Pennsylvania State University
Cumene Plant
Final Assignment
S. Bina, L. Brethauer, C. Janiszewski, E. Reed, J. Snyder
Team 25
0
Executive Summary
The goal of this project was to determine the feasibility of a proposed cumene plant to be
located on the US Gulf Coast. It will be used to produce cumene from a propylene and benzene
feed. The plant consists of a main cumene reactor, a trans-alkylation reactor, and nine
distillation towers. A new catalyst is proposed which makes the selectivity for producing
cumene higher, but may have higher capital and utility costs. The new catalyst proposed from
the R&D department may give the cumene plant a competitive edge compared to other
companies in the industry. The feed to the cumene plant consists of a fresh propylene feed and
a fresh benzene feed with a recycle stream. The plant produces a capacity of 473 MMlb/yr with
a 99.95 wt% purity cumene product.
The estimated capital cost to build the plant is $49MM. The yearly utilities of the plant cost
$7.7MM. The base case economics result in an After Tax Return of 21.75% and a NPW of
%28.7MM. The analysis was based on a standard 3 year sellout period and the prices given by
the Marketing Department for propylene at 50c/lb and benzene at 51.85c/lb. It is predicted
that there will be a compound yearly increase of 4.2% of cumene until the year of 2020. Based
solely on the economic analysis, there is room in the cumene market to become established
and grow successfully.
It is our recommendation to do not proceed for several reasons unless the following is
accomplished.
1. All contracts to sell cumene must be priced with an escalator to the cost of benzene and
proplyene. This safeguards against rising raw materials costs.
2. Market surveys of the cumene market reveal no foreseeable downturn.
3. Removed toulene and benzene are purified and sold for profit.
4. A study should be conducted to determine optimal plant capacity.
There are two main technical difficulties with regards to building the cumene plant: waste
management and the catalyst. The base case does not sell side products that do not go into the
fuel drum, such as benzene and toluene. With multiple waste streams leaving the system, it is
important to ensure proper disposal of the chemicals. This will require extra attention and costs
to the plant. Secondly, there needs to be more research conducted on the catalyst in order to
verify that it gives a higher selectivity to cumene compared to other competitors. This is an
important technical issue because it is vital to know all of the information of the catalyst and
confirm its efficacy before implementing it into multimillion dollar cumene synthesis factory.
With high risk sensitivities, the decision to move forward with the construction of the cumene
plant becomes more complicated. Although the projected economic and market analysis is in
1
our favor, the highly sensitive facts such as price per pound deems this cumene plant as too
risky an investment.
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Table of Contents
I.
II.
Background
Process Description
4
6
BFD
PFD
Cumene Specification Sheet
Material Balance
III. Process & Equipment Design
IV. Case Studies
V. Outside Battery Limit
VI. Environmental & Safety Considerations
VII. Capital Estimate
VIII. Operating Costs
IX. Outstanding Issues
X. Economic Evaluation
XI. Conclusion with Recommendations
XII. References
XIII. Appendix
Equipment Design Calculations
Sigma-Aldrich MSDS
Plant Specification Sheet
3
9
23
26
28
31
33
36
37
41
44
45
Background
The compound cumene belongs in the Industrial Chemical Manufacturing industry. This
industry in the United States has brought in total revenue of $275 billion dollars. This was split
among the 1,500 companies in the US that are a part of this industry. There is a substantial
amount of trade including imports to Canada, China and Germany. The US exports to Mexico,
Canada, Belgium, China, and Brazil. Cumene entered the market in 1944 by Hack and Lang
when they proved cumene could be oxidized to form a hydrocarbon that decomposes to form
phenol and acetone. The demand for cumene increased during World War II in order to help
increase the octane rating of America’s aviation fuel program.
Cumene is used to create two prominent organic chemicals: phenol and acetone. Phenol is used
for Bisphenol A (BPA) which is used to create epoxy resins used in electronic devices including
CDs. Diluted phenol is found in disinfectant products including house cleaners and mouthwash.
Acetone is a low toxicity chemical, and 75% of the acetone produced is used to formulate other
chemicals. Nail polish remover is an everyday product in which acetone is the main component.
The production of organic chemicals has increased just over 2 percent according to the
February 2015 quarterly industry update, which directly affects the production of cumene.
The components reacted and produced in the cumene reactor can be used in a variety of
industries. The reaction of benzene and propylene produces primarily cumene, as well as ethyl
benzene, and butyl benzene. Ethyl benzene, butyl benzene, and leftover propylene combine to
create a fuel source. In order to continue in the development of a cumene plant using new
catalyst, profitability must be shown. Profitability will be evaluated through market trends for
reactants and products. The market has been steadily growing worldwide, particularly in Asia.
The main competitor in the cumene market is Badger, who also reacts benzene and propylene.
The reactions take place in the liquid phase in catalyzed fixed bed reactors. The process is
flexible because the fresh propylene feed entering the process can be a variety of grades. Even
though there are international competitors in the cumene market, there is still a high enough
demand to stay in business and retain customers. The demand for cumene is projected to
4
steadily increase at an annual compound growth rate of approximately 4.2% till 2020. With the
high projected demand for cumene, a new cumene plant entering the market will not struggle
to make money or compete with already established companies.
5
I. Process Description
This chemical process uses benzene and propylene to produce cumene at a high purity and high
conversion. There are a number of side reactions that take place. Some products of the side
reactions can be further reacted to produce cumene, while some are undesirable. It is
important to limit the undesired reactions. This is done by removing certain species from the
effluent of the main reactor, effluent of the trans-alkylation reactor, and from both fresh feed
streams. Below is an illustration of each reaction and side reaction that occurs within the
process.
Note: This Process description will be based numerically off of the PFD for reference.
6
Trans-Alkylation Reactions
The fresh benzene stream (111) is purged of toluene (113), which increases the benzene purity
from 95 wt% to 99.8 wt%. This operation requires a distillation column with 30 trays and duty
of 1.4 X 107 BTU/hr. The fresh propylene stream (101) is purified by 2 distillation columns. The
first and second column removes nearly all ethylene (102) and butene (105) respectively. The
total duty from both columns is 5.6 X 106 BTU/hr. These operations are worth the cost because
of how it eases downstream operation and reduces the formation of undesired products. Both
purified streams are then mixed with the benzene recycle stream. The mixed effluent (121) is
separated based on phase. The vapor phase is compressed to 500 psia, and the liquid phase is
pumped to 500 psia. The streams are reintroduced and heated with high pressure steam to
optimized temperature and pressure for the main reactor. The conditions of the feed to the
main reactor are 470 ̊F and 495 psia.
