glycerol

__Glycerol__

Glycerol forms the backbone of [|triglycerides], and is chiefly produced by [|saponification] of fats as a byproduct of [|soap-making]. 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 (**1**) are treated with an alcohol such as ethanol (**2**) with catalytic base to give ethyl esters of fatty acids (**3**) and glycerol (**4**): Glycerol is also 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. [|[3]] Because of the emphasis on [|biodiesel], where glycerol is a waste product, the market for glycerol is depressed, and the old [|epichlorohydrin] process for glycerol synthesis is no longer economical on a large scale. Glycerol can be removed from the process by using a special enzyme that breaks down phytol and starches. This enzyme is biologically produced using a genetically engineered bacterium. Because there is no glycerin produced as a by-product, the biodiesel purity is greatly improved and costs can be reduced. [|[4]] Only one producer for synthetic glycerol is left, because high-quality glycerol is needed in highly sensitive pharmaceutical, technical and personal care applications. Raw materials used to make glycerol include animal fats, such as beef tallow, and vegetable oils, such as coconut and soybean. [|[5]] Approximately 950,000 tons per annum are produced in the USA and Europe; 350,000 tons of glycerol were produced per year in the United States alone from 2000-2004. [|[6]] Production will increase as the [|EU directive 2003/30/EC] is implemented, which requires the replacement of 5.75% of petroleum fuels with [|biofuel] across all Member States by 2010. It is projected that by the year 2020, production will be six times more than demand. [|[3]]

Glycerol is a sweet tasting compound containing three hydroxyl groups. It is a colorless, odorless, and viscous liquid. It is the main component in a triglyceride.

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.
 * Food Industry**

Glycerol is also used to manufacture mono- and di-glycerides for use as emulsifiers, as well as polyglycerol esters going into shortenings and margarine. It is also used as a humectant (along with propylene glycol labelled as E1520 and/or E422) in the production of snus, a Swedish-style smokeless tobacco product. As used in foods, glycerol is categorized by the American Dietetic Association as a carbohydrate. The U.S. Food and Drug Administration (FDA) carbohydrate designation includes all caloric macronutrients excluding protein and fat. Glycerol has a caloric density similar to table sugar, but a lower glycemic index and different metabolic pathway within the body, so some dietary advocates accept glycerol as a sweetener compatible with low carbohydrate diets.

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, which is made from denatured alcohol, glycerol, sodium castorate (saponified Castor bean oil), saponified cocoa butter, saponified tallow, sucrose, water, and sometimes sodium laureth sulfate. 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. It is possible to make glycerol soap at home. Glycerol can be used as a laxative when introduced into the rectum in suppository or small-volume (2–10 ml)(enema) form; it irritates the anal mucosa and induces a hyperosmotic effect. Topical pure or nearly pure glycerol is an effective treatment for psoriasis, burns, bites, cuts, rashes, bedsores, and calluses. It can be used orally to eliminate halitosis, as it is a contact bacterial desiccant. The same property makes it very helpful with periodontal disease; it penetrates biofilm quickly and eliminates bacterial colonies.
 * Pharmaceutical and Personal Care Applications**

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 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 (which di-atomic alcohols - i.e. ethanolic (grain) alcohol, methanolic (wood) alcohol, etc., does not). 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 REDOX 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.
 * Botanical Extracts**

Glycerol is used to produce nitroglycerin, or glyceryl trinitrate (GTN), which is an essential ingredient of smokeless gunpowder and various explosives such as dynamite, gelignite, and propellants like cordite. Reliance on soap-making to supply co-product glycerine made it difficult to increase production to meet wartime demand. Hence, synthetic glycerin processes were national defense priorities in the days leading up to World War II. GTN is commonly used to relieve //angina pectoris//, taken in the form of sub-lingual tablets, or as an aerosol spray.
 * Chemical Intermediate**

A great deal of research is being conducted to try to make value-added products from crude glycerol (typically containing 20 % water and residual esterification catalyst) obtained from biodiesel production. The use of crude glycerin as an additive to biomass for a renewable energy source when combusted or gasified is also being explored.
 * Hydrogen gas production unit
 * Glycerine acetate (as a potential fuel additive)
 * Conversion to propylene glycol
 * Conversion to acrolein
 * Conversion to ethanol
 * Conversion to epichlorohydrin, a raw material for epoxy resins

Its surface tension is 64.00 mN/m at 20 °C, and it has a temperature coefficient of -0.0598 mN/(m K). The surface tension makes it useful in bubble-blowing solutions.
 * Additional Physical Properties**