Extraction of aliphatic hydrocarbons and formation of new ones at superheated steam temperatures from demineralized anthracite from Vrska Cuka (Serbia)

Extraction of aliphatic hydrocarbons from demineralized coal using superheated steam is a promising method for reducing the industrial production costs. In the present study, extractions were performed at superheated steam temperatures without a catalyst (373 to 473 K; 2-20 h). The greatest yield of extracted organic matter was obtained during the first 2 h (4.0 to 6.1 % of the initial sample mass). At longer times, solubility values varied, suggesting that the release of aliphatic hydrocarbons depends on their location within different structural domains of the organic matrix. The high maturity of the organic matter indicates that the anthracite sample is in the metagenesis phase. Gas chromatography with flame ionization detection showed that extraction yielded n-paraffins, primarily the energetically significant C12 to C19 homologues, comprising 50 to 61 % of extracted compounds after 20 h. Comparison with less mature coals (lignite and brown coal) from the same area revealed a similar trend, though, with increasing coalification, the proportion of n-paraffins decreased and terpenes increased. Fourier transform infrared spectroscopy of the dry residue after extraction showed that methyl groups (2972 cm⁻¹) were lost after 2 hours at all temperatures, while complete removal of aliphatic structures, including ethyl groups (2924, 2852 and 1377 cm⁻¹), occurred after 20 h. The detected paraffins and terpenes originated from methyl and ethyl groups extracted from the organic matrix. Additionally, while lignite and brown coal gave nearly identical results, lignite lacked independently bound methyl groups.