Styrene monome
Formula C8H8
Chemistry
Styrene is a certain organic chemical compound having the
chemical formula C6H5CH=CH2.
Its chemical structure is made up of a vinyl group bonded
onto a benzene ring. This benzene ring makes styrene an
aromatic compound.
Styrene is a clear, colorless liquid that is derived from
petroleum and natural gas by-products
Other names for styrene can be styrol, vinyl benzene,
phenylethene, or phenyl ethylene.
Styrene helps create plastic materials used in thousands of
remarkably strong, flexible, and lightweight products, which
represent a vital part of our health and well being. It's used
in everything from food containers and packaging materials
.to cars, boats, and computers
Figure1. Chemical structure of styrene
Styrene dissolves in some liquids, but dissolve only slightly
in water , It is soluble in alcohol , ether acetone ,and carbon
disulfide ; It is incompatible with oxidizers , catalysts for
vinyl polymers ,peroxides ,strong acids .and aluminum
. chloride
Styrene is dangerous when exposed to flame heat or
oxidation ; it reacts violently with chlorosulfonic acid, oleum
,and alkali metal graphite , and reacts vigorously with
oxidizing materials, It may polymerize if contaminated or
subjected to heat , on decomposition , it emits acrid fumes, it
. usually contains an inhibitor such as tert-butylcatechol
Occurrence, history, and use
Styrene is named after the styrax trees from whose sap
(benzoin resin) it can be extracted. Low levels of styrene
occur naturally in plants as well as a variety of foods such as
fruits, vegetables, nuts, beverages, and meats. The
production of styrene in the United States increased
dramatically during the 1940s, when it was popularized as a
feedstock for synthetic rubber.
The presence of the vinyl group allows styrene to
polymerize. Commercially significant products include
polystyrene, ABS, styrene-butadiene (SBR) rubber, styrene-
butadiene latex, SIS (styrene-isoprene-styrene), S-EB-S
(styrene-ethylene/butylenes-styrene), styrene-
divinylbenzene (S-DVB), and unsaturated polyesters. These
materials are used in rubber, plastic, insulation, fiberglass,
pipes, automobile and boat parts, food containers, and
carpet backing.
Sources
Styrene is one of the most important monomers worldwide,
and its polymers and copolymers are used in an increasingly
.wide range of applications
The major uses are in plastics, latex Paints and coatings,
synthetic rubbers, polyesters and styrene-alkyd coatings
Among the top 50 chemicals worldwide, styrene was
twentieth in 1994 with production of 11 270 million pounds.
Styrene occurs naturally as a degradation product in
cinnamic acid Containing plants, e.g. balsamic trees, and as a
.by-product of fungal and microbial metabolism
Styrene has been detected in the atmosphere in many
locations. Its presence in air is principally due to emissions
from industrial processes involving styrene and its polymers
and Copolymers. Other sources of styrene in the
environment include vehicle exhaust, cigarette smoke and
other forms of combustion and incineration of styrene
.polymers
The concentration of styrene in urban air is relatively low
compared with that of aromatic hydrocarbons, such as
toluene and xylene. This appears to be due to the ready
reactivity of Styrene with ozone to yield benzaldehyde and
peroxides, all of which are irritants; one of the
A peroxide, peroxybenzyol nitrate, is a potent eye irritant.
Styrene is an active component of photochemical smog.
Some liberation of styrene may also take place from recently
manufactured plastic goods. While this may contribute to
indoor levels of styrene, the effect on total emissions to the
.environment is negligible
Applications
Styrene monomer is a basic building block of the plastic
industry. It is used to make a host of downstream derivative
products that go into millions of consumer goods. Primary
derivatives of styrene monomer, in order of demand, include:
polystyrene, expandable polystyrene (EPS) and acrylonitrile-
butadiene-styrene (ABS)/styrene-acrylonitrile (SAN) resins,
styrene butadiene (SB) latex, SB Rubber (SBR), unsaturated
polyester resins (UPR), specialty polymers, co-polymers
and styrene thermoplastic elastomers (TPE) (see Figures 1.3
and 1.4).
