Enzymatic production of biodiesel using lipases immobilized on silica nanoparticles as highly reusable biocatalysts: effect of water, t-butanol and blue silica gel contents

The enzymatic production of biodiesel by methanolysis of canola oil was studied using self-made biocatalysts. Mesoporous SBA-15 nanoparticles were prepared, characterized and functionalized by 3-glycidyloxypropyl trimethoxysilane. Lipases from Candida antarctica (CALB), Thermomyces lanuginosus (TLL) and Rhizomucor miehei (RML) were covalently immobilized onto SBA-epoxy. Thermal stability and the influence of methanol concentration on the catalytic activity were also evaluated. Higher thermal stability and methanol tolerance for immobilized derivatives were achieved compared to the free enzyme. In an optimization study, the effect of water, t-butanol and blue silica gel as water adsorbent on the yield of FAME was considered. For the SBA-RML catalysed reaction, water had little effect in increasing FAME yield, but when 20 wt% water by substrate weight was added to the SBA-TLL catalysed reaction, the methyl ester content reached nearly complete conversion (98% FAME). t-Butanol had a great effect on yield, with almost complete conversion for SBA-RML and SBA-TLL. The effect of blue silica gel also was investigated. The immobilized TLL was quite stable and can be reused for 20 cycles without significant loss in activity (6%). RML and CALB also presented a good reusability, keeping 95% of their initial activities after 7 and 15 cycles of the reaction.