Synthesis of energy rich fuel additive from biomass derived levulinic acid and furfuryl alcohol using novel tin-exchanged heteropoly acid supported on titania nanotubes as catalyst

Biomass feedstocks are available in a wide variety. It is an alternative source to fossil fuels to meet higher energy demand and a renewablefeedstock for many industrial products and chemical substances. Furfuryl alcohol and levulinic acid are both biomass-based chemicals that can be valorized for use in various applications. In the current study, we have introduced esterification reaction of furfuryl alcohol with levulinic acid to produce furan2-ylmethyl 4-oxopentanoate, which can be used to synthesize biofuels, perfumes, flavouring agents, and other industrially useful compounds. For this conversion, a novel and highly efficient catalyst, 20 % (w/w) Sn metal exchanged dodecatungstophosphoric acid (TPA) with titania nanotubes (TNT) support was used under environmentally benign solventless reaction conditions. Partially substituted protons of TPA with Sn (x = 1) increased the acidity of the catalyst, and resulted into higher activity than 20 % (w/w) TPA/TNT. Protons of TPA were substituted with Sn metal at different proportions (i.e., H = 1, 2, 3 of TPA exchanged with Sn = 0.5, 1, 1.5, respectively). Amongst all, 20 % (w/w) Sn1-TPA/TNT was found to be the most efficient catalyst for the esterification reaction of furfuryl alcohol and levulinic acid due to its higher acidity. Fresh and reused catalysts were well-characterized using various analytical techniques. Using LHHW (Langmuir-Hinshelwood-Hougen-Watson) mechanism, a kinetic model was developed. The activation energy was found to be 7.85 and 13.58 kcal/mol for esterification (step 1) and self-etherification (step 2) reactions, respectively. The activation energy of esterification is lower than that of self-etherification and the rate of esterification is higher than that of self-etherification.