Real-Time Small-Angle Neutron Scattering Analysis of Lipase-Catalyzed Biodiesel Production in Microemulsion Systems
Hayes, D. G., V. S. Urban, and S. V. Pingali.  2013.  104th American Oil Chemistsí Society Annual Meeting, Montreal, May 2013.  (invited)

Lipase-catalyzed synthesis of biodiesel is potentially an attractive alternative to alkali-catalyzed transesterification for several reasons: utilizion of free fatty acid (FFA)-rich feedstocks and employment of safer and more sustainable synthesis conditions (lower stoichiometric excess of alcohol, energy cost, and downstream purification requirements, and waste product production. Fundamental research is required to elucidate the partitioning behavior of reactants, products, and intermediates, and its relationship with the observed kinetics, in order to improve the reaction rate and yield (e.g., prevent product inhibition) since this reaction occurs at the liquid-liquid interface in all situations. To achieve this goal, the lipase-catalyzed esterification of lauric acid and 1-butanol has been conducted in water-in-oil microemulsions: a thermodynamically stable solution of aqueous nanodro;plets dispersed in apolar media through the addition of surfactant (Aerosol-OT). The reaction has been monitored using small-angle neutron scattering (SANS) to ascertain (perhaps quantitatively) the effect of partitioning during the time course of reaction, achieved through selective deuteration of media components to acheive a difference in neutron contrasting across the interface. A preliminary analysis of the SANS data shows that the alcohol and fatty acid strongly partition to the interface, demonstrated by a decrease in the thickness of the interface's surfactant monolayer and of the extent of attractive interactions existing between nanodroplets, a trend that is reversed during the time course of reaction, due to the consumption of substrate.