Reactions and Reactors Basic Concepts

2001 ◽  
Author(s):  
L. K. Doraiswamy
Keyword(s):  
Reaction Time ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Reaction Rates ◽  
Heterogeneous Reactions ◽  
Rate Equations ◽  
Continuous Reactor ◽  
Rigorous Treatment ◽  
Reactor Types ◽  
Definition Of

Organic synthesis is replete with countless classes of reactions, including several that are named after their discoverers (the name reactions), but fortunately they can all be conducted in less than a half-dozen broad types of reactors. Choosing a reactor for a given reaction is based on several considerations and combines reaction analysis with reactor analysis. Thus in this chapter we consider the following aspects of reactions and reactors, much of which should serve as an introduction to chemists and a refresher to chemical engineers: reaction rates, stoichiometry, and rate equations; the basic reactor types, as a prelude to a more rigorous treatment of these in Parts III and IV; transport of mass (represented by reactant and product molecules) and heat across phase boundaries for heterogeneous reactions; and types of laboratory reactors used by chemists and chemical engineers for their specific objectives. The first step in any consideration of reaction rates is the definition of reaction time. This depends on the mode of reactor operation, batch or continuous. For the batch reactor, the reaction time is the elapsed time; whereas for the continuous reactor, it is given by the time the reactant spends in the reactor, called the residence time, that is measured by the ratio of reactor volume to flow rate (volume/volume per unit time with units of time). An equally important consideration is the concept of reaction space (which can have units of volume, surface, or weight), leading to different definitions of the reaction rate. We begin this section by considering different ways of defining the reaction rate based on different definitions of reaction time and space. The basis of all reactor design is an equation for the reaction rate.

Photocatalytic degradation of azo dye in TiO2 suspended solution

2001 ◽  
Vol 43 (2) ◽  
pp. 313-320 ◽  
Author(s):  
C.-H. Hung ◽  
P.-C. Chiang ◽  
C. Yuan ◽  
C.-Y. Chou
Keyword(s):  
Reaction Time ◽  
Light Intensity ◽  
Photocatalytic Degradation ◽  
Azo Dye ◽  
Batch Reactor ◽  
Reaction Rates ◽  
Pseudo First Order Reaction ◽  
Degradation Rates ◽  
Orange G ◽  
Degradation Of Azo Dye

The photocatalysis of azo dye, Orange G, by P-25 anatase TiO2 was investigated in this research. The experiments were conducted in a batch reactor with TiO2 powder suspension. Four near-UV lamps were used as the light source. The experimental variables included solution pH level, amount of TiO2, illumination light intensity, and reaction time. A pseudo-first order reaction kinetic was proposed to simulate the photocatalytic degradation of Orange G in the batch reactor. More than 80% of 10 mg/L Orange G decomposition in 60-minute reaction time was observed in this study and fast decomposition of Orange G only occurred in the presence of both TiO2 and suitable light energy. Faster degradation of Orange G was achieved under acid conditions. The degradation rates of Orange G at pH = 3.0 were about two times faster than those at pH = 7.0. Faster degradation of azo dye was observed for greater irradiated light intensity and more TiO present during the reaction. The reaction rates were proportional to TiO2concentration and light intensity with the power order of 0.726 and 0.734, respectively.

Study on Black Liquor Low-temperature Gasification in Fluidized Bed by Eulerian Multiphase Computationally Fluid Dynamics Modeling

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Weiling Li ◽  
Wenqi Zhong ◽  
Baosheng Jin ◽  
Rui Xiao ◽  
Yingjuan Shao ◽  
...  
Keyword(s):  
Low Temperature ◽  
Fluidized Bed ◽  
Reaction Rate ◽  
Solid Phase ◽  
Heterogeneous Reaction ◽  
Black Liquor ◽  
Molar Fraction ◽  
Reaction Rates ◽  
Operating Conditions ◽  
Heterogeneous Reactions

Abstract A three-dimensional Eulerian multiphase based computational model was developed to simulate the black liquor gasification processes in a fluidized bed gasifier (FBG) at low temperature. The standard k-e model and kinetic theory of granular model were used to simulate the gas phase and solid phase, respectively. Black liquor pyrolysis, homogeneous reactions and heterogeneous reactions were taken into account in chemical model. The reaction rates of homogeneous and heterogeneous reaction were determined by Arrhenius–Eddy dissipation reaction rate and kinetic reaction rate. Simulations were carried out at four different operating conditions, i.e. reactor temperature was kept at 550 degree centigrade or 600 degree centigrade, and nitrogen or air was used as fluidizing medium. The calculated results were in well agreement with the experiment used as calibration. Base on the simulation, gas-sold flow patterns and gas species molar fraction distributions were obtained, the relationship of gas composition profiles with the temperature and the fluidizing media were discussed.

