bk-1979-0091.ch004

4

Colloidal Properties of S o d i u m Carboxylates

1

W. H. BALDWIN and G. W. NEAL

2

Downloaded by UNIV OF MELBOURNE on January 17, 2016 | http://pubs.acs.org Publication Date: March 2, 1979 | doi: 10.1021/bk-1979-0091.ch004

Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830

Tall oils are obtained in large quantity from the pulping of soft woods to make paper. Hoyt and Goheen (l) state that in 1964 the yield of fatty and rosin acids exceeded 400, 000 tons. Tall oil contains about 94% total acids and 6% alcohols. The fatty acid fraction contains oleic ~ 24% and linoleic ~ 23%, of which ~4%is conjugated linoleic of the t a l l o i l . The rosin acid fraction contains abietic acid ~ 14% and related acids 33% of the total (2). An extensive literature on general aspects of the colloidal chemistry of compounds in this class is available (see, for example, references 3, 4, 5, and 6). The large supply of t a l l oils and the well-known surface properties of many of the components have led to several suggestions to use them or their derivatives in micellar flooding (7,8, 9). However, there are, so far as we know, no extensive laboratory investigations underway nor plans to test these possibilities in the field. In view of the contribution t a l l oils might make to enhanced recovery i f they could be used, a survey of interfacial tension properties of aqueous/hydrocarbon systems, similar to those which have become common with the petroleum sulfonate and other surfactants under consideration for micellar floods, seemed worthwhile. The recent popularity of interfacial tension measurements is largely attributable to the development of the spinning drop approach into a practical technique by Cayias, Schechter, and Wade (10). Gash and Parrish (11) have increased the utility of the method by designing a variation that is capable of making measurements with several samples simultaneously, with the sacrifice of accuracy of the Cayias, Wade, and Schechter device in some ranges of interfacial tensions, because of the constraint of a single rotational velocity. In the work described here, sodium oleate was selected as 1

Current Address: Rt. 1, Erie, TN

2

Current Address: Apt. #12, 585 E. Parkway S., Memphis, TN This chapter not subject to U.S. copyright. Published 1978 American Chemical Society In Chemistry of Oil Recovery; Johansen, Robert T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

CHEMISTRY

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O F OIL RECOVERY

the model f o r i n t e n s i v e study o f s e v e r a l v a r i a b l e s , and other carboxylates have been included t o i n d i c a t e the e f f e c t o f s t r u c ture .


Experimental The a c i d s : (Figures 1 & 2) 95 and 99% o l e i c , 95% l i n o l e i c , 99% l i n o l e n i c , 99% e l a i d i c and c h o l i c acids "were obtained from chemical supply houses. Mixed r o s i n acids were a commercial pro duct, A c i n t o l R type S (2_). Sodium s a l t s o f f a t t y acids were formed by e l e c t r o m e t r i c t i t r a t i o n o f an aqueous-ethanol s o l u t i o n with sodium hydroxide, evaporated t o dryness t o remove ethanol and stored dry or as an aqueous stock s o l u t i o n . A sample o f mixed r o s i n acids was assayed e l e c t r o m e t r i c a l l y with potassium hydroxide i n benzene-ethanol. A stock s o l u t i o n was then p r e pared i n water from a weighed q u a n t i t y o f A c i n t o l R and the amount o f sodium hydroxide c a l c u l a t e d from t h e assay. Other m a t e r i a l s were reagent grade chemicals. I n t e r f a c i a l t e n s i o n measurements were made on one or both o f the devices mentioned ( 1 0 , 1 1 ) . Spinning o f the samples was con t i n u e d u n t i l successive readings were constant; u s u a l l y 2h hours was s u f f i c i e n t . A l l measurements were made at 30°C. P l o t s o f equivalent alkane number versus i n t e r f a c i a l t e n s i o n were made with pure n-alkanes - no mixtures were used i n r e s u l t s r e p o r t e d here. P r e c i s i o n o f Measurements. A l i q u o t s from a stock s o l u t i o n of 0 . 1 M sodium o l e a t e ( f i v e months old) were used t o prepare aqueous t e s t s o l u t i o n s that were 0 . 0 1 M i n sodium o l e a t e and 0 . 1 M i n sodium c h l o r i d e pH 9 · 5 . I n t e r f a c i a l tensions were measured against n-undecane without p r e - e q u i l i b r a t i o n . The second s o l u t i o n was made and measured one week a f t e r t h e f i r s t and the t h i r d s o l u t i o n two weeks a f t e r the f i r s t . The r e s u l t s i n Table I Table I P r e c i s i o n o f I n t e r f a c i a l Tension Measurements 0 . 0 1 M Sodium Oleate, 0 . 1 M Sodium Chloride pH 9 - 5 vs η-Undecane

