UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The absorptiometric determination of sodium sulphide and the kinetics of its oxidation Hong, Charles Chuan-Chi 1963

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1963_A7 H65 A2.pdf [ 5.76MB ]
[if-you-see-this-DO-NOT-CLICK]
Metadata
JSON: 1.0059072.json
JSON-LD: 1.0059072+ld.json
RDF/XML (Pretty): 1.0059072.xml
RDF/JSON: 1.0059072+rdf.json
Turtle: 1.0059072+rdf-turtle.txt
N-Triples: 1.0059072+rdf-ntriples.txt
Original Record: 1.0059072 +original-record.json
Full Text
1.0059072.txt
Citation
1.0059072.ris

Full Text

THE ABSORPTIOMETRY DETERMINATION OF SODIUM SULPHIDE AND THE KINETICS OF ITS OXIDATION by CHARLES CHUAN-CHI HONG B.S., N a t i o n a l Taiwan U n i v e r s i t y , 1959 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF ' MASTER OF APPLIED SCIENCE i n the Department of CHEMICAL ENGINEERING We accept t h i s t h e s i s as conforming t o the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1963 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that per m i s s i o n f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying, or p u b l i  c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of Chemical E n g i n e e r i n g The U n i v e r s i t y of B r i t i s h Columbia,. Vancouver 8, Canada. Date September l 6 t h 9 1963* i ABSTRACT A study of the Lauth's V i o l e t a b s o r p t i o m e t r y method f o r the a n a l y s i s of sodium sulphide was c a r r i e d out. The order of adding the reactants i n the development of the c o l o r , the use of three d i f f e r e n t methods of t i t r a t i o n f o r s t a n d a r d i z i n g the s o l u t i o n s used f o r determining the c a l i b r a t i o n f a c t o r , and the e f f e c t s of v a r y i n g the concentrations of the reagents were a l l i n v e s t i g a t e d . I n the formation of Lauth's V i o l e t from sodium s u l p h i d e , a d d i t i o n of reactants i n the order base e l e c t r o l y t e , sodium sulphide, and p-phenylenediamine was shown to be best. The arsenious oxide method of t i t r a t i o n was s e l e c t e d f o r determining the concentration of sodium sulphide i n standard s o l u t i o n s used f o r c a l i b r a t i o n . I f the reagents: base e l e c t r o l y t e c o n t a i n i n g f e r r i c c h l o r i d e , and p-phenylenediamine, were used at the concentrations of 0,16% and 5% by weight, r e s p e c t i v e l y , the c a l i b r a t i o n f a c t o r remained constant up to concentrations 16 grams per L i t r e of sodium s u l p h i d e . The a p p l i c a b i l i t y of the Lambert-Beer law and the e f f e c t of sodium t h i o s u l p h a t e on the a b s o r p t i o m e t r y method a l s o were s t u d i e d . i n d e t a i l . The o x i d a t i o n of sodium sulphide was s t u d i e d under atmospheric pressure at various temperatures by use of two d i f f e r e n t apparatuses. From the measurements of the amounts of oxygen absorbed, the o x i d a t i o n of sodium sulphide probably gives d i s u l p h i d e , t h i o s u l p h a t e , s u l p h i t e and sulphate. The sto i c h i o m e t r y corresponds t o t h i o s u l p h a t e being the main product of t h i s r e a c t i o n . The r a t e of absor p t i o n of oxygen with simultaneous, o x i d a t i o n of sodium sulphide was observed to decrease, with i n c r e a s i n g temperature from 25° to 45°C Nevertheless, the maximum Absorption rate: was found at 55°C, and the ab s o r p t i o n rate decreases again w i t h temperature at l e a s t to &5°C. The r e a c t i o n orders f o r the o x i d a t i o n of sodium sulphide depend upon temperature, being second order at 25°C, order of 1.5 at 35° and 45°C., and f i r s t order from 55° t o 85° C. The r e a c t i o n order with respect t o oxygen i s f i r s t order, i r r e s p e c t i v e of temperature. The maximum r a t e of o x i d a t i o n a l s o occurs at 55° C. X ACKNOWLEDGEMENTS The author would l i k e t o express h i s deepest g r a t i t u d e to Dr. S. D. Cavers f o r the valuable a s s i s t a n c e , and h e l p f u l c r i t i c i s m s o f f e r e d throughout the course of t h i s p r o j e c t . The author i s indebted to Dr. J . B. Risk , of B r i t i s h Columbia Research C o u n c i l , f o r s e v e r a l c o n s u l t a t i o n s , and a l s o t o Dr. D.S. Sc o t t , and Mr. V / . Hayduk f o r t h e i r c o n s t r u c t i v e suggestions. A p p r e c i a t i o n i s al s o expressed f o r the t e c h n i c a l a s s i s t a n c e given by Messrs. R. Muelchen, and E.F. Rudischer of the Department of Chemical Engineering. J . J . Byerley, of the Department of M e t a l l u r g y , determined the absor p t i o n spectrum of Lauth's V i o l e t . i i i TABLE OF CONTENTS PAGE PREFACE l a PART I. THE ABSORPTIOMETRY DETERMINATION OF SODIUM SULPHIDE l b INTRODUCTION 1 INITIAL PROCEDURE 2 METHODS OF TITRATION 7 A. Iodimetric Method 7 B. Volhard Method 10 C. Arsenious Oxide Method 11 HYDROLYSIS OF SODIUM SULPHIDE .12 v CALIBRATION FACTORS 16 . ORDER OF ADDING REAGENTS IN FORMING LAUTH'S VIOLET... 19 • APPLICABILITY OF LAMBERT-BEER LAW 23 EFFECT OF CONCENTRATIONS OF REAGENTS 27 EFFECT OF SODIUM THIOSULPHATE ON THE ABSORPTIOMETRY METHOD 36 CONCLUSION 40 PART I I . THE KINETICS OF THE OXIDATION OF SODIUM SULPHIDE 42 INTRODUCTION 43 EXPERIMENTAL METHODS • 45 1. Apparatus 45 2. Procedure 46 THEORY 52 RESULTS AND DISCUSSION 54 i v TABLE OF CONTENTS (Cont'd.) Page 1. The K i n e t i c s of the Oxidat i o n of Sodium Sulphide 54 2. E f f e c t of I n i t i a l Concentration of Sodium Sulphide on Oxi d a t i o n Rate £ 77 3 . E f f e c t of A d d i t i o n of Glass Beads S3 4 . R e p r o d u c i b i l i t y 84 5 . The Absorption of Oxygen 84 6 . Determination of Stoichiometry 103 7. Comparison of the Oxidations of Sodium Sulphide and Black Liquor 110 CONCLUSIONS 112 RECOMMENDATIONS 114 NOMENCLATURE 115 LITERATURE CITED 116 APPENDIX 118 V LIST OF TABLES TABLE Page 1. C a l i b r a t i o n of Tuberculin Syringe 2 2. C a l i b r a t i o n F a c t o r s , I n i t i a l Procedure 17 3. Comparisons of Orders of Adding Reagents i n Forming Lauth 1s V i o l e t 19 4. Test of Lambert-Beer Law 24 5. ' E f f e c t of Concentration of p-Phenylenediamine 30 6. E f f e c t of Concentration of F e r r i c C h l oride 30 7. E f f e c t of Concentration of p-Phenylenediamine 32 .8. C a l i b r a t i o n F actors f o r 0.16$ by Wt. FeCl3 and 5% by Wt. p-Phenylenediamine 33 9. E f f e c t of Sodium Thiosulphate on E x t i n c t i o n 38 10. Key to Figures 12 and 13 45 11. Influence of S t i r r i n g Rates.on Oxid a t i o n Rate ..... 55 12. I n f l u e n c e of S t i r r i n g Rates on O x i d a t i o n Rate 57 13. Influence of Oxygen Feed Rates on Ox i d a t i o n Rate .. 59 14. Influence of Oxygen Feed Rates on Oxidation Rate .. 59 15. E f f e c t of Temperature on O x i d a t i o n Rate (Oxygen used) 62 16. E f f e c t of Temperature on Ox i d a t i o n Rate ( A i r used). 62 17. Percentage Evaporation of Water from S o l u t i o n 63 18. Data Showing Second Order at 25°C 67 19. Data Showing Order of 1.5 at 35°C 67 20. Data Showing Order of 1.5 at 45°C 69 21. S p e c i f i c Reaction Rates at Various Temperatures ... 76 22. E f f e c t of I n i t i a l Concentration of Sodium Sulphide on O x i d a t i o n at 250c (Oxygen used) 78 v i LIST OF TABLES (Continued) TABLE Page 23. E f f e c t of I n i t i a l Concentration of Sodium Sulphide on O x i d a t i o n at 35°C (Oxygen used) 7$ 24. E f f e c t of I n i t i a l Concentration of Sodium Sulphide on Oxid a t i o n at 55°C (Oxygen used) 79 25. Stoichiometry at 25°C 36 26. Stoichiometry at 35°C 87 27 . Stoichiometry at 45°C 87 28. Stoichiometry at 55°C 88 29. Stoichiometry at 650c 89 30. Stoichiometry at 75°C 90 31. Stoichiometry at 85°C 90 32 . E f f e c t of I n i t i a l Concentration of Sodium Sulphide on the Absorption and on the O x i d a t i o n at 25°C .... 100 33 . E f f e c t of I n i t i a l Concentration of Sodium Sulphide on the Absorption and on the Ox i d a t i o n at 25°C .... 103 34. Absorption of Oxygen Without a Chemical Reaction at 25°C • 103 35 . Probable Reactions i n the Ox i d a t i o n of Na2S and NaHS 105 36 . O x i d a t i o n of Sodium Sulphide at Various Temperatures f o r Apparatus i n F i g . 13 *. 109 37. O x i d a t i o n of Sodium Sulphide at 25°C as a Function of I n i t i a l Concentration 109 v i i LIST OF FIGURES FIGURE Page 1„ Absorption Spectrum of Lauth Ts V i o l e t S o l u t i o n .... 5 2. Mole F r a c t i o n s vs. pH f o r the System Na2S-NaHS-H2S. 14 3. C a l i b r a t i o n Curve, I n i t i a l Procedure 18 4. C a l i b r a t i o n Factors Obtained from Two D i f f e r e n t Orders 21 5 . S p e c i f i c E x t i n c t i o n versus Concentration of Lauth's V i o l e t 25 6. E f f e c t of Concentration of p-Phenylenediamine on E x t i n c t i o n 28 7. E f f e c t of Concentration of F e r r i c C h l o r i d e on E x t i n c t i o n 29 8. E f f e c t of Concentration of p-Phenylenediamine on E x t i n c t i o n 31 9. C a l i b r a t i o n f o r Use of 0.16$ F e r r i c C h l oride and 5$•p-Phenylenediamine 34 10. E f f e c t of the Concentration of p-Phenylenediamine and F e r r i c C h l o r i d e Used, on the C a l i b r a t i o n Factor 35 11. Induction Time f o r the Formation of Lauth's V i o l e t . 39 12. Apparatus f o r Determining Reaction Orders with Respect to Sodiurn Sulphide and Oxygen 47 13. Apparatus f o r Determining Stoichiometry and Oxygen Absorption 48 14. Influence of S t i r r i n g Rates on the Ox i d a t i o n Rate of Sodium Sulphide 56 15. I n f l u e n c e of S t i r r i n g Rates on the Ox i d a t i o n Rate of Sodium Sulphide 58 16. Influence of Oxygen Feed Rates on the Oxi d a t i o n Rate of Sodium Sulphide 60 17. Influence of Oxygen Feed Rates on the Oxi d a t i o n Rate of Sodium Sulphide 6 l v i i i LIST OF FIGURES (Continued) FIGURE Page 18. O x i d a t i o n o f Sodium S u l p h i d e a t 2 5 ° , 3 5 ° , and 450C (Oxygen used) 65 1 9 . O x i d a t i o n o f Sodium S u l p h i d e a t 2 5 ° , 3 5 ° , and 45oC ( A i r Used) 66 20. Second Order R e a c t i o n a t 250c 68 2 1 . Order o f 1 .5 a t 35°C 70 22. Order o f 1 . 5 a t 45°C 71 2 3 . F i r s t Order R e a c t i o n a t 55°C 72 2 4 . F i r s t O rder R e a c t i o n a t 65°C 73 2 5 . F i r s t Order R e a c t i o n a t 75°C 74 2 6 . F i r s t Order R e a c t i o n a t 85°C 75 2 7 . E f f e c t o f I n i t i a l C o n c e n t r a t i o n o f Sodium S u l p h i d e on O x i d a t i o n a t 250C (Oxygen Feed) 80 28. E f f e c t o f I n i t i a l C o n c e n t r a t i o n o f Sodium S u l p h i d e on O x i d a t i o n a t 35°C (Oxygen Feed) .... 81 2 9 . E f f e c t o f I n i t i a l C o n c e n t r a t i o n o f Sodium S u l p h i d e on O x i d a t i o n a t 55°C (Oxygen Feed) .... 82 30. S t o i c h i o m e t r y a t 25°C 91 3 1 . S t o i c h i o m e t r y a t 35°C 92 3 2 . S t o i c h i o m e t r y a t 45°C 93 3 3 . S t o i c h i o m e t r y a t 55°C 94 3 4 . S t o i c h i o m e t r y a t 65°C 95 35. S t o i c h i o m e t r y a t 75°C 96 3 6 . S t o i c h i o m e t r y a t 35°C 97 3 7 . E f f e c t o f I n i t i a l C o n c e n t r a t i o n o f Sodium S u l p h i d e on A b s o r p t i o n o f Oxygen a t 250c 99 3 8 . E f f e c t o f I n i t i a l C o n c e n t r a t i o n o f Sodium S u l p h i d e on A b s o r p t i o n and on t h e O x i d a t i o n a t 25°C 101 ix LIST OF FIGURES (Continued) FIGURE Page 3 9 . E f f e c t of I n i t i a l Concentration of Sodium Sulphide on Absorption and on the O x i d a t i o n at 25°C 102 40. O x i d a t i o n of Sodium Sulphide at Various Temperatures f o r Apparatus i n Figure 13 107 41. Ox i d a t i o n of Sodium Sulphide at 25°C as a Function of I n i t i a l Concentration 108 PREFACE This t h e s i s c o n s i s t s of two p a r t s : Part I , The Absor.ptiometric Determination of Sodium Sulphide; and Part I I , The K i n e t i c s of the Oxida t i o n of Sodium Sulphide. In Part I , various e f f e c t s were i n v e s t i g a t e d to improve the Lauth's V i o l e t a b s o r p t i o m e t r y method f o r the a n a l y s i s of sodium s u l p h i d e . In Part I I , the k i n e t i c s of the o x i d a t i o n of sodium sulphide were stud i e d by use of the modified a b s o r p t i o m e t r y method obtained from Part I . The Nomenclature and the L i t e r a t u r e C i t e d , which appear at the end of the t h e s i s , r e f e r to Parts I and I I taken together. PART I THE ABSORPTIOMETRY DETERMINATION OF SODIUM SULPHIDE INTRODUCTION S o d i u m s u l p h i d e c a n be e s t i m a t e d by d e v e l o p i n g i t i n t o a p u r p l e s o l u t i o n c o n t a i n i n g L a u t h ' s V i o l e t , by means o f p - p h e n y l e n e d i a m i n e and a base e l e c t r o l y t e c o n t a i n i n g f e r r i c c h l o r i d e as an o x i d i z i n g a g e n t (U. S t r i c k l a n d and R i s k (1) a p p l i e d t h e method t o t h e p r o b l e m o f t h e d e t e r m i n a t i o n o f s u l p h i d e i n K r a f t p u l p p r o c e s s b l a c k l i q u o r . H o w e v e r , t h e p r e s e n t work i s r e s t r i c t e d t o t h e a n a l y s i s o f s o l u t i o n s o f h y d r o g e n s u l p h i d e i n aqueous s o d i u m h y d r o x i d e s o l u t i o n s . A c c o r d i n g l y , t h e p r o b l e m s a s s o c i a t e d w i t h t h e p r e s e n c e o f l i g n i n and t h e l i k e do n o t a r i s e h e r e . The r e a c t i o n . . m e c h a n i s m s t a k i n g p l a c e i n t h e f o r m a t i o n o f L a u t h ' s V i o l e t c o u l d n o t be f o u n d i n t h e l i t e r a t u r e . H o w e v e r , t h e f o l l o w i n g . s t e p s w o u l d r e p r e s e n t i t s f o r m a t i o n i f t h i s p r o c e e d s s i m i l a r l y t o t h a t o f m e t h y l e n e b l u e (2). H 2 N ~ C 3 " N H 2 + H 2 N - 0 ~ N H 2 C F ° r ] , • r e u 3 p-Phenylenediami ne H 2 N < > N = 0 - N H 2 H 2 N - 0 - N < > N H 2 S H Phenylene Blue Lauth's Violet F e C , 3 H 2N J^S^^NH 2CI 2 The o v e r a l l s t o i c h i o m e t r i c equation was proposed by Werner (3) as f o l l o w s : 2 p-C 6 H 4 (NH 2 ) 2 + 6 F e C | 3 + 6 FeCI2 4- NH4CI + 4 HCI + Cl Lauth's Violet INITIAL PROCEDURE Samples of sulphide s o l u t i o n were taken by means of a 1-ml. t u b e r c u l i n syringe f i t t e d with a brass stop attached t o the plunger so that the volume d e l i v e r e d each time was the same. In the present work t h i s volume was 0.1590 ml., i n accordance with the recommendations of S t r i c k l a n d and Risk. The t u b e r c u l i n syringe was c a l i b r a t e d w i t h d i s t i l l e d water of known temperature, as shown i n Table 1. This syringe was r i n s e d three times with the Table 1. C a l i b r a t i o n of Tuberculin Syringe Run Wt. H2O D e l i v e r e d Temp, of H 20 Density of H 20 Volume 1 0.15^7 g. 2 5 ° C 0.9971 0.1592 ml. 2 0 . 1 5 S 6 " " " 0.1591 " 3 • 0.1575 " " " 0.1580 " 4 0.1593 " " " 0.1593 " Average Volume of Tuberculin Syringe = 0.1590 ml. s o l u t i o n t o be analyzed and was then used to d e l i v e r the exact volume of sample quoted above under the surface of 4 5 ml. of base e l e c t r o l y t e 0.08% * by weight f e r r i c c h l o r i d e contained i n a glass-stoppered graduated c y l i n d e r . The mixture was * See footnote on P. 3 3 s w i r l e d two or three times and allowed t o stand f o r two minutes. Next 2 - ml. of 1% * by weight p-phenylenediamine was added by means of a blow p i p e t . The s o l u t i o n was thoroughly mixed. A f t e r t e n minutes, the r e s u l t i n g Lauth's V i o l e t s o l u t i o n had reached the maximum i n t e n s i t y of c o l o u r . I t was then d i l u t e d t o a s u i t a b l e volume with d i s t i l l e d water, and i t s e x t i n c t i o n , or o p t i c a l d e n s i t y , was measured. In the present study a Beckman DU spectrophotometer was used at a wavelength of 600 m i l l i m i c r o n s and a s l i t width of 0.24-mm. S i l i c a c e l l s w i t h a t h i c k n e s s of 1 cm. were used. The co n c e n t r a t i o n of sodium sulphide was c a l c u l a t e d from the f o l l o w i n g expression : C = E V F / 5 0 1 where C i s the con c e n t r a t i o n of sodium sulphide i n grams per l i t r e , E the e x t i n c t i o n c o r r e c t e d by s u b t r a c t i n g the e x t i n c t i o n of a blank s o l u t i o n ( 1 ) , V the volume i n ml. to which the s o l u t i o n has been d i l u t e d a f t e r colour development but p r i o r to e x t i n c t i o n measurement, and F a c a l i b r a t i o n f a c t o r determined experimentally by t i t r a t i n g f r e s h l y - p r e p a r e d oxygen-free samples of sodium sulphide and a l s o a n a l y z i n g these same s o l u t i o n s a b s o r p t i o m e t r i c a l l y . Before d i l u t i o n the s o l u t i o n has a volume near 50 ml. ( a c t u a l l y c l o s e t o 47 ml.) and the r a t i o V/50 i s then approximately the f a c t o r by which the * The concentrations of f e r r i c c h l o r i d e and p-phenylenediamine mentioned hare are those of S t r i c k l a n d and Ri s k . These were used i n i t i a l l y i n t h i s work. However, as shown l a t e r , others are more s u i t a b l e and f o r the k i n e t i c s s t u d i e s the l a t t e r were used. 4 Lauth's V i o l e t s o l u t i o n has been d i l u t e d . The r a t i o V / 5 0 i s c a l l e d the d i l u t i o n i n t h i s t h e s i s . The a b s o r p t i o n spectrum of Lauth's V i o l e t s o l u t i o n at 3 . 