CZ284681B6 - Process for preparing solutions of n-methylmorpholinoxide with a low content of nitrosomorpholine - Google Patents

Abstract

A method of preparing N-methylmorpholinoxide by oxidising N-methylmorpholine in an aqueous hydrogen peroxide solution at a temperature of 55 to 75 degrees C with a molar ratio of H2O2/amine=0.4 to 0.9, preferably 0.5 to 0.70 possibly in the presence of chelating reagents, possibly in the presence of CO2, with distilling off of unprecipitated N-methylmorpholine under reduced pressure. After adding hydrogen peroxide to the reaction mix and after a decrease in its concentration to 0.05 to 0.15 % of mass, 0.01 to 0.05 % of mass of hydrazine is added, calculated to the reaction mix, and the mixture is kept at reaction temperature for a further half to three hours.

Description

Process for preparing N-methylmorpholine oxide

Technical field

The present invention relates to a process for the preparation of low-color, low-nitrosomorpholine (NOMOR) low-N-methylmorpholine oxide (NMMO) solutions used to prepare cellulosic fibers. For this purpose, a solution containing 50 to 60 wt. N-methylmorpholine oxide containing up to 300 ppb of nitrosomorpholine.

The physical dissolution of cellulose together with the simple and quantitative solvent recovery is a radical innovation compared to the viscose fiber production technology, especially in terms of protection of the working and environment.

BACKGROUND OF THE INVENTION

NMMO is produced by reacting N-methylmorpholine (NMM) with hydrogen peroxide according to Equation 1.

/ ^CH3 * “ON ⁺ f + H ₂ ow V

The reaction proceeds with respect to both reactants in an almost quantitative yield. The patent literature therefore focuses on the quality of NMMO produced.

In the Eastman Kodak Co. patent (US 3,447,939, DE 1694048 02.09.1966), which focuses on the use of cyclic amine oxides as a solvent for macromolecular substances, describes the preparation of cyclic tertiary amine oxides, among them NMMO first. The oxidation of the amine is carried out with an H2O2 / amine ratio of 0.98. In the example of the preparation of NMMO, the peroxide weighing data, according to which the molar ratio H ₂ O ₂ / amine = 0.83, with a yield of oxide per peroxide high above 100%, is erroneous. All other data in the patent suggest the application of an almost equimolecular ratio of reactants.

To NMM containing 8 wt. of water, a 35% solution of H ₂ O ₂ is added over a period of 4 to 5 hours at a temperature of 67 to 72 ° C. The mixture was then kept at the reaction temperature for a further 2 hours and after cooling the excess peroxide was decomposed by the catalase enzyme. The yellow oil was dewatered by azeotropic rectification with benzene and anhydrous NMMO was then poured into acetone, precipitating NMMO crystals in a yield of 89.6%, calculated on NMM. The rest of the NMMO and impurities are likely to remain in the mother liquor.

A similar procedure is described in CS AO 218 714, which also operates at an H 2 / amine ratio of 0.98 and a temperature of 67-72 ° C. The only difference from Eastman Kodak Co is that the reaction mixture is first extracted with acetone to get rid of unreacted NMM and then only dewatered by rectification with benzene. This, however, loses the effect of purifying the NMMO by crystallization.

For the production of fibers, aqueous NMMO solutions are used and it is therefore advisable to avoid dewatering and crystallization in the preparation of NMMO. However, a sufficiently pure NMMO solution should be prepared without crystallization.

One of the requirements for NMMO quality is the coloring of the solution. The procedure of US 3,447,939 gives an orange NMMO solution. In DD 254 199, it is emphasized that in production

The light color NMMO solution must be maintained at +1 K and the H 2 O 2 solution must be gently dispersed into the reaction mixture, for example by means of a nozzle. An equimolecular reactant ratio is used at a temperature of 69-72 ° C.

According to another patent of the same group of authors (DD 259 863) up to 90 wt. The NMM is introduced over a period of 3.5 hours with a 48% H 2 O 2 solution at 75 ° C and then stirred for an additional 5 hours. The stoichiometric ratio of the reactants is used. The reaction mixture is then passed through four cation exchange columns, and phosphoric acid is added to the reaction mixture before entering the 4th column. Unreacted NMM appears to be trapped on the cation exchanger.

