REACTION KINECTIS AND REACTOR DESIGN

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REACTION KINECTIS ANDREACTOR DESIGN

Lecturer : Dr. Rabitah Zakaria Jabatan Kejuruteraan Proses dan

MakananFakulti Kejuruteraan

UPM


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What are the elements of reaction kinetics? Rates of which different reaction occurs Factors that affect reaction rates Reactions mechanisms Rate limiting steps that control the reaction Mathematical model describing reaction rate

Reactor Design?

Exploitation of chemical reaction in commercial scale Sizing of chemical reactor Determination of best process conditions i.e flow,

temperature, pressure for optimum performance Types of reactors: Flow patterns Arrangement of reactors: staged, recycle etc How materials behave (chemically and physically) within a

reactor


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Many chemical reaction occurs during foodprocessing, packaging and storage which

cause changes in composition and attributeof the raw materialsAffect the quality and safety of foodsKnowledge of reaction kinetics will allow usto control the reactions to obtain the bestconditions of a process or storage


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CookingPreparation of fruit jams Sucrose hydrolysis to glucose and fructose Browning of sugar and protein resulting in

darkening and bitter flavors Pectin polymerization resulting in gelationColor formation during meat processingMicrobial growth during food processing

Nutrient degradation during thermalprocessingFermentation process to produce yoghurtHydrogenation of cooking oil


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Microbial growthShelf life predictionNutrient degradations


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Fermentation of sugar and starch to produceethanolHydrolysis of xylose to produce xylitol

Transesterification of triglycerides to producefatty acid methyl esterHydrolysis of triglycerides to free fatty acidsHydrolysis of cellulose to produce biosugar


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Required Text: Levenspiel, O., ChemicalReaction Engineering, Third Edition. JohnWiley and Sons, New York, 1998Additional Recommended Texts: Fogler, H.S., Elements of Chemical Reaction

Engineering, Forth Edition. Prentice-Hall Int. Series,New Jersey, 2005

Earle, R. Earle ,M., Fundamentals of Food ReactionTechnology (www.nzifst.org.nz/foodreactiontechnology/index.htm)


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Test 1 10 %Test 2 20 %Assignment /Quiz 20 %

SCL Project 10 %Final Exam 40 %


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Assignment will generally be assigned on thelecture period on Fridays.Due at the beginning at the specified lectureperiod.

Only selected problems will be gradedIndividual submission. Neatly presented .You are encouraged to work in group but not tocopy other people works. Copying will beconsidered cheating and will lead to disciplinaryaction. Plagiarism: 0 MarksLate homework : 25 % deduction for eachweekday


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Purpose : Review Homework solutions Practice working difficult problems Discuss exam questions

Be prepared to be asked to solve problems onthe whiteboardTime ??


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A comprehensives project involving elementsof chemical reaction engineeringWork in group: group will be determined laterProject will be given midway through thesemesterEvaluation: Written Report


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Chapter 1 : Overview of Chemical ReactionEngineeringChapter 2: Kinetics of Homogenous ReactionsChapter 3: Interpretation of HomogenousReactionsChapter 4: Reactor Design for HomogenousReactionsChapter 5 :Multi Stage ReactorChapter 6: Non ideal reactorChapter 7 : Biochemical ReactionsChapter 8: Biochemical Reactor Systems


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Classification of Reactions

Variables Affecting ReactionDefinition of Reaction rateDefinition of Conversion, Selectivity and Yield


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A typical chemical process:

PhysicalTreatment

i.e. heattransfer,size reduction,

ChemicalReaction

Separation,purifciation

recycle

product


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Homogenous Reactions- take place in ONEPHASE : implying uniform pressure,temperature, and compositionExamples : most liquid-phase reactions i.e.

Glucose fermentation to ethanol

Heterogenous Reactions take place in atleast two phases i.e. attack of solids by acids,

burning of coal-may involve mass transfer limitation as wellas heat transfer limitation


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Nature of reactantsTemperature, PressureConcentration Effect

Surface Area for heterogeneous reactionCatalysts

HW: creative problems


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Based on fluid volumes:

Based on mass of solid in solid-fluid system


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Based on unit interface (two fluid system orsolid in gas solid system)

Based on volume of solid in gas-solid system:


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Based on volume of reactor

Relation of reaction rates:

Fundamentals of reaction rate theory ?


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aA + bB rR + sSA +b/a B r/a R +s/a Q

The rate of reaction of all materials arerelated by :


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aA + bB rR + sSA +b/a B r/a R +s/a S

Parameter to quantify the fraction consumption of the(limiting) reactant A in the reaction


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Parameter to quantify the amount of thedesired product formed with respect to the(limiting ) reactant A supplied , taking thereaction stoichiometry into account

aA + bB pP + sSA +b/a B p/a P +s/a S

Yp = amount of P actually formed =max. possible amount of P


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Parameter to quantify the amount of productformed with respect to the quantity of the(limiting) reactant A consumed , takingreaction stoichiometry into account

SR,A = quantity of P formedquantity of P from A converted


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1.1 and 1.2due


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Suppose a reaction :aA + bB rR + sSA +b/a B r/a R +s/a S


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Homogenous Reaction ?Specificreaction rate


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Example rate law:

Reaction is order with respect to A and orderwith respect to B

Overall reaction order n = +

Other Examples

Rate law is determined from experimentalobservationUnit for specific reaction reaction rate ??

rA = k A C A C B


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r A = k A C A C B

Reaction order of each species is identical with thestoichiometric coefficient of that species as written

Elementary reactions usually indicates single stepreaction


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Example:B +2D 3T is an elementary reaction

-r B =-r D =rT =


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Indicating that the reaction occurs through a series ofelementary reaction


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2B D +C elementary and reversiblerate net = rate forward + rate reverse -r B, forward = k B CB2

rB, reverse = k -B CDCC rB,net = k B CB2 -k -B CDCC

rB,net = k B (CB2 -k -B / k B CDCC)

k -B / k B = Kc = Concentration equilibriumconstant


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For a reversible reaction, the concentration atequilibrium are related by thermodynamic relationshipfor the equilibrium constant

2B D +C

Kc= C DCCCB2

Need to check whether the rate law is thermodynamicallyconsistent at equilibrium

At equilibrium rB= 0

rB,net = k B (CB2 CDCC/ Kc) =0 K c= ?


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http://upload.wikimedia.org/wikipedia/commons/2/24/Activation_energy.svg


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http://e/html/course/lectures/three/audio/audio3-2.mp3


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Commonly cited rule of thumb :rate double with 10 deg C in temperature

Apply to all ?


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How d oes temperature affect reaction withhigh E compared to low E


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Sensitivity decrease with increasingtemperature


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In a continuous liquid sterilising operation , theproduct need to be heated at a holdingtemperature of 118 deg C for 7 min . Onemorning you discover from the product outputthat fluid pumps has unaccountably increased

the flowrate by 30%. The only available way torectify it in the short term to get usable productis to increase the reaction rate of sporedestruction by 30%. This can be done by liftingthe holding temperature. To what temperatureshould you lift it?.E for bacteria spore destruction= 298 KJ/molR = 8.314 J/mol/K

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REACTION KINECTIS AND REACTOR DESIGN