Multifunctional Reactor Research Articles

Development and analysis of a multifunctional reactor for equilibrium reactions: benzene hydrogenation and methanol synthesis

The performances of a multifunctional reactor based on the in situ condensation and separation of the product are investigated for two industrial importance exothermal catalytic synthesis: the benzene hydrogenation into cyclohexane and methanol synthesis from syngas. The condensed product is separated in situ from the reacting medium through a hydraulic seal, in order to drive the equilibrium composition towards the product. The experimental background for the reactor–condenser (axial and radial configurations) is presented. A one-dimensional, steady-state model is developed. The performances of the reactor–condenser are compared to industrial data in the case of the methanol synthesis.

Recent Research in Catalytic Inorganic Membrane Reactors

The two most important, and often the most expensive, steps in a chemical process are usually the chemical reactor and the separation of the product stream. Both the process economics and the efficient use of natural resources could be improved by the combination of these two operations into a single unit operation, leading to potential savings in energy and reactant consumption and reduced by-product formation. One promising way to accomplish this combination is the use of membrane separation and catalytic reaction together in a multifunctional reactor. Until relatively recently, the use of membranes was restricted to low temperature processes with mild chemical environments, which could be tolerated by polymeric materials. Recent advances in inorganic materials have expanded the range of membrane use, to include high temperature and chemically harsh environments. This has allowed inorganic membranes to be integrated into catalytic reactors. This area was reviewed previously by the present author (Dixon, 1999). The present contribution seeks to review literature and new developments in the succeeding four and a half year period, since the end of 1998. Research directions that were previously considered promising are re-evaluated here, and new ideas since then are presented.

Modelling of a Reverse Flow Catalytic Membrane Reactor for the Partial Oxidation of Methane

Gas-To-Liquid (GTL) processes have great potential as alternative to conventional oil and coal processing for the production of liquid fuels. In GTL-processes the partial oxidation of methane (POM) is combined with the Fischer-Tropsch reaction. An important part of the investment costs of a conventional GTL-plant is related to cryogenic air separation. These costs could be substantially reduced by separating air with recently developed oxygen perm-selective perovskite membranes, which operate at similar temperatures as a POM reactor. Integration of these membranes in the POM reactor seems very attractive because oxygen reacts at the membrane surface resulting in a high driving force over the membrane increasing the oxygen permeation.Because the POM-reaction is only slightly exothermic, the natural gas and air feed have to be preheated to high operating temperatures to obtain high syngas yields and because the Fischer-Tropsch reactor operates at much lower temperatures, recuperative heat exchange is essential for an air-based POM process. External heat transfer at elevated temperatures is expensive and therefore recuperative heat exchange is preferably carried out inside the reactor, which can be achieved with the reverse flow concept. To combine the POM reaction, air separation and recuperative heat exchange in a single apparatus a novel, multi-functional reactor is proposed, called the Reverse Flow Catalytic Membrane Reactor (RFCMR). In this reactor a relatively uniform temperature profile should be established at the membrane section and the temperature fronts should be located in the inert in- and outlet sections.To study the RFCMR concept, reactor models have been developed assuming a shell-and-tube geometry, based on models that are commonly used to describe conventional reverse flow reactors. Simulations of the novel reactor concept revealed that a small amount of methane has to combusted on the air side to create the reverse flow behaviour. Also a small amount of steam has to be injected distributively along the perovskite membrane section to maintain the centre of the reactor at nearly isothermal conditions. With these modifications it was found that the desired temperature profile could indeed be created in the RFCMR and that high overall syngas yields can be achieved.

