二氧化碳辅助制备高稳定性支撑型离子液体膜的热力学基础及其表征

A novel method for preparing supported ionic liquid membranes (SILMs) under low temperature assisted by high pressure carbon dioxide (CO2) is proposed, in order to remarkably improve the stability and life of the liquid membrane and to accomplish the controllable preparation of SILMs. High pressure CO2 is able to be dissolved in ILs, and offers advantages of reducing significantly the viscosity of ILs and providing the pressure difference as the driving force for ILs to diffuse into the membrane pores. By making use of the advantages of high pressure CO2,the proposed method is expected to accomplish the controllable preparation of ILs membrane with uniform thickness and loading capacity. With the assistence of CO2, the number of ILs types that are suitable for preparing the SILMs will be expanded greately, and it is of particularly importance to those ILs with a large solubility for acidic gases but with a high viscosity.Furthermore, CO2-assisted method is expected to overcome the limitation of membrane pore size due to ILs' high viscosity and to provide a wider choice of membrane supports. This project will focus on the study of the following fundamental issues in CO2-assisted SILMs: (1) Thermodynamic phase behavior of ILs+CO2 binary systems; (2) The basic rules and controllable parameters on tuning the ILs viscosity by adding CO2; (3) The penetration and diffusion mechanisms of ILs+CO2 mixtures in the porous supports; (4) The investigation and evaluation of the preparation process of the SILMs using high pressure CO2. With these fundamental studies, the project will provide theoretical basis for the design and fabrication of SILMs which are used for the removal of acid gases as well as energy-saving and emission reduction.

为克服现有支撑型离子液体膜(SILMs)制备方法的缺点，本项目提出低温下高压CO2辅助制备SILMs的创新方法，以提高液膜稳定性和使用寿命，实现SILMs的可控制备。该方法偶合降粘减阻和压差驱动原理，借助CO2可溶于离子液体，且能显著降低其粘度提高扩散系数的优势，达到离子液体液膜相厚度、负载量的可控制备，有望极大拓展用于液膜相离子液体的种类，尤其对酸性气体溶解度大的高粘性离子液体更具重要意义；同时有望克服因液膜粘度高对载体孔径的限制，从而扩大基膜材料的选择范围。 项目拟通过对以下科学问题的研究：(1)ILs+CO2二元体系热力学相行为；(2) CO2对ILs粘度调节的基本规律和控制参数；(3)ILs+CO2混合液在多孔介质中的渗透扩散规律；(4)高压CO2辅助制备SILMs过程研究与评价，为酸性气体脱除和节能减排用液膜分离过程设计提供实验依据和理论指导。

离子液体（ionic liquids, ILs）是新兴绿色溶剂，可以溶解CO2、SO2等酸性气体。经氨基修饰功能化后还能进一步提高其脱硫脱碳能力。离子液体粘度高流动性差，影响气体的扩散和吸收。将离子液体与多孔载体组装形成复合材料，如支撑型离子液体膜(SILMs)、负载型离子液体(SILs)等，则可以提高单位质量ILs的脱硫脱碳能力，减少溶剂用量并缩小反应器体积，有利于实现工业化。.制备负载量和分布状态可控的负载型离子液体是过程的关键。难点在于ILs高粘度阻碍了其在介孔和微孔中渗透扩散。传统浸渍法易造成SILMs残留针孔、液膜厚度过大、ILs在SILs中分布不均匀、堵塞孔道等问题。本课题发展了超临界二氧化碳辅助（SFID）制备该类负载型复合材料的新方法。可以有效提高制备质量，获得性能稳定、负载量可控、ILs分布均匀的复合材料。.采用热涂布法制得平均孔径为2.67 nm的γ-Al2O3支撑体。(1)浸渍涂布法制备[BMIM][BF4]液膜，最佳CO2渗透率为3.547 GPU，CO2/N2选择性为32.2。(2)SFID法制备SILMs，在50°C，12MPa，12 h，加入200 mg [BMIM][BF4]和9 mL乙醇，制得[BMIM][BF4]-SILMs ，其CO2渗透率约为1.5 GPU，CO2/N2选择性约为44。特点是保持膜气体渗透率条件下，对气体分离选择性提高到上限。(3)以[BMIM][Ac]为液膜相，结果类似。(4)用分子模拟研究气体在限域ILs中的渗透扩散，发现纳米孔道引起了ILs密度分布不均，在孔道中心形成低密度区，同时引起烷基链平行于壁面，为CO2提供了吸附空间和扩散通道，从而提高了CO2的溶解扩散能力。.采用浸渍法和SFID法制备SILs。(1)SFID法在满足负载量同时能够保持原载体的介孔结构和完整性。(2)乙醇为共溶剂时，制备[BMIM][BF4]-SILs与[BMIM][Ac]-SILs，最佳条件分别为16 MPa，60°C，3 h，6 mL乙醇和16 MPa，50°C，3 h，3 mL乙醇。(3) CO2吸附量随ILs负载量增大而增加，且呈带状分布；SFID法制备的载体，其CO2吸附性能优于传统浸渍法，当[BMIM][Ac]的负载量为63.2%时，吸附量高达48.47 mg/g。(4)再生循环5次后，SILs仍保持其吸附性能。