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Electrochemical oxidation of phenol for waste water treatment Sucre, Vivian Smith de 1979

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ELECTROCHEMICAL OXIDATION OF PHENOL FOR WASTE WATER TREATMENT  by  V I V I A N SMITH de^SUCRE B.Sc.  Universidad  Simon B o l i v a r ,  1975  A THESIS SUBMITTED I N P A R T I A L F U L F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF A P P L I E D  SCIENCE  in THE FACULTY OF GRADUATE Department of Chemical  We a c c e p t to  this  the  thesis  required  STUDIES  Engineering  as  conforming  standard  THE U N I V E R S I T Y OF B R I T I S H COLUMBIA August,  0  Vivian  1979  S m i t h de S u c r e ,  1979  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r  an advanced d e g r e e a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and I f u r t h e r agree that permission  for extensive  study.  copying o f this thesis  f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s .  It i s understood that copying o r p u b l i c a t i o n  o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my written  permission.  Department o f ^UxCcAL  &0&IM£IUA)G  The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5  DE-6  BP 75-51 1 E  ABSTRACT  The e l e c t r o c h e m i c a l cations  was  investigated  l y t i c c e l l was o p e r a t e d s t r e a m s up t o and H S L \ 2  or  showed  complete  Rates  i n both batch  than  that  total  the  lead  a l l the organic  further  percent  and d e c r e a s e d  carbon  as  posed  to  relative  than  initial  feed of Na S0i 2  for  interpret  the  the the  mass t r a n s f e r  by a n o d i z i n g l e a d  r e m o v a l was more  +  for shot.  difficult.  by an a c i d i c p H , b u t products.  a c a t i o n i c membrane f o r  T.O.C.  with increasing  concentration,  In d i v i d e d ions,  removal.  current  electrolyte  cells.  a n a l k a l i n e pH  which allowed m i g r a t i o n of h y d r o x y l  phenol  The  density,  flow  rate,  increased.  experimental  batch  anode  s i m i l a r i n d i v i d e d and u n d i v i d e d  favoured  s i z e were  Comparisons of presented  (T.O.C.)  oxidized increased  and anode p a r t i c l e  are  electro-  i n s o l u t i o n c o u l d be r e a d i l y o x i d i z e d  o x i d a t i o n of intermediate  superior  of phenol  dioxide obtained  phenol  a n a n i o n i c membrane,  p r o v e d t o be  modes w i t h  l e a d d i o x i d e was f o u n d t o b e a b e t t e r  T h e o x i d a t i o n o f p h e n o l was  cells,  and c o n t i n u o u s  The  d i s s o l v e d i n aqueous s o l u t i o n s  o f p h e n o l o x i d a t i o n were  improved the  anodes.  appli-  NaOH.  phenol o x i d a t i o n ,  but  for waste treatment  on l e a d d i o x i d e p a c k e d - b e d  1100 mg/1 p h e n o l  Electrodeposited  Results  o x i d a t i o n of phenol  results  experiments,  results  and a s i m p l i f i e d  from c o n t i n u o u s  and e l e c t r o c h e m i c a l  i i  w i t h a mass t r a n s f e r  experiments  reaction  model i s  model pro-  i n terms of  resistances.  T A B L E OF CONTENTS ABSTRACT  i i  L I S T OF TABLES  v  L I S T OF FIGURES ACKNOWLEDGMENTS  v  Chapter 1 INTRODUCTION  2  i  v  i  i  i  1  1.1  Phenols  as p o l l u t a n t s  1  1.2  Methods of t r e a t m e n t of p h e n o l i c wastes  2  BASES OF THE ELECTROCHEMICAL PROCESS  6  2.1  General concepts  6  2.2  L i t e r a t u r e r e v i e w on t h e e l e c t r o c h e m i c a l o x i d a t i o n of phenol 2.2.1 Reaction products 2.2.2 P r o p o s e d r e a c t i o n mechanisms 2.2.3 Electrode materials tested 2.2.4 E f f e c t of current d e n s i t y 2.2.5 E f f e c t of n a t u r e of the e l e c t r o l y t e . . . . 2.2.6 E f f e c t o f pH The l e a d d i o x i d e e l e c t r o d e  2.3  12 12 13 18 20 21 24 25  3  OBJECTIVES  29  4  EXPERIMENTAL APPARATUS AND METHODS  31  4.1  Apparatus  31  4.1.1 C e l l design 4.1.2 Flow diagram of the apparatus E x p e r i m e n t a l methods 4.2.1 Batch experiments 4.2.2 Continuous experiments A n a l y t i c techniques 4.3.1 Phenol analysis 4.3.2 T o t a l organic carbon a n a l y s i s 4.3.3 Lead a n a l y s i s  31 39 43 43 45 46 46 47 48  4.2  4.3  i i i  5  RESULTS AND DISCUSSION  49  5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12  Electrode materials . E f f e c t o f pH u s i n g t h e d i v i d e d c e l l E f f e c t of c u r r e n t u s i n g the d i v i d e d c e l l C o m p a r i s o n s o f membrane p e r f o r m a n c e s E f f e c t o f pH u s i n g t h e u n d i v i d e d c e l l E f f e c t of current u s i n g the u n d i v i d e d c e l l . . . . C o m p a r i s o n s o f d i v i d e d and u n d i v i d e d c e l l s . . . . E f f e c t of c o n d u c t i v i t y of the e l e c t r o l y t e E f f e c t of i n i t i a l phenol concentration E f f e c t of e l e c t r o l y t e flow r a t e E f f e c t of p a r t i c l e s i z e Comparisons of experimental r e s u l t s w i t h m a t h e m a t i c a l models 5.12.1 Batch experiments 5.12.2 Continuous experiments 5 . 1 3 C u r r e n t e f f i c i e n c i e s , e n e r g y r e q u i r e m e n t s and energy c o s t s f o r phenol o x i d a t i o n 5.13.1 Batch experiments 5.13.2 Continuous experiments 5.13.3 Cost comparisons  49 55 64 65 68 69 75 76 78 83 86  6  CONCLUSIONS  99  7  RECOMMENDATIONS  88 88 89 95 95 96 96  101  NOMENCLATURE  104  BIBLIOGRAPHY  107  APPENDIX 1 2 3 4 5  S p e c i f i c a t i o n of a u x i l i a r y equipment Experimental data M a t h e m a t i c a l models Calculations Relevant p h y s i c a l data  iv  and m a t e r i a l s  .  .  . I l l 116 158 171 181  L I S T OF TABLES  Table 1  R a t e s o f p h e n o l o x i d a t i o n on d i f f e r e n t electrode materials 2 E f f e c t o f c u r r e n t d e n s i t y and t y p e o f e l e c t r o l y t e on C . O . D . r e m o v a l 3 E f f e c t o f t y p e o f e l e c t r o l y t e on p h e n o l o x i d a t i o n . . . . 4 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 . . . 5 C o m p a r i s o n s o f d i v i d e d and u n d i v i d e d c e l l s 6 T y p i c a l c u r r e n t e f f i c i e n c i e s , e n e r g y r e q u i r e m e n t s and energy c o s t s i n batch experiments w i t h u n d i v i d e d c e l l . 7 T y p i c a l c u r r e n t e f f i c i e n c i e s , e n e r g y r e q u i r e m e n t s and energy c o s t s i n continuous experiments w i t h undivided c e l l 8 Operating costs of v a r i o u s treatment methods, estimated f o r 1974 f o r a c a t a l y t i c c r a c k e r e f f l u e n t c o n t a i n i n g 700 m g / 1 p h e n o l Appendix 1 A-l Summary o f t y p i c a l p r o p e r t i e s o f IONAC membranes . . . . Appendix 2 Experimental data tables f o r : Run 1-1 t o R u n 1 - 9 : Divided c e l l , batch experiments w i t h anodized lead Run 2 - 1 t o R u n 2 - 1 1 : Divided c e l l , batch experiments w i t h e l e c t r o d e p o s i t e d Pb02 Run 3 - 1 t o Run 3 - 1 5 : Undivided c e l l , batch experiments with electrodeposited Pb0 Run 4 - 1 t o Run 4 - 8 : Undivided c e l l , continuous experiments with electrodeposited Pb0 Appendix 4 A-2 T h e o r e t i c a l phenol f r a c t i o n a l conversion vs time for a mass t r a n s f e r — c o n t r o l l e d b a t c h s y s t e m A-3 C a l c u l a t i o n o f e x p e r i m e n t a l , mass t r a n s f e r a n d r e a c t i o n r a t e c o n s t a n t s from experiments 4 - 1 , 4 - 2 , 4-3 A-4 C a l c u l a t i o n o f e x p e r i m e n t a l , mass t r a n s f e r a n d r e a c t i o n r a t e c o n s t a n t s f o r experiment 4-4 A-5 C a l c u l a t i o n o f e x p e r i m e n t a l , mass t r a n s f e r and r e a c t i o n r a t e c o n s t a n t s f o r experiment 4-8 A-6 pH o f s o l u t i o n s o f NaOH and H ^ O ^ a t 2 0 ° C A-7 C o n d u c t i v i t i e s o f a q u e o u s s o l u t i o n s o f NaOH, H ^ O ^ and N32S01+ a t 2 0 ° C A-7 % p h e n o l i o n i z e d v s pH  19 21 23 37 76 95  96  97 113  119-123 124-134  2  135-149  2  150-157  v  173 175 176 177 181 181 182  L I S T OF FIGURES  Figure 1 V o l t a g e components i n a d i v i d e d e l e c t r o l y t i c c e l l . . 2 Reaction products 3 Half-wave p o t e n t i a l vs pH, f o r the o x i d a t i o n of 4 x IO phenol 4 Side v i e w of the g e n e r a l d i v i d e d - c e l l arrangement . . 5 F r o n t and s i d e v i e w s o f t h e a n o d e chamber f o r t h e anodized lead electrode 6 F r o n t a n d s i d e v i e w s o f t h e a n o d e chamber f o r t h e e l e c t r o d e p o s i t e d Pb02 e l e c t r o d e 7 D e t a i l of the i n l e t or o u t l e t connection adapted o n t h e e l e c t r o d e p o s i t e d Pb02 on g r a p h i t e a n o d e . . 8 D e t a i l of the mechanism used to h o l d the c e l l 9 Flow diagram of the apparatus 10 E f f e c t o f t y p e o f l e a d d i o x i d e e l e c t r o d e a t 10 A and i n i t i a l pH - 9 . 4 w i t h IONAC M C - 3 4 7 0 membrane 11 Scanning electron-micrographs of the electrodeposited Pb02 p a r t i c l e s a f t e r u s e 12 Scanning electron-micrographs of the anodized l e a d p a r t i c l e s , a f t e r use 13 E f f e c t o f c u r r e n t o n pH and % T . O . C . o x i d a t i o n w i t h IONAC M C - 3 4 7 0 membrane 14 E f f e c t o f c u r r e n t on % p h e n o l o x i d a t i o n a t i n i t i a l pH = 9 . 4 w i t h IONAC M C - 3 4 7 0 membrane 15 E f f e c t o f c u r r e n t on p H , % T . O . C . o x i d a t i o n and % p h e n o l o x i d a t i o n w i t h N A F I O N - 1 2 7 membrane 16 E f f e c t o f pH o n % T . O . C . a n d % p h e n o l o x i d a t i o n a t 20 A w i t h N A F I O N - 1 2 7 membrane 17 T y p e o f membrane-pH e f f e c t on % T . O . C . and % p h e n o l o x i d a t i o n a t 20 A . . . . . . . . . . . . . . . . 18 C u r r e n t e f f e c t on % T . O . C . and % p h e n o l o x i d a t i o n a t pH = 2 . 5 w i t h IONAC M C - 3 4 7 0 19 T y p e o f c a t i o n i c membrane e f f e c t o n % T . O . C . a n d % p h e n o l o x i d a t i o n a t 20 A a n d pH = 2 . 5 20 pH e f f e c t on % T . O . C . a n d % p h e n o l o x i d a t i o n a t 10 A i n a n u n d i v i d e d c e l l 21 pH e f f e c t o n % T . O . C . and % p h e n o l o x i d a t i o n a t 20 A i n a n u n d i v i d e d c e l l 22 E f f e c t o f pH o n % T . O . C . a n d % p h e n o l o x i d a t i o n a t 30 A i n an u n d i v i d e d c e l l • 23 C u r r e n t e f f e c t on % T . O . C . and % p h e n o l o x i d a t i o n at pH - 2 . 5 i n . an u n d i v i d e d c e l l 24 E f f e c t o f c u r r e n t on % T . O . C . and % p h e n o l o x i d a t i o n a t i n i t i a l pH = 1 2 , i n a n u n d i v i d e d c e l l  . .  9 12 24 32  - 4  vi  . . <  34 35 . .  36 38 40 52 53 54 56 59 60 62  .  .  63 66 67 70 71  .  .  72 73 74  25  E f f e c t o f e l e c t r o l y t e c o n d u c t i v i t y a t 20 A ( i n a l k a l i n e and a c i d m e d i a ) 26 E f f e c t o f e l e c t r o l y t e c o n d u c t i v i t y a t 10 A and i n i t i a l pH = 12 27 E f f e c t o f e l e c t r o l y t e c o n d u c t i v i t y a t 10 A and i n i t i a l pH - 2 . 5 28 % phenol o x i d i z e d vs time for v a r i o u s i n i t i a l p h e n o l c o n c e n t r a t i o n s a t 10 A a n d pH = 2 . 5 29 P h e n o l c o n c e n t r a t i o n e f f e c t o n p h e n o l c o n c e n t r a t i o n v s t i m e a t 10 A and 2 . 5 pH 30 E f f e c t o f f l o w r a t e o n t h e s i n g l e p a s s % p h e n o l o x i d a t i o n a t ( a ) 10 A , (b) 20 A 31 E f f e c t o f a n o d e s u r f a c e a r e a - p a r t i c l e s i z e o n t h e % phenol oxidized i n a single-pass vs flow rate . . . 32 - J l n ( l - X ) v s (u) -*- f o r t h e c a l c u l a t i o n o f e x p e r i m e n t a l r a t e constants i n s i n g l e pass experiments Appendix 3 A-l P a c k e d bed r e a c t o r i n p l u g f l o w A-2 Potential distribution i n a particulate electrode . . . A-3 Schematic r e p r e s e n t a t i o n of eq. A-14 A-4 Schematic r e p r e s e n t a t i o n of eq. A-15 A-5 Schematic r e p r e s e n t a t i o n of a batch r e c i r c u l a t i o n system  77 79 80 81 82 85 87  -  vii  91 159 161 164 166 168  ACKNOWLEDGEMENTS  I would l i k e his  to  t h a n k my s u p e r v i s o r  a d v i c e and encouragement  also  grateful  project  to P r o f .  and f o r  patience,  I wish to staff  also  for  their  their  we h a d  interest  my a p p r e c i a t i o n  cooperation  to  the  and a s s i s t a n c e a n d t o  i n the  operation  Russian papers, Mrs. Monica Gutierrez for Nina Thurston for Financial FONINVES  gratefully  t y p i n g the  support  (Fondo p a r a  the  together. sug-  Civil  Chemical Engineering the  of a n a l y t i c a l  the  personnel  Engineering  A l s o acknowledged are M r s . Rima K a p l a n f o r h e r  Mrs.  in  I am  understanding.  express  generous h e l p  for  Gustavo Sucre f o r h i s  E n v i r o n m e n t a l E n g i n e e r i n g L a b o r a t o r y i n the for  sincere  discussions  due t o my h u s b a n d ,  and  Paul Watkinson  the whole of t h i s work.  Oloman f o r h i s  t h e many u s e f u l  Thanks are gestions,  Colin  throughout  Prof.  drafting  of  the  Department  apparatus. translations of f i g u r e s ,  from and  manuscript.  from the V e n e z u e l a n Government  through  l a I n v e s t i g a c i o n e n M a t e r i a de H i d r o c a r b u r o s )  appreciated.  viii  is  CHAPTER 1  INTRODUCTION 1.1  P h e n o l s as  pollutants  "Phenols" i n waste water phenol tain  (CgHsOH), b u t  The m a j o r  Phenols are vents,  wood p r e s e r v a t i v e s ,  p h e n o l i c compounds, the  i n c r e a s i n g use  paint vehicles, plastics,  fertilizers,  of  o f many i n d u s t r i a l w a s t e w a t e r  of p h e n o l i c wastes are  finding  they w i l l  chemical industry.  teristics  i n coatings,  con-  and d r u g s .  undoubtedly  so u s e f u l ,  are  streams.  and coke  plants. sol-  substitutes,  Given the  usefulness  c o n t i n u e t o be a major chemical  also responsible  of product  charac-  for  their  potential.  chlorophenols which are i n the  phenols w i l l  that  s t r i p p i n g agents,  e x p l o s i v e s , rubber  C h l o r i n e used i n d r i n k i n g water  degradable  o i l refineries  U n f o r t u n a t e l y , some o f t h e  t h a t make p h e n o l s  high pollution  aromatic r i n g  only  groups.  constituents  sources  terminology i n c l u d e s not  a l l those d e r i v a t i v e s of the  one o r more h y d r o x y l Phenols are  treatment  persistent  environment.  combines w i t h phenols  pollutants,  C o n c e n t r a t i o n s as  combined w i t h c h l o r i n e ( 1 ) .  P u b l i c H e a l t h S e r v i c e has  set  d r i n k i n g waters  (2).  at  above 2 m g / 1 , but  1 yg/1  the  can cause t a s t e  form  s i n c e they are not  i m p a r t o b j e c t i o n a b l e t a s t e s and o d o u r s  when p h e n o l s a r e  to  l o w as  5 ug/1 of  to d r i n k i n g  For t h i s  easily  reason  waters the U . S .  allowable concentration of phenols Phenols are in fish  1  t o x i c to  f l e s h at  fish  at  levels  concentrations  far  in  2 below the  toxic level  (3).  The c h e m i c a l o x y g e n d e m a n d , (theoretically deplete  the  vegetable  C.O.D.  2 . 4 mg 0 2 / m g p h e n o l )  and a n i m a l  generally  1977 a n d p r o j e c t  1.2  Methods of  treatment  effluent  50 G . P . M .  for  different  least  o f 0 . 0 2 mg/1 f o r  (4,5).  requires  for  native  0.1  wastes. mg/1  (3).  Generally recovery  s u c h as b e n z e n e ,  remaining i n the  varies widely  is  only  further  treatment before  as  applicable of  about  has  been  or b u t y l  99.7%, but  of view. being  Therefore  alcohol.  the  concen-  still  signif-  the  waste  discharged. of  the  of economics.  phenolic Solvent  f o u n d t o be an e x t r e m e l y e x p e n s i v e  content extracalter-  (1).  several  cannot  basis  processes  recovery are  r e c o v e r y or d e s t r u c t i o n  i s made o n t h e  i n many c a s e s  wastes that  aqueous phase a f t e r control point  example,  There are  extraction  butyl acetate,  pollution  a given stream  tion,  1983  to  2000 m g / 1 o f p h e n o l a n d f l o w s i n e x c e s s  The c h o i c e b e t w e e n of  of  by t h e U . S .  phenolic concentrations  show e f f i c i e n c i e s o f r e c o v e r y up t o  from the  stream  can  (2).  These methods  icant  death  industrial  of phenol i n i n d u s t r i a l effluents  organic solvents  trations  causing the  established  P h e n o l s may b e r e c o v e r e d b y l i q u i d - l i q u i d using  concentration  of p h e n o l i c wastes  flow rates  for wastes of at  have been  (E.P.A.)  limited  a standard  The c o n c e n t r a t i o n do t h e  relatively high  species.  E n v i r o n m e n t a l P r o t e c t i o n Agency These g u i d e l i n e s  is  and i n s u f f i c i e n t  oxygen o f a r e c e i v i n g body o f w a t e r  P e r m i s s i b l e l e v e l s of phenols  in  of phenols  c o n v e n t i o n a l methods  for  be e c o n o m i c a l l y r e c o v e r e d .  treating These  phenolic  include  adsorption,  3 incineration,  biological  treatment,  adsorption  applicable  for  is  concentrations.  Thus i t  waste stream before  it  activated make t h e  a finite carbon)  cost  i s a p p l i e d to  for  and e v e n t u a l l y  of the  operation  and r e - u s e d .  The f i r s t  produces  the  the  adsorbed  required  for  this  from the  operation.  (1)  carbon beds  the  b e d becomes  reasonable  the  purpose  (900°C)  the  (3). is  (0.09-0.4 fully  that  phenol stream  the  g phenol/g  loaded.  To re-  regenerations are and t h e  possible.  second  Very high temperatures  and c a r b o n l o s s e s  O p e r a t i n g c o s t s of the  and i t was f o u n d t h a t  phenolic  c a r b o n must be  C h e m i c a l and t h e r m a l  phenol completely.  Carbon  or d i l u t e  carbon process  removing phenols  compared w i t h t h o s e o f o t h e r  study  to p r e t r e a t  activated  a more c o n c e n t r a t e d  destroys  recent  of the  capacity  activated  have been  r e l a t i v e l y l o w (100-200 mg/1)  may b e n e c e s s a r y  The m a i n d i s a d v a n t a g e c a r b o n has  and c h e m i c a l o x i d a t i o n .  o f 5-10% c a n  activated  carbon  are result  process  p r o v e n t r e a t m e n t methods i n a activated  c a r b o n was t h e  most  expensive. Incineration In the  techniques  only a p p l i c a b l e to  case of d i l u t e phenol s o l u t i o n s ,  large  amounts o f w a t e r  tures  for  as  are  the  cost  w o u l d be p r o h i b i t i v e .  concentrated  of energy  to  wastes.  evaporate  Typical operating  c o m b u s t i o n o f p h e n o l t o c a r b o n d i o x i d e and w a t e r  are  tempera-  as  high  800°C. Biological  applicable  for  treatments for  the  degradation  concentrations  up t o  l o g i c a l plants  report  effluents  influent  o f a b o u t 1000 m g / 1  loads  Different activated  treated  biological  sludge,  treatment  trickling  filter,  several  of phenolic wastes  thousands mg/1.  i n the  are  Many  r a n g e o f 0 . 1 mg/1  bio-  for  (6). f l o w schemes,  s u c h as  o r l a g o o n c a n be u s e d ,  alternating but  the  4 activated the  success  system, of  sludge  system i s  of b i o l o g i c a l  t h e most treatment  because the microorganisms  phenol concentration  Therefore,  has  t i o n basin before  the b i o l o g i c a l  logical  are  dose of o x i d i z i n g agent the  c a r b o n d i o x i d e and w a t e r iate,  less  t r e a t m e n t may be r e q u i r e d the  c h e m i c a l o x y g e n demand  Operating  capital  costs of  large  reduce  converted  (C.O.D.)  the  total  to  latter organic  of the waste to  increases  i s required  s i g n i f i c a n t l y the  sium permanganate i s  ratio  for  the  acceptable  i n the  operating  a more d e s i r a b l e  is  that  manganese d i o x i d e t h a t has and i n c r e a s i n g  the  amount  its  cost  the  and  (3),  of peroxide  neces-  The  presence,  oxidation reaction which costs,  and f o r  oxidizing a higher  this  reason  potas-  agent.  oxidant 15.7  r e a c t i o n produces  t o be removed,  (1).  or  levels.  of 2 g H£02/g phenol  oxidation reaction—theoretically  The m a i n d i s a d v a n t a g e  (T.O.C.)  c a n p r o v i d e 99% p h e n o l r e m o v a l  present  P o t a s s i u m permanganate r e q u i r e s  additional  carbon  about 4 g H202/g s u b s t i t u t e d - p h e n o l .  catalyst  to  intermed-  case,  sary  a metal  perox-  D e p e n d i n g on  certain  phenols  of  are  are  costs.  b u t when s u b s t i t u t e d to  bio-  land areas  and c h l o r i n e d i o x i d e .  r e m o v a l when u s i n g a r a t i o  can i n c r e a s e  equaliza-  t r e a t m e n t by h y d r o g e n  I n the  the  range  p h e n o l c a n be c o m p l e t e l y o x i d i z e d  O x i d a t i o n by h y d r o g e n p e r o x i d e a b o u t 40% C . O . D .  to  in  temperature.  t o p r o v i d e an  generally  includes  compounds. to  o f pH and  treatment.  or only p a r t l y  harmful organic  c o n t r o l of shock loads  been n e c e s s a r y  ozone,  aspect  only adaptable to a c e r t a i n  in substantial  potassium permanganate,  A very c r i t i c a l  conditions  Chemical o x i d a t i o n of phenols  the  the  r e l a t i v e l y l o w , but  r e q u i r e d w h i c h may r e s u l t  ide,  is are  and s t a b l e  i n many c a s e s i t  treatment  common.  to phenol g  KMnO^/g  weight phenol.  a precipitate  c o m p l i c a t i n g the  of  operation  5 O z o n i z a t i o n can be v e r y e f f e c t i v e i n the d e s t r u c t i o n of p h e n o l s . For  example, s t a r t i n g a t 2500 mg/1,  min, when u s i n g a r a t i o of 1.7  99% removal  can ba a c h i e v e d i n 60  g ozone/g p h e n o l .  Ozone can o x i d i z e  the  phenol c o m p l e t e l y t o C O 2 and water but the u s u a l p r a c t i c e i s t o p a r t i a l l y o x i d i z e the p h e n o l t o o r g a n i c compounds more e a s i l y b i o d e g r a d a b l e then use a b i o l o g i c a l treatment.  T h i s i s done s i n c e a t low p h e n o l  c e n t r a t i o n s the n e c e s s a r y ozone t o p h e n o l r a t i o omical.  i s too h i g h t o be  p r o d u c t s o f t h e o x i d a t i o n o f phenol by c h l o r i n e d i o x i d e a r e v e r y At near n e u t r a l pHs,  i n the range  d i z e d t o benzoquinone w i t h a t h e o r e t i c a l requirement  7-8,  phenol i s o x i -  of 1.5  g  p h e n o l and above pH 10 the p r o d u c t s a r e m a l e i c and o x a l i c a c i d r a t i o of 3.3.  C h l o r o p h e n o l s a r e not produced  because the benzene r i n g i s c o m p l e t e l y d e s t r o y e d . made on t h e o x i d a t i o n of p h e n o l i c t h e p r o c e s s was  of  c o k i n g wastes by  Cl02/g requiring  by t h i s  An economic CIO2  process study  indicated  e x c e s s i v e l y expensive u n l e s s the o x i d i z i n g agent  a l r e a d y b e i n g produced New  econ-  installed.  dependent on pH.  a weight  con-  I n i t i a l c o s t s a r e r e l a t i v e l y h i g h because t h e ozone g e n e r a t i n g  system has t o be The  and  that  was  on s i t e ( 3 ) .  methods f o r t r e a t i n g p h e n o l i c wastes a r e b e i n g nought, because  the importance  o f the p o l l u t i o n problem  and the h i g h l y  restrictive  f u t u r e p o l l u t i o n c o n t r o l standard. Increasing interest tion  ( 7 ) , wet  a i r , and  i s b e i n g shown i n methods such as Gamma I r r a d i a -  c a t a l y t i c oxidation (8), u l t r a v i o l e t oxidation (9),  and e l e c t r o c h e m i c a l o x i d a t i o n , which i s the s u b j e c t of the p r e s e n t In the f o l l o w i n g c h a p t e r the fundamental  bases  of the e l e c t r o c h e m i c a l  p r o c e s s are p r e s e n t e d a l o n g w i t h a l i t e r a t u r e r e v i e w on p r e v i o u s at e l e c t r o c h e m i c a l o x i d a t i o n c f p h e n o l .  study.  attempts  CHAPTER 2  BASES OF THE ELECTROCHEMICAL PROCESS  2.1  General For  concepts  any e l e c t r o c h e m i c a l r e a c t i o n B + ze"  the  reversible  equilibrium potential  T  where  the  equal  to u n i t y  - * j "  activity coefficient  potential  potential  of the metal of the to  of the  Z A is written  '»  the  electrode  i s defined electrode  (Fig. 1).  as  f^  = a^/C^)  is  = v  Cathode p o t e n t i a l *  = V  brium p o t e n t i a l  between  for reaction j .  j , are  difference  and t h e  potential  between of the  the solution  Thus,  Anode p o t e n t i a l  or d i f f e r e n c e  reaction  (i.e.,  the  a c  = d> - cb ma sa  [2]  = <> j mc  [3]  The r a t e o f a n e l e c t r o c h e m i c a l r e a c t i o n  for  as  I  of each s p e c i e s  r  potential,  form  (10).  The e l e c t r o d e  adjacent  j  j  the  <> j is  electrode  The a n o d i c  sc  a f u n c t i o n of the potential  and c a t h o d i c  and t h e  overequili-  overpotentials  respectively,  n . = v * - v. aj a 3  [4]  The  current density  ( i ) i s d e f i n e d as t h e amount o f c u r r e n t  passing  p e r u n i t a r e a o f t h e e l e c t r o d e , and may be r e l a t e d t o t h e o v e r p o t e n t i a l , e i t h e r l i n e a r l y a t low o v e r p o t e n t i a l s  (n a i ) o r through t h e T a f e l equa-  t i o n at high overpotentials, H. - a. + b. l o g i 3 3 3 In a g i v e n e l e c t r o l y t e , for  [6]  the T a f e l constants  a and b have s p e c i f i c  each e l e c t r o c h e m i c a l r e a c t i o n j o c c u r r i n g on a g i v e n e l e c t r o d e a t  determined c o n d i t i o n s o f pH and temperature. for  values  These have been  common e l e c t r o d e r e a c t i o n s on d i f f e r e n t e l e c t r o d e s  reaction w i l l  occur  reported  (10,11).  A side  i f the p o t e n t i a l of the e l e c t r o d e i s equal t o the  t o t a l p o t e n t i a l r e q u i r e d t o d r i v e the s i d e r e a c t i o n ( e q u i l i b r i u m p o t e n t i a l plus overpotential). l y t i c processes lysis, of  Major s i d e r e a c t i o n s a s s o c i a t e d w i t h e l e c t r o -  i n aqueous s o l u t i o n s a r e t h e r e a c t i o n s o f water e l e c t r o -  that i s , the anodic  formation  o f oxygen and t h e c a t h o d i c  formation  hydrogen. Depending on t h e pH o f t h e e l e c t r o l y t e and p o t e n t i a l o f t h e e l e c t r o d  d i f f e r e n t water e l e c t r o l y s i s r e a c t i o n s , may  (Standard r e d u c t i o n potentials)  Oxygen e v o l u t i o n r e a c t i o n s : 2 0H~ t  % 0  t  % 0  H 0 2  2  + H 0 + 2e~  V° = 0.4010  [Rl]  + 2H  V° = 1.2290  [R2]  V ° =-0.8277  [R3]  V° =0.0000  [R4]  2  2  occur,  +  + 2e"  Hydrogen e v o l u t i o n r e a c t i o n s : H 0 + e~ t 2  H  +  + e~ t  hE  + OH"'  2  h H  2  Side r e a c t i o n s w i l l t i o n f o r current  compete w i t h  the d e s i r e d e l e c t r o c h e m i c a l  reac-  so t h a t t h e a p p l i e d c u r r e n t d e n s i t y w i l l be t h e sum o f  the p a r t i a l c u r r e n t d e n s i t i e s s u p p o r t i n g  each r e a c t i o n .  Considering  8 the  electrochemical reaction  the  o x i d a t i o n o f A i s d e f i n e d as  of  e l e c t r i c i t y needed  amount  (A -* B + z e ) ,  an e x p r e s s i o n f o r  per  equivalent  the  percent  % C.E. = where,  m = number  If  the  sometimes  the  the  efficiency  for  theoretical  o f A , and t h e  amount  actual  of A o x i d i z e d .  of current  efficiency  is:  100  [7]  of moles of A o x i d i z e d .  i s necessary  ( d e p e n d i n g on t h e between  x  o x i d a t i o n of A i s the  it  current  r a t i o between  t o o x i d i z e one e q u i v a l e n t  of e l e c t r i c i t y passed  Thus,  the  the  to  desired  suppress  the  electrochemical reverse  relative reaction rates).  