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Anodic oxidation of phenolics found in coal conversion effluents 1982

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ANODIC OXIDATION OF PHENOLICS FOUND IN COAL CONVERSION EFFLUENTS by MEENAKSHI' CHETTIAR (M.Sc, University of Madras, India 1978) A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Chemical Engineering Department) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December 1981 ( c ) Meenakshi Chettiar, 1981 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or pu b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date ABSTRACT A n o d i c o x i d a t i o n o f t h e m a j o r p h e n o l i c s t h a t a r i s e i n c o a l c o n v e r s i o n e f f l u e n t s was i n v e s t i g a t e d . E x p e r i m e n t s were p e r f o r m e d i n a packed bed anode o f e l e c t r o d e p o s i t e d l e a d d i o x i d e . The p h e n o l i c s were t r e a t e d i n d i v i d u a l l y i n c o n c e n t r a t i o n s r a n g i n g up t o 1 gp l i n aqueous s o l u t i o n s i n a b a t c h r e c i r c u l a t i o n s y s t e m . Compounds s t u d i e d were p h e n o l , 0 - c r e s o l , p - c r e s o l , 2 , 3 - X y l e n o l , 3 , 4 - X y l e n o l , r e s o r c i n o l and c a t e c h o l . The e f f e c t s o f v a r i a t i o n i n i n i t i a l c o n c e n t r a t i o n and a p p l i e d c u r r e n t were s t u d i e d . S o l u t i o n s were a n a l y z e d p r i m a r i l y by gas c h r o m a t o g r a p h y and by t o t a l o r g a n i c c a r b o n a n a l y z e r . The e f f e c t o f t h e o x i d a t i o n p r o c e s s on t he remova l o f c h e m i c a l oxygen demand ( C . O . D . ) and b i o l o g i c a l oxygen demand ( B . O . D . ) was d e t e r m i n e d i n a few c a s e s . O x i d a t i o n o f t h e p h e n o l i c s was f a v o u r e d by i n c r e a s i n g t h e c u r r e n t d e n s i t y and d e c r e a s i n g t h e i n i t i a l c o n c e n t r a t i o n . Comp le te o x i d a t i o n o f t he o r g a n i c c a r b o n i n t he p h e n o l i c s was f ound t o be d i f f i c u l t a l t h o u g h c o m p l e t e remova l o f t h e p h e n o l i c compound was a c h i e v e d i n s e v e r a l c a s e s . No d i r e c t c o r r e l a t i o n was found between t h e r a t e o f a n o d i c o x i d a t i o n on Pb02 and t h e s t r u c t u r e o f t h e p h e n o l i c compounds. A m i x t u r e o f f i v e m o n o h y d r i c p h e n o l s w h i c h were p r e s e n t a t c o n c e n t r a t i o n s r e p o r t e d as t y p i c a l f o r c o a l c o n v e r s i o n w a s t e w a t e r s was a l s o o x i d i z e d . Up t o 95% o x i d a t i o n o f t h e p h e n o l i c s was o b t a i n e d . A gas c h r o m a t o g r a p h / m a s s s p e c t r o m e t e r a n a l y z e r was used t o examine t h e p r o d u c t s o f a n o d i c o x i d a t i o n i n t y p i c a l r u n s . R e a c t i o n r o u t e s were p o s t u l a t e d f o r t h e o x i d a t i o n p r o c e s s . Compar i sons o f t h e e x p e r i m e n t a l r e s u l t s w i t h a mass t r a n s f e r model a r e p r e s e n t e d f o r a few e x p e r i m e n t s . i i TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES v i LIST OF FIGURES v i i ACKNOWLEDGEMENTS x CHAPTER 1 INTRODUCTION 1 1.1 Phenolics in coal processing effluents 1 1.2 Typical composition of coal conversion wastes 1 1.3 Available methods of treatment of phenolic wastes and in t e r e s t for t h i s study 3 2 LITERATURE SURVEY 5 2.1 General concepts 5 2.2 L i t e r a t u r e review on the electrochemical oxidation of selected phenolics 8 2.2.1 Anodic oxidation of phenol 9 2.2.2 E l e c t r o l y t i c oxidation of cresols 9 2.2.3 Anodic oxidation of Xylenols 12 2.2.4 Anodic oxidation of dihydric phenols 13 2.2.5 Oxidation of phenolic mixtures 14 2.3 Importance of choice of experimental conditions ... 15 2.3.1 Nature of electrode materials 15 2.3.2 Current density-anode potential 16 2.3.3 Nature of the e l e c t r o l y t e 18 2.3.4 E f f e c t of pH 18 2.3.5 ^Cell configuration 19 3 BASIS AND EXTENT OF EXPERIMENTAL STUDY 21 i i i CHAPTER Page 4 EXPERIMENTAL APPARATUS AND METHODS 23 4.1 Apparatus 23 4.1.1 Description of equipment 23 4.1.2 Flow diagram of the apparatus 27 4.2 Experimental methods 27 4.2.1 Anodization process 27 4.2.2 Electrochemical oxidation of individual phenol ies 30 4.2.3 Experimental modifications made with c e r t a i n phenolies 31 4.2.4 Anodic oxidation of phenolic mixtures 33 4.3 Ana l y t i c a l techniques 33 4.3.1 Analysis of phenols 33 4.3.2 Total organic carbon analysis 34 4.3.3 B i o l o g i c a l oxygen demand analysis 35 4.3.4 Chemical oxygen demand analysis 35 4.3.5 GC/MS Analysis 36 4.3.6 Accuracy and r e p r o d u c i b i l i t y 37 5 RESULTS AND DISCUSSION 39 5.1 Oxidation of individual phenolies 39 5.1.1 Anodic oxidation of phenol 39 5.1.2 Oxidation of p-cresol 42 5.1.3 Oxidation of 0-cresol 46 5.1.4 Oxidation of 2,3-Xylenol 48 5.1.5 Oxidation of 3,4-Xylenol 52 5.1.6 Oxidation of resorcinol 56 5.1.7 Oxidation of catechol 62 5.2 Comparison of performance of d i f f e r e n t phenolics .. 66 5.2.1 E f f e c t of v a r i a t i o n of i n i t i a l concentration 66 5.2.2 E f f e c t of v a r i a t i o n of applied current 69 5.2.3 Substituent effents 69 5.2.4 E f f e c t of d i f f u s i v i t y 72 5.3 Oxidation of phenolic mixtures 74 5.4 Reaction e f f i c i e n c y f o r a ty p i c a l run 79 iv CHAPTER Page 5.5 Cell voltage 80 5.6 Comparison of experimental r e s u l t s with mathematical models 82 6 CONCLUSIONS 86 7 FURTHER WORK 88 NOMENCLATURE 90 BIBLIOGRAPHY 93 APPENDIX 1 S p e c i f i c a t i o n of a u x i l l i a r y equipment and materials ... 97 2 Experimental data 105 3 Mathematical model 162 4 Calculations 169 5 Relevant data 176 v LIST OF TABLES TABLE Page I Composition of synthetic coal conversion wastewater 2 II Comparison of half wave potential values 10 III E f f e c t of current density and type of e l e c t r o l y t e on C.O.D. removal using Pb02 anode 17 IV Fundamental s p e c i f i c a t i o n s of the e l e c t r o l y t i c c e l l ... 25 V D i f f u s i v i t i e s of the phenolic compounds in water 73 VI Results obtained from the oxidation of mixture of monohydric phenols (run 8-3) 78 VII V a r i a t i o n of Av 81 Appendix-2 Experimental data tables f o r : Run 1-1 to Run 1-5 Anodic oxidation of phenol 105-111 Run 2-1 to Run 2-5 Anodic oxidation of p-cresol 112-116 Run 3-1 to Run 3-5 Anodic oxidation of 0-cresol 117-121 Run 4-1 to Run 4-5 Anodic oxidation of 2,3-Xylenol 122-126 Run 5-1 to Run 5-5 Anodic oxidation of 3,4-Xylenol 127-131 Run 6-1 to Run 6-5 Anodic oxidation of resorcinol 132-136 Run 7-1 to Run 7-5 Anodic oxidation of catechol 137-145 Run 8-1 to Run 8-3 Anodic oxidation of mixture of monohydric phenols of i n t e r e s t 146-151 Run 9-1 to Run 9-8 Anodic oxidation f o r GC/MS analysis 152 Appendix-3 A-l Theoretical 2,3-Xylenol f r a c t i o n a l conversion vs time f o r a mass transfer c o n t r o l l e d batch system 167 A-2 Theoretical resorcinol f r a c t i o n a l conversion vs time f o r a mass transfer c o n t r o l l e d batch system 168 vi LIST OF FIGURES FIGURE Page 1 Components of a simple e l e c t r o l y t i c c e l l 5 2 Side view of the general undivided c e l l arrangement (N.T.S.) Components of the e l e c t r o l y t i c c e l l 24 3 Experimental setrup f o r anodic oxidation 26 4 Various components of the c e l l 26 5 Flow diagram of the apparatus 28 6 Deposition of condensation product during the oxidation of catechol 32 7 Cone, e f f e c t on % phenol oxidized at 10 A 40 8 Current e f f e c t on % phenol oxidized (1 g/1 runs) 40 9 E f f e c t of cone, on rate of oxidation of organic carbon in phenol at 10 A 43 10 Cone, e f f e c t on % p-cresol oxidized at 10 A 44 11 Current e f f e c t on % p-cresol oxidized (1 g/1 runs) 44 12 E f f e c t of cone, on rate of oxidation of organic carbon in p-cresol 45 13 Cone, e f f e c t on % o-cresol oxidized at 10 A 47 14 Current e f f e c t on % o-cresol oxidized (1 g/1 runs) 47 15 E f f e c t of cone, on rate of oxidation of organic carbon in o-cresol 49 16 Cone, e f f e c t on % 2,3-Xylenol oxidized at 10 A 50 17 Current e f f e c t on 2,3-Xylenol oxidized (1 g/1 run) 51 18 E f f e c t of cone, on rate of oxidation of organic carbon in 2,3-Xylenol at 10 A 53 19 E f f e c t of current on rate of oxidation of organic carbon in 2,3-Xylenol (1 g/1 runs) 54 20 Cone, e f f e c t on % 3,4-Xylenol oxidized at 10 A 55 v i i FIGURE Page 21 Current e f f e c t on % 3,4^Xylenol oxidized (1 g/1 runs) .. 55 22 Cone, e f f e c t on % resorcinol oxidized at 10 A 58 23 Current e f f e c t on % resorcinol oxidized (1 g/1 runs) .. 59 24 Ef f e c t of cone, on rate of oxidation of organic carbon i n resorcinol at 10 A 60 25 E f f e c t of current on rate of oxidation of organic carbon in resorcinol (1 g/1 runs) 61 26 E f f e c t of cone, on rate of oxidation of organic carbon i n catechol at 10 A 63 27 E f f e c t of current on rate of oxidation of organic carbon in catechol (1 g/1 runs) 64 28 Va r i a t i o n of f i n a l % oxidized with i n i t i a l concentration of phenolics at 10 A 67 29 Vari a t i o n of i n i t i a l rate with i n i t i a l concentration at 10 A 68 30 Vari a t i o n of f i n a l % oxidized with applied current (1 g/1 runs) 70 31 Vari a t i o n of i n i t i a l rate of oxidation with applied current (1 g/1 runs) 71 32 E f f e c t of nature of phenolics on % oxidation (10 A, 2 hrs; run 8-1) 75 33 E f f e c t of nature of phenolics on % oxidation (10 A, 3 hrs; run 8-2) 76 34 E f f e c t of nature of phenolics on % oxidation (10 A, 5 hrs; run 8-3) 77 35 GC/MS analysis of f i n a l product from phenol oxidation (run 9-1) 154 36 GC/MS analysis of f i n a l product from p-cresol oxidation (run 9-3) 155 37 Mass spectrum showing the presence of 4-Hydroxy-4-Methyl- 2,5-Cyclohexadiene-l-one 156 38 GC/MS analysis df f i n a l product from o-cresol oxidation (run 9-2) 157 v i i i FIGURE Page 39 GC/MS analysis of f i n a l product from 2,3-Xylenol oxidation (run 9-4) 158 40 GC/MS analysis of f i n a l product from 3,4-Xylenol oxidation (run 9-5) 159 41 MS confirmation of traces of 2,3-Dimethyl hydroquinone or isomer 160 42 GC/MS analysis of f i n a l product of oxidation of mixture and Xylenols (run 9-8) 161 Appendix 3 A-l Schematic representation of a multipie pass system 162 ix ACKNOWLEDGEMENTS I wish to place on record my sincere gratitude to Prof. Paul Watkinson, under whose guidance and encouragement t h i s work was c a r r i e d out. My grateful acknowledgement i s due to my husband, Mohan Chettiar for his suggestions and thoughtfulness. Thanks are due to our parents f o r t h e i r cooperation, patience and s a c r i f i c e s . I would l i k e to express my appreciation f o r the assistance of Prof. Colin Oloman and f o r his sincere i n t e r e s t . Also acknowledged are the s t a f f of the Chemical Engineering department and Environmental Engineering Laboratory for t h e i r enthusiastic assistance. Further thanks are due to Tim Ma for helping with GC/MS an a l y s i s , Mrs. Christine Lee f o r typing the manuscript, Mrs. Bea Kirzsan and my husband f o r the dr a f t i n g of fi g u r e s . x 1. CHAPTER 1 INTRODUCTION 1.1 Phenolics in coal processing e f f l u e n t s The term "phenols" i n waste water includes not only phenol (CgHgOH) but an assortment of organic compounds containing one or more hydroxyl groups attached to an aromatic r i n g . Phenols have a high p o l l u t i o n potential due to t h e i r t o x i c i t y . Permissible l e v e l s of phenols i n i n d u s t r i a l wastes have been established by the U.S. Environmental Protection Agency (EPA). These guidelines e s t a b l i s h phenol l e v e l s of 0.1 mg/l for the Best P r a c t i c a l Control Technology Currently Available f o r 1977, and 0.02 mg/l f o r the Best Available Control Technology Economically Achievable f o r 1983 [1]. Coal g a s i f i c a t i o n , coal l i q u e f a c t i o n and coke oven plants have phenolic-waste problems. It has been reported that 60 to 80 percent of the total organic carbon (T0C) in the organic contaminants from coal conversion systems i s phenolic in nature [2]. 1.2 Typical composition of coal conversion wastes Wastewater composition appears to be r e l a t i v e l y independent of process technology and coal feed in the case of phenolic constituents [2]. For p o l l u t i o n control studies, i t i s convenient to define a simulated wastewater which approaches the composition of real coal conversion waste- waters from various processes. Table I provides a ty p i c a l composition of such a synthetic wastewater [3] as might ar i s e from the condensate (gas TABLE I COMPOSITION OF SYNTHETIC COAL CONVERSION WASTEWATER COMPOUND 1. Phenol 2 . Resorc ino l 3. Catechol STRUCTURAL FORMULA OH <§> OH OR OH CONCENTRATION mg/l 2000 1000 1000 4 . A c e t i c Ac id 5. O-Cresol 6. P-Creso l 7. 3 , 4 -Xy leno l 8 . 2 , 3 - X y l e n o l 9. P y r i d i n e 10. Benzoic Ac id 11 . 4 - E t h y l p y r i d i n e 12. 4 -Methy lca techo l CH3C00H OH OH <§> CH. GH„ CH, CH3 3 1CH3 C H 3 COOH C 2 H 5 # OH: OH: 400 400 250 250 250 120 100 100 100 CH„ Only the l i s t o f compounds present i n concen t ra t i ons of 100 mg/l or above i s presented here . The ac tua l composi t ion o f the s y n t h e t i c waste can be found i n Appendix 5. 3. liq u o r ) of a coal g a s i f i e r . For example, the Synthane process produces about 0.4 - 0.6 tons of condensate water of t h i s approximate composition per ton of coal g a s i f i e d [3]. 1.3 Available methods of treatment of phenolic wastes and i n t e r e s t f o r t h i s study The choice between recovery OH destruction of phenolics can be made on the basis of economics. The value of the recovered product should be balanced against both the cost of recovery and the cost of p o l l u t i o n control systems required f o r the destruction of the chemicals. Recovery i s a p p l i - cable only to concentrations i n the percentage range and to flows in excess s of about 50 G.P.M. [1]. Although recovery becomes less c o s t l y as the concentration increases, recovery processes may produce streams which require e f f l u e n t treatment. Treatment processes include i n c i n e r a t i o n techniques, adsorption on activated carbon,various chemical oxidation methods, b i o l o g i c a l oxidation and ion exchange re s i n processes. A review of a l t e r n a t i v e methods of phenol wastewater control [4] and cost comparison between various treatment processes cu r r e n t l y being used [5], reveals that b i o l o g i c a l treatment i s the best available choice to degrade these wastes. However, even i n an - ideal b i o l o g i c a l environment, many operating problems have been associated. Besides, the a b i l i t y of t h i s process to produce e f f l u e n t phenol concen- tr a t i o n s of less than 500 ppb on a consistent basis i s questionable and hence i s not recommended i f phenol removal i s the primary concern [4]. For example, in a series of test runs with phenol i n l e t concentrations ranging from 450 to 4800 ppm [3], i t was found that as the phenol i n l e t concentration was increased, a breakthrough point was reached where 4. additional i n l e t phenol resulted in a s i g n i f i c a n t increase in the e f f l u e n t phenol concentration. New methods for treating phenolic e f f l u e n t s have been attempted [6,7] because of the i n t e n s i t y of the p o l l u t i o n problem and the highly r e s t r i c t i v e future p o l l u t i o n control standards expected. Dephenolization of these e f f l u e n t s by electro-oxidative methods has been attempted [81. Investigation of the f e a s i b i l i t y of anodic oxidation of the major phenolics in Table I i s the subject of the present study. The work i s r e s t r i c t e d to the oxidation of the phenolics present in concen- tratio n s equal to or greater than 250 mg/l in the synthetic waste. This research was motivated by the r e s u l t s of previous work [9] that revealed the p o s s i b i l i t y of e s s e n t i a l l y complete removal of phenol by e l e c t r o - oxidation under c e r t a i n conditions. 5. CHAPTER 2 LITERATURE SURVEY 2.1 General concepts An electrochemical reactor i s a device i n which chemical reactions can be performed d i r e c t l y by the input of e l e c t r i c a l energy. The basic components and fundamental operation of an electrochemical process can be v i s u a l i z e d from F i g . 1. d.c. power supply electrolyte solution diaphragm Fig. 1 Components of a simple electrochemical reactor 6. The anode and cathode are immersed in the e l e c t r i c a l l y conducting e l e c t r o l y t e . The electrodes are connected outside the bath to the terminals of a d.c. power supply. When an emf of s u f f i c i e n t magnitude i s applied, electron t r a n s f e r occurs between the electrodes and the e l e c t r o l y t e . This r e s u l t s in a flow of e l e c t r i c i t y in the external c i r c u i t and chemical reaction at each electrode. In a chemical sense, oxidation occurs at the anode and reduction at the cathode. The diaphragm in i t s simple form acts as a kind of f i l t e r . Consider a general r e v e r s i b l e electrode reaction at equilibrium r 0 + ze R 0) r ' o 0 represents the oxidised form and R represents the reduced form of the same substance. In the case, when r r = r 0 , there i s no net current flow. The rate of the forward reaction, r r i s given by r r = W = k c C o where i c i s the p a r t i a l current density f o r the cathodic reaction, k c i s the electrochemical rate constant and C Q i s the concentration of 0 at the point of discharge. S i m i l a r l y , ro • W - ka <Y where rQ i s the rate of oxidation, i f l i s the p a r t i a l current density f o r the anodic reaction, k, and C are the corresponding electrochemical rate a i constant and concentration of R respectively. 