Chlorination furnace

The chlorination is mostly carried out in fluidized-bed reactors. Whereas the reaction is slightly exothermic, the heat generated during the reaction is not sufficient to maintain it. Thus, a small amount of oxygen is added to the mixture to react with the coke and to create the necessary amount of heat. To prevent any formation of HCl, all reactants entering the reactor must be completely dry. At the bottom of the chlorination furnace, chlorides of metal impurities present in the titanium source, such as magnesium, calcium, and zircon, accumulate. 

Fig. 21. Production diagram of silicon tetrachloride by ferrosilicon chlorination 1 - jaw crasher 2 - bucket elevator 3 - grate 4 - shaft hoist 5 -bin 6 - chlorinating furnace 7 - condenser 8 - scrubber 9 - boiler 10, 14 - condensers 11 - distillation tank 12 - rectification tower 13 - refluxer 15 -collector 16- apparatus for the destruction of solid chlorides 17- hydrolysis chamber 18- absorption column.

The principal steps in this direct chlorination process for converting zircon to ZrCU are shown in Fig. 7.4. Gases from the chlorinating furnace are cooled to around 100°C to condense crude solid ZrCU and FeCU, then cooled further to condense SiCU, TiCU, and AICI3. The crude ZrCU is purified by sublimation with hydrogen in a stainless steel retort. Hydrogen reduces volatile FeCU to nonvolatile FeCU, which remains in the retort with ZrOj and other nonvolatile impurities. This process removes most of the metals associated with zirconium in zircon except hafnium. 

Fio. 2.7. Chlorination furnace TC, thermocouple positions 1, chlorine gas preheater 2, charcoal diffuser bed 3, resistor carbon 4, charge of briquettes 5, graphite electrode 6, split graphite-pipe top heater 7, feed hopper 8, nichrome heater for cross-over pipe 9, nickel-lined condenser 10, water-cooled iron aftercondenser 11, exhaust to scrubbers 12, condenser heating air blower 13, nichrome air heater (Stephens, W. W. and Gilbert H. L. Ref. 62). 

The cells are fed semicontinuously and produce both magnesium and chlorine (see Alkali and chlorine products). The magnesium collects in a chamber at the front of the cell, and is periodically pumped into a cmcible car. The cmcible is conveyed to the cast house, where the molten metal is transferred to holding furnaces from which it is cast into ingots, or sent to alloying pots and then cast. The ingot molds are on continuous conveyors. 

A number of high temperature processes for the production of titanium carbide from ores have been reported (28,29). The aim is to manufacture a titanium carbide that can subsequently be chlorinated to yield titanium tetrachloride. In one process, a titanium-bearing ore is mixed with an alkah-metal chloride and carbonaceous material and heated to 2000°C to yield, ultimately, a highly pure TiC (28). Production of titanium carbide from ores, eg, ilmenite [12168-52-4], EeTiO, and perovskite [12194-71 -7], CaTiO, has been described (30). A mixture of perovskite and carbon was heated in an arc furnace at ca 2100°C, ground, and then leached with water to decompose the calcium carbide to acetjdene. The TiC was then separated from the aqueous slurry by elutriation. Approximately 72% of the titanium was recovered as the purified product. In the case of ilmenite, it was necessary to reduce the ilmenite carbothermaHy in the presence of lime at ca 1260°C. Molten iron was separated and the remaining CaTiO was then processed as perovskite. 

Although there are minor differences in the HCl—vinyl chloride recovery section from one vinyl chloride producer to another, in general, the quench column effluent is distilled to remove first HCl and then vinyl chloride (see Eig. 2). The vinyl chloride is usually further treated to produce specification product, recovered HCl is sent to the oxychlorination process, and unconverted EDC is purified for removal of light and heavy ends before it is recycled to the cracking furnace. The light and heavy ends are either further processed, disposed of by incineration or other methods, or completely recycled by catalytic oxidation with heat recovery followed by chlorine recovery as EDC (76). 

Chlorination. Historically, the production of zirconium tetrachloride from zircon sand involved first a reduction to carbide nitride (see above) followed by the very exothermic reaction of the cmshed carbide nitride with chlorine gas in a water-cooled vertical shaft furnace ... 

Thermal Cracking. Thermal chlorination of ethylene yields the two isomers of tetrachloroethane, 1,1,1,2 and 1,1,2,2. Introduction of these tetrachloroethane derivatives into a tubular-type furnace at temperatures of 425—455°C gives good yields of trichloroethylene (33). In the cracking of the tetrachloroethane stream, introduction of ferric chloride into the 460°C vapor-phase reaction zone improves the yield of trichloroethylene product. 

In 1885, Charles Martin Hall invented his aluminum process and Hamilton Young Castner in 1890 developed the mercury-type alkali-chlorine cell, which produced caustic (sodium hydroxide) in its purest form. Edward G. Acheson in 1891, while attempting to make diamonds in an electric furnace, produced silicon carbide, the first synthetic abrasive, second to diamond in hardness. Four years later, Jacobs melted aluminum oxide to make a superior emeiy cloth. Within two decades, these two abrasives had displaced most natural cutting materials, including naturally occurring mixtures of aluminum and iron oxides. 

Ethylene dichloride from this step is comhined with that produced from the chlorination of ethylene and introduced to the pyrolysis furnace. 

Figure 7-5. The European Vinyls Corporation process for producing vinyl chlo-rlde " (1) chlorination section, (2) oxychlorination reactor, (3) steam stripping and caustic treatment of water effluent, (4) EDC distillation, (5) pyrolysis furnace, (6,7,8) VCM and EDC separation, (10) by-product reactor.

Fig. 7.12 Influence of coal chlorine content on the furnace wall corrosion rates of mild steel tubes in low-pressure coal-fired power plant (Lees, C.E.G.B., private communication)...

On top of this, PVC is by no means the only chlorine source. Other raw materials and (particularly for blast furnaces close to the sea) even the air used in incineration processes may have significant contributions to the chlorine throughput too. 

The permit allows Stahlwerke Bremen to use 500 tonne MPW per day with a chlorine content of up to 1.5% (= ca. 3% PVC) on a daily average. This level seems to be a balance between the need to allow for a reasonable PVC tolerance in MPW (lower values are rare in MPW), and the desire of Bremen Stahlwerke to use a material that is as free of impurities as possible. After all, chlorine has no added value in the process, and may only contribute to problems like corrosion in the blast furnace, etc. In sum, the 1.5% level seems to be a balance between commercial reality and a technical ideal. 

Silicon, like carbon, is relatively inactive at ordinary temperatures. But, when heated, it reacts vigorously with the halogens (fluorine, chlorine, bromine, cmd iodine) to form halides and with certain metals to form silicides. It is unaffected by all acids except hydrofluoric. At red heat, silicon is attacked by water vapor or by oxygen, forming a surface layer of silicon dioxide. When silicon and carbon are combined at electric furnace temperatures of 2,000 to 2,600 °C (3,600 to 4700 °F), they form silicon carbide (Carborundum = SiC), which is an Importeint abrasive. When reacted with hydrogen, silicon forms a series of hydrides, the silanes. Silicon also forms a series of organic silicon compounds called silicones, when reacted with various organic compounds. 

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