Effect of Inorganic Salt Blending on the CO₂ Separation Performance and Morphology of Pebax1657/Ionic Liquid Gel Membranes

Abstract

Gel membranes comprising inorganic salt, molten salt or ionic liquid (IL), and Pebax1657 were prepared by blending the three components in ethanol/water mixture, and their carbon dioxide separation properties were evaluated. To probe the effects of inorganic salt types and concentrations, a small amount of common inorganic salts, such as sodium chloride (NaCl), calcium chloride (CaCl2), and sodium sulfate (Na2SO4) were first doped into neat Pebax membranes. The thermal properties, surface chemistry, and gas separation performance of the free-standing membranes were evaluated using differential scanning calorimetry, Fourier-transform infrared spectroscopy, and gas permeation tests. CaCl2-doped membranes gave the best performance due to the high water content and cross-linking between the salt cation and polyamide segments, which resulted in lower polymer crystallinity. Further incorporation of 1-ethyl-3-methylimidazolium tetrafluoroborate IL into Pebax1657/inorganic salt mixture to form thin film composite gel membranes improved the inorganic salt solubility and enhanced CO2 permeance up to 899 GPU at the expense of CO2/N2 selectivity and mechanical strength. Cyclic permeation tests using humidified feed containing a trace amount of contaminant showed stable performance although no improvement in gas pair selectivity was observed, confirming solution-diffusion mechanism through the gel membranes.

Mixed-Matrix Ion Gel Membranes for Gas Separation

“…For instance, the TFC-HFM prepared by Fam et al, containing GO, showed a 42% decrease in CO 2 permeance, while the CO 2 /N 2 selectivity was preserved, after a 6-month aging period. The same authors also reported a fast physical aging in Pebax/80 wt %IL/CaCl 2 TFC-HFM, with a feed pressure of 10 bar, due to the loss of free volume in the structure of the PTMSP gutter layer . Nonetheless, there is still much work to be done in order to understand how these parameters can influence the performance of mixed-matrix ion gels.…”

“…More recently, Fam et al studied the influence of different inorganic salts (NaSO 4 , NaCl and CaCl 2 ) and [C 4 mim]­[BF 4 ] IL in Pebax 1657-based membranes for CO 2 /N 2 separation. In this case, the authors used a different approach.…”

“…CO 2 separation efficiencies of two- and three-component ion gel membranes represented on (a) CO 2 /N 2 , (b) CO 2 /CH 4 and (c) CO 2 /H 2 Robeson plots. Data from refs , − , , , , , , , , − , , , − , , , and − are illustrated, and the upper bounds were adapted from Robeson and Rowe et al …”

“…A faster withdrawal speed increased the selective layer thickness, and consequently decreased both CO 2 permeance and CO 2 /N 2 selectivity. Using a similar preparation method, the same authors also fabricated TFC-HFMs of ion gels containing different inorganic salts, Pebax1657, and 80 wt % [C 2 mim]­[BF 4 ] IL …”

Ionic Liquids Endowed with Novel Hybrid Anions for Supercapacitors

“…Ionic liquids (ILs), as a state-of-the-art kind of ambient temperature molten salt, have captured intensive insights because of their green characteristic. Close attention to the ILs has been widely paid in various aspects, such as electrolytes, − energy applications, − catalytic reactions, , material modifications, , and efficient gas absorbents. − Compared with the traditional organic electrolytes, they are considered to be more secure because of their negligible vapor pressure, high thermal stability, and nonflammability, which have therefore been considered as a substitute for organic electrolytes in EDLCs. The cations and anions do not match in terms of size and tend to exhibit some degree of charge delocalization due to the weak interaction between the constituent ions, which is usually responsible for their high ionic conductivity.…”