Continuous-stirred reactors

Shell Higher Olefins Process (SHOP). In the Shell ethylene oligomerization process (7), a nickel ligand catalyst is dissolved in a solvent such as 1,4-butanediol (Eig. 4). Ethylene is oligomerized on the catalyst to form a-olefins. Because a-olefins have low solubiUty in the solvent, they form a second Hquid phase. Once formed, olefins can have Htfle further reaction because most of them are no longer in contact with the catalyst. Three continuously stirred reactors operate at ca 120°C and ca 14 MPa (140 atm). Reactor conditions and catalyst addition rates allow Shell to vary the carbon distribution. 

Another nickel cataly2ed process is described ia a Tolochimie patent (28). Reaction conditions claimed are 1—2.4 MPa (150—350 psi) at 100°C minimum. The combination continuous stirred reactor and gravity decanter uses density-driven circulation between the two vessels to recirculate the catalyst to the reaction 2one without the use of filters or pumps. Yield and catalyst usage can be controlled by varying the feed rates. 

The manufacture of siHcone polymers via anionic polymerization is widely used in the siHcone industry. The anionic polymerization of cycHc siloxanes can be conducted in a single-batch reactor or in a continuously stirred reactor (94,95). The viscosity of the polymer and type of end groups are easily controUed by the amount of added water or triorganosUyl chain-terminating groups. 

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... 

An ideal plug flow reactor, for example, has no spread in residence time because the fluid flows like a plug through the reactor (Westerterp etal., 1995). For an ideal continuously stirred reactor, however, the RTD function becomes a decaying exponential function with a wide spread of possible residence times for the fluid elements. 

Non-ideal reactors are described by RTD functions between these two extremes and can be approximated by a network of ideal plug flow and continuously stirred reactors. In order to determine the RTD of a non-ideal reactor experimentally, a tracer is introduced into the feed stream. The tracer signal at the output then gives information about the RTD of the reactor. It is thus possible to develop a mathematical model of the system that gives information about flow patterns and mixing. 

A phenomenon that arises particularly with continuous stirred reactors is the occurrence of more than one steady state. This becomes apparent from the heat and material balances. "Heat generation" is made up of the heat of reaction plus any heat transfer, and the "heat removal" is the sensible and latent heat change of the reaction products. In problem P4.10.13, for instance, both the heat generation and the heat removal are plotted against the temperature. The two lines intersect at three points which represent the steady states. A point at which the slope of the heat generation line is... 

The slurry from the ERH sump is pumped to one of two continuously stirred reactors (two for each ERH, four for the plant) to complete the hydrolysis, if necessary. Because the sodium hydroxide dissolves any aluminum present in the munitions, converting it to aluminum hydroxide, the aluminum hydroxide is prevented from clogging downstream components by neutralizing the completely reacted hydrolysate with hydrochloric or sulfuric acid, causing the dissolved aluminum to form a precipitate, which is then filtered (Step 7). The hydrolysate is sent to holding tanks to await secondary treatment in the SCWO reactors. 

Step 11 is treatment by SCWO of the energetics hydrolysate mixed with hydropulped dunnage. Step 12 of the GATS process is treatment of the agent hydrolysate from the continuously stirred reactors by SCWO. The two steps are evaluated collectively. 

In a continuous stirred reactor maintained at 20 °C, phenol degraded at rates of 0.094 and 0.007/h at feed concentrations of 180 and 360 mg/L, respectively (Beltrame et al., 1984). In the presence of suspended natural populations from unpolluted aquatic systems, the second-order microbial transformation rate constant determined in the laboratory was reported to be 3.3 + 1.2 x 10 ° L/organism-h (Steen, 1991). 

Beltrame, P., Beltrame, P.E., and Cartini, P. Influence of feed concentration on the kinetics of biodegradation of phenol in a continuous stirred reactor, Water Res., 18(4) 403-407,1984. 

