Industrially, propylene glycol is produced from propylene oxide[4] (for food-grade use), and global capacity in 1990 was 900,000 tonnes per year.[5] 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.