The main reactor, at volume 230 ft3, runs at 370 ̊F and pressure drop of 15 psia. The product
stream contains 93 wt% cumene. This spec would not be met without the initial separation of
undesired reactants. The effluent of the reactor stream is cooled with cold water so that it can
be allotted through valve V-201 to reduce pressure from 475 psia to 30 psia. This reduction in
pressure increases the relative volatility of the species from the effluent to be separated more
readily. Catalyst regeneration in the main reactor is done by feeding steam through stream 202
and out stream 203. Valves V-201, V-204, and V-205 remain open during production while
valves V-202 and 203 remain closed until catalyst regeneration is completed.
The main reactor product stream is sent to the first of four separators in the third section of the
plant design (201). The first separator removes benzene and all lighter species (301) so that the
cumene recovered from the reboiler (311) can be purified downstream. The benzene stream is
purified further by removing propane, propene, and lighter undesired species by distillation
(302). The benzene stream is now pure enough to recycle (314) and feed to the trans-alkylation
reactor (315). The heavy stream from the first distillation separator is sent to two separators
(311). The first of the two distillation columns produces the high purity cumene product stream
(322) by removing heavier species including PIBP’s (323). The second column removes the
undesired heavy species, such as terphenyl (325), so that the distillate is a majority of PIPB’s
(324). The purified PIPB and benzene stream (the feeds for the trans-reactor), at a 1:6
7
respective ratio, are prepared for trans-alkylation by pumps and a heater, utilizing high
pressure steam, to be congruent with the trans-reactor pressure and temperature specs as it
moves into the fourth stage of operation.
The feed stream into the trans-alkylation reactor (401) is at 338 ̊F and 250 psia. Since the
benzene feed to the reactor was very pure, based on components lighter than benzene, the
effluent from the trans-reactor (402) can be separated as a fuel product (503) in the fifth stage
of operation. It is pressurized and cooled to 50 psia and 110 ̊F to be sold. The bottoms product
(502) is recycled and mixed with the bottoms product of the first distillation column of the third
operation stage. This recycles the PIPB’s, recovers cumene produced in the trans-reactor, and
removes some heavy species downstream.
8
II. Process and Equipment Design
Introduction
The design of the distillation columns used as the major separation unit operations follows this
procedure: equilibrium diagrams of the key species being separated were examined and from
these, the optimal pressure for the column was selected. Often this was atmospheric pressure
to lower the capital cost of the distillation column. This was selected because cheaper material
is able to be used to construct the column due to minimal pressure differentials between the
inside and outside of the column. Sizing of the column was performed using graph of the reflux
ratio versus the number of theoretical trays. The ‘knee of the curve’ point on the graph was
selected as the optimal compromise between the reflux ratio and number of trays. This allows a
balance between capital cost and continuous operation cost.
The main reactor was designed to have the greatest cumene to propylene conversion ratio in
the reactor. To minimize the size of the main reactor, a packed bed reactor was selected. This
was accomplished by graphing the cumene to propylene conversion ratio and the benzene to
propylene feed ratio, and graphing the cumene to propylene conversion ratio and WHSV at the
selected benzene to feed ratio. The conditions of the main reactor determined from the graphs
were then used to determine duty of the main reactor heat exchanger. This is further discussed
in detail in the main reactor KDV section below.
The trans-alkylation reactor size was determined from the flow of the inlet stream to the
reactor. Specifications of the packed bed trans-alkylation reactor conditions and catalyst were
previously specified. By utilizing the flow of the inlet stream to be reacted and the WHSV ratio
of 4, the mass of catalyst required was calculated. From the mass of catalyst required for the
reactor, the bulk packing of the catalyst, and the void fraction of the catalyst, the volume of the
trans-alkylation reactor was calculated.
Main Reactor Design
The inlet operating pressure was chosen to be 251 psia as it was the lowest operating pressure
that the stream was in liquid phase at the inlet pressure of 300 °F. The determined pressure
drop was found to be 20 psi, the largest pressure drop allowed by specification, was also
calculated from the Ergun equation. The large pressure drop increases the width of the velocity
profile, causing the liquid to have more surface interactions with the catalyst lengthwise. This
increased interaction allows for the minimum conversion of 0.96 for proplyene to cumene to be
achieved in a smaller reactor volume than that of a reactor with a smaller pressure drop.
9
The reactor benzene to propylene feed ratio and the WHSV ratio was determined from graphs
in Figures A and B shown below. Figure A, the graph of the cumene to propylene conversion
ratio versus the benzene to propylene feed ratio was plotted. From Figure A, the peak for
greatest cumene to propylene conversion ratio was chosen at a benzene to propylene feed
ratio of 7. Then, in Figure B, the cumene to propylene conversion ratio was plotted versus the
WHSV (mass flow per mass of catalyst) at the chosen benzene to propylene feed ratio with
different reactor temperatures. From the graph of the multiple curves (each representing a
different reactor operating temperature), the greatest conversion that was less than 1 (because
of interpolation errors in the fitted data) was selected from the curve at the temperature at
which the conversion was the greatest. Finally, the WHSV was then selected from that point on
the curve.
1
1
Cumene/Prop Convesion
Greatest Cumene/Propylene
Conversion
Cumene/Propylene Conversion vs. Bz/C3
Ratio in Main Reactor
0.995
0.99
0.985
0.98
0.975
Cumene/Prop Conv. vs. WHSV @ Bz/Prop
Ratio=7
0.8
0.6
100
0.4
200
300
0.2
0.97
400
0
0.965
0
2
4
6
Bz/C3 Ratio
8
10
Figure A. Comparison of cumene to propylene conversion
ratio and benzene to propylene feed ratio
1
2
3
4
5
6
7
8
10
WHSV
Figure B. Greatest Cumene/Propylene conversion ratio
(less than 1) = 0.9997 at 400°F
Separation Process Design
In order to better understand the Cumene plant, the entire system of separators is broken
down into 3 sections. The first system of separators includes three distillation columns that are
set-up before the main reactor. The second system of separators occurs directly after the first
reactor. The third separating process system is necessary to reach a cumene specification of
0.9995 wt%. A summary table is provided for each separator that lists key parameters such as
the temperature, pressure, mole fractions of the streams along with optimization details about
the distillation columns.
