"An ounce of careful plant design is worth ten pounds of reconstruction."

LECTURE 12: LABORATORY AND INDUSTRIAL CATALYTIC

REACTORS: SELECTION, APPLICATIONS, AND DATA ANALYSIS

I. Introduction A. Why study reactors?

B. Definition and classification of reactors

C. Reactor/process design perspective: from the laboratory to the full-scale plant

D. Selection of reactors in the laboratory and plant

II. Laboratory and Bench Scale Reactors A. Kinds

B. Criteria for selection of lab/bench scale reactors; applications

III. Plant Reactors A. Common types

B. Fixed catalyst bed reactors: characteristics, advantages, limitations

C. Fluidized beds: characteristics, advantages, limitations

D. Criteria for selection

IV. Collecting, Analyzing and Reporting Data from Laboratory Reactors A. General approach and guidelines

B. Criteria for choosing catalyst form and pretreatment, reaction conditions

C. Choosing mode of reactor operation; differential and integral reactors

D. Analyzing and reporting data from laboratory reactors

1. Analysis of rate data: objectives and approach

2. Integral analysis

3. Differential analysis

V. Examples

New HDS Unit, ARCO Carson, CA Refinery

I. Introduction

A. Why study reactors?

1. The design of catalyst and reactor

are closely interrelated.

2. Design of catalytic processes

requires a knowledge reactor

design, operation optimization and

selection

3. Progress in improving our standard

of living depends on our ability to

design reactors

4. Our personal existence depends on

controlling cellular reactions in our

body while that of the human race

hangs on the outcome of enormous

global reactions.

B. Definition and Classification of Reactors

1.What is a Reactor?

a. A device that encloses the reaction space, and which houses the

catalyst and reacting media.

b. A container to which reactants are fed and products removed, that

provides for the control of reaction conditions.

2. Classification of Reactors

a. Size

b. Methods of charging/discharging: batch or steady-state flow

c. Motion of particles with respect to each other

d. Fluid flow type: tubular or mixed-fluid

Table 12.1 Classification of Catalytic Reactors

Basis for Classification Classes Examples

Size Laboratory Bench scale

Pilot scale

Plant scale

0.5 cm diam. tubular microreactor (0.1-1 g catalyst) 2.5 cm diam. x 30-50 cm long tubular reactor (50-200 g catalyst)

7.5 cm diam x 6-10 m long tubular reactor (20-100 kg catalyst)

1-6 m diam x 20-50 m long tubular reactor (20-100 metric tons cat.)

Methods of charging and discharging

Batch Flow, steady state

Stirred liquid and solids a. tubular, fixed catalyst bed

b. slurry, mixed fluid, mixed solids

Motion of catalyst particles relative to each

other

Fixed Relative motion

Tubular fixed solids (fixed bed) a. fluidized bed

b. slurry bubble column

Fluid flow Tubular, plug flow Mixed fluid flow

Turbulent gas in tubular fixed bed Slurry reactor with mechanical stirring

C. Reactor/process

design perspective

Hardware and Software

Scientific & Engineering Tasks

Scientific & Engineering Disciplines

Discover Reaction

Laboratory Reactor

Kinetic Model Development

Chemical Kinetics and Catalysis

Rate/Selectivity & Rate Equation

Reactor Model

Reactor Model Development

Reaction Engineering & Mathematics

Reactor /Process Design

Catalytic Reactor Design

Pilot Plant Reactor

Finl. Plant Design & Economic Studies

Large Scale Plant

Process Design Economics

Intrinsic

Kinetics

Catalyst Prop.

Diff., Mass Trans

Fig. 12.1 Structure of Catalytic Process

Development [adapted from J. M. Smith,

Chem. Eng. Prog., 64, 78 (1968)].

D. Choosing reactors in the lab and plant

Reactors are used for many different purposes:

1. to study the mechanisms and kinetics of chemical reactions to provide data for validation of process simulations

2. to investigate process performance over a range of process variables

3. to obtain design data

4. to produce energy, materials and products.

