Method for depleting 2-methoxyethanol (MOE)

Abstract

A process for the depletion of 2-methoxyethanol (MOE) from a mixture comprising predominantly morpholine (MO) (crude morpholine), wherein crude morpholine is distilled in a distillation column in the presence of an alkali metal compound of the general formula M.sup.+[RO.sup.−] (M.sup.+ is alkali metal cation and R is hydrogen (H), methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl), where MO and a compound of the general formula R—OH are distilled off and an alkali metal methoxyethoxide of the general formula M.sup.+[MeOEtO.sup.−] is obtained in the bottom of the column.

Claims

1. A process for the depletion of 2-methoxyethanol (MOE) from a mixture comprising predominantly morpholine (MO) (crude morpholine), wherein crude morpholine is distilled in a distillation column in the presence of an alkali metal compound of the formula M.sup.+[RO.sup.−] (M.sup.+is alkali metal cation and R is hydrogen (H), methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl), where MO and a compound of the formula R—OH are distilled off and an alkali metal methoxyethoxide of the formula M.sup.+[MeOEtO.sup.−] is obtained in the bottom of the column.

2. The process according to claim 1, wherein the alkali metal compound is used in a 0.1-fold to 5-fold molar amount based, (a) when an alkali metal hydroxide (alkali metal compound in which R is hydrogen (H)) is used, on the MOE (2-methoxyethanol) present in the crude morpholine, (b) when an alkali metal alkoxide (alkali metal compound in which R is not hydrogen (H)) is used, in a batchwise mode of operation, on the MOE (2-methoxyethanol) present in the crude morpholine and optionally water present in the crude morpholine, or in a continuous mode of operation, on the MOE (2-methoxyethanol) present in the crude morpholine.

3. The process according to claim 1, wherein M.sup.+is Li.sup.+, Na.sup.+or K.sup.+.

4. The process according to claim 1, wherein the alkali metal compound is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium propoxide, sodium propoxide, potassium propoxide, lithium isopropoxide, sodium isopropoxide, potassium isopropoxide, lithium n-butoxide, sodium n-butoxide, potassium n-butoxide, lithium isobutoxide, sodium isobutoxide, potassium isobutoxide, lithium sec-butoxide, sodium sec-butoxide, potassium sec-butoxide, lithium tert-butoxide, sodium tert-butoxide, and potassium tert-butoxide.

5. The process according to claim 1, wherein the alkali metal compound is used in the form of a solution in an alcohol of the formula R′—OH, in which R′ is methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl, and R′—OH is likewise distilled off.

6. The process according to claim 5, wherein in the case where an alkali metal alkoxide is used, the radical R′ corresponds to the radical R.

7. The process according to claim 5, wherein the content of the alkali metal compound in the solution is 1% to 50% by weight (based on the total mass of the solution).

8. The process according to claim 5, wherein the alkali metal compound used is sodium methoxide (20% to 40% by weight in methanol) or potassium ethoxide (15% to 35% by weight in ethanol).

9. The process according to claim 1, wherein the crude morpholine is obtained by reaction of diethylene glycol (DEG) with ammonia and subsequent distillative removal of ammonia, water, aminodiglycol (ADG) and DEG from the reaction product.

10. The process according to claim 1, wherein the crude morpholine comprises >85% by weight of morpholine (MO) and 0.1% to 5% by weight of methoxyethanol (MOE).

11. The process according to claim 1, wherein the morpholine (MO) distilled off has a purity of >98.5% by weight and a content of methoxyethanol (MOE) of <0.1% by weight.

12. The process according to claim 1, wherein the top pressure in the distillation column is 0.01 to 12 bar.

13. The process according to claim 1, wherein for a continuous mode of operation crude morpholine and the alkali metal compound are supplied to the distillation column, R—OH is removed overhead and MO is removed via a side draw, and alkali metal methoxyethoxide is discharged via the bottom.

14. The process according to claim 13, wherein the feed for the alkali metal compound and the side draw at which MO is removed are located in the stripping section of the distillation column.

15. The process according to claim 14, wherein the feed for the alkali metal compound is located above the side draw at which MO is removed.

16. The process according to claim 15, wherein the position of the feed for the alkali metal compound in the stripping section of the column is selected such that there is no significant amount of water present there.

Description

EXAMPLES

(1) The APHA color number was determined in accordance with DIN EN 1557.

