Meßtechnik zur Charakterisierung von Gas/Flüssigkeits-Reaktoren

Measuring techniques for characterizing gas/liquid reactors . The article considers measuring techniques for the characterization of the phases in gas/liquid reactors. These include the velocity profile and turbulence in the continuous phase as well as holdup, size, and velocity of the dispersed phase. Also, methods for the determination of the specific interfacial area and the volumetric mass transfer coefficients are discussed. Measuring methods have made enormous advances in recent years. In spite of this, there is a lack of reliable methods, especially for use during reactions without disturbing the state of the reactor. It is suspected that probe technique will gradually fall into disuse and more and more attention will be focussed on contractless methods. This calls for further development of ultrasonic methods and methods relying on emission of light.     

Meßtechniken für Gas/Feststoff-Wirbelschichtreaktoren

Measuring techniques for gas/solid fluidized bed reactors. Significant progress has been made in the field of fluidization in recent years due to its application to the combustion of coal as well as sewage sludges and other residues. The new applications have also created a demand for new measuring techniques. In the present paper the available measuring techniques for fluid mechanical properties are reviewed, ranging from simple measurements for the determination of bed expansion to more sophisticated techniques for the determination of local solids concentrations, velocities, and mass flows. Furthermore, the problem of gas sampling from fluidized bed reactors is discussed. Among others, a measuring technique based on mass spectrometry is presented for local and instantaneous measurements of gas concentrations.     

Neue Erkenntnisse zum Mischverhalten von Submersreaktoren

Mixing behaviour of submersed reactors. New improved measuring techniques lead to new insights into the local mixing behaviour of submerse reactors. As exemplified by airlift tower loop reactors, it is shown that it is possible to obtain more information from gas residence time distributions if the signal-to-noise ratio of the measurement can be improved significantly. Additional information is obtained, e.g., on that part of the gas recirculated around the loop or the circulation time of the gas phase. The recirculated gas significantly influences the gas backmixing in such reactors. A more thorough investigation of the gas phase motion requires locally resolved data. For the properties of the gas phase, local measuring techniques are available, which allow for measurements of the mean bubble velocity profile even during production runs in large aerated stirred tank reactors. The results show that the gas backmixing is acutely dependent on the viscosity of the continuous liquid phase. Complementary measurements on the properties of the continuous liquid phase can be investigated by means of the heat-pulse-technique. This also is applicable in real media, e.g., during biotechnological cultivation runs. Besides the measurement of the mean liquid velocity, one can, furthermore, obtain some information on the locally dominating mixing mechanism. One significant result of such investigations is that in the airlift reactors investigated the bubble-wake mixing mechanism dominates, whereas the isotropic turbulence in terms of the statistical turbulence theory plays a secondary role. This even holds at very high energy inputs.     

Measuring techniques in gas-liquid and gas-liquid-solid reactors

This article offers an overview of the instrumentation techniques developed for multiphase flow analysis either in gas/liquid or in gas/liquid/solid reactors. To characterise properly such reactors, experimental data have to be acquired at different space scale or time frequency. The existing multiphase flow metering techniques described give information concerning reactor hydrodynamics such as pressure, phases holdups, phases velocities, flow regime, size and shape of dispersed inclusions, axial diffusion coefficients. The measuring techniques are presented in two groups: the non-intrusive techniques that deliver global, cross-section-averaged or local data, and the intrusive probes that are dedicated to local measurements. Eventually some examples of multiphase instrumentation development are reported (trickle-bed and slurry bubble column at semi-industrial scale) in the refinery or petrochemical area.     

A solution strategy for the film model for non-isothermal gas–liquid reactions

A general solution strategy for the film model for gas–liquid reaction has been proposed using the boundary element method (BEM) of discretization over subintervals in gas–liquid films. Non-isothermal effects in the film are included and the associated temperature changes near the gas–liquid interface are computed. The accuracy of the solution procedure is first established using some simple isothermal and non-isothermal benchmark problems and with semi-analytical solutions. Then illustrative results are presented for a non-isothermal series reaction system to illustrate effects of various parameters such as Arrhenius number, solubility changes with temperature, effect of volatility of the liquid phase reactant, etc. The proposed solution method provides fast and accurate values for interfacial fluxes and fluxes into the bulk liquid in addition to concentration profiles. Hence the method is extremely useful for coupling local effects of the film model with global effects based on CFD coupled compartmental model for gas–liquid reactors.     

