A new continuous-flow recycle microwave reactor for homogeneous and heterogeneous chemical reactions

A new continuous-flow recycle microwave reactor suitable for organic synthesis has been developed to handle 0.51 quantities of reagents. The apparatus, which is designed for laboratory use, operates at atmospheric pressure in open- or closed-loop mode. It is fitted with a temperature control system. We describe this novel reactor and illustrate its efficiency with examples of organic syntheses carried out using both homogeneous and heterogeneous reactions.     

A new in situ chemical reactor for studying heterogeneous catalysis by NMR: The GRASSHopper

A new device/technique, Gas Reactor And Solid Sample Hopper designated GRASSHopper II, is described as an alternative to magic-angle spinning (MAS) for in situ NMR experiments on reacting heterogeneous systems. It is capable of supporting NMR studies of heterogeneous catalysis in the batch mode, in the flow reactor mode and for measurements of chemical kinetics. This new approach is based on the technique of magic-angle hopping (MAH). Characteristics, advantages, limitations and potential areas of application are described. Preliminary results are shown on the formation, subsequent hydrolysis and then regeneration (via dehydration) of (C₆H₅)₃C⁺ carbocations in zeolite HY cavities, and on the gas–solid polymerization of ethylene on a Cp₂ZrCl₂/MAO/SiO₂ ‘supported' catalyst.     

A Simple technique for microfluidic heterogeneous catalytic hydrogenation reactor fabrication

A simple process is described for the facile production of microfluidic reactors with ‘built-in’ metallic catalysts. This approach provides considerable reductions in cost and complexity when compared to existing catalytic chip designs. The process involves the sputtering of catalytic metals into the channels of microfluidic reactors prior to device bonding. The utility of such microreactors as environments for heterogenous catalytic hydrogenations was tested and demonstrated by applying them to the on-chip reduction of butyraldehyde to butanol and benzyl alcohol to benzaldehyde. The use of such ‘built-in’ systems as microreactors for specific processes was shown to have considerable potential for both fundamental research and industrial application.     

Absorption of acetone in a two-impinging-streams absorber

The effectiveness of various spray absorption configurations (as shown in Fig. 1 of the paper), which are based on the new technique of “absorption in two-impinging-streams” as well as on conventional absorption techniques in a single spray, were tested by absorbing acetone from air into a water spray. The major conclusions are: (1) absorption rates of acetone into two-impinging-streams (configurations “a” and “c” in Fig. 1) are significantly higher (up to a factor of four) than absorption rates into two streams separately operated (configurations “b” and “d”) under identical conditions and (2) absorption rates of acetone in two-impinging-streams are higher than in a single stream (configurations “e”-“h” in Fig. 1), but the enhancement is less pronounced than above.     

Continuous heterogeneous polymerization. I. A laboratory-scale stirred tank reactor

Design, calibration, and operation is described of a unique, 2-liter laboratory-scale continuous stirred tank reactor for the heterogeneous stereospecific polymerization of α-olefins under pressure.     

A new reactor coupling heterogeneous Fenton‐like catalytic oxidation with membrane separation for degradation of organic pollutants

BACKGROUND: There is growing interest in employing heterogeneous Fenton‐like catalysts in slurry to obtain higher activity. However, fine size particles create problems associated with recovery from the treated water. Therefore, it is highly desirable to develop a novel Fenton‐like process that not only has high degradation efficiency of organic pollutants, but also allows for easily reusing the catalysts. RESULT: A new reactor was investigated by coupling the heterogeneous Fenton‐like oxidation with membrane separation. Results showed that the FeY catalyst could be almost filtrated by a submerged micro‐filtration membrane in the reactor to continuously activate H₂O₂. For a FeY dose of 1 g L^?1 and a residence time of 120 min, the degradation efficiency of AO II reached 97%. CONCLUSIONS: In the new reactor, degradation of AO II occurred continuously and efficiently without an additional FeY separation process. The treatment capacity of this FeY catalyst for wastewater containing 100 mg L^?1 AO II in the reactor was estimated to be 82 times that of a reactor in which the catalyst could not be reused. The distinguishing technical feature of this reactor was the reuse of the Fenton‐like catalyst. Copyright © 2011 Society of Chemical Industry     

A catalyst deposited over the external surface of the reactor tubes—A new solution for carrying out heterogeneous catalytic processes

A mathematical model of a new reactor design has been proposed. In the new reactor the catalyst is deposited over the external surface of the tubes, where the coolant flows. The widespread industrial process of oxidation of o‐xylene into phthalic anhydride was investigated. The results obtained show significant advantages of the new design in comparison with the conventional fixed bed reactor operating in the industry. They are: much higher productivity, easily controlled temperature regime, raised selectivity and decrease content of side products, as well as an opportunity for additional feed‐in of the reagent along the reactor height. The technological regime of the oxidation process was optimized.     