Multi-drop constant velocity

I n t e r f a c i a l Tension (dynes/cm) Run I Run I I 0.065 0.1U0 0.058 0.070 0.085 0.068 0.062 0.068 0.070 0.077 0.068 ± 0.009 0 . 0 8 5 ± 0.022 0.098 0.09^

Run I I I 0.062 0.05Ma) 0.062 0.080(a) 0.068 0.06k ± 0.003(b)

Avg O.O8O Single-drop variable velocity Avg. 0 . 0 9 1 ± 0 . 0 0 7 (a) A i r bubbles appeared. Results d i s c a r d e d . (b) The range i s the average d e v i a t i o n from the mean.

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

BALDWIN

AND NEAL

Sodium

FATTY

Carboxylates

ACID

STRUCTURES

OLEIC ACID

c=c CH (CH )/ 3

s

2

(CH ) C00H 2

7

ELAIDIC ACID H /(CH ) C00H N

CH (CH )


3

2

2

7

H

7

LINOLEIC ACID H

,Η H

v

/=c CH (CH ) 3

2

Jn

N

c=c

CH/

4

(CH ) C00H 2

7

LINOLENIC ACID

CH CH 3

C=C N 2

C=C CH/ CH

Figure 1.

V

C=C ( C H ) COOH S

2

2

7

Fatty acid structures

CYCLIC CARBOXYLIC ACIDS ABIETIC ACID

Figure 2.

Cyclic carboxylic acids


78

CHEMISTRY

OF

OIL

RECOVERY

i n d i c a t e a l o v e r average obtained -with the multisample apparatus than with the single-sample u n i t , although s c a t t e r i n the two sets overlapped. Most p o i n t s f a l l w i t h i n ±0.02 dynes/cm of the o v e r a l l average, or w i t h i n about 30%. Although the u n c e r t a i n t y appears l a r g e , the accuracy i s nevertheless adequate t o i d e n t i f y c o n d i t i o n s corresponding t o the m i l l i d y n e values favorable f o r enhanced o i l recovery. These low i n t e r f a c i a l tensions t y p i c a l l y occur only f o r a narrow range of compositions, outside which t e n sions are orders o f magnitude higher than the minimum value.


Results 1. E f f e c t o f Surfactant Concentration. Figure 3 compares r e s u l t s of alkane scans f o r three concentrations of sodium o l e a t e at constant sodium c h l o r i d e concentration and pH. The 0.002 M s o l u t i o n i s derived from 95% o l e i c a c i d , the 0.01 M and the 0.1 M s o l u t i o n s are d e r i v e d from 99% o l e i c a c i d . Both the magnitude and the alkane p o s i t i o n of minimum i n t e r f a c i a l t e n s i o n (n^ = 11) are e s s e n t i a l l y concentration independent under these c o n d i t i o n s . Wade, et a l (12) reported a s i m i l a r i n v a r i a n c e i n n^ with a pure a l k y l benzene s u l f o n a t e , although there was more change i n the minimum value of i n t e r f a c i a l t e n s i o n with the s u l f o n a t e concen t r a t i o n than i s observed w i t h the carboxylate. The i n t e r f a c i a l t e n s i o n at n^ f o r 0.01 M sodium o l e a t e i s i n the range of the values of Table I . Very high i n t e r f a c i a l t e n s i o n (> 10 dynes/cm) was found at 0.0001 M sodium o l e a t e i n 0.1 M sodium c h l o r i d e . T h i s presumably r e f l e c t s the f a c t that the s u r f a c t a n t concentra t i o n i s almost c e r t a i n l y below the c r i t i c a l m i c e l l e concentra t i o n (13). 2. E f f e c t of Sodium Chloride Concentration. Figure k com pares i n t e r f a c i a l tensions o f s e v e r a l d i f f e r e n t s u r f a c t a n t con c e n t r a t i o n s verses n-undecane i n the presence of 0.1 M sodium c h l o r i d e with values obtained without s a l t . S a l t reduces the i n t e r f a c i a l t e n s i o n at a l l s u r f a c t a n t concentrations. Aqueous potassium oleate has a c r i t i c a l m i c e l l e concentration of ^0.001 M (13). I t could be i n f e r r e d from F i g u r e k that 0.001 M sodium o l e a t e with no added s a l t i s below the cmc, because o f the high i n t e r f a c i a l t e n s i o n . I f so, the much lower i n t e r f a c i a l t e n s i o n i n the presence of 0.1 M sodium c h l o r i d e stems from r e d u c t i o n o f the cmc expected i n the presence of added s a l t (ΐΛ). In Figure U , i n t e r f a c i a l tensions at 0.01 and 0.1 M sodium o l e a t e and 0.1 M sodium c h l o r i d e are higher than i n Figure 3. However, the d e s i r e d s u r f a c t a n t concentration i n Figure h was ob t a i n e d by d i s s o l v i n g the r e q u i r e d q u a n t i t y of sodium o l e a t e and pH was not c o n t r o l l e d . Data from F i g u r e k are not d i r e c t l y com parable to F i g u r e 3 f o r t h i s reason. Table I I i l l u s t r a t e s the e f f e c t of v a r y i n g the sodium c h l o r ide concentration on i n t e r f a c i a l t e n s i o n f o r one s u r f a c t a n t con c e n t r a t i o n . Between 0.01 and 0.2 M sodium c h l o r i d e there appears to be a small decrease i n i n t e r f a c i a l t e n s i o n . Increasing the


