Page 292 - Modeling of Chemical Kinetics and Reactor Design

262 Modeling of Chemical Kinetics and Reactor Design

of reactors depends on many factors such as safety, environment, and
profit. Optimization techniques are often employed during the design
stage to establish the optimum design from the profit viewpoint. This
includes factors such as raw materials, initial and operating costs, and
the market value of the finished products. The designer also requires
knowledge of reactor performance before reviewing an optimiza-
tion technique.
Chemical reactions are performed in reactor systems that are derived
from one of the following basic types of model reactors:

• The well-mixed reaction system with uniform composition that is
operated batchwise.
• The semibatch reactor where the incoming and outgoing mass
flows are not equal to each other, and the total mass of the
reacting mixture is not constant.
• The continuously operated stirred tank reaction in which the
composition of the reaction mixture is assumed uniform and equal
to the composition at the outlet.
• The tubular (plug flow) reactor in which piston flow of the
reacting mixture is assumed, and there is neither mixing nor
diffusion in the flow direction.

The following details establish reactor performance, considers the
overall fractional yield, and predicts the concentration profiles with
time of complex reactions in batch systems using the Runge-Kutta
numerical method of analysis.

A GENERAL APPROACH

The rate equation involves a mathematical expression describing the
rate of progress of the reaction. To predict the size of the reactor
required in achieving a given degree of conversion of reactants and a
fixed output of the product, the following information is required:

• Composition changes
• Temperature changes
• Mixing patterns
• Mass transfer
• Heat transfer