Title:
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Application of radiofrequency heating in catalytic reaction engineering
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Radiofrequency (RF) heating of composite magnetic materials enables direct and efficient
transfer of energy to the sites of catalytic reactions within a chemical reactor.
The materials consist of an RF heated magnetic component and a catalytic component.
The two components can be optimised separately according to the demands of the application.
This approach was applied to continuous direct amide formation from amines
and carboxylic acids under flow conditions, a reaction of great interest and potential
to the pharmaceutical industry.
The RF heat generation of NiFe2 04-TiO2 magnetic materials were optimised. Catalyst
screening showed sulfated commercial P 25 Ti02 to give good catalytic activity in the
reaction of 4-phenylbutyric acid with aniline in xylene. The composite material was
prepared mechanochemically from a mixture of the optimised magnetic and catalytic
components.
A continuous RF heated reactor was developed, consisting of a 6 mm diameter insulated
micro packed-bed reactor placed within an RF induction coil. The reactor was
operated at 7 bar and up to 200°C for up to 10 hours. The sulfated composite achieved
t he highest activity of up to 50% conversion in a single pass and the least deactivation.
Temperature profiles obtained from the analytical solutions were combined with a catalyst
kinetic model to form a reactor model, which was validated by the experimental
results. The concentration profiles obtained from the reactor model gave an insight into
the mechanism of the observed process intensification - the temperature rise along the
RF heated reactor axis helped to offset the reduction in the reaction rate as a result
of depletion of the reactants. This novel type of process is therefore most suited to
reactions with high reaction rate orders and it would therefore be of great interest to
investigate other processes where this effect could be demonstrated.
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