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Chapter 19

Effect of Demulsifiers on Interfacial Properties Governing Crude Oil Demulsification 1

Surajit Mukherjee and Arnold P. Kushnick Exxon Chemical Company (ECTD), Houston, TX 77029

Effectiveness of a crude o i l demulsifier is correlated with the lowering of shear viscosity and dynamic tension gradient of the oil-water interface. Using the pulsed drop technique, the interfacial dilational modulii with different demulsifiers have been measured. The interfacial tension relaxation occurs faster with an effective demulsifier. Electron spin resonance with labeled demulsifiers indicate that the demulsifiers form 'reverse micelle' like clusters in bulk oil. The slow unclustering of the demulsifier at the interface appears to be the rate determining step in the tension relaxation process. Crude o i l i s almost always produced as p e r s i s t e n t w a t e r - i n - o i l emulsions which must be r e s o l v e d i n t o two s e p a r a t e phases b e f o r e t h e crude o i l can be accepted f o r t r a n s p o r t a t i o n . The water d r o p l e t s a r e sterically s t a b i l i z e d by t h e a s p h a l t e n e and r e s i n f r a c t i o n s o f t h e crude o i l . These a r e condensed a r o m a t i c r i n g s c o n t a i n i n g s a t u r a t e d carbon c h a i n s and n a p t h e n i c r i n g s as s u b s t i t u e n t s , a l o n g w i t h a d i s t r i b u t i o n o f heteroatoms (S, 0 and N) and m e t a l s ( N i , V ) . I t has been suggested (1) t h a t a s t a b i l i z i n g f i l m p r o t e c t i n g t h e water drops from c o a l e s c e n c e i s c r e a t e d by hydrogen bonding o f t h e N-, 0-, and S- c o n t a i n i n g groups a t t h e water d r o p - - o i l i n t e r f a c e . A l t h o u g h , many o t h e r methods (e.g. e l e c t r o s t a t i c s e p a r a t i o n , h e a t i n g , c e n t r i f u g a t i o n , e t c . ) may be used t o s e p a r a t e t h e o i l and water phases, chemical d e m u l s i f i c a t i o n i s t h e most i n e x p e n s i v e and w i d e l y used t e c h n i q u e t o r e s o l v e crude o i l e m u l s i o n s . The d e m u l s i fiers are oil-soluble water-dispersible non-ionic polymeric 1

Current address: Lever Research, Inc., Edgewater, NJ 07020 0097-6156/89/0396-0364$06.00/0 o 1989 American Chemical Society


19.

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365

(molecular weight 2,000-100,000) s u r f a c t a n t s . They a r e added t o t h e crude o i l i n v e r y small (10-400 ppm) amounts. One o f t h e most commonly used d e m u l s i f i e r i s t h e o x y a l k y l a t e d a l k y l phenol f o r m a l ehyde r e s i n , t h e a l k y l group may be b u t y l , amyl o r nonyl group. The interfacial activity i s c o n t r o l l e d by t h e amounts o f e t h y l e n e and propylene oxides attached t o the r e s i n . The major problem i n d e m u l s i f y i n g crude o i l e m u l s i o n s i s t h e extreme s e n s i t i v i t y t o d e m u l s i f i e r c o m p o s i t i o n . There have been attempts ( 2 , 3) t o c o r r e l a t e d e m u l s i f i e r e f f e c t i v e n e s s w i t h some o f the physical p r o p e r t i e s g o v e r n i n g emulsion s t a b i l i t y . However, o u r understanding i n t h i s area i s s t i l l limited. Consequently, d e m u l s i f i e r s e l e c t i o n has been t r a d i t i o n a l l y based on a ' t r i a l and e r r o r * method w i t h hundreds o f c h e m i c a l s i n t h e f i e l d . Our goal i s t o develop a property-performance r e l a t i o n s h i p f o r different types of demulsifiers. The important interfacial properties governing w a t e r - i n - o i l emulsion s t a b i l i t y a r e shear viscosity, dynamic t e n s i o n and d i l a t i o n a l elasticity. We have studied the r e l a t i v e importance o f these parameters i n demulsification. In t h i s paper, some o f t h e r e s u l t s o f o u r s t u d y a r e p r e s e n t e d . In p a r t i c u l a r , we have found t h a t t o be e f f e c t i v e , a d e m u l s i f i e r must lower t h e dynamic i n t e r f a c i a l t e n s i o n g r a d i e n t and its a b i l i t y t o do so depends on t h e r a t e o f u n c l u s t e r i n g o f t h e e t h y l e n e o x i d e groups a t t h e o i l - w a t e r i n t e r f a c e . E x p e r i m e n t a l Techniques The o i l - w a t e r dynamic i n t e r f a c i a l tensions a r e measured by t h e pulsed drop (4) t e c h n i q u e . The e x p e r i m e n t a l equipment c o n s i s t s o f a syringe pump t o pump o i l , w i t h the demulsifier dissolved i n i t , through a c a p i l l a r y t i p i n a t h e r m o s t a t e d g l a s s c e l l c o n t a i n i n g b r i n e o r w a t e r . The i n t e r f a c i a l t e n s i o n i s c a l c u l a t e d by measuring the p r e s s u r e i n s i d e a small o i l drop formed a t t h e t i p o f t h e capillary. In t h i s t e c h n i q u e , t h e s y r i n g e pump i s stopped a t t h e maximum bubble p r e s s u r e and t h e o i l - w a t e r i n t e r f a c e i s a l l o w e d t o expand r a p i d l y t i l l t h e o i l comes o u t t o form a small drop a t t h e c a p i l l a r y t i p . Because o f t h e sudden e x p a n s i o n , t h e i n t e r f a c e i s initially a t a n o n e q u i l i b r i u m s t a t e . As i t approaches e q u i l i b r i u m , the pressure, A P ( t ) , i n s i d e t h e drop decays. The excess p r e s s u r e i s continuously measured by a s e n s i t i v e p r e s s u r e t r a n s d u c e r . The dynamic t e n s i o n a t time t , i s c a l c u l a t e d from t h e 'Young-Laplace' equation