The three papers just referred to share a further assumption, namely that a steady state is set up in the continuous reactor, so that all time derivatives in the kinetic equations may be equated to zero. Graessley (91) considered the unsteady state during the start-up of a continuous stirred reactor and found that Mw may in certain cases increase without bound instead of reaching a steady state this will occur if a branching parameter exceeds a critical value. His reaction scheme is restricted to mono-radicals, and the effect of loss of radicals from the reactor is not taken into account. If a steady state is set up, the MWD obtained is Beasley s, when termination by combination and branching by copolymerization of terminal double bonds are absent. Since there is reason (92) to doubt the validity of Beasley s conclusions, as discussed above, the same doubt must apply to this work of Graessley s. 

Two other techniques use attached microorganisms for remediation. In a fluidized-bed method, the microorganisms are attached to particles dispersed throughout a continuously stirred reactor. In another arrangement, the microorganisms are attached to rotating discs. 

One of the well-studied systems that illustrates this successive-bifurcation behavior is the Belousov-Zhabotinski reaction. Let me briefly show you the results of some experiments done at the University of Texas at Austin,8 referring for further details to the discussion by J. S. Turner in this volume. The experimental setup of the continuously stirred reactor... 

The model predicts the yield of S Xg = 2S/ (2 S + R) at the end of the reaction (when all B is consumed). It was developed for batch and semi-batch reactors (119, 120), and later extended to continuous stirred reactors via a somewhat complicated procedure (121-112). Some criticism may be adressed, to the MIRE-model, in spite of its great interest arbitrary choice of spherical shape, assimilation of R to half the Kolmogorov microscale (which is not obvious as we have seen above) and above all, assumption that the initial reactant in the particle cannot diffuse outside, which creates an unwanted dissymmetry between A and B when V = Vg. 

Other methods that have been used to determine Koc values are the so-called box method (Macintyre et al., 1991), the continuous stirred reactor method (de Jonge et al., 1999) and headspace methods, which are especially useful for volatile chemicals (Garbarini and Lion, 1985). Delle Site (2001) has recently reviewed the available methods for the determination of Koc values. 

Transitions Between Periodic and Chaotic States in a Continuous Stirred Reactor... 

If tR and tQ are in the same order of magnitude, as in the experiments reported here, Xg depends on all the micromixing states encountered between injection and total using up of the acid, which occurs most of the time when the segregated clumps reach the stirrer region. This situation is somewhat similar to the competition between reaction/micromixing/dilution encountered in continuous stirred reactors (6), the space time being replaced here by the circulation time. 

Yu, H., Hu, Z., and Hong,T. 2003. Hydrogen production from rice winery wastewater by using a continuously-stirred reactor. J. Chem. Eng. Japan, 36,1147-1151. 

When a fluid passes through a packed column, the flow is divided due to the packing. Modelling of these phenomena is carried out by superimposing a dispersion, characterized by a coefficient D on the convective plug flow of velocity U. This is the model for an axial dispersion reactor. This model allows characterisation of a flow with intermediate properties between those of the plug flow reactor and those of a continuous stirred reactor. 

The statistical data shown in Table 5.2 were obtained for an isothermal continuously stirred reactor (CSR) with a spatial time of 1.5 h. With these experimental data, we can formulate a relationship between the reactant conversion (y) and the input concentration (x). For the establishment of a statistical model based on a... 

Ideal continuously stirred reactor (CSTR) for which a volume element entering the CSTR will become uniform dispersed with all the other volume elements in the reactor. The initial outlet will be equal to the ratio of the tracer volume divided by the reactor volume times the initial tracer concentration, and would then exponential decay in time. 

To model a packed bed of wood particles pyrolysis and char conversion schemes can be selected from the database. Homogenous reactions within the void space are modelled by describing each volume cell in the numerical grid of the flow model as a continuous stirred reactor. Due to the lack of reliable kinetic data for the conversion of gaseous species under packed bed conditions, only the conversion of hydrogen and carbon monoxide is currently taken into account. For the combustion of hydrogen an infinite rate is assumed whereas the conversion of carbon monoxide is calculated according to [17]. 

Let us consider a catalyst pellet in a continuous stirred reactor with a... 

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