An experimental study of small pore zeolites for the upgrading of biomass to furfural

Abstract

Furfural derived from lignocellulosic biomass is a valuable platform molecule in the production of renewable liquid fuels and chemicals. With ever-increasing emphasis on reducing dependence on traditional petroleum-derived fuels and chemicals, the production of value-added chemicals from biomass has the potential to have a major global economic and environmental impact. To do so efficiently and sustainably requires the development and evaluation of new catalysts for these applications. These catalysts must not only be effective at catalyzing the conversion of sugars to furfural, but also must be easily separated, regenerated, and reused following each reaction. In this study, several small pore zeolites and metal-organic frameworks (MOFs) were evaluated for use in the dehydration of xylose, glucose, and switchgrass to furfural in a monophasic system of 90/10 gamma-valerolactone (GVL)/water. Based on results of initial experiments, three small pore zeolites, SAPO-34, SAPO-56, and DNL-6, became the major focus of these studies. The pore sizes of these molecules are significantly smaller than the kinetic diameters of xylose and glucose, which would lead one to predict minimal furfural production over these catalysts due to limited acid site access. In spite of that, moderate furfural yields of approximately 40% were achieved over SAPO-34 and SAPO-56 from xylose. Moderate furfural yields were also achieved from non-pretreated switchgrass over the SAPO catalysts in the GVL/water system, with strong evidence that both xylose and glucose were converting to furfural. Furfural degradation in GVL/water was minimal compared to degradation in a purely aqueous solvent. No leaching of acid sites occurred with the SAPO-34 catalyst, and it was recycled multiple times with only a 5% drop in furfural yield from first to final reaction. Most previous research using zeolite catalysts to upgrade biomass has focused on medium and large pore zeolites, as their pore apertures more closely match the kinetic diameters of the relevant component sugars of biomass. The results presented in this study suggest that small pore zeolites are also worthy of ongoing research.