10
9
1st Separation Process System
Separator T-111: Toluene/Benzene
Purpose
The purpose of this first separator is to separate the toluene from benzene. By having a high
mole fraction of toluene separated out from the entire process, the reaction between toluene
and propylene resulting in o-cymene occurs at a minimal amount. This is very beneficial for the
plant because there are fewer impurities that prevent high conversions of cumene and other
products. By minimizing this reaction using the first separator, the sizing of the reactors and
other separators will be smaller.
Operating Conditions
The inlet stream is at atmospheric pressure and a temperature of 110°F. The exiting benzene
stream is at 162.6°F and 11.60 psia while the toluene stream leaving the tower is at 230.5°F and
at atmospheric pressure. The condenser is operating at 11.60 psia. The number of stages for
benzene/toluene separation process is 30 which results in a reflux ratio of 0.855 as seen in
Figure 1. The feed tray in which the reactants enter the separator was found using empirical
calculations in HYSYS. The reactants enter at the 11th tray, which gives a new reflux ratio 0.833.
According to figure 2, the stream of toluene and benzene is entering at atmospheric pressure.
This is a relatively difficult separation to make and therefore requires more stages to make the
separation possible.
70
T-111
60
# of stages
50
40
30
20
10
0
0
1
2
3
4
RR
Figure 1. Reflux ratio versus theoretical number of trays
Figure 2. The X-Y diagram for benzene at 14.7 psia
11
Summary Chart
Separator T-101: Ethylene/ Propane, Propene, Butene
Purpose
The purpose of this separator is to remove the butene from ethylene, propane, and propene.
The propene is desired for downstream operations. The propane and ethylene will eventually
go into a fuel drum storage container for profit. The propene is then used to make cumene. By
separating out butene, butyl benzene will not be made in significant quantity and therefore less
heavier products will be produced. Again, this makes the reactor sizing smaller, and fewer
impurities results in a higher conversion of desired products.
Operating Conditions
The inlet temperature to the separator is -22.09°F and 30.0 psia. The top stream is leaving at 40.35°F at 20 psia while the bottoms are
22
T-101
# of stages
20
18
16
14
12
10
0.15
0.2
0.25
0.3
0.35
0.4
0.45
RR
Figure 4. The X-Y diagram for butane at 29.01 psia
Figure 3. Reflux ratio versus theoretical trays
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leaving at 55.9°F and 30.0 psia. The number of stages for the distillation column is 17 from
figure 3 with a reflux ratio of 0.216. Through empirical calculations, the optimal tray to have the
feed entering is the 7th tray. This gives a new reflux ratio of 0.216.
Summary Chart
Separator T-102: Propene, Propane/1-Butene
Purpose
The purpose of this reactor is to separate the ethylene which will be stored in the fuel drum.
The propane and propene stream will be recycled back into the system because propene reacts
to create cumene. It is important to keep reactants that make cumene, such as propylene in
high concentration in the system in order to maximize the conversion of cumene.
Operating Conditions
The inlet temperature and pressure are at -23.19°F and 30.00 psia. The ethylene stream leaving
the top of the distillation column has a temperature and pressure of -145.5°F and 20.00 psia.
The propane and propene stream leaving the bottom leaves at -22.09°F and 30 psia. The
number of stages for this separator is 15 with a reflux ratio of 63.1 as shown in Figure 5. The
feed should enter at 7th tray, determined by empirical calculations. According to Figure 6, this
is an easy separation because of the big difference between ethylene and the propane/propene
mixture.
13
T-102
# of stages
20
15
10
5
0
55
65
75
85
RR
Figure 6. The X-Y diagram for propene at 20 psia
Figure 5. Reflux ratio versus theoretical trays
Summary Chart
2nd Process Separator System
Separator T-301: Benzene, Propene/Cumene, PIPB
Purpose:
After leaving the main cumene reactor, the reactor effluent is mixed with the trans-alkylation
reactor effluent, creating stream 1 from this separation system. This stream contains large
amounts of cumene. The first separator is used to separate a benzene rich light stream with
propene impurities from a heavy stream of cumene with PIPB impurities.
14
Operating Conditions
The inlet temperature and pressure of this distillation are at 222.1 and 30 psia. The reactor
effluent exists at a higher pressure (200 psia), which causes this separation to be more difficult
and take more energy. The XY equilibriumplot for this separation at 200 psia as well as the XY
equilibrium plot at 30 psia are shown below.
Figure 8. Benzene/Cumene Separation at 210 psia
Figure 7. Benzene/Cumene Separation at 30 psia
Figure 7 illustrates that this separation is easier at atmospheric conditions. Because of this, the
reactor effluent is depressurized before this separation.
The main specification for this separation is the cumene recovery, as the main economic benefit
of this process is cumene sales, and the benzene recycle cannot have more than 1000 ppm
cumene in it. Due to this, this distillation column was set to have a cumene recovery of .999. To
save energy, the reflux ratio was set at 2.
With a reflux ratio of 2, this separation could be run with 25 stages, with the inlet flow fed to
the 13th stage.
15
Summary Chart
Separator T-311: Benzene/Propane and Propene
Purpose
After separating the cumene from the benzene in separator 1, the benzene is still not pure
enough to be recycled to the main reactor and the trans-alkyation reactor. The largest of the
impurities in this stream consist of propene and propane. This separator exists in order to
remove the propane and propene from the benzene stream.
Operating Conditions
The feed to this distillation consists mainly of benzene at 98.72 wt% purity and 14.7 psia.
Without running this separation under a vacuum, 14.7 psia is the lowest pressure at which this
separation can occur, and the separation is easier at lower pressures, thus the pressure will not
be changed before this separation occurs.