Visible and solar light photocatalytic disinfection of bacteria by N-doped TiO2

2014 ◽  
Vol 14 (5) ◽  
pp. 924-930 ◽  
Author(s):  
V. Arya ◽  
Ligy Philip
Keyword(s):  
Batch Reactor ◽  
Reaction Rates ◽  
Water Disinfection ◽  
Continuous Reactor ◽  
Pseudo First Order Reaction ◽  
Doped Tio2 ◽  
Complete Inactivation ◽  
Bicarbonate Ions ◽  
Solar Water Disinfection ◽  
Inactivation Of Bacteria

A water treatment system was developed based on a photocatalytic process, employing immobilized N-doped TiO2, which worked under solar radiation. Batch reactor studies were conducted using an immobilized and suspended form of N-doped TiO2. Activities of Degussa P-25 and N-doped TiO2 were compared. Optimization of catalyst concentration was also carried out. Reaction rates under different working conditions were compared. The bacterial kill followed a pseudo first-order reaction. Continuous reactor studies were carried out using N-doped TiO2 coated glass plates. Three-log inactivation of bacteria was obtained after a contact time of 40 min. The effects of turbidity, bicarbonate ions and organic matter were studied. It was found that the efficiency of the system decreased due to these components. Comparison of the performance of solar water-disinfection (SODIS) and solar photocatalytic treatment for disinfection of water was also carried out. The results showed that the suspended catalyst achieved complete inactivation in 1 h compared to SODIS which took 6 h. Bacterial regrowth was observed in the case of SODIS treatment whereas no bacterial growth was observed after solar photocatalytic treatment.

Thermodynamics and foundations of mass-action kinetics

2005 ◽  
Vol 30 (1-2) ◽  
pp. 3-113 ◽  
Author(s):  
Miloslav Pekař
Keyword(s):  
Chemical Kinetics ◽  
Reaction Rate ◽  
Chemical Potential ◽  
Kinetic Equations ◽  
Reaction Rates ◽  
Equilibrium States ◽  
Mass Action ◽  
Rate Equations ◽  
Mass Action Kinetics ◽  
Non Equilibrium

A critical overview is given of phenomenological thermodynamic approaches to reaction rate equations of the type based on the law of mass-action. The review covers treatments based on classical equilibrium and irreversible (linear) thermodynamics, extended irreversible, rational and continuum thermodynamics. Special attention is devoted to affinity, the applications of activities in chemical kinetics and the importance of chemical potential. The review shows that chemical kinetics survives as the touchstone of these various thermody-namic theories. The traditional mass-action law is neither demonstrated nor proved and very often is only introduced post hoc into the framework of a particular thermodynamic theory, except for the case of rational thermodynamics. Most published “thermodynamic'’ kinetic equations are too complicated to find application in practical kinetics and have merely theoretical value. Solely rational thermodynamics can provide, in the specific case of a fluid reacting mixture, tractable rate equations which directly propose a possible reaction mechanism consistent with mass conservation and thermodynamics. It further shows that affinity alone cannot determine the reaction rate and should be supplemented by a quantity provisionally called constitutive affinity. Future research should focus on reaction rates in non-isotropic or non-homogeneous mixtures, the applicability of traditional (equilibrium) expressions relating chemical potential to activity in non-equilibrium states, and on using activities and activity coefficients determined under equilibrium in non-equilibrium states.

scholarly journals REEXAMINATION OF ASTROPHYSICAL RESONANCE-REACTION-RATE EQUATIONS FOR AN ISOLATED, NARROW RESONANCE

2011 ◽  
Vol 20 (01) ◽  
pp. 165-172
Author(s):  
J. J. HE ◽  
J. HU ◽  
L. Y. ZHANG ◽  
L. LI ◽  
S. W. XU ◽  
...  
Keyword(s):  
Reaction Rate ◽  
Charged Particles ◽  
Rate Equations ◽  
Broad Resonance ◽  
Narrow Resonance ◽  
Resonant Reaction ◽  
Stellar Temperatures ◽  
Definition Of ◽  
Resonance Equation

