CZ284760B6 - Process for preparing solutions of n-methylmorpholinoxide with a low content of nitrosomorpholine - Google Patents

Abstract

A method of preparing a 45 to 70% aqueous solutions of N-methylmorpholine oxide with a low content of nitrosomorpholine of up to 50 ppb by oxidising of N-methylmorpholine in an aqueous hydrogen peroxide solution at a temperature of 60 to 75 degrees C with a molar ratio of H2O2/amine=0.5 to 0.9. Hydrogen peroxide acts on N-methylmorpholine, which contains at least one of three hydrogen peroxide stabilisers from a group including sodium pyrophosphate, sodium salt of ethylenediaminetetraacetic acid, sodium stannate at a total concentration of 0.01 to 0.05 % by weight calculated on the basis of the amount of changed amine and common commercial form of the added stabilisers including crystalline water content. It is an advantage to use N-methylmorpholine as an azeotropic mixture with water.

Description

Technical field

The present invention relates to a process for the preparation of low nitrosomorpholine (NOMOR) solutions of N-methylmorpholine oxide (NMMO), which is 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 I.

/ \ / \ ₊ / ^CH 3

ON — CH ₃ <· H ₂ O ₂ ----- ► O _ * H ₂ O

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, Germany 1694048 September 2, 1966), which is directed to 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 H ₂ O ₂ / amine ratio is 0.83 is erroneous, with the yield of oxide per peroxide being well over 100%. All other data in the patent suggest the application of an almost equimolecular ratio of reactants.

To NMM containing 8 wt. water, an average of 35% H 2 O 2 solution is introduced at a temperature of 67 to 72 ° C for 4-5 hours. 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 with a ratio H 2 O ₂ / amine = 0.98 and a temperature of 67-72 ° C. Eastman Kodak Co. it is only that the reaction mixture is first extracted with acetone, free of unreacted NMM and then 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 quality requirements of NMMO is the coloring of the solution. The procedure of US 3,447,939 gives an orange NMMO solution. NDR 254 199 emphasizes that in the preparation of a light colored NMMO solution, the reaction temperature must be kept within + 1 K and the solution

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H 2 O 2 must be gently dispersed into the reaction mixture, for example by means of a nozzle. An equimolecular ratio of reactants at 69-72 ° C is used.

According to another patent of the same group of authors (GDR 259 863) up to 90 wt. The NMM was introduced over 3.5 hours at 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.

In Hös AG (EP 0 254 803), 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 NMM rectification 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 prior to 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 over two hours. H ₂ O ₂ in the ratio H ₂ O ₂ / amine = 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 NMMO solution obtained contains 2 ppm H ₂ O 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 in 1967, a process for the production of trialkylamine oxides, in particular triethylamine oxide, in which the oxidation of the amine with hydrogen peroxide was catalyzed by an alkali hydrogen carbonate 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 tertiary amine oxides with a single long carbon chain (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 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 dimethyllaurylamine 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 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.

-2GB 284760 Β6

Another Ethyl Corporation patent (EP 320,694, Nov. 22, 1988) protects the preparation of tertiary amine oxides in the presence of CO ₂ and ascorbic acid, both of which have 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, preferred temperature is 45-75 ° C, CO ₂ concentration of 0.05 to 5%, by weight of the amine, and the same is also the ascorbic acid content. Three comparative experiments are presented.

CO _{2 only} AK only both d imethylene itrosamine 96 ppb 37 ppb nedetek. methyldodecylnitrosamine nedetek. 216 ppb nedetek.

Another patent of 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 titanium plate, 96 ppb in the presence of CO _2, and nitrosamines below 10 ppb.

The last of a series of patents Ethyl Corporation (EP 426 084, 30/10 1989) disclose 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, Feb. 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. % of sodium EDTA was obtained as follows: 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) discloses 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. and the weight of the tertiary amine. Effective phosphonates include aminotrismethylene 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 at a stoichiometric H ₂ O ₂ / amine ratio a solution of dimethyl lauryl amine having a nitroso group content of 34 ppb was obtained.

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% by weight of primary and secondary amines. Preferably, unwanted amines are removed by the addition of reagents such as acyl halides, acid anhydrides, sulfonyl halides, etc. The BASF patent alone describes the preparation of low nitrosamine-containing NMMOs. In a comparative experiment, methyl morpholine containing 0.3 wt. primary and secondary amines. 30% w / w was introduced at 70 ° C over two hours. H ₂ O ₂ solution with a molar H ₂ O ₂ / NMM ratio of 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. the NMMO solution it contained

3100 ppb 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 obtained when acetic anhydride was added to the starting N-methylmorpholine in an amount of 0.0045 mol per 1 mol of NMM prior to oxidation and the mixture was allowed to react for 1 hour.

