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Radiolytic transformation of sulfides in sulfate black liquors Chiu, Shui-Tung 1972

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RADIOLYTIC TRANSFORMATION OF SULFIDES IN SULFATE BLACK LIQUORS B Y SHUI-TUNG CHIU B.Sc. Chung-hsing University, Taiwan, 1962 M.F. University of B r i t i s h Columbia, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Forestry We accept this thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA September, 1972 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Br i t ish Columbia, 1 agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of Br i t ish Columbia Vancouver 8, Canada Date M(TU. Z2-1. /?7 7 ABSTRACT The p o t e n t i a l l y v o l a t i l e , malodorous sulfides (HgS, CH^SH, CRVjSCH-j and CH^SSCH^ ) i n sulfate black liquros were transformed to stable compounds by exposure to gamma photon r a d i o l y s i s . The product complex following r a d i o l y s i s of sul f i d e s i n aqueous solution i s partly resolved ass polysulfide (from H 2 S ) * sulfate (from H S, CH SH and CH 0SSCH„), an intermediate, CH SSCEU (from 2 3 3 3 3 -> CH^SH), and a high molecular weight, amorphous substance (especially from CH^SCILj). Variables studied with aqueous solutions and commercial black liquors have included s u l f i d e concentration, solution pH, temperature, oxygen saturation and effects of soluble l i g n i n , a l l of which.adjusted to some extent the sulfide degradation kinetics. Lowering solution pH and increasing i n i t i a l s u l f i d e concentration, temperature and/or oxygen pressure increased apparent degradation yields (G), while l i g n i n ( t h i o l i g n i n ) acted as a r a d i c a l scavenger in the process. In gamma r a d i o l y s i s of strong and weak black liquors (pH 12 0 85 -13«^0) at Gammacell temperature (3^°C), and atmospheric oxygen pressure, the apparent degradation yi e l d s of su l f i d e are propor-ti o n a l to the respective i n i t i a l concentrations. Apparent degradation y i e l d s were 0„001-0 o 003 f o r CEjSCELj at 0 . 2 0 x 10"^ -.1.10 x 1 0~ 3g/l and 0.002-0.0,85 for CH^SSCH^ at O.kk x 1 0~ 3g/l-39.71 x l O ^ g / l concentration. - i i -S i m i l a r l y , i n carbonated black liquors (pH 8 . 2 0 - 9 * 1 5 ) 9 the apparent degradation yields of sulfides s i g n i f i c a n t l y correlated with their i n i t i a l concentration. The apparent s u l f i d e degradation yiel d s are 0 . 0 1 5 to 3*k27 f o r H S at O . 8 9 x 1 0 * " 3 - 2 6 5 . 2 0 x 1 0 ~ 3 g / l , 2 0 . 0 0 6 - 0 . 2 3 0 for CH^SH at 0 . ^ 8 x 1 0 ~ 3 - 2 8 . 7 0 x 1 0 ~ 3 g / l , 0 . 0 0 3 - 0 . 0 2 0 f o r CH^SCH^ at 0 . 6 0 x 1 0 " 3 - 5 . 2 2 x 1 0 ~ 3 g / l and 0 . 0 0 ^ - 0 . 0 3 5 for CH^SSCH^ at 1 . 0 3 x 1 0 ~ 3 - 9 . 1 1 x 1 0 ~ 3 g / l concentration. The presence of oxygen( 1 atmosphere pressure) at higher concentration of ^ .^(2^7.75 x 1 0 " 3 g / l ) and C H 3 S H ( 9 6 7 • 5 0 x 1 0 ' 3 g / l ) i n carbonate black liquor (pH 7 . 5 0 ) showed high apparent degradation yields of 1 7 and 28 for ELS and CH SH, respectively. This i s 3 considered to be due to a chain reaction occurring during degradation of su l f i d e s . Polysulfide may be generated by r a d i o l y s i s of a c i d i f i e d sodium s u l f i d e and sulfate green l i q u o r . The apparent yie l d s of polysulfide excess sulfur were 3 and 5 for a c i d i f i c a t i o n with carbon dioxide ( 1 2 0 psi) and hydrogen s u l f i d e ( 2 7 0 p s i ) , respectively. As part of these studies, new techniques have been developed for recovery and analysis of sulfides at low concentrations i n aqueous solution. i i i ACKNOWLEDGEMENTS The writer wishes to acknowledge the guidance and encourage-ment given by Dr. J.W. Wilson, Professor; and Dr. L. Paszner, Research Associate, Wood and Pulp Science, Faculty of Forestry, University of B r i t i s h Columbia, during the course of planning and experimental phases and during preparation of the thesis document. Grateful acknowledgement i s also made to Dr. R.W. Wellwood, Professor, Faculty of Forestry; Dr. F.E. Murray, Head and Professor, Department of Chemcial Engineering; Dr. D.C. Walker, Associate Professor, Department of Chemistry, University of B r i t i s h Columbia f o r their helpful suggestions and review of the thes i s . Technical help was kindly provided by Mr. U. Rumma and Go Bohnenkamp, technicians, Faculty of Forestry, University of B r i t i s h Columbia. The help of Mr. Y.S. You, graduate student,for the polysulfide experiments, i s also appreciated. Special thanks are expressed for the f i n a n c i a l support provided by the National Research Council of Canada through Dr. J.W. Wilson; the Teaching Assistanships from the Faculty of Forestry, University of B r i t i s h Columbia; and the Forestry Fellowship from the Canada Department of Environment. Last, but not lea s t , the patience and encouragement of my wife throughout these academic years are acknowledged with my sincere affection. i v TABLE OF CONTENTS TITLE PAGE. ABSTRACT i ACKNOWLEDGEMENTS 1 1 1 TABLE OF CONTENTS i v LIST OF TABLES x LIST OF FIGURES 1.0 INTRODUCTION 1 2.0 LITERATURE REVIEW 7 2.1 Process Chemistry of Potential A i r and Water Pollutant Formation i n Sulfate Pulping of Wood . .7 2.1.1 Sulfide reactions i n the digester 8 2.1.2 Sulfides formation i n stock washers 12 2.1.3 Gaseous emissions from the black liquor oxidation tower 12 2.1,k Multiple effect evaporator emissions 13 2.1.5 Emissions from d i r e c t contact evaporators . . . 1 * * 2.1.6 Emissions from the recovery furnace 15 2.1.7 Smelt d i s s o l v i n g tank emissions 17 2.1.8 Emissions from the lime k i l n 18 2.1.9 Summary 18 2.2 Physical and Chemical Treatment of Sulfides i n Aid of A i r and Water Po l l u t i o n Abatement i n Sulfate Pulping of Wood 19 2.2.1 Some physical and chemical properties of sulfate pulp m i l l malodorous sulfide s 20 2.2.2 Oxidation of sulfid e s 20 2.2.3 Chlorination 2k V 2.2.4 Photolysis *26 2.2.4.1 Photolysis of hydrogen s u l f i d e 27 2.2.4.2 Photolysis of methyl raercaptan 128 2.2.4.3 Photolysis of dimethyl s u l f i d e 29 2.2 .4 .4 Photolysis of dimethyl d i s u l f i d e 30 2.3 Gamma Radiolysis of Water 31 2.3.1 Molecular products • • • •33 2.3.2 Primary r a d i c a l species » 34 2.3.3 Radiolysis of oxygenated water ..... 36 2.4 Radiolysis of Sulfides i n Aqueous Solution 38 2.5 Reaction of Sulfides with Hydrocarbons Induced by Gamma Radiation i n Black Liquor *H 2.6 Gamma Radiolysis of Pulp M i l l Effluents 43 3.0 MATERIALS AND METHODS kk 3.1 Model Compounds kk 3.2 Black Liquors ^5 3.3 Analysis of Aqueous Sulfide Solutions 45 3.3*1 Potentiometric determination of sul f i d e s i n sulfate black l i q u o r b6 3.3.1.1 Experimental 49 3.3 .1 .1 .1 Apparatus 49 3.3.1 .1 .2 Theory of s i l v e r n i t r a t e potentiometric t i t r a t i o n 49 3.3 .1 .1 .3 Interpretation of t i t r a t i o n curves . . . 53 3.3 .1 .1 .3 .1 Effect of mercaptide ion concen-t r a t i o n on t i t r a t i o n 55 3.3 .1 .1 .3 .2 T i t r a t i o n of inorganic polysulfide solution • 57 3.3 .1 .1 .3 .3 T i t r a t i o n of oxidized s u l f i d e liquors • . . . . 5 8 v i 3.3 .1 .1 .3 .4 T i t r a t i o n of dimethyl'sulfide and dimethyl d i s u l f i d e i n alka l i n e solution 59 3 .3 .1 .1 .3 .5 T i t r a t i o n of mercaptan i n the presence of elemental sulf u r 60 3.3.2 Gas l i q u i d chromatographic (GLC) determination of organic sulfides i n black li q u o r 62 3.3.2.1 Experimental 68 3.3 .2 .1 .1 Chemicals 68 3.3.2 .1 .2 Gas l i q u i d chromatography (GLC) 68 3.3 .2 .1 .3 Sample procurement f o r gas l i q u i d chromatography 71 3.3 .2 .1 .3 .1 Carbon tetrachloride l i q u i d / l i q u i d extraction 72 3.3 .2 .1 .3 .2 A c i d i f i c a t i o n of black liquor with boric acid 74 3.4 Chemistry and Analysis of Polysulfide 78 3.4.1 Significance of polysulfide as an extension to sulfate pulping 78 3.4.2 Composition and nomenclature of aqueous poly-s u l f i d e solutions • 79 3.4.3 Preparation of aqueous polysulfide solutions .81 3.4.4 Polysulfide determination ........82 3.4.4.1 Gravimetric analysis 82 3.4.4.2 Volumetric analysis 83 3.4.5 Determination of sulfate i n polysulfide •: solution 88 3*5 Black Liquor Characterization . . . 89 3.5.1 Determination of pH 89 3.5.2 Density 89 3.5.3 Total solids 90 V l l 3'5'k Lignin determination 90 3.6 A c i d i f i c a t i o n of Sulfate Black Liquor with Carbon Dioxide . . . . 9 2 3*7 Gamma Radiation 96 3.7.1 Cobalt -60 gamma photon source . . . . 9 6 3»7» 2 Gamma ray dosimetry 97 3.8 Sample Preparation and Analyses f o r Experimental Gamma Radiolysis of Aqueous Sulfide Model Compound Solutions and Sulfate Black Liquors . . . . . . 9 9 3.8.1 Gamma r a d i o l y s i s of aqueous s u l f i d e model c ompounds . . . . . . . . . . . . . . . . 1 0 0 3.8.1.1 Sodium s u l f i d e . . .100 3.8.1.2 Sodium methyl raercaptan 101 3.8.1.3 Dimethyl s u l f i d e and dimethyl d i s u l f i d e ..102 3.8 .1.3.1 Effect of pH 101* 3.8.1 .3 .2 Effect of dissolved l i g n i n 105 3.8 .1.3.3 High temperature and high pressure . . .106 3.8.2 Gamma r a d i o l y s i s of sulfate and polysulfide black liquors .....108 3.8.3 Gamma r a d i o l y s i s of carbonated sulfate and polysulfide black liquors 109 3.8.^ Effect of oxygen, a i r and nitrogen atmosphere on gamma r a d i o l y s i s of sulfides i n the carbon-ated black liquors • 110 3.9 Regeneration of Polysulfide from Sodium Sulfide and Green Liquor I l l k.O RESULTS 113 k.l Gas Liquid Chromatography (GLC) Ca l i b r a t i o n Curves for Sulfides 113 k.2 Black Liquor Characteristics 113 k.3 I r r a d i a t i o n of Aqueous Sulfide Model Compounds . . .113 v i i i 4.3.1 Sodium s u l f i d e 113 4.3.2 Sodium methyl mercaptan . . . . I l 4 4.3.3 Dimethyl s u l f i d e and dimethyl d i s u l f i d e 115 4.3.3.1 Effect of solution pH 117 4.3.3.2 Effect of l i g n i n concentration 118 4.3.3.3 Effect of temperature ...119 4.3.3.4 Effect of oxygen pressure . . . . 1 2 1 4.4 Gamma Radiolysis of Sulfate and Polysulfide Black Liquors (pH 12.85-13.40) 123 4.5 Gamma Radiolysis of Carbonated Sulfate and Poly-s u l f i d e Black Liquors (pH 8 .20-9 .15) 125 4.6 Effect of Nitrogen, A i r and Oxygen Atmospheres on Gamma Radiolysis of Sulfides i n Carbonated Black Liquor (pH 7.50) 12 7 4.7 Regeneration of Polysulfide by Gamma Radiolysis of Sodium Sulfide Solution . . . . 1 2 9 5.0 DISCUSSION 130 5.1 Analysis of Total Sulfides i n Sulfate Pulping Liquors 130 5.2 Gamma Radiolysis of Sulfides i n Aqueous Solution and Sulfate Black Liquor 136 5 .2.1 Hydrogen s u l f i d e 136 5 .2.2 Methyl mercaptan . . . . l 4 l 5.2.3 Dimethyl s u l f i d e and dimethyl d i s u l f i d e 144 5.2.4 Unidentified sulfur compound (X) 154 5.3 Kinetics of Gamma Radiolysis of Sulfides i n Aqueous Solution and Black Liquor 15^ 5.4 Effect of Gamma Radiation on Black Liquor pH . . . . . 1 5 9 5.5 Oxidation of Sulfides i n Black Liquor l6o ix 5.6 Applications 162 5 . 6 . 1 Treatment of digester and blow r e l i e f and evaporator condensates l62 5 . 6 . 2 High s u l f i d i t y and polysulfide recovery processes 163 6 . 0 CONCLUSION 165 6.1 Sulfide Analyses 165 6.2 Gamma Radiolysis of Sulfides i n Aqueous Solution 166 7.0 REFERENCES 1?0 8.0 r.TABLES AND FIGURES 207 X LIST OF TABLES TABLE Page 2.1 Release of v o l a t i l e s u l f u r compounds from digesters and washers .207 2.2 Release of v o l a t i l e sulfur compounds from recovery systems ....208 2.3 Physical c h a r a c t e r i s t i c s of sulfate pulp m i l l malo-dorous sulfide s 209 3.1 Sulfate and polysulfide black liq u o r sources 210 3.2 Effect of i n f l e c t i o n point "a" and "b" i n potentio-metric t i t r a t i o n curve on c a l c u l a t i o n of hydrogen s u l f i d e i n black liq u o r 211 3.3 Accuracy of potentiometric t i t r a t i o n of s u l f i d e i n al k a l i n e solution i n the presence of methyl mercaptan • .....212 3 . 4 Interpretation of the potentiometric t i t r a t i o n curve as a f f e c t i n g the accuracy of s u l f i d e determination by addition of methyl mercaptan 213 3 . 5 Determination of s u l f i d e and bound mercaptan by addition of excess of Na-mercaptan to oxidized alka-l i n e s u l f i d e solution xirith and without t h i o l i g n i n as additive ......214 3 . 6 Potentiometric t i t r a t i o n of methyl mercaptan i n alkaline solution i n the presence of elemental sulfur 215 3 . 7 E f f i c i e n c y of 5 x 10 ml carbon tetrachloride l i q u i d / l i q u i d extraction of the organosulfides from 5 ml sulfate white and black liquors . . . 2 l 6 3.8 E f f i c i e n c y of 20 ml carbon tetrachloride l i q u i d / l i q u i d extraction of organic s u l f i d e compounds from 5 ml boric acid (1 .0) treatment carbonated black liquor (1-1) 217 4.1 Characteristics of sulfate and polysulfide black liquors 218 x i TABLE Page 4.2 Gamma r a d i o l y s i s of sodium s u l f i d e aqueous solution and formation of polysulfide excess sulfur at Gamma-c e l l temperature ( 3 4 ° ) 2 1 9 4.3 Effect of solution pH on gamma radiation degradation y i e l d (G) of polysulfide excess sulfur 220 4 . 4 Gamma r a d i o l y s i s of sodium methyl mercaptan i n various pH solutions at Gaminacell temperature (34°C) 221 4 . 5 Gamma r a d i o l y s i s of model compounds of dimethyl d i -s u l f i d e i n aqueous al k a l i n e solution at Gammacell temperature (34°C) 222 4.6 Gamma r a d i o l y s i s of dimethyl s u l f i d e and .dimethyl d i -s u l f i d e i n sulfate black liquor (2-1) at Gammacell temperature (34°C) 223 4 . 7 Gamma radiation degradation y i e l d s (G) of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n al k a l i n e aqueous solution and black liquor (2-1) 224 4.8 Effect of solution pH on gamma r a d i o l y s i s (3 Mrad) of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n aqueous solution 225 4 . 9 Effect of l i g n i n concentration on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n aqueous alk a l i n e solution 226 4.10 Effect of temperature on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liquor (1-3) under 50 p s i i n i t i a l oxygen pressure 227 4.11 Effect of temperature on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n carbonated black liquor (2-1) under 50 p s i i n i t i a l oxygen pressure .228 4.12 Effect of oxygen pressure on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liq u o r (2-1) at Gammacell temperature (34°C) 229 4.13 Effect of oxygen pressure on gamma r a d i o l y s i s of d i -methyl s u l f i d e and dimethyl d i s u l f i d e i n carbonated black li q u o r (2-1) at Gammacell temperature (34°C).230 x i i TABLE Page 4.14 Potentiometric t i t r a t i o n of mono- and polysulfide i n 4 ml gamma irr a d i a t e d black liquor (3-1) 2 3 1 4.15 Gamma r a d i o l y s i s of dimethyl s u l f i d e i n sulfate and polysulfide black liquors 232 4.16 Gamma r a d i o l y s i s of dimethyl d i s u l f i d e i n sulfate and polysulfide black liquors 233 4.17 Gamma r a d i o l y s i s of unidentified sulfur compound (X) i n sulfate and polysulfide black liquors at Gammacell temperature (34°C) 234 4.18 Gamma radiation degradation y i e l d (G) of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n the various sulfate and polysulfide black liquors 235 4.19 Gamma r a d i o l y s i s of hydrogen s u l f i d e i n carbonated sulfate and polysulfide black liquors at Gammacell temperature (34°C) 236 4.20 Gamma r a d i o l y s i s of methyl mercaptan i n carbonated sulfate and polysulfide black liquors 237 4.21 Gamma r a d i o l y s i s of dimethyl s u l f i d e i n carbonated sulfate and polysulfide black liquors 238 4.22 Gamma r a d i o l y s i s of dimethyl d i s u l f i d e i n carbon-ated sulfate and polysulfide black liquors 239 4.23 Gamma r a d i o l y s i s of unidentified sulfur compound (X) i n carbonated sulfate and polysulfide black liquors 240 4 . 2 4 Gamma radiation degradation y i e l d s (G) of hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and d i -methyl d i s u l f i d e i n the various carbonated black liquors 2 4 l 4.25 Effect of nitrogen, a i r and oxygen atmospheres on gamma r a d i o l y s i s of sulfides in carbonated black liquor ( l - l ) 242 x i i i TABLE Page 4.26 Effect of nitrogen, a i r and oxygen atmospheres on gamma radiation degradation y i e l d (G) of hydrogen s u l f i d e , methyl mercaptan and dimethyl s u l f i d e i n the carbonated black liq u o r ( l - l ) 243 4.27 Gamma r a d i o l y s i s of carbon dioxide and hydrogen s u l f i d e a c i d i f i e d sodium s u l f i d e and sulfate green liqu o r 244 x i v LIST OF FIGURES FIGURE Page 2.1 The spectrum of electromagnetic radiation 2 45 3.1 Potentiometric t i t r a t i o n curves of sulfate and poly-su l f i d e black liquors 246 3.2 Potentiometric t i t r a t i o n curves of sodium s u l f i d e solution, sulfate white liquor (WL, 1-3) and black liquor (BL, 1-2) and added methyl mercaptan 247 3 .3 Potentiometric t i t r a t i o n curves of s u l f i d e i n sulfate white (WL, 1-2) and black liquor (BL, 1-2) i n the presence of methyl mercaptan 248 3 . 4 Potentiometric t i t r a t i o n curves of sodium polysulfide i n presence of methyl mercaptan 249 3«5 Potentiometric t i t r a t i o n curves of sodium s u l f i d e i n 1% t h i o l i g n i n containing a l k a l i n e solution with and without oxidation and addition of sodium methyl mercaptan 250 3.6 Potentiometric t i t r a t i o n curves of dimethyl s u l f i d e , dimethyl d i s u l f i d e , sulfur-mercaptan and methyl mercaptan i n alkaline solution 251 3 . 7 Potentiometric t i t r a t i o n curves of methyl mercaptan with and without added elemental sulfur i n a l k a l i n e solution 252 3 . 8 The c a l i b r a t i o n curves f o r hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e i n carbon tetrachloride 253 3 . 9 The c a l i b r a t i o n curves f o r dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liquor 254 3 . 1 0 Steps of carbon tetrachloride l i q u i d / l i q u i d extraction of dimethyl s u l f i d e and dimethyl d i s u l f i d e from white liquor (WL) and black liquor (BL) . . . 2 5 5 3.11 Effect of solution pH on the e f f i c i e n c y of carbon tetrachloride l i q u i d / l i q u i d extraction 256 X V FIGURE Page 3.12 Change of black liquor (1-4) pH as a function of added boric acid concentration 257 3.13 Gas l i q u i d chromatography (GLC) of carbon t e t r a -chloride extracts of a c i d i f i e d and unacidified black liquor (2-1) samples • 258 3.14 Redox t i t r a t i o n curve of a poly s u l f i d e solution with sodium s u l f i t e i n 90°C saturated sodium chloride solution 259 3.15 Calib r a t i o n curve f o r spectroscopic determination of polysulfide excess sulfur i n 3M NaCI and 0.01M NaOH solution 260 3.16 C a l i b r a t i o n curve of transmittance and concentra-tion f o r sulfate solution 261 3.17 Calib r a t i o n curve of t h i o l i g n i n concentration versus absorbance at 213 nm 262 3.18 Relationship of black liquor (BL) pH and carbon dioxide volume bubbled 263 3.19 Infrared spectrum of the r a d i o l y s i s product of aqueous dimethyl s u l f i d e 264 3 . 2 0 Schematic drawing of high pressure and temperature i r r a d i a t i o n apparatus 265 3.21 Relationship of powerstat setting and pressure vessel temperature • • 266 4.1 Gamma r a d i o l y s i s of sodium s u l f i d e aqueous solution and formation of polysulfide excess sulfur at Gammacell temperature (34°C) 267 4.2 Gamma r a d i o l y s i s of various pH sodium methyl mercaptan solutions at Gammacell temperature (34°C) 268 4.3 Gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n aqueous al k a l i n e solution and black liquor (2-1) at Gammacell temperature (34<>C) . . . 2 6 9 4 . 4 Effect of solution. pH on gamma r a d i o l y s i s (3 Mrad) of dimethyl s u l f i d e and dimethyl d i s u l f i d e 270 xvi FIGURE Page 4 . 5 Effect of solution pH on ratios of gamma radiation (3 Mrad) degradation y i e l d (G) and i n i t i a l concen-t r a t i o n (Co) 271 4.6 Effect of l i g n i n concentration on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n aqueous al k a l i n e solution 2 7 2 4 . 7 Effect of temperature on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black li q u o r (1-3) under 50 p s i i n i t i a l oxygen pressure 273 4 . 8 Effect of temperature on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n carbonated black liq u o r (2-1) under 50 p s i i n i t i a l oxygen pressure.274 4 . 9 Effect of oxygen pressure on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liq u o r (2-1) at Gammacell temperature (34°C) 275 4.10 Effect of oxygen pressure on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n carbon-ated black liquor (2-1) at Gammacell temperature (34°C) 276 4.11 Potentiometric t i t r a t i o n of mono- and polysulfide i n 4 ml gamma ir r a d i a t e d black liquor (3-1) 2 7 7 4.12 Gamma r a d i o l y s i s of dimethyl s u l f i d e i n sulfate and polysulfide black liquors at Gammacell temperature (34°C) 278 4.13 Gamma r a d i o l y s i s of dimethyl d i s u l f i d e i n sulfate and polysulfide black liquors at Gammacell tempera-ture (34°C) 279 4.14 Gamma r a d i o l y s i s of an unidentified s u l f u r compound (X) i n sulfate and polysulfide black liquors at Gammacell temperature (34°C) 280 4.15 Relation of i n i t i a l concentration and gamma radiation y i e l d s of dimethyl s u l f i d e i n black liquors 281 4.16 Relation of i n i t i a l concentration and gamma radia-tion degradation yie l d s of dimethyl d i s u l f i d e i n black liquors 282 x v i i FIGURE P a 2 e 4.17 Gamma r a d i o l y s i s of hydrogen s u l f i d e i n carbonated sulfate and polysulfide black liquors at Gammacell temperature (34°C) 283 4.18 Gamma r a d i o l y s i s of methyl mercaptan i n carbonated sulfate and polysulfide black liquors at Gammacell temperature (34°C) . . 2 8 4 4.19 Gamma r a d i o l y s i s of dimethyl s u l f i d e i n carbonated sulfate and polysulfide black liquors at Gammacell temperature (34°C) 285 4.20 Gamma r a d i o l y s i s of dimethyl d i s u l f i d e i n carbonated sulfate and polysulfide black liquors at Gammacell temperature (34°C) 286 4.21 Gamma r a d i o l y s i s of an unidentified sulfur compound (X) i n carbonated sulfate and polysulfide black liquors at Gammacell temperature (34°C) 287 4.22 Relation of i n i t i a l concentration and gamma radia-tion degradation y i e l d s of hydrogen s u l f i d e i n carbonated black liquors 288 4.23 Relation of i n i t i a l concentration and gamma radia-tion degradation y i e l d s of methyl mercaptan i n carbonated black liquors 289 4.24 Relation of i n i t i a l concentration and gamma radia-t i o n degradation y i e l d s of dimethyl s u l f i d e i n carbonated black liquors 290 4.25 Relation of i n i t i a l concentration and gamma radia-t i o n degradation y i e l d s of dimethyl d i s u l f i d e i n carbonated black liquors 291 4.26 Effect of nitrogen, a i r and oxygen atmosphere on gamma r a d i o l y s i s of hydrogen s u l f i d e i n carbonated black liquor ( l - l ) at Gammacell temperature (34°)-292 4.27 Effect of nitrogen, a i r and oxygen atmospheres on gamma r a d i o l y s i s of dimethyl s u l f i d e i n carbonated black liquor (1-1) at Gammacell temperature (34°)-293 x v i i i FIGURE Page 4.28 Effect of nitrogen, a i r and oxygen atmospheres on gamma r a d i o l y s i s of methyl mercaptan and dimethyl d i s u l f i d e i n carbonated black li q u o r (1-1) at Gammacell temperature (34°C) 294 5.1 Formation of malodorous sulfides from sulfate cooking .295 5*2 Proposed radio-chemical reactions i n gamma radio-l y s i s of sulfate black liquor ..296 - 1 -1.0 INTRODUCTION In North America, the pulp and paper industry occupies a prominent position (ninth) among natural product processing industries such as o i l , mining and food processing industries. Canada alone produced 16.4% of the world's total supply of pulp, furnishing nearly l 6 million short tons in 1969. Of this amount, 9.3 million tons was chemical pulp of which approximately 73% was produced by the sulfate (kraft) process (64). Projections made for chemical pulp production anticipate that; of sulfate pulp w i l l increase by two and" one-half times, and that of the neutral s u l f i t e semichemical (NSSC) process will approximately double the 1968 figures by 1985 in the United States. Sulfite pulp production w i l l likely decrease sl i g h t l y , whereas soda and dissolving pulp production is expected to remain constant ( 8 9 ) . Therefore, the sulfate and NSSC processes are expected to dominate chemical pulping in the future, as they do at present. The main reasons for such potential dominance of the pulping industry by the sulfate process are the comparative simplicity, rapidity of cooking, applicability to a l l wood variations and wood species, favorable pulp and paper properties and,most import-ant of a l l , the availability of an efficient and economic recovery process. These intrinsic advantages have seemed to outweigh the drawbacks, which are the requirement of the high i n i t i a l invest-ment and pollution problems of several types, usually of a complex nature. Opportunities for pollutant formation and escape occur at many points throughout the process. Budgeting for pollution control has become a recognized factor in pulp mill operation today. Expenditures for pollution control by pulp mills have reached phenomenal figures during the past decade. Fortunately, the pulping process,has. been modified and improved through the years in such a manner that stringent recovery of process losses usually defray part of the capital costs for additional equipment. Besides, as a public service, governments have often recognized the need for various forms of assistance to increase pollution abatement. Such subsidies have increased the funds available, not only to public agencies con-cerned with pollution control, but have also provided direct research grants and tax relief to the industry. The causes of air and water pollution relate mainly to dissolved organic wood residues (carbohydrates, lignin and ex-tractives) and subsequent formation of methyl mercaptan, dimethyl sulfide, dimethyl disulfide and hydrogen sulfide in the digester, as well as during the chemical recovery process. Chemical recovery involves black liquor concentration, combustion and reconstitution of the cooking chemicals. During the digester r e l i e f , digester blow, and recovery operations, sulfur-bearing gases may be lost to the atmosphere in varying amounts. Other minor sources of pollutants are particulate matter from the recovery furnace. The possible formation of water pollutants in sulfate pulping relates to digester r e l i e f , blow, and evaporator con-densates, as well as to weak wash waters discharged from bleach plants. These water contaminants constitute sources of biological oxygen demand (BOD), chemical oxygen demand (COD) and may contribute to toxicity of the effluents. It is also recognized that most of the problem causing contaminants relate to the non-cellulosic components released during the course of pulping. Among important pollutants, the sulfide and mercaptide ions have been identified as highly toxic constituents (2 l 4 ) . Recently, various efforts have been made to solve pollution problems associated with sulfate pulp m i l l s . As is often the case, a process designed to resolve one problem may create yet another. Some solutions proposed for abatement of air pollution often create water pollution and vice:versa. Retention and stabilization of sulfur-containing volatile compounds is d i f f i c u l t . Methods practiced or proposed for black liquor digester r e l i e f and blow gas treatments are oxidation (42, 92, 136), chlorination (60, 75, 201, 205), combustion (39, 50, 51) and absorption and desorption (1, 171); but none of these has been shown to be completely successful. Failure of such provisions often relate to the extreme human sensitivity to obnoxious sulfides, possibly -4-evolutionary in nature as an index or warning precaution to food spoilage. Threshold concentration values of sulfide detection by humans lies below or at the detection limits of modern analytical instruments andr while none of the sulfides (except for hydrogen sulfide) has been directly associated with human illnesses/ they do constitute a considerable nuisance to the public. Increased availability of high energy isotopes from reactor by-products provides the possibilities in the near future for industrial processing, and process control developments. Although, applications of industrial radiation processing are, generally speaking, in preliminary stages, the limited results indicate levels of achievements unobtainable by conventional means. The application of ionizing radiation to wood product ~ industries is currently being investigated for wood coatings, wood plastic combinations, prevention of wood chip deterioration in outside storage prior to pulping (43, 71) and wood substance modification to benefit pulp properties and pulping processes (3^, **3, 71, 81, 208). Considerable information has been made available on the effects and uti l i z a t i o n of ionizing radiation for purposes of food and drug processing and new packaging technology. Although limited studies are available on the destruction of micro-organisms and oxidation of organic substances in industrial effluents and waste water streams (118), specific technology and descriptive literature with pulp mill effluent treatments are almost completely lacking. Most works have been only exploratory in nature. Detailed information is available only for sanitary effluent treatments, researched mainly in the United States. Treatment of industrial effluents, using radiation, i s also described for pesticides such as dieldrin and DDT ( 4 l , 74, 206), decolorization of aqueous dye solutions from textile mills (74) and for decolorization and solids precipitation from sulfate and neutral sulfite pulp mill effluents (113). These treatment schemes offer examples of significant reductions in BOD/COD, color, toxicity and improved solids sedimentation and are connected only through highly reactive species created by radiolysis of aqueous solutions. The transformations of volatile malodorous sulfides in sulfate black liquor, and recovery of polysulfide from aqueous sulfide and green liquor as induced by gamma radiation, are l i t t l e studied. The present study is concerned with application of gamma radiation to industrial and laboratory sulfate pulping liquors with the following objectives: 1. To explore influences of gamma photon radiation on the chemical transformations of characteristic sulfides in black liquor and carbonated black liquor. -6-2. To determine the effects of system variables, such as solution pH, lignin concentration, temperature and oxygen pressure, on transformations occurring with various sulfide model compounds. 3 . To explore the possibility of recovering polysulfide from aqueous sodium sulfide solution and sulfate green liquor. k. To estimate the degree of sulfide stabilization attainable by a radiolytic process. 5. To reevaluate and possibly improve the analytical methodology available for determination of inorganic and organic sulfides in alkaline solutions, as well as in sulfate black liquor. < -7-2.0 LITERATURE REVIEW 2.1 Process Chemistry of Potential Air and Water Pollutant Formation in Sulfate Pulping of Wood Waste liquor treatment from pulp and paper mills constitutes a major problem of pollution abatement with this industry (59) • The amount of waste water effluent from sulfate pulp m i l l s , with attached bleach plant, varies between 30,000 to 130,000 US gal/ton of air-dried (AD) pulp. This waste water has a low BOD (biological oxygen demand) when compared to such industries as canneries, breweries, dairies and the like; but i t is the tremendous volume of water that makes pulp mill waste effluent treatment so expensive. Substantial improvements have been made towards upgrading the effluent quality by developing operating procedures which minimize the fibre loss, and nonrecoverable chemical discharge. A considerable amount of research effort and capital expenditure relating to new and alternate methods of effluent control have been added in older mills and are being incorporated into newly designed mills (1, 39, 60, 92, 120, 130, 136, 171, 203). Generally, both effluent toxicity and BOD effects of sublethal: concentrations of mill effluents,are of major;importance, especially i f discharges occur to inland waterways (174), Among the waste and a i r pollutants from sulfate m i l l s , sulfides occupy a special place and command dual attention. In aqueous solution, -8-they are known to be toxic to aquatic fauna (21, 2 l 4 ) , p a r t i c -u l a r l y to f i s h , whereas i n gaseous form released to the atmos-phere, they have drawn loud public outcries because of t h e i r obnoxious nature. Organosulfide emissions from sulfate pulping are associated with the digester r e l i e f , blow tank, pulp washer, oxidation tower, liqu o r concentrators, recovery furnace, smelt d i s s o l v i n g tank and the lime k i l n . While the range of odor causing s u l f i d e emissions may d i f f e r from m i l l to m i l l , the types of compounds i d e n t i f i e d as occurring in the above operations are generally the same. 2.1.1 Sulfide .reactions in the digester The substances mainly responsible for odor emissions from sulfate m i l l s are hydrogen s u l f i d e (R2S) and various forms of organosulfides, o r i g i n a t i n g primarily from reactions with l i g n i n methoxyl groups. F i r s t escape of these compounds from the digester i s permitted i n the form of conden-sates and non-condensible gases during the digester r e l i e f and digester blow operations. Approximate quantities of these compounds are given i n Table 2.1 (15, 90). The hydrogen s u l f i d e i s formed through a hydrolytic e q u i l i b r i a of s u l f i d e ions i n the aqueous sulfate cooking l i q u o r . S~~ + HgO <• • > HS" + 0H~ / 2 - l / HS" + HgO I » HgS + OH" / 2 - 2 / - 9 -T h u s , i t i s o b v i o u s t h a t t h e q u a n t i t y o f h y d r o g e n s u l f i d e e m i t t e d f r o m a n a q u e o u s s y s t e m d e p e n d s o n t h e pH a n d t e m p e r a t u r e o f t h e s o l u t i o n , w i t h l o w e r e m i s s i o n s o c c u r r i n g u s u a l l y a t h i g h p H ( p H 12-13) (176) . H i g h c o o k i n g t e m p e r a t u r e s ( i n e x c e s s o f 180 ° C ) h a v e b e e n s h o w n t o a i d t h e n u c l e o p h i l i c c l e a v a g e o f t h e l i g n i n m e t h o x y l g r o u p d u r i n g s u l f a t e c o o k i n g t o f o r m m e t h y l m e r c a p t a n ( 76 ) . L i g - O C H , + S " ~ > C B , S ~ + L i g - O " 3 3 C H , S " + H o 0 < y C H , S H + 0 H ~ / 2 - 3 / F u r t h e r r e a c t i o n s w i t h t h e n e w l y f o r m e d m e r c a p t i d e i o n s a n d l i g n i n m e t h o x y l s l e a d t o t h e f o r m a t i o n o f d i m e t h y l s u l f i d e . L i g - O C H , + C H - . S " > C H ^ S C H , + L i g - 0 ~ /2-k/ 3 3 3 3 T h e o r d e r o f n u c l e o p h i l e p o w e r o f m e r c a p t i d e a n d h y d r o s u l f i d e i o n s h a s b e e n s h o w n b y G o h e e n ( 7 6 ) a n d T u r u n e n (207) t o b e f a r g r e a t e r t h a n t h a t o f t h e h y d r o x i d e i o n ( 0 H ~ ) , t h u s e x p l a i n i n g t h e l o w m e t h a n o l c o n t e n t o f s u l f a t e c o o k i n g l i q u o r . R e a c t i o n k i n e t i c s o f o r g a n i o s u l f i d e f o r m a t i o n s h a v e b e e n s t u d i e d e x t e n s i v e l y ( 1 1 , 55 , 126, 128) a n d w e r e f o u n d t o d e p e n d o n h y d r o s u l f i d e i o n c o n c e n t r a t i o n (128, 166) , pH ( 1 1 , 1 6 6 ) , c o o k i n g t e m p e r a t u r e ( 1 1 ) , a n d a v a i l a b i l i t y o f l i g n i n m e t h o x y l s (55 , 126). M c K e a n e t a l . (128) w e r e a b l e t o s h o w t h a t d e m e t h y l a t i o n d u r i n g s u l f a t e c o o k i n g f o l l o w e d f i r s t o r d e r r e a c t i o n w i t h r e s p e c t t o h y d r o s u l f i d e i o n c o n c e n t r a t i o n . A n d e r s s o n (11) e s t i m a t e d t h a t a p p r o x i m a t e l y 2 . 