Investigation of the Effect of Supercritical Carbon Dioxide Pretreatment on Sugar Yield Prior to Enzymatic Hydrolysis of Empty Fruit Bunches

Abstract

Supercritical carbon dioxide (SC-CO₂) pretreatment of empty fruit bunches (EFBs) was investigated for its effect on glucose yield following enzymatic hydrolysis. The SC-CO₂ pretreatment of EFBs was performed under various conditions: temperature of 80°C or 130°C; pressure of 150, 200, or 250 bar; moisture content of 0% or 75%; and time of 30 min or 60 min. The SC-CO₂-pretreated EFBs were hydrolyzed using a combination of the enzymes Celluclast 1.5L and Novozyme 188 (Sigma Aldrich, St. Louis, MO) . The chemical compositions of untreated EFBs (% g/g dry biomass) were recorded as 36.7% cellulose, 22.8% hemicellulose, and 24.2% klason lignin. The optimal chemical composition of EFBs for SC-CO₂ pretreatment were 38%, 25.5%, and 23.8% for cellulose, hemicellulose, and klason lignin, respectively. After enzymatic hydrolysis, the glucose yield of untreated EFBs was 17% (17 g/100 g dry biomass). SC-CO₂ pretreatment of EFBs for 60 min at 75% moisture content, 130°C, and 250 bar pressure gave the highest glucose yield of 24%. Pretreatment combined with premixing of the EFBs with alkali (SC-CO₂ + alkaline) yielded glucose and xylose contents of 36.8% and 14.9%, respectively, The results showed an increase in glucose of about 13% for premixed pretreatment compared to SC-CO₂ pretreatment alone. Morphology analysis showed changes on the surface of the treated EFBs, which looked swollen and ruptured compared with the surface of the untreated EFBs.