A Texas lignite was treated with HCl and HF to remove its mineral matter and its cations associated with carboxyl groups, converting them to their acidic form. Part of this demineralized lignite was then treated with metal acetate solutions to exchange hydrogen on some of the carboxyl groups with metal cations, producing Na, K, Mg, Ca and Ba loaded samples. These loaded lignites and the demineralized lignites were then pyrolysed in N2 at 5 °C min-1 up to 1000 °C. The pyrolysis process was monitored by using both chromatography to analyse for the major gases (CO2, H2O, CO, H2 and CH4) and TGA to determine total weight loss. The presence of cations on the lignite produces significant changes in the composition of the gas released but little effect on total weight loss. The role of secondary reactions, which involve participation of the gases initially released from the coal, is discussed.
- ion exchange