Performance Relationships in Surfactants - ACS Publications

6 Relationship of Solubilization Rate to Micellar Properties Anionic and Nonionic Surfactants Downloaded via TUFTS UNIV on August 3, 2018 at 21:04:17 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Y. C. C H I U , Y . C. H A N , and H . M. C H E N G Department of Chemistry, Chung Yuan Christian University, Chung-Li, Taiwan 320, Republic of China

This paper presents a new finding that the o i l solubilization rate is a function of surfactant aggregate size. Light scattering and conductance measurements were used in the experiments. Alcohol ethoxylates and SDS were used as surfactants. The aggregate size was changed by changing the surfactant structure or by adding chemicals. The solubilization rate shows a maximum at a certain aggregate size for a given surfactant and a given o i l . Thus, we have found a measurable and controllable factor (size) in the process of oil solubilization. A theory was proposed to relate solubilization rate with micellar properties and surfactant structure. By using this theory, we can explain the performance of petroleum sulfonate in enhanced oil recovery and improve current formulation in achieving ultra-low interfacial tension. We can also explain the nonionic detergent performance as a function of surfactant structure. This paper presents a new finding that the oil solubilization rate is a function of the surfactant aggregate size. This idea originated from Chiu s observation on solubilization phenomena in tertiary oil recovery. During experiments with petroleum sulfonates in surfactant flooding, it was found that the surfactant solutions in the optimum electrolyte region, contaning large surfactant aggregates, are effective in oil recovery (1). These solutions give fast solubilization of o i l and exhibit ultralow interfacial tension when they are in contact with oil (1). A theory was proposed that the large surfactant aggregates are important in obtaining rapid solubilization and ultralow interfacial tension (1). In order to test this theory, medium molecular weight alcohols were used to replace electrolyte in increasing surfactant aggregate size. The resulting solutions also gave good oil recovery (2_) . This theory has been T

0097-6156/84/0253-0089$08.00/0 © 1984 American Chemical Society

Rosen; Structure/Performance Relationships in Surfactants ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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S T R U C T U R E / P E R F O R M A N C E R E L A T I O N S H I P S IN S U R F A C T A N T S

used t o e x p l a i n t h e d e t e r g e n t performance o f a l c o h o l e t h o x y l a t e s with respect to surfactant structure ( 3 ) . A l t h o u g h t h e proposed t h e o r y has been used e f f e c t i v e l y i n s e v e r a l p r a c t i c a l a p p l i c a t i o n s , no e x p e r i m e n t a l p r o o f h a s b e e n given that the o i l s o l u b i l i z a t i o n rate i s a function of surfactant aggregate s i z e . I n v i e w o f t h e i m p o r t a n c e o f s o l u b i l i z a t i o n and t h e e x i s t e n c e o f p r a c t i c a l methods o f m e a s u r i n g and c o n t r o l l i n g s u r f a c t a n t a g g r e g a t e s i z e , we d e c i d e d t o c o r r e l a t e t h e s o l u b i l i z a t i o n r a t e w i t h m i c e l l a r p r o p e r t i e s f o r some a n i o n i c and n o n i o n i c surfactants. A l t h o u g h s o l u b i l i z a t i o n (4) h a s b e e n a s u b j e c t o f many i n v e s t i g a t i o n s , most o f t h e s t u d i e s w e r e made o n t h e f i n a l e q u i l i b r i u m solubilization. O n l y a few s t u d i e s c o n c e r n a b o u t t h e k i n e t i c s and mechanism. I n r e c e n t p u b l i c a t i o n s , C a r r o l (_5) measured s o l u b i l i z a t i o n r a t e o f n o n p o l a r o i l s by n o n i o n i c s u r f a c t a n t s o l u t i o n s u s i n g a m i c r o s c o p i c o b s e r v a t i o n o f t h e change o f o i l d r o p l e t a d h e r i n g on a f i b e r . Chan e t a l ( 6 , 7 ) s t u d i e d t h e k i n e t i c s and mechanism o f s o l u b i l i z a t i o n i n d e t e r g e n t s o l u t i o n s b y r a d i o t r a c e r technique. T h e s e methods a r e e i t h e r t e d i o u s o r r e q u i r i n g s a f e t y precaution. For l a r g e scale laboratory operation using simple e q u i p m e n t s , we h a v e d e v e l o p e d a l i g h t s c a t t e r i n g t e c h n i q u e t o m e a s u r e t h e s o l u b i l i z a t i o n r a t e and p a r t i c l e s i z e . Experimental L i g h t s c a t t e r i n g t e c h n i q u e was u s e d i n d e t e r m i n i n g t h e o i l s o l u b i l i z a t i o n r a t e . Debye's e q u a t i o n (8) was u s e d i n t h e i n t e r p r e t a tion. The b a s i c p r i n c i p l e i n v o l v e s t h e measurement o f t h e s u r f a c t a n t aggregate s i z e during the s o l u b i l i z a t i o n . A s t h e o i l goes i n t o t h e s u r f a c t a n t m i c e l l e , t h e i n c r e a s e d s i z e w i l l be r e f l e c t e d by t h e t u r b i d i t y o f t h e s o l u t i o n . The i n s t r u m e n t u s e d i n t h e t u r b i d i t y measurement was H a t c h M o d e l 2100 A T u r b i d i m e t e r . A H o t e c h S h a k e r B a t h , M o d e l 901 ( H o t e c h I n s t r u m e n t s C o r p . ) was u s e d i n m i x i n g t h e o i l and s u r f a c t a n t s o l u t i o n . The n o n i o n i c s u r f a c t a n t s , N e w c o l 1 1 0 2 , 1103 and 1105 w e r e p r o d u c e d b y S i n o - J a p a n C h e m i c a l Co., L t d . The a c t i v e i n g r e d i e n t i s dodecanol ethoxylate. Sodium d o d e c y l s u l f a t e (SDS, No. L. 5750, Sigma C h e m i c a l Co. 9 5 % a c t i v e , c o n t a i n i n g 6 5 % C - ^ J 27% C-^4 and 6% C-^) was u s e d a s t h e a n i o n i c s u r f a c t a n t . Oleic A c i d ( E x t r a p u r e r e a g e n t , K a n t o C h e m i c a l Co., T o k y o , J a p a n ) , T r i o l e i n ( g l y c e r o l t r i o l e a t e ( C H C O O ) 3 C 3 H 5 , T e c h n i c a l , BDH C h e m i c a l s , E n g l a n d ) and n-decane ( E . M e r c k , G.C., 95%) were u s e d as o i l . Sodium c h l o r i d e ( E . M e r c k , p u r i t y 100 ± 0.05%) was u s e d as e l e c t r o l y t e . The e x p e r i m e n t was done by a d d i n g a g i v e n amount o f o i l t o 14.0 g o f 0.05% n o n i o n i c s u r f a c t a n t s o l u t i o n . The o i l was f i r s t added t o t h e s u r f a c t a n t s o l u t i o n and d i s p e r s e d i n t o t i n y d r o p l e t s by hand and was t h e n m i x e d w i t h t h e s u r f a c t a n t s o l u t i o n b y t h e H o t e c h S h a k e r a t 120 c y c l e s / m i n f o r 20 m i n u t e s . The t u r b i d i t y o f t h e s o l u t i o n was m e a s u r e d . The s o l u t i o n was s h a k e n and t u r b i d i t y 1 7

