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UBC Theses and Dissertations

DEA degradation in heat exchanger tubes 1984

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DEA D E G R A D A T I O N I N H E A T EXCHANGER T U B E S by \ A M I T A B H A CHAKMA D i p l . I n g . , A l g e r i a n P e t r o l e u m I n s t i t u t e , 1982 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T OF T H E REQUIREMENTS FOR T H E D E G R E E OF MASTER OF A P P L I E D S C I E N C E i n T H E F A C U L T Y OF G R A D U A T E S T U D I E S D e p a r t m e n t Of C h e m i c a l E n g i n e e r i n g We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y OF B R I T I S H C O L U M B I A J u n e 1984 © A m i t a b h a C h a k m a , 1984 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 requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree 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 study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s or her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date A B S T R A C T A q u e o u s d i e t h a n o l a m i n e ( " D E A " ) i s w i d e l y u s e d f o r t h e r e m o v a l o f a c i d g a s e s s u c h a s C 0 2 a n d H 2 S f r o m n a t u r a l g a s a s w e l l a s r e f i n e r y g a s e s . I n a d d i t i o n t o t h e d e s i r e d a b s o r p t i o n a n d d e s o r p t i o n r e a c t i o n s , some s i d e r e a c t i o n s o c c u r b e t w e e n C 0 2 a n d DEA r e s u l t i n g i n t h e f o r m a t i o n o f d e g r a d a t i o n c o m p o u n d s . D e g r a d a t i o n n o t o n l y r e p r e s e n t s a l o s s o f v a l u a b l e D E A , b u t may a l s o l e a d t o o p e r a t i o n a l p r o b l e m s s u c h a s c o r r o s i o n , f o a m i n g a n d f o u l i n g . DEA d e g r a d a t i o n i s a c o m p l e x p r o c e s s a n d d e p e n d s on s o l u t i o n c o n c e n t r a t i o n , raw g a s c o m p o s i t i o n , s o l u t i o n f l o w r a t e a n d (mos t i m p o r t a n t l y ) t e m p e r a t u r e . C a r e f u l l y c o n t r o l l e d DEA d e g r a d a t i o n 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 i n a c o i l e d h e a t e x c h a n g e r t u b e ( 2 . 0 3 2 mm I D , 3 . 1 7 5 mm OD a n d 4 . 8 m l o n g ) h e a t e d by means o f a c o n s t a n t t e m p e r a t u r e h e a t t r a n s f e r f l u i d . T h e o p e r a t i n g c o n d i t i o n s c o v e r e d a r e : 1379 t o 4137 kPa C 0 2 p a r t i a l p r e s s u r e , 60 t o 200 ° C , 20 t o 40 wt% DEA s o l u t i o n s a n d 0 .011 L / s t o 0 . 0 1 7 2 L / s ( 3 . 4 m/s t o 5 . 3 m / s ) s o l u t i o n f l o w r a t e m e a s u r e d a t 60 ° C . T h e DEA d e g r a d a t i o n r a t e was f o u n d t o i n c r e a s e w i t h t e m p e r a t u r e , C 0 2 p a r t i a l p r e s s u r e a n d DEA c o n c e n t r a t i o n a n d d e c r e a s e w i t h s o l u t i o n f l o w r a t e . D e g r a d a t i o n r e s u l t e d i n s e v e r e f o u l i n g o f t h e h e a t e x c h a n g e r t u b e . T h e v i s c o s i t y a s w e l l a s f o a m i n g t e n d e n c y o f t h e s o l u t i o n s were f o u n d t o i n c r e a s e w i t h t h e c o n c e n t r a t i o n o f d e g r a d a t i o n p r o d u c t s . i i T h e f o l l o w i n g s i m p l e m a t h e m a t i c a l m o d e l f o r t h e p r e d i c t i o n o f DEA d e g r a d a t i o n i n h e a t e x c h a n g e r s was d e v e l o p e d : ^ Y y ^ , HEOD DEA + C 0 2 T H E E D • BHEP + C 0 2 T h e r a t e c o n s t a n t s k , , k 2 a n d k 3 a r e g i v e n by : ' l n ( k , ) = 11 . 924 - 6 4 2 1 / T . ' l n ( k 2 ) = 8 . 4 5 0 - 5 5 8 0 / T l n ( k 3 ) = 3 9 . 8 1 3 - 1 5 1 6 0 / T P o t e n t i o d y n a m i c c o r r o s i o n s t u d i e s a s w e l l a s c o n v e n t i o n a l w e i g h t l o s s t e s t s w e r e c a r r i e d o u t a n d d e g r a d e d DEA s o l u t i o n s were f o u n d t o be c o r r o s i v e t o w a r d s A I S I - S A E 1020 c a r b o n s t e e l . 3- ( h y d r o x y e t h y l ) - 2 - o x a z o l i d o n e ( " H E O D " ) was i d e n t i f i e d a s one o f t h e c o r r o s i v e c o m p o n e n t s . S e v e r e p i t t i n g o f A I S I - S A E 1020 c a r b o n s t e e l by HEOD was d e t e c t e d by e l e c t r o n m i c r o g r a p h i c a n a l y s i s . M i n o r p i t t i n g was a l s o n o t i c e d i n t h e c a s e o f BHEP a n d D E A . U s e o f a c t i v a t e d c a r b o n f i l t e r s a n d s o d a a s h t r e a t m e n t were b o t h f o u n d t o be i n c a p a b l e o f r e m o v i n g m a j o r d e g r a d a t i o n p r o d u c t s . A p u r i f i c a t i o n m e t h o d c o n s i s t i n g o f NaOH i n j e c t i o n was d e v e l o p e d a n d f o u n d t o be e f f e c t i v e i n c o n v e r t i n g HEOD a n d N , N , N - t r i s - ( h y d r o x y e t h y l ) e t h y l e n e d i a m i n e ( " T H E E D " ) b a c k t o D E A . H o w e v e r , c o n v e r s i o n o f HEOD t o DEA a p p a r e n t l y d e p e n d s on t h e p r e s e n c e o f o t h e r d e g r a d a t i o n c o m p o u n d s . T A B L E OF CONTENTS ABSTRACT . . i i L I S T OF T A B L E S .. v i i i L I S T OF FIGURES x ACKNOWLEDGEMENTS x i v C h a p t e r 1 INTRODUCTION 1 1.1 The DEA p r o c e s s 2 1.2 DEA d e g r a d a t i o n 5 1.3 O b j e c t i v e s o f p r e s e n t s t u d y 7 2 L I T E R A T U R E REVIEW 8 2.1 A b s o r p t i o n o f C 0 2 i n DEA 8 2 . 2 DEA d e g r a d a t i o n 10 2 . 2 . 1 O t h e r d e g r a d a t i o n p r o d u c t s 14 2 . 3 C o r r o s i o n i n DEA s o l u t i o n s 15 2 . 3 . 1 . C o r r o s i v i t y o f DEA d e g r a d a t i o n p r o d u c t s 17 2 . 4 R o l e o f h e a t e x c h a n g e r v a r i a b l e s 22 2 . 5 F o u l i n g o f h e a t e x c h a n g e r s 23 2 . 6 A n a l y s i s o f DEA s o l u t i o n s 24 3 EXPERIMENTAL EQUIPMENT AND PROCESS. DESCRIPTION 28 3.1 E q u i p m e n t d e s i g n 28 3 .2 P r o c e s s d e s c r i p t i o n 38 3 . 3 E q u i p m e n t d e s c r i p t i o n 32 3 . 3 . 1 A u t o c l a v e 32 3 . 3 . 2 H e a t e x c h a n g e r 33 i v 3.3.3 S o l u t i o n pump 34 3.3.4 Water c o o l e r 34 3.3.5 Flow meter 34 3.3.6 T e m p e r a t u r e c o n t r o l l e r 36 3.3.7 T e m p e r a t u r e measurements 36 3.3.8 Vapor r e c o v e r y s y s t e m 36 3.4 System p r e p a r a t i o n 37 3.5 System l o a d i n g .37 3.6 S t a r t up 39 4 ANALYTICAL PROCEDURE 4 2 4.1 C a l i b r a t i o n of Gas C h r o m a t o g r a p h .42 4.2 O p e r a t i n g c o n d i t i o n s 42 4.3 E r r o r s 46 5 CORROSION STUDIES 4 7 5.1 P r i n c i p l e s of p o t e n t i o d y n a m i c t e c h n i q u e 47 5.2 C a l c u l a t i o n of c o r r o s i o n c u r r e n t 51 5.3 E x p e r i m e n t a l p r o c e d u r e 54 6 MISCELLANEOUS TESTS 55 6.1 V i s c o s i t y measurements 55 6.2 Foaming t e s t s 57 7 MODEL DEVELOPMENT 59 7.1 Heat e x c h a n g e r model ..59 7.1.1 T e m p e r a t u r e p r o f i l e d e t e r m i n a t i o n 59 7.1.2 DEA t r a n s p o r t p r o p e r t i e s 67 7.1.3 Heat t r a n s f e r f l u i d p r o p e r t i e s 68 7.1.4 T h e r m a l c o n d u c t i v i t y of 316 s t a i n l e s s s t e e l 72 7.1.5 P r e s s u r e d r o p d e t e r m i n a t i o n 73 7.1.6 F i l m t h i c k n e s s d e t e r m i n a t i o n 74 7.1.7 Heat e x c h a n g e r model p e r f o r m a n c e 75 v 7 . 2 K i n e t i c m o d e l 77 7 . 2 . 1 D e t e r m i n a t i o n o f r a t e c o n s t a n t s 81 7 . 2 . 2 D e t e r m i n a t i o n o f i n l e t c o n d i t i o n s 83 8 RESULTS AND DISCUSSION OF DEGRADATION EXPERIMENTS 84 8.1 C o m p a r i s o n o f e x p e r i m e n t a l d a t a w i t h m o d e l p r e d i c t i o n 84 8 . 2 E f f e c t s o f o p e r a t i n g v a r i a b l e s on d e g r a d a t i o n 90 8 . 2 . 1 E f f e c t o f f l o w r a t e 90 8 . 2 . 2 E f f e c t o f . t e m p e r a t u r e 97 8 . 2 . 3 E f f e c t o f s o l u t i o n c o n c e n t r a t i o n 97 8 . 2 . 4 E f f e c t o f C 0 2 p a r t i a l p r e s s u r e 101 8 . 3 E f f e c t o f d e g r a d a t i o n on s o l u t i o n v i s c o s i t y 103 8 . 4 E f f e c t o f d e g r a d a t i o n on s o l u t i o n f o a m i n g 103 8 . 5 E f f e c t of d e g r a d a t i o n on s o l u t i o n pH 105 8 . 6 "Heat e x c h a n g e r f o u l i n g 108 8 . 6 . 1 E f f e c t o f t e m p e r a t u r e 108 8 . 6 . 2 E l e c t r o n m i c r o p r o b e a n a l y s i s 110 8 . 6 . 3 A p p a r e n t d e p o s i t t h i c k n e s s 110 8 . 7 E x p e r i m e n t w i t h a new t u b e 111 9 RESULTS AND DISCUSSION OF CORROSION STUDIES 116 9.1 C o r r o s i o n r a t e i n u n d e g r a d e d DEA s o l u t i o n s 116 9 . 2 C o r r o s i o n r a t e i n d e g r a d e d DEA s o l u t i o n s . . . . 1 1 6 9 . 3 E f f e c t o f C 0 2 d i s s o l v e d i n DEA s o l u t i o n s on c o r r o s i o n 119 9 . 4 E f f e c t o f s o l u t i o n c o n c e n t r a t i o n on c o r r o s i o n 120 9 . 5 E f f e c t o f s o l u t i o n pH on c o r r o s i o n 120 9 . 6 E f f e c t o f i n d i v i d u a l d e g r a d a t i o n p r o d u c t s on c o r r o s i o n 121 v i 9 . 7 E f f e c t o f m e t a l c o m p l e x i n g 123 9 . 8 P a s s i v i t y 124 9 . 9 P i t t i n g 125 10 P U R I F I C A T I O N OF DEGRADED DEA SOLUTIONS 131 10.1 Use o f a c t i v a t e d c a r b o n f i l t e r s 131 10 .2 Use o f c h e m i c a l s 133 10 .3 R e m o v a l of HEOD 133 10 .4 R e m o v a l o f THEED 133 10 .5 P u r i f i c a t i o n o f i n d u s t r i a l s ample 135 10 .6 NaOH t r e a t m e n t o f a m i x t u r e o f D E A , HEOD a n d THEED 138 10 .7 Soda a s h t r e a t m e n t 138 11 CONCLUSION AND RECOMMENDATIONS 142 11.1 C o n c l u s i o n s 142 11 .2 R e c o m m e n d a t i o n s 145 11 .3 R e c o m m e n d a t i o n s f o r f u r t h e r work- 148 NOMENCLATURE 149 REFERENCES 153 APPENDIX A L i s t i n g o f t h e c o m p u t e r p r o g r a m f o r t h e c a l c u l a t i o n o f DEA d e g r a d a t i o n r a t e i n t h e h e a t t r a n s f e r t u b e 162 v i i L I S T OF TABLES T a b l e 4.1 O p e r a t i n g c o n d i t i o n s o f t h e gas c h r o m a t o g r a p h ' 43 4 . 2 G . C . r e t e n t i o n t i m e of m a j o r d e g r a d a t i o n compounds 44 7.1 D e n s i t y of S h e l l T h e r m i a O i l - C 69 7 . 2 V i s c o s i t y o f S h e l l T h e r m i a O i l - C 70 7 . 3 C o m p a r i s o n o f o u t l e t t e m p e r a t u r e and i n i t i a l p r e s s u r e d r o p d a t a f o r d i f f e r e n t r u n s 76 8.1 C o m p a r i s o n o f D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 1 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 9 0 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 . 0 1 2 4 L / s , C 0 2 p a r t i a l p r e s s u r e 4137 kPa) 85 8 . 2 C o m p a r i s o n o f D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 2 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 7 0 ° C h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 . 0 1 2 4 L / s , C 0 2 p a r t i a l p r e s s u r e 4137 kPa) . . . 8 5 8 . 3 C o m p a r i s o n o f D E A , HEOD, THEED a n d BHEP c o n c e n t r a t i o n s o f r u n 3 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n • (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0.011 L / s , C 0 2 p a r t i a l p r e s s u r e 4137 kPa) 86 8 . 4 C o m p a r i s o n o f D E A , HEOD, THEED a n d BHEP c o n c e n t r a t i o n s o f r u n 4 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 6 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 . 0 1 7 2 L / s , C 0 2 p a r t i a l p r e s s u r e 4137 kPa) 86 8 . 5 C o m p a r i s o n o f D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 5 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 6 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 .011 L / s , C 0 2 p a r t i a l p r e s s u r e 4137 kPa) 87 v i i i 8 . 6 C o m p a r i s o n , of D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 6 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 4 0 ° C , h e a t i n g f l u i d t e m p . l 9 0 ° C , f l o w r a t e 0 .011 L / s , C 0 2 p a r t i a l p r e s s u r e 4137 kPa ) 87 8 . 7 C o m p a r i s o n o f D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 7 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 .011 L / s , C 0 2 p a r t i a l p r e s s u r e 2758 kPa) 88 8 . 8 C o m p a r i s o n o f D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 8 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0.011 L / s , C 0 2 p a r t i a l p r e s s u r e 1379 kPa) 88 8 . 9 C o m p a r i s o n o f D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 9 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (40 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 .011 L / s , C 0 2 p a r t i a l p r e s s u r e 41 37 kPa) 89 8 . 1 0 C o m p a r i s o n o f D E A , HEOD, THEED and BHEP c o n c e n t r a t i o n s o f r u n 10 w i t h t h e t h e o r e t i c a l m o d e l p r e d i c t i o n (20 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0.011 L / s , C 0 2 p a r t i a l p r e s s u r e 4137 kPa) 89 8 .11 A v e r a g e DEA d e g r a d a t i o n r a t e s . ( I n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 .011 L / s ) 101 9.1 E f f e c t o f C 0 2 on c o r r o s i o n r a t e s . . . 1 1 9 9 . 2 E f f e c t o f DEA c o n c e n t r a t i o n on c o r r o s i o n r a t e s 121 i x L I S T OF FIGURES F i g u r e 1.1 T y p i c a l f l o w s h e e t o f a DEA p l a n t 3 1.2 T y p i c a l f l o w s h e e t o f a DEA p a i n t s h o w i n g a r e a s where c o r r o s i o n u s u a l l y o c c u r s 16 2 . 2 P o u r b a i x p o t e n t i a l - p H d i a g r a m f o r t h e i r o n - w a t e r s y s t e m 19 3.1 F l o w s h e e t o f t h e e q u i p m e n t f o r t h e s t u d y o f DEA d e g r a d a t i o n i n h e a t e x c h a n g e r s 29 3 .2 P h o t o g r a p h o f o v e r a l l v i e w o f t h e e q u i p m e n t 30 3 . 3 P h o t o g r a p h s h o w i n g ma in c o m p o n e n t s o f t h e e q u i p m e n t 31 3 . 4 C a l i b r a t i o n c u r v e f o r t h e c a p i l l a r y f l o w m e t e r 35 3 . 5 S c h e m a t i c d i a g r a m o f t h e f e e d t a n k s y s t e m 38 4.1 C h r o m a t o g r a m o f a d e g r a d e d DEA s a m p l e f rom r u n 3 a f t e r 192 h r , 45 5.1 T y p i c a l a n o d i c p o l a r i z a t i o n p l o t s h o w i n g i m p o r t a n t z o n e s and t r a n s i t i o n p o i n t s 49 5 . 2 T y p i c a l a n o d i c p o l a r i z a t i o n c u r v e s h o w i n g t h e e f f e c t o f e n v i r o n m e n t a n d i n h i b i t o r a d d i t i o n upon t h e c u r v e 50 5 . 3 C a t h o d i c p o l a r i z a t i o n d i a g r a m f o r a c o r r o d i n g m e t a l 52 6.1 S c h e m a t i c d i a g r a m o f t h e v i s c o s i m e t e r 56 6 .2 S c h e m a t i c d i a g r a m o f t h e foam t e s t i n g a p p a r a t u s 58 7.1 S c h e m a t i c d i a g r a m o f t h e t e m p e r a t u r e p r o f i l e a c r o s s a segment o f t h e h e a t e x c h a n g e r t u b e .62 7 . 2 S c h e m a t i c d i a g r a m o f t e m p e r a t u r e p r o f i l e a c r o s s t h e m e t a l t u b e w a l l 65 x 8.1 DEA c o n c e n t r a t i o n as a f u n c t i o n of a n d f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , h e a t i n g o i l t e m p . 2 5 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 91 8 . 2 T e m p e r a t u r e o f t h e DEA s o l u t i o n as a f u n c t i o n o f t h e d i s t a n c e f rom t h e t u b e e n t r a n c e a n d f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 7 0 ° C , h e a t i n g o i l t e m p . 2 5 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 94 8 . 3 DEA c o n c e n t r a t i o n as a f u n c t i o n of t i m e and f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 7 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 95 8 . 4 T h e o r e t i c a l m o d e l p r e d i c t i o n o f DEA c o n c e n t r a t i o n a s a f u n c t i o n o f t i m e and f l o w r a t e ( s i n g l e p a s s ) . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 7 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 96 8 . 5 T h e o r e t i c a l m o d e l p r e d i c t i o n o f t h e f i l m t h i c k n e s s a s a f u n c t i o n o f t h e d i s t a n c e f rom • t h e t u b e e n t r a n c e and f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 7 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 97 8 . 6 DEA c o n c e n t r a t i o n as a f u n c t i o n o f t i m e and h e a t i n g f l u i d t e m p e r a t u r e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , f l o w r a t e 0 .011 L / s , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 99 8 . 7 DEA c o n c e n t r a t i o n as a f u n c t i o n o f t i m e and i n i t i a l DEA c o n c e n t r a t i o n . ( I n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , f l o w r a t e 0.011 L / s , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 100 8 . 8 DEA c o n c e n t r a t i o n as a f u n c t i o n o f t i m e and C 0 2 p a r t i a l p r e s s u r e (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , ) 102 8 . 9 S o l u t i o n v i s c o s i t y a s a f u n c t i o n o f t i m e and d e g r a d a t i o n p r o d u c t c o n c e n t r a t i o n 104 8 . 1 0 T y p i c a l pH c h a n g e o f p a r t i a l l y d e g r a d e d DEA s o l u t i o n as a f u n c t i o n o f t i m e (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . l 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 .011 L / s ) 107 x i 8.11 P r e s s u r e d r o p as a f u n c t i o n o f t i m e and h e a t i n g f l u i d t e m p . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , f l o w r a t e 0 .011 L / s ) 109 8 . 1 2 E l e c t r o n m i c r o g r a p h i c . p h o t o s o f t h e u n c o n t a m i n a t e d a n d c o n t a m i n a t e d s u r f a c e s o f t h e h e a t e x c h a n g e r t u b e (20 x) 112 8 . 1 3 E l e c t r o n m i c r o g r a p h i c p h o t o s o f t h e f o u l e d s u r f a c e o f t h e h e a t e x c h a n g e r t u b e (20 x) a n d a m a g n i f i e d v i e w (400 x) o f t h e same s u r f a c e 113 8 . 1 4 E l e c t r o n m i c r o p r o b e p l o t s o f t h e u n c o n t a m i n a t e d a n d c o n t a m i n a t e d s u r f a c e s o f t h e h e a t e x c h a n g e r t u b e 114 8 . 1 5 A p p a r e n t d e p o s i t t h i c k n e s s a s a f u n c t i o n o f t i m e a n d h e a t i n g f l u i d t e m p e r a t u r e (30 wt% D E A , i n l e t t e m p . 6 0 ° C , f l o w r a t e 0 .011 L / s ) 115 9.1 P o t e n t i o d y n a m i c a n o d i c p o l a r i z a t i o n c u r v e o f 30 wt% u n d e g r a d e d DEA s o l u t i o n ( t e m p . 2 5 ° C ) . . . . 1 1 7 9 . 2 P o t e n t i o d y n a m i c a n o d i c p o l a r i z a t i o n c u r v e o f 30 wt% p a r t i a l l y d e g r a d e d DEA s o l u t i o n c o n t a i n i n g 8 . 7 wt% d e g r a d a t i o n p r o d u c t s ( t e m p . 2 5 ° C ) • 118 9 . 3 E l e c t r o n m i c r o g r a p h i c p h o t o o f an u n c o r r o d e d A I S I 1020 c a r b o n s t e e l t e s t c o u p o n (400 x) 126 9 . 4 E l e c t r o n m i c r o g r a p h i c p h o t o o f A I S I 1020 c a r b o n s t e e l t e s t c o u p o n a f t e r 120 h r . i m m e r s i o n i n 15 wt% DEA s o l u t i o n a t 1 0 0 ° C (400x) 127 9 . 5 E l e c t r o n m i c r o g r a p h i c p h o t o o f A I S I 1020 c a r b o n s t e e l t e s t c o u p o n a f t e r 120 h r . i m m e r s i o n i n 15 wt% BHEP s o l u t i o n a t 1 0 0 ° C (400x) 128 9 . 6 E l e c t r o n m i c r o g r a p h i c p h o t o o f A I S I 1020 c a r b o n s t e e l t e s t c o u p o n a f t e r 120 h r . i m m e r s i o n i n 15 wt% HEOD s o l u t i o n a t 1 0 0 ° C (400x) .129 9 . 7 E l e c t r o n m i c r o g r a p h i c p h o t o o f a p i t a r e a o f A I S I 1020 c a r b o n s t e e l c o u p o n a f t e r 120 h r . i m m e r s i o n i n 15 wt% HEOD s o l u t i o n a t 1 0 0 ° C (2000x) 130 10.1 C h r o m a t o g r a m s o f p a r t i a l l y d e g r a d e d DEA s a m p l e s t a k e n u p s t r e a m a n d d o w n s t r e a m o f an a c t i v a t e d c a r b o n f i l t e r l o c a t e d i n a gas p l a n t i n A l b e r t a 132 10 .2 C h r o m a t o g r a m s o f a p a r t i a l l y d e g r a d e d DEA s a m p l e o f r u n 3 b e f o r e a n d a f t e r NaOH t r e a t m e n t 136 10 .3 C h r o m a t o g r a m s o f a p a r t i a l l y d e g r a d e d DEA s a m p l e f rom a gas p r o c e s s i n g p l a n t b e f o r e a n d a f t e r NaOH t r e a t m e n t 137 10 .4 C h r o m a t o g r a m s o f l a b o r a t o r y made m i x t u r e o f 30 wt% D E A , 12 wt% HEOD a n d 8 wt% THEED b e f o r e and a f t e r NaOH t r e a t m e n t 139 10 .5 C h r o m a t o g r a m s o f a p a r t i a l l y d e g r a d e d DEA s a m p l e f rom a ga s p r o c e s s i n g . p l a n t b e f o r e a n d a f t e r soda a s h t r e a t m e n t 141 x i i i 1 CHAPTER 1 INTRODUCTION N a t u r a l ga s p r o d u c e d f r o m g e o l o g i c a l f o r m a t i o n s i s u s u a l l y s a t u r a t e d w i t h w a t e r v a p o r a n d f r e q u e n t l y c o n t a i n s c a r b o n d i o x i d e a n d / o r h y d r o g e n s u l p h i d e . W a t e r v a p o r a n d a c i d g a s e s must be r e m o v e d f rom t h e n a t u r a l gas p r i o r t o i t s t r a n s p o r t a t i o n and s u b s e q u e n t use i n o r d e r t o a v o i d h y d r a t e f o r m a t i o n , p r e v e n t c o r r o s i o n i n p i p e l i n e s a n d t o m i n i m i s e h e a l t h and p o l l u t i o n p r o b l e m s upon s u b s e q u e n t u s e . The d e g r e e o f r e m o v a l o f t h e s e c o n s t i t u e n t s v a r i e s a c c o r d i n g t o e n d u s e . The a q u e o u s d i e t h a n o l a m i n e (DEA) p r o c e s s , w h i c h b e l o n g s t o t h e a m i n e p r o c e s s g r o u p , was d e v e l o p e d by B o t t o m s [ 1 , 2 ] i n 1930 t o remove a c i d g a s e s ( C 0 2 a n d H 2 S ) f r o m h i g h v o l u m e , h i g h p r e s s u r e n a t u r a l gas s t r e a m s . F o r many y e a r s , t h e amine p r o c e s s e s were v i r t u a l l y t h e o n l y c h o i c e a v a i l a b l e t o ga s p r o s c e s s o r s f o r t h e s w e e t e n i n g o f ( r e m o v a l o f a c i d g a s e s f rom) n a t u r a l ga s u s i n g c h e m i c a l s o l v e n t s . A l t h o u g h numerous new s w e e t e n i n g p r o c e s s e s h a v e been d e v e l o p e d s i n c e t h e n i n e t e e n t h i r t i e s , t h e m a j o r i t y o f t h e gas p r o c e s s i n g p l a n t s use a m i n e s o f one k i n d o r a n o t h e r . The DEA s w e e t e n i n g p r o c e s s has l o n g been f a v o u r e d f o r t h e s w e e t e n i n g o f r e f i n e r y o r m a n u f a c t u r e d g a s e s b e c a u s e DEA r e a c t s o n l y v e r y s l o w l y w i t h c a r b o n d i s u l p h i d e and c a r b o n y l s u l p h i d e , 2 i . e . t y p i c a l c o n t a m i n a n t s o f r e f i n e r y o r m a n u f a c t u r e d g a s e s . H o w e v e r , i n r e c e n t y e a r s , DEA has a l s o become i n c r e a s i n g l y p o p u l a r w i t h n a t u r a l gas p r o c e s s o r s and many MEA p l a n t s h a v e been c o n v e r t e d t o DEA [ 3 - 9 ] . D E A ' s p o p u l a r i t y c a n be a t t r i b u t e d t o t h e f o l l o w i n g f a c t o r s : Low e n e r g y r e q u i r e m e n t , f o r r e g e n e r a t i o n c o m p a r e d w i t h most o t h e r s o l v e n t s ; t h i s i s due t o D E A ' s l o w e r , s p e c i f i c h e a t a n d h e a t o f r e a c t i o n w i t h C 0 2 and H 2 S . Low s o l v e n t l o s s due t o l o w e r v a p o r p r e s s u r e o f D E A . L e s s c o r r o s i o n . Low r a t e o f d e g r a d a t i o n a s a r e s u l t o f i r r e v e r s i b l e s i d e r e a c t i o n s w i t h C 0 2 . A l t h o u g h d i f f i c u l t i e s a r e s o m e t i m e s e n c o u n t e r e d w i t h r e d u c i n g h y d r o g e n s u l p h i d e c o n c e n t r a t i o n t o p i p e l i n e s p e c i f i c a t i o n s , t h e SNPA m o d i f i c a t i o n o f t h e DEA p r o c e s s i s c l a i m e d t o be a b l e t o r e d u c e h y d r o g e n s u l p h i d e c o n c e n t r a t i o n t o a b o u t 1.15 t o 3 . 4 5 m g / s t d m 3 ( 0 . 0 5 t o 0 . 1 5 g r a i n s p e r 100 SCF) [ 1 0 ] . 1.1 The DEA P r o c e s s A t y p i c a l f l o w s h e e t o f an i n d u s t r i a l DEA s w e e t e n i n g u n i t i s shown i n F i g u r e 1 . 1 . The raw s o u r gas e n t e r s t h e u n i t t h r o u g h an i n l e t s e p a r a t o r where e n t r a i n e d h y d r o c a r b o n l i q u i d s and s o l i d p a r t i c u l a t e s a r e r e m o v e d . 1 . 2 . 3 . 4 . SWEET GAS 0 - H CONDENSER ABSORBER A C I D GASES FEED GAS R E B O I L E R F i g u r e 1.1 T y p i c a l f l o w s h e e t o f a DEA p l a n t 4 T h e gas t h e n e n t e r s t h e b o t t o m o f t h e a b s o r b e r a n d f l o w s upward a g a i n s t a c o u n t e r - c u r r e n t s t r e a m o f a q u e o u s D E A . The a c i d g a s e s a r e a b s o r b e d by t h e DEA s o l u t i o n . The s w e e t e n e d g a s , w h i c h i s s a t u r a t e d w i t h w a t e r v a p o u r , l e a v e s t h e t o p o f t h e a b s o r b e r a n d i s u s u a l l y s e n t t o a d e h y d r a t i o n u n i t . The r i c h DEA s o l u t i o n c o n t a i n i n g C 0 2 a n d H 2 S f l o w s f rom t h e b o t t o m o f t h e a b s o r b e r and p a s s e s t h r o u g h t h e l e a n - r i c h h e a t e x c h a n g e r where i t i s h e a t e d by t h e h o t , l e a n DEA s o l u t i o n . I t t h e n e n t e r s t h e t o p o f t h e s t r i p p e r c o l u m n . In some c a s e s a f l a s h t a n k i s i n s t a l l e d u p s t r e a m o f t h e l e a n - r i c h h e a t e x c h a n g e r , where t h e a b s o r b e d h y d r o c a r b o n s a r e d e s o r b e d f rom t h e s o l u t i o n by l e t t i n g down t h e p r e s s u r e o f t h e r i c h DEA s t r e a m . Upon e n t r y i n t o t h e s t r i p p e r , some o f t h e a b s o r b e d a c i d g a s e s a r e f l a s h e d on t h e t o p t r a y o f t h e c o l u m n . The s o l u t i o n t h e n f l o w s downward a g a i n s t a c o u n t e r c u r r e n t f l o w o f s t r i p p i n g v a p o r g e n e r a t e d i n t h e r e b o i l e r . The s t r i p p i n g v a p o r , w h i c h c o n s i s t s m a i n l y o f s t e a m , removes t h e a c i d g a s e s f r o m t h e r i c h DEA s o l u t i o n . The o v e r h e a d p r o d u c t s p a s s t h r o u g h a c o n d e n s e r where most o f t h e s team i s c o n d e n s e d . The a c i d g a s e s a r e s e p a r a t e d f r o m t h e c o n d e n s a t e i n a s e p a r a t o r a n d t h e c o n d e n s a t e i s r e t u r n e d t o t h e t o p o f t h e s t r i p p e r a s r e f l u x . The l e a n DEA s o l u t i o n l e a v i n g t h e b o t t o m o f t h e s t r i p p e r , e x c h a n g e s h e a t w i t h t h e r i c h s o l u t i o n i n t h e l e a n - r i c h h e a t e x c h a n g e r and t h e n p a s s e s t h r o u g h a c o o l e r , where i t i s c o o l e d 5 t o t h e o p e r a t i n g t e m p e r a t u r e o f t h e a b s o r b e r . A s m a l l s i d e s t r e a m o f l e a n DEA s o l u t i o n i s u s u a l l y p a s s e d t h r o u g h an a c t i v a t e d c a r b o n f i l t e r t o p r e v e n t t h e b u i l d - u p o f c o n t a m i n a n t s . 1.2 DEA D e g r a d a t i o n In s p i t e o f D E A ' s s u p p o s e d r e s i s t a n c e t o d e g r a d a t i o n , DEA c a n r e a c t w i t h c a r b o n d i o x i d e t o f o r m some u n d e s i r e a b l e p r o d u c t s . Mos t p l a n t o p e r a t o r s e x p e r i e n c e some l o s s o f DEA due t o d e g r a d a t i o n bu t t h e s e v e r i t y o f d e g r a d a t i o n v a r i e s d e p e n d i n g on raw gas c o m p o s i t i o n a n d p l a n t o p e r a t i o n . D e g r a d a t i o n o f DEA i s u n d e s i r e a b l e n o t o n l y b e c a u s e i t r e p r e s e n t s a l o s s o f v a l u a b l e D E A , b u t a l s o b e c a u s e a c c u m u l a t i o n o f d e g r a d a t i o n compounds r e s u l t s i n f o u l i n g o f p r o c e s s e q u i p m e n t and i n c r e a s e s t h e f o a m i n g t e n d e n c y o f t h e s o l u t i o n i n t h e a b s o r b e r a n d s t r i p p e r . F u r t h e r m o r e , some o f t h e d e g r a d a t i o n compounds a r e b e l i e v e d t o be c o r r o s i v e [ 1 1 - 1 4 ] . P l a n t o p e r a t o r s u s u a l l y t r y t o m i n i m i s e d e g r a d a t i o n o f DEA s o l u t i o n s by c h a n g i n g o p e r a t i n g v a r i a b l e s s u c h as s o l u t i o n c o n c e n t r a t i o n , t e m p e r a t u r e , p r e s s u r e e t c . U n l i k e m o n o e t h a n o l a m i n e , DEA c a n n o t be r e c l a i m e d e c o n o m i c a l l y . A c t i v a t e d c a r b o n f i l t e r s a r e i n s t a l l e d i n most DEA s w e e t e n i n g p l a n t s a n d a r e b e l i e v e d t o be a b l e t o a b s o r b some d e g r a d a t i o n compounds a l o n g w i t h o t h e r c o n t a m i n a n t s [ 1 3 , 1 5 , 1 6 ] . H o w e v e r , l i m i t e d l a b o r a t o r y t e s t s have i n d i c a t e d t h a t a c t i v a t e d c a r b o n f i l t e r s a r e n o t c a p a b l e o f r e m o v i n g any m a j o r d e g r a d a t i o n compounds f rom p a r t i a l l y d e g r a d e d s o l u t i o n s [ 1 7 ] . 6 The strong temperature dependence of DEA degradation has been observed in i n d u s t r i a l o p e r a t i o n s and has been confirmed by l a b o r a t o r y s t u d i e s [17]. Therefore, degradation of DEA i s expected to occur mostly i n equipment operated at e l e v a t e d temperatures such as the l e a n - r i c h heat exchanger and the s t r i p p e r - r e b o i l e r . In order to minimise degradation in heat exchangers, temperature i s c o n s i d e r e d to be the most important v a r i a b l e in the design and o p e r a t i o n of DEA u n i t s . U s u a l l y , bulk s o l u t i o n temperatures are measured and used for process c o n t r o l . However, from the p o i n t of view of degradation as well as c o r r o s i o n , the s k i n temperature i s of g r e a t e s t importance. The f l u i d adjacent to the heat t r a n s f e r s u r f a c e experiences the g r e a t e s t temperature i n c r e a s e and i s t h e r e f o r e most s u s c e p t i b l e to degradation. The s k i n temperature depends not only on the temperature of the heating medium but a l s o on the flow rate of the DEA s o l u t i o n . In a d d i t i o n , the flow r a t e determines the temperature p r o f i l e i n the DEA s o l u t i o n . No i n f o r m a t i o n concerning the e f f e c t of flow rate on DEA degradation i s p r e s e n t l y a v a i l a b l e . Since flow rate i s an important o p e r a t i n g v a r i a b l e over which d e s i g n e r s as w e l l as the operators have some c o n t r o l , the study of the e f f e c t of flow rate on DEA degradation i s of c o n s i d e r a b l e i n d u s t r i a l i n t e r e s t . 7 1.3 O b j e c t i v e s of p r e s e n t s t u d y The o b j e c t i v e s o f t h i s s t u d y may be s u m m a r i z e d a s f o l l o w s : 1 . P e r f o r m c a r e f u l l y c o n t r o l l e d DEA d e g r a d a t i o n e x p e r i m e n t s w h i c h s i m u l a t e t h e c o n d i t i o n s i n i n d u s t r i a l h e a t e x c h a n g e r s and r e b o i l e r s ; 2. D e v e l o p a s i m p l e m a t h e m a t i c a l m o d e l w h i c h p r e d i c t s t h e r a t e of d e g r a d a t i o n o f DEA i n h e a t e x c h a n g e r s u s i n g k i n e t i c d a t a o b t a i n e d i n p r e v i o u s b a t c h - w i s e e x p e r i m e n t s ; 3. S t u d y t h e e f f e c t o f DEA and i t s d e g r a d a t i o n p r o d u c t s on t h e • c o r r o s i o n o f m i l d s t e e l . T h e p r e s e n t work i s r e s t r i c t e d t o C 0 2 a s t h e a c i d g a s . 8 CHAPTER 2 L I T E R A T U R E REVIEW S e v e r a l p a p e r s on t h e p e r f o r m a n c e o f DEA s w e e t e n i n g u n i t s have been p u b l i s h e d [ 1 8 - 2 1 ] . ' The SNPA m o d i f i c a t i o n o f t h e DEA s w e e t e n i n g p r o c e s s , w h i c h u s e s h i g h e r c o n c e n t r a t i o n s o f DEA t h a n c o n v e n t i o n a l DEA s w e e t e n i n g p r o c e s s e s , has been r e p o r t e d by Wendt and D a i l e y [ 1 0 ] . In a d d i t i o n , t h e r e a r e s e v e r a l t e x t b o o k s and h a n d b o o k s a v a i l a b l e w h i c h r e v i e w n a t u r a l - g a s p r o c e s s i n g i n g e n e r a l [22 2 5 ] , V a r i o u s a n a l y t i c a l m e t h o d s f o r r o u t i n e a n a l y s i s o f gas t r e a t i n g s o l u t i o n s a r e d e s c r i b e d i n t h e " G a s C o n d i t i o n i n g F a c t B o o k " [ 2 6 ] . 2.1 ABSORPTION OF CARBON D I O X I D E IN DEA The c h e m i s t r y o f C 0 2 r e a c t i o n s w i t h a q u e o u s DEA s o l u t i o n s i s f a i r l y c o m p l e x a n d n o t y e t f u l l y u n d e r s t o o d . The l i t e r a t u r e on C 0 2 - D E A r e a c t i o n s i s e x t e n s i v e [ 2 7 - 3 9 ] , w i t h B l a u w h o f f e t a l . [40] p r o v i d i n g an e x c e l l e n t r e c e n t r e v i e w . 9 The o v e r a l l C0 2-DEA r e a c t i o n s c a n be r e p r e s e n t e d by t h e f o l l o w i n g e q u a t i o n s [ 3 ] : 2R2NH + H 2 0 + C0 2 =s=as. ( R 2 N H 2 ) 2 C 0 3 [ 2 . 1 ] ( R 2 N H 2 ) 2 C 0 3 + H 2 0 + C02 2R 2NH 2HC0 3 [ 2 . 2 ] Where, R s t a n d s f o r - C 2H„OH. The e q u i l i b r i u m o f t h e a b o v e r e a c t i o n s l i e s t o t h e r i g h t a t low t e m p e r a t u r e a n d h i g h p r e s s u r e a n d l e f t a t h i g h t e m p e r a t u r e and low p r e s s u r e . F o r t h i s r e a s o n , i n d u s t r i a l a b s o r b e r s a r e o p e r a t e d a t low t e m p e r a t u r e and h i g h p r e s s u r e . 10 2 . 2 DEA DEGRADATION B e s i d e s t h e m a i n C 0 2 a b s o r p t i o n r e a c t i o n s , c e r t a i n i r r e v e r s i b l e s i d e r e a c t i o n s may o c c u r and r e s u l t i n u n d e s i r e a b l e c o m p o u n d s ; t h e l a t t e r a r e t e r m e d " d e g r a d a t i o n c o m p o u n d s . " In h i s e x p l o r a t o r y work on o r g a n i c n i t r o g e n b a s e s f o r gas s w e e t e n i n g , w h i c h l e d t o t h e d i s c o v e r y o f amine p r o c e s s e s , B o t t o m s [2] o b s e r v e d t h a t e t h a n o l a m i n e s ( i n c l u d i n g D E A ) , were s t a b l e a t low t e m p e r a t u r e s . H o w e v e r , w h e n t h e p u r e compounds o r t h e i r a q u e o u s s o l u t i o n s were h e a t e d a b o v e 1 5 0 ° C , some d e c o m p o s i t i o n was n o t i c e d . T h i s was p r o b a b l y t h e f i r s t r e p o r t e d i n d i c a t i o n o f a m i n e d e g r a d a t i o n . DEA d e g r a d a t i o n i s a c o m p l e x p h e n o m e n o n . S m i t h and Y o u n g e r [ 7 , 1 3 , 1 8 ] a s w e l l a s N o n h e b e l [14] have r e p o r t e d t h a t d e g r a d a t i o n a p p a r e n t l y d e p e n d s on t e m p e r a t u r e , p r e s s u r e , gas c o m p o s i t i o n ; amine c o n c e n t r a t i o n , s o l u t i o n pH and t h e p r e s e n c e o f m e t a l i o n s . The f i r s t c o m p r e h e n s i v e work on DEA d e g r a d a t i o n was p u b l i s h e d by P o l d e r m a n a n d S t e e l e [12] i n 1956 . T h e i r work c o n s i s t e d o f s a t u r a t i n g a 25 wt% DEA s o l u t i o n w i t h C 0 2 a t 2 5 ° C i n s i d e a s t a i n l e s s s t e e l a u t o c l a v e , s e a l i n g a n d h e a t i n g t h e a u t o c l a v e t o a t e m p e r a t u r e r a n g i n g f rom 100 t o 1 7 5 ° C . The p r e s s u r e i n s i d e t h e v e s s e l v a r i e d f rom 1257 t o 4137 kPa (180 t o 600 p s i ) . A f t e r 8 h r t h e a u t o c l a v e was c o o l e d t o 2 5 ° C and t h e p a r t i a l l y d e g r a d e d s o l u t i o n s were a n a l y s e d by f r a c t i o n a l d i s t i l l a t i o n and c r y s t a l l i z a t i o n . 11 DEA l o s s e s r a n g e d f rom 0% a t 1 0 0 ° C and 1257 kPa t o 97% a t 1 7 5 ° C a n d 4137 k P a . T h e y i d e n t i f i e d N , N - b i s ( h y d r o x y e t h y l ) p i p e r a z i n e ( " B H E P " ) a s a d e g r a d a t i o n compound and p o s t u l a t e d t h e f o l l o w i n g r e a c t i o n scheme f o r i t s f o r m a t i o n : 0 II H O - C 2 H a C \ / \ N - H + C 0 2 5» H O - C 2 H a - N 0 + H 2 0 [ 2 . 3 ] H O - C 2 H „ C H 2 C H 2 " D E A " " H E O D " 0 II C C H 2 - C H 2 / \ / \ 2 H O - C 2 H « - N 0 > H O - C 2 H a - N ^ ^ N - C 2 H a - O H + 2 C 0 2 CH 2 1 •"* CH 2 CH 2 — C H 2 " H E O D " ' " B H E P " [ 2 . 4 ] The a u t h o r s h o w e v e r , d i d n o t i d e n t i f y o t h e r d e g r a d a t i o n compounds due t o t h e l a c k o f s u i t a b l e a n a l y t i c a l t e c h n i q u e s . : In a f o l l o w - u p s t u d y , Hakka e t a l . [ 4 l ] were a b l e t o d e t e c t N , N , N ' - t r i s ( 2 - h y d r o x y e t h y l ) e t h y l e n e d i a m i n e ( " T H E E D " ) i n d e g r a d e d DEA s o l u t i o n s by u s i n g more s o p h i s t i c a t e d a n a l y t i c a l p r o c e d u r e s . A c c o r d i n g t o t h e a u t h o r s , THEED o c c u r r e d f r e q u e n t l y a t c o n c e n t r a t i o n s o f 0 . 5 t o 2 wt% i n t h e DEA s o l u t i o n a n d s h o u l d be r e g a r d e d as a m a j o r d e g r a d a t i o n c o m p o u n d . 1 2 T h e s e a u t h o r s a n d o t h e r s [ 8 , 9 , 1 2 ] f o u n d t h a t b o t h BHEP a n d THEED c a n a b s o r b a c i d g a s e s and t h a t t h e i r b a s i c i t y i s s i m i l a r t o t h a t o f t r i e t h a n o l a m i n e ( " T E A " ) . H o w e v e r , u n d e r n o r m a l i n d u s t r i a l o p e r a t i n g c o n d i t i o n s , o n l y one o f t h e n i t r o g e n a toms i n . t h e BHEP o r THEED m o l e c u l e i s l i k e l y t o r e a c t w i t h a c i d g a s e s . H e n c e , on a m o l e c u l a r b a s i s , t h e a c i d gas r e m o v a l c a p a c i t y o f t h e DEA s o l u t i o n f a l l s w i t h i n c r e a s i n g s o l u t i o n d e g r a d a t i o n . S m i t h a n d Y o u n g e r [13] and o t h e r s [42] h a v e d i s c u s s e d DEA d e g r a d a t i o n a n d m e n t i o n e d s e v e r a l o t h e r d e g r a d a t i o n compounds r e p o r t e d by ga s p l a n t o p e r a t o r s . One o f t h e s e d e g r a d a t i o n compounds was f o u n d t o h a v e t h e same r e t e n t i o n t i m e as t r i e t h a n o l a m i n e ( " T E A " ) i n ga s c h r o m a t o g r a p h i c a n a l y s i s . Choy [ 4 2 , 4 3 ] p e r f o r m e d s e v e r a l c a r e f u l l y c o n t r o l l e d d e g r a d a t i o n e x p e r i m e n t s and f o u n d t h a t DEA d e g r a d a t i o n a p p e a r s t o be g o v e r n e d by a f i r s t o r d e r r e a c t i o n a t t e m p e r a t u r e s and C 0 2 p a r t i a l p r e s s u r e s r a n g i n g f rom 165 - 1 8 5 ° C a n d 1207 t o 4137 kPa (175 t o 600 p s i ) , r e s p e c t i v e l y . He a l s o f o u n d t h a t t h e r a t e o f d e g r a d a t i o n was a f f e c t e d by t h e i n i t i a l DEA c o n c e n t r a t i o n . T h i s c l e a r l y c o n t r a d i c t s t h e s i m p l e f i r s t o r d e r r e a c t i o n c o n c e p t . F u r t h e r m o r e , s e v e r a l u n i d e n t i f i a b l e d e g r a d a t i o n compounds were d e t e c t e d and t h e i r c o n c e n t r a t i o n c h a n g e s w i t h t i m e s u g g e s t e d a s e r i e s o f s i m u l t a n e o u s and c o n s e c u t i v e d e g r a d a t i o n r e a c t i o n s . 1 3 K e n n a r d a n d M e i s e n [ 1 7 , 4 4 ] u n d e r t o o k a c o m p r e h e n s i v e s t u d y on t h e r e a c t i o n m e c h a n i s m s a n d k i n e t i c s o f DEA d e g r a d a t i o n . T h e i r work c o n s i s t e d o f r e a c t i n g C 0 2 w i t h DEA i n a 600 mL s t i r r e d a u t o c l a v e . The t e m p e r a t u r e was v a r i e d f r o m 90 t o 2 5 0 ° C , t h e p r e s s u r e f rom 4 1 3 . 7 t o 6895 kPa a n d t h e i n i t i a l DEA c o n c e n t r a t i o n f r o m 5 t o 100 wt%. T h e y f o u n d t h e r e a c t i o n s b e t w e e n C 0 2 a n d DEA t o be c o m p l e x a n d c o n s i s t i n g o f a c o m b i n a t i o n o f e q u i l i b r i u m , p a r a l l e l , s e r i e s a n d i o n i c s t e p s . T h e y p r o p o s e d a p s e u d o - f i r s t o r d e r e q u a t i o n t o d e s c r i b e t h e o v e r a l l d e g r a d a t i o n r e a c t i o n o f D E A . Among 12 d e t e c t a b l e d e g r a d a t i o n compounds K e n n a r d [51] f o u n d H E O D , T H E E D a n d BHEP t o be t h e main o n e s . He a l s o f o u n d t h a t C 0 2 i s n e i t h e r c o n s u m e d n o r p r o d u c e d d u r i n g t h e d e g r a d a t i o n o f DEA t o THEED a n d B H E P ; t h i s s u g g e s t e d t h a t C 0 2 a c t s a s a c a t a l y s t . HEOD, a l t h o u g h p r o d u c e d f rom DEA and C 0 2 , was shown t o be u n s t a b l e a n d c o u l d be c o n v e r t e d b a c k t o D E A . K e n n a r d [51] p r o p o s e d t h e f o l l o w i n g s i m p l i f i e d r e a c t i o n scheme w h i c h i s v a l i d f o r DEA c o n c e n t r a t i o n s o f 0 t o 100 wt%, t e m p e r a t u r e s o f 90 t o 1 7 5 ° C a n d C 0 2 l o a d i n g g r e a t e r t h a n 0 . 2 g C 0 2 / g D E A . THEED BHEP 1 4 In a r e c e n t s t u d y , B l a n c e t a l . [45] r e a c t e d C 0 2 s e p a r a t e l y w i t h DEA a n d HEOD s o l u t i o n s i n a s e a l e d a u t o c l a v e . - The t e m p e r a t u r e o f t h e a u t o c l a v e was v a r i e d f rom 90 t o 1 3 0 ° C . T h e y p r o p o s e d v a r i o u s m e c h a n i s m s f o r t h e f o r m a t i o n o f H E O D , T H E E D , BHEP a n d o t h e r d e g r a d a t i o n c o m p o u n d s . H o w e v e r , no q u a n t i t a t i v e d a t a were p r e s e n t e d i n s u p p o r t o f t h e s e r e a c t i o n m e c h a n i s m s . 2 . 2 . 1 O t h e r d e g r a d a t i o n p r o d u c t s O t h e r t y p e s o f d e g r a d a t i o n p r o d u c t s known as " h e a t s t a b l e s a l t s " may a l s o f o r m i n t h e p r e s e n c e o f any a c i d i c c o n s t i t u e n t s s t r o n g e r t h a n H 2 S and C 0 2 . S u c h s t r o n g a c i d s , r e p o r t e d by H e n r y and G r e n n e r t [ 4 6 , 4 7 ] i n 1955, were l a t e r i d e n t i f i e d by B l a n c e t a l . [ 4 5 ] a s f o r m i c , a c e t i c , p r o p i o n i c . a n d o x a l i c a c i d s . T h e s e a c i d s r e a c t w i t h DEA by p r o t o n t r a n s f e r . H o w e v e r , t h e a n i o n s o f t h e s e a c i d s a r e n o t c a p a b l e o f a c c e p t i n g t h e p r o t o n b a c k f rom t h e p r o t o n a t e d DEA m o l e c u l e d u r i n g t h e r e g e n e r a t i o n p r o c e s s . The DEA m o l e c u l e w h i c h has been p r o t o n a t e d by a s t r o n g a c i d t h u s becomes n e u t r a l i z e d . F o r m a t i o n o f t h e s e a c i d s has been a t t r i b u t e d t o t h e p r e s e n c e o f o x y g e n , b u t t h e m e c h a n i s m o f t h e i r f o r m a t i o n i s n o t c l e a r l y u n d e r s t o o d . Waterman e t a l . [50] r e p o r t e d t h e p r e s e n c e of h e a t s t a b l e a n i o n s s u c h as a c e t a t e , c h l o r i d e , f o r m a t e , o x a l a t e and t h i o s u l p h a t e i n gas t r e a t i n g DEA s o l u t i o n s . 15 I n d u s t r i a l - g r a d e DEA s o l u t i o n s u s u a l l y c o n t a i n s m a l l amount s o f m o n o e t h a n o l a m i n e ( " M E A " ) . MEA c a n a l s o d e g r a d e [ 4 8 , 4 9 ] t o f o r m o x a z o l i d o n e ( " O Z D " ) , 1- (2- h y d r o x y e t h y l ) i m i d a z o l i d o n e ( " H E I " ) , N , N ' - b i s h y d r o x y e t h y 1 ) u r e a ( B H E U ) , and N - ( h y d r o x y e t h y l ) e t h y l e n e d i a m i n e (HEED) [ 4 8 , 4 9 ] . D e g r a d a t i o n compounds o f h i g h m o l e c u l a r w e i g h t h a v e a l s o been s u g g e s t e d b u t n o t i d e n t i f i e d [ 4 , 1 2 ] . T h e s e compounds a r e b e l i e v e d t o be 1 i n e a r - p o l y c a r b a m i d e s c o n t a i n i n g p o l y a l k y l e n e amine s t u c t u r e s . 2 . 3 CORROSION IN DEA SOLUTIONS C o r r o s i o n i n DEA t r e a t i n g p l a n t s h a v e been w i d e l y r e p o r t e d i n t h e l i t e r a t u r e [ 1 1 - 1 4 ] . C o r r o s i o n p r o b l e m s i n some i n d u s t r i a l DEA t r e a t i n g u n i t s i n W e s t e r n C a n a d a have been r e p o r t e d by F i t z e r a l d and R i c h a r d s o n [ 5 2 ] . H a l l and B a r r o n [53] p r e s e n t e d a d e t a i l e d a n a l y s i s o f c o r r o s i o n p r o b l e m s a t t h e Ram R i v e r Gas P l a n t o p e r a t e d by t h e A q u i t a i n e Company o f C a n a d a . The e f f e c t s o f a c i d gas l o a d i n g a n d h i g h t e m p e r a t u r e on c o r r o s i o n a r e w e l l r e c o g n i s e d [ 3 , 5 4 ] . The h i g h e r t h e a c i d gas l o a d i n g and t h e t e m p e r a t u r e , t h e h i g h e r t h e r a t e o f c o r r o s i o n . The e q u i p m e n t p r o c e s s i n g r i c h DEA a t h i g h t e m p e r a t u r e s , s u c h as t h e r i c h s i d e o f t h e l e a n - r i c h a m i n e h e a t e x c h a n g e r , t h e r e b o i l e r and t h e t o p t r a y s o f t h e r e g e n e r a t o r a r e most p r o n e t o c o r r o s i o n . F i g u r e 2.1 shows t h e a r e a s o f a DEA u n i t where c o r r o s i o n i s most l i k e l y t o o c c u r . SWEET GAS 0-H CONDENSER ABSORBER FEED GAS FLASH TANK WATER COOLER CD ACID GASES _ l J AMINE-AMINE HEAT EXCHANGER REGENERATOR REBOILER i Where c o r r o s i o n o c c u r s . F i g u r e 2.1 T y p i c a l f l ow s h e e t of a DEA p l a n t s h o w i n g a r e a s where c o r r o s i o n u s u a l l y o c c u r s . 1 7 2 . 3 . 1 C o r r o s i v i t y o f DEA d e g r a d a t i o n p r o d u c t s P o l d e r m a n e t a l . [48] h a v e r e p o r t e d t h a t t h e m a j o r MEA d e g r a d a t i o n p r o d u c t s ( i . e . 1 - ( 2 - h y d r o x y e t h y l ) i m i d a z o l i d o n e ( " H E I " ) and N - ( h y d r o x y e t h y l ) e t h y l e n e d i a m i n e ( " H E E D " ) a r e c o r r o s i v e . T h e i r f i n d i n g s were l a t e r c o n f i r m e d by L a n g and Mason [ 5 5 ] . C o r r o s i v e n e s s o f MEA d e g r a d a t i o n p r o d u c t s has g e n e r a l l y been a c c e p t e d t o d a t e [ 5 6 - 5 9 ] , H o w e v e r , i n t h e c a s e o f D E A , t h e c o r r o s i v e n e s s o f t h e d e g r a d a t i o n p r o d u c t s i s s t i l l a m a t t e r . o f c o n t r o v e r s y . P o l d e r m a n e t a l . [12] r e p o r t e d i n 1956 t h a t DEA d e g r a d a t i o n p r o d u c t s were c o r r o s i v e . Moore [11 ] i n 1960 was p r o b a b l y t h e f i r s t t o p u b l i s h some i n d u s t r i a l d a t a on c o r r o s i o n i n DEA s y s t e m s . The a u t h o r r e p o r t e d a s u b s t a n t i a l i n c r e a s e i n t h e r a t e o f c o r r o s i o n w i t h t h e c o n c e n t r a t i o n of d e g r a d a t i o n p r o d u c t s , r e a c h i n g 1 mm/year (40 m p y ) . S i n c e t h e n , t h e c o r r o s i v e n a t u r e o f t h e d e g r a d a t i o n p r o d u c t s h a s been d e s c r i b e d i n v a r i o u s p u b l i c a t i o n s [ 1 3 , 1 4 ] . H o w e v e r , B l a n c e t a l . [45] r e c e n t l y p u b l i s h e d d a t a i n s u p p o r t o f t h e c l a i m t h a t DEA d e g r a d a t i o n p r o d u c t s a r e n o t c o r r o s i v e . T h e y s u g g e s t t h a t , w i t h i n t h e o p e r a t i n g t e m p e r a t u r e r a n g e o f . 20 t o 1 0 0 ° C , t h e pH o f 30 wt% DEA s o l u t i o n l i e s b e t w e e n 11 .5 and 10 d e p e n d i n g on t h e c o n c e n t r a t i o n o f d e g r a d a t i o n p r o d u c t s . 18 T h e y p r o p o s e d t h a t , u n d e r t h e s e c o n d i t i o n s , i r o n and c a r b o n s t e e l a r e e i t h e r n o n - c o r r o s i v e o r p a s s i v e a c c o r d i n g t o t h e P o u r b a i x p o t e n t i a l - p H d i a g r a m [ 6 0 ] . A s c h e m a t i c P o u r b a i x p o t e n t i a l - p H d i a g r a m f o r t h e i r o n w a t e r s y s t e m i s g i v e n i n F i g u r e 2 . 2 . A l t h o u g h P o u r b a i x p o t e n t i a l - p H d i a g r a m s c a n p r o v i d e some i n d i c a t i o n on t h e f e a s i b i l i t y o f c o r r o s i o n u n d e r c e r t a i n c o n d i t i o n s , t h e y do n o t p r o v e t h a t i t a c t u a l l y o c c u r s . To o b t a i n an a c c u r a t e p i c t u r e o f what a c t u a l l y t a k e s p l a c e , one has t o r e s o r t t o e x p e r i m e n t a l k i n e t i c s t u d i e s , s u c h as p l o t t i n g p o t e n t i o d y n a m i c p o l a r i z a t i o n c u r v e s f o r t h e s y s t e m u n d e r c o n s i d e r a t i o n [ 6 0 ] . 19 F i g u r e 2.2 P o u r b a i x p o t e n t i a l - p H d i a g r a m f o r t h e i r o n - w a t e r s y s t e m . 20 The potential-pH diagram to which Blanc et al.[44] referred (see Figure 2.2) is representative of the iron-water system. However, the DEA system, in general, is far more complex due to the following reasons : ^ 1. The system consists of iron, carbon dioxide, hydrogen sulphide, water and DEA. 2. The shape of the potential-pH curve changes substantially with temperature; in the case of the iron-water system, the region of corrosion widens and the region of passivity narrows. 3. Degraded i n d u s t r i a l DEA solutions usually contain heat stable s a l t s . These s a l t s (such as cyanides) may form complexes with the metal thus invalidating the use of Pourbaix potential-pH diagram [60]. Blanc et a l . [45] carried out their corrosion experiment by immersing mild steel coupons in 3N (30 wt%) aqueous DEA solutions at 80°C with a H2S p a r t i a l pressure of 2000 kPa (290 p s i ) . After 500 hours of immersion, the weight loss measurement of the coupons yielded a corrosion rate of 0.05 mm/year (2 mpy). Choy [43], in his work on DEA degradation, found hydrogen sulphide to i n h i b i t DEA degradation. In l i g h t of Choy's work, the results of Blanc et a l . [45] are understandable, as the DEA solution did not degrade noticeably. 21 In a n o t h e r c o r r o s i o n t e s t , B l a n c e t a l . [45] u s e d an a q u e o u s m i x t u r e o f - D E A and BHEP and o b t a i n e d a c o r r o s i o n r a t e o f 0 . 0 2 mm/year ( 0 . 8 m p y ) , l e s s t h a n t h a t o b t a i n e d f o r t h e D E A - H 2 S - Fe s y s t e m . T h e y a t t r i b u t e d t h e l o w e r c o r r o s i o n r a t e t o t h e p r e s e n c e o f B H E P , w h i c h i s a l s o b a s i c i n n a t u r e . H o w e v e r , t h i s i s i n c o n t r a d i c t i o n t o t h e f i n d i n g s o f H a k k a e t a l . [ 4 1 ] . The l a t t e r c o n d u c t e d c o r r o s i o n t e s t s w i t h SAE1010 low c a r b o n s t e e l immersed i n b o i l i n g , a q u e o u s s o l u t i o n s o f 6 wt.% D E A , BHEP, THEED a n d H E E D . T h e y r e p o r t e d a w e i g h t l o s s o f 1.8 mg i n t h e c a s e o f BHEP c o m p a r e d t o a w e i g h t l o s s o f 0 . 4 mg i n t h e c a s e o f D E A . R e c e n t e x t e n s i v e work on DEA d e g r a d a t i o n by M e i s e n and K e n n a r d [10 ] r e v e a l e d t h a t H E O D , T H E E D and BHEP a r e t h e m a j o r DEA d e g r a d a t i o n p r o d u c t s . The s t a t e m e n t by B l a n c e t a l . [45] t h a t DEA d e g r a d a t i o n p r o d u c t s a r e n o t c o r r o s i v e c a n n o t be r e g a r d e d as p r o v e n s i n c e n o t a l l t h e m a j o r DEA d e g r a d a t i o n p r o d u c t s were e x a m i n e d i n t h e i r c o r r o s i o n t e s t s . 22 2 . 4 ROLE OF HEAT EXCHANGER V A R I A B L E S To ' d a t e , no r e s e a r c h ha s been d i r e c t e d t o w a r d s t h e r o l e o f t h e h e a t e x c h a n g e r o p e r a t i o n r e g a r d i n g d e g r a d a t i o n o f D E A . H o w e v e r , i t i s r e c o g n i s e d t h a t t h e DEA s o l u t i o n i s p a r t i c u l a r l y s u s c e p t i b l e t o d e g r a d a t i o n i n t h e r i c h s o l u t i o n s i d e o f l e a n - r i c h h e a t e x c h a n g e r and i n t h e r e b o i l e r . T h i s may be due t o t h e e l e v a t e d t e m p e r a t u r e a n d d i s s o l v e d a c i d ga s l e v e l i n t h e s o l u t i o n . B a l l a r d [61] p u b l i s h e d c o m p r e h e n s i v e g u i d e l i n e s f o r t h e p r o p e r d e s i g n a n d o p e r a t i o n o f amine r e b o i l e r s . He e m p h a s i z e d c o r r o s i o n p r o b l e m s and s u g g e s t e d t h a t : * s t eam t e m p e r a t u r e s a b o v e 1 4 0 ° C ( 2 8 5 ° F ) be a v o i d e d t o p r e v e n t e x c e s s i v e s k i n t e m p e r a t u r e s on t h e t u b e s ; * t h e maximum a l l o w a b l e r e b o i l e r t e m p e r a t u r e be k e p t a t 1 2 7 ° C ( 2 6 0 ° F ) t o p r e v e n t amine d e g r a d a t i o n ; * p a r t i a l f l o o d i n g o f t h e r e b o i l e r t u b e s be a v o i d e d t o p r e v e n t h i g h h e a t l o a d s i n t h e t o p s e c t i o n o f t h e t u b e b u n d l e ; * t h e r e b o i l e r b u n d l e a l w a y s be k e p t c o v e r e d w i t h 0 . 