Discerning molecular-level CO 2 adsorption behavior in amine-modified sorbents within a controlled CO 2 /H 2 O environment towards direct air capture

Sorbents designed for direct air capture (DAC) play a crucial role in the pursuit of achieving net-zero carbon dioxide emissions. This study elucidates CO2 adsorption from dilute, humidified CO2 streams onto an amine-modified benchmark DAC adsorbent via solid-state NMR spectroscopy. Various NMR techniques, including 1D 1H MAS, 13C MAS, 2D 1H-13C HETCOR NMR, and 1H R2 and R1ρ relaxometry reveal the impact of CO2 partial pressure and H2O on CO2 adsorption behavior. We find that CO2 concentration governs the stepwise formation of ammonium carbamate, carbamic acid, and physisorbed CO2, where relative humidity (RH) at a desired low (<400 ppm) CO2 loading affects total CO2 uptake. The relaxation studies reveal the cooperative or competitive nature of H2O-CO2 sorption in CO2-dilute humid gas, and in particular polymer swelling upon humidification. From those results, we demonstrate that the observed absorption capacity enhancement by humidity is caused by pore opening due to sorbent swelling, and not by bicarbonate formation. This NMR-discerned speciation provides insights into sorption behavior at different RHs in dilute CO2 gas streams, simulating real-world atmospheric conditions, and governs the design of efficient and adaptable material-process combinations for solid sorbent DAC

A Rigorous Integrated Approach to Model Electrochemical Regeneration of Alkaline CO₂ Capture Solvents

This work develops a rigorous model for electrochemical regeneration in Aspen Custom Modeler (ACM), designed to seamlessly integrate into ASPEN Plus, allowing to model complete carbon dioxide (CO2) capture – electrochemical regeneration cycles on a single modelling platform. The modelling of CO2 electrochemical cells has gained significant attention in CO2 capture and utilization processes. This emphasizes the importance of modelling in driving the progress of CO2 electrochemical cells which combines absorption by alkaline solvents and electrochemical solvent regeneration. In such process, potassium hydroxide (KOH, or other metal hydroxides) is used as a solvent for CO2 capture. This process involves a series of chemical reactions that result in the formation of potassium carbonate (K2CO3) and potassium bicarbonate (KHCO3). After CO2 is captured through absorption, the K2CO3/KHCO3 solution is directed towards the regeneration cell where an electrochemically driven pH swing takes place facilitating the desorption of CO2. The cell’s primary objective is to lower the pH of the solution by generating protons at the anode, thereby moving its chemical equilibrium towards carbonic acid. Given the limited solubility of CO2 in water, it desorbs once it reaches saturation. The residual solution can be reclaimed in the cathode compartment and recycled. Electrochemistry models are currently unavailable in popular simulation software like ASPEN Plus, thus making the development of integrated process models, in this case for CO2 capture, more challenging. Here, we introduced a rigorous model to be applied in ACM/ASPEN Plus software to simulate the CO2 regeneration process. The model’s validity was assessed against experimental measurements. Following this validation, the model was subsequently employed to design pilot plant campaigns for the Horizon 2020 project ConsenCUS

Discerning molecular-level CO₂ adsorption behavior in amine-modified sorbents within a controlled CO₂/H₂O environment towards direct air capture

Sorbents designed for direct air capture (DAC) play a crucial role in the pursuit of achieving net-zero carbon dioxide emissions. This study elucidates CO2 adsorption from dilute, humidified CO2 streams onto an amine-modified benchmark DAC adsorbent via solid-state NMR spectroscopy. Various NMR techniques, including 1D 1H MAS, 13C MAS, 2D 1H-13C HETCOR NMR, and 1H R2 and R1ρ relaxometry reveal the impact of CO2 partial pressure and H2O on CO2 adsorption behavior. We find that CO2 concentration governs the stepwise formation of ammonium carbamate, carbamic acid, and physisorbed CO2, where relative humidity (RH) at a desired low (&lt;400 ppm) CO2 loading affects total CO2 uptake. The relaxation studies reveal the cooperative or competitive nature of H2O-CO2 sorption in CO2-dilute humid gas, and in particular polymer swelling upon humidification. From those results, we demonstrate that the observed absorption capacity enhancement by humidity is caused by pore opening due to sorbent swelling, and not by bicarbonate formation. This NMR-discerned speciation provides insights into sorption behavior at different RHs in dilute CO2 gas streams, simulating real-world atmospheric conditions, and governs the design of efficient and adaptable material-process combinations for solid sorbent DAC.</p