AP(t)

=

2

° (*) d

(D

R

where i s the radius o f t h e drop. The i n t e r f a c i a l d i l a t i o n a l modulas i s then c a l c u l a t e d by a F o u r i e r T r a n s f o r m a t i o n o f t h e t r a n s i e n t i n t e r f a c i a l t e n s i o n d a t a (see l a t e r ) . The interfacial shear v i s c o s i t i e s a r e measured by t h e deep channel v i s c o u s t r a c t i o n surface v i s c o m e t e r (5) a t t h e I l l i n o i s I n s t i t u t e o f Technology. The o i l - w a t e r e q u i l i b r i u m t e n s i o n s a r e measured by e i t h e r t h e s p i n n i n g drop o r t h e du Nouy r i n g (6) method.

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366

E l e c t r o n Spin Resonances are measured at 9.5 GHz a t room temperature. Demulsifiers are l a b e l e d by r e a c t i n g the t e r m i n a l OH groups with the s p i n - l a b e l 3-chloroformyl 2,2,5,5 tetramethyl p y r r o l i n e 1-oxyl (Figure 5 a ) . T h i s i s done by the Schotten-Baumann reaction ( 7 ) . The c a r b o x y l i c form o f the s p i n - l a b e l ( o b t a i n e d from Eastman Kodak Company) i s d i s s o l v e d i n a b e n z e n e / p y r i d i n e m i x t u r e and i s reacted, i n s i t u , w i t h t h i o n y l c h l o r i d e ( a l s o from Eastman Kodak Company). A f t e r 15 m i n u t e s , vacuum-dried d e m u l s i f i e r i s added t o the m i x t u r e . The s o l u t i o n i s mixed and l e f t o v e r n i g h t . A l l the reactions are c a r r i e d under a n i t r o g e n b l a n k e t . Excess benzene i s then added and the i n s o l u b l e p a r t i s e l i m i n a t e d . The tagged d e m u l s i fier i s s e p a r a t e d from the f r e e l a b e l e i t h e r by p r e c i p i t a t i n g i t w i t h methanol o r by s i z e e x c l u s i o n chromatography. R e s u l t s and

