GB774789A - Process for the production of hexamethylenetetramine - Google Patents

Abstract

Solid hexamethylenetetramine or a concentrated solution of hexamethylenetetramine is obtained by reacting ammonia and formaldehyde in solution in a solvent at the boiling point of the reaction mixture and with utilization of the heat of reaction as heat for evaporation of the solvent from the reaction mixture, the process being characterized by the features that the formaldehyde is used in the form of a gaseous mixture which contains formaldehyde in dilute form, such as is produced in, for example, the catalytic oxidation of methane or methanol, and that the boiling point of the solution is kept between 50 and 80 DEG C. by the choice of suitable pressure conditions or by conducting air or other inert gases through the reaction mixture. In a modification of the process the reaction between the ammonia and formaldehyde is carried out in solution in the solvent at a temperature below the boiling point of the reaction mixture and part of the mixture is continuously removed from the reaction apparatus and passed to an evaporation vessel which is under reduced pressure or in which inert gases are passed through the mixture so that spontaneous boiling of the mixture takes place with evaporation of solvent and resultant cooling of the solution, the cooled solution being wholly or in part returned to the reaction vessel after at least a part of any solid hexamethylene-tetramine which may have been formed has been separated off a part of the formaldehyde present in the mixture of gas and steam from the contact oven, e.g. the mixture obtained when formaldehyde is produced by catalytic oxidation of methane, may be absorbed in a washing column and the residual gas containing the unabsorbed formaldehyde converted into hexamethylenetetramine. When the formaldehyde containing mixture from the oxidation of methanol is used in the hexamethylenetetramine production the unreacted methanol present in the mixture may be recovered from the waste gases after the formaldehyde has been converted to hexamethylenetetramine. In examples: (1) a gaseous mixture containing formaldehyde and steam such as is evolved from a contact oven for the production of formaldehyde by oxidation of methanol or methane is passed together with ammonia into a reaction vessel filled with a solvent, e.g. water, the quantity of ammonia being advantageously regulated in such a manner that a small quantity thereof is contained in the waste gases from the reactor. The reaction temperature is kept at a boiling temperature between 50 and 80 DEG C. by choosing suitable pressure conditions or by conducting air or other inert gas through the reaction solution and the gases and vapours evolved leave the reactor through a column fitted with a reflux condenser. The heat of reaction causes evaporation of the solvent until a concentrated solution of hexamethylenetetramine is formed or until the precipitation of solid hexamethylenetetramine ; (2) as in (1) except that the reaction is effected under normal pressure and at a temperature of about 60 DEG C. The reaction mixture does not boil and a part thereof is continuously transferred into an evaporation vessel which is either under reduced pressure or in which inert gases are passed through the solution. Spontaneous boiling of the solvent occurs in the evaporation vessel with cooling of the reaction solution and part or all of the cooled solution is returned to the reaction vessel. A part of the concentrated solution and any solid hexamethylenetetramine which has separated may be removed from the evaporator and part or all of the reaction solution which is returned to the reaction vessel is pumped through suction filters or centrifuges to separate solid hexamethylenetetramine.