Effect of Reactor Design

As an example, Libanati et al studied catalyst deactivation by exposure to HMDS in a commercial catalyst reactor. The composition of the reactant mixtures was 88% ethanol and 12% n-propyl acetate. The total inlet concentration was approximately 1500 ppm (as Ci hydrocarbon). The design conditions were an inlet catalyst temperature equal to 616 K and a flow rate of 283 NmVmin. Individual catalyst beads of approximately 3.1 mm diameter were packed in a bed with 17.8 cm in depth. The catalyst was Pt-Pd/y-AbOs, impregnated to produce a 50-100 pm active metal eggshell layer on the outside of 3.1 mm beads. 

Light-off curves for the oxidation of hexane in a laboratory reactor (from ref. 2) 

These gaseous precursor compounds diffuse into the bead catalyst and deposit as silica particles in the micropores. This deposition results in silica penetration further into the particle than the outer layer containing the active metals. 

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Effect of reactor design on size and productivity for a gas-liquid reaction... 

Effect of Reactor Design on Size and Productivity for a Gas-Licjuid Reaction (CCPS, 1993a)... 

The kinetic parameters chosen for comparison are rate constants and t1/2. Radiation influences and the effect of reactor design are usually identical when these kinetic data are compared between the various AOPs tested. The values for pseudo first-order kinetics and half-lives for various processes are given in Table 14.3. In most cases, the values of f3/4 are equal to two times those of t1/2 therefore, the reactions obey a first-order kinetics. Figure 14.5. shows that Fenton s reagent has the largest rate constant, e.g., approximately 40 times higher than UV alone, followed by UV/F C and Os in terms of the pseudo first-order kinetic constants. Clearly, UV alone has the lowest kinetic rate constant of 0.528 hr1. 

Several reported chemical systems of gas-liquid precipitation are first reviewed from the viewpoints of both experimental study and industrial application. The characteristic feature of gas-liquid mass transfer in terms of its effects on the crystallization process is then discussed theoretically together with a summary of experimental results. The secondary processes of particle agglomeration and disruption are then modelled and discussed in respect of the effect of reactor fluid dynamics. Finally, different types of gas-liquid contacting reactor and their respective design considerations are overviewed for application to controlled precipitate particle formation. 

This fact is also confirmed by the discussion made earlier regarding the effect of various design parameters on the performance of hydrodynamic cavitation reactors. 

Merchuk, J. C., Ladwa, N., Cameron, A., Bulmer, M., and Pickett, A., Concentric-Tube Airlift Reactors Effects of Geometrical Design on Performance, AIChE J., 40 1105 (1994)... 

Young, J.C. Dhab, M.F. The effect of media design on the performance of fixed bed anaerobic reactors. Water Sci. Technol. 1983, 15, 369. 

The steady-state economic design of a process with this type of reaction requires consideration of the effects of reactor size and temperature on the entire plant. High recycle flowrates of A and a large reactor operating at a low temperature will suppress the production of D. But this will require a large capital investment in the reactor and separation sections of the plant and consume significant energy. 

Figure 2.24 shows the effect of different design levels of conversion on the sizes of the reactor and the condenser. A 90% conversion design produces a 1.68-m3 reactor... 

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. 

It is useful to initially examine the tubular reactor as an isolated unit so that some insight can be gained about the effects of various design and operating parameters on its inherent behavior. The equations describing the steady-state operation of a tubular reactor are presented and illustrated for a specific numerical example. Both adiabatic and nonadiabatic tubular reactors are considered. 

The effect of reactor inlet temperature is shown in Figure 5.3. For an inlet temperature of 446 K, the reaction rate is small. Therefore there is only a small increase in temperature and little consumption of the reactants (low conversion). However, a quite small increase in inlet temperature to 448 K results in very rapid increases in temperature and conversion. With an inlet temperature of 450 K, the reactants are essentially completely consumed. The adiabatic temperature rise is about 330 K This example illustrates one of the difficult problems associated with tubular reactors. They can be very sensitive to reactor inlet temperature. The problem is analogous to that seen in earlier chapters in CSTRs that are designed for low conversions. The reactor inlet stream contains high concentrations of both reactants, so there is plenty of fuel to generate a runaway reaction. If the maximum temperature limitation in the system is 550 K, this runaway could do real damage to the catalyst or result in a vessel meltdown. 

W. L. Luyben, Effect of kinetic, design and operating parameters on reactor gain, hid. Eng. Chem. Research 39, 2384 (2000). 

The area of reactor design has been widely studied, and there are many excellent textbooks that cover this subject. Most of the emphasis in these books is on steady-state operation. Dynamics are also considered, but mostly from the mathematical standpoint (openloop instability, multiple steady states, and bifurcation analysis). The subject of developing effective stable closedloop control systems for chemical reactors is treated only very lightly in these textbooks. The important practical issues involved in providing reactor control systems that achieve safe, economic, and consistent operation of these complex units are seldom understood by both students and practicing chemical engineers. 

Cheng, H., Scott, K. and Christensen, P. A. (2004d) Influence of reactor design on electrochemical hydrodehalogenation of 2, 4-dibromophenol in a paraffin oil - cathode effect. Environ. Sci. 

UOP and Norsk Hydro have jointly developed and demonstrated a new MTO process utilizing a SAPO-34 containing catalyst that provides up to 80% yield of ethylene and propylene at near-complete methanol conversion. Some of the key aspects of the work have included the selection of reactor design for the MTO process and determination of the effects of process conditions on product yield. Evaluation of the suitability of the MTO light olefin product as an olefin polymerization feedstock and demonstration of the stability of the MTO-lOO catalyst have also been determined during the development of this process. 

Considerations based on the known physical phenomena can guide the choice of catalyst porosity and porous structure, catalyst size and shape and reactor type and size. These considerations apply both to the laboratory as well as to large-scale operations. Many comprehensive reviews and good books on the problem of reactor design are available in the literature. The basic theory for porous catalysts is summarized in this book and simple rules are set forth to aid in making optimum choices to obtain fully effective catalyst particles, which give the best performance from an economic point of view. 

Less pronounced effect of reactor diameter and gas distribution design on operation makes scale-up easier. 

Other reactor design considerations may be necessary in special cases. Monomer mass transfer, not normally a problem, can he important if the monomer- aqueous phase interface is small. This is more likely in systems involving gaseous monomers in which the large surface area of the monomer emulsion is not present. In such cases special attention must he paid to gas dispersion and transport. Giher factors that can have a significant effect on reactor design include latex viscosity, heat transfer rates, reaction pressure, and control mechanisms. 

Merchuk, J.C. Ladwa, N. Cameron, A. Bulmer, M. Pickett, A. Concentric-tube airlift reactors effects of geometrical design on performance. AIChE J. 1994, 40 (7), 1105-1117. 

Rewatkar V.B., Joshi J.B., Effect of impeller design on liquid phase mixing in mechanically agitated reactors, Chem. Eng. Comm. 102 (1991), p. 1-33... 

Additional reactor design issues studied during RRT included the effect of petcoke particle size on conversion,and the effect of reactor temperature on gas composition and HiiCO ratio. 

Electrical efficiency of conversion may be considered as the effectiveness in utilizing all or most of the available wattage in the corona reactor. This is a function of reactor design, with particular emphasis... 

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