Series, reactors CSTRs

Cooking extmders have been studied for the Uquefaction of starch, but the high temperature inactivation of the enzymes in the extmder demands doses 5—10 times higher than under conditions in a jet cooker (69). Eor example, continuous nonpressure cooking of wheat for the production of ethanol is carried out at 85°C in two continuous stirred tank reactors (CSTR) connected in series plug-fiow tube reactors may be included if only one CSTR is used (70). 

Continuous stirred tank reactors (CSTRs) are frequently employed multiply and in series. Reactants are continuously fed to the first vessel they overflow through the others in succession, while being thor-... 

Numerical calculations are the easiest way to determine the performance of CSTRs in series. Simply analyze them one at a time, beginning at the inlet. However, there is a neat analytical solution for the special case of first-order reactions. The outlet concentration from the nth reactor in the series of CSTRs is... 

Thus the respective rate expressions depend upon the particular concentration and temperature levels, that exist within reactor, n. The rate of production of heat by reaction, rg, was defined in Sec. 1.2.5 and includes all occurring reactions. Simulation examples pertaining to stirred tanks in series are CSTR, CASCSEQ and COOL. 

In contrast, a continuous reactor process is controlled at steady state, thereby ensuring a homogeneous copolymer composition. Therefore, a diblock prepared in a series of CSTRs has precise block junctions and homogeneous compositions of each block. In this case, effective CCTP gives a polymer with precisely two blocks per chain, instead of the statistical multiblock architecture afforded by dual catalyst chain shuttling systems. 

In an ideal continuous stirred tank reactor, CSTR, the composition and temperature are uniform throughout and the condition of the effluent is the same as that of the tank. When a battery of such vessels is employed in series, the concentration profile is step shaped if the abscissa is total residence time or the stage number. 

SJi. The initial startup of an adiabatic, gas-phase packed tubular reactor makes a good example of how a distributed system can be lumped into a series of CSTRs in order to study the dynamic response. The reactor is a cylindrical vessel (3 feet ID by 20 feet long) packed with a metal packing. The packing occupies 5 percent of the total volume, provides 50 ft of area per of total volume, weighs 400 ib yft and has a heat capacity of 0.1 Btu/lb °F. The heat transfer coefficient between the packing and the gas is 10 Btu/h It "F. 

Figure 3-9 Total residence time from 1 /r plot for a series of CSTR reactors for 1, 2, 3,4, and n equal-volimie...

For any more complex flow pattern we must solve the fluid mechanics to describe the fluid flow in each phase, along with the mass balances. The cases where we can still attempt to find descriptions are the nonideal reactor models considered previously in Chapter 8, where laminar flow, a series of CSTRs, a recycle TR, and dispersion in a TR allow us to modify the ideal mass-balance equations. 

Laboratory studies of the rearrangement process began with semi-continuous operation in a single, 200-mL, glass reactor, feeding 1 as a liquid and simultaneous distillation of 2,5-DHF, crotonaldehyde and unreacted 1. Catalyst recovery was performed as needed in a separatory funnel with n-octane as the extraction solvent. Further laboratory development was performed with one or more 1000-mL continuous reactors in series and catalyst recovery used a laboratory-scale, reciprocating-plate, counter-current, continuous extractor (Karr extractor). Final scale-up was to a semiworks plant (capacity ca. 4500 kg/day) using three, stainless steel, continuous stirred tank reactors (CSTR). 

Table 11.2 gives the total holding times for two values of K, both for a series of CSTRs with minimal total volume and for a series of equal-sized mixed reactors. Total holding times for equal-sized mixed reactors have been calculated using a zero finding routine. The last value in Table 11.2 is the dimensionless holding time for a PFR reactor with Michaelis-Menten kinetics, calculated by means of the following equation ... 

Pertinent examples of the value of dimensional analysis have been reported in a series of papers by Maa and Hsu (19,37,63). In their first report, they successfully established the scale-up requirements for microspheres produced by an emulsification process in continuously stirred tank reactors (CSTRs) (63). Their initial assumption was that the diameter of the microspheres, <7ms, is a function of phase quantities, physical properties of the dispersion and dispersed phases, and processing equipment parameters ... 

In continuous emulsion polymerization of styrene in a series of CSTR s, it was clarified that almost all the particles formed in the first reactor (.2/2) Since the rate of polymerization is, under normal reaction conditions, proportional to the number of polymer particles present, the number of succeeding reactors after the first can be decreased if the number of polymer particles produced in the first stage reactor is increased. This can be realized by increasing emulsifier and initiator concentrations in the feed stream and by lowering the temperature of the first reactor where particle formation is taking place (2) The former choice is not desirable because production cost and impurities which may be involved in the polymers will increase. The latter practice could be employed in parallel with the technique given in this paper. 

An alternative to the series of CSTRs is to have one reactor followed by a distillation column that recycles reactant back to the reactor. The flowsheet of this process is shown in Figure 2.59. The reactor can be small because the concentration of the reactant in the reactor can be large. The per-pass conversion of reactant is not equal to... 

A continuous stirred tank reactor (CSTR) is a vessel to which reactants are added and products removed while the contents within the vessel are vigorously stirred using internal agitation or by internally (or externally) recycling the contents. CSTRs may be employed in series or in parallel. An approach to employing CSTRs in series is to have a large... 

Multistage CSTR Since tubular reactor performance can be simulated by a series of CSTRs, multistage CSTR tracer models are useful in analyzing data from empty tubular and packed-bed reactors. The solution for a tracer through n CSTRs in series is found by induction from the solution of one stage, two stages, and so on. 

Examples of values of Pe are provided in Fig. 19-8. When Pe is large, n =k Pe/2 and the dispersion model reduces to the PFR model. For small values of Pe, the above equation breaks down since the lower limit on n is n = 1 for a single CSTR. To better represent dispersion behavior, a series of CSTRs with backmixing may be used e.g., see Froment and Rischoff (Chemical Reactor Analysis and Design, Wiley, 1990). A model analogous to the dispersion model may be used when there are velocity profiles across the reactor cross-section (eg., for laminar flow). In this case, the equation above will contain terms associated with the radial position in the reactor. 

Continuous stirred-tank reactors (CSTR) are currently used for biodiesel manufacturing. Obviously, a single CSTR would require a huge volume to achieve the performance of a batch or PFR-like reactor, but the use of several CSTRs in series can improve the productivity considerably (Figure 14.12a). Intermediate... 

Another example cited in Luyben and Luyben (1997) is when a large jacketed CSTR is replaced by several smaller CSTRs in series. For most reactions, a series of CSTRs has a lower total volume than a single CSTR for the same production rate and operating temperature. This smaller total reactor volume produces a smaller surface area and a larger AT, resulting in poor temperature control, particularly in the first reactor. 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

Ignore the size of a process unit and multiple process units of the same type in series, such as the number of evaporators for multi-effect evaporation or the number of Continuously Stirred Tank Reactors (CSTRs). 

Consider the following series of CSTRs accomplishing a first-order reaction (reactors of equal size). 

Commercial continuous reactor systems generally consist of a number of continuous stirred-tank reactors (CSTRs) connected in series. The reagents are pumped into the first reactor and the product is removed from the last. Heat is exchanged through reactor jackets and internal cooling surfaces. 

Commercial SBR systems sometimes consist of as many as 12-15 equalsized reactors connected in series. Reactor sizes are 2500-3500 gal with total mean residence times of about 8 hr. More recent SBR systems consist of fewer reactors and some commercial systems contain CSTRs that arc not all the same size. 

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