3 t o 2.5% o f t h e t o t a l s u l f u r c h a r g e ( a t 30% s u l f i d i t y ) i s c o n v e r t e d t o o r g a n i c s u l f i d e s . R e c e n t s t u d i e s b y D o u g l a s s a n d P r i c e (55) s h o w t h a t t h e r a t e o f m e r c a p t a n f o r m a t i o n i s v e r y a c c u r a t e l y p r o p o r t i o n a l t o t h e -10-s u l f i d i t y at constant e f f e c t i v e a l k a l i and liquor to wood r a t i o l e v e l s . McKean et a l . (128) suggested that sulfate cooks could be made at much lower s u l f i d i t y levels (25%) without seriously impairing d e l i g n i f i c a t i o n rates. The formation of organosulfides depends on the a v a i l a b i l i t y of methoxyl groups. Wood methoxyl i s known to vary with wood source. Some observations i n this respect were made by Douglass and Price (55) and McKean e_t a l . (126). At i d e n t i c a l cooking conditions, porous-wood chips (Betula papyrifera Marsh, and Acer  rubrum L.) formed larger quantities of organosulfides than those of coniferous woods (Picea excelsa Link and Pinus taeda L.). In sulfate cooking of porous-woods, approximately 10% more organosulfides are liberated than i n comparable pulping of coniferous wood. The higher methoxyl content and some l a b i l e methoxyl group i n porous-wood l i g n i n ( s y r i n g y l ) , were thought to contribute to the basic differences observed (128). However, the increase i n organo-sulfides was not proportional to the higher methoxyl content of these hardwoods. The pH effect upon l i b e r a t i o n of hydrogen s u l f i d e and methyl mercaptan i s correspondingly indicated i n Eqs./2-2/ and / 2 - 3 / i Since the pH of the cooking li q u o r i s d i r e c t l y proportional to the a l k a l i charge, the release of hydrogen s u l f i d e and methyl mercaptan i s highly dependent on residual a l k a l i n i t y of the black l i q u o r . Based on vapor, pressure vs. pH measurements of hydrogen s u l f i d e and methyl mercaptan at various temperatures, Shih e_t al . (176, 177) found that methyl mercaptan, being a weaker acid than hydrogen s u l f i d e , was highly sensitive to pH changes above pH 10. The vapor pressure curves suggested the d e s i r a b i l i t y of r e t a i n -ing a f i n a l pH of 13. In view of the high s u l f i d e concentration, changes i n the solution above pH 10 can res u l t also i n s i g n i f i c a n t vapor pressure changes of hydrogen s u l f i d e . A drop of pH from 13 to 10 can increase vapor,, pressure of hydrogen s u l f i d e one-hundred-fold, especially under highly e f f i c i e n t steam stripping conditions. Dimethyl s u l f i d e concentration, on the other hand, i s not d i r e c t l y affected by pH because i t s vapor: pressure i s unaffected by the a l k a l i n i t y of the cooking l i q u o r . The dependence of the formation of organosulfides on temperature has been demonstrated by Andersson (11), Douglass and Price (55) t DeHaas and Hansen (51) and McKean ot a_l. (126). Based upon the a c t i v a t i o n energies calculated from Eq. /2-3/and Eq. /2-4/ (11.3 and 7.6 Kcal/Mole, respectively) as compared to that of d e l i g n i f i c a t i o n (30.2 Kcal/Mole), i t i s suggested that a rapid cook at high temperature i s l i k e l y to produce less odor than a slow cook at low temperature. The secondary product, dimethyl d i s u l f i d e (CH^SSC^), originates probably during the l a t e r stages of cooking and/or upon digester r e l i e f and blow operations. Its formation has been traced to oxidation of methyl mercaptan by oxygen at ambient -12-teraperature (55). + + 0 2 + + 2CILjSSCH3 /2-5/ —> kOE~ + 2CH SSCEU'V2-6/ Digester r e l i e f and blow operations are recognized as the largest points of organosulfur emissions within sulfate pulp m i l l s . This i s so because these compounds are primarily formed in the digester; and f i r s t opportunity to escape from this confinement i s by steam stripping with pressure release and blowing. From the foregoing overview i t i s evident that i n the cooking process alone a delicate balance of the main cooking conditions ( s u l f i d i t y , pH and temperature) must be maintained fo r e f f e c t i v e odor c o n t r o l . 2.1.2 Sulfide formation i n stock washers emissions and formation of dimethyl d i s u l f i d e from oxidation of methyl mercaptan as described i n the foregoing section. During brown stock washing, the slurr y pH c l o s e l y approaches ne u t r a l i t y , high rate of a i r flow, turbulence and temperature increase the vapor pressure of v o l a t i l e s u l f i d e s , especially that of hydrogen s u l f i d e , methyl mercaptan, and dimethyl s u l f i d e (Table 2.1) Stock washers can be a ready source of s u l f i d e (15, 90). 2.1.3 Gaseous emissions from the black liquor oxidation tower - 1 3 -Th e major benefit of black liquor oxidation is removal of hydrogen sulfide and methyl mercaptan from the effluent stream by converting the volatile reduced sulfur com-pounds to non-volatile or less volatile states. Thus, inorganic sulfide ions in the waste liquor are converted to thiosulfate and oxidation of methyl mercaptide ions to dimethyl disulfide is obtained with ease. As seen in Table 2.2 sulfur dioxide and hydrogen sulfide emissions from oxidation towers are neglible, dimethyl disulfide being the only major source of emission in this operation. 2.1.4 Multiple effect evaporator emissions Multiple effect evaporators are designed as the f i r s t step in concentrating weak black liquor (12-^15%, solids) to 50-55% solids l e v e l . In effect, water evaporation occurs under vacuum and heat, whereby non-condensible sulfur gases are also vaporized or stripped during boiling. The vapors vented from the multiple effect evaporator are condensed by barometric or surface condensers• Condensates from the barometric condenser of the multiple effect evaporator usually contain a limited quantity of hydrogen sulfide and methyl mercaptan. Discharge of the condensate causes potential water pollution (90). On the other hand, air pollution usually occurs from the surface condenser by which the non-condensible sulfides are separated from the condensate (90). - 1 4 -Sulfur gases or i g i n a t i n g from multiple ef f e c t evaporators represent a major emission source of sulfate pulp m i l l s . Black liquor oxidation preceding evaporation, however, s i g n i f i c a n t l y reduces hydrogen s u l f i d e and methyl mercaptan emissions during evaporation (Table 2.2). Sulfur loses occurring from multiple effect evaporators processing unoxidized black liquor can be described by the following reactions (121): Na S + 2H-0 A > H S + 2NaOH /2-7/ 2 * 2 CH SNa + HO A > CH SH + Na OH /2-8/ 3 2 3 I I 2.1.5 Emissions from d i r e c t contact evaporators Most recovery furnaces are operated i n series with direct-contact evaporators. The sensible heat i n furnace f l u e gases i s used to raise the black li q u o r concentration i n the multiple effect evaporators to the f i r i n g concentration of 65-70% solids (90). Gas emissions from the direct-contact evaporation are caused by s t r i p p i n g of dissolved gases from the black l i q u o r by hot f l u e gases. Further, pH reductions are also believed to take place due to C0 2 and S0 2 content of gas streams or i g i n a t i n g i n the furnace. This causes a considerable s h i f t i n hydrogen s u l f i d e and methyl mercaptan equilibriums. H + + HS" ^ Z Z ± SHg /2-9/ + H + CH^S-^^ CH^SH /2-10/ Some recent studies by Buxton (36) and Thoen et a l . (198) indicate that the d i r e c t contact evaporator i s the major source of hydrogen s u l f i d e , methyl mercaptan and sulf u r dioxide emissions from sulfate m i l l s . However, gaseous sulfu r emissions from oxidized black liquor are considerably reduced (139) • Emission:, ranges from d i r e c t contact evaporation or unoxidized and oxidized black liquor are shown i n Table 2;2 (90). P r a c t i c a l l y odor free operation i s claimed with the so-c a l l e d a i r contact evaporator as described by Hochmuth (93 )• In this new design the f l u e gases are used only f o r preheating the furnace a i r supply which primaz&ly pass through the black li q u o r i n d i r e c t contact evaporator i s used as an evaporation media f o r the black l i q u o r . The process has no e f f e c t i v e change i n black l i q u o r pH. Any sulf u r gases picked up from the evaporator virill be burned i n the furnace, thus black li q u o r oxidation i s not required. 2.1.6 Emissions from the recovery furnace The purpose of the recovery furnace i s to burn the concentrated black liquor, and to recover sodium and s u l f u r as sodium carbonate and sodium s u l f i d e . Useful steam i s also produced at this stage. A recovery furnace i s usually composed of three sections: the drying and pyrolysis zone, the reducing zone, and the o x i d i z -ing zone. Each section i s designed f o r the purpose of supplying the reactants required to achieve the end results (90, 93)• The concentrated black liquor (65-70% s o l i d s ) i s introduced into the furnace drying zone where the remaining water i s evaporated. The pyrolysis of black liquor produces large amounts of hydrogen su l f i d e and a large number of organic sulf u r compounds (33, 56, 68). The pyrolysis reaction combines the oxidation and reduction stages because of introduction of primary a i r . In the pyrolysis zone the su l f u r compounds are either oxidized to the appropriate oxidation state of the p a r t i c u l a r sodium s a l t or reduced to v o l a t i l e s u l f i d e s (140). The oxidized s u l f u r s a l t s w i l l f a l l into the reducing zone where the oxidized state s u l f u r i s further reduced to sodium s u l f i d e . The v o l a t i l e s u l f i d e s formed i n the pyrolysis zone are carried into the upper region of the oxidation zone where the sulfides are either oxidized to sulfur dioxide or are p a r t i a l l y discharged to the atmosphere d i r e c t l y . If the furnace i s properly operated, the v o l a t i l e s u l f i d e s w i l l be oxidized to sulfur dioxide i n the oxidation zone. When the oxidation zone i s improperly operated, complete s u l f i d e oxidation w i l l not occur and the sulfides may escape unchanged from the furnace (iko). This results i n considerable sulf u r loses and a i r p o l l u t i o n i n the form of sulfur dioxide and s u l f i d e s . Variables a f f e c t i n g sulfur emissions from the recovery furnace were extensively studied by Blosser e_t a_l. (30), Harding and Landry (82), Murray and Rayner (1^0) and Thoen e_t a l . (198). A s i g n i f i c a n t c o r r e l a t i o n was found between sulfu r emissions and furnace operation variables, such as black l i q u o r f i r i n g rate, r a t i o of secondary a i r to black li q u o r f i r i n g rate, per cent excess oxygen i n furnace f l u e gases, black li q u o r spray droplet si z e , turbulence within recovery furnace and r a t i o of sodium to s u l f u r i n the black l i q u o r . Recovery furnaces are rarely operated at t h e i r optimum conditions (140). Ranges of emissions as estimated under non-optimum conditions are given i n Table 2.2 (90). Under optimum conditions s u l f u r dioxide (0.04-0.08ppm) was the only sulf u r containing gas detected by Thoen e t . a l . (198). Newer developments, described by Arhippainen and Jungerstam (16), Clement and E l l i o t t (38), and Lankenau and Flores (112), are concerned either with elimination of the d i r e c t contact evaporator (16, 112) or use of newer furnace designs (38). The use of recovery b o i l e r , i n conjunction with economized surface to recover heat from f l u e gases, has been shown to provide acceptably low t o t a l reduced sulf u r emissions and i s claimed to provide f o r odor free sulfate cooking (29). 2.1.7 Smelt d i s s o l v i n g tank emissions Hydrogen s u l f i d e and organosulfide emissions from -18-th e smelt d i s s o l v i n g tank are minor (Table 2.2) (90) and usually command l i t t l e concern. Under normal operating temperatures, the smelt contains only hydrogen s u l f i d e . Organosulfides detected i n the off-gases are incidental and have been traced to dra f t i n g gases from the reducing zone of the furnace into the smelt tank and recycle water coming from evaporator condensates containing organosulfides. 2.1.8 Emissions from the lime k i l n Lime k i l n emissions have been found (39, 215) to include minor amounts of reduced sulf u r (0.01-0.83 lb/ADT of pulp) or i g i n a t i n g both from the lime mud (193) and the f u e l used to f i r e the unit (90). 2.1.9 Summary In the foregoing sections special emphasis was placed on the formation of various forms of bivalent s u l f u r compounds as potential a i r and water pollutants associated with sulfate pulping. While under the normal operating conditions large quantities of these sulfides appear i n the gas phase, equally important concentrations are detected i n aqueous streams orig i n a t i n g as wash waters, condensates, and unavoidable s p i l l s throughout the whole pulping operation (21). Most of these sulfides are formed p r e f e r e n t i a l l y i n aqueous solution. Their confinement and retention throughout recovery yie l d s s u l f u r i n -19-the form of sodium s u l f i d e useful f o r regenerating necessary cooking chemicals. Such treatments not only increase the over a l l economy of pulp production, but also help to reduce a i r and water p o l l u t i o n . 2.2 Physical and Chemical Treatment of Sulfides i n Aid of A i r and Water P o l l u t i o n Abatement i n Sulfate Pulping of Wood In sulfate pulping about one cubic meter (264 gallons) of digester condensates are formed per air-dry ton of pulp (173). The organic components of the condensate, mainly alcohols, acetone, and terpentines greatly contribute to the BOD load of this e f f l u e n t . Approximately 80 to 85% of the condensate t o x i c i t y i s attributed to hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e (18). The multiple effect evaporators contribute about 4-7 m-V air-dry ton of pulp. Although these condensates represent low BOD loads, t h e i r s u l f i d e content was found to contribute heavily to the discharged effluent t o x i c i t y from sulfate pulp m i l l s (173). Considerable e f f o r t s have been expended during the past decade to remove sulfides from condensates by various procedures. Most of these attempts have involved treatment with a i r and steam (97). On hot-air s t r i p p i n g , most of the sulfur compounds are oxidized and v o l a t i l e substances escape. The e f f i c i e n c y of -2 0-s u l f i d e removal from condensates by hot-air s t r i p p i n g i s over 90% (18, 173). Steam str i p p i n g provides higher e f f i c i e n c y f o r removal of alcohols and acetone than hot-air (80°C) str i p p i n g (18). 2.2.1 Some physical and chemical properties of sulfate pulp m i l l malodorous sulfides Hydrogen s u l f i d e and methyl mercaptan are gases, and dimethyl s u l f i d e and dimethyl d i s u l f i d e are v o l a t i l e liquors at ambient temperature (25°C) and pressure. Hydrogen s u l f i d e and methyl mercaptan can dissociate i n aqueous solutions according to the following equilibriums (126, 169, 176). HgS HS" + H + /2-H/ HS S + H /2-12/ CH SH <dl± CH S" + H + /2-13/ 3 3 Dissociation constants at 100°C i n aqueous solution (l69)» b o i l i n g point, explosive concentration ranges i n a i r (54), and odor thres-hold i n ambient a i r (114) are shown i n Table 2.3. 2.2.2 Oxidation of sulfides The gas phase oxidation of the four s u l f i d e s , hydrogen; s u l f i d e , methyl'mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e , by mixing with a i r , i s explosive within the l i m i t i n g concentrations shown i n Table 2.3 (54). Harkness and Murray (84) -21-have indicated that mixtures of oxygen and dimethyl sulfide o explode when heated to 210 C. Oxidation of hydrogen sulfide with oxygen in gas phase forms elemental sulfur (205). ZHgS + 02 > 2IL,0 + 2S /2-14/ Sulfide ions in black liquor are readily oxidized by air, as well as molecular oxygen (17, 73, 133, 135, 202). The practice of sulfate black liquor oxidation prior to evaporation is a well accepted process used to stabilize sulfides and reduce odor problems of sulfate pulp mills. Black liquor oxidation was found to be accelerated by the presence of catalysts such as phenolic elements of thiolignin (115) and/or iron salts from crossion products (137). The mechan-ism of sulfide oxidation has been proposed by Murray (137, 138) and is believed to involve two stages, wherein sulfide ions are first oxidized to polysulfide. l6s~~ + 70o + 14H 0 » 2S + 280H~. . ./2-15/ C. C O Further, the polysulfide ions are oxidized to form elemental sulfur and thiosulfate at a lower temperature (below 6l°C), or only to thiosulfate at higher temperature (over 71°C). 2S "~ + 2li.O + 0o — > 2 Sn + kOR~ /2-l6/ 8 * 2 8 2S^~ + 902 + 12 0H"^ >8S203"" + 61^0 /2-17/ Elemental sulfur formed during low temperature black liquor -22-oxidation disproportionates in storage to reform some of the original sulfide ions (135, 137). This reduces the effective-ness of black liquor oxidation as a means of odor control, especially over long term liquor storage. Sg + 120H~ >4s~~ + 2S203"" + 6 ^ 0 /2-18 Gas phase oxidation of methyl mercaptan with oxygen between 210 and 26o°C has been studied by Cullis" and Roselaar ( 4 4 ) . The products identified included sulfur dioxide, aldehyde, methanol, methane, carbon monoxide and dimethyl disulfide. The oxidation mechanism has been described as follows (44, 83): CH SH + 0 » CH„S- + HO /2-19/ 3 2 3 2 CftjS' + 02 > CH^  + S02 /2-20/ In aqueous phase, the methyl mercaptan can be oxidized to dimethyl disulfide at ambient temperature in the presence of air as described previously in Eqs./2.5/ and /2.6/. Dimethyl sulfide and dimethyl disulfide gases were found to be practically unreactive to oxygen at ambient temperature. However, Cromwell (42) claimed that oxidation of sulfides can be performed by treatment of the foul gases with ozone. The mech-anism of organic sulfide ozonization was also discussed by Douglass ( 5 4 ) . Further, aqueous solutions of dimethyl sulfide are readily oxidized to dimethyl sulfoxide in the presence of 30% hydrogen peroxide below 20°C (211). At high temperature, dimethyl s u l f i d e can be reacted with oxygen. Harkness and Murray (84) have shown that the reaction i s non-explosive at 195°C, exhibiting an i n i t i a t i o n and a main stage. The major oxidation products from this reaction are sulfur dioxide carbon monoxide, and sometimes formaldehyde. S i m i l a r l y , C u l l i s and Roselaar ( 4 5 ) , studying the gas phase oxidation of dimethyl su l f i d e at 200°C temperature, found that sulf u r dioxide, aldehyde, methanol and carbon monoxide were present among the oxidation products. Gas phase oxidation of dimethyl d i s u l f i d e at 24o°C also had been studied by C u l l i s and Roselaar ( 4 6 ) . The oxidation products were sulfu r dioxide, methanol, carbon monoxide and carbon dioxide. The oxidation of dimethyl d i s u l f i d e with molecular oxygen i n a l k a l i n e aqueous solution in the 25 to 152°C range has been studied by Murray and Rayner ( l 4 l ) . The mechanism i s considered to be base-catalyzed disproportionation to form mercaptide and methyl sulfenic acid (CH^SOH). The l a t t e r substance i s readily oxidized further to methyl sulfonic acid (CH^SO^H). However, the p o s s i b i l i t y of methyl d i s u l f i d e reduces the effectiveness of black liquor oxidation under these conditions ( l 4 l ) . B i l b e r g (26) studied the behavior and formation of t h i o s u l f a t from oxidized and nonoxidized polysulfide black liquors by heating with s u l f i t e . He was able to show that non-oxidized liquors had l i t t l e influence on the amount of th i o s u l f a t e formed, -2 k-whereas the oxidized black liquor resulted i n marked increase i n the thiosulfate content. In summary, proper operation of black li q u o r oxidation, combustion of resident s u l f i d e gases col l e c t e d from the oxidation tower, a i r and steam scrubbing of the digester, blow tank and evaporators condensates, are e f f i c i e n t means of pulp m i l l odor control (92). 2.2.3 Chlorination Malodorous sulfides have been found to react readily with chlorine, both i n aqueous ac i d i c and/or al k a l i n e solutions. The most l i k e l y end products of the c h l o r i n a t i o n are elemental su l f u r , methyl sulfonyl chloride (CH^SO^Cl), dimethyl sulfoxide(CBLSOCH^), and methyl sulfonic acid(CH^SO^CH^)(50,169,205). The c h l o r i n a t i o n of hydrogen sul f i d e gas produces elemental su l f u r . Sulfur dioxide and sulfur trioxide were formed when hydrogen s u l f i d e was chlorinated i n aqueous solution (50, 205). The chl o r i n a t i o n of methyl mercaptan goes through a series of complicated reactions. Douglass (5k) indicated that excess chlorine i n the presence of water formed methyl sulfonyl chloride, methyl sulfonic acid and other unstable intermediate compounds. In case of inadequate chlorine supply, the products would be composed of a mixture of methyl sulfonyl chloride, unreacted mercaptan, dimethyl d i s u l f i d e and methyl methane thiosulfonate -25-(CH SO SCH ). Appropriate reaction mechanisms f o r the formation 3 2 3 of these products have also been proposed (5^)« Products from ch l o r i n a t i o n of dimethyl s u l f i d e are deter-mined by the reaction conditions, p a r t i c u l a r l y by the presence or absence of water. Thus, anhydrous c h l o r i n a t i o n proceeds step-wise with replacement of a l l hydrogens on one carbon atom before any attack at the second carbon atom occurs (lSk). Chlorination of dimethyl s u l f i d e i n the presence of water i s said to be a very complicated reaction. Bennett e_t a_l. (23) have shown that this produces dimethyl sulfoxide, methyl sulfonyl chloride, dimethyl sulfone (CEL^SO^Ej) and methyl s u l f i n i c acid (CH-jSOgH). Mechanisms for these reactions were also proposed by the above authors. The c h l o r i n a t i o n of dimethyl d i s u l f i d e i n aqueous solution produces methane, sulfonyl chloride and methyl sul f i n i c acid (50). Oxidation of the combined r e l i e f and blow gases with chlorine has been practiced, and i t also has proven to be an e f f i c i e n t and r e l a t i v e l y inexpensive method of reducing sulfate pulp m i l l a i r p o l l u t i o n (60). Direct chlorine oxidation of digester condensates and non-condensible gases has been practiced (75). The system includes a f i r s t stage of a i r oxidation i n the presence of water, then treatment of the gases i n a ch l o r i n a t i o n tower, and f i n a l l y washing of the gases with water. The process i s claimed to provide completely odor free operation (201, 205). Recovery furnace odor gases also can be s i m i l a r l y treated with a small quantity of chlorine and washed with water (201). Tomlinson and Ferguson (203) reported odor reductions by passing digester non-condensible gases through a scrubber i n which the absorbant contained residual chlorine i n spent bleach l i q u o r . 2.2.4 Photolysis A number of studies have been devoted to the i r r a d i a t i o n and photolysis of sulfide s i n gas and/or l i q u i d phases. Malodorous sulfide s have been i r r a d i a t e d recently f o r the purpose of eliminating the foul smell from sulfate pulp m i l l s (159, 184). Rayner and Murray (159) studied gas phase photolytic oxidation of methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e as induced by long wave (3,600$t) and short wave (2,537Jt) u l t r a v i o l e t radiation. The experiment has shown that oxidation rates are accelerated by radiation at both wave lengths of radiat i o n . The short wave u l t r a v i o l e t radiation rapidly catalyzed the oxidation of methyl mercaptan and dimethyl s u l f i d e . Strafor-e l l i ejb a_l. (184) studied gas phase gamma r a d i o l y s i s of hydrogen s u l f i d e , methyl mercaptan,dimethyl s u l f i d e and dimethyl d i s u l f i d e i n presence of dry a i r and indicated that a l l s u l f i d e s are f i n a l l y oxidized and possibly precipitated on the container walls. Sulfur dioxide was observed as the common intermediate product f o r a l l s u l f i d e s . Maximum sulfur dioxide concentration was observed usually at 0*2 Mrad. Within the concentration ranges of 50-2000 ppm, complete de s u l f u r i z a t i o n required approximately 0.8 to 1.5 Mrad. 2.2.4.1 Photolysis of hydrogen s u l f i d e There i s strong evidence that H»and HS* are primarily formed by photolysis (2050-2288$) of pure hydrogen s u l f i d e gas (153, 157). HgS + hv » H« + HS* / 2 - 2 l / TheSH»and ,H»atoms may subsequently react to form hydrogen and elemental s u l f u r as shown i n the following schemes (49, 58): H» + H 2S—>H g + R& /2-22/ 2HS* —> H S + S* /2-23/ 2 2HS«—» Hg + S 2 /2-24/ S t i l e s ejb a l . (183), studying the photolysis (2,200 -2,800$) of s o l i d hydrogen s u l f i d e at low temperature (77°K), also confirmed that the primary photolytic step with HgS i s loss of a hydrogen atom, which Was detected by electron spin resonance (E.S.R.). Further, the sulfur chain (*Sn) can be detected by E.S.R* spectra when the photolysis products are warmed to 125°K. The l i q u i d or gas phase addition of HS» to an o l e f i n i c double bond, as promoted by short wave u l t r a v i o l e t radiation (2,800A*), between -78°C and room temperature has been i n v e s t i -gated by Vaughan and Rust(210). The t h i o l i s thought to ar i s e via -2 8-the following chain propagation reactions: HS» + RCH=CH > RCHCH,,SH. /2-2 5/ 2 RCHCH SH + H S > RCHLCH SH + HS» . ../2-26/ 2 2 ^ 2 A si m i l a r reaction also has been confirmed by G-riesbaum ejb a l . (80), who studied the free r a d i c a l addition of hydrogen s u l f i d e to allene. 2.2.4.2 Photolysis of methyl mercaptan Electron spin resonance studies following u l t r a v i o l e t r a d i o l y s i s of s o l i d aqueous solution and pure s o l i d methyl mercaptan at 77°K indicated that the primary photochemical process results i n proton loss from the mercaptan and formation of a t h i y l r a d i c a l (213). CH3SH + hv > CE^S* + H» /2-27/ The reaction also has been confirmed by Inaba and Darwent (98) i n studies concerned with the photolysis of gaseous methyl mercaptan. Products of complete methyl mercaptan gas photolysis were analysed by Skerrett and Thompson (178), and were shown to consist of hydrogen (80%) and methane (18%); the condensible products were elemental sul f u r and dimethyl d i s u l f i d e . The quantum y i e l d of methyl mercaptan disappearance was measured to be 1.7. However, Inaba and Darwent (98) stated that methane (CH^) and elemental sulf u r do not appear as a resu l t of o r i g i n a l photolysis of methyl mercaptan but are due to a secondary processes. The following schemes are proposed by Inaba and Darwent (98) to be the most important events in the photolysis of methyl mercaptan. CH SH + hv — > C E S* + H*., /2-28/ 3 3 H« + CILjSH—» CH^ S* + H2 , / 2 - 2 9 / 2CH S' > CH SSCH / 2 - 3 0 / 3 3 3 2.2.4 .3 Photolysis of dimethyl sulfide The primary mechanism of dimethyl sulfide photolysis was found to be exclusively C-S bond cleavage. Mercury photosensitized decomposition of pure dimethyl sulfide vapor was investigaed by Jones ejb al_. ( 1 0 0 ) , using mass spectro-inetric techniques. The products, ethane (4l%), dimethyl disulfide ( 2 9%)» methyl mercaptan (12%) and methane (3%)> together with thiof ormaldehyde (not measured), were accounted for by simple combination-disproportionation reactions of the CH^  and CH^ S" fragments. Similarly, Ogoro and Inaba (148) studied the effect of photolysis time, temperature, pressure and presence of argon or nitric oxide (NO) on the radiolytic degradation of dimethyl sulfide gas. The major products were methane, ethane,' methyl mercaptan and dimethyl disulfide. Ethane and hydrogen sulfide were formed only at high temperature photolysis (above 250°C). -30-Th e possible reactions have been proposed as follows! * /2-31/ /2 -32 / /2-33/ CH^SGH + hv •> CH SCH, 3 CH S* 3 CH» 3 H S (above 250°C) 2.2 .4 .4 Photolysis of dimethyl d i s u l f i d e The d i r e c t photolysis of organic d i s u l f i d e s both i n vapour and l i q u i d phases has been investigated. The primary step of photolytic decomposition was shown to be form-ation of two t h i y l radicals by homolytic S-S bond cleavage. The photolysis of vapor phase dimethyl d i s u l f i d e i n the presence of ethylene (C H, ) and acetylene (C0Ry) was f i r s t 2 4 - * * investigated by Ueno and Takezaki (209). No pressure change was observed i n the reaction with ethylene, while with acetylene an obvious pressure decrease was observed. Smissman and Sorenson (179) were able to demonstrate the E.S.R. spectra of a number of t h i y l radicals (RS») produced by u l t r a v i o l e t i r r a d i a t i o n of several l i q u i d phase d i s u l f i d e s , including that of dimethyl d i s u l f i d e i n chlorobenzene solution at 77°K. These results have been confirmed by Rao ejb a l . (158) i n a study of the effect of pressure (2-25 torr) and temperature (28-l86°C) on the photolysis of dimethyl d i s u l f i d e at 2,300 to 2,800A, and at 2,288$ wave lengths. The following photolytic schemes have been shown to be possible: - 3 1 -CH^SSCH^ + hv—>2CU ^ S * / 2 - 3 ^ / CH SSCH + CHS*—> CH SH + •CHSSCH / 2 - 3 5 / 3 3 3 3 2 3 •C^SSCH^ + CH^SSCH^—> polymer / 2 - 3 6 / Jones e_t a l . ( 1 0 0 ) , i n studies of mercury photosensitized decomposition of dimethyl d i s u l f i d e vapour, found two primary decomposition mechanisms as S-S cleavage (80%) and C-S cleavage (20%). The major products involve dimethyl s u l f i d e (27%), dimethyl t r i s u l f i d e (26%), methyl mercaptan (22%), ethane (13%) and methane (2%). Thioformaldehyde (CH^S), methyl hydrodisulfide (CH^SSH) and carbon d i s u l f i d e are also produced but were proposed by suitable self- and cross-combination and disproportionation reactions of the primary fragments CH^, CH^S», and CH^SS\ 2.3 Gamma Radiolysis of Water Gamma rays are electromagnetic radiation of very short —8 -11 wave length (10 -10 cm) and hence of great photon quantum energy. The r e l a t i v e position of gamma rays i n the spectrum of electromagnetic radiation i s shown i n Fig . 2.1 ( 1 6 3 ) . In gamma radiation, only part of the radiation energy may be transferred at an inter a c t i o n s i t e and the process i s not selective. There i s s u f f i c i e n t energy available to break any bond, but i n practice c e r t a i n bonds are broken p r e f e r e n t i a l l y . The ion i z i n g photon or p a r t i c l e and the displaced electron are often both capable of producing further i o n i z a t i o n . Thus, one incident -32-photon may a f f e c t many thousands of molecules. The passage of gamma radiation (about 1 Mev) through water or d i l u t e aqueous solutions gives i n i t i a l electrons, p o s i t i v e l y charged water ions and excited water molecules which are produced by Compton scattering and by the photoelectric effect (9, 91, 1^7, 180). ^ O A V — > e ~ , HgO*, R"20* /2-35/ The electrons lose energy by further c o l l i s i o n s u n t i l they reach thermal energy (0.025ev) and are then solvated. These events -11 take about 10 second. e" + nH 0 — > e~ /2-36/ 2 aq ' ' The posi t i v e ions, R"20 , are energetically unstable and decompose + -13 to H ions and H0» radicals i n about 10 second. H 0 + > H + + H0» /2-37/ 2 or H 0 + + H 0 > H 0» + HOt /2-38/ 2 2 3 ' ' The excited water molecules may exist f o r microseconds only and then decompose to H« atoms and H0« radicals or perhaps undergo i o n i z a t i o n . ^ 0 * > H» + HO*. /2-39/ H20* > e" + H 20 + /2-kO/ Within the spurs containing e , H« and EOy the various a Q. — + fragments may react to form H , HO , H 0«, OH , H-0 and HUO 2 ^ 2 3 as shown i n the following schemes. -33-H' + H' > 2 H0« HO' ^ H2°2 e~ aq + H 3 O * — » H 0» 3 e aq + 6aq % e aq + HO' > H> HO« > V>,.; 2 OH' /2-44/ 2.3.1 Molecular products The molecular products, hydrogen (H 2) and hydrogen peroxide (H^O^, are formed i n a spur, but both Hg and HgOg are decomposed by a chain reaction. The hydrogen gas escapes readily, whereas the hydrogen i n solution can further react with oxidizing radicals (HO'). H 2 + HO'—> HgO + H* /2-47/ Hydrogen peroxide generally reacts with the reducing species (e~ , H«). aq HgOg + e~ q > H0« + H0~ /2-48/ ^Og + H» > HO* + HgO* /2.49/ and on escape of hydrogen from the solution, oxygen i s produced. H 20 2 + HO' > ^ 0 + H0» /2-50/ HO* + H0|—> E202 + 0 2 /2-51/ H0| + H0»  >E2° + °2 /2~52/ The molecular hydrogen peroxide i s usually retained i n solution, and becomes available for reaction with solutes. -34-2.3.2 Primary r a d i c a l species Both the hydrated electron ( e a q ) and hydrogen atom (H») are powerful reducing agents, while the hydroxyl r a d i c a l (HO) i s a powerful oxidizing agent (123). The solution pH has a considerable effect on formation of primary r a d i c a l species. In neutral solution, the reducing radicals are hydrated electrons and hydrogen atoms. In acid solution, the hydrated electrons are readily converted to hydrogen atoms (104). e" + H + « Z ± RY /2~53/ aq In solution, above pH 13, the hydrated electrons are the only reducing species (124). H« + 0H~ > e~ /2-5^/ aq Both hydrated electrons and hydrogen atoms are present i n the range of pH 4-11, while the hydrogen atom i s the important reducing species below pH 2(l47). Hydrated electrons react with CO^ at a high rate (k 7.7 9 -1 -1 x 10 M sec ) (77). C°2 + % > C ° 2 ~ / 2 " 5 5 / The COg thus formed i s able to add to organic radicals to form carboxylates (172, 217). Saturated hydrocarbons, as well as alcohols, are unreactive toward e . Hydrated electrons were shown to be the most aq J e f f i c i e n t nucleophiles, whereby, they may react with carbon atoms -35-adjacent to any double bond. The f a i r r e a c t i v i t y of e~ with aq aldehydes and ketones i s found to be due to the p o s i t i v e l y polarized carbon on carbonyls. In reaction with aromatic compounds, e acts as a very reactive nucleophilic agent (10, aq 172). The hydrogen atom (H«) i s a reducing agent, but i t i s not as strong as the hydrated electron (1^7)• Main reactions of the hydrogen atom with organic compounds are hydrogen abstraction and additions to double bonds or rings: RH + H » — » H + R» , /2-56/ 2 ArH + H*—» H-ArH /2-57/ The p r i n c i p a l oxidizing species found i n the gamma r a d i o l y s i s of water i s the hydroxyl r a d i c a l (HO' ) (9, 1^7, 180). In the absence of solutes, H0»reacts with reducing r a d i c a l s , as shown in Eqs. /2-45/ and /Z-kSf and addition reaction shown i n Eq. /2-42/. In the presence of solutes, the oxidiz-ing agents undergo four types of reactions, such as charge .transfer, hydrogen abstraction addition or displacement. The presence of hydroperoxyl radicals (HOg^ i n t h e S a m m a r a d i o l y s i s of deaerated water has been demonstrated through the following scheme: H0» + H 20 2 > H 20 + H02 /2-58/ -36-Th e hydroperoxyl r a d i c a l i s an acid with a pK value of 4.5 (47). It i s formed i n acid solution, whereas 0^ i s formed only i n neutral solution (47» 91). + "" HC» H + 0. /2-59/ £ 2 It also gives respectively hydrogen peroxide and water by reaction with i t s e l f and the H 0 »radical. HO* + HO» i—» HO + 0 /2-60/ 2 2* 2 2 2 H0« + HO > HO + 0o /2- 6 l / 2 2 2 2.3.3 Radiolysis of oxygenated water In gamma r a d i o l y s i s of aerated aqueous solution secondary r a d i c a l s , such as 0* , HO* , H 0~ and 0^, are formed * 2 2 (47, 91). The 02 i s formed by reacting molecular oxygen with the hydrated electron: 0 + e~ > Or, /2-62/ 2 aq 2 1 1 The molecular oxygen has been found to be a very e f f i c i e n t scavenger f o r the hydrogen atom to form hydroperoxyl r a d i c a l , the acid form of the product 02• 02 + H. > HO^  /2-63/ Further, hydrogen sesquioxide (IL^O^) i s postulated to form via the following scheme: H0» + HO* * H 0 /2-64/ 2 2 3 The ozonized ion r a d i c a l (0^) i s formed i n the r a d i o l y s i s of the oxygenated alkaline solution (47). In alk a l i n e solution, -37-0H~ reacts with H0» r a d i c a l to form 0~. The ozonized ion r a d i c a l i s further formed by reaction of O with oxygen. OH" + HO' 2Zt HO + 0'. / 2- 65/ 2 0" + 02 > Oy /2-66/ From the foregoing, i t becomes evident that pH has a si g n i f i c a n t effect on the y i e l d of molecular and ra d i c a l y i e l d i n aqueous solutions. Thus the ra d i c a l products of H«and HO', as well as the molecular products H and IL,0 are varied according 2 ^ 2 to d i f f e r e n t pH of the media (87). The hydroperoxyl r a d i c a l (HO^) is formed i n acid solution, but i t s d i s s o c i a t i o n reaction to Oj" occurs i n neutral solution (Eq. /2-59/) (47). The hydroxyl r a d i c a l (H0-) behaves l i k e an acid at high a l k a l i n i t y to form 0~ (Eq. /2-65/) (47). In addition, both hydrogen atoms (H« ) and hydrated electrons (e~ ) exist i n neutral solution. In acid solution, e~ i s converted aq aq to H* (Eq. /2-53/), whereas i n solution above pH 13, H«is readily reacted to form e" (Eq. /2-54/) (10). The yie l d s (G) of radicals and molecular products (e~ , H*, aq HO*, H^, K^O^) i n the gamma i r r a d i a t i o n of water appear to be a function of solution pH (87). A l l yie l d s tend to decrease with increase i n pH, except G(HO-) and G(H») which increase from neutral to acid and from neutral to alka l i n e media. -38-2.4 Radiolysis of Sulfides i n Aqueous Solution Sulfate black liquors usually contain low concentrations of organic malodorous sulfide s and f a i r l y high concentration of inorganic s u l f i d e . Physico-chemical d i s t i n c t i o n s of gamma ra d i o l y s i s of sulfides i n black liquor have not been reported, although radiation chemistry of organic s u l f i d e s , contained i n b i o l o g i c a l systems, have been studied quite widely. It i s this area of interest that provides useful examples to the r a d i o l y s i s of malodorous sulfides as contained i n numerous i n d u s t r i a l effluents, p a r t i c u l a r l y that of kraft m i l l black l i q u o r . Very low concentrations of sulfides were found e a r l i e r to protect other materials against destruction by gamma radiation i n aqueous solution (165, 220). The sulfur linkage i s p a r t i c u l a r l y reactive toward free radicals and i s l i k e l y to be s e l e c t i v e l y damaged by radiation (I87). Considerable information i s available on radiation chemistry of simple organic s u l f i d e solutions, as well as more complicated structures such as sulfhydryl-containing enzymes. The high energy of X- and gamma-ray radiolyses of hydrogen su l f i d e i n aqueous solution forms elemental sulf u r (117, 122). Sulfate was also obtained as the higher oxidation product by -39-Nanobashivili and Gvilava (1^5) and Nanobashivili ejb al_. (l44) on X- and gamma r a d i o l y s i s of various metallic s u l f i d e solutions (sodium, potassium, ammonium, etc.) and aqueous suspensions of su l f i d e minerals (pyrites, sphalerites and galenites). These results were confirmed by Markakis and Tappel (122). The possible intermediate products and reaction rates of hydrogen su l f i d e and radicals produced by pulse r a d i o l y s i s of water were studied by Karmann ej; a_l. (103), who found also that polysulfide ions existed. Radiolysis of mercaptans has also been considerably invest-igated. X- and gamma-ray radiation of butyl-, amyl- and hexyl-mercaptans, and thiophenols formed corresponding d i s u l f i d e s and sulfate ions (l44, l45). The gamma r a d i o l y s i s of amino acid cysteine (HSCEL,CHNHgCOOH) has been extensively studied because of i t s association with b i o l o g i c a l protective agents (20, 48, 186, 219, 220). Swallow (186) investigated the gamma radiation of cysteine hydrochloride solution i n aerated and deaerated aqueous solution. In a i r saturated solutions, irradiation>of cysteine was shown to produce cystine via a chain reaction. These findings were further confirmed by Barron and Flood (20) i n that the oxidation of t h i o l s by gamma radiation may be considerably increased i n oxygenated solutions. -40-Th e formation of hydrogen s u l f i d e from gamma r a d i o l y s i s of cysteine aqueous solution has been investigated by Dale and Davies (48), as well as Whitcher e_t a l . (219). Markakis and Tappel (122) quantitatively i d e n t i f i e d the products of gamma ra d i o l y s i s of aqueous cysteine solutions i n the presence and absence of oxygen. They found cystine, hydrogen s u l f i d e , elemental sulf u r and sulfate ion as the products of r a d i o l y s i s . The chemcial reactions accompanying r a d i o l y s i s of dimethyl s u l f i d e are reduction and oxidation by radicals through water r a d i o l y s i s . Meissner e_t a_l. (129) have determined the absolute rate constants existing between reactions of hydroxyl radicals (H0«) and hydrated electrons (e~ q) formed with respect to pulse r a d i o l y s i s of dimethyl s u l f i d e i n aqueous solutions. The effects of solution pH and oxygen on formation of intermediate products, - - + such as CHtjSCHg, CR^SOCH^ and (CH^SCR^Jg, were discussed. The r a d i o l y s i s of d i s u l f i d e i n form of cystine has been considerably investigated. The d i s u l f i d e bond was found to be p a r t i c u l a r l y sensitive to io n i z i n g radiation. Protein damage i s readily averted by the r a d i o - s e n s i t i v i t y of cystine which i s contained i n usual b i o l o g i c a l systems. The protection against radiation i s generally afforded through the ready reaction of the d i s u l f i d e with the radicals available i n aqueous systems (165). - U n -i o n i z i n g radiation of the organic d i s u l f i d e s cystine i n acid i c aqueous solutions produces the t h i o s u l f u r i c acid (CySSO^H) through f i s s i o n of the C-S bond, s u l f i n i c acid (CySOgH) and cysteic acid (CySO^H) through f i s s i o n of the S-S bond (69, 78, 175). Markakis and Tappel (122) i d e n t i f i e d cysteine (CySH), hydrogen s u l f i d e , elemental sulf u r and sulfate ions from gamma r a d i o l y s i s of a c i d i f i e d cystine aqueous solutions. A more detailed i n v e s t i -gation of gamma r a d i o l y s i s of cystine aqueous solutions has been performed by Purdie (156). Yields (G) were determined f o r the following products: CySO H(0.3-1.7), CySO H(0-1.2), CyS02SH(0.05-2 j c-0.1), CySS03H(0.1-0.1), CySH(0-2.5) and CySSSCy(1.3-5.6). Mechanisms f o r the above radio-chemical reactions were also presented and discussed. Their relevance to the treatment and s t a b i l i z a t i o n of black liquor sulfides through the p a r t i c u l a r r a d i o - s e n s i t i v i t y of the C-S and S-S bonds i s believed, thereby, to be demonstrated. 