Application of Cardo-type polyimide (PI) and polyphenylene oxide (PPO) hollow fiber membranes in two-stage membrane systems for CO2/CH4 separation

Abstract

In this study, a two-stage membrane system for the separation of CH4/CO2 was designed<br><br>based on a series of laboratory-scale experiments obtained using two types of commercial<br><br>hollow fiber membranes including polyphenylene oxide (PPO) and Cardo-type polyimide<br><br>(PI). The former showed high permeability and low to moderate selectivity, while the latter exhibited high selectivity and moderate permeability. In this design, the permeate<br><br>from the first stage - rich in CO2 but containing considerable amount of methane - is fed<br><br>into the second stage to recover its methane content. The performances of double- and<br><br>single-stage system designs were compared in terms of methane loss (the ratio of<br><br>methane content in permeate to that of feed) and recompression needed for the second<br><br>stage at a given retentate CO2 concentration. It was concluded that the methane loss was<br><br>minimum when PI was used in both stages, while the required membrane area was<br><br>minimum when PPO was used in both stages. Since in latter case the obtained methane<br><br>loss was the highest, the proposed design to attain both low methane loss and membrane<br><br>area was using PI in the first and PPO in the second stages.