Adsorption of CO2 by Coal and Activated Carbon: A Study Using In-situ Small-Angle X-ray Scattering and Sorption Manometry

Abstract

Carbon capture and storage in unmineable coal seams has been recognised as one of several possible means for mitigating anthropogenic green-house-gas emissions into the atmosphere. However, implementation of this technology on the industrial scale required to significantly reduce CO2 emissions is inhibited by the lack of understanding of many aspects of the interactions between the injected CO2 fluid and coal microstructure. This thesis introduces and details the aspects of the techniques of sorption manometry and small-angle X-ray scattering applicable to the investigation of CO2 adsorption by coal. The experimental work is divided into three sections: the first investigates a self-consistent method for determining the helium density of a microporous material, the second assesses the reliability of manometric measurements of CO2 uptake by small samples, and the third presents an in-situ small-angle X-ray scattering study of CO2 and Xe adsorption by Baralaba coal and Takeda 4A activated carbon. An established self-consistent method for determining the helium density of a microporous material from gravimetric helium sorption data was reworked for application to manometric sorption data. The method was applied to a data set of four He isotherms obtained for a sample of activated carbon at 77, 87, 195 and 298 K using the manometric technique, yielding an unrealistic helium density value of 1.06 g/cm3. It was found that the sensitivity of the method to sample density was too low to provide a reliable measure of the helium density, owing to insufficient variation in the temperature dependency of the Henry constant for temperatures above room-temperature. Assuming negligible helium adsorption at low-pressure (P ≤ 1 bar) and room-temperature remains the best method at present for determining the helium density of a microporous material. Application of this method yielded a helium density value of 2.01 g/cm3 for the activated carbon sample studied.