oxidized  species  and t h e  reduction  In order  cathode,  reaction, reaction  to avoid  or to prevent  contact  mixing of  a n o l y t e and c a t h o l y t e w i t h p o s s i b l e r e a c t i o n a n i o n e x c h a n g e  membrane  or  a d i a p h r a g m c a n be used  a n o d e and c a t h o d e  chambers  in  a divided  o f i o n s and m o l e c u l e s .  An i o n  e x c h a n g e membrane  t h r o u g h t h e membrane. membranes,  they  catholyte,  since the  the  the  different  anion s e l e c t i v e or c a t i o n s e l e c t i v e ,  or cations Due t o  transport  general  respectively w i l l  the  c a n a l s o be used  t y p e o f membrane  For  transport  c a n be e i t h e r  which case only anions  the  separate the  cell.  A diaphragm a l l o w s the  by  to  [OH ] o r  transported of i o n  pH o f t h e  [H ] ions w i l l +  exchange  anolyte be  and  determined  used.  case of plane  potential  selective properties  to c o n t r o l the  of  be  in  drops  electrodes  through  the  cell  and two s e p a r a t e are  chambers,  illustrated in Fig.  1.  9  If  K  e  , K  a  , and K  e,  diaphragm, as  e  d  are  c  and c a t h o l y t e ,  ig.  1.  the  electrxcal conductivities  .•  V o l t a g e components i n a divided electrolytic cell.  and a r e  o f the  a n o l yJ t e ,  u n i f o r m , the Ohm's l a w can be  written  follows: K i  I A<p I sa  e  1  1  K e  =  the  total  AV . . = A(J> ohmic sa Y  When t h e  anolyte  an e x t r a  potential  K °e  1  c  I A<p I ' <=^ sc  'd  ohmic drop  + A<}), + A<(> d sc Y  I A<j> , I d'  S.  a Therefore,  '  Y  and c a t h o l y t e  is  r  i  1  c  given by:  S .S .£ = i ( - ^ + —S-+ — - ) . K K K ' e e, e a d c have a p p r e c i a b l y  d r o p may e x i s t ,  different  compositions,  called "liquid junction potential" ;  10 (10) b u t  usually i t  The t o t a l  is relatively  electrolysing voltage  AV = V  *  a  |V *|  +  electrolysing voltage  of  the  e l e c t r o l y t i c process  is  directly related  current  is  density  i would  [8]  +  e  c  of importance  depend  be,  on i t s  total voltage  s i n c e the  operating  power r e q u i r e m e n t s  drop through  the  cell  cost  which  at  a given  density.  Practically, than  a current  e., d  a  will  to the  for  i  +  c  e The t o t a l  small.  the  particular  a reference cathode  the  solution.  the  has  potentials  at  the  easier  surface  i n p o t e n t i a l between  to  measure or V  of the  electrode  potential  as w i l l  c  anode  t h e m e t a l and  w h i c h an e l e c t r o c h e m i c a l r e a c t i o n o c c u r s  or  the  depends  b e shown b e l o w .  Consider a s i n g l e r e v e r s i b l e reaction that (anode o r  is  because to measure  to be c o n n e c t e d  difference  The r a t e a t  s t r o n g l y on t h e  electrolysing voltage  electrode  electrode  to detect  total  occurs  on an  electrode  cathode), 1 A X 2  The n e t  the  1: 2:  oxidation reduction  r a t e of e l e c t r o c h e m i c a l r e a c t i o n  modulus o f the of  B + ze  difference  reversible  between  the  over the  m  the  and C„ B  electrode,  reactions  is  r a t e s o f o x i d a t i o n and  2  C  the  reduction  mi  2  -  B  K  r  i  C  are  the  |  A  s  s  electrode  reaction  - = | K r  where C. A  reaction reaction  [9]  s  concentrations  o f A and B a t  the  surface  of  s  mi and m  respectively,  2  are  the  orders  a n d K r i and K r  of the 2  are  the  o x i d a t i o n and  reduction  electrochemical  reaction  rate constants, tial  w h i c h c a n be e x p r e s s e d  i n terms  of the  electrode  by u s i n g an A r r h e n i u s t y p e o f r a t e c o n s t a n t - a c t i v a t i o n  poten-  energy  relationship, Kr  Kr Here Kr£ and K r ° a r e p o t e n t i a l at transfer  1  2  = K r ° exp  = K r ! exp 2  rate constants  standard  1  RT f(l-a)  [10]  — J  |v*r  zF RT  referred  [11]  to a p a r t i c u l a r  c o n d i t i o n s , and a i s a c o n s t a n t  coefficient.  These equations  imply that  electrode  known a s t h e  a f r a c t i o n of  charge  the  • *• e l e c t r o d e p o t e n t i a l ct|V | d r i v e s t h e | V I d r i v e s the  (1-a)  The f a c t tially the  that  on t h e  reverse  the  f o r w a r d r e a c t i o n and t h e  reaction.  electrochemical rate constant  e l e c t r o d e p o t e n t i a l and n o t j u s t  case of a pure chemical r e a c t i o n ,  can be v a r i e d by orders  of-the  electrode w i l l  from the b u l k o f the  the  the  to  ular  electrode  etical  purposes  are  reaction  in rate  potential., at  the ..  surface,  flux  transfer  for  the  as  t h e r a t e o f mass t r a n s f e r .  electrode  = K (C. - C. ) [12] . -\ s c o e f f i c i e n t , c h a r a c t e r i s t i c of the p a r t i c -  c o n f i g u r a t i o n and f l u i d  expressions  exponen-  temperature  concentration of reactant  m  the. mass  on t h e  i l l u s t r a t e s that  be r e l a t e d  s o l u t i o n to  Mass t r a n s f e r where K i s m  depends  o f m a g n i t u d e by s i m p l y a d j u s t i n g t h e  At a given r e a c t i o n rate, surface  remainder  transfer  A  dynamics.  coefficients,  a v a i l a b l e i n standard  texts  (12).  E m p i r i c a l and  suitable for  design  theor-  12 2.2  Literature  r e v i e w on t h e  A substantial  literature  o x i d a t i o n of phenol. reactions reported  findings are  In the  exists  of operating  sometimes  have been proposed,  order  to  literature  is  related  However, owing to  and t h e v a r i e t y  mechanisms  electrochemical oxidation of to  the  the  phenol  electrochemical  complexity of the  c o n d i t i o n s used  contradictory.  i n each  Many d i f f e r e n t  some o f w h i c h a p p e a r h i g h l y  consider possible rate determining p r e s e n t e d h e r e a n d some o f t h e  oxidation study, reaction  speculative.  factors,  a review of  contradictions  are  dis-  cussed. 2.2.1  Reaction  products  T h e a n o d i c o x i d a t i o n o f p h e n o l was e x t e n s i v e l y and. c o - w o r k e r s reported  (13-15)  during the  t h a t when p h e n o l i s  s u l p h u r i c a c i d media the OH  early part  o x i d i z e d at  products QH  studied  of t h i s  by F i c h t e r  century.  They  a lead dioxide electrode  shown i n F i g . 2 a r e  in  involved.  0 CH-COOK rt  OH phenol  hydroquinone  I!  0  p-benzoquinone  OH  2.  maleic  acid  OH  ether of pyrocatechol Fig.  CH-COOH  Reaction  products.  2>4' d i h y d r o x y diphenyi  4,4' dihydroxy diphenyi  13 It was  also found that i f benzene (13) i s electrochemically  oxidized at  a platinum electrode i n sulphuric acid solution some of the same products were encountered, e.g., and o x a l i c acids.  hydroquinone,  It was  p-benzoquinone, catechol, maleic,  suggested (11,13) that probably phenol  was  f i r s t produced as an intermediate i n the oxidation of benzene, even though phenol had not been isolated from the reaction mixture. information  Thus,  concerning benzene electrooxidation can be useful f o r the ,  present study. 2,2.2  Proposed reaction mechanisms a)  Hydroxylation  The formation of hydroquinone and catechol was  attributed to the  introduction of hydroxyl groups into the aromatic r i n g , by the action of anodically generated oxygen. produced i f benzene was  the s t a r t i n g substrate  assumption i s contradicted t i o n of benzene to  By the same mechanism phenol would be (13).  However, t h i s  i n a more recent paper (16) where the oxida-  p-benzoquinone i s reported  at 100%  current e f f i c i e n c y  at potentials below those at which oxygen evolution occurs. explanation  But a c l e a r  of the mechanism i s not given i n the paper. b)  Nuclear linkage  Fichter explained  the formation of diphenyi derivatives by supposing  that a linkage of two aromatic n u c l e i was  brought about by a bond of  oxygen,  [R5]  A s i m i l a r mechanism would produce a l l the diphenyi compounds indicated i n F i g . 2.  Those compounds were f o u n d when lead peroxide anodes were  14 employed at reported  a r e l a t i v e l y low current  that  homologues group.  the  like  more r e c e n t  presence  o f an e l e c t r o n  conditions  among t h e  oxidized  the  further  the  case of s u b s t i t u t e d  always reported  presence  products  reported  products  to  the  o x i d a t i o n upon  current  of d.iphenyl  density.  the  studies  is possible  either  presence  (23,24)  phenol  are hydroquinone, It  benzo-  that  are not  under  formed,  the  Primary electron, transfer  oxidation of phenol,  to e x i s t  i n the  solution,  i n agreement  in  is  with  ionized  (23,25),  first-step due t o  the  m e c h a n i s m s of ability  or u n i o n i z e d form depending  OH  0  of  on t h e pH o f  4-  unionized  form  and a t  h i g h pH v a l u e s w i l l  The f o l l o w i n g mechanisms of  the  In  acidic solutions  tend  H  phenoxide ion  l o w pH i n aqueous s o l u t i o n s p h e n o l s w i l l  form,  or  mechanism  two d i f f e r e n t ,  have been proposed  r  At  the  However,  of coupled products  which i s  In  derivatives  above mentioned e n d - p r o d u c t s .  phenols,  phenol  donating  of o x i d a t i o n of pure  diphenyl derivatives  i n recent  electron transfer phenols  further  also  findings. c)•  In  the  and c a r b o n d i o x i d e .  are  Fichter's  (17-22)  G e n e r a l l y the  quinone, maleic a c i d , reported  to  e l e c t r o l y s i s o r upon i n c r e a s i n g t h e  not been r e p o r t e d  Fichter  2  l i n k a g e , . i s e v e n more p r o n o u n c e d w i t h  o - C r e s o l due t o t h e  publications  solutions.  the  (25A/m ).  The d i p h e n o l s w e r e f o u n d s u s c e p t i b l e  c o n t i n u i n g the  has  nuclear  density  [R6]  tend t o b e i n t h e u n i o n i z e d  t o be a s  a phenoxide ion.  have been p r o p o s e d ,  for  the  first  step  oxidation: the  initial  +  s t e p i n v o l v e s two e l e c t r o n s  where t h e  15  e l e c t r o p h i l i c attack of the aromatic nucleus ion",  produces the "phenoxonium  0  U - ^  - 2e H"  -y  phenoxonium ion (mesomeric)  [R7]  In a l k a l i n e solutions the primary anodic reaction of phenoxide ions i s a one-electron transfer with the formation of a phenoxy free r a d i c a l that i s very r e a c t i v e .  • •  - Ie. phenoxi r a d i c a l  [R8]  In appendix 5, the percentage phenol ionized as a function of pH i s calculated from the d i s s o c i a t i o n constant (K, = 1.28 d  for phenol at 20°C  x 10~ ). 1 0  d)  The divided or undivided  c e l l and the reaction mechanism-  A great deal of information regarding the electrochemical oxidation of phenol e x i s t s because of commercial i n t e r e s t i n the production of hydroquinone or" p-benzoquinone (.19-22). chemical  Covitz studied the e l e c t r o -  oxidation of phenol for hydroquinone production at lead dioxide,  anodes i n an undivided  c e l l i n acid media.  He showed that the reaction  can be c o n t r o l l e d to produce hydroquinone at over 90% y i e l d . The  s i m p l i f i e d mechanism for the e l e c t r o l y t i c process proposed i s  (26, p. .157):  OH It  i s of i n t e r e s t  to  i n t r o d u c e an oxygen atom i n t o  undivided quinone. is  cell  to note that  p-benzoquinone  From t h i s  c a r r i e d out  reaction  i n a divided  p-benzoquinone would not reduced  i n the  membrane,  scheme  cell,  contact  the  starting  i s reduced  back to hydroquinone.  semipermeable  the  anodic r e a c t i o n , water  it  at is  is  utilized  phenol molecule.  I n the  the  cathode  obvious that  b y u s i n g a membrane the  cathode  i f the  or a  and t h e r e f o r e  Covitz reported  only measurable  to produce  (19)  product  hydro-  process  diaphragrc. would not  t h a t when u s i n g  be a  i n the  anolyte  was  is  oxidation cf  p-benzoquinone. Another p o s s i b l e r e a c t i o n  i n an u n d i v i d e d c e l l  hydroquinone back to p-benzoquinone which would for  o x i d a t i o n at  phenol o x i d a t i o n .  the  anode,  thus  lowering the  the  compete w i t h  current  the  efficiency  phenol for  e)  E l e c t r o l y t i c a c t i o n of lead  Some a u t h o r s  (16,23,26)  support  the hypothesis  o x i d a t i o n o f p h e n o l on l e a d d i o x i d e . c h e m i c a l l y by l e a d d i o x i d e and t h e rapidly  Pb0  2  suggested  transfer  organic  from the  i n the  2  studies of  the  products  formed.  organic molecule. w o u l d be n e c e s s a r y reaction  [R13].  whatever  is  species  so f o r m e d  are  or e l e c t r o l y t i c  step.  [R12]  explanation  to  to determine  the  electron  oxidative a b i l i t y  C l a r k e and c o - w o r k e r s  in stirred  p r e v i o u s l y , the  (16)  benzene e m u l s i o n s .  The  and m a l e i c a c i d were  were not  made analysis  rapidly  provided.  same p a p e r c o n t r a d i c t s  the  hypothesis  a mechanism o f i n t r o d u c t i o n o f oxygen i n t o Thus i f P b 0 to replace  Further  2  is  the  supposed  oxygen l o s t  source  o x i d a t i o n of  t o be the  is  the  oxygen c a r r i e r  i n reaction  of oxygen,  it  [R12] by  of course,  the  water,  intermediates  i n f o r m a t i o n c o n c e r n i n g the  last  o x i d a t i o n o f p h e n o l t o open c h a i n o r g a n i c  carbon d i o x i d e i s very  tions  2  The u l t i m a t e  The a v a i l a b l e  to  phenol i s o x i d i z e d  the p r e v a i l i n g mechanism. f)  lytic  c a r r i e d out  However, .numerical r e s u l t s  h y d r o x y l a t i o n as  electrocatalytic  + 2  showed t h a t b e n z o q u i n o n e  As d i s c u s s e d of  Pb0  words,  transfer  as a n a l t e r n a t i v e  absence of c u r r e n t .  with granular  lead  of  molecule.  E x p e r i m e n t s have been Pb0  reduced  + ORGANIC + PRODUCT + P b  T h i s mechanism i s  of  In other  o x i d i z e d b a c k t o Pb02 b y a c h a r g e  1)  dioxide  have been  limited,  concerned w i t h the  s u b s t r a t e for waste treatment  stages of the  compounds  or  eventually  p r o b a b l y b e c a u s e o n l y a few total  destruction  applications  (i.e.,  of the  17,18,25).  electro-  investiga-  organic  A mechanism f o r the However,  i n the  last-stage  r e a c t i o n s has not  early investigations  a t e s were s u s c e p t i b l e to f u r t h e r  (14)  i t was shown t h a t  disintegration.  a high resistance  Fichter high current trolytic  established that  oxygen.  as o x a l i c  acid,  He r e p o r t e d formic a c i d ,  products  elecsuch  agreement  A p a r t i c u l a r l y i n t e r e s t i n g c o n t r o l l e d p o t e n t i a l study i s  presented  the  e l e c t r o l y t i c o x i d a t i o n of benzene  t h e a r o m a t i c r i n g o c c u r s and t h e  Anodically oxidizing the  been  with  at  in  and c a r b o n d i o x i d e p r o d u c t i o n  of  saturated  and c a r b o n m o n o x i d e , w h i c h i s  the p o t e n t i a l i s i n c r e a s e d above t h a t of  is  occurs faster  characteristic final  w i t h some o f t h e p r o d u c t s r e p o r t e d b y G l a d i s h e v a  for  be  (27).  aromatic nucleus less  example,  was shown t o  the decomposition process  d e n s i t i e s , when t h e  for  and p - b e n z o q u i n o n e ,  to chemical o x i d a t i o n ,  r e a d i l y b r o k e n down b y e l e c t r o c h e m i c a l means  proposed.  intermedi-  Catechol,  was w e l l known a s a n e a s i l y o x i d i z a b l e s u b s t r a t e , which offered  ever been  generated  agents,  (17).  (16) where i t  of oxygen e v o l u t i o n ,  current  efficiency  as  fragmentation  for maleic  acid  increases.  o x y g e n i s known a s one o f t h e m o s t p o w e r f u l  a n d seems t o b e r e s p o n s i b l e f o r  intermediates,  i s shown t h a t  even though the  exact  the  further  oxidation  r e a c t i o n mechanism has  not  determined. 2.2.3  Electrode materials  tested  L e a d d i o x i d e h a s b e e n t h e most  commonly u s e d e l e c t r o d e  e l e c t r o c h e m i c a l o x i d a t i o n o f p h e n o l and i n s e v e r a l c a s e s i s as t h e  electrode m a t e r i a l of c h o i c e .  r e v i e w and compare t h e  performances  However, i t of d i f f e r e n t  i a l s were t e s t e d :  nickel,  the  recommended  i s of i n t e r e s t  electrode  I n t h e p a p e r by G l a d i s h e v a and L a v r e n c h u k (17)  in  materials.  s e v e r a l anode  smooth p l a t i n u m , g r a p h i t e ,  to  and l e a d  mater-  dioxide  electrodeposited the  The e x p e r i m e n t s s h o w e d t h a t  same o p e r a t i n g c o n d i t i o n s , t h e h i g h e s t  lead of  on a n i c k e l b a s e .  dioxide electrode.  oxidation is  sities.  g i v e n at  The r e s u l t s  are  o x i d a t i o n r a t e o c c u r r e d on shown i n T a b l e 1 w h e r e t h e  two p h e n o l c o n c e n t r a t i o n s  The c h e m i c a l s t a b i l i t y o f t h e  under  different  a n d two c u r r e n t electrodes  the rate  den-  tested  was  TABLE 1 RATES OF PHENOL OXIDATION ON DIFFERENT ELECTRODE MATERIALS ( 1 7 )  I n i t i a l phenol c o n e , (mg/1)  Electrode material  at  1.0 9.2  3.7 21.6  Graphite  200 1000  0.7 6.3  2.4 17.0  Smooth p l a t i n u m  200  0.4  2.4  Nickel  200  0.2  2.9  densities  T h e - g r a p h i t e a n o d e was f o u n d r e l a t i v e l y s t a b l e between 50-250 A / m but  started  2  t o b r e a k down, f o r m i n g  t o remove by f i l t r a t i o n .  pH = 10 n i c k e l  Nickel  at  The  expected, This  to phenol  f a c t was e x p l a i n e d b y t h e  curthe diffi-  since  oxidation,  and d e s t r o y i n g the  electrode.  of course, electrochemically  t h e r a t e s o f o x i d a t i o n o f p h e n o l w e r e much l o w e r c o n s i d e r i n g t h a t p l a t i n u m has  at  densities  e l e c t r o d e s were u n s u i t a b l e  d i s s o l u t i o n occurred p a r a l l e l  smooth p l a t i n u m e l e c t r o d e was,  but  higher current  s m a l l p a r t i c l e s t h a t were  c o n s u m i n g a s i g n i f i c a n t amount o f c u r r e n t ,  stable  2  200 1000  graphite cult  2  Electro deposited lead dioxide  also discussed. rent  R a t e o f O x i d a t i o n (mg/min] i = 5 0 A /m i = 1000 A / m  than  a h i g h oxygen o v e r p o t e n t i a l .  formation of a tar  film  on t h e  surface  20 of  the  ever,  anode w h i c h d i d n o t the  presence  lead dioxide I n the Fioshin  et  d i s s o l v e i n a l k a l i n e or a c i d  o f s u c h a f i l m was n o t m e n t i o n e d  study (22)  the  same r e s u l t  l e a d d i o x i d e anode,  it  i s known t h a t  s o l u t i o n s are ent  substrate.  powers, o f t h e  However, the  caused by f u r t h e r  was n o t  suggested  2.2.4  factor are  same.  rate  given i n Tables  Pb02 e l e c t r o d e ,  at  suggested  towards  the  quinone. were not  20  current  1 and 2 . the  the  current It  effect  initial  2  the  C.O.D.  have  performed.  densities.  on p h e n o l o x i d a t i o n was  was c o n c l u d e d t h a t among  d e n s i t y was t h e  strongest  the  determining The  results  In Table 1 i t  c a n be o b s e r v e d  on  the  concentration  o f 1000 m g / 1 o f p h e n o l ,  the  that  current  density  times. i n the  sodium sulphate  466 m g / 1 o f c h e m i c a l o x y g e n demand  50 A / m , t h e  organic  This p o s s i b i l i t y  of e l e c t r o c h e m i c a l o x i d a t i o n of phenol.  T a b l e 2 shows t h a t at  same  differ-  density  r a t e o f p h e n o l o x i d a t i o n a p p r o x i m a t e l y d o u b l e d when t h e was i n c r e a s e d  was t h e  on p l a t i n u m c o u l d a l s o  analyses  2  the  was  in acidic  c a r r i e d out over a wide range of current (17)  plat-  to quinone  of these electrodes  two e l e c t r o d e s  products  by  i t was o n l y 5% on p l a t i n u m ,  The r e a s o n  range o f 50-2000 A / m .  studied,  i n the  whereas  d i s i n t e g r a t i o n of the  i n reference  i n the  The c h e m i c a l y i e l d  overpotential  Effect of current  For example,  variables  the  was o b t a i n e d when c o m p a r i n g t h e  lower quinone y i e l d  and o t h e r  S t u d i e s have been  studied  the  p r a c t i c a l l y the  adsorptive  been  case of  of e l e c t r o c h e m i c a l o x i d a t i o n of phenol to quinone  inum and l e a d d i o x i d e e l e c t r o d e s .  although  i n the  How-  electrode.  al  33% o n t h e  solution.  final  dropped  (C.O.D.)  C . O . D . was 420 m g / 1 a f t e r t o 30 mg/T i n o n l y 1 h .  e l e c t r o l y t e , when at  a current  5 h , whereas  at  starting  density  of  2000 A / m  2  21 TABLE 2 EFFECT OF CURRENT DENSITY AND TYPE OF ELECTROLYTE ON C . O . D . REMOVAL ( 1 7 )  Current density A/m 2  2  I II  5 5  307 420  500  I II  3 5  90 120  1000  I II  1 2  30 75  2000  I II  0.5 1.0  0 30  2.2.5  I n i t i a l phenol I n i t i a l C.O.D. Electrolyte I Electrolyte II  c o n c e n t r a t i o n = 200 m g / 1 c o n c e n t r a t i o n = 466 m g / 1 o f 0 - 1 g / 1 N a C l , 1.5 g / 1 N a S 0 i - 3 g/1 Na SO^ 2  on t h e  electrolyte  e l e c t r o x i d a t i o n of phenol for  c h l o r i d e s a l t s were u s e d as  such media the  2  t  2  E f f e c t of nature of the  several studies  treatment, In  F i n a l C.O.D. (mg/1 o f 0 )  50  Notes.  In  Time o f Electrolysis (h)  Electrolyte type  electrolytes  o x i d a t i o n of phenol follows  waste  (17,18,25,28-30).  totally different  reaction  paths. When u s i n g N a C l o r C a C l have been proposed 1.  2  as e l e c t r o l y t e s ,  the  following  reactions  (17)  E v o l u t i o n of c h l o r i d e at 2 Cl" -  2e~ -» C l  2  the  anode, [R14]  22 2.  Formation of hypochlorite with phenol,  a)  Cl  + H 0  2  reaction  H C l + HCl©  2  8 HClO  f o l l o w e d by c h e m i c a l  [R15]  + C H O H •> CH 6  CO-OH  5  II  + 2 C0  CH -  + 8 HCl  2  + H 0 2  CO-OH [R16]  C h l o r i n a t i o n o f - p h e n o l by m o l e c u l a r C l p r o d u c i n g 2 , 4 d i c h l o r o p h e n o l and 2 , 4 , 6 t r i c h l o r o p h e n o l  b)  As c a n be s e e n ,  2  this  p r o c e s s does not  o x i d a t i o n of phenol, production of  instead  it  is  equivalent  o f c h l o r i n e and h y p o c h l o r i t e  electrochemical  to  the  electrolytic  f o l l o w e d by a c h e m i c a l  oxidation  phenol. It  also  these are the  (25)  gives  rise  to undesirable  c l a i m e d t o be c a p a b l e  quinone  ence 2,4  but  represent pure  type,  where  the  removal  experiments  Knowing that itself,  the  were  sodium s u l p h a t e . 2  after  phenols  that  at  the  four  l o w e r when t h e  l y t e was p u r e N a S 0 t . 2  to  the  f  are  with  and the  p-chlorophenol,  percent  removal of  respectively.  electrolyte  than  phenol  does not  appear  rate of  phenol  i f the  support  electrolyte  such  2  also  (17)  shown i n T a b l e 2 w h e r e  current  densities  used,  electrolyte  contained  N a C l t h a n when t h e  However, an a n a l y s i s  t  i n terms of f i n a l  the  of  refer-  o f a m i x t u r e o f N a C l and N a S 0 i  have been compared  The r e s u l t s  give products  a r e more o b j e c t i o n a b l e  t h a n when u s i n g a n i n e r t  electrolytes  starting  p o l l u t i o n problem even  The p e r f o r m a n c e  treatment.  observed always  +  out  82%, 79%, a n d 58%  a d d i t i o n of c h l o r i d e s a l t s  oxidation i s higher  to  Although  T h i s was shown i n  trichlorophenol  chlorinated  the  oxidation,  100%.  carried  ( C . O . D . ) were  t o b e a good s o l u t i o n t o  pure Na S0i  of further  i s never  d i c h l o r o p h e n o l and 2 , 4 , 6  c h e m i c a l o x y g e n demand  chlorination products.  final  of c h l o r i n a t e d  it  C.O.D.  as  and C.O.D. is was  electro-  phenols  which  23 may h a v e b e e n p r o d u c e d was n o t which e l e c t r o l y t e  i s more  Other e l e c t r o l y t e s , a packed bed g r a p h i t e  p r o v i d e d , thus i t  is difficult  to  decide  suitable. s u c h a s Na2Bi 0y, NH3 and H^SO^ w e r e t e s t e d t  electrode  (18).  The r e s u l t s  are  using  shown i n T a b l e  3.  TABLE 3 EFFECT OF TYPE OF ELECTROLYTE ON PHENOL OXIDATION ( 1 8 )  Electrolysis t i m e (h)  Final cone,  pH  0.1 M sodium b o r a t e  9.7  3.5  420  10.0  5.5  400  0.1 M sulphuric acid  1.1  3.7  400  5% s o d i u m c h l o r i d e  5.7  20-0  10  0 . 1 M ammonia  I n i t i a l p h e n o l c o n e . = 1000 m g / 1 V o l u m e o f e l e c t r o l y t e = 700 m l Current = 0 . 6 A (on g r a p h i t e  With the about  phenol (mg/1)  Electrolyte  first  three electrolytes  p h e n o l was r e m o v e d f r o m 1000 m g / 1  400-420 mg/1 i n e l e c t r o l y s i s t i m e s  phenol concentration electrolyte  and a t  reached  the  from 3 to  5 h.  The  to  final  10 m g / 1 o n l y when u s i n g a s o d i u m c h l o r i d e  excessively large  electrolysis  t i m e s a l l o w e d makes  performances  difficult.  In t h i s  low and an e s t i m a t i o n o f the  anode)  the  t i m e o f 20 h .  comparison between  case the  electrode  current  a r e a was n o t  The  different  electrolyte  a p p l i e d was r e l a t i v e l y provided.  24 2.2.6  E f f e c t of pH  The e f f e c t of pH on the oxidation p o t e n t i a l of phenol has been reported (23).  The r e s u l t s of this polarographic study are represented  i n F i g . 3. >  r  < 02  1  1  0  X  1  1  1  1  1  r  1  1  1  : 1  8  A  1  1  12  pH Fig.  3.  Half-wave p o t e n t i a l vs pfi, f o r the oxidation of 4 x 10" M phenol (23). 4  The h a l f wave p o t e n t i a l i s defined as the p o t e n t i a l on a polarographic curve when the current i s equal to one h a l f the mass  transfer  l i m i t i n g current (31). I t can be observed that the h a l f wave p o t e n t i a l decreases when going from acid to basic solutions and eventually s t a b i l i z e s at a constant value for a pH equal to the pK^ (logarithmic of the d i s s o c i a t i o n constant of phenol).  At pH = pK^ a l l the phenol w i l l be i n the ionized form, or  i n other words, protonation w i l l be n e g l i g i b l e .  This means that a high  pH makes the phenol more e a s i l y oxidizable as far as p o t e n t i a l requirements are concerned. The e f f e c t of pH on the rate of phenol oxidation i s not well documented.  In reference  (17), i t was concluded  that the v e l o c i t y of  oxidation was p r a c t i c a l l y independent of pH of the s o l u t i o n i n the range  25 of  pH 6 t o 9 ,  changed  i n absence of c h l o r i d e i o n s .  to 11.9 a r a p i d increase  was r e p o r t e d ,  However, phenol or C . O . D .  isolated  study  from the  in  the  of  intermediate  tions  reviewed  the  a n d more  data  (Table  easily  that  crystal  Each v a r i e t y carefully  i n g to  analyses  concentration  were not  effect  of  reported  o f pH c a n n o t  No d e f i n i t i v e r e s u l t s effect (13)  in  o f pH o n t h e  c a n be p r e p a r e d  conditions  and i s b e t t e r  conforms is  atomic  oxidation solu-  same  h i g h pH  oxygen.  These  orthorombic free  and  differ  according  B-Pb02 i s  from the  other  tetragonal. under  (32). e x a c t l y to  the  stoichiometric  always detected  oxides,  Pb02  ( 3 3 ) , w i t h a-Pb0  lead dioxide i s  than  lead  lead dioxide structure  itself  a good  (26).  2  tend-  (or P o u r b a i x diagrams)  l e a d c a n be u s e d  as  electronic It  is  w i t h the  believed oxygen  (32). show t h e  s t a b i l i t y o f l e a d a n d l e a d compounds  dynamic p r e d i c t i o n s  found  content.  