engleski

The Influence of the Seed Preparation on Granulometric Characteristic and Polymorphism at Glycine Crystallization

Influence of the seeding process on the granulometric characteristics and polymorphism of crystals during batch cooling crystallization was examined. Crystals which were used as seed in the experiments were obtained from different crystallization methods what finally caused different characteristics of obtained crystals. The analyzed material was glycine, which is the simplest amino acid and is found in many proteins and enzymes. It is used in food, pharmaceutical and cosmetic industries. There are three known polymorphic structures of glycine: α, β and γ - glycine. Different additives (1.8 g C2H2O4/100ml, 4.8 g C2H5OH/100ml and 7 g NaCl/100 ml of water) were used in the batch cooling crystallization. Additives present in a growth medium lead almost always to a change in the solubility of the solute. A natural consequence of the change in the solubility of the compounds is that the concentration of ions/molecules of the solute present in the medium and the solute–fluid interfacial energy are altered. All these lead to changes in the metastable zone width and influence the nucleation process and the crystal growth. Therefore, the crystals obtained by adding different additives had different polymorphic forms. XRD analysis confirmed occurrences of γ glycine obtained by adding sodium chloride or oxalic acid, while α polymorphs were achieved by adding ethanol. Obtained crystals were grinded 8 minutes in the planetary ball mill. The seed in one experiment was original salt of glycine ( structure). Distribution of the seed size was 180 – 355 m. Although all experiments were carried out at the same process condition, the obtained kinetic curves and granulometric characteristics of crystals depended on the seed quality. Higher level of supersaturation and wider multimodal crystal size distribution were obtained by using seed from crystallizations with additions of oxalic acid and sodium - chlorides. The original glycine seed yields a regular and narrow crystal size distribution. Crystal habit did not change much after grinding in planetary ball mill. But after seeded crystallization, the change was significant. DSC analysis was confirmed that addition of seeds prepared in a different ways did not affect the formation of different polymorphs.

batch seeded crystallization; glycine; granulometric characteristic of crystal

nije evidentirano