BALDWIN AND NEAL

Sodium

Ί

Carboxylates

I

I

79

I

I

0.1 M SODIUM CHLORIDE, pH = 9.5 1 \—

-

• A •

0.5

0AM SODIUM OLEATE 0 . 0 1 S O D I U M OLEATE 0.002/tf SODIUM OLEATE


0.2

0.1 μ \ !7 Λ

0.05

8

9 10 11 12 13 EQUIVALENT A L K A N E CARBON NUMBER

Figure 3.

Interfacial tension—sodium oleate

I I I 1111

Ί—I

1—I A

I 10

10

3

1—I

I I I 1111

τη

Γ

SODIUM O L E A T E , OAM SODIUM CHLORIDE vs n - U N D E C A N E

•

SODIUM OLEATE vs n-UNDECANE

•

T R S 1 0 - 8 0 , OMM vs n-UNDECANE

I

I I I Mil

-4

I I I 111J

I I I 1111 10

ι

SODIUM CHLORIDE

I I I I ml

2

ι

ι

10"

M O L A R I T Y OF S U R F A C T A N T Figure 4.

Interfacial tension—concentration of surfactant


I I I Ml 10"

CHEMISTRY

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O F OIL RECOVERY

sodium c h l o r i d e concentration much above 0 . 2 M leads t o g e l f o r mation (15.). Table I I I n t e r f a c i a l Tension 0.1

M Sodium Oleate, pH 1 0 . U , vs n-undecane

Sodium C h l o r i d e (m/l) 0.01 0.1 0.2 Downloaded by UNIV OF MELBOURNE on January 17, 2016 | http://pubs.acs.org Publication Date: March 2, 1979 | doi: 10.1021/bk-1979-0091.ch004

