Product Separation after Chemical Interesterification of Vegetable Oils with Methyl Acetate. Part I: Vapor-Liquid Equilibrium

Chemical interesterification of triglycerides with methyl acetate yields biodiesel and triacetin. This reaction is highly reversible, which implies the presence of intermediate compounds such as diacetinmonoglycerides. In addition, the use of methanolic potassium methoxide as the catalyst causes the appearance of diacetin, monoacetin, and glycerol. Vacuum distillation becomes an interesting alternative for the separation of biodiesel and triacetin. Vapor liquid equilibrium (VLE) determination requires information related to the vapor pressures of the different compounds and the nonideality of the liquid phase (activity coefficients). The lack of literature information for some compounds was supplemented with experimental data and predictive models for vapor pressure and activity coefficients (UNIFAC and UNIFAC Dortmund). The suitability of using vacuum distillation was evaluated using the Fenske equation and experimental results from a structured packed distillation column. According to the results, removal of diacetinmonoglycerides can be easily accomplished, unlike the elimination of diacetin, monoacetin, and glycerol, which form azeotropes with triacetin.