Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Hydrogenation of o-nitroanisole to o-anisidine was conducted in a packed-bed microreactor as a model hydrogenation reaction of importance to the pharmaceutical and fine chemicals industries with the aim of investigating the reactor performance and kinetics of the reaction. The effects of different processing conditions viz. hydrogen pressure, o-nitroanisole concentration, temperature, and residence time on the conversion of o-nitroanisole, space-time yield (STY), and selectivity of o-anisidine were studied using 2% Pd/zeolite catalyst. The kinetic study was undertaken in a differential reactor mode keeping the conversion of o-nitroanisole at less than 10%. During the kinetic study, it was observed that the intermediate 2-methoxynitrosobenzene was present in the reactor at low catalyst loading and low conversions because of short residence time in the reactor. Therefore, for the kinetics study, the overall reaction was treated as comprising two separate reactions: first the reduction of o-nitroanisole to 2-methoxynitrosobenzene and then, the reduction of 2-methoxynitrosobenzene to o-anisidine. Internal and external mass and heat transfer limitations in the microreactor were examined. Different rate laws using different mechanisms from the literature were considered to fit the experimental data. Two rate equations for the two consecutive reactions assuming Langmuir–Hinshelwood mechanism provided the best fit to the experimental data. These two rate equations predicted the experimental rates within 10% error. Experiments were also carried out in an integral reactor, and the reactor performance data were found to be in agreement with the predictions of the theoretical models.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... This straightforward and convenient way of catalyst incorporation makes it possible to directly use commercially off-the-self catalysts or conventionally synthesized bulk catalysts in the laboratory, and thus greatly expands the application arena of microreactors in solid-catalyzed multiphase reactions. Table 2 provides a brief overview of heterogeneously catalyzed multiphase reactions in packed-bed microreactors, the majority of which involve the presence of a gas-liquid-solid system [34,35,[86][87][88][89][90][91][92][93], except only 1 example concerning a liquid-liquid-solid system [94]. ...
... Thus processed catalysts can be loaded into the microchannel either by manual filling, or by applying a pump or vacuum at the reaction outlet (e.g., when the catalysts are suspended in a liquid). The packed catalysts are retained inside the reaction microchannel by constrictions at both ends, e.g., using micro-pillars in the case of chip-based microreactors [34,86] or filters in the case of capillary-based microreactors [87]. ...
... Most of the existing gas-liquid-solid reactions explored in packedbed microreactors (as listed in Table 2) were probably carried out under liquid-dominated slug flow pattern (Fig. 3a), since gas-liquid slug flow was usually observed before the catalyst bed [35,[87][88][89][90][91][92][93]. Noteworthy, a recent work highlighted reaction performance under both liquiddominated slug flow and gas-continuous flow patterns [34]. ...
Article
Full-text available
The convergence of continuous flow chemistry and microreactor technology creates numerous possibilities towards the development of an efficient and sustainable chemical synthesis. In this field, the combination of heterogeneous catalysis and multiphase flow processing in microreactors represents an important approach. This review presents a summary of the recent progress on the utilization of wall-coated and packed-bed microreactors for carrying out heterogeneously catalyzed gas-liquid and liquid-liquid reactions, with a focus on the microreactor operation principles and selected reaction examples with promising application potential. Finally, an outlook on the future development trends is provided.
... [18] For hydrogenation with shorter residence times, the reactant cannot be completely transformed into target compound because a portion of the reactant flows out of the reactor before contacting hydrogen on the catalysts, whereas for hydrogenation with longer residence times, there would inevitably be byproducts. [19] In the continuous hydrogenation process, increasing the hydrogen flow rate not only increases the relative molar amount of hydrogen, but can also decrease the residence time and intensify the gas À liquid mixture and mass transfer by changing the turbulence in μPBR, which has noticeable influences on the conversion and selectivity of the reaction. [19] Consequently, it is essential to determine the optimal gas-to-liquid flow rate ratio. ...
... [19] In the continuous hydrogenation process, increasing the hydrogen flow rate not only increases the relative molar amount of hydrogen, but can also decrease the residence time and intensify the gas À liquid mixture and mass transfer by changing the turbulence in μPBR, which has noticeable influences on the conversion and selectivity of the reaction. [19] Consequently, it is essential to determine the optimal gas-to-liquid flow rate ratio. The conversion and selectivity with different ratios of gas to liquid flow rate were studied using Pd(OH) 2 /C catalyst to investigate the effect of gas-liquid flow rate on continuous hydrogenation reaction results, and the results were summarized in Table 4. Table 4 (Entries 1-2) illustrates that when α = 10&20, low conversion and selectivity were observed due to limited H 2 availability (β < 6). ...
Article
Full-text available
Due to the intricacy aromatic dinitro compound hydrogenation processes, it is difficult to attain high conversion and selectivity using merely modified catalysts in batch reactors. The micropacked‐bed reactor (μPBR) offers efficient heat and mass transfer, a precise and controllable reaction process, and a high level of safety. In this work, the hydrogenation of 2,4‐dinitroanisole was selected as the model reaction, and a variety of catalysts were utilized in the continuous flow system based on μPBR for hydrogenation of 2,4‐dinitroanisole. During 960 minutes of operation, the synthesis of 2,4‐diaminoanisole was carried out using a Pd (OH)2/C catalyst and the optimal process condition, yielding 100 % conversion, 99.5 % selectivity, and the favorable durability. For the hydrogenation of relevant aromatic dinitro compounds, the continuous flow system demonstrates exceptional performance.
... Because of reduced length scales, they can offer advantages such as improved temperature control, accelerated heat and mass transfer, and enhanced mixing of reactants. 1,2 Micropacked bed reactors (MPBRs) or microfixed bed reactors, which combine the benefits of microreactors and fixed-bed reactors, have been demonstrated to be promising tools for multiphase catalytic reaction systems in investigating catalyst performance, 3−6 reaction kinetics, 7 and chemical synthesis. 8−11 Enhanced mass transfer in MPBRs has been reported by many researchers (refer to the review by Zhang et al. 12 ). ...
... 26 The correlations for larger scale packed bed reactors are not suitable for predicting the mass transfer in microscale packed bed reactors. 3,7 The main reason for this comes from the fact that viscous and capillary forces are predominant in the MPBRs in comparison with the large-scale packed bed reactors. 4,27 Hydrodynamic behavior of an MPBR (or even a bench-scale trickle-bed reactor) differs from that of an industrial-scale trickle bed, due to the significant effect of capillary forces, and consequently there could be no real trickle flow in a microscale packed bed. 4 In literature, L-S mass transfer studies in MPBRs are scarce. ...
Article
Full-text available
The volumetric liquid–solid (L-S) mass transfer coefficient under gas–liquid (G-L) two-phase flow in a silicon-chip-based micropacked bed reactor (MPBR) was studied using the copper dissolution method and was related to the reactor hydrodynamic behavior. Using a high-speed camera and a robust computational image analysis method that selectively analyzed the bed voidage around the copper particles, the observed hydrodynamics were directly related to the L-S mass transfer rates in the MPBR. This hydrodynamic study revealed different pulsing structures inside the packed copper bed depending on the flow patterns established preceding the packed bed upon increasing gas velocity. A “liquid-dominated slug” flow regime was associated with an upstream slug flow feed. A “sparse slug” flow regime developed with an upstream slug-annular flow feed. At higher gas velocity, a “gas continuous with pulsing” regime developed with an annular flow feed, which had similar features to the pulsing flow in macroscale packed beds, but it was sensitive and easily destabilized by disturbances from upstream or downstream pressure fluctuations. The volumetric L-S mass transfer coefficient decreased with increasing gas velocity under the liquid-dominated slug flow regime and became rather less affected under the sparse slug flow regime. By resolving the transition from the liquid-dominated slug flow to the sparse slug flow and capturing the onset of the gas-continuous with pulsing regime, we gained new insights into the hydrodynamic effects of G-L flows on the L-S mass transfer rates in a MPBR.
... Higher gas-liquid-solid mass transfer rate is also attainable in packed bed microreactors due to smaller particles accommodated [50,60]. Thus, gas-liquid hydrogenation reactions in packed bed microreactors have gained increased research attention over the past decade [36,50,[61][62][63][64][65][66]. In some cases, mass transfer limitations were (almost) eliminated and the reactions were under kinetic control, making packed bed microreactors a promising tool for kinetic investigations [61,63,64]. ...
... Thus, gas-liquid hydrogenation reactions in packed bed microreactors have gained increased research attention over the past decade [36,50,[61][62][63][64][65][66]. In some cases, mass transfer limitations were (almost) eliminated and the reactions were under kinetic control, making packed bed microreactors a promising tool for kinetic investigations [61,63,64]. ...