3 3


C H I U ET A L .

6.

91

Solubilization Rate and Micellar Properties

was measured r e p e a t e d l y u n t i l t h e t u r b i d i t y r e a c h e d a c o n s t a n t value. F o r a n i o n i c s u r f a c t a n t e x p e r i m e n t s , 15.0 g o f 0.5% s u r f a c t a n t s o l u t i o n was u s e d and t h e s h a k i n g t i m e was 5 m i n u t e s . Some e x p e r i m e n t s c o n c e r n i n g t h e s o l u b i l i z a t i o n o f t r i o l e i n i n SDS s o l u t i o n s w e r e done b y a d d i n g t r i o l e i n d r o p w i s e t o t h e s u r f a c t a n t s o l u t i o n . 15.0 g o f 0.5% SDS s o l u t i o n was u s e d . One d r o p o f t r i o l e i n (0.006 ± 0.001 g) was added t o t h e s u r f a c t a n t s o l u t i o n . The o i l was d i s p e r s e d , s h a k e n and t u r b i d i t y measured a s i t was m e n t i o n e d above. When t u r b i d i t y r e a c h e d a c o n s t a n t v a l u e , a n o t h e r d r o p o f t r i o l e i n was added and t h e p r o c e s s r e p e a t e d u n t i l t h e t u r b i d i t y v a l u e d i d n o t change w i t h t h e a d d i t i o n o f t r i o l e i n . I t should be mentioned here t h a t t h e n o n i o n i c s u r f a c t a n t s o l u t i o n s w e r e u s e d w i t h i n 1-10 d a y s a f t e r t h e p r e p a r a t i o n . The a n i o n i c s u r f a c t a n t s o l u t i o n s w e r e u s e d a f t e r a g i n g f o r two d a y s . A l l e x p e r i m e n t s were done a t room t e m p e r a t u r e , 25 ± 1 °C. Result

and D i s c u s s i o n

A Proposed Theory. I n e a r l i e r p u b l i c a t i o n s ( 1 - 3 ) , a t h e o r y was proposed t o c o r r e l a t e s o l u b i l i z a t i o n r a t e , i n t e r f a c i a l t e n s i o n and s i z e o f t h e s u r f a c t a n t a g g r e g a t e : ( 1 ) t h e i n t e r f a c i a l t e n s i o n l o w e r i n g between t h e o i l - s u r f a c t a n t s o l u t i o n i n t e r f a c e i s a f u n c t i o n o f t h e r a t e o f s o l u b i l i z a t i o n o f o i l , and (2) t h e r a t e o f s o l u b i l i z a t i o n (AS/At) i s a f u n c t i o n o f t h e e f f e c t i v e volume f o r solubilization: AS/At = k η V . err

(1)

c

Where

k η V

eff

constant. number o f a g g r e g a t e s i n u n i t v o l u m e o f s u r f a c t a n t solution. e f f e c t i v e volume f o r s o l u b i l i z a t i o n by an a g g r e g a t e , f ( a c c e s s i b l e volume o f t h e h y d r o c a r b o n c o r e , chemical nature of the surfactant molecule,chemical nature of the o i l ) .

The e f f e c t i v e v o l u m e f o r s o l u b i l i z a t i o n may o r may n o t be p r o p o r t i o n a l t o t h e g e o m e t r i c a l s i z e o f t h e a g g r e g a t e . I t depends on t h e p a c k i n g o f t h e m o l e c u l e s i n t h e a g g r e g a t e and t h e m u t u a l c o m p a t i b i l i t y o f t h e s u r f a c t a n t and o i l m o l e c u l e s . I n most c a s e s , V f ξ i s proportional to the s i z e of them i c e l l e (or aggregate). When t h e a g g r e g a t e s i z e i s t o o l a r g e and t h e p a c k i n g o f monomer becomes t o o t i g h t , V f £ may d e c r e a s e w i t h t h e a g g r e g a t e s i z e . e

e

I n t e r p r e t a t i o n o f L i g h t S c a t t e r i n g . We u s e d Debye's e q u a t i o n ( 8 ) f o r m i c e l l a r s o l u t i o n as a b a s i s f o r t h e l i g h t s c a t t e r i n g measurement:

%

Z

( %r)

M (C-C ) 0


(2)

