(135b) An Improved Approach to Make Cyclic Acetals From Glycerol

The production of biodiesel from plant triglycerides leads to formation of byproduct glycerol, a versatile feedstock in itself for producing chemicals such as propylene glycol and epichlorohydrin. It is well known that glycerol can be converted into cyclic acetals via condensation with aldehydes; for example, 2-methyl-4-hydroxymethyl-1,3-dioxolane and 2-methyl-5-hydroxy-1,3-dioxane are formed via reaction of glycerol with acetaldehyde. These compounds have desirable properties as fuel additives via improving pour point and viscosity of biodiesel, and reducing particulate emissions from fuel combustion.

Glycerol acetals can be synthesized directly with aldehydes or by transacetalization with another acetal compound. In this paper, we present results of glycerol acetal synthesis using 1,1-diethoxyethane (DEE). Reaction kinetics and equilibria, along with physical property data such as reactant miscibility, have been studied at different reaction temperatures, reactant molar ratios, and Amberlyst 15 cationic exchange resin catalyst loadings. A kinetic model describing the reaction is presented; results are compared with acetal formation via direct condensation with acetaldehyde.

Results show that acetal formation with 1,1-diethoxyethane is faster and proceeds further to completion than reaction of glycerol with acetaldehyde. In addition, the reaction of 1,1-DEE produces ethanol as a product, thus making the system water-free. However, the disadvantage of transacetalization with 1,1-DEE is that it requires the extra step of making 1,1-DEE from ethanol and acetaldehyde (although the ethanol can be recycled in the process). Based on the comparison of the reaction parameters, the conceptual design of a continuous process to make cyclic glycerol acetals using 1,1-DEE will be presented.