Kinetics and Reactor Design Dr. Khashayar Nasrifar Department of Chemical Engineering Jan. 2015

Contact Details: Office: 5D-42 Lectures: 3 hours per week Lecture room: 2A-9

Course Outcomes 1. To define the meaning of chemical design 2. To describe the meaning of rate of reaction and rate mathematical models 3. To differentiate between different types of reactor system and their calculations 4. To identify the effect of catalyst on rate of reaction and reactor design parameters 5. To apply the fundamentals of reactor design on process selection based on selectivity and profitability

Syllabus Introduction to chemical reaction engineering and mole balance (3 hrs) Expressing the design equation in terms of conversion, finding the size of continuous reactor using Levinspiel diagram (6 hrs) Defining the meaning of reaction rate law, type of rate of reactions, and relation to the stoichiometric equation (6 hrs) Design of isothermal reactors, study the effect of heat on the reaction rate and reactor design (6 hrs) Calculating the reaction rate from experimental data. Find reaction order and reaction constant from experimental data (6 hrs)

Syllabus Design of reactors with multiple reactions. Finding the rate of reaction for multi-component, study the selectivity of the reaction and their effect on the reactor design (6 hrs) Study the reaction mechanism, heterogeneous reactions and introduction to the design of bioreactors (6 hrs) Study the catalysis, defining the catalyst, their role in the reaction (6 hrs) Total: 45 hrs

Assessments Final exam 40% Mid semester test 40% Quiz 10% Assignments 10% Total 100%

Lecture 1 Chapter 1: General Mole Balance Equation Applied to Batch Reactors, CSTRs, PFRs, and PBRs .

Objectives After completing Chapter 1 of the text and associated the reader will be able to: Define the rate of chemical reaction. Apply the mole balance equations to a batch reactor, CFSTR, PFR, and PBR. Describe two industrial reaction engineering systems. Describe photos of real reactors.

Chemical Identity A chemical species is said to have 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. Decomposition CH3CH3  H2 + H2C=CH2 Combination N2 + O2  2NO 3. Isomerization C2H5CH=CH2 CH2=C(CH3)2

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. 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

Reaction Rate 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

NOTE: dCA/dt is not the rate of reaction Reaction Rate For a catalytic reaction, we refer to -rA', which is the rate of disappearance of species A on a per mass of catalyst basis. NOTE: dCA/dt is not the rate of reaction WHY?

Example 1 Is sodium hydroxide reacting? Sodium hydroxide and ethyl acetate are continuously fed to a rapidly stirred tank in which they react to form sodium acetate and ethanol: NaOH CH3COOC2H5 Products CH3COONa + C2H5OH and unreacted NaOH + CH3COOC2H5

Reaction Rate Consider species j: rj is the rate of formation of species j per unit volume [e.g. mol/dm3*s] rj is a function of concentration, temperature, pressure, and the type of catalyst (if any) rj is independent of the type of reaction system (batch, plug flow, etc.) rj is an algebraic equation, not a differential equation We use an algebraic equation to relate the rate of reaction, -rj, to the concentration of reacting species and to the temperature at which the reaction occurs [e.g. -rj = k(T)Cj2].

General Mole Balance

Batch Reactor Mole Balance

Constantly Stirred Tank Reactor

CSTR Mole Balance

Plug Flow Reactor

Plug Flow Reactor Mole Balance This is the volume necessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA.

Packed Bed Reactor Mole Balance This is the weight of catalyst necessary to reduce the entering molar flow rate (mol/s) from FA0 to the exit molar flow rate of FA.

Reactor Mole Balance Summary Differential Algebraic Integral Batch CSTR PFR PBR

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

Solution Mole balance: In - Out + Generation = Accumulation

Example 3 The irreversible liquid phase second order reaction is carried out in a CSTR. The entering concentration of A, CA0, is 2 mol/dm3 and the exit concentration of A, CA is 0.1 mol/dm3. The entering and exiting volumetric flow rate, v0, is constant at 3 dm3/s. What is the corresponding reactor volume?

Solution × ?

WHAT IS WRONG? The entering concentration, CA0 = 2 mol/dm3 of A was substituted into the rate law instead of the exit concentration CA = 0.1 mol/dm3. Because the CSTR is perfectly mixed, the concentration inside the CSTR where the reaction is taking place is the same as that in the exit. The reactor volume is fairly large at about 5 thousand gallons. (3.785 dm3 = 1 US gallon)

Straight Though Transport Reactor

Automotive Catalytic Converter

Sasol Advanced Synthol (SAS) Reactor