ERT 316: REACTION ENGINEERING CHAPTER 1 MOLE 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

Manufacturing of chemical & pharmaceuticals Introduction Application of Chemical Reaction Engineering Waste treatment Microelectronics Nanoparticles Manufacturing of chemical & pharmaceuticals Living system

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 another chemical 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 generation of j by chemical reaction within the system (moles/time) Rate of accumulation of j 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, rj of 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 Batch in out 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 between    W = 0, FA = FA0    W = W1, FA = FA1

Summary of Reactor Mole Balance Differential Form Algebraic Form Integral Form  Comment Batch   No spatial variations, unsteady state CSTR -   - No spatial variations, steady state PFR Steady state PBR

Packed-Bed Reactor at Sasol Limited Chemical 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