United States Patent Us4046556 Direct Gaseous Reduction Of Oxidic Metal Ores With Dual Temperature Cooling The Reduced Product

Author : Chin Sang Rhee
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (15 download)

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Download or read book Kinetics of Formation of Iron Pentacarbonyl from Partially Reduced Iron Oxide written by Chin Sang Rhee and published by . This book was released on 1969 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The kinetics of the formation of iron pentacarbonyl from iron¬ ore flotation tailings have been studied. About 300 grams of solid material was charged into a vertical reactor of 2.5-inch pipe size and reduced with carbon monoxide, usually for two hours, in the following range of operating conditions: pressures from Oto 50 psig., temperatures from 1100 to 1400oF, and gas velocities from 2.4 to 18.8 ft./min. When the reactor was air-cooled to the desired temperature after reduction, the reaction of carbonyl formation was started and maintained usually for two hours. The operating conditions were varied in the range of pressures from 100 to 300 psig., temperatures from 200 to 350°F, and carbon monoxide velocities from 0.27 to 1.02 ft./min. The exhaust gas from the reactor was analyzed by means of chromatography. The formation of iron pentacarbonyl appears to involve three sequential steps; adsorption of carbon monoxide on the iron sites, surface reaction of iron atoms with adsorbed and non-adsorbed carbon monoxide molecules, and desorption of iron pentacarbonyl. The rate of the overall reaction is slow and is controlled by the rate of surface reaction. The experimental data of carbonyl concentration at the bed exit were predicted within 22 percent standard deviation for most runs by the following rate equation: where k and b are the reaction rate constant and the deactivation constant, respectively, and Sis the fractional conversion of free iron to iron pentacarbonyl. The forward reaction term (CCo) usually dominates the concentration dependence of the reaction rate. The magnitude of the overall activation energy depends on the reduction conditions and the type of solid material o For one type of flotation tailings under reduc1·ion conditions of 30 psig o and 1200°F the overall activation energy was 6.03 Kcal./gmol. below 2500F and 1.42 Kcal./gmol. above 2500F. For the other kind of flotation tailings under the same reduction conditions the activation energy was 15. 9 Kcal. /gmol. below 250°F and 6 .ti.o Kcal. /gmol. above 250°F. The deactivation term appears to exist for two reasons. One is increasing difficulty in the interaction between the adsorbed carbon monoxide molecules and the iron atoms as more iron is removed from discrete points of the surface due to the formation of iron pentacarbonyl. The other reason is the occupation of iron sites by other materials such as deposited carbon, produced carbonyl, and traces of impurities in the reactant gas o The magnitude of deactivation constant is much affected by pressure and temperature and also different for different solid materials but is always less than l.5xl0-4 sec. -1 over the operating conditions investigated. In the formation of iron pentacarbonyl, the reactivity of the solid surface was found to be very important. The reduction temperature and pressure much affect the reactivity of reduced iron. The lower the reduction temperature and pressure, the more reactive is the reduced iron. Too low a reduction temperature, however, is not desirable be¬ cause of extensive iron carbide formation. For the two flotation tailings studied the optimum reduction condition is 0-10 psig. and 1200-1300°F. For the pr4ctical application of the pneumatolytic transport of metallic iron, hydrogen reduction and the mixing of a small amount of ammonia with the reactant gas in carbonyl formation are recommended.