Chemical kinetics is the study of chemical reaction rates and reaction mechanisms. The study of chemical reaction engineering CRE combines the study of chemical kinetics with the reactors in which the reactions occur.
Chemical kinetics and reactor design are at the heart of producing almost all industrial chemicals, such as the manufacture of phthalic anhydride shown in Figure It is primarily a knowledge of chemical kinetics and reactor design that distinguishes the chemical engineer from other engineers.
The selection of a reaction system that operates in the safest and most efficient manner can be the key to the economic success or failure of a chemical plant. For example, if a reaction system produces a large amount of undesirable product, subsequent purification and separation of the desired product could make the entire process economically unfeasible.
Figure Manufacture of phthalic anhydride. The Chemical Reaction Engineering CRE principles learned here can also be applied in many areas, such as waste treatment, microelectronics, nano-particles, and living systems, in addition to the more traditional areas of the manufacture of chemicals and pharmaceuticals.
Some of the examples that illustrate the wide application of CRE principles in this book are shown in Figure These examples include modeling smog in the L. Also shown are the manufacture of ethylene glycol anti-freezewhere three of the most common types of industrial reactors are used Chapters 5 and 6and the use of wetlands to degrade toxic chemicals Chapter 7 DVD-ROM.
Other examples shown are the solid-liquid kinetics of acid-rock interactions to improve oil recovery Chapter 7 ; pharmacokinetics of cobra bites Chapter 8 Web Module ; free radical scavengers used in the design of motor oils Chapter 9 ; enzyme kinetics Chapter 9 and drug delivery-pharmacokinetics Chapter 9 DVD-ROM ; heat effects, runaway reactions, and plant safety Chapters 11 through 13 ; increasing the octane number of gasoline and the manufacture of computer chips Chapter Figure The wide world of CRE applications.
Overview—Chapter 1. This chapter develops the first building block of chemical reaction engineering, mole balanceswhich will be used continually throughout the text. After completing this chapter the reader will be able to.
Before entering into discussions of the conditions that affect chemical reaction rate mechanisms and reactor design, it is necessary to account for the various chemical species entering and leaving a reaction system. This accounting process is achieved through overall mole balances on individual species in the reacting system.
After defining the rate of reaction, — r Awe show how the general balance equation may be used to develop a preliminary form of the design equations of the most common industrial reactors:. In developing these equations, the assumptions pertaining to the modeling of each type of reactor are delineated.
Finally, a brief summary and series of short review questions are given at the end of the chapter. The rate of reaction tells us how fast a number of moles of one chemical species are being consumed to form another chemical species. The term chemical species refers to any chemical component or element with a given identity. The identity of a chemical species is determined by the kind, number, and configu-ration of that species' atoms.
For example, the species para-xylene is made up of a fixed number of specific atoms in a definite molecular arrangement or configuration. The structure shown illustrates the kind, number, and configuration of atoms on a molecular level.After you enable Flash, refresh this page and the presentation should play.
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Title: Chapter 6 Design for Single Reaction. Description: These are reactions whose progress can be described and followed adequately by For such reactions product distribution is Potpourri of Multiple Reaction Tags: chapter design potpourri reaction single.
Latest Highest Rated. These are reactions whose progress can be described and followed adequately by using one and only one rate expression coupled with the necessary stoichiometric and equilibrium expressions. For such reactions product distribution is fixed hence, the important factor in comparing design is the reactor size. It has the disadvantage of high labor and handling cost, often considerable shutdown time to empty, clean out, and refill, and poorer quality control of the product.
Thus, the same volume of these reactors is needed to do a given job. On a long-term production basis we must correct the size requirement estimate to account for the shutdown time between batches. The order of reaction, conversion, expansion factor are all related to concentration.
Any other way of feeding is less efficient. Density changes will be assumed to be negligible. How to find the best setup to achieve a given conversion? At high enough conversions the plug flow reactor is superior. The optimum recycle ratio is found by differentiating with respect to R and setting to zero 52 No Transcript 53 No Transcript 54 By selecting proper R, to make 55 Reactor combinations 56 Chapter 7 Design for Parallel Reactions In this chapter, we discuss how to optimize the size of a reactor and product distribution with a pre-condition of constant volume.
