Batch reactors specific reactions

A catalytic hydrogenation is performed at constant pressure in a semi-batch reactor. The reaction temperature is 80 °C. Under these conditions, the reaction rate is lOmmolT s-1 and the reaction may be considered to follow a zero-order rate law. The enthalpy of the reaction is 540 kj moT1. The charge volume is 5 m3 and the heat exchange area of the reactor 10 m2. The specific heat capacity of water is 4.2kJkg 1K 1. 

Specific reactor characteristics depend on the particular use of the reactor as a laboratory, pilot plant, or industrial unit. AH reactors have in common selected characteristics of four basic reactor types the weH-stirred batch reactor, the semibatch reactor, the continuous-flow stirred-tank reactor, and the tubular reactor (Fig. 1). A reactor may be represented by or modeled after one or a combination of these. SuitabHity of a model depends on the extent to which the impacts of the reactions, and thermal and transport processes, are predicted for conditions outside of the database used in developing the model (1-4). 

The batch reactor initially contains 227 kg of acetyiated castor and die initial temperature is 613 K. Complete hydrolysis yields 0.156 kg acetic acid per kg of ester. Eor diis reaction, die specific reaction rate constant k is... 

The desired product is P, while S is an unwanted by-product. The reaction is carried out in a solution for which the physical properties are independent of temperature and composition. Both reactions are of first-order kinetics with the parameters given in Table 5.3-2 the specific heat of the reaction mixture, c, is 4 kJ kg K , and the density, p, is 1000 kg m . The initial concentration of /I is cao = 1 mol litre and the initial temperature is To = 295 K. The coolant temperature is 345 K for the first period of 1 h, and then it is decreased to 295 K for the subsequent period of 0.5 h. Figs. 5.3-13 and 5.3-14 show temperature and conversion curves for the 63 and 6,300 litres batch reactors, which are typical sizes of pilot and full-scale plants. The overall heat-transfer coefficient was assumed to be 500 W m K. The two reactors behaved very different. The yield of P in a large-scale reactor is significantly lower than that in a pilot scale 1.2 mol % and 38.5 mol %, respectively. Because conversions were commensurate in both reactors, the selectivity of the process in the large reactor was also much lower. 

For the case where all of the series reactions obey first-order irreversible kinetics, equations 5.3.4, 5.3.6, 5.3.9, and 5.3.10 describe the variations of the species concentrations with time in an isothermal well-mixed batch reactor. For series reactions where the kinetics do not obey simple first-order or pseudo first-order kinetics, the rate expressions can seldom be solved in closed form, and it is necessary to resort to numerical methods to determine the time dependence of various species concentrations. Irrespective of the particular reaction rate expressions involved, there will be a specific time... 

The vast majority of the reactions carried out in industrial scale batch reactors involve reactants in condensed phases. Since the specific volumes of both liquids and solids are very small, the difference between internal energy and enthalpy for these materials is usually negligible. Thus one often sees the statement that for batch reactions taking place at constant volume ... 

The reaction system, 2A = B = > C, has been studied in a constant volume, batch reactor with the tabulated results. Assuming the orders conform to the stoichiometry, find the specific rates. 

A batch reactor has a 500 lb charge of a solution of acetic anhydride at a concentration of 0.0135 lbmol/cuft. The solution density is 65.5 lb/cuft and its specific heat is 0.9 Btu/(lb)(). The heat of reaction is -90,000 Btu/lbmol and the specific rate is... 

Most combustion processes are chain-branching, but other examples of chain-branching reactions are also found in industrial systems. Chain-branching reaction systems are potentially explosive, and for this reason great care must be taken to avoid safety hazards in dealing with them. The explosion behavior of gaseous fuels as a function of stoichiometry, temperature, and pressure has been an important research area [241]. Experimental data are typically obtained in a batch reactor, a spherical vessel immersed in a liquid bath maintained at a specific temperature. The desire to understand the explosion behavior of various... 

For the consecutive reactions, A B C, the specific rates are equal and B0 = 0, Find the maximum value of B/Aq in (a) Batch reactor (b) Two stage CSTR. 

You might think that the fed-batch technique would work in the single-reactant case considered above. A number of simulations were run, and results showed that there was little improvement when the base case kinetic parameters were used. The problem is illustrated in Figure 4.11. The material initially charged to the reactor is assumed to contain no reactant A (Ca = 0 at time = 0). The concentration of reactant has to buildup to quite high levels (Ca = 6 kmol/m3) because the specific reaction rate k is relatively small (4.045 x 10 4 s 1 at 340 K). Eventually there is enough fuel to cause a runaway. 

If a much higher specific reaction rate is used, the reactant concentration is lower and the tendency for a runaway is reduced. This is illustrated in Figure 4.13, where the preexponential factor k0 is increased by a factor of 10. In this hot reaction case, the reactant concentration CA builds to only 1 kmol/m3 and no runaway occurs. Note that the fresh feed is cut off when the reactor is full (VR = 12.57 m3). The batch is terminated when the desired conversion (99.99%) is attained at 460 min. 

The batch reactor is extremely flexible compared with continuous reactor configurations. For example, temperature can easily be made a function of reaction time. Once the reactor is put into service, operational alternatives are still available. The tank can be operated halffull without affecting product quality, or the reaction time can be modified easily. Both of these changes may cause heat and mass transfer problems in fixed-volume continuous equipment. This flexibility is worthwhile for products that are made in various grades, have seasonal demand, or have subjective specifications such as the taste of beer. 

Catalytic tests have been performed in a 500 ml stainless steel batch reactor under hydrogen pressure using 50 g of presulfided catalyst and 125 g of Safanyia atmospheric residue (SAR), The SAR feed had a specific gravity of 0,977 and contained 4.1 wt % S, 0.25 wt % N, 25 wt ppm Ni, 81 wt ppm V and 15.5 wt % C7-asphaltens, A set of used catalysts (symbol P) has been obtained by varying the pressure between 2 to 15 MPa at reaction temperature of 390 °C, contact time of 1 h and hydrogen flow rate of 30 1/h. Further experimental details are reported elsewhere (30). 

There are many types of chemical reactors which operate under various conditions, such as batch, flow, homogeneous, heterogeneous, steady state, etc. Thus, one general mathematical description which would apply to all types of reactors would be extremely complex. The general approach for reactor design, therefore, is to develop the appropriate mathematical model which will describe the specific reaction system for that particular form of reactor under consideration. For example, if the reaction system is to be evaluated for steady-state... 

Provided that gaseous reactants and products behave ideally and the specific volumes of liquid and solid reactants and products are negligible compared with the specific volumes of the gases, the internal energy of reaction may be calculated from Equation 9.1-5. (lliis quantity is required for energy balances on constant-volume batch reactors.)... 

Kinetic steps are best identified by measuring the initial products formed from individual species (including postulated intermediates) or from simple mixtures. Isotopically labeled species have proved useful in such experiments. Initial products of homogeneous processes are observable in batch reactors at sufficiently short times or in flow reactors at points sufficiently near the inlet. The most advanced systems for initial product detection are molecular beam reactors (Herschbach 1976 Levine and Bernstein 1987) in which specific collisions are observed. Each of these techniques restricts the number of contributing reactions in a given experiment, so that their stoichiometry and rates can often be inferred. 

The time necessary to achieve 90% conversion in a batch reactor for an irreversible first-order reaction in which the specific reaction rate is 10 s is 6.4 h. For second-order reactions we have... 

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