catalytic reactor design - pollution preventioninfohouse.p2ric.org/ref/27/26268.pdf · 17 = - l 1...

J FEATURE REP( )RT

Keep the catalyst in mind from the beginning

CATALYTIC REACTOR

DESIGN

M ost major processes in the chemical process industries are built around heterogeneous chemical reactions. A solid catalyst is an integral part of almost all these operations. In new-construction or

retrofit projects for such plants, process engineers must design and specify not only the reactors but also the catalysts.

Independent design of the two, without concern for how they will mesh, can mean a more costly design, a low production rate and more-frequent shutdowns. It may even cause the catalyst to fail.

Consider, for instance, this debacle at a methanol plant. A carbon-steel pipe had been installed at the en- ,trance to the methanol reactor. High-pressure carbon monoxide in the feed stream reacted with the steel to pro- duce iron carbonyls, which poisoned the catalyst [171. Remedying the situation cost several million dollars.

With the hope of avoiding such situations, we first summarize the principles of catalyst and reactor design, with emphasis on maintaining interdependence between the two activities. Then we apply the principles to industrial reactors.

The focus is solely on heterogeneous catalysis, in which the catalyst (virtually always in solid form) is not in the same phase as the process stream. Even with this limitation, the technology is far too detailed for full pre- sentation here. Instead, our aim is to enable readers to keep the big picture in mind whenever getting immersed in the specifics of a project.

Calvin H. Bartholomew and William C. Hecker Brigham Young University

70 CHEMICAL ENGlNEERlNGiJUNE 1994

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1 Part 1 t‘

Catalyst design eterogeneous catalysts come in a wide variety of forms. Most are H spheres, tablets, rings, pellets of

various shapes, or monolithic honeycomb structures. Generally, this particle or structure consists of an active catalytic species impregnated into or de- posited onto a nominally inert support.

Design involves both the active catalyst and the support. It consists essentially of choosing the right type and form of catalyst for a given situation, then specifying its size, porosity, catalytic-species distribution and other properties.

This design procedure requires the engineer to deal with the catalytic functions, chemical and physical properties, and mechanical and flow properties of the catalyst. These three groupings are highly interrelated.

For instance, catalytic functions include activity, selectivity for desired products, and stability against deactivation; each of these depends on the chemical and physical makeup of the catalyst. Mechanical properties, including particle strength and attrition resistance, depend on the chemical stability and microstructure of the solid and the presence of binders. And flow properties, such as flow distribution and pressure drop, depend on particle shape and size.

The interrelation often generates a need for compromises. For instance, mechanical strength decreases with increasing porosity 151, especially above a porosity of 50%, whereas activity at high conversions (entailing conditions where pore diffusional resistance is high) rises with increasing porosity. Ac- cordingly, the degree of porosity must be a compromise between high activity and high mechanical strength.

Furthermore, moderately active catalysts tend to be chemically more stable than those of high activity. And pressure drop through the system is lowest for large catalyst particles, at the expense of higher pore diffusional resistance and hence lower activity.

An imaginative engineer will be alert for new approaches or materials that at least partially circumvent the need for compromises. For instance, a compara- Amencan Oil Co

