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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Abstract
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.