Direct air CO₂ capture using aqueous ammonia through an experimental investigation using Box-Behnken statistical approach

[Geoengineering News]

https://www.sciencedirect.com/science/article/abs/pii/S1385894725071967

Authors: Neha Tiwari, K. Balamurali Krishna Mayya, Ramesh K. Guduru, Pavan Gurrala

https://doi.org/10.1016/j.cej.2025.166358

05 August 2025

Highlights

•Investigation of aqueous ammonia solutions for the first time in direct air CO₂ capture.

•Effect of airflow rate, concentration, and temperature on DAC.

•Systematic analysis of gas-liquid flow dynamics under ultra-dilute CO₂ conditions

•Predictive models validated with <3.3 % error using Box-Behnken design

•Phase characterization confirms ammonium bicarbonate formation via diffraction analysis

Abstract

Direct Air Capture (DAC) of carbon dioxide (CO₂) is a crucial strategy for achieving net-zero carbon targets. This study investigates the use of an aqueous ammonia solution for DAC, specifically utilizing ambient air with CO₂ concentrations ranging from approximately 400 to 420 ppm. The Box-Behnken method was employed to systematically evaluate the effects of key operating parameters air flow rate, ammonia concentration, and temperature using a steady-state bubble column. The results revealed that CO₂ capture efficiency increased at lower air flow rates and temperatures, while higher ammonia concentrations enhanced both efficiency and absorption rate. The mass transfer coefficient initially increased with air flow rate up to a certain threshold before declining due to bubble coalescence and reduced interfacial area, whereas it consistently increased with ammonia concentration and decreased with temperature. The optimal conditions were identified as an airflow rate of 5.76 L/min, an ammonia concentration of 1.10 M, and a temperature of 12.01 °C, resulting in a CO₂ capture efficiency of 76.42 %, an absorption rate of 51.33 mol/s/m3, and a mass transfer coefficient of 9.20 mmol/s/m3/kPa. Model validation confirmed strong agreement between experimental and predicted results, ensuring the robustness of the developed correlations. Additionally, characterization of the byproducts verified the formation of ammonium bicarbonate as a stable carbon capture product. This study provides a comprehensive understanding of steady-state bubble column absorption for DAC and highlights its potential as a viable CO₂ capture strategy.

Source: ScienceDirect