92


Where

τ μ μ C C M Ν λ

0

Q

= = = = = = = =

Turbidity. r e f r a c t i v e index of the s o l u t i o n . r e f r a c t i v e index of the solvent. concentration (g/ml). c r i t i c a l m i c e l l a r c o n c e n t r a t i o n (CMC). aggregate weight. A v o g a d r o ' s number. wave l e n g t h o f t h e l i g h t . 2

When (dy/dC) ( C - C ) becomes c o n s t a n t , τ w o u l d be p r o p o r t i o n a l t o M. F o r n o n i o n i c s u r f a c t a n t , we u s e d N e w c o l 1 1 0 2 , 1103 and 1105. These s u r f a c t a n t s c o n t a i n d o d e c a n o l e t h o x y l a t e . The l a s t d i g i t i n t h e N e w c o l number r e p r e s e n t s t h e e t h y l e n e o x i d e (EO) number. The CMC v a l u e s f o r p u r e d o d e c a n o l e t h o x y l a t e (3) w i t h EO number f r o m 3 t o 5 a r e i n t h e c o n c e n t r a t i o n r a n g e o f 0.001-0.003%. C v a l u e i n o u r e x p e r i m e n t i s 0.05%. T h e r e f o r e , C-C c a n be c o n s i d e r e d a s c o n s t a n t . V a l u e s ( 3 ) o f μ a s a f u n c t i o n o f C a l s o show t h a t dy/dC i s a l m o s t c o n s t a n t . Thus i n t h e n o n i o n i c s u r f a c t a n t measurement i n t h i s p a p e r , τ i s c o n s i d e r e d t o be p r o p o r t i o n a l t o M. F o r a n i o n i c s u r f a c t a n t , we u s e d s o d i u m d o d e c y l s u l f a t e ( S D S ) . The CMC v a l u e s w e r e m e a s u r e d b y c o n d u c t a n c e method. The CMC v a l u e s w e r e t a k e n f r o m t h e b r e a k s o f c u r v e s f r o m p l o t s o f K/C v e r s u s N"2. Where Κ i s t h e s p e c i f i c c o n d u c t a n c e , C i s m o l a r c o n c e n t r a t i o n and Ν i s t h e e q u i v a l e n c e . F i g u r e 1 shows t h e CMC v a l u e s o f SDS a t 25 °C. The c u r v e s h o w i n g i n t h e l o w e r l e f t s i d e r e p r e s e n t s d a t a t a k e n f r o m l i t e r a t u r e f o r p u r e SDS. The c u r v e s h o w i n g i n t h e u p p e r r i g h t s i d e r e p r e s e n t s measurements f o r o u r impure sample. T a b l e I shows some v a l u e s o f (dy/dC) ( C - C ) f o r p u r e SDS a t 25 °C. The v a l u e s f o r N a C l c o n c e n t r a t i o n s o f 0.03 M t o 0.50 M a r e n o t f a r f r o m c o n s t a n t . T h e r e f o r e , i n t h i s c o n c e n t r a t i o n r e g i o n , τ i s a l s o c o n s i d e r e d t o b e p r o p o r t i o n a l t o M. The C v a l u e u s e d i n o u r e x p e r i m e n t s i s 0.5% (0.0171 M, a v e r a g e m o l e c u l a r w e i g h t was t a k e n a s 2 9 3 ) . Q

Q

Q

Table I . Data System

from F i g . l Lower L e f t: C u r v e c -

H 0 2

0.03M N a C l 0.20M N a C l 0.50M N a C l

Some SDS P r o p e r t i e s a t 25 °C

c

0

Data from

Ref.12

λ = 4358 (dy/dC)

2

(d /dC) (C-C ) y

2

0.0091

0.01426

0.000130

0.0141 0.0163 0.0162

0.01421 0.01339 0.01199

0.000200 0.000218 0.000194


0

CHIU ET AL.


ο.οοφ

0.020,

0.0071

u u

0.0061

0.010

J

0

0.0051

0

L 0,2

NaCl, M

g

0.004|

0.003

•

T h i s work.

Δ

D a t a f r o m R e f e r e n c e 9.

Q

D a t a from R e f e r e n c e 1 0 .

Ο

C a l c u l a t e d from e q u a t i o n in reference 11.

0.002

D a t a f r o m R e f e r e n c e 12 f i t i n w e l l with the others. 0.001

J 0.2

L

J. 0.4

J 0.6

L

0.8

NaCl, M F i g u r e 1.

CMC V a l u e s o f SDS a t 25 C.


