An improved process for the preparation of 1,3-betylene glycol

Abstract: Disclosed are the improvements of a process for the preparation of 1,3-butylene glycol, in which the generation of by-products can be decreased, resulting in being capable of productiong 1,3-butylene glycol having high quality (e.g. an odorless, so-called "cosmetic grade") at a high-yield.

Description: The present invention relates to an improved process for the preparation of 1,3-butylene glycol. In particular, the present invention relates to the improvements of a process for the preparation of 1,3-butylene glycol, in which the generation of by-products can be decreased, resulting in it being capable of obtaining 1,3-butylene glycol having high quality (e.g. odorless) at a high yield. BACKGROUND OF THE INVENTION 1,3-butylene glycol is an organic compound which has a boiling point of 208°C under ordinary pressure, is viscous, colorless, transparent and low odor, exhibits an excellent solubility and a capability of producing chemically-stable derivatives, and is a useful compound as a solvent for coatings, starting materials for various synthetic resins and surfactants, a high-boiling-point solvent and antifreeze, food supplements, animal food supplements, a humectant for tobacco composition and an intermediate for preparation of various other compounds. Recently in particular, high-quality odorless 1,3-butylene glycol has been used as a solvent for toiletry products in the field of cosmetics due to its excellent moisture absorptive property, low volatility, low irritation and low toxicity. However, the scope for the application of 1,3-butylene glycol is limited due to a very minor quantity of residual odor. Most recently in particular, further improvement in the quality and the yield of an odorless, so-called "cosmetic grade" 1,3-butylene glycol has been strongly desired. Heretofore, there have been three widely-known processes for the preparation of 1,3-butylene glycol which are described below. (1) A method (British Patent N° 853266) in which acetaldol is first prepared by aldol condensation of acetaldehyde, and then catalytically hydrogenated to obtain 1,3-butylene glycol. (2) A method in which 1,3-butylene glycol is prepared by a hydration reaction of 1,3-butyleneoxide. (3) A method in which 1,3-butylene glycol is prepared from propylene and formaldehyde by the Prince Reaction. However, method (2) is not yet completed for use as an industrial manufacturing process, and therefore is unpractical. And, method (3) is also unpractical because it gives only a low yield. Therefore, 1,3-butylene glycol has been industrially manufactured by method (1). However, acetaldol is not stable due to its chemical structure. For example, crotonaldehyde is produced by dehydration of acetaldol, resulting in the production of various impure materials as by-products, for example, butanol, 2-butanone, etc. It is known that the above-mentioned acetaldol produced industrially is primarily composed of 2,4-dimethyl-1,3-dioxane-6-ol(aldoxane) which is a trimer of acetaldehyde as described in Industrial Engineering Chemistry 44, 1003 (1952). It is self-evident that if aldoxane is catalytically reduced, it would be decomposed by hydrogenation into 1,3-butylene glycol and ethanol as a reaction mechanism, which makes it objectionable for the purpose of industrially manufacturing 1,3-butylene glycol. As a method for solving the problem, for example, Japanese Patent Unexamined Publications 212384/1987 and 246529/1987 disclose that a crude reaction solution primarily consisting of paraldol is prepared while distilling out acetaldehyde after thermally decomposing aldoxane, followed by catalytically reducing paraldol to prepare 1,3-butylene glycol. Heretofore, unreacted acetaldehyde [a primary component in stream (C) of Figure 1] distilled out in a step [aldoxane decomposing column 1-3 in Figure 1] for preparing a solution [stream (B) of Figure 1] primarily consisting of aldoxane and paraldol in which aldoxane [a primary component in stream (A) of Figure 1] is thermally decomposed, has been recirculated [stream line (F)] to the aldol condensation step (a) [1-1 of figure 1]. In such an acetaldehyde-recirculating method, crotonaldehyde generated in the thermal decomposition step (b) [1-3 of figure 1] of aldoxane is also recirculated to the aldol condensation step together with unreacted acetaldehyde, unpreferably resulting in the generation of various impure components by a reaction with acetaldehyde, etc. in the aldol condensation step. The impure components, in particular, odor-causing impurities cannot be sufficiently removed in succeeding steps [e.g ethanol/butanol distillation columns, water distillation column, etc.], resulting in it adversely affecting to the quality (e.g. odor regulation) of 1,3-butylene glycol products for their uses in the field of cosmetics. Almost all of the water is removed together with the unreacted acetaldehyde through the thermal decomposition step of aldoxane and the simultaneous acetaldehyde distillation as described above, objectionably