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The analysis of the potential to improve performance of a methanol synthesis reactor through forced periodical operations by Nonlinear Frequency Response method is presented. The methanol synthesis in an isothermal and isobaric lab-scale CSTR is considered. First, the analysis was performed for single input modulations (in Part I), which showed that significant improvements can't be achieved. Here, the study is extended to analysis of simultaneous modulations of two inputs. All possible input combinations (6 cases) are analysed and the optimal forcing parameters, maximizing the time-average methanol production, were determined. For all combinations the improvement is possible, but for some cases it is not significant. The highest improvement is predicted for simultaneous modulation of the inlet partial pressure of CO and the inlet volumetric flow rate. This case, for which it is possible to achieve up to 33.51 % of methanol production, is analysed it detail and optimized using multi-objective optimization. This is the peer-reviewed version of the article: Daliborka Nikolić, Carsten Seidel, Matthias Felischak, Tamara Miličić, Achim Kienle, Andreas Seidel-Morgenstern, Menka Petkovska, Forced periodic operations of a chemical reactor for methanol synthesis – the search for the best scenario based on Nonlinear Frequency Response Method. Part II Simultaneous modulation of two inputs, Chemical Engineering Science, 2022, 248, 117133, doi: [https://doi.org/10.1016/j.ces.2021.117133] The published version: [https://cer.ihtm.bg.ac.rs/handle/123456789/4816]

One of the most frequently used governing equations underpinning engineering flow analysis is the renowned Navier–Stokes (NS) equation. Several references regarding the derivation of equation of motion in Cartesian coordinates are available in standard textbooks. However, derivation of above equation in rotational frame is missing in literatures. Flow analysis using NS equation in rotational frame is a prerequisite for analysis of various engineering problems like rotational flow dynamics in chemical reactors, lubricating oil behavior in various rotating machines, electrolyte flow behavior in electrochemical reactors with rotating electrodes, etc. Systematic understanding of each terms in the equation is essential to develop a suitable governing mathematical model of any physical flow problem with various level of complexities. This is possible only if same can be derived from fundamentals, detailing terms behind the equation. A systematic approach is made here to derive NS equation in rotational frame from basic Cartesian form.

The aim of this paper is to develop some novel numerical algorithms for finding roots of one-dimensional non-linear equations. We derive these algorithms by utilizing the main and basic idea of the variational iteration technique. The convergence rate of the suggested algorithms is discussed. It is corroborated that the proposed numerical algorithms possess sixth-order convergence. To demonstrate the validity, applicability, and the performance of the proposed algorithms, we solved different test problems. These problems also include some real-life applications associated with the chemical engineering such as van der Wall’s equation, conversion of nitrogen-hydrogen feed to ammonia and the fractional-transformation in the chemical reactor problem. The numerical results of these problems show that the proposed algorithms are more effective against the other well-known similar nature existing methods. Finally, the dynamics of the suggested algorithms in the form of the polynomiographs of different complex polynomials have been analyzed that reveals the fractal nature and the other dynamical aspects of the suggested algorithms.

International audience; An unconventional modelling methodology based on artificial neural networks is proposed to rapidly develop a model from data obtained during different batch experiments. The objective of the global model is to predict time evolution of concentrations of all species present in the reaction medium. For this, different recurrent neural networks are elaborated to estimate a particular species as a function of operating parameters and concentrations of all species and then assembled in a complex global model.To validate the approach, the esterification reaction of methanol by acetic acid, which presents equilibrium, has been chosen. The kinetic evolution of the chemical species during experiments conducted in batch mode are correctly represented whatever the operating conditions. Finally, the global model based on neural networks is integrated in a hybrid model. This permits to transpose the reaction to a semi-batch chemical reactor which has not been considered during the learning phase.

Power-to-Gas technologies could play an important role in future energy systems, since they make it possible to store surplus electric energy from fluctuating renewable energy sources such as solar and wind. In Power-to-Gas concepts, the first step towards storage is the production of H2 by electrolysis, a possible further step is methanation. The Engler-Bunte-Institute, Fuel Technology at Karlsruhe Institute of Technology is conducting research on catalytic methanation in slurry bubble column reactors, which represent a highly load flexible reactor technology. To obtain experimental data at a semi-industrial scale a methanation pilot plant was built and commissioned. The plant is equipped with various safety valves, which may release the hazardous gases H2, CO and CH4 in the chemical reactor into the environment in the unintended case of overpressure, which may lead to a flammable and/or toxic cloud, threatening the safety of the workers and other humans near the plant. In this work, the safety evaluation of the accidental release in the methanation plant is performed using the numerical tool GASFLOW-MPI. Both toxicity and flammability of the hazardous gas cloud are analyzed and discussed. A local-global two-step simulation strategy, including a local computational model and a global computational model, is employed to calculate the hazardous gas dispersion efficiently and accurately. In the first step, a local detailed computational model with fine mesh is used to calculate the release mass flow through the exhaust tube and the complicated shock waves directly without any further assumption model such as the notional nozzle model. In the second step, a large-scale model with the relatively coarse mesh is chosen to efficiently predict the hazardous gas dispersion around the entire methanation plant. Moreover, the performances of two different types of exhaust pipes are compared and discussed, and the recommended exhaust pipe design is provided. The simulation results show that version B of the exhaust tubes is more recommendable from the viewpoint of safety.

