Catalytic Process For Synthesizing N,N-Dimethyl Glucamine From N Methyl Glucamine

Abstract

The invention relates to a process for synthesizing an aqueous N,N-dimethyl glucamine solution, characterized in that a formaldehyde solution is metered into an N-methyl glucamine solution in the presence of a metal catalyst at hydrogen pressure.

Claims

1. A process for preparing an aqueous N,N-dimethylglucamine solution, wherein an aqueous solution of formaldehyde is metered into an aqueous solution of N-methylglucamine in the presence of a metal catalyst at a hydrogen pressure of 10-200 bar, in which subsequent to a hydrogenation with formaldehyde metering at 35-65° C., a further, after-hydrogenation step is added without formaldehyde metering at 70−110° C.

2. The process as claimed in claim 1, wherein the metal catalyst is Raney nickel.

3. The process as claimed in claim 1, in which the molar ratio of N-methylglucamine to formaldehyde is 1:1 to 1:1.5.

4. The process as claimed in claim 1, wherein the process is carried out at a hydrogen pressure of 20-180 bar.

5. The process as claimed in claim 1, in which the reaction temperature T is from 40-50° C.

6. The process as claimed in claim 1, wherein the Hazen color number of the resulting 50 wt % solution of N,N-dimethylglucamine in water is less than 800.

7. The process as claimed in claim 1, wherein the hydrogenation catalyst is used for more than 5 reaction batches.

8. The process as claimed in claim 1, wherein reaction takes place in a stirred reactor or loop reactor.

9. The process as claimed in claim 1, wherein the residual N-methylglucamine content is <2 wt %.

10. The process as claimed in claim 1, wherein the residual formaldehyde content is <0.1 wt %.

11. The process as claimed in claim 1, wherein subsequent to the hydrogenation a distillation step for removing methanol is appended.

12. The process as claimed in claim 1, in which the molar ratio of N-methylglucamine to formaldehyde is 1:1 to 1:1.2.

13. The process as claimed in claim 1, wherein the process is carried out at a hydrogen pressure of 70-120 bar.

14. The process as claimed in claim 1, wherein the Hazen color number of the resulting 50 wt % solution of N,N-dimethylglucamine in water is less than 400.

15. The process as claimed in claim 1, wherein the residual N-methylglucamine content is <1 wt %.

16. The process as claimed in claim 1, in which the molar ratio of N-methylglucamine to formaldehyde is 1:1.01 to 1:1.08.

17. The process as claimed in claim 1, wherein the Hazen color number of the resulting 50 wt % solution of N,N-dimethylglucamine in water is less than 230.

18. The process as claimed in claim 1, wherein the residual N-methylglucamine content is <0.25 wt %.

Description

EXAMPLES

[0049]

TABLE-US-00001 Hydro- Gardner Hazen genation color at color at Hydro- temp- 50% 50% Form- 1-stage/ genation erature active active NMG Ni aldehyde 2-stage pressure [° C.] content content [%] [ppm] [%] 1 (comp.) 2-stage 30 100 9.4 n.m. 0.91 35 0.03 2 (comp.) 2-stage 100 130 16.9 n.m. 6.0 29 0.01 1 1-stage 28 60 2.5 350 0.06 2 0.02 2 1-stage, 28 60 1.1 200 0.08 2 0.02 repeat 3 1-stage 100 60 0.6 105 0.10 2 0.02 4 1-stage, 100 60 0.6 115 0.05 3 0.01 repeat 3 (comp.) 1-stage 3 60 9 n.m. 0.17 62 0.03 4 (comp.) 1-stage 3 60 8 n.m. 0.9 45 0.03 5 (comp.) 1-stage 85 40 0.5 81 0.13 0.6 0.01 n.m. = not measurable

[0050] Gardner color number and Hazen color number:

[0051] The clear, aqueous dimethylglucamine solutions without any gas bubbles were introduced into 10 mm rectangular cuvettes. The color numbers were measured at room temperature in a LICO 690 colorimeter from Hach Lange.

[0052] Total amine number by acid-base titration:

[0053] The samples, weighed out accurately on an analytical balance, were dissolved in glacial acetic acid and titrated with 0.1 molar perchloric acid in glacial acetic acid, using a titroprocessor from Metrohm.

[0054] Solids content (105° C./2 hours):

[0055] The samples, weighed out precisely, were dried to constant weight in a drying cabinet at 105° C. for two hours by evaporation of the water, and after drying were precisely weighed again.

[0056] Water (Karl Fischer titration):

[0057] The water content of the precisely weighed-out samples was determined by the Karl Fischer titration method using Karl Fischer solvent and Karl Fischer titrant.

