Compositional determination of acidic species in Illinois no. 6 coal extracts by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Coal acids constitute a source of corrosion in coal refining, and carboxylic acids are implicated in retrograde reactions in coal liquefaction. Here, we use electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to provide detailed molecular compositions of acidic species in a pyridine extract as well as in hexane-soluble (coal acids) and hexane-insoluble (acidic asphaltenes) fractions designed to concentrate the acidic components. All three extracts contain similar major heteroatomic classes. For a given heteroatomic class, asphaltenes > pyridine extract > coal acids in aromaticity; the combined acid fractions exhibit wider distributions in carbon number and double bond equivalents than the pyridine extract. Although the pyridine extract contains the widest variety of organics, additional acidic species are found in the other two extracts. The chemical compositions of coal acids are now accessible in unprecedented detail and promise to provide a starting point for more rational analysis of coal origin and processing.