The specific thermal properties of porous silicon (PSi) are discussed in relation to its possible applications. Based on the summary of the experimental approach required for nanomaterials, it is shown that both thermal conductivity and capacity per unit volume of PSi are dramatically decreased in comparison to conventional thermal insulators. The induced thermo-acoustic emission effect has some advantageous features over the conventional transducers, including resonance-free and broad-band dynamic response with a significantly low distortion. The PSi device is useful as a digital speaker, for object sensing in air, as a noncontact actuator, for analyses of bio-acoustic communications, and as a chemical reactor array.

A dataset of high-speed video footage of mercury droplets settling through liquid media of different viscosities is presented. Video footage was taken at 4000 frames per second for mercury droplets at room temperature settling through either deionised water or silicone oil. The data set is useful for validation of computational models of a wide range of systems which include phase separation studies, settling behaviour as well as interfacial phenomena in liquid-liquid systems. The data can serve as an analogue for validation for fluid systems where dimensional similarity exists and experimentation is not possible due to hostile experimental conditions, e.g. settling of molten metal through molten oxide slag in pyrometallurgical furnaces or separation of heavy liquid phases in chemical reactors.

This chapter is a survey of chemical reaction engineering basics: chemical species, reaction rates, representations of chemical reactions, chemical stoichiometry, thermodynamics, energy regularity for biotransformations, multiple reactions, conversion, yield, selectivity and yield factor, mass and energy balances, ideal chemical reactors, and economics of reaction engineering. Basic concepts are introduced, for example, elementary reaction, approximate reaction, coupled reaction, concentrations, specific reaction rate, Roels formula, transitional state, activation energy, chemical equilibrium, Gibbs free energy, enthalpy, and entropy. Also, included are how reaction rates are related between different substrates, different products; why there is only one independent variable in every reaction; what yield factors are, and how all are linked through stoichiometry. You should understand why A → B or S → P is used commonly in a reaction engineering text, instead of more realistic or real-life examples after reading this chapter. The understanding of how chemical reactions are approximated and represented, for example, is the key in understanding the representation of metabolic pathways in microbiology.

Mass transfer plays an important role in chemical engineering applications involving multiphase systems. Several techniques have been developed in the field to measure the global mass concentration in multiphase chemical reactors. However, because of the complexity of multiphase processes, only few techniques are able to provide local and quantitative information. In this study a dual-emission Laser Induced Fluorescent technique (LIF) has been developed to locally measure the mass transfer of a rising CO 2 bubble in a quiescent fluid. Details of the pH field with an overall precision of ± 0.04 pH units, dissolved CO 2 concentration, and the mass transfer evolution in the bubble wake can now be measured quantitatively. It is capable to provide quantitative comparison with simulation results and as such experimental validation of multiphase CFD models.

Gas–liquid flows appear in natural and industrial processes in various forms and often feature complex inter-phase mass, momentum, and energy transfers. One example of naturally occurring gas–liquid flow is the dispersion of marine droplets. Gas–liquid flows are also found in abundance in industrial processes. One significant industrial application is venting of mixture vapors to liquid pools in chemical reactors. This chapter is concerned with gas–liquid flows. Within this flow system, the two phases that coexist simultaneously in the fluid flow often exhibit relative motion among the phases and heat and mass exchanges across the interface boundary. Owing to the complexities of interfaces and resultant discontinuities in fluid properties as well as from physical scaling issues, it is rather customary to apply a statistical, averaged approach in the form of a two-fluid model to resolve such a flow system. Separate transport equations governing the conservation of mass, momentum, and energy are solved for each phase and exchanges that take place at the interfaces between the two phases are explicitly accounted for in which the dynamics of the interaction between the two phases can be effectively described via suitable models of the inter-phase mass, momentum, and energy exchanges. Normally, the coupling between the two phases is very tight, which demands special numerical strategies and solution algorithms to be adopted. This particular flow system is also complicated considerably by the prevalence of particle–particle collisions. A number of population balance methods, along with suitable coalescence and break-up mechanisms, are discussed. In the context of computational fluid dynamics, the application of population balance models to describe the coalescence and break-up dynamics of these gas particles can be coupled with the two-fluid model to predict the wide range of particle sizes within the two-phase flow.

We explore the possibility to actively use the system geometry to search for states of minimum entropy production in a chemical reactor. This idea is inspired by the energy-efficient mass and energy transfer that takes place in the reindeer nose thanks to its complex geometry. A cylindrical plug-flow reactor for oxidation of sulfur dioxide is used as example, while optimal control theory is used to formulate the problem. We hypothesize that the nasal anatomy of the reindeer has evolved to its present shape to help reducing energy dissipation during respiration in extreme ambient temperatures. A comparable optimal diameter-profile in the plug-flow reactor resulted in 11% reduction of the total entropy production, compared to a cylindrical reference reactor. With, in addition, an optimal reactor length, the reduction is 16%. These reductions are largely due to reductions in viscous dissipation. In practice, this translates into smaller pressure drops across the system, which reduce the loads of upstream/downstream compressors. Moreover, the peak in the temperature profile was reduced with respect to that obtained by controlling the temperature of the cooling medium. With today's technological solutions, the optimal diameter profile might be easier to realize than other optimal control strategies. The possible gains from this first example are encouraging, and may serve as inspiration for further applications. © 2019 Institution of Chemical Engineers

Microreactors and micro heat exchangers have very unique characteristics due to the small size of their channels. Our close examination of the properties of microchemical systems has resulted in the finding that microchannel reactor systems have modular structures, a feature which may be exploited to create novel systems. In microreactors, reagents are mixed in a dedicated device while another microchannel is used to exchange heat. For this reason, the chemical reactor, which is conventionally treated as a unit operation, may be decomposed into more elementary operations, thereby enabling the development of new chemical apparatuses by reconfiguring the individual modules. This presentation introduces a conceptual framework for the elementary operation of these chemical apparatuses. An example of the application of these concepts to the development of a new distillation device will be discussed.

