Abstract:

Ionic liquids (ILs) possess the merits of high stability, excellent solubility, designability, facile recovery, and environmental friendliness. Particularly, they exhibit remarkable potential in carbon capture on account of their high solubility for CO₂. However, due to the wide variety and expensive price of ILs, it is time-consuming and laborious to rely on experimental research, and it is crucial to construct a thermodynamic prediction model for ILs systems. Since the UNIFAC predictive model was of great value for ILs selection and convenient for subsequent selection of gas separation tasks and process design and optimization, the UNIFAC model was proposed to predict the activity coefficient of the ILs-CO₂ system. In this work, the experimental data of CO₂ absorption by ILs were collected, the activity coefficient was calculated by combining the phase equilibrium, and the activity coefficient database of ILs-CO₂ system was established. The parameters of UNIFAC model (R_k and Q_k ) were calculated by COSMO method and van der Waals rule, respectively. Based on the experimental values, the UNIFAC interaction parameters were fitted. The prediction performance of the UNIFAC model established by the two methods was compared by the average relative error (AARD). The results showed that the UNIFAC model established by COSMO method (AARD=7.68%) could reduce the prediction error of activity coefficient of ILs-CO₂ system by 4.89 percentage points compared with van der Waals method (AARD=12.57%). On this basis, the activity coefficient UNIFAC model of ILs-CO₂ system was established, and a database of interaction parameters for nearly 100 pairs of groups was obtained. In addition, based on the group contribution characteristics of the UNIFAC model, all group fragments contained in the interaction parameter database could be extended to new ionic liquid systems, so that the established UNIFAC model could be used to predict the activity coefficients of new kinds of ILs-CO₂ systems. Due to the group contribution feature of the UNIFAC model, the UNIFAC model developed in this work could predict the activity coefficients of ILs-CO₂ binary system composed of the groups included in the database, providing a solid basis for the molecular design of the subsequent ILs method for gas absorption.

Key words: ionic liquids, UNIFAC model, group contribution method, activity coefficient

摘要：

离子液体（ILs）具有高稳定性、溶解性能好、可设计性、易回收等优点，尤其因高 CO₂溶解度在碳捕集方面显示了巨大潜力。但由于ILs种类繁多且价格昂贵，依靠实验研究耗时费力，因此构建 ILs 体系的热力学预测模型至关重要。UNIFAC 模型在 ILs 气体分离工艺设计与优化领域具有重要的理论价值和工程应用意义，基于此，本研究构建了应用于 ILs-CO₂ 体系活度系数预测的 UNIFAC 模型。本文系统收集了 CO₂ 在ILs中的溶解度实验数据，并结合相平衡计算出活度系数，建立了ILs-CO₂体系活度系数数据库。采用COSMO方法和van der Waals规则分别获得了 UNIFAC 模型中基团的重要参数（R_k 和Q_k ）。基于实验值，拟合了 UNIFAC 相互作用参数。通过平均相对误差（AARD），比较了两种方法建立的 UNIFAC 模型的预测效果。结果表明：通过 COSMO 方法（AARD=7.68%）建立的 UNIFAC 模型对 ILs-CO₂ 体系的活度系数预测误差比van der Waals方法（AARD=12.57%）降低了4.89个百分点。并在此基础上建立了ILs-CO₂体系 UNIFAC 模型，获得了近100 对基团的相互作用参数数据库。由于 UNIFAC 模型的基团贡献特点，本工作建立的 UNIFAC 模型可预测数据库中包含的基团组成的新型 ILs 与 CO₂ 体系的活度系数，从而为后续 ILs 法气体吸收的分子设计奠定了扎实基础。

关键词: 离子液体, UNIFAC 模型, 基团贡献法, 活度系数