Patent GB-686500-A (GB)
Title: Improvements in and relating to the separation of amines
Filed: 1951-03-09
Abstract: Fractional separation of a mixture of amines containing at least two of the following: mono-, di-, and tri-methylamine and ammonia is effected by treating with a weak acid whose adducts with said compounds decompose below the boiling point of the acid, and expelling the absorbed amines or ammonia by heating or evacuation or both.  The methylation product of ammonia may be treated, advantageously after removal of water and methanol.  By varying the velocity of flow of the mixture or the amount of weak acid, one or two components only may be absorbed.  The process may be repeated to obtain the pure components.  Weak acids include aromatic hydroxy compounds, e.g. phenol, cresols, xylenols, arylphenols, resorcin, naphthols, chlorphenols, and aminophenols, aminocarboxylic acids, and sulphonamides, e.g. alanine and isopropyl-sulphonamide.  The use in known manner of organic solvents or of water, aqueous alkalis or salts, e.g. as described in Specification 475,818, may be combined with the weak acid treatment in the same, a prior or subsequent step. Weak acids with dichlor-, trichloro- or nitro-benzene, hydrogenated naphthalenes, aliphatic or aromatic hydrocarbons, ethers, alcohols, and ketones are suitable for separating ammonia from methylamines and monofrom dimethylamine, while trimethylamine is separated from ammonia-free mixtures with acids+water.  In examples: (1) ammonia+trimethylamine is passed into phenol+o-dichlorbenzene.  After saturation, a gas concentrated in ammonia escapes while the absorbent on heating to 170 DEG  C. gives a gas concentrated in the tert. amine.  By continued repetition, pure components are obtained; (2) ammonia and dimethylamine are separated similarly using molten a - and b -naphthols; (3) the solvent mixture of (1) is saturated with a mixture of ammonia and the tert. amine.  Pure tert amine is passed to give a gas concentrated in ammonia while the solution on heating gives the tert. amine; (4) m-cresol is contacted with a mixture of ammonia, di- and tri-methylamines, practically pure ammonia escaping; (5) the gas obtained by heating the absorbent of (4) is treated with m-cresol to separate the two amines; (6) commercial cresol is used to separate ammonia and the tert. amine from prim. and sec. amine which are absorbed.  After expulsion, the latter are separated with phenol and o-dichlorobenzene; (7) a mixture of ammonia, and the 3-methylamines is contacted with caustic soda to separate the tert. amine.  The gas expelled from the absorbent is treated with cresol to separate ammonia, and the absorbed prim. and sec. amines are separated in a further stage; (8) phenol +o-dichlorbenzene are used to absorb the amines from ammonia, caustic soda is then used to remove mono- and difrom tri-methylamine, and these two are separated as in (6); (9) caustic soda is the first absorbent, acetonitrile then selectively absorbs the prim. and sec. amine, and further extractions give the pure components; (10) caustic soda is the first absorbent, the escaping gas being treated with further absorbent sufficient only to dissolve mono- and di-methylamine; (11) the increased selectivity of cresol for mono-and di-methylamine by increasing the volume or by saturating with water is illustrated. Specification 435,200 also is referred to.