1 5 - 0 . 2 0 m (6 - 8 i n c h e s ) o f l i q u i d t o p r e v e n t l o c a l i s e d d r y i n g a n d o v e r h e a t i n g . T h e s e g u i d e l i n e s s h o u l d m i n i m i s e n o t o n l y c o r r o s i o n b u t a l s o d e g r a d a t i o n by p r e v e n t i n g l o c a l h o t s p o t s ( o r h i g h s k i n t e m p e r a t u r e s ) . 23 M c M i n and F a r m e r [54] a l s o e m p h a s i z e t h e i m p o r t a n c e o f m e t a l s k i n t e m p e r a t u r e s i n c o n n e c t i o n w i t h c o r r o s i o n . A m i n e s a r e known t o a c t a s c o r r o s i o n i n h i b i t o r s by f o r m i n g f i l m s on m e t a l s u r f a c e s [ 6 1 ] . F o r t h i s r e a s o n , t h e r e i s a g e n e r a l t e n d e n c y t o k e e p s o l u t i o n v e l o c i t i e s i n h e a t e x c h a n g e r s a n d p i p e s l o w . In a d d i t i o n , h i g h e r s o l u t i o n v e l o c i t i e s may l e a d t o b r e a k o u t o f a c i d g a s e s f rom t h e s o l u t i o n and t h u s c a u s e c o r r o s i o . n [ 5 3 , 6 2 , 6 3 ] . B a l l a r d [61 ] recommends maximum s o l u t i o n v e l o c i t i e s o f 0 . 6 m / s e c (2 f t / s e c ) i n h e a t e x c h a n g e r s , 3 - 6 m/ sec (10-20 f t / s e c ) i n p i p e s a n d 4 . 5 - 6 m / s e c (15 -20 f t / s e c ) i n v a l v e s . 2 . 5 FOULING OF HEAT EXCHANGERS A l t h o u g h t h e a c c u m u l a t i o n o f i m p u r i t i e s u s u a l l y i n c r e a s e s t h e f o u l i n g r e s i s t a n c e i n h e a t e x c h a n g e r s , no p a r t i c u l a r a t t e n t i o n ha s been f o c u s e d on DEA h e a t e x c h a n g e r s . H a l l a n d B a r r o n [53] r e p o r t e d f o u l i n g o f s u c h h e a t e x c h a n g e r s but d i d n o t i d e n t i f y i t s c a u s e . H o w e v e r , t h e y d i d m e n t i o n t h e e x i s t e n c e o f c o r r o s i o n a n d d e g r a d a t i o n p r o d u c t s . F o u l i n g i n DEA h e a t e x c h a n g e r s i s most l i k e l y c a u s e d by c h e m i c a l r e a c t i o n f o u l i n g . T e m p e r a t u r e e f f e c t s t e n d t o d o m i n a t e c h e m i c a l r e a c t i o n r a t e s and f o u l i n g t h e r e f o r e i n c r e a s e s e x p o n e n t i a l l y w i t h a b s o l u t e t e m p e r a t u r e [ 6 4 ] . W a t k i n s o n a n d E p s t e i n [65] r e p o r t e d e x p o n e n t i a l i n c r e a s e s i n f o u l i n g r a t e s w i t h w a l l t e m p e r a t u r e s and h e a t f l u x . T h e y a l s o r e p o r t e d a d e c r e a s e i n f o u l i n g r a t e w i t h i n c r e a s i n g f l o w r a t e . Shah e t . 24 a l . [66] r e p o r t e d t h a t f o u l i n g r a t e s were h i g h e r i n t u b e s of s m a l l d i a m e t e r . T h e s e f i n d i n g s may a l s o have i m p o r t a n t i m p l i c a t i o n s i n t h e f o u l i n g o f DEA h e a t e x c h a n g e r s . 2 . 6 A N A L Y S I S OF DEA SOLUTIONS Q u a n t i t a t i v e a n a l y s i s o f p a r t i a l l y d e g r a d e d DEA s o l u t i o n s has p r o v e n t o be r a t h e r d i f f i c u l t due t o t h e f a c t t h a t t h e d e g r a d a t i o n compounds h a v e f a i r l y low v a p o r p r e s s u r e s , decompose a t e l e v a t e d t e m p e r a t u r e s , a r e h i g h l y p o l a r a n d o c c u r i n low c o n c e n t r a t i o n s . H e n r y a n d G r e n n e r t [ 4 6 , 4 7 ] were among t h e f i r s t r e s e a r c h e r s i n t e r e s t e d i n t h e d e t e c t i o n a n d m e a s u r e m e n t s o f h e a t s t a b l e s a l t s i n r e f i n e r y s a m p l e s . T h e y i n v e s t i g a t e d f o u r t y p e s o f a c i d i c m a t e r i a l s : o r g a n i c a c i d s ; c h l o r i d e s ; c y a n i d e s and t h i o c y a n a t e s ; s u l p h i t e s , s u l p h a t e s , and t h i o s u l p h a t e s . T h e y u s e d p o t e n t i o m e t r i c t i t r a t i o n f o r t h e d e t e c t i o n o f o r g a n i c a c i d s . T h e y a l s o d i s c u s s e d c o n v e n t i o n a l wet c h e m i c a l methods ( s u c h aS t i t r a t i o n and K j e l d a h l t o t a l n i t r o g e n d e t e r m i n a t i o n ) a s w e l l as o t h e r m e t h o d s f o r t h e d e t e r m i n a t i o n o f t o t a l s u l p h u r , s u l p h i d e , m e r c a p t i d e , s u l p h a t e , t h i o c y a n a t e , c y a n i d e , c h l o r i d e , c a r b o n a t e , a l k a l i n i t y and s o d i u m . H o w e v e r , t h e i r s t u d y f a i l e d t o d e t e c t t h e p r e s e n c e o f DEA d e g r a d a t i o n c o m p o u n d s . 25 C o n v e n t i o n a l wet c h e m i c a l m e t h o d s f o r a n a l y s i n g DEA s o l u t i o n a r e a l s o d e s c r i b e d i n r e f e r e n c e [ 2 6 ] . A g a i n t h e s e m e t h o d s a r e n o t c a p a b l e o f i d e n t i f y i n g DEA d e g r a d a t i o n c o m p o u n d s . P o l d e r m a n and S t e e l e [12] a t t e m p t e d t o a n a l y s e t h e DEA d e g r a d a t i o n compounds by f r a c t i o n a l d i s t i l l a t i o n a n d c r y s t a l l i z a t i o n and were a b l e t o i s o l a t e a n d i d e n t i f y N , N ' - b i s ( h y d r o x y e t h y l ) p i p e r a z i n e ( " B H E P " ) . Hakka e t a l . [41] u s e d i n f r a r e d s p e c t r o s c o p y , mass s p e c t r o s c o p y , gas c h r o m a t o g r a p h y a n d t h i n l a y e r c h r o m a t o g r a p h y t o d e t e c t T H E E D . Gough [67] p r o v i d e d a c o m p r e h e n s i v e s t u d y on t h e a n a l y s i s o f DEA s o l u t i o n s . He d e s c r i b e d two a n a l y t i c a l s c h e m e s : a) a c o m p r e h e n s i v e scheme f o r c o m p o n e n t a n a l y s i s , t o o b t a i n d e t a i l e d i n f o r m a t i o n on c o m p o s i t i o n , b) a s i m p l e scheme f o r q u a l i t y e v a l u a t i o n , a p p r o p r i a t e f o r r o u t i n e a n a l y s i s . H o w e v e r , t h e s e p r o c e d u r e s were n o t s u i t a b l e f o r d e t e c t i n g o r i d e n t i f y i n g i n d i v i d u a l d e g r a d a t i o n c o m p o u n d s . B r y d i a and P e r s i n g e r [68] d e s c r i b e d a c h r o m a t o g r a p h i c t e c h n i q u e , u s i n g d e r i v a t i z a t i o n f o r t h e a n a l y s i s o f e t h a n o l a m i n e s o l u t i o n s . T r i f l u o r o a c e t y l a n h y d r i d e was u s e d t o c o n v e r t n o n - v o l a t i l e a m i n e s i n t o v o l a t i l e a m i n e t r i f l u o r o a c e t y l d e r i v a t i v e s p r i o r t o c h r o m a t o g r a p h i c s e p a r a t i o n . A l t h o u g h t h e m e t h o d was f a i r l y s i m p l e and r a p i d , t h e a u t h o r s r e p o r t e d d i f f i c u l t i e s w i t h r e p r o d u c i b i l i t y , p r e c i s i o n , a n d t h e p r e s e n c e o f w a t e r . 26 P i e k o s e t a l . [69] e l i m i n a t e d t h e s h o r t c o m i n g s e x p e r i e n c e d by B r y d i a e t a l . [68] by c o n v e r t i n g t h e a l k a n o l a m i n e s t o t r i m e t h y l s i l y l d e r i v a t i v e s . N , 0 - b i s ( t r i m e t h y l s i l y l ) a c e t a m i d e was u s e d a s a s i l y l a t i o n r e a g e n t , w h i c h r e a c t s w i t h b o t h t h e a m i n o a n d h y d r o x y l g r o u p s o f t h e a l k a n o l a m i n e s . T h i s m e t h o d p r o d u c e s f a i r l y s t a b l e compounds w h i c h a r e more e a s i l y s e p a r a t e d a n d i d e n t i f i e d by gas c h r o m a t o g r a p h y . T h e a d d i t i o n o f a t r i m e t h y l s i l y l g r o u p . a l s o d e c r e a s e s t h e p o l a r i t y o f t h e a l k a n o l a m i n e s a n d r e d u c e s h y d r o g e n b o n d i n g . S i l y l a t e d compounds a r e more v o l a t i l e a n d more s t a b l e due t o r e d u c t i o n o f r e a c t i v e s i t e s . The a u t h o r s were a b l e t o s e p a r a t e M E A , D E A and TEA d e r i v a t i v e s and f o u n d t h a t t h e p r e s e n c e o f up t o 5% w a t e r c o u l d be t o l e r a t e d p r o v i d e d t h e s i l y l a t i o n a g e n t i s p r e s e n t i n e x c e s s . Saha e t a l . [ 70 ] d e s c r i b e d t h e p r o b l e m s o f d e r i v a t i z a t i o n o f a m i n e s p r i o r t o ga s c h r o m a t o g r a p h i c a n a l y s i s . Among t h e i n c o n v e n i e n c e s m e n t i o n e d w e r e : t i m e c o n s u m i n g p r o c e s s o f d e r i v a t i v e p r e p a r a t i o n , p r o b a b i l i t y o f i n c o m p l e t e d e r i v a t i z a t i o n a n d i n s t a b i l i t y o f t h e d e r i v a t i v e s f o r l o n g p e r i o d s . C o n s e q u e n t l y , t h e y i n v e s t i g a t e d t h e use o f o r g a n i c p o l y m e r b e a d s as c o l u m n p a c k i n g a n d f o u n d t h a t T e n a x G . C . , a p o r o u s p o l y m e r b a s e d on 2 , 6 * - d i p h e n y l p a r a p h e n y l e n e o x i d e , was a b l e t o s e p a r a t e a l k a n o l a m i n e s w i t h e x c e l l e n t r e s u l t s . T h e y were a b l e t o s e p a r a t e an a q u e o u s m i x t u r e o f M E A , D E A a n d TEA i n l e s s t h a n e i g h t m i n u t e s u s i n g a 3 . 1 7 5 mm O . D . , 1.2192 m l o n g ( 1 / 8 " O . D . , 4 f t l o n g ) s t a i n l e s s s t e e l c o l u m n . No s ample p r e p a r a t i o n was r e q u i r e d and t h e c o l u m n was n o t a f f e c t e d by w a t e r . 27 Choy and M e i s e n [42 ] were t h e f i r s t t o i n v e s t i g a t e s p e c i f i c a l l y t h e a n a l y s i s o f DEA and i t s d e g r a d a t i o n p r o d u c t s . T h e y a d o p t e d a t e c h n i q u e w h i c h c o n s i s t e d o f f i r s t d r y i n g t h e d e g r a d e d DEA s a m p l e by a i r s t r i p p i n g , t h e n d i s s o l v i n g i t i n d i m e t h y l f o r m a m i d e a n d f i n a l l y s i l y l a t i n g i t w i t h N , 0 - b i s ( t r i m e t h y l s i l y l ) a c e t a m i d e . The s i l y l a t e d compounds were t h e n s e p a r a t e d u s i n g a 3 .175 mm O . D . , 1 .8288 m l o n g ( 1 / 8 " , 6 f t l o n g ) s t a i n l e s s s t e e l c o l u m n p a c k e d w i t h 8% OV17 on 8 0 / 1 0 0 mesh c h r o m o s o r b f o l l o w e d by f l a m e i o n i z a t i o n d e t e c t i o n . N i t r o g e n was u s e d a s t h e c a r r i e r g a s . A l t h o u g h t h e method was a c c u r a t e and r e l i a b l e , i t was t i m e c o n s u m i n g , r e q u i r e d c o n s i d e r a b l e c a r e d u r i n g s i l y l a t i o n p a r t i c u l a r l y w i t h r e g a r d t o r e m o v a l o f w a t e r . C o n s e q u e n t l y , i t was n o t s u i t a b l e f o r p l a n t u s e . K e n n a r d [51 ] d e v e l o p e d a s i m p l e , r e l i a b l e a n d d i r e c t gas c h r o m a t o g r a p h i c t e c h n i q u e f o r t h e a n a l y s i s o f DEA and i t s d e g r a d a t i o n c o m p o u n d s . He u s e d Tenax G . C . a s t h e c o l u m n p a c k i n g . He was a b l e t o d e t e c t 14 compounds i n d e g r a d e d DEA s o l u t i o n s a n d l a t e r i d e n t i f i e d them by u s i n g c o m b i n e d gas c h r o m a t o g r a p h y a n d mass s p e c t r o m e t r y . He was a b l e t o d e t e c t DEA a n d known d e g r a d a t i o n p r o d u c t s a t c o n c e n t r a t i o n s a s low as a b o u t 0 . 5 wt%. The r e p r o d u c i b i l i t y was t y p i c a l l y ± 5%. 28 CHAPTER 3 EXPERIMENTAL EQUIPMENT AND PROCESS D E S C R I P T I O N 3.1 EQUIPMENT DESIGN A p r i n c i p a l o b j e c t i v e o f t h e p r e s e n t work was t o p e r f o r m c a r e f u l l y c o n t r o l l e d DEA d e g r a d a t i o n e x p e r i m e n t s u n d e r f l o w c o n d i t i o n s t y p i c a l l y e n c o u n t e r e d i n i n d u s t r i a l h e a t t r a n s f e r e q u i p m e n t s u c h as l e a n - r i c h h e a t e x c h a n g e r s a n d r e b o i l e r s . The f l o w s h e e t o f t h e e q u i p m e n t d e v e l o p e d f o r t h i s p u r p o s e i s shown i n F i g u r e 3 . 1 . The e q u i p m e n t e s s e n t i a l l y c o n s i s t s o f a h e a t e x c h a n g e r t u b e , a h i g h p r e s s u r e a u t o c l a v e , a pump, a w a t e r c o o l e r and a s s o c i a t e d i n s t r u m e n t a t i o n . F i g u r e 3 .2 i s a p h o t o g r a p h o f t h e e n t i r e e q u i p m e n t w h e r e a s F i g u r e 3 .3 shows t h e m a i n c o m p o n e n t s o f t h e e q u i p m e n t . 3 .2 PROCESS D E S C R I P T I O N The a q u e o u s DEA s o l u t i o n i s f i r s t s a t u r a t e d w i t h C 0 2 i n t h e h i g h p r e s s u r e a u t o c l a v e . I t i s t h e n f i l t e r e d and pumped u n d e r h i g h p r e s s u r e t h r o u g h t h e h e a t e x c h a n g e r t u b e . The h e a t e x c h a n g e r t u b e i s t h e h e a r t o f t h e e q u i p m e n t where DEA i s h e a t e d t o t h e d e s i r e d t e m p e r a t u r e by means o f a h e a t t r a n s f e r f l u i d i n an a l u m i n u m t a n k . The h e a t t r a n s f e r f l u i d i t s e l f i s h e a t e d by an i m m e r s i o n h e a t e r . The t e m p e r a t u r e o f t h e h e a t t r a n s f e r f l u i d i s k e p t u n i f o r m by means o f a s t i r r e r . F i g u r e 3.1 Flow s h e e t of t h e equipment f o r t h e s t u d y of DEA d e g r a d a t i o n i n h e a t e x c h a n g e r s . 30 F i g u r e 3 . 2 P h o t o g r a p h of o v e r a l l v i e w of t h e e q u i p m e n t . 3 1 F i g u r e 3.3 P h o t o g r a p h s h o w i n g ma in c o m p o n e n t s of t h e e q u i p m e n t . 32 D e g r a d a t i o n r e a c t i o n s t a k e p l a c e i n s i d e t h e h e a t t r a n s f e r t u b e . T h e t e m p e r a t u r e o f t h e DEA s o l u t i o n i s t h e n l o w e r e d a g a i n t o t h e a u t o c l a v e t e m p e r a t u r e by h e a t e x c h a n g e i n a w a t e r c o o l e r . The a u t o c l a v e t e m p e r a t u r e , h e a t e x c h a n g e r i n l e t a n d o u t l e t t e m p e r a t u r e s , a n d w a t e r c o o l e r i n l e t a n d o u t l e t t e m p e r a t u r e s a r e m e a s u r e d by t h e r m o c o u p l e s . The a u t o c l a v e p r e s s u r e , h e a t e x c h a n g e r i n l e t and o u t l e t p r e s s u r e s a r e m o n i t o r e d by means o f B o u r d o n p r e s s u r e g a u g e s . T h i s p r o c e s s o f h e a t i n g and c o o l i n g o f t h e DEA s o l u t i o n i s c a r r i e d o u t c o n t i n u o u s l y f o r a l o n g p e r i o d o f t i m e ( t y p i c a l l y a b o u t 120 t o 240 h r ) . 10 mL s a m p l e s a r e w i t h d r a w n a t l e a s t ' eve ry 24 h o u r s and a n a l y z e d f o r d e g r a d a t i o n compounds by gas. c h r o m a t o g r a p h y . 3 . 3 EQUIPMENT D E S C R I P T I O N 3 . 3 . 1 A u t o c l a v e The a u t o c a l v e i s a 4 L , 316 s t a i n l e s s s t e e l v e s s e l ( A u t o c l a v e E n g i n e e r s , E r i e , P A . ) c a p a b l e o f w i t h s t a n d i n g p r e s s u r e s up t o 3 4 . 5 MPa (5000 p s i ) . I t i s u s e d as t h e s o l u t i o n c o n t a i n e r a s w e l l a s t o s a t u r a t e t h e s o l u t i o n w i t h c a r b o n d i o x i d e a t t h e d e s i r e d p r e s s u r e a n d t e m p e r a t u r e . I t i s p r o v i d e d w i t h 6 p o r t s , w h i c h c a n be u s e d as i n l e t and o u t l e t p o r t s f o r i n c o m i n g and o u t g o i n g s t r e a m s . T o p r e v e n t e x c e s s i v e p r e s s u r e b u i l d u p , one o f t h e a u t o c l a v e p o r t s i s c o n n e c t e d t o an a d j u s t a b l e p r e s s u r e r e l i e f v a l v e . 33 3 . 3 . 2 H e a t e x c h a n g e r The . h e a t e x c h a n g e r s e t - u p c o n s i s t s o f a s i n g l e h e a t e x c h a n g e r t u b e , an a l u m i n u m t a n k c o n t a i n i n g h e a t t r a n s f e r f l u i d , a s t i r r e r and an i m m e r s i o n h e a t e r . The h e a t e x c h a n g e r t u b e i s a h e l i c a l c o i l 4 . 8 0 m l o n g , 3 . 1 7 5 mm OD, a n d 2 . 0 3 2 mm I D . The t u r n i n g r a d i u s o f t h e t u b e i s 0 . 4 0 6 4 m (16 i n c h ) . The t u b e , w h i c h was made o f 316 s t a i n l e s s s t e e l , was immersed i n t h e a l u m i n u m t a n k ( 0 . 7 m I D , 0 . 7 5 m h i g h ) . The t a n k was f i l l e d w i t h a p p r o x i m a t e l y 150 L c o m m e r c i a l S h e l l T h e r m i a O i l - C , a p e t r o l e u m - b a s e d h e a t t r a n s f e r f l u i d . The t a n k was f i t t e d w i t h 1/3 HP v a r i a b l e s p e e d (100 - 1625 rpm) L i g h t n i n S t i r r e r ( G r e e y M i x i n g E q u i p m e n t , T o r o n t o , M o d e l NS-1 ( E V S ) ) . The t a n k was c o n n e c t e d t o a v a p o r r e c o v e r y s y s t e m ( see S e c t i o n 3 . 3 . 8 ) . The s t i r r e r was a t t a c h e d t o a 0 . 9 1 4 m l o n g , 12 .7 mm d i a . , 304 s t a i n l e s s s t e e l s h a f t w h i c h was c o n n e c t e d t o a s i n g l e 0 . 1 0 1 6 m d i a m e t e r m a r i n e p r o p e l l e r t y p e b l a d e . A 10 kw o v e r - t h e - s i d e i m m e r s i o n h e a t e r ( C h r o m a l o x C a n a d a , R e x d a l e , O n t a r i o , M o d e l K T L O - 3 1 0 - 1 ) was u s e d t o h e a t t h e h e a t t r a n s f e r f l u i d . The h e a t e r i s made up o f 3 s t e e l - s h e a t h e d t u b u l a r h e a t i n g e l e m e n t s w e l d e d i n t o a j u n c t i o n b o x . The h e a t e r was f i t t e d w i t h t h r e e 0 . 1 0 1 6 m l o n g s l u d g e l e g s and was p l a c e d i n s i d e t h e a l u m i n u m t a n k . A 3 p h a s e , 240 v o l t s power l i n e p r o v i d e d t h e r e q u i r e d e l e c t r i c i t y . 34 3 . 3 . 3 S o l u t i o n pump The s o l u t i o n pump i s a m a g n e t i c a l l y d r i v e n g e a r pump ( M i c r o p u m p , C o n c o r d , C T . , M o d e l 210-513 ) d r i v e n by a 1/6 HP e x p l o s i o n - p r o o f m o t o r . The w e t t e d p a r t s were made o f 316 s t a i n l e s s s t e e l . The pump i s c a p a b l e o f o p e r a t i n g u n d e r h i g h p r e s s u r e and i s r a t e d up t o 10 .3 MPa (1500 p s i ) a t a t e m p e r a t u r e of 1 3 5 ° C (275 ° F ) . 3 . 3 . 4 W a t e r c o o l e r The w a t e r c o o l e r i s a 12 .19 m (40 f t ) l o n g h e l i c a l c o i l , 12 .7 mm ( 0 . 5 i n c h ) OD, 10 .92 mm ( 0 . 4 3 0 i n c h ) I D , 316 s t a i n l e s s s t e e l t u b e , p l a c e d i n s i d e a 0 . 5 0 8 m (20 i n c h ) d i a m e t e r , 0 . 9 1 4 4 m (3 f t ) h i g h PVC s h e l l . The h o t DEA s o l u t i o n p a s s e s downwards i n t h e c o i l and i s c o o l e d by an upward f l o w o f water , f l o w i n g t h r o u g h t h e PVC s h e l l . 3 . 3 . 5 F l o w m e t e r The m e t e r u s e d t o m e a s u r e t h e DEA f l o w r a t e c o n s i s t s o f a 1.75 mm ( 0 . 0 6 9 i n c h ) I D , - 3 . 1 7 mm ( 0 . 1 2 5 i n c h ) OD, 5 0 . 8 mm (2 i n c h e s ) l o n g c a p i l l a r y t u b e c o n n e c t e d t o a d i f f e r e n t i a l p r e s s u r e gauge ( O r a n g e R e s e a r c h I n c . , M i l f o r d , C T . , M o d e l 1502 D G ) . F l o w r a t e was m e a s u r e d a t 60 ° C a t t h e i n l e t o f t h e t h e h e a t t r a n s f e r t u b e . The p r e s s u r e gauge was c a l i b r a t e d t o g i v e f l o w r a t e as a f u n c t i o n o f p r e s s u r e d r o p . The c a l i b r a t i o n c u r v e i s shown i n F i g u r e 3 . 4 . se 36 The c a l i b r a t i o n was done by m e a s u r i n g t h e f l o w o f 30 wt% DEA s o l u t i o n f o r a g i v e n t i m e a t a p a r t i c u l a r m e t e r r e a d i n g by means o f a s t o p w a t c h and a g r a d u a t e d c y l i n d e r . The a v e r a g e of a t l e a s t 10 r e a d i n g s were t a k e n f o r e a c h f l o w r a t e i n o r d e r t o m i n i m i s e t h e e r r o r . 3 . 3 . 6 T e m p e r a t u r e c o n t r o l l e r The t e m p e r a t u r e c o n t r o l l e r i s a p r o p o r t i o n a l c o n t r o l l e r (Omega, S t a m f o r d , C T . , M o d e l 4 9 ) . I t was c o n n e c t e d t o a t h e r m o c o u p l e p l a c e d a b o u t 10 mm f rom t h e h e a t i n g e l e m e n t s t o measure t h e t e m p e r a t u r e o f t h e h e a t t r a n s f e r f l u i d . The c o n t r o l l e r t h e n c o m p a r e s t h e m e a s u r e d t e m p e r a t u r e w i t h t h e s e t p o i n t a n d t a k e s c o r r e c t i v e p r o p o r t i o n a l a c t i o n by c o n t r o l l i n g t h e e l e c t r i c i t y s u p p l y t o t h e h e a t e r . 3 . 3 . 7 T e m p e r a t u r e m e a s u r e m e n t s T e m p e r a t u r e s were m e a s u r e d by t h e r m o c o u p l e s ( J - t y p e , I r o n - c o n s t a n t a n ) c o n n e c t e d t o a d i g i t a l t e m p e r a t u r e i n d i c a t o r ( D o r i c , T r e n d i c a t o r 41 OA) by means o f a m u l t i p l e r o t a r y s w i t c h . 3 . 3 . 8 V a p o r r e c o v e r y s y s t e m The v a p o r r e c o v e r y s y s t e m c o n s i s t e d of a c o n d e n s e r , a 2L c o l l e c t i o n t a n k a n d a w a t e r e j e c t o r . V a p o r g e n e r a t e d i n t h e h e a t t r a n s f e r f l u i d t a n k was c o n d e n s e d i n a w a t e r c o n d e n s e r 37 p l a c e d a t t h e t o p o f t h e t a n k . The o t h e r end o f t h e c o n d e n s e r was c o n n e c t e d t o a c o l l e c t o r t a n k , where t h e c o n d e n s e d h e a t t r a n s f e r f l u i d i s c o l l e c t e d . In o r d e r t o p r e v e n t l e a k a g e o f v a p o r f r o m t h e t a n k , t h e v a p o r r e c o v e r y s y s t e m was c o n n e c t e d .to a w a t e r e j e c t o r , w h i c h e n s u r e d t h a t a l l t h e v a p o r g e n e r a t e d i n t h e t a n k p a s s e d t h r o u g h t h e c o n d e n s e r . 3 . 4 SYSTEM PREPARATION In o r d e r t o p r e v e n t o x y g e n f rom c o m i n g i n c o n t a c t w i t h t h e DEA s o l u t i o n , t h e h e a t t r a n s f e r t u b e i s p u r g e d w i t h c a r b o n d i o x i d e f o r a b o u t 2 min b e f o r e e a c h r u n . A f t e r p u r g i n g , a s l i g h t p o s i t i v e p r e s s u r e 205 t o 239 kPa (15 - 20 p s i g ) i s m a i n t a i n e d i n o r d e r t o e x c l u d e t h e p o s s i b i l i t y o f a i r r e - e n t e r i n g t h e s y s t e m . 3 . 5 SYSTEM LOADING A f e e d t a n k o f 4L c a p a c i t y , shown i n F i g u r e 3 . 5 was u s e d f o r l o a d i n g t h e s y s t e m . The f e e d t a n k , u s u a l l y f i l l e d w i t h 2 . 5 L o f a q u e o u s DEA s o l u t i o n o f t h e d e s i r e d c o n c e n t r a t i o n was p u t u n d e r p o s i t i v e p r e s s u r e , s l i g h t l y h i g h e r t h a n t h a t o f t h e s y s t e m 170 kPa (10 p s i g ) by i n t r o d u c i n g c a r b o n d i o x i d e . The o u t l e t p o r t o f t h e f e e d t a n k was t h e n c o n n e c t e d t o t h e i n l e t p o r t of t h e a u t o c l a v e . The s y s t e m t h e n c o u l d be l o a d e d s i m p l y by o p e n i n g v a l v e s VA01 and VA02 ( s e e F i g u r e 3 . 5 ) . FEED TANK V A 0 2 AUTOCLAVE H X H V A 0 1 C O , SUPPLY F i g u r e 3.5 S c h e m a t i c d i a g r a m o f t h e f e e d t a n k s y s t e m . oo 39 T h i s m e t h o d a l l o w e d l o a d i n g o f t h e s o l u t i o n w i t h o u t i n t r o d u c i n g a i r i n t o t h e s y s t e m . L o a d i n g u s u a l l y r e q u i r e d a b o u t 10 - 15 m i n . A f t e r s o l u t i o n l o a d i n g was c o m p l e t e d , t h e a u t o c l a v e i n l e t v a l v e was s h u t o f f , and t h e f e e d t a n k d i s c o n n e c t e d f rom t h e s y s t e m . The t o t a l l i q u i d i n v e n t o r y was k e p t s m a l l t o m i n i m i s e t h e t o t a l t i m e r e q u i r e d f o r e a c h r u n . H o w e v e r , e n o u g h l i q u i d i n v e n t o r y was p r o v i d e d f o r a d e q u a t e c i r c u l a t i o n t h r o u g h o u t t h e s y s t e m as w e l l a s f o r s o l u t i o n s a m p l i n g . The minimum l i q u i d i n v e n t o r y was f o u n d t o be a b o u t 2 . 5 L . 3 . 6 START UP A f t e r l o a d i n g t h e s y s t e m w i t h DEA s o l u t i o n , t h e f o l l o w i n g s t e p s were t a k e n : 1 . The w a t e r i n l e t v a l v e t o t h e h e a t e x c h a n g e r t a n k o v e r h e a d c o n d e n s e r was o p e n e d . 2 . The s t i r r e r s p e e d was r a i s e d t o a b o u t 200 r p m . 3 . The t e m p e r a t u r e c o n t r o l l e r s e t p o i n t was s e t t o 50 ° C and t h e e l e c t r i c h e a t e r was s w i t c h e d o n . 40 The t e m p e r a t u r e of t h e he a t t r a n s f e r f l u i d was g r a d u a l l y r a i s e d t o t h e d e s i r e d t e m p e r a t u r e ( t y p i c a l l y a b o u t 250°C) by g r a d u a l l y i n c r e a s i n g t h e t e m p e r a t u r e c o n t r o l l e r s e t p o i n t and t h e s t i r r e r s p e e d . The s o l u t i o n b y - p a s s v a l v e FCV2 was f u l l y opened. The s y s t e m p r e s s u r e was r a i s e d t o 791 kPa ( l O O p s i g ) by o p e n i n g t h e c a r b o n d i o x i d e s u p p l y v a l v e FCV3. The pump was s t a r t e d w i t h t h e by p a s s v a l v e FCV2 f u l l y o pen. T h i s i s not o n l y r e q u i r e d f o r t h e s t a r t u p of t h e pump, but a l s o h e l p s i n s a t u r a t i n g t h e DEA s o l u t i o n w i t h c a r b o n d i o x i d e . The s y s t e m p r e s s u r e was g r a d u a l l y i n c r e a s e d by o p e n i n g t h e c a r b o n d i o x i d e s u p p l y v a l v e FCV3 t o t h e d e s i r e d v a l u e , i . e . t y p i c a l l y 4238 kPa (600 p s i g ) . The f l o w t h r o u g h t h e h e a t e x c h a n g e r t u b e was s t a r t e d and g r a d u a l l y i n c r e a s e d t o i t s maximum t o b r i n g t h e a u t o c l a v e t e m p e r a t u r e up t o t h e d e s i r e d t e m p e r a t u r e ( t y p i c a l l y 60 ° C ) , by o p e n i n g t h e f l o w c o n t r o l v a l v e FCV1 and c l o s i n g t h e b y - p a s s v a l v e FCV2. 