resulting in it becoming unsuitable of practical operation due to viscosity increase or crystallization of the crude solution discharged from the bottom of the decomposition column. Furthermore, conventional 1,3-butylene glycol products prepared by the hydrogenation of paraldol after removing crotonaldehyde as described above include minor amounts of odor-causing impurities even after being refined through the conventional refining steps described below. The conventional refining steps primarily have included an ethanol distillation step, a butanol distillation step, a water distillation step, a salts-removing step, a step for removing high-boiling-point ingredients and a step for removing low-boiling-point ingredients, leading to the production of a refined 1,3-butylene glycol. On the other hand, it is known (e.g. Japanese Examined Patent Publication N° 80139/1991) that very minor amounts of odor-causing impurities can be acceleratedly removed by distillation while charging water so as to obtain an odorless 1,3-butylene glycol (e.g. a product having a purity of 99.7-99.97%) from a 1,3-butylene glycol product having odor (e.g. a commercially supplied product having a purity of more than 98%). Even though the method described in the Publication n° 80139/1991 is carried out, the odorless 1,3-butylene glycol can be obtained only at a yield of 50 to 60%. The present invention has been completed as a result of studies by the present inventor to solve the above-described problems. SUMMARY OF THE INVENTION The object of the present invention is to provide a process for the preparation of 1,3-butylene glycol having a high quality and at a high yield. The feature of the present invention is an improved process for the preparation of 1,3-butylene glycol by steps (a), (b) and (c); (a) aldol condensation of acetaldehyde in the presence of an alkali catalyst to obtain a reaction crude solution primarily containing aldoxane, acetaldehyde and water; (b) thermal decomposition of aldoxane to obtain paraldol while distilling off a distillate containing acetaldehyde, water and small amounts of crotonaldehyde from the reaction crude solution; (c) hydrogenation of paraldol to obtain 1,3-butylene glycol in the presence of a catalyst; characterised in that fresh water is charged into the top of a distillation column while removing water after having removed ethanol and butanol from a crude 1,3-butylene glycol solution containing ethanol and butanol generated in said hydrogenation step (c). According to an advantageous embodiment, said fresh water is deionized water. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram exhibiting a process for preparing aldoxane and paraldol in which steps (a) and (b) are combinedly shown. Step (a) includes an aldol condensation reactor (1-1), and also as a supplement includes a neutralization tank (1-2). Step (b) includes an aldoxane decomposition column (1-3), and supplementarily includes an acetaldehyde-refining column (1-4). Figure 2 is a block diagram exhibiting a process for preparing 1,3-butylene glycol in which step (c) is shown. Step (c) includes a hydrogenation reactor (2-1) and alcohols distillation column (2-2). Figure 3 is a block diagram exhibiting a step for refining a crude 1,3-butylene glycol, in which a water-distillation column (3-1), a salts-removing column (3-2) and a distillation column (3-3) for removing high-boiling-point ingredients and a distillation column (3-4) for removing low-boiling-point ingredients. Figure 4 is a graph in which the distillation yield of odorless 1,3-butylene glycol products is shown in the ordinate, and the amount of by-produced alcohols based on 1000 of odorless 1,3-butylene glycol products is shown in the abscissa. DETAILED DESCRIPTION OF THE INVENTION The present invention is described hereinafter in more detail based on accompanying Figures 1 to 3 which are a block diagram exhibiting a process for preparing 1,3-butylene glycol in which steps (a), (b) and (c) are combinedly shown. In accordance with the present invention, there is provided an improved process for the preparation of 1,3-butylene glycol by steps (a), (b) and (c); (a) aldol condensation step of acetaldehyde in the presence of an alkali catalyst to obtain a crude reaction solution primarily containing aldoxane, acetaldehyde, water and small amounts of crotonaldehyde ; (b) thermal decomposition step of aldoxane to obtain paraldol while distilling off a distillate containing acetaldehyde, water and small amounts of crotonaldehyde from the crude reaction solution ; (c) hydrogenation step of paraldol to obtain 1,3-butylene glycol in the presence of a catalyst; characterised in that fresh water is charged into the top of a distillation column while removing water after having removed ethanol and butanol from a crude 1,3-butylene glycol solution containing ethanol and butanol obtained in said hydrogeneation step (c). A crude 1,3-butylene glycol solution obtained in the hydrogeneration step (c) usually contains ethanol, butanol, water, salts generated in neutralization tank (1-2) other