Kinetic and Catalytic Aspects in Propene Oxide Production

Propene oxide synthesis has a relative long history. Many processes have already been developed and some of them even applied at the industrial scale. By comparing them, one of the most promising is the HPPO process (Hydrogen Peroxide Propene Oxide), because hydrogen peroxide is used as direct oxidant in propene oxidation and only water is obtained as theoretical byproduct. The reaction is catalyzed by TS-1, a titanium silicalite MFI zeolite, it is carried out under mild conditions of temperature and propene pressure (40°C, 20 bars). Methanol is used as solvent. Since 25 years now, this process is under development and recently some industrial plants, based on this technology, are already running. Despite the industrial interest, only few papers have been published till now dealing with the kinetics of the reactions involved in the process, paying attention only on the main reaction and without taking into account the mechanism proposed by other authors. The first part of this thesis is devoted to the kinetic investigation of the overall reaction network of the HPPO process, considering both the main and the side reactions, taking care on the mechanism suggestions reported in the literature. The study has been performed in a fed-batch reactor. The collected runs have been interpreted by adopting a reliable mechanism and reaction scheme. By taking into account also the mass transfer phenomena, it has been possible to investigate the kinetics of the reaction system and to obtain the kinetic rate laws with related kinetic parameters. The second part of the work is devoted to the design and realization of a continuous lab-scale pilot plant, that includes the possibility to work with several continuous reactors such as continuous stirred tank reactor (CSTR), adiabatic tubular reactor and jacketed tubular reactor. In this way, by using a CSTR, the kinetic model found in the previous step of this thesis has been validated and the correct strategy to enhance the hydrogen peroxide conversion and propene oxide selectivity has been evaluated. Finally, the third part of this work is strictly related to the waste water effluents treatment coming from the HPPO plant, that contain unreacted hydrogen peroxide. A detailed catalytic investigation has been performed on the hydrogen peroxide decomposition and the best catalysts tested in continuous too, paying attention to the intensification of this last step of the HPPO process