8/9/2019 Seminar 28

1/31

Seminar Presentation on

REACTIONS INSERIES:

Prepared By : Guided By :Prepared By : Guided By :

H.M. Joshipura M.H. JoshipuraH.M. Joshipura M.H. Joshipura

8/9/2019 Seminar 28

2/31

IntroductionIntroduction CRE :CRE : Various reactions are to be dealt withVarious reactions are to be dealt with

ClassificationClassification

1. wrt Phase1. wrt Phase

Homogeneous reactionsHomogeneous reactions

Heterogeneous reactionsHeterogeneous reactions2. wrt Catalyst2. wrt Catalyst

Catalytic reactionsCatalytic reactions

NonNon--catalytic reactionscatalytic reactions

3. wrt Equilibrium3. wrt Equilibrium

Reversible reactionsReversible reactions

irreversible reactionsirreversible reactions4. wrt Concentration4. wrt Concentration

Single reactionSingle reaction

Multiple reactionsMultiple reactions Series reactionsSeries reactions

-- Parallel reactionsParallel reactions

8/9/2019 Seminar 28

3/31

Mathematical CharacterizationMathematical Characterization

The simplest case of series in which every reaction in theThe simplest case of series in which every reaction in thesequence obeys firstsequence obeys first--order kinetics, may be represented in termsorder kinetics, may be represented in termsof following equation ;of following equation ;

kk11 kk22 kk33 kk44AA BB CC DD ....

The differential equations that govern kinetic systemsThe differential equations that govern kinetic systemsof this type are solved by working in terms ofof this type are solved by working in terms of

concentration derivatives.concentration derivatives.As we go on to derive the equations for theAs we go on to derive the equations for theconcentrations for A & B, depicting the relationconcentrations for A & B, depicting the relationbetween concentration and time, we get them asbetween concentration and time, we get them as

8/9/2019 Seminar 28

4/31

As we go on to derive the equations for theAs we go on to derive the equations for theconcentrations for A & B, depicting the relationconcentrations for A & B, depicting the relation

between concentration and time, we get them asbetween concentration and time, we get them as

A = AA = A00 ee kk

11tt &&

B = BB = B00ee--kk

22tt + [(k+ [(k11AA00/(k/(k22 kk11)) (e)) (e

kk11tt ee kk22

tt)])]

The time corresponding to a maximumThe time corresponding to a maximum

concentration of B is given byconcentration of B is given by

ttmaxmax = (1/(k= (1/(k22 kk11)) *)) *

ln[kln[k22

/k/k11

(1 + B(1 + B00

/A/A00

kk22

BB00

/k/k11

AA00

)])]

8/9/2019 Seminar 28

5/31

The graphs below show the change in concentration ofThe graphs below show the change in concentration ofB wrt time, for different casesB wrt time, for different cases

CaseCase 1 when B1 when B00

= 0= 0

8/9/2019 Seminar 28

6/31

CASE 2 Two modes of behavior for B when B0 = 0.5A0

8/9/2019 Seminar 28

7/31

Qualitative discussion about Product distribution :

Consider following two cases elaborated in following two graphsCase - 1

8/9/2019 Seminar 28

8/31

Case - 2

8/9/2019 Seminar 28

9/31

For irreversible reactions in series the mixing ofFor irreversible reactions in series the mixing of

fluid of different composition is the key to thefluid of different composition is the key to theformation of intermediate.formation of intermediate.

The maximum possible amount of any and allThe maximum possible amount of any and all

intermediates is obtained if fluids of differentintermediates is obtained if fluids of differentcompositions and at different stages ofcompositions and at different stages of

conversion areconversion are notnot allowed to mix.allowed to mix.

8/9/2019 Seminar 28

10/31

Quantitative treatment for Plug flow andQuantitative treatment for Plug flow and

mixed flow reactormixed flow reactor

Equations depicting the behavior ofEquations depicting the behavior of

components :components :

For P

FR:

For P

FR:

CCAA/C/CA0A0 = e= e-- kk

11

CCRR/C/CA0A0 = (k= (k11/k/k22 kk11)(e)(e

--kk11

ee--kk22))

CCR,maxR,max/C/CA0A0 = (k= (k11/k/k22))

kk22/(/(kk22

kk11))

p, optp, opt = ln(k= ln(k22/k/k11)/(k)/(k22 kk11))

8/9/2019 Seminar 28

11/31

For MFR : Equations depicting the behavior ofFor MFR : Equations depicting the behavior of

components :components :

CCAA/C/CA0A0 = 1/(1 + k= 1/(1 + k11mm))

CCRR/C/CA0A0 = (k= (k11 mm)/[(1 + k)/[(1 + k11 mm)(1 + k)(1 + k22 mm)])]

CCR,maxR,max/C/CA0A0 = 1/[(k= 1/[(k22/k/k11))

1/21/2 + 1]+ 1]22

m, optm, opt

= 1/(k= 1/(k11

kk22

))1/21/2

8/9/2019 Seminar 28

12/31

Quantitative treatment for plug flow or batchQuantitative treatment for plug flow or batch

reactor and mixed flow reactorreactor and mixed flow reactor

The concentrationThe concentration--time curves :time curves :

For PFR :For PFR :

8/9/2019 Seminar 28

13/31

For MFR :For MFR :

8/9/2019 Seminar 28

14/31

Relative concentration of the reactionRelative concentration of the reactioncomponents, for PFR :components, for PFR :

8/9/2019 Seminar 28

15/31

Relative concentration of reaction componentsRelative concentration of reaction components

For MFR :For MFR :

8/9/2019 Seminar 28

16/31

Comparison of the fractional yields of R inComparison of the fractional yields of R in

MFR & PFR.MFR & PFR.