[0058] N-methylglucamine, N,N-dimethylglucamine and sorbitol (GC):

[0059] The samples were completely acetylated with a very large excess of acetic anhydride/pyridine at 80° C. The N-methylglucamine, N,N-dimethylglucamine and sorbitol contents were determined by gas chromatography on a 60 m Agilent HP-5 column, using decanol as internal standard and using an FID detector.

[0060] Methanol (GC):

[0061] The methanol content was determined by a gas-chromatographic method for volatile substances, using isobutanol as internal standard and using a TCD detector.

[0062] Formaldehyde (free and chemically bonded):

[0063] To release the chemically bonded formaldehyde, the samples were heated with aqueous sulfuric acid in the presence of 2,4-dinitrophenylhydrazine. Through the reaction of the formaldehyde with 2,4-dinitrophenylhydrazine, 2,4-dinitrophenylhydrazone was formed. The 2,4-dinitrophenylhydrazone content was subsequently determined by HPLC liquid chromatography. The free formaldehyde and chemically bonded formaldehyde content was captured as a sum total.

[0064] Nitrosamines (total NNO):

[0065] The samples were analyzed for total nitrosamine content in a method based on the ATNC (apparent total nitrosamine content) method. With chemical denitrosation in an acidic medium, nitrogen monoxide was released from the nitrosamines and was subsequently determined quantitatively using a very sensitive detector specific for nitrogen monoxide. Calculation and indication of content were made in the form of the NNO content (>N—N═O with molar mass 44 g/mol).

[0066] Nickel (ICP-OES):

[0067] The nickel content of the samples was determined by ICP-OES (inductively coupled plasma optical emission spectrometry) in a method based on DIN EN ISO 11885.

[0068] Formic acid (free and chemically bonded, IC):

[0069] The samples were pretreated with heating in an aqueous-alkaline medium in order by hydrolysis to liberate the formic acid, bonded chemically in the form of ester and amide. The amount of formic acid or salts thereof already present before the alkaline hydrolysis, and of formic acid and/or salts thereof liberated only by the alkaline hydrolysis, was determined as a sum total by ion chromatography (IC).

Comparative Example 1: Example 2 from EP-0614881

[0070] In a 2 liter round-bottom glass flask equipped with stirrer, thermometer and electrical heating under atmospheric pressure, 1500 g of a 43%, aqueous N-methylglucamine solution were produced by diluting a 60% N-methylglucamine solution (Gardner color number 1.7, Hazen color number 263). The 43%, aqueous N-methylglucamine solution was heated to 35° C. with stirring. From a dropping funnel, with further stirring, a total of 288.7 g of a 36.5%, aqueous formaldehyde solution were added dropwise over the course of half an hour at 35° C. The reaction to give the N-methylglucamine-formaldehyde adduct was slightly exothermic. The Gardner color number of the pale-yellow, clear, aqueous N-methylglucamine-formaldehyde adduct solution was 0.8 and the Hazen color number was 151.

[0071] Immediately after the end of the dropwise addition, a portion of the aqueous N-methylglucamine-formaldehyde adduct solution amounting to 1300 g was taken from the 2 liter round-bottom glass flask and was introduced at room temperature into a 2 liter stirred autoclave.

[0072] The 2 liter stirred autoclave was equipped with stirrer, heating, cooling, supply lines for hydrogen and nitrogen, temperature measurement, pressure measurement, and safety valve. 20.4 g of Raney nickel were introduced under nitrogen into the 2 liter stirred autoclave.

[0073] The 2 liter stirred autoclave was closed. Three times, 10 bar of nitrogen were injected, with depressurization each time. Thereafter, three times, 10 bar of hydrogen were injected, with depressurization each time. After the leak test and depressurization, the stirring speed was set to 800 rpm. With further stirring, heating took place to 100° C. and then hydrogen was supplied. The exothermic hydrogenation took place, with renewed injection of the hydrogen consumed, at 800 rpm, 100° C. and a hydrogen pressure of 30 bar. After the end of the evident absorption of hydrogen, stirring was continued for two hours at 100° C. and a hydrogen pressure of 30 bar. This was followed by cooling to 30° C., depressurization, purging with nitrogen, and the emptying of the 2 liter stirred autoclave. The Raney nickel catalyst was separated off by a pressure filtration under nitrogen. The liquid filtrate was dark brown and had a Gardner color number of 8.

