Design Project 3: Optimization of
Toluene – Benzene Reactor
CHE 433: Process Design and Optimization I
Group Members: Maytham Alzayer, Ramdeep Multani, Ravinder Singh
October 30, 2013
Table of Contents
Introduction
1
Summary
2
Discussion
3-15
Conclusion
16
Assumptions
16
References
17
Appendix
18-21
Introduction
The objective of this project was to optimize and design a benzene producing system. A base
case system was given to optimize the conversion of toluene to benzene and minimize diphenyl
byproduct from a side reaction. The two reactions are shown below:
+
toluene
H
+
H
hydrogen
CH4
benzene
methane
Figure 1: Main Reaction: Thermal Hydrodealkylation
+
benzene
diphenyl
H
H
hydrogen
Figure 2: Side Reaction: Benzene Dealkylation
Preliminary economic conditions were given to estimate net profit for various conversions and therefore
find optimal conversion. The case base assumed perfect separation but the system needed to be
designed for realistic separation. The base case was modified and equipment was sized and a cost
analysis was done. Hand calculations needed to be done to set up the modified process equipment in
Aspen. The Aspen design was further modified to get the desired product purities. The final Aspen
design would then be compared with the base case.
1
Summary
The optimum conditions were found to be at a conversion rate of 70 percent for toluene which
had a selectivity of 97.7 percent at a purge ratio of 1:1 of hydrogen and methane. To optimize the
process, one additional flash drum, distillation column, and 2 pumps and 2 throttles were added to the
base case design. The final optimized case had a 99.99% purity benzene stream compared to the base
case which had a purity of 100%, which was unrealistic while optimizing the process. The optimized case
had a toluene recycle stream containing 2.07% benzene compared to the base case which contained 0%
benzene. The quench streams for both the optimized and the modified bas case resulted in being 21% of
the stream coming out of the first flash drum. While doing a cost analysis, the net profit ended up being
$638,650.97 less for the optimized case compared to the base case. The manufacturing cost for the
optimized case ended up being $94,523 more compared to the base case. The equipment on the other
hand ended up being $560,000 cheaper for the optimized case compared to the base case.
Base Case
Fixed Capital
Final Optimized Case
10,541,754.28
Fixed Capital
cents/gal
($/yr)
Subtotal VC
144.13
39772086.96
Subtotal VC
Subtotal FC
6.53
1801454.80
Subtotal FC
Total Manufacturing Cost
150.66
41573541.76 Total Manufacturing Cost
Revenue
163.83
45207941.44
Revenue
GP
13.17
3634399.68
GP
NP
7.90
2180639.81
NP
Dep
3.82
1054175.43
Dep
CF
11.72
3234815.24
CF
Payout
3.26
Payout
10,541,754.28
cents/gal
144.48
6.53
151.00
160.32
9.31
5.59
3.82
9.41
4.06
($/yr)
39866610.16
1801454.80
41668064.96
44238046.35
2569981.40
1541988.84
1054175.43
2596164.27
Table 1: Cost Analysis (For details cost analysis, see Appendix E)
Base Case
Equipment
Fired Heater
Reactor
steam generator 1
steam generator 2
Heat Exchanger
Flash Drum
Distillation Column 1
Distillation Column 2
Condenser (Distilation column 1)
Reboiler (Distilation column 1)
Reboiler (Distilation column 2)
Condenser (Distilation column 2)
2 Comperssors
Total Cost
Capital Invesment
Lang Factor
Final Optimized Case
Equipment
Fired Heater (Heater)
Reactor
steam generator 1 (B14)
steam generator 2 (B15)
Heat Exchanger (B16)
Flash Drum (Flash1)
Flash Drum 2 (B12)
Distillation Column 1 (B10)
Distillation Clolumn 2 (B5)
Distillation Clolumn 3 (B20)
Condenser (Distilation column 1) (B10 cond)
Reboiler (Distilation column 1) (B10 reb)
Reboiler (Distilation column 2) (B5 reb)
Condenser (Distilation column 2) (B5 cond)
Reboiler (Distilation column 3) (B20 reb)
Condenser (Distilation column 3) (B20 cond)
2 Comperssors
3,506,342 Total Cost
10,541,754 Capital Invesment
3.0 Lang Factor
Cost ($)
1,064,703
774,398
14,450
9,887
76,050
51,707
1,052,763
155,142
10,647
25,857
18,252
9,126
243,360
Cost ($)
1034282.787
757021.7548
11900
33600
91000
32900
18900
380000
4400
51000
34200
190000
16500
7700
17700
9900
255,528.00
2946532.542
10,541,754
3.58
Table 2: Equipment Cost Analysis
2
Discussion
Background
The base case for this project had a perfect separation for the toluene-benzene reaction. The
hydrogen and toluene feed went into a reactor with a 5:1 ratio. Prior to the reactor, the reactor feed
was heated in a fired heater. The products of the reactor went into three heat exchangers to be cooled.