than 1,3-butylene glycol which is the desired product. Accordingly, ethanol and butanol have been firstly removed and then water has been removed by distillation while being partially refluxes at the top of the distillation column, followed by removing the salts, the high-boiling-point ingredients and low-boiling-point ingredients, resulting in being capable of obtaining a 1,3-butylene glycol product [e.g. described in Japanese Unexamined Patent Publication N°156738/1988]. However, odor-causing impurities cannot be sufficiently removed only by the above-mentioned conventional water distillation, undesirably resulting in being incapable of obtaining an odorless 1,3-butylene glycol product at a high-yield. An odorless 1,3-butylene glycol can be prepared at a high-yield through the combination of the present invention with the removal of the salts, the high-boiling-point ingredients and low boiling-point ingredients. In Figures 3, 3-1 is a water distillation column, 3-2 is a salts-removing column (e.g. a thin-layer evaporator), 3-3 is a column for removing the high-boiling-point ingredients, 3-4 is a column for removing low-boiling-point ingredients. A crude 1,3-butylene glycol solution after the removal of alcohols primarily containing 1,3-butylene glycol, water, the high-boiling-point ingredients, the low-boiling-point ingredients and salts is charged into the water-distillation column (3-1). Although a perforated plate column and a bubble-cap column, etc. are to be preferably used as the water-distillation column (3-1), there can be more preferably used a packed column having low-pressure loss, in which a packing material is contained such as Sultzer-packing or Melapack (a trade name of Sumitomo Heavy Industries), etc. in order to maintain the distillation temperatures to as low as possible, which otherwise would cause the thermal decomposition of 1,3-butylene glycol above 200°C resulting in adversely affecting it with regard to oder [described in Japanese Unexamined Patent Publication n°156738/1998]. Furthermore, subjecting 1,3-butylene glycol to heated conditions for a long time (retention time) would result in adversely affecting it with regard to odor. Accordingly, preferably used is a reboiler having a short retention time in the side of process fluids, for example, a thin-layer evaporator such as a naturally falling-film type thin-layer evaporator or a force-scraping type thin-layer evaporator, etc. The present invention is characterised in that fresh water is charged into the top portion of the column (3-1) while distilling off water. The fresh water may include tap water, preferably pure water (e.g. deionized water), and more preferably distilled water from the view point of an advanced refining process. A crude 1,3-butylene glycol after removing the alcohols has to be charged into the vicinity of a middle portion of the water-distillation column (3-1). When the portion is excessively higher, the concentration of 1,3-butylene glycol in the distillate increases, unpreferably resulting in the loss of 1,3-butylene glycol. On the other hand, when it is excessively lower, the water content in the liquid discharged from the bottom of the column (3-1) would unpreferably increase. The liquid which includes 1,3-butylene glycol containing salts and high-boiling ingredients is discharged from the bottom of the column (3-1), and then it is transferred to a salts-removing column (3-2). The amount of the fresh water to be charged into the top portion of the water-distillation column (3-1) is from 1 to 200 parts by weight, preferably from 5 to 50 parts by weight based on the amount of the crude liquid to be charged. In the case when it is less than 1 part, impurities which adversely affect the odor of a 1,3-butylene glycol product cannot be sufficiently removed. On the other hand, in the case when it is more than 100 parts, although the impurities can be sufficiently removed, the thermal energy load in the reboiler would unpreferably increase. Reflux in the top of the water-distillation column (3-1) may be carried out or not. In the case that reflux is not carried out, the fresh water is preferably charged into the vicinity of the top of the water-distillation column (3-1). On the other hand, in the case that reflux is carried out, the fresh water is preferably charged into the vicinity of a middle portion of the water-distillation column (3-1). The fresh water at room temperature can be charged without any problems. The pressures of the top of the water-distillation column (3-1) are generally reduced pressures of less than 0.133 bar (100 Torr), preferably 0.0267-0.080 bar (20 to 60 Torr). In the case that the pressures are less than 0.0267 bar (20 Torr), the cooling energy load in a condenser would unpreferably increase. When the water distillation and the charging of the fresh water are carried out at the above-mentioned pressures, the temperatures in the distillation column would be inevitably kept within a range of 20 to 40°C at the bottom portion of the column. As described above, compounds which are removed due