PROCESS FOR PREPARING METAL ALKOXIDES BY TRANSALCOHOLISATION

Abstract

A process for preparing metal alkoxides by transalcoholisation, comprising: feeding a lower metal alkoxide and a higher alcohol into a reactive distillation column; removing a solution of a higher metal alkoxide in the higher alcohol from the bottom of the column or from a recycle stream taken from the bottom of the column; and removing a gaseous lower alcohol from the top of the column, at least partially condensing the gaseous lower alcohol, and recirculating a part of the condensate to the top of the column; wherein an auxiliary alcohol is provided in the reactive distillation column, the boiling point of the auxiliary alcohol being between the boiling point of the lower alcohol and the boiling point of the higher alcohol at the pressure prevailing in the reactive distillation column. The process allows for high conversion of a lower metal alkoxide to a higher metal alkoxide while limiting the formation of solid deposits in the column, while having low energy requirements.

Claims

1.-15. (canceled)

16. A process for preparing metal alkoxides by transalcoholisation, comprising: feeding a lower metal alkoxide and a higher alcohol into a reactive distillation column; removing a solution of a higher metal alkoxide in the higher alcohol from the bottom of the column or from a recycle stream taken from the bottom of the column; and removing a gaseous lower alcohol from the top of the column, at least partially condensing the gaseous lower alcohol, and recirculating a part of the condensate to the top of the column; wherein an auxiliary alcohol is provided in the reactive distillation column, the boiling point of the auxiliary alcohol being between the boiling point of the lower alcohol and the boiling point of the higher alcohol at the pressure prevailing in the reactive distillation column.

17. The process according to claim 16, wherein the lower alkoxide is fed into the reactive distillation column via a side feed.

18. The process according to claim 16, wherein the higher alcohol is fed into the bottom of the column and/or the recycle stream taken from the bottom of the column.

19. The process according to claim 16, wherein the solution of the higher metal alkoxide comprises at most 1% by weight of the lower alcohol, relative to the total weight of the solution of the higher metal alkoxide.

20. The process according to claim 16, wherein the higher metal alkoxide solution comprises 3 to 90% by weight of the higher metal alkoxide, relative to the total weight of the higher metal alkoxide solution.

21. The process according to claim 16, wherein the column comprises a forced circulation reboiler and the higher alcohol is fed into a stream supplied to the forced circulation reboiler in liquid form.

22. The process according to claim 16, wherein the condensate of the gaseous lower alcohol comprises at most 1% by weight of the higher alcohol, relative to the total weight of the condensate.

23. The process according to claim 16, wherein the lower metal alkoxide is fed into the column as a solution in the lower alcohol and the solution comprises 20 to 40% by weight of the lower metal alkoxide, relative to the total weight of the solution of the lower metal alkoxide.

24. The process according to claim 16, wherein the lower metal alkoxide is an alkali metal alkoxide.

25. The process according to claim 24, wherein the lower metal alkoxide is a sodium alkoxide or a potassium alkoxide.

26. The process according to claim 16, wherein the higher alcohol is selected from 3-methyl-3-methoxybutanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol, 3-methyl-3-hexanol, and 3,7-dimethyl-3-octanol.

27. The process according to claim 16, wherein the boiling point of the auxiliary alcohol is at least 10 C. above the boiling point of the lower alcohol at the pressure prevailing in the reactive distillation column.

28. The process according to claim 16, wherein the boiling point of the auxiliary alcohol is at least 10 C. below the boiling point of the higher alcohol at the pressure prevailing in the reactive distillation column.

29. The process according to claim 16, wherein the auxiliary alcohol is selected from 1-methoxy-2-propanol, 2-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, tert-butanol, in particular 2-butanol, 1-methoxy-2-propanol, and 3-methyl-2-butanol.

30. The process according to claim 16, wherein the higher metal alkoxide is liquid at a temperature of 20 C. and a pressure of 1 bar absolute.

Description

[0092] The invention is further illustrated by the enclosed FIGURE and the following examples.

[0093] FIG. 1 shows a plant suitable for the production of metal alkoxides by the process of the invention.

