GB646959A - Solvent extraction process - Google Patents

Abstract

Liquid aliphatic secondary amines are recovered from multi-component liquid systems including the by-products of their manufacture, by adding to the system a selective hydrocarbon solvent for the amine to form an extract of the amine in the solvent, washing with a second solvent substantially immiscible with the selection solvent, the second solvent removing the other components of the said system, separating the extract from the second solvent and the amine from the extract, preferably by distillation. The operation may be carried out in a continuous countercurrent fashion and suitable apparatus is illustrated. The invention is of particular importance in the recovery of di-isopropylamine obtained by the vapour phase reaction of ammonia and isopropyl alcohol when isopropylamine, acetone, water, methyl isobutyl carbinol, methyl isobutyl ketone and unused reactants are also present in the reaction mixture. Water is the preferred wash solvent. The purity of the amine recovered decreases with an increase of its concentration in the extract and whilst in general water/solvent ratios of 0.5-10.0/1 may be used in the recovery of di-isopropylamine ratios of 0.75-2.0/1 are preferred. The amount of amine obtained depends on the number of extraction stages used but the purity is a function of the number of back-wash stages and it is preferred that one backward stage is provided for every five extraction stages and more particularly for every two of such stages. For complete di-isopropylamine recovery the minimum volume of hydrocarbon solvent used is between 10 and 50 per cent of the combined volume of amine feed and backwash, when the ratio of feed to backwash is low, e.g. 1/20, the minimum volume of solvent approaches 10 per cent of their combined volumes, when high, e.g. 1/2, the corresponding volume is 50 per cent. Good results are obtained using 3-30 volumes of solvent per volume of desired component in the crude feed, although for diisopropylamine 5-7 volumes are preferably used. Temperature affects both recovery and purity. Thus within the range 30-50 DEG C. which is preferred, a temperature increase results in an increase in recovery but a decrease in purity. A temperature of about 40 DEG C. is particularly preferred although temperatures of 0-100 DEG C. are also mentioned. Preferably the hydrocarbon phase is dispersed in the water phase although the reverse process may be employed. The process may be worked as a batch process. Hydrocarbon solvents specified are paraffins boiling between 0 DEG and 250 DEG C., preferably 150 DEG and 250 DEG C., e.g. butane, pentane, heptane, octane, nonane, decane, hexadecane, dodecane, tridecane and tetradecane and mixtures thereof. Preferably a solvent is used which allows of efficient product recovery by fractional distillation and of solvent recovery from impurities. For some solvents the process must be worked under pressure. Di-isopropylamine may be recovered from the solvent by first passing over a dehydrating agent, e.g. anhydrous calcium sulphate or activated aluminium before distillation. If distillation is effected without initial drying water-amine and alcohol-amine azeotropes are obtained, these azeotropes being returned to the distillation unit. n-Pentane may also be added to remove water and isopropyl alcohol as azeotropes therewith. Other recoverable amines are di-sec.-butyl, diethyl-, di-n-propyl- and di-n-butyl-amine. Fourteen examples are provided of the recovery of di-isopropylamine from other products obtained in its manufacture from isopropyl alcohol and ammonia, the effect of variations of temperature, flow rates and quantities of extracting solvents (in (1) n-pentane and in all others a paraffinic hydrocarbon cut of B.R. 150-200 DEG C. is used) and water, and numbers of backwash stages per extraction stage are illustrated. The Specification as open to inspection under Sect. 91 refers generally to the recovery of one component from a multi-component system by the above method. It also refers to the recovery of primary, secondary and tertiary amines in general, tri-sec.- and sec.-butyl-, ethyl-, n-propyl-, n-butyl-, triethyl-, tri-n-propyl-, tri-n-butyl- and bis-1,3-dimethylbutylamines being specified in addition to those above mentioned. It is stated that ethers may similarly be recovered from the reaction product obtained from alcohols and sulphuric acid, the backwash liquid being a mixture of an alcohol such as ethyl alcohol and ethylene glycol, and water, e.g. of composition 5 to 35 per cent water and 95 to 65 per cent alcohol, water-alcohol mixtures containing 5 to 30 per cent of water by volume being preferred. This subject-matter does not appear in the Specification as accepted.