i n fact  P o t e n t i a l - p H diagrams thermodynamic  further  w o u l d be u n s t a b l e a t  h i g h e l e c t r i c a l c o n d u c t i v i t y may b e c o n n e c t e d i n the  c o u l d be  suggested that i n a l k a l i n e  substantially  an oxygen d e f i c i e n c y  deficiency  be  o x i d a t i o n w o u l d p r o b a b l y be t h e  a-Pb02 i s  show a l o w e r o x y g e n  the  the  p-benzoquinone  structure.  controlled  conductor,  (18)  l e a d d i o x i d e commonly e x i s t .  C o n t r a r y t o most m e t a l  that  i n the  solution  electrode  Lead d i o x i d e never formula,  of the  o x i d i z a b l e by t h e  The l e a d d i o x i d e  the  3).  Fichter  primary products but  al  about the  products.  Two t y p e s o f to  by T a r j a n y i e t  literature  i n a c i d media,  2.3  of the  pH was  case. In the  as  o p t i c a l density  w h i c h was e x p l a i n e d b y a n i n c r e a s e  hydroquinone. this  i n the  H o w e v e r , when t h e  an anode a t  (34). high  regions From  of  thermo-  electrode  26 potentials  f o r pH v a l u e s  Under such c o n d i t i o n s Delahay et lead  are  From t h e s e ,  (35)  2  Pb +  t h e most  + 2e~ + 4 H  SOLT  The r e a c t i o n s opposite  2  constructed ions  the  studied  (1 g - i o n / 1 ) .  reactions  lead acid storage + SOu~  +  are  occur i n the  b l o c k i n g of the  Pb0  2  t i o n s may a l s o b e o f  2  Pb0 . 2  form the  surface  (23).  V° = 1 . 6 8 5  [R17]  V° = - 0 . 3 5 6  [R18]  It  and i n  i s w e l l known t h a t  presence of excess  i n the  of  battery,  with a deposit  importance  and p H s .  basis  indicated d i r e c t i o n during discharge  i n the  for  electrode  potentials  those that  2  d i r e c t i o n during charging of Pb0  Many  different  t PbSOi* + 2 H 0  2  corrosion.  p o t e n t i a l - p H diagram  t PbSOtt + 2e~  anism of discharge  acid  have  appreciable  be c o v e r e d w i t h a l a y e r o f  thermodynamically p o s s i b l e at  u n i v e r s a l l y used Pb0  0 and 12 w i t h o u t  the metal w i l l  i n the presence of s u l f a t e  reactions  the  al  between  sulfate  the  the  mech-  involves  o f PbSOLv ( 3 2 ) .  These  o x i d a t i o n of phenol i n  reac-  sulphuric  media. The s u i t a b i l i t y o f l e a d d i o x i d e as a n a n o d e m a t e r i a l h a s b e e n k n o w n  f o r many y e a r s .  It  is  clear  that  prolonged high anodic p o t e n t i a l s undergoes d e g r e d a t i o n ) . oxygen o v e r v o l t a g e  Also,  (10,36)  lead dioxide i s able  more e f f e c t i v e l y t h a n  to  withstand  graphite  (which  lead dioxide possesses a r e l a t i v e l y high  of the  same o r d e r  of magnitude  as  platinum  a n d i s much c h e a p e r . Preparation. anodization, a) put  the  or deposited  Anodization.  until  acquired  the  onto other The m o s t  lead i n contact  flow of current l e a d has  Lead d i o x i d e can be p r e p a r e d metals  by  as  a c o a t i n g on l e a d  electrodeposition.  c o n v e n t i o n a l a n o d i z a t i o n method  w i t h an aqueous H S0t| e l e c t r o l y t e 2  oxygen e v o l u t i o n i s p l a i n l y v i s i b l e , characteristic  by  is  and p r o v i d e and t h e  b l a c k deposit of lead d i o x i d e  to a  grey (26,33).  It  i s w e l l known t h a t  layer  oxygen i s  o f l e a d d i o x i d e has  electrode  should not  be l e f t  by r e d u c t i v e p r o c e s s e s possible  been  e v o l v e d f r o m a l e a d a n o d e o n l y when a laid  down ( 3 2 ) .  i n contact  After  with sulfate  anodization,  ions to avoid  ( R e a c t i o n R17) and s h o u l d be used as  soon  the losses  as  (26).  Some a u t h o r s preparation  (37,38)  have p o s t u l a t e d  that  o f Pb02 b y a n o d i z a t i o n o f Pb i s  o c c u r s between  the  Pb02 and t h e  a shortcoming of  that  a solid  phase  u n d e r l y i n g Pb t o p r o d u c e  the  the reaction  less  con-  d u c t i v e PbO, Pb0 However,  another'study  + Pb t  2  (39)  reports  z a t i o n o f l e a d i n H2SO4 o b s e r v e d B-Pb0  2  and PbSOt+j b u t  s t o r a g e of the i s proposed at  the  the  i n the  Pb/PbSO^ p o t e n t i a l ,  is  the  (36)  Electrodeposition.  d e p o s i t i o n o f Pb02 on i n e r t Some o f t h e m e t h o d s a r e Pb02 has graphite. easy the  been  that  Most other  oxidation (26).  are  2  from e l e c t r o l y t e s  and o f t h e s e ,  the and  the  tolerate  the  disintegrate. the  electro-  containing  lead.  (32).  tantalum,  platinum,  carbon,  because of t h e i r  Several types of e l e c t r o l y t e s  deposition of P b 0 ,  8-Pb02  s e v e r a l methods f o r  unsuitable  to  f r o m Pb  a-Pb02-  summarized i n r e f e r e n c e  metals  to  of  a mechanism  formed  rises  anodized l e a d can not  on n i c k e l ,  ct-Pb02,  same s t u d y  transforms  to  anodi-  s e v e r a l weeks  potential  d i r e c t l y to  There are  deposited  of the  F i r s t , PbSO^ i s  PbSOij f i l m  metals  In the  when t h e  presence of c h l o r i d e ions which cause i t b)  even a f t e r  dry s t a t e .  converted  reported  only products  by x - r a y d i f f r a c t i o n , were  and l a t e r  value,  underlying grid metal has been  the  a n o d i z a t i o n of l e a d .  oxygen o v e r p o t e n t i a l  It  that  [R19]  no PbO was d e t e c t e d ,  electrode  for  2 PbO  lead nitrate  inherently  have been used  has been  or  found to  for give  28 the.best  deposits  The l a r g e s t  (40). producers  anodes i n the w o r l d are  of commercial e l e c t r o d e p o s i t e d  Pacific  anode,  the  breakthrough  greatest  electrodeposition a lead nitrate  produced  anodized  f o r m a t i o n has been  The e l e c t r o d e p o s i t i o n  is  2  the  form found  baths.  from a l k a l i n e s o l u t i o n s  U n l i k e the effectively  2  lead,  the  manufacture.  on g r a p h i t e  '  uses  (41).  less  common and  can  (26,36).  electrodeposited  i n chloride concentrations  the  c o m m e r c i a l anodes  The a - f o r m i s  close  l e a d d i o x i d e anodes p r o d u c e d by P a c i f i c  perchlorate  i n the  graphite  shown i n  i n a c i d m e d i a as d e s c r i b e d b y G i b s o n  from a c i d l e a d n i t r a t e  be d e p o s i t e d  the  3-Pb0  for Pb0  (36).  electrolyte  The t e t r a g o n a l  Japan.  by P a c i f i c w i t h a l e a d d i o x i d e c o a t e d  interest  process  dioxide  E n g i n e e r i n g and P r o d u c t i o n C o . o f N e v a d a  a n d Sanwa C h e m i c a l C o . L t d . , o f T o k y o , Since the  lead  to  Pb0  2  can  saturation.  a n d Sanwa C o . a r e  operate In  fact  i n use  for  CHAPTER 3  OBJECTIVES  The a i m o f t h i s w o r k was t o  study  the  e l e c t r o c h e m i c a l o x i d a t i o n of  phenol for waste treatment a p p l i c a t i o n s . selected cell  because i t  provides  volume compared  ularly  important  equipment effect  reported  to c a r r y  out  of important  electrode  to a simple f l a t  where d i l u t e  The r e s e a r c h  larger  the  plate  solutions  operating  surface  to be  the  These v a r i a b l e s  lead versus  electrodeposited  ( d i v i d e d or undivided c e l l ) ,  ( a n i o n i c or c a t i o n i c ) ,  particle  size.  out  study  this  electrolyte,  the  The p e r f o r m a n c e is  compared  to  compare  current  29  the  also  ion-selective electrolyte,  flow-rate,  and to  carry  lead  dioxide  some t e s t s w e r e made  resistance. is  of importance, the  of  dioxide),  anode m a t e r i a l  further  l i t t l e information i n the  effects.  of  2.  r e a c t i o n mechanism f o r  There i s  of  lead  o f a n o d i z e d l e a d and e l e c t r o d e p o s i t e d  them i n t e r m s o f c o r r o s i o n  partic-  i n c l u d e type  pH o f t h e  the  reasons given i n Chapter  may c o m p l e t e l y c h a n g e t h e  such  as  i n terms of phenol o x i d a t i o n but  intermediates.  of  phenol concentration,  The u s e o f a d i v i d e d o r u n d i v i d e d c e l l  of  type  applied,  L e a d d i o x i d e was s e l e c t e d for  study  variables.  cell  c o n d u c t i v i t y of the  This i s  treated.  and a n e x p e r i m e n t a l  (anodized  membrane  unit  d e s i g n and c o n s t r u c t i o n  l e a d d i o x i d e anode configuration  areas per  electrode.  are  here includes process  A p a c k e d b e d a n o d e was  since  it  oxidation  literature  on  The e l e c t r o l y t e s m i x t u r e s o f Na2S0i  t o be u s e d f o r t h e  and H^SO^ o r Na2S0L; and NaOH, t o b e a b l e t o  +  i n d e p e n d e n t l y pH a n d c o n d u c t i v i t y o f t h e From t h e p o i n t d e t e r m i n e what  o x i d a t i o n of phenol consist  of view of waste  treatment,  it  is  o r how much o r g a n i c c a r b o n r e m a i n s  i n solution after  treatment.  of the  not  the  o n l y i n terms of p h e n o l o x i d a t i o n but  carbon  (T.O.C.)  oxidation.  have been r e p o r t e d . been r e p o r t e d .  In the  But t h i s  Relatively 1100 m g / 1 )  i n order  the  a l s o on t h e  i s not  electrochemical  total  an a d e q u a t e t e c h n i q u e  to  to  dioxide,  important v a r i a b l e s  reviewed l i t e r a t u r e  is  reported  organic  no T . O . C .  analyses  (C.O.D.)  have  of a n a l y s i s i n  the  (42).  low phenol concentrations  phenol o x i d a t i o n i s  investigate  achieved for  are used  the process  in this  until  study  (up  to  practically total  the range of o p e r a t i n g  c o n d i t i o n s of  experiments. 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 was s e l e c t e d  study the understood uous  of i n t e r e s t  I n some c a s e s c h e m i c a l o x y g e n demand  c a s e o f a r o m a t i c compounds  the  effect  vary  electrolytes.  f r a c t i o n of the phenol i s converted to carbon  Therefore,  of  effect  o f some o f t h e v a r i a b l e s .  as  the  Once t h e  o p e r a t i n g mode s y s t e m was  a n d c o n t r o l l e d , some e x p e r i m e n t s w e r e p e r f o r m e d  i n the  to  better contin-  mode. Finally,  pared with  the  t h e mass t r a n s f e r  and a s i m p l i f i e d presented  experimental f r a c t i o n a l conversions of phenol are  model f o r a batch r e c i r c u l a t i o n o p e r a t i o n ,  model i n c l u d i n g 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 t r o l  i n order  to analyze the data  and c o m p a r e t h e mass t r a n s f e r  com-  from t h e  continuous  and e l e c t r o c h e m i c a l r e a c t i o n  is  experiments resistances.  CHAPTER 4  EXPERIMENTAL APPARATUS AND METHODS  4.1  Apparatus 4.1.1  Cell  design  The e l e c t r o l y t i c c e l l series  it  permits  or undivided c e l l ) a)  Basically,  the  packings.  cell  and a r e  the  divided  consists  which are  separated  flexible  design  arrangements  electrode  arrangement  o f two f l a t  i n contact  with  contained  to prevent  is  plates,  in is  (divided  materials,  the  shown i n F i g . 4 .  the  anode  a n o d i c and  and  cathode  cathodic  i n 3 mm t h i c k s l o t t e d  from each o t h e r  neoprene  b y a n i o n - s e l e c t i v e membrane  a n o l y t e and c a t h o l y t e .  The c a t h o d i c  t h e membrane f r o m s a g g i n g due t o t h e  weight  anodic packing.  The a n o l y t e a n d c a t h o l y t e cell  cell  the mixing of the  p a c k i n g i s used  arranged  cell  Both packings are  which prevents  of  the assembly of d i f f e r e n t  Divided  feeders,  This  and s i m p l i f i e s work w i t h  A s i d e view of the  gaskets  of a stack of elements  and compressed by a clamp mechanism.  used because  current  consists  and t h e  that w i l l  outlets  at  the  inlets  top,  be produced d u r i n g the  l e a d d i o x i d e anode p l a t e s and e l e c t r o d e p o s i t e d In the  case  are  l o c a t e d at  to f a c i l i t a t e the electrolysis.  are used  in this  of the  of the  the  gases kinds of  anodized lead  sheet  plate.  anodized lead electrode 31  exit  Two d i f f e r e n t  study:  l e a d d i o x i d e on g r a p h i t e  the bottom of  the  current  feeder  plate  Legend a = 1.6 mm t h i c k n e o p r e n e  insulator  b = 1.6 mm t h i c k c a t h o d i c f e e d e r ( s . s . 316 p l a t e )  plate  c = 3 mm t h i c k s l o t t e d n e o p r e n e g a s k e t containing cathodic packing d = i o n s e l e c t i v e membrane a g a i n s t protective p l a s t i c screen (variable thickness) e = 3 mm t h i c k s l o t t e d n e o p r e n e containing anodic packing f  Fig.  4.  Side view of the  general  divided-cell  = anodic current feeder: 3 mm t h i c k l e a d p l a t e , o r lead dioxide coated graphite 3 cm t h i c k  gement.  (no  scale)  gasket  plate  33 was  c u t from a 0.3 cm t h i c k l e a d s h e e t .  The d e t a i l e d f r o n t and s i d e  views o f t h e anode chamber when u s i n g such e l e c t r o d e a r e shown i n F i g . 5. A neoprene gasket that w i l l  determines t h e c r o s s s e c t i o n a l a r e a o f t h e f e e d e r p l a t e  be t r a n s p o r t i n g t h e c u r r e n t .  The s i d e view shows t h a t an  e x t r a s t a i n l e s s s t e e l p l a t e i s used m a i n l y t o f a c i l i t a t e the i n l e t to  and o u t l e t connectors  the lead sheet.  the welding of  t o t h e c e l l and a l s o t o g i v e more s t r e n g t h  The f r o n t and s i d e views o f t h e cathode chamber a r e  the same as t h e anode chamber, except t h a t t h e t h i c k n e s s o f t h e s . s . 316 cathode f e e d e r was 0.16 cm. The  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 on g r a p h i t e p l a t e was o b t a i n e d  from P a c i f i c E n g i n e e r i n g and  Co.  The t o t a l t h i c k n e s s o f t h e p l a t e i s 3 cm  t h e t h i c k n e s s o f t h e l e a d d i o x i d e c o a t i n g on each s i d e o f t h e g r a p h i t e  i s 0.2 cm.  Some m o d i f i c a t i o n s had t o be made t o t h e o r i g i n a l  e l e c t r o d e t o adapt i t t o t h e c e l l and  design being  used.  commercial  The f i n a l  front  s i d e views o f t h e e l e c t r o d e d e p o s i t e d P b 0 2 anode a r e shotvn i n F i g . 6.  To a v o i d p o s s i b l e c r a c k i n g o f t h e P b 0 2 c o a t i n g , t h e e l e c t r o d e was l e f t with  i t s o r i g i n a l w i d t h o f 15 cm. A m o d i f i c a t i o n had t o be made i n o r d e r  f l o w through t h e g r a p h i t e coated adapted i s shown i n F i g . 7.  plate.  to introduce the e l e c t r o l y t e  A d e t a i l of t h e c o n n e c t i o n  The e l e c t r o l y t e never comes i n c o n t a c t  the g r a p h i t e base p l a t e because t h e n y l o n c o n n e c t i o n means o f a neoprene washer.  T h i s type o f c o n n e c t i o n  with  was i n s u l a t e d by prevents  c o r r o s i o n ..  o f t h e g r a p h i t e base and e v e n t u a l d e t e r i o r a t i o n o f t h e l e a d d i o x i d e l a y e r . Some fundamental s p e c i f i c a t i o n s o f t h e d i f f e r e n t elements o f t h e c e l l a r e g i v e n i n T a b l e 4.  The. dimensions o f t h e anode and cathode chambers  were never changed, b u t d i f f e r e n t The:cathodic  packing  s i z e s o f anodic  p a c k i n g s were used.  consisted of s e v e r a l s t a i n l e s s steel-304  screens  Legend a = l e a d s h e e t anode  feeder  b = s l o t t e d neoprene  gasket  c = electrolyte  outlet  d = anode p a c k i n g ( l e a d e = electrolyte f  = neoprene  shot)  inlet  insulator  g = s t a i n l e s s s t e e l 316 p l a t e (where c o n n e c t o r s a r e welded)  Fig.  5.  F r o n t and s i d e v i e w s o f t h e a n o d e chamber f o r t h e a n o d i z e d lead electrode. (no s c a l e ) .  Legend a = uncoated graphite anode f e e d e r b = electrolyte  s e c t i o n of  the  outlet  c = anode p a c k i n g d = slotted  neoprene  gasket  e = e l e c t r o d e p o s i t e d Pb02 s e c t i o n the feeder p l a t e f  = electrolyte  g = neoprene  Fig.  6.  of  inlet  insulator  F r o n t and s i d e v i e w s o f t h e anode chamber f o r t h e e l e c t r o d e p o s i t e d PbC>2 e l e c t r o d e , (no s c a l e )  2.54 cm  A  Legend a = nylon  connection  b = stainless c = neoprene  s t e e l mesh washer  d = lead dioxide e = g r a p h i t e base f  layer plate  = compressing nut  (threaded)  6.3 mm Fig.  7.  D e t a i l o f t h e i n l e t o r o u t l e t c o n n e c t i o n a d a p t e d on t h e e l e c t r o d e p o s i t e d Pb02 on g r a p h i t e anode. (no s c a l e )  u> ON  TABLE 4 FUNDAMENTAL S P E C I F I C A T I O N S  Dimensions  of the  a n o d e and  OF THE E L E C T R O L Y T I C C E L L  cathode  Length Width Thickness Anodic packings:  size  (mm)  2 1.7-2.00 0.7-1.1  packing:  s t a i n l e s s steel-304 screens cross s e c t i o n a l area of the  (20 x 20 mesh) s c r e e n s (38 x 5 ) c m  Membranes: cationic:  IONAC MC 3142 IONAC MC 3470 NAFION 127 IONAC MA 3475  anionic: Protective  = 38 cm = 5 cm = 3 mm Particle  lead shot (to anodize) electrodeposited lead dioxide  Cathodic  chambers:  screens:  saran polypropylene  2.54 cm  C:  Jl  E o O  OJ  E o •3-  m c\j  E o  G:  CM . 6  -6 cm  2 mm  CLAMP  WELDED  SQUARE  TO  G=  TUBES  0  i -5 cm-  la) Fig.  8.  PLAN  Detail  (b)  VIEW .  of the mechanism used to h o l d  the  cell.  (no  FRONT scale)  VIEW  39 (20 mesh) so t h a t  cut  the  to  the  total  s i z e of the  thickness  i o n s e l e c t i v e membranes along w i t h the teristics  of the  tested  protective  cathode  chamber  p a c k i n g was 0 . 3  in this  study  are  p l a s t i c screens.  of these m a t e r i a l s  as  (5  38 c m )  x  and j o i n e d  2  cm.  The  different  l i s t e d i n Table  The p r o p e r t i e s  and  s u p p l i e d by the m a n u f a c t u r e r s  4, charac-  are  given  i n A p p e n d i x 1. A d e t a i l of the mechanism used cell  is  g i v e n i n F i g . 8.  which are welded to introduced  through  C-clamp screws are gaskets,  It  consists  of the  tightened,  four  the  seal  a c e r t a i n range,  various parts of steel  Style 81).  p r e s s mechanism,  square  the  cell.  thickness  and a l s o  This  the  tubes  The c e l l  is  and once  the  square tubes compress  for  i n the  the  of four m i l d  the upper p a r t  press design permits v a r i a t i o n s within  compress  s i x C-clamps (Jorgensen,  p r o v i d i n g an e f f e c t i v e  materials  to  the  neoprene  versatile  and w i d t h o f t h e  cell  c a n be r a p i d l y o p e n e d  and  closed. b)  Undivided  A s i d e view of the represented  i n F i g . 4,  cathodic packing are side are case,  undivided c e l l except  that  the  e l i m i n a t e d and t h e  c l o s e d by u s i n g a cathode  arrangement  4.1.2  cathodic  feeder  Flow diagram of the  Figure 9 is  the  schematic  is  similar  to  i o n s e l e c t i v e membrane inlet  feeder  and o u t l e t  that  and  of the  plate without holes.  o n l y a p l a s t i c screen (saran or p o l y p r o p y l e n e )  a n o d i c bed and t h e  are  cell  the  cathode In  i s p l a c e d between  this the  plate.  apparatus flow diagram.  Equipment  specifications  g i v e n i n A p p e n d i x 1. Two m a i n f l o w c i r c u i t s e x i s t .  At the  r i g h t hand s i d e o f t h e  electro-  J  lytic  cell  is  the  anolyte  flow  circuit.  Pump P U - 1 d e l i v e r s  the  anolyte  Fig.  9.  Flow diagram of  the  apparatus.  o  41 Legend f o r F i g .  9.  P.S.)  Power s u p p l y  (D.C.)  V)  Voltmeter  E.C.)  Electrolytic  cell  T-l)  Anolyte tank  (contains phenol  T-2)  Anodization  T-3)  Catholyte  T-4)  Washing  PU-1)  A n o l y t e pump  PU-2)  Catholyte  R-l)  Anolyte  R-2)  Catholyte  P-l)  A n o l y t e p r e s s u r e and  P-2)  Catholyte  F-l)  Anolyte  F-2)  Catholyte  GL-1)  Gas-liquid separator for  the  anolyte  GL-2)  Gas-liquid separator  the  catholyte  V-1)  Anolyte tank shut-off  V-2)  Anodization tank shut-off  V-3)  Catholyte  V-4)  Washing tank s h u t - o f f  V-5)  Anolyte flow control  V-6)  Catholyte  V-7)  Cathode  V-8)  Liquid  sample  V-9)  Liquid  l e v e l control valve i n GL-1  V-10)  Liquid  level control valve  solution)  tank  tank  tank  pump  rotameter rotameter temperature  p r e s s u r e and  gauges  temperature  gauges  filter filter  for  valve  tank shut-off  valve valve  valve valve  flow control  valve  chamber p r e s s u r e - c o n t r o l  valve  valve  i n GL-2  42 from t a n k s T - l o r T - 2 t o t h e anode chamber.  The l i q u i d  flow rate  is  c o n t r o l l e d by a d j u s t i n g v a l v e V - 5 and i s measured w i t h r o t a m e t e r R - l . P r e s s u r e and t e m p e r a t u r e chamber a r e m e a s u r e d Filter collect  F-l  a n o l y t e at  the  i s l o c a t e d at  the  o f t h e anode chamber,  small  gas b u b b l e s p r o d u c e d i n t h e  to f a c i l i t a t e the  separator  gas  liquid  separation  for  the  gas b u b b l e s .  of G L - 1 , to ensure  liquid  flow.  that  at  the bottom of the  then r e l e a s e d  tanks  at  the  to c o l l e c t  the r e s u l t s  agglomeration  liquid  liquid  to the a n o l y t e c i r c u i t  control  the pressure  ization  at  differences  level  the  experiments.  liquid  cell.  flows  samples  after  The d o t t e d  passage  the  thus  in  is  a n o l y t e and c a t h o l y t e chambers  the  line use. cell.  basically  Valve V-7 serves  a v o i d i n g too high  in  The  through the  catholyte circuit  above d e s c r i b e d .  o f t h e membrane,  between the  the  towards  i n the c a t h o l y t e chamber, p r o v i d i n g p r e s s u r e  both sides  at  c a r r i e d out w i t h  of the  t o p o f G L - 1 and t h e  The f l o w d i a g r a m c o r r e s p o n d i n g t o t h e analogous  bigger  gas-liquid  t h e r e c y c l e l i n e when t h e a n o d i z a t i o n t a n k T - 2 i s  Valve V-8 serves  also  i n a p r o g r e s s i v e a c c u m u l a t i o n o f gas  ( T - l o r T - 2 ) t o be r e c y c l e d t o  represents  thus  serves  provides extra  gas b u b b l e s a r e n o t  This would r e s u l t  cell,  to  electrolysis into  V a l v e V - 9 c o n t r o l s the  t h e a n o l y t e l i n e w h i c h may a f f e c t  feed  anolyte  in GL-1.  G L - 1 i n w h i c h a bed o f g l a s s beads  outlet  is  outlet  This glass-wool f i l t e r  The g a s - l i q u i d m i x t u r e e n t e r s  gas  of the  in P - l .  t h e pump f r o m damage.  to agglomerate  surface  entrance  s m a l l p a r t i c l e s t h a t m i g h t be w i t h d r a w n f r o m t h e  protecting  ones  of the  to  equal-  pressure  t h a t may  result  i n membrane b r e a k i n g . When t h e  c e l l was a s s e m b l e d w i t h o n l y one c h a m b e r ,  c i r c u i t was u s e d .  only the  anolyte  The c a t h o l y t e c i r c u i t was e l i m i n a t e d b y c l o s i n g  the  43 catholyte  inlet  and o u t l e t  to the  cell.  The c e l l was p o w e r e d b y a 1 KVA D . C . power s u p p l y The c e l l  current  drop across  4.2  the  was r e a d  from the  electrodes  power-supply meter,  was m e a s u r e d  (Appendix 1 ) . and t h e  voltage  independently.  E x p e r i m e n t a l methods 4.2.1  Batch  experiments  The e x p e r i m e n t a l p r o c e d u r e chambers-cell operation, considered  Before lysis  s i n c e the  as a p a r t i c u l a r a)  to  t h e more c o m p l i c a t e d two  cell  operation  can  the  first,  l e a d e l e c t r o d e was a n o d i z e d b y  ensure that  t h e a n o d e was e q u a l l y  electro-  active  run.  V a l v e s V - 1 and V - 4 were shut w i t h a 20% H2S01+ s o l u t i o n .  o f f and t a n k s  T - 2 and T - 3 w e r e  The D . C . power s u p p l y was t u r n e d  the  same t i m e .  About 2 & of s o l u t i o n coming out  s e p a r a t o r s was w i t h d r a w n a t anolyte Five  and c a t h o l y t e  each s i d e to purge  f l o w s were r e c y c l e d to  the  tanks  from the  Immediately the liquid  current  was a d j u s t e d  to  T - 2 and T - 3  t i m e was a l l o w e d , b u t t i m e was 1 h . as  for  successive  (Choice of the  shown i n C h a p t e r  5.)  the  first  experiments  the  respectively. process.  = 5 2 6 . 3 A / m ) and 2  time,  a 12 h  the  standard  the  valve V-7. anodization  a n o d i z a t i o n t i m e was j u s t i f i e d After  activated  anodization  p r e s s u r e s i n b o t h chambers were e q u a l i z e d by a d j u s t i n g  When l e a d was t o b e a n o d i z e d f o r  tally,  10 A ( c . d .  Valves  gas-liquid  system before  l o f r^SOtj s o l u t i o n r e m a i n e d i n e a c h t a n k f o r t h e  filled  on.  V - 2 and V - 3 w e r e t h e n o p e n e d and b o t h p u m p s , P U - 1 and P U - 2 , w e r e at  be  process  each e x p e r i m e n t ,  every  one-chamber  case of the  Anodization  i n 20% l ^ S O ^ ( 4 3 ) ,  before  i s described for  a n o d i z a t i o n , b o t h pumps  anodization experimenwere  44 simultaneously turned tanks  o f f a n d v a l v e s V - 2 and V - 3 w e r e c l o s e d .  T - l and T-4 were f i l l e d  with d i s t i l l e d  P U - 1 and P U - 2 r e s p e c t i v e l y .  water  increased  i n d i c a t i n g that  and c o n n e c t e d  The c e l l was w a s h e d u n t i l  d r o p p e d p r a c t i c a l l y t o z e r o and t h e p o t e n t i a l  Then,  difference  the  to  pumps  current  through the  e s s e n t i a l l y no e l e c t r o l y t e was c o n t a i n e d  cell  in  the  cell. b) After prepared  the  Phenol electrochemical oxidation c e l l was t h o r o u g h l y w a s h e d ,  i n tank T - l .  process  8 I o f a n o l y t e s o l u t i o n were  T h e c o n c e n t r a t i o n o f p h e n o l , t h e pH and t h e  ductivity  of the  a n o l y t e were set  to the  d e s i r e d l e v e l s by a d d i n g  necessary  v o l u m e s o f s t o c k s o l u t i o n s o f p h e n o l , NaOH o r ^ S O ^ , a n d  N32S01+, w h i c h h a d b e e n p r e v i o u s l y p r e p a r e d . before  the  initial  and r e a d j u s t e d  if  s a m p l e was t a k e n ,  f o r each experiment  s o l u t i o n was t h e n p r e p a r e d  respectively.  Pressure  Immediately  current  the  from the  s y s t e m and a l s o  tion. of  operating  to the  T-3 are  by a d j u s t i n g  flow  v a l v e s V - 5 and V - 6  e q u a l i z a t i o n was p r o v i d e d a d j u s t i n g v a l v e V - 7 . was s e t  at  the  liquid  desired  t o p r o v i d e some t i m e f o r  A t t h e moment t h e  value. 3 i of the  solutions  s e p a r a t o r s were d i s c a r d e d i n o r d e r f l o w s and c u r r e n t  l i q u i d s were r e c y c l e d to t a n k s  e l e c t r o l y t e remained i n each tank.  measured  data  c o r r e s p o n d i n g pumps a n d  c o n d i t i o n s were b e i n g set  gas  i n tank  A n o l y t e and c a t h o l y t e  r a t e s o f a n o l y t e and c a t h o l y t e were s e t  coming out  measured  i n Appendix 2.  T a n k s T - l and T - 3 w e r e c o n n e c t e d  As the  agitated  and pH a n d c o n d u c t i v i t y w e r e  and c o n d u c t i v i t y a n d pH w e r e m e a s u r e d .  the  the  necessary.  An e q u a l volume o f c a t h o l y t e  recorded  The t a n k was w e l l  con-  f r o m t h e moment when t h e  to  purge  stabiliza-  T - l and T - 3 , 5 H  T h e e l e c t r o l y s i s t i m e was  a n o l y t e was r e c y c l e d t o t a n k T - l .  