Mustafa Nasser, PhD, MSc, BSc Chemical Engineering CHE402: Kinetics and Reactor Design CHAPTER ONE Mole Balances in Reacting Systems & Reactor Design Equations Mustafa Nasser, PhD, MSc, BSc Chemical Engineering Dr Mustafa Nasser 2012

Objectives Describe photos of real reactors. Define the rate of chemical reaction. Apply a general mole balance to a batch reactor, a continuous stirred tank reactor (CSTR), a plug flow reactor (PFR), and a packed bed reactor (PBR). Dr Mustafa Nasser 2012

Industrial Reactors Dr Mustafa Nasser 2012

Industrial Reactors Dr Mustafa Nasser 2012

Industrial Reactors Dr Mustafa Nasser 2012

Spherical Reactors Dr Mustafa Nasser 2012

Industrial Reactors Dr Mustafa Nasser 2012

Industrial Reactors Dr Mustafa Nasser 2012

Industrial Reactors Dr Mustafa Nasser 2012

Industrial Reactors Dr Mustafa Nasser 2012

Packed Bed Reactor Packed Bed Reactor in use for a Fisher-Tropsch synthesis reaction at Sasol Limited Chemical. Dr Mustafa Nasser 2012

Straight Through Transport Reactor Straight Through Transport Reactor (STTR) in use for a Fisher-Tropsch synthesis reaction at Sasol Limited Chemical. Dr Mustafa Nasser 2012

Laboratory CSTR/Batch Reactor Dr Mustafa Nasser 2012

Laboratory CSTR Dr Mustafa Nasser 2012

RC1e Reaction Calorimeter Dr Mustafa Nasser 2012

Chemical Identity A chemical species has reacted when it has lost its chemical identity. The identity of a chemical species is determined by the kind, number, and configuration of that species' atoms. Dr Mustafa Nasser 2012

Loss of Chemical Identity Decomposition; AB  A + B Combination; A + B  AB Isomerization; A  B single displacement (substitution); A + BC  AC + B double displacement (metathesis); AB + CD  AD + CB Dr Mustafa Nasser 2012

Reaction Rate The reaction rate is the rate at which a species looses its chemical identity 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. Reaction rates are associated with reaction stoichiometry, which describe molar relationships Dr Mustafa Nasser 2012

Reaction Rate Consider species A: rA = rate of formation of A per unit vol -rA = rate of a disappearance of A per unit vol For a catalytic reaction, -rA' is the rate of disappearance of species A on a per mass of catalyst basis. NOTE: dCA/dt is not the rate of reaction Dr Mustafa Nasser 2012

Reaction Rate Consider in general terms, species j… The rate, rj is the rate of formation of species j per unit volume a function of concentration, temperature, pressure, and the type of catalyst (if any) independent of the type of reaction system (batch, plug flow, etc.) an algebraic equation, not a differential equation Dr Mustafa Nasser 2012

Reaction Rate rA = the rate of formation of species A per unit volume Consider species A: A  B rA = the rate of formation of species A per unit volume -rA = the rate of a disappearance of species A per unit volume rB = the rate of formation of species B per unit volume EXAMPLE: A  B If B is being formed at 0.2 moles per decimeter cubed per second, ie, rB = 0.2 mole/dm3/s Then A is disappearing at the same rate: -rA= 0.2 mole/dm3/s The rate of formation (generation of A) is rA= -0.2 mole/dm3/s Dr Mustafa Nasser 2012

Which reaction type characterizes the combusion of ethane Which reaction type characterizes the combusion of ethane? 2 C2H6 + 7 O2  4 CO2 + 6 H2O combination isomerization decomposition single displacement double displacement E Dr Mustafa Nasser 2012

Which statement is always false? D Dr Mustafa Nasser 2012

General Mole Balance Equation Gj Fjo Fj where N is the moles of j in the system at time t. Dr Mustafa Nasser 2012

General Mole Balance Equation Gj Fjo Fj if all variables are spatially uniform Dr Mustafa Nasser 2012

General Mole Balance Equation If rj varies with position in the system, rj,1 V1 rj,2 V2 Dr Mustafa Nasser 2012

General Mole Balance Equation Gj Fjo Fj Dr Mustafa Nasser 2012

Reaction Rate and Rate Law Dr Mustafa Nasser 2012

Reaction Rate and Rate Law Dr Mustafa Nasser 2012

GMBE Applied to Batch Reactors For a batch reactor (no flows): GMBE reduces to: Dr Mustafa Nasser 2012

GMBE Applied to Batch Reactors Assuming perfect mixing: Batch Reactor Design Equation Dr Mustafa Nasser 2012

GMBE Applied to Batch Reactors For the simple reaction A  products: In a constant volume reactor, Dr Mustafa Nasser 2012

GMBE Applied to Batch Reactors For the simple reaction A  products: In a constant pressure reactor, Dr Mustafa Nasser 2012

Batch Reactors Dr Mustafa Nasser 2012

Which is NOT a characteristic of an ideal batch reactor ? Absence of concentration gradients (i.e., perfect mixing) Steady state operation No material crosses system boundary (i.e., no flows) Derivative with respect to time B Dr Mustafa Nasser 2012