The patent of Hiils AG (EP 0 254 803) states that the purity of NMMO is increased when the initial NMM is first rectified with water to a 74% azeotrope which is then oxidized.

The effect of rectification of NMM prior to oxidation on NMM purity is understandable because NMM, like other tertiary amines, yellows upon storage under atmospheric oxygen. The question is, however, whether the purification of the starting material before the chemical reaction is even patentable. In the example, the NMM is rectified with the same amount of water on the column. 35% by weight of the resulting azeotropic mixture were introduced within two hours. Η ₂ Ο ₂ in FECE / amine ratio = 0,82. The mixture was then stirred at 68 ° C for 6 hours. Finally, unreacted NMM and some of the water were distilled off under vacuum so that the solution contained 60 wt. NMMO. The obtained NMMO solution contains 2 ppm Η ₂ Ο ₂ , 0.1 wt. NMM and the acid number is 0.1 mg KOH / g. The solution is yellowish. The cited patent protects a molar H ₂ O ₂ / NMM ratio of 0.75 to 0.90, ensuring complete peroxide reaction. Removal of unreacted NMM by vacuum distillation is easy.

Already incl. In 1967, a process for the production of trialkylamine oxides, in particular triethylamine oxide, in which the oxidation of the amine with hydrogen peroxide is catalyzed by an alkali bicarbonate and an alkaline polyphosphate, was patented (US 3,333,000). Polyphosphates and other chelating agents prevent the breakdown of peroxide into water and oxygen. When triethylamine was oxidized without the catalyst system, the yield of H 2 O 2 was only 30.8%, in the presence of catalysts the yield was theoretical.

Of particular importance are the single long carbon chain tertiary amine oxides (especially dimethyl laurylamine) used as surfactants. In oxidizing these amines with hydrogen peroxide, carbon dioxide has been found to have a greater catalytic effect than bicarbonate (US 4,247,480, 1981). The CO ₂ content should be 0.01 to 2% by weight, based on the tertiary amine. At the same time peroxide stabilizers such as polyphosphates, ethylenediaminetetraacetic acid (EDTA), tin stannates etc. are added. The H ₂ O ₂ / amine ratio is 1.05 to 1.1, because the fatty amine cannot be separated from the oxide solution and has to react .

French Patent 2,632,638 (1988) protects the use of CO ₂ as a catalyst in the oxidation of tertiary amines with hydrogen peroxide, the first aspect of the invention being identical to US 4,247,480, which is not disclosed in the prior art. Examples are directed to triethylamine oxide.

More recently, the quality of oxides has been evaluated according to the nitrosamine content, which varies between 50 and 10,000 ppb. Oxidation of dimethyl lauryl amine produces carcinogenic dimethylnitrosamine and Nnitroso-N-methyllaurylamine. In the preparation of NMMO mainly N-nitrosomorpholine (NOMOR) is produced.

A first procedure for the preparation of low nitrosamine amine oxides is described in EP 307184 (8.9.1987) of Ethyl Corporation. According to the patent, tertiary amines are oxidized with hydrogen peroxide in the presence of CO ₂ at a temperature below 45 ° C. While a product containing 96 ppb dimethylnitrosamine was obtained in the presence of CO ₂ at 65 ° C and a 10% excess of H ₂ O ₂ , at a temperature below 40 ° C the nitrosamine content was below the detection limit. 3 to 7 wt. CO ₂ by weight of amine. It can be argued that already U.S. Pat. No. 4,247,480 describes the preparation of oxides in the presence of CO ₂ at 40 to 80 ° C.

