Method for producing metal alcoholates

Abstract

Process for preparing metal alkoxides by means of transalcoholization, wherein a lower metal alkoxide is fed via a side feed into a reactive distillation column comprising a rectifying section situated above the feed and a stripping section situated below the feed; a higher alcohol is fed into the stripping section, the bottom and/or a bottoms circuit of the column; a solution of a higher metal alkoxide in the higher alcohol is taken off at the bottom of the column and/or from the bottoms circuit; and a vapor comprising lower alcohol is taken off at the top of the column, the vapor is at least partially condensed and a substream of the condensate is recycled to the top of the column as reflux. The process enables the preparation of metal alkoxides with a reduced energy requirement.

Claims

1. A process for preparing metal alkoxides by means of transalcoholization, wherein a lower metal alkoxide is fed via a side feed into a reactive distillation column comprising a top, a bottom, a rectifying section situated above the feed and a stripping section situated below the feed; a higher alcohol is fed into the stripping section, the bottom and/or a bottoms circuit of the column; a solution of a higher metal alkoxide in the higher alcohol is taken off at the bottom of the column and/or from the bottoms circuit; and a vapor comprising lower alcohol is taken off at the top of the column, the vapor is at least partially condensed and a substream of the condensate is recycled to the top of the column as reflux; wherein the higher alcohol has a higher boiling point than the lower alcohol.

2. The process according to claim 1, wherein the higher alcohol is fed into the bottom and/or the bottoms circuit of the column in liquid form.

3. The process according to claim 1, wherein the solution of the higher metal alkoxide comprises not more than 1.0% by weight of the lower alcohol, based on the total weight of the solution of the higher metal alkoxide.

4. The process according to claim 1, wherein the solution of the higher metal alkoxide comprises 3% to 60% by weight of the higher metal alkoxide, based on the total weight of the solution of the higher metal alkoxide.

5. The process according to claim 1, wherein the column has a forced circulation evaporator and the higher alcohol is fed in liquid form into the feed to the forced circulation evaporator.

6. The process according to a claim 1, wherein the top condensate comprises not more than 0.8% by weight of the higher alcohol, based on the total weight of the top condensate.

7. The process according to claim 1, wherein the lower metal alkoxide is fed in as a solution in the lower alcohol and the solution comprises 20% to 40% by weight of the lower metal alkoxide, based on the total weight of the solution of the lower metal alkoxide.

8. The process according to a claim 1, wherein the lower metal alkoxide is an alkali metal alkoxide.

9. The process according to claim 8, wherein the lower metal alkoxide is a sodium alkoxide or a potassium alkoxide.

10. The process according to claim 9, wherein the lower metal alkoxide is sodium methoxide or potassium methoxide.

11. The process according to claim 1, wherein the higher alcohol is selected from isopropanol, sec-butanol, 2-methyl-2-butanol, tert-butanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol and 3-methyl-3-hexanol.

Description

BRIEF DESCRIPTION OF FIGURES

(1) The invention is illustrated further by the appended figures and the following examples.

(2) FIG. 1 shows a comparison plant suitable for the preparation of metal alkoxides.

(3) FIG. 2 shows a plant suitable for the preparation of metal alkoxides by means of the process according to the invention.

(4) According to FIG. 1, the plant comprises a reactive distillation column 101. Into this is fed a solution of a lower metal alkoxide via conduit 102 together with a higher alcohol from conduit 103.

(5) At the top of column 101, a vapor comprising lower alcohol is taken off via conduit 104 and condensed in condenser 105. A first substream of the condensed vapor is discharged from the process via conduit 106, while a second substream of the condensed vapor is recycled to the top of the column via conduit 107.

(6) A solution of the higher metal alkoxide in the higher alcohol is taken off at the bottom of the column. A first substream of the solution of the higher metal alkoxide is discharged from the process via conduit 108, while a second substream of the solution of the higher metal alkoxide is recycled to the bottom of the column via conduit 109, evaporator 110 and conduit 111.

(7) According to FIG. 2, the plant comprises a reactive distillation column 201. Into this is fed a solution of a lower metal alkoxide via conduit 202. A higher alcohol is fed into the bottoms circuit via conduit 203 and evaporator 210.