GMBE Applied to Flow Reactors Continuous Stirred-Tank Reactor (CSTR): reactants steady state perfect mixing volumetric flow rate products Dr Mustafa Nasser 2012

GMBE Applied to Flow Reactors Continuous Stirred-Tank Reactor (CSTR): reactants steady state perfect mixing CSTR Design Equation products Dr Mustafa Nasser 2012

Which is NOT a characteristic of an ideal CSTR? Absence of concentration gradients (i.e., perfect mixing) Steady state operation Material crosses system boundary (i.e., flows in and out) Derivative with respect to time D Dr Mustafa Nasser 2012

GMBE Applied to Flow Reactors Tubular (Plug Flow) Reactor (PFR): y y+y y reactants products V Fj(y) Fj(y+y) Dr Mustafa Nasser 2012

GMBE Applied to Flow Reactors Tubular (Plug Flow) Reactor (PFR): steady state spatially uniform V V Fj(y) Fj(y+y) Dr Mustafa Nasser 2012

GMBE Applied to Flow Reactors Tubular (Plug Flow) Reactor (PFR): steady state spatially uniform V uniform cross-section Dr Mustafa Nasser 2012

GMBE Applied to Flow Reactors Tubular (Plug Flow) Reactor (PFR): PFR Design Equation Dr Mustafa Nasser 2012

Which IS a characteristic of an ideal Plug Flow Reactor? Absence of concentration gradients (i.e., perfect mixing) Steady state operation Material crosses system boundary (i.e., flows in and out) Derivative with respect to time C Dr Mustafa Nasser 2012

GMBE Applied to Packed Bed Reactors PBR used for fluid/solid catalytic reaction: W W+W W FAo FA W FA(W) FA(W+W) Dr Mustafa Nasser 2012

GMBE Applied to Packed Bed Reactors PBR used for fluid/solid catalytic reaction: dimensions of generation term W FA(W) FA(W+W) Dr Mustafa Nasser 2012

GMBE Applied to Packed Bed Reactors PBR used for fluid/solid catalytic reaction: PBR Design Equation When pressure drop and catalyst decay can be neglected, integral form can be used: Dr Mustafa Nasser 2012

Which IS a characteristic of an ideal Packed Bed Reactor? Absence of concentration gradients (i.e., perfect mixing) Steady state operation No material crosses system boundary (i.e., no flows) Derivative with respect to position D Dr Mustafa Nasser 2012

Design Equation Summary Batch CSTR PFR PBR Dr Mustafa Nasser 2012

Example 2: Batch Reactor Times A  B Calculate the time to reduce the number of moles by a factor of 10 (NA = NA0/10 ) in a batch reactor for the above reaction with -rA = kCA,  when k = 0.046 min-1 Dr Mustafa Nasser 2012

Solution Mole balance: In - Out + Generation = Accumulation Dr Mustafa Nasser 2012

Dr Mustafa Nasser 2012

Example 3 Dr Mustafa Nasser 2012

Solution Dr Mustafa Nasser 2012

Some General Quiz 1. In the formula for CSTR, if the rate of reaction is not constant and is dependent on the concentration, should we take to mean? the integral mean?

Some General Quiz Because the reactor is well-mixed, the concentrations, temperature, and rate of reaction are the same throughout the reactor volume, including the point at which it exits the reactor. Consequently, the concentrations, temperature, and rate of reaction in the reactor are all evaluated at the exit conditions of the CSTR.

P1-8 Dr Mustafa Nasser 2012

P1-8 Solution (a) Batch Reactor - Closed system, No Input or output streams. - Well mixed and no spatial variation in system properties. - Constant Volume or constant Pressure. (b) CSTR - Steady state - No spatial variation in concentration, temperature, or reaction rate through the vessel. (c,d) PFR and PBR Steady State No Radial variation in properties of the system Dr Mustafa Nasser 2012

P1-8 Solution (e) State the meaning of - rA is the number of Moles of A reacting (disappearing) per unit of time per unit of volume. - rA’ is the number of Moles of A reacting (disappearing) per unit of time per unit of mass of catalyst (or Surface Area). rA’ is the number of Moles of A generated per unit of time per unit of mass of catalyst (or Surface Area). In General: Rate of reaction is an intensive property that is, it is a function of concentration, temp, pressure and the type of catalyst if any. And is defined at any point (location) within the system. It is independent of the amount of reactants. Dr Mustafa Nasser 2012

P1-13A(Fogler) Complete the table: Type of reactor characteristics phases present uses advantages disadvantages Batch CSTR PFR PBR Dr Mustafa Nasser 2012

P1-13A(Fogler) Batch Reactor Dr Mustafa Nasser 2012

P1-13A(Fogler) CSTR Dr Mustafa Nasser 2012

P1-13A(Fogler) PFR Dr Mustafa Nasser 2012

P1-13A(Fogler) PBR Dr Mustafa Nasser 2012

P15a (CSTR)

P15a (PFR)

P1-15b (CSTR)

P1-15b (PFR) P1-15c (Take home)

Try now: (c) (a) (b) Dr Mustafa Nasser 2012

Dr Mustafa Nasser 2012