(550g) Carbon Dioxide Adsorption at Elevated Temperatures for Vehicle Exhaust Gas Treatment

To forestall the effects of climate change, due to an excess of carbon dioxide in the atmosphere, scaled carbon capture and storage (CCS) operations are needed to separate CO₂ from the exhaust gases generated by fossil fuel combustion at electric power plants and from the internal combustion engines of automobiles. Many different classes of porous materials have been considered for use as carbon capture adsorbents. Many published studies of these materials focus on their CO₂ adsorption capabilities at near-ambient conditions; e.g., at 25 °C and 1 atm [1]. However, higher discharge temperatures, in the range from 40 to 75°C, are relevant for CO₂ removal from combustion stack gases and vehicle exhaust streams. Fewer studies have been reported [2-4] for CO₂ uptake on adsorbents at these elevated temperatures.

To assess the performance of prospective carbon capture adsorbents at the higher temperatures characteristic of vehicle exhaust trains, CO₂ uptake measurements were performed on eight commercially available porous adsorbents at temperatures of 25, 40, 55, and 70 °C using a Micromeretics ASAP 2050 extended adsorption gas analyzer. The materials tested included two activated carbons, two zeolite molecular sieves, two metal-organic framework adsorbents (MOFs), one zeolitic imidazolate framework (ZIF), and one elastic-layered MOF (ELM). The CO₂ adsorption capacities of the two zeolites were additionally evaluated at temperatures of 85 and 100 °C. A decrease of 23% to 27% in the CO₂ adsorption capacity was observed at 1 atm pressure for each 15 °C stepwise increase in the measured isotherm. From application of the Clausius-Clapeyron equation to the adsorption isotherms, isosteric heats of adsorption are obtained for each of the porous solids that are in good agreement with adsorption enthalpies reported for these materials at lower temperatures. Among the materials considered, the reduction in CO₂ adsorption capacity with increasing temperature is most pronounced for zeolites 5A and 13X, which correspondingly have the largest heats of adsorption for carbon dioxide.

1. Keskin, S., van Heest, T. M., & Sholl, D. S. (2010). Can Metal–Organic Framework Materials Play a Useful Role in Large‐Scale Carbon Dioxide Separations. Chemistry and Sustainability, 3, 879-891.

2. Yazaydın, A. O., Snurr, R. Q., Park, T. H., Koh, K., Liu, J., LeVan, M. D., & Low, J. J. (2009). Screening of metal− organic frameworks for carbon dioxide capture from flue gas using a combined experimental and modeling approach. Journal of the American Chemical Society, 131, 18198-18199.

3. Singh, V. K., & Kumar, E. A. (2016). Comparative studies on CO₂ adsorption kinetics by solid adsorbents. Energy Procedia, 90, 316-325.

4. Yong, Z., Mata, V. G., & Rodrigues, A. E. (2001). Adsorption of carbon dioxide on chemically modified high surface area carbon-based adsorbents at high temperature. Adsorption, 7, 41-50.