CZ118895A3 - Process for preparing n-methylmorpholinoxide with a low content of nitrosomorpholine - Google Patents

Abstract

A method for production of 50 to 70% by weight of N-methylmorpholine-N-oxide with a content of nitrosomorpholine up to 100 ppb through oxidation of N-methylmorpholine by hydrogen peroxide at a temperature from 55 to 75 degrees C and molar ratio of H2O2/N-methylmorpholine equalling 0.5 to 0.9 and reaction time of 5 to 8 hours according to formula I. After distilling off un-reacted N-methylmorpholine from the reaction mixture, a solution with 50 to 70 % by weight of N-methylmorpholine-N-oxide is extracted by a solvent from the group of aromatic hydrocarbons with 6 to 8 carbon atoms, ketones with 4 to 8 carbon atoms or organic acid esters having a total carbon atom number of 4 to 8 at a temperature ranging from 10 to 60 degrees C.<IMAGE>

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 cellulose fibers. A solution containing 50 to 60% by weight of N-methylmorpholine oxide containing up to 300 ppb of nitrosomorpholine is used for this purpose.

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 environmental environment.

BACKGROUND OF THE INVENTION

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

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) directed to the use of cyclic amine oxides as a solvent for macromolecular substances, the preparation of cyclic tertiary amine oxides, among them NMMO, is described. The amine oxidation is carried out with a ratio of H ₂ O ₂ / amine = 0.98. In the example of preparation of NMMO, the peroxide weighing data is wrong, according to which the molar ratio of H ₂ O ₂ / amine would be 0.83, 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. of water is added over a period of 4 to 5 hours with a 35% solution of H ₂ O ₂ 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 drained by azeotropic rectification with benzene and the anhydrous NMMO was>

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The L ' ^{3 was} then poured into acetone to precipitate the NTTMO4 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, where ~ also works with a ratio of θ2 / ^3Π, * ^{η =} 0.98 and a temperature of 67 to 72 θθ. Unlike the Eastman Kodak Co. patent 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 requirements for NMMO quality 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 H 2 O 2 solution must be finely dispersed into the reaction mixture, for example by means of a nozzle. The equimolecular ratio of the reactants is used at a temperature of 69-72 ° C.

According to another patent of the same group of authors (GDR 259 863) up to 90 wt. The NMM was introduced as a 3.5 hour 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 Huls 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 purity of NMM is understandable because NMM, like other tertiary amines, becomes yellow when stored under the influence of 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. The resulting azeotropic mixture was charged with 35% w / w F 2 Cl 2 ^{in a} ratio of? 2 C / amine = 0.82 over two hours. 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 contained 2 ppm H2O2, 0.1 wt. NMM and the acid number is 0.1 mg KOH / g. The solution is yellowish. The cited patent protects the H2O2 / NMM molar ratio = 0.75 to 0.90, ensuring complete peroxide reaction. . ·.

Unreacted NMM by vacuum distillation is easy.

As early as 1967, a process for producing &gt;

trialkylamine oxides, in particular triethylamine oxide, in which _______I.

-o xi d ace - -am i; nu '' peróiai the conductor of catalysis is an alkali bicarbonate and an alkaline polyphosphate. 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% with the theoretical yield in the presence of catalysts.

Of particular importance are the single long carbon chain tertiary amine oxides (especially dimethyllaurylamine) used as surfactants. It has been found that, when oxidizing these amines with peroxide, hydrogen, carbon dioxide has a greater catalytic effect than bicarbonate (US 4,247,480, 1981). The CO2 content should be 0.01 to 2% by weight. calculated on tertiary amine. Simultaneously added peroxide stabilizers such as polyphosphates, ethylenediaminetetraacetic acid (EDTA), stannates, etc.. Works with ratio Η2θ2 / ^{3Π, ί} η ⁼ 1.05 to 1.1, because the fatty amine can not be separated from the solution oxide has completely reacted, and .

French patent 2,632,638 (1988) protects the use of CO2 as a catalyst in the oxidation of tertiary amines with hydrogen peroxide, the first point of the invention being identical to US 4,247,480, which is not disclosed in the prior art. Examples are directed to triethylamine oxide.

