Preconditioning of a virginiamycin solution for crystallization

Crystallization of antibiotics and other biologically active substances from water solutions represents an important stage of their biotechnological production. The process is based on a sharp reduction of a target compound solubility caused by either temperature decrease, or supersaturation of a solution. A preconditioning of a solution, i.e., its evaporation with a simultaneous temperature decrease seems to be an optimal technical solution, especially advantageous for the treatment of thermolabile substances. This paper describes the technology and equipment for the pre-crystallization treatment of solutions of various substances produced by the biotechnological and chemical industries. The proposed preconditioning technology includes ultrasonic dispersion of a solution and formation of an aerosol with a large integral evaporation surface followed by condensation. Comparing to common tubular evaporators used in various industrial processes, this technology provides about equal productivity and, at the same time, lower energy consumption, since it does not require the heating and the further cooling of a solution needed to evaporate and condensate the solvent, respectively, that prevents undesirable effect of high temperature on thermolabile compounds. In addition, the technology prevents the damage of thermolabile compounds, improves the efficiency of the further crystallization process due to the ultrasound-stimulated formation of crystallizing nuclei, and provides a solvent distillate suitable for the further re-use. The designed device for preconditioning has been successfully tested using culture broth of Streptomyces sp. containing a feed antibiotic virginiamycin; such treatment with the further crystallization in standard crystallizers has resulted in the efficient formation of equal-sized antibiotic crystals.