DESC:Field of Invention
The present invention relates to a process for preparation of 1,3-butylene glycol and product thereof.

Background of the invention
1,3-butylene glycol is viscous, colourless, transparent, highly hygroscopic and has a low odor. It has a wide range of applications such as producing chemically stable derivatives, useful as a solvent for coating industry, as a monomer for various synthetic resins, and as a chain lengthening agent (chain extender). 1,3-butylene glycol also has excellent moisturizing properties and hence, its requirement is increasing in cosmetic industry.

1,3-butylene glycol is generally produced by any one of the three known processes described below.

First, a method in which acetaldol is first prepared by aldol condensation of acetaldehyde and then catalytically hydrogenated to obtain 1,3-butylene glycol using Raney Nickel metal catalyst. Further, purification of the obtained 1,3-butylene glycol is carried out by conventional distillation to separate the odor causing impurities. Furthermore, the process requires the addition of alkali metal hydroxides such as sodium hydroxide or potassium hydroxide, or alkali metal borohydrides such as sodium borohydride for removal of impurities having high boiling points. The drawbacks of this process are that it is a batch process particularly, the step of hydrogenation of acetaldol and purification of 1,3-butylene glycol are performed in batch-wise manner, higher consumption of hydrogen in the hydrogenation step, and incomplete removal of odor causing impurities by conventional distillation.

Second, a method in which 1,3-butylene glycol is prepared by a hydration reaction of 1,3-butylene oxide. This process is not used for manufacturing 1,3-butylene glycol industrially.

Third, a method in which 1,3-butylene glycol is prepared from propylene and formaldehyde by the Prince reaction. This process gives low yield of 1,3-butylene glycol.

JP 4397495 discloses a process for producing 1,3-butylene glycol where acetaldol is catalytically hydrogenated under acidic conditions to prevent corrosion of the equipment. However, the process requires addition of alkali metal hydroxides and alkali metal borohydrides for removal of impurities having high boiling points.

Acetaldehyde used in the aldol condensation reaction for preparation of acetaldol enters the product stream of acetaldol such that the crude product may contain up to 50% by weight (% wt.) of more of acetaldehyde which is not present in free form but is reversibly combined with the acetaldol itself. The presence of acetaldehyde causes decomposition of acetaldol into crotonaldehyde when heated to higher temperatures such as in the hydrogenation step. The following prior art mention about separation of acetaldehyde from acetaldol.

WO 2005/068408 describes a method for preparation of 1,3-butylene glycol using acetaldehyde having low concentration of carboxylic acid (up to 0.04%). This application describes a process step where after the aldol condensation, the product stream is treated with acid to neutralize the alkali agent used in the aldol condensation and acetaldol and acetaldehyde are separated using a stripper distillation column. However, in this document, 1,3-butylene glycol obtained after hydrogenation is subjected to further steps of distillation and vacuum distillation for purification of the product.

US 2521204 describes a process for concentration of acetaldol. The process involves neutralizing crude acetaldol to a pH in a range of 6.5 to 7.5. Then passing said crude acetaldol in form a liquid free-flowing film over a surface heated to a temperature of 90°C to 110°C to separate acetaldehyde by vaporization.

WO 2005/068408 and US 2521204 do not teach to remove impurities from 1,3-butylene glycol.

Japanese patents JP 6979473 and JP 6979544 describe a 1,3-butylene glycol product, where after its synthesis 1,3-butylene glycol is subjected to further steps of dehydration, desalting, distillation, alkalization, dealkalization and dehydration. The 1,3-butylene glycol product has high content of hydrides of the trimer of acetaldehyde and acetal compounds of 1,3-butylene glycol and acetaldol.

None of the above applications describe a process wherein hydrogen consumption is reduced during the hydrogenation step.

There is a need for an improved process for preparation of 1,3-butylene glycol that has reduced hydrogen consumption during the hydrogenation step, and further removes colour and odor causing impurities.

Summary of the invention
In an aspect, the invention relates to a process preparation of 1,3-butylene glycol, the process comprising:
a. stripping off acetaldehyde from a crude mixture comprising acetaldol acetaldehyde and water, at a temperature in a range from 80°C to 90°C, to produce a concentrated acetaldol,
b. hydrogenating the concentrated acetaldol to produce a crude 1,3-butylene glycol, and
c. subjecting the crude 1,3-butylene glycol to azeotropic distillation.

