Homogeneous continuous stirred tank reactor

To clarify the above points we consider a simple homogeneous continuous stirred tank reactor (CSTR), in which consecutive exothermic reactions... 

HCSTR = homogeneous continuous stirred tank reactor. 

From Gerrens [1976]. BR = batch reactor PER = plug flow reactor HCSTR = homogeneous continuous stirred tank reactor = perfectly mixed flow reactor of this chapter SCSTR = segregated continuous stirred tank reactor. 

The MWD resulting from semi-batch operations of a stirred tank reactor with monomer feed under various conditions is treated in Refs. 77-82. In a homogeneous continuous stirred tank reactor (HCSTR), the steady-state concentrations of monomer and initiator can be derived from the monomer and initiator mass bal-... 

Automatic Continuous Online Monitoring of Polymerization Reactions was adapted to monitoring a homogeneous continuous stirred tank reactor (HCSTR) to verify the quantitative predictions concerning f, M, and r, as a function of the flow and kinetic parameters, to determine the kinetic parameters themselves, to ascertain the ideality of mixing in the reactor, to assess the effects of feed and reactor fluctuations, and to approximate a fully continuous tube-type reactor [38],... 

Ideal CSTR (continuous stirred tank reactor) behavior is approached when the mean residence time is 5-10 times the length of time needed to achieve homogeneity, which is accomplished with 500-2000 revolutions of a properly designed stirrer. 

The ideal continuous stirred tank reactor is the easiest type of continuous flow reactor to analyze in design calculations because the temperature and composition of the reactor contents are homogeneous throughout the reactor volume. Consequently, material and energy balances can be written over the entire reactor and the outlet composition and temperature can be taken as representative of the reactor contents. In general the temperatures of the feed and effluent streams will not be equal, and it will be necessary to use both material and energy balances and the temperature-dependent form of the reaction rate expression to determine the conditions at which the reactor operates. 

An excellent production figure for (R)-mandelonitrile (2400 g/1 per day) was achieved by Kragl et al. [105] using a continuously stirred tank reactor in which an ultrafiltration membrane enables continuous homogenous catalysis to occur from an enzyme (PaHnl) which is retained within the reaction vessel. In order to quench the reaction the outlet of this vessel was fed into a vessel containing a mixture of chloroform and hydrochloric acid, which allowed for accurate product analysis. 

In the continuous stirred tank reactor (CSTR) instant mixing to achieve a homogeneous reaction mixture is assumed so that the composition throughout the reactor is uniform. During the reaction, monomer is fed into the system at the same rate as polymer is withdrawn. The heat problem is somewhat diminished because of the constant removal of heated products and the addition of nonheated reactants. 

Chapter 1 reviews the concepts necessary for treating the problems associated with the design of industrial reactions. These include the essentials of kinetics, thermodynamics, and basic mass, heat and momentum transfer. Ideal reactor types are treated in Chapter 2 and the most important of these are the batch reactor, the tubular reactor and the continuous stirred tank. Reactor stability is considered. Chapter 3 describes the effect of complex homogeneous kinetics on reactor performance. The special case of gas—solid reactions is discussed in Chapter 4 and Chapter 5 deals with other heterogeneous systems namely those involving gas—liquid, liquid—solid and liquid—liquid interfaces. Finally, Chapter 6 considers how real reactors may differ from the ideal reactors considered in earlier chapters. 

The mean residence time for a continuous stirred-tank reactor of volume Vc may be defined as Vc/v in just the same way as for a tubular reactor. However, in a homogeneous reaction mixture, it is not possible to identify particular elements of fluid as having any particular residence time, because there is complete mixing on a molecular scale. If the feed consists of a suspension of particles, it may be shown that, although there is a distribution of residence times among the individual particles, the mean residence time does correspond to Vc v if the system is ideally mixed. 

The classical problem of multiple solutions and undamped oscillations occurring in a continuous stirred-tank reactor, dealt with in the papers by Aris and Amundson (39), involved a single homogeneous exothermic reaction. Their theoretical analysis was extended in a number of subsequent theoretical papers (40, 41, 42). The present paragraph does not intend to report the theoretical work on multiplicity and oscillatory activity developed from analysis of governing equations, for a detailed review the reader is referred to the excellent text by Schmitz (3). To understand the problem of oscillations and multiplicity in a continuous stirred-tank reactor the necessary and sufficient conditions for existence of these phenomena will be presented. For a detailed development of these conditions the papers by Aris and Amundson (39) and others (40) should be consulted. 

Piret, E. L., and Trambouze, P. J. 1959. Continuous stirred tank reactors Designs for maximum conversions of raw material to desired product. Homogeneous reactions. A.I.Ch.E. Journal 5, 384-390. 

One type of reactor which can be useful for kinetic measurements is the continuous stirred tank reactor (CSTR). The kinetic model is identical with that for the recirculation reactor and the designs are based on the reactors used for homogeneous reactions. Carberry et have described a CSTR which... 

The reaction takes place in a continuously stirred tank reactor, thus reaching the activity and selectivity found in homogeneous reactions. The liquid is contacted with a nanofiltration (NF)-membrane that allows products to permeate but rejects the dissolved catalyst. This set-up is made possible by the development of solvent resistant NF-membranes having a molecular weight cut-off (MWCO) in the range 200-700 Da and working conditions below 40 °C and 35 bar. 

Example 4-8 An ideal continuous stirred-tank reactor is used for the homogeneous polymerization of monomer M. The volumetric flow rate is O, the volume of the reactor is V, and the density of the reaction solution is invariant with composition. The concentration of monomer in the feed is [M]o. The polymer product is produced by an initiation step and a consecutive series of propagation reactions. The reaction mechanism and rate equations may be described as follows, where is the activated monomer and P2, . . , P are polymer molecules containing n monomer units ... 

Although the oscillatory behavior of continuously stirred tank reactor had been discussed in chemical engineering long before the current studies on homogeneous chemical systems, [see G G], it is recently that the role of stirring and of a CSTR environment in reactions such as the B-Z and others has been recognized and used extensively in experiments. 

Compared to batch processes, continuous processes often show a higher space-time yield. Reaction conditions may be kept within certain limits more easily. For easier scale-up of some enzyme-catalyzed reactions, the Enzyme Membrane Reactor (EMR) has been developed. The principle is shown in Fig. 7-26 A. The difference in size between a biocatalyst and the reactants enables continuous homogeneous catalysis to be achieved while retaining the catalyst in the vessel. For this purpose, commercially available ultrafiltration membranes are used. When continuously operated, the EMR behaves as a continuous stirred tank reactor (CSTR) with complete backmixing. For large-scale membrane reactors, hollow-fiber membranes or stacked flat membranes are used 129. To prevent concentration polarization on the membrane, the reaction mixture is circulated along the membrane surface by a low-shear recirculation pump (Fig. 7-26 B). 

Examples of continuous stirred tank reactors are presented in Figure 1.14. Such a system can be applied for both homogeneous and heterogeneous systems. Figure 1.19 illustrates the differences between batch and CSTR reactors. 

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