styrene and polystyrene
TRANSCRIPT
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Organic Chemistry Report
Polystyrene
Mr.Teerapat Jerawattanakaset (ID. 5722781515)
Ms.Praewa Virameteekul (ID. 5722782778)
Ms.Nutnicha Singhapunt (ID. 5722792223)
CHS 211: Organic Chemistry for Engineers
Dr. Siwarutt Boonyarattanakalin (Assistant Professor)
Sirindhorn International Institute of Technology (SIIT)
Thammasat University
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List of illustration
Figure 1: The structure of monomer styrene.
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.
Figure 15: Overall polystyrene polymerization process.
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List of illustration
List of table
Figure 16: Configuration of polystyrene.
Figure 17: Stick model of polystyrene.
Figure 18: Reaction of alkane moiety withinitiator radical (In•) or polystyrene radical (R•)
Figure 19: Hydrogen abstraction by initiatorradical (In•) or polystyrene radical (R•)
Figure 20: Expandable polystyrene (EPS).
Figure 21: Shape molding EPS.Figure 22: Block molding EPS.
Figure 23: Extruded polystyrene (XPS).
Fig 24: Polystyrene paper (PSP).
Figure 25: The resin identification code symbolfor polystyrene.
Table 1: Properties of styrene
Table 2: Annual styrene production capacities (1,000 t)
Table 3: Properties of polystyrene
Table 4: Annual polystyrene production capacities(1,000 t)
Table 5: Half life periods of organic peroxidesreproduced with permission from Akzo Noble PolymerChemical
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ABSTRACT
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
the small rate of the hazardous waste.
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Styrene
INTRODUCTION
Styrene, or ethenylbenene, also known as vinylbenzene, and phenylethene, is an
organic compound with chemical formular C 6H5CH=CH. This derivative of benzene is
colourless oily liquid that evaporates easily with a sweet smell.
Styrene is an important feedstock in variety if polymer products. Of the total amount
of styrene produced, almost 50% is used to make polystyrene, 20% for elastomers,
thermosetting resins and polymer dispersions, 15% in ABS and SAN copolymer, 10% is
expanded polystyrene (EPS), and the remainder in a variety of copolymers and specialitymaterials.
Figure 1: The structure of monomer styrene.
MECHANISM OF STYRENE
Industrial production of styrene from ethylbenzene
Styrene is a product of dehydrogenation process of ethylbenzene which is produced
by combining benzene and ethylene in acid-catalyst: C 6H6 + C 2H4 → C6H5CH 2CH 3
by alkylation of benzene.
Figure 2: Alkylation reaction of benzene.
Before alkylation, ethylene must in the form of electrophile which reacted with an acid:
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The chloride ion is immediately picked up by the aluminum chloride to form an AlCl 4 ̅. Then
electrophile substitution of benzene with CH 3CH 2+:
Figure 3: Electrophile substitution of benzene with CH 3CH 2+ mechanism.
The hydrogen is removed by AlCl 4 ̅ which was formed at the same time as the CH 3CH 2
+
electrophile. The aluminum and hydrogen chloride catalysts are re-generated in this second
step in Figure 3.
Figure 4: The structure of ethylbenzene.
The hydrogenation reaction of ethylbenzene to styrene is endothermic and equilibrium
limited
Figure 5: Dehydrogenation reaction of ethylbenzene forming a styrene.
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INDUSTRIAL SCALE PREPARATION
At room temperature, the reaction equilibrium is located far towards the educts side. It
can be shifted towards the product side by increasing the temperature, which increases the
equilibrium constant due to the van’t Hoff relationship and by reducing the pressure, since
two moles of product are formed from one mole of ethylbenzene. Therefore the technical
Styrene synthesis is run at around 600°C with an excess of steam, the steam-ethylbenzene
mixtures has a molar ratios from 5:1 to 12:1. Styrene plants run their reactors under
isothermal or adiabatic conditions with flow rates that ensure short contact times in order to
prevent polymerization of Styrene.
Figure 6: Adiabatic dehydrogenation of ethylbenzene (EB)
a) Steam superheater, b) Reactor, c) High-pressure Steam,
d) Low-pressure Steam, e) Condenser, f) Heat exchanger.
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Figure 7: Isothermal dehydrogenation of ethylbenzene (EB)
a) Heater, b) Steam superheater, c) Reactor,
d) Heat exchanger, e) Condenser
The equilibrium ethylbenzene conversion at 600°C and 0.1 bar pressure is about 83%, and
conversions between 50 and 60% are obtained in technical reactors. The typical byproducts
of the ethylbenzene dehydrogenation are (~1%) benzene and (~2%) toluene formed by
catalytic dealkylation and hydrodealkylation of ethylbenzene, respectively, or they also can
be formed by steam dealkylation. All these reactions are accompanied by the formation of
coke that can deactivate the catalysts. This coke is removed by combustion with steam
according to the water-gas shift reaction.