as a Function o f Sodium Chloride

I n t e r f a c i a l Tension (dynes/cm) 0.33 0.26 0.23

Measurements with a commercial petroleum sulfonate surfactant are included i n Figure h f o r comparison with sodium o l e a t e . 3. E f f e c t o f pH. A l k y l c a r b o x y l i c acids are weak e l e c t r o l y t e s , the d i s s o c i a t i o n constant i n general becoming smaller with i n c r e a s i n g molecular weight. I t t h e r e f o r e seemed appropriate t o determine the e f f e c t o f the pH o f the aqueous s o l u t i o n on i n t e r f a c i a l tension. Figure 5 summarizes the r e s u l t s f o r two concentrations o f sodium o l e a t e o f varying the pH on i n t e r f a c i a l t e n s i o n . One trend i s that the lower the s o l u t i o n pH the lower the i n t e r f a c i a l t e n s i o n . Harkins et a l ( l 6 ) have demonstrated that the i n t e r f a c i a l t e n s i o n between benzene and aqueous sodium oleate i s lower when the benzene l a y e r contains o l e i c a c i d . Since the p a r t i t i o n coe f f i c i e n t o f o l e i c a c i d between alkane and aqueous sodium o l e a t e g r e a t l y favors the alkane phase (lT)> any o l e i c a c i d from hydrolys i s would tend t o p a r t i t i o n i n t o the alkane phase. Thus lowering the s o l u t i o n pH would consequently increase the concentration o f o l e i c a c i d i n the alkane phase and b r i n g about lower i n t e r f a c i a l tension. Another t r e n d i n Figure 5 i s that the 0 . 0 1 M sodium o l e a t e i s more s e n s i t i v e t o pH e f f e c t s than the 0 . 1 M sodium o l e a t e . M a n s f i e l d (17) found that an aqueous s o l u t i o n o f high i o n i c strength or o f high pH i n h i b i t e d the t r a n s f e r o f o l e i c a c i d from p a r a f f i n o i l t o the a l k a l i n e aqueous phase. The higher i n t e r f a c i a l tensions o f the 0 . 0 1 M sodium o l e a t e s o l u t i o n s i n comp a r i s o n with 0 . 1 M sodium o l e a t e at pH above 1 0 . 5 may r e f l e c t a lower concentration and i o n i c strength. Or i f , as M a n s f i e l d suggests, k i n e t i c s o f t r a n s f e r between phases at high pH i s slow, e q u i l i b r i u m may not have been reached i n these experiments. In Table I I I the r e s u l t s of adding excess a c i d t o sodium o l e a t e s o l u t i o n s are given. These data are not d i r e c t l y comparable t o Figure 5 since the aqueous phase contains cosolvent and the s o l u t i o n s were p r e e q u i l i b r a t e d before t e s t i n g . However, the trend t o lower i n t e r f a c i a l t e n s i o n with i n c r e a s i n g a d d i t i o n s o f o l e i c a c i d (and thus lower pH) i s p a r a l l e l t o Figure 5-


4.

BALDWIN AND NEAL

Sodium

Carboxylates

81

Table I I I I n t e r f a c i a l Tension as a Function 0.01

o f Added O l e i c A c i d

M Sodium Oleate, 0 . 1 M Sodium C h l o r i d e ,

5% I s o b u t y l A l c o h o l P r e - e q u i l i b r a t e d with


Equal Volume o f n-undecane O l e i c A c i d Added (m/l aqueous) 0 0.001 0.002 0.005 0.008 0.01

I n t e r f a c i a l Tension (dynes/cm) 0.65 0.53 0.U2 0Λ8 0.32 0.23

h. E f f e c t s of A l c o h o l s . Alcohols are common a d d i t i v e s t o many surfactant formulations being considered f o r o i l recovery. Wade ( 1 2 ) has studied the e f f e c t o f a l c o h o l a d d i t i o n s on i n t e r f a c i a l p r o p e r t i e s and phase behavior f o r pure a l k y l benzene sulfonates. S a l t e r ( l 8 ) d i v i d e s the alcohols i n t o three main groups on the b a s i s o f t h e i r o i l / w a t e r s o l u b i l i t y . Isopropyl a l c o h o l i s o f the water s o l u b l e group, i s o b u t y l a l c o h o l i s of the intermediate group, and 2-hexanol i s o f the o i l s o l u b l e group. Table IV gives some r e s u l t s f o r a l c o h o l s of each c l a s s . No strong e f f e c t was seen. We have p r e v i o u s l y reported (15.) on the a b i l i t y o f a l c o hols t o reduce the v i s c o s i t y o f sodium oleate g e l s . Table IV E f f e c t o f Added Alcohols Sodium Oleate, 0 . 1 M Sodium C h l o r i d e , pH 1 0 Λ vs. n-undecane Sodium Oleate (m/l) 0.01 0.1

Co-Solvent (% aqueous) None 5% I s o b u t y l a l c o h o l None 1% Isopropyl a l c o h o l 1% 2-Hexanol

I n t e r f a c i a l Tension (dynes/cm) 0.19 0.62 0.26 0.33 0.17

5. E f f e c t of Unsaturation. Alkane scans f o r C-^q c a r b o x y l i c a c i d s a l t s are compared i n Figure 6 . The alkane p o s i t i o n o f m i n i mum i n t e r f a c i a l t e n s i o n (n^) increases with the degree o f unsatu ration. Increasing i n t e r f a c i a l tensions are found i n the order o l e a t e , l i n o l e n a t e , l i n o l e a t e . Sodium s t e r e a t e , the corresponding


CHEMISTRY

O F OIL RECOVERY

g en 0.01 /tf SODIUM OLEATE, 0.1 M SODIUM CHLORIDE, VS n-UNDECANE


< ο

0.1 M SODIUM OLEATE, 0.1 /tf SODIUM CHLORIDE, VS n-UNDECANE

bk-1979-0091.ch004

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