Presentation on theme: " 제1장 Mole Balance Chemical Reaction Engineering 반응공학 I."— Presentation transcript:
1 제1장Mole BalanceChemical Reaction Engineering반응공학 I
2 Chapter 1. Mole Balance 1.1 Definition of the Rate of Reaction, -rA 1.2 The General Mole Balance Equation1.3 Batch Reactors1.4 Continuous-Flow Reactors1.4.1 Continuous-Stirred Tank Reactor1.4.2 Tubular Reactor1.4.3 Packed-Bed Reactor1.5 Industrial Reactors
3 Socrates (470-399 B.C.) The first step to knowledge The first step to knowledgeis to know that we are ignorant
4 Objectives Chapter 1. Mole Balance After completing Chapter 1, the reader will be able to: Define the rate of chemical reaction. Apply the mole balance equations toa batch reactor, CSTR, PFR, and PBR. Describe two industrial reaction engineering systems. Describe photos of real reactors.
5 The identity of a chemical species The species nicotine is made up of a fixed number of a specific atoms in the specific atoms in a definite molecular arrangement or configuration. The structure shown illustrates the kind, number, and configuration of atoms in the species nicotine on a molecular level.
6 The identity of a chemical species cis-2-butene trans-2-butene 2-butene has four carbon atoms and eight hydrogen atoms; however the atoms in this compound can form two different arrangements.cis-2-butene trans-2-buteneAs a consequence of the different configurations, these two isomers display different chemical and physical properties. Therefore, we consider them as two different species.HHHCH3C=CC=CCH3CH3CH3H
7 When has a chemical reaction taken place? We say that chemical reaction has taken place when a detectable number of molecules of one or more species have lost their identity and assumed a new form by a change in the kind or number of atoms in the compound and/or by a change in structure or configuration of these atoms.The identity of a chemical species is determined by the kind, number, and configuration of that species’ atoms.
8 A species can lose its identity by 3 reactions Three basic chemical reactions:1. Decomposition (분해반응)2. Combination (결합반응)3. Isomerization (이성질화반응)
9 When has a chemical reaction taken place? Three basic chemical reactions:CH(CH3)2+ C3H6DecompositionCombinationCH2=C-CH2CH3CH3CH3C=CHCH3Isomerization분자가 그들의 화학적 동일성을 잃을 때 어떤 특정 화학성분의 분자의 일정 개수가 반응 또는 소실되었다고 말한다.
10 Reaction rate rA: the rate of formation of species A per unit volume The rate of a reaction can be expressed as the rate of disappearance of a reactant or as the rate of appearance of a product.Consider species A:A → BrA: the rate of formation of species A per unit volume-rA: the rate of disappearance of species A per unit volumerB: the rate of formation of species B per unit volume
11 What is –r A (–r´A )?2C6H5Cl CCl3CHO (C6H4Cl)2CHCCl H2OChlorobenzene Chloral DDT (Dichloro Diphenyl-Trichloroethane)Fuming H2SO4The numerical value of the rate of reaction, -rA, is defined asthe number of moles of chloral reacting (disappearing)per unit time per unit volume [mol/dm3·s].Solely a function of properties of reacting materials.(Concentration, temperature, pressure, catalyst or solvent)An intensive quantity.An algebraic function of concentration. such as.for homogeneous system:for heterogeneous system:
13 Ideal Reactor Type Batch Reactor -uniform composition everywhere in the reactor-the composition changes with timeContinuous-Stirred Tank Reactor (CSTR)-uniform composition everywhere in the reactor (well mixed)-same composition at the reactor exitTubular Reactor (PFR)-fluid passes through the reactor with no mixing of earlierand later entering fluid, and with no overtaking.-It is as if the fluid moved in single file through the reactor-There is no radial variation in concentration (plug-flow reactor)
14 Is Sodium Hydroxide Reacting? NaOH + CH3COOC2H5 CH3COONa + C2H5OHCSTRNaOHCH3COOC2H51P.M. = 3P.M.C2H5OH,CH3COONa, andunreactedNaOH andCH3COOC2H5Steady state: the product is continuously withdrawn from the tank at a rate equal to the total feed rate.
15 Balance on control volume NjGj = rj · VFj0FjA mole balance on species j, at any time, t, yieldsRate of flow of j into the system (mole/time)Rate of flow of j out of the system (mole/time)Rate of generation of j by chem. rxn within the system (mole/time)Rate of accumulation of j within the system (mole/time)-+=in out generation = accumulation
16 Rate of formation of species j by chem. rxn Suppose that the rate of formation of species j for the reaction varies with the position in the control volume. The rate of generation, DGj1, in terms of rj1 and sub-volume DV1 isDV1DV2Vrj1rj2If the total control volume is divided intoM sub-volume, the total rate of generation isBy taking the appropriate limits (i.e., let M → and DV → 0) and making use of the definition of integral, we can rewrite the foregoing equation in the formFrom this equation, we can see that r j will be an indirect function of position, since the properties of the reacting materials (e.g., conc., temp.) can have different values at difference locations in the reactor.