The method of direct interaction of metal vapors and organic compounds on liquid-nitrogen-cooled walls of the reaction vessel (metal vapor cryosynthesis) allows the synthesis of diverse metal complex compounds and solvated metallic nanoparticles. In this review, state-of-the-art experimental works in this direction since 2000 are revisited. Analysis of the literature data highlights the following mainstream directions for the development of this approach: (i) the use of unstable intermediates, which are formed at the instant of the low-temperature co-condensation, as precursors of target products; (ii) control over the growth of metallic nanoparticles due to secondary physicochemical transformations after cryosythesis; (iii) the use of the low-temperature co-condensation products as functional materials, homogeneous, microheterogeneous, and supported heterogeneous catalysts. Further development of this method requires a marked leap forward in the development of innovative facilities, which involves the state-of-the-art design of the advanced low-energy equipment with high performance and low consumption of coolants.

Turbulent combustion and reaction are widely encountered in air and water pollution, chemical reactors, iron and steel-making furnaces, industrial and utility furnaces, gas-turbines, rocket engines, ramjet engines, and internal engine combustors, plasma chemical reactors, and reentry of spacecraft. There are strong turbulence–chemistry interactions. The chemical reaction may affect turbulence by the density variation due to heat release. On the other hand, the turbulence not only enhances heat and mass transfer but also increases the time-averaged reaction rate by intensifying the mixing among different reactants and combustion products. In this chapter, various turbulent combustion models will be discussed.

We outline various tools coming from fields of thermodynamics, kinetics, and optimization that are useful in dynamical modelling and optimal control of chemical (electrochemical) reactors. In the first part, we analyse thermal and (electro)chemical transport processes, where the transport steps may be regarded as peculiar reactions described by appropriate affinities. Rate and transport equations contain terms exponential with respect to Planck's potentials and the temperature reciprocal. In each elementary step, kinetic mass action law implies the presence of two competing unidirectional fluxes. While they are equal in the thermodynamic equilibrium, their difference off equilibrium constitutes an observed flux or a resulting rate. A generalized affinity emerges as a driving force. Correspondence with classical Butler–Volmer kinetics is shown for electrochemical systems. Near thermodynamic equilibrium, the theory converges to the standard linear kinetics described by Onsager's equations. In the second part, we transfer to the chemical realm the method of thermodynamic optimization that was developed in earlier chapters for thermal machines. The method is aimed here at the maximum production of chemical power, and after suitable extension, it may be applied to electrochemical flow systems, in particular fuel cells. With the thermodynamic knowledge and methods of dynamic optimization (especially the dynamic programming), kinetic limits are estimated with an optimal work function Wmax that extends a familiar quasistatic work Wrev for finite rates. Optimization leads to energy limits more restrictive than classical because of the rate penalty effects. These results are extended to fuel cells and electrochemical systems in the next chapter.

Optimal control of chemical reactors represents a challenging task, as their behaviour is nonlinear, asymmetric, and highly affected by various uncertainties. The paper presents multivariable control of a laboratory chemical reactor, in which acetic acid reacts with sodium hydroxide and the neutralization process runs in the reaction mixture. The challenge is to optimize the set-point tracking of pH in the presence of parametric uncertainties. The control inputs are the volumetric flow rates of acid and base. The robust model predictive control was designed to fulfil the control task. To make the optimization problem more tractable, the LMI-based formulation of the convex optimization problem is implemented. The optimization problem has a special structure to ensure offset-free control performance and satisfaction of constraints on control inputs. Moreover, optimal control actions are calculated considering the multiple input system. As only the controlled output is measured, the state observer was designed and used. The main contribution of the paper is the experimental investigation of the LMI-based and state-observer-based robust model predictive control with integral action designed subject to input constraints. Control performance of the laboratory neutralization chemical reactor satisfies all control requirements.

Chemical looping reforming (CLR) processes offer textbook examples for challenges in chemical engineering with respect to transport limitations. Phenomena that potentially need to be considered in a rigorous reactor model include (i) diffusion in solids and nanometer-scale pores, (ii) heat and mass transfer between suspended particles and the ambient gas, (iii) meso-scale phenomena such as clustering, as well as (iv) large-scale phenomena such as particle and gas-phase dispersion in the reactor’s axial direction. Here we summarize key scientific advances made in the “NanoSim” project, which established a computational platform that enables modelling a large range of these phenomena. Specifically, we show that already at the particle scale significant uncertainties are introduced when modelling chemical reactors in very detail. This is due to the nature of gas-particle flow, i.e., the spontaneous formation of heterogeneities (i.e., so-called meso-scale structures) that impact flow, species transport and reactions. The key finding is that these heterogeneities must be accounted for in typical CLR applications to correctly predict reaction rates in an industrial-scale reactor.

