绿液预处理对棉秆化学成分及酶水解糖化的影响

摘要

Green liquor consists of sodium carbonate and sodium sulfide and is generated in chemical recovery system of a kraft mill. Cotton stalk was pretreated by green liquor （GL） at different total titrateable alkali （TTA） charge, sulfidity and temperature. The pretreated materials were hydrolyzed with different enzyme dosages to evaluate the effects of GL pretreatment on sugar yield improvement. The results show that the cooking yield drops with the increase of TTA charge. A reasonable increase of the pretreatment TTA charge and suifidity can promote the sugar conversion ratio efficiently. A strong pretreatment leads to a serious degradation of carbohydrate and lowers sugar recovery in the following enzymatic hydrolysis. In addition, cotton bark accounts for a larger proportion of cotton stalk, leading to a low final yield of total sugar hydrolysis. The conversion ratio of glucan, xylan and total sugar in cotton stalk pretreated by 16% TTA and sulfidity 32% at 120℃ reached up to 74.0%, 61.3%, and 68.5%, respectively, while cellulase load was 20 FPU/g substrates.%绿液的主要成分是Na2CO3和Na2S，可在硫酸盐浆厂碱回收系统中循环产生。将新疆棉秆在不同温度、硫化度和用碱量下经绿液预处理后，在不同酶用量下进行酶水解，并测定酶水解液中总糖得率以评价预处理效果。结果表明，原料预处理得率随用碱量的增加而下降。适当地提高蒸煮温度和用碱量，可以增加木质素脱除量，有利于后续酶水解的进行，但过于剧烈的预处理条件将导致碳水化合物的过度降解，因而降低酶水解糖的转化率。另外，由于新疆棉秆细小，棉秆皮占全秆比例较大，原料总糖含量较低，导致最终酶水解总糖得率偏低。在温度120℃，用碱量16％，硫化度32％条件下绿液预处理，酶水解糖转化率达到最大值，当酶水解酶用量为20FPU／g（对浆料）时，葡聚糖、木聚糖和总糖的转化率分别为74．0％、61．3％和68．5％。