survey of industrial chemestry - chapter 9

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Chapter

9

Derivatives

of Ethylene

Over

100

billion Ib

of

chemicals

and

polymers

per

year

are

made from

ethylene, by far the most im portant organic chemical. Over 40% of all

organic chemicals by volume are derived from ethylene. Unfortunately, we

cannot describe the interesting chemistry and uses for all the important

derivatives of ethylene. W e will limit our detailed discussion to those

chemicals made from ethylene that appear in the top 50 , which amount to 8

important organic chem icals. These are listed in Table 9.1.

Again we are faced with the question of what order to treat these

chemicals:

by

rank, alphabetically,

and so on.

Some

of

these chemicals

can

be grouped by m anufacturing process, since one m ay be made from another,

and both originally

from

ethylene, in a m ultistep synthetic sequence. W e

take advantage of this manufacturing relationship in our choice of order

since it

groups these chemicals together

in one

important feature that

we

wish to em phasize: their chem istry of m anufacture. The discussions of

these chem icals w ill be different from that for inorganics. For inorganics the

Table

9 .1

Ethylene Derivatives

in the T op 50

Ethylene dichloride

Vinyl chloride

Acetic acid

Vinyl

acetate

Ethylbenzene

Styrene

Ethylene oxide

Ethylene glycol



ethylene

ethylene

dichloride

vinyl

chloride

acetaldehyde

acetic

acid

vinyl acetate

ethy benzene

styrene

ethylene

glycol

ethylene oxide

Figure 9 .1 Synthesis of ethylene deriva tives in the top 50 chemicals.



emphasis was on the

simple

reaction, the

engineering aspects

of the

chemical's manufacture, uses,

and

economics. Because there

are

more

organics than inorganics

in the top 50, we

must sacrifice some details

in

engineering and

economics

but

still stress

the

chemistry

of

manufacture

(including mechanism when known) and uses of the chemicals. Let us recall

at this point that nearly half

of all

ethylene

is

polymerized

to

polyethylene.

This

process

and the

polymer will

be

discussed

in a

later chapter. Other than

this th e

main large-scale industrial reactions

of

ethylene

are

summarized

in

this chapter. Fig. 9.1 gives an outline of this chemistry with the order that

we

will

use to

consider these chemicals. They

are in

four pairs, since vinyl

chloride is made from ethylene dichloride, vinyl acetate is made from acetic

acid,

styrene

is processed from ethylbenzene, and ethylene glycol is

manufactured

from

ethylene oxide.

1. ETHYLENE DICHLORIDE EDC)

Cl-CH

2

-CH

2

-Cl

Ethylene dichloride is one of the highest-ranked derived organic

chemicals

and is

made

in excess of 20

billion

Ib/yr.

There

are two

major

manufacturing

methods for this chemical, each of which contributes about

50% to the total

production

of

EDC.

The

classical method

for EDC

manufacture is the electrophilic addition of chlorine to the double bond of

ethylene.

The

yield

is

good (96-98 );

it can be

done

in

vapor

or

liquid

phase at

40-5O

0

C

using ethylene dibromide a s a solvent, and the product is

easily

purified

by

fractional distillation.

The

mechanism

is

well understood

and is a

good example

of the

very general addition

of an

electrophile

to a

double bond. Here th e intermediate is the bridged chloronium ion, since in

this structure

all

atoms have

a

complete

octet. A

primary carbocation

is

less

stable. Polarization

of the

chlorine-chlorine bond occurs

as it

approaches

the

T

cloud

of the

double bond. Backside attack

of

chloride

ion on the

bridged

ion

completes

the

process.

Reaction

Mechanism

slow



In contrast to this direct chlorination there is the oxychlorination of

ethylene using hydrogen chloride and oxygen, the other

major

method now

used.

Since

th e

chlorine supply

is

sometimes short

and it is difficult to

balance the caustic soda and chlorine demand (both are made by the

electrolysis

of brine),

hydrogen chloride provides

a

cheap alternate source

for the chlorine atom. Most of the ethylene dichloride manufactured is

converted into vinyl chloride by eliminating a mole of HCl, which can then

be

recycled

and

used

to

make more

EDC by

oxychlorination.