tively new catalyst composed of a ceramic honeycomb monolith with a thin catalyst wash-coat inside its channels provides both low pressure drop and low pore diffusional resistance, i.e., high activity. Eight steps: A stepwise procedure for catalyst design follows. The appropriate interweaving of this procedure with reactor design is explained beginning on the next page. (1) Spell out the reactants, products and operating conditions for the process (2) Identify and list all possible chemical reactions (including undesired ones) and categorize them according to the type of bond changes. Examples of reactions include dehydrogenation, hydrogenation, oxidation, carbon monoxide insertion, dehydration, and group addition (3) Assess the feasibility and energetics of each reaction in Step 2, by calculat- ing its enthalpy change, free-energy change and other relevant thermodynamic parameters (4) For the reactions that Step 3 shows to be significant, visualize the actual molecular changes, the elementary reactions on the catalyst surface, and the active intermediates. From this, pre- dict the important reaction paths (5) Determine what kinds of catalytic functions or sites (for example, adsorp- tive, desorptive, hydrogenative, acidic) will be necessary. For instance, low- temperature methane combustion calls for catalytic sites that dissociatively chemisorb oxygen and methane but easily desorb water (6) Seek catalyst materials that offer the appropriate catalytic functions (e.g., platinum or nickcl for hydrogcnn- tion, and zeolites for cracking), the necessary thermal stability, and resistance to poisoning or fouling. Look also for a stable, compatible support material, as well as promoters to enhance activity or stability (7) Specify the catalyst microstructure in terms of crystallinity, surface area, porosity and similar parameters that govern catalyst strength and attrition resistance. Also, specify catalyst particle size and shape, and choose binders to give the particle strength and attrition resistance.

In this step, keep in mind the impor- tance of minimizing pressure drop. Apart from the decrease with increasing catalyst-particle size, the pressure drop per unit height of catalyst bed can be decreased by factors as high as ten through careful choice of monoliths or uniquely lobed or star-shaped pellets. At a constant particle diameter, pressure drop increases in the following order: lobes, rings, extrudates, tablets, spheres (8) In most cases, Steps 1-7 generate several potential catalyst candidates. Test these experimentally for activity, selectivity and stability

Databases can be valuable at many points in this eight-step process [lo]. In Steps 3-6, for instance, computerized data banks containing thermodynamic data, reaction mechanisms, surface- chemistry data, and catalyst properties greatly speed the selection process.

Reactor design Design of a reactor combines material

balances, energy balances and kinetic rate expressions to come up with the optimum reaction conditions and type and size of reactor (or reactors) for a given process. “Optimum” usually means the minimum vessel volume for a single-reaction process, or the best selectivity or product distribution for a process with multiple (parallel or series) reactions. Material balance: Sometimes called the species-continuity equation or the reactor-performance equation, this tells how any given reaction species is distributed in space and time. The material balance presupposes a particular reactor type.

Detailed discussion of material balances (and of energy balances and E- netic rate expressions) is beyond the scope of this article. A material balance may be as complicated as Equation 1 in Table 1, which describes a transient, two-dimensional reactor in which axial dispersion is important. Or, it may be as simple as the performance equation for the continuous stirred-tank reactor (CSTR), Equation 2, derived from Equation 1 by assuming steady-state, uniform concentration in the radial di- rection and no axial dispersion. For a typical one-dimensional reactor, the material balance predicts conversion as

CHEMICAL ENGINEERING/JUNE 1994 71

TABLE 1. THREE KEY RELATIONSHIPS FOR REACTOR DESIGN

1. Material Balance - Reactor Performance Equation

2. Energy Balance - Conservation of Energy

3. Rate Expression - Rate Equation

no mass transfer influence :

17 = - 1 j D e f f -(strong pore resistance, 1st order) (8) L k“‘

a function of the distance z into the reactor and of the reaction rate ( -rA).

In principle, there is one material- balance equation for each species in the system. However, for a single reaction the species are all tied together by the

. stoichiometric relationship (e.g., A t B = C + D), and thus, only one balance is needed to fully describe the system. For multiple reactions, there must be one additional mass balance equation for each additional stoichiometric reaction that describes the reaction network. Energy balance: This spells out how temperature varies in space and time throughout the reactor. A description of the temperature field is important, because the reaction rate is in most instances a strong

exothermicity and heat losses to the sur- roundings are all important. Conversely, it may be as simple as Equation 4, which applies to a one-dimensional adiabatic

