Oxidative reactions to form ethyl methacrylate via a phase specific iron phosphate catalyst .
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Date
2012
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Abstract
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.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.
Keywords
Oxidation., Ether., Catalysis., Theses--Chemistry.