Direct Air Capture (DAC)-Sourced CO₂ and Green Hydrogen: A Synergistic Route to Sustainable E-Fuels

The increasing urgency of climate change mitigation has led to growing interest in Direct Air Capture (DAC) as a viable solution for reducing atmospheric CO₂ levels. This study focuses on the modeling of a DAC process employing an alkali sorbent, specifically implementing a modified Kraft process. The objective is to develop a simulation of the upscaled Carbon Engineering ‘s DAC plant assessing its energy consumption and integration with downstream CO₂ utilization. The captured CO₂ is subsequently used in methanol synthesis process combining it with green hydrogen, exploring a potential pathway for sustainable e-fuel production. The process was modeled using Aspen Plus®, a professional software developed by AspenTech, with a focus on replicating the thermodynamic and operational characteristics of the large-scale DAC system. Special attention was given to thermal integration strategies aimed at recovering thermal energy in order to reduce consumption. The DAC model was validated by comparing its energy demand per unit of CO₂ captured against reference values from literature and existing pilot-scale systems. Additionally, an analysis was conducted to evaluate energy conversion efficiencies, particularly, regarding the utilization section, properly methanol conversion ratio and electrical conversion into chemical power were assessed. The results provide valuable insights into the feasibility of large-scale DAC deployment and its integration with e-fuel production, clarifying the implications of utilization strategies for DAC systems. Specifically, the study calculates energy consumption per unit of methanol produced and per unit of CO₂ captured, offering a clear estimate of the energy requirements involved. Additionally, the analysis includes a detailed comparison between plants with and without the utilization facility, highlighting how the energy demand increases with the utilization process and how other factors are impacted. These factors include the potential removal of obsolete auxiliary components and changes in the purity of some streams like the CO₂ available. The findings underscore key considerations that provide a basis for future research, aimed at improving energy efficiency and assessing the role of DAC technologies within a sustainable carbon management framework.