5 5 grams per l i t r e sodium sulphide was measured. The e x t i n c t i o n reached a sharp maximum at 6 0 0 m i l l i m i c r o n s , as shown i n Figure 1. This r e s u l t confirms the recommendation of S t r i c k l a n d and Risk (1) that a wavelength of 6 0 0 m i l l i m i c r o n s be used. In preparing the base e l e c t r o l y t e the "Roccal" w e t t i n g agent suggested by S t r i c k l a n d and Risk was l e f t out f o r the present case of a n a l y s i s of sodium sulphide s o l u t i o n s . ("Roccal" i s necessary i n the a n a l y s i s of black l i q u o r which forms a p r e c i p i t a t e on a c i d i f i c a t i o n ( D . ) The volume of d i l u t e d Lauth's V i o l e t s o l u t i o n can be measured more a c c u r a t e l y without the w e t t i n g agent present because of a marked r e d u c t i o n i n foaming. For o b t a i n i n g the c a l i b r a t i o n f a c t o r F, sodium sulphide s o l u t i o n s were prepared by i n j e c t i n g hydrogen sulphide i n t o a standard sodium hydroxide s o l u t i o n . S t o i c h i o m e t r i c c a l c u l a t i o n s revealed that 0 . 2 N sodium hydroxide, proposed by Wright et a l ( 2 ) ^ s too d i l u t e f o r preparing samples of sodium sulphide w i t h concentrations higher than 7 . 8 gms. per l i t r e . Therefore, 0 .4 N sodium hydroxide has been used i n the present work. To f r e s h l y b o i l e d d i s t i l l e d water, s u f f i c i e n t carbonate- f r e e sodium hydroxide s o l u t i o n of 50% by weight conce n t r a t i o n (4) was added to prepare a s o l u t i o n of 0 .4 N sodium hydroxide. A 400 450 500 550 WAVELENGTH, millimicrons Igure 1. Absorption Spectrum of Lauth's Violet Solution. 6 0 0 700750 6 30-ml. v i a l was f i l l e d with the 0.4 N sodium hydroxide s o l u t i o n and n i t r o g e n (99.993% p u r i t y ) was bubbled through the s o l u t i o n by being passed through two syringe needles, one below and the other above the surface of the s o l u t i o n , f o r twenty minutes i n order to s t r i p the oxygen from the s o l u t i o n . Pure hydrogen sulphide from a gas c y l i n d e r was then i n j e c t e d i n t o the s o l u t i o n by means of a 100-ml. hypodermic s y r i n g e . The sodium sulphide s o l u t i o n s thus prepared were used immediately f o r c a l i b r a t i o n , i n an attempt to prevent any p o s s i b l e o x i d a t i o n of sodium sulphide by a i r . I f the s o l u t i o n s are contaminated with oxygen, the sodium sulphide i s g r a d u a l l y o x i d i z e d t o sodium t h i o s u l p h a t e ( 5 ) . As shown l a t e r , the t h i o s u l p h a t e i n t e r f e r e s with the t i t r a t i o n method by which the f i n a l c a l i b r a t i o n has been made. To o b t a i n the value of the c a l i b r a t i o n f a c t o r F, the sodium sulphide s o l u t i o n s i n i t i a l l y were standardized by an i o d i m e t r i c method as proposed by Wright et a l ^ ) # However, an i n v e s t i g a t i o n of t h i s and other methods of s t a n d a r d i z a t i o n of sodium sulphide s o l u t i o n s i n d i c a t e d t h a t a much b e t t e r method of a n a l y s i s of these could be used. This i n v o l v e d the use of arsenious oxide followed by back t i t r a t i o n w ith i o d i n e s o l u t i o n to a s t a r c h end point The present work was done to i n v e s t i g a t e the Lauth's V i o l e t method from two p o i n t s of view: the method of s t a n d a r d i z i n g the s o l u t i o n s of sodium sulphide used i n determining the c a l i b r a t i o n f a c t o r F, and the a b s o r p t i o m e t r y method i t s e l f . 7 The l a t t e r part of the work co n s i s t e d of studying the order of adding together the reagents i n the colour formation of Lauth's V i o l e t , the a p p l i c a b i l i t y of the Lambert-Beer law, the e f f e c t of concentrations of p-phenylenediamine and f e r r i c c h l o r i d e on the e x t i n c t i o n , and the e f f e c t of any sodium t h i o s u l p h a t e present i n the s o l u t i o n s analyzed. METHODS OF TITRATION T i t r a t i o n i s necessary t o e s t a b l i s h the value of c a l i b r a t i o n f a c t o r F. Many methods of t i t r a t i n g s u l p h i d e , both chemical and pote n t i o m e t r i c v , have been published i n the l i t e r a t u r e . Three methods of chemical t i t r a t i o n were considered i n the present work: the i o d i m e t r i c method ( 2 ^, the Volhard method , and the arsenious oxide method A. I o d i m e t r i c Method: The use of the i o d i m e t r i c method as proposed by Wright et a l ^ "2^ produced a curve of c a l i b r a t i o n f a c t o r F versus the co n c e n t r a t i o n of sodium s u l p h i d e , which was a concave upward. In other words, high values of the c a l i b r a t i o n f a c t o r ware obtained f o r both high and low concentrations of sodium sulphide i n the v i a l s of sodium sulphide s o l u t i o n s prepared as p r e v i o u s l y d e s c r i b e d . Further more, the curve was found t o be not r e p r o d u c i b l e . ' In view of the poor r e p r o d u c i b i l i t y of the c a l i b r a t i o n curve, the s t a b i l i t y of the Beckman DU spectrophotometer used was doubted. To check i t s s t a b i l i t y , a red glass f i l t e r , which t r a n s m i t s r a d i a t i o n mainly i n the range 580 to 640 m i l l i m i c r o n s , was used as a standard " s o l u t i o n " of constant o p t i c a l d e n s i t y . The spectrophotometer was found to be quite s t a b l e ; the readings of e x t i n c t i o n of the f i l t e r kept e s s e n t i a l l y constant on d i f f e r e n t days. Thus the doubt of the s t a b i l i t y of the spectrophotometer was d i s s i p a t e d . The Lauth's V i o l e t s o l u t i o n was found s t a b l e a l s o , as i t s e x t i n c t i o n reading remained constant f o r s e v e r a l hours a f t e r i t was d i l u t e d with d i s t i l l e d water. As a check on the r e l i a b i l i t y of the r e s u l t s obtained by the i o d i m e t r i c method, the concentration of sodium sulphide i n each v i a l used as a standard was obtained by a c c u r a t e l y measuring the increase i n weight r e s u l t i n g from the i n j e c t i o n of the hydrogen sulphide i n t o the s o l u t i o n of sodium hydroxide of measured volume i n the v i a l . The c o n c e n t r a t i o n of sodium sulphide was c a l c u l a t e d , and the r e s u l t was compared with that obtained i o d i m e t r i c a l l y . The concentrations found by the i o d i m e t r i c method were always higher than those c a l c u l a t e d from weighing. The d i f f e r e n c e was as much as 100% at 0.5-gm, per l i t r e sodium s u l p h i d e , and decreased with i n c r e a s i n g c o n c e n t r a t i o n , being only 3% at 7.3 gm. per l i t r e . The i o d i m e t r i c method i n v o l v e s the o x i d a t i o n of sodium sulphide by i o d i n e to form p r e c i p i t a t e d sulphur, and the back t i t r a t i o n of the i o d i n e i n excess with sodium 9 thiosulphate solution, starch being used as an indicator. The f i r s t reaction proceeds as follows: Na2S + l 2 • 2 Nal + S I 2 Two major sources of error are believed to be the cause of the high F values already noted as being obtained by t h i s method. These are vaporization of iodine into a i r (4), and enclosure of iodine by the sulphur precipitated i n the solution (6). The former was probably more important at low concentrations of sodium sulphide, whereas the l a t t e r was probably the major cause of the high values of F at large concentrations. Loss of iodine by enclosure by the precipitated sulphur i s known to be important at sulphide concentrations greater than 0.80-gm. per l i t r e (6). The highest concentration of sulphide s o l u t i o n prepared f o r the present work was 15.72 gms. per l i t r e , much higher than the l i m i t i n g concentration. The iodine loss can be minimized by using concentration of iodine of 0.02 N * rather than the concentration of 0.1 N proposed by Wright et a l (2). In addition, the iodine loss can be kept down to a minimum, when iodine i s used as s l i g h t l y i n excess as possible. The fact that t h i s suggestion was not always followed at low concentrations of sodium sulphide i n the present work probably explains the high F values at such concentrations. * 0.02 N iodine solution was suggested verbally by Dr. J. B. Risk of B.C. Research Council. B. Volhard Method: The use of Volhard method (k) produced more accurate r e s u l t s than d i d the i o d i m e t r i c method when the weighing method was taken as the standard f o r comparison. However, the end point i n the back t i t r a t i o n of the Volhard procedure i s not e a s i l y d e t e c t a b l e , because of the presence of white s i l v e r thiocyanate p r e c i p i t a t e : Ag* + SCN~ - AgSCN \ 3 In a d d i t i o n , the method i s time consuming as compared with the other two methods. The Volhard method has one advantage over the i o d i m e t r i c method or the arsenious oxide method t o be described s h o r t l y i n that i t may be used to measure the conce n t r a t i o n of sodium sulphide i n s o l u t i o n s which have undergone p a r t i a l a i r o x i d a t i o n . I n both the i o d i m e t r i c method and the arsenious oxide method the presence of sodium t h i o s u l p h a t e , produced as a r e s u l t of a i r o x i d a t i o n of sodium sulphide according to the equation 2 Na 2S + 2 0 2•+ H 20 N a 2 S 2 0 3 + 2 NaOH 4 means t h a t , i n the i o d i m e t r i c method, l e s s than the proper amount of sodium t h i o s u l p h a t e would be added i n the back t i t r a t i o n , and t h a t , i n the arsenious oxide method, e x t r a standard i o d i n e s o l u t i o n would be required i n the back t i t r a t i o n step to o x i d i z e the t h i o s u l p h a t e . This d i f f i c u l t y does not a r i s e when the Volhard method i s used, since redox r e a c t i o n s are not in v o l v e d i n e i t h e r the p r e c i p i t a t i o n of the s u l p h i d e , 2 Ag + + S = • Ag 2S J 5 I : or the back t i t r a t i o n of the extra s i l v e r ions added (Equation 3). C. Arsenious Oxide Method: In the present study, the arsenious oxide method was found t o be an e x c e l l e n t one f o r the t i t r a t i o n i n v o lved i n determining the c a l i b r a t i o n f a c t o r F. A c c o r d i n g l y , the c a l i b r a t i o n f a c t o r s reported i n t h i s work have been determined i n t h i s way. A known volume ( 5 ml.) of the sodium sulphide s o l u t i o n prepared as described e a r l i e r , i s added by a c a l i b r a t e d syringe t o an excess of standard sodium a r s e n i t e s o l u t i o n (0.02 N) below the surface i n order to prevent any p o s s i b i l i t y of a i r o x i d a t i o n of sodium sul p h i d e , and the mixture i s then a c i d i f i e d with h y d r o c h l o r i c a c i d . The mixture of the p r e c i p i t a t e which i s formed and the s o l u t i o n i s then d i l u t e d t o 200 ml. i n a volumetric f l a s k , and shaken thoroughly. The r e a c t i o n t a k i n g place i s A s 2 0 3 + 3 Na2S + 3 H20 As 2S 3 J + 6 NaOH 6 The mixture i s f i l t e r e d i n t o a dry v e s s e l through a dry f i l t e r paper. One hundred ml. of the f i l t r a t e i s removed, n e u t r a l i z e d with sodium bicarbonate, and back t i t r a t e d w i t h standard 0.02 N iodine i n the presence of starch to the f i r s t blue c o l o u r . The q u a n t i t y of the arsenious oxide consumed i s c a l c u l a t e d by s u b t r a c t i n g the amount of the r e s i d u a l oxide from that o r i g i n a l l y employed. The arsenious oxide method was found to give concentrations of sodium sulphide only s l i g h t l y l e s s than those obtained by the weighing method. This r e s u l t i s i n cont r a s t to the r e s u l t s obtained i o d i m e t r i c a l l y which were higher than those of the weighing method. The negative discrepancy seems to be more reasonable than the p o s i t i v e one i n the r e s u l t s f o r the sodium sulphide c o n c e n t r a t i o n , since part of the hydrogen sulphide i n j e c t e d i s probably present i n the gas phase i n the v i a l . HYDROLYSIS OF SODIUM SULPHIDE Since sodium sulphide i s a s a l t of weak a c i d and strong base, i t has a tendency to hydrolyze i n aqueous s o l u t i o n . The e q u i l i b r i a i n v olved are S = — S = (S = ) = K 0 ( S = ) K 0 = l 7 S = + H + = « H S " ( H S - ) = K , ( S = ) ( H * ) K| = 8 x l o ' 2 * g S = + 2 H + « H 2 S ( H 2 S ) = K 2 ( S = ) ( H + ) 2 K 2 = 9 x l 0 1 9 * 9 A m a t e r i a l balance f o r the t o t a l sulphur i n the s o l u t i o n i s C = (S=) + (HS~) + ( H 2 S ) 10 where C = t o t a l c o n c e n t r a t i o n of sulphur, moles / l i t r e . S u b s t i t u t i o n of equations 7, and 9 i n t o 10 gives C = (S = ) [ l + 8 x l O l 2 ( H + ) + 9 x l O , 9 ( H + ) 2 ] By d e f i n i t i o n mole f r a c t i o n s of the three s u l p h u r - c o n t a i n i n g components i n the s o l u t i o n are defined as X S= = (S = ) / C , X H S - = ( H S " ) / C , X H 2 s = ( H 2 S ) / C . Therefore, X S = |+ 8 x l O , 2 ( H + ) + 9 x l O , 9 ( H + ) 2 1 1 * K-,is c a l c u l a t e d from tha data of Reference 8 and K2, from t h a t of References 8 and h. 13 8 x l Q l 2 ( H + )  X H S " ~ j + 8 x l O l 2 ( H + ) + 9 x l O l 9 ( H + ) 2 1 2  9 x l 0 ' 9 ( H + ) 2 A H 2 S - , + 8 x,o l 2(H+) -H 9 x l O , 9 ( H + ) 2 ^ The three equations above are graphically- represented i n Figure 2. The hydrogen i o n co n c e n t r a t i o n ( H + ) i n these equations i s , of course, the e q u i l i b r i u m value. I t i s seen from Figure 2 tha t at pH's l e s s than 4, the sulphur i s present e s s e n t i a l l y as hydrogen sulphide molecules . S i m i l a r l y the sulphur i s almost completely i n the hydro- sulphide form at pH equal t o 10 , and i n the sulphide form at pH's greater than 15 . The e q u i l i b r i u m value of hydroxyl i o n c o n c e n t r a t i o n (OH ) or of hydrogen i o n c o n c e n t r a t i o n (H + ) can be r e l a t e d to the i n i t i a l c o n c e n t r a t i o n of sodium hydroxide s o l u t i o n and the t o t a l moles of sulphur present. When hydrogen sulphide i s i n j e c t e d i n t o an excess of sodium hydroxide s o l u t i o n , the hydroxyl i o n c o n c e n t r a t i o n w i l l decrease by an amount equal t o the hydrogen i o n produced per u n i t volume due to the formation of sul p h u r - c o n t a i n i n g ions from hydrogen s u l p h i d e . Therefore, ( 0 H - ) o - ( 0 H " ) = (HS~) + 2 (S = ) 14 where (OH )0 = the i n i t i a l c o ncentration of hydroxyl i o n . When the pH i s greater than t e n , hydrogen sulphide d i s s o l v e d i n the s o l u t i o n i s n e g l i g i b l e . Thus, C = ( H S " ) + (S = ) 15 15 Equations for the i o n i z a t i o n of the hydrosulphide ion and for the i o n i z a t i o n of water,, with t h e i r respective i o n i z a t i o n constants ( 8 , 4 ) , are H S " H + + S = KQ 2 = I . 2 5 x I O " 1 3 16 H 2 O ^ H + + O H " K w = l x l 0 " 1 4 17 Subtracting equation 17 from equation 16 and rearranging gives Now, S 3 + H 2 0 = H S " + O H " 18 v- K « - I x l 0 ~ 1 4 _ | r r 2 1 d K = - — = , o g , ^ - | 3 = 8 x 1 0 * lga KQ 2 1.25X10 1 3 i . e . < H S " > < O H " > - 8 x l O - » (S = ) or (S=) _ (0H~) 19 (HS") 8 x I O " 2 Combining equations 14, 15 and 19 to eliminate (HS ) and (S") y i e l d s ( 0 H " ) 2 + [ 2 C - ( 0 H " ) o + 0.08] (OH") + 0.08 [ C - ( 0H ' ) o ] = 0 20 By use of equation 20 i t i s possible to calculate the equilibrium hydroxyl ion concentration (OH ) i f the concentration of the t o t a l sulphur C and the i n i t i a l concen t r a t i o n of sodium hydroxide ( 0 H " ) o are known. The r a t i o of the concentrations of sulphide to hydrosulphide ions can be estimated by sub s t i t u t i n g the calculated (OH ) into equation 19 or reading d i r e c t l y from F i g . 