Optimization of biodiesel production from waste lard by a two-step transesterification process under mild conditions

The aim of this work is to investigate a two-step homogenous catalyzed waste lard transesterification reaction for low cost biodiesel production. For this purpose, two 23 full factorial design of experiments was applied. Six variables, namely esterification time (60–120 min), H2SO4 concentration (20–40 wt.%), MeOH:FFA (15:1–23:1), transesterification time (30–60 min), KOH concentration (1–2 wt.%), and MeOH:triglycerides (6:1–9:1), that typically affect the production process were studied. The esterification step is significantly affected mostly by the reaction time and the MeOH:FFA ratio value. Specifically, their increase brings a reduction of the FFA acidity. Likewise, the transesterification step is positively affected primarily by three independent variables, namely reaction time, KOH concentration and MeOH:triglyceride ratio. Furthermore two empirical models describing evolution of the two-step transesterification reaction were developed. They can become useful tools for further scaling-up the process by predicting its reaction yield within a 95% of confidence level.