2. 1.1Introduction to Ethyl Benzene (EB):
Ethyl benzene is an organic chemical compound which is an aromatic hydrocarbon
(HC). Its major use is in th petrochemical industry as an intermediate compound for
the production of styrene, which in turn is used for making polystyrene, a commonly
used plastic material. Although often present in small amounts in crude oil, ethyl
benzene is produced in bulk quantities by combining the petrochemicals benzene and
ethylene in an acid-catalyzed chemical reaction. Catalytic hydrogenation of the ethyl
benzene then gives hydrogen gas and styrene, which is vinyl benzene. Ethyl benzene is
also an ingredient in some paints.
Ethyl Benzene is used almost exclusively as intermediate in the production of styrene
monomer. It is produced by liquid phase alkylations or vapour phase alkylation’s of
benzene with ethylene. Commercial production started in the 1930s and has grown to
over 23 million metric annually (MTA)
1.2 History of Ethyl Benzene:
The alkylation of HC with olefins in the presence of AlCl3 catalyst was first practiced
by M.Balsohn in 1879. However, Charles Friedel & James M. Crafts pioneered much
of early research on alkylation & AlCl3 catalyst .Over a century later, the process that
employ the classic Friedel-Crafts reaction chemistry remain a dominant source of EB.
Ethyl benzene was first produced on a commercial scale in the 1930s by Dow
Chemical in US and by BASF in the Federal Republic of Germany.
Until 1980s , almost all ethyl benzene was manufactured with an aluminium chloride
catalyst using a Freidal Crafts reaction mechanism . A few EB production units
employed a different Freidal-Crafts catalyst, boron trifluoride. Small amount of EB
also recovered as a by product from mixed xylenes streams using a very intensive
distillation process. In 1980s ,the first commercial facility using a zeolite based process
and the absence of maintenance and environmental problems associated with the
Freidal-Crafts catalyst have allowed zeolite catalyst and to completely displace the
order catalyst in all modern production facilities. The4first zeolite process was based
on vapour –phase reactor at temp. of over 4000C. In this temperature range, reaction
such as isomerisation/cracking and hydrogen transfer produce a number of by products
that contaminate the EB product.
Efforts were made to reduce by-product formation by changing reaction condition, but
it was not until the advent of liquid phase processes operating at temperatures lower
than 2700C that zeolite –catalysed processes were truly capable of producing high
purity EB . The first high purity zeolite based on technology developed by UOP and
ABB Lummus Global , started up in the 1990.
2
3. The Ethyl benzene- Styrene industry remained relatively insignificant until World War
2. The tremendous demand for synthetic SBR during world war prompted accelerated
technology improvements and tremendous capacity expansion. This enormous wartime
effort led to the construction of several large scale factories, turning styrene production
quickly in to a giant industry. In 1965, 10% of EB production was from super fraction
of on a commercial scale in the 1930s by Dow Chemical in US and by BASF in the
Federal Republic of Germany.
1.3 Natural Occurrences:
Ethyl benzene is a colourless, flammable liquid that smells like gasoline. It is naturally
found in coal tar and petroleum and is also found in manufactured products such as
inks, pesticides, and paints.
3
5. 2.1 Current Applications:
All commercial EB production is captive consumed for the manufacture of styrene
monomer Styrene is used in the production of poly styrene and a wide range of other
plastics. Of the other minor applications, the most significant in the paint industry as a
solvent.
Even smaller volumes go towards the production of acetophenone, diethyl benzene & ethyl
anthraquinone.
2.2 Product Specification
The product specification on EB is set to provide a satisfactory feedstock to the associated
styrene unit.
Objectionable impurities in the EB can be grouped in to two categories: a)
Halides
b) Diethylbenzene
Purity 99.5 wt% min.
