Preventing Aerosol Emissions in a CO2 Capture System: Combining Aerosol Formation Inhibition and Wet Electrostatic Precipitation

Mass Transfer-Reaction Modeling of CO2 Capture Mediated by Immobilized Carbonic Anhydrase Enzyme on Multiscale Supporting Structures

Immobilized carbonic anhydrase (CA) enzyme enhances CO2 absorption in potassium carbonate (PC) solutions, offering an attractive alternative to amine-based processes for postcombustion carbon capture. In this work, the cross-scale models of mass transfer coupled with absorption reactions were developed to evaluate the structural impacts of different enzyme immobilization supporting materials, including nonporous nanoparticle carriers (nano scale), porous microparticle carriers (micro scale), and fixed packing structures (macro scale), on the rate enhancement effect of the immobilized CA. Increasing enzyme activity was demonstrated to be an effective approach to promoting the CO2 absorption rate; however, there was an upper limit due to the limitation of CO2 diffusion in the liquid phase, either adjacent to the gas-liquid interface or the liquid-solid interface. The size of particle carriers is another critical factor affecting the CO2 absorption rate. Only nanoscale particle carriers could directly enter the region within the liquid film of mass transfer, thus providing effective enzymatic enhancement. When the particle size was reduced to below 0.35 μm, the PC promoted with the immobilized CA outperformed the benchmark monoethanolamine solution. The solid-side mass transfer resistance became dominant as the particle size decreased. Modeling results also showed that using stagnant packing materials in a fixed bed as a supporting structure for CA immobilization would be impractical for accelerating CO2 absorption.

Reducing aerosol and ammonia emission in post-combustion CO2 capture: Additives as key solutions

Advancement of the absorbent for CO2 capture is essential in optimizing the performance and reducing the negative environmental effects associated with this technology. Despite ammonia's promise as an absorbent, the volatility limits its practical application and creates potential environmental pollution. Therein, we assess various additives (amino acids, carbonates, and alkanolamines) for ammonia-based solvents using multi-stage circulation absorber from the viewpoints of aerosol emission, ammonia emission, and CO2 capture efficiency. Experimental findings reveal that ammonia volatilization can be inhibited by the protonation of free ammonia by carboxyl groups and the formation of hydrogen bonding between amino/hydroxyl groups and ammonia, with ammonia emission reduced by 21.7 %, aerosol emission reduced by 26.5 %, and CO2 capture efficiency increased to a maximum of 87.8 % under the condition of adding histidine. Moreover, the experiment highlights a positive correlation between total ammonia emission and aerosol concentration/diameter. Additionally, tests combining source abatement with water wash exhibit up to 50.5 % aerosol removal efficiency and up to 76.6 % ammonia removal efficiency. To further mitigate emissions, a comprehensive approach is proposed, achieving an 84.4 % reduction in ammonia emission and a 61.9 % reduction in aerosol emission. Finally, a method for recycling ammonia for desulfurization is suggested.

Insights into Aerosol Emission Control in the Postcombustion CO2 Capture Process: From Cluster Formation to Aerosol Growth

Aerosols produced in the amine carbon capture process can lead to secondary environmental pollution. This study employs molecular dynamics (MD) simulations to investigate cluster formation, amine behavior, and aerosol growth of amines, essential for reducing amine aerosol emissions. Results showed that the cluster evolution process can be divided into cluster formation and growth in terms of molecular content, and the nucleation rate for the present systems was estimated in the order of 1028 cm-3 s-1. CO2 absorption was observed alongside successful nucleation, with CO2 predominantly localizing in the cluster's outer layer postabsorption. Monoethanolamine (MEA) exhibited robust electrostatic interactions with other components via hydrogen bonding, leading to its migration toward regions where CO2 and H2O coexisted within the cluster. While MEA presence markedly spurred cluster formation, its concentration had a marginal effect on the final cluster size. Elevating water content can augment the aerosol growth rate. However, altering the gas saturation is possible only within narrow confines by introducing vapor. Contrarily, gas cooling introduced dual, opposing effects on aerosol growth. These findings, including diffusion coefficients and growth rates, enhance theoretical frameworks for predicting aerosol formation in absorbers, aiding in mitigating environmental impacts of amine-based carbon capture.