For this separation, the main variables that are important are the purity of benzene as well as
the amount of benzene kept in the system. This separation is set to make the benzene purity at
99.7 wt%, with hexane making up the majority of the impurities (the hexane is approximately
2900 ppm, which is below specifications for reactor inlets). The other specification set for this
distillation is a benzene recovery of 99%, so that little benzene is lost with the propene and
propane.
16
The knee of the curve method was used to determine that this separation should be run with 8
stages and a reflux ratio of 0.725. The graph of reflux ratio vs. number of stages is shown below
in Figure 11.
T-311
30
# of Stages
25
20
15
10
5
0
0
2
4
6
8
10
Reflux Ratio
Figure 10. Stages vs. Reflux Ratio for Separator 2
This graph shows that the minimum stages necessary for this separation is approximately 3,
while the reflux ratio hits a minimum at about 0.624. Using the knee of the curve method, it
was determined that 8 stages were ideal for this separation, as adding more stages would not
heavily affect the reflux ratio.
Summary Chart
Temperature (inlet, top, bottom) °F
Pressure (inlet, top, bottom) psia
138.5 ; 45.52 ; 194.9
14.7, 14.7, 20
Feed tray pressure psia
18.36
Feed tray temperature °F
Feed composition (mole fraction)
Benzene
Propene
146.4
0.9872
0.0068
Benzene (bottom) mole fraction
0.997
Benzene (top) mole fraction
0.0916
Number of stages; feed tray
8;3
Reflux ratio
0.725
17
Separator T-331: Cumene/PIPB
Purpose
After the cumene is separated from benzene, it must be purified to meet the specifications for
the consumer (99.95 wt% pure). Similarly, the PIPB must be separated in order to send to the
trans-alkylation reactor.
Operating Conditions:
At atmospheric pressure, this separation is much easier than at any higher pressure, so the inlet
feed is left at its previous value of 20 psia as this is fairly close to atmospheric, and would keep
capital costs down for a pressure drop. The temperature as this feed enters the tower is in the
middle of the range for the tower, and thus little energy is needed to change the temperature
when it is added.
The specifications for this distillation column were created in order to obtain the necessary
purity of cumene with a minimal loss of cumene. In order to achieve this, the top of the column
was set to have a cumene purity of 99.95% by weight. In order to minimize cumene loss, The
other specification set for this separation was a cumene recovery of 99.9%.
This separation is run using 20 stages and a reflux ratio of 1.06. Below is a graph of the number
of stages in the separation vs. the reflux ratio.
40
T-331
35
# of stages
30
25
20
15
10
5
0
0
0.5
1
1.5
2
2.5
3
Reflux Ratio
Figure 11. Reflux ratio versus theoretical trays
This graph shows that the minimum number of stages possible for this separation is about 14,
while the minimum reflux is about 0.6. Using 20 stages and a reflux ratio of 1.06 minimizes the
run cost as much as can be done without adding too much capital.
18
Summary Chart
Temperature (inlet, top, bottom) °F
Pressure (inlet, top, bottom) psia
335.5 ; 308.2 ; 458
20 ; 14.7 ; 20
Feed tray pressure psia
19.84
Feed tray temperature °F
Feed composition (mole fraction)
Cumene
PIPB
333.2
0.9216
0.555
Cumene (top) mass fraction
0.998
PIPB (bottom) mole fraction
0.7106
Number of stages; feed tray
20 ; 10
Reflux ratio
1.06
Separator T-332: Heavies/PIPBs
Purpose
The purpose of this separator is to remove the heavies from the PIPB stream. This is an
important process because it prevents the heavies from entering the trans-alkylation reactor,
which would decrease the amount of conversion to cumene. Heavies also build up in the
reactors, so this will help to prevent some extra maintenance.
Operating Conditions
The inlet pressure to this separation is left at below atmospheric pressure in order to make the
separation utilize less energy. The temperature of this feed is inside the temperature range for
the distillation column, so it does not take much energy to heat or cool the feed after it has
entered the distillation column. The flowrate entering the distillation column is 372 lbs/hr,
which is relatively small compared to other streams in the system.
19
30
T-332
# of stages
25
20
15
10
5
0
0
10
20
30
40
50
Reflux Ratio
Figure 12. Reflux ratio versus theoretical trays
Summary Chart
Temperature (inlet, top, bottom) °F
Pressure (inlet, top, bottom) psia
409.4 ; 164.3 ; 308.3
20.0 ; 7.0 ; 9.0
Feed tray pressure psia
7.8
Feed tray temperature °F
Feed composition (mole fraction)
Heavies
PIPBS
0.519
0.7648
PIPBs (top) mole fraction
0.8144
Heavies (bottom) mole fraction
0.5714
Number of stages; feed tray
15 ; 7
Reflux ratio
411.9
10
3rd Separation Process System
Separator T-501: Cumene, PIPBs/Benzene
Purpose
The purpose of the separator is to recycle the bottom cumene and PIPB stream back into the
system. The top stream is mostly benzene, which will be sent to the fuel drum. This separation
is important because by recycling pure amount of PIPBs and cumene back into the system there
is a more pure final cumene product.
20
Summary Chart
Temperature (inlet, top, bottom) °F
195.9 ; 176.1 ; 360.3
Pressure (inlet, top, bottom) psia
20 ; 14.7 ; 20
Feed tray pressure psia
18.79
Feed tray temperature °F
Feed composition (mole fraction)
Benzene
Cumene
191.5
0.9828
0.0086
Benzene/hexane (top) mole fraction
0.9999
Cumene (bottom) mole fraction
0.6824
Number of stages; feed tray
20 ; 10
Reflux ratio
1.07
Separator T-601: Cumene Purification
Purpose
The purpose of this final separator is to reach the cumene specification in order to sell it to the
customers. The separation involves benzene and cumene. The benzene will go to waste
because it does not meet the specification to sell it.
Operating Conditions
This is the last separation in the system and it is important to keep the tower optimized at the
point in which the final cumene product leaving meets the specification of 99.95 wt%. There is
a mass flow rate of 57201 lbs/hr flowing into the separator. The mass flowrate of cumene
leaving the bottoms is 56298 lbs/hr. The mass percent of cumene entering the reactor is
already relatively high, so only a small impurity of benzene needs to be removed from the
system in order to reach specification.