The well-known astrophysical resonant-reaction-rate (RRR) equations for an isolated narrow resonance induced by the charged particles have been reexamined. The validity of those assumptions used in deriving the classical analytic equations has been checked, and found that these analytic equations only hold for certain circumstances. It shows the customary definition of "narrow" is inappropriate or ambiguous in some sense, and it awakes us not to use those analytic equations without caution. As a suggestion, it is better to use the broad-resonance equation to calculate the RRR numerically even for a narrow resonance of a few keV width. The present conclusion may influence some work in which the classical narrow-resonant equations were used for calculating the RRRs, especially at low stellar temperatures for those previously defined "narrow" resonances.

CFD Modelling of Biomass Gasification in Fluidized-Bed Reactor Using the Eulerian-Eulerian Approach

2014 ◽  
Vol 592-594 ◽  
pp. 1903-1908 ◽  
Author(s):  
Issac Thankachan ◽  
S. Rupesh ◽  
C. Muraleedharan
Keyword(s):  
Reaction Rate ◽  
Biomass Gasification ◽  
Reaction Rates ◽  
Volatile Matter ◽  
Heterogeneous Reactions ◽  
Diffusion Reaction ◽  
Fluidised Bed ◽  
Cfd Modelling ◽  
Euler Model ◽  
Fluidised Bed Reactor

A comprehensive two dimensional numerical model has been developed to simulate the biomass gasification in a fluidised bed reactor. Gas-solid flows as well as the chemical reactions are considered. Euler-Euler model is adopted to describe the multiphase flow regime inside the reactor. The standard k-є model is used to model the turbulence for each phase. The particle motion inside the reactor is modelled using various drag laws derived from Kinetic Theory of Granular Flow. Biomass fuel after pyrolysis is fed as char and volatile matter. The reaction rates of homogeneous reactions and heterogeneous reactions are determined by Eddy dissipation reaction rate and Arrhenius-Diffusion reaction rate, respectively. Gas velocities, flow patterns, composition of gas product and distribution of reaction rates are obtained. Results are compared with experimental data and found to be in agreement.

Ionisationsmessung hinter Stoßwellen in Argon mittels Mikrowellen und einer gepulsten Langmuir-Sonde / Ionization Measurements behind Shocks in Argon with Microwaves and a Pulsed Langmuir Probe

1972 ◽  
Vol 27 (12) ◽  
pp. 1717-1730
Author(s):  
K Schneider ◽  
H Grönig
Keyword(s):  
Plasma Density ◽  
Langmuir Probe ◽  
Reaction Rate ◽  
Collision Frequency ◽  
Reaction Rates ◽  
Electron Collision ◽  
Rate Equations ◽  
Excitation Process ◽  
Density Profiles ◽  
Electron Collision Frequency

The ionization of shock heated argon was measured by means of the attenuation and phase shift of transmitted microwaves of 2.5 and 8 mm at shock Mach numbers 7.5 ≦ Ms ≦ 11.8 and initial pressures 3 ≦ p1/Torr ≦ 20. Taking into account the boundary layer at the shock tube wall it is possible to evaluate the plasma density and electron collision frequency from specially prepared attenuation-phase angle-diagrams. A pulsed Langmuir probe has been tested regarding its feasibility to measure the plasma density and the electron temperature. The reaction rate equations of Jahn and Harwell including the ionization of impurities have been solved in order to interpret the plasma density profiles. The theoretically required reaction rates for the ionization of argon by an excitation process, k* and k1+, and for ionization by collisions between electrons and argon atoms, k3+, have been experimentally determined.

Optimization of Chemical Reaction Processes in Microreactors Using Reaction Rate Analyses

2011 ◽  
Author(s):  
Yukako Asano ◽  
Shigenori Togashi ◽  
Yoshishige Endo
Keyword(s):  
Reaction Time ◽  
Quantum Chemical Calculations ◽  
Solvent Effects ◽  
Quantum Chemical ◽  
Reaction Rate ◽  
Side Reaction ◽  
Reaction Rates ◽  
Sandmeyer Reaction ◽  
Diffusion Controlled ◽  
Bromination Reaction

