PROCESS FOR MAKING A SUBSTANTIALLY NITROSAMINE-FREE, SUBSTANTIALLY PEROXIDE-FREE, SUBSTANTIALLY COLORLESS AMINE OXIDE

Abstract

A process for making a substantially nitrosamine-free, substantially peroxide-free, substantially colorless amine oxide solution comprises reacting a tertiary amine capable of forming an amine oxide with a less than stoichiometric amount of aqueous hydrogen peroxide in an aqueous medium while imposing on the aqueous medium a vapor space having a carbon dioxide partial pressure p(CO.sub.2) of less than 0.75 bar absolute. The process allows for obtaining amine oxides which are substantially nitrosamine-free, substantially peroxide-free, and substantially colorless. This unique combination of desirable features has not been achieved so far in a process only comprising oxidation and distillation.

Claims

1.-17. (canceled)

18. A process for making a substantially nitrosamine-free, substantially peroxide-free, substantially colorless amine oxide solution, said process comprising reacting a tertiary amine capable of forming an amine oxide with a less than stoichiometric amount of aqueous hydrogen peroxide in an aqueous medium while imposing on the aqueous medium a vapor space having a carbon dioxide partial pressure p(CO.sub.2) of less than 0.75 bar absolute, wherein the aqueous hydrogen peroxide is metered into an aqueous solution of the tertiary amine at a hydrogen peroxide dosage rate r(H.sub.2O.sub.2) in the range of from 0.035 to less than 1 mol per 1 mol of tertiary amine and hour, and the carbon dioxide partial pressure p(CO.sub.2) in bar absolute is given by $\left(C{O}_2\right)=r\left(H_2{O}_2\right)/z$ wherein z is a variable in the range of from 1 to 4 h.sup.1 bar.sup.1.

19. The process of claim 18, wherein a sweep of a diluent gas is maintained in the vapor space above the aqueous medium and carbon dioxide is bubbled through the aqueous medium.

20. The process of claim 19, wherein the diluent gas is an inert gas.

21. The process of claim 18, wherein the concentration of tertiary amine in the aqueous medium is in the range of from 40 to 95 vol.-%.

22. The process of claim 18, wherein the process comprises adding 10 to 70 wt.-% aqueous hydrogen peroxide to the aqueous medium.

23. The process of claim 18, wherein the total amount of hydrogen peroxide used is 50 to 99 mol-% per mol of tertiary amine.

24. The process of claim 18, which is conducted at a temperature of 20 to 90 C.

25. The process of claim 18, wherein the tertiary amine forms a minimum boiling azeotrope with water at a pressure in the range of from 0.01 to 5 bar absolute.

26. The process of claim 25, wherein the tertiary amine is N-methylmorpholine.

27. The process of claim 25, comprising subjecting the tertiary amine oxide solution to distillation to remove water and/or water-azeotrope of unreacted tertiary amine.

28. The process of claim 27, wherein the distillation is carried out at a pressure in the range of from 50 to 300 mbar.

29. The process of claim 27, wherein the removed water-azeotrope of unreacted tertiary amine is recycled to the reaction with hydrogen peroxide.

30. The process of claim 18, wherein the amine oxide has a nitrosamine content of less than 50 ppb, relative to the weight of amine oxide.

31. The process of claim 18, wherein a 50 wt.-% aqueous solution of the amine oxide has an extinction of less than 2%/cm at 450 nm.

32. The process of claim 31, wherein a 50 wt.-% aqueous solution of the amine oxide has an APHA color number of less than 100.

Description

EXAMPLES

[0050] The present invention can be further explained and illustrated on the basis of the following examples.

Example 1

[0051] An aqueous solution of N-methylmorpholine (NMM, 63 wt.-%; 1.01 kg, 1.0 eq.) was placed in a 1.6 L double-walled glass reactor. Said reactor was equipped with a crossbar stirrer, a reflux condenser, a thermometer, a frit-fitted glass tube connected to a CO.sub.2 (3.0) line, a gas inlet (w/o tube) connected to a N.sub.2 (technical) line and a H.sub.2O.sub.2 dosage line (Teflon tube connected to a diaphragm metering pump). H.sub.2O.sub.2 was fed from a glass reservoir. The reaction was carried out at 1.0 bar absolute.

[0052] The aqueous solution was heated to a temperature of 50 C. under a constant stream of nitrogen (1.5 L/h). After the temperature of 50 C. was reached, dosage of CO.sub.2 was started at a stream of 0.15 L/h. From the ratio of the streams and the total pressure, a CO.sub.2 partial pressure of 91 mbar can be calculated.