94


During the s o l u b i l i z a t i o n experiment, o i l c o n t i n u e s to s o l u b i l i z e i n t h e s u r f a c t a n t m i c e l l e and t h e M v a l u e c o n t i n u e s t o increase. The change o f M i s r e f l e c t e d by t h e change o f τ. And d x / d t ( t = t i m e ) i s t a k e n as t h e r a t e o f s o l u b i l i z a t i o n i n o u r experiments. The c o n t r i b u t i o n t o τ by e m u l s i f i e d o i l i n o u r e x p e r i m e n t s i s c o n s i d e r e d n e g l i g i b l e i n t h e n o n i o n i c s u r f a c t a n t s o l u t i o n s due t o t h e v e r y l o w CMC v a l u e s . I n SDS s o l u t i o n s , t h e e m u l s i f i c a t i o n o c c u r s a t t h e v e r y b e g i n n i n g when no N a C l i s added t o t h e s o l u t i o n and t h e t u r b i d i t y i n t r o d u c e d by e m u l s i f i c a t i o n d o e s n o t change w i t h t i m e . When N a C l i s added t o SDS s o l u t i o n s , t h e CMC becomes l o w and e m u l s i f i c a t i o n becomes u n i m p o r t a n t as i t w i l l be shown i n the f o l l o w i n g s e c t i o n s . S o l u b i l i z a t i o n i n Nonionic Surfactant. F i g u r e 2 shows t h e s o l u b i l i z a t i o n of o l e i c a c i d i n Newcol n o n i o n i c s u r f a c t a n t s . Turbidity was p l o t t e d a g a i n s t s h a k i n g t i m e . The f i r s t number on t h e c u r v e represents the s u r f a c t a n t . 1102 means d o d e c a n o l e t h o x y l a t e c o n t a i n i n g 2 EO. The s e c o n d number on t h e c u r v e r e p r e s e n t s t h e amount o f o l e i c a c i d added t o t h e s u r f a c t a n t s o l u t i o n . F o r d o d e c a n o l e t h o x y l a t e , when EO number i s l a r g e r t h a n 8, t h e a g g r e g a t e w e i g h t d e c r e a s e s w i t h t h e i n c r e a s e i n EO number ( 1 3 ) . F o r t h e l o w EO members, w a t e r s o l u b i l i t y becomes l o w . F o r example, when EO = 4, t h e c l o u d p o i n t (3) i s a b o u t 8 °C. When EO = 5, t h e c l o u d p o i n t (3) i s a b o u t 30 °C. I n F i g u r e 2, t h e t u r b i d i t y i n zero shaking time r e f l e c t s the aggregate weight i n the s u r f a c t a n t s o l u t i o n b e f o r e the a d d i t i o n of o i l . The t u r b i d i t y i s v e r y h i g h i n 1102 i n d i c a t i n g l a r g e a g g r e g a t e s i n t h e s o l u t i o n . The t u r b i d i t y f o r t h e o r i g i n a l s o l u t i o n i s s l i g h t l y h i g h e r f o r 1103 t h a n 1105 i n d i c a t i n g l a r g e r aggregates e x i s t i n g i n 1103 s o l u t i o n . dx/dt (slope of the curve) i n F i g u r e 2 r e p r e s e n t s s o l u b i l i z a t i o n r a t e and t h e s t e a d y t u r b i d i t y s h o w i n g a t t h e end o f e a c h curve s i g n i f i e s the s o l u b i l i z a t i o n of o i l at that p a r t i c u l a r condition. Among t h e s e 6 c u r v e s , t h e 1102 c u r v e s h o u l d be d i s cussed s e p a r a t e l y . S i n c e o u r e x p e r i m e n t s were c a r r i e d o u t a t 25 °C, t h e t e m p e r a t u r e i s f a r above t h e 1102 c l o u d p o i n t . A l though the a g g r e g a t e s i z e i s l a r g e , the a g g r e g a t e i s packed t i g h t and s h o u l d have l o w s o l u b i l i z a t i o n v o l u m e . The a d d i t i o n o f a s m a l l amount o f o l e i c a c i d (0.002 g) i n c r e a s e s t h e a g g r e g a t e s i z e tremendously. F u r t h e r a d d i t i o n of o l e i c a c i d r e s u l t s i n c o a g u l a t i o n and d e c r e a s e s t u r b i d i t y . F o r c u r v e s r e p r e s e n t i n g N e w c o l 1103 and 1105, s e v e r a l t r e n d s a r e shown i n F i g u r e 2: (1) f o r s u r f a c t a n t s o l u t i o n s c o n t a i n i n g t h e same amount o f o l e i c a c i d , d x / d t i s h i g h e r f o r 1103 t h a n 1105, s h o w i n g good agreement w i t h E q u a t i o n 1 and (2) when t h e same s u r f a c t a n t i s u s e d , d x / d t i s h i g h e r f o r more o i l addition. T h i s i s expected from k i n e t i c s r u l e s . F i g u r e 3 shows t h e s o l u b i l i z a t i o n o f t r i o l e i n i n N e w c o l s u r factants. F i g u r e 4 shows t h e s o l u b i l i z a t i o n o f n-decane i n t h e same s u r f a c t a n t s o l u t i o n s . The g e n e r a l c h a r a c t e r i s t i c s o f t h e c u r v e s i n F i g u r e s 3 and 4 a r e t h e same as t h o s e shown i n F i g u r e 2.


CHIU ET A L .



96


Α. 1102, 0. 004 g Β. 1102, 0. 002 g C. 1103, 0. 006 g D.

1103, 0. 004 g

Ε. 1105, 0 012 g F. 1105, 0 009 g 600

500

G. 1105, 0 .006 g

1

400

•H •Η

•s ο Η

80

120

S h a k i n g Time, M i n . F i g u r e 3.

S o l u b i l i z a t i o n of T r i o l e i n i n Nonionic

Surfactant.


C H I U ET A L .


A.

1102, 0 006 g

B.

1102, 0 002 g

C.

1103, 0 010 g

D. 1103, 0 006 g E.

1103, 0 002 g

F. 1105, 0 015 g G.

1105, 0 006 g

500

400

4-1

•H

300

-υ Ή

U Η

200

40

80

120

160


Solubilization

o f n-Decane i n N o n i o n i c

Surfactant.



98

From t h e l o w e r t u r b i d i t y v a l u e s shown i n F i g u r e s 3 and 4, one may estimate that the s o l u b i l i z a t i o n of o l e i c a c i d i s higher than t r i o l e i n o r n-decane i n N e w c o l s u r f a c t a n t s o l u t i o n s . I t i s d i f f i c u l t t o make f u r t h e r d i s t i n c t i o n b e t w e e n t r i o l e i n and n-decane f r o m F i g u r e s 3 and 4. S o l u b i l i z a t i o n i n A n i o n i c S u r f a c t a n t . F i g u r e s 5 and 6 show t h e s o l u b i l i z a t i o n o f o l e i c a c i d i n SDS s o l u t i o n s . The s u r f a c t a n t aggregate s i z e i s v a r i e d by changing NaCl c o n c e n t r a t i o n i n t h e surfactant solution. T a b l e I I shows t h e a g g r e g a t i o n number o f SDS m i c e l l e s a t 25°C a s r e p o r t e d b y v a r i o u s a u t h o r s . The a g g r e g a t i o n number i s i n g e n e r a l i n c r e a s e s w i t h t h e N a C l c o n c e n t r a t i o n . When t h e N a C l c o n c e n t r a t i o n i s above 0.4M, t h e a g g r e g a t i o n number i n c r e a s e s more r a p i d l y . The m i c e l l a r shape changes f r o m s p h e r i c a l to r o d ( 1 4 , 1 5 ) . Table I I .

