Adaptation of the microscopic properties of redox catalysts to the type of gas-solid reactor

Catalysts of selective oxidation usually work in a simultaneous redox mode in reactant/air cofed reactors. The solid must provide selective lattice oxygen according to a kinetic mechanism depending on operating conditions that differ from one reactor to another. Better catalytic performance can be obtained in a recirculating solids reactor because it allows separate optimization of the reduction and oxidation steps. Among the microscopic properties of the catalyst, the crystal morphology is to be taken into account because it influences its reactivity on stream. These considerations lead to a new approach of the catalyst-reaction-reactor trio.     

Influence of structural properties of catalysts at various stages of selective oxidation: from catalyst preparation to catalytic reactors

Solid oxides selective in mild oxidation exhibit a definite crystal morphology. Each crystal face displays a surface crystal field which rules the transformation of the reactant to a given product. The catalytic metastability of the surface which has to be maintained in the operating conditions prevailing in reactors depends on the reactivity of the bulk, because of oxygen diffusion process. Application to VPO, the catalyst for oxidation of n-butane to maleic anhydride, gives the opportunity to examine these properties in the series preparation–activation–catalysis–ageing, in relation to the type of catalytic reactor. This revised version was published online in August 2006 with corrections to the Cover Date.     

厌氧氨氧化反应器的启动方法研究进展

厌氧氨氧化反应器的启动时间过长是制约厌氧氨氧化在工程实践中发展和应用的一个关键性因素,因此实现厌氧氨氧化反应器的快速启动对于该项技术的推广意义十分重大。分析比较了选取不同类型的反应器和接种不同类型的污泥对于厌氧氨氧化反应器启动时间及脱氮效果的影响,并对今后的研究方向提出了建议。     

Numerical evidence for a “highway in state space” for reactors with minimum entropy production

We report on the nature of the state of minimum entropy production. Thousands of solutions for this state in chemical reactors controlled by the temperature of the coolant medium, show that the solutions fall more or less on what we have called a “highway in state space”. The solutions were found using optimal control theory for reactors that produce a fixed amount of product. A subset of the solutions, for the oxidation of sulphur dioxide, is presented. Each solution gives the most energy-efficient way of operating a reactor for the given boundary conditions. For reasonable process intensities, the highway is characterised by approximately constant entropy production and driving forces, but not necessarily by linear flux-force relations. Knowledge about the highway has implications for energy-efficient reactor design. The results give theoretical support to engineering practices.     

METHANE COUPLING USING CATALYTIC MEMBRANE REACTORS

The purpose of this review article is to provide readers with an extensive account on methane-coupling reactions performed in membrane reactors available in literature up to 2000. The principles, advantages or disadvantages, and crucial problems of all kinds of membrane reactors used in methane coupling are discussed. Some areas such as solid oxide membrane reactors for methane oxidative coupling are treated less extensively, as it has always been reviewed by other researchers. More emphasis has been placed in catalytic proton or mixed proton and electron-hole conducting membrane reactors, as they have greater potentials and have received less attention in the literature.     

METHANE COUPLING USING CATALYTIC MEMBRANE REACTORS

The purpose of this review article is to provide readers with an extensive account on methane-coupling reactions performed in membrane reactors available in literature up to 2000. The principles, advantages or disadvantages, and crucial problems of all kinds of membrane reactors used in methane coupling are discussed. Some areas such as solid oxide membrane reactors for methane oxidative coupling are treated less extensively, as it has always been reviewed by other researchers. More emphasis has been placed in catalytic proton or mixed proton and electron-hole conducting membrane reactors, as they have greater potentials and have received less attention in the literature.     

Reactors for hydrogenation of edible oils

Due to the characteristics of the hydrogenation of edible oil, by far the most common type of reactor has been the batch-type shurry hardener. Although continuous reactors offer several advantages compared to batch reactors, they are seldom used in the industry. This review paper describes the most commonly used full-scale reactors, both batch and continuous. Several different laboratory reactors are also described. The experimental results obtained from those reactors indicate that it is possible to achieve selectivites and reaction rates in a continuous reactor as high as in a slurry batch reactor.     