41 10 . Maximum f l o w was c o n t i n u e d u n t i l t h e s o l u t i o n t e m p e r a t u r e i n t h e a u t o c l a v e r e a c h e d t h e d e s i r e d t e m p e r a t u r e ( t y p i c a l l y 60 ° C ) . U s u a l l y t h i s was a c h i e v e a b l e w i t h i n 5 m i n . 11 . The s o l u t i o n f l o w r a t e was r e d u c e d t o t h e d e s i r e d v a l u e by a d j u s t i n g t h e b y - p a s s v a l v e . The w a t e r i n l e t v a l v e t o t h e w a t e r c o o l e r was o p e n e d and s e t t o o b t a i n a DEA o u t l e t t e m p e r a t u r e o f 6 0 ° C . " 12. The o p e r a t i n g v a r i a b l e s were c a r e f u l l y m o n i t o r e d a n d r e g u l a t e d i n o r d e r t o a c h i e v e s t e a d y s t a t e o p e r a t i o n o f t h e e q u i p m e n t . U s u a l l y , s t e a d y s t a t e was r e a c h e d i n a b o u t 15 m i n . The e x p e r i m e n t was t h e n c o n t i n u e d f o r e x t e n d e d p e r i o d s ( a b o u t 150 - 200 h r ) w h i l e m o n i t o r i n g a l l v a r i a b l e s a s r e q u i r e d . 13 . A 1OmL s a m p l e o f t h e DEA s o l u t i o n was w i t h d r a w n e v e r y 24 h r ( o r more f r e q u e n t l y ) and a n a l y s e d by gas c h r o m a t o g r a p h y . 14. A t t h e e n d o f e a c h r u n , t h e s y s t e m was f l u s h e d w i t h d i s t i l l e d w a t e r i n o r d e r t o p r e p a r e i t f o r t h e n e x t r u n . 42 CHAPTER 4 A N A L Y T I C A L PROCEDURE The ga s c h r o m a t o g r a p h i c t e c h n i q u e d e v e l o p e d by K e n n a r d [51] was a d o p t e d f o r t h e a n a l y s i s o f DEA and i t s d e g r a d a t i o n p r o d u c t s i n t h i s w o r k . 4.1 C A L I B R A T I O N OF GAS CHROMATOGRAPH C a l i b r a t i o n c u r v e s f o r D E A , H E O D , T H E E D a n d BHEP were o b t a i n e d f r o m K e n n a r d ' s t h e s i s [51] and c h e c k e d f r o m t i m e t o t i m e t o e n s u r e t h a t t h e c a l i b r a t i o n c u r v e s were s t i l l a p p l i c a b l e . 4 . 2 OPERATING CONDITIONS The o p e r a t i n g c o n d i t i o n s o f t h e Gas C h r o m a t o g r a p h a r e s u m m a r i z e d i n T a b l e 4 . 1 . 43 T a b l e 4.1 O p e r a t i n g c o n d i t i o n s o f t h e gas c h r o m a t o g r a p h , Gas C h r o m a t o g r a p h M a n u f a c t u r e r M o d e l D e t e c t o r C h r o m a t o g r a p h i c Co lumn M a t e r i a l D i m e n s i o n s P a c k i n g O p e r a t i n g c o n d i t i o n s C a r r i e r gas C a r r i e r gas f l o w I n j e c t i o n p o r t t emp. D e t e c t o r p o r t t e m p . C o l u m n t e m p . S y r i n g e M a n u f a c t u r e r M o d e l I n j e c t e d s ample s i z e H e w l e t t P a c k a r d 5830A H y d r o g e n f l a m e i o n i z a t i o n S t a i n l e s s s t e e l 1/8" O . D . , 6 ' l o n g T e n a x G . C . , 60 /80 mesh N i t r o g e n 2 5 m l / m i n 3 0 0 ° C 3 0 0 ° C I s o t h e r m a l a t 1 5 0 ° C f o r 0 . 5 m i n . , t h e n t e m p e r a t u r e r a i s e d a t 8 ° C / m i n t o 3 0 0 ° C . H a m i l t o n C o . , R e n o , N e v a d a . 7 0 1 , 1 0 M 1 , w i t h f i x e d n e e d l e and C h a n e y a d a p t e r 1 M L 44 T y p i c a l l y 1 LIL s a m p l e s o f d e g r a d e d DEA s o l u t i o n were i n j e c t e d d i r e c t l y i n t o t h e c o l u m n w i t h a p r e c i s i o n s y r i n g e f i t t e d w i t h a C h a n e y a d a p t e r . The a d a p t e r h e l p e d i n e n s u r i n g t h a t a c o n s t a n t v o l u m e o f s ample was i n j e c t e d i n t o t h e c o l u m n . A n e e d l e g u i d e was u s e d a t t h e i n j e c t i o n p o r t , w h i c h n o t o n l y p r o t e c t e d t h e f r a g i l e s y r i n g e n e e d l e b u t a l s o s e r v e d as a s p a c e r f o r n e e d l e p e n e t r a t i o n and h e l p e d l e n g t h e n t h e sep tum l i f e . The m a j o r d e g r a d a t i o n p r o d u c t s c o u l d be d e t e c t e d i n a b o u t 20 m i n . H o w e v e r , t h e a n a l y s i s was c a r r i e d o u t f o r a b o u t 30 m i n . i n o r d e r t o e n s u r e t h e e l u t i o n o f h e a v y c o m p o u n d s . A f t e r e a c h r u n t h e c o l u m n had t o be c o o l e d f r o m 3 0 0 ° C t o 1 5 0 ° C w h i c h t o o k a b o u t 5 m i n . A c h r o m a t o g r a m o f a d e g r a d e d DEA s o l u t i o n f rom r u n 3 i s shown i n F i g u r e 4 . 1 . T a b l e 4 . 2 g i v e s t h e GC r e t e n t i o n t i m e s o f compounds i n d e g r a d e d DEA s o l u t i o n s . T a b l e 4 . 2 R e t e n t i o n t i m e o f m a j o r d e g r a d a t i o n c o m p o u n d s . Compound R e t e n t i o n t ime (min) DEA 7 . 8 0 - 7 . 95 BHEP 14 .30 - 14. 40 HEOD 1 4 . 9 0 - 15 . 1 0 THEED 17 .80 - 18 . 00 DEA g u r e 4.1 C h r o m a t o g r a m o f a d e g r a d e d DEA sample f rom r u n 3 a f t e r 192 h r . 46 4 . 3 ERRORS The m a j o r s o u r c e o f e r r o r i n t h e G . C . a n a l y s i s - i s t h e i n j e c t i o n - t i m e o f t h e s a m p l e ( i . e . t h e t i m e s p e n t by t h e n e e d l e i n s i d e t h e c o l u m n p o r t d u r i n g i n j e c t i o n ) . S l i g h t i n c r e a s e s i n i n j e c t i o n t i m e r e s u l t i n l a r g e r peak a r e a s due t o t h e v a p o r i z a t i o n o f t h e s m a l l amount o f l i q u i d n o r m a l l y h e l d i n t h e n e e d l e . The e x t e n t o f t h i s e r r o r d e p e n d s on t h e s k i l l o f t h e o p e r a t o r . To m i n i m i s e t h i s e r r o r , a t l e a s t s i x i n j e c t i o n s o f t h e same s a m p l e were made and t h e a v e r a g e a r e a s were t h e n u s e d f o r t h e d e t e r m i n a t i o n o f c o n c e n t r a t i o n s by means o f t h e c a l i b r a t i o n c h a r t s . A n o t h e r s o u r c e o f e r r o r was t h e c h a n g e i n t h e f l o w r a t e o f c a r r i e r g a s . As t h e c o l u m n became c l o g g e d , t h e f l o w r a t e f e l l . T h i s p r o b l e m was o v e r c o m e by c h e c k i n g t h e c a r r i e r gas f l o w r a t e a n d m a k i n g t h e n e c e s s a r y a d j u s t m e n t s on a d a i l y b a s i s . A n o t h e r e r r o r was a s s o c i a t e d w i t h t h e a u t o m a t i c i n t e g r a t i o n o f peak a r e a s by t h e c h r o m a t o g r a p h . I f t h e p e a k s t e n d t o t a i l .or b u n c h , t h e a u t o m a t i c i n t e g r a t o r may make s m a l l e r r o r s i n d e c i d i n g where t o b e g i n a n d end i n t e g r a t i o n . F i n a l l y , t h e r e i s some e r r o r a s s o c i a t e d w i t h e s t a b l i s h i n g and r e a d i n g t h e c a l i b r a t i o n c u r v e s . H o w e v e r , t h i s fo rm o f e r r o r i s m i n o r c o m p a r e d t o t h a t p r o d u c e d by t h e v a r i a t i o n i n s a m p l e i n j e c t i o n t i m e . 47 CHAPTER 5 CORROSION STUDIES 5.1 P R I N C I P L E S OF POTENTIODYNAMIC TECHNIQUE When a m e t a l s p e c i m e n i s immersed i n a c o r r o s i v e medium, b o t h o x i d a t i o n a n d r e d u c t i o n r e a c t i o n s o c c u r on i t s s u r f a c e . T y p i c a l l y , t h e m e t a l c o r r o d e s due t o o x i d a t i o n a n d t h e medium i s r e d u c e d w i t h t h e l i b e r a t i o n o f h y d r o g e n . The m e t a l a c t s a s b o t h a n o d e a n d c a t h o d e . C o r r o s i o n u s u a l l y i s a r e s u l t o f a n o d i c c u r r e n t s . To g e t a b e t t e r u n d e r s t a n d i n g o f c o r r o s i o n p r o c e s s e s , i t i s a d v a n t a g e o u s t o m a k e t h e m e t a l s p e c i m e n a c t e i t h e r a s an a n o d e or a s a c a t h o d e ( b u t n o t b o t h ) . When a m e t a l i s immersed i n a c o r r o s i v e l i q u i d , i t a s sumes a p o t e n t i a l E c o r r , known as t h e " f r e e c o r r o s i o n p o t e n t i a l " r e l a t i v e t o a r e f e r e n c e e l e c t r o d e [ 7 1 ] . A t t h i s f r e e c o r r o s i o n p o t e n t i a l , b o t h a n o d i c a n d c a t h o d i c c u r r e n t s h a v e e x a c t l y t h e same m a g n i t u d e and t h e r e i s no n e t c u r r e n t . The m e t a l c a n be made more a n o d i c by use o f an e x t e r n a l v o l t a g e and t h e a n o d i c c u r r e n t t h e n p r e d o m i n a t e s o v e r t h e c a t h o d i c c u r r e n t . S i m i l a r l y , t h e c a t h o d i c c u r r e n t c a n be made t o p r e d o m i n a t e by s h i f t i n g t h e p o t e n t i a l i n t h e n e g a t i v e d i r e c t i o n . The c o r r o s i o n c h a r a c t e r i s t i c s o f a m e t a l s p e c i m e n i n a g i v e n e n v i r o n m e n t c a n be s t u d i e d by p l o t t i n g t h e c u r r e n t 48 r e s p o n s e as a f u n c t i o n o f a p p l i e d p o t e n t i a l . T h i s p l o t i s known as " P o t e n t i o d y n a m i c P o l a r i z a t i o n P l o t . " A p o t e n t i o d y n a m i c a n o d i c p o l a r i z a t i o n p l o t c a n y i e l d i m p o r t a n t i n f o r m a t i o n s u c h a s : 1. The a b i l i t y o f t h e m a t e r i a l t o s p o n t a n e o u s l y p a s s i v a t e i n t h e p a r t i c u l a r m e d i u m ; ( P a s s i v a t i o n i s d e f i n e d as t h e t r a n s f o r m a t i o n o f an a c t i v e m e t a l i n t h e Emf s e r i e s i n e l e c t r o c h e m i c a l b e h a v i o u r t o t h a t o f an a p p r e c i a b l y l e s s a c t i v e o r n o b l e m e t a l ) 2 . The p o t e n t i a l r e g i o n o v e r w h i c h t h e s p e c i m e n r e m a i n s p a s s i v e ; , 3 . The c o r r o s i o n r a t e i n t h e p a s s i v e r e g i o n . A t y p i c a l a n o d i c p o l a r i z a t i o n p l o t i s shown i n F i g u r e 5 . 1 . ' I m p o r t a n t z o n e s a n d t r a n s i t i o n p o i n t s a r e l a b e l l e d . The m e t a l c o r r o d e s i n c r e a s i n g l y f rom A t o B . A t p o i n t B t h e c o r r o s i o n c u r r e n t r e a c h e s a maximum a n d f o r m a t i o n o f a p a s s i v e f i l m b e g i n s . F r o m B t o C , t h e c o r r o s i o n c u r r e n t d e c r e a s e s r a p i d l y due t o t h e f o r m a t i o n o f a p r o t e c t i v e m e t a l o x i d e l a y e r . T h e r e i s no c h a n g e i n c o r r o s i o n c u r r e n t f r o m C t o D and t h e m e t a l r e m a i n s p a s s i v e . A t p o i n t E , t h e p r o t e c t i v e f i l m s t a r t s t o b r e a k down as t h e p o t e n t i a l i s i n c r e a s e d . F i g u r e 5 . 2 shows t h e e f f e c t o f e n v i r o n m e n t upon t h e p o l a r i z a t i o n c u r v e . As c a n be s e e n f rom F i g u r e 5 . 2 , r a i s i n g t h e t e m p e r a t u r e , a c i d i t y o f t h e s o l u t i o n and t h e f o r m a t i o n o f m e t a l c o m p l e x e s i n c r e a s e t h e c o r r o s i o n c u r r e n t . By c o n t r a s t , a l l o y i n g and i n h i b i t o r a d d i t i o n d e c r e a s e t h e c o r r o s i o n c u r r e n t . 49 CURRENT (Log scale) F i g u r e 5 . 1 T y p i c a l a n o d i c p o l a r i z a t i o n p l o t s h o w i n g i m p o r t a n t z o n e s a n d t r a n s i t i o n p o i n t s . 50 CA o > HI I - O Q. I n c r e a s i n g t e m p e r a t u r e , a c i d i t y o r m e t a l c o m p l e x i n g i n c r e a s e s t h e minimum p a s s i v e c u r r e n t . Minimum p a s s i v e c u r r e n t I n h i b i t o r a d d i t i o n d e c r e a s e s t h e c o r r o s i o n c u r r e n t . I n c r e a s i n g t e m p e r a t u r e i n c r e a s e s t h e c r i t i c a l c u r r e n t . C r i t i c a l c u r r e n t CURRENT (Log scale) F i g u r e 5 . 2 T y p i c a l a n o d i c p o l a r i z a t i o n c u r v e s h o w i n g t h e e f f e c t o f e n v i r o n m e n t and i n h i b i t o r a d d i t i o n upon t h e c u r v e . 51 5 . 2 C A L C U L A T I O N OF CORROSION CURRENT The c o r r o s i o n c u r r e n t c a n be c a l c u l a t e d f rom p o l a r i z a t i o n d a t a by u s i n g t h e S t e r n - G e a r y e q u a t i o n [ 7 1 ] . A s s e e n f rom F i g u r e 5 . 3 , i f a c o r r o d i n g m e t a l i s p o l a r i z e d c a t h o d i c a l l y by r a i s i n g an e x t e r n a l l y a p p l i e d p o t e n t i a l f rom 0 c o r t o 0 ' , t h e c a t h o d i c c u r r e n t ( I c ) i n c r e a s e s a c c o r d i n g t o t h e f o l l o w i n g r e l a t i o n s h i p : I c = l a + I a p p l i e d [ 5 . 1 ] S i m i l a r l y , f o r a n o d i c p o l a r i z a t i o n ; l a = Ic - I a p p l i e d [ 5 . 2 ] where l a - A n o d i c c u r r e n t I c - c a t h o d i c c u r r e n t I a p p l i e d - a p p l i e d c u r r e n t . The c h a n g e i n p o t e n t i a l due t o p o l a r i z a t i o n c a n be e x p r e s s e d a s f o l l o w s : F o r c a t h o d i c p o l a r i z a t i o n ; Ic 0 c o r - 4>' = A<£ = /3c l o g [ 5 . 3 ] I c o r S i m i l a r l y f o r a n o d i c p o l a r i z a t i o n ; l a L\<J> = - /3a l o g [ 5 . 4 ] I c o r Where /3a - a n o d i c T a f e l c o n s t a n t , /3c - c a t h o d i c T a f e l c o n s t a n t , I c o r - c o r r o s i o n c u r r e n t . 52 F i g u r e 5 . 3 C a t h o d i c p o l a r i z a t i o n d i a g r a m f o r a c o r r o d i n g m e t a l . 53 F r o m e q u a t i o n s 5.1 a n d 5 . 2 ; I a p p l i e d = I c - I a T h e r e f o r e , (A0/0c) (A0//3a). I a p p l i e d = I c o r [10 - 10 ] [ 5 . 5 ] (A0/0c) (A</>//3a) 10 and 10 c a n be e x p r e s s e d as s e r i e s as f o l l o w s 2 (Atf>//3c) ( - 2 . 3 ( A 0 / / 3 c ) ) 10 = 1 + 2 . 3 (A0/0c) + + . . . [ 5 . 6 ] 2! a n d 2 -(A0/0a) (-2.3(A0//5a) ) 10 = 1 - 2 . 3 (Atf>//3a) + - . . . [ 5 . 7 ] 2! A s s u m i n g A#//3c and A</>//3a t o be s m a l l , t h e h i g h e r t e r m s c a n be n e g l e c t e d a n d e q u a t i o n 5 . 5 c a n be a p p r o x i m a t e d by : I a p p l i e d = 2 . 3 I c o r A0 ( 1 //3c + l / 0 a ) o r , 1 I a p p l i e d /3a /3b I c o r = — — ( ) [ 5 . 8 ] 2 . 3 &<j> /3a + /3c E q u a t i o n 5 . 8 i s t h e S t e r n G e a r y e q u a t i o n . 54 5 . 3 EXPERIMENTAL PROCEDURE P o l i s h e d m i l d s t e e l s p e c i m e n s , e a c h w i t h a s u r f a c e a r e a o f 6 . 4 4 c m 2 were immersed i n a c o r r o s i o n c e l l c o n t a i n i n g a q u e o u s DEA s o l u t i o n . A c a l o m e l e l e c t r o d e w i t h s a t u r a t e d KC1 s o l u t i o n was u s e d a s t h e r e f e r e n c e e l e c t r o d e . The c o r r o s i o n c e l l was t h e n c o n n e c t e d t o a c o r r o s i o n m e a s u r e m e n t s y s t e m ( P r i n c e t o n A p p l i e d R e s e a r c h , P r i n c e t o n , N J , M o d e l 3 5 0 A ) , e q u i p p e d w i t h a m i c r o c o m p u t e r . P o t e n t i o d y n a m i c p o l a r i z a t i o n c u r v e s were o b t a i n e d a t 1 m v / s e c s c a n n i n g r a t e and t h e f r e e c o r r o s i o n r a t e was d e t e r m i n e d v i a T a f e l s l o p e d e t e r m i n a t i o n a n d e x t r a p o l a t i o n . The e x p e r i m e n t s were c o n d u c t e d a t 2 5 ° C . 55 CHAPTER 6 MISCELLANEOUS T E S T S 6 . 1 V I S C O S I T Y MEASUREMENTS The v i s c o s i t y o f p a r t i a l l y d e g r a d e d DEA s o l u t i o n s were m e a s u r e d by means o f a r o t o v i s c o m e t e r (Haake R o t o v i s c o , B e r l i n , West G e r m a n y , M o d e l RV12) u s i n g a s m a l l - g a p - c l e a r a n c e bob a n d c u p c o m b i n a t i o n ( N V ) . A s c h e m a t i c d i a g r a m o f t h e v i s c o s i m e t e r i s g i v e n i n F i g u r e 6 . 1 . The t e m p e r a t u r e o f t h e s o l u t i o n was m a i n t a i n e d a t t h e d e s i r e d v a l u e by c i r c u l a t i n g w a t e r f r o m a c o n s t a n t t e m p e r a t u r e w a t e r b a t h t h r o u g h t h e t e m p e r i n g , b a t h and t h e c u p ' s i n n e r c o r e . At l e a s t t h r e e r e a d i n g s a t v a r i o u s r o t a t i o n a l s p e e d s were t a k e n and t h e a v e r a g e o f t h e t h r e e r e a d i n g s was u s e d t o m i n i m i s e t h e i n s t r u m e n t a l a n d e x p e r i m e n t a l e r r o r s . The minimum v i s c o s i t y w h i c h c o u l d be d e t e r m i n e d a c c u r a t e l y was 2 c p . S i n c e t h e v i s c o s i t y d e c r e a s e s w i t h i n c r e a s i n g t e m p e r a t u r e , a l l v i s c o s i t y m e a s u r e m e n t s were c a r r i e d o u t a t 2 5 ° C i n o r d e r t o k e e p t h e v i s c o s i t y o f t h e d e g r a d e d DEA s o l u t i o n s a b o v e t h e minimum r e a d a b l e l i m i t o f t h e R o t o v i s c o m e t e r . © Basic instrument ROTOVISCO RV 12 © Recorder: xy/t ® Speed programmer PG 142 & Measuring-drive-units: M 150, M 500, M 1500 - choose one or more to cover the full range of your samples. ® Stand d Temperature vessel © Thermal liquid constant temperature circulator. A refrigerated circulator model is best suited for viscosity measurements at or below room tempera-ture. @ Sensor system: 40 alternatives to choose from for optimal test conditions and results. SENSOR SYSTEM NV Rotor (BOB) radius R 2 ; R3 (mm) height I (mm) 17.85; 20.1 60 STAT0R (CUP) radius ; R4 (mm) 17.5 ; 20.5 RADII RATIO R 4/Rj 1.02 SAMPLE VOLUME V (cm 3) 9 TEMPERATURE: max. (°C) min. (°C) 150 -30 CALCULATION FACTORS A (Pa/sc i le grad.) M (min/s) G (mPa-s/scale grad.-min) 0,5356 5,41 98,65 • F i g u r e 6 . 1 S c h e m a t i c d i a g r a m o f t h e v i s c o s i m e t e r . 57 6 . 2 FOAMING T E S T A s t a n d a r d i n d u s t r i a l t e c h n i q u e [26] was u s e d f o r t h e d e t e r m i n a t i o n o f f o a m i n g c h a r a c t e r i s t i c s o f d e g r a d e d DEA s o l u t i o n s . The f o a m i n g a p p a r a t u s ( s ee F i g u r e 6 . 2 ) c o n s i s t e d o f a 1000 mL g r a d u a t e d c y l i n d e r , an e x t r a c o a r s e f r i t t e d g l a s s gas d i s p e r s i o n t u b e (8 mm d i a m e t e r , 20 mm l o n g ) a n d a wet gas m e t e r . The gas d i s p e r s i o n t u b e was p l a c e d i n s i d e t h e g r a d u a t e d c y l i n d e r and p a s s e d t h r o u g h a s t o p p e r . 200mL o f d e g r a d e d DEA sample was p o u r e d i n t o t h e c y l i n d e r . An a i r s u p p l y t u b e was c o n n e c t e d t o t h e gas d i s p e r s i o n t u b e a n d o i l - f r e e a i r a t a r a t e o f 4 L / m i n was p a s s e d f o r 5 m i n . The a i r s u p p l y was t h e n s t o p p e d a n d t h e foam h e i g h t and t h e t i m e f o r t h e foam t o b r e a k c o m p l e t e l y were n o t e d . A l t h o u g h t h i s m e t h o d d o e s n o t p r o v i d e a q u a n t i t a t i v e r e l a t i o n s h i p b e t w e e n f o a m i n g t e n d e n c y and t h e c o n c e n t r a t i o n o f d e g r a d a t i o n p r o d u c t s i n t h e s o l u t i o n , i t d o e s i n d i c a t e w h e t h e r t h e a c c u m u l a t i o n o f d e g r a d a t i o n p r o d u c t s ha s a s i g n i f i c a n t e f f e c t on f o a m i n g . 58 A I R IM N o . 1 2 S t o p p e r G A S D I S P E R S I O N T U B E 1 0 0 0 9 0 0 C Y U I N D E R - G a s D i s p e r s i o n T u b e C y l i n d r i c a l , F r i t t e d G l a s s E x t r a C o a r s e . 8 x 5 5 0 - m m . :oo F i g u r e 6 .2 S c h e m a t i c d i a g r a m o f t h e foam t e s t i n g a p p a r a t u s . 59 CHAPTER 7 MODEL DEVELOPMENT A t h e o r e t i c a l m o d e l was d e v e l o p e d i n o r d e r t o p r e d i c t t h e r a t e o f DEA d e g r a d a t i o n i n s i d e t h e h e a t t r a n s f e r t u b e . The m o d e l c o n s i s t s o f two m a j o r p a r t s : 1. H e a t e x c h a n g e r m o d e l , 2 . K i n e t i c m o d e l . 7.1 HEAT EXCHANGER MODEL A s u c c e s s i v e summat ion m e t h o d was u s e d f o r t h e h e a t e x c h a n g e r c a l c u l a t i o n . The h e a t e x c h a n g e r t u b e l e n g t h was d i v i d e d i n t o s m a l l s e g m e n t s a n d e a c h segment was t r e a t e d a s an i n d i v i d u a l h e a t e x c h a n g e r u n i t . T r a n s p o r t p r o p e r t i e s were e v a l u a t e d a t t h e b u l k s o l u t i o n t e m p e r a t u r e o f e a c h s e g m e n t . T h i s a p p r o a c h m i n i m i s e s t h e e r r o r a s s o c i a t e d w i t h e v a l u a t i n g t h e t r a n s p o r t p r o p e r t i e s a t t h e a v e r a g e b u l k s o l u t i o n t e m p e r a t u r e f o r t h e e n t i r e h e a t e x c h a n g e r a n d t h u s a l l o w s t h e p r e d i c t i o n o f a more a c c u r a t e t e m p e r a t u r e p r o f i l e . 7 . 1 . 1 T e m p e r a t u r e p r o f i l e d e t e r m i n a t i o n In o r d e r , t o d e t e r m i n e t h e t e m p e r a t u r e p r o f i l e , i t was n e c e s s a r y t o c a l c u l a t e t h e o v e r a l l h e a t t r a n s f e r c o - e f f i c i e n t . 60 The i n s i d e f i l m c o - e f f i c i e n t was c a l c u l a t e d by t h e f o l l o w i n g e q u a t i o n [72 ] : Tk 0 . 8 1/3 M 0 . 1 4 h i = 0 . 0 2 3 ( ) (Re ) ( P r ) ( ) [ 7 . 1 ] D i c c M W The c o r r e s p o n d i n g o u t s i d e f i l m c o - e f f i c i e n t was c a l c u l a t e d by t h e f o l l o w i n g e q u a t i o n [ 7 3 ] : Tk 0 . 6 7 0 . 3 7 Db 0 . 1 do 0.5 M m ho =0 . 1 7 (. ) (Re ) (Pr ) ( ) ( ) ( ) [ 7 . 2 ] Do O o Dt Dt M W where -0 . 2 1 m = 0 . 7 1 4 M and t h e o u t s i d e R e y n o l d s number i s d e f i n e d as : D b 2 x RPS x po Re = o M O where Db = b l a d e d i a m e t e r (m) Dt = t a n k d i a m e t e r (m) RPS = s t i r r e r s p e e d po = d e n s i t y o f t h e h e a t t r a n s f e r f l u i d ( k g / m 3 ) M O = v i s c o s i t y o f t h e h e a t t r a n s f e r f l u i d ( p a . s ) . 6-1 The o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t ( b a s e d on t h e i n s i d e d i a m e t e r ) f o r a s t r a i g h t t u b e , was c a l c u l a t e d f rom [ 7 2 ] : 1 TJi = [ 7 . 3 ] ( 1 / h i ) + ( 1 / h o ) ( D i / D o ) + ( x m / T k m ) ( D i / D l m ) S i n c e t h e p r e s e n t e x p e r i m e n t a l work i n v o l v e d a c o i l e d h e a t t r a n s f e r t u b e , t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t f o r t h e c o i l e d t u b e had t o be f o u n d . T h i s was done by means o f t h e f o l l o w i n g e q u a t i o n [74] : Uc = U i (1 + 3 . 5 ( D i / D c ) ) [ 7 . 4 ] The h e a t e x c h a n g e r t u b e was a s sumed t o c o n s i s t o f " n " o f s m a l l h e a t e x c h a n g e r s egment s o f l e n g t h " x " . E a c h segment was c o n s i d e r e d as an i n d i v i d u a l h e a t e x c h a n g e r u n i t . H e a t t r a n s f e r c a l c u l a t i o n s were t h e n p e r f o r m e d on s u c c e s s i v e h e a t e x c h a n g e r s e g m e n t s . The s c h e m a t i c d i a g r a m o f t h e t e m p e r a t u r e p r o f i l e a c r o s s any s m a l l h e a t e x c h a n g e r segment i s shown i n F i g u r e 7.1 6 2 Th To Ti o X F i g u r e 7.1 S c h e m a t i c d i a g r a m o f t h e t e m p e r a t u r e p r o f i l e a c r o s s a segment o f t h e h e a t e x c h a n g e r t u b e . The h e a t b a l a n c e f o r a s m a l l h e a t e x c h a n g e r segment o f l e n g t h " x " , may be w r i t t e n a s : W = Mass f l o w r a t e o f t h e DEA s o l u t i o n , Cp = s p e c i f i c h e a t o f t h e DEA s o l u t i o n , dT = t e m p e r a t u r e d i f f e r e n c e o f t h e DEA s o l u t i o n , T h = h o t f l u i d t e m p e r a t u r e , T = b u l k s o l u t i o n t e m p e r a t u r e , dA = e l e m e n t a l h e a t t r a n s f e r a r e a , Uc = o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t . W Cp dT = Uc dA ( T h - T) [ 7 . 5 ] Where 63 We c a n w r i t e dA = IT D i d x , so t h a t E q u a t i o n 7.5 becomes : W Cp dT = Uc ff D i dx (Th -T) [ 7 . 6 ] A s s u m i n g t h a t Uc and Cp a r e c o n s t a n t a nd i n t e g r a t i n g g i v e s , w h e r e , IC d e n o t e s t h e i n t e g r a t i o n c o n s t a n t . A t , x = 0, I n (Th - T i ) = IC where, T i d e n o t e s t h e i n l e t t e m p e r a t u r e . ! Uc ir D i x j > + I n (Th - T i ) W Cp } ! Uc TT D i x) / [ 7 . 7 ] W Cp ) The b u l k s o l u t i o n t e m p e r a t u r e i n e a c h i n d i v i d u a l segment c a n t h e r e f o r e be f o u n d p r o v i d e d Th and T i a r e known. 64 S i n c e t h e t e m p e r a t u r e of t h e DEA s o l u t i o n a t t h e i n l e t of t h e h e a t e x c h a g e r t u b e i s known a l o n g w i t h o t h e r p e r t i n e n t i n f o r m a t i o n , t h e o u t l e t t e m p e r a t u r e of t h e f i r s t segment can be c a l c u l a t e d e a s i l y . The o u t l e t t e m p e r a t u r e , To, of t h e f i r s t segment t h e n becomes t h e i n l e t t e m p e r a t u r e , T i , of t h e s e c o n d segment and so f o r t h . The f o l l o w i n g e q u a t i o n r e l a t e s t h e o u t l e t t e m p e r a t u r e of a segment t o t h e i n l e t t e m p e r a t u r e of t h e f o l l o w i n g segment : T i = To ; 1 < j < n [7.8] j j-1 where T i - i n l e t t e m p e r a t u r e To - o u t l e t t e m p e r a t u r e n - number o f segments. t e m p e r a t u r e of t h e l a s t segment r e p r e s e n t s t h e e x i t of t h e DEA s o l u t i o n l e a v i n g t h e h e a t t r a n s f e r t u b e . The c a l c u l a t i o n s of t h e o u t s i d e and i n s i d e w a l l t e m p e r a t u r e s r e q u i r e an a n a l y s i s o f i n d i v i d u a l h e a t t r a n s f e r r e s i s t a n c e s . F i g u r e 7.2 shows t h e t e m p e r a t u r e p r o f i l e a c r o s s t h e h e a t e x c h a n g e r t u b e w a l l . The o u t l e t t e m p e r a t u r e 65 DEA Solution Twi T — Heat transfer f l u id Th Two F i g u r e 7 .2 S c h e m a t i c d i a g r a m o f t e m p e r a t u r e p r o f i l e a c r o s s t h e m e t a l t u b e w a l l . 66 C o n s i d e r i n g t h e i n d i v i d u a l r e s i s t a n c e s and t e m p e r a t u r e d r o p s a c r o s s e a c h o f t h e r e s i s t a n c e s , t h e f o l l o w i n g e q u a t i o n c a n be w r i t t e n : T h - T Th - Two Two - Twi Twi - T = : ; = = [ 7 . 9 ] ( 1 / U c ) ( 1 / h o ) ( D i / D o ) ( x m / T k m ) ( D i / D l m ) ( 1 / h i ) From e q u a t i o n 7 . 8 i t f o l l o w s t h a t Th - Two = ( 1 / h o ) ( D i / D o ) ( T h - T) Uc o r Two = T h - (Th - T ) ( 1 / h o ) ( D i / D o ) Uc S i m i l a r l y , Two - T w i = ( x m / T k m ) ( D i / D l m ) ( T h - T) Uc o r Twi = Two - (Th - T ) ( x m / T k m ) ( D i / D l m ) Uc F r o m e q u a t i o n 7 . 