[0074] This dark brown filtrate was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 51% and DI water content of 49% by addition of DI water with thorough mixing at 60° C. This product solution was subjected to analysis. Apart from the losses involved in emptying the autoclave and working up the solution, the yield of dissolved N,N-dimethylglucamine in the DMG 50 was virtually quantitative.

[0075] The product obtained was characterized as follows:

TABLE-US-00002 Appearance at 20° C.: clear, liquid, dark brown Gardner color number: 9.4 Hazen color number: not measurable, since too dark Total amine number (titration): 133 mg KOH/g Solids content (105° C./2 hours): 51.4% (m/m) Water (Karl-Fischer titration): 49% (m/m) N-Methylglucamine (GC): 0.91% (m/m) N,N-Dimethylglucamine (GC): 44.5% (m/m) Sorbitol (GC): 0.6% (m/m) Methanol (GC): <0.1% (m/m) Formaldehyde (free and chemically 0.026% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 35 μg/g Formic acid (free and chemically 0.70% (m/m) bonded)

Comparative Example 2: As Per Example 3 from EP-0614881

[0076] In a 2 liter round-bottom glass flask equipped with stirrer, thermometer and electrical heating under atmospheric pressure, 1500 g of a 43%, aqueous N-methylglucamine solution were produced by diluting a 60%, technical N-methylglucamine solution (Gardner color number 1.7, Hazen color number 263) with DI water.

[0077] The 43%, aqueous N-methylglucamine solution was heated to 35° C. with stirring. From a dropping funnel, with further stirring, a total of 288.7 g of a 36.5%, aqueous formaldehyde solution were added dropwise over the course of half an hour at 35° C. The reaction to give the N-methylglucamine-formaldehyde adduct was slightly exothermic. Thereafter the clear, pale yellow reaction mixture was additionally stirred further for an hour at 35° C. The Gardner color number of this pale-yellow, aqueous N-methylglucamine-formaldehyde adduct solution was 0.8 and the Hazen color number was 162.

[0078] Thereafter, a portion of the aqueous N-methylglucamine-formaldehyde adduct solution amounting to 1300 g was taken from the 2 liter round-bottom glass flask and was introduced at room temperature into a 2 liter stirred autoclave.

[0079] The 2 liter stirred autoclave was equipped with stirrer, heating, cooling, supply lines for hydrogen and nitrogen, temperature measurement, pressure measurement, and safety valve. 20.4 g of Raney nickel were introduced under nitrogen into the 2 liter stirred autoclave.

[0080] The 2 liter stirred autoclave was closed. Three times, 10 bar of nitrogen were injected, with depressurization each time. Thereafter, three times, 10 bar of hydrogen were injected, with depressurization each time. After the leak test and depressurization, the stirring speed was set to 800 rpm. With further stirring, heating took place to 125° C. and then hydrogen was supplied. The exothermic hydrogenation took place, with renewed injection of the hydrogen consumed, at 800 rpm, 130° C. and a hydrogen pressure of 100 bar. After the end of the evident absorption of hydrogen, stirring was continued for two hours at 130° C. and a hydrogen pressure of 100 bar. This was followed by cooling to 30° C., depressurization, purging with nitrogen, and the emptying of the 2 liter stirred autoclave. The Raney nickel catalyst was separated off by a pressure filtration under nitrogen. The liquid filtrate was deeply dark brown and had a Gardner color number of 13.4.

[0081] This deeply dark brown filtrate was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 51% and DI water content of 49% by addition of DI water with thorough mixing at 60° C. The resulting product solution was subjected to analysis. Apart from the losses involved in emptying the autoclave and working up the solution, the yield of dissolved N,N-dimethylglucamine in the DMG 50 was virtually quantitative.

[0082] The product obtained was characterized as follows:

TABLE-US-00003 Appearance at 20° C.: clear, liquid, deeply dark brown Gardner color number: 16.9 Hazen color number: not measurable, since too dark Total amine number (titration): 133 mg KOH/g Solids content (105° C./2 hours): 52.6% (m/m) Water (Karl-Fischer titration): 49% (m/m) N-Methylglucamine (GC): 6.0% (m/m) N,N-Dimethylglucamine (GC): 35.9??% (m/m) Sorbitol (GC): 0.6% (m/m) Methanol (GC): <0.1% (m/m) Formaldehyde (free and chemically 0.012% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 29 μg/g Formic acid (free and chemically 0.90% (m/m) bonded)