The two requirements, small size and maximization of desired product, may run counter to each other. In such a situation an economic analysis will yield the best compromise. If a1gta2 or the desired reaction is of higher order than unwanted reaction, high reactant concentration is desirable. As a result, a batch or plug flow reactor would favor formation of product R and would require a minimum reactor size.
But this would also require large mixed flow reactor. If a1a2 or the two reactions are of same order. It is simply a matter of convenience which definition is used. Thus in general, we define as the instantaneous fractional yield of M, based on the disappearance or formation of N.
The maximum possible amount of any and all intermediates is obtained if fluids of different compositions and at different stages of conversion are not allowed to mix. As with reactions in parallel, a rise in reactant concentration of favors the higher-order reaction a lower concentration favors lower-order reaction.
Consider the reversible first-order reactions No Transcript No Transcript 8. Image we have two beakers, one holding A and the other holding B. In case athe performance is a reaction in series In case b and cit looks like From this discussion we propose the general rule Irreversible series-parallel reactions can be analyzed in term of their constituent series reactions and parallel reactions in that optimum contacting for favorable product distribution is the same as for the constituent reaction.
T plot has the general shape shown below No Transcript The size of reactor for a given duty and for a given temperature progression is found as follows 1. Draw the reaction path on the XA vs.Reactive components are pumped together at a mixing junction and flowed down a temperature-controlled pipe or tube. This provides some major advantages such as faster reactions, cleaner products, safer reactions and easy scale-up.
Flow reactors are easily pressurized e. This process is called superheating. Flow reactors enable excellent reaction selectivity. The rapid diffusion mixing avoids the issues found in batch reactors. The high surface area to volume ratio x greater than a batch reactor enables almost instantaneous heating or cooling and therefore ultimate temperature control.
Flow chemistry allows only a small amount of hazardous intermediate to be formed at any instant. The high surface area also allows excellent control of exotherms.
Week 7. Design for Single Reaction
Reaction products exiting a flow reactor can be flowed into a flow aqueous workup system or solid phase scavenger column. From there they can be analyzed either in line e. Flow Chemistry with automation enables the quick variation of reaction conditions on a very small scale e. Parameters such as reaction time, temperature, ratio of reagents, concentration and reagents themselves can all be rapidly varied.
One reaction can follow another, separated by solvent, each cleaning out the previous reaction. Scale-up issues are minimized due to maintaining excellent mixing and heat transfer. Higher flow rates and correspondingly larger reactors can be used to easily produce kilogram quantities. Multi-step procedures such as a rapid low-temperature deprotonation followed instantaneously by the addition of an electrophile high temperature are made easy.
This section provides information about the application of flow chemistry. Please use the navigation to the left to access more specialist flow chemistry information. Here are two examples shown below:. This paper describes reaction conditions for the oxidation of alcohols in continuous flow using a column reactor packed with polymer-supported tetra-N-alkylammonium perruthenate. Author Steven V. Ley, Ian R. Baxendale, Jon Deeley, Charlotte M. Tranmer University of Cambridge. We purchased an Asia flow chemistry reactor in Juneand are reaping the benefits of using flow chemistry techniques.
The pharmaceutical industry has been leading the way in its use of flow chemistry technology for research and development and manufacturing of new drugs, and Gedeon Richter is no exception. Using a Syrris Asia Flow Chemistry system, researchers have been able to create new heterocyclic scaffolds — chemistry that was impossible to them before adopting flow chemistry techniques.Tubular reactors filled with static mixing elements are often used as plug flow reactors for both high and low viscosity chemical reaction systems.
In many cases and for various reasons, a batch tank reaction system may be best for a particular chemical synthesis and operating plant environment and should continue to be used. It is sometimes desired to operate continuously in order to eliminate batch-to-batch variations, produce a consistent product at all times and to have a compact dedicated continuous reactor to free up use of existing batch tank equipment.
