Glycerin (Glycerol)

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Infobox on Glycerin (Glycerol)
Example of Glycerin (Glycerol)
Glycerin.jpg
Facts
Origin -
Stowage factor (in m3/t) 1,70 m3/t (drums)
Humidity / moisture -
Ventilation -
Risk factors See text

Description

Glycerol (or glycerine, glycerin) is a simple polyol compound. It is a colourless, odourless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids known as triglycerides. Glycerol is sweet-tasting and of low toxicity.

Triglycerides found in Fats and Oils are by definition esters of glycerol with long-chain carboxylic acids; the hydrolysis (saponification) or transesterification of these triglycerides produces stoichiometric quantities of glycerol. In this scheme, glycerol is produced as a co-product in the production of long-chain carboxylate salts used as soaps.

It is also a byproduct of the production of biodiesel via transesterification. This form of crude glycerin is often dark in appearance with a thick, syrup-like consistency. Triglycerides are treated with an alcohol such as ethanol with catalytic base to give ethyl esters of Fatty Acids and glycerol.

Glycerol from triglycerides is produced on a large scale, but the crude product is of variable quality, with a low selling price. It can be purified, but the process is expensive. As a result, a good fraction of crude glycerol is disposed of as waste. Some glycerol is burned for energy, but the heat value is low.

That said, crude glycerol from the hydrolysis of triglycerides can be purified by treatment with Activated Carbon to remove organic impurities, alkali to remove unreacted glycerol esters, and ion exchange to remove salts. High purity glycerol (> 99.5%) is obtained by multi-step distillation; vacuum is helpful due to the high boiling point of glycerol (290°C).

Synthetic glycerol refers to material obtained from non-triglyceride sources. Glycerol may also be produced by various routes from propylene. The epichlorohydrin process is the most important; it involves the chlorination of propylene to give allyl chloride, which is oxidized with hypochlorite to dichlorohydrins, which reacts with a strong base to give epichlorohydrin. Epichlorohydrin is then hydrolyzed to give glycerol. Chlorine-free processes from propylene include the synthesis of glycerol from acrolein and propylene oxide.

Because of the emphasis on biodiesel, where glycerol is a waste product, the market for glycerol is depressed, and these old processes are no longer economical on a large scale. In fact, due to the glycerol glut, efforts are being made to convert glycerol to its precursors, such as acrolein and epichlorohydrin.

Derivation
(1) Byproduct of soap manufacture;(2) from propylene and chlorine to form allyl chloride which is converted to the dichlorohydrin with hypochlorous acid; this is then saponified to glycerol with caustic solution (3) isomerization of propylene oxide to allyl alcohol, which is reacted with peracetic acid; the resulting glycidol is hydrolysed to mglycerol (4) hydrogenation of carbohydrates with nickel catalyst (5) from acrolein and Hydrogen Peroxide.

Method of purification
Redistillation, ion-exchange techniques.

Application

Food industry
In foods and beverages, glycerol serves as a humectant, solvent, and sweetener, and may help preserve foods. It is also used as filler in commercially prepared low-fat foods (e.g., cookies), and as a thickening agent in liqueurs. Glycerol and water are used to preserve certain types of leaves. As a sugar substitute, it has approximately 27 kilocalories per teaspoon (sugar has 20) and is 60% as sweet as sucrose. It does not feed the bacteria that form plaques and cause dental cavities. As a food additive, glycerol is labeled as E number E422. It is added to icing (frosting) to prevent it setting too hard.

Pharmaceutical and personal care applications
Glycerol is used in medical and pharmaceutical and personal care preparations, mainly as a means of improving smoothness, providing lubrication and as a humectant. It is found in allergen immunotherapies, cough syrups, elixirs and expectorants, toothpaste, mouthwashes, skin care products, shaving cream, hair care products, soaps and water-based personal lubricants. In solid dosage forms like tablets, glycerol is used as a tablet holding agent. For human consumption, glycerol is classified by the U.S. FDA among the sugar alcohols as a caloric macronutrient.

Glycerol is a component of glycerin soap. Essential Oils are added for fragrance. This kind of soap is used by people with sensitive, easily-irritated skin because it prevents skin dryness with its moisturizing properties. It draws moisture up through skin layers and slows or prevents excessive drying and evaporation.[citation needed] With similar benefits, glycerin is a common ingredient in many bath salts recipes. However, some assert that due to glycerin's moisture absorbing properties, it can be more of a hindrance than a benefit.

Glycerol can be used as a laxative.