Choosing the right reactor is critical to the engineering

process and is dictated by many different variables such as

• reaction type

• rate of deactivation

• economics

• other process requirements

II. Common Lab and Bench Scale Reactors

1. fixed bed tubular

2. stirred gas, fixed bed

3. stirred liquid/gas, stirred catalyst

4. fluid bed

5. fixed bed, transient gas flow

Laboratory and bench-scale reactors vary greatly in size,

complexity, cost, and application.

Table 12.2 Laboratory and Bench-Scale Catalytic Reactors Classes Class Examples Features

Fixed bed tubular Laboratory differential/integral

Bench-scale integral

0.5 cm diam tubular microreactor (0.1-1 g catalyst, solid catalyst, gas fluid; glass or metal

2.5 cm diam. x 30-50 cm long tubular reactor (50-200 g

catalyst); solid catalyst, gas or liquid fluid; metal

Stirred gas, fixed bed Stirred batch Batch recycle

Berty

Carberry

microreactor, 1 g catalyst, glass or met. microreactor, 1 g catalyst, glass or met.

bench-scale, 2-200 g cat., 10-100 atm, stainless steel,

circulating gas

bench-scale, 2-200 g cat., 10-100 atm, stainless steel,

spinning catalyst basket

Stirred liquid/gas, stirred catalyst

Stirred batch Bubble slurry

bench-scale, 2-50 g cat., 1-200 atm, glass or metal heterogeneous or homogeneous catalyst

Fluid bed

Laboratory Bench-scale transport

Recirculating transport

microreactor, 1-5 g cat, 1 atm, glass bench-scale, 50-200 g catal, 1-10 atm, metal

Fixed bed, transient gas flow

Pulse flow TPD/TPSR

Radio tracer exchange

MS/Transient response

Frequency response

microreactor, 0.1-1 g catalyst, glass or metal, 1 atm

Fig. 12.2 Features of representative laboratory

reactors [Levenspiel, 1979].

10/30 female joint

10/30 male joint

9 mm O-ring joint

4 ft. preheater coil of2 mm capillary tubing

Thermocouple guide of2mm capillary tubing

7"

Fritted disc

Catalyst space

Figure 12.3 Laboratory Pyrex FBR reactor (courtesy of the BYU

Catalysis Laboratory).

Figure 12.4 Berty internal recycle reactor.

Gas-Liquid CSTR (UCSB) Batch Reactor (UCSB)

Bench scale reactor (courtesy of Shell Corp.)

II. Laboratory and Bench Scale Reactors

B. Criteria for selection of lab and bench-scale reactors; applications

1. Satisfying intended application

2. Avoiding deactivation

3. Avoiding inter- and intra- particle heat and mass transport limitations

4. Minimizing temperature and concentration gradients

5. Maintaining ideal flow patterns

6. Maximizing the accuracy of concentration and temperature

measurements

7. Minimizing construction and operating costs

Table 12.3 Seven Criteria for Selection of Laboratory and Bench-Scale

Catalytic Reactors

Criterion Issues Involved/Measures of/Methods to Meet Criterion

1. Satisfy purpose of measurement (i.e., application)

Measure: (1) intrinsic activity/selectivity, (2) kinetics of reaction and deactivation

Obtain mechanistic understanding

Simulate process

2. Avoid catalyst deactivation where possible; where not, decide if fast or

slow

See Chap. 5 (B&F) on avoiding different kinds of catalyst deactivation Fast decay causes activity and selectivity disguises and requires use of

transient or transport reactor

Slow decay best studied using CSTR or differential reactor

3. Avoid inter- and intra-particle heat and mass transport limitations

Thiele modulus less than 0.5; small particles or thin catalyst layer Minimize film thickness with high flow rates, turbulence