-2 CZ 284681 B6

Another patent of Ethyl Corporation (EP 320,694, Nov. 22, 1988) protects the preparation of tertiary amine oxides in the presence of CO ₂ and ascorbic acid, both having a synergistic effect on the reduction of nitrosamines. A H ₂ O ₂ / amine ratio of 1.0 to 1.5 is recommended, 1.1 to 1.2 is preferred. The reaction temperature is 0 to 100 ° C, preferably 45 to 75 ° C, a CO ₂ concentration of 0.05 to 5%, based on the weight of the amine, and the content of ascorbic acid is the same. Three comparative experiments are presented.

only CO ₂ only AK both dimethylenitrosam and methyldodecylnitrosamine ppb 37 ppb 216 ppb nedetek. nedetek.

Another patent by Ethyl Corporation (EP 356,918, Aug 29, 1988) protects the preparation of nitrosamine-free amine oxides by oxidation of tertiary amines with hydrogen peroxide in the presence of titanium metal. Both titanium-free and CO ₂ -free, a 30% oxide solution is obtained from dimethyllaurylamine containing about 700 ppb of both nitrosamines, containing 310 ppb of nitrosamines in the presence of a titanium plate, 96 ppb in the presence of CO _2, and nitrosamines below 10 ppb.

The last of a number of patents of Ethyl Corporation (EP 426 084, October 30, 1989) describes the preparation of amine oxides in the presence of CO ₂ diluted with at least an equal volume of inert gas. At a content of 60 wt. CO ₂ or more in the gas above the reaction mixture gave an orange product using a gas containing 20 to 40 wt. CO ₂ is a yellowish oxide solution only.

Albright and Wilson Limited protects (GB 2,252,320, February 2, 1991) the stabilization of amine oxide solutions against nitrosamine formation during production and storage by the addition of 2.5 to 20 wt. bicarbonate or carbonate, calculated on the weight of the amine. It is said that carbon dioxide does not protect nitrosamines perfectly, especially when storing solutions. During oxidation it is recommended to add chelating agents to prevent decomposition of hydrogen peroxide. In the examples, the content of NO groups is given. When oxidizing a tertiary amine of the trade mark Empigen AB at a H ₂ O ₂ / amine ratio of 0.9 at 40 ° C, with the addition of 0.4 wt. sodium EDTA was obtained the following dependence:

% wt. NaHCO ₃ per amine 0 0,71 1,8 3,6 7,15 10 ppb NO 314 611 406 237 64 66

Another patent of the same company (EP 553 800, January 31, 1992) describes the synergistic effect of bicarbonate or carbonate and organic phosphonate. The patent protects the bicarbonate concentration from 0.05 to 20 wt. % and phosphonate 0.005 to 5 wt. by weight of the tertiary amine. Effective phosphonates include aminotrimethylene phosphonate, ethylenediaminotetrakismethylene phosphonate and the like. In oxidation, it is useful to add chelating agents that stabilize hydrogen peroxide and accelerate oxidation, but do not affect the formation of nitrosamines. With a combination of 0.1 wt. % phosphonate and 1 wt. NaHCO ₃ per amine and a stoichiometric H ₂ O ₂ / amine ratio yielded a solution of dimethyl lauryl amine having a nitroso group content of 34 ppb.

In its patent (EP 545,208, December 6, 1991), BASF states that the nitrosamine content of the oxide solution depends on the content of primary and secondary amines in the starting tertiary amine. The patent protects a process starting from tertiary amines containing less than 0.05 wt.

primary and secondary amines. Preferably, unwanted amines are removed by the addition of reagents such as acyl halides, acid anhydrides, sulfonyl halides and the like.

BASF alone describes the preparation of NMMO with a low nitrosamine content. In a comparative experiment, methyl morpholine containing 0.3 wt. primary and secondary amines.

-3 CZ 284681 B6

30% w / w was introduced at 70 ° C over two hours. H ₂ O ₂ solution with a molar ratio H ₂ O ₂ / NMM = 0.9. The mixture was then stirred at 70 ° C for 7 hours. The unreacted NMM was distilled off at 10 kPa to give 57 wt. NMMO solution containing 3100 ppb of nitrosamines. When NMMO was prepared from NMM, purified by distillation to a content of 0.02 wt. primary and secondary amines, then contained below 50 ppb of nitrosamines.

