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

Ultrasound-assisted continuous crystallization of metastable polymorphic pharmaceutical in a slug-flow tubular crystallizer

Metastable polymorphic pharmaceuticals have garnered significant attention in recent years due to their enhanced physicochemical properties, including solubility, bioavailability, and intellectual property considerations. However, the manufacturing of metastable form pharmaceuticals remains a formidable challenge. The stable preparation of metastable carvedilol (CVD) form Ⅱ crystals during CVD production is elusive, leading to substantial inconsistencies in product quality and regulatory compliance. In this study, we successfully prepared metastable CVD Form Ⅱ crystals using a continuous tubular crystallizer. Our findings demonstrate that the tubular crystallizer exhibits high efficiency and robustness for generating metastable crystal Form Ⅱ. We optimized the crystallization process by incorporating air bubble segments and employing ultrasonic irradiation strategies to overcome blockages and wall sticking issues encountered during operation. Ultimately, we developed an ultrasound-assisted continuous slug-flow tubular crystallization method and evaluated its performance. The results indicate that the CVD crystals produced through this process are resilient, sustainable, and uninterrupted products with promising potential for producing metastable polymorphic pharmaceuticals while effectively addressing encrustation problems associated with continuous tubular crystallization.

Process Analytical Technology for the Production of Parenteral Lipid Emulsions According to Good Manufacturing Practices

The good manufacturing practices (GMP) and process analytical technology (PAT) initiatives of the US Food and Drug Administration, in conjunction with International Council for Harmonisation (ICH) quality guidelines Q8, Q9, and Q10, ensure that manufacturing processes for parenteral formulations meet the requirements of increasingly strict regulations. This involves the selection of suitable process analytics for process integration and aseptic processing. In this article, we discuss the PAT requirements for the GMP-compliant manufacturing of parenteral lipid emulsions, which can be used for clinical nutrition or for the delivery of lipophilic active ingredients. There are risks associated with the manufacturing processes, including the potential for unstable emulsions and the formation of large droplets that can induce embolisms in the patient. Parenteral emulsions are currently monitored offline using a statistical approach. Inline analytics, supplemented by measurements of zeta potential, could minimize the above risks. Laser scanning technology, ultrasound attenuation spectroscopy, and photo-optical sensors combined with image analysis may prove to be useful PAT methods. In the future, these technologies could lead to better process understanding and control, thus improving production efficiency.

Continuous Crystallization Using Ultrasound Assisted Nucleation, Cubic Cooling Profiles and Oscillatory Flow

Continuous tubular crystallizers have the potential to reduce manufacturing costs and increase product quality. However, designing tubular crystallizers is a complex and challenging task as crystallization is a complex, multiphase process with a propensity for fouling and clogging. While several designs have been proposed to overcome these issues, these designs are either unproven or poorly scalable and complex. In this work a continuous crystallizer is designed and evaluated to mitigate these issues. The tubular crystallizer combines a novel method to obtain a cubic cooling profile to control the supersaturation, ultrasound to induce nucleation and oscillatory flow to improve mixing and minimize fouling and sedimentation. The results show that the crystallizer was able to operate for more than 4 h without clogging, with high yields and a narrow particle size distribution. The design proposed here is therefore considered a viable approach for continuous crystallizers.

Enhanced crystallisation kinetics of edible lipids through the action of a bifurcated streamer

The processing of healthy foods remains a challenge and any technology with the ability to tailor the physical properties of new materials is in demand. High-intensity ultrasound (HIU) has been identified as a useful processing technique for such activities particularly for edible lipids. HIU has been known to alter the crystallisation kinetics and in turn the resultant physicochemical properties for specific food applications. The role of cavitation dynamics during treatment of oils with HIU is of interest, with the knowledge gained allowing for insight into the complex and still undefined mechanism of action. To this end, the crystallisation kinetics of an edible lipid were investigated in the presence of several distinctly different cavitation conditions. Several cavitation clusters, including a bifurcated streamer (BiS), located on the surface of a piston-like emitter (PLE) were studied, each generated by a specific ultrasonic power level. Only samples crystallised at a low supercooling (ΔT_SC) value display significant differences in induction time for each of the selected HIU powers, at least 5 minutes earlier than without exposure to HIU. Substantially better energy efficiencies were seen for the BiS regime (ΔT_SC = 5 °C) which coincided with maximal crystal growth rates. An increase in melting enthalpy and elastic modulus is reported in the presence of HIU for all crystallisation temperatures, this effect is larger overall with increasing ultrasonic power. In addition, sonicated samples in the presence of the BiS event were composed of fewer smaller crystals compared to higher HIU powers after 60 minutes at 30 °C. Bubble dynamics recorded during a 10 s sonication period exhibited a greater acoustic attenuation effect for the highest ultrasonic power (75 W). The results suggest that the dynamics of the cluster and the presence of the BiS event are important in terms of energy efficiency and the physical properties of the crystallised lipid material.

