The performance of affordable and stable cellulose-based poly-ionic membranes in CO2/N2 and CO2/CH4 gas separation
2018
Nikolaeva, Daria | Azcune, Itxaso | Tanczyk, Marek | Warmuzinski, Krzysztof | Jaschik, Manfred | Sandru, Marius | Dahl, Paul Inge | Genua, Aratz | Loïs, Sandrine | Sheridan, Edel | Fuoco, Alessio | Vankelecom, Ivo F.J.
The majority of commercial membrane units for large-scale natural gas sweetening are based on cellulose acetate (CA). However, the low selectivity and risk for and plasticisation affect adversely the performance of CA-based systems. Herein, we present a new class of CA-derived poly(ionic liquid) (PIL) as a thin film composite (TFC) membrane for CO₂ separations. CA is modified with pyrrolidinium cations through alkylation of butyl chloride, substituting the hydroxyl group in the polymer backbone, and further anion exchange to bis(trifluoromethylsulfonyl)imide, P[CA][Tf₂N]. The synthesised PIL material properties are extensively studied. The CO₂ separation performance of the newly synthesised materials is evaluated by gravimetric gas sorption experiments, single gas time-lag experiments on thick membranes, and mixed-gas separation experiments on TFC membranes. The results are compared to the parent material (CA) as well as a reference PIL (poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl)imide (P[DADMA][Tf₂N])). The ideal CO₂/N₂ sorption selectivity of P[CA][Tf₂N] is constant up to 10 bar. The single gas transport measurements in P[CA][Tf₂N] reveal improved ideal CO₂ selectivity for the CO₂/N₂ gas pair and increased CO₂ permeability for the CO₂/CH₄ gas pair compared to the reference PIL. Mixed-gas permeation tests demonstrated that P[CA][Tf₂N]-based membranes with a 5 µm thick selective layer has a two-fold higher CO₂ flux compared to conventional CA. These results present CA modification into PILs as a successful approach promoting the higher permeate flows and improved process stability in a wide range of concentrations and pressures of CO₂/N₂ and CO₂/CH₄ gas mixtures.
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