Co-reporter:E. Kertalli, N. Kosinov, J.C. Schouten, T.A. Nijhuis
Chemical Engineering Journal 2017 Volume 307(Volume 307) pp:
Publication Date(Web):1 January 2017
DOI:10.1016/j.cej.2016.07.084
•Packed bed membrane reactor for propylene oxide (PO) direct synthesis in a liquid phase.•Safe and mild operating reaction conditions.•Improvement of PO selectivity by reducing the propylene hydrogenation.•Influence of the reactor configuration on the hydrogen efficiency.In the present work, the direct synthesis of propylene oxide (PO) in the liquid phase is successfully performed in a packed bed membrane reactor. We show that this engineering device can be implemented under mild reaction conditions (low temperature and pressure) and outside the explosive regime (low hydrogen concentration), making it appealing for industrial applications. The ceramic membrane allows for a separate feed of the reactants, therefore addressing the PO selectivity issue related to the propylene hydrogenation. The reaction is operated in a continuous methanol flow fed with propylene inside the tubular membrane; hydrogen and oxygen are fed through the porous material. We observe that the feeding strategy of the reactants has an important effect on key parameters such as PO selectivity and productivity. By separating propylene from hydrogen, the propane formation was reduced with respect to conventional packed bed reactors. Moreover, the addition of small amounts of NaBr to the reaction medium increases the catalytic activity to PO, but also to propane formation. Therefore, this study provides a good starting point in the design of a membrane reactor device for the direct synthesis of PO where the main limitations such as propylene hydrogenation and water formation can be addressed.
Co-reporter:L.A. Truter, V. Ordomsky, J.C. Schouten, T.A. Nijhuis
Microporous and Mesoporous Materials 2016 Volume 226() pp:424-432
Publication Date(Web):15 May 2016
DOI:10.1016/j.micromeso.2016.02.016
•A method for the incorporation of zeolite coatings in glass chip-microreactors is described.•A glass pretreatment provides a single step for the activation of the microchannel surface resulting in an improved zeolite coating.•The zeolite coatings formed are uniform, have a high surface area and Brønsted acidity.A method for the incorporation of zeolite coatings in glass chip-based microreactors has been developed. The use of a fluoride-based hydrothermal pretreatment method provides a microchannel surface with high roughness, good wettability, and a silica nutrient source in a single pretreatment step. This pretreated glass surface is ideal for the subsequent in-situ zeolite hydrothermal synthesis which enables the formation of zeolite coatings within the chip-based microreactor. The optimization of the zeolite precursor suspension in terms of aluminium and silica source and amount, allows for the formation of zeolite coatings which are uniform, have high surface area and high Brønsted acidity.
Co-reporter:Klaas T. Zuidhof; Mart H. J. M. de Croon; Jaap C. Schouten;Johan T. Tinge
Journal of Chemical & Engineering Data 2015 Volume 60(Issue 4) pp:1056-1062
Publication Date(Web):March 12, 2015
DOI:10.1021/je500836b
We have determined the density, dynamic viscosity, and surface tension of liquid phase Beckmann rearrangement mixtures, consisting of ε-caprolactam and fuming oleum. These important properties have been measured in wide ranges of both temperature and molar ratios of acid and ε-caprolactam, covering conditions that are of relevance for industrial production of ε-caprolactam from cyclohexanone oxime, i.e., T = (293 to 393) K and ([H2SO4] + [SO3])/[ε-caprolactam] = (1.4 to 2.6). The results were correlated as functions of temperature and composition. The density of oleum/ε-caprolactam mixtures shows a linear relationship with both temperature and composition. A modification of the traditional Reynolds model proved to be the most suitable way to represent the dynamic viscosity of these Beckmann rearrangement mixtures. The reduction of the surface tension with temperature is described with a power law expression, while the decrease of the surface tension with increasing molar ratios of acid over ε-caprolactam is described with a linear relationship. These results can be applied to design liquid phase Beckmann rearrangement processes on both large scale and microscale.
Co-reporter:Jun Yue, Evgeny V. Rebrov and Jaap C. Schouten
Lab on a Chip 2014 vol. 14(Issue 9) pp:1632-1649
Publication Date(Web):12 Feb 2014
DOI:10.1039/C3LC51307F
We report a three-phase slug flow and a parallel-slug flow as two major flow patterns found under the nitrogen–decane–water flow through a glass microfluidic chip which features a long microchannel with a hydraulic diameter of 98 μm connected to a cross-flow mixer. The three-phase slug flow pattern is characterized by a flow of decane droplets containing single elongated nitrogen bubbles, which are separated by water slugs. This flow pattern was observed at a superficial velocity of decane (in the range of about 0.6 to 10 mm s−1) typically lower than that of water for a given superficial gas velocity in the range of 30 to 91 mm s−1. The parallel-slug flow pattern is characterized by a continuous water flow in one part of the channel cross section and a parallel flow of decane with dispersed nitrogen bubbles in the adjacent part of the channel cross section, which was observed at a superficial velocity of decane (in the range of about 2.5 to 40 mm s−1) typically higher than that of water for each given superficial gas velocity. The three-phase slug flow can be seen as a superimposition of both decane–water and nitrogen–decane slug flows observed in the chip when the flow of the third phase (viz. nitrogen or water, respectively) was set at zero. The parallel-slug flow can be seen as a superimposition of the decane–water parallel flow and the nitrogen–decane slug flow observed in the chip under the corresponding two-phase flow conditions. In case of small capillary numbers (Ca ≪ 0.1) and Weber numbers (We ≪ 1), the developed two-phase pressure drop model under a slug flow has been extended to obtain a three-phase slug flow model in which the ‘nitrogen-in-decane’ droplet is assumed as a pseudo-homogeneous droplet with an effective viscosity. The parallel flow and slug flow pressure drop models have been combined to obtain a parallel-slug flow model. The obtained models describe the experimental pressure drop with standard deviations of 8% and 12% for the three-phase slug flow and parallel-slug flow, respectively. An example is given to illustrate the model uses in designing bifurcated microchannels that split the three-phase slug flow for high-throughput processing.
Co-reporter:Narendra G. Patil, Faysal Benaskar, Evgeny V. Rebrov, Jan Meuldijk, Lubertus A. Hulshof, Volker Hessel, and Jaap C. Schouten
Organic Process Research & Development 2014 Volume 18(Issue 11) pp:1400-1407
Publication Date(Web):July 17, 2014
DOI:10.1021/op500064k
A new scale-up concept for microwave assisted flow processing is presented where modular scale-up is achieved by implementing microwave cavities in series. The scale-up concept is demonstrated for case studies of a packed-bed reactor and a wall-coated tubular reactor. With known kinetics and reaction temperature, a packed-bed reactor gave a conversion of 99% with the highest production rate of 170 kgprod/kgcat·h for esterification of acetic acid and ethanol catalyzed by ion-exchange resin in 18 cavities. A similar approach for a multicomponent reaction of benzaldehyde, piperidine, and phenylacetylene catalyzed by a thin Cu film in a wall-coated tubular reactor gave 99% conversion with the highest production rate of 7740 kgprod/kgcat·h in 28 cavities. In both cases, the pseudo first order reaction rate with respect to the limiting reactant yielded a typical rise in conversion and production rate. In a packed-bed reactor-heat exchanger operated at a temperature between 343 and 348 K, the conversion in the esterification reaction increased from 22% to 88% when the number of cavities was increased from one to eight. The experimental conversions matched the predictions of a packed bed reactor model within 5%. The production capacity in flow reactors, restricted to smaller sizes due to a limited microwave penetration depth and dominated mainly by the reaction kinetics, was increased by modular scale-up with implementation of the microwave multicavity assembly.
Co-reporter:Narendra G. Patil;Faysal Benaskar;Evgeny V. Rebrov;Jan Meuldijk;Lumbertus A. Hulshof†;Volker Hessel;Jaap C. Schouten
Chemical Engineering & Technology 2014 Volume 37( Issue 10) pp:1645-1653
Publication Date(Web):
DOI:10.1002/ceat.201400118
Abstract
A feasibility study in state-of-the-art multi- and monomode microwave cavities was conducted to outline important functionalities necessary in a microwave setup for continuous fine-chemicals synthesis. For multimode operation, the heating efficiency depends on the position as well as on the volume distribution of the load. For monomode operation, the heating efficiency does not depend on the axial position and has a maximum with respect to the load diameter. Based on this study, a microwave setup consisting of four cavities was designed and constructed. The setup provided a defined microwave field pattern and allowed focusing of the microwave power. A near-uniform distribution of microwave energy in all four cavities of the setup was achieved at reduced grid to applicator losses.
