Suresh Gudimetla
ETHYLENE GLYCOL
Glycols are compounds which have two hydroxyl groups attached to two
separate carbon atoms in ann aliphatic chain. Glycols are mainly composed of
Carbon, hydrogen and oxygen.
Ethylene glycol is a product of water and ethylene oxide. The other glycols are
Diethylene glycol, triethylene glycol and tetraethylene glycol.
Properties
Ethylene glycol is a colorless, odorless liquid which is completely miscible with
water and many other organic solvents.
The physical properties of ethylene glycol are given below.
Formula : HOCH2CH2OH
Molecular weight : 62.07
Specific Gravity : 1.1155
Boiling point : 197.6
Melting point : -13.0
Viscosity : 20.9
Refractive index : 1.4318
Ethylene glycol is difficult to crystallize. When it is cooled it forms a highly
viscous, supercooled mass which solidifies to form a glass like substance.
Chemical properties:
1. Ethylene glycol oxidisies to form a number of aldehydes and carboxylic acid
by oxygen,nitric acid and some other oxidizing agents. The important
products formed from ethylene glycol are glycolaldehyde, glycolic acid,oxalic
acid, formaldehyde and formic acid. When the reactions are varied , we can
get a selcted oxidation product
2. Ethylene gl;ycol reacts with dicarboxylic acid to form linear polysters .
3. Transesterfication of carbnonates with ethylene glycol gives ethylene
carbonate.
CH3O-CO-O CH3 + HOCH2CH2OH ------------ 2CH3OH +CO3
4. Ethylene glycol give 1,4-di-oxane by acid catalyzed dehydration to form
diethylene glycol followed by cyclisation.
5. Ethylene glycol is alkylated or acylated to form ethers and esters.
6. Ethylene glycol reacts with ethylene oxide to form di, tri, tetra and other
polyethylene glycols.
Manufacturing of Ethylene Glycol:
Ethylene Glycol is manufactured by hydrolysis of Ethylene Oxide. Ethylene Oxide
is formed by direct oxidation of Ethylene with air or oxygen. Ethylene Oxide is
thermally hydrolysed to Ethylene Glycol. The Ethylene Oxide water mixture is
preheated to 200 C where upon it is converted to Ethylene Glycol. The by-
products formed in this reaction are di, tri, tetra, poly ethylene glycols.
The process diagram is shown below:
Ethylene
Gylcol
Ethylene Oxide and water are sent to the reactor where the reaction takes place
at 200 C. After the formation of the desired product, the mixture is sent to the
distillation columns with decreasing pressures. Water is first removed and
recycled back to the reactor. The mono, di, tri ehtylene glycols are separated in
the other distillation columns by vacuum distillation. Tetra ehtylene glycol which
is formed in low quantities cannot be separated. The reaction in the reactor is
exothermic and the heat produced in the reactor is used to heat the distillation
columns. Generally a plug flow reactor is used.
H2COCH2 + H2O HOCH2CH2OH
nH2COCH2 + HOCH2CH2OH HO(CH2CH2O) n+1 -H
where n = 1, 2, 3
Alternative processes for Ethylene Glycol Production:
1.Ethylene is oxidised in presence of a catalyst in acetic acid to form ethylene
glycol.
CHH4 + AcOH CH2OAc HOCH2CH2OH
The main drawback of this process is high corrosion problems.
2.Ethylene glycol can be produced by reacting carbon monoxide and hydrogen
directly at a very high pressure. The drawback of this process is the reaction is
slow and the catalyst is both very sensitive and expensive.
3.Ethylene oxide reacts with carbon dioxide solution to form ethylene carbonate.
Hydrolysis of Ethylene carbonate gives Ethylene Glycol. The drawbacks are
catalyst feeback and product separation.
Uses of Ethylene Glycol:
1.It is used as an anti-freeze component.
2.Used in manufacturing of ethers and esters which are frequently used as
reaction media and absorption fluids and solvents for dyes, lacquers and other
cellulose products.
References:
Encyclopedia of Chemical Engineering , Kirk Othmer.
Ullman’s Encyclopedia of Chemistry.