Carbon membranes derived from polymer blend of polyetherimide and polyethylene glycol for gas separation

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Date
2015-11-01
Authors
Wan Nurul Huda Wan Zainal
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Membrane technology offers many advantages over conventional gas separation methods such as simplicity and ease operation. Carbon membrane has a high thermal resistance and good chemical stability in corrosive environments. In the present study, in order to enhance the gas permeability, carbon membrane was synthesized from polymer blend of polyetherimide (PEI) and polyethylene glycol (PEG). The PEG/PEI carbon membrane was synthesized on the alumina support coated with an Al2O3 intermediate layer. The effect of different preparation parameters on the carbon membranes properties and separation performance were studied by varying the blend ratios (0, 0.1, 0.2, 0.3 and 0.4 PEG:PEI), carbonization temperatures (550, 600, 650 and 700 °C), heating rates (1, 3, 5 and 7 °C/min) and soaking times (1, 2 and 3 h). The PEG/PEI carbon membrane with the best separation performance was further tested at the different permeation temperatures (25, 50, 75 and 100 °C) and feed pressures (2.0, 2.5, 3.0 and 3.5 bar). The PEG/PEI carbon membrane separation performance was further investigated with the binary gas mixtures of the CO2/CH4, CO2/N2 and O2/N2. From the characterization results, the PEG/PEI carbon membranes consist of three distinguish layers; a carbon layer, Al2O3 intermediate layer and alumina support. The XRD results revealed that the PEG/PEI carbon membrane has an amorphous structure. The BET surface area of the carbon membrane derived from 0.1 PEG:PEI blend ratio (denoted as PEG1/PEI carbon membrane) increased to 544.07 m2/g ratio rather than 248.75 m2/g by pure PEI carbon membrane. The CO2 and O2 permeability of the PEG1/PEI carbon membrane increased to 1685 and 927 barrer, respectively rather than 421 and 262 barrer exhibited by PEI carbon membrane, respectively. The carbon membrane derived from 0.1 PEG:PEI blend ratio and carbonized at temperature of 650 °C with heating rate of 1 °C/min and 2 h of soaking time showed the best separation performance with the highest of the CO2/CH4, CO2/N2 and O2/N2 ideal selectivities of 64.72, 38.02 and 5.05, respectively. For binary gas mixtures, this sample exhibited the CO2/CH4, CO2/N2 and O2/N2 selectivities of 38.10, 34.74 and 3.98, respectively. The carbon membrane performance was affected by the effect of membrane aging. After regeneration at temperature of 300 °C, the PEG1/PEI carbon membrane restored about 80 % of the original CO2 and O2 permeability with CO2/CH4, CO2/N2 and O2/N2 ideal selectivity of 75.23, 45.54 and 6.09, respectively. Overall, the PEG1/PEI carbon membranes exhibited better separation performance with enhanced gas permeability and ideal selectivity compared to pure PEI carbon membrane.
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