Evaluation of diatomaceous earth supported lipase sol–gels as a medium for enzymatic transesterification of biodiesel

Immobilized lipase has the potential to be the catalyst of choice for biodiesel production since it is efficient, effective, and environmentally friendly; however, the stability and activity of lipase must be addressed before enzymatic biodiesel production processes can be industrially accepted. This study investigates an enzyme immobilization procedure that immobilizes lipase in a sol–gel supported on diatomaceous earth (Celite® R632), and determines its potential for biodiesel production in terms of achievable conversion and apparent stability. Four immobilized materials (lipase sol–gels with and without Celite® at two protein loading levels) were compared in terms of their immobilized protein content, conversion of methanol to methyl oleate, lipase activity, long term stability, and glycerol–water adsorption. The Celite® R632 sol–gel with high protein loading achieved the maximum conversion in the 6-h reaction period (90%). A drying step was found to be advantageous prior to the reaction, and the absorption of glycerol–water on the Celite® was only found to be significant at high levels of glycerol. The material was found to be very stable upon storage at 4 °C for up to 1.5 years, losing only about 15% of its percent conversion capacity per year. Based on this study, the supported immobilization technique shows significant potential as a novel catalyst for biodiesel production.