{"Affiliation":[{"label":"Affiliation","value":"Forestry, Faculty of","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","classmap":"vivo:EducationalProcess","property":"vivo:departmentOrSchool"},"iri":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","explain":"VIVO-ISF Ontology V1.6 Property; The department or school name within institution; Not intended to be an institution name."}],"AggregatedSourceRepository":[{"label":"AggregatedSourceRepository","value":"DSpace","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","classmap":"ore:Aggregation","property":"edm:dataProvider"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","explain":"A Europeana Data Model Property; The name or identifier of the organization who contributes data indirectly to an aggregation service (e.g. Europeana)"}],"Campus":[{"label":"Campus","value":"UBCV","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","classmap":"oc:ThesisDescription","property":"oc:degreeCampus"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","explain":"UBC Open Collections Metadata Components; Local Field; Identifies the name of the campus from which the graduate completed their degree."}],"Creator":[{"label":"Creator","value":"Chiu, Shui-Tung","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/creator","classmap":"dpla:SourceResource","property":"dcterms:creator"},"iri":"http:\/\/purl.org\/dc\/terms\/creator","explain":"A Dublin Core Terms Property; An entity primarily responsible for making the resource.; Examples of a Contributor include a person, an organization, or a service."}],"DateAvailable":[{"label":"DateAvailable","value":"2011-03-02T03:28:26Z","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"edm:WebResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"DateIssued":[{"label":"DateIssued","value":"1972","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/issued","classmap":"oc:SourceResource","property":"dcterms:issued"},"iri":"http:\/\/purl.org\/dc\/terms\/issued","explain":"A Dublin Core Terms Property; Date of formal issuance (e.g., publication) of the resource."}],"Degree":[{"label":"Degree","value":"Doctor of Philosophy - PhD","attrs":{"lang":"en","ns":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","classmap":"vivo:ThesisDegree","property":"vivo:relatedDegree"},"iri":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","explain":"VIVO-ISF Ontology V1.6 Property; The thesis degree; Extended Property specified by UBC, as per https:\/\/wiki.duraspace.org\/display\/VIVO\/Ontology+Editor%27s+Guide"}],"DegreeGrantor":[{"label":"DegreeGrantor","value":"University of British Columbia","attrs":{"lang":"en","ns":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","classmap":"oc:ThesisDescription","property":"oc:degreeGrantor"},"iri":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","explain":"UBC Open Collections Metadata Components; Local Field; Indicates the institution where thesis was granted."}],"Description":[{"label":"Description","value":"The potentially volatile, malodorous sulfides (H\u2082S, CH\u2083SH,\r\nCH\u2083SCH\u2083 and CH\u2083SSCH\u2083) in sulfate black liquros were transformed\r\nto stable compounds by exposure to gamma photon radiolysis. The\r\nproduct complex following radiolysis of sulfides in aqueous\r\nsolution is partly resolved ass polysulfide (from H\u2082S) sulfate\r\n(H\u2082S, CH\u2083SH, and CH\u2083SSCH\u2083), an intermediate, CH\u2083SSCH\u2083 (from CH\u2083SH), and a high molecular weight, amorphous substance (especially from CH\u2083SCH\u2083).\r\nVariables studied with aqueous solutions and commercial black liquors have included sulfide concentration, solution pH, temperature, oxygen saturation and effects of soluble lignin, all of which.adjusted to some extent the sulfide degradation kinetics. Lowering solution pH and increasing initial sulfide concentration, temperature and\/or oxygen pressure increased apparent degradation yields (G), while lignin (thiolignin) acted as a radical scavenger in the process.\r\nIn gamma radiolysis of strong and weak black liquors (pH 12.85 -13.40) at Gammacell temperature (34\u00b0C), and atmospheric oxygen pressure, the apparent degradation yields of sulfide are proportional\r\nto the respective initial concentrations. Apparent degradation yields were 0.001-0.003 for CH\u2083SCH\u2083 at 0.20 x 10\u207b\u00b3 -1.10 x 10\u207b\u00b3g\/l and 0.002-0.085 for CH\u2083SSCH\u2083 at 0.44 x 10\u207b\u00b3g\/l-39.71 x 10\u207b\u00b3g\/l concentration. \r\n\r\nSimilarly, in carbonated black liquors (pH 8.20 \u2013 9.15), the\r\napparent degradation yields of sulfides significantly correlated\r\nwith their initial concentration. The apparent sulfide degradation\r\nyields are 0.015 to 3.427 for H\u2082S at 0.89 x 10\u207b\u00b3-265.20 x 10\u207b\u00b3g\/l,\r\n0.006-0.230 for CH\u2083SH at 0.48 x 10\u207b\u00b3- 28.70 x 10\u207b\u00b3g\/l, 0.003 - 0.020 for CH\u2083SCH\u2083 at 0.60 x 10\u207b\u00b3 - 5.22 x 10\u207b\u00b3g\/l and 0.004-0.035 for CH\u2083SSCH\u2083 at 1.03 x 10\u207b\u00b3-9.11 x 10\u207b\u00b3g\/l concentration.