Co-reporter:Joost Rooze, Evgeny V. Rebrov, Jaap C. Schouten, Jos T.F. Keurentjes
Ultrasonics Sonochemistry 2013 Volume 20(Issue 1) pp:1-11
Publication Date(Web):January 2013
DOI:10.1016/j.ultsonch.2012.04.013
The physics and chemistry of nonlinearly oscillating acoustic cavitation bubbles are strongly influenced by the dissolved gas in the surrounding liquid. Changing the gas alters among others the luminescence spectrum, and the radical production of the collapsing bubbles. An overview of experiments with various gas types and concentration described in literature is given and is compared to mechanisms that lead to the observed changes in luminescence spectra and radical production. The dissolved gas type changes the bubble adiabatic ratio, thermal conductivity, and the liquid surface tension, and consequently the hot spot temperature. The gas can also participate in chemical reactions, which can enhance radical production or luminescence of a cavitation bubble. With this knowledge, the gas content in cavitation can be tailored to obtain the desired output.Highlights► The manuscript describes literature work on the influence of gas content and gas properties in cavitation. ► Experimental and theoretical research on single and multi-bubble cavitation is presented. ► The relevant gas parameters are designated and discussed.
Co-reporter:Faysal Benaskar, Volker Engels, Narendra G. Patil, Evgeny V. Rebrov, Jan Meuldijk, Volker Hessel, Lumbertus A. Hulshof, Andrew E. H. Wheatley, and Jaap. C. Schouten
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 51) pp:18206-18214
Publication Date(Web):December 2, 2013
DOI:10.1021/ie402956n
A parametric study of the factors that influence C–O bond formation reactions has been carried out to elucidate the mechanism by which copper mediates the Ullmann-type nucleophilic aromatic substitution (SNAr) of 4-chloropyridine with potassium phenolate. Process conditions such as temperature, reactant concentrations, catalyst concentration, and amounts of solubilizing additive were varied to obtain the kinetic data. Both reactant and product concentration were found to have a significant effect on the reaction rate. An increased concentration of 18-crown-6 ether, used as an alkali metal solubilizing agent for potassium phenolate, proved to be effective only for low conversions, whereas an inhibited phenolate complexation at high product concentrations was observed. An apparent activation energy of 55 kJ·mol–1 was observed for a Cu0 catalyst in the liquid-phase coupling reaction in a temperature range of 100–150 °C. It was demonstrated that a Langmuir–Hinshelwood kinetic model is mechanistically most likely to be obeyed for this type of surface reaction. A maximum adsorption enthalpy on Cu was found for the product, 4-phenoxypyridine, followed by the reactants phenolate and 4-chloropyridine, respectively.
Co-reporter:M. Al-Rawashdeh, J. Zalucky, C. Müller, T. A. Nijhuis, V. Hessel, and J. C. Schouten
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 33) pp:11516-11526
Publication Date(Web):2017-2-22
DOI:10.1021/ie4009277
This paper provides a proof of concept for the capability of the barrier-based micro-/millichannels reactor (BMMR) to number-up gas–liquid Taylor flow under reactive flow conditions. The hydrogenation of phenylacetylene to styrene and ethylbenzene using homogeneous cationic rhodium catalysts [Rh(NBD)(PPh3)2]BF4] (NBD = norbornadiene) was used as a model reaction. First, a parametric study in a semicontinuous batch reactor was made by changing the hydrogen pressure, the catalyst concentrations, and the initial concentrations of phenylacetylene and styrene. A mechanism for this reaction system has been proposed by Esteruelas et al. ( J. Org. Chem. 1998, 49−53). This mechanism was extended here to develop a kinetic model which predicts the experimental result within an accuracy of 20%. Catalyst deactivation was observed and incorporated in the kinetic model. Second, the reaction was conducted in the BMMR. The reactant and product concentrations of a single channel were compared to those of eight parallel channels combined. For 95% of the obtained results, the difference in concentrations between the single channel and the eight channels was within ±10% and depended on the gas and liquid flow rates. As a proof of concept, the number-up concept of gas–liquid Taylor flow in the BMMR under reactive flow conditions has been successfully realized.
Co-reporter:N. T. Zuidhof;M. H. J. M. de Croon;J. C. Schouten;J. T. Tinge
Chemical Engineering & Technology 2013 Volume 36( Issue 8) pp:1387-1394
Publication Date(Web):
DOI:10.1002/ceat.201300088
Abstract
Beckmann rearrangement of cyclohexanone oxime dissolved in cyclooctane with oleum to ϵ-caprolactam was demonstrated in a microreactor setup with internal recirculation operated in continuous mode. The core of the setup comprised a 316 stainless-steel micromixer consisting of 17 split-and-recombine units connected to a delay loop, a 316 stainless-steel microchannel reactor with an internal diameter of 0.250 mm and a length of 0.50 m. At 100 °C, the conversion of cyclohexanone oxime was complete and the selectivity towards ϵ-caprolactam was approximately 99 %. The solvent cyclooctane reduces the observed purity of the produced oleum/ϵ-caprolactam. This reduction in purity might be a severe hurdle for usage of a solvent on the industrial scale in the Beckmann rearrangement of cyclohexanone oxime in oleum to ϵ-caprolactam.
Co-reporter:J. Yue;T. A. Nijhuis ;J. C. Schouten
Chemical Engineering & Technology 2013 Volume 36( Issue 4) pp:611-626
Publication Date(Web):
DOI:10.1002/ceat.201200559
Abstract
Numerical analysis is presented for gas absorption accompanied by a second-order reaction into a liquid layer of finite thickness in laminar flow, with the gas-phase mass transfer resistance and the axial decrease of the gas-phase solute concentration due to absorption being taken into account. Both cocurrent and countercurrent flow modes are analyzed, where the presence of significant resistance or axial decrease of the solute concentration in the gas phase can lead to substantially lower rates of gas absorption than those found when the influence of gas-phase mass transfer is not considered. Approximate expressions describing the exact numerical solution to the enhancement factor in the cocurrent flow mode are developed and can be extrapolated for estimating the enhancement factor in a more general case of a (1, n)-th-order reaction in which the influence of gas-phase mass transfer cannot be neglected.
Co-reporter:Frans Visscher, André Bieberle, Markus Schubert, John van der Schaaf, Mart H. J. M. de Croon, Uwe Hampel, and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 51) pp:16670
Publication Date(Web):November 30, 2012
DOI:10.1021/ie301439s
This paper presents the volume fractions of n-heptane and water measured in a rotor-stator spinning disc reactor. The volume fractions were measured using γ-ray tomography and photographic image analysis. The volume fractions were determined as a function of rotational disc speed, flow ratio, position in the reactor, and rotor material. In addition, the effect of the density difference between water and n-heptane was determined by dissolving potassium iodide in the water phase. Below a rotational disc speed of 75 rpm the volume fraction measured by tomography and photographic image analysis are within 10% deviation. For low rotational disc speeds, the n-heptane volume fraction decreases slightly with increasing rotational disc speed: the centrifugal force accelerates the larger n-heptane droplets to the center. At higher rotational disc speeds the droplets become smaller accordingly, the friction between the phases determines the flow, and the n-heptane volume fraction becomes equal to the n-heptane to total flow ratio. An increase in density difference from 0.31 to 0.79 kg dm–3 did not influence the volume fractions.
Co-reporter:Narendra G. Patil, Faysal Benaskar, Evgeny V. Rebrov, Jan Meuldijk, Lumbertus A. Hulshof, Volker Hessel, and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 44) pp:14344
Publication Date(Web):October 3, 2012
DOI:10.1021/ie300754z
The productivity of microwave-assisted continuous specialty chemical synthesis has been brought to a commercially interesting scale of 1 kg/day. To that end, a counter-current multitubular millireactor/heat exchanger (MTMR) assembly has been developed with the reactant flow through millitubular reactors, while the coolant flows in the shell side. The efficiency of microwave absorption under continuous operation in a single mode microwave cavity has been improved with the deposition of a thin (350 ± 40 nm) Cu film on the inner walls of the reactor tubes. This design ultimately resulted in an enhanced product (1,3-diphenyl-2-propynyl piperidine) yield of a multicomponent reaction (of piperidine, benzaldehyde, and phenylacetylene). The Cu film also improved the uniformity of microwave energy absorption in the reactor tubes along the radial direction. A near-isothermal operation was achieved by cooling with a counter-current flow of a microwave transparent coolant in the outer shell of the MTMR. A production rate of 333 ± 11 kgprod/(kgcat·h) was achieved in a single microwave cavity at 373 ± 5 K and at a total reactant flow rate of 1.66 × 10–9 m3/s. The average production rate of 1,3-diphenyl-2-propynyl piperidine in the MTMR assembly (six parallel tubes in a shell and tube reactor/heat exchanger) was 93% of the production rate in a single tube due to a slightly uneven flow and temperature distribution. Kinetically determined mean Cu film temperature was 477 ± 10 K. Although the reactor tubes were placed at an equal distance from axial symmetry (six parallel tubes in a hexagonal arrangement), a maximum temperature deviation of 8.0 ± 0.5 K was observed over the reactor tubes. The parallelization approach was demonstrated to be successful for scale up of continuously operated microwave reactors.
