Cassells B, Karhumaa K, Sànchez I Nogué V, Lidén G
Department of Chemical Engineering, Lund University, Box 124, 221 00, Lund, SE, Sweden.
Novozymes A/S, Krogshoejvej 36, 2880, Bagsvaerd, SE, Denmark.
Appl Biochem Biotechnol. 2017 Feb;181(2):536-547. doi: 10.1007/s12010-016-2229-y. Epub 2016 Sep 8.
Wheat straw is one of the main agricultural residues of interest for bioethanol production. This work examines conversion of steam-pretreated wheat straw (using SO as a catalyst) in a hybrid process consisting of a short enzymatic prehydrolysis step and a subsequent simultaneous saccharification and fermentation (SSF) step with a xylose-fermenting strain of Saccharomyces cerevisiae. A successful process requires a balanced design of reaction time and temperature in the prehydrolysis step and yeast inoculum size and temperature in the SSF step. The pretreated material obtained after steam pretreatment at 210 °C for 5 min using 2.5 % SO (based on moisture content) showed a very good enzymatic digestibility at 45 °C but clearly lower at 30 °C. Furthermore, the pretreatment liquid was found to be rather inhibitory to the yeast, partly due to a furfural content of more than 3 g/L. The effect of varying the yeast inoculum size in this medium was assessed, and at a yeast inoculum size of 4 g/L, a complete conversion of glucose and a 90 % conversion of xylose were obtained within 50 h. An ethanol yield (based on the glucan and xylan in the pretreated material) of 0.39 g/g was achieved for a process with this yeast inoculum size in a hybrid process (10 % water-insoluble solid (WIS)) with 4 h prehydrolysis time and a total process time of 96 h. The obtained xylose conversion was 95 %. A longer prehydrolysis time or a lower yeast inoculum size resulted in incomplete xylose conversion.
小麦秸秆是生物乙醇生产中主要的农业残余物之一。本研究考察了在一个混合工艺中，以蒸汽预处理小麦秸秆（使用SO作为催化剂），该混合工艺包括一个简短的酶促预水解步骤以及随后与酿酒酵母木糖发酵菌株进行的同步糖化发酵（SSF）步骤。一个成功的工艺要求在预水解步骤中对反应时间和温度以及在SSF步骤中对酵母接种量和温度进行平衡设计。在210℃下使用2.5%SO（基于水分含量）蒸汽预处理5分钟后获得的预处理物料在45℃时显示出非常好的酶解消化率，但在30℃时明显较低。此外，发现预处理液对酵母有相当大的抑制作用，部分原因是糠醛含量超过3g/L。评估了在该培养基中改变酵母接种量的影响，在酵母接种量为4g/L时，在50小时内葡萄糖实现了完全转化，木糖实现了90%的转化。对于在混合工艺（10%水不溶性固体（WIS））中具有此酵母接种量、4小时预水解时间和96小时总工艺时间的过程，乙醇产量（基于预处理物料中的葡聚糖和木聚糖）达到0.39g/g。获得的木糖转化率为95%。更长的预水解时间或更低的酵母接种量会导致木糖转化不完全。