Benzene 0.1-0.3%
Toluene 0.1-0.3%
O-xylene+cumene 0.02% max
m,p-xylene 0.02% max
Allylbenzene 0.2%
Diethylbenzene 20mg/kg max
Total chlorides 1-3 mg/kg max
Total original sulphur 4 mg/kg max
Reactivity density@150 C 0.869-0.872
APHA color 15 max
5
7. Manufacturing Capacities:
PRODUCER CAPACITY*
BP Chemicals, Texas City, TX 1,100
Chevron, St. James, LA 1,800
Cos-Mar, Carville, LA 2,200
Dow, Freeport, TX 1,900
Huntsman, Odessa, TX 350
Lyondell Chemical, Channelview, TX 3,000
Nova, Bayport, TX 1,400
Sterling, Texas City, TX 2,000
Westlake, Lake Charles, LA 380
Total 14,130
*Millions of pounds per year of Ethyl benzene (EB).
In INDIA
(From Chemical Weekly Buyers Guide 2011)
Pashim Petrochem Ltd, Vadodara
Amol Chemicals & Polymers, Mumbai
Chemaroma Drug House , Mumbai
Chemico, Kolkata
Forum Enterprizes, Mumbai
Ganesh Trading Co., Mangalore
Manish Chemicals, Ahmedabad
Aquapure & Perfect Chemicals, Bengaluru
Solvchem, Maharashtra
7
8. 3. MARKET SURVEY
3.1 Current & Projected Demand:
Demand ( till 2010):
1999: 13,193 million pounds
2000: 13,444 million pounds
2004: 14,552 million pounds
2010: 17,075 million pounds
Growth
Historical (2004 - 2010): 2.7 percent per year.
Strength
EB demand runs parallel to that of styrene, and styrene is a mature and stable
commodity, used in many homo-polymer, copolymer and ter-polymer applications.
These applications cover a wide scope in industrial, consumer and medical products.
Weakness
EB’s major shortcoming is that it is essentially a one market segment product - styrene.
Moreover, as the styrene is produced with captive EB there is not much noticeable
market activity.
3.2 Price & Price Variations:
PRICE
Historical (1995 - 2000):
High, $0.25 per pound, bulk, f.o.b. Houston, TX, list ($ 0.5511 / Kg) By
Friday 8 August, 2010:
EB was valued at $1,554-1,570/tonne FOB NWE ($ 1.554—1.570 / Kg) Price
8
9. Variations:
The US unit sales value of EB in $/Kg from 1960 – 1986:
Year Sales ( $/Kg)
1960 0.13
1965 0.09
1970 0.09
1973 0.11
1974 0.37
1975 0.20
1978 0.24
1979 0.35
1980 0.50
1983 0.51
1986 0.48—0.51
3.3 Application wise Consumption Pattern:
Application Consumption ( in % )
Styrene Production 99 %
Paint industry as a solvent < 1%
Production of Acetophenone,
Diethylbenzene,Ethyl < 1%
anthraquinone
9
11. 4.1 Physical Properties:
Under ordinary conditions, EB is a clear liquid with a characteristic aromatic odor. EB is
an irritant to the skin & eyes and is ordinary toxic by ingestion and skin adsorption.
The properties are as follows:
IUPAC Name Ethylbenzene
Other names Ethylbenzol, EB, Phenylethane
Identifiers [100-41-4]
CAS Number DA0700000
RTECS Number c1ccccc1CC
SMILES C8H10
Molecular Formula 106.167 g/mol
Molar Mass Colourless liquid
Appearance 0.87139 g/cc
Density (at 150 c) 0.8669 g/cc
Density ( at 200 c) 0.86262 g/cc
Density ( at 250 c) -94.949 0 c
M.P. 136.860 c
B.P. ( at 101.3 K Pa) 1.49588
Refractive index (at 200 c) 1.49320
Refractive index ( at 250 c ) 3609 K Pa (36.09 bar)
Critical pressure 344.02 0 c
Critical temperature 150 c
Flash point 4600 c
Auto ignition temperature 1.0%
Flammability limit ( lower) 1.5%
Flammability limit ( Upper) -----
Latent heat ( fusion) 86.3 j/kg
Latent heat ( vaporization) 335 j/kg
Heating value ( gross) 42999 j/kg
Heating Value ( net) 40928 j/kg
Kinematic viscosity (at 37.8 0 c ) 0.6428 * 10 -6 m2 / s
11
12. Kinematic viscosity (at 98.90 c ) 0.390 * 10 -6 m2 / s
Surface Tension 28.48 mN/m
Specific heat capacity ( ideal gas, 250 C) 1169 kg-1 K-1
Specific heat capacity ( liquid, 250 C) 1752 kg-1 K-1
Acentric factor 0.311
Critical compressibility 0.264
LEL 1.2 %
UEL 6.8 %
4.2 Chemical Properties:
The most important chemical reaction of EB is its dehydrogenation to Styrene.