2.5 Reaction of Sulfides with Hydrocarbons Induced by Gamma Radiation i n Black Liquor Black li q u o r i s a very complicated solution. In addition to sulfur compounds, i t contains various organic components and component fragments such as sugars, l i g n i n , extractives and th e i r derivatives. During gamma r a d i o l y s i s of black liquor, organic radicals can be formed either d i r e c t l y by photon attack or -42-i n d i r e c t l y by hydrogen atom abstraction as i n i t i a t e d by H>and HO made available through r a d i o l y s i s of water. Organic radicals are considered to be very reactive toward su l f i d e compounds. The reactions operate either through abstraction of one hydrogen atom from the su l f i d e compounds to form s u l f i d e r a d i c a l s , or by addition to the su l f i d e compounds by di r e c t attack on the su l f i d e bond. The addition reaction, as the most favorable reaction, has been demonstrated by Pryor and Guard (15^)» and Pryor and Pickering (155), although the reaction mechanism i s s t i l l not cl e a r f o r this process i n black l i q u o r . Pryor and Pickering (155) have demonstrated, however, that the reaction may occur with p o l y s t y r y l radicals and various d i s u l f i d e s (methyl, ethyl ... etc.) at the S-S bond and by a reaction that could be regarded as a d i r e c t displacement: M« + RSSR—» M-SR + RS': /2-67/ Pryor and Guard (15*0 demonstrated the reaction of phenyl radicals with d i s u l f i d e i n two schemes: either by attack on the d i s u l f i d e bond (Eq. /2-67/ or by hydrogen abstraction (Eq. /2-68/). M« + RSSR > M-H + RSSR*. /2-68/ The attack of radicals on the d i s u l f i d e bond usually occurs to a larger extent than hydrogen abstraction. Pryor and Guard (15*0 confirmed that the reaction rates of phenyl ra d i c a l s with d i s u l f i d e bonds i n dimethyl- and die t h y l d i s u l f i d e were as high as 98% and 93%, respectively. -k3-Other possible reactions able to increase the molecular weight of sul f i d e s are addition of t h i y l radicals (HS» and CELTS') to large molecular weight hydrocarbons. Addition of the methane sulfenyl r a d i c a l (CH^ S*) to derivatives of cyclohexene and but y l -methyl sulfides have been i l l u s t r a t e d by Readio and Sk e l l ( l 6 l ) and Huyser and Kellogg (96). Addition of benzenethiol (CgH^S*) to allene has also been shown by Heiba (88). The sulfhydryl radicals (HS*) which are able to add to allene and conjugated o l e f i n s , have been demonstrated by Griesbaum et. a l . (80). 2.6 Gamma Radiolysis of Pulp M i l l E f f luents Only one previous publication (113) treats r a d i o l y s i s of aqueous pulp m i l l e f f l uents. However, the work does not deal d i r e c t l y with i o n i z i n g radiation effects on chemical reactions, but investigated some p r a c t i c a l aspects (residual color and'COD, ) of i r r a d i a t e d e f f l u e n t s . Thus Lenz e_t a l . (113) investigated the effects of gamma radiation of aerated, strong and weak effluents o r i g i n a t i n g from effluent streams of sulfate linerboard and neutral s u l f i t e semichemical (NSSC) m i l l s . The extensive treat-ment (approximately 16-32 Mrad) s i g n i f i c a n t l y removed and even eliminated effluent color, and simultaneously reduced the l e v e l of chemical oxygen demand (COD) to 50 to 80% of the o r i g i n a l . Further, the treatment brought the solution pH within the neutral range and promoted f l o c c u l a t i o n and p r e c i p i t a t i o n of s o l i d s . 3.0 MATERIALS AND METHODS 3.1 Model Compounds Recent chemical analyses of sulfate black liquors con-s i s t e n t l y show the presence i n varying amounts of hydrogen su l f i d e ( H 2 S ) , methyl mercaptan (CH^SH), dimethyl s u l f i d e (CH^SCH^), and dimethyl d i s u l f i d e (CH^SSCH^) (67). Hydrogen sul f i d e and methyl mercaptan are present as sodium s a l t s i n a dissolved state under alkaline conditions, but are e a s i l y freed from the solution upon neutralization and a c i d i f i c a t i o n . Dimethyl s u l f i d e and dimethyl d i s u l f i d e can be stripped quantitatively from t h e i r respective alkaline solutions both by degassing with nitrogen or by l i q u i d / l i q u i d extraction techniques. Due to the complexity of black liquors, the c a l i b r a t i o n of a n a l y t i c a l techniques, as well as most r a d i o l y s i s experiments of the present study, were carr i e d out on model systems including the above mentioned substances. Further reagents, such as sodium hydroxide (NaOH), s i l v e r n i t r a t e (AgNO^), 95% ethanol (CgH^OH), k0% hydrochloric acid (HCl), boric acid (H^BO^), carbon dioxide (C02) and oxygen gas were secured from l o c a l chemical supply houses. A l l chemicals were reagent grade and the water used f o r d i l u t i o n / d i s s o l u t i o n was d i s t i l l e d water. -45-3.2 Black Liquors For p r a c t i c a l extrapolation of results some commercial black liquors were analysed. Further, to observe the range of. the v a r i a t i o n i n the four major sulfate black liq u o r s u l f i d e s (HgS, CHL SH, CH SCH and CH SSCEL ), liquor samples were secured from 3 3 3 3 ^ four d i f f e r e n t m i l l s of one company and one further sample was obtained from another company, as well as one from p i l o t cooking conducted by the Western Forest Products Laboratory (Vancouver), Pulping Section. In addition, two polysulfide black liquors were obtained from vapor and l i q u i d phase cookings done by the Pulp and Paper Research Institute of Canada, Montreal, P.Q. The respective black liquors were shipped i n polyethylene containers during the winter months (November, December), immediately recharged upon a r r i v a l into sealed glass containers and stored i n a cold storage room at 5°C i n the dark. The source and composition of respective black liquors can be found i n Table 3.1. 3*3 Analysis of Aqueous Sulfide Solutions On reviewing the pertinent l i t e r a t u r e on s u l f i d e analysis two points became c l e a r : (1) The a n a l y t i c a l techniques hitherto proposed are f a r from quantitative, and (2) f o r complete analysis of sulfides i n aqueous al k a l i n e solutions at least two methods have to be used. Reasons for this were b r i e f l y mentioned i n the introduction of model compounds. Thus, under these conditions -46-two methods of analysis were used fo r characterising black liq u o r s u l f i d e s . 3.3.1 Potentiometric determination of sul f i d e s i n sulfate black liquor The pulping industry i s not the f i r s t to run into problems of s u l f i d e analysis (182). Early papers o r i g i n a t i n g with the petroleum industry deal with this problem as related to MSweetening": .or' deaulf.urizaltion of gasoline. The a l k a l i n e extracts of raw gasoline are found to contain sodium s u l f i d e , mercaptans and organic sulfides and are thus, except fo r l i q u i d and other organic solutes, somewhat similar to sulfate pulping black l i q u o r s . F i r s t e f f o r t s of potentiometric p r e c i p i t a t i o n of heavy metal sulfides are reported by Dutoil and Weiss (57) • The use of s i l v e r n i t r a t e as t i t r a n t was f i r s t reported by Treadwell and Weiss (204) i n 1919, and applied to pulping black li q u o r analysis by Borlew and Pascoe (31) i n 1946. The s i l v e r n i t r a t e method was substantially improved by Tamele and co-workers (190, 191, 192) f o r hydrogen s u l f i d e i n mixture with mercaptans and was further refined f o r the analysis of dissolved s u l f i d e s i n pulping black liquors by Bilberg (26) and C o l l i n s (40). The great popularity of the s i l v e r n i t r a t e method i s due to the large i n s o l u b i l i t y and easy f l o c c u l a t i o n of s i l v e r s u l f i d e i n -k7-ammoniacal a l k a l i n e solution and the accuracy by which potential changes accompanying formation of such precipitates can be followed. For c l a s s i c a l t i t r a t i o n s the analysis i s c a r r i e d out in sodium acetate buffered solutions using a potential c a l i b r a t e d s u l f i d e coated s i l v e r electrode (190). To date, d i f f i c u l t i e s were reported i n locating the proper end points i n s u l f i d e ion t i t r a -tions by c l a s s i c a l methods. Since the t i t r a t i o n curve i s asymmetrical, an unusually large and rapid drop i n potential i s shown without a readily detectable i n f l e c t i o n point just p r i o r to reaching the equivalence point. To further aggrevate the problem, sat i s f a c t o r y results are obtained only with 0.002 M or greater s u l f i d e concentrations; large errors arise below this l i m i t i n g concentration of s i l v e r s u l f i d e (111). To resolve some of these d i f f i c u l t i e s several modifications of the s i l v e r n i t r a t e method have been proposed. The TAPPI Standard T625 ts-64 (13) gives the closest procedure to that proposed by Borlew and Pascoe (31). Coshen and Bauman (37) determined s u l f i d e and mercaptan i n black li q u o r by employing a< vacuum tube c i r c u i t and a "magic eye" or tuning control tube f o r detecting the sharp potential i n f l e c t i o n occuring at the equiva-lence points. Olsson and Samuelson (1^9) used anion exchange re s i n to separate the s u l f i d e from the organic constituents (non-sulfur) of black l i q u o r . The sulfides retained on the resi n -48-are sequentially eluted and quantitatively determined by potentiometric t i t r a t i o n with mercuric chloride (HgCl 2) i n the presence of sodium hydroxide. Swartz and Light (188) studied the s u l f i d e ion-selective electrode as an a n a l y t i c a l tool f o r the analysis of s u l f i d e i n black liquor, and claimed that s i l v e r reduction also occurred. Bilberg (26), comparing the black liquor potentiometric t i t r a t i o n of s i l v e r n i t r a t e , mercuric chloride and cadmium sulfate (CdSO.), found that the method based on mercuric chloride 4 t i t r a t i o n gave the least effect with components i n black liquors other than the s u l f i d e . Frant and Ross (70) recently proposed the use of an anti-oxidant solution for storing black l i q u o r . Further, a known cadmium a c t i v i t y solution i s added to the black liquor and the s u l f i d e i s determined quantitatively by measuring the decrease of cadmium a c t i v i t y i n the solution with a cadmium a c t i v i t y electrode. Other methods, such as that by Bethge e_t a l . (24) f o r the colorimetric determination of hydrogen s u l f i d e and mercaptans i n i n d u s t r i a l effluents, have been proposed recently. Although precision and accuracy were found to be s a t i s f a c t o r y f o r hydrogen s u l f i d e , inaccuracies were reported i n simultaneous determinations with methyl mercaptan due to the expected short l i f e of mercaptan complexes formed i n the presence of hydrogen s u l f i d e and some interference of oxygen. Thus, the potentiometric -49-t i t r a t i o n with s i l v e r n i t r a t e i s accepted as the easiest and most accurate s u l f i d e determination method i f correct i n t e r -pretation of the t i t r a t i o n curve i s made. 3.3.1«1 Experimental 3<3*1«1*1 Apparatus The potentiometric t i t r a t i o n apparatus used i n these studies was manufactured by the Radiometer Cooperation, Copenhagen, Denmark, and consisted of a Model TTT-11 Automatic T i t r a t o r and Type ABU-1 Autoburette unit coupled with an X-Y recorder for automatically recording t i t r a n t volume and associated change i n p o t e n t i a l . The electrodes were Corning t r i p l e purpose glass electrode (No. 476024) (119) and Radiometer type s i l v e r -s i l v e r electrode (P4011, KT). The s i l v e r s u l f i d e electrode was prepared by e l e c t r o l y t i c a l l y coating a layer of s i l v e r s u l f i d e (AgS) on the s i l v e r electrode (31). 3.3.1.1.2 Theory of s i l v e r n i t r a t e potentiometric t i t r a t i o n The s o l u b i l i t y product or ion product constant of s i l v e r s u l f i d e i s extremely low (K = 1.6 x IO"**9. 25°C). The sp a c t i v i t y product (a ) of the s i l v e r ions (a f t +) and the s u l f i d e S p A g ions (a — ) i s constant at a p a r t i c u l a r temperature: s - 2 . a = a + • a / 3 - l / -50-Th e t i t r a t i o n c e l l consists of a s i l v e r s u l f i d e - s i l v e r electrode and a high pH glass reference electrode. The c e l l may-be written as; Ag/AgCl/' 0.1N HCl// Sample Solution// AggS/Ag /3-2/ The difference of potential between the two electrodes when both are immersed i n a solution containing s u l f i d e ions (S ) can be expressed as: E = K + ^ l n a A g+ or E x = K - - f f l n a s " _ /3-3/ Where: E^ = potential = constant R = gas constant T = absolute temperature F = faraday It should be noted that the su l f i d e ion a c t i v i t y (a — ) i n S Eq. /3-3/, being a strong base, w i l l contribute to the acid/base balance i n accordance with the following schemes: -51-Eq. /3.3/ also indicates that the potential difference (E ), i s dependent on the s u l f i d e ion a c t i v i t y ( a — ) . Tamele 1 a  et a l . (190), studying behaviour of the s i l v e r electrode i n potentiometric t i t r a t i o n of su l f i d e ions i n cases of extreme d i l u t i o n , indicated that i f the solution contains hydrosulfide ion (HS~) concentrations below 10~^N, the high negative potential drops abruptly on further d i l u t i o n and approaches a low constant value. Thus, the l i m i t i n g concentration f o r normal s u l f i d e ion response i n potentiometric t i t r a t i o n becomes lO'-^N or greater, i f spurious behaviour i s to be avoided. In t y p i c a l analysis, to a 150 ml beaker equipped with a magnetic s t i r r e r , 20 ml of 20% sodium hydroxide, together with 5 ml of about 30% aqueous ammonium hydroxide solution, and a layer of paraffine o i l was needed. Under continued s t i r r i n g an aliquot of the s u l f i d e sample containing at least 0.005 g of sodium s u l f i d e (equivalent to about 2 ml of strong black liquor) was injected into the solution by using a 5 ml syringe. The sample was then t i t r a t e d with 0.05 or 0.1 N s i l v e r n i t r a t e solution. The volume of t i t r a n t and potential read-out were recorded automatically on the recorder in the X-Y mode. The end point f o r the mono-sulfide was read at the f i r s t i n f l e c t i o n of the t i t r a t i o n curve. The reactions f o r the t i t r a t i o n are as followst S"~ + 2Ag+ > Ag 2S (black ppt)... CH^S" + Ag +—>CH SAg (yellow ppt) /3-6/ /3-7/ -52-The following calculations give s u l f i d e and mercaptan i n grams per l i t e r ( g / l ) : ml of AgNO (0.05N) Na2S = 1.951 x /3-8/ ml of liquo r sample ml of AgNO (0.05N) or H S = 0.852 x 3 /3-9/ 2 ml of liquor sample ml of AgNO (0.05N) CH3SNa = 3.505 x i /3-10/ ml of liquor sample ml of AgNO (0.05N) or CH^SH = 2.405 x 3 / 3 - l l / ml of liquor sample The potentiometric t i t r a t i o n curves f o r four sulfate and two polysulfide black liquors are shown i n Fig« 3*1. Obviously, two i n f l e c t i o n points "a" and "b" can be i d e n t i f i e d as s u l f i d e t i t r a t i o n end points. According to usual reading of these curves, black liquor shows mercaptan content. By convention (67, 188), i n f l e c t i o n point "b" i s taken as endpoint f o r c a l c u l a t i n g the solution s u l f i d e content. The difference of reading between i n f l e c t i o n points M a w and wb" can af f e c t the s u l f i d e c a l c u l a t i o n as shown i n Table 3.2. This indicates that gross errors are -53-introduced by the practice of reading i n f l e c t i o n "b" f o r mono-sul f i d e c a l c u l a t i o n s . This w i l l be discussed further i n a la t e r section. 3.3.1.1.3 Interpretation of t i t r a t i o n curves The behavior of s u l f i d e ions i n black liq u o r i s complicated. Trace quantities of elemental s u l f u r may exist i n both white and black l i q u o r s . The elemental s u l f u r also may be formed by oxidation of black liquor monosulfides on contact with a i r . The secondary reaction with methyl mercaptan i s considered as follows (102): CH S~ + S° » CH^SS" /3-12/ S~" + so; , > S~~ /3-13/ n-1 n Their effect on su l f i d e determination by s i l v e r n i t r a t e potentiometric t i t r a t i o n i s proposed as (102): + 2CEL.SS + 2Ag 2CH 3SSA g 2CH SSAg > Ag S + CH SSSCH 3 2 3 3 2CH SS~ + 2Ag + > Ag S + CH SSSCH Ij-lkl 3 2 3 3 + S n + 2 A g > A g 2 S n Ag 2S n > Ag 2S + 5 ° ^ S~~. + 2Ag + > Ag S + S° /3-15/ n 2 n-1 -54-T i t r a t i o n curves of Fig* 3.2 show sodium s u l f i d e i n a l k a l i n e solution, white liquor (WL 1-3), and black liquor (BL 1-2) samples with and without CH^SNa addition as t i t r a t e d with s i l v e r n i t r a t e . S i m i l a r l y , Table 3*3 shows the accuracy of s u l f i d e determination with known quantities of hydrogen s u l f i d e and methyl mercaptan i n a l k a l i n e solution, with and without 1% t h i o l i g n i n as additive. On the t i t r a t i o n curve i n f l e c t i o n point "a" i s taken f o r c a l c u l a t i o n of s u l f i d e , ,,a,I-•,b,, f o r bound mercaptan^ M b " - " c f o r free mercaptan. These results confirm that i n f l e c t i o n point "a" i s due to mono-sulfide, and i n f l e c t i o n Mb" originates from bound mercaptan. This also indicates that one mole of bound mercaptan i s precipitated by one equal mole of s i l v e r n i t r a t e i n stoichimetric r a t i o as shown by calculations i n Eq. /3-l4/. The addition of 1% thio-l i g n i n did not seem to a f f e c t the t i t r a t i o n r e s u l t s . Fig. 3.2 c l e a r l y indicates that alkaline s u l f i d e solution, as well as k r a f t liquor, give similar potentiometric traces to those obtained with black l i q u o r . This also indicates that i n f l e c t i o n "b" i s caused by presence of the mercaptide ion. T i t r a t i o n curves of s u l f i d e and mercaptan mixtures having no i n f l e c t i o n at "b" were shown by Tamele e_t a l . (192), as well as Cashen and Bauman (37). However, F e l i c e t t a e_t a_l. (67) reported that i n f l e c t i o n Mb" was indeed present f o r mixtrues of s u l f i d e and -55-mercaptan. Their reasoning, and decision to calculate the s u l f i d e content from i n f l e c t i o n point "b", was unclear and can not be followed. For quantitative demonstration, a 10 g / l sodium s u l f i d e solution was prepared by dissolv i n g the appropriate amount of reagent grade sodium s u l f i d e i n 1 N NaOH solution with and without 1% t h i o l i g n i n added. One ml of the sodium s u l f i d e solution gave a t i t r a t i o n curve t y p i c a l f o r excess free mercaptan. The i n f l e c t i o n points at "a" and "b" were read f o r c a l c u l a t i o n of sodium s u l f i d e with results tabulated i n Table 3.4. The data indicate that sodium s u l f i d e calculated from i n f l e c t i o n point "a" agrees well with the o r i g i n a l quantity of s u l f i d e added. Honrever, great error was found i f sodium s u l f i d e was calculated from i n f l e c t i o n M b M . Bilbe r g (26) proposed that the presence of aromatic polyhydroxy compounds (such as l i g n i n or th i o l i g n i n ) i n black liq u o r reduces the s i l v e r ion which may contribute to errors with s i l v e r n i t r a t e t i t r a t i o n . From Table 3.4, i t i s obvious that there i s l i t t l e difference i n t i t r a t i o n responses of alk a l i n e s u l f i d e l i q u o r samples with and without added t h i o l i g n i n . 3.3.1.1.3.1 Effect of mercaptide ion concentrations on t i t r a t i o n The potentiometric t i t r a t i o n of s u l f i d e and mercaptide ion mixture i s based on s i l v e r s u l f i d e being precipitated -56-f i r s t at a high negative potential followed by considerable change i n potential a f t e r a l l of the s u l f i d e ion has reacted. The p r e c i p i t a t i o n of s i l v e r mercaptan commences at a lower potential and on completion of mercaptide ion p r e c i p i t a t i o n , another sharp change i n potential occurs. Again, elemental sulf u r interferes with this procedure as i t reacts with the mercaptide ion and i t s product, as shown i n Eq. /3-12/, imparts to the electrode a potential close to that observed from the mono-su l f i d e ion. In order to demonstrate the effect of the presence of mercaptide ion on outcome of the s u l f i d e determination, a c e r t a i n volume of commercial pulp m i l l white liquor (WL 1-3) and black liqu o r (BL 1-2) were pipetted into the t i t r a t i o n c e l l . In a series of t i t r a t i o n s (using the above mixture as stock solution) various quantities of sodium mercaptan solution were added and the solution was t i t r a t e d immediately with 0.1 N s i l v e r n i t r a t e . The t i t r a t i o n curves reproduced i n Fig* 3.3, show c l e a r l y the case of excess elemental sulf u r and i t s effect on mercaptan, whereby a l l the mercaptide ions are converted to organo poly-s u l f i d e (CH^SS -). The excess elemental sulf u r remains unreacted. By increasing the quantity of mercaptan solution to react with excess elemental sulfur, free mercaptan i n f l e c t i o n s were obtained on the t i t r a t i o n curve. Thus i t i s reasoned that there are few i f any methyl mercaptide ions i n black liquor, since most of the -57-mercaptide ions are converted to organopolysulfide i n black l i q u o r . 3.3.1.1.3.2 T i t r a t i o n of inorganic polysulfide solution As shown i n Eq. /3-l5/» p o l y s u l f i d e -s u l f i d e i s precipitated and elemental sulfur i s released by t i t r a t i o n of polysulfide solutions with s i l v e r n i t r a t e . A poly-s u l f i d e sample was prepared by d i s s o l v i n g 0.164 g of elemental su l f u r i n 20 ml of 10 g / l sodium s u l f i d e a l k a l i n e solution under nitrogen atmosphere. The solution was shaken f o r three days on o an automatic shaker at room temperature (25 C). A golden-yellow polysulfide solution was obtained. For t i t r a t i o n 0.25 ml samples of the polysulfide solution were transferred with microsyringe to the t i t r a t i o n c e l l and t i t r a t e d with 0.1 N s i l v e r n i t r a t e . For a further series of t i t r a t i o n s , varying amounts of sodium mercaptan were added to 0.25 ml portions of polysulfide solution. As seen i n Fig» 3.4, two i n f l e c t i o n points are found again on these t i t r a t i o n curves of inorganic polysulfide solutions. A s i m i l a r pattern was reported e a r l i e r by Bilberg (26), and recently by Papp (151) and Murray e_t a_l., (142) f o r t i t r a t i o n of a solution containing s u l f i d e and po l y s u l f i d e . B i l b e r g (26) and Papp (151) further showed that when the polysulfide solution was pretreated with sodium s u l f i t e , the i n f l e c t i o n "b" disappeared. The following chemical reaction i s thought to be involved: S~" + (n-l)S0~~ > ( n - l ) S 2 0 3 " + S"~ /3-l6/ -58-By adding varying amounts of sodium mercaptan, i n f l e c t i o n point "b" gradually became the constant value "b/w (Fig* 3 « * 0 . This i s taken as further proof that i n f l e c t i o n point ,'b" of the black liqu o r t i t r a t i o n curve i s due to the presence of organic and inorganic polysulfides i n the solution, rather than mono-sulfide alone. 3.3.1.1.3.3 T i t r a t i o n of oxidized s u l f i d e liquors Black liquor was oxidized i n a 500 ml ja r equipped with a rubber stopper and with i n l e t and outlet tubes. A kOO ml liquor sample containing about 10 g / l sodium s u l f i d e i n 1 N sodium hydroxide, with and without 1% t h i o l i g n i n added, was purged with oxygen through a porous glass gas-dispersion tube immersed i n the solution. The oxygen flow rate (kk ml/min) was controlled by means of a reducing valve and measured with a cali b r a t e d rotameter. Simultaneous to oxygen purging the solution was s t i r r e d by a magnetic s t i r r e r . Foam was reduced by adding a few drops of octanol. The change i n sodium s u l f i d e concentration was determined from time to time by withdrawing one ml samples of solut i o n . These were mixed with k ml of 16.6 g / l sodium mercaptan solution, and the mixed solutions were then t i t r a t e d with 0.1 N s i l v e r n i t r a t e . Changes i n s u l f i d e and bound mercaptan concentrations due to the -59-treatment are shown i n Table 3.5. As expected, quantities of dissolved s u l f i d e and bound mercaptan gradually decreased as oxidation progressed. The potentiometric t i t r a t i o n of oxidized sodium s u l f i d e with 1% t h i o l i g n i n i n alkaline solution before addition of sodium mercaptan shows that the s u l f i d e end point was well defined (Fig. 3.5). 3.3.1.1.3.4 T i t r a t i o n of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n a l k a l i n e solution Black li q u o r usually contains a small quantity of dimethyl s u l f i d e and dimethyl d i s u l f i d e . Swartz and Light (188) claimed that the end-point break i n s i l v e r n i t r a t e potentiometric t i t r a t i o n of black liquor i s caused by the presence of organosulfide compounds, such as methyl mercaptan and dimethyl s u l f i d e , which may supply ions to the system. It i s agreed that there i s a considerable effect of mercaptide ions on the t i t r a t i o n procedure. In order to test the interference caused by dimethyl s u l f i d e , an experiment was done including the mixing of 1.0 ml of dimethyl s u l f i d e with 100 ml 1 N sodium hydroxide solution. The solution was t i t r a t e d with s i l v e r n i t r a t e a f t e r having been s t i r r e d f o r 30 min at room temperature. This solution gave no su l f i d e ion p o t e n t i a l . The same procedure was applied to dimethyl d i s u l f i d e and, as expected, i t gave organo-sulfide p o t e n t i a l . For comparison, potentiometric t i t r a t i o n curves of dimethyl s u l f i d e , dimethyl - 6 o -d i s u l f i d e , elemental sulfur-mercaptan and methyl mercaptan alk a l i n e solutions are shown i n Fig. 3 . 6 . The potential; of ionized d i s u l f i d e (Curve II) and sulfur-mercaptan (Curve III) al k a l i n e solutions are very close. Accordingly, the reaction of dimethyl d i s u l f i d e i n a l k a l i n e solution may be proposed as follows: CH SSCH + OH" > CH SS" + CH^OH /3-17/ 3 3 3 * 3 . 3 . 1 . 1 . 3 . 5 T i t r a t i o n of mercaptan i n the presence of elemental sulf u r Potentiometric t i t r a t i o n of mercaptan i n black liquor results i n poorly defined t i t r a t i o n curves (Fig, 3 . 1 ) . As previously discussed, this may be explained as due to presence of elemental sulf u r i n solution, since this i s capable of reacting further with mercaptide ions and forming organopolysulfides (Eq. / 3 - 1 2 / ) . In order to test this point, d i f f e r e n t amounts of elemental sulf u r were dissolved i n aliquot portions of 20 ml methyl mercaptan al k a l i n e solution by shaking f o r three days under nitrogen atmosphere at room temperature. The s i l v e r n i t r a t e potentiometric t i t r a t i o n was conducted by sampling 4 . 0 ml of the prepared solution. T i t r a t i o n curves are reproduced i n Fig. 3 . 7 , while bound sulfur and bound mercaptan were calculated from Eq. / 3 - 1 0 / and are tabulated i n Table 3 . 6 . The potentiometric t i t r a t i o n of mercaptan i n the presence of elemental s u l f u r was -61-dependent on the ra t i o of mercaptan to elemental s u l f u r . As shown i n Table 3.6, as long as the amount of elemental s u l f u r was greater than the corresponding mercaptan concentration no free mercaptan i n f l e c t i o n point was detected on the t i t r a t i o n curves. The excess elemental s u l f u r remains unreacted or dissolved i n the strong alkaline solution i n the form of su l f i d e (Eq. /2-18/). This i s also indicated by data of Table 3.6, as well as Fig. 3*7 (Curves II and I I I ) . Conversely, when mercaptan concentration i s greater than elemental su l f u r , organo-sulfide and free mercaptan are shown by the t i t r a t i o n curves such as Fig,. 3.7 (Curve I I ) . As a result of this i t may be proposed to keep the ra t i o of elemental sulf u r to mercaptan sulfu r greater than,one during sulfate cooking by adding small amounts of elemental s u l f u r . Thereby the methyl mercaptide ions should react with sulf u r to form organopolysulfide before they react further to form dimethyl s u l f i d e and dimethyl d i s u l f i d e . Organopolysulfide i s considered to be less v o l a t i l e than methyl mercaptan. Part of the a i r p o l l u t i o n problem associated with sulfate pulp cooking might be abated by reducing methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i -de .to the less v o l a t i l e organopolysulfides. In summary, sulfate black liquor potentiometric t i t r a t i o n yields two i n f l e c t i o n points: The f i r s t break ("a") i s considered -62-to be raono-sulfide, the second i n f l e c t i o n f"b") i s thought to be due to the presence of organopolysulfides i n unoxidized and organic/inorganic polysulfides i n oxidized black l i q u o r s . Most of the mercaptide ion i n black liquor may be bound by traces of elemental sulf u r present i n black liquor to form organopolysulfide which also contributes to the potentiometric t i t r a t i o n . Determination of methyl mercaptan by potentiometric t i t r a t i o n i n sulfate black liquor i s most d i f f i c u l t , as mentioned above. Correct interpretation of the t i t r a t i o n curve gives considerable promise f o r accurate determination of s u l f i d e i n oxidized black l i q u o r . It i s proposed that p a r t i a l abatement of a i r p o l l u t i o n o r i g i n a t i n g with the sulfate pulping process might be obtained by adjusting the elemental sulf u r to mercaptide s u l f u r r a t i o during the cooking stage. The mercaptide should be bound by elemental s u l f u r to form organopolysulfides which are less v o l a t i l e than methyl mercaptan. 3.3*2 Gas; l i q u i d chromatographic (GLC) determination of organic sulfides i n black li q u o r During the sulfate pulping process approximately 2.3 to 2.5% of the sulfur charge i s converted to organosulfur compounds, mainly methyl mercaptan, dimethyl s u l f i d e and dimethyl -63-d i s u l f i d e . These, on escape from the black liquor, constitute the main sources of malodorous emissions (11). Part of this spectrum of s u l f i d e emissions, suitably i d e n t i f i e d and determined by potentiometric t i t r a t i o n techniques, has been discussed at length i n the foregoing section. Although mercaptide ions do respond to potentiometric t i t r a t i o n t h e i r concentration l i m i t a t i o n s cause severe problems, especially below 0.002 M concentration. This i s due to the limited response of the s i l v e r s u l f i d e electrode below the above concentration. Thus, this technique becomes unsuited f o r analysis of mercaptans i n commercial black liquors where the usual concentration does not exceed 0.002 M. Colorimetric analysis of hydrogen s u l f i d e and methyl mercaptan i n sulfate effluents* has been reported, but the technique has been found to be extremely tedious for black li q u o r analysis (24). Other techniques, such as that of Bialkowsky and DeHaas (25) employing wet-chemistry and F e l i c e t t a e_t a l . (67) who combine mass spectroscopy and t i t r a t i o n methods, although capable of quantitative analysis, were found to be too involved and unsuited f o r routine black liquor analysis. In recent years a large number of papers have been published on gas l i q u i d chromatography of sulfides (2, 3, 33, 52, 55, 86, 95, 125, 127, 13^, 160, 184, 199, 200, 205, 218). Ma ny of the papers - 6k-deal d e s c r i p t i v e l y with chromatographic conditions (2, 3, 86, 127, 134, 169, 205), while others concentrate on improvements in sampling techniques (55, 66, 95, l6o, 221). The d i r e c t analysis of sulfides i n d i l u t e aqueous solution (such as kraft black liquor) presents numerous problems i n gas chromatography. Considerable interference i s experienced from the water peak, which usually requires s p e c i a l l y selected sample preconditioning attachments at the chromatograph sampling port. Only li m i t e d attempts have been made on d i r e c t determination of malodorous sulfu r compounds i n aqueous effluents. The techniques developed to l i b e r a t e the v o l a t i l e solutes from aqueous solution, followed by gas chromatography without water interference, include d i s t i l l a t i o n either at elevated temperature (62) and/or reduced pressure (146). Stripping with a stream of inert gas was developed by Swinnerton ej; a l . (185) and considerably improved upon by Rayner et a l . (160). Rayner et al_. (160) determined methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e by f i r s t c o l l e c t i n g the samples i n a s t r i p p i n g c e l l to eliminate the considerable dispersion of samples i n continuous gas streams. Douglass and Price (55) described a novel s t r i p p i n g technique which takes advantage of changing s o l u b i l i t y c h a r a c t e r i s t i c s of sulfide s with solution pH. They followed s u l f i d e formation k i n e t i c s - 65-by a c i d i f y i n g a known quantity of pulping liquor with excess s u l f u r i c acid. Using chromatography, the vapor above the aqueous solutions was sampled and analyzed and the results converted to quantitative figures with the aid of conversion (liberation) f a c t o r s . While r e p r o d u c i b i l i t y of the technique was quite acceptable, i t does not account f o r more than one-third to one-fourth of the mercaptan o r i g i n a l l y present i n the sample. In a sim i l a r study McKean ejb a_l. (127) described dimethyl s u l f i d e analysis by a s l i g h t l y d i f f e r e n t technique. A c a l i b r a t i o n curve i s prepared f o r the compound by heating the aqueous solution of known dimethyl s u l f i d e concentration to a constant temperature and .subsequently sampling the vapour phase with a microsyringe through a septum. Gas chromatograph analysis followed. This technique requires a c a l i b r a t i o n curve f o r each (heating) temperature. Recently, Matteson e_t al_. (125) reported that malodorous sulfur compounds can be extracted with carbon tetrachloride from steam d i s t i l l a t e s of kraft black l i q u o r . Thereby, they repeatedly extracted the o i l y d i s t i l l a t e with carbon tetrachloride and subjected the extract to gas l i q u i d p a r t i t i o n chromatography (GLC). Further improvements of this technique were reported by Andersson and Bergstrb'm (12), who a c i d i f i e d the black liquor-carbon tetrachloride mixture to a pH of 9.3 with saturated boric acid solution. The organic layer was sampled and the s u l f i d e content - 6 6 -determined by GLC. It was claimed that both dimethyl s u l f i d e and dimethyl d i s u l f i d e are rapidly and almost completely extracted (98%) into the carbon tetrachloride layer by this technique but only part of the methyl mercaptan could be recovered. Thus, a conversion factor has been developed for methyl mercaptan. On the hardware side, important improvements have been made available with columns and packings (3» 33» l 6 o ) and especially detectors. Among known detectors, Thermal Conductivity Detector (TCD) was often employed, since i t responds universally to a l l types of compounds. Low s e n s i t i v i t y of TCD, however, has been a great handicap to accurate analyses. Especially poor response was obtained f o r low concentrations of organosulfides such as found i n black l i q u o r s . Large advances were made v/ith the Flame Ioniza-tion Detector (Fill) itfhich has shown high s e n s i t i v i t y (1000 times lower detection l i m i t s than with TCD) f o r hydrocarbons and a l k y l s u l f i d e s , but weak responses to hydrogen s u l f i d e and sulfur d i -oxide (2,33» l 6 o ) . It gives no response to carbon d i s u l f i d e and water. It i s known that i n the presence of sulfur, halogens i n the organic structure cause s i g n i f i c a n t reduction i n s e n s i t i v i t y , where-by the detector becomes of limited value i n work with s u l f i d e s . Possibly the largest recent improvements i n sulfur detection were made with introduction of the Flame Photometric Detector (FPD) i n 1966. The FPD i s the f i r s t inexpensive detector, operated on - 6?