[0053] After 60 min, dosage of H.sub.2O.sub.2 was started (50 wt.-% aqueous H.sub.2O.sub.2, 395 g, 0.9 eq.) at a stream of H.sub.2O.sub.2 of 0.93 mL/min (i.e. 0.15 mol/(mol.Math.h); z=1.65 h.sup.1 bar.sup.1). During dosage of H.sub.2O.sub.2, the temperature was maintained at 50 C. and dosage of CO.sub.2 and N.sub.2 was continued.

[0054] After the dosage of H.sub.2O.sub.2 was finished, the concentration of H.sub.2O.sub.2 in the reaction mixture was determined by cerimetric titration. Stirring at 50 C. and dosage of CO.sub.2 and N.sub.2 was maintained until the concentration of residual H.sub.2O.sub.2 in the reaction mixture was less than 50 ppm (about 1 h).

[0055] Subsequently, dosage of CO.sub.2 was stopped, and the reaction mixture was allowed to cool to room temperature. The reflux condenser was exchanged by a distillation apparatus (condenser and vacuum pump) and water and NMM were distilled off at a sump temperature of 50 C. (2 fractions, first fraction, collected at about 150 mbar: 133 g, second fraction, collected at about 80 mbar: 188 g).

[0056] Water (308 g) was added to the distillation residue giving 1328 g of a 49.6 wt.-% aqueous solution of N-methylmorpholine N-oxide (NMMO) having an APHA color number of 22, an extinction at 450 nm of 1.2%, and a N-nitroso morpholine content of less than 20 ppb.

Example 2

[0057] An aqueous solution of N-methylmorpholine (NMM, 63 wt.-%; 1.01 kg, 1.0 eq.) was placed in a 1.6 L double-walled glass reactor. Said reactor was equipped with a crossbar stirrer, a reflux condenser, a thermometer, a frit-fitted glass tube connected to a CO.sub.2 (3.0) line, a gas inlet (w/o tube) connected to a N.sub.2 (technical) line and a H.sub.2O.sub.2 dosage line (Teflon tube connected to a diaphragm metering pump). H.sub.2O.sub.2 was fed from a glass reservoir. The reaction was carried out at 1.0 bar absolute.

[0058] The aqueous solution was heated to a temperature of 50 C. under a constant stream of nitrogen (1.5 L/h). After the temperature of 50 C. was reached, dosage of CO.sub.2 was started at a stream of 0.50 L/h. From the ratio of the streams and the total pressure, a CO.sub.2 partial pressure of 250 mbar can be calculated.

[0059] After 60 min, dosage of H.sub.2O.sub.2 was started (50 wt.-% aqueous H.sub.2O.sub.2, 395 g, 0.9 eq.) at a stream of H.sub.2O.sub.2 of 0.93 mL/min (i.e. 0.15 mol/(mol.Math.h); z=0.6 h.sup.1 bar1). During dosage of H.sub.2O.sub.2, the temperature was maintained at 50 C. and dosage of CO.sub.2 and N.sub.2 was continued.

[0060] After the dosage of H.sub.2O.sub.2 was finished, the concentration of H.sub.2O.sub.2 in the reaction mixture was determined by cerimetric titration. Stirring at 50 C. and dosage of CO.sub.2 and N.sub.2 was maintained until the concentration of residual H.sub.2O.sub.2 in the reaction mixture was less than 50 ppm (about 30 min).

[0061] Subsequently, dosage of CO.sub.2 was stopped, and the reaction mixture was allowed to cool to room temperature. The reflux condenser was exchanged by a distillation apparatus (condenser and vacuum pump) and water and NMM were distilled off at a sump temperature of 50 C. (2 fractions, first fraction, collected at about 150 mbar: 145 g, second fraction, collected at about 80 mbar: 162 g).

[0062] Water (312 g) was added to the distillation residue giving 1318 g of a 50.1 wt.-% aqueous solution of N-methylmorpholine N-oxide (NMMO) having an APHA color number of 296, an extinction at 450 nm of 4.3%, and a N-nitroso morpholine content of less than 20 ppb.

Example 3

[0063] An aqueous solution of N-methylmorpholine (NMM, 63 wt.-%; 1.01 kg, 1.0 eq.) was placed in a 1.6 L double-walled glass reactor. Said reactor was equipped with a crossbar stirrer, a reflux condenser, a thermometer, a frit-fitted glass tube connected to a CO.sub.2 (3.0) line, a gas inlet (w/o tube) connected to a N.sub.2 (technical) line and a H.sub.2O.sub.2 dosage line (Teflon tube connected to a diaphragm metering pump). H.sub.2O.sub.2 was fed from a glass reservoir. The reaction was carried out at 1.0 bar absolute.