1 0 a n d 7 . 1 1 , b o t h t h e o u t s i d e and i n s i d e w a l l t e m p e r a t u r e s c a n be c a l c u l a t e d p r o v i d e d U , h , T e t c . a r e known. H o w e v e r , t o d e t e r m i n e U , h and T , we need t o know, t h e o u t s i d e a n d i n s i d e w a l l t e m p e r a t u r e s Two a n d T w i . The l a t t e r were f o u n d by a t r i a l a n d e r r o r m e t h o d ; a c o m p u t e r p r o g r a m was w r i t t e n f o r t h i s p u r p o s e ( s e e A p p e n d i x A ) . [ 7 . 1 0 ] [ 7 . 1 1 ] 67 7 . 1 . 2 DEA t r a n s p o r t p r o p e r t i e s T r a n s p o r t p r o p e r t i e s o f DEA s o l u t i o n s a r e r e q u i r e d t o c a l c u l a t e t h e h e a t t r a n s f e r c o - e f f i c i e n t s . D a t a on t h e p h y s i c a l p r o p e r t i e s o f DEA s o l u t i o n s h a v e been p u b l i s h e d i n g r a p h i c a l f o r m [ 2 6 , 7 5 ] . S i n c e a c o m p u t e r - b a s e d s u c c e s s i v e s u m m a t i o n m e t h o d was u s e d t o p e r f o r m t h e h e a t e x c h a n g e r c a l c u l a t i o n , i t was p r e f e r a b l e t o p r e d i c t t h e p r o p e r t i e s by means o f e q u a t i o n s . The f o l l o w i n g s i m p l e e q u a t i o n s were t h e r e f o r e d e v e l o p e d t o p r e d i c t t h e d e n s i t y , v i s c o s i t y , t h e r m a l c o n d u c t i v i t y and s p e c i f i c h e a t o f a q u e o u s DEA s o l u t i o n s : ' p = 9 9 8 . 0 - 0 . 0 0 4 0 3 T 2 + C ( 3 .-4-0 . 00025 T 1 , a 5 ) - C 1 - 1 9 [ 7 . 1 2 ] In**' = ( 0 . 0 6 7 6 6 6 C - 6 . 8 2 0 8 6 7 ) / ( 1 - 0 . 0 0 4 3 9 5 C) - ( T ( 0 . 0 1 4 0 6 6 + 0 . 0 0 0 1 0 5 C ) / ( 1 - 0 . 0 0 4 9 6 5 ) ) [ 7 . 1 3 ] k = ( 0 . 4 6 7 5 - 0 . 0062 c a 8 5 3 8 ) T a o 8 [ 7 . 1 4 ] Cp = 4 . 1 7 6 + 0 . 0 0 0 4 6 T - 0 . 0 0 1 8 3 7 C + 0 . 0 0 0 0 5 4 C T [ 7 . 1 5 ] where p = d e n s i t y ( k g / m 3 ) M = v i s c o s i t y ( P a . s ) k = t h e r m a l c o n d u c t i v i t y ( W / m ° C ) Cp= s p e c i f i c h e a t ( J / g ° C ) T = t e m p e r a t u r e ( ° C ) C = DEA c o n c e n t r a t i o n (wt%) 68 In a l l cases the percentage d i f f e r e n c e between the p u b l i s h e d and p r e d i c t e d values i s l e s s than 5% and i n most cases i t i s l e s s than 2% f o r temperatures between 20 and 100 °C and c o n c e n t r a t i o n s between 0 and 100 wt%. 7.1.3 Heat t r a n s f e r f l u i d p r o p e r t i e s The only i n f o r m a t i o n on the p r o p e r t i e s of S h e l l Thermia O i l - C was provided by S h e l l Canada [76]. Using the l i m i t e d i n f o r m a t i o n provided, i t s p r o p e r t i e s were evaluated as f o l l o w s : Density Density at 15°C was given as 874.6 kg/m3 [76]. The f o l l o w i n g equation was developed from F i g u r e 16-11 of G.P.S.A. Engineering Data Book [77] using d e n s i t y at 15°C. 1000 ( 0.886662 - 0.000750 T ) [7.16] where po d e n s i t y of the heat t r a n s f e r f l u i d (kg/m 3) T temperature (°C) 69 D e n s i t y was d e t e r m i n e d e x p e r i m e n t a l l y and c o m p a r e d w i t h t h e t h e v a l u e s p r e d i c t e d by e q u a t i o n 7 . 1 5 . The c o m a p r i s o n i s shown i n T a b l e 7 . 1 . The a c c u r a c y was f o u n d t o be w i t h i n ± 1 % . T a b l e 7.1 D e n s i t y o f S h e l l T h e r m i a O i l - C Temp (C) D e n s i t y ( k g / m 3 ) M e a s u r e d P r e d i c t e d 1 5 8 7 4 . 6 8 7 5 . 4 20 8 7 2 . 0 871 . 7 40 8 5 2 . 5 . 8 5 6 . 7 1 00 8 0 8 . 5 8 1 1 . 7 1 40 7 8 0 . 0 781 . 7 1 60 7 6 4 . 8 7 6 6 . 7 200 7 3 2 . 5 7 3 6 . 7 70 V i s c o s i t y ASTM v i s c o s i t y c h a r t s [ 7 8 ] , c a n be u s e d t o o b t a i n v i s c o s i t i e s o f p e t r o l e u m o i l s a t any t e m p e r a t u r e p r o v i d e d t h e v i s c o s i t i e s a t two d i f f e r e n t t e m p e r a t u r e s a r e known. The v i s c o s i t i e s o f S h e l l T h e r m i a O i l - C were d e t e r m i n e d e x p e r i m e n t a l l y f o r d i f f e r e n t t e m p e r a t u r e s and t h e e x p e r i m e n t a l p r o c e d u r e i s d e s c r i b e d i n C h a p t e r 6 . The f o l l o w i n g e q u a t i o n was t h e n o b t a i n e d f o r t h e v i s c o s i t y d e t e r m i n a t i o n : I n(MO) = - ( 2 . 2 1 7 7 + 0 . 0 1 8 8 T ) [ 7 . 1 7 ] where MO = v i s c o s i t y o f t h e h e a t t r a n s f e r f l u i d ( P a . s ) T = t e m p e r a t u r e ( ° C ) T a b l e 7 . 2 p r o v i d e s a c o m p a r i s o n be tween v i s c o s i t i e s d e t e r m i n e d e x p e r i m e n t a l l y and t h o s e p r e d i c t e d by e q u a t i o n 7 . 1 7 . T h e a c c u r a c y i s w i t h i n ± 10%. T a b l e 7 . 2 V i s c o s i t y o f S h e l l T h e r m i a O i l - C Temp(C) V i s c o s i t y ( p a . s ) M e a s u r e d P r e d i c t e d 40 0 . 0 5 1 4 0 . 0 5 1 4 1 00 0 . 0 1 5 4 0 . 0 1 6 7 1 50 0 . 0 0 7 0 0 . 0 0 6 5 200 0 . 0 0 2 5 0 . 0 0 2 6 71 T h e r m a l c o n d u c t i v i t y No d a t a on t h e t h e r m a l c o n d u c t i v i t y were p r o v i d e d by S h e l l Canada; but i t was recommended t o use t h e f o l l o w i n g U.S. B u r e a u of S t a n d a r d s e q u a t i o n [79] : Where; Tk = t h e r m a l c o n d u c t i v i t y ( B T U / f t 2 / h r / ° F / i n c h ) , T = t e m p e r a t u r e ( ° F ) , d = s p e c i f i c g r a v i t y 60/60°F The t h e r m a l c o n d u c t i v i t y can t h e n be c o n v e r t e d t o S . I . u n i t s (W/m°C) s i m p l y by m u l t i p l y i n g by a c o n v e r s i o n f a c t o r of 0.1441314. W i t h i n t h e s p e c i f i c g r a v i t y range o f 0.740 and 1.00 and a t t e m p e r a t u r e s between -17.8 t o 426 °C t h e a c c u r a c y i s c l a i m e d t o be +10%. S p e c i f i c h e a t S p e c i f i c h e a t d a t a were a l s o u n a v a i l a b a l e . The f o l o w i n g U.S. B u r e a u of S t a n d a r d s e q u a t i o n [79] was u s e d t o c a l c u l a t e t h e s p e c i f i c h e a t : Tk [0.821 - 0.000244]/d [7.18] Cp = [0.388 + 0.00045 T ] / d 0 5 [7.19] Where; Cp = s p e c i f i c h e a t ( B T U / l b / ° F ) , T = t e m p e r a t u r e ( ° F ) , d = s p e c i f i c g r a v i t y . 72 The s p e c i f i c h e a t t h u s o b t a i n e d can t h e n be c o n v e r t e d t o S . I . u n i t s (j/kg°C) by m u l t i p l y i n g by a c o n v e r s i o n f a c t o r of 4184. The s t a t e d a c c u r a c y i s w i t h i n ± 4 % . 7.1.4 T h e r m a l c o n d u c t i v i t y of s t a i n l e s s s t e e l T h e r m a l c o n d u c t i v i t y o f s t a i n l e s s s t e e l i s not s t r o n g l y d e pendent on t e m p e r a t u r e between 150 and 250°C, t h e p r e s e n t e x p e r i m e n t a l r a n g e . However, i n o r d e r t o p e r f o r m t h e h e a t t r a n s f e r c a l c u l a t i o n s and e s p e c i a l l y t o p r e d i c t t h e tube w a l l t e m p e r a t u r e , t h e f o l l o w i n g e q u a t i o n was d e v e l o p e d by f i t t i n g t h e d a t a from t h e M e t a l s R e f e r e n c e Book [ 8 0 ] . : km = 15.60 + 0.006289 T [7.20] where km = -thermal c o n d u c t i v i t y of 316 s t a i n l e s s s t e e l (W/m°C) T = m e t a l t e m p e r a t u r e (°C) The a c c u r a c y i s w i t h i n ± 0 . 5 % . 73 7 . 1 . 5 P r e s s u r e d r o p d e t e r m i n a t i o n The C o l e b r o o k e q u a t i o n was u s e d t o c a l c u l a t e f r i c t i o n f a c t o r s [81] : 1 e 4 . 6 7 = - 4 . 0 l o g ( + ) + 2 . 2 8 [ 7 . 2 1 ] y i D i Re y r The s o l u t i o n o f e q u a t i o n 7.21 r e q u i r e s an i n i t i a l e s t i m a t e o f t h e f r i c t i o n f a c t o r " f " f o l l o w e d by a t r i a l and e r r o r s o l u t i o n . The i n i t i a l f r i c t i o n f a c t o r was e s t i m a t e d by t h e f o l l o w i n g e q u a t i o n [81 ] : f = 0 . 0 4 ( R e ) ' 0 1 6 [ 7 . 2 2 ] The i n i t i a l s u r f a c e r o u g h n e s s f a c t o r " e " was d e t e r m i n e d as 0 .012 mm f r o m p r e s s u r e d r o p m e a s u r e m e n t s o f w a t e r f l o w i n g t h r o u g h a 0 . 5 m l o n g s e c t i o n o f t h e h e a t e x c h a n g e r t u b e . A f t e r c a l c u l a t i n g t h e f r i c t i o n f a c t o r " f " , t h e p r e s s u r e d r o p f o r t h e s t r a i g h t p i p e was c a l c u l a t e d by [ 8 1 ] : A P s t = 2 p v 2 f L / D [ 7 . 2 3 ] 74 The p r e s s u r e d r o p i n t h e c o i l e d t u b e was d e t e r m i n e d f rom : T h i s e q u a t i o n was c h o s e n by a n a l o g y w i t h e q u a t i o n 7 . 4 w h i c h r e l a t e s h e a t t r a n s f e r c o e f f i c i e n t o f a c o i l e d t u b e t o t h a t o f s t r a i g h t t u b e ( s ee E q u a t i o n 7 . 4 ) [ 7 4 ] . 7 . 1 . 6 F i l m t h i c k n e s s d e t e r m i n a t i o n The h e a t t r a n s f e r f i l m t h i c k n e s s " 6L " was c a l c u l a t e d by e q u a t i n g t h e c o n d u c t i v e a n d c o n v e c t i v e t e r m s i n t h e h e a t f l o w e q u a t i o n : From e q u a t i o n 7.1 a n d n e g l e c t i n g t h e v i s c o s i t y r a t i o t e r m , t h e f o l l o w i n g e q u a t i o n c a n be d e r i v e d t o g i v e t h e f i l m t h i c k n e s s " 5L " a s a f u n c t i o n o f f l u i d t r a n s p o r t p r o p e r t i e s , t u b e d i a m e t e r a n d mass f l o w r a t e o f t h e s o l u t i o n . APc = A P s t + (1 + 3 . 5 ( D i / D c ) ) [ 7 . 2 4 ] dQ = k dA d T / 6 L = h dA dT H e n c e , 6L = k / h [ 7 . 2 5 ] k 5L = = h 4 3 . 4 7 8 d 1 - 8 [ 7 . 2 6 ] 75 7 . 1 . 7 H e a t e x c h a n g e r m o d e l p e r f o r m a n c e The p e r f o r m a n c e o f t h e h e a t e x c h a n g e r m o d e l may be e v a l u a t e d by c o m p a r i n g t h e e x p e r i m e n t a l o u t l e t t e m p e r a t u r e s w i t h t h o s e p r e d i c t e d by t h e m o d e l f o r v a r i o u s r u n s . S i m i l a r l y , i n i t i a l p r e s s u r e d r o p m e a s u r e m e n t s c a n a l s o be c o m p a r e d . The p r e d i c t e d o u t l e t t e m p e r a t u r e s were f o u n d t o be e x t r e m e l y c l o s e t o t h e m e a s u r e d o n e s . T h i s i s s u r p r i s i n g , c o n s i d e r i n g t h e f a c t t h a t a number o f c o r r e l a t i o n s were i n c l u d e d i n t h e m o d e l . P r o b a b l y t h e e r r o r s a s s o c i a t e d w i t h t h e s e c o r r e l a t i o n s c a n c e l l e d one a n o t h e r t o some e x t e n t . I n i t i a l p r e s s u r e d r o p p r e d i c t i o n s were a l s o i n g o o d a g r e e m e n t w i t h t h e e x p e r i m e n t a l r e s u l t s . T h i s i s p r o b a b l y due t o t h e f a c t t h a t t h e i n i t i a l s u r f a c e r o u g h n e s s was d e t e r m i n e d e x p e r i m e n t a l l y ( a l b e i t u s i n g w a t e r a t a m b i e n t t e m p e r a t u r e ) . T a b l e 7 . 3 shows t h e c o m p a r i s o n s o f o u t l e t t e m p e r a t u r e s and i n i t i a l p r e s s u r e d r o p s f o r v a r i o u s r u n s . 76 T a b l e 7 . 3 C o m p a r i s o n o f o u t l e t t e m p e r a t u r e a n d i n i t i a l p r e s s u r e d r o p d a t a f o r d i f f e r e n t r u n s . Run N o . O u t l e t t e m p . ( C ) E x p t . M o d e l I n i t i a l AP (kPa) E x p t . M o d e l 1 1.90 1 92 690 718 2 1 70 174 1 207 1 237 3 195 200 552 572 4 1 65 171 552 1 339 5 1 65 171 552 574 6 1 40 141 552 581 7 195 200 552 572 8 1 95 200 552 572 9 1 95 200 552 602 1 0 1 95 200 552 548 77 7 . 2 K I N E T I C MODEL K e n n a r d ' s [51] s i m p l i f i e d m o d e l f o r DEA d e g r a d a t i o n may be w r i t t e n a s f o l l o w s : BHEP K e n n a r d r e p o r t e d t h a t t h e d e g r a d a t i o n r a t e i s u n a f f e c t e d by C 0 2 p a r t i a l p r e s s u r e s p r o v i d e d t h e C 0 2 c o n c e n t r a t i o n i n t h e DEA s o l u t i o n e x c e e d s 0 . 2 g C 0 2 / g D E A . He a l s o r e p o r t e d t h e d e p e n d e n c y o f t h e d e g r a d a t i o n r a t e on t h e i n i t i a l DEA c o n c e n t r a t i o n a n d p l o t t e d p s e u d o f i r s t o r d e r r a t e c o n s t a n t s k , a n d k 2 a s a f u n c t i o n o f t e m p e r a t u r e a n d DEA c o n c e n t r a t i o n . He f o u n d k 3 t o be i n d e p e n d e n t o f t h e DEA c o n c e n t r a t i o n b u t d e p e n d e n t on t h e t e m p e r a t u r e . C o n s e q u e n t l y , he d i d n o t i n c l u d e t h e e f f e c t o f C 0 2 p a r t i a l p r e s s u r e i n h i s m o d e l . H o w e v e r , u n d e r i n d u s t r i a l c o n d i t i o n s ( e s p e c i a l l y i n r e b o i l e r s ) , t h e C 0 2 l o a d i n g may be much l o w e r t h a n 0 . 2 g C 0 2 / g D E A . T h e r e f o r e , t h e n e e d t o i n c l u d e a t e r m w h i c h t a k e s i n t o a c c o u n t t h e C 0 2 p a r t i a l p r e s s u r e a s w e l l a s DEA c o n c e n t r a t i o n i s c l e a r . B o t h C 0 2 p a r t i a l p r e s s u r e a n d DEA c o n c e n t r a t i o n d e t e r m i n e t h e s o l u b i l i t y o f C 0 2 i n DEA s o l u t i o n s a t a g i v e n t e m p e r a t u r e . Hence t h e C 0 2 s o l u b i l t y i s a p a r a m e t e r w h i c h s h o u l d be a b l e t o t a k e i n t o a c c o u n t t h e v a r i a t i o n i n C 0 2 p a r t i a l p r e s s u r e as w e l l 78 as DEA concentration. It was therefore decided to include a C 0 2 s o l u b i l i t y term in the rate equations. Kennard [51] reported that DEA degradation changes with DEA concentration. He i d e n t i f i e d three regions : 1. 0 - 1 0 wt% DEA, where the main degradation route is ion i c . 2. 10 - 30 wt% DEA, where the degradation route is a combination of molecular and ionic routes. 3. 30 - 100 wt% DEA, where the main degradation route i s molecular. Recognising that i t was impractical to develop a single equation for predicting the rate constants for a DEA concentration range of 0 - 100 wt%, i t was decided to develop an equation for the intermediate range of 20 to 40 wt% which is of greatest i n d u s t r i a l importance. Kennard's model [51] was modified as follows : k 3 THEED > BHEP + C0 2 The following equations represent the above kinetic model d[DEA] = - k j D E A ] [ C 0 2 ] - k 2 [ D E A ] [ C 0 2 ] [ 7 . 2 7 ] dt d[HEOD] dt = k,[DEA ] [ C 0 2 ] [ 7 . 2 8 ] 79 d [ T H E E D ] = k 2 [ D E A ] [ C 0 2 ] " k 3 [ T H E E D ] [ 7 . 2 9 ] d t d [ B H E P ] = k 3 [ T H E E D ] [ 7 . 3 0 ] d t d [ C 0 2 ] A s s u m i n g = 0 , i n t e g r a t i o n o f e q u a t i o n 7 . 2 7 y i e l d s , d t [DEA] = [DEA]o e x p { - ( k 1 + k 2 ) [ C 0 2 ] t } [ 7 . 3 1 ] E q u a t i o n 7 . 2 8 on s u b s t i t u t i o n a n d i n t e g r a t i o n y i e l d s , d [HEOD] d t = k . [ C 0 2 ] [ D E A ] o e x p { - ( k 1 + k 2 ) [ C 0 2 ] t } k , [HEOD] = [ D E A ]o ( 1 - e x p { - ( k , + k 2 ) [ C 0 2 ] t } ) ( k , + k 2 ) + [ H E O D ] 0 [ 7 . 2 3 ] E q u a t i o n 7 . 2 9 c a n be w r i t t e n as f o l l o w s : d [ T H E E D ] d t d [ T H E E D ] = k z [ C 0 2 ] [ D E A ] o e x p { - ( k , + k 2 ) [ C 0 2 ] t } - k 3 [ T H E E D ] + k 3 [ T H E E D ] = k 2 [ C 0 2 ] [ D E A ] 0 e x p { - ( k , + k 2 ) [ C 0 2 ] t } d t [ 7 . 3 4 ] The a b o v e e q u a t i o n i s a f i r s t o r d e r l i n e a r d i f f e r e n t i a l e q u a t i o n and c a n be s o l v e d by m u l t i p l y i n g by an i n t e g r a t i o n f a c t o r e x p { k 3 t } [THEED] e x p { k 3 t } = Jk2[C02][DEA]0exp{(k3-(k,+k2)[C02])t}dt k 2 [ C 0 2 ] [ D E A ] 0 = ( : — ) e x p { ( k 3 - ( k , + k 2 ) [ C 0 2 ] ) t } + IC1 [ 7 . 3 5 ] k 3 - ( k , + k 2 ) [ C 0 2 ] where IC1 d e n o t e s i n t e g r a t i o n c o n s t a n t . 80 A t t = 0 , [THEED] = [ T H E E D ] 0 k 2 [ C 0 2 ] [ D E A ] 0 [ THEED ] o = + IC1 k 3 - ( k , + k 2 ) [ C 0 2 ] k 2 [ C 0 2 ] [ D E A ] 0 T h e r e f o r e , IC1 ,= [ T H E E D ] 0 - k 3 - ( k , + k 2 ) [ C 0 2 ] E q u a t i o n 7 . 3 5 c a n t h e n be w r i t t e n a s : k 2 [ C 0 2 ] [ D E A ] 0 [THEED] = ( ) ( e x p { - ( k , + k 2 ) [ C 0 2 ] t } - e x p { - k 3 t } ) k 3 - ( k , + k 2 ) [ C 0 2 ] + [ T H E E D ] 0 e x p { - k 3 t } [ 7 . 3 6 ] E q u a t i o n 7 . 3 0 c a n t h e n be s o l v e d a s f o l l o w s d [ B H E P ] d t = k 3 [ T H E E D ] k 2 k 3 [ C 0 2 ] [ D E A ] 0 ( e x p { - ( k , + k 2 ) [ C 0 2 ] t } - e x p { - k 3 t } ) k 3 - ( k , + k 2 ) [ C 0 2 ] + [ T H E E D ] 0 e x p { - k 3 t } / * k 2 k 3 [ C 0 2 ] [ D E A ] 0 [BHEP] = / ( e x p { - ( k 1 + k 2 ) [ C 0 2 ] t } - e x p { - k 3 t } ) d t J K 3 - ( k , + k 2 ) [ C 0 2 ] r + / [ T H E E D ] 0 e x p { - k 3 t } d t k 2 k 3 [ C O 2 ] [ D E A ] o e x p { - ( k , + k 2 ) [ C 0 2 ] t [BHEP] = (- k 3 - ( k ,-+k2) [ C 0 2 ] • ( k , + k 2 ) [ C 0 2 ] 1 1 + e x p { - k 3 t } ) - [ T H E E D ] 0 e x p { - k 3 t } + IC2 k 3 k , where IC2 d e n o t e s i n t e g r a t i o n c o n s t a n t . 81 A t t=0 , [ B H E P ] = [ B H E P ] 0 k 2 k 3 [ C O 2 ] [ D E A ] 0 k 3 - ( k . + k 2 ) [ C 0 2 ] [THEED] [ B H E P ] 0 = ( ) + IC2 k 3 - ( k , + k 2 ) [ C 0 2 ] k 3 ( k 1 + k 2 ) [ C 0 2 ] k 3 k 2 [ D E A ] o [ T H E E D ] 0 IC2 = + + [ B H E P ] 0 ( k . + k 2 ) k 3 k 2 k 3 [ C 0 2 ] [ D E A ] 0 e x p { - ( k , + k 2 ) [ C 0 2 ] t } e x p { - k 3 t } [BHEP] = ( + ) k 3 - ( k , + k 2 ) [ C 0 2 ] ( k , + k 2 ) [ C 0 2 ] k 3 k 2 [ D E A ] 0 [ T H E E D ] 0 + + ( 1 - e x p { - k 3 t } ) + [ B H E P ] 0 [ 7 . 3 7 ] ( k , + k 2 ) k 3 7 . 2 . 1 D e t e r m i n a t i o n o f r a t e c o n s t a n t s In o r d e r t o d e t e r m i n e t h e r a t e c o n s t a n t s , C 0 2 s o l u b i l i t y d a t a were n e e d e d . In t h e a b s e n c e o f any r e l i a b l e s o l u b i l i t y m o d e l , t h e l i m i t e d d a t a o f L e e e t a l . [82] were u s e d . In some c a s e s , i n t e r p o l a t i o n was n e e d e d . T h i s k i n d o f a p p r o a c h i s n o t v e r y d e s i r e a b l e f o r a c c u r a t e p r e d i c t i o n o f r a t e c o n s t a n t s bu t i t was u n a v o i d a b l e . New v a l u e s o f k , and k 2 were g e n e r a t e d f r o m K e n n a r d ' s [51 ] r a t e c o n s t a n t s ( i d e n t i f i e d by an a s t e r i s k ) a s f o l l o w s : k , = k , * / [ C 0 2 ] k 2 = k 2 * / [ C 0 2 ] The v a l u e s t e m p e r a t u r e s . o f k , a n d k 2 were c a l c u l a t e d f o r v a r i o u s V a l u e s o f k 3 were o b t a i n e d f rom K e n n a r d ' s t h e s i s . 82 I t s h o u l d be n o t e d t h a t most o f K e n n a r d ' s r a t e d a t a were o b t a i n e d a t C 0 2 p a r t i a l p r e s s u r e s o f 4137 kPa and t h u s t h e r e i s some u n c e r t a i n t y when t h e C 0 2 p a r t i a l p r e s s u r e i s d i f f e r e n t . T h e f o l l o w i n g e q u a t i o n s f o r p r e d i c t i n g k 1 f k 2 and k 3 a s a f u n c t i o n o f t e m p e r a t u r e were t h e n o b t a i n e d by l e a s t s q u a r e f i t t i n g : l n ( k , ) = 11 .924 - 6 4 2 1 / T [ 7 . 3 8 ] l n ( k 2 ) = 8 . 4 5 0 - 5 5 8 0 / T [ 7 . 3 9 ] l n ( k 3 ) = 3 9 . 8 1 3 - 15160 /T [ 7 . 4 0 ] where T d e n o t e s t h e a b s o l u t e t e m p e r a t u r e i n d e g r e e s K e l v i n . B u l k s o l u t i o n t e m p e r a t u r e was u s e d f o r t h e c a l c u l a t i o n o f t h e r a t e c o n s t a n t s . A t t e m p t s were made t o d e v e l o p an e m p i r i c a l m o d e l f o r t h e p r e d i c t i o n o f C 0 2 s o l u b i l i t y i n a q u e o u s DEA s o l u t i o n s . H o w e v e r , m a i n l y due t o t h e l a c k o f a d e q u a t e d a t a , i t was n o t s u c c e s s f u l . I t was t h e r e f o r e d e c i d e d t o use t h e C 0 2 s o l u b i l i t y u n d e r t h e i n i t i a l s a t u r a t i o n c o n d i t i o n s i n t h e a u t o c l a v e . I t t h e n became p o s s i b l e t o p r e d i c t t h e r a t e o f DEA d e g r a d a t i o n f a i r l y a c c u r a t e l y , c o v e r i n g t h e t e m p e r a t u r e r a n g e o f 60 t o 200 ° C , C 0 2 p a r t i a l p r e s s u r e r a n g e o f 1379 t o 4137 kPa a n d DEA c o n c e n t r a t i o n r a n g e o f 20 t o 40 wt%. 83 7 . 2 . 2 D e t e r m i n a t i o n o f t u b e i n l e t c o n d i t i o n s a n d r e s i d e n c e t i m e F o r t h e c o m p u t e r c a l c u l a t i o n s t h e i n l e t c o n d i t i o n s a t as w e l l a s t h e r e s i d e n c e t i m e i n t h e h e a t t r a n s f e r t u b e n e e d t o be known. K n o w i n g t h e v o l u m e o f t h e h e a t t r a n s f e r t u b e and s o l u t i o n f l o w r a t e t h e t i m e r e q u i r e d t o p r o c e s s one h e a t t r a n s f e r t u b e v o l u m e e q u i v a l e n t DEA s o l u t i o n c a n be d e t e r m i n e d . T h i s t i m e i s t h e r e s i d e n c e t i m e f o r a s i n g l e p a s s , r t . The t i m e r e q u i r e d f o r a l l t h e DEA s o l u t i o n t o p a s s t h r o u g h t h e h e a t e x c h a n g e r t u b e o n c e i s d e n o t e d by t s p . The t o t a l n o . o f p a s s e s N c a n t h e n be d e t e r m i n e d a s f o l l o w s : N = t / t s p The t o t a l r e s i d e n c e t i m e o f t h e DEA s o l u t i o n i n t h e h e a t t r a n s f e r t u b e i s t h e n g i v e n b y : RT = r t x N T h e c o n c e n t r a t i o n c h a n g e s f o r a s i n g l e p a s s a r e v e r y l o w . In a d d i t i o n , t h e q u a n t i t y o f DEA s o l u t i o n i n t h e h e a t t r a n s f e r t u b e i s s m a l l c o m p a r e d t o t h e t o t a l DEA s o l u t i o n i n v e n t o r y i n s i d e t h e a u t o c l a v e . T h e r e f o r e , t h e c o n c e n t r a t i o n c h a n g e a s a r e s u l t o f m i x i n g o f p a r t i a l l y d e g r a d e d DEA s o l u t i o n f r o m t h e h e a t t r a n s f e r t u b e w i t h t h e DEA s o l u t i o n i n t h e a u t o c l a v e i s v e r y s m a l l . C o n s e q u e n t l y , i t was a s sumed t h a t a l l t h e DEA s o l u t i o n p a s s e s t h r o u g h t h e h e a t t r a n s f e r t u b e b e f o r e m i x i n g o c c u r s i n t h e a u t o c l a v e and t h e n e x t p a s s b e g i n s . T h i s a p p r o x i m a t i o n i s n o t e x p e c t e d t o a f f e c t t h e a c c u r a c y o f t h e c o m p u t e r p r e d i c t i o n s s i g n i f i c a n t l y . 84 CHAPTER 8 RESULTS AND DISCUSSION OF DEGRADATION EXPERIMENTS 8.1 COMPARISON OF THE EXPERIMENTAL DATA WITH MODEL PREDICTION The c o m p a r i s o n s o f e x p e r i m e n t a l d a t a w i t h t h o s e p r e d i c t e d by t h e m o d e l a r e g i v e n i n T a b l e 8.1 t o T a b l e 8 . 1 0 . The m o d e l p r e d i c t i o n s w i l l a l s o be c o m p a r e d w i t h t h e e x p e r i m e n t a l d a t a i n g r a p h i c a l f o r m l a t e r i n t h e c h a p t e r . As c a n be s e e n , t h e a g r e e m e n t be tween t h e p r e d i c t i o n s and t h e e x p e r i m e n t a l v a l u e s a r e q u i t e g o o d bu t n o t p e r f e c t . T h e r e a s o n s f o r t h e d i f f e r e n c e s a r e n o t f u l l y known but may be a t t r i b u t e d t o t h e f o l l o w i n g f a c t o r s : * I n a c c u r a c i e s in t h e r a t e c o n s t a n t s , * The s i m p l i f i c a t i o n i n v o l v e d i n t h e r e a c t i o n s cheme , * I n a c c u r a c i e s i n t h e C 0 2 s o l u b i l i t y d a t a , * I n a c c u r a c i e s i n t h e e x p e r i m e n t a l m e a s u r e m e n t s , e s p e c i a l l y t h e low BHEP c o n c e n t r a t i o n s . 85 T A B L E 8.1 RUN NO.1 : 30WT% D E A , TIN=60C, TOUT=190C, T 0 U T C = 1 9 2 . 4 C FLOW RATE=0 .0124 L / s , DELP=690 k P a , C A L D P = 7 1 7 . 9 kPa C 0 2 P A R T I A L PRESSURE = 4137 k P a , TH=250C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 .00 3 . 0 0 _ 2 4 . 0 2 .92 2.91 0 . 0 5 0 . 0 6 - 0.01 - - 4 8 . 0 2 . 8 3 2 . 8 2 0.11 0 . 1 2 - 0 . 0 3 - - 7 2 . 0 2 . 7 3 2 . 7 2 0 . 1 6 0 . 1 8 0 . 0 5 0 . 0 4 - - 9 6 . 0 2 .64 2 . 6 3 0 . 2 2 0 . 2 4 0 . 0 6 0 . 0 5 - 0.01 1 2 0 . 0 2 . 5 6 2 . 5 4 0 . 3 0 0 . 3 0 0 . 0 7 0 . 0 6 - 0.01 144 .0 2 . 5 0 2 . 4 5 0 . 3 5 0 . 3 6 0 . 0 9 0 . 0 8 - 0.01 168 .0 2.41 2 . 3 5 0 . 4 0 0 . 4 2 0.11 0 . 0 9 0 . 0 5 0 .01 192 .0 2 . 2 7 2 . 2 6 0 . 4 7 0 . 4 9 0 . 1 3 0 . 1 0 0 . 0 5 0 .01 T A B L E 8 . 2 RUN N O . 2 : 30WT% D E A , TIN=60C, T O U T = 1 7 0 C , T O U T C = 1 7 3 . 7 C FLOW R A T E = 0 . 0 1 6 5 L / s , DELP=1207 k P a , CALDP=1237 kPa C 0 2 P A R T I A L PRESSURE = 4137 kPa TH=250C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 .00 3 . 0 0 — 2 4 . 0 2 . 9 4 2 . 9 3 - 0 . 0 3 - 0.01 - -4 8 . 0 2 . 8 7 2 . 8 7 0 . 0 6 0 . 0 7 - 0 . 0 2 - • - 7 2 . 0 2.81 2 . 8 0 0 . 1 0 o. to - 0 . 0 2 - 0.01 9 6 . 0 2 . 7 6 2 . 7 4 0 . 1 2 0 . 1 4 0 . 0 2 0 . 0 3 0.01 0 .01 120 .0 2 . 6 9 2 . 6 7 0 . 1 6 0 . 1 7 0 . 0 4 0 . 0 4 0 .02 0 . 0 2 144 .0 2 . 6 3 2.61 0 . 1 9 0 . 2 0 0 . 0 4 0 . 0 5 0 .02 0 .02 168 .0 2 . 5 5 2 . 5 4 0 . 2 2 0 . 2 4 0 . 0 5 0 . 0 6 0 . 0 3 0 . 0 2 1 9 2 . 0 2 . 5 0 2 . 4 8 0.2jS 0 . 2 7 0 . 0 6 0 . 0 7 0 . 0 3 0 . 0 3 86 T A B L E 8 . 3 RUN N O . 3 : 30WT% D E A , T I N = 6 0 C , TOUT=195C,TOUTC=200C FLOW RATE=0 .0110 l / s , DELP=552 k P a , CALDP=57 1.9 kPa C O 2 P A R T I A L PRESSURE = 4137 k P a , TH=2 50 C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 . 0 0 3 .00 _ 2 4 . 0 2 . 8 9 2 . 8 9 0 . 0 5 0 . 0 8 - 0 . 0 2 - 4 8 . 0 2 . 7 5 2 . 7 8 0 . 1 4 0 . 1 5 - 0 . 0 3 - 7 2 . 0 2 . 6 8 2 . 6 7 0 . 2 0 0 . 2 3 - 0 . 0 5 0 .01 9 6 . 0 2 . 5 7 2 . 5 7 0 . 2 8 0 . 3 0 0 . 0 5 0 . 0 6 0 .01 120 .0 2 . 4 6 2 . 4 6 0 . 3 5 0 . 3 8 0 . 0 5 0 . 0 8 0 .01 144 .0 2 . 3 5 2 . 3 5 0 . 4 4 0 . 4 6 • 0 . 0 7 0 . 1 0 0 . 0 2 168 .0 2 . 2 5 2 . 2 4 0 . 52 0 . 5 3 0 . 0 8 0.11 0 . 0 2 0 . 0 2 1 9 2 . 0 2 . 1 3 2 . 1 3 0 . 5 8 0.61 0 . 1 0 0 . 1 2 0 . 0 2 0 . 0 2 T A B L E 8 . 4 RUN N O . 4 : 30WT% D E A , T I N = 6 0 C , T O U T = 1 6 5 C , T O U T C = 1 7 0 . 9 C FLOW RATE=0 .0172 L / s , DELP=1 .31 MPa , CALDP=1 .34 MPa C 0 2 P A R T I A L PRESSURE = 4137 k P a , TH=250C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 . 0 0 3 .00 _ _ 2 4 . 0 2 . 9 4 2 . 9 4 - 0 . 0 3 - 0.01 - - 4 8 . 0 2 . 8 8 2 . 8 7 0 . 0 6 0 . 0 6 - 0 . 0 2 - - 7 2 . 0 2 . 8 4 2.81 0 . 1 0 0 . 0 9 - 0 . 0 2 - 0.01 9 6 . 0 2 . 7 8 2 . 7 5 0 . 1 2 0 . 1 3 0 . 0 2 0 . 0 3 0.01 0.01 120 .0 2 . 7 2 2 . 6 9 0 . 1 5 0 . 1 6 0 . 0 4 0 . 0 4 0 . 0 2 0.01 144 .0 2 . 6 4 2 . 6 2 0 . 1 8 0 . 1 9 0 . 0 4 0 . 0 5 0 . 0 2 0 . 0 2 168 .0 2 . 5 7 2 . 5 6 0.21 0 . 2 2 0 . 0 5 0 . 0 5 0 . 0 3 0 . 0 2 192 .0 2.51 2 . 5 0 0 . 