Co-reporter:M.H. Halabi, M.H.J.M. de Croon, J. van der Schaaf, P.D. Cobden, J.C. Schouten
International Journal of Hydrogen Energy 2012 Volume 37(Issue 5) pp:4516-4525
Publication Date(Web):March 2012
DOI:10.1016/j.ijhydene.2011.12.003
This paper presents an experimental study for a newly modified K2CO3-promoted hydrotalcite material as a novel high capacity sorbent for in-situ CO2 capture. The sorbent is employed in the sorption enhanced steam reforming process for an efficient H2 production at low temperature (400–500 °C). A new set of adsorption data is reported for CO2 adsorption over K-hydrotalcite at 400 °C. The equilibrium sorption data obtained from a column apparatus can be adequately described by a Freundlich isotherm. The sorbent shows fast adsorption rates and attains a relatively high sorption capacity of 0.95 mol/kg on the fresh sorbent. CO2 desorption experiments are conducted to examine the effect of humidity content in the gas purge and the regeneration time on CO2 desorption rates. A large portion of CO2 is easily recovered in the first few minutes of a desorption cycle due to a fast desorption step, which is associated with a physi/chemisorption step on the monolayer surface of the fresh sorbent. The complete recovery of CO2 was then achieved in a slower desorption step associated with a reversible chemisorption in a multi-layer surface of the sorbent. The sorbent shows a loss of 8% of its fresh capacity due to an irreversible chemisorption, however, it preserves a stable working capacity of about 0.89 mol/kg, suggesting a reversible chemisorption process. The sorbent also presents a good cyclic thermal stability in the temperature range of 400–500 °C.Highlights► K2CO3-promoted hydrotalcite material is experimentally studied as a novel high capacity sorbent for in-situ CO2 capture. ► The sorbent shows fast adsorption rates and attains a relatively high sorption capacity. ► The sorbent shows good cyclic and thermal stability in the temperature range of 400–500 °C.
Co-reporter:Jovan Jovanović, Evgeny V. Rebrov, T. A. (Xander) Nijhuis, M. T. Kreutzer, Volker Hessel, and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 2) pp:1015-1026
Publication Date(Web):November 16, 2011
DOI:10.1021/ie200715m
The capillary microreactor, with four stable operating flow patterns and a throughput range from grams per hour to kilograms per hour, presents an attractive alternative to chip-based and microstructured reactors for laboratory- and pilot-scale applications. In this article, results for the extraction of 2-butanol from toluene under different flow patterns in a water/toluene flow in long capillary microreactors are presented. The effects of the capillary length (0.4–2.2 m), flow rate (0.1–12 mL/min), and aqueous-to-organic volumetric flow ratio (0.25–9) on the slug, bubbly, parallel, and annular flow hydrodynamics were investigated. Weber-number-dependent flow maps were composed for capillary lengths of 0.4 and 2 m that were used to interpret the flow pattern formation in terms of surface tension and inertia forces. When the capillary length was decreased from 2 to 0.4 m, a transition from annular to parallel flow was observed. The capillary length had little influence on slug and bubbly flows. The flow patterns were evaluated in terms of stability, surface-to-volume ratio, throughput, and extraction efficiency. Slug and bubbly flow operations yielded 100% thermodynamic extraction efficiency, and increasing the aqueous-to-organic volumetric ratio to 9 allowed for 99% 2-butanol extraction. The parallel and annular flow operating windows were limited by the capillary length, thus yielding maximum 2-butanol extractions of 30% and 47% for parallel and annular flows, respectively.
Co-reporter:M.H. Halabi, M.H.J.M. de Croon, J. van der Schaaf, P.D. Cobden, J.C. Schouten
International Journal of Hydrogen Energy 2012 Volume 37(Issue 6) pp:4987-4996
Publication Date(Web):March 2012
DOI:10.1016/j.ijhydene.2011.12.025
This paper presents an experimental investigation for an improved process of sorption-enhanced steam reforming of methane in an admixture fixed bed reactor. A highly active Rh/CeαZr1−αO2 catalyst and K2CO3-promoted hydrotalcite are utilized as novel catalyst/sorbent materials for an efficient H2 production with in situ CO2 capture at low temperature (450–500 °C). The process performance is demonstrated in response to temperature (400–500 °C), pressure (1.5–6.0 bar), and steam/carbon ratio (3–6). Thus, direct production of high H2 purity and fuel conversion >99% is achieved with low level of carbon oxides impurities (<100 ppm). A maximum enhancement of 162% in CH4 conversion is obtained at a temperature of 450 °C and a pressure of 6 bar using a steam/carbon molar ratio of 4. The high catalyst activity of Rh yields an enhanced CH4 conversion using much lower catalyst/sorbent bed composition and much smaller reactor size than Ni-based sorption enhanced processes at low temperature. The cyclic stability of the process is demonstrated over a series of 30 sorption/desorption cycles. The sorbent exhibited a stable performance in terms of the CO2 working sorption capacity and the corresponding CH4 conversion obtained in the sorption enhanced process. The process showed a good thermal stability in the temperature range of 400–500 °C. The effects of the sorbent regeneration time and the purge stream humidity on the achieved CH4 conversion are also studied. Using steam purge is beneficial for high degree of CO2 recovery from the sorbent.Highlights► Sorption-enhanced methane steam reforming is experimentally demonstrated. ► A highly active Rh/CeαZr1−αO2 catalyst and K2CO3-promoted hydrotalcite are utilized. ► The process is studied in response to temperature (400–500 °C), pressure (1.5–6.0 bar), and steam/carbon ratio (3–6). ► Direct production of high H2 purity and fuel conversion >99% is achieved with low level of carbon oxides impurities (<100 ppm).
Co-reporter:J. Yue;E. V. Rebrov;J. C. Schouten
Chemical Engineering & Technology 2012 Volume 35( Issue 8) pp:1473-1485
Publication Date(Web):
DOI:10.1002/ceat.201200160
Abstract
Numerical analysis on gas absorption accompanied by an instantaneous reaction or a second-order reaction into a liquid layer of finite thickness in laminar flow is presented. A similar influence of the reactant diffusivity ratio, the Fourier number, and the Hatta number on the enhancement factor is reported compared to the ideal situation in which the liquid layer is in plug flow motion. Approximate enhancement factor expressions are developed for both reaction cases by analogy to the plug flow situation, where the predictions according to the original penetration theory tend to give erroneous results in the enhancement factor at Fourier numbers above 0.1. The developed expressions in the case of a second-order reaction can be extrapolated for estimating the enhancement factor in the more general case of a (1, n)-th-order reaction.
Co-reporter:N. T. Zuidhof;M. H. J. M. de Croon;J. C. Schouten;J. T. Tinge
Chemical Engineering & Technology 2012 Volume 35( Issue 7) pp:1257-1261
Publication Date(Web):
DOI:10.1002/ceat.201100550
Abstract
The selectivity and conversion of the sulfuric acid-catalyzed Beckmann rearrangement of cyclohexanone oxime, dissolved in cyclooctane, to ϵ-caprolactam are determined in a microreactor for conditions with a high concentration of ϵ-caprolactam. The microreactor consists of a low-temperature mixing zone followed by a high-temperature reaction zone. The mixing is conducted in a split-and-recombine micromixer and a microchannel at 65 °C, followed immediately by a second microchannel at 100–127 °C to obtain complete conversion. Under these conditions a selectivity of 99 % is achieved. The residence time of the reactants in the microreactor setup is about 10 s. In literature, a selectivity of about 95 % for the same reaction in a similar setup is reported, but at a uniform temperature of 120–130 °C for mixing and reaction. So, suppressing the reaction during mixing is a major tool to enhance the selectivity to ϵ-caprolactam.
Co-reporter:J. Yue;E. V. Rebrov;J. C. Schouten
Chemical Engineering & Technology 2012 Volume 35( Issue 5) pp:859-869
Publication Date(Web):
DOI:10.1002/ceat.201200071
Abstract
Gas absorption accompanied by an irreversible chemical reaction of first-order or second-order in a liquid layer of finite thickness in plug flow has been investigated. The analytical solution to the enhancement factor has been derived for the case of a first-order reaction, and the exact solution to the enhancement factor has been obtained via numerical simulation for the case of a second-order reaction. The enhancement factor in both cases is presented as a function of the Fourier number and tends to deviate from the prediction of the existing enhancement factor expressions based on the penetration theory at Fourier numbers above 0.1 due to the absence of a well-mixed bulk region in the liquid layer. Approximate enhancement factor expressions that describe the analytical and exact solutions with an accuracy of 5 % and 9 %, respectively, have been proposed.