In the last era, the quality was. The oxi has a nitrosamine content of between 50 and 10,000 ppb. The oxidation of dimethyllaurylamine produces carcenogenic dimethylnitrosamine and furthermore J

N-nitroso-N-methyllaurylamine. In the preparation of NMMO mainly N-nitrosomorpholine (NOMOR) is produced.

First preparation procedure. Low nitrosamine amine oxides are described in EP307184 (8.9.1987) of Ethyl Corporation.

According to the patent, tertiary amines are oxidized with hydrogen peroxide in the presence of CO2 at a temperature below 45 ° C. While in the presence of CO 2 at 65 ° C and a 10% excess of H 2 O 2, a 96 ppb dimethylnitrosamine product was obtained, below 40 the nitrosamine content was below the detection limit. 3 to 7 wt. CO2 per amine weight. It can be argued that already U.S. Pat. No. 4,247,480 describes the preparation of oxides in the presence of CO2 at 40 to 80 ° C.

Next

The presence of a synergistic H2O2 ratio temperature is the concentration patent of Ethyl Corporation (EP 320 694, protects the preparation of tertiary amine oxides in

CO2 and ascorbic acids, both having a reduced nitrosamine content. / Amine = 1.0 to 1.5 is preferred, 1.1 to 1.2 is preferred. Reaction to 100 ° C, preferably 45 to 75 ° C,

CO2 0.05 to 5% calculated on the weight of the amine, and the content of ascorbic acid is the same. Three comparative experiments are presented.

dimethylnitrosamine methyldodecylnitrosamine only CO2 96 detects.

only AK 37

216 both of them. 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 CO2-free are obtained from dimethyllaurylamine a 30% oxide solution containing about 700 ppb of both nitrosamines, in the presence of titanium plate containing a solution of -310 ppb nitrosamines, in the presence of CO2 of 96 ppb and .

The last of a series of patents of Ethyl Corporation (EP 426 084, October 30, 1989) describes the preparation of amine oxides in the presence of CO2 diluted with at least an equal volume of inert gas. With a content of 60 wt. CO2 and more in the gas above the reaction mixture gave an orange product, using a gas containing 20 to 40% by weight. The carbon dioxide solution was only yellowish.

Albright and Vilson Limited protects (GB 2,252,320,

Stabilization of amine oxide solutions against formation of nitrosamines during production and storage by addition of 2.5 to 20 wt.

bicarbonate or carbonate, calculated on the weight of the amine.

Carbon dioxide does not protect against the formation of nitrosamines perfectly, especially when storing solutions, to add chelating agents to hydrogen. In the examples it is given

In oxidation, it is recommended - to prevent decomposition - peroxide content of NO groups. When oxidizing a tertiary amine of the trade mark Empigen AB at a ratio of H 2 O 2 / amine · = 0.9 at -40 θΟ, ku addition of 0? % sodium EDTA was obtained by the following% wt. NaHCO ₃ to amine 0 - ~ 0.71 1.8 3.6 7.15 10 "__pp.bu NO - ai - ₄ - ₆ ip - - - - 4015 ^^^^ 37 ^^ 67 ^^ 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% by weight and the phosphonate from 0.005 to 5% by weight. by 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. When combined 0.1 wt. % phosphonate and 1 wt. NaHCO 3 to amine and a stoichiometric H 2 O 2 / amine ratio yielded a solution of dimethyl lauryl amine containing 34 ppb nitroso groups.

In its patent (EP 545,208, Dec. 6, 1991), BASF states that the nitrosamine content of an 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. primary and secondary amines. Preferably, unwanted amines are removed by addition of reagents such as. they are acyl halides, acid anhydrides, sulfonyl halides, etc. The BASF patent alone describes the preparation of low nitrosamine-containing NMMOs. In the comparative experiment, methyl morpholine containing 0.3% by weight of primary and secondary amines was oxidized. H2O2 solution with H2O2 / NMM molar ratio = 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 ppb 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 moles per mole of NMM and the mixture was allowed to react for 1 hour.

