			Home About us Contact

Chemical Reactors (chemical + reactor)

Distribution by Scientific Domains

Chemistry	55%
Engineering	38%

Selected Abstracts

Modellierung und Simulation von Chemiereaktoren , Aspekte einer zeitgemäßen Ingenieurausbildung

CHEMIE-INGENIEUR-TECHNIK (CIT), Issue 1-2 2005
J. Hagen Prof.
Abstract Die Durchführung chemischer Prozesse in der Technik unter möglichst optimalen Bedingungen setzt ein Grundverständnis für die Arbeitsweise von Chemiereaktoren voraus. Grundlage der Modellierung von Chemiereaktoren sind die Stoff- und Wärmebilanz und die Kinetik der Reaktion. Nur in einfachen Fällen lassen sich analytische Lösungen für Problemstellungen aus der Praxis durch Integration der Differentialgleichungen finden. Das in der Chemieingenieurausbildung eingesetzte Softwarepaket POLYMATH ist sehr anwenderfreundlich und einfach zu erlernen. Es wird u.,a. eingesetzt, um gekoppelte Differentialgleichungen simultan zu lösen und Datenanalyse durch Regression durchzuführen. Mit einem einmal aufgestellten Modell lässt sich der Einfluss verschiedener Reaktionsparameter auf den Gesamtprozess leicht nachvollziehbar simulieren. Modeling and Simulation of Chemical Reactors , Aspects of a Modern Education of Engineers Understanding how chemical reactors work lies at the heart of almost every chemical processing operation. Basis information for modeling and simulation of chemical reactors is needed from mass transfer, heat transfer and chemical kinetics. Only simple problems from practice can be solved analytically by means of integration of the differential equations. POLYMATH is a extremely user-friendly software package which makes modeling easy for the education of chemical engineers and chemists. POLYMATH is used to numerically solve coupled differential equations simultaneously or to find kinetic parameters in rate expressions by regression. Using an identified model the influence of various reaction parameters on the overall process can be simulated easily. [source]

Integrated on-chip derivatization and electrophoresis for the rapid analysis of biogenic amines

ELECTROPHORESIS, Issue 14 2004
Nigel P. Beard
Abstract We demonstrate the monolithic integration of a chemical reactor with a capillary electrophoresis device for the rapid and sensitive analysis of biogenic amines. Fluorescein isothiocyanate (FITC) is widely employed for the analysis of amino-group containing analytes. However, the slow reaction kinetics hinders the use of this dye for on-chip labeling applications. Other alternatives are available such as o -phthaldehyde (OPA), however, the inferior photophysical properties and the UV ,max present difficulties when using common excitation sources leading to a disparity in sensitivity. Consequently, we present for the first time the use of dichlorotriazine fluorescein (DTAF) as a superior in situ derivatizing agent for biogenic amines in microfluidic devices. The developed microdevice employs both hydrodynamic and electroosmotic flow, facilitating the creation of a polymeric microchip to perform both precolumn derivatization and electrophoretic analysis. The favorable photophysical properties of the DTAF and its fast reaction kinetics provide detection limits down to 1 nM and total analysis times (including on-chip mixing and reaction) of <60 s. The detection limits are two orders of magnitude lower than current limits obtained with both FITC and OPA. The optimized microdevice is also employed to probe biogenic amines in real samples. [source]

Moment independent and variance-based sensitivity analysis with correlations: An application to the stability of a chemical reactor

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2008
E. Borgonovo
Recent works have attracted interest toward sensitivity measures that use the entire model output distribution, without dependence on any of its particular moments (e.g., variance). However, the computation of moment-independent importance measures in the presence of dependencies among model inputs has not been dealt with yet. This work has two purposes. On the one hand, to introduce moment independent techniques in the analysis of chemical reaction models. On the other hand, to allow their computation in the presence of correlations. To do so, a new approach based on Gibbs sampling is presented that allows the joint estimation of variance-based and moment independent sensitivity measures in the presence of correlations. The application to the stability of a chemical reactor is then discussed, allowing full consideration of historical data that included a correlation coefficient of 0.7 between two of the model parameters. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 687,698, 2008 [source]

Clustering multivariate time-series data

JOURNAL OF CHEMOMETRICS, Issue 8 2005
Ashish Singhal
Abstract A new methodology for clustering multivariate time-series data is proposed. The new methodology is based on calculating the degree of similarity between multivariate time-series datasets using two similarity factors. One similarity factor is based on principal component analysis and the angles between the principal component subspaces while the other is based on the Mahalanobis distance between the datasets. The standard K -means clustering algorithm is modified to cluster multivariate time-series datasets using similarity factors. Simulation data from two nonlinear dynamic systems: a batch fermentation and a continuous exothermic chemical reactor, are clustered to demonstrate the effectiveness of the proposed technique. Comparisons with existing clustering methods show several advantages of the proposed method. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Thermal and mass transients in the developing region of a homogeneous tubular chemical reactor