2 6 0 . 2 5 0 . 0 6 0 . 0 6 0 . 0 4 0 . 0 2 87 T A B L E 8 . 5 RUN N O . 5 : 30WT% D E A , TIN=60C, T O U T = 1 6 5 C , T O U T C = 1 7 1 . 5 C FLOW R A T E = 0 . 0 1 1 0 L / s , DELP=552 k P a , C A L D P = 5 7 3 . 2 k P a C 0 2 P A R T I A L PRESSURE = 4137 k P a , TH=225C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 . 0 0 3 . 0 0 2 4 . 0 2 . 9 5 2 . 9 4 - 0 . 0 4 - 0.01 - - 4 8 . 0 2 . 9 0 2 . 8 8 0 . 0 7 0 . 0 7 - 0 . 0 2 - -7 2 . 0 2 . 8 4 2.81 0.11 0..1 1 - 0 . 0 3 - - 9 6 . 0 2 . 7 9 2 . 7 5 0 . 1 2 0 . 1 5 0 . 0 2 0 . 0 3 0.01 - 1 2 0 . 0 2 . 7 4 2 . 6 9 0 . 1 6 0 . 1 9 0 . 0 4 0 . 0 4 0 . 0 2 0.01 1 4 4 . 0 2 . 6 7 2 . 6 3 0.21 0 . 2 2 0 . 0 4 0 . 0 5 0 . 0 2 0.01 1 6 8 . 0 2.61 2 . 5 7 0 . 2 4 0 . 2 6 0 . 0 5 0 . 0 6 0 . 0 3 0.01 192 .0 2 . 5 4 2 . 5 0 0 . 2 8 0 . 30 0 . 0 6 0 . 0 7 0 . 0 3 0.01 T A B L E 8 . 6 RUN N O . 6 : 30WT% D E A , T I N = 6 0 C , T O U T = 1 4 0 C , T O U T C = 1 4 2 . 1 C FLOW R A T E = 0 . 0 1 1 0 L / s , DELP=552 k P a , CALDP=581 kPa C 0 2 P A R T I A L PRESSURE= 4137 k P a , TH=190C T I M E CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 . 0 0 3 . 0 0 2 4 . 0 2 . 9 8 2 . 9 7 - 0.01 - - - 4 8 . 0 2 . 9 4 2 . 9 3 - 0 . 0 3 - 0.01 - 7 2 . 0 2 . 9 2 2 . 9 0 0 . 0 5 0 . 0 4 - 0.01 - 9 6 . 0 2 . 8 7 2 . 8 6 0 . 0 5 0 . 0 6 - 0 . 1 5 -120 .0 2 . 8 2 2 . 8 3 0 . 0 5 0 . 0 7 0 . 0 2 0 . 0 2 0 . 0 2 1 4 4 . 0 2 . 8 0 2 . 7 9 0 . 0 6 0 . 0 8 0 . 0 2 0 . 0 2 0 . 0 3 1 6 8 . 0 2 . 7 7 2 . 7 6 0 . 0 7 0 . 1 0 0 . 0 4 0 . 0 3 0 . 0 4 0.01 1 9 2 . 0 2 . 7 2 2 . 7 2 0 . 0 9 0.11 0 . 0 4 0 . 0 3 0 . 0 4 0.01 88 T A B L E 8 . 7 RUN N O . 7 : 30WT% D E A , T I N = 6 0 C , TOUT=195C,TOUTC=200 C FLOW R A T E = 0 . 0 1 1 0 L / s , DELP=552 k P a , CALDP=572 kPa C 0 2 P A R T I A L PRESSURE = 2758 k P a , TH=250C TIME CONCENTRATION ( M O L E S / L ) DEA HEOD THEED BHEP EXP i CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 . 0 0 3 .00 _ _ — 2 4 . 0 2.91 2.91 0 . 0 5 0 . 07 - 0.01 - - 4 8 . 0 2 . 8 2 2 . 8 0 0 . 1 5 0 .14 - 0 . 0 3 - - 7 2 . 0 2.71 2 . 6 9 0 . 2 0 0.21 - 0 . 0 4 - 0.01 9 6 . 0 2 . 6 0 2 . 59 0 . 3 0 0 . 2 9 0 . 0 5 0 . 0 6 - 0.01 120 .0 2 . 5 0 2 . 4 9 0 . 3 5 0 . 3 6 0 . 0 6 0 . 0 7 0.01 0.01 144 .0 2 . 4 0 2 . 3 9 0 . 4 5 0 . 4 3 0 . 0 8 0 . 0 9 0 . 0 2 0.01 168 .0 2 . 3 0 2 . 2 9 0 . 5 0 0 . 5 0 0 . 1 0 0 . 1 0 0 . 0 3 0.01 192 .0 2 . 2 0 2.18 0 . 5 8 0 . 57 0 . 1 0 0.11 0 . 0 3 0.01 T A B L E 8 . 8 RUN N O . 8 : 30WT% D E A , T I N = 6 0 C , TOUT=195C,TOUTC=200 C FLOW R A T E = 0 . 0 1 1 0 L / s , DELP=552 k P a , CALDP= 572 kPa C 0 2 P A R T I A L PRESSURE =1379 kPa , TH=250C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 3 . 0 0 3 .00 2 4 . 0 2 . 9 4 2.91 - 0 . 07 - 0.01 - - 4 8 . 0 2 . 8 3 2.81 0 . 1 0 0 . 1 3 - 0 . 0 3 - - 7 2 . 0 2 . 7 4 2 . 7 2 0 . 1 6 0 . 1 9 - 0 . 0 4 - 0.01 9 6 . 0 2 . 6 4 2 . 6 3 0 . 2 5 0 . 2 6 0 . 0 5 0 . 0 5 - 0.01 120 .0 2 . 5 6 2. 53 0 . 3 0 0 . 32 0 . 0 5 0 . 0 7 - 0.01 144 .0 2 . 4 7 2 . 4 4 0 . 4 0 0 . 39 0 . 0 7 0 . 0 8 - 0.01 168 .0 2 . 3 8 2 . 3 5 0 . 4 6 0 . 4 5 0 . 1 0 0 . 0 9 0.01 0 . 0 2 192 .0 2 . 2 8 2 . 2 5 0 . 5 0 0 .52 0 . 1 0 0 . 1 0 0.01 0 . 0 2 89 T A B L E 8 . 9 RUN N O . 9 : 40WT% D E A , TIN=60C, TOUT= 1 95C , TOUTC = 20 0' C FLOW R A T E = 0 . 0 1 1 0 L / s , DELP=552 k P a , CALDP= 602 kPa C 0 2 P A R T I A L PRESSURE = 4137 kPa , TH=250C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 4 . 0 0 4 . 0 0 2 4 . 0 3 .84 3 .84 0 . 1 0 0 . 1 2 - 0 . 0 2 - - 4 8 . 0 2 . 6 6 3 .68 0 . 2 0 0 . 2 4 0 . 0 5 0 . 0 5 - - 7 2 . 0 2 . 52 3 .52 0 . 3 4 0 . 3 6 0 . 0 7 0 . 0 7 - 0.01 9 6 . 0 2 . 3 6 3 .35 0 . 5 0 0 . 4 8 0 . 1 0 0 . 1 0 0.01 0.01 1 2 0 . 0 2.21 3 . 1 9 0 . 6 0 0 . 6 0 0 . 1 2 0 . 1 2 0 . 0 2 0.01 144 .0 2 . 1 0 3 .03 0 . 7 0 0 . 7 2 0 . 1 6 0.15 0 . 0 3 0 . 0 2 168 .0 2 . 8 9 2 . 8 7 0 . 8 0 0 . 8 3 0 . 2 0 0 . 1 7 0 . 0 3 0 . 0 2 192 .0 2 . 7 2 2.71 0 . 9 2 0 . 9 5 0 . 2 0 0.19 0 . 0 4 0 . 0 2 , T A B L E 8 . 1 0 RUN N O . 1 0 : 20WT% D E A , T I N = 6 0 C , TOUT=195C,TOUTC=2 00 C FLOW R A T E = 0 . 0 1 1 0 L / s , DELP=552 k P a , CALDP= 572 kPa C 0 2 P A R T I A L PRESSURE = 4 1 3 7 kPa , TH=250C TIME CONCENTRATION ( M O L E S / L ) h r DEA HEOD THEED BHEP EXP CALC EXP CALC EXP CALC EXP CALC 0 0 . 0 2 . 0 0 2 . 0 0 _ 2 4 . 0 1 . 94 1 . 94 - 0 . 0 4 - - 0.01 - - 4 8 . 0 1 . 8 9 1 .88 0-.06 0 . 0 8 0.01 0 . 0 2 - 0.01 72 . 0 1 .82 1.81 0 . 1 0 0.11 0 . 02 0 . 0 2 - 0.01 9 6 . 0 1 .76 1 .75 0 . 1 5 0 . 1 5 0 . 0 2 0 . 0 3 - 0 . 0 2 120 .0 1 . 70 1 . 69 0 . 2 0 0 . 1 9 0 . 0 3 0".04 - 0 . 0 2 144 .0 1 .64 1 .63 0 . 2 2 0 . 2 3 0 . 0 5 0 . 0 5 - 0 . 0 2 168 .0 1 . 57 1 .57 0 . 2 5 0 . 2 6 0 . 0 5 0 . 0 5 0.01 0 . 0 3 192 .0 1 . 52 1 .50 0 . 2 8 0 . 30 0 . 0 6 0 . 0 6 0.01 0 . 0 3 90 8 . 2 E F F E C T S OF OPERATING V A R I A B L E S ON DEGRADATION The e f f e c t s o f t e m p e r a t u r e , s o l u t i o n c o n c e n t r a t i o n , C 0 2 p a r t i a l p r e s s u r e a n d e s p e c i a l l y o f s o l u t i o n f l o w r a t e on DEA d e g r a d a t i o n were s t u d i e d . 8 . 2 . 1 E f f e c t o f f l o w r a t e In o r d e r t o e x a m i n e t h e e f f e c t o f f l o w r a t e on DEA d e g r a d a t i o n , two s e t s o f e x p e r i m e n t s were c a r r i e d o u t . In f i r s t s e t , t h e f l o w r a t e was v a r i e d w h i l e k e e p i n g t h e t e m p e r a t u r e o f t h e h e a t i n g f l u i d c o n s t a n t . The t e m p e r a t u r e o f t h e DEA s o l u t i o n l e a v i n g t h e h e a t t r a n s f e r c o i l was a l l o w e d t o v a r y . The r e s u l t s a r e p l o t t e d i n F i g u r e 8 . 1 . As m i g h t be e x p e c t e d , l o w e r f l o w r a t e s r e s u l t e d i n h i g h e r d e g r a d a t i o n r a t e s . The i n c r e a s e i n DEA d e g r a d a t i o n c a n be a t t r i b u t e d t o t h e c o m b i n e d e f f e c t o f t h e r e s i d e n c e t i m e f o r s i n g l e p a s s i n t h e t u b e a n d t h e s o l u t i o n t e m p e r a t u r e . S i n c e t h e d e g r a d a t i o n r a t e i n c r e a s e s r a p i d l y w i t h t e m p e r a t u r e , t h e t e m p e r a t u r e i n t h e o u t l e t s e c t i o n c a n be a s sumed t o e x e r t t h e p r e d o m i n a t i n g i n f l u e n c e . In o r d e r t o e l u c i d a t e t h e e f f e c t o f f l o w r a t e o n l y , a s e c o n d s e t o f e x p e r i m e n t s was c a r r i e d o u t . 91 3 | ' i 1 1 1 r • - 0 . 0 1 6 5 L/s • - 0 . 0 1 2 4 L/s CM co " A - 0.0110 L/s Model o » I I- ' I I i ' 0 4 0 8 0 1 2 0 1 6 0 2 0 0 2 4 0 TIME (Hours) F i g u r e 8.1 DEA c o n c e n t r a t i o n as a f u n c t i o n o f t i m e and f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , h e a t i n g o i l t e m p . 250 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 92 The f l o w r a t e s were v a r i e d w h i l e t h e o u t l e t t e m p e r a t u r e was k e p t c o n s t a n t by r e g u l a t i n g t h e h o t f l u i d t e m p e r a t u r e . Two f l o w r a t e s were c h o s e n , one a t 0 . 0 1 7 2 L / s ( 5 . 3 m/s ) a n d t h e o t h e r a t 0 .011 L / s ( 3 . 4 m / s ) . T h e t e m p e r a t u r e p r o f i l e s r e s u l t i n g f r o m t h e two f l o w r a t e s a r e shown i n F i g u r e 8 . 2 . As c a n be s e e n , t h e y a r e a l m o s t i d e n t i c a l . DEA c o n c e n t r a t i o n s a s a f u n c t i o n o f t i m e a r e p l o t t e d i n F i g u r e 8 . 3 . DEA d e g r a d a t i o n r e m a i n s a l m o s t t h e same f o r b o t h f l o w r a t e s . The m o d e l p r e d i c t i o n s o f t h e c o n c e n t r a t i o n p r o f i l e s f o r t h e two f l o w r a t e s a r e p l o t t e d i n F i g u r e 8 . 4 . As c a n be s e e n , f o r a s i n g l e p a s s , t h e d e g r a d a t i o n r a t e i s h i g h e r a t l o w e r f l o w r a t e s (0 .011 L / s ) . A l t h o u g h t h e d e g r a d a t i o n r a t e f o r a s i n g l e p a s s a t t h e l o w e r f l o w r a t e i s h i g h e r , t h e o v e r a l l d e g r a d a t i o n r a t e s f o r a g i v e n p e r i o d ( a n d when t h e f l u i d s a r e r e c i r c u l a t e d ) a r e a l m o s t t h e same f o r b o t h f l o w r a t e s . T h i s i s due t o t h e " t o t a l r e s i d e n c e t i m e " , w h i c h i s t h e same i n b o t h c a s e s . The e f f e c t o f r e s i d e n c e t i m e c a n be e x p l a i n e d by c o n s i d e r i n g two f l o w r a t e s W, a n d W 2 (W, < W 2 ) a n d d e f i n i n g : w, = = l o w e r f l o w r a t e w2 = = h i g h e r f l o w r a t e N , = = t o t a l n o . o f p a s s e s a t f l o w r a t e W, N 2 = = t o t a l n o . o f p a s s e s a t f l o w r a t e W 2 R T , = = t o t a l r e s i d e n c e t i m e a t f l o w r a t e W, R T 2 •• = t o t a l r e s i d e n c e t i m e a t f l o w r a t e W 2 r t , = = r e s i d e n c e t i m e f o r s i n g l e p a s s a t f l o w r a t e W, r t 2 = = r e s i d e n c e t i m e f o r s i n g l e p a s s a t f l o w r a t e W 2 93 The r e s i d e n c e t i m e f o r a s i n g l e p a s s t r , a t t h e l o w e r f l o w r a t e W, i s h i g h e r t h a n t h e r e s i d e n c e t i m e t r 2 a t t h e h i g h e r f l o w r a t e W 2 . H o w e v e r , f o r a g i v e n t i m e T , t h e number o f p a s s e s N , t h r o u g h t h e t u b e i s l o w e r t h a n N 2 o f t h e h i g h e r f l o w r a t e . We c a n w r i t e : R T , = r t , x N , , a n d R T 2 = r t 2 x N 2 I f r t , x N , = r t 2 x N 2 , t h e n t h e t o t a l r e s i d e n c e t i m e i s t h e same f o r b o t h f l o w r a t e s W, a n d W 2 . T h i s i s t h e c a s e f o r f l o w r a t e s o f 0 .011 L / s ( 3 . 4 m/s ) and 0 . 0 1 7 2 L / s ( 5 . 3 m / s ) . B a s e d on h y d r o d y n a m i c c o n s i d e r a t i o n s , one more f a c t o r h a s t o be e x a m i n e d . T h i s i s t h e s o - c a l l e d " b o u n d a r y f i l m " , i . e . t h e l a y e r a d j a c e n t t o t h e h e a t e x c h a n g e r t u b e w a l l . The f i l m t h i c k n e s s d e c r e a s e s w i t h i n c r e a s i n g f l o w r a t e . A l a r g e f i l m t h i c k n e s s means t h a t a h i g h e r p r o p o r t i o n o f t h e l i q u i d i s i n c o n t a c t w i t h t h e s u r f a c e o f t h e h e a t e x c h a n g e r a n d , c o n s e q u e n t l y , r e s u l t s i n h i g h e r r a t e s o f d e g r a d a t i o n . F i l m t h i c k n e s s e s a s p r e d i c t e d by t h e t h e o r e t i c a l m o d e l a r e shown i n F i g u r e 8 . 5 . F i l m t h i c k n e s s e s a r e v e r y t h i n b e c a u s e o f t h e s m a l l d i a m e t e r t u b e a n d h i g h e r R e y n o l d s number u s e d i n t h e e x p e r i m e n t s . T h e r e f o r e , t h e d e g r a d a t i o n r a t e c o u l d be p r e d i c t e d a c c u r a t e l y u s i n g t h e b u l k s o l u t i o n t e m p e r a t u r e . However i n i n d u s t r i a l h e a t e x c h a n g e r s , t h e f i l m t h i c k n e s s e s may be l a r g e and t h e r e f o r e , m e t a l w a l l t e m p e r a t u r e may h a v e t o be u s e d f o r c a l c u l a t i n g t h e r a t e c o n s t a n t s . 94 O oo r- r • - 0 . 0 1 7 2 L / s - 0 . 0 1 1 0 L / s o ± JL X 1 2 3 4 5 DISTANCE FROM TUBE ENTRANCE (m) F i g u r e 8 .2 T e m p e r a t u r e o f t h e DEA s o l u t i o n as a f u n c t i o n o f t h e d i s t a n c e f rom t h e t u b e e n t r a n c e a n d f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 7 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 95 co CM CO E Z o co eg r - < I - Z CO UJ OJ o z O O < UJ o CM CM CM O CM I r • - 0JD110 L/s • - 0.0172 L/s F i g u r e 8 . 3 X X 40 80 120 160 TIME (Hours) 200 240 DEA c o n c e n t r a t i o n as a f u n c t i o n o f t i m e and f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t emp . 1 7 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 96 F i g u r e 8 . 4 M o d e l p r e d i c t i o n o f DEA c o n c e n t r a t i o n a s a f u n c t i o n of t i m e a n d f l o w r a t e ( s i n g l e p a s s ) . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 7 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 97 — r - r T - 0.0110 L/s • - 0.0172 L/s CO h o ' » J I I I 0 1 2 3 4 5 DISTANCE FROM TUBE ENTRANCE (m) F i g u r e 8 . 5 M o d e l p r e d i c t i o n o f t h e f i l m t h i c k n e s s a s a f u n c t i o n o f ' t h e d i s t a n c e f rom t h e t u b e e n t r a n c e and f l o w r a t e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 7 0 ° C , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 Mpa) 98 8 . 1 . 2 E f f e c t o f t e m p e r a t u r e The r a t e o f DEA d e g r a d a t i o n i s known t o be s t r o n g l y d e p e n d e n t on t e m p e r a t u r e . DEA c o n c e n t r a t i o n s a r e p l o t t e d i n F i g u r e 8 . 6 . a s a f u n c t i o n o f t i m e f o r t h r e e d i f f e r e n t h e a t t r a n s f e r f l u i d t e m p e r a t u r e s . The f l o w r a t e was k e p t c o n s t a n t and t h e h e a t t r a n s f e r t u b e o u t l e t t e m p e r a t u r e was a l l o w e d t o v a r y w i t h t h e t e m p e r a t u r e o f h e a t t r a n s f e r f l u i d . As c a n s e e n f r o m F i g u r e 8 . 6 , t h e DEA c o n c e n t r a t i o n f a l l s w i t h i n c r e a s i n g t e m p e r a t u r e . T h i s i s c o n s i s t e n t w i t h p r e v i o u s f i n d i n g s . 8 . 2 . 2 E f f e c t o f s o l u t i o n c o n c e n t r a t i o n T h r e e e x p e r i m e n t s were c a r r i e d o u t w i t h 2 0 , 30 a n d 40 wt% DEA s o l u t i o n s a t a c o n s t a n t f l o w r a t e o f 0 .011 L / s . T h e s e c o n c e n t r a t i o n s were c h o s e n t o r e f l e c t t y p i c a l i n d u s t r i a l c o n d i t i o n s . F i g u r e 8 . 7 shows t h e DEA c o n c e n t r a t i o n a s a f u n c t i o n o f t i m e f o r t h e s e e x p e r i m e n t s . I t i s c l e a r f r o m t h i s f i g u r e t h a t t h e d e g r a d a t i o n r a t e i n c r e a s e s w i t h t h e s o l u t i o n c o n c e n t r a t i o n . S i n c e t h e t e m p e r a t u r e o f t h e s o l u t i o n v a r i e d a l o n g t h e h e a t t r a n s f e r t u b e , i t was n o t p o s s i b l e t o c a l c u l a t e t h e r a t e o f d e g r a d a t i o n a c c u r a t e l y . However f o r c o m p a r i s o n p u r p o s e s , a v e r a g e v a l u e s o f d e g r a d a t i o n r a t e s were c a l c u l a t e d u s i n g i n i t i a l a n d f i n a l DEA c o n c e n t r a t i o n s and a r e p r e s e n t e d i n T a b l e 8 . 1 1 . 99 0 F i g u r e 8 . 6 4 0 8 0 1 2 0 1 6 0 TIME (Hours) 2 0 0 2 4 0 DEA c o n c e n t r a t i o n as a f u n c t i o n h e a t i n g f l u i d t e m p e r a t u r e . (30 r a t e 0.011 L / s , i n l e t temp, p r e s s u r e 4 . 1 4 Mpa) of t i m e , a n d wt% D E A , f l o w 6 0 ° C , c 0 2 p a r t i a l 1 00 CD r 1 — — 1 1 1 r A - 40 wt% • - 30 wt% m - • - 20 wt% Model o> o o I I 1 1 1 1 1 0 40 80 120 160 200 TIME (Hours) F i g u r e 8 . 7 DEA c o n c e n t r a t i o n as a f u n c t i o n of t i m e a n d i n i t i a l DEA c o n c e n t r a t i o n . ( I n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0 .011 L / s , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 1 101 T a b l e 8.11 A v e r a g e d e g r a d a t i o n r a t e s . ( I n l e t t e m p . 60 C , o u t l e t t e m p . 195 C , h e a t i n g f l u i d t e m p . 250 C , f l o w r a t e 0 .011 L / s ) S o l u t i o n c o n e . D e g r a d a t i o n r a t e wt% m o l e s / ( L h r ) 20 0 . 0 0 2 5 30 - 0 . 0 0 4 5 40 0 . 0 0 6 5 The i n c r e a s e i n d e g r a d a t i o n r a t e may be e x p l a i n e d i n t e r m s o f h i g h e r s o l u t i o n s t r e n g t h and C 0 2 d i s s o l v e d i n t h e DEA s o l u t i o n . The h i g h e r t h e DEA c o n c e n t r a t i o n , t h e h i g h e r t h e a l k a l i n i t y and c o n s e q u e n t l y t h e q u a n t i t y o f C 0 2 d i s s o l v e d i n t h e DEA s o l u t i o n . F o r e x a m p l e , a t 1 0 0 ° C a n d a C 0 2 p a r t i a l p r e s s u r e o f 690 k P a , t h e C 0 2 c o n c e n t r a t i o n i n 3 . 5 N (30 wt%) DEA i s 1.883 N ( 0 . 5 3 8 mole C 0 2 / m o l e DEA) as c o m p a r e d t o 1.290 N ( 0 . 4 9 0 m o l e C 0 2 / m o l e DEA) o f 2 N (20 wt%) DEA [ 8 2 ] . A t h i g h e r s o l u t i o n c o n c e n t r a t i o n s , more C 0 2 i s d i s s o l v e d i n t h e s o l u t i o n a n d t h i s c a u s e s t h e d e g r a d a t i o n r a t e t o r i s e . 8 . 2 . 4 E f f e c t o f C 0 2 p a r t i a l p r e s s u r e E x p e r i m e n t s u s i n g 30 wt% DEA a t 4 1 3 7 , 2758 , a n d 1379 kPa o f C 0 2 p a r t i a l p r e s s u r e s were c a r r i e d o u t i n o r d e r t o s t u d y t h e i r e f f e c t on d e g r a d a t i o n . The DEA c o n c e n t r a t i o n s f o r t h e s e t h r e e r u n s a r e p l o t t e d i n F i g u r e 8 . 8 a s a f u n c t i o n o f t i m e . 1 02 CO CO A o co T " r 1.38 MPa 2.76 MPa 4.14 MPa — Model JL 0 F i g u r e 8 . 8 40 80 120 160 TIME (Hours) 200 240 DEA c o n c e n t r a t i o n as a f u n c t i o n o f t i m e a n d C 0 2 p a r t i a l p r e s s u r e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 9 5 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0.011 L / s ) 1 03 As e x p e c t e d , t h e d e g r a d a t i o n r a t e was f o u n d t o i n c r e a s e w i t h C 0 2 p a r t i a l p r e s s u r e . A g a i n t h i s i n c r e a s e c a n be a t t r i b u t e d t o t h e • i n c r e a s e i n d i s s o l v e d C 0 2 i n t h e DEA s o l u t i o n s a t h i g h e r C 0 2 p a r t i a l p r e s s u r e s . 8 . 3 E F F E C T OF DEGRADATION ON SOLUTION V I S C O S I T Y The a c c u m u l a t i o n o f d e g r a d a t i o n p r o d u c t s i n c r e a s e s t h e v i s c o s i t y o f DEA s o l u t i o n s . The v i s c o s i t y c h a n g e s o f t y p i c a l r u n s a r e shown i n F i g u r e 8 . 9 . A l t h o u g h t h e v i s c o s i t y i n c r e a s e i s n o t v e r y s i g n i f i c a n t (4 t o 12% o f t h e i n i t i a l s o l u t i o n v i s c o s i t y ) , i f l e f t u n a t t e n d e d , i t m i g h t h a v e some v e r y s e r i o u s c o n s e q u e n c e s on p l a n t p e r f o r m a n c e s u c h as u n s a t i s f a c t o r y o p e r a t i o n o r h i g h e r power c o n s u m p t i o n by t h e DEA s o l u t i o n pumps . I t a l s o d e c r e a s e s t h e h e a t t r a n s f e r c o e f f i c i e n t o f t h e h e a t e x c h a n g e r s . F u r t h e r m o r e mass t r a n s f e r c o - e f f i c i e n t s d e c r e a s e w i t h v i s c o s i t y . T h e r e f o r e , v i s c o s i t y i n c r e a s e s w i l l l i k e l y r e s u l t i n p o o r p e r f o r m a n c e o f t h e C 0 2 a b s o r b e r i n i n d u s t r i a l f a c i l i t i e s . 8 . 4 E F F E C T OF DEGRADATION ON SOLUTION FOAMING In o r d e r t o d e t e r m i n e w h e t h e r d e g r a d a t i o n h a s a n y e f f e c t on s o l u t i o n f o a m i n g , f o a m i n g t e s t s a s d e s c r i b e d i n C h a p t e r 6 were c a r r i e d o u t . The r e s u l t s a r e p r e s e n t e d i n T a b l e 8 . 1 2 . F i g u r e 8.9 S o l u t i o n v i s c o s i t y as a f u n c t i o n of t i m e and d e g r a d a t i o n p r o d u c t c o n c e n t r a t i o n . 1 05 T a b l e 8 .12 R e s u l t s o f f o a m i n g t e s t s w i t h 30 wt% DEA Sample d e s c r i p t i o n Foam h e i g h t mL Foam b r e a k d o w n t i m e ( s ) 0 . 0 wt% d e g r a d e d DEA 40 5 5 . 0 wt% d e g r a d e d DEA 50 30 7 . 3 wt% d e g r a d e d DEA 80 70 8 . 7 wt% d e g r a d e d DEA 1 00 100 As c a n be s e e n f rom t h e r e s u l t s , a c c u m u l a t i o n o f d e g r a d a t i o n p r o d u c t s i n c r e a s e s t h e f o a m i n g t e n d e n c y o f t h e s o l u t i o n . H o w e v e r , i t was n o t p o s s i b l e t o d e t e r m i n e w h i c h d e g r a d a t i o n c o m p o u n d ( s ) a r e p r i m a r i l y r e s p o n s i b l e f o r f o a m i n g 8 . 5 E F F E C T OF DEGRADATION ON SOLUTION pH When DEA d e g r a d e s , t h e c o n c e n t r a t i o n o f DEA i n t h e s o l u t i o n d e c r e a s e s a n d t h e c o n c e n t r a t i o n o f d e g r a d a t i o n p r o d u c t s i n c r e a s e s . The a l k a l i n i t y o f t h e two p r i n c i p a l d e g r a d a t i o n compounds (BHEP and THEED) i s l o w e r t h a n t h a t o f DEA and i s e q u i v a l e n t t o TEA [ 4 1 ] . T h e r e f o r e , a s DEA d e g r a d e s , t h e pH o f t h e s o l u t i o n d e c r e a s e s . F u r t h e r m o r e , f o r m a t i o n o f o t h e r d e g r a d a t i o n compounds i s a l s o p a r t l y r e s p o n s i b l e f o r t h e d e c r e a s e i n pH o f t h e DEA s o l u t i o n . H a l l and B a r r o n [53] 106 p r e s e n t e d i n d u s t r i a l d a t a s h o w i n g a g r a d u a l . r e d u c t i o n i n s o l u t i o n pH w i t h t h e f o r m a t i o n o f h e a t s t a b l e s a l t s . T h e s e h e a t s t a b l e s a l t s a r e f o r m e d as a r e s u l t o f n e u t r a l i z a t i o n o f c a r b o x y l i c a c i d s w i t h DEA [45] t h e r e b y r e d u c i n g t h e b a s i c i t y o f t h e s o l u t i o n . T h e s e f i n d i n g s a r e c o n f i r m e d by t h e e x p e r i m e n t a l r e s u l t s o b t a i n e d f r o m d e g r a d a t i o n e x p e r i m e n t s i n w h i c h t h e s o l u t i o n pH was m e a s u r e d a s a f u n c t i o n o f t i m e . ( s e e , f o r e x a m p l e , F i g u r e 8 . 1 0 ) The i n i t i a l s h a r p d r o p i n pH c a n be a t t r i b u t e d t o t h e a b s o r p t i o n o f C 0 2 . The g r a d u a l d e c r e a s e t h e r e a f t e r r e p r e s e n t s t h e l o s s o f b a s i c i t y due t o t h e l o s s o f DEA a c c o m p a n i e d by t h e f o r m a t i o n o f l e s s b a s i c d e g r a d a t i o n p r o d u c t s BHEP a n d T H E E D . 1 07 80 120 160 TIME (Hours) 200 240 F i g u r e 8 . 1 0 T y p i c a l pH c h a n g e of p a r t i a l l y d e g r a d e d DEA s o l u t i o n as a f u n c t i o n o f t i m e . (30 wt% D E A , i n l e t t e m p . 6 0 C , o u t l e t t e m p . l 9 5 C , h e a t i n g f l u i d t e m p . 2 5 0 C , f l o w r a t e 0.011 L / s ) 108 8 . 6 HEAT EXCHANGER FOULING H e a t e x c h a n g e r f o u l i n g c r e a t e s a r e s i s t a n c e t o f l o w w h i c h r e s u l t s i n i n c r e a s e d p r e s s u r e d r o p s . T h e r e f o r e p r e s s u r e d r o p m e a s u r e m e n t s c a n p r o v i d e i n f o r m a t i o n on f o u l i n g . In o r d e r t o s t u d y t h e e f f e c t o f s o l u t i o n d e g r a d a t i o n on f o u l i n g o f h e a t e x c h a n g e r s , t h e p r e s s u r e d r o p a c r o s s t h e h e a t e x c h a n g e r c o i l was r e c o r d e d f o r e a c h r u n . 8 . 6 . 1 E f f e c t o f t e m p e r a t u r e The t e m p e r a t u r e o f t h e h o t h e a t t r a n s f e r f l u i d seems t o i n f l u e n c e t h e f o u l i n g r a t e . In t h r e e d i f f e r e n t r u n s p e r f o r m e d a t t h e same f l o w r a t e (0 .011 L / s ) , t h e h o t f l u i d t e m p e r a t u r e was v a r i e d a n d t h e o u t l e t t e m p e r a t u r e was a l l o w e d t o c h a n g e a c c o r d i n g l y . F i g u r e 8 .11 shows t h e p r e s s u r e d r o p as a f u n c t i o n of t i m e f o r t h e s e t h r e e r u n s . As c a n be s e e n f rom F i g u r e 8 . 1 1 , t h e f o u l i n g r a t e r i s e s w i t h i n c r e a s i n g t e m p e r a t u r e and r e a c h e s a c o n s t a n t v a l u e i n e a c h c a s e . A l l t h e s e r u n s were c a r r i e d o u t i n t h e t u r b u l e n t r e g i o n , where v i s c o u s f o r c e s p l a y a m i n o r r o l e . T h e r e f o r e , i n s p i t e o f s l i g h t v i s c o s i t y i n c r e a s e s a s a r e s u l t o f s o l u t i o n d e g r a d a t i o n , t h e i n c r e a s e i n p r e s s u r e d r o p c a n be a t t r i b u t e d m o s t l y t o f o u l i n g . F o u l i n g may i n c r e a s e t h e p r e s s u r e d r o p by r e d u c i n g t h e e f f e c t i v e t u b e d i a m e t e r due t o s c a l e f o r m a t i o n a n d a l s o by i n c r e a s i n g t h e s u r f a c e r o u g h n e s s o f t h e t u b e . 109 O o o o o • - 250 °C • - 225 °C - 4-190 °C • A 4 O o m o o -L 4 6 TIME (Days) 8 10 F i g u r e 8 .11 P r e s s u r e d r o p as a f u n c t i o n o f t i m e a n d h e a t i n g f l u i d t e m p e r a t u r e . (30 wt% D E A , i n l e t t e m p . 6 0 ° C , h e a t i n g f l u i d t e m p . 2 5 0 ° C , f l o w r a t e 0.011 L / s , C 0 2 p a r t i a l p r e s s u r e 4 . 1 4 MPa) 1 10 E l e c t r o n m i c r o g r a p h i c p h o t o s o f t h e s u r f a c e s o f an u n c o n t a m i n a t e d a n d a c o n t a m i n a t e d t u b e s e c t i o n a r e shown F i g u r e 8 . 1 2 . F i g u r e 8 . 1 3 show t h e e l e c t r o n m i c r o g r a p h i c p h o t o s o f a c r o s s s e c t i o n , o f t h e c o n t a m i n a t e d t u b e a n d a m a g n i f i e d v i e w (400 x ) , o f t h e f o u l i n g s c a l e . 8 . 6 . 2 E l e c t r o n m i c r o p r o b e a n a l y s i s E l e c t r o n m i c r o p r o b e a n a l y s i s o f t h e f o u l e d h e a t e x c h a n g e r s u r f a c e r e v e a l e d t h e p r e s e n c e o f a l u m i n u m i n t h e f o u l i n g s c a l e . H o w e v e r , t h e s o u r c e of a l u m i n u m c o u l d n o t be d e t e r m i n e d . I t s h o u l d be n o t e d t h a t no a l u m i n u m was u s e d i n t h e f l o w c i r c u i t . E l e c t r o n m i c r o p r o b e p l o t s o f t h e c o n t a m i n a t e d a n d u n - c o n t a m i n a t e d s u r f a c e s a r e shown i n F i g u r e 8 . 1 4 . 8 . 6 . 3 A p p a r e n t d e p o s i t t h i c k n e s s A p p a r e n t d e p o s i t t h i c k n e s s was c a l c u l a t e d f r o m t h e p r e s s u r e d r o p d a t a . I t was a s sumed t h a t t h e i n c r e a s e i n t h e p r e s s u r e d r o p was o n l y due t o t h e d e c r e a s e i n t h e e f f e c t i v e t u b e d i a m e t e r a s a r e s u l t o f s c a l e f o r m a t i o n . D e p o s i t t h i c k n e s s e s a r e p l o t t e d i n F i g u r e 8 . 1 5 as a f u n c t i o n o f t i m e . 111 8 . 7 EXPERIMENT WITH A NEW TUBE Run 1 (30 wt% D E A , i n l e t t e m p . 6 0 ° C , o u t l e t t e m p . 1 9 0 ° C , f l o w r a t e 0 . 0 1 2 4 L / s , h e a t i n g f l u i d t e m p . 2 5 0 ° C and C 0 2 p a r t i a l p r e s s u r e 4137 kPa) was r e p e a t e d u s i n g a new u n c o n t a m i n a t e d t u b e o f same d i m e n s i o n ( 4 . 