Poly(4-methyl-1-pentene) Membrane for CO2 Separation: Performance Comparison of Dense and Anisotropic Membrane

Concerns about climate change, the greenhouse gases effect and global warming have become the motivation to explore new technology to separate CO₂ gases. In this work, poly(4-methyl-1-pentene) (PMP) was fabricated to determine its feasibility to separate CO₂ from N₂ gas and to elucidate the influence of the membrane structure on its separation performance. This study consists of two main parts where a full dense PMP membrane with various PMP concentrations was fabricated first as a controlled sample. 5 wt% PMP fabricated at 20 °C was the best condition to fabricate the membrane based on the gas permeance test. The CO₂ and N₂ permeance is 5.91 GPU (76.46 Barrer) and 0.51 GPU (6.61 Barrer), respectively, and the CO₂/N₂ selectivity is 11.57. To prepare a membrane with the anisotropic structure, a non-solvent induced phase separation method was employed. Similar PMP concentration and drying conditions to the dense membrane were used to fabricate the anisotropic PMP membrane for comparison purposes. The influence of dry phase inversion time was tested. It was found that the dry phase inversion time has a significant impact on the porosity of the substructure but not the thickness of the dense layer. Nevertheless, 40 s dry phase inversion time appears to be the best duration to fabricate the anisotropic PMP membrane. The CO₂ permeance was improved by 10 times compared to the full dense membrane. However, the CO₂/N₂ selectivity is halved to the dense PMP membrane, mainly due to the thin dense layer and porous substructure of the membrane.