GB788297A - Improved process for separating and purifying condensation products - Google Patents

Abstract

<PICT:0788297/III/1> Apparatus for the production of polyamides comprises a pressure vessel 12 heated by element 11 and so arranged that the lower part is at a lower temperature than the remainder whereby low molecular weight polymer separates from a supernatant aqueous layer containing impurities (see Group IV (a)). The temperature differential may be obtained by omitting insulation from the bottom of the vessel or by providing the bottom of the vessel with cooling fins or, as shown, by means of a cooling coil 20 through which air or liquid may be circulated. The cooling liquid may be the polyamide forming material itself in which case the coil opens at an intermediate part of the vessel and the material is continuously fed in, low polymer being continuously removed from the bottom of the vessel and water also by any suitable means. Thermometers 14-16 are provided. Specifications 763,994, [Group IV (a)], and 788,298 are referred to.ALSO:In the preparation of polyamides, water-soluble impurities are removed from the raw materials by the following procedure: The raw materials are heated with water to polyamide-forming temperatures under sufficient pressure to prevent the water boiling, in a reaction vessel the lowermost zone of which is maintained at a temperature below that in the remainder of the vessel, until a water-insoluble low molecular weight polyamide is obtained in the lowermost zone substantially separated from an overlying layer of water and substantially free from water-soluble impurities. This polyamide is then withdrawn either in the molten or solid condition. The process may be operated continuously, the raw materials and water being fed into an intermediate part of the vessel. The feed, suitably preheated, serves to maintain the lowermost zone at the required reduced temperature. The low polymer is continuously tapped off at the bottom and the water, together with impurities, at the upper part of the vessel. The invention is described with reference to the polymerization of 11-amino undecanoic acid as a 50 per cent paste with water, the lowermost zone being at 220 DEG C. and the remainder of the vessel at 262-265 DEG C. The low polymer is formed after heating for an hour and a half, nine-tenths of the polymer being then withdrawn and the vessel refilled after withdrawing the water. The process is stated to be suitable also for obtaining polyamides from lactams and from diamines and dibasic acids. The Specification describes suitable apparatus, the apparatus forming the subject-matter of Specification 788,298, [Group III]. Specification 763,994 also is referred to.