(27c) Systems Design and Economic Analysis of Direct Air Capture of CO2  through Temperature Vacuum Swing Adsorption on Metal Organic Frameworks

Authors: 
Sinha, A., Georgia Institute of Technology
Darunte, L. A., Georgia Institute of Techology
Jones, C. W., Georgia Institute of Technology
Kawajiri, Y., Georgia Institute of Technology
Realff, M., Georgia Institute of Technology
The rising levels of CO2 concentration in the atmosphere poses a serious threat to global climate stability. To mitigate this threat, efforts needs to be made for reduction of CO2 levels. One of the strategy is to capture CO2 from stationary, point, sources. These point sources accounts for approximately only one-third of the global emissions. Another strategy is to capture CO2 directly from ambient air which, if successfully implemented, could result in capture of CO2 from disperse emission sources. In contrast to CO2 capture from stationary sources, Direct Air Capture (DAC) plants are location independent and can be scaled more easily. Thus, the DAC plant can be set up near a sequestration or utilization site, eliminating the need for CO2transportation infrastructure.

Our work proposes comparison of two metal organic frameworks, namely, MIL-101(Cr)-PEI and mmen-Mg2(dobpdc) [1] for DAC through temperature vacuum swing adsorption (TVSA). Isotherm parameter estimation for CO2 adsorption was carried out for both the adsorbents using published and original data and a kinetic study was performed through empirical correlations [2] to estimate the mass transfer rates for the process . The adsorbents are grown as films inside 900 cpsi (cells per square inch) monolith. To achieve a temperature swing, steam is used as a stripping agent during the desorption step. In this thermal desorption operation, it is believed that the amines groups present in the metal organic frameworks are prone to oxidative degeneration at higher temperatures[3]. To overcome this challenge, we propose a five step process: adsorption, evacuation, pressurization, desorption and cooling. In the proposed process, evacuation and cooling steps are implemented through vacuum swing to remove the oxygen in the channels when the temperature is high. In order to model this system, partial differential algebraic equations have been implemented in gPROMS, which is a commercial dynamic process modeling and optimization software. The linear driving force (LDF) model is used to approximate the rate of CO2adsorption [2].

This talk will discuss the energy requirements and overall economics of this DAC process. Different components which contribute to consumption of energy are identified and the TVSA model is simulated to estimate the net energy requirement for MIL-101-PEI-50 and mmen-Mg2(dobpdc). Operating costs during the five steps (adsorption, evacuation, pressurization, desorption and cooling) and capital costs for metal organic frameworks and monoliths have been estimated for both the adsorbents. It has been shown that lifetime of the adsorbent is critical in estimating the net cost and a sensitivity analysis of the adsorbentâ??s lifetime has been performed to analyze the DAC economics for both the adsorbents. We have identified sensitive parameters such as gas flow rate, cycle time, film thickness etc. which effects the overall energy requirements and net economics of the DAC process.

1. McDonald, T.M., et al., Capture of carbon dioxide from air and flue gas in the alkylamine-appended metal-organic framework mmen-Mg2(dobpdc). J Am Chem Soc, 2012. 134(16): p. 7056-65.

2. Y. Y. Li, S.P.P., B. D. Crittenden, Zeolite monoliths for air separation Part 2: Oxygen Enrichment, Pressure Drop and Pressurization. Trans IChemE, 1998. 76: p. 931-941.

3. Heydari-Gorji, A. and A. Sayari, Thermal, Oxidative, and CO2-Induced Degradation of Supported Polyethylenimine Adsorbents. Industrial & Engineering Chemistry Research, 2012. 51(19): p. 6887-6894.