Example 1

[0083] A 10 liter stirred autoclave equipped with temperature measurement, pressure measurement, safety valve, gas-introduction stirrer and immersed tube was charged under a countercurrent of nitrogen with 4.95 kg of 57.3% N-methylglucamine solution in water at 60° C., Gardner color number: 0.9, Hazen color number: 158, and 200 g of water-moist Raney nickel (containing 40% water). Rinsing took place with 200 g of DI water. The 10 liter stirred autoclave was closed. Three times, 10 bar of nitrogen were injected, with depressurization each time. Thereafter, three times, 10 bar of hydrogen were injected, with depressurization each time. After the leak test, the stirring speed was set to 1100 rpm, the internal temperature to 60° C. and the hydrogen pressure to 28 bar. Over the course of 4 hours and 10 minutes, 1.245 kg of aqueous formaldehyde solution (36.8% formaldehyde dissolved in water with methanol) were metered continuously, using a pump, into the 10 liter stirred autoclave. The molar ratio of N-methylglucamine to the total formaldehyde after the end of formaldehyde metering was 1.00:1.05. The stirring speed was held at 1100 rpm and the internal temperature at 59-64° C. The hydrogen consumed was replaced by supplying fresh hydrogen and in this way the hydrogen pressure in the 10 liter stirred autoclave was held at 25-28 bar. After the end of absorption of hydrogen, stirring was continued for 3 hours at 60° C. and 28 bar, followed by heating to 90° C. and stirring for a further 3 hours at 90° C. and 28 bar. After that, cooling took place to 30° C. and the stirrer was switched off. For an hour, the Raney nickel settled. The major part of the crude, aqueous N,N-dimethylglucamine was slowly pressed out of the 10 liter stirred autoclave, via an immersed tube reaching not quite to the base, and was separated from small fractions of the suspended Raney nickel by means of pressure filtration. The major part of the Raney nickel remained, with a small residue of aqueous N,N-dimethylglucamine, beneath the immersed tube in the 10 liter stirred autoclave, for the next batch.

[0084] The filtered, aqueous N,N-dimethylglucamine was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 50% and DI water content of 50% by addition of DI water with thorough mixing at 60° C. Apart from the amount remaining under the immersed tube in the 10 liter stirred autoclave and the samples taken, the yield of dissolved N,N-dimethylglucamine was virtually quantitative.

[0085] The product obtained was characterized as follows:

TABLE-US-00004 Appearance clear, liquid, yellow Gardner color number: 2.5 Hazen color number: 350 Total amine number (titration): 129 mg KOH/g Solids content (105° C./2 hours): 50.0% (m/m) Water (Karl-Fischer titration): 50% (m/m) N-Methylglucamine (GC): 0.06% (m/m) N,N-Dimethylglucamine (GC): 43.5% (m/m) Sorbitol (GC): 1.0% (m/m) Methanol (GC): <0.01% (m/m) Formaldehyde (free and chemically 0.015% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 2 μg/g Formic acid (free and chemically 0.024% (m/m) bonded) (ion chromatography after alkaline hydrolysis, IC)

Example 2

[0086] The 10 liter stirred autoclave with aqueous N,N-dimethylglucamine and used Raney nickel beneath the immersed tube from the previous batch (example 1) was charged under a countercurrent of nitrogen with 4.95 kg of liquid, 57.3% N-methylglucamine solution in water at 60° C. (Gardner color number: 0.9, Hazen color number: 158) and 30 g of fresh, water-moist Raney nickel (containing 40% water). Rinsing was carried out with 200 g of DI water. The 10 liter stirred autoclave was closed. Three times, 10 bar of nitrogen were injected, with depressurization each time. Thereafter, three times, 10 bar of hydrogen were injected, with depressurization each time. After the leak test, the stirring speed was set to 1100 rpm, the internal temperature to 60° C. and the hydrogen pressure to 28 bar. Over the course of 3 hours and 50 minutes, 1.244 kg of aqueous formaldehyde (36.8% formaldehyde dissolved in water with methanol) were metered continuously, using a pump, into the 10 liter stirred autoclave. The molar ratio of N-methylglucamine to the total formaldehyde after the end of the formaldehyde metering was 1.00:1.05. The stirring speed was held at 1100 rpm and the internal temperature at 55-64° C. The hydrogen consumed was replaced by a supply of fresh hydrogen and in this way the hydrogen pressure in the 10 liter stirred autoclave was held at 25-28 bar. The continuous formation of the N-methylglucamine/formaldehyde adduct and the continuous catalytic hydrogenation of this product to form N,N-dimethylglucamine took place simultaneously. After the end of absorption of hydrogen, stirring was continued for 3 hours at 60° C. and 28 bar, followed by heating to 90° C. and stirring for a further 3 hours at 90° C. and 28 bar. This was followed by cooling to 30° C., and the stirrer was switched off. The Raney nickel settled for an hour. Via an immersed tube reaching not quite to the base, the major part of the crude, aqueous N,N-dimethylglucamine was pressed out slowly from the 10 liter stirred autoclave and separated from small fractions of the suspended Raney nickel by means of pressure filtration. The major part of the Raney nickel remained, with a small residue of aqueous N,N-dimethylglucamine, beneath the immersed tube in the 10 liter stirred autoclave, for the next batch.