21
# of stages
15
14
13
12
11
10
9
8
7
6
T-601
15
20
25
Reflux Ratio
Summary Chart
22
30
35
III. Case Studies
Design Case I
In the final design of the cumene plant, there are three separators before the reactants enter
the main cumene reactor. The products separated or being purged out of the system for fuel
storage includes ethylene, butene, and propane in the fresh propene feed. The separation of
ethylene and butene out of the system in order to purify the propene stream requires two
separators. After analyzing the boiling points of each reactant, it was determined that the two
separators can be combined into one separator with a total of three streams leaving. The top
product in the new distillation
tower would be ethylene with a
boiling point of -154°C. The middle
stream leaving the separator would
be propene with a boiling point of 53°C. The purified propene stream
stays in the system by going to the
cumene reactor to produce
cumene. Finally, the bottom stream
leaving the distillation tower would
be butene with a boiling point of 21°C. None of the reactants have a similar boiling point, which
makes the separation relatively easy. Therefore, the new distillation tower does not need to be
too complex with the amount of trays in order to make the separations possible. Butene and
ethylene are both sent to the fuel drum for storage and to sell as product. This design would
overall benefit the cumene plant in a cost effective way. By turning the job of two towers into a
single column reduces the amount of equipment needed for the plant. This makes a difference
in maintenance of the entire system, particularly during shut down for maintenance. The fresh
feed stream flow rate is 21760 lbs/hr, therefore the new tower will need to be sized to fit such
a high flowrate.
In conclusion, the amount of butylene in the feed is minimal compared to the amounts of
propylene and ethylene. Separating the propylene and ethylene to high purity is possible, but
the final bottom butylene stream will be mostly propene not providing the desired separation.
This conclusion is supported by observation of the flow rates from each of the three streams
emulated in HYSYS. The flow rate of ethylene out is 163lb/hr with an ethylene purity of 99.95
wt%. The flow of propylene out is 21 lb/hr with a purity of 93.94 wt% propylene. The bottoms
flow of butylene out is 21580 lb/hr with a propylene purity of 93.25 wt% with most of the
butylene exiting with this stream at a purity of 0.29 wt% butylene. This separation would be
useful if the propylene fresh feed was of lower purity with greater ratios of butylene and/or
ethylene. It is possible that a less costly and lower purity propylene feed could be used to lower
the overall cost to produce cumene by using this separation. Comparing the utility cost of the
two towers with the one tower, the condenser will use over half the energy (6.94E6Btu/hr total
for both condensers vs. 3.2E6Btu/hr for the single condenser) and the reboiler will use over
23
three times less energy than both reboilers (5.456E6Btu/hr for both reboilers vs. 1.7E6Btu/hr
for the single reboiler).
Design Case II
The distillate leaving T-311 is a mix of propene and propane. As of now in the main
design, the stream will be sent to the fuel drum. Propene is used throughout the cumene plant
in order to make cumene, so it is not ideal to send excess to the fuel drum. In order to utilize a
greater percentage of the incoming propene, rather than allowing it to escape the process with
the propane, a new distillation column could be added to the system after propane and
propene are separated from benzene. This new distillation would keep a larger amount of
propene in the process, granting a greater yield of cumene. Also, the propane leaving the
system would then be more pure, and thus could be sold as a side product. The total mass
distillation flowrate leaving the tower is 1716 lbs/hr. The mass fractions of propane and
propene are 0.8489 and 0.1457. This is a small amount of propene leaving the system, although
the propane would be sold for a small profit. The added distillation column would add more
capital cost for the system. Also, the separation of propene from propane is relatively difficult,
and would likely take a lot of energy in order to keep propane impurities from accumulating
through the system. Instead of storing the propane as fuel, the propane could be purified to
sell. This requires a specification of 99.5 wt%. This would require a lot of adjustment in the
distillation tower in order to accommodate a high specification. Finally, it should be noted that
the majority of the propene is used during a single pass, which would make the amount
recycled very small.
This separation was modeled using HYSYS as an extension of our base case. In this case, a
separator was added to the vapor stream coming from distillation tower T-302 in order to
separate propene from propane. With a 95 wt.% amount of propene (the purity that was
initially fed to the system) in the distillate, the maximum amount of propene that can be
24
obtained was 6.25 lbmol/hr, which is slightly larger than 1% of the amount of propene fed to
the system. In order to obtain this, a minimum of 47 stages are necessary (using a reflux ratio of
over 10,000). A more realistic number of stages for this separation would be using 60 stages,
which gives a reflux ratio of 53. For such a small amount of propene that would be salvaged, an
extra 60 stage distillation tower would be far too expensive in just capital cost. There is not
enough benefit from this separation to warrant the construction and maintenance of this
tower, especially as it would have more stages than any other tower in this plant. That is
without even mentioning the energy cost of running the tower. Quantitatively, the tower itself
would cost approximately 486000 USD in capital costs alone. This tower would also need to
cool the distillate to -421.1 F, using about 900,000 BTU/hr. This refrigeration cost would dwarf
the cost of the propene that would be saved.
25
IV. Outside Battery Limit
The Out of Battery Limit, or OBL, comprises all equipment and costs not associated with process
equipment. While not directly affecting the process, the OBL is necessary for the site to start up
and operate continually. Site development deals with the costs associated with clearing the
desired plant location, excavating the desired site location, ensuring the site has proper runoff,
and beautifying the site once construction is complete. Excavation, while not a technically
difficult task, requires large amounts of man power and equipment. Landscaping and
beautifying of the site after construction is also important as it keep the plant appearance up
and also helps prevent runoff during storms. Site development did not need to be scaled up as
it was not based on any process flows and the base price was evaluated in 2014.
OBL utilities encompass lighting for buildings, cold water pumps, low pressure steam for steam
tracing, water utilities for various buildings and power for out of process pumps. These utilities
essentially keep the building inhabitable for workers and ensure that all necessary utilities, such
26
as cold water, to reach the heat exchangers they run through. Utilities had to be scaled up for
two reasons. The base price was evaluated in 2012, so the price had to be scaled up to present
day prices. This was done by multiplying the base price by 1.03N, where N= the number of
years between the current year and the base price year. To scale up for the size of the process,
the utilities price was multiplied by the ratio of the process feed to the utilities base feed.