(8) At the top of column 201, a vapor comprising lower alcohol is taken off via conduit 204 and condensed in condenser 205. A first substream of the condensed vapor is discharged from the process via conduit 206, while a second substream of the condensed vapor is recycled to the top of the column via conduit 207.

(9) A solution of the higher metal alkoxide in the higher alcohol is taken off at the bottom of the column. A first substream of the solution of the higher metal alkoxide is discharged from the process via conduit 208, while a second substream of the solution of the higher metal alkoxide is recycled, together with the higher alcohol from conduit 203, to the bottom of the column via conduit 209, evaporator 210 and conduit 211.

Examples

(10) Experiments were conducted for the preparation of sodium alkoxides by means of transalcoholization from sodium methoxide and higher alcohols, the higher alcohols used being isopropanol, 2-butanol and 2-methyl-2-butanol.

(11) Methods

(12) A. Determination of the Concentration of the Higher Alcohol in the Top Condensate

(13) To determine the content of higher alcohol in the top condensate, a sample was taken, 1,4-dioxane as internal standard was added and the sample was analyzed for its alcohol content by gas chromatography (RTX-5 Amine separating column, length 30 m, internal diameter 0.32 mm, film thickness 1.5 ?m). The detection limit was approx. 500 mg/kg.

(14) B. Determination of the Methanol Concentration in the Bottoms Discharge

(15) B.1 Higher Alcohol: Isopropanol or 2-Butanol

(16) To determine the methanol content in the bottom of the column, 150 mg (when using isopropanol as higher alcohol) or 60 mg (when using 2-butanol) of a sample were weighed into a 22.5 ml headspace glass vessel.

(17) 1 ml of tap water was added to the sample, and the sample was sealed gas-tight with an aluminum cap and analyzed by headspace GC (DB-1 separating column, length 30 m, internal diameter 0.25 mm, film thickness 1.0 ?m). Quantification was effected using the standard addition method. The detection limit was less than 100 mg/kg.

(18) In the standard addition method, the sample is subjected to a multiple determination, for example a double determination. Here, a specific amount of the substance to be determined (the higher alcohol) is added multiple times to each sample and the sample is measured after each addition. The increase in the substance signal is ascertained. The concentration of the higher alcohol in the original sample can be calculated by linear regression.

(19) The solubility of the samples must be tested in advance. If two phases form, the amount weighed in must be reduced.

(20) B.2 Higher Alcohol: 2-Methyl-2-Butanol

(21) To determine the methanol content in the bottom of the column, 500 mg of a sample were taken and allowed to cool to room temperature. The sample was mixed with 1 ml of water and 0.5 mg of tert-butanol in dioxane (1 ml, as internal standard), a drop of phosphoric acid was added thereto and the sample was diluted with 3 ml of dioxane (without internal standard) in order to obtain a diluted sample. In the case of solid samples, these were melted at 60? C. before mixing with water, tert-butanol, phosphoric acid and dioxane. The diluted sample was analyzed for its alcohol content by gas chromatography (DB-1 separation column, length 30 m, internal diameter 0.25 mm, film thickness 1.0 ?m). The detection limit was approx. 200 mg/kg.

(22) C. Determination of the Alkoxide Concentration in the Bottoms Discharge

(23) To determine the alkoxide 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/l in 2-propanol). The amount of hydroxides and carbonate was determined by means of volumetric Karl Fischer titration (KFT), since these constituents react with the KF components in the KFT and form water. The contribution of hydroxides and carbonates is subtracted from the total content of bases in order to ascertain the content of alkoxide.

Examples 1 to 5 and Comparative Examples 1 to 3

(24) The examples were carried out in a plant which comprised an 80-tray glass bubble-cap tray column and a forced circulation flash evaporator. Tables 1A and 1B show the specific parameters of the examples. The evaporator was heated with a commercial thermostat (Julabo HT6) with a maximum heating power of 5700 W. The diameter of the column was 50 mm. Sodium methoxide (30% by weight in methanol) was fed into the column from the side. To avoid heat losses, the column was heated isothermally with an electric guard heater.

(25) The higher alcohol was fed either upstream of the evaporator or to a tray in the stripping section or together with sodium methoxide from the side into the column. The amount of higher metal alkoxide or methanol in the solution of the higher metal alkoxide taken off at the bottom was determined.

