Purity-constrained TVSA modeling of Lewatit VPOC 1065 for direct air capture: bridging cured thermodynamics, process design and geometrical analysis

Abstract

Direct air capture (DAC) is a leading carbon dioxide removal (CDR) technology that extracts CO₂ directly from ambient air, independent of emission sources. Among the various process designs, temperature–vacuum swing adsorption (TVSA) has emerged as the most mature technology and is currently deployed at commercial scale, particularly in its steam-assisted configuration. However, the DAC-TVSA process has often been evaluated using incomplete models, where critical aspects such as the O₂ purity constraint were ignored or the condenser energy cost was neglected, potentially leading to misleading feasibility assessments. This work develops a comprehensive TVSA modeling framework that unifies detailed adsorption thermodynamics for both dry and humid conditions, refined heat-transfer descriptions accounting for wall-driven regeneration, realistic treatment of auxiliary equipment, and explicit oxygen-purity constraints. The model was benchmarked against literature data, demonstrating that the omission of stricter process constraints can severely underestimate the actual energy–productivity trade-offs. Additionally, the study identified the pre-heating step required to meet the O₂ specification as the critical bottleneck in both wall-heated and steam-assisted configurations. The impact of this limitation was further analyzed by systematically varying the adsorber aspect ratio. This revealed the existence of an optimal region, governed by the trade-off between enhanced heat transfer in flatter geometries and increased pressure drop associated with longer beds. In parallel, the benefits of steam injection were visualized through minimum work envelopes, which clearly highlighted the performance gains achievable by improving the desorption step. Overall, the results highlight the substantial potential that can be realized by directly addressing the critical bottlenecks of DAC.