Stirred continuous flow

The previous chapters have discussed the behaviour of non-linear chemical systems in the two most familiar experimental contexts the well-stirred closed vessel and the well-stirred continuous-flow reactor. Now we turn to a number of other situations. First we introduce the plug-flow reactor, which has strong analogies with the classic closed vessel and which will also lead on to our investigation of chemical wave propagation in chapter 11. Then we relax the stirring condition. This allows diffusive processes to become important and to interact with the chemistry. In this chapter, we examine one form of the reaction-diffusion cell, whose behaviour can be readily understood by comparison with the responses observed in the CSTR. 

Mahan and Solo studied the reaction in a stirred continuous flow reactor, in which O atoms produced by a microwave discharge through pure O2 or 02-inert gas mixtures reacted with CO. O atom concentrations were measured by titration with NO2. They found that radiation accompanied reaction 0.29 % of the time for the process at 298 °K, and concluded that the reaction was second-order. They proposed the mechanism... 

In an attempt to explain the horatian oscillations due to the B-Z reaction in a well-stirred continuous flow reactor reported by R. A. Schmitz et al., Iwamoto and Seno (1981) proposed a reaction model and a two dimensional mathematical model. 

H.J. Kim and A. Beskok, Numerical Modeling of Chaotic Mixing in Electroosmotically Stirred Continuous Flow Mixers, ASME J. Heat Transfer 131(9) 092403 (2009). 

The final experimental reports were by Freter al. (21, 22, 23), who studied growth of Vibrio cholerae in mouse and rabbit large intestine (see Figure 5 and Table 3. Here three strains were compared the chemotactic wild type, an immotile mutant strain, and a nonchemotactic but randomly motile mutant strain. In well-stirred continuous flow culture, all three strains grew in proportion. In the intestinal loops, the nonchemotactic strain was rapidly displaced by the chemotactic wild type. Most interestingly, in another experiment the randomly motile strain was also rapidly displaced by the immotile strain. Apparently, in this situation at least, motility without chemo-taxis was a liability for the cells. 

The mass balance. A perfectly stirred continuous flow reactor inside the loop of a recirculating system, as described in section 6.6.1, s was used. As is shown in the section on calculating procedure for the reaction rate, a rigorous mass balance for this system gives... 

At this point in our discussion of well-stirred continuous-flow bioreactors it is helpful to consider a straightforward extension of our analysis to encompass the possibility of using more than a single feed stream. Illustration 13.5 considers a situation in which a supplementary feed stream is suppUed to the second CSTBR. This illustration lets us address situations in which it is desirable to include additional components (e.g., inducers) in the growth medium to enhance the selectivity of the cascade for the production of desired product species. Induction enhances the production of secondary metabolites becanse of the presence of particular chemical species in the growth medium. 

In these experiments we used a well-stirred continuous-flow reactor in which the test specimen was mounted. A sapphire window on the top of the reactor permitted the passage of infrared radiation to the thermal imager. The contents were mechanically stirred with an impeller whose shaft entered the reactor through a gas-tight seal. Hydrogen and oxygen entered the reactor at a rate controlled by electronic mass-flow controllers, and the exit stream was continuously analyzed for product concentration (water vapor in this case) which was recorded on a strip chart. 

In bofh CW and pulsed lasers fhe dye solution musf be kepf moving to prevenf overheating and decomposition. In a pulsed laser fhe dye is continuously flowed fhrough fhe confaining cell. Alternatively, magnetic stirring may be adequate for low repetition rates and relatively low power. In a CW laser fhe dye solution is usually in fhe form of a jef flowing rapidly across fhe laser cavify. 

Specific reactor characteristics depend on the particular use of the reactor as a laboratory, pilot plant, or industrial unit. AH reactors have in common selected characteristics of four basic reactor types the weH-stirred batch reactor, the semibatch reactor, the continuous-flow stirred-tank reactor, and the tubular reactor (Fig. 1). A reactor may be represented by or modeled after one or a combination of these. SuitabHity of a model depends on the extent to which the impacts of the reactions, and thermal and transport processes, are predicted for conditions outside of the database used in developing the model (1-4). 

Batch reactors often are used to develop continuous processes because of their suitabiUty and convenient use in laboratory experimentation. Industrial practice generally favors processing continuously rather than in single batches, because overall investment and operating costs usually are less. Data obtained in batch reactors, except for very rapid reactions, can be well defined and used to predict performance of larger scale, continuous-flow reactors. Almost all batch reactors are well stirred thus, ideally, compositions are uniform throughout and residence times of all contained reactants are constant. 

Continuous-Flow Stirred-Tank Reactor. In a continuous-flow stirred-tank reactor (CSTR), reactants and products are continuously added and withdrawn. In practice, mechanical or hydrauHc agitation is required to achieve uniform composition and temperature, a choice strongly influenced by process considerations, ie, multiple specialty product requirements and mechanical seal pressure limitations. The CSTR is the idealized opposite of the weU-stirred batch and tubular plug-flow reactors. Analysis of selected combinations of these reactor types can be useful in quantitatively evaluating more complex gas-, Hquid-, and soHd-flow behaviors. 

