Changes to the organic functional groups of an inertinite rich medium rank bituminous coal during acid treatment processes

• Published in: Fuel processing technology Vol. 92; no. 4; pp. 764 - 770
• Main Authors: Strydom, C.A., Bunt, J.R., Schobert, H.H., Raghoo, M.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01-04-2011; Elsevier
• Subjects: Acid treatment; Applied sciences; Bituminous coal; carbon dioxide; coal; Energy; Energy. Thermal use of fuels; Exact sciences and technology; FTIR; Fuels; hydrochloric acid; leaching; nitric acid; nitrogen; Organic functional groups; oxygen; Reactivity; temperature; Acid treatment; Reactivity; Organic functional groups; FTIR; Bituminous coal; Carbon dioxide; Nitric acid; Mineral matter; Inertinite; Infrared spectrometry; Reaction time; Lixiviation; Protonation; Surface area; Coal rank; Functional group
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2010.09.008

A South African inertinite rich medium rank bituminous coal was subjected to a series of acid treatment steps using concentrations of HF and HNO
3 ranging between 1.5 and 4
M, temperatures between 65 and 80
°C and reaction time between 1.5 and 3
h for each acid. A HF and HCl procedure was used to reduce mineral matter to less than 2.5%. Analyses indicate that oxygen and nitrogen containing species are incorporated in the coal structure during the HF/HNO
3 leaching processes, but not during the HCl/HF/HCl procedure. The HF/HNO
3 methods lead to increased amounts of =
N–OH groups formed on the remaining coal structure, whereas the HCl/HF/HCl procedure did not. The –COOH content upon HCl/HF/HCl treatment increased slightly possibly due to protonation of COO
− groups by HCl. The results show that the CO
2 reactivity doubled after the HF/HNO
3 procedures and increased by a factor of 2.5 for the HCl/HF/HCl treatment. Surface areas of the treated coal samples increased with the highest increase for the HCl/HF/HCl method. The increased surface areas may cause the increased CO
2 reactivity. The results indicate that the described acid treatment procedures with mixtures containing nitric acid have slight, but measurable, effects on the coal structure.