21 Micellar Solubilization of Methanol and Triglycerides
Downloaded by PENNSYLVANIA STATE UNIV on February 16, 2013 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch021
A. W. Schwab and Ε. H . Pryde Northern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL 61604
Micellar and pre-micellar solutions of methanol in triolein were studied with three different surfactant systems using 2-octanol as a co-surfactant. Surfactants evaluated by viscosity, conductivity, density, refractive index and particle size data along with polarizing microscopic examinations were bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate and tetradecyldimethylammonium linoleate. Data show phase equilibria regions of liquid crystalline phases as well as micellar solutions. All systems were effective for solubilizing methanol in triolein. The order of effectiveness for water tolerance is: Tetradecyldimethylammonium linoleate> Bis(2-ethylhexyl) sodium sulfosuccinate> Triethylammonium linoleate Micelles and microemulsions, terms perhaps unfamiliar to the American farmer, are important to his needs for an emergency fuel derivable from agriculturally renewable resources to run his direct injection diesel engine during planting and harvesting seasons. Unfortunately, vegetable oils such as soybean and safflower oils as such are not entirely satisfactory fuels, partly because of their incomplete combustion, but mainly because of their high viscosities (1). Research at the Northern Regional Research Center has been directed toward lowering the viscosity by micro-emulsification of vegetable oil with other materials to form hybrid fuels. Previously, we have reported on triglyceride-aqueous ethanol microemulsions (2) and triglyceride-methanol microemulsions (3). These were nonionic systems, and we have now extended our studies to include ionic and known micellar systems. Micelle formation of bis (2-ethylhexyl) sodium sulfosuccinate in water is well documented. In polar solvents such as methanol, however, it has been generally assumed that micellization either does not This chapter not subject to U.S. copyright. Published 1986, American Chemical Society
In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Downloaded by PENNSYLVANIA STATE UNIV on February 16, 2013 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch021
284
P H E N O M E N A IN M I X E D S U R F A C T A N T S Y S T E M S
o c c u r o r , i f i t does, t h e a g g r e g a t i o n number i s v e r y s m a l l ( 4 ) . One o f our o b j e c t i v e s i s t o s t u d y m i c e l l i z a t i o n i n b o t h methanol and 2 - o c t a n o l . F r i b e r g (5) has n o t e d t h a t m i c e l l a r s o l u t i o n s do not m e r i t t h e name m i c r o e m u l s i o n s . Among t h e systems s t u d i e d were b i s ( 2 - e t h y l h e x y l ) sodium s u l f o s u c c i n a t e , triethylammonium l i n o l e a t e and tetradecyldimethylammonium l i n o l e a t e u s i n g 2 - o c t a n o l as a co-surfactant. This s e l e c t i o n represents three d i f f e r e n t classes o f s u r f a c t a n t s . B i s ( 2 - e t h y l h e x y l ) sodium s u l f o s u c c i n a t e , commonly r e f e r r e d t o as A e r o s o l OT, i s o f t h e a n i o n i c t y p e which c a r r i e s a sodium c a t i o n . T h i s p a r t i c u l a r s u r f a c t a n t would n o t be recommended f o r use i n a d i e s e l engine because o f i t s p o t e n t i a l a s h d e p o s i t . Triethylammonium l i n o l e a t e i s a l s o an a n i o n i c type s u r f a c t a n t , and the h y d r o p h o b i c m o i e t y i s d e r i v a b l e from a g r i c u l t u r e r e s o u r c e s and the c a t i o n i s an o r g a n i c amine which s h o u l d n o t c r e a t e a p o t e n t i a l ash problem. Tetradecyldimethylammonium l i n o l e a t e was i n c l u d e d because i t r e p r e s e n t s a new c l a s s o f d o u b l e - c h a i n s u r f a c t a n t s . I n a related study, Ruckenstein (6) n o t e d that optimum m i c r o e m u l s i f i c a t i o n r e s u l t s were o b t a i n e d w i t h a c o m b i n a t i o n o f s i n g l e - and d o u b l e - c h a i n e d s u r f a c t a n t s . T r i o l e i n was s e l e c t e d as a r e p r e s e n t a t i v e t r i g l y c e r i d e because i t s c h e m i s t r y i s c l o s e l y r e l a t e d t o t h a t o f soybean o i l , and i t i s c u r r e n t l y a v a i l a b l e i n high p u r i t y . Soybean o i l i s a l i k e l y c a n d i d a t e as an a l t e r n a t e f u e l , s i n c e i t i s an a g r i c u l t u r a l l y renewable p r o d u c t w i t h heat c o n t e n t o f about n i n e t y p e r c e n t t h a t o f #2 d i e s e l f u e l . Materials
and Methods
2S 25 Triolein (tri-cis-octadecenoin d = 0.9091; η = 1.4662) was o b t a i n e d from Nu Chek Prep. , I n c . and was 99+% pure by QLC a n a l y s i s . Methanol (99.9+%, HPLC grade) and 2 - o c t a n o l (98%, n = 1.4234; d = 0.819) were a c q u i r e d from A l d r i c h and were p u r i f i e d over type 4A m o l e c u l a r s i e v e s (Union C a r b i d e ) and f i l t e r e d b e f o r e u s e . K a r l F i s h e r t i t r a t i o n s f o r H^O on b o t h a l c o h o l s p r i o r t o usage gave v a l u e s o f
