Effect of decomposition of oxygen-containing structures on the conversion of lignite in the presence of hydrogen donor solvent

In this paper, pyrolysis behaviors of oxygen-containing structures of Xilinhaote (XLHT) lignite in hydrogen donor solvent (HDS) were investigated to reveal the effect of HDS on the pyrolysis sequence characteristics of XLHT and the difference of the pyrolysis behaviors of oxygen-containing structures in the presence or absence of HDS. Results showed that coal conversion was closely associated to the decomposition of oxygen-containing structures of lignite, and HDS could promote the cleavage of oxygen-containing groups and inhibit the resolidification of decomposed products, while its effect on the pyrolysis sequence of different structures of lignite was tiny. Thermal cleavage of weak aryl-alkyl ether bonds and carbonyl groups of lignite at relatively low temperatures of 280 - 380 degrees C contributed to the depolymerization of XLHT lignite to form preashphaltene (PA) with coal conversion and PA yield increasing from 12.85 % and 1.98 % to 64.58 % and 13.08 %, respectively. As the temperature rose to 430 degrees C, coal conversion was up to 84.13 %, and HDS could promote the cleavage of relatively stable oxygen-containing groups, aryl-aryl ethers, and methylene structures, which was the major contributor to increase coal conversion at relatively high temperatures during liquefaction. Besides, C-O and C=O moieties retained on the surface of LR at 430 degrees C, which netted 12.54 % and 3.52 % of carbon single bond forms, respectively.