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This is a review article on chemical reactors: definitions, basic configurations, computational techniques and discussion of reactor types used in practice.

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REACTORS IN PROCESS ENGINEERING

Gary L. Foutch

Arland H. Johannes Oklahoma State University

I. Reactor Classifications

II. Primary Reactors

III. Generalized Reactor Design

IV. Special Reactor Configurations

GLOSSARY

Adiabatic reactor: Vessel that is well insulated to minimize heat transfer and has an

increase or decrease in temperature from the initial inlet conditions due solely to the

heats of reaction.

Batch reactor: Vessel used for chemical reaction that has no feed or effluent streams.

The reactor is well stirred and usually run either isothermally or adiabatically. The

main design variable is how much time the reactants are allowed to remain in the

reactor to achieve the desired level of conversion.

Catalyst: Substance that increases the rate of a chemical reaction without being

consumed in the reaction.

Continuous stirred tank reactor: Sometimes called a continuous-flow stirred-tank

reactor, ideal mixer, or mixed-flow reactor, all describing reactors with continuous

input and output of material. The outlet concentration is assumed to be the same as

the concentration at any point in the reactor.

Conversion: Fraction or percentage that describes the extent of a chemical reaction.

Conversion is calculated by dividing the number of moles of a reactant that reacted

by the initial moles of reactant. Conversion is defined only in terms of a reactant.

Elementary reaction: Reaction that has a rate equation that can be written directly

from a knowledge of the stoichiometry.

Isothermal reactor: Any type of chemical reactor operated at constant temperature.

Mean residence time: Average time molecules remain in the reactor. Note that this is

different from space time.

Multiple reactions: Series or parallel reactions that take place simultaneously in a

reactor. For example, A + B → C and A + D → E are parallel reactions, and A + B

→ C + D → E + F are series reactions.

Plug flow reactor: Sometimes called a piston flow or a perfect flow reactor. The plug

flow reactor has continuous input and output of material. The plug flow assumption

generally requires turbulent flow. No radial concentration gradients are assumed.

Product distribution: Fraction or percent of products in the reactor effluent.

Rate constant: Constant that allows the proportionality between rate and concentration

to be written as a mathematical relationship. The rate constant is a function of

temperature only and is generally modeled by an exponential relationship such as the

Arrhenius equation.

Rate equation: Mathematical expression that is a function of both concentration of

reactants or products, and temperature.

Reaction mechanism: Series of elementary reaction steps that when combined, gives

the overall rate of reaction.

Space time: Time to process one reactor volume based on inlet conditions.

Yield: Moles of a desired product divided by moles of a limiting reactant.

A chemical reactor is any type of vessel used in transforming raw materials to desired

products. The vessels themselves can be simple mixing tanks or complex flow reactors.

In all cases, a reactor must provide enough time for chemical reaction to take place.

The design of chemical reactors encompasses at least three fields of chemical

engineering: thermodynamics, kinetics, and heat transfer. For example, if a reaction is

run in a typical batch reactor, a simple mixing vessel, what is the maximum conversion

expected? This is a thermodynamic question answered with knowledge of chemical

equilibrium. Also, we might like to know how long the reaction should proceed to

achieve a desired conversion. This is a kinetic question. We must know not only the

stoichiometry of the reaction but also the rates of the forward and the reverse reactions.

We might also wish to know how much heat must be transferred to or from the reactor to

maintain isothermal conditions. This is a heat transfer problem in combination with a

thermodynamic problem. We must know whether the reaction is endothermic or

exothermic.

After chemical reaction a series of physical treatment steps is usually required to purify

the product and perhaps recycle unreacted material back to the reactor. The quantity of

material to be processed is a key factor in determining what type of reactor should be

used. For small-lot quantities, a batch reactor is commonly used in industry. For large,

high-volume reactions, such as in the petroleum industry, flow reactors are common.

I. Reactor Classifications

Reactors may be classified by several different methods depending on the variables of

interest. There is no single clear cut procedure for reactor classification. As a result,

several of the more common classification schemes are presented here.

A. OPERATION TYPE

The operational configuration for the reactor can be a primary method of classification.

1. Batch

Batch reactors are operated with all the material placed in the reactor prior to the start of

reaction, and all the material is removed after the reaction has been completed. There is

no addition or withdrawal of material during the reaction process.

2. Semibatch

The semibatch reactor combines attributes of the batch and the continuous-stirred tank.

The reactor is essentially batch but has either a continuous input or output stream during

operation.

3. Continuous Flow Reactors

Continuous flow reactors represent the largest group of reactor types by operational

classification. Several continuous flow reactors are used industrially.

a. The continuous-stirred tank reactor (CSTR) involves feeding reactants into a

wellmixed tank with simultaneous product removal.

b. The plug flow reactor (PFR) consists of a long pipe or tube. The reacting mixture

moves down the tube resulting in a change in concentration down the length of the

reactor.

c. In the recycle reactor part of the outlet stream is returned to the inlet of the reactor.

Although not a typical reactor classification by type, the recycle reactor allows for

continuous operation in regimes between CSTR and PFR conditions.

B. NUMBER OF PHASES

Reactors can also be classified by the number of phases present in the reactor at any

time.

1. Homogeneous

Homogeneous reactors contain only one phase throughout the reactor.

2. Heterogeneous

Heterogeneous reactors contain more than one phase. Several heterogeneous reactor

types are available due to various combinations of phases .

a. Gas-liquid

b. Gas-solid

c. Liquid-solid

d. Gas-liquid-solid

Multiphase reactor configurations are strongly influenced by mass transfer operations.

Any of the reactor types presented above can be operated as multiphase reactors.

C. REACTION TYPES

Classification of reactors can also be made by reaction type.

1. Catalytic

Reactions that require the presence of a catalyst to obtain the rate conditions necessary

for that particular reactor design.

2. Noncatalytic

Reactions that do not include either a homogeneous or heterogeneous catalyst.

3. Autocatalytic

Reaction scheme whereby one of the products increases the overall rate of reaction.

4. Biological

Reactions that involve living cells (enzymes, bacteria, or yeast), parts of cells, or

products from cells required for the reaction scheme.

5. Polymerization

Reactions that involve formation of molecular chains, whether on a solid support or in

solution.

D. COMBINATION OF TERMS

Any combination of the above classifications can be used to describe a reactor: for

example, a heterogeneous-catalytic-batch reactor.

II. Primary Reactors

There are five primary reactor designs based in theory: batch, semibatch, continuous-

stirred tank, plug flow, and fluidized bed. The operating expressions for these reactors

are derived from material and energy balances, and each represents a specific mode of

operation. Selected reactor configurations are presented in Fig. 1.

A. BATCH

DESCRIPTION. Batch processes are the easiest to understand since they strongly

relate to "cookbook" technology. You put everything in at the beginning and stop the

reaction at some time later. This cookbook technology allows for immediate production

of a new product without extensive knowledge of the reaction kinetics. [See BATCH

PROCESSING (CHEMICAL ENGINEERING) .]

The reactor is characterized by no addition of reactant or removal of product during the

reaction. Any reaction being carried out with this constraint, regardless of any other

reactor characteristic, is considered batch. The assumptions for batch operation are (1)

the contents of the tank are well mixed, (2) reaction does not occur to any appreciable

degree until filling and startup procedures are complete, and (3) the reaction stops when

quenched or emptied. The reactor can be operated with either a homogeneous or

heterogeneous reaction mixture for almost any type of reaction.

CLASSIFICATION. The batch reactor, one of the five primary reactor configurations,

is the oldest reactor scheme.

DESIGN PARAMETERS. The design parameters for a batch reactor can be as simple

as concentration and time for isothermal systems. The number of parameters increases

with each additional complication in the reactor. For example, an additional reactant

requires measurement of a second concentration, a second phase adds parameters, and

variation of the reaction rate with temperature requires additional descriptors: a

frequency factor and an activation energy. These values can be related to the reactor

volume by the equations in Section III.

FIG. 1. Selected reactor configurations: (a) batch, (b) continuous stirred-tank reactor, (c)

plug flow reactor, (d) fluidized bed, (e) packed bed, (f) spray column, and (g) bubble

column.

APPLICATIONS. Application of the batch reactor design equations requires integration

over time. Along with the simplicity of cookbook chemistry, this is one of the major

advantages of the batch reactor: concentrations are not averaged over time. Initially,

when concentrations are at their highest, the corresponding rates of reaction are also high.

This gives the greatest amount of conversion in the shortest time. The integral reactor

design form makes the batch reactor attractive for higher-order reactions. Batch is also

good for reactions in series (if the reaction can be quickly quenched), where large

amounts of an intermediate can be produced quickly before it has time to react away to a

by-product.

The batch reactor is extremely flexible compared with continuous reactor

configurations. For example, temperature can easily be made a function of reaction time.

Once the reactor is put into service, operational alternatives are still available. The tank

can be operated half-full without affecting product quality, or the reaction time can be

modified easily. Both of these changes may cause heat and mass transfer problems in

fixed-volume continuous equipment. This flexibility is worthwhile for products that are

made in various grades, have seasonal demand, or have subjective specifications such as

the taste of beer.

Batch reactors are used extensively in industries where only small quantities of product

are made, such as pharmaceuticals. For small amounts, the economy of scale hurts flow

reactors, which typically have a higher initial investment for controls and plumbing.

ADVANTAGES-DISADVANTAGES. The primary advantages of the batch reactor

are simplicity of design, which allows for tremendous flexibility, and integration of the

performance equation over time. The simplicity of design, usually a stirred tank, makes

operation and monitoring easy for the majority of reactions. The integrated form of the

performance equation has varied significance depending on the particular reaction

scheme being performed. For example, molecular weight distributions in polymerization

reactions can be controlled more precisely in batch reactors.

One of the traditional disadvantages of the batch reactor has been the labor required

between runs for emptying and filling the tank. With recent advances in computer

control, this disadvantage no longer exists. If the advantages of batch are significant, the

capital expense of computer control is essentially negligible. Due to computer control,

the batch reactor should no longer be looked upon as something to be avoided. If the

kinetics and design parameters indicate that batch is a competitive design, then use it.

