A study of the adsorption potential of CO₂on South African ash.

Kholumo, Mookho
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As the global demand for energy increases, CO2 discharge will also increase due to power stations andother coal-dependent industries. It therefore becomes necessary to develop processes that willenable the capture and storage of CO2 from flue gas in combustion processes, in order to mitigate the undesirable consequences of CO2emission. It is for this reason that research on carbon capture and storagehas receivedconsiderable attention recently. Adsorption of CO2 onto coal ash is a potentially attractive alternative to capturing CO2 from stationary sources in the context of carbon capture and storage technologies. Four coal ash samples were used as CO2 adsorbents in this study, obtained from three different industries, namely: 1) coal power station 2) a petrochemical industry and, 3) a metallurgical plant. Thermogravimetric analysis, X-ray diffraction spectroscopy, and BET isotherms were used to analyse the nature of the samples prior to the adsorption process. A volumetric adsorption system was used to facilitate the adsorption process. The pulverized fuel ash sample had the highest CO2adsorption capacity, followed by the spreader stoker ash sample, the chain grate ash sample, and finally the gasification ash sample.The as received ash was found to have a potential to uptake CO2in a capacity range of 0.17 – 2.8 Mt CO2, meaning that 1.28 % of the annual sequestrableCO2 produced in South Africa could be captured using all of the ash produced in one year in South Africa. Coal ash is a suitable material for the adsorption of CO2,however its adsorption capacity needs to be improved by treatment with acids and amines in order to introduce active functional groups.