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Figure 2: Alkylation reaction of benzene.Figure 3: Electrophile substitution of benzene withCH3CH2+ mechanism.
Figure 4: The structure of ethylbenzene.
Figure 5: Dehydrogenation reaction of ethylbenzeneforming a styrene.
Figure 6: Adiabatic dehydrogenation of ethylbenzene
(EB) a) Steam superheater, b) Reactor, c) High-pressureSteam, d) Low-pressure Steam, e) Condenser, f) Heatexchanger.
Figure 7: Isothermal dehydrogenation of ethylbenzene(EB) a) Heater, b) Steam superheater, c) Reactor, d) Heatexchanger, e) Condenser
Figure 8: Reaction network (products and byproduct) inthe dehydrogenation of ethylbenzene. Toluene and
benzene are formed by (1) dealkylation reaction, (2)hydrodealkylation reaction and (3) steam dealkylation.The Coke formation and gasification with steam is alsoshown (4).
Figure 9: Schematic drawing of the catalytic oxidativedehydrogenation over carbon nanofilaments, (1)-adsorption of ethylbenzene, (2)-dehydrogenation at basiccenters, (3)-desorption of Styrene, (4)- adsorption ofoxygen and reaction with OH groups, (5)- desorption of
water
Figure 10: Structure of polystyrene.
Figure 11: Mechanism of Polystyrene where Ph grouprepresents an aryl ring.
Figure 12: Initiation of polymerization of polystyrene.
Figure 13: Propagation of polymerization of polystyrene.
Figure 14: Termination of polymerization ofpolystyrene.
Now-a-day, there is one type of material used as packaging material which good hate
carrier and good at force absorption and this is always called “foam” in Thai or ‘Styrofoam”
in trading name; Polystyrene. Polystyrene is a synthetic polymer made from monomer
styrene, a benzene derivative which made from benzene and ethylene.
Polystyrene is a clear glassy solid material, hard and rather brittle which is
thermoplastic that has wide liquid phase temperature so it is easy to form a various shape.
Polystyrene is one of the most widely used plastic, the scale of its production being several
billion kilograms per year made from petrochemical. Polystyrene is synthesized by
polymerization of monomer styrene by several of catalyst and initiator. There are many typeof polystyrene for different of using by addition of some material to change its physical
properties such as hardness, flexibility, heat inductivity etc. or can be colored with colorants.
As a thermoplastic polymer, it flows if heated above about 100ºC and becomes rigid again
when cooled. With this limit of using, attention is required when working with polystyrene
because its composition that hazard to environment and human’s life.
This day there is still no way to destroy polystyrene with no danger to environment
and human because of its composition and physical properties. So in the industrial they are
trying to find the way for recycling polystyrene and the production of polystyrene that release
Alternative processes for styrene synthesis (Oxidative dehydrogenation of EB)
Oxidative dehydrogenation is one of the many alternative techniques which have been
proposed to overcome some of the disadvantages of the styrene synthesis by EB
dehydrogenation like the high endothermicity of the reaction and product separation.
Alkhazov et al. proposed that carbonaceous deposits which were formed in the first hours of
time on stream on the surface of acidic catalysts act as the real active centers for the oxidative
dehydrogenation of ethylbenzene to Styrene.
C6H5CH 2CH 3 + 1/2O 2 C6H5CH=CH 2 + H 2O
The formation of water as a byproduct makes the process exothermic and thermodynamically
enables complete conversion. This also reduces the energy consumption for the Styrenesynthesis over iron oxide catalysts considerably. In more recent studies various carbon
materials exhibited higher activities and selectivities than iron oxide based catalysts at much
lower reaction temperatures than 600°C.
Figure 9: Schematic drawing of the catalytic oxidative dehydrogenation over carbon
nanofilaments, (1)- adsorption of ethylbenzene, (2)-dehydrogenation at basic centers,
(3)-desorption of Styrene, (4)- adsorption of oxygen and reaction with OH groups,
From a stereochemical point of view, the type of polystyrene produced by radical or
anionic methods is consequently not crystallizable. As Figure 15 shows, polystyrene can bedivided into three classes: atactic, isotactic and syndiotactic. Catalysts which could be used to
produce hemitactic polystyrene have not been described to date.
Figure 16: Configuration of polystyrene.
Atactic polystyrene is used as general purpose polystyrene (GPPS). The partially crystalline,
isotactic polystyrene (IPS), which can be prepared with the aid of Ziegler-Natta catalysts and
has a relatively high melting point of 240 ºC, is of virtually no commercial interest. It has an
extremely slow crystallization rate and consequently cannot be used for industrial processing
Pure polystyrene is brittle, but hard enough that a fairly high-performance product can
be made by giving it some of the properties of a stretchier material, such as polybutadiene
rubber. The two such materials can never normally be mixed because of the small mixing
entropy of polymers (see Flory-Huggins solution theory), but if polybutadiene is added
during polymerization it can become chemically bonded to the polystyrene, forming a graft
copolymer, which helps to incorporate normal polybutadiene into the final mix, resulting in
high-impact polystyrene or HIPS, often called "high-impact plastic" in advertisements.
Several other copolymers are also used with styrene. Acrylonitrile butadiene styrene or ABS
plastic is similar to HIPS: a copolymer of acrylonitrile and styrene, toughened with
polybutadiene. Most electronics cases are made of this form of polystyrene, as are manysewer pipes. HIPS can is used for producing disposable plastic cutlery and dinnerware, CD
and many other objects where a rigid, economical plastic is desired.
Polystyrene paper (PSP)
As same as EPS, but form the shape by extruding by heated screw (screw extrusion).
When PS melted by the heat, it will be added butane gas that makes PS expands the rolled assheet like paper. Then this polystyrene paper form will get molded by heat (thermal foaming)