8/9/2019 Seminar 28

17/31

Comparison of yields in PFR & MFR(CSTR)Comparison of yields in PFR & MFR(CSTR)

For PFR : the maximum concentration of intermediateFor PFR : the maximum concentration of intermediateisis

CCR,maxR,max/C/CA0A0 = (k= (k11/k/k22))

kk22/(k/(k

22 kk

11))

and the time at which it occurs isand the time at which it occurs isttp,optp,opt = ln(k= ln(k22/k/k11)/(k)/(k22 kk11))

For MFR :For MFR :

CCR

,maxR

,max

/C/CA0A0

= 1/[(k= 1/[(k22

/k/k11

))1/21/2 + 1]+ 1]22

AndAnd

ttm,optm,opt = 1/(k= 1/(k11kk22))1/21/2

8/9/2019 Seminar 28

18/31

Taking the ratio of the equations for CTaking the ratio of the equations for CR,maxR,max/C/CA0A0

for MFR(CSTR) to PFRwe havefor MFR(CSTR) to PFRwe have

YYCSTRCSTR/Y/YPFRPFR = 1/[{1 + (k= 1/[{1 + (k22/k/k11))1/21/2}}22(k(k11/k/k22))kk22/(k/(k22-- kk11))

The graph in next slide shows comparison ofThe graph in next slide shows comparison of

maximum yields for series reactions in stirredmaximum yields for series reactions in stirredtank and plug flow reactors.tank and plug flow reactors.

8/9/2019 Seminar 28

19/31

8/9/2019 Seminar 28

20/31

Reactions in series producing by products :Reactions in series producing by products :

Reaction system :Reaction system :

FEEDFEED PRODUCTPRODUCT

PRO

DUCT

PRO

DUCT

BYPRO

DUCT

BYPRO

DUCT

Reactor performance :Reactor performance :

FEEDFEED PRODUCT rPRODUCT r11

= k= k11CCFEDFED to powerto power 11PRODUCTPRODUCT BYPRODUCT rBYPRODUCT r22= k= k22CCPRODUCTPRODUCT to powerto power 22

8/9/2019 Seminar 28

21/31

Where rWhere r11,r,r22 = rates of reaction for primary and= rates of reaction for primary and

secondary reactionssecondary reactions

KK11,k,k22 = reaction rate constants= reaction rate constantsCCFEEDFEED = molar concentration ofFEED= molar concentration ofFEED

CCPRODUCTPRODUCT = molar concentration of PRODUCT= molar concentration of PRODUCT

11, , 22 = constants (order of reaction) for= constants (order of reaction) for

primary and secondary reactionsprimary and secondary reactions

8/9/2019 Seminar 28

22/31

Idealized reactor models :Idealized reactor models :

There are three idealized models used for reactorThere are three idealized models used for reactordesigns.designs.

Ideal batch model, Continuous wellIdeal batch model, Continuous well--stirred model,stirred model,The plug flow model.The plug flow model.

For a certain reactor conversion system, the feedFor a certain reactor conversion system, the feedshould have a corresponding residence time in theshould have a corresponding residence time in thereactor.reactor.

so batch or plug flow reactor give a high selectivityso batch or plug flow reactor give a high selectivityfor the given conversion in case of series reactionsfor the given conversion in case of series reactions

8/9/2019 Seminar 28

23/31

Reactor concentration :Reactor concentration :

The series reaction producing byproducts can beThe series reaction producing byproducts can be

inhibited by low concentrations of PRO

DUCT

.inhibited by low concentrations of PRO

DUCT

. If reaction involves more than one feed, thenIf reaction involves more than one feed, then

using an excess of one of the feeds enablesusing an excess of one of the feeds enables

operation with a relatively high conversion ofoperation with a relatively high conversion of

other feed material, and still inhibits seriesother feed material, and still inhibits series

reactions.reactions.

8/9/2019 Seminar 28

24/31

Reactor temperature :Reactor temperature : If kIf k11 increases faster than kincreases faster than k22,operate at high,operate at high

temperature.temperature.

If kIf k22 increases faster than kincreases faster than k11,operate at low,operate at lowtemperature.temperature. Reactor pressure :Reactor pressure : If there is a significant difference between the effect ofIf there is a significant difference between the effect of

pressure on the primary and secondary reactions, thepressure on the primary and secondary reactions, the

pressure should be chosen to reduce as much possiblepressure should be chosen to reduce as much possiblethe rate of the secondary reaction relative to primarythe rate of the secondary reaction relative to primaryreaction.reaction.