Formulation of Reduced-Order Models for the Dynamic and Stability Analyses of Autothermal Radial Flow Reactors

Autothermal radial flow reactors typically consist of a reactor setup of multiple catalyst-beds with internal heat exchange. These reactors are widely used because of their high efficiency due to the internal heat exchange, and radial flow arrangements are preferred due to their low pressure drops. Although an efficient multi-functional reactor arrangement, this setup has shown to provide for an additional destabilizing mechanism via the heat feedback. Thus, additional stability considerations are necessary when operating autothermal or non-adiabatic reactors at high conversions. This work proposes the formulation of a simplified model to investigate the effect of the heat transfer feedback on the stability of autothermal radial flow reactors. The present work focuses on a lumping approach to reduce the order of a complex distributed parameter system. The model is complex enough so as to preserve the intricacies of this reactor arrangement, but still yield a tractable dynamic formulation. The industrial ammonia synthesis process has been chosen as a case study to illustrate the proposed methodology. The lumped model predictions are qualitatively compared against numerical simulations of a detailed mathematical model.

Influence of Reaction Kinetics on the Performance of a Chromatographic Reactor

In general, the economic use of chromatographic reactors depends on the reaction and separation parameters. In this work, the continuous annular chromatograph as multifunctional reactor (CACR) and the CACR with upstream tube reactor (TUBR + CACR) were investigated.

New Modular Integral Pilot Reactors for Information Retrieval on Fixed‐Bed Catalytic Gas‐Phase Reactions

The integral reactor is most critical for experimental reaction engineering. However, its design does not come up to current requirements. Based on a tested modular construction principle, new modules for multifunctional integral pilot reactors with a wide range of applications were developed. These modules allow to configure both single and combination reactors for implementing varied methodical objectives. Two examples illustrate the advantages for the user.

Introduction of fusion driven subcritical system plasma design

Fusion driven subcritical nuclear system (FDS) is a multifunctional hybrid reactor, which could breed nuclear fuel, transmute long-lived wastes, producing tritium and so on. This paper presents an introduction of FDS plasma design. Several different advance equilibrium configurations have been proposed and a 1.5-D discharge simulation of FDS was also present.

The Claus process: teaching an old dog new tricks

The potential of integrating reaction with adsorption in a single piece of equipment to favourably displace chemical equilibria has attracted considerable attention in recent years. In contrast to the most such multifunctional reactor concepts investigated so far, the aim of our work is to study an industrially relevant chemical system with all its peculiarities. The feasibility of enhancing conversion in fixed-bed adsorptive reactors has been evaluated for the Claus reaction used in sulphur recovery, which is usually carried out in a multistage process, to counteract the severe equilibrium limitations at high conversions. Both experimental and simulation results indicate that the adsorption/reaction kinetics and the adsorbent capacity have to exhibit appropriate and compatible values in order to overcome the equilibrium limitation and attain high conversions in a single-step process. A crucial point is the selection of suitable reaction conditions, since the occurrence of undesirable side-reactions (e.g. suppression of COS elimination in the case of the Claus process) may be amplified by the distorted concentration profiles in adsorptive reactor operation. In industrial applications such by-products may be of particular importance and thus exert a decisive influence on the concentration profile modifications possible.

Innovative means for the catalytic regeneration of particulate traps for diesel exhaust cleaning

Catalytic traps for diesel particulate removal are multifunctional reactors coupling filtration and catalytic combustion of soot. This paper reviews the most recent developments carried out at Politecnico di Torino concerning two different trap types: zirconia-toughened-alumina foams catalysed with Cs–V catalysts, operating according to a deep filtration mechanism, and cordierite or SiC wall-flow filters catalysed with perovskite catalysts (e.g. LaCr 0.9O 3), enabling shallow-bed filtration. The preparation and characterisation of these two trap types are described and the performance of the traps (filtration efficiency, pressure drops, etc.) evaluated on a diesel engine bench under various operating conditions. A final critical assessment points out that most chances of practical application in mobile sources lie in wall-flow type traps for their superior filtration efficiency (>95%) and their compatibility with active trap regeneration means (e.g. fuel post-injection) that can occasionally rise on purpose the exhaust gas temperature to accelerate the catalytic combustion of trapped soot. Conversely, completely passive solutions based on deep filtration catalytic traps show only promise for stationary applications at temperatures higher than 350°C, due to insufficient catalyst activity at lower temperatures.

