Varga Enikõ, Klinke Helene B, Réczey Kati, Thomsen Anne Belinda
Budapest University of Technology and Economics, Department of Agricultural Chemical Technology, H-1521 Budapest, Szt Gellért tér 4, Hungary.
Biotechnol Bioeng. 2004 Dec 5;88(5):567-74. doi: 10.1002/bit.20222.
In this study ethanol was produced from corn stover pretreated by alkaline and acidic wet oxidation (WO) (195 degrees C, 15 min, 12 bar oxygen) followed by nonisothermal simultaneous saccharification and fermentation (SSF). In the first step of the SSF, small amounts of cellulases were added at 50 degrees C, the optimal temperature of enzymes, in order to obtain better mixing condition due to some liquefaction. In the second step more cellulases were added in combination with dried baker's yeast (Saccharomyces cerevisiae) at 30 degrees C. The phenols (0.4-0.5 g/L) and carboxylic acids (4.6-5.9 g/L) were present in the hemicellulose rich hydrolyzate at subinhibitory levels, thus no detoxification was needed prior to SSF of the whole slurry. Based on the cellulose available in the WO corn stover 83% of the theoretical ethanol yield was obtained under optimized SSF conditions. This was achieved with a substrate concentration of 12% dry matter (DM) acidic WO corn stover at 30 FPU/g DM (43.5 FPU/g cellulose) enzyme loading. Even with 20 and 15 FPU/g DM (corresponding to 29 and 22 FPU/g cellulose) enzyme loading, ethanol yields of 76 and 73%, respectively, were obtained. After 120 h of SSF the highest ethanol concentration of 52 g/L (6 vol.%) was achieved, which exceeds the technical and economical limit of the industrial-scale alcohol distillation. The SSF results showed that the cellulose in pretreated corn stover can be efficiently fermented to ethanol with up to 15% DM concentration. A further increase of substrate concentration reduced the ethanol yield significant as a result of insufficient mass transfer. It was also shown that the fermentation could be followed with an easy monitoring system based on the weight loss of the produced CO2.
在本研究中，乙醇由经碱性和酸性湿式氧化（WO）（195℃，15分钟，12巴氧气）预处理的玉米秸秆生产，随后进行非等温同步糖化发酵（SSF）。在SSF的第一步，在50℃（酶的最佳温度）加入少量纤维素酶，以便由于一些液化作用获得更好的混合条件。在第二步，在30℃加入更多纤维素酶并与干面包酵母（酿酒酵母）混合。富含半纤维素的水解产物中存在亚抑制水平的酚类（0.4 - 0.5克/升）和羧酸（4.6 - 5.9克/升），因此在对整个浆液进行SSF之前无需解毒。基于湿式氧化玉米秸秆中可用的纤维素，在优化的SSF条件下获得了理论乙醇产量的83%。这是在底物浓度为12%干物质（DM）的酸性湿式氧化玉米秸秆、30 FPU/克DM（43.5 FPU/克纤维素）酶负载量的条件下实现的。即使酶负载量为20和15 FPU/克DM（分别对应29和22 FPU/克纤维素），乙醇产量也分别达到了76%和73%。在SSF 120小时后，达到了最高乙醇浓度52克/升（6体积%），这超过了工业规模酒精蒸馏的技术和经济极限。SSF结果表明，预处理玉米秸秆中的纤维素可以有效地发酵成乙醇，底物浓度可达15% DM。由于传质不足，底物浓度的进一步增加显著降低了乙醇产量。还表明，可以通过基于产生的二氧化碳重量损失的简易监测系统跟踪发酵过程。