(2) The water content was determined in accordance with DIN EN 51777 (K. Fischer). GC conditions: 30 m Db-1, temperature program with 60° C. starting temperature, 4° C./min heating rate, 190° C. final temperature.

Example 1 (Distillation of Morpholine (MO) in the Presence of Sodium Methoxide)

(3) Column type: 1.0 m Sulzer DX packing, Diameter 42 mm (A=13.85 cm.sup.2) Number of theoretical plates: 25-30

(4) The reactor was initially charged with 1503 g of crude morpholine (comprising 0.048% by weight of water and 0.4% by weight of MOE) and 32 g of 30% sodium methoxide solution (corresponding to a 1.5-fold molar amount based on MOE and water in the crude morpholine) were added thereto with stirring. The resulting mixture is referred to as feedstock. This was heated to boiling at standard pressure (SP=1.013 bar) and the column was refluxed for 60 minutes. Methanol was removed with a reflux ratio (RR) of 10. After reaching a top temperature of 128° C., the column was switched over to the main run. The two fractions were analyzed by means of gas chromatography (GC).

(5) TABLE-US-00001 TABLE 1 Distillation results for sodium methoxide Feedstock Fraction 1 Fraction 2 Mass/g 1535 107 1276 Pressure (top) SP SP Temperature/° C. 129 129-137 (bottom) Temperature/° C. 65-128 128 (top) Temperature/° C. 20 20 (cooler) APHA color number 10 11 Water 0.00 0.07 0.02 Methanol/ 1.47 19.70 0.05 GC area % 2-Methoxyethanol/ 0.39 0.00 0.00 GC area % 1,2-ethylenedia- 0.00 0.57 0.00 mine/GC area % Morpholine/ 97.51 79.71 99.96 GC area % Morpholine/g 1497 85 1275
Result:

(6) Using sodium methoxide, the methoxyethanol was able to be bound in the bottoms during the entire distillation. After the methanol removal, morpholine having a high purity and low color number (fraction 2) could be distilled. The distillation yield for fraction 2 was 85%.

Example 2 (Distillation of Morpholine (MO) in the Presence of Potassium Ethoxide)

(7) The same column type as in example 1 was used.

(8) A reactor was initially charged with 1683 g of crude morpholine (comprising 0.023% by weight of water and 0.4% by weight of MOE) and 58 g of a 24% potassium ethoxide solution (corresponding to a 1.5-fold molar amount based on MOE and water in the crude morpholine) were added thereto with stirring. The resulting mixture is referred to as feedstock. This was then heated to boiling at standard pressure (SP) and the column was refluxed for 60 minutes. Ethanol was removed with a reflux ratio (RR) of 10 to 15. After reaching a top temperature of 128° C., the column was to the main run. The fractions were analyzed by means of GC.

(9) TABLE-US-00002 TABLE 2 Distillation results for potassium ethoxide Feedstock Fraction 1 Fraction 2 Fraction 3 Mass/g 1741 268 160 1193 Pressure (top) SP SP SP Temperature/° C. 128-129 129 129 (bottom) Temperature/° C. 77-127 127-128 128 (top) Temperature/° C. 20 20 20 (cooler) APHA color number 11 Water 0.00 0.016 Ethanol/ 2.53 17.72 0.77 0.10 GC area % 2-Methoxyethanol/ 0.39 0.00 0.00 0.00 GC area % 1,2-ethylenedia- 0.00 0.00 0.00 0.00 mine/GC area % Morpholine/ 96.29 80.44 98.93 99.85 GC area % Unknown/ 0.00 0.04 0.27 0.04 GC area % Morpholine/g 1677 216 158 1191
Result:

(10) Using potassium ethoxide, the methoxyethanol was able to be bound in the bottoms during the entire distillation. After the ethanol removal, morpholine having a high purity and low color number could be distilled. The distillation yield for fraction 3 was 71%.

Example 3 (Distillation of Morpholine (MO) in the Presence of Sodium Hydroxide)

(11) The same column type as in example 1 was used.

(12) A reactor was initially charged with 1682 g of crude morpholine (comprising 0.4% by weight of MOE and 0.00% by weight of water) and 28.4 g of a 23.3% methanolic NaOH solution (corresponding to a 1.86-fold molar amount based on MOE in the crude morpholine) were added thereto with stirring. The mixture was then heated to boiling at SP and the column was refluxed for 60 minutes. Methanol was removed with an RR of 15. From a top temperature of 128° C., the column was switched over to the main run. The top cooler was operated at a temperature of 75° C. (partial condenser).