In this chapter primary attention is paid to uncontrolled fluid–solid noncatalytic and catalytic systems with particulate solids. The scientific information is largely based on a book in Polish by Szarawara, J., Skrzypek, J., Gawdzik A. 1991. Podstawy Inzynierii Reaktorow Chemicznych ( Fundamentals of Chemical Reactor Engineering ), second ed. Warszawa, WNT, whose English counterpart is not available to date. Basic regimes of a heterogeneous processes (kinetic, diffusional, and intermediate) are distinguished. The notion of chemical resistance is defined and its significance for heterogeneous reactors is exemplified. The so-called model of shrinking grain is formulated and its main implications are described. Some special cases of this model are analytically solved and numerous application examples to industrial processes are presented. Statics and kinetics of sorption processes are considered. The equation of heterogeneous surface kinetics is derived and its “decelerating kinetics” is explained by the detrimental product rates in the denominator of this equation. Effects of concentration and temperature on the general rate of contact reaction are discussed for both exothermal reactions and exothermic reactions. Issues associated with diffusion in porous channels, Thiele modulus, and the influence of internal diffusion on the general chemical rate are discussed. The popular notion of effectiveness coefficient of a contact, attributed to the exploitation of the internal surface of grain, is defined. Charts characterizing internal diffusion under nonisothermal conditions are analyzed. While the effects of catalyst and sorbent deactivation are ignored, the chapter describes the main mechanisms of catalyst decay and, as such, it provides an introduction to further chapters which analyze systems with deactivating sorbents and catalysts to minimize the detrimental effect of catalyst deactivation.

Chemical looping combustion (CLC) is a promising carbon capture technology where cyclic reduction and oxidation of a metallic oxide, which acts as a solid oxygen carrier, takes place. With this system, direct contact between air and fuel can be avoided, and so, a concentrated CO2 stream is generated after condensation of the water in the exit gas stream. An interesting reactor system for CLC is a packed bed reactor as it can have a higher efficiency compared to a fluidized bed concept, but it requires other types of oxygen carrier particles. The particles must be larger to avoid a large pressure drop in the reactor and they must be mechanically strong to withstand the severe reactor conditions. Therefore, oxygen carriers in the shape of granules and based on the mineral ilmenite were subjected to thermal cycling and creep tests. The mechanical strength of the granules before and after testing was investigated by crush tests. In addition, the microstructure of these oxygen particles was studied to understand the relationship between the physical properties and the mechanical performance. It was found that the granules are a promising shape for a packed bed reactor as no severe degradation in strength was noticed upon thermal cycling and creep testing. Especially, the addition of Mn2O3 to the ilmenite, which leads to the formation of an iron-manganese oxide, seems to results in stronger granules than the other ilmenite-based granules.

Ammonia as an alternative fuel and hydrogen carrier has received increased attention in recent years. To explore the potential of co-firing ammonia with methane for power generation, studies involving robust mathematical analyses is required to progress towards industrial implementation. To explore the chemical kinetic mechanisms best suited to ammonia/methane combustion in gas turbines, five different detailed mechanisms are compared to assess their efficacy in representing the reaction kinetics under practical gas turbine combustor operating conditions. Ignition delay time is compared with recently published predictions showing that the mechanisms of Tian and Teresa exhibit the best accuracy over a large range of conditions. A one-dimensional simulation was also conducted using a Chemical Reactor Network (CRN) model, thus providing a relatively quick estimation of the combustion mechanisms under swirling combustion conditions. The simulation of NOx emissions indicate that the Tian mechanism performs better than the others considered. Hence, the Tian mechanism was selected as the most appropriate for further studies of ammonia/methane combustion through a set of experiments carried out at various equivalence ratios and pressure conditions. Finally, sensitivity and pathway analyses were also performed to identify important reactions and species under high-pressure conditions, areas that need more attention for model development and emission control in future studies.

The main goal is to design a hybrid reactor that exhibits nonlinear behaviour, i.e., multiplicity of steady states or limit cycles. Then, the hybrid system can be used for testing new control algorithms. In the hybrid reactor, the reactor vessel and jacket are real, but the chemical reaction is simulated by means of the electric heater. To intensify the nonlinear effects in the designed system, a mathematical model of the hybrid reactor is developed and analyzed. It is assumed that the reactor content in not well-mixed and the reactor volume can be divided into two compartments. It is also assumed that the reaction heat (simulated by the heater) is constrained by its maximum value. Then, the dynamical behaviour of the system was studied based on the bifurcation analysis and the main bifurcation parameter was the flow rate Fj of coolant in the reactor jacket. Limit cycles and hysteresis were observed in a wider range of flow rates Fj after increasing the imperfect mixing effects in the mathematical model. Qualitatively the same results were obtained for a greater enthalpy of reaction. The obtained results have shown how to intensify the nonlinear effects in the designed hybrid reactor.

In chemical reactors, an enormous variety of possible regimes, both non-steady-state (transient) and steady-state can be observed. Steady-state reaction rates can be characterized by maxima and hystereses. Non-steady-state kinetic dependences may exhibit many phenomena of complex behavior, such as “fast” and “slow” domains, ignition and extinction, oscillations and chaotic behavior. These phenomena can be even more complex taking into account transport processes in three-dimensional media. In this case, waves and different spatial structures can be generated.

A reactive CFD model has been developed and implemented numerically in an in-house code for a coupled double loop circulation fluidized bed reactor. In the current work it is utilized for the chemical looping combustion (CLC) process but the model can easily be modified for exploring some other chemical looping processes. The air reactor and the fuel reactor are operated in fast fluidization regime and simulated separately in a simultaneous mode. The connections between the two reactors are realized through time-dependent inlet-outlet boundary conditions. The model predictions are validated by comparison with experimental data reported in the literatures. Good agreement is observed between the experiments and simulations. Using this model, fluid dynamics and chemical process performance of the double loop reactor is investigated. The results show that the methane is rapidly consumed at a very short entrance section of the reactor and the axial distribution of the oxygen is more smooth. Higher reactant residence time and fuel reactor temperature increase the conversion of methane and oxygen. The methane conversion could reach 95% during the current study. This is a submitted manuscript of an article published by Elsevier Ltd in Chemical Engineering Journal, 16 March 2017.

