MODERN CATALYTIC TECHNOLOGIES FOR CONVERTING BIOMASS DERIVED SUGARS TO CHEMICALS: AN OVERVIEW OF THE CATALYSIS CENTER FOR ENERGY INNOVATION

摘要

Utilization of lignocellusic biomass for the production of fuels or chemicals is extremely attractive due to the minimal competition with the food production chain. Cellulose and hemi-cellulose, the two major fractions of lignocellulosic biomass, can be depolymerized by acid-hydrolysis or by enzymatic decomposition to form glucose and xylose respectively. The efficient transformation of these hexose and pentose molecules to 5-hydroxymethyl-furfural (HMF) and furfural, which are considered as two valuable platform chemicals, poses several challenges that need to be addressed. For example, the difficulty of converting glucose to furans is one major obstacle that has to be overcome. Currently, a costly and slow enzymatic route is employed for the conversion of glucose to fructose, which can easily be dehydrated to HMF. The parallel path in the case of pentoses is the isomerization of xylose to xylulose followed by xylulose dehydration to furfural. The development of new heterogeneous catalytic materials for the efficient conversion of glucose to fructose and xylose to xylulose that might replace the enzymatic processes is an important stepping stone. Another important challenge is related to the low selectivity of the fructose and xylulose dehydration reactions. In particular, the acid catalyzed dehydration in an aqueous environment is accompanied by side reactions which lead to the formation of acyclic dehydration and fragmentation products, insoluble humins and rehydration products. The use of other solvents or co-solvents might significantly improve furan yields (i.e., DMSO, water or DMSO - water mixture). On the other hand, HMF yields higher than 90% can be achieved in DMSO. Unfortunately, issues related to the separation of HMF from DMSO render this solvent unattractive for commercial applications. In order to identify other solvents with similar effects on reactivity but without the issues related to separation, it is initially necessary to understand the solvation of reactants and products in the solvents currently tested.