The reaction is carried out at:
1. High temprature ( 600-6700 c)
2. Usually over an iron oxide catalyst
3. Steam is used as dilutent
Commercially, selectivities to styrene range from 89-96%with per rpass conversion 65-70%.
Another reaction of commercial importance is the oxidation of EB by air to hydroperoxides
C6H5CH(OOH)CH3
The reaction takes place in the liquid phase , with no catalyst required. With a suitable
catalyst EB can be converted to xylenes. Commercial processes for isomerizing
xylenes usually involve the catalytic isomerization or dealkylation of EB. EB may be
dealkylated catalytically or thermally to benzene.
12
13. 4.3 Environmental & Health Effects:
Emergency Overview:
Clear, colourless liquid with a characteristic, sweet, gasoline-like, aromatic odour.
Flammable liquid and vapour. Liquid can accumulate static charge by flow, splashing
and agitation. Vapour is heavier than air and may spread long distances. Distant
ignition and flashback are possible. Liquid can float on water and may travel to distant
locations and/or spread fire. Closed containers may rupture and explode in heat of fire.
TOXIC. May be harmful if inhaled. Central nervous system depressant. Vapour may
cause headache, nausea, dizziness, drowsiness, confusion, unconsciousness and
possibly death. SKIN IRRITANT. May cause skin irritation. Aspiration hazard.
Swallowing or vomiting of the liquid may result in aspiration (breathing) into the
lungs. POSSIBLE CANCER HAZARD - may cause cancer, based on animal
information.
Potential Health effects:
Effect of short Term Exposure:
Inhalation:
Ethylbenzene readily forms high vapour concentrations and should be considered toxic
by this route of exposure. Inhalation of the vapour or mists can irritate the nose and
throat and produce symptoms of central nervous system depression such as mild
unsteadiness, headache, nausea, dizziness and a feeling of drunkenness at
approximately 100-200 ppm. Much higher concentrations can cause more severe
symptoms including unconsciousness and death. Human volunteers exposed to 85 ppm
for 8 hours reported no adverse health effects. Above 100 ppm, mild unsteadiness,
sleepiness and headache were reported. In another report, approximately 100 ppm
(cited as 400 mg/m3) produced a slight irritating effect on the respiratory tract,
occasional headaches, sleepiness, slight drowsiness after 8 hours. More pronounced
irritation, frequent headaches, sleepiness and a feeling of drunkenness were observed
at 200 ppm (860 mg/m3). At 1150 ppm (5000 mg/m3), irritation of nose and throat
was experienced. Exposure to 1000-2000 ppm (0.1-0.2%) for 6 minutes caused
irritation of the nose and throat, fatigue and increasing unsteadiness, chest constriction
and dizziness in 4-6 male volunteers. Exposure to 5000 ppm (0.5%) was considered
intolerable.
Skin Contact:
The liquid can cause moderate irritation, based on animal information. Ethylbenzene is
absorbed through the skin to a small extent, but harmful effects are not expected to
occur by this route of exposure.
13
14. Eye Contact:
The liquid can cause mild to moderate irritation, based on limited animal information.
Volunteers reported that exposure to approximately 100 ppm was slightly irritating to
the eyes. At 1000 ppm (0.1%) the vapour was very irritating to the eyes of 4-6
volunteers, producing smarting and burning, accompanied by profuse tearing. This
irritation, gradually decreased until, after a minute or two, it was barely noticeable. At
2000 ppm (0.2%), the irritation was almost intolerable upon first exposure, but again
became less irritating upon continued exposure, while 5000 ppm (0.5%) was
considered intolerable.
