Gas Permeation and Separation in Functionalized Polymers of Intrinsic Microporosity: A Combination of Molecular Simulations and Ab Initio Calculations
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- 作者：Weijie Fang ; Liling Zhang ; Jianwen Jiang
- 刊名：Journal of Physical Chemistry C
- 出版年：2011
- 出版时间：July 28, 2011
- 年：2011
- 卷：115
- 期：29
- 页码：14123-14130
- 全文大小：989K
- 年卷期：v.115,no.29(July 28, 2011)
- ISSN：1932-7455
文摘
We combine molecular simulations and ab initio calculations to investigate the permeation and separation of CO2/N2 in polymers of intrinsic microporosity (PIMs) with different functional groups (cyano, trifluoromethyl, phenylsulfone, and carboxyl). A robust equilibration protocol is proposed to construct model membranes with predicted densities very close to experimental data. The fractional free volumes (FFVs) in PIM-1 (with cyano), TFMPS-PIM (with both trifluoromethyl and phenylsulfone), and CX-PIM (with carboxyl) are 45.2%, 42.1%, and 38.7%, respectively. Hydrogen bonding is observed to form among carboxyl groups and contributes to the lowest FFV in CX-PIM. From wide-angle X-ray diffractions, the estimated d-spacing distances agree well with available experimental results, and the chain-to-chain distance in CX-PIM is the shortest among the three membranes. Ab initio calculations reveal that the interaction energies between the functional groups and CO2 decrease as carboxyl > phenylsulfone > cyano > trifluoromethyl; consistently, the simulated solubility coefficient of CO2 is the largest in CX-PIM. The simulated diffusion coefficient decreases with reducing FFV and correlates well with FFV. While the sorption selectivity of CO2/N2 increases in the order of PIM-1 < TFMPS-PIM < CX-PIM, the diffusion selectivity remains nearly constant; consequently, the permselectivity follows the same hierarchy as the solubility selectivity. This computational study provides microscopic insight into the role of functional groups in gas permeation and suggests that strong CO2-philic groups should be chosen to functionalize PIM membranes for high-efficiency CO2/N2 separation.