Raw material/product storage was necessary to store materials away from the plant to ensure
safety. This protects the materials against plant explosion and the plant against any chemical
spills. The storage tanks will be placed outside on cement pad sites outside of the possible blast
radius of the plant. Pumps will be required to pump the raw materials into the plant. The cost
of the pumps and their utilities are included in the OBL utilities costs. Storage for product will
also be located there, allowing random pickup of product without disturbance of the process.
Raw material/product storage costs had to be scaled up. The base price was evaluated in 2010,
so the price had to be scaled up to present day prices. This was done by multiplying the base
price by 1.03N, where N= the number of years between the current year and the base price
year. To scale up for the size of the process, the storage price was multiplied by the ratio of the
process feed to the assumed process feed.
Environmental OBL costs include costs to ensure that we meet required EPA specifications and
are doing no harm to the surrounding community. This includes waste water treatment if
necessary, air quality control, spill control, and hazard prevention and preparedness.
Environmental OBL did not need to be scaled up as it does not have direct ties to the process or
its capacity.
27
V. Environmental & Safety Considerations
General safety guidelines
These guidelines are put in place to eliminate hazards and catastrophes that can occur
in this chemical plant. Proper precautions must be taken to ensure a safe environment
and working conditions. Guidelines for safety are as listed:
Guidelines
Identify a hazard
Assess the hazard
Avoid hazard
Reduce hazard source severity
Reduce the likelihood of hazard
With these steps in place we can determine when to use passive, active, or procedural
safeguards to prevent said hazard. Passive safeguards are the easiest to implement and
take little to no maintenance. A simple drain or dyke qualifies as a passive safeguard.
Active safeguards are put in place to measure a system and report if it detects a hazard.
A safeguard like a temperature probe or pressure gauge require periodic evaluation.
Procedural safeguards outline how a certain hazard is dealt with step by step.
Procedural safeguards include systematic disposal of dangerous material as well as what
to do after the plant undergoes emergency shutdown. The equipment and process was
analyzed and these three safeguards were implemented as we see fit.
Process Safety
There are a few safety measures that will be implemented to avoid hazards. The
following list encompasses the general safety of the process:
Process Safety:
Insulation of pipes that have high temperatures
Small batch volumes to reduce the amount of flammable liquid in one place
28
Segregation of the reactors from each other and other equipment to reduce
up/downstream damage
Detection systems for construction and human error:
eg: leaks from bad welds or operator mistakes
Equipment Safety
Reactors
Both reactors experience an exothermic catalytic reaction. Identified hazards include thermal
runaway, spilling, and the abundance hot surfaces.
To guard against thermal runaway it is important to have control systems in place that will
control downstream processes to limit reactions in the reactor. If these systems fail to
recognize a thermal runaway in time we must quench the reaction by dumping the reactor
contents into a knockout drum. Quenching will be carried out initially by water (high heat
capacity) as an active safeguard. Cascade quenching may be necessary to completely stop the
thermal runaway. Sulfuric acid will be next to quench followed by another quench of either
water or acid, depending on the effectiveness of the two previous quenches. Cascade
quenching is and procedural safe guard because the third quench is determined by the
operator according to the effectiveness of the two previous quenches.
Fire safety is very important to assess and can reduce plant damage substantially. To prevent a
fire caused by the exothermic reactions we plan to implement a foam sprinkler system. Foam
can suppress the fire by separating the fuel from the air. Surrounding systems will be coated so
that the fire cannot spread.
Spills arise from leaks and leaks will continue to secrete chemicals until they are sealed. Leaked
chemicals will be drawn down a drain by ditches and dykes. The drain will collect the hazardous
material for proper disposal.
Distillation
We have 9 distillation columns that run at relatively low pressures. Buying columns with lower
maximum pressure ratings is economical. Though some margin for safety is considered when
buying a column, steady state operation is commonly the condition considered. It is important
to note that flow in the system is fast and at high volume. Therefore, integration of pressure
controls to monitor the internal environment of the columns is essential.
Fluid backup can cause a pressure increase that the column is not rated for. Larger diameter
piping downstream can be used to reduce the likelihood of hazards like this. Some columns run
29
at very high temperatures which may also induce over pressurization. External fire and hot
ambient conditions are two examples that will increase the pressure within a column. In
extreme measures, crash cooling of the column will be used to eliminate the hazard of
overheating. To immediately alleviate the pressure in a column, burst disks are used when the
column is under relative extreme pressure.
The effluent from the burst disks need to be assessed based on column environment. A flare
will be utilized on specific columns where the flow rate is low. If the flow rate is high and the
leak is waste it will go to a knockout drum. The drum will be cooled, sealed, and disposed of
according to safety procedure. Any leak with fluid that is desired in downstream operation will
be sent to do so, after being made conditionally congruent with the mixing point.
To reduce the corrosion within the column we may decide to use some type of cathodic
protection. This precaution may not be pertinent. Corrosion will be monitored so that we can
make an economic decision sometime later.
Pumps/Compressors & Heat Exchangers
Simple operations such as pumps and exchangers are commonly replaced if they fail. When a
pressure system fails the stream is diverted to another pressure system to keep operations in
motion. This will avoid any hazards caused by the failed pump. To guard against hazard, pumps
with an adequate safety margin are to be used.
Etc.
Concrete floors guard against ground water contamination. No process uses water so little
waste water treatment is needed.
For specific information on each component in the system, please refer to the Appendix for a
full MSDS on each chemical.
30
VII. Capital Estimate
The capital estimate was developed through HYSYS Economic Analysis Software. All equipment
was evaluated based on sizing determined from the methods discussed in the Equipment
Design section. All equipment was assumed to be made out of carbon steel, the cheapest
material. This assumption was safe as no equipment had large enough pressures or
temperatures that carbon steel could not handle the stress of. All process equipment, including
heat exchangers, pumps, compressors, distillation towers, and reactors, was considered inside
battery limit (IBL). HYSYS software was used to only estimate IBL equipment. All IBL equipment
costs were assumed to be present day, eliminating the need for escalation. Engineering and
installation costs for all IBL equipment were calculated as well and are included in the
summary.
