Patent GB-700682-A (GB)
Title: Treatment of paraformaldehyde to reduce its water content
IPC: C08G2/08
Filed: 1950-10-27
Abstract: The water content of paraformaldehyde is reduced by a process which comprises subjecting it to treatment first with the vapour of an organic base or hydrogen chloride so as to cause some of the substance to be absorbed by the paraformaldehyde and then with a current of heated air to evaporate water from the treated paraformaldehyde.  Specified organic bases are triethylamine, N - methyl pyrrolidine and other tertiary amines which do not react with formaldehyde.  The organic base or hydrogen chloride is preferably applied to the paraformaldehyde by contacting the latter with a current of air containing the vapourous substance, the treated paraformaldehyde being then subjected to a further treatment with a current of heated air to evaporate water.  In a modification of the process an air stream containing the organic base or hydrogen chloride is employed for the initial treatment of the paraformaldehyde and a heated air stream containing the organic base or hydrogen chloride is employed for the subsequent drying operation. Before the paraformaldehyde is treated with the current of heated air, the paraformaldehyde containing the organic base or hydrogen chloride may be given a preliminary drying treatment by direct heating in air, e.g. to 100 DEG C. for 1 to 2 hours.  The process may be effected by treating particles of paraformaldehyde with a stream of air at 25 to 50 DEG C. and containing 0.1 to 10 per cent. by volume of, for example, hydrogen chloride or triethylamine for 1 to 30 minutes and the treated particles may then be given a preliminary drying treatment by heating in air as above and then dried in a current of air heated to 80 to 170 DEG C. and containing from 0 to 10 per cent. or even up to 25 per cent. by weight of water vapour.  The treatment of the paraformaldehyde containing the organic base or hydrogen chloride with the current of heated air may be carried out while the paraformaldehyde is in the form of a fluidized bed of particles, fluidization being effected by the heated air stream.  In this case the velocity of the air stream may be adjusted so that a portion of the paraformaldehyde particles is continuously carried upward and into a cyclone separator in which the dried particles are separated from the moving air stream.  In examples: (1) extruded paraformaldehyde particles containing 9.6 per cent. by weight of water are exposed to an air stream containing hydrogen chloride for 3 minutes and the particles then dried for two hours at 100 DEG C. in a steam heated drier open to the air; the particles are then ground and dried in the form of a fluidized bed using air at 130 DEG C. and containing 7 per cent. of moisture, the dried paraformaldehyde particles which are separated in the cyclone separator containing 2 per cent. by weight of moisture; (2) this example is similar to (1) except that the initial treatment is effected by exposure to an air stream containing triethylamine for about 30 minutes whilst the air in the cylindrical drier is heated to 160 DEG C. and contains 5 per cent. by weight of water vapour.