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Figure 8: Reaction network (products and byproduct) in the 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 also shown (4).
Industrial catalyst composition
The dehydrogenation of EB to St in industry is carried out over potassium promoted
iron oxide catalysts as shown in Figure 5. About 23 million tons of Styrene are produced per
year worldwide, which makes even small improvements of the catalysts profitable. Potassium
was found to increases pure Fe 2O3 (hematite) catalysts by one order of magnitude, and is
believed to play a role in the removal of carbonaceous surface deposits, by catalyzing the
combustion of coke with steam. Potassium carbonate (K 2CO 3) is believed to be the active site
for the coke gasification process.
Technical catalysts are prepared from about 80 wt% of iron oxide Fe 2O3 (hematite)
and at least 10 wt% of potassium oxide. Small amounts of alumina and chromia act as
structural promoters and increase the lifetime of the catalysts. Oxides of V, Ce, W or Mo
improve the selectivity, but their effect is only moderate. Therefore any catalyst model can be
restricted to systems consisting of iron and potassium oxides.
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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,
(5)- desorption of water
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Table 1: Properties of styrene
Properties of styrene
IUPAC name PhenyletheneChemical formula C 8H8 (C 6H5CH=CH 2)
Molar mass 104.15 g/mol
Appearance Colorless oily liquid
Odor Sweet
Density 0.909 g/cm 3
Melting point -30 ºC (-22 ºF; 243 K)
Boiling point 145 ºC (293 ºF; 418 K)Solubility in water 0.03% (at 20 ºC)
Vapor pressure 5 mmHg (at 20 ºC)
Refractive index (n D) 1.5469
Viscosity 0.762 cP (at 20 ºC)
Table 2: Annual styrene production capacities (1,000 t)
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Polystyrene
INTRODUCTION
Polystyrene (PS) 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 can be rigid (in low temperature) or formed (when compressed with air or
gasses.) Polystyrene is a synthetic aromatic polymer made from the monomer styrene, a
liquid petrochemical. Polystyrene is rather poor barrier to oxygen and water vapor and can be
naturally transparent, but can be colored with colorants.
Figure 10: Structure of polystyrene.
MECHANISM OF POLYSTYRENE
The synthesis of polystyrene is similar to the other polymer which is produced by
chain growth polymerization process such as polyethylene, polypropylene etc.
The catalyst for polymerization may be an acid (Lewis or Br ø nsted), a lewis base, or a
Free Radicle Initiator like a benzoyl radical RO• as shown in Figure 10:
Figure 11: Mechanism of Polystyrene where Ph group represents an aryl ring.
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Polymerization of Polystyrene:
Initiation: Using initiator to start the reaction by adding a initiator group to the monomer to
make an intermediary. The initiator can be carbocation, radical, or carbanion. In the
following Figure represents the using of radical to make a radical intermediary (as known as
active center).
Figure 12: Initiation of polymerization of polystyrene.
Chain Propagation: During chain propagation, up to several thousand monomer molecules
add to the the chain. A new active center is formed at the end of the chain after each addition.
Figure 13: Propagation of polymerization of polystyrene.
Chain termination: In styrene polymerization, bimolecular combination is the dominant
termination mechanism at temperatures up to 160 ºC. However, there is evidence that at
higher temperatures disproportionation can account for up to 40%.
Termination of polymerization usually occurs through bimolecular reactions between two
polymer radicals. There are two modes: combination and disproportionation. In the first, two
polymer radicals combine to form a single molecule. In the second, a hydrogen atom is
transferred from one polymer radical to the other to form two polymer molecules, one of
which has a terminal double bond.
Figure 14: Termination of polymerization of polystyrene.
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Figure 15: Overall polystyrene polymerization process.
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
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methods, such as injection moulding. By contrast, syndiotactic polystyrene (SPS) crystallizes
immediately, has a melting point of about 270 ºC and a glass transition temperature of 100 ºC.
Figure 17: Stick model of polystyrene.
Table 3: Properties of polystyrene
Properties of polystyrene
IUPAC name Poly(1-Phenylethene)
Chemical formula (C 8H8)n
Density 0.96-1.04 g/cm
Melting point
~ 240ºC (464 ºF; 513 K)
(decomposes at lowertemperature)
Thermal conductivity0.033 W/(m.K)
(foam, ρ 0.05 g/cm 3)
Refractive index (n D)1.6; dielectric constant 2.6
(1kHz – 1 GHz)
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Table 4: Annual polystyrene production capacities (1,000 t)
INDUSTRIAL SCALE PREPARATION
Production of Standard Polystyrene
Continuous thermal polymerization is carried out using pure styrene in the presence of
5 to 10% of ethylbenzene at temperatures of 130 to 140 º C. Throughputs of from 0.05 to 134
kg/l.h are achieved. The mean molar mass is fixed by the choice of temperature, which
consequently determines the properties of the polystyrene.
