Carbon Dioxide Removal from Natural Gas Stream Using Polycarbonate Membrane

This report presents a research study on application of membrane system in removal carbon
dioxide from natural gas stream which represented by methane in this project. The
morphology of asymmetric membrane is very important factor in order to produce membrane
with desirable properties that able to remove carbon dioxide from natural gas stream. The
objectives of this research study are to study the effect of various preparation conditions on
the morphologies of asymmetric polycarbonate (PC) membrane and its relation to CO2/CH4
separation characteristic. Dry/wet phase inversion technique was used to fabricate
asymmetric PC membranes. The effect of solvent-non-solvent pair on membrane
morphologies and separation characteristic were investigated. The chemical used are
dichloromethane (DCM) as more volatile solvent while methanol (MeOH), ethanol (EtOH)
and propanol (PrOH) were selected as non-solvents. In addition, methanol (MeOH) and
tetrahydrofuran (THF) were used as coagulant and less volatile solvent, respectively. Based
on the literatures studied, the propanol and butanol-based membranes showed promising
performance. Fourier Transform Infrared (FTIR) Spectroscopy is used for analyzing organic
materials in order to obtain specific information about the chemical bonding and also the
molecular structures of the membrane. Scanning electron microscopy (SEM) is used to
observe the membrane morphologies. Gas permeation unit was used to evaluate the
performance of membrane. Experimental results showed that high boiling point of PrOH was
responsible in forming highly porous substructure with macrovoid formation in the DCMbased
membranes prepared using PrOH as non-solvent. The performance of asymmetric PC
membranes was evaluated by measuring CO2 and CH4 permeances as well as CO2/CH4 ideal
selectivity. The results showed that CO2 and CH4 were strongly dependent upon membrane
morphologies formed during fabrication. A highly porous membrane prepared from DCMPrOH
and was found to give higher CO2 and CH4 permeance (CO2:182 GPU; CH4:141 GPU)
as compared to MeOH (CO2:149 GPU; CH4:104 GPU) and EtOH (CO2:165 GPU; CH4:129
GPU) membranes. In term of selectivity, the highest CO2/CH4 ideal selectivity of the
fabricated asymmetric PC membrane is approximately 1.54. In conclusion, asymmetric PC membranes show promising performance and have high potential to be used for CO2/CH4
separation.