AICHE JOURNAL, Issue 3 2010
Mohammad K. Alkam
Abstract The current investigation presents a finite difference simulation of a homogeneous tubular reactor under laminar flow conditions. The present simulation considers the unsteady operation where transients in flow hydrodynamics, temperature field, and species concentrations have been considered. Flow development in the entrance region of the present reactor has been considered. Present results exhibit reactant concentration and mixing cup temperature profiles for a variety of operating conditions. Effects of several parameters on the performance of the current reactor have been examined, including, reaction parameter, order of reaction, and Schmidt number. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Semi-adaptive control of convexly parametrized systems with application to temperature regulation of chemical reactors

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2001
Alexander Fradkov
In this paper, we are interested in the problem of adaptive control of non-linearly parametrized systems. We investigate the viability of defining a stabilizing parameter update law for the case when the plant model is convex on the uncertain parameters. We show that, when the only prior knowledge is convexity, there does not exist an adaptation law,derivable from the standard separable Lyapunov function technique of Parks,applicable for all the state space. Therefore, we propose a semi-adaptive state feedback controller where adaptation takes place only in the region of the state space where convexity can be used to reduce parameter uncertainty. In the remaining part of the state space we freeze the adaptation and switch to a robust controller. This scheme ensures semi-global stability for convexly parametrized non-linear systems with matched uncertainty. The proposed controller is then applied to the problem of temperature regulation of continuous stirred exothermic chemical reactors where reaction heat is convex in the uncertain parameters. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Thermal decomposition of tert -butyl peroxide in a gas chromatographic reactor: A comparison of kinetic approaches

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2004
Peter J. Skrdla
The thermal decomposition of tert -butyl peroxide is investigated utilizing both the column and the injection port of a commercial gas chromatograph (GC) as chemical reactors. Using the injector liner as the reactor, the chromatographic peak areas of the reactant, measured at various injector temperatures, are used in the determination of the activation energy of the decomposition (Ea). With the column serving as the reactor, both the reactant peak areas and the product peak shapes are similarly utilized for this purpose. Values of Ea obtained using different mathematical treatments for each of the three approaches are found to range from 115 to 164 kJ/mol. Of these methods, the column reactor approach utilizing peak area measurements (referred to as PACR, for "peak area, column reactor") is found to be far superior in terms of its speed, robustness, and its accuracy in determining Ea. The PACR method's effectiveness can be largely attributed to the mathematical treatment that is described in the approach. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 386,393, 2004 [source]

Linear PI control of batch exothermic reactors with temperature measurement

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 3 2006
Jose Alvarez-Ramirez
Abstract A wide variety of speciality materials and fine chemicals such as plastics, pharmaceutical and microelectronics components are produced in batch reactors. The nonlinear, transient and finite-time features of the batch reactors give rise to complex process and control design problems. In particular, the safe operation of exothermic reactors depends on the adequate functioning of a temperature tracking controller, and to a good extent, the same is true for the attainment of a suitable compromise between productivity and product quality attributes. While the stabilization problem of continuous exothermic chemical reactors has been recently addressed with rigorous asymptotic-stability methods, the same kind of studies have not yet been performed for the finite-time batch reactor case. In this paper, the problem of designing a temperature tracking controller for an exothermic batch reactor, with n species and m reactions, is addressed under the following premises: (i) only the reactor temperature is measured, (ii) the (typically uncertain) reaction rate and heat exchange nonlinear functions are unknown, (iii) the controller must be linear and easy to tune, and (iv) the closed-loop reactor motion must be stable in a suitable sense. The combination of industrial-oriented inventory control concepts in conjunction with singular perturbation results yields a linear controller with a combined feedforward-PI feedback structure, antireset windup scheme, and conventional-like tuning rules. The controller: (i) tracks, arbitrarily fast and close, a prescribed temperature trajectory, with admissibly deviated concentration motions, and (ii) quickly recovers the behaviour of an exact model-based nonlinear I/O linearizing controller. The proposed design is put in perspective with the geometric and IMC nonlinear control approaches. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Composition cascade control for chemical reactors

