【作者】 辛琴；

【导师】 刘洪来；

【作者基本信息】 华东理工大学 ， 物理化学， 2011， 博士

【摘要】 生物质的预处理是由生物质制备生物燃料过程中非常重要的关键步骤之一。然而,当前相关技术的效率和成本效益仍然有待突破。本文针对离子液体预处理生物质过程,系统研究了链状流体的分子热力学模型、含离子液体系统的相平衡及离子液体在生物质预处理中的应用,为离子液体预处理生物质过程的工程化进行了前期探索,积累了相关的基础数据和工艺优化所必需的分子热力学模型。在链状流体的分子热力学模型构建方面,我们完成了以下工作：(1)基于密堆积格子构建了一个新的随机共聚高分子溶液的混合亥氏函数模型。模型主要包含三个方面的贡献：高分子和溶剂的无热混合熵贡献、多元组分单体间相互作用能贡献和高分子拆分及高分子成链的贡献。第一项贡献采用了Guggenheim模型计算；杨建勇等建立的多元Ising格子模型用于计算第二项的贡献；高分子链贡献则由化学缔合统计力学理论计算。该模型预测值与计算机Monte Carlo(MC)模拟结果几乎吻合一致,且能很好的应用于实际随机共聚物溶液的液液相平衡计算。(2)在上述模型的基础上,通过增加考虑所有高分子链自身的长程相关性,开发了一个适用于多元链状流体的混合亥氏函数模型。与计算机MC模拟结果比较,该模型较Flory Huggins理论(FHT)和Revised Freed理论(RFT)有了很大的改善,能用于计算含离子液体和链状高分子系统的各种复杂液液相图。在关联实际系统时,可用二元系统关联得到的参数直接预测不同温度下的三元相平衡。(3)鉴于密堆积格子模型不能描述压力对相平衡影响的缺陷,开发了一个改进的Percus-Yevick范德华状态方程。方程中所包含的纯流体参数α和6可由其蒸发焓、密度和分子量等物性估算得到,唯一可调的两元参数a12可由挥发性的非电解质亨利常数获得。除了一些系统在低离子液体浓度区域内出现比较大的偏差,该状态方程对含离子液体两元系统的计算结果与实验值吻合很好；对两元系统液液平衡的关联效果也令人满意。在含离子液体系统的相平衡及其在生物质预处理中的应用研究方面,我们完成了以下工作：(1)实验测定了22℃下含离子液体[C2mim][Ac]或[C4mim][Ac]三元系统的液液相平衡数据,同时发展了相关模型并对这些含离子液体系统的液液相平衡数据进行了关联计算。结果发现,离子液体[C2mim][Ac]或[C4mim][Ac]与磷酸钾溶液(K3P04)形成的双水相系统(Aqueous Biphasic Systems,简称ABS)最高可回收95.0%以上的离子液体。我们结合模型关联结果对含离子液体系统液液分相的机理进行了定性解释。(2)考察了不同离子液体溶解生物质组分的能力。选用1-乙基-3-甲基咪唑乙酸盐([C2mim][Ac])对芒属(Miscanthus)生物质进行了溶解试验,研究发现：通过添加K3P04溶液作为反溶剂可以形成离子液体与盐的ABS,并将离子液体中的溶解物沉淀出来,经液液平衡分离可以回收离子液体和磷酸钾盐,再由固液分离及两次水洗沉淀物后,在50℃下对处理过的生物质成分进行生物酶水解。与其它预处理方法获得的结果比较显示,该方法是一个新的有潜力的生物质预处理过程。预处理过的芒属木质素和半纤维素含量较低,使得酶解得到葡萄糖的速率和产率都很高,在12小时内就能达到85.0%的产率,24小时后几乎100%的产率；回收后的离子液体和磷酸钾盐可重复使用,用回收的离子液体处理生物质,其酶解结果也挺令人满意,在12小时内可达到70.0%的产率。(3)针对木质素在离子液体中富集影响溶解能力的问题,采用乙酸乙酯(EtOAc)、1,4-二氧杂环已烷(1,4-dioxane)和四氢呋喃(THF)三种有机溶剂对离子液体[C2mim][Ac]水溶液中的不同木质素成分进行了萃取分离。研究发现分子量越小的木质素越容易被萃取至有机相；THF有着相对较好的萃取能力；同时降低pH值可一定程度上提高木质素的分配系数值。更多还原

