<P> The freezing point of water is depressed when mixed with propylene glycol, owing to the effects of dissolution of a solute in a solvent (freezing - point depression). In general, glycols are non-corrosive, have very low volatility and very low toxicity; however, the closely related ethylene glycol (a key ingredient in antifreeze) is toxic to humans and to many animals . </P> <P> Industrially, propylene glycol is produced from propylene oxide (for food - grade use), and global capacity in 1990 was 900,000 tonnes per year . 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 (302 ° F) to 180 ° C (356 ° F) in the presence of ion exchange resin or a small amount of sulfuric acid or alkali . </P> <P> Final products contain 20% propylene glycol, 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 . This starting material is usually reserved for industrial use because of the noticeable odor and taste that accompanies the final product . </P> <P> S - Propanediol may be synthesized from D - mannitol, through the following scheme: </P>

Is polypropylene glycol the same as propylene glycol