Boron-embedded hydrolyzed PIM-1 carbon membranes for synergistic ethylene/ethane purification

For the first time, boron embedded carbon membranes have shown superior C₂H₄ permeability and C₂H₄/C₂H₆ selectivity to the upper bound line under both pure and mixed gas tests. The precursors of the carbon membranes were prepared by incorporating various boron compounds with different molecular sizes into a hydrolyzed polymer of intrinsic microporosity (PIM-1) and then carbonized at 700 °C. The increments in C₂H₄ permeability and C₂H₄/C₂H₆ selectivity followed the order of molecular size of the boron compounds. Both PALS results and CO₂ adsorption isotherms confirmed the enlarged pore size and increased pore amount. The enhancements in C₂H₄ permeability and C₂H₄/C₂H₆ selectivity were mainly due to the higher C₂H₄ diffusivity and greater diffusion selectivity resulting from proper choices of boron additives and carbonization conditions. When 9,9-dihexylfluorene-2,7-diboronic acid (DHFDA) was embedded into the hydrolyzed PIM-1 and then carbonized at 700 °C, the C₂H₄ permeability and C₂H₄/C₂H₆ selectivity of the carbonized membrane under mixed gas tests increased from 7.5 to 13.7 Barrer and from 9.3 to 9.7, respectively.