Operate at low conversions

Use CSTR or differential reactor

4. Minimize temperature and concentration gradients

Gradients cause activity and selectivity disguises Maximize mixing in batch reactor and CSTR; use inerts

Use CSTR or differential reactor where possible

5. Maintain ideal flow patterns Minimize mixing and laminar flow in tubular reactors; Maximize mixing and minimize gradients in CSTR

Avoid gas or liquid holdup in multi-phase reaction systems

6. Maximize accuracy of concentration and temperature measurements

Sensitive analytical methods and well-placed, sensitive probes Sufficiently high product concentrations

7. Minimize construction and operating costs

Select the least expensive reactor that will satisfy the other criteria Consider ways of minimizing size of catalyst and volume of reactant gas

Table 12.4 Applications of Lab/Bench Test Reactors Reactor Type Catalyst Selection

Activity/Selectivity

Reactor/Design Fundamental

Mechanism

Process

Simulation

Life Kinetics

Integral

Adiabatic X (overall avg. conv.) X X

Isothermal X (overall conv. at T) X X

Differential

Single Pass X (intrinsic) X (intrinsic) X (eliminate)

Recycle X (intrinsic) X (intrinsic) X (eliminate)

Stirred gas X (intrinsic) X (kinetics) X (intrinsic) X (eliminate) X (model)

Fluid bed/ Transport

X (fast deact.) X (fast deact.) X (fast deact.)

X

Micro-pulse X (comparative, initial) X

Transient X (elem. steps)

X X (model)

Common Types of Catalytic Plant Reactors

1.Fixed-bed Reactors a. Packed beds of pellet or monoliths

b. Multi-tubular reactors with cooling

c. Slow-moving pellet beds

d. Three-phase trickle bed reactors

2.Fluid-bed and Slurry Reactors a. “Stationary” gas-phase

b. Gas-phase

c. Liquid-phase i. Slurry

ii. Bubble Column

iii. Ebulating bed

Table 12.5 Characteristics of Plant-Scale Fixed Bed Reactors

Advantages

1. Ideal plug (or mixed) flow

2. Simple analysis

3. Low cost, low maintenance

4. Little loss or attrition

5. Greater variation in operating conditions and contact times is possible

6. Usually a high ratio of catalyst to reactants

long residence time complete reaction

7 Little wear on catalyst and equipment

8. Only practical, economical reactor at very high pressures

Disadvantages

1. Poor heat transfer in a large fixed bed.

a. Temp. control and measurement difficult

b. Thermal catalyst degradation

c. Non uniform rates.

2. Non uniform flow patterns e.g. channeling 3. Swelling of the catalyst; deformation of the reactor

4. Regeneration or replacement of the catalyst is

difficult - shut down is required.

5. Plugging, high pressure drop for small beads or

pellets - ∆P is very expensive. 6. Pore diffusional problems intrude in large pellets

Overcoming the Disadvantages

1. Monolithic supports overcome disadvantages 2, 5 & 6

2. Temperature control problems are overcome with:

a. Recycle

b. Internal and external heat exchanges

c. Staged reactors d. Cold shot cooling

e. Multiple tray reactor - fluid redistributed & cooled between stages.

Catalyst is easily removed - varied from tray to tray.

f. Use of diluents

g. Temperature self regulation with competing reactions, one endo and one exothermic. h. Temp control by selectivity and temporarily poisoning the catalyst

B. Fixed-bed reactors: characteristics, advantages,

limitations

Advantages:

• Flexible- large variation in operating conditions and contact times

is possible

• Efficient- long residence time enables a near complete reaction

• Generally low-cost, low-maintenance reactors

Disadvantages:

• Poor heat transfer with attendant poor temperature control

• Difficulty in regenerating or replacing spent catalyst

Product

Feed

Inert balls

Catalyst

Reactants Inlet

Liquid OrGaseous

Bath

ReactorTube

Gas OrLiquidFlow

OutletProduct

ReactorTube

a..