Article
Full-text available
The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was performed in perfluoroalkoxy alkane capillary microreactors packed with a carbon-supported ruthenium (Ru/C) catalyst with an average particle diameter of 0.3 or 0.45 mm. The reaction was executed under an upstream gas-liquid slug flow with 1,4-dioxane as the solvent and H2 as the hydrogen donor in the gas phase. Operating conditions (i.e., flow rate and gas to liquid flow ratio, pressure, temperature and catalyst particle size) were varied in the microreactor to determine the influence of mass transfer and kinetic characteristics on the reaction performance. At 130 °C, 12 bar H2 and a weight hourly space velocity of the liquid feed (WHSV) of 3.0 gfeed/(gcat·h), 100% LA conversion and 84% GVL yield were obtained. Under the conditions tested (70 – 130 °C and 9 – 15 bar) the reaction rate was affected by mass transfer, given the notable effect of the mixture flow rate and catalyst particle size on the LA conversion and GVL yield at a certain WHSV. A microreactor model was developed by considering gas-liquid-solid mass transfer therein and the reaction kinetics estimated from the literature correlations and data. This model well describes the measured LA conversion for varying operating conditions, provided that the internal diffusion and kinetic rates were not considered rate limiting. Liquid-solid mass transfer of hydrogen towards the external catalyst surface was thus found dominant in most experiments. The developed model can aid in the further optimization of the Ru/C catalyzed levulinic acid hydrogenation in packed bed microreactors.
... In comparison, the development of flow microreactors with superior rates of heat and mass transport and improved safety 3-7 enable isothermal kinetic studies. 5,[8][9][10] Flow reactors are now often combined with online analysis to provide data-rich experimental platforms. Online flow analysis methods reported in the literature include GC, [11][12][13][14] HPLC, [15][16][17][18][19][20][21][22][23] MS, 16,[23][24][25][26] UV, 13 IR, [27][28][29][30][31][32] Raman, 33,34 X-ray absorption spectroscopy 28 and NMR 35 as well as viscosity measurements. ...
... The MBDoE problem is an optimisation problem to find the values of the design vector φ, within a pre-defined allowable design space, which minimise a certain measure of the expected covariance matrix using one of the previously described methods of quantifying the size of a matrix 2 as shown in eqn (10). ...
Article
Full-text available
An autonomous flow microreactor platform was developed that was able to conduct reaction experiments and measure the outlet reactant and product concentrations using HPLC without user supervision. The platform performed unmanned kinetic experiments with the aim of precisely estimating the parameters of a kinetic model for the esterification between benzoic acid and ethanol catalysed by sulfuric acid. The capabilities of the autonomous platform were demonstrated on three different experimental scenarios: 1) performing steady-state experiments, where the experimental reaction conditions were pre-defined by the user; 2) performing steady-state experiments, where the conditions were optimised online by Model-Based Design of Experiments (MBDoE) algorithms, with the aim of improving parameter precision; 3) executing transient experiments, where the conditions were pre-selected by the user. For the steady-state experiments, the platform automatically performed online parameter estimation and MBDoE with a pre-selected kinetic model. It was demonstrated that a campaign of steady-state experiments designed using online MBDoE algorithms led to more precise parameter estimates than a campaign of experiments designed by the traditional factorial design. Transient experiments were shown to expedite kinetic parameter estimation and use less reagents than campaigns of steady-state experiments, as it was no longer necessary to wait for the system to reach steady-state. In general, the transient experiments offered less precise parameter estimates than the steady-state campaigns, however the experiments could be completed in just 2 h instead of the 8 h required for a campaign of steady-state experiments.
... The catalyst dosage will affect the heat and mass transfer of substrates and products. 43 Upon increasing Be/FA dosage, the viscosity of the medium may increase gradually, and the mass and heat transfer are limited. Excessive water molecules produce competitive hydrolysis reaction near the active site. ...
... [5][6][7] The μPBRs also play the pivotal roles in kinetics study and fast catalyst screening. 8,9 Outstandingly, the μPBRs have been successfully applied to various gas-liquid-solid reactions, including hydrogenation, 10 oxidation, 11 and Fischer-Tropsch synthesis, 12 and so on. ...
Article
Full-text available
Micro‐packed bed reactors (μPBRs) have the advantages of high heat and mass transfer efficiency and excellent safety, and they have been successfully applied to hydrogenation and oxidation reactions. However, the study of gas–liquid flow regimes in the μPBR, which is essential for the mass transfer modeling and reactor scale‐up, is still insufficient due to the limitation of micro‐scale and complexity of capillary force. In this work, the flow regimes in the two‐dimensional μPBR were systematically studied by visual method utilizing a high‐performance camera. Four typical flow regimes and characteristics were captured, and flow regime transition was revealed. Effects of gas and liquid superficial velocities, liquid physical properties, and particle sizes on liquid spreading areal fraction and pressure drop were investigated. Flow regime transition correlation of churn flow and pseudo‐static flow in the μPBR was provided for the first time based on the summary of the current and previous published results.
... Alkene hydrogenation to alkane using Pt or Pd metal supported on zeolite or silica as a catalyst has been done [7][8][9][10]. In contrast, Ni metal as a hydrogenation catalyst was used by Fernández et al. [11]. ...
Conference Paper
In this presented work, hierarchical zeolite supported Ni catalysts were synthesized in their reduced form and applied to the hydrogenation of methyl eugenol as an attractant. Efficiently, attractant was produced from methyl eugenol directly. However, as it has carcinogenic properties, a synthesis method of attractants from other resources is necessary. 1,2-dimethoxy-4-propyl-benzene, which can be formed through the hydrogenation process of methyl eugenol substrate is a potential source for attractant production. Hierarchical zeolite (HZ) catalysts displayed better physical properties compared to natural zeolite itself. This work aims to determine the effect of reaction pressure and time on the hydrogenation of methyl eugenol into 1,2-dimethoxy-4-propyl-benzene. GCMS analysis composition shows increased conversion of methyl eugenol and selectivity of 1,2-dimethoxy-4-propyl-benzene, increasing the initial H2 pressure.
... Methods that reveal the flow and transport phenomena in electrosynthesis microreactors are limited, and those reported are mainly derived from traditional microfluidic studies such as microscopic observation and computational fluid dynamics (CFD) simulation. Similar to previous microreactors with wall loaded catalysts [49,50], the crucial transport direction is vertical to the channel walls of electrosynthesis microreactors, but the effect of electromigration should be considered when dealing with ionic mass transfer issues. Here follows a summary of typical investigations into the flow patterns and mass transfer controls in electrosynthesis microreactors to elucidate the features of miniaturized electrosynthesis devices. ...
Article
Full-text available
Electrochemical methods are environmentally friendly and have unique advantages in the synthesis of organic chemicals. However, their implementation is limited due to the complex transport problems posed by traditional electrochemical reactors. Recently, the application of microreaction technology in electrosynthesis studies has reduced the transport distance of ions and increased the specific surface area of electrodes, leading to efficient, successive, and easily scaled-up electrosynthesis technologies. In this review article, engineering advantages of using microchannels in electrosynthesis are discussed from process enhancement perspective. Flow patterns and mass transfer behaviors in recently reported electrochemical microreactors are analyzed, and prototypes for the reactor scale-up are reviewed. As a relatively new research area, many scientific rules and engineering features of electrosynthesis in microreactors require elucidation. Potential research foci, considered crucial for the development of novel electrosynthesis technology, are therefore proposed.
... The external mass transfer resistance was studied in hydrogenation of o-nitroanisole to o-anisidine in a MFBR over a Pd/zeolite catalyst [74]. Different bed lengths were used to change the residence time. ...
... The gas-liquid two-phase mass transfer widely occurs in many chemical processes such as absorption, reaction, rectification and membrane separation (Sotowa et al., 2009). Microreactors have shown many advantages for mass and heat transfer (Jahnisch et al., 2000;Kin Yeong et al., 2004;Tadepalli et al., 2007;Yue et al., 2007). The effect of micro scale could cause the rapid increases of concentration gradient, pressure gradient and temperature gradient in channel, meanwhile, the specific surface area is usually 10~100 times larger than that of the traditional reactor (Fu, 2016). ...
Article
The intensification of mass transfer of CO2 absorption into [Bmim][BF4] aqueous solution by continuous sudden expansion units was investigated experimentally in microchannels. The influences of two-phase flow rates and the number of sudden expansion units on pressure drop and volumetric mass transfer coefficient were studied systematically. The results indicate that the sudden expansion structure could remarkably enhance gas-liquid mass transfer. The enhancement factor of mass transfer increases with increasing the number of sudden expansion units and gas-liquid flow rate ratio, while the pressure drop has only slight elevation. The effective mass transfer enhancement efficiency was assessed according to the energy consumption and enhancement factor, which could achieve from 1.2 to 2.4, showing excellent mass transfer intensification effect of the sudden expansion structure. Moreover, a new correlation was proposed for predicting liquid side volumetric mass transfer coefficient.
... In other cases researchers avoid modelling the micropacked bed reactor at all, instead they check that the reactor is not limited by heat or mass transfer resistances and they operate in differential mode with conversion less than 10%. They can then calculate the rate of reaction as the rate of product formation divided by the mass of catalyst, and they can fit kinetic models directly to this rate data [29,45,[264][265][266]. Alternatively, a common approach, and the approach used in this work, is to make a number of simplifying assumptions when modelling the reactor, and then to operate at only a single gas liquid flowrate so that greater focus can be directed towards the kinetics [168,169,267,268]. ...
