Effect of impurity gases in carbon dioxide on sorption behavior and mineral matter in an Australian bituminous coal

Injection of CO2 into coal seams is considered a potential approach for sequestering it. However, the carbon dioxide that is injected into seams may contain other gases that could potentially react with the coal and change its sorption behavior. Here we exposed samples of a moistened bituminous coal to small amounts of SO2, H2S, NO2, NH3 and a number of potential amine capture agents in sealed containers for up to 2 years, evacuated them and measured their sorption behavior and determined their mineralogy using low temperature ashing followed by quantitative X-ray diffraction analysis of the residue. Exposure of the coal to amines, H2S or NO2 had no effect on the sorption characteristics of the coal. However, SO2 markedly reduced the CO2 sorption capacity of the coal (by 25%).The minerals in the coal consisted mainly of quartz, kaolinite, illite and carbonates. Of the gases tested, only SO2 modified the mineral matter extensively. It attacked the clays as well as carbonates, producing a range of sulfate minerals and amorphous material. This shows that the effects of SO2 on sorption behavior and mineralogy of the coals need to be included in any prediction of sorption potential of coals if it is present in the CO2 that is to be injected into the coal.

Research highlights
► Impact of impurity gases in CO2 on a coal was studied.
► H2S, NO2, CO2, NH3, amine capture agents had little effect on sorption or mineral matter.
► SO2 reduced sorption capacity of the coal by 25%.
► SO2 attacked clays and carbonates in the coal, forming sulfates.