Ingestion:
Ethylbenzene has relatively low toxicity following ingestion. As a central nervous
system (CNS) depressant, it can cause nausea, vomiting, headache and dizziness. Very
large amounts may cause unconsciousness and death. Ethylbenzene can cause severe
lung damage or death if the liquid is accidentally breathed into the lungs (aspirated),
based on physical properties. There are no reports of aspiration occurring in humans.
Ingestion is not a typical route of occupational exposure.
Effects of Long-Term (Chronic) Exposure:
Nervous System:
A number of human population studies involving painters and other occupational
groups exposed to a wide range of solvents, including ethylbenzene, have led to some
investigators to conclude that long-term exposure to solvents may cause permanent
effects on the central nervous system (CNS). The signs and symptoms are ill-defined
and include headaches, memory loss, fatigue and altered emotional reactivity. This
syndrome is commonly known as Organic Solvent Syndrome. There are no specific
studies that implicate ethylbenzene as a causal agent, although it is present in many of
the paints and other solvent-containing products. The available studies tend to have a
number of deficiencies including concurrent exposure to many different chemicals, and
lack of exposure data. In a limited study, most workers exposed to up to 11.5 ppm
(cited as 0.05 mg/L) complained of headaches, irritability and of tiring rapidly.
Functional nervous system disturbances were found in some workers employed for
over 7 years.
14
15. Skin:
Repeated or prolonged contact may cause dry, red, chapped skin (dermatitis).
Skin Sensitization:
No allergic skin reaction was observed among 25 volunteers exposed to 10% ethylbenzene in
petrolatum.
Hearing:
Studies in rats have shown that simultaneous exposure to ethyl benzene and noise
increases the potential for hearing damage above that for noise exposure alone. Guinea
pigs do not appear to be sensitive to these effects.(54,55) The relevance of these
observations to human exposures is not known.
4.4 Handling, Storage & Transportation:
EB is a flammable liquid.
It is stored & transported in steel containers.
The US DOT identification number is UN 1175.
Foam, Carbon dioxide, dry chemical, halon & water ( fog pattern) are used in fighting EB
fires.
The use of NIOSH approved respirators is recommended at high concentration.
Skin contact should be avoided.
15
17. Currently, the primary source of ethyl benzene is the alkylation of benzene with
ethylene. The only other source, the super fractionation of mixed C8 aromatic streams,
supplies only a small portion of the ethyl benzene produced. Two distinct types of
ethyl benzene alkylation processes are currently used commercially: liquid- phase
alkylation and vapor-phase alkylation.
5.1 Liquid Phase Alkylation:
Liquid phase aluminum chloride processes have been the dominant source of
ethylbenzene since the 1930s. Several companies have developed variations of this
technology. Processes currently in use include those of Dow chemical, BASF, shell
chemical, Monsanto, societe chimique des cahrbonnages, and union carbide/ badger.
The Monsanto process is currently the most modern commercially licensed aluminum
chloride alkylation technology. Alkylation of benzene with in the presence of an
aluminum chloride catalyst complex is exothermic (∆H-114 kJ/mol); the reaction is
very fast and produces almost stoichiometric yields of ethy lbenzene. In addition to
AlCl3, a wide range of Lewis acid catalysts, including AlBr3, FeCl3, and BF3, have
been used. Aluminum chloride processes generally use ethyl chloride or hydrogen
chloride as a catalyst promoter. These halide promoters reduce the amount of AlCl3
required. The reaction mechanism has been studied in detail Alkylation:
In the conventional AlCl3 process (see Fig 1), three phases are present in the reactor.
Aromatic liquid, ethylene gas, and a liquid catalyst complex phase (a reddish brown
material called red oil). A mixture of catalyst complex, dry benzene, and recycled
polyalkyl benzenes is continuously fed to the reactor and agitated to disperse the
catalyst complex phase in the aromatic phase. Ethylene and the catalyst promoter are
injected into the reaction mixture through spargers, and essentially 100% of the
ethylene is converted. Low ethylene: Benzene ratios are used to give optimum overall
yield of ethylbenzene.
Commercial plants typically operate at ethylene: because molar ratios of ca.0.3-0.35.
