Scale-up concept for modular microstructured reactors based on mixing, heat transfer, and reactor safety

Microstructured reactors are characterized by rapid mixing processes and excellent temperature control of chemical reactions. These properties allow the safe operation of hazardous chemistry in intensified processes. Problems occur during scale-up of these processes, where heat transfer becomes the limiting effect. With high flow rates and transitional or even turbulent flow regimes in small channels, rapid mixing and excellent heat transfer can be maintained up to high production rates. For exothermic reactions, limits for parametric sensitivity and safe operation are shown from literature and combined with convective heat transfer for consistent scale-up. Good knowledge of reaction kinetics, thermodynamics and heat transfer is essential to determine runaway regions for exothermic reactions. From these correlations, consistent channel design and continuous-flow reactor setup is shown.     

多相反应体系的微界面强化简述

加氢、氧化等气液慢反应过程广泛存在于现代过程工业之中,这些反应过程一般受传质速率控制。因此,对这类多相反应体系的传质强化一直是研究热点之一。但总体而言,除外场和微通道（微流控）强化等一类强化反应器外,以往的研究大多集中于界面尺度为毫-厘米级的传统反应器的搅拌与混合方式、气泡分布状态、流体流型、构效关系等方面,而鲜有将研究视角投放到传统以米为直径计量单位的反应器平台上如何构建尺度为微米级的界面体系及其特殊效应方面。探讨了多相反应体系的微界面反应强化理念,并简述了微界面的涵义、微界面反应强化与构效调控方法、微界面反应器的结构与形成原理、微界面体系的微颗粒测试与相界面表征技术、微界面反应强化面临的问题与挑战等,以与本领域同行共同研讨。     

THE CHARACTERIZATION OF COMPLEX SYSTEMS OF CHEMICAL REACTIONS

A method is presented for the enumeration of possible overall chemical reactions and mechanisms, based on an initial choice of elementary reactions connecting a set of chemical species. Such a procedure furnishes an important tool for the study of complex reaction systems. The method is presented in such a way as to be readily implemented by computer solution, which is indispensable for many systems.     

Chemical reaction engineering in the chemical processing of metals and inorganic materials

The advances made in the field of chemical engineering as applied to the processing of metals and other inorganic materials are reviewed. The reactions involved in this field are heterogeneous in nature, the fluid-solid noncatalytic reactions being the most important group of examples. In these heterogeneous reactions, interfacial chemical reactions are always accompanied by the transfer of mass and heat between the reaction interface and the bulk fluid. The interplay of these steps determines the overall characteristics and analysis of the reaction rate. The review examines the developments in the quantitative rate analysis of various fluid-solid reaction systems. Examples are largely drawn from the work of the author and coworkers, which has led to the formulation of the Law of Additive Reaction Times and its application to a wide range of fluid-solid reactions. The serious effects of thermodynamics on fluid-solid reaction with small equilibrium constants, in terms of the overall rate and the falsification of activation energy, have been examined based on a careful quantitative analysis.     

Dynamics of open chemical systems and the algebraic structure of the underlying reaction network

While there has been a longstanding interest in stability of non-isothermal reactors there has only recently developed a comparable interest in the dynamics of open isothermal reactors with complex chemical reaction networks. In the recent literature there has been paid particular attention to the study of biological reaction systems which might exhibit sustained oscillations (biological clocks) or bistability (biological switches). Results are presented which bear upon the relationship between the algebraic structure of the underlying reaction network and the extent to which reactors might give rise to such “exotic” dynamics.     

