Phase Behavior of a Pure Alkyl Aryl Sulfonate Surfactant - ACS

3

Phase Behavior of a P u r e

Alkyl

Aryl

Sulfonate Surfactant

Downloaded by UNIV OF MICHIGAN ANN ARBOR on September 19, 2015 | http://pubs.acs.org Publication Date: March 2, 1979 | doi: 10.1021/bk-1979-0091.ch003

Ε. I. FRANSES, H. T. DAVIS, W. G. MILLER, and L. E. SCRIVEN Departments of Chemical Engineering & Materials Science, and of Chemistry, University of Minnesota, Minneapolis, MN 55455

The phase behavior of surfactants in water and hydrocarbon is the key to understanding the water- and oil-dissolving power of certain surfactant systems and the interfacial tension between the phases that form in these systems (1,2). Ultralow tensions less than ΙΟμΝ/m (0.01 dyn/cm) are required by one of the important mechanisms in various processes for enhancement of petroleum recovery. Much information is now in the literature (3,4,5,6), but most of the data are for commercial surfactants which are complex mixtures of surface-inactive as well as surface -active components (7). Recently a University of Texas group synthesized a number of isomerically pure alkyl aryl sulfonate surfactants (8) which are structurally similar to components of practically important petroleum sulfonate surfactant products (8,9). The Texas group established (9) and we confirmed (10) that ultralow tensions can be achieved with certain of these pure surfactants, provided the right combination of surfactant concentration, sodium chloride concentration, hydrocarbon, temperature and experimental pro cedure is employed. Few studies of pure alkyl aryl sulfonate surfactants have appeared (8,11c,12). The interpretation of phase behavior and interfacial tension data for pure, single surfactants and well -defined surfactant mixtures is expected to be easier than for complex and poorly-defined mixtures. Fundamental studies on pure surfactants will shed light on the behavior of practically important surfactant systems which are impure. Using one of the pure alkyl aryl sulfonates with water, sodium chloride and decane, we are investigating simultaneously the phase behavior, the structure of the phases, and the inter facial tensions between them. Ultralow tensions are observed in this system (10), and i t is important to know why they occur, when they do (13). Our first aim is to establish the equilibrium phase diagram of surfactant-water-decane as a function of 0-8412-0477-2/79/47-091-035$10.00/0 © 1978 American Chemical Society In Chemistry of Oil Recovery; Johansen, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

CHEMISTRY

36

temperature

and sodium c h l o r i d e c o n c e n t r a t i o n .

O F OIL RECOVERY

In t h i s paper

we

r e p o r t t h e m a i n methods we a r e a p p l y i n g t o p h a s e b e h a v i o r , some o f w h i c h p e r t a i n t o s t r u c t u r e a s w e l l , and o u r r e s u l t s t o d a t e . Interfacial

tension

measurements w i l l


The methods a r e t h e f o l l o w i n g 14):

be r e p o r t e d

Spectroturbidimetry i s simply measuring o f a l i g h t beam b y a b s o r p t i o n a n d s c a t t e r i n g a sample. I n terms o f t r a n s m i t t a n c e T, t h e t o i n c i d e n t i n t e n s i t y , and t o t a l a b s o r b a n c e

A , abs

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~

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+

elsewhere (10).

( f o r a d d i t i o n a l d e t a i l s see Ref. the l o s s o f i n t e n s i t y as i t p a s s e s t h r o u g h r a t i o of transmitted Α Ξ -log-j^T,

A scat le

where i s a b s o r b a n c e due t o a b s o r p t i o n , A g i s t h a t due to s c a t t e r i n g (also c a l l e d t u r b i d i t y ) , £ i s t h e p a t h l e n g t h (cm) and c i s the concentration (g/cm^). Since s p e c i f i c absorption, abs/^ ' l i k e the scattering contribution scat/^ ' ^ l 9 ly i n d e p e n d e n t o f t h e s i z e s and c o n c e n t r a t i o n s o f p a r t i c l e s a n d aggregates p r e s e n t ( i n o r d i n a r y s o l u t i o n s i t f o l l o w s Beer's law and i s c o n s t a n t ) , v a r i a t i o n s o f A / £ c w i t h r e s p e c t t o c o n c e n t r a t i o n , t e m p e r a t u r e o r h i s t o r y r e f l e c t changes i n s i z e s and amount o f d i s p e r s e d m a t e r i a l ( 1 5 ) . T h u s t h e method c a n g i v e a 'fingerprint' of a dispersion. I t i s n o t s e n s i t i v e enough, however, t o d e t e c t s m a l l t u r b i d i t i e s a r i s i n g from o r d i n a r y m i c e l l e s o r comparable m o l e c u l a r aggregates, f o r which a l i g h t s c a t t e r i n g method i s r e q u i r e d ( 1 6 J . B u t f o r t h i s r e a s o n spectroturbidimetry can e a s i l y d i s c r i m i n a t e a f i n e , n o n - s e t t l i n g d i s p e r s i o n from an e q u i l i b r i u m m i c e l l a r s o l u t i o n . c a t