7. The current density, i i s given by the modulus of the difference between i„ and i . The rate constants k and k, can be expressed in terms c a c a of the electrode potential [10 ] , by the formulae .0 . _ azFlV* k a = k o e x p (l-a^F|V , ( 3 ) where k° and k° are rate constants referenced to a p a r t i c u l a r electrode c a r potential under standard conditions and a i s a constant known as the charge transfer c o e f f i c i e n t . Equations (2) and (3) imply that a f r a c t i o n of the electrode potential |V | drives the forward reaction and the remainder (1-a)|V | drives the reverse reaction. As the electrochemical rate constant depends exponentially on the electrode potential as well as the temperature, adjustment of the potential would lead to a wide v a r i a t i o n of reaction rate. * * The tot a l e l e c t r o l y s i n g voltage, AV which i s the sum of V 3 and V a c and the to t a l ohmic drop i s easier to measure than the anode potential * * * * V, or. cathode potential V . In order to measure V, or V . a reference a a a c electrode has to be connected at the surface of the anode or cathode and the difference in potential between the electrode under consideration and the solution should be measured. The total e l e c t r o l y s i n g voltage i s of importance because the operating cost of the e l e c t r o l y t i c process w i l l depend on i t s power requirement, which i s d i r e c t l y related to the voltage drop through the c e l l at a given current density. Besides, i f the potential of the electrode i s in the r i g h t range, many side reactions such as the anodic formation of oxygen and cathodic formation of hydrogen can occur 8. in aqueous solutions, r e s u l t i n g in the loss of current e f f i c i e n c y . The concentration of a reactant A, at the surface of the electrode i s related to both the rate of the electrochemical reaction and the rate of mass transf e r from the bulk of the solution to the electrode surface, Mass transf e r flux=k m(C/\^ - ) (4) where k.m i s the mass t r a n s f e r - c o e f f i c i e n t . For a given species, km i s a function of the electrode configuration and f l u i d dynamics. For design purposes, empirical and t h e o r e t i c a l expressions f o r t r a n s f e r c o e f f i c i e n t s can be obtained from standard texts [ 1 1 ] . In very d i l u t e systems, i t might be expected that the rate of electrochemical reaction i s dictated by mass transfer processes. At t h i s l i m i t i n g current condition, the current e f f i c i e n c y w i l l tend to be low. There must therefore be a p r a c t i c a l l i m i t of concentrations below which electrochemical oxidation would become very i n e f f i c i e n t . Some coupling of electrochemical and chemical or biochemical processes might be of i n t e r e s t in these s i t u a t i o n s . 2.2 L i t e r a t u r e review on the electrochemical oxidation of selected phenolies A substantial l i t e r a t u r e e x i s t s in t h i s f i e l d . This l i t e r a t u r e covers a v a r i e t y of anodes, current d e n s i t i e s , e l e c t r o l y t e s and other operating conditions. And not unexpectedly, a wide range of oxidation products have been obtained. The a v a i l a b l e information concerning the l a s t stages of the anodic oxidation of phenolics to open chain compounds or eventually to carbon dioxide i s very l i m i t e d because most oxidation studies were aimed at 9. synthesis of compounds and e l u c i d a t i o n of the reaction mechanisms rather than at destruction of the organics for waste treatment. 2.2.1 Anodic oxidation of phenol Early studies of the anodic oxidation of phenol were done by Fichter and co-workers [12-16]. They reported that phenol oxidation at a lead dioxide electrode in sulphuric acid media r e s u l t s in the formation of hydroquinone, p-benzoquinone, catechol, maleic a c i d , monophenyl ether of pyrocatechol, 2,4' dihydroxy diphenyl and 4,4' dihydroxy diphenyl. The f i n a l products obtained were oxalic a c i d , formic a c i d , carbon monoxide and carbon dioxide. A few suggestions have been made about the mechanism of the oxidation [12]. In more recent publications [15-20] the presence of diphenyl derivatives has not been reported. 2.2.2 El e c t r o l y t i c ; oxidation of cresols The r e l a t i v e ease of oxidation of various phenolic compounds depends on the substituents present on the r i n g . The half wave potential value i s an i n d i c a t i o n of the e f f e c t of adding d i f f e r e n t substituent groups to the phenolic r i n g . The half wave p o t e n t i a l , {E1 ) i s defined as the potential on the polarographic curve when the current i s equal to one half the mass transfer l i m i t i n g current. When electron-donating substituents l i k e OH and a l k y l groups are present, the E^ i s s h i f t e d towards more negative values and t h i s should be accompanied by an increase in the ease of oxidation. The e f f e c t of the substituents i s greatest at the ortho and para po s i t i o n s . The E1 values f o r the phenols of i n t e r e s t are presented in Table II. Based on the half-wave potential values, TABLE II COMPARISON OF HALF WAVE POTENTIAL VALUES Name of phenolic compound £-2 v o l t Conditions of measurement - Reference Phenol p-Cresol O-Cresol Catechol Resorcinol Hydroquinone 2,4-Xylenol 3.4- Xylenol 3.5- Xylenol 0.633 0.543 0.556 0.139 0.490 0.018 0.459 0.513 0.587 Acetate buffer pH 5.6; graphite electrode wax-impregnated graphite anode Acetate buffer pH 5.6; graphite electrode [21] [21] [21] [25] [25] [25] [21] [21] [21] Note: A l l half-wave potentials are reported with reference to the S.C.E. p-cresol should be more susceptible to anodic oxidation than phenol [22]. p-cresol oxidation at polished lead electrodes (PLE) in sulphuric acid media in a c e l l with a diaphragm [23] resulted in the following products detected by n.m.r an a l y s i s . OH p-cresol (£) CH 3 4-Hydroxy-4methylcyclohexa-2, 5-dienone (ft) 40% 20% HO CH 3 0 p-Benzoquinone (ft) 33% 0 0 Methyl-p-benzoquinone (jjf 3 7% 0 Extraction of the lead anode with hot methylene chloride yielded a f t e r evaporating a mixture of coupling products of the type; OH CH 3 OH OH t£) n = 0,1,2 etc. CH 3 n OH Similar e l e c t r o l y s i s of 0-cresol [23] yi e l d e d OH 0-cresol t O j C H 3 12% 0 Methyl-p-benzoqui none C^T™3 75% 0 OH Methyl hydroquinone (0 3 13% OH 12. Extraction of the anode with hot methylene choride yielded tars which n.m.r indicated to be coupling products of O-cresol. In a study of the e f f e c t of anode material, PbOg-C anode (prepared by anodic p r e c i p i t a t i o n of lead dioxide on a carbon rod) i s reported to behave in a s i m i l a r manner to the PLE with respect to the rate of conversion and % y i e l d of c e r t a i n products. An increase in i n i t i a l concentration of p-cresol resulted in the production of larger percentages of coupling products on a PLE [23]. In a comparison of anodic oxidation of cresols [24], p-cresol i s reported to have a larger % conversion (96%) than O-cresol (90%) under s i m i l a r conditions. On the basis of c y c l i c voltammetric studies on a lead dioxide anode [23] i t was concluded that the phenol i s oxidised chemically by lead dioxide on the anode surface, and the reduced lead species thus formed i s oxidised (via d i r e c t charge transfer) r a p i d l y back to Pb (IV), as i t i s part of the anode i t s e l f . 2.2.3 Anodic oxidation of Xylenols Electrooxidation of 2,4-Xylenol and 2,6-Xylenol under conditions reported for the cresols with a PLE has been reported [23]. The following products were obtained from 2,4-Xylenol and 2,6-Xylenol. OH OH OH. (J^r C H3 (2,2'-dihydroxy-3,3'5,5 ,-tetramethyl biphenyl) H3C CH 3 0 2,4-Xylenol (4-hydroxy-2,4-dimethylcyclohexa-2,5-dienone) HO CH. 3 13. 2,6-dimethyl-p-benzoquinone) H3C CH'3 o^f)r(5^:0 (3,3' ,4,4'-tetramethyldiphenoquinone) Although 2,3-Xylenol and 3,4-Xylenol are the Xylenols of greatest importance in coal wastewaters, no data are available on anodic oxidation of these compounds. However, corresponding products analogous to the above mentioned ones can be expected. 2.2.4 Anodic oxidation of dihydric phenols As evidenced by their half-wave potentials [Table II], the dihydric phenols, resorcinol and catechol are easier to oxidise than phenol itself. Nash, Skauen and Purdy [25] report a similar trend in half-wave potential values of dihydric phenols as obtained in reference 26. It has been suggested [26] that during the oxidation of resorciinbl, radicals are generated which then may polymerize and deposit on the electrode. The kinetics and mechanism of coulometric oxidation of catechol at controlled potential have been investigated [27]. The oxidation is said to proceed as a two-electron process: .e 0 - C6H4(0H)2 — 0 - C6H402 + 2H+ + 2e (5) It has been pointed out by several investigators [28,29] that - O-benzoquinone in aqueous solutions decomposes giving catechol and 2-hydroxyquinone or 4-hydroxyquinone, the stoichiometric course of which i s given by Eq. (6). 2C 6H 40 2 + H 20 - C 6H 4(0H) 2 + C 6H 30 2(0H) (6) The l a t t e r product (2-hydrpxyquinone or 4-hydroxyquinone) i s said to condense r a p i d l y giving a substance of high molecular weight and unknown chemical composition. The reaction i s reported [28,29] to be accelerated both by hydroxyl ions and excess amounts of catechol at pH values from 5 to 8. However, at low pH conditions, the c a t a l y t i c e f f e c t of catechol i s n e g l i g i b l e [27]. 2.2.5 Oxidation of phenolic mixtures A number of electrode reactions are possible when several phenolics are present in the reactant solution or, when d i f f e r e n t phenols are produced as intermediates during the oxidation. It i s of i n t e r e s t to know which electrode reactions are favoured. An analysis of the e f f e c t of potential and electrode k i n e t i c parameters on reaction s e l e c t i v i t y and on current and rate d i s t r i b u t i o n has been made for plug-flow and back mixed electrochemical reactors [30] in which a sequence of reactions takes place, however a p p l i c a t i o n of such an analysis to the present case i s a complex mathematical problem. In an attempt [8] to oxidise a phenol and trichlorophenol mixture i t was found that both constituents were attacked at about the same rate. Otherwise there i s l i t t l e information on the oxidation of phenolic mixtures such as those a r i s i n g in coal conversion e f f l u e n t s . 15. 2.3 Importance of choice of experimental conditions The factors which determine the rate and product d i s t r i b u t i o n of the anodic oxidation of phenolics a t a given temperature and flowrate are as follows. ( i ) nature of anode material ( i i ) current density - anode potential ( i i i ) nature of the e l e c t r o l y t e (iv) e f f e c t of pH (v) c e l l configuration The e f f e c t s of these f a c t o r s are as follows. 2.3.1 Nature of electrode materials Gladisheva and Lavrenchuk [15] have compared the performance of d i f f e r e n t anode materials such as n i c k e l , smooth platinum, graphite and ele c t r o deposited lead dioxide. Their experiments showed that under the same operating conditions, the highest oxidation rate occurred on the lead dioxide electrode. The lead dioxide anode was found to be superior to others in terms of s t a b i l i t y and ease of operation. The same r e s u l t was obtained by Fioshin et al [20] when comparing platinum and lead dioxide electrodes in the study of electrochemical oxidation of phenol to quinone. It has been suggested that the adsorptive powers of the electrodes towards the organic substrate plays a major r o l e in addition to the overpotential of the electrodes. Sucre and Watkinson [31] reported that electrodeposited lead dioxide i s a better anode than anodised lead shot in terms of phenol oxidation and corrosion resistance f o r phenolic waste treatment a p p l i c a t i o n s . A packed bed anode i s a good choice for oxidation of d i l u t e phenolic solutions because i t provides larger electrode surface areas per unit c e l l 16. volume compared to simple f l a t plate electrode [32]. However, the use of very fin e p a r t i c l e s which would give large external surface areas might lead to c e l l blockage in applications where so l i d s are present in the wastewater or are produced by the oxidation. Also spatial electrode potential variations in packed bed c e l l s can be so large that loss of reaction s e l e c t i v i t y w i l l r e s u l t . Considering the nature of electrodeposited lead dioxide, methods used for the electrodeposition of PbC^ on i n e r t substrate from e l e c t r o l y t e s containing lead have been summarized in reference [33]. Electrodeposited Pbn2> uniformly coated on a graphite substrate has been recommended [19,31] for t h i s case. These anodes are being commercially made by P a c i f i c Engineering and Production Co. of Nevada. 2.3.2 Current density - anode potential From a study of the e f f e c t of d i f f e r e n t variables on phenol oxidation, 2 i t was concluded that in the range of 50-2000 A/m , the current density was the strongest rate determining factor [15]. The re s u l t s are given in Table I I I . From the table i t can be seen that, s t a r t i n g with 466 mg/l of chemical oxygen demand (C.O.D.) at a current density of 50 A/m , the f i n a l C.O.D. was 420 mg/l aft e r 5 h, whereas at 2000 A/m2 the C.O.D. dropped to 30 mg/l in 1 hour. Similar effects of current density have been reported elsewhere [31]. Experiments may be performed under a constant anode potential using a potentiostat. But i t appears to be much easier to control the current density. TABLE III EFFECT OF CURRENT DENSITY AND TYPE OF ELECTROLYTE ON C.O.D. REMOVAL USING Pb0 2 ANODE Current density A/m2 E l e c t r o l y t e Time of E l e c t r o l y s i s (h) Final C.O.D. (mg/l of 0 2) 50 I 5 307 II 5 420 500 I 3 90 II 5 120 1000 I 1 30 II 2 75 2000 I 0.5 0 II 1.0 30 Notes: I n i t i a l phenol concentration = 200 mg/l I n i t i a l CO. ,D. concentration = 466 mg/l of 0 2 E l e c t r o l y t e I - 1 g/1 NaCl, 1. 5 g/1 Na 2S0 4 E l e c t r o l y t e II - 3 g/1 Na 2S0 4 18. 2.3.3 Nature of the electrolyte Chloride salts have been used as electrolytes in phenolic waste treatment studies [Table III]. This electrolyte gives rise to undesirable chlorination products. As chlorinated phenols are more objectionable than phenol itself, it appears desirable to use an inert supporting electrolyte such as sodium sulphate. From the point of view of reduction in C.O.D., however sodium chloride would be preferable as seen in Table III. Other electrolytes, such as Mrfi^Oj,NH^ and H2SO4 have also been " tested using a packed bed graphite electrode [16]. Sucre [31] showed that the rate of phenol oxidised is unchanged by increasing the conductivity of the electrolyte. 2.3.4 Effect of pH From the relationship between half wave potential and pH for the oxidation of phenol [34] it can be expected that a high pH would make phenol more easily oxidizable. Due to the ability of phenols to exist in the ionized or unionized form depending on the pH of the solution, pH is believed to play a major role in the mechanism of electron transfer during the oxidation process. No definitive results could be found in the reviewed literature about the effect of pH on further oxidation of intermediate products. However Sucre and Watkinson [31] report that oxidation of phenol was more rapid under acidic conditions but the oxidation of the total organic carbon was favoured by alkaline conditions. 2.3.5 Cell configuration In the study of electrochemical oxidation of phenol for hydroquinone production, Covitz [17] reported that the reaction can be co n t r o l l e d to produce hydroquinone at over 90% y i e l d in an undivided c e l l in acid media. The mechanism proposed for the e l e c t r o l y t i c process i s as follows [35]. Anodic reaction (7) Cathodic reaction (8) + ^ Overall reaction (9) From t h i s reaction scheme, i t is obvious that i n an undivided c e l l p-benzoquinone can be reduced at the cathode to produce hydroquinone. If the process i s ca r r i e d out in a divided c e l l , p-benzoquinone would not contact the cathode and therefore no hydroquinone would be produced. Another i n t e r e s t i n g possible reaction in an undivided c e l l is the oxidation of hydroquinone back to p-benzoquinone, which would compete with the phenol for oxidation at the anode, thus lowering the current e f f i c i e n c y for phenol oxidation. Reference [31] provides valuable informa- tion in t h i s connection. Rates of phenol oxidation were reportedly s i m i l a r OH + H 20 - + 4 Ii + 4 e 0 ...+ [I ll + 2 H + 2 e o 0H OH in divided and undivided c e l l s . Even in terms of T.O.C. removal, no improvement was obtained with the divided c e l l even under optimum pH controlled conditions provided by an anionic membrane. Thus i t appears that there would be no p a r t i c u l a r advantage in choosing divided c e l l operation. Due to the lack of av a i l a b l e information about the e f f e c t of c e l l configuration factors on the anodic oxidation of other phenolics of i n t e r e s t , these e f f e c t s have been discussed f o r phenol (C5H5OH) alone. Similar e f f e c t s may be expected for other phenolics. CHAPTER 3 BASIS AND EXTENT OF EXPERIMENTAL STUDY The aim of th i s work was to study the f e a s i b i l i t y of electrochemical oxidation of the major phenolics in coal processing e f f l u e n t s . Experimental studies of the anodic oxidation of phenol, ortho c r e s o l , para c r e s o l , 2,3-Xylenol, 3,4-Xylenol, r e s o r c i n o l , and catechol are reported. For each of the phenolics, the e f f e c t of v a r i a t i o n of i n i t i a l concentration and applied current was studied by r e c i r c u l a t i n g solution from a feed tank through a packed bed c e l l . The e f f e c t s of the above variables are reported in terms of the fr a c t i o n a l oxidation of both the phenolics and the total organic carbon (T.O.C.) versus time. As this work is oriented towards waste treatment, the ef f e c t s of the oxidation on chemical oxygen demand (C.O.D.) and b i o l o g i c a l oxygen demand (B.O.D.) have been reported in selected cases. Gas chromatograph/ Mass spectrometer analysis was used to i d e n t i f y the products of oxidation and to obtain the percentages of the oxidation products from each of the phenolics studied. Synthetic mixtures of phenolics of in t e r e s t made up by mixing the monohydric phenolics in proportions outlined in Table I were oxidized under chosen conditions to study t h e i r s u s c e p t a b i l i t y to oxidation in the mixture. The nature and quantities of oxidation products from the mixture are reported. Comparisons have been made among the various phenolics to correlate t h e i r behaviour in response to variations in applied current density and i n i t i a l concentration. F i n a l l y , the data from a few of the experimental 22. runs have been analyzed by comparison with mathematical models to understand the c o n t r o l l i n g factors governing the process. On the basis of a prior study on phenol [31] the following operating conditions were fixed during t h i s work. Anode Cell configuration Supporting e l e c t r o - l y t e Operating mode pH Period of oxidation Packed bed of electrodeposited lead dioxide, packing p a r t i c l e size - 0.7-1.1 m.m Undivided Sodium sulphate, 5g/l + H2SO4 2 i [ e l e c t r i c a l conductivity 8 x 10" {Q, c.m)~ ] Batch-recirculation system 2-3 2 hours CHAPTER 4 EXPERIMENTAL APPARATUS AND METHODS 4.1 Apparatus 4.1.1 Description of equipment The apparatus of Sucre [31] was retained with r e l a t i v e l y minor a l t e r a t i o n s . The side view of the general d i v i d e d - c e l l arrangement i s represented in Fig. 2. B a s i c a l l y , the c e l l consists of two f l a t plates, the anode and cathode current feeders. The anode current feeder i s in contact with the anodic packing, which i s contained in a 3 mm thick slo t t e d neoprene gasket separated from the cathode by a saran screen. The anolyte i n l e t is located at the bottom of the c e l l and the o u t l e t i s at the top. This f a c i l i t a t e s the e x i t of any gases produced during the e l e c t r o l y s i s . A commercial anode consisting of an electrodeposited lead dioxide coating on a graphite plate i s used as the anode current feeder. To prevent corrosion and eventual d e t e r i o r a t i o n of the lead dioxide layer, suitable precautions were taken at the point of introduction of the e l e c t r o l y t e through the graphite coated plate. The d e t a i l s of the i n l e t and o u t l e t connections adapted for t h i s purpose can be obtained from reference [31]. S p e c i f i c a t i o n s of the d i f f e r e n t elements of the c e l l are provided in Table IV. Fig. 3 shows the a u x i l i a r y equipment used in the process. The sequence of arrangement of the various layers in the c e l l displaying the various steps in c e l l assembly i s shown in Fig. 4. F i g . 