Discussion

I n t e r f a c i a l Shear V i s c o s i t y The d e m u l s i f i c a t i o n p r o c e s s i n v o l v e s c o a l e s c e n c e o f s m a l l e r water droplets i n t o l a r g e r ones. During t h i s p r o c e s s , the o i l i n the liquid f i l m between the d r o p l e t s d r a i n s o u t , t h e r e b y t h i n n i n g the f i l m and f i n a l l y rupturing i t . The f a s t e r the f i l m t h i n s , the greater i s the d e m u l s i f i c a t i o n e f f e c t i v e n e s s . The l i q u i d d r a i n a g e rate depends, among o t h e r f a c t o r s , on the interfacial shear v i s c o s i t y . A high (>1 surface p o i s e ) i n t e r f a c i a l shear v i s c o s i t y s i g n i f i c a n t l y slows down the l i q u i d d r a i n a g e . C o n s e q u e n t l y , the e m u l s i o n i s s t a b l e . But the r e v e r s e i s not t r u e . Emulsions have been found t o be s t a b l e (8) even w i t h a low i n t e r f a c i a l v i s c o s i t y . Our r e s u l t s suggest t h a t the l o w e r i n g o f i n t e r f a c i a l shear v i s c o s i t y , a l t h o u g h n e c e s s a r y , i s not a s u f f i c i e n t c r i t e r i o n f o r e f f e c t i v e d e m u l s i f i c a t i o n . In a d d i t i o n , a d e m u l s i f i e r must a l s o r a p i d l y dampen any f l u c t u a t i o n s i n the o i l - w a t e r i n t e r f a c i a l t e n s i o n . The d e m u l s i f i c a t i o n data with four d i f f e r e n t demulsifiers f o r a crude oil-water system (Table I) support t h i s conclusion. S t r u c t u r a l l y , the d e m u l s i f i e r PI and RO are o f moderate (MW - 2,0005,000) m o l e c u l a r w e i g h t s , whereas PI and P2 are l a r g e (MW >50,000) three dimensional s t r u c t u r e s . The r e s u l t s show t h a t a l t h o u g h a l l the d e m u l s i f i e r s l o w e r the shear viscosity, they d i f f e r w i d e l y in their demulsification e f f e c t i v e n e s s , as measured by the r e s i d u a l bottom sediment and water content (Figure 1) (BS and W%) o f the d e h y d r a t e d o i l . For example, the d e m u l s i f i e r 0P1, a l t h o u g h i t l o w e r s both the equilibrium interfacial tension (Figure 2) and the shear v i s c o s i t y ( T a b l e I ) , nevertheless i s i n e f f e c t i v e . T h i s i s because i t t a k e s a much l o n g e r t i m e f o r the o i l - w a t e r i n t e r f a c i a l t e n s i o n t o reach e q u i l i b r i u m w i t h 0P1 than w i t h PI o r P2 (see l a t e r ) . In g e n e r a l , t h e r e i s no c o r r e l a t i o n between the t e n s i o n and the shear v i s c o s i t y o f an o i l - w a t e r i n t e r f a c e . However, f o r systems containing d e m u l s i f i e r s , a low i n t e r f a c i a l t e n s i o n (IFT) o f t e n l e a d s t o a l o w e r i n g o f the shear v i s c o s i t y . D e m u l s i f i e r s , i n g e n e r a l , are large disordered m o l e c u l e s and when t h e y are p r e s e n t at the i n t e r f a c e t h e y c r e a t e a m o b i l e , low v i s c o s i t y zone. However, a low IFT i s not a n e c e s s a r y c o n d i t i o n f o r a low v i s c o s i t y i n t e r f a c e . A l a r g e d e m u l s i f i e r such as P I , a l t h o u g h not v e r y s u r f a c e a c t i v e , can s t i l l l o w e r the shear v i s c o s i t y t o a v e r y low v a l u e ( T a b l e I ) .

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367


60

10

30

50

DEMULSIFIER CONCN.(PPM) PI + P2 •

•

OP1

F i g u r e 1: Residual water content o f a b r i n e - i n - c r u d e o i l e m u l s i o n w i t h t h e d e m u l s i f i e r s P I , P2 and 0P1. 30

z

2

-|

1

1

0

1

20 •

1

1

1

40 P1

F i g u r e 2: Interfacial P I , P2 and 0P1.

DEMULSIFIER CONCN.(PPM) + P2 O

r

M 0P1

t e n s i o n o f b r i n e v s t h e crude o i l w i t h

10

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T a b l e I . Comparison o f E f f e c t i v e n e s s and I n t e r f a c i a l P r o p e r t i e s o f D i f f e r e n t D e m u l s i f i e r s i n a Crude O i l - W a t e r System Concn.