The heat exchangers used 450 psig saturated water, 50 psig saturated water, and 80°C cooling water,
respectively to cool the reactor outlet stream. Then the stream went into a flash drum where the
methane and hydrogen were completely separated from the benzene, toluene, and diphenyl. A 1:1 ratio
of methane and hydrogen were purged from the flash drum vapor stream before being recycled into the
fresh hydrogen feed. The liquid stream of the flash drum, composed of benzene, toluene, and diphenyl,
went through two distillation columns before the recovered toluene would be recycled into the fresh
toluene feed stream. The first distillation column was used to separate only the benzene product. The
second distillation column was used to separate the diphenyl from toluene. The flash drum and
distillation columns were assumed to have perfect separation. See Appendix A, Figure A1 for the process
flow diagram.
Economics and Optimization
The base case system needed to be optimized to find the optimal conversion of toluene. Five
different conversions and their respective selectivity’s were compared. For each case, the stream tables
were made to determine the flow rate of each component throughout the system with a 100 mol
toluene fresh feed basis. The stream tables in Appendix D show how much product and byproduct is
produced and how much feed was needed for the five cases. Using the preliminary economics given, the
net profit could be determined, as seen in Appendix D. The preliminary economics could be used to find
the manufacturing cost, and revenue generated and thus net profit for the five different conversions.
The toluene conversion of 0.7 and a selectivity of 0.977 were found to be the most optimal with a net
profit of 7.9 cent/gal toluene. It allowed the most profit by maximizing benzene product and minimizing
diphenyl byproduct, as seen in Figure 3.
Net Profit (cents/gal T fed)
Net Profit Comparison
8.5
7.5
6.5
5.5
4.5
0.5
0.6
0.7
0.8
0.9
Conversion
Figure 3: Net Profit Comparison
3
Process Flow Diagram & Process Description
The process starts with fresh toluene and hydrogen going into a fired heater with a 1:5 ratio.
The fired heater heats the components to 1150°F prior to entering a plug flow reactor. The toluene and
hydrogen enter the reactor, which causes primary and side reactions occur. The outlet stream goes
through three heat exchangers to cool the stream. The heat exchangers used 450 psig saturated water,
50 psig saturated water, and 80°C cooling water, respectively to cool the outlet reactor stream. The
products of the reactor were sent to a flash drum to separate the methane and hydrogen from benzene,
toluene, and diphenyl. Some of the vapor methane and hydrogen stream was purged while the
remaining was recycled into the fresh hydrogen stream. Bottoms of the flash drum went through two
distillation columns to separate the three components. Before the bottoms of the flash drum went into
the distillation column, 21% of the liquid stream from the flash was used to quench the outlet reactor
stream before the stream leaving the reactor entered the heat exchangers. The goal of the quenching
the stream was to stop the reaction immediately by cooling it down. The first distillation column
separated benzene from the toluene and diphenyl. The second distillation column separated the toluene
and diphenyl. The recovered toluene was then recycled back into the fresh toluene stream.