8/9/2019 Seminar 28

25/31

For liquidFor liquid--phase reactions the Pressure is likelyphase reactions the Pressure is likelyto be chosen toto be chosen to

Prevent Vaporization of the productsPrevent Vaporization of the products

Allow vaporization of one of liquid so that itAllow vaporization of one of liquid so that itcan be condensed & refluxed back to the reactorcan be condensed & refluxed back to the reactoras a means of removing the heat of reactionas a means of removing the heat of reaction

Allow vaporization of one of the componentsAllow vaporization of one of the componentsin a reversible reaction in order that removalin a reversible reaction in order that removalincreases maximum conversion.increases maximum conversion.

8/9/2019 Seminar 28

26/31

Industrial Applications :Industrial Applications :

The below mentioned cases are prominent applications of theThe below mentioned cases are prominent applications of theReactions in Series.Reactions in Series.

The Chlorination ofToluene:The Chlorination ofToluene:

CC66HH55CHCH33 + Cl+ Cl22 CC66HH55CHCH22Cl + HClCl + HClToluene Chlorine Benzyl ChlorideToluene Chlorine Benzyl Chloride

CC66HH55CHCH22Cl + ClCl + Cl22 CC66HH55CHClCHCl22 + HCl+ HCl

Benzyl chloride Benzal dichlorideBenzyl chloride Benzal dichloride

CC66HH55CHClCHCl22 + Cl+ Cl22 CC66HH55CClCCl33 + HCl+ HCl

Benzal dichloride BezotrichlorideBenzal dichloride Bezotrichloride

8/9/2019 Seminar 28

27/31

The manufacture of ethylene glycol from ethylene oxideThe manufacture of ethylene glycol from ethylene oxideand water:and water:

CC22HH44 + Cl+ Cl22 ClCHClCH22CHCH22OH + HClOH + HCl

Ethylene ChlorohydrinEthylene ChlorohydrinClCHClCH22CHCH22OH + 1 /2 Ca(OH)OH + 1 /2 Ca(OH)22

CC22HH44O + 1 /2 CaClO + 1 /2 CaCl22 + H+ H22OO

Chlorohydrin Ethylene oxideChlorohydrin Ethylene oxide

CC22HH44O + HO + H22OO HOCHHOCH22CHCH22OHOH

Ethyleneoxide Ethylene GlycolEthyleneoxide Ethylene Glycol

8/9/2019 Seminar 28

28/31

The manufacture of Ethanolamine.The manufacture of Ethanolamine.

NHNH33 + CH+ CH22OCHOCH22 NHNH22CHCH22CHCH22OHOH

AmmoniaE

thyleneoxideAmmoniaE

thyleneoxideMonoethanolamine,MEAMonoethanolamine,MEA

NHNH22CHCH22CHCH22OH + CHOH + CH22OCHOCH22

N(CHN(CH22CHCH22OH )OH )33MonoethanolamineMonoethanolamine

Triethanolamine,TEATriethanolamine,TEA

8/9/2019 Seminar 28

29/31

The manufacture of Glycol Ethers:The manufacture of Glycol Ethers:

CC22HH55OH + CHOH + CH22OCHOCH22

OHCHOHCH22CHCH22OCOC22HH55Ethyl alcohol Ethyleneoxide CellosolveEthyl alcohol Ethyleneoxide Cellosolve

OHCHOHCH22CHCH22OCOC22HH55 + CH+ CH22OCHOCH22

CHCH22OCOC22HH55 CHCH22OCHOCH22 CHCH22OHOH

CellosolveCellosolve

CarbitolCarbitol

8/9/2019 Seminar 28

30/31

Summary :Summary :

For series reactions mathematical characteristics areFor series reactions mathematical characteristics arelearned and behaviors of proceeding components inlearned and behaviors of proceeding components inseries reactions are studied.series reactions are studied.

The concentrationThe concentration--time relations for PFRas well as fortime relations for PFRas well as forMFRare studied, so the conversion relationships.MFRare studied, so the conversion relationships.

Different criteria for designing the reactor in which theDifferent criteria for designing the reactor in which thereactions in series are carried out are studiedreactions in series are carried out are studied

All above can be applied for advances in the field of theAll above can be applied for advances in the field of thereactions in series.reactions in series.

8/9/2019 Seminar 28

31/31

ReferencesReferences

[ 1 ] Chemical Process Design byRobin Smith.[ 1 ] Chemical Process Design byRobin Smith.

[ 2 ] Elements of Chemical Reaction Engineering[ 2 ] Elements of Chemical Reaction Engineering

(Third Addition) by H. Scott Fogler.(Third Addition) by H. Scott Fogler.

[ 3 ] ChemicalE

ngineering Kinetics &R

eactor Design By[ 3 ] ChemicalE

ngineering Kinetics &R

eactor Design ByC.G. Hill.C.G. Hill.

[ 4] Chemical Reactor Design byE.B. Nauman.[ 4] Chemical Reactor Design byE.B. Nauman.

[ 5 ] Chemical Reaction Engineering (Third Addition )[ 5 ] Chemical Reaction Engineering (Third Addition )

byOctave Levenspiel.byOctave Levenspiel.