Outside Battery Limit (OBL) equipment base prices were given. The cost of these goods was
scaled up to meet the requirements of the plant design. Scale was performed by first scaling up
the given prices to the base year. The base price was multipled by 1.03N, where N= the number
of years between the current year and the base price year. To scale up for the size of the
process, the OBL price was multiplied by the ratio of the process feed to the OBL base feed.
31
The most expensive piece of equipment is the compressor required to compress
propane/propene vapor so that it can be safely stored and sent to a fuel drum. While
expensive, at $953,000, the compressor is necessary for safety regulations. Money can also be
made from the fuel drum, so the capital cost of the compressor is offset by the profits brought
in from the fuel drum. Contributing the large cost is the large size of the compressor,
approximately 1500 ft3. Two compressors in series could help reduce cost as the load for each
would be significantly less. All other equipment was appropriately sized and reasonably priced.
32
VIII. Operating Costs
Operating Costs:
The most important costs are raw material costs, as these have the ability to change
drastically based on the market. Benzene and propene are the largest components of raw
materials costs. Benzene prices are directly correlated to oil prices as it is recovered from
cracking crude oil. While benzene prices have fluctuated over the past decade, there has been
a steady increase, with prices topping $4.82/gal in 2014, a $2.00 jump since the last reported
price of $2.82/gal in 2010. This large jump in price can be attributed to high crude oil prices in
the past two years as well as the high demand for benzene as the world continues to consume
plastics rapidly.
70
Benzene
60
50
¢/lb
40
30
20
10
0
1990
2000
Year
2010
Figure 14. Pricing of Benzene from 1990 to
2015
Like benzene, propylene prices have been steadily increasing for the past decade. Propene is
the other major component of the raw materials costs. Raw material costs are drastically
important because if the price of raw materials have the ability to change easily. If the prices of
benzene and propene were to spike, the plant may have to increase the sale price of cumene to
remain profitable. This could drive business elsewhere and thus profits for the plant would
plunge even lower.
33
80
Propylene
¢/lb
60
40
20
0
1990
1995
2000
2005
2010
2015
Year
Figure 15. Prices of propylene from 1990 to 2015
Operating costs for energy will remain somewhat constant as the energy requirements for
equipment will not change drastically. Energy costs could affect the profitability of the plant if
the drastically increase through the change in oil prices. However, energy prices have remained
fairly stagnant in recent years due to an overproduction of oil, new discovery of natural gas in
America, and renewable energy sources continuing to rise in popularity and availability.
Total energy operating costs were $12.6 million per year.
Utility costs for the process were as follows:
34
Utilities costs affect the process much less than raw materials and utilities costs. They are
necessary to the process and cannot be waived. Pending a drought, water prices will remain
constant with inflation. Catalyst costs are dictated from the manufacturer and will remain fairly
constant in order for the company to maintain business. Catalyst also only needs to be bought
every few years, allowing the cost to actually decrease per year due to inflation. Utilities costs
will also consistently remain low due to the ability to sell used steam. This drastically reduces
the cost by almost $5 million in current estimates. Out of all operating costs, utilities costs
represent the smallest fraction.
35
IX. Outstanding Issues
Disposal of Waste Streams
The cumene plant does not sell any effluents leaving the separators besides the cumene. In
order to sell the effluent streams, the purity must be 99.5 wt %. This results in multiple waste
streams of somewhat high purities of chemicals. This is an issue because there are many
policies in place to ensure the safe disposal of chemicals. There is the possibility to have even
hazardous waste streams reused or recycled. As stated by Congress, the objectives of the
Resource Conservation and Recovery Act (RCRA) are "to promote the protection of health and
the environment and to conserve valuable material and energy resources." With these goals in
mind, EPA developed the hazardous waste recycling regulations to promote the reuse and
reclamation of useful materials in a manner that is safe and protective of human health and the
environment. The disposal of chemical waste is not only a safety issue, but an economic one as
well considering outsourced waste management companies are needed to properly dispose of
the chemicals. The following chemicals are found in the waste streams leaving the cumene
plant.
Toluene & Benzene
Toluene and Benzene are both an odorless liquid at room temperature. They are highly
flammable as a liquid and vapor. According to Sigma Aldrich, burning it in a chemical incinerator
equipped with an afterburner and scrubber is the best way to dispose of the waste. It is
necessary to take extra precaution during this process because the chemical is highly
flammable. Contacting a licensed professional waste disposal service to dispose of this material
is recommended for both chemicals.
Toluene
Benzene
36
X. Economic Evaluation
Assumptions
In order to perform an economic evaluation of this process, various assumptions needed to be
made. First of all, the price of raw materials and products was assumed to hold firm through
the next fifteen years of operation. Specifically, the price for each material was set to be the
average price from the last five years. This made benzene $0.519/lb, propene $0.50/lb, toluene
$0.212/lb, propane $0.297/lb, ethylene $0.503/lb, and cumene $0.628/lb.
Other assumptions for economic data are as follows:
Capacity
On-Stream Time
Project Life
Market Build
Capital Spending
Depreciation
Escalation
Discount Rate
Income Tax rate
Working Capital
SG&A
473 MMlb/year
8400 hours/year
15 years from startup
40% / 75% / 100%
15% / 35% / 50%
MACRS (20%, 32%, 19.2%, 11.5%, 11.5%, 5.8%)
2.7% per year
12%
35%
10% of Revenues
1% of Sales
This plant requres 4 separate shifts with 6 operators in each. The operators will have a salary of
$70,000/man-yr, and any overhead will be set using 150% of the labor cost.
Repair and maintenance is set at 1.5% of the capital, property taxes are 2.5% of the capital, and
Insurance costs .5% of the capital.
Base Case
The following summary sheet shows the various costs and returns of the base case for this
system:
37
Working with the assumptions of this base case, this plant would have a net present value of
28.7 million dollars, giving a rate of return (after taxes) of 21.75%, well above the minimum of
15%. The main cost of this process as shown is the cost of raw materials, costing $0.5661 per
pound of cumene produced. Compared to this, the cost of utilities, fixed costs, and the price of
sold byproducts (0.0164, 0.0147, and 0.0105 $/lb cumene respectively) are very small.
