Advanced crosslinkable polyimide membranes for aggressive sour gas separations

The glassy copolyimide 6FDA-DAM:DABA was investigated as a polymer backbone for membranes used in aggressive sour gas separation applications. An esterification crosslinking mechanism enabled the synthesis of materials with augmented H₂S/CH₄ selectivity and plasticization resistance. These materials make use of polyethylene glycol (PEG) crosslinking agents and are referred to as PEGMC polymers. Rigorous dense film characterization of the novel crosslinkable materials indicates that excellent H₂S/CH₄ selectivity (24) is achievable while still maintaining high CO₂/CH₄ selectivity (29) under high pressure ternary mixed gas (CO₂/H₂S/CH₄) feeds. Defect-free asymmetric hollow fiber membranes were formed and appropriate crosslinking conditions were determined, allowing for the characterization of these fibers under realistic sour gas feed conditions. Also, a PDMS post-treatment was used to give ultra-high permselectivity for aggressive feeds. Using several mixed gas feeds containing high concentrations of CO₂ and H₂S at feed pressures up to 700 psig, it is shown that the crosslinked asymmetric hollow fiber membranes developed and manufactured through this work are capable of maintaining excellent separation performance even under exceedingly taxing operating conditions. For example, CO₂/CH₄ and H₂S/CH₄ permselectivity values of 47 and 29, respectively, were obtained for a 5% H₂S, 45% CO₂, 50% CH₄ feed at 35°C with 700 psig feed pressure. An extremely aggressive 20% H₂S, 20% CO₂, 60% CH₄ mixed gas feed with 500 psig feed pressure was also used; the maximum CO₂/CH4 and H₂S/CH₄ permselectivity values were found to be 38 and 22, respectively.Ph.D

Polyimide hollow fiber membranes for CO2 separation from wet gas mixtures

Matrimid®5218 hollow fiber membranes were prepared using the dry-wet spinning process. The transport properties were measured with pure gases (H2, CO2, N2, CH4 and O2) and with a mixture (30% CO2 and 70% N2) in dry and wet conditions at 25 ºC, 50 ºC, 60 ºC and 75 ºC and up to 600 kPa. Interesting values of single gas selectivity up to 60 ºC (between 31 and 28 for CO2/N2 and between 33 and 30 for CO2/CH4) in dry condition were obtained. The separation factor measured for the mixture was 20% lower compared to the single gas selectivity, in the whole temperature range analyzed. In saturation conditions the data showed that water influences the performance of the membranes, inducing a reduction of the permeance of all gases. Moreover, the presence of water caused a decrease of single gas selectivity and separation factor, although not so significant, highlighting the very high water resistance of hollow fiber membrane modules

Cross-Linkable Polyimide Membranes for Improved Plasticization Resistance and Permselectivity in Sour Gas Separations

A series of cross-linkable membrane materials based on the 6FDA-DAM:DABA (3:2) polyimide backbone were synthesized for improved sour gas separation performance, in terms of both membrane stability and permselectivity. Short-chain poly­(ethylene glycol) (PEG) molecules were used as cross-linking agents in an esterification-based cross-linking reaction. Pure and mixed gas permeation and pure gas sorption experiments were performed on dense films of these materials. Compared to unmodified 6FDA-DAM:DABA (3:2), higher sour gas permselectivity and membrane stability were achieved under aggressive feed conditions. H₂S-induced plasticization was not evident until pure H₂S feed pressures greater than approximately 6–8 bar. Pure CO₂-induced plasticization only occurred at feed pressures greater than about 25 bar. Under mixed gas feed conditions with 20% H₂S, 20% CO₂, and 60% CH₄ at 35 °C, attractive selectivities above 22 and 27 for H₂S/CH₄ and CO₂/CH₄, respectively, were observed for a feed pressure of 62 bar with both triethylene glycol and tetraethylene glycol cross-linking agents