The major disadvantage of batch reaction now is the hold-up time between batches.

Although the actual reaction time necessary to process a given amount of feed may be

substantially less than for a time-averaged reactor such as a CSTR, when the hold-up

time is added, the total process time may be greater. Other disadvantages of the batch

reactor are dependent on the particular type of reaction being considered, such as whether

the reaction is in parallel or serles.

B. SEMIBATCH

DESCRIPTION. The semibatch reactor is a cross between an ordinary batch reactor

and a continuous-stirred tank reactor. The reactor has continuous input of reactant

through the course of the batch run with no output stream. Another possibility for

semibatch operation is continuous withdrawal of product with no addition of reactant.

Due to the crossover between the other ideal reactor types, the semibatch uses all of the

terms in the general energy and material balances. This results in more complex

mathematical expressions. Since the single continuous stream may be either an input or

an output, the form of the equations depends upon the particular mode of operation.

Physically, the semibatch reactor looks similar to a batch reactor or a CSTR. Reaction

occurs in a stirred tank, with the following assumptions: (1) the contents of the tank are

well mixed, and (2) there are no inlet or outlet effects caused by the continuous stream.

CLASSIFICATION. The semibatch reactor is one of the primary ideal reactor types

since it can not be accurately described as either a continuous or a batch reactor. A

semibatch reactor is usually classified as a type of transient reactor.

DESIGN PARAMETERS. The major design parameters for a semibatch reactor are

similar to a batch reactor with the addition of flow into or out of the tank.

APPLICATIONS. The advantage of this reactor, with feed only, is for the control of

heat of extremely exothermic reactions. By inputting the feed gradually during the

course of the reaction, the concentration of feed in the reactor can be kept lower than in

normal batch operation. Also, the temperature of the feed stream, when cooler than the

reaction mixture, has a quenching effect. Some of the heat released during the reaction is

used to heat the feed material, thereby reducing the required capacity of the heating coils.

The semibatch can also be used to control the kinetics in multiple reaction sequences.

The selectivity may be shifted to one reaction by adding a reactant slowly. This keeps

one reactant concentration high with respect to the other.

The semibatch can also be used for continuous product removal, such as vaporization of

the primary product. This can increase yield in equilibrium limited reactions.

ADVANTAGES-DISADVANTAGES. The temperature-controlling features of this

reaction scheme dominate selection and use of the reactor. However, the semibatch

reactor does have some of the advantages of batch reactors: temperature programming

with time and variable reaction time control.

The temperature conditions and the batch nature of this reactor are the primary

operational difficulties and make the reactor impractical for most reactions, even for

computer-controlled systems. The majority of reactions considered for semibatch are

highly exothermic and, as such, are dangerous and require special attention.

C. CONTINUOUS-STIRRED TANK

DESCRIPTION. The continuous-stirred tank reactor (CSTR) has continuous input and

output of material. The CSTR is well mixed with no dead zones or bypasses in ideal

operation. It may or may not include baffling. The assumptions made for the ideal CSTR

are (1) composition and temperature are uniform everywhere in the tank, (2) the effluent

composition is the same as that in the tank, and (3) the tank operates at steady state. [See

FLUID MIXING.]

We traditionally think of the CSTR as having the appearance of a mixing tank. This

need not be the case. The above assumptions can be met even in a long tube if the

mixing characteristics indicate high dispersion levels in the reactor. This is particularly

true of gassed liquids where the bubbling in the column mixes the liquid.

CLASSIFICATION. The continuous-stirred tank reactor is one of the two primary

types of ideal flow reactors. It is also referred to as a mixed-flow reactor, back-mix

reactor, or constant-flow stirred-tank reactor.

DESIGN PARAMETERS. The CSTR is not an integral reactor. Since the same

concentration exists everywhere, and the reactor is operating at steady state, there is only

one reaction rate at the average concentration in the tank. Since this concentration is low

because of the conversion in the tank, the value for the reaction rate is also low. This is

particularly significant for higherorder reactions compared with integral reactor systems.

Time is still an important variable for continuous systems, but it is modified to relate to

the steady-state conditions that exist in the reactor. This time variable is referred to as

space time. Space time is the reactor volume divided by the inlet volumetric flow rate. In

other words, it is the time required to process one reactor volume of feed material. Since

concentration versus real time remains constant during the course of a CSTR reaction,

rate-data acquisition requires dividing the difference in concentration from the inlet to the

outlet by the space time for the particular reactor operating conditions.

APPLICATIONS. The CSTR is particularly useful for reaction schemes that require

low concentration, such as selectivity between multiple reactions or substrate inhibition

in a chemostat (see Section IV). The reactor also has applications for heterogeneous

systems where high mixing gives high contact time between phases. Liquid-liquid

CSTRs are used for the saponification of fats and for suspension and emulsion

polymerizations. Gas-liquid mixers are used for the oxidation of cyclohexane. Gas

homogeneous CSTRs are extremely rare.

ADVANTAGES-DISADVANTAGES. The advantages for CSTRs include (1) steady-

state operation, (2) back mixing of heat generated by exothermic reactions, which

increases the reaction rate and subsequent reactor performance, (3) avoidance of reactor

hot spots for highly exothermic reactions, making temperature easier to control, (4)

favoring lower-order reactions in parallel reaction schemes, (5) economical operation

when large volumes require high contact time, and (6) enhancement of heat transfer by

mixing.

For the kinetics of decreasing rate with increasing conversion (most reactions),

isothermal CSTRs have lower product composition than plug flow reactors. Additional

disadvantages of CSTR are that larger reactor volumes are usually required, compared

with other reactor schemes, and that energy for agitation is required in the tank,

increasing operating costs .

D. PLUG FLOW

DESCRIPTION. This reactor has continuous input and output of material through a

tube. Assumptions made for the plug flow reactor (PFR) are (1) material passes through

the reactor in incremental slices (each slice is perfectly mixed radially but has no forward

or backward mixing between slices; each slice can be envisioned as a miniature CSTR),

(2) composition and conversion vary with residence time and can be correlated with

reactor volume or reactor length, and (3) the reactor operates at steady state.

The PFR can be imagined as a tube, but not all tubular reactors respond as PFRs. The

assumptions need to be verified with experimental data.

CLASSIFICATION. The plug flow reactor is the second primary type of ideal flow

reactor. It is also erroneously referred to as a tubular reactor.

DESIGN PARAMETERS. The parameters for PFRs include space time, concentration,

volumetric flow rate, and volume. This reactor follows an integral reaction expression

identical to the batch reactor except that space time has been substituted for reaction

time. In the plug flow reactor, concentration can be envisioned as having a profile down

the reactor. Conversion and concentration can be directly related to the reactor length,

which in turn corresponds to reactor volume.

APPLICATIONS. For normal reaction kinetics the plug flow reactor is smaller than the

continuous-stirred tank reactor under similar conditions. This gives the PFR an

advantage over CSTR for most reactions. These conditions are best met for short

residence times where velocity profiles in the tubes can be maintained in the turbulent

flow regime. In an empty tube this requires high flow rates; for packed columns the flow

rates need not be as high. Noncatalytic reactions performed in PFRs include high-

pressure polymerization of ethylene and naphtha conversion to ethylene. A gas-liquid

noncatalytic PFR is used for adipinic nitrile production. A gas-solid PFR is a packed-bed

reactor (Section IV). An example of a noncatalytic gas-solid PFR is the convertor for

steel production. Catalytic PFRs are used for sulfur dioxide combustion and ammonia

synthesis.

ADVANTAGES-DISADVANTAGES. The advantages of a PFR include (1) steady

state operation, (2) minimum back mixing of product so that concentration remains

higher than in a CSTR for normal reaction kinetics, (3) minimum reactor volume in

comparison with CSTR (since each incremental slice of the reactor looks like an

individual CSTR, we can operate at an infinite number of points along the rate curve), (4)

application of heat transfer in only those sections of the reactor where it is needed

(allowing for temperature profiles to be generated down the reactor), and (5) no

requirement for agitation and baffling.

The plug flow reactor is more complex than the continuous-stirred tank alternative with

regard to operating conditions. There are a few other disadvantages associated with the

PFR. For the kinetics where rate increases with conversion (rare), an isothermal plug

flow reactor has lower product composition than a CSTR. For highly viscous reactants,

problems can develop due to high-pressure drop through the tubes and unusual flow

profiles.

E. FLUIDIZED BED

DESCRIPTION. Fluidization occurs when a fluid is passed upward through a bed of fine

solids. At low flow rates the gases or liquids channel around the packed bed of solids,

and the bed pressure drop changes linearly with flow rate. At higher flow rates the force

of the gas or liquid is sufficient to lift the bed, and a bubbling action is observed. During

normal operation of a fluidized bed the solid particles take on the appearance of a boiling

fluid. The reactor configuration is usually a vertical column. The fluidized solid may be

either a reactant, a catalyst, or an inert. The solid may be considered well mixed, while

the fluid passing up through the bed may be either plug flow or well mixed depending on

the flow conditions. Bubble size is critical to the efficiency of a fluidized bed. [See

FLUIDIZED BED COMBUSTION.]

CLASSIFICATION. Fluidized reactors are the fifth type of primary reactor

configuration. There is some debate as to whether or not the fluidized bed deserves

distinction into this classification since operation of the bed can be approximated with

combined models of the CSTR and the PFR. However, most models developed for

fluidized beds have parameters that do not appear in any of the other primary reactor

expressions .

DESIGN PARAMETERS. In addition to the usual reactor design parameters, height of

the fluidized bed is controlled by the gas contact time, solids retention time, bubble size,

particle size, and bubble velocity.

APPLICATIONS. Fluidized beds are used for both catalytic and noncatalytic reactions.