2 ELECTROLYTE OUTLET ELECTROLYTE INLET a = 1.6 mm THICK NEOPRENE INSULATOR b = 1.6 mm THICK CATHODIC FEEDER P L A T E (S.S. 316) c = SARAN SCREEN TO HOLD ANODIC PACKING d = ANODIC PACKING - ELECTRODEPOSITED LEAD DIOXIDE PARTICLES SIZE 0.7 < dp < I.I mm e = ANODIC CURRENT FEEDER • LEAD DIOXIDE COATED GRAPHITE PLATE 3 cm THICK a b c d t a Side view of the general undivided c e l l arrangement (N.T.S.) TABLE IV FUNDAMENTAL SPECIFICATIONS OF THE ELECTROLYTIC CELL Dimensions of the anode and cathode chambers: Length = 38 cm Width = 5 cm Thickness = 3 mm Anode p a r t i c l e s - crushed PEPCON electrodeposited Pb0 2 p a r t i c l e s i z e - 0.7-1.1 mm weight - 250 gm Anode backing plate - PEPCON Pb02 coated graphite Protective screen - saran Cathode - 316 SS plate * P a c i f i c Engineering and Production Co. of Nevada Fig. 4 Various components of the c e l l 27. 4.1.2 Flow diagram of the apparatus A schematic flow diagram of the equipment is represented i n Fig. 5. Pump PU-1 del i v e r s the e l e c t r o l y t e from tanks T-1, T-2 or T-3 to the c e l l , the l i q u i d flow rate i s controlled by adjusting valve V-4 and is measured with rotameter R - l . Pressure and temperature at the entrance are measured in P - l . F i l t e r F - l , located at the outlet of the c e l l is used to c o l l e c t small p a r t i c l e s that might be car r i e d out of the c e l l and which might damage the flow c i r c u i t . This glass wool f i l t e r also f a c i l i t a t e s the gas l i q u i d separation in GL-1 by agglomerating small gas bubbles produced in the e l e c t r o l y s i s . In GL-1, a bed of glass beads provides extra agglomeration surface for the gas bubbles. I f the gas bubbles are car r i e d out with the l i q u i d flow, the progressive accumulation of gas in the e l e c t r o l y t e would a f f e c t the r e s u l t s of the experiments. The gas i s released at the top of GL-1 and the l i q u i d flows to the heat exchanger, H.E., where the heat generated in the c e l l i s removed by cooling water. From the heat exchanger, the l i q u i d flows back to the feed tanks T-1 or T-2. The c e l l was powered by a 1 KVA D.C power supply, P.S. (Appendix 1). The c e l l current was adjusted with the power-supply meter, and the voltage drop across the electrodes was measured by the voltmeter, V. 4.2 Experimental methods 4.2.1 Anodization process Before each experiment, the Pb02 was anodized by e l e c t r o l y s i s in 20% F^SO^ [36], to minimize changes i n a c t i v i t y over time. When the packing F i g . 5 F l o w d i a g r a m o f t h e a p p a r a t u s Legend f o r F i g . 5 ( P . S . ) - POWER SUPPLY (V) - VOLTMETER ( E . C . ) - ELECTROLYTIC CELL ( T - 1 ) - ELECTROLYTE TANK (CONTAINS PHENOLICS) (T-2) - ANODISATION TANK (T-3) - WATER TANK ( P U - 1 ) - PUMP ( R - l ) - ROTAMETER ( P - l ) - P R E S S . & TEMP. GAUGE ( F - l ) - F ILTER ( G L - 1 ) - G A S - L I Q . SEPARATOR ( V - l ) - ELECTROLYTE TANK SHUT OFF VALVE (V-2) - ANODISATION TANK SHUT OFF VALVE (V-3) - WATER TANK SHUT OFF VALVE (V-4) - ELECTROLYTE FLOW CONTROL VALVE (V-5) - LIQUID SAMPLE VALVE ( V - 6 ) - L IQUID LEVEL CONTROL VALVE IN GL-1 ( H . E . ) - HEAT EXCHANGER ( C - l ) - COOLING WATER INET (C-2) - COOLING WATER OUTLET (D) - DRAIN was anodized for the f i r s t time, a 12 h anodization time was allowed, but for successive experiments the standard anodization time was 1 h as recommended by Sucre [31]. To carry out the anodization, valves V-l and V-3 were shut o f f and tank T-2 was f i l l e d with 20°/ H 2S0 4. The D.C. power supply was turned on. Valve V-2 was opened and Pump PU-1 was started up simultaneously. The current was adjusted to 10A ( c d - 526.3 A/m ). About 21 of s o l u t i o n was drained o f f through D to purge the system and then r e c y c l i n g to tank T-2 was c a r r i e d on for 1 h. After anodization, the pump was shut o f f and simultaneously V-2 was shut o f f . Valve V-3 was opened and d i s t i l l e d water from T-3 was pumped through the c e l l . The c e l l was washed u n t i l the current dropped to p r a c t i c a l l y zero and the potential difference through the c e l l increased i n d i c a t i n g that e s s e n t i a l l y no e l e c t r o l y t e was contained in the c e l l . 4.2.2 Electrochemical oxidation of individual phenolics Before each run, the c e l l was thoroughly washed in d i s t i l l e d water. In Tank T-1, the e l e c t r o l y t e was prepared by adding a constant quantity (5g/l) of sodium sulphate and sulphuric acid (0.44 g/1). The desired amount of the phenolic compound was then dissolved in d i s t i l l e d water, added to T-1, and the tot a l volume was made up to 8 1. The tank was well agitated by means of a magnetic s t i r r e r . The i n i t i a l pH of the e l e c t r o l y t e was measured and readjusted i f necessary with NaOH or H2S0 4. The actual quantities of the phenolic compound added in each of the runs are recorded in Appendix 2. The valve V-l was opened and the required flow rate was set by - adjusting valve V-4. Immediately the current was set at the desired value. In order to provide some time for the s t a b i l i z a t i o n of flows and current, 3 1 of the e l e c t r o l y t e was discarded a f t e r passing through the c e l l , rather than re c y c l i n g i t to T - l . The e l e c t r o l y s i s time was measured from the moment the e l e c t r o l y t e was recycled to tank T - l . Samples of about t h i r t y ml were withdrawn through V-5 at in t e r v a l s of 15 min for a n a l y t i c a l purposes. The e l e c t r o l y s i s was car r i e d on for 2 h. Then the c e l l was washed with d i s t i l l e d water. In order to avoid the reduction of the PbO^ anode, the current was on while the washing step proceeded. 4.2.3 Experimental modifications made with c e r t a i n phenolics Among the phenolics studied, the p-cresol was insoluble in d i s t i l l e d water. Therefore a few p e l l e t s of NaOH were added to obt a i n the p - c r e s o l solution and a suitable quantity of H2S0^ was added to get the desired pH range. The xylenols were soluble only in hot water ( ̂  50°C). Hence the e l e c t r o l y t e was made up to 8 1 with hot water. The cooling water to the heat exchanger was c a r e f u l l y lowered during the anodic oxidation of the Xylenols because in the higher concentration runs (1 g/1 runs), the xylenols came out of the solution when the e l e c t r o l y t e was cooled during the run. With the c r e s o l s , 2,3-Xylenol and catechol as there was excessive foaming, the e l e c t r o l y t e began to overflow from GL-1. To avoid the loss of e l e c t r o l y t e , a two-holed rubber stopper provided with an a i r vent was used to cover GL-1. From the stopper, a tube was connected to T - l , to recycle the overflowing l i q u i d . During experiments with catechol, in addition to excessive foaming, a brownish black, insoluble condensation product was formed in runs with i n i t i a l concentrations equal to or greater than 0.5 g/1. This product blocked the glass wool in the f i l t e r , decreased the voidage in the packed bed anode, caused problems in the gas-liquid separator and resulted in small values for maximum attaina b l e flow rates. The saran screen was also blocked as can be seen in Fig. 6. Therefore, the screen had to be changed a f t e r the catechol runs. To overcome the problem of excessive foaming and pushing Fig. 6 Deposition of condensation product during the oxidation of catechol up of the glass beads from GL - 1 , glass beads were replaced by glass wool and the i n l e t and o u t l e t of the e l e c t r o l y t e to GL-1 were interchanged. 4.2.4 Anodic oxidation of phenolic mixtures Mixtures of phenol, cresols and xylenols were made up by weighing out the phenolics in the same proportions as they are found in synthetic coal conversion wastewaters (Table I) and di s s o l v i n g them i n d i v i d u a l l y in d i s t i l l e d water. Addition of ̂ £ 5 0 ^ , H^SO^ and adjustment of pH were made and a l l the steps elaborated in 4.2.2 were followed. In these runs, the t o t a l e l e c t r o l y s i s time alone was varied. For one of these runs (run 8-3), in addition to the analysis of phenols and T.O.C., C.O.D. and B.O.D. analysis were performed on the i n i t i a l and f i n a l sample . Wherever B.O.D. analysis r e s u l t s are reported, 1 I samples were c o l l e c t e d , both at the beginning of the run before r e c y c l i n g to T-1 was started and a f t e r the e l e c t r o l y s i s was complete. 4.3 A n a l y t i c a l techniques The samples c o l l e c t e d were analyzed for phenols, tota l organic carbon and in some cases C.O.D. and B.O.D. Products of oxidation of typ i c a l runs were i d e n t i f i e d by GC/MS where possible. 4.3.1 Analysis of phenols Concentration of the phenols was determined by gas chromatography using a flame i o n i z a t i o n detector. D i f f e r e n t columns were used for mono- hydric phenols and for dihydric phenols. Equipment s p e c i f i c a t i o n s and operating conditions are given in Appendix 1. Fresh standard solutions of the phenols in the desired range were prepared by accurately weighing out the phenols used to prepare the e l e c t r o l y t e for the experiments. Before the i n j e c t i o n of the samples, phenol standards were injected under the same conditions and the calibration;! curve of peak heights vs . \ phenol concentration was constructed. As the phenol peaks were narrow, the peak heights rather than peak areas were used d i r e c t l y . In a few cases, peaks of one or two oxidation products were observed. These peaks did not i n t e r f e r e with the analysis of the phenols, and they were not further i d e n t i f i e d . When mixtures of monohydric phenols were analysed, the column temperature was sui t a b l y adjusted to obtain retention times that had reasonable time i n t e r v a l s between the d i f f e r e n t peaks. The samples were analysed within a day to avoid degradation [31]. For the analysis of resorcinol [37] the peaks were broad, but uniform. Hence the peak heightswere again used. Large errors would be expected in this case at lower concentrations. In a l l cases, however, standards and samples were injected u n t i l the v a r i a t i o n in peak heights was only 2-3%. In the analysis of catechol attempts with the carbowax column used for resorcinol proved to be unsuitable even at conditions of maximum d e t e c t a b i l i t y with the flame i o n i z a t i o n detector. Hence the catechol concentration could not be determined except in one case where a rough estimate was made. Attempts of methylating the samples with TMAH (T r i methyl anilinium hydroxide) followed by analysis of the methyl d e r i v a t i v e of catechol with the column material OV-17 also proved f u t i l e . 4.3.2 Total organic carbon analysis The total organic carbon analyzer contains two furnaces: one for total * Catechol i n the samples was extracted with ether followed by evaporation of the ether and addition of calculated quantities of the methylating agent. carbon and one for inorganic carbon. The tota l carbon furnace operates at a temperature of 1000°C to convert a l l the carbon present in the sample to carbon dioxide. The inorganic carbon furnace operates at 150°C to convert only the inorganic carbon in the sample to carbon dioxide. The amount of carbon dioxide produced i s detected in an infrared analyzer [38]. The tota l organic carbon (T.O.C.) in the sample i s calculated by subtracting the inorganic carbon from the total carbon. Under the pH conditions used, i t was found that the concentration and v a r i a t i o n of inorganic carbon present in the samples was n e g l i g i b l e . Hence in a l l cases only the tota l carbon has been reported as T.O.C. The c a l i b r a t i o n procedure was s i m i l a r to that used in gas chromato- graphy. Variation in peak height in successive i n j e c t i o n of a certain. ' sample was~<2%. For T.O.C. an a l y s i s , i t was possible to use the same standards used in the analysis of the phenols knowing the f r a c t i o n of organic carbon present in 1 g of the phenol. S p e c i f i c a t i o n and operating conditions of the T.O.C. analyzer are also given in Appendix 1. 4.3.3 B i o l o g i c a l oxygen demand analysis In cases where the b i o l o g i c a l oxygen demand (B.O.D.) i s reported the analysis was performed by Wood Laboratory Ltd. The seed bacteria for B.O.D. analysis were grown by an enrichment process using B.O.D. water supplemented with phenolics. 4.3.4 Chemical oxygen demand analysis The chemical oxygen demand (C.O.D.) determination provides a measure of the oxygen equivalent of that portion of the organic matter in a sample 36. that is susceptible to oxidation by a strong chemical oxidant [38]. Where the e f f l u e n t contains only r e a d i l y a v a i l a b l e organic bacterial food and no toxic matter, the C.O.D. value can be used to approximate the ultimate carbonaceous B.O.D. values. C.O.D. was determined by the dichromate reflux method outlined in v reference [39]. The test was repeated for each sample to test the repro- d u c i b i l i t y . The ca l c u l a t i o n s are presented in Appendix 4. 4.3.5 GC/MS analysis A Hewlett-Packard gas chromatograph /'mass spectrometer combination equipped with a f u l l y i n t e r a c t i v e data system (HP-1000 series computer) was used to analyse the composition and nature of the f i n a l sample from a few of the typ i c a l oxidation runs. For th i s purpose one run was performed _2 with each of the phenolics studied at a current density of 526.3 A/m , for 2 hrs with an i n i t i a l concentration of 1g/1 (Appendix 2). One sim i l a r run was performed with a mixture of monohydric phenols of composition s i m i l a r to that used in run 8-3. The f i n a l sample from a l l of the above runs were given for the GC/MS analysis. This analysis was performed by Mr. Tim Ma. The r e s u l t s are reported in Appendix 2. The operating condi- tions and equipment s p e c i f i c a t i o n s can be found in Appendix 1 . A l l the products were i d e n t i f i e d with standard data obtained for the compounds in the mass spectrometer. In cases where the p o s s i b i l i t y of two isomers has been reported, the mass spectrometer data was i n s u f f i c i e n t to d i s t i n g u i s h between them. An example for such a case has been enclosed (Appendix 2). The samples for the analysis were prepared by the following procedure. 10 ml samples of the f i n a l samples were i n d i v i d u a l l y extracted twice with 37. 50 ml of methylene c h l o r i d e . The organic phase was separated,dried with anhydrous MgSO^ and evaporated in a rotary evaporator.. The residue was dissolved in 10 ml of methylene chloride and given for GC/MS an a l y s i s . In the case of resorcinol and catechol no products were detected. v For catechol the clear layer and the suspended black product were separately extracted with methylene c h l o r i d e . However in these cases the extraction in to the methylene chl o r i d e phase was i n e f f i c i e n t . With the av a i l a b l e column, the solvent choice was l i m i t e d , and therefore other solvents were not t r i e d . An a l t e r n a t i v e attempt was made with a s o l i d probe in order to introduce the sample d i r e c t l y in to the mass spectrometer. No d e f i n i t e i d e n t i f i c a t i o n s were made in th i s attempt. 4.3.6 Accuracy and r e p r o d u c i b i l i t y Care was taken to maintain accuracy in a l l the analyses. The repro- d u c i b i l i t y of r e s u l t s was checked. For the analysis of the phenolics and T.O.C, in j e c t i o n s were repeated u n t i l the vari a t i o n s in peak heights were within 3%. Repr o d u c i b i l i t y of the oxidation process was tested and found to be good. For example in repeated runs of phenol and resorcinol oxidation at 10 A with an i n i t i a l concentration of 1 g/1, the following r e s u l t s were obtained a f t e r 2 hours of oxidation. % oxidised Name of Compound T r i a l I T r i a l II phenol 89.6 89.2 resorcinol 71 .6 68.2 The r e s u l t s obtained with a few of the phenol runs were compared with the corresponding r e s u l t s obtained by Sucre [31]. As seen below, there i s a reasonable agreement. % oxidation a f t e r 60 mins, working at 10 A with i n i t i a l phenol concentration of 0.1 gm/1 % oxidation a f t e r 120 mins, working at 10 A with i n i t i a l phenol concentration of 1 gm/1 Source Ref [31] Present study 98 (Run 3-3) 100 (Run 1-4) 100 (Run 3-31) 89.6 (Run 1-1) CHAPTER 5 RESULTS AND DISCUSSION 5.1 Oxidation of individual phenolics 5.1.1 Anodic oxidation of phenol A t y p i c a l plot of r e s u l t s of the r e c i r c u l a t i n g batch oxidation runs i s shown in Fig. 7 where % phenol oxidized i s plotted versus time f o r three d i f f e r e n t values of i n i t i a l phenol concentration. As the i n i t i a l phenol concentration was increased from 108'mg/l to 683 mg/l and to 910 mg/l, the % phenol oxidized a f t e r 30 minutes decreased from 88.9% to 55.3% to 30.2% although the absolute amount of phenol oxidized in a given time generally increased. However, in run 1-5, the % phenol oxidized l e v e l l e d o f f a f t e r 1 hour. When the c e l l was opened, the cathode surface was found to be covered with a deposit of yellow t a r - l i k e material. This tar must have been formed primarily by the oligomerization and polymerization of p-benzoquinone and by i t s reaction with the phenolic compounds present. Tar formation has been encountered in l i t e r a t u r e 117,19]and an .attempt to overcome t h i s problem has been reported [19]. Fig. 8 shows the e f f e c t of increasing the applied current at a constant i n i t i a l concentration of phenol. The e f f e c t of increasing the current i s to r a i s e the i n i t i a l rate of phenol oxidation as shown by the slopes of the curves at the beginning of the runs. However, the i n i t i a l rate i s not proportional to the current since there i s a larger increase in rate as the current i s increased from 5A to 1 OA than from 10A to 15A. A possible reason f o r t h i s i s that with increasing currents more hydro-  quinone i s produced and i t s oxidation to p-benzoquinone may carry increasing f r a c t i o n s of the current. Stated in another way, the current e f f i c i e n c y for phenol oxidation f a l l s o f f with increasing applied current and the production of p-benzoquinone probably increases. This postulate i s perhaps supported by the observation that the i n t e n s i t y of the yellow colouration and smell due to p-benzoquinone appeared to increase in the treated solution as the applied current was increased. The GC/MS analysis of the treated phenol solution however showed only (Appendix 2) the following constituents: unreacted phenol 12.6%, p-benzoquinone 69.5%, catechol 7% and hydroquinone 10.9%. No coupling products (dimers) were detected. The absence of such products rules out the ra d i c a l mechanism f o r the reaction [40]. Based on the products obtained, the following reaction scheme i s proposed. The f i r s t step i s the formation of "phenoxonium ion" by e l e c t r o p h i 1 i c attack of the aromatic nucleus, followed by the formation of catechol or hydroquinone. Hydroquinone gets oxidized further by the loss of 2 electrons to form p-benzoquinone. The f a c t that 6 times more p-benzoquinone than hydroquinone i s formed shows that under present conditions the oxidation of hydroquinone to p-benzoquinone i s favoured. The cathodic reduction of p-benzoquinone i s not as important. An explana- tion f or t h i s i s presented in Section 5.4. OH 0 0 OH © j HOH OH 0 OH 0 During the anodic oxidation of phenol under conditions chosen for the study, i t i s obvious that phenol goes through various oxidation states and r e s u l t s p a r t l y i n the formation of carbon dioxide. As seen from F i g . 