2. In t h i s work, the i n i t i a l concentration of sodium hydroxide solution used was 16 0.4 M. The : r a t i o s o f (S=)/(HS~) c o r r e s p o n d i n g t o t h i s i n i t i a l c o n c e n t r a t i o n were c a l c u l a t e d as 1.16 and 45 .4 f o r C = 0 . 2 M and 0.02 M, r e s p e c t i v e l y . I n v i e w o f t h e f a c t t h a t t h e c o n c e n t r a t i o n o f s u l p h i d e i s h i g h e r t h a n t h a t o f h y d r o - s u l p h i d e , t h e l a t t e r w i l l be c a l c u l a t e d as sodium s u l p h i d e f o r t h e purpose o f r e p o r t i n g r e s u l t s . (On t h i s b a s i s t h e c o n c e n t r a t i o n s C o f 0 .2 M and 0.02 M r e s p e c t i v e l y , j u s t q u o t e d , a r e 15.6 gm./l. and 1.56 gm./l. o f sodium s u l p h i d e , r e s p e c t i v e l y . ) a r s e n i o u s o x i d e method a r e shown i n T a b l e 2. These a p p l y t o t h e c o n c e n t r a t i o n s o f r e a g e n t s used i n i t i a l l y as mentioned e a r l i e r . Between 0 and 6 gm./l. o f sodium s u l p h i d e F remains c o n s t a n t a t a v a l u e o f 0.614 w i t h a s t a n d a r d d e v i a t i o n o f 0.015 ( c o r r e s p o n d i n g t o a c o e f f i c i e n t o f v a r i a b i l i t y o f 2.4%). A b e s t l i n e was drawn by use o f t h e method o f l e a s t squares i n t h i s range o f c o n c e n t r a t i o n s . S i n c e t h e l i n e p asses t h r o u g h the o r i g i n , i t i s c o m p l e t e l y s p e c i f i e d by i t s s l o p e , which i s d e t e r m i n e d , i n ac c o r d a n c e w i t h t h e p r i n c i p l e o f l e a s t s quares ( 9 ) , by d i v i d i n g t h e SUB& o f c o n c e n t r a t i o n s by t h e sum o f t h e p r o d u c t s o f e x t i n c t i o n and d i l u t i o n . The s l o p e i s e q u a l t o the c a l i b r a t i o n f a c t o r F. CALIBRATION FACTORS The c a l i b r a t i o n f a c t o r s o b t a i n e d by means o f t h e £ ( E V / 5 0 ) (below 6 . 0 3 g./l.) Table 2. C a l i b r a t i o n Factors, I n i t i a l Procedure (Volume of Na 23 solution: 0.159 ml.) gm./l. Na 2S EV/50. F 0.86 1.35 0.637 1 . 3 0 2.06 0.631 1.49 2 . 3 0 0.643 2.54 4.10 0.620 2.59 4.H 0.630 3.55 5.33 0.609 3.39 6.44 0.604 4.49 7.28 0.617 4 . 6 2 7.41 0.623 5.52 9.20 0.600 5.75 9.64 0.596 6 . 0 3 9.74 0.619 6.71 10.84 0.619 7.28 11.42 0.637 7.44 12.02 0.619 7.62 11.97 0.637 8.22 12.30 0.642 9.90 14.55 0.680 10.08 14 . 6 2 0.630 11.24 16.35 0.687 11.39 16 . 2 4 0.701 12.34 17.43 0.708 12.41 17.33 0.714 13.10 18.80 0.697 13.71 18.93 0.722 When the concentrations are greater than 6 gm./l., F increases with increasing concentration of sodium sulphide. Figure 3 shows the concentration of sodium sulphide i n the various v i a l s plotted against the product of extinction and E V d i l u t i o n : — A straight l i n e r e l a t i o n s h i p exists even 0 2 4 6 8 10 12 14 16 18 20 E V / 5 0 , EXTINCTION x DILUTION f igure 3. Calibration Cuiwe?e;t i f t i t i a i ftwcedure. at concentrations greater than 6 gm./l. However, the s t r a i g h t l i n e does not pass through the o r i g i n at such con c e n t r a t i o n s . The c a l i b r a t i o n curve of F i g . 3 i s repr o d u c i b l e w i t h i n the experimental e r r o r . I t i s based on a t u b e r c u l i n syringe d e l i v e r i n g a sample volume of 0.159 ml. I t i s po s s i b l e to c a l c u l a t e the c a l i b r a t i o n f a c t o r s based on other sample volumes, since the product of the c a l i b r a t i o n f a c t o r and the sample volume i s a constant i f the sample volume taken i s i n the neighbourhood of 0.15 ml. . In an attempt t o e x p l a i n why the c a l i b r a t i o n f a c t o r s increase at high con c e n t r a t i o n l e v e l s , the a b s o r p t i o m e t r y method was i n v e s t i g a t e d i n more d e t a i l . ORDER OF ADDING REAGENTS IN FORMING LAUTH'S VIOLET With three reagents, there are s i x p o s s i b l e orders i n which these reagents can be brought together. These orders are l i s t e d i n Table 3 together with an i n d i c a t i o n of Table 3 . Comparisons of Orders of Adding Reagents i n Forming Lauth's V i o l e t . Order Mutual D e s t r u c t i o n O x i d a t i o n of Na 2S of B and P by A i r B-P-N - X P-B-N X N-B-P X N-P-B X B-N-P P-N-B B = Base E l e c t r o l y t e , P=p-Phenylenediamine, N = Na 2S c e r t a i n d i f f i c u l t i e s t h a t a r i s e f o r v a r i o u s o r d e r s . As p o i n t e d out by S t r i c k l a n d and Risk , p-phenylenediamine and f e r r i c c h l o r i d e r e a c t with each other very r a p i d l y , so t h a t when they have been t o g e t h e r f o r l e s s than t h i r t y seconds, s u f f i c i e n t mutual d e s t r u c t i o n has taken place f o r a low e x t i n c t i o n t o be found a f t e r subsequently adding s u l p h i d e . T h e r e f o r e the orders B-P-N, and P-B-N, i n Table 3 can be d i s c a r d e d . The orders N-B-P, and N-P-B, i n which the other reagents are added to the sodium s u l p h i d e , r e s u l t i n o x i d a t i o n of the sodium s u l p h i d e by a i r . Low e x t i n c t i o n readings r e s u l t as a consequence o f t h i s o x i d a t i o n so t h a t these o r d e r s are a l s o t o be r e j e c t e d . Only the two o r d e r s : B-N-P, and P-N-B, remain f o r fconsider&tipn. The c a l i b r a t i o n f a c t o r s F were determined e x p e r i  m e n t a l l y as a f u n c t i o n of c o n c e n t r a t i o n f o r each o f these two o r d e r s . The a r s e n i o u s oxide method of t i t r a t i o n and .the c o n c e n t r a t i o n s of reagents g i v e n under I n i t i a l Procedure were used. The r e s u l t s are shown i n F i g . 4 which i n d i c a t e s t h a t the c a l i b r a t i o n f a c t o r s f o r the B-N-P order remain e s s e n t i a l l y constant over the range of c o n c e n t r a t i o n s i n v e s t i g a t e d , but t h a t the c a l i b r a t i o n f a c t o r s f o r the P-N-B order i n c r e a s e with c o n c e n t r a t i o n . A l s o , the v a l u e s of F f o r the P-N-B order are somewhat lower than those f o r the B-N-P o r d e r . In other words, the P-N-B order y i e l d s h i g h e r e x t i n c t i o n v a l u e s . These r e s u l t s s t r o n g l y suggest t h a t when the B-N-P order i s used, p a r t of the sodium s u l p h i d e i s o x i d i z e d by f e r r i c c h l o r i d e to compounds, perhaps 1.0 0.8 o o < UL 0.6 o AT I 0.4 cc m < 0.2 o • •» B-N-P ORDER ^ P - M - R ORDER J L 0 1 2 3 4 5 CONCENTRATION OF Na 2 S, g . / l 8 Figure 4» Calibration Factors -Obtained from too different Order®:. sodium t h i o s u l p h a t e f o r i n s t a n c e , which do not give L a u t h T s V i o l e t when p-phenylenediamine i s added. For both the B-N-P and the P-N-B orders the odour of hydrogen s u l p h i d e could be d e t e c t e d d u r i n g the a d d i t i o n of p-phenylenediamine and base e l e c t r o l y t e t o the r e s p e c t i v e mixtures. However, s i n c e the minimum p e r c e p t i b l e c o n c e n t r a t i o n o f hydrogen s u l p h i d e i s approximately one p a r t per b i l l i o n (10), the l o s s of s u l p h i d e i n the form of hydrogen s u l p h i d e gas i s probably n e g l i g i b l e . T h e r e f o r e , even i f the l o s s should not be r e p r o d u c i b l e , i t should not a f f e c t the constancy of the c a l i b r a t i o n f a c t o r F. For the B-N-P order, the c a l i b r a t i o n f a c t o r s are approximately constant i n the r e g i o n of c o n c e n t r a t i o n s i n v e s t i g a t e d , as shown i n F i g . 4. Hence the s u l p h i d e l o s t as hydrogen s u l p h i d e i s e i t h e r a constant p r o p o r t i o n of t h a t o r i g i n a l l y present or the l o s s e s are n e g l i g i b l e as suggested. The B-N-P order i s b e l i e v e d t o be p r e f e r a b l e to the P-N-B order even though the l a t t e r produces h i g h e r e x t i n c t i o n s . A constant v a l u e of F i m p l i e s a l i n e a r r e l a t i o n s h i p between e x t i n c t i o n and c o n c e n t r a t i o n . The advantage of such a l i n e a r r e l a t i o n s h i p i s considered to be p r e f e r a b l e t o t h a t of the e x i s t e n c e of h i g h e r e x t i n c t i o n s . Admittedly, however, the B-N-P order i s probably only v e r y s l i g h t l y b e t t e r than the P-N-B order when i t i s r e c a l l e d t h a t the former pro v i d e s a l i n e a r r e l a t i o n s h i p between c o n c e n t r a t i o n and the product of e x t i n c t i o n and d i l u t i o n up to only about 6 gms./l. o f sodium s u l p h i d e , as shown i n F i g . 3. ( T h i s remark a p p l i e s only to the reagent concentrations given under the I n i t i a l Procedure. The P-N-B order has not been tested with the higher reagent concentrations proposed i n a l a t e r section.) The B-N-P order was that used by Strickland and Risk (1), that used i n obtaining the c a l i b r a t i o n factors reported e a r l i e r i n t h i s thesis, and that used i n a l l the work described from t h i s point onward. APPLICABILITY OF LAMBERT-BEER LAW According to the Lambert-Beer law (11), the extinction E, corrected by subtracting the extinction of a blank (1), of the sample i s d i r e c t l y proportional to concentration C: log -p = E = kbC 21 I f the law i s obeyed, the s p e c i f i c extinction k should be a constant, irrespective of the concentration C of Lauth's V i o l e t .•» Lauth's V i o l e t solutions, prepared from sodium sulphide solutions at 1.14, 4.55, 5.70, 7.25, 6*. 74, 12.36, 14.10 gms./l. respectively, by means of the procedure already described ( I n i t i a l Procedure), were each diluted to several d i f f e r e n t volumes. The extinction of each d i l u t e d solution was measured by use of c e l l s with thickness 1.0 cm., or of 0.1 cm. i f the extinction was high. The results are summarized i n Table 4 and F i g . 5, i n which the concentration of the Lauth's V i o l e t i s expressed as p.p.m. of sodium sulphide which means that i n the diluted solution whose extinctio n was measured the concentration of sodium sulphide would have been the value quoted had the sodium sulphide not 24 Table 4 . Test of Lambert-Beer Law (sample volume = 0.159 ml.) Cone. Na 2S i n standarc s o l u t i o n , gms./l. 1.14 4.55 5.70 7.25 3.74 12.36 14.10 D i l u t e d Cone. C e l l E x t i n c t i o n S p e c i f ii Volume, Lauth's Thickness E ( c o r r e c t e d E x t i n c t : ml. V i o l e t , b, cm. .for the ex k, p>p.m. Na 0S t i n c t i o n of (p.p.m. a blank) (cm.)-* 100 1.31 1.0 0.900 0.585 200 0 .92 t! 0.463 0.590 400 0 .46 IT 0.233 0.604 300 0.23 Tr 0.125 0.631 250 2.39 1.0 1.376 0.498 500 1.45 tt 0.726 0.523 1,000 0.72 tt 0.372 0.539 2,000 0 .36 Tt 0.193 0.553 . 50 13.24 0 .1 0.603 0.330 100 9.12 Tt 0.355 0.389 200 , 4 .56 tf 0.207 0.453 400 2.23 ft 0.115 0.504 300 1.14 1.0 0.533 0.511 1,600 0.57 rt 0.290 0.508 3,200 0.29 tt 0.146 0.512 100 11.50 0.1 0.436 O.388 200 5.75 tr 0.262 0.455 400 2.83 tt 0.142 O.483 300. 1.44 1.0 0.693 0.435 1,600 0.72 tr O.36O 0.500 3,200 0.36 tr 0.133 0.508 100 13.92 0 .1 0.513 0.368 200 6.96 rt 0.300 0.431 400 3 .43 tt 0.161 O.463 300 1.74 1.0 0.837 O .48I 1,600 0.37 tt 0.435 0.500 3 ,200 0.44 rt 0.221 0.508 1,000 1.96 1.0 0.849 0.441 2,000 0.9$ tt 0.434 0.451 4,000 0.49 Tf 0.223 O.463 1,000 2.24 1.0 0 .952 0.432 2,000 1.12 ft 0.484 0.440 4 , 0 0 0 0.56 f» 0.245 0.437 -1 • ~ 1.0 £ o i 1 0.8 Q . CL 0.6 o i — x Ld O U. O LU 0. CO 0.4 0.2 CONCENTRATION OF Na 2S IN STANDARD SOLUTION, g/1. O 1.14 Q 5.70 9 8.74 O 14.10 64 .55 © 7.25 © 12.36 • • i 1 i 1 1 1 0.1 0.5 I 5 10 20 CONCENTRATION OF LAUTH'S VIOLET, p.p.m. Na 2S ure 5. Specific Extinction versus e v e n t r a t i o n o f ^ afh»s V i o l e t (calculated «» parte- million1-©;*; sodiina sulphMe i a the M i n t e d solu&ioa-)-•- 63 been converted i n t o Lauth.'s V i o l e t . F i g . 5 shows that the Lambert^Beer law i s obeyed f a i r l y w e l l w i t h respect to the con c e n t r a t i o n of the Lauth's V i o l e t up to concentrations l e s s than 3 p.p.m. (expressed as sodium s u l p h i d e ) , the constant slope of the f a m i l y of the p a r a l l e l l i n e s i n d i c a t i n g the d e v i a t i o n of the law with respect to Lauth's V i o l e t c o n c entrations. The maximum d e v i a t i o n between values of k's f o r a giv e n , c o n c e n t r a t i o n of standard sodium sulphide s o l u t i o n was estimated from F i g . 5 as only 5.3% i f the Lauth's V i o l e t s o l u t i o n was so d i l u t e d that the e x t i n c t i o n readings f e l l i n the range of 0.9 to 0.2 when c e l l s w i t h a thi c k n e s s of 1.0 cm. were used. The curve shows a f a l l i n g o f f at high c o n c e n t r a t i o n of the Lauth's V i o l e t , and the Lambirt-Beer law breaks down, as shown i n F i g . 5. The Lambert-Beer law, however, appears not to be obeyed wi t h respect to the con c e n t r a t i o n of sodium sulphide i n the standard s o l u t i o n , since the p a r a l l e l l i n e s shown i n F i g . 5 f a i l t o c o i n c i d e w i t h one another. I t i s of i n t e r e s t to note t h a t the low concentrations of sodium sulphide i n the standard s o l u t i o n s used y i e l d high values of s p e c i f i c e x t i n c t i o n , and^ v i c e v e r s a , i f the amounts of reagents used are those suggested by S t r i c k l a n d and R i s k (1). Therefore, i t becomes apparent t h a t the concentrations of reagents, p-phenylenediamine and base e l e c t r o l y t e , are not s u f f i c i e n t l y high to convert a l l of the sodium sulphide i n t o Lauth's V i o l e t , and t h i s f a c t r e s u l t s i n the increase described p r e v i o u s l y , of the c a l i b r a t i o n f a c t o r F at high l e v e l s of 2 7 sodium sulphide c o n c e n t r a t i o n i n the standard s o l u t i o n . EFFECT OF CONCENTRATIONS OF REAGENTS A study was made of the e f f e c t on the e x t i n c t i o n of changing the concentrations of p-phenylenediamine and f e r r i c c h l o r i d e i n the a n a l y t i c a l procedure. S t r i c k l a n d and Risk (1) suggested the use of 4 5 ml. of 0.08% by weight f e r r i c c h l o r i d e and 2 ml. of 1% by weight p-phenylenediamine, to develop 0 . 1 5 ml. of sodium sulphide s o l u t i o n i n t o Lauth's V i o l e t . .When these concentrations were used the c a l i b r a t i o n f a c t o r s were found to be high at high co n c e n t r a t i o n l e v e l s of sodium s u l p h i d e , as mentioned e a r l i e r . I f the concent r a t i o n of f e r r i c c h l o r i d e i s kept at 0.08% by weight, the e x t i n c t i o n times d i l u t i o n , EV / 5 0 , i s found to increase with i n c r e a s i n g concentrations of p-phenylenediamine used, as shown i n F i g . 6. This i s e s p e c i a l l y so at high concentrations of sodium s u l p h i d e . I f , now, the con c e n t r a t i o n of p-phenyenediamine i s kept at 1% by weight, the e x t i n c t i o n times d i l u t i o n i s found to i n c r e a s e , then decrease, w i t h i n c r e a s i n g concentrations of f e r r i c c h l o r i d e , as shown i n F i g . 7. The maximum e x t i n c t i o n times d i l u t i o n occurs very roughly at 0.16% by weight of f e r r i c c h l o r i d e . The i n c r e a s i n g ordinate p o r t i o n of the curves i s c o n s i s t e n t w i t h f e r r i c c h l o r i d e being one of the a c t i v e agents i n the formation of Lauth's V i o l e t from sodium s u l p h i d e . However, i f the concentration of f e r r i c c h l o r i d e used i s increased beyond about 0.16%, perhaps o x i d a t i o n takes place o f some of the sodium sulphide to a compound which gives 2$ 32 30 28 26 24 22 t -20 i « x 161- o 14 i- £ 12 x 10 LU - 8 o ^ 6 £ 4 PARAMETER: CONCENTRATION OF Na 2 S IN THE STANDARD SOLUTION USED 9 4.51 g./l. 0 1 2 3 CONC. OF p-PHENYLENEDIAMINE USED, wt. % figure ©. Sffffet of CtofiieototmM©.© of p*Pfefpyiea©$&atMTO ©tft SSstiaetiop '<0o<3>$% -fey i7t^.of solution WSG«2) PARAMETER: CONCENTRATION OF No 2S IN THE STANDARD SOLUTION USED 12.90 g./l. 9.52 g./l. 4.51 g./l . w 0.08 0.16 0.24 CONC. OF FeCI 3 USED, wt. % to§r_tr&, of p*pta©raylesi©dliaHainj6 u s e d ' ) no colour when p-phenylenediamine i s added and the ext i n c t i o n at a given d i l u t i o n decreases as implied i n F i g . 