Flow reactors concentrations

Equation (100) applies also to a continuous-flow reactor in which the contents experience no back-mixing (equiveilent to plug flow) time has been eliminated from the expressions. When complete back-mixing is achieved in a continuous-flow reactor, concentration gradients are absent and we have... 

Fig. 1.25. Reaction in series—batch or tubular plug-flow reactor. Concentration Cr of intermediate product P for consecutive first order reactions, A -> P -> Q...

The parameters for PFRs include space time, concentration, volumetric flow rate, and volume. This reactor follows an integral reaction expression identical to the batch reactor except that space time has been substituted for reaction time. In the plug flow reactor, concentration can be envisioned as having a profile down the reactor. Conversion and concentration can be directly related to the reactor length, which in turn corresponds to reactor volume. 

A chaotic state of the Belousov-Zhabotinskii reaction may be generated in a flow reactor. Concentrations of the reagents were found to vary randomly for the following reagent concentrations in the influent streams at 39.6°C, see Table 6.4. The changes in Ce(IV) concentration occurring during... 

It will be clear from the above that the space-velocity (equation (2.85)) and the space-time yield (equations (2.105) and (2.111)) are dependent upon the degree of conversion and upon the initial (batch reactor) or inlet (plug flow reactor) concentrations. In order to compare the performance of reactors involving different or values, it is therefore useful to define normalized s and... 

Multiple reactions in parallel producing byproducts. Consider again the system of parallel reactions from Eqs. (2.16) and (2.17). A batch or plug-flow reactor maintains higher average concentrations of feed (Cfeed) than a continuous well-mixed reactor, in which the incoming feed is instantly diluted by the PRODUCT and... 

Another possibility to improve selectivity is to reduce the concentration of monoethanolamine in the reactor by using more than one reactor with intermediate separation of the monoethanolamine. Considering the boiling points of the components given in Table 2.3, then separation by distillation is apparently possible. Unfortunately, repeated distillation operations are likely to be very expensive. Also, there is a market to sell both di- and triethanolamine, even though their value is lower than that of monoethanolamine. Thus, in this case, repeated reaction and separation are probably not justified, and the choice is a single plug-flow reactor. 

Plug-flow reactors have a decreasing concentration gradient from inlet to outlet, which means that toxic compounds in the feed remain undiluted during their passage along the reactor, and this may inhibit or kill many of the microorganisms within the... 

A useful classification of lands of reaclors is in terms of their concentration distributions. The concentration profiles of certain limiting cases are illustrated in Fig. 7-3 namely, of batch reactors, continuously stirred tanks, and tubular flow reactors. Basic types of flow reactors are illustrated in Fig. 7-4. Many others, employing granular catalysts and for multiphase reactions, are illustratea throughout Sec. 23. The present material deals with the sizes, performances and heat effects of these ideal types. They afford standards of comparison. 

In another land of ideal flow reactor, all portions of the feed stream have the same residence time that is, there is no mixing in the axial direction but complete mixing radially. It is called a.plugflow reactor (PFR), or a tubular flow reactor (TFR), because this flow pattern is characteristic of tubes and pipes. As the reaction proceeds, the concentration falls off with distance. 

Example 5 Application of Effectiveness For a second-order reaction in a plug flow reactor the Thiele modulus is ( ) = SVQ, and inlet concentration is C50 = 1.0. The equation will he integrated for 80 percent conversion with Simpsons rule. Values of T) are... 

Plug Flow Reactor (PFR) A plug flow reactor is a tubular reactor where the feed is continuously introduced at one end and the products continuously removed from the other end. The concentration/temperature profile in the reactor varies with position. 

In a catalytic reactor, concentrations and temperature change along the flow path of the reactants, and in some cases also normal to the flow. The sum of all these changes over the catalyst-filled volume in time will give the production of the reactor. There are several methods to account for all these changes, illustrated on Figure 8.1.1. 

Both kinetic and equilibrium experimental methods are used to characterize and compare adsorption of aqueous pollutants in active carbons. In the simplest kinetic method, the uptake of a pollutant from a static, isothermal solution is measured as a function of time. This approach may also yield equilibrium adsorption data, i.e., amounts adsorbed for different solution concentrations in the limit t —> qo. A more practical kinetic method is a continuous flow reactor, as illustrated in Fig. 5. 

