Novel polyethylene glycol methyl ether substituted polysiloxane membrane materials with high CO2 permeability and selectivity

Abstract

Membrane gas separation is a promising technology for CO₂ capture. However, one of the key challenges is the development of stable-in-time and highly permeable materials with increased CO₂ permselectivity. In this study, two series of novel polysiloxanes with linear (methyl oligoethyleneglycol allyl ether (PEG8)) and branched (vinyl-bis- [methyltriethyleneglycol] (B-PEG4)) oxygen-containing side substituents were synthesized. By crosslinking PEG-substituted polymethylsiloxanes with polydimethylsiloxane (PDMS), a series of CO₂-highly selective membrane materials with a PDMS content of 6.5–50 wt% was obtained for the first time. The effect of the side chain geometry on the sorption and transport properties of these membranes for different gases (N₂, O₂, CO₂, CH₄, C₂H₆) was evaluated. The specific interactions between the PEG substituents and CO₂ that contribute to the enhanced selectivity of these materials were identified. The introduction of both linear and branched PEG substituents leads to in an increase in the selectivity of diffusion, solubility, and CO₂/gas permeability, compared to PDMS.

The CO₂/N₂ and CO₂/CH₄ permselectivities and diffusion selectivities are increases, as well as the permeability coefficients of the membrane materials for all gases are decreases, as the PDMS content reduces from 50 % to 6.5 % wt. Within the PDMS concentrations range between 6.5 and 12.5 % wt., there was a sharp increase in diffusion and permeability coefficients of membrane materials. For this polysiloxanes with linear PEG substituents, an unexpectedly high diffusion selectivity for CO₂ was observed. Such value determined the maximum CO₂ permselectivity among the polysiloxanes studied. The most promising membrane material from these series was identified as PEG8-substituted polysiloxane with 12.5 wt% PDMS. It has a CO₂ permeability coefficient of 1300 Barrer, CO₂/N₂ selectivity of 37 and CO₂/CH₄ selectivity of 10.