7. It was expected from F i g . 6 that, i f the concen t r a t i o n of f e r r i c chloride were kept at 0.16% by weight, the exti n c t i o n times d i l u t i o n would increase from the values predicted by Fig . 7 i f the concentration of the p-phenylene diamine used were increased above the value of 1% which applied to F i g . 7. The res u l t s of experiments to test t h i s assumption appear i n F i g . 8. The results expected were obtained and F i g . 8 shows also that at 5% by weight of p-phenylenediamine, the ext i n c t i o n times d i l u t i o n i s beginning to l e v e l out. In fa c t , t h i s i s the maximum extinc t i o n obtained by using the B-N-P order i n t h i s work. The numerical data corresponding to Figures 6, 7, and 8 are summarized i n Tables 5, 6, and 7. Table 5. Effect of Concentration of p-Phenylenediamine (FeCl3 = 0.08% by wt., 45 ml. used) Cone, of Na^S i n Values of Extinction X D i l u t i o n f or Three Standard Solution, Cones, of p-Phenylenediamine (2 ml. used) gms./l. 1% 2% 3% 4.51 7.38 7.44 7.78 9.52 14.32 15.12 15.24 12.90 18.10 19.55 21.40 Table 6. Effect of Concentration of Ferric Chloride (p-phenylenediamine =1% by wt., 2 ml. used) Cone, of Na2S i n Values of Extinction X D i l u t i o n f o r Standard Solution, Three Cones, of F e r r i c Chloride (45 ml. used) gms./l. 0.08% 0.16% 0.24% 4.51 7.38 7.74 7.34 9.52 14.32 14.66 14.26 12.90 18.10 18.95 18.00 3 2 1 - 30 28 26 24 :22 1"» z 214 | l 2 xIO UJ o I f ) 8 6 > u i 4 0 PARAMETER: CONCENTRATION OF Na 2S IN THE STANDARD SOLUTION USED 4.51 g./l. 0 1 2 3 4 5 6 CONC. OF p-PHENYLENEDIAMINE USED,wt.% F i g u r e 8,. Effect .of Concentration o f p*Ph©nyl©ne«3iaiaine on S k t i n c t i o n (0..!©?6 EfcClg s o i n t i o n rased)..-Table 7. E f f e c t of Concentration of p-Phenylenediamine (FeCl3 = 0.16% by wt., 45 ml. used) Cone, of Na2S i n Values of E x t i n c t i o n X D i l u t i o n f o r Three Standard S o l u t i o n , Cones, of p-Phenylenediamine (2 ml. used) gms./l. i % .3% 5% 4.51 7.74 8.OS 8.43 9.52 14.66 16.46 17.06 12.90 13 .95 22.50 23.23 A new c a l i b r a t i o n g i v i n g the concentration of sodium sulphide as a f u n c t i o n of the product of e x t i n c t i o n and d i l u t i o n was made by using 45 ml. of 0.16% by weight f e r r i c c h l o r i d e and 2 ml. of 5% by weight p-phenylenediamine i n s t e a d of the lower concentrations of these reagents given under the heading I n i t i a l Procedure. A l i n e a r r e l a t i o n s h i p was e s t a b l i s h e d throughout a l l of the concentrations i n v e s t i  gated, from 0 up to 15.72 gms. per l i t r e of sodium s u l p h i d e . These r e s u l t s are given i n Figure 9 and Table 8. Based on a sample volume of 0.159 ml., the average c a l i b r a t i o n f a c t o r i s 0 .541 , with a standard d e v i a t i o n of 0.011 and a c o - e f f i c i e n t of variance of 2.0%. As a colour-developing reagent, p-phenylenediamine w i l l s h i f t the r e a c t i o n e q u i l i b r i u m forward t o form more Lauth's V i o l e t i f i t i s used i n more concentrated'.', form. In order to reproduce the c a l i b r a t i o n completely i t i s suggested that p-phenylenediamine i n the form of dihydro- c h l o r i d e be weighed a c c u r a t e l y with a chemical balance and d i l u t e d with d i s t i l l e d water by use of a p i p e t . I t i s po s s i b l e i n t h i s way to prepare the p-phenylenediamine at the Table 8. C a l i b r a t i o n F a c t o r s f o r 0.16% by Wt. FeCLj and 5% by Wt. p-Phenylenediamine (Volume o f Na 2S sample = 0.159 ml.) Cone, of Na 2S i n EV „ „ Standard S o l u t i o n '3U F Remarks gms./l. 1.12 2.12 0.528 2.62 4 .40 0.592 3.14 6.12 0.513 4.52 8 .43 0.533 4.60 3.44 0.545 5.73 10.56 0.547 6.29 11.60 0.542 7.60 14.55 0.523 9.43 17.37 0.543 *<* 9.53 17.06 0.551 10 . 80 19.76 0.546 12.35 22.96 0.533 12.58 23.46 0.536 12.89 23.28 0.554 14.10 26.56 0.531 15.72 29.20 0.533 verage C a l i b r a t i o n F a c t o r F = = 0.541 * r e p r e s e n t s the sodium s u l p h i d e s o l u t i o n with the presence of sodium t h i o s u l p h a t e . same c o n c e n t r a t i o n each time. T h i s procedure was used i n o b t a i n i n g the c a l i b r a t i o n curve of F i g u r e 9. In the case of f e r r i c c h l o r i d e , the s h i f t of the e q u i l i b r i u m cannot e x p l a i n the experimental r e s u l t s f u l l y , s i n c e a secondary r e a c t i o n i n v o l v i n g o x i d a t i o n o f sodium s u l p h i d e by f e r r i c c h l o r i d e probably occurs a l s o . 22 . -20 18 O Na 2S SOLUTION WITHOUT N a 2 S 2 0 3 P Na 2S SOLUTION WITH N a 2 S 2 0 3 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 E V / 5 0 , EXTINCTION x DILUTION figure 9 , CaiiteratioB f o r Use ef. 0.16% fterrie €feiei?ade awi 5& p-PfeensrleBediaiaiBe., CP.CD 0 . 0 8 % FeCI3 + I % p-C 6 H 4 (NH 2 ) 2 9,0 0.16 %FeCI 3 + 5 % p -C 6 H 4 (NH 2 ) 2 < 0.4 - tr m o 0.2 - 0 2 4 6 8 10 12 14 CONCENTRATION OF N a 2 S , g . / l . i r e 10. Effect of the Concentration of p-Phenylenedi#iaine and F e r r i c Chloride Used, on the Calibration Factor. . The e f f e c t of the concentrations of p*phenylenediamdne and f e r r i c c h l o r i d e i s v i s u a l i z e d by p l o t t i n g the c a l i b r a t i o n f a c t o r s against the concentrations of sodium sulphide with the concentrations of the two reagents as a parameter, as shown i n F i g . 10. The c a l i b r a t i o n f a c t o r s obtained by use of 5% p-phenylenediamine and 0.16% f e r r i c c h l o r i d e remain at a constant value up to 15.72 gms./l. of sodium s u l p h i d e . For the k i n e t i c s s t u d i e s of the oxidatjion of sodium s u l p h i d e , these concentrations of the reagents were used to determine the concentration of sodium sulphide i n the r e a c t i o n s o l u t i o n . The f o l l o w i n g equation was a p p l i e d . C = 0 . 5 4 1 ( E V / 5 0 ) 22 EFFECT OF SODIUM THIOSULPHATE ON THE ABSORPTIOMETRY METHOD Upon o x i d a t i o n of sodium s u l p h i d e , the compound formed i s sodium t h i o s u l p h a t e , as shown i n Equation 4. Sodium t h i o s u l p h a t e was studied t o see whether i t would i n t e r f e r e with the determination of sodium sulphide by the absor p t i o m e t r i c method. S t o i c h i o m e t r i c c a l c u l a t i o n s based on Equation 4 showed th a t complete o x i d a t i o n of 156 grams of sodium sulphide gives 158 grams of sodium t h i o s u l p h a t e . Since the weight r a t i o of sodium t h i o s u l p h a t e to sodium sulphide o x i d i z e d i s ne a r l y u n i t y , a s o l u t i o n of sodium sulphide and a s o l u t i o n of sodium t h i o s u l p h a t e were prepared s e p a r a t e l y , each having the same concentration expressed as 37 grams per l i t r e of the r e s p e c t i v e compound. M i x i n g these s o l u t i o n s then gave a s o l u t i o n which simulated a p a r t i a l l y o x i d i z e d sodium sulphide s o l u t i o n . The sodium sulphide s o l u t i o n was prepared f i r s t . As u s u a l , hydrogen sulphide was i n j e c t e d i n t o a 0.4 N sodium hydroxide. This s o l u t i o n was found t o contain 15.72 grams per l i t r e of sodium sulphide by the a b s o r p t i o m e t r y method [5% p-phenylenediamine and 0.16% f e r r i c c h l o r i d e ) . The sodium t h i o s u l p h a t e s o l u t i o n was prepared at t h i s same concent r a t i o n (15.72 gms./l. of sodium t h i o s u l p h a t e ) by s l i g h t l y d i l u t i n g a standard 0.1 N sodium t h i o s u l p h a t e s o l u t i o n . The two s o l u t i o n s then were mixed -in various p r o p o r t i o n s , by use of a c a l i b r a t e d s y r i n g e , i n serum b o t t l e s i n which the a i r had been replaced by pure n i t r o g e n . The concentrations of sodium sulphide and sodium t h i o s u l p h a t e i n each r e s u l t i n g mixed s o l u t i o n were c a l c u l a t e d from the known volumes and the concentrations of the two compounds which had been mixed. The value of EV/50 corresponding to the c a l c u l a t e d c o n c e n t r a t i o n of sodium sulphide i n each mixed s o l u t i o n was then read from the c a l i b r a t i o n s i n Figures 3 and 9 . The EV/50 thus obtained represented the e x t i n c t i o n times d i l u t i o n of sodium sulphide without t h i o s u l p h a t e . The a c t u a l EV/50 al s o was determined by the a b s o r p t i o m e t r y method, and t h i s represented the e x t i n c t i o n times d i l u t i o n of sodium sulphide with t h i o s u l p h a t e present. The e f f e c t of sodium t h i o s u l p h a t e 38 on the a b s o r p t i o m e t r i c method can be observed by comparing the EV/50's obtained from the c a l i b r a t i o n curve and with those obtained by a c t u a l a n a l y s e s . The r e s u l t s are shown i n Table 9, which i n d i c a t e s t h a t the presence of sodium Table 9. E f f e c t o f Sodium T h i o s u l p h a t e on E x t i n c t i o n Na 2S and Na2S 20 3 R e s u l t s o f EV/50 R e s u l t s of EV/50 f o r i n Mixed S o l u t i o n f o r 0.08% FeClo + 0.16% F e C l 3 + 5% 1% p-phenylenediamine p-phenylenediamine g . / l . g.A. N a 2 s w i t h - Na 2S with Na2S w i t h - Na 2S with Na 2S Na 2S 203 out Na 2S 203 N a 2 S 2 0 3 out Na 2S203 N a 2 S 2 0 ^ 0 15.72 0 0 0 0 3.H 12.58 5.14 5.12 5.80 6.12 6.29 9.43 10.22 9.62 11.60 11.60 9.43 6.29 14.23 13.86 17.37 17.37 12.58" 3.14 -17.75 17.64 23.20 23.46 15.72 0 21.12 21.12 29.20 29.20 t h i o s u l p h a t e i n the s o l u t i o n decreased the e x t i n c t i o n some what i f 0.08% f e r r i c c h l o r i d e and 1% p-phenylenediamine are used; hvit does not a f f e c t the e x t i n c t i o n s i g n i f i c a n t l y i f 0.16% f e r r i c c h l o r i d e and 5% p-phenylenediamine are employed. T h i o s u l p h a t e a c t s as a c h a i n breaker i n the cha i n r e a c t i o n o c c u r r i n g i n the o x i d a t i o n o f p-phenylenediamine by f e r r i c c h l o r i d e d u r i n g the f o r m a t i o n of Lauth's V i o l e t (12). The i n d u c t i o n time i s approximately p r o p o r t i o n a l to the concen t r a t i o n of the t h i o s u l p h a t e i n the s o l u t i o n , as shown i n F i g . 11. I f the c o l o u r development was prolonged from the time of 10 minutes, used r o u t i n e l y , to 15 minutes, the i n c r e a s e i n e x t i n c t i o n was found to be n e g l i g i b l e , o n l y 1.4% on the average. 39 8 SUM OF CONCENTRATIONS OF Na 2S AND NazS203:15.72 g./l. PARAMETER: REAGENT CONCENTRATIONS USED IN LAUTH'S VIOLET PROCEDURE in Q> ••— ."3 4 C E LU 3 2 ! O 2 h - C J Z ) Q 2 ! 1 0 0.2 0.4 0.6 0.8 MASS Na 2 S / (MASS Na 2S + N a 2 S 2 0 3 ) figure %%•" Itidttctloh Tim© for the fosnaatioto of &auth'& V i o l e t . Equation 4 shows sodium hydroxide i s a product of the o x i d a t i o n of sodium sulphide a l s o . However, the change i n the concentration of sodium hydroxide seems t o have l i t t l e e f f e c t . The sodium sulphide s o l u t i o n s prepared as standards are apparently subject to a i r o x i d a t i o n even though the s o l u t i o n s removed from the v i a l s are replaced w i t h n i t r o g e n . I t was found that i f such a s o l u t i o n was allowed to stand i n the v i a l f o r days, the e x t i n c t i o n tended to decrease with time. The use f o r c a l i b r a t i o n purposes of f r e s h l y prepared (and oxygen-free) sodium sulphide s o l u t i o n i s th e r e f o r e important, i n order that no th i o s u l p h a t e be present to c o n f l i c t with arsenious oxide i n the back t i t r a t i o n w ith i o d i n e . The f a c t that the Lauth's V i o l e t method produces, f o r a given v i a l of standard sodium sulphide s o l u t i o n , decreasing concentrations with time i s c o n s i s t e n t with the f a c t that the method i s independent of the presence of sodium t h i o s u l p h a t e . CONCLUSIONS In determining the c a l i b r a t i o n f a c t o r s f o r use with the Lauth's V i o l e t a bsorptiometric determination of so l u b l e s u l p h i d e s , the arsenious oxide method of t i t r a t i o n (6) i s c e r t a i n l y more s a t i s f a c t o r y than i s the i o d i m e t r i c method (2) and i s probably b e t t e r than the Volhard method (4). In t h i s c a l i b r a t i o n procedure the sodium sulphide s o l u t i o n s should be prepared oxygen free, and should be used when freshly prepared i n order that thiosulphate produced by a i r oxidation of the sulphide does not destroy the accuracy of the arsenious oxide determination. The reagents are best brought together i n the order: base e l e c t r o l y t e , sodium sulphide and p-phenylene diamine. I f 45 ml. of 0.16% by weight f e r r i c chloride base e l e c t r o l y t e , and 2 ml. of 5% by weight p-phenylenediamine are used for a volume of sodium sulphide of 0.15 ml., the c a l i b r a t i o n factor i s constant up to 16 gms. per l i t r e of sodium sulphide. The Lauth's V i o l e t method i t s e l f i s independent of the presence of sodium thiosulphate i n the solution. PART I I THE KINETICS OF THE OXIDATION OF SODIUM SULPHIDE INTRODUCTION Odour c o n t r o l i n the K r a f t pulping process has been a subject of i n t e r e s t f o r s e v e r a l decades. In 1939 Bergstrom and Trobeck (13) f i r s t proposed the o x i d a t i o n of black l i q u o r to reduce the malodour from the pulping operations. The advantages f o r the o x i d a t i o n of sulphate black l i q u o r , o u t l i n e d by C o l l i m s (14), in c l u d e : 1. Maintenance of the s u l p h i d i t y of cooking l i q u o r . 2. Reduction i n the amount of lime required f o r c a u s t i c i z i n g . 3 . Reduction of the odour nuisance from evaporators and the recovery furnace. 4. P o s s i b i l i t y of s u b s t i t u t i o n f o r s a l t cake of soda ash or c a u s t i c soda as p a r t i a l a l k a l i make-up. 5. Improving the s u i t a b i l i t y f o r rubber compounding of l i g n i n p r e c i p i t a t e d from black l i q u o r . 6. More uniform operation of the vacuum evaporators. 7. Reduction of c o r r o s i o n i n evaporators and scrubbers. 8. Production of a f u e l i n the form of dry l i q u o r which i s more s u i t a b l e than that prepared from unoxidized l i q u o r . In regard to the k i n e t i c s of the o x i d a t i o n of black l i q u o r , i n s u f f i c i e n t knowledge i s a v a i l a b l e so f a r , even though many c o n t r i b u t o r s have published t h e i r experimental r e s u l t s . Wright (15) found that the r e a c t i o n i s pseudo f i r s t order by measuring the r a t e of absorption o f o x y g e n f r o m m o i s t a i r a t one a t m o s p h e r e t o t a l p r e s s u r e by s u l p h a t e b l a c k l i q u o r b e t w e e n 4 0 ° a n d 9 0 ° C . He a l s o f o u n d t h a t s o d i u m s u l p h i d e i s o x i d i z e d more r a p i d l y i n b l a c k l i q u o r t h a n i n aqueous a l k a l i , p r o b a b l y b e c a u s e o f t h e p r e s e n c e o f c a t a l y s t s d e r i v e d f r o m t h e wood. M u r r a y ( 1 6 ) f o u n d t h a t t h e r a t e s o f o x i d a t i o n v a r i e d i n a c o m p l e x manner d e p e n d i n g upon t h e p a r t i a l p r e s s u r e o f o x y g e n , t h e s o d i u m s u l p h i d e c o n c e n t r a t i o n , t h e r a t e o f l i q u o r s t i r r i n g , and t h e c h e m i c a l r e a c t i o n t a k i n g p l a c e u n d e r t h e p r e v a i l i n g e x p e r i m e n t a l c o n d i t i o n s . Z i e g e l m e y e r and F e i s c h l ( 5 ) f o u n d t h e f u l l a g r e e  ment f o r t h e p r o c e s s o c c u r r i n g d u r i n g t h e o x i d a t i o n w i t h t h e s u p p o s e d r e a c t i o n e q u a t i o n . 