B 12
S1
B 11
S3
B 13
15
S2
B6
S4
9
1
B1
B3
3
5
B4
B85
4
2
B2
10
B7
B9
B8
10 I
11
10 RE
B 10
12
14
Figure 4: Base Case Perfect Separation
4
B18
S2
S3
B12
B19
S1
B8
15
9
7-2
S4
8
B1
F-HEATER
1
B7
REACT O
5
HEAT ER
4
B2
7
B5
B4
B3
B6
7-4
7-1
2
10RE
B9
3
13
10
10OR
B10
7-3
B11
11
12
14
Figure 5: Base Case without Perfect Separation
Equipment Design and Aspen Simulation
Once the non-perfect base case, meaning no perfect separation, was inputted into Aspen, the
purities were not in the range required for this project. In order to meet the required purities, an
additional distillation column and flash drum was added to the design. The additional flash drum served
to separate the majority of the methane from the liquid mixed stream coming out of the first flash
drum. Next, to achieve optimal benzene the pressure needed to be reduced. Also, by reducing the
pressure in the distillation columns, it was found to give more manageable temperatures. Also, this
resulted in being able to decrease the number of stages, meaning the distillation columns would be
cheaper.
The final design equipment, as seen in Figure 6, used three distillation columns, two flash drums,
two pumps, two throttles, three heat exchangers, one adiabatic plug flow reactor, one fired heater, two
compressors, five splitters/mixers, and a quench stream. First a fire heater was used to raise the
temperature of the mixture streams to 1150°F before the stream entered the plug flow reactor. Once
the mixture stream entered the plug flow reactor, the goal of the reactor was to help facilitate a
reaction to develop the desired product benzene. The products leaving the plug flow reactor ended up
having a temperature of 1148.58°F while keeping the pressure constant at 500psia. Next, three heat
exchangers were introduced and their goal was to cool down the product coming out of the plug flow
reactor. The first heat exchanger used water coming in as saturated liquid and coming out as saturated
vapor at 455°F and 443.5psia. By using 126.29 lbmol/hr of water, the product stream combined with the
quench stream, labeled “7-1” in the process flow diagram, was able to be cooled down from 1148.58°F
5
to 1120.78°F. Then to cool down the stream even more, the second heat exchanger used water coming
in as saturated liquid and coming out as saturated vapor at 281.124°F and 50psia. By using 1110.19
lbmol/hr of water, the product stream leaving the second heat exchanger, labeled “7-3” in the process
flow diagram, was able to be cooled down from 1120.78°F to 810.48°F. Finally, one more heat
exchanger was used but instead of saturated water, cooling water was used. The cooling water came
into the third heat exchanger at 80°F and exited the heat exchanger at 120°F. By using 24475 lbmol/hr
of cooling water, the exiting product stream, labeled “7-4” in the process flow diagram, was able to be
cooled down to 100°F. Also, to reduce energy costs, the heat (Q) generated by the second heat
exchanger was used to operate the reboiler in the first distillation column labeled “B10” and the heat
generated by the first heat exchanger was used to operate the reboiler in the second distillation column
labeled “B20.” The heat generated by the distillation columns was the basis in calculating the flow rates
of the water entering the first two heat exchangers.
Once the products were cooled down to 100°F, they were then sent to a throttle to reduce the
pressure from 500psia to 450psia. Then a flash drum was used to separate the methane and hydrogen
from the rest of the products. The hydrogen and methane left the flash drum as a gas while the rest of
the products remained a liquid. The gas stream leaving the flash drum was then sent to a separator, in
which 17% of the methane and hydrogen were removed from the process and the rest would be
recycled back with the fresh hydrogen feed stream. Two compressors were used in parallel and a
separator was used to send half of the mixture to one compressor while the other half of the mixture
would be sent to the second compressor. The compressors operated at 500psia because the feed
stream was set at 500psia and to prevent a pressure difference it is good to have mixing streams mix at
the same pressure.
The liquid stream leaving the flash drum was then split into a quench stream, which would help
cool down the product stream leaving the reactor, and another liquid stream which would be sent to
another flash drum. The quench stream ended up being 21% of the liquid coming out of the flash drum
and mixing with the stream leaving the plug flow reactor. Before the quench stream could mix with the
stream leaving with the plug flow reactor, a pump was used to bring the quench stream pressure back
up to 500psia from 450psia. The other liquid stream, labeled “10OR”, was then sent through a throttle
to reduce its pressure from 450psia to 40psia because it was found that this stream could be easily
flashed at 40psia and remove most of the remaining methane and hydrogen from the system. The
temperature was kept the same as the stream entering the flash drum which was 100°F.
