The evolution of pellet size and shape during spheronisation of an extruded microcrystalline cellulose paste

Shaping of Porous CeO2 Powders into Highly Active Catalyst Carriers

CeO₂ is attracting more and more attention because of its outstanding performance in heterogeneous catalysis, as an active support and a reaction promoter in reactions of industrial interest. We herein describe a novel and scalable manufacturing process of mm-sized CeO₂ spheres by a combination of extrusion and spheronization of CeO₂ porous powders. In this study, wet paste formulation and fabrication procedures were optimized, and as a result methylcellulose was identified as the best plasticizer for paste extrusion to provide well-defined spherical shapes and smooth surfaces, as well as reproducible batches. After nickel impregnation (10 wt %), the catalytic performance of CeO₂ supports was evaluated in the CO₂ methanation reaction (T = 250-350 °C, P = 5 bar·g) and compared with that of commercial Al₂O₃ spheres doped or not with CeO₂. These novel CeO₂-based catalysts are easily reduced at a moderate temperature and more active than the Al₂O₃ analogues, particularly at low reaction temperatures and small reactor volumes, properties that make their implementation in emerging reactor configurations very promising.

Applicability of Image Analysis to Support QbD driven Development of Pellets

Objective The stages of preparing high drug loaded pellets were investigated using static and dynamic imaging techniques to provide a greater understanding and ease the scale up process. Significance: An example of a real case laboratory and production scale Quality by design (QbD) based development of pellets is demonstrated. Potential Process analytical technology (PAT) approaches by dynamic image analysis (DIA) are presented in various process phases. Methods: Pellets were prepared at laboratory and production scale (high shear granulation, extrusion/spheronization, drying, coating). The influence of process parameters on pellet properties (aspect ratio, yield, pellet size, and their distribution) was investigated using static and dynamic image analysis. During coating, we focused on the coating thickness and identification of potential agglomeration. Results and conclusions: The effects of kneading time, amount of water, extrusion screen plate (ESP) opening diameter and thickness on pellet properties were confirmed in accordance with literature. In terms of screw speed, spheronization speed and time, no considerable influence on pellet properties was observed in the range of studied process parameters, thereby confirming the design space. . In addition to the ESP thickness and opening diameter, quality of the ESP impacts the pellet properties. Lastly, coating thickness measurements with dynamic and static image analysis were comparable and an exemplary case of in-line agglomeration detection was presented. Real time evaluation with PATVIS APA is an effective PAT tool for the evaluation of spheronization (pellet size distribution, aspect ratio, yield) and coating (coating thickness, agglomeration detection).

Elucidation of mass transfer mechanisms in pellet formation by spheronization

Previously published mechanisms of pellet formation during extrusion-spheronization include a transfer of material between different granules. This research aimed to specify the origin of this transfered mass, enabling further insight into the extrusion-spheronization process. Granules of various diameters were rounded simultaniously in a spheronizer to ascertain if mass transfer between smaller and larger granules is truly in balance, or if mass transfer from smaller to larger granules is preferred. Granules were also marked with a fluorescent tracer to enable quantification of mass transfer. By using differently sized and shaped granules as starting material, different modes of mass transfer were investigated. Samples were taken after various process durations to investigate the kinetics of the tranfer mechanism. It was found that both small and large granules dispense and receive mass during spheronization. In general, small granules increase their size, while large granules maintain their size or show a slight size decrease, resulting in the particularly narrow monomodal size distribution.

Scale-up of the rounding process in pelletization by extrusion-spheronization

Previously described scaling models for the spheronization process of wet extrudates are incomplete, often concluding with an adjustment of the plate speed according to the spheronizer diameter, but neglecting to give guidelines on the adjustment of the load or the process duration. In this work, existing scaling models were extended to include the load and the process time. By analyzing the final particle size and shape distributions as well as the rounding kinetics for various loads and plate speeds in spheronizers with plate diameters of 0.12 m, 0.25 m and 0.38 m, the found scaling model was validated. The peripheral speed was found to be the main influence on the rounding kinetic, while the load and the plate diameter only showed minor influence. Higher peripheral speeds, higher loads and a larger spheronizer diameter led to an increase in rounding kinetic, allowing for shorter residence times and increased throughput. However, lower peripheral speed, lower loads and lower plate diameters led to particles of increased sphericity.

Influence of extruder screws speed and process temperature on the extrudate shape changes of the maize-spelt blends

The objective of the study was examination of changes in the shape factors of extruded products, which occur as a result of different settings of the extrusion process variables. Samples analysed included products created by means of the extrusion process from a mixture of spelt flour and cornmeal, with the share of spelt at 70 to 100%. The samples were made with the use of a co-rotating twin screw extruder. Two speeds of extruder screw rotation (300 and 350 rpm) as well as two levels of temperature (120 and 140°C) were set during the investigation. The samples obtained were photographed in a light box, following which they underwent an image analysis with the use of specialist vision software. Four shape-related factors were determined: area, elongation factor, Heywood circularity factor and compactness factor. It was determined that the product shape changed significantly depending on the share of spelt flour in the mixture. Moreover, it was observed that change in the screw rotation speed within the analysed range may cause material changes in the shape of particular extrudates.

Spheronization of solid lipid extrudates: Elucidation of spheroid formation mechanism

To explain the rounding mechanism of extrudates by spheronization method, two main concepts are found in literature: one proposed by Rowe (1985) and one proposed by Baert et al. (1993). These concepts are based on wet extrusion-spheronization method using microcrystalline cellulose as mains excipient. However, there are no concepts for the spheronization mechanism of extrudates based on solid lipids as spheronization aid. Therefore, the aim of this study is to systematically investigate the mechanism of pellet formation of lipid based extrudates by lipid spheronization method. Different lipid based extrudate formulations were spheronized and particle size distribution and shape of the pellets, at each minute of the process, were characterized. Additionally, visual investigations of the morphological alterations were performed by optical and scanning electron microscopy. Two main material temperature phases were identified as presenting important influence on the pellet formation during the process: (1) a "brittle phase", where the extrudates are broken into smaller particles and (2) a "plastic phase", where the material starts to partially melt, allowing the particles to deform. By the same token, different morphological stages, from cylindrical rods to sphere-shaped passing through a dumbbell-shaped particle, were observed and showed to be highly dependent on temperature and process time. Moreover, a new particle shape, defined as "two-spheres", was recognized and a sequential material overlapping (covering) phenomenon was identified. This particular dislocation of material, from the edges to the central region of the particles (increasing their mean diameter), was recognized at longer process times and led to the formation of a smooth surface and the final spherical shape. At the end, a new concept of pellet formation from lipid extrudates is presented considering the observed changes in the morphology and particle size of the pellets during the spheronization process.