Conference Paper
Microreactor technology was applied to the study of catalytic systems because their high rates of heat and mass transport, improved safety and ease of automation makes them particularly effective research tools in this area. A multistep flow system for the synthesis of benzylacetone from benzyl alcohol via oxidation, aldol condensation and reduction reactions was developed by utilising three micropacked bed reactors and a gas liquid membrane separator. This reaction had previously been conducted in batch cascade, however, the multistep flow system enabled the achievement of higher yields with lower catalyst contact times because separating each reaction into its own reactor allowed greater freedom to tailor the operating conditions for each reaction. The multistep system also allowed the catalysts to be studied in a process wide environment, leading to the identification of significant catalyst inhibition due to by and co-products from upstream reactions. An automated closed loop microreactor platform was developed which utilised Model-Based Design of Experiments (MBDoE) algorithms for rapid kinetic modelling of catalytic reactions. The automated platform was first applied to the homogenous esterification of benzoic acid with ethanol using a sulfuric acid catalyst, where a campaign of steady-state experiments designed by online MBDoE led to the estimation of kinetic parameters with much higher precision than a factorial campaign of experiments. This reaction was then conducted with MBDoE designed transient experiments, which dramatically reduced the experimental time required. The same reaction was studied using a heterogeneous Amberlyst-15 catalyst, and by combining factorial designs, practical identifiability tests and MBDoE for model discrimination and parameter precision, a practical kinetic model was identified in just 3 days. The automated platform was applied to the oxidation of 5-hydroxymethylfurfural in a micropacked bed reactor with gas-liquid flow using AuPd/TiO2 catalysts, however due to poor experimental reproducibility, a kinetic model was not identified.
... [305] Many other conventional (non-biobased) hydrogenation reactions have been performed using heterogeneous catalysts in wall-coated or packed bed microreactors. [180,181,[306][307][308] In packed bed microreactors the use of small catalyst particles is inevitable, potentially causing high pressure drop. Wall-coated microreactors can maintain enhanced mass transfer without higher pressure drop generation, [180] making them potentially suitable for the processing of highly viscous biomass sources such as in the HDO of glycerol or thick bio-oils. ...
Article
Full-text available
Biomass as a renewable and abundantly available carbon source is a promising alternative to fossil resources for the production of chemicals and fuels. The development of biobased chemistry, along with catalyst design, has received much research attention over recent years. However, dedicated reactor concepts for the conversion of biomass and its derivatives are a relatively new research field. Continuous flow microreactors are a promising tool for process intensification, especially for reactions in multiphase systems. In this work, the potential of microreactors for the catalytic conversion of biomass derivatives to value‐added chemicals and fuels is critically reviewed. Emphases are laid on the biphasic synthesis of furans from sugars, oxidation and hydrogenation of biomass derivatives. Microreactor processing has been shown capable of improving the efficiency of many biobased reactions, due to the transport intensification and a fine control over the process. Microreactors are expected to contribute in accelerating the technological development of biomass conversion and have a promising potential for industrial application in this area.
... These devices perform gas-liquid-solid reactions that benefit from the small volumes and an improved heat and/or mass transfer. [7][8][9][10][11][12][13] Kashid and Kiwi-Minsker 14 have reviewed the different potential applications of packed bed microreactors for gas-liquid-solid reactions. ...
Article
We describe the co-current flow pattern of gas and liquid through micro-fabricated beds of solid and pillars under variable (i) capillary number, (ii) contact angle or wettability and (iii) pillar arrangement, i.e. modifying the distance between pillars or their size and comparing regular with more chaotic systems. Laser-induced fluorescent microscopy and image analysis are used to study the hydrodynamic interactions in terms of dynamics, liquid hold-up, and gas-liquid interfacial area per reactor volume. Those parameters provide insights into the multiphase flow patterns in these systems, how to control them, maximize mass transfer rate and unlock the potental of microreactors to reveal further intrinsic information.
... Kinetic investigations in a microreactor setup require a precise and efficient procedure for the determination of conversion-time curves. 14,33,34 Our setup ( Fig. 1) allowed for fully automated steady-state experiments with flow rate variation, continuous quenching, and sampling. ...
Article
Full-text available
We investigated solvent-free synthesis of the ionic liquid 1-butyl-3-methylimidazolium bromide in a microreactor setup. Time-conversion curves were used to derive a model for the liquid-liquid two-phase system taking both heat transfer and mass transfer into account. Simulations conducted with parameter variations were used to evaluate the general influence of mass and heat transfer coefficients on the conversion and temperature profiles in a flow reactor. A scale-up of the microreactor experiments to production in a millistructured plate reactor can be limited by insufficient heat removal, which results in parametric sensitivity. Thus, a general stability criterion was applied to the reactor model to derive stability diagrams from the calculated temperature profiles. These diagrams provide parameter ranges that ensure stable reactor operation, and can be used to predict the effectiveness of different scale-up concepts. Several concepts were combined in the design of a reaction-specific optimized multi-injection flow reactor with a channel geometry that could be adapted to the predicted local rate of heat generation.
... [12][13][14][15] The flow behavior and mass transfer characteristics have been discussed in various flow regimes and under various operating conditions. Compared to the homogeneous reaction of CO 2 absorption, heterogeneous reactions (e.g., hydrogenation, 16 oxidation, 17 and Fischer-Tropsch synthesis 18 ) are more common in practice. Taking the Taylor flow condition as an example, the processes for homogeneous and heterogeneous reactions are largely different. ...
Article
The hydrodynamic characteristics of gas-liquid two-phase flow can significantly affect the performance of gas-liquid-solid microreactors. Using nitrobenzene hydrogenation as the reference heterogeneous catalytic reaction, the two-phase reacting flow behavior was visualized and characterized. Distinct differences in the length evolution and migration velocity and residence time of gas slugs were noticed for the reaction and non-reaction cases. The interface retraction of gas slug was observed, which was mainly due to the hydrogen consumption at the gas pressure accumulation stage. Moreover, effects of the gas and liquid flow rates as well as the inlet nitrobenzene concentration on the two-phase flow behaviors and microreactor performance were also investigated. The results suggested that increasing the gas flow rate could enhance nitrobenzene conversion, but this effect was impaired by the reduced residence time at high gas flow rate. Higher nitrobenzene concentration could enhance the interface retraction and extend the residence time, together promote aniline production but in a trade-off with the conversion. This work reveals the intrinsic interaction between two-phase flow behaviors and catalytic reaction in microreactors, which can play a significant role in the development of microreactor technology.
... 8,9 Generally, for microreactors with catalysts, effective control of the chemical reaction rate is crucial for the reactions 3,10 with desired conversion, 11,12 purity, 13 selectivity, 14 and safety. 7 Usually, the chemical reaction rate in microreactors can be regulated by adjusting certain parameters like concentration, 15 pressure, 16 temperature, 17 and flux. 9 However, all these approaches are passively relying on manual operations; i.e., the current microreactors cannot make an initiative adjustment for reactions responding to the change in environments. ...
Conference Paper
Nowadays efficient and reliable control of highly exothermic reactions to effectively prevent overheating or even explosions still remains a challenging task, although newly developed microreactor technology has shown promise. Here, we report a novel smart microreactor system equipped with responsive catalytic nanoparticles on microchannels for self-regulated control over highly exothermic reactions by responding to the reaction-generated heat. On the basis of shrinking/ swelling behaviors of polymeric networks in the responsive catalytic nanoparticles, the smart microreactor could respond to the change of reaction temperature to tune the catalysis activity of catalytic particles in a thermo-feedback process. As a breakthrough result, highly exothermic reactions carried out in such a microreactor can be wellcontrolled in a self-regulation process without any manual assistance, efficiently ensuring the safety of the reaction. Such smart responsive catalytic systems have high potential and are attractive as a new generation of efficient tools that feature a selfregulation property for highly exothermic catalytic reactions.
... 8,9 Generally, for microreactors with catalysts, effective control of the chemical reaction rate is crucial for the reactions 3,10 with desired conversion, 11,12 purity, 13 selectivity, 14 and safety. 7 Usually, the chemical reaction rate in microreactors can be regulated by adjusting certain parameters like concentration, 15 pressure, 16 temperature, 17 and flux. 9 However, all these approaches are passively relying on manual operations; i.e., the current microreactors cannot make an initiative adjustment for reactions responding to the change in environments. ...
Conference Paper
Metal particles with dimensions in nanoscale as ideal candidates of catalysts have shown instinctively superior properties compared with bulk ones owing to their high surface-to-volume ratio. Usually the single-structured metal nanocatalysts with abundant active-sites exposed on surface only enable reactions monotonously occur faster or slower. However, ideally the catalysts are required to independently respond to the change in reaction environments to achieve smart self-regulation for effectively controlling the chemical reaction process, especially for safety considered when used for ultrafast high exothermic reactions with vast amount of gas and heat generated. Here we utilize in situ growth of silver nanoparticles embedded in the outer networks of the thermo-responsive polymeric nanogels to build a new class of metal/polymer nanocomposites. Based on the shrinking/swelling behaviors of the polymeric networks in the responsive nanocatalysts, the as prepared smart responsive nanocatalysts acting like “living” catalyst can tune and control the exposed active site of the embedded metal catalysts responding to the reaction heat, in which the overheating and explosion for high exothermic reactions can be self-regulatively prevented without any manual assistance in both batch reactors and continuous-flow of microchannel reactors, and thus the safety of such reactions can be effectively ensured. Furthermore, feedback signals in the reaction environment like pH, ionic and glucose, etc. can also be designed as new generation of efficient smart nanocatalsts by incorporating diverse functional polymers.