[0064] The aqueous solution was heated to a temperature of 50 C. under a constant stream of nitrogen (1.5 L/h). After the temperature of 50 C. was reached, dosage of CO.sub.2 was started at a stream of 0.05 L/h. From the ratio of the streams and the total pressure, a CO.sub.2 partial pressure of 32 mbar can be calculated.

[0065] After 60 min, dosage of H.sub.2O.sub.2 was started (50 wt.-% aqueous H.sub.2O.sub.2, 395 g, 0.9 eq.) at a stream of H.sub.2O.sub.2 of 0.93 mL/min (i.e. 0.15 mol/(mol.Math.h), z=4.69 h.sup.1 bar.sup.1). During dosage of H.sub.2O.sub.2, the temperature was maintained at 50 C. and dosage of CO.sub.2 and N.sub.2 was continued.

[0066] 6 h after the dosage of H.sub.2O.sub.2 was finished, dosage of CO.sub.2 was stopped, and the reaction mixture was allowed to cool to room temperature. The reflux condenser was exchanged by a distillation apparatus (condenser and vacuum pump) and water and NMM were distilled off at a sump temperature of 50 C. (2 fractions, first fraction, collected at about 150 mbar: 143 g, second fraction, collected at about 80 mbar: 170 g).

[0067] Water (322 g) was added to the distillation residue giving 1329 g of a 49.6 wt.-% aqueous solution of N-methylmorpholine N-oxide (NMMO) having an APHA color number of 10, an extinction at 450 nm of 0.5%, a H.sub.2O.sub.2 content of 1200 ppm and a N-nitroso morpholine content of 180 ppb.

Comparative Example 1

[0068] N-Methylmorpholine (NMM, 101.1 g, 1.0 eq.) and water (37.5 mL; yielding a mixture of 73 wt.-% NMM and 27 wt.-% water) were placed in a 250 mL double-walled glass reactor. Said reactor was equipped with a crossbar stirrer, a reflux condenser, a thermometer, a frit-fitted glass tube connected to a CO.sub.2 (3.0) line and a H.sub.2O.sub.2 dosage line (Teflon tube connected to a diaphragm metering pump). The head space above the aqueous phase inside the reactor (including the condenser) was about 500 mL H.sub.2O.sub.2 was fed from a glass reservoir. The reaction was carried out at 1.0 bar absolute.

[0069] The aqueous solution was heated to a temperature of 50 C. under a constant stream of CO.sub.2 (1.0 L/h) for 2 hours without stirring. In total, 2 L of CO.sub.2 were fed during that time which corresponds to about 4 times the headspace volume of the reactor and thus was sufficient to essentially replace the previous atmosphere by pure CO.sub.2.

[0070] Then, dosage of H.sub.2O.sub.2 was started (50 wt.-% aqueous H.sub.2O.sub.2, 61.2 g, 0.9 eq.) at a stream of H.sub.2O.sub.2 of 0.21 mL/min (i.e. 0.225 mol/(mol.Math.h); z=0.23 h.sup.1 bar.sup.1). During dosage of H.sub.2O.sub.2, the temperature was maintained at 50 C. and dosage of CO.sub.2 was continued at a stream of 0.1 L/h.

[0071] After the dosage of H.sub.2O.sub.2 was finished, the concentration of H.sub.2O.sub.2 in the reaction mixture was determined by cerimetric titration. Stirring at 50 C. and dosage of CO.sub.2 were maintained until the concentration of H.sub.2O.sub.2 was below 50 ppm (about 10 min).

[0072] Subsequently, dosage of CO.sub.2 was stopped, and the reaction mixture was allowed to cool to room temperature. The reflux condenser was exchanged by a distillation apparatus (condenser and vacuum pump) and water and NMM were distilled off at a sump temperature of 50 C. (2 fractions, first fraction, collected at about 150 mbar: 21.9 g, second fraction, collected at about 80 mbar: 25.7 g).

[0073] Water (59.2 g) was added to the distillation residue giving 208.4 g of a 50.1 wt.-% aqueous solution of N-methylmorpholine N-oxide (NMMO) having an APHA color number of 297, an extinction at 450 nm of 4.9%, and a N-nitroso morpholine content of less than 20 ppb.

Comparative Example 2

[0074] N-Methylmorpholine (NMM, 101.1 g, 1.0 eq.) and water (37.5 mL; yielding a mixture of 73 wt.-% NMM and 27 wt.-% water) were placed in a 250 ml double-walled glass reactor. Said reactor was equipped with a crossbar stirrer, a reflux condenser, a thermometer, a frit-fitted glass tube connected to a CO.sub.2 (3.0) line and a H.sub.2O.sub.2 dosage line (Teflon tube connected to a diaphragm metering pump). H.sub.2O.sub.2 was fed from a glass reservoir. The reaction was carried out at 1.0 bar absolute.