EDC and

vinyl chloride plants usua lly are physically linked . Most plants are 50:50

direct chlorinationroxychlorination to balance the output of HCl.

50 %

CH

2

=CH

2

+

2HCl

+

X

2

O

2

^

Cl-CH

2

-CH

2

-Cl

+

H

2

O

Cl-CH

2

-CH

2

-Cl >

CH

2

=:

CH-Cl + HCl (recycle)

50%

CH

2

=CH

2

+ Cl

2

^ Cl-CH

2

-CH

2

-Cl

Cl-CH

2

-CH

2

-Cl *• CH

2

=CH-Cl + HCl (recycle)

What probably happens in the oxychlorination process is that chlorine is

formed

in situ. The reaction of hyd roge n chloride and oxygen to give

chlorine and water was discovered by Deacon in 1858. Once the chlorine is

formed,

it

then adds

to

ethylene

as in the

direct chlorination mechanism.

Cu

+2

is the catalyst and helps to m ore rapidly react HCl and O

2

because of its

ability

to

undergo reduction

to

Cu

+1

and

reoxidation

to

C u

+2

.

KCl is

present

to

reduce

the

volatility O f C u C l

2

.

2HCl + 2Cu

+2

>• Cl

2

+ 2Cu

+

+

2H

+

2Cu

+

+

V

2

O

2

+

2H

+

2Cu

+2

+ H

2

O

Ethylene dichloride is a colorless liquid with a bp of 84

0

C. As with m any

chlorinated hydrocarbons,

it is

quite toxic

and has a TLV

value

of 10 ppm

(TWA).

It is on the

list

of

"Reasonably Anticipated

to Be

Human

Carcinogens.

Nearly all ethylene dichloride is made into vinyl chloride, which is

polymerized to the important plastic poly(vinyl chloride) (PVC).

Perchloroethylene (perc) is used as a dry cleaning agent (55%), a chemical

intermediate (29%), and a metal cleaning agent (11%). Perc has a 75% share

of the dry cleaning business. M ethyl chloroform is one of a few chlorinated

compounds that has low toxicity, but it is being phased out because of its

ozone depleting potential. Som etim es called 1,1,1, it is used as a chemical

intermediate (60%), a metal cleaning agent (25%), and as an ingredient in



adhesives, coatings, and inks (8%). V inylide ne chloride is polym erized to a

plastic (Saran®). The ethylenediamines are used as chelating agents, the

most important being ethylenediaminetetracetic acid (EDTA).

vinyl chloride perchloroethylene methyl chloroform

vinylidene

chloride ethyleneamines

Despite these minor uses, the economics of EDC is linked to the demand

for PV C plastic.

2. VINYL

CHLORIDE

VINYL

CHLORIDE

MONOMER, VCM)

CH

2

=CH-Cl

Although there

are two

manufacturing methods

for

ethylene dichloride,

all

the

vinyl chloride

is

made

by a

single process, thermal dehydro-

chlorination of ED C. This takes place at tem peratures of 480-51O

0

C under a

pressure of 50 psi with a charcoal catalyst to give a 99% yield. V inyl

chloride is a gas at ambient pressure with a bp of -13

0

C.

It is separated from

ethylene dichloride by fractional distillation. V inyl chloride readily

polymerizes so it is stabilized with inhibitors to prevent polymerization

during storage.

The

mechanism

of

formation

is a

free-radical chain process

as

shown below. A lthough

th e

conversion

is

low, 50-60%, recycling

th e

EDC allows an overall 99% yield.

Reaction



The largest use of vinyl chloride is in the manufacture of poly(vinyl

chloride)

plastic, which

finds

diverse applications

in the

building

and

construction industry

as

well

as in the

electrical, apparel,

and

packaging

industries. Poly(v inyl chloride) does degrade relatively fast for a polymer,

but various heat, ozone,

and

ultraviolet stabilizers make

it a

useful polymer.

A wide variety of desirable properties can be obtained by using various

amounts

of

plasticizers, such that both rigid

and

plasticized

PV C

have large

markets. PV C takes up 98% of all vinyl chloride with only 2% being used

for chlorinated solvents and po ly(vinylidene chloride).