【Abstract】 The biomass pretreatment is one of the most important steps in the process of manufacturing biofuels from biomass. While the modern technology is not that efficient and still waiting for big break. In this paper, to develop the ionic liquids pretreatment process, we have developed the molecular thermodynamic model for chain-like fluid system and studied the phase equilibrium for systems containing ionic liquids and its application in the biomass pretreatment process. These previous exploration has provided fundamental information and necessary molecular thermodynamic models for optimizing ionic liquids pretreatment process.Mainly, the theory work includes the following three parts:(1) A new molecular thermodynamic model of mixing Helmholtz energy for random copolymer solutions based on close-packed lattice has been developed. The model contains three contributions:the contribution from athermal mixing of polymer chain and solvent, the Helmoltz energy of mixing in a multi-component Ising lattice, and the contribution from dissociation of polymer and association of monomers. The Guggenheim model is used to calculate the athermal mixing entropy, Yang et al.’s multicomponent Ising lattice model is used to calculate the mixing Helmholtz energy of multi-component Ising lattice and the statistical association theory of Cummings, Zhou and Stell is used to calculate the Helmholtz energy due to dissociation of polymer and association of monomers, respectively. It is shown that comparisons between show that the agreement between Monte Carlo (MC) simulated coexistence curves and that predicted by this model is nearly perfect. The model can be satisfactorily used to correlate the liquid-liquid equilibrium of practical random copolymer solutions.(2) Based on previous model, we have generally extended it to the multicomponent chain-like fluid mixtures by considering all the long-range interactions in each single chain. The liquid-liquid phase equilibrium of ternary chain-like mixtures predicted by this model are in good agreement with MC simulation results and much better than that calculated by Flory Huggins theory (FHT) and Revised Freed theory (RFT) obviously. This model can describe types 1-3 phase separations of Treybal classification satisfactorily. Meanwhile, model parameters correlated from the binary system can be further used to predict the corresponding liquid-liquid equilibrium of ternary mixtures, including systems containng ionic liquids or chain-like polymers.(3) Since the closed-packed lattice model can’t describe the effect of pressure on the phase equilibrium, we have developed a revised Percus-Yevick-van der Waals equation of state. Pure-component parameters a and b in the equation are estimated from the enthalpy of vaporization and liquid-density data of pure-component. The only adjustable binary parameter a12 can be obtained from Henry’s constant for the nonelectrolyte. Calculated total pressures of ionic liquid solutions are in good agreement with experimental data although in a few systems observed total pressures are slightly higher than those calculated in the region where the ionic liquid is dilute. The results of correlating a few binary systems with a miscibility gap are also quite satisfying.For the application of ionic liquids in biomass pretreatment process, we have done the following three experimental works:(1) At 22℃, we have measured the ternary liquid-liquid equilibrium data for aqueous biphasic systems containing [C2mim][Ac] or [C4mim][Ac]. The results show that using the potassium phosphate solution (K3PO4) is able to recycle at least 95.0% ionic liquids. Meanwhile, to better understand the phase separation mechanism of these systems, we have used our model to calculate and correlate the experimental data.(2) We have studied the solubility of biomass in different ionic liquids and chose 1-ethyl-3-methylimidazole acetate ([C2mim][Ac]) as the candidate solvent to dissolve Miscanthus. The results show that the K3PO4 solution is able to be used as an anti-solvent to precipitate biomass and an aqueous biphasic system of IL phase and salt phase is formed. After separating the liquids and solid, the solid phase has been washed by water twice before an enzymatic hydrolysis step carrying out to convert cellulose to glucose at 50℃. The results of this new process show that it is a very potential pretreatment method for Miscanthus, which gives a pellet with relative low content of lignin and hemicellulose and has obtained a high rate and high yield of glucose conversion from cellulose. The yield of 85.0% was obtained in 12h and nearly 100% after 24h. Meanwhile, the [C2mim][Ac] and K3PO4 solutions were recycled and reused after simple treatment. The two re-runs have also given a pretty good result,70.0% yield in 12h.(3) To solve the accumulation problem of lignin in IL-rich phase, we have studied three organic solvents:ethyl acetate (EtOAc),1,4-dioxane and tetrahydrofuran (THF) to extract and separate different kinds of lignin from [C2mim][Ac] aqueous solution. The results show that the smaller the molecular weight of lignin, the easier be extracted to the organic phase. THF has turned out to be the best solvent among these three. Lower pH is able to increase the partition coefficients.更多还原