A

c

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c

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P o l a r i z i n g microscopy i d e n t i f i e s biréfringent phases, f o r example l i q u i d c r y s t a l l i n e p h a s e s (17,18), and r e v e a l s d i s p e r s e d p a r t i c l e s , p r o v i d e d they a r e l a r g e r than about l y ( u l t i m a t e s e n s i t i v i t y i s about 0.3μ). Vapor s o r p t i o n measurements y i e l d e q u i l i b r i u m c o m p o s i t i o n and f u g a c i t y o r c h e m i c a l p o t e n t i a l ; t h e i s o p i e s t i c v e r s i o n (19) i s used t o determine t h e uptake o f a pure vapor by a n o n v o l a t i l e material. This technique determines e q u i l i b r i u m composition o f a p h a s e w h i c h c a n n o t be s e p a r a t e d q u a n t i t a t i v e l y f r o m t h e l i q u i d phase i n e q u i l i b r i u m w i t h i t . I n o u r a p p l i c a t i o n , a n o n v o l a t i l e c r y s t a l l i n e s u r f a c t a n t specimen S i s e q u i l i b r a t e d with vapor of V, w h i c h i s , i n t u r n , a t e q u i l i b r i u m w i t h a s y s t e m o f S a n d V c o n s i s t i n g o f two p h a s e s , o n e r i c h i n S, a n d o n e r i c h i n V. A t e q u i l i b r i u m , t h e Gibbs-Duhem r e l a t i o n g u a r a n t e e s .that t h e i n i t i a l specimen o f S t a k e s up enough V from t h e vapor phase t h a t t h e c h e m i c a l p o t e n t i a l o f S, a s w e l l a s o f V, i s t h e same as i n t h e b i p h a s i c system, and so t h e c o m p o s i t i o n o f t h e phase f o r m e d b y v a p o r s o r p t i o n i s t h e same a s t h a t o f t h e S - r i c h p h a s e . T h i s c o m p o s i t i o n i s e a s i l y d e t e r m i n e d by w e i g h t measurement. I f t h e t e m p e r a t u r e were a t r i p l e p o i n t , i . e . t h r e e p h a s e s a t

In Chemistry of Oil Recovery; Johansen, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

3.

FRANSES E T A L .

Alkyl

equilibrium,

a

Si

with

and

solid

saturated

surfactant

the

l e

Thus i t h a s


s o r p t i o n i s the

Sulfonate

37

Surfactant

s o l u t i o n and

two

s u r f a c t a n t - r i c h phases,

same c h e m i c a l p o t e n t i a l o f

would

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Aryl

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V

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t o be same as

verified that

that

i n the

V,

composition

then S2

c o n s i s t o f phases the

V

p h a s e p r o d u c e d by

biphasic

the

is and vapor

dispersion.

C a r b o n - 1 3 N u c l e a r M a g n e t i c R e s o n a n c e S p e c t r o s c o p y (20) gives i n f o r m a t i o n about motion — whether f a s t o r slow, i s o t r o p i c o r anisotropic — o f s p e c i f i c carbons i n the m o l e c u l a r s p e c i e s t h a t make up a s a m p l e . P r o v i d e d a phase has a d i s t i n g u i s h i n g spectrum, i t s p r e s e n c e (above a l i m i t i n g mass f r a c t i o n ) c a n be e s t a b l i s h e d , whether or not i t i s f i n e l y d i s p e r s e d i n a second phase. Thus t h i s i s a p o w e r f u l t o o l f o r l o c a t i n g p h a s e t r a n s i t i o n s and p r o b i n g the phase diagram. I t c a n a l s o be u s e d t o h e l p e l u c i d a t e t h e m i c r o s t r u c t u r e o f l i q u i d c r y s t a l l i n e p h a s e s and m i c e l l a r aggregates (21). Conductimetry of s u r f a c t a n t s which are

