Page 61 - Plant design and economics for chemical engineers

# PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS
require additional information? What approximations would be necessary if data are
not available to resolve these questions?
6. Ethylene is produced commercially in a variety of different processes. Feed stocks
for these various processes range from refinery gas, ethane, propane, butane, natural
gasoline, light and heavy naphthas to gas and oil and heavier fractions. Prepare three
different qualitative flow sheets to handle a majority of these feed stocks. What are
the advantages and disadvantages of each selected process?
7. Gather all the available information on one of the ethylene processes for which a
flow sheet was prepared in the preceding problem and make a preliminary material
balance for the production of 50 million lb/yr of ethylene. Assume an operating
factor of 90 percent.
8. One method of preparing acetaldehyde is by the direct oxidation of ethylene. The
process employs a catalytic solution of copper chloride containing small quantities of
palladium chloride. The reactions may be summarized as follows:
WCI,
C,H, + 2CuC1, + H,O - CH,CHO f 2HCl+ 2CuCl
2CuCl+ 2HCl+ ;O, - 2CuC1, + H,O
In the reaction, PdCl, is reduced to elemental palladium and HCl, and is reoxidized
by CuCl,. During catalyst regeneration the CuCl is reoxidized with oxygen. The
reaction and regeneration steps can be conducted separately or together.
In the process, 99.8 percent ethylene, 99.5 percent oxygen, and recycle gas are
directed to a vertical reactor and are contacted with the catalyst solution under slight
pressure. The water evaporated during the reaction absorbs the exothermic heat
evolved, and make-up water is fed as necessary to maintain the catalytic solution
concentration. The reacted gases are water-scrubbed and the resulting acetaldehyde
solution is fed to a distillation column. The tail gas from the scrubber is recycled to
the reactor. Inerts are eliminated from the recycle gas in a bleed stream which flows
to an auxiliary reactor for additional ethylene conversion.
Prepare, in the form of a flow sheet, the sequence of steps in the development
of a plant to produce acetaldehyde by this process. An analysis of the points to be
considered at each step should be included. List the additional information that will
be needed to complete the preliminary design evaluation.
9. Prepare a simplified equipment flow sheet for the acetaldehyde process outlined in
Prob. 8. Identify temperature, pressure, and composition, wherever possible, at each
piece of equipment.
10. Prepare a material balance and a qualitative flow sheet for the production of 7800
kg/h of acetaldehyde using the process described in the previous problem. Assume
an operating factor of 90 percent and a 95 percent yield on the ethylene feed. Both
ethylene and oxygen enter the process at 930 kPa.
11. Using the information developed in Prob. 10, make a basic energy balance around
each piece of equipment and for the entire process. Prepare, a quantitative flow
sheet to outline the results of the basic energy balance.
12. Prepare a material balance for the production of 7800 kg/h of acetaldehyde using
the process described in Prob. 8. However, because 99.5 percent oxygen is unavail-
able, it will be necessary to use 830%Pa air as one of the raw materials. What steps
of the process will be affected by this substitution in feed stocks? Assume an
operating factor of 90 percent and a 95 percent yield on the ethylene feed.