Photochemical heterogeneous catalytic reaction at recirculated reactor system

A study was undertaken to examine the possibility of combining a batch-recirculated photoreactor with a ceramic membrane filter for heterogeneous photocatalysis applications. D-cargo red GS (GS) was used as the test substrate and titanium dioxide was used as photocatalyst for this study. The dark adsorption of GS on the TiO₂ particle surface was also analyzed. The adsorption trends of GS at various initial concentrations followed the Langmuir isotherm trend. The GS were decolorized from 20% to 70% by the dark adsorption with various concentrations. The photodegradation of GS after the dark adsorption showed the behavior of Langmuir-Hinshelwood model. The variation of recirculation flow rate did not much influence photocatalysis. Variation tendencies of GS concentration were almost similar after about 90 minutes illumination in spite of the flow rate change. The values ofk (apparent first order rate constant) also varied with increase of the recirculation flow rate, but there were no observable significant differences between them. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

A new CVD reactor for semiconductor film deposition

The concept and design of a new chemical vapor deposition (CVD) reactor is presented for both epitaxial and nonepitaxial film deposition in semiconductor processing. The reactor is designed in such a way that a stagnant semiconductor source fluid of uniform concentration is provided for the film deposition without causing free or forced convection. The supply of the source gas for the deposition is by diffusion through a porous material such as quartz or graphite. Compared to the low pressure CVD (LPCVD) reactor with mounted wafer configuration, the new reactor should give a better film thickness uniformity and about an order of magnitude reduction in the amount of the source gas required. Further, at least for polycrystalline silicon deposition, the deposition rate can be much higher than is currently practiced with the LPCVD reactor. Design equations for the reactor are given. Details on the design for the polycrystalline silicon deposition are also given.     

Hybrid modeling of ethylene to ethylene oxide heterogeneous reactor

In this research a dynamic grey box model (GBM) of ethylene oxide (EO) fixed bed reactor has been presented. In the first step of the study, kinetic model of the existing reactions was obtained using artificial neural network (ANN) approach. In order to build the ANN model industrial data of a typical EO reactor were employed. Time, C₂H₄, C₂H₄O, CO₂, H₂O and O₂ mole fractions were network inputs and the multiplication of reaction rate and catalyst deactivation (r * a)was ANN output. From 164 data, 109 data were employed to train ANN. After employing different training algorithms, it was found that, the radial basis function network (RBFN) training algorithm provides the best estimations of the data. This best obtained network was tested against fifty five unseen data. The network estimations were close to unseen data which confirmed generalization capability of the obtained network.In the next step of study, (r * a) was estimated with ANN and then the hybrid model of the reactor was solved. Simulation results were compared with EO mechanistic model and also with plant industrial data. It was found that GBM is 8.437 times more accurate than the mechanistic model.     

Modeling of transient heterogeneous two-dimensional catalytic packed bed reactor

A two-dimensional transient catalytic packed bed model, incorporating all transport parameters and resistances, along with boundary conditions based on a catalytic single pellet has been developed. Thermal conduction through the solid phase is included in the model. The overall steady state reactor performances of packed bed reactor using a model proposed in this study are compared with those from different models which are often used for a packed bed reactor. The model presented is very useful in the presence of internal temperature and concentration gradients in the catalyst pellets. The dynamic behavior in feed temperature change is examined during ethane hydrogenolysis. A transient thermal runaway is observed by feed temperature decrease. The sensitivities of the computation to each physical parameter and the effects of some simplifying assumptions in the model are also analyzed. The magnitude and position of hot spot in catalytic packed bed reactor are relatively sensitive to thermal parameters and characteristic parameters of a catalyst pellet.     

废水处理光催化反应器的发展

光催化是一项很有前途的水处理技术,光催化反应器是影响光催化反应效率的重要因素之一。作者对影响光催化反应器效率的因素如光源种类、反应器结构、催化剂状态等进行了分析,并总结了近年来在国内外研制及应用的一些典型的光催化反应器．给出了其结构图．并对其优缺点进行了评价。     

Fast binary reactions in a heterogeneous catalytic batch reactor

When heterogeneous chemical reaction is sufficiently fast, transport of reactants becomes limiting. In a well stirred, batch reactor, macroscopic concentration gradients can be eliminated as a factor limiting the rate of reaction, leaving only the mesoscopic mass transfer of reactants to the surface of the catalyst as limiting, if the reaction does not occur inside a porous support. Here, a transformation of the governing equations for the time-dependence of bulk and surface concentrations results in second order ODE in time and a single nonlinear constraint with boundary values at the initial and infinite times for two auxiliary variables termed modified Thiele moduli. This system of two equations—one differential, one algebraic—and two unknowns is an exact consequence of the governing equations (three ODEs and three algebraic constraints). The power of this formulation is demonstrated by analytic solutions for irreversible and nearly irreversible theories. These solutions are corroborated by full nonlinear numerical computations of the boundary value problem, for the case when asymmetric mass transfer coefficients admit the possibility that the mode of operation switches from relative surface depletion of one reactant to depletion of the other in a binary reaction. The modified Thiele modulus formulation reveals the time scale for the switch over, as well as giving a reliable prediction for the time scale for 99% conversion based on the switch time identified from the irreversible theory.     