In another aspect, the invention relates to 1,3-butylene glycol comprising less than or equal to 0.002% of ethanol, less than or equal to 0.01% each of acetic acid and 2-ethyl butanol, less than 0.5% of water, and less than 0.05% of a mixture comprising n-butanol, 1,3-butanediol acetate, 1,3-dioxane-2-heptyl-4-methyl, 2-methyl-1-[1-(2-methylbutoxy)ethoxy] butane, hexanol and 2,4-pentanediol-3methyl.

Detailed Description of the invention
The present invention relates to a process for preparation of 1,3-butylene glycol comprising the steps:
a. stripping off acetaldehyde from a crude mixture comprising acetaldol acetaldehyde and water, at a temperature in a range from 80°C to 90°C, to produce a concentrated acetaldol,
b. hydrogenating the concentrated acetaldol to produce a crude 1,3-butylene glycol, and
c. subjecting the crude 1,3-butylene glycol to azeotropic distillation.

The process comprises preparing the crude mixture by aldol condensation of acetaldehyde in an aqueous medium till less than 60% wt. of acetaldehyde is converted to acetaldol. Aldol condensation is carried out using an alkali hydroxide as a catalyst, such as sodium hydroxide and an alkaline (basic) pH in a range from 10 to 14. The catalyst is added to acetaldehyde as a dilute aqueous solution having a concentration of 1% wt. to 5% wt. Addition of catalyst in excess is avoided to prevent formation of colour and odor forming impurities. Water is present in an amount to adjust acetaldehyde concentration to be in a range from 50% wt. to 80% wt.

Subsequently, the crude mixture is neutralized by the addition of an organic acid selected from acetic acid, propionic acid or butyric acid to an acid content up to 0.5% wt. or an acidic pH in a range from 5 to 6. Preferably, the crude mixture is neutralized by the addition of acetic acid.

In an embodiment, the aldol condensation of acetaldehyde is carried out such that crude mixture contains 25% wt. to 30% wt. of acetaldehyde, and 40% wt. to 50% wt. of acetaldol, preferably 40% wt. to 42% wt. The acetaldehyde in the crude mixture refers to the unreacted acetaldehyde from the aldol condensation.

The crude mixture further comprises crotonaldehyde, 2-vinyl crotonaldehyde, sorbaldehyde, high boiling (HB) point compounds and salts of aldehydes thereof.

The crude mixture is subjected to stripping as described in step (a). This step is carried out in a rising film evaporator at atmospheric pressure. Preferably, step (a) is carried out at a temperature in the range from 88°C to 90°C.

The concentrated acetaldol comprises 60% wt. to 65% wt. of acetaldol, 8% wt. to 10% wt. or 10% wt. to 12% wt. of acetaldehyde.

In an embodiment, the concentrated acetaldol further comprises 3% wt. to 5% wt. of crotonaldehyde, 0.5% wt. to 0.6% wt. of acetic acid, 3% wt. to 5% wt. of HB, 10% wt. to 13% wt. of water, and other compounds.

The concentrated acetaldol is subjected to hydrogenation as described in step (b). This step is carried out in absence of a solvent and in presence of a nickel catalyst such as Raney nickel. The catalyst is initially added in an amount in a range from 0.1% wt. to 1% wt. and hydrogenation is carried out at a temperature in range from 55°C to 120°C, using hydrogen pressure of 10-25 atmosphere (atm). Preferably, step (b) is carried out at a temperature in range from 75°C to 80°C.

In an embodiment, step (b) is followed by digestion at 120°C or 130°C for 3 hours.

Preferably, step (b) is carried out with hydrogen in an amount of 0.65 m3 per kg of 1,3-butylene glycol.

In step (b), the acetaldehyde and crotonaldehyde present the concentrated acetaldol are converted to ethanol and butanol. The crude 1,3-butylene glycol contains ethanol, butanol, acetals, esters, and salt (generated by neutralization of the aldol condensation catalyst).

The catalyst in step (b) is regenerated and may be reused, requiring 0.1% wt. of fresh catalyst to be used along with the regenerated catalyst in the next reaction. This makes the process commercially viable.

