Pre-reactor

One of the most promising ways of dealing with conversion oscillations is the use of a small-particle latex seed in a feed stream so that particle nucleation does not occur in the CSTRs. Berens (3) used a seed produced in another reactor to achieve stable operation of a continuous PVC reactor. Gonzalez used a continuous tubular pre-reactor to generate the seed for a CSTR producing PMMA latex. 

P 69] No details on the solvent used and concentrations are given in [127], as the process most likely is proprietary (Figure 4.96). Probably the process is solvent-free as obviously one of the reactants has also the function of dissolving the other. The temperature for micro-channel processing was set to 0 °C. The residence time between the pre-reactor and micro mixer was 1 s and between the micro mixer and quench 5 s, totalling 6 s. 

OS 89] [R 19] [P 69] Using a special reactor configuration with an interdigital micro-mixer array with pre-reactor, subsequent tubing and a quench, a yield of 95% at 0 °C was obtained [127]. The industrial semi-batch process had the same yield at -70 °C. 

The catalyst is prepared in a pre-reactor from nickel salts with boron hydrides as the reductant under a pressure of ethene and then ligand is added. 

Figure 5 represents a typical example of the variation of the number of polymer particles with mean residence time 0. The solid line shows the theoretical value predicted by the Nomura and Harada model with e= 1.28x 10 . The dotted line is that predicted by the Gershberg model(or the Nomura and Harada model with Case C for ), where Eq. (23) was used instead of Eq.(16) for Ap. The value of Nt produced at longer mean residence time differs, therefore, by a factor of T(5/3) between the solid and dotted lines in Figure 5. From the comparison between the experimental and theoretical results shown in Figure 5, it is confirmed that the steady state particle number can be maximized by operating the first stage reactor at a certain low value of mean residence time max which is considerably lower than that in the succeeding reactors. This is so-called "pre-reactor principle". It is, therefore, desirable to operate the first reactor at such mean residence time as producing something like a maximum number of polymer particles in order to increase the rate of polymerization in the succeeding reactors. This will result in a decrease in the number of necessary reactors and hence, in the capital cost.

MF = 0.01 g/cc-water because the residence times of both reactors are fixed at 0= 20 minutes. From this theoretical and experimental results, therefore, a plug flow type reactor with a divided monomer feed is recommended for the first stage reactor(pre-reactor), because the volume of the reactor can be decreased by decreasing monomer concentration in a feed stream. Nevertheless, the steady state particle number attained in this reactor can be increased. 

Kurita, R., Hayashi, K., Fan, X., Yamamoto, K., Kato, T., Niwa, O., Microfluidic device integrated with pre-reactor and dual enzyme-modified microelectrodes for monitoring in vivo glucose and lactate. Sensors Actuators B 2002, 87, 296-303. 

Acetylcholineesterase and choline oxidase A glassy C electrode surface was modified with osmium poly (vinyl-pyridine) redox polymer containing horseradish peroxidase (Os-gel-HRP) and then coated with a co-immobilized layer of AChE and ChO. A 22 pL pre-reactor, in which ChO and catalase were immobilized on beads in series, was used to remove choline. The variation in extracellular concentration of ACh released from rat hippocampal tissue culture by electrical stimulation was observed continuously with the online biosensor combined with a microcapillary sampling probe. Measurement of ACh and Ch was carried out by using a split disc C film dual electrode. 

The theory and the experimental data from this study demonstrates that in a train of CSTRs, essentially all of the particles form in the first reactor. Therefore, it is possible to maximize the monomer conversion in the latex leaving the first reactor by keeping the temperature and the residence time at the first reactor as low as possible in order to produce the maximiun number of polymer particles and so increase the rate of polymerization in the succeeding stages. This is the so-called pre-reactor concept. 

This can be explained by the fact that the flow in the CCTVFR became closer to plug flow as the Taylor number was dropped closer to. Therefore, the steady-state particle number and the steady-state monomer conversion could be arbitrarily varied by simply varying the rotational speed of the inner cylinder. Moreover, no oscillations were observed, and the rotational speed of the inner cylinder could be kept low, so that the possibility of shear-induced coagulation could be decreased. Therefore, a CCTVFR with these characteristics is considered to be highly suitable as a pre-reactor for a continuous emulsion polymerization process. In the case of the continuous emulsion polymerization of VAc carried out with the same CCTVFR, however, the situation was quite different [365]. Oscillations in monomer conversion were observed, and almost no appreciable increase in steady-state monomer conversion occurred even when the rotational speed of the inner cylinder was decreased to a value close to. Why the kinetic behavior with VAc is so different to that with St cannot be explained at present. 

When a monomer split-feed operation based on the experimental result shown in Fig. 32 was applied, for example, to a continuous tubular pre-reactor with some backmixing, the number of polymer particles increased by about 30% at Mpi=0.02 g/cm -water, compared to the number produced in a batch reactor, as shown in Fig. 33. 

The monomer split-feed operation was also shown to work in a continuous stirred-tank pre-reactor. When certain conditions are fulfilled, the split-feeds... 

Except for the reactor zones, autoclave and tubular processes are very similar (3, 4). Peripherals in both cases are designed pre-reactor to ramp pressures and temperatures to very high levels and post-reactor to reduce temperatures and lower pressures to near ambient conditions to enable product isolation. Simplified process flow diagrams for the autoclave and tubular processes are shown in Figures 7.1 and 7.2, respectively. 

A further process for which reactive distillation is commonly used in industrial practice is the synthesis of methyl-tert-butyl ether (MTBE) which is an additive for gasoline. MTBE is produced by etherification ofisobutene with methanol. The process based on reactive distillation leads to conversions of 99%. Isobutene and methanol are fed into the pre-reactor where the equilibrium conversion is obtained. The stream leaving the pre-reactor is fed into the reactive distillation column where MTBE is obtained as the bottom product. 

Multiple CSTRs with a pre-reactor such as a small CSTR, a single-pass tube or a spiral-flow cylinder ... 

Comparing the performance of the three different RD processes considered, one can conclude that a non-RD section on top of reactive total reboiler seems to be the best configuration for both productivity and reliability of design. The minimum reflux ratio of this configuration can be estimated from (5.17) and (5.15). This R,ni value can be significantly reduced by installation of a pre-reactor 1). A fully RD column often suffers from splitting of the product in the upper column section owing to backward reaction. 

Figure 5.6. Dependence of relative difference of inclusion volume fraction of TiCU-Al(i-C4H9)3 catalyst particles on the axis of tubular turbulent pre-reactor of divergent-convergent design and its peripheral part on particles diameter d2 and linear rate of reaction mixture...

In this case catalyst is introduced via nipple 1 by inside canal 2 of pre-reactor (Fig. 6.4) and solvent via nipple 3. The flow after passing via turbulization section 4 equalizes catalyst concentration over flow volume and introduces into 5. By inside canal the flow comes to the divergent-convergent section 6 where its turbulization occurs and then to the nozzle 7, where flow additionally acquires non-stable hydrodynamic current. At output of nozzle the flow reaches Veber s criterion 0,5 and as a result of interaction with gas medium begins to break but not earlier than at 50 mm from nozzle head. 

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