2.1.1. Materials

The tested biomass was silver fir sawdust. All HTC experiments were performed using demineralized water (σ = 0.005 mS/cm). Potassium hydroxide (Sigma-Aldrich Comporation US, grade ACS reagent, Reg. Ph. Eur.) and HCl (Sigma-Aldrich grade puriss, 24.5%–26.0%) were used for the activation of the hydrochar.

## 2.1.2. Experimental Apparatus

The HTC apparatus was designed and realized on purpose. Details of the piping and control instrumentation are reported elsewhere [34]. The 316-stainless steel batch reactor has an internal volume of about 200 mL and is equipped with a valve for the air initial evacuation and gaseous product withdrawal. A thermocouple and a pressure-meter allow monitoring and controlling the process temperature and pressure, respectively.