[0087] The filtered, aqueous N,N-dimethylglucamine was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 50% and DI water content of 50% by addition of DI water with thorough mixing at 60° C. Apart from the samples taken, the yield of dissolved N,N-dimethylglucamine was virtually quantitative.

[0088] The product obtained was characterized as follows:

TABLE-US-00005 Appearance clear, liquid, yellow Gardner color number: 1.1 Hazen color number: 200 Total amine number (titration): 139 mg KOH/g Solids content (105° C./2 hours): 50.1% (m/m) Water (Karl-Fischer titration): 49.8% (m/m) N-Methylglucamine (GC)*: 0.08% (m/m) N,N-Dimethylglucamine (GC): 46.7% (m/m) Sorbitol (GC): 1.1% (m/m) Methanol (GC): <0.01% (m/m) Formaldehyde (free and chemically 0.021% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 2 μg/g Formic acid (free and chemically bonded) (ion chromatography after alkaline hydrolysis, IC)

Example 3

[0089] A 10 liter stirred autoclave equipped with temperature measurement, pressure measurement, safety valve, gas-introduction stirrer and immersed tube was charged under a countercurrent of nitrogen with 4.97 kg of liquid, 57.3% N-methylglucamine solution in water at 60° C. (Gardner color number: 0.9, Hazen color number: 158) and with 200 g of water-moist Raney nickel (containing 40% water). Rinsing was carried out with 200 g of DI water. The 10 liter stirred autoclave was closed. Three times, 10 bar of nitrogen were injected, with depressurization each time. Thereafter, three times, 10 bar of hydrogen were injected, with depressurization each time. After the leak test, the stirring speed was set to 1100 rpm, the internal temperature to 60° C. and the hydrogen pressure to 90 bar. Over the course of 3 hours and 15 minutes, 1.249 kg of aqueous formaldehyde (36.8% formaldehyde dissolved in water with methanol) were metered continuously, using a pump, into the 10 liter stirred autoclave. The molar ratio of N-methylglucamine to the total formaldehyde after the end of formaldehyde metering was 1.00:1.05. The stirring speed was held at 1100 rpm and the internal temperature at 55-61° C. The hydrogen consumed was replaced by a supply of fresh hydrogen, and in this way the hydrogen pressure in the 10 liter stirred autoclave was held at 97-101 bar. The continuous formation of the N-methylglucamine/formaldehyde adduct and the continuous catalytic hydrogenation of said product to form N,N-dimethylglucamine took place simultaneously. The conversion was monitored by samples taken and analysis of said samples by GC, NMR, and titration for determining the amine number. After the end of absorption of hydrogen, stirring was continued for 3 hours at 60° C. and 100 bar, followed by heating to 90° C. and stirring for a further 3 hours at 90° C. and 105 bar. After that, cooling took place to 30° C. and the stirrer was switched off. The Raney nickel settled for an hour. Via an immersed tube reaching not quite to the base, the major part of the crude aqueous N,N-dimethylglucamine was pressed out slowly from the 10 liter stirred autoclave and was separated from small fractions of the suspended Raney nickel by means of pressure filtration. The major part of the Raney nickel remained, with a small residue of aqueous N,N-dimethylglucamine, beneath the immersed tube in the 10 liter stirred autoclave, for the next batch.

[0090] The filtered, aqueous N,N-dimethylglucamine was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 50% and DI water content of 50% by addition of DI water with thorough mixing at 60° C. Apart from the amount remaining under the immersed tube in the 10 liter stirred autoclave and the samples taken, the yield of dissolved N,N-dimethylglucamine was virtually quantitative.

