Direct conversion of furfuryl alcohol to butyl levulinate using tin exchanged tungstophosphoric acid catalysts

To decrease the dependence on crude oil, biomass derived liquid transportation fuels are highly desirable. Butyl levulinate is a potential cellulose-derived biofuel additive with properties similar to diesel and low water solubility. Herein we report a direct one-pot production of levulinic acid ester, butyl levulinate, from furfuryl alcohol by alcoholysis using n-butanol. The partial tin exchanged tungstophosphoric acid (TPA) supported on montmorillonite K-10 catalysts showed facile alcoholysis of furfuryl alcohol to levulinate ester under mild temperature conditions. Partially exchanging the H⁺ ion of TPA with Sn (x = 1) resulted in enhanced acidity of the catalyst and showed an increase in the catalytic activity as compared to TPA/K-10 catalyst. A series of tin exchanged tungstophosphoric acid (20 % w/w) supported on montmorillonite K-10 clay (Sn_x-TPA/K-10, where x = 0.5–1.5) were synthesized and thoroughly characterized by using XRD, FT-IR, UV-VIS, titration and SEM techniques. Among various catalysts, Sn_1^-TPA/K-10 was found to be the most active catalyst for butyl levulinate synthesis. Two different clay supports and varying tin loadings were used to study the effects on surface acidity as well as catalytic activity in butyl levulinate synthesis. Effects of different reaction parameters were studied and optimized to get high yields of butyl levulinate. Under mild reaction conditions at 110 °C, complete conversion of furfuryl alcohol with 98 % selectivity to butyl levulinate was achieved. The prepared catalyst could be recycled at least five times without significant loss of activity. The overall process is green and clean.