The crude 1,3-butylene glycol is subjected to step (c). The azeotropic distillation is carried out by the addition of 0.2 to 0.4 parts of water per 1 part of 1,3-butylene glycol obtained in the distillate.

In step (c) azeotropic distillation is carried out by adding crude 1,3-butylene glycol and water are added in a reactor comprising a top portion and a bottom portion. Azeotropic distillation is carried out in the reactor under vacuum at a pressure in a range from 450 mm to 500 mm of Hg or 720 mm of Hg. Preferably, the temperature of the top portion of the reactor is maintained in a range from 70°C to 80°C, and the bottom portion of the reactor is maintained in a range from 80°C to 100°C.

Azeotropic distillation removes the odor causing impurities such as acetaldehyde, crotonaldehyde, acetals and esters from the crude 1,3-butylene glycol.

The process of the present invention by step (a) provides a concentrated acetaldol having lower concentration of acetaldehyde (8% wt. to 10% wt. or 10% wt. to 12% wt.) than the crude mixture (25% wt. to 30 % wt. of acetaldehyde). This reduces the hydrogen required during hydrogenation of the concentrated acetaldol in step (b). For instance, carrying out step (b) with the crude mixture requires hydrogen in an amount of 1 m3 or more per kg of 1,3-butylene glycol. Whereas, carrying out step (b) with the concentrated acetaldol significantly reduces the hydrogen required in step (b) to 0.65 m3 per kg of 1,3-butylene glycol.

Further, the process, by recycling acetaldehyde obtained in step (a), and reusing the catalyst regenerated in step (b), has low wastage. This allows the process to be carried out in a continuous mode and increases the efficiency of the process, thereby making it cost-effective.

Furthermore, the process of the present invention by step (c) removes the impurities such as butyraldehyde, crotonaldehyde, acetals and esters which are not completely removed by conventional distillation. Also, the process eliminates the need for addition of alkali metal hydroxides or alkali metal borohydrides to remove the high boiling point impurities.

The process of the present invention provides 1,3-butylene glycol with high yield and high purity. 1,3-butylene glycol produced by the process has a purity in a range from 99.50% to 99.85%. Further, the 1,3-butylene glycol produced by the process of the present invention has low acid content during storage and thus, is colourless and has no or low odor over time.

The process provides 1,3-butylene glycol having high purity that finds its applications in cosmetics, personal care and FMCG industry among other industrial applications.

In a preferred embodiment, prior to step (c), conventional distillation of the crude 1,3-butylene glycol is carried out to remove the low and high boiling point impurities. The conventional distillation is flash distillation, vacuum distillation or simple distillation. Ethanol and butanol are removed followed by water by vacuum distillation with keeping refluxes at top of the column in a continuous mode in the first distillation column followed by removing the salts in the second distillation column by vacuum distillation. Low boiling and high boiling impurities are removed in the third distillation column resulting in being capable of obtaining a 1,3-butylene glycol product.

In another preferred embodiment, after step (c), 1,3-butylene glycol is further treated in batch-wise manner with granular activated charcoal, followed by filtration to obtain 1,3-butylene glycol.

The granular activated charcoal/carbon has a normal particle size of form 12 x 40 mesh, the activated charcoal has an apparent density of from 300 kg/m3 to 500 kg/m3 and the activated carbon has a surface area of from 1000 m2/g to 1500 m2/g, the activated carbon has iodine number of at minimum 1000 mg/g.

Preferably, the present invention relates to a process for preparation of 1,3-butylene glycol, the process comprising:
a. preparing a crude mixture, comprising 40% wt. to 42% wt. of acetaldol and 25% wt. to 30% wt. of acetaldehyde, by aldol condensation of acetaldehyde in an aqueous medium,
b. neutralizing the crude mixture, by adding an organic acid selected from acetic acid, propionic acid or butyric acid to an acid content of up to 0.5% wt. or pH in a range from 5 to 6,
c. stripping off acetaldehyde from the crude mixture comprising acetaldol acetaldehyde and water, at a temperature in a range from 80°C to 90°C, to produce a concentrated acetaldol,
d. hydrogenating the concentrated acetaldol to produce a crude 1,3-butylene glycol,
e. subjecting the crude 1,3-butylene glycol to azeotropic distillation by adding 0.2 to 0.4 parts of water per 1 part of 1,3-butylene glycol in the distillate.