Demulsifier NONE RO PI P2 0P1 RO: PI: P2: 0P1:

BS&W

(ppm)

(vo!%)

200 60 60 40

50 16 0.2 0.6 50

Oxyalkylated Oxyalkylated Cross-linked Oxyalkylated

Dynamic I n t e r f a c i a l

IFT

28 9 21 20 4

nonyl phenol r e s i n c r o s s - l i n k e d polypropylene polypropylene g l y c o l t r i m e t h y l o l propane

Tension

Shear V i s c o s i t y

(Dvnes/cm)

(Surface

Poise)

2.0 X 1Q" 8 X 10"* 1 X lO"? 1 X lO'l I X 10

1

_ z

glycol

Gradient

When t h e i n t e r f a c i a l f i l m between two d r o p l e t s t h i n s , t h e l i q u i d i n the f i l m f l o w s o u t towards t h e p l a t a e u b o r d e r r e g i o n . Such a f l o w removes some o f t h e s u r f a c t a n t s from t h e i n t e r f a c e t h u s c r e a t i n g an uneven c o n c e n t r a t i o n o f t h e s u r f a c t a n t a l o n g t h e i n t e r f a c e ( 9 , 1 0 ) . Furthermore, t h e i n t e r f a c i a l f i l m o f t e n t h i n s unevenly t h u s c r e a t i n g l o c a l l y t h i n and t h i c k r e g i o n s ( 1 1 ) . A l o c a l t h i n n i n g i m p l i e s an increase i n the i n t e r f a c i a l a r e a and hence a d e c r e a s e i n t h e surfactant concentration. On t h e o t h e r hand, t h e s u r f a c t a n t concentration increases i n the t h i c k region. This nonuniform surfactant concentration at the i n t e r f a c e leads t o l o c a l v a r i a t i o n s i n t h e i n t e r f a c i a l t e n s i o n s which produces a f l o w o f l i q u i d from t h e high t o t h e low t e n s i o n regions. This i s known as t h e 'Gibbs-Marangoni' e f f e c t . T h i s interfacial t e n s i o n induced flow opposes t h e outward d r a i n a g e i n the f i l m . I t also helps t o 'heal' the f i l m t o i t s o r i g i n a l uniform t h i c k n e s s . The n e t r e s u l t i s a reduced r a t e o f f i l m t h i n n i n g and c o n s e q u e n t l y a more s t a b l e emulsion. In o r d e r t o be e f f e c t i v e , a d e m u l s i f i e r has t o reduce t h e 'Gibbs-Marangoni* r e s i s t i v e l i q u i d flow. I t does so by m i g r a t i n g from t h e i n t e r i o r t o t h e i n t e r f a c e , e q u a l i z i n g t h e i n t e r f a c i a l s u r f a c t a n t c o n c e n t r a t i o n and b r i n g i n g t h e i n t e r f a c i a l t e n s i o n o f t h e f i l m t o i t s e q u i l i b r i u m value. As p o i n t e d out by Ross and Haak (12), i f this process i s f a s t e r than t h e s u r f a c t a n t m i g r a t i o n induced f l o w along t h e i n t e r f a c e , t h e l o c a l t h i n s p o t s i n t h e f i l m are n o t 'healed' and t h e l i q u i d d r a i n a g e i n the f i l m continues unabated. C o n s e q u e n t l y , t h e drop c o a l e s c e n c e r a t e i s enhanced and the e m u l s i o n i s r a p i d l y d e s t a b i l i z e d . The importance of rapid relaxation i n demulsification e f f e c t i v e n e s s can be seen w i t h t h e crude o i l - w a t e r dynamic t e n s i o n r e s u l t s w i t h P2 ( F i g u r e 3) and 0P1 ( F i g u r e 4 ) . As can be seen, i t takes o n l y about 60 seconds f o r t h e i n t e r f a c e t o reach i t s e q u i l i b r i u m s t a t e w i t h t h e e f f e c t i v e d e m u l s i f i e r P2, whereas w i t h l e s s e f f e c t i v e d e m u l s i f i e r 0 P 1 , t h e e q u i l i b r i u m i s reached o n l y a f t e r 800 seconds.

369


19. MUKHERJEEANDKUSHNICK 60


50 -

40

-

30

-

20

10 -

0 _|

,

1

0

1

20

1

1

40

1

1

1

60

1

1

80

1

100

1

120

TIME (SECONDS)

F i g u r e 3: Dynamic i n t e r f a c i a l t e n s i o n o f t h e crude o i l - b r i n e i n t e r f a c e as a f u n c t i o n o f t i m e , w i t h 40 ppm P2.

n 0

1

1

1

0.2

0.4

1

1

0.6 (Thousanda) Time (SECONDS)

1

1

0.8

1

r 1

F i g u r e 4: Dynamic i n t e r f a c i a l t e n s i o n o f t h e crude o i l - b r i n e i n t e r f a c e as a f u n c t i o n o f t i m e , w i t h 40 ppm 0P1.


