(83d) Application of Radiofrequency Heating for Process Intensification in Pd Catalysed Hydrogenation Over Composite Magnetic Microparticles

Application
of radiofrequency heating for process intensification in Pd catalysed hydrogenation
over composite magnetic microparticles

Thomas
K. Houlding, Pengzhao Gao, Evgeny V. Rebrov

School of Chemistry & Chemical Engineering,
Queen's University Belfast, Stranmillis Road, BT9
5AG, Belfast, UK

Recently, much research
in process intensification has been focussed on the development
multi-functional reactors, improving processes by system integration [1]. The
use of NiZn ferrite nanoparticles embedded in a mesoporous microparticles for
radiofrequency (RF) heating, magnetic separation and enhancement of mass
transfer in the laminar flow within a continuous flow system provides a novel
process intensified platform for system integration. The objective of this
study was to explore novel Pd-based supported catalysts for selective and
economically viable fine chemical synthesis.

The composite titania
microparticles were prepared by sol-gel method from titania precursor in the
presence of a structure directing agent and NiZn ferrite nanoparticles (grain
size 15-25 nm) in the sol following earlier developed methodology [2,3].  After
calcination at 300°C, the porous network was filled with a Pd precursor by
incipient wetness impregnation. Then the microparticles were dried, calcined
and reduced in hydrogen flow.

The heating rate of
composite microparticles in the AC field (100-400 kHz, current 20-100 A) was determined
of powders and slurries containing the desired amount of solid material. Induction
coils with either 4, 5 or 6 turns were used as applicators to generate RF fields
with different frequencies.  During operation the induction coil was cooled
from inside by circulating water at 10^oC. The heating rates were
studied as a function of ferrite composition (Ni and Zn content), the total
loading of ferrite onto titinia microparticles as well as of the field strength
and frequency. The temperature was measured with a fibre optic probe. The
highest heating rate was observed over microparticles containing NiZn ferrite
nanoparticles with low coercivity, with average powder heating rates of up to 40
K/min. Specific absorption rates (SAR) of up to 10 W/g were observed for composite
microparticles containing magnetite nanoparticles.

Figure 1. Specific
absorption rate of SiO₂@magnetite microparticles as a function of
current and coil type

The catalytic activity
of composite catalysts in hydrogenation reactions was determined in a reactor
made of PEEK at a total H₂ pressure of 3 bar. Reference experiments
were carried out using conventional heating with a thermostat. During
experiments under RF-heating, the liquid temperature remains considerably below
the catalyst temperature, which was estimated from the Arrhenius plot for the reaction
rate of several selected transformations.

References

[1] Hessel
V. Novel Process Windows ? Gate to Maximizing Process Intensification via Flow
Chemistry. Chem. Eng. Technol. 2009;32:1655-1681.

[2] Rebrov
EV, Berenguer-Murcia A, Skelton HE, Johnson BFG, Wheatley AEH, Schouten JC.
Capillary microreactors wall-coated with mesoporous titania thin film catalyst
supports. Lab Chip. 2009;9:503-506.

[3] Protasova
LN, Rebrov EV, Skelton HE, Wheatley AEH, Schouten JC. A kinetic study of the
liquid-phase hydrogenation of citral on Au/TiO2 and Pt?Sn/TiO2 thin films in
capillary microreactors. Appl. Catal. A. 2011;399:12-21.