纤维素水解液膜蒸馏浓缩与同步脱毒的机理与过程研究

A low glycose concentration and existence of various fermentation inhibitors in cellulosic hydrolysate are the main reasons that cause a low bioethanol concentration in fermentation and high energy-consumption during concentration. However, few reports on concentration and synchronous detoxification of cellulosic hydrolysate are available. Thus, a study on membrane based concentration of low energy-consumption and synchronous detoxification can promote the bioethanol concentration in fermentation. This project attempts to apply membrane distillation and investigates the feasibility and mechanism of concentration and synchronization detoxification of cellulosic hydrolysate. Firstly, the thermal efficiency of low-level heat such as solar energy and waste hot heat is evaluated. Secondly, the feasibility of low-level heat in the process of membrane distillation concentrate of cellulosic hydrolysate is analyzed. Thirdly, the efficiency and mechanism of various typical inhibitors removal are investigated based on the vapor-liquid phase equilibrium on the membrane surface. At last, the vapor-liquid phase equilibrium on the membrane surface is changed by means of adding the “salt-out” components in liquid phase or filling adsorbents in vapor phase, which then enhances the mass transfer impetus and improves the detoxification effect. This project applies membrane distillation technology and proposes concentration and synchronization detoxification of cellulosic hydrolysate as a novel idea, aiming at promoting the development of bioethanol.

纤维素水解液中糖浓度低、存在多种发酵抑制物是导致最终发酵液中生物乙醇浓度过低、浓缩能耗高的主要原因，而现有对纤维素水解液进行浓缩及同步脱毒(去除抑制物)的研究鲜有报道。因此，开展基于膜过程的低耗浓缩和同步脱毒研究有助于提高发酵液中纤维素乙醇的浓度。本项目拟以膜蒸馏为关键技术，利用低品位热源开展纤维素水解糖液的浓缩与同步脱毒的可行性与机理研究，包括：评价太阳能、纤维素预处理过程中产生的废蒸汽等热效率，分析低品位热用于膜蒸馏浓缩水解液过程的可行性；基于膜蒸馏过程中膜界面处汽液平衡原理，考察纤维素水解液中不同的典型发酵抑制物去除效率及其机理；通过添加具有盐效应的第三组分，或者在膜蒸馏组件下游填充吸附剂改变膜界面汽液平衡，提高传质推动力，增强脱毒效果，并研究该过程的强化机制。本项目以膜蒸馏作为主要技术手段，提出了低能耗纤维素水解液浓缩与脱毒结合的新思路，有望促进纤维素生物乙醇的发展。

为提高纤维素乙醇的发酵浓度以降低后续分离浓缩的成本，纤维素水解糖液的浓缩和脱毒至关重要。膜蒸馏作为一种新型的膜分离技术，可在较低的温度下把非挥发性物质浓缩至极高的浓度同时去除溶液中的挥发性组分，在纤维素水解糖液浓缩和脱毒应用方面拥有巨大的潜力。本项目首次采用真空膜蒸馏法(VMD)对纤维素水解糖液的浓缩和脱毒进行了初步研究，并在此基础上实现高效发酵制备纤维素乙醇。.首先考察了料液温度、料液流速和料液浓度等操作参数对VMD浓缩模拟糖时通量和截留率的影响。膜通量随料液流速和温度的升高而增加，随料液浓度升高而降低，确定浓缩的最佳条件为温度65℃，流速1.0m/s，下游真空度5kPa，并在此条件下把初始浓度为5g/L的模拟葡萄糖溶液浓缩10倍，整个过程对葡萄糖的截留率大于99.5%，有效组分损失小。.其次研究了VMD对抑制物糠醛和乙酸的去除效果。当葡萄糖浓度为5g/L，乙酸和糠醛浓度为1.25g/L时，在料液温度70℃，下游压力5kPa条件下，由于低浓度范围内糠醛-水相对挥发度远大于乙酸-水的相对挥发度，糠醛和乙酸的去除率相差很大，分别为96.25%和24.79%。为提高乙酸的去除率，采用盐效应和吸附法来改变乙酸-水的气液平衡。实验结果表明：在料液中添加第三组分盐对改变乙酸气液平衡来提高乙酸对水的相对挥发度影响不大，而在组件下游侧填充吸附剂可以有效的提高乙酸的去除率，添加活性炭和树脂后，乙酸的去除率从28.9%分别提高到42.8%和73.2%，为无吸附剂时的1.48和2.53倍。.最后对经VMD浓缩及脱毒的玉米秸秆酶解液的发酵情况进行了考察，未经浓缩和2倍浓缩糖液的发酵乙醇最高浓度分别为15.99g/L和28.69g/L，3倍浓缩糖液由于碳源充足，抑制物糠醛完全脱除，发酵36h后达到最高浓度42.18g/L，是前两者的2.64和1.47倍。发酵结果表明VMD可有效地浓缩纤维素水解糖液至合适的发酵浓度(>100g/L)同时去除抑制物，提高乙醇的发酵浓度。

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