In the catalytic category, there are fluidized catalytic crackers of petroleum, acrylonitrile

production from propylene and ammonia, and the chlorination of olefins to alkyl

chlorides. Noncatalytic reactions include fluidized combustion of coal and calcination of

lime.

ADVANTAGES-DISADVANTAGES The fluidized bed allows for even heat

distribution throughout the bed, thereby reducing the hot spots that can be observed in

fixed-bed reactors. The small particle sizes used in the bed allow high surface area per

unit mass for improved heat and mass transfer characteristics. The fluidized

configuration of the bed allows catalyst removal for regeneration without disturbing the

operation of the bed. This is particularly advantageous for a catalyst that requires

frequent regeneration.

Several disadvantages are associated with the fluidized bed. The equipment tends to be

large, gas velocities must be controlled to reduce particle blowout, deterioration of the

equipment by abrasion occurs, and improper bed operation with large bubble sizes can

drastically reduce conversion.

III. Generalized Reactor Design

Design of a chemical reactor starts with a knowledge of the chemical reactions that take

place in the reactor. The ultimate product of the design is the reactor and the supporting

equipment such as piping, valves, control systems, heat exchangers, and mixers. The

reactor must have sufficient volume to handle the capacity required and to allow time for

the reaction to reach a predetermined level of conversion or yield.

A. APPROACH, CONSIDERATIONS, AND METHODS

1. Use of the Reaction Coordinate or Molar Extent of Reaction

In chemical reactor design, an understanding of the reactions and mechanisms involved is

required before a reactor can be built. In general, this means the chemical reaction

equilibrium thermodynamics must be known before the reactor is even conceptualized.

Any chemical reaction can be written as

a A + b B + ... = r R + s S + ...

where A and B are the reactants, R and S the products, and a, b, r, s are defined as the

stoichiometric coefficients. In general, these stoichiometric coefficients are given a value

of v i (stoichiometric numbers). An arbitrary sign convention is given to the

stoichiometric numbers to make them consistent with thermodynamics: positive signs for

products, negative signs for reactants.

An example for the reaction of methane with ethylene to give butane plus hydrogen is

written as

2 CH4 + C2H4 → C4H10 + H2

Here the stoichiometric number of methane is -2, ethylene -1, butane +1, and hydrogen

+1. If we look at the change in the number of moles of one component, there is a direct

relationship between stoichiometry and the change in the number of moles of any other

component.

N∆

===

∆L

For a differential amount

ε==== d

where ε is the reaction coordinate or molar extent of reaction.

Note that

()

n=i

i...,,2,1dε≡

This equation, with the boundary conditions.

0for

0=ε N=N i

ε=ε for

N=N i

on integration gives

()

n...,,,=ivNN iii 21

0ε+=

The reaction coordinate provides a relationship between the initial number of moles

Ni0 , the reaction coordinate ε , and the number of moles Ni at any point or stage in the

reaction Since the units of the stoichiometric numbers vi are dimensionless, the reaction

coordinate has the same units as Ni (for example, mol, kg mol, or kg mol/sec).

Example. For the gas phase reaction,

2A + B = R + S

seven moles of A are reacted with four moles of B in a batch reactor. A gas-mixture

analysis after reaction showed the final mixture contained 20 mol% R. Calculate the

mole fractions of the other components.

Knowns:

1. NA0 = 7

2. NB0 = 4

3. YR = 0.20

4. NR0 = 0, NS0 = 0

Let: N T = final number of moles. N0 = initial total number of moles, and v = Σ vi .

ε−=ε+=

ε+=ε+=

ε−=ε+=

S0SS

R0RR

B0BB

A0AA

vNN

Since

ε−

=≡

ε−

=≡

But

ε−

=== 11

2.0

so ε = 1.83. Therefore, Ys = 0.20 (as expected from stoichiometry) and

∑=

00.1Y

24.0Y

36.0Y

20.0Y

A similar analysis can be made for many reactions occurring simultaneously. If we have

r independent reactions with n species, their stoichiometric coefficients can be termed vi,

j, with i =1, 2, ..., n species and j = I, II, ..., r reactions. In this case,

ji,

j i,

dN ...,

...,

,II







ε=

and

ji,

dN ...,

...,

II,







∑ε=

Integration gives Ni = Ni 0 + ∑ j vi,j εj

Example.

C2H4 + 2

1 O 2 = C 2 H 4 O

C2 H4 + 3 O 2 = 2 CO 2 + 2 H 2 O

Initially, one mole of C2 H4 and three moles of air (~21% O 2 ) react. Derive an expression

relating the mole fractions of each of the components. For the reactions

A +

1 B = C

εI (extent of reaction, 1st reaction)

and

A + 3 B = 2 D + 2 E

ε II (extent of reaction, 2nd reaction)

Knowns:

1. N A0 = 1 mol

2. N B0 = (.21) (3) = .063 mol

NC0 = ND0 = NE0 = 0

N2 is an inert, that is, NI0 = Nl = (0.79)

(3) = 2.37 mol

In genera1,

Ni = Ni0 +

()

II,IJ

j=ε

∑

jji,

NA = N A0 + v A,I ε I + v A,II ε II = 1 - ε I - ε II

NB = NB0 + vB,I εI + v B ,II εII = 0.63 - 2

1ε I - 3 ε II

NC = NC0 + v C ,I εI + vC,II εII 0 + εI

ND = ND0 + v D, I εI + vD,II εII = 0 + εII

NE = NE0 + vE,I εI + vE, II εII = 0 + εII

NI = NI0 + vI,I εI + vI,II εII = 2.37 + 0εI + 0εII

NT = NT0 + vi,j εj = 4 -

∑∑

ij 2

1 ε I

Therefore,

III

Aε−

ε−ε−

= Y

and

63.0

Bε−

−ε−

= Y

Similar expressions are prepared for the remaining components.

In general, the reaction coordinate or molar extent of reaction is a bookkeeping method.

Numerical values of the reaction coordinate depend on how we write the chemical

reaction. When the initial moles are unknown or when preliminary calculations are done,

a basis of one mole of feed is usually assumed. The numerical value of the reaction

coordinate depends on this basis but cancels out when mole fractions are calculated.

Another commonly used method for determining the extent of reaction is conversion.

Conversion is based on initial and final molar quantities of a reactant. This molar basis

can be written in terms of either total moles of reactant or in terms of molar flow rate. In

equation form,

A0A

X−

where XA is the conversion of reactant A between 0 and 1, N A0 the initial moles of

reactant A or initial molar flow rate of A, and NA the final number of moles or outlet

molar flow rate of A.

For single reactions, fractional conversion is normally the preferred measure of the

extent of reaction. However, for multiple reactions the reaction coordinate is the method

of choice. The relationship that exists between conversion and the reaction coordinate is

Xε

−=

2. Rate Expressions

Before designing a chemical reactor, one must know the reaction(s) rate. Rates of

reaction can be written in intrinsic form or in terms of a specific reactant of interest. An

intensive measure, based on a unit volume of fluid, is normally used for homogeneous

reacting systems. Thus, the general definition of reaction rate can be written as













=dt

where ri is the number of moles of component i that appear or disappear by reaction per

unit volume and time in kg mol liter -l sec -l , Vt the total volume of reacting fluid in liters,

Ni the number of moles of component i in kg mol, and t the time in seconds. The rates of

formation of products R, S, T ,... are related to the rates of disappearance of reactants A,

B,..., by the stoichiometric numbers,

r=====

With the normal sign convention (positive for products, negative for reactants), a rate is

negative for a reactant (-rA ) and positive for a product (rR ).

Rates of reactions are functions of the thermodynamic state of the system. For a simple

system, fixing temperature and composition fixes the rest of the thermodynamic

quantities or the state. Thus, the rate can be written in terms of a temperature-dependent

term called the rate constant k (constant at fixed temperature) and a concentration term or

terms Ci .

Example.

AA C kr =−

Rates of reaction vary with changes in temperature or concentration. All reactions are

reversible (i.e., have a forward and a reverse reaction). When the rate of the forward

reaction equals the rate of the reverse reaction, there is no net change in concentrations of

any component, and the system is said to be at thermodynamic equilibrium. This

condition represents a minimum free energy of the system and determines the limits of

conversion. The overall rate of reaction equals zero at equilibrium. A relationship can

be derived between the forward and reverse rate constants and the overall thermodynamic

equilibrium constant. For example, consider the reaction

A + B R + S

→ ←

If the forward rate equals k 1CACB, and the reverse rate equals k 2 CRCS, the overall rate of

disappearance of component A is -r A = k l CACB - k 2 CRCS . At equilibrium, -r A ≅ 0,

k≡=

where K c is defined as the thermodynamic equilibrium constant based on concentration.

Reactions that have very high values of the equilibrium constant are termed irreversible

since the value of k2 must be very small. Without much loss of accuracy, these equations

can be modeled as dependent only on the forward rate. In this example, if the reaction is

essentially irreversible, -rA = k l CAC B .

Rate expressions must ultimately come from an analysis of experimental data. We

cannot normally write a rate equation by inspection of the stoichiometric reaction

equation; however, a reaction is termed elementary if the rate expression can be written

by inspection based on the stoichiometric numbers.

Consider the following reversible reaction

A + B = 2 R

→ ←

If this reaction is elementary, the rate expression can be written as

A1 CkCCk

r−=−

In general, an elementary reaction has the form:

KK sCR

vvvv −=−

Reactions are classified by their order depending on the sum of the stoichiometric

coefficients of each term.

Examples.

-rA = k zero order

-rA = k CA first-order irreversible

-rA = k C2A second-order irreversible

-rA = k 1 CA - k 2 CR first-order reversible

A+

=− r complex

complex

7.0

3.0

AA CkCr =−

3. Use of Kinetic Data

To design a chemical reactor the rate expression must be known. Assuming the

reaction is known not to be elementary, we must search for a mechanism that describes

the reaction taking place or use experimental data directly. Mechanisms can be

hypothesized as the sum of a series of elementary reactions with intermediates. Using

methods developed by physical chemists, we can hypothesize whether the proposed

mechanism fits the actual experimental evidence. If no inconsistencies are found, the

hypothesized mechanism is possibly the actual mechanism. However, agreement of the

mechanism with the experimental data does not necessarily mean that the proposed

mechanism is correct, since many mechanisms can be hypothesized to fit such data.

