【作者】 吕学斌；

【导师】 邹竞； 张毅民；

【作者基本信息】 天津大学 ， 化学工艺， 2009， 博士

【摘要】 木质纤维素转化为乙醇是生物质能源转化过程中研究的热点。本文对秸秆转化为生物乙醇过程中的预处理、酶水解和发酵以及乙醇的分离等关键问题进行了研究。通过对低温条件下玉米秸秆中半纤维素水解动力学的研究,得到了半纤维素的最佳水解条件。应用Seaman模型对实验数据进行分析,得到80-121℃下木糖的生成和降解速率,以及葡萄糖和糠醛的生成速率。通过对所得响应曲面进行分析得出各温度下的最佳水解条件分别为:在80℃下,硫酸浓度5%,反应时间240 min,最终木糖浓度为13.21 g/L;在100℃下,硫酸浓度5.5%,反应时间60 min,最终木糖浓度为18.73 g/L;在121℃下,硫酸浓度2%,反应时间60 min,最终木糖浓度为17.95 g/L。并应用阿累尼乌斯方程计算得到该温度范围内秸秆预处理过程的活化能为56.3 kJ/mol。采用稀酸预处理方法对油菜秸秆进行预处理,通过中心组合实验设计方法设计实验,对影响油菜秸秆预处理过程的硫酸浓度,预处理时间以及固体浓度等因素进行优化。结果发现,在180℃预处理条件下,硫酸浓度为1%,预处理时间为10 min,固体浓度为20%时,木糖产率为68.4%,木糖浓度达到27.3 g/L,较固体浓度为10%增大了一倍。而在121℃预处理条件下,固体浓度对预处理结果影响较大,当硫酸浓度为2%,预处理时间为60 min,固体浓度为10%时,木糖产率为73.6%,而此条件下木糖浓度只有14.7 g/L。扫描电镜结果进一步证明纤维素的结构在高温条件下更容易破坏。考察了固体浓度对油菜秸秆酶水解和发酵过程的影响。结果发现适当地增大固体浓度,对酶水解和发酵过程影响不显著,而葡萄糖和乙醇的最终浓度却显著增大。180℃预处理后的秸秆可以在25%的固体浓度下进行酶水解和发酵过程,最终的乙醇浓度可以达到4.6%,与10%固体浓度比较,乙醇浓度提高了2.05倍;而在低温预处理后的秸秆可以在20%的固体浓度下进行酶水解和发酵过程,最终的乙醇浓度达到了3.5%,与10%固体浓度所得的结果比较,乙醇浓度提高了1.76倍。选用膜蒸馏装置同时发酵和分离乙醇,考察了不同发酵方式对乙醇的生产速率、最终浓度以及乙醇产率。结果表明,与常规发酵过程比较,选用膜蒸馏装置同时发酵和分离乙醇,可以消除发酵过程中产生的乙醇对后续发酵过程的抑制,这样不仅可以提高乙醇的生产效率,同时乙醇生成速率也显著增大,最终乙醇的浓度也有了一定程度的提高。更多还原

【Abstract】 Lignocellulose converted to bioethanol is currently a hot subject in bioenergy conversion research. In this thesis, the key problems included pretreatment; enzymatic hydrolysis; fermentation and ethanol distillation in bioethanol conversion from straw were studied.Kinetic studies of hemicellulose hydrolysis of corn stover at low temperature were investigated in this thesis. Seaman model was used to analyze the experiments data and the kinetic parameters for xylose, glucose and furfural were obtained at different temperatures. The optimal conditions at different temperatures were obtained from the analysis of response surfaces, which were 5% H2SO4 at 80℃for 240 min with 13.21 g/L xylose; 5.5% H2SO4 at 100℃for 60 min with 18.73 g/L xylose and 2% H2SO4 at 121℃for 60min with 17.95 g/L xylose. Arrhenius equation was used to calculate the activity energy which was 56.3 kJ/mol.The central composite design was used to optimize the effect of acid concentration, treatment time and solid content on dilted sulfuric acid pretreatment of rapeseed strw at two temperatures. The results showed that the solid content was not significant on pretreatment at high temperature. After pretreated at 180℃, the xylose yield reached 68.4% and the concentration of xylose was 27.3 g/L at 1% sulfuric acid for 10 min, which was one time hiher than that of 10% solid content. However, the pretreatment was great affected by solid content at low temperature. After pretreated at 121℃, the xylose yield got to 73.6% at 10% solid content and the xylose concentration was 14.7 g/L at 2% sulfuric acid for 60 min. Scanning electron microscope(SEM) results showed that cellulose structure was more easily destroyed at high temperature than at low temperature.The effects of solid content on enzymatic hydrolysis and fermentation were studied in this thesis. The results showed that an acceptably higher solid content coul not prevent the enzymatic hydrolysis and fermentation process and on the contrary it could improve the final concentration of glucose and ethanol. The enzymatic hydrolysis and fermentation of rapeseed straw could be carried out at 25% solid content after pretreated at high temperature. And the final concentration of ethanol could get to 4.6% which was 2.07 times higher than that of 10% solid content. Moreover, the solid content could also reached 20% during enzymatic hydrolysis and fermentation after pretreated at low temperature and the final ethanol concentration was 3.5% which was 1.76 times higher than that of 10% solid content.Simultaneous ethanol fermentation and separation was carried out in a membrane distillation reactor. The ethanol production efficency, production rate and final ethanol concentration were compared between different fermentation mode, with membrane distillation and without membrane distillation. The results showed that fermentation with membrane distillation could separate ethanol from the broth which eliminated the inhibition of high ethanol concentration on fermentation. And the production efficency, production rate and final ethanol concentration were greatly improved in the fermentation with membrane distillation.更多还原