In another aspect, the present invention relates to 1,3-butylene glycol comprising less than or equal to 0.002% of ethanol, less than or equal to 0.01% each of acetic acid and 2-ethyl butanol, less than 0.5% of water, and less than 0.05% of a mixture comprising n-butanol, 1,3-butanediol acetate, 1,3-dioxane-2-heptyl-4-methyl, 2-methyl-1-[1-(2-methylbutoxy)ethoxy] butane, hexanol and 2,4-pentanediol-3methyl.

Further, 1,3-butylene glycol comprises less than 0.5 ppm of acetaldehyde, less than 5 ppm of crotonaldehyde, more than 0 ppm to 10 ppm or less of hydrides of the trimer of acetaldehyde, 50 ppm or less of acetals of 1,3-butylene glycol and acetaldol, 50 ppm or less of esters of acetic acid and 1,3-butylene glycol, and 0.0032% weight of acetic acid.

Preferably, 1,3-butylene glycol has a value of 10 i.e., colourless, on American Public Health Association (APHA) colour scale and is odorless.

In a further aspect, the invention relates to a personal care composition comprising 1,3-butylene glycol of the present invention.

The process of the present invention is described below by non-limiting examples.

Examples
Example 1
After stripping off acetaldehyde by Step (a), 4000 gm concentrated acetaldol containing 65% wt. of acetaldol, 10% wt. of acetaldehyde, 10% wt. of crotonaldehyde and dehydrated aldol, 4% wt. of High Boiling (HB) compounds (2-vinyl crotonaldehyde, trans sorbaldehyde and higher aldehyde), and 11% wt. water was hydrogenated (Step (b)) without a solvent in the presence of 1% wt. of nickel catalyst at hydrogen pressure 20 atm and temperature 78°C, to produce crude 1, 3-butylene glycol. This was followed by digestion to convert higher aldehyde at 120°C for 3 hours.

The crude 1, 3-butylene glycol was distilled in a column under reduced pressure to remove ethanol, butanol, water, salts, and high boiling impurities. Then, azeotropic distillation (Step (c)) was carried out by addition of 0.2 parts of demineralized water i.e., 400 gm of demineralized water, to remove odor causing impurities. The azeotropic distillation was carried out under reduced pressure (720 mm Hg) in the distillation column. 1,3-butylene glycol in the distillate was obtained from the kettle bottom in a quantity of 2000 gm having purity of 99.85% and was odorless and colourless (APHA scale value 10).

Example 2
The process described in Example 1 was repeated except 2000 gm concentrated acetaldol was used in step (b), and azeotropic distillation (Step (c)) of crude 1,3-butylene glycol was carried out by addition of 0.2 parts of demineralized water i.e., 200 gm demineralized water.

Colourless 1,3-butylene glycol (APHA scale value 10) having low odor in the distillate was obtained from kettle bottom in a quantity of 1000 gm having purity of 99.85%.

Then, the obtained 1,3-butylene glycol was treated with granular activated carbon in a fixed bed at temperature 40°C with residence time 1 to 2 hours. The activated carbon had normal particle size of form 12 x 40 mesh, minimum apparent density of 430 kg/m3, surface area of 1150 m2/g, and iodine number of 1100 mg/g.

Example 3
A crude mixture (6154 gm) was obtained after subjecting 4658 gm of acetaldehyde to aldol condensation. The crude mixture contained 25% wt. to 30 % wt. of acetaldehyde, 40% wt. to 42% wt. of acetaldol, 3% wt. to 5% wt. of crotonaldehyde, and 3% wt. of a mixture of 2-vinyl crotonaldehyde, sorbaldehyde, and high boiling (HB) compounds its salt.

The crude mixture was subjected to stripping (Step(a)) at a temperature of 90°C in a rising film evaporator to remove acetaldehyde and to form 4000 gm concentrated acetaldol. The concentrated acetaldol contained 2600 gm of acetaldol and 400 gm of acetaldehyde.