2 Na 2S + 2 0 2 + H 20 N a 2 S 2 0 3 + 2 Na OH ^ H o w e v e r , B i l b e r g and Landmark (17) f o u n d t h e o x i d a t i o n p r o d u c t s o f b l a c k l i q u o r c o n t a i n p o l y s u l p h i d e s , t h i o s u l p h a t e s u l p h i t e , and s m a l l amounts, o f s u l p h a t e . S i n c e t h e b l a c k l i q u o r c o n t a i n s a v a r i e t y o f o r g a n i c and i n o r g a n i c compounds, a c o m p l e t e a n a l y s i s o f b l a c k l i q u o r i s d i f f i c u l t . I n v i e w o f t h i s c o m p l e x i t y , t h e p r e s e n t s t u d y was r e s t r i c t e d t o t h e o x i d a t i o n o f s o d i u m s u l p h i d e , w h i c h i s t h e m a i n component o f t h e b l a c k l i q u o r o x i d i z e d . The p r e s e n t work i s a i m e d a t t h e d e t e r m i n a t i o n s o f r e a c t i o n o r d e r s w i t h r e s p e c t t o b o t h sodium s u l p h i d e and o x y g e n , r a t e s o f o x y g e n a b s o r p t i o n , and t h e s t o i c h i o m e t r y o f r e a c t i o n s t a k i n g p l a c e d u r i n g t h e o x i d a t i o n o f s o d i u m s u l p h i d e at d i f f e r e n t temperatures. A b r i e f comparison i s made between the o x i d a t i o n s of sodium s u l p h i d e and o f bl a c k l i q u o r p u b l i c i z e d i n the l i t e r a t u r e . EXPERIMENTAL METHODS 1. Apparatus The two d i f f e r e n t apparatuses used i n t h i s work are shown i n F i g u r e s 12 and 1 3 . The apparatus i n F i g . 12 was used to study the k i n e t i c s of the o x i d a t i o n of sodium s u l p h i d e by b u b b l i n g oxygen or a i r whereby the o v e r a l l r e a c t i o n orders with r e s p e c t t o the c o n c e n t r a t i o n s of sodium s u l p h i d e and oxygen could be determined. The apparatus i n F i g . 13 was used t o determine the r a t e of oxygen a b s o r p t i o n with simultaneous o x i d a t i o n o f sodium s u l p h i d e , and i t s s t o i c h i o m e t r y at v a r i o u s temperatures. The key to F i g u r e s 12 and 13 i s shown i n Table 1 0 . Table 1 0 . Key to F i g u r e s 12 and 13 1, 2 , 3 , k, 5 - stopcocks A pressure r e g u l a t o r B purge meter C s a t u r a t o r D r e a c t o r E soap bubble meter F water bath G s t i r r e r f o r water bath H thermometer I f r i t t e d d i s k J magnet K thermoregulator L h e a t i n g element M magnetic s t i r r e r N water r e s e r v o i r 0 gas buret Table 10. - (Continued) P Q R S T manometer glass tube preheating c o i l breaker A l l e n screw 2. Procedure The r e a c t i o n orders f o r the o x i d a t i o n of sodium sulphide were determined by means of the apparatus shown i n F i g . 12. Oxygen or a i r was used as gas feed. The gas from a c y l i n d e r was passed through a pressure r e g u l a t o r A, a purge meter B with a brass d i f f e r e n t i a l pressure r e g u l a t o r to c o n t r o l the constant flow r a t e s , and an absorption bulb C which contained water and was used as a s a t u r a t o r . The gas was bubbled through a f r i t t e d d i s c I of coarse p o r o s i t y (nominal maximum pore s i z e : 40 - 60 microns),20 mm. i n diameter, i n t o the r e a c t o r D. The r e a c t o r was a Pyrex round-bottom f l a s k of 500 ml. c a p a c i t y , and contained 250 ml. of sodium sulphide s o l u t i o n . (The sulphide s o l u t i o n was prepared by bubbling hydrogen sulphide through a g l a s s tube i n t o 0.4 N sodium hydroxide s o l u t i o n i n a storage b o t t l e . A i r was purged out of the b o t t l e through another g l a s s tube above the surface of the s o l u t i o n by t h i s stream of hydrogen s u l p h i d e . I t took very roughly one minute t o purge out a i r from the b o t t l e . 250 ml. of the sulphide s o l u t i o n were poured i n t o the r e a c t o r . The run was s t a r t e d immediately). The gas fl o w r a t e s were measured with a soap bubble meter E by measuring the time with a stop-watch Figure $3, 4ppa#atw© f c * Bfeferraiiiiog Stoiehioineiyy and Gss^gen Jibeoiptioa. r e q u i r e d f o r a soap f i l m to pass through 50 ml. The gas flow r a t e s were c a l c u l a t e d from the r e a c t i o n temperatures and the barometric pressure on a dry-gas b a s i s (the gas as measured was assumed to be s a t u r a t e d with water). The r e a c t i o n temperature was c o n t r o l l e d with a Col o r a U l t r a Thermostat, with an accuracy of i 0.01°C. I t c o n s i s t e d o f a thermo-regulator K, two h e a t i n g elements L, and a high-speed s t i r r e r G f o r the water bath. The water bath F had a dimension of 12 i n . x 20 i n . x 11 i n . h i g h , and was f i l l e d with 5 i n . of water. I t was made of g l a s s so t h a t the s t i r r i n g r a t e of the magnet J i n the s o l u t i o n c ould be measured with a N i c h o l s probostrobe. The magnet, 5/16 i n . diam. x 1.5 i n . , was p l a s t i c - c o a t e d , and s t i r r e d with a magnetic s t i r r e r M below the water bath. The samples of sodium s u l p h i d e s o l u t i o n were withdrawn at 30-min. i n t e r v a l s . The sampling was done by use of a c a l i b r a t e d t u b e r c u l i n s y r i n g e (volume: 0.159 ml.) through a rubber serum b o t t l e cap att a c h e d to one of the f o u r 10/30 t a p e r s e a l j o i n t s ' o n the r e a c t o r . The concen t r a t i o n s of the sodium s u l p h i d e s o l u t i o n s were determined by the a b s o r p t i o m e t r i c method u s i n g 0.16 % f e r r i c c h l o r i d e and 5% p-phenylenediamine as reagents, as a l r e a d y d e s c r i b e d i n Part I . The c o n c e n t r a t i o n s o f sodium s u l p h i d e , i n gram moles per l i t r e , were c a l c u l a t e d from the f o l l o w i n g e quation C = 0 . 0 0 6 9 3 6 ( E V / 5 0 ) 23 The a p p a r a t u s o f F i g . 13 was used t o s t u d y the r a t e o f oxygen a b s o r p t i o n and t h e s t o i c h i o m e t r y f o r t h e o x i d a t i o n o f sodium s u l p h i d e . Both t h e gas b u r e t 0 ( 1 , 0 0 0 ml. i n c a p a c i t y and h a v i n g 1 0-ml. d i v i s i o n s ) , and t h e manometer P were f i l l e d w i t h w a t e r . Oxygen from a c y l i n d e r was passed t h r o u g h the system f o r a few m i n u t e s , w i t h s t o p  cocks 1 and 5 opened, and 2 , 3 , and 4 c l o s e d . When t h e a i r i n t h e g l a s s tube Q ( 1 / 4 i n . I . D . ) , and i n t h e r e a c t o r D had been r e p l a c e d by oxygen, s t o p c o c k 2 was opened, and t h e w a t e r r e s e r v o i r N ( 4 . 5 i n . diam. and 6 i n . h i g h ) was lowe r e d s l o w l y . Care was t a k e n t h a t no a i r was sucked i n t o t h e system by o b s e r v i n g t h e b u b b l i n g of oxygen i n the w a t e r c o n t a i n e d i n t h e beaker S. When t h e gas b u r e t had been f i l l e d w i t h oxygen, s t o p c o c k s 1 and 5 were c l o s e d s i m u l t a n e o u s By means o f s t o p c o c k 4 t h e w a t e r t h e n was d r a i n e d p a r t i a l l y f r o m t h e manometer. The p r e s s u r e i n t h e system was a d j u s t e d by t u r n i n g t h e k n u r l e d wheel below t h e water r e s e r v o i r . The gas b u r e t r e a d i n g was r e c o r d e d when the p r e s s u r e i n t h e system was t h e same as t h e a t m o s p h e r i c p r e s s u r e . The sodium s u l p h i d e s o l u t i o n i n t h e r e a c t o r was s t i r r e d i m m e d i a t e l y a t a r a t e o f 1 , 3 2 0 r.p.m. The s t i r r i n g r a t e s and t h e sodium s u l p h i d e a n a l y s e s were d e t e r m i n e d by t h e same methods used f o r t h e a p p a r a t u s o f F i g . 1 2 . When t h e p r e s s u r e i n t h e system had d e c r e a s e d by an i n c h o r so o f w a t e r , because o f t h e a b s o r p t i o n o f oxygen by t h e sodium s u l p h i d e s o l u t i o n , t h e p r e s s u r e was r e s t o r e d t o atmospheric pressure by r a i s i n g the water r e s e r v o i r . The gas buret reading was recorded w i t h the corresponding reading time. Before the apparatus i n F i g . 13 was used f o r experiments, i t had been t e s t e d f o r l e a k s . The system was sealed, and brought to 3 . 2 4 i n . of water below atmospheric pressure. A f t e r eleven hours, the same pressure d i f f e r e n c e was observed. The absence of leaks was the r e s u l t of the f a c t t h a t the whole system was made of glassware, with t a p e r - s e a l j o i n t s each coated with Dow Corning high vacuum grease. The j o i n t s a l s o were sealed t i g h t l y by use of T e f l o n s l e e v e s . I n a d d i t i o n , rubber bands were connected between hooks on each s i d e of the j o i n t s . For the apparatus of F i g . 13 only oxygen was used as gas feed. Therefore, there i s no r e s i s t a n c e i n the gas phase except, perhaps, at the beginning of a run before the oxygen has had time to reach s a t u r a t i o n . A i r was not used as gas feed f o r the apparatus of F i g . 1 3 , since the p a r t i a l pressure of oxygen i n the gas phase would change p e r s i s t e n t l y w i t h time as the o x i d a t i o n of sodium sulphide proceeded i n the r e a c t i o n zone. The i n t e r f a c i a l area between the two phases was supposed to be the same i n each run at constant s t i r r i n g speed, even though a vortex was formed. The d i f f u s i o n a l r e s i s t a n c e occurs mainly i n the l i q u i d phase.. The i n s t a l l a t i o n of c o i l R i n the apparatus of F i g . 13, had the purpose of preheating the e n t e r i n g oxygen. The g l a s s tube connecting the heating c o i l and the r e a c t o r was not immersed i n the water bath except i n a t r i a l run. In t h i s run, the high-vacuum grease coated between the j o i n t s melted and flowed to the r e a c t o r . The presence of a surface a c t i v e agent at the g a s - l i q u i d i n t e r f a c e i n the r e a c t o r could cause marked r e d u c t i o n i n the r a t e of mass t r a n s f e r of oxygen across the i n t e r f a c e . Therefore the tube was not immersed f o r the runs f o r which data have been r e p o r t e d . For each run, the temperature i n the r e a c t o r remained constant when the a i r above the l i q u i d i n the r e a c t o r was replaced w i t h the preheated oxygen. No condensation on water vapor was found i n the c o i l , i n the tube between the c o i l and the r e a c t o r , or i n the tube Q, even at thehighest temperature, 85°C, i n v e s t i g a t e d . THEBRY Since equation h i s the dominant r e a c t i o n i n the o x i d a t i o n of sodium sul p h i d e , I t i s necessary t o c a l c u l a t e the chemical e q u i l i b r i u m constant f o r t h i s r e a c t i o n t o see i f the r e a c t i o n i s r e v e r s i b l e or i r r e v e r s i b l e . Therrao- dynaraically, the e q u i l i b r i u m constant, c a l c u l a t e d from the f r e e energy of formation, was found to be 1 x l O 1 ^ at 25°C The e q u i l i b r i u m constant is. so lar g e t h a t the reactiomsmay be regarded as u n i d i r e c t i o n a l . The e x p e r i m e n t a l l y determined data f o r the c o n c e n t r a t i o n s o f sodium s u l p h i d e as f u n c t i o n s of r e a c t i o n time were t r e a t e d a c c o r d i n g l y . When the c o n c e n t r a t i o n of oxygen i n the s o l u t i o n i s c o n s t a n t , the r a t e o f o x i d a t i o n of sodium s u l p h i d e may be expressed by the f o l l o w i n g e q u a t i o n (11): = k r n oi dt K n C . 2 4 where C = c o n c e n t r a t i o n of sodium s u l p h i d e at time t . n = r e a c t i o n order with r e s p e c t t o sodium s u l p h i d e . k n= s p e c i f i c r e a c t i o n r a t e , t = r e a c t i o n time. I n t e g r a t i o n o f equ a t i o n 24 and s u b s t i t u t i o n of the i n i t i a l c o n d i t i o n , C = Co at t = 0, g i v e s i-n l-n • C - Co = (n-l)knt 25 The v a l u e o f n may be any p o s i t i v e number not n e c e s s a r i l y an i n t e g e r (except one i n Equa t i o n 25). For the f i r s t o r der, n = 1, equation 24 g i v e s In C = k,t t i n C 0 26 The r e a c t i o n order with r e s p e c t to the c o n c e n t r a t i o n of oxygen may be determined by comparing the r a t i o o f the s p e c i f i c r e a c t i o n r a t e obtained by u s i n g oxygen as a gas feed b u b b l i n g i n t o the s u l p h i d e s o l u t i o n with t h a t obtained by s i m i l a r l y u s i n g a i r . When the o x i d a t i o n of sodium s u l p h i d e o c c u r s , the r a t e of oxygen a b s o r p t i o n i s i n c r e a s e d as compared to the p h y s i c a l a b s o r p t i o n i n t o pure water without a simultaneous chemical r e a c t i o n . From the amount of oxygen absorbed and the amount of sodium s u l p h i d e o x i d i z e d , i t i s p o s s i b l e to e v a l u a t e the s t o i c h i o m e t r y of the r e a c t i o n s as the o x i d a t i o n of sodium s u l p h i d e proceeds. A l l o f the experimental c o n c e n t r a t i o n versus time data w i l l be handled by the approach of the i n t e g r a t i o n method (11). RESULTS AND DISCUSSION 1. The K i n e t i c s of the O x i d a t i o n of Sodium Sulphide In order to study the r e a c t i o n k i n e t i c s of the o x i d a t i o n of sodium s u l p h i d e the experiments were c a r r i e d out with the apparatus shown i n F i g . 12. In o r d i n a r y heterogeneous g a s - l i q u i d r e a c t i o n s , the o v e r a l l r a t e s may be c o n t r o l l e d by the p h y s i c a l t r a n s p o r t of the gas from the gas phase to the l i q u i d phase, by the chemical r e a c t i o n i t s e l f , or by both f a c t o r s working t o g e t h e r . The experimental c o n d i t i o n s f o r the apparatus i n F i g . 12 were e s t a b l i s h e d i n such a way t h a t the mass t r a n s f e r r e s i s t a n c e would not complicate the o v e r a l l r e a c t i o n r a t e by c o n s i d e r a t i o n o f two f a c t o r s (20): (a) The i n f l u e n c e of s t i r r i n g r a t e on the o x i d a t i o n r a t e . (b) The i n f l u e n c e of oxygen feed r a t e on the o x i d a t i o n r a t e . Both the s t i r r i n g r a t e and the oxygen feed r a t e were increased,to certain respective values; from these values onward the reaction rate was found to be independent of them. Under such conditions, the sodium sulphide solution may be regarded as saturated with the gas, and the concentration of the gas dissolved i n the solution may be taken as constant at a given temperature. Since the rate of the d i f f u s i o n of gas i s low at low temperature, the two factors were established at 2 5 ° C , rather than at higher temperatures. The i n i t i a l s p e c i f i c reaction rates were compared at various s t i r r i n g rates with a fixed oxygen feed rate, and also, at various oxygen feed rates with a fixed s t i r r i n g rate. Since the reaction order with respect to sodium sulphide at 25°C. was s t i l l uncertain at t h i s stage, t h i s was taken to be f i r s t order at t h i s temperature for convenience. The influence of s t i r r i n g rates on oxidation rate was studied at an a r b i t r a r y oxygen feed rate of 3 1 4 ml./min. (on a dry-gas basis) at standard conditions (OOC. and 760 mm. IHg). The results are summarized i n Table 11 and graphically represented i n F i g . 14. The i n i t i a l s p e c i f i c reaction rates Table 11. Influence of S t i r r i n g Rates on Oxidation Rate Temp.: 25°C; Oxygen Feed Rate: 314 ml./min. Time, Cone, of Na 2S, gm. mole/litre min. 1 3 5 r.p.m. 800 r.p.m. 1,030 r.p.m. 1,220 r.p.m 0 0.0668 0.0733 0.0761 0.0771 30 0.0535 0.0590 0.0621 , 0.0621 60 0.0442 0.0430 0.0496 0.0438 90 0.0365 0.0411 0.0420 0.0424 .20 o § 0 2 .01 TEMPERATURE: 2 5 ° C. OXYGEN FEED RATE: 314 ml./min. (DRY GAS AT 0°C. AND I ATM.) PARAMETER : STIRRING RATE 0 60 120 180 240 300 TIME, minutes 360 420 480 Figure 14. Influence of Stirring Rates on the Oxidation Sate of Sodium Sulphide, were c a l c u l a t e d and shown i n Table 12 and F i g . 15, which show tha t when oxygen was bubbled i n t o the sulphide s o l u t i o n at 314 ml./min., the r e a c t i o n r a t e was independent of the Table 12 . Influence of S t i r r i n g Rates on O x i d a t i o n Rate Temp.: 25°C; Oxygen Feed Rate: 314 raX/min0 r.p.m. I35 800 1,030 1,220 i n i t i a l k x l O ^ m i n " 1 6.68 6.47 6.70 6.84 s t i r r i n g r a t e s between 135 and 1,220 r.p.m. I n other words, when the s o l u t i o n was s t i r r e d at r a t e s between 135 and 1,220 r.p.m., s u f f i c i e n t l i q u i d turbulence was obtained f o r thorough mixing of the s o l u t i o n with the bubbling oxygen. The s t i r r i n g r a t e was kept at 1,000 r.p.m. while studying the i n f l u e n c e of oxygen feed r a t e s on the o x i d a t i o n r a t e s of sodium s u l p h i d e . At 1,000 r.p.m. of the s t i r r e r , the ra t e of o x i d a t i o n was found to depend on the oxygen feed rates /up to 450 ml./min. However, beyond 450 ml./min., the i n i t i a l s p e c i f i c r e a c t i o n rate remains constant, as shown i n Tables 13 and 14, and Figures 16 and 17. The 0 ml./min. of oxygen • feed r a t e corresponded to the use of oxygen above the l i q u i d phase without bubbling i t through the s o l u t i o n . From the experimental r e s u l t s i l l u s t r a t e d i n Tables 13 and 14, i t may be concluded t h a t at oxygen feed r a t e s higher than 450 ml./min. and at s t i r r i n g r a t e s higher ro - O H 9 < * 8 l 0 F " TEMPERATURE: 2 5 ° C. OXYGEN FEED RATE : 314 ml./min. o i= 7 3.6 L U cr t 4 o L U Q_ 3 if) _ j 2 < b I (DRY GAS AT 0°C, AND I ATM.) O ( j o o 0 200 400 600 800 1,000 1,200 1,400 1,600 STIRRING R A T E , r.p.m. figure M. Influence- ©f Stirring: Itetes -on t i e Oxidation fete of Sodium Sulphide. 