Direct ocean capture via a pH-swing integrated hollow fiber membrane contactor

[Geoengineering News]

‎https://www.sciencedirect.com/science/article/abs/pii/S1385894726058407

Authors: Chihyuk Ahn, Sang Moon Shin, Tae-Hyun Bae

14 June 2026

Highlights

•Continuous CO2 extraction from seawater via pH-swing hollow fiber membrane contactor process.

•Transport model quantifying mass transfer resistances and enabling scale-up.

•Stable operation in natural seawater without fouling or wetting.

•Cost drivers and optimization pathways revealed by techno-economic analysis

Abstract

Direct ocean capture (DOC) has emerged as a promising negative-emissions pathway that exploits the ocean's natural carbon reservoir to remove CO2 from seawater rather than from air. Here, we demonstrate a DOC system that integrates a pH-swing process with a hollow fiber membrane contactor (HFMC), enabling continuous CO2 extraction under ambient temperature and pressure. Acidification shifts the dissolved inorganic carbon equilibrium toward molecular CO2, which is selectively removed across a gas-permeable, water-repellent membrane driven by a concentration gradient. The HFMC architecture provides a high specific interfacial area while maintaining complete phase separation, allowing stable operation in natural seawater without observable fouling. Combined experimental measurements and transport modeling elucidate the hydrodynamic dependence of gas–liquid mass transfer and quantify the relative contributions of liquid-, membrane-, and gas-side resistances, establishing a predictive framework for HFMC scale-up. Techno-economic and life-cycle analyses indicate a baseline net levelized cost of capture (Net LCOC) of 703 USD tCO2−1, primarily driven by acid consumption and membrane costs. With near-term improvements in acid utilization efficiency, renewable electricity supply, and membrane performance, the Net LCOC can be reduced to approximately 127 USD tCO2−1. Further cost reductions are achievable through integration with coastal industrial processes, potentially lowering capture costs to 100 USD tCO2−1 or below. Overall, this study demonstrates that coupling pH-swing chemistry with gas–liquid membrane contactors enables a low-energy, scalable approach to oceanic CO2 removal and provides a viable pathway toward practical negative-emissions deployment at coastal industrial sites.

Source: ScienceDirect 

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