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• A new method for transforming from a CLD to a PSD is proposed. • Image processing algorithms were used to construct the transformation method. • Crystallization kinetic parameters of L-carnitine acid were estimated and validated. • The accuracy of transforming CLD to PSD was verified by experiment. Crystallization kinetics and thermodynamics are fundamental in the development of crystallization processes. This work systematically measured the kinetic parameters during cooling crystallization in pure and mixed solvent systems of L-carnitine (LC) by the using of process analysis technologies (PATs). Chord length distribution (CLD) of crystals in the system was collected using Focused Beam Reflectance Measurement (FBRM) and was converted to crystal size distribution (CSD). A fast and simple converting method was established by combining the FBRM's working principle and image recognition techniques, considering both crystal orientation and non-spherical morphology. Further, the kinetic parameters were evaluated using an optimizing objective function merging changes in solution concentration and CSD. It reveals that LC crystal growth more likely follows size-independent growth mechanism. The accuracy of the kinetic parameter estimation was verified by comparing the experimental results to that obtained via process simulation using the estimated kinetic parameters under the same operating conditions. [ABSTRACT FROM AUTHOR]

Abstract Background Crystallization is used as a purification process in majority of the industries such as pharmaceuticals, food products, chemicals, catalysts, and cosmetics. Crystallization of active pharmaceutical ingredients is carried out to increase the dissolution rate and attain sufficient bioavailability in pharmaceutical industries. It can also enhance the flow properties and drug dosage control of the active pharmaceutical ingredients. Single crystals give us a lucid understanding of the intrinsic properties of a material. A material made up of many crystals will have grain boundaries which do not allow us to measure properties such as thermal and electrical resistance effectively. Single crystals will not have defects or impurities in them. Thus, help us in making comparisons with other materials and contribute to a better understanding of particular behaviors. Therefore, it is important to investigate the growth of single crystals. Sulphanilamide is a sulpha class drug used as an intermediate and starting material for the production of various drugs. It is an antibacterial agent and is often used in pharmaceutics and cosmetics. In this study, we wanted to obtain sulphanilamide crystals by two different crystallization methods and compare the results gathered. Sulphanilamide usually crystallizes in the form of needles, thus is ideal for the purpose of this study. In this work, crystallization of sulphanilamide was carried out by cooling method and solvent evaporation method. In Cooling method as temperature was brought down the crystals separated out. On the other hand, in solvent evaporation method, the solvent evaporated leaving behind the crystals. The process parameters that varied included stirring rate of the solution at a constant temperature, concentration of the solute in a constant volume of solvent, solvent systems chosen-acetone, methanol and ethanol, and time allowed for crystallization. Results Crystals were obtained under the varying conditions. Characterization of the crystals formed was carried out using X-ray diffraction method, scanning electron microscopy, and differential scanning calorimetry. The size and morphology of the crystals formed was observed and the results were compared. It was found that the crystals obtained from using methanol as solvent, with high concentration of solute, gave the most uniform and large-sized cubic crystals under solvent evaporation method. The surface of the crystal was also seen to be smooth with well-defined edges as shown in the SEM images. Stirring reduced the size of crystals formed, and longer time of crystal formation resulted in larger crystals. Solvent evaporation method gave more uniform crystals compared to cooling method. Conclusion This study gives us an understanding of how each parameter affects crystal growth. Thus, optimum conditions for crystal growth can be determined.

Spherical crystallization can be an important technological step in the production of a solid form active agent. By the production of spherical crystals, direct compression tablet making can be applied to the powder material. This method makes the tableting process quicker, shorter and more economical with reduced amounts of additives and a reduced number of technological steps. This way, the granulation method can be avoided, which is also advantageous for a moisture sensitive drug. In this paper, we presented Focused Beam Reflectance Measurement (FBRM) studies applied in the case of the non-typical spherical crystallization methods of the active pharmaceutical ingredient ambroxol hydrochloride. Spherical agglomeration and controlled cooling crystallization methods were carried out based on our previous studies regarding these methods and the crystal formation processes were investigated with FBRM probe. Critical agglomeration periods and other mechanisms, such as the breakage of the agglomerates and the precipitation of small particles, were investigated. Chord length values were observed continuously and samples were taken out in certain points of the crystallization. Particle size analysis was carried out in each case to obtain information on the particle size enlargement caused by the crystallization methods. With the application of light microscopic analysis, aspect ratio and roundness values were also determined to obtain pieces of information on the sphericity-changes of the particles throughout the crystallization and large improvements were presented either for these parameters (aspect ratio from ~ 1.7 to ~ 1.3; roundness from ~ 2.4 to ~ 1.5) and the mean particle size (from ~13 μm to 120–400 μm). Among others, it was revealed that after the spherical agglomeration method (SA), mostly crystal agglomerates were formed, while slow cooling crystallization with alternating temperature profile (ATP) yielded larger and probably harder individual crystals. [ABSTRACT FROM AUTHOR]