17 1.2 The General Mole Balance Equation (GMBE)With this GMBE, we can develop the design equations for the various types of industrial reactors: batch, semi-batch, and continuous-flow. Upon evaluation of these equations we can determine the time (batch) or reactor volume (continuous-flow) necessary to convert a specified amount of reactants to products.
18 1.3 Batch Reactors A → B NA (1-5) t If the reaction mixture is perfectly mixed so that there is no variation in the rate of reaction throughout the reactor volume, we can take rj out of the integral and write the GMBE in the formNo spatial variations in the rate of reactionNA0A → BNA(1-5)t
19 What time is necessary to reduce the initial number of moles from NA0 to NA1?Integrating with limits thatat t = 0, NA = NA0at t = t1, NA = NA1(1-6)
22 1.4.1 Continuous-Stirred Tank Reactor (CSTR) Fj0The CSTR is normally run at steady state andis assumed to be perfect mixed.- No temporal, spatial variations in conc., temp., or rxn rate throughout the vessel- Conc. and temp at exit are the same as they are elsewhere in the tank- Non-ideal mixing, residence-time distribution model is neededFjNo spatial variations in the rate of reactionDesign Equation for a CSTR
23 1.4.1 Continuous-Stirred Tank Reactor (CSTR) Fj0Design Equation for a CSTRFj
24 1.4.2 Tubular Reactor - The reaction rate will also vary axially. - To develop the PFR design equation, we shall divide (conceptually) the reactor into a number of sub-volumes so that within each sub-volume DV, the reaction rate may be considered spatially uniform.Let Fj(y) represent the molar flow rate of species j into volume DV at yFj(y+D y) represent the molar flow rate of species j out of volume DV at (y+D y)In a spatially uniform sub-volume DV,
25 Tubular ReactorSteady state(1-8)rj is a function of reactant concentration, which is function of the position y down the reactor.Substitute DV into Eq. 1-8 and divide by Dy to yieldTaking the limit as Dy approaches zero, we obtain
26 Tubular ReactorIt is usually most convenient to have the reactor volume V rather than the reactor length y as the independent variable. Using dV=Ady,The tubular reactor design equation can be applied to the PFR with variable and constant cross-sectional area.
27 Tubular ReactorIt is usually most convenient to have the reactor volume V rather than the reactor length y as the independent variable. Using dV=Ady,The tubular reactor design equation can be applied to the PFR with variable and constant cross-sectional area.
29 Packed-Bed Reactor (PBR) For a fluid-solid heterogeneous system, the rate of reaction of a substance A is defined asThe mass of solid is used because the amount of the catalyst is what is important to the –r’AIn out generation = accumulationNo pressure dropNo catalyst decay
30 Example 1-1 How large is it? (PFR) CA0 v0CAVrA=-kCAThe first-order reaction (liquid phase rxn)A Bis carried out in a tubular reactor in which the volumetric flow rate, v0, is constant.(1) Derive an equation relating the reactor volume (V) to the entering concentration of A (CA0), the rate constant k, and the volumetric flow rate v0.(2) Determine the reactor volume necessary to reduce the exiting concentration (CA) to 10% of the entering concentration (CA0) when the volumetric flow rate (v0) is 10 ℓ/min and the specific reaction rate, k, is 0.23 min-1.
31 Example 1-1 How large is it? (PFR) (GMBE for tubular reactor)(first-order reaction)Tubular, 1st order rxn
32 P1-6B How large is it? (CSTR) VrA=-kCAFj0FjThe first-order reaction (liquid phase rxn)A Bis carried out in a CSTR in which the volumetric flow rate, v0, is constant.(1) Derive an equation relating the reactor volume (V) to the entering concentration of A (CA0), the rate constant k, and the volumetric flow rate v0.(2) Determine the reactor volume necessary to reduce the exiting concentration (CA) to 10% of the entering concentration (CA0) when the volumetric flow rate (v0) is 10 ℓ/min and the specific reaction rate, k, is 0.23 min-1.
33 P1-6B How large is it? (CSTR) For CSTR,the mole balance on species A was shown to beVrA=-kCAFj0FjThe CSTR is almost 4 times larger than the PFR for getting 90% conversion
34 Mole Balance on Different Reactor Reactor Differential Algebraic IntegralBatchCSTRPFRPBR
35 HomeworkP1-7AP1-9AP1-11BP1-15BDue Date: Next Week