NOMENCLATURE A Aconstant I

Ci Concentration of species i C, Heat capacity at constant

DAB Diffusivity of A into B E Energy of activation FA,, Inlet molar flowrate of A AH, Heat of reaction k Thermal conductivity (Eq.3);

rate constant (Eq. 6,8) Ki Constants L Characteristic length of catalyst

q Heatrates r Radial distance r, t Time T Temperature v, Radial velocity v, Axial velocity V Volume X, Fractional conversion of A z Axial distance 7 Effectiveness factor p$ Term accounting for viscous

dissipation p . Density

pressure

pellet

Rate of generation of A

function of the temperature. The energy balance may be as compli-

cated as Equation 3 in Table 1, which describes the temperature profile in a transient, two-dimensional reactor in which axial dispersion, viscous dissipation,

72 CHEMICAL ENGINEERING/JUNE 1994

reactor. For a typical one-dimensional reactor this relationship predicts temperature as a function of distance z and reaction rate -rA. Since conversion (XA) is also a function of these two variables, under some circum- stances temperature becomes a unique function of conversion, as shown in Equa- tion 4 [ 121. I

The energy balances just dis- clxssed describe macroscopic temperature gradients across the length and width of the reactor. One must sometimes carry out additional energy bal-

ances on single catalyst pellets, to determine temperature gradients between the gas phase and the catalyst surface or within the pellet or both. Kinetic rate expression: This describes how the reaction rate of each species de-

pends on concentrations, temperature, and catalyst properties. The rate expres- sioncan bevery complex; for instance, see Equation 5 in Table 1, which is for a re- versible, temperature-dependent Lang- muir-Hinshelwood-type reaction (see Folger, H.S., “Elements of Chemical Re- action Engineering,” 2nd ed., Prentice Hall, 1992). For a much less complex example, see Equation 6, covering simple first-order irreversible reactions. If the system has a deactivating catalyst, an equation for activity as a fundion oftime should also be included.

Whenever internal or external mass- transfer influences affect the reaction rate, it can be adjusted by multiplying the intrinsic rate expression by an effectiveness factor as shown in Equa- tions 7 and 8 for internal influence. The resulting “global” or “observed” rate should then be used in material and energy balances.

For systems with strong internal- pore-diffusion resistances (quite com- mor, ir, industrial catalytic-reactw systems), the effectiveness factor is a function of catalyst diameter and catalyst pore sizes. The relationship is ex- pressed via the effective diffusivity, Deff; see Equation 8. This is one of the key links between reactor design and catalyst design, as the physical and chemical properties of the catalyst influence the reactor design directly by affecting the rate expression

Catalytic reactor design As already emphasized, proper design of the catalytic reactor must be a care-

,

fi FEATURE REPORT

fully arranged marriage of catalyst and reactor. This interdependence shows up in several ways.

For example, a more-active catalyst enables operation at milder conditions of temperature and pressure; moreover it minimizes the required reactor volume and cost. A catalyst whose activity is very stable (with a life on the order of months or years) can be matched with a relatively lower-cost tubular bed reactor rather than a more expensive fluid bed system, because it need not be re- placed ofien. High-pressure conditions are likely to require selection of a ro- bust packed-bed reactor and a catalyst in monolith or large-pellet form to minimize pressure drop.

A practical sequence to achieve the optimal combination of catalyst and reactor is as follows:

1. For various candidate reactor types that seem promising, use the previously outlined reactor-design relationships to specify the reactor size (including the amount of catalyst needed), the concentrztioii aid temperature profiles, the quantity of heat that must be added or removed, and the rate of deactivation

2. Choose among the candidates, using these criteria:

(a) Minimize the volume of catalyst, and therefore reactor size, required. For instance, in the case of an irreversible first-order reaction, a tubular reactor requires a lesser volume than does either a slurry reactor or a fluid- bed reactor

(b) Provide for eficient heat transfer when dealing with strongly exo- or en-

dothermic reactions. Slurry or fluid-bed reactors are attractive in this regard

(c) Also for strongly exo- or endothermic reactors, consider reactors or at least catalyst trays in series, with in- terstage heating or cooling [12]

(d) In situations in which the catalyst becomes deactivated rapidly (in sec- onds to hours), provide for rapid, conve- nient regeneration

3. Choose the catalyst type and form that will:

(a) Maximize activity, selectivity and stability

(b) Minimize pressure drop and maximize access of reactants to the porous catalyst interior. Lobed extrudates are

attractive for this; so are monoliths wash-coated with catalyst [B, 111.

