Review Chapters (1 – 6) CHPE550: Catalysis and Catalytic Processes Lecturer: Dr Qazi Nasir Office : 5D-40, College of Engineering Email: qazinasir@gmail.com

Introduction to reaction engineering Chemical kinetics is the study of chemical reaction rates and reaction mechanisms. The study of chemical reaction engineering (CRE) combines the study of chemical kinetics with the reactors in which the reactions occur Phthalic anhydride

Introduction to reaction engineering Manufacture of Phthalic anhydride

Introduction to reaction engineering Water Treatment Microelectronics Nanoparticles Living system Manufacture of chemicals and pharmaceuticals

Introduction to reaction engineering Smog Hippo Digestion Molecular CRE

Introduction to reaction engineering Oil Recovery Pharmacokinetics Cobra Bites

Introduction to reaction engineering Reaction Rate The reaction rate is the rate at which a species looses its chemical identity per unit volume The identity of a chemical species is determined by the kind, number; and configuration of that species' atoms For example. the species nicotine (a bad tobacco alkaloid) is made of a fixed number of specific atoms in a definite molecular arrangement or configuration

Introduction to reaction engineering Reaction Rate Even though two chemical compounds have exactly the same number of atoms of each element, they could still be different species because of different configurations. For example, 2-butene has four carbon atoms and eight hydrogen atoms; however, the atoms in this compound can form two different arrangements

Introduction to reaction engineering 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 a disappearance of species A per unit volume rB = the rate of formation of species B per unit volume

Introduction to reaction engineering Reaction Rate There are three basic ways a species may lose its chemical identity: decomposition. combination. and isomerization. Decomposition: For example. if benzene and propylene are formed from cumene molecule

Introduction to reaction engineering Reaction Rate Combination: A second way that a molecule may lose its species identity is through combination with another molecule or atom

Introduction to reaction engineering Reaction Rate The third way a species may lose its identity is through isomerization, such as the reaction

Introduction to reaction engineering Reaction Rate Consider the reaction of chlorobenzene and chloral to produce the insecticide DDT (dichorodiphenyl-tricholoethane) in the presence of fuming sulphuric acid

Introduction to reaction engineering Reaction Rate The numerical value of the rate of disappearance of reactant A, -rA is a positive number e.g. -rA = 4 mol A/dm3.s The rate of reaction, -rA is the number of moles of A (e.g.. chloral) reacting (disappearing) per unit time per unit volume (mol/dm3.s). Symbol A represent chloral, B be chlorobenzene, C be DDT, and D be H2O

Introduction to reaction engineering Reaction Rate The heterogeneous reactions involve more than one phase. In heterogeneous reaction systems, the rate of reaction is usually expressed in measures other than volume, such as reaction surface area or catalyst weight.

Introduction to reaction engineering Reaction Rate The rate equation (i.e., rate law) for rj is an algebraic equation that is solely a function of the reacting materials and reaction conditions (e.g., concentration, temperature, pressure or type of catalyst at a point in a system) The rate equation is independent of the type of reactor (e.g., batch or continuous) in which reaction occurs

Introduction to reaction engineering Reaction Rate The chemical reaction rate law is essentially an algebraic equation involving concentration, not a differential equation The algebraic form of the rate law for –rA for the reaction may linear function of conc or

Introduction to reaction engineering General Mole Balance Equation To perform a mole balance on any system, the system boundaries must first be specified. To perform a mole balance on species j in a system volume where species j represents the particular chemical species of interest, such as water or NaOH Balance on system volume

Introduction to reaction engineering General Mole Balance Equation A mole balance on species j at any instant in time. t. yields the following equation:

Introduction to reaction engineering General Mole Balance Equation Gj. is just the product of the reaction volume V. and the rate of formation of species j, rj Suppose now that the rate of formation of species j for the reaction varies with the position in the system volume

Introduction to reaction engineering General Mole Balance Equation Dividing up the system volume, V

Introduction to reaction engineering General Mole Balance Equation The rate of generation, ∆Gj1, in terms of rj1 and sub volume ∆V1 is Similarly the expression can be written for ∆Gj1 and other sub volumes The total rate of generation within the system volume is the sum of all the rates of generation in each of the sub volumes

Introduction to reaction engineering General Mole Balance Equation By taking the appropriate limits (i.e., let M →∞ and ∆V→0) and making use of the definition of an integral and rewrite the foregoing equation in the form General mole balance equation we can develop the design equations for various types of reactors

Reactor Mole Balance Summary Differential Algebraic Integral Batch CSTR PFR (Plug flow reactor) PBR (Packed bed reactor)

Reactor Sizing CSTR CSTR is modeled as being well mixed such that there are no spatial variations in the reactor. The CSTR mole balance when applied to species A in the reaction Simplifying, we get CSTR volume required to achieve specific conversion X X = conversion

Reactor Sizing CSTR Given – rA as a function of conversion, – rA=f(X), one can size any type of reactor. We do this by constructing a Levenspiel plot. 0.2 0.4 0.6 0.8 10 20 30 40 50 Here we plot either as a function of X. X XEXIT For vs. X, the volume of a CSTR is: X = conversion

Space Time Space time, τ, is obtained by dividing reactor volume (V) by the volumetric flow rate entering the reactor (vo): The space time is the time necessary to process one reactor volume of fluid based on entrance conditions. Consider a tubular reactor which is 20 m long & 0.2 m3 in volume. The dash line represent 0.2 m3 of fluid goes directly upstream of reactor.

Space Time Typical space time for industrial reactors

Space Time Sample industrial space times

Space Velocity Space velocity, SV, is obtained by dividing the volumetric flow rate entering the reactor by the reactor volume : The SV is the reciprocal of the space time. Two velocity used in industry is LHSV and GHSV