离子液体预处理生物质中液液相平衡的实验与理论研究

In the process of manufacturing second-generation bioethanol from biomass, the product yields can be effectively improved by pretreatment of biomass using ionic liquid (IL) with polar aprotic solvent. Due to its high cost, it is necessary to recycle and reuse IL to make the process more economical. The IL-based aqueous biphasic system (ABS) in the presence of solvent will be formed using inorganic salt to recover IL. However, the separation and recovery process of IL cannot be conducted without the reliable phase equilibrium data. In this proposal, experimental and theoretical study on the liquid-liquid equilibrium (LLE) for this quaternary system will be conducted. In experimental study, a new LLE apparatus will be developed with a temperature range from 293.15 to 353.15 K and normal pressure. LLE data will be obtained as well as the physicochemical properties (e.g. viscosity, density and pH) of the IL-based ABS; the microscopic images and spectrograms will be acquired. The factors influenced the phase behavior will be analyzed from the macroscopic and microscopic identification studies. Therefore, optimum conditions will be identified to make the recovery process as efficient as possible. In theoretical study, based on the experimental studies, the e-NRTL model will be modified for the application to quaternary system containing IL. This fundamental study will present the LLE data for the recovery process of IL as well as the theoretical foundation for the phase behavior in the ABS.

在第二代生物乙醇制备中，利用离子液体混合非质子极性溶剂预处理生物质，可有效提高产率。为了降低离子液体带来的高成本，采用无机盐与含溶剂离子液体形成双水相体系的方法，对离子液体进行分离回收。准确、可靠的相平衡数据是开展离子液体回收利用理论研究和工程实践的基础。本项目将围绕四元双水相体系的液液相平衡展开实验和理论方面的研究。实验方面，研制一套新的液液相平衡实验系统（测量压力：常压，温度范围：293.15-353.15 K），宏观上获得四元相平衡的实验数据及相平衡体系中各相的物理化学性质（如黏度、密度、pH值等），微观上获得各相的显微图及谱图；从宏观和微观上分析各因素对相行为的影响规律，进而优化反应条件，提高离子液体的回收率。理论方面，基于实验数据及微观分析，修正e-NRTL模型以适用于含离子液体的四元体系。本项目的开展为离子液体的回收利用提供基础的相平衡数据，为四元体系相行为的理解提供理论指导。

离子液体被视为新型的绿色溶剂，在生物能源、有机合成、材料制备、催化与分离等领域得到了广泛的研究。本项目主要的研究内容及结果如下：（1）建立了三元体系相平衡分子热力学模型，混合物中含有缔合作用成分及溶剂化作用成分，即形成配位化合物，利用模型计算了氮气在丙酮和氯仿混合物的溶解度，考虑亨利常数的不确定性，计算值与实验数值的平均相对偏差为3.35%，吻合良好；（2）改进了毛细管黏度计，借助红外光谱仪，从宏观和微观上，研究了溶剂对降低离子液体黏度的影响规律；（3）基于收集的166种离子液体热物性数据，建立了基于修正的自由体积理论的离子液体黏度模型，最大偏差在4.01%内、相对偏差的绝对平均值在1.54%内；（4）在实验室条件下，制备38-46%的浓盐酸，并利用浓盐酸对生物质进行处理，效果理想。