Optimization of a two stage process for biodiesel production from shea butter using response surface methodology

The challenges of biodiesel production from high free fatty acid (FFA) shea butter (SB) necessitated this study. The reduction of %FFA of SB by esterification and its subsequent utilization by transesterification for biodiesel production in a two stage process for optimization studies was investigated using response surface methodology based on a central composite design (CCD). Four operating conditions were investigated to reduce the %FFA of SB and increase the %yield of shea biodiesel (SBD). The operating conditions were temperature (40–60°C), agitation speed (200–1400 rpm), methanol (MeOH): oil mole ratio: 2:1–6:1 (w/w) for esterification and 4:1–8:1 (w/w) for transesterification and catalyst loading: 1–2% (H2SO4, (v/v) for esterification and KOH, (w/w) for transesterification. The significance of the parameters obtained in linear and non-linear form from the models were determined using analysis of variance (ANOVA). The optimal operating conditions that gave minimum FFA of 0.26% were 52.19°C, 200 rpm, 2:1 (w/w) and 1.5% (v/v), while those that gave maximum yield of 92.16% SBD were 40°C, 800 rpm, 7:1 (w/w) and 1% (w/w). The p-value of <0.0001 for each of the stages showed that the models were significant with R2 of 0.96 each. These results indicate the reproducibility of the models and showed that the RSM is suitable to optimize the esterification and transesterification of SB for SBD production. Therefore, RSM is a useful tool that can be employed in industrial scale production of SBD from high FFA SB.