Pure Batch Reactor

All of reactant A is charged to the vessel at the beginning of the batch at a temperature T0 = 294 K. The amount of the initial charge fills the vessel. In the discussion below, different heat transfer areas are considered, starting with the jacket heat transfer area and increasing the area if necessary by using an external heat exchanger. 

To illustrate some of the design and control issues, a vessel size (DR = 2 m, VR = 12.57 m3, jacket heat transfer area Aj = 25.13 m2) and a maximum reactor temperature (7j) ax = 340 K) are selected. The vessel is initially heated with a hot fluid until the reaction begins to generate heat. Then a cold fluid is used. A split-range-heating/ cooling system is used that adds hot or cold water to a circulating-water system, which is assumed to be perfectly mixed at temperature Tj. The setpoint of a reactor temperature controller is ramped up from 300 K to the maximum temperature over some time period. 

Batch Reactor Equations The dynamic equations describing the batch reactor are similar to those of a CSTR except that the feed and product streams are missing  

Constant liquid density and physical properties are assumed, so the volume of liquid in the reactor is constant with time, as is the volume in the cooling system (jacket or external heat exchanger). Equations (4.4)-(4.6) become 

The setpoint of the temperature control SP is ramped from 300 to 340 K over a period of time. The effect of this ramp rate is investigated below. If the ramp rate is too fast, the reactor temperature may run away because the heat removal system may not be able to remove the heat generated with the high initial concentrations of reactant A. If the ramp rate is too slow, the batch time will be long and therefore reduce productivity. 

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Several types of batch reactors are considered in this chapter. In a pure batch reactor all the reactants are charged initially to the vessel. The reactor is heated to the desired reaction temperature and products are formed. At the termination of the batch cycle, the products are removed. The inherent problem with this type of batch reactor is that all the fuel is sitting in the vessel. If temperature is increased too quickly or if adequate heat transfer area is not available, an exothermic reaction can easily cause a runaway. 

As mentioned earlier, the inherent problem with the pure batch reactor is that at the beginning of the batch all the reactant is available for reaction at a high concentration. If the initial reactant concentration is lower, there is less likelihood of a runaway. This is... 

The results presented above illustrate the effects of various parameters on a pure batch reactor. High initial reactant concentrations, large heats of reaction, large vessels, small controller gains, and high ramp rates can lead to reaction mnaways. 

For batch reactors in which two reactants are involved, the problems encountered with a pure batch reactor can sometimes be reduced if only one of the reactants is initially charged to the vessel and the other reactant is fed gradually at a rate such that the heat removal capacity is not exceeded. We will study this mode of operation in the next section. 

The results presented in the previous section are for the simple reaction A — B. In this section we consider the reaction A + B —> C. For the pure batch reactor in which the two reactants are initially charged to the vessel, the results are quite similar to those found in the simple A — B reaction. The effects of various design and kinetic parameters are essentially the same because both reactants are charged in their stoichiometric amounts. 

For purely batch reactors, the reference time is naturally the residence time, as a function of which the conversion in the reactor is usually described. This batch time can also be used for analysis of semi-batch reactors. Nevertheless, as the reactant introduction in semi-batch reactors can have a drastic influence on the reactor performance, the feed time is more preferably used as the reference time 4]. 

In actual practice pure batch reactors are rarely used, but semi-batch reactors find very wide application. They have the obvious advantage that the reaction rate can be controlled by the feed rate of one reactant. 

When two or more reactants are brought together in a single phase, where they will react with each other, it is often not possible to separate the effects of mixing from chemical reaction, either in space or in time. In exceptional cases it may be possible to mix the reactants at a sufficiently low temperature, where no reaction takes place, and heat the mixture until the reaction starts. This may be done in pure batch reactors, but these are rarely applied in industry. In most technical processes chemical reactions are carried out in such a way that at least one of the reactants is introduced into a mixture where the reaction is already taking place. In these situations the rate of the chemical reaction is in principle dependent on the rate of mixing. There are two well known examples of single phase reactors where this applies ... 

A pure batch reactor, used for a rapid exothermic reaction, is inherently very unstable. A well known example of such a reactor is a bomb. When we want to control a chemical reaction effectively, also in the laboratory, the semi-batch mode is usually preferred. A certain amount of one reactant (A) is put into the reactor, and heat to a temperature that makes the reaction possible. The other reactant (B) is introduced into the reactor with a controlled rate. When the reactor has adequate cooling, the reactor temperature can be kept effectively within desired limits. The practical problem is a how to adjust the cooling rate to the strongly varying reaction rate. 

In the first and second intervals, the particles behave like semi-batch reactors in the third interval, as pure batch reactors. The third interval resembles suspension polymerization, but the particles are much smaller. There is usually little or no coalescence, so that the particle number remains approximately the same after the end of interval I. 

The batch process is similar to the semibatch process except that most or all of the ingredients are added at the beginning of the reaction. Heat generation during a pure batch process makes reactor temperature control difficult, especially for high soHds latices. Seed, usually at 5—10% soHds, is routinely made via a batch process to produce a uniform particle-size distribution. Most kinetic studies and models are based on batch processes (69). 

Suppose the reaction is performed in a batch reactor of constant volume V(m ) at a constant temperature T(K), beginning with pure A... 

