Conversion of Lignocellulosic Biomass to Reducing Sugars in High Pressure and Supercritical Fluids: Greener Alternative for Biorefining of Renewables

Abstract Supercritical fluids offer great potential to be employed in lignocellulosic biomass (LCB) fractionation in biorefinery. Supercritical carbon dioxide and water are greener alternatives compared with conventional reagents and have been investigated for the pretreatment and hydrolysis of lignocellulosic biomass. This review is focused on examining the fundamentals that govern the function of supercritical fluids in the pretreatment stage, as well as in the main hydrolysis reaction. Sub/supercritical carbon dioxide is used in pretreatment and sub/supercritical water has been the solvent of choice in hydrolysis of LCB. Significant research has gone into understanding the effect of process parameters such as temperature, pressure, cosolvent, and use of external catalyst on the sugar yield in biorefining of the LCB in supercritical fluids. It is shown that processes with reduced environmental impact and energy consumption can significantly enhance biorefining of LCB at commercial scale. Enzymatic hydrolysis of LCB in supercritical carbon dioxide is a promising approach that can accommodate mild reaction conditions. Developing an understanding of the performance of enzymes in high pressure systems and designing carriers for enzyme immobilization and further recycling is expected to enable one pot pretreatment and hydrolysis and is an important milestone in processing renewable resources for deriving biofuel and value‐added chemicals.