Continuous-flow stirred-tank reactors ia series are simpler and easier to design for isothermal operation than are tubular reactors. Reactions with narrow operating temperature ranges or those requiring close control of reactant concentrations for optimum selectivity benefit from series arrangements. 

Continuous-Flow Stirred-Tank Reactors. The synthesis of j )-tolualdehyde from toluene and carbon monoxide has been carried out using CSTR equipment (81). -Tolualdehyde (PTAL) is an intermediate in the manufacture of terephthabc acid. Hydrogen fluoride—boron trifluoride catalyzes the carbonylation of toluene to PTAL. In the industrial process, separate stirred tanks are used for each process step. Toluene and recycle HF and BF ... 

Experimental data taken from the chlorination of toluene in a continuous stirred tank flow reactor at 111°C and irradiated with light of 500 nm wavelength yield a product distribution shown in Table 1 (1). 

Continuous-flow Stirred Tank Reactor (CSTR) A reaction vessel in which the feed is continuously added, and the products continuously removed. The vessel (tank) is continuously stirred to maintain a uniform concentration within the vessel. 

Various experimental methods to evaluate the kinetics of flow processes existed even in the last centuty. They developed gradually with the expansion of the petrochemical industry. In the 1940s, conversion versus residence time measurement in tubular reactors was the basic tool for rate evaluations. In the 1950s, differential reactor experiments became popular. Only in the 1960s did the use of Continuous-flow Stirred Tank Reactors (CSTRs) start to spread for kinetic studies. A large variety of CSTRs was used to study heterogeneous (contact) catalytic reactions. These included spinning basket CSTRs as well as many kinds of fixed bed reactors with external or internal recycle pumps (Jankowski 1978, Berty 1984.)... 

CONTINUOUS FLOW ISOTHERMAL PERFECTLY STIRRED TANK REACTOR... 

A continuous flow stirred tank reactor (CFSTR) differs from the batch reactor in that the feed mixture continuously enters and the outlet mixture is continuously withdrawn. There is intense mixing in the reactor to destroy any concentration and temperature differences. Heat transfer must be extremely efficient to keep the temperature of the reaction mixture equal to the temperature of the heat transfer medium. The CFSTR can either be used alone or as part of a series of battery CFSTRs as shown in Figure 4-5. If several vessels are used in series, the net effect is partial backmixing. 

CONTINUOUS FLOW STIRRED TANK REACTOR (CFSTR) ... 

Fig ure 5-23. Battery of continuous flow stirred tank reactors. 

Fig ure 6-22. Temperature versus conversion for a first order irreversible reaction in an adiabatic continuous flow stirred tank reactor. 

CESTR Continuous flow stirred tank reactor... 

The name continuous flow-stirred tank reactor is nicely descriptive of a type of reactor that frequently for both production and fundamental kinetic studies. Unfortunately, this name, abbreviated as CSTR, misses the essence of the idealization completely. The ideality arises from the assumption in the analysis that the reactor is perfectly mixed, and that it is homogeneous. A better name for this model might be continuous perfectly mixed reactor (CPMR). 

The use of acidic chloroaluminates as alternative liquid acid catalysts for the allcy-lation of light olefins with isobutane, for the production of high octane number gasoline blending components, is also a challenge. This reaction has been performed in a continuous flow pilot plant operation at IFP [44] in a reactor vessel similar to that used for dimerization. The feed, a mixture of olefin and isobutane, is pumped continuously into the well stirred reactor containing the ionic liquid catalyst. In the case of ethene, which is less reactive than butene, [pyridinium]Cl/AlCl3 (1 2 molar ratio) ionic liquid proved to be the best candidate (Table 5.3-4). 

In the continuous hydrovinylation experiments, the ionic catalyst solution was placed in the reactor R, where it was in intimate contact with the continuous reaction phase entering from the bottom (no stirring was used in these experiments). The reaction phase was made up in the mixer from a pulsed flow of ethylene and a continuous flow of styrene and compressed CO2. 

Frequently, stirred tanks are used with a continuous flow of material in on one side of the tank and with a continuous outflow from the other. A particular application is the use of the tank as a continuous stirred-tank reactor (CSTR). Inevitably, there will be a vety wide range of residence times for elements of fluid in the tank. Even if the mixing is so rapid that the contents of the tank are always virtually uniform in composition, some elements of fluid will almost immediately flow to the outlet point and others will continue circulating in the tank for a very long period before leaving. The mean residence time of fluid in the tank is given by ... 

An Experimental Study Using Feed Perturbations for a Free-Radically Initiated Homogeneous Polymerization in a Continuous-Flow Stirred-Tank Reactor... 

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