Acido Acrilico

Energy Balances and Numerical Methods
Design Project
Production of Acrylic Acid
Process Description
Figure 1 is a preliminary process flow diagram (PFD) for the acrylic acid production process.
The raw materials are propylene and oxygen. Steam in added to provide thermal ballast. The
propylene feed may be assumed pure vapor at 446 kPa. The air feed, which may be considered to
contain onlyoxygen, nitrogen, and water is also at 446 kPa. The steam is saturated at 446 kPa.
The feeds are mixed and sent to the reactor (R-301) in which acrylic acid is formed. There
reactions which occur are shown below. The reactor effluent is sent to a separation unit (S-301)
in which all light gases (oxygen, nitrogen, carbon dioxide, and propylene) are separated as vapor
in Stream 7. Stream 7 issplit into Streams 8 and 9. Stream 8 is a recycle stream containing
propylene, oxygen, nitrogen, and carbon dioxide. A pump is required in this stream which is not
shown. Stream 9 is incinerated. Stream 10, containing water and acrylic acid is sent to a
distillation column (T-301) to produce purified acrylic acid. The desired acrylic acid production
rate is 50,000 metric tons/yr.

ProcessDetails
Feed Streams
Stream 1: propylene, pure vapor, 25°C and 446 kPa
Stream 2: air at 218°C and 446 kPa
(it has been compressed from atmospheric pressure causing the temperature
increase - the annual cost for this compression is $1.22M per compressor)
water present in amount to saturate air at 25°C and 1 atm
Stream 3: low-pressure steam
Stream 4: feed mixture should have the followingcomponents:
air (containing oxygen, nitrogen, and water vapor) 55 mole %
steam (added as steam) 40 mole%
propylene 5 mole %
you must determine the stream temperature
Effluent Streams
Stream 9: waste gas stream to incinerator, credit may be taken for LHV of fuel

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Stream 11: waste water stream, treatment cost $50.00/106 kg
must contain less than 0.05 wt % acrylic acid
Stream 12: acrylicacid product, 99.9 wt% purity.
Equipment
Reactor (R-301):
The following reactions occur:
C3 H6 + 15O2 → C3 H 4O2 + H 2O
.
propylene
acrylic acid
C3 H6 + 4.5O2 → 3CO2 + 3H 2O
Selectivities and conversions at various temperatures are given in Table 1. These values
are for the reactor operating pressure of 446 kPa and are independent of the amount of
oxygen present, as long as propylene isthe limiting reactant. Part of your assignment is to
determine the best exit reactor temperature.
Table 1
Selectivity and Conversion at Different Temperatures
Temperature
(°C)
200
250
300
350
400
450
500
550
600
650

Selectivity
(moles acrylic/ moles CO2)
10.0
10.0
9.77
8.91
7.24
4.90
2.45
0.891
0.655
0.610

Conversion of Propylene

0.04
0.05
0.11
0.22
0.36
0.500.63
0.76
0.83
0.86

Separator (S-301):
In this separator, all components other than acrylic acid and water exit in Stream 7. The
acrylic acid and water vapor are partitioned between Streams 7 and 10 according to
Raoult’s law. Part of your task is to determine the optimum temperature and pressure for
this separator. The separator pressure must be below 446 kPa. Note: The vapor pressureexpression given in last semester’s design project is not applicable here. You must
determine such an expression on your own.

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Distillation Column (T-301):
In this distillation column, the water and acrylic acid in Stream 10 are separated. The
column operates at vacuum conditions. Specifications are as follows. The column
pressure is determined by the boiling point of acrylic acid atits maximum allowable
temperature, 90°C. This is also the temperature of Stream 12. The temperature of
Stream 11 is the boiling point of water at the pressure of the column. Energy
requirements are described with the heat exchange equipment, below.
Heat Exchanger (E-301):
In this heat exchanger, you may assume that one-half of the flow of Stream 12, containing
pure acrylic acid, is...