Supercritical CO2 pretreatment of lignocellulose enhances enzymatic cellulose hydrolysis

The supercritical carbon dioxide …SC±CO2† pretreatment of lignocellulose for enzymatic hydrolysis of cellulose was investigated. Aspen (hardwood) and southern yellow pine (softwood) with moisture contents in the range of 0±73% (w/w) were pretreated with SC±CO2 at 3100 and 4000 psi and at 112±165°C for 10±60 min. Each pretreated lignocellulose was hydrolyzed with commercial cellulase to assess its enzymatic digestibility. Untreated aspen and southern yellow pine (SYP) gave ®nal reducing sugar yields of 14:5 2:3 and 12:8 2:7% of theoretical maximum, respectively. When no moisture was present in lignocellulose to be pretreated, the ®nal reducing sugar yield from hydrolysis of SC±CO2-pretreated lignocellulose was similar to that of untreated aspen. When the moisture content of lignocellulose was increased, particularly in aspen, signi®cantly increased ®nal sugar yields were obtained from enzymatic hydrolysis of SC±CO2-pretreated lignocellulose. When the moisture content of lignocellulose was 73% (w/w) before pretreatment, the sugar yields from the enzymatic hydrolysis of aspen and southern yellow pine pretreated with SC±CO2 at 3100 psi and 165°C for 30 min were 84:7 2:6 and 27:3 3:8% of theoretical maximum, respectively. The SC±CO2 pretreatments of both aspen and SYP with moisture contents of 40, 57, and 73% (w/w) showed signi®cantly higher ®nal sugar yields compared to the thermal pretreatments without SC±CO2