Chapter 17
Recovery of a Dialkyl Diphenyl Ether Disulfonate Surfactant from Surfactant Flush Solutions by Precipitation 1
Yuefeng Yin, John F. Scamehorn , and Sherril D. Christian
Downloaded by UNIV OF MINNESOTA on June 13, 2013 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0594.ch017
Institute for Applied Surfactant Research, University of Oklahoma, Norman, OK 73019
Surfactant precipitation i s one method of separating and concentrating surfactant for reuse from a subsurface surfactant-based remediation process. One class of surfactants which has been shown to be very effective in this application i s d i a l k y l d iphenylether disulfonates. In this work, the precipitation and coacervation phase boundaries for a surfactant mixture which i s primarily didecyldiphenylether disulfonate as a function of concentration of added NaCl and KCl are reported. The Krafft temperature (lowest temperature at which precipitation occurs) i s only mildly affected by the added electrolyte. The fraction of surfactant precipitated i s shown to be r e l a t i v e l y small except at very high added electrolyte levels. The rate of precipitation i s slow except at very high added electrolyte levels; e.g., more than a week i s sometimes required for e q u i l i b r a t i o n . One of the most attractive aspects of these surfactants for use in subsurface remediation i s their low tendency to precipitate. This i s a disadvantage when precipitation i s necessary for surfactant recovery.
In order f o r surfactant-enhanced subsurface remediation o p e r a t i o n s t o be an economic s o l u t i o n t o s o i l contamination, recovery of the s u r f a c t a n t f o r reuse i s necessary (1). P r i o r t o s e p a r a t i n g the organic or i o n i c p o l l u t a n t from the s u r f a c t a n t , these components can be concentrated i n the
1
Corresponding author
0097-6156/95A)594-O231$12.00A) © 1995 American Chemical Society
In Surfactant-Enhanced Subsurface Remediation; Sabatini, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
232
SURFACTANT-ENHANCED SUBSURFACE REMEDIATION
flush s o l u t i o n using micellar-enhanced ultrafiltration (MEUF) (2z4). In MEUF the s o l u t i o n i s t r e a t e d by u l t r a f i l t r a t i o n w i t h membrane pore s i z e s small enough t o b l o c k the passage of m i c e l l e s with s o l u b i l i z e d organic p o l l u t a n t s or bound i o n i c contaminants (of opposite charge t o t h a t of the surfactants). The permeate s o l u t i o n p a s s i n g through the membrane can be r e i n j e c t e d i n t o the a q u i f e r s i n c e i t contains low s u r f a c t a n t c o n c e n t r a t i o n s . The retentate s o l u t i o n not p a s s i n g through the membrane can be t r e a t e d t o separate the s u r f a c t a n t from the p o l l u t a n t t o permit reuse of the s u r f a c t a n t . A t y p i c a l r e t e n t a t e s o l u t i o n contains about 0.3 M s u r f a c t a n t , s i n c e above t h a t concentration, c o n c e n t r a t i o n p o l a r i z a t i o n causes f l u x through the membrane t o be unacceptably low. For nonionic surfactants, an a l t e r n a t i v e t o MEUF i s t o heat the s o l u t i o n above the c l o u d p o i n t where the s o l u t i o n phase separates i n t o a dense coacervate s o l u t i o n c o n t a i n i n g a high c o n c e n t r a t i o n of s u r f a c t a n t and p o l l u t a n t and a d i l u t e s o l u t i o n which can be r e i n j e c t e d (5). There are s e v e r a l options f o r t h i s r e t e n t a t e (or coacervate) treatment step which are h i g h l y dependent on the nature of the s u r f a c t a n t and the p o l l u t a n t . (A) : An i o n i c s u r f a c t a n t can be p r e c i p i t a t e d by a d d i t i o n of e l e c t r o l y t e or r e d u c t i o n of temperature. This s u r f a c t a n t can then be separated by f i l t r a t i o n , c e n t r i r r i g a t i o n , or g r a v i t y s e t t l i n g . The s u r f a c t a n t can then be r e d i s s o l v e d f o r reuse. The p o l l u t a n t may phase separate i n t o a separate l i q u i d phase which can be skimmed o f f as i t s s o l u b i l i t y decreases as the s u r f a c t a n t i s removed from s o l u t i o n upon p r e c i p i t a t i o n . I f the p o l l u t a n t forms a dense l i q u i d phase or a dense p r e c i p i t a t e , t h i s technique i s not e f f e c t i v e . T h i s method i s d i s c u s s e d f o r a s p e c i f i c s u r f a c t a n t i n t h i s paper and has been analyzed f o r other s u r f a c t a nts i n other p u b l i c a t i o n s (6.7). (B) : I f the p o l l u t a n t i s a v o l a t i l e organic s o l u t e , the r e t e n t a t e can be vacuum, a i r , or steam s t r i p p e d (4.8.9) . In t h i s case, the p o l l u t a n t i s removed overhead from the s t r i p p e r and i s condensed f o r d i s p o s a l as a l i q u i d or f e d d i r e c t l y t o an i n c i n e r a t i o n u n i t . The bottoms stream from the s t r i p p e r contains the s u r f a c t a n t i n concentrated form, which can be d i r e c t l y reused. (C) : I f the p o l l u t a n t i s a metal or m e t a l l i c complex (e.g., z i n c or chromate), e l e c t r o l y t e can be added t o s o l u t i o n or the pH adjusted t o cause the p o l l u t a n t t o be p r e c i p i t a t e d from s o l u t i o n . A f t e r removal of the s o l i d p r e c i p i t a t e f o r d i s p o s a l , the remaining s u r f a c t a n t s o l u t i o n can be reused. (D) : An organic e x t r a c t a n t phase can be contacted w i t h the r e t e n t a t e t o e x t r a c t the p o l l u t a n t or a l t e r n a t i v e l y the surfactant. The solvent requires regeneration (e.g., d i s t i l l a t i o n ) f o r reuse. Back e x t r a c t i o n of the s o l v e n t i n t o the aqueous s o l u t i o n i s a l s o of concern, p a r t i c u l a r l y
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In Surfactant-Enhanced Subsurface Remediation; Sabatini, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Downloaded by UNIV OF MINNESOTA on June 13, 2013 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0594.ch017
17.