An interpretation of batch or flow reactor data is used to fit an empirical rate

expression. For example, in a simple batch reactor, concentration is measured as a

function of time. Once the experimental data are available, two methods can be used to

fit a rate expression.

The first, called the integral method of data analysis, consists of hypothesizing rate

expressions and then testing the data to see if the hypothesized rate expression fits the

experimental data. These types of graphing approaches are well covered in most

textbooks on kinetics or reactor design.

The differential method of analysis of kinetic data deals directly with the differential

rate of reaction. A mechanism is hypothesized to obtain a rate expression and a

concentration-versus-time plot is made. The equation is smoothed, and the slopes, which

are the rates at each composition, are evaluated. These rates are then plotted versus

concentration; and if we obtain a straight line passing through the origin, the rate

equation is consistent with the data. If not, another equation is tested. Kinetic data can

also be taken in flow reactors and evaluated with the above methods and the reactor

design equation.

4. Temperature Dependence of the Rate Constant

On a microscopic scale, atoms and molecules travel faster and, therefore, have more

collisions as the temperature of a system is increased. Since molecular collisions are the

driving force for chemical reactions, more collisions give a higher rate of reaction. The

kinetic theory of gases suggests an exponential increase in the number of collisions with

a rise in temperature. This model fits an extremely large number of chemical reactions

and is called an Arrhenius temperature dependency, or Arrhenius' law. The general form

of this exponential relationship is

RTE

0−

=ekk

where k is the rate constant, k 0 the frequency factor of pre-exponential, E the activation

energy, R the universal gas constant, and T the absolute temperature. For most reactions,

the activation energy is positive, and the rate constant k increases with temperature.

Some reactions have very little or no temperature dependence and therefore activation

energy values close to zero. A few complex reactions have a net negative activation

energy and actually decrease with temperature. These reactions are extremely rare.

The Arrhenius temperature dependency for a reaction can be calculated using

experimental data. The procedure is to run a reaction at several different temperatures to

get the rate constant k as a function of absolute temperature. From the previous equations

ln k = ln k 0 - E/RT; the natural log of k is then plotted versus the reciprocal of the

absolute temperature. The slope of this line is then -E/R, and the intercept is the ln k 0 .

B. DESIGN EQUATIONS

1. General Reactor Design Equation

All chemical reactors have at least one thing in common: Chemical species are created or

destroyed. In developing a general reactor design equation, we focus on what happens to

the number of moles of a particular species i . Consider a region of space where chemical

species flow into the region, partially reacts, and then flows out of the region. Doing a

material balance, we find

rate in - rate out + rate of generation

= rate of accumulation

In equation form

i=+− G

0&&

where is the molar flow rate of i in, the molar flow rate of i out, G

0 i

&i the rate of

generation of i by chemical reaction, and dNi /dt the rate of accumulation of i in the

region. The rate of generation of i by chemical reaction is directly related to the rate of

reaction by

∫dVr

2. Ideal Batch Reactor Equation

A batch reactor has no inlet or outlet flows, so . 0

ii nn && Perfect mixing is

assumed for this ideal reactor, and the rate ri is independent of position. This changes

our generation term in the general reactor design equation to

∫= t

0Vrr ii dV

Then, by the general design equation, our ideal batch reactor equation becomes

dN r

This equation does not define the rate ri , which is an algebraic expression independent of

reactor type such as ri = kCi 2 .

a. Constant Volume Batch Reactors. For the special case of constant volume or

constant density (usually values for the mixture, not the reactor), we can simplify the

ideal batch reactor equations. Starting with the ideal batch reactor equation

the volume is placed inside the differential and changed to concentration:

/VNd ==

[constant

Vt , ideal batch reactor].

This equation is usually valid for liquid-phase reactions and for gas reactions where the

sum of the stoichiometric numbers equals zero, but it is invalid for constant pressure gas-

phase reactions with mole changes.

When the rate expression is known, this equation yields the major design variable, time,

for a batch reaction of given concentration or conversion.

Example. A → B + C (irreversible, aqueous reaction). The rate expression can be

written as

A = -kC A

Using this rate expression and the constant density ideal batch reactor equation gives

AkC

dC −=

Integrating with an initial concentration CA0 at t = 0 gives

ln kt

−

A= [constant volume, Vt ]

where t is the time for the batch reaction.

It is often convenient to work with fractional conversion of a reactant species. Let i = A,

a reactant, then

A0A

A/VN

/VN/VN

X−

−

and if Vt is constant,

AAO

X−

= [constant Vt ]

Substituting into the ideal batch reactor equation gives

A0 r

C=− [constant Vt ]

Example. A → B + C (elementary, constant volume reaction). The rate expression can

then be written as

)

AA0AA x1kCkCr

−=−=

where CA = CA0 (1 - XA ). Therefore,

()

AA0

A0 X1kC

C−−=−

Integrating with the boundary condition XA = 0 at t = 0, gives

-ln (1 - XA ) = kt [constant V t ]

Given a rate constant k and a desired conversion, the time for the batch reaction can be

calculated.

b. Variable Volume Batch Reactors. In general, the equations developed previously

assumed constant volume or constant density. For gas-phase reactions such as A + B = C,

the total number of moles decrease, and the volume (or density) changes.

Our ideal batch reactor equation, written in terms of any reactant A, can be changed to

reflect a change in volume. For example,

r−=−=−











+− dt

=− r











+−=− dt

From thermodynamics, assuming ideal solutions, we can derive an expression relating the

volume at any conversion with the original volume,























∑

+= A

where Vi is the molar specific volume of component i. This expression is usually

simplified by defining an expansion factor in terms of any reactant; for A,

VvN ii

∑

≡

and

Vt = Vt0 (1 + EA XA )

This changes the ideal batch reactor equation to

=−

where

VvC

Eii

∑

≡

and assumes constant temperature, pressure, and ideal solutions.

For the special case of an ideal gas mixture,

Ci == and

which leads to an easy formula to calculate the change in volume factor.

where YA0 is the initial mole fraction of A, v the sum of the stoichiometric numbers, and

vthe stoichiometric number of component A.

Example. A → 3 R. Given that the feed is 50% A and 50% inerts, calculate EA . By

stoichiometry,

()()

0.1

25.0

50.0

213

100A

−

∑=−==

=−=

c. Summary of Ideal Batch Reactor Design Equations.

General Case.

tt r

i≡=

VdC

dC r

ln t

A0A

X−

≡ [for reactant A]

0A r −=













Constant Temperature and Pressure Ideal Solution.

i0A

VvC

∑

≡

AA0A

0A r −=













+dt

CEC

ldeal Gas.

E≡

0A r

1−=













+dt

Constant Volume.

dC r =

0A r −=

3. Single Ideal Flow Reactor

For batch reactors, time is the key design variable. The batch reactor design equations

answer the question: How long does it take to obtain a specified conversion or

concentration?

With flow reactors, volume is the key design variable. For a given feed rate,

how big must the reactor be to get a specified conversion?

a. Ideal Continuous-Stirred Tank Reactor Design Equations. Very well

mixed unreacted material flows into a vessel, reacts, and exits the reactor along

with converted product. Starting with the general reactor design equation, several

assumptions are made to reduce the equation to a usable form.

dVrnn i

iii =

∫

+− t

0&&

CSTR Assumptions.

1. There is no accumulation in the reactor of any species i . This implies the

reactor is at steady-state flow conditions.

0 =

dN i

2. There is perfect mixing in the reactor. This implies no spatial variations of

rate in the reactor, and the composition of the exit stream is the same as the

composition anywhere in the reactor.

0VrdVr ii =

∫

These assumptions then give the ideal CSTR design equation

ii nn

t&& −

If this equation is written for a reactant species A, the resulting equation is

A0A

r −

−

=nn &&

Noting that

)

A0AA 1Xnn −= && , we can rewrite the ideal CSTR design equation

in terms of conversion of reactant A, as

0AA

r −

=nX &

For the special case of constant density or constant volume of the reacting fluid,

this equation is written

)

()

A0A

A0A0A

0AA

rr −

−

CCnnX &&

b. Ideal Plug Flow Reactor Design Equation. Unreacted material flows into

the reactor, a pipe or tube that has a large enough length and volume to provide

sufficient residence time for the fluid to react before exiting. The assumption of

ideal plug flow indicates that the composition in the reactor is independent of

radial position. Unlike in a stirred-tank reactor, the composition changes as the

fluid flows down the length of the reactor. The design equation for an ideal PFR

is derived by a differential material balance assuming steady-state flow in the

reactor. This gives

()

∫=+−+ t

iiii ndndVrn &&&

Upon simplification the resulting ideal plug flow reactor equation is

In terms of a reactant A and conversion, this equation can be written as

∫−

For the special case of a constant density PFR, the preceding equation can be

simplified by noting that

A0A

X−

dX −= [constant volume]

Therefore,

∫−

−= A

0A A

For the special case of a packed bed catalytic reactor with plug flow, the equation

is rewritten in terms of catalyst weight,

∫′

where W c is the weight of catalyst in kg and ri ' the rate constant based on a unit

volume of catalyst in mol sec- 1 kg- 1 catalyst.

4. Space Time

It is useful to have a measure of time for a flow reactor even though the major

design variable is reactor or fluid volume. A commonly used quantity in

industrial reactor design is space time. Space time is defined as the time required

to process one reactor volume of feed, measured at some set of specified

conditions. The normal conditions chosen are the inlet concentration of a reactant

and inlet molar or volumetric flow rate.

Volumetric flow rate into the reactor is defined as

&≡

Since time is obtained when total volume is divided by volumetric flow rate, a

quantity r called space time is defined

&==

Since space time is defined for the inlet conditions, it is constant no matter what

happens in the reactor. Our design equations for a CSTR and a PFR can be

modified to reflect this quantity.

