International audienceIn spite of a great number of industrial applications, the thermal design of contact dryers for sewage sludge remains empirical. To improve the understanding of drying mechanisms, the penetration theory developed by Schlünder and co-workers for mono and multi dispersed packing is used to represent the experimental results from a laboratory scale dryer. For granular packing, the only adjustment parameter of the model is the mixing number, which characterizes the dryer and its stirrer. For pasty-like materials, the pasty phase is assumed to be a saturated particulate phase. As the calculation of the effective properties calculation is cumbersome for a multi-granular packing, the particulate phase is considered as a mono-dispersed packing, whose dimension is unknown. To identify the two adjustment parameters, the mixing number was quantified from experiments performed on activated alumina balls, for which physical and thermal characteristics are known, and then the characteristic dimension of the sludge was determined by adjustment of experimental drying kinetics measured in a batch agitated dryer. According to this model, drying is exclusively controlled by the contact resistance between the wall and the biggest particles contained in the dewatered sludge. The model allows to find most of the tendencies experimentally observed for different operating conditions

a b s t r a c tThis study aims at better understanding the wet granulation process of a binary mixture composed of microcrystalline cellulose (water insoluble) and lactose (water soluble). It investigates the effect of formulation (proportion of the different components in the mixture) on the granule growth kinetics, the evolution of granule morphology during granulation, the wet mass consistency and dry granule strength of the end product. Additionally the influence of mixer design has been studied by up scaling the process from the 1.9 L Mi-pro high shear mixer used as the reference scale to a 6 L Diosna P1-6 high shear mixer. The scale-up rules investigated were constant impeller tip speed and constant Froude number. Our results allowed us to draw the following conclusions: -The increase in MCC content is found to increase the optimum binder requirement for granulation, wet mass consistency and dry granule strength.-Granule growth takes place in three distinct stages: wetting, nucleation and growth. These stages can be identified with the help of the recorded torque values during the granulation process or by the evolution of granule size and granule morphology.-The characterization of the starting materials by moisture sorption isotherms brings more insight to the role of each component during the granulation process.-The increase of the granulation scale has little influence on the observed growth mechanism. However bimodality of the granule size distribution is increased, wet mass consistency and dry granule strength are decreased with increasing scale of operation.

The effect of the main means of agitation in a high shear mixer has been investigated in this study. Granulation runs have been performed on a fine cohesive microcrystalline cellulose powder (Avicel 105, d 50 = 20 μm) often used as a pharmaceutical excipient in tablet formulations in two bowls of a Mi-Pro® laboratory high shear mixer with a capacity of 0.9 and 1.9 L, respectively. Torque curves recorded during granulation are found to allow good control of the process while increasing impeller speed is found to generally reduce granule size and the onset of breakage seems to occur for similar values of impeller tip speed. As a general rule, the chopper allows for better binder distribution in the Mi-Pro® and is found to be necessary for successful granulation at low to moderate impeller speeds. For high impeller speeds in excess of 4.4 m/s with or without a chopper, similar granule sizes and growth mechanisms are observed. Granule roundness was found to increase with impeller speed up to a certain speed after which granule roundness has been found to decrease with increasing impeller speed most probably because of increased breakage of the granules. Dry granule strength has been found to increase with increasing impeller speed, presenting only a slight decrease at the highest impeller speed studied.

a b s t r a c t Keywords:High shear mixer granulator Torque curves Work of adhesion Viscosity Scale-up The effect of binder properties on torque curves, granule growth kinetics, wet mass consistency and dry granule strength has been investigated in this study. Granulation runs have been performed on a fine cohesive microcrystalline cellulose powder (Avicel 105, d 50 = 20 μm) in two types of laboratory high shear mixers: a MiPro high shear mixer using a 1.9 L bowl and a 6 L Diosna high shear mixer. Binders used included ultra-pure water and solutions of varying concentrations of PVP and HPMC allowing us to cover different values for parameters like viscosity and work of adhesion. Torque curves recorded during granulation are found to allow good control of the process. Optimum liquid requirement for granulation has been found to vary with binder type and decrease with increasing viscosity while granule growth kinetics has been found to be to be related to the work of adhesion for low viscosity binders. Granule strength has been evaluated for wet granules by the means of wet mass consistency measurements on a mixer torque rheometer and for dried granules by means of uniaxial compression tests on a Texture Analyser mechanical testing machine. For low viscosity binders both wet mass consistency and dry granule strength have been found to depend on the work of adhesion. For high viscosity binders higher wet mass consistencies but lower dry granule strengths have been observed. Granulating on the larger 6 L scale has shown that constant impeller tip speed offers good agreement in terms of mean granule size however granule size distribution seems to be scale dependant.

Purpose: Understanding and predicting the flow of bulk pharmaceutical materials could be key in enabling pharmaceutical manufacturing by continuous direct compression (CDC). This study examines whether, by taking powder and bulk measurements, and using statistical modelling, it would be possible the flow of a range of materials likely to be used in CDC. Methods: More than 100 materials were selected for study, from four pharmaceutical companies. Particle properties were measured by static image analysis, powder surface area and surface energy techniques, and flow by shear cell measurements. The data was then analysed and a range of statistical modelling techniques were used, to build predictive models for flow. Results: Using the results from static image analysis a model could be built which allowed the prediction of likely flow in a shear cell, which can be related to performance in a CDC system. Only a small amount of powder was required for the image analysis. Surface area did not add to the precision of the model, and the available surface energy technique did not correlate with flow. Conclusions: A small sample of powder can be examined by Static image analysis, and this data can be used to give an early read on likely flow of a material in a CDC system or other pharmaceutical process, allowing early intervention (if necessary) to improve the characteristics of a material, early in development.