Abstract:
In common industrial process, mass transfer control (mixed control) or dissolution control can be invlved for designing process equipment or determining the mechanisms of chemical reactions. A jet-impingement apparatus has been used to study dissolution rates by directing a jet of water onto a pellet of the material of interest at high velocity to ensure that dissolution is controlling. The apparatus has been used to measure the dissolution rate constant of magnetite under the conditions of power system coolants - often a controlling parameter in steel corrosion. For unequivocal measurement of the dissolution rate constant, the mass transfer characteristics of the apparatus need to be known in order to extrapolate mass transfer coefficients to the conditions of interest. Accordingly, mass transfer in our impingement system is being studied at atmospheric pressure with materials of a moderate dissolution rate. Cast pellets of plaster of Paris of different purities and single crystals of the same compound (gypsum-CaSO4 2H2O), and pellets of trans-cinnamic acid, potassium bitartrate and aspartic acid have been used in this study. The dissolution rate constants for single crystal and aspartic acid were determined and the commercial plaster result gave mass-transfer correlation of jet-impinging apparatus in reasonable agreement with published correlation. However, the commercial plaster tended to have a higher solubility tham pure plaster or gypsum crystals; its dissolution rates were higher than those of the other materials studied, which were in the same range.