CSTR,

A0A

−

PFR, ∫−

For the special cases of constant density, these equations simplify to

CSTR,

A0A

C-C

−

[constant volume or density]

PFR, ∫−

−= A

[constant volume or density]

5. Transient Stirred-Tank Reactors

Design equations for unsteady-state operation are needed for start-up of CSTRs

or for semibatch operation. These equations must have the ability to predict

accurately the concentration or conversion changes before steady-state flow is

obtained. Starting with the general design equation, and assuming perfect mixing,

we obtain

Vrnn i

iii =+− t

0&&

Since

Cni =

000

VCN

VCn

and

VdN ≡

tt dVCdC iii +

upon substitution the resulting equation is

=−

−+

iii r

VCdtdVVC

dC &&

C. DESIGN CONSIDERATIONS

1. Batch Versus Flow Reactors

Commercial-scale batch reactors are generally used for small-lot or specialty

items. This includes chemicals such as paints, dyes, and pharmaceuticals. Batch

reactors are very simple and flexible. Vessels used to make one compound can be

washed and reused to make other products. The ease of cleaning and maintaining

batch reactors along with low capital investment and low instrumentation costs

make the batch reactor particularly attractive in industrial applications.

The batch reactor also has disadvantages. These include high labor cost, manual

control, poor heat transfer conditions, and mixing problems. Poor heat transfer

results from relatively low area-to-volume ratios. This can be avoided with the

use of internal coils or external recycle heat exchangers. Batch reactors are

generally not suitable for highly endothermic or highly exothermic reactions.

These heat effects can be partially avoided by running in a semibatch operation.

Good mixing is required for approaching theoretical conversion. Depending on

impeller design, a power of 0.5-1.0 kW/m3 produces 90% of the calculated

theoretical conversion. Care must be taken to design batch reactors with a

heightto-diameter ratio close to one. For larger ratios, pump circulation or

baffling is required. For high-pressure reactions, sealing problems may be

encountered on the agitator shaft.

Perhaps the biggest disadvantage of a batch reactor is the difficulty encountered

for isolation of intermediates. For series reactions such as A → B → C, where B

is the desired product, it is difficult to stop the reaction (quench) without

overshooting.

Continuous tubular flow reactors are most commonly used for large quantity

items such as chemicals manufactured in the petroleum industry. There are many

advantages of continuous tubular flow reactors. Labor costs are very low, and

automatic control is easy to implement. Liquid- or gas-phase homogeneous

reactions are routine for all temperature and pressure ranges. Heterogeneous

reactions, such as solid-catalyzed reactions, are easily run in packed beds or

packed tube reactors. Intermediates are easy to isolate for any desired conversion,

since the reactor length can be adjusted. Heat transfer is relatively good with

large area-to-volume ratios and can be made as large as required by using smaller

tubes. For large heat effects, the reactor can be designed as a counter-current heat

exchanger or as a single jacketed reactor. For highly endothermic reactions, the

reactor tubes can be placed in a furnace and heated radiantly or with hot

combustion gases.

Tubular flow reactors are usually inflexible. Normally they are designed and

dedicated to a single process. They are typically hard to clean and maintain, have

high capital costs, and depending on materials and geometry, are rarely stock

items.

To achieve desired conversions predicted by ideal design equations, plug flow is

required. This implies turbulent flow and higher energy costs if packing is used.

Mass transfer can also be a problem. Axial diffusion or dispersion tends to

decrease residence time in the reactor. High values of the length-to-diameter

ratios (L/D > 100) tend to minimize this problem and also help heat transfer.

Continuous-stirred tank reactors lie somewhere between tubular and batch

reactors. Mixing and heat transfer problems are similar to those of batch reactors.

However, many of the stirred-tank reactors have benefits of the tubular flow

reactors. These include isolation of intermediates, automatic control, and low

labor costs .

2. Heat Effects

Most reactors used in industrial operations run isothermally. For adiabatic

operation, principles of thermodynamics are combined with reactor design

equations to predict conversion with changing temperature. Rates of reaction

normally increase with temperature, but chemical equilibrium must be checked to

determine ultimate levels of conversion. The search for an optimum isothermal

temperature is common for series or parallel reactions, since the rate constants

change differently for each reaction. Special operating conditions must be

considered for any highly endothermic or exothermic reaction.

3. Design for Multiple Reactors

Common design problems encountered in industrial operations include size

comparisons for single reactors, multiple reactor systems, and recycle reactors.

a. Size Comparisons of Single Isothermal Flow Reactors. The rate of

reaction of a CSTR is always fixed by the outlet concentrations. Since the rate is

constant (first- or second-order, etc.), a large volume is required to provide

enough time for high conversion. In general, a plug flow reactor is much more

efficient and requires less volume than a stirred-tank reactor to achieve the same

level of conversion. In a plug flow reactor, the rate changes down the length of

the reactor due to changes in reactant concentrations. High initial rates prevail in

the front of the reactor with decreasing rates near the end. The overall integration

of these rates is much higher than the fixed rate in a CSTR of equal volume. For

complex kinetics such as autocatalytic reactions, where the concentrations of both

reactants and products increase the forward rate of reaction, stirred-tank reactors

are preferred and require less volume. Under most common kinetics, a series of

three or four stirred-tank reactors of equal volume in series approaches the

performance of a plug flow reactor.

b. Reactors in Series and Parallel.

i. PLUG FLOW REACTORS. Plug flow reactors are unique in the sense that

operation in parallel or series give the same conversion if the space time is held

constant. This implies, for example, that if a 20-m reactor of fixed diameter is

required to achieve a given conversion, the same conversion and capacity can be

achieved by running ten 2-m reactors in series or ten 2-m reactors in parallel. The

split of the feed in the parallel case must be one tenth of the total to keep the same

space time. In industrial applications the geometry chosen is a function of cost of

construction, ease of operation, and pressure drop. Parallel operation is normally

preferred to keep the pressure drop at a minimum.

ii. STIRRED-TANK REACTORS IN SERIES AND PARALLEL. Stirred-tank

reactors behave somewhat differently from plug flow reactors. Operation of

CSTRs in parallel, assuming equal space time per reactor, gives the same

conversion as a single reactor but increases the throughput or capacity

proportional to the number of reactors.

This is not the case for multiple CSTRs in series. CSTRs operated in series

approach plug flow and therefore give much higher levels of throughput for the

same conversion. When we have two reactors of unequal size in series, highest

conversion is achieved by keeping the intermediate concentration as high as

possible. This implies putting the small CSTR before the large CSTR.

c. Plug Flow and Stirred Tank Reactors in Series. When two reactors, a plug

flow and a stirred tank are operated in series, which one should go first for

maximum conversion? To solve this problem the intermediate conversion is

calculated, the outlet conversions are determined, and the best arrangement

chosen. Keeping the intermediate conversion as high as possible results in the

maximum conversion. Concentration levels in the feed do not affect the results of

this analysis as long as we have equal molar feed.

4. Recycle Reactors

In a recycle reactor, part of the exit stream is recycled back to the inlet of the

reactor. For a stirred-tank reactor, recycle has no effect on conversion, since we

are essentially just mixing a mixed reactor. For a plug flow reactor, the effect of

recycle is to approach the performance of a CSTR. This is advantageous for

certain applications such as autocatalytic reactions and multiple reaction

situations where we have a PFR but really require a CSTR.

IV. Special Reactor Configurations

Additional reactors exist that are either completely or partially based on the five

primary reactor types discussed in Section II. They receive special attention due

to specific applications and/or unique mass transfer characteristics.

A. AUTOCLAVE

DESCRIPTION. The autoclave reactor is a small cylindrical reactor, built to

withstand high pressures, used to evaluate the kinetics of hightemperature, high-

pressure reactions and the production of small quantities of specialty chemicals.

The reactor is typically packed with a supported catalyst, and reactant is added by

injection. Pressure in the system is elevated by increasing the temperature of the

autoclave. Additional pressure, if needed, can be obtained with the injection of

additional gaseous reactant or an inert.

CLASSIFICATION. The autoclave is usually a heterogeneous batch reactor

mainly used for high-pressure kinetic studies. The autoclave is typically a solid

catalyzed gas-liquid reaction system.

APPLICATIONS. This reactor allows easy data collection for high-

temperature, high-pressure reaction systems that have difficult flow properties.

This includes reactants that are solid at room temperature or mixtures of solids

and liquids. Typical reactions performed in autoclaves are coal liquefaction,

petroleum residuals and coal liquids upgrading, and high molecular weight

hydrogenation experiments.

B. BLAST FURNACE

DESCRIPTION. The blast furnace, a vertical shaft kiln, is the oldest industrial

furnace. Reactant enters in the top of the shaft and falls down through a

preheating section, a calcinating section, past oil, gas, or pulverized coal burners,

through a cooling section, with the product ash falling through a discharge gate.

CLASSIFICATION. The blast furnace operates continuously although the

individual particles see a batch mode of reaction. The actual reaction conditions

must be based on the batch reactor sequence for the particles since complete

conversion is desired. This requires control of the mass throughput in the

furnace, but primarily it requires accurate temperature control. Control of the

solids is maintained at the bottom discharge port. Gas flow rate is controlled by

blowers or by a stack discharge fan.

APPLICATIONS. Blast furnaces are used for the production of iron from ore

and phosphorus from phosphate rock.

C. BUBBLE COLUMN

DESCRIPTION. The bubble column is a tower containing primarily liquid

(>90%) that has a gas or a lighter liquid sparged into the bottom, allowing

bubbles to rise through the column. The column may contain staging, which

enhances the mass transfer characteristics of the reactor. In countercurrent

operation the reactor is particularly attractive for slightly soluble gases and liquid-

liquid systems. With cocurrent flow and a highly baffled column, the reactor has

mass transfer characteristics similar to those of a static mixer. The reactor may

sometimes contain a solid suspended in the liquid phase.

