Semi reactor

Using a batch reactor, a constant concentration of sulfuric acid can be maintained by adding concentrated sulfuric acid as the reaction progresses, i.e., semi-batch operation. Good temperature control of such systems can be maintained, as we shall discuss later. 

Stirred-tank reactors can be operated in batch, semi-batch, or... 

The Amoco reactor operates at 70—80°C and 2 MPa (300 psi) reactor pressure. The existence of several partially isolated compartments allows a semi-iadependent control of temperature as well as comonomer and hydrogen concentrations within each section, which ia turn offers a substantial control of the molecular weight and MWD of resias. Amoco technology also accommodates a large variety of polymerization catalysts, including Phillips and Ziegler catalysts. 

Process Control. The progress of the alkyd reaction is usually monitored by periodical deterrninations of the acid number and the solution viscosity of samples taken from the reactor. The frequency of sampling is commonly every half-hour. Deterrnined values are plotted against time on semi-1 ogarithmic coordinates, as shown in Figure 4. 

Semi-Batch Reactor In a semi-batch reactor, some reactants are added to the reactor at the start of the batch, while others are fed intermittently or continuously during the course of the reaction. 

To check the effect of integration, the following algorithms were tried Euler, explicit Runge-Kutta, semi-implicit and implicit Runge-Kutta with stepwise adjustment. All gave essentially identical results. In most cases, equations do not get stiff before the onset of temperature runaway. Above that, results are not interesting since tubular reactors should not be... 

The design frequency of regeneration is normally from three to six months for semi-regenerative units, and one reactor every 24 hours in cyclic units. For either case, an increase in regeneration frequency would result in a reduction in average catalyst coke level. Thus, gasoline yields would increase and catalyst requirements decrease. 

The common practice in semi-regenerative Powerformers is to desulfurize the reactor feed. This reduces the deactivation rate of the Powerforming catalyst,... 

Figure 4-4 shows a semi-batch reactor with outside circulation and the addition of one reactant through the pump. Semi-batch reactors have some reactants that are charged into the reactor at time zero, while other reactants are added during the reaction. The reactor has no outlet stream. Some reactions are unsuited to either batch or continuous operation in a stirred vessel because the heat liberated during the reaction may cause dangerous conditions. Under these... 

A semi-batch reactor has the same disadvantages as the batch reactor. However, it has the advantages of good temperature control and the capability of minimizing unwanted side reactions by maintaining a low concentration of one of the reactants. Semi-batch reactors are also of value when parallel reactions of different orders occur, where it may be more profitable to use semi-batch rather than batch operations. In many applications semi-batch reactors involve a substantial increase in the volume of reaction mixture during a processing cycle (i.e., emulsion polymerization). 

Thermal runaway reactions are the results of chemical reactions in batch or semi-batch reactors. A thermal runaway commences when the heat generated by a chemical reaction exceeds the heat that can be removed to the surroundings as shown in Figure 12-5. The surplus heat increases the temperature of the reaction mass, which causes the reaction rate to increase, and subsequently accelerates the rate of heat production. Thermal runaway occurs as follows as the temperature rises, the rate of heat loss to the surroundings increases approximately linearly with temperature. However, the rate of reaction, and thus the... 

Whether the reactor operates in batch or semi-batch mode... 

Some batch reactions have the potential for very high energy levels. If all the reactants (and sometimes catalysts) are put into a kettle before the reaction is initiated, some exothermic reactions may result in a runaway. The use of continuous or semi-batch reactors to limit the energy present and to reduce the risk of a runaway should be considered. The term semi-batch refers to a system where one reactant and, if necessary, a catalyst is initially charged to a batch reactor. A second reactant is subsequently fed to the reactor under conditions such that an upset in reacting conditions can be detected and the flow of the reactant stopped, thus limiting the total amount of potential energy in the reactor. 

Small scale test runs prior to preparative irradiation experiments may be carried out in tubes which are either taped to the lamp housings (immersion wells) depicted in Figures 13-1 and 13-2 or placed in turntable reactors ( merry-go-rounds ). These arrangements permit the simultaneous irradiation of several samples, but only a fraction of the available light emission is used. In Figure 13-4 a simple reactor is shown which focusses almost all the emitted light into one sample which can be scaled up also to semi-preparative volumes. In this way the necessary irradiation time can be reduced sharply. 

Wachi and Jones (1991b) used a gas-liquid flat interface reactor as a semi-batch precipitation cell for the experimental measurement of calcium carbonate precipitation, as shown in Figure 8.15. 

In a continuous steady state reactor, a slightly soluble gas is absorbed into a liquid in which it dissolves and reacts, the reaction being second order with respect to the dissolved gas. Calculate the reaction rate constant on the assumption that the liquid is semi-infinite in extent and that mass transfer resistance in the gas phase is negligible. The diffusivity of the gas in the liquid is 10" 8 m2/s, the gas concentration in the liquid falls to one half of its value in the liquid over a distance of 1 mm, and the rate of absorption at the interface is 4 x 10"6 kmol/m2 s. 

With semi-continuous (more properly, semi-batch) reactors only part of the charge is added at the beginning of the cycle. Usually some reaction time is allowed to pass before the remaining part of the charge is added in a controlled manner. Sometimes... 

The influence of inhibitor on the performance of a semi-continuous reactor can be, in some ways, similar to both batch and continuous systems. A dead time is usually observed upon addition of the initial charge. When the secondary stream flow is started after some reaction of the initial charge, additional inhibitor flows into the reactor and the initiation rate drops. When this programmed addition is stopped the initiation rate increases sometimes enough to cause temperature control problems. 

Semi-continuous reactors can be used to produce very narrow or quite broad particle size distributions depending on the nature of the secondary feed stream and how it is added to the reactor. 

Compositional drift in continuous reactor trains can be altered by introducing feed streams of the more reactive monomer between reactors. This procedure is equivalent to programmed addition of the more reactive monomer in a semi-continuous system. 

The proceeding discussion of polymer composition was based on the assumption that essentially all polymer is formed in the organic phases of the reaction mixture. If a water-soluble monomer, such as some of the functional monomers, is used, the reactions taking place in the aqueous phase can contribute to variation in polymer composition. In fact, in extreme cases, water soluble polymer can be formed in the aqueous phase. This can happen in batch, semi-continuous or continuous reactors. The fate of functional monomers could be considerably different among the different reactor types, but detailed studies on this phenomenon have not been reported. 

Recipe additions can also be important with semi-continuous reactors. Addition rates influence reactor performance, and incorrect addition location can lead to non-uniform reaction within the reactor, localized flocculation, and reactor short-circuiting. 

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