Novel CO2 selectively permeating membranes containing PETEDA dendrimer

Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance (1H NMR) spectroscopy. The composite membranes for selectively permeating CO2 were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO2 and CH4 gases and the gas mixture containing 10 vol.% CO2 and 90 vol.% CH4, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO2 permeance of 8.14 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 and CO2/CH4 selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO2 permeance reaches 3.56 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 and CO2/CH4 selectivity is 19. For the gas mixture, the membrane has a CO2 permeance of 6.94 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 with a CO2/CH4 selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO2 permeance of 3.29 × 10−5 cm3 (STP) cm−2 s−1 cmHg−1 with a CO2/CH4 selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO2/CH4 gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO2 permeance and CO2/CH4 selectivity increase and CH4 permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS).