2- mole balances_stu

Chemical Reaction Engineering (CRE) is the field that…

TODAY’S LECTURE

Introduction

Definitions

General Mole Balance Equation

Chemical Reaction Engineering

Chemical reaction engineering is at the heart of virtually every chemical process. It separates the chemical engineer from other engineers.

Let’s Begin CRE

Chemical Reaction Engineering (CRE) is the field that …..

• A chemical species is said to have reacted when it has lost its chemical identity.

Chemical Identity

• A chemical species is said to have reacted when it has lost its chemical identity.

1. Decomposition

Chemical Identity

• The reaction rate is the rate at which a species looses its chemical identity per unit volume.

Reaction Rate

Reaction Rate

Consider the isomerization AB

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: AB If Species B is being formed at a rate of

0.2 moles per decimeter cubed per second, ie,

rB = 0.2 mole/dm3/s

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.

(mol/gcat/s)

Reaction Rate

Consider species j:

• rj is the rate of formation of species j per unit volume [e.g. mol/dm3/s]

General Mole Balance

General Mole Balance

Batch Reactor Mole Balance

Batch Reactor Mole Balance

Continuously Stirred Tank Reactor Mole Balance

CSTR (Cont.)

Plug Flow Reactor

PFR Mole Balances

PFR:

PFR Mole Balances (Cont.)

PFR Mole Balances (Cont.)

PFR:

The integral form is:

V dFAr

AFA 0

FA

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

PBR

PBR Mole Balances (Cont.)

PBR

FA0 FA r AdW dNA

dt

Reactor Mole Balance Summary

KEEPING UP

Separations

These topics do not build upon one another

Filtration Distillation Adsorption

Reaction Engineering

These topics build upon one another

Mole Balance Rate Laws Stoichiometry

Mole Balance Rate Laws

Mole Balance

Rate Laws

Stoichiometry

Isothermal Design

Heat Effects

Homework 1: A 200-dm3 constant-volume batch reactor is pressurized to 20 atm with a mixture of 75% A and 25% inert. The gas-phase reaction is carried out isothermally at 227 C.

V = 200-dm3

P = 20 atmT = 227 C 

a. Assuming that the ideal gas law is valid, how many moles of A are in the reactor initially? What is the initial concentration of A? b. If the reaction is first order:

Calculate the time necessary to consume 99% of A.c. If the reaction is second order:

Calculate the time to consume 80% of A. Also calculate the pressure in the reactor at this time if the temperature is 127 C.

Homework 2: