DEV-CPPS · DEVELOPMENT OF THE CONTINUOUS POWDER PRODUCTION SYSTEM

Final Activity Report Summary - DEV-CPPS (Development of the Continuous Powder Production System)

The technology we have analysed allows us to generate powders with properties that are difficult or even impossible to achieve by traditional methods like milling, crystallisation, spray drying or agglomeration. In addition to particle size in powders, the morphology of particles has become more and more important. The processes we analysed allow us to generate particles with designed particle properties. The process we analysed experimentally and numerically for this project allows for the micronisation of chemical reactive and heat sensitive substances. In most experiments and analyses, carbon dioxide was used as compressed gas. Thus the processing of oxygen-sensitive substances in an inert atmosphere can be realised easily. To understand and develop the process, two major methods were selected: computer modelling and semi-industrial scale experimental analysis. These enabled us to analyse and control the more important to design tailor-made particle systems which allow for, among other things, the controlled release of reactive substances or offer durable protection of sensitive substances. Conditions for two types of dispersion were obtained and analysed. The matrix or shell substance of the composite has to be solid at ambient conditions, whereas the encapsulated or core substance can by either liquid or solid. The different substances needed to produce a composite are stored in separate vessels. The substances can be in a liquid, molten or dispersed state. Depending on the pressure and temperature as well as viscosity of the components, very different morphologies can be obtained. The range of preferred conditions for selected materials was evaluated. Particles with dispersed droplets or dispersed solids are formed. The use of the compressed gas allows for the formation of different morphologies. By adjusting the key process parameters like spray pressure, spray temperature and gas ratio to product ratio it is possible to form spheres, sponges, fibres, hollow spheres and foams. The system also allows for the pulverisation of the reactive components of the powder, which is possible because the reactive materials are mixed in a static mixer very fast and for a very short time after the components have been melted separately in discrete vessels. One of the key parameters in the static mixer was to obtain the 'resident time' in static mixer by using numerical modelling and numerical analysis. This was necessary to reduce the possible reaction time and maximise the components' mixed intensity. The liquid polymer/carbon dioxide blend is then depressurised through a nozzle. While depressurising, the polymer blend breaks up into small droplets and the droplets simultaneously freeze, thus forming a fine powder. We next produced the proper modelling of the spray in the spray nozzle together with heat transfer analysis in the spray tank. Several numerical and experimental models were tested and analysed for this part. In both numerical and experimental analyses the influence of high magnetic field was introduced and LES/DNS particle analysis carried out. Finally, a few possible conditions were selected and verified in laboratory-scale experiments. Also the influence of the chosen process parameters (such as the temperature, magnetic field and pressure of the melt) on the resulting powders was examined via experiments with a few model systems. The developed plant was optimized and finally able to carry even highly reactive and high temperature materials. For the experiments, polymer-systems with varying properties were used. In this way the influence of the material properties on the particle generation was examined. Rheology and calorimetry-measurements were used to characterise the materials.

Data: CORDIS, © European Union