Overall Process Considerations for Using Dilute Acid Cellulose Hydrolysis Technology to Produce Ethanol from Biomass

Recent advances in reactors designed for the dilute acid thermochemical treatment of biomass have resulted in the development of process alternatives in which both cellulose and hemicellulose are hydrolized in soluble sugars in high yields. The optimal extent of cellulose hydrolysis will depend on both the performance and economics of the thermochemical treatment operation, and on subsequent unitoperations in the bioethanol production process. Examples of subsequent unit operation interactions include the extent to which cellulase enzymes are used to hydrolyze any remaining cellulose, kinetics and conditions of a largely soluble mixed sugar confermentation, and the extent to which removal of compounds that inhibit fermenting microorganisms is required. In addition, a number of processoperation and economic considerations affect the ultimate economic viability of this type of biomass hydrolysis process. These considerations include reactor design issues to accommodate the kinetic parameters of the various hydrolysis and sugar degradation reactions, liquid volume requirements to achieve acceptable sugar yields, sugar concentrations that result from such a process and theirimpact on subsequent fermentation volumes and ethanol recovery operations, potential co-product opportunities that result from solubilized lignin, and process steam requirements. Several potential whole-process configurations are presented and key process and economic issues for each are discussed.