As the ratio is increased, more side reactions, such as transalkylation and isomeric
rearrangement, occur. Further alkylation of ethylbenzene leads to the reversible
formation of lower molecular mass polyalkylbenzenes. The loss in net yield due to
residue is minimized by recycling this material to the alkylation reactor. In addition,
because the reaction occurs close to thermodynamic equilibrium, the traditional
processes use a single reactor to alkylate benzene and transalkylate polyalkylbenzenes.
The reaction temperature is generally limited to 1300C; a higher temperature rapidly
deactivates the catalyst and favors formation of non aromatics and polyalkyllbenzenes,
which are preferential absorbed by the highly acidic catalyst complex, resulting in
byproduct formation. Sufficient pressure is maintained to keep the reactants in the
liquid phase. High –alloy materials of construction are also required for the piping and
handling systems. The liquid reactor effluent is cooled and discharged into a settler,
17
18. where the heavy catalyst phase is decanted from the organic liquid phase and recycled.
The organic phase is washed with water and caustic to remove dissolved AlCl3 and
promoter. The aqueous phase from these treatment steps in first neutralized and then
recovered as a saturated aluminum chloride solution and wet aluminum hydroxide
sludge.
Removal of dissolved catalyst from the catalyst from the organic stream has long been
a problem for ethylbenzene producers. Recently CdF chime found that more complete
recovery of AlCl3 could be achieved by first contacting the organic phase with
ammonia instead of sodium hydroxide.
Separation: Purification of the ethyl benzene product is usually accomplished in a
series of three distillation columns. The unreacted benzene is recovered by the first
columns as an overhead distillate. The second column separates the ethyl benzene
product from the heavier polyalkylated components. The bottoms product of the
second column is fed to a final column, where the recyclable polyalkylbenzenes are
stripped from non recyclable high molecular mass residue compounds. The residue or
flux oil, consisting primarily of polycyclic aromatics, is burned as fuel. Because the
alkylation mixture can tolerate only minor amounts of water, the recycled benzene and
fresh benzene must be dried thoroughly prior to entering the reactor. Water not only
increases corrosion, but also decreases catalyst activity. Benzene dehydration is
accomplished in a separate column.
The improved Monsanto process has distinct advantages compared to conventional
AlCl3 processes. The most of these is a significant reduction in the AlCl3 catalyst use,
thus lessening the problem of waste catalyst disposal. Monsanto found that by an
increase in temperature and by careful control of ethylene addition, the required AlCl3
concentration could be reduced to the solubility limit, thereby eliminating the separate
catalyst complex phase. Therefore, alkylation occurs in a single homogeneous liquid
phase instead of the two liquid phases is earlier processes.
Monsanto claims that a separate catalyst complex phase may actually prevent the
attainment of maximum reactor yields. With a few exceptions, the flow scheme of the
Monsanto process is nearly the same as that of more traditional processes. The process
is also capable of operating with low- concentration ethylene feed. The process is also
capable of operating with low concentration ethylene feed. Typically, the alkylation
temperature is maintained at 160-1800C. This higher operating temperature enhances
catalyst activity, with the additional benefit that the heat of reaction can be recovered
as low- pressure steam. Whereas the traditional process accomplishes alkylation and
transalkylation in a single reactor, the homogenous catalyst system must employ a
separate transalkylation reactor. At lower catalyst concentrations, the recycle of
substantial amounts of polyalkylbenzenes terminates the alkylation reaction.
Therefore, only dry benzene, ethylene, and catalyst are fed to the alkylation reactor.
The recycle polyethylbenzene stream is mixed with the alkylation reactor effluent prior
to entering the transalkylation reactor. The transalkylation reactor is operated at much
lower temperature than the primary alkylation reactor. After transalkylation, the
reaction products are washed and neutralized to remove residual AlCl3. With the
homogenous process, all of the catalyst remains in solution. The catalyst-free organic
reaction mixture is then purified using the sequence described previously for the
18
19. conventional AlCl3 process. As with other AlCl3 process, the organic residue is used
as fuel and the aluminium chloride waste streams are usually sold, or sent to treatment
facilities.
