Production of Monosugars from Lignocellulosic Biomass in Molten Salt Hydrates: Process Design and Techno-Economic Analysis

ZnCl2 hydrate, the main molten salt used in biomass conversion, combined with low concentration HCl is an excellent solvent for the dissolution and hydrolysis of the carbohydrates present in lignocellulosic biomass. The most recalcitrant carbohydrate, cellulose, is dissolved in a residence time less than 1 h under mild conditions without significant degradation. This technology is referred to as BIOeCON-solvent technology. Separation of the sugars from the solution is the main challenge. The earlier conclusion regarding the potential of zeolite beta for selective adsorption has been used as the basis of a scale-up study. The technology of choice is continuous chromatographic separation (e.g., simulated moving bed, SMB). The sugar monomers are separated from the sugar oligomers, allowing the production of monosugars at high yield, using water as an eluent. Results of a pilot plant study are presented showing a stable operation at high selectivity. Several process designs are discussed, and the techno-economic performance of the BIOeCON-solvent technology is demonstrated by comparison with the state-of-the-art technology of NREL (National Renewable Energy Laboratory), which is based on enzymatic conversion of cellulose. It is concluded that the BIOeCON-solvent technology is technically and economically viable and is competitive to the NREL process. Because the BIOeCON-solvent process is in an early stage of development and far from fully optimized, it has the potential to outperform the existing processes.