... 8,9 Generally, for microreactors with catalysts, effective control of the chemical reaction rate is crucial for the reactions 3,10 with desired conversion, 11,12 purity, 13 selectivity, 14 and safety. 7 Usually, the chemical reaction rate in microreactors can be regulated by adjusting certain parameters like concentration, 15 pressure, 16 temperature, 17 and flux. 9 However, all these approaches are passively relying on manual operations; i.e., the current microreactors cannot make an initiative adjustment for reactions responding to the change in environments. ...
... When using even smaller catalyst particles, in particular, smaller than 200 mm, internal diffusion limitations can be reduced and the flow becomes more stable due to capillary effects. However, practical applications might be limited by a high pressure drop and a strong tendency toward clogging with decreasing particle size [21][22][23][24][25]. ...
Article
The continuous hydrogenation of a mixture of L-arabinose and D-galactose over a Ru/C catalyst was investigated in a miniaturized packed bed reactor. The reaction is one important step of the transformation process of the naturally occurring hemicellulose arabinogalactan (AG) into valuable sugar alcohols. Process intensification was accomplished by reducing the reactor dimensions to a few millimeters, thus leading to better mass and heat transfer performance. The effect of temperature, pressure and liquid flow rate on the yield as well as byproduct formation will be discussed. Based on a kinetic model derived from batch experiments, a model of the continuous reactor was developed and used for scale-up purposes.
Article
Hundred-gram scale of highly selective catalytic hydrogenation of folic acid has been developed, which is adopted continuous-flow technology with Raney Ni as a catalyst. Through optimization of the reaction condition, a high conversion rate of folic acid (> 99%) and a high selectivity (99%) of tetrahydrofolate have been achieved. Additionally, a high-purity calcium-6S-5-methyltetrahydrofolate (6S-5-MTHF.Ca) has been synthesized from tetrahydrofolate obtained by continuous hydrogenation through chiral resolution, methylation, salting and recrystallization (purity: 99.5%, de: 97.6%). Compared to known methods, this method provides a feasible procedure using simple, inexpensive, and readily available reagents, making it a step-economical and cost-effective alternative strategy for production of tetrahydrofolate and its active derivatives. For Table of Contents Only
Article
Full-text available
In heterogeneous catalysis, heterolytic H2 activation for (selective) hydrogenation and hydroprocessing reactions involves the dissociation of adsorbed H2 molecules into proton (Hδ+) and hydride (Hδ−) on the catalyst surface. This approach offers several advantages, including high selectivity for polar bond (s), a low energy barrier for H2 dissociation, a high capacity for reaction‐favorable H2 adsorption, and reduced catalyst poisoning. This requires the construction of frustrated Lewis pairs on the catalyst surface, satisfying specific criteria, such as having an abundant quantity of Lewis pairs with steric hindrance and maintaining a certain distance of 3–5 Å between the pairs. This review highlights intrinsic catalyst properties for heterolytic H2 activation based on state‐of‐the‐art reports. The main components necessary for this activation include supports with strong basic sites and/or oxygen vacancies, and/or metals of single atom. For this purpose, designed catalytic materials aim to strengthen the Lewis acidity and basicity, improve the polarization of Lewis pairs, enrich oxygen vacancies, maximize the interfacial area between metal species and Lewis base, and enhance metal–support interaction. Therefore, heterogeneous catalysts retaining such heterolytic H2 activation characteristics will be significantly effective in various hydrogenation and hydroprocessing reactions.
Article
Since the 1930s, fixed bed reactors (FBR) have been operated for continuous hydrogenation reactions in the petrochemical/fine chemical industries, with publications each year detailing engineering principles, scientific breakthroughs, equipment design and setup, from these industries. Only in the last two decades, FBR have started to be utilized in the pharmaceutical industry as a result of sustainability commitment and growing demand of complex and specialized drugs. Most of the engineering knowledge is transferable across industries; however, there are differentiators inherent to each industry, with the pharmaceutical industry having its own unique challenges. One of the main differentiators between industries is the reactor scale and, consequently, reactor catalyst requirements. Petrochemicals or fine chemicals operate on a large industrial scale, with up to 72 m high reactors, with an internal diameter on the order of 5 m (China Petroleum & Chemical Corporation), and require large volumes of catalysts because of the high product demand for thousands of tonnes per year, while for the pharmaceutical industry, a smaller scale reactor is required for product demand in the thousands of kilograms per year range. It is the reactor size that defines catalyst specifications, such as particle size and geometry. Many transformations have emerged from academic and medicinal chemistry groups utilizing the ThalesNano H-Cube; however, there are relatively few reported processes that have been scaled within the pharmaceutical industry. This Perspective outlines a review of continuous flow hydrogenation technologies; focusing on the trickle bed reactor (TBR) and the respective process operation and effect of process variables on reaction rate requirements for the pharmaceutical industry; it also reflects on transformation examples using TBR across the pharmaceutical industry.
Article
A continuous flow system based on a micro-packed bed reactor was developed for hydrodechlorination, and the hydrogenation of chlorobenzene was selected as the model reaction. With the optimal reaction conditions, a conversion and selectivity of 100% were obtained.
Article
Oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) is of great importance for the production of biopolymer. It is regarded as a representative of the heterogeneous process, in which the reactant in the gas phase and liquid phase interact with each other over the solid catalysts. Due to the low mass-transfer efficiency and co-existence of O2 and organic compounds in the batch reactor, low catalytic efficiency and safety concerns hiders the commercial application. Herein, a micropacked-bed reactor was used to realize the efficient and ultrafast continuous-flow synthesis of FDCA. Au/CeO2 was used as a catalyst and O2 was used as a green oxidant. Owing to the enhanced gas−liquid mass transfer efficiency, an HMF conversion of 100% and an FDCA selectivity of 90 % were achieved within only 41 s, which represents a space-time-yield of 1−2 orders of magnitude higher than that of traditional reactors. By virtue of the minimized internal and external mass transfer resistances, kinetic parameters of the reaction were determined. The rate constants were more than one order of magnitude higher than those of other strategies. In addition, the oxidation of HMFCA to FFCA was determined to be the rate-controlling step. Overall, this work not only delineates an efficient strategy for synthesizing FDCA from HMF, but also opens a new avenue for enhancement of heterogeneous reactions suffering from limited mass transfer.
Article
In recent years, self-optimization strategies have been gradually utilized for the determination of optimal reaction conditions owing to their high convenience and independence from researchers' experience. However, most self-optimization algorithms still focus on homogeneous reactions or simple heterogeneous reactions. Investigations on complex heterogeneous gas-liquid-solid reactions are rare. Based on the Nelder-Mead simplex method and Bayesian optimization, this work proposes a reaction optimization framework for optimizing complex gas-liquid-solid reactions. Three gas-liquid-solid reactions including the hydrogenations of nitrobenzene, 3,4-dichloronitrobenzene, and 5-nitroisoquinoline are investigated, respectively. Reaction parameters (temperature, hydrogen pressure, liquid flow rate, and gas flow rate) are optimized. Compared with the traditional OVAT method, the proposed Bayesian based optimization algorithm exhibits remarkable performance with higher yields (0.998, 0.991 and 0.995, respectively) and computational efficiency.
Article
The kinetics of the glycerol steam reforming reaction catalyzed by a nickel-promoted metallurgical residue was studied in a fixed-bed reactor at atmospheric pressure. The temperature was varied between 480°C and 580 °C. The experimental reaction rates were correlated via different heterogeneous kinetic models based on Langmuir-Hinshelwood-Hougen-Watson mechanisms that consider single- or dual-site adsorption of the reactants. The mechanism that provided the most mathematically accurate and thermodynamically consistent results is initiated by dissociative adsorption of glycerol, which cause the breaking of two C-C bonds in the glycerol molecule upon adsorption. This model claims that the dehydrogenation of an adsorbed glycerol intermediate is the rate-determining step of the global reaction. A macroscopic analysis of the glycerol to gas consumption rates also validated the activation energies identified by the successful heterogeneous model by fitting the experimental data to a straightforward power law model. The activation energy was found to be 66.1 kJ·mol⁻¹ with a partial order with respect to glycerol of 0.63.
Article
The selective hydrogenation of halogenated nitroaromatic compounds is of great importance in the fine chemical industry. However, the hydrogenation reactions in commonly utilized batch reactors suffer from the undesired dehalogenation, resulting in higher requirement for subsequent separation processes and severe corrosion to industrial fatalities. In this work, a H-flow system with the micropacked bed reactor was developed for the selective hydrogenation of halogenated nitroaromatic compounds and the reduction of 3,4-dichloronitrobenzene was selected as the model reaction. With the optimal hydrogenation conditions, the yield of 3,4-dichloroaniline was obtained as high as 99.8% under mild conditions. With this strategy this flow system was successfully employed to the reduction of other chlorinated nitroaromatics also demonstrating low dehalogenation. The H-flow system enables negligible dehalogenation and remarkable yield of target product with higher efficiency and lower energy cost compared with the batch reactor.
Article
As an important form of reactors for gas/liquid/solid catalytic reaction, trickle bed reactors (TBRs) are widely applied in petroleum industry, biochemical, fine chemical and pharmaceutical industries because of their flexibility, simplicity of operation and high throughput. However, TBRs also show inefficient production and hot pots caused by non-uniform fluid distribution and incomplete wetting of the catalyst, which limit their further application in chemical industry. Also, process intensification in TBRs is necessary as the decrease in quality of processed crude oil, caused by increased exploitation depths, and more restrictive environmental regulations and emission standards for industry, caused by increased environment protection consciousness. In recent years, lots of strategies for process intensification in TBRs have been proposed to improve reaction performance to meet the current and future demands of chemical industry from the environmental and economic perspective. This article summarizes the recent progress in techniques for intensifying gas/liquid/solid reaction in TBRs and application of intensified TBRs in petroleum industry.
Article
An automated flow platform based on tube-in-tube contactor and micropacked bed reactor is developed to measure the kinetics of gas-liquid-solid hydrogenation reactions. The liquid flowing in the inner tube of the tube-in-tube contactor is rapidly saturated to ensure a constant H2 concentration before entering the micropacked bed, which transforms the gas-liquid-solid system to a liquid-solid system. A ramping strategy is adopted in which the continuously varied residence time and the corresponding conversion data are obtained in a single experiment. Two reactions including hydrogenation of α-methylstyrene and nitrobenzene are chosen to demonstrate the accuracy and efficiency of this automated platform. Varying the flow rate ramping shows that accurate kinetic determination requires a specific range of flow rate ramps. A kinetic curve of conversion versus residence time (more than ten thousand data points) can be obtained in a single experiment within 50 min. The kinetic parameters obtained with this strategy agree well with literature values. The automated flow platform with flow rate ramping enables accurate determination of gas-liquid-solid reaction kinetics with higher efficiency and lower reagent cost compared with other methods.
Article
An autonomous reactor platform was developed to rapidly identify a kinetic model for the esterification of benzoic acid with ethanol with the heterogeneous Amberlyst-15 catalyst. A five-step methodology for kinetic studies was employed to systematically reduce the number of experiments required to identify a practical kinetic model. This included (i) initial screening using traditional factorial designed steady-state experiments, (ii) proposing and testing candidate kinetic models, (iii) performing an identifiability analysis to reject models whose model parameters cannot be estimated for a given experimental budget, (iv) performing online Model-Based Design of Experiments (MBDoE) for model discrimination to identify the best model from a list of candidates, and (v) performing online MBDoE for improving parameter precision for the chosen model. This methodology combined with the reactor platform, which conducted all kinetic experiments unattended, reduces the number of experiments and time required to identify kinetic models, significantly increasing lab productivity.
Article
Full-text available
Intensified trickle bed reactors were developed for catalytic wet air oxidation (CWAO) of phenol, by generating microbubbles before gas/liquid fluid flows along catalyst packed‐beds. By coupling gas‐liquid microdispersion module, phenol disappearance rate significantly increases under the same operating conditions and phenol conversion reaches 92% in 22 seconds at 160°C and 1000 kPa. Effects of operating conditions were studied systematically and results demonstrated characteristics of high‐interaction regime at low Reynolds number. Comparison of effects among mass transfer and reaction steps shows CWAO reaction is controlled by resistance to liquid‐solid mass transfer of phenol in most cases, while gas‐liquid mass‐transfer‐resistance is ignorable. A dimensionless correlation, Sh = 2.29φ−0.91(ReL + ReG)0.04, was established, by considering influences of liquid film thickness and fluid flow situations on liquid‐solid mass transfer coefficient in microbubble‐in‐liquid/catalyst‐particle system. The study would provide an effective method for intensifying CWAO and other liquid‐solid‐mass‐transfer‐resistance‐controlled gas/liquid/solid catalytic reactions and help understand mass transfer mechanism in new gas/liquid/solid system.
Article
Oxidation of crotonaldehyde to crotonic acid is an important chemical reaction process because crotonic acid, its derivative and copolymer are ubiquitous in the productions of chemical, cosmetic, and medicines. However, the reactor safety and process efficiency are still not satisfactory. In order to solve such problems, a novel reactor of gas-liquid-solid mini-fluidized bed with bed inner diameter of 3 mm was developed to carry out the selective catalytic oxidation reaction. The effects of operation conditions and solid particle properties on the conversion rate of reactant crotonaldehyde and the selectivity of product crotonic acid were investigated. The causes of these effects are explained from the standpoint of residence time and gas-liquid mass transfer flux. Moreover, the comparison of reactor performance between the three-phase mini-fluidized bed and the batch stirred tank reactor as a traditional one was made to evaluate the performance of such a reactor. Experimental results show that the average reaction or conversion rate of the mini-fluidized bed is about 30 times much higher than that of batch stirred tank reactor to evaluate the improved performance. But the selectivity is less affected by the operation conditions and solid particle bed properties. The size reduction of three-phase mini-fluidized bed decreases the mass transfer distance of molecular diffusion, and the solid particles and mini-bubbles not only provide the higher specific interface area but also cause hydrodynamics changes that is to intensify the interface disturbance, which effectively accelerate the mass transfer.
Article
Nowadays, one of the major challenges for the chemical industry is the development of innovative processes with less by‐product formation, improved product yields, and high‐energy efficiency. Microreactor technology provides unique solutions to meet these requirements. As an important means for process intensification, microchemical technology is expected to have a number of advantages for chemicals production. The high heat‐ and mass‐transfer rates in microreactors enable many highly exothermic, fast reactions to be operated under nearly isothermal conditions, thereby better selectivity or yield can be reached as compared to conventional reactors.This chapter is a summary of recent developments in microreactor technology for gas–liquid catalytic reactions that constitute up to 20% of all reactions used in fine chemicals industry. The fundamentals of design and operation of microreactors are explained. Various design concepts are discussed and key features are illustrated, and examples of successful applications are given.
Article
The 2-chloro-4-nitroaniline liquid-phase hydrogenation kinetics on supported palladium and platinum catalysts differing in the nature of the carrier and the active metal content was studied for the first time. The experiment was carried out at elevated hydrogen pressures in the range of 9 - 12 atm and 303 K in solvents 2-propanol-water and ethyl acetate in the reactor such as Vishnevsky autoclave. The main kinetic parameters of the reaction have been determined, and the influence of various parameters on the regularities of the process has been established. It is shown that an increase in the active metal content in the catalyst leads to an increase in the rate of the hydrogenation reaction of 2-chloro-4-nitroaniline. When using platinum supported catalysts, the rate of hydrogenation of 2-chloro-4-nitroaniline is significantly higher than when using supported palladium catalysts. The replacement of the liquid phase of the catalyst system with 2-propanol by ethyl acetate adversely affects the reaction rate. The influence of the catalytic system nature and composition on the target product dehalogenation degree was determined. It was found that when carrying out the reaction at elevated hydrogen pressures, it is preferable to use low-percentage platinum catalysts, rather than palladium catalysts, since the former provide less dehalogenation of the target product. For citation: Klimushin D.M., Krasnov A.I., Filippov D.V., Sharonov N.Yu. Hydrogen pressure, solvent and catalyst nature influence on 2-chloro-4-nitroaniline hydrogenation regularities. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 9-10. P. 30-35
Article
Process intensification commonly enables reaction acceleration and therefore continuous-flow/PAT is urgently needed. The low volumes typical for micro-flow pose challenges for online sampling operations in analytics. In this paper, a very fast process is combined with a modified ultra-high-performance liquid chromatography (UHPLC) system allowing for very fast sampling and analysis. Low-volume online sampling according to the needs posed by PAT for pharma quality control, is introduced here for UHPLC analysis of the photo-Claisen rearrangement in micro-flow. Chances and challenges are critically reviewed, including the reproducibility and robustness of the sampling. Furthermore, the ability and speed of the chosen set-up in order to capture process changes and adjust the process parameters properly is investigated. With the applied online sampling system, it was possible to perform, almost unattended and spending 12 times less sampling volume, a full factorial analysis of all relevant reaction conditions (243 experiments) in three days. Such quality-in-the-process-line (QuIProLi) online sampling avoided random errors due to automation.
Article
Nowadays efficient and reliable control of highly exothermic reactions to effectively prevent overheating or even explosion still remains a challenging task, although newly-developed microreactor technology has shown a promising way. Here we report a novel smart microreactor system equipped with responsive catalytic nanoparticles on microchannels for self-regulated control over highly exothermic reactions by responding to the reaction-generated heat. Based on shrinking/swelling behaviors of polymeric networks in the responsive catalytic nanoparticles, the smart microreactor could respond to the change of reaction temperature to tune the catalysis activity of catalytic particles in a thermo-feedback way. As a breakthrough result, highly exothermic reactions carried out in such a microreactor can be well controlled in a self-regulation way without any manual assistance, ensuring the safety of the reaction efficiently. Such smart responsive catalytic systems are highly potential and attractive as new generation of efficient tools that featured with self-regulation property for highly exothermic catalytic reactions.