Co-reporter:J. Yue;E. V. Rebrov;J. C. Schouten
Chemical Engineering & Technology 2012 Volume 35( Issue 4) pp:679-692
Publication Date(Web):
DOI:10.1002/ceat.201100686
Abstract
An approximate analysis of gas absorption with instantaneous reaction in a liquid layer of finite thickness in plug flow is presented. An approximate solution to the enhancement factor for the case of unequal diffusivities between the dissolved gas and the liquid reactant has been derived and validated by numerical simulation. Depending on the diffusivity ratio of the liquid reactant to the dissolved gas (γ), the enhancement factor tends to be either lower or higher than the prediction of the classical enhancement factor equation based on the penetration theory (Ei,pen) at Fourier numbers typically larger than 0.1. An empirical correlation valid for all Fourier numbers is proposed to allow a quick estimation of the enhancement factor, which describes the prediction of the approximate solution and the simulation data with a relative error below 5 % under the investigated conditions (γ = 0.3–4, Ei,pen = 2–1000).
Co-reporter:M.H. Halabi, M.H.J.M. de Croon, J. van der Schaaf, P.D. Cobden, J.C. Schouten
Fuel 2012 Volume 99() pp:154-164
Publication Date(Web):September 2012
DOI:10.1016/j.fuel.2012.04.016
This paper presents a fundamental model-based analysis for the applicability of integration of a highly active Rh/CeαZr1−αO2 catalyst with two candidate CO2 sorbents for pure H2 production in low temperature sorption-enhanced steam reforming of methane. K-promoted hydrotalcite and lithium zirconate solids are considered in the investigation as CO2 sorbents. The process is analyzed using multi-scale modeling levels of a heterogeneous particle-based model, a heterogeneous bulk-scale model, and a homogenous bulk-scale model. The presence of this active catalyst dictates strict requirements on the sorbent in terms of fast adsorption kinetics for an efficient process performance. The maximum CH4 conversion enhancement is determined to be a strong function of sorption kinetics. This enhancement is not affected by a higher sorbent capacity at slow adsorption kinetics. The process is studied using two fixed bed configurations of an integrated dual function particle and an admixture bed of catalyst/sorbent particles. Optimal operating conditions for the hydrotalcite-based system are identified to provide CH4 conversion of 98% with high H2 purity of 99.8% and low CO2 contamination (<250 ppm). The lithium zirconate-based system can provide CH4 conversion and H2 purity of 99.9% at identical conditions. Based on the end application of H2 produced, the process can be tuned to feed gas turbine cycles, fuel cells, or petrochemical plants.Highlights► Pure H2 production using low temperature sorption-enhanced steam reforming of methane. ► The applicability of integration of a highly active Rh/CeαZr1−αO2 catalyst with two candidate CO2 sorbents is studied. ► Multi-level modeling scales are constructed. ► The maximum CH4 conversion enhancement is a strong function of sorption kinetics.
Co-reporter:Faysal Benaskar;Dr. Volker Engels;Dr. Evgeny V. Rebrov;Narendra G. Patil;Dr. Jan Meuldijk;Dr. Peter C. Thüne;Dr. Pieter C. M. M. Magusin;Brahim Mezari;Dr. Volker Hessel;Dr. Lumbertus A. Hulshof;Dr. Emiel J. M. Hensen;Dr. Andrew E. H. Wheatley;Dr. Jaap C. Schouten
Chemistry - A European Journal 2012 Volume 18( Issue 6) pp:1800-1810
Publication Date(Web):
DOI:10.1002/chem.201102151
Abstract
New routes for the preparation of highly active TiO2-supported Cu and CuZn catalysts have been developed for CO coupling reactions. Slurries of a titania precursor were dip-coated onto glass beads to obtain either structured mesoporous or non-porous titania thin films. The Cu and CuZn nanoparticles, synthesized using a reduction by solvent method, were deposited onto calcined films to obtain a Cu loading of 2 wt %. The catalysts were characterized by inductively coupled plasma (ICP) spectroscopy, temperature-programmed oxidation/reduction (TPO/TPR) techniques, 63Cu nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (S/TEM-EDX) and X-ray photo-electron spectroscopy (XPS). The activity and stability of the catalysts obtained have been studied in the CO Ullmann coupling of 4-chloropyridine and potassium phenolate. The titania-supported nanoparticles retained catalyst activity for up to 12 h. However, catalyst deactivation was observed for longer operation times due to oxidation of the Cu nanoparticles. The oxidation rate could be significantly reduced over the CuZn/TiO2 catalytic films due to the presence of Zn. The 4-phenoxypyridine yield was 64 % on the Cu/nonporous TiO2 at 120 °C. The highest product yield of 84 % was obtained on the Cu/mesoporous TiO2 at 140 °C, corresponding to an initial reaction rate of 104 mmol gcat−1 s−1. The activation energy on the Cu/mesoporous TiO2 catalyst was found to be (144±5) kJ mol−1, which is close to the value obtained for the reaction over unsupported CuZn nanoparticles (123±3 kJ mol−1) and almost twice the value observed over the catalysts deposited onto the non-porous TiO2 support (75±2 kJ mol−1).
Co-reporter:Serdar Celebi, T. Alexander Nijhuis, John van der Schaaf, Frank A. de Bruijn, Jaap C. Schouten
Carbon 2011 Volume 49(Issue 2) pp:501-507
Publication Date(Web):February 2011
DOI:10.1016/j.carbon.2010.09.048
Homogeneous deposition precipitation (HDP) of nickel has been investigated for the growth of carbon nanofibers (CNFs) on carbon paper for use in proton exchange membrane fuel cells as a gas diffusion layer. Selective CNF growth on only one side of carbon paper is required to transfer the generated protons on platinum catalyst fast enough to avoid any proton mass transfer losses. For this purpose, a mask deposition holder was designed to deposit the nickel hydroxide which is reduced to nickel with hydrogen before catalyzing the CNF growth. The deposition time effect on the catalyst loading and the effect of the catalyst loading variation on the yield of CNF growth on carbon paper were investigated. Both effects had linear dependence in the region of interest. The HDP of nickel on the carbon paper ensured strong attachment of nickel crystals on the carbon paper fibers keeping the porosity at a promising level with an acceptable BET area of CNFs. The HDP method provides fine-tuning in the CNF layer thickness only on one side of the carbon paper with good reproducibility in the deposition of nickel.Graphical abstractResearch highlights► An advanced catalyst support layer using CNF is developed for PEM fuel cells. ► Nickel hydroxide is deposited controllably on a single side of carbon paper. ► CNFs are grown on reduced nickel leaflet layers.
Co-reporter:L. N. Protasova, E. V. Rebrov, K. L. Choy, S. Y. Pung, V. Engels, M. Cabaj, A. E. H. Wheatley and J. C. Schouten
Catalysis Science & Technology 2011 vol. 1(Issue 5) pp:768-777
Publication Date(Web):26 May 2011
DOI:10.1039/C1CY00074H
Vertically aligned ZnO nanowires (NWs) with a length of 1.5–10 μm and a mean diameter of ca. 150 nm were grown by chemical vapour deposition onto a c-oriented ZnO seed layer which was deposited by atomic layer deposition on Si substrates. The substrates were then spin-coated with an ethanol solution containing Pd nanoparticles with an average size of 2.7 and 4.5 nm. A homogeneous distribution of the Pd nanoparticles on ZnO NWs has been obtained using both Pd particle series. The catalytic activity of the ZnO NWs and Pd/ZnO NWs catalysts was measured in the semihydrogenation of 2-methyl-3-butyn-2-ol at 303-343 K and a pressure of 2–10 bar. The effect of the solvent used on the catalytic performance of the Pd/ZnO NWs catalyst was studied. The Pd/ZnO catalysts showed alkene selectivity of up to 95% at an alkyne conversion of 99%. A kinetic model is proposed to explain the activity and selectivity of the ZnO support and Pd/ZnO catalysts.
Co-reporter:Joost Rooze, Evgeny V. Rebrov, Jaap C. Schouten, Jos T.F. Keurentjes
Ultrasonics Sonochemistry 2011 Volume 18(Issue 1) pp:209-215
Publication Date(Web):January 2011
DOI:10.1016/j.ultsonch.2010.05.007
The sonochemical oxidation efficiency (ηox)(ηox) of a commercial titanium alloy ultrasound horn has been measured using potassium iodide as a dosimeter at its main resonance frequency (20 kHz) and two higher resonance frequencies (41 and 62 kHz). Narrow power and frequency ranges have been chosen to minimise secondary effects such as changing bubble stability, and time available for radical diffusion from the bubble to the liquid. The oxidation efficiency, ηoxηox, is proportional to the frequency and to the power transmitted to the liquid (275 mL) in the applied power range (1–6 W) under argon. Luminol radical visualisation measurements show that the radical generation rate increases and a redistribution of radical producing zones is achieved at increasing frequency. Argon, helium, air, nitrogen, oxygen, and carbon dioxide have been used as saturation gases in potassium iodide oxidation experiments. The highest ηoxηox has been observed at 5 W under air at 62 kHz. The presence of carbon dioxide in air gives enhanced nucleation at 41 and 62 kHz and has a strong influence on ηoxηox. This is supported by the luminol images, the measured dependence of ηoxηox on input power, and bubble images recorded under carbon dioxide. The results give insight into the interplay between saturation gas and frequency, nucleation, and their effect on ηoxηox.