(c) Be compatible with the reactor- design needs; for instance, with high thermal conductivity for highly endothermic or exothermic reactions, and with sufficient mechanical strength so that catalyst at the bottom of the reactor can withstand the full weight of material above it 4. Choose the reactor-catalyst combi-

nations that will minimize capital cost and overall production costs. In this connection, be aware that the price of a catalyst is usually a relatively minor consideration in comparison to its activity, selectivity, and stability 0

n order to use these design principles effectively, the engineer must be familiar with the types of reactors

actually available in practice. These can be divided into two general classes, fixcd-bcd am! hidizec! cr slurry bed.

Fixed vs. fluid In fixed-bed reactors, the catalyst re- mains essentially stationary until it is to be reactivated or discarded. It may, for instance, be confined within the tubes of a tubular reactor, or it may be placed on trays.

The advantages of fixed-bed reactors, especially in comparison with fluidized or slurry-bed reactors, include:

Approximation of ideal plug-flow operation, and thus high conversion ef- ficiency

Simplicity, giving low cost and minimal maintenance

Allowance for greater variation in operating conditions and contact times, and hence in conversion

giving longer residence time and thus more-complete reaction *Minimal wear on catalyst and equip- ment

Practical operation at very high pressures Conversely, fluidized-bed and slurry reactors offer these advantages over fixed-bed versions:

Easier catalyst regeneration and replacement

Rapid mixing, which facilitates eficient heat transfer and, thus, isother- mal operation (Continues)

High ratio a€ cata!yst to rea.cta.nnrs,

-~


FEATURE REPORT

1. Catalyst deactivation behavior; regeneration policy a. Fixed beds are favored if the life of the catalyst is longer than about 3 mo b. Fluidized or slurry beds are favored in process situations that involve rapid deactivation and the need to regenerate the catalyst

2. Reaction conditions: Fixed beds are favored for high pressures; fluid or slurry beds are favored for strongly exo- or endothermic reactions.

Low pore-diffusional resistance, due to the small size of catalyst particles typically used

Temperature control in fixed-bed reactors can be improved, at additional cost, through such measures as inter- stage cooling or heating. Judicious use of competing reactions or partial poi-

3. Catalyst strength and attrition resistance: Fixed-bed catalysts must be strong enough to avoid being crushed at reactor bottom. Severe attrition rules out use in a fluid bed

4. Process economics: a. Capital cost depends on the complexity of design, cost of materials, reactor fabrication, and catalyst cost b. Operating cost depends mainly on pressure drop, maintenance, regeneration costs and heat-transfer duty

soning of the catalyst can serve the same purpose.

For instance, in the oxidative dehydrogenation of methanol to for maldehyde, the reaction with oxygen (CH30H + 0.5 0, .= HCHO + H,O) is highly exothermic (-156 kJ/mol), whereas the direct dehydrogenation (CH30H = HCHO + H,) is quite en-

also influence the choice of reactor. For example, catalysts used in fixed beds typically must offer a crush strength of at least 3 kdparticle (or an axial crush strength of 50-80 kg/cm2). Otherwise the pellets at the bottomofthereactor may be crushed to fines, causing unacceptably high pressure drop across the reactor.

relate mainly to the reactor type cho- sen; others concern the nature of the catalyst or the process. Many are explained best by considering specific examples. Fixed-bed reactors: In these, it is par- ticularly important to maximize catalyst strength and porosity, minimize

dcthermic (85 kJ/ mole). Accordingly, the reaction temperature of the system can be regulated by controlling the oxygen concentration and the oxygen-to-steam ratio.

