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Understanding and Enhancing the Catalytic Production of 5-Hydroxymethylfurfural from Fructose in Aqueous Cosolvent Systems

  • Author(s): Svenningsen, Glen
  • Advisor(s): Christopher, Phillip
  • et al.
Abstract

US interest in biomass as an alternative energy source continues to increase in demand with growing political, economic and environment concerns with fossil fuels. One potential route for converting cellulosic biomass to fuels is through the dehydration of fructose to produce 5-hydroxymethylfurfural (HMF), followed by the catalytic conversion of HMF to renewable fuels, such as dimethylfuran (DMF). Economically viable production of HMF from fructose requires high yields. The formation of HMF has been thought to occur through the acid-catalyzed dehydration of the furanose form of fructose, while other fructose tautomers likely lead to unwanted side products. The tautomeric composition of fructose is highly dependent on the reaction temperature and solvent system; thus, HMF production is likely sensitive to these factors. In order to develop detailed insights into the factors that control HMF yields, we executed extensive kinetic analysis using a variety of solvent systems, reaction conditions, acid types and acid concentrations to determine the mechanism and selectivity controlling factors in fructose dehydration to HMF by homogeneous acid catalysts. Through these studies we were able to strongly support the hypothesis that selectivity in fructose conversion to HMF is controlled by the tautomeric distribution. Furthermore, we found that dimethyl sulfoxide (DMSO) solutions produce the highest HMF selectivity, (up to 85%) and fastest conversion rates of any solvent system; however, DMSO is highly energy intensive to separate. To overcome separation costs, we aimed to develop novel heterogeneous catalysts which mimic the desirable solvation effects of DMSO in low boiling, aqueous co-solvent mixtures. We grafted DMSO-like functional groups near acidic sites on the surface of supports generate local conditions which mimic bulk solutions of DMSO, which increased HMF selectivity by ~30%. To synthesize these catalysts, the surface of silica was first functionalized by (3-mercaptopropyl)-trimethoxysilane. The grafted thiols were then converted into 1, 3-methyl propyl sulfoxides to mimic DMSO at the surface and characterized by RAMAN spectroscopy. A techno-economic analysis was performed on the conversion of fructose to dimethylfuran (DMF) by heterogeneous catalysts in aqueous tetrahydrofuran solutions, using Aspen Plus. We report a minimum selling price (MSP) of DMF of 1.74 $/kg, with fructose feedstock, DMF yield, catalyst cost, and water treatment being the main contributors to the MSP.

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