New Catalyst Synthesis and Multifunctional Reactor Concepts for Emerging Technologies in the Process Industry

In order to promote the introduction of emerging technologies in the process industry, it has been established the two types of supporting R&D activities can be effectively pursued in parallel: (1) new catalyst synthesis methods that eliminate or minimize mass transfer limitations; and (2) multi-functional reactors by integrating catalysis, heat transfer and/or separation. Catalyst Synthesis: In this paper, several methods of catalyst tailoring will be described that can minimize mass transfer limitations at industrially relevant conversion levels. Three (3) specific examples have been selected to demonstrate what can be achieved: (1) micro-engineered catalyst that enables enhanced inter-phase transfer; (2) new mesoporous catalysts with ultra large pores to accommodate slowly diffusing reactants; and (3) customized zeolites of extremely small particles to achieve high effectiveness factors while retaining the virtues of shape selectivity. Multi-functional Reactors: Applying process intensification principles, mature high-volume petrochemical processes can be improved dramatically, beyond the expected progress. This will be described using three (3) specific examples: (1) intra-reactor oxidative reheat for the production of styrene, by staging endothermic and exothermic reactions in series; (2) simultaneous operation of endothermic, dissociative adsorption of methane with exothermic, oxidative removal of carbon during catalytic partial oxidation; and (3) catalytic distillation for the production of ethers, ethyl benzene and the selective hydrogenation of highly unsaturated components in olefins streams.     

Structured catalysts for partial oxidations

The objective of the present work is centred on the analysis of the behaviour of fixed-bed reactors packed with structured catalysts when a partial oxidation takes place. The fluid flow within an element, formed by the intersection of two adjacent corrugated plates, was mathematically modelled and numerical simulations were performed in order to study possible optimising of the catalyst structure. A simple model, involving the continuous stirred tank approach, was used to simulate the performance of the catalyst in an industrial reactor. The profiles of temperature, concentration, velocity and pressure along the reactor were obtained through the global mass balance, partial molar balances, conservation of moment, energy balance and mechanical energy balance. These equations were applied to an exothermic reactional system, the selective oxidation of methanol to formaldehyde, in order to evaluate the possibility of application of these catalysts in industry. Various parameters specific to the catalyst and the reactional system were tested in order to achieve a better understanding of the behaviour of these structured packing. The comparison with the heterogeneous model predictions for a random packing and with industrial values pointed out that the choice of parameters is fundamental to the performance of the catalyst. The adjustments to the parameters allows for significant improvements in some of the more troublesome aspects of the reactional system. Lowering the hot-spot, reducing the progress of the secondary reaction and reducing the pressure drop are the main enhancements that these structured catalysts can offer.     

Hydrogen production from propane in Rh-impregnated metallic microchannel reactors and alumina foams

Rh-impregnated alumina foams and metallic microchannel reactors have been studied for production of hydrogen-rich syngas through short contact time catalytic partial oxidation (POX) and oxidative steam reforming (OSR) of propane. Effects of temperature and residence time have been compared for the two catalytic systems. Temperature profiles obtained along the central axis were valuable in understanding the different behaviour of the reactor systems. Gas phase ignition occurs in front of the metallic monolith at furnace temperatures above 700 °C, leading to lower hydrogen selectivity. Lowering the residence time below 10 ms for the microchannel monolith increases the syngas selectivity. This probably due to quenching of the gas phase reactions at high linear gas velocity, and suggests that microchannel reactors have potential for isolating kinetic effects and minimising gas phase contributions. The Rh/Al₂O₃ foam systems show higher initial syngas selectivity than the Rh-impregnated microchannel reactors, but deactivate rapidly upon temperature cycling, especially when steam is added as a reactant.     

Intensification of cavitational activity in sonochemical reactors using different additives: Efficacy assessment using a model reaction

Sonochemical reactors offer excellent promise for the intensification of different chemical processing applications. The current work deals with intensification of cavitational activity using different additives with an objective of decreasing the processing cost as well as enhancing the applicability of sonochemical reactors for different applications. Potassium iodide oxidation has been used as a model reaction. Experiments have been carried out in a laboratory scale ultrasonic horn reactor. The effects of different additives such as air, solid particles (cupric oxide and titanium dioxide), salts (sodium chloride and sodium nitrite) and radical promoters (hydrogen peroxide, ferrous sulphate, iron metal, carbon tetrachloride and t-butanol) on the degradation of potassium iodide have been investigated. Combination of additives has also been investigated for examining the possible synergistic effects in comparison to the use of individual additions. It has been observed that based on the type of additive, optimum concentration needs to be selected and it may not be desirable always to use different additives in combination. It is desirable to select an additive which can give additional reaction mechanism in the system to aid the desired application under question.     

