Page 290 - Modeling of Chemical Kinetics and Reactor Design

260 Modeling of Chemical Kinetics and Reactor Design

CHAPTER FIVE

Introduction to Reactor

Design Fundamentals

for Ideal Systems

INTRODUCTION

In Chapter 4, the various types of laboratory and industrial reactors
were reviewed. Reactor design is primarily concerned with the type
and size of reactor and its method of operation for the required
process. Important considerations are given at an early stage in the
design of any process where chemical reaction is required. Designers
must first consider the thermodynamics involving the equilibrium of
reaction before investigating the chemical kinetics in relation to the
reaction mechanisms. Figure 5-1 succinctly illustrates the logic of this
approach. In this figure, consideration is given to the possibility of
using either a gas phase or liquid phase reaction, whether the reaction
is endothermic (i.e., absorbing heat) or exothermic (i.e., releasing heat),
and whether or not the reaction is reversible.
There are advantages to using the liquid phase rather than the gas
phase operation. For example, for the desired product the reactor may
be smaller. This is because the physical properties of liquids are greater
than those for gases, namely the heat capacities and thermal con-
ductivities, factors which increase the heat transfer. Additionally, the
equipment size is small resulting in lower power requirements and
capital costs. The main disadvantages are corrosion and catalyst losses.
In considering a liquid system, all operating conditions must fall within
the two-phase region. If the critical temperature is not significantly
above the desired reaction temperature, high operating pressures are
potentially hazardous and expensive to contain, especially if one
of the reactants is a noncondensable gas, which is required at high
partial pressure.

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