Co-reporter:Maria A. Leon, Roman Tschentscher, T. Alexander Nijhuis, John van der Schaaf, and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 6) pp:3184-3193
Publication Date(Web):February 15, 2011
DOI:10.1021/ie101962g
Rotating foam stirrer reactors have a promising application in multiphase reactions. In this reactor, highly porous open-celled materials, solid foams, are used both as a catalyst support and as stirrer blades. One of the advantages of such a foam stirrer is easy catalyst handling. This paper presents a preparation method for catalysts on solid foam supports. The performance of the alumina foam catalysts is tested in the hydrogenation of a functionalized alkyne. A stable and homogeneous catalytic coating was deposited on aluminum foams by a combination of anodization and wash coating using the slurry method. Anodization produced a rough and porous material that improved the adhesion of the catalytic coating. The use of a slurry with a bimodal particle size distribution increased the catalytic coating stability. The mass loss of the catalytic coating after applying ultrasonic vibrations was less than 10 wt %, which indicates a good adhesion. A high specific surface area was achieved by increasing the foam cell density, that is, the number of pores per linear inch (ppi), and the catalytic coating thickness. With the wash-coating method, catalytic coatings were produced having a thickness between 10 and 40 μm, a porosity of around 50%, and a specific surface area up to 28.5 m2/gfoam. The hydrogenation of 3-methyl-1-pentyn-3-ol was chosen as the test reaction. Internal and external mass transfers limit the reaction rate of this fast reaction. High activity and selectivity were reached by combining a high specific surface area with a thin catalytic coating on the foam. Increasing the foam cell density up to 20 ppi led to enhanced liquid−solid mass transfer because of the high specific surface area combined with the fast refreshment of the catalyst surface. Coating thicknesses of less than 20 μm led to improved internal mass transfer due to shorter diffusion paths.
Co-reporter:J. Jovanovi&x107;;W. Hengeveld;E. V. Rebrov;T. A. Nijhuis;V. Hessel;J. C. Schouten
Chemical Engineering & Technology 2011 Volume 34( Issue 10) pp:1691-1699
Publication Date(Web):
DOI:10.1002/ceat.201100118
Abstract
An interdigital mixer-redispersion capillary assembly was applied to prevent the liquid-liquid bubbly flow coalescence in microreactors. The redispersion capillary consisted of 1-mm-long 0.25 mm inner-diameter constrictions, placed every 0.50 m along the channel length. The system was tested on the phase transfer-catalyzed esterification to produce benzyl benzoate. The application of constrictions to prevent coalescence resulted in a better reproducibility and higher conversion compared to a capillary without constrictions. The bubbly flow generated by the interdigital mixer-redispersion capillary assembly was found to be independent of the redispersion capillary inner diameters (0.50 and 0.75 mm) while being highly dependent on the flow rates. By controlling the total flow rate and the aqueous-to-organic ratio, the bubbly flow surface-to-volume ratio could be increased up to 230 700 m2m–3. Compared to the conventional phase transfer-catalyzed esterification, the continuous operation in the interdigital mixer-redispersion capillary assembly eliminated the use of solvents and bases, removing an energy-intensive step of distillation while increasing process safety.
Co-reporter:F. Visscher, W. A. Gaakeer, P. Granados Mendoza, M. H. J. M. de Croon, J. van der Schaaf, and J. C. Schouten
Journal of Chemical & Engineering Data 2011 Volume 56(Issue 9) pp:3630-3636
Publication Date(Web):August 5, 2011
DOI:10.1021/je200478p
Equilibrium data at (293 ± 2) K are presented for benzoic acid in water and three different organic phases (heptane, methylbenzene, and trichloroethylene). The monomeric partition constant, KPMON, and the dimerization constant, KD, for the organic phase were determined at 293 K. For the heptane/water benzoic acid system, KPMON equals (0.209 ± 0.049) m3AQ·m–3ORG, and KD equals (1.33 ± 0.68) m3·mol–1. For the methylbenzene/water benzoic acid system, KPMON equals (1.17 ± 0.92) m3AQ·m–3ORG, and KD equals (0.39 ± 0.64) m3·mol–1. For the trichloroethylene/water benzoic acid system, KPMON equals (0.808 ± 0.295) m3AQ·m–3ORG, and KD equals (1.18 ± 0.89) m3·mol–1. Equilibrium constants were obtained from UV–vis spectroscopy and conductivity experiments. The equilibrium data of these extraction systems can be used to quantify liquid–liquid mass transfer rates with extraction systems that require low flammability risk (trichloroethylene), low costs (methylbenzene), or setups constructed from polymethyl methacrylate (heptane).
Co-reporter:Marco Meeuwse, Sanne Lempers, John van der Schaaf, and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 21) pp:10751-10757
Publication Date(Web):May 11, 2010
DOI:10.1021/ie1003366
The heterogeneously catalyzed oxidation of glucose is performed in a rotor−stator spinning disk reactor. One side of the rotor is coated with a Pt/C and Nafion catalytic layer, resulting in a liquid−solid interfacial area of 274 mi2 mR−3. At the lowest rotational disk speed, 26 rad s−1, the reaction is liquid−solid mass transfer limited; at the highest rotational disk speed, 180 rad s−1, the intrinsic kinetics are rate determining. The experimental overall reaction rates are fitted with a resistances in series model, with the activation energy, pre-exponential factor, and volumetric liquid−solid mass transfer coefficient as parameters. The volumetric liquid−solid mass transfer coefficient, kLSaLS, increases from 0.02 to 0.22 mL3 mR−3 s−1 for a rotational disk speed of 26 to 157 rad s−1. These values are high in comparison to conventional reactors, like packed beds, in spite of the low liquid−solid interfacial area used in this study. The values of the liquid−solid mass transfer coefficient kLS are 1 order of magnitude higher compared to values reported for packed beds. The Sherwood number for the liquid−solid mass transfer in the rotor−stator spinning disk reactor depends on the Reynolds number to the power 2 in the range 1 × 105 < Re < 7 × 105. In this range, the transition of laminar flow to turbulent flow takes place, resulting in a change of the mass transfer mechanism.
Co-reporter:R. Tschentscher, R. J. P. Spijkers, T. A. Nijhuis, J. van der Schaaf, and J. C. Schouten
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 21) pp:10758-10766
Publication Date(Web):May 6, 2010
DOI:10.1021/ie100385n
The liquid−solid mass transfer rate is studied for two three-phase reactor configurations, a stirred reactor and a rotating solid foam reactor, using the dissolution of copper by potassium dichromate as a model reaction. For the stirred reactor consisting of a Rushton stirrer and a slurry with small particles, the particle density has a large influence on the liquid−solid mass transfer rate. Heavy particles show high slip velocities, as their path is less influenced by the liquid turbulence. Furthermore, the mass transfer is enhanced by neighboring particles passing each other. In the case of solid copper particles, a kLS value of 3 × 10−3 ms−1 was observed. For particles having a density comparable to industrial catalyst supports, the kLS value is 1 order of magnitude lower. For the rotating foam block stirrer also, high kLS values of 2.5 × 10−3 ms−1 could be achieved due to the high liquid velocity along the foam struts. The influence of several parameters on the hydrodynamics and the liquid−solid mass transfer was studied. Among these, the foam block height, the foam pore size, and the space above the foam block stirrer have a large effect on the liquid circulation, the bubble formation, and therefore on the liquid−solid mass transfer. The reduction of the foam pore size has two counterbalancing effects, resulting only in a slight increase of the rate of mass transfer: (i) the liquid−solid interfacial area is increased; (ii) the liquid circulation is, however, reduced due to the higher frictional pressure drop. Gas bubbles passing the foam struts affect the liquid−solid mass transfer by inducing liquid velocity fluctuations. For the foam block stirrer, a maximum kLSaLS value of 0.6 s−1 was obtained. This shows great potential for further optimization of the liquid flow and therefore the mass transfer. An additional advantage of the foam stirrer reactor is that the solid phase is fixed and the catalyst does not need to be separated downstream from the reactor.