[0091] The product obtained was characterized as follows:

TABLE-US-00006 Appearance clear, liquid, pale yellow Gardner color number: 0.6 Hazen color number: 105 Total amine number (titration): 133.5 mg KOH/g Solids content (105° C./2 hours): 50.2 Water (Karl-Fischer titration): 49.6% (m/m) N-Methylglucamine (GC) 0.10% (m/m) N,N-Dimethylglucamine (GC): 43.4% (m/m) Sorbitol (GC): 1.1% (m/m) Methanol (GC): <0.01% (m/m) Formaldehyde (free and chemically 0.024% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 2 μg/g Formic acid (free and chemically 0.015% (m/m), depending on bonded) (ion chromatography after the NMG grade alkaline hydrolysis, IC)

Example 4

[0092] The 10 liter stirred autoclave with aqueous N,N-dimethylglucamine and used Raney nickel beneath the immersed tube from the previous batch (example 3) was charged under a countercurrent of nitrogen with 4.98 kg of liquid, 57.3% N-methylglucamine solution in water at 60° C. (Gardner color number: 0.9, Hazen color number: 158) and 30 g of fresh, water-moist Raney nickel (containing 40% water). Rinsing was carried out with 200 g of DI water. The 10 liter stirred autoclave was closed. 10 bar of nitrogen was injected three times, with depressurization after each injection. After that, 10 bar of hydrogen was injected three times, with depressurization after each injection. Following the leak test, the stirring speed was set to 1100 rpm, the internal temperature to 60° C., and the hydrogen pressure to 90 bar. Over the course of 3 hours and 50 minutes, 1.252 kg of aqueous formaldehyde (36.8% formaldehyde dissolved in water with methanol) were metered continuously, using a pump, into the 10 liter stirred autoclave. The molar ratio of N-methylglucamine to the total formaldehyde after the end of the formaldehyde metering was 1.00:1.05. The stirring speed was held at 1100 rpm and the internal temperature at 57-62° C. The hydrogen consumed was replaced by a supply of fresh hydrogen and in this way the hydrogen pressure in the 10 liter stirred autoclave was held at 96-99 bar. The continuous formation of the N-methylglucamine/formaldehyde adduct and the continuous catalytic hydrogenation of this product to form N,N-dimethylglucamine took place simultaneously. By taking samples and analyzing these samples by GC, NMR and titration for determining the amine number, the conversion was monitored. After the end of absorption of hydrogen, stirring was continued for 3 hours at 60° C. and 100 bar, followed by heating to 90° C. and stirring for a further 3 hours at 90° C. and 108 bar. This was followed by cooling to 30° C., and the stirrer was switched off. The Raney nickel settled for an hour. Via an immersed tube reaching not quite to the base, the major part of the crude, aqueous N,N-dimethylglucamine was pressed out slowly from the 10 liter stirred autoclave and separated from small fractions of the suspended Raney nickel by means of pressure filtration. The major part of the Raney nickel remained, with a small residue of aqueous N,N-dimethylglucamine, beneath the immersed tube in the 10 liter stirred autoclave, for the next batch.

[0093] The filtered, aqueous N,N-dimethylglucamine was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 50% and DI water content of 50% by addition of DI water with thorough mixing at 60° C. Apart from the samples taken, the yield of dissolved N,N-dimethylglucamine was virtually quantitative.

[0094] The product obtained was characterized as follows:

TABLE-US-00007 Appearance: clear, liquid, pale-yellow Gardner color number: 0.6 Hazen color number: 115 Total amine number (titration): 132 mg KOH/g Solids content (105° C./2 hours): 49.9% Water (Karl-Fischer titration): 50.3% (m/m) N-Methylglucamine (GC)*: 0.05% (m/m) N,N-Dimethylglucamine (GC): 45.0% (m/m) Sorbitol (GC): 1.0% (m/m) Methanol (GC): 0.01% (m/m) Formaldehyde (free and chemically 0.012% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg, depending on the NMG grade Nickel (ICP-OES): 2 μg/g, depending on the NMG grade Formic acid (free and chemically 0.024% (m/m), depending on bonded) (ion chromatography after the NMG grade alkaline hydrolysis, IC)

Comparative Example 3 (Low Hydrogen Pressure)