Solution Water 0.01M N a C l 0.02M N a C l 0.03M N a C l 0.1OM N a C l 0.15M N a C l 0.20M N a C l 0.30M N a C l 0.40M N a C l 0.45M N a C l 0.50M N a C l 0.55M N a C l 0.60M N a C l 0.80M N a C l

Aggregation

Ref .9 80

94 100 112

118

126

-

Number o f SDS M i c e l l e s a t 25°C Aggregation R e f . 10

70-77

97-101

148

174-528 1630

Number R e f . 12 62

72

-

Ref.

14

90

101

-

-

110

200

142

-

-

600 940

-

The t u r b i d i t y v a l u e s a t z e r o s h a k i n g t i m e r e f l e c t s t h e t u r b i d i t y f o r t h e SDS s o l u t i o n s b e f o r e t h e a d d i t i o n o f o i l . U s u a l l y , hand d i s p e r s i o n o f o i l does n o t i n c r e a s e t u r b i d i t y o f the s u r f a c t a n t s o l u t i o n . T u r b i d i t y i n c r e a s e s o n l y when m e c h a n i c a l s h a k i n g i s a p p l i e d . B u t i n SDS s o l u t i o n s when no N a C l i s a d d e d , the d i s p e r s i o n o f o l e i c a c i d b y hand i n c r e a s e s t u r b i d i t y and s u b s e q u e n t m e c h a n i c a l s h a k i n g c a u s e s no f u r t h e r c h a n g e . The i n i t i a l t u r b i d i t y f o r SDS s o l u t i o n c o n t a i n i n g 0-0.4 M N a C l b e f o r e t h e a d d i t i o n o f o i l r a n g e s f r o m 1-3 and i s h a r d l y d i s t i n g u i s h a b l e i n t h e d r a w i n g . F i g u r e s 5 and 6 show s i m i l a r c h a r a c t e r i s t i c s . E a c h c u r v e i n F i g u r e 5 r e p r e s e n t s t h e s o l u b i l i z a t i o n o f 0.050 g o l e i c a c i d i n SDS s o l u t i o n c o n t a i n i n g t h e s p e c i f i e d N a C l . In F i g u r e 6, 0.062 g o l e i c a c i d i s u s e d . I n general, higher t u r b i d i t y i s o b s e r v e d i n F i g u r e 6 t h a n i n F i g u r e 5.


6.

99


CHIU ET AL.

700h

0

5

10

15

20

25

30

35

40


Solubilization of Oleic Acid i n Anionic

Surfactant.


100


0.1 M N a C l


S o l u b i l i z a t i o n of O l e i c A c i d i n A n i o n i c

Surfactant.