Article
Hydrodynamic study was performed on the gas-liquid-solid micro-fluidized beds with 0.8 mm bed diameter and multi-bubbles through high speed camera recording system. Flow regimes including dispersed bubble flow, coalesced bubble flow and slug flow were identified from the multi-bubble flow. Wall effect at the small bed-to-particle diameter ratio led to the occurrence of bubble coalescence and flow regime transition at lower solid holdups. Obvious bed contraction appeared only at lower liquid velocities or higher gas velocities. The diameter range of the spherical micro-bubbles in the micro-fluidized beds was 200 - 500 μm. The bubble size in dispersed bubble flow was normally distributed and slightly increased with the solid holdup. And in coalesced bubble flow, the bubble size was decided by the overall coalescence probability and presented a special step distribution. The larger coalesced bubbles concentrated the distribution of bubble terminal velocity. And the bubble terminal velocity decreased with the solid holdup and inversely with the bubble size. In dispersed bubble flow regime, there was positive linear relationship between the apparent viscosity and the solid holdup. Three-phase micro-fluidized beds meet the further development of micro-reactors, and this study on the hydrodynamic characteristics contributes to their wider application.
Article
Full-text available
Hydrogenation of o-nitroanisole to o-anisidine was investigated using Pd-C catalyst in a stirred slurry reactor. The initial rate data were analyzed to check the importance of mass transfer effects. A batch reactor model has been derived and the performance compared with experiments. The use of the batch reactor model in evaluation of kinetics and mass transfer parameters has been discussed.
Article
Full-text available
This paper deals with the modelling of a multiphase batch reaction: catalyzed nitrobenzene hydrogenation. The reactor's gas–liquid mass transfer parameters in the absence of any reaction are first identified, and the solubility of hydrogen in the reactional medium is also measured. A reaction kinetics and heat parameter identification method is then developed. This method is based on a light experimental procedure, requiring measurement of only temperature and pressure variations in the batch reactor.This study is carried out in an isothermal batch and semi-batch reactor, whose initial temperature varies between 283 and 333K. A simplified model associating the hydrodynamic gas–liquid mass transfer parameters and the chemical kinetics processes is developed. The key parameters that can influence the reaction development are the hydrogen pressure, the coolant temperature, the quantity of catalyst pellets and the stirring speed. The developed model also allows the precise simulation of the extent of reaction and the temperature evolution of the studied multiphase catalytic reaction.
Article
Full-text available
Hydrogenation of 2,4-dinitrotoluene (DNT) to 2,4-diaminotoluene (DAT) has been carried out over a 5% Pd/C catalyst. Gas chromatography and liquid chromatography have been used to detect the reaction intermediates. 4-Hydroxylamine,2-nitrotoluene (4HA2NT) is the main reaction intermediate. The two amino-nitro compounds 4-amino,2-nitrotoluene (4A2NT) and 2-amino,4-nitrotoluene (2A4NT) are the other relevant intermediates found. 4HA2NT decomposes by exposure to air and in the GC injector thus complicating the analysis of the reaction mixture. A simple procedure has been developed to perform the GC analysis without interference of the hydroxylamine. A kinetic study has been also carried out and a reaction pathway has been proposed. Intermediates are formed from DNT through three parallel reactions. They are then hydrogenated to the final product DAT by a series of consecutive reactions.
Article
Full-text available
A review of recent developments in multiphase catalytic processes for the manufacture of pharmaceutical and fine chemicals, and an overview of reaction engineering principles needed for analysis of the local and overall reaction rate for reactor design and interpretation of performance is presented. The first section gives an overview of recent applications in pharmaceuticals and fine chemicals where heterogeneous and homogeneous catalyzed multiphase chemistries have been identified that are more efficient and represent safer operation with decreased environmental impact when compared to existing processes. The next three sections describe a scheme for classification of the various types of reactions that are typically encountered, along with distinguishing features of these reactions and commonly used multiphase reactor types. This is followed by a review of reaction engineering principles needed for describing the local overall rate of reaction, including a summary of typical models for evaluation of the intrinsic reaction kinetics, incorporation of transport-kinetic interactions, methods for identification of the controlling reaction regime and assessment of the relative contribution of transport effects. The next two sections set forth basic reactor models for commonly used reactor types, including mechanically agitated reactors and bubble column reactors. A brief summary of commonly used correlations for estimation of mass transfer coefficients in these reactors for gas-liquid and liquid-liquid systems is also given. The final section is devoted to a summary of key reaction engineering issues that occur in pharmaceutical and fine chemical multiphase catalytic processes, along with some thoughts on future needs and challenges.
Article
Full-text available
A kinetic study into the styrene hydrogenation over a palladium on alumina catalyst has been made. Styrene was used as a model component for pyrolysis gasoline. A kinetic rate expression has been derived and the inhibiting e6ect of sulfur components has been included. Using this kinetics and mass-transfer models compiled from literature, the performance of two types of reactors for the styrene (pyrolysis gasoline) hydrogenation has been evaluated. A structured reactor such as a monolith has large advantages over a conventional trickle-bedreactor. For the monolithic reactor a more than 3 times higher volumetric productivity is obtainedwith much less catalyst. The modeling results indicate that deactivation by gum formation should be significantly less due to much better hydrogen mass transfer in the reactor.
Article
A new development in the field of internals in packed columns is the use of structured packing types. Recently, a new structured packing type coated with a thin alumina layer (KATAPAKTM) has been developed. In this report, the results of an experimental and theoretical study concerning the possible applicability of this new packing material for hydrogenation processes in a trickle-bed reactor is presented. The palladium catalyzed hydrogenation of α-methylstryrene is used as a model reaction to study hydrodynamics and mass transfer characteristics in a trickle-bed reactor under reactive conditions. Converstions at several process conditions are measured in a pilot plant in which 3 mm spheres as well KATAPAKTM is applied as packing materials. A comparison of the results of some physical absorption experiments with the results of hydrogenation experiments showed that the resistance in series model—in which the total resistance against mass transfer is calculated from the separate resistances—is not valid in systems where heterogeneous reactions at the solid surface can enhance the mass transfer-rate at the gas-liquid interphase. With the aid of a developed trickle-bed reactor model, based on liquid diffusion, simultaneous reaction at the solid surface and zero volume mixing points, the mass transfer phenomena in trickle-bed reactors in conditions where the resistance in series model fails can be explained and described. The numerically solved model calculates the hydrogen profiles in the liquid films of the reactor and over all single pass conversions at several process conditions. These conclusions are confirmed by the results of the simulation of a model reactor, i.e. the laminar film reactor with a catalytically active wall. From the results of the measurements it could be concluded that in trickle-flow conditions, the application of KATAPAKTM does not significantly improved on the overall performance of trickle-bed reactors. The increase of the physical absorption rate due to better mass transfer characteristics of structured packings compared to dumped packing types—as reported in literature—will be eliminated to a certain extent in reactive systems due to the enhancement effect of heterogeneous reactions in trickle-flow operation.
Article
A precise knowledge of solubility of gases in liquids is essential for analyzing gas-liquid and gas-liquid-solid reactions. This paper presents solubility data of hydrogen in o-nitroanisole, o-nitroanisole-methanol mixtures, and o-anisidine under various conditions of temperature and pressure. The data are important in the design of a reactor for o-anisidine which is manufactured by catalytic hydrogenation of o-nitroanisole. No data have been published for the solubility of hydrogen in o-nitroanisole and o-anisidine. The solubility of hydrogen in o-nitroanisole, onitroanisole-methanol mixtures, and o-anisidine was studied in the range of interest for hydrogenation, namely, 40-80 °C, 7-50 atm, and 3-8 M concentration.
Article
A differential packed-bed reactor microfabricated in silicon is presented for heterogeneous gas phase catalyst testing. A novel cross-flow design achieves uniform flow distribution over a wide (25.5 mm) but shallow (400 μm long × 500 μm deep) catalyst bed to realize differential conversions with sufficient reaction to allow monitoring with conventional analysis techniques. The use of catalyst particles (diameters 53–71 μm) implies that conventional synthesis procedures can be used and experimental results translated to catalysts in macroscopic reactors. A set of shallow microfabricated channels maintains a spatially uniform pressure drop irrespective of variations in catalyst packing. Experiments and finite element simulations confirm the bed is isobaric with even distribution of flow. Quantitative analysis of transport effects indicates the microreactor also suppresses thermal and mass gradients in the catalyst bed. These characteristics make the cross-flow microreactor a useful tool for experiments to obtain kinetics and optimize reaction conditions. Experiments with CO oxidation confirm the ability of the microreactor to obtain kinetic and mechanistic information that compare well with parameters previously determined in macroscale systems. Reactor modeling also indicates that the catalyst bed operates differentially even at total conversions that would be considered large in traditional plug flow reactors, adding to the utility of the cross-flow microreactor as a laboratory tool.
Article
Dimensionless criteria are derived for evaluating the significance of interphase and interparticle temperature gradients in fixed bed catalytic reactors. Comparison of the criteria reveals that the magnitudes of the heat transport resistances are generally in the order: interparticle > interphase > intraparticle. The criteria show the critical importance of decreasing the diameters of the reactor and the catalyst particles to minimize transport limitations. Dilution of the bed with inert solids is shown to be advantageous only at Reynolds numbers sufficiently low that the effective thermal conductivity of the bed is insensitive to the flow rate.
Article
Catalytic hydrogenations of aromatic nitro compounds are known to be potentially hazardous reactions. Their safety depends both on the properties of compounds and on the operating conditions. The focus of this paper is on thermal hazards. Firstly, the thermal stability of the reaction mixtures determines the temperature range in which the reaction can be run safely. Secondly, accumulation of hydroxylamine is a potential hazard as it can lead to undesired side-reactions, which are highly exothermic and, in contrast to the hydrogenation, cannot be controlled by the hydrogen supply. Using a reaction calorimeter, the thermal data of the reactions, i.e. overall heat and heat flow during the reaction, can be measured. Conclusions on the accumulation of intermediates in the reaction mixture can also be drawn from these data. Finally, the thermal behaviour of the reactor in the case of a cooling failure can be predicted with a high accuracy.
Article
The Pd-catalysed hydrogenation of 2-butyne-1,4-diol has been studied in the monolith CDC and in a single channel capillary reactor in (I) the pressure range 100–300kPa, (II) the temperature range 298–328K using a 30%v/v 2-propanol/water solvent. The monolith reactor was operated in downflow mode such that the reaction fluid was either single phase or in Taylor Flow. The latter was also employed in the single-capillary reactor. The kinetics were found to be a function of the hydrodynamic conditions. This was not found to be due to transport problems but to a function of the surface concentration of reacting species. Reaction rates varied from a positive order (0.13) to zero order to negative orders (-0.34 to -0.38) in 2-butyne-1,4-diol concentration. A model based upon a Langmuir–Hinshelwood mechanism was applied and found to predict reasonably well reaction rates and product distribution. High selectivity values towards the 2-butene-1,4-diol were found in both the single- and multiple-capillary reactor even at 100% conversion of the alkyne.
Article
The state-of-the-art of the gas-liquid mass transfer characteristics in trickle-bed reactors was summarized and its quantification methods were reevaluated based on a wide-ranging data base of some 3200 measurements. A set of three unified whole-flow-regime dimensionless correlations for volumetric liquid- and gas-side mass transfer coefficients, and gas–liquid interfacial area, each of which spanned four-order-of-magnitude intervals, were derived. The correlations involved combination of artificial neural networks and dimensional analysis. The dimensionless interfacial area, ShL and ShG were expressed as a function of the most pertinent dimensionless groups: ReL, ReG, WeL, WeG, ScL, ScG, StL, XG, MoL, FrL, Eom, Sb.
Article
A novel catalytic gas–liquid reactor configuration, consisting of a monolithic reactor with a liquid-motive ejector as gas–liquid distributor is introduced as a retrofit or alternative to an agitated slurry reactor. The ejector distributes gas and liquid to the channels of a monolith reactor at velocities greater than those attainable with gravity-driven flow, intensifying mass transfer and reaction in a compact reactor. Pressure drops measured using this configuration do not conform to models from the literature. A strong effect of liquid coalescence properties was observed. Until fully predictive pressure drop and gas–liquid distribution models become available, successful scale-up will depend on pressure-drop data measured with industrial process conditions and fluids. Current literature models for mass transfer underpredict laboratory autoclave reaction results, indicating a need for further model development, and in the interim requiring pilot-scale testing for scale-up purposes.
Article
The mass transfer characteristics of monolith reactors in gas-liquid-solid applications have been investigated. A model is proposed which gives correlations based on different mass transfer steps for Taylor flow in capillaries. The fast hydrogenation of x-methylstyrene over Pd monolith catalysts of different cell densities (200-600 cpsi) was used as a test reaction in a pilot reactor. The reaction could be carried out in the internal and external mass transfer limited regime, as has been verified by a change in activation energy plots. Depending on the operating conditions, the overall mass transfer group k(ov)a ranged from 0.5 to 1.5 s(-1) which shows that excellent mass transfer can be achieved for gas-liquid-solid reactions in monolith reactors. (C) 2001 Elsevier Science Ltd. All rights reserved.
Article
The rate of hydrogenation of para-substituted nitrobenzene over colloidal platinum obeys the same kinetic equation found applicable to the hydrogenation over colloidal rhodium and palladium catalysts.1 The hydrogenation of aliphatic nitrocompounds seems to be poisoned by the reaction products. Another difference is that with the addition of acid or base the rate of hydrogenation of aromatic nitrocompounds increases whereas the rate for aliphatic nitrocompounds decreases.
Article
Scaling up of the monolithic three-phase reactor has been studied in the hydrogenation step of anthraquinones for large-scale production of hydrogen peroxide. The influence of flow pattern (bubble flow and slug flow), flow distribution, pressure drop, and mass transfer has been investigated. It is illustrated that the segmented gas-liquid flow (slug flow) gives the highest production rate with very small scale-up effects.
Article
A microchemical device has been built in silicon and glass by using microfabrication methods including deep-reactive-ion etch technology, photolithography, and multiple wafer bonding. The microchemical system consists of a microfluidic distribution manifold, a microchannel array, and a 25-μm microfilter for immobilizing solid particulate material within the reactor chip and carrying out different heterogeneous chemistries. Multiple reagent streams (specifically, gas and liquid streams) are mixed on-chip, and the fluid streams are brought into contact by a series of interleaved, high-aspect-ratio inlet channels. These inlet channels deliver the reactants continuously and cocurrently to 10 reactor chambers containing standard catalytic particles. The performance of the microfabricated “packed-bed” reactor is compared to that of traditional multiphase packed-bed reactors in terms of fluid flow regimes, pressure drop, and mass transfer. The hydrogenation of cyclohexene is used as a model reaction to measure the mass transfer resistances. Overall mass transfer coefficients (KLa) are measured to range from 5 to 15 s-1nearly 2 orders of magnitude larger than values reported in the literature for standard laboratory-scale reactors.
Article
Diagnostic tests for detecting heat and mass-transfer effects in experimental catalytic reactors are reviewed and updated. New perturbation criteria are presented for intraparticle, interphase, and interparticle transport in both single- and mixed-phase flow in fixed beds. Emphasis is placed on the proper choice of reactor parameters to minimize deviations from isothermal plug-flow performance.
Article
Hydrogenation of nitrobenzene and m-nitrotoluene in mixture was performed in a monolithic Pd catalyst reactor and with ground catalyst in a slurry reactor. The gas-liquid flow in the narrow channels of the monolithic catalyst was a segmented two-phase flow. The mass transfer of hydrogen directly from the gas plugs to the channel wall was found to be the dominating transport step. This direct transport corresponded to more than 70% of the total transport of hydrogen to the channel wall in a typical run. The decreased selectivity of aniline formation found in the hydrogenations in the monolithic catalyst was explained by the influence of the film transport resistance near the channel wall. Hydrogenation of m-nitrotoluene was strongly delayed in the presence of nitrobenzene. Fitting different rate equations to the experimental data indicated that the reaction mechanism is complicated.
Article
Monolith catalyst supports are attractive as fixed bed reactors that, at the scale of the catalyst dimension, exhibit the mass transfer characteristics of slurry reactors. This paper presents a reactor design study for the single-pass conversion of dinitrotoluene in a loop configuration with an external heat exchanger. The advantage of such a loop system is the elimination of a solvent, which in turn allows more reaction heat to be recovered. The advantages of using a monolith are the low pressure drop at high recycle ratio, while maintaining good mass transfer characteristics. The modelling includes internal diffusion limitation, external mass transfer characteristics, heat effects, maldistribution and flow stability. The optimal design is found at the lowest hydrodynamic stable flow rates, where the mass transfer is fastest and the residence time in the column maximal.
