What Is Monopropylene Glycol?
Monopropylene glycol (also known as propylene glycol, PG, propan1, 2diol and MPG) is a clear, colourless and viscous liquid with a characteristic odour and has the formula C3H8O2. This solvent is soluble in water and holds hygroscopic properties, meaning it can attract hard water molecules.
It is used across a wide range of industries as it has low toxicity, coupled with a freezing point which is depressed upon mixing with water.
Chemical and physical properties of mono propylene glycol:
Molecular Formula: C3H8O2 / CH3CH(OH)CH2OH
Synonyms: MPG, Propylene Glycol, PG, Propan1, 2diol, Propane-1,2-Diol, 1,2-Dihydroxypropane 1,2Propandiol
Cas Number: 57-55-6
Molecular Mass: 76.095 g·mol−1
Exact Mass: 76.052429 g/mol
Flashpoint: 210 °F / 98.9 °C
Boiling Point: 370.8 °F / 188.2 °C
Melting Point: −74 °F / −59 °C
Vapour Pressure: 0.13 mm Hg at 25 °C
Water Solubility: Miscible
Density: 1.0361 g/cu cm at 20 °C
Log P: -1.34
How is it produced?
Mono propylene glycol is produced from propylene oxide. The most common process is by the non-catalytic hydrolysis of propylene oxide in a high-temperature and high-pressure environment. The second method is the catalytic one, which can proceed at 150 °C, in the presence of ion exchange resin, or a small amount of sulphuric acid or alkali. It can also be produced from glycerol which is a bio-diesel by-product.
The demand for, and consumption of, mono propylene glycol is high with an estimated 1.2 million tonnes produced yearly by plants situated around the world.
How is it handled, stored distributed?
Mono propylene glycol is stored and moved in stainless steel or mild steel tanks and can be transported by tank trucks. It is not classified as dangerous for any mode of transport and is not hazardous to health. It has a flash point of 103 °C (closed cup) and a specific gravity of 1.04.
Monopropylene Glycol Uses
There are many uses for mono propylene glycol across many different industries and some chemical manufacturers produce two grades of MPG to meet these varied needs.
The first grade is used in the food industry for food colourings and flavourings and is also a classified humectant food additive (E1520). There are also many applications in the cosmetics industry that use this solvent, specifically personal care products including shampoos, bubble baths, baby wipes and as a moisturiser in make-up.
The second is industrial grade MPG which has a variety of uses but the main application is as an antifreeze and aircraft wing and runway de-icer which is because its freezing point lowers upon mixing with water. It is also used in heat transfer liquids such as engine coolants.
Monopropylene Glycol is additionally used in the pharmaceutical industry, examples include as a chemical intermediate in the production of high-performance unsaturated polyester resins used in paints and varnishes and as an excellent solvent utilised in printing inks. It is also used in the manufacturing of non-ionic detergents which are used in the petroleum, sugar-refining, and papermaking industries, the cryonics industry and as an additive in pipe tobacco, preventing dehydration
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