We applied microreactors to the three following reactions: a consecutive bromination reaction, the two-step Sandmeyer reaction, and an acetylation reaction including solvent effects. We obtained the reaction rate constants from few experimental data or quantum chemical calculations and optimized the reaction conditions such as the reaction times and temperature. We then experimentally validated them by microreactors. A consecutive bromination reaction, where the objective reaction was followed by the side reaction, was one of the processes. The reaction temperature played an important role in the effects of a microreactor. The yield of the objective product was improved by about 40% using a microreactor. The two-step Sandmeyer reaction was also applied, where the 1st-step reaction was followed by the 2nd-step reaction to produce the objective product. The 1st-step reaction had the diffusion-controlled process, while the 2nd-step reaction had the reaction-controlled one. The yield of the objective product was improved when microreactors were used and the reaction time for the 2nd-step reaction was set appropriately. Moreover, an acetylation reaction including solvent effects on reaction rates was considered and the solvent effects could be predicted from quantum chemical calculations. The calculation suggested that acetic acid with the larger electron-accepting property gave more stability to the species formed in the transition state. The reaction time was shortened using a microreactor, when the reaction process was changed from reaction-controlled to diffusion-controlled by changing the solvent used.

THE EFFECT OF REACTANTS' INITIAL TEMPERATURES ON THE RATE CONSTANT AND CONVERSION OF SAPONIFICATION REACTION TAKING PLACE IN A NON-ISOTHERMAL AND NON-ADIABATIC BATCH REACTOR

2020 ◽  
Vol 3 (2) ◽  
pp. 25-33
Author(s):  
Nader Kamal Nasar ◽  
Adli Omar Alznati ◽  
Abdulozez Arzoga
Keyword(s):  
Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Reaction Rates ◽  
Reaction Rate Constant ◽  
Time Intervals ◽  
Isolation System ◽  
Reaction Conversion ◽  
Temperature Rate ◽  
Electrical Conductivity Data

This experimental research studied the saponification reaction of ethyl acetate with sodium hydroxide, which was carried out in a well-agitated non-isothermal and non-adiabatic batch reactor. As no isolation system was provided in this experiment, this study investigated other routes for boosting the reactants conversion. Subsequently, the effect of initial feed temperatures on the reaction rate constant and reaction conversion was assessed. For this purposes, the reaction rates of equimolar reactants were measured when they were heated from 20°C (ambient temperature) to 30°C, 40°C and 50°C. The decrease in the reactants concentrations throughout the reaction durationwas determined at equal time intervals by recording the electrical conductivity data of the reaction mixture. The results were represented graphically for time-conversion, temperature-conversion and temperature-rate constants profiles. They had shown that the reaction rate constant increased with rising of the initial feed temperatures. Even though, the conversion was boosted when the reactants were initially heated above 20°C, no significant change in conversion was achieved between 30, 40, and 50°C. The resulted value of activation energy was about 50 % less than the most accurate published values.

Location-thinking, value-thinking, and graphical forms: combining analytical frameworks to analyze inferences made by students when interpreting the points and trends on a reaction coordinate diagram

2021 ◽  
Author(s):  
Alexander P. Parobek ◽  
Patrick M. Chaffin ◽  
Marcy H. Towns
Keyword(s):  
Reaction Rate ◽  
Research Study ◽  
Reaction Rates ◽  
Reaction Coordinate ◽  
Structured Interviews ◽  
Chemistry Students ◽  
Qualitative Research Study ◽  
The Impact ◽  
Analytical Frameworks ◽  
Chemical Representations

Reaction coordinate diagrams (RCDs) are chemical representations widely employed to visualize the thermodynamic and kinetic parameters associated with reactions. Previous research has demonstrated a host of misconceptions students adopt when interpreting the perceived information encoded in RCDs. This qualitative research study explores how general chemistry students interpret points and trends on a RCD and how these interpretations impact their inferences regarding the rate of a chemical reaction. Sixteen students participated in semi-structured interviews in which participants were asked to interpret the points and trends along provided RCDs and to compare relative reaction rates between RCDs. Findings derived from this study demonstrate the diversity of graphical reasoning adopted by students, the impact of students’ interpretations of the x-axis of a RCD on the graphical reasoning employed, and the influence of these ideas on inferences made about reaction rate. Informed by analytical frameworks grounded in the resources framework and the actor-oriented model of transfer, implications for instruction are provided with suggestions for how RCDs may be presented to assist students in recognizing the critical information encoded in these diagrams.

Sign in / Sign up

Export Citation Format

Share Document