Maleic anhydride (MA) occurs as colourless or white crystalline flakes with strong acrid (pungent) odour. It is soluble in acetone, ether, petroleum fractions and reacts with water, evolving heat and forming MA. It also dimerises to 1,2,3,4 -cyclobutane tetracarboxylic acid dianhydride in the presence of UV light.
MA is mostly used to make unsaturated polyester resins (UPRs). UPRs are used in a wide range of applications including bathroom fixtures and automobiles.
The second-largest outlet for MA is 1,4 butanediol (BDO) and derivatives tetrahydrofuran (THF) and gamma-butyrolactone (GBL).
MA is available as liquid (molten) or solid (flake): the liquid form dominates and accounts for 90-95% of the market, which is not easily transportable.
MA is produced commercially by the oxidation of benzene or butane. The butane-based process is considered to have superior economics and is the preferred route by most producers. However, a small amount is produced by the benzene route.