9, the actual quantity of phenol oxidized completely to carbon dioxide i s about 22% and 18% in runs 1-4 and 1-5 re s p e c t i v e l y . [It should be noted that whenever % T.O.C. oxidized has not been reported, the net change in T.O.C. was p r a c t i c a l l y undetectable due to the high concentration of carbon present in s o l u t i o n s ] . 5.1.2 Oxidation of p-cresol Effects of v a r i a t i o n of concentration and current shown in F i g . 10 and 11 are found to be s i m i l a r to those observed in the case of phenol. However at every stage, the % p-cresol oxidized i s lower than that observed with phenol i t s e l f . A s i m i l a r r e s u l t i s observed in % t o t a l organic carbon (Fig. 12) oxidized. These trends are contrary to expectations based on the half-wave potential values. This might be ei t h e r due to the unreactive nature of p-cresol under the conditions of present work or due to the retarding influence of the cathodic reduction of the oxidized product r e s u l t i n g in regeneration of p-cresol. In the GC/MS analysis a larger percentage (84.2) of unoxidized p-cresol was i d e n t i f i e d in comparison to the oxidation product (15.8). Besides the expected oxidation product, 4-hydroxy-4-methyl-cyclohexa-2,5, diene-l-one (which has been confirmed from the mass spectrum), no other oxidation product such as methyl-p-benzoquinone has been i d e n t i f i e d . Hence the required ideal conditions of time, potential or electrode a c t i v i t y f o r the complete anodic oxidation of p-cresol were not provided in t h i s study. F i g . 9 E f f e c t of cone, oh rate of oxidation o f organic carbon i n phenol at 10 A. _.  Fig. 1 2 Effect of cone, on rate of oxidation of organic carbon in p-cresol.  cn 46. 5.1.3 Oxidation of 0-cresol In the study of the e f f e c t of i n i t i a l concentration on the oxidation of 0-cresol (Fig. 13) i t i s observed that in run 3-4, the rate l e v e l s o f f a f t e r 96.8% oxidation showing the expected retarding influence due to a more favoured competitive reaction. This reaction i s probably oxygen evolution. In F i g . 14, where the i n i t i a l concentration i s about 1 gpl of 0-cresol, the percent oxidized i s e s s e n t i a l l y l i n e a r l y dependent on time. In addi- t i o n , the % oxidation/unit time increases with applied current in a near l i n e a r manner unlike the trend observed with phenol and p-cresol. Products reported in the l i t e r a t u r e {23] (see Chapter 2) are detected in s i m i l a r proportions in the present work, v i z . 69.8% methyl benzoquinone 19.0% methyl hydroquinone and 11.3% s t a r t i n g compound, 0-cresol. Observation of intense yellow colouration i s supported by the large concentration of methyl benzoquinone observed in the treated s o l u t i o n . The anodic oxidation path appears to be s i m i l a r to that reported for phenol by the formation of "phenoxonium ion". The formation of the reported products would be as follows: -2e 0-cresol methyl hydroquinone Methyl Benzoquinone No tar or coupling products formation was observed with 0-cresol. As methyl benzoquinone, the main product of anodic oxidation has F i g . 13 Cone, e f f e c t on % o-cresol oxidized at 10 A F i g . 14 Current e f f e c t on % o-cresol oxidized (1 g/1 runs) the same quantity of organic carbon as the s t a r t i n g material, the % organic carbon oxidized changes very l i t t l e (Fig. 15) as the process i s c a r r i e d on. 5.1.4 Oxidation of 2,3-Xylenol Based on the structure of 2,3-Xylenol, s u b s t i t u t i o n of the methyl groups in the ring should increase the electron density at the carbon atom to which the hydroxyl group i s attached, making i t more susceptible to anodic oxidation than phenol and the c r e s o l s . Experiments with 2,3-Xylenol did show increased s u s c e p t i b i l i t y . F i g . 16 shows that 2,3-Xylenol gets oxidized completely within two hours even at the higher i n i t i a l concentrations.of 380 and 625 mg/l. The current e f f e c t (Fig. 17) i s however more c r i t i c a l with the rate of oxidation being extremely slow in 5A run. Unlike the other runs with 2,3-Xylenol there was no excessive gas evolution and foaming in the above run (run 4-2). The lower voltage corresponding to the low applied current might have an important role in reducing the gas evolu- t i o n and the rate of oxidation. It should be noted, however that the usual concentration e f f e c t also comes into play in Fig. 17. Although runs 4-1, 4-2 and 4-3 were intended to have the same i n i t i a l concentration equal i n i t i a l concentrations were not achieved because of non-uniform d i s s o l u t i o n and evaporation of 2,3-Xylenol in hot water. Otherwise the curve f o r run 4-1 would have been farther removed from that of run 4-3, in F i g . 17. The % T.O.C. oxidized could be measured in a l l runs with 2,3-Xylenol The i n i t i a l concentrations from G.C. and T.O.C. analysis do not agree in t h i s case. This could be due to the vigorous reaction which started 30 KEY RUN NO. INITIAL CONC. ppm • 3-4 95 • 3-5 505 Q U (0 5 TIME (min) F i g . 15 E f f e c t - o f cone, on rate of oxidation of organic carbon tn o-cresol ; ; 50. «OOL Fig. 16 Cone, e f f e c t on % 2,3-Xylenol oxidized at 10. A . .. TIME (min) F i g . 17 Current e f f e c t on % 2,3-Xylenol oxidized (1 g/1 run) well before r e c y c l i n g was started. Besides, contrary to expectation, with an increase i n i n i t i a l concentration, a larger % T.O.C. i s oxidized (Fig. 18). The e f f e c t of current on % T.O.C. oxidized can be observed in Fig. 19. There i s a s i g n i f i c a n t increase in % T.O.C. oxidized when the current i s raised from 5A to 10A although the trend between 10A and 15A i s not clear - c u t . The treated solution when subjected to GC/MS analysis showed the following compounds OH 0 0 CH 3 PM TT CH 0 L°3 0 3 H3C OH 17.6% 79.8% 2.6% . 2,3-Xylenol 2,3-dimethyl 4-hydroxy-2,4- benzoqui.none dimethyl, 2,5-cyclo- hexadiene-1-one and traces of 2,3-dimethyl hydroquinone. Based on the products i d e n t i f i e d , the mechanism of the oxidation i s probably s i m i l a r to that outlined f o r phenol. The presence of only traces of 2,3-dimethyl hydroquinone shows that the loss of 2 electrons from 2,3-dimethyl hydroquinone i s rapid, with the equilibrium s h i f t e d in such a way as to make th i s reaction almost i r r e v e r s i b l e . 5.1.5 Oxidation of 3,4-Xylenol Based on i t s structure, 3,4-Xylenol should be as reactive as 2,3-Xylenol. The Ex of 3,4-Xylenol (0.513 V) i s much lower [21] than that of phenol. The usual well marked trends are observed i n the plots of the concentration e f f e c t (Fig. 20) and the current e f f e c t (Fig. 21). 30 o (A O O 20) 0 K < z 4 U OC o 10 KEY RUN NO. INITIAL CONC. ppm 4- 1 625 • 4-5 380 • 4 - 4 97 60 TIME (min) 120 Fig. 18 E f f e c t of cone, on rate of oxidation of organic carbon in 2,3-Xylenol at 10 A. tn to  •gg The T.O.C. analysis showed that there was less than 5% oxidation of the organic carbon i n a l l the runs and hence these r e s u l t s have not been reported. The poor r e s u l t s obtained i n the anodic oxidation of 3,4-Xylenol under the present conditions could be because of the low s o l u b i l i t y of 3,4-Xylenol in water. A few insoluble o i l y droplets were noted in the e l e c t r o l y t e which also could have affected the whole process. The f a c t that there i s no measurable decrease i n T.O.C. further supports the observation that 3,4-Xylenol i s r e s i s t a n t to anodic oxidation under the conditions used. The low oxidation of organic carbon could not be due to the formation of some non-oxidisable oxidation product because the only products that were i d e n t i f i e d in the treated solution were the st a r t i n g compound, 3,4-Xylenol at 77.9%, and the following compound 4-hydroxy, 2,4-dimethyl, 2-5-cyclohexadiene-l-one at 22.1% The above'mentioned product was obtained from the oxidation of 2,3-Xylenol and has also been obtained [23] from the anodic oxidation of 2,4-Xylenol. Therefore i t must have a stable configuration among the possible isomers of the oxidation products obtainable from various xylenols. 5.1.6 Oxidation of Resorcinol Substitution of a hydroxyl group in the meta po s i t i o n of phenol decreases the half wave p o t e n t i a l . Due to the electron donating nature of the substituent, resorcinol should be more e a s i l y oxidized during anodic oxidation. This was found to be true. As seen from Fig. 22, resorcinol i s destroyed completely in 60 minutes provided the i n i t i a l concentration i s lower than 500 mg/l. Increasing the i n i t i a l concentra- tion to 1200 mg/l has a well pronounced e f f e c t in decreasing the percen- tage oxidation i n a given time. The e f f e c t of current on the rate of oxidation (Fig. 23) follows the usual trend. Anodic oxidation of resorcinol i s very i n t e r e s t i n g from the point of view of achieving carbon dioxide formation. F ig. 24 shows that with a decrease in i n i t i a l concentration of r e s o r c i n o l , there i s an increase i n % organic carbon oxidized. With an increase in applied current, although there i s a s l i g h t increase in % organic carbon oxidized, the exact trend i s unclear (Fig. 25). As mentioned in section 4.3.5, none of the oxidation products of resorcinol could be i d e n t i f i e d by GC/MS analysis even when a s o l i d probe was used. Thus no d e f i n i t e conclusion can be made about the reaction route in t h i s case. However a few comments can be made based on the observations made during the runs. In spite of the f a c t that there was an observable rate of oxidation of organic carbon, there was no foaming or noticeable gas evolution. This suggests that the foaming observed i n the 0-cresol runs and 2,3-Xylenol runs was perhaps due to the formation of some surface active compounds rather than being simply due to gas evolution. During the resorcinol runs the e l e c t r o l y t e remained colourless fo r the f i r s t 30 minutes and became yellow thereafter. Also the samples c o l l e c t e d at the beginning of the runs were yellow during c o l l e c t i o n and slowly became colourless in f i v e minutes. This suggests that the reaction  F i g . 23 Current e f f e c t on % r e s o r c i n o l o x i d i z e d (1 g/1 runs) cn T 100 h KEY RUN NO. INITIAL CONC. ppm • 6 - 4 87 • 6 - 5 490 • 6 - 1 1200 z TIME (min) Fig. 24 E f f e c t of cone, on rate of oxidation of organic carbon in resorcinol at 10 A KEY RUN NO. 1 (A) • 6-2 5 • 6- 1 10 T 6-3 15 TIME (min) Fig. 25 Effect of current on rate of oxidation of organic carbon in resorcinol (1 g/1 runs) leading to the formation of the yellow oxidized product of resorcinol has i t s equilibrium s h i f t e d towards the forward reaction only at high concen- tr a t i o n s of the i n i t i a l oxidation product. 5.1.7 Oxidation of catechol Anodic oxidation of catechol was found to be very vigorous as expected from i t s structure. Among the phenolics studied, catechol proved to be most susceptible to complete oxidation leading to the formation of carbon dioxide. The maximum oxidation of organic carbon (62.7%) was achieved in run 7-5 (Fig. 26). With higher i n i t i a l concentrations of catechol (1000 mg/l), the curve l e v e l s o f f a f t e r 90 minutes of oxidation showing that probably an e l e c t r o - i n a c t i v e compound or a compound that i s highly r e s i s t a n t to anodic oxidation under the present conditions i s formed. Besides, as expected [27] the c a t a l y t i c e f f e c t of catechol described i n Section 2.2.4 seems to be n e g l i g i b l e under the low pH conditions of the experiment. An increase i n applied current does not quite seem to favour the oxidation of organic carbon because the trends followed i n run 7-1 (10A) and 7-3 (15A) are s i m i l a r (Fig. 27) although a lower rate of oxidation of organic carbon i s observed i n the case of 5A run. As indicated e a r l i e r , (Chapter 4), the concentration of catechol i n the runs could not be determined by the usual GC technique which was inapplicable f o r concentrations below 200 mg/l. However, under typic a l conditions (run 7-1, 1000 mg/l, i n i t i a l c o n e , 10A), i t was found by This i s supported by the f a c t that the reaction appeared to be less vigorous, with less gas evolution and foaming a f t e r the f i r s t 90 minutes.  Fig. 27 E f f e c t of current on rate of oxidation of organic carbon in catechol (1. g/1 runs) GC using the carbowax column that about 150 mg/l of catechol remained a f t e r 2 hours of anodic oxidation in which there was 45.6% oxidation of the organic carbon. A black product of polymerization was produced i n a l l runs except i n run (7-4) where the lowest (100 mg/l) i n i t i a l concen- t r a t i o n of catechol was used. Attempts to characterize the black p r e c i - pitate were not successful. The observations made in the catechol runs suggest that the i n i t i a l two-electron process leading to the formation of 0-quinone i s followed immediately by i t s decomposition and condensation. The pale yellow solution c o l l e c t e d in the i n i t i a l stage of the process spontaneously formed the condensation product which pr e c i p i t a t e d out of the samples. Unfortunately, none of the products of oxidation could be i d e n t i f i e d in the GC/MS ana l y s i s . In order to evaluate the anodic oxidation process from the point of view of e f f l u e n t treatment of waste containing catechol, B.O.D. and C.O.D. r e s u l t s are reported. (Appendix 2, runs 7-2, 7-3). As expected, there i s a larger % reduction in B.O.D. at a higher current. However between the two extreme values of current used (5A and 15A), there i s only a small difference in reduction of B.O.D. achieved during the experiment. The treatment brings about 81% reduction in B.O.D. value at an applied current of 15A. The change in the C.O.D. values as a r e s u l t of the oxidation i s comparable with the % oxidation of organic carbon^ but the'effect of increase i n the reduction of C.O.D. values with increase in current i s more s i g n i f i c a n t . 66. 5.2 Comparison of performance of d i f f e r e n t phenolics 5.2.1 E f f e c t of v a r i a t i o n of i n i t i a l concentration An increase in the i n i t i a l concentration of the phenolics studied i s accompanied by a drop in the % of oxidation in 2 hours (Fig. 28). The phenol runs do not follow the trend due to the deposition of tars on the cathode surface in run 1-5 as mentioned e a r l i e r . 2,3-Xylenol was however oxidized completely at a l l the i n i t i a l concentrations studied. In order to discuss rates l o g i c a l l y , c o ntrolled-potential e l e c t r o - l y s i s (cpe) c a r r i e d out with a potentiostat should be performed rather than constant current experiments as the f a c t o r a f f e c t i n g the rate constant i s the p o t e n t i a l . In the present study, the c a l c u l a t i o n of the i n i t i a l rate was based on the time interval during which % phenolic compound oxidized increased l i n e a r l y with time. Except in the case of 2,3-Xylenol, the i n i t i a l oxidation rates f o r a l l the phenolics go through a maximum value with increasing concentration (Fig. 29). This indicates that at an i n i t i a l concentration of about 500 mg/l, the best rate of oxidation can be obtained. The actual values of the i n i t i a l rates, however do not seem to have a d i r e c t c o r r e l a t i o n to the structure of the phenolics. This indicates that besides the nature of the substituents, other factors l i k e d i f f u s i o n a l e f f e c t s , nature of the oxidation products, adsorption e f f e c t s and optimum potential range can perhaps play a major role in the anodic process. An increase in the i n i t i a l concentration seems to accelerate the rate of oxidation of 2,3-Xylenol in the concen- t r a t i o n range studied. too oc O 80 x (Vi a « 60 x o KEY NAME OF COMPOUND V PHENOL • o - C R E S O L p - C R E S O L • RESORCINOL o 2,3 XYLENOL • 3 ,4 XYLENOL 40 20 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 6 3 INITIAL CONC. OF PHENOLICS XIO mole / m 16.0 F i g . 28 V a r i a t i o n o f f i n a l % o x i d i z e d w i t h i n i t i a l c o n c e n t r a t i o n o f p h e n o l i c s a t 10 A  5.2.2 E f f e c t of v a r i a t i o n of applied current With an increase i n applied current, there i s an increase i n the f i n a l % oxidation a f t e r 2 hours operation in a l l cases (Fig. 30). The f i n a l % of oxidation increases in the order 3,4-Xylenol, p - c r e s o l , 0-cresol, r e s o r c i n o l , phenol, 2,3-Xylenol. This e f f e c t i s more s i g n i f i c a n t when the increase i s between 5A and 10A than in the case of increase from 10A to 15A. The i n i t i a l rate of oxidation(Fig. 31) increases with increase in applied current except in the case of p-cresol where the increase in rate between 5A and 10A i s i n s i g n i f i c a n t . In t h i s study of the e f f e c t of applied current, the data obtained with d i f f e r e n t phenolics indicates that the trend followed with the i n i t i a l rates i s d i f f e r e n t from that obtained with the f i n a l % oxidized. This indicates that the k i n e t i c s and the transport phenomena associated with each process are complex and deserve further i n v e s t i g a t i o n . 