Oxidative reactions to form ethyl methacrylate via a phase specific iron phosphate catalyst .
The importance of alkyl methacrylates has been firmly established within the chemical industry. For example, free radical polymers, which contain the methacrylate backbone are more rigid than acrylate polymers. Several methods have been reported for the production of alkyl methacrylates. The aim of this project is focused on isolating a phase specific iron phosphate catalyst and thereafter testing its efficacy in oxidative reactions to form ethyl methacrylate in a one step process in the gas phase using a fixed bed continuous flow reactor. The catalyst was characterized by using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), Brunauer-Emmett-Teller (BET) surface area measurements, Attenuated Total Reflection-Infrared (ATR-IR) Spectroscopy, Scanning Electron Microscopy (SEM), Temperature Programmed Reduction (TPR), Temperature Programmed Oxidation (TPO), Energy Dispersive X-ray (EDX) determination, Temperature Programmed Desorption (TPD), Room Temperature X-ray Diffraction (XRD), In situ X-ray Diffraction (In situ XRD), Thermogravimetric/Differential Thermal Analysis (TGA/DTA), Transmission Electron Microscopy (TEM), Mössbauer Spectroscopy and Raman Spectroscopy. A further venture included employing certain of the above techniques to characterize the cesium promoted iron phosphate catalyst as well as the spent catalysts. The catalytic activity of the iron phosphate based catalyst synthesized was investigated for the oxidative dehydrogenation (ODH) of ethyl isobutyrate (EIB) to ethyl methacrylate (EMA). Reaction conditions which were considered included variation in the contact time, co-feeding water at varying contact times, co-feeding ethanol at varying ratios, as well as co-feeding both ethanol and water and catalyst lifetime and regeneration studies. The cesium promoted iron phosphate catalyst was tested at optimal reaction conditions. The findings of the investigation showed that the tridymite-like FePO4 phase was the most suitable precursor to allow for the formation of the active α-phase during catalytic testing. It was found that the catalyst performed optimally at a contact time of 0.8 seconds and the beneficial effect of co-feeding water and ethanol primarily on conversion and selectivity towards EMA respectively, was demonstrated. Optimal results were obtained at a EIB:EtOH ratio of 1:5 with a conversion of 57 % and a yield of 34 mol %. The lifetime and regeneration studies showed that water had a significant effect on the regeneration of the catalyst after a specific time on stream and a shorter time on stream (i.e. 25 hours) prior to regeneration, minimized rapid deactivation of the catalyst. The characterization results obtained for the spent catalysts showed that under the reaction conditions considered with respect to co-feeds, the active α-phase and the Fe2P2O7 phase dominated. The cesium promoted iron phosphate catalyst was synthesized to favour stabilization of the tridymite-like structure. The results showed that a mixture of phases was observed for the synthesized promoted catalysts and there was an increase in EIB conversion as well as EMA selectivity with a decrease in cesium loading. However, the promoted catalyst with the lowest cesium loading (Cs/Fe = 0.10), showed a lower selectivity towards EMA relative to the unpromoted iron phosphate catalyst.