(26) The vapor was discharged at the top of the column and condensed in a condenser. The amount of higher alcohol in the top condensate was determined.

(27) Comparative example 1 was initially performed like example 1. Once a steady state had been established, the feed of isopropanol upstream of the evaporator was halted and isopropanol was instead fed in together with sodium methoxide. The composition of the top condensate and of the sodium isopropoxide taken off at the bottom was determined after re-establishing the steady state.

(28) Comparative example 2 was initially performed like example 2. Once a steady-state had been established, the feed of sec-butanol upstream of the evaporator was halted and sec-butanol was instead fed in together with sodium methoxide. The composition of the top condensate and of the sodium sec-butoxide taken off at the bottom was determined after re-establishing the steady state.

(29) Comparative example 3 was performed analogously to example 5, with the difference that 2-methyl-2-butanol was not fed in upstream of the evaporator but instead together with sodium methoxide to tray 30. The composition of the top condensate and of the sodium 2-methyl-2-butoxide taken off at the bottom was determined after establishing the steady state.

(30) TABLE-US-00001 TABLE 1A Experimental test data for examples 1 and 2 and comparative examples 1 and 2. Comparative Comparative example 2 Example 1 example 1 Example 2 Version 1 Version 2 Version 3 Version 4 Higher alcohol Isopropanol 2-Butanol Na methoxide feed [kg/h] 0.23 0.23 0.49 0.49 0.49 0.49 0.49 Na methoxide feed point Tray 40 Tray 40 Tray 30 Tray 30 Tray 30 Tray 30 Tray 30 Higher alcohol feed [kg/h] 1.226 1.125 1.814 1.742 1.800 1.874 1.918 Higher alcohol feed point Upstream of Tray 40 Upstream of Tray 30 Tray 30 Tray 30 Tray 30 evaporator evaporator Top takeoff [kg/h] 0.171 0.180 0.427 0.420 0.418 0.424 0.428 Bottom takeoff [kg/h] 1.286 1.172 1.869 1.809 1.871 1.94 1.977 Bottoms circuit [kg/h] 150 150 150 150 150 150 150 Reflux [kg/h] 1.341 1.343 0.700 0.700 0.835 0.900 1.001 Reflux ratio 7.84 7.46 1.64 1.67 2.00 2.12 2.34 Ratio of feed/reflux 0.172 0.171 0.700 0.700 0.587 0.544 0.4905 T (column top) [? C.] 63.0 62.2 62.2 62.6 62.1 62.2 62.3 T (column bottom) [? C.] 83.8 83.8 103 103 103 103 103 T (feed) [? C.] 47.9 54.5 52.5 54.0 54.0 54.0 54.5 Top pressure [mbar, absolute] 949 949 949.5 949.5 949.5 949.6 949.4 Column differential pressure [mbar] 81.3 82.2 73.8 76.2 78.2 79.8 82.5 Alkoxide in bottom [% by weight] 7.8 9.2 14.4 14.5 14.1 13.5 13.5 Methanol in bottom [% by weight] 0.04 2.0 0.07 0.7 0.4 0.2 0.1 Higher alcohol in top condensate 0.15 0.4 0.360 1.04 n.d. * n.d. * n.d. * [% by weight] * n.d.: below the detection limit