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The t i m e i t t a k e s f o r an o i l - w a t e r i n t e r f a c e t o reach e q u i l i b r i u m depends s t r o n g l y on the e t h y l e n e o x i d e c o n t e n t o f the d e m u l s i f i e r m o l e c u l e . The i n t e r f a c i a l tension decay p r o c e s s can often be an o r d e r o f magnitude l o n g e r than what i s observed i n systems where the s u r f a c t a n t d i f f u s i o n from b u l k t o i n t e r f a c e i s the rate determining step. Demulsifiers form ' r e v e r s e - m i c e l l e * l i k e structures i n the b u l k o i l w i t h the e t h y l e n e o x i d e groups c l u s t e r i n g together t o minimize t h e i r i n t e r a c t i o n s with t h e o i l phase. We believe, the unclustering o f the e t h y l e n e o x i d e groups as w e l l as rearrangement o f the d e m u l s i f i e r m o l e c u l e s a t the i n t e r f a c e are the r a t e d e t e r m i n i n g s t e p s i n the t e n s i o n r e l a x a t i o n p r o c e s s . S i m i l a r interfacial tension b e h a v i o r has been observed (13) w i t h l a r g e o i l - s o l u b l e w a t e r - i n s o l u b l e s u r f a c t a n t such as C h o l e s t e r o l . E l e c t r o n Spin

Resonance

We have s t u d i e d d e m u l s i f i e r a s s o c i a t i o n by t h e e l e c t r o n spin resonance (ESR) t e c h n i q u e . The s p i n l a b e l i s c o v a l e n t l y a t t a c h e d (Figure 5a) t o t h e d e m u l s i f i e r . N o r m a l l y , the ESR spectrum o f a f r e e l y tumbling n i t r o x y l r a d i c a l c o n s i s t s o f three sharp peaks (Figure 5b). However, the spectrum f o r a tagged e t h o x y l a t e d nonyl phenol r e s i n ( F i g u r e 6a o r 6b) shows o n l y a s i n g l e broad peak. The r e s u l t s may be e x p l a i n e d i n the f o l l o w i n g manner. The s p i n l a b e l s a r e attached next t o the e t h y l e n e o x i d e groups. C l u s t e r i n g o f t h e e t h y l e n e o x i d e groups b r i n g s the n i t r o x i d e r a d i c a l s i n c l o s e proximity with other. As the o r b i t a l s c o n t a i n i n g u n p a i r e d e l e c t r o n from d i f f e r e n t l a b e l s o v e r l a p , t h e r e i s a s p i n exchange which l e a d s t o a s i n g l e resonance peak. S i m i l a r exchange b r o a d e n i n g has been observed (14) i n l i p i d f i l m s i n which s p i n probes are e x c l u d e d t o form a g g r e g a t e s . With s t r o n g e r i n t e r a c t i o n , the s i n g l e resonance peak narrows. The e t h y l e n e o x i d e c l u s t e r i n g depends on the p o l a r i t y o f the medium. The p e a k - t o - t r o u g h s e p a r a t i o n gives an i n d i c a t i o n o f the clustering strength. A smaller separation implies stronger c l u s t e r i n g . We have found t h a t i n t o l u e n e ( F i g u r e 6a) the s e p a r a t i o n is 15 gauss whereas i n i s o p r o p y l a l c o h o l ( F i g u r e 6b) i t i n c r e a s e s t o 25 gauss. T h i s suggests a weaker c l u s t e r i n g o f the e t h y l e n e o x i d e groups w i t h i n c r e a s i n g p o l a r i t y o f the medium. I n t e r f a c i a l D i l a t i o n Modulus The complex i n t e r f a c i a l d i l a t i o n a l modulus ( * ) i s a key fundamental property g o v e r n i n g foam and emulsion s t a b i l i t y . I t i s d e f i n e d as the interfacial tension increment (da) per u n i t f r a c t i o n a l i n t e r f a c i a l a r e a change (dA/A) i . e . , e

c

*(f)- -(fH -(f)-j^j e

e

- ATA

2

A where e ' ( f ) and e " ( f ) are the r e a l and the i m a g i n a r y components a t a f r e q u e n c y f . We have used a procedure ( 4 ) , where the complete f r e q u e n c y spectrum i s o b t a i n e d by a F o u r i e r T r a n s f o r m o f the dynamic interfacial tension data. The r e l e v a n t relationships are:


19.

