IV-1 - Introduction - no polym

8/14/2019 IV-1 - Introduction - no polym

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June 5, 2008 FILS Chemical ReactorsPreparatory Notions Revisited

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BIBLIOGRAPHYBIBLIOGRAPHY

Octave Levenspiel, Chemical Reaction Engineering, Third

Edition, John Wiley & Sons, New York, 1999

Ronald W. Missen, Charles A. Mims, Bradley A. Saville,Introduction to Chemical Reaction Engineering and Kinetics,

John Wiley & Sons, New York, 1999

E. Bruce Nauman, Chemical Reactor Design, Optimization, and

Scale-up, McGraw-Hill, New York, 2002

Lanny D. Schmidt, The Engineering of Chemical Reactions,

Oxford University Press, New York, 1998

Chemical ReactorsChemical Reactors


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BIBLIOGRAPHY (Cont.)BIBLIOGRAPHY (Cont.)

Holland, C.D., Anthony, R.G., Fundamentals of Reaction Engineering,

Prentice-Hall Inc., Englewood Cliffs, 1979. Froment, G.F., Bischoff, K.B., Chemical Reactor Analysis and Design, John

Wiley & Sons, New York, 1979. Lee, H.H., Heterogeneous Reactor Design, Butterworth Publishers, Boston,

1985. Levenspiel, O., The Chemical Reactor Omnibook+, OSU Book Stores Inc.,

Corvallis, 1984. Danckwerts, P.V., Gas-Liquid Reactions, McGraw-Hill, New York, 1970. Denbigh, K.G., Turner, J.R., The Chemical Reactor Theory - an Introduction,

2

nd

edition, Cambridge Univ. Press, 1971. Hill, C.G. jr., An Introduction to Chemical Kinetics and Reactor Design, John

Wiley & Sons, New York, 1977. Tarhan, M.O., Catalytic Reactor Design, McGraw-Hill, New York, 1983 Lavric, V., Chemical Reactors, 1996 (UPB lithography)



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ExaminationExamination

Written test multiple choices, five variants to select from; free access to alldocumentation

The rules of grading:

A) no answer checked, Zero points;

B) all answers checked, Zero points;

C) for the rest, the following formula applies:

where gstands for the number ofgood answers checked,pgstands for the weight

fraction of the answergand b stands forbad answers checked.

Examples:C.1 in all, three good answers ( weight each), all checked: since no

bad answer is checked;

C.2 two good answers and one bad:

C.3 no good answer and one bad answer: Zero


1gg pP

b

13 3 10 1

P

12 13

1 1 3P


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Definition:

The Chemical Reactor is the confined space where a

chemical process develops, resulting in transformation of

some species (reactantsreactants) in others (productsproducts), under strict

observation of the mass conservation laws.


Every industrial chemical process aims towards economicalleconomicallyfabricating a desired productdesired product from a variety of starting materials

through a succession of treatment steps, which can be abstracted in

a general processing flowsheet.

The Hybrid Chemical Reactor, ensures in situseparation of

the valuable product or intermediate, not only lowering the

overall production costs, but increasing the process rate due

to higher chemical driven forces.


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The flowsheet of a typical chemical process


Products

Row materials

Pre-chemical

processing physi-

cal treatment Chemical processingstages

Post-chemical

processingphysical treat-

ment steps


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Design of the chemicalreactor - many alternatives

can be proposed for a process.

Optimum solution concerns

not just the chemical reactor.

One design may have lowchemical reactor cost, but the

materials leaving the unit may

be such that their treatment

requires much higher costs.

The economics of the over-all

process must be considered


Predictions not suffi-

ciently close to reality

Abstraction

RealityThe process to be known

and studied

Mathematical Model

The reality as we

are able to predict it

Physical ModelThe reality as we

are able to grasp

Simplifying

Assumptions

Boundary

Conditions

Improvement


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Information used in chemical reactor modeling


Automation

& ControlThermo-

dynamics

Stoichiome

try & Ki-

netics

Balance

equations

Chemical

Reactor

Modeling

Momentum

transport

Heat

transport

Mass

transport

Phases

flow


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Classification of chemical reactions useful in reactor modeling