T h i r t y m l s a m p l e s w e r e t a k e n i n i n t e r v a l s o f 15 m i n f o r p h e n o l a n a l y s i s by o p e n i n g v a l v e V - 8 . pleted, still  the  When t h e u s u a l e l e c t r o l y s i s t i m e o f 2 h was  c e l l was w a s h e d w i t h d i s t i l l e d  flowing  t o a v o i d r e d u c t i o n o f t h e Pb02  The samples w e r e f i r s t  s a m p l e s when i n t r o d u c i n g t h e  to t e s t  the  effect  i n the  of varying  t a n k T - l w a s 20 After  the  o r a n o d i z a t i o n was c a r r i e d o u t b y  the  20% H 2 S O 4 a t  10 A f o r  was p r e p a r e d  t o t a l volume of the  initial  e l e c t r o l y t e s a m p l e was t a k e n , to  the  f l o w r a t e was t h e n f i x e d was s e t .  process. repeated,  the  In  i n the  same  electrolyte  the  the  in  first  the  liquid  A  by a d j u s t i n g v a l v e V - 5 , and t h e  s a m p l e was t a k e n , flow  D . C . power  cell.  Four I o f e l e c t r o l y t e were withdrawn at  A different until  1 h.  and c o n d u c t i v i t y  desired values,  s u p p l y was t u r n e d o n , a n d t h e e l e c t r o l y t e w a s f e d t o  GL-1 before  the  L  a n d pH w e r e m e a s u r e d a n d a d j u s t e d  current  (without  f l o w on p h e n o l o x i d a t i o n i n a  the p h e n o l s o l u t i o n t o be t r e a t e d  manner d e s c r i b e d p r e v i o u s l y b u t  c o n t i n u o u s mode  cell.  . s t a n d a r d method o f e l e c t r o l y s i s w i t h  liquid  the  Continuous experiments  The e l e c t r o d e p r e t r e a t m e n t  case  a n d l a t e r pH  pH a n d c o n d u c t i v i t y p r o b e s .  s i n g l e pass through the u n d i v i d e d  this  was  to avoid p o s s i b l e contamination of  Some e x p e r i m e n t s w e r e c a r r i e d o u t recycle),  current  anode.  a n a l y z e d f o r p h e n o l and T . O . G .  and c o n d u c t i v i t y were measured,  4.2.2  water w h i l e the  com-  to  r a t e was t h e n flow r a t e range  ensure set  desired  the o u t l e t  s t a b i l i z a t i o n of  up a n d t h e  same  the  procedure  p r o v i d e d by rotameter  R - l was  covered. In Appendix 2 the cell  experiments  a s s e m b l y and o p e r a t i n g mode.  are  of  d i v i d e d by groups a c c o r d i n g to  46 4.3  Analytic  techniques  The s a m p l e s centrations  taken at  the o u t l e t  of the  c e l l were a n a l y z e d f o r  o f p h e n o l , t o t a l o r g a n i c c a r b o n , a n d i n some c a s e s ,  4.3.1  con-  lead.  Phenol analysis  Phenol concentrations  i n the  s a m p l e s w e r e d e t e r m i n e d b y gas  tography u s i n g a flame i o n i z a t i o n specifications  detector.  chroma-  The a n a l y t i c e q u i p m e n t  and o p e r a t i n g c o n d i t i o n s u s e d a r e  given i n Appendix  1.  S t a n d a r d p h e n o l s o l u t i o n s r a n g i n g from 0-116 mg/1 were p r e p a r e d p i p e t t i n g f r o m t h e same p h e n o l s o l u t i o n u s e d t o p r e p a r e for  the  experiments.  degradation  enough so t h a t  b e l o w t h e p e a k was n o t n e c e s s a r y , the  a n a l y s i s of the  Standards  the e s t i m a t i o n of the  and peak h e i g h t s  bio-  c o u l d be  area  used. standards  c a l i b r a t i o n c u r v e o f peak h e i g h t s vs p h e n o l  and samples were i n j e c t e d u n t i l 2-3%.  s c a l e corresponded to about  the v a r i a t i o n i n  peak  T h i s means t h a t when t h e r e c o r d e r  100 m g / 1 t h e maximum a l l o w e d v a r i a t i o n  full repre-  ± 2 m g / 1 , a n d t h e r e c o r d e r d e t e c t a b i l i t y was 1 m g / l / d i v i s i o n .  No p e a k s o t h e r  than the  o t h e r w o r d s no i n t e r f e r e n c e in  an  constructed.  h e i g h t was n o t more t h a n  sented  them from p o s s i b l e  samples from each r u n , the p h e n o l  w e r e a l w a y s i n j e c t e d and t h e c o n c e n t r a t i o n was  to preserve  to  (42).  P h e n o l peaks were t h i n  Before  electrolyte  C o p p e r s u l f a t e was a d d e d t o t h e s t a n d a r d s  approximate c o n c e n t r a t i o n o f 1 g/1 logical  the  by  the G . C . a n a l y s i s .  s o l v e n t and p h e n o l p e a k s w e r e o b s e r v e d , o f t h e p h e n o l o x i d a t i o n p r o d u c t s was  Phenol detention  in  detected  t i m e was a p p r o x i m a t e l y 30  seconds. All  the  samples were a n a l y z e d on t h e  t h o u g h i t was shown t h a t  day o f t h e  experiment,  the c o n c e n t r a t i o n of phenol i n the  even  sample d i d  47 not v a r y a f t e r  one week o f  For those experiments than  100 m g / 1 t h e  to work w i t h 4.3.2 All  the  same s t a n d a r d s and  organic  i n the  Civil  furnace  and t h e  carbon furnace carbon  carbon  i n the  thus produced  The t o t a l subtracting different  to  the  for  the  the  i n the  sample  (T.O.C.)  The i n o r g a n i c  convert  i n the  carbon i n the  of the  and the  samples  calibration  c u r v e of mg/1  The  inorganic carbon  (44).  calculated therefore  two  The  ranged  by  stan-  standards between  from each r u n ,  the  total  c a l i b r a t i o n c u r v e peak h e i g h t  exceeded  ranged  to  of  same p h e n o l  Carbon content  i n successive  vs injec-  2%.  carbon s t a n d a r d s were p r e p a r e d  standards also  the  one f o r e a c h c h a n n e l .  from a s t o c k  o f Na2C03 a n d NaHC03 c o n t a i n i n g 1000 m g / 1 o f c a r b o n , ic  is  carbon,  V a r i a t i o n s i n peak h e i g h t  sample never  carbon  The amount  sample  total  only  analyzer  carbon a n a l y s i s were the  mg/1 c a r b o n c o n s t r u c t e d . of a c e r t a i n  required,  injected  total  total  to carbon d i o x i d e .  i n an i n f r a r e d  analysis  the  a temperature of 1000°C  150°C to  chromatograph.  Before the  the  detected  are  order  o n a Beckman  Basically,  carbon d i o x i d e .  total  carbon s t a n d a r d s were  tions  operates at  i n o r g a n i c carbon from the  calibrate  0-90 mg/1.  were c a r r i e d out  sample to  carbon  calibrations  dards used used  organic  in  furnace.  o p e r a t e s at  is  factor  detectability.  o f two f u r n a c e s :  contained  furnace  contained  necessary  higher  analysis  consists  i n o r g a n i c carbon  dioxide  carbon  i n o r g a n i c carbon  a l l the  phenol concentrations  E n g i n e e r i n g Department.  carbon analyzer  convert  at  carbon analyses  organic  The t o t a l  performed  were d i l u t e d by the  Total organic  total  analyzer  samples  storage.  between  so t h a t  0-90 mg/1.  i n o r g a n i c c a r b o n v s peak h e i g h t  solution  the  inorgan-  After was  the  constructed,  48 the  samples were  ations  injected  i n peak h e i g h t  Knowing t h a t compare t h e  i n the  inorganic channel.  f o r a same s a m p l e w e r e o f t h e  phenol contains  phenol concentration  concentration  A g a i n maximum v a r i -  0.7657  g C/g phenol,  o b t a i n e d b y gas  c a l c u l a t e d from the  T.O.C.  order  ysis  i n the  analytical  All  the  are  g i v e n i n A p p e n d i x 1.  analysis,  for  after  standards,  and t h e  the  analysis after  T.O.C. 4.3.3  Lead  To t e s t  samples  initial  the  sample.  r a n g e o f 2-3% w h i c h  c o n d i t i o n s of the  T.O.C.  anal-  The p h e n o l s t a n d a r d s f o r T . C . a n a l y s i s  one m o n t h o f s t o r a g e when c o m p a r e d w i t h f r o m one e x p e r i m e n t  d i d not  fresh  show v a r i a t i o n i n  one w e e k .  analysis  electrode  were a n a l y z e d f o r  c o r r o s i o n , the  samples  f r o m some o f t h e  lead using atomic absorption  Lead s t a n d a r d s were p r e p a r e d 1000 m g / 1 o f l e a d . chosen a c c o r d i n g to  the  c o n d i t i o n s are  lead content of  the  experiments  spectrophotometry.  by d i l u t i n g a s t o c k s o l u t i o n c o n t a i n i n g  The r a n g e o f c o n c e n t r a t i o n s  The s p e c i f i c a t i o n s operating  the  with  to  results.  s p e c i f i c a t i o n s and o p e r a t i n g  showed no a l t e r a t i o n  is possible  chromatography  D e v i a t i o n s between b o t h a n a l y s i s were u s u a l l y i n the gives confidence  it  o f 2%.  of the  of the  standards  was  samples.  atomic absorption  g i v e n i n A p p e n d i x 1.  a p p a r a t u s used and  its  CHAPTER 5  RESULTS AND DISCUSSION  5.1  Electrode  materials  Some p r e l i m i n a r y e x p e r i m e n t s electrode  materials  affecting  the  Appendix  before  process.  starting  Results  a n d 1-2 w e r e removal.  produced  indicates  that  c a r r i e d out The r e s u l t s  approximately  the  1 h anodization  showed a f a i r l y  was t e s t e d to t e s t  showed t h a t  variables  f o r each  run  in  After  i s probable  the  a n o d i z a t i o n p e r i o d and w h i l e t h e  i f some f i n e it  solution.  water,  particles  liquid  from the  was c o n s i d e r e d A series  the  the  at  Experiments concentrations  1-4  outlet  electrode  to  and p H s .  to  test  49  the  electrode  the  coating  washed  t o o k on a b r o w n c o l o u r  for to  were e n t e r i n g  the  water.  lead concentration investigate  as  in  what  anolyte.  1-8 w e r e p e r f o r m e d The r e s u l t s  that  c e l l was b e i n g  surface  o f t e s t s were c a r r i e d out  presence of l e a d i n the  to coat  time.  the  necessary  time  This  each of these runs the It  1.  anodization  removed vs t i m e .  After  distilled  anodization  group N o .  of a n o d i z a t i o n  1 h and 12 h  the  governed  table  effect  same % T . O . C .  u n i f o r m brown c o a t i n g . longer  the  for  Therefore  other  i n experiments  thicker  with  possible  time i s probably s u f f i c i e n t  l e a d shot w i t h a l a y e r o f Pb02-  is  g i v e n i n the  test  2.  on T . O . C . times  to  to i n v e s t i g a t e  are  The a n o d i z e d l e a d e l e c t r o d e Runs 1-1  were performed  are  under  different  s u m m a r i z e d on p .  electrolyte 122.  in a l l  50  these runs  the  with  i n d i c a t i n g that  time,  electrode are  able  concentration  first  the  reducing the  those runs  the  occurred  i n the  anolyte  corrosion rate  conies i n c o n t a c t  to pass to  therefore  of lead  w i t h the  catholyte  spontaneously  through  of the  as w i l l  to  decrease  i s p r o b a b l y h i g h e r when  solution.  chamber  lead content  tended  Also,  the  anolyte.  the  lead  the ions  cation-membrane ( T h e pH c h a n g e s  be e x p l a i n e d i n the  next  in  sec-  tion.) I n R u n 1-4 c e l l without centration  the  an a p p l i e d c u r r e n t  of lead  except  that  fed.to  the  cell.  which indicates  is  potentials  was 4 . 2  the  tively).  under  to  the  rapidly,  and as  drop decreased. brown c o a t i n g ,  of  lead  the  at  the  a 5 g/1 Na S0i 2  higher  t  a result  to  the  at  pH o f  or  t h e maximum l e a d was  +  g/1)  the  pH-(Runs 1-6, the  amount  1-7  response of  (Run 1 - 3 ) .  It  pressure increased  c e l l was o p e n e d  o f some l e a d  lead  electrode.  30 g / 1 N a 2 S 0 i , a n d i t  the  underlying  was  mg/1.  positive  9.8  electrode  showing the  electrolyte  normal hydrogen  because the  When t h e  repeated,  1.7  electrolyte.  study  anolyte  r u n was  the  the  maximum c o n -  p o t e n t i a l - p H diagram for  o f N a 2 S 0 i | (30 initial  through  i n s o l u t i o n was 2 . 7  same i n i t i a l  a 5 g/1 NaCl e l e c t r o l y t e  covered with a deposit  Later this  mg/1 when w o r k i n g a t  experiment  highest  was a p p l i e d b e f o r e  with respoct  A n a t t e m p t was made t o  electrode finish  at  the  tbermodynamically stable  same c o n c e n t r a t i o n  s o l u t i o n was h i g h e r  produced  (140 m g / 1 ) .  i n agreement w i t h  mg/1 when w o r k i n g w i t h At  and i t  T h e maximum amount  a n d 1-6 s h o w e d t h a t  concentration  (5 g / 1 NaOH) was r e c i r c u l a t e d  difference  t h a t Pb02 i s  electrode  R u n s 1-5  in solution  a potential  This observation  anodic  electrolyte  grey  the  lead,  compound.  a n d 1-8 the  and  anodized  to  and t h e had  in  respec-  was n o t  c o a t i n g began  electrode  of lead  lead  possible dissolve voltage  lost  t h e membrane  its was  51 The p e r f o r m a n c e s  o f a n o d i z e d l e a d and e l e c t r o d e p o s i t e d  c o m p a r e d f r o m Runs 1-9 formed under  the  (IONAC M C - 3 4 7 0 ) results  same e x p e r i m e n t a l  are represented  corresponding to  i n F i g . 10.  the  anodized l e a d .  (experiments  of the  The  ten  i s above t h a t removed v s t i m e  but  to zero towards  the  r e a c h i n g 2 mg/1 a f t e r  show t h a t are  flaking  end o f t h e  curves  t h e maximum c o n -  times higher  i n the  electrodeposited  are  reported  case of  Pb0  particles  2  i n many o t h e r Pb0  2  experiwas  used.  from the  The a n o d i z e d l e a d e l e c t r o d e  i s possible that  a n o d i z i n g the current  o f the  lead concentration  anodized lead p a r t i c l e s  film occurred.  2  cell  Once t h e  (Fig.  t h e y w o u l d d i s s o l v e more e a s i l y  c o u l d become more r e s i s t a n t  resistance  or a f t e r to  long periods  in  to  corro-  of use.  Also  c o r r o s i o n c o u l d be i m p r o v e d by  and l o n g e r a n o d i z a t i o n t i m e s .  formation of cracks  built  electrode  l e a d v e r y s l o w l y u s i n g more d i l u t e H 2 S O 4 s o l u t i o n s ,  densities  found  potential.  anodizations  its  The o n l y e x c e p t i o n was  and  90 m i n u t e s .  applied anodic  successive  run.  was a p p l i e d and t h e  of the P b 0  c a r r i e d out  absence of the  sion after  vs  curve  e a c h c a s e t h e maximum l e a d c o n c e n t r a t i o n was l o w e r t h a n 0 . 4 m g / 1 ,  flakes  it  membrane  (0.6).  G r o u p s 2 and 3) w h e r e e l e c t r o d e p o s i t e d  Scanning e l e c t r o n micrographs  the  electrode  2  The % T . O . C .  Lead analyses  i n Run 2 - 3 w h e r e n o c u r r e n t  12)  same c a t i o n i c  per-  lead.  shown i n F i g . 1 1 .  tended  up,  Pb0  o f l e a d i n s o l u t i o n was a b o u t  anodized  ments, In  the  were  The c u r v e f o r % p h e n o l o x i d i z e d  electrodeposited  Scanning electronmicrographs are  conditions,  p r a c t i c a l l y c o i n c i d e n t a l for both electrodes,  centration the  Both experiments  and a p p r o x i m a t e l y e q u a l v o i d a g e f r a c t i o n  t i m e when u s i n g t h e  are  and 2 - 2 r e s p e c t i v e l y .  Pb02 c a n be  lower  .This might prevent  (where c o r r o s i o n p r o b a b l y s t a r t s )  that result  the  from a  52  d 20 d H  io  -A -O  -A"  -o-  =8*  8"  0 100  80  Q LU 60 X  o _J Z 40 UJ X CL  KEY  RUN  N2  O  1-9  ANODIZED  A  2-2  ELECTRODEPOSITED P b 0  20  0  I  i  30  10.  l  LEAD  .  60  TIME Fig.  ELECTRODE  (min)  E f f e c t o f t y p e o f l e a d d i o x i d e e l e c t r o d e a t 10 A and i n i t i a l pH = 9 . 4 w i t h IONAC M C - 3 4 7 0 membrane.  2  I  00  Fig.  11.  S c a n n i n g e l e c t r o n - m i c r o g r a p h s o f t h e e l e c t r o d e p o s i t e d PbC>2 p a r t i c l e s a f t e r use. ( p a r t i c l e s i z e s b e t w e e n 1 . 7 - 2 . 0 0 mm)  Fig.  12.  Scanning electron-micrographs of the anodized after use. ( p r e p a r e d f r o m 2 mm l e a d s h o t )  lead  particles,  55 perhaps too strong  anodizing action.  A n a t t e m p t was made t o a n d 10 A , b u t considerably  i n two h o u r s and a f t e r  i t a t e was p l u g g i n g t h e Tungsten 10 A .  carbide  The a n o l y t e  trode  and t h e  total  test  a packed bed n i c k e l  the v o l t a g e  opening the  drop  cell,  through  electrode the  cell  i t was o b s e r v e d  b e d and c o v e r i n g t h e  at  pH = 12  increased  that  a  precip-  membrane.  (WC) p a r t i c l e s w e r e a l s o  tested  at  pH = 12 a n d  took a grey  colour i n d i c a t i n g d i s s o l u t i o n of the  elec-  carbon test  revealed  in  i n c r e a s i n g amount  of carbon  solution. From t h e s e p r e l i m i n a r y t e s t s deposited of  the  higher  5.2  P b 0 2 was t h e m o s t  experiments  o f pH u s i n g t h e  electrooxidation  effect  consider  some i m p o r t a n t  first  the  anodized  the  remainder and  its  lead.  cell  u s i n g the  literature  the  effect  divided  cell.  e l e c t r o o x i d a t i o n of phenol, observations  about  the  about  Before it  phenol  o f a b a s i c pH discussing  i s necessary  pH b e h a v i o u r  c a t i o n membrane MC-3470 w h i c h i s the  sataple  at  the  to  9.4.  outlet  w o r k i n g at. 10 A ( R u n 2 - 2 , as  suitable  a n o l y t e p h e n o l c o n c e n t r a t i o n was s e t  p H was a d j u s t e d  ditions  c a r r y out  electro-  in  to  the  cell.  electrolytes,  the  divided  the  corrosion resistance  in alkaline electrolytes,  o f pH on t h e  Using the  of  better  l a c k of information i n the  r a n g e was i n v e s t i g a t e d  the  choice to  % p h e n o l o x i d a t i o n when compared t o  Effect  divided  convenient  because of i t s  Because o f the  the  i t was c o n c l u d e d t h a t  i n Run 2 - 2 w e r e  It  was o b s e r v e d  of the  F i g . 13). repeated  that  c e l l had dropped Later,  the  but w i t h o u t  at  after  for  alkaline  100 mg/1  and  15 m i n t h e p H  to about  3, when  same e x p e r i m e n t a l  con-  phenol being present  and  the  same pH d r o p was o b s e r v e d .  side reactions  Thus,  the  pH d r o p a p p e a r s t o be due  o f oxygen e v o l u t i o n , and not  t o p r o d u c t i o n o f an  to  acid  from p h e n o l o x i d a t i o n . What p r o b a b l y h a p p e n s i s first  at  the  changes  electrode,  and t h e n  the  through  t h e membrane,  concentration  pH d r o p .  towards  the  produced the net  end o f t h e  the  cell  decreases  If  the  side reactions  o b s e r v e d pH b e h a v i o u r , current  it  compared at  other are  to  follows  3.7  f o r Run 2 - 2 .  unexpected  result.  had i n c r e a s e d  when t h e  ally  it  that  current  currents  the  (0,  3,  6,  11.7.  are  i n these experiments  o n l y a l l o w s the  increase  i n the  in  observed  conductivity  transport  responsible  drop  for  must be  occur  The pH v s t i m e  6 A (Run 2 - 5 )  same t e n d e n c y  sample at  was t h e  any c u r r e n t for  will  the  this  t h e pH  described  outlet  c a t i o n i c MC-3470, the  of  an the  observed  applied  as  the  produced  effect.  of p o s i t i v e ions but  was  curves  The same b e h a v i o u r was  proposed  the  related  and 10 A ) w i t h a l l  o f 3 A (Run 2 - 4 )  s o l u t i o n was r e c i r c u l a t e d w i t h o u t  used  at  trans-  The pH r e s p o n s e  When w o r k i n g a t  I n 15 m i n t h e pH o f t h e to  rate of  side reactions  applied.  A lower current  from 9.4  rate  the v o l t a g e  pH r e s p o n s e  i n 15 m i n , s h o w i n g t h e  Two p o s s i b l e e x p l a n a t i o n s membrane  a result  r a t e at which the  i n F i g . 13.  previously  cell  electrolyte  conditions held constant.  also represented from 9.4  the  is a progressive  o f oxygen e v o l u t i o n are  different  experimental  dropped  effect  than  the  2-2).  u l t i m a t e l y be d e t e r m i n e d b y t h e then  i s higher  r u n and a s  (Run  because the  discharged  If  of hydrogen i o n s , which would r e s u l t  through  the  ions are  the mechanism o f oxygen e v o l u t i o n  T h i s w o u l d a l s o e x p l a i n why t h e  increases  to  the h y d r o x y l  ( R e a c t i o n s R I o r R2) p r o d u c i n g h y d r o g e n i o n s .  which the hydrogen ions are port  that  (Run 2 - 3 ) . Since  the  theoreticionic  58 selectivity  i s not  100%, i t  ions passed  to the  a n o l y t e from the  the  pH.  is  possible  Another p o s s i b i l i t y i s  a lead dioxide reaction. was d e t e c t e d  without  presence  that  the  associated  i n the  suddenly  the  changed  from 11.8 to observed  ions generating  3.8  from 3 to  that  b u t when t h e percent (Fig.  13).  three curves  current  of the  at  enhancement  of T.O.C.  90 m i n i n Run 2 - 4 .  To i n v e s t i g a t e  dropped  f r o m 12 t o  than  the  were  current  was  pH d r o p p e d  same b e h a v i o u r  of  pH-current  2-4,  and 2 - 5 ,  it  r e m o v e d i n 90 m i n ,  for  this  d i f f e r e n c e was t h e first  higher  i n d i c a t i o n of  an  high pH.  experiment  starting  i n Run 2 - 2  at  i n the  pH r e s p o n s e  2 - 8 was c a r r i e d  when a  out.  pH = 12 and 10 A t h e pH  ( F i g . 15).  After  15 m i n t h e  pH h a d  2.  I n Run 2 - 1 0 t h e  pH was k e p t  is  i n t e r v a l f r o m 90 t o 120 m i n  T h i s was t h e  c a t i o n membrane was u s e d ,  dropped even f a s t e r  in  shown i n F i g . 1 4 .  i f t h e r e was any d i f f e r e n c e  U s i n g t h e N A F I O N - 1 2 7 membrane,  the  t o a 17% T . O . C .  i n the  reason  r e m o v a l at  electrode  i n R u n 2 - 4 f r o m 3 t o 10 A , a h i g h e r  c a r b o n was o x i d i z e d  The m o s t p r o b a b l e  con-  (Reaction R17).  the  The e f f e c t  lead  the  observed  r e m o v e d i n Runs 2 - 2 ,  tended  was c h a n g e d  pH o b s e r v e d  different  15 m i n , f o l l o w i n g  rate of phenol o x i d a t i o n i s  the  and t h e  90 m i n and a g a i n t h e  (Fig. 13).  % T.O.C.  pH c h a n g e s  d u r i n g Run 2 - 4  10 A , a f t e r  d u r i n g the next  When c o m p a r i n g t h e observed  different  with  difference  Pb02 r e d u c e s  a flow of current  applied current,  i n Runs 2 - 2 a n d 2 - 5 on t h e  the  the  raising  associated  In other words,  where  hydroxyl  therefore  is  (Run T a b l e 2 - 3 )  run.  lead battery  to ensure t h a t  with  pH i n c r e a s e  of  T h i s w o u l d e x p l a i n why a p o t e n t i a l  an a p p l i e d c u r r e n t  of sulphate  In order  changes  as  a c e r t a i n amount  alkaline catholyte,  c e n t r a t i o n was b u i l d i n g up d u r i n g t h e may h a v e b e h a v e d  that  i n the  b a s i c range f o r a longer  period  59  Fig.  14.  E f f e c t o f c u r r e n t on % p h e n o l o x i d a t i o n a t w i t h IONAC M C - 3 4 7 0 membrane.  initial  pH = 9 . 4  60  61 of  t i m e , by s t a r t i n g  started  to drop a f t e r  the next In  of  a pH o f 1 2 . 8 .  45 m i n , a n d w e n t  the  same f i g u r e ,  severely  from 12.2 to a v a l u e of 2.2  it  c a n a l s o be o b s e r v e d  l i m i t e d by a h i g h p H .  o n l y a 10% o f t h e  the  A s shown i n F i g . 16 t h e pH  p h e n o l had been  p h e n o l had a l r e a d y been o x i d i z e d  On t h e  other  to  h i g h pH r u n i s a b o v e t h e  the  in  15 m i n u t e s .  phenol i s 2-10)  at  hand,  the  that  the  o x i d a t i o n of  A t 15 m i n and pH = 1 2 . 7 oxidized,  whereas  after  same t i m e  curve for % T.O.C. % T.O.C.  the  at  removed v s t i m e  pH -  (Run 2, 65%  (Run 2 - 9 ) .  corresponding  curve corresponding to  the  low  pH r u n . It cell, the  s h o u l d be n o t e d  a n d when t h e  cell  lation cult,  (higher  tank. but  that  t h e pH i s m e a s u r e d  pH d r o p i s r e c o r d e d  pH a t  the  entrance),  T h i s makes t h e  still  the  outlet  of  the  t h e r e must be a pH p r o f i l e and a v a r i a b l e pH i n t h e  interpretation  there i s a d e f i n i t e  at  of the  enhancement  results  i n T.O.C.  within  recircu-  more  diffi-  removal  at  h i g h pH. These experiments l o w pH' a t  i n d i c a t e d t h a t a n o p t i m u m pH s e q u e n c e w o u l d b e  the b e g i n n i n g of the  h i g h pH a t  the  end,  favouring T.O.C.  a n a n i o n s e l e c t i v e membrane  removal.  and t h r o u g h  t h e membrane w e r e s u f f i c i e n t  2 to 12, d u r i n g the o f r u n c o u l d be With t h i s  the that  the  desired  that  o f h y d r o x y l i o n s f r o m t h e NaOH  course  of a run,  to produce at  catholyte,  a pH i n c r e a s e  a given current,  from  an optimum  possible.  objective,  a n i o n i c membrane  This i d e a suggested  a  c o u l d p r o v i d e p r e c i s e l y s u c h a n o p t i m u m pH  If  type  transport  f a v o u r i n g p h e n o l o x i d a t i o n , and  sequence.  about  the  run,  a  s e v e r a l p r e l i m i n a r y t e s t s were performed  IONAC M A - 3 4 7 5 .  increase  I n F i g . 1 7 , Run 2 - 1 1 , i t  i n pH i n d e e d o c c u r s ,  and a t  is  30 m i n u t e s  with observed  90% o f  62  63  64 the phenol had been oxidized, before the pH started to increase.  When  the pH increase was produced, the T.O.C. started to be oxidized at a higher rate than i n Run 2-10. I t should be noted that i n the high pH range the oxidized organic carbon remains i n solution i n the form of inorganic carbon (e.g., Run 2-11) probably carbonates, due to the higher s o l u b i l i t y of carbon dioxide i n a l k a l i n e solutions. P a r t i c u l a r l y i n t e r e s t i n g colour changes were observed during these experiments.  The e l e c t r o l y t e at the outlet of the c e l l showed a brown-  reddish colour when the pH was a l k a l i n e (higher than 9.4), and i n those runs where the pH dropped spontaneously, the colour changed to l i g h t yellow.  For example, i n Pom 2-10 the e l e c t r o l y t e took a deep brown-  reddish colour u n t i l 60 min and when the pH drop was produced, the outlet showed the l i g h t yellow colour while tank was s t i l l brown.  These colour  reactions, when the pH was changed, were also observed i n a pure benzoquinone solution, prepared f o r comparison.  5.3  E f f e c t of current using the divided c e l l In experiments 2-3, 2-4, and 2-5, current and pH were dependent  variables and therefore the unique e f f e c t of the current can not be analyzed separately.  However, i n F i g . 13 i t can be seen that the runs  at 6 and 10 A showed approximately s i m i l a r pH drops and therefore the current e f f e c t can be compared. for  The % T.O.C. removed vs^ time curves  those two runs are p r a c t i c a l l y coincidental. From F i g . 14 i t i s observed that at 10 A and 15 min, 12% more of the  phenol had been oxidized than at 6 A.  At 10 A, t o t a l phenol conversion  was achieved i n 90 min, but at 6 A, 120 min were necessary to oxidize the  65 phenol  completely.  Two r u n s w e r e c a r r i e d o u t w i t h t h e study  the  2-7).  effect  of the  The r e s u l t s  are  current  without  plotted  i n F i g . 1 8 , where  % phenol o x i d i z e d vs time curves sion  i s achieved at  analyses  revealed  5.4  same  75 m i n f o r b o t h c u r r e n t s .  that  at  20 A , 47% o f t h e  The p e r f o r m a n c e s  results  are  At  plotted  removed v s  i n F i g . 19.  removal i s  b o t h at  IONAC M C - 3 4 7 0 ,  time curves  20 A and pH = 2 .  about  concerned,  as d e s c r i b e d  77% o f t h e  the best  because i t  unknown, but experienced  it  after  provides  (Fig. 17).  Run 2 - 1 1 .  i s possible that  o x i d a t i o n , or that  it  curves  not  the  had  But at  a c h i e v e d w i t h b o t h membranes.  are very c l o s e but  previously  c e l l was o p e n e d  The  phenol  65% when u s i n g N A F I 0 N - 1 2 7 .  t h e membrane was f o u n d t o be c h a n g e d  when t h e  conver-  c a r b o n had been o x i d i z e d t o  exactly  75 m i n  The % coincidental.  r u n w i t h IONAC M C - 3 4 7 0 . performance the  as  far  as  f a v o u r a b l e pH  I n 15 m i n , p h e n o l  70%, a n d t o t a l p h e n o l o x i d a t i o n was a l s o a c h i e v e d  ever,  the  T.O.C.  The % p h e n o l o x i d i z e d v s t i m e  The a n i o n i c membrane M A - 3 4 7 5 g a v e  was  phenol  However, the  120 m i n , 10% more c a r b o n was o x i d i z e d i n t h e  increase  that  10 A o n l y a 12% h a d b e e n o x i d i z e d  f r o m Runs 2 - 6 a n d 2 - 9 ,  p h e n o l c o n v e r s i o n had been  T.O.C.  i s observed  2-6,  performances  b e e n o x i d i z e d i n 15 m i n v e r s u s  T.O.C.  it  (Runs  o f c a t i o n i c membranes IONAC M C - 3 4 7 0 and NAFION 127  showed t h a t when u s i n g t h e  total  pH c h a n g e s  to  time.  