a q u e o u s s o l u t i o n s and d i s p e r s i o n s o f i o n i c s t r o n g e l e c t r o l y t e s i n monomer f o r m i s a

s e n s i t i v e i n d i c a t o r o f t h e i r s t a t e o f a g g r e g a t i o n , because the e q u i v a l e n t c o n d u c t i v i t y o f e v e n an e x t r e m e l y f i n e d i s p e r s i o n i s much s m a l l e r t h a n t h a t o f e q u i l i b r i u m m i c e l l e s w h i c h , i n t u r n , i s smaller than that of m o l e c u l a r l y d i s p e r s e d ions i n water ( l i b ) . The c o n d u c t i v i t y o f a m i c e l l a r s o l u t i o n i s due p a r t l y t o t h e s u b s t a n t i a l p e r c e n t a g e o f the g e g e n i o n s w h i c h a r e n o t bound t o the m i c e l l e s , w h e r e a s a d i s p e r s e d p h a s e must r e t a i n so much l a r g e r a p e r c e n t a g e as t o l e a v e f a r f e w e r g e g e n i o n s . The p e r c e n t a g e o f f r e e g e g e n i o n s i n m i c e l l a r s o l u t i o n s d e p e n d s on t h e s u r f a c t a n t head group, m i c e l l e s i z e , and c o n c e n t r a t i o n . T y p i c a l values are 10 t o 40% (lib,22). Furthermore, m i c e l l e s contribute signific a n t l y to the c o n d u c t i v i t y (23), whereas the l a r g e p a r t i c l e s o f d i s p e r s e d p h a s e do n o t . Ultracentrifugation

and

ultrafiltration

are

means

a

of

s e p a r a t i n g d i s p e r s e d p a r t i c l e s o f one p h a s e f r o m a n o t h e r and estimating p a r t i c l e size. O r d i n a r y s m a l l m i c e l l e s do n o t sediment q u i c k l y ; moreover they r e - e q u i l i b r a t e c o m p a r a t i v e l y r a p i d l y a f t e r u l t r a c e n t r i f u g a t i o n . The n a t u r e o f u l t r a f i l t r a t i o n membranes u s e d i n o u r a p p l i c a t i o n i s d e s c r i b e d i n R e f . 24. APPARATUS AND

used.

PROCEDURES

A C a r y 15 U V - V i s i b l e (200 t o 800 nm) The c e l l h o l d e r was t h e r m o s t a t t e d

S p e c t r o p h o t o m e t e r was (±0.2°C). Temperatures

up t o 60°C w e r e m e a s u r e d w i t h a B a i l e y s u r f a c e m i c r o p r o b e ( ± 1 ° C ) ; t h o s e b e t w e e n 6 0 ° C and 9 0 ° C were e s t i m a t e d (±2°C) f r o m t h e thermostat temperature. C e l l t e m p e r a t u r e was homogeneous w i t h i n these l i m i t s . T o t a l a b s o r b a n c e s were m e a s u r e d w i t h a n a c c u r a c y o f 0.003 and a s e n s i t i v i t y o f 0.002. They were u s u a l l y t a k e n a t w a v e l e n g t h s b e t w e e n 750 and 350 nm, where s c a t t e r i n g i s d o m i n a n t . However, t o h a v e s e n s i t i v i t y i t was s o m e t i m e s n e c e s s a r y t o work b e t w e e n 350 and 240 nm, where a b s o r p t i o n b y t h e s u r f a c t a n t


CHEMISTRY O F OIL RECOVERY

38

becomes s i g n i f i c a n t . T h e l a t t e r was e v a l u a t e d a t c o n c e n t r a t i o n s s o l o w t h a t s c a t t e r i n g was n e g l i g i b l e . A b s o r b a n c e s a t t h e UV a b s o r p t i o n maxima

(271.5,

267, 261, 255 a n d 223 nm) w e r e

also

measured and used f o r a n a l y t i c a l p u r p o s e s a f t e r b e i n g c o r r e c t e d f o r s c a t t e r i n g , as d e t e r m i n e d b y e x t r a p o l a t i o n from t h e nonabsorbing r e g i o n o f t h e spectrum. C o n c e n t r a t i o n s found s h o u l d n e v e r b e more t h a n 1 0 % a b o v e t h e t r u e v a l u e .