A heterogeneous chemical reactor analysis and design laboratory: The kinetics of ammonia decomposition

A laboratory module for senior-level reaction engineering/reactor design students is described. Students use low-conversion experimental data to explore and characterize the kinetics of ammonia decomposition over various supported catalysts at atmospheric pressure in a packed-bed reactor. Each student team is assigned one of four catalyst types, a reactor temperature, and a series of feed flow rates and compositions. Aggregate data from all student groups is then summarily analyzed per catalyst type. In each experimental trial, the reactor conversion is determined by a thermal conductivity measurement applied to the feed (reactor bypass) and reactor effluent gases. An analysis of the reaction rate across a range of temperatures and varying feed gas partial pressures allows students to test various reaction mechanisms, to suggest rate-determining steps, and to statistically determine rate law parameters. Students typically use the Langmuir–Hinshelwood–Hougen–Watson (LHHW) approach to derive rate law expressions, and determine rate constants through application of the Arrhenius equation. High student numbers (ca. 140) are accommodated through the availability of four experimental stations — each sharing a common source of feed gas and equipped with independent flow controllers and gas analyzers.     

A new model for a hollow fibre enzyme reactor

A new model based on the concept of axial dispersion has been developed for predicting the performance of a hollow fibre enzyme reactor. It is shown that a simple closed form analytical solution for the prediction of the reactor performance results. The model parameters are obtained a priori from the welldefined hydrodynamic conditions. The agreement between the model predictions and the numerical solutions is excellent over a wide range of variables. The comparison of the model predictions with the experimental data shows good agreement. The model can be easily extended to include further complications. The extension to non-Newtonian substrates is discussed and results for reactor performance under these conditions are given.     

Liquid-liquid heterogeneous mixing efficiency in a rotating packed bed reactor

Mixing of two immiscible liquids consists of two sections that are liquid-liquid dispersion and mass transfer intraphase or interphase. It plays a crucial role in the liquid-liquid heterogeneous reactions. Here, the liquid-liquid heterogeneous mixing efficiency in RPB reactor is experimentally assessed by a consecutive-competitive chemical probe system. The diameters of dispersed phase droplets in RPB were measured and a correlation to predict the mean diameters were obtained. Based on the dispersed phase size and mass transfer characteristic, a model for predicting the segregation index of liquid-liquid heterogeneous mixing in RPB was established with a deviation <20%. Based on this model, the characteristic time of liquid-liquid heterogeneous mixing in RPB is determined to be in the range of 0.01–1 s. RPB exhibits a great process intensification potential for heterogeneous mixing process.     

Non-equilibrium effects on fast reactions in a heterogeneous batch reactor

Recent studies by the authors of the heterogeneous catalysis of fast binary reactions have taken a dynamical systems approach, assuming that fast enough reactions are confined to a manifold upon which surface equilibrium holds. This approximation makes substantial simplification possible, for instance in the case of a batch reactor, it allows a naturally sixth order system to be approximated by a two dimensional manifold for the dynamics of two modified Thiele moduli. Nevertheless, a proper assessment of how much faster must the velocity of surface reaction be than the velocity of mass transfer to the catalytic surface before the quasi-equilibrium on the surface holds should be made. In this paper, a theory for the systematic correction to infinitely fast reactions is made for large but finite velocity reactions. It is compared to full numerical solutions to the model equations. Recommendations about the regime of applicability of the quasi-equilibrium approximation are made. In general, the predictions of the quasi-equilibrium theory hold for ratios of mass transfer coefficients to reaction velocity ξ of less than 1/1000, with qualitative agreement in regimes of less than 1/100. The general trend, however, is that the stronger the kinetic asymmetry between the mass transfer coefficients of the reactants, the slower the reaction rate can be and still have the quasi-equilibrium theory hold. A perturbation analysis demonstrates that the quasi-equilibrium theory is a regular limit of the fast non-equilibrium theory. In the irreversible case, a matched asymptotic analysis gives the same prediction for the switch time from effective surface depletion of one reagent to the other as the quasi-equilibrium theory. Furthermore, it gives an estimate of the smoothing out of the transition zone with a temporal width of ξ^1/2. It should be noted that the continual drive for improved catalyst activities inevitably leads to mass transfer limited reactions, and thus this regime is not uncommon.