\r\n\r\nThe presence of oxygen( 1 atmosphere pressure) at higher\r\nconcentration of H\u2082S (247.75 x 10\u207b\u00b3g\/l) and CH\u2083SH(967.50 x 10\u207b\u00b3g\/l)\r\nin carbonate black liquor (pH 7.50) showed high apparent degradation\r\nyields of 17 and 28 for H\u2082S and CH\u2083SH, respectively. This is\r\nconsidered to be due to a chain reaction occurring during degradation of sulfides.\r\n\r\nPolysulfide may be generated by radiolysis of acidified sodium sulfide and sulfate green liquor. The apparent yields of polysulfide excess sulfur were 3 and 5 for acidification with carbon dioxide (120 psi) and hydrogen sulfide (270 psi), respectively.\r\n\r\nAs part of these studies, new techniques have been developed for recovery and analysis of sulfides at low concentrations in aqueous solution.","attrs":{"lang":"en","ns":"http:\/\/purl.org\/dc\/terms\/description","classmap":"dpla:SourceResource","property":"dcterms:description"},"iri":"http:\/\/purl.org\/dc\/terms\/description","explain":"A Dublin Core Terms Property; An account of the resource.; Description may include but is not limited to: an abstract, a table of contents, a graphical representation, or a free-text account of the resource."}],"DigitalResourceOriginalRecord":[{"label":"DigitalResourceOriginalRecord","value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/31925?expand=metadata","attrs":{"lang":"en","ns":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","classmap":"ore:Aggregation","property":"edm:aggregatedCHO"},"iri":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","explain":"A Europeana Data Model Property; The identifier of the source object, e.g. the Mona Lisa itself. This could be a full linked open date URI or an internal identifier"}],"FullText":[{"label":"FullText","value":"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\u201e), 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\u00ab^0) at Gammacell temperature (3^\u00b0C), 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\u201e001-0 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 \u2022 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 \u2022 \u2022 \u2022 \u202233 2.3.2 Primary r a d i c a l species \u00bb 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 \u2022 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 \u2022 . . . . 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 \u2022 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 \u2022: 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\u00bb7\u00bb 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 \u2022 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 \u2022 .....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 \u00b0 ) 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C).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\u00b0C) 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\u00b0C) 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\u00ab5 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 \u2022 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\u00b0C 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 \u2022 \u2022 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0C) . . 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\u00b0C) 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\u00b0C) 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\u00b0C) 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\u00b0)-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\u00b0)-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\u00b0C) 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) \u2022 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 <\u2022 \u2022 > HS\" + 0H~ \/ 2 - l \/ HS\" + HgO I \u00bb 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 \u00b0 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\/ \u2014> 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\u2022 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 \u00b1 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) \u2022 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 )\u2022 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)\u2022 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\u00b0C) 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\u00b0C) 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