The main compounds of plant biomass, i.e., cellulose, lignin and hemicellulose, were submitted to hydrothermal carbonisation (HTC) in ranges of temperature and time of 140-240ºC and 0.5-24 h, respectively. Those parameters were combined into a single one, the severity factor, and its effect on hydrochar yield on the one hand, and on pH, yield and composition of the liquid fraction on the other hand, was investigated in depth. The production of furanic and phenolic compounds was correlated with both severity and pH. The kinetics of furfural (FU) and 5-hydroxymethylfurfural (5-HMF) production and consumption were also investigated and modelled, and the results were compared to those reported in the literature. The production of nine phenolic compounds from lignin HTC was also considered.