The vapor-liquid equilibria of the aluminum chloride-titanium tetrachloride system
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Communications The Vapor-Liquid Equilibria of the Aluminum Chloride-Titanium Tetrachloride System
The potential use of A1C13 for energy efficient reduction to the metal requires a very pure chloride feed material. Direct chlorination of any aluminum-containing mineral would produce some unwanted chloride byproducts as well as the desired A1C13. The Bureau of Mines has reported the vapor-liquid equilibria of the A1C13-FeC13 system,1 showing the possibility of removing the troublesome chlorination byproduct, FeC13, from A1C13 by distillation. Titanium, too, can be a problem when it exists in aluminum resource materials and is chlorinated along with the aluminum fraction. As shown recently, 2 the separation of TiCL from A1C13 is not as simple as one would expect from examination of the respective vapor pressures. For example, at 20, 100, and 140 ~ the ratios of the vapor pressures of TIC14 to that of A12C16 (the dimer of A1C13 and the predominant vapor constituent at lower temperatures) are approximately 250,000, 220, and 20, respectively. At about 207 ~ the two chlorides have the same vapor pressure, approximately 5.32 bar (4000 torr), and above this point the vapor pressure of TiCI4 is lower than that of A1C13. To complicate further the equilibria of this system, A1C13 melts at 192 ~ a temperature at which its vapor pressure is 2.66 bar (2000 torr), while TIC14 melts at - 3 0 ~ and boils at 136 ~ Finally, A1C13 has a solubility in TiCI4 which varies substantially with temperature. Notwithstanding these complexities, vapor-liquid equilibria have been determined. The apparatus and methods have been described I in conjunction with the A1C13-FeC13 system. Slight differences were found in working with TiCI4, the major one being a significant loss of the more volatile TiCI4 during preparation of the samples. This made it more difficult to prepare exactly desired compositions. Table I gives the analyses of aluminum and titanium in acidified solutions of the condensed phases as calculated A1C13 weight percentages. The data are plotted in Figure 1 as vapor composition against liquid composition, and in Figure 2 as the equilibrium boiler temperature against weight percentages of A1C13 in the vapor and liquid phases. It must be noted that the data were not obtained at constant pressure, as is the usual practice in developing vapor-liquid equilibria. Because the apparatus was sealed upon filling with the hygroscopic chlorides and during equilibration, it was not possible to monitor pressure. Instead, boiler temperatures were set somewhat above the melting point of the A1C13-TiCI4 mixture in each test. The curves drawn in each figure should not be taken as true equilibria at one constant pressure but as close approximations that are subject to correction for pressure, and hence temperature. H.C. KO, Research Chemist, and A. LANDSBERG, Chemical Engineer, are with United States Bureau of Mines, Albany Research Center, Albany, OR 97321. Manuscript submitted March 25, 1986. METALLURGICALTRANSACTIONS B
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