Obtaining levulinic acid from fructose over acidic ion-exchange resins catalysts

Abstract

Diesel compositions must be reformulated in order to fulfil new EU standards, where oxygen content must be, of at least, 15% by 2020. By other way, the new diesels can reach the consideration of biofuels if they are obtained from biomass. An important platform chemical obtained from biomass is levulinic acid, which is the most widely used reactant to obtain alkyl levulinates. These alkyl levulinates are found to be possible oxygenated chemicals additives that could upgrade fuel’s quality, turning into in “greener” ones. The absence in the literature of information of acid ion-exchange resins as catalysts for the dehydration of fructose to 5-hydroxymethylfurfural and subsequent rehydration to obtain levulinic acid, make the study of the behaviour of these catalysts useful and interesting. The reaction system was studied using dioxane as solvent, a fixed composition of reactants (14% wt. fructose and 4% wt. water) and in the temperature range between 90 ºC and 110 ºC. Two sets of resins are used during the study in the catalysts screening: a set of macroreticular resins (Amberlyst 15 and Amberlyst 39) and another one of gel-type (Dowex 50x8, Dowex 50x4 and Dowex 50x2). The experimental set was a discontinuous pressurized batch reactor and high-performance liquid chromatography. Fructose conversion, selectivity towards levulinic acid (LA) and 5-hydroxymethylfurfural (HMF), and yields of each product are calculated. The gel-type resin Dowex 50x2 is the most selective resin between the studied operation conditions. From the results of two sets of resins it can be concluded that less content of cross-linker divinylbenzene leads to higher yields. Yield of HMF and global yield reaction are better at lower temperatures, while LA yield increase at higher temperatures. Humic acids formation is the cause of the noticeable reduction of the global reaction yield. The highest yield reached for HMF is 72,4% at 90 ºC with Dowex 50x4 and 34,4% for LA at 100 with Dowex 50x2.