The concentrated acetaldol was hydrogenated (Step (b)) without a solvent in the presence of 1% wt. of nickel catalyst at hydrogen pressure 20 atm and temperature 78°C to produce crude 1,3-butylene glycol. This was followed by digestion to convert higher aldehyde at 120°C for 3 hours.

Then the crude 1,3-butylene glycol was distilled in a column under reduced pressure to remove ethanol, butanol, water, salts, and high boiling impurities. Then, azeotropic distillation (Step (c)) was carried out by addition of 0.20 parts of demineralized water i.e., 440 gm to 460 gm of demineralized water, to remove odor causing impurities. The azeotropic distillation was carried out under reduced pressure (720 mm Hg) in the distillation column. 1,3-butylene glycol in the distillate was obtained from the kettle bottom in a quantity of 2200 gm to 2300 gm having purity of 99.85%.

Example 4
A crude mixture was prepared by subjecting 4658 gm of acetaldehyde to an aldol condensation in a reactor containing 1439 gm of water, and in presence 104 gm of an aqueous solution of (1% to 2.5% w/w) sodium hydroxide as a catalyst. The pH of the reaction mixture was basic. The reaction was carried out until 60% wt. to 65% wt. of acetaldehyde was converted to acetaldol.

The crude mixture (6154 gm) was then neutralized by addition of acetic acid such that the acid content was 0.50% i.e., the pH of the crude mixture was acidic. The crude mixture contained 1500-1650 gm acetaldehyde, 2700-2800 gm acetaldol and 51 gm of a mixture of crotonaldehyde, 2-vinyl crotonaldehyde, sorbaldehyde, HB compounds and its salts.

The crude mixture after neutralization was subjected to stripping (Step(a)) at a temperature of 90°C in a rising film evaporator to remove acetaldehyde and to form 4000 gm concentrated acetaldol. The concentrated acetaldol contained 2600 gm of acetaldol and 400 gm of acetaldehyde.

Then, the concentrated acetaldol was hydrogenated (Step (b)) without a solvent in presence of 1% wt. of nickel catalyst at hydrogen pressure 20 atm and temperature 78°C, to produce crude 1,3-butylene glycol. This was followed by digestion to convert higher aldehyde at a temperature of 130°C for 3 hrs.

Then, the crude 1,3-butylene glycol was distilled in column under reduced pressure to remove ethanol, butanol, water, salts, and high boiling impurities. Then, azeotropic distillation (Step (c)) was carried out by addition of 0.2 parts of demineralized water i.e., 400 gm of demineralized water, to remove odor causing impurities. The azeotropic distillation was carried out under reduced pressure (720 mm Hg) in the distillation column. 1,3-butylene glycol in the distillate was obtained from the kettle bottom in a quantity of 2000 gm having purity of 99.85%.

Comparative Example A
The process described in Example 1 of the present invention was repeated except stripping of acetaldehyde (Step (a)) was not performed. Hence, the crude mixture containing 40 % wt. of acetaldol, 30 % wt. of acetaldehyde, 7% wt. of crotonaldehyde and 2% wt. of HB compounds described above in Example 1, and 21% wt. water, was subjected to hydrogenation (Step (b)) and (Step (c)) as described in Example 1.

Comparative Example B
The process described in Example 1 was repeated except step (c) was not performed. 1, 3-butylene glycol obtained was not odorless.

Example 5
Determination of hydrogen consumption during hydrogenation (Step(b) of the process)
As described above, concentrated acetaldol subjected to hydrogenation in Examples 1 to 4 of the present invention and Comparative Example B contained 65% wt. of acetaldol. Whereas the crude mixture subjected to hydrogenation in Comparative Example A contained 40% wt. of acetaldol.

Table 1 shows the hydrogen consumption in step (b) by the process of Examples 1 to 4 of the present invention. Table 2 shows the hydrogen consumption in step (b) by the process of Comparative Example A. Hydrogen consumption by the process Comparative Example B was similar to that of Examples 1 to 4 of the present invention. The calculation of hydrogen consumption is based on 1 kg of 1,3-butylene glycol. In the examples 93.2% of 1,3-butylene glycol was isolated from the crude 1,3-butylene glycol.