After

some tough years

in the

1970s vinyl chloride

had a

good economic

gain in the 1980s. The 1997 production of approximately 15 billion Ib is

expected to increase by about 3% per year in the near

future.

At a price of

210/lb that gives

a

total commercial value

of

$3.2

billion. One of the

reasons vinyl chloride

has had

some

bad

years

is the

recent

findings of

toxicity. It causes liver cancer and is on the list of chem icals that are

"Known to Be Hum an Carcinogens." In 1973 its TLV w as 200 ppm. This

was

reduced

in

1974

to 50 ppm and in

1980

the TWA was 5

ppm.

In

2000

it

is 1 ppm . However, apparently this causes no health problems for poly(vinyl

chloride) uses. On ly

th e

monomer

is a

health hazard.

As a

result,

the

economic

situation looks good.

3. ACETIC

ACID

ETHANOIC

ACID, GLACIAL

ACETIC ACID)

Mechanism

If there is a prime example of an organic chem ical that is in a state of flux

and

turnover

in

regards

to the

m anufacturing method,

it is

probably acetic

acid. There are now three industrial processes for m aking acetic acid.

Domestic capacity in

1978

was almost equal among acetaldehyde

oxidation,



«-butane

oxidation, and m ethanol carbonylation. In 1980 m ethanol

carbonylation exceeded 40% of the capacity and will continue to increase in

its share of capacity because of economic advantages. In 1998 methanol

carbonylation was 64% of capacity. Acetic acid will also be covered in the

derivatives

of

methane chapter,

but it is

appropriate

to

cover

it

here since

both it and vinyl acetate are still made from ethylene.

Ethylene is the exclusive organic raw material for making acetaldehyde,

70%

of which is further oxidized to acetic acid or acetic anhydride . The

Wacker process, named after

a

German company,

for

making acetaldehyde

involves

cupric chloride and a small amount of palladium chloride in

aqueous solution

as a

catalyst.

The

inorganic chemistry

of

this reaction

is

understood:

(1) A

T

complex between ethylene

and

palladium chloride

is

formed and decomposes to acetaldehyde and palladium metal; (2) the

palladium is reoxidized to palladium chloride by the cupric chloride; and (3)

the cuprous chloride thus formed

is

reoxidized

to the

cupric state

by

oxygen

fed

to the

system.

The

three equations that follow indicate

the

series

of

redox reactions that occur. W hen added together they give

the

overall

reaction. The yield is 95%.

(1)

(2)

(3)

overall:

The details of the organic chemistry of the reaction of ethylene with

PdCl

2

(equation

(1 )

above)

are

also known

and are

shown

in

Fig. 9.2.

The

palladium ion

complexes with ethylene

and

water molecules

and the

water

adds across the bond while

still

complexed to palladium. The palladium

then serves as a hydrogen acceptor wh ile the doub le bond reform s. Keto-

enol tautomerism takes place, followed by release of an acetaldehyde

molecule

from

the palladium .

When it was a

major

source for acetic acid, acetaldehyde was in the top

50

at about 1.5 b illion Ib. Now it is under a billion pounds but it is still used

to

manufacture acetic acid

by

further oxidation. Here

a

m anganese

or

cobalt

acetate catalyst

is

used with

air as the

oxidizing agent. Tem peratures range

from

55-8O

0

C

and

pressures

are 15-75

psi.

The

yield

is

95%.



Figure 9.2 Mechanism

of the

W acker reaction. (Source: White)

Although the oxidation reaction is

simple,

the mechanism is quite

complex and involves the formation of peracetic acid first.

Some of the

peracetic acid decomposes with

the

help

of the

catalyst

and

the

catalyst is regenerated by this process.



Most of the peracetic acid decomposes via a cyclic reaction with

acetaldehyde to form two m oles of acetic acid.

A second manufacturing method for acetic acid utilizes butane from the

€4

petroleum stream rather than ethylene. It is a very com plex oxidation

with

a variety of products formed, but conditions can be controlled to allow

a large percentage of

acetic

acid to be formed. Cobalt

(best),

manganese, or

chromium acetates

are

catalysts with temperatures

of 50-25O

0

C and a

pressure

of 800

psi.

