Pressure and time effect over semi-continuous gasification of zootechnical sludge near critical condition of water for green chemicals production

•Near critical condition of water.•Thermodynamic evaluations for the production of green chemicals.•Operative condition effect on the SCWG process.

Aim of the paper is the analysis of experimental data from digestate from buffalo sewage gasification carried out at high pressure, close water critical condition. Experiments were performed in a semi-continuous reactor, by loading the biomass, continuously feeding the pressurised water and removing the gas product from the reaction vessel. At a fixed value of temperature (310 °C), two pressure levels were investigated across the water critical pressure (110 bar and 320 bar). According to the expectation, from the treatment of this type of biomass a liquid fraction, containing some components that can be used as chemicals for the “green industries”, was obtained. Aldehydes and carboxylic acids were the main product obtained and the liquid phase composition was revealed to be sensitive to the pressure level, since a more concentrated product was obtained at lower pressure level. In addition, a reaction pathways is proposed coherently to the observed evolution of the liquid phase composition.