Unveiling the complexity of salt(s) in water under transcritical conditions

Abstract

Processes using water at sub-and supercritical conditions (T > 300°C) are used in industrial wastewater treatment, chemical recycling of wastes, biomass conversion and also in material synthesis, because of their rapidity and high efficiency. However, the salts injected or generated during the processes can lead to complex multiphasic water-salts systems with a behavior far to be understood in all the cases. Drastic changes of physics and chemistry of the systems are expected from water intrinsic properties; however, the formation of new phases, sometimes unexpected, near the critical point of water (374°C; 22.1 MPa) also has a direct effect on the properties of the system. It is thus important to be conscious of the existence of these new phases to have the best control as possible on the physico-chemistry occurring inside the reactor. The aim of this review paper is to give an overview of these poorly-known new phases and to show that they are more encountered in SCW than it is thought.

Behavior of Silicon Carbide Materials under Dry to Hydrothermal Conditions

“…The oxidation behavior of the (110,111,311, 511 and 100) faces of silicon single crystals Lewis and Irene obtained different oxidation rates for the thermal oxidation of single crystal Si depending on the crystal faces (110,111,311, 511 and 100). It appears that, for thin oxide film, the growth of silica depends on the density of atoms, which is specific to each orientation.…”

“…Furthermore, it is interesting to note that single crystals of SiC are often hexagonal (α) and that CVD-SiC samples generally crystallize in the cubic (β) crystalline. The different crystal structures and the different atomic natures of the C-and Si-faces lead to different oxidation behaviors which is not the case for silicon crystals [49] The oxidation behavior of the (110,111,311, 511 and 100) faces of silicon single crystals Lewis and Irene obtained different oxidation rates for the thermal oxidation of single crystal Si depending on the crystal faces (110,111,311, 511 and 100). It appears that, for thin oxide film, the growth of silica depends on the density of atoms, which is specific to each orientation.…”

“…The distance between water molecules increases, which weakens the hydrogen bonds and dipole electrostatic interactions. Therefore, low-density water acts as a non-polar solvent, in which salts precipitate, in the supercritical region [110]. However, for a constant temperature of 400 • C, the density, ionic and dielectric constants increase with the pressure.…”

Geoinspired syntheses of materials and nanomaterials

“…In other words, oil is soluble in supercritical water but not salts. 85,86 Another interesting behaviour concerns the evolution of the ionic product of water (Fig. 10B), which is about three orders of magnitude higher at 250 1C than at room temperature under 250 bars.…”

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling

“…A properly designed SCWO system has an advantage over incineration in the treatment of toxic organic waste because the lower operating temperatures inhibit the production of NO x , SO 2 , and particulate matter (PM). The main challenges in adopting the technology are related to thermal management of the reactor, corrosion control, and salt precipitation. − However, recent research has shown that with proper management of the SCWO process, the limitations can be minimized. − The insights into the reactor operation, such as temperature profiles of the fluid and the reactor components (wall, liner, injectors, etc. ), the spatial distribution of reacting species, and the location of the liquid/supercritical phase transition are essential in the reactor design and optimization of its operational parameters.…”