Continuous flow stirred tank reactors defined

Another noteworthy achievement is the report of a systematically designed oscillating system, in which two autocatalytic subsystems, arsenite-iodate and chlorite-iodide, were linked in a continuous flow stirred-tank reactor. These two subsystems have been studied independently of each other. The arsenite-iodate subsystem has been thoroughly examined in a CSTR and shown to exhibit bistability under a range of conditions. The oscillations of iodide concentration involved a variation by a factor of more than 10 during each oscillation In an unstirred system, well-defined waves were observed. The chlorite-iodide reaction has also been studied. ... 

The residence time distribution (RTD), also referred to as the distribution of ages, is based on the assumption that each element traveling through the column takes a different route and will therefore have a different residence time. Different methods are developed to determine the RTD in a module or in a reactor [190]. The RTD of a chromatographic column is defined by a function E (Figure 3.20), such that E dt is the fraction of material in the exit stream with an age between t and f - - dt. The -curve lies between the extremes of plug flow and continuously stirred tank reactor. The surface below the curve between f = 0 and t = oo has to be equal to unity E t) dt = 1, because all elements that enter the module must also exit the module. 

The reactor in which chemical reactions lake place is fhe mosl imporlanl piece of equipmenl in each chemical planl. A variety of reactors are used in induslry, bul all of Ihem can be assigned to cerlain basic types or a combination of fhese ideal reactors [53] (1) bafch slirred-lank reactor, (2) continuous slirred-lank reactor, and (3) lubular reactor. The ideal slirred-lank bafch reactor is characterized by complete mixing, while in the ideal tubular reactor, plug flow is assumed. In contrast to the stirred-tank batch reactor with well-defined residence time, the continuous stirred-tank reactor has a very broad residence-time distribution. In... 

Ideal mixing and plug flow. The batch, contlnuous-stirred-tank, and plug-flow reactors are defined by certain idealized assumptions on the fluid flow. The batch and continuous-stirred-tank reactors are assumed to be ideally well mixed, which means that the temperature, pressure and species concentrations are independent of spatial position within the reactor. The plug-flow reactor describes a special type of flow in a itube in which the fluid.is well.mixed in the radial direction and varies... 

We will begin with the case of the batch reactor. In this case the vessel defines the control volume. We will move to systems with flow in and both flow in and out. The former is the case of semibatch operation while the latter will be treated as the continuous stirred tank reactor (CSTR) and the plug flow reactor (PFR). All the chemical kinetics that we will need can be introduced within the context of these four different kinds of reactors. 

For the first criterion, one compares the reactor volumes based on the average residence time for a given extent of reaction or final conversion. The average residence time depends on the reaction kinetics and therefore the reaction rate, which in turn depends on whether the reaction takes place at constant volume or variable volume. In a system at constant volume, one obtains directly a ratio between the volumes, because the average residence time is equal to space time which is defined as the ratio between reactor volume and inlet volumetric flow in the reactor. For the same conversion, the ratio between volumes is proportional. Since the average residence time in a PFR reactor is similar to the reaction time in a batch reactor, we may assume that they have similar behaviors and then we compare only the ideal tubular reactors (PFR — plug flow reactor) to the ideal tank reactors (CSTR—continuous stirred-tank reactor). 

Indeed, PAAc cryogels coupled with a bromate oscillator oscillated between swollen and collapsed states [31]. The reactions of bromate, sulfite, and ferrocyanide ions were conducted in an open continuously stirred tank reactor. Four feed solutions (potassium bromate, sodium sulfite, potassium ferrocyanide, and sulfuric acid) were supplied continuously to the reactor, during which the pH of the reaction solution was monitored as a function of time. The flow rate of the feed solutions is an important parameter in determining the extent of pH oscillations. In Fig. 21, pH versus time plots are shown for four different reduced flow rates k, defined as the flow rate of the feed solutions divided by the reaction volume. It is seen that the pH of the solution oscillates between 6.2-6.9 and 3.2-3.8. The dissociation degree a of a weak electrolyte relates to pH by ... 

Analogy between the above equations and the continuous-stirred tank reactor (CSTR) model can be easily realized, and from this analogy, we can define the modified flow rate with the following physical significance ... 

Fig. 7.2. Schematic diagram of the apparatus. Each solution, one corresponding to one stable stationary state and the other to the other stationary state, is stored in one of two continuous-stirred tank reactors (CSTR) and pumped at a determined and variable rates through the laminar flow reactor (LFR), where they are brought in contact with each other in a sharp well-defined boundary. For the remainder of the definitions see the text. Prom [1]...

The mesh reactor is an alternative continuous-phase microcontactor, where the gas and liquid flow through separate channels separated by a thin membrane. To provide stable operation, the fluid interface is immobilized by well-defined openings obtained with a thin mesh [72]. Interfadal forces help to stabilize the fluid interface within the openings, while fluid layers are thin enough to facilitate mass transfer. The meniscus shape at the interface between the two phases defines the available area for mass transfer and is a function of contact angle, pore geometry, and pressure difference between phases. The open area of the micromesh contactor is about 20-25%, which leads to a gas-liquid interfacial area of 2000 well above the values obtained in traditional stirred tank reactors. This... 

In Chapter 4, we defined the characteristics of two ideal continuous reactors, the ideal plug-flow reactor (PFR) and the ideal continuous stirred-tank reactor (CSTR). We use the term ideal to refer to these reactors because the conditions of mixing and fluid flow in them are defined very precisely. To recap... 

We show an example of shape insensitivity by comparing the behavior of the two commonly used models shown in Figure 8.5 continuous stirred tank reactors, CSTRs, and plug flow reactors, PFRs. Here, the mean residence time of the test system is again defined as... 

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