气液冷等离子体多相反应器基础研究与应用进展

等离子体作为物质存在的一种基本形态,因其特有的高活性而不同于固、液、气三种形态,逐渐应用于多个领域,并发展成了一门新兴学科。由于冷等离子体参与的气液化学反应能产生更多的活性物质,而且液体的流动性能够强化活性物质的传递,因此,气体放电产生的冷等离子体与液相反应在许多领域表现出重要的应用价值,更具有探究意义。综述了几种冷等离子体的放电形式以及表征技术,重点阐述了气液冷等离子体多相反应器的不同结构以及应用,并对气液冷等离子体技术发展进行了展望。     

Hydrogenation of 2‐ethylanthraquinone under Taylor flow in single square channel monolith reactors

The hydrogenation of 2‐ethylanthraquinone (EAQ) to 2‐ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz‐glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas‐liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two‐phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi‐empirical formula were used to predict gas‐solid, gas‐liquid, and liquid‐solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Gas‐Lift Reactors for Rapid Reactions with Appreciable Gas Consumption

Gas‐lift reactors offer important advantages for a number of gas/liquid and gas/liquid/solid reactions. However, the design and operation of these reactors can be complex when there is a substantial change in the molar gas flow rate along the length of the reactor, e.g., when a gaseous reactant is converted into a liquid product. In this situation, there is a strong coupling between reactor hydrodynamics and reaction kinetics, which arises from the fact that the rate of liquid circulation through the reactor and the longitudinal profile of gas holdup in the riser are mutually dependent. Several one‐dimensional models have been developed to describe kinetic/hydrodynamic coupling in gas‐lift reactors. These models offer useful insights into the parameters that affect reactor performance. The models can also be used to explore different approaches to scale‐up.     

气-液-固三相循环流化床中的液相轴向扩散

The effects of liquid viscosities, solid circulating rates, liquid and gas velocities and phase holdups on the axial dispersion coefficient, Dax, were investigated in a gas-liquid-solid circulating fluidized bed (GLSCFB).Liquid viscosity promotes the axial liquid backmixing when solid particles and gas bubbles are present. Increases in gas velocities and solid circulating rates lead to higher Dax. The effects of liquid velocity on Dax are associated with liquid viscosity. Compared with conventional expanded beds, the GLSCFBs hold less axial liquid dispersion,approaching ideal plug-flow reactors.     

A Review of Catalytic Membrane Layers for Gas/Liquid Reactions

This paper summarises the main ideas of how to use membranes with built-in catalytic function for performing catalysed gas/liquid reactions. Mass transfer effects on catalyst performance and other decisive factors for the design of industrial gas/liquid and gas/liquid/solid reactors are briefly reviewed. Various concepts for applying catalytic membrane layers in multiphase reactors are introduced and the motivation behind their use is explained. What follows is an assessment of the present achievements in using such concepts for gas/liquid reactions. The results available in literature are critically evaluated, focussing mainly on the field of liquid-phase hydrogenations and oxidations, which constitute the major areas where catalytic membranes have been applied to date to gas/liquid systems. The aim of such treatment is to point out the targets, to elaborate on how far the whole field has developed and what challenges remain, rather than to cover a multitude of specific aspects of the many different studies reported in literature.     

Numerische Simulation disperser Gas/Flüssig‐Strömungen in Blasensäulen bei hohen Gasgehalten mit OpenFOAM® Teil 1 – Grundlagen der Modellierung

Various chemical products are synthesized in processes using gas/liquid reactors with bubbly flows. Hence, there is significant interest in a more efficient process design as well as in process intensification with a strong focus on this reactor class. However, the design of industrial gas/liquid reactors requires more detailed information about the flow structures and characteristics of two‐ or multiphase systems. The basic models for two‐fluid model simulations of dispersed gas/liquid flows in bubble columns at high gas fractions are presented..     

