Modified COSMO‐UNIFAC model for ionic liquid–CO₂ systems and molecular dynamic simulation

Abstract

A new predictive molecular thermodynamic model (i.e., modified COSMO-SAC-UNIFAC) was first proposed and extended to predict the solubility of CO 2 in pure and mixed ionic liquids (ILs) at the temperatures down to 263.2 K. It is interesting to discover that with equimolar amounts, the solubility of CO 2 in such 1:was consistent at the same temperature and pressure in the case of exchanging their respective cations and anions. The molecular dynamic (MD) simulation for CO 2 + mixed ILs was performed to deeply analyze and explain this intriguing phenomenon. Not only the CO 2 gas drying experiment with the ILs ([C2mim][OAc], [C2mim][dca], and [C2mim][OAc] + [C2mim][dca])as absorbents but also the corresponding process simulation and optimization were made to stress the effectiveness and applicability of the new thermodynamic model.

Computer-Aided Molecular Design of Ionic Liquids as Advanced Process Media: A Review from Fundamentals to Applications

“…In addition to liquid solutes, Lei's group also extended the UNIFAC model to cover gas solutes namely CO 2 , CO, and H 2 by correlating the solubility data of the gases in ILs at different temperatures. 8,370,375 It was verified that the extended UNIFAC model can be used for predicting the gas solubility in a wide temperature and pressure range. As summarized in a revision and extension in 2020, 33 conventional main groups and 50 IL main groups have been covered by the UNIFAC model extended by Lei's group (see Figure 19).…”

“…71,370,372−374 In the case of modified UNIFAC, the R k and Q k were proposed to be fitted from experimental data together with interaction parameters by the model originators; 362 however, one could also use the same method as that in the original UNIFAC model extension due to the solid physical basis of this approach and usually the small amount of experimental data available. 373,375 After determining the van der Waals parameters of all involved (sub)groups, the binary interaction parameters between different main groups can be regressed by correlating the UNIFAC models to experimental activity coefficient data. For the model extension to IL-involved systems, the binary interaction parameters between conventional main groups can be kept identical to those previously reported in literature; the interaction parameters between IL main groups could be assumed to be zero due to the strong interaction and weak dissociation of ion pairs.…”

“…For the extension of the UNIFAC models, the van der Waals parameters of already existing groups can be directly taken from current literature, and those for new groups such as IL (sub)groups in the original UNIFAC can be estimated from R k = V k × N A V V W Q k = A k × N A A V W where N A is Avogadro’s number, 6.023 × 10 23 /mol; V VW (15.17 cm 3 mol –1 ) and A VW (2.5 × 10 9 cm 2 mol –1 ) are the standard segment volume and surface area as suggested by Bondi; V k and A k denote the volume and surface area of group k , respectively, which can be estimated by correlating to molecular volumes and surface areas or by quantum chemical calculations. ,,− In the case of modified UNIFAC, the R k and Q k were proposed to be fitted from experimental data together with interaction parameters by the model originators; however, one could also use the same method as that in the original UNIFAC model extension due to the solid physical basis of this approach and usually the small amount of experimental data available. , …”

“…So far, several researchers have reported the extensions of UNIFAC models to IL-involved systems, which differ from each other in the group decomposition method, the data set used for model regression, and the range of covered groups. ,,,,,,,− Some of the representative UNIFAC extensions are summarized as follows.…”

Condensable Gases Capture with Ionic Liquids

“…Another important application of the COSMO-RS model in gas separation is to calculate free volume ( V f ) and free volume fraction ( FFV ). , V f includes atom-sized defects and holes generated by random stacking of atoms, providing space for motion between the atoms and molecules. FFV is defined as the ratio of free space to occupied space F F V = V normalm − 1.3 V vdW V normalm where V m is the molar volume of the IL, and V vdW is the van der Waals volume of IL.…”