Recent Progress in Alkaline CO₂ Capture Using Airlift Reactors: Fundamentals, Hydrodynamics, and Mass Transfer Enhancement

Nael Hassan; A. Al-Farraji

doi:10.71229/rwsh9b56

Authors

Nael Hassan Department of Chemical Engineering, College of Engineering, Al-Nahrain University, Jadriya, Baghdad, Iraq
A. Al-Farraji Department of Chemical Engineering, College of Engineering, Al-Nahrain University, Jadriya, Baghdad, Iraq

DOI:

https://doi.org/10.71229/rwsh9b56

Keywords:

CO₂ capture, Alkaline absorbents, Airlift reactor, Gas–liquid mass transfer, Hydrodynamics, Packing materials, Process intensification

Abstract

The increasing concentration of atmospheric carbon dioxide (CO₂) has intensified the need for efficient and sustainable carbon capture technologies. Among the available approaches, chemical absorption remains one of the most established methods for post-combustion CO₂ capture, while alkaline absorbents such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) have attracted considerable attention because of their rapid reaction kinetics, high CO₂ reactivity, low volatility, and favorable absorption characteristics. This review critically examines recent developments in CO₂ capture using alkaline absorbents, with particular emphasis on their integration with airlift reactor technology. The fundamental mechanisms of reactive CO₂ absorption and gas–liquid mass transfer are discussed, together with the influence of key hydrodynamic parameters, including gas holdup, liquid circulation velocity, bubble dynamics, and volumetric mass transfer coefficients. Particular attention is given to external-loop airlift reactors and the incorporation of packing materials as a process-intensification strategy. Packing can enhance gas dispersion, suppress bubble coalescence, increase gas–liquid interfacial area, and improve overall mass transfer performance. The effects of major operating parameters, including gas flow rate, absorbent concentration, temperature, and reactor configuration, are also evaluated. Comparative analysis indicates that effective CO₂ capture depends on the coupled interactions among absorbent chemistry, reactor hydrodynamics, interfacial mass transfer, and operating conditions. Finally, current research gaps and future directions are identified, particularly regarding reactor optimization, packing configuration, absorbent regeneration, scale-up, and the development of energy-efficient alkaline absorption systems. This review provides an integrated framework for understanding and improving alkaline CO₂ capture in airlift reactors.

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