[0075] The aqueous solution was heated to a temperature of 50 C. under a constant stream of CO.sub.2 (0.082 L/h) and nitrogen (0.353 L/h) for 2 hours with stirring. From the ratio of the streams and the total pressure, a CO.sub.2 partial pressure of 188 mbar can be calculated

[0076] Then, dosage of H.sub.2O.sub.2 was started (50 wt.-% aqueous H.sub.2O.sub.2, 71.4 g, 1.05 eq.) at a stream of H.sub.2O.sub.2 of 0.34 mL/min (i.e. 0.362 mol/(mol.Math.h); z=1.92 h.sup.1 bar1). During dosage of H.sub.2O.sub.2, the temperature was maintained at 50 C. and dosage of CO.sub.2 and N.sub.2 was continued.

[0077] After the dosage of H.sub.2O.sub.2 was finished, stirring at 50 C. and dosage of CO.sub.2 and N.sub.2 were maintained for 16 hours. Subsequently, dosage of CO.sub.2 was stopped, and the reaction mixture was allowed to cool to room temperature.

[0078] 24.0 g of water were added yielding 233.3 g of a 50.1 wt.-% aqueous solution of N-methylmorpholine N-oxide (NMMO) having an APHA color number of 33, an extinction at 450 nm of 0.6%/cm, and a N-nitroso morpholine content of less than 20 ppb. The mixture contained 0.716 wt.-% of hydrogen peroxide.

[0079] To an aliquot of this mixture (about 100 g) manganese dioxide (0.5 g) was added which resulted in vigorous gas formation. As gas formation had ceased, the mixture was essentially hydrogen peroxide free (as determined by cerimetric titration) but APHA color number was 236. Upon standing for 4 days at room temperature, APHA color number further increased, eventually exceeding the scale (>1000) and extension was 6.9%/cm. To another aliquot of this mixture (about 100 g) platinum on charcoal (2.0 g, 57 wt.-% water, Pt-content: 5.0 wt.-% of solids) was added which resulted in vigorous gas formation. As gas formation had ceased, the mixture was essentially hydrogen peroxide free (as determined by cerimetric titration) and APHA color number was 78. Upon standing for 4 days at room temperature, APHA color number increased to 527 and extension was 3.9%/cm.

Example 4

[0080] Triethylamine (101.3 g, 1.0 eq.) and water (10.0 mL; giving a mixture of 91 wt.-% NMM and 9 wt.-% water) were placed in a 250 mL double-walled glass reactor. Said reactor was equipped with a crossbar stirrer, a reflux condenser, a thermometer, a frit-fitted glass tube connected to a CO.sub.2 (3.0) line and a H.sub.2O.sub.2 dosage line (Teflon tube connected to a diaphragm metering pump). H.sub.2O.sub.2 was fed from a glass reservoir. The reaction was carried out at 1.0 bar absolute.

[0081] The aqueous mixture was heated to a temperature of 50 C. under a constant stream of nitrogen (0.70 L/h). After the temperature of 50 C. was reached, dosage of CO.sub.2 was started at a stream of 0.164 L/h. From the ratio of the streams and the total pressure, a CO.sub.2 partial pressure of 190 mbar can be calculated.

[0082] After 60 min, dosage of H.sub.2O.sub.2 was started (50 wt.-% aqueous H.sub.2O.sub.2, 61.2 g, 0.9 eq.) at a stream of H.sub.2O.sub.2 of 0.286 mL/min (i.e. 0.30 mol/(mol.Math.h); z=1.57 h.sup.1 bar1). During dosage of H.sub.2O.sub.2, the temperature was maintained at 50 C. and dosage of CO.sub.2 and N.sub.2 was continued.

[0083] After the dosage of H.sub.2O.sub.2 was finished, the concentration of H.sub.2O.sub.2 in the reaction mixture was determined by cerimetric titration. Stirring at 50 C. and dosage of CO.sub.2 were maintained until the concentration of H.sub.2O.sub.2 was below 50 ppm (about 180 min).

[0084] Subsequently, dosage of CO.sub.2 was stopped, and the reaction mixture was allowed to cool to room temperature. The reflux condenser was exchanged by a distillation apparatus (condenser and vacuum pump) and water and triethylamine were distilled off at a sump temperature of 50 C. (1 fraction, collected at about 100 mbar: 35.3 g).

[0085] Water (47.6 g) was added to the distillation residue giving 210.1 g of a 49.7 wt.-% aqueous solution of triethylamine N-oxide having an APHA color number of 29, an extinction at 450 nm of 0.8%, and a N-nitroso diethylamine content of less than 20 ppb.