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Toward Sustained Product Formation in the Liquid-Phase Hydrogenation of Mandelonitrile over a Pd/C Catalyst
journal contribution
posted on 2020-05-18, 18:41 authored by Mairi
I. McAllister, Cédric Boulho, Colin Brennan, Stewart F. Parker, David LennonThe
liquid-phase hydrogenation of the aromatic cyanohydrin mandelonitrile
(MN, C6H5CH(OH)CN) over a carbon-supported Pd
catalyst to produce the primary amine phenethylamine (PEA, C6H5CH2CH2NH2) is investigated
with respect to the transition from operation in single-batch mode
to repeat-batch mode. While a single-batch reaction returns a complete
mass balance, product analysis alongside mass balance measurements
for a six-addition repeat-batch procedure shows an attenuation in
the rate of product formation and an incomplete mass balance from
the fourth addition onward. This scenario potentially hinders possible
commercial operation of the phenethylamine synthesis process, so it
is investigated further. With reference to a previously reported reaction
scheme, the prospects of sustained catalytic performance are examined
in terms of acid concentration, stirrer agitation rate, catalyst mass,
and hydrogen availability. Gas–liquid mass transfer coefficient
measurements indicate efficient gas → liquid transfer kinetics
within the experimental constraints of the Henry’s law limitation
on hydrogen solubility in the process solvent (methanol). Deviations
from the optimized product selectivity are attributed to mass transport
constraints, specifically the H2(solv) → 2H(ads)
transition, which is ultimately restrained by the availability of
H2(solv). Finally, in an attempt to better understand the
deactivation pathways, inelastic neutron scattering measurements on
a comparable industrial-grade catalyst operated in an analogous reaction
in fed-batch mode indicate the presence of an oligomeric overlayer
postreaction. This overlayer is thought to be formed via oligomerization
of hydroxyimine or imine species via specific pathways that are identified
within a postulated global reaction scheme.
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stirrer agitation ratesingle-batch reaction returnsmodeoligomeric overlayer postreactionC 6 H 5 CH 2 CH 2 NH 2H 2phenethylamine synthesis processmass balance measurementsmass transport constraintsSustained Product Formationmass balanceMNcarbon-supported Pd catalystsix-addition repeat-batch procedureoptimized product selectivityreaction scheme
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