After filling and closing one of the reactors, pressure and temperature on the biomass will be exerted. These constant externally managed process conditions lead to defined reaction mechanisms.
In the search for the energetically most favorable state (principle of the smallest constraint (according to Le Chatelier)) and the first set of thermodynamics that the energy of a closed system is always constant, the biomass first dissolves completely and goes into a suspension with overlapping gas phases. Up to the end of the reaction, depending on the equilibrium reactions, temperatures, pressures, masses, pH values and intermediates change. When the energetically most favorable state and the optimum operating point are reached, the spherical HTC coal is formed by polymerization from the suspension phase.
For heavy metal containing biomasses, e.g. sewage sludge, this optimum time is chosen in a way that the heavy metal precipitation coincides with the polymerization of the HTC coal. With this process, 95% of the heavy metals are embedded in the coal, thus removing them from the liquid phase with its nutrients and valuable materials. The heavy-metal-containing HTC coal obtained by separation is activated and recycled as adsorbent into the sewage treatment plant. Here, it replaces the 4th cleaning stage for removing microparticles from peeling and nanoproducts as well as drug and hormone residues.