CLASSIFICATION. The bubble column is a typical gas-liquid heterogeneous

reactor with the design also applicable to liquid-liquid systems. The bubbles rise

through the liquid in plug flow. The liquid is well mixed by the bubbling gas and

seldom follows plug flow assumptions.

APPLICATIONS. The bubble column can withstand high gas velocities and

still maintain high mass transfer coefficients. This column is particularly

attractive for reactions that do not require large amounts of gas absorption or

require well-mixed liquids.

There are numerous applications for bubble columns, for example, gas-liquid

columns include the absorption of isobutylene in sulfuric acid, and liquid-liquid

columns are used for nitration of aromatic hydrocarbons.

D. CHEMOSTAT—TURBIDOSTAT

DESCRIPTION. The chemostat is a biological CSTR where the substrate

concentration in the tank is maintained constant. The turbidostat is similar to the

chemostat except that the cell mass in the reactor is kept constant. The primary

distinction between the two reactors is the control mechanism used to maintain

continuous operation. A unique feature of a biological CSTR is the washout

point. When the flow rate is increased so that the microbes can no longer

reproduce fast enough to maintain a population, the microbes wash out of the

tank, and the reaction ceases. This washout point represents the limits of

maximum flow rate for operation.

CLASSIFICATION. The chemostat is a biological heterogeneous CSTR. The

microbes are considered a solid phase, and for aerobic fermentations, oxygen or

air is bubbled through the tank to allow oxygen mass transfer into the media,

resulting in a three-phase reactor.

APPLICATIONS. Continuous fermentation processes are primarily used in the

research and development stage. However, more chemostat operations are being

used at the production level as the understanding of this reactor increases.

Examples include ethanol fermentation for the production of fuel grade ethanol

and single-cell protein production from methanol substrates.

E. DIGESTOR

DESCRIPTION. The digestor is a biological reactor used mainly for the

treatment of municipal and industrial wastes. Wastes are fed continuously to the

digestor, where some solids settle to the bottom of the tank, and other solids are

matted and lifted to the surface by the gases produced during the fermentation. In

an aerobic digestor the mat is broken and mixed by gas circulation. The solid

sludge in the bottom of the tank is raked down a conical bottom and pumped from

the tank. A fraction of the sludge is recycled back to the digestor to maintain a

steady microbial population.

CLASSIFICATION. The digestor is classified as a continuous biological

heterogeneous reactor. Liquid flow through the digestor roughly follows the

CSTR assumptions. Digestion of the solids is a complex mechanism that requires

empirical design equations to describe.

APPLICATIONS. The digestor is mainly restricted to the treatment of

municipal and industrial wastes. Substantial research has been done on using

anaerobic digestion of biomass for the production of methane gas. These systems

are limited to small-scale applications where alternative energy sources are

inadequate. Some current anaerobic digestors use the methane produced as a by-

product to supply heat for operation of the digestor.

F. EXTRUDER

DESCRIPTION. For reactions that require high temperature and pressure for

short periods of time, the extruder is ideal. The reactant is fed to a screw type

device that narrows toward the exit. Friction in the extruder produces high

temperatures and pressures, and the product is forced out dies at the end of the

extrusion tube. This type of extruder is referred to as a dry extruder. If steam is

injected along the extrusion tube, the reactor is referred to as a wet extruder.

CLASSIFICATION. The extruder is essentially a plug flow reactor. Although

the material is being well mixed, this mixing is primarily in the radial and

circumferential directions rather than axially. Due to the extreme conditions in

the extruder, solids can liquefy, resulting in heterogeneous operation.

APPLICATIONS. The extruder is used extensively in the food processing

industry. Grains and starches can be hydrolyzed easily.

G. FALLING FILM

DESCRIPTION. Falling-film reactors have a liquid reactant flowing down the

walls of a tube with a gaseous reactant flowing up or down (usually

countercurrent). This reactor is particularly advantageous when the heat of

reaction is high. The reaction surface area is minimal, and the total reaction heat

generated can be controlled.

CLASSIFICATION. This reactor may follow the plug flow assumptions, or it

may be equilibrium limited depending on the operating conditions.

APPLICATIONS. An example of a reaction performed in a falling-film reactor

is the sulfonation of dodecyl benzene.

H. FERMENTOR

DESCRIPTION. The term fermentation is used to describe the biological

transformation of chemicals. In its most generic application, a fermentor may be

batch, continuous-stirred tank (chemostat), or continuous plug flow (immobilized

cell). Most industrial fermentors are batch. Several configurations exist for these

batch reactors to facilitate aeration. These include sparged tanks, horizontal

fermentors, and biological towers.

CLASSIFICATION. The most traditional application of the fermentor is in

batch mode. In anaerobic fermentations the reactor looks like a normal batch

reactor, since gas-liquid contact is not an important design consideration.

Depending on the reaction, the microbes may or may not be considered as a

separate phase. For aerobic fermentations, oxygen is bubbled through the media,

and mass transfer between phases becomes one of the major design factors.

APPLICATIONS. Since the characteristics of microbes lead to the batch

production of many products, examples of fermentors are numerous. They

include beer vats, wine casks, and cheese crates as anaerobic food production

equipment. The most significant aerobic reactor is the penicillin fermentor.

I. GASIFIERS

DESCRIPTION. A gasifier is used to produce synthesis gas from carbonaceous

material. The solid is packed in a column, and gas is passed up through the bed,

producing a mixture of combustible products, primarily methane, hydrogen

and carbon monoxide, with a low to medium BTU content.

CLASSIFICATION. A gasifier is a continuous gas process in conjunction with

either a batch of solids or continuous solids feed and product removal. The gas

phase passing up through the bed obeys plug flow behavior. In continuous solids

handling, the bed is fed from the top and emptied from the bottom. These solids

also obey plug flow assumptions with flow countercurrent to the gas phase.

APPLICATIONS. Coal gasifiers are used for the production of synthesis gas;

however, any carbon source could be used. Biomass is receiving attention as a

carbon source.

J. IMMOBILIZED CELL

DESCRIPTION. The washout problems associated with continuous

fermentation are eliminated by attaching the microbes or enzymes to a solid

support, preventing them from leaving the reactor. The attachment procedures

vary, and as a result, the flow scheme in the reactor may differ depending on the

choice of attachment. Encapsulation allows shear at the surface of the support so

that fluidization techniques can be used. Attachment onto a surface usually limits

the flow conditions to a packed-bed configuration.

CLASSIFICATION. An immobilized cell reactor is classified as a continuous

biological system that may follow either plug flow theory or fluidized-bed theory

depending on the mode of operation.

APPLICATIONS. The use of immobilizedcell systems is applicable to all

fermentation schemes and is being researched extensively for the production of

alcohols, chemicals, and biological products.

K. JET TUBE

DESCRIPTION. For rapid exothermic reactions that require continuous stirred-

tank operating conditions for good reaction control, a jet tube reactor can be used.

This reactor gives thorough mixing despite the extremely short residence times

involved in these reactions. One reactant is injected into the other through a jet,

orifice, or venturi. This gives high turbulence to insure a well-mixed condition.

Large-scale testing is needed to select the reactor conditions accurately, since

minor errors in kinetic constants are magnified due to the high activation energies

of the reactions. Jets can handle both gas and liquid feed and are usually built in

multiple jet configurations.

CLASSIFICATION. Since reaction does not occur until one reactant is jetted

into the other, the actual jet does not become involved in the kinetics, it is strictly

a method for contacting reactants quickly. The actual reactor performance is

based on CSTR assumptions.

APPLICATIONS. Oil burners are jet tube reactors. Jet washers are used for

fast reactions such as acid-base reactions. An example is the absorption of

hydrochloric acid in sodium hydroxide-sodium sulfite solutions.

L. LAGOON

DESCRIPTION. Lagoons are used for the deposition and degradation of

industrial and human wastes. The waste, in water, is pumped into a holding

lagoon. Water in the lagoon usually evaporates but may be pumped out under

some conditions. The advantage of a biological lagoon is long holding times for

the degradation of compounds that have extremely slow reaction rates.

There are three modes of operation for lagoons. They may be either anaerobic,

aerobic, or facultative (which is a combination of aerobic and anaerobic).

Aerobic lagoons require the additional cost of aerators and compressors for

continuous bubbling of air, oxygen, or ozone into the lagoon.

CLASSIFICATION. The biological lagoon is difficult to categorize since a

reaction and a separation process are occurring simultaneously. Water flow

through the system should ideally be at steady state; however, variable input,

climatic conditions, and rain all affect the water in the system as a function of

time. Chemical concentrations are similar to semibatch operation but may be at a

relatively steady state.

APPLICATIONS. Lagoons are a simple, lowcost reaction system for

wastewater treatment. Anaerobic lagoons are capable of handling

highconcentration wastes but then require an aeration lagoon to treat the water

effluent. Effluent from aerobic lagoons with low-concentration feed usually

requires no additional treatment to meet water quality standards.

M. LOOP REACTOR

DESCRIPTION. For reactions where highpressure requirements do not allow

large diameter tanks for homogeneous reaction kinetics, a loop reactor can be

used. The loop is a recycle reactor made of small diameter tubes. Feed can be

supplied continuously at one location in the loop and product withdrawal at

another.

CLASSIFICATION. Despite its complex construction, the loop is essentially a

stirred-tank reactor. By recirculating fast enough the system can be considered

well mixed. For this to be the case, the rate of recycle must be much greater than

the rate of product withdrawal.

APPLICATIONS. An example for the loop reactor is the oxidation of normal

butane.

N. PACKED BED

DESCRIPTION. The packed bed reactor is used to contact fluids with solids. It

is one of the most widely used industrial reactors and may or may not be catalytic.

The bed is usually a column with the actual dimensions influenced by temperature

and pressure drop in addition to the reaction kinetics. Heat limitations may

require a small diameter tube, in which case total throughput requirements are

maintained by the use of multiple tubes. This reduces the effect of hot spots in

the reactor. For catalytic packed beds, regeneration is a problem for continuous

operation. If a catalyst with a short life is required, then shifting between two

columns may be necessary to maintain continuous operation.