(13) TABLE-US-00003 TABLE 3 Distillation results for sodium hydroxide Feedstock Fraction 1 Fraction 2 Fraction 3 Mass/g 1710 185 147 1261 Pressure (top) SP SP SP Temperature/° C. 130 129 129-145 (bottom) Temperature/° C. 114-128 128 128 (top) Temperature/° C. 75 75 75 (cooler) APHA color number 0.04 Water 0.00 0.016 Methanol/ 1.27 13.33 0.51 0.10 GC area % 2-Methoxyethanol/ 0.39 0.00 0.00 0.03 GC area % 1,2-ethylenedia- 0.00 0.00 0.00 0.00 mine/GC area % Morpholine/ 97.95 86.47 99.38 99.83 GC area % Unknown/ 0.00 0.11 0.12 0.00 GC area % Morpholine/g 1675 160 146 1259
Result:

(14) Using NaOH, the methoxyethanol was for the most part able to be bound in the bottoms during the entire distillation. After the methanol removal (fractions 1 and 2), morpholine having a high purity and low color number (fraction 3) could be distilled. The distillation yield for fraction 3 was 75%.

Example 4 (Continuous or Semi-Batchwise Distillation of Morpholine (MO) in the Presence of Sodium Methoxide)

(15) Column type: 1.5 m Sulzer DX packing, Diameter 30 mm Number of theoretical plates: 30-45
Continuous Mode of Operation (Fraction 1):

(16) The reactor was initially charged with 500 g of crude morpholine (comprising 0.02% by weight of water and 0.26% by weight of MOE) and 4.8 g of 30% sodium methoxide solution were added thereto with stirring. The resulting mixture was then heated to boiling at SP and the column was refluxed for 30 minutes. Morpholine was distilled with an RR of 3. At the same time, MOE-containing morpholine and sodium methoxide were metered into the bottom of the distillation. In order to selectively remove methanol, the top cooler was operated as a partial condenser at approx. 80° C. Fraction 1 was condensed, with the predominant portion of the methanol remaining in the gas phase. The methanol was then condensed in a second, downstream condenser. After 26 h, the experiment was stopped. The results show a marked depletion of methoxyethanol in fraction 1.

(17) Semi-Batchwise Mode of Operation (Fractions 2 and 3):

(18) The reactor was initially charged with 730 g of crude morpholine (comprising 0.02% by weight of water and 0.26% by weight of MOE) and 48.5 g of 30% sodium methoxide solution were added thereto with stirring. The resulting mixture was then heated to boiling at SP and the column was refluxed for 30 minutes. Morpholine was distilled with an RR of 3. At the same time, MOE-containing morpholine was metered into the bottom of the distillation. The methanol was removed in exactly the same way as in the continuous mode of operation. The results show a marked depletion of methoxyethanol in fraction 2.

(19) After 8 h, the feed amount of morpholine was increased from 300 to 400 g/h and the purified morpholine was collected as fraction 3. After 9 h, the experiment was ended. An increased content of methoxyethanol can be observed in fraction 3 compared to fractions 1 and 2. This is associated with the fact that no further new sodium methoxide was added, that is to say the sodium methoxide was no longer available in an amount sufficient to quantitatively bind the methoxyethanol in the bottoms. This proves that the binding of the methoxyethanol in the bottoms can be attributed to the presence of the sodium methoxide.

(20) TABLE-US-00004 Feedstock Fraction 1 Fraction 2 Fraction 3 Mass/g 12 805 g 185 147 1261 of crude MO and 128 g of Na methoxide Pressure (top) SP SP SP Temperature/° C. 129-130 129-130 130 (bottom) Temperature/° C. 126 126 126-127 (top) Temperature/° C. 75-80 80 80 Partial condenser Temperature/° C. 20 20 20 (cooler) APHA 5    10 11 10 color number Water 0.020 0.065 0.006 0.002 Methanol/ 0.560 0.492 0.099 0.027 GC area % 2-Methoxyetha- 0.261 0.008 0.003 0.023 nol/GC area % 1,2-ethylenedia- 0.00  0.036 0.018 0.011 mine/GC area % Morpholine/ 98.939  99.453 99.870 99.932 GC area % Morpholine/g 12 669     5444 2534 2884

(21) The values given in the “Feedstocks” column relate to the feed stream into the column

(22) The distillation yield for the fractions 1 to 3 was 86%.