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 13 2002
Jose Alvarez-Ramirez
Abstract Eventhough the composition control of chemical reactors is an old, widely studied, and still relevant problem in chemical process control, it still presents some aspects that remain unexplored or unresolved. For instance, a unifying approach is needed to systematize the existing ad hoc controller constructions, to rigorously explain their remarkable robustness property, and to explore the possibility of improving their construction and functioning. In this paper, some aspects of these control problems are addressed by resorting to recently developed approaches in constructive non-linear control, yielding a systematic controller construction coupled to a simple tuning scheme that can be executed with standard tuning rules, a closed-loop stability criterion, and an explanation of the closed-loop dynamics behaviour. Specifically, a linear cascade (master/slave) control configuration is proposed, which leads to global internal stability of the controlled system with asymptotic regulation of the output-stream composition about a given desired setpoint. A simulation example is used to illustrate the results. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Reachability of nonlinear fed-batch fermentation processes

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 12 2002
G. Szederkényi
Abstract The reachability of a simple nonlinear fed-batch fermentation process model is investigated in this paper. It is shown that the known difficulties of controlling such processes are primarily caused by the fact that the rank of the reachability distribution is always less than the number of state variables. Furthermore, a co-ordinates transformation is calculated analytically that shows the nonlinear combination of the state variables which is independent of the input. The results of the reachability analysis and that of the co-ordinates transformation are independent of the source function in the system model. The results are extended to the four state variable non-isotherm case, and to nonlinear fed-batch chemical reactors with general reaction kinetics. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Single-particle motion and heat transfer in fluidized beds

AICHE JOURNAL, Issue 12 2006
Yee Sun Wong
Abstract Fluidized beds are particularly favored as chemical reactors because of their ability to exchange heat through immersed heat-exchange surfaces. However, little is known about how the heat-exchange process works on a single-particle level. The most commonly applied theory of fluidized bed heat exchange is that developed by Mickley and Fairbanks in the 1950s,the so-called packet model. The work described in this article is an attempt to understand the process of heat transfer by solids convection, using positron emission particle tracking to follow the trajectory of a single tracer particle in the bed. In particular, the residence time of particles in the vicinity of the surface is determined here for the first time. Using these data, the observed heat-transfer variations are interpreted mechanistically. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Design and scale-up of chemical reactors for nanoparticle precipitation

AICHE JOURNAL, Issue 5 2006
Daniele L. Marchisio
Abstract In recent years there has been a growing interest in production on an industrial scale of particles with size in the sub-micron range (40-200 nm). This can be done by controlling particle formation in order to nucleate very small particles and by tailoring the particle surface in order to avoid particle aggregation and produce stable suspensions. In this work we focus on the role of turbulent mixing on particle formation in confined impinging jet reactors. In particular, we show how computational fluid dynamics and simple precipitation models could be used to derive scale-up criteria for the production of nanoparticles. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Passive control design for distributed process systems: Theory and applications

AICHE JOURNAL, Issue 8 2000
Antonio A. Alonso
A recently developed theory linking passivity with the second law of thermodynamics was used to develop a robust control design methodology for process systems with states distributed in time and space. Asymptotic stabilization of the infinite dimensional state thus can be accomplished for convection,diffusion processes with nonlinear production terms. Two examples representative of these phenomena were considered: chemical reactors and thermal treatments induced by electromagnetic fields. The first case shows how mixing and reactor size are critical control design parameters. If mixing is complete, at least in some direction, exponential stabilization can be achieved by high gain control. If not, stabilization is still possible for reaction domains smaller than a critical volume. In the second case, the electromagnetic field power supplied can always be manipulated to preserve passivity for any domain size. Two important consequences are that the infinite dimensional state can be reconstructed at arbitrary precision by robust observers and that control of the energy inventory will suffice to provide asymptotic stabilization. Theoretical justification of these findings is given on a general framework and illustrated through simulation experiments. [source]

Optimal control of non-linear chemical reactors via an initial-value Hamiltonian problem

OPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 1 2006
V. Costanza
Abstract The problem of designing strategies for optimal feedback control of non-linear processes, specially for regulation and set-point changing, is attacked in this paper. A novel procedure based on the Hamiltonian equations associated to a bilinear approximation of the dynamics and a quadratic cost is presented. The usual boundary-value situation for the coupled state,costate system is transformed into an initial-value problem through the solution of a generalized algebraic Riccati equation. This allows to integrate the Hamiltonian equations on-line, and to construct the feedback law by using the costate solution trajectory. Results are shown applied to a classical non-linear chemical reactor model, and compared against suboptimal bilinear-quadratic strategies based on power series expansions. Since state variables calculated from Hamiltonian equations may differ from the values of physical states, the proposed control strategy is suboptimal with respect to the original plant. Copyright © 2005 John Wiley & Sons, Ltd. [source]