Page 76 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

An explanation of the function of each block in Figure 2.4(a) is given below.
1. Reactor Feed Preparation Block: In most cases, the feed chemicals entering a process come
from storage. These chemicals are most often not at a suitable concentration, temperature, and
pressure for optimal performance in the reactor. The purpose of the reactor feed preparation
section is to change the conditions of these process feed streams as required in the reactor.
2. Reactor Block: All chemical reactions take place in this block. The streams leaving this block
contain the desired product(s), any unused reactants, and a variety of undesired by-products
produced by competing reactions.
3. Separator Feed Preparation Block: The output stream from the reactor, in general, is not at a
condition suitable for the effective separation of products, by-products, waste streams, and
unused feed materials. The units contained in the separator feed preparation block alter the
temperature and pressure of the reactor output stream to provide the conditions required for the
effective separation of these chemicals.
4. Separator Block: The separation of products, by-products, waste streams, and unused feed
materials is accomplished via a wide variety of physical processes. The most common of these

techniques are typically taught in unit operations and/or separations classes—for example,
distillation, absorption, and extraction.
5. Recycle Block: The recycle block represents the return of unreacted feed chemicals, separated
from the reactor effluent, back to the reactor for further reaction. Because the feed chemicals
are not free, it most often makes economic sense to separate the unreacted reactants and recycle