Production of furfural and 5-hydroxymethyl furfural from Camellia oleifera fruit shell in [Bmim]HSO4/H2O/1,4-dioxane biphasic medium

Abstract

The high-value utilization of Camellia oleifera fruit shell (CFS), which is an important waste in edible tea oil processing, is of great significance for the sustainable development of Camellia oleifera industry. In this study, the CFS after being simply pretreated (PCFS) to remove crude fat, pigment, et al., was used as material to produce furfural (FF) and 5-hydroxymethyl furfural (5-HMF) catalyzed by 1-butyl-3-methylimidazole hydrogen sulfate ([Bmim]HSO4). On the basis of comparing the superiority of microwave heating and traditional oil bath heating, on the basis of comparing the in-situ extraction of FF and HMF with four common solvents including 1,4-dioxane, methyl isobutyl ketone (MIBK), benzene, and cyclohexane, the [Bmim]HSO4/H2O/1,4-dioxane biphasic catalytic reaction system assisted by microwave irradiation was established. In this reaction system, FF was the chief product and 5-HMF was the chief by-product. The highest yields of FF and 5-HMF were 67.54 mol% and 20.97 mol%, respectively. The yield of FF was much higher than that of 5-HMF under the same reaction conditions. The kinetic analysis indicated that the hemicellulose hydrolysis to xylose catalyzed by [Bmim]HSO4 was the rate-limiting step in the production of FF. The cellulose hydrolysis to glucose and the subsequent isomerization of glucose to fructose were the rate-limiting steps in the production of 5-HMF. The rapid formation of other by-products was also one of the reasons for low yield of 5-HMF. [Bmim]HSO4 still performed excellent stability and catalytic activity after three times of cycles. FF with a purity of 95.26% could be obtained from the 1,4-dioxane phase under vacuum distillation. The relative contents of hemicellulose and cellulose and the crystallinity index of cellulose in PCFS residues decreased with the enhancement of reaction temperature and retention time. The biphasic medium used in this study was efficient for the production of FF from CFS.