How (Carbon) Negative Is Direct Air Capture? Life Cycle Assessment of an Industrial Temperature-Vacuum Swing Adsorption Process

Abstract

Current climate targets require negative emissions. Direct air capture (DAC) is a promising negative emission technology, but energy and materials demands lead to trade-offs with indirect emissions and other environmental impacts. Here, we show by Life Cycle Assessment (LCA) that the first commercial DAC plants in Hinwil and Hellisheiði can achieve negative emissions already today with carbon capture efficiencies of 85.4 % and 93.1 %. Climate benefits of DAC, however, depend strongly on the energy source. When using low-carbon energy, as in Hellisheiði, adsorbent choice and plant construction become important with up to 45 and 15 gCO<sub>2e</sub> per kg CO<sub>2</sub> captured, respectively. Large-scale deployment of DAC for 1 % of the global annual CO<sub>2</sub> emissions would not be limited by material and energy availability. However, current small-scale production of amines for adsorbent production would be needed to be scaled up by an order of magnitude. Other environmental impacts would increase by less than 0.057 %. Energy source and efficiency are essential for DAC to enable both negative emissions and low-carbon fuels.<br>