I II III IV

1 2 3 4

Fresh feed

Recycle gas

b.

Fig. 12.6 Commercial fixed-bed reactor designs for controlling

temperature: (a) multi-tubular heat-exchange reactor, (b) series of

fixed-bed, adiabatic reactors with interstage heating or cooling.

Figure 12.5 Commercial

fixed-bed, adiabatic catalytic

reactor.

Advantages

1. Frequent regeneration of the catalyst

possible.

2. Rapid mixing of solids in fluid beds means

uniform gas composition.

3. Isothermal operation and efficient

temperature control is practical.

4. Small-diameter particles in fluid minimize

pore diffusional resistance.

5. Improved thermal efficiency because of

high heat transfer rates.

6. In the case of highly exothermic, liquid

phase reactions, slurry reactors are less

complex and less expensive than heat-

exchange-tubular systems.

Disadvantages

1. Fluidized beds are complicated systems

involving multiple reactors, heat exchangers,

extensive valving and piping to provide

continuous system.

2. $$ Extensive investment. Maintenance is

high.

3. Fluid flow is complex in fluidized and slurry

bubble columns - less than ideal contacting.

Product distribution is changed - less

intermediate formed in a series reaction.

4. Only a small variation in residence time

possible. Low residence times. Conversion

may be limited.

5. Attrition & loss of Catalyst.

Table 12.6

Characteristics of Plant-Scale Fluidized and Slurry Bed Reactors

Deentrainedvapor

Product

Spentcatalyst

Hydro-clone

Freshcatalyst

Feed

a.

Continuousphase

Product

Dispersedphase

b.

Figure 12.7 Liquid-phase slurry reactors: (a) forced-circulation,

slurry-bed reactor, (b) bubble-column, slurry-bed reactor.

H2

reactants + H2

products

shaft heater

liquid

P

productwithdrawal

suspendedcatalystparticles

rotor

pressurevessel

to heat source

H2 from reservoir

(consumption measured)

Figure 12.8 Batch-slurry reactor for hydrogenation

of specialty chemicals.

Product

Steam stripping

Flue gas

Fluid-bedregenerator

Air

Transfer line

Feed

Transfer-line reactor

Fig. 12.9 Design of typical FCC transfer-line (riser)

reactor with fluidized-bed regenerator.

Products

Riserreactor

Catalyststripper

Steam

Reactorfeed

Steam

Air

Overflowwell

Regenerator

Fluegas

Cyclone

a. Products

Cyclone

Reactor

Catalyst stripper

Steam

Air

Reactor

Regenerator

Flue gas

feed

b.

Figure 12.10 Commercial FCC riser reaction designs (a) Exxon, (b) UOP.

Fluid Cat Cracker (Chevron) Stacked Fluid Cat Cracker (UOP)

Shell Cat-Cracker All-riser Cracking FCC Unit

Criteria for Selection of Plant Reactors

1.General Criteria.

a.deactivation rate and regeneration policy

b.reaction conditions

c.catalyst strength and attrition resistance

d.process economics

2.Role of Cp/(-∆∆∆∆Hr)

slope =

T

XA

Cp

-∆HR

1rA

XA

1

100

10

1000

T

XA 1rA

XA

c

d

a

b

Fig. 12.11 (a) Operating line for a

highly exothermic reaction in an ideal

tubular reactor with pure reactant and

(b) corresponding reciprocal rate versus

conversion curve and area V/FAo for a

CSTR. (c) Operating line for a highly

exothermic reaction in an ideal tubular

reactor with dilute reactant and (d)

corresponding reciprocal rate versus

conversion curve and area V/FAo for a

PFR.

3. Optimal Temperature Progression

Figure 12.12 Optimum temperature progression (and locus of

maximum rates) of (a) reversible endothermic reaction and (b)

reversible exothermic reactions.

