A contribution to the study of acidic ion-exchange resins to produce butyl levulinate from fructose and butyl alcohol

Abstract

Biomass is the only renewable resource on the earth that can derive liquid fuel and fine chemicals to replace the petroleum-based chemicals. In recent years, the development of bioenergy concerning the synthesis of levulinate esters from biomass via chemical/catalytic process has attracted more and more interests, and extensive research is being carried out worldwide. Levulinate esters, like methyl levulinate, ethyl levulinate, and butyl levulinate, are a kind of important intermediates and energy chemicals having high reactivity and widespread application in many fields. Alkyl levulinates are proposed as oxygenates of potential interest as diesel fuel components. In blends with commercial gasoil it has been shown that cold flow properties of blends are substantially upgraded and particulate emissions greatly decrease. These green diesel fuel enhancers can be synthesized by the acid catalysed reaction of levulinic acid with alcohol32. Direct conversion of carbohydrates to levulinate esters using solid acids such as NaY, 𝑆𝑂#$%/ZrO2, 𝑆𝑂# $%/TiO2, are described in the literature, but direct conversion of fructose to esters of levulinic acid using ion-exchange resins has never been attempted to the best of our knowledge. In this study, the catalytic performances of ion-exchange resins (Dowex 50Wx2, Dowex 50Wx4, Amberlyst 39, Amberlyst 16, Amberlyst 15) in the direct conversion of carbohydrates such as fructose to butyl levulinate in butanol-water media were investigated. With temperature above 100ºC, almost 100% of fructose conversion was obtained irrespective of the catalyst employed. However, different catalysts showed different activity and selectivity towards the production of butyl levulinate. Among these catalysts employed, gel-type resins (especially Dowex 50Wx2) were found to be a type of potential catalysts for prospective utilization, which showed the highest selectivity and yield to butyl levulinate. The catalyst range assayed showed spurious effect on the reaction rates. The higher temperatures led to higher reaction rates but also presented higher formation of by-products such as butyl formate and BMF. Although, no humins were detected during the investigation. Catalysts with less degree of cross-linking present higher selectivity towards levulinate esters. The reuse of Dowex 50Wx2, after reconditioning them with deionised water and methanol, showed lesser catalytic activity after each use due to the loss of acid sites above the surface of catalyst, providing less catalytic activity for the reaction. Overall, this study indicated that acidic ion-exchange resins are promising catalysts for the direct production of levulinate esters from fructose and can be employed for the large-scale synthesis of butyl levulinate from renewable carbohydrates in the future