Glycols

Mono Propylene Glycol

Mono propylene glycol (also known as propylene glycol, PG, propan1, 2diol and MPG) is a clear, colourless, and viscous liquid with a characteristic odour.  It has the formula C3H8O, is soluble in water, and has hygroscopic properties.  MPG 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.

Production

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.

Storage and Distribution

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.

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, cosmetics, and pharmaceutical industries.  MPG is used as a solvent for food colourings and flavourings, and is also a classified humectant food additive (E1520).  In the personal care industry it is used as a moisturiser in make-up, shampoo, bubble bath and baby wipes, to name but a few examples.  The pharmaceutical industry uses MPG as a solvent in oral, injectable, and topical formulations.

Industrial grade MPG also has a variety of uses but the main application is as an antifreeze and aircraft wing and runway de-icer.  This is because the freezing point of MPG lowers upon mixing with water.  It is also used in heat transfer liquids such as engine coolants.

It can also be used as a chemical intermediate in the production of high performance unsaturated polyester resins used in paints and  varnishes.  It is also an excellent solvent that is utilised in printing inks and it is also used in the manufacture of non-ionic detergents which are used in the petroleum, sugar-refining, and paper making industries.  It can also be used in the cryonics industry and can be used as an additive in pipe tobacco as it prevents dehydration.