59 Table 13. Influence of Oxygen Feed Rates on Oxidation Rate Temp.: 2 5°C; S t i r r i n g rate: 1,000 r.p.m. Time, Cone, of Na^S, gm. mole/litre min. 0 ml./min. 46 ml./min. 168 ml./min. 314 ml./min. 709 ml./min, 0 0.228 0.237 0.237 0.243 0.224 30 0.225 0.211 0.203 0.209 0.190 60 0.221 0.192 0.178 0.172 0.144 90 0.214 0.167 0.154 0.139 0.120 120 0.220 0.154 0.137 0.118 0.102 150 0.206 0.139 0.115 0.0999 0.0840 180 0.206 0.121 0.0985 0.0849 0.0756 210 0.201 0.110 0.0857 0.0749 0.0660 Table 14. Influence of Oxygen Feed Rates on Oxidation Rate Temp.: 2 5°C; S t i r r i n g rate: 1,000 r.p.m. 0 2 Feed Rate, ml./min. 0 46 168 314 709 I n i t i a l kxl03, min." 1 0.438 3.65 4.88 5.77 6.05 than 135 r.p.m., no rate determining influence of mass transfer i s to be expected. For studying the effect of temperature on the oxidation rate of sodium sulphide, the s t i r r i n g rate and the oxygen feed rate therefore were maintained at 1,000 r.p.m. and 500 ml./min. of dry gas at 0°C. and 1 atrn., respectively. Although the experiments just described were made with oxygen as a gas feed, and although a mass transfer resistance could have been present in the gas phase when a i r was so used, the same feed rate and the same s t i r r i n g rate were used with a i r as with oxygen. It i s shown l a t e r that no mass transfer resistance was present under these conditions even when a i r was the feed. ._: .20 ^.06 o o ° . 0 2 .0 1 0 TEMPERATURE: 2 5 ° C. STIRRING RATE : 1,000 r.p.m. PARAMETER : OXYGEN FEED RATE (DRY GAS AT 0°C. AND I ATM.) 60 120 180 240 300 T I M E , minutes 360 420 480 Figure 16. feflpeac© of Oxygen ./feed Rates on the fcxidation fete pt Sodium Sulphide, "o" 1 0 TEMPERATURE: 25 C. STIRRING RATE : 1,000 r.p.m. O 1 100 - 200 300 400 500 600 700 800 OXYGEN FEED R A T E , ml./min. at 0 °C . and I atm. ' E^igpy© 111?, .EaftBteae© of fisygem- Feed fet@s oa th<s ©sldaMosa Hate of Sodttea $ q & B b i d & « {«=» The effect of temperature on the oxidation rates of sodium sulphide was investigated between 25°C. and 85°C. for each of oxygen and a i r as gas feeds to the sulphide solution. The concentration versus time data are given i n Tables 15 and 16. Table 15. Effect of Temperature on Oxidation Rate (Oxygen used) S t i r r i n g rate: 1,000 r.p.m.; Feed Rate: 500 ml./min. Time, Cone, of Na 9S, gm. mole/litre min. 25°C 35°C 45°C 55°C 6 5 0 c . 75°C 85°C 0 0.181 0.170 JD.178 0.181 0.181 0.180 0.135 30 0.145 0.120 0.128 0.128 0.129 0.120 0.137 60 0.112 0.0835 0.0913 0.0860 0.0873 0.0892 0.102 90 0.0970 0.0603 0.0675 0.0611 0.0668 0.0617 0.0779 120 0.0804 0.0455 0.0521 0.0417 0.0499 0.0431 0.0571 150 0.0726 0.0359 0.0406 0.0261 0.0353 0.0315 0.0411 ISO 0.0640 0.0275 0.0325 0.0137 0.0237 0.0166 0.0250 210 0.0564 0 .0251 0.0211 0.0200 240 0 .0520 0 .0226 0.0160 270 0.0484 0.0191 0.0119 300 0.0433 0.0161 0.0068 Table 16. Effect of Temperature on Oxidation Rate (A i r used) S t i r r i n g rate: 1,000 r.p.m.; A i r Feed Rate: 500 ml./min. Time, Cone, of Na2S, gm. mole/litre min. 25°C. 35°C. 450C. 55°C 650C. 75°C 35°C. 0 0.170 0.169 0.169 0.161 0.172 0.174 0.173 30 0.160 0.155 0.153 0.152 0.157 0.160 0.159 60 0.149 0.139 0.142 0.135 0.145 0.147 0.153 90 0.135 0.125 0.129 0.126 0.133 0.134 0.140 120 0.130 0.114 0.120 0.115 0.121 0.122 0.133 150 0.120 0.106 0.109 0.106 0.116 0.116 0.123 180 0.111 0.0990 0.103 0.0961 0.105 0.103 0.111 210 0.106 0.0931 0.0954 0.0373 0.100 0.0950 0.104 240 0.100 0.0840 0.0873 0.0813 0.0951 0.0920 0.100 270 0.0940 0.0774 0.0821 0.0733 0.0885 0.0869 0.0980 300 0.0907 0.0713 0.0762 0.0677 0.0833 0.0850 63 Since part of the water i n the sulphide s o l u t i o n was evaporated at temperatures higher than 65°C, the concen t r a t i o n s reported i n Tables 15 and 16 at 650, 7 5 ° , and 85° C. have been corrected f o r evaporation, which amounted at the end of the runs to 3% to 14% of the o r i g i n a l 250 ml. of s o l u t i o n . (These percentages r e f e r to evaporation only. An a d d i t i o n a l percentage, approximately 2%, was removed as samples). The percentage evaporation at each temperature i s given i n Table 17 f o r each gas feed used. At the end of Table 17. Percentage Evaporation of Water from S o l u t i o n Gas Feed Percentage Evaporation 650C 75°C 85°C Oxygen 4% 3% H% A i r 3% 9% 5% each run, the volume of the s o l u t i o n was measured with a graduated c y l i n d e r . This volume was subtracted from 250 ml. (250 ml. of sodium sulphide s o l u t i o n was placed i n a graduated c y l i n d e r and poured from t h i s i n t o the r e a c t i o n v e s s e l at the s t a r t of a run). The evaporation of water from the sulphide s o l u t i o n was estimated by s u b t r a c t i n g the volume of the samples withdrawn from the d i f f e r e n c e c a l c u l a t e d . Since the gas f l o w r a t e was maintained constant, the evapor a t i o n was assumed d i r e c t l y p r o p o r t i o n a l t o time f o r the purpose of c o r r e c t i n g concentrations. The evaporation of water from the sulphide s o l u t i o n at temperatures higher than 65°C took place because of the 1 f a c t that the e n t e r i n g gas was only p a r t i a l l y saturated w i t h water vapor i n the s a t u r a t o r . At the temperatures between 25°C and 55°C, the evaporation of water from the r e a c t i o n v e s s e l was n e g l i g i b l e . The decrease i n volume of the s o l u t i o n was only 2%, mainly because of the volume of samples taken f o r analyses (no c o r r e c t i o n was a p p l i e d ) . The data given i n Tables 15 and 16 f o r the temperatures from 2 5 ° t o 45°C d i d not y i e l d s t r a i g h t l i n e s on semi-logarithmic c h a r t s . Since the formation of t h i o  sulphate i s the main r e a c t i o n i n the o x i d a t i o n of sodium sulph i d e , and since the chemical e q u i l i b r i u m constant, c a l c u l a t e d from thermodynamic data, i s very l a r g e , the decreasing slope* on the semi-logarithmic charts of the curves r e l a t i n g c oncentration t o r e a c t i o n time f o r 2 5 ° , 3 5 0 , and 45°C (Figures 18 and 1 9 ) , i s b e l i e v e d to have been caused, not by r e v e r s i b i l i t y of the r e a c t i o n , but r a t h e r by mechanisms being i n v o l v e d over t h i s temperature range d i f f e r e n t from those a p p l i c a b l e from 5 5 ° to 85°C, since f o r the l a t t e r range the semi-logarithmic p l o t s were s t r a i g h t l i n e s (See F i g s . 23 to 26 i n c l u s i v e ) . A good s t r a i g h t l i n e was obtained f o r 25°C when the data were p l o t t e d as l/C versus time ( F i g . 2 0 ) . These r e s u l t s i n d i c a t e that the r e a c t i o n i s of second order with respect to sulphide at 25°C. The data are given i n Table 18. * The slope of each curve of Figures 18 and 19 decreases with time. 480 f i g u r e TIME, minutes 5. Oxidation of Sodium Sulphide at 23^, 3 8 * * and 45 eG ( A i r Used). Table 18. Data Showing Second Order at 25°C. S t i r r i n g Rate: 1,000 r.p.m.; Gas Feed Rate: : 500 m l . / i Time, Oxi d a t i o n with Op Oxi d a t i o n w i t h A i r min. C,gm.mole/1.* l/C,l./gm.mole C,gm.mole/l.* l/C,l./gm 0 0.131 5.52 0.170 5.33 30 0.145 6.90 0.160 6 .25 60 0.112 3.93 0.149 6.71 90 0.0970 10.31 0.135 7.41 120 0.0804 12.44 0.130 7.69 150 0.0726 13.73 0.120 3.33 180 0.0640 15.63 0.111 9.01 210 0.0564 17.73 0.106 9.44 240 0.0520 19.23 0.100 10.00 270 0.0434 20.66 0.0940 10.64 300 0.0433 23.09 0.0907 11.02 * Data t r a n s f e r r e d from Tables 15 and 16. However, f o r 35°C and 45°C, the data d i d not give s t r a i g h t l i n e s on l/C versus time c h a r t s . A r e a c t i o n order of 1.5 was assumed, and the order was confirmed when the concentration versus time data d i d y i e l d e x c e l l e n t s t r a i g h t l i n e s on p l o t s of l/C^ » 5 versus time, as shown i n Figures 21 and 22. Tables 19 and 20 give the corresponding data. Table 19. Data Showing Order of 1.5 at 35°C S t i r r i n g Rate: 1,000 r.p.m.; Gas Feed Rate: 500 ml./min Time, O x i d a t i o n w i t h O2 Oxidat i o n with A i r min. C,gm.mole/1.* l/C ° . 5 (l./gm. C,gm.mole/l.* l / c 0 » 5 , ( l . / g mole)0.5 mole) 0 0.170 2 .42 0.169 2.41 30 0.120 2.83 0.155 2.54 60 0.0835 3.46 0.139 2 .68 90 0.0603 4 .06 0.125 2.83 120 0.0455 4.69 0.114 2.96 150 0.0359 5.28 0.106 3.07 180 0.0275 6.03 0.0990 3.13 210 0.0931 3.23 240 0.0840 3.44 270 0.0774 3.59 300 0.0713 3.74 3 2 - 2 8 - 24L 0 60 120 180 240 300 REACTION T I M E , minutes © Figure 20. Second Order Reaction at 23 €'•• Table 20. Data Showing Order of 1.5 at 45°C S t i r r i n g Rate: 1,000 r.p.m.; Gas Feed Rate: 500 ml./min Time, Oxidation with O2 Oxidation with A i r min. C, gm.mole/1.* l/C°»5,(l./gm. C,gm.mole/l.* l/(j0v5,(l./ mole) 0 ,5 mole) 0 0.17S 2.37 0.169 2.43 30 0.12S 2.SO 0.153 .2.52 60 0.0913 3.30 0.142 2.65 90 0.0675 3.36 0.129 2.73 120 0.0521 4 . 3 3 0.120 2.88 150 0.0406 4.96 0.109 3.03 ISO 0.0325 5.55 0.103 3.11 210 0.0251 6.31 0.0954 3.24 240 0.0226 6.65 0.0873 3.33 270 0.0191 7.23 0.0821 3.49 300 0.0161 7.37 0.0762 3.62 Data transferred from Tables 15 and 16. For the temperatures from 55° to 85°C, the oxidation of sodium sulphide follows the f i r s t order with respect to the concentration of sodium sulphide, as i l l u s  trated i n Figures 23 to 26. The s p e c i f i c reaction rates f o r the oxidation of sodium sulphide by use of oxygen and a i r as gas feeds at various temperatures are summarized i n Table 21 . I f the Henry's law i s assumed, and i f the reaction i s of the f i r s t order with respect to the concentration of oxygen i n the sulphide s o l u t i o n , the r a t i o of the s p e c i f i c reaction rates with oxygen and with a i r as gas feeds w i l l be 4 . 7 6 . This reasoning makes i t a f i r s t order reaction, since the r a t i o of s o l u b i l i t i e s of oxygen i n the solution by bubbling ?o CM 5 0 60 120 180 240 300 REACTION TIME, minutes Figure 3 i . Order of | . 9 at 33 C. 0 60 120 180 240 300 REACTION TIME, minutes Figure 22. Order of 1.5 at 45°C. a> o E E REACTION TIME, minutes 23., Fi^ e t ©Mm ^ a g t i o n at 53@<t. 2 .01 0 60 120 180 240 300 REACTION T IME, minutes Figure 23. F i r s t Order Reaction at ?S°G. o E REACTION TIME, minutes Figure 26. F i r s t Order Reaction at 85°C. 76 Table 21 . S p e c i f i c Reaction Rates at Various Temperatures S t i r r i n g Rate: 1,000 r.p.m.; Gas Feed Rate: 500 ml./min. Temp., Reaction O x i d a t i o n w i t h 0 2 O x i d a t i o n with A i r (k)p ? * °C Order ( k ) 0 ( k ) a i rkTay w.r.t. Na 2S * _ 25 2 5.67 X 10" 2 1.68 x IO- 2 3.38 35 1.5 4.05 X 10" 2 0.887 x IO" 2 4.56 45 1.5 3.68 X IO" 2 0.776 x 1 0 - 2 4.74 55 1 12.9 X 10-3 2.88 x 10-3 4 . 4 8 65 1 10.7 X 10-3 2.45 x 10-3 4 .36 75 1 12.2 X 10-3 2.75 x 10-3 4.44 85 1 9.92 X 10-3 2.36 x 10-3 4.20 U n i t s of k's: 2nd order: l./(gm.mole)(min.) order of 1.5: l.°«5/(gm.mole)°*5(min.) 1st order: r n i n . - ^ * I f Henry's law i s a p p l i c a b l e , t h i s r a t i o i s 4 .76 pure oxygen and a i r ( c o n t a i n i n g 21% of oxygen by volume), r e s p e c t i v e l y , i s 4 . 7 6 . The experimental r e s u l t s obtained f o r t h i s r a t i o at various temperatures show tha t the o x i d a t i o n of sodium sulphide f o l l o w s the f i r s t order with respect to oxygen, i r r e s p e c t i v e of the temperature i n v e s t i g a t e d . The r a t i o s are a l l very c l o s e to 4 . 7 6 , except f o r the somewhat smaller value at 25°C. The good agreement of the experimental values of the r a t i o s with the t h e o r e t i c a l l y p r e d i c t e d value shows not only that the r e a c t i o n i s of f i r s t order with respect to oxygen, but al s o t h a t the s o l u t i o n i s saturated w i t h oxygen, whether the feed i s oxygen or a i r , f o r a s t i r r i n g r a t e of 1 ,000 r.p.m. and a gas feed r a t e of 500 ml./ min. Therefore the mass t r a n s f e r r e s i s t a n c e i n the gas phase can be ignored even when a i r i s used as the gas feed for these conditions of contacting. I t can be seen from Table 21 that the influence of temperature on the oxidation rate of sodium sulphide i s not very pronounced. There are two opposing effects involved i n the heterogeneous gas-liquid reaction: reaction of solutes and s o l u b i l i t y of oxygen. At high temperature the reaction rate may be increased; however, the s o l u b i l i t y of the gas i n the solution w i l l be decreased. The maximum oxidation rate of sodium sulphide occurs at 55°C As w i l l be seen l a t e r , the maximum absorption rate observed for oxygen also occurred at 55°C when the apparatus shown i n Fig . 13 was used. 2. Effect of I n i t i a l Concentration of Sodium Sulphide on the Oxidation Rate. The experimental r e s u l t s for various i n i t i a l concentrations of sodium sulphide are shown i n Tables 22, 23 and 24 for 25°, 35°, and 55°C The data are shown also i n Figures 27, 2S, and 29. These re s u l t s show that at low i n i t i a l concentrations the s p e c i f i c reaction rate i s comparatively high. This phenomenon suggests that the oxidation of sodium sulphide probably involves reactions i n addition to that described by equation 4. This statement i s j u s t i f i e d l a t e r i n the determination of the stoichiometry. Table 2 2 . E f f e c t of I n i t i a l Concentration of Sodium Sulphide on O x i d a t i o n at 25°C (Oxygen used) S t i r r i n g Rate: 1,000 r.p.m.; Oxygen Feed Rate: 500 ml./min. Time, C,* l / C , C, l / C , C, l / C , min. gm.mole/l. l./gm. gm. l./gm. gm. l./gm. mole m o l e / l . mole mol e / l . mole 0 0.181 5.52 0.0990 10.10 0.0485 20.6 30 0.145 6.90 0.0704 14.20 0.0400 25.0 60 0.112 8.93 0.0535 18.70 0.0323 31.0 90 0.0970 10.31 0.0437 22.90 0.0266 37.6 120 0.0804 12.44 0.0349 28.65 0.0232 43.1 150 0.0726 13.78 0.0298 33.55 0.0193 51.8 180 0.0640 15.63 0.0277 36.10 O.OI69 59.1 210 O.O564 17.73 0.0219 45.70 240 0.0520 19.23 270 0.0484 20.66 300 0.0433 23.09 k? 5.67 x IO" 2 15.2 x IO" 2 19.6 x I O - 2 l./(gm. mole) (min.) * Data t r a n s f e r r e d from Table 15. Table 23. E f f e c t of I n i t i a l Concentration of Sodium Sulphide on Ox i d a t i o n at 35° (Oxygen used) S t i r r i n g Rate: 1,000 r.p.m.; Oxygen Feed Rate: 500 ml./min. Time, C,* 1/C°»5, C, l/C 0'5, min. gm.mole/l. (l./gm. gm.mole/l. (l./gm. mole)0.5 mole)0.5 0 0.170 2.42 0.0737 3.68 30 0.120 2.88 0.0525 4.36 60 0.0835 3.46 O.O368 5.21 90 0.0603 4.06 0.0305 5.73 120 0.0455 4.69 0.0238 6.48 150 0.0359 5.23 0.0196 7.15 130 0.0275 6.03 O.OI58 7.95 k1.5„ r 4.05 x IO" 2 4,63 x 10-2 (l.)°-5 mole)u»-J, . % (mm.) 79 Table 24. Effect of I n i t i a l Concentration of Sodium Sulphide on Oxidation at 55° C (Oxygen used) S t i r r i n g Rate: 1,000 r . p . m . ; Oxygen Feed Rate: 500 ml . /min . Time, Cone. of Na 2 S, gm. m o l e / l . min. 0 0.131 * 0.116 0.0559 30 0.123 0.0762 0.0237 60 0.0360 0.0475 0.0186 90 0.0611 0.0277 0.0135 120 0.0417 0.0195 150 0.0261 180 0.0137 k l , - i 12.9 x 10-3 14 .8 x 10-3 17 .1 x 10 mm. * Data i n t h i s column transferred from Table 15. 60 120 180 240 300 REACTION TIME, minutes Filgure 27, Effect of l a i t i a l GoBcentratiosu of Sodium Sulphide on ©Kidation at 28<>C . ( Oxygen Feed). 0 60 120 180 240 300 REACTION TIME, minutes Figure 23* . Effect of In i t i a l 'Concent ra t ion of Sodium Sulphide on Cteidatiop at 35®C. (©Jsygea Feed). 2 _0> o E 0 Figure 2©<! 6 0 120 180 240 REACTION T IME, minutes Effect o f Initial. Concentration of. Sodium o'n' ttsidation '&€ 56°C* (Oxygen Feed). 3 0 0 3 . E f f e c t of A d d i t i o n o f G l a s s Beads To t e s t whether g l a s s w i l l c a t a l y z e t h e o x i d a t i o n o f sodium s u l p h i d e , two runs were done by a d d i n g r e f i n e d g l a s s beads ( s u p p l i e d by A.3 . L a P i n e & Co., Chicago) t o t h e s o l u t i o n i n t h e Pyrex r e a c t o r . I n t h e f i r s t r u n , 2 . 6 8 gms. o f 500 microns average d i a m e t e r were added, and i n t h e second, 0 . 