Page 403 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

b. Recycles that reduce impurities in products

Recycles are also used for the following purposes. Identify four examples of each.

a. Heat removal

7.
b. Flowrate control

c. Improvement of separation

d. Reduction of utility requirements

From your previous courses and experience, identify four process recycle streams that serve different
8.
purposes from those identified in 7 (a)–(d).

What information is needed about the available utilities before a choice between them can be made
9.
for a specific heating duty?

Take a flowsheet for one of the processes in Appendix B and identify the reactor feed preparation,
10. reactor, separator feed preparation, separator, recycle, and environmental control sections. Is there
any ambiguity concerning the demarcation of these sections? Explain.

How many simple distillation columns are required to purify a stream containing four components
11.
into four “pure” products? Sketch all possible sequences.

How many simple distillation columns are required to purify a stream containing five components
12.
into five “pure” products? Sketch all possible sequences.

Illustrate a system (PFD and McCabe-Thiele diagrams) to purify two components (A and B) from a
binary, homogeneous, minimum-boiling azeotrope that is pressure sensitive. The feed concentration
13.
of A is greater than the azeotropic composition at the pressure of the column receiving the feed. The
azeotropic composition of A decreases with increasing pressure.

In the production of dimethyl carbonate from methanol, it is necessary to separate methanol from
formal (also known as methylal—C H O ). However, an azeotrope exists between these two
3 8 2
components. Using a process simulator, examine the equilibrium curves (x-y plots) between 100 kPa
and 1000 kPa to determine a strategy for purifying these two components. Compare your results for
the following thermodynamic packages for the K-value:

a. Ideal
14.
b. NRTL

c. UNIFAC

d. SRK

What do you learn from this comparison?