Polyetherimide/multiwall carbon nanotube mixed matrix hollow fiber membrane for gas separation

Abstract

Mixed matrix membrane (MMM) which incorporated with polymeric and inorganic materials has become an interest to engineers in the early twenty due to its potential in advancing the gas separation properties of the polymeric-based membrane. The main objective of this study is to establish an effective approach for mixing and dispersing carbon nanotube (CNT) into the matrix of polyetherimide (PEI) to obtain MMM with optimized gas separation performance efficiency. The changes in gas permeability and selectivity of the fabricated flatsheet MMM was correlated with three different functionalizations on CNT. It was found that aminopropyl-triethoxysilane treated CNT homogeneously dispersed CNT in the polymer solution and gave the best separation on CO2 molecules. The result found that MMM exhibited CO2/CH4 selectivity of 30.59, which is significantly higher than the intrinsic value of PEI ever reported (common PEI CO2/CH4 selectivity = 29.66). Next, using the polymeric solution formulation with the optimum filler loading, hollow fiber (HF) MMM was tailored. The spinning parameters such as extrusion rate and air gap distance during dry phase inversion were optimized. It was found that the produced asymmetric membrane exhibited high permeance and selectivity. The average CO2 permeance obtained was 67.72 GPU with CO2/CH4 selectivity of 58.89. Additionally, increasing the shear rate by a higher extrusion rate resulted in a membrane with higher selectivity. Moreover, the selectivity of all the MMM fabricated surpassed 80% of the recognized intrinsic value, implying that the membrane produced in the study can be considered as defect-free membrane. The best HF MMM was obtained by incorporating 0.5wt% CNT into dope containing 25wt% PEI and extruding the dope at 4 cm3/min using air gap of 300 mm. The optimal HF MMM showed 28 times increment in permeance of pure gas CO2 and 2 times higher selectivity of CO2/CH4, compared to that of neat PEI. A comparative study with other PEI MMM revealed that CNT with proper functionalization and fabrication technique indeed could impart a strong influence in improving the matrix properties for further in-depth development.