ERT 316: REACTION ENGINEERING CHAPTER 1 MOLE BALANCES

ERT 316: REACTION ENGINEERINGCHAPTER 1MOLE BALANCES Lecturer: Miss Anis Atikah Ahmad Email: anisatikah@unimap.edu.my Tel: +604-976 3245

OUTLINE • Introduction • Chemical Species • Chemical Reaction • Rate of Reaction • General Mole Balance Equation • Batch Reactor • Continuous-Flow Reactors • Industrial Reactors

Introduction • Application of Chemical Reaction Engineering

1. Chemical species What are chemical species? • Any chemical component or element with a given identity. • Identity of a chemical species is determined by the kind, number, and configuration of that species’ atoms. • Kind of species- methane, butene, butane • Number of atoms- eg: CH4: 1 C, 4 H • Configuration of atoms- arrangement of the atoms

Can they be considered as different SPECIES? Kind: Same (Butene) Number of atoms: Same (C4H8) Configuration: Different arrangement ANSWER: Yes. We consider them as two different species because they have different configurations.

2. Chemical reaction • Chemical reaction is any reaction when one or more species lost their identity and produce 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. HOW????

2. Chemical reaction • Species may lose its chemical identity by: 1) Decomposition (by breaking down the molecule into smaller molecule) Eg: C ⇌ A + B 2) Combination (reverse of decomposition) 3) Isomerization ( neither add other molecule nor breaks into smaller molecule)

It tells how fast a number of moles of one chemical species to form anotherchemical species. 3. Rate of Reaction, ,the rate of reaction: is the number of moles of A reacting (disappearing) per unit time per unit volume ( ). , is the rate of formation (generation) of species A. , is a heterogeneous reaction rate: the no of moles of A reacting per unit time per unit mass of catalyst ( catalyst)

4. The General Mole Balance Equation • A mole balance of species j at any instant time: Rate of accumulation of j within the system (moles/time) Rate of generation of j by chemical reaction within the system (moles/time) Rate of flow of j into the system (moles/time) Rate of flow of j out of the system (moles/time) In - Out + Generation = Accumulation Fj0 - Fj + Gj = Fj0 - Fj + =

4. The General Mole Balance Equation Consider a system volume : System volume Fj0 Gj Fj General mole balance: Fj0 - Fj + Gj = dNj/dt In - Out + Generation = Accumulation

The General Mole Balance Equation Condition 1: • If all the the system variables (eg: T, C) are spatially uniform throughout a system volume: Gj = rj.V

The General Mole Balance Equation Condition 2: • If the rate of formation, rjof a species j for the reaction varies with position in the system volume: • The rate of generation ∆Gj1: ∆Gj1=rj1∆V1 ∆V1 rj1 rj2 ∆V2 Fj0 Fj

4. The General Mole Balance Equation • The total rate of generation within the system volume is the sum of all rates of generation in each of the subvolumes. • Taking the limit M∞, and ∆V0 and integrating,

TYPE OF REACTORS in out Batch REACTORS Continuous Flow

5. Batch Reactors • The reactants are first placed inside the reactor and then allowed to react over time. • Closed system: no material enters or leaves the reactor during the time the reaction takes place. • Operate under unsteady state condition. • Advantage: high conversion the conditions inside the reactor (eg: concentration, temperature) changes over time

5. Batch Reactors: Derivation • Batch reactor has neither inflow nor outflow of reactants or products while the reaction is carried out: FA0 = FA = 0 • General Mole Balance on System Volume V FA0 - FA+ =

5. Batch Reactors: Derivation • Assumption: Well mixed so that no variation in the rate of reaction throughout the reactor volume: • Rearranging; • Integrating with limit at t=0, NA=NA0 & at t=t1, NA=NA1,

6. Continuous-Flow Reactors: steady state 1. Continuous-Stirred Tank Reactor (Backmix/ vat) • open system: material is free to enter or exit the reactor • reactants are fed continuously into the reactor. • products are removed continuously. • operate under steady state condition • perfectly mixed: have identical properties (T, C) everywhere within the vessel. • used for liquid phase reaction

6.1 Continuous-Stirred Tank Reactor DERIVATION • General Mole Balance: • Assumption: 1.steady state: 2. well mixed: • Mole balance: FA - FA + = 0 FA0 - FA+ = design equation for CSTR

6. Continuous-Flow Reactors: steady state 2. Plug Flow/Tubular Reactor • Consist of cylindrical hollow pipe. • Reactants are continuously consumed as they flow down the length of the reactor. • Operate under steady state cond. • No radial variation in velocity, conc, temp, reaction rate. • Usually used for gas phase reaction

6.2 Plug Flow Reactor DERIVATION • General Mole Balance: • Assumption: 1.steady state: • Differentiate with respect to V: FA0 - FA+ = FA0 - FA+ = 0

6.2 Plug Flow Reactor DERIVATION • Rearranging and integrating between V = 0, FA = FA0 V = V1, FA = FA1

6. Continuous-Flow Reactors: steady state 3. Packed-Bed Reactor (fixed bed reactor) • Often used for catalytic process • Heterogeneous reaction system (fluid-solid) • Reaction takes place on the surface of the catalyst. • No radial variation in velocity, conc, temp, reaction rate

6.3 Packed Bed Reactor DERIVATION • General Mole Balance: • Assumption: 1.steady state: • Differentiate with respect to W: the reaction rate is based on mass of solid catalyst, W, rather than reactor volume FA0 - FA+ = FA0 - FA+ = 0

6.2 Packed Bed Reactor DERIVATION • Rearranging and integrating betweenW = 0, FA = FA0 W = W1, FA = FA1

Summary of Reactor Mole Balance

Industrial Reactors Packed-Bed Reactor at Sasol Limited Chemical

Industrial Reactors Fixed-Bed Reactor at British Petroleum (BP): using a colbalt-molybednum catalyst to convert SO2 to H2S

Industrial Reactors Fluidized Catalytic Cracker at British Petroleum (BP): using H2SO4 as a catalyst to bond butanes and iso-butanes to make high octane gas

ERT 316: REACTION ENGINEERING CHAPTER 1 MOLE BALANCES