The

m echanism

of

this reaction involves free radical oxidation

of

butane

to butane hydrop eroxide, w hich decomposes to acetaldehyde via p scissions.

It is similar to the oxidation of cyclohexane to cyclohexanol and

cyclohexanone, w hich w ill be discussed in Ch apter 11, Section 4.

The

third

and now

preferred method

of

acetic acid manufacture

is the

carbonylation of m ethano l (Monsanto process), invo lving reaction of

methanol

and carbon monoxide (both derived from m ethane). This is

discussed in

Chapter

12,

Section

3.



Table

9.2

Uses

of

Acetic Acid

Vinyl acetate

60%

Cellulose

acetate

10

Acetic

esters

10

Solvent for TA/DMT 10

Miscellaneous

10

Source: Chemical

Profiles

Although

we have included acetic acid manufacture under ethylene

derivatives, as you can see it is made from three of the seven basic organics:

ethylene, C

4

hydrocarbons, and methane, with the most important method

being

from

m ethane. Pure 100% acetic acid is sometimes called glacial

acetic because when cold it will solidify into layered crystals similar in

appearance to a glacier. It is a colorless liquid with a pungent, vinegar odor

and sharp acid taste, bp

118

0

C ,

and mp

17

0

C .

Table

9.2

summarizes

the

uses

of

acetic acid. V inyl acetate

is

another

top 50 chem ical. Acetic anhyd ride is used to make cellulose

acetate

and at

times has been in the top 50 chem icals itself. Ce llulose acetate is a polymer

used mainly

as a fiber in

clothing

and

cigarette

filters.

Ethyl acetate

is a

common organic solvent. Acetic acid

is

used

as a

solvent

in the

manufacture

of terephthalic acid (TA) and dimethyl terephthalate (DMT), which are

monomers for the synthesis of poly(ethylene terephthalate), the polyester

of

the

textile industry.

A

minor household

use of

acetic acid

is as a

3-5%

aqueous solution, which

is

called vinegar.

4. VINYL ACETATE

Vinyl

acetate is one of many compounds where classical organic

chemistry has been replaced by a catalytic process. It is also an example of

older

acetylene chemistry becoming outdated by newer processes involving

other basic organic building blocks. Up to 1975 the preferred m anufacture

of

this important monomer was based on the addition of acetic acid to the

triple bond of acetylene using zinc amalgam as the catalyst, a universal

reaction

of

alkynes.



In

1969,

90% of

vinyl

acetate

was

manufactured

by

this

process.

By

1975

only 10% was made from

acetylene,

and in

1980

it was obsolete.

Instead,

a

newer method based

on

ethylene replaced this

old

acetylene

chemistry.

A

Wacker catalyst

is

used

in

this process similar

to

that

fo r

acetic

acid. Since the

acetic

acid can also be made from ethylene, the basic raw

material is solely ethylene, in recent years very economically advantageous

as com pared to acetylene chem istry. An older liquid-phase process has been

replaced by a vapor-phase reaction run at 70-140 psi and 175-20O

0

C.

Catalysts may be (1) C-PdCl

2

-CuCl

2

, (2) PdCl

2

-Al

2

O

3

, or (3) Pd-C

KOA c. The product is distilled; water, acetaldehyde, and some po lym er are

separated. The acetaldehyde can be recycled to acetic acid. The pure

colorless vinyl acetate is collected at

72

0

C .

It is a lachrymator (eye irritant) .

The yield is 95%. The m echanism of this reaction is the same as the W acker

process

for

ethylene

to

acetic acid, except that acetic acid attacks rather than

water. You should develop this mech anism similar to Fig.

9.2,

subtituting

acetic acid

for

water.

Table 9.3 gives the uses of vinyl acetate. Poly(v inyl acetate) is used

primarily

in adhesives, coatings, and paints, especially those that are water-

based. This percentage of use has increased dramatically in recent years.

The

shift

to

water-based coatings

has

certainly helped vinyl acetate

production.

