Alkali-assisted coal extraction with polar aprotic solvents

• Published in: Fuel processing technology Vol. 90; no. 4; pp. 591 - 598
• Main Authors: Makgato, M.H., Moitsheki, L.J., Shoko, L., Kgobane, B.L., Morgan, D.L., Focke, W.W.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.04.2009; Elsevier
• Subjects: Applied sciences; Coal; Coal and derived products; Coke; Energy; Exact sciences and technology; Fuels; Graphite; Solvent extraction; Structure, chemical and physical properties; South Africa; Africa; Solvent extraction; Coke; Coal; Graphite; Organic solvent; Sulfides; Sodium; Ash content; Ash; Dissolution; Sodium hydroxide
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2008.12.016

Coal extraction experiments were conducted using a coal, containing ca. 10% ash, from the Tshikondeni mine in South Africa. This coal dissolves only to a limited extent in pure polar aprotic solvents such as dimethylformamide (DMF) and N-methyl-2-pyrrolidinone (NMP). However, the addition of a strong base, e.g. sodium hydroxide (NaOH) or sodium tert-butoxide increased the degree of coal dissolution in these organic solvents. Depending on the extraction conditions, carbon extraction efficiencies of up to 90% were obtained. Carbon precursor material was recovered from the solution as a gel by precipitation with water. Ash content was reduced from 10% in the coal to less than 1.6% in the coal extracts. Sodium sulfide (Na 2S) addition further reduced ash content and aided the recovery of carbon precursors that led to graphitizable cokes but the degree of extraction was significantly reduced.