Making the choice Long catalyst life (greater than 3 mo) favors fixed bed reactors. On the other hand, a rapidly deactivating catalyst that needs frequent replacement or regeneration mandates the use of a fluidized or slurry bed reactor, because in such a system the deactivated catalyst can be removed and fresh catalyst added during operation.

The next priority in the selec process is to consider reaction conditions, especially catalyst temperature. Been,*"-. ,ct+ -fir\.. tLfi-- a u u c UI l,I G puur Wl.a1114! conduct:i;- ity of a typical ceramic-supported solid catalyst, a large fixed bed reactor more than a few inches in diameter behaves essentially adiabatically, so control of reaction temperature is not possible for a highly exo- or endothermic reaction. Any resultant overheating can degrade the catalyst or lower its selectivity. On the other hand, the well-mixed behavior of fluidized and slurry reactors facilitates efficient convective heat transfer and temperature control, as has already been noted.

Catalyst strength and attrition may

74 CHEMICAL ENGINEERING/JUNE 1994

In fluidized or slurry bed reactors, attrition of just a few percent of the total catalyst charge per day leads to uneco- nomical loss of catalyst. And in a slurry reactor, it upsets the catalyst separa- tion process.

Capital cost is affected by complexity of the design. For example, in the highly exothermic Fischer-Tropsch syntheses (involving production of liquid hydrocarbons from carbon monoxide and hydrogen), a single liquid- phase slurry reactor involves substantially less material and fabrication costs than a fixed bed reactor containing hundreds of small diameter, catalyst filled tubes [MI. Conversely, fluidized beds can incur high capital

fluidization. Operating cost depends greatly on

the pressure drop through the reactor. This dependence also affects capital cost, because it determines the size of the process compressor or pump. Among the other significant determi- nants of operating cost are maintenance, catalyst regeneration and heat- transfer duty.

costs for the equipiileilt associated with

Some pointers The engineer should also keep the following practical points in mind. Some

pressure drop, minimize pore diffusional resistance, and maximize catalyst life. As already noted, several of these features are obtained at the expense of each other.

Consider pellets, for example. Be- cause pressure drop decreases and crush strength increases with increasing particle diameter while the pore diffusional re-

sistance increases, it makes sense to choose lobes or rings, so as to obtain lower pressure drop per given particle diameter. Thus, three- and four-lobed particles are used in hydrodesulfuriza- tion to minimize both pressure drop and pore diffusional resistance.

In low-temperature methanation or Fischer-Tropsch synthesis, high meso- porosity is needed to obtain extensive metal surface area, and high macrop- orosity is needed for reactant access while minimizing pore diffusional resistance. But catalyst strength is not a big issue, because reaction conditions are mild and the catalyst beds are not high. Accordingly these catalysts are typically supported on extruded pellets

area gamma-alumina of moderate crush strength and relatively moderate resistance to hydrothermal sintering.

On the other hand, nickel catalysts used in high temperature steam re- forming must be strong and hydrother- mally stable. Accordingly, relatively large nickel crystallites are supported on pressed pellets or rings consisting of a low-surface-area calcium or magne- sium aluminate or alpha alumina, all three of these offering high strength and high hydrothermal stability. Monoliths: For catalytic processes of

CL + ^I^ ̂ ^__^^^ wab ait: ~uii~pusai: ~f ii high-s&ice-

! Part 1 ,

high gas throughput or space velocity, monoliths can be employed to great ad- vantage over pellets because they incur a lower pressure drop. Both the pressure drop and the geometrical surface area (GSA) of the monoliths decrease with an increase in the monolith chan- nel diameter.