3.2 Vapor Phase Alkylation:
Vapor-phase alkylation has been practiced since the early 1940s, but at that time
processes were unable to compete with liquid-phase aluminum chloride based
technology. The alkar process developed by UOP, based on boron trifluoride catalyst,
had modest success in the 1960s, but fell from favor because of high maintenance costs
resulting from the severe corrosion caused by small quantities of water. Nevertheless,
some ethylbenzene units continue to use this process.
The Mobil –badger ethylbenzene process represents the latest and most successful
vapor phase technology to be introduced. The process was developed in the 1970s
around Mobil’s versatile ZSM-5 synthetic zeolite catalyst. Earlier attempts at using
zeolite or molecular sieves for benzene alkylation had suffered from rapid catalyst
deactivation because of coke formation and poor transalkylation capabilities. The
Mobil catalyst combines superior resistance to coke formation with high catalytic
activity for both alkylation and transalkylation by American Hoechst Corp. at their
408x10-3/t/a Bayport, Texas plant. Currently nine commercial plants have been
licensed, representing ca. 3x10106 t/a of production capacity.
ALKAR PROCESS:
This process produces a high purity ethylbenzene product and can use dilute ethylene
feed stock. If the entry of water into the process is strictly prevented, the corrosion
problems associated with aluminum chloride processors are avoided. However, even
small amounts of water (<1mg/kg) hy6drolze the BF, catalyst. The alkyation reaction
takes place at high pressure (2.5-3.5 Mpa; 25-35 bar) and low temperature
(1001500C). Dehydrated benzene, ethylene, and make up BF3, catalysts are fed to the
reactor. Typically, ethylene; benzene molar ratios between 0.15 and 0.2 are used. The
reactor inlet temperature is controlled by recycling a small portion of the reactor
effluent.
Transalkylation takes place in a separate reactor. Dry benzene, BF3 catalyst, and
recycled polyethlybenzene are fed to the transalkylation reactor. The effluent streams
from the two reactors are combined and passed to a benzene recovery column, where
benzene is separated for recycle to the reactors. Boron trifluoride and light
hydrocarbons are taken over head as a vapour stream from which the BF3, is recovered
for recycle. The bottom for the benzene recovery column is sent to a product column,
where ethyl benzene of > 99.9% purity is taken overhead.
A final column serves to recover polyethylbenzenes for recycle to the transalkylation
reactor. The alkar process can operate with ethylene feed containing as low as 8-10
mol% ethylene, enabling a variety of refinery and coke-oven gas streams to be used.
19
20. However, purification of these streams is necessary to remove components that poison
the BF3 catalyst, e.g., trace amounts of water sulfur compound, and oxygenates.
ALKAR PROCESS FLOWSHEET
Mobil-Badger Process:
The fixed –bed ZSM-5 catalyst promotes the same overall alkylation chemistry as
those used in the other processes; however, the reaction mechanism is different.
Ethylene molecules are adsorbed onto the Bronsted acid sites within the catalyst,
which activates the ethylene molecule and allows bonding with benzene molecules to
occur. Hence, the range of higher alkylated aromatic byproducts formed by the Mobil
– Badger process is somewhat different than that for the Friedel Crafts processes.
These components do not affect the ethyl benzene product purity and are recycled to
the reactor for transalkylation or dealkylation. The Mobil-Badger heterogeneous
catalyst system offers several advantages when compared to the other commercially
available processes.
The most important are that it is noncorrosive and non-polluting. The catalyst is
essentially silica – alumina, which is environmentally inert. Because no aqueous waste
streams are produced by the process, the equipment for waste treatment and for
20
21. catalyst recovery is eliminated. In addition, carbon steel is the primary material of
construction, high-alloy materials and brick linings are not required. The reactor
typically operates at 400-4500C and 2-3 MPa (20-30 bars). At this temperature >99%
of the net process heat input and exothermic heat of reaction can be recovered as
steam.
MOBIL-BADGERPROCESS FLOWSHEET
The reaction section includes two parallel multi-bed reactors, a fired heater, and heat
recovery equipment. The high-activity catalyst allows transalkylation and alkylation to
occur simultaneously in a single reactor. Because the catalyst slowly deactivates as a
result of coke formation and requires periodic regeneration, two reactors are included
to allow uninterrupted production: one is on stream while the other is regenerated.
