Direct Air Capture via Counter-Current NaOH Absorption System: Evolution of pH for Subsequent Plasma-Enhanced CO₂ Utilization

Abstract

Direct air capture (DAC) technologies offer a promising approach to mitigate anthropogenic climate change by enabling net negative emissions. CO₂ absorption using NaOH represents an efficient solution within the proposed BlueFire carbon cycle, which integrates DAC with plasma technology for syngas production. Optimizing a DAC plant control relies on understanding the pH profile as a key parameter. A bubble column absorption model with pure CO₂ was experimentally adapted for a counter-current flow setup with ambient air, reproducing a staged pH decrease. An optimal absorption endpoint was determined by identifying the maximum slope of the pH decline, indicating high reaction progress. X-ray diffraction analysis of the absorption products validated the theoretical model of carbonate formation.