CMS membranes from PBI/PI blends: temperature effect on gas transport and separation performance

José Manuel Pérez-Francisco, José Luis Santiago-García, María Isabel Loría-Bastarrachea, Donald R. Paul, Benny D. Freeman, Manuel Aguilar-Vega

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Abstract

This study reports pure gas permeability and diffusion coefficients for carbon molecular sieve membranes (CMSM) derived from dense membranes based on blends of a rigid polyimide PI DPPD-IMM (PI) and polybenzimidazole (PBI), PI/PBI, at different concentrations. The permeability, diffusion and selectivity for PI/PBI blend CMS membranes was systematically tested as a function of concentration and temperature. CMS membrane derived from pure PI DPPD-IMM membrane (PI100-600) exhibited the highest permeability coefficients (PHe = 960 Barrer, PCO2 = 503 Barrer) and the highest separation factors (αO2/N2 = 8.3 and αCO2/CH4 = 56.5). Increasing PI concentration in the membranes blend precursors shows a positive effect on CMS membranes permeability, diffusion coefficients and selectivity. These results are attributed to an increase in micropores dimension that was reflected by the emergence of a d-spacing shift from 5.9 Å to 7.1 Å. It was also found that large concentrations of PBI (>50 wt%) in the precursor showed a negative effect on permeability and also in gas pair selectivity for carbon membranes which was attributed to carbazole-type strands densification of the structure. As PI concentration increases in PI/PBI CMS membranes, they present higher entropic selectivity and low energetic selectivity leading to the best permeability/selectivity relationship surpassing 2008 Robeson's upper bound for O2/N2 and CO2/CH4 gas pairs.

Original languageEnglish
Article number117703
Number of pages11
JournalJournal of Membrane Science
Volume597
DOIs
Publication statusPublished - 1 Mar 2020
Externally publishedYes

Keywords

  • Blend precursors
  • CMS membrane
  • Entropic selectivity
  • Gas separation
  • Graphenic stuctures

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