Method for the preparation of 1,4-butane diol having an APHA color index of less than 30

Abstract

Method for preparing 1,4-butanediol having an APHA color index of less than 30 by treating substance mixtures comprising 1,4-butanediol by distillation of the 1,4-butanediol in the presence of complex hydrides.

Claims

1. A method for preparing 1,4-butanediol having an APHA color index of less than 30 comprising treating a substance mixture comprising 1,4-butanediol by distillation of the 1,4-butanediol in the presence of a complex hydride.

2. The method according to claim 1, wherein the complex hydride used is NaBH.sub.4.

3. The method according to claim 2, wherein NaBH.sub.4 is used as an aqueous alkaline solution.

4. The method according to claim 1, wherein the distillation of the 1,4-butanediol is operated continuously.

5. The method according to claim 4, wherein the distillation is operated using a dividing wall column.

6. The method according to claim 1, wherein the pH of the mixture of substance mixture comprising 1,4-butanediol and hydride has a pH of 4 to 14 at a minimum water content of 10%.

7. The method according to claim 2, wherein the pH of the mixture of substance mixture comprising 1,4-butanediol and hydride has a pH of 4 to 14 at a minimum water content of 10%.

Description

EXPERIMENTAL SECTION

Example 1

(1) In a 1 liter round-bottomed flask, 750 g of crude butanediol were initially charged, which comprised, in addition to ca. 49% 1,4-butanediol, ca. 45% water, ca. 0.3% gamma-butyrolactone, 0.15% acetal, 0.05% 4-hydroxybutyraldehyde, ca. 1% methanol, ca. 1.1% propanol, ca. 1.3% n-butanol, ca. 0.1% formaldehyde acetals and hemiacetals, ca. 0.1% 2-methyl-1,4-butanediol and also some partly unknown high and low boilers. The mixture had a color index of 175 APHA and a pH of 7.1. 5 g of a Borol? solution (Dow Chemicals, VenPlus Solution) were added under an inert gas (nitrogen). ca. 94 g of low boilers, initially at 500 mbar, then at 100 mbar and bottom temperatures of 112-134? C. were distilled off from the mixture. After change of the fraction, the bottom temperature was increased to ca. 150? C., and at 50 mbar ca. 65 g of intermediate fraction (ca. 32% water, content by GC, calculated as anhydrous, of butanediol: 98.1%, color index 6 APHA) were distilled off. Subsequently, at ca. 40 mbar, ca. 520 g of main fraction were distilled off at ca. 150? C. The 1,4-butanediol from the main fraction had a purity by GC of 99.85%, 2-methylbutanediol 0.092%, acetal content was 0.077%, gamma-butyrolactone was undetectable. The color index was 8 APHA. The sample was filled into a sheet metal can (material 1.0425) and stored at 50? C. After 24 h, the color index was unchanged at 8 APHA.

Comparative Example 1

(2) Example 1 was repeated but without the addition of Borol?. After removal of the main amount of low boilers and water, ca. 85 g of intermediate fraction were obtained (color index 7 APHA, water content ca. 80%, content by GC, calculated as anhydrous, of butanediol: ca. 60%). ca. 4 g were obtained as main fraction. The 1,4-butanediol from the main fraction had a purity by GC of 99.54%, 2-methylbutanediol 0.095%, acetal content was 0.219%, gamma-butyrolactone 0.014%. The color index was 6 APHA. The sample was filled into a sheet metal can (material 1.0425) and stored at 50? C. After 24 h, the color index was 35 APHA.

Example 2

(3) In a 1 liter round-bottomed flask, 750 g of crude butanediol were initially charged, which comprised, in addition to ca. 84% 1,4-butanediol, ca. 15% water, ca. 0.01% gamma-butyrolactone, ca. 0.15% acetal, 0.01% acetaldehyde and acetal and hemiacetal thereof with butanediol and also some further unknown high and low boilers. The mixture had a color index of 75 APHA and a pH of 9. 5 g of a Borol? solution (Dow Chemicals, VenPlus Solution) were added under an inert gas (nitrogen). ca. 94 g of low boilers, initially at 500 mbar, then at 100 mbar and bottom temperatures of 112-134? C. were distilled off from the mixture. After change of the fraction, the bottom temperature was increased to ca. 150? C., and at 50 mbar ca. 65 g of intermediate fraction (ca. 32% water, content by GC, calculated as anhydrous, of butanediol: 98.1%, color index 6 APHA) were distilled off. Subsequently, at ca. 40 mbar, ca. 520 g of main fraction were distilled off at ca. 150? C. The 1,4-butanediol from the main fraction had a purity by GC of 99.895%, acetal content was 0.071%, gamma-butyrolactone was undetectable. The color index was 6 APHA. The sample was filled into a sheet metal can (material 1.0425) and maintained at a temperature of 50? C. After 24 h, the color index was unchanged at 6 APHA.

Comparative Example 2

(4) Example 2 was repeated but without the addition of Borol? (pH of ca. 6.5). After removal of the main amount of water, ca. 78 g of intermediate fraction were obtained (color index 15 APHA, water content ca. 39%, content by GC, calculated as anhydrous, of butanediol: 97.5%). ca. 529 g were obtained as main fraction. The 1,4-butanediol from the main fraction had a purity by GC of 99.693%, acetal content was 0.175%, gamma-butyrolactone 0.014%. The color index was 6 APHA. The sample was filled into a sheet metal can (material 1.0425) and maintained at a temperature of 50? C. After 24 h, the color index was 51 APHA.

Example 3

(5) In a 1 liter round-bottomed flask, 750 g of crude butanediol were initially charged, which comprised, in addition to ca. 98% 1,4-butanediol, ca. 0.5% water, ca. 0.5% gamma-butyrolactone, 0.13% acetal and also some further unknown high and low boilers. The mixture had a color index of 25 APHA. 0.5 g of LiAlH4 was added under inert gas (nitrogen). At a bottom temperature of ca. 150? C. and 50 mbar, ca. 50 g were distilled off from the mixture. This fraction comprised ca. 8% water, content by GC, calculated as anhydrous, of butanediol 93.2%, color index 8 APHA). Subsequently, at ca. 40 mbar, ca. 620 g of main fraction were distilled off at ca. 150? C. The 1,4-butanediol from the main fraction had a purity by GC of 99.912%, acetal content was 0.054%, gamma-butyrolactone was undetectable. The color index was 5 APHA. The sample was filled into a sheet metal can (material 1.0425) and heated to 50? C. After 24 h, the color index was unchanged at 5 APHA.

Comparative Example 3

(6) Example 3 was repeated but without the addition of LiAlH4. As first fraction, ca. 45 g were obtained (color index 9 APHA, water content ca. 9%, content by GC, calculated as anhydrous, of butanediol: 92.5%). ca. 623 g were obtained as main fraction. The 1,4-butanediol from the main fraction had a purity by GC of 99.731%, acetal content was 0.151%, gamma-butyrolactone 0.024%. The color index was 6 APHA. The sample was filled into a sheet metal can. After 24 h, the color index was 12 APHA.