Multiple Reaction Systems Research Articles

A simple chemical equilibrium algorithm applied for single and multiple reaction systems

AbstractThermodynamics is a branch of physics of high importance for engineering applications but is usually considered by most students as a rather obscure field, full of abstract concepts. Therefore, simple algorithms, which can exemplify the use of thermodynamic principles for practical situations, should be viewed as valuable teaching tools with large applications in engineering undergraduate courses. This point served as motivation for the present work, which proposes an alternative and simple computational approach for solving chemical equilibrium problems via successive reaction quotient calculations, both for single and multireactional systems. The code was written using MATLAB software; its fundamental theory was explained through a step‐by‐step approach and applied to both Shift and Boudouard reactions. Comparisons with ASPEN HYSYS and HSC Chemistry simulations corroborate its versatility and thermodynamic consistency. The full script is available in its entirety at the as supporting information together with the necessary text (.txt) files. Also, a user guide was provided to help students to replicate the results presented in the article.

The CRISPR/Cas System: A Customizable Toolbox for Molecular Detection.

Clustered regularly interspaced short palindromic repeats (CRISPR) and their associated proteins (Cas) are promising molecular diagnostic tools for rapidly and precisely elucidating the structure and function of genomes due to their high specificity, programmability, and multi-system compatibility in nucleic acid recognition. Multiple parameters limit the ability of a CRISPR/Cas system to detect DNA or RNA. Consequently, it must be used in conjunction with other nucleic acid amplification techniques or signal detection techniques, and the reaction components and reaction conditions should be modified and optimized to maximize the detection performance of the CRISPR/Cas system against various targets. As the field continues to develop, CRISPR/Cas systems have the potential to become an ultra-sensitive, convenient, and accurate biosensing platform for the detection of specific target sequences. The design of a molecular detection platform employing the CRISPR/Cas system is asserted on three primary strategies: (1) Performance optimization of the CRISPR/Cas system; (2) enhancement of the detection signal and its interpretation; and (3) compatibility with multiple reaction systems. This article focuses on the molecular characteristics and application value of the CRISPR/Cas system and reviews recent research progress and development direction from the perspectives of principle, performance, and method development challenges to provide a theoretical foundation for the development and application of the CRISPR/CAS system in molecular detection technology.

The Stoichiometric Uniqueness of Multiple Chemical Reaction Systems in Chemical Thermodynamics, Kinetics and Catalysis – Contributions of Professor Ilie Fishtik

The main scientific achievements of great significance accomplished by Professor Ilie Fishtik at the University of Iowa and the Worcester Polytechnic Institute, in several fields of the physical chemistry as chemical thermodynamics, kinetics and heterogeneous catalysis were revealed and briefly analysed. Fundamental equations of chemical thermodynamics within the De Donder (stoichiometric) approach were reformulated in terms of a special class of chemical reactions, called as response reactions. Using this approach, the unusual behaviour of chemical equilibrium systems, to interpret the apparent contradictions to Le Chatelier principle and to discover hitherto unnoticed thermodynamic identities, was rationalised. The stabilities of chemical species were formulated in terms of a certain class of stoichiometrically unique chemical reactions and their thermochemical characteristics. A completely new approach for the generation and simplification of kinetic mechanisms for complex reaction systems was developed and applied. Based on a new type of reaction networks, referred to as reaction route graphs, a systematic method of analysis and reduction of a microkinetic mechanism was established and employed.

Immobilization of Cellulase from Trichoderma Reesei on Multiwall Carbon Nanotubes (MWCNTs)

Cellulase is an enzyme commonly used to break down cellulose to beta-glucose. The demand of cellulase has been arisen due to its extensive range of applications in the industries such as detergents, foods and biofuel production. In present study, cellulase from Trichoderma reesei was immobilized on a functionalized multiwall carbon nanotube (MWCNTs) by physical adsorption method. Fourier Transform Infrared (FTIR) was used to confirm the successful functionalization of MWCNTs and immobilization of cellulase. In this approach, effects of pH and temperature for both free and immobilized cellulase were evaluated. Practically, the immobilized cellulase showed an improvement in pH and thermal stability compared to free cellulase at optimum condition of 50°C and pH 5 with 12% and 8% of increments respectively. For reusability study on CMC analysis, the bionanoconjugate retained 60% of its initial activity even after 3rd cycle of analysis. This feature is beneficial to the industrial applications because of its potential to be easily separated from the end product at the end of the reaction, reuse for several times and helps in development of multiple enzyme reaction systems.

Analysis of Experimental Conditions, Measurement Strategies, and Model Identification Approaches on Parameter Estimation in Plug Flow Reactors

Continuous flow reactors such as plug flow reactors (PFRs) have been used in the identification of reaction systems (Moore, J. S.; Jensen, K. F. Angew. Chem. 2014, 126, 480−483). It is important to understand the impact of operating conditions, measurement strategies, and kinetic model identification methods on the identification of reaction systems in a PFR. Typically, for kinetic model identification using the simultaneous identification approach, concentrations are measured as a function of residence time under isothermal operating conditions in a PFR. On the other hand, concentrations and temperature are required to be measured as a function of residence time under non-isothermal conditions for kinetic model identification of multiple reaction systems in a PFR. In this work, we extend the incremental method for identification of kinetic and heat transport models using measurements from non-isothermal steady-state PFRs. This work investigates the role of experimental conditions, measurement strategies ...

Design trade-offs in a column with side-reactor configuration for improving selectivity in multiple reaction systems

The configuration of columns with side-reactors (SRC) can effectively enhance the performance of reaction–separation processes, particularly where the operational limitations of conventional multifunctional reactors, such as reactive distillation systems, negate the overall benefits. Industrial manufacturing processes often use multiple reaction schemes that result in both desired and undesired products. The selectivity and yield of the desired product are usually improved by using large reaction vessels or high recycle flow rates of excess reactant. Therefore, in multiunit chemical processes, the foremost design trade-off is between the reaction vessel volume and the recycle flow rate. In this study, we investigate the competition of these parameters in SRC configurations in achieving specific conversion or yield criteria. Two real chemical processes involving side-reactors of non-reactive distillation columns and recycle streams are considered and their optimal design configurations are detailed. The results affirm the importance of this trade-off and its quantitative analysis to obtain the optimal SRC configuration.

Dynamic Performance Optimization of a Pilot-Scale Reactive Distillation Process by Economics Optimizing Control

The most prominent example of process intensification by process integration is reactive distillation (RD), which can realize a high reactant conversion and a high purity of the target product in equilibrium-limited reaction systems. Reactive distillation is mostly used for single reactions, but realizations for multiple-reaction systems leading to more than one target product can also be found. In multipurpose chemical processes, the target product of a multiple-reaction system can be switched during the production. When combining fluid separation and multiple-reaction systems, e.g., in a RD column, it is challenging to find operating conditions that lead to the most profitable operation of the process. Economics optimizing control where an economic objective is employed in a model-predictive control framework has the potential to drive the process to the economic optimum during operation based upon a process model and online measurements. However, so far only few applications of such advanced process co...

A comprehensive chemical model for the preliminary steps of the thermal stabilization process in a carbon fibre manufacturing line

A multistage comprehensive chemical model predicts the kinetic parameters and simulates the thermal stabilisation process.

Cooling and stirring failure for semi-batch reactor: Application to exothermic reactions in multiphase reactor

Thermal safety assessment for multiple exothermic reaction systems in multiphase reactors is challenging. One of the first step is to determine the presence or absence of secondary reactions producing non-condensable gaseous products. Then, a kinetic and thermal study should be performed to evaluate the value of the heat-flow rates due to chemical reactions. Epoxidation of a free fatty acid by a percarboxylic acid produced in-situ was studied. A classical approach by determining the adiabatic temperature rise (ΔTad) and the time to maximum rate under adiabatic conditions (TMRad) by microcalorimetry was used. Then, different cooling and stirring failure scenarii in a semi-batch lab-scale reactor under isoperibolic mode were performed. It was confirmed that the formation of peroxyformic acid governs the overall reaction kinetics and the reaction temperature. It was confirmed that in case of cooling failure, mechanical agitation should be maintained.

Steady-state and dynamic hysteresis effects during lean co-oxidation of CO and C3H6 over Pt/Al2O3 monolithic catalyst

A global kinetic model is developed for the co-oxidation of CO and C3H6 over a Pt/Al2O3 diesel oxidation monolithic catalyst based on a recent bench flow reactor study (Abedi et al., 2012). A monolith reactor model containing these kinetics is used to elucidate the dynamic and steady state hysteresis behavior observed during oxidation of a CO+C3H6 mixture on Pt/Al2O3. Dynamic hysteresis is observed during temperature-programmed oxidation which involves ramping the feed gas temperature up and down at a constant ramp rate. The predicted solid temperature spatial profile during ramp-up and ramp-down shows how the catalyst temperature lags behind the inlet temperature change, especially during the ramp-down. The dynamic hysteresis loop, whose width increases with the ramp rate and effective heat Peclet number (Peh,eff), is mainly a result of disparate time scales of thermal front propagation and temperature ramp and will be present even for reactions with negligible heat release. Steady state hysteresis can also be explained based on adiabatic temperature rise (ΔTad) and Peh,eff, i.e. thermokinetic multiplicity. The region of steady state hysteresis loop expands with an increasing ΔTad which is proportional to the feed concentrations of CO and C3H6. For fixed ΔTad, the steady state multiplicity disappears as Peh,eff increases or when there is negligible thermal feedback due to intra or interphase heat transfer. Finally, the model is used to construct a map that may be used to assess the light-off features of multiple reaction systems in monolith reactors.

