CSD and the kinetic parameters of crystallization of K2SO4
Advancing the chemical engineering fundamentals
Crystallization (T2-9P)
Keywords: batch crystallization, CSD, crystallization kinetic, potassium sulphate
A study of a cooling crystallization of a potassium sulphate water solution in a batch reactor is described in this paper. The effect of hydrodynamics conditions on the crystallization process was investigated by using different type of impellers. Two types of impellers were investigated; the four-pitched blade impeller which generates axial flow and the six blades Rusthon turbine which generates radial flow. The experiments were performed at mixing rate of 700 rpm, in order to ensure well mixing conditions in the reactor and at four different linear cooling rates in the range from 8-20 °C/h for both types of impeller. Crystal size distributions were determined and approximated with log – normal function for all experiments. The shape of crystals was studied from photographs obtained on light microscope Olympus BX50.
Influence of the cooling rates to the metastable zone width was investigated. The experimental data shows that higher cooling rate expands the metastable zone for all types of impeller and influences the crystal size distribution. At low cooling rates, supersaturation was kept at constant value for a long period. It results improved conditions for mass transfer and crystals would grow. Bigger crystals were obtained at lower cooling rates.
Also, it is stated that radial flow (Rusthon turbine) is particularly inappropriate for nucleation process, and for crystallization. Nucleation started at lower temperature and higher supersaturation. This conditions result with high nucleation’s rate and large number of nucleation centre. Crystal size distributions are shift to the smaller size. Also, the obtained crystals were settling on the wall of the reactor, baffles and stirrer. The great part of obtained crystals was agglomerated.
Nucleation order, n and constant of nucleation, kn were determinate for different cooling rates. Relation between the rate of concentration drop in a solution and supersaturation has been approximated with a power low equation, where K is a growth rate constant and g is reaction order.
Presented Wednesday 19, 13:30 to 15:00, in session Crystallization (T2-9P).