Next, the liquid stream entering the distillation column had barely any hydrogen, a little bit of
methane, and the rest was benzene, toluene, and diphenyl. The goal of this distillation column was to
separate the toluene and the benzene so the toluene could be recycled back with the fresh toluene
stream and the benzene could be removed from the system, so it could be sold as a final product. The
first distillation column, labeled “B10”, was found to do the best separation at 40psia, reflux ratio of 2.5
(calculated), distillate rate of 265.877 lbmol/hr, 30 stages, and the feed entering at stage 21, giving just
enough time for enough separation to occur. This distillation sent almost all the benzene and the
remaining methane to the distillate part of the distillation column. Another distillation column was used
to purify the stream even more because a minimum of 99.97% of purity was required for benzene. The
6
other distillation column, labeled “B5”, ended up having 99.999% pure benzene as a liquid product. The
operating conditions for this distillation column ended up having 4 stages with the feed entering at stage
2, pressure of 40psia, a reflux ratio of 1.5 (calculated), and a distillate rate of 2.4 lbmol/hr.
The liquid stream (labeled 12) leaving the first distillation column, labeled “B10”, ended up going
into a distillation column to remove the diphenyl from the mixture before being recycled with the fresh
toluene feed stream. The distillation column ended up operating at 10 stages with the feed location at
stage 10, reflux ratio of 0.128 (calculated), distillate rate of 116 lbmol/hr, and a pressure being constant
at 40psia. The toluene recycle stream ended up having a toluene purity of 97.93% purity with a benzene
purity of 2.07%, meeting the requirements of this project. Before the recycle stream could be mixed
with the initial toluene feed stream, the pressure needed to be increased back up to 500 psia and a
pump was used to increase the pressure to 500 psia.
All equipment design and equipment cost can be seen in Appendix F.
B18
S11
B17
9
15
S8
S12
B8
B19
S14
S7
S13
8
S5
S9
B1 3
HEATER
REAC TOR
B14
B3
1
5
7-1
7
7-2
B15
S6
B16
B4
FLASH1
7-3
HEAT ER
B2
2
4
S15
S10
10
B22
B9
10RE
10OR
B6
S3
S2
S16
B5
S18
B10
11
B12
S1
S4
B20
B23
14
12
13
Figure 6: Final Aspen Design
7
Capital Investment
While doing a cost analysis, it was found that an adiabatic plug flow reactor was cheaper to use
compared to an isothermal plug flow reactor. This was because the reaction is exothermic and it is more
realistic to have a adiabatic reactor compared to an isothermal reactor. The volume for the isothermal
reactor ended up being 217 m3 at 1150°F and 21 m3 at 1300°F. The reason of using multiple
temperatures was to get the range of volumes for the isothermal reactor design. The adiabatic reactor
volume ended up being 94 m3 and the outlet reactor temperature ended up being 1138°F. See sample
calculations for details. The reactor volume in Aspen ended up being 92.3 m3. The lower the volume for
the reactor, the cheaper it ends up being.
Based on equipment design, the final Aspen design ended up being cheaper to produce.
Although more equipment was added, it was cheaper because the conditions were changed at which
the plant operates. The final costs can be seen in Table 4 below using the equipment design
specifications as seen in Table 3.