8 0 m l o n g , 3 . 1 7 5 mm OD, 2 . 0 3 2 mm ID and a t u r n i n g r a d i u s o f 0 . 4 0 6 4 m ) . D e g r a d a t i o n a s w e l l a s p r e s s u r e d r o p d a t a m a t c h e d a c c u r a t e l y w i t h t h e p r e v i o u s r e s u l t s . b) C o n t a m i n a t e d F i q u r e 8 .12 E l e c t r o n m i c r o g r a p h i c p h o t o s o f t h e u n c o n t a m i n a t e d and c o n t a m i n a t e d s u r f a c e s of t h e h e a t e x c h a n g e r t u b e . (20 x) 113 F i g u r e 8 . 1 3 E l e c t r o n m i c r o g r a p h i c p h o t o s o f t h e f o u l e d s u r f a c e of t h e h e a t e x c h a n g e r t u b e (20 x) and a m a g n i f i e d v i e w (400 x) o f t h e same s u r f a c e Fe A l Cr Mn + C r Fe N i • *• • •**" • • N i a) C o n t a m i n a t e d s u r f a c e • . • Cr Mn + Cr Al •••••• y . b) U n c o n t a m i n a t e d s u r f a c e Fe Fe N i N i F i g u r e 8 .14 E l e c t r o n m i c r o p r o b e p l o t s o f t h e c o n t a m i n a t e d and u n c o n t a m i n a t e d s u r f a c e s o f t h e h e a t e x c h a n g e r t u b e . 1 1 5 CM TIME (Days) F i g u r e 8 . 1 5 A p p a r e n t d e p o s i t t h i c k n e s s as a f u n c t i o n o f t i m e and h e a t i n g f l u i d t e m p e r a t u r e . (30 wt% D E A , i n l e t t e m p . 6 0 C , f l o w r a t e 0.011 L / s ) 1 1 6 CHAPTER 9 RESULTS AND DISCUSSION OF CORROSION STUDIES 9.1 CORROSION RATE IN UNDEGRADED DEA SOLUTIONS The c o r r o s i o n r a t e o f c a r b o n s t e e l i n t h e u n - d e g r a d e d - s o l u t i o n , a s d e t e r m i n e d by p o t e n t i o d y n a m i c t e s t ( s e e F i g u r e 9 . 1 ) , was 0 . 0 6 mm/year ( 2 . 4 6 m p y ) , T h i s i s q u i t e c l o s e t o t h e c o r r o s i o n r a t e o f 0 . 0 5 mm/year (2 mpy) o b t a i n e d by B l a n c e t a l . [45] i n one o f t h e i r t e s t s u s i n g t h e F e ~ H 2 S - D E A s y s t e m . The c o r r o s i o n r a t e s a r e p r a c t i c a l l y t h e same. I t s h o u l d be n o t e d t h a t C 0 2 was n o t u s e d i n t h e i r c o r r o s i o n t e s t s . S i n c e H 2 S i s known t o i n h i b i t DEA d e g r a d a t i o n [ 4 3 ] , t h e i r DEA s o l u t i o n , w h i c h was s a t u r a t e d o n l y w i t h H 2 S , d i d n o t d e g r a d e n o t i c e a b l y . 9 . 2 CORROSION RATES IN DEGRADED DEA SOLUTIONS A d e g r a d e d s a m p l e o f DEA s o l u t i o n c o n t a i n i n g a b o u t 8 . 7 % d e g r a d a t i o n p r o d u c t s y i e l d e d a c o r r o s i o n r a t e o f 0 . 4 mm/year (16 .1 m p y ) , a b o u t 6 . 5 t i m e s h i g h e r t h a n t h a t o f u n ' - d e g r a d e d s o l u t i o n . T h i s i n d i c a t e s t h a t d e g r a d e d DEA s o l u t i o n s c o n t a i n i n g HEOD, THEED a n d BHEP a r e , i n f a c t , c o r r o s i v e t o w a r d s c a r b o n s t e e l a n d t h e r e b y c o n t r a d i c t s e a r l i e r c l a i m s [ 4 5 ] . I •• . I DO - - • . S H D - R R E R MI//SEC EC0RR E . HH I - I . 5 D D I I - • . S O D R E S U L T S C T C D . 5 3 H R T C a.oas J -CBRRC S . 7 S I E 3 MPY 2 . E S H :C0RR - • . 3 3 7 I D 5 I D 3 N R / C M 2 F i g u r e 9.1 P o t e n t i o d y n a m i c a n o d i c p o l a r i z a t i o n c u r v e of 30 wt% u n d e g r a d e d DEA s o l u t i o n . ( t e m p . 2 5 C) - • . S H d - . 3 B 0 - S R M P L E D R T E R R E R I? N I / / S E C E C 0 R R 2 • 2 . • I E . H H I - I . E D O I I - • . 7 B D R E S U L T S C T C • . I 7 7 R T C N 0 7 F 0 U N D I C 0 R R C 3 . H 3 D E H MPY E C 0 R R V - • . S D H - • . 2 3 0 • . 2 H H • . 3 3 2 I . E I D E I - 0 . 0 3 2 N R / C M 2 3 . 3 B H E S 5 . B I I E H 2 . H S S E H 2 . E 7 0 E H • 9 N R / C l i 2 F i g u r e 9 .2 P o t e n t i o d y n a m i c a n o d i c p o l a r i z a t i o n c u r v e o f 30 wt% p a r t i a l l y d e g r a d e d DEA s o l u t i o n c o n t a i n i n g 8 . 7 wt% d e g r a d a t i o n p r o d u c t s . (Temp. 25C) oo 1 19 9 . 3 E F F E C T OF CQ 2 DISSOLVED IN DEA SOLUTIONS ON CORROSION DEA s o l u t i o n s i n t h e a b s e n c e o f C 0 2 a r e no t c o r r o s i v e . H o w e v e r , when t h e y a r e s a t u r a t e d w i t h C 0 2 , t h e y become c o r r o s i v e . T h i s c a n be c o n c l u d e d f r o m T a b l e 9.1 by c o m p a r i n g t h e c o r r o s i o n r a t e s o b t a i n e d w i t h 40 wt% DEA s o l u t i o n s w h i c h a r e e i t h e r f r e e o f o r i n i t i a l l y s a t u r a t e d w i t h C 0 2 a t a t m o s p h e r i c p r e s s u r e a n d 100 ° C . T a b l e 9.1 E f f e c t o f C 0 2 on c o r r o s i o n r a t e s Sample C o r r o s i o n r a t e s mm/year mi l s / y e a r 40 wt% DEA 0 . 0 0 3 0. 1 40 wt% DEA + CO 2 1 .840 7 2 . 3 2 1 20 9 . 4 E F F E C T OF SOLUTION CONCENTRATION When DEA c o n t a i n s C 0 2 , t h e c o r r o s i o n r a t e i n c r e a s e s w i t h t h e DEA c o n c e n t r a t i o n . W e i g h t l o s s r e s u l t s c o n d u c t e d a t v a r i o u s DEA c o n c e n t r a t i o n s a r e p r e s e n t e d i n T a b l e 9 . 2 . T h e y c l e a r l y i n d i c a t e t h a t t h e c o r r o s i o n r a t e i n c r e a s e s w i t h DEA c o n c e n t r a t i o n . T a b l e 9 .2 E f f e c t o f DEA c o n c e n t r a t i o n on c o r r o s i o n r a t e s Sample C o r r o s i o n r a t e s mm/year m i l s / y e a r 30 wt% DEA + C 0 2 1 .60 6 3 . 1 40 wt% DEA + C 0 2 1 .840 7 2 . 3 2 60 wt% DEA + C 0 2 2 . 0 7 0 8 1 . 6 0 9 . 5 E F F E C T OF SOLUTION pH ON CORROSION P o u r b a i x p o t e n t i a l - p H d i a g r a m f o r F e - H 2 0 s y s t e m [60 ] c a n p r o v i d e q u a l i t a t i v e i n f o r m a t i o n on t h e e f f e c t o f pH on c o r r o s i o n . As s e e n f r o m F i g u r e 2 . 2 , t h e r e e x i s t two d i s t i n c t r e g i o n s o f c o r r o s i o n , one a t pH g r e a t e r t h a n 13 and t h e o t h e r a t pH l o w e r t h a n 9 . A t i n t e r m e d i a t e pH v a l u e s , t h e c o r r o s i o n r a t e w o u l d be m i n i m a l due t o t h e f o r m a t i o n o f m e t a l o x i d e on t h e s u r f a c e . 1 2 1 T h e r e f o r e , any d e c r e a s e i n s o l u t i o n p H , t e n d s t o l e a d t h e s y s t e m g r a d u a l l y t o w a r d s t h e c o r r o s i o n r e g i o n and t h e r e f o r e i n c r e a s e s t h e c o r r o s i o n r a t e . As d i s c u s s e d i n C h a p t e r 8, t h e pH o f DEA s o l u t i o n s i n i t i a l l y d e c r e a s e r a p i d l y a s a r e s u l t o f C 0 2 a b s o r p t i o n a n d t h e r e a f t e r d r o p g r a d u a l l y due t o t h e f o r m a t i o n o f d e g r a d a t i o n p r o d u c t s . T h e r e f o r e , s o l u t i o n s a r e e x p e c t e d t o become more c o r r o s i v e a s d e g r a d a t i o n o c c u r s . 9.6 E F F E C T OF INDIVIDUAL DEGRADATION PRODUCTS A f t e r n o t i c i n g t h e c o r r o s i v e n a t u r e o f d e g r a d e d DEA s a m p l e s , i t was d e s i r e a b l e t o i d e n t i f y w h i c h d e g r a d a t i o n p r o d u c t s a r e p r i m a r i l y r e s p o n s i b l e f o r c o r r o s i o n o f c a r b o n s t e e l . W e i g h t l o s s t e s t s were c a r r i e d o u t w i t h d i f f e r e n t a q u e o u s s o l u t i o n s c o n t a i n i n g HEOD and BHEP s e p a r a t e l y a s w e l l a s w i t h m i x t u r e s o f DEA p l u s HEOD and DEA p l u s B H E P . T a b l e 9.3 s u m m a r i z e s t h e r e s u l t s o f t h e s e w e i g h t l o s s t e s t s . . 1 22 T a b l e 9 . 3 E f f e c t o f i n d i v i d u a l d e g r a d a t i o n compound on c o r r o s i o n Sample C o r r o s i o n r a t e s mm/year m i l s / y e a r 15 wt% DEA + C 0 2 0 . 1 3 5.1 15 wt% BHEP + C 0 2 0 . 16 6 . 3 15 wt% HEOD + C 0 2 1 . 95 7 6 . 6 30 wt% DEA + C 0 2 1 .60 6 3 . 1 30 wt% DEA + 5 wt% BHEP + C 0 2 1 .57 6 2 . 0 30 wt% DEA + 5 wt% HEOD + C 0 2 1 .91 7 5 . 0 The c o r r o s i o n r a t e i n t h e s o l u t i o n c o n t a i n i n g DEA and B H E P , i s s l i g h t l y l o w e r t h a n t h a t o f DEA a l o n e . T h i s i n d i c a t e s t h e n o n - c o r r o s i v e n a t u r e o f B H E P . i n DEA s o l u t i o n s a n d i s i n a g r e e m e n t w i t h t h e f i n d i n g s o f B l a n c e t a l . [ 4 5 ] . H o w e v e r , BHEP s o l u t i o n s (on a c o n s t a n t w e i g h t b a s i s ) a r e more c o r r o s i v e t h a n DEA on i t s own. T h i s c a n be s e e n by c o m p a r i n g t h e w e i g h t l o s s d a t a f o r 15 wt% DEA a n d 15 wt % BHEP s o l u t i o n s , r e s p e c t i v e l y . T h i s i s a l s o i n a g r e e m e n t w i t h t h e f i n d i n g s o f Hakka e t a l . [ 4 1 ] . The c o r r o s i o n r a t e s i n t h e s o l u t i o n c o n t a i n i n g DEA p l u s HEOD were h i g h e r t h a n t h o s e c o n t a i n i n g DEA a l o n e a n d DEA p l u s B H E P . T h i s i n d i c a t e s t h e c o r r o s i v e n a t u r e o f HEOD. 1 23 9 . 7 E F F E C T OF METAL COMPLEXING A q u e o u s DEA s o l u t i o n s c a n be r e g a r d e d as m i x t u r e s o f i o n i s e d s p e c i e s i n e q u i l i b r i a , c o n s i s t i n g m a i n l y o f H + , O H " , H C O 3 - , R 2 N C O O ~ , a s w e l l a s C 0 2 and R 2 N H + [ 5 1 ] . Among t h e a b o v e m e n t i o n e d s p e c i e s , O H " , H C 0 3 ~ , R 2 N C O O " and R 2 N H + a r e c a p a b l e o f f o r m i n g m e t a l c o m p l e x e s w i t h c a r b o n s t e e l . M a j o r DEA d e g r a d a t i o n p r o d u c t s , HEOD and THEED a r e a l s o l i k e l y t o f o r m m e t a l c o m p l e x e s . O t h e r c o n t a m i n a n t s , s u c h as h y d r a z i n e , c y a n i d e s , s u l p h i d e s , e t c . , i f p r e s e n t , may a l s o a c t a s c o m p l e x f o r m i n g l i g a n d s . Comeaux [57] r e p o r t e d t h e f o r m a t i o n o f i r o n c h e l a t e s w i t h p o l y a m i n e s s u c h as e t h y l e n e d i a m i n e , N - ( H y d r o x y e t h y l ) - E t h y l e n e d i a m i n e e t c . (A c h e l a t e i s a c o m p l e x i n g a g e n t w h i c h a t t a c h e s t o a m e t a l i o n a t more t h a n one p o i n t ) . H a l l a n d B a r r o n [53] r e p o r t e d t h e p r e s e n c e o f i r o n c h e l a t e s , w h i c h t i e up i r o n , i n i n d u s t r i a l DEA s o l u t i o n s . C o n s i d e r i n g t h e p r e s e n c e o f a l l t h e s e s p e c i e s w i t h c o m p l e x f o r m i n g a b i l i t i e s i n d e g r a d e d DEA s o l u t i o n s , i t i s v e r y l i k e l y t h a t m e t a l c o m p l e x e s o f one k i n d or a n o t h e r a r e p r o d u c e d w i t h t h e m e t a l i o n s i n t h e s o l u t i o n . The ma in e f f e c t o f c o m p l e x i n g i s t h e r e d u c t i o n o f t h e p o t e n t i a l o f t h e m e t a l - i o n / m e t a l e q u i l i b r i u m r e p r e s e n t e d by t h e f o l l o w i n g r e a c t i o n : F e 2 + + 2 e ' - Fe [ 9 . 1 ] The r e d u c t i o n i n t h i s e q u i l i b r i u m p o t e n t i a l e n l a r g e s t h e c o r r o s i o n r e g i o n s i n t h e p o t e n t i a l - p H d i a g r a m . 1 24 F o r m a t i o n o f m e t a l c o m p l e x e s s t a b i l i s e s m e t a l i o n s i n t h e s o l u t i o n , and t h e r e f o r e , r e s u l t s i n an i n c r e a s e i n t h e s o l u b i l i t y o f t h e m e t a l . I t may a l s o p r o m o t e b r e a k d o w n o f p a s s i v e f i l m s ; t h e e x t e n t o f t h e b r e a k d o w n d e p e n d s on t h e c o n c e n t r a t i o n o f t h e c o m p l e x e s i n s o l u t i o n . 9 . 8 P A S S I V I T Y An e x a m i n a t i o n o f p o l a r i z a t i o n c u r v e s f o r b o t h t h e u n d e g r a d e d and t h e d e g r a d e d s a m p l e s ( s e e , F i g u r e 9.1 a n d 9 . 2 , r e s p e c t i v e l y ) , i n d i c a t e s t h a t a l t h o u g h r e g i o n s o f p a s s i v i t y do e x i s t o v e r a wide p o t e n t i a l r a n g e , t h e y a r e n o t q u i t e s t a b l e . P a r t i c u l a r l y i n t h e c a s e o f u n d e g r a d e d DEA ( s e e F i g u r e 9 . 1 ) , t h e f i l m seem t o be v e r y u n s t a b l e . More i m p o r t a n t i s t h a t t h e c o r r o s i o n c u r r e n t i n t h e p a s s i v e r e g i o n i s v e r y c l o s e t o t h e c r i t i c a l c o r r o s i o n c u r r e n t a n d c o n s e q u e n t l y d o e s n o t p r o v i d e a d e q u a t e p r o t e c t i o n . T h e r e f o r e , t h e i d e a o f m a i n t a i n i n g l o w e r s o l u t i o n v e l o c i t i e s , i n o r d e r t o p r o t e c t t h e p r o t e c t i v e p a s s i v e f i l m on t h e m e t a l s u r f a c e i s q u e s t i o n a b l e . H o w e v e r , t h e r e a r e o t h e r f a c t o r s , s u c h as a c i d g a s b r e a k o u t , t o be c o n s i d e r e d i n t h i s r e s p e c t . 125 9 . 9 P I T T I N G The p i t t i n g p o t e n t i a l o f u n d e g r a d e d DEA s o l u t i o n s was n o t f o u n d t o be v e r y d i s t i n c t ( s e e F i g u r e 9 . 1 ) . H o w e v e r , i n t h e c a s e of d e g r a d e d DEA s o l u t i o n s , t h e p i t t i n g p o t e n t i a l i s c l e a r l y v i s i b l e . T h i s seems t o i n d i c a t e t h a t d e g r a d e d DEA s o l u t i o n s m i g h t i n d u c e p i t t i n g c o r r o s i o n u n d e r c e r t a i n c o n d i t i o n s . E l e c t r o n m i c r o g r a p h i c p h o t o s o f t h e t e s t c o u p o n s u s e d i n d i f f e r e n t c o r r o s i o n t e s t s , i n f a c t show p i t t i n g v e r y c l e a r l y ( see F i g u r e s 9 . 3 t o 9 . 6 r e s p e c t i v e l y ) . P i t t i n g i s most s e v e r e i n t h e c a s e o f t h e t e s t c o u p o n immersed i n HEOD. I n t r a g r a n u l a r c o r r o s i o n i s a l s o e v i d e n t . A 2000 x m a g n i f i c a t i o n o f a p i t a r e a i s shown i n F i g u r e 9 . 7 . F i g u r e 9.3 E l e c t r o n m i c r o g r a p h i c p h o t o of an u n c o r r o d e d A I S I 1020 c a r b o n s t e e l t e s t c o u p o n . ( 4 0 0 x ) 1 27 Figure 9.4 Electron micrographic photo of AISI 1020 carbon steel test coupon after 120 hr immersion in in 15 wt% DEA solution at 100 C. (400x) 1 28 F i g u r e 9 . 5 E l e c t r o n m i c r o g r a p h i c p h o t o of A I S I 1020 c a r b o n s t e e l t e s t coupon a f t e r 120 h r . immersion i n 15 wt% BHEP s o l u t i o n a t 100 C . U O O x ) F i g u r e 9 . 6 E l e c t r o n m i c r o g r a p h i c p h o t o o f A I S I 1020 c a r b o n s t e e l t e s t c o u p o n a f t e r 120 h r . i m m e r s i o n i n 15 wt% HEOD s o l u t i o n a t 100 C . U O O x ) F i g u r e 9 . 7 E l e c t r o n m i c r o g r a p h i c p h o t o o f a p i t a r e a o f AIS I 1020 c a r b o n s t e e l t e s t c o u p o n a f t e r 120 h r . i m m e r s i o n i n 15 wt% HEOD s o l u t i o n a t 100 C . (2000x) 131 CHAPTER 10 P U R I F I C A T I O N OF DEGRADED DEA SOLUTIONS U n l i k e MEA, d e g r a d e d DEA s o l u t i o n s c a n n o t be p u r i f i e d by d i s t i l l a t i o n a t a t m o s p h e r i c p r e s s u r e . The r e a s o n f o r t h i s i s t h a t DEA and i t s d e g r a d a t i o n p r o d u c t s have s i m i l a r v a p o r p r e s s u r e s . 10.1 USE OF CARBON F I L T E R S A c t i v a t e d c a r b o n f i l t e r s a r e w i d e l y u s e d t o p u r i f y d e g r a d e d DEA s o l u t i o n s . T h e y c a n remove s u s p e n d e d s o l i d s , h e a v y h y d r o c a r b o n s and p r o b a b l y some o f t h e h e a t s t a b l e s a l t s [ 5 1 ] . A l t h o u g h t h e i r s u c c e s s f u l o p e r a t i o n ha s been r e p o r t e d by s e v e r a l a u t h o r s [ 1 2 , 1 5 , 1 6 ] , M e i s e n a n d K e n n a r d ' s l i m i t e d l a b o r a t o r y t e s t s i n d i c a t e d t h a t a c t i v a t e d c a r b o n f i l t e r s do n o t remove any m a j o r DEA d e g r a d a t i o n c o m p o u n d s . C h r o m a t o g r a m s o f DEA s a m p l e s t a k e n u p s t r e a m and d o w n s t r e a m o f a c t i v a t e d c a r b o n f i l t e r s i n a gas t r e a t i n g p l a n t l o c a t e d i n A l b e r t a a r e shown i n F i g u r e 1 0 . 1 . T h e s e c h r o m a t o g r a m s a l s o c o n f i r m t h a t none o f t h e m a j o r DEA d e g r a d a t i o n p r o d u c t s were removed by t h e a c t i v a t e d c a r b o n f i l t e r . 1 32 HEM a) Sample t a k e n u p s t r e a m o f f i l t e r b) Sample t a k e n d o w n s t r e a m o f f i l t e r F i g u r e 10.1 C h r o m a t o g r a m s o f p a r t i a l l y d e g r a d e d DEA s a m p l e s t a k e n u p s t r e a m and d o w n s t r e a m o f an a c t i v a t e d c a r b o n f i l t e r l o c a t e d i n a gas p l a n t i n A l b e r t a . 1 33 10 .2 USE OF CHEMICALS S c h e i r m a n [15] r e p o r t e d t h e use o f s o d a a s h ( N a 2 C 0 3 ) f o r t h e r e m o v a l o f h e a t s t a b l e s a l t s . He a l s o s u g g e s t e d t h e p o s s i b l e use o f s o d i u m h y d r o x i d e (NaOH) and p o t a s s i u m compounds i n s t e a d o f s o d a a s h . H a l l a n d B a r r o n [53 ] r e p o r t e d t h e u se o f b o t h a c t i v a t e d c a r b o n f i l t e r s a n d NaOH i n t h e Ram R i v e r Gas P l a n t . T h e y p r e s e n t e d d a t a i n d i c a t i n g a r e d u c t i o n i n t h e h e a t s t a b l e s a l t c o n t e n t as a r e s u l t o f t h e s e t r e a t m e n t s . S i n c e c o r r o s i o n t e s t s i n d i c a t e d t h a t BHEP i s n o t c o r r o s i v e , p r e s e n t e f f o r t s were d i r e c t e d t o w a r d s t h e r e m o v a l o f HEOD and T H E E D . 10 .3 REMOVAL OF HEOD A c c o r d i n g t o K e n n a r d [ 5 1 ] , " H E O D i s f o r m e d by t h e d e h y d r a t i o n o f DEA c a r b a m a t e . 0 I I R-N-C- jO" I C 2 H „ - 0 - i H 0 H* i * • N 0 + H 2 0 [10 .1 ] C H 2 - C H 2 DEA C a r b a m a t e HEOD 1 34 K e n n a r d [51 ] s u g g e s t e d t h a t NaOH a d d i t i o n t o HEOD s o l u t i o n s c a n c o n v e r t most o f t h e HEOD t o D E A . T h i s i s due t o t h e f a c t t h a t t h e HEOD r i n g i s u n s t a b l e a n d t h e e l e c - t r o n d e f i c i e n t c a r b o n y l a tom o f t h e r i n g i s e a s i l y a t t a c k e d by O H " . + O H ' + H + HEOD 0 II -> R - N - C - O H I C 2 H , - O H [ 1 0 . 2 ] DEA C a r b a m a t e When NaOH i s a d d e d , HEOD i s c o n v e r t e d back t o DEA c a r b a m a t e a n d DEA c a n be r e g e n e r a t e d by d r i v i n g o f f C 0 2 f rom t h e c a r b a m a t e upon a p p l y i n g h e a t . 0 II R - N - C - O H > R 2 N H + C 0 2 [ 1 0 . 3 ] I C 2 H 4 - O H DEA C a r b a m a t e DEA 135 10 .4 REMOVAL OF THEED NaOH i s a l s o c a p a b l e o f r e m o v i n g THEED f r o m d e g r a d e d s o l u t i o n s . A l t h o u g h t h e m e c h a n i s m i s u n c l e a r , t h e o v e r a l l r e a c t i o n a p p e a r s t o be a s f o l l o w s : R R R R \ / \ / N - C 2 H a - N + O H ' ^ N - H + O H - C 2 H « - N [ 1 0 . 4 ] / \ / \ R H R H THEED DEA DEA NaOH was a d d e d t o a t y p i c a l d e g r a d e d DEA s o l u t i o n and t h e m i x t u r e was h e a t e d a t 80 C f o r a b o u t 2 m i n . The c h r o m a t o g r a m s o f t h i s s o l u t i o n b e f o r e a n d a f t e r NaOH t r e a t m e n t a r e shown i n F i g u r e 1 0 . 2 . As c a n be s e e n , THEED was removed c o m p l e t e l y and HEOD was removed a l m o s t c o m p l e t e l y . H o w e v e r , a new peak seems t o a p p e a r . T h i s new peak ha s a r e t e n t i o n t i m e s i m i l a r t o N - ( h y d r o x y e t h y l ) i m i d a z o l i d o n e ( " H E I " ) . 10 .5 P U R I F I C A T I O N OF INDUSTRIAL SAMPLE NaOH was a l s o a d d e d t o a d e g r a d e d DEA s a m p l e o b t a i n e d f rom a gas p r o c e s s i n g p l a n t and was h e a t e d a t 80 C f o r a b o u t 2 m i n . The c h r o m a t o g r a m s o f t h e DEA s a m p l e b e f o r e a n d a f t e r NaOH t r e a t m e n t a r e shown i n F i g u r e 1 0 . 3 . Once a g a i n , THEED was removed c o m p l e t e l y , HEOD was r e m o v e d p a r t i a l l y a n d a new peak a p p e a r e d . 136 a) B e f o r e NaOH t r e a t m e n t DEA -L New peak b) A f t e r NaOH t r e a t m e t F i g u r e 10.2 Ch r o m a t o g r a m s o f a p a r t i a l l y d e g r a d e d DEA sample o f r u n 3 b e f o r e and a f t e r NaOH t r e a t m e n t . 1 37 DEA HEM Yr—T- a) B e f o r e NaOH t r e a t m e n t DEA HEM New peak b) A f t e r NaOH t r e a t m e n t F i g u r e 10 .3 C h r o m a t o g r a m s o f a d e g r a d e d f rom a gas p r o c e s s i n g p l a n t b e f o r e and a f t e r NaOH t r e a t m e t . 1 38 Once a g a i n , THEED was removed c o m p l e t e l y , HEOD was removed p a r t i a l l y and a new peak a p p e a r e d . T h i s p a r t i a l r e moval of HEOD was somewhat s u r p r i s i n g and may have been due t o the p r e s e n c e of N- ( h y d r o x y e t h y l ) e t h y l e n e a m i n e ("HEM"), wh i c h was not p r e s e n t i n the l a b o r a t o r y sample. 10.6 NaOH TREATMENT OF A MIXTURE OF DEA, HEOD AND THEED Because of t h e i n a b i l i t y t o remove HEOD c o m p l e t e l y from t h e l a b o r a t o r y and e s p e c i a l l y from t h e i n d u s t r i a l sample, i t was d e c i d e d t o p r e p a r e a 20 mL m i x t u r e of 30 wt%, 12 wt% and 8 wt% of DEA, -HEOD and THEED, r e s p e c t i v e l y , i n t h e l a b o r a t o r y i n t h e ab s e n c e of o t h e r c o n t a m i n a n t s . 2 mL of 1 N NaOH was t h e n added t o t h e s o l u t i o n and t h e m i x t u r e was h e a t e d a t 80°C f o r 2 min. The a p p r o p r i a t e chromatograms a r e shown i n F i g u r e 10.4. T h i s t i m e , a l m o s t c o m p l e t e r e m o v a l o f HEOD was a c h i e v e d . THEED re m o v a l was c o m p l e t e and t h e new peak a p p e a r e d a g a i n . C o n s e q u e n t l y , t h e HEOD r e m o v a l e f f i c i e n c y by NaOH t r e a t m e n t a p p e a r s t o depend on the p r e s e n c e of o t h e r c o n t a m i n a n t s . 1 39 DEA HEOD i — r a) B e f o r e NaOH t r e a t m e n t DEA b) A f t e r NaOH t r e a t m e n t F i g u r e 10 .4 C h r o m a t o g r a m s o f l a b o r a t o r y made m i x t u r e o f 30 wt % D E A , 12 wt% HEOD and 8 wt% THEED b e f o r e a n d a f t e r NaOH t r e a t m e n t . 1 40 10 .7 SODA ASH TREATMENT Soda a s h ( N a 2 C 0 3 ) i s o c c a s i o n a l l y u s e d f o r t h e r e m o v a l o f d e g r a d a t i o n c o m p o u n d s , e s p e c i a l l y t h e h e a t s t a b l e s a l t s f r o m d e g r a d e d DEA s o l u t i o n s . In o r d e r t o a s s e s s t h e e f f e c t o f N a 2 C 0 3 a d d i t i o n upon t h e r e m o v a l o f m a j o r d e g r a d a t i o n c o m p o u n d s , N a 2 C 0 3 was a d d e d t o an i n d u s t r i a l DEA s o l u t i o n sample a n d t h e m i x t u r e was h e a t e d a t 80 C f o r a b o u t 2 m i n . The c h r o m a t o g r a m s o f t h e s a m p l e b e f o r e a n d a f t e r N a 2 C 0 3 t r e a t m e n t a r e shown i n F i g u r e 1 0 . 5 . As c a n be s e e n , none o f t h e m a j o r d e g r a d a t i o n compounds was r e m o v e d . On t h e c o n t r a r y , a n o t h e r peak a p p e a r s w h i c h ha s t h e same r e t e n t i o n t i m e a s t h e " n e w " peak m e n t i o n e d a b o v e . 141 HEM a) B e f o r e s o d a a s h t r e a t m e n t b) A f t e r soda a s h t r e a t m e n t F i g u r e 10 .5 C h r o m a t o g r a m s o f a d e g r a d e d DEA sample f rom a ga s p r o c e s s i n g p l a n t b e f o r e and a f t e r soda a s h t r e a t m e n t . 1 42 CHAPTER 11 CONCLUSION AND RECOMMENDATIONS 11.1 CONCLUSIONS; 1 . D e g r a d a t i o n o f DEA i n h e a t e x c h a n g e r s m a i n l y d e p e n d s on t e m p e r a t u r e , C 0 2 p a r t i a l p r e s s u r e a n d DEA c o n c e n t r a t i o n . 2 . A c c u m u l a t i o n o f DEA d e g r a d a t i o n c o m p o u n d s , i n c r e a s e s t h e s o l u t i o n v i s c o s i t y . 3 . DEA d e g r a d a t i o n r e s u l t s i n s e v e r e f o u l i n g o f p r o c e s s e q u i p m e n t . 4 . DEA d e g r a d a t i o n a l s o i n c r e a s e s t h e f o a m i n g t e n d e n c y o f t h e s o l u t i o n . 5 S k i n t e m p e r a t u r e a n d n o t t h e b u l k s o l u t i o n t e m p e r a t u r e l a r g e l y d e t e r m i n e s t h e DEA d e g r a d a t i o n r a t e . 6 . S o l u t i o n f l o w r a t e c a n be u s e d as an o p e r a t i n g v a r i a b l e i n m i n i m i s i n g s k i n t e m p e r a t u r e . H i g h e r s o l u t i o n f l o w r a t e c a n m i n i m i s e t h e r a t e o f d e g r a d a t i o n by d e c r e a s i n g t h e f i l m t h i c k n e s s o f t h e s o l u t i o n a d j a c e n t t o t h e m e t a l w a l l . 143 7. Kennard's s i m p l i f i e d k i n e t i c model was not a b l e t o p r e d i c t DEA d e g r a d a t i o n under v a r i a b l e C 0 2 p a r t i a l p r e s s u r e s . H i s model p r o v i d e s d i f f e r e n t r a t e c o n s t a n t s f o r t h r e e d i f f e r e n t c o n c e n t r a t i o n ranges. In o r d e r t o p r e d i c t the DEA d e g r a d a t i o n r a t e under v a r i a b l e C 0 2 p a r t i a l p r e s s u r e and DEA c o n c e n t r a t i o n s , Kennard's model was m o d i f i e d as f o l l o w s : ^ J ^ ^ HEOD DEA + C0 2 k 3 THEED >• BHEP + C0 2 The pseudo r a t e c o n s t a n t s k,,k 2 and k 3 can be c a l c u l a t e d as a f u n c t i o n of temperature by u s i n g the f o l l o w i n g e q u a t i o n s : l n ( k , ) = 11.924 - 6451/T(K) l n ( k 2 ) = 8.450 - 5580/T(K) l n ( k 3 ) = 39.813 - 15160/T(K) Us i n g the above model, i t was p o s s i b l e t o p r e d i c t the r a t e of DEA d e g r a d a t i o n f o r the temperature range of 60 t o 200 °C, the C0 2 p a r t i a l p r e s s u r e . r a n g e of 1379 t o 4137 kPa, and DEA s o l u t i o n c o n c e n t r a t i o n range of 20 t o 40 wt%. 1 4 4 8. HEOD, one o f t h e m a j o r DEA d e g r a d a t i o n p r o d u c t s was f o u n d t o be c o r r o s i v e t o w a r d s m i l d s t e e l . 9. HEOD, THEED and some o t h e r m i n o r d e g r a d a t i o n compounds c a n be c o n v e r t e d back t o DEA by a d d i n g NaOH a n d a p p l y i n g h e a t . 1 0 . The HEOD r e m o v a l e f f i c i e n c y by NaOH a p p a r e n t l y d e p e n d s on t h e p r e s e n c e o f o t h e r d e g r a d a t i o n c o m p o u n d s . 