Article
A study is presented on the performance potential of gas–liquid–solid multiphase catalytic reactions in small-size structured catalyst/reactor channels. A hydrogenation reaction is performed over the Ni/alumina monolith catalyst module with a model feed consisting of styrene, 1-octene, and toluene. The gas/liquid feed stream is directly delivered into a single, representative channel of the multichannel monolith catalyst module to eliminate any flow distribution problem. The reaction tests are conducted with different channel sizes, wall structures, and feed compositions. The cocurrent downflow operation is compared to the cocurrent upflow. The olefin hydrogenation reaction is found to be severely limited by mass-transfer rates. Because of intensified mass transfer inside the small catalyst channel, substantial olefin conversion (>50%) is achieved even at unconventionally high LHSV (∼2000 v/v/h). Liquid and gas superficial linear velocities were varied over a wide range (UL = 1–50 cm/s, UG = 1–2000 cm/s) to elucidate effects of possibly different flow regimes on the reaction performance. The mass-transfer rate constant of liquid reactant from bulk fluid onto the channel surface in a 1-mm reaction channel is found to be related to the flow conditions by a simple equation, akLS (1/s) = 0.094(UL + 0.1UG)0.788. The mass-transfer equation is useful for selection of suitable flow conditions for a given catalytic reaction rate. © 2005 American Institute of Chemical Engineers AIChE J, 2005
Article
Silicon microreactors with Pt/Al2O3 thin-film wall catalyst were adopted for kinetic studies of CO preferential oxidation (PrOx). The activity of this catalyst was compared to that of other catalyst systems based on similar formulation. Internal and external mass-transport and heat-transport limitations of the microreactor were examined and comparisons were made to minimized packed-bed reactors (m-PBRs). We found that at lower temperatures (<220°C), the microreactor shows negligible mass- and heat-transport resistance, implying direct access to intrinsic kinetics. However, external mass transport begins to play a significant role in limiting overall reaction rates above 220°C for PrOx. A microkinetic reaction model for PrOx was used for the study of reaction pathways and the analysis of surface intermediate species, which are difficult to study experimentally. Reaction mechanisms are discussed with these modeling results as a guide. Afterward, the results of a separate, nonisothermal reactor model using the finite-difference method are discussed to understand differences in performance of the microreactor and m-PBRs with respect to the CO conversion vs. temperature characteristic. As a result, we discovered that the temperature gradients in m-PBRs favor the reverse water–gas shift (r-WGS) reaction, thus causing a much narrower range of permissible operating temperatures compared to that of the microreactor. Accordingly, the extremely efficient heat removal of the microchannel/thin-film catalyst system eliminates temperature gradients and efficiently prevents the onset of the r-WGS reaction. © 2005 American Institute of Chemical Engineers AIChE J, 2005
Article
The rapid development of microfabrication techniques creates new opportunities for applications of microchannel reactor technology in chemical reaction engineering. The extremely large surface-to-volume ratio and the short transport path in microchannels enhance heat and mass transfer dramatically, and hence provide many potential opportunities in chemical process development and intensification. Multiphase reactions involving gas/liquid reactants with a solid as a catalyst are ubiquitous in chemical and pharmaceutical industries. The hydrodynamics of the flow affects the reactor performance significantly; therefore it plays a prominent role in reactor design. For gas/liquid two-phase flow in a microchannel, the Taylor slug flow regime is the most commonly encountered flow pattern. The present study deals with the numerical simulation of the Taylor flow in a microchannel, particularly on gas and liquid slugs. A T-junction empty microchannel with varying cross-sectional width (0.25, 0.5, 0.75, 1, 2 and 3 mm) served as the model micro-reactor, and a finite volume based commercial computational fluid dynamics (CFD) package, FLUENT, was adopted for the numerical simulation. The gas and liquid slug lengths at various operating and fluid conditions were obtained and found to be in good agreement with the literature data. Several correlations in the T-junction microchannel were developed based on the simulation results. The slug flows for other geometries and inlet conditions were also studied.
Article
Nitrobenzene hydrogenation over palladium catalyst was performed in a microstructured falling film reactor at a range of flowrates (0.5–3 ml/min) and pressure (1–6 bar). Confocal microscopy was used to measure liquid film thickness. Comparison with film thickness prediction equations showed an overprediction of 10–30%. The kLa of this system was estimated to be 3–8 s−1 with interfacial surface area per reaction volume 9000–15000 m2/m3. Conversion was found to be affected by both liquid flowrate and hydrogen pressure, and the reactor operated between the kinetic and mass transfer controlled regimes.
Article
Hydrogenation of nitrobenzene to aniline in ethanol was performed continuously in a microstructured falling film reactor at 60 °C, 1–4 bar hydrogen pressure and residence time 9–17 s. Palladium catalyst was deposited as films or particles via sputtering, UV-decomposition of palladium acetate, incipient wetness or impregnation. Deactivation was observed and was particularly pronounced for the sputtered and UV-decomposed catalysts. Catalysts prepared through incipient wetness or impregnation were more stable and activity could be recovered by oxidation at 130 °C. The main causes of deactivation were determined to be deposition of organic compounds and palladium loss.
Article
The formation of nitroso-, azo- and azoxy-aromatics depends of a relatively complex scheme involving consecutive reactions. However, all different products can be produced in good yields with palladium catalysts, using optimised kinetics, selective poisoning or alloying. These reactions show different dependencies of the reaction rate on Pd particle size and alloying. Solvents have different roles, in addition to the usual one consisting in the solubilisation of the reactants: they can change the solubility of hydrogen, compete with the reactants for adsorption at the metal surface or catalyse side reactions.
Article
The catalytic transfer hydrogenation of o-nitro anisole to o-anisidine was studied in the temperature range 35–85 °C with ammonium formate as H-donor and iso-propanol as solvent using Pd/C as catalyst above agitation speed 1000 rpm. The substrate feed concentration was varied in the range from 0.068 to 0.341 kmol/m3 while catalyst loading was in the range 1.25–10% (w/w) of o-nitro anisole. The intermediate, hydroxylamine, was detected. In 130 min, all o-nitro anisole was converted with 99% selectivity towards o-anisidine. The catalyst has considerable reusability and was regenerated after deactivation without any significance loss in activity. Reliable methods for product separation and treatment of aqueous stream obtained after washing and solvent recovery are proposed. The possibility of Fenton Chemistry to treat aqueous waste stream was explored and found suitable.
Article
Our recent studies of CO preferential oxidation (PrOx) identified systematic differences between the characteristic curves of CO conversion for a microchannel reactor with thin-film wall catalyst and conventional mini packed-bed lab reactors (m-PBR's). Strong evidence has suggested that the reverse water-gas-shift (r-WGS) side reaction activated by temperature gradients in m-PBR's is the source of these differences. In the present work, a quasi-3D tubular non-isothermal reactor model based on the finite difference method was constructed to quantitatively study the effect of heat transport resistance on PrOx reaction behavior. First, the kinetic expressions for the three principal reactions involved were formed based on the combination of experimental data and literature reports and their parameters were evaluated with a non-linear regression method. Based on the resulting kinetic model and an energy balance derived for PrOx, the finite difference method was then adopted for the quasi-3D model. This model was then used to simulate both the microreactor and m-PBR's and to gain insights into their different conversion behavior.Simulation showed that the temperature gradients in m-PBR's favor the reverse water-gas-shift (r-WGS) reaction, thus causing a much narrower range of permissible operating temperature compared to the microreactor. Accordingly, the extremely efficient heat removal of the microchannel/thin-film catalyst system eliminates temperature gradients and efficiently prevents the onset of the r-WGS reaction.
Article
Direct fluorination of toluene, pure or dissolved in either acetonitrile or methanol, using elemental fluorine was investigated in gas/liquid microreactors, namely a falling film microreactor and a micro bubble column. The experiments included measurements at high substrate concentrations and at high fluorine contents diluted in a nitrogen carrier gas, e.g. up to 50 vol.% fluorine. Results obtained were compared to the performance of a laboratory bubble column which served as a technological benchmark.Due to the formation of liquid layers of only a few tens of micrometers thickness, the microreactors provide very large interfacial areas, e.g. up to 40,000 m2/m3. These values exceed by far those of the laboratory bubble column as well as all other devices applied in practice.The potential for enhancing mass and heat transfer was verified by several experiments resulting in an increase in conversion and selectivity for the microreactors compared to the laboratory benchmark. For the falling film microreactor, yields of up to 28% of monofluorinated ortho and para products for a degree of toluene conversion of 76% were obtained. These values are of the same order as described for the industrially applied Schiemann process. Space-time yields of the microreactors, when referred to the reaction channel volume, were orders of magnitude higher than those of the laboratory bubble column. Taking into account the construction material needed, the corresponding figures of merit, for an idealized geometry as well as the existing total reactor geometry, still indicate technological and economic benefits.A variation of operating conditions for the direct fluorination revealed that conversion can be increased in the microreactors by using higher fluorine-to-toluene ratios and reaction temperatures. The choice of solvent is also essential, with acetonitrile yielding much better results than methanol.
Article
The use of segmented flow in capillaries, also known as Taylor flow, for reaction engineering purposes has soared in recent years. On the one hand, Taylor flow has been used in honeycomb monolith catalyst supports. On the other hand, Taylor flow is the common flow pattern in multiphase microchannel reactors. This contribution reviews the fluid mechanical aspects of this flow pattern in quite general terms, with an emphasis on the underlying principles. From very simple analysis, design estimates for mass transfer, pressure drop and residence time distribution may be obtained with relative ease and—for multiphase reactors—surprising accuracy.
Fine Chemicals through Heterogeneous Catalysis Solubility of hydrogen in o-nitroanisole, o-nitroanisole-methanol mixtures and o-anisidine
  • H U Blaser
  • U Siegrist
  • H Steiner
  • Wiley
  • Vch
  • Weinheim
Blaser, H.U., Siegrist, U., Steiner, H., 2001. Fine Chemicals through Heterogeneous Catalysis. Wiley/VCH, Weinheim. p. 389. Brahme, P.H., Vadgaonkar, H.G., Ozarde, P.S., Parande, M.G., 1982. Solubility of hydrogen in o-nitroanisole, o-nitroanisole-methanol mixtures and o-anisidine. Journal of Chemical and Engineering Data 27, 461–462.
Use of a monolith catalyst for the hydrogenation of dinitrotoluene to toluenediamine
  • R M Machado
  • D J Parrillo
  • R P Boehme
  • R R Broekhuis
Machado, R.M., Parrillo, D.J., Boehme, R.P., Broekhuis, R.R., 1999. Use of a monolith catalyst for the hydrogenation of dinitrotoluene to toluenediamine. US Patent 6005143.
Immobilizing heterogeneous catalysts in microchannel reactors
  • R Födisch
  • A Kursawe
  • D Hconicke
Födisch, R., Kursawe, A., HConicke, D., 2002. Immobilizing heterogeneous catalysts in microchannel reactors. In: Proceedings of the Sixth International Conference on Microreaction Technology, New Orleans, pp. 140–146.