Article

Tuning microcavities in thermally rearranged polymer membranes for CO2 capture

School of Chemical Engineering, College of Engineering, Hanyang University, Seoul, Republic of Korea.
Physical Chemistry Chemical Physics (Impact Factor: 4.2). 04/2012; 14(13):4365-73. DOI: 10.1039/c2cp23729f
Source: PubMed

ABSTRACT Microporous materials have a great importance in catalysis, delivery, storage and separation in terms of their performance and efficiency. Most microporous materials are comprised of inorganic frameworks, while thermally rearranged (TR) polymers are a microporous organic polymer which is tuned to optimize the cavity sizes and distribution for difficult separation applications. The sub-nano sized microcavities are controlled by in situ thermal treatment conditions which have been investigated by positron annihilation lifetime spectroscopy (PALS). The size and relative number of cavities increased from room temperature to 230 °C resulting in improvements in both permeabilities and selectivities for H(2)/CO(2) separation due to the significant increase of gas diffusion and decrease of CO(2) solubility. The highest performance of the well-tuned TR-polymer membrane was 206 Barrer for H(2) permeability and 6.2 of H(2)/CO(2) selectivity, exceeding the polymeric upper bound for gas separation membranes.

Download full-text

Full-text

Available from: Jong Geun Seong, Apr 27, 2015
0 Followers
 · 
269 Views
  • Source
    Procedia Engineering 01/2012; 44:3–4. DOI:10.1016/j.proeng.2012.08.280
  • [Show abstract] [Hide abstract]
    ABSTRACT: This study demonstrates that thermal treatment of ortho-hydroxy containing polyimides (HPIs) in the solid state certainly leads to the formation of polybenzoxazoles (PBOs). Thermal conversion protocol, including temperature and dwell time, and the form of the sample (film or powder) determine the rearrangement reaction rate of HPI into PBO. Thermal rearrangement kinetics seems to be faster for film samples rather than for powder ones. Also, mild thermal treatment conditions (i.e., low temperatures and short times) seem to result in negligible or low degrees of conversion to PBO. Moreover, synthetic routes of HPI do not alter in any way the thermal conversion pathway. These findings validate the widely reported imide-to-benzoxazole thermal rearrangement mechanism, and contradict the alternative rearrangement pathway, proposed recently, of HPI into poly(biphenylene bisimide) polymers.
    European Polymer Journal 07/2012; 48(7):1313–1322. DOI:10.1016/j.eurpolymj.2012.04.007 · 3.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The presence of water vapor in a membrane gas separation system is known to cause plasticization and/or competitive sorption with other gas species. Using appropriate mathematical models to interpret such a multi-component system is of considerable practical importance. In an earlier publication, we reported the permeation properties of water vapor and its impact on the membrane performance for two polyimides; 2,2′-bis(3,4′-dicarboxyphenyl) hexafluoropropane dianhydrid-2,3,5,6-tetramethyl-1,4-phenylenediamine (6FDA-TMPDA) and poly(3,3′-4, 4′-benzophenone tetracarboxylic-dianhydride diaminophenylindane) (Matrimid® 5218) under mixed gas/water vapor feed streams (CH4, CO2 and H2O). In this work, mathematical models based on proven sorption and transport models for glassy polymers were derived to successfully describe and characterize the permeation of water vapor and the associated changes of membrane performance in such a multi-component system. Water vapor induced-plasticization effects were not predicted by these models for either polyimide. Instead, as vapor activity increased, these models predicted a decrease in diffusion coefficient. This decline could be related to vapor-induced pore filling, which was further verified using positron annihilation lifetime spectroscopy (PALS) measurements. Pore filling by water molecules or possibly water clusters affected not only the self-diffusional pathway but also that for other penetrating gas molecules (CH4 and CO2). The increasing trend of water vapor permeability over the range of vapor activity for both polyimides was caused by the net effect of increasing vapor solubility and decreasing vapor diffusivity.
    Journal of Membrane Science 08/2012; s 409–410:96–104. DOI:10.1016/j.memsci.2012.03.047 · 4.91 Impact Factor
Show more