Heterogeneous catalysis with continuous flow microreactors

Li, Xiaoying; Ünal, Barış; Jensen, Klavs F.

doi:10.1039/c2cy20260c

Cited by 69 publications

(43 citation statements)

References 35 publications

(36 reference statements)

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“…27,28 These are typically offset through the use of high pressures of up to 100 bar, which increases the associated explosion risks. Small-scale microreactors offer a safer, alternative approach to high-pressure hydrogenations with molecular hydrogen, and in conjunction with continuous flow processing offers significant benefits compared to batch processes, related to the unique gas-liquid-solid triphasic reaction conditions present in such transformations, improved safety, and process intensification.…”

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confidence: 99%

Platinum-catalysed cinnamaldehyde hydrogenation in continuous flow

2015

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Platinum is one of the most widely used hydrogenation catalysts. Here we describe the translation of batch reactions to continuous flow, affording tunable C=O versus C=C hydrogenation over a Pt/SiO2 catalyst, resulting in high steady state activity and singlepass yields in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol under mild conditions. Negligible catalyst deactivation occurs under extended flow operation due to removal of reactively-formed poisons from the reaction zone. Process intensification imparts a four-fold enhancement in cinnamyl alcohol productivity.Chemoselectivity underpins 21 st century catalysis, 1, 2 permitting the targeted modification of specific functional groups within complex starting materials, 3-7 notably from biomass-derived feedstocks. 8 Catalytic hydrogenation of organic compounds possessing multiple unsaturated bonds such as α,β-unsaturated aldehydes is particularly challenging, 9-11 necessitating active sites able to discriminate and preferentially activate closely related moieties. Platinum is widely employed in heterogeneously catalysed hydrogenation of diverse functional groups including C=C, 12 C≡C, 13 C=O, 13 C≡N, 14 NO2 15 and aromatics. 15 The selective hydrogenation of allylic and benzylic aldehydes to unsaturated alcohols is a commercially important industrial process within the flavour, fragrance, agrochemical and pharmaceutical sectors, 9, 16 in which active and selective heterogeneous catalysts for such transformations are essential to circumvent the greater thermodynamic stability of C=O relative to C=C bonds. 9 The liquid phase, selective hydrogenation of cinnamaldehyde (CinnALD) to cinnamyl alcohol (CinnOH) illustrated in Scheme 1 is of significant interest due to the widespread use of this allylic alcohol in perfumes and flavourants. [16][17][18][19] Platinum is a promising catalyst for this challenging reaction, in which hydrogenation of the C=C bond is both kinetically and thermodynamically more favourable than the C=O function, 20 and hence the influence of the physicochemical properties of platinum nanoparticles is a topic of much intensive recent investigation in batch reactors. Particle size effects upon CinnOH selectivity have proved controversial, with oleic acid/oleylamine stabilised mono-and bimetallic colloidal Pt nanoparticles reported to exhibit a strong size dependence of CinnOH selectivity, with low coordination sites favoring C=C hydrogenation, 21, 22 whereas Zhu and Zaera reported that CinnOH selectivity was insensitive to the size of silica supported Pt nanoparticles albeit over a narrow size range. 23 Guo et al have shown that confinement of Pt nanoclusters within the cavity of metal-organic frameworks also promotes CinnOH selectivity; with steric constraints on CinnALD believed to hinder C=C planar adsorption with consequent preferential C=O activation. 24 Kinetics of CinnALD hydrogenation are also a function of support properties 25 and hydrogenation pressure. We recently reported a detailed mechanistic study of the structura...

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Platinum-catalysed cinnamaldehyde hydrogenation in continuous flow

2015

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“…In numerous applications in the fine chemical and pharmaceutical industries [15][16][17][18], the properties of the final product depends greatly on mass transfer to the catalyst particle surface [19]. Due to the laminar flow conditions prevalent in microchannels, the transport of reactants to the catalyst surface is often limited by diffusion due to the formation of thick hydrodynamic and mass transfer boundary layers around catalytic particles [20].…”

Section: Introductionmentioning

confidence: 99%

Magnetic actuation of catalytic microparticles for the enhancement of mass transfer rate in a flow reactor

Lisk

Bonnot

Rahman

et al. 2016

Chemical Engineering Journal

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Permanent WRAP URL:http://wrap.warwick.ac.uk/81857 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP URL' above for details on accessing the published version and note that access may require a subscription. AbstractThe effect of periodic changes in particle velocity on mass transfer to the reacting surface of a magnetic particle with a diameter 225 m in laminar flow has been investigated in a microfluidic reactor. The periodic particle motion in a fluid was investigated under a sinusoidal magnetic field generated by a quadrupole arrangement of electromagnets around the reactor. The effect of operating frequency of the rotating magnetic field, intensity of the magnetic field, and phase shift between the two sets of magnets on particle dynamics has been studied. Three particle motion modes have been observed depending on the frequency of the applied field. The mass transfer rate was estimated under steady velocity and variable velocity of the particle using a mass transfer correlation by Feng and Michaelides (Int. J. Heat Mass Transfer 44 (2001) 4445). The validity of this correlation for the case of variable particle velocity has been confirmed with a 2D numerical model, describing actual hydrodynamics and mass transfer towards the particle surface. The mass transfer coefficient *Revised Manuscript (clean for typesetting) Click here to view linked References 2 depends both on the mean particle velocity and the deviation of velocity from the mean value.The periodic movement with variable particle velocity reduces the mass transfer coefficient by 7.6% as compared to steady state motion with the same mean velocity.

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“…It enables the systematic optimization of reaction times and thus helps to avoid side and consecutive reactions, a major goal, e.g., in the preparation of pharmaceuticals and fine chemicals or platform molecules from biomass. [21][22][23] Until now, high-resolution reaction time control is only implemented for open-tubular microreactors, where reactions proceeding via non-catalytic or homogeneously catalyzed pathways usually start by mixing two reaction components and are quenched thermally or chemically. 1,[24][25][26] Inefficient heating, cooling, and mixing may bias the processed data.…”

Section: Introductionmentioning

confidence: 99%

High-performance monoliths in heterogeneous catalysis with single-phase liquid flow

et al. 2017

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Hierarchical, macro-mesoporous silica monoliths with domain sizes (sum of mean macropore size and skeleton thickness) of ∼1 μm are highly efficient supports in heterogeneous catalysis with single-phase liquid flow. Their unprecedented performance regarding low backmixing, the elimination of internal and external diffusive transport limitations, as well as the simultaneous realization of a large (internal and external) surface area of the monolith skeleton allow reactor operation under exclusive reaction control. For experimental characterization, the Knoevenagel condensation was employed with an aminopropylated silica monolith integrated into an on-line coupled, high-pressure reaction-analysis system. It allows precise, fully automated adjustment and control of all relevant reaction parameters and promises a boost in the rapid, reproducible determination of the intrinsic reaction kinetics, in general. Hydrodynamic and reaction kinetic parameters identify extreme plug-flow conditions with this high-surface-area, compact type of microreactor and quasi-homogeneous operation in continuous-flow mode.

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Heterogeneous catalysis with continuous flow microreactors

Cited by 69 publications

References 35 publications

Platinum-catalysed cinnamaldehyde hydrogenation in continuous flow

Platinum-catalysed cinnamaldehyde hydrogenation in continuous flow

Magnetic actuation of catalytic microparticles for the enhancement of mass transfer rate in a flow reactor

High-performance monoliths in heterogeneous catalysis with single-phase liquid flow

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