M e a s u r e m e n t s were r e c o r d e d o n l y a f t e r

total

t h i s way

absorbance

v a l u e s a t s e v e r a l w a v e l e n g t h s w e r e c o n s t a n t f o r a t l e a s t two hours. F o r b i p h a s i c d i s p e r s i o n s t h i s was done a t s e v e r a l temp e r a t u r e s a n d a s o l u b i l i t y p h a s e b o u n d a r y was t a k e n t o b e t h e t e m p e r a t u r e a t w h i c h t h e a b s o r b a n c e due t o s c a t t e r i n g f a l l s s h a r p l y t o 0.02 o r l e s s . This i s the 'synthetic method f o r 1

determining s o l u b i l i t i e s

(_25) .

M i l l i p o r e (M) a n d N u c l e p o r e (N) u l t r a f i l t r a t i o n membranes w i t h p o r e s i z e s 0.05 t o 0.22y w e r e u s e d t o s e p a r a t e d i s p e r s e d particles. A l t e r n a t i v e l y o r i n a l t e r n a t i o n a Beckman L3-50 p r e p a r a t i v e u l t r a c e n t r i f u g e w i t h a n SW-1 s w i n g i n g b u c k e t r o t o r was u s e d . I n i t i a l s o l u t i o n s a n d d i s p e r s i o n s w e r e s t i r r e d magn e t i c a l l y f o r a t l e a s t 12 h o u r s . A L e i t z p o l a r i z i n g microscope equipped with a Nikon photom i c r o g r a p h i c a t t a c h m e n t was e m p l o y e d w i t h e i t h e r a s l i d e c o v e r s l i p arrangement o r a square c a p i l l a r y specimen c o n t a i n e r . Some s p e c i m e n s were t a k e n f r o m e q u i l i b r a t e d b i p h a s i c s y s t e m s a n d some w e r e p r o d u c e d b y v a p o r s o r p t i o n o f w a t e r o r d e c a n e b y p u r e surfactant. F o r v a p o r s o r p t i o n measurements a t h e r m o s t a t t e d v a p o r s o r p t i o n a p p a r a t u s (Worden Q u a r t z P r o d u c t s , I n c . ) was u s e d ( 2 6 ) . A s m a l l p a n c o n t a i n i n g a b o u t 100 mg o f s u r f a c t a n t was s u s p e n d e d b y a q u a r t z s p r i n g , t h e e x t e n s i o n o f w h i c h was f o l l o w e d b y means of a t r a v e l i n g microscope. The s p r i n g was c a l i b r a t e d u n d e r vacuum. P u r e s o l v e n t s (water o r decane) were u s e d i n s t e a d o f s a t u r a t e d s o l u t i o n s i n the vapor s o r p t i o n experiment, because v a p o r p r e s s u r e l o w e r i n g d u e t o d i s s o l u t i o n o f s u r f a c t a n t was e s t i m a t e d t o b e l e s s t h a n 0.01%, w h e r e a s t e m p e r a t u r e v a r i a t i o n s o f 0 . 0 1 ° C c h a n g e t h e v a p o r p r e s s u r e o f w a t e r b y 0.06%. To a v o i d weight e r r o r because o f c o n d e n s a t i o n on t h e s p r i n g o r on t h e s u r f a c t a n t c r y s t a l , t h e s u r f a c t a n t s p e c i m e n was k e p t a b o u t 1°C above t h e t e m p e r a t u r e o f t h e s o l v e n t . Thus a s m a l l s y s t e m a t i c r e l a t i v e e r r o r o f 5 t o 10% i n t h e s o r b e d amount was i n t r o d u c e d . The s t e a d y s p r i n g r e a d i n g , u s u a l l y a t t a i n e d w i t h i n 4 t o 12 h o u r s a f t e r a i r e v a c u a t i o n , was t a k e n t o be t h e e q u i l i b r i u m v a l u e . T h i s was c o n f i r m e d b y r e p e t i t i o n , p a r t i a l d e s o r p t i o n a n d r e e q u i l i b r a t i o n and temperature c y c l e s . A V a r i a n XLFT-100 F o u r i e r T r a n s f o r m nmr S p e c t r o m e t e r i n t e r f a c e d w i t h a V a r i a n 620-L m i n i c o m p u t e r w i t h m a g n e t i c t a p e s t o r a g e provided high-resolution, proton-decoupled spectra o f natural a b u n d a n c e c a r b o n - 1 3 a t 25.2 MHz. F o r i d e n t i f i c a t i o n o f carbon p e a k s , c h l o r o f o r m - d s o l u t i o n s o f s u r f a c t a n t ( s o l u b i l i t y a b o u t 20 wt%) were p r e p a r e d . Chloroform-d also served f o ra deuterium f i e l d lock. S a m p l e s o f s u r f a c t a n t i n w a t e r o r d e c a n e were p l a c e d


3.

