Description
Glycol: any of a class of organic
chemicals characterized by having separate two hydroxyl (-OH)
groups, contribute to high water solubility, hygroscopicity and
reactivity with many organic compounds, on usually linear and
aliphatic carbon chain. The general formula is CnH2n(OH)2 or
(CH2)n(OH)2. The wider meaning names include diols, dihydric
alcohols, and dihydroxy alcohols. Polyethylene glycols and
polypropylene glycols are sometimes called polyglycols which are
derived by polymerization of ethylene oxide and propylene oxide
respectively. Polyethylene glycols are water-soluble at all
molecular weights, but polypropylene glycols become increasingly
less water-soluble at high molecular weights. Ethylene glycol,
HOCH2CH2OH, is the simplest member of the glycol family. Mono-, di-
and triethylene glycols are the first three members of a homologous
series of dihydroxy alcohols. They are colourless, essentially
odourless stable liquids with low viscosities and high boiling
points. Ethylene glycol is a colourless, odourless, involatile and
hygroscopic liquid with a sweet taste. It is somewhat viscous
liquid; miscible with water; boiling point **8 C, melting point *3
C; soluble in ethanol, acetone, acetic acid, glycerine, pyridine,
aldehydes; slightly soluble in ether; insoluble in oil, fat,
hydrocarbones. It is prepared commercially by oxidation of ethylene
at high temperature in the presence of silver oxide catalyst,
followed by hydration of ethylene oxide to yield mono-, with di-,
tri-, and tetraethylene glycols as co-products. The yields of
ethylene glycol are depend on pH conditions. The acid-catalyzed
condition in the presence of excess water provides the highest
yield of monoethylene glycol. Because of its low freezing point,
involatility and low corrosive activity, it is widely used in
mixtures of automobile antifreeze and engine-cooling liquids.
Ethylene glycol has become increasingly important in the plastics
industry for the manufacture of polyester fibers and resins,
including polyethylene terephthalate, which is used to make plastic
bottles for soft drinks (PET bottles). MEG is the raw material in
the production of polyester fiber, PET resins, alkyd, and
unsaturated polyester. Diethylene glycol, CH2OHCH2OCH2CH2OH, is
similar in properties to MEG, but with a higher boiling point,
viscosity, and specific gravity. Diethylene glycol is used in the
manufacture of unsaturated polyester resins, polyurethanes and
plasticizers. It is a water-soluble liquid; boiling point **5
C; soluble in many organic solvents. It is used as a humectant in
the tobacco industry and in the treatment of corks, glue, paper and
cellophane. Diethylene glycol (DEG) is derived as a co-product with
ethylene glycol and triethylene glycol. The industry generally
operates to maximize MEG production. Ethylene glycol is by far the
largest volume of the glycol products in a variety of applications.
Availability of DEG will depend on demand for derivatives of the
primary product, ethylene glycol, rather than on DEG market
requirements. Triethylene glycol, HO(C2H4O)3H, is a colourless,
odourless, non-volatile, and hygroscopic liquid. It is
characterised by two hydroxyl groups along with two ether linkages,
which contribute to its high water solubility, hygroscopicity,
solvent properties and reactivity with many organic compounds. DEG
is used in the synthesis of morpholine and 1,*-dioxane. TEG is
displacing diethylene glycol in many of these applications on
account of its lower toxicity. TEG finds use as a vinyl
plasticizer, as an intermediate in the manufacture of polyester
resins and polyols, and as a solvent in many miscellaneous
applications. Triethylene glycol (TEG) is derived as a coproduct in
the manufacture of ethylene glycol from ethylene oxide, and from
"on-purpose" TEG production using diethylene glycol. Some
capacities are based on total capacity for ethylene glycols. The
main uses for TEG depend upon its hygroscopic properties. Air
conditioning systems use TEG as dehumidifiers and, when
volatilized, as an air disinfectant for bacteria and virus control.
Glycols, having high boiling point and affinity for water, are
employed as liquid desiccant for the dehydration of natural gas.
The dehydration means the removal of water vapor in refinery tower
so that dry hydrocarbon gases can exit from the top of the tower.
There are wide range of glycol ethers which have bifunctional
nature of ether and alcohol. cellosolves are monoether derivatives
of ethylene glycol. They are excellent solvents, having solvent
properties of both ethers and alcohols. Glycol family products are
versatile compounds used in the fields include;
- Anti-freezing and anti-icing
additive
- Intermediate in polymer production and chemical
reaction
- Solvent or plasticizer for plastic, lacquer,
paint and varnish
- Hydraulic, brake, thermal exchange fluids and
fuel additive
- Humidifying and plasticizing
- Dehydrating
- Coupling printing inks
- Textile conditioning
- Solvent for dyes in textile and leather
finishing
- Agricultural formulation
- General purpose cleaners
- Explosives manufacture
- Electrolytic component
- Humectant
- Water-based coating
Preservative, rust
remover, and disinfectant
