Dehydration of glucose over sulfate impregnated ZnO (hexagonal-monoclinic) catalyst in dimethyl sulfoxide (DMSO) medium: Production, separation, and purification of 5-hydroxymethylfurfural (5-HMF) with high purity

Abstract

Dehydration of glucose for the production and separation of 5-hydroxymethylfurfural (5-HMF) with high purity has been performed. For selective production of 5-HMF from glucose, a new sulfated-ZnO catalyst with a combined hexagonal-monoclinic phase was developed and characterized by several techniques. The catalyst characterization results demonstrated a significant variation of physicochemical properties of hexagonal ZnO after sulfate impregnation. The glucose dehydration was performed in a glass reactor in a dimethyl sulfoxide (DMSO) medium. The effect of several important reaction parameters including temperature (120–160 °C), time (1–8 h), catalyst loading (25–100 wt%), and sulfate loading on ZnO with respect to glucose (1.5–4.5M) was evaluated. Results demonstrated that the sulfated-ZnO catalyst containing both the Brønsted (B) and Lewis (L) acid sites was very active and selective to 5-HMF compared to pure hexagonal ZnO containing only Lewis acidic sites (LAS). It was also observed that the higher (B + L) acidity of catalysts propagated the rehydration process, which led to the formation of various unwanted side products. The maximum glucose conversion of 96.2% with ~35% yield of 5-HMF was obtained at 160 °C after 6 h of reaction, with 2.5M-SO42−/ZnO catalyst. Among all others, the 2.5M-SO42−/ZnO catalyst was the best due to the presence of an optimum acidity with an appropriate B/L ratio. Further, the catalyst separation and recycling studies were performed. The results revealed that the 2.5M-SO42−/ZnO catalyst could be recycled multiple times without substantial loss of catalytic activity and 5-HMF yield. Furthermore, a liquid-liquid extraction process was developed, demonstrating that almost 100% of 5-HMF could be extracted from the product solution with ~97% purity.