CHBE 457 Process Synthesis
Department of Chemical and Biological Engineering
The University of British Columbia
Assignment 1 Due: Friday, 26 September 2014, 4:30pm CHBE Main Ofce
1. Nitrobenzene (a precursor for aniline) is made by nitration of benzene in the presence of sulfuric
acid:
NO
2
+ HNO
3
+ H
2
O
[H
2
SO
4
]
(R1)
US Patent 4,772,757 describes a process with recycle of nitrating acid.
(a) Search the literature and prepare a qualitative owsheet for the nitrobenzene plant. Explain
the plant operation.
(b) Create a preliminary database, with the following parameters for all major components: Den-
sity, Normal Boiling Point, Heat Capacity, Heat Conductivity, and Critical properties. List
your sources (Perrys Chemical Engineers Handbook, process simulators, the Internet, etc.).
(c) Show an input-output diagram for this process with capacity of 100 000 (tonnes/yr).
(d) What is the maximum gross prot attainable?
Source of prices of commodity chemicals: a weekly publication ICIS Chemical Business at
http://www.icis.com/StaticPages/Students.htm
(Reported prices are mostly from 2006.) Reports (~6 months old) available at
http://www.icispricing.com/il_shared/il_splash/chemicals.asp?llink%
2. Consider the owsheet for the manufacture of vinyl chloride in Figure 4.8 of our textbook:
Figure 1: Flowsheet showing task integration for the vinylchloride process
1
(a) If the pyrolysis furnace and the distillation towers are operated at the same pressure as the
chlorination reactor (1.5 atm), what are the principal disadvantages? Hint: Check the boiling
points and critical constants for the major chemicals, Table 1.
(b) Is it possible to use some of the heat of condensation from the C
2
H
4
Cl
2
condenser to drive
the reboiler of the rst distillation column? Explain your response.
(c) Consider the rst reaction to make dichloroethane. Show the distribution of chemicals when
ethylene is 25% in excess of the stoichiometric amount and the chlorine is entirely converted.
Assume that 100 000 lb/hr of vinyl chloride are produced.
Table 1: Boiling points and critical constants
Normal Boiling Point Boiling point (
C) Critical constants
Chemical at 1 atm (
C) 4.8 atm 12 atm 26 atm T
c
(
C) P
c
(atm)
HCl 84.8 51.7 26.2 0 51.4 82.1
C
2
H
3
Cl 13.8 33.1 70.5 110 159 56
C
2
H
4
Cl
2
83.7 146 193 242 250 50
3. It is desired to produce a hot vapour stream of benzene to feed a reactor for a certain petrochem-
ical process. The benzene is available from an off-site storage facility at 1 atm and 25
C. The
reactor requires the benzene to be at 250
C and 10 atm. Two possible process schemes are being
considered to heat and pressurize the feed: (1) pump the liquid benzene to 10 atm and then heat
it up/vapourize in a heat exchanger, or (2) vapourize the benzene rst and then compress it to the
desired pressure. Use a process simulator to compare the cost of the two proposed schemes to
feed 1000 kg/h of benzene to the reactor. Assume that the cost of heating is $15/GJ and that the
electricity cost (to power the pump or the compressor) is $0.10/kWh.
4. The production of ammonia using the Haber process takes place at temperatures of around 500
C
and pressures of 250 atm using a porous iron catalyst according to the following highly exothermic
reaction:
N
2
(g) +3 H
2
(g) 2 NH
3
(g)
(a) Give possible reasons for the high temperature and pressure used for this reaction.
(b) Use a process simulator to determine the equilibrium conversion obtained in the reactor for
the given conditions. The feed is a mixture of N
2
and H
2
in stoichiometric proportion.
(c) Explain how the temperature and pressure should be adjusted to increase the conversion and
the penalties for making these changes. Support your explanations with the simulation re-
sults.
2