38
Economic Sensitivities
Changes in Capital
The capital estimate was developed using ASPEN Icarus, but there is the potential that the price
could be quite different from what was predicted based on contractor costs, market changes,
and various other unforeseeable issues. For the base case, the capital cost of this process is $49
million, giving an ATROR of 21.75%. In order to maintain the minimum ATROR allowed (15%),
the maximum amount of money that could be spent on capital (keeping all other factors the
same) would be $72 million, which would constitute a 46.9% change. It is highly unlikely that
the capital cost would rise higher than this amount.
Changes in Reactant Cost
Historically, the prices of both benzene and propene have been lower by over 10 cents/lb,
however, these prices have risen dramatically in the last few years (likely due to increases in oil
prices). In order to maintain an ATROR of 15%, the price of Benzene may rise by 1.8 cents/lb, or
3.5%. If the benzene price stays the same, the price of propene may rise by 3.3 cents/lb, or
6.6%. With the rising prices of benzene and propene, it is quite possible that these prices may
be exceeded at least one time during the 15 year project life. However, the price of cumene has
been rising in a similar pattern to propene and benzene, and thus these rising prices will likely
be mitigated by the rise in cumene prices.
Changes in Cumene Cost
As stated previously, the prices of cumene have been rising in recent years, however, it is
possible that cumene prices could dip in the future for various reasons. Keeping all values as
stated in the base case, the cumene cost may drop by approximately 1.3 cent/lb, or 2% and
keep the ATROR above 15%. A drop in cumene cost, however, is unlikely due to current market
trends and current changes in crude oil prices.
Historical Pricing
Historically, the prices of cumene, propene, and benzene have been much lower than the last
five years. While all of these prices are fairly well correlated, the lower these prices are, the less
negligible the capital, utility, and plant costs become. Below is a table of the ATROR and NPW of
the plant using average cumene, propene, and benzene costs from various 5 year periods in
recent history.
39
This table shows that, in recent history, this process would not be viable. The recent upsurge in
prices of benzene, propene, and cumene are what make this process viable. Should prices hold
to the amounts they have had since about 2006, this would be not be viable. The recent
upsurge in prices of benzene, propene, and cumene are what make this process viable.
Changes in Sellout Rate
Due to potential changes in market demand, it is possible that the sellout of this plant’s
capacity could happen faster or slower than predicted. Given that all other factors hold firm
(capital cost, materials cost, etc), if the plant capacity takes 6 years to sell out instead of 3 years
in the base case following a scale up of 20%/35%/50%/75%/80%/100%, the ATROR falls to
16.76%. This allows for the plant capacity to take up to double the expected amount of time to
sell out.
Conversely, if the capacity is sold faster than expected (a rate of 50%/100%) selling out by the
second year, the ATROR may rise as high as 23.21%.
40
XI. Conclusion with Recommendations
Based on this study, it is clear that the cumene business is a growing market, yet profit
margins are currently very tight. The market for cuemene is expected to grow at an annual
compound growth rate of 4.2% until 2020, allowing room for new companies to enter the
market without major impact from competitors. However, small changes in benzene and
propene costs, both directly correlated to fuel costs, make the profit margins narrow.
Technologically, the plant has no foreseeable issues. All distillation columns run at low
pressures, making them cheap in capital costs and operating costs while making the process
safe. Some further work for downstream tower control systems is needed, as controls based
on product purity flow rate would increase quality control. Capital costs to build the plant are
approximately $49 million and operating costs are approximately $12 million/year. The current
PW is $28.7 million after 19 years.
The following table summarizes the economic analysis:
41
The project appears to be marginal at best, as profit margins are highly sensitive. The Base
Case calls for an ATROR of 19.9%, comfortably above the required 15% ATROR. However, with
only a 3.5% increase in benzene prices or a 6.6% increase in propene prices, the ATROR falls to
15%. These costs are directly tied to oil prices, and while oil prices have been on the steady
decline in the past 12 months, they are highly unpredictable. If current trends in the oil market
stabilize over the next two years, the recommendation could change from not build to build. A
2.05% decline in cumene prices also returns the ATROR to 15%. While the cumene market and
its demand are projected to rise steadily over the next 20 years, further economic studies on
the market to ensure no foreseeable market decline would be necessary in order to move
forward. A few things could be done to improve these economics. Capital costs can rise 47%
before the ATROR falls to 15%, so a scale up of the plant could be done to increase cumene
production and thus widen sensitivities.
42
Competition from other plants does not seem to pose a threat. The market for cuemene, and
specifically its derivates phenol and acetone have large, varied markets. Phenol and acetone
are used in applications from household products to industrial scale chemicals, safeguarding
their market should one sector no longer be applicable.
Based solely on the tight economic margins, it is recommended that we do not build unless the
following can be accomplished:
1. All contracts to sell cumene must be priced with an escalator to the cost of benzene and
proplyene. This safeguards against rising raw materials costs.
2. Market surveys of the cumene market reveal no foreseeable downturn.
3. Removed toulene and benzene are purified and sold for profit.
4. A study should be conducted to determine optimal plant capacity.
43
XII. References
"Sigma-Aldrich." Sigma-Aldrich. Web. 31 Jan. 2015. <http://www.sigmaaldrich.com/unitedstates.html>.
" Cumene :: Badger." Cumene :: Badger. Web. 31 Jan. 2015.
<http://www.badgerlicensing.com/TechServices_PC_Cumene.html>.
"Energy and Cost Calculator for Heating Water." Water Treatment Solutions. Lenntech, 7 Jan.
2015. Web. 15 Feb. 2015.
"The Best Heat Transfer Fluids for Liquid Cooling." Lytron. Lytron Industries, 18 May 2012. Web.
16 Feb. 2015.
Jakobsen, Hugo A. "Packed Bed Reactors." Chemical Reactor Modeling (2008): 953-84. Springer
Link. Web. 16 Feb. 2015.
Robert Nedwick, “Chemical Engineering 470 Blue Book” 2015.
44
Appendix
Equipment Design Calculations
Sigma-Aldrich MSDS
Plant Specification Sheet
45