Hydrothermal flames

Steeper, R.R., Methane and methanol oxidation in supercritical water chemical kinetics and hydrothermal flame studies, Sandia Rep., Sand96-8208.UC-1409, 1-150, 1996. 

B. Wellig, K. Lieball and P. R. von Rohr, Operating Characteristics of a Transpiring-wall SCWO Reactor with a Hydrothermal Flame as Internal Heat Source, J. Supercrit. Fluids, 34 35-50, 2005. 

ETH Zurich developed the concept of a film-cooled coaxial hydrothermal reactor [36]. Two coaxial tubes form the reactor, waste water enters the central tube, and the oxidant enters the outer tube. The walls of the reactor are cooled by a water film of 80-250°C to retard precipitation of solids and corrosion of the pressure vessel. Hydrothermal flames, estimated at 1700-2200°C can be observed through windows. The plant was designed for 15 kg/h at 42 MPa and 600°C and was patented by Sulzer Chemtech AG 1995 in the USA [37]. 

Serikawa, R., Usui, T., Nishimura, T., et al. (2002). Hydrothermal flames in supercritical water oxidation investigation in a pilot scale continuous reactor. Fuel, 81, pp. 1147-1159. 

Various methods are applied to the synthesis of titania particles including sol-gel method, hydrothermal method [2], citrate gel method, flame processing and spray pyrolysis [1]. To utilize titania as a photocatalyst, the formation of ultrafme anatase titania particles with large crystallite size and large surface area by various ways has been studied [4]. 

Another distinguishing feature of titania prepared by flame spray pyrolysis is the draar e of anatase crystallite size with the increase of flame temperature. Generally, the increase of preparation temperature increases the crystallite size in other processes such as sol-gel method, hydrothermal method [2, 3], flame processing and conventional spray pyrolysis. The decrease of crystallite size was directly related to the decrease of particle size. Fig. 5 shows SEM and TEM images of titania particles prepared by flame spray pyrolysis. 

PP-g-MA) silicate nanocomposites and intercalated thermoset silicate nanocomposites for flame-retardant applications were characterised by XRD and TEM [333], XRD, TEM and FTIR were also used in the study of ID CdS nanoparticle-poly(vinyl acetate) nanorod composites prepared by hydrothermal polymerisation and simultaneous sulfidation [334], The CdS nanoparticles were well dispersed in the polymer nanorods. The intercalation of polyaniline (PANI)-DDBSA (dodecylbenzene-sulfonate) into the galleries of organo-montmorillonite (MMT) was confirmed by XRD, and significantly large 4-spacing expansions (13.3-29.6A) were observed for the nanocomposites [335],... 

It could be expected, that combustion reactions and possibly flames can be produced in such dense supercritical mixtures. Technical aspects of hydrothermal oxydation at moderate pressures have already been tested and discussed [7,8]. The study of combustion and flames in supercritical phases offers several possibilities 1. The variation of pressure over wide ranges should influence reaction mechanisms and flame characteristics because the density can be changed from low, gas-like, to high, liquid-like, values. 2. The variable temperature of the dense, fluid environment can have an influence on reactions and flames. 3. The chemical and physical character of this environment can be varied considerably, for example by using supercritical water as the major component, as in the present experiments. Certainly, the knowledge of transport coefficients of gases involved is desirable. For water the viscosity has been determined to... 

Other methods including hydrothermal precipitation, flame hydrolysis, thermal decomposition of Fe(CO)s and high temperature reaction of Fe " chloride with iron, are used only on a small scale to obtain specialty products (see Chap. 19). 

Hydrothermal processes, i. e. the heating of suspensions of ferrihydrite in alkaline media under pressure, have been used to produce large platy crystals of hematite. This process gives vell formed crystals, but is expensive. The crystals can be reduced to produce isomorphous magnetite plates. Flame hydrolysis involves burning Fe " chloride at 400-800 °C to iron oxide. Owing to the many technical difficulties associated with this process, it is not commercially important. 

German C. R., Richards K. J., Rudnicki M. D., Lam M. M., Charlou J. L., and FLAME scientific party (1998b) Topographic control of a dispersing hydrothermal plume. Earth Planet. Sci. Lett. 156, 267—273. 

German C. R., Thursherr A. M., Radford-Kroery J., Charlou J.-L., Jean-Baptiste P., Edmonds H. N., Patching J. W., and the FLAME 1 II science teams (2003) Hydrothermal fluxes from the Rainbow vent-site, Mid-Atlantic Ridge new constraints on global ocean vent-fluxes. Nature (submitted). 

Kriechbaum GW, Kleinschmit P (1989) Suptafine oxide powdtrs—flame hydrolysis and hydrothermal S5mthesis. Angewandte Chemie-Int Ed Engl 28 1416-1423... 

---