GB681127A - Formaldehyde polymers - Google Patents

Abstract

Paraformaldehyde is made by contacting formaldehyde with a cool liquid which is a non-solvent for both and contains a polymerizing catalyst which may be basic, e.g. triethylamine, sodium carbonate or hydroxide, or acidic, e.g. sulphuric acid. The quenching liquid may be acetone, methylal, diethyl ether or tetrahydrofurane. Vapours of aqueous formaldehyde containing at least 60, e.g. 60-90 per cent by weight formaldehyde, with other diluents such as methanol, methane or carbon oxides according to the source, may be used. Products of vapour phase oxidation of methanol or methylal are suitable. The amount of polymerizing catalyst is varied according to the degree of polymerization desired and is preferably such that dilution of the quenching liquid with an equal weight of water gives a pH of 4-8 with an alkali or less than 2 with an acid catalyst. Preferably, the liquid is at 10-40 DEG C. The liquid containing the polymer may pass to a settling chamber, the polymer being removed as a slurry and the supernatant liquid recycled after cooling. The slurry is pressed or centrifuged, dried, melted and flaked or spray dried. The build-up of water or methanol is avoided when using oxidation products by taking off a side stream from the used quenching liquid, distilling to recover an acetone-methanol azeotrope which is recycled, methanol which is again oxidized, and dilute formaldehyde which is concentrated and mixed with the feed.