Title Promoter Affiliations Abstract "Ultrasound-Assisted Synthesis of Zeolite Catalysts" "Tom Van Gerven" "Process Engineering for Sustainable Systems (ProcESS)" "Zeolites are aluminosilicate minerals with a microporous structure used as adsorbents and catalysts. They are conventionally synthesized by hydrothermal methods in batch systems. However, this process exhibits several disadvantages, such as long synthesis times and non-uniform qualities of product from batch to batch. There is a strong interest from the zeolite manufacturing industry to reduce the synthesis time and achieve a continuous process without affecting the profit-earning capacity. The slow reaction kinetics, characteristic of the aluminosilicate chemistry, and the formation of solid particles during the synthesis render the transition from batch to continuous processes difficult. Ultrasound-assisted synthesis of zeolites is a promising approach to reduce the synthesis time by acceleration of the reaction kinetics as well as a way to control the particle size distribution of final crystals. Besides, oscillatory baffled reactors have been demonstrated to be suitable for the handling of solid particles.                  Therefore, this research project focused on the development of the reactive crystallization of submicronic zeolite crystals in a continuous process assisted by ultrasound. To accomplish this goal, the effects of ultrasound on zeolite synthesis were first studied to identify different scenarios for the improvement of the conventional process. In parallel, a continuous flow process for the synthesis of zeolites, integrating an oscillatory baffled reactor, was developed. Further optimization of the process involved process parameters, such as flow rate, temperature and oscillation conditions. Finally, the scale-up of ultrasound to the continuous flow process was examined for controlling the particle size distribution.                  This doctoral research demonstrated that ultrasound can be applied during the crystallization step of zeolite synthesis at high temperature, reducing the reaction time by ~ 33 % compared to a standard crystallization. It was found that ultrasound accelerates the reaction kinetics if applied during the pre-organization of aluminosilicate species, modifying the solubility and concentration levels in the synthesis system. Moreover, ultrasound can be used as a post-treatment technique after the crystallization for controlling the particle size distribution and agglomeration degree of the final powder. The irradiation volume, time and sonication power were identified as ultrasound parameters to tune the agglomeration degree. Combination of high power and long irradiation time resulted in a more dispersed powder without changing the single crystal morphology (size and shape). Ultrasound was able to turn some agglomerates into single crystals and reduce the size of the largest ones.                  Ultrasound was able to improve the dispersion of metallic particles during the preparation of catalysts by ion-exchange process. The particles were smaller allowing a proper incorporation into the zeolite channels. The catalysts were evaluated for non- oxidative methane dehydroaromatization with a catalytic activity comparable to the conventional impregnation method.                  Moreover, this doctoral research accomplished, for the first time, a continuous flow synthesis of zeolites in a pilot scale. It was found that the combination of seed- assisted method, in-line mixing of reactants at high temperature and an oscillatory baffled reactor allows a stable continuous operation during 5 h. It was possible to reproduce the same reaction kinetics in continuous flow as in the batch laboratory scale. This represents an advantage for further scale-up of the process and fills the gap between laboratory and production scale. The quality of the final product was similar in terms of purity and single crystal size. Nevertheless, bigger agglomerates were formed over time resulting probably from the supposed different mobility of the seeds in the suspension. Optimal oscillation conditions were identified to reduce this effect and guarantee a proper handling of solids, reducing the risk of clogging.                  Finally, the scale-up and integration of ultrasound into the continuous synthesis pilot was performed for controlling the agglomeration degree of the final powder. An ultrasound probe prototype was integrated in the last section of the reactor, corresponding to the end of the crystallization process. The agglomerates were ~ 20 % smaller compared to agglomerates without treatment. Based on comparisons between the post-treatment performed in batch and in continuous operation, the irradiation time was identified as a key parameter when moving from batch to continuous and from laboratory to pilot scale. New opportunities arise from the findings of this doctoral research for a future industrial implementation of a continuous flow process for the synthesis of zeolites. Moreover, the ultrasound deagglomeration results give the basis for a future scale-up of ultrasound to accelerate the reaction kinetics and develop efficient zeolite synthesis processes taking into account the principles of Process Intensification."