Identification and study of descriptors of boehmite paste kneading for innovative solids conception

The control of alumina support textural properties is a very important task in the framework of innovative catalytic material manufacturing.  Mass transport in the porous medium is strongly affected by the microstructure and could decrease the impregnation efficiency of the active phase and the resulting catalytic activity. Alumina support is constituted of elementary crystals (a few Å) formed during the precipitation step, that stick together to form aggregates (a few nm). These clusters can stick together to form agglomerates (from 100 nm to 1 μm average size).The resulting assembly constitutes the overall porous complex network which combines different spatial scales and leads to a wide distribution of pores diameter. Support manufacturing procedure consists in many unit operations starting form a colloidal suspension to a final shaped solid particle (scale: mm). Among them, kneading (or paste mixing) has a high impact on the final textural properties. One of the main issue is to control this process: coupling of physicochemical, rheological and hydrodynamic phenomena in the kneader makes it difficult to optimize the operating conditions, to scaleup the process or to change the technology. In order to go further than the empirical rules, the objective of this PhD’s work is to model the involved phenomena (aggregates cracking and agglomeration, rheological behavior, …) and to validate them thanks to dedicated experimentation and characterization (DRX, N2 and Hg porosimetry, MET, SAXS, DLS, rheology, …). Then, the resulting elementary bricks will be put together in a complex flow in order to simulate a kneader. A comparison between the coupled model and the experimental results obtained on the kneader will validate this multi-scale approach. This PhD’s work will contribute to a bigger goal: developing a kneader simulator. It will predict the textural properties of the catalytic support as a function of operating conditions and boehmite properties. This simulator will be used to find technological and operating innovation ideas and to develop new alumina catalytic support.