FRANSES E T

AL.

Alkyl

Aryl Sulfonate

39

Surfactant

i n 12 mm nmr t u b e s w i t h a c a p i l l a r y i n s e r t c o n t a i n i n g e i t h e r D2O o r a c e t o n e - d ^ as l o c k s o l v e n t . The c h e m i c a l s h i f t r e f e r e n c e s were TMS ( t e t r a m e t h y l s i l a n e ) i n c h l o r o f o r m - d a n d a c e t o n e - d ^ , and TSP ( 2 , 2 , 3 , 3 , t e t r a d e u t e r o - 3 ( t r i m e t h y l s i l y l ) - p r o p i o n i c a c i d s o d i u m s a l t , b y M e r c k , S h a r p and Dohme) i n D 0 . Same s a m p l e s ( S p e c t r a 1,2,5 and 6 shown b e l o w ) were p u t i n 5 mm NMR t u b e s and t h e n an e x t e r n a l l o c k on F was e m p l o y e d . The t r u e s p e c t r a l w i d t h was 5120 Hz ( o r 5656 H z ) , t h e a c q u i s i t i o n t i m e was 0.8s (or 0.727s, r e s p e c t i v e l y ) , and t h e s e n s i t i v i t y e n h a n c e m e n t t i m e c o n s t a n t was 0.8s. F o r m o s t s p e c t r a , t h e RF p u l s e w i d t h was 60 y s , c o r r e s p o n d i n g t o a 45° p u l s e f o r a l i p h a t i c c a r b o n s and a s m a l l e r one f o r a r o m a t i c s ; t h e e x c e p t i o n s a r e S p e c t r a 18 and 19, 100 y s , and S p e c t r u m 5, 113 y s . O r d i n a r i l y no p u l s e d e l a y was u s e d . The F o u r i e r t r a n s f o r m l e n g t h was a l w a y s 8192 w o r d s . S a m p l e s were s p u n a t a b o u t 20 Hz. 2


1 9

B i p h a s i c s o l u t i o n s were h o m o g e n i z e d by b a r - s t i r r i n g a f t e r l o a d i n g i n t o nmr t u b e s . S i n g l e - p h a s e , s u r f a c t a n t - r i c h samples were p r e p a r e d b y e q u i l i b r a t i n g s u r f a c t a n t c r y s t a l s i n s i d e t h e nmr t u b e s w i t h w a t e r o r d e c a n e v a p o r (200h f o r S p e c t r u m 6, 150h f o r S p e c t r u m 13) u n t i l w e i g h t r e m a i n e d c o n s t a n t . The temp e r a t u r e o f most o f t h e nmr s p e c t r a i s 3 7 ° C , t h e t e m p e r a t u r e t o w h i c h t h e s a m p l e s a r e h e a t e d by t h e RF power o f t h e d e c o u p l e r when t h e r e i s no t e m p e r a t u r e c o n t r o l . However, t e m p e r a t u r e was c o n t r o l l e d f o r one-phase systems. The number o f t r a n s i e n t s (T) and t e m p e r a t u r e s (°C) a r e r e p o r t e d b e l o w w i t h e a c h s p e c t r u m . S o l u t i o n r e s i s t a n c e s w e r e m e a s u r e d a t 1000 Hz w i t h an AC W h e a t s t o n e b r i d g e ; an HP 200 AB o s c i l l a t o r p r o v i d e d t h e i n p u t a t u n e d a m p l i f i e r w i t h a n u l l d e t e c t o r was u s e d t o f i n d t h e b r i d g e b a l a n c e ( w i t h s i m u l t a n e o u s r e s i s t a n c e and c a p a c i t a n c e balancing). A homemade c e l l w i t h P t e l e c t r o d e s was u s e d , s i m i l a r t o t h e one d e s c r i b e d i n R e f . 27a. The c e l l was calib r a t e d w i t h 0.10N NaCl s o l u t i o n s .

