Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
  • C07C209/82—Purification; Separation; Stabilisation; Use of additives
  • C07C209/86—Separation

Definitions

• the invention relates to a process for isolating amines from aqueous solutions by continuous distillation of aqueous solutions of the amines by a two-pressure process for the rectification of homogeneously azeotropic two-component mixtures.
• Two liquids that are completely soluble in one another and that form azeotropes, the composition of which depends on the pressure, can be separated by distillation without the aid of an additive.
• Such a separation process by rectification of the liquid ischungen in two columns, which are operated at different pressures, is referred to as a two-pressure process, cf. Klaus Sattler, "Thermal Separation Processes, Fundamentals, Design, Apparatus", 2nd edition, Verlag Chemie, Weinheim, New York, Basel, Cambridge, Tokyo, 1995, pages 147ff.
• aqueous solutions of amines are obtained, from which the amines must be obtained in anhydrous form. Since the amines form an azeotrope with water, they cannot easily be isolated by distillation from aqueous solutions in anhydrous form.
• the recovery of pure amines from aqueous, salt-containing solutions is important for the economy of processes in which the amines are used as bases. In this process, the amines must be recovered from the aqueous solutions of their ammonium salts formed during the reaction.
• the invention has for its object to provide a process for the isolation of amines in the most anhydrous form possible from aqueous solutions of the amines.
• the object is achieved according to the invention with a process for isolating amines from aqueous solutions by continuous distillation of aqueous solutions of the amines by a two-pressure process for the rectification of homogeneously azeotropic two-component mixtures, if aqueous solutions of amines which form an azeotrope with water, the composition of which is pressure-dependent, distilled in two columns at different pressures
• the pressure in the second column is at least 0.5 bar higher than in the first column
• the aqueous amine solution is fed in a side stream to the first column and water and portions which are higher than the amines or are non-volatile are removed from the bottom of the column
• a mixture of amine and water is taken off at the top of the first column and in conducts a side stream into the second column
• d) takes an azeotrope of water and amine from the top of the second column and returns it to the first column
• e) removes the purified amines from the bottom of the second column.
• the energy required for the evaporation of the azeotrope is introduced into the lower part of this column in the first column by introducing water vapor, and water and portions which are higher than the amines are discharged from the bottom of the column boiling or non-volatile, and removes at the upper part of the first column volatile components which boil lower than the amines.
• the pressure in the first column is set, for example, to values from 10 mbar to 10 bar, and is usually 0.1 to 3 bar. A method of operation in which the pressure in the first column is set to atmospheric pressure is particularly preferred.
• the pressure in the second column is set at least 1 bar higher than in the first column. In the particularly preferred embodiment of the invention, the pressure in the second column is set at least 6 bar higher than in the first column.
• the pressures and the other conditions for the distillation e.g. temperature of the heat transfer medium such as cooling water, brine or steam, diameter of the columns and size of the recycle stream between the columns
• the pressures and the other conditions for the distillation are preferably selected so that an optimal solution for the isolation of the process and economic aspects Amines is achieved.
• all the amines which form an azeotrope with water can be isolated in practically anhydrous form by the process according to the invention.
• the water content of the amines isolated from the aqueous solutions is, for example, 10 to 200 pp, preferably 20 to 60 ppm.
• the use of N, N-dimethylisopropylamine is particularly preferred.
• Such amines are used, for example, in the above-mentioned processes, for example in the production of alkyl ketene dimers, in the most anhydrous form possible.
• the ammonium salts formed are separated off and treated with aqueous solutions of bases in order to release the amines from the corresponding ammonium salts.
• bases are, for example, sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide and barium hydroxide.
• N, N-dimethylisopropylammonium hydrochloride For example, so much aqueous sodium hydroxide solution is added to an aqueous solution of N, N-dimethylisopropylammonium hydrochloride until the pH of the aqueous ammonium salt solution is at least 11. As a result, N, N-dimethylisopropylamine is released from the ammonium salt solution and sodium chloride is formed. N, N-dimethylisopropylamine can then be isolated from this mixture in practically water-free form by continuous distillation by the process according to the invention.
• Aqueous solutions of the amines which may also contain impurities such as low-boiling components or neutral salts such as sodium chloride, can, for example, be distilled using the two-pressure process as follows: An aqueous solution of amines containing neutral salts which form an azeotrope with water, the composition of which is pressure-dependent , is continuously fed in a side stream to a first column which is operated under atmospheric pressure.
• the side stream can be introduced, for example, in the middle of the column.
• the column has trays, preferably sieve trays, as separation devices.
• the number of theoretical plates of the column is e.g. 5 to 15, preferably 8 to 12.
• the aqueous amine solution to be distilled, which is fed to the first column can be a
• the energy required for the distillation can be supplied to the system using an evaporator at the bottom of the column or by introducing steam.
• the bottom draw of the first column contains water and parts which boil higher than the amines or are nonvolatile, such as, for example, neutral salts.
• the top draw from the first column which consists of a mixture of amine and water (for example 95% by weight of amine and 5% by weight of water), is removed continuously and passed in a side stream, for example into the upper half of the second column, in the pressure is, for example, 7 bar.
• An almost anhydrous amine is also obtained continuously in the bottom of the second column.
• An azeotrope of water and amine (for example 89% by weight of amine and 11% by weight of water) is continuously taken off at the top of the second column and for example returned to the upper half of the first column. Volatile constituents can optionally be continuously removed from the upper part of the first column.
• the practically anhydrous amine can be used again, for example, in the synthesis of alkyl ketene dimers from carboxylic acid chlorides.
• the reflux ratio is, for example, 0.5 to 3, preferably 0.5 to 2 in the first column and 1 to 4, preferably 1 to 2 in the second column.
• the dimethylisopropylammmonium chloride obtained in the production of alkylketene dimer from a long-chain carboxylic acid chloride (eg stearic acid chloride) and N, N-dimethylisopropylamine is brought to a pH as an approximately 50% strength by weight aqueous solution by adding 25% strength by weight aqueous sodium hydroxide solution -Value set at 11, heated to a temperature of 50 ° C. and fed continuously in a side stream to a column with 25 sieve trays operated under atmospheric pressure.
• the heating is carried out by continuously introducing direct steam at a temperature of approx. 150 ° C. into the lower part of the column.
• the amount of steam is approximately 20% of the amount of amine solution which is fed to the first column.
• a side draw is set up in the rectifying section of the first column, through which contaminants which are more volatile than water are continuously removed.
• the bottom of the second column is heated using an evaporator.
• pure N, N-dimethylisopropylamine is continuously drawn off, which contains about 40 ppm of water.
• the second column At the top of the second column there is an azeotrope which contains 89% by weight of N, N-dimethylisopropylamine and 11% by weight of water.
• the reflux ratio in the second column is 1.5. That on the head the azeotrope obtained in the second column is fed continuously to the first column in a side stream above the metering point of the aqueous N, N-dimethylisopropylamine solution.
• the condenser of the second column is vented into the rectifying section of the first column, which is operated under normal pressure.

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• 2002
  • 2002-11-12 JP JP2003543996A patent/JP2005509022A/ja active Pending
  • 2002-11-12 CA CA002465811A patent/CA2465811A1/en not_active Abandoned
  • 2002-11-12 WO PCT/EP2002/012603 patent/WO2003042159A1/de not_active Application Discontinuation
  • 2002-11-12 EP EP02791672A patent/EP1451142A1/de not_active Withdrawn
  • 2002-11-12 US US10/494,042 patent/US20050000790A1/en not_active Abandoned
  • 2002-11-12 CN CNA028226836A patent/CN1585741A/zh active Pending

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