6. C H I U ET A L .

101


Among t h e SDS s o l u t i o n s w i t h d i f f e r e n t N a C l c o n c e n t r a t i o n s , t h e m i c e l l a r p r o p e r t i e s i n t h e s e s o l u t i o n s r e q u i r e some d i s c u s s i o n . From F i g u r e 1, one c a n s e e t h e CMC v a l u e s o f o u r SDS s o l u t i o n s i n t h e u p p e r r i g h t s i d e . S i n c e t h e c o n d u c t a n c e method f o r CMC d e t e r m i n a t i o n c a n be used o n l y i n e l e c t r o l y t e c o n c e n t r a t i o n o f n o t more t h a n 0.1 M, we may u s e t h e v a l u e s o b t a i n e d o n l y i n t h i s c o n centration region. I n SDS s o l u t i o n w i t h o u t N a C l , t h e CMC v a l u e i s 0.56-0.60%. F o r N a C l c o n c e n t r a t i o n o f 0.025-0.1 M, CMC v a l u e s a r e a r o u n d 0.15%. From l i t e r a t u r e d a t a s h o w i n g i n t h e same f i g u r e , one may p r e d i c t o n l y s m a l l d e c r e a s e o f CMC w o u l d o c c u r i n N a C l c o n c e n t r a t i o n r a n g e o f 0.1-0.4 M. I n t h e SDS s o l u t i o n s we u s e d i n t h e e x p e r i m e n t s , t h e s u r f a c t a n t c o n c e n t r a t i o n i s 0.5%. T h i s v a l u e l i e s b e l o w t h e CMC when no N a C l i s added. I n t h e p r e s e n c e o f 0.1-0.4 M N a C l , 7 0 % o f t h e s u r f a c t a n t w i l l b e i n t h e m i c e l l a r form. When no N a C l i s added t o t h e SDS s o l u t i o n , t h e t u r b i d i t y i n c r e a s e w i t h s l i g h t d i s p e r s i o n o f o l e i c a c i d i s p r o b a b l y due t o t h e monomer e m u l s i f i c a t i o n o f t h e o l e i c a c i d . The p r o c e s s does n o t seem t o r e q u i r e a s much t i m e and e n e r g y a s s o l u b i l i z a t i o n . I n t h e SDS s o l u t i o n s c o n t a i n i n g 0.1-0.4 M N a C l , t h e t u r b i d i t y i n c r e a s e i s m a i n l y due t o m i c e l l a r s o l u b i l i z a t i o n . The s o l u b i l i z a t i o n r a t e ( d x / d t ) o f t h e s o l u t i o n s seems t o b e i n t h i s o r d e r : 0 . 1 M > 0 . 2 M > 0 . 3 M > 0 . 4 M NaCl. The f i n a l s o l u b i l i z a t i o n o f t h e s o l u t i o n s i s a l s o i n t h e same o r d e r . The s i z e o f t h e p u r e SDS m i c e l l e s i n s o l u t i o n s c o n t a i n i n g N a C l h a s b e e n shown t o i n c r e a s e w i t h t h e N a C l c o n c e n t r a t i o n ( T a b l e I I ) . Our i n s t r u m e n t i s n o t s e n s i t i v e enough t o d i s t i n g u i s h t h e s i z e b e t w e e n t h e s e s m a l l m i c e l l e s a t d i f f e r e n t NaCl c o n c e n t r a t i o n s . I n the s o l u b i l i z a t i o n o f o l e i c a c i d i n 0.5% SDS s o l u t i o n s , t h e maximum V f f seems t o o c c u r when t h e N a C l c o n c e n t r a t i o n i s a r o u n d 0.1 M. The maximum may o c c u r i n N a C l c o n c e n t r a t i o n b e l o w 0.1 M o r b e t w e e n 0.1 M and 0.2 M w h i c h we h a v e n o t s t u d i e d . F i g u r e 7 shows some t u r b i d i t y d a t a a s a f u n c t i o n o f t r i o l e i n a d d i t i o n i n SDS s o l u t i o n s c o n t a i n i n g v a r y i n g amount o f N a C l . Each p o i n t was t a k e n f r o m e x p e r i m e n t s s u c h a s d e s c r i b e d i n t h e e x p e r i mental s e c t i o n by dropwise a d d i t i o n o f t r i o l e i n . The t u r b i d i t y i n c r e a s e s w i t h t h e a d d i t i o n o f t r i o l e i n t o a steady value f o r a l l SDS s o l u t i o n s c o n t a i n i n g d i f f e r e n t amount o f N a C l . The h i g h e s t t u r b i d i t y ( o r t h e h i g h e s t s o l u b i l i z a t i o n ) and t h e h i g h e s t s o l u b i l i z a t i o n r a t e ( d x / d t ) o c c u r a t 0.5 M N a C l . A t higher NaCl concent r a t i o n s , c o a g u l a t i o n o c c u r s w i t h s h a k i n g and t u r b i d i t y d e c r e a s e s . F i g u r e 7 a l s o shows some d a t a t a k e n f r o m e x p e r i m e n t s p e r f o r m e d i n t h e same way a s d e s c r i b e d a b o v e f o r t h e s o l u b i l i z a t i o n o f o l e i c a c i d i n SDS s o l u t i o n s . I n t h e s e e x p e r i m e n t s , 0.050 g t r i o l e i n was added t o t h e SDS s o l u t i o n c o n t a i n i n g a s p e c i f i e d amount o f NaCl. The f i n a l t u r b i d i t y v a l u e s w e r e p l o t t e d a l o n g t h e l i n e c o r r e s p o n d i n g t o 0.050 g t r i o l e i n a d d i t i o n w i t h t h e s p e c i f i e d NaCl c o n c e n t r a t i o n . These v a l u e s a r e n o t t o o f a r f r o m t h e v a l u e s o b t a i n e d b y d r o p w i s e a d d i t i o n o f t r i o l e i n a s shown i n t h e same diagram. e


102



6.

C H I U ET A L .


103

Up t o t h i s moment we h a v e s t u d i e d t h e s o l u b i l i z a t i o n r a t e o f s e v e r a l o i l y m a t e r i a l s i n some n o n i o n i c a n d a n i o n i c s u r f a c t a n t s . I n g e n e r a l we f o u n d t h a t t h e o i l s o l u b i l i z a t i o n r a t e i s a f u n c t i o n of the s u r f a c t a n t aggregate s i z e . The maximum V £ £ f o r a s e r i e s o f s u r f a c t a n t s o l u t i o n s seems t o o c c u r a t t h e c o n d i t i o n t h a t t h e s u r f a c t a n t a s s o c i a t e s t o t h e maximum a g g r e g a t e volume w i t h o u t i n c r e a s i n g t h e d e n s i t y o f t h e a g g r e g a t e . The V £ £ v a l u e seems to p a r a l l e l the f i n a l s o l u b i l i z a t i o n v a l u e o f the s u r f a c t a n t . A l l t h e r e s u l t s we o b t a i n e d a r e q u a l i t a t i v e i n n a t u r e . The m a t e r i a l s u s e d i n t h e e x p e r i m e n t s a r e m o s t l y n o t 100% p u r e b u t should be u s a b l e i n comparing performance r e s u l t o f i n d u s t r i a l applications. And t h e c o n c l u s i o n s we o b t a i n e d do n o t h a v e t h e l i m i t a t i o n o f a pure o i l (or s u r f a c t a n t ) o r a p a r t i c u l a r o i l (or surfactant). One i m p o r t a n t f a c t o r we h a v e n o t d i s c u s s e d i s t h e electrical effect. T h i s may c o n t r i b u t e s i g n i f i c a n t l y i n a n i o n i c s u r f a c t a n t s o l u b i l i z a t i o n w i t h p o l a r o i l . We h a v e n e i t h e r d i s c u s s e d t h e mechanism o f s o l u b i l i z a t i o n n o r t h e s p e c i f i c e f f e c t of a c e r t a i n o i l t o a c e r t a i n s u r f a c t a n t . To u n d e r s t a n d c l e a r l y s u c h s p e c i f i c e f f e c t s a n d t o d e r i v e more q u a n t i t a t i v e r e l a t i o n s g o v e r n i n g t h e r e s u l t o f s o l u b i l i z a t i o n , we a r e p l a n n i n g t o c o n d u c t f u t u r e experiments w i t h pure sample. e