Polystyrene is one of the easiest plastics to use to produce
commodity packages and consumer goods. It is primarily used
in insulation, packaging, appliances, furniture, toys and
cassettes. It consumed 49 percent of the world production of
styrene monomer based on 2004 data.
Expandable polystyrene (EPS) beads are produced from
styrene monomer and non-CFC (chlorinated fluorocarbons)
blowing agents. It is primarily used in food packaging,
insulation and cushion packaging. Resins of ABS/SAN are
used in construction materials, appliances, business machines
and transportation. Expandable polystyrene and ABS/SAN
resins accounted for 30 percent of the world production based
on 2004 data. Other applications include paper and textile
coatings and carpet backing (SB latex), production of tires
(SBR), construction and marine applications (UPR), adhesives
and polymer modification (TPEs), etc.
Polystyrene products are recyclable. In the past, polystyrene
companies routinely recycled plant scraps to make their
manufacturing processes as efficient as possible. More recently,
with growing concerns about how it disposes of its wastes, the
polystyrene industry has started recycling post consumer
polystyrene packaging. Polystyrene is being recycled back into
packaging, as well as durable goods such as office supplies,
house and garden products, construction materials, video
cassettes and other useful products.
Production of Styrene
1) Dehydrogenation of ethyl benzene
Ethyl benzene is dehydrogenated to styrene by the
following reaction:
This is the desired selective reaction; however, various non-
selective reactions will occur. For example, a reactor
effluent contains an average of 0.7% benzene and 1.0%
toluene.
The crude styrene, with an average composition of 37%
styrene, 61% ethyl benzene, 1.0% toluene, 0.7% benzene,
and 0.3% tars, is passed through a pot containing sulfur or
some other polymerization inhibitor and is then fed into a
vacuum column system. The overhead from a primary
fractionating column is fractionated to separate the ethyl
benzene, which is Recycled, from the benzene and toluene,
which are separated by distillation. The bottoms from a
primary fractionating column are distilled to obtain the pure
styrene product .
The reactions for styrene production are as follows:
C6 H 5 C2 H 5 ⃗ CHCH
→
2 6 5 2 3 + H2
ethylbenzene styrene hydrogen (1)
C6 H 5 C2 H 5 →CH 6 + C2 H4
6
ethylbenzene benzene ethylene (2)
C6 H 5 C2 H 5 + H 2 →C 6 H 5 CH 3 + CH 4
ethylbenzene hydrogen toluene methane (3)
2) Co-product with propylene oxide
Ethyl benzene is oxidized to the hydro peroxide, which is
then reacted with propylene to yield the propylene oxide
and a co-product, methyl phenyl carbinol. The carbinol is
then dehydrated to styrene . Expected impurities may
include propylbenzene, isopropyl benzene, and alpha-
.methyl styrene
From pyrolysis gasoline )3
4) Dehydrates of 1-phenylethanol
An obsolete process for styrene production involved
oxidation of ethyl benzene to acetophenone and 2-
phenylethanol, followed by hydrogenation of the
acetophenone to 1-phenylethanol, this dehydrates easily to
styrene.
5) Oxydehydrogenation of 4-
vinylcyclohexene
Dow has proposed a route to styrene by
oxydehydrogenation of 4-vinylcyclohexene prepared by
butadiene dimerization. The dimerization is performed in
the gas phase at 100°C and 25 bar over a proprietary
catalyst consisting of copper loaded Y-zeolite.
The second step is oxydehydrogenation of vinylcyclohexene
to styrene. This reaction is catalyzed by mixed-metallic
oxides in the vapor phase at about
400°C and 2.4 bar.
A variant of this process, developed by DSM, converts the
vinylcyclohexene to ethyl benzene, and the dehydrogenation
can then be carried out in a conventional plant. The DSM
process employs liquid-phase butadiene dimerization to 4-
vinylcyclohexene catalyzed by iron dinitrosyl chloride–zinc
complex [Fe (NO2) Cl/Zn], while the dehydrogenation to
ethyl benzene is catalyzed by palladium on magnesium
oxide. Final conversion of ethyl benzene to styrene can be
carried out with conventional dehydrogenation catalysts.