Fired Heater (duty) (kw)
Reactor volume (m3)
Quench steam percentage of original (BTU/hr)
steam generator 1 (duty) (BTU/hr)
steam generator 2 (duty) (BTU/hr)
Heat Exchanger duty (BTU/hr)
Flash Drum dimensions
Distillation Colum 1 dimensions
Distillation Colum 2 dimensions
Condenser 1 duty (BTU/hr)
Condenser 2 duty (BTU/hr)
Reboiler 1 duty (BTU/hr)
Reboiler 2 duty (BTU/hr)
Compressor Duty (hp)
Hand Calculations (base design) Aspen Results (final desing)
17,380.00
16106.02012
94.7
92.3
0.21
0.21
10635571
1748377
2761826
18485766
52292895
40720041
A=.76 m2, h=4.9 m
A=.49 m2, h=4.9 m
hieght: 208 ft, D: 0.93 m
hieght: 108 ft, D: 2.11 m
hieght: 28 ft, D: 0.48 m
hieght: 22 ft, D: 0.5 m
9838765
17854743
1893702
1730028
10674847
18533452
2761826
1750950
107.2
115.3
Table 3: Base Design vs. Aspen Design (final) Equipment Design Specifications
8
Base Case
Equipment
Fired Heater
Reactor
steam generator 1
steam generator 2
Heat Exchanger
Flash Drum
Distillation Column 1
Distillation Column 2
Condenser (Distilation column 1)
Reboiler (Distilation column 1)
Reboiler (Distilation column 2)
Condenser (Distilation column 2)
2 Comperssors
Total Cost
Capital Invesment
Lang Factor
Final Optimized Case
Equipment
Fired Heater (Heater)
Reactor
steam generator 1 (B14)
steam generator 2 (B15)
Heat Exchanger (B16)
Flash Drum (Flash1)
Flash Drum 2 (B12)
Distillation Column 1 (B10)
Distillation Clolumn 2 (B5)
Distillation Clolumn 3 (B20)
Condenser (Distilation column 1) (B10 cond)
Reboiler (Distilation column 1) (B10 reb)
Reboiler (Distilation column 2) (B5 reb)
Condenser (Distilation column 2) (B5 cond)
Reboiler (Distilation column 3) (B20 reb)
Condenser (Distilation column 3) (B20 cond)
2 Comperssors
3,506,342 Total Cost
10,541,754 Capital Invesment
3.0 Lang Factor
Cost ($)
1,064,703
774,398
14,450
9,887
76,050
51,707
1,052,763
155,142
10,647
25,857
18,252
9,126
243,360
Cost ($)
1034282.787
757021.7548
11900
33600
91000
32900
18900
380000
4400
51000
34200
190000
16500
7700
17700
9900
255,528.00
2946532.542
10,541,754
3.58
Table 4: Base Case vs. Aspen Design (Final) Equipment Capital Cost
9
Health and Safety Considerations
Some health and safety considerations are that benzene can cause cancer. Also, methane and hydrogen are
extremely flammable. Any other safety considerations can be seen in the tables provided below ranging from Tables
5-11. A What If scenario was run to let the plants to know what would have if certain situations were to occur, as
seen in Table 5.
Table 5: Representative, simplified What-If analysis for the process.
Causes
Consequences
Safeguards & Recommendations
What If ...


Flash drum
raptures

Fire starts
inside the plant

Pumps
overheat


Sudden increase in
the pressure
Fatigue in the flash
wall

Spark from one of
the electrical
components (pump
or compressor)
Human error (e.g.
smoking in
undesignated area)
Lack of lubrication
Blockage of gas
flow in the
upstream pipe






Benzene, toluene and
diphenyl will spell on the
floor.
Large quantities of methane
and hydrogen will
contaminate the air.
The flammable materials
causes explosion and may
damage the whole plant.
Fatalities may occur

Damage to the compressor.
Personal injuries to the
workers (burns)
Backward flow of the
compressed gas




As a precaution, make sure the
flash’s wall thickness is a little
higher than what is recommended.
Make sure the flash is inspected
frequently.
Make sure safety measures are
strictly followed by the workers.
Pumps and compressors should be
equipped with spark prevention
mechanism
Make sure the compressors are
properly lubricated and inspected
frequently.
Table 6: List of starting materials, additives, products, and known by-products for the process.