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371

FREE PROBE

F i g u r e 5: a) Chemical s t r u c t u r e o f a nonyl phenol r e s i n and the s p i n l a b e l 3 - c h l o r o f o r m y l 2,2,5,5 t e t r a m e t h y l p y r r o l i n e 1 - o x y l ; b) ESR o f a f r e e l a b e l i n t o l u e n e .

F i g u r e 6: ESR o f the l a b e l e d nonyl phenol r e s i n i n a) t o l u e n e and i n b) i s o p r o p y l a l c o h o l .


n -2.2

1

1

1

-2

1

1

-1.8 •

ELASTIC

1

1

-1.6 Log Frequency (Hz) +

1

-1.4

1

1

-1.2

1

r -1

VISCOUS

Figure 7: Elastic ( i n - p h a s e ) and v i s c o u s (out-of-phase) components o f crude o i l - b r i n e interfacial d i l a t i o n a l modulus w i t h 40 ppm P2.

Q

•

ELASTIC

Log Frequency (Hz) O

VISCOUS

Figure 8: Elastic ( i n - p h a s e ) and v i s c o u s (out-of-phase) components o f crude o i l - b r i n e interfacial d i l a t i o n a l modulus w i t h 40 ppm 0P1.


19. MUKHERJEEANDKUSHNICK

e

*(f)

=

Aa(t)e

0 o/

-

°° A l n A ( t ) e


2nf

e

27rift -

373

dt

27rift

(3) dt

e»(f) - AlnA

Im FT (Aa)

(4)

2*f AlnA

Real FT (Aa)

(5)

"(f) -

1

The real component, e ( f ) , i s t h e d i l a t i o n a l e l a s t i c modulus ( F i g u r e 7 ) . I t i s t h e i n t e r f a c i a l t e n s i o n g r a d i e n t t h a t i s i n phase with t h e a r e a change. A t a l o w f r e q u e n c y , t h e i n t e r f a c i a l f i l m behaves as a s o l u b l e monolayer. I n t e r f a c i a l c o n c e n t r a t i o n and t h e tension a r e then governed by t h e b u l k c o n c e n t r a t i o n and so remain i n v a r i a n t t o a change i n a r e a . On t h e o t h e r hand, a t a v e r y high frequency t h e i n t e r f a c i a l f i l m behave as a c o m p l e t e l y i n s o l u b l e monolayer and t h e v a r i a t i o n i n i n t e r f a c i a l t e n s i o n r e s u l t i n g from a l o c a l change i n a r e a i s v i r t u a l l y instantaneous. The i m a g i n a r y component, e"(f)> i s the d i l a t i o n a l viscosity modulus. T h i s a r i s e s when t h e d e m u l s i f i e r i n t h e monolayer i s sufficiently soluble i n t h e bulk l i q u i d , so t h a t t h e t e n s i o n gradient created by an a r e a c o m p r e s s i o n / e x p a n s i o n can be s h o r t circuited by a t r a n s f e r o f d e m u l s i f i e r s t o and from t h e s u r f a c e . I t i s 90° o u t o f phase w i t h t h e a r e a change. The shape o f t h e c u r v e s f o r t h e d i l a t i o n a l modulus ( F i g u r e s 7 and 8) s u g g e s t s a s i n g l e r e l a x a t i o n mechanism, p r o b a b l y t h e unfolding o f t h e d e m u l s i f i e r m o l e c u l e s a t t h e i n t e r f a c e . The f r e q u e n c y peak i n t h e " ( f ) p l o t i s a measure o f t h e c h a r a c t e r i s t i c r e l a x a t i o n t i m e . A s h o r t e r r e l a x a t i o n t i m e , by i n d u c i n g f a s t e r f i l m drainage, increases demulsification e f f i c i e n c y . The dynamic response d a t a f o r PI and P2 ( F i g u r e 7) a r e s i m i l a r . They a r e , however, q u i t e d i f f e r e n t from t h a t o f 0P1 ( F i g u r e 8 ) . The c h a r a c t e r i s t i c r e l a x a t i o n times f o r PI and P2 a r e 50 and 69 seconds r e s p e c t i v e l y , whereas w i t h 0P1 i t i s 158 seconds. T h i s i n d i c a t e s that with PI and P2, t h e o i l - w a t e r i n t e r f a c e w i l l have much s h o r t e r response time l e a d i n g t o an improved d e m u l s i f i c a t i o n e f f e c t i v e n e s s . e

