A. Nusret Bulutcu

Effect of surface charge distribution on the crystal growth of sodium perborate tetrahydrate

Growth and dissolution rates of sodium perborate crystals have been measured in a flow-type single-crystal cell. Sodium perborate grows dendritically at any level of supersaturation and shows growth and dissolution rate dispersion. Both the growth and dissolution rates of sodium perborate were found to be controlled by surface charge distribution which is represented by applied voltages in an electrostatic separator. It was determined that high surface charge dominates the crystal growth rate when compared with low surface charge under identical conditions. The results obtained showed that the formation of dendritic structure is not a function of supersaturation but a function of surface charge. The rate of dissolution of a crystal with a high surface charge is greater than that with a low surface charge.

Application of genetic algorithm for determination of mass transfer coefficients

Abstract The mass transfer coefficient, k d , surface reaction constant, k r , and reaction rate order, r , have been calculated by applying the genetic algorithm analysis. This analysis provides the parameter estimations as new data are recorded and consequently yields the time variability of the parameters. In this study, the application of the genetic algorithm procedure is presented for determining the coefficients and their relative standard deviation. The relative standard deviation does not exceed 0.9% taking into account the crystal growth rate, R g calculated from the equation R g =k r (Δ C−R g /k d ) r and the one experimentally obtained and represented by the equation R g =k g (Δ C) g , where k r is the rate constant for the surface reaction, k d is the mass transfer coefficient, r is the reaction order, k g is the overall crystal growth rate constant, Δ C is the supersaturation and g is the overall crystal growth rate order. This new proposed method is compared with the previous methods for the cases of growth of NiSO 4 and CuSO 4 ·5H 2 O crystals in a fluidized bed crystallizer.

Determination of growth and dissolution mass rate of boric acid crystals by a simple computer program

Growth and dissolution rates of boric acid were measured in a laboratory-scale fluidized-bed crystallizer under well-established conditions of supersaturation, undersaturation, temperature and fluidization. It was found that the overall growth rate of boric acid is controlled by both diffusion and reaction steps. But reaction step is the main controller of the crystal growth of boric acid. It was also determined that the dissolution region of boric acid, apart from other known materials is controlled by diffusion and reaction steps. An improved computer program procedure was used to determine the effect of diffusion and reaction steps on the growth and dissolution rates of boric acid crystals. This simple program gives a high accuracy of determination of the mass transfer coefficient, kd, the surface reaction constant, kr and the surface reaction order r. The relative standard deviation between the equation RG=kr(ΔC−RG/kd)r and those experimentally obtained and represented by the equation RG=KG(ΔC)g do not exceed 0.08% for both growth and dissolution region.

Production of high bulk density anhydrous borax in fluidized bed granulator

Abstract Production of anhydrous borax from borax pentahydrate was investigated in a fluidized bed calcinator. Single step calcination gives a puffed product with very low density. In order to obtain high bulk density product dehydration should be carried out at least in two stages. The most important step dominating the final bulk density is the first step. Dehydration of borax pentahydrate up to around 80% Na2B4O7 content at temperatures lower than 393 K in the first step gives high bulk density anhydrous borax at the final stage. After this critical point, thermal shock imposed on the particle has only slight effect on the final bulk density value and anhydrous borax with a bulk density higher than 0.6 g cm−3 may easily be obtained at temperatures less than 800 K.