A study of the mechanisms of the salt catalyzed carbochlorination of kaolin
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INTRODUCTION
RESEARCH has been conducted by the Bureau of Mines on using domestic kaolin as an alternative to imported bauxite as a source of aluminum. In addition to Bureau work on the production of reduction-grade alumina, studies of the direct carbochlorination of kaolin to produce a feed for the energy efficient Alcoa smelting process L,2showed important effects on the rate, selectivity, and extent of reaction related to calcining and reaction temperatures, type of reductant used, addition of NaCI catalyst, and contact with SiCI4. The complexity of the carbochlorination of domestic kaolin has prevented its immediate use for the production of anhydrous A1C13. The object of the present research is not to develop a process, but to continue to investigate the nature of the carbochlorination reaction and to provide information for a conceptual design. The work reported here is divided into four parts that affect the rate, selectivity, and extent of the reaction: reductant, catalysts, SiCI4, and sample size and configuration.
in 0.1 g. This apparatus is shown in Figure 1. Successful operation of the system was maintained by preventing condensation of the reaction products before they were exhausted at the bottom of the reactor. All samples were calcined [
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E X P E R I M E N T A L PROCEDURES
ARNE LANDSBERG, Chemical Engineer, and R.D. WILSON, Chemist, are with Albany Research Center, United States Bureau of Mines, Albany, OR 97321. Manuscript submitted April 5, 1984.
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protection tube ,..,.~ Experimental data were obtained by weighing samples continuously during chlorination. In the case of small samples (up to 2 g), a bucket or basket holding the sample was suspended by a quartz fiber from a recording balance. In this apparatus, described in a previous paper ] but not shown here, the sample and holder were enclosed within a vertical 25-ram-diameter quartz tube. Inert gas was passed into an enclosure around the balance and downward over the sample. Chlorine was added at the top of the vertical tube just above a tube furnace that maintained the gases and sample at the desired temperature, A therrnocouple protected in a 6-ram-diameter quartz tube projected upward from the bottom of the reaction tube to within a few millimeters of the sample. Optimum reaction temperatures based on reaction rate were determined for each reductant used. Exhaust gases passed through a lower side arm of the reaction tube and through a bubbler containing sulfuric acid before being admitted to an exhaust hood. Volatile reaction products condensed in a cooler glass wool plug in the bottom of the reaction tube. For samples consisting of a bed of pellets, the weight of the reactor and its contents was recorded continuously with-
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