Glycerol

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HS number	Crude: 1520.00.00 Pure: 2905.45.00
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Food energy	4.32 kcal/g
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Chemical infobox

Glycerol, also well known as glycerin and glycerine, and less commonly as propane-1,2,3-triol, 1,2,3-propanetriol, 1,2,3-trihydroxypropane, glyceritol, and glycyl alcohol is a colorless, odorless, hygroscopic, and sweet-tasting viscous liquid. Glycerol is a sugar alcohol and has three hydrophilic alcoholic hydroxyl groups (-OH) that are responsible for its solubility in water. Glycerol is prochiral. Glycerol is used in glycerol soap, in cosmetics and creams, in foods, in chemistry, and in glycerol fog machine mist. Glycerol is produced from dihydroxyacetone phosphate (DHAP) by the enzyme glycerol three-phosphate dehydrogenase (Gpd p) in the mitochondrion of the eukaryotic cell during glycolysis.^*

Glycerol and triglycerides

When referring to its function in living organisms, the term glycerol is preferred. Glycerol is an important component of triglycerides (i.e. fats and oils) and of phospholipids. Glycerol is a three-carbon substance that forms the backbone of fatty acids in fats.(1) When the body uses stored fat as a source of energy, glycerol and fatty acids are released into the bloodstream. The glycerol component can be converted to glucose by the liver and provides energy for cellular metabolism.

A byproduct of saponification and transesterification to obtain biodiesel, this is produced by hydrolysis of three ester linkages and loss of three equivalents of fatty acid from fat or biological oil.

Fats and oils are insoluble in water, because the OH groups of glycerol are replaced by ester groups. They are hydrophobic.

Glycerol and biodiesel

As a byproduct of biodiesel production, each of the OH sites in HO-CH₂-CH(-OH)-CH₂-OH is one of the three places where a fatty acid chain is broken off the triglyceride molecule.

See: transesterification.

Purification

Like biodiesel by-product, the purification of the lower glycerol phase involves: neutralisation, separation of unreacted methanol, dilution with wash liquid stream coming from methylester washing, splitting of soaps and final concentration up to 80%. Partially refined glycerol can be delivered as such to specialized distillers.

Feedstock pre-treatment and upgrading of glycerol to pharmaceutical grade (>99.7%) can be optionally implemented within the biodiesel factory itself.

When used in food, care should be taken to use only pure vegetable glycerol that is specifically labeled for use in food. "External use only" warnings should be heeded.

Applications

Drugs

Used in medical and pharmaceutical preparations, mainly as a means of improving smoothness, providing lubrication and as a humectant. Also may be used to lower intracranial and intraocular pressures.
Laxative suppositories, cough syrups, elixirs and expectorants.

Personal care

Serves as an emollient, humectant, solvent and lubricant in personal care products
Competes with sorbitol although glycerol has better taste and higher solubility.
Toothpaste, mouthwashes, skin care products, hair care products and soaps

Glycerol is a component of glycerol soap, which is made from denatured alcohol, glycerol, sodium castorate (from castor), sodium cocoate, sodium tallowate, sucrose, water and parfum (fragrance). Sometimes one adds sodium laureth sulfate. This kind of soap is used by people with sensitive, easily irritated skin because it prevents skin dryness with its moisturize properties.

When used as an emollient, glycerol should never be applied undiluted to the skin. The same powerful hygroscopic property that draws moisture out of the air to moisten the skin will draw moisture out of the skin if the glycerol is too concentrated. A minimum of two or three parts water should be added to one part glycerol.

Foods and beverages

Serves as humectant, solvent and sweetener, may help preserve foods.
Solvent for flavors (such as vanilla) and food coloring.
Humectant and softening agent in candy, cakes and casings for meats and cheeses.
Manufacture of mono- and di-glycerides for use as emulsifiers
Used in manufacture of polyglycerol esters going into shortenings and margarine.
Used as filler in low-fat food products (i.e., cookies).

Glycerol has approximately 27 food calories per teaspoon and is 60% as sweet as sucrose. Although it has about the same food energy as table sugar, it does not raise blood sugar levels, nor does it feed the bacteria that form plaques and cause dental cavities. Glycerol should not be consumed undiluted, as unhydrated glycerol will draw water from tissues, causing blistering in the mouth and gastric distress. As food additive, glycerol is also known as E number E422.

Polyether polyols

One of the major raw materials for the manufacture of polyols for flexible foams, and to a lesser extent rigid polyurethane foams
Glycerol is the initiator to which propylene oxide/ethylene oxide is added

Alkyd resins (plastics) and cellophane

Used in surface coatings and paints
Used as a softener and plasticizer to impart flexibility, pliability and toughness
Uses include meat casings, collagen casings (medical applications)and nonmeat packaging
Plasticizer in cellophane.

Absolute alcohol

There is an absolute alcohol production process by dehydration using glycerol.

Other applications

Manufacture of paper as a plasticizer, Nitroglycerin, humectant and lubricant
Humectant for pet foods to retain moisture and enhance palatability
Used in lubricating, sizing and softening of yarn and fabric
Used in de-/anti-icing fluids, as in vitrification of blood cells for storage in liquid nitrogen
Patent applications have been filed for detergent softeners and surfactants based on glycerol (i.e., alkyl glyceryl ethers) instead of quaternary ammonium compounds.
A way to preserve leaves is to submerge them in a solution of glycerol and water.

Use a mixture of one part glycerol to two parts water. Place the mixture in a flat pan, and totally submerge the leaves in a single layer in the liquid. You'll have to weigh them down to keep them submerged. In two to six days, they should have absorbed the liquid and be soft and pliable. Remove them from the pan and wipe off all the liquid with a soft cloth. Done correctly, the leaves will remain soft and pliable indefinitely.

Can be added to solutions of water and soap to increase that solution's ability to generate soap bubbles that will last a long time.

Used as an antifreeze or a cryoprotectant in cryogenic process.

Used in fog machine fluids

Used in hookah tobacco mixtures (called "ma'assel" or "shisha" tobacco), often along with molasses and/or honey.

Counteracts phenol burns

External links

Sources

Health.gov dietary guidelines

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