Molten-metal bath reactors

Recently, several new processes for methane thermal decomposition were reported in the literature. In one report, the authors proposed a methane decomposition reactor consisting of a molten metal bath.8 Methane bubbles through molten tin or copper bath at high temperatures (900°C and higher). The advantages of this system are efficient heat transfer to a methane gas stream and ease of carbon separation from the liquid metal surface by density difference. In... 

For the depolymerization of PMMA, molten metal bath, dry distillation, extruder processes and fiuidized-bed processes are used [19], The depolymerization reactor of a molten metal bath consists essentially of a gas- or oil-heated metal bath. The metals used are those which have a low melting point such as tin and lead. The PMMA regrind is fed from the storage silos onto the stirred metal bath. Bath temperature and a residence time of some minutes are important for good yield and quality of the MMA. 

In contrast to this, the residence time of the products in a fluidized bed lies between 1 and 5 s [20]. Buekens [21] studied the influence of the residence times in technical fluidized-bed processes. One of the main advantages in using a fluidized bed reactor for depolymerization is that it involves no contamination of organometallic compounds in the products and less environmental problems [1]. Therefore, companies are looking to use fluidized-bed processes especially for filled PMMA. The filler will contaminate the molten metal bath while in a fluidized bed the often expensive fillers can be recovered. 

Batch Mode - Batch reactions have also been carried out to examine the decomposition of polymers in the presence of catalysts. The polymer and the catalyst are both placed in the reactor, and the reactor is immersed in a molten metal bath or a fluidized sand bath at a given temperature for a specified period of time. In some cases, a shaking apparatus is used to promote contact of the catalyst, the polymeric reactant and the decomposition products. After the reaction time is complete, the reactor is opened, and the reaction products are typically analysed by chromatographic techniques. For example, in order to probe the full range of decomposition products, we developed an analytical... 

EFG - entrained flow gasifier SBR - spouted bed reactor MMB - molten metal bath supercritical fluid FXB - fixed bed... 

Dispersion of bubbles in a molten metal bath and the induced flow strongly influence the performance of gas-agitated steelmaking processes. Unfortunately, measurements of the bubble and molten metal flow characteristics are quite difficult in real steelmaking processes. Hence water model experiments have been extensively employed for such investigations, as discussed in detail in Chap. 1 [17,18]. The vessels used for such model experiments are usually fully wetted by water, whereas in the actual steelmaking processes, the wettability of the reactor wall is generally poor. When the wall material, i.e., refl actory, is wetted by the molten metal, some chemical reactions may occur between them, and consequently, the molten metal may be contaminated by the refractory. As mentioned earlier, the wettability is evaluated in terms of 0a [19]. 

In contact with molten salts, the nickel-base alloys behave much more satisfactorily than is the general experience with molten metals. For this reason they are considered as structural materials in atomic reactors using fluoride mixtures as coolants and are used as vessels for heat-treatment salt baths, as thermocouple sheaths and in similar applications. 

A suitable temperature at the walls of the metal reactor can be maintained by means of a molten salt bath containing fused sodium and potassium nitrates and nitrites. The reactor is immersed in the bath and heat is applied... 

ARP [Advanced Reactor Process] A process for making aluminum metal. A molten slag bath containing alumina and carbon produces aluminum carbide that is reacted with more alumina. Under development by Alcoa and Elkem Technology, but not commercialized by 2011. See also Thermical. 

Molten-Tin Process for Reactor Fuels (16). Liquid tin is being evaluated as a reaction medium for the processing of thorium- and uranium-based oxide, carbide, and metal fuels. The process is based on the carbothermic reduction of UO2 > nitriding of uranium and fission product elements, and a mechanical separation of the actinide nitrides from the molten tin. Volatile fission products can be removed during the head-end steps and by distilling off a small portion of the tin. The heavier actinide nitrides are expected to sink to the bottom of the tin bath. Lighter fission product nitrides should float to the top. Other fission products may remain in solution or form compounds with... 