e

R e l a t i o n Between S t r u c t u r e and P e r f o r m a n c e o f S u r f a c t a n t s . In a d e t e r g e n t p a p e r ( 3 ) , we h a v e r e p e a t e d t h e d e t e r g e n c y w o r k o f The P r o c t o r and Gamble Company o f some n a r r o w r a n g e d o d e c a n o l e t h o x y l a t e s w i t h EO number f r o m 2 t o 8. A d e t e r g e n c y maximum a t EO number 4 f o r 24 °C ( a t EO number 5 f o r 38 °C) was f o u n d f o r t r i o l e i n removal. For o l e i c a c i d removal, a steady increase o f d e t e r g e n c y was f o u n d f o r d o d e c a n o l e t h o x y l a t e s f r o m EO number 2 t o EO number 5 a t 38 °C and no s i g n i f i c a n t change f r o m EO number 5 t o EO number 8. From c l o u d p o i n t measurement, i t was f o u n d t h a t the temperature a t which the i n d i c a t e d s u r f a c t a n t showing the maximum d e t e r g e n c y i s 7-15 °C above t h e s u r f a c t a n t c l o u d p o i n t . S i n c e t r i o l e i n i s r e l a t i v e l y n o n - p o l a r , i t s r e m o v a l depends mainly on s o l u b i l i z a t i o n . The l a r g e a g g r e g a t e s formed a t temp e r a t u r e somewhat above t h e c l o u d p o i n t a r e o b v i o u s l y v e r y e f f e c t i v e i n s o l u b i l i z a t i o n . We h a v e a t t r i b u t e d t h i s t o t h e i n c r e a s e of s o l u b i l i z a t i o n r a t e w i t h the s u r f a c t a n t aggregate size. The e v i d e n c e has b e e n shown b y t h i s p a p e r . C a r r o l l (5) s t u d i e d t h e k i n e t i c s o f s o l u b i l i z a t i o n o f n o n p o l a r o i l b y n o n i o n i c s u r f a c t a n t s o l u t i o n s and f o u n d t h a t t h e s o l u b i l i z a t i o n r a t e i s s t r o n g l y temperature dependent i n the r e g i o n o f the n o n i o n i c c l o u d p o i n t : 15 °K b e l o w t h e c l o u d p o i n t , t h e r a t e i s extremely s m a l l r e l a t i v e t o that a t the cloud p o i n t . Nakagawa and T o r i (16) h a v e f o u n d a tremendous i n c r e a s e i n a g g r e g a t e w e i g h t f o r n o n i o n i c s u r f a c t a n t s near the c l o u d p o i n t and the i n c r e a s e i n aggregate weight c o r r e l a t e d w i t h increased s o l u b i l i z a t i o n o f long c h a i n a l k y l compounds a t c o n s t a n t t o t 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 . These i n d e p e n d e n t s t u d i e s show more e v i d e n c e s t o what we h a v e j u s t d e s c r i b e d i n t h i s paper.


104


S i n c e o l e i c a c i d i s r e l a t i v e l y p o l a r , i t may become e m u l s i f i e d by t h e s u r f a c t a n t monomer. The r e m o v a l o f o l e i c a c i d comes m a i n l y f r o m two c o n t r i b u t i o n s : monomer e m u l s i f i c a t i o n and m i c e l l a r s o l u bilization. A l t h o u g h t h e V f £ has b e e n d e c r e a s e d w i t h i n c r e a s i n g EG number i n d o d e c a n o l e t h o x y l a t e s , i n h i g h e r EO numbers t h a n 5, t h i s f a c t o r has b e e n compensated by t h e i n c r e a s e o f monomer w i t h i n c r e a s i n g EO number (CMC d e c r e a s e s w i t h EO n u m b e r ) . The l e v e l l i n g o f d e t e r g e n c y o f d o d e c a n o l e t h o x y l a t e s f r o m EO number 5 t o EO number 8 h a s b e e n i n t e r p r e t e d by t h e s e r e a s o n s . The monomer e m u l s i f i c a t i o n o f o l e i c a c i d has b e e n c l e a r l y shown i n t h i s p a p e r i n SDS s o l u t i o n . The n o n i o n i c s u r f a c t a n t s we u s e d h e r e h a v e l o w EO numbers and show m a i n l y t h e e f f e c t o f s o l u b i l i z a t i o n . I t a l s o appears that l a r g e r s o l u b i l i z a t e p r e f e r s l a r g e r micelles for solubilization. T h i s i s shown i n t h e SDS s o l u b i lization. T r i o l e i n s o l u b i l i z e s more e f f e c t i v e l y i n SDS s o l u t i o n s c o n t a i n i n g h i g h e r NaCl c o n c e n t r a t i o n w h i l e o l e i c a c i d s o l u b i l i z e s b e t t e r i n lower NaCl c o n c e n t r a t i o n . The d i s t i n c t i o n o f t h e s i z e p r e f e r e n c e b e t w e e n d i f f e r e n t s o l u b i l i z a t e s i s n o t so o b v i o u s i n t h e n o n i o n i c s u r f a c t a n t s o l u t i o n s r e p o r t e d h e r e . W i t h EO number b e t w e e n 2-5, t h e s i z e s o f t h e n o n i o n i c s u r f a c t a n t a g g r e g a t e s a r e so much l a r g e r t h a n t h e SDS m i c e l l e s ( o r t h e o i l m o l e c u l e s ) t h a t e v e n t h e s m a l l e s t n o n i o n i c a g g r e g a t e s a r e more e f f e c t i v e s o l u b i l i z e r s t h a n t h e SDS m i c e l l e s . Thus t h e y show a l e v e l l i n g e f f e c t f o r the d i f f e r e n t s o l u b i l i z a t e s . The e l e c t r i c a l c h a r g e on a n i o n i c s u r f a c t a n t s may a l s o h a v e some c o n t r i b u t i o n t o t h e d i f f e r e n c e i n s o l u b i l i z a t i o n o f o l e i c a c i d and t r i o l e i n . A n o t h e r example s h o w i n g t h e p r e f e r e n c e f o r l a r g e s u r f a c t a n t a g g r e g a t e s i s d e m o n s t r a t e d i n t e r t i a r y o i l r e c o v e r y ( 1 ) . When a 5% B r y t o n 430 p e t r o l e u m s u l f o n a t e s o l u t i o n was u s e d , t h e u l t r a l o w i n t e r f a c i a l t e n s i o n b e t w e e n o i l and w a t e r and f a s t s o l u b i l i z a t i o n o f c r u d e o i l a p p e a r e d a r o u n d 0.3 M N a C l . By C o u l t e r c o u n t e r measurement, s u r f a c t a n t a g g r e g a t e s a r o u n d 1 μ i n s i z e was f o u n d . B e l o w 0.3 M N a C l , t h e a g g r e g a t e s i z e s w e r e s m a l l e r and t h e s o l u b i l i z a t i o n r a t e s w e r e s l o w e r . Above 0.3 M N a C l , t h e a g g r e g a t e s became u n s t a b l e and t e n d e d t o w a r d s e p a r a t i o n f r o m w a t e r . We h a v e n o t had an o p p o r t u n i t y t o measure t h e s o l u b i l i z a t i o n r a t e o f petroleum sulfonate s o l u t i o n s . The s t a t e m e n t made h e r e i s m a i n l y f r o m o b s e r v a t i o n . The o i l s o l u b i l i z a t i o n i n 5% B r y t o n 430 c o n t a i n i n g 0.3 M N a C l i s t o o f a s t t o be measured by o r d i n a r y methods. In order to b r i n g the s o l u b i l i z a t i o n r a t e i n a measurable range, we u s e d much s m a l l e r s u r f a c t a n t a g g r e g a t e s (SDS) i n t h e e x p e r i ments. The phenomenon e x h i b i t e d by t r i o l e i n s o l u b i l i z a t i o n r e s e m b l e d t h e phenomenon o b s e r v e d i n B r y t o n 430 e x c e p t t h e r a t e was much s l o w e r . I t i s w e l l known t h a t SDS and many c o m m e r c i a l s u r f a c t a n t s c a n n o t be u s e d t o r e c o v e r o i l . I n our o p i n i o n t h e s e s u r f a c t a n t s c a n n o t a s s o c i a t e t o f o r m l a r g e enough a g g r e g a t e s i s one i m p o r t a n t reason. I n most c a s e s , when e l e c t r o l y t e i s added t o t h e s u r f a c t a n t s o l u t i o n to i n c r e a s e the s i z e of the aggregate, s u r f a c t a n t s e p a r a t i o n o c c u r s b e f o r e l a r g e enough a g g r e g a t e s c a n be b u i l t up. e


