Download Ethylene glycol is a major constituent of motor vehicle antifreeze

ETHYLENE GLYCOL
Introduction [1]:
Glycols are dihydric alcohols having an aliphatic carbon chain. They have the general
chemical formula CnH2n(OH)2. Ethylene glycol is the simplest and the most important of
the glycols. It is a colorless, nearly odorless, sweet-tasting, hygroscopic liquid. The
chemical formula of ethylene glycol is: C2H6O2.
Ethylene glycol was first produced in 1859 by Wurtz. He saponified ethylene glycol
diacetate with potassium hydroxide. Three years later he made ethylene glycol by
hydration of ethylene oxide. This glycol encounted a commercial importance in 1925
when it was first manufactured in large scale quantities from ethylene oxide through the
intermediate ethylene chlorohydrin.
Some of the physical properties of the ethylene glycol are shown in Table 1.1.
Ethylene glycol
Molecular weight, g/gmol
62.07
Freezing point, 0C
-13
Boiling point, 0C
197.2
Solubility at 200C., wt.%
In water
Complete
Water in
Complete
Table 1.1 Physical properties of Ethylene glycol
Ethylene glycol is relatively nonvolatile and viscous. It is also soluble in common
alcohols and phenol.
Manufacture [1]:
I. Most of the ethylene glycol produced today is obtained by hydration of ethylene oxide.
The reaction is:
CH2-O-CH2 + H2O  CH2-OH-CH2-OH
Ethylene oxide is readily converted to ethylene glycol by either of the following methods:
-
by the action of a dilute aqueous solution of a strong acid
-
by reaction with water at elevated temperature and pressure
The ethylene glycol which results from these methods is concentrated by evaporations
and further purified by vacuum distillations.
II. A second commercial method of producing ethylene glycol is based on the reaction of
formaldehyde and a mixture of carbon monoxide and water at high pressure and
temperature to produce glycolic acid.
CH2 + CO + H2O  CH2-OH-CH2-OH
The latter is esterified with methanol or n-propanol to form the corresponding alkyl
glycolates. These are then hydrogenated to glycol in the presence of a catalyst containing
copper and magnesium oxides at temperatures of 125-3250C and pressure above 100 atm.
Ethylene glycol is recovered from the reaction mixture by fractional distillation.
III. Ethylene glycol has been produced in Germany from ethyl alcohol via ethylene and
ethylene dichloride. The latter is saponified by heating with aqueous solution of sodium
bicarbonate, ferric oxide or some similar agent. This process was used for manufacturing
glycol in small quantities for explosives during the World War.
IV. Other methods have been tried for the production of ethylene glycol but they were
not proved commercially attractive. These methods are: direct hydroxylation of ethylene,
decomposition and hydrogenation of sugars and polyhydroxy compounds and direct
hydrolysis of ethylene chlorohydrin to ethylene glycol.
V. On a laboratory scale, ethylene glycol is readily formed by the hydrolysis of ethylene
dihalides or ethylene diacetate.
1.2 Uses (Applications) [1]:
Ethylene glycol is one of the most important of all synthetic organic chemicals. It has
widespread applications in many branches of industry :
-
Its most important use are as an nonvolatile, permanent-type antifreeze.
-
The antifreeze grade of ethylene glycol is used in sprinkler systems for unheated
buildings and in place of salt solutions in heat exchange systems where corrosion is a
factor.
-
It is incorporated into water-containing products such as asphalt-emulsion paints to
prevent breaking of the emulsion by freezing of the water.
-
Ethylene glycol is as an intermediate in the production of ethylene glycol dinitrate for
use in low-freezing dynamites.
-
It is also used as a high-temperature coolant in aircraft engines, x-rays tubes, machine
guns and army tanks.
-
It permits operations at considerably high temperature than water when it is used as
the coolant.
-
Solutions of boric acid or its salts in ethylene glycol are widely used to form the
electrolyte in electrolytic condensers employed in midget radio sets, induction
motors, radar equipment and other electronic devices.