-p r i n c i p l e s of spectroscopy, f o r sulfur and phosphorous containing compounds to be coupled with gas chromatography. The use of this detector was f i r s t reported by Stevens e_t al^. (181) as an automated gas chromatographic analysis system f o r sub-ppm level s of sulfur compounds i n ambient a i r . The a n a l y t i c a l system developed for gas analysis required the use of 36-feet of 0.085 i n (ID) Teflon column on 30/60 mesh Teflon coated with polyphenyl ether and 0.5 g of orthophosphoric acid. Further improvements and results on this system are described by Mulik e_t a_l. (134). The detector i s comprized e s s e n t i a l l y of a burner j e t , r e f l e c t i v e (collimating) mirror and narrow pass f i l t e r (39^ nm for S, and 526 nm for P). The photomultiplier tube responds to the chemoluminescent c h a r a c t e r i s t i c l i g h t emitted by S at 394 nm wave length when sulfu r i s burned i n a hydrogen-rich flame. The li g h t monitored by the photomultiplier tube i s fed to an electro-meter and recorder. The FPD i s a mass flow rate dependent detector and as such the detector w i l l y i e l d a peak area independent of the volume of c a r r i e r gas eluted with the sample. It requires a p a r t i c u l a r c a l i b r a t i o n curve f o r every compound, as i t has no l i n e a r portion at a l l (straight lines are obtained on log-log plots with slopes between 1.5 to 2.0 which has been found to be constant over a 500 f o l d range). While i t s s p e c i f i c i t y to hydrocarbons i s good, the -68-detector s e n s i t i v i t y f o r S i s 10,000 f o l d the s e n s i t i v i t y f o r hydrocarbons (86). The f i l t e r s are not completely sele c t i v e as to S and P, with the sulfur f i l t e r phosphorus also detected at 100 f o l d lower s e n s i t i v i t y . The good ppb detection f o r S i s obtained only under careful tuning of the instrument as described by Stevens e_t a l . (181) 3.3.2.1 Experimental 3.3.2.1.1 Chemicals Dimethyl s u l f i d e (bp. 37-38°C) and dimethyl d i s u l f i d e (bp. 109-111°C) were obtained from Eastman Organic Chemicals; hydrogen sulfide, (bp. -6l.8°C) and methyl mercaptan (bp. 7.6°C) from Matheson of Canada Ltd.; boric acid and carbon tetrachloride were reagent grade. The sulfate black liquor (2-1) was obtained from Canadian Forest Products Ltd., Port Mellon, B.C. and the white liquor (3-1) containing 38 g / l ef f e c t i v e a l k a l i and l k . k g / l sodium s u l f i d e was obtained from Department of Environment, Western Forest Products Laboratory, Vancouver, B.C. 3.3.2.1.2 Gas l i q u i d chromatography (GLC) A MicroTek MT-150 gas chromatograph, equipped with a Melpar flame photometric detector (FPD) and flame io n i z a t i o n detector (FID), dual channel electrometer and dual pen -69-recorder was used f o r these studies. The column was prepared by using a c o i l e d glass column 7 feet long and % i n (OD) packed with didecylphthalate on 60/8O mesh Chromosorb P (25:75 by weight). The chromatograph operating parameters were as follows: Carrier gas: Nitrogen, 45 ml/min 40 psi i n l e t pressure Oven temperature: 4 min at 25°C f o r HgS and CH^SH Program: Oven temperature r i s e from 25°C to 125°C & 22°c/min f o r CH^SCH and CH3SSCH3 Detector temperature: 150°C Detector gas flow: H"2 : 150 ml/min A i r : 30 ml/min 02: 15 ml/min The c a l i b r a t i o n curves f o r E^S and C^SH were prepared d i r e c t l y by taking measured volumes of the gases with gas tight micro syringes at known pressure and temperature. The samples were taken through f l e x i b l e rubber hoses connected to a manometer on one end and to lecture bottles of the gas on the other. The gas samples so taken were injected through rubber septums into an inverted volumetric f l a s k containing 100 ml CCl^. S i m i l a r l y , l i q u i d s u l f i d e samples (dimethyl s u l f i d e and dimethyl d i s u l f i d e ) were withdrawn with appropriate microsyringes and mixed with CC1, i n the above manner. Thus d i l u t i o n series were prepared f o r a l l four sulfid e s and injected d i r e c t l y into the gas chromatograph. Under the above described conditions t y p i c a l chromatograms were obtained which could be further evaluated as to c h a r a c t e r i s t i c retention times and detector response with changing concentrations. Retention times of s u l f i d e peaks eluting under the p a r t i c u l a r chromatographic conditions are described as follows: Hydrogen s u l f i d e (H S) 1 min 50 sec 2 Methyl mercaptan (CH^SH) 5 min 25 sec Dimethyl s u l f i d e (CRjSCKLj) 8 min 30 sec Dimethyl disulfide . (CH SSCH„) 18 min 25 sec 3 3 C a l i b r a t i o n curves constructed from the information obtained i n the above described manner are presented i n F i g . 3*8. As anticipated the concentration vs. detector response relationships were a l l straight l i n e s when plotted on log-log scale (within the described concentration range). Ca l i b r a t i o n curves for determining dimethyl s u l f i d e and d i -methyl d i s u l f i d e i n black liquor (above pH 12) were also prepared. One hundred ml of the black li q u o r (2-1) was thoroughly extracted with 8 x 50 ml carbon tetrachloride and then further stripped with nitrogen gas at room temperature f o r 12 hours. The treated black liquor was tested f o r no residual organic sulfid e s by extraction of 5 ml samples with 5 x 5 ml carbon tetrachloride which was combined and examined by GLC analysis. The organic sulfid e s free i c e-water-cooled black liquor was transferred into a 25 ml volumetric f l a s k equipped with a rubber septum. Appropriate amounts of dimethyl s u l f i d e and dimethyl d i s u l f i d e were then injected into the black liquor samples. The solution was thoroughly shaken and stored i n the cold (5°C) overnight. Further 5 ml of the organo-su l f i d e solution was syringed into a 20 ml separation funnel and thoroughly extracted with 5 x 5 ml carbon tetrachloride. The c a l i b r a t i o n curves of black liquor organosulfide concentrations vs. detector response (represented by peak height) are shown i n Fig. 3.9. 3.3.2.1.3 Sample procurement f o r gas l i q u i d chromatography (GLC) As stressed e a r l i e r , no convenient single technique i s available f o r simultaneously and quantitatively determining a l l black liquor s u l f i d e s . Following a c r i t i c a l examination of the available techniques, l i q u i d / l i q u i d extraction with carbon tetrachloride^. as o r i g i n a l l y proposed by Matteson e_t al_. (125) and l a t e r modified by Andersson and Bergstro'm (12), was chosen as most suited f o r sample procurement and analysis by gas l i q u i d chromatography. -72-3.3.2.1.3.1 Carbon tetrachloride l i q u i d / l i q u i d extraction Before applying the l / l technique, extraction e f f i c i e n c i e s on both enriched white and black liquors were determined. While white liquor needed no preparation f o r this determination, 100 ml portions of the black liquor were pre-extracted f i v e times with 100 ml portions of CCl^ followed by strip p i n g with nitrogen gas f o r 24 hours i n order to remove sulfides present. Extraction e f f i c i e n c i e s were tested on two repl i c a t e 5 ml liquor samples to which varying amounts of dimethyl s u l f i d e -3 -3 (0.845 x 10 to 0.212 x 10 g) and dimethyl d i s u l f i d e (1.057 x -3 -3 10 to 0.264 x 10 g) were added. The solutions were prepared i n 20 ml separatory funnels equipped with silicone-neoprene rubber septums. The heterogeneous l i q u o r - s u l f i d e mixture was shaken by hand f o r 2 min and allowed to stand f o r at least 15 min. Following standing, the mixture was successively extracted f i v e times with 10 ml CC1 by shaking each time f o r 1 min and allowing s u f f i c i e n t 4 time (usually 15 min) for cle a r separation of the two layers. The combined organic layer (bottom) was drained into a 25 ml volumetric f l a s k and immediately made up to mark with fresh CCl^. The sul f i d e content of the supernatant .liquid was determined by gas l i q u i d chromatography. Recovered quantities and e f f i c i e n c i e s are -73-indicated i n Table 3«7 and Fig. 3.10. For determining dimethyl s u l f i d e and dimethyl d i s u l f i d e i n experimental black li q u o r samples, the same procedure was followed except that 10 ml of cooled black liquor (-5°C) was extracted with 5 x 5 ml CC1 i n 20 ml capacity separatory funnels. 4 Carbon tetrachloride extraction seems to be selec t i v e to sulfur compounds i n black l i q u o r . As shown i n Table 3»7> the extraction e f f i c i e n c y of dimethyl s u l f i d e and dimethyl d i s u l f i d e i s s i m i l a r f o r both white and black l i q u o r s . This indicates l i t t l e , i f any, interference by dissolved l i g n i n and carbohydrates or other organic and inorganic solutes usually found i n commercial black l i q u o r s . The extraction e f f i c i e n c i e s f o r dimethyl s u l f i d e and dimethly d i s u l f i d e , however, were s i g n i f i c a n t l y d i f f e r e n t being in the order 90 to 9^% and 78 to 81% respectively. It also appears that change i n concentration over the four f o l d range of 0.212 x -o -3 10 -> to 0.845 x 10 g i n 5 ml sample had no detectable effect on extraction e f f i c i e n c y of dimethyl s u l f i d e by carbon tetrachloride. Similar observation was made on dimethyl d i s u l f i d e as shown i n Table 3.7. In order to test effect of solution pH on extraction e f f i c i e n c y of dimethyl s u l f i d e and dimethyl d i s u l f i d e , the buffered solutions were prepared between pH 1.5 to 13.5 by mixing c e r t a i n portions of 0.1 M potassium hydrogen phosphate with 0.1 -7 k-M HCI or 0.1 M NaOH as described i n the Handbook of Chemistry and Physics (9*0. Aqueous solutions of 100 p i dimethyl s u l f i d e and dimethyl d i s u l f i d e i n 100 ml d i s t i l l e d water were cooled to 5°C overnight. To 5 ml buffered solution 1.0 ml of the aqueous solution was added in a 20 ml test tube equipped with a rubber septum. The solution was well mixed with the syringe, shaken several times and cooled to 5°C. The solution thus prepared was extracted f i v e times with 10 ml aliquots of CC1 . Sulfide concentrations were further k determined by gas l i q u i d chromatography. The e f f i c i e n c y of CC1 l i q u i d / l i q u i d extraction of dimethyl k s u l f i d e and dimethyl d i s u l f i d e was considerably affected by pH of the solution as shown i n Fig 3.11. There was r e l a t i v e l y l i t t l e change i n e f f i c i e n c y between pH 1.5 to 7«0 where nearly 100% of dimethyl s u l f i d e and 95% of dimethyl d i s u l f i d e was recovered. A rather sharp drop was observed by increasing the pH from 7.0 to 10.0 where the e f f i c i e n c i e s dropped 10% f o r dimethyl s u l f i d e and 15% for dimethyl d i s u l f i d e . There was r e l a t i v e l y l i t t l e change between pH 10.0 to 13.5. 3.3.2.1.3.2 A c i d i f i c a t i o n of black liquor with boric acid The analysis of carbon tetrachlor-ide extracts by gas l i q u i d p a r t i t i o n chromatography was designed to -75-provide both q u a l i t a t i v e and quantitative information on.black liquor s u l f i d e s . I d e n t i f i c a t i o n of a given s u l f i d e compound involved evaluation of comparative and r e l a t i v e retention time data as provided by standard reference compounds. Further substantiation of a l l peaks obtained from black liquor extracts was made by enhancement of the i n i t i a l peak through addition of known quantities of known compound to the black l i q u o r before the extraction step. The rather disturbing inaccuracy of the methyl mercaptan determination i n black liquor by the previously described potentio-metric t i t r a t i o n technique prompted further search f o r a more accurate method. As indicated by the experiments of Douglass and Price (55) and Andersson and Bergstrdm (12), both dissolved hydrogen s u l f i d e and methyl mercaptan can be stripped from aqueous solutions a c i d i f i c a t i o n of the black l i q u o r . This can be followed by CC1 l i q u i d / l i q u i d extraction. 4 For this experiment, extraction was done a f t e r adjusting liquor pH to approximately 6.5 with boric acid (H^BCvj). This also coincides with maximum extraction e f f i c i e n c y as determined for dimethyl s u l f i d e and dimethyl d i s u l f i d e (Fig. 3.11). Boric acid i s a t r i b a s i c acid. Dissolved i n water the various hydrogen atoms undergo d i s s o c i a t i o n to d i f f e r e n t extents. The three d i s s o c i a t i o n constants at 20°C(K1> Kg and ) can be calculated from the following equations (94): H B O —> H + + H B O 3 3 + 2 H 2 B O ; <-—> H + H B O ~ H B O 3 —> H + + B O ; -76-K = 7.3 x IO" 1 0 /3-18/ K = 1.8 x 10~ 1 3..../3-19/ 2 K3 = 1.6 x I0" 1 2 f. . . ./3-20/ Since the boric acid i s a weak el e c t r o l y t e , the law of mass action may be followed f o r the respective d i s s o c i a t i o n (94): (H +) x (H2BO-)/(H3B03)= K± /3-2l/ (H +) x (HB03"")/(H2BO~) = Kz /3-22/ (H +) x (BO-—)/(HBO") = K /3-23/ 3 3 3 The magnitude of the di s s o c i a t i o n constants indicates the extent of i o n i z a t i o n at given.concentrations. The relationship between black liquor (BL 1-4) pH and boric acid addition i s shown i n Fig. 3.12. Above pH 6.8 the black li q u o r pH i s a function of boric acid concentration while below pH 6.8 only small change i n pH i s observed with increased amounts of boric a c i d . This allows f a i r l y good control of black liquor pH when pH 6.5 i s chosen as target a c i d i t y for treated samples. Changes i n gas chromatograms due to black li q u o r a c i d i f i c a t i o n are i l l u s t r a t e d i n Fig. 3.13. The appearance of H S and CH SH i s 2 3 quite obvious while position of the e a r l i e r peaks remained unchanged following a c i d i f i c a t i o n . The boric acid a c i d i f i c a t i o n of black liquor was carried out i n a vessel, hermetically closed with the aid of a rubber septum. The predetermined amount of -77-s o l i d boric acid (1.1 g) was weighed into the vessel together with 20 ml of CC1 . The black liquor (5 ml) was added with a syringe through the rubber septum. Contents of the vessel were shaken vigorously u n t i l a l l the boric acid dissolved. The vessel and contents were then frozen overnight i n an inverted position and the organic layer sampled and analyzed by gas l i q u i d chromatography next day. During the course of GLC analysis of the various black liquors the expected compounds, hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e were i d e n t i f i e d i n accordance with e a r l i e r findings of F e l i c e t t a ejt a_l. (67) and others. No further compounds were detected with the exception of "X" (Fig. 3.13) although Thomas (200) reported propyl mercaptan, ethyl d i s u l f i d e and propyl d i s u l f i d e i n digester blow and r e l i e f gases entering the lime k i l n . Similar results were indicated by Thoein and Nicholson (199) following infrared analysis of r e l i e f gases. In addition the possible existence of methyl hydrogen d i s u l f i d e (CH^SSH) i n black liquor pyrolysates has been proposed by Brink e_t a l . (32). In this study an unidentified compound "X" (Fig. 3*13) was found as a constant and rather large component of the l i q u i d / l i q u i d extraction of black liquor. The compound was present i n CC1, extracts of both normal and a c i d i f i e d black liquors of a l l -78-sources (including polysulfide black l i q u o r ) . In some samples the concentration of the unkown was quite high. Limited further experiments indicated that the unknown contains no ionizable hydrogen and i s a v o l a t i l e s u l f u r compound with a b o i l i n g point s l i g h t e r higher than that of dimethyl s u l f i d e . 3.4 Chemistry and Analysis of Polysulfide 3.4.1 Significance of polysulfide as an extention to sulfate pulping Polysulfide pulping i s one of the few methods by which s t a b i l i z a t i o n of wood carbohydrates occurs during a l k a l i n e pulping. This results i n y i e l d increases and some improved physical properties of pulps produced thereby. By impregnation of wood chips with polysulfide liquor the carbonyl end groups of polysaccharides are oxidized to carboxyl groups, thus s t a b i l i z i n g the carbohydrates against a l k a l i n e degradation (8, 196, 132). The a b i l i t y of a polysulfide solution to s t a b i l i z e polysaccharides increases with the concentration of elemental sulfur and with the r a t i o of polysulfide excess sul f u r to s u l f i d e sulfur i n alkaline solution (109, 197). The y i e l d increases of polysulfide pulping are caused to a large extent by retention of glucomannan i n coniferous woods (109, 167) and xylan i n porous woods (110, 167). The modification of l i g n i n by formation of carbonyl groups i s believed to increase the rate of -79-d e l i g n i f i c a t i o n (131, 1^3, l 6 7 ) . Pulp y i e l d increases are found to depend mainly on the amount of elemental sulfur added, degree of impregnation, pulping conditions, and wood species being pulped (108). Maximum pulp y i e l d increases are usually i n the range of 2-5%, based on oven-dry wood (53, 108, 167, 212). The pulp y i e l d increases of porous wood are moderate and only about one-half of those obtained with coniferous woods. It may be that xylan i n porous woods i s not as e f f e c t i v e l y s t a b i l i z e d by polysulfide cooking as glucomannan i n coniferous woods (167). As f o r pulp properties, Sanyer and Laundrie (167) reported that the strength properties of l o b l o l l y pine (Pinus taeda L.) polysulfide pulps were comparable with those of sulfate pulp, except f o r the s l i g h t l y lower tear strength. Requirements for bleaching chemicals were about the same as those expected f o r sulfate pulps of the same Kappa number. D i l l e n and Noreus (53) indicated that Scots pine (pinus s y l v e s t r i s L.) polysulfide process pulps have of higher v i s c o s i t y for cooks c a r r i e d to low Kappa numbers than similar pulps o r i g i n a t i n g from conventional sulfate cooks. 3.4.2 Composition and nomenclature of aqueous polysulfide solutions The anions i n an aqueous polysulfide solution are considered to be HS~, S , 0H~ and a variety of polysulfide ions -80-generally designated as S S . A whole series of polysulfide n ions from SS ~ to S^S~~ has been isolated i n c r y s t a l l i n e form as sodium or potassium sa l t s (197). E l e c t r o l y t i c procedures were also developed by which reduction of sulfur can : _ provide^ mixtures of s t i l l higher homologs of S S and either S^S or 8 o S^S (65). According to the nomenclature of Teder (197), each polysulfide ion can conveniently be considered to consist of one atom of sul f i d e s u l f u r /S(-II)/ and n atoms of polysulfide excess sulfur /s(0)/. S(-II) = (SH") + (S"") + £ ( s n s " ~ ) /3-2V S(0) =Zn(SnS~") /3-25/ Total amounts of su l f i d e and excess sulfur can be determined a n a l y t i c a l l y . The average number of excess sulfur atoms per polysulfide ion(n) i s expressed as: n = Z n ( S n S " " ) / 2 I ( S n S " ~ ) /3-26/ The average number (n) i s a theoretical concept which cannot be obtained from conventional chemcial analysis of polysulfide solutions. In practice, X , the rat i o of polysulfide excess sulfur s S(0) to sul f i d e sulfur S(-II) i s used to characterize polysulfide solutions. X g = S(0)/S(-II) = Z>(S nS~)//( HS') + (S~~) + X(S nS~~)/ /3-27/ Small values of n are observed with solutions of high a l k a l i n i t y -81-and low X g, while large n values occur with solutions of high X and low a l k a l i n i t y . By p r a c t i c a l considerations i n technical s polysulfide solution n i s always considerably larger than X g (197). Aqueous polysulfide solutions have deep color ranging from yellow to red with increasing S n i n the chain. When polysulfide solutions are a c i d i f i e d slowly to below pH 9» the polysulfide decomposes into HS~" and elemental s u l f u r . Thermal decomposition over 9 0° of polysulfide i n a l k a l i n e aqueous solution i s strong due to decomposition into s u l f i d e and thiosulfate (195)• 3.4.3 Preparation of aqueous polysulfide solutions Polysulfide solutions can be prepared by d i s s o l v i n g elemental sulf u r i n pure s u l f i d e solution. Direct solution of elemental s u l f u r into sulfate ; white liquor, which i s highly a l k a l i n e , causes extensive thiosulfate formation (189, 195). By p a r t i a l oxidation of white liquor with a i r i n the presence of black liquor, polysulfide can be formed. Besides the polysulfides, large amounts of thios u l f a t e , and small amounts of s u l f i t e and sulfate are produced simultaneously (27). Barker (19) claimed that s u l f i d e i n white liquor can be s e l e c t i v e l y oxidized to poly-s u l f i d e with manganese oxide. Other ways of producing polysulfides have been proposed, such as e l e c t r o l y s i s of sodium s u l f i d e or expelling hydrogen s u l f i d e from green liquor by carbon dioxide and recovery of -82-elemental s u l f u r by Claus* process (212). P a r t i a l reduction of sulfate and cathode reduction of sulfur dioxide to form poly-s u l f i d e have been reported (7» 35 )• Hydrogen s u l f i d e can be decomposed to elemental sulfur by i r r a d i a t i o n with u l t r a v i o l e t , alpha-particles or by passing the gas through an e l e c t r i c arc (35 )• The recovered elemental sulfur may be dissolved i n s u l f i d e solution f o r the preparation of po l y s u l f i d e . As a new approach, gamma r a d i o l y t i c generation of poly-s u l f i d e i n carbon dioxide and hydrogen s u l f i d e a c i d i f i e d s u l f i d e solution was attempted i n these studies. 3.4.4 Polysulfide determination The analysis of polysulfide i n aqueous solutions became important with the discovery of advantages provided by the presence of polysulfide i n sulfate pulping liquors (197 )• The determination of polysulfide s u l f u r /S(0)/ presents numerous problems (28, 197 )• The c l a s s i c a l methods of analysis were reviewed and summarized by Blasius e_t a_l. (28) i n 1968. 3.4.4.1 Gravimetric analysis The technique i s based on converting poly-sulfides into hydrogen s u l f i d e and elemental s u l f u r . The l a t t e r i s determined gravimetrically. The reaction schemes can be expressed as: -83-H + quartz catalyst Na S > H S > HgS + (n-l)S ../3-28/ 2 n 2 n $0 C 3.4.4.2 Volumetric analysis Total sulfur i n polysulfide can be determined by iodometric t i t r a t i o n i n acid solution: H0S + I_ > 2HI + nS /3-29/ 2 n 2 In alkaline solution, the sulfur i s quantitatively oxidized to sul f a t e . Thus the polysulfide s u l f u r can be calculated from the difference of t o t a l sulfur and su l f i d e s u l f u r . Polysulfide sulfur can be reduced quantitatively to s u l f i d e with sodium amalgam: Na SS + 2n NaHg > (n+l)Na,S + 2nHg • ../3-30/ 2 n m c. m Thus the polysulfide sulfur can be calculated from the difference of iodine consumption of mono-sulfide sulfur and the t o t a l reduced s u l f i d e s u l f u r . The reaction of polysulfide sulfur with s u l f i t e to form thiosulfate i s also known: Na 2SS n + n Na^SO^ > Na2S + n Na2S20,j /3-3l/ The thiosulfate can be determined iodometrically when the s u l f i d e ++ ++ and the excess s u l f i t e are precipitated by Zn and Sr , respec t i v e l y . -8k-S i m i l a r l y , the polysulfide sulfur w i l l react quantitatively with cyanide to form thiocjniate and the thiocyanate can be analysed by iodometric t i t r a t i o n . Na 2SS n + n CN~ > Na2S + n SCN~ /3-32/ The above described methods are usually too d i f f i c u l t to perform for d i r e c t analysis of polysulfide cooking liquors, as they become involved and time consuming, due to interference from the impurities found i n such l i q u o r s . Recently, several methods have been developed which allow quantitative determination of polysulfide sulfur i n white or black l i q u o r s . Johnsen (99) developed an acidimetric method for the deter-mination of polysulfide sulfur i n sulfate white and black liquors by using hydrochloric acid t i t r a t i o n . S i m i l a r l y , Ahlgren (5) modified the Scandinavian standard procedure (Scan-N 2:63) (170) f o r the analysis of polysulfide sulfur, hydroxide, s u l f i d e and carbonate i n polysulfide cooking l i q u o r . This new technique uses hydrochloric acid as t i t r a n t . Olsson and Samuelson (1^9) developed a quantitative method for determination of s u l f i d e , t h i o s u l f a t e and polysulfide i n black liquors by subjecting the liquor sample to anion exchange chromatography fo r the separation of inorganic su l f u r compounds from organic impurities i n the sample effluent. Further separation of thiosulfate and most of the s u l f i d e s i s made by elution from the anion exchange resin with NaN0~. Polysulfide -85-and the remaining sulfides are subsequently eluted with a mixture of Na2S03 and NaNO^ solution. During elution, the polysulfide s u l f u r i s transferred into t h i o s u l f a t e . Both eluates contain s u l f i d e and thiosulfate which can be determined potentiometrically. Rice and Zimmermann (l62) determined sodium s u l f i d e , t h i o s u l f a t e , s u l f i t e or polysulfide i n white liquor by combination of argento-metric, acidic iodine and alkaline iodine (hypoiodite) t i t r a t i o n . The TAPPI method (T624 ts - 66) (lk) analyses polysulfide s u l f u r by reacting the excess sulfur with s u l f i t e to form thiosulfate which can be t i t r a t e d quantitatively by acidic iodine. In this study, the polysulfide s u l f u r was determined by redox t i t r a t i o n , described by Ahlgren and LeMon (6), and spectrophoto-metry (195)» For the redox t i t r a t i o n , the apparatus consisted of a Radiometer pH meter, equipped with Platium (Sargent S-30440) and Calomel electrodes. The equipment was completed by adding an automatic t i t r a t o r and X-Y recorder. The polysulfide sample (sodium t e t r a s u l f i d e ) was obtained from Hooker Chemical Corporation, New York. The sample (0.9 ml) for analysis was transferred into a vessel containing 50 ml of saturated sodium chloride solution and conditioned i n a water bath at 9 0° + 1°C. The t i t r a t i o n c e l l can be expressed as; Pt//NaCl(sat.) J J J j J ^ / / KC1, H g C l 2 / H g C l 2 (S) / Hg /3-33/ Then, the solution was t i t r a t e d slowly with 0.5 M sodium s u l f i t e -86-(ca, 2 ml/min). The potential change due to addition of the t i t r a n t was recorded automatically. The end point was determined by reading the volume of s u l f i t e solution consumed at the i n f l e c t i o n point of the t i t r a t i o n curve as shown i n Fig 3.1^. The end point i s also indicated by disappearance of yellow color i n the sample solution. The polysulfide excess sulf u r i s c a l c u l -ated according to the following formula (6)j S nS + n SO" + H20 (> > n S 20~~ + HS" + 0H~.../3-34/ Results of f i v e determinations gave an average of 313.1 +3.0 g / l excess sulfur f o r the samples prepared. Comparing results of the above redox t i t r a t i o n of polysulfide sulfur with d i f f e r e n t methods such as iodometric, acidimetric, ion exchange following potentio-metric t i t r a t i o n and copper column method, the value obtained i s in good agreement with those reported above (6). Excess sulf u r i n polysulfide was determined spectroscopically according to the procedure described by Teder (195) • The c a l i b r a t i o n curve of polysulfide sulfur was prepared by mixing varying amounts _2 of commercial polysulfide with 3 M NaCI and 10 M NaOH aqueous solutions. The prepared polysulfide sulfur concentrations ranged from 79.1 x 10~^ to k?k.5 x 10~** g / l . Absorption curves were obtained f o r the solution on a Unicam Sp. 800 spectrophotometer with 1 cm sample and reference c e l l (containing a blank solution -2 of 3 M NaCI and 10 M NaOH aqueous solutions). The average of -87-two absorbance replications at 285 nm wave length was plotted against excess sulfur concentration and i s shown i n Fig. 3«15» This wave length (285 nm) was selected f o r reasons of least interference on absorptivity of varying hydroxyl ion concentra-tions and the r a t i o of the polysulfide sulfur to that of s u l f i d e s u l f u r concentration (195)» It was pointed out by Teder (195) that generally good agreement i s obtained between the spectro-photometry procedure and acidimetric or redox t i t r a t i o n of poly-s u l f i d e solutions without the l i g n i n present. The accuracy of the spectrophotometric method i s not affected by the presence of other bases, such as carbonate ions i n the sample, whereas the acidimetric method w i l l be disturbed by the presence of high base content. Polysulfide samples with high l i g n i n concentrations were found to be less suitable f o r analysis by the spectrophotometric method (195)• However, the spectrophotometric method proved to have great advantages as i t i s less complicated and time consuming than other methods such as iodometric, acidimetric, ion exchanges followed by potentiometric t i t r a t i o n and redox t i t r a t i o n . The s u l f i d e sulfur / S(-II)/ i s determined by pretreatment of the polysulfide solution with excess s u l f i t e solution at 50°C u n t i l disappearance of the yellow color. The monosulfide sulfur can be analysed by s i l v e r n i t r a t e potentiometric t i t r a t i o n as described previously. -88-3»4.5 Determination of sulfate i n polysulfide solution The sulfate i n the polysulfide solution, obtained as oxidative component from the gamma r a d i o l y s i s of a c i d i f i e d s u l f i d e solutions, can be accurately determined by turbidimetry (63). The method i s based on conversion of sulfate ions to barium sulfate (BaSO^) under conditions which lead to a c o l l o i d a l suspension. The method i s v a l i d f o r concentrations as low as parts per m i l l i o n (ppm) (63). The c a l i b r a t i o n curve*; for sulfate determination was constructed by pipetting 2, 5, 10, 25, and 50 ml of a standard potassium sulfate solution (0.0905 g/l) to 50 ml volumetric f l a s k s . The measured solutions were diluted to the mark with d i s t i l l e d water. The sulfate solution was then poured into a 100 ml beaker contain-ing 10 ml of sa l t - a c i d - g l y c e r o l (500 ml 20% NaCI : 10 ml cone. HCl : 500 ml glycerol) conditioning solution and 0.3 g of barium chloride (BaClg^HgO) were added. The mixed solution was s t i r r e d for one min, l e t stand k rain and transmittance was measured at k60 nm wavelength with a Spectronic-20 spectrophotometer. A blank solution f o r zero adjustment was also prepared with the same procedure except without adding potassium sulfate solution. The c a l i b r a t i o n curve of transmittance (%) vs. HgSO^ concentration i s shown i n Fig, 3.l6. In t y p i c a l analysis of the sulfate i n poly s u l f i d e solution -89-i s determined by placing 5-10 samples of polysulfide solution into a 100 ml beaker containing 10 ml of 10% hydrochloric acid solution. The solution i s boiled for 10 min to expel carbon dioxide and hydrogen s u l f i d e gases, f i l t e r e d and dil u t e d to 50 ml with d i s t i l l e d water. The barium sulfate c o l l o i d suspension was further prepared according to the procedure described above fo r the c a l i b r a t i o n curve preparation. 3.5 Black Liquor Characterization The various i n d u s t r i a l and experimental sulfate black liquors (Table 4.1) were analysed as to pH, density, t o t a l solids and l i g n i n concentration p r i o r to storage. These data were thought to indicate o r i g i n and history of cooking, of which only limited information was ava i l a b l e . 3*5*1 Determination of pH A Radiometer pH meter, equipped with a Corning high pH glass electrode (No. 476024) was used. Calib r a t i o n of the meter was effected with a pH 12.72 buffer solution (Fisher S c i . ) . A l l pH determinations were done at room temperature (25°C) within one week of receipt of the samples. 3.5.2 Density The density of black liquors v/as determined at -90-25°C with the aid of a calibrated pycrometer (50 ml). Density values were determined r e l a t i v e to d i s t i l l e d water (at 25°C). The average densities were calculated from three re p l i c a t i o n s f o r black l i q u o r . 3.5.3 Total solids Total black liquor solids were determined by TAPPI Standard T625 ts-6k (13). According to this method 10 ml of black liquor i s weighed into a tared weighing b o t t l e to the nearest 0.0001 g. The sample i s dried overnight i n an oven at 1 0 5° + 3°C (2k h r . ) . The samples are then cooled and the residue reweighed at room temperature. Average s o l i d content was calculated from four independent replications of each black l i q u o r . This technique received severe c r i t i c i s m recently and has been discussed at length by Parker e_t al_. (152). The problem associated with the TAPPI standard (13) are ascribed to incomplete evaporation of water and a i r oxidation during drying both of which result i n higher y i e l d s . Several temporary remedies to these problems were suggested by Parker ejb al_. (152), however, the method remained substantially the same. 3 » 5 » ^ Lignin determination The accurate and rapid determination of dissolved l i g n i n in pulping waste liquors i s of considerable i n t e r e s t . -91-For this purpose various techniques have been suggested, but u l t r a v i o l e t spectroscopy has gained most popularity for both fundamental and applied l i g n i n analysis (101, 105, 106, 107). Most studies on l i g n i n u l t r a v i o l e t spectroscopy are limited to the 280 nm absorption. Unfortunately, absorption at this wavelength i s also strongly influenced by dissolved carbohydrates and t h e i r degradation products (106, 107). L i t t l e information i s available on the disturbed wavelength region between 205 to 280 nm (101, 105, 106, 107). While s u l f i t e spent liquors show c h a r a c t e r i s t i c absorbancies at 205 and 280 nm, sulfate black liquors have an absorption maxima only at 205 nm. The absorption at 280 to 290 nm i s much less defined and i s usually related to carbohydrate degradation products. Evidence of such effects was given by Kleinert and Joyce (106)• The d i s t i n c t maximum at 205 nm was shown to originate from the aromatic nucleous of l i g n i n (105), which was found to give good l i n e a r response with change i n concentration (101). Black liquor l i g n i n concentrations were determined by comparing absorbancies of ethanol diluted black liquors with a c a l i b r a t i o n curve prepared with p u r i f i e d t h i o l i g n i n . The t h i o l i g n i n was prepared by a c i d i f i c a t i o n of a spruce sulfate pulping liquor (3-1) with 10% hydrochloric acid to pH 3-4. The precipitated t h i o l i g n i n was co l l e c t e d by centrifuging -92-(6,620 G) and repeatedly washed with d i s t i l l e d water u n t i l no further brown color was detectable i n the wash water. The centrifuged t h i o l i g n i n was air-^dried and p u r i f i e d by f i l t r a t i o n from ethanol solutions followed by evaporation to dryness. The procedure of p u r i f i c a t i o n i n ethanol solution was repeated twice and the residue washed with dry ether followed by vacuum drying. The c a l i b r a t i o n curve i n Fig. 3.17 was prepared by dis s o l v i n g various amounts of the dried t h i o l i g n i n i n 95% ethanol and p l o t t i n g the concentrations against absorbancy obtained at 213 nm. Black liquor samples were dil u t e d to 2500 and 5000 parts with 95% ethanol. The absorbancies were measured with a Unicam Sp. 800 spectrophotometer using a 1 cm quartz c e l l and 95% ethanol as reference. Similar absorption curves were obtained f o r a l l sulfate and polysulfide black liq u o r s . A l l liquors examined exhibited the d i s t i n c t absorption maximum at 213 nm and a f l a t shoulder at 285 nm. Slight s h i f t s i n absorption maxima were observed with l i g n i n concentration i n black liquors; s h i f t s occurring towards the shorter wavelength (210 nm) with decreasing concentrations. 