5.2.3 Subsitutuent e f f e c t s As referred e a r l i e r , (sections 2.2.2) most studies of substituent e f f e c t s are based on s h i f t s of half-wave p o t e n t i a l s . However from the present study, i t i s obvious that there i s no d i r e c t c o r r e l a t i o n between the half-wave potential values (Table II) and f i n a l % oxidized. The half-wave potential does take the d i f f u s i o n and a c t i v i t y c o e f f i c i e n t s of the oxidized and reduced forms into account as shown by the following equation [41] RT nF In ( D D ox Red Red (10) ox where D ox and D Red are the d i f f u s i o n c o e f f i c i e n t s of the oxidized and 100 so ce O X CM S 60 a u KEY NAME OF COMPOUND V PHENOL • o - CRESOL p - CRESOL • RESORCINOL • 2,3 XYLENOL O 3,4 XYLENOL X o 40 20 6 8 APPLIED CURRENT 10 14 16 (A) F i g . 30 V a r i a t i o n o f f i n a l % o x i d i z e d w i th a p p l i e d c u r r e n t (1 g/1 runs) 22.0 20.01 C 16.0 M « E (0 o 12.0 u i-< cc -I < p 2 8.0 I 4.0 0.01 KEY NAME OF COMPOUND • PHENOL • o-CRESOL • p-CRESOL • RESORCINOL A 2,3 XYLENOL O 3,4 XYLENOL _i_ 6 8 APPLIED CURRENT 10 12 14 16 (A) Fig. 31 Variation of i n i t i a l rate of oxidation with applied current (1 g/1 runs) reduced forms, r e s p e c t i v e l y , and f and f ^ are the a c t i v i t y c o e f f i c i e n t s . But the s h i f t of the half-wave potential (AEj )v caused by introducing 2̂ A the substituent X in to the parent molecule chosen as a reference compound, in which X = H i s related [41] to the equilibrium constants f o r the reaction by eq. (11) ' ( A E % ) x = ^ r 1 ( A 1 ° 9 K>x - W where K i s the equilibrium constant of the reaction 0 + ze R, and A log K = log - log Kp, where K Q represents the value f o r the reference system f o r which X = H. Although the s h i f t in Ei i s related to the reaction k i n e t i c s , in the determination of half-wave p o t e n t i a l s , i t i s assumed that the overall rate of the reaction .is l i m i t e d by the rate of d i f f u s i o n of the reactant to the electrode, which may not be exactly true with the present cases. The overall rate of the reactions may be c o n t r o l l e d by the processes occurring at the electrode surface. Besides, gas evolution, further oxidation of the intermediates and adsorption e f f e c t s a l l of which need further i n v e s t i g a t i o n may play a r o l e . 5.2.4 E f f e c t of d i f f u s i v i t y The t h e o r e t i c a l d i f f u s i v i t y values (Appendix 4) have been presented in Table V. On the basis of d i f f u s i v i t y , i f the reactions are c o n t r o l l e d \ by the rate of mass transport of the phenolic molecules to the electrode, the ease of oxidation should be as follows. phenol > dihydric phenols > cresols > xylenols 73. In the present study, at an applied current of 10A, with an i n i t i a l concentration of lgpl of the phenolic compound, the i n i t i a l rate of oxidation follows the order (Fig. 31). phenol > 2,3-Xylenol > resorcinol > p-cresol > 3,4-Xylenol > O-cresol TABLE V DIFFUSIVITIES OF THE PHENOLIC COMPOUNDS IN WATER Name of phenolic compound Molal volume of the phenolic compound at i t s normal b o i l i n g point 3 cm /g.mole * cnr/sec x 10 6 cm2/s Phenol 105 8.5 p-cresol 126 7.7 O-cresol 126 7.7 2,3-Xylenol 147 7.4 3,4-Xylenol 147 7.4 resorcinol 112 8.3 catechol 112 8.3 This trend conforms to the order expected from the d i f f u s i v i t y values except f o r 2,3-Xylenol which takes precedence over resorcinol and 3,4-Xylenol which has a higher i n i t i a l rate than O-cresol. Consi- dering the % oxidized i n two hours (Fig. 30) under s i m i l a r conditions the order seems to be d i f f e r e n t from above. Therefore, even though * Calculation outlined in Appendix 4. 74. d i f f u s i v i t y might control the rate of oxidation in the i n i t i a l stages of oxidations other factors which deserve further attention do play a r o l e . 5.3 Oxidation of phenolic mixtures When the monohydric phenolics are mixed in about the same concen- tratio n s as they are found in the wastewater of Table I, the extent to which the phenolics were oxidized in a given time decreased in the following order as shown in F i g . 32-34. OH OH OH OH OH phenol o-cresol 2,3-Xylenol p-cresol 3,4-Xylenol This leads us to the following conclusion. 1) Substitution of methyl (electron donating group) decreases the ease of oxidation. 2) Substitution in the ortho position i s preferable to s u b s t i t u - tion in the para p o s i t i o n . 3) No d e f i n i t e conclusion can be drawn about the preference of para p o s i t i o n over meta. Mass transfer e f f e c t s would have also aided in the oxidation of phenol and 0-cresol as t h e i r i n i t i a l concentration i s higher than the r e s t . The mixture oxidation runs (runs 8-1, 8-2, 8-3) prove that as the period of treatment i s increased, better oxidations can be obtained. Even a f t e r 95.8% oxidation of the phenolic mixture (run 8-3), the curve did not f l a t t e n out showing that by increasing the period of oxidation or by using more optimal conditions, v i r t u a l l y complete oxidation might be obtained. Fig, 32 E f f e c t of nature of phenolics on % oxidation (1 OA, 2 hrs; run 8-1) ;  Fig. 34 Effect of nature of phenolics on % oxidation (10 A, 5 hrs; run 8-3) From the GC/MS analysis of the treated s o l u t i o n , a l l the products obtained from the indi v i d u a l phenolic runs were i d e n t i f i e d . No product r e s u l t i n g from the in t e r a c t i o n of the oxidation products of d i f f e r e n t phenolics was i d e n t i f i e d . This could be due to one of the following causes: 1) Conditions of the experiment were not favourable for the occurrence of any coupling reaction between the products. 2) Products of such interactions did not show up on the chromato- graph e i t h e r due to t h e i r d i f f e r e n t nature or due to t h e i r presence in ne g l i g i b l e concentrations. Although the phenolics maintain t h e i r individual behaviour even in the mixture, there i s an i r r e g u l a r gradation in t h e i r rates of oxidation i n a l l cases. This could be due to the d i f f e r e n t competing reactions taking place simultaneously. A comparison i s made between the T.O.C, B.O.D. and C.O.D. analysis of the i n i t i a l and the treated sample from Run 8-3 in Table VI. TABLE VI RESULTS OBTAINED FROM THE OXIDATION OF MIXTURE OF MONOHYDRIC PHENOLS (RUN 8-3) i = 526 A/m"2 Time T.O.C. C.O.D. B.O.D. min mg/l mg/l mg/l 0 1480 4291 2783 300 1160 3502 1210 % Reduction 21.6 18.4 56.5 It can be noticed that the T.O.C. and C.O.D. reduction values are small and comparable whereas B.O.D. value i s brought down to a value less than half the i n i t i a l value. This B.O.D. reduction i s comparable to the value obtained in b i o l o g i c a l treatment f o r f i v e days [42], 5.4 Reaction e f f i c i e n c y f o r a typical run It i s apparent that the mechanism of anodic oxidation i s complex. For example, consider the oxidation of phenol, run 9-1. The oxidation products reported are p-benzoquinone, hydroquinone and catechol. Besides about 4% of the organic carbon was converted into carbon dioxide and carbon monoxide. Benzoquinone i s generated in the anode compartment with catechol, hydroquinone, carbon dioxide and oxygen, and i t may be converted to hydroquinone at the cathode. If the process proceeds to produce only •, the above compounds, the sum of the current e f f i c i e n c i e s f o r the forma- tio n of these products on the anode should be 1 . 0 . As gas analysis was not done, the f r a c t i o n of carbon oxidized to CO and C0£ i s unknown, therefore current e f f i c i e n c y i s reported assuming extreme values of the carbon monoxide to carbon dioxide r a t i o s . The current e f f i c i e n c y (Appendix 4) i s found to be 0.43 - 0.63 depending on the r a t i o of CO to CO2 formed. Presumably there are other reactions occurring which account f o r the res t of the current. These reactions could be the formation of oxygen from water e l e c t r o l y s i s or the formation of some other oxidation product that has not been i d e n t i f i e d . Moreover, as no precaution has been taken to decrease the convection of benzoquinone to the cathode, reduction of benzoquinone to hydroquinone followed by the non-productive oxidation of that hydroquinone back to benzoquinone could account f o r a loss in current e f f i c i e n c y . However, 80. hydrogen evolution at the cathode would compete with the thermo- dynamically favoured reduction of benzoquinone at the cathode. From the carbon balance, i t can be seen that 21% of the carbon has not shown up in the products identified. Presumably there are other unidenti- fied products which account for this discrepancy. Carbon loss could have also occurred due to deposition of tar products on the electrodes during the process. 5.5 Cell voltage The cell voltage V-is given by AV = V . + TI + In I + V . (12) mm 'a 1 'c1 ohm The variation between V. ,.. . , and V-. , may be particularly i n i i i a I Tl na i dependent on V ^ m for a constant applied current. The potential drop across the packed bed should have been ideally measured by using probes at various points in the bed. However this drop was found to be very small in similar experiments when the potential profile was measured in a packed bed copper electrode under the conditions of constant current electrolysis [43]. Vohm (Appendix 4) increases with the applied current. It is difficult to compare the change in cell voltage at different applied currents for a particular phenolic compound on the basis of V Q n m at different currents because ri and n in eq. 12 will change with applied a c current. From Table VII it can be seen that the cell voltage increases during the anodic oxidation of 2,3-Xylenol, 3,4-Xylenol and catechol. With 2,3-Xylenol and catechol there was an excessive foaming and gas evolution. This would decrease the effective electrolyte conductivity according to the following equation TABLE VII VARIATION OF AV Name o f phenol ic compound ( I n i t i a l cone. 1 gp l ) 5A runs 1 OA runs 15A runs I n i t i a l AV v o l t s F ina l AV vol ts I n i t i a l AV v o l t s F i n a l AV v o l t s I n i t i a l -AV vol ts F ina l AV vol t s Phenol 6.15 6.0 7.1 7.1 12.7 10.7 p-Creso l 5.4 5.4 7.9 7.5 12.4 10.8 O-Cresol 6.0 5.9 9.2 8.0 11.3 9.1 2 , 3 - X y l e n o l 5.0 5.9 6.5 8.3 8.6 10.6 3 ,4 -Xy leno l 4.4 4 .8 5.9 6.3 7.4 7.5 r e s o r c i n o l 5.5 5.2 7.4 6.7 10.8 9.7 ca techo l 3.8 4.4 5.3 6.2 6.9 7.0 K e g = K e (1 - f)°/c (13) where f i s the f r a c t i o n of gas in the e l e c t r o l y t e . It has been reported that depending on the gas loading, the e f f e c t i v e conductivity of the e l e c t r o l y t e in the fixed bed can be lowered from 10-90% [441. Therefore the ohmic drop would increase considerably and the c e l l voltage thus shows a d i s t i n c t increase in these cases. The presence of the screen and water e l e c t r o l y s i s increase t h i s e f f e c t . With 3,4-Xylenol a s i m i l a r increase in resistance i s expected as indicated e a r l i e r (section 5.1.5). A decrease in c e l l voltage i s observed in several cases. This may be a t t r i b u t e d to one of the following e f f e c t s which can counteract the e f f e c t of gas evolution. 1) Increase in conductivity of the e l e c t r o l y t e due to e i t h e r heating in the c e l l or due to the nature of the products formed. The conductivity of the e l e c t r o l y t e was found to increase in s i m i l a r experiments [31]. 2) An intermediate cathode reaction f o r example cathodic reduction of p-benzoquinone in phenol runs can occur at a high cathodic potential thus decreasing the e f f e c t i v e c e l l voltage. 3) Physical changes may occur in the current feeders or the bed p a r t i c l e s . 5.6 Comparison of experimental r e s u l t s with mathematical models To t e s t whether mass transfer of the phenolic compound from the bulk e l e c t r o l y t e to the surface of the electrode controls the rate of disappearance of the phenolic compound, c a l c u l a t i o n s were performed with 83. 2,3-Xylenol and resorcinol runs, in a manner s i m i l a r to the ca l c u l a t i o n s of Sucre [31]. Fractional conversion of the phenolic compound X was related with mass transfer groups (Appendix 3) by the following equation X = 1 - exp [ {exp ( J L _ ) - 1 } | - - J l _ ] ( 1 4) The sample c a l c u l a t i o n s (Tables A-l and A-2) are represented as a band of conversion vs time in Figs. 16, 17, 22 and 23. In F ig. 16, i t can be seen that the curve corresponding to the lowest i n i t i a l concentration (97 mg/l) approaches the mass tra n s f e r - c o n t r o l l e d region i n 15 minutes. Between 30 and 45 minutes, the theore- t i c a l and experimental curves coincide in this case, while with the i n i t i a l concentration of 625 mg/l, the curve almost coincides with the theoretical region a f t e r 60 minutes. Thus in the case of 2,3-Xylenol runs where enhancement of mass transport by foaming may be expected as described by Nam's et al [45]', the rate of oxidation seems to be con t r o l l e d by mass transfer at i n i t i a l concentrations i n the range of 0.1 g/1. In f a c t in run 4.4 ( i n i t i a l concentration 97 mg/l), i n about 45 minutes the experimental curve exceeds the theoretical region. At th i s point, i t i s hard to conclude whether t h i s can be at t r i b u t e d to the excessive gas evolution, although i t seems l i k e l y from Fig. 17 where the curve representing the rate of oxidation at an applied current of 5A i s f a r below the mass transfer c o n t r o l l e d region. It may be r e c a l l e d that i n thi s p a r t i c u l a r run, gas evolution was not d i s t i n c t . At the highest applied current (15A) the experimental curve approaches the theoretical region only a f t e r 90 minutes with higher i n i t i a l concentrations (1 g/1). Considering the e f f e c t of increasing the i n i t i a l concentration in the runs with resorcinol (group 6) Fig. 22 where there was no foaming or noticeable gas evolution the experimental curves are closer to the mass transfer controlled region. It should be remembered, however that the d i f f u s i v i t y of resorcinol molecules i s larger than that of 2,3-Xylenol although the change in d i f f u s i v i t y has been taken into account in c a l c u l a t i n g the t h e o r e t i c a l mass transf e r region. F i g . 23 leads again to the suspicion about the role of gas evolution in mass tra n s f e r . It can be observed that at higher i n i t i a l concentration of r e s o r c i n o l , unlike the observation made with 2,3-Xylenol the experimen- t a l curve i s f a r below the theoretical region even at the highest applied current (Run 6-3). Any discussion of the above e f f e c t s depends on the accuracy or a p p l i c a b i l i t y of the mass transfer c o e f f i c i e n t c o r r e l a t i o n used. Although the equation of Pickett and Stanmore [46] used in Ref. 31 has been modified to improve i t s a p p l i c a b i l i t y to present case by considering .the correction with a double layer of packed bed based on the suggestions in Ref. 10, pg.161, i t i s s t i l l a poor c o r r e l a t i o n f o r a gas evolving, randomly packed bed electrode. The equations used i n .the present study to determine k m are Sh - 0.66 Re 0.56 Sc 0.33 (15) Sh = 0.62 Re 0.56 Sc 0.33 (16) There are c o r r e l a t i o n s [47] r e l a t i n g the volume of gas evolved to mass transfer c o e f f i c i e n t which show that when there i s hydrogen or oxygen evolution, the rate of mass transfer increases. Correlations are also a v a i l a b l e for electrochemical processes involving gaseous reactants [48]. The overall capacity c o e f f i c i e n t for mass transfer in the present set up can be calculated from equations of the type k Qa = k ma (1 + Vg) n (17) where Vg, the volume of gas evolved would be needed. As the pressure drop was not measured, a more accurate c a l c u l a t i o n of mass transfer c o e f f i c i e n t has not been attempted. CHAPTER 6 CONCLUSIONS An in v e s t i g a t i o n was made of the anodic oxidation of major phenolics in coal processing waste from the point of view of e f f l u e n t treatment. Experiments were performed with phenol, O-cresol, p - c r e s o l , 2,3-Xylenol, 3,4-Xylenol, r e s o r c i n o l , catechol and mixtures of the f i v e monohydric phenols. 1. Generally, the percentage oxidation of the phenolics in a given time was favoured by increasing the applied current and decreasing the v i n i t i a l concentration of the phenolics. 2. Complete oxidation of the organic carbon under present condi- tions of 5 1 of phenolic solution with concentration range 0.1 g/1 to 1 g/1 of phenolic compound r e c i r c u l a t e d f o r a two hour period, occurred to a s i g n i f i c a n t extent only i n the case of 2,3-Xylenol, resorcinol and catechol. 3. From the comparison of the performance of d i f f e r e n t phenolics, there i s no simple c o r r e l a t i o n of the rates of oxidation with the structure and d i f f u s i v i t y of the phenolic compounds. The observed order of decreas- ing reaction rate at an applied current of 10A with an i n i t i a l concentra- ti o n of 1 gpl of the phenolic compounds was phenol, 2,3-Xylenol, r e s o r c i n o l , p - cresol, 3,4-Xylenol, o-cresol. 4. When the synthetic mixture of f i v e monohydric phenols present at concentrations corresponding to a ty p i c a l coal conversion waste was oxidized, about 96% of the phenolics were oxidized i n 5 hours. The ease with which the phenolics were oxidized was as follows 87. phenol > 0-cresol > 2,3-Xylenol > p-cresol > 3,4-Xylenol As a r e s u l t of the treatment, T.O.C. and C.O.D. were reduced by about 20% while the reduction in the B.O.D. value was about 56%. 5. The products of the oxidation process were i d e n t i f i e d for typic a l runs of the individual phenolics and phenolic mixture. From the nature of the products and observations made in the runs, possible routes f o r the oxidations were proposed in most cases. Most of the oxidation products were in the form of quinones or hydroquinones. None of these oxidation products have been included [49] in the EPA l i s t of organic p r i o r i t y pollutants. 6. Comparison of the experimental r e s u l t s from two d i f f e r e n t sets of runs with a mass transfer model indicated that the depletion of phenolics i s con t r o l l e d by mass transfer when the concentration of the phenolic compound i s low. CHAPTER 7 FURTHER WORK Further investigation of the electrochemical treatment of coal conversion effluents would contribute the establishment of the technical f e a s i b i l i t y of the process. To obtain a complete understanding of the process, the following recommendation are made on the basis of th i s study. 