1 1 . I n d u s t r i a l l y u s e d a c t i v a t e d c a r b o n f i l t e r s a r e n o t a b l e t o remove any m a j o r DEA d e g r a d a t i o n p r o d u c t s . 12. N a 2 C 0 3 t r e a t m e n t i s n o t a b l e t o remove B H E P , HEOD or THEED f rom d e g r a d e d DEA s o l u t i o n s . 1 45 11.2 RECOMMENDATIONS : a) The e f f e c t o f t e m p e r a t u r e : T e m p e r a t u r e i s t h e most i m p o r t a n t o p e r a t i n g v a r i a b l e t o be c o n t r o l l e d i n o r d e r t o m i n i m i s e DEA d e g r a d a t i o n . E l e v a t e d t e m p e r a t u r e s , e s p e c i a l l y h i g h m e t a l s k i n t e m p e r a t u r e s and l o c a l h o t s p o t s , s h o u l d be a v o i d e d t h r o u g h o u t t h e p l a n t . In d e s i g n i n g h e a t e x c h a n g e r s f o r amine t r e a t i n g p l a n t s , c o n s i d e r a t i o n s h o u l d be g i v e n t o m e t a l s k i n t e m p e r a t u r e . T h i s c a n be done by s e l e c t i n g i n d i v i d u a l h e a t t r a n s f e r r e s i s t a n c e s s u c h t h a t h e a t t r a n s f e r r e q u i r e m e n t s a r e met w i t h o u t c r e a t i n g h i g h m e t a l s k i n t e m p e r a t u r e . M e t a l s k i n t e m p e r a t u r e s s h o u l d p r e f e r a b l y be l i m i t e d t o 1 2 0 ° C and be m o n i t o r e d c a r e f u l l y . A t l e a s t two t h e r m o c o u p l e s , one a t t h e i n l e t a n d t h e o t h e r a t t h e o u t l e t s h o u l d be a t t a c h e d t o t h e h e a t t r a n s f e r s u r f a c e f o r t h i s p u r p o s e . I f t h e m e t a l s k i n t e m p e r a t u r e i n c r e a s e s due t o any p r o c e s s u p s e t d u r i n g p l a n t o p e r a t i o n , i t s h o u l d be b r o u g h t u n d e r c o n t r o l e i t h e r by i n c r e a s i n g t h e s o l u t i o n f l o w r a t e o r by d e c r e a s i n g t h e t e m p e r a t u r e o f t h e h e a t i n g m e d i u m . H o w e v e r , i n c r e a s i n g t h e f l o w r a t e w o u l d p r o v i d e a s w i f t e r a n d b e t t e r t e m p e r a t u r e c o n t r o l t h a n l o w e r i n g t e m p e r a t u r e o f t h e h e a t i n g medium. .1 46 b) E f f e c t o f d i s s o l v e d C 0 2 : C 0 2 c a t a l y s e s DEA d e g r a d a t i o n r e a c t i o n s . In t h e a b s e n c e o f C 0 2 , DEA d e g r a d a t i o n i s n o t a p p r e c i a b l e . S i n c e , t h e h i g h e s t t e m p e r a t u r e i s e x p e r i e n c e d by DEA i n t h e r e g e n e r a t o r r e b o i l e r , a l l t h e d i s s o l v e d C 0 2 s h o u l d be s t r i p p e d o u t o f t h e s o l u t i o n i n t h e r e g e n e r a t o r t r a y s . The r e b o i l e r s h o u l d s e r v e o n l y t o p r o v i d e t h e n e c e s s a r y s t eam f o r r e g e n e r a t i o n , bu t n o t t o s t r i p d i s s o l v e d C 0 2 i n t h e r e b o i l e r . I f t h e DEA s o l u t i o n e n t e r i n g t h e r e b o i l e r c o n t a i n s v e r y l i t t l e d i s s o l v e d C 0 2 , t h e n d e g r a d a t i o n i n t h e r e b o i l e r w o u l d be m i n i m a l . In o r d e r t o see w h e t h e r t h e r e g e n e r a t o r i s s t r i p p i n g o u t a l m o s t a l l t h e d i s s o l v e d C 0 2 , t h e e f f i c i e n c y o f t h e s t i p p i n g o p e r a t i o n s h o u l d be c h e c k e d . T h i s c a n be done by a n a l y s i n g l e a n DEA s a m p l e s l e a v i n g t h e r e g e n e r a t o r a n d DEA s a m p l e s e n t e r i n g t h e r e b o i l e r f o r d i s s o l v e d C 0 2 . The C 0 2 c o n c e n t r a t i o n s i n b o t h s a m p l e s s h o u l d be t h e same. I f t h e C 0 2 c o n t e n t o f t h e DEA s o l u t i o n e n t e r i n g t h e r e b o i l e r i s f o u n d t o be h i g h e r t h a n t h a t o f t h e l e a n DEA s o l u t i o n , s t e p s s h o u l d be t a k e n t o i n c r e a s e t h e s t r i p p i n g e f f i c i e n c y o f t h e r e g e n e r a t o r . T h i s s h o u l d be d o n e by i n c r e a s i n g t h e r e f l u x r a t e , n o t by i n c r e a s i n g t h e t e m p e r a t u r e . 147 c ) C o r r o s i o n c o n t r o l : S o l u t i o n pH has a s t r o n g e f f e c t on c o r r o s i o n of m i l d s t e e l . T h e r e f o r e t h e pH o f t h e r i c h DEA s o l u t i o n l e a v i n g t h e C 0 2 a b s o r b e r s h o u l d be m o n i t o r e d , p r e f e r a b l y w i t h an o n - l i n e pH m e t e r . The s o l u t i o n pH s h o u l d n o t be a l l o w e d t o go b e l o w 9 . C o r r o s i v e d e g r a d a t i o n compounds s u c h as HEOD s h o u l d be removed f rom t h e s o l u t i o n and f o r m a t i o n o f o r g a n i c a c i d s s h o u l d be m i n i m i s e d by p r e v e n t i n g o x y g e n f rom c o m i n g i n c o n t a c t w i t h t h e DEA s o l u t i o n . d) S o l u t i o n P u r i f i c a t i o n : B o t h a c t i v a t e d c a r b o n f i l t e r a n d NaOH i n j e c t i o n may be e m p l o y e d a s means o f s o l u t i o n p u r i f i c a t i o n . The a c t i v a t e d c a r b o n f i l t e r removes s u s p e n d e d p a r t i c l e s . NaOH i n j e c t i o n s e r v e s two p u r p o s e s : i t removes HEOD and THEED t o some e x t e n t and i t a l s o h e l p s m a i n t a i n t h e s o l u t i o n pH a b o v e 9 . As a r e s u l t o f NaOH a d d i t i o n s o d i u m s a l t s w o u l d g r a d u a l l y b u i l d up i n s i d e t h e s y s t e m . A r e c l a i m e r m i g h t be u s e d t o s e p a r a t e t h e s e s a l t s f r o m t h e DEA s o l u t i o n i f t h e s a l t b u i l d up becomes e x c e s s i v e . DEA s o l u t i o n s s h o u l d be r o u t i n e l y a n a l y s e d f o r d e g r a d a t i o n p r o d u c t s a n d NaOH , s l i g h t l y a b o v e s t o i c h i o m e t r i c r e q u i r e m e n t f o r t h e r e m o v a l o f HEOD, THEED and o t h e r o r g a n i c a c i d s ( i f p r e s e n t ) , s h o u l d be a d d e d . 1 48 11 .3 RECOMMENDATIONS FOR FURTHER WORK: a) K i n e t i c M o d e l : The k i n e t i c m o d e l d e v e l o p e d i n t h i s t h e s i s n e e d s some i m p r o v e m e n t . The f o l l o w i n g i s recommended f o r t h i s p u r p o s e : C 0 2 c o n c e n t r a t i o n i n t h e DEA s o l u t i o n i s an i m p o r t a n t p a r a m e t e r i n t h e m o d e l . A t h e o r e t i c a l t h e r m o d y n a m i c m o d e l f o r t h e p r e d i c t i o n o f s o l u b i l i t y i n DEA s o l u t i o n n e e d s t o be d e v e l o p e d and i n c o r p o r a t e d w i t h t h e k i n e t i c m o d e l . K i n e t i c d a t a a t l o w e r C 0 2 p a r t i a l p r e s s u r e and t e m p e r a t u r e r a n g e o f 40 C t o 120 C s h o u l d be o b t a i n e d f rom b a t c h w i s e e x p e r i m e n t s . T h i s , c o m b i n e d w i t h C 0 2 s o l u b i l i t y d a t a , c a n t h e n be u s e d t o c a l c u l a t e t h e p s e u d o - r a t e c o n s t a n t s . P o t e n t i o d y n a m i c c o r r o s i o n s t u d i e s s h o u l d be c a r r i e d o u t i n o r d e r t o i d e n t i f y o t h e r c o r r o s i v e d e g r a d a t i o n compounds and t o s t u d y t h e c o r r o s i o n m e c h a n i s m s i n DEA s o l u t i o n . b) P u r i f i c a t i o n o f DEA s o l u t i o n : A l t h o u g h NaOH a d d i t i o n c a n a i d i n t h e r e g e n e r a t i o n o f DEA f rom some o f t h e d e g r a d a t i o n c o m p o u n d s , i t s e x c e s s i v e use m i g h t h a v e some a d v e r s e a f f e c t on t h e s t r i p p i n g e f f i c i e n c y o f t h e r e g e n e r a t o r . T h e r e f o r e , i t i s d e s i r e a b l e t o h a v e some i n f o r m a t i o n on t h e e f f e c t o f NaOH a d d i t i o n on v a p o r - l i q u i d e q u i l i b r i a o f D E A - C 0 2 s y s t e m u n d e r t h e r e g e n e r a t o r c o n d i t i o n s . 149 NOMENCLATURE A H e a t t r a n s f e r s u r f a c e a r e a (m 2 ) BHEP N , N - B i s ( h y d r o x y e t h y l ) p i p e r a z i n e BHEU N , N - B i s ( h y d r o x y e t h y l ) u r e a C DEA c o n c e n t r a t i o n (wt%) Cp S p e c i f i c h e a t o f DEA s o l u t i o n ( J / g ° C ) Cpo S p e c i f i c o f h e a t i n g f l u i d ( J / g ° C ) d S p e c i f i c g r a v i t y Db S t i r r e r b l a d e d i a m e t e r (m) Dc T u r n i n g d i a m e t e r o f t h e h e a t t r a n s f e r t u b e (m) D i I n s i d e d i a m e t e r o f t h e h e a t t r a n s f e r t u b e (m) Dim L o g mean d i a m e t e r ( D o - D i ) / I n [ D o / D i ] Do O u t s i d e d i a m e t e r o f t h e h e a t t r a n s f e r t u b e (m) Dt D i a m e t e r o f t h e t a n k c o n t a i n i n g h e a t t r a n s f e r f l u i d (m) DEA D i e t h a n o l a m i n e E c o r r F r e e c o r r o s i o n p o t e n t i a l ( V o l t s ) f F r i c t i o n f a c t o r , e q u a t i o n 7 . 2 2 h i I n s i d e h e a t t r a n s f e r c o e f f i c i e n t ( J / m 2 s ° C ) HEED N - ( h y d r o x y e t h y l ) e t h y l e n e d i a m i n e HEI N - ( h y d r o x y e t h y l ) i m i d a z o l i d o n e HEM N - ( h y d r o x y e t h y l ) e t h y l e n i m i n e HEOD 3 - ( h y d r o x y e t h y l ) - 2 - o x a z o l i d o n e ho O u t s i d e h e a t t r a n s f e r c o e f f i c i e n t ( J / m 2 s ° C ) Ia A n o d i c c u r r e n t (Amps) Ic C a t h o d i c c u r r e n t (Amps) I c o r r C o r r o s i o n c u r r e n t (Amps) 1 50 k T h e r m a l c o n d u c t i v i t y o f a q u e o u s DEA s o l u t i o n ( W / m ° C ) K i , K 2 , k 3 R a t e c o n s t a n t s u s e d i n t h e k i n e t i c m o d e l f o r t h e d e g r a d a t i o n o f DEA ( L / m o l e s h r ) km T h e r m a l c o n d u c t i v i t y o f t h e t u b e m e t a l ( W / m ° C ) L L e n g t h o f t h e h e a t t r a n s f e r t u b e (m) MEA M o n o e t h a n o l a m i n e N N o . o f p a s s e s t h r o u g h t h e h e a t t r a n s f e r t u b e OZD O x a z o l i d o n e P P r e s s u r e (kPa) Q H e a t d u t y ( k J / s ) R - C 2 H a - O H RPS R e v o l u t i o n s p e r s e c o n d r t R e s i d e n c e t i m e f o r a s i n g l e p a s s ( h r ) RT T o t a l r e s i d e n c e t i m e ( h r ) t T i m e ( h r ) T B u l k s o l u t i o n t e m p e r a t u r e ( ° C ) TEA T r i e t h a n o l a m i n e THEED N , N , N - T r i s ( h y d r o x y e t h y l ) e t h y l e n e d i a m i n e T i H e a t t r a n s f e r t u b e i n l e t t e m p e r a t u r e ( ° C ) Tk T h e r m a l c o n d u c t i v i t y o f h e a t i n g o i l ( W / m ° C ) To H e a t t r a n s f e r t u b e o u t l e t t e m p e r a t u r e ( ° C ) Th H e a t t r a n s f e r f l u i d t e m p e r a t u r e ( ° C ) t s p T i m e r e q u i r e d t o p a s s t o t a l DEA i n v e n t o r y t h r o u g h t h e h e a t t r a n s f e r t u b e i n a s i n g l e p a s s ( h r ) 151 Twi I n s i d e w a l l t e m p e r a t u r e of t h e h e a t t r a n s f e r t u b e (°C) Two O u t s i d e w a l l t e m p e r a t u r e of t h e he a t t r a n s f e r t u b e (°C) U i O v e r a l l h e a t t r a n s f e r c o e f f i c i e n t b a s e d on i n s i d e s u r f a c e of t h e s t r a i g h t h e a t t r a n s f e r tube ( J / m 2 s ° C ) Uc O v e r a l l h e a t t r a n s f e r c o e f f i c i e n t f o r t h e c o i l e d h e a t t r a n s f e r tube ( J / m 2 s ° C ) w Mass f l o w r a t e ( k g / s ) x L e n g t h of a s m a l l segment of t h e h e a t t r a n s f e r tube xm Heat t r a n s f e r tube w a l l t h i c k n e s s (m) DIMENSIONLESS GROUPS Nu N u s s e l t Number, hD/k Pr P r a n d t l . 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F . , " E f f e c t o f H y d r a u l i c F l o w on Amine P l a n t C o r r o s i o n , " P r o c . of Gas C o n d i t i o n i n g C o n f e r e n c e , U n i v e r s i t y o f O k l a h o m a , N o r m a n , O k l a h o m a , M a r c h 5 - 7 , 1984 . 6 3 . M a d d o x , R . N . , a n d M a i n s , G . J . , " D a t a and D e s i g n f o r Amine t r e a t i n g , " P r o c . o f Gas P r o c e s s o r s A s s o c i a t i o n A n n u a l M e e t i n g , New O r l e a n s , 1984. 6 4 . C h r i t t e n d e n , B . D . , " C h e m i c a l R e a c t i o n F o u l i n g , " C o n t i n u i n g E d u c a t i o n C o u r s e N o t e s on The F o u l i n g o f H e a t E x c h a n g e r s , I n s t . o f C h e m i c a l E n g i n e e r s a n d The C h e m i c a l E n g i n e e r i n g D e p t . o f The U n i v o f B i r m i n g h a m , M a r c h 1 9 - 2 0 , 1981 . 6 5 . W a t k i n s o n , A . P . , a n d E p s t e i n , N . , P r o c . 4 t h I n t . 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H . , " C o r r o s i o n a n d C o r r o s i o n C o n t r o l , " 3 r d P r i n t i n g , J o h n W i l e y and S o n s , I n c . , New Y o r k , 1965 . 7 2 . K e r n , D . Q . , " P r o c e s s H e a t T r a n s f e r , " M c G r a w - H i l l Book C o . , New Y o r k , 1950. 7 3 . O l d s h u e , J . Y . , a n d G r e t t o n , A . T . , " H e l i c a l C o i l H e a t T r a n s f e r i n M i x i n g V e s s e l s , " Chem. E n g . P r o g . , 50 ( 1 2 ) , 615 , D e c e m b e r , 1 9 5 4 . 7 4 . McAdams, W . H . , " H e a t T r a n s m i s s i o n , " T h i r d E d i t i o n , McGraw H i l l Book C o . , New Y o r k , 1954. 7 5 . "Gas T r e a t i n g C h e m i c a l s " , U n i o n C a r b i d e E t h y l e n e O x i d e D e r i v a t i v e D i v i s i o n , D a n b u r y , C T . , 1980 . 7 6 . " L u b e R e p o r t - T . I . P . 3 . 2 1 . 4 . " , S h e l l C a n a d a . 7 7 . G . P . S . A . E n g i n e e r i n g D a t a B o o k , 9 t h E d i t i o n , Gas P r o c e s s o r s S u p p l i e r s A s s o c i a t i o n , T u l s a , O K . , 1976. 161 7 8 . S t a n d a r d s o f T u b u l a r E x c h a n g e r M a n u f a c t u r e r s A s s o c i a t i o n (TEMA) 6 t h E d i t i o n , T E M A , New Y o r k , 1978. 7 9 . U . S . B u r e a u o f S t a n d a r d s M i s c e l l a n e o u s P u b l i c a t i o n s 9 7 . 8 0 . S m i t h e l l s , C . J . , " M e t a l s R e f e r e n c e B o o k " , V o l . I l l , 4 t h E d i t i o n , B u t t e r w o r t h s , L o n d o n , 1967 . 8 1 . D e n n , M . N . , " P r o c e s s F l u i d M e c h a n i c s " , P r e n t i c e - H a l l , I n c . , E n g l e w o o d C l i f f s , New J e r s e y , 1980. 8 2 . L e e , I . J . , O t t o , F . D . a n d M a t h e r , A . E . , " S o l u b i l i t y o f C a r b o n D i o x i d e i n A q u e o u s D i e t h a n o l a m i n e S o l u t i o n s a t H i g h P r e s s u r e s , " J . o f C h e m i c a l E n g i n e e r i n g D a t a , j_7 ( 4 ) , 4 6 5 , 1972. 1 62 APPENDIX - A L i s t i n g o f t h e c o m p u t e r p r o g r a m f o r t h e d e t e r m i n a t i o n o f t e m p e r a t u r e p r o f i l e , p r e s s u r e d r o p , f i l m t h i c k n e s s and t h e DEA d e g r a d a t i o n r a t e i n t h e h e a t e x c h a n g e r t u b e . c c c c c c c c c c c c c c c c c c c c c c c c c PROGRAM TO P R E D I C T T E M P E R A T U R E P R O F I L E , P R E S S U R E D R O P , F I L M T H I C K N E S S , D E A , H E O D . T H E E D AND B H E P C O N C E N T R A T I O N S IN T H E H E A T T R A N S F E R T U B E OF T H E DEA D E G R A D A T I O N E X P T . T H = T E M P E R A T U R E OF T H E H E A T I N G MEDIUM ( C ) T S = T E M P E R A T U R E OF T H E A U T O C L A V E ( C ) T W I N = I N S I O E WALL T E M P E R A T U R E OF T H E C O I L ( C ) T C L = T O T A L C O I L L E N G T H (M) T L V = T O T A L L I O U I O I N V E N T O R Y ( C U . M ) T S P S = T I M E FOR A S I N G L E P A S S THRU H E X . ( S E C ) D E A L ' O N T Y . OF D E G R A D E D DEA IN 1 P A S S D E A N P = D E A C O N C . A F T E R NP P A S S E S H E O N P = H E O D C O N C . T H E N P = T H E E D C O N C . " T O T H R = T O T A L T I M E ( H R ) N P T = T O T A L N O . OF P A S S E S N P H R = N O . OF P A S S E S PER HOUR X = C O I L L E N G T H (M) D E A L T = L O S S OF D E A AT T H E ENO OF E A C H I N C R E M E N T H E O D T = HEOD C O N C . T H E E D T = T H E E D C O N C . " D E A C T = D E A C O N C . F F T = F R I C T I O N F A C T O R T O L E R A N C E K = C O L E B R O O K C O N S T . 0 E L P = P R E S S U R E DROP ( P A . ) R E A L N P R C . N P R O , N P T , N P H R , NPNHR D A T A D O T , D B , R P H / 0 . 7 1 1 2 , 0 . 1 0 1 G D A T A V O L S / O . 0 0 0 0 1 1 0 0 / D A T A 0 1 , 0 0 . D C , XW / 0 . 0 0 2 0 3 2 T L V / 2 0 0 . . 4 X I N C , F F T / 1 10 D A T A T O T H R . T C L D A T A T I N C , T E P S C 0 2 = 3 . 2 0 0 O E A O = 3 0 . 0 0 D E A O T = D E A O D E A L T = D E A O H E O D T = 0 . 0 T H E E D T = 0 . 0 B H E P T = 0 . 0 SUMOP = 0 . 0 R E A L K , K 1 , K 2 , K = 0 . 0 0 0 0 1 2 P I = 4 . * A T A N ( 1 . ) I N I T I A L WALL T E M P E R A T U R E T S = 6 0 . 0 T = 6 0 . 0 T1 = TS T H = 2 5 0 . 0 TWOUT = T H TWIN = TH - TW • TWIN X = 0 . 0 0 DX = 0 . 1 WRITE ( 6 . 1 0 ) FORMAT ( 1X , 1 ' ' R E ' , 8 . / . O . 0 0 3 1 7 5 . 8 , . 0 0 2 5 / . . . 0 0 1 , . 0 . 4 0 6 4 . 0 . 0 0 0 7 1 5 / 0 . 0 0 1 / K 3 , L N K 1 . L N K 2 , L N K 3 1 0 . 0 ' L E N G T H ( m ) ' , 2X . 6X , ' DEA C O N C . ' ' W A L L T ( C ) ' , 2X 6X , ' D E L X * E 5 ' , ' S O L . T ( C ) ' . 5 X , / / ) 1 63 c C C A L L S U B R O U T I N E THERM TO C A L C U L A T E P R O P E R T I E S OF S H E L L T H E R M I A C C A L L T H E R M ( T H , C P O . T K O , R H O O . V I S O ) C C C A L L S U B R O U T I N E DPROP TO C A L C U L A T E DEA P R O P E R T I E S C C A L L D P R O P ( T S . D E A O , R H O S . V I S S . T K S , C P S ) C A L L D P R O P ( T , D E A O , R H O , V I S , T K , C P ) GO TO 3 0 2 0 C A L L D P R O P ( T , D E A O . R H O , V I S , T K , C P ) 3 0 C A L L D P R O P ( T W I N , D E A O . RHOW, V I S W , TKW, CPW) C A L L T H E R M ( T W O , C P O , T K O , V I S O W ) C C C A L L S U B R O T I N E S S P R O P TO C A L C U L A T E T H . C O N D . OF M E T A L WALL C C A L L S S P R O P ( T W , T K M ) C C C A L C U L A T E P R O C E S S S I D E H E A T T R A N S F E R C O E F F I C I E N T C V O L T = V O L S * ( R H O S / R H O ) WT = V O L S * RHOS V E L T = ( 4 . * W T ) / ( R H 0 * P I * D I * * 2 . ) G = ( 4 . * W T ) / ( P I * D I * * 2 . ) R E C = ( D I * G ) / V I S NPRC = ( C P * V I S ) / TK HI = 0 . 0 2 3 * ( T K / D I ) * ( R E C * * 0 . 8 ) * ( N P R C * * 0 . 3 3 3 3 3 3 3 ) * ( V I S / V I S W ) 1 * * 0 . 1 4 D E L X = 4 3 . 5 * DI * * 1 .8 / ( ( ( 4 . * W T ) / ( P I * V I S ) ) * * 0 . 8 * ( N P R C * * 0 . 1 3 3 3 3 3 3 ) ) D E L X = D E L X * 1 0 0 0 0 0 . C C C A L C U L A T E T H E O U T S I D E H E A T T R A N S F E R C O E E F F I C I E N T C REO = DB * * 2 . * RPH * RHOO / V I S O NPRO = C P O * V I S O / TKO V I S E X = 0 . 1 * ( V I S 0 * 8 . 6 2 1 E - 0 5 ) * * ( - 0 . 2 1 ) HO = 0 . 1 7 * ( T K O / D O ) * ( R E O * * 0 . S 6 6 7 ) * ( N P R O * * 0 . 3 3 3 3 ) * ( D B / O O T ) 1 * * 0 . 1 * ( D O / D O T ) * * . 5 * ( V I S O / V I S O ) * * V I S E X C C C A L C U L A T E L O G MEAN 0 1 A M E T E R C DL = (DO - D I ) / ( A L O G ( D O / D I ) ) C C C A L C U L A T E T H E O V E R A L L H E A T T R A N S F E R C O E F F I C I E N T C U » 1. / ( ( 1 . / H I ) + ( ( 1 . / H O ) * ( D I / D O ) ) + ( ( X W / T K M ) * ( O I / D L ) ) ) UC = U * ( 1 + 3 . 5 * ( D I / D C ) ) C C C A L C U L A T E T H E B U L K T E M P E R A T U R E OF DEA S O L N . C T = T H - ( T H - T I ) * E X P ( ( - U C * P I * D I * 0 X ) / ( W T " C P ) ) C C A L C U L A T E I N S I D E WALL T E M P E R A T U R E AND C H E C K WITH A S S U M E D V A L U E C TWOUT = T H - ( ( T H - T ) * ( 1 . / H O ) *.( D I / D O ) * U C ) TWINC = TWOUT - ( ( T H - T ) * ( X W / T K M ) * ( D O / D L ) * U C ) I F ( ( T W I N C - T ) . L T . 0 . 0 0 0 0 0 0 1 ) GO TO 5 0 I F ( A B S ( T W I N C - T W I N ) . L T . T E P S ) GO TO 6 0 I F ( A B S ( T W I N C - T W I N ) . G T . T E P S ) GO TO 4 0 4 0 TWIN = TWINC TW = ( T W I N + TWOUT) / 2 . GO TO 2 0 5 0 TWIN = T 6 0 THR = X I N C / V E L T THR = THR / 3 6 0 0 . C C P R E S S U R E DROP C A L C U L A T I O N C C I N I N I A L E S T I M A T E OF F R I C T I O N F A C T O R C F I = 0 . 0 4 * R E C * * ( - 0 . 1 6 ) C C C A L C U L A T I O N OF F R I C T I O N F A C T O R BY C O L E B R O O K FORMULA C 7 0 F = ( 1 . / ( - 4 , 0 * A L 0 G 1 0 ( ( K / D I ) + ( 4 . 6 7 / ( R E C * F I * * 0 . 5 ) ) ) + 2 . 2 8 ) ) * * 2 . I F ( A B S ( F - F I ) . L T . - F F T ) GO TO 9 0 I F ( A B S ( F - F I ) . G T . F F T ) GO TO 8 0 8 0 F I = F GO TO 7 0 9 0 D E L P = ( 2 . * R H 0 * V E L T * * 2 . * F * X I N C ) / DI D E L P = D E L P * ( 1 . + 3 . 5 * ( D I / D C ) ) D E L P = D E L P / 1 0 0 0 . SUMDP = SUMDP + D E L P C C A L L S U B R O U T I N E R A T E TO C A L C U L A T E C O N C . P R O F I L E FOR 1 P A S S C C A L L R A T E ( T , T H R . D E A O T . C 0 2 , D E A X , H E O D X , T H E E D X , T H E E D T . B H E P X ) D E A L T = D E A L T - D E A X H E O D T = H E O D T + HEODX T H E E D T = T H E E D X B H E P T = B H E P X D E A C T = D E A O T - D E A L T W R I T E ( 6 , 1 0 0 ) X , T W I N . T , R E C , D E A X , D E L X 100 F O R M A T ( 1 X . F 5 . 2 . 4 X , F 8 . 3 , 4 X , F 8 . 3 . 2 X , F 1 0 . 2 . 3 X . F 8 . 4 , 3 X . 1 F 1 0 . 4 , / ) X = X + 0 . 1 0 0 I F (X . G E . T C L ) GO TO 120 I F (X . L T . T C L ) GO TO 110 1 1 0 D E A O T = D E A X T1 = T GO TO 2 0 1 65 c C * C A L C U L A T E T I M E FOR T O T A L L I Q U I D V O L . T O P A S S * C 120 T S P S = T L V / V O L S W R I T E ( 6 , 1 3 0 ) T S P S 130 FORMAT ( 1 X , ' T S P S = ' . F 1 2 . S , / / ) T O T S = TOTHR * 3 6 0 0 . P S I = SUMDP / 6 . 8 9 4 7 5 7 W R I T E ( 6 , 1 4 0 ) S U M D P , P S I 140 FORMAT ( 1 X , ' T O T A L P R E S . D R O P , k P a = ' , F 1 2 . 4 , 2 X , ' P S I = ' . F 1 2 . 4 , / / ) N P T = T O T S / T S P S W R I T E ( 6 . 1 5 0 ) V O L S , T H -150 FORMAT ( 2 X , ' V O L . FLOW R A T E =' , F 1 0 . 7 , 4 X , ' H O T F L U I D T E M P . = ' , 1 F 8 . 2 . / / ) W R I T E ( 6 . 1 6 0 ) D E A O , C 0 2 160 FORMAT ( 1'X, ' I N I T I A L DEA C O N C . = ' , F 6 . 2 . 4 X . ' [ C O ] L = ' . F 6 . 2 , / / 1 ) C C C A L C U L A T E O E A . H E O O & T H E E D C O N C . FOR NP P A S S E S C W R I T E ( 6 , 1 7 0 ) 170 FORMAT ( ' 1 ' , 2 X , ' T I M E ( h r ) ' , 4 X . ' R T ( s e c ) ' , 4 X , ' D E A C O N C . ' , 4 X , 1 ' H E O O C O N C , 4 X , ' T H E E D C O N C . ' . 4 X , ' B H E P C O N C . / / ) HR = 0 . NPHR = 3 6 0 0 . / T S P S 180 NPNHR = NPHR * HR R T S = THR * NPNHR * 3 6 0 0 . D E A L = D E A O - D E A X D E A N P = D E A O - ( O E A O - O E A X ) * NPNHR HEONP = H E O D T * NPNHR T H E N P = T H E E D T * NPNHR B H E N P = B H E P T * NPNHR W R I T E ( 6 . 1 9 0 ) H R , R T S . D E A N P . H E O N P , T H E N P . BHENP 190 FORMAT ( 1 X . F 1 0 . 4 . 1X , F 1 0 . 4 , 2 X . F 1 0 . 4 . 3 X , F 1 0 . 4 . 4 X . F 1 0 . 4 . 4 X . 1 F 1 0 . 4 , / / ) HR = HR + 2 4 . IF (HR . G E . T O T H R ) GO TO 2 0 0 I F (HR . L T . T O T H R ) GO TO 180 2 0 0 S T O P END C C S U B R O U T I N E DPROP TO C A L C U L A T E DEA P R O P E R T I E S C S U B R O U T I N E D P R O P ( T , D E A O , R H O , V I S , T K , C P ) RHO = 9 9 8 . 0 - 0 . 0 0 4 0 3 * T * * 2 + D E A O * ( 3 . 4 - 0 . 0 0 0 2 5 * T * * 1 . 4 5 ) - 1 D E A 0 * * 1 . 1 9 V I S 1 = ( 0 . 0 6 7 6 6 6 * D E A 0 - 6 . 8 2 0 8 6 7 ) / ( 1 . - 0 . 0 0 4 3 9 5 * D E A O ) V I S 2 = T * ( ( 0 . 0 1 4 0 6 6 + 0 . O O O O 1 0 5 * D E A O ) / ( 1 . - 0 . 0 0 4 9 6 5 * D E A O ) ) V I S = E X P ( V I S 1 - V I S 2 ) TK = ( 0 . 4 6 7 5 - 0 . 0 0 6 2 * D E A O * * 0 . 8 5 3 8 ) * T * * 0 . 0 8 C P * 4 . 1 7 6 + 0 . 0 0 0 4 6 * T - 0 . 0 1 8 3 7 * D E A O + 0 . 0 0 0 0 5 4 * D E A O * T CP = CP * 1 0 0 0 . R E T U R N END 1 6 6 K 2 L N K 3 ( 1 0 0 0 . / ( T + 2 7 3 . ) ) ( 1 0 0 0 . / ( T + 2 7 3 . ) ) K 2 ) * C 0 2 * T H R ) K 2 ) K 2 ) * C 0 2 ) 0 3 = E = S U B R O U T I N E R A T E ( T , T H R , D E A O . C 0 2 , D E A X , H E O D X , T H E E D X , T H E E O T . B H E P X ) R E A L K 1 . K 2 . K 3 , L N K 1 , L N K 2 , L N K 3 D A T A A 1 , A2 / 1 1 . 9 2 4 , - 6 . 4 5 1 / D A T A A 3 , A 4 / 8 . 4 5 , - 5 . 5 8 / D A T A A 5 . A 6 / 2 0 . 6 4 0 . - 6 . 5 2 / LNK1 = A1 + A 2 * ( 1 0 0 0 . / ( T + 2 7 3 . ) ) K1 = E X P ( L N K 1 ) L N K 2 = A3 +• A4 E X P ( L N K 2 ) A 5 + A6 K 3 = E X P ( L N K 3 ) A = E X P ( - ( K 1 B = K 1 / (K1 + C = K 2 * C 0 2 / ( K 3 - (K1 D = K 2 / (K1 + K 2 ) D 1 = K 2 * K 3 * C 0 2 * D E A 0 / ( K 3 - ( K 1 + K 2 ) * C 0 2 ) D2= 1 . / ( ( K 1 + K 2 ) * C 0 2 ) 1 . / K 3 K 3 / ( K 3 - (K1 + K 2 ) * C 0 2 ) F = ( ( K 1 + K 2 ) * C 0 2 ) / ( K 3 - (K1 + K 2 ) * C 0 2 ) G = E X P ( - K 3 * T H R ) C 2 = T H E E D T * G C 3 = ( T H E E D T / K 3 ) * ( 1 . - G ) C A L C U L A T E S D E A C O N C E N T R A T I O N D E A X = D E A O * A H E O D X = D E A O * B * ( 4 . - A ) T H E E D X = D E A O * C * (A - G ) + C 2 B H E P X = D 1 * ( ( - A « D 2 ) + ( D 3 * G ) ) - C 3 + ( D E A O * D ) + B H E P T R E T U R N END S U B R O U T I N E S S P R O P C A L C U L A T E S T H . C O N D . OF M E T A L S U B R O U T I N E S S P R O P ( T W , T K M ) TKM = 1 5 . 6 0 + 0 . 0 0 6 2 8 9 * TW R E T U R N END S U B R O U T I N E T H E R M C A L C U L A T E S T H E P R O P E R T I E S OF S H E L L T H E R M I A S U B R O U T I N E T H E R M ( T H , C P O , T K O , R H O O , V I S O ) C P O = ( 0 . 3 8 8 + 0 . 0 0 0 4 5 * ( T H * ( 9 . / 5 . ) + 3 2 . ) ) / 0 . 9 3 5 2 C P O = C P O * 4 184 TKO = " ( 0 . 8 2 1 - 0 . 0 0 0 2 4 4 * ( T H * ( 9 . / 5 . ) + 3 2 . ) ) / 0 . 8 7 4 2 T K O = T K O * 0 . 1 4 4 1 3 1 4 RHOO = 0 . 8 8 6 6 6 2 - 0 . 0 0 0 7 5 0 * T H RHOO = RHOO * 1 0 0 0 . V I SO = - ( 2 . 2 1 7 7 + 0 . 0 1 8 8 * T H ) V I SO = E X P ( V I S O ) R E T U R N END P U B L I C A T I O N S C h a k m a , A . a n d M e i s e n , A . , " P r e d i c t i n g D e n s i t y , V i s c o s i t y , T h e r m a l C o n d u c t i v i t y a n d S p e c i f i c H e a t o f A q u e o u s DEA S o l u t i o n s " , H y d r o c a r b o n P r o c e s s i n g , i n p r e s s . , - C h a k m a , A . a n d M e i s e n , A . , " D e g r a d a t i o n o f A q u e o u s DEA S o l u t i o n s i n H e a t T r a n s f e r T u b e s " , t o be p r e s e n t e d a t t h e 1984 A n n u a l M e e t i n g o f A . I . C h . E . , San F r a n c i s c o , N o v . , 1984 . C h a k m a , A . a n d M e i s e n , A . , " C o r r o s i v i t y o f DEA S o l u t i o n s a n d t h e i r D e g r a d a t i o n P r o d u c t s " , t o be p r e s e n t e d a t t h e 3 4 t h C a n a d i a n C h e m i c a l E n g i n e e r i n g C o n f e r e n c e , Quebec C i t y , C a n a d a , O c t . 1984 .

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