GB760215A - Manufacture of alkanolamines - Google Patents

Abstract

Alkanolamines are prepared from ammonia and ethylene oxide or 1 : 2-propylene oxide by continuously passing a liquid mixture of ammonia in aqueous solution, containing 5 to 90 per cent by weight of water, and the alkylene oxide, which mixture contains not more than 50 per cent by weight of the alkylene oxide and from 1 to 45 mols. of ammonia for every three mols. of alkylene oxide present, through a reaction zone maintained at a temperature ranging from a minimum of 80 DEG to 150 DEG C. to a maximum of 275 DEG C., under a pressure which ensures that the reaction mixture is maintained in the liquid state throughout the reaction zone, the contact time within the reaction zone not exceeding 30 minutes and the amount of water in the mixture and the temperature of the reaction zone being so adjusted in relation to each other that substantially complete reaction of the alkylene oxide takes place. In a modification, all or part of the water in the reaction mixture is replaced by an equivalent amount in terms of hydroxyl content of an organic compound containing only carbon, hydrogen and one or more alcoholic or phenolic hydroxy groups, e.g. methanol, ethanol, ethylene glycol, glycerol or phenol. Preferably, the reaction zone is first heated to 80-150 DEG C. and then cooled to maintain a temperature of about 150 DEG C. or lower. The proportions of mono-, di- and tri-alkanolamines in the product may be varied by adjustment of the ratio of ammonia to alkylene oxide. Thus, a ratio of ammonia to ethylene oxide of greater than 4 : 1 gives mono-ethanolamine predominantly; a ratio of 1 : 1 to 4 : 1 gives optimum proportions of diethanol amine; a ratio of 1 : 3 using very dilute aqueous ammonia favours triethanolamine formation. The products contain some tri-alkanolamine glycol ethers; formation of those derived from triethanolamine may be suppressed by including minor amounts of acidic materials such as sulphuric, phosphoric or boric acids or carbon dioxide in the reaction mixture. A preferred embodiment comprises the use of aqueous ammonia containing 40-80 per cent in a reaction mixture containing not more than 35 per cent by weight of alkylene oxide and heating to an initial temperature of 100-150 DEG C., which allows a contact time of 120 seconds or less to be used and yields predominantly mono-alkanol amines. The mono-and di-alkanolamines obtained by the present process may be further reacted with the alkylene oxides. Suitable apparatus is described comprising proportionating pumps which feed aqueous ammonia and alkylene oxide to a mixer from which the resulting mixture is fed through a long stainless steel coil completely immersed in a liquid, e.g. water, boiling under reflux. The boiling liquid heats the reactants to the boiling temperature and the exothermic heat of the subsequent reaction is consumed in further boiling the controlling liquid. The reacted mixture leaves the reactor, at a pressure of, e.g., 60 atmospheres, through a let-down valve, and is fractionated to separate the excess ammonia, water and alkanolamines. Numerous examples are given of process employing this apparatus wherein aqueous ammonia is reacted with ethylene or propylene oxide yielding mixtures of the corresponding three trialkanolamines, and in some cases the crude products containing aqueous excess ammonia or an isolated ethanolamine are further reacted with the alkylene oxide. Other examples describe similar reactions of ethylene oxide with ammonia in methanol, aqueous methanol or n-butanol. According to the Provisional Specification, the process may be carried out at temperatures as high as 300 DEG C.; the reaction mixture should contain more than 1 per cent by weight of water and the contact time should be such that complete reaction of the alkylene oxide occurs and may be 2 hours. Additional examples are given wherein a molar ratio of ammonia to ethylene oxide of 25 : 1 and a 95 per cent aqueous ammonia solution are used. Also, the organic compounds which may replace the water wholly or in part may be any hydroxy compound including mono-, di- or tri-alkanolamines produced by the process and examples are given wherein mixtures of ammonia with mono- or di-ethanolamine are reacted with ethylene oxide. Specifications 448,373, [Group IV], 642,950, 655,580 and U.S.A. Specification 2,373,199 are referred to.