The interfacial compatibility between a potential CO₂ separation membrane and capture solvents

Water-lean solvents are considered as a promising solution for carbon dioxide (CO₂) capture. Candidate CO₂ capture molecules include N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA), 3-methoxy-N-(pyridine-2-ylemthyl)propan-1-amine (MPMPA), and 1-((1,3-Dimethylimidazolidin-2-ylidene)amino)propan-2-ol (1-IPADM-2-BOL). When integrating the water-lean solvents with the separation membrane to form a hybrid system, it would have a higher driving force to pull CO₂ through a membrane. In addition, including a membrane in the direct air capture (DAC) system would reduce the evaporation of capture solvents. Therefore, it is important to understand the chemical compatibility of the solvents with the separation membranes to better integrate them into the process for DAC of CO₂. Characteristic peaks of water-lean solvents and separation membrane were observed in the static spectral measurements of time-of-flight secondary ion mass spectrometry (ToF-SIMS). For example, m/z⁺ 217.190 C₁₁H₂₅N₂O₂⁺, m/z⁺ 181.129 C₁₀H₁₇N₂O⁺, and m/z⁺ 172.145 C₈H₁₈N₃O⁺, are the protonated 2-EEMPA, protonated MPMPA, and protonated 1-IPADM-2-BOL, respectively. Similarly, the fragment of CO₂ separation membrane, m/z⁺ 263.082 C₁₆H₁₁N₂O₂⁺, a synthesized PEEK-ionene, was observed, showing molecular detection of ToF-SIMS. In addition, x-ray photoelectron spectroscopy (XPS) was performed to quantitatively verify the change of carbon ratio at the interface, indicating the interactions between water-lean solvents and the separation membrane. These findings show that the interface between the CO₂ separation membrane and water-lean solvents should be studied at the molecular level, because they provide insights into how we could design hybrid systems comprised of CO₂ separation membranes and capture solvents.