Oxidation of SO2

to SO3

Reduction of iron ore to

iron and steel

Cracking of crude oilGas-liquid absorption with

reaction

Attack of solids by acids

Oxidation of ammonia to produce

nitric acid

Roasting of ores

Ammonia synthesisBurning of coal

Hetero-geneous

Enzyme and microbial reactions

Reactions in colloidal systemsFast reactions such as burning

of a flame

Most liquid-phase reactionsMost gas-phase reactions

Homo-

geneous

CatalyticNon-catalytic


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chemical species are denoted byAj, wherej=1,,Swith Sbeing the number

of all chemical species involved in the chemical process;

stoichiometric coefficients are denoted by j, for a single reactions and ij for

multiple reactions, with i=1,,R, where Rstands for the total number of

chemical reactions between the Schemical species; the stoichiometric coefficients for products are positive, while for reactants

are negative, to show the progression of the chemical process

Elements of systematicElements of systematic

stoichiometrystoichiometry

Single reactions1

0S

j j

j

A

Multiple reactions1 1

0R S

i j j

i j

A

0A rank


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Measuring the progress of a chemical process - quantifying the degree of

participation of a molecular species in this chemical process

intensive units - normalized value, independent of the starting point

extensive units/variables their values will depend upon the initial quantity

of each and every species participating at the chemical process

As intensive variable, theconversion is the widest used;

As extensive variable, the degree of advancement or the reaction extentarethe

widest used.

The rule of thumb advocates that, for a single reaction chemical process,

conversion is the appropriate measure of transformation, while the degree of

advancement should be used for all other cases.

Measuring the progress of theMeasuring the progress of the

chemical processchemical process


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The conversion

Single reaction chemical process



1

0S

j j

j

A

dr

k

ka A b B q Q s S K K

The degree of transformation for each reactant species is given by

the fractional conversions

0 0

0 0

; A A B BA BA B

N N N N X X

N N

0

0

AB A

B

NbX X

a N

0 1 A A A N N X

0 B A BA A

b N N M X

a

0Q A QA A

q N N M X

a

0S A SA A

s N N M X

a

0

0

jA

jA

A

NM

N

Limiting reactant


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The degree of advancement / The extent




1

0S

j j

j

A

0

; 1, 2, ,

j jA A

j

N N

j S

K

0j j A A jN N

Multiple reaction chemical process

0

; 1, 2, ,j jA A i

i

ij

N Ni R

K

0

1

j j

R

A A ij i

i

N N

0

1 1

S R

T ij i

j i

N N

1 1

0R S

i j j

i j

A


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Molar concentration

Single reaction chemical process constant volume

Composition of the chemical mixtureComposition of the chemical mixture

Single reaction chemical process variable volume

j

j

A

A

NC

V

0j

j

A A jA AC C M X a

0

0

0 1 1j

jj

A jA A jA A

A A

A A A A

N M X M Xa aC C

V x X

0 1

00 1

0 1 0

1

for gas phase reactions

for liquid phase reactions

A A

AA A

A A A

A

X X

XX X

A

X X X

X

N N

NV V

V


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Molar fraction


Composition of the chemical mixtureComposition of the chemical mixturej

j

A

A

T

Ny

N

0

0

1 1

j

jj

A jA A jA A

AS Sj j

A jA A jA A

j j

N M X M Xa ay

N M X M X a a

Multiple reaction chemical process

0 0

1 1

0

1 1 1 1

1

j j

j

R R

A ij i A ij M ii i

A S R S R

ij i ij M i

j i j i

N yy

N


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ThermodynamicsThermodynamics the heat liberated or absorbed during the chemical process

the maximum possible extent of reaction

ThermodynamicsThermodynamics

0 0

1

lnj

S

j A

j

G G RT K

,1

j

S

p j p Aj

C C


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Chemical kineticsChemical kinetics concerned with the rates and mechanisms of chemical reactions;

search for the factors that influence the rate of reaction;

tool for: gaining insight into the reacting systems nature, understanding how

chemical bonds are made/broken, and estimating their energies and stability;

the mode of reaction of compounds provides clues to their structure;

the basis for important theories in combustion and dissolution;

permit satisfactory design of equipments to effect the reactions on a technical

scale

in polymerization processes: the stoichiometry and kinetics are complex. A

polymer is always a mixture of macromolecules having different chain lengths -statistics can be used, to simplify the mathematical treatment, lumping the infinite

number of conservation equations (polymers and/or free radicals) into an easier

mathematical model, focused on several characteristics of the molecular mass

distribution, like mean, dispersion and symmetry;

Chemical kineticsChemical kinetics


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Equilibrium of Elementary Reversible Reactions

Chemical kineticsChemical kinetics

,d

r

k

Ck

A B Q S K

forward d A Br k C C reverse r Q S r k C C

, , 0S forward S reverser r Equilibrium

d R SC

r A B

k C CK

k C C

Molecularity and Order of Reaction Homework

Temperature dependent term of a rate equation Homework


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Chemical Processes KineticsChemical Processes Kinetics

Searching for a mechanism (Lavric, 1996)

homework

IV-1 - Introduction - no polym

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