Table 1
Basis : 1 Kg of 1,3-butylene glycol (BG)
Acetaldol 65% Qty# (gm) Conc.
(% wt.) 100% Basis (gm) Hydrogen Gas (m3)
Acetaldehyde 2000 10% 200 0.10
Crotonaldehyde as such plus Dehydrated aldol 10% 200 0.12
Acetaldol 65% 1300 0.33
HB compounds* (2-VC & Trans Sorb & Higher Aldehyde) 4% 80 0.06
0.61
Product Isolation Efficiency 93.2 0.65$ m3/Kg of 1,3-BG
*2-VC: 2 vinyl crotonaldehyde, trans sorb: trans sorbaldehyde
#2000 gm of concentrated acetaldol provides 1kg of 1,3-BG (as described in Example 2).
$: The value includes hydrogen consumption for 1,3-BG lost during isolation from the crude 1,3-BG.

The hydrogen gas consumption for each of the compounds was calculated as below:

1 mol of hydrogen= 0.002 kg of hydrogen.
As per Avogadro’s Law, 1 kg.mol of gas = 22.4 m3 of gas,
1 kg mol of hydrogen= 2 kg of hydrogen,
Therefore, 1 kg of hydrogen= 0.5 kg.mol of hydrogen= 11.2 m3 of hydrogen.

Amount of hydrogen (m3) =Moles of compound x moles of hydrogen used x 11.2

Acetaldehyde (MW= 44.05): 1 mole of acetaldehyde requires 1 mol of hydrogen for hydrogenation, i.e., 0.10 m3 of hydrogen per gm of Acetaldehyde.

(200/44.05)*0.002*11.2 = 0.10 m3 of hydrogen per gm of Acetaldehyde.

Similarly, 1 mole of crotonaldehyde (MW=70) requires 2 mol of hydrogen for hydrogenation, i.e., 0.12 m3 of hydrogen per gm of Crotonaldehyde.

(200 /70.0)*0.004*11.2= 0.12 m3 of hydrogen per gm of Crotonaldehyde.

1 mol of Acetaldol (MW=88) requires 1 mol of hydrogen for hydrogenation, i.e., 0.33 m3 of hydrogen per gm of Acetaldol.

(1300/88)*0.002*11.2= 0.33 m3 of hydrogen per gm of Acetaldol.

HB
1 mol of each of 2-VC (MW=96) and Trans Sorb (MW=96) requires 3 mol of hydrogen for hydrogenation, i.e., 0.06 m3 of hydrogen per gm of HB

(80/96)*0.006*11.2 = 0.056= 0.06 m3 of hydrogen per gm of HB.

Table 2
Basis : 1 Kg of butylene glycol (BG)
Acetaldol 40% Qty# (gm) Conc.
(% wt.) 100% Basis Hydrogen Gas (m3)
Acetaldehyde 3000 30% 900 0.46
Crotonaldehyde 7% 210 0.13
Acetaldol 40% 1200 0.31
HB compounds* (2-VC & Trans Sorb & Higher Aldehyde) 2% 60 0.04
0.94
Product Isolation Efficiency 93.2 1.00$ m3/Kg of 1,3-BG
*2-VC: 2 vinyl crotonaldehyde, trans sorb: trans sorbaldehyde
# 3000 gm of crude mixture provides 1 kg of 1,3-BG.
$: The value includes hydrogen consumption for 1,3-BG lost during isolation from the crude 1,3-BG.

Table 3
Examples 1 to 4 of the present invention Comparative Example A Comparative Example B
Hydrogen consumption in step (b)
(m3/kg of product) 0.65 1 0.65

Evaluation of 1,3-butylene glycol
1,3-butylene glycol obtained in Examples 1 to 4 of the present invention and Comparative Examples A and B was evaluated as below:
a. Determination of impurities: Odor causing impurities such as acetaldehyde and crotonaldehyde were determined by Gas Chromatography- Mass spectroscopy. The results are shown in Table 4.

