Solvent Assisted Biodiesel Production by Co-processing Beef Tallow and Soybean Oil Over Calcium Catalysts

Due to sustainability issues, biodiesel must be produced from low-grade fats and the conventional homogeneously-catalyzed processes must be replaced by more efficient and more profitable production processes such as heterogeneous ones. Biodiesel (fatty acids methyl esters, FAME) was produced from a mixture (50 wt%) of soybean oil and non-edible beef tallow over heterogeneous calcium-based catalysts obtained by calcination of scallop shells. In order to improve the catalytic performances, solvent assisted methanolysis was conducted using alcohols (ethanol, 1-propanol, isopropanol and isobutanol), acetone, methylcyclohexane, and tetrahydrofuran (THF) with Vmethanol/Vsolvent = 2.8. Catalytic data revealed that alcohol solvents adsorb competitively with methanol on the catalyst active sites reducing the FAME yield due to their slower alcoholysis rates. Hexane and methylcyclohexane are inadequate for methanolysis reactions since they are immiscible with methanol. THF and acetone are immiscible with the co-produced glycerin, which favors methyl esters formation by displacing the chemical equilibrium towards reaction products. Acetone performs better than THF (FAME yield gain of 14% against 3%) because of its higher miscibility with methanol. THF was the most effective solvent to avoid fat adsorption on the catalyst surface, a key factor for catalyst stability, and to improve the glycerin purity.