Measurement and enhancement of gas-liquid mass transfer in milliliter-scale slurry reactors

Due to the limited availability of chemical reactants in the early process development of pharmaceuticals and fine chemicals, and sometimes the high-cost of catalyst, it is increasingly popular to use milliliter-scale slurry reactors with reaction volumes of 20 ml or less to screen catalyst candidates for three-phase reactions. To ensure the success of catalyst screening, it is advantageous to run reactions under kinetically controlled conditions so that the activities of different catalysts can be compared. Because catalysts with small particle sizes are used in slurry reactors, the reactions are susceptible to gas-liquid mass transfer limitations. This work presents an efficient way of enhancing gas-liquid mass transfer in milliliter-scale reactors through the use of magnetically driven agitation with complex motion. In the reactor described here, gas-liquid mass transfer coefficients can be doubled over those obtained with the agitation technique used in commercial milliliter-scale units. In addition, the reactor can achieve the top range of mass transfer coefficients obtained in a full-scale reactor. This work also presents the first measurements of gas-liquid mass transfer coefficients in milliliter-scale reactors, which are two orders-of-magnitude smaller than systems for which mass transfer coefficients have been reported earlier. Both physical and chemical absorption techniques are used.     

Dynamics of continuous isobutylene cationic polymerizations

Polyisobutylene can be produced in either continuous cationic precipitation or solution polymerization reactors. It is known that the open-loop behavior of polymerization reactors may be very complex and may lead to oscillatory behavior, which is usually caused by thermal positive feedback (due to the large heats of reaction of polymerization reactions) and high viscosity effects (such as the gel effect in radical polymerization reactors and the decrease of heat transfer coefficients at high polymer concentrations). Oscillatory behavior may be observed in industrial isobutylene reactors, and it is intended to know whether these oscillations are inherent to the kinetic mechanism. Based on published experimental data, mathematical models are developed for both solution and precipitation processes. Steady-state solutions are calculated and steady-state stability is analyzed. Dynamic simulations and stability results reveal that only single stable steady-state solutions are possible for such reactors at usual operation conditions, which means that oscillatory behavior is not intrinsic to the reaction mechanism. © 1996 Wiley & Sons, Inc.     

Microstructured reactors and supports for ionic liquids

Different types of microstructures and their applications with respect to the synthesis and the use of ionic liquids are presented. Microstructured reactors are suitable for reactions with fast intrinsic kinetics, requiring high mass and heat transfer performances. Chemical synthesis can be performed safely under operating condition (e.g. high temperature, pressure, etc.) difficult to obtain in traditional reactors. The examples presented clearly indicate that microstructured reactors offer superior performance for the synthesis of ionic liquids in comparison to conventional equipment. For the use of ionic liquids as reaction media, existing ionic liquids show some limitations due to their higher viscosity compared to conventional solvents. Therefore, future research should be focused on the development of low viscosity ionic liquids.The approaches to use ionic liquids in microstructured reactors and in combination with microstructured supports for catalytic reactions show many advantages in view of high product selectivity and yield. The use of supported ionic liquids on microstructured materials seems to be particularly promising for gas phase as well as for gas/liquid reactions.     

Electro-membrane reactor: A powerful tool for green chemical engineering

Electro-membrane reactors use electro-membranes for preferentially diffusive/electrophoretic migration or electroosmotic separation of in-situ reactive products, thereby maximizing the reaction rate and transport efficiencies of the products. These reactors are widely employed in the chemical engineering sectors such as green chemical synthesis, biorefining, electrocatalytic reduction/oxidation, and water treatment. In this review article, we provide an overview of the recent advances in three categories of electro-membrane reactors in chemical engineering sectors from three categories: (1) Electro-membrane reactors based on stacked ion-exchange membranes for resources recovery; (2) Electro-membrane reactors via Faraday reactions on functional anodes/cathodes for substance transformation; and (3) Closed-loop chemical reactions and substance separation via coupling of Faraday reactions and stacked membranes. The increasing demand for low-carbon economy has accelerated the advancement of environmentally friendly chemical engineering and sustainable processes and necessitates the use of electro-membrane processes. The macro perspective provides a timely reference for researchers and engineers.     