1. Routine analysis of the gaseous products by orsat or gas chromatographic analysis should be attempted. The oxidation products should be monitored p e r i o d i c a l l y and a complete GC/MS analysis should be performed on a l l the samples. This would lead to a) Presentation of a complete study on the e f f e c t of current density [50] and % current e f f i c i e n c y u t i l i z e d i n the formation of d i f f e r e n t anodic oxidation products. b) Formation of d e f i n i t e conclusions about e f f l u e n t q u a l i t y under d i f f e r e n t operating conditions. 2. Electrode potential variations should be determined by using reference electrodes located at cer t a i n points in the bed. This would a s s i s t with the modelling of the process. 3. The rot a t i n g d i s c electrode can be used with a l l of the above phenolics to elucidate the kinetic s of electrooxidation under d i f f e r e n t operating conditions. 4. For future experiments with the packed bed a series of f i l t e r s provided with valves should be added to the recycle loop of the equipment to prevent the buildup of the suspended condensation product during prolonged periods of operation. 5. The work should be extended to the study of treatment of a l l the chemicals in coal processing e f f l u e n t s and hence the actual e f f l u e n t . 6. As an electrochemical process has several advantages over chemical oxidation process [51] the present process should be scaled up for continuous runs. As a part of the water p u r i f i c a t i o n system f or i n d u s t r i a l wastes, a larger c e l l assembly with a m u l t i p l i c i t y of treating zones would be required. 7. Studies should be performed to te s t the app l i c a t i o n of anodic oxidation as a f i n a l polishing step a f t e r b i o l o g i c a l or any other t r e a t - ment that i s not capable of destroying the phenolics completely. A packed bed, i f s u f f i c i e n t l y long and appropriately polarized, can possibly function as an electrochemical f i l t e r which w i l l reduce the concentration of a l l electrochemically oxidisable species to a level that can be desirably low for optimum b i o l o g i c a l treatment. This suggests the p o s s i b i l i t y of use of anodic oxidation as a p r i o r step to any other treatment. 90. NCMENCXATURE C.E Co CA s Cr dp D DOx,> DRed E AE F fox, fRed I k r \ k a o Keg K specific surface area of the bed current density referred to the surface area of the feeder plate current efficiency concentration of the oxidized form at the point of discharge concentration of reactant in the bulk of solution concentration of reactant at the surface of the electrode concentration of the reduced form at the point of discharge average particle diameter diffusivity of the phenolic compound in water diffusion coefficients half wave potential shift in half wave potential Faraday's constant activity coefficients applied current electrochemical reaction rate constant mass transfer coefficient overall capacity coefficient effective electrolyte conductivity equilibrium constant Typical units 2,3 m /m A/m2 mg/l mg/l mg/l mg/l m m2/s V coul/g equiv. A m/s m/s (Km) -1 91 Typical units L length of the cel1 m 3 N e l e c t r o l y t e flow rate m /s R universal gas constant kJ/k mol °K Re, Reynolds number based on p a r t i c l e p diameter Sc Schmidt number S thickness of the bed (in the d i r e c t i o n m of current) T temperature °K t time of e l e c t r o l y s i s S * t dimensionless time t residence time in the mixing tank S m 3 u s u p e r f i c i a l v e l o c i t y m/s V a anode potential V * V c cathode potential V V .„ minimum c e l l voltage V mi n a AV total c e l l voltage V V Q n m i r drop in e l e c t r o l y t e V W width of the bed m X phenol f r a c t i o n a l conversion y variable length of the bed m z number of electrons associated with the anodic oxidation Greek Letters a 0 transfer c o e f f i c i e n t experimental flow rate of e l e c t r o l y t e m /sec 9 2 . T y p i c a l un i t s e voidage of the bed £ shape f a c t o r f o r the p a r t i c l e s k aL e — d imens ion less mass t r a n s f e r group 2 v k inemat ic v i s c o s i t y o f water (cm / s ) n a o v e r p o t e n t i a l f o r the anodic r e a c t i o n s V n c o v e r p o t e n t i a l f o r the ca thod ic r eac t i ons V <1> a s s o c i a t i o n parameter o f s o l v e n t y. v i s c o s i t y cp 93. BIBLIOGRAPHY 1. Lanouette, K. "Treatment of phenolic wastes." Chem. Eng. 84, 99 (Oct. 1977). 2. "Control technology assessment." Environmental review of synthetic fuels 2, 3 (May 1979). 3. Assessment of coal conversion wastewaters: Characterization and preliminary b i o t r e a t a b i l i t y , PB-294338, EPA-600/7-78-181, 94 (Sept. 1978). 4. Throop, M.W. "Alternative methods of phenol waste water c o n t r o l . " Journal of Hazardous Materials 1, 319 (1975/77). 5. Katzer, J . , Sadana, A., and Ficke, H. "Aqueous phase c a t a l y t i c oxidation as a waste water treatment technique." Eng. Ext. Series 145, 29 (1974). 6. Kazuo, S., Kazuto, T., and Satoru, T. "Degradation of aqueous phenol solutions by gamma i r r a d i a t i o n . " Environmental Science and Technology U, No. 9, 1043 (1978). 7. Zeff, J. "UV. ox. process f o r the e f f e c t i v e removal of organics in waste water." A.I.Ch.E. Symposium Series 73_, No. 167, 206 (1976). 8. S u r f l e t t , B. " E l e c t r o l y t i c destruction of i n d u s t r i a l e f f l u e n t s . " The E l e c t r i c i t y Council Research Centre. Report No. 204 (Oct. 1969). 9. Smith De Sucre, V., and Watkinson, A.P. "Anodic oxidation of phenol f o r waste water treatment." Can. J. Chem. Eng. 5_9, 52 (1981 ). 10. Pic k e t t , D.J. Electrochemical reactor design. E l s e v i e r , Amsterdam (1977). 11. Sherwood, T.K., Pigford, R.L., and Wilke, CR. Mass Transfer. McGraw H i l l , New York (1975). 12. F i c h t e r , F. "Electrochemical oxidation of aromatic hydrocarbons." Trans Amer. Electrochem. Soc. 45_, 107 (1924). 13. Fic h t e r , F., and Stocker, R. "Electrochemical oxidation of aromatic hydrocarbons and phenols." Chem. Abstr. 8, 3037 (1914). 14. F i c h t e r , F., and Brunner, E. "New products of the electrochemical oxidation of phenol." Chem. Abstr. 10_, 2873 (1916). 94. 15. Gladisheva, A.I., and Lavrenchuck, V.I. "Electrochemical oxidation of phenol." ( o r i g i n a l t i t l e in Russian). Uch. Zap. Tsent. Nauch. Issled. Inst. Glovyan. Prom, No. 1, 68 (1966); Chem. Abstr. 67, 28639X (1967). 16. T a r j a n j i , M. et a l . "Decreasing the phenolic content of l i q u i d s by an electrochemical technique." U.S. Pat. 3,730,864 (May 1, 1973). 17. Covitz, F. "Electrochemical oxidation of phenol." U.S. Pat. 3,509,031. (Apr. 28, 1970). 18. Jones, G.C., et a l . " E l e c t r o l y t i c oxidation of phenol at lead thaiium anodes." U.S. Pat. 4,035,253 (July 12, 1977). 19. Jones, G.C., and Payne, D.A. "Electrochemical oxidation of phenol." U.S. Pat. 3,994,788. (Nov. 30, 1976). 20. Fioshin, M.Y., et a l . "Electrochemical oxidation of phenol to quinone." Electrokhimiya 1_3, No. 3, 381 (1977). 21. Swantoni, J . C , Synder, R.E., and Clark, R.O. "Voltammetric studies of phenol and a n i l i n e ring s u b s t i t u t i o n . " Anal. Chem. 33_, 1894 (1961 ). 22. Ross, D.S., Fimkelstein, M., Rudd, J.E. Anodic Oxidation. Academic Press, New York (1975). 23. Nilson, A., Ronlan, A., and Parker, V. "Anodic oxidation of phenolic compounds." Journal Chem. Soc. Perkin trans. I 20, 2337 (1973); Chem. Abstr. 80, 115431k (1974). 24. Ronlan, A. "Phenols." Encyclopaedia of electrochemistry of the elements. M. Dekkar, New York, Vol. XI, 270 (1978). 25. Nash, R.A., Skauen, D.M., and Purdy, W.C. "The polarographic behaviour of c e r t a i n antioxidants at the wax impregnated graphite electrode." J. Amer. Pharm. Ass. .47, 433 (1958).- 26. Elwing, P.J., and K r i v i s , A.F. "Voltammetric studies with the graphite i n d i c a t i n g electrode." Anal. Chem. 30, 1645 (1958). 27. Sivaramiah, G., and Krishnan, V.R. "Kinetics and mechanism of controlled potential coulometric oxidation of catechol." Indian J . Chem. 4, 541 (1966). 28. Dawson, C.R., and Nelson, J.M. "The influence of catechol on the s t a b i l i t y of 0-benzoquinone in aqueous solutions." J. Amer. Chem. Soc. 60, 245 (1938). 29. Wagreich, H., and Nelson, J.M. "On the mechanism of the catechol- tyrosinase reaction." J. Amer. Chem. Soc. 60, 1545 (1938). 95, 30. Sakellaropoulos, ; P.G. " C r i t e r i a f o r s e l e c t i v e path promotion in electrochemical reaction sequences." AIChE Journal, 25_, No. 5, 781 (1979). 31. Sucre, V.S. "Electrochemical oxidation of phenol for waste water treatment." M.A.Sc. th e s i s . The University of B r i t i s h Columbia (Aug. 1979). 32. Chu, A.K.P., Fleischmann, M., and H i l l s , G.J. "Packed bed electrodes. I. The electrochemical extraction of copper ions from d i l u t e aqueous soluti o n s . " J . App. Electrochem. 4, 323 (1974). 33. Carr, J.P., and Hampson, N.A. "The lead dioxide electrode." Chem. Rev. 72, No. 6, 679 (1972). 34. Ronlan, A., "Phenols." Encyclopaedia of electrochemistry of the elements. M. Dekkar, New York, Vol. XI, 242 (1978). 35. R i f i , M.R., and Covitz, F.H. Introduction to organic electrochemistry. M. Dekkar, New York (1974). 36. Shields, J.R., and C o u l l , J . "Rate studies in the electrochemical oxidation of phenol." Trans. Am. Electrochem. Soc. 80_, 113 (1941). 37. Vladimir, K. "Analysis of dihydric phenols by gas chromatography." J. Chromatogr. 5_7, 132 (1971 ). 38. Wesley, W. Water q u a l i t y engineering f o r p r a c t i c i n g engineers. Barnes & Noble, New York, (1970). 39. Standard methods f o r the examination of water and waste water. Thirteenth e d i t i o n , APHA.AWWA.WPCF (1971). 40. Papouchado, L., et a l . "Anodic oxidation pathways of phenolic compounds, Part 2 Stepwise electron transfers and coupled hydro- oxylations." J. Electroanal. Chem. 65, 275 (1975). 41. Zuman, P. The eluci d a t i o n of organic electrode processes. Academic Press, New York (1969). 42. Singer, P.C., et a l . Report Summary: T r e a t a b i l i t y and assessment of coal conversion wastewaters: Phase 1, EPA-600/7-79-248 (June 1980). 43. Yoshizava, S., et a l . "Cathodic reduction of nitrobenzene on the packed bed copper electrode." B u l l e t i n of the Chemical Society of Japan, 49,, No. 11 , 2889 (1976). 44. Neale, G.H., and Nader, W.K. "Prediction of transport processes within porous media: D i f f u s i v e flow processes within an homogeneous swarm of spherical p a r t i c l e s . " A.I.Ch.E. Journal, 19, 112 (1973). 96. 45. Nam's, L., and McLaren, F. "Rapid mass transport to electrodes in foamed e l e c t r o l y t e . " J . Electrochem. Soc. 117, 1527 (1970). 46. Pickett, D.J., and Stanmore, B.R. "An experimental study of a single layer packed bed cathode in an electrochemical flow reactor." J . App. Electrochem. 5_, 95 (1975). 47. Sedahmed, G.H. "Mass transfer behaviour of gas evolving p a r t i c u l a t e - bed electrode." J . App. Electrochem. 9_, 37 (1979). 48. 01oman, C. " T r i c k l e bed electrochemical reactors." J . Electrochem. Soc. 126, No. 11, 1885 (1979). 49. Patterson, J.W., and Kodukala, P.S. "Biodegradation of hazardous organic poll u t a n t s . " CEP, 77_, No. 4, 48 (1981 ). 50. Oloman, C. "Electro-oxidation of benzene in a f i x e d bed reactor." J. App. Electrochem. 1_0, 553 (1980). 51. Weinberg, N.L., and Weinberg, H.R. "Electrochemical oxidation of organic compounds." Chem. Rev. 68_, No. 4, 445 (1968). 52. L i , K.Y., Kuo, C.H., and Weeks, J.L. "Kinetic study of ozone-phenol reaction in aqueous solutions." A.I.Ch.E. Journal, 25_, No. 4, 583 (1979). 53. Brockmann, H.E., and Oke, T.O. "Gas chromatography of barbiturates, phenolic a l k a l o i d s and xanthene bases, f l a s h heater methylation by means of trimethyl anilinium hydroxide." J. of Pharm. S c i . 58_, 370 (1969). 54. Perry, R.H., and C h i l t o n , CH. Chemical engineers handbook. F i f t h e d i t i o n , McGraw H i l l , New York (1973). 55. Reid, C.R., and Sherwood, T.K. The properties of gases and l i q u i d s . Second e d i t i o n , McGraw H i l l , New York (1966). 56. Hayduk, W., and Laudie, H. "Prediction of d i f f u s i o n c o e f f i c i e n t s f o r nonelectrolytes in d i l u t e aqueous solutions." A.I.Ch.E. Journal 20_, 611 (1974). APPENDIX 1 Sp e c i f i c a t i o n of A u x i l l i a r y Equipment and Materials Power supply Sorenson DCR 4D-25B Voltmeter range: 0-40V Ammeter range: 0-30A (smallest d i v i s i o n = 1 A) Voltmeter Central S c e i n t i f i c Co., D.C. Voltmeter Scales: 0-1.5 Volts (smallest d i v i s i o n 0-15 Volts (smallest d i v i s i o n Rotameter Brooks, f u l l view i n d i c a t i n g rotameter Type: 7-1110 Tube No.: R-7M-25-1 Float: 316 s t a i n l e s s steel Max. flow: 1400 cc/min (s.g. = 1) Scale: 0-100% l i n e a r Gas l i q u i d separators 2.5 cm I.D. and 60 cm long glass tube. Liquid o u t l e t located at 40 cm from the bottom (except for group VII where the i n l e t and outlet were interchanged) bed: 2 mm diameter glass beads. = .010 V) = .10 V) 98. F i l t e r 3.0 cm I.D. and 15 cm long glass tube f i l l e d with glass wool (Merck). Pressure gauge Marsh-type 3-100-SS with 316 st a i n l e s s steel tube scale 0-30 psi (% psi/div) Pump Barrish Pumps Co., N.Y. Model type: 12A-60-316 Flow data: 21 G.P.H. at 40 psid, 29 G.P.H. at 0 psid. (psid indicates d i f f e r e n t i a l pressure) Pump preset at 45 psid. pH meter Corning, Model 701A / d i g ital ionalyzer (accuracy ± 0.01 pH) Electrode: BJC-combination electrode Tubings 1. Imperial Eastman "Poly Flo" 66-P-3/8". 2. PVC h" schedule 40 piping. Valves 1. Whitey, forged body regulating, 316 S.S. 3/8" connections. 2. PVC-%" valve (chemline p l a s t i c ) . . 99. F i t t i n g s Swagelok compression tubing f i t t i n g 316 S.S. 3/8" P l a s t i c screen Supplied by Chicopee Manufacturing Co., Georgia Saran type Max. operating temperature = 125°F Chemical resistance: good resistance to acids and most a l k a l i s top layer, s t y l e 6100900, weight/sq.yd. = 7 oz. bottom layer, s t y l e 61010XX, weight/sq.yd. = 10.6 oz. Analytic equipment and operating conditions s p e c i f i c a t i o n s a) Gas chromatography s p e c i f i c a t i o n s Gas chromatograph Manufacturer: Varian Aerograph Model: 1440 s e r i e s , single column model Detection: flame i o n i z a t i o n detector Chromatographic columns Supplier: Western Chromatography Supplies, New Westminster, B.C. Material : glass 1. Column used for analysis of monohydric phenols Dimensions: 2 mm I.D., 6.4 mm O.D., 6 f e e t long - Packing: 10% SP-2100 on 100/120 Supelcoport ( d e t a i l s of the packing 1 0 0 . are given in B u l l e t i n 742D by Supelco, Inc.). Operating conditions Injector port temperature 150°C Column temperature 130°C (brought to 115°C for analysis of phenolic mixtures) Detector temperature 175°C Ca r r i e r gas N 2 pr He . Carrier gas flow 30 ml/min A i r flow 300 ml/min H 2 flow 30 ml/min Attenuation - varied for d i f f e r e n t concentrations Recorder Model: Sargent SRG-GC, Se r i a l number 237 0073 Response 1 mV f u l l scale 2. Column used for analysis of dihydric phenols Dimensions: 2 mm I.D., 6.4 mm O.D., 1 m long Packing: Porapak P (80/100 mesh) - support Carbonax 20 M - stationary phase Operating conditions Injector port temperature 260°C Column temperature 220°C Detector temperature 280°C C a r r i e r gas He (oxygen content under 10 p.p.m) Carrier gas flow 22 ml/min Air flow 300 ml/min H 9 flow 37 ml/min Recorder Model : Watanabe MC 641, Serial number 575283 Response 1 mV f u l l scale 3. Column attempted for catechol analysis [52,53] Dimensions: 2 mm I.D., 6.4 mm O.D., 1 m long Packing: 3% OV-17 on chromosorb W (HP) 80/100 mesh Operating conditions Injection port temperature 300°C Column temperature 140°C Detector temperature 300°C Carrier gas He Ca r r i e r gas flow 40 ml/min A i r flow 300 ml/min H 2 flow 40 ml/min Recorder Model: hp 17505 A Range 0.1-100 MV Syringe Supplier: Unimetrics Sample s i z e : 1 yl T.O.C. analysis s p e c i f i c a t i o n s Model: Beckman 915 t o t a l organic carbon Analyzer: Beckman 865 infrared analyzer Operating Conditions Temperature of the t o t a l carbon channel 1000°C Oxygen flow 250 ml/min Syringe Hamilton with automatic plunger Sample siz e 50 ul Recorder Model: Hewlett Packard 7127A Response: 1 mV f u l l scale Chart speed: 1 cm/min GC/MS Analysis s p e c i f i c a t i o n s Manufacturer: Hewlett-Packard Model: 5985B (Quadropole mass spectrometer) F u l l y i n t e r a c t i v e data system HP-1000 series computer Chromatographic column Supplier: Hewlett-Packard Material: Fused s i l i c a c a p i l l a r y Dimensions: 0.32 mm I.D. 25 metres long Liquid phase: SE-54 ( S i l i c o n e gum) Operating conditions Injection port temperature 260°C Temperature program 30°C to 260°C at 8°C/min Car r i e r gas He Linear v e l o c i t y : 50-80 cm/sec Mass spectrometer conditions Mode of i o n i z a t i o n : Electron Impact (70 eV) Ion source temperature: 200°C Electron m u l t i p l i e r : 1600-2000 V (1) Run time 40 (2,3,4) St a r t , stop masses 41,500 amv (6) A/D Measurements per datum point [ 3.0]i (7) Threshold 40 min (8) Scan s t a r t delay i (14) Ion source temperature [202.0] So l i d Probe Inlet conditions Temperature program: 30°C to 250°C at 25°C/min Reagents Phenol - loose c r y s t a l s , reagent grade Matheson Coleman & Bell p-Benzoquinone - P r a c t i c a l Matheson Coleman & Bell S i l v e r Nitrate - Fine reagent MBW Chemicals Sodium Sulfate - Anhydrous, granular, An a l y t i c a l grade Mallinckrodt Sodium Hydroxide - p e l l e t s , reagent American S c i e n t i f i c and. Chemical S u l f u r i c agent - reagent A.C.S. A l l i e d Chemical Buffer - Fisher S c i e n t i f i c (2 ± 0.02) p-cresol, 0-cresol - c r y s t a l l i n e BDH Laboratory Chemicals group Resorcinol - laboratory grade Fisher S c i e n t i f i c Company < Catechol - Pyrocatechin (resublimed) Fisher S c i e n t i f i c Company 2.3- Dimethyl phenol _ 1 a b o r a t o r v a r a d e 3.4- Dimethyl phenol laboratory grade Fisher S c i e n t i f i c Company Magnesium Sulfate - Anhydrous, powder, Analytical reagent Ma 11inckrodt Methylene chloride - Dow Chemical of Canada Ltd. Methylating agent (Methelute) Pierce Chemicals Co. Rockford Water for solutions - Laboratory, single d i s t i l l e d water APPENDIX 2 Experimental Data Ch a r a c t e r i s t i c s for a l l experiments a) Mode of operation: Batch experiments using undivided c e l l b) Cell d e s c r i p t i o n : Cathode: s t a i n l e s s steel 316 plate Anode: Pb0 2 electrodeposited on graphite feeder plate P a r t i c l e s : electrodeposited Pb0 2 crushed and sized (obtained from P a c i f i c Engineering and Production Co., Nevada) Size: 0.7 < dp < 1.1 mm Weight: 250 gm V o l u m e : n.337 5°g/c.c = 2 2 c " 3 [54] Void f r a c t i o n (e) = 5 ^ 2 2 = 0.59 Separation: two layers of saran screen between cathodic plate and Pb0 2 p a r t i c l e s . E l e c t r o p l a t e r s tape used for adhesion where necessary. Group I Anodic oxidation of Phenol Group II Anodic oxidation of p-Cresol Group III Anodic oxidation of 0-Cresol Group IV Anodic oxidation of 2,3-Xylenol Group V Anodic oxidation of 3,4-Xylenol Group VI Anodic oxidation of Resorcinol I 1 0 6 . Group VII Anodic oxidation of catechol Group VIII Anodic oxidation of mixture of monohydric phenolics of i n t e r e s t Group IX Anodic oxidations f o r GC/MS analysis Temperatures A l l experiments were set up at a temperature of 22-24°C with the use of heat exchanger except in the groups IV, V and VIII which were carried out at 40-45°C. Anodization Before each experiment the anode was treated with 20% ^SO^ at 10 A (2.5-3.5 Volts) f o r 1 hour. RUN 1-1 E l e c t r o l y t e KA) i(A/m" 2) (c .c/min) I n i t i a l pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 770 1 .9 1 gm/1 phenol t (min) AV (volts) phenol mg/l % • oxidized 0 7.10 910 0 15 7.10 750 17.6 30 7.10 635 30.2 45 7.10 480 47.3 60 7.10 350 61 .5 75 7.10 300 67.0 90 7.10 200 78.0 105 7.10 140 84.6 120 7.10 95 89.6 Comment: The net change in T.O.C. was p r a c t i c a l l y undetectable due to the high amount of carbon present in s o l u t i o n . RUN 1-2 E l e c t r o l y t e 1(A) i(A/m" 2) (c.c/min) I n i t i a l pH 5 g/1 Na2S0 4 0.44 g/1 H 2S0 4 5 263.2 719.25 2.16 1 g/1 phenol t AV phenol (min) ( v o l t s ) mg/l % o x i d i z e d 0 6.15 970 0 15 6.15 875 9.8 30 6.15 750 22.7 45 6.10 670 30.9 60 6.10 595 38.7 75 6.05 533 45.1 90 6.00 432 55.5 105 6.00 330 66.0 120 6.00 291 70.0 RUN 1-3 E l e c t r o l y t e 1(A) i(A/m" 2) (c.c/min) I n i t i a l pH 5 g/1 Na 2S0 4 0.44 g/1 H2SO4 15 789.5 679 2.11 1 g/1 phenol t AV (min) ( v o l t s ) 0 12.70 15 12.70 30 12.65 45 11.50 60 11.30 75 11 .00 90 11.00 105 10.60 120 10.70 phenol mg/l % o x i d i z e d 1010 0 805 20.3 545 46.0 480 52.5 350 65.4 265 73.8 195 80.7 130 87.1 80 92.1 RUN 1-4 El e c t r o l y t e 1(A) i(A/m ) 4> I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 770 2.33 0.1 g/1 phenol t (min) AV (volts) phenol mg/l % oxidized T.O.C. mg/l % oxidized 0 7.40 108 0 84.5 0 15 7.20 46 57.4 82.0 3.0 30 6.90 12 88.9 79.0 6.0 45 6.65 2 98.2 78.0 7.0 60 6.60 0 100.0 73.5 13.0 75 6.50 72.0 14.0 90 6.50 70.3 17.0 105 6.40 69.0 18.0 120 6.40 66.0 22.0 Comment: T.O.C. reported i s a c t u a l l y the total carbon because the concentration of inorganic carbon and i t s v a r i a t i o n was n e g l i g i b l e in a l l cases. RUN 1-5 E l e c t r o l y t e 1(A) i(A/m" ) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 784 2.56 0.5 g/1 phenol t AV phenol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 8.40 683 0 555 0 15 8.35 467 31.6 535 4.0 30 8.40 305 55.3 525 6.0 45 8.40 208 69.6 520 7.0 60 8.60 168 75.4 508 9.4 75 8.65 160 76.6 498 11.4 90 8.70 168 75.4 485 14.0 105 8.70 168 75.4 475 16.0 120 8.70 168 75.4 455 18.0 RUN 2-1 E l e c t r o l y t e KA) i(A/m~ 2) (c.c/min) I n i t i a l pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 623 2.3 1 g/1 p-cresol t AV (min) (volts) 0 7.9 15 8.20 30 8.00 45 7.80 60 8.30 75 8.15 90 7.50 105 7.70 120 7.50 p-cresol mg/l % oxidized 823 0 780 5.2 625 24.1 540 34.4 485 41 .1 433 47.4 390 52.6 355 56.9 305 62.9 113. RUN 2-2 E l e c t r o l y t e KA) i(A/m" 2) (c.c/min) I n i t i a l PH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 1 g/1 p-cresol 5 263.2 64.1 2.1 t AV p-cresol (min) (volts) mg/l % oxidized 0 5.40 1100 0 15 5.60 960 12.7 30 5.45 920 16.4 45 5.45 860 21.8 60 5.50 740 32.7 75 5.45 720 34.6 90 5.45 710 35.5 105 5.45 640 41.8 120 5.40 590 46.4 RUN 2-3 E l e c t r o l y t e KA) i(A/m" 2) (c.c/min) I n i t i a l pH 5 g/1 Na 2S0 4 0.44 g/1 H2'S04 15 789.5 616 2.40 1 g/1 p-cresol t AV (min) (volts) 0 12.4 15 11.6 30 11.1 45 11.1 60 11.0 75 10.9 90 11.0 105 10.8 120 10.8 p-cresol mg/l % oxidized 1100 0 775 29.6 625 43.2 545 50.5 535 51.4 470 57.3 450 59.1 365 66.8 325 70.5 115 . RUN 2 -4 E l e c t r o l y t e 1(A) i(A /m ) * ' I n i t i a l ( c . c / m i n ) pH 5 g/1 N a 2 S 0 4 0 . 4 4 g/1 H 2 S 0 4 10 5 2 6 . 3 672 1.74 0.1 g/1 p - c r e s o l t AV p - c r e s o l T . O . C . (min) ( v o l t s ) m g / l % o x i d i z e d m g / l % o x i d i z e d 0 8 . 0 0 69 0 7 2 . 0 0 15 7 . 5 0 40 4 1 . 3 7 0 . 2 2 . 5 30 7 . 4 0 26 6 1 . 6 6 9 . 3 3 . 8 45 7 . 3 0 19 7 2 . 5 6 8 . 4 5 . 0 60 7 . 2 0 15 7 9 . 0 68 .1 5 . 4 75 7 . 3 0 11 8 4 . 8 6 6 . 7 7 .4 90 7 . 4 0 9 8 7 . 0 6 2 . 9 1 2 . 6 105 7 . 5 0 8 8 8 . 4 61 .1 1 5 . 2 120 7 . 5 0 6 91 . 3 60 .1 1 6 . 6 RUN 2-5 E l e c t r o l y t e 1(A) i(A/m ) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 668.5 2.36 0.5 g/1 p-cresol t AV p-cresol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 8.7 355 0 300 0 15 8.5 300 15.5 300 0 30 8.3 223 37.2 300 0 45 8.0 208 41 .4 300 0 60 7.9 193 45.6 300 0 75 7.8 168 52.7 300 0 90 7.5 140 60.6 300 0 105 7.7 125 64.8 299 0.3 120 7.6 115 67.6 292 2.7 RUN 3-1 E l e c t r o l y t e KA) i(A/m" 2) (c.c/min) I n i t i a l PH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 658 2.34 1 g/1 0-cresol t AV (min) (volts) 0 9.2 15 8.6 30 8.0 45 7.9 60 8.0 75 8.0 90 8.0 105 8.0 120 8.0 0-cresol mg/l % oxidized 853 0 790 7.4 735 13.8 600 29.7 555 34.9 470 44.9 405 52.5 368 56.9 300 64.8 RUN 3-2 E l e c t r o l y t e ' 1(A) ifA/m"*) $ I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 5 263.2 658 2.43 1 g/1 O-cresol t AV O-cresol (min) (volts) mg/l % oxidized 0 6.0 995 0 15 5.9 978 1.7 30 6.0 905 9.1 45 6.0 770 22.6 60 6.0 742 25.4 75 5.9 715 28.1 90 5.9 620 37.7 105 5.9 572 42.5 120 5.9 535 46.2 RUN 3.-3 E l e c t r o l y t e 1(A) i(A/m' 2) 4> (c.c/min) I n i t i a l PH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 15 789.5 630 2.61 1 g/1 0-cresol t AV 0-cresol (min) (volts) mg/l % oxidized 0 11.3 905 0 15 10.0 855 5.5 30 9.5 657 25.4 45 9.3 585 35.4 60 9.1 515 43.1 75 9.0 400 55.8 90 9.0 310 65.8 105 9.0 220 75.7 120 9.1 170 81 .2 RUN 3-4 E l e c t r o l y t e 1(A) i(A/m~^) <f> I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 686 2.35 0.1 g/1 O-cresol t AV O-cresol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 8.0 95 0 90 0 15 7.8 65 31.6 85 5.6 30 7.6 33 65.3 83 7.8 45 7.5 17 82.1 83 7.8 60 7.5 13 86.3 - - 75 7.5 7 92.6 82 8.9 90 7.5 5 94.7 81 10.0 105 7.7 3 96.8 80 11.1 120 7.7 3 96.8 80 11.0 RUN 3 - 5 E l e c t r o l y t e 1(A) i ( A / m ) <J> I n i t i a l ( c . c / m i n ) pH 5 g/1 N a 2 S 0 4 0 . 4 4 g/1 H 2 S 0 4 10 5 2 6 . 3 669 2 . 4 8 0 . 5 g/1 0 - c r e s o l t AV 0 - c r e s o l T . O . C . (min) ( v o l t s ) m g / l % o x i d i z e d m g / l % o x i d i z e d 0 8.1 505 0 570 0 15 7 .7 395 2 1 . 8 545 4 . 3 9 30 7 . 5 320 3 6 . 6 545 4 . 3 9 45 7 . 3 265 4 7 . 5 545 4 . 3 9 60 7 . 3 238 5 2 . 9 545 4 . 3 9 75 7 . 2 198 6 0 . 8 545 4 . 3 9 90 7 . 2 165 6 7 . 3 545 4 . 3 9 105 7 . 2 115 7 7 . 2 528 7 .37 120 7 . 2 88 8 2 . 6 520 8 . 7 7 RUN 4-1 E l e c t r o l y t e 1(A) i(A/m~*) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 784 2.54 1 g/1 2,3-Xylenol t AV 2,3-Xylenol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 6.5 625 0 578 0 15 6.6 455 27.2 560 3.1 30 6.8 325 48.0 550 4.8 45 7.3 205 67.2 525 9.2 60 7.7 140 77.6 515 10.9 75 7.9 75 88.0 500 13.5 90 8.1 22 96.5 495 14.4 105 8.2 0 100.0 483 16.4 120 8.3 0 100.0 458 20.8 RUN 4-2 E l e c t r o l y t e 1(A) i(A/m~ £) 4» I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 5 263.2 777 2.5 1 g/1 2,3-Xylenol t AV 2,3-Xylenol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 5.0 830 0 714 0 15 5.1 712 14.2 712 0.4 30 5.2 625 24.7 710 0.7 45 5.3 595 28.3 707 1.1 60 5.4 515 38.0 705 1 .4 75 5.5 450 45.8 702 1.8 90 5.6 375 54.8 700 2.1 105 5.7 310 62.7 695 2.8 120 5.9 260 68.7 687 3.9 RUN 4-3 E l e c t r o l y t e 1(A) i(A/m* ) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 15 789.5 791 2.58 1 g/1 2,3-Xylenol t AV 2,3-Xylenol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 8.6 780 0 707 0 15 8.9 555 28.9 705 0.3 30 9.7 380 51.3 697 1 .4 45 10.3 235 69.9 686 2.7 60 10.6 155 80.1 663 6.2 75 10.7 95 87.8 620 12.3 90 10.7 50 93.6 592 16.3 105 10.7 30 96.2 585 17.3 120 10.6 0 100.0 580 18.0 RUN 4-4 E l e c t r o l y t e 1(A) i(A/m - 2) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 791 2.36 1 g/1 2,3-Xylenol t AV 2,3-Xylenol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 7.0 97 0 73.5 0 15 6.8 46 52.6 73.5 0 30 7.0 24 75.8 73.5 0 45 7.3 15 84.5 73.5 0 60 7.4 6 93.8 73.5 0 75 7.4 0 100.0 71.3 3.1 90 7.4 0 100.0 69.0 6.1 105 7.4 0 100.0 66.0 10.2 120 7.4 0 100.0 66.0 10.2 RUN 4-5 E l e c t r o l y t e 1(A) i(A/m" ) $ I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 864.5 2.3 0.5 g/1 2,3- Xylenol t AV 2,3-Xylenol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 7.4 380 0 251 .3 0 15 7.2 295 22.4 251 .3 0 30 ' 7.9 160 57.9 251 .3 0 45 8.5 82 78.4 251.3 0 60 8.8 33 91.3 243.8 3.0 75 8.9 17 95.5 240.0 4.5 90 8.7 5 98.7 237.8 5.4 105 8.5 0 100.0 232.5 7.5 120 8.4 0 100.0 219.0 12.8 RUN 5-1 E l e c t r o l y t e 1(A) i(A/m" ) • I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 819 2.32 1.2 g/1 3,4- Xylenol t AV (min) (volts) 0 5.9 15 6.5 30 6.5 45 6.5 60 6.5 75 6.4 90 6.4 105 6.3 120 6.3 3,4-Xylenol mg/l % oxidized 1110 0 1025 7.7 900 18.9 825 25.7 785 29.3 690 37.8 655 41.0 623 43.9 600 46.0 RUN 5-2 E l e c t r o l y t e 1(A) i(A/m ) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 5 263.2 805 2.34 1.2 g/1 3,4- Xylenol t AV 3,4-Xylenol (min) (volts) mg/l % oxidized 0 4.4 1290 0 15 4.7 1250 3.1 30 4.8 1218 5.6 45 4.8 1140 11 .6 60 4.8 1085 15.9 75 4.8 1030 20.2 90 4.8 1000 22.5 105 4.8 965 25.2 120 4.8 915 29.1 RUN 5-3 El e c t r o l y t e 1(A) i(A/ni ) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 15 789.5 805 2.25 1.2 g/1 3,4- Xylenol t AV 3,4-Xylenol (min) (volts) mg/l % oxidized 0 7.4 1175 0 15 7.8 890 24.3 30 7.7 765 34.9 45 7.6 675 42.6 60 7.6 581 50.6 75 7.6 515 56.2 90 7.6 465 60.4 105 7.6 423 64.0 120 7.5 395 66.4 RUN 5-4 E l e c t r o l y t e 1(A) i(A/m" ) cf) I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 10 526.3 819 2.33 0.44 g/1 H 2S0 4 0.1 g/1 3,4- Xylenol t AV (min) (volts) 0 6.6 15 6.3 30 6.3 45 6.4 60 6.4 75 6.4 90 6.4 105 6.4 120 6.3 3,4-Xylenol mg/l % oxidized 103 0 67 35.4 48 53.9 33 68.0 27 73.8 22 79.1 19 81.6 17 83.8 14 86.9 RUN 5-5 E l e c t r o l y t e 1(A) i(A/m" 2) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 784 2.32 0.5 g/1 3,4- Xylenol t AV 3,4-Xylenol (min) (volts) mg/l % oxidized 0 6.6 515 0 15 6.4 393 23.7 30 6.2 290 43.7 45 6.1 230 55.3 60 6.1 196 61.9 75 6.1 165 68.0 90 6.0 143 72.2 105 5.9 130 74.8 120 6.0 108 79.0 RUN 6-1 E l e c t r o l y t e 1(A) i(A/m"*) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 805 2.16 1 g/1 Resorcinol t AV Resorcinol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 7.4 1200 0 725 0 15 7.2 1130 5.8 715 1.4 30 7.2 970 19.2 665 8.3 45 7.0 855 28.8 660 9.0 60 7.0 695 42.1 653 9.9 75 7.0 635 47.1 635 12.4 90 7.0 545 54.6 625 13.8 105 6.9 420 65.0 625 13.8 120 6.7 380 68.3 625 13.8 RUN 6-2 Electrolyte 1(A) i(A/m"2) <J> Initial (c.c/min) pH 5 g/1 Na2S04 0.44 g/1 H2S04 5 263.2 763 2.3 1 g/1 Resorcinol t AV Resorcinol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 5.5 1230 0 750 0 15 5.5 1190 3.3 - 750 0 30 5.4 1150 6.5 700 6.7 45 5.3 1105 10.2 700 6.7 60 5.3 1000 18.7 700 6.7 75 5.3 980 20.3 675 10.0 90 5.2 930 24.4 675 10.0 105 5.3 855 30.5 658 12.3 120 5.2 810 34.2 658 12.3 RUN 6-3 E l e c t r o l y t e 1(A) i(A/m ) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 15 789.5 784 2.23 1 g/1 Resorcinol t AV Resorcinol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 10.8 1205 0 715 0 15 9.9 1070 11.2 715 0 30 9.3 890 26.1 670 6.3 45 9.3 755 37.3 640 10.5 60 9.0 650 46.1 635 11.2 75 9.3 510 57.7 630 11.9 90 9.4 425 64.7 615 14.0 105 9.5 310 74.3 578 19.2 120 9.7 200 83.4 585 18.2 RUN 6-4 E l e c t r o l y t e 1(A) i(A/m~ £) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 / 526.3 816 2.59 0.1 g/1 Resorcinol /• — t AV Resorcinol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 8.2 87 0 66 0 15 8.0 40 54.0 55 14.5 30 7.8 0 100.0 52 20.6 45 7.7 0 100.0 47 28.2 60 8.0 0 100.0 41 37.4 75 8.5 0 100.0 37 44.3 90 8.8 0 100.0 33 49.9 105 9.0 0 100.0 31 52.7 120 9.0 0 100.0 ' 26 61.1 RUN 6-5 E l e c t r o l y t e 1(A) i(A/m~ ) <f> I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 798 1.45 0.5 g/1 Resorcinol t AV Resorcinol T.O.C. (min) (volts) mg/l % oxidized mg/l % oxidized 0 3.4 490 0 377 0 15 3.5 285 41 .8 330 12.5 30 3.5 145 70.4 308 18.3 45 3.5 20 95.9 288 23.6 60 3.5 0 100.0 267 29.2 75 3.5 0 100.0 245 35.0 90 3.5 0 100.0 245 35.0 105 3.5 0 100.0 255 32.4 120 3.5 0 100.0 230 39.0 RUN 7-1 El e c t r o l y t e KA) i(A/m' 2) (c.c/min) I n i t i a l pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 798 2.39 1 g/1 Catechol t (min) AV (volts) T.O.C. mg/l % oxidized 0 5.3 800 0 15 6.5 755 5.6 30 6.6 635 20.6 45 6.5 575 28.1 60 6.5 515 35.6 75 6.4 468 41.5 90 6.3 400 50.0 105 6.2 410 48.8 120 6.2 435 45.6 Comment: A l l the samples were centrifuged and T.O.C. analysis was performed on the centrifugate in the case of catechol runs. 138. RUN 7-2 El e c t r o l y t e KA) i(A/m~ 2) (c.c/min) Ini t i a l PH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 1 g/1 Catechol 5 263.2 823 2.34 t AV T.O.C. (min) (volts) mg/l % oxidized 0 3.8 720 0 15 4.3 705 2.1 30 4.5 635 11.8 45 4.6 570 20.8 60 4.6 535 25.7 75 4.5 495 31.3 90 4.5 455 36.8 105 4.4 410 43.1 120 4.4 390 45.8 RUN 7-3 E l e c t r o l y t e 1(A) i(A/min~^) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 15 789.5 840 2.30 0.44 g/1 H 2S0 4 1 g/1 Catechol t AV (min) (volts) 0 6.9 15 7.2 30 7.4 45 7.3 60 7.2 75 7.1 90 7.1 105 7.0 120 7.0 T.O.C. mg/l % oxidized 535 0 463 13.5 410 23.4 365 31 .8 343 35.9 318 40.6 308 42.4 263 50.8 270 49.5 14:0. RUN 7-4 El e c t r o l y t e 1(A) i(A/m~ 2) (c.c/min) I n i t i a l PH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 84.4 2.34 0.1 g/1 Catechol t AV T.O.C. (min) (volts) mg/l % oxidized 0 5.8 84 0 15 5.9 78 7.1 30 5.9 75 10.7 45 5.9 69 18.5 60 5.9 65 22.6 75 5.9 60 28.6 90 5.8 46 45.2 105 5.8 43 48.8 120 5.8 39 53.6 RUN 7-5 E l e c t r o l y t e 1(A) i(A/m" 2) * I n i t i a l (c.c/min) pH 5 g/1 Na 2S0 4 0.44 g/1 H 2S0 4 10 526.3 833 2.52 0.5 g/1 Catechol t AV (min) ( v o l t s ) 0 5.5 15 5.8 30 5.9 45 5.8 60 5.7 75 5.7 90 5.6 105 5.6 120 5.6 T.O.C. mg/l % o x i d i z e d 335 0 295 11.9 255 23.9 200 40.3 180 46.3 175 47.8 160 52.2 155 53.7 125 62.7 142. B.O.D. Analysis (Runs 7-2, 7-3) B.O.D. Analysis r e s u l t s Run 7-2 (5 amps) B.O.D. (5 days at 20°C) ppm: I n i t i a l sample (t = 0 min) 930 Final sample (t = 120 min) 240 % Reduction in B.O.D. 74 B.O.D. Analysis r e s u l t s Run 7-3 (15 amps) B.O.D. (5 days at 20°C) ppm: I n i t i a l sample (t = 0 min) 600 Final sample (t = 120 min) 117 % Reduction in B.O.D. 81 143. C.O.D. Analysis (Runs 7-2, 7-3) Sample Description D i l u t i o n ( i f any) Titre-FAS Blank-Sample (m.l) (m.l) C.O.D. .(mg/D Average C.O.D. mg/l I n i t i a l sample (run 7-2) (t = 0 min) 20 10 23.90 21.05 2.85 5.70 2103.3 2103.3 2103.3 Final sample (run 7-2) (t = 120 min) 20 10 24.70 23.00 2.05 3.75 1512.9 1383.8 1448.3 % Reduction in C.O.D. 31 .1 I n i t i a l sample (run 7-3) (t = 0 min) 20 10 24.30 22.25 2.45 4.50 1884.5 1660.5 1772.5 Final sample (run 7-3) (t = 120 min) 20 10 25.4 24.3 1 .35 2.45 996.3 904.1 950.2 % Reduction in C.O.D. 46 .4 144. COMPARISON OF PERFORMANCE OF DIFFERENT PHENOLICS 1. Variation of final % oxidized with initial concentration of phenolics at 10 A 2. Variation of initial rate with initial concentration at 10 A 3. Variation of final % oxidized with applied current (1 g/1 runs) 4. Variation of initial rate of oxidation with applied current (1 g/1 runs) Name of Compound % Final oxidized Initial cone, ppm Initial cone. mole/m3 x 106 Initial rate ppm/min Initial rate g.mol/sec x 10° Phenol 100.0 108 1.15 4.13 3.66 75.4 683 7.26 14.40 12.75 89.6 910 9.67 10.67 9.45 O-Cresol 96.8 95 0.88 2.00 1 .54 82.6 505 4.68 7.33 5.66 64.8 853 7.90 4.20 3.24 p-Cresol 91 .3 69 0.64 1 .93 1 .47 67.6 355 3.29 3.67 2.83 62.9 823 7.62 2.87 2.21 Resorcinol 100.0 87 0.78 2.90 2.20 100.0 490 4.45 11 .50 8.70 68.3 1200 10.90 7.67 5.81 2,3-Xylenol 100.0 97 0.80 3.40 2.32 100.0 380 3.12 5.67 3.87 100.0 625 5.12 11 .33 7.74 3,4-Xylenol 86.9 103 0.84 2.40 1 .66 79.0 515 4.22 8.13 5.55 46.0 m o 9.10 5.67 3.87 Note: Similar data could not be obtained from catechol runs because concen- trations of catechol samples were not determined. ./cont'd 145. COMPARISON OF PERFORMANCE OF DIFFERENT PHENOLICS/cont1d Name of Compound Applied current (Amps) Fi na 1 % oxidized I n i t i a l rate ppm/mi n I n i t i a l rate g.mol/sec x 10° Phenol 5 70.0 6.33 5.61 10 89.6 10.67 9.45 15 92.1 13.67 12.11 O-Cresol 5 46.2 3.00 2.32 10 62.9 3.93 3.03 15 81 .2 7.67 5.92 p-Cresol 5 46.4 6.00 4.63 10 50.0 6.60 5.09 15 70.5 15.83 12.21 Resorcinol 5 34.2 2.78 2.10 10 68.3 7.67 5.81 15 83.4 10.00 7.57 2,3-Xylenol 5 68.7 7.87 5.38 10 100.0 11 .33 7.74 15 100.0 15.00 10.25 3,4-Xylenol 5 29.1 2.40 1 .64 10 46.0 7.00 4.78 15 66.4 13.67 9.34 Note: The rates were determined from the l i n e a r portion of the curves in a l l cases. Elec t ro ly te 1(A) i (A/m" 2 ) 5 g/1 Na 2 S0 4 0.16 g/1 p-Cresol 0.44 g/1 H 2 S0 4 0.20 g/1 2,3-Xylenol 10 526.3 1.37 g/1 phenol 0.17 g/1 3,4-Xylenol 0.28 g/1 0-cresol ^ t AV (min) (volts) 0 5.5 15 5.6 30 5.8 45 5.9 60 6.0 75 6.0 90 6.0 105 6.0 120 6.0 Phenol mg/l * oxidized 1250 0 1190 4.8 1110 11.2 998 20.2 850 32.0 798 36.2 745 40.4 678 45.8 615 50.8 0-Cresol mg/l % oxidized 248 0 240 3.2 234 5.7 208 16.1 181 27.0 179 27.8 167 32.7 158 36.3 152 38.7 RUN 8-1 $ I n i t i a l c .c /min pH 823 2.48 p-Cresol mg/l % oxidized 122 0 116 4.9 115 5.7 110 9.8 101 17.2 98 19.7 101 17.2 101 17.2 98 19.7 2,3-Xylenol mg/l % oxidized 137 0 131 4.6 124 9.5 115 16.1 98 28.5 97 29.2 93 32.1 90 34.3 89 35.0 3,4-Xylenol mg/l * oxidized 139 0 131 5.8 139 0 139 0 129 7.2 134 3.6 126 9.4 134 3.6 134 3.6 Total Total mg/l * oxidized 1896 0 1808 4.6 1722 9.2 1570 17.2 1359 28.3 1306 31.1 1232 35.0 1161 38.8 1088 42.6 RUN 8-2 E lec t ro ly te I c d . Average flow rate I n i t i a l (A) (A/m" 2) c.c/min pH 5 g/1 Na 2 S0 4 0.18 g/1 p-cresol 0.44 g/1 H 2 S 0 4 0.16 g/1 2,3-Xylenol 10 526.3 793 2.36 1.33 g/1 phenol 0.17 g/1 3,4-Xylenol 0.30 g/1 O-cresol t (min) (vol ts) Phenol 0-cresol P- Cresol 2,3-Xylenol 3,4-Xylenol Total mg/l Total % oxidized mg/l % oxidized mg/l % oxidized mg/1 % oxidized mg/l % oxidized mg/1 % oxidized 0 5.2 1200 0 291 0 143 0 124 0 131 0 .1889 0 15 5.5 1093 8.9 269 7.6 137 4 .2 117 5 .7 130 0.8 1746 7.6 30 5.7 948 21 .0 240 17.5 120 16 1 103 16 9 116 11 .5 1527 19.2 45 5.8 898 25.2 238 18.2 121 15 4 103 16 .9 128 2.3 1488 21.2 60 5.8 840 30.0 220 24.4 116 18 9 99 20 2 125 4.6 1401 25.8 75 5.8 735 38.8 212 27.2 114 20 3 95 23 4 123 6.1 1279 32.3 90 5.9 700 41.7 208 28.5 116 18 9 99 20 2 131 0 1254 33.6 105 5.9 605 49.6 184 36.8 108 24 5 87 29 8 123 6.1 1107 41.4 120 5.9 520 56.7 164 43.6 102 28 7 82 33 9 124 5.3 992 47.5 135 5.9 475 60.4 157 46.1 102 28 7 80 35 5 126 3.8 941 50.2 150 5.9 400 66.7 143 50.9 99 30 8 76 38 7 128 2.8 846 55.2 165 5.9 350 70.8 126 56.7 93 35 0 73 41 1 130 0.8 773 59.1 180 5.9 305 74.6 111 61.9 88 38 5 67 46 0 119 9.2 690 63.5 RUN 8-3 E l e c t r o l y t e I Average flow rate I n i t i a l (A) (A/m" 2) c .c /min pH 5 g/1 Na ,so 4 0.14 g/1 p-cresol 0.44 g/1 H 2 S 0 4 0.14 g/1 2,3-Xylenol 10 526.3 794.5 2.38 1.14 g/1 phenol 0.14 g/1 3,4-Xylenol 0.27 g/1 O-cresol t AV Phenol 0-Cresol P- Cresol 2,3-Xylenol 3,4-Xylenol Total Total (min) (vol ts) mg/l % oxidized mg/l % oxidized mg/1 % oxidized mg/l % oxidized mg/l % oxidized mg/l % oxidized 0 5.2 1070 0 246 0 127 0 109 0 122 0 1674 0 15 5.4 1005 6.1 228 7.3 127 0 101 7.3 112 8.2 1573 6.0 30 5.5 970 9.4 223 9.4 125 1.6 99 9.2 117 4.1 1534 8.4 45 5.6 885 17.3 217 11 .8 123 3.2 104 4.6 122 0 1451 13.3 60 5.7 735 31 .3 192 22.0 103 18.9 96 11.9 114 6.6 1240 25.9 75 5.8 593 44.6 154 37.4 90 29.1 83 23.9 101 17.2 1013 39.5 90 5.8 563 47.4 143 41 .9 90 29.1 88 19.3 118 3.3 1002 40 . l ' 105 5.8 520 51.4 140 43.1 80 37.0 80 26.6 97 20.5 917 45.2 120 5.8 428 60.0 118 52.0 79 37.8 70 35.8 106 13.1 801 52.2 .cont 'd RUN 8-3/cont 'd t (min) &V (volts) Phenol 0- Cresol P- Cresol 2,3-Xylenol 3,4-Xylenol Total mg/l Total % oxidizt mg/l % oxidized mg/1 % oxidized mg/1 % oxidized mg/l t oxidized mg/l % oxidized 135 5.8 332 69.0 94 61.8 73 42.5 62 43.1 106 13.1 667 60.2 150 5.7 260 75.7 76 69.1 65 48.8 55 49.5 93 23.8 549 67.2 165 5.7 198 81.5 69 72.0 60 52.8 50 54.1 91 25.4 468 72.0 180 5.6 142 86.7 61 75.2 52 59.1 39 64.2 83 32.0 377 77.5 1 1 195 5.6 95 91.1 36 85.4 48 62.2 35 67.9 83 32.0 297 82.3 i 210 5.6 78 92.7 21 91.5 42 66.9 25 77.1 72 41 .0 238 85.8 j 225 5.6 55 94.9 18 92.7 39 69.3 21 80.7 70 42.6 203 87.9 240 5.6 43 96.0 9 96.3 38 70.1 14 87.2 54 55.7 158 90.6 j 255 5.6 28 97.4 7 97.2 34 73.2 12 89.0 56 54.1 137 91 .8 270 5.6 10 99.1 4 98.4 29 77.2 9 91.7 45 63.1 97 94.2 j 285 5.6 0 100.0 0 100.0 28 78.0 7 93.6 48 60.7 83 95.0 300 5.6 0 100.0 0 100.0 24 81.1 4 96.3 43 65.2 71 95.8 1 — ; i j i I j • j i i <JZ> 150. T.O.C. Analysis r e s u l t s , Run 8-3 t T.O.C. (min) mg/l % oxidized 0 1480 0 60 1380 6.8 120 1320 10.8 180 1290 12.8 240 1260 14.9 300 1160 21 .6 B.O.D. Analysis r e s u l t s , Run 8-3 B.O.D. (5 days at 20°C) ppm: I n i t i a l sample(t = 0 min) 27.83 Final sample (t = 300 min) 1210 % Reduction in B.O.D. 56.52 15.1 C.O.D. Analysis r e s u l t s , Run 8-3 Sample Description D i l u t i o n Titre-FAS Blank-Samp!e C.O.D. Average ( i f any) (m.l) (m.l) (mg/l) C.O.D. mg/l I n i t i a l sample 10 14.20 11 .20 4310 (t = 0 min) 4291 10 14.30 11.10 4271 Final Sample 10 16.20 9.20 3540 (t = 300 min) 3502 10 15.40 9.00 3463 % Reduction in C.O.D. 18.4 RUN 9-1 E l e c t r o l y t e K A ) i ( A / m " 2 ) (c . c / m i n ) I n i t i a l pH 5 g/1 N a 2 S 0 4 0 .44 g/1 H 2 S 0 4 10 5 2 6 . 