Patent GB-1088435-A (GB)
Title: Process for preparing highly purified formaldehyde
IPC: C07C47/045
Filed: 1966-05-11
Abstract: <PICT:1088435/C3/1> <PICT:1088435/C3/2> Polyoxymethylene, particularly those having the infra-red analysis shown in Fig. 3 and the differential thermal analysis shown in Fig. 4, polymers and acetylation derivatives thereof are prepared by polymerization of highly purified formaldehyde absorbed in a hydrocarbon solvent (e.g. toluene or toluene and hexane or heptane) at low temperatures (e.g. -20 DEG  to -30 DEG  C.) in the presence of a polymerization catalyst (e.g. phenyl-isonitrile, n-dibutyl - tin - dilaurate, 1 - morpholino - 1 - propene, 1,2 - di - n - butyl - 3 - methyldiazilidine or pyridine) and isolation of the polymer which may be acetylated (e.g. with acetic anhydride in pyridine).  The products, for which viscosity and thermal stability are reported, may be formed into films or filaments optionally containing 4,41 - butylidene - bis - (3 - methyl-6-tributyl-phenol). The highly purified formaldehyde is obtained by further polymerizing low molecular weight polyoxymethylene (e.g. paraformaldehyde or a -oxymethylene) by heating in a closed system, optionally in the presence of a catalyst and/or solvent medium, at a temperature of from 80-165 DEG  C., drying the resultant polyoxymethylene of increased molecular weight to reduce its absorbed water content and thermally decomposing the resultant dried polyoxymethylene to formaldehyde.ALSO:Highly purified formaldehyde is produced by further polymerizing a low molecular weight polyoxymethylene by heating in a closed system at a temperature of from 80 DEG  to 165 DEG  C., drying the resultant polyoxymethylene of increased molecular weight to reduce its absorbed water content and thermally decomposing the resulting dried polyoxymethylene to form the highly purified formaldehyde.  The first stage of the process is preferably carried out in an autoclave by heating a low molecular weight polyoxymethylene, such as a paraformaldehyde or a-polyoxymethylene polymer having an absorbed and bound water content of not more than 20%, e.g. at a temperature of 115 DEG  to 165 DEG  C. to cause the desired further polymerization and reduction in the proportion of bound water.  This first stage is optionally carried out in the presence of a diluent medium and/or catalyst.  The diluent medium may comprise one or more specified hydrocarbon, chorinated hydrocarbons, ethers, esters, ketones, nitriles, amides or sulphoxides.  The catalyst, which is usually present in an amount of less than 10% by weight of the low molecular weight polyoxymethylene, may be an inorganic or organic acid or base, for example hydrogen halides, halogen oxyacids, carboxylic acids, benzene sulphonic acid, boron trifluoride complexes, inorganic hydroxides, ammonium or phosphonium salts, amines, Schiff's bases or amino acids.  The treated polyoxymethylene, which is subsequently dried by conventional means to remove absorbed water, may have a degree of polymerization of from 60 to 200 and be at least 95% pure, e.g. material more than 99% pure can be attained. The product is decomposed to formaldehyde in known manner.