Analysis of Equilibrium-Based TSA Processes for Direct Capture of CO2 from Air

Abstract

Direct capture of CO 2 from air is a concept that, if successfully implemented, could lead to capture of CO 2 from disperse sources. We have developed process models to consider the viability of adsorption-based air capture technologies. Our models focus on using an amino-modified silica adsorbent, TRI-PE-MCM-41, and a structured monolithic contactor unit. We have studied several different temperature swing adsorption processes using the purity of CO 2 and annual product throughput as metrics for comparing process performance. This analysis identifies some of the operational parameters, adsorbent characteristics, and other factors that have a significant effect on the performance of the process. Using the total energy requirement of the process and available sources of energy, such as low pressure steam and electricity, we carry out an economic analysis to obtain a net operating cost for air capture of CO 2 . We identify a process with a daily throughput of ∼1.1 t CO 2 at 88.5% purity using standard shipping container sized air capture units. The total energy required (6745 MJ/t CO 2 ) is dominated by the parasitic losses—sensible heat requirements of the contactor (40%) and the adsorbent (28%) and not by the mechanical energy associated with air flow (∼5%). On the basis of our analysis of factors such as source of electricity, availability of low pressure steam, and geographic location, the net operating cost of capture is estimated to be ∼$100/t CO 2 . These cost estimates do not include capital expenses necessary to construct or maintain the air capture units. Potential strategies for further reducing the energy and monetary cost of these processes are identified. Our analysis supports continued work to establish the technological and economic feasibility of adsorption-based air capture.