C o m p a r i s o n s o f membrane  can be compared  significant  a r e v e r y c l o s e and t o t a l  c a r b o n d i o x i d e i n 120 m i n , w h e r e a s a t d u r i n g the  c a t i o n i c membrane M C - 3 4 7 0  oxidation  i n 75 m i n .  How-  i n c o l o u r from y e l l o w to The a c t u a l  reason  for  polymer s t r u c t u r e of the  interacted  this  brown, is  membrane  i n some way w i t h t h e  phenol  66  Fig.  18.  C u r r e n t e f f e c t on % T . O . C . and % p h e n o l o x i d a t i o n pH = 2 . 5 w i t h IONAC M C - 3 4 7 0 .  at  67  Fig.  19.  T y p e o f c a t i o n i c membrane e f f e c t on % T . O . C . % p h e n o l o x i d a t i o n a t 20 A and pH = 2 . 5 .  and  oxidation products.  T h e s e c h a n g e s may a f f e c t  the  lifetime  o f t h e mem-  brane. The c a t i o n i c membrane M C - 3 1 4 2 was o n l y experiments perforated For t h i s  with  anodized lead.  reason,  that  its  Another disadvantage  MA3475 w e r e s t r o n g e r  the  and t h i c k n e s s e s  The p o l y p r o p y l e n e s c r e e n ,  its  drops than the  saran  first  IONAC membranes MC3470 a n d  two o w i n g t o t h e i r  as p h e n o l and T . O . C .  removal i s  These experiments does not  the r e s u l t s  the  as  far  c a n be s e e n drop as  fast  t h a t when as i n  the  I n R u n 3 - 2 t h e pH o n l y d r o p p e d f r o m 12 t o 1 1 . 5 i n two i n c o r r e s p o n d i n g Run 2-8  2 i n 15 m i n .  The r e a s o n  for  case of the u n d i v i d e d c e l l ,  t a k i n g p l a c e at electrolyte.  affect  show t h a t  to  concerned.  pH v s t i m e c u r v e i n F i g . 2 0 , i t  cell.  hours whereas  the  sup-  1).  w o r k i n g w i t h o n l y one c h a m b e r t h e p H d o e s n o t  in  different  o f pH u s i n g t h e u n d i v i d e d c e l l  From t h e  12 t o  Problems of  c l o t h u s e d i n Run 2 - 2 , p r o b a b l y due  p l a s t i c screens  divided  i n NaOH s o l u t i o n s .  u s e d i n R u n 2 - 1 , p r o d u c e s much h i g h e r  use o f the d i f f e r e n t  Effect  membrane  IONAC M C - 3 1 4 2 membrane  w i t h use  the  (Appendix  c l o s e l y packed screen s t r u c t u r e .  5.5  circuits.  t h a n t h e N A F I O N - 1 2 7 a n d IONAC M C 3 1 4 2 .  b r e a k i n g never occurred w i t h  potential  of the  deteriorate  of mechanical r e s i s t a n c e ,  port materials  i n short  a p l a s t i c s c r e e n was i n t r o d u c e d b e t w e e n t h e  nylon support w i l l  I n terms  d u r i n g the p r e l i m i n a r y  On s e v e r a l o c c a s i o n s t h e membrane was  by p r o t r u d i n g p a r t i c l e s , w h i c h r e s u l t e d  and t h e p a r t i c l e s . is  tested  the  cathode  changes  (Fig.  this  15 ) t h e pH d r o p p e d  different  from  pH b e h a v i o u r i s  that  the r e a c t i o n of hydrogen e v o l u t i o n the h y d r o x y l  ion balance  in  the  When s t a r t i n g  at  pH = 9 . 5  sents a s m a l l e r drop than starting  at  pH = 2 . 5 ,  the  i n the  case of the  o x i d i z e d vs time curves  In  3.8 w h i c h a l s o  divided  t h e pH was h e l d p r a c t i c a l l y  A s was f o u n d i n e x p e r i m e n t s  that  pH d r o p p e d t o  at  with  10 A f o r  the  the  p h e n o l i s o x i d i z e d much f a s t e r  at  oxidized  at  the h i g h pH.  pH = 2 . 5 , w h e r e a s remained  at  divided  cell,  undivided c e l l  The pH e f f e c t and t h e  i n o r g a n i c carbon  showed t h e  f a v o u r e d b y a l o w pH w h e r e a s  is  improved at observed  on T . O . C .  5.6  a high pH. that  as t h e  o x i d a t i o n than  Effect  of current  that  l o w pH ( 2 . 5 ) , during the  constant  at  runs  current  4°C t e m p e r a t u r e i n c r e a s e  a high pH. compared  h a n d , more T . O . C .  was  c a r b o n was o x i d i z e d  (e.g.,  further  but  20 a n d 30 A ( F i g s . Phenol o x i d a t i o n  o x i d a t i o n of  the  at  Run 3 - 2 ) .  same t e n d e n c y .  the  undivided  effect  20,  intermediates  21 a n d 22 i t  pH h a s  is  a greater  effect  10 A , t h e  cell  o f 1 0 , 2 0 , and 30 A c u r r e n t s a h i g h pH ( 1 2 ) .  temperature of the  It  c a n be d e t e c t e d  When w o r k i n g a t  i n the  occurs,  (e.g.,  Runs 3 - 6  increases  s m a l l and t h e  side effects  remains  r e c i r c u l a t i o n tank  and 3 - 7 ) .  These  due t o t e m p e r a t u r e  con-  noted  and  30 A , a p p r o x i m a t e l y a 1 2 ° C  is registered  at  s h o u l d be  electrolyte  A t 20 A s l i g h t h e a t i n g  ture increase are  show  c a r b o n had been o x i d i z e d  increases,  and F i g . 24 a t at  (Fig. 20),  on p h e n o l o x i d a t i o n .  room t e m p e r a t u r e .  120 m i n o p e r a t i o n .  other  When c o m p a r i n g F i g s .  u s i n g the  F i g u r e 23 d e s c r i b e s stant  the  %•phenol  pH was 2 . 5 ,  was a l s o s t u d i e d when w o r k i n g a t  is  also  On t h e  A t 120 m i n , 19% o f t h e  results  the  a l o w pH t h a n a t  pH = 1 2 , a 32% o f t h e  i n s o l u t i o n as  21 a n d 2 2 )  pH was 1 2 .  a n d when  constant.  15 m i n , 70% o f t h e p h e n o l was o x i d i z e d when t h e  w i t h o n l y a 33% when t h e  cell,  repre-  a after  tempera-  temperature  variations  70  Fig.  20.  pH e f f e c t on % T . O . C . and % p h e n o l i n an u n d i v i d e d c e l l .  o x i d a t i o n at  10 A  Fig  21.  pH e f f e c t o n % T . O . C . and i n an u n d i v i d e d c e l l .  % phenol  oxidation  at  20 A  I  JL  100 r-  KEY  RUN  O  3-6  2.5  X  3-7  12.0  MASS  N2  PH  TRANSFER -  CONTROLLED  20  REGION  1  1  1  30  60  90  TIME ( m i n ) Fig.  22.  Effect of pH on % T.O.C. and % phenol oxidation at 30 A in an undivided c e l l .  i 120  74 100  120  100  —a 80  O  UJ  N Q X  O  60  UJ  JO. CL  KEY  40  • O  20  0  0  30  N2  I (A)  3-2  10  3-5  20  3-7  30  _L 60  TIME 24.  RUN  JL 90  (min)  E f f e c t o f c u r r e n t o n % T . O . C . and % p h e n o l a t i n i t i a l pH = 1 2 , i n a n u n d i v i d e d c e l l .  oxidation  120  75 can probably be neglected. In F i g . 23 and F i g . 24 the e f f e c t of increasing current i s to substantially  r a i s e the i n i t i a l rate of phenol oxidation, thus  decreasing  the time to complete oxidation and to increase the % of T.O.C. removed. These e f f e c t s are not proportional to the current since there i s a bigger increase i n T.O.C, removal and i n the rate of phenol oxidation i n going from 10 A to 20 A than i n going from 20 A to 30 A ( i . e . , F i g . 24). It can also be observed that i n F i g . 23 the % phenol oxidized vs time curves are closer together  than i n F i g . 24, which indicates that at  high pH the current has a greater e f f e c t on phenol oxidation than at low pH. The maximum % T.O.C* oxidation i s encountered i n Run 3-7, for the highest current and a l k a l i n e pH, where 92% of the carbon was oxidized i n 120 minutes,  5.7  Comparisons of divided and undivided  cells  It i s possible to evaluate the performances of divided and undivided c e l l s under s i m i l a r conditions.  Table 5 shows the operating  condition  and r e s u l t s of three comparisons. Cationic membranes IONAC MC-3470 and NAFION 127 gave s i m i l a r performances  to  the undivided  c e l l s i n terms of phenol oxidation.  Con-  sidering that 2% error a r i s e s i n the determinations of.phenol and T.O.C. .... i t can be said that the r e s u l t s seem to favour the undivided  cell  slightly  i n terms of T.O.C. removal. Run Run  2-11, with anionic membrane MA-3475, can be either compared with  3-4 or with Run 3-5.  Because i n Run 2-11 the pH increased from 2.4  to 12, higher % T.O.C. oxidation was achieved  than i n Run 3-4, but  76 TABLE 5 COMPARISONS OF D I V I D E D AND UNDIVIDED CELLS  Run N o . (cell configuration)  Conditions 1(A) pH  70  11  10  2.5  Run 3 - 3 (undivided)  70  19  10  2.5  Run 2 - 9 (NAFION  77  47  20  2.5  Run 3 - 4 (undivided)  75  53  20  2.5  Run 2 - 1 1 (IONAC MA 3 4 7 5 )  72  67  20  Run 3 - 5 (undivided)  53  127)  it  a c h i e v e d i n Run 3 - 5 , due t o  the  ments w i t h t h e  observed  even i f the  that higher  T.O.C.  12  (at  a  o x i d a t i o n was  % phenol o x i d i z e d at  i t was d e c i d e d  undivided  15 m i n was  lower  A t a pH o f 1 2 ,  t i v i t y was c h a n g e d  effect  to perform the  undivided c e l l rest  of the  is  experi-  electrolyte  of e l e c t r o l y t e  c o n d u c t i v i t y when w o r k i n g  i n Runs 3-5 and 3 - 1 1 ,  f r o m 8 * 10  -3  to  a n d 30 g / 1 o f N a 2 S 0 i , r e s p e c t i v e l y . +  and b e c a u s e t h e  cell.  of c o n d u c t i v i t y of the  F i g u r e 25 shows t h e 20 A .  20  When c o m p a r i n g Run 2 - 1 1 w i t h Run 3 - 5  of these r e s u l t s  to operate,  Effect  is  73  higher pH.  On t h e b a s i s simpler  2.4 12  to  % phenol oxidation.  c o n s t a n t pH o f 1 2 )  at  % T.O.C. ox. a t 120 m i n  Run 2 - 7 (IONAC M C - 3 4 7 0 )  similar  5.8  % Phenol ox. a t 15 m i n  32 x 10  -3  the  (ft.cm)  The r e s u l t s  electrolyte -1  conduc-  , by a d d i n g 5  showed t h a t  the  g/1  increase  i n c o n d u c t i v i t y d i d not removal.  affect  Both experiments  the  phenol o x i d a t i o n , nor the  gave a l m o s t  perfectly  c o i n c i d e n t a l curves  % p h e n o l o x i d i z e d v s t i m e and o f % T . O . C . v s t i m e . o b t a i n e d when t h e  c o n d u c t i v i t y was c h a n g e d ,  at  T.O.C.  The same r e s u l t  pH = 2 . 5  of was  i n Runs 3 - 4  and  3-10. H o w e v e r , when w o r k i n g a t c o n d u c t i v i t y produced  10 A , a n d pH = 1 2 ,  an e x t r a  at  same i n c r e a s e  20% c a r b o n o x i d i z e d a f t e r  % phenol o x i d i z e d vs time curve remained Similarly,  the  10 A , and pH = 2 . 5  120 m i n , b u t  p r a c t i c a l l y unchanged  ( F i g . 27)  about  in  (Fig.  8% more c a r b o n  the 26).  was -3  oxidized after  120 m i n when c o n d u c t i v i t y was c h a n g e d  -3 30  x  10  from 8.4  x 10  to  -1 (fi.cm)  , but  again,  the  % phenol o x i d i z e d vs time curve  showed  no v a r i a t i o n . An e x p l a n a t i o n in  c o n d u c t i v i t y of the  and t h e r e f o r e in  electrode  further  a higher potential  electrode results  i s much h i g h e r  change the  net  change i s d e t e c t e d 5.9  electrolyte  Effect  i n the  of i n i t i a l  F i g u r e 28 r e p r e s e n t s  the  the  increase  potential,  A t 10 A , s u c h a n change i n the 20 A , t h e  increase rate of metal  decrease i n s o l u t i o n p o t e n t i a l appreciably,  and t h e r e f o r e  did  no  removed.  % phenol o x i d i z e d vs time f o r  concentrations  the  initial  phenol concentration  38% and t o 27%.  a lower s o l u t i o n  But at  CO2.  An  concentration  initial  1100 m g / 1 , t h e  to  potential  ent  to  produces  % of T.O.C.  phenol  these observations.  i n an a p p r e c i a b l e  so t h a t  electrode  for  potential.  o x i d a t i o n of intermediates  potential not  c a n be p r o p o s e d  of phenol  (Runs 3 - 3 ,  was i n c r e a s e d  % phenol o x i d i z e d after H o w e v e r , i n F i g . 29 i t  3-12,  three  and 3 - 1 3 ) .  f r o m 93 m g / 1 t o  15 m i n d e c r e a s e d is possible  to see  525  differAs mg/1  f r o m 70% t o that a given  79  Fig.  26.  E f f e c t of e l e c t r o l y t e and i n i t i a l pH = 1 2 .  conductivity  at  10 A  80  Fig.  27.  E f f e c t of e l e c t r o l y t e a n d i n i t i a l pH - 2 . 5  conductivity  at  10 A  81  100  Q UJ N X  o  UJ X 0_  60 TIME Fig.  28.  (min)  % phenol o x i d i z e d vs time for v a r i o u s i n i t i a l p h e n o l c o n c e n t r a t i o n a t 10 A and pH = 2 . 5 .  PHENOL  CONCENTRATION  (mg/L )  N5 VO  o  —  "2. m 3  CO ho  time the net  amount  increases.  Thus,  compared t o figure  it  of phenol o x i d i z e d  i s h i g h e r as  350 m g / 1 o f p h e n o l w e r e o x i d i z e d  the  concentration  i n 15 m i n i n Run  200 m g / 1 i n R u n 3 - 1 2 and o n l y 75 m g / 1 i n R u n 3 - 3 .  is  easier  to observe  For example,  i f the  c u r v e f o r Run 3 - 1 2 was d i s p l a c e d a l o n g t h e  axis until  i t matched  the  the  p a r a l l e l i s m between  the  same r e s u l t s  removal i s r e l a t i v e l y low.  phenol,  the higher  5.10  the net  But f o r  change  concentration  under  results  with  otherwise  initial  11% when t h e  of carbon present  flow at  conditions,  £/min.  73% i n R u n 3 - 1 5 .  w e r e 53% a n d 54% r e s p e c t i v e l y .  large  shows t h a t  flow rate  The % T . O . C . (Refer  at  r e c i r c u l a t i o n tank.  both  due  to  t o Run t a b l e s  £/min, flow  oxidized  after  oxidized  i s masked by the  h i g h e r c o n v e r s i o n would be e x p e c t e d circulation,  mg/1  A comparison  f l o w , was 1 . 1 2  T h u s , p h e n o l was 75% o x i d i z e d  atively  o f 1100  rate  t h o s e f r o m Run 3-4 w h e r e t h e  of the  concen-  in solution.  a flow r a t e of 0.55  equal operating  zero.  T.O.C.  initial  concentration  t i m e were o b t a i n e d .  The e f f e c t  curves  c o n c e n t r a t i o n was 93 m g / 1 ,  same % p h e n o l v s t i m e a n d % T . O . C .  and a b o u t  both  the  rates p r a c t i c a l l y the  3-4  time  i n T . O . C . was p r a c t i c a l l y u n d e t e c t a b l e  Effect of electrolyte  the  the  curves.  i n Run 3 - 1 2 f r o m t i m e  initial  this  w o r d s , a f t e r ' 30 m i n o f R u n  10 A and pH = 2 . 5 ,  When t h e  Run 3 - 1 5 was p e r f o r m e d of  at  as  c a r b o n was r e m o v e d i n 2 h v e r s u s  t r a t i o n was 525 m g / 1 . of  In other  w o u l d be o b s e r v e d  As t h e s e r u n s w e r e p e r f o r m e d  25% o f t h e  three  c u r v e c o r r e s p o n d i n g t o Run 3 - 1 3 ,  w o u l d be p r a c t i c a l l y c o i n c i d e n t a l . 3-13,  the  In  3-13  vs  15 m i n i n Run  after  120 m i n  i n Appendix 2.)  presence  of the  rel-  In a s i n g l e pass experiment,  a  at  re-  a l o w e r f l o w r a t e means i t  a lower flow r a t e . t a k e s more t i m e f o r  With  a given  84 e f f e c t to be detected i n the r e c i r c u l a t i o n tank a n a l y s i s .  The effect of  both i n l e t concentration and flow rate, i s more e a s i l y examined i n single pass experiments where the c e l l operates i n steady state.  Thus  some s i n g l e pass experiments were carried out. Figure 30 represents the % phenol oxidized i n a single pass through the c e l l vs flow rate, at d i f f e r e n t i n i t i a l concentrations, when operating at 10 A and pH = 2.5.  Runs 4-1, 4-2, and 4-3 were carried out at  e s s e n t i a l l y the same phenol concentration of 100 ± 5 mg/1 to check reproducibility.  They produced p r a c t i c a l l y c o i n c i d e n t a l % phenol o x i -  dized vs flow rate curves.  About 90% of the phenol was oxidized at a  flow rate of 0.11 £/min, and as the flow rate was increased the % of phenol oxidized dropped, reaching a 20% at a flow rate of 1.1 2,/.mini Run 4-4 was performed under the same conditions (pH = 2.5, I = 10 A) but s t a r t i n g at the higher phenol concentration of 580 mg/1. analysis showed that about  The phenol  70% was oxidized when the l i q u i d flow rate  was 0.11 Ji/min and that the % phenol oxidized decreased with increasing flow rate, to about 8% when the flow rate reached 1.1 2,/min. Similar e f f e c t s were observed when operating at a current of 20 A, for i n i t i a l concentrations of 110 and 510 mg/1. The table for Run 4-1 shows that when the flow rate was 0.11 £/min at 10 A, the temperature of the e l e c t r o l y t e was raised from 24°C at the i n l e t to  32°C at the outlet of the c e l l .  But when the flow was  increased to 0.25 £/min the outlet temperature increased only 4°C above the i n l e t temperature.  The operation can be considered  practically  isothermal f o r a l l flows equal or higher than 0.25 il/min. At 20 A ( i . e . , Run 4-5) the temperature at the outlet increased more than at 10 A, as could be expected, but the operation can be  100 (a) KEY  RUN  N2  80 O Q UJ U O X  4- 1 4-2 4-3 4-4  + 60  •  PHENOL C 0 (mg/l)  105 95 100 580  o o  Z LU X  40  0_  20  0  0.2  0.4  J. 0.6 FLOWRATE  100  0.8  1.0  1.4  (L/min)  T 1  KEY  RUN  N2  80 Q LU N  9 X  1.2  •  4- 5 4-6  0.8  1.0  PHENOL C 0 (mg/L)  110 510  60  o  LU 40 X  0_  20  0  02  0.4  06 FLOWRATE  30.  (L/min)  E f f e c t o f f l o w r a t e on t h e s i n g l e pass % phenol o x i d a t i o n a t ( a ) 10 A , ( b ) 20 A .  1.2  1.4  86 considered  practically  i s o t h e r m a l f o r flows above o r e q u a l t o 0.55 £/min.  I n r e t r o s p e c t , i t would have been b e t t e r t o r e p o r t a l l t h e r e s u l t s under c o n s t a n t due  room temperature t o e l i m i n a t e any p o s s i b l e s i d e  t o temperature v a r i a t i o n s .  of a t o t a l l y d i f f e r e n t  effect  However, t h i s would r e q u i r e the d e s i g n  c e l l w i t h a b u i l t - i n heat exchanger t o remove t h e  heat r e l e a s e d by t h e c u r r e n t .  5.11  Effect of p a r t i c l e  size  F i g u r e 31 shows t h e % o f phenol o x i d i z e d v s f l o w u s i n g t h r e e ent anode s u r f a c e a r e a s .  The lower curve  where no p a r t i c l e s were p r e s e n t on g r a p h i t e p l a t e .  c o r r e s p o n d s t o experiment 4-8,  and the anode was j u s t  The i n t e r m e d i a t e  differ-  curve  the lead d i o x i d e  c o r r e s p o n d s t o the average %  p h e n o l o x i d i z e d from Runs 4-1, 4-2, and 4-3 where a p a r t i c l e s i z e between 1.7 and 2.0 mm was used and t h e upper curve was o b t a i n e d when working w i t h p a r t i c l e s i z e s between 0.7 and 1.1 Taking  mm.  as a reference, the f l o w o f 0.4 A/min, where t h e o p e r a t i o n i s  p r a c t i c a l l y i s o t h e r m a l , i t i s observed t h a t when working without t h e s p e c i f i c a r e a was 3.3 cm ^ and o n l y  particles  20% o f t h e phenol was o x i d i z e d ,  whereas f o r a s p e c i f i c a r e a o f 20.6 cm ^ u s i n g t h e l a r g e r p a r t i c l e s , about a 59% o x i d a t i o n was a c h i e v e d . 0.7-1.1 mm)  With t h e s m a l l e r p a r t i c l e s  (sizes =  about a 67% o f t h e p h e n o l was o x i d i z e d and t h e s p e c i f i c  was 41.5 cm ^.  (Calculations of the s p e c i f i c  e l e c t r o d e areas  area  a r e found  i n Appendix 4.) These e f f e c t s w i l l be d i s c u s s e d m a t i c a l models f o r the p r o c e s s .  i n t h e next s e c t i o n based on mathe-  87  0  0.2  0.4  06 FLOWRATE  F i g . 31.  0.8  1.0  (I/min)  E f f e c t o f anode s u r f a c e a r e a - p a r t i c l e s i z e on t h e % phenol o x i d i z e d i n a s i n g l e - p a s s vs flow r a t e .  1.2  1.4  88 5.12  Comparisons of e x p e r i m e n t a l 5.12.1 If  of for  Batch  the  results  rate of phenol disappearance  r e c i r c u l a t i o n system,  phenol f r a c t i o n a l groups  to  the  is  the  c o n t r o l l e d b y mass  surface  following  conversion with dimensionless  o f the  equation  -K  t  is  specific  the  exp ( e x p  time the  surface  superficial  area of the  electrolyte  v e r s i o n vs t i m e , from the  a L  m  electrode, relates  t i m e a n d mass  K -  electrolyte  then  the  transfer  1)— t m  a L m  u  spends i n the m i x i n g tank,  electrode,  L the  electrode  are  r e p r e s e n t e d as  t a k i n g i n t o account  empirical equation  height,  for  t h a t a 10% e r r o r  t h e mass t r a n s f e r  c a n be  for  this  of X vs t  case,  are  as d i s c u s s e d  presented  F i g u r e 28 shows t h e  deviations  m o d e l when o p e r a t i n g  responding  to  the  closest  the  to  approximately  at  10 A .  initial  experimental  chemical reaction k i n e t i c s  model.  controls  the  Calcu-  results  As e x p e c t e d ,  the  from  curve  (93 m g / 1 )  the cor-  is  r e g i o n w i t h a 15 m i n c o n v e r s i o n model.  o f p h e n o l was 1100 m g / 1  % phenol o x i d i z e d after  b y t h e mass t r a n s f e r  As w e l l ,  Table A - 2 .  phenol concentration  concentration  con-  coefficient  15% l o w e r t h a n p r e d i c t e d b y t h e mass t r a n s f e r  experimental  predicted  initial  of the  mass t r a n s f e r - c o n t r o l l e d  Where t h e  the  expected  i n A p p e n d i x 3 , page 1 6 0 .  i n Appendix 4,  mass t r a n s f e r  lowest  and u  coefficient.  c o r r e l a t i o n c h o s e n may u n d e r e s t i m a t e t h e mass t r a n s f e r  lations  the  a band o r r e g i o n o f  the  particular  a  velocity.  The m o d e l c a l c u l a t i o n s  the  transfer  (Appendix 3 ) .  X = 1 -  Here,  models  experiments  p h e n o l from the b u l k e l e c t r o l y t e a batch  with mathematical  15 m i n i s  (Run  a b o u t 55% b e l o w  This implies that  the  3-13) that  electro-  rate of phenol o x i d a t i o n  under  89 such c o n d i t i o n s .  However, as the phenol c o n c e n t r a t i o n drops d u r i n g t h e  c o u r s e o f t h e experiments, model. at  t h e curves approach t h a t o f t h e mass t r a n s f e r  I n o t h e r words, t h e p r o c e s s i s c o n t r o l l e d by r e a c t i o n  kinetics  t h e b e g i n n i n g and as phenol d e p l e t e s , mass t r a n s f e r becomes t h e con-  t r o l l i n g mechanism. F i g u r e s 21 and 22 show t h a t as t h e c u r r e n t i s i n c r e a s e d a t an initial  phenol  c o n c e n t r a t i o n o f t h e o r d e r o f 100 mg/1  (Runs 3-4, 3-6) t h e  e x p e r i m e n t a l % phenol o x i d i z e d v s time curve moves c l o s e r t o t h e mass t r a n s f e r r e g i o n as might be expected. is  still  A t 20 A, t h e e x p e r i m e n t a l  curve  below t h e mass t r a n s f e r r e g i o n u n t i l about 75 min when t h e con-  v e r s i o n was complete.  But a t 30 A t h e mass t r a n s f e r band e n c l o s e s t h e  e x p e r i m e n t a l c u r v e from Run 3-6, a t 30 min time. For b o t h  20 and 30 A c u r r e n t s , t h e curve a t low pH i s c l o s e r t o  the mass t r a n s f e r model than t h e c u r v e c o r r e s p o n d i n g t o t h e h i g h pH r u n . It  s h o u l d be noted  that the experimental curves obtained w i t h  the d i v i d e d o r t h e u n d i v i d e d c e l l region.  either  a r e never above t h e mass t r a n s f e r  The c l o s e s t e x p e r i m e n t a l curve t o t h e mass t r a n s f e r model i s  t h a t o f Run 3-6 a t 30 A and pH = 2.5. 5.12.2  Continuous  experiments  F o r a . s i n g l e pass through appears,  the packed bed r e a c t o r where phenol  by a r a t e p r o c e s s f i r s t  assumption  of plug flow y i e l d s  o r d e r i n phenol  (Appendix  dis-  c o n c e n t r a t i o n , the  3)  - Jtn(l - X) = K a L/u where X i s t h e f r a c t i o n o f p h e n o l o x i d i z e d and K i s t h e o v e r a l l r a t e c o n s t a n t , which can be r e l a t e d t o t h e mass t r a n s f e r and e l e c t r o c h e m i c a l r a t e c o n s t a n t s by u s i n g t h e concept chemical r e s i s t a n c e s as,  o f a d d i t i v e mass t r a n s f e r and e l e c t r o -  90  Using the data from those experiments performed  i n the continuous mode,  i t i s possible to evaluate an experimental rate constant.  When - &n(l - X)  i s plotted vs -jj a straight l i n e i s obtained ( F i g . 32) and the experimental rate constant K can be determined  from the slope.  Thus, using a v a i l a b l e  correlations f o r K , K can be determined. m r The nature of the electrochemical rate constant K  was alluded to i n r  Chapter 2.  Unlike a chemical reaction rate constant, i t i s dependent on  electrode p o t e n t i a l .  As discussed i n Appendix 3, when operating at a  f i x e d current rather than at a fixed p o t e n t i a l , changes i n phenol concent r a t i o n , flow rate, surface area, etc. w i l l r e s u l t . i n changes i n p o t e n t i a l and hence i n K . Therefore, the analysis of r e s u l t s i n terms of K to be r r 3  presented here, i s of limited usefulness except to indicate what resistance (mass transfer or electrochemical k i n e t i c s ) i s more important under determined conditions. variables on K  However, considerations of the e f f e c t s of the process  does show q u a l i t a t i v e agreement with what i s expected  from  the simple model, as w i l l be shown with the following examples. Taking the average f r a c t i o n a l conversion from experiments 4-3, performed  4-1,  4-2,  at 10 A and i n i t i a l concentrations of phenol of 100 ± 5  with p a r t i c l e sizes between 1.7 and 2.00 mm,  the  mg/1,  experimental:rate con-  stant i s obtained from the corresponding straight l i n e represented i n F i g . _3  32.  The r e s u l t i n g value of K i s 3.1 x 10  cm/s.  Using the c o r r e l a t i o n  by Pickett and Stanmore (45) for mass transfer c o e f f i c i e n t i n e l e c t r o chemical packed bed reactors K  and K m  (Table A-3).  are calculated at various flows r  91  92 For example, at  0.25 V m i n  : K = 3.9 x 1 0 ~ m  3  at  1.10  : K = 8.8 x i o " m  3  A/min  This implies  that  o x i d a t i o n because  at  cm/s, K = 15.7 x i o " ' r cm/s, K  the low flow r a t e ,  t h e mass t r a n s f e r  80% o f t h e o v e r a l l r e s i s t a n c e . the r e s i s t a n c e to r e a c t i o n  resistance  (~~) m  c o n t r o l s the  represents  other hand, at  represents  phenol  about  the h i g h flow  a 65% o f t h e o v e r a l l  an rate,  resis-  (tr).  tance  The same c a l c u l a t i o n p r o c e d u r e was a p p l i e d when t h e  initial  constant  was 1.4  x 10  cm/s.  In t h i s  (Table A-4) 0.25  case the  A/min  : K = 3 . 8 x 10 m  -3  electrochemical reaction  resistance  cm/s, K  at  = 2 . 2 1 x 10  r  all  -3  a t 1 . 1 0 l/mln : Km = 8 . 8 x i o " 3 c m / s , Kr = 1 . 6 7 x 1 0 ~ The r e s u l t s  f r o m Run 4 - 4  The r e s u l t i n g e x p e r i m e n t a l r a t e  r e s i s t a n c e was h i g h e r t h a n t h e mass t r a n s f e r  at  to the data  c o n c e n t r a t i o n was 580 m g / 1 , w o r k i n g u n d e r o t h e r w i s e e q u a l  c o n d i t i o n s as i n t h e p r e v i o u s e x a m p l e . _3  i.e.,  cm/s.  3  mass t r a n s f e r  On t h e  (~)  = 4.8 x i o "  r  c m / s , and '  3  from b o t h examples a r e  cm/s  cm/s.  3  i n q u a l i t a t i v e agreement  flows  w i t h the  of the model, s i n c e at a constant i n i t i a l c o n c e n t r a t i o n , K ' r s h o u l d d e c r e a s e when t h e f l o w r a t e i n c r e a s e s , a n d a t a c o n s t a n t f l o w  pre-  dictions  K  r  s h o u l d a l s o d e c r e a s e when t h e  described i n Appendix  initial  size  as  3.  The e x p e r i m e n t a l r a t e c o n s t a n t particle  concentration increases  rate,  ( 0 . 7 - 1 . 1 mm).  was a l s o e v a l u a t e d f o r t h e  Using the r e s u l t s  f r o m Run 4 - 8 ,  smaller  the  experi-  -3 mental rate constant transfer at  i s K = 1.8  x 10  and r e a c t i o n c o e f f i c i e n t s a t  0.25 £/min  : K = 5.3 x 1 0 ~ m  1.10  : K = 12.1 x i o " m  A/min  cm/sec the  ( T a b l e A - 5 ) , and t h e  extreme flows  cm/s, K = 2.68 x 1 0 ~ ' r  3  3  are, cm/s  3  cm/s, K = 2.09 x i o " ' r  3  cm/s.  mass  93 These d a t a  indicate that  t h a n mass t r a n s f e r .  