The essence of the invention

The process for producing NMMO with a low NOMOR content by oxidation of NMM with hydrogen peroxide at 55-75 ° C with a H2O2 / NMM molar ratio of 0.5 to 0.9 at a reaction time of 5-8 hours according to the invention is characterized in that unreacted NMM is distilled off. a solution of 50 to 70 wt. The NMMO extracts with a solvent that groups of aromatic hydrocarbons, C4 to C8 ketones or organic acid esters with a total carbon number of 4 to 8 at a temperature of 10 to 60 ° C.

According to the invention, the molar ratio H2O2 / NMM is 0.5 to 0.9. It has been found that, with increasing ratio, the NOMOR content of the reaction mixture increases in the stated molar ratio range from 150 to 500 ppb NOMOR. In the same direction, the extraction intensity is increasing. The level of nitrosamines extraction from the NMMO solution is given by the number of extraction steps and the solvent / oxide solution ratio. It is therefore preferable to work with a lower H2O2 / NMM ratio.

A suitable solvent must not only extract NOMOR well, but must also dissolve poorly in the oxide solution and, conversely, the oxide must be poorly soluble in the solvent. When oxidizing NMM with hydrogen peroxide according to Cs. AO 218 714 removes unreacted NMM by extraction with acetone, whereupon part of the water is said to be transferred to acetone. The authors of the cited invention did not monitor the content of NOMOR, according to our measurements, a significant part of NOMOR was removed by acetone extraction. However, acetone is unsuitable as an extractant. NMMO is quite soluble in acetone and solubility is further enhanced by water and NMM contained therein. According to the example cited in the patent specification, 10 to 13 wt. prepared by NMMO. This dissolved NMMO is heavily contaminated with nitrosamine and is unusable. Of the ketones, methylisobutyl ketone has good properties, which is relatively inexpensive and dissolves only 0.17% by weight when extracted. NMMO calculated on solvent.

Aromatic hydrocarbons also have suitable extraction properties.

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Benzene is not recommended for its toxicity, toluene and xylenes are suitable.

According to the invention, suitable extraction agents are carboxylic acid esters. The lower esters too dissolve NMMO, similar to acetone. Butyl acetate is suitable, in which 0.4 to 0.5 wt. NMMO, according to the concentration of the extracted NMMO solution. / Alcohols such as butanol are too soluble in NMMO solution and are therefore not suitable.

The less preferred ethereality of the diethyl ether was distilled off under vacuum only with deep temperature condensation, which is technically disadvantageous. Methyl tert-butyl ether already has a relatively low partition coefficient (eg 6.5 times lower than methyl isobutyl ketone) and yet its boiling point of 55 ° C is still too low for vacuum distillation. Higher ethers have an even worse partition coefficient.

Chlorinated hydrocarbons have good extraction properties but are not suitable due to their toxicity.

Based on our measurements, methylisobutylketone, toluene and butyl acetate are the optimum extracting agents in terms of partition coefficient, phase-solubility, toxicity and cost.

Extraction should only be carried out after distilling off unreacted NMM from the oxide solution. The presence of NMM would increase the solubility of NMMO in the extraction agent and, moreover, NMM is difficult to separate from the listed extraction agents. '

The extraction can be carried out by all known methods: single-step extraction with a larger amount of solvent, repeated extraction with smaller portions of solvent, and continuous countercurrent extraction, which is the most economical.

A small amount of the solvent contained in the extracted NMMO solution is removed by vacuum distillation at the boiling point of the 60-80 ° C oxide solution. A solution of 60% by weight boils at atmospheric pressure. NMMO solution at 115 ° C, when there is a risk of oxide decomposition.

Example 1.

Azeotropic NMM-water mixture containing 73%. , amine. was oxidized with 35% H2O2 at 65 ° C. The peroxide was dosed evenly for 3 hours and then reacted for a further 4 hours. The H2O2 / NMM ratio was 0.7.

