Optimization of magnetic actuation protocol to enhance mass transfer in solid/liquid microfluidic systems

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The dynamic properties of a 250 m magnetic microparticle in a time varying magnetic field have been studied in a PDMS microreactor with a diameter of 13 mm using a dual coupled quadrupolar arrangement of electromagnets. A sinusoidal applied magnetic field has dictated a circular motion of the particles in the microreactor in the frequency range below 0.6 Hz. Different circular motion modes have been observed at higher frequencies of the applied field. The particular symmetric arrangement of the magnets has allowed a non-steady-state motion with variation in velocity between magnetic poles. The motion of magnetic particle has been described in terms of average velocity and mean square deviation from average velocity. The effect of actuation protocol parameters (frequency, magnetic field strength and phase shift) on particle velocity and acceleration has been investigated. The maximum average velocity of 0.016 m/s has been observed under an optimized actuation protocol. The mass transfer rate towards the particle surface is mainly influenced by the average velocity while the effect of acceleration/deceleration of the particle has an order of magnitude less influence

Magnetic zeolites: novel nanoreactors through radiofrequency heating

Many catalytic applications use conventional heating to increase the temperature to allow the desired reaction. A novel methodology is presented for the preparation of magnetic zeolite-based catalysts, allowing more efficient radiofrequency heating. These nanoreactors are tested in the isomerisation of citronellal with successful results and without any apparent deactivation

The enhancement of direct amide synthesis reaction rate over TiO 2 @SiO 2 @NiFe 2 O 4 magnetic catalysts in the continuous flow under radiofrequency heating

A series of TiO2@SiO2@NiFe2O4 composite magnetic catalyst with a core-double shell structure was synthesized by a sol-gel method. The morphology of the catalysts was studied by XRD, SEM, N2 physisorption and their magnetic properties were examined with magnetometry, and specific absorption rate measurements. The catalytic activity was determined in a direct amide synthesis reaction between aniline and phenylbutyric acid at 150 °C in a fixed bed flow reactor under radiofrequency heating. The intermediate silica layer of the catalyst increased the porosity of the outer titania layer and the specific absorbance rate of the catalyst. The initial reaction rate increased by 61% as compared to a similar core-shell TiO2@NiFe2O4 catalyst showing the detrimental effect of nickel ferrite on titania. The reaction rate was further increased by a factor of 3.5 after a sulfation treatment due to an optimum Lewis acid site strength. The highest specific reaction rate over TiO2@SiO2@NiFe2O4 was observed at a 7.5 wt% sulfate loading which was 2.6 times higher as compared to a mechanical mixture of the same composition. The initial reaction rate decreased by 36% after a period of 55 h on stream. The catalyst activity was restored after a treatment with a H2O2 solution

Active site isolation in bismuth-poisoned Pd/SiO₂ catalysts for selective hydrogenation of furfural

Active site isolation in furfural (FA) hydrogenation was studied by poisoning a Pd catalyst with bismuth. A solution of FA in water was hydrogenated over a 5 wt% Pd/SiO₂ catalyst in a batch reactor at various reaction temperatures and pressures. Furfuryl alcohol (FAL) was an intermediate product which was further hydrogenated into tetrahydrofurfuryl alcohol (TFAL) or cyclopentanone (CPA) and cyclopentanol (CPOL). While application of hydrogen pressure above 30 bar had little effect on the hydrogenation kinetics, a reaction temperature affected product distribution and the main product changed from TFAL (at 50 °C) to FAL (100 and 150 °C). Poisoning the catalyst with Bi decreased the number of available active sites but had little effect on the turn-over frequencies, most likely because of the absence of electronic effects of Bi on Pd nanoparticles. The main reaction product over the Bi-poisoned catalyst was FAL with no FA oligomerisation products. At a reaction temperature of 150 °C, CPA was formed with a 57% yield. Considering that Bi preferentially poisons step sites of Pd, the comparison of the product distribution between the Pd and Pd-Bi catalyst as well as the literature data for the alloy Pd-Cu catalysts indicates that the active site isolation observed in the Pd-Bi catalysts is responsible for the increasing FAL and CPA selectivities and elimination of oligomer by-products

Performance of novel CaO-based sorbents in high temperature CO2 capture under RF heating

The problem of CO₂ mitigation on a small and medium scale can be resolved by developing a combined system of CO₂ capture and its consecutive conversion into valuable products. The first stage of CO₂ looping, however, should be reliable, effective and easy to control and radiofrequency heating, as a new advanced technology, can be used to improve the process. CO₂ absorption and desorption RF units can be installed within power plants and powered during the periods of low energy demand thus stabilizing the electrical grid. In this work, a CaO sorbent produced by template synthesis was studied as a sorbent for a CO₂ looping system under RF heating which offers short start-up times, highly controlled operation, high degree of robustness and low price. The sorbent reached its stable CO₂ capacity of 15.4 wt.% already after 10 temperature cycles (650/850 °C) under RF heating. Higher CO₂ desorption rate and lower degree of the sorbent sintering was observed under RF heating as compared to conventional heating

The enhancement of direct amide synthesis reaction rate over TiO₂@SiO₂@NiFe₂O₄ magnetic catalysts in the continuous flow under radiofrequency heating

A series of TiO₂@SiO₂@NiFe₂O₄ composite magnetic catalyst with a core-double shell structure was synthesized by a sol-gel method. The morphology of the catalysts was studied by XRD, SEM, N₂ physisorption and their magnetic properties were examined with magnetometry, and specific absorption rate measurements. The catalytic activity was determined in a direct amide synthesis reaction between aniline and phenylbutyric acid at 150 °C in a fixed bed flow reactor under radiofrequency heating. The intermediate silica layer of the catalyst increased the porosity of the outer titania layer and the specific absorbance rate of the catalyst. The initial reaction rate increased by 61% as compared to a similar core-shell TiO₂@SiO₂@NiFe₂O₄ catalyst showing the detrimental effect of nickel ferrite on titania. The reaction rate was further increased by a factor of 3.5 after a sulfation treatment due to an optimum Lewis acid site strength. The highest specific reaction rate over TiO₂@SiO₂@NiFe₂O₄ was observed at a 7.5 wt% sulfate loading which was 2.6 times higher as compared to a mechanical mixture of the same composition. The initial reaction rate decreased by 36% after a period of 55 h on stream. The catalyst activity was restored after a treatment with a H₂O₂ solution

Highly dispersed supported Pt-Sn/TiO2 catalysts derived from mixed metal cluster precursors for selective hydrogenation of [alpha],[beta]-unsaturated aldehydes

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