SI9111221A - Process for separating aminooxides from aqueous solutions - Google Patents

Abstract

To separate off amine oxides, in particular N-methylmorpholine, from aqueous solutions, in particular from effluents which are produced during processing of cellulose, the solutions are brought into contact with a cation exchanger resin, the anchor groups of which comprise carboxyl groups, in order to charge the cation exchanger with the amine oxides, whereupon the charged cation exchanger is washed and treated with an aqueous solution of a weak acid having a pKa of greater than 3.0, in order to elute the amine oxides.

Description

Procedure for the determination of amino acids from aqueous solutions

The invention relates to a process for the determination of amine oxides, in particular N-methylmorpholinoxide (NMMO), from aqueous solutions, in particular from wastewater obtained from the processing of cellulose, in which solutions are contacted with a cation exchange resin to coat the cation exchanger with amino acids , after which the coated cation exchanger is washed and the amino acids are eluted.

They are known to introduce cellulose into aqueous solutions of amino acids, in particular N-methylmorpholinoxide (NMMO), and to prepare spinning homogeneous cellulose solutions. By precipitation of these solutions in water, they obtain a foil, fiber or mold on a cellulose basis. The post-treatment of the products produces wastewater containing up to 4% by weight of NMMO. The NMMOs contained therein must be decided as much as possible before these wastewater can be released.

SU-A-1 427 011 discloses a process of the type described above. In this process, they adsorb NMMOs on a strongly acidic cation exchanger. Ammoniacal aqueous isopropyl alcohol is used as the elution agent. After elution, the cation exchanger with sulfuric acid must be converted to acid form again.

This method has proven to be technically and energetically very complicated, as NMMOs contain a mixture of ammonia, water and isopropyl alcohol, which must be distilled. Volatile constituents (ammonia and isopropyl alcohol) are the first to decide, and then the remaining aqueous NMMO solution is further concentrated by distillation into NMMO monohydrate. Furthermore, when regenerating the cation exchanger, a strong acidic solution of ammonium sulfate is obtained, which must be neutralized with ammonia and then treated to solid ammonosulfate by evaporation.

It is an object of the invention to remove these defects and to make available a process of the kind described above that can be performed without a neutralizing step and without energy-demanding separation and regeneration stages.

This object of the invention is achieved by using a cation exchanger whose anchor groups are carboxyl groups in the process of the aforementioned species, and treating the cation exchanger with an amine oxide with an aqueous weak acid with a pK _a value above 3.0 to elute the amino acids . From the eluate, amino acids can be eliminated by distillation, and condensed vapors can again be used as the eluant.

The process of the invention has been shown to be particularly suitable for the treatment of solutions with up to 4% by weight of NMMO, since it enables the practical quantitative determination of NMMO from wastewater.

A preferred variant of the process of the invention is the use of a weak acid whose boiling point is below 120 ° C. As such, the formic or acetic acid contained in the aqueous solution is preferably between 8 and 15% by weight. Carbonic acid, if present in an aqueous solution in a concentration of between 2 and 20% by weight, preferably between 10 and 15% by weight, has also been shown to be suitable.

The process of the present invention will be further described in the following examples.

EXAMPLE 1

100 ml of weakly acidic cation exchanger with carboxyl groups as anchor groups (Lewatit CNP 80 (basic frame: polyacrylate); manufacturer: Bayer AG) is coated in a 5-volt (BV) flow column, i.e. 500 ml of 1% aqueous NMMO solution at a flow rate of 10 BV / h. The NMMO was then eluted with 10 BV of aqueous 10% acetic acid solution, and the cation exchanger was regenerated and subsequently washed with 15 BV of water (speed: 5 BV / h). NMMO cannot be demonstrated in the rinse water by conventional methods (titration and HPLC).

The resulting mixture of NMMO and acetic acid (1000 ml) was heated in vacuo (100 mbar) to 100 ° C and distilled 950 ml. Distillate again gives 98% of the acetic acid used; The NMMO solution was concentrated to 10%.

EXAMPLE 2

It is carried out as described in Example 1; and coated with 8 BV of 0.5% NMMO solution. NMMO cannot be demonstrated in the rinse water. The eluate was treated as described in Example 1. The NMMO / acetic acid mixture was evaporated to 50 ml; in the distillate 100% acetic acid was again obtained, and the NMMO concentration at the bottom increased to 8%.

EXAMPLE 3

It is carried out as described in Example 1; it is coated with 2 BV of 4% NMMO solution and washed with 15 BV of water. NMMO cannot be demonstrated in the rinse water.

The eluate was treated as described in Example 1. The NMMO / acetic acid mixture was evaporated to 300 ml, then 200 ml of water was added and the mixture was evaporated to 50 ml; in the distillate 97% of acetic acid is again obtained, and the NMMO concentration at the bottom increases to 16%.

EXAMPLE 4

100 ml of weakly acidic cation exchanger with carboxyl groups as anchor groups (Dowex CCR-2 (basic framework: polyacrylate); manufacturer: Dow Chemical) was coated in a 7 BV 1 ml aqueous NMMO flow column with a flow rate of 10 BV / h. The NMMO was then eluted with 10 BV of aqueous 10% acetic acid solution and the cation exchanger was regenerated and subsequently washed with 15 BV of water (speed: 5 BV / h). NMMO cannot be demonstrated in the rinse water by conventional methods (titration and HPLC).

The eluate was treated as described in Example 1. The NMMO / acetic acid mixture was evaporated to 80 ml; in the distillate 97% of acetic acid is again obtained, and the NMMO concentration at the bottom rises to 8.5%.

EXAMPLE 5

100 ml of weakly acidic cation exchanger with carboxyl groups as anchor groups (Duolite C 433 (basic frame: polyacrylate); manufacturer: Rohm und Haas) is coated in a 4 BV 1 ml aqueous NMMO flow column with a flow rate of 10 BV / h. The NMMO was then eluted with 10 BV of aqueous 10% acetic acid solution and the cation exchanger was regenerated and subsequently washed with 10 BV of water (speed: 5 BV / h). NMMO cannot be demonstrated in the rinse water by conventional methods (titration and HPLC).

The eluate was treated as described in Example 1. The NMMO / acetic acid mixture was evaporated to 40 ml; 100% acetic acid is again obtained in the distillate and the NMMO concentration at the bottom increases to 10%.

Claims (4)

PATENT APPLICATIONS Claims 1. A method for the decomposition of amino acids, in particular N-methylmorpholinoxide, from aqueous solutions, in particular from wastewater obtained from the processing of cellulose, in which the solutions are contacted with a cation exchange resin to coat the cation exchanger with the cation exchange coated washed and amino eluted, characterized in that a cation exchange resin, whose anchor groups exist from carboxyl groups, is used, and the cation exchanger coated with the amino acid is treated with an aqueous weak acid with a pK _a value above 3.0 to elute the amino acids. Process according to claim 1, characterized in that a weak acid having a boiling point below 120 ° C is used. Process according to claim 2, characterized in that formic or acetic acid is used as a weak acid, the aqueous solution preferably containing between 8 and 15% by weight of acid. Process according to claim 2, characterized in that carbonic acid, which is present in the aqueous solution at a concentration of from 2 to 20% by weight, preferably between 10 and 15% by weight, is used as a weak acid.