Co-reporter:Patrick W. A. M. Wenmakers, John van der Schaaf, Ben F. M. Kuster and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 11) pp:5353-5366
Publication Date(Web):April 30, 2010
DOI:10.1021/ie900644e
In this paper, the performance of two types of advanced foam packings (viz., Hairy Foam and washcoated Solid Foam) is compared with that of a packed bed of porous spherical particles. The comparison is done for two different types of reactions (viz., the slow hydrogenation of cinnamaldehyde and the fast hydrogenation of 3-methyl-1-pentyn-3-ol) and under two flow conditions (viz., upflow and downflow), in terms of selectivity, conversion, pressure drop, and reactor height. Under similar operating conditions, the simulation results show that, for both reactions, the Hairy Foam and Solid Foam packings reach higher selectivities and conversions than the packed bed of particles. However, in the case of the slow reaction, the pressure drop for the Hairy and Solid Foam packings is significantly larger than that for the bed of particles. This is due to the lower solids holdup, and thus lower catalyst concentration, of the Hairy Foam and Solid Foam packings. Therefore, larger reactors are required for the hairy foam and solid foam packings, resulting in a higher total pressure drop.
Co-reporter:Jovan Jovanović, Evgeny V. Rebrov, T. A. (Xander) Nijhuis, Volker Hessel and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 6) pp:2681-2687
Publication Date(Web):February 16, 2010
DOI:10.1021/ie9017918
Precise control over the interfacial area of aqueous and organic slugs in segmented flow in a microchannel reactor provides an attractive means to optimize the yield and productivity of a phase-transfer-catalyzed reaction. Herein, we report the selective alkylation of phenylacetonitrile to the monoalkylated product in a microchannel of 250-μm internal diameter operated in a continuous and solvent-free manner in the slug-flow regime. The conversion of phenylacetonitrile increased from 40% to 99% as a result of a 97% larger slug surface-to-volume ratio when the volumetric aqueous-to-organic phase flow ratio was raised from 1.0 to 6.1 at the same residence time. The larger surface-to-volume ratio significantly promoted catalyst phase transfer but decreased selectivity because of the simultaneous increase of the rate of the consecutive reaction to the dialkylated product. There exists an optimum flow ratio with a maximum productivity. Conversion and selectivity in the microchannel reactor were both found to be significantly larger than in a stirred reactor.
Co-reporter:Marco Meeuwse, John van der Schaaf and Jaap C. Schouten
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 4) pp:1605-1610
Publication Date(Web):December 31, 2009
DOI:10.1021/ie901301m
This paper presents a new type of spinning disk reactor configuration for gas−liquid operations. It combines the features of a classical spinning disk with a liquid film on the rotor [e.g., Aoune, A.; Ramshaw, C. Int. J. Heat Mass Transfer 1999, 42, 2543−2556] and those of a rotor−stator spinning disk unit with a single gas inlet in the bottom stator [Meeuwse, M.; van der Schaaf, J.; Kuster, B. F. M.; Schouten, J. C. Chem. Eng. Sci. 2010, 65 (1), 466−471]. In this new configuration, gas and liquid are cofed through an inlet in the top stator. It is shown that gas−liquid mass transfer mainly takes place in the dispersed region between the rotor and the bottom stator. kGLaGLVR in this region is up to a factor of 6 larger than in the region with the liquid film on the rotor. Simulation of gas desorption from a saturated liquid shows that the gas−liquid mass transfer in this cofed configuration is considerably improved in comparison to the separate reactors, at similar operating conditions. The new reactor has also a higher potential for scaling up: gas and liquid can be cofed from one rotor−stator unit to another without the need for redistribution of the gas.
Co-reporter:Faysal Benaskar, Volker Engels, Narendra Patil, Evgeny V. Rebrov, Jan Meuldijk, Volker Hessel, Lumbertus A. Hulshof, David A. Jefferson, Jaap. C. Schouten, Andrew E.H. Wheatley
Tetrahedron Letters 2010 Volume 51(Issue 2) pp:248-251
Publication Date(Web):13 January 2010
DOI:10.1016/j.tetlet.2009.10.126
The action of nanoparticulate copper catalysts with a mean particle size of 10 nm in the Ullmann ether synthesis is reported using multimode microwave heating and employing stable chloropyridine salts and unactivated phenol, with stabilized copper nanoparticles outperforming other copper catalysts in terms of stability and reusability.The action of nanoparticulate copper catalysts with a mean particle size of 10 nm in the Ullmann ether synthesis is reported using multimode microwave heating and employing stable chloropyridine salts and unactivated phenol, with stabilized copper nanoparticles outperforming other copper catalysts in terms of stability and reusability.
Co-reporter:Faysal Benaskar, Volker Engels, Narendra Patil, Evgeny V. Rebrov, Jan Meuldijk, Volker Hessel, Lumbertus A. Hulshof, David A. Jefferson, Jaap. C. Schouten, Andrew E.H. Wheatley
Tetrahedron Letters 2010 Volume 51(Issue 44) pp:5849
Publication Date(Web):3 November 2010
DOI:10.1016/j.tetlet.2010.09.001
Co-reporter:S. R. A. de Loos;J. van der Schaaf;R. M. Tiggelaar
Microfluidics and Nanofluidics 2010 Volume 9( Issue 1) pp:131-144
Publication Date(Web):2010 July
DOI:10.1007/s10404-009-0525-3
Most heterogeneously catalyzed gas–liquid reactions in micro channels are chemically/kinetically limited because of the high gas–liquid and liquid–solid mass transfer rates that can be achieved. This motivates the design of systems with a larger surface area, which can be expected to offer higher reaction rates per unit volume of reactor. This increase in surface area can be realized by using structured micro channels. In this work, rectangular micro channels containing round pillars of 3 μm in diameter and 50 μm in height are studied. The flow regimes, gas hold-up, and pressure drop are determined for pillar pitches of 7, 12, 17, and 27 μm. Flow maps are presented and compared with flow maps of rectangular and round micro channels without pillars. The Armand correlation predicts the gas hold-up in the pillared micro channel within 3% error. Three models are derived which give the single-phase and the two-phase pressure drop as a function of the gas and liquid superficial velocities and the pillar pitches. For a pillar pitch of 27 μm, the Darcy-Brinkman equation predicts the single-phase pressure drop within 2% error. For pillar pitches of 7, 12, and 17 μm, the Blake-Kozeny equation predicts the single-phase pressure drop within 20%. The two-phase pressure drop model predicts the experimental data within 30% error for channels containing pillars with a pitch of 17 μm, whereas the Lockhart–Martinelli correlation is proven to be non-applicable for the system used in this work. The open structure and the higher production rate per unit of reactor volume make the pillared micro channel an efficient system for performing heterogeneously catalyzed gas–liquid reactions.
Co-reporter:M. J. F. Warnier;M. H. J. M. de Croon;E. V. Rebrov
Microfluidics and Nanofluidics 2010 Volume 8( Issue 1) pp:
Publication Date(Web):2010 January
DOI:10.1007/s10404-009-0448-z
In this paper, a model is presented that describes the pressure drop of gas–liquid Taylor flow in round capillaries with a channel diameter typically less than 1 mm. The analysis of Bretherton (J Fluid Mech 10:166–188, 1961) for the pressure drop over a single gas bubble for vanishing liquid film thickness is extended to include a non-negligible liquid film thickness using the analysis of Aussillous and Quéré (Phys Fluids 12(10):2367–2371, 2000). This result is combined with the Hagen–Poiseuille equation for liquid flow using a mass balance-based Taylor flow model previously developed by the authors (Warnier et al. in Chem Eng J 135S:S153–S158, 2007). The model presented in this paper includes the effect of the liquid slug length on the pressure drop similar to the model of Kreutzer et al. (AIChE J 51(9):2428–2440, 2005). Additionally, the gas bubble velocity is taken into account, thereby increasing the accuracy of the pressure drop predictions compared to those of the model of Kreutzer et al. Experimental data were obtained for nitrogen–water Taylor flow in a round glass channel with an inner diameter of 250 μm. The capillary number Cagl varied between 2.3 × 10−3 and 8.8 × 10−3 and the Reynolds number Regl varied between 41 and 159. The presented model describes the experimental results with an accuracy of ±4% of the measured values.
Co-reporter:Evgeny V. Rebrov, Angel Berenguer-Murcia, Helen E. Skelton, Brian F. G. Johnson, Andrew. E. H. Wheatley and Jaap C. Schouten
Lab on a Chip 2009 vol. 9(Issue 4) pp:503-506
Publication Date(Web):17 Nov 2008
DOI:10.1039/B815716B
A new method for catalyst deposition on the inner walls of capillary microreactors is proposed which allows exact control of the coating thickness, pore size of the support, metal particle size, and metal loading. The wall-coated microreactors have been tested in a selective hydrogenation reaction. Activity and selectivity reach values close to those obtained with a homogeneous Pd catalyst. The catalyst activity was stable for a period of 1000 h time-on-stream.