Chemical-looping combustion can be carried either in circulating fluidized bed reactors or in dynamically operated packed bed reactors. In this work, the influence of the reactor selection on the overall process efficiency has been estimated. The CLC reactors are fed with syngas at 20 bar, which is produced from coal gasification. In the fluidized bed system, the oxygen carrier particles are transferred from the air to the fuel reactor and vice versa. Uniform reactor temperatures can be maintained due to internal solids circulation and vigorous mixing. Due to the large solids circulation and low reaction enthalpy in the syngas-fed fuel reactor, small temperature differences result between the reactors. A case where NiO/Al2O3 is used as oxygen carrier has been considered and an LHV efficiency of 41.4% has been calculated, assuming the fuel conversion at chemical equilibrium, leading to some unconverted CO and H2 in the reaction products. If full gas conversion is obtained by using another oxygen carrier operating at the same maximum temperature of 1200 °C, this efficiency can be increased to 41.8%. In the packed bed case, large temperature gradients inside the reactors are obtained and the CO2 and steam is produced at a lower (time-)average temperature. In addition, thanks to the lower average reaction temperature during fuel oxidation, the selectivity of the reduction reactions with nickel is not an issue. On the other hand, in this case a significant amount of steam has to be added or recycled to avoid carbon deposition, leading to an LHV efficiency of 41.1%. If a carrier is selected with a low kinetic activity for the Boudouard reaction, the efficiency can be increased by 1.1% point up to 42.2% of LHV. Other differences between the two systems are related to the number of vessels needed and the volume of the solids inventory, which is expected to be lower in the circulating fluidized bed system. An initial investment cost estimation demonstrates that the oxygen carrier costs are important, so that a low cycle time and a cheap oxygen carrier is preferred. The process efficiency for both reactor configurations is at the same level, 41–42% of LHV. Therefore, it can be concluded that the reactor selection will not be made based on the process efficiency, but on the availability, operability and cost of high temperature and high pressure reactor systems, that are still under development and both present pros and cons.

International audience; Kinetics is essential for chemical reactor modelling, in particular to reduce the inherent risks of extrapolation going along with scaling-up. Pharmaceutical industries are especially concerned. However, when chemical systems are very complex, development of good models may lead to prohibitively expensive and time consuming experiments. The aim of this paper is to describe an efficient experimental design strategy for discrimination of stoichio-kinetic models. The proposed methodology is based on model-based experimental design(optimal design), which uses information already acquired on models to determine the best conditions to implement a new experiment with the highest discrimination potential. The combination with microreactor technology is also proposed in this work. The whole procedure for model discrimination is firstly described in detail and then, applied to a numerical study case, consisting of a chemical synthesis carried out in a microreactor. The discrimination procedure efficiently leads to the determination of the single adequate model among the various potential models proposed before the implementation of the designed experiments.It is verified that the procedure does not depend on the set of preliminary experiments and is time-saving when compared to a classical factorial plan.

Catalysis is of crucial importance for the chemical industry. The number of catalysts applied in industry is very large, and catalysts come in many different forms, from heterogeneous catalysts in the form of porous solids to homogeneous catalysts dissolved in the liquid reaction mixture to biological catalysts in the form of enzymes. Catalysis is a multidisciplinary field requiring efforts of specialists in different fields of chemistry, physics and biology to work together to achieve the goals set by mankind. There is a direct link between chemical kinetics and catalysis; according to the very definition of catalysis, it is a kinetic process. Despite the fundamental differences between elementary steps in catalytic process on surfaces with enzymes or homogeneous organometallic complexes, there are striking similarities in terms of chemical kinetics. A general overview of different types of catalysis is presented and discussed in this chapter. Basic definitions related to formal kinetics and acquisition of kinetic data are introduced. Different kinds of chemical reactors along with respective mass balances are presented. Finally, a relationship between kinetics and thermodynamics is discussed.

In this chapter, we apply dimensional analysis to chemical processes. We use homogeneous batch reactions, plug flow reactions, and porous solid–catalyzed reactions as examples. We show how to derive the dimensionless parameters for these examples, then we show how to combine them to form the Group I, II, III, and IV Damkohler numbers, as well as the Reynolds number. These numbers are used during process upscaling.

Chemical industry, more than any other, is perceived as a threat. This negative feeling is enhanced because of major accidents, which have occurred during its history, involving catastrophic effects on both human health and environment: Oppau (1921), Texas City (1947), Seveso (1976), and Bhopal (1984) are some of tragic examples.

In this chapter we discuss various theoretical and practical aspects of chemical reactor analysis, synthesis, and optimization. In particular we stress the role of dynamic modeling and optimal control methods in optimization of chemical, electrochemical, and biological reactors. We analyze in sequence: stoichiometric coefficients, driving forces of transport and rate processes, nonlinear macrokinetics of chemical processes, chemical Ohm’s law, heterogeneities, stability, instabilities, limit cycles, chemical fluctuations, and the role of chaos and fractals in the chemical word. Particular attention is given to the power yield problems in chemical engines (the second part of this chapter).

A numerical feasibility study was performed on the integral performance of dual function catalyst particles in a packed bed reactor equipped with a porous membrane for distributive feeding of oxygen. The exothermic oxidative coupling and the endothermic steam reforming of methane (for simultaneous production of ethylene and synthesis gas) are integrated at the level of a porous catalyst particle with distributed activity, where the presence of the intraparticle heat-sink strongly reduces the total reaction heat and the temperature gradients in the reactor, eliminating the need for expensive conventional cooling of the reactor. Numerical simulations, with reaction kinetics taken from the literature, revealed that with distributive oxygen feeding via membranes indeed the local oxygen concentration in the packed bed membrane reactor can be kept low, which combined with a high Thiele modulus for oxidative coupling makes dual function catalysis possible. Using a reforming core diameter of approximately 15–40 μm, the steam reforming and oxidative coupling reaction rates could be effectively tuned to achieve autothermal operation, while the methane conversion was enhanced from 34 to 48% at optimum C 2 production rates. In addition, it was shown that the temperature profiles in the reactor can be strongly reduced by employing the dual function catalyst and that the use of axial oxygen membrane flux profiles enables the use of a single particle configuration to approach autothermal operation in the entire reactor.

