Lignocellulosic biomass steam explosion

Because the hemicellulose fraction of biomass materials can be separated from lignin and cellulose by dilute acid treatment, cellulose becomes more reactive towards cellulase. Hemicellulose hydrolysis rates vary with acid concentration, temperature, and solid-to-liquid ratio. With most lignocellulosic materials, complete hemicellulose hydrolysis can be achieved in 5-10 min at 160°C or 30-60 min at 140 °C. Dilute acid hydrolysis forms the basis of many pretreatment processes for example, autohydrolysis and steam explosion are based on high-temperature dilute acid catalyzed hydrolysis of biomass. 

The pretreatment of any lignocellulosic biomass is cmcial before enzymatic hydrolysis. The objective of pretreatment is to decrease the crystallinity of cellulose which enhances the hydrolysis of cellulose by cellulases (17). Various pretreatment options are available to fractionate, solubilize, hydrolyze and separate cellulose, hemicellulose and lignin components (1,18-20). These include concentrated acid (27), dilute acid (22), SOj (25), alkali (24, 25), hydrogen peroxide (26), wet-oxidation (27), steam explosion (autohydrolysis) (28), ammonia fiber explosion (AFEX) (29), CO2 explosion (30), liquid hot water (31) and organic solvent treatments (52). In each option, the biomass is reduced in size and its physical structure is opened. Some methods of pretreatment of Lignocellulose is given in Table I. 

Carbon dioxide explosion is a pre-treatment process that uses supercritical carbon dioxide to break down the biomass structure. In aqueous solution, carbon dioxide forms carbonic acid which depolymerizes lignocellulosic materials. As a small molecule, carbon dioxide can penetrate into the pores of the biomass better than ammonia. When carbon dioxide explodes due to the change of pressure, it breaks the cellulosic structure. This process is usually operated under high pressure but low temperature to prevent monosaccharide degradation. But in comparison to steam explosion and ammonia explosion processes, the sugar recovery yield from this process is... 

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