CO₂ removal in humid environment by ion‐exchange membranes

Abstract

Many CO2 sorbents have performance degradation issues in humid environment. The recently developed moisture swing sorbent, initially used for CO2 capture from ambient air, faces the same problem of high moisture sensitivity in the adsorption environment with very dilute CO2 concentration (i.e., air). However, the performance of the sorbent, especially its moisture sensitivity, at relative high concentrations of CO2, is still unknown. In this work, the adsorption performance of a resin‐based ion‐exchange membrane loaded with CO32− (a typical moisture swing sorbent) was investigated in a series of isothermal equilibrium experiments at varying CO2 concentrations and relative humidity. The results showed that the moisture sensitivity of the adsorption capacity of the ion‐exchange membrane decreased with the initial CO2 concentration, especially when the initial CO2 concentration was above 4%. The competition mechanism of H2O and CO2 molecules in the membrane material was analyzed by the modified dynamic adsorption model. The present work indicates that the resin‐based ion‐exchange membrane could be used for carbon dioxide removal in a lot humid environments with relatively high CO2 concentration, such as fruit and vegetable storage room, raw natural gas, and flue gas.

Quaternized Plant-Based Porous Biochar for Direct Air Capture of CO2 by Moisture-Swing Adsorption

“…The adsorbent’s particle size was decreased during grinding, increasing the contact surface area and binding efficiency, which improved the adsorption kinetics and raised the adsorption capacity. Besides, as mentioned above, the moisture-swing adsorption process of the particle-based adsorbents shows diffusion-controlled kinetics according to the shrinking core adsorption model. , The augmented porosity and exposing surface could promote the diffusion of H 2 O and CO 2 molecules, reduce the mass transfer resistance, and thus accelerate the adsorption kinetics. , …”

“…Figure a–d shows the SEM images of the as-prepared four quaternized biochars, where all of them present the morphology containing numerous pores and folds. This kind of structure greatly enhances the gas–solid contact area, which facilitates the diffusion of CO 2 and H 2 O molecules within the adsorbent . The pore size distribution is presented in Figure e where all four biochar adsorbents’ pore sizes were mainly concentrated in the range of 1–50 nm.…”

“…Besides, the carbon capture system is simplified since the heating unit or pressurization unit are not necessary . The typical moisture-swing sorbents are the anion-exchange resin (AER) particles , or membranes − where the resin powder is embedded inside a matrix polymer, and their adsorption capacity usually varies between 0.1 and 1.0 mmol/g. AER carries quaternary ammonium groups as the positive site balanced by negative carbonate ions.…”

Carbon Capture Beyond Amines: CO2Sorption at Nucleophilic Oxygen Sites in Materials

“…[143] Solid‐state NMR (SS NMR) studies support the formation of HCO 3 − upon exposure of OH − ‐rich polymers to dry CO 2 [149] . Remarkably, exposure of the CO 2 ‐saturated material to air with >50% relative humidity (RH) greatly decreases the favorability of CO 2 sorption, leading to desorption (Figure 6, desorption) [143,150,151] . It was originally proposed that desorption is triggered by shifting the equilibrium in Figure 7 from two adjacent bicarbonates to one carbonate and free CO 2 [13,143,146,152] .…”

“…[149] Remarkably, exposure of the CO 2 -saturated material to air with > 50% relative humidity (RH) greatly decreases the favorability of CO 2 sorption, leading to desorption (Figure 6, desorption). [143,150,151] It was originally proposed that desorption is triggered by shifting the equilibrium in Figure 7 from two adjacent bicarbonates to one carbonate and free CO 2 . [13,143,146,152] Although this is counterintuitive -water lies on the product side of this equilibrium -it is likely that CO 3 2À hydrogen-bonds with nanoconfined water more strongly than HCO 3 À , favoring CO 3 2À formation (and CO 2 desorption) in the presence of water.…”