Polymerisationstechnik

Polymerization engineering. Polyreactions are complex chemical reactions which are generally conducted in liquid phase. The characteristic feature of polyreactions is the pronounced increase in viscosity of the reactants during the reaction. The increase in viscosity influences numerous reaction and process parameters, such as the reaction kinetics, the transfer of mass, heat, and momentum, the degree of mixing of the reactants, and the residence time distribution of continuous reactors. Thus the increase in viscosity influences the performance, selectivity, and safety of the reactor. The choice of reactor for performing polyreactions can be based on various aspects. Of decisive importance are the performance and selectivity of the reactor. For the cases of simple and complex polyreactors, various kinds of reactors are compared with respect to their performance and selectivity, with the molar mass distribution of the resulting polymers serving as example of the selectivity of polyreactions. In the case of simple polymerizations, the molar mass distribution of the polymers depends unequivocally on the type of reactor and the various reactor types can be arranged in appropriate order. This is no longer the case for more complex polymerizations because the concentration conditions in the reactors play an increasingly important role.     

Insights into gas-liquid-solid reactors obtained by magnetic resonance imaging

Magnetic resonance imaging (MRI) is emerging as a measurement tool with unique capabilities in the field of reaction engineering—in particular, the ability to study three-dimensional, optically opaque systems, and to quantify the physics and chemistry that is occurring at multiple length-scales within such systems. Here we highlight recent developments in developing MRI methods for application to studying both hydrodynamics and chemical conversion in gas-liquid-solid reactors. Examples are taken from parallel channel, structured reactors and fixed beds. In the former case it is now possible to image liquid velocities up to within individual channels within a ceramic monolith. In the context of fixed beds, the ability of MRI to reveal the mechanism of the trickle-to-pulse transition is reviewed. A new application of MRI to image the changing liquid holdup between individual packing elements within a bed during periodic operation is then presented. Finally, the state-of-the-art in mapping chemical conversion in trickle-bed reactors is discussed.     

Experimental and Theoretical Studies on Hydrogenation in Multiphase Fixed‐Bed Reactors

Multiphase fixed‐bed reactors have complex hydrodynamic and mass transfer characteristics. The modeling and scale‐up are therefore difficult. The present work focuses on the role of mass transfer on the effective reaction rate. The catalytic 1‐octene hydrogenation was taken as a model reaction. The reaction rate in the trickle‐bed reactor is by a factor of 20 smaller than (theoretically) in the absence of any mass transfer limitations. For high octene concentrations (> 10 %), the effective reaction rate is limited by the H₂ consumption, above all by the gas/liquid and liquid/solid mass transfer. For lower octene concentrations the reaction is zero order with respect to H₂ and only depends on the octene consumption, i.e., on the interplay of chemical reaction, L/S and intraparticle mass transfer of octene.     

Thermodynamic optimization of energy transfer in (bio)chemical reaction systems

The engineering science literature on energy-transfer processes (heat engines, heat pumps, etc.) for the production of mechanical energy, electricity, cold or heat has produced some remarkable results on maximum power and efficiency optimization. We have wondered in how far these results can be extended to include chemical reaction systems to describe living and possibly future-industrial energy-transfer systems. With elements of non-linear irreversible thermodynamics and chemical kinetics, we have arrived at some interesting results on optimizing the performance of chemical energy transfer. We discuss thermodynamic efficiency, energy-transfer rate, entropy-generation rate, and optimum-performance characteristics of (bio)chemical energy transfer.     

Tube-wall reactor modelling for multiple reaction networks with non-linear kinetics and volume change

Tube-wall reactors are gaining importance for highly exothermic and fast chemical reactions because of their simple construction and improved temperature control. A generalized mathematical model of the non-isothermal annular tube-wall reactors for simultaneous catalytic reactions with mixed type non-linear reaction kinetics and volume change is developed. Numerical solutions of two-dimensional component transfer equations, heat transfer equation and fluid flow equation may be obtained with appropriate boundary conditions using a recently developed orthogonal collocation method for annular geometries. The model has been successfully applied to the tube-wall reactors for the Fischer-Tropsch Synthesis. Comparison between model predictions and previous experimental results is good.     

