【作者】 幸婷；

【导师】 张富春；

【作者基本信息】 新疆大学 ， 生物化学与分子生物学， 2008， 硕士

【摘要】 乙醇工业在国民经济中占有重要的地位。随着世界石油储量的锐减和我国环境保护工作的加强,车用燃料乙醇需求逐年增加。世界上90%的乙醇都是由发酵生成,发酵法生产乙醇的过程中,产物乙醇会对微生物的生长产生抑制,在线分离乙醇是消除产物抑制最有效的途径之一,可以提高发酵效率,同时简化分离和纯化工艺。为改进传统的乙醇发酵工艺,本文系统地研究了酿酒酵母、马克思克鲁维酵母生产乙醇的发酵特性,将两个酵母菌混合发酵,结合循环气提法在线分离产物,在前人研究的基础上改进了乙醇发酵循环气提耦合工艺,增加了低温循环水浴槽,使得提取产物乙醇的回流装置处于低温状态,克服了传统气提酒精发酵工艺中的不足,从化工分离与发酵工程两方面着手强化其单元操作特性,进一步提高气提在线分离乙醇效率,同时降低乙醇提取工艺中的能耗及废液量,并最终降低乙醇的生产成本。研究表明该工艺使得乙醇发酵水平得到了明显的提高。本文首先通过对酿酒酵母（Saccharomices cerevisiae）、马克思克鲁维酵母（Kluyveromyces marxianus）的发酵特性的研究,结合两个菌种的发酵特点,提出了乙醇混合菌发酵,通过研究混合菌发酵的接种方式、通气条件、流加补料策略提高乙醇生产得率,并得出混合菌批式发酵的基本条件:自然pH条件下,混合培养,发酵温度为35℃,通气量为0.5vvm进行发酵。其次,本文在乙醇批式发酵的基础上,对CO₂循环气提在线分离乙醇发酵工艺进行了考察,针对醇水溶液体系中不同循环气量、气提初始乙醇浓度以及低温循环水浴槽的温度对气提效率的影响进行了考察,得出循环气量、低温循环水浴槽的温度分别与乙醇移出速率成线性关系,而乙醇初始浓度与乙醇移出效率成抛物线性关系;采用低温收集回流乙醇,可得到浓度高达400 g?L-1的乙醇,其分离效果明显优于常温收集;结合实际发酵中最优发酵条件,得到乙醇发酵-耦合循环气提工艺的最优条件为:在乙醇浓度达到70 g?L-1左右时开始气提,气提循环气量为0.5vvm,低温水浴槽温度控制为2℃,该条件下,既能保证较高的乙醇生产强度,又能使乙醇生产的能耗为最低,从而降低乙醇的生产成本。将该循环气提工艺应用至真实乙醇发酵体系中,耦合混合菌发酵,结果表明可将发酵过程中的乙醇浓度控制在35 g·L-1左右,从而有效的消除产物抑制,酵母菌长期保持较高活力,发酵时间可延长至360 h;同时,乙醇对糖的得率为0.44 g·g-1,为流加补料批式发酵的1.22倍,乙醇的生产强度为4.32 g·L-1h-1,为流加补料批式发酵的2.29倍。更多还原

【Abstract】 The ethanol industry accounts for important role in national economy. With the increasing crisis of energy source and strengthening power of environmental protection, the demands of fuel ethanol consumption have grown very quickly in recent years. Ninety percent of the whole ethanol production in the world is generated by fermentation, but a main problem in fermentation is the product inhibition effect by the ethanol metabolized from the yeast in the process. One of the most effective method for alleviating product inhibition is in-situ ethanol separation, which can not only improve the efficiency of fermentation, but simplify the process of separation and purification. For improving the traditional ethanol fermentation technics of current alcohol industry of our country, the characteristics of Saccharomices cerevisiae and Kluyveromyces marxianus were systematically studied in this thesis, then the mixed fermentation were carried out by two yeast strains. Combined with cycled gas stripping to separate products in situ and the previous studies, the cycled gas stripping equipment were improved—a condenser was installed, so that the circumfluence equipment was all under a low temperature environment, the aim is to improve the disadvantages in the traditional fermentation with gas stripping. The study is mainly based on the characteristics of chemical engineering separation, and fermentation engineering to reduce the energy cost for ethanol distillation and the amount of the liquor wastes, the final goal is to decrease the cost. The results suggested that the new process could greatly improve the ethanol fermentation efficiency.Firstly, the characteristics of S. cerevisiae and K. marxianus, which were employed in all experiments, were studied, and mixed-yeasts fermentation was suggested based on the results. The ethanol production rate was expected to be improved by investigation of the mixed fermentation inoculation mode, air flow flux and fed-batch strategies The basal conditions of mixed-yeasts ethanol fermentation were obtained as: natural pH conditions, mixed cultivation, 35℃of fermentation temperature and 0.5 vvm of airflow flux for fermentation.Secondly, CO₂ cycle gas-stripping for separation of ethanol in situ was studied in ethanol batch or fed-batch fermentation. In this process, CO₂ produced in ethanol fermentation was circulated between fermentor and separation instrument. From the results in a gas stripping experiment with ethanol-water solution as medium, we concluded that the recycle rate of CO₂ or the temperature in the condenser was linear correlation to the efficiency of gas stripping respectively, while the concentration of ethanol in fermentor presented as a parabolic curve. In the condenser for collection of returning ethanol at low-temperature, the concentration of ethanol can reach to 400 g·L-1, which is significantly higher than that at normal temperature. Combined above results, the optimal conditions for gas stripping is: 70g·L-1 of ethanol concentration when gas-stripping started, the gas flow for the cycle at 0.5vvm, the condenser temperature at 2℃, if all the conditions were met, it could be guaranteed a higher ethanol productivity and a minimum energy consumption, thereby reducing the cost in ethanol production.The results of simulated gas stripping experiments indicated that when collecting ethanol at low temperature, the ethanol concentration in the condenser can reach to 400g·L-1. In ethanol fermentation with gas stripping, the ethanol productivity was 4.32g·L-1 h-1, which was 2.29 times to that in the fed-batch fermentation without gas stripping.更多还原