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The relationship between the rigidity, microporosity and the ideal gas separation properties of polymers of intrinsic microporosity (PIM) is very important but seldom studied in detail. Herein, we designed a novel bromine substituted intrinsic microporosity polyimide (PIM-DB-PI), and compared its gas separation properties with a more rigid and microporous PIM-PI-1 (680 vs 435 m2 g−1) from −30 to 30 °C for the first time. Both PIM-PIs showed improved ideal gas separation properties with their performance for H 2 /N 2 , O 2 /N 2 , CO 2 /N 2 and CO 2 /CH 4 changed from well below the 2008 trade-off lines to approach or even above their latest trade-off lines upon decreasing temperature. The PIM-PI-1 with higher microporosity and rigidity showed higher gas permeability, diffusion and solubility coefficients as well as larger activation energy of permeation (E p) and diffusion (E d) than PIM-DB-PI, whereas PIM-DB-PI exhibited higher gas pair selectivity derived from its larger diffusion selectivity (a D), which was attributed to its higher enthalpic selectivity. Besides, the PIM-DB-PI showed a much larger critical penetrate size ((f/c) 1/2 ) than PIM-PI-1 due to its higher flexibility. The above finding indicates that both rigidity and microporosity are very important in fine-tuning the gas transport through the polymer membrane. The microporosity has dominant effect on the gas diffusion selectivity of the membrane and the rigidity has more effect on the critical diffusion penetrate size ((f/c) 1/2 ) of PIM-PI membranes. [Display omitted] • Gas separation properties of two PIM-PIs were reported from 30 to −30 °C. • PIM-PI-1 with higher surface area and rigidity showed larger permeability and lower selectivity than PIM-DB-PI. • The PIM-PI-1 showed higher activation energy of permeation and diffusion than PIM-DB-PI. • The microporosity had much stronger effect than rigidity on the diffusion selectivity due to higher enthalpic selectivity. • The rigidity is dominant in determine the critical diffusion penetrate size ((f/c) 1/2 ) of the PIM-PI membranes. [ABSTRACT FROM AUTHOR]

Sub-ambient temperature membrane-based separation is attracting more and more attention in solving the industrial energy intensive separation challenges. However, the research on low temperature gas separation properties of polymeric membranes is limited. Here, gas separation performance of an intrinsic microporous polymer (PIM-1) at temperatures of −30, −20, −10, 0, 10, and 30 °C were fully characterized for the first time. As the temperature decreases, there was a continuous drop in He, H 2 , N 2 , O 2 , CH 4 and CO 2 permeability coupled with a sharply increased ideal gas pair selectivity with the overall performance gradually outperformed the latest trade-off curves for H 2 /N 2 , O 2 /N 2 , CO 2 /CH 4 and CO 2 /N 2. In which, the O 2 and CO 2 permeability of PIM-1 at −30 °C reached as much as 159 and 1380 Barrer, combined with O 2 /N 2 and CO 2 /N 2 ideal selectivity of 9.35 and 81.2, respectively. The drop in permeability originated from the decresaed diffusion coefficients that overweigh the solubility increase, whereas the increased ideal selectivity was due to the enhanced ideal diffusion selectivity (a D), especially the energetic factor of the ideal diffusivity selectivity upon decreasing temperatures. The higher performance induced by low temperatures derived from the shrinkage of the micropore in PIM-1 to more size sieving ultra-micropore region. Additionally, an O 2 permeability of 157 Barrer and O 2 /N 2 selectivity of 8.0 for mixed-gas at −20 °C under upstream pressure of 16 bar was observed. The results indicate that PIM-1 operates at sub-ambient temperature has great perspective in gas separation applications. Image 1 • Sub-ambient temperatures gas separation properties of PIM-1 were evaluated. • The performance of PIM-1 increased significantly with decreasing temperatures. • PIM-1 showed an unprecedented O 2 permeability of 159 Barrer and O 2 /N 2 selectivity of 9.35 at −30 °C. • The performance improvement originated from the enhanced diffusion selectivity. • An extremely high O 2 /N 2 mixed-gas selectivity of 8 and O 2 permeability of 157 Barrer was observed at 16 Bar and −20 °C. [ABSTRACT FROM AUTHOR]

Bromination/debromination provided a highly efficient method to improve the ultra-microporosity and gas separation property of PIM-PIs and their CMS membranes, showing great opportunities in achieving high performance gas separation membranes. [Display omitted] • Bromination/debromination is an efficient way to adjust polymer ultra-microporosity. • DBPI significantly enhanced ultra-microporosity and ∼ 8-fold higher permeability. • Debrominated DBPI-550 exhibited unprecedented P CO2 of 20639 Barrer. • The bromination enhanced E p by increasing activation energy of diffusion (E d). • The debromination improved E p by decreasing heat of sorption (ΔH s). Tailoring the ultra-microporosity of polymer and carbon molecular sieve membranes (CMSM) is vital to their gas separation properties. Herein, we adopted a simple novel bromination/debromination method to tune the ultra-microporosity and gas separation properties of a triptycene-based polyimide of intrinsic microporosity (PIM-PI) and its derived CMSM. The brominated PIM-PI showed higher free volume, larger surface area, and ∼ 8 times gas permeability without scarifying selectivity. This is due to the bromine introduction in the main chain induced huge increased ultra-microporosity that caused strong molecular sieving effect. After debromination at 550 °C, the CMSM from the brominated PIM-PI displayed larger pore volume, narrower pore size, ∼ 9-fold enhanced gas permeability and same selectivity than the non-brominated counterpart. The corresponding DBPI-550 demonstrated an unprecedented CO 2 permeability of 20639 Barrer combined with CO 2 /N 2 and CO 2 /CH 4 selectivity of 29.2 and 30.9, respectively. Thermal dynamic results showed that this main chain bromination enhanced separation property by improving the activation energy of diffusion (E d). The diffusion transition state theory suggested this is contributed by the energetic factor of selectivity (E enthalpic). The debromination improved activation energy of permeation originated from its decreased heat of sorption (ΔH s). This bromination/debromination technique provided a facile method to editing the ultra-microporosity of the resulting membranes, and shed light on the future designing of high performance industrial gas separation membranes. [ABSTRACT FROM AUTHOR]

Resolving the relationships between the molecular structure and gas separation properties of microporous polymers and their derived carbon molecular sieve membranes (CMSMs) are extremely important in obtaining highly efficient gas separation polymer membranes and CMSMs. To elucidate the correlations, we designed two microporous polyimides (CTPI and MTPI) derived from two triptycene-based diamine isomer monomers, that is, 2,6-triptycene diamine (C 2 symmetry, CTA) and 2,7-triptycene diamine (C s symmetry, MTA). The MTA shows a higher dipole moment than CTA (2.47 vs 1.83 Debye). As a result, the MTPI derived from MTA exhibits a slightly higher density (1.25 vs 1.23 cm3 g−1), smaller fractional free volume (0.250 vs 0.262), lower surface area (148 vs 193 m2 g−1) and smaller micropore size (7.5 vs 9.0 Å), higher glass transition temperature (345.8 vs 329.3 °C) and lower gas permeability but a slightly higher gas pair selectivity than CTPI. The MTPI also demonstrates a higher maximum derivative of weight loss temperature (547.6 vs 546.4 °C) than CTPI, and the 550 °C pyrolyzed MTPI (MTPI-550) shows a higher surface area (772 vs 703 m2 g−1) and larger micropore (6.4 vs 5.4 Å) than the corresponding CTPI-550. Consequently, the MTPI-550 shows higher gas permeability than CTPI-550. The CO 2 permeability of MTPI-550 is 9878 Barrer combined with CO 2 /CH 4 ideal selectivity of 44.5, which is one of the best performances among reported CMSMs. The barometric sorption results indicate that the higher permeability of CMSMs than the PIM-PI precursors is due to the larger diffusion and solubility coefficients because of huge enhanced microporosity, and the higher selectivity is attributed to their diffusion selectivity by the smaller pore size of CMSMs. The above findings clearly show that the larger dipole moment isomer leads to a compacter polymer chain packing of the corresponding PIM-PI, and a more open structure in the resulting CMSM due to the larger dipole-dipole interaction delayed its decomposition speed during the CMSM formation. [Display omitted] • Two intrinsic microporous polyimides were synthesized from two diamine isomer monomers. • CTPI showed a looser chain packing than MTPI because of smaller dipole interaction. • The 550 °C pyrolyzed MTPI showed a larger micropore but narrow pore size than CTPI. • The MTPI-550 showed a CO 2 permeability of 9878 Barrer and CO 2 /CH 4 selectivity of 44.5. • The CMSMs showed both higher P and a X/Y than PIM-PIs due to larger micropore volume and smaller pore size. [ABSTRACT FROM AUTHOR]

One of the biggest challenges in membrane-based gas separation application is how to obtain highly efficient membranes with both high permeability and selectivity. To achieve this target, we reported a novel simple method to modify polymer of intrinsic microporosity (PIM-1) membranes by direct sulfonation using sulfur trioxide (SO 3)/dichloromethane solution to get a series of sulfonated PIM-1 (SPIM-1) membranes. The SO 3 H group was bonded to the main chain of the SPIM-1 and distributed homogeneously in the entire membrane that was confirmed by FTIR, XPS and SEM/EDS mapping. As the sulfonation time increased from 2 to 6 min, the concentration of sulfonic acid (SO 3 H) group in the repeat unit increased from 12.3% to 30.1%. The introduction of SO 3 H groups resulted in a decreased surface area and denser polymer chain packing. The resulting SPIM-1 membranes exhibited huge improved selectivity with separation performance much better than the pristine PIM-1. In which, the 6 min sulfonated PIM-1 membrane (SPIM-1-6) showed excellent gas separation properties with its performance approaches or even exceeds the latest trade-off curves for O 2 /N 2 , CO 2 /N 2 , H 2 /N 2, and CO 2 /CH 4. This is due to the SO 3 H group induced a compact packing of polymer main chain that remarkably enhanced the diffusion selectivity. The 60 days aged SPIM-1-6 demonstrated even higher gas pair selectivity, and the H 2 /N 2 and O 2 /N 2 selectivity reached as much as 125 and 8.43 coupled with H 2 and O 2 permeability of 1077 and 73.4 Barrer, respectively. Additionally, the SPIM-1-6 also showed excellent mixed-gas separation properties, with CO 2 /CH 4 mixed-gas selectivity over 40 coupled with CO 2 permeability of 296 Barrer even at the upstream pressure of 20 bar. These results suggested the great potential for this mild sulfonation method and sulfonated PIM-1 membranes in advanced membrane-based gas separation applications. [Display omitted] • PIM-1 membrane was sulfonated by SO 3 /dichloromethane solution at mild condition for the first time. • SPIM-1 membranes showed a denser chain packing than that of PIM-1. • SPIM-1-6 exhibited a H 2 /N 2 separation property above the latest upper bound. • 60 days aged SPIM-1-6 showed remarkable O 2 /N 2 and CO 2 /CH 4 selectivity of 8.53 and 65. • SPIM-1-6 showed both high P CO2 of 296 Barrer and a CO2/CH4 of 40 for mixed-gas testing at 20 bar. [ABSTRACT FROM AUTHOR]