Current knowledge on the preparation of NMMO solutions with low nitrosomorpholine content can be summarized as follows:

In the oxidation of tertiary fatty amines with hydrogen peroxide, it has been found that carbon dioxide effectively catalyzes the reaction while reducing the nitrosamine content. It is expedient to combine the action of CO ₂ with other substances such as titanium metal, ascorbic acid and aminophosphonates. Sodium bicarbonate has a similar effect to CO ₂ . In patents describing the effect of CO ₂ and bicarbonates in the oxidation of tertiary amines with hydrogen peroxide, there is no single example of the oxidation of NMM. Our experiments confirmed that CO ₂ increases the rate of NMM oxidation by 10 to 100 times (depending on CO ₂ concentration) and decreases the formation of nitrosomorpholine by a significant order.

The data of the BASF patent (EP 545 208) that NMMs with primary and secondary amines below 0.05% yield a NMMO solution with a very low nitrosamine content during oxidation were not confirmed by our experiments.

NMM behaves differently than trialkylamines when oxidized with hydrogen peroxide. Even without the addition of chelating agents, a high yield of NMMO on hydrogen peroxide is obtained. The reaction proceeds at a sufficient rate even without catalysts such as CO ₂ or sodium bicarbonate, although patents for the preparation of surfactant oxides usually also include NMMs in the starting amine list, these processes, which work with a stoichiometric amount of H ₂ O ₂ , are not suitable. , on the preparation of NMMO.

SUMMARY OF THE INVENTION

Process for preparing a NMMO solution with a very low NOMOR content and at the same time a very slight coloration (colorless or only yellowish) by oxidation of NMM with hydrogen peroxide at a temperature of 60 to 75 ° C and a molar H ₂ O ₂ / NMM ratio of 0.5 to 0.9 The invention is characterized in that from 0.01 to 0.05 wt. a hydrogen peroxide stabilizer selected from the group consisting of sodium pyrophosphate, sodium ethylenediaminetetraacetic acid (EDTA) or sodium tin stannate, or a combination thereof, based on the mass of NMM: The concentration refers to the commercial form of the substances including any crystal water.

In the case of the oxidation of fatty tertiary amines, the patent literature explicitly states that chelating agents prevent the decomposition of H ₂ O ₂ and accelerate the oxidation process, but do not affect the nitrosamine content (EP 553 800). Oxidation of NMM proceeds differently: oxidation does not decompose even without H ₂ O ₂ chelating agents and chelating agents do not accelerate oxidation. According to our experimental findings, chelating agents reduce the formation of nitrosamines by an order of magnitude. However, the stabilizers contained in the commercial H ₂ O ₂ solution are not sufficient to suppress the formation of nitrosamines.

The advantage of chelating agents over CO ₂ is that it is easier to handle and, in particular, to better color the product. Since CO ₂ strongly catalyzes oxidation, it is recommended to operate below 40 ° C, which is disadvantageous in terms of heat dissipation.

A stabilizer is added to the present NMM, preferably in the form of an azeotrope with water, and a solution of H ₂ O ₂ , preferably 35%, is added over a period of 2 to 1 hours, and the peroxide is allowed to react for a further 2.5 to 5 hours. Unreacted NMM is separated by vacuum rectification as an azeotrope with water.

-4GB 284760 B6

In most cases, one or a combination of several stabilizers is added to commercial H2O2 solutions. The concentration of stabilizer in commercial hydrogen peroxide at a concentration of 35 wt. H ₂ O ₂ tends to be 100 to 200 ppm, which is not sufficient to suppress the formation of NOMOR below 100 ppb in the final NMMO solution. Based on the NMM employed, it is only 0.005 to 0.01 wt.% At a molar ratio of H ₂ O ₂ / NMM = 0.6. stabilizer.

The peroxide stabilizer is added to the present NMM, but can also be added to the H ₂ O ₂ solution, which gives less effect. Therefore, the stabilizer contained in the commercial peroxide also reduces the formation of NOMOR relatively little.

