Purification of Methyl Acetate/Water Mixtures from Chemical Interesterification of Vegetable Oils by Pervaporation

Abstract

Biodiesel production through chemical interesterification of triglycerides requires an excess of methyl acetate that must be recovered once the reaction is finished and the catalyst is neutralized. The present study concerns with the purification of methyl acetate by pervaporation. PERVAP 2201 was chosen as pervaporation membrane due to its high hydrophilic character that makes it suitable for the elimination of water in methyl acetate. Runs were started from concentrations in the feed of 2–8 wt.% of water and working temperatures close to the boiling point of methyl acetate (50, 60, and 70 °C), to get the main design parameters, i.e., permeate flux and selectivity. High temperature favored the permeate flux without compromising the selectivity. However, the flux declines significantly when water contained in the feed is below 2 wt.%. This implies that pervaporation should be used, only to decrease the water content to a value lower than in the azeotrope (2.3% by weight). A solution-diffusion model relating the flux of the permeating compound with the activity of the compound in the feed and the operating temperature has been proposed. The model obtained can be used in the design of the pervaporation stage, thus allowing to know the permeate flux for the different operating conditions.