GB722434A - Process for the production of hexamethylenetetramine - Google Patents

Abstract

Hexamethylenetetramine is obtained by reacting ammonia and formaldehyde in solution in a solvent, the reaction being carried out at the boiling-point of the reaction mixture and the heat of reaction that is evolved being utilized as heat for effecting evaporation of the solvent containing the reactants. The heat of reaction is defined as the total heat produced by the absorption and by the solution of the reactants in addition to that of the reaction proper. By selecting suitable pressure conditions, i.e. reduced or increased pressure, with, if required, the addition of another gas, the boiling-point can be fixed as required for the most favourable reaction temperature. Specified solvents are water and alcohol. In carrying out the reaction the reactants may be brought together as follows: (a) formaldehyde is dissolved in water or aqueous alcohol and gaseous ammonia is passed into the solution or otherwise brought into contact with the solution, e.g. in a trickling tower; (b) the ammonia is dissolved in water or aqueous alcohol and gaseous aldehyde is introduced into the ammoniacal solution; (c) gaseous ammonia and gaseous aldehyde are introduced into a solvent such as water or aqueous alcohol or into a solution containing dissolved reaction product; (d) dissolved ammonia and dissolved formaldehyde are interacted. The process can be made continuous by proportioning the formaldehyde and ammonia by means of suitable regulating apparatus, e.g. pH-regulating apparatus, polarographs or conductivity meters. In examples: (1) a 30 per cent aqueous solution of formaldehyde at 20 DEG C. trickles through a trickling tower and meets an ascending current of gaseous ammonia introduced at the bottom. The pressure is adjusted to about 150 mm. of mercury corresponding to a boiling temperature of about 60 DEG C. or to such other pressure as will enable the reaction to be carried out within the preferred temperature range of 50-70 DEG C. The evaporated solvent is condensed and the hexamethylenetetramine formed leaves the column as a 27 per cent aqueous solution which is then evaporated in a vacuum evaporator to form solid hexamethylenetetramine. The ammonia added is proportioned by means of a pH regulating apparatus to a neutral outflowing solution; (2) a 27 per cent solution of hexamethylenetetramine is prepared as in (1) and is evaporated down to give a concentrated solution into which gaseous ammonia is introduced whereby the solubility of the hexamethylenetetramine is lowered and pure hexamethylenetetramine is precipitated and separated from the ammoniacal mother liquor which is again reacted with a 30 per cent formaldehyde solution at a pressure of 156 mm. of mercury, corresponding to a boiling temperature of 61 DEG C. whereby the ammonia dissolved in the mother liquor is converted into hexamethylenetetramine. The outgoing vapours are condensed and the solution of hexamethylenetetramine flowing out of the reaction apparatus is again introduced to yield a further quantity of hexamethylenetetramine.