Basismodelle für Reaktoren — eine kritische Bilanz

In the literature of chemical reaction engineering, the basic models for reactors are deduced in different ways. This paper demonstrates that the authors do not always stringently differentiate between fluid mechanics and chemical reaction engineering methods. Thus misinterpretations may arise. As this publication shows, it would be more precise to use instead of ideal reactors the term completely/radially mixed reactors (mixing vessel/pipe). In addition, attention is directed to convection reaction models. They give an idea of the local concentration profiles in reactors for a small mathematical effort. The models give predictions superior to those of the ideal reactor models and of the dispersion model, both of which can only give mean values.     

Gas–liquid interfacial areas in three-phase fixed bed reactors

A simple model, based on the theory of liquid emulsions, is proposed to develop correlations suitable for estimating gas–liquid interfacial areas for the bubble flow regime in three-phase fixed bed reactors operated with gas and liquid flowing cocurrently upflow. The model is also employed for trickle-bed reactors for estimating the increase in gas–liquid interfacial areas when these reactors are operated under high pressure conditions. It is found that developed correlations account satisfactorily for most of the data of gas–liquid interfacial areas available in the literature for cocurrent upflow three-phase fixed bed reactors and for trickle-bed reactors operated at high pressure conditions.     

Definition und Messung der Mischgüte in flüssigen Gemischen

Definition and measurement of quality of mixing in liquid mixtures. The relative deviation from homogeneity of a mixture can be defined in various ways. These expressions are adapted to the various methods of measuring the degree of mixing and the mixing time: probe methods; color change of chemical indicators; decoloration proportional to the conversion of a reaction; increase in temperature arising from heat of reaction. A comparative study of the various methods is presented (see also [1] in English language).     

Katalytische Suspensions-Reaktoren

Catalytic suspension reactors . Reactions occurring in slurries are frequently encountered in industrial chemistry. The field of application of suspension reactors and their advantages and disadvantages compared with other catalytic reactors are underlined. It should be borne in mind when calculating space-time yields that several drag components (gas/liquid and liquid/solid mass transfer, as well as pore diffusion inhibition) precede the actual reaction. They are best accounted for by the concept of series switching of partial resistances. In the case of highly active and finely divided catalysts, however, absorption acceleration may take place. Methods are presented for determining reaction and transport parameters and correlations of mass and heat transfer are considered. Particular attention is devoted to the question whether the characteristic quantities of heat and mass transfer in a three-phase system can be estimated from the experimental data for two-phase systems (gas/liquid and liquid/solid). This is shown to be feasible in many cases with an accuracy adequate for practical purposes. Reactor and catalyst performance show opposing trends in suspension reactors. Guidelines for optimal operation can be derived on the basis of simplified model concepts.     

Mean residence time of gas in mechanically agitated gas–liquid contactors

In the present study of gas–liquid contactors, mean residence/contact time was calculated from knowledge of superficial velocity and the gas phase hold-up, for various gas rates and impeller geometry and speeds, and compared with values obtained from RTD measurements. A new correlation, involving Flow Number, Froude Number, system geometry and the physical properties, is proposed. This uses the authors data and those available in literature.     

微反应器的研究与进展

微反应器是20世纪90年代初发展起来的新型的化学反应结构元件。本文对微反应器按液-液相、气-液相和气-液-固二相等反应体系对务种新型做反应器作了简要介绍;阐述了微反应器所具有的一系列超越传统反应器的优越性。最后对其未来的发展作了展望。     

喷射式气-液反应器的型式及应用

气体和液体以喷射形式进料 ,是喷射式气液反应器的显著特征 ;喷射式气液反应器是一种多相反应器 ,具有较好的传热、传质和混合特性。对喷射式气—液反应器的型式及应用作了概要介绍     

Experimental studies of interphase mass transfer with chemical reaction — Saponification of esters

This study concerns the transfer of ethyl acetate from a supernatant still liquid into a lower layer of caustic solution in which a saponification reaction occurs. Apparatus and techniques for measuring the concentration profiles which develop in the turbulent reaction layer in the aqueous phase at the liquid-liquid interface are described. In particular, the effects of turbulence on the reaction layer propagation, the reaction zone in the turbulent layer, and the concentration distribution of various components of the system were observed and measured. From these data, mass transfer rates and enhancement factors were deduced. The effects of turbulence in the aqueous phase were presented in terms of an eddy diffusivity model.