Optimization and kinetic studies on conversion of rubber seed (Hevea brasiliensis) oil to methyl esters over a green biowaste catalyst

Abstract

The goal of the study was to establish the optimal condition for the transesterification process for Hevea brasiliensis oil (HBO) conversion into H. brasiliensis oil methyl esters (HBOME) using a novel base heterogeneous catalyst synthesized from a biowaste (kola nut pod husk). Thus, the influence of concentration of catalyst, MeOH:HBO molar ratio, reaction time and reaction temperature on the HBOME yield was identified using Taguchi orthogonal array design approach. Also, the overall reaction rate constant (k) and reaction order (n) for the process was determined as a way to develop a kinetic model. The results showed that HBOME yield of 96.97 wt% could be achieved using catalyst amount of 3.5 wt%, MeOH:HBO molar ratio of 6:1, reaction time of 75 min and reaction temperature of 65 °C. Performance evaluation of the process input variables suggests reaction time had the highest influence on the HBOME yield. The values of n and k were determined to be 1 and 0.0034 min^-1, respectively via kinetic modeling of the transesterification process. The cetane number, kinematic viscosity and acid value of the HBOME produced were 59.54 ± 0.15, 4.98 ± 0.12 mm²/s and 0.22 ± 0.00 mg KOH/g oil, respectively, which compared well with the standard specifications for biodiesel. Thus, HBO and kola nut pod husk could serve as cheap bioresources for biodiesel production.

Keywords: Biodiesel; Kinetics; Modeling; Optimization; Rubber seed oil; Taguchi design.