Fig. 6. Breakthrough curves for aqueous acetone (10 mg 1" in feed) flowing through exnutshell granular active carbon, GAC, and PAN-based active carbon fibers, ACF, in a continuous flow reactor (see Fig. 5) at 10 ml min" and 293 K [64]. C/Cq is the outlet concentration relative to the feed concentration. Reprinted from Ind. Eng. Chem. Res., Volume 34, Lin, S. H. and Hsu, F. M., Liquid phase adsorption of organic compounds by granular activated carbon and activated carbon fibers, pp. 2110-2116, Copyright 1995, with permission from the American Chemical Society.

After the rates have been determined at a series of reactant concentrations, the differential method of testing rate equations is applied. Smith [3] and Carberry [4] have adequately reviewed the designs of heterogeneous catalytic reactors. The following examples review design problems in a plug flow reactor with a homogeneous phase. 

The inlet concentration of component A at the entrance of the plug flow reactor is... 

Glasser, D., Hildebrandt, D., and Crowe, C. (1987). A geometric approach to steady flow reactors The attainable region and optimization in concentration space. Ind. Eng. Chem. Res., 26, 1803-1810. 

There are three idealized flow reactors fed-batch or semibatch, continuously stirred tank, and the plug flow tubular. Each of these is pictured in Figure 1. The fed-batch and continuously stirred reactors are both taken as being well mixed. This means that there is no spatial dependence in the concentration variables for each of the components. At any point within the reactor, each component has the same concentration as it does anywhere else. The consequence... 

In contrast to the first two reactors, concentrations within the tubular flow reactor are... 

The performance data for plug versus mix reactor were obtained. The data were collected as the inverse of qx vs inverse of substrate concentration. Table E.1.1 shows the data based on obtained kinetic data. From the data plotted in Figure E.1.1, we can minimise the volume of the chemostat. A CSTR works better than a plug flow reactor for the production of biomass. Maximum qx is obtained with a substrate concentration in the leaving stream of 12g m 3. 

In Fig. 28, the abscissa kt is the product of the reaction rate constant and the reactor residence time, which is proportional to the reciprocal of the space velocity. The parameter k co is the product of the CO inhibition parameter and inlet concentration. Since k is approximately 5 at 600°F these three curves represent c = 1, 2, and 4%. The conversion for a first-order kinetics is independent of the inlet concentration, but the conversion for the kinetics of Eq. (48) is highly dependent on inlet concentration. As the space velocity increases, kt decreases in a reciprocal manner and the conversion for a first-order reaction gradually declines. For the kinetics of Eq. (48), the conversion is 100% at low space velocities, and does not vary as the space velocity is increased until a threshold is reached with precipitous conversion decline. The conversion for the same kinetics in a stirred tank reactor is shown in Fig. 29. For the kinetics of Eq. (48), multiple solutions may be encountered when the inlet concentration is sufficiently high. Given two reactors of the same volume, and given the same kinetics and inlet concentrations, the conversions are compared in Fig. 30. The piston flow reactor has an advantage over the stirred tank... 

The interpretation of the above data on iodination has been questioned by Buss and Taylor217, and by Grovenstein et a/.218,219. The former workers studied the iodination of 2,4-dichlorophenol at about 25 °C using a stirred flow reactor, the advantages of which are that once a steady state has been reached there is no change in the concentration of the reactive species in the reactor with time and the rate of reaction is simply a product of extent of reaction multiplied by the reciprocal ol the contact time hence it is possible to use unbuffered solutions and low iodide ion concentrations. They found general catalysis by the base component of added phosphate buffers and the observed rate coefficients varied with [H+ ] according to... 

Although many industrial reactions are carried out in flow reactors, this procedure is not often used in mechanistic work. Most experiments in the liquid phase that are carried out for that purpose use a constant-volume batch reactor. Thus, we shall not consider the kinetics of reactions in flow reactors, which only complicate the algebraic treatments. Because the reaction volume in solution reactions is very nearly constant, the rate is expressed as the change in the concentration of a reactant or product per unit time. Reaction rates and derived constants are preferably expressed with the second as the unit of time, even when the working unit in the laboratory is an hour or a microsecond. Molarity (mol L-1 or mol dm"3, sometimes abbreviated M) is the preferred unit of concentration. Therefore, the reaction rate, or velocity, symbolized in this book as v, has the units mol L-1 s-1. 

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