-
Ethylene glycol is the diluent in many types of hydraulic-brake and shock-absorber
fluids.
-
It is also a component of the aqueous-base, nonflammable hydraulic fluids known as
“hydrolubes”.
-
It acts as a softening agent for cellophane and as a stabilizer in the soybean liquidbase airfoam used in extinguishing oil and chemical fires.
-
It is the starting material in the commercial production of glyoxal and in the
production of the unsaturated ester type of alkyd resins.
-
It is a component of carbon-removal formulations for cleaning aluminum pistons, of
non-grain-raising wood strains and of electropolishing solutions for steel and
aluminum.
-
It is a raw material for the preparations of a large variety of synthetic resins,
plasticizers and elastomers.
1.3 Production of ethylene glycol
1.3.1 Minimal process requirements
One process alternative is to produce ethylene glycol from ethylene oxide. The minimal
requirements for such an alternative process include one reactor, two separators and one
distillation column. The schematic representation of this process is shown in Figure 1.3.
Ethylene
glycol
H 2O
(CH2)2
O
Reactor
Ethylene oxide
separation
Water
separation
D
i
s
t
i
l
l
a
t
i
o
n
Di-and triglycols
Figure 1.3 Schematic diagram of a process to manufacture ethylene glycol [2].
Ethylene oxide and water are introduced in the reactor, the product of the reaction is
ethylene glycol. The product stream will contain, besides ethylene glycol, other materials
(unreacted water and/or ethylene oxide, di- and triethylene glycol). (The di-and
triethylene glycols are formed because the hydroxyl group is very reactive). For this
reason in the process are included other units: a unit that removes water (water
separations), one that removes unreacted ethylene oxide (ethylene oxide separation). The
distillation column unit permits the separation of the ethylene glycol from di- and
triglycol.
1.3.2 Additional requirements
A more complete process is shown in Figure 1.4.
Vacuum
Vacuum
H2O
Ethylene
oxide
D
C
H2O
H2O
S1
M
Ethylene glycol
S2
R
H2O
Ethylene glycol
Diethylene glycol
Triethylene glycol
Diethylene glycol
Triethylene glycol
Ethylene glycol
Diethylene glycol
Triethylene glycol
Figure 1.4 Schematic representation of a process to manufacture ethylene glycol [3].
The process includes a mixer, M, where the ethylene oxide and the water, stored in a unit,
are mixed. The amount of ethylene oxide and water that are going into the mixer are
controlled by valves. From the mixer, the mixed product is going into the rector, R,
where the glycols are formed. A controller, C, is used to manipulate the ratio of water to
ethylene oxide. From reactor, the product stream is going into the distillation column, D,
which in this process is steam heated. The condensers are collected at the top of the
column and recycled in the water unit. At the bottom of the column are collected the
unreacted materials: water, ethylene glycol, di- and triethylene glycol. The process
includes two separators. The first one, S1, separates the unreacted water from the rest of
the products. The second separator, S2, separates the ethylene glycol from the rest of the
products.
The separators are provided with boilers and condensers.
To separate the di-and triethylene glycols two more separators will be needed.
1.4 Benefits of Modeling:
A mathematical representation of the process (a model) can be useful for many different
purposes. For example, the daily operation of the plant can be both planned and
scheduled. The performance of the units can be assessed. Studies related to productivity,
cost, and safety can be performed using the data from the process but without disturbing
the plant. If a dynamic model is available, transient and control studies can be easily
conducted to investigate the behavior of the process during start-ups and shut-down
operations. Another important use of the models is for troubleshooting the process.
References:
[1] Jacqueline I. Kroschwitz (executive editor); Mary Howe-Grant (editor), Encyclopedia
of Chemical Technology , 4th Edition, New York : Wiley, c1991, At head of title: KirkOthmer
[2] T.W.Fraser Russell and Morton M. Denn, Introduction to Chemical Engineering
Analysis, John Wiley & Sons, Inc., New York 1972
[3] Ullmann's Encyclopedia of Industrial Chemistry, Weinheim, Germany; New York:
VCH, c1994-c1996.