Entrained-flow chlorination of titaniferous slag to produce titanium tetrachloride
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RODUCTION
PREFERRED commercial processes for producing titanium metal and titanium dioxide use titanium tetrachloride as an intermediate. Although fluid-bed technology is used to produce titanium tetrachloride, there are strict feedstock requirements that limit the use of fluid-bed processing. Titanium ore feedstocks must fall within a narrow particle size range. Smaller particles will be elutriated from the fluid bed before sufficient residence time for reaction. Larger particles are difficult to fluidize. Fluid-bed feedstocks should contain very low amounts of alkaline earth metals. Especially calcium oxide, and to a lesser extent magnesium oxide, chlorinate to form low vapor pressure, liquid metal chlorides that tend to build up in the fluid bed. This can lead to defluidization, localized overheating, and fusion of the bed. Fluid-bed feedstocks should also contain low levels of chlorinationinert components such as silica, which tends to accumulate in the bed. The purpose of this study is to investigate a chlorination process for producing titanium tetrachloride that would overcome feedstock limitations of the fluid bed. There is very little to be found in the literature regarding the production of titanium tetrachloride by an entrained-flow chlorination process. There are several patents,[1–4] however, that describe such a process. Also, an entrained-flow chlorination process using very different chemistry has been reported.[5] II. EXPERIMENTAL A. Definitions “SF Slag/Cl2” is the stoichiometric factor for the slag/Cl2 ratio during a run. A value of 1.0 means that the ratio is stoichiometric; that is, if chlorination of slag is complete, there would be no free Cl2 remaining. A value of 1.20 means that there is a 20 pct excess of slag over that required to react with all of the Cl2. JAMES P. BONSACK, formerly Senior Scientist, Millennium Inorganic Chemicals, Research Center-Baltimore, is retired. FRED E. SCHNEIDER, Technologist, is with Millennium Inorganic Chemicals, Research CenterBaltimore, Glen Burnie, MD 21060. Manuscript submitted November 2, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
“SF C/Slag” is the stoichiometric factor for the C/Slag ratio in feedstocks. A value of 1.0 means that if chlorination of slag is complete, there would be no carbon remaining. A value of 1.20 means that if all of the slag is chlorinated, there will be a 20 % excess of carbon remaining. Since the CO2/CO ratio varied from run to run, the SF C/Slag value was calculated after each run. Gas/vapor retention times are based on a chlorination zone 7 cm in diameter and 91 cm in height, or 3500 cm3 in volume. Gas/vapor flow rates through the reactor were corrected for temperature and the change in the number of moles of gas/ vapor due to reaction. The average flow rate was used: [(cm3 /s)in ⫹ (cm3 /s)out]/2 The calculated gas retention time is estimated to be accurate within ⫾10 pct, due mainly to the variation in CO2/CO ratio and inaccuracies in gas flow meters. “% Cl2 Reacting” was calculated from the Cl2/N2 mole ratio fed to the
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