Of the three stabilizers, sodium ethylenediaminetetraacetate has the best properties, which not only radically reduces the formation of NOMOR, but also provides an almost colorless NMMO solution. When using a tin (IV) stannate with a concentration according to the invention, the final NMMO solution has a white tin hydroxide opalescence. However, the solution is also colorless. Therefore, it is preferred to use a combination of stabilizers, e.g. % sodium ethylenediaminetetraacetate and 10 wt. sodium stannate.

It has been found that the NOMOR content of the oxide increases with increasing molar H ₂ O ₂ / NMM ratio and therefore it is recommended to work with a ratio of 0.4 to 0.7. This knowledge can also be used when working with the addition of a stabilizer, which makes it possible to reduce the concentration of the stabilizer. However, the effect of the stabilizer on suppressing NOMOR formation is so strong that it allows the oxidation of NMM with a molar ratio of up to 0.9. The higher the molar ratio, the higher the stabilizer concentration must be within the range of the invention.

Examples

Example 1

Four comparative experiments of oxidation of azeotropic NMM-water mixture (73 wt% NMM) with unstabilized 30% hydrogen peroxide and one trial with standardly stabilized 35% peroxide were performed. Solution containing 35 wt. H ₂ O ₂ , was stabilized at the manufacturer by sodium pyrophosphate decahydrate at a concentration of 150 ppm and 3 ppm sodium hexahydroxotinate.

In a 1 L sulfonation flask equipped with a stirrer and placed in a thermostat, 400 g of NMM azeotrope containing 0.01 wt. morpholine. In experiments with individual stabilizers, 0.1 g of stabilizer was added to the azeotrope. At 65 ° C, the H ₂ O ₂ solution was uniformly fed for 3 hours with a molar H ₂ O ₂ / NMM ratio of 0.6.

After the peroxide was introduced, the mixture was stirred at the reaction temperature for 3 hours while the peroxide concentration dropped to about 50 ppm. Unreacted NMM was then distilled off in vacuo using a column of 8 theoretical plates and at the same time the NMMO solution was concentrated to 60 + 1% by weight. The results are summarized in the table.

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No Pok. stabilizer peroxide wt. Content NOMOR ppb NMMO staining 49 none 30% nestab. 292 yellow orange. 50 Na4P ₂ O ₇ .10H ₂ O 30% nestab. 19 Dec yellowish 51 Na ₂ Sn (OH) ₆ 30% nestab. <10 colorless opalescence 52 EDTA 30% nestab. <10 colorless 53 none 35% stabil. 200 yellow

Example 2

The azeotropic NMM-water mixture was oxidized with a commercial stabilized H ₂ O ₂ solution (pyrophosphate + tin stannate) at 65 ° C with a molar ratio of H ₂ O ₂ / NMM = 0.9. 0.04 wt.% Was added to the present azeotrope. sodium ethylenediaminetetraacetate (dihydrate), calculated on NMM. Peroxide was dosed for 3.5 hours, the reaction time was 5 hours. After the unreacted NMM was distilled off, a colorless 60% NMMO solution containing 20 ppb NOMOR was obtained.

Example 3

Azeotrope NMM - water was oxidized at 65 ° C a commercial stabilized 35% H ₂ O ₂ at a molar ratio of H ₂ O ₂ / NMM = 0.6. 0.017 wt.% Was added to the present azeotrope. % EDTA (dihydrate) and 0.006 wt. sodium hexahydroxotinate. The peroxide was dosed for 3 hours and then the reaction mixture was stirred for an additional three hours at the reaction temperature. After the unreacted NMM was distilled off under vacuum, a colorless solution of 60 wt. NMMO containing 10 ppb NOMOR.

Industrial applicability

The invention is applicable to the production of low nitrosomorpholine N-methylmorpholine oxide, which is used for the preparation of cellulose fibers.

Claims (2)

PATENT CLAIMS Process for the preparation of 45 to 70% by weight aqueous solutions of low-nitrosomorpholine-containing N-methylmorpholine oxide to 50 ppb by oxidation of N-methylmorpholine with an aqueous hydrogen peroxide solution at a temperature of 60 to 75 ° C with a molar H ₂ O ₂ / amine ratio of 0.5 to 0.9, characterized in that N-methylmorpholine is treated with hydrogen peroxide, which contains at least one of the three hydrogen peroxide stabilizers consisting of sodium pyrophosphate, sodium ethylenediaminetetraacetate, sodium stannate in a total concentration of 0.01 to 0.05% by weight . calculated on the loaded amine, and the conventional commercial form of added stabilizers, including crystalline water. The process according to claim 1, wherein the hydrogen peroxide is treated with N-methylmorpholine in the form of an azeotrope with water.