GATE & PSUs CHEMICAL ENGINEERING

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CHEMICL ENGINEERING [GTE-019] Postal Correspondence GTE &

Postal Correspondence Packages call at 0-9990657855 018

ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India

1 CHEMICL ENGINEERING [GTE-019] Postal Correspondence GTE & PSUs CHEMICL ENGINEERING CHEMICL RECTION ENGINEERING- To Buy Postal Correspondence Packages call at ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [1] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

2 CHEMICL ENGINEERING [GTE-019] GTE Syllabus: Chemical Engineeng - CH. Chemical Reaction Engineeng: Theoes of reaction rates; kinetics of homogeneous reactions, interpretation of kinetic data, single and multiple reactions in ideal reactors, non-ideal reactors; residence time distbution, single parameter model; non-isothermal reactors; kinetics of heterogeneous catalytic reactions; diffusion effects in catalysis. C O N T E N T 1. INTRODUCTION ND BSIC CONCEPT KINETICS OF RECTION INTERPRETTION OF BTCH RECTOR DT DESIGN EQUTION FOR IDEL RECTORS DESIGN FOR SINGLE RECTION DESIGN FOR MULTIPLE RECTIONS TEMPERTURE ND PRESSURE EFFECTS BSIC SPECTS OF NON IDEL FLOW HETEROGENEOUS RECTION QUESTION BSED ON GTE PPER MODEL TEST PPER-I WITH SOLUTION PRCTICE SET PRCTICE SET PRCTICE SET-3 Subjective Question ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

3 CHEMICL ENGINEERING [GTE-019] CHPTER-1 INTRODUCTION ND BSIC CONCEPT Every industal chemical processs is designed to produce economically a desired product from a vaety of starting mateal through a succession of treatment steps. Figure: Typical chemical process. Raw mateal undergoes a number of physical steps to put them in the form in which they can be reacted chemically. Then mateal passes through the reactor. The products of reaction must then undergo for further treatment. In chemical reaction engineeng subject we are concerned with chemical treatment step of a process. combines the study of chemical kinetics (reaction rates and reaction mechanisms) with the reactors in which the reaction occurs. Chemical Reaction: When any chemical starts to losing their identity, then we can say it reacts. Chemical reaction takes place by decomposition, combination or change in configuration of molecules. Chemical reaction may be classified depending upon so many factors, given below: Based upon number of phase involved: Homogeneous and Heterogeneous reaction. Based upon catalyst used or not: Catalytic and non-catalytic reaction. Based upon the moleculaty i.e. number of molecules that takes part in the reaction: Unimolecular, bimolecular and t-molecular reaction. Based upon heat evolved or absorbed: Exothermic and endothermic reaction Based upon reaction takes place in one or both directions: Reversible or irreversible reaction. Based upon order of reaction: First order, second order and third order reaction. Based upon single or multiple reaction takes place: Single and multiple reaction. Based upon number of stepss present in a reaction: Elementary and non-elementary reaction Rate of Reaction: We define rate of reaction in terms of component. If the rate of change in number of moles dn of this component due to reaction is i then, 1 dni Moles of i formed V(Volume of fluid)(time) i.e., the number of moles of component i formed per unit time per unit volume (mol/dm 3 s). If species i is a reactant, the numecal value of r i is a negative number (e.g. r i = 3mol/dm 3.s or rr i = 3mol/dm 3.s) If species i is a product, then r i = will be a positive number. The rate of reaction can be a large value to essentially zero. For constant volume system : 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [3] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