The N-acetyl-D,L-amino acid precursors are conveniently accessible through either acetylation of D,L-amino acids with acetyl chloride or acetic anhydride in a Schotten-Baumann reaction or via amidocarbonylation I801. For the acylase reaction, Co2+ as metal effector is added to yield an increased operational stability of the enzyme. The unconverted acetyl-D-methionine is racemized by acetic anhydride in alkali, and the racemic acetyl-D,L-methionine is reused. The racemization can also be carried out in a molten bath or by an acetyl amino acid racemase. Product recovery of L-methionine is achieved by crystallization, because L-methionine is much less soluble than the acetyl substrate. The production is carried out in a continuously operated stirred tank reactor. A polyamide ultrafiltration membrane with a cutoff of 10 kDa retains the enzyme, thus decoupling the residence times of catalyst and reactants. L-methionine is produced with an ee > 99.5 % and a yield of 80% with a capacity of > 3001 a-1. At Degussa, several proteinogenic and non-proteinogenic amino acids are produced in the same way e.g. L-alanine, L-phenylalanine, a-amino butyric acid, L-valine, l-norvaline and L-homophenylalanine. 

The sodium reduction of titanium tetrachloride was actually carried out as early as 1939 in Germany, and about 670 kg was produced by the Deutsche Gold and Silber Scheideanstalt, during the 1939-45 war. The process, now obsolete, involved reduction in a molten bath of 50 per cent sodium chloride and 50 per cent potassium chloride at 800°C in an atmos phere of hydrogen. The reactors consisted of expendable welded sheet-iron cylindrical vessels, 50 cm diameter by 70 cm deep and 2 mm thick. These rested loosely in a stout iron crucible, fitted into a gas-fired furnace. A portable stirrer was used to agitate the reactor contents. Approximately 20 kg batches of titanium were reduced by distilling 85 kg of titanium tetrachloride at a controlled rate into a melt of 15 kg sodium chloride and 15 kg of potassium chloride, covered with a layer of 46 kg of molten sodium. The titanium sank to the bottom of the molten salts, and at the end of the reaction was recovered from the crushed solidified melt by leaching with dilute hydrochloric acid, in a ceramic-lined vessel. It was finally washed in water and dried at a moderate temperature. The same plant was also used for the production of zirconium metal by the sodium reduction of potassium fluorozirconate (KaZrF ]. 

Preparation of uranium metal. As discussed previously, some nuclear power plant reactors such as the UNGG type have required in the past a nonenriched uranium metal as nuclear fuel. Hence, such reactors were the major consumer of pure uranium metal. Uranium metal can be prepared using several reduction processes. First, it can be obtained by direct reduction of uranium halides (e.g., uranium tetrafluoride) by molten alkali metals (e.g., Na, K) or alkali-earth metals (e.g.. Mg, Ca). For instance, in the Ames process, uranium tetrafluoride, UF, is directly reduced by molten calcium or magnesium at yoO C in a steel bomb. Another process consists in reducing uranium oxides with calcium, aluminum (i.e., thermite or aluminothermic process), or carbon. Third, the pure metal can also be recovered by molten-salt electrolysis of a fused bath made of a molten mixture of CaCl and NaCl, with a solute of KUFj or UF. However, like hafnium or zirconium, high-purity uranium can be prepared according to the Van Arkel-deBoer process, i.e., by the hot-wire process, which consists of thermal decomposition of uranium halides on a hot tungsten filament (similar in that way to chemical vapor deposition, CVD). 

For high-temperature operations, materials, and fuels are key technologies. There is a century of large-scale experience in the use of fluoride molten salts. Aluminum is made by electrolysis of a mixture of bauxite and sodium aluminum fluoride salts at 1000 C in large graphite baths. Fluoride salts are compatible with graphite fuels. A smaller nuclear experience base exists with molten fluoride salts in molten salt reactors. Nickel alloys such as modified Hastelloy-N have been qualified for service to 750 C. A number of metals and carbon-carbon composites have been identified for use at much higher temperatures however, these materials have not yet been fully developed or tested for such applications. 

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