Kinetic study of synthesis of bio-fuel additives from glycerol using a hetropolyacid

Abstract

Concerns about the ever increasing quantities of glycerol produced as a by-product of the process of manufacture of bio-diesel serve as a fuel for research about the alternative uses of glycerol. The esterification of glycerol with acetic acid over Cesium supported heteropolyacid (CsPWA) serving as the catalyst was carried out. The products obtained were mono, di and tri acetins which have wide application as biofuels. A series of experiments were carried out with CsPWA as catalyst and parameters considered for studies were temperature, molar ratio of reactants (acetic acid:glycerol) and the catalyst loading weight percent. Each parameter was varied keeping the other two constant and the results were recorded. Temperature was varied from 80°C to 110°C; molar ratio of glycerol to acetic acid is between 3:1 and 9:1 and catalyst loading of 3%w/w to 7%w/w. The yield and conversion varied for different conditions, but in general, the yield of diacetin and triacetin increased with time. Optimum parameters were adjudged to be 110°C with a molar ratio of 9:1 of the reactants and catalyst loading being 5% weight of reaction mixture where maximum glycerol conversion of 98% was obtained. The results obtained indicate that the esterification of glycerol with acetic acid is a consecutive reaction and the kinetic model was developed based on homogeneous first order reaction series by optimization method using MATLAB, and rate constants (k₁, k₂ and k₃) were determined. From the rate constants at different temperatures, using Arrhenius equation the activation energies (E₁, E₂ and E₃) were also determined.