Free-Radical Polymerization
Bulk and solution polymerization is carried out using oil-soluble initiators. Essentially
akzo initiators and peroxides, hydroperoxides, peresters or perketals can be used. The choice
of a suitable initiator depends not only on its decomposition characteristic, but also on the
formation of decomposition product and byproducts, the industrial handling properties and
approval of the initiator under food regulations, as well as its grafting activity when used for
rubber-modified polystyrene, and the thermal stability of the end products. A distinction is
made between mono-, di- and multifunctional initiators. Depending on the exposure of the
initiator under reaction conditions, the level of active initiator decreases with time, as
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demonstrated by the half-life periods of various peroxides at different temperatures as
presented in Table 5.
Table 5: Half life periods of organic peroxides reproduced with permission from Akzo
Noble Polymer Chemical
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Figure 18: Reaction of alkane moiety with initiator radical (In•) or polystyrene radical (R•)
Figure 19: Hydrogen abstraction by initiator radical (In•) or polystyrene radical (R•)
BACKGROUND OF PRODUCT
The various properties of polystyrene make it useful for our life. With several ofpreparation, polystyrene appears in many roles these days.
Expandable Polystyrene (EPS)
Expandable polystyrene is polystyrene foam (PS Foam) is rigid and tough, white
color and looks like cell. Using pentane or butane as a blowing agent (instead of using CFCs
as before to avoid leaking of greenhouse gas) added to polystyrene while polymerization
process. Then it expands when receiving an amount of heat from steam (molding). EPS is
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used for many applications e.g. trays, plates, bowls and fish boxes, which has very low
density because of expanding of gas in the process.
Figure 20: Expandable polystyrene (EPS).
There are 2 of forming of EPS: Shape molding and Block molding.
1. Shape molding can be used as ice boxes, fish boxes or else containers.
Figure 21: Shape molding EPS.
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2. Block molding, EPS blocks or boards used in building construction are commonly cut
using hot wires.
Figure 22: Block molding EPS.
Extruded polystyrene (XPS)
Extruded polystyrene foam (XPS) consists of closed cells, offers improved surface
roughness and higher stiffness and reduced thermal conductivity. The density range is about
28–45 kg/m 3. Because of the extrusion manufacturing process, XPS does not require facers to
maintain its thermal or physical property performance. It can easily get burnt and destroyed
by UV ray. And because of higher stiffness, XPS can more resist water vapor better than EPS
so this makes it more suitable to wetter environments than EPS.
Figure 23: Extruded polystyrene (XPS).
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Copolymer
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
"jewel" cases, smoke detector housings, license plate frames, plastic model assembly kits,
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)
and will be used as trays or food boxes etc.
Fig 24: Polystyrene paper (PSP) .
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ENVIRONMENTAL ISSUES
Recycling
Most polystyrene products are currently not recycled due to the lack of incentive to
invest in the compactors and logistical systems required. Due to the low density of
polystyrene foam, it is not economical to collect. However, if the waste material goes through
an initial compaction process, the material changes density from typically 30 kg/m3 to 330
kg/m3 and becomes a recyclable commodity of high value for producers of recycled plastic
pellets. Expanded polystyrene scrap can be easily added to products such as EPS insulation
sheets and other EPS materials for construction applications; many manufacturers cannot
obtain sufficient scrap because of collection issues. When it is not used to make more EPS,
foam scrap can be turned into products such as clothes hangers, park benches, flower pots,
toys, rulers, stapler bodies, seedling containers, picture frames, and architectural molding
from recycled PS.
Figure 25: The resin identification code symbol for polystyrene.
Liter
Polystyrene foam is a major component of plastic debris in the ocean, where it
becomes hazardous to marine life and "could lead to the transfer of toxic chemicals to the
food chain". Animals do not recognize this artificial material and may even mistake it for
food. Polystyrene foam blows in the wind and floats on water, and is abundant in the outdoor
environment. It can be lethal to any bird or sea creature that swallows significant quantities.
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Conclusion
Polystyrene is made from the monomer styrene that used wildly in the industries. To produce
the product the industries have to select the type for the raw material and process that they
want to form a product depends on the properties and the quantities of product. Expandable
polystyrene is similar to Polystyrene paper but Polystyrene paper used screw extrusion to
form the shape. However, Polystyrene paper must be expands when receiving an amount of
heat from steam after added to polystyrene while polymerization process. Extruded
polystyrene foam can more resist water vapor better than Expandable polystyrene, but
Extruded polystyrene foam can get burnt and destroyed by UV ray easier than Expandable
polystyrene. For Copolymer product can be made by the properties of a stretchier material.
Nowadays, Expandable polystyrene have often been using in the reality to make products and
convenience stuffs for comfortable in the real our life.