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Chapter 3 Mass Balance Balance on Reactive Processes System.

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Presentation on theme: "Chapter 3 Mass Balance Balance on Reactive Processes System."— Presentation transcript:

1 Chapter 3 Mass Balance Balance on Reactive Processes System

2 Content  Stoichiometry  Limiting and Excess Reactant, Fractional Conversion and Extent of Reaction  Chemical Equilibrium  Multiple Reaction, Yield and Selectivity  Balance on Reactive System

3 Stoichiometry  Stoichiometry – theory of proportions in which chemical species combine with one another.  Stoichiometric equation of chemical reaction – statement of the relative number of molecules or moles of reactants and products that participate in the reaction. 2 SO 2 + O 2 ---> 2 SO 3  Stoichiometric ratio  ratio of species stoichiometry coefficients in the balanced reaction equation  can be used as a conversion factor to calculate the amount of particular reactant (or product) that was consumed (produced). 2 mol SO 3 generated2 mol SO 2 consumed 2 mol SO 2 consumed1 mol O 2 consumed

4 Test Yourself C 4 H O > 4 CO H 2 O 1.Is the stochiometric equation balance?  Yes 2.What is stochiometric coefficient for CO 2 44 3.What is stochiometric ratio of H 2 O to O 2 including it unit  4 mol H 2 O generated/ 6 mol O 2 consumed 4.How many lb-moles of O 2 reacted to form 400lb-moles CO 2  600 lb-moles O 2 reacted mol/min C 4 H 8 fed into reactor and 50% is reacted. At what rate water is formed?  200 mol/min water generated

5 Limiting Reactant & Excess Reactant  The reactant that would run out if a reaction proceeded to completion is called the limiting reactant, and the other reactants are termed excess reactants.  A reactant is limiting if it is present in less than its stoichiometric proportion relative to every other reactant.  If all reactants are present in stoichiometric proportion, then no reactant is limiting.

6 Example C 2 H 2 + 2H > C 2 H 6 Inlet condition: 20 kmol/h C 2 H 2 and 50 kmol/h H 2 What is limiting reactant and fractional excess? (H 2 :C 2 H 2 ) o = 2.5 : 1 (H 2 :C 2 H 2 ) stoich = 2 : 1 H 2 is excess reactant and C 2 H 2 is limiting reactant Fractional excess of H 2 = (50-40)/40 = 0.25

7 Fractional Conversion  Fractional Conversion (f)

8 Extent of Reaction  Extent of Reaction, ξ ξ = extent of reaction n i = moles of species i present in the system after the reaction occurred n io = moles of species i in the system when the reaction starts v i = stoichiometry coefficient for species i in the particular chemical reaction equation

9 Example N 2 + 3H > 2NH 3 Reactor inlet: 100 mol N 2 /s; 300 mol H 2 /s; 1 mol Ar/s If fractional conversion of H 2 0.6, calculate extent of reaction and the outlet composition. Unreacted H 2 or H 2 outlet= (1-0.6) 300 = 120 mol H 2 /s Solve for extent of reaction : 60 mol/s

10 Test Yourself Page C 2 H 4 + O >2 C 2 H 4 O The feed to a reactors contains 100kmol C 2 H 4 and 100kmol O 2. a) which is limiting reactant? C2H4C2H4 b) Percentage of excess? {(100-50)/50 }x100%=100% c) O 2 out? C 2 H 4 formed? Extent of reaction? 50kmol100kmol C 2 H 4 50kmol d) if fractional conversion for limiting reactant is 50%, what is outlet composition and extent of reaction? 50kmol C 2 H 4 ; extent of reaction = 25 kmol;75 kmol O 2 50 kmol C 2 H 4 O e) if reaction proceed to a point where 60kmol O 2 left, what is fractional conversion for C 2 H 4 ? Fractional conversion of O 2 and extent of reaction? f C2H4 =0.8f O2 =0.4extent of rxn=40 kmol

11 Great work is done by people who are not AFRAID to be great

12 Class Discussion Example 4.6-1

13 Chemical Equilibrium  For a given set reactive species and reaction condition, two fundamental question might be ask: 1.What will be the final (equilibrium) composition of the reaction mixture? – chemical engineering thermodynamics 2.How long will the system take to reach a specified state short of equilibrium? – chemical kinetics  Irreversible reaction  reaction proceeds only in a single direction (from reactants to products)  the concentration of the limiting reactant eventually approaches zero.  Reversible reaction  reactants form products for forward reaction and products undergo the reverse reactions to reform the reactants.  Equilibrium point is a rate of forward reaction and reverse reaction are equal  However the discussion to get the chemical equilibrium point is not covered in this text- learn in chemical engineering thermodynamic

14 Class Discussion Example CO + H2O CO2 + H2 nco= 1-ξ nH2O=2- ξ n CO2= ξ nH2= ξ ntotal= 3 K=yCO2 yH2 / y CO y H2O=1 yY CO2= ξ/3 yH2= ξ/3 y CO= (1- ξ)/3 y H2O= (2- ξ)/3

15 Multiples Reaction, Yield & Selectivity  Some of the chemical reaction has a side reaction which is formed undesired product- multiple reaction occurred.  Effects of this side reaction might be: 1.Economic loss 2.Less of desired product is obtained for a given quantity of raw materials 3.Greater quantity of raw materials must be fed to the reactor to obtain a specified product yield. selectivity= moles of desired product moles of undesired product

16 Yield  3 definition of yield with different working definition Yield= Moles of desired product formed Moles that would have been formed if there were no side reaction and the limiting reactant had reacted completely Yield= Moles of desired product formed Moles of reactant fed Yield= Moles of desired product formed Moles of reactant consumed

17 Extent of Reaction for Multiple Reaction  Concept of extent of reaction can also be applied for multiple reaction  only now each independent reaction has its own extent.

18 Class Discussion Example 4.6-3

19 Balance of Reactive Processes  Balance on reactive process can be solved based on three method: 1.Atomic Species Balance 2.Extent of Reaction 3.Molecular Species Balance

20 MUFLIS DALAM HARTA HANYA KEMISKINAN YANG SEMENTARA DI DUNIA, MUFLIS DALAM WATAK ADALAH KEMISKINAN TERBURUK DI DUNIA. IA AKAN DI BAWA BERSAMA KE AKHIRAT

21 Atomic Species Balance No. of unknowns variables -No. of independent atomic species balance -No. of molecular balance on indep. nonreactive species -No. of other equation relating the variable ============================= No. of degree of freedom =============================

22 Extent of Reaction No. of unknowns variables +No. of independent chemical reaction -No. of independent reactive species -No. of independent nonreactive species -No. of other equation relating the variable ============================= No. of degree of freedom =============================

23 Molecular Species Balance No. of unknowns variables +No. of independent chemical reaction -No. of independent molecular species balance -No. of other equation relating the variable ============================= No. of degree of freedom =============================

24 ANY QUESTION?


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