0 2 3 gm. of 4 2 m i c r o n s maximum d i a m e t e r . I n both r u n s , t h e a d d i t i o n o f the g l a s s beads i n c r e a s e d t h e a r e a of c o n t a c t between the s o l u t i o n and g l a s s by about t e n t imes. The o x i d a t i o n of sodium s u l p h i d e was c a r r i e d out a t 55°C by the use o f oxygen as gas f e e d i n t h e a p p a r a t u s shown i n F i g . 1 2 . The .observed f i r s t o r d e r s p e c i f i c r e ' a c t i o n r a t e s were 5 . 7 9 x 1 0 _ 3 1 and 5 . 8 8 x 10"" 3 min.-''" When compared w i t h t h e o x i d a t i o n w i t h o u t t h e presence o f g l a s s beads a t 55°C ( 1 2 . 9 x 10~3 m i n . - 1 ) , t h e a d d i t i o n o f g l a s s beads t o t h e s o l u t i o n d i d not i n c r e a s e t h e r e a c t i o n r a t e . I n f a c t , t h e r e a c t i o n r a t e was d e c r e a s e d by 55% and 5 4 % , r e s p e c t i v e l y , by the a d d i t i o n . T h e r e f o r e , t h e o x i d a t i o n o f sodium s u l p h i d e was not c a t a l y z e d by g l a s s . The d e c r e a s e i n the o x i d a t i o n r a t e i n the presence o f g l a s s beads may have been due t o the i n h i b i t i o n by g l a s s o f t h e o x i d a t i o n o f sodium s u l p h i d e . However, i n view o f t h e f a c t t h a t i n c r e a s i n g t h e area o f c o n t a c t by t e n t i m e s , a whole o r d e r o f magnitude, d e c r e a s e s the s p e c i f i c r e a c t i o n r a t e o n l y by a f a c t o r o f two, s u g g e s t s t h a t f o r p r e s e n t purposes any i n h i b i t i o n perhaps can be i g n o r e d . 4 . R e p r o d u c i b i l i t y To t e s t the r e p r o d u c i b i l i t y of the work, the run at 55°C i n the apparatus of F i g . 12 w i t h no glas s beads present was done a second time. The s p e c i f i c r e a c t i o n r a t e s was 12.5 x 10~3 min.--*- whereas, i n the e a r l i e r run, the value was 12.9 x 10""3 min."*-'- as mentioned i n connection with the work where g l a s s beads were added. Agreement of the two values of the s p e c i f i c r e a c t i o n r a t e was thus w i t h i n kfo. The good r e p r o d u c i b i l i t y i s r e f l e c t e d a l s o i n the constancy of the r a t i o of s p e c i f i c r e a c t i o n r a t e s obtained by us i n g oxygen and a i r as r e s p e c t i v e gas feeds. 5. The Absorption of Oxygen. The ab s o r p t i o n of oxygen i n t o sodium sulphide s o l u t i o n s was i n v e s t i g a t e d by use of the apparatus shown i n F i g . 13 w i t h a s t i r r i n g r a t e of 1,320 * r.p.m. As im p l i e d by F i g . 16, the r a t e of oxygen abs o r p t i o n as w e l l as the r a t e of the o x i d a t i o n of sodium s u l p h i d e , measured by t h i s apparatus, in c l u d e . t h e e f f e c t of r e a c t i o n k i n e t i c s plus t h a t of a mass t r a n s f e r r e s i s t a n c e i n the l i q u i d phase. (Although F i g . 16 a p p l i e s t o a s t i r r i n g r a t e of 1,000 r.p.m. inst e a d of 1,320 r.p.m., i t would seem q u i t e l i k e l y that a mass t r a n s f e r r e s i s t a n c e would s t i l l be i n v o l v e d at the higher r a t e of s t i r r i n g , since bubbling at 450 ml./min. of oxygen was needed to remove the mass t r a n s f e r r e s i s t a n c e at 1,000 r.p.m. That mass t r a n s f e r r e s i s t a n c e i s in v o l v e d i s confirmed l a t e r . ) The r a t e of oxygen abs o r p t i o n was evaluated * a p p l i e s to Figures 30 to 41 i n c l u s i v e . by f i n d i n g the volume of oxygen absorbed measured at the known room temperature and barometric pressure. The r e s u l t s , obtained at various r e a c t i o n temperatures, are given i n Tables 25 to 3 1 , together with the amounts of sodium sulphide o x i d i z e d c a l c u l a t e d from the analyses. The r e s u l t s are shown g r a p h i c a l l y i n Figures 30 to 36 . Both t a b l e s and graphs are l a b e l l e d " s t o i c h i o m e t r y " although t h e i r use i n t h i s connection i s described l a t e r . A comparison of the slopes of the a b s o r p t i o n curves of oxygen i n Figures 30 t o 36 shows that the o v e r a l l average r a t e of a b s o r p t i o n of oxygen i n t o the sodium sulphide s o l u t i o n decreases with temperature from 25° t o 4 5°C However, when the temperature i s increased t o 55°G, the absorption r a t e increases a b r u p t l y to a maximum, 1.06 x 10""4 gm. mole/min. f o r an i n i t i a l c o n c e n t r a t i o n of 0.164 gm. mole/ l i t r e of sodium sul p h i d e . The absorption r a t e then decreases again with i n c r e a s i n g temperature. This phenomenon i s c o n s i s t e n t with the assumption, mentioned i n the f i r s t s e c t i o n of Results and D i s c u s s i o n , that d i f f e r e n t r e a c t i o n mechanisms are involved f o r each of the two temperature ranges, 25° to 45° C, and 55° t o 85°C. Acco r d i n g l y , d i f f e r e n t orders of r e a c t i o n w i t h respect to sodium sulphide were observed f o r these two temperature ranges, as already described. Table 25. S t o i c h i o m e t r y at 25°C S t i r r i n g r a t e : 1,320 r.p.m.; T ime, C umulat i v e min. gm. mole Na 2S Oxidized 0 0 30 0.0028 60 0.0088 90 0.0108 120 0.0143 150 0.0163 ISO 0.0188 210 0.0201 240 0.021§ 270 ' 0.0230 300 0.0244 330 0.0260 360 0.0267 I n i t i a l c o n e : 0.185 gm. mole Time, Cumulative min. gm. mole 0 Absorbed ^ 0 0 25 0.0016 43 0.0034 63 0.0054 83 0.0071 100 0.0088 120 0.0107 145 0.0131 166 0.0151 185 0.0169 206 0.0188 229 0.0208 256 0.0229 279 0.0247 301 0.0264 324 0.0282 346 0.0299 360 0.0309 Table 26. Stoichiometry at 35°C S t i r r i n g r a t e : 1,320 r.p.m.; I n i t i a l cone.: 0.193 gm Time, Cumulative Time, Cumulative ,min. gm. mole Na 2S min. gm. mole 0 O x i d i z e d Absorbed 0 0 0 0 30 0.0018 51 0.0019 60 0.0052 75 0.0041 90 0.0038 94 0.0059 120 0.0121 113 0.0076 150 0.0151 138 0.0099 ISO 0.0181 165 0.0123 210 0.0203 135 0.0141 240 0.0228 203 0.0153 270 0.0240 226 0.0177 300 0.0256 243 0.0196 330 0.0271 266 0.0213 360 0.0285 287 0.0230 309 0.0248 335 0.0271 360 0.0292 Table 27. Stoichiometry at 45°C S t i r r i n g r a t e : 1,320 r.p.m.; I n i t i a l c o n e : 0.191 gm.i Time, Cumulative Time, Cumulat ive min. gm. mole Na2S min. gm. mole 0 O x i d i z e d Absorbed 0 0 0 0 30 0.0015 55 0.0018 60 0.0040 33 0.0038 90 0.0060 110 0.0058 120 O.OO9O 136 0.0073 150 0.0123 167 0.0102 ISO 0.0153 190 0.0121 210 0.0180 215 0.0141 240 0.0193 244 0.0163 270 0.0213 269 0.0183 300 0.0223 294 0.0202 330 0.0237 319 0.0221 360 0.0251 344 0.0239 36O 0.0253 Table 28. Stoichiometry at 55°C S t i r r i n g r a t e : 1,320 r.p.m.; I n i t i a l c o n e : O .I64 gm.mole Time, Cumulative Time, Cumulative min. gm. mole Na 2S min. gm. mole O2 Oxidized ' Absorbed 0 0 0 0 30 0.0035 31 0.0019 60 0.0083 50 0.0039 90 0.0110 65 O.OO56 120 0.0143 83 0.0075 150 O .OI64 104 0.0097 ISO 0.0175 124 0.0119 210 0.0194 143 0.0140 240 0.0215 167 0.0164 270 0.0233 135 0.0182 300 0.0235 204 0.0202 330 0.0264 222 0.0222 360 0.0263 235 0.0233 257 0.0256 273 0.0273 302 0.0301 325 0.0324 345 0.0343 360 0.0358 Table 29 . Stoichiometry at 65°C S t i r r i n g r a t e : 1 ,320 r.p.m.; I n i t i a l c o n e : 0.169 gm.mole Time, Cumulative Time, Cumulative min. gm. mole Na 2S min. gm. mole 0 2 Oxidized Absorbed 0 0 0 0 30 0.0045 22 0.0020 60 0.0080 46 0.0043 90 0.0108 65 0.0061 120 0.0123 87 0.0083 150 0.0158 110 0.0101 180 0.0168 136 0.0127 210 0.0180 160 0.0148 240 0.0200 175 0.0164 270 0.0226 194 0.0184 300 0.0232 215 0.0206 330 0.0241 230 0.0223 360 0.0252 251 0.0243 274 0.0264 298 0.0286 319 0.0306 338 0.0322 360 0.0337 Table 30 . Stoichiometry at 75°C S t i r r i n g r a t e : 1 ,320 r.p.m.; I n i t i a l c o n e : 0.171 gm.mole/1. Time, Cumulative Time, Cumulative min. gm. mole Na 2S min. gm. mole 0 2 Oxidized Absorbed 0 0 0 0 30 0.0035 30 0.0018 60 0.0073 50 ' O.OO36 90 0.0105 75 0 .0062 120 0.0128 93 0 .0082 150 0.0153 113 0 .0102 ISO 0.0173 141 0 .0134 210 0.0188 158 0 .0151 240 0.0206 174 0.016S 270 0 .0214 194 0.0136 300 0 .0221 220 0.0203 330 0.0235 267 0 .0228 360 0 .0243 290 0 .0244 321 0 .0261 360 0 .0283 Table 31 . Stoichiometry at 35°C S t i r r i n g r a t e : 1,320 r.p.m.; I n i t i a l c o n e : 0 .172 gm. Time, Cumulative Time, Cumulative min. gm. mole Na2S min. gm. mole 0g Oxidized Absorbed 0 0 0 0 30 0.0020 41 0 .0019 60 0 .0038 80 0 .0041 90 0.0050 110 0.0060 120 0.0063 156 0 .0083 150 0 .0075 210 0 .0102 180 0 .0085 255 0.0125 210 0 .0098 293 0.0141 240 0.0110 335 0 .0160 270 0 .0128 360 0.0172 300 0.0130 330 0.0133 360 0.0158 .04 INITIAL CONC. OF Na 2S : 0.185 gm.mole/l. REACTION TIME, minutes ||gur® 30. Sioftcfciioaietry at 23®Cl* INITIAL CONC. OF Na 2S 0.198 gm.mole/l. 0 60 120 180 240 300 360 REACTION TIME, minutes re* $1. StoMli&oaetry at 3i®£,' INITIAL CONC. OF Na 2 S: 0.191 gm. mole / I. 60 120 180 240 300 360 REACTION TIME, minutes .04 L REACTION TIME, minutes f&gwfe S3-.: Stoicaioaetipy at SS°C.. .04 .03 Q LU r- O < LU CE UJ _J O .02 < o.OI INITIAL CONC. OF Na 2S 0.169 gm. mole/ l . 60 120 180 240 300 360 REACTION TIME, minutes p©>'34...' - SttficJ&'iopeiry -at' 65*€« INITIAL CONC. OF Na2S 0.171 gm. mole/I. PA O w 60 120 180 240 300 360 REACTION TIME, minutes 97 .04 .03 o § • 0 2 y o < cr o.O I INITIAL CONC. OF Na 2S: 0.172 gm. mole/1. 0 60 120 180 240 300 360 REACTION TIME , minutes Figure 36. Sioichiome'iry at 83°e. 98 The r a t e of oxygen absorption was found to be slow i n the f i r s t hour of r e a c t i o n . The r a t e themrLncreased t o a constant value which was maintained f o r s e v e r a l hours, and then decreased g r a d u a l l y as the o x i d a t i o n of sodium sulphide continued. High i n i t i a l c oncentrations of sodium sulphide produce a comparatively high absorption r a t e . As the i n i t i a l c o n c e n t r a t i o n decreases so does the absorption r a t e as i m p l i e d by F i g . 37. The curve marted w i t h 0 gm. m o l e s / l i t r e of sodium sulphide i n F i g . 37 was obtained by using 250 ml. of 0.^ - N sodium hydroxide s o l u t i o n without the i n j e c t i o n of hydrogen s u l p h i d e * This curve represents the r a t e of absorption of oxygen without a simultaneous o x i d a t i o n of sodium s u l p h i d e . Figures 30, 38, and 39 show the o x i d a t i o n of sodium sulphide and the absorption of oxygen f o r i n i t i a l c o ncentrations of 0.185, 0.0906, and 0.040 gm. m o l e s / l i t r e of sodium s u l p h i d e . The experimental data are summarized i n Table 25, 32, 33, and 3*+. (The oxygen absorption data are the same as t h a t shown i i n F i g . 37). I t has been mentioned already taht at low i n i t i a l c o n centrations of sodium sulphide the s p e c i f i c r e a c t i o n r a t e f o r the disappearance of sodium sulphide i s comparatively h i g h . This r e s u l t i s i n c o n t r a s t w i t h the r e s u l t f o r the r a t e of oxygen a b s o r p t i o n . This paradox a l s o suggests that the o x i d a t i o n of sodium sulphide does not i n v o l v e a s i n g l e r e a c t i o n , a statement which w i l l be j u s t i f i e d i n the next s e c t i o n . * Only i n t h i s case has oxygen not been p a r t i a l l y s t r i p p e d from the s o l u t i o n by hydrogen s u l p h i d e . 0 60 120 180 240 300 360 REACTION TIME, minutes Figure 37. ' Effect o f i n i t i a l Concentration of Sodium SulpMde on A^aorption Of Oxygen at 25 #€. 100 The decrease i n the volume of sodium sulphide s o l u t i o n , due t o the withdrawals of samples f o r analyses, was n e g l i g i b l e , being l e s s than 2% when the apparatus of F i g . 13 was used. This small decrease i n the volume of s o l u t i o n would have l i t t l e e f f e c t on e i t h e r the ab s o r p t i o n r a t e or the o x i d a t i o n r a t e . Table 32. E f f e c t of I n i t i a l Concentration of Sodium Sulphide on the Absorption and on the Oxi d a t i o n at 2 5 0 c . S t i r r i n g r a t e : 1,320 r.p.m.; I n i t i a l c o n e : 0.0906 gm.mole/l. Time, Cumulative Time, Cumulatr min. gm. mole Na 2S min. gm. mole Oxidized Absorbe< 0 0 0 0 30 0 .0009 50 0.0020 60 0 .0035 75 0 .0039 90 0 .0055 95 0.0057 120 0.0072 117 0.0074 150 0 .0090 140 0 .0091 180 0 .0095 164 0.0110 210 0.0117 200 0 .0131 240 0 .0119 230 0.0148 270 0 .0124 265 0.0166 270 0.0168 .03 INITIAL CONC. OF Na 2S : 0 .0906 gm. mole/I. Q . 0 2 LU H O < LU cr LU - J o < cr o .0! 60 120 180 240 300 REACTION TIME, minutes 5; Wi&i 02 'Initial GonoSBtiration Sodium fibsfirptioEi and on the ©Eidaiioto a4 2S°G* .e on R E A C T I O N T I M E , minutes f i g u r e $9* E f f e c t off I n i t i a l Gencepfcraiion of Sodium Sulphide on • • y ^Sjsoiption and o n t h e Oxidation at 25 C,*, Table 3 3 . E f f e c t of I n i t i a l Concentration of Sodium Sulphide on the Absorption and on the Ox i d a t i o n at 25°C S t i r r i n g r a t e : 1,3.20 r.p.m.; I n i t i a l c o n e : 0.040 gm. mol e / l . Time, Cumulative min. gm. mole Na 2S Oxidized 0 0 30 0.0007 60 0.0017 90 0.0028 120 0.0035 150 0.0044 180 0.0050 210 0.0056 240 0.0060 270 0.0064 300 0.0065 Time, min. 0 65 105 145 187 230 281 300 Cumulative gm. mole 0 2 Absorbed 0 0.0019 0.0039 0.0058 0.0076 0.0092 0.0108 0.0114 Table 34. Absorption of Oxygen Without a Chemical Reaction at 25°C S t i r r i n g r a t e : 1,320 r.p.m.; 0 .4 N NaOH: 250 ml. Time, min. 0 60 120 180 240 Cumulative gm.mole 0 2 0 1.2 1.6 3.3 4 .9 Absorbed x 105 300 7 .0 6 . Determination of Stoichiometry From Figures 3° t o 36 , i t i s seen th a t sodium t h i o s u l p h a t e i s the main product when the o x i d a t i o n of sodium sulphide proceeds, since one mole of oxygen i s re q u i r e d per mole of sodium sulphide o x i d i z e d (equation 4 ) . However, i n the i n i t i a l stages of o x i d a t i o n , the a c t u a l q u a n t i t y of oxygen absorbed i s l e s s than the t h e o r e t i c a l value f o r the formation of the t h i o s u l p h a t e . This i n d i c a t e s that at l e a s t one p a r a l l e l r e a c t i o n , which consumes l e s s oxygen, takes place i n c o m p e t i t i o n with the formation of the t h i o s u l p h a t e . Booth (18) g i v e s the equation f o r the f o r m a t i o n o f d i s u l p h i d e f o r which r e a c t i o n o n l y 1/4 mole of oxygen i s r e q u i r e d per mole of sodium s u l p h i d e o x i d i z e d , and perhaps t h i s r e a c t i o n i s the one i n com p e t i t i o n here with the f o r m a t i o n of t h i o  s u l p h a t e . Of course, when d i s u l p h i d e ions move t o the i n t e r f a c e or more oxygenated p a r t o f the s o l u t i o n , they w i l l be o x i d i z e d f u r t h e r i n s t a n t l y ( 1 8 ) . In the l a t e r stages of o x i d a t i o n , i n c o n t r a s t t o the e a r l y s t a g e s , the consumption of oxygen i s g r e a t e r than the t h e o r e t i c a l value f o r the fo r m a t i o n of sodium t h i o s u l p h a t e , perhaps because the sodium s u l p h i d e a l s o i s o x i d i z e d to sodium s u l p h i t e and s u l p h a t e . (19) I t should be emphasized here t h a t when the pH of a sodium s u l p h i d e s o l u t i o n l i e s between 10 and 15, as shown i n F i g . 2, the s o l u t i o n , i n f a c t , c o n s i s t s o f a mixture of s u l p h i d e and h y d r o s u l p h i d e . S i m i l a r r e a c t i o n s to the o x i d a t i o n o f sodium s u l p h i d e are expected f o r the o x i d a t i o n o f the hy d r o s u l p h i d e . A l l of the probable r e a c t i o n s f o r the o x i d a t i o n of s u l p h i d e and hydrosulphide are summarized i n Table 35 . The f a c t t h a t at l e a s t t e n r e a c t i o n s o f d i f f e r e n t importance probably are i n v o l v e d i n the o x i d a t i o n o f sodium s u l p h i d e s o l u t i o n , as giv e n i n Table 35 , presumably e x p l a i n s t h e phenomenon t h a t t h e o x i d a t i o n r a t e o f s u l p h i d e i n c r e a s e s as t h e i n i t i a l c o n c e n t r a t i o n o f s o d i u m s u l p h i d e i s d e c r e a s e d , i n c o n t r a s t t o t h e d e c r e a s e i n t h e r a t e o f a b s o r p t i o n o f o x y g e n o b s e r v e d as t h e c o n c e n t r a t i o n o f s o d i u m s u l p h i d e i s d e c r e a s e d . T a b l e 3 5 . P r o b a b l e R e a c t i o n s i n t h e O x i d a t i o n o f N a 2 S and HaHS A . F o r N a 2 S : 2 S = + 2 0 2 + H 2 0 S 2 0 3 = + 2 O H " 27 2 S = + 1/2 0 2 + H 2 0 S 2 + 2 0 H " 28 S 2 = + I. 5 0 2 S 2 0 3 = 29 2 S = + 3 0 2 2 S 0 3 = 30 S 0 3 = + 1/2 0 2 S 0 4 = 31 B . F o r NaHS: 2 S H " + 2 0 2 S 2 0 3 = + H 2 0 32 2 S H " + l / 2 0 2 — — S 2 = -+* H 2 0 33 S 2 = + 1.5 0 2 - • S 2 0 3 = 34 2 S H " + 3 0 2 + 2 OH " 2 S 0 3 = + 2 H 2 0 35 S 0 3 = + 1/2 0 2 S 0 4 = 36 I n s t e a d o f a s i n g l e r e a c t i o n g i v i n g s o d i u m t h i o  s u l p h a t e as t h e p r o d u c t , t h e o x i d a t i o n o f s o d i u m s u l p h i d e , i n f a c t , l i k e l y i n v o l v e s a s e r i e s o f r e a c t i o n s , p a r a l l e l , c o n s e c u t i v e , i r r e v e r s i b l e , and p r o b a b l y r e v e r s i b l e ' . These r e a c t i o n s , a l t h o u g h o f m i n o r i m p o r t a n c e as compared t o t h e f o r m a t i o n o f t h e t h i o s u l p h a t e , c o m p l i c a t e t h e s t u d y o f t h e r e a c t i o n . F u r t h e r m o r e , i n t h e r a n g e o f pH i n v e s t i g a t e d , t h e s o l u t i o n a c t u a l l y c o n t a i n s b o t h s u l p h i d e and h y d r o s u l p h i d e . T h i s a l s o r e n d e r s t h e i n v e s t i g a t i o n d i f f i c u l t . I t was described already t h a t the use of the apparatus i n F i g . 