Simultaneous Dehydration of Glucose and Xylose Present in a Process-Relevant Biorefinery Hydrolysate to Furfurals Using Heterogeneous Solid Acid Catalysts
Ashutosh Mittal, Daniel A. Ruddy, Xiaowen Chen, David K. Johnson
Abstract
High Resolution Image Download MS PowerPoint Slide In this work, we report the simultaneous dehydration of glucose and xylose present in a process-relevant biorefinery hydrolysate to furfural and 5-hydroxymethylfurfural (HMF) using heterogeneous solid acid catalysts in a microwave reactor. Initially, several solid acid catalysts with varied Brønsted and Lewis acidity were screened to evaluate their activity and selectivity in dehydration of pure glucose to HMF. A noticeable improvement in HMF yield from dehydration of 8 wt % glucose was obtained by combining an acidic ion-exchange resin (Purolite CT-275DR) with an amorphous silica-alumina catalyst (Davicat-3115) resulting in HMF yields of 27–33% using a homogeneous solvent system of aqueous dioxane (dioxane/water, 2:1 v/v) at 195 °C in 5 min. Under the same reaction conditions, catalysts, and solvent system but with the addition of NaCl in catalytic amounts (33–100 mM), a more than 2-fold increase in HMF yields (66–70%) was achieved for the dehydration of 8 wt % glucose, whereas furfural yields approaching 95% were achieved for the dehydration of 6 wt % xylose, when conducted separately. Notably, using the same catalyst and solvent system while slightly modifying the reaction conditions to 197 °C and 5 min, simultaneous dehydration of 4 wt % xylose and 9 wt % glucose present in a process-relevant corn stover hydrolysate resulted in furfural and HMF yields of 96 and 74%, respectively, resulting in a combined furfural yield of 80%. The results further showed that the pH of the reaction solution played an important role in maximizing product yields. A pH < 2 resulted in low HMF yields due to the increased formation of HMF degradation products, whereas a pH 2–3 gave high HMF yields by possibly stabilizing the reaction intermediates and product, suppressing the occurrence of side reactions.