Volume of batch reactors

V = superficial linear velocity of gas (based on cross-sectional area of empty tower), ft/s Vb = volume of batch reactor, ft3 VB = volume of back-mix reactor, ft3... 

The concept of a well-stirred segregated reactor which also has an exponential residence time distribution function was introduced by Dankwerts (16, 17) and was elaborated upon by Zweitering (18). In a totally segregated, stirred tank reactor, the feed stream is envisioned to enter the reactor in the form of macro-molecular capsules which do not exchange their contents with other capsules in the feed stream or in the reactor volume. The capsules act as batch reactors with reaction times equal to their residence time in the reactor. The reactor product is thus found by calculating the weighted sum of a series of batch reactor products with reaction times from zero to infinity. The weighting factor is determined by the residence time distribution function of the constant flow stirred tank reactor. 

The most important characteristic of an ideal batch reactor is that the contents are perfectly mixed. Corresponding to this assumption, the component balances are ordinary differential equations. The reactor operates at constant mass between filling and discharge steps that are assumed to be fast compared with reaction half-lives and the batch reaction times. Chapter 1 made the further assumption of constant mass density, so that the working volume of the reactor was constant, but Chapter 2 relaxes this assumption. 

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

The liquid phase hydrolysis reaction of acetic anhydride to form acetic acid is carried out in a constant volume, adiabatic batch reactor. The reaction is exothermic with the following stoichiometry... 

As a vessel of a given shape increases in size, both the surface area and the volume increase, but they do not increase at the same rate. For a sphere the surface area is a function of the diameter squared and the volume is a function of the diameter cubed. This is also true for a cylinder whose height is a multiple of its diameter. The polymerization of styrene is an exothermic reaction. The amount of energy released at any time is dependent on the volume of the reactor, and the rate of removal of that heat is dependent on the surface area. Unless the heat is removed, the temperature will rise and the reaction rate will increase. The result will be an uncontrolled reaction that not only may ruin the batch but could also damage the reactor and might cause a tire or explosion to occur. 

A liquid-phase reaction, A products, was studied in a constant-volume isothermal batch reactor. The reaction rate expression is (-rA) = kAcA, and k = 0.030 min 1. The reaction time, t, may be varied, but the down-time, td, is fixed at 30 min for each cycle. If the reactor operates 24 hours per day, what is the ratio of reaction time to down-time that maximizes production for a given reactor volume and initial concentration of A What is the fractional conversion of A at the optimum ... 

The participant A is identified by subscript a. Thus the concentration is Ca, the number of mols is na, the fractional conversion is xa, the partial pressure is pa, the rate of decomposition is ra. The capital letter A also is used on occasion instead of Ca. The flow rate in terms of mols is na but the prime ( ) is left off when the meaning is clear, The volumetric flow rate is V, reactor volume is Vr or simply V of batch reactors, the total pressure is... 

To avoid massive dilution of the reaction mixture in the fed-batch reactor, the initial reactor volume was rather large relative to the flow rate of the feed streams. However, the initial volume of the reactor affects the amounts of enzymes that are required. As shown in Section 4.1.4.1, large amounts of enzymes are needed for each volume unit in the reactor, and in order to work with reasonable amounts of enzymes, this volume was limited to 50 mL. 

Regarding reactor sizes, a comparison of Eqs. 5.4 and 5.19 for a given duty and for s = 0 shows that an element of fluid reacts for the same length of time in the batch and in the plug flow reactor. Thus, the same volume of these reactors is needed to do a given job. Of course, on a long-term production basis we must correct the size requirement estimate to account for the shutdown time between batches. Still, it is easy to relate the performance capabilities of the batch reactor with the plug flow reactor. 

A batch reactor is defined as a closed spatially uniform system which has concentration parameters that are specified at time zero. It might look as illustrated in Figure 2-4. This requires that the system either be stirred rapidly (the propeller in Fig. 24) or started out spatially uniform so that stirring is not necessary. Composition and temperature are therefore independent of position in the reactor, so that the number of moles of species in the system Nj is a function of time alone. Since the system is closed (no flow in or out), we can write simply that the change in the total number of moles of species j in the reactor is equal to the stoichiometric coefficient Vj multiplied by the rate multiphed by the volume of the reactor. 

For a constant volume container (batch reactor), V = Vi and thus, eq. (3.91) can be used to calculate the pressure inside the reactor as a function of temperature and conversion. 

Calculation of the time required to reach a particular conversion is the main objective in the design of batch reactors. Knowing the amount of reactant converted, i.e. the amount of the desired product formed per unit volume in this reaction time, the volume of reactor required for a given production rate can be found by simple scale-up as shown in the example on ethyl acetate below. 

The reaction mixture will be discharged when the conversion of the acetic acid is 30 per cent. A time of 30 min is required between batches for discharging, cleaning, and recharging. Determine the volume of the reactor required. 

The gas-phase decomposition of sulfuryl chloride, S02C12 — S02 + Cl2, is thought to follow a first order rate law. The reaction is performed in a constant volume, isothermal batch reactor, and the concentration of S02C12 is measured at several reaction times, with the following results. 

Chemical B is to be manufactured in a batch reactor at an average rate of 5 kmol h 1 through the liquid phase isomerisation reaction A - B. At the end of each run, it takes 5 h to empty the reactor, carry out any repairs and maintenance work and refill the reactor. For a working year of 7000 h, determine the volume of the reactor and the number of batches. 

Continuous processes will generally not be used for acrylic surface coating latexes, adhesives, and other low tonnage products. Scmibatch processes are frequently used in which not all the ingredients are added initially. Continuous systems are favored for large-volume polymers like SBR in order to increase the reactor output and reduce fluctuations in product properties. Such continuous reactor trains usually consist of a series of batch reactors each connected with bottom inlets and top outlets and operated with continuous overflow. 

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