Density continuous reactors

The balances for the continuous reactor are as follows The total mass balance, assuming constant density is... 

Low density polyethylene is made at high pressures in one of two types of continuous reactor. Autoclave reactors are large stirred pressure vessels, which rely on chilled incoming monomer to remove the heat of polymerization. Tubular reactors consist of long tubes with diameters of approximately 2.5 cm and lengths of up to 600 m. Tubular reactors have a very high surface-to-volume ratio, which permits external cooling to remove the heat of polymerization. 

A batch reactor and a single continuous stirred-tank reactor are compared in relation to their performance in carrying out the simple liquid phase reaction A + B —> products. The reaction is first order with respect to each of the reactants, that is second order overall. If the initial concentrations of the reactants are equal, show that the volume of the continuous reactor must be 1/(1 — a) times the volume of the batch reactor for the same rate of production from each, where a is the fractional conversion. Assume that there is no change in density associated with the reaction and neglect the shutdown period between batches for the batch reactor. 

The same reactions considered in Prob. 6.17 are now carried out in a single, perfectly mixed, isothermal continuous reactor. Flow rates, volume and densities are constant,... 

Reactors have volume V. Continuous-flow reactors have volumetric flow rate V, and constant-density reactors have residence time X = V/v. Until Chapter 8 all continuous reactors are either completely mixed (the CSTR) or completely unmixed (the PFTR). 

For a continuous reactor, y is the molar flow, for batch reactors it is the molar amount of substance or concentration. For systems with a constant density, the molar quantities can simply be replaced by concentrations. Thus, any model predicts the stoichiometric relation y, = To +vi< On the other hand, experimentally recorded concentrations exist for the... 

Given the two continuous reactors in this chapter, the CSTR and the PFR, it is natural to compare their steady-state efficiencies in converting reactants to products. For simplicity, consider a constant-density, liquid-phase reaction with nth-order, irreversible reaction rate... 

The same consecutive reactions considered in Problem 2.13 are now carried out in two perfectly mixed continuous reactors. Flow rates and densities are constant. The volumes of the two tanks (V) are the same and constant. The reactors operate at the same constant temperature. 

Having thus described the elements appearing in the drawing, operation of the device illustrated may now be explained. As is well-known in the art, at any level of 30 power operation the neutron flux density within the reactor 2 is not uniform therein. The maximum flux density occurs at the center of the active portion 4 thence the flux density diminishes. It is much smaller at the periphery of the active portion 4 than at the center. The 35 neutron flux density continues to diminish throughout the shield 6. It will readily be seen that a neutron absorber which is placed at the center of the active portion 4 has a much greater effect upon the neutron... 

Ethylene and comonomer are purified, then dried and fed with recycled diluent with a catalyst slurry to a double loop continuous reactor. Polsrmer forms as discrete particles on catalyst grains and is allowed to settle briefly at the bottom of settling legs to increase concentration from about 40% in main loop to 50-60% in the product discharge (77). Reactor temperatures are usually 70-110°C and reactor pressures are between 3 and 5 MPa (450 and 720 psi). Diluent and residual monomers are flashed off for recycle and polymer is conveyed for pelletization. Production of low density pol5uners was not practicable due to solubility of low density/low molecular weight polymer molecules in the diluent, but the use of chromox catalysts that produce broad molecular weight LLDPE and metallocene catalysts that produce mLLDPE have broadened the product portfolio for slurry-phase polymerization. 

Spielman and Levenspiel (1965) appear to have been the earliest to propose a Monte Carlo technique, which comes under the purview of this section, for the simulation of a population balance model. They simulated the model due to Curl on the effect of drop mixing on chemical reaction conversion in a liquid-liquid dispersion that is discussed in Section 3.3.6. The drops, all of identical size and distributed with respect to reactant concentration, coalesce in pairs and instantly redisperse into the original pairs (after mixing of their contents) within the domain of a perfectly stirred continuous reactor. Feed droplets enter the reactor at a constant rate and concentration density, while the resident drops wash out at the same constant rate. Reaction occurs in individual droplets in accord with nth-order kinetics. 

In addition to phase behaviour, it is also important to evaluate the density of the reaction mixture. This variable plays a major role in both reaction equilibrium and kinetics. The control of density is more complex in supercritical reactors, where it can change dramatically with small perturbations in temperature, pressure or composition. The more direct application of density, in the case of continuous reactors, is to calculate the residence time of the reaction mixture for a given operating pressure and temperature. It is important to keep in mind that the volumetric flow measured downstream of the reactor can be very different from the flow inside the reactor due to the high variability of the density at supercritical conditions. In the case of batch reactors there are two... 

Delgado, A. G., Fajardo-Williams, D., Popat, S. C., Torres, C. I. Successful operation of continuous reactors at short retention time results in high-density, fast-rate Dehalococ-coides dechlorinating cultures. Appl Microbiol Biotech 2014, 98,2729-2737. 

To increase the efficiency of EC in a continuous reactor, the mean residence time should be increased. The experiments showed that this effect is reached in the case of a relatively high value of current density and weak value of the inlet flow-rate. This study highlighted the hydrodynamic aspect of the flow in the external airlift reactor functioning as a batch and continuous reactor. The design of this kind of reactor should be improved to allow the reactant to follow the compartment in which the reaction takes place (riser). 

When the fluid density is constant, then r(= V/u) is the average residence time that the fluid spends in the reactor. This is true for the CSTR, and for any other continuous reactor operating at steady state. 

If the mass density of the flowing fluid is the same at every position in the reactor, the subscript 0 can be dropped from t and v. As noted in the discussion of the ideal CSTR,/or the case of constant density, t(= V/d) is the average residence time of the fluid in the reactor. This is true for any continuous reactor operating at steady state. However, for the ideal PFR, t has an even more exact meaning. Not only is z the average residence time of the fluid in the reactor, it is also the exact residence time that each and every fluid element spends in the reactor. For an ideal PFR, there is no mixing in the direction of flow, i.e., adjacent fluid elements caimot mix with or pass each other. Therefore, every element of fluid must spend exactly the same time in the reactor. That time is t, when the mass density is constant For the case of constant density, Eqn. (3-29) becomes... 

The graphical interpretation of the design equations for the two ideal continuous reactors has been illustrated using fractional conversion to measure the progress of the reaction. The analysis could have been carried out using the extent of reaction with Eqns. (3-18) and (3-34). Moreover, for a constant-density system, the analysis could have been carried out using the concentration of Reactant A, Ca, with Eqns. (3-24) and (3-37). 

We will begin the discussion of continuous reactors with the ideal CSTR, first with a constant-density example and then with a variable-density example. The ideal PFR then will be treated, for the constant-density and then the variable-density case. To point out the differences between constant- and variable-density systems, and the differences between how the different reactors are treated, all of our analysis will be based on Reaction (4-B) and the rate equation given by Eqn. (4-13). 

Taking into account the fission densities of reactor fuels, lO fission cm /sec, the values of irradiation damages are very high, particularly when compared to the values obtained in the tubing alloys and all the more with respect to the tank. For a rate of combustion of the order of 45 GWd f, the irradiation damage is 2 to 5,000 dpa, at a speed corresponding to a few dpa per day. Such a rate of creation of defects evidently calls for a continuous process of timely restoration of these point defects. 

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. 

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