Summary For e f f e c t i v e d e m u l s i f i c a t i o n o f a w a t e r - i n - o i l e m u l s i o n , both shear viscosity as w e l l as dynamic t e n s i o n gradient o f the water-oil i n t e r f a c e have t o be lowered. The i n t e r f a c i a l d i l a t i o n a l modulus data i n d i c a t e that the i n t e r f a c i a l r e l a x a t i o n process occurs f a s t e r with an e f f e c t i v e d e m u l s i f i e r . The e l e c t r o n s p i n resonance w i t h l a b e l e d d e m u l s i f i e r s suggests t h a t d e m u l s i f i e r s form c l u s t e r s i n t h e bulk o i l . The u n c l u s t e r i n g and rearrangement o f t h e d e m u l s i f i e r a t the i n t e r f a c e may a f f e c t t h e i n t e r f a c i a l r e l a x a t i o n p r o c e s s .

OIL-FIELD CHEMISTRY

374


Acknowledqment The a u t h o r s w i s h t o thank t h e Exxon Chemical Company f o r p e r m i s s i o n t o p u b l i s h t h i s paper. We thank Dr. Darsh T. Wasan and Mr. Chandrashekhar S h e t t y a t I I T , Chicago f o r measuring some o f t h e interfacial shear v i s c o s i t i e s . A special thanks t o Ms. Layce Gebhard o f Exxon Research and E n g i n e e r i n g f o r measuring t h e ESR spectra. F i n a l l y , a special thanks t o Ms. Rose Mary Rangel o f Energy Chemicals (Exxon Chemical Company) f o r t h e p r e p a r a t i o n o f t h e manuscript.

Literature Cited 1.

Oren, J . J.; Mackay, D. M. Fuel. 1977, 56, 382.

2.

Burger, P. D.; Hsu, C.; Arendele, J . P. SPE 16285, SPE International Symposium on Oilfield Chemistry. San Antonio, Texas. February 4-6, 1987; p 457.

3.

Blair, C. M. Chem. Ind. 1960, 538.

4.

Clint, J . H . ; Neustadter, E. L . ; Jones, T. J. Proc. 3rd. Eur. Symp. on Enhanced Oil Recovery, Bournemouth, U.K., 1981, p 135.

5.

Wasan, D. T.; Gupta, L . ; Vora, M. K. AICHE J. 1971, 17(6), 1287.

6.

Adamson, A. W. Physical Chemistry of Surfaces, 3rd Ed.; J. Wiley and Sons.: New York, 1976; Chapter 1.

7.

Tormala, 481.

8.

Neustadter, E. L . ; Whittingham, K. P.; Graham, D. E. In Surface Phenomena in Enhanced Oil Recovery; Shah, D. O., Ed.; Plenum Press: New York, 1981; p 307.

9.

Zapryanov, Z . ; Malhotra, A. K.; Adrengi, N . ; Wasan, D. T. Int. J. Multiphase Flow. 1983, 9, 105.

P.;

Lattila,

H . ; Lindberg,

J . J . Polymer. 1973, 14,

10. Ivanov, I. B.; Jain, R. K. In Dynamics and Instability of Fluid Interfaces; Sorensen, T. S. Ed.; Lecture Notes in Physics Series No. 105; Springer Verlag: Berlin, W. Germany, 1979; p 120. 11. Jain, R. K . ; Ivanov, Ibid; p 140.

I.

B.; Maldarelli, C.; Ruckenstein, E.

12. Ross, S.; Haak, R. M. J. Phys. Chem. 1969, 73, 2828. 13. Van Hunsel, J.; 1986, 114, 432.

Bleys, G.; Joos, P. J. Colloid Interface S c i .

14. Smith, I. C. P.; Butler, K. W. In Spin Labeling: Theory and Practice, Berliner, L. J., Ed.; Academic Press: New York, 1976; Vol. 1, p 423. Received December 21, 1988

Oil-Field Chemistry - American Chemical Society

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