Exothermic reversible Exothermic irreversible Endothermic

Qin Q

Optimum

Tmax

T T T

Tmax

Coldfeed

Furnace

Adiabaticreactors

Coldproduct

A B C

D E

F G

Q Q Q

XA

a

b

Fig. 12.13 (a) Use of staged adiabatic tubular fixed-bed reactors with interstage cooling to achieve optimum

temperature progression in the cases of exothermic reversible, exothermic irreversible and endothermic

reactions. (b) Design schematic for staged adiabatic fixed-bed reactors with interstage furnace heating for a strongly endothermic reaction such as reforming of methane.

Collecting, Analyzing and Reporting Data

from Laboratory Reactors

Different purposes:

1. activity/selectivity and life data for catalyst selection

2. chemical reaction mechanistic and kinetic data for understanding the

reaction at a fundamental level, modeling the reaction process, and/or

designing reactors

3. process variable data over a wide range of conditions for purposes of

designing large-scale reactors, experimentally validating models and

optimizing the catalytic process.

Data collection typically involves three major steps (Fig. 12.14):

1. selection of a reaction and catalyst

2. selection of a reactor type

3. analysis of the data

SelectReaction

andCatalyst

Criteria Data

Select reactorand conditions Data Analysis

IntegralDifferentialInitial Rates

BatchFlow CSTR Plug - integral or differential

mechanismrate expressionprocess optimization

new experiments

Figure 12.14 Process of obtaining rate and kinetic data; note that

statistical methods are used in Steps 2 and 3 and in the recycle process.

Table 12.7 Proposed Guidelines for Choosing Catalyst Form, Pretreatment, and Reaction Conditions and for Reporting of Data [Ribiero et al., 1996].

1. Catalyst Properties and Characterization

a. Catalysts/surfaces should be carefully prepared and pretreated so as to be free of solid contaminants such as sulfur, chlorides, and carbon that might affect activity.

b. Support effects should be avoided by studying reactions on single crystals of the active catalytic phase, e.g., metal, metal films, and/or relatively highly-concentrated, poorly-dispersed supported metals. Preparation methods should be used which minimize decoration of the metal surface, e.g., decomposition of metal carbonyls on supports. Supported base metal catalysts need to be well-reduced to avoid complications due to unreduced metal oxides.

c. In the case of structure-sensitive reactions, effects of surface structure and/or dispersion need to be taken into account.

d. Metal dispersion/surface area should be measured using proven and/or standard (ASTM) methods, e.g., hydrogen chemisorption or titration rather than CO chemisorption for metals.

e. Methods of preparation and characterization should be reported in detail. Methods for calculating surface area and dispersion should also be carefully reported. Reporting these methods and the surface area or dispersion of catalyst samples should be a requirement for publication of specific activity data.

Table 12.7 Continued

2. Reaction Conditions

a. TOF and kinetic data must be measured in the absence of pore diffusional restrictions, film mass transfer limitations, and heat transfer limitations (generally at low temperature and low conversion). Experimental evidence and calculations based on well-known criteria (e.g., the Thiele modulus for pore diffusional resistance) should be provided in publications to demonstrate that the data were obtained in the absence of these effects.

b. TOF and kinetic data must be measured in the absence of deactivation effects, e.g., poisoning, coking, and sintering. The burden of proof that such effects are absent should be on the authors of a publication.

c. TOF data should be collected over wide ranges of temperature and reactant concentrations to facilitate valid comparison with data from other laboratories and to provide meaningful data for determining temperature and concentration dependencies.

d. TOF data should be reported at specified conditions of temperature, reactant concentrations, and conversion. These specifications should be used by reviewers and editors as a minimum reporting requirement for publication in a journal.