13 Involves the e f f e c t of r e a c t i o n k i n e t i c s plus a mass t r a n s f e r r e s i s t a n c e of oxygen i n the l i q u i d phase. This i s confirmed by comparing the slopes of the curves i n F i g . 40 w i t h those of the corresponding curves appearing i n Figures 18, 23, 2 4 , 2 5 , and 2 6 . The former i s always l e s s than the l a t t e r . This r e s u l t i n d i c a t e s that mass t r a n s f e r r e s i s t a n c e i s i n v o l v e d i n a f f e c t i n g the o v e r a l l r a t e besides the r e a c t i o n k i n e t i c s . The experimental data corresponding to F i g . 40 are shown i n Table 36. The use of the apparatus i n F i g . 13 a l s o shows that the s p e c i f i c r e a c t i o n r a t e increases as the i n i t i a l c o n c e n t r a t i o n of sodium sulphide i s decreased, as im p l i e d by the data of Table 37 which are p l o t t e d i n F i g . 41. The e f f e c t of temperature on the o x i d a t i o n r a t e i s d i f f i c u l t t o c o r r e l a t e by means of an Arrhenius equation, since the temperature e f f e c t i s not pronounced, and since the r e s u l t s depend upon the i n i t i a l concentrations of sodium sul p h i d e . PARAMETER : TEMPERATURE , C. 120 240 360 480 6 0 0 720 8 4 0 960 T IME, minutes O x i d a t i o n o f S o d i u m S u i c i d e a t V a r i o u s T e B ^ e r a t u r e e f o r A p p a r a t u s i n F i g u r e 1.3, 109 Table 36 . O x i d a t i o n of Sodium Sulphide at Various Temperatures f o r Apparatus i n F i g . 13. S t i r r i n g r a t e = 1 ,320 r.p.m. Time, Cone, of Na 2S, gm. m o l e / l i t r e min. 25°C 350c 45°C 55°C 65°C 75°C 85°C 0 0.135 0.198" 0.191 O .I64 0 .169 0.171 0.172 30 0.174 0.191 0.185 0.150 0 .151 0.157 0.164 60 0 .150 0.178 0.175 0.131 0 .137 0.142 0.157 90 0.142 0.163 0.167 0.120 0.126 0.129 0 .132 120 0.128 0.150 0.155 0.107 0.120 0.120 0.147 150 0.120 0.138 0.142 0.0984 0.106 0.110 0.142 ISO 0.110 0.126 0.130 0.0940 0.102 0.102 0.133 210 0.105 0.117 0.119 O.O865 0.0970 0.0960 0.133 240 0.100 0 .107 0.114 0.0730 0.0892 0.0885 0.128 270 0.0935 0.102 0.106 0.0710 0.0795 0.0355 0.121 300 C.0879 0.0956 0.102 0.0700 0.0762 0.0326 0.120 330 0.0815 O.O896 0.0961 0.05S5 0.0725 0.0771 0.119 360 0.0785 0.0S40 0.0905 0.0570 0.0681 0.0737 0 .109 Table 37. Ox i d a t i o n of Sodium Sulphide at 25°C as a Function of I n i t i a l Concentration. S t i r r i n g r a t e = 1 ,320 r.p.m. Time, min. Cone, of NagS, gm. mo l e / l . 0 0.185 0.0906 0.0400 30 0.174 0.0871 0.0373 60 0.150 O.O765 0.0333 90 0.142 0.0635 0.0239 120 0.128 0.0618 0.0262 150 0.120 0.0552 0.0223 180 0.110 0.0525 0.0202 210 0.105 0.0433 0.0175 24O 0.100 0.0430 0.0160 270 0.0935 0.0409 0.0144 300 0.0379 0.0140 330 0.0315 360 0.0735 110 7. Comparison of the Oxidations of Sodium Sulphide and Black L i q u o r . The o x i d a t i o n of hydrogen sulphide d i s s o l v e d i n sodium hydroxide s o l u t i o n behaves s i m i l a r l y to the o x i d a t i o n of sodium sulphide i n black l i q u o r . The main d i f f e r e n c e l i e s i n the r a t e s of o x i d a t i o n . Ziegelmeyer and F e i s c h l (5) showed th a t black l i q u o r s c o n t a i n organic substances, which increase the r a t e of o x i d a t i o n by 20 to 30 times. B i l b e r g and Landmark (17) found t h a t the o x i d a t i o n products of black l i q u o r i n c l u d e p o l y s u l p h i d e s , t h i o s u l p h a t e , s u l p h i t e , and small amounts of sulphate. In the present work, from the s t o i c h i o m e t r i c determination of oxygen absorbed, the formation of the same products of the o x i d a t i o n of the sulphide s o l u t i o n i s i m p l i e d . Venemark (21) found t h a t the r a t e of oxygen abs o r p t i o n i n t o b l a c k l i q u o r i n each run i s to a l a r g e extent independent of time from the beginning of o x i d a t i o n , a r e s u l t which i s i n agreement with the r e s u l t s obtained from the present work f o r the treatment of s o l u t i o n s of s u l p h i d e . Murray (15) s t u d i e d the o x i d a t i o n of black l i q u o r between 50° and 91°C. Although c a t a l y s i s i n h i s s t u d i e s may r e s u l t i n q u i t e d i f f e r e n t mechanisms of r e a c t i o n from those a p p l i c a b l e i n the present work, i t would seem i n t e r e s t i n g to compare h i s r e s u l t s with those of the present work, Murray (15) found that the rate of the oxidation of weak black l i q u o r may be expressed by a semi-empirical f i r s t order equation with respect to sulphide. In the present work at temperatures between 55° and 85°C the oxidation of sodium sulphide also was found to be of f i r s t order with respect to the concentration of sodium sulphide. Murray (15) did not study the oxidation at lower temperatures. Shchukarev and Kireeva-Tuzulakhova (19) studied the oxidation of sodium sulphide at 20° and 40OC, and found that the reaction order was anomalous. In regard to the reaction order with respect to the concentration of oxygen, the present work establishes i t as f i r s t order, irrespective of the temperature, f o r the oxidation of sulphide. Murray (15), however, gave the . r a t i o of oxidation rates with oxygen to those obtained using a i r as feed gas as a function of temperature and the concentration. The r a t i o ranged from 1,71 to 3.11. The way Murray calculated t h i s r a t i o was i n e f f e c t i v e . He obtained the oxidation rates i n the units of grams per unit time. Only i f the reaction were of zero order would the values of the r a t i o be expected to remain constant. In the present work the s p e c i f i c reaction rates were compared. The s p e c i f i c reaction rate i s independent of time and concen t r a t i o n , whereas the oxidation rate, expressed as mass per unit time, i s a strong function of both time and concentration. Murray ( 1 5 ) used the method of a n a l y s i s of the present work f o r determining the content of sulphide i n black l i q u o r except that the concentrations of base e l e c t r o l y t e and p-phenylenediamine were those suggested by S t r i c k l a n d and Risk (1) instead of the higher concen t r a t i o n s used here. This f a c t may account f o r the d i f f e r e n t r e s u l t s i n the two studie s with respect to the r e a c t i o n order f o r oxygen. Murray (15) c o r r e l a t e d h i s data by adding the p a r t i a l pressure of oxygen i n the gas phase, m u l t i p l i e d by an a r b i t r a r y constant, t o the concentration of s u l p h i d e . This approach i s e n t i r e l y e m p i r i c a l , and the order w i t h respect to oxygen i s not easy to v i s u a l i z e . Murray (15) found that the change with temperature i n the r a t e of the o x i d a t i o n of sodium sulphide i n black l i q u o r i s very s l i g h t . H is r e s u l t s show that the maximum o x i d a t i o n r a t e occurs at a temperature between 61° and 7l°C. For the o x i d a t i o n of sodium s u l p h i d e , the maximum ra t e was found from t h i s work t o be at 55°C. CONCLUSIONS The experimental r e s u l t s , as a whole, are s a t i s  f a c t o r y , since the two d i f f e r e n t apparatuses gave the co n s i s t e n t r e s u l t s . The use of the higher concentrations of reagents, base e l e c t r o l y t e and p-phenylenediamine, f o r the development 113 of Lauth's V i o l e t from sulphide s o l u t i o n , i s s a t i s f a c t o r y f o r the study of the k i n e t i c s of the o x i d a t i o n of sodium su l p h i d e . One advantage i s that the concent r a t i o n of sodium sulphide can be c a l c u l a t e d d i r e c t l y from the c a l i b r a t i o n f a c t o r without using the c a l i b r a t i o n curve, since the c a l i b r a t i o n f a c t o r remains constant up t o 16 gms. per l i t r e of sodium sul p h i d e . The o x i d a t i o n of sodium sulphide i s s i m i l a r to that of black l i q u o r , except t h a t the r e a c t i o n i s much slower, due t o the absence of the organic substances which c a t a l y z e the r e a c t i o n . Besides the t h i o s u l p h a t e , o x i d a t i o n of sodium sulphide may give d i s u l p h i d e , s u l p h i t e and sulphate. The r a t e of oxygen abs o r p t i o n i s increased a p p r e c i a b l y by the simultaneous o x i d a t i o n of sodium sulphide i n the s o l u t i o n . The r a t e of oxygen absorption decreases with temperature from 2 5 ° t o 45°C, but increases a b r u p t l y to a maximum at 55°C, and then decreases again. Although the absorption r a t e of oxygen i s t o a great extent independent of the concentr a t i o n change of sodium sulphide d u r i n g an o x i d a t i o n experiment, i t does depend upon the i n i t i a l c o n c e n t r a t i o n of the s u l p h i d e . The r e a c t i o n orders w i t h respect t o sodium sulphide depend upon the temperature: second order at 25°C, order of 1 . 5 at 3 5 ° and 45°C, and f i r s t order from 5 5 ° t o 85°C. The r e a c t i o n order with respect t o oxygen i s always f i r s t order, independent of the temperature. The maximum o x i d a t i o n r a t e a l s o occurs at 55°C. RECOMMENDATIONS The f o l l o w i n g recommendations are proposed f o r f u r t h e r experimental work on the o x i d a t i o n of sodium sulphide or of black l i q u o r : (a) For the study of r e a c t i o n k i n e t i c s , the apparatus shown i n F i g . 12 can be modified by r e p l a c i n g the s a t u r a t o r with a condenser connected t o the o u t l e t s of the gas. In t h i s way, the water vapor c a r r i e d by the gas from the s o l u t i o n w i l l r e f l u x to the r e a c t o r without causing s e r i o u s change of the concentration of the sulphide due t o evaporation at high temperature. ( C a l c u l a t i o n s show a l o s s of only 0.5% of a 250 ml. volume from the rea c t o r i n 5 hours i f the e x i t gas were cooled to 7°C.) (b) A study of the o x i d a t i o n of sodium sulphide could be c a r r i e d out with various "appropriate organic substances present to c a t a l y z e the o x i d a t i o n . Perhaps information would r e s u l t as t o those compounds which are important i n the o x i d a t i o n of sodium sulphide i n black l i q u o r . (c) The reason, why the r e a c t i o n orders w i t h respect to the concent r a t i o n of sodium sulphide depend upon the temperatures, may be c l a r i f i e d by use of the E . S . R . technique t o detect and determine the d i f f e r e n t unpaired f r e e r a d i c a l s which probably are involved at d i f f e r e n t temperatures. 115 NOMENCLATURE Symbols B Base E l e c t r o l y t e b C e l l Thickness, cm . C Concentration of Sodium Sulphide, gms./l. or gm.rnoles, A . or co n c e n t r a t i o n of Lauth's V i o l e t , p.p.m. Na^S. C 0 I n i t i a l Concentration of Sodium Sulphide, gms./l. or gm. moles/1. E E x t i n c t i o n a l o g I Q / I . kbC - Absorbance F C a l i b r a t i o n Factor - 50 C / E V I I n t e n s i t y of tran s m i t t e d l i g h t or r a d i a n t energy a t s i n g l e wavelength I 0 I n t e n s i t y of i n c i d e n t l i g h t or r a d i a n t energy at s i n g l e wavelength k S p e c i f i c e x t i n c t i o n or s p e c i f i c absorbance, (p.p.m.) "I (cm.)"*1 K Chemical e q u i l i b r i u m constant k^ S p e c i f i c r e a c t i o n r a t e , (gm. moles/1.) 1 ~ n ( i n i n . J " 1 N Sodium sulphide n Reaction order P p-Phenylenediamine t Reaction time, min. V D i l u t e d volume of Lauth's V i o l e t s o l u t i o n , ml. V /50 D i l u t i o n x Mole f r a c t i o n LITERATURE CITED (1) S t r i c k l a n d , J.D.H., and R i s k , J.B., TAPPI 40, 9 1 (1957) (2) Wright, R.H., Schoening, M.A., and Hayward, A.M., TAPPI jk> 2^9 (195D (3) Werner, A.E., Canadian Pulp and Paper Industry 16, No. 3 35 (1963) (4) S w i f t , E.H., A System of Chemical A n a l y s i s , P r e n t i c e - H a l l I nc., New York (1946) (5) Ziegelmeyer, F., and F e i s c h l , 0., Das Papier 12, 122 (1958) ~ (6) Vogel, A.I., Q u a n t i t a t i v e Inorganic A n a l y s i s , Longmans Green & Co., New York (1951) (7) P h i l i p p , B., and Hoyme, H., Faserforschung und T e x t i l t e c h n i k Jahrgang 8, Heft 9, 354 (1957) (8) Goates, J.R., Gordon, M.B., and Faux, N.D., J . Am. Chem. SW. 74, 735 ( 1 9 5 2 ) (9) Hougen, O.A., and Watson, K.M., Chemical Process P r i n c i p l e s , Part 3, John Wiley & Sons, Inc., New York (1947) (.10) 'Wright, R.H., B r i t i s h Columbia Research C o u n c i l , T e c h n i c a l B u l l e t i n No. 2 7 , "The Reduction of Odors from K r a f t Pulp M i l l s " (undated) (11) Glasstone, S., and Lewis, D., Elements of P h y s i c a l Chemistry, 2nd E d i t i o n , D. Van Nostrand Co., Inc., New York (i960) (12) R i s k , J.B., and S t r i c k l a n d , J.D.H., Anal. Chem. 29, 434 (1957) (13) Bergstrom. H., and Trobeck, K.G., Svensk Papperstidn, 22, 554 (1939) (14) C o l l i n s , T.T., J r . , Paper Trade J . 131, No. 15, 30 (1950) (15) Wright, R.H., TAPPI 2j>, No. 6, 2 7 6 (1952) (16) Murray, F.E., TAPPI 42, No. 9, 76l (1959) (17) B i l b e r g , E. f and Landmark, P., Norsk S k o g i n d u s t r i 15, No. 5, 221 (1961) (18) Booth, H., J . Soc. Leather Trades' Chemists 40, 226(1956! — (19) Shchukarev, S.A., and Kireeva-Tuzulakhova, E.M., J . Gen. Chem. (U.S.S.R.) 1, No. 8-9, 1125 (1931), (20) Van de Vusse, I r . J.G., F i r s t European Symposium on Chemical Engineering, Amsterdam (May 1957) (21) Venemark, Av E., Svensk Papperstidn. _5_2, 629 (1956) 118 APPENDIX The c o r r e c t i o n of the c o n c e n t r a t i o n of sodium sulphide f o r the evaporation of water from the r e a c t o r i n a few of the runs compensates f o r the f a c t t h a t , without the c o r r e c t i o n , the c o n c e n t r a t i o n at any time would be the r e s u l t not only of r e a c t i o n , but a l s o of evaporation. However, the r e a c t i o n r a t e observed at any time i s that corresponding to the a c t u a l concentrations i n the r e a c t o r which are higher than the c o r r e c t e d ones. This defect i n the c o r r e c t i o n i s probably not s e r i o u s except toward the ends of 1swo or three of the runs. The experimental c o n d i t i o n s f o r n e g l i g i b l e r e s i s t a n c e to mass t r a n s f e r i n the apparatus of F i g . 12 were e s t a b l i s h e d at low temperature under sa t u r a t e d c o n d i t i o n s . At higher temperatures, d i f f u s i o n may be important since the gas i s not saturated i n the s a t u r a t o r . The evaporation of vrater i n t o a gas bubble might here present a s i g n i f i c a n t r e s i s t a n c e t o mass t r a n s f e r . In any f u r t h e r work t h i s p o i n t should be checked. Operation w i t h a condenser f o l l o w i n g the r e a c t o r , suggested i n Recommendations, would not be p o s s i b l e w i t h a s a t u r a t o r ahead of the r e a c t o r since a gain of water i n the r e a c t o r w i t h time would r e s u l t . Hence i f a condenser were used dry gas would be needed, and the problem of p o s s i b l e mass t r a n s f e r r e s i s t a n c e as a r e s u l t of evaporation of water i n t o the gas bubbles i n the r e a c t i o n would need even more c a r e f u l examination. 

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
Japan 23 0
United States 17 1
China 12 10
India 4 11
Malaysia 2 2
Germany 2 3
Iran 2 0
Indonesia 1 1
City Views Downloads
Tokyo 23 0
Unknown 10 18
Maynard 7 0
Shenzhen 6 10
Beijing 6 0
Ashburn 4 0
Mountain View 3 0
University Park 1 0
Mumbai 1 3
Dallas 1 0
Coimbatore 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}
Download Stats

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0059072/manifest

Comment

Related Items