Regeneration takes ca. 36h and is necessary after 6-8 weeks of operation. The catalyst
is less sensitive to water, sulfur, and other poisons than the Lewis acid catalysts. The
reactor effluent passes to the purification section as a hot vapor. This steam is used as
the heat source for the first distillation column, which recovers the bulk of the
unreacted benzene for recycle to the reactor. The remaining benzene is recovered from
a second distillation column.
The ethybenzene product is taken as the overhead product from the third column. The
bottoms product from this column is sent to the last column, where the recyclable
alkylbenzenes and polyalkylbenzenes are separated from heavy nonrecyclable residue.
The low-viscosity residue stream, consisting mainly of diphenylmethane and
diphenylethane, is burned as fuel. The Mobil-Badger process also can use dispute
21
22. ethylene feedstocks. In semi commercial applications, the process has operated on
streams containing as little as 15 mol% ethylene.
5.3 New Developments:
Dow Chemical and Snamprogetti are developing a process for making ethyl
benzene/styrene from ethane and benzene. The process combines the dehydrogenation
of ethane and ethyl benzene in one unit and integrates the processes for preparing
ethylene, ethyl benzene and styrene. This process is claimed to have lower costs than
the conventional route to styrene, largely stemming from the low cost of ethane in
relation to ethylene. A pilot plant has been operating since 2002 and commercialisation
could be possible by the end of the decade.
5.4 Comparison between Processes:
Although both the alkylation process i.e. liquid phase & vapor phase are of equal use
commercially. Yet there are some differences:
1. In vapour phase alkylation, the reactors operates at higher temperatures(400—4500
c) which causes catalytic deactivation by fouling as a result catalyst required periodic
regeneration.
2. In vapour phase alkylation process two reactors will be required so that processing and
regeneration can proceed alternatively without interrupting production.
3. All the ethylene feedstock is reacted completely in the liquid benzene, thus eliminating off
gas recovery equipment.
4. Ethyl benzene yield is 99.7% in liquid phase alkylation process while in vapour phase
alkylation it is around 98%.
5. Zeolite as a catalyst can be used in any of the processes.
6. Up to 99.95wt% product purity in the with no xylene formation, in liquid phase alkylation
process.
22
24. The liquid phase alkylation process for ethyl benzene production is selected, and the
detailed discussion of the process is as follows:
Introduction to process:
Efforts were made to reduce by-product formation by changing reaction condition but
it was not until the advent of liquid phase at temperature lower than 2700 c that zeolite
–catalyzed processes were truly capable of producing. The first high purity zeolite
based EB plant , based on technology developed by UOP & ABB Lummus Global
started up in 1990.
Technology Supplier: UOP & ABB Lummus Global
Current Status: Currently 16 plants are using this technology.
Raw Materials: Ethylene & Benzene
Product quality achievable: 99.95wt% pure EB can be produced.
Catalyst: Zeolite
Material of construction: Carbon Steel
Process Effluents: Inert component of ethylene feed which will appear as benzene column
vent.
6.1 Process Chyemistry:
EB made by the alkylation of benzene with ethylene in the presence of zeolite catalyst.
Successive alkylation also
occurs to minor extent, producing diethylbenzens, collectively termed polyethylene benzene
(PEB)
Benzene + Ethylene → EB (Ethyl benzene)
EB + Ethylene →DEB (Di- ethyl benzene) Process
Description:
Benzene alkylated with the ethylene to yield a mixture of alkylated benzenes. This
mixture is distilled to recover product EB, and higher ethylated benzenes (PEB). The
liquid phase alkylation reactor consists of multi[le beds of zeolite catalyst operating
adiabatically. Process conditions are selected to keep the aromatic reaction mixture in
the liquid phase. Excess benzene is used, and ethylene is injected before each bed.
Multiple ethylene injection points improve selectively and enhance catalyst stability. In
the alkylation reactor, ethylene reacts completely, leaving only the inert constituents of
24
25. the feed, such as ethane. These inters pass through the reactor and are from the plant at
a convenient point.
