Understanding and Development of Type II Porous Liquids using Molecular Simulations
Author(s)
Chang, Chao-Wen
Advisor(s)
Editor(s)
Collections
Supplementary to:
Permanent Link
Abstract
Solvent-based gas separation systems suffer from various issues like low gas capacities, high regeneration energies, and large capital costs. Despite these limitations, the field has seen little innovation in decades. Porous liquids offer a transformative opportunity to overcome these issues. In particular, Type II porous liquids—composed of intrinsically porous molecules dissolved in a liquid solvent—combine the adsorption capabilities of porous materials with the practical advantages of liquid handling. However, several critical gaps remain. First, the identification of suitable solvents for porous liquids has largely relied on labor-intensive experimental testing. Second, the mechanisms governing CO2 uptake in porous liquids are not yet well understood. Finally, the formation of porous liquids is currently constrained by the use of bulky solvents, whereas most common solvents are relatively small.
To address the first challenge, we demonstrate an efficient screening approach for this task that uses COSMO-RS calculations, predictions of solvent pKa values from a machine-learning model, and several other features and apply this approach to select solvents from a library of more than 11,000 compounds. This method is shown to give qualitative agreement with experimental observations for two molecular cages, CC13 and TG-TFB-CHEDA, identifying solvents with higher solubility for these molecules than had previously been known. Ultimately, this screening algorithm streamlines the downselection of suitable solvents for porous organic cages to enable more rapid discovery of Type II porous liquids.
To tackle the second challenge, we use molecular simulations and experiments to examine CO2 uptake by a prototypical porous liquid composed of porous organic cages (CC13) in 2’-hydroxyacetophenone (2’-HAP). Our simulations are in reasonable agreement with experimental measurements of CO2 solubility and provided unambiguous information on the partitioning of CO2 within microenvironments in the liquid. Analysis of CO2 dynamics was performed using these simulations, including assessing the self-diffusivity of CO2 in both the neat solvent and porous liquid. This offers insights into the kinetics of CO2 uptake and transport in Type II porous liquids. Experiments with Type II porous liquids formed by dissolving CC13 in three different size-excluded solvents showed non-additive CO2 absorption relative to predictions based on ideal volume additivity. This non-additive absorption behavior was also observed in simulations. We also demonstrated non-additive gas uptake from Type II porous liquids based on another porous cage, CC19.
For the third challenge, we present a novel entropy-driven variant of Type II porous liquids, focusing on the behavior of imine-based porous organic cages (POCs) dissolved in chloroform. We explore how entropy effects, often observed in porous solids, can be leveraged to create liquids with intrinsic porosity despite using small solvents like chloroform, which traditionally penetrate and eliminate cage porosity. We further reveal that under specific conditions, chloroform is displaced from the cages, allowing CO₂ adsorption within the cages and the solvent. The findings suggest that this approach could expand the range of solvent/cage combinations, providing insights into designing more effective porous liquids for gas sorption and separation applications.
Sponsor
Date
2025-07-31
Extent
Resource Type
Text
Resource Subtype
Dissertation