3.6 A c i d i f i c a t i o n of Sulfate Black Liquor with Carbon Dioxide Preliminary experiments showed that sodium s u l f i d e and sodium mercaptan are quite inert to gamma i r r a d i a t i o n i n aqeous alkaline solution at high pH levels (pH 12-13.5). However, below -93-pH 9, both hydrogen s u l f i d e and mercaptan are readily decomposed by gamma-radiation. Further, p r a c t i c a l reason f o r a c i d i f i c a t i o n of such liquors i s due to the fact that sodium su l f i d e concentration i s but l i t t l e changed (20-30%) during sulfate cooking (73, l 6 8 ) . A high s u l f i d i t y cooking liquor gives high sulfur to sodium oxide r a t i o (S/Na^O) i n the combustion furnace, whereby large amounts of hydrogen s u l f i d e and sulfur dioxide are emitted to the atmosphere. At the same time this also produces a smelt with undesirably high melting point (72, 79). This problem i s generally remedied by a c i d i f i c a t i o n of the black liquor to aid recovery;: of an appreciable proportion of the su l f i d e charge as hydrogen s u l f i d e . The a c i d i f i c a t i o n can be conducted by carbonation of black liquor using pulp m i l l stack gases (COg) (l66); and the evolved hydrogen s u l f i d e can be absorbed i n green liquor (l68). During a c i d i f i c a t i o n , l i g n i n phenolic groups are liberated, r e s u l t i n g i n l i g n i n p r e c i p i t a t i o n (166). It i s further assumed that the residual hydrogen s u l f i d e and organic sulfid e s can be eas i l y s t a b i l i z e d by exposure to gamma radiation. In a c i d i f i e d black liquor, odor of the precipitated l i g n i n was found to be eliminated by gamma radiation. A c i d i f i c a t i o n of black liquor was o r i g i n a l l y patented by -9k-Gray e_t a_l. (79). According to t h e i r method the black l i q u o r i s pressure carbonated and the treatment i s followed by s t r i p p i n g with vacuum. The procedure was reported to aid recovery of 55-62% of the t o t a l sulfur from black l i q u o r . The carbon dioxide a c i d i f i c a t i o n apparatus used i n the present experiments consisted of a 50Q'ml glass vessel f o r containing kOO ml black liquor and a magnetic s t i r r e r . Carbon dioxide gas was admitted through a dispersion tube and degree of a c i d i f i c a t i o n was monitored with a pH meter. The CO flow rate was controlled by a 2 rotometer reducing valve which had set at 5^ ml/min. The f i v e 100 ml capacity gas traps each contained 25 ml carbon tetrachloride and 25 ml of 20% NaOH. During black liquor a c i d i f i c a t i o n , changes i n pH were recorded automatically. The rel a t i o n s h i p of pH change and the volume of 00^ bubbled through 400 ml samples of various black liquors at 25°C i s shown i n Fig. 3.18. Carbonation i s considered to be completed when black li q u o r pH reached about 7.4. The s u l f i d e content of a c i d i f i e d black liquor (ELS, CH SH, d 3 CH^SCH^and CH^SSCEj) was determined by syringing 5 ml of ice-water-cooled liquor into a 25 ml volumetric f l a s k through a rubber septum. The f l a s k contained 20 ml carbon tetrachloride and 1.0 g boric acid. The solution was then shaken vigorously several times during inverted storage i n a -5°C freezer f o r 7 to 8 hours. -95-Sulfides c o l l e c t e d i n the carbon tetrachloride layer were analyzed quantitatively by GLC and the results read from the c a l i b r a t i o n curve presented i n Fig. 3 » 8 . The boric acid contained i n the carbon tetrachloride further a c i d i f i e s the carbonated black liquor to about pH 6.5» Concentr-ations 'of hydrogen s u l f i d e and methyl mercaptan i n the carbonated black liquor are too loiv to be determined accurately by s i l v e r n i t r a t e potentiometric t i t r a t i o n . However, the above procedure has been found convenient and accurate for sulfides determination. The e f f i c i e n c y of hydrogen s u l f i d e and methyl mercaptan carbon tetrachloride l i q u i d / l i q u i d extraction was not determined. However, the results appear to be reasonably quantitative by considering that the s o l u b i l i t y of hydrogen s u l f i d e i s 4l.9 g/l i n carbon tetrachloride and only 3.8 g / l i n water at 20°C and 1 atmosphere pressure ( l l 6 ) , while the methyl mercaptan i s highly soluble i n carbon tetrachloride (no data available) and only s l i g h t l y soluble i n water (9^). Thus most of the hydrogen s u l f i d e and methyl mercaptan should be easily transferred into the organic solvent phase. The e f f i c i e n c i e s of dimethyl s u l f i d e and dimethyl d i s u l f i d e extractions were tested by preparing 50 ml organosulfide (k2.k x 10~3 g / l C^SCH^ and 52.8 x 10~3 g / l CttjSSCRj ) enriched carbonated black liquor (1-1). The black liquor had been preextracted with -96-5 x 50 ml carbon tetrachloride p r i o r to enrichment. Five ml of the prepared solution were syringed into a 25ml volummetric f l a s k which contained 1.0 g boric acid suspended i n 20 ml carbon tetrachloride. The solution was then shaken vigorously several times during inverted storage in a -5°C freezer for 7 to 8 hours. GLC analysis followed and the sulfides were determined according to the c a l i b r a t i o n curves presented i n Fig,3*8. The results are compiled i n Table 3.8. Average e f f i c i e n c i e s of dimethyl s u l f i d e and dimethyl d i s u l f i d e were 92.9% and 86.9% respectively. 3.7 Gamma Radiation 3.7.1 Cobalt-60 gamma photon source The gamma ray source used i n these studies, was a Gammacell 220, manufactured by Atomic Energy of Canada Limited (AECL). The Gammacell was i n i t i a l l y loaded with 8610 curies cobalt-60 as p e l l e t s i n 6 pencils and 6,860 curies of cobalt-60 as slugs ( t o t a l , 15^70 c u r i e s ) . The radiation s h i e l d consists of a large steel-encased lead b a r r i e r with provision f o r housing the cobalt-60 source. Cobalt-60 has a half l i f e of 5.24 years. Dose rate measure-ments according to ferrous sulfate chemical dosimetry on March 26, 1968 gave 1.26 x 106 + 2.5% rad/hr radiation i n t e n s i t y being -97-c e r t i f i e d by AECL. The sample chamber dimensions of this i r r a d i a t o r are 8.13-in i n height and 6-in diameter. The i r r a d i a t o r controls consist of drawer movement control switch (for r a i s i n g or lowering the sample drawer manual control, a d i g i t a l timer (calibrated in hours, minutes and seconds) and mode selector switch for selection of time range. The Gammacell ambient temperature i s 34°C. 3«7.2 Gamma ray dosimetry The l i n e a r energy absorption c o e f f i c i e n t varies considerably f o r d i f f e r e n t absorber materials. Absorption of gamma rays i s a function of absorber mass. Thus the gamma ray intensity within the steel vessel used for treatments of the present study must be affected by the wall thickness of the steel vessel. In order to determine the dose available to samples processed i n the vessel, ferrous sulfate dosimetry was conducted. Methods described by Weiss (2l6), Spinks and Woods (180) as well as O'Donnell and Sangster (1^7) were followed. The technique c a l l s for t r i p l y d i s t i l l e d water f o r d i l u t i o n and preparation of dosimetry solutions. This was prepared by using d i s t i l l e d water which was further d i s t i l l e d from 2% reagent grade potassium permanganate (KMnO ) and potassium dichromate k (KCr 0 ) solutions, followed by exposure to gamma rays for 20 - 9 8 -Mrad. The dosimetry solution contains 0.0014 M reagent grade ferrous sulfate (FeSO,), 0.001 M sodium chloride and 0 .4 M 4 spectro grade s u l f u r i c acid. A pre-irradiated 2 x 7.5 cm glass test tube containing 20 ml of the prepared dosimetry solution was saturated with oxygen by bubbling oxygen through the sample f o r 2 min. The tube thus prepared was placed i n the st e e l vessel and irr a d i a t e d for 24l sec on October 19» 1970. Simultaneously, an aliquot dosimetry sample was ir r a d i a t e d outside the vessel f o r the same period of time. The f e r r i c ion ( F e + + + ) concentration formed was determined by spectrophotometry on a Unicam Sp. 800 u l t r a v i o l e t spectrophotometer at 305 nm wave length. The absorbed dose (D) was calculated as follows: O.965 x 1 0 9 (A) D = •- — • • rad e d p G ( F e + + + ) Where: A = absorbance at 305 nm e = 2204 l/mol.cm, absorptivity of f e r r i c ion at 25°C (180) d = 1 cm, sample thickness p = 1.024 g/ml, density of dosimetry solution at 25°C G ( F e + + + ) = 1 5 , 5 m o 1 / 1 0 0 ev(l80) As f o r absorbance measurement, an aliquot of the non-irradiated stock solution was used as blank and the absorbance determined 0 at room temperature (25 C). The absorbed dose (D) calculated from the three re p l i c a t i o n s -99-of ferrous sulfate dosimetry outside the vessel were 106.18, 105.70 and 106.65% based on the value calculated from the AECL c e r t i f i e d value. In contrast, the absorbed dose (D) inside the vessel was 9^.48, 93.66 and 92.14% of the c e r t i f i e d value. Thus the average difference between inside and outside the vessel i s 12.75%. This indicates that the steel vessel reduced the absorbed gamma ray dose by 12.75%. A l l further dose calculations were based on these values by taking the above losses into account where applicable. 3.8 Sample Preparation and Analysis f o r Experimental Gamma Radiolysis of Aqueous Sulfide Model Compound Solutions and Sulfate Black Liquors The four major sulfides (Na 2S, CH SWa, CIL^SC^ and C^SSCELj) which contribute to sulfate pulp m i l l odor problems, have been studied at ambient Gammacell temperature (3k°C) and normal oxygen pressure. The r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n aqueous solution and black liquor (2-1) were also studied extensively with response to a number of obviously important variables such as solution pH, l i g n i n concentration, temperature and oxygen pressure. In these studies, the sulfides were i r r a d i a t e d at concentrations c l o s e l y resembling the conditions under which the compounds occur i n black liquor. The experiments were designed to follow major changes i n concentration with increasing doses of absorbed radiation energy. -100-Th e model experiments were conducted on s u l f i d e s , obtained from regular chemical suppliers as described i n Section 3*1* Further to the analyses, potentiometric t i t r a t i o n always refers to the procedure described i n Section 3*3*1» the gas l i q u i d chromatography (GLC), the modified boric acid a c i d i f i c a t i o n and carbon tetrachloride extraction technique as described i n Section 3*3.2, and turbidimetry as described i n Section 3*4.5. Modifications of these procedures w i l l be indicated where necessary i n the following sections. 3*8.1 Gamma r a d i o l y s i s of aqueous su l f i d e model compounds The gamma r a d i o l y s i s of su l f i d e model compounds involves aqueous solutions of sodium s u l f i d e (Na^S), methyl mercaptan (CH^SH), dimethyl s u l f i d e (CH^SCH^) and dimethyl d i s u l f i d e (CH^SSCELj. 3*8.1.1 Sodium su l f i d e Sodium s u l f i d e solutions were prepared at two pH levels (pH 12.46 and 8.38). The pH 12.46 solution was made by d i s s o l v i n g lOg of reagent grade Na S^HgO i n one l i t e r of d i s t i l l e d water. The solution at pH 8.38 was prepared by dis s o l v i n g l5g Na 2S«9H 20 i n one l i t e r of d i s t i l l e d water. Adjustment to pH 8.38 was achieved by a c i d i f i c a t i o n with O.lN hydrochloric acid. A l i g h t yellow colour was observed a f t e r a c i d i f i c a t i o n , i n d i c a t i n g - 101-that part of the sul f i d e had been oxidized to elemental s u l f u r . Five ml samples of the sodium s u l f i d e solution were transferred into 10 ml test tubes through rubber septums. The samples were ir r a d i a t e d with an absorbed dose of 0, 0.1, 0.3» 0.5, 0.7» 0.9» 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 Mrad at Gammacell ambient temperature. Analysis for residual sodium s u l f i d e was made by s i l v e r n i t r a t e potentiometric t i t r a t i o n (Section 3.3.1) while polysulfide sulfur was determined by UV spectrophotometry (Section 3.4.4). 3.8.1.2 Sodium methyl mercaptan Sodium methyl mercaptan solutions of pH 13*54, 12.54 and 10.70 were prepared by bubbling methyl mercaptan gas into an ice-water-cooled 2.JJ sodium hydroxide solution. The pH of the solution was adjusted by adding 0.1N hydrochloric acid. Five ml of the cooled sodium methyl mercaptan solution were then syringed through septum to ice-water-cooled and oxygen-flushed 10 ml test tubes. The aqueous mercaptan solutions were i r r a d i a t e d at ambient Gammacell temperature i n the closed tubes to one of 0, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1.5, 2.0, 2.5 and 3.0 Mrad absorbed doses. The sodium-methyl mercaptan was analyzed by s i l v e r n i t r a t e potentiometric t i t r a t i o n (Section 3.3.1). Formation of dimethyl d i s u l f i d e was determined f o r the mercaptan solution of pH 13.54 -102-by GLC analysis. The pH of the samples was also measured. Sulfate formation also has been found as a r a d i o l y s i s product of methyl mercaptan. Ten ml of the pH 10.70 methyl mercaptan solution were syringed into an oxygen flushed 50 ml test tube and i r r a d i a t e d up to k Mrad at Gammacell temperature. The i r r a d i a t e d solution was further a c i d i f i e d to about pH 3 by adding 0.1 N hydrochloric acid, boiled f o r 10 min to expel the residual methyl mercaptan and f i l t e r e d through a f i l t e r paper to obtain a clear solution. Three ml of 3 M barium chloride were then added whereby p r e c i p i t a t i o n of sulfate was observed. 3.8.1.3 Dimethyl s u l f i d e and dimethyl d i s u l f i d e A comparative study was made by r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n a l k a l i n e solution and i n a commercial sulfate black liquor (2-1). The dimethyl s u l f i d e a l k a l i n e solution was prepared by syringing 55 p l dimethyl s u l f i d e through septum to an ice-water-cooled and oxygen saturated volumetric f l a s k containing 500 ml 0.25 N sodium hydroxide solution. The same procedure was also followed f o r preparation of the dimethyl d i s u l f i d e a l k a l i n e solution. The organic s u l f i d e black liquor solution was prepared by d i s s o l v i n g 80 jul of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n 500 ml of cooled, oxygen saturated black liquor (2-1) contained i n a volumetric f l a s k . The solutions thus prepared were thoroughly -103-mixed by shaking and then refrigerated at -5°C f o r three days. The i n i t i a l pH values of the solutions were 13.12 and 13.1k f o r the alkaline and black liquor, respectively. From these stock solutions 10 ml portions were syringed through septum to i c e -water-cooled and oxygen flushed 50 ml test tubes. The sample were then i r r a d i a t e d to 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.5, 2.0, 2.5 3.0, 3.5, 4.0, and 4.5 Mrad at ambient Gammacell temperature. Residual s u l f i d e concentrations aft e r i r r a d i a t i o n were determined by the GLC method. In order to i s o l a t e larger quantities of the products from the gamma ir r a d i a t e d dimethyl s u l f i d e a l k a l i n e solution, 5 ml dimethyl s u l f i d e dissolved i n 50 ml 0.25 N sodium hydroxide solution was s t i r r e d and i r r a d i a t e d f o r 5 Mrad i n a 500 ml volume t r i e f l a s k . Following i r r a d i a t i o n the solution was placed i n a 6o°C water bath f o r 4 hours to d i s t i l l off the residual dimethyl s u l f i d e . The solution was then thoroughly extracted with chloro^ form. The organic layer was further washed with d i s t i l l e d water three times. On evaporation of the excess chloroform the residue was dried i n vacuum at room temperature, which provided a white amorphous substance. The infrared spectrum of the substance was obtained by d i s s o l v i n g the sample i n small amounts of ether and applying the paste to a potassium bromide window. The infrared spectrum was run on a Perkin Elmer Model 21 double beam spectro--10k-photometer. A sample spectrum from the product i s shown i n Fig.3.19, No sulfate p r e c i p i t a t i o n was observed by adding 3M barium chloride to the a c i d i f i e d aqueous solution (pH 3). A similar procedure was also followed f o r the r a d i o l y s i s of dimethyl d i s u l f i d e i n alk a l i n e solution. However, the chloroform extract could not be isolated; whereas p r e c i p i t a t i o n of sulfate has been observed on addition of barium chloride to the a c i d i f i e d , i r r a d i a t e d solution. Due to the fact that aqueous dimethyl s u l f i d e and dimethyl d i s u l f i d e solutions are r e l a t i v e l y inert to gamma radiation, variables such as solution pH, dissolved l i g n i n content, temper-ature and oxygen pressure were studied. These are considered as af f e c t i n g the r a d i o l y s i s degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e according to the following processes. 3.8.1.3.1 Effect of pH Due to d i f f i c u l t i e s found with black liquor, pH was studied on buffered solutions of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n model systems. Solutions with varying pH were prepared by mixing desired proportions of 0.1 M hydro-c h l o r i c acid (HCI), potassium dihydrogen phosphate (KHoP0,,) and 2 M" sodium hydroxide (NaOH) (94). The dimethyl s u l f i d e solution was prepared by di s s o l v i n g about -105-5 u l dimethyl s u l f i d e i n 50-60 ml oxygen saturated buffer solutions. S i m i l a r l y , dimethyl d i s u l f i d e solution was prepared by mixing about 8 u l dimethyl d i s u l f i d e to 50-60 ml oxygen saturated buffer solution. From the above stock solutions 5 ml portions of ice-water-cooled organic s u l f i d e solutions were then syringed through septum to 10 ml capacity oxygen flushed test tubes. The samples were ir r a d i a t e d to 3 Mrad at ambient Gammacell temperature. The i n i t i a l and f i n a l (after 3 Mrad i r r a d i a t i o n ) organic s u l f i d e concentrations were determined by GLC analysis following the usual 5 x 10 ml carbon tetrachloride extraction. No change was found in the pH of the buffer solution a f t e r 3 Mrad gamma-radiation. 3.8.1.3.2 Effect of dissolved l i g n i n Concentration of dissolved t h i o l i g n i n could not be e f f e c t i v e l y controlled i n black liq u o r without d i l u t i o n or condensation. Thus, by necessity, the effect of dissolved t h i o l i g n i n was best studied again on aqueous solutions of dimethyl s u l f i d e and dimethyl d i s u l f i d e . Five hundred ml aliquot samples of 165.O x 10~^g/l dimethyl s u l f i d e and 190.0 x 10~ 3g/l dimethyl d i s u l f i d e solutions were prepared i n O.25 N sodium hydroxide. The sodium hydroxide solutions were saturated with molecular oxygen at ice-water -106-temperature. The solutions thus obtained were mixed thoroughly and stored i n a freezer ( 5°C) for three days. To 5 ml portions of these stock solutions various quantities of t h i o l i g n i n (Section 3.7.4) were added to provide a concentration range of 10-120 g / l by weighing the appropriate amount of t h i o l i g n i n into 10 ml test tubes. Then, 5 ml of ice-water-cooled organic sulfides, containing the a l k a l i n e solution, was syringed through a septum to the test tubes. The rnixturre was shaken thoroughly u n t i l the t h i o l i g n i n was dissolved, and kept i n the freezer (5°C) f o r two days. The samples were then i r r a d i a t e d to 1.5 and 3.0 Mrad. The residual dimethyl s u l f i d e and dimethyl d i s u l f i d e concentrations were estimated by GLC following 5 x 10 ml carbon tetrachloride extraction. The pH of the 3 Mrad i r r a d i a t e d solutions was also measured. 3.8.1.3*3 High temperature and high pressure A portion (30 ml) of cooled black liquor (1-3* 2-1) samples was introduced into a pre-cooled and oxygen flushed stainless steel pressure vessel (3*5 x 8.7 cm, wall thickness, 0.7 cm) through a rubber septum which could be inserted into the vessel outlet. This was designed f o r transfering samples in/out of the vessel by a syringe. The high pressure and temperature apparatus used i n the -107-present studies i s shown i n Fig. 3.20. Gas connections were 3l6 stainless steel l / 8 - i n diameter tubing joined by Swedge-Lock connectors. Temperature control was achieved by a ca l i b r a t e d power regulator. Automatic temperature records were obtained with the aid of thermocouples (iron-constantan) and strip- c h a r t recorder. I r r a d i a t i o n of samples thus prepared was done i n the Gammacell at a nominal dose rate of 1.26 x 10^ rad/hr (March 26, 19-68). A proper dose correction factor f o r the steel pressure vessel has been applied as determined by Fricke dosimetry (Section 3.7.2). I r r a d i a t i o n temperatures of black liquor samples were controlled by a heating mantle and power regulator. The r e l a t i o n between set t i n g and temperature i s shown i n Fig. 3.21. Five hundred m i l l i l i t e r s of the organosulfide enriched black liquor (1-3) and carbonated black liquor (2-1) samples contained . in a septumed volumetric f l a s k were thoroughly shaken and stored i n the freezer (5°C) for three days. From the stock solution, 30 ml of the cooled black liquor was syringed into an ice-water-cooled and oxygen flushed steel pressure vessel and placed under 50 p s i oxygen pressure. The solution was s t i r r e d magnetically f o r a period of 10 min. The closed vessel was then i r r a d i a t e d to a to t a l of 3 Mrad dose at heating mantle power regulator settings of -108-20, 25, 30, 40 and 45 (50 to 120°C). The effect of oxygen pressure (between 25 to 100 psi) on the r a d i o l y t i c degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liquor (2-1) and carbonated black liquor (2-1) portions was also studied at ambient Gammacell temperature (34°C). The control samples were prepared by the same procedure except without gamma i r r a d i a t i o n . After i r r a d i a t i o n , the vessel was removed from the Gammacell o chamber and cooled to -5 C overnight. The excess pressure was then released while the sample was frozen within the container. The sample was further stored i n the vessel and allowed to thaw in ice-water. The solution was sampled with a 10 ml syringe for further analyses by GLC. 3.8.2 Gamma r a d i o l y s i s of sulfate and polysulfide black liquors Two 120 ml open glass beakers containing 80 ml black liquor (3-1) were ir r a d i a t e d at ambient Gammacell tempera-ture (3'+°C) to 0, 0.06, 0.12, 0.24, 0.37, 0.49, 0 . 6 l , 0.92, 1.22, 1.52, 1.83, 2.13 and 2.44 Mrad. The solution was p e r i o d i c a l l y sampled for analysis by potentiometric t i t r a t i o n of monosulfide and p o l y s u l f i d e . Four ml of the black liquor sample were p e r i o d i c a l l y withdrawn by a pipette f o r s i l v e r n i t r a t e potentiometric t i t r a t i o n . -109-Th e consumption of 0.05 N s i l v e r n i t r a t e at i n f l e c t i o n "a" and "b" was taken to correspond to the monosulfide and poly-s u l f i d e species, respectively. In another series of experiments, the effects of .gamma radiation on dimethyl s u l f i d e , dimethyl d i s u l f i d e and the unidentified sulfur compound (X) i n the various sulfate and polysulfide black liquors were studied. Ten ml of the ice-water-cooled black liquor were syringed into oxygen flushed and cooled (0°C) 50 ml test tubes which were equipped with rubber septums. The samples were then i r r a d i a t e d i n the Gammacell for 0, 1.0, 2.0, 3.0, 4.0 and 5.0 Mrad, then c h i l l e d i n ice water. In the meantime • the control samples (0 Mrad) were conditioned in a 34 + 0.5°C water bath. The organosulfides were determined by 5 x 5 ml carbon tetrachloride extraction followed by GLC analysis (Fig 3.9) • The quantity of the unidentified s u l f u r compound (Xv) was estimated from dimethyl s u l f i d e c a l i b r a t i o n curve (Fig 3.9). 3.8.3 Gamma r a d i o l y s i s of carbonated sulfate and polysulfide black liquors The various sulfate and polysudfide black liquors were carbonated by saturation with carbon dioxide. From these stock solutions 10 ml samples were syringed into oxygen flushed and ice-water-cooled 50 ml test tubes. Radiation doses of 0, 1.0, -110-2.0, 3*0, 4.0 and 5.0 Mrad were used. Following i r r a d i a t i o n , the samples were immediately c h i l l e d i n ice-water. S i m i l a r l y , the control samples (0 Mrad) were conditioned i n a 34 + 0.5°C water bath. The sulfides were analysed by i n j e c t i n g 5 ml of the appropriate sample into a 25 ml septumed volumetric f l a s k con-taining 20 ml carbon tetrachloride and appropriate quantity of boric acid (1.0 g) a c i d i f i e s the carbonated sample to pH 6.5. The sulfides such as hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e , dimethyl d i s u l f i d e and the unidentified sulfur compound (X) were determined d i r e c t l y by GLC by comparing the detector response plotted i n the c a l i b r a t i o n curves (Fig. 3*8)• The unidentified sulfur compound (X) was also estimated from the c a l i b r a t i o n curve of dimethyl s u l f i d e (Fig. 3*8). 3.8.4 Effect of oxygen, a i r and nitrogen atmosphere on gamma r a d i o l y s i s of sulfides i n the carbonated black liquors A 500 ml carbon-dioxide-acidified black liquor (1-1) was prepared i n a septum sealed volumetric f l a s k . The solution was further enriched with sulfides by bubbling hydrogen s u l f i d e , methyl mercaptan, and adding 100 jul dimethyl s u l f i d e and 150 pi dimethyl d i s u l f i d e to the solution. The solution thus obtained was shaken vigorously and stored i n a freezer (5°C) f o r - I l l -three days. Ice-water-cooled 50 ml test tubes were flushed with oxygen, a i r or nitrogen,as required f o r various experiments, and sealed with rubber septums. Ten ml of the a c i d i f i e d black li q u o r was syringed to each test tube. The samples were then homogenized and i r r a d i a t e d at Gammacell temperature to 0, 0.5, 1.0, 2.0 and 3.0 Mrad. The control samples (0 Mrad) were also prepared by the same procedure and conditioned i n a water bath held at 34 + 0.5°C. After the treatment, control and gamma ir r a d i a t e d samples were cooled i n ice-water and stored i n a -5°C freezer f o r four hours. Five ml portions of the cooled solution were syringed to 50 ml septumed volumetric flasks containing 45 ml carbon tetrachloride and an appropriate amount of boric acid (1.0 g) to reduce the solution pH from 7*5 to 6.5. The s u l f i d e s were then analyzed quantitatively by GLC. 3.9 Regeneration of Polysulfide from Sodium Sulfide and Green Liquor During the course of these investigations i t was discovered through chemical analysis that i r r a d i a t e d sodium s u l f i d e solutions contained substantial amounts of p o l y s u l f i d e . This indicated that increased s t a b i l i t y of aqueous sodium s u l f i d e solutions i s attained not only through an oxidation of s u l f i d e toward higher valence states of sulfur (SO ), but also through formation of p o l y s u l f i d e . -112-Th i s phenomenon may provide a new opportunity for i n d u s t r i a l manufacture or regeneration of pol y s u l f i d e . Experiments were conducted i n a 50 ml stainless steel vessel (3.5 x 15 cm, wall thickness 0.7 cm). A proper dose correction factor has been determined for the vessel by ferrous sulfate dosimetry (Section 3.7.2). Forty-ml of various concentrations of aqueous sodium s u l f i d e and a pulp m i l l green liquor (1-2) were placed i n the vessel and irra d i a t e d at Gammacell temperature up to 70 Mrad. The i r r a d i a t i o n apparatus was simi l a r to that depicted in Fig. 3.20. An a i r pressure driven magnetic s t i r r e r was used for mixing of the sulfide, solution and carbon dioxide or hydrogen s u l f i d e gas. After i r r a d i a t i o n , the excess gas pressure was relieved and one gram of sodium hydroxide was added to s t a b i l i z e the residual hydrogen s u l f i d e . The polysulfide excess sulfur was determined by u l t r a v i o l e t spectrophotometry as described i n Section 3.4.4„ The formation of sulfate was measured as t u r b i d i t y produced by treatment of the solution with barium chloride (Section 3.4.5). -113-4.0 RESULTS 4.1 Gas Liquid Chromatography (GLC) Calib r a t i o n Curves f o r Sulfides The c a l i b r a t i o n curves f o r hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e , generally found i n a c i d i f i e d black liquor, are shown i n Fig, 3 « 8 , whereas the c a l i b r a -tion curves presented i n Fig. 3*9 were prepared for dimethyl s u l f i d e and dimethyl d i s u l f i d e as obtained by l i q u i d / l i q u i d extraction with carbon tetrachloride from unacidified black liquor (2-1). 4.2 Black Liquor Characteristics A limited number of sulfate black liquor c h a r a c t e r i s t i c s , such as pH, so l i d s , density, l i g n i n content and various sulfides have been determined. The results are given i n Table 4.1. 4.3 I r r a d i a t i o n of Aqueous Sulfide Model Compounds The degradation of sulfides induced by gamma radiation, was studied on sodium s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e as model compounds. The effects of such variables as solution pH, l i g n i n concentration, temperature and oxygen pressure were investigated. 4.3.1 Sodium sulfate The gamma r a d i o l y s i s of aqueous su l f i d e solutions -114-of pH 12.46 and 8.38 were studied. Degradation of sodium s u l f i d e i s exponential with dose. Changes i n sodium s u l f i d e concentration and formation of polysulfide excess sulfur are shown i n Table 4.2 and Fig. 4.1. The yie l d s of sulf i d e degradation (G(-Na 2S)) and formation of polysulfide excess sulfur (G(S)) are determined with the aid of i n i t i a l slopes of curves found i n Fig. 4.1. The relationship between s u l f i d e solution pH and G(-Na2S) and G(S) are shown i n Table 4.3. The solution pH greatly affected the degradation y i e l d of sulfides and y i e l d of polysulfide excess s u l f u r . The sodium su l f i d e degradation yie l d s (G(-Na 2S)) increase from 5»0 to 7»5» when solution pH i s decreased from 12.46 to 8.38. Meanwhile, the yields of polysulfide excess sulfur (G(S)) increased from 0.1 to 1.1 when the solution pH was decreased from 12.46 to 8.38 (Table 4.3). 4.3.2 Sodium methyl mercaptan Gamma r a d i o l y s i s of methyl mercaptan i n aqueous solutions of pH 13*54, 12.54 and 10.70 was studied. The mercaptan degradation as induced by gamma radiation, the observed pH changes and formation of dimethyl d i s u l f i d e from mercaptan solution of pH 13.5** are shown i n Table 4.4 and Fig. 4.2. The apparent methyl mercaptan degradation yields (G(-CELSNa)) were calculated from the -115-i n i t i a l slopes of curves i n Fig. 4.2 and are given i n Table 4.3. The exponential plot of mercaptan degradation rate (slope) obviously increases as the i n i t i a l solution pH i s decreased from 13.54 to 12.54 and 10.70 (Fig. 4.2). Similarly, values of mercaptan degradation yie l d s are greatly affected by solution pH; G^-CH^SNa)) of 2.5, 11.3 and 15.4 correspond to solution pH 13.54, 12.54 and 10.70 (Table 4.3). Two products, dimethyl d i s u l f i d e (Fig. 4.2) and sulfate, were discovered i n i r r a d i a t e d aqueous methyl mercaptan solutions. The actual quantity of sulfate was not determined. 4.3.3 Dimethyl sul f i d e and dimethyl d i s u l f i d e The results of gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n a selected black liquor (2-1, pH 13.14) and alkaline solution (pH 13.12), are presented i n Fig. 4.3. Numerical values and respective pH changes are shown i n Tables 4.5 and 4.6. The apparent degradation yie l d s of dimethyl s u l f i d e (Gf-CH^SCH^ ) ) and dimethyl d i s u l f i d e (Gf-CH^SSCIij ) ), calculated from the i n i t i a l slopes of curves found i n Fig. 4.3, are tabulated i n Table 4.7. The results indicate that r a d i o l y t i c degradation of dimethyl su l f i d e and dimethyl d i s u l f i d e i n black liquor as well as i n alka l i n e solution i s exponential with dose. Degradation yie l d s -116-were s i g n i f i c a n t l y higher i n aqueous alkaline solution than i n black l i q u o r . As shottrn i n Table 4.7, the corresponding degrada-tion y i e l d s of dimethyl s u l f i d e and dimethyl d i s u l f i d e were 0.73, 0.89 for aqueous alkaline solution, and only 0.50, 0.43 f o r black liquor, i . e . , a d e f i n i t e protective effect i n black liquor i s observed. The experiment also indicates that up to 4.5 Mrad dose the pH of black liquor i s only s l i g h t l y affected by the gamma radiation treatment (Table 4.6). Sulfate has been found to be a product of gamma r a d i o l y s i s of dimethyl d i s u l f i d e aqueous solution but the concentration i s too low to be determined quantitatively by the usual wet chemistry (barium s a l t gravimetric) method. On the other hand, sulfate could not be detected i n irr a d i a t e d dimethyl s u l f i d e solutions, however, an unidentified amorphous carbonyl group containing substance was detected and analysed by infrared spectrum reproduced i n Fig, 3.19* The effect of solution pH, l i g n i n concentration, temperature and oxygen pressure on the degradation yields of dimethyl s u l f i d e and dimethyl d i s u l f i d e were studied i n some d e t a i l as indicated i n the following s e r i e s . -117-4.3.3.1 Effect of solution pH The r e l a t i o n of solution pH versus percentage decomposition of su l f i d e s , degradation yie l d s (Gr), and degradation y i e l d to i n i t i a l concentration (mole) r a t i o ( G / C O ) are shown i n Table 4.8 as well as Figs. 4.4 and 4.5. The results show a high c o r r e l a t i o n of solution pH on degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e as induced by gamma radiation. The per cent degraded dimethyl s u l f i d e (91.2 to 44.0%) decreased l i n e a r l y as solution pH was increased from acid (pH 0.5) to strong base (pH 13.5). S i m i l a r l y , the degradation percentage of dimethyl d i s u l f i d e (82.3 to 65*0%) decreased almost l i n e a r l y as solution pH was increased from pH 1.5 to 10.1, then i t s l i g h t l y increased from 70.3 to 73.8% as the pH was further increased from pH 11.5 to 13.0. The degradation y i e l d of dimethyl s u l f i d e (Gt-CH^SCH^)) decreased l i n e a r l y from 0.43 to 0.17 as the solution pH was increased from strong acid (pH 0.5) to strong base (pH 13.5). While the degradation yields of dimethyl d i s u l f i d e (G(-CH SSCBL)) 3 3 increased s l i g h t l y from 0.47 to 0.50 when solution pH was increased from 1.5 to 5.5, the y i e l d decreased from 0.48 to 0.36 when the solution pH was increased from 5*5 to 10.1. Again, the y i e l d increased s l i g h t l y from 0.36 to 0.39 as solution pH was increased from 10.1 to 13«5» -118-Since i n i t i a l concentrations of dimethyl sulfide and/or dimethyl d i s u l f i d e were varied i n the samples having various solution pH(Table 4.8), i t would be more l o g i c a l to compare the respective degradation rates by yields to i n i t i a l s u l f i d e concentrations (G/Co). A S shown in Fig. 4.5, dimethyl s u l f i d e G/Co also decreases l i n e a r l y as the solution pH i s changed from strong acid to strong base, whereas G/Co of dimethyl d i s u l f i d e i s decreased almost l i n e a r l y from strong acid to pH 10.1 and G/Co then s l i g h t l y increases from pH 10.1 to 13«5» 4.3.3.2 Effect \of l i g n i n concentration The relationship of l i g n i n concentration to percentage decomposition, and degradation y i e l d s (G) of dimethyl s u l f i d e and dimethyl d i s u l f i d e following i r r a d i a t i o n between 1,5 to 3*0 Mrad are shown i n Table 4.9 and Fig. 4.6. The results reveal that the presence of l i g n i n ( t h i o l i g n i n ) affects the radiation degradation of the organosulfides i n diverse ways. The l i g n i n in solution may gradually i n h i b i t radiation degradation of the organosulfides as l i g n i n concentration increases progressively up to about 50 g / l . On further increase of the l i g n i n concentration from 50 to 120 g / l , the percentage of s u l f i d e decomposition increases s l i g h t l y for both 1.5 and 3.0 Mrad dose. S i m i l a r l y , the average degradation y i e l d (G) of dimethyl s u l f i d e and dimethyl d i s u l f i d e decreased obviously from 0.53 to 0.34, as l i g n i n -119-concentration was gradually increased from 0 to 50 g / l , there-a f t e r on further increase of l i g n i n concentration (50 to 120 g/l) the degradation y i e l d increases only s l i g h t l y . 