There are many equipment types and arrangements used to achieve continuous operations such as with the use of empty pipe reactors, cascades of stirred tanks, extruders, scraped surface reactors, etc.
For this to be achieved, all the material within the reactor must be well mixed and have the same residence time plug flow. When fluid viscosities are water like, empty pipe reactors operating in deep turbulent flow most often work well. With increasing viscosity resulting in laminar flow operating conditions in the pipe reactor, static mixing elements will require to be installed in the pipe to assure good mixing of the reacting materials.
In slow chemical reaction systems, long residence times are required to complete the reaction. In addition, secondary reactants may require to be added after initial reaction and heat may be required to be added or removed. Because slow chemical reaction systems normally require long residence times, tubular reactors will operate in deep laminar flow regardless of fluid viscosity.
The tubular reactors are typically skid mounted in a sloped horizontal back-and-forth configuration Figure 1 or in a vertical up-flow followed by a vertical down-flow configuration.
A tubular reactor is a fundamentally simple continuous reactor where there are no moving parts other than pumps that deliver the reactants. In a typical slow chemical reaction system where long residence times are required, the fluids passing through a tubular reactor are in the laminar flow regime even when the materials are low viscosity water-like fluids. An empty tube is unfortunately not suitable as a chemical tubular reactor in slow chemical reaction systems when the material processed is in the laminar flow regime.
The addition of static mixing elements inside the tubular reactor creates the ideal conditions of radial mixing and near plug flow conditions necessary to perform chemical reactions in the laminar flow regime.
In an empty tube, viscous material in laminar flow will exhibit no radial mixing Figure 5 top where material will exit the pipe in virtually the same position as where it was introduced into the pipe.
Addition of GX mixing elements in the same tube will create a high degree of radial mixing Figure 5 bottom.
In addition to excellent radial mixing, continuous reactors require plug flow conditions. Plug flow conditions means that all the material processed through the reactor must have the same residence time so that the chemicals exiting the reactor have witnessed the same reaction conditions of reactive species contact-time aging-temperature history.
As shown in Figure 6, an empty pipe operating in the laminar flow regime red curve is a poor continuous reactor because the material in the center of the pipe travels at approximately twice the average velocity while material at the wall travels very-very slowly dead-zone aged material.
This results in poor plug flow characteristics as shown in the Step-Response experiment of Figure 7 when processing high viscosity material in laminar flow with little diffusion. The addition of High Performance GX static mixing elements in the same pipe processing viscous materials dramatically improves plug flow characteristics Figure 6 and 7-Green Line where the bulk of the material exits the pipe in 2.
The blue curve shows ideal plug flow. In low viscosity chemical reaction systems, the velocity profile of Figure 6 continues to exist which necessitates the use of static mixer inserts to achieve good plug flow characteristics.
However, a low viscosity environment allows for diffusion of the reacting species where in high viscosity systems diffusion between species is very low to non-existent. This means that in low viscosity chemical reaction systems, plug flow characteristics improve because diffusion occurs between the bulk fluid and wall material and is not exclusively dependent on radial mixing created by the static mixing elements.
This diffusion phenomenon occurring with low viscosity chemical reaction systems allows for the use of Medium Performance Type HT Helical static mixers which are less costly and consume lower pressure drop than the High Performance GX static mixers which is the only design suitable for high viscosity plug flow reactors where diffusion of chemical species is very low.
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Chemical reactor selection and design - PowerPoint PPT Presentation
Figure 1: Typical layout of a skid-mounted small diameter long residence time static mixer plug flow reactor. Figure 2: GX static mixer used in plug flow reactors for viscous materials.Copy embed code:. Automatically changes to Flash or non-Flash embed. WordPress Embed Customize Embed. URL: Copy. Presentation Description No description available. And on of the typical situation the engineer is faced with a host of question: how to select a reasonable design from the many available alternatives.
Design of the reactor is no routine matter. Reactor design uses information, knowledge, and experience from a variety of areas — thermodynamics, chemical kinetics, fluid mechanics, heat transfer, mass transfer, and economics.
