Enhanced CO2 capture using amine-based extractants in liquid-liquid hollow fiber membrane contactors for direct ocean capture

Abstract

One of the novel direct ocean capture (DOC) proposed to achieve negative carbon emissions is the liquid-liquid hollow fiber membrane contactor (LL-HFMC). The ocean, with a CO₂ concentration approximately 150 times higher than that of the atmosphere, provides a more energy-efficient and cost-effective alternative to direct air capture (DAC). Despite its advantages, there is a lack of research on the effects of membranes and extractants in the DOC process. This study aims to optimize extractants for LL-HFMC in the DOC process through a systematic evaluation of amine-based extractants. The performance of monoethanolamine (MEA), ethylenediamine (EDA), diethylenetriamine (DETA), and triethylenetetramine (TETA) were compared alongside sodium hydroxide (NaOH), a benchmark extractant in LL-HFMC processes. Polypropylene hollow fiber membranes were used as the contactor medium. Among the extractants, DETA exhibited the highest CO₂ capture efficiency. In addition, the effects of concentration and the flow rates (seawater and extractant) using DETA on system performance were investigated. These findings underscore the importance of material and process optimization, reaffirming that DOC – leveraging its inherently higher CO₂ concentration – offers a more economical and scalable carbon capture medium than DAC. This study provides valuable insights into enhancing DOC efficiency and advancing carbon capture methodologies.