oa Towards Pyrolysis of Lignite Lithotypes and Main Structural Constituents of Coal-Precursor Vegetation

Pyrolysis coupled “off-line” with thermal desorption gas chromatography–mass spectrometry (TD-GC/MS) were used to specify qualitatively/quantitatively organic functionalities in pyrolysates of “Maritsa-Iztok” lignite lithotypes, i.e. humoclarain, xylain, humovitrain, liptain. Further, main constituents of coal forming vegetation (cellulose, hemicellulose and lignin) were pyrolyzed. The aim of the study was to specify organic volatiles and to assign identified components to the lignocellulose biomass building blocks of coal forming vegetation.

Identified and quantified compounds were grouped in chemical series, i.e. aromatics, S- and O- containing compounds, coal biomarkers. Samples immaturity reflects in high diversity of phenols, methoxy phenols (only guaiacyl structures), furans, etc. maximizing at xylain lithotype. Carbohydrate degradation products, i.e. furaldehydes, 2-cyclopenten-1-ones, etc. were identified as well. Some particularities in pyrolysates of coal forming vegetation were recognizable: (i) volatiles of cellulose are dominated by furaldehydes, furans and 2-cyclopentene homologs; (ii) 3-furaldehyde is dominant in xylan volatiles; (iii) in lignin pyrolysate alkylated PAHs and phenols are preponderant, hydrocarbons (nC7-nC14) and S-containing compounds are present as well.

Pyr-TD/GC-MS allows to get a hint on the degradation and conservation rates of organic debris from coal precursors and to assess the extent of their incorporation into the structure of immature coal organic matter.