Multifunktionale Reaktoren

In multifunctional reactors chemical and physical unit operations are carried out simultaneously. Traditionally chemical reaction engineering considers mass and heat transfer processes in combination with chemical reactions. However, the term multifunctional reactor points to an extended and more detailed view of process integration. By application of these reactors it is possible to save investment and/or operating costs, to meet environmentally relevant limits or to improve process safety. Mechanical and thermal unit operations are especially good candidates for integration with a chemical reaction step. In this contribution selected multifunctional reactors are presented, which were either adopted from the literature or are the subject of the authors' own research activities.     

Inference of chemical reaction networks

This paper demonstrates how, in principle, a chemical reaction mechanism (reaction network) can be inferred using relatively simple systematic mathematical and statistical analyses of experimental data obtained from chemical reactors. This method involves specifying a global ordinary differential equation (ODE) model structure capable of representing an entire set of possible chemical reactions. Mathematical and statistical tests are then used to reduce the ODE model structure to a subset of reactions. Finally, a model rationalisation procedure, relying on exploiting the basic rules of reaction chemistry, is used to obtain a consistent set of reactions which are combined to give the overall reaction network. The identification procedure is demonstrated for pure batch operation with a worked example using simulated noisy data from an extended Van de Vusse reaction network consisting of five species and four elementary reactions [Van de Vusse, J.G., 1964. Plug-flow type reactor versus tank reactor. Chemical Engineering Science 19, 994-997]. A further case study of a semi-batch (fed batch) system using simulated data from a simplified biodiesel system, with six chemical species involved in three elementary reactions, is provided. It is shown that the method is able to correctly identify the underlying structure of the network of chemical reactions and provide accurate estimates of the network rate constants.     

微型流化床反应分析的方法基础与应用研究

准确测试气-固反应特性、求算动力学参数和推导反应机理是能源、化工、冶金等过程工程领域的重要研究课题。通过分析现有气-固反应分析测试方法与测试仪器优缺点,本文作者提出了利用微型流化床(MFB,micro fluidized bed)实现低扩散、快速升温条件下的反应微分化和等温分析的测试方法,系统研究了反应器内的流体力学特性,研制了微型流化床反应分析仪(MFBRA,micro fluidized bed reaction analyzer),验证和展示了其对热解、燃烧(氧化)、气化、还原、催化、吸收等典型气-固反应的应用,充分揭示了微型流化床反应分析仪强化传热传质、降低扩散抑制、实现实时在线微分分析的特性,尤其为快速复杂反应提供了有效的研究分析手段,并且拓展了水蒸气气氛、在线颗粒采样、串联反应解耦等系列气-固反应研究与表征功能,形成了与热重分析互补的气-固反应分析方法和分析仪。     

Microcatalytic reactors: Kinetics and mechanisms with isotopic tracers

Pulsed microcatalytic reactors have found extensive application in the petroleum and chemical industries where rapid catalyst screening and evaluation are demanded. Automated, continuous-operation test units allow the accumulation of considerable amounts of data in a minimum of time. The technique is also useful in research where the small pulse size enables one to study “initial” interactions between surface and reactants. In this way, information about many kinetic parameters, such as intrinsic reaction rates, orders, poisoning effects, and catalyst deactivation, can be obtained. Both stable and radioactive isotopic tracers may be used economically in microcatalytic reactors to provide significant mechanistic information which cannot be obtained conveniently by other methods. For example, one can explore the chemical nature and number of active sites, as well as the fate of individual atoms and molecules as they interact with the catalyst. Although the technique may be applied to both “simple” and complex catalytic reaction systems, the discussion will be limited to a review of data obtained from (1) “unimolecular” reactions such as cyclopropane and butene isomerization and cumene dealkylation over the mixed oxides silica-alumina, silica-magnesia, and zeolites and (2) “bimolecular” reactions such as ethylene hydrogenation over alumina. Some of the limitations of microcatalytic reactors will also be given.