Kinetics of coal fly ash chlorination by phosgene
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The kinetics of the reaction between phosgene and a fly ash composed of 97 weight percent alumina and silica has been studied over a temperature range of 450 to 800(DEGREES)C and a phosgene partial pressure range of 0.02 to 0.9 atm. A microbalance was used in obtaining initial conversion rate and extended conversion-time data, and B.E.T. surface areas and specific phosgene chemisorption weights as functions of conversion. Intrinsic kinetic parameters and a constant alumina to silica molar reaction ratio were determined over a fly ash conversion range of 0 to 0.375. The reaction is first order with respect to phosgene partial pressure. The shrinking-core model was successfully applied to predict fly ash conversion versus time data for the full phosgene partial pressure range and for temperatures up to 600(DEGREES)C. An activation energy of 40.8 kcal/g-M and a frequency factor of 4.7EO7 cm/min were used in the model;The results of the kinetic study were utilized in the preliminary design of a fly ash chlorination reactor. It is predicted that four reactors with beds 3 m in diameter and 2.36 m tall could process the 27 2,000 metric tons of fly ash collected annually by a 1000 megawatt power station. Spherical pellets with a diameter of 0.25 cm would be reacted at 700(DEGREES)C to recover 67 percent of the alumina and 13 percent of the silica.