4.3.3.3 Effect of temperature Black liquor (1-3) and carbonated black liquor (2-1) enriched with dimethyl s u l f i d e and dimethyl d i s u l f i d e were i r r a d i a t e d f o r 3 Mrad under 50 psi i n i t i a l oxygen pressure between 60 to 115°C. The effect of solution temperature on decomposition rate of dimethyl s u l f i d e and dimethyl d i s u l f i d e , degradation y i e l d s (G), and r e l a t i o n of s u l f i d e degradation, the change of black liquor pH of gamma irr a d i a t e d and control (without i r r a d i a t i o n ) samples was compared i n Tables 4.10 and 4.11 as well as Figs. 4.7 and 4.8. The results indicate a s i g n i f i c a n t effect of temperature on degradation rate of organosulfides, i n both i r r a d i a t e d and control black liquors, as well as carbonated black liquor samples. However, the temperature did not confound the effect of radiation as the rate of organosulfide degradation of the i r r a d i a t e d liquors was considerably f a s t e r than that observed on the control samples. The percentage of dimethyl s u l f i d e and dimethyl d i s u l f i d e decomposition i n black liquor (1-3) under 50 p s i i n i t i a l oxygen -120-pressure, following administration of 3 Mrad (305 min) radiation dose, shows that increasing the temperature from 60 to 115°C s i g n i f i c a n t l y increased the decomposition rate of dimethyl s u l f i d e from 52.88 to 77.45% f o r the gamma radiation treatment and by the same r e l a t i v e amount of 34.79 to 56.25% for the control samples. Concurrently, dimethyl d i s u l f i d e decomposition increased from 71.98 to 100% for the irra d i a t e d samples and only from 5 ^ . 7 9 to 83.27% for the control samples. S i m i l a r l y , dimethyl s u l f i d e degradation y i e l d (Gf-CH^SCRj )) increases l i n e a r l y from 0.44 to 0.64 as the temperature was increased from 60 to 115°C. The dimethyl d i s u l f i d e degradation y i e l d (Gi-CH^SSCH^)) also increased l i n e a r l y from 0.34 to 0.46 with increase i n temperature from 60 to 83°C (Table 4.10). Dimethyl s u l f i d e and dimethyl d i s u l f i d e i n carbonated black liquor under 50 p s i i n i t i a l oxygen pressure, i r r a d i a t e d with a 3 Mrad (297 min) dose, also shows that an increase of temperature from 77 to 115°C greatly increases dimethyl s u l f i d e decomposition percentage from 59.24 to 87.68% f o r the gamma radiation treatment and only 33.86 to 59.22% for control samples. With the same temperature changes, dimethyl d i s u l f i d e decomposition percentage increased from 53.82 to 97.79% f o r the ir r a d i a t e d samples and only 36.17 to 78.86% for control samples. Sim i l a r l y , the dimethyl s u l f i d e degradation y i e l d (G(-CHSCH_ ) ) increases l i n e a r l y from -121-0.17 to 0.25 and dimethyl d i s u l f i d e degradation y i e l d (Gf-CH^SSCftj) ) increases from 0.18 to 0.34, when the maximum temperature was increased from 77 to 115°C (Table 4.11). Black liquor (3-1) pH is considerably decreased by i r r a d i a t i o n at elevated temperature. On the irra d i a t e d samples (3 Mrad) pH decreased from 12.51 to only 11.42, when the maximum temperature was increased from 60 to 115°C and samples were kept under 50 p s i i n i t i a l oxygen pressure (Table 4.10). This indicates that gamma i r r a d i a t i o n s i g n i f i c a n t l y lowers the black liquor' pH when i t i s irr a d i a t e d at higher temperature. On the other hand, the carbon-ated black liquor pH was l i t t l e affected by gamma i r r a d i a t i o n under the temperature range (Table 4.11). 4.3.3*4 Effect of oxygen pressure Dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liquor (2-1) and carbonated black liquor (2-1) were ir r a d i a t e d f o r 3 Mrad at Gammacell temperature (34°C) under various oxygen pressures (25-100 p s i ) . The effect of oxygen pressure on decomposition percentage of dimethyl s u l f i d e and dimethyl d i s u l f i d e , degradation yields (G), and comparisons of sulfi d e degradation between ir r a d i a t e d and control samples, are tabulated i n Tables 4.12 and 3.13 and presented graphically i n Figs.4.9 and 4.10. The results reveal that degradation of organosulfides i n both -122-black liquor and carbonated black liquor increases obviously as oxygen pressure i s increased. In contrast, the degradation of organosulfides, as induced by gamma radiation, i s usually considerably higher than that obtained with comparable control sarnpl es. Decomposition percentage of dimethyl s u l f i d e i n black liquor ( 2 - l ) ; a t ambient Gammacell temperature following 3 Mrad (297 min) dose, shows that v a r i a t i o n of oxygen pressure from 25 to 100 p s i increased the degradation l i n e a r l y from 66.16 to 87.67% f o r gamma irr a d i a t e d samples, and only from 29.33 to 57.4l% f o r the comparable control black l i q u o r . The rate of dimethyl d i s u l f i d e decomposition increased from 46.72 to 77.87% f o r i r r a d i a t e d black liq u o r samples and only from 30.22 to 42.08% f o r the comparable control samples when the oxygen pressure was increased from 25 to 100 p s i . S i m i l a r l y , the apparent degradation y i e l d (G^CH^SCH^)) of dimethyl s u l f i d e nearly doubled (0.l6 to 0.31) and the apparent degradation y i e l d of dimethyl d i s u l f i d e also increased from 0.08 to 0.l4, when the oxygen pressure was increased from 25 to 100 p s i (Table 4.12). The decomposition percentage of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n irr a d i a t e d carbonated black liquor (2-1) was also investigated under 25 to 100 p s i oxygen pressure. For ir r a d i a t e d dimethyl s u l f i d e samples the decomposition percentage increased -123-from 66.16 to 87.67% and only 29.33 to 57.^1% f o r the comparable control samples. The decomposition percentage of dimethyl d i s u l f i d e increased from 46.72 to 77.87% and 30.22 to 57.03% f o r gamma irr a d i a t e d and comparable control samples, respectively, when the oxygen pressure was increased from 25 to 100 p s i . S i m i l a r l y , the calculated degradation y i e l d of dimethyl s u l f i d e (Gf-CH^SCH^ ) ) increased from 0.21 to 0.28 and 0.l6 to 0.26 f o r dimethyl d i s u l f i d e as the oxygen pressure was increased from 25 to 100 p s i . These yields are d e f i n i t e l y modest considering the substantially excess quantity of available oxygen. 4.4 Gamma Radiolysis of Sulfate and Polysulfide Black Liquor (pH 12.85-13.40) Black liquor (3-1) was irr a d i a t e d at Gammacell ambient temperature. Four ml samples were p e r i o d i c a l l y withdrawn and analysed f o r monosulfide (S ~) and polysulfide (S S ) by s i l v e r n nitr a t e potentiometric t i t r a t i o n . The consumption of 0.05N s i l v e r n i t r a t e for monosulfide (-430 mv) decreased to almost zero and polysulfide (-250 mv) gradually increased to a t t a i n maximum when the black liquor was irra d i a t e d to about 1 Mrad. Further i r r a d i a t i o n i s expected to induce polysulfide degradation (Table 4.14 and Fig 4.11) due to possible competing reactions i n the mixture. The pH of the black liquor was found to be l i t t l e affected by -124-gamma radiation up to 2.44 Mrad (Table 4 . l 4 ) . Gamma radiation induced degradation of dimethyl s u l f i d e , dimethyl d i s u l f i d e and the unidentified s u l f u r compound (X) i n various black liquors i s shown i n Tables 4.15, 4.l6 and 4.17 as well as i n Figs. 4.12, 4.13 and 4.l4, respectively. The degradation of dimethyl s u l f i d e (Fig. 4.12) and dimethyl d i s u l f i d e (Fig. 4.13) are also exponential with dose. Apparent degradation yields of dimethyl s u l f i d e (Gf-CRjSCH-j) ) and dimethyl d i s u l f i d e (Gt-CH^SSCH^)) of the various black liquors were calculated from the i n i t i a l slopes of respective s u l f i d e degradation curves as shown i n Figs. 4.12 and 4.13. The results are also shown i n Table 4.18. Due to the low concentration of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n process black liquors (Table 4.1), the s u l f i d e degradation yie l d s are considered to be greatly affected by the i r i n i t i a l concentration. The p l o t t i n g of dimethyl s u l f i d e and dimethyl d i s u l f i d e degradation y i e l d (Tables 4.5. 4.6 and 4.18) vs. i n i t i a l organosulfidee concentrations (Tables 4.1, 4.5 and 4.6) are shown graphically i n Figs. 4.15 and 4.16 for dimethyl s u l f i d e and dimethyl d i s u l f i d e , respectively. The results show that the degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liquors was exponential with dose (Figs. 4.12 and 4.13). The gamma radiation degradation yie l d s of dimethyl s u l f i d e (G(-CH SCH ) ) and dimethyl d i s u l f i d e (G(-CH_SSCIL,) - 1 2 5 -i n black liquor are very low and range from 0o001 to 0 . 0 0 3 for dimethyl s u l f i d e and 0 . 0 0 2 to 0.085 f o r dimethyl d i s u l f i d e (Table 4.18). As shown i n Figs. 4.15 and 4 . l 6 , the apparent degradation yi e l d s correlate strongly with the i n i t i a l concentration of organosulfides. Dimethyl sul f i d e degradation y i e l d s increased considerably from 0.002 to O.56 when i t s i n i t i a l concentration i n black liquor (2-1) was increased from O.56 x 10~ 3 to 171.8 x 1 0 ~ 3 g / l (Fig. 4 . 1 5 ) . S i m i l a r l y , dimethyl d i s u l f i d e degradation y i e l d (0.045 to 0.885) i n black liquor (2-1) greatly increased as the concentration was boosted from 17.08 x 10~ 3 to 207.5 x 1 0 " 3 g / l (Fig. 4 . 1 5 ) . 4 . 5 Gamma Radiolysis of Carbonate Sulfate and Polysulfide Black Liquors (pH 8 . 2 0 - 9 1 5 ) The extent of r a d i o l y t i c degradation of hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e , dimethyl d i s u l f i d e and of the unidentified sulfur compound (X) i s shown i n Tables 4 . 1 9 , 4 . 2 0 , 4 . 2 1 , 4.22 and 4.23 as well as i n Figs. 4 . 1 7 , 4.18, 4 . 1 9 , **.20 and 4 . 2 1 . The exponential degradation patterns of hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e were further plotted i n Figs. 4 . 1 7 , 4.18, 4.19 and 4 . 2 0 , respectively. Apparent degradation yi e l d s given i n Figs. 4 . 1 7 , 4.18, 4.19 and 4 .20 of hydrogen s u l f i d e (G(-H"2S), methyl mercaptan (Gf-CH^SH) ), dimethyl s u l f i d e (Gt-CH^SCaj ) )' and dimethyl d i s u l f i d e (Gf-CRjSSCH^ ) ) -126-i n various carbonated black liquors, were calculated from the i n i t i a l slopes of the respective s u l f i d e degradation curves. The degradation yields of the sulfides are further shown i n Table 4.24. The, results indicate that the degradation of hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e i n the carbonated black liquors was exponential with dose (Figs, 4.17, 4.18, 4.19 and 4.20). The i n i t i a l concentration of sulfides i n the carbonated black liqu o r varied according to d i f f e r e n t sources. The s u l f i d e degradation yields (Table 4.24) were also plotted against the i n i t i a l concentration of sulfides i n the respective liquors from Tables 4.19, 4.20, 4.21 and 4.22. The correlations of su l f i d e degradation yie l d s and their i n i t i a l concentration are shown i n Figs. 4.22, 4.23, 4.24 and 4.25 f o r hydrogen s u l f i d e , methyl mercap-tan, dimethyl s u l f i d e and dimethyl d i s u l f i d e , respectively. The s u l f i d e degradation y i e l d varies with s u l f i d e species and highly correlates with i t s i n i t i a l concentration exi s t i n g i n the carbonated black l i q u o r . Hydrogen s u l f i d e degradation yie l d s (G(-H 2S)), as shown i n Fig. 4.22, increased l i n e a r l y from 0.015(1-2) to 3.427(4-lL) when the i n i t i a l concentrations were increased from -3 _3 0.89 x 10 to 265 x 10 g / l . Methyl mercaptan degradation yie l d s (G(-CH SH)) increased s i m i l a r l y from 0.006(4-2v) to 0.230(1-3) when -127-_3 the i n i t i a l concentration was increased from 0.48 x 10 to 28.70 x 10 g / l ( F i g . 4.23). The dimethyl s u l f i d e degradation y i e l d (Gf-CH^SCH^)) showed a l i n e a r relationship with increasing y i e l d from 0.003(1-4) to 0.020(1-2) when the i n i t i a l concentration was increased from 0.60 x 10 - 3 to 5.22 x 10~ 3g/l (Fig 4.26). S i m i l a r l y , dimethyl d i s u l f i d e degradation yield(Gt-CH^SSCH^)) increased l i n e a r l y from 0.004(1-2) to 0.035(2-1) as i t s i n i t i a l concentration was increased from 1.03 x 10~3 to 9.11 x 10""3 g / l (Fig. 4.25). 4.6 Effect of Nitrogen, A i r and Oxygen Atmospheres on Gamma Radiolysis of Sulfides i n Carbonated Black Liquor (pH 7*50) The carbonated black li q u o r (1-1) enriched with hydrogen sulfide, methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e was ir r a d i a t e d i n nitrogen, a i r or oxygen atmosphere. The comp-arative effects of nitrogen, a i r and oxygen atmospheres on gamma radiation degradation of the sulfides are shown i n Table 4.25 as well as Figs. 4.26, 4.27 and 4.28. The exponential degradation patterns of hydrogen s u l f i d e , dimethyl s u l f i d e and methyl mercaptan are also plotted i n Figs. 4.26, 4.27 and 4.28, respectively. The apparent degradation yields of EL.S, CH^SCH^ and CH^SH -in nitrogen, a i r and oxygen were calculated from the i n i t i a l slope of respective s u l f i d e degradation curves as found i n Figs. 4.26, 4.27 and 4.28. The comparison of nitrogen, a i r and oxygen on -128-degradation y i e l d of hydrogen s u l f i d e , methyl mercaptan and dimethyl s u l f i d e i s shown i n Table 4.26. In this case, dimethyl d i s u l f i d e i s either degraded by gamma radiation or generated by ra d i o l y s i s of methyl mercaptan. The degradation of methyl mercaptan and dimethyl s u l f i d e i n nitrogen, a i r and oxygen i s graphically presented i n Fig. 4.28. There are indications that the degradation of hydrogen s u l f i d e , dimethyl s u l f i d e and methyl mercaptan i s also exponential with dose i n nitrogen, a i r and oxygen atmospheres. As shown i n Table 4.26, the su l f i d e degradation yi e l d s i n nitrogen, a i r and oxygen atmospheres are correspondingly 8.5, 9»7 and l6.7 f o r hydrogen s u l f i d e , 10.2, 18.5 and 28.0 for methyl mercaptan, and 0.19, 0.43 and 0.74 for dimethyl s u l f i d e . The degradation of dimethyl d i -su l f i d e as shown i n Fig. 4.28 i s greatly affected by the presence of nitrogen, a i r and oxygen i n carbonated black liquor; a i r and oxygen have the greatest effect on the degradation rate of dimethyl d i s u l f i d e . In the presence of oxygen i n carbonated black li q u o r , the high degradation yields of hydrogen s u l f i d e (16.7) and methyl mercaptan (28.0) indicate that the degradation reactions of the sul f i d e s , induced by gamma radiation, created chain reactions. -129-4.7 Regeneration of Polysulfide by Gamma Radiolysis of Sodium Sulfide Solution A preliminary test shows that only i n s i g n i f i c a n t amounts of polysulfide are formed by dir e c t r a d i o l y s i s of sodium s u l f i d e solutions and green liquor (at pH above 12). However, i f the solutions are a c i d i f i e d by carbon dioxide or hydrogen s u l f i d e , the polysulfide y i e l d greatly increases. The formation of polysulfide excess sulfur and sulfate by gamma r a d i o l y s i s of sodium s u l f i d e solutions and green liquor (1-2) under 120 psi carbon dioxide or 270 p s i hydrogen s u l f i d e pressure i s shown i n Table 4.27. The apparent yields of polysulfide excess sulfur (G(S)) ranged from 1.47 to 2.96 f o r carbonated sodium s u l f i d e solution; and 3.06 to 4.92 for hydrogen s u l f i d e a c i d i f i e d aqueous sodium s u l f i d e solutions and green l i q u o r . The apparent yiel d s of sulfate (G(H SO )) are r e l a t i v e l y modest, from 0.l6 to 2 4 0.40 for the carbonated s u l f i d e solutions and only 0.03 to 0.08 for the hydrogen sul f i d e a c i d i f i e d s u l f i d e solution. This shoivs that the y i e l d of polysulfide excess sulfur i s much higher than the y i e l d of sulfate formation. -130-5.0 DISCUSSION 5.1 Analysis of Total Sulfides i n Sulfate Pulping Liquors The mechanisms of formation and available a n a l y t i c a l techniques of malodorous sulfides have been described at length by Sarkanen e_t a_l. (169), Douglass and Price (55) » and McKean et a l . (128). The main steps i n these reactions leading to the various sulfides can be summarized as shown i n Fig. 5*1. In this work, an unidentified sulfur compound (X) present i n substantial quantities i n both natural black liquor and a c i d i f i e d black liquor was shown by carbon tetrachloride l i q u i d / l i q u i d extraction and GLC analysis. The presence of this unknown (X) has not been reported i n the l i t e r a t u r e . It i s believed that i t i s not an a r t i f a c t of storage and analysis. This statement i s based on the observation that i f fresh black li q u o r was stripped with nitrogen gas, ~ GLC analysis of the co l l e c t e d gas also showed the presence of the unknown (X) i n the gas phase. The few tests indicated that the unknown compound (X) contains no ionizable hydrogen. Its retention time i n GLC i s very close to that of dimethyl s u l f i d e (Fig. 3.12), thus i t should be a v o l a t i l e organic sulfur compound with a b o i l i n g point s l i g h t l y higher than that of dimethyl s u l f i d e . Exact i d e n t i f i c a t i o n of the unknown (X) was not accomplished. -131-Organic polysulfides i n black liquor may be largely formed by reaction of the mercaptide ion with elemental s u l f u r . A possible scheme may be proposed as (102): CH^S' + S > CH3SS" / 5-l/ This reaction i s also indicated by experiments i n which methyl mercaptan was added to black liquor and white liquor at room temperature. Analysis followed by s i l v e r n i t r a t e potentiometric t i t r a t i o n i n which the i n f l e c t i o n point "b" i n the t i t r a t i o n curves was resolved to be due to the presence of organic poly-s u l f i d e (Fig. 3"2). Another, possibly new reaction was also observed by s t i r r i n g dimethyl d i s u l f i d e i n 1 N NaOH solution at room temperature, whereby al k a l i n e hydrolysis of the sul f i d e leads to the d i s u l f i d e ions CH^SSCH^ + 0H~ »CH 3SS~ + CR^OH ->->/5-2/ This reaction has been demonstrated by potentiometric t i t r a t i o n (Fig. 3.6) and was discussed at length i n Section 3.3. However, in a l k aline hydrolysis of dimethyl d i s u l f i d e , the formation of methyl mercaptan can not be observed from Fig. 3.6. This seems to be i n agreement with findings of Murray and Rayner ( l 4 l ) i n that dimethyl d i s u l f i d e i s not hydrolyzed to mercaptan by treatment with 0.1 N NaOH at room temperature, but that mercaptide i s formed o only at 100 C under nitrogen. -132-Considerable d i f f i c u l t i e s were met during these investigations with respect to selection of suitable techniques which would provide means of assessment of t o t a l sulfides and adequate sen-s i t i v i t y needed f o r the description of i n t r i c a t e valence changes in s u l f i d e energetics taking place in i r r a d i a t e d black l i q u o r s . To this end no single technique was available i n the l i t e r a t u r e which could account f o r a l l the sulfides i n black l i q u o r . For the purpose of this study, analysis of sulfides i n unacidified black liquor was followed by s i l v e r n i t r a t e potentio-metric t i t r a t i o n for hydrogen s u l f i d e ( i n f l e c t i o n point "a") and organic polysulfide and inorganic polysulfide ( i n f l e c t i o n point "b") as discussed i n Section 3.3. A technique of corrected interpretation of the potentiometric t i t r a t i o n curve was developed quite independently from other researchers whose findings appeared just recently i n the l i t e r a t u r e (142, 151). The results herein indicate that during the potentiometric t i t r a t i o n of six sulfate and two polysulfide black liquors (Fig. 3.1) obviously two i n f l e c t i o n points Ca" and *b") appear as s u l f i d e end points. According to the older convention, i n f l e c t i o n point "b" i s taken as end point for s u l f i d e and no existence of mercaptan was assumed. The difference of readings between points "a" and "b" -133-can be up to 112% but is, on the average, between 10 to 20% (Table 3.2). The v a l i d i t y of these observations was checked with aqueous al k a l i n e model solutions (Section 3.3.1.4). The results c l e a r l y indicate that both the model solutions and white.liquor give similar t i t r a t i o n curves as black l i q u o r . It i s also indicated that the i n f l e c t i o n point "b" i s caused by the presence of the mercaptide ion i n that one mole of found mercaptan i s precipitated by an equal quantity of s i l v e r n i t r a t e , as shown by the calculations i n Eq. / 3 » l 4 / . Although discrepancy o r i g i n a t i n g from using i n f l e c t i o n "b" for c a l c u l a t i n g the su l f i d e content i n aqueous solutions was reported by F e l i c e t t a e_t a l . (67), recently published figures by Murray e_t al_. (l42) and Papp (151) support the above observations. Data obtained on model solutions and tabulated i n Table 3.4 now c l e a r l y indicate the correctness of this procedure. It should be pointed out that most of the mercaptide ion i n black li q u o r i s converted to organopolysulfide (CH^SS-) by reaction with elemental sulfur as shown i n Eq. /3.12/. The addition of elemental sulfur to sodium s u l f i d e solution formed polysulfide which also developed an i n f l e c t i o n point "b" by s i l v e r n i t r a t e potentiometric t i t r a t i o n as discussed i n Section 3.3.1.1.3.2. This further supports the observation that the i n f l e c t i o n point "b" i n the black li q u o r t i t r a t i o n curve i s due to the presence of organic and inorganic polysulfides i n the solution rather than to the mono-sulfide ion. -134-For the unionizable organosulfides such as dimethyl s u l f i d e , dimethyl d i s u l f i d e and the unidentified sulfur compound (X), the technique of carbon tetrachloride l i q u i d / l i q u i d extraction and GLC were adapted. Further, i t was found that methyl mercaptan could also be determined by low temperature a c i d i f i c a t i o n of black liq u o r , with excess of boric acid suspended i n carbon tetrachloride solution and followed by GLC analysisjSection 3.3.2). In carbonated black liquor samples the t o t a l sulfides (H 2S, CILjSH, CH^SCH, CH^SSCH^and X) were d i r e c t l y determined by the low temperature boric acid a c i d i f i c a t i o n and quantitative l i q u i d / l i q u i d extraction of the sulfides with carbon tetrachloride followed by GLC analysis (Section 3*6). L i q u i d / l i q u i d extraction with carbon tetrachloride of dimethyl s u l f i d e , and dimethyl d i s u l f i d e from unacidified black liquor, has been found to have quite acceptable e f f i c i e n c y and recovery rates (80-90%) depending on the type of organosulfide involved (Section 3.3.2.1.3.1). On carbonated black l i q u o r , the extraction e f f i c i e n c y was further improved up to 3-7% by boric acid treatment (Table 3.11). The concentration of methyl mercaptan i n unac i d i f i e d black liquor (Table 4.1), as well as that of hydrogen s u l f i d e and methyl mercaptan i n carbonated black liquor (Tables 4.19 and 4.20), were found to be too low to respond to s i l v e r n i t r a t e potentiometric -135-t i t r a t i o n (Section 3.3.1). However, the carbon tetrachloride 1 i q u i d / l i q u i d extraction procedure was found convenient and accur-ate enough f o r interpretation of the s u l f i d e energetics even at these low concentrations. Although the e f f i c i e n c y of hydrogen s u l f i d e and methyl mercaptan carbon tetrachloride l i q u i d / l i q u i d extraction was not determined due to technique d i f f i c u l t i e s , the method i s considered to be reasonably quantitative when the high respective solubility,.-, of hydrogen sulfide and methyl mercaptan in carbon tetrachloride solution are considered. As discussed previously (Section 3.6), the s o l u b i l i t y of hydrogen s u l f i d e i s 4l.9 g/l i n carbon tetrachloride and only 3.8 g / l i n water at 20°C and 1 atmosphere; whereas the s o l u b i l i t y of methyl mercaptan i n carbon tetrachloride i s very high (no data a v a i l a b l e ) , and i t i s only sl i g h t l y soluble i n water (12). Thereby, most of the sulfides should be easily transferred into the carbon tetrachloride phase on l i q u i d / l i q u i d extraction. It was f e l t that methods suggested earlier for l i b e r -ation (62, 146), stripping (55, l6o, 185) and extraction (12, 125) were either too technical or largely inadequate for the purposes of this investigation. Although the method f i n a l l y adopted could never duplicate the e f f i c i e n c i e s (98%) of the Andersson and Berg-strOm (12) technique, i t was f a r superior to the method suggested by Douglass and Price (55) and McKean e_t a_l. (127) i n both - I n -e f f i c i e n c y and reproducibility„ The great sensitivity of the flame photometric detector (FPD) operated i n conjunction with the MT-150 gas chrornatograph contributed greatly to the success of this a n a l y t i c a l techniques. 5.2 Gamma Radiolysis of Sulfides i n Aqueous Solution and Sulfate Black Liquor In order to study the degradation of sulfides i n black liquor, s u l f i d e model compounds such as sodium s u l f i d e (Na^S), sodium methyl mercaptan (CH^SNa), dimethyl s u l f i d e (CH^SCH^) and dimethyl d i s u l f i d e (CH^SSCH^) were ir r a d i a t e d i n aqueous solution and black liquor at various pertinent experimental conditions. Black liquors usually contain a high concentration of inorganic s u l f i d e , organic components and minor amounts of organic sulfid e s (Table 4.1). The organic components are complicated i n black liquor; they consist of various forms of carbohydrates (cellulose and hemicellulose residues), l i g n i n , extractives and th e i r d erivatives. The radicals formed through gamma r a d i o l y s i s of water, and the organic components of .. black liquor,may be p a r t i c u l a r l y reactive toward the sul f i d e linkage. 5.2.1 Hydrogen Sulfide Only a few investigations on sodium s u l f i d e r a d i o l y t i c degradation yields i n aqueous solution have been -137-reported i n the past. In this study, the apparent degradation y i e l d of s u l f i d e (Gf-Na^S)) i n aqueous solution i s pH dependent. Values of G(-Na S) are found to range between 5-0 and 7.5 f o r 2 s u l f i d e solutions at pH 12.46 and 8.38, respectively (Table 4.3). Further investigations of apparent degradation yields of hydrogen su l f i d e (Gf-RgS)) in carbonated black liquors (Fig.4.24) show that the degradation yields (0.015 to 3.427) correlate s i g n i f i c a n t l y with i n i t i a l hydrogen s u l f i d e concentrations (0.89 x 10 ^ to 265.20 x 10~ 3g/l). The comparison of hydrogen s u l f i d e degradation y i e l d of a carbonated black liquor ( l - l ) i n presence of nitrogen, a i r and oxygen are corresponding 8.5, 9«7 and 16.7 (Table 4.26). The degradation of su l f i d e i n aqueous solution and carbonate black liquor i s exponential with dose (Figs, 4.1, 4.17 and 4.26). The formation of polysulfide and sulfate by gamma r a d i o l y s i s of sodium s u l f i d e aqueous solution was found to pr e v a i l i n this study (Table 4.2 and 4.27). This i s i n agreement with e a r l i e r reports by Loiseleur (117) who reported i n 1942 that elemental sulfur was formed by X-ray r a d i o l y s i s of hydrogen s u l f i d e i n aqueous solution. Further, Markakis and Tappel (122) reported that in gamma radiolysis .,Of 6 x l 0 - 3 M hydrogen s u l f i d e aqueous solution with a dose of 107 rad, 60% of the sulfur was recovered as elemental sulfur and 5% as sulfat e . Only limited information i s available on the y i e l d of -138-polysulfide from gamma r a d i o l y s i s of aqueous s u l f i d e solution. Herein i t was found that the y i e l d of polysulfide excess sulfur (G-(S)) was pH dependent (Table 4.4). The polysulfide excess sulfur generated from aqueous sodium sul f i d e solution a c i d i f i e d with COS, (120 psi) and H S (2 70 psi) , was determined as a function ci 2 of i r r a d i a t i o n dosage, i n i t i a l s u l f i d e concentration and pre-i r r a d i a t i o n a c i d i f i c a t i o n treatment (Table 27). The response to the dose effect was found to increase l i n e a r l y at constant i n i t i a l s u l f i d e concentration when aqueous su l f i d e solutions wer„e a c i d i f i e d by C0 2 or HgS (Table 4.27). The hydrogen s u l f i d e gas a c i d i f i e d s u l f i d e solutions gave considerably higher yields of excess sulfur (G(S) = 3•06 to 4.92) than those expected i n carbon dioxide a c i d i f i e d liquors (G(S) = 1.47 to 2.96). This may be due to increase of sul f i d e concentra-tion by H 2S gas treatment. Other experiments (Table 4.27) show the effect of gamma r a d i o l y t i c generation of polysulfide from sulfate green liq u o r (35 g / l Na 2S) a c i d i f i e d by hydrogen s u l f i d e gas. The y i e l d of polysulfide excess sulfur attained at 30.0 and 60.0 Mrad was 3.8 and 6.6 g/l(G(S) = 3.81, 3.34) respectively. While the optimum conditions for generation of su l f i d e to polysulfide by gamma radiation has not been obtained i n this -139-study, the results indicate that conditions may be optimized to obtain maximum excess sulfur and minimum sulfate y i e l d s . Such limit a t i o n s are prerequisite to maximum generation of polysulfide by gamma r a d i o l y s i s from s u l f i d e solution and sulfate green liq u o r . The mechanism of formation of elemental sulfur and polysulfide by gamma r a d i o l y s i s of su l f i d e aqueous solution may be proposed from the schemes of su l f i d e reaction with H»and HO radicals as formed by the r a d i o l y s i s of water. HO- + HgS—>HS» + H20 j5-31 H* + HgS »HS« + H 2 /5-4/ 2HS > HgS + S 15-51 2HS » H 2S 2 /5-6/ Karmann e_t a_l. (103), studying pulse r a d i o l y s i s of hydrogen su l f i d e i n aqueous solution, found that H» , H0« and e^^ reaction with HgS i s very f a s t . fc(H' + HgS) = 109 M~ 1sec _ 1 15-71 k(H0« + H 2S) = 1.1 x 101 0 M" 1sec~ 1 /5-8/ lc(e~ q + H 2S) = 1.3 x 101 0 M~ 1sec" 1 15-91 The reaction of e with H S i s shown as: aq 2 e" + H S > SH" + H 15-101 aq 2 ' ' > S' + H 2 15-111 The rate constant of k(H0«+ HgS) i s independent of pH within -i4o-the pH range of 2 to 6. In alkaline solution HgS i s dissociated to HS~ which i s able to react with HO* to form the intermediate (SHOH)~. HO* + SH" > (SHOH)~ /5-12/ k(HO- + SH~ ) = 5*^ x 109 M~1sec~1 ..../5-13/ Only S~ can be formed by gamma ra d i o l y s i s of alk a l i n e s u l f i d e solution. (HS.OH)' + SH" • H^ O + HSj" / 5 - l ^ / HS~~ > S" + SH" 15-15/ Therefore, there i s no overall change i n r a d i o l y s i s schemes of sul f i d e i n alk a l i n e solution. This affords an explanation f o r the low y i e l d of excess sulfur from gamma r a d i o l y s i s of high pH su l f i d e solutions. In this study, the apparent yields of sulfate (G(H2SO^)) from gamma r a d i o l y s i s of carbon dioxide a c i d i f i e d sodium s u l f i d e solution range between 0.l6and 0.40; and even lower sulfate yields were obtained between 0.03 to 0.08 i n hydrogen s u l f i d e gas (270 psi) a c i d i f i e d aqueous s u l f i d e solution (Table 4.27). This r e l a t i v e l y higher y i e l d of sulfate i n carbon dioxide a c i d i f i e d s u l f i d e solution as compared to that of hydrogen s u l f i d e gas a c i d i f i e d s u l f i d e solution i s rather d i f f i c u l t to explain. However, i t i s worthy of note that the sulfate y i e l d by gamma radiation i s controllable to a minimum by hydrogen s u l f i d e gas -141-a c i d i f i c a t i o n of su l f i d e solutions. The yields of sulfate i n this investigation were substantially lower than that reported by Nanobashvili and Gvilava (l45). They showed that gamma r a d i o l y s i s of 0.005 - 0.5 M sodium s u l f i d e solution gave sulfate yields (G(H2S0^)) up to 60. They also proposed that the chain reaction of sul f i d e oxidation to sulfate may be fundamentally maintained by the R0» r a d i c a l through r a d i o l y s i s of water (145)• 5.2.2 Methyl mercaptan Gamma r a d i o l y s i s of methyl mercaptan i n aqueous solution i s scarcely reported; but io n i z i n g radiation (X- and gamma rays) of cysteine aqueous solutions has been considerably investigated due to interests i n r a d i o s t a b i l i t y of b i o l o g i c a l systems(9, 186). The results of gamma r a d i o l y s i s of methyl mercaptan i n aqueous al k a l i n e solutions (Table 4.4 and Fig. 4.2) show that the degradation of mercaptan i s pH dependent. The mercaptan degrada-tion y i e l d s (G(-CH^SNa)) i n the presence of a i r are 2.5, 11.3 and 15.4 f o r pH 13.54, 12.54 and 10.70, respectively. The products of ra d i o l y t i c transformation were found to be dimethyl d i s u l f i d e and sulfate. Further, investigations on the degradation y i e l d of -142-mercaptan (Gf-CH^SH) ) i n carbonated black liquor (Fig.4.23) indicate that the degradation yields (0.006 to 0.230) are also s i g n i f i c a n t l y correlated with i n i t i a l concentrations of methyl -3 _3 mercaptan (0.40 x 10 to 28.70 x 10 g / l ) . Degradation of mercaptan was obviously affected by the presence of oxygen. Difference i n mercaptan yie l d s was observed with i r r a d i a t e d carbonated black liquor (1-1) i n the presence of nitrogen,air and oxygen atmospheres. The corresponding Gf-CH^SH) was 10.2, 18.5 and 28.0 (Table 4.26) at i n i t i a l pH of 7.50. Degradation of mercaptan in aqueous solution and carbonated black liquor was found to be exponential with dose (Fig«4.2, 4.18 and 4.28). These results are i n agreement with the gamma r a d i o l y s i s of cysteine i n aqueous solution by Swallow (186). In a i r saturated solution, the y i e l d of cystine (CySSCy) from gamma r a d i o l y s i s of cysteine-hydrochloride solution (pH 1.9 - 3.3) may reach as high as 24. In deaerated solutions, the y i e l d of cystine^ i s reduced to 3. Furthermore, Alle n (9) also reported that cystine yields from r a d i o l y s i s of cysteine solution were a function of oxygen, pH and i n i t i a l concentration of cysteine,. In oxygenated solutions, the -1^3-cystine yields (G(CySSCy)) increased with increasing cysteine concentration; while i n neutral solutions cystine y i e l d s as high as 60 were obtained under cert a i n conditions, whereas the yi e l d s i n acid and alk a l i n e solutions were loiirer. The extensive l i t e r a t u r e on the r a d i o l y s i s of -SH functional group containing compounds has well established the fact that free r a d i c a l attack at the -SH i s the main i n i t i a t i n g process(4, 6 l , 150, 156, 187). The high y i e l d i n the oxidation cysteine to cystine i n the presence of oxygen i s reported to be the resul t of a chain reaction. Sxvallow (186) has postulated the following schemes s RS H + HO- ^ RS' + H,p 0 o « o o o o a o . o « . . o o . o o a / 5 — 1 ^ / RS» + RSH—>RSSR + H' , a . . . . . /5-17/ HO* + RSH > RS» + H 2 ° 2 < - . . < > . / 5 - 1 9 / However, the release of H« as indicated by Eq. 15-171 seems unli k e l y . Thus the following schemes are proposed to be pre-dominant i n this process. Unfortunately, they f a i l to explain the pH effect (14). RS* 0 1 ^  iRSO , o o o o o o o o o o««oeo0O« o a o o e o e o a 2 2 RS02 + RSH—>RSSR + H02 > .../5-2l/ Nanobashvili et a l . (lkk) i l l u s t r a t e d that d i s u l f i d e s and certai n -144-sulfo compounds were obtained from r a d i o l y s i s of b u t y l - , amyl-, hexyl- and other raercaptans. The higher oxidation stage i s observed by the increasing yields of sulfate ions, and consequently decreasing pH of the aqueous solutions. 5.2.3 Dimethyl s u l f i d e and dimethyl d i s u l f i d e As shown i n Table 4.7, the degradation yields i n alkaline model solutions were Gf-CftjSCR^j) 0.730, G(-CH^SSCll^) 0.885. Relatively speaking, these yields are considerably higher than those obtained i n black liquor Gf-CH^SCH^ ) 0.503 , Gf-CH^SSCHj) 0.427 at the similar pH values (pH 13.12 - I3«l4) and i r r a d i a t i o n l e v e l s . This indicates a scavenging and protective effect of black liquor organic components on the degradation of organosulfides. The degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e model compounds i n alk a l i n e solution and black liquor i s also exponential with dose (Fig, 4.3). The effect of dimethyl s u l f i d e and dimethyl d i s u l f i d e degradations induced by gamma radiation i s greatly affected by solution pH (Figs, 4.4 and 4.5), l i g n i n concentration (Fig.4.6), temperature (Figs. 4.7 and 4.8) and oxygen pressure (Figs, 4.9 and 4.10). As shown i n Table 4.8, as well as i n Fig,4.5, the dimethyl -145-s u l f i d e degradation y i e l d to i n i t i a l concentration (G/Co) decreased l i n e a r l y when solution pH was decreased from strong acid (pH 0.5) to strong alkaline solution (pH 13.5). While G/Co of dimethyl d i s u l f i d e was also decreased almost l i n e a r l y from strong acid to pH 10.1, then i t increased s l i g h t l y from pH 10.1 to pH 13.5. The products and mechanisms of gamma r a d i o l y s i s of dimethyl su l f i d e have not been investigated. Meissner e_t a_l. (129) were able to measure the rate constants i n the reaction of dimethyl s u l f i d e with hydrated electrons (e~ ) and hydroxyl r a d i c a l (HO* ) aq by pulse radiation. The reaction rate constant of dimethyl su l f i d e and HO- (K(H0« + CH^SCH^ ) ) i s 260 times higher than that ° f eaq (KKq + C ^ S C ^ ) ). K(H0« + CH^SCHg) = 5.2 x 10 9M* 1sec- 1 /5~22/ K ( e a q + CH^SCH^) = 2.0 x 10 7M~ 1sec" 1 /5-25/ As discussed i n Section 2.3, higher concentration of H0»was found i n acid solution, whereas higher concentration of e~ existed only a q i n a l k aline solution. The s l i g h t increase of G/Co of dimethyl d i s u l f i d e i n strong alkaline solution (pH 10-13.5) i s d i f f i c u l t to understand due to the unclear degradation mechanism. However, the higher yi e l d s of oxidizing, species (H0« , H0| and H202 ) in ra d i o l y s i s of ^ aqueous acid solutions may increase degradation yields of dimethyl s u l f i d e and -146-dimethyl d i s u l f i d e i n low pH (acid) solutions. As shown i n Table 4 . 