Screening of Acidic Ion-Exchange Resins to Produce Butyl Levulinate from Fructose and Butyl Alcohol

Abstract

Alkyl levulinates are esters with the same boiling point as the lightest fraction of diesel fuel and can be obtained from lignocellulosic materials; therefore, introducing them in the formulation of commercial biodiesel fuels could potentially improve their properties. Thee aim of the present work is to perform a screening of acidic ion-exchange resins for their use as catalysts for the industrial production of butyl levulinate, taking butanol and fructose as raw materials. Experiments were performed at 120ºc under 21.5 bar of pressure, working with reaction mixtures of 60 mL butanol, 10 mL water, 1,5 g fructose and 1 g catalyst. Resins with low DVB content were selected for the screening process, namely Amberlyst 31, Dowex 50WX2, Dowex 50WX4, Dowex 50WX8 and Purolite CT-124, all of them with a particle size of 100–200 mesh. Fructose conversions were around 95% for Amberlyst 31 and CT-124, whilst Dowex resins reached roughly 100%. The best performance was achieved with Dowex 50WX2, and Dowex 50WX4; the last one was finally chosen with a selectivity towards butyl levulinate of around 35%. The performance of the chosen resin was then studied at five different temperatures between 100ºc and 140ºc. Its yield towards BL decreased to 30% at high temperatures, possibly due to the less stability of the ester in these conditions; lower temperatures, on the contrary, were discarded due to the slow reaction rate. the selected ideal temperature was therefore 120ºc. Finally, the composition of the feed was changed by varying the fructose concentration (0.75 g and 3 g were tried). Higher concentrations produced severe darkening of the reaction mixture, revealing the formation of undesired by-products, dibutyl ether among them. Lower concentrations, on the other side, did not improve significantly the yield and resulted in overly dilute products. Consequently, a mass fraction of fructose around 2,5% was deemed adequate. In these conditions, a yield towards the desired product of over 3555% was achieved, with fructose conversions of roughly 100%