A novel reactor concept with autothermal operation is presented for the simultaneous production of ethylene by oxidative coupling (OCM) and synthesis gas by steam reforming of methane (SRM). A detailed reactor model was developed and used to gain insight in the complex behavior of the reactor comprising two separate reaction chambers which are thermally coupled. The OCM is carried out in packed bed reverse flow membrane reactor tubes submerged into a fluidized bed where the unconverted methane and by-products, from which the valuable C2 (C2H4 and C2H6) components have been separated, are reformed together with some additional steam, thus producing synthesis gas and consuming the reaction heat liberated by the exothermic OCM. On basis of detailed simulations it has been shown that indeed the exothermic OCM and endothermic SRM can be very efficiently coupled permitting autothermal operation with cyclic steady state C2 yields up to 30% at full methane conversion with a CH 4 / O 2 molar ratio of 2–2.5 and a H2O/CH4 molar ratio of 3 in the SRM fluidized bed reactor.

Recently, many novel reactor concepts based on membrane fluidized bed reactors have been proposed. In this work, the effects of gas permeation through flat membranes on the hydrodynamics in a pseudo-2D membrane-assisted gas–solid fluidized bed have been investigated experimentally. A combination of the non-invasive techniques (Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA)) was employed to simultaneously investigate solids phase and bubble phase properties in great detail. Counter-intuitively, addition of secondary gas via the membranes, that constituted the confining walls of a gas–solid suspension at conditions close to incipient fluidization, did not result in a larger, but in a smaller equivalent bubble diameter, while gas extraction on the other hand, resulted in a larger equivalent bubble diameter, although in this case the effect was less pronounced. This could be explained by changes in the larger scale particle circulation patterns due to gas extraction and addition via the membranes.

Fluidized beds employing fine powders are finding increased application in the chemical and petrochemical industry because of their excellent mass and heat transfer characteristics. However, in fluidized bed chemical reactors axial gas back mixing can strongly decrease the conversion and selectivity. By insertion of membranes in fluidized beds large improvements in conversion and selectivity can be achieved, firstly by optimizing axial concentration profiles via distributive feeding of one of the reactants or selective withdrawal of one of the products, and secondly, by decreasing the effective axial dispersion via compartmentalization of the fluidized bed. Moreover, insertion of membrane bundles in a suitable configuration impedes bubble growth, thereby reducing reactant by-pass via rapidly rising large bubbles. In this work the influence of the presence and configuration of membrane bundles and the effect of gas addition via the membranes on the effective axial dispersion was studied experimentally. Steady state concentration profiles were measured where a CO2-tracer was injected at different locations through a probe (point injection) or via the membranes (line injection) into a square fluidized bed (0.15 m × 0.15 m × 0.95 m) containing glass particles (75-110 µ m, 2550 kg/m3) fluidized with nitrogen distributed via a porous plate. Different bed configurations, viz. without internals, with vertical or horizontal membrane bundles were investigated and the effects of overall fluidization velocity and gas flow ratio of gas fed through the membrane bundles and the porous plate distributor were studied. Experimental results revealed that the insertion of vertical and horizontal membrane bundles decreases the effective axial dispersion considerably compared to a bed without internals. The point injection experiments indicated the importance of a non-uniform lateral emulsion phase velocity profile. The line injection experiments clearly pointed out the importance of bubble-to-emulsion phase mass transfer limitations. Gas addition through the membrane bundles decreases the effective axial gas dispersion enormously by almost annihilating the solids down flow along the walls and by decreasing the average bubble size and bubble fraction. © 2007 Elsevier Ltd. All rights reserved.

By placing together the pieces of the design and control puzzle we developed a novel methodology that allows the screening and selection of feasible integrated designs at an early stage. The structure reactor–separator–recycle (R–S–R) system is a central design objective. The key piece of equipment remains the chemical reactor that should be large enough to ensure feasible and flexible operation. Multiple states are possible solely due to the effect of material recycles, but thermal effects may bring more complicated non-linearities. The so-called snowball effect is merely a matter of design than control. The behaviour depends on the reactor size and plantwide control structure. Larger reactors behave better than smaller ones. A clear distinction is made between self-regulation and regulation-by-feedback control structures. Usually, using the recycles to change the production rate is better than fixing the fresh feeds. By means of the phenol hydrogenation case study, we show that indeed the best control strategies are based on manipulating both reactants recycles.

Novel energy efficient chemical reactor technology is proposed. High pressure and temperature are generated by means of rapid compressive heating of gases by liquids with the following rapid cooling during the expansion stage. The compression-expansion of gas bubbles was studied experimentally in a reactor utilizing the principle of hydraulic ram phenomenon. The pressure measured in water with dispersed air bubbles was used to calculate compression of the bubbles containing mixture of methane with hydrogen or argon. It was found that the liquid compression technology might be an effective practical route to convert natural gas to valuable chemicals such as ethylene and acetylene.