and

MATERIALS The s u r f a c t a n t i s t h e s o d i u m s a l t o f 8 - p h e n y l n - h e x a d e c y l p - s u l f o n a t e ( m o l e c u l a r w e i g h t 404.6 d a l t o n ) . One s a m p l e was g e n e r o u s l y p r o v i d e d by P r o f . W. H. Wade o f t h e U n i v e r s i t y o f Texas, A u s t i n . A n o t h e r b a t c h ( R e s e a r c h Sample 8727J) was k i n d l y p r o v i d e d b y C o n t i n e n t a l O i l Company, P o n c a C i t y , Oklahoma. T h i s 'Conoco s a m p l e was f o u n d t o c o n t a i n an i m p u r i t y i n s o l u b l e in chloroform. The c h l o r o f o r m e x t r a c t was e v a p o r a t e d and d r i e d i n a vacuum o v e n . The p u r i f i e d C o n o c o s a m p l e g a v e i d e n t i c a l 13c nmr s p e c t r a ( s e e F i g u r e 6 ) , t h e same UV a b s o r p t i o n maxima, and t h e same p o l a r i z i n g m i c r o s c o p e t e x t u r e s a s t h e T e x a s s a m p l e . The p h a s e b e h a v i o r and i n t e r f a c i a l t e n s i o n s w e r e s i m i l a r , a l t h o u g h n o t a l w a y s t h e same ( 1 0 ) . B e c a u s e t h e f i r s t s a m p l e was l i m i t e d i n amount, t h e Conoco s a m p l e was u s e d f o r some o f t h e e x p e r i m e n t s r e p o r t e d h e r e , a s i n d i c a t e d by a s t e r i s k s . Both a p p e a r e d t o be o f h i g h p u r i t y i n t h e l i g h t o f t h e s y n t h e s i s 1


CHEMISTRY OF

40

OIL

RECOVERY


1 3

method (8_,9) and their C nmr s p e c t r a , w h i c h e v i d e n c e d no c a r bon p e a k s o t h e r t h a n t h o s e a t t r i b u t a b l e t o t h e p r e s u m e d s t r u c t u r e (see F i g u r e 6 ) . The o r i g i n o f t h e y e l l o w i s h n e s s o f b o t h s a m p l e s was n o t i d e n t i f i e d . Spectroturbidimetry was c o n d u c t e d a t s u c h low c o n c e n t r a t i o n s ( λ > 350 nm. In t h i s range a b s o r p t i o n by t h e s u r f a c t a n t i s n e g l i g i b l e and a b s o r b a n c e i s due a l m o s t e x c l u s i v e l y t o s c a t t e r i n g . T h i s w a v e l e n g t h dependence c o r r e s p o n d s t o R a y l e i g h - D e b y e o r Mie s c a t t e r i n g (15), w h i c h i n d i c a t e s p a r t i c l e s i z e s g r e a t e r t h a n 0.1μ (14), w h e r e a s s m a l l e r p a r t i c l e s g i v e R a y l e i g h s c a t t e r i n g , w i t h w a v e l e n g t h d e p e n d e n c e Ι/λ^ (15).

(ii)

A b s o r b a n c e s t h o u g h c o n s t a n t o v e r measurement p e r i o d s o f h o u r s d e p e n d e d on t h e o r d e r o f m i x i n g , age, and t h e r m a l h i s t o r y o f s p e c i m e n s o f t h e same o v e r a l l composition.

(iii)

The t u r b i d i t y , i . e . s p e c i f i c a b s o r b a n c e due t o s c a t t e r i n g , (A-A k )/lc a t 436 nm was l a r g e r t h a n 15 c m / g . As e s t i m a t e d f r o m d a t a on s o d i u m d o d e c y l s u l f a t e (16), t h i s c o r r e s p o n d s t o many t h o u s a n d s o f s u r f a c t a n t m o l e c u l e s p e r p a r t i c l e i f a l l o f t h e s u r f a c t a n t i s a g g r e g a t e d and t h u s t o p r o p o r t i o n a t e l y more p e r p a r t i c l e i f o n l y a f r a c t i o n o f the 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 i s aggregated i n t o particles. I n any c a s e t h i s t u r b i d i t y i n d i c a t e s p a r t i c l e s c o n s i d e r a b l y l a r g e r than even the l a r g e s t r e p o r t e d e q u i l i b r i u m m i c e l l e s i n s i m i l a r systems ( l i b ) . When a b s o r b a n c e s had t o be m e a s u r e d a t l e s s t h a n 436 nm t h e r e s u l t s were e x t r a p o l a t e d t o 436 nm i n o r d e r t o a p p l y t h i s criterion. 2