[0094] According to FIG. 1, the plant comprises a reactive distillation column 101, in which an auxiliary alcohol is provided. A solution of a lower metal alkoxide is fed into column 101 via line 102. A higher alcohol is fed to the bottom of column 101 via line 103, reboiler 110 and line 111. The auxiliary alcohol is typically provided prior to start-up of column 101 via a line located between lines 102 and 111 (not shown in FIG. 1), and auxiliary alcohol is continuously fed to column 101 via said line in the course of the reaction to maintain an effective concentration of auxiliary alcohol in column 101.

[0095] At the top of column 101, a gaseous lower alcohol is removed via line 104 and condensed in condenser 105. A first stream of the condensed lower alcohol is removed from the process via line 106, while a second stream of the condensed lower alcohol is returned to the top of column 101 via line 107.

[0096] A solution of a higher metal alkoxide in the higher alcohol is removed from the bottom of the column. A first stream of the solution of the higher metal alkoxide is removed from the process via line 108, while a second stream of the solution of the higher metal alkoxide is returned to the bottom of the column via line 109 and reboiler 110 together with the higher alcohol from line 103 via line 111.

[0097] Examples and Methods

[0098] Experiments were carried out on the production of sodium tetrahydrolinaloolate by transalcoholisation from sodium methoxide and tetrahydrolinalool (THL), using 2-butanol, 1-methoxy-2-propanol and 3-methyl-2-butanol as auxiliary alcohols.

[0099] Methods

[0100] A. Determination of Higher Alcohol and Auxiliary Alcohol in the Top Condensate

[0101] A sample of the top condensate was taken, 1,4-dioxane was added as internal standard and the sample was analyzed for its THL and auxiliary alcohol content by gas chromatography (separation column RTX-5 Amine, length 30 m, internal diameter 0.32 mm, film thickness 1.5 m, TCD detector). The detection limit was approximately 500 mg/kg.

[0102] B. Determination of Lower Alcohol and Auxiliary Alcohol in the Bottom Output

[0103] B.1 Auxiliary Alcohol: 2-Butanol

[0104] 500 mg of a sample of the solution of the product metal alkoxide were taken and allowed to cool to room temperature (approximately 23 C.). The sample was mixed with about 0.5 mg 2-methyl-2-butanol (as internal standard) in 1 mL ethanol, and 4 mL ethanol (without internal standard) were added to obtain a diluted sample. In cases where the sample was solid, it was melted at 60 C. before mixing with 2-methyl-2-butanol and ethanol.

[0105] The diluted sample was analyzed by gas chromatography (separation column DB-1, length 30 m, inner diameter 0.25 mm, film thickness 1.0 m). Quantification was carried out using the standard addition method. The detection limit was 200 mg/kg.

[0106] B.2 Auxiliary Alcohol: 1-Methoxy-2-Propanol

[0107] 500 mg of a sample of the solution of the product metal alkoxide were taken and allowed to cool to room temperature (approximately 23 C.). The sample was mixed with about 0.5 mg sec-butanol (as internal standard) in 1 mL ethanol, and 4 mL ethanol (without internal standard) were added to obtain a diluted sample. In cases where the sample was solid, it was melted at 60 C. before mixing with sec-butanol and ethanol.

[0108] The diluted sample was analyzed by gas chromatography (separation column DB-1, length 30 m, inner diameter 0.25 mm, film thickness 1.0 m). Quantification was carried out using the standard addition method. The detection limit was 200 mg/kg.

[0109] B.3 Auxiliary Alcohol: 3-Methyl-2-Butanol

[0110] 500 mg of a sample of the solution of the product metal alkoxide were taken and allowed to cool to room temperature (approximately 23 C.). The sample was mixed with about 0.5 mg n-hexane (as internal standard) in 1 mL isopropanol, a drop of phosphoric acid was added, and 3 mL isopropanol (without internal standard) were added to obtain a diluted sample. In cases where the sample was solid, it was melted at 60 C. before mixing with hexane, phosphoric acid and ethanol.

[0111] The diluted sample was analyzed by gas chromatography (separation column DB-1, length 30 m, inner diameter 0.25 mm, film thickness 1.0 m). Quantification was carried out using the standard addition method. The detection limit was 200 mg/kg.