Controlling particle size is essential for crystal quality in the chemical and pharmaceutical industry. Several articles illustrate the potential of ultrasound to tune this particle size during the crystallization process. This paper investigates how ultrasound can control the particle size distribution (PSD) of acetaminophen crystals by continuous seed generation in a tubular crystallizer followed by batch growth. It is demonstrated that the supersaturation ratio at which ultrasound starts seed generation has a substantial effect on the final PSD while the applied power is insignificant in the studied conditions. The higher the supersaturation ratio, the smaller the final crystals become up to a supersaturation ratio of 1.56. Furthermore, it was shown that ultrasound can also impact the final PSD when applied during the growth phase. Frequencies of 850 kHz or below reduce the final particle size; the lower the applied frequency, the smaller the crystals become. In conclusion, one could state that ultrasound is able to control the particle size during seed generation and subsequent growth until the final particle size. [ABSTRACT FROM AUTHOR]

2D population balance model is presented for stirred cooling crystallizer of high aspect ratio crystals including primary and secondary nucleation, size-dependent growth of the two characteristic crystal facets and linear and nonlinear breakage along the crystal length. Three breakage mechanisms are modelled: crystal-impeller and crystal-wall collisions linear and crystal–crystal collisions nonlinear breakage processes. The 2D population balance equation is reduced into a system of moment equations for the mixed moments of length and width variables which is closed applying the quadrature method of moments and solved by using a three point QMOM-ODE method. It was shown that strong interactions exist between the secondary nucleation, crystal growth and breakage processes connected by the CSD. The stirring rate has strong impact on crystallization of high aspect ratio crystals forming the crystalline product directly by breakage. The crystal-impeller breakage proved to be the dominant process but the crystal–crystal breakage also play significant role. [ABSTRACT FROM AUTHOR]

In this paper calibration model building based on using an ATR-FTIR spectroscopy is investigated for in-situ measurement of the solution concentration during a cooling crystallization process. The cooling crystallization of L-glutamic Acid (LGA) as a case is studied here. It was found that using the metastable zone (MSZ) data for model calibration can guarantee the prediction accuracy for monitoring the operating window of cooling crystallization, compared to the usage of undersaturated zone (USZ) spectra for model building as traditionally practiced. Calibration experiments were made for LGA solution under different concentrations. Four candidate calibration models were established using different zone data for comparison, by using a multivariate partial least-squares (PLS) regression algorithm for the collected spectra together with the corresponding temperature values. Experiments under different process conditions including the changes of solution concentration and operating temperature were conducted. The results indicate that using the MSZ spectra for model calibration can give more accurate prediction of the solution concentration during the crystallization process, while maintaining accuracy in changing the operating temperature. The primary reason of prediction error was clarified as spectral nonlinearity for in-situ measurement between USZ and MSZ. In addition, an LGA cooling crystallization experiment was performed to verify the sensitivity of these calibration models for monitoring the crystal growth process. [ABSTRACT FROM AUTHOR]

Combined rainbow Schlieren deflectometry (RSD) and liquid crystal thermography (LCT) served as in situ non-intrusive techniques to determine local concentration and temperature fields based on refractive index gradients in solution during crystallization of sodium sulfate from aqueous solution. The combination of RSD with LCT allowed the decoupling of concentration and temperature effects. Convective mass transport happened during periods of fast, dendritic growth, but even higher levels occurred during the densification of the dendritic crystals, indicating significant mass deposition in this phase. The convection developed mainly as a result of concentration gradients as opposed to temperature gradients. A supersaturation field map was generated and growth kinetics of the sodium sulfate salt was determined. The kinetics followed a power law relationship, with constants in line with those in the literature. [ABSTRACT FROM AUTHOR]

Continuous small-scale production is currently of utmost interest for fine chemicals and pharmaceuticals. For this purpose, equipment and process concepts in consideration of the hurdles for solids handling are required to transfer conventional batch processing to continuous operation. Based on empirical equations, pressure loss constraints, and an expandable modular system, a coiled flow inverter (CFI) crystallizer with an inner diameter of 1.6 mm was designed. It was characterized concerning its residence time behavior, tested for operation with seed crystals or an ultrasonic seed crystal unit, and evaluated for different purging mechanisms for stable operation. The residence time behavior in the CFI corresponds to ideal plug flow behavior. Crystal growth using seed crystals was demonstrated in the CFI for two amino acids. For fewer seed crystals, higher crystal growth rates were determined, while at the same time, secondary nucleation was observed. Feasibility for the interconnection of a sonicated seeding crystal unit could be shown. However, the hurdles are also identified and discussed. Prophylactic flushing combined with a photosensor for distinguishing between solvent and suspension phase can lead to stable and resource-efficient operation. The small-scale CFI technology was investigated in detail, and the limits and opportunities of the technology are presented here. [ABSTRACT FROM AUTHOR]

Millimeter-sized α-glycine crystals were generated from continuous non-seeded cooling crystallization in slug flow. The crystallization process is composed of three steps in sequence: slug formation, crash-cooling nucleation, and growth. Stable uniform slugs of three different aspect ratios (slug length/tubing inner diameter) were formed, by adjusting the flow rates of both the solution and air streams. Besides supersaturation, the slug aspect ratio can also affect primary nucleation outcome. Stable slug flow can accommodate a relative supersaturation (C/C*) of up to 1.5 without secondary nucleation. Large glycine crystals can grow to millimeter size within 10 min, inside millimeter-sized slugs without reducing the slug quality. [ABSTRACT FROM AUTHOR]