4 CHEMICL ENGINEERING [GTE-019] d Ni d dci () Ci V where, C i is the concentration of species i in reaction mixture. Relative rates of reaction: For the reaction: a bb cc dd The relation between the rate of participants, B, C, D in chemical reaction with their stoichiometc coefficient r rb r C rd is: a b c d r C lso, if we compare r a c a r rc c Rate of disappearance of = a c (R Rate of formation of C) Factors affecting rate of reaction: Many vaable may affect the rate of a chemical reaction. In homogeneous system the temperature, pressure and composition affect the rate of reaction. In heterogeneous system factors that affect the rate of reaction are rate of mass transfer i.e., heat transfer nature of catalyst if present. Note (1) Rate of reaction can also be given as: i) Based on unit mass of solid in fluid-solid system, 1 dni moles of i formed ' W (mass of solid)( (time) ii) iii) iv) Based on unit interfacial surface in two-fold systems or based on unit surface of solid in gas-solid system, 1 dni moles of i formed " S (surface)(time) Based on unit volume of solid in gas-solid systems, 1 dni moles of i formed "' V (volume of solid)(time) s Based on unit volume of reactor, if different from the rate based on unit volume of fluid, 1 dni moles of i formed '''' V (volume of reactor)(time) r () Relation between different rate of reactions: ()( r V')( ")( r W"')( r"") S r V r V i i i i Rate law: n algebraic equation that relates the reaction rate and concentration is known as rate law. B PRODUCTS r()( k,) T f C C r n B or k C C B k Rate constant/ specific reaction rate s i r 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [4] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

5 CHEMICL ENGINEERING [GTE-019] Order of reaction (n) = + For the reaction where all the stoichiometc coefficients are 1, e.g. + B C + D k kb kc kd k Important. Rate Laws re determined by expemental observation. 1. homogeneous reaction is one which takes place in only one phase; i.e., all the reacting mateal and products and catalyst (if any) will be present in a similar phases. Example: NO() g 1 O() g NO() g hetrogeneous reaction is one which involves the presence of more than one phase. 1 V O() 5 s Example: SO() g O() g SO() 3 g. Catalytic reaction are those reaction which involves use of catalyst to enhancee the rate of reaction. Example: CH4 Ethylene H Non catalytic reactions are those reaction which does not involve use of catalyst. 1 Example: NO O NO 3. (a) Unimolecular Reaction: Reaction of single molecule. HC CH Decomposition Example: CH4 H C CH (b) Bimolecular Reaction: Reaction between two molecules. (c) Tmolecular Reaction: Decomposition HI()g I() NO O 4. The reaction may be classified as exothermic and endothermic reaction. Exothermic reaction is one in which heat is evolved. Example: CO H CH3 OH Heat Endothermic reaction is one in which heat is absorbed C H OH C ion H4 HO Heat l 3 5 Dehydrati ethyl alcohol 5. The reaction may be classified as reversible and irreversible reaction. Reversible reaction are those in which forward and reverse reaction takes place simultaneously. CH5OH CH3COOH H CH3 COOCH5 HO Irreversible reaction are those which can proceed only in one direction. C H HNO C H NO H O C H Ni Heat 6 Ethane gh() NO Oxidation Cu 6. The reaction may be classified as first order, second order and third order reaction. First order reaction: Decompositionon 1 Example: NO5 NO + O g 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [5] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

6 CHEMICL ENGINEERING [GTE-019] Second order reaction: (Saponification of ester) Example: CH3COOCH5 NaOH CH3COONa CH5OH Third order reaction: Example: NO H 7. Single and Multiple Reaction: (a) When a single stoichiometc equation and single rate equation are chosen to represent the progress of the reaction, we have a single reaction. (b) When more than one rate equations are chosen to represent the progress of the reaction, we have a multiple reaction. Multiple reaction may be classified as. Sees Reaction: B S Parallel Reaction: Complicated Reaction: B C C B D Here reaction proceeds in parallel with respect to B but in sees with respect to, C and D. 8. Elementary and Non Elementary Reaction: Consider a single reaction with stoichiometc equation B C ccording to rate law, rate of disappearance of is given by r K C C Such reaction in which the rate equation corresponds to a stoichiometc of equation are called elementary reaction. When there is no direct corresponding rate and stoichiometc, then the reaction is called non-elementary reaction. In other words, elementary reaction is a single step reaction whereas non-elementary reaction is multistep reaction. The best example of a non-elementary reaction is that between hydrogen and bromine. H Br HBr Which has rate expression: Competitive Type r S HBr B N O H O and B 1 1 K [H ][Br ] [HBr] K + [Br ] B C S Side by side Moleculaty and Order of Reaction: The moleculaty of an elementary reaction is the number of molecules involved in the reaction and this has been found to have the values of one, two or occasionally three. Moleculaty refers only to an elementary reaction. 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [6] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