Table 4
Examples 1 to 4 of the present invention Comparative Example B
Acetaldehyde Less than 0.5 ppm More than 5 ppm
Crotonaldehyde Less than 5 ppm More than 50 ppm

The content of impurities by the process of Comparative Example A was similar to that of Examples 1 to 4 of the present invention.

b. Determination of acid content: The acid content of 1,3-butylene glycol was determined by alkalimetric titration using 0.025N NaOH. The acid content of 1,3-butylene glycol was determined immediately after production and after storage for 2 years at a temperature of 15°C to 32°C, in a dry area kept out of direct exposure to sunlight.

The acid content of Examples 1 to 4 of the present invention was 50 ppm (0.005%). There is no change in the acid content of 1,3-butylene glycol produced by Examples 1 to 4 of the present invention when determined immediately after production and after storage for 2 years.

Table 3 shows that the process of the present invention by including step (a) significantly reduced hydrogen consumption during the hydrogenation carried out in step (b) in comparison to the process of Comparative Example A. Further, Table 4 shows that 1,3-butylene glycol produced by the process of the present invention by including step (c) had significantly less colour and odor causing impurities than Comparative Example B, thereby avoiding further downstream processing of 1,3-butylene glycol to make it colourless and odorless. Hence, the process of the present invention provided both reduced hydrogen consumption and 1,3-butylene glycol with reduced colour and odor causing impurities.

Further, 1,3-butylene glycol of the present invention was analysed by gas chromatography method described in JP patents JP 6979473 /JP 6979544 as described in Table 5.

Table 5:
Analytical Column: a column with dimethylpolysiloxane as a stationary phase (a film thickness of 1.0 µm, a length of 30 m, and an inner diameter of 0.25 mm);
Heating Conditions: heating from 80° C to 120° C at 5° C/min, then heating again to 160° C at 2° C/min and maintaining for 2 minutes, and further heating to 230° C at 10° C/min and maintaining at 230° C for 18 minutes;
Sample Introduction Temperature: 250° C;
Carrier Gas: helium;
Column Gas Flow Rate: 1 mL/min; and
Detector and Detection Temperature: a flame ionization detector (FID), 280° C.

Upon gas chromatography analysis, the relative retention time (RRT) of hydrides of the trimer of acetaldehyde was 0.65, RRT of acetals of 1,3-butylene glycol and acetaldol was 2.3 to 2.4, RRT of esters of acetic acid and 1,3-butylene glycol was 1.35 to 1.45.

The results of gas chromatography were compared with those of the Japanese patents as shown in Table 6.

Table 6
JP 6979473 JP 6979544 Present invention
Hydrides of the trimer of acetaldehyde RRT* of 1.6 to 1.8
More than 0 ppm to 1000 ppm or less RRT* of 1.6 to 1.8
More than 0 ppm to 600 ppm or less RRT* of 0.65
More than 0 ppm to 10 ppm or less
Acetals of 1,3-butylene glycol and Acetaldol having RRT* from 2.3 to 2.4 1000 ppm or less 150 ppm or less 50 ppm or less
*RRT- relative retention time

Table 6 shows that 1,3-butylene glycol of the present invention has significantly less concentration of hydrides of the trimer of acetaldehyde, and acetal compounds which are responsible for causing odor, than the 1,3-butylene glycol of the JP patents. Thus, 1,3-butylene glycol as per the present invention was odorless.

The impurity profile of 1,3-butylene glycol of the present invention as determined by gas chromatography is shown in Table 7.

Table 7:
Chemical name Maximum percentage concentration Percentage content
1,3-Butylene glycol 100 99.80
Water < 0.05 0.07
Acetic acid < 0.01 0.005
Ethanol < 0.002 0.001
2-ethyl butanol < 0.01 0.001
n-butanol Aggregate Content
< 0.05 Aggregate Content
< 0.05
1,3-butane diol acetate
1,3-Dioxane-2heptyl-4-methyl
2-Methyl-1-[1-(2-methylbutoxy)ethoxy] butane
Hexanol
2,4-pentanediol 3-methyl

Table 7 shows that ethanol, acetic acid, 2-ethyl butanol, water, n-butanol, 1,3-butanediol acetate, 1,3-dioxane-2-heptyl-4-methyl, 2-methyl-1-[1-(2-methylbutoxy)ethoxy] butane, hexanol and 2,4-pentanediol-3methyl are present as trace impurities in 1,3-butylene glycol.

The foregoing description of the disclosure has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.