9 , as well as i n Fig. 4.6, the presence of l i g n i n i n al k a l i n e solution shows a s i g n i f i c a n t scavenging effect due to competition for reaction radicals (produced through water i r r a d i a t i o n ) between l i g n i n and organosulfides. It seems l i k e l y that the great energy absorbing capacity of aromatic l i g n i n protects organosulfides from degradation. Lignin concen-trations i n sulfate black liquor usually range from 18 to 48 g / l (Table 4.1). According to Fig. 4.6, decomposition values of both dimethyl s u l f i d e and dimethyl d i s u l f i d e decrease consistently with up to 50 g / l t h i o l i g n i n concentration, with some inconsistencies being evident f o r dimethyl d i s u l f i d e at higher i r r a d i a t i o n dosages. Similar observations can be made for Gt-CH^SCHVj) and Gf-CH^SSCH^) i n that a clear scavenging trend i s indicated only for the average G values at 50 g / l l i g n i n concentration. The degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e by gamma radiation i s also a function of temperature and oxygen pressure. At the i n i t i a l oxygen pressure of 50 p s i , the organo-sulf ide degradation yields increased l i n e a r l y as the temperature was increased from 6o to 115°C for the black li q u o r (T able 4.10, F i g . 4.7) and carbonated black liquor (Table 4.11, Fig. 4.8). On the other hand, at Gammacell ambient temperature (34°C), the organosulfide degradation yields also increased l i n e a r l y as oxygen -147-pressure was increased from 25 to 100 psi for black liquor (Table 4.12, Fig.4.9) as well as carbonated black liquor (Table 4.13, Fig.4.10). As discussed i n Section 2.3.3 on gamma r a d i o l y s i s of water, oxygen i s a very e f f i c i e n t scavenger for reducing species such as H-and e aq5 a n < l various oxidation species (H0.J, C\j, 0*, and U^O^) are generated. Thereby, the degradation yields of dimethyl s u l f i d e and dimethyl d i s u l f i d e are greatly affected by the oxygen pressure. This has been confirmed by Purdie (156), Markakis and Tappel (122), and Forbes e_t a l . (69), on r a d i o l y s i s of cystine aqueous solutions. They were able to demonstrate that oxidation products were greatly increased i n the aerated solutions. In this study, due to low i n i t i a l concentrations of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liquors, the apparent degradation yields were low. They do, however, correlate s i g n i -f i c a n t l y with their respective i n i t i a l concentrations i n black liquors (Table 4.18, and Figs. 4.15 and 4.l6) and carbonated black liquors (Table 4.24, and Figs. 4.24 and 4.25). The effect of nitrogen, a i r and oxygen atmospheres on gamma ra d i o l y s i s of dimethyl s u l f i d e i n carbonated black liquor ( l - l ) i s shown i n Table 4.25 as well as Fig. 4.27. Dimethyl s u l f i d e degradation i n nitrogen, a i r and oxygen i s exponential with dose -148-(Table 4.25 and Fig. 4.28). The degradation yields (Gf-CH^SCH^ ) ) are 0.185, 0.426 and 0.741 f o r presence of nitrogen, a i r and oxygen, respectively. Gamma ra d i o l y s i s of dimethyl d i s u l f i d e , i n conjunction virith methyl mercaptan i n the presence of nitrogen, a i r and oxygen i n carbonated black liquor, shown i n Fig. 4.28, suggests that the presence of oxygen and a i r promoted the formation of dimethyl d i s u l f i d e i n the r a d i o l y s i s of methyl mercaptan and greatly elevated the degradation of dimethyl d i s u l f i d e . These results conform with the e a r l i e r observations that the presence of oxygen i s very b e n e f i c i a l to the increase of methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e degradation rates. The infrared spectrum reproduced i n Fig. 3.19 reveals that a product of gamma ir r a d i a t e d dimethyl s u l f i d e shows strong absorp-tion at 1710cm which i s assigned to the carbonyl group. The product i s a nonvolatile, stable, amorphous substance. However, sulfate ions have not been detected from the gamma r a d i o l y s i s of dimethyl s u l f i d e aqueous solution, whereas they were present i n irra d i a t e d solutions of dimethyl d i s u l f i d e . This i s further evidence that s t a b i l i z a t i o n of organosulfides i n black liq u o r can be obtained by gamma radiation. The products and mechanisms of gamma r a d i o l y s i s of dimethyl -Iks-s u l f i d e and dimethyl d i s u l f i d e i n aqueous solution have not been investigated, except by Meissner e_t al_. (129), who showed some intermediate compounds from pulse r a d i o l y s i s of dimethyl s u l f i d e aqueous solutions. Radiation of cystine has been studied i n considerable depth. The effects of solution pH and oxygen on radiation degradation of the organosulfide and thei r possible mechanisms, are thoroughly discussed i n the following sections to help to explain the degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n model solution and black l i q u o r s . Change i n the three absorption maxima of the intermediate compounds were observed following impingement of the pulse by Meissner e_t a_l. (129). Pulse r a d i o l y s i s of dimethyl s u l f i d e i n alkaline solution produces absorption maximum at 3500A*. Further absorptions occur at 2900$ and k7Q0% % H0» + CH^SCH^ > CH^SOHCRj /5-24/ CH^SOHCH^ > CH^SOCH^ (3500A) + H + /5-25/ HO. + CH^ SCHL. > CH SCH- (2900A*) + HgO /5-26/ 2H0« + 201^50^ > (CH^SCH^) ZC*700A) + 2 OH .... /5-%7/ The i n t e n s i t i e s at these absorption maxima (intermediate products) were shoxvn to be dependent on solution pH and presence of oxygen. In oxygenated solutions, the absorption maximum at 2900$ disappeared, because the 0^ was shown to react readily with -150-CH SCH' r a d i c a l s . With increasing pH from 7 to 13. the absorp-pH was raised to 9« The d i s u l f i d e bond i s p a r t i c u l a r l y sensitive to io n i z i n g radiation. The radicals formed through gamma r a d i o l y s i s of water attacked the -S-S-group as the main i n i t i a l process (4, 150, 156, 187). Due to the limited s o l u b i l i t y , r a d i o l y s i s of dimethyl d i s u l f i d e has not been favored f o r theoretical studies. However, the r a d i o l y s i s of cystine (CySSCy) aqueous solutions has been considerably investigated by many researchers. Markakis and Tappel k (122) determined the products of gamma r a d i o l y s i s (between 10 -8 x 7 -k 10 rad) of cystine i n 100 x 10 M hydrochloric acid solutions and found cysteine (CySH), hydrogen s u l f i d e , elemental sulf u r and sulfate. In these experiments the yield s of cysteine (0-11 x 10~^M) and hydrogen s u l f i d e (0-1.8 x 10~^M) were lower than the yields — k U of elemental sulf u r (0-lk0 x 10 M) and sulfate (0-85 x 10 M). For the s t a b i l i z a t i o n of d i s u l f i d e s i t i s p a r t i c u l a r l y important to note that the formation of sulfate was increased greatly i n aerated cystine solutions (122). 3 2 The d e t a i l s of i n i t i a l products r e s u l t i n g from gamma r a d i --151-k o l y s i s (8 x 10 rad) of cystine a c i d i f i e d aqueous solutions (3 x 10 M) were f i r s t analyzed by Grant et al_. (78), using paper chromatography and electrophoresis. The sulfur products of the oxygenated or aerated solutions were cystine disulfoxide (CySOgCy) with y i e l d (G) of less than 0.1, cysteic acid (CySO^H) with y i e l d of 0.3-1.5, cysteine s u l f i n i c acid (CySOgH) with y i e l d s of 0.1 or less, and cysteine (CySH) with yields of 0.1 to 0.9. Similar studies were also conducted by Forbes e_t a_l. (69). The yi e l d s of oxidized s u l f u r compounds were affected by factors such as radiation dose, solution pH and the presence of a i r . During the io n i z i n g radiation (X- and Y-rays) treatment of cystine, the products were derived from both f i s s i o n of the S-S bond (e.g. CySOgH and CySO^H) and f i s s i o n at the S-C bond (e.g. CySSO^H). Purdie (15°) studied the gamma r a d i o l y s i s (10 rad) of 3 x 10 M cystine water solutions. The products, which have been determined, were cystine disulfoxide, cysteic acid, cysteine s u l f i n i c acid, cysteine, cystine thiosulfonic acid (CySOgSH), cysteine t h i o s u l f u r i c acid (CySSO^H) and cystine t r i s u l f i d e (CySSSCy). The p r i n c i p a l oxidation products i n aerated solutions were CySO^G = 0.9-1.7) and CyS0 3H(G = 0.7-1.2). In deaerated solutions, the yiel d s of CyS0 2H(G = 0.3-1.2) were r e l a t i v e l y lower, and CySO^H was present i n only trace amounts. S i m i l a r l y , only trace amounts of cysteine were detected i n aerated solutions (G = 0T0.7). Substantially higher yi e l d s of cysteine were -152-obtained i n deaerated solutions (G = 0.4-2.5). Cystine t r i -s u l f i d e , on the other hand, was produced i n .significant amounts i n both aerated (G = 0.4-0.6) and deaerated (G = 1.0) solutions. The yields of minor products of CySSO^H and CySOgSH correspond to 0.1 and 0.05 f o r both aerated and deaerated solutions. Several schemes have been proposed for the r a d i o l y s i s of cystine and the related d i s u l f i d e s i n aqueous solution (69, 78, 156, 175) • These reactions may provide an explanation of the oxidation of dimethyl d i s u l f i d aqueous solutions as induced by gamma radiation. The d i s u l f i d e bond i s readily attacked by HO* to form sulfenic acid (RS0H). RSSR + HO >RS0H + RSr, /5-2 8/ The sulfenic acid i s very reactive and may react i n various ways i n aerated solutions to form RSO^ and sulfenic acid (RSO^H)-RS0H + 0~ > RS0~ + H /5-29/ 2 3 2RS0H > RS02H + RSH /5-30/ RS0H + H 0 > RS0 H + E- /5-3l/ 2 2 2 The formation of sulfenic acid and thiosulfonic acid are also proposed via a displacement reaction (69)? RSSR + H02 > RS02H + RS* /5-32/ RSSR + HO- > RSS0 H + R* /5-33 / 2 2 Purdie (156) proposed the following reactions of formation - 1 5 3 -disulfoxide (RSO^SR), sulfenic acid (RS02H) and sulfonic acid (RSO^H) i n aerated solutions RS- + 0 >RSO«, / 5 - 3 1 * / 2 ^ RSO* + RS >RS02SR 15-3 51 2RSC- > RS0oS0.,R /'5-36 / 2 2 2 RSO„SO R + HoO >RS0o H + RSO^H 15-371 2 2 £ 2 j The t r i s u l f i d e (RSSSR) i s formed during the r a d i o l y s i s of cystine both i n aerated and deaerated solutions (156)s RS* + RSSR > RSSSR + R» / 5 - 3 8 / The formation of sulfate was observed from the gamma ra d i o l y s i s of dimethyl d i s u l f i d e i n aqueous al k a l i n e solution. Markakis and Tappel (122) also confirmed that sulfate was formed by the gamma r a d i o l y s i s of cystine aqueous acidic solutions. Forbes e_fc a_l. (69) indicated that t h i o s u l f u r i c acid (RSSO^H) i s an intermediate f o r the formation of sulfate from the i o n i z i n g i r r a d i a t i o n of d i s u l f i d e i n neutral or al k a l i n e solution. 2RSS03H + 2H20 > 2RSH + ^ S O ^ 15-331 These processes indicate the strong tendency of sul f i d e s t a b i l i z a t i o n i n aqueous solutions via various oxidation trans-formations. The mechanisms should be d i r e c t l y applicable to gamma r a d i o l y s i s of sulfides i n sulfate black l i q u o r s . -154-5.2.4 Unidentified s u l f u r compound (X) The gamma radiation degradation of the unidentified s u l f u r containing compound (X) i n unacidified (Table 4.17, Fig 4.l4) and a c i d i f i e d (Table 4.23, Fig. 4.21) sulfate and poly s u l f i d e black liquors has folloxired a pattern similar to that observed with the radiation degradation of organosulfides, discussed i n d e t a i l i n the previous sections. 5.3 Kinetics of Gamma Radiolysis of Sulfides i n Aqueous Solution and Black Liquor The i n d i r e c t action of radicals from water decomposition alone i s not s u f f i c i e n t to explain the mechanism of the gamma r a d i o l y s i s of s u l f i d e s i n black l i q u o r . The sulfate black li q u o r contains very high concentration and complicated inorganic and organic compounds, i n the highly concentrated aqueous solution, and the hydration shells of the hydrated molecules or ions are overlapping. This affects a number of physico-chemical properties and profoundly changes the microscopic volumes of the solution at the moment of energy d i s s i p a t i o n in the tracks or spurs of io n i z i n g p a r t i c l e s (22 ). Radicals produced from the r a d i o l y s i s of water and hydrocarbons i n black liquor are able to react with the sulfides i n numerous ways. As radiation proceeds, the reacted s u l f i d e molecules w i l l -155-l i k e l y remain i n the solution, s t i l l capable of further reaction with other radicals with a frequency equal to the unreacted su l f i d e molecules, A complete description of the chemical reactions by gamma r a d i o l y s i s of black liquor i s impossible. However, tentative schemes are i l l u s t r a t e d i n Fig. 5° 2° The fundamental r a d i o l y t i c reactions of sulfides i n black liquor are proposed as follows? k I H^  0 A w ^ H* "t HO* «.»o»ooo»oooeoo»»oooooo»*/5 — 4 0 / k Q I RH( organic ) ^ R« + Hv..ooo<>«oo.e«o<.oooooo(.os / 5~ 4 l / k S H* ' ' P f O C L l I C t e o * 0 o o o o o o o o o o o o o 9 o » o o a e j^—Uf'ti / S HO* ^ P r O C L l J C t o * > o o o e o o o o o o * ) o < i o « « o e o e o o / 5"^3 / k3 S *^  R* P r O d l J C t oooo««o»oo»o»oo»oooeoooo/5™*^'^'/ k (S - S) + H» > Product .<,.....»./5-^5/ o k 2 (S Q S) + HO* > Product .,,,..o.,.o.o.../5-^6/ k (S Q S) + R» =2—> Product . . . . . . . . . . / J - ^ / k RH + H* Product ..o,.,,,,,, /5 -W/ k5 RH + H0# =—> Product /5-^9/ k RH + R» > Product » . . o » ,»*,»»» 0 / 5-50/ -1 -156-Where, I = dose rate, absorbed energy in t e n s i t y , i n 100 ev/g t k , k , k , and k, 0 = sp e c i f i c rate constant, i n M w ° 1-6 1-3 1 min"^ S = i n i t i a l s u l f i d e concentration, i n molecules o S = su l f i d e remaining i n solution a f t e r i r r a d i a t i o n time t, i n molecules S Q - S = concentration of the transformed s u l f i d e , i n molecules Let, = primary y i e l d of gamma r a d i o l y s i s of water, i n molecules /100 ev G Q = primary y i e l d of gamma r a d i o l y s i s of organic compounds, in molecules/100 ev d ' } = G W I + G 0 I - k1(S)(H>) - k^(S 0-S)(H. ) - k 4(RH)(H-) /5-5l/ d(H0« ) • , d t G wI - k 2(S)(H0. ) - k 2 (S Q-S) (HO. ) - k5(RH)(H0-) ..../£-52/ > = G I - k 3(S)(R-) - k 3(S Q-S)(R. ) - k 6(RH)(R-) 15-531 ~ ^ d t ^ = ( k l ( H * ) + k 2 ( H 0 « ) + k 3(R.))(S) 15-5^1 The reactions are rapid, and the system can reach a steady state in a small f r a c t i o n of a second. If Eqs. /5-5l/, /5-52/ and /5-53/ are taken as zero, the system of equations can be solved f o r the various radicals as shown below. -157-GWI + GQI (H.) -k1(S) + k^(SQ-S) + k^(RH) (HO.) = —t  k (S) + k2(SQ-sj + k^(RH) G QI (R.) = • ; I*'5*' k3(S) + k3(SQ-S) + kg(RH) The steady, state values of (H* )» (H0» ) and (R. ) (/5~55/, /5-56/ and f5-571) are substituted into Eq. /5-5^/. The radicals react as readily with the transformed s u l f i d e molecules as with the s u l f i d e i n i t s o r i g i n a l form. Thus these are assumed: i t CO kj, k2 Oj k2 and k^  C/) k^  d ( B) + » o D k2GwI k 3G 0I " dt = ~ + ~1 + : ( k[(SQ) + k^(RH) k 2 ( S Q ) + k 5(RH) k 3 ( S Q ) + kg(RH) 0./5-58/ In pure water, (RH) = 0, G QI = 0 d(S) 2G I = _ K { S ) dt (so) When t = 0, (S) = (S Q) ln(S) = ln(S Q) - 2 & w I t (S Q) -158-log ( s ) = log(S ) - 0.868_^L_ I t 15-591 Where It = D(Dose) This indicates that there i s a li n e a r relationship of logarithmic s u l f i d e concentration and radiation time(t) f o r the gamma ra d i o l y s i s of su l f i d e at constant dose r a t e ( I ) . According to Eq. /5-58/, the degradation of sul f i d e i n black liquor which usually contains high organic components, i s expressed by Eq. /5-6o/s . d ( s ) / «y+ v v v dt (S) (S ) + k z » ( R H ) , , k5< R H ) k6(RH) '1 k2 k i When t = 0, (S) = (S ) o log (S) = log (s ) - o.434y o G + G G w o . w /5-6o/ O f k, k 2 Go kg(RH) (s ) + — 2 -/ I* • /5-6l/ -159-Where It = D(Dose). It i s also i l l u s t r a t e d that the logarithm of s u l f i d e concentration decreases l i n e a r l y with radiation tirne(t) at constant dose r a t e ( l ) . The presence of organic components give scavenging effect and reduce the yields of su l f i d e degradation. In this study, the dose r a t e ( l ) i s constant, so that the plot of logarithmic s u l f i d e concentration versus i r r a d i a t i o n time (t) i s a straight l i n e f o r sulfides i n both pure water solutions (Tables 4.2, 4.3 and 4.5 as well as Figs 4.1, 4.2, and 4.3) and black liquors (Tables 4.6, 4.15, 4.16, 4.19, ^.20, 4.21, 4.22, and 4.25 as well as Figs. 4.3, 4.12, 4.13, 4.17, 4.18, 4.19, 4.20, 4.26, 4.27 and 4.28). 5.4 Effect of Gamma Radiation on Black Liquor pH The pH of black liquor i s l i t t l e changed when black liquor i s i r r a d i a t e d at Gammacell ambient temperature (Tables 4.6 and 4.12). However, a s i g n i f i c a n t decrease i n the pH of black liquor was observed f o r both control and gamma irr a d i a t e d samples (Table 4.10) as the solution temperature was increased from room temperature to 115°C (under 50 p s i i n i t i a l oxygen pressure). Decrease of pH with the irr a d i a t e d samples was greater than that the control samples under similar oxygen pressure. On the other hand, the temperature effect on the pH change was not s i g n i f i c a n t -i6o-f o r either i r r a d i a t e d and control samples of carbonated black liquor (Table 4.11). In gamma r a d i o l y s i s of the oxygenated black liquor, the oxygen molecules are considered to add to the organic radicals to form r e l a t i v e l y stable peroxy ra d i c a l s ; R- + 0 > RO- ...... 15-62/ 2 2 Under certa i n conditions these organic peroxy radicals are able to abstract hydrogen from the substrate of organic components-RO^  + RH >R0 2H + R- /5-63/ The schemes presented i n Eqs. /5-62/ and /5-63/ are chain reactions. Autooxidation proceeding i n the above schemes also may be suspected due to heating the black liquor under oxygen pressure. In addition, organic molecules i n aqueous solution may be oxidized to 00^ and H^ O when they are exposed to radiation f o r a s u f f i c i e n t l y long time (91). Thus the pH of black liquor decreases by oxidation at elevated temperature with or without radiation. However, since gamma radiation can speed up the oxidation process of both carbohydrates and possibly the l i g n i n fractions in black liquor, the pH i s greatly decreased. 5*5 Oxidation of sulfides i n black liquor The gamma r a d i o l y s i s of sodium s u l f i d e solution at pH 12.46 - l 6 i -showed the lowest degradation rate (Fig. 4.1). When black liquor (3-1, pH 13.27) was ir r a d i a t e d i n an open vessel i n free contact with a i r , the consumption of s i l v e r n i t r a t e (AgNO^) decreased rapidly to almost zero, as indicated by the i n f l e c t i o n point "a" on potentiometric t i t r a t i o n curve, whereas f o r the i n f l e c t i o n point "b" i t increased to a maximum and then decreased as shown in Table 4.l4 and Fig. 4.11. These results are sim i l a r to those observed on black liquor oxidation by Murray e_t a_l. (l42). They stated that oxidation of su l f i d e ions i n black l i q u o r proceeded in two steps. The f i r s t step involves oxidation of s u l f i d e into an inorganic and/or organic polysulfide ( i n f l e c t i o n point "b"). The second step involves the oxidation of polysulfide ion to the f i n a l oxidation products (thiosulfate and elemental s u l f u r ) . As f o r organic s u l f i d e s , the methyl mercaptide ion i n black liquor i s readily oxidized to dimethyl d i s u l f i d e at ambient temperature i n the presence of a i r . Extensive oxidation of dimethyl s u l f i d e and dimethyl d i s u l f i d e was also observed i n black liquor (1-3) and carbonated black liquor (2-1). Under 50 p s i i n i t i a l oxygen pressure, the oxidation degradation rates of the organic sulfides increased greatly as the temperature was increased from 60 to 115°C (Figs. 4.7 and 4.8). At constant temperature (34 bC), the rate of degradation of organic s u l f i d e s increased with increasing oxygen pressure from 25 to 100 p s i -162-(Figs. 4.9 and 4.10). 5.6 Applications This pioneering research for treatment of sulfate pulp m i l l effluents to eliminate p o l l u t i o n and recover polysulfide from green liquor may f i n d useful applications i n various ways. 5.6.1 Treatment of digester and blow r e l i e f , and evaporator condensates The sulfate pulp m i l l r e l i e f condensates contain malodorous sulfur compounds such as hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e , and various v o l a t i l e organic compounds formed during the course of pulping, along with minor amounts of black liquor and f i b r e s (95$ 120, 125). The amount of condensates i s about one cubic meter per air-dry ton of pulp. The BOD load i s mainly attributed to the presence of high methanol content (173). Gamma r a d i o l y s i s of aerated digester and blow r e l i e f condensates w i l l reduce the t o x i c i t y and BOD load because methanol i n the condensate i s readily oxidized to aldehyde and formic acid by gamma radiation (85). Amount of evaporator condensates i s about 4 to 7 cubic meters per air-dry ton of pulp (173). Though i t does not contribute to -163-BOD to a large extent, i t contains poisonous s u l f i d e s . With respect to purity, of course, the condensates can be recycled i n pulp m i l l s f o r preparing the cooking liquor, but only half the available amount of t o t a l condensates i s required for this purpose. The t o x i c i t y of the evaporator condensates can be greatly reduced by gamma r a d i o l y s i s of the aerated solution before i t i s discharged to sewers. 5.6.2 High s u l f i d i t y and polysulfide recovery processes Carbonation of high s u l f i d i t y black liquor and stripping of hydrogen sulfide before combustion w i l l reduce the emissions of sulfur dioxide and hydrogen s u l f i d e from the combustion furnace, as well as reduce the ratio of smelt sulfur to sodium oxide (S/Na^O). According to the method of Gray £t a l . (79)» black liquor i s carbonated with lime k i l n and flu e gases,under pressure, followed by vacuum stripping of hydrogen s u l f i d e . This process can recover 55 to 65% of black liquor t o t a l s u l f u r . By gamma ra d i o l y s i s of the aerated, a c i d i f i e d black liquor, the residual sulfides compounds i n the carbonated black li q u o r are stable enough f o r further treatment such as condensation. The treated sulfate black liquor i s fermentable with yeast; the recoverable t h i o l i g n i n has no obnoxious smell. -164-Th e regenerated hydrogen s u l f i d e i n carbonated black liqu o r may be either absorbed i n white liquor for the preparation of conventional sulfate cooking liquor or pressurized i n green liquor and i r r a d i a t e d to form po l y s u l f i d e . Regeneration of polysulfide from gamma r a d i o l y s i s of green liquor can be effected by a c i d i f i c a t i o n either with carbon dioxide or hydrogen s u l f i d e . Hydrogen s u l f i d e a c i d i f i c a t i o n usually gives higher e f f i c i e n c y of polysulfide formation than carbon dioxide. The regenerated polysulfide,containing carbonate;can be causticized by calcium oxide or calcium hydroxide, as practiced with conventional green liquor c a u s t i c i z a t i o n f o r sulfate cooking (194). -165-6.0 CONCLUSION The work contained herein describes new, improved methods of t o t a l s u l f i d e analysis of adequate s e n s i t i v i t y and quantitative r e p r o d u c i b i l i t y required to describe gamma radiation i n i t i a t e d changes i n s u l f i d e energetics occurring i n sulfate black liquors and carbonated black l i q u o r s . Model experiments were run f o r the investigation of variables influencing the rate of s u l f i d e s t a b i l i z a t i o n i n aqueous solutions. The information gathered from these model experiments was used i n formulating a proposal fo r an i n d u s t r i a l black liquor s t a b i l i z a t i o n process, based on the r a d i o l y t i c oxidation of sulfides i n aqueous solution i n the presence of excess oxygen. 6.1 Sulfide Analyses Sulfate and polysulfide black liquor analysis by s i l v e r n i t r a t e potentiometric t i t r a t i o n shows two equivalent end points. It i s shown that the two equivalence points ari s e from two d i f f e r e n t forms of s u l f i d e ; namely, the f i r s t i n f l e c t i o n point (-430 rnv) i s considered to be monosulfide, the second i n f l e c t i o n (-250 mv) i s due to presence of organic and inorganic p o l y s u l f i d e s . The organic polysulfide i s formed by the reaction of methyl mercaptide ion with elemental s u l f u r . Inorganic polysulfide i s generated by the oxidation of s u l f i d e ions. -166-In black liquor, methyl mercaptan can not be d i r e c t l y analyzed by potentiometric t i t r a t i o n due to i t s low concentration. However, the quantitative determination i s afforded by a c i d i f i c a t i o n of the black liquor sample to pH 6.5 with suspensions of boric acid i n carbon tetrachloride and analysis of the organic layer with gas l i q u i d chromatography (GLC). Dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liquor can be determined by carbon tetrachloride l i q u i d / l i q u i d extraction and GLC analysis. Residual sulfid e s i n carbonated black liquor, such as hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e , may be quantitatively determined by GLC following adjustment of the sample pH to 6.5 with boric acid and low tempera-ture extraction with carbon tetrachloride ( l i q u i d / l i q u i d extraction. 6.2 Gamma Radiolysis of Sulfides i n Aqueous Solution Part of the products res u l t i n g from the gamma r a d i o l y s i s of sul f i d e model compounds i n aqueous solution have been i d e n t i f i e d . Polysulfide and sulfate are formed from r a d i o l y s i s of sodium s u l f i d e , dimethyl d i s u l f i d e and sulfate from methyl mercaptan. An amorphous substance was obtained from dimethyl s u l f i d e , and sulfate from dimethyl d i s u l f i d e . This indicates that oxidation of sulfides -167-i s the most important reaction of gamma r a d i o l y s i s of sulfides i n aqueous solution. The apparent degradation yields of sodium s u l f i d e (Gf-Na^S) in aqueous solution are pH dependent. In sul f i d e solutions at pH 8.38, G(-Na 2S) i s 7.5» gradual reduction i n degradation y i e l d s (G(-Na 2S) = 5.0) i s observed with solutions at strongly alkaline (pH 12.46) condition. The apparent degradation yields of sodium methyl mercaptan are also greatly affected by solution pH; G^CH^SNa) values of 2.5, 11.3 and 15»4 were calculated correspond-ing to solution pH values of 13.54, 12.54 and 10.70, respectively. Again, degradation of this compound shows the same trend as above. The apparent degradation yields of dimethyl s u l f i d e (Gf-CH^SCH^ ) ) and dimethyl d i s u l f i d e (Gf-CEjSSCH^)) i n alkaline solutions (pH 13.12) were obviously higher than i n black li q u o r (pH 13.14). The degradation yie l d s of dimethyl s u l f i d e and dimethyl d i s u l f i d e correspond to 0.73 and O.89 f o r aqueous alk a l i n e solutions and only 0.50 and 0.43 f o r black l i q u o r . Further, lower solution pH and l i g n i n concentration, increased temperature and oxygen pressure promoted development of higher degradation y i e l d s . In gamma r a d i o l y s i s of sulfate black liquor, sodium s u l f i d e concentration i s generally decreased as i t i s converted to poly--168-sulfideo In this study, maximum polysiilfides were obtained about 1 Mrad at 34°C, and then degraded for further radiation. The apparent degradation yields of dimethyl s u l f i d e (0.001-0.003) and dimethyl d i s u l f i d e (0,002-0.085) were s i g n i f i c a n t l y correlated with th e i r i n i t i a l concentration i n black liquors (pH 12.85-13.40). Degradation yie l d s of hydrogen s u l f i d e (0.015-3.427), methyl mercaptan (0.006-0.230 ) , dimethyl s u l f i d e (0.003-0.020) and dimethyl d i s u l f i d e (0.004-0.035) i n the sulfate and polysulfide carbonated black liquors (pH 8.20-9,15) were also shown to be s i g n i f i c a n t l y correlated with th e i r i n i t i a l concentration. The presence of oxygen i n the sulfi d e enriched carbonated black liq u o r (pH 7.50) increased the r a d i o l y t i c degradation yields of hydrogen s u l f i d e (l6,7), methyl mercaptan (28.0), dimethyl s u l f i d e (0.7*0 ° The higher degradation yie l d s of hydrogen s u l f i d e and methyl mercaptan are considered to be due to chain reactions. Degradation of hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e by gamma radiation i n aqueous solution and carbonated black liquor i s exponential with dose. Si m i l a r l y , the exponent with dose was also found to characterize the degradation of dimethyl s u l f i d e and dimethyl d i s u l f i d e in the -169-various unacidified black liq u o r s . In radio-chemical reactions of oxygenated black liquors and carbonated black liquors, the degradation of malodorous sulfides i s considered to be oxidation, polyaddition and combination of oxidation and polyaddition products. The v o l a t i l e malodorous sulfides are thus s t a b i l i z e d i n the black liquor a f t e r gamma radiation treatment. Advantages of these reactions i n processing of black li q u o r are proposed to relate to abatement of a i r p o l l u t i o n from sulfate pulp m i l l s . Gamma radiation induced oxidation of s u l f i d e and mercaptide ions, and organic components i n the aerated sulfate pulp m i l l effluent, i s further expected to reduce t o x i c i t y and b i o l o g i c a l oxygen demand (BOD) of pulp m i l l e f f l uents. Thus, the radiation treatment i s also proposed to reduce major problems of water p o l l u t i o n . Polysulfide can be generated by gamma radiation of carbon dioxide or hydrogen s u l f i d e a c i d i f i e d sodium s u l f i d e and sulfate green l i q u o r s . The apparent yields of polysulfide excess sulfur (G(S)) were 2.96 and 4.92 for a c i d i f i c a t i o n with carbon dioxide (120 psi) and hydrogen s u l f i d e (270 p s i ) , respectively. However, further optimization of the reaction condition to obtain higher yie l d s of poly s u l f i d e i s necessary fo r i n d u s t r i a l polysulfide cooking liquor regeneration. -170-7o0 REFERENCES 1. Adams, D.F. 1965. A survey of European kraft m i l l odor systems. Tappi 48(5) : 83A -87A. 2. . 1969. Analysis of malodorous sulfur-containing gases. Tappi 52 1 5 3 - 5 8 . 3. , and R.X. Koppe. 1959= Gas chromatographic analysis of hydrogen s u l f i d e , sulfur dioxide, mer-captan and a l k y l sulfides and d i s u l f i d e s . 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Svensk Papperstid. 70 .8 500-506. 195. _. 1967<> Spectrophotometric determination of poly-sul f i d e excess sulf u r i n aqueous solutions. Svensk Papperstid. 70 g 197-200. 196. . 1968. Redox potential of polysulfide solutions and carbohydrate s t a b i l i z a t i o n . Svensk Papper-s t i d 71 s l49-l60. 197. . 1969. Some aspects of the chemistry of poly-s u l f i d e pulping. Svensk Papperstid. 72 % 29k-302. -203-198. Thoen, G.N., G.G. DeHaas, R.G. Tallent and A.S. Davis. 1968. The effect of combustion variables on the release of odourous sulfu r compounds from a kraft recovery unit. Tappi 51 s 329-333. 199. and D.C. Nicholson. 1970. Infrared analysis of k r a f t pulping gases. Tappi 53 5 224-226. 200. Thomas, E.W. 1964. Direct determination of hydrocarbon sulfides i n kraft gases by gas l i q u i d chroma-tography. Tappi 47 ; 587-588. 201. Tirado, A. and V. Gonzales. 1969. Ten years experience i n odor control at the Loreto Y Pena Robre kraft m i l l . Tappi 52 s 853-856. 202. 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Warther, J.F. and Ambery, H.R. 1969. The status of odor control i n the kraft pulp industry. Paper Presented at AIC&E Meeting, Portland, Oregan. 216. Weiss, J. 1952. Chemical dosimetry using ferrous and eerie sulfates. Nucleonics 10(7) s 28-31. 217. Weiss, J.J. 1964. Polyfunctional simple molecules s chemical i n t e r e s t . Radiation Res. Suppl. 4 ; 141-149. 218. Wenzel, H.F.J, and O.V. Ingruber. 1967. Controlling problems of a i r and water contamination. Paper Trade J. 15(2) s 42-47. -2 06-219. Whitcher, S.L., M. Rotheram and N. Todd. 1953. Radiation Chemistry of cysteine solution. Nucleonics 11(8) g 30-33. 220. Wilkening, V.G., M. L a i , M. Arends and D.A. Armstrong. 1967. The y- r a d i o l y s i s of cysteine i n deaerated IN HC10. solutions. Can. J. Chem. 45 8 1209-4 1214. 221. Williams, I.H. and F.E. Murray. 1966. Studies on the gas chromatographic analysis of kraft m i l l s u l f i d e s . Part 1. C o l l e c t i o n and analysis of gaseous samples. Pulp Paper Mag. Can. 67 % T3k7- T352. 222. Wilson, D.F. and B.F. Hrutfiord. 1971. SEKOR IV. Formation of v o l a t i l e organic compounds i n the kraft pulping process. Tappi 5^ s 1094-1098. Table 2.1 Release of v o l a t i l e sulfur compounds from digester* and washers Release lb/air-dry ton of pulp. M i l l SO, Skoghall (Batch) Kopraanhojmen* (Batch) Norrsundet (Continuous) Lovholmen (Continuous) (Batch) H2S CRjSH 0.070 0.450 0.049 0.118 0.081 o.o44 0.021 0.045 CEjSSCH^ 0.080 0.008 0.001 Total Ref 0.231 1 5 0.502 15 0.070 15 0.164 15 Brown Stock 0.01-0,02 0.01-0.12 0.10-0.25 Washers 0.01-0.12 0.002-0.004 0.40-2.50 0.20-1.50 0.72-4.12 90 0.01-0.02 0.01-0.02 0.14-0.43 90 1 ro o From condensate (turpentine and blow condensates) only. Table 2.2 Release of v o l a t i l e sulfur compounds from sulfate recovery systems ( 9 0 ) . Release, lb/air-dry ton of pulp SO_ H 2 ! CEL^ SH CftjSCRj CH^SSCR^ Total Oxidation tower Multiple effect evaporators A. B. Conta c t Evaporators A. B. 0 - 0 . 0 1 0 . 0 1 - 0 . 0 2 0 . 0 5 - 0 . 1 0 0 . 0 2 - 0 . 0 8 0.05-0.15 Recovery furnac e Smelt tank Lime k i l n 0 - 0 . 0 1 0 - 0 . 0 1 0 . 1 0 - 3 . 0 0 . 0 1 - 0 . 0 2 2 . 0 - 8 . 0 5 . 0 - 3 0 . 0 2 . 0 - 8 . 0 0 . 1 0 - 2 . 0 1 0 . 0 - 1 5 . 0 1 . 0 - 5 . 0 0 . 0 - 0 . 0 1 0 . 0 2 - 0 . 0 5 No data ava i l a b l e . 0 . 1 0 - 1 . 5 0 . 0 5 - 0 . 0 8 0 . 0 1 - 0 . 0 2 0 . 1 0 - 0 . 3 0 0 . 0 5 - 0 . 1 5 0 . 0 5 - 0 . 1 5 0 . 5 0 - 2 . 5 0 0 . 1 0 - 0 . 3 0 0.10-0.40 0 . 0 5 - 0 . 2 5 0 . 0 1 - 0 . 1 0 0 . 0 1 - 0 . 2 0 0 . 1 - 0 . 1 0 0 . 0 1 - 0 . 0 2 0 . 0 1 - 0 . 0 2 0 . 0 2 - 0 . 0 5 0 . 0 1 - 0 . 0 2 0 - 0 . 0 1 0 . 1 3 - 0 . 3 5 0 . 2 6 - 4 . 6 1 0 . 2 1 - 0 . 6 3 7.70-41.20 2.17-10.55 11*03-20.14 0 . 0 5 - 0 . 1 4 A. Unoxidized black liquor, B. Oxidized black liquor. Table 2^3 Physical c h a r a c t e r i s t i c s of sulfate pulp m i l l malodorous s u l f i d e s . Compound B o i l i n g point , °C Explosive cone, range i n a i r , fo (54) Dissociation const, at 100°C (169) Odor threshold i n ambient a i r ppm (114) -61.80 4.3-45.5 K± =2.1 x 10-7 (A) 0.00047 K2 <10~lk (B) Cft^SH 7.6 2.2-9.2 K = 4.3 x 10 1 1 (C) 0.0021 CH SCH 3 3 37.0-38.0 3.9-21.8 0.001 CH^SSCEj 109-111 No data available A. HgS HS" + H / 2 - l l / . - K2j __ + ' 3 • HS S *H H t * » • o «* o« » / C. CH SH<A> CH s" + H + ..../2-13/ Table 3.1 Sulfate and polysulfide black liquor sources. Code Wo. Company Location Wood Species Sulphidity Kappa No. 1 - 1 W*ey e rha eu s e r Everett Douglas-fir 30 26.7 1 - 2 Weyerhaeuser Longview Douglas-fir 19.2 22.7 1 - 3 Weyerhaeuser New Bern N.C. 65% L o b l o l l y pine 35% Pond pine 21.0 1 - 4 Weyerhaeuser Springfield Douglas-fir 21.4 50.0 2 - 1 Canadian Forest Products Port Mellon B.C. 3 - 1 Forest Products Laboratory Vancouver B.C. Sprue e 4 - n Pulp Paper Res. Inst, of Can. Montreal P.Q. 4 - i v Pulp Paper Res. Inst, of Canada Montreal P.Q. Table 3.2 Effect of i n f l e c t i o n point "a" and "b" i n potentiometric t i t r a t i o n curves on c a l c u l a t i o n of hydrogen sul f i d e i n black liquor. H S Calculation, g / l Black Liquor I n f l e c t . I n f l e c t . Differenc es Sourc es pt "a" pt "b" g / l % 1 - 1 4.25 4.76 0.50 11.8 1 - 2 0.95 1.50 0.55 57.3 1 - 3 3.42 3.84 0.42 12.3 1 - 4 2.42 2.86 0.44 18.2 2 - 1 2.63 3.19 0.56 21.3 3 - 1 1.71 2.83 1.12 65.2 4,- 1L 8.80 9.4l 0.61 7.0 4 - IV 0.81 1.72 0.91 111.7 Table 3*3 Accuracy of potentiometric t i t r a t i o n of sulfide i n alkaline solution i n the presence of methyl mercaptan. Added, mg Found, mg Source Na S CH SNa Thio- Na S i n f l e c t . % l i g n i n 2 pt "a" Bound Na- mer-captan i n f l e c t , a - b Free Na-mercap-tan Total A<S*'t for 10.0 66.5 Na2S Solution* l o . o 67.7 19.9 56.8 1% 9.3 9.8 19.9 93.0 19.1 45.1 64.2 96.5 98.0 21.2 44.5 100 23.1 35.7 65.7 97.0 58.8 103.5 White Liquor (1-3) 22.6 19.9 55.1 57.8 18.7 19.5 82.7 40.3 16.1 98.0 37.7 20.1 56.4 102.3 57.8 100.0' * Reagent grade Na„5 i n IN NaOH Solution, Table 3.4 Interpretation of the potentiometric t i t r a t i o n curve as af f e c t i n g the accuracy of su l f i d e determination by addition of methyl mercaptan. Added Found Na 2 S, mg Th i o l i g n i n , fo N a 2 s i n f l e c t i o n Error, % Na2s inflection Error pt "a", mg pt ttbn, mg 10.0 - 9*3 10.0 - 10.7 10.0 1.0 9.8 10.0 1.0 9.8 -7 22.1 +120.5 +7 22.9 +129.1 -2 22.0 +119.7 -2 22.4 +124.4 -21k-Table 3*5 Determination of s u l f i d e and bound mercaptan by-addition of excess of Na-mercaptan to oxidized a l k a l i n e s u l f i d e solution with and without t h i o l i g n i n as additive. Oxidation** With 1% time, min. 0 5 10 20 50 70 80 t h i o l i g n i n Na2S, g / l * 9*8 9.3 8.8 6.2 1.2 O.k Bound Na-mercap-tan, g / l * 21.2 37.6 27.4 20.5 17.8 17.4 Without 1% t h i o l i g n i n Na S, g / l * 12.4 10.0 9.0 5-5 4.0 2 Bound Na-mercap-tan, g / l * 22.8 29.4 20.9 19.5 10.9 *n = 2. **0 flow rate = 44 ml/min i n 400 ml liq u o r sample. -2i5-Table 3.6 Potentiometric t i t r a t i o n of methyl mercaptan i n a l k a l i n e solution i n the presence of elemental s u l f u r . CH SNa 11.22 11.22 11.22 11.22 11.22 11.22 S i n 3 Elemental 0 4.0 8.0 20.0 38.4 457.0 Sample Sulfur *mg Approx. Mercap. 