吸收-吸附耦合法捕集烃类气体过程传质机理及动力学研究

Separation of gas mixtures that contain light hydrocarbons is widely concerned in petrochemical industry. We have recently proposed a so called absorption-adsorption hybrid method, in which carefully chosen porous materials were dispersed in liquids to form suspension slurries. This method achieves promising high separation efficiency for common gas mixtures. However, the separation mechanism for the mentioned gases is not fully clear and there are no available kinetic theory research reports for this method up to date. The aims of this work are, first, systematic measurement of the ab(d)sorption characteristic of common light hydrocarbons, nitrogen and hydrogen in ZIF-8/liquid slurries at different operation conditions, and to perform phase equilibrium separation experiments for gas mixtures constituted by these gas components by means of the aforementioned slurry, from which there will be obtained the main factors affecting hydrocarbons’ dissolution ability in ZIF-8 slurries, and the optimum operation conditions for gas separation; second, take advantage of microscopic characterization techniques as AFM, FT-IR, Raman et al., to investigate the interaction between liquid molecules and the functional groups on the surface of suspended ZIF-8 particles. Thus, from the molecular level it will be possible to understand the gas-liquid-solid multiphase mass transfer mechanism of gas molecules during their dissolution process in the slurry, and also to explain the mechanism of separation of gas mixtures containing hydrocarbons by means of this slurry; last, based on the obtained experimental results, to develop efficient gas sorption kinetic models. The obtained results should be of great benefit for the improvement and practical application of this new proposed gas separation technology.

实现对含烃混合气的有效分离是石化行业的一个研究重点。吸收-吸附耦合分离法作为一种新型气体分离技术，通过选择合适的多孔介质和液体介质混合形成悬浮浆液可以实现对常见混合气的有效分离。但相应的气体分离机理尚不完全明确，相关动力学理论研究尚未开展。因此本项目拟首先系统测定不同操作条件下典型烃类气体、H2和N2在ZIF-8/液体介质混合浆液中溶解吸收特征和浆液体系对常见含烃混合气的分离效果，获得相应的气体吸收动力学数据和相平衡分离实验数据，确定影响浆液体系捕集烃类气体能力的主要因素和适宜的操作工况；然后利用原子力显微镜和红外、拉曼等微观表征技术分析液体介质与ZIF-8骨架表面官能团之间作用力大小和作用机制，从分子水平确定气体吸收过程气-液-固多相传质机理和ZIF-8浆液对常见含烃混合气分离机理；最后在所得动力学实验数据和微观表征结果基础上开发有效的气体吸收动力学模型。为该技术的完善和推广建立可靠的理论基础。

本项目以有效分离回收裂解干气（C2H4/CH4）中C2H4、煤层气（CH4/N2）和焦炉煤气（CH4/H2）中CH4为研究背景，以ZIF-8、水和乙二醇混合浆液为分离媒介。主要内容包括分析ZIF-8、水和乙二醇分子之间作用机制；掌握气体组分在ZIF-8浆液中溶解吸收机理；建立烃类气体组分在ZIF-8浆液中溶解吸收动力学模型；系统评价ZIF-8浆液分离目标含烃混合气性能等。获得研究结果包括：（1）基于ZIF-8/水-乙二醇浆液偏关显微分析照片和水、乙二醇液滴与ZIF-8颗粒压片之间接触角关系，明确了ZIF-8材料的疏水、亲乙二醇特性，且乙二醇分子会在ZIF-8颗粒外表面富集成液层现象；（2）综合不同气体组分在ZIF-8/水、ZIF-8/乙二醇浆液中溶解特征以及含水ZIF-8湿材料在低温、高压下储CH4特性，一方面明确了水分子不能进入到ZIF-8孔道中这一认识；另一方面得出气体组分在ZIF-8浆液中的溶解-扩散-吸附的传质机理（3）进行了C2H4、CH4在ZIF-8/水浆液中溶解吸收动力学实验，结合溶解传质机理，建立了同时考虑受乙二醇液层溶解扩散和ZIF-8吸附扩散控制的CH4、C2H4在ZIF-8/水、ZIF-8/水-乙二醇浆液中的溶解吸收动力学模型，模拟值与实验值吻合良好；（4）优选ZIF-8/水浆液，对C2H4/CH4、CH4/N2和CH4/H2进行系统分离研究，指出ZIF-8浆液分离效果明显优于干ZIF-8材料，利用浆液流动性可以在分离装置中实现一个多级、连续分离操作，并推荐了相应的操作条件。（5）研究了2-甲基咪唑-乙二醇混合液对常见混合气中CO2的捕集效果，明确了相关机理。所得研究结果证明ZIF-8/水、ZIF-8/水-乙二醇(20 wt%)浆液完全可用来分离回收目标混合气中烃类组分、2-甲基咪唑-乙二醇混合液可用来捕集烟道气、沼气等中CO2，具有很好应用前景。