The same effect was achieved if, prior to oxidation, acetic anhydride was added to the starting N-methylmorpholine in an amount of 0.0045 mol per 1 mol of NMM and the mixture was allowed to react for 1 hour.

In the preparation of NMMO and in the case of fatty amine oxides (surfactants) the color of the product is of great importance. The oxide solutions obtained are usually yellow to orange in color. It is described in the literature that catalysis of the tertiary amine oxidation with carbon dioxide gives yellow to orange products. Several of the patents cited herein focus on the coloring of oxide solutions.

In all procedures that pursue preparation of as light as possible NMMO solutions, an approximately equimolecular H ₂ O ₂ / NMM ratio is employed. In our experience, a small excess of peroxide indeed maintains the bright color of the reaction mixture. However, the cited patents do not disclose the content of residual H ₂ O ₂ in the NMMO solution. At the same time, fiber producers demand a H ₂ O ₂ content below 50 ppm. Working with the equimolecular ratio of reactants also generates an inadmissible amount of carcinogenic nitrosomorpholine, up to an order of magnitude higher than that permitted by fiber manufacturers (300 ppb).

SUMMARY OF THE INVENTION

The process for preparing a colorless or only slightly yellow NMMO solution by oxidizing NMM with hydrogen peroxide at 55 to 75 ° C with a molar ratio of H ₂ O ₂ / NMM = 0.4 to 0.9 according to the invention consists in that after the peroxide solution and its reacting to a level of 0.1 + 0.05 wt. H ₂ O ₂ in the reaction mixture adds 0.01 to 0.05 wt. hydrazine, calculated on the weight of the reaction mixture, and allowed to react at the reaction temperature for a further 1 to 3 hours. Unreacted NMM is separated by a known method, i.e. by vacuum rectification.

The reaction mixture turns yellow only when the H ₂ O ₂ concentration falls below 0.1 wt. If yellow substances are formed before, they are bleached with peroxide. The addition of hydrazine according to the invention partially decomposes H ₂ O ₂ , but at the same time prevents the formation of yellow substances. Was tested, other reducing agents that react sH ₂ O _2, no harvest, did not give a colorless solution of NMMO, some, such as ascorbic acid, cause browning of the solution.

According to our measurements of the course of the H ₂ O ₂ concentration, peroxide reacts only partially with hydrazine, while most reacts with NMM. Therefore, the addition of hydrazine may not even correspond to the stoichiometry of the equation

NH ₂ NH ₂ + 2 H ₂ O ₂ -> N ₂ + 4 H ₂ O

After unreacted NMM was distilled off, the final NMMO solution remained below 0.01% by weight. hydrazine. Low hydrazine content can have a positive effect on inhibition of peroxide formation in NMMO solution in the production of cellulose fiber. Hydrazine is toxic to activated sludge and wastewater containing up to 1 ppm of hydrazine may be fed to biological treatment. Due to the properties of hydrazine and the fiber production process, wastewater with a hydrazine concentration higher than 1 ppm cannot be produced.

-4GB 284681 B6

Due to the coloring of the NMMO solution, hydrazine can be used in oxidation with a relatively high molar ratio of Η ₂ Ο ₂ / ΝΜΜ to 0.9. However, with respect to the NOMOR content, it is expedient to work with an H ₂ O ₂ / NMM ratio of 0.4 to 0.7. Greater excess NMM is also advantageous in terms of H ₂ O ₂ reaction rate. For the same reasons, the optimum temperature is 60 to 65 ° C.

Particular preference is given to combining the addition of hydrazine with chelating agents such as sodium pyrophosphate, sodium ethylenediaminetetraacetate or sodium stannate. In this case, an absolutely colorless NMMO solution is obtained which contains below 50 ppb of nitrosomorpholine.