In t h i s  was 100 m g / 1 a n d a l l t h e size,  were e q u a l to  coefficients example, on  K are m  due t o  the  smaller  particles),  higher  at  first  dependance  of the  the  achieved at  electrode the  potential w i l l  cell,  increase  of the  area  the net  effect  is  the  s p e c i f i c surface  s h o u l d be e m p h a s i z e d  each experiment, a larger the  different  from the  the  coefficient  obtained  same n e t  obtained  from the  of K  larger area  with  theoretical (smaller same  are  r  K is  potential  the  conversions  bed,  are  (Fig. 31), from 20.6  to  equation:  reported  set  (or the  input,  here for  the  o f c o n d i t i o n s used  sizes  than used i n  average  according to  value) the  a n o d e was t h e  (without p a r t i c l e s ) ,  slope of the  obtained  u  the values for  expected.  particles  of the  input  K a  exp  same p a r t i c l e  current  plate  the  that higher  plug flow  from Run 4-7 where t h e  feeder  the  s h o u l d n o t be u s e d i n a s c a l e - u p ,  the  electrode  data  Pb02 on g r a p h i t e  particular  even w i t h  average for  that  and t h e r e f o r e  cell  Using the  constant  first  o v e r a l l rate constant  than w i t h  This i s expected  rate constants are  study,  are  be l o w e r f o r  r  for  transfer  i n the  r  phenol  particle  o f the bed  and thus l o w e r v a l u e s  X = 1 -  tion  of  e m p i r i c a l mass t r a n s f e r  s p e c i f i c surface  a given flow rate  4 1 . 5 cm \  It  for  The mass  i n q u a l i t a t i v e agreement w i t h  smaller p a r t i c l e s ,  due t o t h e  example.  lower r e a c t i o n c o e f f i c i e n t s K  is also  a p p l i e d to  the  resistance  concentration  a given flow r a t e than  Even though a l o w e r v a l u e o f the with  initial  experimental c o n d i t i o n s except  since for a higher  current  the  a higher  particles.  This result model,  reaction offered  case,  those i n the  p a r t i c l e s i z e , but  the  the  straight  the  reacin  since this will  be  model. electrodeposited  experimental  l i n e o n F i g . 32  is  rate  K = 5  10  x  _3  cm/sec.  For the ranges  t h e Re n u m b e r s r e f e r r e d lower than 700. transfer  to the h y d r a u l i c diameter,  For R e ^  coefficient  e  experiments  de = 2 S W / ( S + W) a r e  < 2000, an a p p l i c a b l e c o r r e l a t i o n f o r the  i n a parallel plate reactor  m  D For l i q u i d  o f flows used i n the  = 1.47  (Re, de  v  is  S c ^ L  (page 1 3 3 , R e f .  % ) S  1  /  mass 10)  3  f l o w r a t e s between 0 . 2 5 and 0 . 1 1 J l / m i n ,  this correlation -4  results  i n mass t r a n s f e r  coefficient  v a l u e s b e t w e e n 4 x 10  and  -4 7  x  10  cm/sec w h i c h a r e about  experimental constant. higher  Since the o v e r a l l  t h a n t h e mass t r a n s f e r  t h e mass t r a n s f e r  ten times lower than the c a l c u l a t e d  coefficient  coefficient,  t h e r e i s an enhancement  e v o l u t i o n , which i s not  i t means t h a t  It  stationary  i n t h e mass t r a n s f e r  It  flat  coefficient  under-  i n pracdue t o  gas  coefficients i n  gas case of  e l e c t r o l y t e is only provided  i s known t h a t mass t r a n s f e r  by  c o e f f i c i e n t s under  times greater  than the  mass  c o e f f i c i e n t s from c o n v e n t i o n a l f r e e - c o n v e c t i o n c o r r e l a t i o n s i n  plates  (10).  But f o r the an e m p i r i c a l the r e s u l t s  case of forced  c o n v e c t i o n and gas e v o l v i n g  c o r r e l a t i o n c o u l d n o t be f o u n d  i n the  seem t o i n d i c a t e t h a t mass t r a n s f e r  p h e n o l o x i d a t i o n on t h e ficients  the values of  e l e c t r o d e s have been developed f o r the  gas e v o l u t i o n a r e between f o u r o r f i v e transfer  be  t a k e n i n t o a c c o u n t by t h e c o r r e l a t i o n .  s o l u t i o n where m i x i n g o f the  t h e gas b u b b l e s .  can never  c o u l d be suggested t h a t  M o s t o f t h e c o r r e l a t i o n s f o r mass t r a n s f e r evolving p a r a l l e l plate  constant  o b t a i n e d by t h e c o r r e l a t i o n a r e an  e s t i m a t i o n of the r e a l s i t u a t i o n . tice  rate  flat  plate,  electrodes,  literature.  c o n t r o l s the  However,  r a t e of  s i n c e e v e n i f t h e mass t r a n s f e r  were i n c r e a s e d by a f a c t o r o f f i v e ,  the r e s u l t i n g  values  coef-  95  would s t i l l be lower than the experimental rate constant. 5.13  Current e f f i c i e n c i e s , energy requirements and energy costs f o r phenol oxidation 5.13.1  Batch experiments  Typical current e f f i c i e n c i e s , energy requirements, and costs are estimated for batch experiments nos. 3-3, 3-12, 3-13, after r e c i r c u l a t i o n times of 15 and 90 min. page 178.  A sample c a l c u l a t i o n i s given i n Appendix 4,  For the estimation of the % C.E. i t was assumed that four  electrons are transferred from the phenol molecule as proposed by Covitz (Reaction R9).  Energy per g mol phenol oxidized i s calculated taking  $0.02/Kw-h as a basis. Table 6 shows that f o r lower i n i t i a l concentrations of phenol or higher r e c i r c u l a t i o n times, the % C.E. are r e l a t i v e l y lower and the energy costs are higher. TABLE 6 TYPICAL CURRENT EFFICIENCIES, ENERGY REQUIREMENTS AND ENERGY COSTS IN BATCH EXPERIMENTS WITH UNDIVIDED CELL (Q=1.12 £/min)  Run No.  3-3  \ (mg/1)  AV (volts)  t (min)  % (mg/1)  X C.E. (%) (%)  Energy Kw-h s ^g moi  Electrical costs ($/g mol)  r  ;  93  8.6  15 90  28 0  70 100  11 3  6.7 22.6  0.14 0.45  3-12  525  8.3  15 90  320 5  39 99  36 19  2.5 4.8  0.05 0.10  3-13  1100  8.5  15 90  792 22  28 98  54 35  1.7 2.4  0.03 0.05  96 Run 3 - 3 a t  C. 0  =93  A  $0.45/g mol o x i d i z e d p h e n o l was p r e s e n t 5.13.2  mg/1, y i e l d s  f o r the  after  t h e maximum e n e r g y c o s t o f  90 m i n o p e r a t i o n , w h e r e p r a c t i c a l l y  treatment.  Continuous experiments  U s i n g t h e d a t a from Runs 4 - 3 and 4 - 4 , C.E.  no  and energy c o s t s  A sample c a l c u l a t i o n are presented  for various flows  it  i s p o s s i b l e to estimate %  i n a s i n g l e pass through the  i s g i v e n i n A p p e n d i x 4 , page 1 8 0 , and the  cell.  results  i n T a b l e 7.  TABLE 7 T Y P I C A L CURRENT E F F I C I E N C I E S , ENERGY REQUIREMENTS AND ENERGY COSTS I N CONTINUOUS EXPERIMENTS WITH UNDIVIDED C E L L  C  C  Run No.  (mg/1)  4-3  95  4-4  580  1  The  Q (A/min)  AV (V)  (mg/1)  0.25 0.55 1.1  8.7 8.3 7.4  0.25 0.55 1.10  8.6 7.9 7.0  electrical  4-4 at  39 63 76  59 34 20  9.6 12.2 14.3  9.7 7.4 5.6  0.195 0.148 0.110  365 470 526  37 19 9  36.7 41.5 39.3  2.5 2.0 1.9  0.050 0.041 0.037  cost of treatment  and  f r o m Run 3 - 1 2 a f t e r  0 . 2 5 5,/min, i t  decreases  5.13.3 It  Cost  as t h e  initial  increased.  Comparing  those  i n terms of c u r r e n t  both s i t u a t i o n s are p r a c t i c a l l y  from Run efficiences  equivalent.  comparisons  i s of interest  the operating costs  are  r  15 m i n ( T a b l e 6) w i t h  can be seen t h a t  energy requirements,  Electrical costs ($/g mol)  C.E. (%)  p h e n o l c o n c e n t r a t i o n and e l e c t r o l y t e f l o w s the r e s u l t s  Energy Kw-h . ^g m o l ' '  X (%)  2  to  compare t h e  for other  estimated e l e c t r i c a l  treatments  g i v e n by K a t z e r  costs  (8).  with Table 8  97 TABLE 8 OPERATING COSTS OF VARIOUS TREATMENT METHODS, ESTIMATED FOR 1974 FOR A C A T A L Y T I C CRACKER EFFLUENT CONTAINING 700 m g / 1 PHENOL ( 8 )  Treatment Process  ($/1000 g a l )  Oxidation p o n d ^ Activated  0.14-0.51  sludge^  Activated sludge, with dilution {  0.24  ($/g  mol)  ( 5 )  0.005-0.018 0.009  2.4  }  costs  0.090  (3) Carbon a d s o r p t i o n  0.86  0.031  Catalytic  0.57  0.020  (4) oxidation '  Electrochemical oxidation  2.00  U / )  (JJ) 0.08^ '  (1) $ 0 . 3 8 / 1 0 g a l i n 1967; o p e r a t i n g c o s t s of b i o l o g i c a l o x i d a t i o n ponds at B i l l i n g Montana O i l R e f i n e r y ; e x t r a p o l a t i o n t o 1974 g i v e s $0.51/10 gal. C a p i t a l investments not i n c l u d e d . 3  3  (2) E x t r a p o l a t e d f r o m 1968 t o 1974 u s i n g a f a c t o r o f 1 . 3 4 ; i f dilution of e f f l u e n t i s r e q u i r e d cost of treatment w i l l i n c r e a s e ; 10:1 dilution factor results i n $2.4/10 gal. 3  10 gal/day design for treating u n f i l t e r e d activated e f f l u e n t t o p r o d u c e w a t e r w i t h 8 mg/1 C . O . D . 6  (4)  Calculated  sludge  plant  f o r a 99% p h e n o l r e m o v a l b y c a t a l y t i c o x i d a t i o n .  ^ " ^ C a l c u l a t e d f r o m t h e o r i g i n a l p a p e r ( R e f . 8) a s s u m i n g t h a t p h e n o l c o n v e r s i o n was a c h i e v e d i n a l l t h e e x a m p l e s . ^ C a l c u l a t e d in this (Appendix 4 ) .  study for t r e a t i n g  a 51 v o l u m e w i t h  total  99% r e m o v a l  C a l c u l a t e d i n t h i s s t u d y b y i n t e r p o l a t i n g f r o m T a b l e 6 f o r 700 m g / 1 phenol i n i t i a l c o n e , using a f a c t o r of $0.02/Kw-h for e l e c t r i c a l energy c o s t .  98 shows t h e  1974 c o s t s  700 m g / 1 p h e n o l . costs  are  for  treating  For the  interpolated  a c a t a l y t i c cracker effluent  electrochemical process,  from T a b l e 6 u s i n g the  mg/1 p h e n o l )  and Run 3-13  v e r s i o n s are  98-99%.  (1100 m g / 1 p h e n o l )  To t r e a t  an e f f l u e n t  data at  electrical  with  700 m g / 1 p h e n o l ,  estimated  e l e c t r i c a l cost  per volume of waste  the d a t a by K a t z e r .  Electrical  times higher than the a c t i v a t e d sludge cost the  order of the a c t i v a t e d sludge cost  cost  of other  processes  cost;  for  a half  ($0.03/g mol).  It  estimated  for  used i n the  the  arbitrary  experiments.  the process would r e q u i r e capital  cost  dations  for  estimate the  energy  $2.00/10  cost  the  is required. estimated  ten  c o s t s w o u l d be l e s s  cell  characteristics  and o p e r a t i n g  To d r a w f i r m c o n c l u s i o n s a b o u t  processes. 7.  than  been  conditions  feasibility  an o p t i m i z a t i o n o f o p e r a t i n g c o s t s  of  electrical  ( $ 0 . 0 8 / g mol) has  given i n Chapter  gal,  3  The  e l e c t r i c a l cost  and the o t h e r  is  i s about  the  of t h i s  former are  i n about  i f dilution  a p p e a r t o be l o w e r t h a n  that  In Appendix 4  i n normal c o n d i t i o n s , but  example, carbon a d s o r p t i o n o p e r a t i n g  s h o u l d be n o t e d  (525  90 m i n , when p h e n o l c o n -  $ 0 . 0 8 / g m o l p h e n o l w o u l d be n e c e s s a r y .  t o compare w i t h  energy  from Run 3-12  approximately the  containing  of  and a  Some r e c o m m e n -  CHAPTER 6  CONCLUSIONS  An i n v e s t i g a t i o n was made o f t h e on l e a d d i o x i d e p a c k e d b e d a n o d e s .  electrochemical In a l l the  experiments  p h e n o l o x i d a t i o n o c c u r r e d more e a s i l y  than  mediate organics  carbonates.  to  carbon  The c o n c l u s i o n s 1.  Electrodeposited the  anodized  dioxide or  of t h i s  study  are  the  o x i d a t i o n of  further  summarized  phenol  performed,  o x i d a t i o n of  inter-  below.  l e a d d i o x i d e was f o u n d t o b e a b e t t e r  anode  l e a d s h o t i n terms o f p h e n o l o x i d a t i o n and  than  corrosion  resistance. 2.  The o x i d a t i o n o f p h e n o l was m o r e r a p i d u n d e r a c i d i c c o n d i t i o n s the  removal of o x i d i z e d products  carbon)  was f a v o u r e d  (measured by t h e  by a l k a l i n e c o n d i t i o n s .  operated w i t h r e c i r c u l a t i o n of s o l u t i o n , on t h e  type  ion selective  membrane u s e d .  w h i c h p r o v i d e d a pH i n c r e a s e  from a c i d i c to  superior 3.  of  organic  In divided electrolyte  cells, pH d e p e n d e d  A n a n i o n i c membrane a l k a l i n e proved to  t o a c a t i o n i c membrane i n t e r m s o f T . O . C .  with  the  In terms of T . O . C . divided cell  p r o v i d e d by t h e  r e m o v a l no improvement  density  at  were  obtained  conditions  membrane.  The e x t e n t s o f p h e n o l and T . O . C . current  was  e v e n u n d e r o p t i m u m pH c o n t r o l l e d  anionic  be  removal.  The r a t e s o f p h e n o l o x i d a t i o n i n d i v i d e d a n d u n d i v i d e d c e l l s similar.  4.  the  total  but  oxidation increased  h i g h or low pH. 99  But at  with  applied  high pH, current  density  changes a f f e c t e d t h e r a t e o f phenol o x i d a t i o n more s t r o n g l y than a t low  pH. -3  5.  An i n c r e a s e i n e l e c t r o l y t e c o n d u c t i v i t y from 8 x 10 (ft.cm) ^ had no e f f e c t  -3 t o 32 x 10  on t h e r a t e s o f phenol o r T.O.C. o x i d a t i o n a t  h i g h o r low pH a t c.d. = 1052.6 A/m , 2  but a t 526.3 A/m  2  c.d., t h e  same i n c r e a s e i n c o n d u c t i v i t y produced h i g h e r T.O.C. o x i d a t i o n r a t e s , even though t h e phenol o x i d a t i o n r a t e s remained 6.  constant.  The e f f e c t o f i n c r e a s i n g t h e i n i t i a l phenol c o n c e n t r a t i o n i n a s i n g l e pass was t o reduce t h e % phenol o x i d i z e d a t a g i v e n time o r i n a s i n g l e pass.  However, t h e c u r r e n t e f f i c i e n c y f o r p h e n o l o x i d a t i o n  increased. 7.  I n c r e a s i n g e l e c t r o l y t e f l o w r a t e reduced t h e s i n g l e pass p h e n o l conversion  at a given i n l e t  phenol c o n c e n t r a t i o n i n continuous  experi-  ments. 8.  I n c r e a s i n g t h e s p e c i f i c s u r f a c e a r e a o f t h e anode i n t h e range o f 3.3 to  41.5 cm /cm 2  3  produced h i g h e r  g i v e n f l o w r a t e and i n l e t 9.  s i n g l e - p a s s phenol conversions  at a  phenol c o n c e n t r a t i o n of the e l e c t r o l y t e .  Comparisons o f t h e e x p e r i m e n t a l  r e s u l t s from b a t c h  experiments w i t h  the mass t r a n s f e r model i n d i c a t e d t h a t t h e o x i d a t i o n o f p h e n o l i s . ..-• c o n t r o l l e d by 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 a t t h e b e g i n n i n g phenol d e p l e t e s , t h e e x p e r i m e n t a l t h a t of t h e mass t r a n s f e r model.  and as  % p h e n o l o x i d i z e d v s time approach Continuous experiments showed t h a t  the e l e c t r o c h e m i c a l r e a c t i o n r e s i s t a n c e becomes more important higher and 10.  e l e c t r o l y t e flow r a t e s , higher  smaller p a r t i c l e  Electric  inlet  phenol  at  concentrations  sizes.  energy c o s t s e s t i m a t e d  c o s t s of other processes. reduced w i t h f u r t h e r work.  were g e n e r a l l y h i g h e r  than  However, power c o s t s can l i k e l y  operating be  CHAPTER 7  RECOMMENDATIONS  I n v e s t i g a t i o n of other tion  of phenol could p o s s i b l y r a i s e  process. ibility  Improvements  to y i e l d  to  regarding the  basis  prospective  of this  study,  the  following  a more c o m p l e t e k n o w l e d g e o f t h e  Analysis  f e a s i b i l i t y of to the  definite  of the  phenol o x i d a t i o n  fraction  The T . O . C .  of the  Measurements Reference  feas-  to determine  of electrode  the  oxidation products  q u a l i t y under  form of each  to  different  effect  of e l e c t r o d e  different  operating  one t o d e t e r m i n e  on t h e  I t w o u l d be o f  potential  on the  conditions.  of i n t e r e s t  for  the  electrolyte  e l e c t r o l y t i c c e l l would 101  interof  Also process  temperature:  b u i l t i n the  bed,  kind  modelling.  A heat exchanger  what  compound.  certain points  operating  p o t e n t i a l measurements a r e  C o n t r o l of the  draw  potential:  potential variations.  under  made,  (benzoquinone,  s h o u l d be a t t e m p t e d ,  s h o u l d be l o c a t e d a t  electrode  to determine  electrode  effluent  i n the  are  products:  a n a l y s i s would permit  carbon i s  electrodes  recommendations  phenol o x i d a t i o n products,  c o n c l u s i o n s about  conditions.  3.  the  process.  h y d r o q u i n o n e and p o s s i b l y m a l e i c a c i d )  est  electrochemical oxida-  the model would l e n d confidence  Routine a n a l y s i s of the  2.  the  calculations.  On t h e  1.  factors  permit  102 temperature c o n t r o l w i t h i n However,  the  exchanger 4.  Analysis  cell  c o n s t r u c t i o n of a c e l l  m i g h t be of the  equipped w i t h  experiments. such a heat  gases produced d u r i n g e l e c t r o l y s i s : technique  the  It  process.  i n s i n g l e pass  difficult.  A gas a n a l y s i s  c o u l d be a s s e s s e d  would permit  a total  for complete m o n i t o r i n g of  carbon balance.  Also  a  measurement  of the  r a t e o f g a s p r o d u c t i o n w o u l d be o f i n t e r e s t  include the  effect  o f gas  After  e v o l u t i o n i n the  these experimental  some o f t h e  other  important  p h e n o l m i g h t be s t u d i e d , the  the  p o t e n t i a l on t h e The f o l l o w i n g  modeling.  improvements were a s s e s s e d ,  factors  e.g.,  the  kind of o x i d a t i o n products,  trode  process  on t h e effect  and the  mathematical modeling of the  the  of d i f f e r e n t  of  effect  anode m a t e r i a l s  o f t e m p e r a t u r e and  i n a d d i t i o n to  on  elec-  intermediates.  would a l l o w improvements  process  effect  electrochemical o x i d a t i o n of  r a t e s o f o x i d a t i o n o f p h e n o l and  recommendations  to  to  the  furthering  general  u n d e r s t and i n g . 5.  The e f f e c t  o f gas  be s t u d i e d . transfer 6.  Cell  8.  c o n t r o l l e d c o u l d be u s e d f o r  l e n g t h , w i d t h , and t h i c k n e s s of electrode  would permit  one t o d e t e r m i n e  a uniform or average  E x p e r i m e n t s c o u l d be s e t electrode  potential  operating  conditions.  The e f f e c t  coefficient  Another e l e c t r o c h e m i c a l r e a c t i o n that  Measurements  of 7.  e v o l u t i o n o n t h e mass t r a n s f e r  o f gas  this  purpose  i s p u r e l y mass (45).  o f t h e bed s h o u l d be v a r i e d .  potential  at  different  points  on t h e  under which c o n d i t i o n s the  electrode  should  potential  up t o d e t e r m i n e  the  is  assumption  reasonable.  relationship  and e l e c t r o c h e m i c a l r a t e c o n s t a n t  e v o l u t i o n and e l e c t r o l y t e  bed  between  under  c o n d u c t i v i t y on  different  the  103 electrode  potential  mathematical 9.  process,  conditions  to  include these effects  in  the  models.  Computer methods the  c o u l d be s t u d i e d  c o u l d be u s e d t o c o r r e l a t e  and d e t e r m i n e  costs  to optimize operating  of energy costs.  a l l the v a r i a b l e s under  different  affecting  operating  104  NOMENCLATURE Typical a  specific  surface  area  a.,b. ~*  constants of the T a f e l reaction j  c d .  current  J  of  the  o f t h e bed  2  equation for  the  to the  surface  area  plate  A/m  2  C.E.  current  C.  initial  C^  i n l e t phenol concentration  mg/1  outlet  mg/1  C. A  %  C^ s  w  efficiency phenol concentration i n batch experiments  phenol concentration  mg/1  2  C.  C  phenol c o n c e n t r a t i o n i n the b u l k of s o l u t i o n  mg/1  phenol c o n c e n t r a t i o n at electrode  mg/1  the surface  of  the  concentration associated with a water electrolysis reaction  /-i  mg/1  dp  average p a r t i c l e diameter  D  diffusivity  F  Faraday's constant  coul/g  i^  local  current  density for phenol oxidation  A/m  i  local  current  d e n s i t y c a r r i e d by t h e  A/m  local  current  d e n s i t y c a r r i e d by t h e m e t a l  i  g  m  mm  of phenol i n water  cm /s 2  solution  A /m  2  i^  average  current  density for phenol o x i d a t i o n  A/m  i  average  current  density f o r water  A/m  2  A/m  2  w  2  V  density referred feeder  cm /cm  units  i  t o t a l average  current  I  applied current  density  electrolysis  A  equiv.  electrical  c o n d u c t i v i t y of the  anolyte  electrical  c o n d u c t i v i t y of the  catholyte  electrical  c o n d u c t i v i t y o f the  metal  electrical  c o n d u c t i v i t y o f the  solution  electrochemical reaction mass t r a n s f e r overall  constant  coefficient  or experimental  length of  rate  the  rate  constant  cell  pressure electrolyte universal Reynolds Schmidt  flow  gas  rate  constant  number number  thickness  of the  bed  ( i n the  d i r e c t i o n of  current)  temperature time of  electrolysis  dimensionless residence  time i n the m i x i n g  superficial anode  time tank  velocity  potential  cathode  potential  reversible equilibrium potential reaction j  for  standard  the  total  reduction potential  voltage  volume o f the  drop through mixing  tank  for  the  cell  the  reaction  j  106 W  w i d t h of the  X  phenol f r a c t i o n a l  y  variable  z  number o f e l e c t r o n s oxidation  Greek  bed  cm conversion  l e n g t h of the bed  cm  associated  with  letters  a  transfer  E  voidage of the  rij  overpotential  E,  shape f a c t o r  9  K a L / u d i m e n s i o n l e s s mass t r a n s f e r m  v  kinematic v i s c o s i t y of water  cf> ma  metal p o t e n t i a l  sa mc sc  phenol  coefficient bed for for  the the  anode  of the  of the  solution potential  j  particles  of the  solution potential metal p o t e n t i a l  reaction  anolyte  cathode  of the  catholyte  group (cm /s) 2  V V V V  107  BIBLIOGRAPHY  1.  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The C h e m i c a l R u b b e r  Ill  APPENDIX 1  Specification Power  of A u x i l i a r y  Equipment  and  Materials  supply  S o r e n s o n DCR 4 0 - 2 5 B Voltmeter range: 0-40V Am m e t e r r a n g e : 0-25A Voltmeter Central S c i e n t i f i c Co., D.C. Scales: 0-1.5 v o l t s 0-15 v o l t s  Voltmeter  Rotameters a)  Anolyte:  Brooks, f u l l view i n d i c a t i n g rotameter Type: 7-1110 Tube N o . : R-7M-25-1 Float: 316 s t a i n l e s s s t e e l Max. f l o w : 1400 c c / m i n ( s . g . = 1) Scale: 0-100% l i n e a r b)  Catholyte:  Brooks, f u l l view i n d i c a t i n g Type: 8-1110 Tube N o . : R-8M-25-2 Float type: 8-RS-8 Max. f l o w : 1 U.S. G.P.M. Scale: 0 - 2 5 0 mm l i n e a r Gas l i q u i d  rotameter  (s.g.  = 1)  separators  2 . 5 cm I . D . and 60 cm l o n g g l a s s t u b e . L i q u i d o u t l e t l o c a t e d a t 40 cm f r o m t h e b o t t o m . P a c k e d t o a p p r o x i m a t e l y 20 cm d e p t h w i t h 2 mm diameter glass beads. Filters 3.0  cm I . D . a n d  Pressure  15 cm l o n g g l a s s t u b e f i l l e d  w i t h glass wool  gauges  M a r s h - t y p e 3 - 1 0 0 - S S w i t h 316 s t a i n l e s s Scale: 0-30 p s i (1/4 p s i / d i v ) .  steel  tube  (Merck).  112 Pumps B a r r i s h Pumps Model type: Flow data: cates outlet 45 p s i d b u t  Co., N.Y. 12A-60-316 21 6 . P . H . a t 40 p s i d , 29 6 . P . H . a t 0 p s i d . p r e s s u r e minus i n l e t p r e s s u r e . ) Pumps a r e a r e a d j u s t a b l e t o 65 p s i d max.  (psid preset  indiat  pH m e t e r C o r n i n g , M o d e l 101 ( a c c u r a c y ± 0 . 0 0 1 pH) Electrode: Fisher, p l a s t i c body-protected Model No. 13-639-97 Conductivity  bulb  type  meter  S e i b o l d , M o d e l L T A . P r o v i d e d w i t h a d j u s t a b l e maximum r a n g e s 1 mmho cm -'- t o 100 mmho cm -'- maximum) C o n d u c t i v i t y c e l l c o n s t a n t = 0 . 8 8 cm -'-  (from  -  -  Tubing I m p e r i a l Eastman  "Poly F l o "  66-P-3/8"  Valves W h i t e y , f o r g e d body r e g u l a t i n g 316 s t a i n l e s s s t e e l . 3/8" connections Fittings Swagelok compression tube f i t t i n g s 316 s t a i n l e s s s t e e l 3 / 8 " Membranes a)  IONAC membranes The IONAC membranes a r e s u p p l i e d b y I o n a c C h e m i c a l S y b r o n C o r p o r a t i o n , Birmingham, N . J . T a b l e A - l i n c l u d e s some o f t h e s p e c i f i c a t i o n s e n t b y t h e m a n u f a c t u r e r .  b)  N A F I 0 N 127 membrane S u p p l i e d b y d u P o n t de Nemours & C o . , D e l a w a r e . NAFION 127 c o n s i s t s o f a n homogeneous f i l m o f 1200 e q u i v a l e n t w e i g h t polymer, 7 mils t h i c k (perfluorosulfonic acid polymer). Supports a r e made f r o m t e f l o n . D e t a i l s o f membrane p r o p e r t i e s s u c h as s t r e n g t h , i o n i c t r a n s p o r t , w a t e r p e r m e a b i l i t y e t c . , a r e a v a i l a b l e i n a p u b l i c a t i o n s u p p l i e d by t h e manufacturer (46).  113 TABLE A - l SUMMARY OF T Y P I C A L PROPERTIES OF IONAC MEMBRANES  C a t i o n E x c h a n g e Membranes MC-3142 MC-3470  Property  A n i o n Exchange Membranes MA-3475  E l e c t r i c a l Resistance (ohm-cm , A . C . measurement) O.IN NaCl l.ON NaCl  14 5  12 6  17 8  % Perselectivity (0.5N N a C l / l . O N NaCl) (0.2N N a C l / O . l N NaCl)  94.1 99.0  96.2  99.0  2  Water P e r m e a b i l i t y (ml/hr/ft. /5 psi)  negligible  2  Mullen Burst Strength (minimum p s i . ) Membrane (mils)  oz./yd g/m  2  2  Capacity meq/g  30)  (less than  175  200  200  7  15  15  6 202  12 405  12 405  30)  Stability  Size A v a i l a b l e nominal sheet s i z e s (inches  recommended  0.70  1.22  1.08  Dimensional S t a b i l i t y ( a b i l i t y to rewet a f t e r drying)  *Not  than  Thickness  Approx. Density Net as s h i p p e d  Chemical H2S01+ HCl NaOH Salt  (less  good  good  good  up t o 6 0 ° C up t o 5% up t o 4% NR* OK a t a l l cone.  up t o 1 2 5 ° C up t o 35% cone. H C l 50% NaOH OK a t a l l cone.  up t o 1 2 5 ° C Superior to MC-3470 i n l o w and h i g h pH media  40 x 120  40 x 120 30 x 96  40 x 120  114 Plastic  screens  S u p p l i e d by C h i c o p e e M a n u f a c t u r i n g C o . , G e o r g i a Saran type Max. o p e r a t i n g t e m p e r a t u r e = 1 2 5 ° F Chemical r e s i s t a n c e : g o o d r e s i s t a n c e t o a c i d s and m o s t a l k a l i s Style: 6100900 Weight/sq.yd. = 7 oz. Polypropylene type Max. o p e r a t i n g t e m p e r a t u r e : 180°F Chemical resistance: e x c e l l e n t r e s i s t a n c e t o most a c i d s and a l k a l i s w i t h e x c e p t i o n o f c h l o r o s u l f o n i c a c i d s and o x i d i z i n g a g e n t s Style: 60070XX W e i g h t / s q . y d . = 8.7 o z . C a t h o d e chamber p a c k i n g m a t e r i a l S t a i n l e s s s t e e l 304 - 20 x 20 mesh  Analytic a)  equipment  and o p e r a t i n g  conditions  specifications  Gas c h r o m a t o g r a p h y specifications Gas c h r o m a t o g r a p h Manufacturer: V a r i a n Aerograph Model: 1440 s e r i e s , s i n g l e c o l u m n m o d e l Detector: H2 f l a m e i o n i z a t i o n d e t e c t o r Chromatographic column Supplier: W e s t e r n C h r o m a t o g r a p h y S u p p l i e s , New W e s t m i n s t e r , B . C . Material: glass Dimensions: 2mm I . D . , 6 . 