Characterization of dairy manure hydrochar and aqueous phase products generated by hydrothermal carbonization at different temperatures

•The optimum temperature of dairy manure of HTC was 200-220 °C.•Py-GC/MS gave more complete understanding of hydrochar composition.•Phenolic compounds is the major component of aqueous phase at 280 °C.•Carbon microspheres were prepared from dairy manure at 240 °C.

The effects of reaction tempreture on hydrochar and aqueous phase products were investigated in this paper. The hydrochars were obtained from hydrothermal carbonization of dairy manure at 200-280 °C for 4 h (maintain 1:20 manure-to-water ratio, stir at 600 rpm). The characteristics of hydrochar were determined by elemental analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and pyrolysis gas chromatography-mass spectroscopy (Py-GC/MS). Hydrothermal carbonization decreased the hydrochar yield from 58.34% mass fraction at 200 °C to 43.48% mass fraction at 280 °C. The higher heating value of the hydrochar increased with temperature. Py-GC/MS was used to semi-quantify and simulate fast pyrolysis heating rates and to study potential key light and medium volatile decomposition products found in hydrochar obtained at different temperatures. Microspheres were observed on the surface of hydrochar obtained at 240 °C. The chemical composition of light bio-oil produced at different temperatures was analyzed by GC-MS. It was mainly contained aldehydes, phenols, ketones, acids, and some small molecules and heterocyclic compounds. The reaction temperature had the most significant impact on dairy manure hydrothermal carbonization.