醋酸水解玉米芯中木聚糖的动力学

Kinetics of acetic acid hydrolysis for xylan from corn cobs

利用醋酸作为催化剂水解玉米芯中半纤维素来制备还原糖,测定了温度在160—200℃、固液质量比为1:15、搅拌速度为500r/m in下,不同水解时间水解液中还原糖的收率以及副产物糠醛的收率。利用半纤维素高温液态水的Garrote模型拟合还原糖生成过程。实验表明,该模型能够较好地描述还原糖生成过程以及副产物糠醛的产生过程。通过曲线拟合确定了不同水解温度下还原糖的生成速率以及降解速率,同时利用Arrhen ius方程确定木聚糖降解活化能为98.538 kJ/mol以及还原糖降解活化能为172kJ/mol。综合比较不同温度下水解液中的还原糖以及糠醛质量浓度,确定使用质量分数为5%的醋酸于180℃下水解19min为最佳水解条件。在此条件下水解液中还原糖收率可达45.135%,糠醛收率可维持在2.35%以下。

The hemicellulose in corn cobs was hydrolyzed for preparing reducing sugars with acetic acid as catalyst.The yields of reducing sugars and furfural were measured in different hydrolysis time under reaction conditions of 160-200 ℃,solid/liquid mass ratio 1∶15,stirring speed 500 r/min.By using the Garrote model of the hemicellulose hydrolysis with hot liquid water the formation process of reducing sugar was fitted.The results show that the model can better describe the formation of reducing sugar and the degradation of furfural as a by-products.Reducing sugars formation and degradation rate at different hydrolysis temperatures were identified through the curve fitting.At the same time,the hydrolysis activation energy of xylan is 98.538 kJ/mol and the activation energy of reducing sugars degradation is 172 kJ/mol determined with Arrhenius equation.Comprehensive comparison of reducing sugars and furfural mass concentrations in hydrolysate at different temperatures indicate that hydrolysis with acetic acid of mass fraction 5% at 180 ℃ for 19 min are optimum reaction conditions under which the yield of reducing sugars and furfural can reach 45.135% and 2.35%,respectively.