Chemical structure analysis and fast micro-pyrolysis study of hydrochar derived from hydrothermal treatment of municipal solid waste

Hydrothermal treatment (HTT) experiments were conducted at 210^○C and 230^○C with 30, 60 and 90 min residence times. Fourier transform infrared spectroscopy (FT-IR) and ¹³C solid-state nuclear magnetic resonance (NMR) were employed to elucidate the effect of HTT on the chemical structure of municipal solid waste. FT-IR results clearly demonstrate that decarboxylation and aromatization reactions occurred during HTT. Fewer types of carbon skeleton structures were observed in the ¹³C solid-state NMR of hydrochars. The aliphaticity yield increased from 74.84% to 91.57% with increasing experiment parameters. In addition, the aromatization reaction was more dramatic in the early stage time, while carbonyl compounds decomposed during the HTT process. Pyrolysis gas chromatography mass spectrometry analysis showed that HTT had positive effects on the simplification of the pyrolytic gas component. In addition, all hydrochars were significantly inhibited to the formation of aromatic compounds with a minor relative peak area of 19.89%. Moreover, hydrochars obtained at a relatively low temperature could achieve a higher yield of hydrocarbons, and hydrocarbons could be partly purified after the HTT process. Overall, the available values of fast pyrolysis products were upgraded by the HTT process.