青贮对柳枝稷制取燃料乙醇转化过程的影响

Effect of ensilage on bioconversion of switchgrass to ethanol based on liquid hot water pretreatment

摘要:

青贮是一种传统的生物质原料保存方法，广泛应用于纤维素乙醇炼制领域尚需要考察其对原料品质和下游乙醇转化过程的影响。文中以秋季 (初、中和末) 收割的柳枝稷为原料，通过青贮、高温水热 (LHW) 预处理、纤维素酶水解和同步糖化与发酵 (SSF) 实验对上述问题予以回答。结果显示，秋季初收割的柳枝稷以不同湿度青贮后pH均小于4.0，干重损失小于2%，各主要成分与青贮前相比无明显变化；LHW预处理中青贮样品半纤维素水解率普遍高于未贮存样品，但青贮同样使原料获得了更高的发酵抑制物产生水平；青贮柳枝稷葡萄糖、木糖和半乳糖产量 (预处理+酶水解) 高于未贮存柳枝稷；经过168 h的SSF，青贮样品乙醇浓度为12.1 g/L，未贮存的秋季初、秋季中和秋季末柳枝稷为底物的浓度分别为10.3 g/L、9.7 g/L和10.6 g/L。综上，青贮有助于提高柳枝稷LHW预处理效率、酶水解率和乙醇产量。

Abstract:

Ensilage is a traditional way of preserving fresh biomass. However, in order to apply ensilage to the ethanol biorefinery, two parameters need to be evaluated: quantity and quality changes of the biomass; and its effects on bioconversion process. To study these two aspects, switchgrass harvested on three different time points (Early, mid and late fall) were used as feedstock. The early fall harvested biomass was ensiled at 5 moisture levels ranging from 30% to 70%. Silage of 40% moisture and 3 other raw switchgrass were pretreated with liquid hot water, followed by enzymatic hydrolysis as well as simultaneous saccharification and fermentation. After 21 days storage pH values of all silages decreased below 4.0 and the dry matter losses were less than 2.0%, and structural sugars contents did not change dramatically. Liquid hot water caused more hemicellulose dissolution in the silage than in unensiled switchgrass. However, ensilage also increased the risk of releasing more sugar degradation products; After enzymatic hydrolysis, silage obtained higher total glucose, xylose and galactose yields than raw materials; After simultaneous saccharification and fermentation, ethanol concentration in silage was 12.1 g/L, higher than the unensiled switchgrass (10.3 g/L, 9.7 g/L and 10.6 g/L for early, mid and late fall respectively). Our results suggest that ensilage helps increase pretreatment efficiency and sugar yield, which increases final ethanol production.