Reactor batch-mass

Various reactor combinations are used. For example, the product from a relatively low solids batch-mass reactor may be transferred to a suspension reactor (for HIPS), press (for PS), or unagitated batch tower (for PS) for finishing. In a similar fashion, the effluent from a continuous stirred tank reactor (CSTR) may be transferred to a tubular reactor or an unagitated or agitated tower for further polymerization before devolatilization. 

Batch Mass Reactors. The batch-mass reactors used in these processes are of two types low conversion agitated kettles and high conversion static reactors with extended cooling surfaces. 

Because of the difficulties of presses with HIPS cited earlier, it is usual to transfer the syrup to a suspension reactor containing water and a suspending agent for the completion of polymerization. Design problems for suspension reactors will be discussed in the next section. Design problems for HIPS prepoly batch-mass reactors are analogous to HIPS continuous reactors as discussed in Section 2.3. 

Major reactor problems in batch-mass reactors are ... 

Practical considerations of unloading play a major role in batch-mass reactors. For "low conversion reactors, a suitably sized dump line must be chosen, based on acceptable N2 dump pressure in the reactor, or discharge pump capability, as well as consideration for limiting reaction in the line between batches. 

High Conversion Batch Mass Reactors. Because of the very high viscosities at high conversion, these reactors are unagitated. Temperature control therefore depends upon conduction through the polymer to extended heat transfer surfaces. Most common are the cooled plates of the plate and frame... 

Classification of Processes and Reactors. Most styrene polymers are produced by batch suspension or continuous mass processes. Some are produced by batch mass processes. Mass in this sense includes bulk polymerization of the polymer... 

Process flow for a typical batch-mass polystyrene process(1) is shown in Figure 1. Styrene monomer is charged to the low conversion prepolymerization reactor with catalyst and other additives, and the temperature is increased stepwise until the desired conversion is reached. It is then transferred into the press. Polycycles are 6 to 14 hours in the low conversion reactor, and 16 to 24 hours in the press. At completion, the cakes are then cooled with water and removed from the press to be ground and then (usually) extruded into pellets. 

This must be done with care to avoid lifting the batch and plugging the vent. To safeguard the kettle, a proper vent line on the rupture disc must be provided. This must be sized to allow relieving under the worst conditions of exothermic reaction where a large volume of water vapor must be vented, as well as a viscous liquid layer caused by loss of suspension. Fortunately, the venting problem here is still not as severe as in mass reactors. 

Willeman et al. [26] modeled the enzyme-catalyzed cyanohydrin synthesis in a stirred batch tank reactor. Assumption of a mass transfer limitation (Figure 9.3b) is made, which results in a low concentration of substrate in the aqueous phase, thus suppressing the non-enzymatic reaction. In a well-stirred biphasic system the enzyme concentration was varied, keeping the phase ratio constant A maximum rate of conversion is reached at the concentration where mass transfer of the substrate becomes limiting. Further increase of enzyme concentration does not enhance the reaction rate [27]. The different results achieved by the two groups are explained by the different process strategies. No mass transfer limitation could be detected by Hickel et al. because the stirring rate in the aqueous phase was not varied [26]. 

If relief sizing is for a continuous or semi-batch reactor, then it may be appropriate to use isothermal calorimetry to determine the amount of reactant accumulation under worst case conditions. The mass of the accumulation, rather than the "all-in 1 batch mass, can then be used for relief system sizing and this can reduce the required relief system size. It should sbe noted that it will still be necessary to carry out suitable adiabatic tests, as described below. Further information is given by Singh1101. 

Reactor and Process Types. It is interesting to subdivide previous work not covered by reactor and process type (Table II). This could be considered a particular two-dimensional projection of the multidimensional space along the coordinates of reactor type and process type. The number of references in each subsection of the field is shown. Obviously, the greatest amount of work has been done in batch, mass/solution polymerization. This is undoubtedly because of the relative simplicity of the mathematical formulation as much as the commercial importance of this case. The same comment applies to the extension of mass/solution... 

Batch suspension reactors are, theoretically, the kinetic equivalent of water-cooled mass reactors. The major new problems are stabilization of the viscous polymer drops, prediction of particle size distribution, etc. Particle size distribution was found to be determined early in the polymerization by Hopff et al. (28, 29,40). Church and Shinnar (12) applied turbulence theory to explain the stabilization of suspension polymers by the combined action of protective colloids and turbulent flow forces. Suspension polymerization in a CSTR without coalescence is a prime example of the segregated CSTR treated by Tadmor and Biesenberger (51) and is discussed below. In a series of papers, Goldsmith and Amundson (23) and Luss and Amundson (39) studied the unique control and stability problems which arise from the existence of the two-phase reaction system. 