The alkylation effluents are fed to the benzene column, where benzene is taken as the
over head product for recycle to the reactor. The benzene column bottoms feed the
ethyl benzene column. Here EB is taken as the overhead product.
The reboiler of the distillation columns may used hot oil, high-pressure steam, or direct
firing. Overhead vapors are condensed in waste heat boilers, generating valuable steam
useful in a downstream SM or propylene oxide/styrene monomer plant. The EB unit
has considerable flexibility to mmet a verify of local site conditions in an efficient
manner. If no stream export is required, the net heat import can be reduced
considerably
6.3 Plant Capacity:
The Ethyl benzene plant capacity is 1000MTPY(109 kg per year) based on:
er capacities of other Ethyl benzene operating plants.
25
27. 7.1 Process information:
1. Stream (1) – Benzene is pure
2. Stream (2) – ethylene contains 7 mole % ethane as impurity. Ethane dose not react but moves
in the process as inerts and vent in the light column.
3. Stream (3) – B: E ratio is adjusted to control reaction selectivity , 8:1.
4. Reactor (R-1) – the limiting reactant achivees 100% conversion.
5. Stream (8) –composition is;
Inerts – 45% mole
Benzene - 55% mole
6. Efficiency of T – 1 is such that 99.9% of benzene that is fed is in the overhead.
7. Stream(11) –
Ethyl benzene = 99.9% wt
Benzene= 0.1% wt
8. All the EB fed in to the EB column (T—2) is in overhead.
7.2 Mass balance Calculations:
The plant capacity for ethyl benzene plant = 1000 MTPA
(number of working days per annum is taken as 330)
For which we are suppose to produce the product as follows:- The
product ethyl benzene which we will produce will contain:-
1190 kmol/hr ethyl benzene
and 1.6 kmol/hr benzene
Since we are using liquid phase alkylation process for ethyl benzene production, for which
yield and conversion are as follows:
Yield=99.7%
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28. Conversion=100% (w.r.t ethylene)
Now consider PFD for ethyl benzene plant
Stream (11)
Ethyl benzene=1190 kmol/hr
Benzene = 1.6 kmol/hr
Now we are coming to the reaction part, here we have reactor:-
Now we know that:-
Yield = [{(moles of product produced)*(stochiomertric coefficient)} /(moles of reactant
converted)]/100
=99.7/100=1190/moles of reactant converted
Moles of reactant converted (ethylene)= 1193.5 kmol/hr
Now the reactions in the reactor are:-
C6H6 + C2H4 → C6H5-C2H5
benzene ethylene Ethyl benzene
C6H5-C2H5 + C2H4 → C6H4-(C2H5)2 Ethyl
benzene ethylene Diethyl benzene
here, For 1 mole of Ethyl benzene = 1 mole of ethylene needed
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29. and For 1 mole of diethyl benzene = 2 moles of ethylene needed.
Now after reactor 1190 mol of ethyl benzene produced
So ethylene consumed is = 1190 mol
Thus rest ethylene is = 1193.5 - 1190
= 3.5 mol of ethylene
Since conversion is 100%
It means that all ethylene had converted in to ethyl benzene and rest ethylene converted in to
diethyl benzene.
Now
2 moles of ethylene will produce = 1 moles of diethyl benzene
So, 3.5 mol will produce = 3.5/2
= 1.75 kmol/hr of diethyl benzene (DEB)
Now, to minimize the production of DEB we have chosen high B : E ratio i.e. 8:1
Thus total benzene requirement is = 8 *1193.5
= 9548 kmol/hr
Since Ethylene is not pure it is having only 93mole % ethylene
Thus total ethylene stream (ethylene+ ethane) requirement is:-
=1193.5/0.93 = 1283.3 kmol/hr
Inert = 1283.3– 1193.5
= 89.8 moles/ hr
After reactor will also have un-reacted benzene which will be :-
=Benzene fed – benzene consumed
= 9548-1193.5-1.75
= 8356.25 mol /hr (unreacted)
Now consider reactor-1 (R-1) again:- Inputs:
Benzene = 9548 mol
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