Partial inventory control of the CSTR via reaction-dependent generalized inventories

Motivated by considering structurally dynamical properties of reaction systems, we develop an approach to deal with the nonlinear control of an unstable CSTR. More precisely, this paper shows that the CSTR dynamics can be split into reaction variant and reaction invariant dynamics modes through the use of linear combinations of system variables (called inventories). Since the reaction invariant dynamics mode is exponentially stable, the control design for an exponential stabilization of the reactor is simply solved together with (partial) inventory control on the basis of controlling the reaction variant dynamics mode. An extension of the approach to multiple chemical reaction systems is briefly outlined. Simulation results for a first order chemical reaction with multiplicity behavior are given to illustrate the theoretical development.

Reactive Distillation for Multiple-Reaction Systems: Optimisation Study Using an Evolutionary Algorithm

Abstract Reactive distillation (RD) has already demonstrated its potential to significantly increase reactant conversion and the purity of the target product. Our work focuses on the application of RD to reaction systems that feature more than one main reaction. In such multiple-reaction systems, the application of RD would enhance not only the reactant conversion but also the selectivity of the target product. The potential of RD to improve the product selectivity of multiple-reaction systems has not yet been fully exploited because of a shortage of available comprehensive experimental and theoretical studies. In the present article, we want to theoretically identify the full potential of RD technology in multiple-reaction systems by performing a detailed optimisation study. An evolutionary algorithm was applied and the obtained results were compared with those of a conventional stirred tank reactor to quantify the potential of RD to improve the target product selectivity of multiple-reaction systems. The consecutive transesterification of dimethyl carbonate with ethanol to form ethyl methyl carbonate and diethyl carbonate was used as a case study.

Reactive Distillation for Multiple Reaction Systems

AbstractDie Reaktivdestillation (RD) wird gegenwärtig vor allem zur Umsatzsteigerung in gleichgewichtslimitierten Reaktionssystemen verwendet, die häufig nur eine Hauptreaktion aufweisen. Diese Arbeit hingegen beschäftigt sich mit dem Einsatz der RD in chemischen Systemen mit mehr als einer Hauptreaktion. In solchen Multi‐Reaktionssystemen ist nicht nur der Umsatz der Edukte, sondern auch die Selektivität des Zielprodukts durch das chemische Gleichgewicht begrenzt. Ungeachtet, ob das Zielprodukt als Zwischenprodukt oder nach mehreren aufeinanderfolgenden Reaktionen gebildet wird, kann die RD zur Überwindung solcher Selektivitätslimitierungen beitragen. Dieses Potenzial wird am Beispiel der konsekutiven Umesterung von Dimethylcarbonat mit Ethanol untersucht. Die Ergebnisse umfassender experimenteller Studien in einer Technikumskolonne werden präsentiert, um den Einfluss entscheidender Betriebsparameter auf das Prozessverhalten zu untersuchen.

Buffer capacity in multiple chemical reaction systems involving solid phases

The buffer capacity of a chemical species in a multiple chemical reaction system is discussed in terms of a special class of stoichiometrically unique reactions referred to as response reactions (RERs). More specifically, it is shown that the buffer capacity may be partitioned into a sum of contributions associated with RERs. This finding provides a deeper understanding of the factors that determine the buffer capacity. In particular, the main contributions to the buffer capacity come from the RERs involving the most abundant species. Concomitantly, the RERs approach provides a simple stoichiometric algorithm for the derivation and analysis of the buffer capacity that may be easily implemented into a computer software.Key words: buffer capacity, response reaction, heterogeneous system, stoichiometric coefficient.

Chemical equilibria of multiple-reaction systems from reaction ensemble Monte Carlo simulation and a predictive equation of state: Combined hydrogenation of ethylene and propylene

Successful application of the reaction ensemble Monte Carlo (REMC) method to compute multiple-reaction chemical equilibria requires a reasonably high acceptance probability for all forward and backward reaction moves during the production stage of a simulation run. To achieve this for a system that involves almost irreversible multiple reactions, it is necessary to choose a thermodynamically-equivalent alternative set of linearly independent reactions, such that the occurrence of very large chemical equilibrium constants is avoided for as many reactions in the set as possible. In this work, the need for such a strategy is justified and applied to the combined hydrogenation of ethylene and propylene, which involves six components and requires a set of four linearly independent reactions. Already validated effective pair potential models were used: one-center Lennard–Jones (1CLJ) models for hydrogen and methane, two-center LJ plus point quadrupole (2CLJQ) models for ethylene, ethane and propylene, and a three-center LJ (3CLJ) model for propane. No binary adjustable parameters were needed to compute the unlike-pair LJ interactions. Simulation results were obtained for the effect of temperature and pressure on the conversions of ethylene and propylene, yield of methane, and density of the system at equilibrium. These results were found to be in very good agreement with calculations using the PSRK group contribution equation of state.