6.

C H I υ E T AL.


105

This paper p r e s e n t s a v e r y b a s i c p r i n c i p l e i n s u r f a c t a n t solubilization. More q u a n t i t a t i v e measurement i n c o r r e l a t i n g s o l u b i l i z a t i o n r a t e w i t h m i c e l l a r p r o p e r t i e s and more a p p l i c a t i o n s of t h i s p r i n c i p l e t o improve performance o f v a r i o u s s o l u b i l i z a t i o n p r o c e s s e s remain the s u b j e c t o f our i n v e s t i g a t i o n . Acknowledgments Shu-Mei Ann, V e n i c e Hu, D a o - S h i n n Hwang, P e t e r Hwang, J i n g - M i n g Hsu, T i a n - T s a i n Wu, Huann-Jang Hwang and R u e y - J i n g Cheng have made c o n t r i b u t i o n t o t h i s p a p e r .

Literature Cited 1. Chiu, Y. C. in "Solution Behavior of Surfactants: Theoretical and Applied Aspects"; Mittal, K. L.; Fendler, E. J., Ed.; Plenum: New York, 1982; Vol. II, pp. 1415-1440. 2. Chiu, Y. C. Oilfield and Geothermal Chemistry Symposium, Denver, Co., U.S.A., June 1-3, 1983; SPE paper 11783. 3. Benson, H.L.; Chiu, Y. C. "Relationship of Detergency to Micellar Properties for Narrow Range Alcohol Ethoxylates", Technical Bulletin, SC: 443-80, Shell Chemical Co. Houston, Texas, U.S.A., 1980. 4. McBain, M.E.; Hutchinson, E. "Solubilization and Related Phenomena"; Academic Press: New York, 1955. 5. Carroll, B. J. J. Colloid and Interface Sci. 1981, 79, 126. 6. Chan, A. F.; Evans, D. F.; Cussler, E. L. AICHE 1976, 22, 1006. 7. Shaeiwitz, J. Α.; Chan, A. F-C.; Cussler, E. L.; Evans, D. F. J. Colloid and Interface Sci. 1981, 84, 47. 8. Debye, P. Ann. Ν. Y. Acad. Sci. 1949, 51, 575. 9. Phillips, J. N. Trans. Faraday Soc. 1955, 51, 561. 10. Hayashi, S.; Ikeda, S. J. Phys. Chem. 1980, 84, 744. 11. Emerson, M. F.; Holtzer, A. J. Phys. Chem. 1967, 71, 1898. 12. Mysels, K. J.; Princen, L. H. J. Phys. Chem.1959, 63, 1696. 13. Becher, P. J. Colloid Sci. 1961, 16, 49. 14. Mazer, Ν. Α.; Benedek, G. B.; Carey, M. C. J. Phys. Chem. 1976, 80, 1075. 15. Missel, P. J . ; Mazer, Ν. Α.; Benedek, G. B.; Young, C. Y.; Carey, M. C. J. Phys. Chem. 1980, 84, 1944. 16. Nakagawa, T.; Tori, K. Koll. Z. 1960, 168, 132. RECEIVED January 20, 1984


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