Co-reporter:Lidia N. Protasova, Evgeny V. Rebrov, Zinfer R. Ismagilov, Jaap C. Schouten
Microporous and Mesoporous Materials 2009 Volume 123(1–3) pp:243-252
Publication Date(Web):1 July 2009
DOI:10.1016/j.micromeso.2009.04.006
Ethanol adsorption–desorption isotherms on well-organized mesoporous silica and titania films with hexagonal pores structure were studied by ellipsometric porosimetry. The mesopore volume was calculated from the change of the effective refractive index at the end points of the isotherm. An improved Derjaguin–Broekhoff–de Boer (IDBdB) model for cylindrical pores is proposed for the determination of the pore size. In this model, the disjoining pressure isotherms were obtained by measuring the thickness of the ethanol film on a non-porous film with the same chemical composition. This approach eliminates uncertainties related to the application of the statistical film thickness determined via t-plots in previous versions of the DBdB model. The deviation in the surface tension of ethanol in the mesopores from that of a flat interface was described by the Tolman parameter in the Gibbs–Tolman–Koening–Buff equation. A positive value of the Tolman parameter of 0.2 nm was found from the fitting of the desorption branch of the isotherms to the experimental data obtained by Low Angle X-ray Diffraction (LA-XRD) and Transmission Electron Microscopy (TEM) measurements in the range of pore diameters between 2.1 and 8.3 nm.
Co-reporter:Patrick W. A. M. Wenmakers, John van der Schaaf, Ben F. M. Kuster and Jaap C. Schouten
Journal of Materials Chemistry A 2008 vol. 18(Issue 21) pp:2426-2436
Publication Date(Web):2008/03/12
DOI:10.1039/B718673H
This paper describes the synthesis of carbon nanofibers (CNFs) on solid carbon foam (“Hairy Foam”) by catalytic decomposition of ethylene. The effect of nickel loading on fiber diameter and morphology, CNF coverage, and fiber layer thickness is studied using SEM and N2/Kr-physisorption. The surface area increased from 0.12 m2support g−1support for reticulated vitreous carbon (RVC) to 146 m2support g−1support for “Hairy Foam”. A nickel concentration of 0.5 gNig−1RVC results in fibers with a diameter of 30 to 90 nm. Increasing the nickel concentration results in fiber diameters of 30 to 1100 nm. Complete CNF coverage is obtained for a nickel deposition time ≥240 min and a nickel concentration ≥2.5 gNig−1RVC.
Co-reporter:M.J.M. Mies, E.V. Rebrov, J.C. Jansen, M.H.J.M. de Croon, J.C. Schouten
Microporous and Mesoporous Materials 2007 Volume 106(1–3) pp:95-106
Publication Date(Web):1 November 2007
DOI:10.1016/j.micromeso.2007.02.032
Highly crystalline zeolite Beta coatings in a range of Si/Al ratios of 12–23 were synthesized on a surface-modified molybdenum substrate by hydrothermal synthesis. The average thickness of the coatings was ca. 2 μm corresponding to a coverage of 2.5 g m−2. The coatings were obtained from a viscous Na, K, and TEAOH containing aluminosilicate precursor mixture with silica sol as reactive silicon source. A mechanism for the in situ growth of zeolite Beta coatings is proposed. According to this mechanism, the deposition of an amorphous gel layer on the substrate surface in the initial stage of the synthesis is an important step for the crystallization of continuous zeolite Beta coatings. The heating rate of the precursor mixture and the synthesis temperature were optimized to control the level of supersaturation and to stimulate the initial formation of a gel layer. At a Si/Al ratio of 23, fast heating and a temperature of 150 °C are required to obtain high coverage, while at a Si/Al ratio of 15, hydrothermal synthesis has to be performed with a slow initial heating rate at 140 °C.
Co-reporter:J. C. Schouten Dr.;A. I. Stankiewicz Dr.
Chemie Ingenieur Technik 2007 Volume 79(Issue 9) pp:
Publication Date(Web):18 SEP 2007
DOI:10.1002/cite.200750273
Co-reporter:E. R. Delsman;M. H. J. M. de Croon;G. D. Elzinga;P. D. Cobden;G. J. Kramer;J. C. Schouten
Chemical Engineering & Technology 2005 Volume 28(Issue 3) pp:
Publication Date(Web):7 MAR 2005
DOI:10.1002/ceat.200407126
Microstructured reactors most often contain a large number of micrometer-sized, parallel channels, instead of a large undivided reaction volume. Individual microchannels behave as plug-flow reactors without significant axial dispersion and with excellent heat and mass transfer properties. However, since the reaction takes place in a large number of parallel channels, it is important that all channels provide equal residence time and amount of catalyst volume. These issues depend not only on the flow distributor design, but also, for example, on the manufacturing tolerances. Correlations are derived to express the conversion of a multichannel microreactor explicitly as a function of the variance of a number of reactor parameters, viz. the channel flow rate, the channel diameter, the amount of catalyst in a channel, and the channel temperature. It is shown that the influence of flow maldistribution on the overall reactor conversion is relatively small, while the influences of variations in the channel diameter and the amount of catalyst coating are more pronounced. The model outcomes are also compared to experimental results of two microreactors with different catalyst distributions, which show that the presented method is able to provide a quick, though rough estimation of the influence of differences between channels on microreactor performance.
Co-reporter:S.A. Kuznetsov, S.V. Kuznetsova, E.V. Rebrov, M.J.M. Mies, M.H.J.M. de Croon, J.C. Schouten
Surface and Coatings Technology 2005 Volume 195(2–3) pp:182-188
Publication Date(Web):31 May 2005
DOI:10.1016/j.surfcoat.2004.05.021
The formation of various coatings in molybdenum–boron and molybdenum–silicon systems was investigated. Boronizing and siliciding treatments were conducted in molten salts under inert gas atmosphere in the 850–1050 °C temperature range for 7 h. The presence of boride (e.g. Mo2B, MoB, Mo2B5) and silicide (MoSi2, Mo5Si3) phases, formed on the surface of Mo plates, was confirmed by X-ray diffraction analysis. The distribution of elements was determined by means of wavelength dispersive spectroscopy (WDS) spectra of the surface and line-scan analyses from surface to interior. Depending on the process type (diffusional or electrochemical) and temperature, the thickness of the protective layers formed on the substrate ranged from 6 to 40 μm. The oxidation resistance of obtained phases was investigated in an air–water mixture in the temperature range of 500–700 °C for a period up to 400 h. An improved oxidation behavior of coated plates in comparison with that of pure molybdenum was observed.
Co-reporter:E.V. Rebrov;M.H.J.M. De Croon;J.C. Schouten
Chemie Ingenieur Technik 2001 Volume 73(Issue 6) pp:
Publication Date(Web):12 JUL 2001
DOI:10.1002/1522-2640(200106)73:6<676::AID-CITE6762222>3.0.CO;2-0
Co-reporter:F. Visscher, R.T.R. Nijhuis, M.H.J.M. de Croon, J. van der Schaaf, J.C. Schouten
Chemical Engineering and Processing: Process Intensification (September 2013) Volume 71() pp:107-114
Publication Date(Web):1 September 2013
DOI:10.1016/j.cep.2013.01.015
Liquid–liquid flow patterns in an impeller–stator spinning disc reactor are qualitatively described. The liquid–liquid flow is studied by contacting water and n-heptane at rotational speeds up to 900 RPM, an axial disc spacing of 1.0 × 10−3 m, and aqueous volume fractions between 0 and 1mAQ3mL−3. The liquid–liquid flow is characterized by six different flow regimes. Each regime is characterized by its continuous liquid phase and the degree of dispersion of the dispersed liquid phase. Regime transitions depend on the formation of boundary layers on the impeller and the stator, the shear stress intensity and the aqueous volume fraction. The impeller is able to selectively pump n-heptane through the reactor, whilst it is intensively mixed with water that remains in the reactor. Combining mixing and separation in one compact reactor is an important step toward a countercurrent operated impeller-based centrifugal extractor.Highlights► Liquid–liquid flow in an impeller–stator spinning disc reactor is described. ► Six different flow regimes were observed between the impeller and the bottom stator. ► Regime transitions depend on shear stress intensity, and aqueous volume fractions. ► Mixing and separation is achieved in one compact reactor. ► This is an important step toward a countercurrent operated spinning disc reactor.
