A novel analytical approach for oxygen speciation in coal-derived liquids
Since the production of crude oil may not meet the increasing demand in the next future, coal liquefaction products have sparked great interest as one of the possible substitutes of petroleum in the transportation field. Speciation of oxygen in direct coal liquefaction products is essential considering the important role of oxygenated compounds in coal conversion reactions. This study attempts to characterize them as fully as possible. The originality of this approach is based on the development of complementary analytical tools to describe the composition of two coal-derived distillates: a naphtha cut and a gasoil cut. Two-dimensional gas chromatography (GC × GC), high resolution mass spectrometry (FT-ICR/MS), nuclear magnetic resonance (NMR), and UV–visible spectroscopy were applied to these two matrices. This analytical scheme shows that among 2.89%w/w of elemental oxygen present in the naphtha cut, 1.78%w/w O corresponds to phenols, 0.08%w/w O to alcohols and 0.21%w/w O to ketones. Concerning carboxylic acids, they are negligible (<0.01%w/w). Thus, a total of 2.07%w/w O is quantified what represents 72% of the oxygenated compounds contained in the naphtha cut. Similarly, in the gasoil cut, among the 0.80%w/w O of elemental oxygen, 0.62%w/w O are attributed to phenols, 0.07%w/w O to alcohols, and 0.015%w/w O to ketones. Benzo and dibenzofurans may represent the species which have not been quantified. Quantification of alcohols and phenols by carbon atom number is also allowed by GC × GC–FID using response factors. It shows that the carbon atom number varies from 6 to 11 for phenols and from 4 to 9 for alcohols. Similarly, carboxylic acids distribution by alkylation degree can be obtained by combining FT-ICR/MS and NMR results. This unique multi-technical approach offers a detail level which was never reached so far in terms of oxygenated compounds characterization for such products. This information is crucial to evaluate the potential of these liquids as a substitute for fuel and envisage their upgrading. âº A detailed quantification of phenols, alcohols, acids, and ketones was established. âº 72% w/w of the oxygen content was quantified in a coal-derived naphtha. âº 88% w/w of the oxygen content was quantified in a coal-derived gasoil. âº Four analytical techniques were used: GCxGC, FT-ICR/MS, UV–visible, and NMR 31P.