to being accompanied by the newly charged fresh water primarily include butanol, 2-ethylbutanol, 2,4-dimethyldioxane, etc. which are produced as by-products in a hydrogenation reaction of the crude solution primarily containing aldoxane and paraldol. As a result of the removal, the purity and yield of a 1,3-butylene glycol product are improved, resulting in effectively obtaining a high quality 1,3-butylene glycol not containing odor-causing ingredients. In the following, although Synthesis Examples, Examples and Comparative Examples are described in order to more specifically illustrate the present invention, the scope of the present invention is not limited to the Examples. Examples and comparative examples There were carried out aldol condensation reaction, aldoxane decomposition reaction, acetaldehyde distillation, [acetaldehyde refining (removal of crotonaldehyde)], (refined) acetaldehyde recirculation to aldol condensation step, and hydrogenation reaction of a solution discharged from an aldoxane decomposition column-bottom (1-3) to prepare 1,3-butylene glycol, through steps as shown in Figure 1. It is noted that a water content was quantitatively measured by Karl Fisher's method, and other ingredients were quantitatively measured with a gas-chromatograph and NMR analyser. Example 1 A 1-litre jacketed aldol condensation reactor (1-1) was charged with 500 g of acetaldehyde aqueous solution (acetaldehyde/water = 90/10 by weight), after which it was cooled at temperatures ranging from 15 to 20°C. Crotonaldehyde in new acetaldehyde charged into the reactor was not detected. Subsequently, 10 g of 0.5 % caustic soda aqueous solution was gradually added dropwise as an alkali catalyst while vigorously stirring, was then allowed to react while maintaining at 20°C for 7 hours to obtain a crude reaction solution primarily containing aldoxane, acetaldehyde, water and minor amounts of crotonaldehyde. After completion of the reaction (aldol condensation reaction) and letting it stand for 2 hours, neutralization was carried out with a diluted acetic acid in order to precisely adjust the pH to 6.2 in a neutralization vessel (1-2), followed by letting it stand for 2 hours. Subsequently, a continuous flash evaporator [aldoxane decomposition column (1-3)] was charged with the crude reaction solution [corresponding to stream (A)] having 24.88 % by weight of acetaldehyde, 63.74 % by weight of aldoxane, 10.46 % by weight of water, 0.30 % by weight of crotonaldehyde and 0.62 % by weight of other ingredients after neutralization. A distillate containing acetaldehyde, water and small amounts of crotonaldehyde was distilled off from the flash evaporator in the solution temperature of 80°C while adjusting heating temperatures for 86 minutes (based on discharging). The relative amount of the obtained distillate [corresponding to stream (C)] was 46.5 %. There was discharged a solution [corresponding to stream (B)] having 54.50 % by weight of aldoxane, 31.35 % by weight of paraldol, 10.56 % by weight of water, 1.63 % by weight of crotonaldehyde and 1.95% by weight of other ingredients from the evaporator (1-3). The distillate containing acetaldehyde, water and small amounts of crotonaldehyde distilled off from the flash evaporator was charged into an acetaldehyde-refining column (1-4) equipped with a discharging line (1-4-5), a condenser (1-4-3), a decanter (1-4-4) and a recirculating line (1-4-6) while maintaining the temperature of the top of the evaporator at approximately 20°C, and that of the bottom of the evaporator at approximately 100°C and ordinary pressures to obtain 192 g of a refined acetaldehyde containing crotonaldehyde of less than 0.1% by removing crotonaldehyde from the discharging line (1-4-5). The refined acetaldehyde was used in Example 2. Subsequently, 200 g of the solution discharged form the evaporator bottom (1-3) was charged into a 1-litre autoclave, and then 15% by weight of a Raney nickel catalyst based on the solution was charged, followed by hydrogenation reaction in the pressure of 80 kg/cm 2 and the temperature of 120°C for 30 minutes. A crude reaction solution obtained was refined through an alcohol distillation column (2-2), a water-distillation column (3-1), a salts-removing column (3-2), a column (3-3) for removing high-boiling-point ingredients and a column (3-4) for removing low-boiling-point ingredients to obtain an odorless 1,3-butylene glycol product with a distillation yield of 76.6 %, and 200 of alcohols were by-produced on 1000 of 1,3-butylene glycol. It is noted that there were conducted the odor evaluation tests in which 5 expert inspectors immediately smelled to compare in atmosphere. Example 2 Similar procedures as described in Example 1 were repeated, except that the refined acetaldehyde obtained in Example 1 was used by applying the operating conditions in the aldoxane decomposition column (1-3) as shown in Table 1. The distillation yield of an odorless 1,3-butylene glycol product was 78.0 %. Other results are shown in Table 1, and 280 of alcohols were by-produced based on 1000 of the 