The use of the hydrazine according to the invention in combination with the catalytic action of CO ₂ is also suitable. However, carbon dioxide catalyses the oxidation of tertiary amines so strongly that after the introduction of peroxide its concentration is below 0.05% by weight. and the addition of hydrazine decreases the color intensity, but not to the extent that hydrazine is added in accordance with the invention at a time when the peroxide concentration is about 0.1% by weight. It is therefore expedient to apply a CO ₂ concentration of up to 1 wt. to the weight of the amine and further reduce the reaction temperature to e.g. 60 ° C. Normally, the NMM is oxidized at a temperature of about 65 ° C. By setting a suitable combination of the H ₂ O ₂ feed rate, the CO ₂ concentration and the reaction temperature, the concentration of H ₂ O _{2 may} be 0.1 to 0.2 wt. and then hydrazine can be successfully applied.

Examples

Example 1

A 2 liter sulfonation flask equipped with a stirrer was charged with 1200 g of the NMM-water azeotrope containing 73 wt. NMM. After heating the thermostat in which the flask was placed and flushing the apparatus with nitrogen, a 35% H ₂ O ₂ solution was injected. The H ₂ O ₂ solution was dosed at a steady rate for three hours with a molar H ₂ O ₂ / NMM ratio of 0.6. A temperature of 60 ° C was maintained during peroxide dosing and post-reaction. The reaction mixture was stirred vigorously. After all peroxide was introduced, the flask was purged with nitrogen.

After the introduction of the H ₂ O ₂ solution, the mixture was kept at the reaction temperature for 1.5 hours, when the H ₂ O ₂ concentration dropped to 0.1 wt. At this time, 0.4 g of hydrazine hydrate was added to the reaction mixture, and the mixture was stirred at 60 ° C for 1.5 hours. The peroxide content decreased to 0.007 wt.

The colorless reaction mixture was transferred to the rectification apparatus and N-methylmorpholine and a portion of water were distilled off at 20 to 13 kPa. A colorless 60% NMMO solution remained in the flask. The yield of NMMO on the converted NMM was 100%, on H ₂ O ₂ 97%.

In a comparative experiment without addition of hydrazine, a yellow NMMO solution was obtained.

Example 2

The NMM was oxidized under the conditions of Example 1 except that 0.3 g Na ₄ P ₂ O ₇ 10 H ₂ O was added to the amine and the reaction temperature was 67 ° C. 1 hour after the solution was introduced

H ₂ O ₂ contained 0.09 wt. H ₂ O ₂ was added, at which time a 30% solution of hydrazine hydrate was added in an amount of 1.5 g. After another hour, the H ₂ O ₂ concentration dropped below 0.01% by weight. and the reaction mixture was worked up as in Example 1. A solution with 60 wt. NMMO, which was completely colorless and contained 20 ppb of nitrosomorpholine.

-5 CZ 284681 B6

Example 3

The NMMO was oxidized as in Example 1, but with the addition of 1 wt. The CO ₂ , calculated on the amine, was the H ₂ O ₂ / NMM ratio of 0.7. After the peroxide solution was introduced, the reaction mixture contained 0.28% H ₂ O ₂ and after a further 20 minutes 1.5 g of a 30% hydrazine hydrate solution was added. After half an hour, the H ₂ O ₂ concentration dropped below 0.01 wt%. and the mixture was rectified as in Example 1. Only a slightly yellowish solution with 60 wt. NMMO containing 25 ppb nitrosomorpholine.

Industrial applicability

The invention is applicable to the production of low nitrosomorpholine-containing N-methylmorpholine oxide which is used to prepare cellulosic fibers.

Claims (1)

PATENT CLAIMS A process for the preparation of N-methylmorpholine oxide by oxidizing N-methylmorpholine with an aqueous hydrogen peroxide solution at a temperature of 55 to 75 ° C with a molar ratio of H ₂ O ₂ / amine = 0.4 to 0.9, preferably 0.5 to 0.70, optionally in the presence of chelating agents, optionally in the presence of CO ₂ , by distilling off unreacted N-methylmorpholine under reduced pressure, characterized in that after the introduction of hydrogen peroxide into the reaction mixture and after its concentration has decreased to 0.05 to 0.15 wt. 0.01 to 0.05 wt. hydrazine, calculated on the reaction mixture, and the mixture is left at the reaction temperature for a further half to three hours.