Effects of hydrothermal treatment on physico-chemcial structures and liquefaction behaviors of lignite

Abstract

The effects of hydrothermal treatment on physico-chemcial structures and liquefaction behaviors of lignite were studied in this paper. The lignite after demineralization was hydrothermally pretreated at 70–280 °C under N2 atmosphere, and physico-chemcial structures of pretreated coal were determined. The results showed that hydrothermal treatment at 130–190 °C could inhibit the reduction of H and O contents and the decomposition of carboxyl groups and phenolic hydroxyl groups in lignite. It was also beneficial to the increase of H content, the formation of mesopores, and decomposition of C-O in lignite. After hydrothermal treatment, the pretreated coal was liquefied at 430 °C under H2 atmosphere. The results showed that the yields of preasphaltene (PA) and oil of pretreated coal at appropriate temperatures (130–190 °C) were higher than those of demineralized coal. These indicated that the hydrothermal treatment played positive roles in the formation of PA, and conversion of asphaltene (AS) to low molecular compounds. The components of liquefaction oil showed that hydrothermal treatment could promote the transfer from polycyclic aromatic hydrocarbons to monocyclic aromatic hydrocarbons, thus leading to a decrease in molecular weight of liquefaction oil. During the liquefaction process, the increases of pore volume and surface area were beneficial to hydrogen transfer, thus improving the liquefaction activity of lignite.