Novel triptycene-based polyimides showed promising results to be candidate membrane materials for removal of CO2 from natural gas, specifically for enhanced oil recovery applications. The gas permeation properties of two novel PIM-polyimides (TDA1-DMN) and (TDA1-APAF) prepared from 9,10-dimethyl-2,3,6,7-triptycene tetracarboxylic dianhydride (TDA1) with commercially available 3,3สน-dimethylnaphthidine (DMN) and 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF) diamine monomers are reported. The triptycene building block with bridgehead methyl side groups provides TDA1-DMN with high BET surface area and very high gas permeabilities (CO2 = 3700 Barrer) but with only moderate selectivities (CO2/CH4 selectivity = 17). Thus, an ortho-hydroxyl-functionalized polyimide (TDA1-APAF) was designed to enhance selectivities, while maintaining high gas permeability. TDA1-DMN and TDA1-APAF had BET surface areas based on nitrogen adsorption of 760 m2 g-1 and 260 m2 g-1, respectively. A freshly prepared sample of TDA1-APAF exhibited excellent gas permeation properties: H2 permeability of 94 Barrer with H2/CH4 selectivity of 129 and CO2 permeability of 40 Barrer coupled with CO2/CH4 selectivity of 55. Physical aging over 250 days resulted in enhanced H2/CH4 selectivity of 183 with only ~ 25% loss in H2 permeability. Aged TDA1-APAF exhibited 5-fold higher pure-gas CO2 permeability (30 Barrer) and 2-fold increase in CO2/CH4 permselectivity (~75) over conventional dense cellulose triacetate membranes at 2 bar. Gas mixture permeation experiments with a 1:1 CO2/CH4 feed mixture demonstrated higher mixed- than pure-gas selectivity (~88) and plasticization resistance up to 30 bar. Moreover, the aged membrane exhibited N2/CH4 selectivity of 2.3 which potentially offers the opportunity of simultaneous removal of N2 and CO2 for natural gas upgrading.
See more of this Group/Topical: 2018 North American Membrane Society Meeting: Oral Submissions