The unreacted NMM was distilled off from the reaction mixture on a column of 8 theoretical plates at a final pressure of 13 kPa and a liquid boiling point of 69 ° C. The obtained 60% NMMO solution was yellow and contained 250 ppb NOMOR.

Various extractants were tested using the obtained NMMO solution. 100 ml of the oxide solution was extracted with 20 ml of solvent at 25 ° C. The NOMOR content of the extract was determined by GLC and the partition coefficient for NOMOR between the two liquid phases was calculated from the mass balance. The dissolved NMMO content was determined by evaporation of the solvent at 3 kPa at 100 ° C. The content of dissolved solvent in the oxide layer was determined by GLC so that the solvent was extracted into another solvent and only this solution was chromatographed. Extraction results

measurements are summarized in the table. Extracting agent Rel. div. NMMO content Reagent content coefficient in the extract in NMMO % wt. % wt.

toluene 1 0.04 0.48 methylisobutylketone '3,2 0.17 0.69 butyl acetate 1.14 0.49 0.38 methyl tert-butyl ether 0.4 0,16- 0.47

Example 2.

The NMMO solution was prepared by oxidizing an azeotropic mixture of NMM wt. H2O2 solution at 60 [deg.] C. with a molar ratio

H 2 O 2 / NMM = 0.5. The peroxide solution was dosed for 3 hours and the mixture was

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allowed to react for peroxide for another 4 hours. ^Mixtures Z'realccnl was distilled off under reduced pressure, the unreacted portion of NMM, and water as the rest to obtain a solution of 61% wt. NMMO containing

275 ppb NOMOR. -------- ------- 110 ml of the oxide solution were extracted three times with 10 ml of toluene each. The oxide solution then contained 47 ppb NOMOR. A small amount of dissolved toluene was removed from the NMMO solution by vacuum rectification on a column with an efficiency of 8 theoretical plates. The oxide loss to toluene was 0.02 wt. calculated for processingExample 3.

In the same manner as in Example 2, the NMMO solution was extracted with butyl acetate. NOMOR content of the extracted oxide; was 40 ppb, the loss of oxide to the solvent was 0.3%.

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Example 4.

50 ml of methyl isobutyl ketone was injected into the continuous 20 mm diameter extraction column packed with a 1 m metal coil layer and 150 ml of 55 wt. NMMO containing 600 ppb NOMOR per hour.

30 ppb of NOMOR was detected in the extracted NMMO solution that was discharged from the bottom of the extractor. From a NMMO solution, 10% by volume was distilled off on a small column at a pressure of 13 kPa to remove all methyl isobutyl ketone.

The methylisobutyl ketone used for the extraction was regenerated on a column with an efficiency of 8 theoretical plates at 20 kPa. The distillation residue remained at 2% per ketone used. NMMO losses in the distillation residue p re d s t u v u 0.1% per. Treated oxide - - ··

Industrial applicability

The invention can be used for the preparation of N-methylmorpholine oxide which is used for the preparation of cellulose fibers.

Claims (4)

Patent claims 1. A process for the preparation of aqueous solutions of N-methylmorpholine oxide with low Obah nitrosomorfolinu oxidation of N-methylmorpholine aqueous hydrogen peroxide solution at 55 to 75 ° C with a molar ratio 2®2 ^ ^ ^or ^ ^{n =} θ * 5 0.9 at a reaction time of 5 to 8 hours, characterized in that, after distilling off unreacted N-methylmorpholine by rectification under reduced pressure, a solution of 50 to 70% by weight is obtained. The N-methylmorpholine oxide is extracted with a solvent selected from the group of aromatic hydrocarbons, ketones C4 to C8, or organic acid esters having a total carbon number of 4 to 8 at a temperature of 10 to 60 ° C. 2. A process according to claim 1, wherein the N-methylmorpholine oxide solution is extracted in batches in two to four stages, 5 to 30% by weight being used in each stage. of solvent calculated on the volume of the oxide solution. 3. Process according to claim 1, characterized in that toluene, methyl isobutyl ketone or butyl acetate are preferably used as the solvent. 4. Process according to Claims 1 and 3, characterized in that the extraction is carried out continuously and countercurrently.