Refined glycerine, also known as glycerol or glycerin, is a
simple straight chain sugar alcohol which has three hydroxyl groups, which
results in glycerine being water-soluble and hygroscopic. It is a clear,
colorless and odorless liquid that is viscous with a high boiling point. It
tastes sweet naturally and has low toxicity. It has typical melting and boiling
points of 17.8 ◦C and 290 ◦C respectively. It is derived naturally and from
petrochemical feedstock. Due to its low toxicity and environmental
friendliness, it is used in many applications, such as food, pharmaceuticals,
cosmetics and personal care items. It is also a versatile and valuable by
product from biodiesel production. Around 950,000 tons are produced in the
United States and Europe annually.
Glycerine is obtained from the saponification or
transesterification of triglycerides. Triglycerides are esters of glycerol with
long chain carboxylic acids, which are found in fats and oils. The by-product
formed is salts of long chain carboxylic acid. Crude glycerine also comes from
the production of biodiesel through the transesterification process.
Triglycerides are reacted with an alcohol, for example ethanol with a small
amount of base as a catalyst to give esters of fatty acids and glycerol.
Synthetic glycerine can be obtained from sources other than
triglycerides, such as from propylene, via the chlorine process or epichlorohydrin
process, and the chlorine free processes. For the epichlorohydrin process,
propylene is chlorinated to form allyl chloride, which is oxidized to give
dichlorohydrins with hypochlorite. Dichlorohydrin then reacts with strong base
to give epichlorohydrin, which is hydrolyzed to give glycerine. The chlorine
free process involves obtaining glycerine from acrolein and propylene oxide.
Glycerol is used in foods and beverages to keep foods moist, to
sweeten foods, as a solvent and it may be used as a food preservative. It is
used as filler in commercial low fat foods such as cookies, and also as a
thickening agent in food products such as liqueurs. It is used as a substitute
for sugar because it does not result in cavities as bacteria do not feed on
Glycerol is used to improve smoothness and lubricating
properties, and to retain moisture. It is found in a wide range of medical and
pharmaceutical products, such as cough syrups, and also in personal care products
such as mouthwashes. It is also a component of glycerin soap with essential
oils added for fragrance, and the soap is used by people with sensitive skin
due to glycerineâ€™s water retaining properties.
Glycerine is able to form strong hydrogen bonds with water and
thus glycerol-water bonds are preferred over water-water hydrogen bonds. Thus,
the formation of ice is hindered unless the temperature is made very low. Such
antifreezing agents are used in automobiles due to glycerine being non-toxic
despite it being replaced by ethylene glycol.
Glycerine is used to produce other chemicals such as
nitroglycerin, which is used in explosives and propellents. It is used to
produce allyl iodide from the elements phosphorus and iodine, which is used in
products such as polymers, preservatives, organometallic catalysts and