Analysis of a novel reverse-flow reactor concept for autothermal methane steam reforming

One of the main shortcomings of existing multifunctional reactor concepts for the autothermal coupling of endothermic and exothermic reactions is inefficient heat integration leading to excessive maximum temperatures or poor reactor performance. For the asymmetric operation of a reverse-flow steam reforming reactor, conditions under which these shortcomings can be overcome are proposed. The asymmetric process is based on the formation of travelling reaction zones. The features of these transient phenomena are analysed by means of a simplified model. During the endothermic semicycle, the heat consumption forms a temperature wave with an expansive low-temperature and a compressive high-temperature part. During the exothermic semicycle a proper axial distribution of the heat supply is necessary in order to maintain a favourable temperature profile in the cyclic operation mode. The results obtained with the simplified model are verified by direct dynamic simulation.

Innovative Membrane-Based Catalytic Process for Environmentally Friendly Synthesis of Oxygenates

Synthesis of liquid oxygenates from light alkanes (C1--C3) is achieved in a multifunctional three-phase catalytic membrane reactor (3PCMR) operating under mild conditions (TR, 80-120 °C; PR, 140 kPa). The features of superacid catalytic membranes mediated by the Men+/H2O2 Fenton system in activating C1-C3 alkanes are presented. The effect of operating conditions ([H2O2], [Men+]) on the catalyst activity is outlined. A general reaction pathway accounting for the activation of the CH bond of the alkane molecule on the superacid sites and the subsequent reaction of the activated alkane with primary reactive intermediates, generated from the Men+/H2O2 system, is proposed. The suitability of the 3PCMR in enabling simultaneous reaction and product separation is discussed.

Kinetic analysis of selective catalytic NOx reduction (SCR) in a catalytic filter

A multifunctional reactor allows substitution of two or more process units with a single reactor, where all the operations of interest are executed simultaneously. For example, when ceramic filter materials, used in flue gas cleaning, are doped with compounds of transition metals, high efficiencies in particulate separation and catalytic activity for the removal of NOx, CO and CHx are obtained. The present study addresses a kinetic analysis of NOx reduction occurring in the catalytic filter material, including experimental data reported in the literature. A numerical model, based on available knowledge of SCR kinetics, is developed, validated with catalytic filter data and with honeycomb profiles, and finally used for case studies regarding design variables (GHSV, inlet concentration). The results indicate that NOx conversion typically required is possible on time scales of gas flow through a catalytic filter medium in the temperature range 250–350 °C, with strong temperature effects due to the competition of the desired SCR reaction and NH 3 oxidation with O 2. Application of the model and parameter values derived from the catalytic filter analysis to a SCR honeycomb situation constitutes a sort of indirect validation.

Heterogeneous catalysts for the production of anthraquinone from 2-benzoylbenzoic acid

In the present paper, the dehydration reaction of 2-benzoylbenzoic acid (BBA) has been investigated in the presence of different heterogeneous catalysts, based on heteropoly acids (polyoxometalates), by using, in a first approach, a batch reactor for screening the best catalysts and, in a second step, a pseudo-continuous multifunctional reactor for determining reaction yields, catalysts productivity and deactivation of the catalyst selected in the first part of the research. The pseudo-continuous reactor works also as evaporator and condenser for separating and collecting produced anthraquinone (AQ) at a high level of purity, while water continuously evaporates in the atmosphere. A productivity comparison has also been reported with respect to solid acid catalysts, i.e. Y and β zeolites and acidified bentonite, tested previously. A kinetic model with vapour–liquid partition, liquid-phase non-ideality and catalyst deactivation, has been developed to correlate the experimental runs.