a

s

r

R e p r e s e n t a t i v e r e s u l t s a r e shown i n T a b l e I and F i g u r e s 2 and 3. A t 0.014 and 0.025 wt% s u r f a c t a n t no s c a t t e r i n g was d e t e c t a b l e and t h e s e s y s t e m s s a t i s f i e d none o f t h e t h r e e criteria. F u r t h e r m o r e t h e i r s p e c i f i c a b s o r b a n c e s a t 300 nm were i n d e p e n d e n t o f c o n c e n t r a t i o n (so were t h e i r s p e c i f i c a b s o r b a n c e s a t t h e UV a b s o r p t i o n maxima ( 1 4 ) ) . I t was c o n c l u d e d that



FRANSES

ET AL.

Alkyl

Aryl Sulfonate

Surfactant

Figure 1. Photomicrograph (χΙΟΟ), with crossed polarizers, of liquid crystals produced by equilibrating dry surfactant crystals with 0.3 wt % aqueous solution of NaCl between two ghss slides. The appearance is the same at NaCl concentra tions from 0 to 1 wt %.

i.o 0.8

0.6

c

0.4 x Increasing Temperatures

0.2

0.0

•

Decreasing Temperatures

20

30

40

50

60

70

80

90

Temperature, C Figure 2. Temperature dependence of total absorbance at 600 nm over 1 cm path length of a biphasic dispersion of 0.70 wt % surfactant in water: bars indi cate fluctuations about average absorbance, which was steady for 2 hr or more; arrows indicate direction of temperature change.


CHEMISTRY

46

OF

OIL

RECOVERY

a b s o r b a n c e s o f t h e s e d i l u t e s y s t e m s were due t o a b s o r p t i o n a l o n e and c o u l d be u s e d t o c o r r e c t f o r a b s o r p t i o n i n a r r i v i n g a t t h e t u r b i d i t i e s (A-A^^/lc o f the h i g h e r c o n c e n t r a t i o n samples. The s a m p l e s w i t h 0.061, 0.14 and 0.70 wt% s u r f a c t a n t were t h u s f o u n d t o h a v e t u r b i d i t i e s a t 436 nm l a r g e r t h a n 15 c m / g . Moreover, t h e y showed w a v e l e n g t h d e p e n d e n c e w e a k e r t h a n Ι / λ . F o r example, a t 0.14 wt% t h e r a t i o o f t u r b i d i t i e s a t 350 and 700 nm i s 8 ± 2 i n comparison with (700/350) = 1 6 . So b y c r i t e r i a ( i ) and (iii) t h e s e systems a r e b i p h a s i c . The d i f f e r e n c e s i n t u r b i d i t y and i t s wave-length dependence i n t h e s e t h r e e systems r e f l e c t e d wide v a r i a t i o n s i n t h e mean and d i s t r i b u t i o n o f p a r t i c l e s i z e s ( 1 5 ) . I t s h o u l d be n o t e d t h a t t h e s p e c i m e n w i t h 0.061 wt% l o o k e d q u i t e transparent. 2