YIN ET AL.
Recovery of α Dialkyl Diphenyl Ether Disulfonate Surfactant
i f s u r f a c t a n t i s l e f t i n t h i s aqueous s o l u t i o n t o allow m i c e l l a r s o l u b i l i z a t i o n of the s o l v e n t . S u r f a c t a n t p r e c i p i t a t i o n would be the most g e n e r a l l y a p p l i c a b l e of these methods s i n c e i t i s not as a f f e c t e d by the nature of the p o l l u t a n t and mixed o r g a n i c / i o n i c p o l l u t ants could be t r e a t e d . I t i s p a r t i c u l a r l y desirable to produce l a r g e , dense p r e c i p i t a t e c r y s t a l s which s e t t l e out of s o l u t i o n r e a d i l y so t h a t inexpensive g r a v i t y s e t t l e r s can be used t o remove the c r y s t a l s from the s o l u t i o n . Use of d i v a l e n t counterions (e.g., calcium f o r a n i o n i c s u r f a c t a n t s ) tends t o l e a d t o c o l l o i d a l p r e c i p i t a t e (6.10), so t h i s work has emphasized monovalent counterions. A new c l a s s of s u r f a c t a n t s r e f e r r e d t o as "Gemini" s u r f a c t a n t s (11-14) have the c h a r a c t e r i s t i c s of a hydrocar bon chain, an i o n i c group, a spacer, a second i o n i c group, and another hydrocarbon t a i l . The l i n e a r d i d e c y l d i p h e n y l e t her d i s u l f o n a t e (C10-DADS) used here i n v o l v e an ether oxygen as a f l e x i b l e spacer. The d i a l k y l d i p h e n y l e t h e r d i s u l f o n a t e s have been shown t o e x h i b i t e x c e l l e n t p r o p e r t i e s f o r subsur face remediation, i n c l u d i n g a low tendency t o p r e c i p i t a t e and a low adsorption onto s o i l s (15) . These s u r f a c t a n t s have a l s o been shown t o be very promising f o r use i n groundwater remediation u s i n g MEUF (4) . Therefore, this work i n v e s t i g a t e s the use of p r e c i p i t a t i o n t o recover a t y p i c a l s u r f a c t a n t from t h i s c l a s s from aqueous s o l u t i o n . Experimental M a t e r i a l s . The s u r f a c t a n t used i n t h i s work was a r e s e a r c h sample s u p p l i e d by Dow Chemical Company (XU40490.75). T h i s sample was concentrated i n C10-DADS, the primary component i n the commercial product DOWFAX 3B2. The sample was r e p o r t e d t o c o n t a i n 28.5 wt. % C10-DADS, 2 wt. % monoalkyldi p h e n y l e t h e r d i s u l f o n a t e , and 1 % other s u r f a c t a n t s (other isomers, homologues, monosuifonates, etc.) which were u n s p e c i f i e d , 1.1 wt. % Na S0 , and water making up the remainder. The a l k y l a t i o n was r e p o r t e d as >98% pure and 96.5 % of the sulf©nation product were d i s u l f o n a t e s . The samples were d e s a l t e d (99.3 % removal of NaCl and Na S0 ) u s i n g u l t r a f i l t r a t i o n with a membrane of molecular weight c u t - o f f of 500 Daltons (small enough t o block the s u r f a c t a n t monomer as w e l l as m i c e l l e s ) a t 40°C. Sodium chloride and potassium c h l o r i d e were reagent grade. Since these m a t e r i a l s were hygroscopic, both c r y s t a l s were d r i e d i n a oven at 240°C for s i x hours f o r dehydration. Water used i n a l l the experiments was double d e i o n i z e d and t r e a t e d by a carbon filter. 2
4
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Methods. To determine the K r a f f t temperature, s u r f a c t a n t sample s o l u t i o n s at concentrations above the CMC were f i r s t subcooled long enough t o allow p r e c i p i t a t i o n t o occur. The
In Surfactant-Enhanced Subsurface Remediation; Sabatini, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
233
In Surfactant-Enhanced Subsurface Remediation; Sabatini, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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Downloaded by UNIV OF MINNESOTA on June 13, 2013 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0594.ch017
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17. YIN ET AL
Recovery ofa Dialkyl Diphenyl Ether Disulfonate Surfactant 235
temperature was then r a i s e d i n c r e m e n t a l l y w i t h t h e i n t e r v a l about 2°C when T
