The role of aqueous ammonia in direct air capture: insights into evaporation and CO₂ interactions

This study investigates the potential of aqueous ammonia as a solvent for Direct Air Capture (DAC) of CO₂, leveraging its high solubility and reactivity with CO₂ despite its known volatility compared to conventional alkaline solutions such as NaOH and KOH. The research focuses on the evaporation behaviour of aqueous ammonia when air and inert gases are bubbled through a liquid column at varying flow rates. Results indicate that increased airflow enhances both CO₂ capture and ammonia evaporation. Experimental analysis were conducted across different ammonia concentrations, and the amount of ammonia utilised for CO₂ capture were evaluated based on both evaporation data and direct CO₂ sensor measurements. Notably, good agreement between the two methods was observed at fixed airflow rates. To systematically assess and optimise the effects of ammonia concentration and airflow rate, statistical analysis using response surface methodology (RSM) was performed, identifying optimal conditions that balance CO₂ absorption efficiency and ammonia loss. The findings underscore the dual role of ammonia in atmospheric CO₂ capture and highlight the trade-off posed by evaporation losses, offering valuable insights for improving ammonia-based DAC systems and informing broader applications in agriculture and chemical processing. HIGHLIGHTSExplores the use of aqueous ammonia solutions for Direct Air Capture (DAC).Investigates ammonia evaporation and atmospheric CO₂ capture across different concentrations, and at a fixed airflow rate the calculated CO₂ capture values closely matched with direct sensor measurements.Ammonia evaporation and CO₂ absorption are strongly influenced by airflow rate and ammonia concentration, which were statistically optimised using response surface methodology. Explores the use of aqueous ammonia solutions for Direct Air Capture (DAC). Investigates ammonia evaporation and atmospheric CO₂ capture across different concentrations, and at a fixed airflow rate the calculated CO₂ capture values closely matched with direct sensor measurements. Ammonia evaporation and CO₂ absorption are strongly influenced by airflow rate and ammonia concentration, which were statistically optimised using response surface methodology.