木薯酒精渣的预处理及补料同步糖化发酵制取乙醇

摘要

Processing cassava alcohol residues(CAR)is one of the bottlenecks of the large scale application of the cassava based alcohol production. This study focused on the ethanol production using CAR as raw material by pretreatment of CAR and simultaneous saccharification and fermentation (SSF). The chemical compositions of cassava alcohol residues were analyzed. Pretreatment was conducted by different methods such as aqueous ammonia pretreatment,sodium hydroxide pretreatment and the combined pretreatment with aqueous ammonia and dilute sulfuric acid. The effect of different pretreatment methods on enzymatic digestibility of CAR were studied. The structural feature of CAR was analyzed by X-ray diffraction(XRD)and scanning electron microscope(SEM). The fed-batch method was combined with simultaneous saccharification and fermentation(SSF)to enhance ethanol concentration further and reduce enzyme loading. The results showed that among the three pretreatment methods the combined pretreatment was more effective on increasing cellulose and digestibility of cellulose. Cellulose increased 111.26% and lignin decreased 35.05% after being pretreated by the combined pretreatment. Compared with no pretreated cassava alcohol residues, cellulose conversion rate increased from 42.10% to 61.71% at 72h of enzyme hydrolysis when the CAR pretreated by combined pretreatment were used as substrate. After pretreatment by aqueous ammonia,the lignin decreased,the cellulose and crystallinity increased,and the surface of CAR became rougher. The ethanol concentration was 51.0g/L at 120h by fed-batch combined with SSF when the initial substrate concentration was 100.0g/L and the final substrate concentration of 400.0g/L by adding aqueous ammonia pretreated CAR at 20h,40h and 60h,respectively.%木薯酒精渣的处置是制约木薯燃料乙醇大规模产业化的问题之一.本文立足于探索木薯酒精渣利用途径,分析了木薯酒精渣的主要成分,对比了氨水、氢氧化钠、氨水组合稀硫酸3种预处理方式对于木薯酒精渣纤维素和木素含量及纤维素酶水解效率的影响,分析了处理前后木薯酒精渣的表面结构及纤维素结晶度,并以氨水处理后的木薯酒精渣为底物,进行了同步糖化发酵.结果表明,3种预处理方法中组合预处理能更好地增加纤维素含量和提高纤维素酶水解效率,与未处理原料相比,组合预处理后纤维素含量增加了111.26%,木素下降了35.05%,酶水解72h纤维素转化率从42.10%增加到61.71%.氨水预处理后,原料的木素含量降低,处理后木薯酒精渣的表面变得更加粗糙,纤维素结晶度有所增加,以氨水处理后的木薯酒精渣为底物进行分批补料同步糖化发酵,当初始底物浓度为100.0g/L,分别在20h、40h、60h进行补料至最终底物浓度为400.0g/L时,发酵120h乙醇浓度达到51.0g/L.