7 CHEMICL ENGINEERING Consider a reaction a b B cc d D P then rate expression r K C C C C where a, b,.. d are not necessaly related to the stoichiometc coefficient. We call the power to which the concentration are raised the order of reaction. Hencee the reaction is - ath order with respect to - bth order with respect to B - nth order overall Since the order refers to the empically found rate expression, it may not to be an integer and can have a fractional value. But, the moleculaty of a reaction must be an integer because it refers to mechanism of reaction and applies only to elementary reaction. Rate constant (K): The rate constant of a chemical reaction is a measure of the rate of reaction when all the reactants are at unit concentration. So, for any reaction say B r k C If we assume that the concentrationn are equal to unity then r K Where K is rate constant. The rate constant K depends on the temperature. It increasees with temperature. K is also called specific rate constant. The units of K depends upon the units of time and concentration. Suppose : r K C n Then we know units of () r mol/l. sec and C mol lit. a b c d B C D [GTE-019] a + b + c + d = n mol se ec. lit. 1 mol k (sec) n mol lit. lit. k (time)(concentration) 1 n 1 1 n where, n is the order of reaction. 9. For reversible reactions: B C k Equilibum constant (k C ) = k FORWRD BCKWRD k Rate constant of forwardrd reaction k - Rate constant of backward reaction k Dung the course of a chemical reaction, the rate of a reaction decreases as the reaction proceeds 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [7] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

8 CHEMICL ENGINEERING [GTE-019] Q.1. ns. c Solved Example For a homogeneous reaction system, where C i is the concentration of i at time t, N i is the no. of moles of i at time t, V is the reaction volume at time t and t is the reaction time. The rate of reaction for species i is defined as (a.) dc i (b.) Q.. For an elementary reaction B 3C (a.) Rate of appearance of C is equal to rate of disappearance of (b.) Rate of disappearance of is equal to rate of disappearance of B. (c.) Rate of appearance of C is equal to rate of disappearance of B. (d.) Rate of appearance of C is 3 times rate of disappearance of. NS: c r rb r C Relative Rates 1 3 of reaction r = rate of disappearance of r B = rate of disappearance of B r C = rate of appearance of C r 3() r C dci k (c.) 1 dni V (d.) 1 dni V Q.3. Rate expression of reaction r 3 0.0C mol/cm min If concentration is to be expressed in mol/l and time in hours, the value of rate constant would be (a.) 0.1hr -1 (mol/l) -1 (b.) 0.01hr -1 (mol/ l) -1 (c.) 1hr -1 (mol/ l) -1 (d.) 1.hr -1 (mol/ l) -1 NS: (c) 1L = 10cm 3 1hr = 60min mol r 0.0C 1 1 hr mol r 0.0C 600 l hr 1 1 r 1C mol l hr Clearly k 1 r unit of k C 1 1 moll hr mol l 1 1 k 1( hr /) mol l 1 1 unit of k mol l hr 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [8] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

9 CHEMICL ENGINEERING [GTE-019] Q.4. The rate of reaction for a gas phase reaction is expressed as dp.56 P atm / hr The Units of rate constant are 1 1 (a.) hr () atm (b dp / / NS: (a) atm hr k atm p atm Q.5. For a gas reaction at T(K), the rate is given by: dp k ' p atm / hr If the rate equation is expressed as: 1 dn r kc( mol /) L hr V The rate constant k is given by (a.) k = k rt (b.) k = k (c.) k = k (RT) (d.) k = k /RT NS: (a) dp k ' p d () C RT '() k C dc RT k '() C RT RT dc k '() C RT r k '() C RT '() kc k C RT 1 3 b.) hr () atm C 1 1 hr p RT k k '() RT Q.6. The irreversible reaction is the special case of reversible reaction if concentration of reactant at equilibum condition is NS: zero (c.) hr 1 atm 1 1 (d.) hr ( mol /) L 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [9] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

10 CHEMICL ENGINEERING [GTE-019] 018 ENGINEERS INSTITUTE OF INDI.ll Rights Reserved GTE+PSU s : Classroom, POSTL, ll India TEST Sees [10] 61C, Kalu Sarai Hauz Khas, New Delhi Ph

Chemical Kinetics. Chapter 13. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chemical Kinetics. Chapter 13. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Kinetics Chapter 13 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Kinetics Thermodynamics does a reaction take place? Kinetics how fast does