In mass-transfer-controlled reactions, such as CO oxidation on Pt-alumina in automotive converters, GSA should be maximized; accordingly, there must be a trade-off between low AP and high GSA. Because of the inher- ently low AP of thin-walled ceramic and metal monoliths, it is possible to design converters for high GSA (40 cm2/cm3) with a fine mesh size (93 squares/cm2) while keeping AP adequately low for efficient auto exhaust operation. To fur- ther enhance the access of reactants to metal crystallites inside the catalyst pores (in other words, minimize the pore diffusional resistance or maximize the catalyst effectiveness), the catalyst is wash-coated in a thin layer of about 0.01 mm thickness inside the monolith channels.

By contrast, monoliths used in selective catalytic reduction (SCR) of NO in power plants on the hot side of the boiler are designed with a large mesh size and low GSA (2-4 squares/cm2 and 7-14 cm2/cm3), to prevent plugging with fly ash. They also have thick catalyst- containing walls to prevent loss of activity due to erosion of the catalyst by fly ash particulates. For this applica- tion, wash-coated catalysts would quickly lose activity as the catalyst eroded away. Fluidized or slurry bed reactors:. In these, the particle size is generally small (in the range of 30-200 microme- terra), ani: gwei-iied by the operzting conditions of the process necessary to maintain an expanded, fluid bed. With these reactors, the catalyst design fo- cuses on maximizing activity, selectivity, and resistance to attrition and spalling.

This resistance is achieved by the appropriate combination of catalyst porosity, support-material type and particle size, and type of binder (e.g., silica or carbon). In developing this combination, the engineer must design not only for high strength but also to avoid any phase changes or reactions

(e.g. carbiding or hydration) that in themselves would bring about spalling or particle disintegration. Catalyst distribution in particles: As noted near the beginning of this article, a catalyst particle consists of an active catalytic species and an inert support. Activity losses due to transport limitations and deactivation can be minimized by careful specification of the catalytic-species distribution throughout the support.

According to Becker and Wei [22], the optimum catalyst distribution depends on relative rates of reaction and deacti-

References 1. “Catalysts Looks to the Future,” National Re-

search Council Panel, National Academy Press, Washington, D.C., 1992.

2. Hegedus, L.L. “Catalytic Technologies for Air Pollution Control,” U.S. Russia Workshop on Environmental Catalysis, Wilmington, Del., Jan. 14-16,1994,

3. Dowden, D.A. Schenll, C.R., and Walker, G.T., “The Design of Complex Catalysts,” Fourth In- ternational Congress on Catalysis, ed. High- tower, J.W., Rice University, Houston, 1968, p. 1120.

4. Trimm, D.L., “Design of Industrial Catalysts,” Chemical Engineering Monographs, 11, Else- vier, 1980.

5. Sleight, A.W., and Chowdhry, U., Catalyst De- sign and Selection, in Leach, B.E., ed, “Applied Industrial Catalysis,” Academic Press, 1983, Vol. 2, Chapter 1, pp. 1-25.

6. Hegedus, L.L. (ed.), “Catalyst Design,” Wiley, 1984.

7. Hegedus, L.L. e t al, “Catalyst Design, Progress and Perspectives,” Wiley, 1987.

8. Richardson, J.T., “Principles of Catalyst Devel- opment,” Plenum Press, 1989.

9. Inui, T., ed, “Successful Design of Catalysis,” Stud. Surf. Sei. Catal., 44, Elsevier, 1989.

10. Becker, E.R., and Pereira, C.J., eds, “Com- puter-Aided Design of Catalysts,” Marcel Dekker, 1993.

11. Satterfield, C.N., “Heterogeneous Catalysis in Industrial Practice,” 2nd ed, McGraw-Hill, 1991, Chapter 4.

12. Levenspiel, O., “Chemical Reaction Engineer- ing,” 2nd ed, Wiley, 1972.

vation. For instance, in the case of fast reaction and fast poisoning, the optimum distribution (or catalyst profile) is an active band between a thin inert outer shell and inert center. This has been called the middle-egg-white profile. For fast reaction and slow poisoning, the optimum profile is a thin outer coating or shell of active catalyst at the exterior surface, called the eggshell profile. The predictions of Becker and Wei have been borne’ out experimentally in several catalytic processes [23,

