Methanal (formaldehyde) is usually used as an aqueous solution containing 37% (w/w) methanal, known as formalin. It contains a small amount of methanol and an inhibitor (often an ethenyl (vinyl) polymer) to prevent the aldehyde from forming long chain polymers on storage.
Uses of methanal (formaldehyde)
Figure 1 Uses of methanal.
Other polymers, based on the polymerization of methanal are discussed below.
Annual production of methanal (formaldehyde), as formalin
Manufacture of methanal (formaldehyde)
Most methanal is produced from methanol by a process that involves both dehydrogenation and oxidation:
A mixture of methanol vapour and air at ca 1000 K and just above atmospheric pressure is passed over a catalyst of finely divided silver or molybdenum(VI) oxide on an inert support.
The resulting methanal is absorbed in water. The byproduct, hydrogen, is used as a fuel for the process.
Polyoxymethylene resins (polyacetal resins)
The polymerization of anhydrous methanal leads to the formation of the polyoxymethylene (or acetal) resins, which are thermoplastics.
They are either made as a homopolymer, to which ethanoic acid is added to terminate the chains:
Alternatively, they are produced as a co-polymer, with epoxyethane:
Both the homopolymer and co-polymer are very tough and resistant to abrasion. They are used, instead of metals, in, for example, bearings and gears and in plumbing.
Date last amended: 18th September) 2013