Investigation of the Effects of L-Proline and L-Asparagine Amino Acids on the Growth and Dissolution Rate of Diammonium Hydrogen Phosphate in Fluidized Bed Crystallizer

The growth and dissolution rates of diammonium hydrogen phosphate crystals were investigated in a fluidized bed crystallizer. The experiments were carried out in pure media and in the presence of the amino acids at the different concentration levels. L-proline and L-asparagine amino acids were used as additives. The growth rate was evaluated according to supersaturation levels. The results show that the growth rates of diammonium hydrogen phosphate crystals in the presence of L-proline and L-asparagine are slightly suppressed compared to the pure medium, while dissolution rates are significantly reduced. Damk？hler numbers and efficiency factors are calculated by using the growth rate data in order to evaluate the relative effectiveness of diffusion and integration resistances on crystal growth. According to the efficiency factor results, it is revealed that both diffusion and integration steps contributed to the growth controlling mechanism of diammonium hydrogen phosphate crystals in pure media and in the presence of amino acids. But, it is determined that efficiency of integration step is slightly higher than efficiency of diffusion step in the pure media. However, it is found that efficiency of the diffusion step in the presence of amino acids slightly increase in comparison with the pure media. This effect is observed prominently in the highest concentration of L-proline amino acid. In addition, it is seen from images taken in the optical microscope that the morphology of diammonium hydrogen phosphate crystals growing in the presence of amino acids significantly change