Kinetic identification and experimental validation of continuous plug flow crystallisation

Recent Advance of Melt Crystallization, Towards Process Intensification and Techniques Development

Melt crystallization has been considered as a green separation technique and widely applied in industry and manufacture due to several attractive features, including no need for solvent, achieving specific product...

Effect of Process Conditions on Particle Size and Shape in Continuous Antisolvent Crystallisation of Lovastatin

Lovastatin crystals often exhibit an undesirable needle-like morphology. Several studies have shown how a needle-like morphology can be modified in antisolvent crystallisation with the use of additives, but there is much less experimental work demonstrating crystal shape modification without the use of additives. In this study, a series of unseeded continuous antisolvent crystallisation experiments were conducted with the process conditions of supersaturation, total flow rate, and ultrasound level being varied to determine their effects on crystal size and shape. This experimental work involved identifying acetone/water as the most suitable solvent/antisolvent system, assessing lovastatin nucleation behaviour by means of induction time measurements, and then designing and implementing the continuous antisolvent crystallisation experiments. It was found that in order to produce the smallest and least needle-like particles, the maximum total flow rate and supersaturation had to be combined with the application of ultrasound. These results should aid development of pharmaceutical manufacturing processes where the ability to control particle size and shape would allow for optimisation of crystal isolation and more efficient downstream processing.

Structure of 2-chloro-N-(p-tol-yl)propanamide

Two independent samples of the title compound, alternatively 2-chloro-N-(4-methylphenyl)prop-an-amide, C10H12ClNO, 1, were studied using Cu Kα, 1a, and Mo Kα, 1b, radiation as part of a continuous crystallization study. The mol-ecule crystallizes with disorder in the Cl/terminal methyl positions [occupancies for the major disorder component of 0.783 (2) in 1a and and 0.768 (2) in 1b] and exhibits N-C bond lengths of 1.3448 (19), 1.344 (2) Å, C=O bond lengths of 1.2233 (18) and 1.2245 (19) Å and an acetamide moiety C-N-C-C torsion angle of 179.00 (13), 178.97 (14) ° for 1a and 1b, respectively. In the crystal, chains along the a axis are formed via N-H⋯O hydrogen bonds between acetamide groups, as well as C-H⋯O inter-actions. These chains arrange themselves into parallel running stacks which display weak C-Cl⋯O=C halogen bonding as well as weak C-H⋯π inter-actions.

Reducing the Induction Time Using Ultrasound and High-Shear Mixing in a Continuous Crystallization Process

Continuous crystallization in tubular crystallizers is of particular interest to the pharmaceutical industry to accurately control average particle size, particle size distribution, and (polymorphic) shape. However, these types of crystallizers require fast nucleation, and thus, short induction times at the beginning of the flow process, which is challenging for larger and complex organic molecules. High shear and/or the presence of bubbles were identified to influence the nucleation behavior. This work investigates the effects of both high-shear mixing and ultrasound on the anti-solvent crystallization of paracetamol in acetone–water. Both devices generate intense amounts of shear and gas bubbles. Generally, the results show that increasing input power decreases the induction time significantly for both the rotor–stator mixer and ultrasound probe. However, the induction time is almost independent of the supersaturation for the ultrasound probe, while the induction time significantly increases with decreasing supersaturation for the rotor–stator mixer. In contrast, the particle size distribution for the rotor–stator mixer is independent of the supersaturation, while increasing supersaturation decreases the particle size for the ultrasound probe.

Determination of Supercooling Degree, Nucleation and Growth Rates, and Particle Size for Ice Slurry Crystallization in Vacuum

Understanding the crystallization behavior of ice slurry under vacuum condition is important to the wide application of the vacuum method. In this study, we first measured the supercooling degree of the initiation of ice slurry formation under different stirring rates, cooling rates and ethylene glycol concentrations. Results indicate that the supercooling crystallization pressure difference increases with increasing cooling rate, while it decreases with increasing ethylene glycol concentration. The stirring rate has little influence on supercooling crystallization pressure difference. Second, the crystallization kinetics of ice crystals was conducted through batch cooling crystallization experiments based on the population balance equation. The equations of nucleation rate and growth rate were established in terms of power law kinetic expressions. Meanwhile, the influences of suspension density, stirring rate and supercooling degree on the process of nucleation and growth were studied. Third, the morphology of ice crystals in ice slurry was obtained using a microscopic observation system. It is found that the effect of stirring rate on ice crystal size is very small and the addition of ethylene glycoleffectively inhibits the growth of ice crystals. The results in this paper can provide theoretical guidance and technical support for the development of vacuum icemakers.