[0095] A 10 liter stirred autoclave equipped with temperature measurement, pressure measurement, safety valve, gas-introduction stirrer and immersed tube was charged under a countercurrent of nitrogen with 5.024 kg of liquid, 57.3% N-methylglucamine solution in water at 60° C. (Gardner color number: 0.9, Hazen color number: 158) and 200 g of water-moist Raney nickel (containing 40% water). Rinsing was carried out with 200 g of DI water. The 10 liter stirred autoclave was closed. 10 bar of nitrogen was injected three times, with depressurization after each injection. After that, 10 bar of hydrogen was injected three times, with depressurization after each injection. Following the leak test, the stirring speed was set to 1100 rpm, the internal temperature to 60° C., and the hydrogen pressure to 3 bar absolute. Over the course of 2 hours and 45 minutes, 1.263 kg of aqueous formaldehyde (36.8% formaldehyde dissolved in water with methanol) were metered continuously, using a pump, into the 10 liter stirred autoclave. The molar ratio of N-methylglucamine to the total formaldehyde after the end of the formaldehyde metering was 1.00:1.05. The stirring speed was held at 1100 rpm and the internal temperature at 54-63° C. The hydrogen consumed was replaced by a supply of fresh hydrogen and in this way the hydrogen pressure in the 10 liter stirred autoclave was held at 2.9-3.2 bar absolute. The continuous formation of the N-methylglucamine/formaldehyde adduct and the continuous catalytic hydrogenation of this product to form N,N-dimethylglucamine took place simultaneously. The conversion was monitored by taking samples and analyzing these samples by GC, NMR and titration for determining the amine number. After the end of absorption of hydrogen, stirring was continued for 3 hours at 60° C. and 3.5 bar absolute, followed by heating to 90° C. and stirring for a further 3 hours at 90° C. and 3.9 bar absolute. This was followed by cooling to 30° C., and the stirrer was switched off. The Raney nickel settled for an hour. Via an immersed tube reaching not quite to the base, the major part of the crude, aqueous N,N-dimethylglucamine was pressed out slowly from the 10 liter stirred autoclave and separated from small fractions of the suspended Raney nickel by means of pressure filtration. The major part of the Raney nickel remained, with a small residue of aqueous N,N-dimethylglucamine, beneath the immersed tube in the 10 liter stirred autoclave, for the next batch.

[0096] The filtered, aqueous N,N-dimethylglucamine was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 50% and DI water content of 50% by addition of DI water with thorough mixing at 60° C. Apart from the amount remaining beneath the immersed tube in the 10 liter stirred autoclave and the samples taken, the yield of dissolved N,N-dimethylglucamine was virtually quantitative.

[0097] The product obtained was characterized as follows:

TABLE-US-00008 Appearance: clear, liquid, brown Gardner color number: 9 Hazen color number: >1000 Total amine number (titration): 3.54 meq/g Solids content (105° C./2 hours): 50.3 Water (Karl-Fischer titration): 49.8% (m/m) N-Methylglucamine (GC): 0.17% (m/m) N,N-Dimethylglucamine (GC): 44.3% (m/m) Sorbitol (GC): 0.8% (m/m) Methanol (GC): <0.01% (m/m) Formaldehyde (free and chemically 0.029% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 62 μg/g Formic acid (free and chemically 0.15% (m/m) bonded) (ion chromatography after alkaline hydrolysis, IC)

Comparative Example 4 (Low Hydrogen Pressure)

[0098] The 10 liter stirred autoclave with aqueous N,N-dimethylglucamine and used Raney nickel beneath the immersed tube from the preceding batch (example 5) was charged under a countercurrent of nitrogen with 5.026 kg of liquid, 57.3% N-methylglucamine solution in water at 60° C. (Gardner color number: 0.9, Hazen color number: 158) and 30 g of fresh, water-moist Raney nickel (containing 40% water). Rinsing was carried out with 200 g of DI water. The 10 liter stirred autoclave was closed. 10 bar of nitrogen was injected three times, with depressurization after each injection. After that, 10 bar of hydrogen was injected three times, with depressurization after each injection. Following the leak test, the stirring speed was set to 1100 rpm, the internal temperature to 60° C., and the hydrogen pressure to 3 bar absolute. Over the course of 3 hours and 30 minutes, 1.264 kg of aqueous formaldehyde (36.8% formaldehyde dissolved in water with methanol) were metered continuously, using a pump, into the 10 liter stirred autoclave. The molar ratio of N-methylglucamine to the total formaldehyde after the end of the formaldehyde metering was 1.00:1.05. The stirring speed was held at 1100 rpm and the internal temperature at 56-63° C. The hydrogen consumed was replaced by a supply of fresh hydrogen and in this way the hydrogen pressure in the 10 liter stirred autoclave was held at 3.5-3.9 bar absolute. The continuous formation of the N-methylglucamine/formaldehyde adduct and the continuous catalytic hydrogenation of this product to form N,N-dimethylglucamine took place simultaneously. The conversion was monitored by taking samples and analyzing these samples by GC, NMR and titration for determining the amine number. After the end of absorption of hydrogen, stirring was continued for 3 hours at 60° C. and 3.9 bar absolute, followed by heating to 90° C. and stirring for a further 3 hours at 90° C. and 3.8 bar absolute. This was followed by cooling to 30° C., and the stirrer was switched off. The Raney nickel settled for an hour. Via an immersed tube reaching not quite to the base, the major part of the crude, aqueous N,N-dimethylglucamine was pressed out slowly from the 10 liter stirred autoclave and separated from small fractions of the suspended Raney nickel by means of pressure filtration. The major part of the Raney nickel remained, with a small residue of aqueous N,N-dimethylglucamine, beneath the immersed tube in the 10 liter stirred autoclave, for the next batch.