Chemical reactors are pieces of equipment in which the feedstock is converted into the desired product. When selecting chemical reactors for specific tasks, economic costs, yield, purity, and pollution must be taken into account. Generally, reactors are chosen that will meet the requirements imposed by the reaction mechanisms, rate expression and the required production capacity. An important factor in reactor operation is the outlet degree of conversion. The degree of conversion affects the economics of separating the reaction mixture and the costs of returning the unconverted reactant back into the reaction. Operating conditions such as temperature, pressure, and degree of agitation are related to the most economic operation. Batch or continuous processes, and combinations of reactor types or multiple reactors in series or parallel can be used to optimize the output. It is also important to determine whether the mode of operation involves either isothermal or an adiabatic conditions.

Combining membrane technology with chemical reactors to enhance the conversion and yield of equilibrium-limited reactions has been taken into account in a wide variety of chemical reactions as a promising method. In this chapter, classified information regarding the application of membrane concepts in some of the important industrial reactions is provided.

Solid foam materials combine high voidage and high surface area. These two properties are advantageous for use in chemical reactors due to the low frictional pressure drop and relatively high surface area that may be used for catalyst deposition. Hydrodynamic parameters such as liquid holdup, pressure drop, and flow regimes similar to those for packed beds, have been obtained for the gas and liquid flows through these solid foam packings. The open-celled solid foam packings used were in the range of 5–40 pores per linear inch (ppi). The regimes studied are two high liquid holdup regimes and a low liquid holdup regime (trickle flow regime). Also the flooding points for counter-current flow have been determined. (7th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering )

In this paper the concept of micro-fluidized beds is introduced. A cylindrical quartz reactor with an internal diameter of only 1 mm is used for process conditions up to Click to view the MathML source and 244 bar. In this way, fast, safe, and inherently cheap experimentation is provided. The process that prompted the present work on miniaturization is gasification of biomass and waste streams in hot compressed water (SCWG). Therefore, water is used as fluidizing agent. Properties of the micro-fluid bed such as the minimum fluidization velocity (Umf), the minimum bubbling velocity (Umb), bed expansion, and identification of the fluidization regime are investigated by visual inspection. It is shown that the micro-fluid bed requires a minimum of twelve particles per reactor diameter in order to mimic homogeneous fluidization at large scale. It is not possible to create bubbling fluidization in the cylindrical micro-fluid beds used. Instead, slugging fluidization is observed for aggregative conditions. Conical shaped micro-reactors are proposed for improved simulation of the bubbling regime. Measured values of Umf and Umb are compared with predictions of dedicated 2D and 3D discrete particle models (DPM) and (semi)-empirical relations. The agreement between the measurements and the model predictions is good and the model supports the concept and development of micro-fluid beds.

Process alternatives for continuous crystallization, i.e., cascades of mixed suspension, mixed product removal crystallizers (MSMPRCs) and plug flow crystallizers (PFCs), as well as batch crystallizers are discussed and modelled using population balance equations. The attainable region approach that has previously been used in the design of chemical reactor networks and separation systems is applied to the above-mentioned alternatives for crystallization processes in order to identify attainable regions in a diagram of mean product particle size vs. total process residence time. It is demonstrated that the boundaries of these attainable regions can be found numerically by solving appropriate optimization problems and that the region enclosed by these boundaries is fully accessible. Knowing the attainable region of particle sizes, it is possible to generate feasible process alternatives that allow specific particle sizes to be obtained in a given process configuration. The influence of uncertainty in the kinetic parameters required for the determination of such attainable regions is also investigated as well. These concepts are illustrated using a case study on the cooling crystallization of paracetamol grown from ethanol.

In this chapter fundamental features of processes with hydrothermal and supercritical water are discussed. Such processes need a reaction vessel that can withstand the operating conditions. Although very similar in principle, the pressure vessels are different with respect to size, purpose, and construction, as discussed. Although, there are many different processes, as discussed in the other chapters of the book “Hydrothermal and Supercritical Water Processes,” the basic processing steps for hydrothermal and supercritical water systems are similar. They comprise the introduction of the feed into the high-pressure vessel and establishing and maintaining operating conditions. The process has to be carried out that leads to the products wanted, the reaction products are retrieved and separated, and water, as the working fluid, is recycled or cleaned for discharge. Experimental processes on a laboratory size, typically are concerned mainly with the process step itself. Production processes are operated to deliver products, contrary to experimental processes, for which the determination of optimal process parameters is the main objective and produced sample products are used for analysis and for presentation. At a first glance, production processes differ from experimental processes mainly by size. While in experimental processes samples of the size of less than grams to maximal kilograms are produced, production processes may begin at a production rate of hundreds of kilograms for very high-priced materials and may reach a yearly production rate of hundreds of thousands of tons. This difference in size brings along a number of problems, mostly engineering problems, but not only. Other problems to be solved are the supply of the feed and the disposal of wastes, as the major logistic problems, financing as an economical problem, acquiring acceptance for the process and the product, as a sociological problem. From the point of view of technology, the main difference between an experimental process and a production process is complexity. Many more steps, some of them of total other aspects than hydrothermal processing, become important, in production processes. This is illustrated by examples for processes with hydrothermal and supercritical water.

This chapter presents elements from chemical reaction engineering necessary to consider in the conceptual design of a process as a system. The selection and the design of the reactor must be done in the context of interactions with the whole process, particularly with the separation system. The preliminary section reviews basic concepts with regard to stoichiometry, kinetics and chemical equilibrium. Then, design principles are discussed in the field of homogeneous reactions with reference to ideal reactor models, followed by heterogeneous reactions, where specific modelling problems are highlighted. Attention is paid to thermal design issues, related to safety and heat integration. Guidelines for the reactor selection are presented. The final section is devoted to new systematic methods developed by the process systems community.