Cop olymers of poly(viny l acetate) with poly(vinyl chloride) are

ased in

flooring

and PVC

pipe. Poly(vinyl alcohol)

is

used

in

textile sizing,

adhesives,

emulsifiers,

and paper coatings. Poly(vinyl butyral) is the plastic

inner

liner

of

most safety glass.

Table 9.3 Uses of Vinyl Acetate

Poly(vinyl

acetate)

55%

Poly(vinyl

alcohol)

19

Poly(vinyl butyral)

12

Copolymers 8

Miscellaneous 6

Source: Chemical Profiles



Vinyl

acetate is a good example of an ethylene chemical with a high

percentage of exports, sometimes near

30%.

The United States now has a

cost advantage in ethylene production and many ethylene derivatives have

high export percentages.

ETHYL ENZENE

Despite the use of new catalyses for manufacturing some industrial

organic chemicals, many well-known classical reactions still abound.

The

Friedel-Crafts

alkylation

is one of the

first reactions studied

in

electrophilic

aromatic substitution.

It is

used

on a

large scale

fo r

m aking

ethy benzene.

or

zeolites

Note that ethylbenzene is a derivative of two basic organic chemicals,

ethylene and benzene. A vapor-phase m ethod with boron

trifluoride,

phosphoric acid, or alumina-silica as catalysts has given away to a liquid-

phase reaction w ith alu m inu m chloride at

9O

0

C

and atmospheric pressure. A

new Mobil-Badger zeolite catalyst at 42O

0

C and 175-300 psi in the gas

phase may be the method of choice for

future

plants to avoid corrosion

problems. The mechanism of the reaction involves complexation of the



ethylene with the Lewis acid catalyst, attack of the electrophilic carbon on

the

aromatic ring, loss

of the

proton

to

rearomatize,

and desorption of the

catalyst with subsequent protonation

in the

side chain.

Excess benzene must

be

used.

A

common

benzene:ethylene

ratio

is

1.0:0.6. This avoids

th e

formation

of di- and

triethylbenzenes.

The

first

ethyl group, being electron donating inductively

as

compared

to

hydrogen,

will activate

the

benzene ring toward electrophilic attack

by

stabilizing

the

intermediate

carbocation.

The

benzene when

in excess

prevents this since

it

+

ortho

(predominant isomer)

increases

th e

probability

of the

attack

on

benzene rather than

on

ethylbenzene,

but

some polyethylbenzenes

are

formed,

and

these

can be

separated

in the

distillation process

and

burned

for fuel.

Alternatively,

disubstituted isomers

can be

transalkylated with benzene

to

give

two

moles

of m onosubstituted product. The benzene is recycled.

Ethylbenzene

is a

colorless

liquid, bp 136

0

C.

Despite

the

elaborate

separations required, including washing with caustic

and

water

and

three

distillation

columns,

th e

overall yield

of

ethylbenzene

is

economically

feasible at

98 .

Almost all

ethylbenzene (99 )

is

used

to

manufacture

styrene.

Only

1%

is

used

as a

solvent.



6.

STYRENE VINYLBENZENE, PHENYLETHENE)

Approximately

79% of the styrene

produced

in the

United

States is

made

from ethylbenzene by dehy drogenation. This is a high- temp erature reaction

(63O

0

C) with various metal oxides as catalysts, including zinc, chromium,

iron, or magnesium oxides coated on activated carbon, alumina, or bauxite.

Iron

oxide on potassium carbonate is also used. Most dehydrog enations do

not

occur readily even at high temperatures. The driv ing force for this

reaction is the extension in conjugation that results, since the double bond on

the side chain is in conjugation with the ring. Conditions must be controlled

to avoid polymerization of the styrene. Sulfur is added to prevent

polymerization.

The

crude product

has

only

37%

styrene

but

contains

61 %

ethylbenzene.

A

costly vacuum distillation through

a

70-plate column

at

9O

0

C and 35

torr

is

needed

to

separate

the

two.

The

ethylbenzene

is

recycled.

Usually

a styrene plant is combined with an ethylbenzene plant

when designed. The yield is 90% .

metal oxide

Because styrene readily polymerizes it is immediately treated with an

antioxidant such

as/>-/-butylcatechol at 10

ppm.