4 m m 0 . D . , 6 f t l o n g Packing: 10% S P - 2 1 0 0 ON 1 0 0 / 1 2 0 S u p e l c o p o r t ( d e t a i l s o f t h e p a c k i n g a r e g i v e n i n B u l l e t i n 742D b y S u p e l c o , I n c . ) Operating conditions I n j e c t o r p o r t temperature 150°C Column t e m p e r a t u r e 1 2 0 ° C Detector temperature 175°C C a r r i e r gas N C a r r i e r gas f l o w 30 m l / m i n A i r f l o w 300 m l / m i n H f l o w 30 m l / m i n A t t e n u a t i o n s e t t i n g 4 x 10 Recorder Model: C o r n i n g 840 s e r i e s R e s p o n s e 1 mv f u l l s c a l e Chart speed: 1 cm/min Syringe Supplier: Unimetrics Sample s i z e : 1 uil 2  2  115 b)  T.O.C. analysis specifications Model: Beckman 915 t o t a l o r g a n i c c a r r o n Analyzer: Beckman 865 i n f r a r e d a n a l y z e r Operating conditions Temperature of the t o t a l carbon channel 1000°C Temperature of the i n o r g a n i c carbon channel 150°C O x y g e n f l o w i n e a c h c h a n n e l 250 m l / m i n Syringe Hamilton w i t h automatic plunger S a m p l e s i z e 50 y £ Recorder Model: H e w l e t t P a c k a r d 7127A Response: 1 mv f u l l scale Chart speed: 1 cm/min  c)  Atomic absorption specifications Manufacturer: J a r r e l A s h , D i v i s i o n of F i s h e r S c i . Co. Model: 810 A t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t e r Lead lamp: Westinghouse h o l l o w l e a d cathode Wave l e n g t h : 2170 A Flame: rich (air-acetylene) Recorder H e w l e t t P a c k a r d 7127A Speed: variable Range: 1 o r 2 mv f u l l s c a l e Reagents P h e n o l — l i q u i f i e d reagent M a t h e s o n C o l e m a n & B e l l M a n u f . Chem. Code: PX 5 1 1 - C B - 1 0 4 0 Assay: m i n 88% p h e n o l , max 12% H2O NaOH—pellets, reagent American S c i e n t i f i c Chemical Code: SS 350 Assay: NaOH m i n 98% H S0 —reagent A.C.S. A l l i e d Chemical Code: 001180-009580 Assay: 95.5-96.5% 2  4  Na2S0i —anhydrous reagent grade A m e r i c a n S c i e n t i f i c a n d C h e m i c a l SS 530 t  Buffers:  F i s h e r S c i e n t i f i c (2 ± 0 . 0 2 ) A m e r i c a n S c i e n t i f i c and C h e m i c a l (10 ±  Lead s t a n d a r d s o l u t i o n f o r atomic F i s h e r S c i e n t i f i c , 1 0 0 0 ppm Water  for  solutions:  absorption:  single d i s t i l l e d  water  0.01)  116  APPENDIX 2 Experimental Data 1.  C h a r a c t e r i s t i c s o f each group o f  experiments  Group N o . 1 a)  b)  Mode o f o p e r a t i o n : B a t c h e x p e r i m e n t s u s i n g t h e d i v i d e d c e l l and t h e a n o d i z e d l e a d electrode Cell description: Cathode: S t a i n l e s s s t e e l 316 p l a t e a n d mesh Anode: F r e s h l e a d f e e d e r p l a t e and p a r t i c l e s Particles: lead spheres Size: dp = 2 mm Weight: 250 g " ° 11.337 Void f r a c t i o n : Membranes t e s t e d : IONAC M C - 3 1 4 2 o r Volume:  f — = 22 c m ( r e f 49) g/cc e = (57 - 2 2 ) / 5 7 = 0 . 6 1 3  IONAC M C - 3 4 7 0 p r o t e c t e d  by s a r a n  screen  Group No. 2 a)  b)  Mode o f o p e r a t i o n : B a t c h e x p e r i m e n t s u s i n g t h e d i v i d e d c e l l and t h e e l e c t r o d e p o s i t e d Pb02 e l e c t r o d e Cell description: Cathode: S t a i n l e s s s t e e l 316 f e e d e r p l a t e and mesh Anode: Pb02 e l e c t r o d e p o s i t e d o n g r a p h i t e f e e d e r p l a t e Particles: e l e c t r o d e p o s i t e d Pb02 c r u s h e d and s i z e d Size: 1.7 < dp < 2 . 0 mm Weight: 215 g Volume: 23 c m V o i d f r a c t i o n (e) =0.6 Membranes t e s t e d : C a t i o n i c membranes: IONAC M C - 3 4 7 0 NAFION 127 A n i o n i c membrane: IONAC MA 3475 I n a l l r u n s , a s a r a n s c r e e n was l o c a t e d b e t w e e n p a r t i c l e s a n d membrane t o p r e v e n t membrane b r e a k i n g a n d s h o r t c i r c u i t . The o n l y e x c e p t i o n was R u n 2 - 1 w h e r e a p o l y p r o p y l e n e s c r e e n was u s e d . 3  Group No. 3 a)  Mode o f o p e r a t i o n : Batch experiments u s i n g the u n d i v i d e d c e l l t h e e l e c t r o d e p o s i t e d Pb02 e l e c t r o d e  ( o n l y one c h a m b e r )  and  117 b)  Cell description: Cathode: s t a i n l e s s s t e e l 316 p l a t e (no p a c k i n g mesh u s e d t o a v o i d by-passing of the l i q u i d ) Anode: f e e d e r a n d p a r t i c l e s a r e t h e same a s d e s c r i b e d i n g r o u p No. 2. Separator: two p i e c e s o f s a r a n s c r e e n b e t w e e n c a t h o d i c p l a t e a n d Pb02 p a r t i c l e s  Group N o . 4 a)  b)  2.  Mode o f o p e r a t i o n : C o n t i n u o u s e x p e r i m e n t s ( s i n g l e p a s s ) u s i n g the u n d i v i d e d c e l l and e l e c t r o d e p o s i t e d Pb02 anode Cell description: The same a s i n g r o u p N o . 3 w i t h e x c e p t i o n s o f Runs 4 - 7 and 4 - 8 . I n Run 4 - 7 : t h e a n o d e was t h e f e e d e r p l a t e o n l y ( w i t h o u t p a r t i c l e s ) I n Run 4 - 8 : t h e p a r t i c l e s had t h e f o l l o w i n g c h a r a c t e r i s t i c s : Size: 0 . 7 < dp < 1.1 mm Weight: 230 g Volume: 2 4 . 5 cm V o i d f r a c t i o n ( e ) : ( 5 7 - 24.5)7,57 = 0 . 5 7  Volume, For  flow pressure  groups N o . 1 and N o . 2 ( u n l e s s  Electrolyte Anolyte Catholyte +Pressures Note:  and t e m p e r a t u r e  Volume 5 5  (£)  Flows  of the  electrolytes  otherwise  U/min) 1.12 1.54  P  stated) +  (kPa) 2.40 2.40  may v a r y ± 20 k P a due t o g a s e v o l u t i o n .  The s y m b o l (*) w h i c h a p p e a r s i n e a c h Run t a b l e ( G r o u p s 1 a n d 2) i n d i c a t e s t h a t t h e c a t h o l y t e pH a n d e l e c t r i c a l c o n d u c t i v i t y r e p o r t e d w e r e m e a s u r e d on s a m p l e d i l u t e d b y a f a c t o r o f t e n .  F o r g r o u p N o . 3 t h e e l e c t r o l y t e v o l u m e f l o w a n d p r e s s u r e a r e t h e same g i v e n f o r t h e a n o l y t e i n g r o u p s N o . 1 and 2 w i t h e x c e p t i o n o f Run 3 - 1 5 where d a t a are r e c o r d e d . I n e x p e r i m e n t s g r o u p N o . 4 t h e e l e c t r o l y t e f l o w was v a r i e d and t h e r e fore the p r e s s u r e , too. Data are then r e p o r t e d i n each p a r t i c u l a r Run t a b l e . Temperatures A l l t h e e x p e r i m e n t s w e r e s e t up a t r o o m t e m p e r a t u r e (22 t o 2 4 ° C ) . D u r i n g the b a t c h experiments (groups 1 , 2 , 3 ) at c u r r e n t s below or e q u a l t o 10 A t h e e l e c t r o l y t e t e m p e r a t u r e s r e m a i n e d c o n s t a n t . But f o r a l l t h o s e e x p e r i m e n t s p e r f o r m e d a t 20 A ( i . e . , R u n s 3 - 4 , 3 - 5 ) a t e m p e r a t u r e i n c r e a s e o f 4 ° C was a l w a y s d e t e c t e d i n t h e r e c i r c u l a t i o n t a n k ( a f t e r t h e 120 m i n r u n ) . A l s o , when w o r k i n g a t 30 A t h e e l e c t r o l y t e t e m p e r a t u r e r o s e a b o u t 1 2 ° C ( i . e . , Runs 3 - 6 and 3 - 7 ) .  118 F o r t h e c o n t i n u o u s e x p e r i m e n t s ( g r o u p N o . 4) t h e t e m p e r a t u r e v a r i a t i o n s a t a g i v e n c u r r e n t a r e a f u n c t i o n o f t h e f l o w a n d w i l l be r e p o r t e d i n each experiment t a b l e .  3.  Anodization  B e f o r e e a c h e x p e r i m e n t t h e a n o d e was t r e a t e d w i t h 20% H 2 S O 4 a t 10 A f o r 1 hour. ( R e f e r t o e x p e r i m e n t a l method s e c t i o n . ) Any e x c e p t i o n t o the standard procedure i s given i n the p a r t i c u l a r run t a b l e .  119 RUN Membrane:  IONAC M C - 3 1 4 2  Anodization:  Electrolytes  S t a r t i n g from the f r e s h l e a d p a r t i c l e s f o r 1 h (at the specified conditions)  Approx.  Cone.  P  H  Anolyte  1% H S0i+ •  1.5  Catholyte  10% H S0i+  1.0*  2  2  I = 20 A  Comments:  1-1  c.d.  = 1052.6 A / m  2  t (min)  AV (V)  T.O.C. (mg/1)  0  7.3  72  0  15  6.8  68  6  30  6.5  62  14  60  5.7  59  17  90  5.7  57  21  120  5.6  52  28  % T.O.C.  ,  P a r t i c l e s showed a n homogeneous b r o w n c o l o u r a f t e r 1 h anodization.  *Indicates that f a c t o r of 10.  the  pH was m e a s u r e d  on a sample  d i l u t e d by a  the  120 RUN Membrane:  MC-3142  Anodization:  Electrolytes  S t a r t i n g from f r e s h l e a d p a r t i c l e s f o r 12 h ( a t the specified conditions)  Approx.  pH  Cone.  Anolyte  1% H2SO4  1.5  Catholyte  10% H S0tj  1.1*  I  = 20 A  t (min)  Comments:  1-2  2  c d .  AV T.O.C. (V) . (mg/1)  = 1 0 5 2 . 6 A/m  % T.O.C.  (Pb) (mg/1)  0  7.3  80  0  15  6.9  75  6  30  6.4  72  11  0.8  60  5.8  66  18  0.7  90  5.6  61  24  0.6  120  5.5  5  30  0.4  0  P a r t i c l e s showed h o m o g e n e o u s b r o w n c o a t i n g a p p e a r a n c e t h a n a f t e r Run 2 - 1 )  ( w i t h the  same  121 RUN Membrane:  IONAC M C - 3 1 4 2  Anodization:  The b e d was o r i g i n a l l y a n o d i z e d f o r 12 h and t h e n was r e a n o d i z e d for 1 h before the run  Electrolyt e  Cone.  pH  Anolyte  5 g/1 NaCl  5.4  Catholyte  10% H S0i+  1.0*  I = 10 A  t (min)  Comments:  1-3  2  c. d.  AV (V)  = 526.3 A / m  2  T.O.C. mg/1  (%)  0  10  73  0  15  5  55  24  30  3  52  28  I t was o b s e r v e d t h a t t h e g l a s s w o o l f i l t e r c o l l e c t e d s m a l l f r a g m e n t s t h a t had f l a k e d o f f t h e e l e c t r o d e , and the s o l u t i o n took a dark grey c o l o u r , i n d i c a t i n g t h a t t h e e l e c t r o d e was r a p i d l y d i s s o l v i n g . When t h e c e l l was o p e n e d t h e e l e c t r o d e h a d l o s t t h e b r o w n o x i d e ^ c o a t i n g showing the u n d e r l a y i n g grey l e a d . The membrane was f o u l e d w i t h d e p o s i t s .  RUNS 1-4  to  1-8  ( C o r r o s i o n s t u d i e s on a n o d i z e d Membrane:  lead)  IONAC MC3142  Anodization time: 12 h s t a r t i n g f r o m f r e s h l e a d , and 1 h p r i o r t o e a c h I = 10 A c . d . = 526.3 A / m Catholyte: 25 g / 1 NaOH ( p H * = 1 2 . 7 K * = 14 x 10 (ft c m ) " ) c  run  2  1  Run N o .  1-4  1--5  Anolyte  5 g / 1 NaOH  5 g/1 Na S0it NaOH t o a d j . pH 2  t (min) 0 15 30 45 60 75 90  (Pb) (mg/1) 1  pH 12.7 12.6 12.5 12.4 11.8  140 36 24 13 3  (Pb) (mg/1)  1--7  30 g / 1 NaaSOtt NaOH t o a d j . pH  30 g / 1 N a S 0 i t NaOH t o a d j . pH 2  (Pb) (mg/1)  pH  (Pb) (mg/1)  PH  (Pb) (mg/1)  9.8 2.9 2.7 2.6 2.5 2.4 2.3  0.0 1.7 1.6 1.4 1.3 1.1 0.8  9.8 3.2 2.9 2.8 2.7 2.6 2.5  0.0 4.2 3.5 2.7 2.0 1.7 1.4  12.0 3.4 2.9 2.6 2.5 2.4 2.3  0.0 5.0 5.0 4.3 3.3 3.0 2.3  T h e e l e c t r o l y t e s were r e c i r c u l a t e d w i t h o u t a p o t e n t i a l a p p l i e d . A p o t e n t i a l was a p p l i e d b e f o r e t h e e l e c t r o l y t e s e n t e r e d t h e c e l l . * M e a s u r e d on a s a m p l e d i l u t e d b y a f a c t o r o f 1 0 . :  2  1--8  pH  2  0.0 2.7 1.7 1.7 0.7  1--6  30 g / 1 N a S 0 i t NaOH t o a d j . p H 2  pH  (Pb) (mg/1)  7.0 2.5 2.22.0 1.9 1.8  0.0 3.4 3.0 2.3 2.2 2.0  RUN Membrane: I = 10 A  IONAC M C - 3 4 7 0 c d . = 526.3 A / m  2  K Electrolytes Anolyte  Catholyte  Concentration  25 g / 1  0 15 30 45 60 75 90  6.4  16*  ° a (fi cm)  6.0 6.0 5.7 5.4 5.2 5.0 5.0  6.4 7.9 9.0 10.5 11.5 12.0 12.7  l  pH 9.41  pH  AV (V)  X  3  (n  NaOH  K  t (min)  x 10 _ i cm)  e  5 g / 1 N32S01+ NaOH t o a d j u s t  1-9  12.6*  Phenol  3  e  1  P  a  9.41 3.00 2.80 2.70 2.63 2.58 2.54  (mg/1) 104 55 42 33 27 19 11  T.O.C. (%)  47 60 68 74 82 89  (mg/1) 80 74 72 71 70 68 67  (Pb)  (%)  8 11 13 14 15 16  (mg/1)  2.2 1.7 1.5 0.9 0.3 0.3  RUN Membrane: I = 10 A  IONAC M C - 3 4 7 0 a g a i n s t c . d . = 526.3 A / m  polypropylene screen  2  K Electrolyte Anolyte  Catholyte  x 10 e (ft cm)  Concentration 5 g / 1 Na2S0i+ NaOH t o a d j u s t 25 g / 1  t (min)  AV (V)  0 15 30 45 60 75 90 105 120  12.9 15.0 16.0 16.0 15.0 14.0 14.0 13.5 13.5  P  6.4  H  9.44  14*  xlO  12.7*  (ft a cm) _  T.O.C.  Phenol  3  e  6.4 8.1 9.4 11.0 12.0 12.5 13.0 13.5 14.0  3  pH  NaOH  K  Comments:  2-1  1  pH  a  (mg/1)  9.44 3.04 2.80 2.67 2.58 2.52  102.0 51.0 29.0 9.0 1.0 0.0  r  2.48 2.42  The p o l y p r o p y l e n e s c r e e n p r o d u c e s saran screen.  (%)  50 71 91 99 100  (Pb)  (mg/1)  (%)  (mg/1)  78  0  72  8  0.0 0.2 0.1  67  14  0.1  65  16  0.1  62  21  0.0  a h i g h e r p o t e n t i a l drop compared w i t h  the  RUN 2 - 2 Membrane: I = 10 A  IONAC M C - 3 4 7 0 a g a i n s t c d . = 526.3 A / m  saran  screen  2  K  x 10 - i (fi cm)  pH  6.5  9.42  3  e  Electrolyte Anolyte  Catholyte  Concentration 5 g/1 Na S0i NaOH t o a d j u s t 2  25 g / 1  t  pH  NaOH  K  14*  xlO  t (min)  AV (V)  a ($2 cm)  0 15 30 45 60 75 90 105 120  8.0 8.0 8.0 7.9 7.5 7.3 7.1 7.0 7.0  6.5 7.8 8.8 9.5 10.5 11.0 11.5 12.0 12.0  12.6*  Phenol  3  T.O.C.  (Pb)  e  1  P  a  9.42 3.12 2.9 2.82 2.75 2.68 2.60 2.58 2.56  (mg/1) 100 45 25 11 5 2 0  (%) 55 75 89 95 98 100  (mg/1)  (%)  77 72 70 68 66 65 64 63 61  6 9 13 14 16 17 18 21  (mg/1) 0.0 0.2 0.1 0.1 0.0 0.0 0.0  RUN  2-3  Membrane: IONAC M C - 3 4 7 0 1 = 0 (no c u r r e n t a p p l i e d )  Electrolyte Anolyte  Catholyte  Concentration 5 g / 1 N32S01+ NaOH t o a d j u s t 25 g / 1  0 15 30 45 60 75 90  Comments:  AV (V) 0.8 0.75 0.7 0.01  x 10  (ft cm) 6.5  3  pH 9.47  pH  NaOH  K t (min)  K  14*  xlO  12.7*  3  Phenol  T.O.C.  (Pb)  (mg/1)  (mg/1)  (mg/1)  95 95 95 95 95 95  73 73 73 73 73 73  0.0 0.5 0.7 1.0 1.2 1.5 2.0  e  (ft a cm)  P a  6.5 5.7 6.1 6.3 6.6 6.6 6.6  9.47 10.74 11.22 11.47 11.64 11.8 11.9  H  No a p p r e c i a b l e c h a n g e i n p h e n o l o r T . O . C . c o n c e n t r a t i o n was d e t e c t e d , b u t w h i l e t h e f i r s t 31 w e r e w i t h d r a w n ( t o p u r g e t h e s y s t e m ) , t h e s o l u t i o n showed t h e b r o w n i s h c o l o u r c h a r a c t e r i s t i c o f t h e o x i d a t i o n of phenol.  RUN Membrance: I = 3 A  IONAC M C - 3 4 7 0 c d . = 157.9 A / m  2-4  2  K  x  10 - i (ft cm)  pH  6.2  9.44  3  e  Electrolyte Anolyte  Concentration 5 g / 1 Na S0i+ NaOH t o a d j u s t 2  Catholyte  25 g / 1  NaOH  K t [min)  AV (V)  0 15 30 45 60 75 90 105 120 135 150  4.7 4.7 4.7 4.5 4.5 4.5 4.5 7.9 7.9 7.7 7.5  Note:  -  pH 15*  xio  e 3  (ft  cm) 6.2 7.0 7.2 7.2 8.0 9.0  12.6*  Phenol  3  -1  p H  a  9.44 11.70 11.77 11.82 11.83 11.84 11.88 3.38 3.00 2.80 2.73  (mg/1) 100 83 68 58 53 49 43 18 6 2 0  T.O.C. (%)  (mg/1)  _ 17 32 42 47 51 57 82 94 98 100  C u r r e n t was c h a n g e d t o 10 A a t 90 m i n t o o b s e r v e pH r e s p o n s e . i n t e r v a l t h e s o l u t i o n had a b r o w n - r e d d i s h c o l o u r and a f t e r the changed to l i g h t y e l l o w .  77 76 73 70 66 64 63 58 44 40 37  (Pb) (%)  (mg/i;  1 5 9 14 17 18 25 43 48 52  0.1 0.4 0.4 0.4 0.4 0.4 0.4 . 0.4 0.3 0.2 0.2  D u r i n g the pH d r o p t h e  h i g h pH colour  RUN 2 - 5 Membrane: I = 6 A  IONAC M C - 3 4 7 0 c . d . = 315.8 A / m  2  K Electrolyte Anolyte  Catholyte  ,  Concentration 5 g / 1 Na SOi+ NaOH t o a d j u s t  6  6.2  15*  xlO  t (min)  AV (V)  a (ft cm)  0 15 30 45 60 75 90 105 120  5.8  6.2  5.7  6.5  5.6  7.1  5.5  8.3  5.5  8.5  pH 9.42  pH  NaOH  K  3  N - l  (ft cm)  2  25 g / 1  x 10  12.6*  Phenol  3  T.O.C.  e  L  p H  a  9.42 3.74 3.50 3.21 3.05 2.88 2.80 2.78 2.76  (mg/1) 85 49 28 19 12 7 5 2 0  (%)  (mg/1)  42 67 78 86 92 94 98 100  65 62 59 56 54 53 53 52  4 7 10 14 17 18 18 20  KJ OO  RUN 2 - 6 Membrane: I = 20 A  IONAC M C - 3 4 7 0 c d . = 1052.6 A / m  2  K Electrolyte Anolyte  Concentration 5  Na S0it  g/1  0.44  2  g/1  Catholyte  25 g / 1  (min)  ... AV (V)  0 15 30 45 60 75 90 105 120  12.7 12.4 9.7 8.9 8.7 3.4 8.2 7.9 7.8  x  10  3  (ft cm)  PH  8.5  2.45  H2SO4  NaOH  K  14*  e  xlO  a (ft c m ) 8.5  12.7*  3  Phenol  T.O.C.  1 _ 1  P  a  2.45  12.5  1.80  15.5  1.67  17.0  1.58  17.5  1.50  .  (mg/1) 105 24 5 2 1 0  (%)  77 95 98 99 100  (mg/1) 81 81 80 78 72 66 59 52 42  0 1 4 11 18 27 36 48  RUN 2 - 7 Membrane: I = 10 A  IONAC M C - 3 4 7 0 c . d . = 526.3 A / m  2  K  x 10 - i (ft cm)  3  e  Electrolyte Anolyte  Concentration 5 g / 1 Na S0i+ 0.44 g/1 H S0it  8.3  2  pH 2.46  2  Catholyte  25 g / 1 NaOH  K  14*  xlO  e  t (min)  AV (V)  (ft cm)  0 15 30 45 60 75 90 105 120  7.5  a  12.7*  Phenol  3  -1  P a  (mg/1)  8.3  2.46  6.7  10.5  1.96  6.3  12.5  1.81  100 30 8 4 2 0  6.0  14.0  5.9  15.0  T.O.C. (mg/1)  <%:  75  0  74  1  74  1  1.72  72  4  1.66  67  11  R  (%) 0 70 92 96 98 100  RUN Membrane: I = 10 A  NAFION 127 c d . = 526.3 A / m  2  K Electrolyte  5 g/1 Na S0ix 0 . 4 4 g / 1 NaOH  Catholyte  25 g / 1  NaOH  t (min)  AV (V)  0 15 30 45 60 75 90 120 150  5.3  a  (ft cm) 8.0  12.6*  Phenol  3  -1  p H  a  5.5  9.0  12.03 2.1 1.8  5.2  11.0  1.54  5.1 5.0 4.9  13.0 14.5 15.0  1.38 1.29 1.26  C o l o u r change observed  PH 12.03  14*  xlO  e  3  8.0  2  K  Note:  x 10 e (ft cm)  Concentration  Anolyte  2-8  (mg/1) 95 53 20 7 3 1 0  from brown r e d d i s h  T.O.C. (%)  44 79 93 97 99 100  t o y e l l o w when t h e  (mg/1)  (%)  76 75 74  1 3  73  4  70 67 66  8 12 13  pH  dropped.  RUN 2 - 9 Membrane: I = 20 A  NAFION 127 c . d . = 1052.6 A / m  2  K Electrolyte  Concentration  Anolyte  5 g/1 Na2S0LL 0 . 4 4 g/1 H S 0 t 2  Catholyte  x 10  (ft cm) 8.2  3  PH 2.48  t  25 g/1 NaOH  15*  K t (min)  AV (V)  0 15 30 45 60 75 90 105 120  8.5 7.5 6.8 6.4 5.9 5.5 5.5 5.5 5.5  xio^ a _ (ft cm)  12.7*  Phenol  T.O.C.  e  1  8.2  P  a  2.48  12.5  1.7  15.0  1.67  16.5  1.64  17.5  1.62  (mg/1)  (%)  102 37 4 1 0 0  64 91 98 100 100  (mg/1) 85 84 82 77 72 67 63 58 53  (%)  1 3 9 15 21 26 32 38  to  RUN 2 - 1 0 Membrane: I = 20 A  NAFION 127 c . d . = 1052.6 A / m  2  K x IO , - l (ft cm) 3  e  Electrolyte  Concentration  Anolyte  5 g/1 Na S0i 5 g / 1 NaOH  Catholyte  25 g / 1 NaOH  2  t  K t (min)  AV (V)  0 15 30 45 60 75 90 105 120 135 150  3.9 3.9 4.9 5.0  Comments:  5.0 5.0 5.0 5.0 5.0 5.0  xlO a _ (ft cm)  pH  30  12.84  15*  12.7  3  6  1 1  p  H  a  Inorg. Carbon (mg/1)  T.O.C. (mg/1)  (%)  0 2 4 8 5 2 3  82 80 78 74 67 60 52  2 5 10 18 26 37  1.28  43  0  43  48  1.26  39  0  39  52  12.84 12.66 12.54 12.24 2.15 1.56 1.40  13.5 14.0  electrolyte  102 92 69 36 15 3 0  Total Carbon (mg/1) 82 82 82 82 72 62 55  30.0 23.5 17.0 11.0 7.0 9.5 11.0  The c o l o u r o f t h e was p r o d u c e d .  Phenol (mg/1) (%)  changed  0 10 32 65 85 97 100  from brown r e d d i s h  t o y e l l o w when t h e  pH d r o p  RUN Membrane: I = 20 A  IONAC M A - 3 4 7 5 ( a n i o n i c ) c . d . = 1052.6 A / m 2  K Electrolyte  Concentration  Anolyte  5 g/1 Na S0ii 0 . 4 4 g / 1 H^SOtt  Catholyte  25 g / 1  x 10 e (ft .cm)  2  NaOH  K  x  AV  (min)  (V)  (ft cm)  0 15 30 45 60 75 90 120 150  7.7  8.0  7.6  8.1  7.4  8.2  7.1 7.0 6.6  8.3 9.5 10.0  e  3  pH  8  2.4  15*  12.7*  10^  t  Comment:  2-11  a  .  _ P  Phenol a  2.40 2.80 3.15 8.33 11.20 11.75 12.08 12.38 12.53  The a n i o n i c membrane showed  (mg/1) 94 26 9 4 2 0  (%) 0 72 90 96 98 100  Carbon Total 78 78 78 78 78 78  a change i n c o l o u r  (mg/1)  Inorg. 0 2 3 7 18 33 45 52 60  (from y e l l o w t o brown)  T.O.C. 78 76 75 71 60 45 33 26 18  after  0 3 4 9 23 42 58 67 77  the  run.  RUN  Electrolyte  1(A)  5 g / 1 Na2S0it NaOH t o a d j u s t  t (min) 0 15 30 45 60 75 90 120  c.d.  10  (A/m  2  3-1  )  526.3  pH  AV (V) 9.7 10.5 9.7 9.1 8.9 8.7 8.5 8.5  K '  x  10  e cm) (ft 6.2 6.5 6.7 6.8 6.9 6.9 7.0 7.0  Phenol  3  H  (mg/D  9.46 3.78 3.62 3.52 3.46 3.42 3.39 3.36  110 60 40 19 9 3 1 0  P  T.O.C. (%)  45 64 83 92 97 99 100  (mg/1) 84 80 78 77 75 71 67 60  (%:  5 7 8 11 15 20 29  RUN 3 - 2  Electrolyte  1(A)  5 g / 1 Na SOtx 0 . 4 4 g / 1 NaOH  c d .  10  2  t (min)  AV (V)  0 15 30 45 60 75 90 120  6.5 6.4 6.3 6.3 6.3 6.4 6.5 6.6  (A/m  2  )  526.3  K  x 10 -1 (ft cm)  Phenol  3  Carbon  (mg/1)  6  8.0 7.5 7.2 7.0 6.9 6.8 6.8 6.7  pH 11.98 11.88 11.81 11.72 11.67 11.58 11.57 11.54  (mg/1)  (%)  106 71 52 34 18 12 9 5  33 51 68 83 89 92 95  Total 81 81 81 81 81 81 81 81  Inorg.  T .O.C.  % T.O.C.  0 5 7 8 10 13 18 26  81 76 74 73 70 68 63 55  7 9 10 13 16 22 32  RUN  Electrolyte  1(A)  5 g / 1 Na2S0i+ 0.44  g/1  c d .  10  (A/m  3-3  )  526.3  H S0LL 2  t (min)  AV (V)  0 15 30 45 60 75 90 120 150  7.8 7.3 7.2 6.9 6.7 6.5 6.4 6.4 6.4  A T 7  K  x 10 e (ft c m ) " 8.4 8.6 8.8 8.9 8.9 8.9 8.9 8.9 8.9  Phenol  3  1  pH  (mg/1)  2.50  93 28 12 4 2 1 0  2.45 2.43 2.41 2.39 2.38  T.O.C. (%)  70 86 95 98 99 100  (mg/1) 75 75 74 71 69 68 65 61 56  (%)  0 1 5 7 9 13 19 25  RUN  Electrolyte  1(A)  5 g / 1 Na2S0ix 0 . 4 4 g / 1 H2SO11  t (min) 0 15 30 45 60 75 90 120 150  (Pb)" =  20  c d .  (A/m  )  1052.6  AV (V)  K x 10 (ft c m )  9.6 9.7 9.2 8.4 8.2 8.2 8.2 9.3 10.7  8.5 9.1 9.2 9.2 9.2 9.3 9.4 9.5 9.6  undetectable.  3-4  T  3  - 1  Phenol  pH  (°c)  (mg/D  2.47 2.28 2.28 2.27 2.25 2.24 2.22 2.20 2.19  23  95 23 10 3 2 1 0  25 26 27 28 28  T.O.C. (%)  75 89 97 98 99 100  (mg/1)  (%:  73 71 68 64 59 54 47 34 23  3 7 12 19 26 36 53 68  RUN  Electrolyte  1(A)  5 g / 1 Na S0i+ 0 . 4 4 g / 1 NaOH 2  t (min) 0 15 30 45 60 75 90 120 150  AV (V) 9.2 9.1 8.9 8.9 9.0 9.4 10.4 11.4 12.0  c d .  20  (A/m  3-5  )  1052.3  K  e  (a  x  io  cm) 8.2 7.9 7.7 7.5 7.2 7.1 7.1 7.1 7.0  3  pH 12.04 11.91 11.76 11.56 11.26 10.76 10.26 9.56 8.84  T (°C) 24 25 26 27 28 28  Phenol (mg/1) 102 48 26 12 3 0  (%)  53 75 88 97 100  Carbon Total 86 84 84 84 84 84 84 83 81  (mg/1)  Inorg.  T,. O . C .  (%)  0 6 13 22 30 37 46 60 62  86 78 71 62 54 46 38 23 19  0 9 17 28 37 46 56 73 78  (Pb) (mg/1] 0.0 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.0  RUN 3 - 6  _Electrolyte  1(A)  5 g / 1 NaaSOit 0.44  g/1  t (min) 0 15 30 45 60 75 90 120  (Pb):  c.d.  30  _2 (A/m )  1578.9  H2SO4  AV (V) 14.0 11.9 11.6 11.4 13.0 14.0 15.0 15.5  undetectable  K  x 10 e cm) (ft 8.6 8.9 9.1 9.3 9.5 9.6 9.7 9.8  Phenol  3  pH  T (°C)  2.48 2.40 2.36 2.32 2.30 2.28 2.26 2.25  24 26 28 29 31 33 34 36  (mg/1) 96 20 4 1 0 0  T.O.C. (%)  79 96 99 100 100  (mg/1)  (%)  76 71 68 61 47 37 28 24  7 11 20 38 51 63 69  RUN 3-7  Electrolyte  1(A)  5 g / 1 Na SOL 0 . 4 4 g / 1 NaOH 2  t (min) 0 15 30 45 60 75 90 120  [Pb]:  f  AV (V)  c.d.  30  (A/m  )  1578.9  K  x 10 e (ft cm)  11.9 10.7 10.4 10.5 12.9 13.4 13.5 13.6  undetectable  8.1 7.6 7.2 7.3 7.0  Phenol  3  pH 12.08 ' 11.97 11.80 11.47 10.80 10.43 10.18 9.5  T (°C) 23 25 26 28 29 31 32 35  (mg/1) 110 36 12 1 0  Carbon (%)  0 67 89 99 100  Total 86 74 61 48 32 25 16 7  (mg/1)  Inorg.  T.O.C.  (%:  0 10' 22 35 51 58 64 73  86 74 61 48 32 23 16 7  0 14 29 44 63 73 81 92  RUN  Electrolyte 5 g/1 Na SOi 2  0.44  g/1  1(A)  c d .  10  +  (A/m  3-8  )  526.3  H S0LL 2  K  10 -1 (ft cm) x  Phenol  3  t (min)  AV (V)  0 15 30 45 60 75 90 120  4.5  30.5  2.5  4.2  31.0  2.44  4.1  31.5  2.42  4.1 4.1  31.5 31.5  2.40 2.38  pH  (mg/1) 108 33 13 5 1 0  T.O.C. (%) 0 70 88 95 99 100  (mg/1)  (%:  83 80 79 77 72 68 67 61  0 4 5 7 13 18 19 27  RUN  Electrolyte  1(A)  5 g / 1 Na S0i+ 0 . 4 4 g / 1 NaOH  c.d.  10  2  AV  (A/m  3-9  )  526.3  K  e  X  1  0  Phenol  3  (min)  (V)  (ft c m ) "  0 15 30 45 60 75 90 120 150  4.6 4.6 4.6 4.6 4.6 4.6 4.6 4.6 4.6  32 32 32 32 32 32 32 32 32  1  pH 12.06 11.88 11.81 11.64 11.41 10.96 10.36 9.24 7.7  (mg/1) 105 72 48 38 18 7 1 0  Carbon (%)  31 54 64 83 93 99 100  Total 80 80 80 80 80 80 80 80 72  (mg/1) Inorg.  T.O.C.  0 2 5 8 14 20 27 40 45  80 78 75 72 66 60 53 40 27  (%) 0 3 6 10 18 25 34 50 66  RUN  Electrolyte 30 g / 1 N32S01+ 0.44 g / 1  1(A)  3-10  c . d . (A/m 1052.6  20  10 - i (ft cm)  PH  T (°C)  6.6  32  2.46  25  6.1  32  2.42  25  6.0  32  2.40  26  6.2 6.4 6.7  32 32 32  2.38  28  2.36  28  t (min)  AV (V)  o' 15 30 45 60 75 90 120 150  K  x  3  e  Phenol (mg/1) 98 20 7 3 1 0  T.O.C. (%) 0 80 93 97 99 100  (mg/1) 80 77 75 70 65 58 54 40 28  (%: 0 4 6 13 19 28 33 50 65  RUN  1(A)  Electrolyte 30 g / 1 N32S01, 0 . 4 4 g / 1 NaOH  c d . (A/m  20  3-11  )  1052.6  x 10 e (ft cm)  K  Phenol  3  t (min)  AV (V)  0 15 30 45 60 75 90 120 150  4.4  32.0  12.03  4.4  31.5  11.93  4.5  31.0  11.70  4.6 4.7  30.5 30.0  11.16 10.42  pH  (mg/1) 113 54 29 14 3 0  Carbon (%) 0 52 74 88 98 100  Total 87 87 87 87 87 87 87 87 87  (mg/1) s  Inorg.  T.O.C.  0 7 13 22 32 40 51 65 70  87 80 74 65 55 47 36 22 17  (%)  8 15 25 37 45 59 75 80  RUN 3 - 1 2  Electrolyte  KA)  5 g/1 N a S 0 0 . 4 4 g / 1 H2S0I+ 2  t (min)  10  4  AV (V)  -2. (A/m )  c.d.  526.3  K  e (ft  x 10  Phenol  3  s-1  pH  (mg/1) 525 320 175 75 25 15 5 0  cm) 0 15 30 45 60 75 90 120  8.7  8.0  2.43  8.6  8.7  2.25  8.5  9.3  2.18  8.2 7.8  9.3 9.3  2.16 2.14  T.O.C. (%)  0 39 67 86 95 97 99 100  (mg/1)  (%:  395 380  4  375  5  370 350  8 11  RUN  Electrolyte  KA)  5 g/1 Na S0Lj g/1  526.3  H2S01+  t (min)  AV (V)  0 15 30 45 60 75 90 120  9.3  Comment:  _2 (A/m )  c.d.  10  2  0.44  3-13  K  x 10 e (ft cm)  Phenol  3  pH  (mg/1)  8.7  2.42  8.3  8.9  2.32  8.0  8.9  2.28  7.9 7.8  9.1 9.2  2.27 2.26  1100 792 506 341 187 88 22 5  1  (%) 0 28 54 69 83 92 98 100  The n e t c h a n g e i n T . O . C . was p r a c t i c a l l y u n d e t e c t a b l e due t o t h e h i g h amount o f c a r b o n p r e s e n t i n s o l u t i o n .  RUN 3 - 1 4  KA)  Electrolyte 5 g / 1 Na SOi+  10  2  2.2  g/1  _2 (A/m )  c.d.  526.3  H2S01+  t (min)  AV (V)  0 15 30 45 60 75 90 120  5.4 5.2 5.1 5.0 4.9 4.9 4.9 4.9  K  x 10 - i (ft cm)  Phenol  3  T.O.C.  e  13.5 13.7 14.0 14.2 14.3 14.5 14.5 14.5  pH 1.8 1.78 1.75 1.75 1.75  (mg/1) 90 30 9 3 1 0  <%)  67 90 97 99 100  (mg/1) 77 74 73 72 69 68 66 64  (%:  4 5 6 10 12 14 17  RUN 3 - 1 5  Electrolyte  c.d.  1(A)  5 g / 1 NaaSOi, 0 . 4 4 g / 1 H S0i+  20  (A/m  )  Q (£/min)  1052.6  0.55  P(Kpa) 145  2  t (min) 0 15 30 45 60 75 90 120  .„ AV (V)  K  x 10 e (ft cm)  1  Phenol  3  pH  (mg/1) 105 28 9 2 1 0  12.1  8.3  2.5  10.5  8.5  2.43  10.9  8.7  2.40  11.1 12.0  8.8 8.9  2.38 2.37  T.O.C. (%)  0 73 91 98 99 100  (mg/1)  (%)  79 74 71 69 62 55 48 36  0 6 10 13 22 30 39 54  RUN  K Electrolyte 5 g / 1 Na S0i4 2  0.44  g/1  1(A) 10  c.d.  (A/m~ ) 2  526.3  4-1  6  x 10  (ft c m ) " 7.9  3  1  pH 2.5  T. in (°C) 24  Phenol C  ( r a i n  g  100  H2SO4  Q (Jo/min)  AV (V)  P (kPa)  T °™  0.11 0.25 0.40 0.55 0.85 1.10  8.7 8.6 8.3 7.9 7.4 7.1  108 120 129 143 184 232  32 28 26 25 24 24  C „  Phenol (mg/1)  9 42 55 67 75 79  / : L )  (%)  91 58 45 33 25 21  RUN 4 - 2  K Electrolyte  1(A)  5 g / 1 N32S04 0.44 g/1 H S0i 2  10  c d .  (A/m~ ) 2  x IO  3  (ft. c m ) "  1  6  526.3  8.1  T. in (°C)  pH 2.5  Phenol C  24  i n  (  m  g  105  t  Q (A/min)  AV (V)  P (kPa)  0.25 0.40 0.55 0.85 1.10 1.30  8.6 8.5 8.3 7.8 7.3 7.0  119 129 143 184 232 280  T C  27 26 25 25 24 24  Phenol (mg/1)  (%)'  43 60 71 80 85 90  60 44 34 26 21 17  /  RUN  4-3  K Electrolyte  1(A)  5 g / 1 UazSOn 0 . 4 4 g / 1 H S0i+  10  c d .  (A/m" ) 2  g  x IO  T  3  (ft c m ) " )  pH  1  526.3  8.0  Phenol  (°C)  2.5  C  in  (  n  23  AV (V)  P (kPa)  0.250 0.400 0.550 0.850 1.100 1.300  8.7 8.6 8.3 7.9 7.4 7.1  108 120 129 143 184 232  T  Phenol  (°C) 27 25 24 24 23 23  C  out  (  m  39 53 63 72 76 81  g  /  1  )  g  95  2  Q U/min)  i  (  %  59 44 34 24 20 17  )  /  1  )  RUN  K Electrolyte  1(A)  5 g/1 N a S 0 0 . 4 4 g / 1 H S0i+ 2  10  4  c.d.  (A/m" ) 2  4-4  x 10  3  (ft c m ) "  1  g  526.3  8  T  Phenol  pH  (°C)  2.45  23  c  ^ s/^) lA  ±a  580  2  Flow U/min)  AV (V)  P (kPa)  0.11 0.25 0.40 0.55 0.85 1.10  8.7 8.6 8.3 7.9 7.4 7.0  108 120 129 143 184 234  T  Phenol  (°C) 31 27 26 25 23 23  C  out 8 > ( m  / 1  175 365 435 470 510 526  ( % )  70 37 25 19 12 9  RUN 4 - 5  K Electrolyte  1(A)  5 g / 1 Na S0 0.44 g / 1 H S0it 2  20  k  c d .  (A/m" ) 2  1052.6  g  x 10  (ft c m ) " 7.9  T  3  1  Phenol  pH  (°C)  2.43  24  C  in  (  m  g  ^  110  2  Q (4/min)  .11 .25 .40 .55 .85 1.10  AV (V)  13.4 13.4 13.3 12.6 11.5 10.8  P (kPa)  T ™\  110 122 129 145 185 234  48 38 32 27 26 25  C  Phenol Amg/1) (%)  7 40 62 73 80 90  94 63 44 34 27 19  RUN 4 - 6  K Electrolyte  KA)  5 g / 1 Na S0i+ 0 . 4 4 g / 1 NaOH  20  2  Q (£/min)  0.11 0.25 0.40 0.55 0.85 1.10  AV (V)  12.2 11.8 11.3 10.8 10.1 9.7  c.d.  _2 (A/m )  x 10 - i (ft cm)  pH  T. in (°C)  7.9  2.45  24  3  e  1052.6  P (kPa)  110 121 129 145 185 234  T  out (°C) 48 38 30 27 25 24  C  out  C  Phenol (mg/1)  56 260 335 390 430 450  Phenol (mg/1) in 515  (%)  89 49 35 24 16 12  H  1  RUN 4 - 7  K Electrolyte  1(A)  5 g / 1 N32S04 0 . 4 4 g / 1 H2S01+  Q (£/min)  0.11 0.25 0.40 0.55 0.85 1.10  Note:  10  c d .  (A/m~ ) 2  g  x IO  (ft c m ) "  523.6  AV (V)  P (kPa)  5.9 5.9 5.9 5.9 5.9 5.9  110 115 115 115 115 115  8.1  T  3  1  (°C)  2.43  25  C  Phenol  n  pH  T  30 28 27 26 25 25  i  C  Phenol (mg/1)  68 87 98 100 103 106  i n  (  m  g  110  (%)  38 21 11 9 6 4  The a n o d e u s e d was t h e f e e d e r p l a t e o n l y ( r e f e r t o g e n e r a l specifications). T h e r e f o r e , t h e p r e s s u r e was p r a c t i c a l l y c o n s t a n t a t 115 K p a .  /  RUN  4-8  K Electrolyte  KA)  5 g / 1 Na SOi+ 0 . 