Shift of Multiple Incompatible Equilibriums by a Combination of Heterogeneous Catalysis and Membranes

摘要

Many organic reactions are equilibriums, in which a large excess of one reagent is required to shift them to completion. One example of industrial interest is biodiesel production by the base-catalyzed transesterification of triglycerides.[ 1] This reaction consists of a sequence of three equilibriums (Scheme 1a–c) with low equilibrium constants,[2] which makes it necessary to use a large excess of methanol. One alternative would be the use of the modern technology of membrane systems[3] to eliminate the concomitant product from the reaction mixture, in this case glycerol. However, to the best of our knowledge, the separation of glycerol in an excess of methanol would not be possible with any type of membrane. Given the very high efficiency of some membranes to eliminate water[4] they have been used in reactions, such as esterification,[5] in which water is the concomitant product. Therefore a possible way to use membranes in biodiesel production could be by the addition of another equilibrium reaction to the series and, thereby, transforming glycerol into a new, valuable product with water as the only byproduct.