Development of high performance carbon molecular sieve membranes via tuning the side groups on PI precursors

In the current study, three 6FDA 1 /BPDA 1 -based polyimides (PIs) containing different diamine moieties (DMB, TCDB, TFDB) were selected to prepare CMS membranes (CMSMs), providing a systematic study of PIs with different side group functionalization. The resultant CMSMs were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and CO 2 absorption measurements. Pure gas (N 2 , O 2 , CH 4 , CO 2 ) and mixed gas (CO 2 /CH 4 ) permeability tests were also conducted. The resultant CMSMs exhibited attractive gas separation performance. Compared to DMB-based PI, TFDB-based with trifluoromethyl (-CF 3 ) side groups exhibited ultra-high permeability (P CO2  = 14938 Barrer, P O2  = 3146 Barrer) and moderate selectivity (α CO2/CH4  = 20.3, α O2/N2  = 4.5), while CMSMs prepared from PI with chlorine functionalization showed higher gas permeability (P CO2  = 6031 Barrer, P O2  = 1311 Barrer) and selectivity (α CO2/CH4  = 46.2, α O2/N2  = 6.5). The results indicated that side group functionalization on PIs exerts a considerable influence on the gas permeation properties of CMSMs.