4 4 g / 1 H SOi+  10  2  c d .  -2 (A/m )  x  10 - i (ft cm)  T.  3  e  8.0  526.3  H  (°C)  2.43  24  P  Phenol C  i n  (  m  g  /  1  )  100  2  Q (Jo/min)  AV (V)  P (kPa)  «.  T  out  (°c) 0.11 0.25 0.40 0.55 0.85 1.10  Note:  6.3 6.0 5.9 5.8 5.7 5.6  112 128 143 162 204 271  31 28 27 26 25 25  C  out  Phenol (mg/1)  (%)  5 33 47 55 66 71  95 67 53 45 34 29  T h i s run corresponds to the s m a l l e r p a r t i c l e s i z e F o r bed d a t a r e f e r t o g e n e r a l s p e c i f i c a t i o n s .  (0.7  < dp < 1.1  mm)  158  APPENDIX 3  Mathematical Models The electrochemical oxidation of phenol i s a heterogeneous process that takes place on the surface of the anode.  A s i m p l i f i e d picture of  the process i s that the disappearance of phenol i s the r e s u l t of  two  steps which occur i n s e r i e s : a)  the transfer of phenol molecules or phenoxonium ions from the bulk of the s o l u t i o n to the surface c f the electrode  b)  an electrochemical reaction by which the phenol i s converted  into  some oxidation products as discussed i n Chapter 2. Two  l i m i t i n g cases are considered  i n which either of the two  are so slow that they control the o v e r a l l rate of the process.  steps  Such  models assume that adsorption phenomena and transfer of oxidation products from the electrode surface are not r a t e - l i m i t i n g .  A t h i r d case i s also  presented where both the resistance to mass transfer and to e l e c t r o chemical reactions are comparable i n magnitude.  1.  Mass transfer controlled model The model presented here deals with a packed bed  electrochemical  reactor operating continuously i n plug flow. Assumptions - The resistance to the electrochemical reaction i s n e g l i g i b l e compared with the resistance to mass t r a n s f e r .  In other words, the concen-  t r a t i o n of phenol at the surface of the electrode i s n e g l i g i b l e  159 compared w i t h t h e Variations  concentration of phenol i n the  i n phenol concentration  the  flow  are  neglected  the  d i r e c t i o n of  All  the bed  is  compared  i n the  to  bulk of  directions  the v a r i a t i o n s  the  solution.  perpendicular  to  of concentration  in  flow.  active  for phenol  oxidation.  Mass b a l a n c e  for  a differential  height.  Q,C Q dC  = - K  A  b  a(S W dy)(C  -  D  11  )  The s u p e r f i c i a l v e l o c i t y r e f e r r e d cross  sectional  area of the  [A.l]  " s  bed i s  to  the  giver.  by: u = Q/W S Neglecting  ,  ( E q . A . l ) c a n be  expressed  s  Q,C Fig.A-1 Plug-flow packed bed reactor d  c  K = _ .3  .  a dy u  C  i  A.  integrating,  c (y) dC A  K  m  a dv u  A  In  l  C.(y) A '  K a v m  which can a l s o  and  [ A . 2]  u be e x p r e s s e d  _  Aj _  i n terms o f the  _  A _  2  A — 2  -  1 -  fractional  conversion X,  for  [ A . 3]  160 then, K a L Jon(l - X ) = - - 5 L  The s p e c i f i c surface  surface  area of the  area of the feeder  particles,  as  where 5 i s  a shape f a c t o r  voids  bed i s  plate plus  for  the  [A.4]  g i v e n by the  the  specific  particles,  and  surface  e is  correlation  by P i c k e t t  coefficient  and S t a n m o r e  K dp -2=— =  equation  (45)  as  (u dp 0 . 56  0.83  was d e v e l o p e d  experimental It  included  s h o u l d be n o t e d  the  fraction  of  1/3  V  [A.6]  IJ layer  that  the  Studies  effect  by gas  For the  present  mass t r a n s f e r  i n gas  It  case of  the  literature.  However,  of  the  mass t r a n s f e r  coefficient  circulation.  evolution is  o f mass t r a n s f e r  was  found  forced  (47),  on but  that  the  not  gas-evolving for  electrolyte  convection,  evolving particulate  convection,  correlated  the  case of  i n the  cell  r a t e o f mass  is  trans-  evolution.  in  than i n free  o f s p h e r e s and  o f gas  motion of the  bubbles.  increased  23 < Re < 520  ± 10%.  s o l u t i o n where the  o n l y p r o v i d e d b y gas was  A.6.  the  follows,  e l e c t r o d e s h a v e b e e n made r e c e n t l y  a stationary  ical  area of  v  using a single  data within  i n equation  packed bed  fer  specific  c a n be e s t i m a t e d u s i n g  for  the  the  the  (49). The a v e r a g e mass t r a n s f e r  This  sum o f  since  it  e l e c t r o d e s could not  i s reasonable to due  the  to  a correlation  expect  gas b u b b l i n g i s  electrolyte  that less  be  for found  enhancement significant  i s m a i n l y moved b y  mechan-  161 2.  Electrochemical reaction  c o n t r o l l e d model  Assumptions -  The r e s i s t a n c e tration  electrochemical  of phenol at  centration -  to  at  the  surface  the b u l k of  The o x i d a t i o n r e a c t i o n  the  is  reaction of  the  is  so h i g h t h a t  particles  is  the  equal  to  concenthe  con-  solution.  assumed  t o be f i r s t  order  i n phenol  concen-  tration. -  The  electrode  This assumption reality the  t o be u n i f o r m a l l o v e r t h e  a significant  s i m p l i f i c a t i o n because  distribution  exists  indicated  length  of  in Fig.  the  anode,  the  in  along  distribution  A-2.  PACKED BED.ANODE  k  1  -• OO )  i  ma  K  m = i  s  e  e  s  m  d<f> o -r^ dx — dx  + i  m  The p o t e n t i a l  7?  in  UJ  =-K  s L  the  . distribution  x direction  origin-  j  O  0  0.  ates because the at  x=0 A-2.  w i t h i n and  potential  i  Fig.  cell.  (10).  CURRENT FEEDER '  assumed  potential  a differential  w o u l d be as  is  represents  an e l e c t r o d e  electrode In  potential  Potential distribution particulate electrode.  X=SQ in  a  a central  both  total  x is  the m e t a l  and  charge  carried the  by  solution.  162 The t o t a l the  feeder  plate  charge  but  at  at  x = 0 is  x = S  the  entirely  current  c a r r i e d by t h e m e t a l  is entirely  c a r r i e d by  of  the  3.  solution. gradient of  the  This implies that at  x = 0 and t h e  curves  than  line.  that  tial  than  V * = <> j T  -  to  is  indicated  z e r o and i s  therefore  the metal p o t e n t i a l  m  tends to  increase  the  but  drop.  Thus,  feeder  has  been  towards  x = S .  to o c c u r at  developed  the  For the  (48)  the  for  greater drop would  electrode  poten-  T h i s means t h a t  current,  a concentric  cell.  affecting  case where  the  t h e mass b a l a n c e Q dC %  The e l e c t r o c h e m i c a l r e a c t i o n potential  poten-  horizontal  i s much  edge o f t h e  solution involved is  exists within  of a l l the v a r i a b l e s  step,  figure,  the  packed  bed  electrode.  the mathematical  trode p o t e n t i a l  limiting  shape  a  a r e more l i k e l y  the  the  concentration  cylindrical  a simple  is  in a differential  of c e l l  r  elec-  correla-  process.  electrochemical reaction  = - K  elec-  complicated.  some a v e r a g e  This permits  the  and  extremely  The m o d e l t o be p r e s e n t e d h e r e assumes t h a t  tion  the  solution potential  A two d i m e n s i o n a l m o d e l f o r p o t e n t i a l ,  trode,  i n the  r e p r e s e n t e d by the  s  distributions  maximum  x = S , so t h a t a  c o n d u c t i v i t y of the metal  electrolyte,  cb  side reactions opposite  the m e t a l  G e n e r a l l y , the  of the  be g r e a t e r  as  at  presents i t s  i d e a l case of a m e t a l of i n f i n i t e c o n d u c t i v i t y , the  drop through  dotted  solution potential  <> j v s x and c> j vs x are m s  In the tial  the metal p o t e n t i a l  length  the  a S W dy C A  rate is: [ A . 7]  -  coefficient  K r  is related  by d e f i n i t i o n °A A a Z  V  F  to  the  electrode  163 Under  the  assumption  of uniform electrode  potential  and C  = C s  eq.  A . 7 can be i n t e g r a t e d  , %  ( w i t h u = Q/W S ) ,  c (y) A  K  dC  a dy r  K a y  An C ( y ) A  A  A  r  [A.9]  Al  for  c  y = L  A  (y)  =  C  a n d  a)  £n(l -  Single  a L  J^A  X) = -  [A.10]  u  reaction  If  the  only reaction  o c c u r r i n g at  chemical o x i d a t i o n of phenol, electrode  Ai  K then,  = 1  x  A 2  a local  the  electrode  reaction  rate  is  the  (referred  to  A  T for  C.(y)  =  T  from e q .  r  K  C  true  current  "  K  [A.11]  ^  r  C  e A  X  i n equation A.11  a y r  ~TY~ true  (  K  A  average  A  A . 9 and s u b s t i t u t i n g  i (y)  the  the  a r e a ) w o u l d be g i v e n b y :  i (y)  Solving  electro-  A  [A.12]  p  l  density  through  the  cell  X  A  =  a"  is,  i (y) A  X  A  dy  =  dy  [A.13]  164 S u b s t i t u t i n g eq.  A.12 into  r e a c t i o n r a t e c a n be o b t a i n e d  eq.  A . 1 3 and i n t e g r a t i n g ,  increased will eq.  h o l d i n g a l l the  be l o w e r t o s u s t a i n A.8 is  average Fig.  rate,  i f the other  the  Fig  If (C. ) Al  concentration  parameters constant,  same c u r r e n t A . 1 4 , to  and t h e  electrode  the  is  the v a l u e o f  flowing.  find  of phenol  To i l l u s t r a t e  r e l a t i o n between  potential,  as  this,  the  represented  in  1  at  A-3  the  V* Schematic  initial  a constant  will  increased, also  representation  concentration  current  input,  be l o w e r , a n d t h e r e f o r e  Analogous reasoning  A.14  initial  A-3.  (V*)'  (V*)'  [A.14]  combined w i t h eq.  reaction  a u  * a L A  Equation A.14 implies that  average  as: K  A . z F X  an  or i f a i s  shows  increased  i m p l i e s t h a t when t h e  at  of  of phenol i s  the the that  eq.  increased  v a l u e of the value of K K  r  will  a constant  electrode  A.14  electrode  will  also  from C. A]  drop  potential too.  decrease i f u  applied current.  p o t e n t i a l , tends to  to  is  Equation  infinity,  the  165 C  r a t e of r e a c t i o n i ^ / z F w i l l  b)  M o r e t h a n one e l e c t r o c h e m i c a l r e a c t i o n o c c u r s a t If,  parallel  f o r example, a s i d e r e a c t i o n of water to the phenol o x i d a t i o n ,  g i v e n b y t h e sum o f t h e If  t e n d t o a maximum g i v e n b y  water  average  the average  current  e l e c t r o l y s i s i s represented  b a l a n c e w o u l d be e x p r e s s e d i  F  A  A  = i . + i A w  K  C, u Ai  a L r  1 -  1 =  a L  the  electrode  current  density w i l l  d r i v i n g each  in be  reaction.  s u b s c r i p t w, the  current  by, where  Using eq. A.14 f o r both p a r t i a l average  Z  u  e l e c t r o l y s i s occurs  densities  w i t h the  A  exp  A  z  u  i =  I/a  currents,  w  F C u w a L'  K 1 -  exp  r  a L w u [A.15]  where  K r  = K A  A  a. z V * F A A a R T  exp A A  r  a and  K r  Therefore, bed,  = K w the  exp  r w  average  c a n be r e l a t e d  where i t greater  w  z  V* F w a R T  current  to the  density,  referred  take p l a c e at  F i g u r e A-4 shows t h a t  p o t e n t i a l at which i . + i  to the  true area  e l e c t r o d e p o t e n t i a l as r e p r e s e n t e d  i s assumed t h a t b o t h r e a c t i o n s than zero.  [A.8]  = i  f o r each set  all  i n F i g . A-4,  a,  electrode L, u,  C  A w  If  the  initial  other  parameters  total  average  current  A]^  concentration of phenol i s  constant,  the  potentials  t h e r e i s o n l y one of parameters  of  increased holding  a lower value of V* w i l l  density i .  s u s t a i n the  all  same  .  v* Fig.A-4  Schematic  Analogously» means t h a t  representation  i f u or a  the values  of the  is  of  eq.  A.15  i n c r e a s e d V* s h o u l d a l s o d e c r e a s e ,  reaction rate  constants  K  and K  which  would  be  w  A lower.  3.  Mass t r a n s f e r The most  transfer  and e l e c t r o c h e m i c a l r e a c t i o n  general  case t o . c o n s i d e r  developed), transfer of  the  cell  length Q dC  area  of the  K  A  a S-W d y  = K  *b under  -  \  p r o f i l e s have  will  mass  been  r a t e o f mass  be e q u a l i n a  differential  C A  A  )  [A.l]  s [A.7]  a S W dy C.  r  A  s  steady-state, K  the  (C.  m  — Q dC.  which permits  concentration  electrode,  to  (dy),  \  Therefore,  (when t h e  i  comparable.  r a t e o f e l e c t r o c h e m i c a l r e a c t i o n and t h e  per u n i t  -  of  i s when b o t h r e s i s t a n c e s  and t o e l e c t r o c h e m i c a l r e a c t i o n a r e  Under s t e a d y - s t a t e  c o n t r o l l e d model  to express  concentration  m  (C. A, b  the  C ) = K C. A r A s s A  concentration  i n the b u l k of  at  solution,  the  surface  as  a  function  167 K  C.  *b  m  X Substituting  eq.  A.16 into  s  eq.  C (y) dC.  K  y = L,C.(y) ' A  K m r (K + K ) u r  Ai  = C  hz  J  A  a  K  K  where  the  cept of  K  overall  rate  resistances  to  electrolysis current z.  l =  eq.  K m r (K + K ) m r  a L  K  m  u  m  r + K  [A.17]  a L [A.18]  u  [A.19] r  K  applying  the  con-  [A.20] r  g e n e r a l c a s e when a s i d e r e a c t i o n o f  occurs i n p a r a l l e l given  u exp  found  as:  K m  A . 1 5 , i n the  1 -  y  K  in series  d e n s i t y w o u l d be F C.  dy  c o n s t a n t , w h i c h c o u l d a l s o be  K Analogous  integrating,  and w i t h X = 1 - — C  A n ( l - X) = -  is  a  m  K  c (y) J  J  and  ^  A  for  Q = u/W S ,  K r (K + K ) 0 m r  A  An  A . l with  y  A  C  [A.16]  (K + K ) m r  K a L u  to  phenol  oxidation,  the  total  water  average  by,  z  F C u w w a L  K 1 -  exp  r  a L w u [A.21]  168 Note that K  i s used f o r the water e l e c t r o l y s i s r e a c t i o n , since i t w  i t i s an a c t i v a t i o n c o n t r o l l e d process and would not be affected by mass transfer. C. l A  In t h i s case, an increase i n the phenol i n l e t concentration  or i n the s p e c i f i c surface area of the bed, would r e s u l t i n lower  values of previously.  (or V*) f o r a same average current density, as discussed However, an increase i n the s u p e r f i c i a l v e l o c i t y u would  r e s u l t i n increased mass transfer c o e f f i c i e n t s time, lower reaction rate constants K  4.  r  A  ,K ' r  (eq. A . 6 ) but at the same  should be expected.  w  Mass transfer model f o r a batch r e c i r c u l a t i o n  system  If the c e l l i s operated i n a batch r e c i r c u l a t i o n system, as shown i n F i g . A-5 both i n l e t and outlet concentrations w i l l be a function of time. + C  A  (t)  F i g . A-5 Schematic repres e n t a t i o n o f a b a t c h system  It i s possible to f i n d an expression to c o r r e l a t e the i n l e t and outlet concentrations with time, u t i l i z i n g the approach of P i c k e t t  (32, p. 325)  From equations A . 3 and A . 4 , K J  A  exp  m  a L u  2  [A.22]  An instantaneous material balance over the r e c i r c u l a t i o n tank would be written as, dC. C  A  - C,  t  2  Aj  = t  m dt  [A.23]  169 with  t  [A.24]  = V /Q m  m  C o m b i n i n g e q u a t i o n A . 22 w i t h A . 2 3 w o u l d  K C . exp Al  m  a L  - c  give,  = t  A  Ai  m  at  integrating, rt  J  f  K  exp  dC,  >  m  a L  -  u  Ai  dt t m  1  J  J  A  Ai  0  yields, (  Ai In  K a L m  exp :  A  u  Substituting  C. A  = C. A  exp  exp  0  from e q .  l  A.25 into  f  C. A  defining,  2  = C. A  t*  t  1  t m  0  f C. Al  -  f  eq.  K a l l m u  exp  exp 0  *  K a L] m - 1 u  -  t  [A.25]  m^  A . 22, K a L m u  t  i -  t  m  = dimensionless  =  t  [A.26]  time  m K  a L  m  A  = d i m e n s i o n l e s s mass t r a n s f e r  0  A  Equation  A . 2 6 c a n be w r i t t e n X = 1 -  2  = fractional  X =  group  conversion  as,  exp [ ( e x p  (-0) -  1)  t*  -  0]  [A.27]  Note that mathematical possible, changes  i f the  reaction controls  solution for  a constant  because the v a l u e of  with time,  as  discussed  the process,  applied current  will  change as  from e q . A . 1 4 .  the  an  analogous  operation  is  concentration  not  171  APPENDIX 4  Calculations  1.  B a t c h experiments.  C a l c u l a t i o n o f t h e o r e t i c a l phenol  c o n v e r s i o n i f mass t r a n s f e r  fractional  controls.  T h i s e s t i m a t e w i l l be s u i t a b l e t o compare a l l t h o s e experiments i n groups No. 2 and No. 3, performed under t h e f o l l o w i n g e x p e r i m e n t a l c o n d i tions, Flow r a t e  1.12 £./min  Particle size  1.7 < dp < 2.00 mm  P a r t i c l e weight  250 g  P a r t i c l e volume =  Void f r a c t i o n  250 e . " , — r = 23 cm 9.375* g/cm &  n  3  o  * d e n s i t y o f Pb02 from f . (49)  3  r  e  (57-23)/57 = 0.60  S p e c i f i c s u r f a c e a r e a o f t h e bed (eq. A.5)  a  =  l  +  6  S  *•(!% x dp  e)  t a k i n g £ = 0.75 f o r A and, from r e f . ( 4 9 ) , and dp = 0 . 1 8 5 1  a =  . 6 x ( l - Q.57) , -1 1— r» "7c ^ n - i c e = /U.o cm 0.3 cm 0.75 x 0.185 o  n  -T—Z  D e t e r m i n a t i o n o f t h e mass t r a n s f e r c o e f f i c i e n t K  m  cm.  = 0.83 f dp  (Re)°-  5 6  (Sc)  from eq. A.6,. .  .  1 / 3  U s i n g an e q u a t i o n f o r d i f f u s i v i t y o f l i q u i d s g i v e n by W i l k e ( 5 0 ) . (Original  nomenclature.)  D =  = y V °-6 A  D = 7.4 x I P '  ( 2 . 6 x 1 8 ) ^ x 297  8  1 x (105)°-  =  ^  x  1 Q  -6  c  m  2  /  s  6  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 =  1  ,  1  2  £  /  m  l  x (I0 cm /Jo)  n  5 x 0.3 cm Re -  u dp -=  12.4 cm/s x 0.185 cm  c  c  =  V  m  o o r  2  0.01 cm /s 2  =  9.2 x 10  K  , . = 229.4  0.01 cm /s  V  S  x (1 min/60 s) = 12.4 cm/s  3  3  2  Q  = 0.83 x  1  0  g  6  cm /s 2  9 x m"^ * r\ i QC U.lo5  —^ (229.4) (1086) = 8.7 x 10 cm/s ± 1 0 % J  Extreme v a l u e s o f K , t a k i n g i n t o account t h e 10% e r r o r i n c o r r e l a t i o n A.6, K~ = 0.078 cm/s m The d i m e n s i o n l e s s  e  =  +  mass t r a n s f e r group i s g i v e n by  K _m  a L =  u Therefore,  K = 0.0096 cm/s m  K _ni  20.6 cm"  1  38 cm  12.4 cm/s  t h e extreme v a l u e s o f 0 w i l l be  e~  = 0.49  6  +  = 0.60  The p h e n o l f r a c t i o n a l c o n v e r s i o n f o r mass t r a n s f e r c o n t r o l i s g i v e n by, X= with  t t* = — t m  1 - e x p [ ( e x p ( - 6 ) - 1) t * - 6] and  5 I t = , , „ . , — = 4.464 min. m 1.12 £ / m m  [A.27]  173 Using the the at  range  extreme v a l u e s  of t h e o r e t i c a l  a g i v e n t i m e , as  o f 6,  e q u a t i o n A . 2 7 i s used t o  calculate  f r a c t i o n a l c o n v e r s i o n f o r mass t r a n s f e r  control  shown i n T a b l e A - 2 .  TABLE A - 2 THEORETICAL PHENOL FRACTIONAL CONVERSION VS TIME FOR A MASS TRANSFER- -CONTROLLED BATCH SYSTEM  t  (min)  X~  X  +  0  .00  0.39  . 0.45  15  3.36  0.83  0.88  30  6.72  0.95  0.97  45  10.08  0.99  0.99  60  13.44  1.00  1.00  A t h e o r e t i c a l mass which i s  t*  transfer  represented  controlled region i s  i n F i g . 28 f o r  obtained  comparison w i t h  the  in this  manner  experimental  results. 2.  Continuous experiments.  and r e a c t i o n r a t e s  D e t e r m i n a t i o n o f e x p e r i m e n t a l , mass  transfer,  constants.  Procedure a)  According to the  plug flow  equation,  A n ( l - X) = -  If  -  line  J i n / (1 - X ) v s  from the  experimental data,  s h o u l d be o b t a i n e d , w i t h a s l o p e e q u a l t o K a L .  rate constant area  is plotted  [ A . 18]  of the  c a n be d e t e r m i n e d  electrode  is  from t h e  slope.  c a l c u l a t e d from e q . A . 5 .  a  straight  The e x p e r i m e n t a l  The s p e c i f i c  surface  174 b)  U s i n g the  e m p i r i c a l e q u a t i o n f o r t h e mass t r a n s f e r  coefficient,  estimated: K  c)  m  = 0.83  dp  (Re)°'  The r e a c t i o n r a t e c o n s t a n t  resistances  in  is  (Sc)  1 / 3  22 < Re < 520  t h e n c a l c u l a t e d from the  equation of  series: 1 K  where  5 6  _1 K r K  K  r  K  m m  [A.20] m K - K  is  TABLE A - 3 CALCULATION OF E X P E R I M E N T A L , MASS TRANSFER AND REACTION RATE CONSTANTS FROM EXPERIMENTS 4 - 1 , 4 - 2 , 4 - 3 * (USING AVERAGE PHENOL FRACTIONAL CONVERSION) K  -1  Q ,/min)  u (cm/s)  (cm/s)  0.25  2.78  0.360  0 . 59  0.40  4.44  0.225  0.55  6.11  0.85 1.10 1.30  C  Re  0.89  51.4  3 . 85 x 1 0 "  3  0 . 44  0.58  82.1  5. 01 x 1 0 ~  3  0.163  0 . 34  0.42  113.0  5 . 98 x 1 0 ~  3  9.44  0.106  0 . 25  0.29  174.6  7 . 64 x 1 0 ~  3  12.22  0.082  0 . 21  0.24  226.0  8 . 82 x 1 0 "  3  4 . 7 6 x 10'  267.0  9 . 69 x  - 3  4 . 5 4 x 10'  14.44  *For these  -1  -  X  0 . 17  0.069  £ n ( l - X)  0.19  From F i g . 3 2 :  1.7  < dp < 2 . 0 0 mm  Slope = 2.42  a=20.6  K  m  u dp u x 0 . 1 8 5 cm = j-.— v 0.01 cm /s 1 1  n  = 0.83 - f dp  z  (Re) ' 0  5 6  cm"  cm/sec = K = — 2 . 4 2 cm/s 2 0 . 6 cm  Re =  r (cm/s)  10  1 5 . 6 5 x 10' 8.06  10'  x  6 . 3 9 x 10' 5 . 1 9 x 10'  experiments:  = 100 ± 5 m g / 1  Ao  K  m (cm/s)  U  x  ( f r o m p a g e 171)  =  3  >  Q  9  x  1 Q  -3  c  m  /  g  38 cm  . = 18.5 u  (Sc)  n  1 / 3  r  = 0.83 x  9  - \ \ l f U.LoD  x Re°'  5 6  (1086)  1 / 3  = 4 . 2 4 x 10"  TABLE A - 4 CALCULATION OF E X P E R I M E N T A L , MASS TRANSFER AND REACTION RATE CONSTANTS FOR EXPERIMENT ( 4 - 4 ) *  Q (Jl/min) 0.25  u  K  1  u (cm/s)  (cm/s)  2.78  0.36  X  -  £ n ( l - X)  Re  0.46  51.4  0.37  0.40  4.44  0.225  0.25  0.29  0.55  6.11  0.163  0.19  0.21  0.85  9.44  0.106  0.12  0.082  0.09  1.10  12.22  *In  experiment  C.  = 580 m g / 1  A  K  m (cm/s)  82.1  3.85  r (cm/s)  io" io" io"  3  X  2.21  X  10'  3  1.95  X  10'  3  1.84  X  10"  1.72  X  10  1.67  X  10  5.01  X  113.0  5.98  X  0.13  174.6  7.64  X  IO"  0.09  226.0  8.82  X  io"  3  3  (4-4): 1.7  < dp < 2 . 0 0 mm  a = 20.6 c m "  1  "(from p a g e  171)  0  From F i g . 3 2 :  S l o p e = 1.1  cm/s =  K =  ! • ! cm/s 2 0 . 6 cm  x  with, Re = 1 8 . 5 u and  K  = 4.24 x 10~  4  Re°"  5 6  (as  i n Table A-3)  =  38 cm  1  <  4  0  5  x  1 0  ~3  c  m  /  s  TABLE A - 5 CALCULATION OF E X P E R I M E N T A L , MASS TRANSFER AND REACTION RATE CONSTANT FOR EXPERIMENT ( 4 - 8 ) *  u  -1  K  K  Q (il/min)  u (cm/s)  0.25  2.78  0.36  0.67  1. 11  25  5.3  x 10~  3  0.40  4.44  0.225  0.53  0 . 76  40  6.9  x 10"  3  0.55  6.11  0.163  0.45  0 . 60  55  8.2  x 10~  3  0.85  9.44  0.106  0.34  0 . 42  85  10.5 x 1 0 "  1.10  12.22  0.082  0.29  0 . 34  110  12.1 x 10~  0.7  < dp < 1.1  *In  experiment  (cm/s)  (4-8)  C. A  Specific  surface  1 * 0 . 3 cm  a  X  1  area  = 100 m g / 1  0  o f the bed  (1 - 0 . 5 7 ) x 6 ( 0 . 7 5 ) ( 0 . 0 9 ) cm "  From F i g . 3 2 :  Slope -  K  m  .  0.83  x  9  -  2  * " U.uy cm 1  0  6  c  m  2  2.68 x 1 0 ~  3  2.40 x 1 0 "  3  2.27 x  10  3  2.14 x  lo"  3  2.09 x  10  x 10~  cm/s  s  3  - 3  e = 0.57  , 1  -1 0  c  m  K  :  f (41.5cm 2  ,  8  1  - 1.78  m / s  )(38cm)  = 9 u  /  - 3  (eq. A . 5 ) :  2 . 8 1 cm/s =  Re =«= u d p / v = u 0 . 0 9 / 0 . 0 1  Re  A n ( l - X)  r (cm/s)  m (cm/s)  (Re°-  5 6  )(1086)  1 / 3  = 8.72  x lo"  4  (Re) ' 0  5 6  3  178 3.  Estimates  a)  Batch  of t y p i c a l % current  experiments % C.E. =  Assuming a 4 - e l e c t r o n Covitz  (Reaction R . l l ) ,  calculation,  it  is  the  final  recorded  at  total  (  m  ^  °*  S  from the  i n the at  the  that  i  d  i  z  e  d  >  x 100  [Eq.  p h e n o l m o l e c u l e as p r o p o s e d  % C . E . c a n be Run 3 - 1 3 ,  concentration 15 m i n  Z  supposed  and the volume r e m a i n i n g state  F  transfer  Sample c a l c u l a t i o n : the  efficiency  7] by  calculated.  r e c i r c u l a t i o n t i m e = 15 m i n . after  tank i s  15 m i n , r e c i r c u l a t i o n i s  treated  outlet  For  is  continuously.  assumed  to be e q u a l  stopped  The to  steady  the  time.  electrolysis  moles pphheenn o l = (1100-792)mg/l oxidized  t i m e = 15 m i n + 5 A / 1 . 1 2 A / m i n = 1 9 . 5 m i n  x 5A x 1 g m o l / 9 4 g x 1 g / 1 0  mg = 1 6 . 4 x 1 0  3  g mol  _3 _ 96500 c o u l / e q x 4 e q / m o l x 1 6 . 4 x 1 0 10 A x 1 9 . 5 m m x 60 s e c / m m This i s  a sample  c a l c u l a t i o n f o r T a b l e 6, where  a n d 90 m i n r e c i r c u l a t i o n b)  Continuous  g mol  ..  n  n  % C.E. is  n  given after  15  times,  experiments F z Q X C. A  % C.E. = Therefore,  current  a function  of flow,  -  efficiencies conversion,  l  x 100  for phenol oxidation i n a s i n g l e pass, initial  phenol concentration,  and  current  applied. Sample c a l c u l a t i o n :  %  =  96500 c o u l / e q  at  x 4 eq/mol x 0.25  10 A x 1 0 % C.E. = 36.7.  Run 4 - 4 ,  3  Q = 0.25  A/min,  A/min x 0.37  m g / g x 94 g / g m o l x 60 s e c / 1  x 580 m g / 1 min  x  are  1  0  Q  179 4.  Estimate  a)  Batch  of  typical electrical  e n e r g y r e q u i r e m e n t s and  experiments Energy requirements _ I AV t Moles of phenol o x i d i z e d V (C. m AQ K  Sample c a l c u l a t i o n : it  costs  was a s s u m e d i n t h e  tank volume i s  previous  treated  Total  Run 3 - 1 3 ,  recirculation  section,  after  the  C. ) A 2  t i m e = 15 m i n .  batch  operation  As the  continuously.  electrolysis  t i m e = 15 m i n + 5 1/1.12 A / m i n = 1 9 . 5  min  A v e r a g e AV = 8 . 5 V Energy mol  10 A * 8 . 5 V x 1 k w / 1 0 w * 1 9 . 5 m i n x 1 h / 6 0 m i n 5A x ( 1 1 0 0 - 7 9 2 ) m g / 1 x i / l 0 m g x 1 g m o l / 9 4 g 3  =  3  g  g mol Power c o s t s are  taken  Cost = 1 . 6 9  as  2^/kw-h for  kw-h/g mol x 0.02  E n e r g y r e q u i r e m e n t s and c o s t s a r e experiments Nos. tion  3-3,  illustration,  3-12,  3-12  $/kw-h = 0 . 0 3  presented at  i n Table  10 A , a f t e r  $/g mol 6 for  the  15 a n d 90 m i n  batch recircula-  time. In Table  8 the  energy requirements per  as  follows:  at  90 m i n r e c i r c u l a t i o n Total  Energy = O J  i n Runs 3 - 1 2  electrolysis  and  3-13,  99% a n d 98% p h e n o l r e m o v a l  time. t i m e = 90 mm + 5 A / 1 . 1 2 A / m i n = 9 4 . 5 m i n  10 A x 8 . 5  V x 9 4 . 5 min x lp3 . , 5A x 60 m m / 1 h  g 0  y  volume of waste i s  / n  k  w  /  w  = 0.027  Energy = 0.027 kw-h/A x 3.785 A/1 g a l = 0.1022  kw-h/A  kw-h/gal  is  estimated achieved  180 The e l e c t r i c a l c o s t  for  treating  102.2 kw-h/1000 g a l x 0.02 T h i s w o u l d be t h e  approximate  99% p h e n o l r e m o v a l , u n d e r  the  cost  10  g a l of waste would be:  $/kw-h = 2 $/1000  for  treating  operating  gal  a 700 m g / 1 e f f l u e n t  conditions  of experiments  with a  3-12  or  3-13. b)  Continuous  experiments energy r e q u i r e d mol phenol o x i d i z e d  I AV Q (C. - C. ) Ai A 2  Sample c a l c u l a t i o n :  Run 4 - 4 a t  E  n  6  r  g  y  £/min,  10 A x 8 . 5 V x 1 0 k w / w x 1 0 m g / g x 94 g / g m o l " 0 . 2 5 £/mln * ( 5 8 0 - 3 6 5 ) m g / l x 60 m i n / 1 h 3  v  Q - 0.25  Cost of e l e c t r i c a l energy 0.02  .  3  per mol of phenol o x i d i z e d :  $/kw-h x 2.51 kw-h/g mol = 0.05  $/g mol  =  2  . '  5  1  k  w  . , ~  h  /  g  . m  o  1  181  APPENDIX 5  Relevant Physical  Data  TABLE A - 6  pH OF SOLUTIONS OF NaOH AND H ^ O ^ AT 2 0 ° C  A qg. / 1NaOH s o l u pH tions  N  (51)  A qg. / 1H ^ O ^ s o l upH tions  .1  40.0  14  49.0  0.3  0.1  4.0  13  4.9  1.2  0.01  0.4  12  0.49  2.1  TABLE A - 7 CONDUCTIVITIES OF AQUEOUS SOLUTIONS OF NaOH, H S0i+ AND N a S O AT 2 0 ° C ( 5 1 ) 2  2  NaOH  cone. (g/1)  l +  H S0i 2  K  x 10 e (ft cm)  1  3  cone. (g/1)  Na SOi  t  2  K x 10 e (ft cm) 1  3  cone. (g/1)  +  K  x 10 e (ft cm)  24.8  5.0  24.3  5.0  5.9  10.1  48.6  10.0  47.8  10.1  11.2  15.2"  71.3  15.1  70.3  15.2  15.7  20.4  93.1  20.2  92.0  20.3  19.8  25.5  23.9  30.8  27.9  5  3  182 % p h e n o l i o n i z e d v s pH a t  dissociation K  d  20°C  constant  " 1.28  = [if] [ C H 0 ~ ] / 6  Ionized fraction Ionized fraction  =  l  6  [  [ R  d +  R D  =  ]  1 Q  5  c  J  _ "  (51)  [C H OH]  5  r  x 10 ^  d -pH  =  ]  0  1.28  x 10 -pH  = 1 Q  % ionized = fraction/(fraction  + 1)  x  u  x ioo  TABLE A - 8 % PHENOL IONIZED VS pH  pH  2  4  i o n i z e d to unionized fraction  1.28  x 10  % ionized  1.28  x io"  _  6  _/-  f i  6  1.28  x 10  1.28  x io"  8  _/  4  1.28  x 10  1.28  x io"  10  12  1.28  128  _o  2  1.28  x 10  1.16  x iff  1  56  99  

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