Page 98 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

2.8 Summary

In this chapter, the development of a process flow diagram has been investigated. The first step in
synthesizing a PFD was to establish and examine all possible chemical routes that form the desired
product(s). The next step was to establish whether the process should operate in a batch or continuous
manner. Guidelines to make this decision were presented in Table 2.1. The next step was to establish the
input/output structure of the process. The process concept diagram was introduced that only required the
identification of the raw materials, products, and stoichiometry of all the reactions that take place. At the
process level, it was shown that all processes possess the same basic structure given in the generic block
flow diagram.

The recycle structure of the PFD was introduced, and the three basic methods of recycle were discussed.
Reasons and examples were provided to illustrate why inert material or products are sometimes recycled
with unreacted raw materials. Difficulties in separating streams of products and reactants were given, and
these were shown to influence the recycle structure and type of separation used.

The separation of products and unreacted raw materials and the integration of energy were covered
briefly and are covered in greater depth in Chapters 12 and 15, respectively. An example showing how
process alternatives are generated using the methods outlined in this chapter was provided, and several
process alternatives were illustrated for this example using generic block flow diagrams. Finally, a list of
resources was presented to help guide the reader to obtain basic data on chemical reactions and

processes.