Pure- and mixed-gas CO2/CH4 separation properties of PIM-1 and an amidoxime-functionalized PIM-1

• Published in: Journal of membrane science Vol. 457; pp. 95 - 102
• Main Authors: Swaidan, Raja, Ghanem, Bader S., Litwiller, Eric, Pinnau, Ingo
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.05.2014; Elsevier
• Subjects: Amidoxime; Applied sciences; artificial membranes; carbon dioxide; Chemistry; CO2/CH4 mixed-gas permeation; Colloidal state and disperse state; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Functionalized PIMs; Gas separation; General and physical chemistry; hydrogen bonding; Intrinsic microporosity; Membranes; methane; microstructure; natural gas; permeability; Polymer industry, paints, wood; polymers; Porous materials; Technology of polymers; Gas separation; Functionalized PIMs; Intrinsic microporosity; CO2/CH4 mixed-gas permeation; Amidoxime; Methane; Polymeric membrane; Gas mixture; Separation; CH; Carbon dioxide; Permeation; CO; Porous material; mixed-gas permeation; Microporosity
• ISSN: 0376-7388
• DOI: 10.1016/j.memsci.2014.01.055

The prototypical solution-processable polymer of intrinsic microporosity, PIM-1, and derivatives thereof offer combinations of permeability and selectivity that make them potential candidate materials for membrane-based gas separations. Paramount to the design and evaluation of PIMs for economical natural gas sweetening is a high and stable CO2/CH4 selectivity under realistic, mixed-gas conditions. Here, amidoxime-functionalized PIM-1 (AO-PIM-1) was prepared and examined for fundamental structure/property relationships. Qualitative NLDFT pore-size distribution analyses of physisorption isotherms (N2 at -196 oC; CO2 at 0 oC) reveal a tightened microstructure indicating size-sieving ultra-microporosity (<7Å). AO-PIM-1 demonstrated a three-fold increase in αD(CO2/CH4) over PIM-1, surpassing the 2008 upper bound with P(CO2)=1153Barrer and ideal α(CO2/CH4)=34. Under a 50:50 CO2:CH4 mixed-gas feed, AO-PIM-1 showed less selectivity loss than PIM-1, maintaining a mixed-gas α(CO2/CH4) ~21 across a 20bar pressure range. Conversely, PIM-1 endured up to 60% increases in mixed-gas CH4 permeability over pure-gas values concurrent with a selectivity of only ~8 at 20bar. A pervasive intermolecular hydrogen bonding network in AO-PIM-1 predominantly yields a rigidified microstructure that mitigates CO2-induced matrix dilations, reducing detrimental mixed-gas CH4 copermeation. [Display omitted] •PIM-1 develops ultra-microporous sieving texture upon amidoxime functionalization.•Extensive hydrogen-bonding network induces 3-fold increase in αD(CO2/CH4).•PIM-1: 60% increase in Pmix(CH4) relative to Ppure(CH4) (strong plasticization).•AO-PIM-1: Stable mixed-gas selectivity (~21) over 20bar range (versus 8, PIM-1).•Intermolecular interactions attenuate matrix dilations and losses in αmix(CO2/CH4).