CO2/CH4 Separation Using Synthesized Cross-linkable Co-polyimide Membranes

Using a cross-linkable co-polyimide (6FDA-Durene/DABA (9/1)), we have developed new flexible and high- performance gas separation membranes that can enhance both membrane permeability and plasticization resistance simultaneously by grafting various sizes of cyclodextrin to the polyimide matrix and then decomposing them at elevated temperatures. The gas permeability of thermally treated pristine polyimide (referred as the original PI) and CD grafted co-polyimide (referred as PI-g-CDs) has been determined using CO2, and CH4, at 35 °C. The permeability of gases increases with an increase in thermal treatment temperature from 200 to 425 °C. However, permeability increases more for those grafted with bigger size CD. Permeability of the original PI thermally treated at 425 °C is about 4-6 times higher than that treated at 200 °C. The permeability increase jumps to 8-10 times for PI-g-α-CD and 15-17 times for PI-g-γ-CD due to CD decomposition at high temperatures and bigger CD creating bigger micro-pores. Interestingly, the permeability ratios of PI-g-α-CD to PI-g-γ-CD and PI-g-β-CD to PI-g-γ-CD at 400 and 425 °C are around 0.6 and 0.8, respectively. These numbers are almost the same as the cavity diameter ratios of α-CD to γ-CD and β-CD to γ-CD. Permselectivity decreases first with an increase in thermal treatment temperature up to 350 °C and then increases. In addition, for co-polyimide membranes grafted by CDs, the higher thermal treatment temperature results in membranes with the better plasticization resistance to CO2 and the better separation performance for 50:50 CO2/CH4 mixed gases.

کلیدواژه ها:

Thermal cross-linkable co-polyimide ، Cyclodextrin ، CO2/CH4 Separation