CLASSIFICATION. A packed bed reactor is a continuous heterogeneous

reactor. The gas or liquid phase obeys plug flow theory. The solids are

considered batch, with even long-life catalyst beds losing activity over time.

APPLICATIONS. Noncatalytic packed bed reactors have been discussed

separately in other sections of this article. They include blast furnaces,

convertors, roasting furnaces, rotary kilns, and gasifiers.

O. RECYCLE

DESCRIPTION. A recycle reactor is a mode of operation for the plug flow

reactor in reaction engineering terms. Recycle may also be used in other

configurations involving a separation step. In plug flow some percentage of the

effluent from the reactor is mixed back into the feed stream. The reason for this is

to control certain desirable reaction kinetics. The more recycle in a plug flow

reactor, the closer the operation is to a stirred-tank reactor. Therefore, with

recycle it is possible to operate at any condition between the values predicted by

either CSTR or PFR. There is no advantage in operating a CSTR with recycle

unless a separation or other process is being performed on the recycle stream,

since the CSTR is already well mixed.

CLASSIFICATION. The recycle reactor is used to reach an operating condition

between the theoretical boundaries predicted by the continuous stirred tank

reactor and the plug flow reactor.

APPLICATIONS. The recycle reactor is used to control the reaction kinetics of

multiple reaction systems. By controlling the concentration present in the reactor,

one can shift selectivity toward a more desired product for nonlinear reaction

kinetics.

P. ROASTING FURNACE

DESCRIPTION. Roasting furnaces are in a class of reactors used by the

metallurgical industry in a preparatory step for the conversion of ores to metals.

There are three widely used roasted furnaces: multiple hearth, fluidized bed, and

flash roasters. In the multiple hearth configuration hot gases pass over beds of

ore concentrate. The flash roaster injects pulverized ore with air into a hot

combustion chamber. The fluidized bed roaster operates as described in a

separate heading.

CLASSIFICATION. All of these roasting furnace reactors operate

continuously. They are noncatalytic gas-solid heterogeneous reactors. The

multiple hearth has characteristics similar to plug flow operation. The flash

roaster approaches CSTR, and the third option is a fluidized bed configuration.

APPLICATIONS. Roasting furnaces are used to react sulfides to produce metal

oxides, which can be converted to metals in the next process step. The sulfides

are used as a reducing agent in nonferrous metallurgy for the recovery of metals.

The process has been used for metals such as copper, lead, zinc, nickel,

magnesium, tin, antimony, and titanium.

Q. ROTARY KILNS

DESCRIPTION. The rotary kiln is a long tube that is positioned at an angle

near horizontal and is rotated. The angle and the rotation allow solid reactants to

work their way down the tube. Speed and angle dictate the retention time in the

kiln. Gas is passed through the tube countercurrent to the solid reactant. The kiln

is operated at high temperatures with three or four heating zones depending on

whether a wet or dry feed is used. These zones are drying, heating, reaction, and

soaking. Bed depth is controlled at any location in the tube with the use of a ring

dam.

CLASSIFICATION. The rotary kiln is a continuous countercurrent

heterogeneous reactor. Solids traveling down the kiln are in plug flow, as are the

gases passing upward.

APPLICATIONS. The most common reactor of this type is the lime kiln. This

is a noncatalytic reaction where gas reacts with calcium carbonate moving down

the kiln. Other reactions performed in the rotary kiln include calcination,

oxidation, and chloridization.

Use of rotary kilns for hazardous waste incineration is becoming more common

for disposal of chlorinated hydrocarbons such as polychlorinated biphenyls

(PCBs). Flow in these kilns is cocurrent. Major advantages include high

temperature, long residence time, and flexibility to process gas, liquid, solid, or

drummed wastes.

R. SLURRY TANK

DESCRIPTION. The slurry tank is a threephase reactor where gas is bubbled

up through a liquid-solid mixture. The slurry tank has the advantage of uniform

temperature throughout the mixture. This temperature control is extremely

important for highly exothermic reactions. Another advantage of the slurry tank

is the low intraparticle diffusion resistance for this contacting pattern. As a

disadvantage, low mass transfer rates occur in liquids when compared with gases,

requiring that small solid particles be used. These particles can clog screens in

the effluent stream used to keep solids in the tank, thus making catalyst retention

difficult.

CLASSIFICATION. The slurry tank, when well mixed, can be considered a

continuousstirred tank reactor for both the gas phase and the liquid phase. When

the solid is retained in the reaction vessel, it behaves in a batch mode; however,

catalyst can be removed and regenerated easily in a slurry tank, so activity can be

maintained.

APPLICATIONS. A major application of the slurry tank is the polymerization

of ethylene. Gaseous ethylene is bubbled through a slurry of solvent and

polymer.

S. SPRAY TOWERS

DESCRIPTION. A spray tower is a continuous gas-liquid reactor. Gases pass

upward through a column and contact liquid reactant sprayed into the column.

The spray tower represents the opposite extreme from a bubble tower. The spray

tower has greater than 90% of the volume as gas. This allows for much reduced

liquid-handling rates for highly soluble reactants.

CLASSIFICATION. The spray tower is a heterogeneous gas-liquid reactor.

The gas passing up the column obeys plug flow conditions, and the liquid sprayed

into the column behaves either as plug flow or as batch for individual droplets

falling down the tower.

APPLICATIONS. Spray towers can be used to absorb gaseous reactants. The

most widely used spray tower is for flue gas desulfurization. SO2 in a combustion

gas is passed upward through an alkaline solution that usually contains calcium

oxide. The SO2 is absorbed into the liquid, which then reacts to calcium sulfite

and continues on to calcium sulfate.

T. TRICKLE BED

DESCRlPTlON. A trickle bed is a continuous three-phase reactor. Three

phases are normally needed when one reactant is too volatile to force into the

liquid phase or too nonvolatile to vaporize. Operation of a trickle bed is limited

to cocurrent downflow to allow the vapor to force the liquid down the column.

This contacting pattern gives good interaction between the gaseous and liquid

reactants on the catalyst surface.

CLASSIFICATION. The trickle bed reactor allows for plug flow reactor

assumptions even at extremely low liquid-flow rates. The trickle bed is classified

as a continuous heterogeneous catalytic reactor.

APPLICATIONS. This reactor also allows for easy laboratory scale operation

for determining rate data, since the flow rate is low. Experimental-scale trickle

beds can be on the order of 0.5 in. in diameter. Trickle bed reactors are used for

the hydrodesulfurization of liquid petroleum fractions.

BIBLIOGRAPHY

Froment, G. F., and Bischoff, K. B. (1979). "Chemical Reactor Analysis and

Design." Wiley, New York.

Levenspiel, O. (1972). ''Chemical Reaction Engineering,'' 2nd ed. Wiley, New

York.

Perry, R. H., and Green, D. W., eds. (1984). ''Perry's Chemical Engineers'

Handbook," 6th ed. McGraw-Hill, New York.

Rase, H. F. ( 1977). ''Chemical Reactor Design for Process Plants," Vol. 1,

Principles and Techniques. Wiley Interscience, New York.

Rase, H. F. (1977). ''Chemical Reactor Design for Process Plants," Vol. 2, Case

Studies and Design Data. Wiley Interscience, New York.

Smith, J. M. (1975). ''Chemical Engineering Kinetics." McGraw-Hill, New

York.

Smith, J. M., and Van Ness, H. C. (1975). ''Introduction to Chemical

Engineering Thermodynamics." McGraw-Hill, New York.

Van't riet and Tramper, J. (1991). "Basic Bioreactor Design." Marcel Dekkar,

New York.

... More examples include water evaporation, melting ice cubes, baking breads, and dissolution of salt in water. In modelling the endothermic reaction, some existing researches vary the model parameters around their nominal values instead of sampling them from some distributions, and only consider reacting tank temperature and concentration as state variables or reacting tank temperature, cooling/heating jacket temperature and concentration with the treatment of the volume as a constant [8,9,10,11]. It is with these reasons, there is a need to develop an endothermic CSTR model with varying volume and using advanced sampling technique to study and analyse the uncertainty quantification of model parameters. ...

... 7 : A Densities ( ρ ) and specific heat capacities ( p c ) are constants. 8 : A There is negligible momentum on the system since there is also negligible external stress acting on the system. Based on the eight assumptions above, the system of Ordinary Differential Equations that governs the dynamics of the deterministic variable-volume model for endothermic CSTR is formulated and it is given by Equation (1); ...

This paper deals with the formulation and the identifiability of the variable-volume deterministic model for the endothermic continuously stirred tank reactor (CSTR). The identifiability of physical parameters of the formulated model is done by using the least squares and the delayed rejection adaptive algorithm version of the Markov chain Monte Carlo (MCMC) method. The least square estimates are used as prior information for the MCMC method. To measure the model output associated with the perturbed model parameters, we use global sensitivity analysis implemented in Latin Hypercube Sampling method. The obtained results from partial rank correlation coefficients show that six parameters are very sensitive and correlated with the model outputs. Finally, we show that the least square and the MCMC numerical results impart the model to be realistic, reliable and worthwhile to describe the dynamics of CSTR processes as physical parameters of the model are well identified and their uncertainties in the model response are analysed and quantified.

... Effect of baffles in reactor. For large rectors, the installation of baffles is common practice to provide more effective mixing and heat transfer in the reactor 34 . Without baffles, the fluid would spin freely without achieving good mixing and reaction yield. ...

... For the baffled reactor, only about 10 min was required. This finding confirms the hypothesis that the reactor with rapidly-spinning blades also requires baffles to help improve the heat and mass transfer, as well as flow pattern of liquid resulting in rapid temperature rise causing the endothermic reaction to move forward 34 . They work by disrupting the flow pattern and keeping the movement of the top to the bottom fluid to promote radially axial circulation of the fluid 37 . ...