Many phenols, especially "hindered phenols" such as butylated hydroxy

toluene

(BHT),

are

good antioxidants. They

act as

radical scavengers

by

readily

reacting with stray radicals

to

give very stable radicals

via

resonance.



The

alkyl

radicals then cannot initiate the polymerization of substances such

as styrene.

This happens:

Instead

of:

A

new

alternate m ethod

for the

manufacture

of

styrene, called

the

oxirane

process,

now

accounting

for

21%

of

production, uses ethylbenzene.

It is

oxidized to the hydroperoxide and reacts with propylene to give

phenylmethylcarbinol (o r methyl benzyl alcohol, MBA) and propylene

oxide,

the

latter being

a top 50

chemical itself.

The

alcohol

is

then

dehydrated at relatively low temperatures

(180-40O

0

C)

using an acidic silica

gel

or titanium dioxide catalyst, a much cleaner and less energy-dependent

reaction than

the

dehydrogenation. Other olefins besides propylene could

be

used

in the

epoxidation reaction,

but it is

chosen because

of the high

demand

for the epoxide. Some acetophenone is separated and hyd rogen ated back to

MBA.



Table 9 .4

Uses

of

Styrene

Polystyrene

62%

ABS

resins

11

SB

latex

8

Unsaturated polyester resins 7

SBR

6

Miscellaneous 6

Source: Chemical Profiles

Table 9.4 shows the uses of

styrene.

These are dom inated by polymer

chemistry

and

involve polystyrene

and its

copolymers.

W e

will study these

in detail

later,

but the primary uses of polystyrene are in various molded

articles such

as toys,

bottles,

and jars, and

foam

fo r

insulation

and

cushioning. Styrene manufac ture is a large business. W ith a production of

11.4 billion Ib and a price of 300/lb styrene has a commercial value of

approximately $3.4

billion.

7. ETHYLENE OXIDE

Another example

of a famous

organic chemical reaction being replaced

by

a

catalytic process

is

furnished

by the

manufacture

of

ethylene oxide.

For

many

years

it was

made

by

chlorohydrin formation followed

by

dehydrochlorination to the epoxide. A lthough the chlorohydrin route is still

used

to convert propylene to propylene oxide, a more efficient air

epoxidation

of

ethylene

is

used

and the

chlorohydrin process

fo r

ethylene

oxide

m anufacture

has not

been used since 1972.

Old method:



The

higher yields (85%)

in the

chlorohydrin method

are not

enough

to

outweigh the waste of chlorine inherent in the process. Although the yields

in the direct oxidation method (75%) are lower, the cheap oxidant

atmospheric oxygen is hard to beat for econom y. Some overoxidation to

carbon

dioxide and water occurs. Good temperature control at 270-29O

0

C

and pressures of 120-300 psi with a 1 sec contact time on the catalyst are

necessary. Tubular reactors containing several thousand tubes of 20-50 m m

diameter

are

used. Even though m etallic silver

is

placed

in the

reactor,

the

actual

catalyst

is silver oxide under the conditions of the reaction. Ethylene

oxide is a gas at room tem perature w ith a bp of 1 4

0

C .

Table

9.5

lists

the

uses

of

ethylene oxide. Ethylene glycol

is

eventually

used

in two

prim ary types

of end

products: polyesters

and

antifreeze. About

half the ethylene glycol is used fo r each end product. Poly(ethylene

terephthalate)

is the

leading synthetic

fiber and has

other important

applications in plastic

film

and bottles. Ethylene glycol is a common

antifreezing agent especially in automobile radiators.

As

a

hospital sterilant

for

plastic m aterials, ethylene oxide

w as

ideal since

radiation or steam cannot be used. It is in this application that evidence of

high miscarriage rates (3x normal) of women on hospital sterilizing staffs

caused a lowering of the TLV to 1 ppm . The chemical was most often used

in closed systems

but in

this application incidental exposures were said

to go

as high as 250 ppm . Since 1984 ethylene oxide is no longer used as a

hospital sterilant. It is now on the "Known to Be Human Carcinogens list.

