Zeolite-promoted hydrolysis of cellulose in ionic liquid, insight into the mutual behavior of zeolite, cellulose and ionic liquid

Abstract

In this paper, a variety of H-type zeolites were demonstrated as efficient catalysts for hydrolysis of cellulose in ionic liquid (IL) to afford high yield of glucose under mild condition without a pretreatment process. By supplying water gradually as the reaction progresses, HY with the acid amount of 11.1mol% promoted the highest glucose yield of 50.0% at 130°C, and the yield of the three main products (glucose, cellobiose and 5-hydroxymethylfurfural) was up to 97.2%. It was found that the pore size, the acid amount, the water amount and the timing of water addition are critical factors for high hydrolysis efficiency. XRD characterization suggested that the framework structure of zeolite was particularly stable in 1-butyl-3-methylimidazolium chloride ([BMIm]Cl), while the cell parameter were enlarged due to the dilatation effect of [BMIm]Cl. Elemental analysis of the IL-treated HY demonstrated that IL entered the channel of HY. As such, part of the intra-channel space of HY was occupied, making the average pore diameter, pore volume and the BET surface area of IL-treated HY all decreased, which were demonstrated by physisorption characterization. FT-IR through pyridine adsorption showed that H+ cations generated in-situ from the Brönsted acid sites of zeolite were the key active species for the good hydrolysis performance, while the Lewis acid sites did not exhibit high activity. By simple calcination, the recovered HY showed excellent reusability. Finally, the proposed reaction pathway and recycle of the catalyst were presented.