4


4

The d e p e n d e n c e o f t u r b i d i t y on t e m p e r a t u r e and t h e r m a l h i s t o r y i s shown i n F i g u r e 2 f o r 0.70 wt% s u r f a c t a n t , w h i c h i s c o m p l e t e l y d i s s o l v e d a t 9 0 ° C , and i n F i g u r e 3 f o r 0.14 wt%, w h i c h i s c o m p l e t e l y d i s s o l v e d a t 45°C. A f t e r a s t e p i n c r e a s e i n tem p e r a t u r e , a v e r a g e a b s o r b a n c e r e q u i r e d a few h o u r s t o become s t e a d y , w h e r e a s a f t e r a s t e p d e c r e a s e t h e t i m e r e q u i r e d was f r o m 5 t o 48h. O c c a s i o n a l l y the absorbance would f l u c t u a t e around a steady average v a l u e . T h i s i s i n d i c a t e d i n F i g u r e 2 by b a r s . F l u c t u a t i o n s a r o s e f r o m v a r y i n g s c a t t e r e r amount i n t h e v o l u m e t r a v e r s e d b y t h e l i g h t beam. S o l u b i l i t i e s were d e t e r m i n e d by a p p l y i n g t h e f o r e g o i n g c r i t e r i a t o a s p e c i m e n drawn f r o m t h e u p p e r m o s t l a y e r o f e a c h s y s t e m a f t e r i t had b e e n s t i r r e d w e l l (by m a g n e t i c s t i r r i n g b a r ) and a l l o w e d t o s e t t l e f o r two d a y s o r more. T a b l e I I summarizes the r e s u l t s : the v a l u e s l i s t e d are the h i g h e s t c o n c e n t r a t i o n s a t w h i c h a s e c o n d p h a s e was n o t d e t e c t e d b y e a c h o f t h e methods listed. When a s e c o n d p h a s e h a d p r e c i p i t a t e d , c o n c e n t r a t i o n s were d e t e r m i n e d by UV a b s o r p t i o n . The e f f e c t o f t h e o r d e r o f m i x i n g o f s u r f a c t a n t and s a l t i n w a t e r was f o l l o w e d w i t h s p e c i a l a t t e n t i o n b e c a u s e o f a c o r r e s p o n d i n g e f f e c t on t h e i n t e r f a c i a l t e n s i o n o f r e s u l t i n g s y s t e m a g a i n s t a d r o p o f d e c a n e (10) . F i g u r e 4 shows t h e t i m e d e p e n d e n c e of t o t a l absorbance a t s e v e r a l wavelengths, o f a system which i s b i p h a s i c i n e q u i l i b r i u m a f t e r t h e s a l t c o n c e n t r a t i o n was r a i s e d f r o m 0 t o 0.3 wt%. T u r b i d i t y c o n t i n u e d t o r i s e f o r 80h, e s p e c i a l l y a t lower wavelengths, a t which s c a t t e r i n g i s s t r o n g e r . A l t h o u g h t h e s y s t e m b e g a n s e t t l i n g a f t e r 80h, t h e t u r b i d i t y c o n t i n u e d i n c r e a s i n g f o r a week, and i t a l s o c o n t i n u e d t o i n c r e a s e after ultrafiltration. Ultracentrifugation

and U l t r a f i l t r a t i o n

Tests

T a b l e s I I I , IV, and V show u l t r a v i o l e t a b s o r p t i o n - b a s e d d e t e r m i n a t i o n s o f c o n c e n t r a t i o n s a f t e r c e n t r i f u g a t i o n (C), u l t r a c e n t r i f u g a t i o n (UC) and u l t r a f i l t r a t i o n ( U F ) . The e f f e c t o f t h e o r d e r o f m i x i n g on s i z e o f d i s p e r s e d p a r t i c l e s , a s e v i d e n c e d b y d i f f e r e n t r e s p o n s e s t o t h e same t r e a t m e n t , i s p l a i n i n T a b l e I I I .


3.

FRANSES E T A L .

Alkyl

Aryl Sulfonate

47

Surfactant

0.4 r x,+ Increasing Temperatures

? 0.3h ΓΟ

•

Decreasing Temperatures


0.2 h

ο.ι O.OL

10

20

30

40

50

60

70

80

Temperature, °C Figure 3. Temperature dependence of total absorbance at 340 nm over 1 cm path length of a biphasic dispersion of 0.14 wt % surfactant in water: each point is the steady value observed for 2 hr or longer; arrows indicate direction of tem perature change.

ive,

h

Figure 4. Time dependence of absorb ance over 1 cm path length at several wavelengths, of precipitating surfactant system of 0.070 wt % surfactant and 0.30 wt % NaCl in water, prepared by adding 3.0 wt % NaCl solution in time zero to 0.077 wt % surfactant in water (transparent). The initial total absorb ance is predominantly by absorption, the increase by scattering from the separat ing phase.

American Chemical Society Library 1155 16th St. N. W. In Chemistry of Oil Recovery; R., et al.; Washington, D.Johansen, C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

CHEMISTRY O F OIL RECOVERY


48

Table I I .

Temperature °C

NaCi. wt%

S o l u b i l i t y (wt%) o f s u r f a c t a n t i n water and s a l t water as determined by d i f f e r e n t c r i t e r i a

Criteria Spectroturbidimetry

c

Visual

Microscopy

25

0

0.10-0.14

0.06

30

0

0.1

3

0.10

45

0

0.2

2

0.14

60

0

90

0

°· ι

0.23

0.7

0.70

3

5

25

0. 30

Phase Behavior of a Pure Alkyl Aryl Sulfonate Surfactant - ACS

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