Chemical reaction engineering is the synthesis of all these factors with the aim of properly designing a chemical reactor. Design of reactors invariable relies on experimentally determined rates. Gas phase 2. Liquid phase 3. Liquid Solid 1. Small scale production 2. Intermediate or one shot production 3. Pharmaceutical 4. Fermentation 1. High conversion per unit volume for one pass 2. Flexibility of operation-same reactor can produce one product one time and a different product the next 3.
Easy to clean 1. High operating cost 2. Liquid phase 2. Gas-liquid rxns 3. Solid-liquid rxns 1. When agitation is required 2. Series configurations for different concentration streams 1. Continuous operation 2. Good temperature control 3.
Easily adapts to two phase runs 4. Good control 5. Simplicity of construction 6 Low operating labor cost 7.Continuous Stirred Tank Reactor Overview
Lowest conversion per unit volume 2. If the element is small, then spatial variations in r A are negligible, and Flow of A into Element Flow of A out of Element Slide Type of Reactor Characteristics Steady — state flow Arranged as one long reactor or many short reactors in a tube bank ; no radial variation in reaction rate concentration ; concentration changes with length down the reactor Kinds of Phases Present Usage Advantages Disadvantages 1.
Primarily Gas Phase 1. Large Scale 2.After you enable Flash, refresh this page and the presentation should play. Get the plugin now. Toggle navigation. Help Preferences Sign up Log in. To view this presentation, you'll need to allow Flash. Click to allow Flash After you enable Flash, refresh this page and the presentation should play. View by Category Toggle navigation. Products Sold on our sister site CrystalGraphics.
Title: Chemical reactor selection and design. Tags: chemical design reactor selection sintering. Latest Highest Rated. CHE 4th year 2 Introduction Almost all chemical engineering process contains three operations. What does chemical reactor design means?
Batch- uniform composition everywhere in reactor but changes with time 2. Semi batch- in semi-batch one reactant will be added when reaction will proceed 3. Continuous reactor Mixed flow- this is uniformly mixedsame composition everywhere, within the reactor and at exit Plug flow- flow of fluid through reactor with order so that only lateral mixing is possible.
When conversion is small, the reactor performance is only slightly affected by flow type. Density variation during reaction affects design, however it is normally of secondary importance compared to the difference in flow type. Number of mixed flow reactor of equal size in series may be used when we need high conversion and cant perform in a single reactor. From the given graph, for first order reaction, conversion for series of equal size reactor can be find 11 Mixed flow reactor of different size in series From the fig it is clear that for plug flow reactor volume can be find by dashed area and for mixed flow whole area.
When we are have to use mixed flow reactor, then we can use different size mixed flow reactor so, that over all volume would be small To optimized or to find how different size of mixed flow reactor should used we have to maximized lower dashed rectangle.
This optimization gives the slope of diagonal of the rectangle should be equal to slope of curve at intersection of these two reactor. Levenspielhas proved that after overall economic consideration equal size reactors in series are economical. In mixed flow reactor at fixed product concentration for high yield, efficiency of reactor will be very low. For no recycle for low product concentration mixed flow reactor will be preferred and for high conversion plug flow. For optimum efficiency we can use a recycle or back mixing plug flow reactors.
For a particular exit concentration a particular optimum recycle ratio should be used. Fig-2 Fig-2 Fig-3 Fig-4 13 Design for parallel reaction When a reactant gives two product desired, and undesired simultaneously with different rate constant then this is called a parallel reaction. To keep maximum amount of desired product we can take following steps.
Ifa1gta2 or the desired reaction is of higher order then keep reactant concentration high for high product concentration. If a1lta2 than for desired reaction keep reactant concentration low.
For a1a2 change in reactant concentration will not affect the product then, because rate constant k1 and k2 are different at different temperature so, we can keep our temperature such that desired product will be high or use of catalyst would be a option which are selective in nature. In irreversible reaction in series like the mixing of fluid of different composition is the key to formation of intermediate.Which scheme do we choose?
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