High activated carbon loading mixed matrix membranes for gas separations

Abstract

Mixed matrix membranes (MMMs) containing highest amounts of activated carbon (AC) reported to date were prepared for gas separation. A polymeric phase of semicrystalline polyvinyl chloride (PVC) was loaded with different amounts (from 23 to 60 wt%) of AC, and then was crosslinked using an aromatic diamine. Thermal treatment was used to complete the crosslinking reaction. Uncrosslinked MMMs were also prepared. FT-IR, SEM microscopy, X-ray diffraction, thermal degradation, and differential scanning calorimetry characterization techniques were used to verify the extent of crosslinking, crystalline structure, and the thermal resistance of the membranes. Crosslinked PVC membrane has higher both permeation flux and selectivity than the uncrosslinked one. It was observed the crosslinking process favored the formation of a less permeable porous structure in all MMMs. A decrease in the polymer crystallinity as the carbon content increased was also observed. This effect was more pronounced in absent of crosslinking. Crosslinked MMMs showed higher thermal resistance than uncrosslinked ones and pure PVC. Permeation tests showed crosslinked MMMs were more selective; i.e., the gas pair H 2/CH 4 selectivities varied from diffusion to Knudsen mechanisms (αH 2/CH 4 11.87-2.25), whereas the selectivity of uncrosslinked MMMs varied from Knudsen to viscous mechanisms (αH 2/CH 4 2.42-1.89). High AC content MMMs possessed permeability values comparable to those of pyrolytic carbon membranes.