Comparison of Soda and Kraft Cooking as a Pretreatment Method for Enzymatic Hydrolysis of Softwood Lignocellulosic Materials

Abstract

Lignocellulosic materials are composed of cellulose, hemicellulose and lignin. Since cellulose is surrounded by lignin, a pretreatment is required to enhance the contact with enzyme for enzymatic hydrolysis. So far, several methods: grinding, steaming, steam explosion, microwave treatment and so on have been studied for wood, however, it is still difficult to saccharify softwood very efficiently. In this study, soda and kraft cooking for chemical pulping were applied for the pretreatment of softwood (Japanese cedar) shaving. The lignin content of kraft pulp ranged from 12% to 3% with increasing cooking time from 1 to 3 hours. Saccharification efficiency after 1 day increased from 90% to 98% with decreasing the lignin content of kraft pulp. The soda and kraft pulp with the same lignin content showed similar saccharification efficiencies. The longer cooking time realized the smaller lignin content, but at the same time, the loss of carbohydrates was larger. As a result, the yields of sugar to wood were almost constant (40%) with a lignin content up to 10% whether the pretreatment was soda or kraft cooking. Even soda cooking is useful enough as a pretreatment method for saccharification of softwood.