Edited by Nicholas P. Chopey 24,251. I

13. Smith, J.M., “Chemical Kinetics,” 3rd ed, Mc- Graw-Hill, 1981.

14. Lee, H.H., “Heterogeneous Reactor Design,” Buttenvorth, 1985.

15. Froment, G.F., and Bischoff, K.B., “Chemical Reactor Analysis and Design,” 2nd ed, Wiley, 1990.

16. Fogler, H.S., “Elements of Chemical Reaction Engineering,” 2nd ed, Prentice Hall, 1992.

17. Collier, C.H., “Catalysis in Practice” Reinhold, 1957.

18. Bartholomew, C.H., in “New Trends in CO Ac- tivation,” Studies in Surface Sei. and Cataly- sis, 64, ed. L. Guczi, Elsevier, 1991.

19. “Reactor Technology,” Kirk-Othmer Encyclo- pedia of Chemical Technology, 3rd ed., Vol.. 19, Wiley, 1982, pp. 880-914.

20. Boer, F.B., et al, Chem. Tech., 312, May 1990. 21. Bhatt, B.L.,et al, “Liquid Phase Fischer-Trop-

sch Synthesis in a Bubble Column,” presented at the DOE Liquefaction Contractors’ Review Conference, Pittsburgh, Pa, Sept. 22-24, 1992.

22. Becker, E.R., and Wei, J., J. Catal,. 46, 365, 372 (1977).

23. Hegedus, L.L., and McCabe, R.W., ‘‘Catalyst Poisoning,” Marcel Dekker, 1984.

24. Oh, S.H., Catalyst Converter Modeling for Au- tomotive Emission Control, in Becker, E.R. and Pereira, C.J., eds, “Computer-Aided De- sign of Catalysts,” Chap. 8, Marcel Dekker, 1993.

25. Iglesia, E., e t al, Reaction-Transport Selectiv- ity Models and the Design of Fischer-Tropsch Catalysts, in Becker, E.R., and Pereira, C.J., op. at., Chap 7.

The authors Calvin H. Bartholomew, Jr., is Professor of Chemical Engneermg at Brigham Young U (BW), and head of the B W Catalysis Labora- tory. He was previously a Se- nior Chemical Engmeer for Corning Corp., Corning, N Y He has conducted research for 25 years in catalysis and combustion, with emphasis on activitv-structure relationships, deactivation, chemisorption, and catalysis for syngas conversion and for selective reduction of NOx. Bartholomew has written two books and over 100 papers, and consulted with over 20 firms. He received the American Chemical Soc.’s Utah Award in 1991. He holds a B.S. in chemical engineering from BYU, as well as a Ph.D. from StanFord U.

William C. Hecker is an As- sociate Professor of Chemical Engineering at BYU, Associ- ate Head of the Catalysis Lab- oratory and head of the Char Oxidation Group. Before join- ing BYU, he was with Chevron Research Corp. and Dow Chemical Co. He has nearly 30 publications and 3 patents, and has been presenter or eo-presenter of 92 tech- nical papers. Research interests include kinetics, heterogeneous catalysis, coal char Oxidation, NO reduction, auto emissions control, and infrared spectroscopy of surfaces. In 1986, he received an AIChE national award as outstanding student- chapter counselor. He holds B.S. and M.S. de- grees from BYU and a Ph.D. from the U. of Cali- fornia a t Berkeley, all in chemical engineering.


FEATURE REPORT

FIGURE 1. The heart of any static-mixing reactor, such as the one being as- sembled here, is its array of stationary guiding elements within the vessel

76 CHEMICAL ENGINEERINGNUNE 1994

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