离子液体在萃取精馏法精制苯与回收噻吩中的热力学调控机制研究

Xinjiang is in rich coal resources, and a large number of coking crude produced in coal chemical industry and coal coking industry every year. As an important source of producing benzene, coking benzene always contains alkanes, alkenes and thiophene, which could form azeotropic mixture with benzene. The mixture which have a similar boiling point or forms azeotropic liquid cannot be separated by normal distillation, but the extractive distillation sometimes can solve this problem. The thiophene in coking benzene has not been recycled in both sulfuric acid washing method and catalytic hydrogenation method. The wastes of desulfurization in both methods are not only wasting of the high value resources but also a potential threat to the entironment of Xinjiang. The key of the extractive distillation is the choice of solvent. Comparing with the conventional organic solvents, ionic liquids (ILs) have non-volatile, good solvent selectivity，adjustable structural and environmental-friendly properties, which makes it a potentially excellent “green”distillation extraction solvent. .The aim of this project is to determine thermodynamic parameters of a series of ILs by inverse gas chromatography, such as infinite dilution activity coefficient, solubility coefficient, selection coefficient, and so on. Then，ILs were selected as the solvents by the experiments for the four parts of the extractive distillation process, including the process of removing toluene and xylene，the process of removing alkanes and alkenes, the process of refining benzene and the process of purifying thiophene. The simulation model of extractive distillation of coking benzene was also established by the data obtained from the vapor-liquid equilibrium experiments. In order to explore the relationship between the thermodynamic parameters of ILs and the components of distillation, four extractive distillation experiments were taken. In addition, some methods were taken to enlarge the adjustment of ILs thermodynamic parameters to obtain the adaptive solvent for the extractive distillation including changing consists of the ions, mixing two type of ILs, adding ILs to organic solvents together.

新疆煤炭资源丰富，煤化工、煤焦化等项目每年都产生大量焦化苯（CB）。作为工业生产用苯的重要来源，CB中含有多种烷烃及烯烃及噻吩等可与苯形成共沸物，普通精馏方法难以达到有效分离。并且，传统上采用硫酸洗涤和催化加氢等方法脱噻吩未加以回收利用，不仅造成资源浪费还会对生态环境产生威胁。采取萃取精馏法则可解决该问题，关键在选取适合的萃取精馏剂。与有机溶剂相比，离子液体（ILs）不挥发、选择性好、性质可调、环境友好，使其成为优良的“绿色”萃取精馏剂来源。.本题通过反气相色谱法测定系列ILs的热力学参数，针对CB萃取精馏实验的四个阶段分别选取ILs萃取精馏剂，通过汽液平衡法建立ILs参与下的热力学模型，并经相应实验探索ILs热力学性质与精馏成分的关系。此外，还通过调整ILs萃取精馏剂的阴阳离子组成、二元混合ILs、ILs复合有机溶剂等方式，实现在更大范围内对萃取精馏体系进行调控。

焦化苯（CB）是工业生产用苯的重要来源，同时也含有噻吩等高附加值组分，有效获取高质量精苯产品并高效回收噻吩具有重要价值。精馏萃取法相较于其他分离方法对CB组分中共沸或近沸体系的分离具有更大优势，但传统萃取精馏剂以有机溶剂为主，存在污染环境、待选溶剂种类少、易挥发和毒性大等缺点。本项目针对CB萃取精馏法精制苯与回收噻吩过程中，选用新型“绿色溶剂”离子液体（ILs）作为萃取精馏剂，通过以IGC法探究ILs的热力学参数，探索调控ILs其热力学性质机制入手，建立起快速筛选ILs作为萃取精馏溶剂的方法。并结合汽液平衡法建立ILs参与下萃取精馏过程的热力学模型，并通过调控ILs热力学性质优化CB分段萃取精馏工艺。.项目采用HSPiP软件和IGC法获取了ILs的溶解度参数，发现两种方法得到的溶解度参数相近。且对于不同的阴离子的ILs，随着阴离子变更，溶解度参数色散力分量δd基本保持不变，ILs的极性力分量δp和氢键力分量δh变化较大。反之，则随着阳离子碳链长度的变化，δd发生变化。针对不同需求，可通过改变ILs阴、阳离子组合结构实现其热力学性质的调控。随后以苯-环己烷、苯-正己烷共沸体系，苯-噻吩近沸体系为研究对象，探究了ILs热力学性质对萃取精馏实验得影响。通过IGC法测算了ILs的，计算了无限稀释下的选择性系数、容量因子以及综合萃取性能指数(PI∞)来评价ILs对三种共沸体系的分离能力并通过实验进行了验证，发现对于一个未知性质的IL，通过其热力学性质，就可初步判断与待分离体系的分离效果。此外，研究还发现基于IGC方法能快速准确得到物质与ILs之间的相互作用参数。相较于传统气液相平衡具有较大的优势，IGC法一次实验得到多种物质的二元交互作用参数，缩短了试验周期并且具有较高准确性。.通过本项目的执行，扩展了“相似相容”原则在CB精细化分离领域的应用，建立了采用IGC方法快速筛选ILs作为萃取精馏溶剂的方法。本项目的研究成果不仅为精制苯与回收噻吩提供热力学基础数据，还可完善ILs萃取精馏CB技术的理论体系。