Taken orally (often mixed with fruit juice to reduce its sweet taste), glycerol can cause a rapid, temporary decrease in the internal pressure of the eye. This can be a useful initial emergency treatment of severely elevated eye pressure.

Botanical extracts
When utilized in 'tincture' method extractions, specifically as a 10% solution, glycerol prevents tannins from precipitating in ethanol extracts of plants (tinctures). It is also used as an 'alcohol-free' alternative to ethanol as a solvent in preparing herbal extractions. It is less extractive when utilized in a standard tincture methodology. Glycerol is approximately 30% more slowly absorbed by the body resulting in a much lower glycemic load. Alcohol-based tinctures can also have the alcohol removed and replaced with glycerol for its preserving properties. Such products are not 'alcohol-free' in either a scientific or consumable sense, but should in all instances more accurately be referred to as "Alcohol-Removed" products. Fluid extract manufacturers often extract herbs in hot water before adding glycerin to make glycerites.

When used as a primary 'true' alcohol-free (e.g. no alcohol (i.e. ethanol) ever being used) botanical extraction solvent in innovative non-tincture based 'dynamic' methodologies, glycerol has been shown, both in literature and through extraction applications, to possess a high degree of extractive versatility for botanicals including removal of numerous constituents and complex compounds, with an extractive power that can rival that of alcohol and water/alcohol solutions. That glycerol possess such high extractive power assumes that glycerol, with its tri-atomic structure, is utilized with dynamic methodologies as opposed to standard passive 'tincturing' methodologies that are better suited to alcohol's di-atomic structure. Glycerol possesses the intrinsic property of not denaturing or rendering a botanical's constituents inert (as di-atomic alcohols – i.e. ethanolic (grain) alcohol, methanolic (wood) alcohol, etc., do). Glycerol is a stable preserving agent for botanical extracts that, when utilized in proper concentrations in an extraction solvent base, does not allow inverting or reduction-oxidation of a finished extract's constituents, even over several years. Both glycerol and ethanol are viable preserving agents. Glycerol is bacteriostatic in its action, and ethanol is bactericidal in its action.

Antifreeze
Like ethylene glycol and propylene glycol, glycerol is a non-ionic kosmotrope that forms strong hydrogen bonds with water molecules, competing with water-water hydrogen bonds. This disrupts the crystal lattice formation of ice unless the temperature is significantly lowered. The minimum freezing point temperature is at about −36°F / −37.8°C corresponding to 70% glycerol in water.

Glycerol was historically used as an anti-freeze for automotive applications before being replaced by ethylene glycol, which has a lower freezing point. While the minimum freezing point of a glycerol-water mixture is higher than an ethylene glycol-water mixture, glycerol is not toxic and is being re-examined for use in automotive applications.

In the laboratory, glycerol is a common component of solvents for enzymatic reagents stored at temperatures below 0 °C due to the depression of the freezing temperature of solutions with high concentrations of glycerol. It is also used as a cryoprotectant where the glycerol is dissolved in water to reduce damage by ice crystals to laboratory organisms that are stored in frozen solutions, such as bacteria, nematodes, and mammalian embryos.

Chemical intermediate
Glycerol is used to produce nitroglycerin, which is an essential ingredient of various explosives such as dynamite, gelignite, and propellants like cordite.

Metabolism
Glycerol is a precursor for synthesis of triacylglycerols and of phospholipids in the liver and adipose tissue. When the body uses stored fat as a source of energy, glycerol and fatty acids are released into the bloodstream. In some organisms, the glycerol component can be converted into glucose by the liver and, thus, provide energy for cellular metabolism.

Shipment / Storage

Pure glycerine – Storage should be in stainless steel, 99,5% pure aluminium, epoxy resin lined or glass lined tanks or drums. Storage in mild steel tanks or drums lead to rapid deterioration which will require re-processing to restore the original purity. Is hygroscopic and, therefore, absorbs moisture from the air, resulting in the reduction of the percentage glycerine. When exposed in this manner, re-processing is necessary to restore the original purity.

Crude glycerine – Storage can be in mild steel tanks or drums since the subsequent refining processes will remove any resultant impurities. Is not subject to damage by exposure to air unless this be for a lengthy period. Glycerine should be stored away from excessive heat or cold, the first leading to product deterioration and, therefore, subsequent re-processing costs. When handling glycerine, local overheating can be avoided by the use of warm water (60°C) heating coils. Contact with oxidizing or nitration agents should be avoided.

Risk factors

Check the IMDG Code (International Maritime Dangerous Goods Code) for overseas transport particulars.

See also: http://www.chemicalland21.com/lifescience/foco/GLYCEROL.htm