Co-reporter:Lidia N. Protasova, Evgeny V. Rebrov, Tatiana S. Glazneva, Angel Berenguer-Murcia, Zinfer R. Ismagilov, Jaap C. Schouten
Journal of Catalysis (4 May 2010) Volume 271(Issue 2) pp:161-169
Publication Date(Web):4 May 2010
DOI:10.1016/j.jcat.2009.07.013
A new method of sol–gel polymer template synthesis of mesoporous catalytic thin films has been proposed which allows controlling the chemical nature of the film, the porosity, thickness and loading with an active species. The mesoporous films with a long-order structure can be obtained in a narrow range of surfactant-to-metal precursor molar ratios from 0.006 to 0.009. The catalytic film thickness was varied from 300 to 1000 nm while providing a uniform catalyst distribution with a desired catalyst loading (1 wt. % Au nanoparticles) throughout the film. The films were characterized by TEM, SEM, ethanol adsorption and contact angle measurements. The calcination of the as-synthesized films at 573 K reduced Ti4+ sites to Ti3+. A 300 nm thick Au-containing film showed an initial TOF of 1.4 s−1 and a selectivity towards unsaturated alcohols as high as 90% in the hydrogenation of citral. Thicker films demonstrated a high selectivity towards the saturated aldehyde (above 55%) and a lower intrinsic catalytic activity (initial TOF of 0.7–0.9 s−1) in the absence of internal diffusion limitations.Control of the thickness of mesoporous Au/TiO2 films was achieved by multiple spin-coating. A 300 nm thick Au-containing film showed high initial TOF of 1.4 s−1 and a selectivity towards unsaturated alcohols as high as 90% in the hydrogenation of citral.Download high-res image (99KB)Download full-size image
Co-reporter:M.A. Leon, T.A. Nijhuis, J. van der Schaaf, J.C. Schouten
Chemical Engineering Science (27 September 2014) Volume 117() pp:8-17
Publication Date(Web):27 September 2014
DOI:10.1016/j.ces.2014.06.016
•A multistage horizontal rotating foam stirrer reactor is used for hydrogenation purposes.•The reactor model consists of stirred tanks in series with backflow and dead volume.•The reactor exhibits a dead volume of 23% and a backflow ratio between 1 and 2.•Plug flow behavior is achieved when six stages are used.•The selectivity of the hydrogenation is enhanced due to plug flow behavior.The performance of a multistage horizontal rotating foam stirrer reactor in semi-continuous operation was studied for the selective hydrogenation of functionalized alkynes to alkenes, an important process in the fine chemicals industry. This new type of multiphase reactor consists of a horizontal vessel compartmentalized by vertical baffles and equipped with an impeller in each compartment. The impeller is a donut-shaped foam block, which is also used as catalyst support. The advantage of this reactor configuration compared to batch slurry reactors is the better catalyst handling, since the catalyst is fixed on the stirrer. In addition, a higher selectivity towards the desired product is achieved as a result of a narrower residence time distribution. A reactor model consisting of stirred tanks in series with backflow and dead volume was used to describe the liquid flow behaviour. The effects of liquid flow rate, backmixing and number of stages for the hydrogenation reaction are discussed, and optimal operation conditions are suggested.
Co-reporter:E. Kertalli, J.C. Schouten, T.A. Nijhuis
Applied Catalysis A: General (25 May 2017) Volume 538() pp:131-138
Publication Date(Web):25 May 2017
DOI:10.1016/j.apcata.2017.03.023
Co-reporter:M.J.M. Mies, E.V. Rebrov, J.C. Jansen, M.H.J.M. de Croon, J.C. Schouten
Journal of Catalysis (25 April 2007) Volume 247(Issue 2) pp:328-338
Publication Date(Web):25 April 2007
DOI:10.1016/j.jcat.2007.02.007
A method for the hydrothermal synthesis of a single layer of zeolite Beta crystals on a molybdenum substrate for microreactor applications has been developed. Before the hydrothermal synthesis, the surface of the substrate was modified by an etching procedure that increases the roughness at the nanoscale level without completely eliminating the surface lay structure. Then, thin films of Al2O3 (170 nm) and TiO2 (50 nm) were successively deposited by atomic layer deposition (ALD) on the substrate. The internal Al2O3 film protects the Mo substrate from oxidation up to 550 °C in an oxidative environment. The high wettability of the external TiO2 film after UV irradiation increases zeolite nucleation on its surface. The role of the metal precursor (TiCl4 vs TiI4), deposition temperature (300 vs 500 °C), and film thickness (50 vs 100 nm) was investigated to obtain titania films with the slowest decay in the superhydrophilic behavior after UV irradiation. Zeolite Beta coatings with a Si/Al ratio of 23 were grown at 140 °C for 48 h. After ion exchange with a 10−4 M cobalt acetate solution, the activity of the coatings was determined in the ammoxidation of ethylene to acetonitrile in a microstructured reactor. A maximum reaction rate of 220 μmol C2H3N g−1 s−1 was obtained at 500 °C, with 42% carbon selectivity to acetonitrile.
Co-reporter:C.M.L. Scholz, V.R. Gangwal, M.H.J.M. de Croon, J.C. Schouten
Applied Catalysis B: Environmental (15 February 2007) Volume 71(Issues 3–4) pp:143-150
Publication Date(Web):15 February 2007
DOI:10.1016/j.apcatb.2006.08.018
Co-reporter:Nilenindran S. Govender, F. Gideon Botes, Mart H.J.M. de Croon, Jaap C. Schouten
Journal of Catalysis (10 December 2008) Volume 260(Issue 2) pp:254-261
Publication Date(Web):10 December 2008
DOI:10.1016/j.jcat.2008.10.008
The methanation reaction mechanism under Fischer–Tropsch conditions is investigated with the Steady State Isotopic Transient Kinetic Analysis (SSITKA) technique over a precipitated iron-based catalyst. The 13CH4 transients resulting from a CO12→CO13 switch (330 °C, 1.2 bar, and H2/CO=15) provided kinetic information for the methanation reaction. Six methanation models were screened and only three of these could describe the methane transient. These models were subsequently extended to account for the Fischer–Tropsch higher hydrocarbon products by considering CC coupling reactions and the kinetic rate parameters were estimated. The result was two indistinguishable mechanisms which could describe the methane transient as well as the experimental steady-state concentrations. Both mechanisms have two active pools of carbon (Cα and Cβ) on the catalyst surface with both leading towards the formation of methane. The Cβ pool is 25 to 50 times less active than the Cα pool for methanation and occupies 92% of the total CHx coverage (0.25 ML). The CC coupling reaction was shown to involve both the Cα and Cβ pools. The concentration of molecularly adsorbed CO on the Fe-based catalyst is shown to be extremely low, with an estimated surface coverage of 9×10−4ML.
Co-reporter:L.A. Truter, V. Ordomsky, J.C. Schouten, T.A. Nijhuis
Applied Catalysis A: General (10 April 2016) Volume 515() pp:72-82
Publication Date(Web):10 April 2016
DOI:10.1016/j.apcata.2016.01.039
Co-reporter:C.M.L. Scholz, B.H.W. Maes, M.H.J.M. de Croon, J.C. Schouten
Applied Catalysis A: General (1 November 2007) Volume 332(Issue 1) pp:1-7
Publication Date(Web):1 November 2007
DOI:10.1016/j.apcata.2007.04.023
Co-reporter:L. N. Protasova, E. V. Rebrov, K. L. Choy, S. Y. Pung, V. Engels, M. Cabaj, A. E. H. Wheatley and J. C. Schouten
Catalysis Science & Technology (2011-Present) 2011 - vol. 1(Issue 5) pp:NaN777-777
Publication Date(Web):2011/05/26
DOI:10.1039/C1CY00074H
Vertically aligned ZnO nanowires (NWs) with a length of 1.5–10 μm and a mean diameter of ca. 150 nm were grown by chemical vapour deposition onto a c-oriented ZnO seed layer which was deposited by atomic layer deposition on Si substrates. The substrates were then spin-coated with an ethanol solution containing Pd nanoparticles with an average size of 2.7 and 4.5 nm. A homogeneous distribution of the Pd nanoparticles on ZnO NWs has been obtained using both Pd particle series. The catalytic activity of the ZnO NWs and Pd/ZnO NWs catalysts was measured in the semihydrogenation of 2-methyl-3-butyn-2-ol at 303-343 K and a pressure of 2–10 bar. The effect of the solvent used on the catalytic performance of the Pd/ZnO NWs catalyst was studied. The Pd/ZnO catalysts showed alkene selectivity of up to 95% at an alkyne conversion of 99%. A kinetic model is proposed to explain the activity and selectivity of the ZnO support and Pd/ZnO catalysts.
Co-reporter:Patrick W. A. M. Wenmakers, John van der Schaaf, Ben F. M. Kuster and Jaap C. Schouten
Journal of Materials Chemistry A 2008 - vol. 18(Issue 21) pp:NaN2436-2436
Publication Date(Web):2008/03/12
DOI:10.1039/B718673H
This paper describes the synthesis of carbon nanofibers (CNFs) on solid carbon foam (“Hairy Foam”) by catalytic decomposition of ethylene. The effect of nickel loading on fiber diameter and morphology, CNF coverage, and fiber layer thickness is studied using SEM and N2/Kr-physisorption. The surface area increased from 0.12 m2support g−1support for reticulated vitreous carbon (RVC) to 146 m2support g−1support for “Hairy Foam”. A nickel concentration of 0.5 gNig−1RVC results in fibers with a diameter of 30 to 90 nm. Increasing the nickel concentration results in fiber diameters of 30 to 1100 nm. Complete CNF coverage is obtained for a nickel deposition time ≥240 min and a nickel concentration ≥2.5 gNig−1RVC.
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