In a batch slurry reactor, the liquid-solid mass-transfer coefficient can be measured by dissolving a sparingly soluble solid in liquid. The concentration of dissolved solid in liquid (Bt) can be measured as a function of time, preferably by a continuous analytical device. Systems such as the dissolution of benzoic acid, jS-naphthol, naphthalene, or KMn04 in water can be used. A plot of B( as a function of time and the slope of such plot at time t = 0 can give ks as... 

It is necessary to consider the mass balances over the electrochemical cell and the reservoir to describe the temporal evolution of COD in the batch recirculation reactor system given in Fig. 1.5. Considering that the volume of the electrochemical reactor Ve (m3) is much smaller than the reservoir volume Vr (m3), we can obtain from the mass balance on COD for the electrochemical cell the following relation ... 

In the case of polyester synthesis from divinyl esters, hydrolysis of the vinyl end group partly took place, resulting in the limitation of the polymer growth.201 A mathematical model showing the kinetics of the polymerization predicts the product composition. On the basis of these data, a batch-stirred reactor was designed to minimize temperature and mass-transfer effects.202 The efficient enzymatic production of polyesters was achieved using this reactor poly(l,4-butylene adipate) with Mn 2 x 104 was synthesized in 1 h at 60 °C. 

Example 7-6. Load the Living Example Problem, (1) Plot the concentration up to a lime of 24 hours. Did you observe anything unusual If so. what (2) Modify the code to carry out the fermentation in a fed-batch (semibalch reactor) in which the substrate is fed at a rate of 0.5 dm 4i and at concentration of 5 g/dm to an initial liquid volume of 1.0 dm containing a cell mass with an initial concentration of = 0.2 mg/dm and an initial substrate concentration of C,y = 0.5 mg/dm . Plot the concentration of cells, substrate, and product as a function of time along w-ith the mass of product up to 24 hours. Compare your results with (1) above. (.3) Repeat (2) when the growth uncompeiitively inhibited by the substrate with K/ = 0,7 g/dm , (4) Set Cp = 10.000 g/dm- and compare your results with the ha.se ca.se. 

THE PROBLEM A batch laboratory reactor with an electrolyte volume of 700 cm and an electrode area of 30 cm is used to deposit a divalent metal from an aqueous solution in a potentiostatic mode. Initial concentration of the metal is O.lkmol/m. The reactor mass transfer coefficient has been measured as 3.3 x 10" m/s. Hydrogen evolution occurs as a parallel reaction according to the equation % = H p [ — ], where kn = 1.30 X 10" A/m and = 12 If the metal deposition is operated at its limiting current density at an electrode potential of —0.9 V (SCE), determine how conversion, total current density, and current efficiency vary with time, in a potentiostatic mode. What will be the current efficiency at the final... 

Solution Polymerization. In this process an inert solvent is added to the reaction mass. The solvent adds its heat capacity and reduces the viscosity, faciUtating convective heat transfer. The solvent can also be refluxed to remove heat. On the other hand, the solvent wastes reactor space and reduces both rate and molecular weight as compared to bulk polymerisation. Additional technology is needed to separate the polymer product and to recover and store the solvent. Both batch and continuous processes are used. 

In a batch process (176), a glass-lined jacketed iron vessel is charged with either sulfur monochloride or sulfur dichloride and about 1% of antimony trichloride as a catalyst. Chlorine is introduced into the reactor near the bottom. Liquid oleum is added to the reactor at such a rate that the temperature of the reaction mass is held at ca 25°C by the use of cooling water in the jacket. 

When the batch is completed, a slight excess of oleum and chlorine is added to reduce to a minimum the residual SCI2. Because thionyl chloride combines readily with sulfur trioxide to form the relatively stable pyrosulfuryl chloride, it is necessary to maintain the concentration of sulfur trioxide in the reaction mass at a low level hence, the addition of oleum to sulfur chloride rather than the reverse. When all of the reactants are added, heat is appHed to the jacket of the reactor and the batch is refluxed until most of the sulfur dioxide, hydrogen chloride, and chlorine are eliminated. The thionyl chloride is then distilled from the reactor. 

The majority of the cyanuric acid produced commercially is made via pyrolysis of urea [57-13-6] (mp 135°C) primarily employing either directiy or indirectly fired stainless steel rotary kilns. Small amounts of CA are produced by pyrolysis of urea in stirred batch or continuous reactors, over molten tin, or in sulfolane. The feed to the kilns can be either urea soHd, melt, or aqueous solution. Since conversion of urea to CA is endothermic and goes through a plastic stage, heat and mass transport are important process considerations. The kiln operates under slight vacuum. Air is drawn into the kiln to avoid explosive concentrations of ammonia (15—27 mol %). 

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