CAKING OF KCL-NACL POWDER AND ITS PREVENTION BY AMINO-ACIDS

Prevention of the caking of KCl-NaCl powder produced by a spray-dryer was investigated. The spray-dried powders of both a simple KCl-NaCl mixture and a mixture of KCl and NaCl with an amino acid that was less soluble than KCl and NaCl and that had hydrophobic functional groups were obtained in the form of particles that were hollow spheres. When stored in high humidity, the first powder soon caked, but the second did not. This difference could be explained by the solubility and polarity of the amino acid added. When the solubility of the amino acid added was higher than that of KCl or NaCl, the surface of the spray-dried particles was crystalline and porous. When the amino acid had hydrophobic functional groups and its solubility was lower than that of KCl or NaCl, the surface of the spray-dried powder was smooth and not porous; this result suggests that the surface of the spray-dried particles was covered with amino acid molecules. We concluded that the solubility and the functional groups of the amino acids that were added to a KCl-NaCl mixture could be used to control caking of the spray-dried powder.