The changes in the gaseous, liquid, and solid products obtained from hydrothermally treated lignite and hydrothermally treated solid products treated by the following mechanical expression were investigated. Furthermore, a microscopic description of the changes was present. Gaseous, liquid, and solid products were characterized by gas chromatography, total organic carbon analyzer, inductively coupled plasma atomic emission spectroscopy, high-performance liquid chromatography, and Fourier transform infrared spectrometer, respectively. The results showed that at temperatures above 173°C for hydrothermal treatment, freezable water, and some organic and inorganic compounds were removed from lignite, and acidic groups first dissolved and decomposed at 100°C. For the following mechanical expression treatment, freezable and nonfreezable water and organic and inorganic compounds were removed, and the concentration of acidic groups changed little. Within temperatures range 175–250°C, for hydrothermal treatment, nonfreezable water and inorganic and organic compounds continued to be removed, and the detection of CO2 is because of decarboxylation. For the following mechanical expression treatment, the main removed water was nonfreezable water, and changes in organic and inorganic compounds, acidic groups, and volatile matter were similar to that of samples treated by mechanical expression at temperatures below 173°C.
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