The nature of solvent extracts from vitrinite-rich and inertinite-rich South African bituminous coals

Daniel Van Niekerk, Jonathan P. Mathews

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Coal-to-liquids is a re-emerging technology that can provide alternatives to oil-derived and natural gas-derived fuels as well as specialty chemicals. Solvent extraction is one such approach to obtain liquid feeds. Two similar (carbon content, rank and age), yet diverse South African coals, Waterberg (vitrinite-rich, 91% point count) and Highveld (inertinite-rich, 87% point count), were evaluated as feedstocks by Soxhlet extraction. Solvents used were pyridine and Nmethylpyrrolidone (NMP). Molecular weight distributions of the parent coals and corresponding residues and solvent extracts were analyzed using laser-desorption ionization time-of-flight mass spectrometry. Both coals had the bulk of the observable molecular weight distributions ranging to approximately 1,700 m/z with a maximum abundance of ~450 m/z for Waterberg and ~550 m/z for Highveld. Very small quantities of very high molecular weight material (160,000 m/z) were also observed. Waterberg and Highveld showed the highest extraction yield with NMP (extraction of 31% and 21%, daf respectively). Both NMP extracts were close analogs (molecular weight distribution) of the parent coals with the highest abundance shifted to a lower mass region (from ~550 to ~350 m/z for Highveld, from ~450 to ~320 m/z for Waterberg). The extraction yields for Waterberg and Highveld with pyridine were lower (7% daf). Waterberg pyridine extracts show a narrow molecular weight distribution (between 200 to 500 m/z with a maximum abundance of 300 m/z). Highveld pyridine extract had a wider weight distribution with a maximum abundance of 340 m/z. NMP is a more favorable solvent if a higher yield and comparable liquid analog of the parent coal is desirable. Pyridine is a more favorable solvent for extracting lower molecular weight material, but with a lower yield. Solvent swelling was also quantified using the packed-bed method. A greater extent of swelling was observed in the Waterberg coal (120 % for Waterberg vs. 60 % for Highveld) using NMP. The same trend was observed using pyridine (110 % for Waterberg vs. 60 % for Highveld). Petrography was conducted on the extracts and a porous pitch-like material was observed.

Original languageEnglish (US)
Title of host publication24th Annual International Pittsburgh Coal Conference 2007, PCC 2007
Pages1497-1506
Number of pages10
StatePublished - Dec 1 2007
Event24th Annual International Pittsburgh Coal Conference 2007, PCC 2007 - Johannesburg, South Africa
Duration: Sep 10 2007Sep 14 2007

Publication series

Name24th Annual International Pittsburgh Coal Conference 2007, PCC 2007
Volume3

Other

Other24th Annual International Pittsburgh Coal Conference 2007, PCC 2007
CountrySouth Africa
CityJohannesburg
Period9/10/079/14/07

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology
  • Geotechnical Engineering and Engineering Geology

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  • Cite this

    Van Niekerk, D., & Mathews, J. P. (2007). The nature of solvent extracts from vitrinite-rich and inertinite-rich South African bituminous coals. In 24th Annual International Pittsburgh Coal Conference 2007, PCC 2007 (pp. 1497-1506). (24th Annual International Pittsburgh Coal Conference 2007, PCC 2007; Vol. 3).