A contribution to the study of butyl levulinate synthesis in the liquid-phase on ion-exchange resins.

Abstract

Alkyl levulinates are biomass derived chemicals with a large spectrum of applications. They have the potential to substitute compounds currently derived from petro-chemical routes as components of conventional diesel or gasoline because of their physicochemical properties. Alkyl levulinates are synthesized most often from levulinic acid, but also from furfuryl alcohol or directly from cellulose and monosaccharide sugars. Levulinic acid is a platform chemical formed from hydrolysis of lignocellulose, the most readily available form of biomass, using the Biofine process. The most widely studied alkyl levulinate is ethyl levulinate, both its synthesis pathways and possible applications have been explored thoroughly. Comparatively, the potential of butyl levulinate has been left untapped. As an additive for automotive diesel fuel, butyl levulinate is even more promising than ethyl levulinate: butyl levulinate remains in diesel solution down to the diesel cloud point; butyl levulinate blends have very small particulate matter emissions; it has a lower solubility in water than ethyl levulinate; good lubricity and conductivity; and a low but better cetane number. Esterification of levulinic acid with butanol over several types of catalysts such as zeolites, lipases and heteropolyacids (HPA) supported on acid-treated clay montmorillonite (K10) has been described in literature, but the catalysis with acidic ion-exchange resins has never been attempted to the best of our knowledge. The present work studies the behavior of different sulfonated polystyrene-divinylbenzene resins in the synthesis of butyl levulinate from levulinic acid. The conducted experiments confirm that acidic polymer catalysts can be used in order to obtain very high conversion and selectivity in the esterification of levulinic acid with butanol to butyl levulinate. Selectivity toward butyl levulinate remains always over 98% for all tested catalysts in the range of temperatures studied, and the most relevant by-product is dibutyl ether. The catalyst with highest activity was Dowex 50Wx2, and overall, gel-type resins presented better yields than macroporous ones. Because of the high polarity of levulinic acid and the formation of water, resins with greater capacity for swelling would favor levulinic acid esterification. Thus resins with a lesser degree of cross-linking present higher reaction rates.Globally, reaction rates improve as the degree of polymer cross-linking diminishes and roughly correspond with large specific volume of swollen polymer.