subscripts a = ambient f = moving front jl f2 f; = i-th moving front fj h = hydrocarbon i j 1 = liquid m = moving front no. 1 = moving front no. 2 = moving front closest to X = 0 = region i or i-th isotherm = regionj or in the region closest to X = 0 = isotherm closest to X = 1 0 = initial temperature S = at complete solidification u: = water Superscripts n = n-th time step
Baker, C. G. J.; Bergougnou, M. A. Can. J . Chem. Eng. 1972, 50, 695. Kim, S. D.; Baker, C. 0. J.; Bergougnou, M. A. Can. J. Chem. Eng. 1975, 53, 134. KO&, K.; MarWka, S.; Ueyama, K.; Matsurra, A.; Yamashlta. F.; Iwamoto, S.; Kato, Y.; Inoue. H.; Shloeta. M.; Suzuki, S.: Akehata, T. J . Chem.The effect of pH on the removal of pyritic sulfur in airlwater chemical coal cleaning was investigated. The pH was varied by adding sulfuric acid or sodium carbonate to a coal-water slurry. The effect of nearby neutral pH (-7) was determined in a buffer solution of sodium dihydrogen phosphate and disodium hydrogen phosphate. Data were taken in the temperature range of 130 to 190 OC, oxygen partial pressure of 0.32 to 1.36 MPa, and reaction times up to 3600 s. The rate of pyrite oxidation was found to be minimum at the nearby neutral conditions. Under otherwise identical conditions, the rate of pyrite oxidation was greater in basic pH than in acidic pH. The enhancement in the rate of pyrite oxidation is explained on the basis of electrochemil reactions. Under nearly neutral conditions, the overall reaction is shown to be controlled by the surface reaction, whereas under acidic as well as basic conditions, diffusion of oxygen through the product ash layer as well as the surface chemical reaction seems to be important.
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