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.