0 2.8 1.4 0.6 0.3 0.02 S/So Apparent Sulfide 0 0.51 0 1.01 1.11 1.4l Bound S 0 3 .62 6.83 10.42 11.24 11.22 S Found Total 0 4.13 6.83 11.82 12.43 12.62 mg % 0 103.3 85.4 59.1 32.1 2.8 Bound Mercap-tan 0 3.62 4.42 11.22 11.24 11.22 Apparent Mercaptan S 11.22 7.21 6.83 0 0 0 Mercap-tan S Total 11.22 10.83 11.25 11.22 11.64 11.22 Found % 100.0 96.5 100.3 100.0 103.7 100*0 mg *pH = 13.3 - 13.6 n=2. -216-Table 3.7 E f f i c i e n c y of 5 x 10 ml carbon tetrachloride l i q u i d / l i q u i d extraction of the organosulfid from 5 ml sulfate white and black l i q u o r s . Liquor Sulfur compound added Sulfur compound found CHjSCIIj CH^SSCaj CI^SCRj % e R V j S S C H ^ 1° -T -3 -3 -3 xlO -3g xlO  Jg xlO g xlO - g White liquor (pH = 13.6") 0.845 1.057 0.766 90.7 0.825 78.1 " M 0.766 90.7 0.835 79.0 " " 0.769 91.0 0.82 6 78.1 " " 0.764 90.4 0.825 78.0 Average O.766 90.7 0.828 78.3 0.423 0.529 0.400 94.6 0.427 80.7 " »• 0.390 92.2 0.415 78.4 Average 0.395 93.4 0.421 79-6 0.212 0.264 0.200 94.3 0.215 81.4 " 0.195 92.0 0.206 78.0 Average 0.198 93.4 0.211 79*9 Black li q u o r (pH = 13.1) 0.845 1.057 0.774 91.5 0.805 76.2 " " 0.780 92.3 0.855 80.9 Average 0.777 91.9 0.830 78.5 0.423 0.529 0.405 95.7 0.421 79.6 w " 0.394 93.1 0.430 81.4 Average 0.400 94.6 0.426 80.5 0.212 0.264 0.190 89.6 0.208 78.8 " " 0.200 94.3 0.206 78.0 Average 0.195 92.0 0.207 78.4 -217-Table 3.8 E f f i c i e n c y of 20ml carbon tetrachloride l i q u i d / l i q u i d extraction of organic s u l f i d e compounds from 5 ml boric acid (l.Og) treatment carbonated black liquor ( l - l ) . Organosulfides added cajSCIL, ClijSSCELj -3 x 10 JS Organosulfides found CELjSCRj CELjSSCIlj x 10~3g 0.212 0.264 0.198 93.6% 0.234 88.6% 0.191 90.1% 0.222 84.1% 0.201 95.0% 0.232 87.9% Average 0.197 92.9% 0.229 86.9% 1 Table 4.1 Characteristics of sulfate and polysulfide black liquors. Sulfides, x 10"3 g / l Source pH Solids, Density Lignin H S CBLSH CILSCBU "XB CH SSCH % (n=4) g/ml, 25°C g / l 2 3 3 (n=3) (n=2) (n=4) (n=3) (n=3) (n=3) (n=3) 1 - 1 13.21 20.1 1.0953 37.5 4254.8 53.57 0 6.49 7.58 1 - 2 12 .87 12.4 1.0657 33.9 953.1 14.90 1.10 10.73 6.53 1 - 3 13.07 13.4 1.0706 44.3 3419.6 49.67 0 8.10 3.00 1 - 4 12.85 14.1 1,0727 37.0 2422.8 34.07 0.25 0.36 0.44 2 - 1 13.25 13.3 1.0695 35.7 2625.1 50.43 0.56 102.00 17.08 3 - 1 13.27 12.6 I.0668 30.3 1714.6 12.87 0.20 85.00 2.10 4 - 1L 13.40 14.1 1.0744 48.6 8796.5 83.67 0.39 50.21 39-71 4 - 2V 13.22 5.5 1.0304 18.6 811.5 11.23 0 4.48 5.06 -219-Table 4.2 Gamma ra d i o l y s i s of sodium s u l f i d e aqueous solution and formation of polysulfide excess sulfu r at Gammacell temperature (34°C). Dose Mrad Ka 2S g / l Molecu. 20 xlO PH Poly-S* xl0" 2g/l Na2S g / l Molecu. x l O 2 0 pH Poly-S* xl0" 3g/l 0.0 3.37 260.2 8.38 16.3 3.19 246.4 12 .46 0.0 0.1 3.29 254.2 8.73 16.9 3.17 244.6 12.48 0.5 0.3 3-13 241.5 8.49 17-5 3.03 234.0 12.46 3-5 0.5 3.03 233.7 8.59 18.9 2.96 228.4 12.52 5.1 0.7 2.87 221.6 8.84 21.8 2.88 221.9 12.42 6.1 0.9 2.76 213.2 8.89 22.0 2.75 212.0 12 .49 7.6 1.5 2.61 201.2 9.32 26.3 2.80 216.2 12.49 11.6 2.0 2.49 191.5 8.71 30.1 2.79 214.9 12.53 14.7 2.5 2.39 184.3 8.80 32.8 2.70 208.3 12.44 16.00 3.0 2.29 176.5 9.03 34.0 2.66 205.1 12.49 16.5 3.5 2.21 170.5 9.25 34.2 2.64 204.5 12.51 18.5 4.0 2.16 166.8 9.07 39.0 2 .62 202.1 12.47 19.0 k.5 2.05 158.4 9.14 41.6 2.60 201.7 12.33 20.2 Replications, n=2. * Polysulfide excess su l f u r . -220-Table 4.3 Effect of solution pH on gamma radiation degradation y i e l d (G) * of sodium s u l f i d e and sodium methyl mercaptan and y i e l d (G)* of polysulfide excess su l f u r . I n i t i a l pH# 8.38 12.46 Na2S cone. , # g / l 3.37 3.19 G(-Na2S) + 7.5 5.0 G(S) + 1.1 0.1 I n i t i a l pH# 10.70 12.54 13.54 CH^SWa cone. , # g / l 6.59 7.46 8.6 i G(-CHVjSKa ) + 15.4 11.3 2.5 * Apparent G, Molecules/100 ev. # From Tables 4.2 and 4.4. + G calculated from i n i t i a l slope of curve i n Fig$4.1 and 4.2. G(S) Y i e l d of polysulfide excess s u l f u r . Table 4.4 Gamma r a d i o l y s i s of sodium methyl mercaptan in various pi solutions at Gammacell temperature (3^°C). Dose Mrad 8.6l 8.60 8.59 8.55 8.51 8.47 8.45 8.48 8.21 8.26 740.0 739.^ 737.7 734.3 731.3 727.9 726.4 728.2 705.5 709.8 6.67 9.25 11.35 13.60 15.15 15.90 17.00 17.47 18.58 20.47 13.54 13.55 13.53 13.53 13.5^ 13.55 13.48 13.46 13.42 13.35 7.46 7.16 7.09 6.76 6.71 6.51 ' 6.42 6.45 6.27 6.21 641.3 6i4.8 608.8 580.8 576.5, 559.2 551.2 554.2 538.7 533.5 12.54 12.46 12.45 12.42 12.43, 12.35 12.37 12.34 12.32 12.27 CH^SNa, g/l 6 # 5 g 6.42 6.03 6.17 5-64 5.26 5.13 5.21 4.80 4.48 Molecu. x i o 2 0 566.2 551.2 535.2 530.0 484.9 451.7 44l.l 447.9 412.6 385.0 PH 10.70 10.85 10.93 10.95 11.03 11.10 11.24 11.41 11.48 11.57 CH SNa, g/l 3 20 Molecu. x 10 CH^SSCH^ x 10~ 3g/l pH CILjSNa,. g/l Molecu. x 10 pH Replications, n=2. -222-Table 4.5 Gamma ra d i o l y s i s of model compounds of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n aqueous alka-l i n e solution at Gammacell temperature (3^°C). Dose Mrad xl0~3g Jl Molecu.xlO 2 0 xl0"3g; / l Molecu.xlO 2 0 0.0 9l.o 8.82 163.6 10.46 13.12 0.1 86.5 8.38 153.3 9.81 13.15 0.3 78.2 7.58 136.5 8.73 13.13 0.5 69.8 6.76 125.0 8.00 13.13 0.7 59.5 5.77 117.0 7.48 13.15 0.9 51.5 ^.99 105.5 6.75 13.17 1.5 36.3 3.52 84.1 5.38 13.15 2.0 30.2 2.93 75.8 4.85 13.16 2.5 24.0 2.32 61.9 3.96 13.15 3.0 21.2 2.05 52.9 3.38 13.17 3.5 16.0 1.55 47.8 3.05 13.15 4.0 10.5 1.01 42.1 2.69 13.14 k.5 6.3 0.6l 33.5 2.14 . 13.13 Replications, n=4. -223-Table 4.6 Gamma ra d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n sulfate blacj^ liquor (2-1) at Gammacell temperature (34 C)» Dose Mrad CRjSCKj —3 2 0 xlO g/l Molecu.xlO xlO~ 3g, CILjSSCH^ / 2 0 / l Molecu.xlO pH 0.0 171.8 16.65 207.5 13.27 13.14 0.1 171.4 l 6 . 6 l 203.6 13.02 13.14 0.3 169.3 16.42 2 02 .9 12.97 13.14 0.5 162.5 15.77 200.6 12.83 13.14 0.7 161.0 15.61 195.8 12.52 13.14 0.9 135.8 13.16 180.1 11.52 -1.5 127.9 12.40 178.6 11.42 13.14 2.0 121.9 11.82 I69.8 10.86 -2.5 117.5 11.40 145.3 9.29 13.12 3.0 99.8 9.67 l4o.6 8.99 -3.5 94.0 9.11 133.9 8.56 13.12 4.0 89.0 8.63 128.6 8.18 -4.5 82.8 8.0 117.8 7.53 13.10 Replications, n=4 „ -224-Table 4.7 Gamma radiation degradation yields(G) of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n alk a l i n e aqueous solution and black liquor (2-1). Sources. Gf-CH^SCH^) Gf-CRjSSCF^ ) Aq. Solution 0.73 0.89 (pH 13.12 ) Black liquor 0.50 0.43 (pH 13.14) * Apparent G, Molecules/lOOev. G Calculated from i n i t i a l slope of curves i n Fig. 4.3. Table 4.8 Effect of solution pH on gamma r a d i o l y s i s (3 Mrad) of dimethyl s u l f i d e and dimethyl d i s u l f i d e . I n i t i a l PH 0.5 2.5 4.4 5-5 6.5 7.5 8.4 9.7 10.1 11.5 13;0 13.5 -3 CH^SC^, x 10 g / l I n i t i a l Cone. 91.0 91.0 91.0 91.0 91.0 88.0 80.0 75.0 75.0 75.0 75.0 75.0 Final cone. 8.0 16.0 22.5 25.5 24.2 26.0 29.o 29.5 33.0 35.0 37.0 42.0 Decomp., % 91.2 82.4 75.3 72.0 73.5 70.5 63.8 60.7 56.0 53-3 50.7 44.0 G* 0.43 0.39 0.36 0.34 0.35 0.32 0.26 0.24 0.22 0.21 0.20 0.17 G/Co 293.5 266.2 245.7 232.1 238.9 226.0 201.9 198.8 182.3 174.0 165.7 140.9 I n i t i a l PH 1 . 5 2 . 5 4 . 4 5 . 5 7 . 0 8 . 4 9 . 7 1 0 . 1 1 1 . 5 1 2 . 5 1 3 . 0 1 3 . 5 CH SSCH , x l 0 " 3 g / l 3 3 I n i t i a l 165.O 170.0 178.O 182.0 184.0 170.0 160.O 160.0 160.0 160.0 160.O 160.O c one. Final 29.0 26.5 32.5 36.0 44.5 50.0 54.5 56.0 47.5 44.0 42.0 47.0 cone. Decomp., % 82.4 84.4 81.7 80.2 75.8 70.6 65.9 65.0 70.3 72.5 73.8 70.6 G>* 0.47 0.49 0.50 0.50 0.48 0.4l 0.36 0.36 0.38 0.4o 0.40 O.39 G/Co** 286.3 271.5 264.6 258.8 245.8 227.2 211.9 211.9 223.7 235.4 235.4 229.5 * Molecules/lOOev. ** Molecules/Mol. lOOev. -22 6-Table 4.9 Effect of l i g n i n concentration on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n aqueous alka l i n e solution. Lignin Cone, g / l 0.0 10.0 30.0 50.0 70.0 100.0 120.0 1.5 Mrad, CB^ s c ^ i n i t i a l cone. , Co=l65.0 x 10"3 g / l CHjSC^.xlO - 3 g / l 105.8 119.6 131.3 133.3 126.1 - 128.7 Decomp., % 35.88 27.52 2 0.42 19.21 23.58 - 22 .00 G'M-CH^SCH^ ) 0.6l 0.47 0.35 0.33 0.4o - 0.38 3.0 Mrad -3 CH^SCH^.xlO g/ l 69.0 85.0 96.0 95.0 88.0 82 .0 81.1 Decomp., % 58.18 50.00 41.82 42.42 46.67 50.31 50.91 G<-CH3SCH3 ) 0.50 o.4i O.36 O.36 o.4o 0.43 0.44 1.5 Mrad, CEj SSCH3 i n i t i a l cone » » Cp= 190.0 x l O ~ 3 g / l C E J S S C H J . X I O " 3 g / l 102.5 139.0 i 4 o . o 139.0 145.0 135.0 130.0 Decomp., % 46.05 26.84 26.31 26.85 23.68 28.95 36.84 Gf-CIL^SSCHj ) 0.60 0.35 0.34 0.35 0.31 0.38 0.47 3.0 Mrad C H SSCH ,xlO~ 3 3 3 g / l 75.00 104.0 102.0 96.0 90.0 86.0 91.5 Decomp., % 60.35 45.26 46.23 49.47 52.63 54.74 51.84 Gf-CI-^SSCftj ) 0.39 O.29 0.30 0.32 0.33 0.36 0.3^ Average G** 0.53 0.38 0.34 0.3** 0.36 0.39 0.4l pH 3 Mrad 13.12 13.07 12.81 12 .10 10.90 10.12 9.08 *Molecules/l00ev. ** Average G value of dimethyl s u l f i d e and dimethyl d i s u l f i d e . -227-Table 4.10 Effect of temperature on gamma r a d i o l y s i s of dimethyl su l f i d e and dimethyl d i s u l f i d e i n black liquor (1-3) under 50 psi i n i t i a l oxygen pressure. Max Temp. °C. 60 77 83 103 115 3 Mrad, CH^SCIij i n i t i a l cone ., Co=l6o .00x10" dL JSCR J,xlO~ 3g/l 75.83 60.00 53.08 50.42 36.08 Decomp., % 52 .88 62.50 66.83 68.28 77.45 G*C-CH3SCH3 ) 0.44 0.52 0.55 0.57 0.64 Control, 305 min, CR^SCH i n t i a l c o n e , Co=l60.00xl0~Jg/l CH 3SCH 3,xl0" 3g/l 104.55 87.08 73*75 71.76 70.00 Decomp., % 34.79 45.58 53.91 55.21 56.25 3 Mrad, CI^SSC^ i n i t i a l c o n e , Co=l30.00xl0~ g / l CH 3SSCH 3,xl0 - 3g/l 36.42 13.50 1.77 0.60 0.00 Decomp., % 71.98 89.62 98.64 99.54 100.00 G* (-CH3SSCH3 ) 0.34 0.42 0.46 Control, 305 min, CH SSCH3 i n i t i a l c o n e , Co=130.00xl0~3g/l CH 3SSCH 3,xl0" 3g/l 56.17 45.00 34.92 36.47 21.75 Decomp., % 56.79 65.38 73.14 71.95 83.27 3 Mrad 12.51 12.26 11.18 11.11 10.00 pH Control 12.67 12.61 12.45 12.47 11.42 Replications, n=3 * Molecules/lOOev. -228-Table 4.11 Effect of temperature on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n carbonated black liquor (2-1) under 50 psi i n i t i a l oxygen pressure. Max. Temp. °C. 77 83 103 115 3 Mrad, CH^SCH i n i t i a l c o n e , Co=54.17xl0"3g/l CRjSCEL^xlO^g/l 22 .08 16.25 11.92 6.67 Decomp., % 59-24 70.00 78.00 87.68 Gr* (-CH^SCH^ ) 0.17 0.20 0.22 0.25 Control, 299 min, CELjSCIij i n i t i a l cone ., Co=54.17xl0 _ 3g/l CHjSCH^ ,xlO"" 3g/l 35.83 29.13 23.08 21.37 Decomp., % 33.86 46.22 57.39 59.22 3 Mrad, CH^SSCH^ i n i t i a l cone. , Co=97.92xl0~3g/l CH 3SSCH 3,xlO~ 3g/l 45.21 10.25 4.09 2.16 Decomp., % 53.82 89.53 95.82 97.79 G*(^CH3SSCH3 ) 0.18 O.29 0.31 0.34 Control, 297 min, CHjSSCilj i n i t i a l c o n e , Co=97.92xlC >-3g/l CH 3SSCH 3,xlO _ 3g/l 62.50 38.33 25.67 20.71 Decomp., % 36.17 60.80 73.78 78.86 Mrad pH Control 7.94 8.19 8.12 8.00 8.07 8.14 7.92 8.10 Replications, n=3 •Molecules /lOOev, -229-Table 4.12 Effect of oxygen pressure on gamma r a d i o l y s i s of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black liqu o r (2-1) at Gammacell temperature (34 C). Oxygen Pressure p s i 25 50 75 100 3 Mrad, CH SCH i n i t i a l c o n e , Co= 3 3 63.01x10-3 g / l CH 3SCH3,xl0"°g/l 31.50 11.17 7.51 3.95 Decomp., % 50.00 81.70 87.99 93.73 G*(-CH3SCH3 ) 0.16 0.27 0.29 0.31 Control, 294 min, Ca^SC^ i n i t i a l cone., Co= 63.01xl0~ CH 3SCH 3,xlO~ 3g/l 45.58 35.17 23.17 18.08 Decomp., % 22 .90 44.18 63.23 71.31 3 Mrad, CHjSSC^ i n i t i a l cone., Co =43.63x10" 3 g / l CH 3SSCH 3,xlO~ 3g/l 19.08 12.25 6.00 4.58 Decomp., % 56.26 71.92 86.25 89.50 G*(-CH3SSCH3 ) 0.08 0.11 0.13 o.i4 Control, 294 min, CH^SSCKj i n i t i a l c one ., Co =43.63x10 " 3 g / i c ^ s s c i y x i o - ^ g / i 35.42 27.68 22.25 9.71 Decomp., %* 18.79 36.56 49.00 77.74 Replications, n=3. * Molecules/lOOev. -230-Table 4 . 1 3 Effect of oxygen pressure on gamma r a d i o l y s i s of dimethyl sul f i d e and dimethyl d i s u l f i d e i n carbon-ated black liquor (2 - 1 ) at Gammacell temperature ( 3 4°C). Oxygen pressure 2 ^ ^ 1 0 0 psi  3 Mrad, CRjSCIij i n i t i a l c o n e , Co=54.17xl0~3g/l CH 3SCH 3,xl0~ 3g/l 18.33 10.27 6.67 Decomp., % 66.l6 81.04 87.67 G*(^CH3SCKLj) 0.21 0.26 0.28 Control, 294 min, CH^SCE^ i n i t i a l c o n e , Co=54.17xl0~3g/l CH^SCH^,xl0~ 3g/l 38.28 26.00 23.07 Decomp., % 29.33 52.00 57.4l 3 Mrad, CH^SSCE^ i n i t i a l c o n e , Co=97.92xl0-3g/l CH 3SSCH 3,xl0 _ 3g/l 52.17 38 . 64 21.67 Decomp., % 46.72 60.72 77.87 G*(-i.CH3SSCE^ ) 0.16 0.20 0.26 Control, 294 min, CE^SSCE^ i n i t i a l c o n e , Co=97• 92xl0~ 3g/l _3 CE^SSCE^.xlO g / l 68.33 64.17 42.08 Decomp., % 30.22 Jk.k7 57.03 Replications, n=3. *Molecules/l00ev. -231-Table 4.14 Potentiometric t i t r a t i o n of mono-and polysulfide i n 4 ml gamma irra d i a t e d black li q u o r (3-1) . Dose Mrad Consumption Monosulfide a of 0.05N AgNO^, P o l y s u l f i d e b ml pH 0.0 7.24 4.52 13.32 0.06 6.64 4.60 13.32 0.12 6.56 4.65 13.32 0.24 6.42 4.96 13.31 0.37 5.20 5.12 13.31 0.49 4.4o 5.46 13.32 0 .6l 2.74 6.14 13.32 0.92 0.32 6.80 13.31 1.22 0.26 5.85 13.29 1.52 0.19 4.05 13.29 1.83 3.64 13.30 2.13 2.79 13.25 2.44 1.87 13.25 Replications, n=2. Radiolysis at Gammacell temperature (34°C) a. I n f l e c t i o n "a" of potentiometric t i t r a t i o n curve. b. I n f l e c t i o n "b" of potentiometric t i t r a t i o n curve. -232-Table 4.15 Gamma r a d i o l y s i s of dimethyl s u l f i d e i n sulfate and polysulfide black l i q u o r s . Dose Mrad 0.0 1.0 2.0 3.0 4.0 5.0 1 - 2 -3 CH^SCBLj.xlO • ,g/ l 1.10 0.96 0.73 0.60 0.46 0.37 T- 7 Molecu.xlO"' 106.6 93.4 70.8 57.8 44.6 36.2 CH^SCH^.xlO •> .g / l 0.25 0.21 0.11 0.06 0.01 -17 Molecu.xlO 24.2 20.4 10.3 3.5 1.0 -2 - 1 -3 CH^SCElj.xlO J , g / l 0.56 0.45 0.30 0.19 0.14 0.07 Molecu.xlO 1 7 54.6 43.6 29.1 18.4 13.6 6.5 3-1 ~ CH SCH ,xl0~^ 3 3 Molecu.xlO 1 7 , g / l 0.20 19.4 0.09 12 .0 0.06 5.8 0. 02 2.3 - -4-1L CRjSCEj.xlO"-^ ,g/ l 0.39 0.31 0.21 0.07 0.04 0.01 Molecu.xlO 1 7 38.1 29.1 20.4 6.8 3.6 1.0 Replications, n=3„ -233-Table 4.l6 Gamma ra d i o l y s i s of dimethyl d i s u l f i d e i n sulfate and polysulfide black l i q u o r s . Dose Mrad < 0.0 1.0 2.0 3.0 4.0 5.0 1-1 CH^SSCEj ,xlO" 18 Molecu.xlO '3, g / l 7.58 48.5 4.30 27.5 3.44 22.0 2.96 18.7 1.71 10.9 1.06 6.8 1-2 CH^SSCH^ ,xl0" ' 3 , g / l 6.53 5.00 3.67 2.90 1.03 0.71 18 Molecu.xlO 19.2 15.4 9-3 5.1 4.4 3.1 1-3 CH SSCHo,xl0" 3 3 -1 Q Molecu.xlO •3 3.00 41.8 2.41 32.1 1.4i 23.0 0.81 18.5 0.69 6.6 0.49 4.5 1-4 CH SSCKj ,xlO" 18 Molecu.xlO "3, g / l 0.44 2.8 0.27 1.8 0.15 1.0 0.09 0.6 0.03 0.2 0.01 0.1 2-1 C H 3 S S C H 3 ,xlO~ "3, g / l 17.08 15.42 11.36 9.15 7.65 5.58 18 Molecu.xlO 109.3 98.6 72.7 58.5 48.9 35.7 3-1 C B ^ S S C E J . X I O " '3, g / l 2.10 O.69 0.44 0.27 0.16 0.07 1 8 Molecu.xlO 13 .4 4.4 2.8 1.7 1.0 0.4 4-1L CH^SSCH^jXlO* , 3 , g / l 39.71 35.90 30.29 23.87 21.15 18.66 Molecu.xlO 1 8 253.9 229.6 193.7 152.8 135.3 119.3 4-2 V CRjSSCH^ ,xlO~ 3 , g / l 5.06 4.63 3.16 2.27 1.34 0.52 1 8 Molecu.xlO 32.4 29.6 20.2 14.5 8.6 3.3 Replications, n=3. / -234-Table 4.17 Gamma r a d i o l y s i s of unidentified sulfur compound (X) in sulfate and polysulfide black liquors at Gammacell temperature (34 0) Dose Mrad 0.0 1.0 2.0 3.0 4.0 5.0 1-1 « X,xlo"° .e/i 6.49 5.11 3.58 1.91 0.64 0.28 1-2 _ X,xl0~^ ,g/i 10.73 6.98 4.38 2.30 1.08 O.69 1-3 _ 3 X,xlO .g/i 8.10 6.37 1.31 0.36 0.22 0.11 1-4 X,xlO J .e/i 0.36 0.21 0.'09 0.05 0.02 0.01 2 ~ X -3 X,xl0 > .g/i 102.00 92.15 79.12 69.38 62.50 59.17 3-1 _3 X,xlO ,g/i 85.00 56.10 47.39 33.50 24.51 2 0.34 4-1L ~ X,xlO~J .g/i 50.21 44.58 25.63 23.33 18.54 12.17 4-2 V 3 X,xl0"° .g/i 4.48 2.67 I.63 1.05 0.78 0.53 Replications, n=3. Quantitative determination from dimethyl s u l f i d e c a l i b r a t i o n curve. -235-Table 4.18 Gamma radiation degradation y i e l d ( G ) * of dimethyl s u l f i d e and dimethyl d i s u l f i d e i n the various sulfate and polysulfide black l i q u o r s . Sources Gt-CH^SC^ ) G(-•CH^SSCftj ) 1-1 0.034 1-2 0.003 0.006 1-3 0.016 1-4 0.001 0.002 2-1 0.002 0.045 3-1 0.001 0.014 4-lL 0.002 0.085 4-2 V 0.005 * Apparent G, G Calculated Molecules/lOOev. either from i n i t i a l slope of curves i n Figs. 4.12 4.13 or estimated from Table 4.15* -236-Table 4.19 Gamma ra d i o l y s i s of hydrogen s u l f i d e i n carbonated sulfate and polysulfide black liquors at Gammacell temperature (34°C). Dose Mrad 0.0 1.0 2.0 3.0 4.0 5.0 1 - 1 -3 H2S, xlO , g / l 116.44 34.65 15.45 7.00 2 .21 O.69 Molecu.xlO 1 9 205.8 61.2 27.3 12.4 3.9 1.2 1-2 o HgSjXlO , g/l 0.89 0.42 0.23 0.15 0.10 o.o4 Molecu.xlO 1 9 1.6 0.7 0.4 0.3 0.1 0.1 1-3 o HgS.xlO'^jg/l 182.19 94.71 30.93 16.10 8.00 2.04 Molecu.xlO 1 9 322.0 167.4 54.7 28.5 14.1 3.6 H2S, x l O _ J > , g / l 2.57 0.74 0.42 0.23 0.13 0.08 Molecu.xlO 1 9 4.5 1.3 0.7 0.4 0.2 0.1 2-1 „ HgS.xlO^jg/l 16.23 9.28 2.79 1.67 0.59 0.30 Molecu.xlO 1 9 28.7 16.4 4.9 3.0 1.0 0.5 3-1 -H 2S,xlO _ J >,g/l 2.87 1.00 0.54 0.4l 0.20 0.13 Molecu.xlO 1 9 5.1 1.8 1.0 0.7 0.3 0.2 4-1L „ E ^ x l O ^ . g / l 265.20 159.45 131.40 81.19 15.42 6.99 19 Molecu.xlO 468.7 281.8 232.2 143.5 27.3 12.3 4-2 V HgS.xlO^.g/l 3.11 1.18 0.56 0.4l 0.18 0.14 Molecu.xlO 1 9 5.5 2.1 1.0 0.7 0.3 0.3 Replications, n=3, -237-Table 4.20 Gamma r a d i o l y s i s of methyl mercaptan i n carbonated sulfate and polysulfide i black liquors • Dose Mrad 0.0 1.0 2.0 3.0 4.0 5.0 C&jSH.xlO-^g/l 4.13 1.70 0.65 0.46 0.30 0.17 Molecu.xlO 1 8 51.8 21.3 8.2 5.7 3.7 1.4 1-2 3 CRjSH.xlO - g / l 1.57 0.70 0.35 0.18 0.08 o.o4 18 Molecu.xlO 19.6 8.6 4.1 2.3 1.0 0.5 1-3 o CH3SH,xlO g / l 28.70 17.25 11.05 8.00 3.63 1.22 18 Molecu.xlO 359.3 216.0 138.4 100.1 ^5.5 15.3 1-4 CHjSH.xlO-^g/l 7.30 4.16 1.55 O.67 0.36 0.19 18 Molecu.xlO 91.4 52.1 19.5 8.4 •4.5 2.4 2 - 1 3 CHjSH.xlO-^g/l 13.15 7.84 4.27 1.40 0.67 0.35 18 Molecu.xlO 164.7 98.2 53.5 17.5 8.4 4.2 3-1 _3 CEjSH.xlO g / l 18 Molecu.xlO 1.25 15.7 0.59 7.4 0.33 4.1 0.19 2.4 0.10 1.2 0.05 0.6 4-1L „ CH SH,xlO"°g/l 3 18 Molecu.xlO 73.87 925.0 ^9.75 623.O 32.73 409.9 22.55 282.4 : 10.38 129.9 6.80 85.1 4-2 V CH3SH,xlO""'g/l 0.48 0.21 0.10 0.06 0.03 0.01 i 8 Molecu.10 6.0 2.6 1.3 0.8 0.4 0.1 Replications, n=3. -238-Table 4.21 Gamma r a d i o l y s i s of dimethyl s u l f i d e i n carbonated sulfate and polysulfide black l i q u o r s . Dose Mrad 0.0 1.0 2.0 3.0 4.0 5.0 1-1 -3 CH^SCH^jXlO Molecu.xlO 1 7 1.16 112.1 0.90 87.6 0.49 47.5 0.23 22 .6 0.07 6.8 0.03 2.9 1 - 2 -3 C H ^ S C I L ^ x l O J 5.22 3.96 2.64 1.97 1.20 0.81 Molecu.xlO 1 7 506.0 383.9 255.9 191.0 116.0 79.5 1-3 _3 C H ^ s c a j . x i o 1.62 0.91 0.69 0.46 0.31 0.13 17 Molecu.xlO 156.7 88.5 67.2 44.6 30.4 12.6 1-4 C H S C H^.xlO J 17 Molecu.xlO 0.60 58.2 0.42 4o.7 0.19 18.4 0.13 12.6 0.04 4.2 0.02 1.6 2 - 1 -3 C H ^ S C H^.xlO J 1.62 1.05 0.66 0.54 0.31 0.23 Molecu.xlO 1 7 156.7 108.3 63.7 52.3 30.4 22.0 3-1 _3 C H ^ S C B t j.xlO 3.27 2.48 1.83 1.10 0.79 0.69 17 Molecu.xlO 313.4 240.1 177.7 106.3 76.3 66.6 4-1L _ o c n ^ s c a ^ x i o 4.53 3.32 2.15 0.94 0.61 0.49 17 Molecu.xlO 439.5 321.5 205.2 90.8 59.1 47.5 4-2V 3 C H ^ S C H ^ ,xlO 0.95 O.76 0.42 0.17 0.08 o.o4 17 Molecu.xlO 92 .1 73.7 40.7 16.5 7.8 3.9 Replications, n=3. -239-Table 4.22 Gamma r a d i o l y s i s of dimethyl d i s u l f i d e i n carbonated sulfate and polysulfide black l i q u o r s . Dose Mrad 0.0 1.0 2.0 3.0 4.0 5.0 1-1 C R J S S C R J . X I O " " 3 , g / l 4.81 2.40 1.65 1.35 0.65 0.39 17 Molecu.xlO 3P7.<* 153.7 105.5 86.3 41.6 25.2 1-2 CH SSCR^xlO" ' 3 , g / l 1.03 0.60 0.38 O.25 0.16 0.10 17 Molecu.xlO 65.7 38.6 24.1 15.6 10.1 6.6 1-3 CH^SSCH^.xlO" " 3 , g / l 2.06 1.43 1.04 0.55 0.28 0.15 17 Molecu.xlO 131.7 91.4 66.5 34.3 18.1 9-6 1-4 CftjSSCttj.xlO" " 3 , g / l 1.80 0.92 0.48 0.26 0.12 0.06 17 Molecu.xlO 114.9 59.0 30.5 16.8 7.7 3.6 2-1 C^SSCH-^xlO" ' 3 , g / l 9.11 5.70 4.80 3.93 2.83 I.65 Molecu.xlO 1 7 582.5 364.5 306.9 251.1 181.2 105.5 3-1 CftjSSCBj ,xlO " 3 , g / l 1.11 1.09 0.62 0.33 0.26 0.14 Molecu.xlO 1 7 105.9 69.9 39.6 27.1 15.1 8.7 4-L C^SSCttj.xlO" ' 3 , g / l 8.00 4.72 2.68 1.83 1.53 1.03 17 Molecu.xlO 511.6 301.8 171.4 116.8 98.1 65.9 4-2 V CH3SSCH3,xlO" ' 3 , g / l 2.93 1.62 1.12 0.64 0.35 0.21 Molecu. xlO"*"7 187.6 103 .6 71.8 40.7 22.4 13.4 Replications, n=3« -240-Table 4.23 Gamma r a d i o l y s i s of unidentified s u l f u r compound: (X) i n carbonated sulfate and polysulfide black l i q u o r s . Dose Mrad 0 . 0 1 . 0 2 . 0 3 . 0 4 . 0 5 . 0 _ X , x i 0 - J > 0 . 4 7 0 . 3 2 0 . 1 4 0 . 0 6 0 . 0 3 0 . 0 1 I -2 o X, xlO J 1 . 3 8 0 . 6 0 0 . 3 8 0.17 0 . 0 2 0 . 0 6 1 - 3 , X, x l 0 _ ; > 6 . 2 2 4.28 3 . 7 8 2.95 2.25 1 . 1 8 1- k X, xlO--* 0 . 3 6 0.18 0 . 1 2 0 . 0 8 0.04 0 . 0 1 2 - 1 -3 X, x i o J 3.70 2.47 1.42 1 . 2 7 0 . 9 0 0 . 4 4 3- 1 _3 X, xlO  J 2 . 8 8 1 . 8 9 1.08 0 . 7 3 0 . 3 2 0 . 1 1 4 - 1 L r. X, x l 0 ~ J 1 8 . 1 5 1 4 . 3 8 1 0 . 0 0 5 . 2 3 3 . 7 9 3 . 0 1 4 - 2 V -X, XlO 1.31 0 . 9 ^ 0.44 0 . 2 0 0 . 1 4 0 . 0 6 Replications, n=3. Quantitative determination from dimethyl s u l f i d e c a l i b r a t i o n curve. -24l-Table 4.24 Gamma radiation degradation y i e l d s ( G ) * of hydrogen s u l f i d e , methyl mercaptan, dimethyl s u l f i d e and dimethyl d i s u l f i d e i n the various carbonated black l i q u o r s . Sources pH # Gf-HgS) G(-CH3SCH) Gf-CH^SCILj ) Gf-CRjSSCt 1-1 8.20 2 .72 0 0.049 0.004 0.025 1-2 8.50 0.015 0.018 0.02 0 0.004 1-3 8.75 3.147 0.230 0.010 0.007 1-4 8.45 0.051 0.063 0.003 0.009 2-1 9.00 0.306 0.107 0.008 0.035 3-1 8.50 0.053 0.013 0.012 0.006 4-1L 9-15 3.427 0.518 0.02 0 0.034 4-2 V 8.20 0.055 0.006 0.003 0.014 * Apparent G, Molecules/lOOev. G Calculated either from i n i t i a l slope of curves i n Figs»4.17, 4.18, 4.19 and 4.20, or estimated from Tables 4.19, 4.20, 4.21, and 4.22. # I n i t i a l pH. -242-Table 4.25 Effect of nitrogen, a i r , and oxygen atmospheres on gamma r a d i o l y s i s of sulfides i n carbonated black l i q u o r { l - l ) . . Dose Mrad 0.0 0.5 1.0 2.0 3.0 H2S, xl0" 3g/l N2-atmo. 607.50 472.50 342 .00 146.92 105.00 Molecu.xlO 2 0 107.4 83.5 60.4 26.0 18.6 Air-atmo. 387.00 256.OO 109.33 8.45 2.93 Molecu.xlO 2 0 68.4 45.3 19.3 1.5 0.5 02-atmo. 247.75 21.34 14.68 6.99 1.93 2 0 Molecu.xlO 43.8 3.8 2.6 1.2 0.3 CajSEUxlO-^g/l N2-atmo. 1935.00 1741.50 1665.00 1135.50 1035.00 Molecu.xlO 2 0 242.3 218.1 208.5 142.2 129.6 Air-atmo. 1645.00 1246.50 976.50 335.50 98.25 ? n Molecu.xlO 206.0 156.1 122.3 42.0 12.3 02-atmo. 967.50 481.50 323.25 229.95 32.41 Molecu.xlO 2 0 121.2 60.3 40.5 28.8 4.1 CRjSCfij ,xlO~ 3g/l N2~atmo. 108.00 103.25 95.45 86.40 81.90 19 Molecu.xlO 104.7 100.1 92.5 83.8 79.4 Air-atom. 107.40 85.95 80.35 58.80 52.88 Molecu.xlO 1 9 104.1 83.3 77.9 57.0 51.3 02-atmo. 106.25 81.45 75*55 54.00 38.82 19 Molecu.xlO 103.0 79.0 73.2 52.3 37.6 CH 3SSCH 3,xlO~ 3g/l N2-atmo. 2295.00 2340.00 2070.00 1752.00 1305.50 20 Molecu.xlO 146.8 149.6 132.4 112 .0 83.5. Air-atom. 2565.00 2 835.00 2695.00 2272.50 1287.00 MolecuxxlO 2 0 164.0 181.3 172.3 145.3 82.3 02-atrno. 3217.50 3195.00 2835.00 2137.50 967.50 Molecu.xlO 2 0 205.7 204.3 I81.3 136.7 61.9 Replications, n=2 I n i t i a l pH 7.50 -243-Table 4.26 Effect of nitrogen, a i r and oxygen atmospheres on gamma radiation degradation y i e l d ( G ) * of hydrogen s u l f i d e , methyl mercaptan and dimethyl s u l f i d e i n the carbonated black l i q u o r ( l - l ) . Atmospheres Gf-HgS) Gf-C&jSH) G(-CH3SCH3 ) Nitrogen 8.5 10.2 0.19 A i r 9-7 18.5 0.43 Oxygen 16.7 28.0 0.74 * Apparent G, Molecules/lOOev. G Calculated from i n i t i a l slope of curves i n Figs. 4.26, 4.27 and 4.28. -2 44-Table 4.27 Gamma ra d i o l y s i s of carbon dioxide and hydrogen su l f i d e a c i d i f i e d sodium s u l f i d e and sulfate green liq u o r . Treatment I n i t i a l Dose Poly-S HgSO^ Na 2S,g/l Mrad g / l G(S) g / l GfHgSO^ C02, 12 0 p s i during i r r a d i a t i o n , Na2S solution. A. 20 11.8 0.875 2.23 0.218 0.18 5 min* 20 11.8 0.975 2.49 0.189 0.16 B. 20 11.8 0.575 1.47 0.222 0.19 B. 20 1.2 0.060 1.53 B. 20 5.9 0.310 1.58 0.240 0.40 C0 2, 12 0 p s i during i r r a d i a t i o n , NagS solution. 1 hr.* 20 5.9 0.375 1.91 0.188 0.31 2 hr.* 20 5.9 0.525 2.68 3 hr.* 20 5.9 0.515 2.63 4 hr. * 20 5.9 0.580 2.96 0.160 0.27 5 hr.* 20 5.9 0.375 1.91 0.182 0.30 A. 20 5.9 0.485 2.48 0.183 0.31 HgS, 270 psi during i r r a d i a t i o n , Na2S solution. 1 hr.* 80 11.8 1,200 3.06 B. 80 11.8 1.550 3.95 B. 4o 17.2 2.450 4.92 0.118 0.07 B. 80 70.8 9.400 4.09 0.5^0 0.08 H2S, 270 psi during i r r a d i a t i o n , green l i q u o r ( l --2) B. 35.1 30.0 3.800 3.81 0.204 0.07 B. 35.1 60.0 6.625 3.34 0.197 0.03 A s Non-preirradiation s t i r r i n g . B : S t i r r i n g during i r r a d i a t i o n . * : Pr e - i r r a d i a t i o n s t i r r i n g only. G : Molecules/lOOev. - 2 4 5 -Figure 2.1 The spectrum of electromagnetic radiation(163) 1 mf 1 ke Frequency, cycles/sec 10 2 2 10 2 1 1 0 » 10 1 9 10 1 S 10 , : 1 0 ' « 10>5 10! 10»3 10' 2 10" -10"1 10D UP -\(f' lCr> -10'' Name of radiation Gamma rays (Hard) X-rays (SofO Ultraviolet Infrared ^—Visible light T ( U H F ) .Shortwave Photon energy, rv 107 10''' 105 w 102 10 1 IO"1 i o -2 i o -3 io-< i o -5 • ]()-T Long wave ( V L F ) Wavelength, angstroms 10-3-l O " 2 10-' 1 — 10 - io-° - I O " 1 0 i o - " -1 X-unit, XI" -1 angstrom, A -1 millimicron, mn -1 micron, ^ 10— 10-1U:' 10 4-103 10" 10s 1 centimeter, cm - 10° 1010-—1 meter, m 10" 10 1 2 j(ji3—j kilometer, km I O ' 4 " Figure 3.1 Potentiometric titration curves of sulfate and polysulfide black liq a a a a a a o a Figure 3 . 2 Potentiometric t i t r a t i o n curves of sodium sulfide solution, sulfate white liquor(WL,1-3) and black liquor ( B L ,1 - 2 ) and added methyl mercaptan. SAMPLE, ml SAMPLE, ml SAMPLE, ml I i i J , I i -J I I i i j_„ 0 3.75 7.50 1125 0 3.25 7.50 1125 0 3.75 7.50 1125 0.1N AgN03j ml Figure 3 . 3 Potentiometric t i t r a t i o n curve-? nt C „ I M J „ A -, „ . and black liquor(BL 1 I) It s u l ^ in sulfate white liquor(WL, 1-2) O K xiquorKUL, 1 - 2 ; in the presence of methyl mercaptan. -450 -250 - 50 + 150 +350 0 SAMPLE, ml WL CHjSNa I 0.5 0 10 2.0 3.0 WW i n 1 /// IV 375 7.50 1125 15.00 0 3.75 0.1 N AgNOj, ml SAMPLE, ml BL CHjSNa I 5.0 0 II 5.0 1.0 III 5.0 20 IV 5.0 3.0 7-50 11.25 15.00 1 ro Co I -249-Figure 3.4 Potentiometric t i t r a t i o n curves of sodium polysulfide in presence of methyl mercaptan. -750 - 50 +250-+3 5 Oh SAMPLE, mi Na-polysulfide Na-mercaptan I 0.25 II 0.25 III 0.25 IV 0.25 II III 0.1 N AgNOj, ml 0.0 LO 4.0 10.0 0 250 500 750 3 5 Potentiometric t i t r a t i o n curves of sodium sulfide i n 1% thiolignin containing alkaline solution with and without oxidation and addition of sodium methyl mercaptan. 0 2.50 5.00 7.50 1000 1250 1500 0.1N AgN03l rd - 2 5 1 -Figure 3.6 Potentiometric t i t r a t i o n curves of dimethyl sulfide, dimethyl di s u l f i d e , sulfur-mercaptan and methyl mercaptan in alkaline solution. SAMPLE, ml -450r 0 I 1.0(CH3SCH3) II W(CH3SSCH3) III 0.0016 g(S) IV 100'PN NaOH) 100 ON NaOH) 4.0(Na-mercaptan) 4.0(Na-mercaptan) Z50 500 O.lN AgNOj, ml - 2 5 2 -Figure 3.7 Potentiometric t i t r a t i o n curves of methyl mercaptan with and without added elemental sulfur in alkaline solution. -450\~ -350 -250-- 150 - 50Y * 50Y + 150Y 250b 350 h SAMPLE Elemental S Na-mercaptan g ml I 0.0 II 0.000b m 0004 i n in 01NAgN03, ml 4.0 4.0 4.0 2.50 500 7.50 - 2 5 3 -Figure 3 . 8 The calibration curves for hydrogen sulfide, methyl mercaptan, dimethyl sulfide and dimethyl disulfide in carbon tetrachloride. w5t 10' ti ct o U J 6 w h 0.1 H25 CH3SH CH3SCH3 CH35SCH3 • i i ' ) 111 1.0 10 CONCENTRATION, g, xW • i i i 1 1 1 i i i i i Ki i ' 18 100 1000 9 - 2 5 4 -Figure 3.9 The c a l i b r a t i o n curves for dimethyl s u l f i d e and dimethyl d i s u l f i d e i n black l i q u o r . io-W4 I/) W3 * ti cc :> o W2 CTI Uj • ti Uj U J CL w CH3SCH3 x CH3SSCH3 © J — l ' M i n i i ' i • i 11 0.1 1.0 10 11111 i i i I I i n L . 100 woo CONCENTRATION, g, x10~ - 2 5 5 -Figure 3.10 Steps of carbon tetrachloride l i q u i d / l i q u i d extractio of dimethyl sulfide and dimethyl disulfide from white liquor ( W L ) and black l i q u o r ( B L ) . Original Added, xW59 CH.SCH, ^ 8 4 5 J J A--A 63.4 CHJSSCHJ o — o 105.7 WL, pH 13.6 40 _1 60 0 BL, pH 13.1 20 40 60 VOLUME OF CCl4, ml -256-Figure 3.11 Effect of solution pB on the efficiency of carbon tetrachloride liquid/liquid extraction. _ L I I _ J i i i 2.0 4.0 6.0 8.0 10.0 12.0 SOLUTION pH Figure 3.13 Gas liquid chromatography(GLC) of carbon tetrachloride extracts of acidified and unacidlfied black liquor ( 2 - 1 ) samples. H2S IT) CH,SH CHjSCHi Acidified Black Liquor(2-1, phi 65) CH?SSCHo I N T t — > < <0 4 6 8 Time, min. I CH3SCH3 >< 1/ 7(9 12 14 16 18 20 22 Black Uquor(2-l pH 135) X CH3SSCH3 25 69 113 125 Temperature, °c i ro co i Figure 3.14 Redox titration curve of a polysulfide solution with sodium sulfite in 9 0 C saturated sodium chloride solution. + 550\-590 ^ +630 5 +670 750 1 Titration Cell Pt/NaClfsatl Sample/KCI, Hg^/Hg^ljsj/Hg 0 4.0 8.0 12.0 16.0 20.0 24.0 0.5M Na2S03J ml Figure 3 . 1 5 Calibration curve for spectroscopic determination of polysulfide excess sulfur in 3M NaCI and 0.01M NaOH solution. Figure 3 . 1 6 Calibration curve of transmittance and concentration for sulfate soluti Figure 3.17 Calibration curve of thiolignin concentration versus absorbance at 213nra. Figure 3 . 1 8 Relationship of black liquor(EL) pH and carbon dioxide volume bubbled. 13.0V 12.0 11.0 5.70.01 9.0 8.0 7.0 0 BL SAMPLE LEGEND 7 - 7 © 7 - 2 A 7 - 3 X 7-4 A 2- 7 a 3 - 7 © 4 - 1L o 4 - 21/ Q Average 0 © 0 Q © 0 D A • + « , © • - 0 © o A ra A A ^ D 10 2.0 3.0 C02 V0LUME(25 C, latm), ml/ml -©+ • X I U M i Figure 3.20 Schematic drawing of high pressure and temperature irradiation apparatus. Gammacell 220 A. Gas supply B. Reducing valve C. Gas release system a-valve b-gas trapiNaOH, 20%) D. Blow-out assembly E Pressure gage F. Flexible tube G. Pressure vessel and heating mantle H. Temperature recording a-thermocouple . b-ice bottle c-recorder L Temperature control a-powerstat b-power supply Figure 3 . 1 9 Infrared spectrum of the radiolysis product of aqueous dimethyl sulfide. -266-Figure 3.21 Relationship of powerstat s e t t i n g and pressure vessel temperature. I I ! i ' 0 10 2.0 3.0 4.0 5.0 Time(hr) Figure 4.1 Gamma radiolysis of sodium sulfide aqueous solution and formation of polysulfide excess sulfur at Gammacell temperature(34 C). 3.4\ 3.2 3.0 26 2.41 22] JO Initial pH i—A 12.46 o 638 14 _JL_ 2.8 i Q 4.2c? i Na2S degradation !°g{S) -^s. dose plot ^ 3 •g Timefminl 979X10 ev/l/m!n JL J L JL 60 160 240 o p° Polysulfide S formation 14 2.8 4.2 24 18 12 % to* o 0 I i Dose(Mrad), 6372min/Mrad Figure 4.2 Gamma radiolysis of varigus pH sodium methyl mercaptan solutions at Gammacell temperature(34 C). Initial pH °—o 1J54 ^ - A 7254 o—o 10-70 Dose(Mrad), 63-58min/Mrad 20-0 7> 150 % ^00 o 50 pH 13-54 CHJSSCHJ formation -Dose(Mrad), 63-58min/Mrad 4<9 7.(9 20 3-0 u n a 8 CHjSNa degradation <NI (5ih to<7(SJ vs. c/ose p/of o zfr0-0-0-0-• co 1 Timefminl 9-81X10 ev/l/min Figure 4.3 Gamma radiolysis of dimethyl sulfide and dimethyl disulfide in aqueous alkaline solution and black liquor(2-1) at Gammacell temperature. DosefMrad), 65.23min/Mrad Timefminl 9.75x10 ev/l/min Figure 4.4 Effect of solution pH on gamma radiolysis (3 Mrad) of dimethyl sulfide and dimethyl d i s u l f i d e . A CH3SCH3 o o CH3SSCH3 0.55 XKT' 0 2.0 4.0 6.0 8.0 10.0120 14.0 0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 SOLUTION pH i ro o i Figure 4.5 Effect of solution pH on ratios of gamma radiation(3 Mrad) degradation yield(G) and i n i t i a l concentration(Co). ' » ' i 1 J ! 2.0 4.0 6.0 8.0 10.0 12.0 14.0 SOLUTION pH - 2 7 2 -Figure 4.6 Effect of lignin concentration on gamma radiolysis of dimethyl sulfide and dimethyl disulfide in aqueous alkaline solution. T l ' 1 L L X J 1 J -JL 0 40 80 120 0 40 80 120 THIOLIGNIN, g/l -273-Figure 4.7 Effect of temperature on gamma radiolysis of dimethyl sulfide and dimethyl disulfide i n black liquor(1-3) under 50 psi i n i t i a l oxygen pressure. 100 90 80 ^ 70 to o I 6 50 40 30 20 ® 0.70h 0.60 A & Control n u aru A — A 3 Mrad C H 3 5 C H 3 o o control* r/-i SSCH-D ® • 3 Mrad 3 3 *305 min "LL X JL 030-L l i 60 77 83 103 115 60 77 83 103 115 MAXIMUM TEMPERATURE, °C -274-Figure 4.8 Effect of temperature on gamma radiolysis of dimethyl sulfide and dimethyl disulfide i n carbonated black liquor(2-1) under 50 psi i n i t i a l oxygen pressure. 10 0\-30 20 040 0.35 030 o to t S 025 020 Ur—&control CHiSCHi A3 Mrad o ° c o n t r o i * C H S S C H ® ® 3 Mrad J J 0.15 _L * 297min ± JL 7 7 83 103 115 77 83 103 115 MAXIMUM TEMPERATURE, °C 275-Figure 4.9 Effect of oxygen pressure on gamma radiolysis of dimethyl sulfide and dimethyl disulfide in black liquor(2 - 1) at Gammacell temperature(34 C). WOr 90 80 70 2> to 8 o o 40 30 20 t=^ c3TJdCH35CH3 o -o control ru ecru • © 3MradCH355CH3 *• 294 min 030 0.25 ° 0.20 V 0.15 0.10 25 50 75 100 25 50 75 100 OXYGEN PRESSURE, psi - 2 7 6 -Figure 4 .10 Effect of oxygen pressure on gamma radiolysis of dimethyl sulfide and dimethyl disulfide inQcarbonated black liquor ( 2 - 1 ) at Gammacell temperature(34 c). 100 90 60 5> O O I 60-50-40-30 20 -ACOntrol ru aru 3Mrad^H35CH3 0 ocontrol r u ecru © ®3MradCH355CH3 * 294 min 0.30h -U n n/r I/) o I io 0.20 o CD 0.15-"L_L 25 50 75 100 25 50 OXYGEN PRESSURE, psi 75 100 -277-Figure 4.11 Potentiometric t i t r a t i o n of mono- and polysulfide in 4 ml gamma irradiated black liquor(3-l). Dose(Mrad), 64.5d min/Mrad Figure 4 . 1 2 Gamma radiolysis of dimethyl sulfide in sulfate and polysulfide bla liquors at Gammacell temperature(34 C). Figure 4.13 Gamma radiolysis of dimethyl disulfide in sulfate and polysulfide black liquors at Gammacell temperature(34 C). log IS) vs. dose plot 42.0 36.0 30.0 0 7.0 2.0 3.0 4.0 5.0 Dose(Mrad), 66.77min/Mrad 0 WO 200 300 Timefminl 9.35X1020ev/l/min i r\> -o I -280-Figure 4 . H Gamma radiolysis of an unidentified sulfur corapound(X) in sulfate and polysulfide black liquors at Gammacell temperature(34 C). 108.0 0 7.0 2.0 3.0 4.0 DosefMrad), 6677min/Mrad - 2 8 1 -Figure 4 . 1 5 Relation of i n i t i a l concentration and gamma radiation yields of dimethyl sulfide i n black liquors. 0-dh 0.7 (Aq. solution, pH 13.12) data from Table 4-7 ft 0-5 o o 0.4 (2-1) + 0.005 12 60 120 180 CH3SCH3 initial concentration, g/l, xlO3 - 2 8 2 -Figure 4.16 Relation of i n i t i a l concentration and gamma radiation degration yields of dimethyl disulfide in black liquors. 1.20 -(Aq. solution, pH 13-12) + data from Table 4-7 osoY Figure 4 .1? Gamma radiolysis of hydrogen sulfide in carbonated sulfate and polysulfide black liquors at Gammacell tempers.ture(34 C). log (5) vs. dose plot 0 7.0 20 30 4.0 5.0 Dose(Mrad), 69.50min/Mrad 100 200 , 300 , 4 0 0 Time(min), 8.98XW20e v/l/min Figure 4 .18 Gamma radiolysis of methyl mercaptan in carbonated sulfate and polysul black liquors at Gammacell tempera;ure(34 C). Dose(Mrad)t 69.50min/Mrad 7 " — L Figure 4.19 Gamma radiolysis of dimethyl sulfide i n carbonated sulfate and polysulfide black liquors at Gammacell temperature(34 C). 0 10 2.0 3.0 4.0 50 Dose(Mrad). 69.50min/Mrad Figure if.20 Gamma radiolysis of dimethyl disulfide inocarbonated. sulfate and polys black liquors at Gammacell temperature(34 C). - 2 8 7 -Figure 4 . 2 1 Gamma radiolysis of an unidentified sulfur corapound(X) in carbonated sulfate and polysulfide black liquors at Gamma-c e l l temperature(34°C). • • X =—— o 1 i 3.0 4.0 5.0 0 10 2.0 Dose(Mrad)t 69.50min/Mrad Figure 4.22 Relation of i n i t i a l concentration and gamma radiation degradation yields of hydrogen sulfide in carbonated black liquors. Figure 4.23 Relation of i n i t i a l concentration and gamma radiation degradation yields of methyl mercaptan in carbonated black liquors. Figure 4.24 Relation of i n i t i a l concentration and gamma radiation degradation yields of dimethyl sulfide in carbonated black liquors. (1-4)(4-2V) I ; i i i i i i L_ 0 0.8 16 2.4 3.2 4.0 4.8 5.6 CHJSCHJ initial concentration, g/l, xW3 ! Figure 4.25 Relation of i n i t i a l concentration and gamma radiation degradation yields of dimethyl disulfide in carbonated black liquors. 0-2) I i JI i i » i » i - i 0 7.0 2.0 3.0 4.0 5.0 6.0 70 6.0 9-0 CHJSSCHJ initial concentration, g/l, xlO Figure 4.26 Effect of nitrogen, a i r and hydrogen sulfide i n carbona (34°C). Dose(Mrad), 66.55min/Mrad oxygen atmospheres on gamma radiolysis of ed black l i q u o r ( l - l ) at Gammacell temperature 0 60 120x 160 -j M ' » I — l 1 1 S— Time(minl 9.WXl020ev/(/min Figure 4.27 Effect of nitrogen, air and oxygen atmospheres on gamma radiolysis of dimethyl sulfide in carbonated black liquor(l-l) at Gammacell temperature (34 C). • X J L 0 /V> atm. A — A Air atm. o-0? atm. x--o -x DosefMrad), 6855min/Mrad 1— 8 i S » 10 2.0 3.0 20 log {5) vs. dose plot Time(min)t 9-10X1 Oev/l/min — a 1 8 » » » 0 60 1 ro 1 120 160 Figure 4.28 Effect of nitrogen, a i r and oxygen atmospheres on gamma radiolysis of methyl mercaptan and dimethyl disulfide i n carbonated black liquor(1-1) at Gammacell temperature(34 C). DosefMradl 6855min/Mrad Time(min), 910X10 ev/l/min Figure 5 . 1 Formation of malodorous sulfides from sulfate cooking. fyO-1--^ e" H20* H20* R (ORGANICS) Rr + Ro H2S CH3SH CH3SCH3 s> CH3SSCH3 OXIDATION and POLYADDITION POLYADDITION VOLATILE SULFIDES STABILIZATION Figure 5 . 2 "Proposed radio-chemical reactions in gamma radiolysis of sulfate black liquor. 

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