The decomposition of nitrous oxide (NjO) to nitrogen and oxygen is preformed in a 5.0 1 batch reactor at a constant temperature of 1,015 K, beginning with pure NjO at several initial pressures. The reactor pressure P(t) is monitored, and the times (tj/2) required to achieve 50% conversion of N2O are noted in Table 3-19. Use these results to verify that the N2O decomposition reaction is second order and determine the value of k at T = 1,015 K. 

Figure 2. Gas Phase Propylene Polymerization with catalysts of various activities (batch reactor, 1L, 80°C, 441 psia, 99% pure C,He)...

To run the residence time distribution experiments under conditions which would simulate the conditions occurring during chemical reaction, solutions of 15 weight percent and 30 percent polystyrene in benzene as well as pure benzene were used as the fluid medium. The polystyrene used in the RTD experiment was prepared in a batch reactor and had a number average degree of polymerization of 320 and a polydispersity index, DI, of 1.17. 

Example 2.11 Suppose initially pure A dimerizes, 2A —> B, isothermally in the gas phase at a constant pressure of 1 atm. Find a solution to the batch design equation and compare the results with a hypothetical batch reactor in which the reaction is 2A B - - C so that there is no volume change upon reaction. 

Suppose a homogeneous, gas-phase reaction occurs in a constant-volume batch reactor. Assume ideal gas behavior and suppose pure A is charged to the reactor. 

In case of exothermic reactions, the heat-exchange capacities of the reactor allow to rapidly evacuate the heat generated by the reaction and therefore to perform a transposition of a pure batch operating mode into a continuous one. The main point is the ability to avoid, as far as possible, an initial increase of the temperature as soon as the reactants are mixed. 

Clearly, the oxidation reaction could not have been implemented in a pure batch operating reactor. Indeed, heat removal capacity would not have been sufficient (100—1200 kW m removed versus 20 x 10 kW m generated). As a consequence, a semibatch mode is necessarily required. Besides, Table 12.10 shows that the feeding times are much higher than the residence time of the Shimtec reactor (around 15 s). 

The density of ethanol at 20 °C is 0.789 g/cm3, and its heat capacity is 2.85 J/g °K. These properties may be assumed to be constant over the temperature range of interest. The solution is so dilute that one may assume that its property values are essentially equal to those of pure ethanol. Batch reactor operation is assumed. 

Pure phosphine is to be admitted to a constant volume batch reactor and allowed to undergo decomposition according to the above reaction. If pure phosphine enters at 672 °C and the initial pressure is 1 atm, determine the times necessary to decompose 20% of the original phosphine for both isothermal and adiabatic operation. 

Commercial plastics HDPE, PP, PS and PVC in granulate form have been used as model feed. The degradation of pure polymers was followed using either at thermoanaly-tical method (MOM Derivatograph Q) or in a laboratory batch reactor system with gaschromatographic product analysis. 

The gas phase reaction, 2A = B, occurs in a batch reactor at a constant pressure of 5 atm under adiabatic conditions. Initially the reactor contains 2 Ibmol of pure A at 600 R. Heat... 

The nonfertilizer calcium phosphates are manufactured by the neutralization of phosphoric acid with lime. The processes for different calcium phosphates differ substantially in the amount and type of lime and amount of process water used. Relatively pure, food-grade monocalcium phosphate (MCP), dicalcium phosphate (DCP), and tricalcium phosphate (TCP) are manufactured in a stirred batch reactor from furnace-grade acid and lime slurry, as shown in the process flow diagram of Figure 3. Dicalcium phosphate is also manufacmred for livestock feed supplement use, with much lower specifications on product purity. 

The [YCo] systems catalyze this reaction only above 130°C, and hence, the reaction must be carried out in dilute benzene or toluene solutions to keep the TON values below —500. Only very active catalysts can be used for the reaction of Eq.(13) when carried out in pure acrylonitrile. Every cobalt catalyst sufficiently active below 125°C was tested in a batch reactor. A solution of the catalyst in pure acrylonitrile was saturated with acetylene at —2.0 MPa and then heated to 130°C (for experimental procedures, see 84MI5). The TON values after 2 hrs are summarized in Table II. The best results were obtained with the i7 -phenylborininato complex (9), which produced 2.78 kg VP/g Co. 

The following data are obtained at 0°C in a constant-volume batch reactor using pure gaseous A ... 

At 100°C pure gaseous A reacts away with stoichiometry 2A a constant volume batch reactor as follows ... 

These come from simple application of the mass-balance equation dCj jdx = Yli which you should verify. Differential equations always need initial or boundary conditions, and for the batch reactor these are the initial concentrations of A, B, and C. For this system, the feed may be expected to be pure A, so Ca = Cao and Cbo Cco 0-... 

T0093 Bio Solutions, Inc., Soil Slurry-Sequencing Batch Reactor T0138 Calgon Carbon Corporation, Perox-Pure T0195 DAHL Associates, Inc., ThermNet... 

If the above condition is not met, the calculations based solely on overall material balance do not take into account the dissolved unreacted A and B that remain in the liquid phase after the reaction in a batch reactor, or which may flow out of the reactor with the liquid in a continuous-flow system. This way, it is assumed that the removal of a reactant is purely a result of the reaction. 

The dehydrogenation of iso-butane was carried out in a recirculating batch reactor.12 Reaction products were analyzed by gas chromatography using flame ionization. The vanadium and vanadium carbide powder materials were purchased from Aldrich Chemical Co. Their bulk compositions were confirmed by the X-ray diffraction measurements. Prior to the dehydrogenation reactions, these powder materials were heated for 1 h at 900 K in pure H2 at a flow rate of 200 cm3 per minute. 

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