3 760 2 . 3 4 1 gm/1 Pheno l t AV phenol (min) ( v o l t s ) m g / l % o x i d i z e d 0 5 .60 975 0 15 5 . 6 5 850 1 2 . 8 30 5 .60 675 3 0 . 8 45 5 . 6 0 565 42.1 60 5 . 6 0 390 6 0 . 0 75 5 . 6 5 305 6 8 . 7 90 5 . 7 5 200 7 9 . 5 105 5 . 7 5 145 85 .1 120 5 . 7 5 105 8 9 . 2 153. Other phenolic runs for GC/Ms analysis 1 g/1, i = 526.3 A/m runs, 2 hours' oxidation Run No. Name of phenolic compound (and i n i - t i a l pH) I n i t i a l Final dp voltage voltage c.c/min vol ts Comments 9-2 9-3 9-4 9-5 9-6 9-7 9-8 O-Cresol (2.35) p-Cresol (2.38) 2.3- Xylenol (2.31) 3.4- Xylenol (2.34) Resorcinol (2.39) Catechol (2.40) 6.2 6.15 5.85 6.05 6.10 5.75 Phenol-9gms 0-Cresol-2gms p-Cresol-1gm 2.3- Xylenol- 1 gm 3.4- Xylenol - l gm (2.3) 5.35 6.55 6.25 9.35 6.15 6.35 6.5 5.85 826 812 777 847 819 840 630 Foaming-increasing as oxidation proceeded. Foaming-increasing as oxidation proceeded. Excessive foaming, solution turned yellow. Clear, pale brown solu- tion obtained. Vigorous reaction, solution turned deep yellow, brown and black in 15 mins, foaming associated with formation of black p r e c i p i t a t e . Solution turned pale yellow with s l i g h t foaming towards the end. ^KEEHIPHENOL OXIDRTION (SAMPLE' " I " 0.5 UL SE-54) H i l t - j i g Q5008 D500S msaa 5003 11; | PHENOL OH "- r r r •" i - f" 7512 :-l}07.7 108.6 17895:] P-EEN20QUIN0NE R=264.52 . CATECHOL OH - O H HYi'ROQU I NONE OH X. iniffir»iiT4nn OH n 1 1 1 i 1 1 r 80 159 236 316 395 474 554 i-l-: - i 1 T r — i r 'IB 79 0 S 6 9 9 4 8 1 O £ 8 11 0 7 Fig. 35 GC/MS analysis of f i n a l product from phenol oxidation (run 9-1) Area Table Entries: FRN 5008 Entry Time Mass Area % 1 4.8 94.0 4793. 12.6 2 3.6 108.0 26452. 69.5 3 8.8 110.0 2660. 7.0 4 10.1 110.0 4131. 10.9 >-CRESOL O X I D A T I O N (F IN f iL SRMPLE) S E - 5 4 2UL pgatl 5804 METHYL HYDROQUINONE OR 4 - H Y D R 0 X Y - 4 - M E T H Y L - 2 , S - C Y C L O H E X f l D I N E N E - 1 - O N E 234 467 934 11&S 1335 1629 18 362 2696 2329 2 5 6 3 2 ? 9 6 3W3U F i g . 36 GC/MS analysis of f i n a l product from p-cresol oxidation (run 9-3) Area Table Entries: FRN 5004 Entry Time Mass Area %' 1 6.9 124.0 14282. 15.8 2 6.5 108.0 76352. - 84.2 P-CRESOL OXIDATION (FINOL SAMPLE) SE-54 2UL 11381 5884 100-, I 4 - M E T H Y L - 2 , 5 - C V C L 0 H E X H D IE N E - 1 - 9 H E 60 6. ya 46 H 57 si 71 Lu_ 1 a 9 1 09 124 126 140 153 Fig. 37 Mass spectrum showing the presence of 4-Hydroxy-4-Methyl- 2,5-Cyclohexadiene-l -one - •MaaaaO-CRESOL OXIDPTION (SE-54 2UL) •5W5M30 - 260 8C/MIN HJJ;I sues 1387 10 7. 7 108.6 1 157 M430 B p 5103. ,H •"' 1 1 ~ T 0-CRESOL —i 1 1 1 —i 1 1 1 r METHYL BEHZOQUI NONE ( 2 , E.-CYCLOHEXHli I EHE- 1 , 4-D I ONE , 2-METHYL ) METHYL HYDR0QUIH0NE OR 4-HYDR0XY-4-METHYL - C Y C L 0 H E X fi D I E H E - 1 - 0 N E n 1 1 1 20Q 401 601 801' 1802 1202 1402 1603 U 1 1 n— 1998 2198 2398 F i g . 38 GC/MS analysis of f i n a l product from o-cresol oxidation (run 9-2) Area table e n t r i e s : FRN 5005 Entry Time Mass Area % 1 6.0 108.0 5103 11.17 2 5.1 122.0 31879 69.80 3 11.2 124.0 8687 19.02 158. •a3aM2 . 3 X Y L E N O L ( 2 U L S E - 5 4 ) 3 2 3 6 •Jan see? ; 1 3 5 . 7 . 1 3 6 : 6 264 347 2 , 3 - X Y L E N O L 1 1 1 " i " 1 . 1 1 r -1 1 1 r 1 2,3-D I METHYL B E N Z O Q U I N O N E 4 - H Y D R 0 X Y - 2 , 4 - D IM E T H Y L 2,5-C Y C L 0 H E X fi It I E H E - 1 - 0N1 —1— r - i i 1 1 1 1 1 1 1 1 1 1 1 129 172 215 259 361 345 387 429 473 516 559 6Ui 645 fcB'd F i g . 39 GC/MS analysis of f i n a l product from 2,3-Xylenol oxidation (run 9-4) Area table e n t r i e s : FRN 5007 Entry Time Mass Area % 1 8.2 122.0 7423. 17.59 2 7.0 136.0 33709. 79.82 3 12.8 138.0 1021. 2.59 •HgnS3,4XYLEN0L OXIDATION (2UL SE-54) 1248 , 137.7 138.6 80728 EH2Q 5886 4-HYDR0XY-2,4-DIMETHYL-2, 5-CYCLOHEXSDIENE-1-ONE 0=14121 -| 1 1 1 1 n i i r 3,4-«YLEN0L 0=497.49. u fi -i "i—1 1 1 r—"—i 1 V 1 1 1 r 1 •-: 1 261 38ft 519 AR0 780 911 1042 1 169 1299 1430 1561 lfeyii Fig. ,40; GC/MS analysis of f i n a l product from 3,4-Xylenol oxidation (run 9-5) Area table e n t r i e s : FRN 5006 Entry Time Mass Area c lo 1 9.6 138.0 14121. 22 .11 2 8.6 122.0 49749. 79 .89 TRACE AMOUNT OF 2 , 3-D I METHYL-HYDROQU I HONE OR 135 ISOMER 91 54 104 65 117 1' ' i' " 50 60 70 3S •aa 188 116 1 I 1 1 " I " 1 ' 1 41 MS confirmation of traces of 2,3-Dimethyl hydroquinone F i g . 42 GC/MS a n a l y s i s / o f , . f i n a l p r o d u c t o f o x i d a t i o n o f m i x t u r e and X y l e n o l s ( r un 9 - 8 ) : PHENOL ,CRESOLS AND XYLENOLS OXIDATION (2UL SE - 5 4 ) •-.)Pt»a39-269 8CMIN 123.. > 124". 6 4^y»i<»*,4-r1ETrtYL-2,S-CYCL0HEXADIENE-l-0NE 1 CATECHOL AND HYDROQUINONE METHYL | BENZO I QUINONE fl j| 2 , 3 AND 3 , 4 XYLENOLS | DIMETHY HYDROQUINONE OR ISOMER | DIOCTYL SEBACATE INTERFERENCE ION 1 2,3-D IMETHY BENZOQUI NONE OR ISOMER ' P AND 3-CRESOLS *P-BENZ ti. OQUINONE 1 PHENOL 2 33 466 700 9 33 1166 1399 1632 1365 209? 2332 2565 2793 30 31 H R E A T H E L E E N T R I E S : F R N 5003 16.1 Ent ry T i m e Mass. 1 7.0 124.0 29 17. 1.. 0 10.2 110. 0 3 7 5 6 3 . 1 3. 4 3 3.7 110.0 14724. 5. 4 5. 1 122. 0 221 5 4 . 7. 9 5 3.2 122. 0 13130. 4. 7 6 3.5 122. 0 3 1 4 3 3 . 1 1 . •2 7 9.3 1 33. 0 1 . <y 3 7.3 136. 0 9 3 1 1 . •J 9 3. 4 103. 0 31 3 7 6 . 1 1. 2 10 6.4 103. 0 17290. 6. 2 1 1 6. 0 103.0 16670. 5. 12 4.9 94.0 3 0 7 4 1 . ii 3 . CflLCULflTE y. DM ENTRY t*: OMPOUNDS : OH OH OH OH OH 6 <§> &CH; C H , C H , CH, C H : OXIDATION PRODUCTS 0 0 • 0 0 or OH OH OH . . 0 OH <? Art 0, 108 0 122 CH, 0 J HO CH 3 136 138 OH 138 110 OH 110 124 124 I 162. APPENDIX 3 Mathematical Model In t h i s study, a multiple-pass system i s used i n a fixed volume (5 1) of sol u t i o n c i r c u l a t e d continuously through the bed. Under these conditions, i f the packed bed electrode i s connected to a rese r v o i r containing solution of volume V , the concentration of the phenolic compound decreases with the time of ele c t r o - o x i d a t i o n . (+) Flow rate = N (-) Volume = V m Fig.A-1 Schematic representation of a multiple- pass system . At any instant, the i n l e t concentration i s and the o u t l e t concen- t r a t i o n i s Co." As approached by Pickett Ref. 10, p. 178, f o r ideal l i m i t i n g conditions.C-j and C 2 can be related as follows k A . r - r r ~„r, / IT) H l l n \ , C 2 = C| [ exp ( ) ] (A.l) The anodic oxidation of the phenolic compound can be c o n t r o l l e d by 163 mass t r a n s f e r o r t h e e l e c t r o c h e m i c a l r e a c t i o n . An a t t e m p t t o o b t a i n a m a t h e m a t i c a l model when t he r e a c t i o n i s c o n t r o l l e d by t he l a t t e r p r o c e s s wou ld be v e r y c o m p l i c a t e d because as C-j and C 2 v a r y the e l e c t r o d e p o t e n t i a l and k r , t h e e l e c t r o c h e m i c a l r e a c t i o n c o n s t a n t w i l l v a r y t o o . Hence o n l y a. mass t r a n s f e r c o n t r o l l e d model has been t r e a t e d h e r e . F o l l o w i n g t he a p p r o a c h made by S u c r e 31 , C 2 can be r e l a t e d t o t h e i n i t i a l pheno l c o n c e n t r a t i o n CQ a s f o l l o w s k aL . k aL C ? = C N exp [ { exp - ( ) - 1 } f • ] ' ( A . 2 ) E q . A . 2 c a n be s i m p l i f i e d by u s i n g the f o l l o w i n g s u b s t i t u t i o n s * t t = — = d i m e n s i o n l e s s t i m e m k aL Q =vr^— = d i m e n s i o n l e s s mass t r a n s f e r g roup whence : CQ - Cp X = - ^ p = f r a c t i o n a l c o n v e r s i o n L 0 X = 1 - exp [ {exp ( -Q) - 1} t * - Q] E s t i m a t i o n o f mass t r a n s f e r c o e f f i c i e n t . Due t o t h e l a c k o f p r o p e r c o r r e l a t i o n s f o r mass t r a n s f e r c o e f f i c i e n t s u n d e r t he c o n d i t i o n s o f the p r e s e n t s t u d y , t he app roach made by P i c k e t t and Stanmore u s i n g a s i n g l e l a y e r packed bed e l e c t r o d e has been used [ 4 6 ] , Sh = 0 . 8 3 R e 0 - 5 6 S c 0 , 3 3 ( A . 3 ) I t has been r e p o r t e d [10] t h a t d a t a by S tanmore on a d o u b l e l a y e r o f r e g u l a r l y packed e l e c t r o d e i n d i c a t e d t h a t v a l u e s o f k m o b t a i n e d were 164. about 20-25% lower than that given by eq. A.3. Thus ca l c u l a t i o n s were based on the equation Sh = a R e 0 " 5 6 S c 0 " 3 3 (A.4) with upper and lower bounds of a = 0.66 and a = 0.62 re s p e c t i v e l y . A sample c a l c u l a t i o n i s given below. 165. Calculation of theo r e t i c a l f r a c t i o n a l conversion i f mass transfer controls S p e c i f i c surface area of the bed, 5= 0.59 (Appendix 2) Assume § = 0.75 [54] - J _ 6(1 - 0.59) a 0.3 + 0.75 x 0.09 = 9.41 c m - 1 S u p e r f i c i a l v e l o c i t y of the l i q u i d , u = 5 1 x 0.3 cm 0.8 1/tnin 1 mi n 60 sec =8.89 cm/s D2,3-Xylenol = 7.0 x 10  6 cm2/s [Table V] D = 8.3 x 10" 6 cm2/s [Table V] resorcinol (see Section 2,i Appendix 4 f o r c a l c u l a t i o n of d i f f u s i v i t y values) 166. Re = ^J2. = 8.89 cm/s x 0.09 cm _ 8 Q v 0:01 cm2/s consider group-4 s = v • 0-01 cm2/s = 1 4 2 g c U 7.0 x 10' b cm2/s expanding eq. A.4, k dp n . 0.56 0.33 m - n aa r ̂ dp , r V k m = o.66 x 7 - ° 0 * 0 9 Q ~ 6 x 8 0 0 ' 5 6 x 1 4 2 9 0 " 3 3 = 6.61 x 10" 3 cm/s The lower l i m i t of k i s obtained from eq. A.5 as follows m k = 0 . 6 2 x 7 - ° n X n Q ° " 6 x SO 0' 5 6 x 1 4 2 9 0 " 3 3 m 0 . 0 9 = 6.19 x 10" 3 cm/s -3 -3 Therefore k ranges from 6.61 x 10 cm/s to 6.19 x 10 cm/s m ° k aL k 9.41 cm"1 38 cm n _ m _ JTJ 4 u 8.89 cm/s The extreme values of Q would therefore be Q1 = 0.25 Q 2 = 0.27 167. The 2,3-Xylenol f r a c t i o n conversion f o r mass transfer i s given by X = 1 - exp [{exp (-Q) -1 } t * - Q ] ** = t 7 tm 5 1 t m = N Q i = 6.250 mm m 0.8 1/rmn The range of theoretical f r a c t i o n a l conversion f o r mass transfer control at various time i n t e r v a l s are shown in Table A - l . TABLE A-l Theoretical 2,3-Xylenol f r a c t i o n a l conversion vs time for a mass transfer c o n t r o l l e d batch system t(min) t X l x 2 0 0 0.22 0.24 15 2.4 0.54 0.57 30 4.8 0.73 0.76 45 7.2 0.84 0.86 60 9.6 0.91 0.92 75 12.0 0.94 0.96 90 14.4 0.97 0.98 105 16.8 0.98 0.99 120 19.2 0.99 0.99 168. Similar treatment f o r group 6 experiments S c = ° - 0 1 C m ^ S : , = 1 2 0 4 8.3 x 10 cm2/s k = 9.25 x 10" 3 cm/s m Q1 = 0.28 Q 2 = 0.30 The resorcinol f r a c t i o n a l conversion f o r mass transfer control i s shown in Table A-2. TABLE A-2 Theoretical time f o r a resorcinol f r a c t i o n a l conversion vs mass transfer controlled batch system t(min) * t X l X2 0 0 0.24 0.26 15 2.4 0.58 0.60 30 4.8 0.76 0.79 45 7.2 0.87 0.89 60 9.6 0.92 0.94 75 12.0 0.96 0.97 90 14.4 0.98 0.98 105 16.8 0.99 0.99 120 19.2 0.99 0.99 169. APPENDIX 4 C a l c u l a t i o n s 1. C .O.D. a n a l y s i s - sample c a l c u l a t i o n s (run 8-3) Sample D i l u t i o n T i t r e - F A S Blank-Sample COD Average COD D e s c r i p t i o n ( i f any) (ml) (ml) (mg/ l ) (mg/ l ) I n i t i a l 10 14.2 11.2 4310 sample 4291 (t=0 min) 10 14.3 11 .1 4271 F i n a l 10 16.2 9.2 3540 sample 3502 (t=300 min) 10 16.4 9.0 3463 i . e . 18.4% reduc t ion in C.O.D. T i t r e - F A S ( i n ml) Values f o r the Blank and Standard Samples Blank Sample Standard Sample 25.45 26.00 25.35 26.00 Average: 25.4 26.00 For the s tandard sample v a l u e s , 2 5 2 5 N FAS = T i t r e - F A S ( m l ) " " 26T0 = ° - 0 9 6 1 N p A S x 8000 x D i l u t i o n f a c t o r ( i f any) ' r a c t o r Sample vol ume (ml) = 0.0962 x 8000 x 10 = 3 g 4 8 C.O.D. (mg/1) = Fac tor x Blank-Sample 170. 2. Calculation of d i f f u s i v i t y of phenolics The d i f f u s i v i t y of the phenolics were calculated by using the r e l a t i o n s h i p of WiIke and Change [55] o = 7.4 x 10" 8 (0 K 2 ) h T D12 y 2 where = mutual d i f f u s i o n of solute 1 in solvent 2 at very low solute concentration, cnr/sec * " . 0 X = "association parameter" of solvent [IT] M2 = molecular weight of solvent T = temperature, K 1̂2 = v i s c o s i t y of s o l u t i o n (solvent), cp V.| = molal volume of the solute at i t s normal b o i l i n g point 3 in cm /g mole , / D12 phenol = 7.4 x l O - 8 (2.26 x 18)* x 297 ( r e f e r t Q p > 3 ^ R E F > 5 5 ) 1 x ( 1 0 5 ) U - b = 8.5 x 10" 6 cm2/,s Improved value of association parameter put f o r t h by Hayduk and Laudie [56,] has been used. Note: D?„ Xylenols c a l c u l a t e d a t 40°C 171. 3. Calculation of current e f f i c i e n c y for a ty p i c a l phenol run The stoichiometry of the predominant processes which occurs i n the oxidation of phenol (run 9-1) are as follows OH 6 1. [I +11 H 20 — 6 C0 2 + 28 H + + 28 e" OH + HoO — || ll + 4 H + + 4 e" 0 OH OH + HoO - II :i + 2 H + + 2 e" OH OH OH (f^j + H 20 - ([̂ r0H+ 2 H + + 2 e' OH + 5 H 20 — 6 CO + 16 H + + 16 e" Consider a carbon balance. Amount of phenol oxidized = (975-105) = 870 mg/l Results from GC/MS analysis of f i n a l sample % Phenol 12.6 Benzoquinone 69.5 Hydroquinone 10.9 Catechol 7.0 Actual quantity of phenol = 105 mg/l Actual quantity of benzoquinone = 579.2 mg/l Actual quantity of hydroquinone = 90.8 mg/l Actual quantity of catechol =58.3 mg/l Cone, of organic carbon in s t a r t i n g solution = 71.4 x 975 93.3 = 746.1 mg/l cone, of organic carbon i n the products = 105 x + 579.2 x T 7 7 j i ^ + (90.8 + 58.3) = 562.7 mg/l cone, of organic'carbon that l e f t the soltuion (from T.O.C. analysis) = 29.8 mg/l cone, of organic carbon unaccounted from carbon balance = 153.6 mg/l = (21%) Calculation of current e f f i c i e n c y * % C.E. for the formation of benzoquinone = 579.2 mg/l x 5 1 x Ig mole 107.4 g x x 96500 coul/eq x 4 eq/mole x 100 10 A x 120 min x 60 sec min = 14.5 % C.E. f o r formation of catechol and hydroquinone = 149.1 mg/l x 5 1 x Ig mole 109.4 x 10° mg x 96500 coul/eq x 2 eq/mole x 100 1.0. A x 120 min x 60 Sec mi n * % C.E. = F Z (moles oxidized) x 100 It 173. = 1.83 % C.E. f o r the formation of CC^ [Assume 100% conversion to C021 = 29.8 mg/l x 5 1 x 1 ^ m ° 1 e x \ 9 x 96500 coul/eq x 28 eq/mole x 100 l d 9 10 mg 10 A x 120 min x 6 0 ^ = 46.6 % C.E. f o r the formation of CO Assume 100 % conversion to CO 29.8 mg/l x 5 1 x 1 9 m ° 1 e x 1 9 x 96500 coul/eq x 16 eq/mole x 100 u 9 10 mg 10 A x 120 min x 6 0 ^ 26.6 Total current e f f i c i e n c y = 42.9 - 62.9 depending on C0:C0 *Gas analysis by G.C. corresponding to the time of collection of the final sample was as follows: %H2, 68.42; %C02, 6.54; %02, 24.73; %CO, 0.31 CO:CO2 was found to vary as follows 1:7.4 (after 90 minutes of oxidation) 1:21.0 (after 120 minutes of oxidation) 4 . C a l c u l a t i o n o f V ^ m i n t he e l e c t r o l y t e 174. cathode saran screen Vohm . V o h m = i ' V S a + i - r d . - S d + i ^ c - S c - V L where V'^ i s t h e l i q u i d f u n c t i o n p o t e n t i a l The l a s t two f a c t o r s a r e n e g l i g i b l e . ; i r ^ S ^ wou ld depend on the q u a n t i t y o f gas e v o l v e d and t y p e o f s c r e e n . C o n s i d e r i r a S a a c r o s s t he b e d . I t can be a p p r o x i m a t e d as f o l l o w s . a K K e l e c t r o l y t e ebed ^ebed sj 0 (due t o t he h i g h c o n d u c t i v i t y o f bed) A v e r a g e c o n d u c t i v i t y o f the e l e c t r o l y t e [31] = 0.895(f2m)' ; = 1 .12 ohm.m e l e c t r o l y t e Vohm- ('5 A runs) yohm (l0 A runs) Vohm ( 1 5 A runs) 263.2 A/m x 1.12 ohm m x 0.003 m 0.88 v o l t s 526.3 A/m2 x 1.12 ohm.m x 0.003 m 1.77 v o l t s 789.5 A/m2 x 1.12 ohm.m x 0.003 m 2.65 v o l t s \ 176. APPENDIX 5 Relevant Physical data ACTUAL COMPOSITION OF SYNTHETIC COAL CONVERSION WASTEWATER OUTLINED IN TABLE I Compound Concentration, mg/l 1. Phenol 2000 2. Resorcinol 1000 3. Catechol 1000 4. Acetic Acid 400 5. o-Cresol 400 6. p-Cresol 250 7. 3,4-Xylenol 250 8. 2,3-Xylenol 250 9. Pyridi ne 120 10. Benzoic Acid 100 11 . 4-Ethyl pyridine 100 12. 4-Methylcatechol 100 13. Acetophenone 50 14. 2-Indanol 50 15. Indene 50 16. Indole 50 17. 5-Methylresorcinol 50 18. 2-Naphthol 50 19. 2,3,5-Trimethylphenol 50 20. 2,-Methylquinoline 40 177. Compound Concentration 21 . 3,5-Xylenol 40 22. 3-Ethylphenol 30 23. A n i l i n e 20 24. Hexanoic Acid 20 25. 1-Naphthol 20 26. Qui no!ine 10 27. Naphthalene 5 28. Anthracene 0.1 29. MgS04.7H20 22.5 30. CaCl 2 27.5 31 . FeNaEDTA 0.34 32. NH4C1 3820 33. Phosphate buffer: KH 2P0 4 170 K 2HP0 4 435 Na 2HP0 4.7H 20 668

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