ID
Chemical
Name(s)
1
Benzene
2
Toluene
3
4
Diphenyl
Hydrogen
5
Methane
6
water
Function in the Process
• The desired product
• component in the outlet stream of the reactor and in the feed to the first distillation
The raw material (reactatnt)
Fed to the reactor and recycled and combined with the freash feed after seperating it from
the other components
By-product in the process
Reactant fed to the reactor with some recycled
Product of the reaction
Portion is purged while the other is recycled
Heating and cooling
10
Chemical ID
Table 7: List of physical and chemical properties of Benzene
1
Chemical Name
Chemical Formula
Molecular Weight (g/mol)
Appearance
Density (ambient conditions)
(g/cm3)
Viscosity (cP)
Melting Point (°C)
Boiling Point (°C)
Decomposition Temperature
(°C)
Flash Point (°C)
Auto-Ignition Temperature
(°C)
Lower Flammable Limit, LFL
(%vol)
Upper Flammable Limit, UFL
(%vol)
Health Rating, NFPA
Flammability Rating, NFPA
Instability Rating, NFPA
Special Hazards Rating, NFPA
Benzene
C6H6
78.11
Clear colorless liquid
0.878
.318
5.5
80.1
NA
-11.1
497
1.2
7.8
2
3
0
NA
Odor Threshold
TWA
STEL
IDLH
Hazards and Health Risks
Compatible Gloves
Required PPE
Spill or Leak Measures
Disposal method
Known Chemical
Incompatibilities
4.68 ppm
0.5
2.5 ppm
NA
Dangerous in case of eye contact and inhalation, carcinogen
Natural Latex
NA
Small leaks: absorb with inert material
Large spills: absorb with sand. Don’t touch. Keep away from heat
Appropriate waste disposal
Oxidizing agents, acides

Source(s)


http://www.cpchem.com/bl/aromatics/enus/Documents/Benzene_2005_Rev_1.pdf
http://www.sciencelab.com/msds.php?msdsId=9927339
http://www.aps.anl.gov/Safety_and_Training/User_Safety/gloveselection.html
11
Table 8: List of physical and chemical properties of Toluene
Chemical ID
2
Chemical Name
Chemical Formula
Molecular Weight (g/mol)
Appearance
Density (ambient
conditions) (g/cm3)
Viscosity (cP)
Melting Point (°C)
Boiling Point (°C)
Decomposition
Temperature (°C)
Flash Point (°C)
Auto-Ignition Temperature
(°C)
Lower Flammable Limit,
LFL (%vol)
Upper Flammable Limit,
UFL (%vol)
Health Rating, NFPA
Flammability Rating,
NFPA
Instability Rating, NFPA
Special Hazards Rating,
NFPA
Toluene
C7H8
92.14
colorless liquid
0.863
.59
-59
111
NA
4.44
480
1.1
7.1
2
3
0
NA
Odor Threshold
TWA
STEL
IDLH
Hazards and Health Risks
Compatible Gloves
Required PPE
Spill or Leak Measures
Disposal method
Known Chemical
Incompatibilities
Source(s)
1.6 ppm
200
500
NA
Dangerous in case of eye contact and inhalation, carcinogen, toxic
Neoprene
NA
Small leaks: absorb with inert material
Large spills: absorb with sand. Don’t touch. Keep away from haet
Appropriate waste disposal
oxidizing agents,


http://www.aps.anl.gov/Safety_and_Training/User_Safety/gloveselection.html
http://www.cen.iitb.ac.in/cen/usage-policies/msds/toluene.pdf
12
Chemical ID
Table 9: List of physical and chemical properties of Diphenyl
3
Chemical Name
Chemical Formula
Molecular Weight (g/mol)
Appearance
Density (ambient conditions)
(g/cm3)
Viscosity (cP)
Melting Point (°C)
Boiling Point (°C)
Decomposition Temperature
(°C)
Flash Point (°C)
Auto-Ignition Temperature
(°C)
Lower Flammable Limit, LFL
(%vol)
Upper Flammable Limit, UFL
(%vol)
Health Rating, NFPA
Flammability Rating, NFPA
Instability Rating, NFPA
Special Hazards Rating, NFPA
Diphenyl
C12H10
154.12
White solid
1.04
NA
68.9
254
NA
112.8
540
0.6
5.8
2
1
0
NA
Odor Threshold
TWA
STEL
IDLH
Hazards and Health Risks
Compatible Gloves
Required PPE
Spill or Leak Measures
Disposal method
Known Chemical
Incompatibilities
Source(s)
NA
.2
NA
NA
Dangerous in case of eye contact and inhalation, toxic to nervous system
Neoprene
NA
NA
Appropriate waste disposal
oxidizing agents, reducing agents


http://www.aps.anl.gov/Safety_and_Training/User_Safety/gloveselection.html
http://www.sciencelab.com/msds.php?msdsId=9927456
13
Chemical ID
Table 10: List of physical and chemical properties of Hydrogen
4
Chemical Name
Chemical Formula
Molecular Weight (g/mol)
