Interesterification of triglycerides with methyl acetate for the co-production biodiesel and triacetin using hydrotalcite as a heterogenous base catalyst

Abstract

Biodiesel is a renewable fuel with several advantages over petro-based fuels and is conventionally produced by the transesterification of triglycerides with alcohols. Chemical interesterification of triglycerides is a good alternative as compared to transesterification, as it yields a value-added compound, triacetin, as a co-product instead of the already abundant commodity, glycerol. In this work, interesterification of soybean oil was carried out with methyl acetate to co-produce biodiesel and triacetin, using calcined hydrotalcite as a heterogeneous base catalyst. Several base catalysts were tested for this reaction. Calcined Mg-Al hydrotalcite (Mg:Al mole ratio – 3:1) was found as the best catalyst for achieving 95.9 % conversion of soybean oil triglycerides in 4 h and yielding 5.3 % selectivity of triacetin along with the value-added intermediates - monoacetindiglycerides and diacetinmonoglycerides, produced with a selectivity of 46 % and 48.7 %, respectively. The optimum reaction conditions were found at an oil to methyl acetate mole ratio of 1:50, catalyst loading of 0.04 g/cm3 and a temperature of 200 ºC. The catalysts were fully characterized before and after the reaction, and were found to possess high surface area with both basic and acidic sites. The effect of various reaction conditions on the rate of reaction, conversion of triglycerides and selectivity of triacetin were studied. The concentration profiles of the reactants, intermediates and products obtained at different temperatures were used to obtain the kinetic rate constants and the activation energy of each parallel step was evaluated. Reusability studies showed that the catalyst was stable and reusable up to three cycles.