Supercritical Water Oxidation/Synthesis
Related publications, More applications
Supercritical water is now widely recognized for its capacity to destroy
toxic or hazardous materials. Supercritical water is also an interesting
medium for chemical synthesis. We have extensive capabilities and
experience in working with supercritical water solutions. At PNNL
there are various facilities available for bench- to pilot-scale studies
of supercritical water systems. For example there is bench-top flow
reactor (up to 600°C) that can be used to measure kinetics and pathways
for both oxidation and synthesis reactions. In situ spectroscopic
techniques include NMR, FTIR, and X-ray absorption or scattering.
For instance, infrared spectroscopy is a fast, elegant method of making
in situ measurements of reaction rates at elevated temperatures and
pressures. This technique combined with the off-line assay allows
us to quickly assess the feasibility of a conversion by supercritical
|Hydrothermal flow reactor for studying
kinetics and pathways at temperatures up to 600°C
In the supercritical oxidation process a solution containing the
hazardous component is heated to near-critical or supercritical
conditions in the presence of appropriate oxidizers. Since the critical
point of water is relatively high (374°C) waste components can be
"burned" to simple byproducts. Under hydrothermal processing conditions
the main components of the waste are converted to three harmless
byproducts; carbon dioxide, nitrogen and water. Significant control
over the reaction can be obtained by varying the temperature or
pressure of the supercritical or near-critical solution. Supercritical
water exists at conditions above its critical temperature (374°C)
and pressure (217 atm); its properties are highly dependent upon
pressure when the system is near the critical point. In supercritical
fluids, the density, dielectric constant, and viscosity, as well
as other properties, can be varied over a wide range by manipulating
pressure. This offers added flexibility for controlling the reaction
pathways and reaction rates. Often the most difficult components
to destroy in a waste stream are the nitrate/nitrites. Earlier work
at PNNL has demonstrated that nitrate is effectively destroyed using
ammonium ion as the reductant.
The advantages of the supercritical water oxidation over more
conventional disposal techniques are
- the "combustion" processes occurring under supercritical water
conditions are known to be highly efficient at converting the
waste to harmless byproducts (>99.9%)
- it is a closed system that has no emissions to the atmosphere
- the system is easily controlled and can be shut down quickly
- the required equipment is relatively simple so that the commercial-scale
unit is small enough for local installations.
|Dysprosium hydroxyfluoride fibers produces at 450°C, 450 bar.
We have also used supercritical water chemistry for the synthesis of nanofibers and nanoparticles of different morphologies for use as novel optical materials and as high-strength materials.
|Dy/W/O platelets formed at 450°C, 530 bar.
For information about supercritical fluid capabilities at PNNL,
please contact Clement Yonker, at (509) 372-4748, firstname.lastname@example.org.