Appearance
Density (ambient conditions) (lb/ft3)
Viscosity (cP)
Melting Point (°C)
Boiling Point (°C)
Decomposition Temperature (°C)
Flash Point (°C)
Auto-Ignition Temperature (°C)
Lower Flammable Limit, LFL (%vol)
Upper Flammable Limit, UFL (%vol)
Health Rating, NFPA
Flammability Rating, NFPA
Instability Rating, NFPA
Special Hazards Rating, NFPA
Odor Threshold
TWA
STEL
IDLH
Hazards and Health Risks
Compatible Gloves
Required PPE
Spill or Leak Measures
Disposal method
Known Chemical Incompatibilities
Source(s)
Hydrogen
H2
2
Gas
0.00521
NA
-259
-253
NA
NA
500 to 517
4
76
NA
NA
NA
NA
NA
NA
NA
NA
Irritant in case of eye contact, skin contact
NA
NA
Stop leak immediately
NA
Oxidizing agents
http://www.airgas.com/documents/pdf/001026.pdf
14
Chemical ID
Table 11: List of physical and chemical properties of Methane
5
Chemical Name
Chemical Formula
Molecular Weight (g/mol)
Appearance
Density (ambient conditions) (lb/ft3)
Viscosity (cP)
Melting Point (°C)
Boiling Point (°C)
Decomposition Temperature (°C)
Flash Point (°C)
Auto-Ignition Temperature (°C)
Lower Flammable Limit, LFL (%vol)
Upper Flammable Limit, UFL (%vol)
Health Rating, NFPA
Flammability Rating, NFPA
Instability Rating, NFPA
Special Hazards Rating, NFPA
Odor Threshold
TWA
STEL
IDLH
Hazards and Health Risks
Compatible Gloves
Required PPE
Spill or Leak Measures
Disposal method
Known Chemical Incompatibilities
Source(s)
Methane
CH4
16
Gas
0.04325
NA
-182
-161
NA
-188
539
5
15
NA
NA
NA
NA
NA
1000
NA
NA
Dangerous in case of eye contact, skin contact and inhalation
NA
NA
Stop leak immediately
NA
Oxidizing agents
http://www.airgas.com/documents/pdf/001033.pdf
15
Conclusion and Recommendations
In conclusion, the final design used three distillation columns, two flash drums, two pumps, two
throttles, three heat exchangers, one adiabatic plug flow reactor, one fired heater, two compressors,
five splitters/mixers, and a quench stream. This design had additional equipment compared to the base
case system. The base case system did not offer the desired purities as expected with hand calculations.
The pumps, compressors, and throttle allowed the flash drums and distillation columns to operate at
optimal conditions with reasonable sizing and desired separations. The additional flash drum and
distillation column serve to remove the methane from the product stream. The final design output
benzene was at essentially 100% purity and toluene recycle purity was 98%. The comparison of hand
calculations to final Aspen design results shows that additional equipment must be used to achieve
perfect or desired separation, as expected.
It is recommended that when designing the process, check the temperatures of the streams to
see if they are reasonable. For example, one distillation column had a temperature of negative 353°F,
which is unreasonable. So check the temperatures to see if they are reasonable and realistic. To make
the temperatures more realistic, the pressures can be varied in order to get the desired results. Another
recommendation is that if there are three products in the mixture and the user wants to remove one of
them, the best method is to flash the stream in order to remove majority of one component from the
mixture. The final recommendation is that when combining the recycle stream with any stream on
Aspen, it is a good idea to increase the number of iterations so the system converges.
Assumptions
- Steady-state
- The Plug Flow Reactor was perfectly adiabatic
- Assume no heat is lost to the environment in the heat exchanger
- Flash Drums are isothermal
- The heat produced by the heat exchangers are used for the reboilers in the distillation columns
16
References
1. Felder, Richard M. and Ronald W. Rousseau. “ Elementary Principles of Chemical Processes.”
2. Peters, Max and Klaus Timmerhaus and Ronald West. “Plant Design and Economics for Chemical
Engineers Fifth Edition.”
3. Seader, J. D. and Ernest J. Henley and D. Keith Roper. “Separation Process Principles.”
17