Enzymatic saccharification of lignocellulosic materials after treatment with supercritical carbon dioxide

Lignocellulosic materials, such as agricultural residues, are abundant renewable resources for bioconversion to sugars. The sugar cane bagasse was studied here to obtain simple sugars for the production of alcohols and other chemicals. The crystalline structure of cellulose and the lignin that physically seals the surrounding cellulose fibers makes enzymatic hydrolysis difficult by preventing the contact between the cellulose and the enzyme. Two different samples of sugar cane (bagasse pulp and skin) were used and compared with microcrystalline cellulose (Avicel). The investigated samples were pretreated with SC-CO₂ explosion before hydrolysis. The experiments were conducted at 12, 14 and 16 MPa at a temperature of 60 °C. In this process, particles of celluloses within the size range from 0.25 to 0.42 mm were placed in defined amounts inside the experimental vessel, CO₂ was injected and let stand for 5 and 60 min. The explosion pretreatment of cellulosic materials by SC-CO₂ was performed in an apparatus of a static type with 300 ml of volume. The hydrolysis reaction using cellulose enzyme was carried at 55 °C for 8 h. After the pretreatment, the glucose yield increased in 72% to the bagasse sample. The SC-CO₂ pretreatment together with alkali increased the glucose yield in 20% as compared with alkali only. X-ray, microscopy and thermal analysis were used to investigate the effect of the pretreatment.