Optimal Synthesis of Sal (Shorea robusta) Oil Biodiesel Using Recycled Bentonite Nanoclay at High Temperature

Abstract

Fresh and recycled bentonite nanoclay was used as a basic catalyst for the optimal synthesis of sal oil methyl ester biodiesel at high temperature. Bulk and surface properties of fresh and recycled catalyst were determined to check the recyclability. A catalyst concentration dependent lumped-parameter kinetic model was proposed for the transesterification of sal oil, and a simple genetic algorithm was used to determine the rate constants. Proposed rate constants were able to predict the experimental conversion of sal oil accurately under varying catalyst and methanol concentrations. A multiobjective optimization problem involving conflicting objectives (i.e., minimization of transesterification time, and minimization of undesirable intermediates) was formulated and solved using a nondominated sorting genetic algorithm. The temperature trajectory over the entire transesterification period was considered as a decision variable to obtain the fixed conversion of sal oil. A set of nondominated optimal Pareto solutions was obtained for the problem studied. For optimal synthesis, a higher isothermal temperature trajectory (≥503 K) was preferred for a short transesterification time (i.e., ≤35 min), whereas a nonisothermal temperature trajectory with lower reaction temperature (446.7–470.7 K) was required to keep undesirable intermediates at a minimum level (i.e., ≤0.0825 mol L–1) for 96.5% conversion of sal oil.