Haiyan Qu

In this work, the solubility of a non-steroidal anti-inflammatory drug (NSAID), piroxicam, is investigated. The polymorphic form II, which is the most stable form at room temperature, was investigated in seven different solvents with various polarities. It has been found that the solubility of piroxicam in the solvents is in the following order: chloroform > dichloromethane > acetone > ethyl acetate > acetonitrile > acetic acid > methanol > hexane. Crystallization of piroxicam from different solvents has been performed with evaporative crystallization and cooling crystallization; the effects of solvent evaporation rate and solute concentration have also been studied. Both form I and form II could be produced in cooling and evaporative crystallization, and no simple link can be identified between the operating parameters and the polymorphic outcome. Results obtained in the present work showed the stochastic nature of the nucleation of different polymorphs as well as the complexity of the crystallization of a polymorphic system.

A novel process consisting of ozonation and crystallization for the recovery of calcium phosphates with improved purity from digester supernatant was tested in a 2.5 L ozonation column and 1 L stirred tank crystallization reactor. The kinetics of natural organic matter (NOM) degradation has been studied and the optimal dose of ozone was determined to be 1.25 mg O₃ per mg of total organic carbon (TOC). Ozonation at pH 2.8 was the most effective in terms of P-recovery rate (86.4%) and product crystallinity improvement, due to the simultaneous stripping of CO₂. Ozonation at pH 8.1 did not have a significant effect on the P-recovery rate but resulted in the best improvement of product purity. A significant effect of NOM partial degradation on product purity and visual characteristics has been proven. With less than 15% of TOC reduction during the ozonation, the organic carbon content in final solid products decreased by approx. 50%. Thereafter, the process was preliminary scaled up to a 10 L set-up with a fluidized bed reactor. For the large set-up, the optimal dose of ozone was 2.2 mg O₃ per mg TOC. During crystallization in the fluidized bed reactor, the dosing of chemicals through the center of the reactor resulted in better control over nucleation and delayed flocculation of the NOM present in the supernatant. It leads to an increase of the P-recovery rate (73–75%) compared to the dosing from the bottom of the reactor (61–67%). In all experiments, low crystallinity hydroxyapatite (HAp)/amorphous calcium phosphate (ACP) were obtained.

Cephradine monohydrate (CPH) crystallizes with a needle‐like shape which leads to severe agglomeration and slow filtration. Effects of different operating conditions on the particle size and shape as well as the filterability of the crystal products are described. The solubility and stability of one anhydrate of cephradine (CPA1) and CPH as a function of temperature and water activity was investigated in different methanol and water mixtures. A solvent‐mediated transformation from CPH to CPA1 was observed at water mole fractions below 0.2–0.35 depending on the temperature. The crystallization behavior of CPH was studied by linear cooling and antisolvent crystallization. Lowering the cooling rate and addition of seeds led to an increase in particle size and improvement of filterability.