[0112] In the standard addition method, a multiple determination of the sample is performed, for example a double determination. A specific amount of the substance to be determined (the reactant alcohol) is added to each sample several times and the sample is measured after each addition. The increase of the substance is determined. The concentration of the reactant alcohol in the original sample can be calculated by linear regression.

[0113] The solubility of the samples must be checked in advance. If two phases are formed, the weight of the sample must be reduced.

[0114] C. Determination of the Concentration of Sodium Alkoxide Tetrahydrolinaloolate in the Bottom Output

[0115] To determine the amount of sodium alkoxide tetrahydrolinaloolate in the bottom of the column, a sample was taken and the total content of bases consisting of alkoxide, hydroxides and carbonate was determined by titration in 2-propanol with trifluoromethanesulfonic acid (0.1 mol/I in 2 propanol). The amount of hydroxides and carbonates was determined by volumetric Karl Fischer titration (KFT), since these components react with the KF components in the KFT and form water. The contribution of hydroxides and carbonates were subtracted from the total base content to determine the alkoxide content.

EXAMPLES

[0116] The examples were carried out in a plant according to FIG. 1, comprising a reactive distillation column with 80 bubble cap trays made of glass and a forced circulation flash reboiler. Table 1 shows the specific parameters of the examples.

[0117] The reboiler was heated with a commercial thermostat (Julabo HT6) with a maximum heating power of 5700 W. The diameter of the column was 50 mm. To avoid heat loss, the column was heated isothermally with an electrical protective heating system.

[0118] Prior to start-up, the column was filled with auxiliary alcohol and reactant alcohol. When the operating temperature was reached, sodium methoxide and reactant alcohol were fed to the column.

[0119] Sodium methoxide (30% by weight in methanol) was fed into the column from the side (tray 40 or 60). Tetrahydrolinalool (THL) was fed into the column before the reboiler or to tray 30.

[0120] The amount of product metal alkoxide, auxiliary alcohol and methanol in the solution of the product metal alkoxide removed at the bottom of the column (bottom output) was determined.

[0121] At the top of the column, gaseous methanol was removed and condensed in a condenser. The amount of reactant alcohol and auxiliary alcohol in the top condensate was determined.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 auxiliary alcohol 2-butanol 1-methoxy- 3-methyl- 2-propanol 2-butanol amount of auxiliary alcohol in column [kg] 0.221 0.417 0.459 auxiliary alcohol feed [kg/h] 0.009 0.009 0 location of auxiliary alcohol feed tray 40 tray 40 tray 38 sodium methoxide feed [kg/h] 0.08 0.08 0.25 location of sodium methoxide feed tray 60 tray 60 tray 40 THL feed [kg/h] 0.358 0.138 0.266 location of THL feed tray 30 tray 30 reboiler stream removed at top of column [kg/h] 0.08 0.071 0.214 stream removed at bottom of column [kg/h] 0.375 0.165 0.307 bottom circulation [kg/h] 150 150 150 reflux [kg/h] 0.4 0.58 0.2 reflux ratio 5 8.2 0.935 ratio of sodium methoxide feed to reflux 0.2 0.138 1.25 T (column head) [ C.] 59.9 60 46.8 T (column bottom) [ C.] 188.3 194.6 206.5 T (sodium methoxide feed) [ C.] 41.4 39.6 43.8 pressure (column head) [mbar, absolute] 698 697 499 differential pressure of column [mbar] 86.2 92.7 67.9 sodium tetrahydrolinaloolate in bottom output 24.8 49 76.4 [wt.-%] methanol in bottom output [wt.-%] <0.02 0.02 <0.02 auxiliary alcohol in bottom output [wt.-%] <0.02 0.11 <0.01 THL in top condensate [wt.-%] 0 0 0 auxiliary alcohol in top condensate [wt.-%] 15 8 0

[0122] In a comparative Example 4 carried out in a similar way to Example 2, but without auxiliary alcohol, a stable operation was not possible, as solid deposits formed in the column within 1 to 2 h and clogged the trays of the column.

[0123] It is evident that the presence of an auxiliary alcohol allows for a stable operation of the column. Moreover, the solution of sodium tetrahydrolinaloolate in tetrahydrolinalool is essentially free of both methanol and the auxiliary alcohol.