Effect of PEG-MEA and graphene oxide additives on the performance of Pebax®1657 mixed matrix membranes for CO2 separation

Abstract

In this work, a series of mixed matrix membranes (MMMs) consisting of Pebax® 1657 as the main polymer matrix, poly(ethylene glycol) (PEG) derivatives with low molecular weights as additives, and graphene oxide (GO) with different loadings as a nanofiller, were prepared for CO2/N2 separation. Changes in the amorphous and crystalline regions of Pebax®/PEG blend membranes and in the free volume of GO-embedded MMMs were estimated based on differential scanning calorimetry (DSC) thermograms. The fractional free volume and density of the Pebax®/PEG blend membranes were investigated according to additive models. Particularly, blending poly(ethylene glycol) methyl ethyl acrylate (PEG-MEA) with the Pebax® matrix significantly improved CO2 permeability without sacrificing high CO2/N2 selectivity. Incorporating GO nanosheets up to 0.3 wt% into the Pebax®/PEG-MEA matrix was found to have a considerable impact on increasing CO2/N2 selectivity, due to largely in part to an increase in the CO2 solubility coefficients. Upon a further increase in GO loading, both CO2 permeability and CO2/N2 selectivity decreased as a result of increasing tortuosity for gas diffusion and also GO aggregation at high GO loading content. More importantly, the Pebax®/PEG-MEA blend membrane with the optimized loading of GO, i.e., 0.3 wt% indicated outstanding anti-CO2 plasticization resistance up to 10 bar as well as long-term stability over 100 days without significant deterioration of CO2/N2 separation performance.