1,3-butylene glycol product. Comparative examples 1 and 2 Similar procedures as described in Example 1 were repeated, except that a distillate from the aldoxane decomposition column (1-3) was directly recirculated into the aldol condensation step without passing through the acetaldehyde-refining column (1-4). The distillation yield of an odorless 1,3-butylene glycol product was 59.6 % in comparative example 1 and 70.0% in comparative example 2, respectively, and 200 and 280 of alcohols were by-produced based on 1000 of the 1,3-butylene glycol product in comparative examples 1 and 2, respectively. Other results are shown in Table 1. Operating conditions and results are shown together with the results in the Examples in Table 1. Example 3 Similar procedures as described in Example 2 were repeated, except that temperature in the aldoxane decomposition column was changed to 85°C. The distillation yield of an odorless 1,3-butylene glycol product was 65.0%, and 150 of alcohols were by-produced based on 1000 of the 1,3-butylene glycol product. Comparative example 3 Similar procedures as described in comparative example 1 were repeated, except that temperature in the aldoxane decomposition column was changed to 85°C. The distillation yield of an odorless 1,3-butylene glycol product was 34.1%, and 150 of alcohols were by-produced based on 1000 of the 1,3-butylene glycol product. EXAMPLE COMPARATIVE EXAMPLE 1 2 1 2 *Operating conditions in the aldoxane decomposition column Temperature (°C) 80 75 80 75 Pressure (bar) [Torr] (1) [760] (1) [760] (1) [760] (1) [760] Retention time (min) 86 86 86 86 *Composition of a solution [stream (F)] recirculated to the aldol condensation reactor (1-1) Acetaldehyde/water 90/10 88/12 87/13 85/15 Crotonaldehyde content (%) in starting acetaldehyde 0 <0.1 3.60 2.34 *Composition (wt%) of a solution [stream (A)] charged into the aldoxane decomposition column Acetaldehyde 24.88 25.19 25.06 22.29 Aldoxane 63.74 61.96 59.76 65.04 Paraldol - - - - Water 10.46 11.93 12.00 11.00 Crotonaldehyde 0.30 0.45 1.61 0.81 Other ingredients 0.62 0.91 1.57 1.10 *Composition (wt%) of a crude solution [stream (B)] discharged from the aldoxane decomposition column Acetaldehyde - - - - Aldoxane 54.50 41.44 38.92 56.71 Paraldol 31.35 44.12 43.44 28.39 Water 10.56 11.16 11.50 10.50 Crotonaldehyde 1.63 1.59 2.46 1.70 Other ingredients 1.95 1.68 3.68 2.69 * Composition (wt%) of a crude reaction solution after hydrogenation Ethanol 14.00 10.81 19.03 13.03 Water 11.42 18.39 11.76 10.75 Butanol 1.63 1.68 2.51 1.74 1,3-butylene glycol 71.14 67.01 68.12 65.11 High boiling point ingredients 1.62 1.72 3.53 2.62 Other ingredients 0.19 0.39 1.06 0.77 Example 4 Similar procedures as described in Examples 1 to 3 were repeated, except that water distillation was carried out while charging fresh water into the top of the water distillation column (3-1). Yield was 89% by weight based on the amount charged into the column (3-3) for removing the high-boiling-point ingredients. Yield was 93% by weight based on the amount charged into the column (3-4) for removing the low-boiling-point ingredients. Comparative Example 4 Similar procedures as described in Example 4 were repeated, except that water distillation was carried out without charging fresh water into the top of the water distillation column (3-1). Yield was 83% by weight based on the amount charged into the column (3-3) for removing the high-boiling-point ingredients. Yield was 89% by weight based on the amount charged into the column (3-4) for removing the low-boiling-point ingredients. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can made therein without departing from the scope thereof.

Claims: A process for the preparation of 1,3-butylene glycol by steps (a), (b) and (c) ; (a) aldol condensation step of acetaldehyde in the presence of an alkali catalyst to obtain a crude reaction solution primarily containing aldoxane, acetaldehyde, water and small amounts of crotonaldehyde ; (b) thermal decomposition step of aldoxane to obtain paraldol while distilling off a distillate containing acetaldehyde, water and small amounts of crotonaldehyde from the crude reaction solution; (c) hydrogenation step of paraldol to obtain 1,3-butylene glycol in the presence of a catalyst; characterised in that fresh water is charged into the top of a distillation column while removing water after having removed ethanol and butanol from a crude 1,3-butylene glycol solution containing ethanol and butanol obtained in said hydrogenation step (c). The process according to claim 1, characterised in that said fresh water is deionised water. The process according to claim 1 or 2, characterised in that said fresh water is charged in the top portion of the water-distillation column (3-1) from 1 to 200 parts by weight, preferably from 5 to 50 parts by weight, based on the amount of the crude liquid to be charged.

Inventors: NISHIGUCHI KAZUHISA, NISHIGUCHI, KAZUHISA
Applicants: DAICEL CHEM, DAICEL CHEMICAL INDUSTRIES, LTD.
Application year: 1993
Main classification: C07C31
IPC codes: C07D319, C07C29