This work presents a comprehensive conceptual design of a Ni-based chemical looping combustion process (CLC) carried out in fixed bed reactors. The process is intended to exploit the well-known advantages of the Ni/NiO redox system for CLC applications in terms of high reactivity, O2 carrying capacity and chemical and thermal stability. Solutions to the problem of heat management in fixed bed reactors at high temperature and high pressure are described, while a continuous flow of nitrogen for driving a gas turbine is produced. Each reactor involved in the process goes through a cyclic sequence of five reaction and heat transfer stages. Cool product gas recirculations are incorporated into the Ni oxidation and NiO reduction stages in order to moderate the maximum temperatures in the beds and control the displacement of the reaction and heat transfer fronts. A preliminary conceptual design of the process has been carried out to determine the minimum number of reactors needed for continuous operation in typical large-scale CO2 capture systems. Basic reactor models and assumptions based on an ideal plug flow pattern have been used in all the reactors during the chemical reactions and the heat transfer operations. This has made it possible to identify reasonable operating windows for the eight fixed-bed reactors that make up the CO2 capture system, and has demonstrated not only its technical viability but also its great potential for further development., This work is financed under the R+D Spanish National Program organised by the Spanish Ministry of Economy and Competitiveness under project ENE2012-37936- C02-02 and by CSIC 201280E017

This paper investigates hydrogen and methane generation from large hydraulic plant, using an original multilevel thermo-economic optimization approach developed by the authors. Hydrogen is produced by water electrolysis employing time-dependent hydraulic energy related to the water which is not normally used by the plant, known as “spilled water electricity”. Both the demand for spilled energy and the electrical grid load vary widely by time of year, therefore a time-dependent hour-by-hour one complete year analysis has been carried out, in order to define the optimal plant size. This time period analysis is necessary to take into account spilled energy and electrical load profiles variability during the year. The hydrogen generation plant is based on 1 MWe water electrolysers fuelled with the “spilled water electricity”, when available; in the remaining periods, in order to assure a regular H 2 production, the energy is taken from the electrical grid, at higher cost. To perform the production plant size optimization, two hierarchical levels have been considered over a one year time period, in order to minimize capital and variable costs. After the optimization of the hydrogen production plant size, a further analysis is carried out, with a view to converting the produced H 2 into methane in a chemical reactor, starting from H 2 and CO 2 which is obtained with CCS plants and/or carried by ships. For this plant, the optimal electrolysers and chemical reactors system size is defined. For both of the two solutions, thermo-economic optimization results are discussed and compared with particular emphasis to energy scenario, economic aspects, system size, capital costs and related investments. It is worth noting that the results reported here for this particular large H 2 plant case represents a general methodology, since it can vary according to their different sizes, primary renewable energy, plant location, and different H 2 utilization.

The various factors influencing the regime transition point in gas-liquid bubble columns are examined. Increasing gas density delays regime transition. This phenomenon is described in a qualitative way by the correlations of Reilly [1] and Wilkinson [2] of which the Reilly correlation is found to be more accurate. However, both correlations are unable to account for the influence of the addition of small quantities of surface tension reducing agents. The Reilly and Wilkinson correlations are also not adequate to describe the influence of the addition of catalyst particles on the transition point for a bubble column slurry reactor.

In this chapter we outline various tools coming from thermodynamics, kinetics, and optimization, useful in dynamic modeling and optimal control of chemical, electrochemical, and biological reactors. In the first part we analyze nonlinear chemical and thermal transport processes in which transport steps are treated as peculiar chemical reactions described by appropriate affinities. Rate and transport equations contain terms exponential with respect to Planck's potentials and temperature reciprocal. In each elementary step, of transport or rate nature, kinetic mass action law leads to the identification of two competing unidirectional fluxes. While they are equal in the thermodynamic equilibrium, their nonvanishing difference off the equilibrium constitutes the observed flux of the resulting rate of the process. A generalized affinity emerges as a suitable driving force. Correspondence with Butler–Volmer kinetics is shown in electrochemical systems. Near the thermodynamic equilibrium the theory converges to the standard linear kinetics described by the Onsager equations.

In this work the inverse model based temperature control of a batch chemical reactor is presented. The controller combines feed-forward and feedback elements. The feed-forward part is the constrained direct inverse, while multiple feedback structures are studied. Since we have a model with good correspondence with the physical system, the inverse of it can produce the manipulated variable. The feedback is needed to eliminate the effect of modeling errors that is especially important in steady-state. For the compensation of modeling error the following channels can be used: the manipulated variable, the set-point and the model parameters. The difference between each channel is how direct they act, and how fast can the consequences of manipulation be seen. These channels do not exclude each other, usually a faster feedback and a slower adaptation is applied where the control problem requires it. The example on which the controller strategies are presented is a 1 liter batch chemical reactor. The reactor has duplicated wall, and a laboratory thermostat supplies cooling/heating medium that flows through on the jacket of the reactor. The manipulated variable is the set-point of the thermostat, and the controlled variable is the inner temperature of the reactor. Simulation experiments support that the developed controller strategy is superior to conventional feedback loops, as it contains handling of measured disturbances, manipulator constraints, dead time and nonlinearity.

The objectives of this chapter are to enlighten the reader with the current status of compact and micro-sized heat exchangers. Heat exchangers of these types were among the first process sector unit operations to be intensified, and many chemical reactors are based upon their structural features. A good knowledge of available heat exchanger concepts is a useful precursor to the introduction of more complex and combined unit operations based upon such compact heat exchangers. Out with the process sector, the challenges to heat transfer in the aerospace and electronics areas have also greatly encouraged the development of such heat exchangers.