Styrene and Polystyrene

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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



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.



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:



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.



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.



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.



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.



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



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)



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.



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.



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



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)



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



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



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



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.



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).



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) .



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.



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.

Documents

Styrene and Polystyrene