Fatty acid methyl esters (FAMEs) are sustainable biofuel that can alleviate high oil costs and environmental impacts of petroleum-based fuel. A modified 1200 W high-efficiency food blender was employed for continuous transesterification of various refined vegetable oils and waste cooking oil (WCO) using sodium hydroxide as a homogeneous catalyst. The following factors have been investigated on their effects on FAME yield: baffles, reaction volume, total reactant flow rate, methanol-oil molar ratio, catalyst concentration and reaction temperature. Results indicated that the optimal conditions were: 2000 mL reaction volume, 50 mL/min total flow rate, 1% and 1.25% catalyst concentration for refined palm oil and WCO, respectively, 6:1 methanol-to-oil molar ratio and 62–63 °C, obtaining yield efficiency over 96.5% FAME yield of 21.14 × 10–4 g/J (for palm oil) and 19.39 × 10–4 g/J (for WCO). All the properties of produced FAMEs meet the EN 14214 and ASTM D6751 standards. The modified household food blender could be a practical and low-cost alternative biodiesel production apparatus for continuous biodiesel production for small communities in remote areas.

... The effect of operating conditions on the CSTR's performance with a saponification experiment was conducted in [20] and the results showed that the increase in conversion scale may depend on the increase in CSTR's volume. The neural network approach was used in [21] in order to identify the dynamics of two states, namely the temperature and the concentration of the CSTR's model, and reasonable and precise results were obtained. ...

In this paper, a variable-volume Continuously Stirred Tank Reactor (CSTR) deterministic exothermic model has been formulated based on the Reynold Transport Theorem. The numerical analysis of the formulated model and the identifiability of its physical parameters are done by using the least squares and the Delayed-Rejection Adaptive Metropolis (DRAM) method. The least square estimates provide the prior information for the DRAM method. The overall numerical results show that the model gives an insight in describing the dynamics of CSTR processes, and 14 parameters of the CSTR are well identified through DRAM convergence diagnostic tests, such as trace, scatter, autocorrelation, histograms, and marginal density plots. Global sensitivity analysis was further performed, by using the partial rank correlation coefficients obtained from the Latin hypercube sampling method, in order to study and quantify the impact of estimated parameters, uncertainties on the model outputs. The results showed that 7 among the 14 estimated model parameters are very sensitive to the model outcomes and so those parameters need to be handled and treated carefully.

The degradation of a model compound (p-nitrophenol - PNP) was evaluated by a heterogeneous Fenton process using iron supported on N-doped activated carbon (Fe-ACM) as catalyst in a continuous stirred tank reactor - CSTR. The stability of the catalyst was verified during reutilization and long-term tests, without any iron loss from the catalyst. The presence of a hydroxyl radical scavenger in solution led to a decrease in the process efficiency, showing that PNP degradation and intermediates mineralization is essentially due to a radical mechanism via the hydroxyl species, but the contributes of hydrogen peroxide, and other radicals, should be taken into account. The effect of some relevant operating conditions of the heterogeneous Fenton process, namely the liquid hourly space velocity (LHSV), the residence time (τ) and the dose of oxidant fed in the removal of PNP, mineralization (in terms of reduction of total organic carbon - TOC) and consumption of the oxidant (H2O2) was also assessed by performing a parametric study. The best operating conditions found (pH = 3, T = 50 °C, LHSV = 6.25 min⁻¹, τ = 120 min and [H2O2]feed = 0.75 g/L) enabled to achieve, at steady-stage, removals of PNP, TOC and COD (chemical oxygen demand) of 94, 83% and 86%, respectively, while a nontoxic effluent (0% of inhibition towards Vibrio fischeri) was generated with enhanced biodegradability (improvements of BOD – biological oxygen demand – from <1.0 to 47.5 mgO2/L and BOD:COD ratio from <0.001 to 0.41). The identification and quantification of reaction intermediates was also carried out, being found that the contribution of oxalic acid, in addition to PNP, to the remaining TOC was above 98%.

Asuncion Quintanilla
Gonzalo Vega
Pablo López
Jose A. Casas

Three-dimensional (3D) Fe/SiC monoliths with parallel interconnected channels and different cell geometries (square, troncoconical, and triangular) were manufactured by robocasting and used as catalytic reactors in hydroxylation of phenol using hydrogen peroxide to produce dihydroxybenzenes; the reaction was performed at Cphenol,0 = 0.33 M, Cphenol,0:CH2O2,0 = 1:1 M, WR = 3.7 g, T = 80-90 °C, and τ = 0-254 gcat·h·L-1 with water as a solvent. The values of the apparent kinetic rate constants demonstrated the superior performance of the triangular cell monoliths for hydrogen peroxide decomposition, phenol hydroxylation, and dihydroxybenzene production reactions. A computational fluid dynamic model was validated with the experimental results. It demonstrated that the triangular cell monoliths, with a lower channel hydraulic diameter and not-facing interconnections, provided a higher internal macrotortuosity that induced an oscillating flow of the liquid phase inside the channels, leading to an additional transverse flow between adjacent parallel channels. This behavior, not observed in the other two geometries, resulted in a better overall performance.

Roberto Icken Hernández López

Transketolase (TK) is an interesting enzyme for the biotechnology industry because it can catalyse the formation of specific carbon-carbon bonds with high stereospecificity and selectivity. These characteristics make TK interesting for the formation of high-value chemicals and pharmaceutical intermediates such as those used to synthesise antibiotics and others according to the substrates on the bioconversion. However, its application within large-scale processes is currently limited by low activity on new reactions, and poor stability at the high temperatures often used during industrial processes. One route to overcome these limitations is to use site-directed mutagenesis or directed evolution to improve the enzyme function and stability. The success of directed evolution relies upon designing a suitable screening method that can directly identify the best mutants from large numbers of variants, with the desired set of attributes. This thesis aims to develop an improved screening platform by adaptation of a previous screening method based upon colorimetric reactions. To assess and quantify TK activity towards the conversion of lithium hydroxypyruvate (Li-HPA) and propionaldehyde (PA) to (3S)-1,3-dihydroxypentan-2-one (HK), over a wide range of substrate concentrations. Moreover, several experiments were performed to establish the best conditions to grow E. coli for TK production, protein extraction methods and quantification of TK. In addition, PCR conditions were established for the development of mutagenic libraries using the MEGAWHOP. Finally, five different truncated TK variants were generated, all of them showed activity using Li-HPA, glycolaldehyde (GA) and PA as substrates. Results obtained in this project set up the basis to generate TK variants with better stability and activity, screen large numbers of variants using the high-throughput platform developed and finally it was shown that truncated versions of TK could keep its activity.

Krit Somnuk

A tubular reactor with ultrasound clamps (US reactor) was used to produce methyl ester from refined palm oil (RPO) as a continuous process. The US reactor had 16 units of ultrasound clamps attached to the tube wall. The clamps were operated at 20 kHz fixed frequency with maximally 400W power per clamp. The ultrasound clamps were fixed 100 mm apart along the length of the reactor. The effects of varying methanol content (5, 10, 15 or 20 vol.%) and KOH loading (4, 6, 8, 10 or 12 g L−1) on the purity of methyl ester were investigated. The results show that the lowest 5 vol.% methanol content tested was unable to convert the glycerides in RPO to over 64.2 wt.% methyl ester purity at any of the KOH loadings. The maximum 99.9 wt.% purity of methyl ester was achieved with 10 g L−1 KOH loading, 10 vol.% methanol, and 400 mm reactor tube length. However, the methyl ester reached its equilibrium level at 300 mm reactor length. Regarding the average energy consumption, 0.035 kW h L−1 was required to produce biodiesel when using ultrasound clamps on the tubular reactor.

Microgels are commonly synthesized in batch experiments yielding quantities sufficient to perform characterization experiments for physical property studies. With increasing attention on the application potential of microgels, little attention is yet payed to the question whether (a) they can be produced continuously on a larger scale, (b) whether synthetic routes can be easily transferred from batch to continuous synthesis and (c) their properties can be precisely controlled as a function of synthesis parameters under continuous flow reaction conditions. We present a new continuous synthesis process of two typical but different microgel systems. It is compared in depth their size, size distribution and temperature responsive behavior to microgels synthesized using batch processes, as well as the influence of premixing and surfactant. For the surfactant-free Poly(N-vinylcaprolactam) (PVCL) and Poly(N-isopropylacrylamide) (PNIPAm) systems, microgels are systematically smaller, while the actual size is depending on the premixing of the reaction solution. But by use of a surfactant, the size difference between batch and continuous preparation diminishes, resulting in equal-sized microgels. Temperature-induced swelling-deswelling of microgels synthesized under continuous flow conditions was similar to their analogues synthesized in batch polymerization process. Additionally, investigation of the internal microgel structure using static light scattering (SLS) showed no significant changes between microgels prepared under batch and continuous conditions. The work encourages synthetic concepts of sequential chemical conditions in continuous flow reactors to prepare precisely tuned new microgel systems.

J. M. Smith
Hendrick C. Van Ness

Preface 1 Introduction 2 The First Law and Other Basic Concepts 3 Volumetric Properties of Pure Fluids 4 Heat Effects 5 The Second Law of Thermodynamics 6 Thermodynamic Properties of Fluids 7 Applications of Thermodynamics to Flow Processes 8 Production of Power from Heat 9 Refrigeration and Liquefaction 10 Vapor/Liquid Equilbrium: Introduction 11 Solution Thermodynamics: Theory 12 Solution Thermodynamics: Applications 13 Chemical-Reaction Equilibria 14 Topics in Phase Equilibria 15 Thermodynamic Analysis of Processes 16 Introduciton to Molecular Thermodynamics Appendixes A Conversion Factors and Values of the Gas Constant B Properties of Pure Species C Heat Capacities and Property Changes of Formation D Representative Computer Programs E The Lee/Kesler Generalized-Correlation Tables F Steam Tables G Thermodynamic Diagrams H UNIFAC Method I Newton's Method Author Index Subject Index

Source: https://www.researchgate.net/publication/241765470_Reactors_in_Process_Engineering

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