(31) TABLE-US-00002 TABLE 1B Experimental test data for Examples 3 to 5 and Comparative Example 3. Comparative Example 5 example 3 Example 3 Example 4 Version 1 Version 2 Version 3 Version 1 Version 2 Higher alcohol 2-Butanol 2-Methyl-2-butanol Na methoxide feed [kg/h] 0.49 0.49 0.15 0.225 0.10 0.15 0.10 Na methoxide feed point Tray 30 Tray 30 Tray 30 Tray 30 Tray 30 Tray 30 Tray 30 Higher alcohol feed [kg/h] 1.864 1.861 1.036 1.23 0.531 0.469 0.325 Higher alcohol feed point Upstream of Tray 15 Upstream of Upstream of Upstream of Tray 30 Tray 30 evaporator evaporator evaporator evaporator Top takeoff [kg/h] 0.430 0.432 0.139 0.187 0.091 0.099 0.068 Bottom takeoff [kg/h] 1.912 1.916 1.057 1.278 0.569 0.511 0.342 Bottoms circuit [kg/h] 150 150 150 150 150 150 150 Reflux [kg/h] 0.860 0.840 0.835 1.000 1.000 1.330 1.000 Reflux ratio 2.00 1.94 7.19 5.35 14.62 10.10 19.56 Ratio of feed/reflux 0.570 0.583 0.150 0.225 0.075 0.150 0.075 T (column top) [? C.] 62.4 62.3 62.7 63 62.6 62.3 62.3 T (column bottom) [? C.] 103 103 103.7 104.2 104.5 106.5 106.5 T (feed) [? C.] 50.3 50.0 47.4 49.9 47.7 52.2 51 Top pressure [mbar, absolute] 949.5 949.5 949.3 949.3 949.1 949.8 949.9 Column differential pressure [mbar] 78.7 78.2 81.8 83.7 88.9 80.6 88.1 Alkoxide in bottom [% by weight] 13.4 13.4 9.6 12.1 10.1 16.7 17.4 Methanol in bottom [% by weight] 0.012 0.09 0.27 0.76 0.04 0.82 0.16 Higher alcohol in top condensate 0.3 n.d.* 8.85 1.19 6.28 n.d.* n.d.* [% by weight] *n.d.: below the detection limit

(32) It can be seen from the comparison of example 1 with comparative example 1 that feeding the higher alcohol in upstream of the evaporator, compared to feeding in the higher alcohol together with the lower alkoxide to tray 40 of the column, results in a lower methanol concentration in the bottom for the same ratio of feed to reflux.

(33) It can in turn be seen from the comparison of example 2 with comparative example 2 (version 1) that feeding the higher alcohol in upstream of the evaporator, compared to feeding in the higher alcohol together with the lower alkoxide to tray 30 of the column, results in a lower methanol concentration in the bottom for the same ratio of feed to reflux. Even with an increase in the reflux in versions 2 to 4 of comparative example 2 from 0.7 kg/h to 1.0 kg/h, the methanol concentration on the bottom only falls to 0.1% by weight, compared to 0.07% by weight in example 2.

(34) In example 3, the higher alcohol was fed in upstream of the evaporator. In example 4, the higher alcohol was fed in to tray 15 in the stripping section. In comparative example 2 (version 2), the higher alcohol was fed in together with the lower alkoxide to tray 30. The reflux ratios were comparable in these three experiments. It can be seen that the methanol concentration in the bottom in examples 3 and 4 was significantly lower than in comparative example 2 (version 2). This shows that feeding the higher alcohol in upstream of the evaporator or in the stripping section of the column, compared to feeding in the higher alcohol together with the lower alkoxide to tray 30 of the column, results in a lower methanol concentration in the bottom for the same ratio of feed to reflux. It is particularly advantageous to feed the higher alcohol in upstream of the evaporator.

(35) It can be seen from the comparison of example 5, version 1, with comparative example 3, version 1, that feeding the higher alcohol in upstream of the evaporator, compared to feeding in the higher alcohol together with the lower alkoxide to tray 30 of the column, results in a lower methanol concentration in the bottom for the same ratio of feed to reflux. This can also be seen from the comparison of example 5, version 3, with comparative example 3, version 2.

(36) The specific heating power of the preparation process was additionally determined for selected examples on the basis of the temperature of the heating oil (KORASILON M 10 oil; spec. heat capacity cp (120? C.): 1.74 kJ/(kg K)) in the feed and in the return. The results are shown in table 2.

(37) TABLE-US-00003 TABLE 2 Specific heating power Comparative Comparative example 2, Example 5, example 3, Example 2 version 4 Version 2 version 1 Methanol in bottom 0.07 0.1 0.76 0.82 [% by weight] Feed oil temperature 120.1 122.8 122.5 127.7 [? C.] Return oil 115.4 117.6 117.5 121.2 temperature [? C.] ?T feed/return [? C.] 4.7 5.2 5 6.5 Oil mass flow rate 331.0 322.3 319.1 190.1 [kg/h] Evaporator heating 752 810 771 597 power [W] Specific heating 10.1 10.9 18.0 25.2 power [J/g]

(38) It can be seen that the process according to the invention for a comparable separation task requires a lower specific heating power than when the higher alcohol is fed in together with the lower metal alkoxide.