Yield and component distribution of biodiesel by methanolysis of soybean oil with lipase-immobilized mesoporous silica

The activity and stability of mesoporous and macro-mesoporous silica immobilized with lipases PS and AK was investigated in methanolysis of soybean oil to biodiesel. Intermediate saturated heavy components of fatty acid methyl esters, linoceric and arachidic acid methyl esters were formed during the reaction. These were ultimately transformed to unsaturated (relatively fast) and saturated (slowly) acid methyl esters. Reaction time (∼72 h), reaction temperature (∼25 °C), pore size (∼80 nm), surface modification with OTES and an appropriate amount of water (1 mL per 0.33 g catalysts) resulted in high selectivity of unsaturated fatty acid methyl esters as well as high total yield. More than the critical mass of catalysts did not affect the total yield but raised the selectivity of the unsaturated components. Excessive increase in the number of methanol addition increased the total yield mainly by the formation of the heavy components. The addition of water as described also substantially increased the stability of the lipase-immobilized catalysts by the water residing inside pores, keeping the lipases to activate interfacially for their reuses.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Mesoporous and macro-mesoporous silica immobilized with lipases PS and AK were used to investigate the effect of variables on their activity and stability towards methanolysis of soybean oil. Macro-mesoprous catalyst always gave higher total yield and FAME quality unless the lipases were leached out. ► Linolenic acid branch in the oil probably attacked some other branches and formed linoceric and arachidic components. These transformed relatively fast to linoleic and oleic, and slowly to palmitic and stearic components. The linoceric was therefore found at the initial stage of the reaction or when the reaction proceeded with lowered activity of lipases. ► Raising the reaction temperature above 25 oC reduced the total yield but left the composition of FAME unchanged. The total yields were not increased once the critical mass of catalysts was used but the selectivity to the unsaturated components was enhanced with the mass of catalysts. ► The total yield of FAME was increased with the number of methanol addition keeping the total amount of addition constant. However, the frequent addition degraded the qualities of the FAME produced due to the formation of linoceric acid methyl ester, requiring more reaction time. ► Appropriate amount of water added at the first-cycle use of the catalyst penetrated into the pores of the catalysts and created the interface activation of the lipases to enhance both the activity and the stability or life of the immobilized catalysts.