甲酸-水共沸体系下的杨木组分分离

Separation of Poplar Components under Formic Acid-Water Azeotrope

利用杨木甲酸法制浆,研究了甲酸-水共沸体系下杨木半纤维素的溶出规律。结果表明,废液中的木糖和低聚木糖源于半纤维素的水解,占废液中总碳水化合物的73%~77%,废液中低聚木糖的比例由70%(1.5 h)降低至13%(4 h),说明随蒸煮的进行,低聚木糖逐步水解为木糖。半纤维素的阿拉伯聚糖在甲酸-水共沸体系下较易水解,主要以单糖形式存在于废液中,相对原料质量其溶出率低于0.37%。甘露聚糖在蒸煮2 h内以低聚糖形式溶出,在蒸煮4 h时废液中低聚甘露糖和甘露单糖各占58%和42%。废液中低聚葡萄糖和葡萄糖的总量低于原料质量的0.7%,说明蒸煮过程中纤维素水解微弱。物料平衡分析表明:纸浆得率随蒸煮时间延长而逐渐下降,废液中可溶性固形物逐渐上升并于3 h后趋于平衡,过程物料损失低于3%。废液中可溶性固形物由木素和碳水化合物组成,分别占70%和30%,且碳水化合物93%源于半纤维素,这说明甲酸-水体系对原料中木素的溶出较聚糖(纤维素+半纤维素)强烈,且具有保留纤维素的脱木素特征。

The dissolution of poplar hemicellulose in formic acid-water azeotrope was studied by formic acid pulping. The results showed that the xylose and oligo-xylose in the waste liquor were derived from hydrolysis of hemicellulose,which accounted for 73% ~ 76% of the total carbohydrate in the waste liquid. The proportion of oligo-xylose in the waste liquid was reduced from 70%（ 1. 5 h） to 13%（ 4 h）,indicating that with the progress of cooking,oligo-xylose were gradually hydrolyzed to xylose. The hemicellulose arabinan is more easily hydrolyzed in the formic acid-water azeotrope system,mainly in the form of monosaccharide in the waste liquid. The dissolution rate of the raw material is below 0. 37%. The mannan was dissolved in the form of oligosaccharides for 2 h during cooking,and 58% and 42% of oligo-mannose and mannose in the waste liquid at 4 h. The total amount of oligoglucose and glucose in the waste was lower than 0. 7% of the mass of the raw material,indicating that the cellulose hydrolysis was weak during the cooking process. The results show that the yield of pulp gradually decreases with the prolonging of cooking time,and the soluble solids in the waste liquid gradually increase and tend to balance after 3 hours,and the process material loss is less than 3%. The soluble solids in the waste consisted of lignin and carbohydrate,accounting for 70% and 30%,respectively,and 93% of the carbohydrate was derived from hemicellulose,indicating that that the dissolution of lignin in the raw material of the formic acid-water system is stronger than that of the polysaccharide（ cellulose ＋ hemicellulose） and has a delignification feature that retains cellulose.