Membrane Separation Technology in Direct Air Capture

Abstract

Direct air capture (DAC) is an emerging negative CO₂ emission technology that aims to introduce a feasible method for CO₂ capture from the atmosphere. Unlike carbon capture from point sources, which deals with flue gas at high CO₂ concentrations, carbon capture directly from the atmosphere has proved difficult due to the low CO₂ concentration in ambient air. Current DAC technologies mainly consider sorbent-based systems; however, membrane technology can be considered a promising DAC approach since it provides several advantages, e.g., lower energy and operational costs, less environmental footprint, and more potential for small-scale ubiquitous installations. Several recent advancements in validating the feasibility of highly permeable gas separation membrane fabrication and system design show that membrane-based direct air capture (m-DAC) could be a complementary approach to sorbent-based DAC, e.g., as part of a hybrid system design that incorporates other DAC technologies (e.g., solvent or sorbent-based DAC). In this article, the ongoing research and DAC application attempts via membrane separation have been reviewed. The reported membrane materials that could potentially be used for m-DAC are summarized. In addition, the future direction of m-DAC development is discussed, which could provide perspective and encourage new researchers' further work in the field of m-DAC.

Keywords: carbon dioxide; direct air capture; high permeance; membrane.

Figure 1

Sample diagram of typical gas separation membrane layers.

Figure 2

Chemical structures of high permeable copolymers, with CO₂ permeabilities ≥ 1000 Barrer or with CO₂/N₂ Selectivity’s ≥ 30 at temperatures ≤ 35 °C. (a) PIM-BTrip [41], (b) KAUST-PI-1 [40], (c) SFX-PIM-33 (m/n = 1/2) [42], (d) PIM-bpy-x [77], (e) PTCNSi(OMe)₃ [45], (f) VAP7 [44], (g) BPM-50 [43].

Figure 3

Chemical structures of copolymers with post modification (CO₂ permeabilities ≥ 1000 Barrer or with CO₂/N₂ selectivity’s ≥ 30 at temperatures ≤ 35 °C). (a) TZPIM [48], (b) MTZ100-PIM [50], (c) AO-PIM-1 [49], (d) Thioamide-PIM-1 [51], (e) cPIM-1 [71].

Figure 4

Examples of high permeable MMMs with MOF and Silica nanoparticles (CO₂ permeabilities ≥ 1000 Barrer or with CO₂/N₂ Selectivity’s ≥ 30 at temperatures ≤ 35 °C). (a) UiO-66-CN@sPIM-1 [57], (b) PAO-PIM-1/NH₂-UiO-66 [61], (c) S-SN [95], (d) 6FDA-durene/Si-5 [53].

Figure 5

Schematic of the mechanism for gas travel through MMMs with GO fillers.

Figure 6

Schematic of Pebax/PPEGMEA membranes obtained via the free radical polymerization of PEGMEA in Pebax in the presence of BPO. Reprinted with permission from Ref. [99]. Copyright 2022 Elsevier.

Figure 7

CO₂/N₂ separation through the facilitated transport membrane [12,104].

Figure 8

Examples of post-capture utilization pathways for CO₂ depending on purity.