Separation and concentration of CO2 from air using a humidity-driven molten-carbonate membrane

[Geoengineering News]

https://www.nature.com/articles/s41560-024-01588-6

Authors 

Ian S. Metcalfe, Greg A. Mutch, Evangelos I. Papaioannou, Sotiria Tsochataridou, Dragos Neagu, Dan J. L. Brett, Francesco Iacoviello, Thomas S. Miller, Paul R. Shearing & Patricia A. Hunt 

Citations: Metcalfe, I.S., Mutch, G.A., Papaioannou, E.I. et al. Separation and concentration of CO2 from air using a humidity-driven molten-carbonate membrane. Nat Energy (2024). https://doi.org/10.1038/s41560-024-01588-6

19 July 2024

Abstract

Separation processes are substantially more difficult when the species to be separated is highly dilute. To perform any dilute separation, thermodynamic and kinetic limitations must be overcome. Here we report a molten-carbonate membrane that can ‘pump’ CO2 from a 400 ppm input stream (representative of air) to an output stream with a higher concentration of CO2, by exploiting ambient energy in the form of a humidity difference. The substantial H2O concentration difference across the membrane drives CO2 permeation ‘uphill’ against its own concentration difference, analogous to active transport in biological membranes. The introduction of this H2O concentration difference also results in a kinetic enhancement that boosts the CO2 flux by an order of magnitude even as the CO2 input stream concentration is decreased by three orders of magnitude from 50% to 400 ppm. Computational modelling shows that this enhancement is due to the H2O-mediated formation of carriers within the molten salt that facilitate rapid CO2 transport.

Fig. 1: Transport in biological membranes and the humidity-driven synthetic membrane.

a, In biological membranes, transport is typically passive, down a concentration gradient (uniport, symport and antiport); however, in active transport, uphill transport against a concentration gradient for one species (red) can be achieved via an intimate coupling with downhill transport of a second species (blue). b, A three-dimensional reconstruction of micro-computed X-ray tomography scans of a synthetic, supported molten-salt membrane, comprising an alumina (Al2O3) support with a ternary eutectic mixture of molten carbonates ((Li/Na/K)2CO3) held in laser-drilled artificial pores. A humidity difference (wet air and dry air) is harnessed to pump CO2 from one air stream to the other, against its concentration gradient, to produce a CO2-enriched output stream.

Source: nature energy