Rational design of solid-acid catalysts for cellulose hydrolysis using colloidal theory

Solid-acid catalysts functionalized with catalytic groups have attracted intense interest for converting cellulose into soluble products. However, design of solid-7 acid catalysts has been guided by molecular level interactions and the actual mechanism of cellulose-solid-acid catalyst particles adsorption remains unknown. Here, colloidal stability theory, DLVO, is used to rationalize the design of solid acids for targeted cellulose adsorption. In nearly all cases, an energy barrier, arising from electrostatic repulsion and much larger than the energy associated with thermal fluctuations, prevents close contact between the solid acid and cellulose. Polymer-based solid-acid substrates such as polystyrene and Nafion are especially ineffective as their interaction with cellulose is dominated by the repulsive electrostatic force. Carbon and metal oxides have potential to be effective for cellulose-solid-acid interaction as their attractive van der Waals interaction can offset the repulsive electrostatic interaction. The effects of reactor temperature and shear force were evaluated, with the finding that reactor temperature can minimize the catalyst-cellulose interaction barrier, promoting coagulation, but that the shear force in a typical laboratory reactor cannot. We have evaluated strategies for enhancing cellulose-catalyst interaction and conclude that raising reaction temperature or synthesizing acid/base bifunctional catalysts can effectively diminish electrostatic repulsion and promote cellulose-catalyst coagulation. The analysis presented here establishes a rational method for designing solid acid catalysts for cellulose hydrolysis.

Nucleation kinetics for primary, secondary and ultrasound-induced paracetamol crystallization

Investigation into the effect of different nucleation mechanisms on the nucleation rate for paracetamol crystallization in stirred microvials.

Sonocrystallization as an Efficient Way to Control the Size, Morphology, and Purity of Coordination Compound Microcrystallites: Application to a Single-Chain Magnet

The size, morphology, and purity control of coordination compound powders is a key stage for their conversion into materials and devices. In particular, surface science techniques require highly pure bulk materials with a narrow crystallite-size distribution together with straightforward, scalable, and reproducible crystallization procedures. In this work we demonstrate how sonocrystallization, i.e. the application of ultrasound during the crystallization process, can afford very quickly powders made of crystallites with controlled size, morphology, and purity. We show that this process drastically diminishes the crystallite-size distribution (low polydispersity indexes, PDI) and crystallite aspect ratio. By comparing sonicated samples with samples obtained by various silent crystallization conditions, we unambiguously show that the improvement in the crystallite morphology and size distribution is not due to any thermal effect but to the sonication of the crystallizing media. The application of sonocrystallization on crystallization batches of single-chain magnets (SCMs) maintains the chemical integrity of the SCMs together with their original magnetic behavior. Moreover, luminescent measurements show that sonocrystallization induces an efficient micromixing that drastically enhances the purity of the SCM powders. We thus propose that sonocrystallization, which is already used on organic or MOF compounds, can be applied to (magnetic) coordination compounds to readily afford bulk powders for characterization or shaping techniques that require pure, morphology- and crystallite-size-controlled powder samples.

Determination of the Nucleation and Growth Kinetics for Aqueous L-glycine Solutions from the Turbidity Induction Time Data

As the turbidity induction time measurements are influenced by the size distribution of the nuclei at the detection point, these data should provide important information on both nucleation and growth. A model is developed in this work to determine the nucleation and growth kinetics of aqueous L-glycine solutions using the turbidity induction time data for various supersaturations from 293.15 K to 313.15 K. The photomicroscopic growth experiments of aqueous L-glycine solutions are also conducted to determine the growth kinetics of nuclei under the same conditions for comparison. The results indicate that the interfacial energy obtained from this model is consistent with that obtained based on the traditional method by assuming t i − 1 ∝ J . The growth kinetics, including the growth activation energy and the kinetic growth parameter, obtained from this model using the induction time data are close to those obtained from the photomicroscopic growth experiments performed in this work.