,CLAIMS:
1. A process for preparation of 1,3-butylene glycol, the process comprising:
a. stripping off acetaldehyde from a crude mixture comprising acetaldol acetaldehyde and water, at a temperature in a range from 80°C to 90°C, to produce a concentrated acetaldol,
b. hydrogenating the concentrated acetaldol to produce a crude 1,3-butylene glycol, and
c. subjecting the crude 1,3-butylene glycol to azeotropic distillation.

2. The process as claimed in claim 1, comprising preparing the crude mixture by aldol condensation of acetaldehyde in an aqueous medium till less than 60% wt. of acetaldehyde is converted to acetaldol, and neutralizing the crude mixture, by adding an organic acid selected from acetic acid, propionic acid or butyric acid to an acid content up to 0.5% wt. or pH in a range from 5 to 6.

3. The process as claimed in claim 1, wherein the crude mixture in step (a) comprises 25% to 30% wt. of acetaldehyde and 40% wt. to 50% wt. of acetaldol.

4. The process as claimed in claim 1, wherein step (a) is carried out at the temperature in the range of 88°C to 90°C.

5. The process as claimed in claim 1, wherein the concentrated acetaldol comprises 60% wt. to 65% wt. of acetaldol and 8% wt. to 10% wt. or 10% wt. to 12% wt. of acetaldehyde.

6. The process as claimed in claim 1, wherein step (b) is carried out with hydrogen at a pressure in a range from 10 to 25 atmosphere and at a temperature in a range from 55°C to 120°C, in presence of Raney Nickel catalyst in a range from 0.1% wt. to 1% wt.

7. The process as claimed in claim 6, wherein step (b) is carried out with hydrogen in an amount of 0.65 m3 per kg of 1,3-butylene glycol product.

8. The process as claimed in claim 1, wherein azeotropic distillation is carried out by adding 0.2 to 0.4 parts of water per 1 part of 1,3-butylene glycol in the distillate.

9. The process as claimed in claim 1, wherein the 1,3-butylene glycol has purity in a range from 99.50% to 99.85%.

10. 1,3-butylene glycol comprising less than or equal to 0.002% of ethanol, less than or equal to 0.01% each of acetic acid and 2-ethyl butanol, less than 0.5% of water, and less than 0.05% of a mixture comprising n-butanol, 1,3-butanediol acetate, 1,3-dioxane-2-heptyl-4-methyl, 2-methyl-1-[1-(2-methylbutoxy)ethoxy] butane, hexanol and 2,4-pentanediol-3methyl.

11. 1,3-butylene glycol as claimed in claim 10 comprising less than 0.5 ppm of acetaldehyde, less than 5 ppm of crotonaldehyde, more than 0 ppm to 10 ppm or less of hydrides of the trimer of acetaldehyde, 50 ppm or less of acetals of 1,3-butylene glycol and acetaldol, and 50 ppm or less of esters of acetic acid and 1,3-butylene glycol.

12. 1,3-butylene glycol as claimed in claim 11, is characterized by gas chromatography analysis, the hydrides of the trimer of acetaldehyde have a relative retention time (RRT) of is 0.65, the acetals of 1,3-butylene glycol and acetaldol have a RRT of 2.3 to 2.4, the esters of acetic acid and 1,3-butylene glycol have a RRT of 1.35 to 1.45,
the conditions for the gas chromatography are
Analytical Column: a column with dimethylpolysiloxane as a stationary phase (a film thickness of 1.0 µm, a length of 30 m, and an inner diameter of 0.25 mm),
Heating Conditions: heating from 80°C to 120°C at 5°C/min, then heating again to 160°C at 2°C/min and maintaining for 2 minutes, and further heating to 230°C at 10° C/min and maintaining at 230°C for 18 minutes,
Sample Introduction Temperature: 250°C,
Carrier Gas: helium; Column Gas Flow Rate: 1 mL/min, and
Detector and Detection Temperature: a flame ionization detector (FID), 280° C.

13. 1,3-butylene glycol as claimed in claim 10 or 11 has a colour 10 on American Public Health Association (APHA) colour scale and is odorless.

14. A personal care composition comprising 1,3-butylene glycol as claimed in any one of the preceding claims 10 to 13.