Advancements in droplet reactor systems represent new opportunities in chemical reactor engineering: A perspective

Traditional chemical reactors, such as batch reactors, continuous reactors, and semi-batch reactors, have been extensively studied and frequently act as central components of modern chemical plants. Recently, various advances in reaction times, surface-to-volume ratios, required amounts of reagents, and throughput have led to new directions in the design of miniaturized chemical reactors. In this Perspective, we provide an overview of the progress from traditional to miniaturized chemical reactors by summarizing the characteristics and applications of different types of reactors. Furthermore, we compare classical chemical reactors and miniaturized droplet reactors to highlight advancements in the design of droplet reactor systems based on open functional surfaces. Finally, we provide an outlook on the research directions of miniaturized droplet reactors.     

A Review of Process Aspects and Modeling of Ebullated Bed Reactors for Hydrocracking of Heavy Oils

The main characteristics of ebullated bed reactors have been reviewed in this work. Key factors of the application of these reactors to hydrocracking of heavy petroleum fractions, such as sediments formation, catalyst attrition and catalyst deactivation, have been clearly discussed. Mathematical representation of ebullated bed systems has been organized into hydrodynamics, scaling down and reactor modeling. Only a few reports dealing with the topic of this review were found in the literature, which employ different levels of sophistication to establish the model equations. These literature reports were summarized and properly discussed, from which it has been recognized that modeling of ebullated bed reactors is a complex task and deserves more attention.     

Applying monolith reactors for hydrogenations in the production of specialty chemicals—process and economic considerations

Monolith catalysts, mainstays in gas-phase automotive and environmental process applications, have found new potential in replacing three-phase slurry reactors for the production of specialty chemicals, especially when their advantages are fully utilized in recirculation loop approaches. Many economic and logistical benefits for removing slurry catalysts drive the investment into monolith technology, both for new capacity and for retrofits onto existing stirred tank reactors. Benefits are most pronounced for fast reaction chemistries, where monolith catalysts can achieve volumetric activities several times higher than slurry reactors. This paper demonstrates how engineering design and scale-up can be performed using fundamental equations and literature correlations in combination with pilot plant measurements and presents an economic analysis emphasizing monolith catalyst life as a critical variable. Efforts to develop replacement catalysts must therefore integrate efficient catalyst fabrication and lab testing into the evaluation process.     

New Catalyst Synthesis and Multifunctional Reactor Concepts for Emerging Technologies in the Process Industry

Abstract

In order to promote the introduction of emerging technologies in the process industry, it has been established the two types of supporting R&D activities can be effectively pursued in parallel: (1) new catalyst synthesis methods that eliminate or minimize mass transfer limitations; and (2) multi‐functional reactors by integrating catalysis, heat transfer and/or separation. Catalyst Synthesis: In this paper, several methods of catalyst tailoring will be described that can minimize mass transfer limitations at industrially relevant conversion levels. Three (3) specific examples have been selected to demonstrate what can be achieved: (1) micro‐engineered catalyst that enables enhanced inter‐phase transfer; (2) new mesoporous catalysts with ultra large pores to accommodate slowly diffusing reactants; and (3) customized zeolites of extremely small particles to achieve high effectiveness factors while retaining the virtues of shape selectivity. Multi‐functional Reactors: Applying process intensification principles, mature high‐volume petrochemical processes can be improved dramatically, beyond the expected progress. This will be described using three (3) specific examples: (1) intra‐reactor oxidative reheat for the production of styrene, by staging endothermic and exothermic reactions in series; (2) simultaneous operation of endothermic, dissociative adsorption of methane with exothermic, oxidative removal of carbon during catalytic partial oxidation; and (3) catalytic distillation for the production of ethers, ethyl benzene and the selective hydrogenation of highly unsaturated components in olefins streams.     

Periodic Operation of Three — Phase Catalytic Reactors

Periodic operation of three phase reactors has been explored for more than two decades. This type of forcing changes selectivity and can increase either conversion or throughput. Experiments and simulation demonstrate periodic flow interruption or variation enhances reaction rates for concurrent trickle beds provided reactants are in the gas phase or can be volatilized under bed operating conditions. Temperature excursions in trickle beds can be controlled by either flow variation or switching the feed between an inert and a reactant. Several approaches to increasing rate through faster mass transfer using flow pulsing have been studied. Pulsing flow can be induced by low amplitude modulation. Periodic switching of flow direction in airlift reactors increases gas hold up and thereby the mass transfer rate. Periodic operation of three phase reactors, thus, appears to be a fertile area for engineering research.     

