Separation of CO2-N2 gas mixtures: Membrane combination and temperature influence
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Novel mixed matrix membranes (MMM) with different characteristics are experimentally evaluated in a two-stage membranes-in-series bench-scale setup for the separation of CO2-N2 gas mixtures. For stage 1, a high permeability (higher than 1000 Barrer) and low selectivity (about 5–10) membrane is chosen: the [emim][Ac]-Chitosan (IL-CS) hybrid membrane developed in our laboratory and the Pervap 4060 (Sulzer) composite membrane. For stage 2, we chose our Zeolite A/PTMSP MMM, whose selectivity is higher than 20 even at up to 343 K, the CO2 permeability not lower than 5000 Barrer, which allows skipping the use of the intermediate compressor. The influence of membrane intrinsic properties (i.e. selective membrane material), number of modules in series, and feed concentration on separation performance is evaluated experimentally. In this system, a 10% CO2 feed is concentrated to 43%, 26 and 40% for the Zeolite A/PTMSP MMM – Zeolite A/PTMSP MMM, IL-CS – Zeolite A/PTMSP and Pervap 4060 – Zeolite A/PTMSP in stage 1 and stage 2, respectively. The agreement of the experimental results with a mathematical model at the low CO2 feed concentration of flue gas allows estimating the membrane area needed for each membrane material to achieve a given CO2 purity and removal efficiency. The very large membrane areas needed to reach the 90% CO2 purity and removal efficiency target are drastically reduced if the CO2 removal efficiency required is set to 70%, especially for the combinations with different membranes in each stage, which gives scope for attempting further development of novel membrane materials for CO2capture processes.