Development and modelling of mixed matrix membranes incorporating large pore size clay for gas separation

Abstract

The objective of this study is to develop Polyetherimide (PEI) mixed matrix membranes (MMM) by incorporating large pore size fillers. This study was divided into two main parts. In the first part, the existing MMM permeation models were evaluated and based on series-parallel resistors approach, a new model has been developed. The developed model was capable to predict gas permeation for all wellknown MMMs morphologies and a good agreement was achieved between the model and the experimental data from open literature. The first part was extended by proposing a morphological map which by virtue the prediction of MMMs morphologies was achievable. The second part of the work was performed to investigate the effect of incorporation of montmorillonite (MMT) and halloysite nano tubes (HNT) as large pore size filler in MMMs for gas separation. MMMs were fabricated using a dry/wet casting technique. The chemical modification of HNTs involved silylation and Ag+ ion exchange treatment. The silylated HNTs was prepared by treating them with N-b-(aminoethyl)-g-aminopropyltrimethoxy silane agent. The results from thermal gravimetric analysis (TGA) and Fourier transform infra red spectroscopy (FTIR) confirmed that chemical modification on clay surface has taken place successfully. A perfect compatibility between the polymer matrix and filler was observed from field emission scanning electron microscopy (FESEM) micrographs. The outcomes showed that, 0.5% loading of silylated-HNT resulted in 27% enhancement in CO2 permeability and 8% increase in selectivity relative to the neat polymer membrane. In order to apply the facilitated transport properties in MMMs, Ag+ ion exchange treatment was performed because of its high affinity toward CO2 rather than CH4. Results showed that silane can successfully enhance the HNTs cation exchange capacity, which led to higher concentration of Ag+ ions in the modified HNTs. Ag+ ion exchange exhibited about 250% enhancement in CO2 permeability. The effect of montmorillonite nano-clay fillers on PEI MMM was also studied. The gas permeation results revealed the following order in terms of selectivity for CO2/CH4 separation: Cloisite 15A > general MMT > hydrophilic MMT > hydrophobic MMT > raw MMT. In conclusion, the best results were achieved at 0.5% of Cloisite 15A loading where permeability and selectivity enhancements were 24% and 28% respectively.