Propylene Glycol C3H8O2 HO-CH2-CHOH-CH3
CAS No. 57-55-6, propane-1, 2-diol, propylene glycol, α-propylene glycol, 1, 2-propanediol, 1,2-Dihydroxypropane, methyl ethyl glycol (MEG), methylethylene glycol, PG, Sirlene, Dowfrost
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol and known universally as CAS No. 57-55-6 is an organic compound (a diol or double alcohol) with formula C3H8O2 or HO-CH2-CHOH-CH3. It is a colorless, nearly odorless, clear, viscous liquid with a faintly sweet taste, hygroscopic and miscible with water, acetone, and chloroform.
Industrially propylene glycol is produced from propylene oxide. Different manufacturers use either non-catalytic high-temperature process at 200°C (392°F) to 220°C (428°F), or a catalytic method, which proceeds at 150°C (3O2°F) to 180°C (356°F) in the presence of ion exchange resin or a small amount of sulfuric acid or alkali.
Final products contain 20% 1,2-propanediol, 1.5% of dipropylene glycol and small amounts of other polypropylene glycols. Further purification produces finished industrial grade or USP/JP/EP/BP grade propylene glycol that is typically 99.5% or greater. Propylene glycol can also be converted from glycerol, a biodiesel byproduct.
Propylene glycol is used:
- As a solvent in many pharmaceuticals, including oral, injectable and topical formulations. Notably, diazepam, which is insoluble in water, uses propylene glycol as its solvent in its clinical, injectable form.
- As a humectant food additive, labeled as E number E1520
- As an emulsification agent in Angostura and orange bitters
- As a moisturizer in medicines, cosmetics, food, toothpaste, shampoo, mouth wash, hair care and tobacco products
- As a carrier in fragrance oils
- As an ingredient in massage oils
- In hand sanitizers, antibacterial lotions, and saline solutions
- In smoke machines to make artificial smoke for use in firefighters' training and theatrical productions
- In electronic cigarettes, as a vaporizable base for diluting the nicotine liquid
- As a solvent for food colors and flavorings
- As an ingredient, along with wax and gelatin, in the production of paintballs
- As a moisture stabilizer (humectant) for snus (Swedish style snuff).
- As a cooling agent for beer and wine glycol jacketed fermentation tanks
- As a non-toxic antifreeze for winterizing drinking water systems, and in applications where the used antifreeze eventually will be drained into the soil, water, or a septic system.
- As a less-toxic antifreeze in solar water heating systems
- As a solvent used in mixing photographic chemicals, such as film developers
- In cryonics
- As a working fluid in hydraulic presses
- As a coolant in liquid cooling systems
- To regulate humidity in a cigar humidor
- As the killing and preserving agent in pitfall traps, usually used to capture ground beetles
- As an additive to pipe tobacco to prevent dehydration.
- To treat livestock ketosis
- As the main ingredient in deodorant sticks.
- To de-ice aircraft.
- Â As an ingredient in UV or black light tattoo ink
- As a lubricant in air conditioning compressors.
- As a wetting agent, used to determine drying time in paints and coatings
Propylene glycol has properties similar to those of ethylene glycol (monoethylene glycol, or MEG). (Note: Infrequently propylene glycol may also use the acronym MEG, but as an abbreviation of methyl ethyl glycol- the industry standard acronym for propylene glycol is PG or MPG (monopropylene glycol)). The industrial norm is to replace ethylene glycol with propylene glycol when safer properties are desired.
Propylene glycol is a component in newer automotive antifreezes and de-icers used at airports. Like ethylene glycol, the freezing point of propylene glycol is depressed when mixed with water due to disruption of hydrogen bonding. Unlike ethylene glycol, propylene glycol is of very low toxicity. Both are readily biodegradable.