Reactive distillation: Non-ideal flow behaviour of the liquid phase in structured catalytic packings

Reactive distillation, the combination of chemical reaction and multistage distillation, is one of the most important industrial applications of the multifunctional reactor concept. The most promising column internals for reactive distillation are the so-called structured catalytic packings that combine favourable characteristics of traditional structured packings and heterogeneous catalysts. The non-ideal flow behaviour of the gas and the liquid phase is a fundamental aspect in multiphase reactor design since it has a strong influence on the reactor performance. In this study, liquid phase residence time distributions for the catalytic structured packing MULTIPAK ® were measured by means of conductivity measurements under different liquid and gas flow rates and evaluated with differential models.

Membrane reactors for hydrogenation and dehydrogenation processes based on supported palladium

Membrane reactors applied to catalytic reactions are currently being studied in many places world-wide. Significant developments in membrane science and the vision of process intensification by multifunctional reactors have stimulated a lot of academic and industrial research, which is impressively demonstrated by more than 100 scientific papers on catalytic membrane reactors being published per year. Palladium as a noble metal with exceptional hydrogen permeation properties and, at the same time, broad applicability as a catalyst, first of all for hydrogenation, is part of many of these developments. This paper discusses two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst. Dense palladium composite membranes can be used for hydrogen separation from packed-bed catalysts in gas-phase hydrocarbon dehydrogenation reactions. Mesoporous membranes containing dispersed bimetallic Pd/X-clusters can be employed as so-called catalytic diffusers for liquid-phase hydrogenation, e.g. of nitrate and nitrite in water. The principles of both concepts are introduced, recently obtained experimental data are evaluated in connection with literature results, and the perspectives for further development are highlighted.

The Reaction Column as a Multifunctional Reactor — Always the Best Choice for Reactive Distillation?

The Reaction Column as a Multifunctional Reactor — Always the Best Choice for Reactive Distillation?

Simultaneous Synthesis and Separation of a Product by Cooling Crystallization into a Multifunctional Reactor

Simultaneous Synthesis and Separation of a Product by Cooling Crystallization into a Multifunctional Reactor

Multi-functional Trickle Bed Reactor for Alkylacetates Synthesis

Multi-functional Trickle Bed Reactor for Alkylacetates Synthesis

The partial oxidation of methane to syngas in a palladium membrane reactor: simulation and experimental studies

Among numerous potential applications of inorganic membrane reactors, the partial oxidation of methane (POM) may offer an alternative route, with respect to steam reforming of methane, for producing synthesis gas. Inorganic membrane reactors are considered to be multifunctional reactors because they are able to combine catalytic reactions with membrane separation properties. In particular, dense palladium membranes are characterised by the fact that: (1) only hydrogen might permeate through them; (2) both Arrhenius and Sievert laws are followed. In this investigation, a dense palladium membrane reactor (PMR) concept is analysed referring both to experimental data and to simulation study. The partial oxidation of methane (POM) reaction to produce synthesis gas was chosen as a model reaction to be investigated. A membrane reactor model that includes the membrane, the gas phase and the catalyst activity is proposed. The experimental results in terms of methane conversion obtained by using a pin-hole free palladium membrane permeable to hydrogen only were compared with model predictions. The effect of reaction temperature on methane conversion at different time factors and sweep gas flow rates was considered. In particular, the effects of temperature profiles on the methane conversion are taken into account in the kinetic model.

Synthesis and purification of anthraquinone in a multifunctional reactor

In the present paper the reaction of 2-benzoylbenzoic acid dehydration has been studied in the presence of different catalysts by using a batch reactor for screening the best catalysts and a pseudo-continuous multifunctional reactor for determining catalysts productivity, reaction yields, catalysts deactivation and regeneration on the previously selected catalysts that are acid bentonite, Y- and β-zeolites. This last reactor works also as evaporator and condenser for separating and collecting produced anthraquinone at a high level of purity, while water continuously formed evaporates in the atmosphere. A kinetic model with vapour–liquid partition and catalyst deactivation has been used to interpret the experimental runs. The liquid reacting mixture showed strong non-ideality favouring the evaporation and collection of pure anthraquinone.