Quantifying capital-energy trade-offs in bipolar membrane electrodialysis for atmospheric and oceanic carbon removal

Abstract

Coupling bipolar membrane electrodialysis (BPMED) with direct air capture (DAC) and direct ocean capture (DOC) presents promising carbon removal pathways. We develop, validate, and integrate process and techno-economic models to assess this integration under variable power scenarios. We find that differences in dissolved inorganic carbon content introduce an energy-size trade-off, leading to smaller BPMED areas via DAC, compared with DOC-BPMED, at the expense of 100-fold higher current densities. Consequently, DAC-BPMED is more sensitive to operational costs, whereas DOC-BPMED is more sensitive to capital costs. Estimated grid-connected capture cost ranges are US$304–US$1,281/t-CO₂ and US$535–US$2,220/t-CO₂ for DAC-BPMED and DOC-BPMED, respectively. Selling excess NaOH and concentrating the CO₂ feedstock could potentially alleviate some CO₂ capture costs via DOC-BPMED, while off-grid renewable power integration increases capture costs in both routes. These findings offer novel insights into BPMED-based carbon removal and motivate further research that advances performance while improving cost-effectiveness.