Application of electrochemical oxidation for treatment of industrial wastewater — the influence of reactor hydrodynamics on direct and mediated processes

The influence of kinetic and hydrodynamic factors in electrochemical reactors used in the removal of pollutants from industrial wastewater is shown, distinguishing between the two main types of reactions, namely direct and mediated electro‐oxidation. The effect of stirring during treatment of four different types of wastewater is reported. Whilst for direct electro‐oxidation of pollutants, the influence of agitation on the performance of the reactor can be easily predicted from a mass transfer correlation, its effect during electro‐oxidation mediated in the homogeneous phase by a redox couple is not straightforward. The Hatta number can be a useful criterion to apply to electrochemical reactors performing mediated oxidation of compounds (in analogy to gas–liquid reactions), so as to define whether the reaction occurs in the bulk of the reactor or near the electrode, and thus can be affected differently by stirring. The hydrodynamic conditions in the reactor for treatment of industrial wastewater can affect the differential selectivity of the removal of pollutants and this can be used for optimising the performance of the reactor with respect to a target pollutant. Copyright © 2006 Society of Chemical Industry     

Modeling and optimization of the cyclic steady state operation of adsorptive reactors

Adsorptive reactors(AR),in which an adsorptive functionality is incorporated into the catalytic reactors,offer enhanced performance over their conventional counterparts due to the effective manipulation of concentration and temperature profiles.The operation of these attractive reactors is,however,inherently unsteady state,complicating the design and operation of such sorption-enhanced processes.In order to capture,comprehend and capitalize upon the rich dynamic texture of adsorptive reactors,it is necessary to employ cyclic steady state algorithms describing the entire reaction-adsorption/desorption cycle.The stability of this cyclic steady state is of great importance for the design and operation of adsorptive reactors.In this paper,the cyclic steady state of previously proposed novel adsorptive reactor designs has been calculated and then optimized to give maximum space–time yields.The results obtained revealed unambiguously that an improvement potential of up to multifold level could be attained under the optimized cyclic steady state conditions.This additional improvement resulted from the reduction of the regeneration time well below the reaction-adsorption time,which means,in turn,more space–time yield.     

A Novel Radial‐Flow,Spherical‐Bed Reactor Concept for Methanol Synthesis in the Presence of Catalyst Deactivation

A radial‐flow, spherical‐bed reactor concept for methanol synthesis in the presence of catalyst deactivation, has been proposed. This reactor configuration visualizes the concentration and temperature distribution inside a radial‐flow packed bed with a novel design for improving reactor performance with lower pressure drop. The dynamic simulation of spherical multi‐stage reactors has been studied in the presence of long‐term catalyst deactivation. Model equations were solved by the orthogonal collocation method. The performance of the spherical multi‐stage reactors was compared with a conventional single‐type tubular reactor. The results show that for this case study and with similar reactor specifications and operating conditions, the two‐stage spherical reactor is better than other alternatives such as single‐stage spherical, three‐stage spherical and conventional tubular reactors. By increasing the number of stages of a spherical reactor, one increases the quality of production and decreases the quantity of production.     

Catalytic oxidation of methanol to formaldehyde: an example of kinetics with transport phenomena in a packed-bed reactor

In the present work the partial oxidation of methanol to formaldehyde has been studied as an example of strongly exothermic reaction affected by internal diffusion in order to deep the topic of mass and heat transfer in packed-bed catalytic reactors both at particle level, introducing the calculation of the effectiveness factor for complex reactions network, and at reactor level, for what concerns long range gradients of composition and temperature. The aim of the work is to stress the impact of the use of rigorous numerical methods, today possible for the high performances reached by the computers, in the solution of a simultaneous set of many differential equations that are necessary to describe completely the mentioned system. A complete mathematical model of the particle and the reactor is presented and a solution strategy is reported for the chosen reaction by considering a reliable kinetic law and evaluating related parameters from experimental data reported by the literature. Calculation results are reported for both particle internal profiles and reactor simulation. The described approach can easily be extended to many other devices and reactors geometry such as, e.g., the ones used in the field of environmental catalysis.