Ethylene

oxide

is

important

in the

manufacture

of

many nonionic detergents

to be discussed in a later chapter. It is a feedstock fo r synthesizing glycol

ethers (solvents

for

paints, brake fluids)

and

ethanolam ines (surfactants

and

Table 9 .5 Uses of Ethylene Oxide

Ethylene glycol 58%

Ethoxylate surfactants

12

Ethanolamines 10

Di, tri, & polyethylene glycols 9

Glycol ethers 6

Polyether polyols

3

Miscellaneous 2

Source: Chemical

Profiles

New

method:



gas

scrubbing

of

refineries

to

remove acids).

The

manufacturing chemistry

of

these

two

materials

is

given below.

Diethylene

and

triethylene glycol (DEG

and

TEG)

are

produced

as by-

products

of

ethylene glycol.

DEG and TEG are

used

in

polyurethane

and

unsaturated polyester resins

and in the

drying

of

natural gas.

DEG is

also

used

in

antifreeze

and in the

synthesis

of

morpholine,

a

solvent, corrosion

inhibitor, antioxidant, and pharmaceutical intermediate.

diethylene

glycol (DEG)

triethylene glycol (TEG)

morpholine

8. ETHYLENE GLYCOL ETHAN-1,2-DIOL)

HO-CH

2

-CH

2

-OH

The

primary manufacturing method

of

making ethylene glycol

is from

acid-

or thermal-catalyzed hydration and ring opening of the oxide. Nearly

all

the

glycol

is

made

by

this process. Either

a

0.5-1.0

H

2

SO

4

catalyst

is

used at 50-7O

0

C for 30 min or, in the

absence

of the

acid,

a

temperature

of

1 95

0

C and 185 psi for 1 hr

will form

th e diol. A 90%

yield

is

realized when



the ethylene

oxideiwater

molar ratio

is

1:5-8.

The

advantage

of the

acid-

catalyzed reaction is no high pressure; the thermal reaction however needs

no corrosion resistance and no acid separation step.

The ethylene glycol, bp

198

0

C,

is readily vacuum distilled and separated

from

the DEG, bp 246

0

C

5

and TEG, bp

288

0

C .

The m echanism of the

reaction follows the general scheme for acid-catalyzed ring openings of

epoxides.

Research is being conducted on the direct synthesis of ethylene glycol

from synthesis gas. In one process very high pressures of 5,000 psi with

very expensive catalysts

Rh

x

(CO) are being studied. An ann ual loss of

rhodium

catalyst

of

only 0.000001% must

be

realized before this process

will

compete econom ically. At least

five

other alternate syntheses of

ethylene glycol that bypass toxic ethylene oxide

are

being researched.

Table

9.6

shows

the use

profile

for

ethylene glycol.

In

1950 only

48% of

antifreeze was

ethylene glycol, whereas

in

1962

it

accounted

for 95% of all

Table

9.6 Uses of Ethylene G lycol

Antifreeze

30 %

Polyester fiber

27

Polyester bottles 25

Industrial uses 10

Polyester film 4

Miscellaneous 4

Source:

Chemical

Profiles



antifreeze. Its ideal properties of low melting point, high boiling point, and

unlimited water solub ility make it a good m aterial for this application. The

polyester bottle market is rising rapidly. Ten years ago it was a small

percentage of ethylene glycol use. Now one

fourth

of all glycol goes to this

type

of

polyester market.

The

polyester bottle market

is

expected

to

increase

>8%

per

year

in the

near future, while

fiber

grows only

at

3-4%

per

year.

A

production of 6.5 billion Ib and a price of 290/lb for ethylene glycol gives a

commercial value

of

$1.8 billion.

Suggested

Readings

Chemical

Profiles

in

Chemical Marketing Reporter,

2-9-98, 2-16-98,

4-20-

98, 11-2-98, and

11-9-98.

Kent, Riegel s Handbook of Industrial Chemistry, pp. 809-830.

Szmant,

Organic Building Blocks of th e Chemical Industry, pp.

188-264.

White, Introduction to Industrial Chemistry, pp. 62-79.

Wiseman, Pe trochemicals, pp. 43-63, 102-103, 151-152, and 163-164.

Wittcoff and Reuben, Industrial Organic Chemicals, pp. 88-148.

survey of industrial chemestry - chapter 9

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