Thermodynamic Stability Relations in Redox Systems

Graphical stability relations in redox systems known as Pourbaix diagrams are analyzed employing the concept of overall stability of chemical species in multiple chemical reaction systems recently developed by us (Fishtik, I. J. Phys. Chem. B 2005, 109, 3851). The overall stability approach provides a simple and systematic algorithm for generating thermodynamically and stoichiometrically consistent Pourbaix diagrams that are referred to as overall Pourbaix diagrams. The conditions under which the conventional Pourbaix diagrams coincide with the overall Pourbaix diagrams are also discussed.

Phase Stability Relations in Invariant Systems

Except for the trivial case of one-component systems, the conventional Schreinemakers phase stability analysis in invariant systems is shown to be thermodynamically and stoichiometrically inconsistent in that the partition of the stability relations into contributions coming from univariant subsystems is formulated only qualitatively. Although the stability relations in invariant systems are essentially additive (i.e., the stability relations in invariant system may be partitioned into a sum contributions coming from univariant subsystems), the quantitative form of this partition has never been considered. On the basis of a new approach to the stability of chemical species in multiple chemical reaction systems that has been recently developed by us (Fishtik, I. J. Phys. Chem. B, 2005, 109, 3851), we show how the stability relations in invariant systems may be uniquely partitioned into contributions coming from univariant reactions. This finding provides a simple algorithm for the construction of various types of thermodynamically consistent stability diagrams.

Thermodynamic Stability of Chemical Species in Multiple Reaction Systems

A general thermodynamic and stoichiometric method, recently developed by us to study subtle forms of stability/instability relations among chemical species, such as resonance and strain energies (Fishtik, I.; Datta, R. J. Phys. Chem. A 2004, 108, 5727-5739), is extended to stability relations in multiple chemical reaction systems. Namely, a new definition as well as a new algorithm of evaluation of the stabilities of chemical species, referred to as the overall stabilities, is proposed. It is further shown that the overall stabilities may be partitioned into a sum of contributions associated with a complete set of stoichiometrically unique response reactions (RERs). This finding reveals that the conventional stability analysis is stoichiometrically and thermodynamically inconsistent in that it involves only a part of RERs.

A novel strategy for the design of multiple reaction systems for genetic analysis

Heat-transfer considerations are critical in the design of multiple reaction microdevices. We present a new methodology for the design and fabrication of multiple reaction systems using the concept of heat integration. In our application, we use heat integration to minimize the overall power consumption in multiple-reaction device operation by optimizing component placement. Designs based on heat integration rely on the use of steady-state temperature gradients developed in the substrate by the actuation of a single reaction chamber to initiate several reactions at progressively lower temperatures. The use of thermal gradients in this manner places design constraints on component placement, but eliminates the need to heat each individual reaction chamber and actively control the temperature of those chambers, and eliminates the power requirement for active cooling. Complete thermal isolation of components in a device, on the other hand, requires higher power input for overall device cooling and local heating but, unlike designs based on heat integration, does not constrain geometry of reaction chambers or their placement.

Optimal determination of rate coefficients in multiple-reaction systems

Abstract An efficient methodology is developed for parameter estimation and is applied by fitting 6 unknown rate coefficients. The estimation procedure is generally applicable to any system, although development has currently been limited to first-order systems of ordinary differential equations (ODE), such as those describing multiple chemical reactions. The objective is to find parameter values so as to minimize the sum of squared error (SSE), where each error term is the difference between the calculated system solution at a point and a selected data value. Since the calculated solution is generally quite nonlinear, an iterative solution is required. At each iteration, parameter values are supplied, the system is solved, and the SSE is determined. In addition, efficient algorithms require the SSE gradient (with respect to the vector of unknown parameters) in order to provide updated parameter estimates. Using conventional techniques, determination of this gradient involves solution of an ODE system for each parameter to be estimated. ff more than a few parameters are involved, the cost could be prohibitive. However, a procedure using adjoint operators is developed in which the SSE gradient can be calculated by solving only one additional ODE system, regardless of the number of parameters being optimized. Combined with a quasi-Newton updating system, an efficient methodology results. This methodology has been applied to a set of six chemical reactions describing the aqueous speciation (hydrolysis) of iodine.