Apostolopoulou, E; (2013) Micro-contactors for kinetic estimation of multiphase chemistries. Doctoral thesis (PhD), UCL (University College London).

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Abstract

The revolutionary Alpha process developed by Lucite International (LI) is an industrially advantageous process over the traditional route of acetone cyanhydrin for the production of methyl methacrylate (MMA). The Alpha process entails two stages. The first stage is an homogeneous catalysis process, a methoxycarbonylation reaction which produces methyl propionate (MeP) from ethylene, CO and methanol using a Pd catalyst stabilised with the 1,2-bis(di-tert-butylphosphinomethyl)benzene (dtbpx) phosphine ligand developed by LI. As it is known, kinetics are important for reactor modelling and simulation, interpretation of reaction mechanisms and catalytic phenomena. The kinetics of the methoxycarbonylation reaction are the subject of this research project and have been studied using a 2 L autoclave reactor and a 0.573 ml volume and 11.7 m length capillary microreactor with similar results. A bespoke experimental rig was designed and built to accommodate the micro devices. A theoretical investigation on the significance of mass transfer effects was undertaken to assess the significance of mass transfer limitations and both reactors were found to operate in the kinetic regime. A hydrodynamics study of Taylor flow under reaction conditions in a 6 m, 0.25 mm ID capillary microreactor was conducted to provide better understanding of the flow and improve its characteristics before the execution of kinetic experiments. The effects of methanol and Pd concentration, CO and ethylene partial pressure on the reaction rate have been studied. The reaction was found to be first and zero order with respect to methanol and ethylene respectively while the fractional order of 0.74 was derived with respect to Pd. CO inhibition kinetics were observed for high CO partial pressures and the reaction order was found to shift from positive to negative at pCO equal to 1.8 bar. The effect of temperature has been investigated in the range 80-120 oC and the activation energy was found to be 53 kJ/mol. A molecular level approach was used to derive a rate equation assuming the methanolysis step as the rate-controlling step. A software package was employed for the estimation of the rate parameters at the reaction conditions of 100 oC and 10 bar of gas pressure. Finally, a significant part of this research was spent on the design and development of a mesh microreactor of rectangular shape with dimensions 3 cm x 3 cm x 1.4 mm incorporating a 2 μm silicon nitride mesh with the aim to perform kinetic experiments but unfortunately this device was proved unsuitable for operation at high pressure.

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