Analyzing and reporting data from laboratory

reactors

1. Analysis of rate data: objectives

a. finding a rate equation

b. determining catalyst activity, selectivity and activity stability

c. determining the effects of important process variables such as

temperature, pressure, reactant concentrations, and space velocity

on activity, selectivity and stability

2. Extracting rate constants and concentration dependencies

a. Integral analysis

b. Differential analysis

WF

dx(-rA)

x

x

xx

x

x

o

Figure 12.15

Test for integral analysis of rate data involving plot of

W/FAo versus integrated reciprocal rate.

Integral analysis of rate data involves the following steps:

1. A series of runs are made in a packed bed at a fixed initial concentration CAo and a fixed temperature

while varying the catalyst mass W and/or the initial molar flow rate FAo to generate a range of W/FAo

values at different conversions (XA).

2. A candidate rate equation is selected for testing using the design equation for plug flow. First try simpler rate equations, e.g. zero-, first- and second-order irreversible and use differential analysis to scope out possible reaction orders.

3. The left-hand side (W/FAo) and right-hand side (the integral of 1/−rA) of the design equation are each evaluated numerically and plotted against each other, as shown in Figure 4.19 to test for linearity.

4. Linearity of the plot (e.g. Figure 12.15) is used as the criterion for judging if the candidate rate equation is a useful model of the data, i.e. consistent with the data.

5. This should be followed by a nonlinear regression with statistical analysis to determine kinetic parameters.

Integral Analysis of Rate Data

Differential Analysis of Rate Data

X

slope = α

ln CA

b

ln (-rA)

W/FA0

XA

1.0

0.5 X

X XXX

XX

X

X

0

slope = -rA'a

XX

X

Fig. 12.16

(a) Differential analysis to obtain

reaction rates. (b) Plot to obtain

reaction orders.

Differential analysis of rate data involves the following steps:

1. The identical series of runs (as in integral analysis) are made in a packed bed at a fixed initial

concentration CAo and fixed temperature while varying the catalyst mass W and/or the initial molar flow rate FAo to generate a range of W/FAo values at different conversions (XA).

2. A plot of conversion XA versus W/FAo data is made for each set of runs at a fixed temperature. A best fit of the data is made using a simple quadratic or cubic equation, and the corresponding curve is plotted on

the same figure, as illustrated in Figure 4.20(a).

3. Tangents to the curve are drawn at regular intervals along the curve corresponding to the best fit, and the

slopes of these tangents are evaluated (Figure 12.16a); the slopes on this plot correspond to the reaction rate, i.e. dXA = (−rA)[d(W/F)]. Tangents can be evaluated more accurately by differentiating the equation

for the best fit of the data and evaluating the derivative at various intervals over the data set.

4. Values of −rA versus XA are plotted on linear or log-log plots to determine reaction orders. For example,

for an irreversible reaction in which data are fitted by a simple power rate law, −rA = k CAα, a plot of

ln(−rA) versus ln(CA) is linear with a slope α (Figure 12.16b).

5. Differential analysis is a useful scoping tool to explore forms of the rate expression; however, in the end a nonlinear regression and rigorous statistical analysis is required to obtain kinetic parameters with

acceptable accuracy.

References

1. O. Levenspiel, Chemical Reaction Engineering, 2nd and 3rd Eds., John

Wiley and Sons, 1972, 1999.

2. O. Levenspiel, The Chemical Reactor Minibook, OSU Bookstores, 1979.

3. J.M. Smith, Chemical Engineering Kinetics, 3rd Ed., McGraw Hill, 1981.

4. "Reactor Technology," Kirk-Othmer: Encyclopedia of Chemical Technology, Vol. 19, 3rd Ed, John Wiley, 1982, pp. 880-914.

5. G.F. Froment and K.B. Bischoff, Chemical Reactor Analysis and Design, John Wiley, 1990.

6. O. Levenspiel, The Chemical Reactor Omnibook, 1993, OSU Bookstores, 1993.

7. C. H. Bartholomew and R. J. Farrauto, Fundamentals of Industrial Catalytic Processes, Chapman and Hall, 2005, Chap. 4.