[0099] The filtered, aqueous N,N-dimethylglucamine was subjected to initial distillation in a rotary evaporator at 60° C. under a pressure of 20 mbar. The distillate contained primarily water, a little methanol, and traces of other low boilers. The viscous N,N-dimethylglucamine having undergone initial distillation was adjusted to an active ingredient content of 50% and DI water content of 50% by addition of DI water with thorough mixing at 60° C. Apart from the samples taken, the yield of dissolved N,N-dimethylglucamine was virtually quantitative.

[0100] The product obtained was characterized as follows:

TABLE-US-00009 Appearance clear, liquid, brown Gardner color number: 8 Hazen color number: >1000 Total amine number (titration): 3.53 meq/g Solids content (105° C./2 hours): 50.5% Water (Karl-Fischer titration): 49.8% (m/m) N-Methylglucamine (GC): 0.9% (m/m) N,N-Dimethylglucamine (GC): 42.1% (m/m) Sorbitol (GC): 0.8% (m/m) Methanol (GC): <0.01% (m/m) Formaldehyde (free and chemically 0.033% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 45 μg/g Formic acid (free and chemically 0.13% (m/m) bonded) (ion chromatography after alkaline hydrolysis, IC)

Example 5

[0101] A nitrogen-inertized 50 liter stirred autoclave, equipped with temperature measurement, pressure measurement, safety valve, gas-introduction stirrer and immersed tube, was charged with 1.9 kg of water-moist Raney nickel (containing 40% water). The nitrogen atmosphere was then replaced by a hydrogen atmosphere. Subsequently 20.0 kg of 40.0% N-methylglucamine solution in water at 40° C. (Gardner color number: 1.4, Hazen color number: 202) were metered into the reactor. Following the leak test, the reactor stirrer was taken into operation, the internal temperature was adjusted to 40° C. and the hydrogen pressure to 85 bar. Over the course of 3 hours, 3.49 kg of aqueous formaldehyde solution (36.9% formaldehyde dissolved in water with max. 1.5% methanol) were metered continuously, using a pump, into the 50 liter stirrer autoclave. The molar ratio of N-methylglucamine to the total formaldehyde after the end of formaldehyde metering was 1.05. The stirring speed was held at 490 rpm and the internal temperature at 39-43° C. The hydrogen consumed was replaced by a supply of fresh hydrogen, and in this way the hydrogen pressure in the 50 liter stirred autoclave was held at 80-85 bar. After the end of hydrogen absorption, the after-reaction began. For this reaction, heating took place for 1 hour from 40° C. and 85 bar with stirring to 90° C., after which stirring was continued at 90° C. for 1, with cooling from 90° C. to 40° C. in 1 hour. After the end of the after-reaction, cooling took place to 30° C. and the stirrer was switched off. The Raney nickel settled for an hour. This was followed by a pressure filtration at 4 bar.

[0102] The filtered, aqueous N,N-dimethylglucamine was subjected to initial distillation in a batch process at 90° C. under a pressure of 600 mbar until the strength of the DMG solution was 50% (DMG-50). The distillate contained primarily water, a little methanol, and traces of other low boilers. Apart from the samples taken, the yield of dissolved N,N-dimethylglucamine was virtually quantitative.

[0103] The product obtained was characterized as follows:

TABLE-US-00010 Appearance clear, liquid, pale-yellow Gardner color number: 0.5 Hazen color number: 81 Total amine number (titration): 132 mg KOH/g Solids content (105° C./2 hours): 50.2% Water (Karl-Fischer titration): 50.0% (m/m) N-Methylglucamine (GC) 0.13% (m/m) N,N-Dimethylglucamine (GC): 45.3% (m/m) Sorbitol (GC): 0.7% (m/m) Methanol (GC): <0.01% (m/m) Formaldehyde (free and chemically 0.005% (m/m) bonded, LC): Nitrosamines (total NNO): <50 μg/kg Nickel (ICP-OES): 0.6 μg/g Formic acid (free and chemically 0.04% (m/m) bonded) (ion chromatography after alkaline hydrolysis, IC)

[0104] The influence of the hydrogenation pressure on the color number of the resulting product is evident from the inventive and comparative examples. A product with acceptable Hazen color number is obtained only in the pressure range from 10 to 200 bar hydrogen pressure.