Lecture 12 Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place.

Today’s lecture Multiple Reactions Selectivety and Yield Series Reactions Complex Reactions

4 Types of Multiple Reactions Series: A → B → C Parallel: A → D, A → U Independent: A → B, C → D Complex: A + B →C + D, A + C → E With multiple reactors, either molar flow or number of moles must be used (no conversion!)

Selectivity and Yield There are two types of selectivity and yield: Instantaneous and Overall. Instantaneous Overall Selectivity Yield

Selectivity and Yield Example: Desired Product: Undesired Product: To maximize the selectivity of D with respect to U run at high concentration of A and use PFR.

Gas Phase Multiple Reactions

Multiple Reactions Chapter 8 A) Mole Balance of Each Species Flow Batch

Multiple Reactions Chapter 8 A) Rates: a) Rate law for each reaction b) Net Rates c) Relative Rates

Multiple Reactions Chapter 8 Stoichiometry: Example: A → B → C (1) A → B k1 (2) B → C k2

Multiple Reactions Chapter 8 1) Mole Balance: V=V0 (constant batch)

Multiple Reactions Chapter 8 Laws Net rates 2) Rates: Relative rates

Batch Series Reactions example: A → B → C (1) A → B (2) B → C t topt Ci A B C 1) Mole balances:

Batch Series Reactions 2) Rates: Laws: Relative:

Batch Series Reactions 3) Combine: Species A: Species B:

Batch Series Reactions Using the integrating factor, at t = 0, CB=0

Batch Series Reactions When should you stop the batch series reaction to obtain the maximum amount of B? Let’s see. t topt Ci A B C

Example: CSTR Series Reactions ABC what is the optimal ? 1) Mole Balance:

Example: CSTR Series Reactions ABC 2) Rates: Laws: Net: Relative:

Example: CSTR Series Reactions ABC 3) Combine:

Example: CSTR Series Reactions ABC Find maximum concentration of B

Net Rate of Reaction for species A For N reactions, the net rate of formation of species A is: For a given reaction i: (i) aiA+biB ciC+diD:

Example A: Liquid Phase PFR Complex Reactions Example A: Liquid Phase PFR NOTE: The specific reaction rate k1A is defined with respect to species A. The complex liquid phase reactions follow elementary rate laws NOTE: The specific reaction rate k2C is defined with respect to species C.

Example A: Liquid Phase PFR The reaction takes place in a PFR. The feed is equal molar in A and B and FA0=200 mol/min and the volumetric flow rate is 100 dm3/min. The reaction volume is 50 dm3 and the rate constants are: Plot FA, FB, FC, FD and SC/D as a function of V.

Example A: Liquid Phase PFR Mole Balances:

Example A: Liquid Phase PFR Net Rates: (5) (6) (7) (8) Rate Laws: (9) (10)

Example A: Liquid Phase PFR Relative Rates: Reaction 1 (11) (12) Reaction 2 (13) (14)

Example A: Liquid Phase PFR Selectivity If one were to write SC/D=FC/FD in the Polymath program, Polymath would not execute because at V=0, FC=0 resulting in an undefined volume (infinity) at V=0. To get around this problem we start the calculation 10-4 dm3 from the reactor entrance where FD will not be zero and use the following IF statement. (15)

Example A: Liquid Phase PFR Stoichiometry: (16) (17) (18) (19) Parameters: (20) (21) (22)

End of Lecture 12

Supplementary Material - Blood Coagulation

Notations

Notations

Mole Balance

Mole Balance

Mole Balance

Result

Blood Coagulation Many metabolic reactions involve a large number of sequential reactions, such as those that occur in the coagulation of blood. Cut → Blood → Clotting Figure A. Normal Clot Coagulation of blood (picture courtesy of: Mebs, Venomous and Poisonous Animals, Medpharm, Stugart 2002, Page 305)

Schematic of Blood Coagulation

Cut A + B C D E F Clot