6) Production of styrene from toluene and
methanol
Styrene can be produced from toluene and methanol, which
are cheaper raw materials than those in the conventional
process. Historically, however, this process has suffered
from low selectivity due to competing decomposition of
methanol. Exelus Inc. claims to have developed this process
with commercially viable selectivities, at (400-425) °C and
atmospheric pressure, by forcing these components through
a proprietary zeolitic catalyst. It is reported that an
approximately 9:1 mixture of styrene and ethylbenzene is
obtained, with a total styrene yield of over 60%.
7) Production of styrene via benzene and
ethane
Another developing route to styrene is via benzene and
ethane. This process is being developed by Snamprogetti
S.p.A. and Dow. Ethane, along with ethyl benzene, is fed to a
dehydrogenation reactor with a catalyst capable of
simultaneously producing styrene and ethylene. The
dehydrogenation effluent is cooled and separated and the
ethylene stream is recycled to the alkylation unit. The
process attempts to overcome previous shortcomings in
earlier attempts to develop production of styrene from
ethane and benzene, such as inefficient recovery of
aromatics, production of high levels of heavies and tars, and
inefficient separation of hydrogen and ethane. Development
of the process is ongoing.
8) Dehydration of phenylmethylcarbino
The process is similar to the oxidation of cumene to cumene
hydro peroxide and isobutane to tert-butyl hydroperoxide.
Magnesium carbonate is added to adjust the pH to 7 to
reduce the decomposition of the hydroperoxide. Selectivity
of about 65% is possible only at a low conversion of 15–
17%. Above that concentration, byproducts including
phenylmethylcarbinol and acetophenone increase
appreciably. Meanwhile, acetophenone can be converted to
styrene by hydrogenation to phenylmethylcarbinol and
subsequent dehydration.
The epoxidation stage is also similar to the production of
tert-butyl hydroperoxide, a molybdenum naphthenate
catalyst playing an important role. However, this requires
milder conditions of 100–130°C in the liquid phase under
ambient pressure. Selectivity of propylene to propylene
oxide is about 91%. Byproducts include dimers of propylene,
whose formation can be inhibited by antioxidants. The
vaporphase dehydration of phenylmethylcarbinol to styrene
takes place over a catalyst at 200–280°C. Titania and
alumina are typical catalysts.
9) By oxidative dehydrogenation.
This styrene process has not been commercialized, although
Dow described an improved catalyst in the mid-1990s (see
note at the end of this chapter). A catalyst with large ligands
that suppresses 4-vinylcyclohexene formation is nickel in
combination with tris-O-phenyl phenyl phosphite. At 80°C
and 1 bar, selectivity to 1, 5- cyclooctadiene is 96%. DSM has
developed a related approach to styrene via butadiene.
Vinylcyclohexene is dehydrogenated in the gas phase over a
proprietary Pd/MgO catalyst to give ethyl benzene.
The ethyl benzene can then be converted to styrene by
conventional techniques.
The Dow process for conversion of butadiene to styrene
involves dimerization of butadiene to vinylcyclohexene
followed by an oxidative dehydrogenation of the
vinylcyclohexene to styrene. The dimerization is catalyzed
by copper loaded Y zeolite. The oxidative hydrogenation
uses proprietary mixed-oxide catalysts. A DSM process has
three steps, the first being dimerization and the second
dehydrogenation to ethylbenzene followed by further
dehydrogenation to styrene. The first dehydrogenation uses
a Pd/MgO catalyst. The ethyl benzene–styrene conversion is
conventional.
10) Styrene from toluene
Toluene is dehydrocoupled to stilbene followed by a
metathesis reaction with ethylene. The first step takes place
at 600°C in the presence of a lead magnesium aluminate
catalyst and the second at 500°C with calcium oxide–
tungsten oxide catalyst on silica.
