Method for preparing pharmaceutical grade 1, 2-propylene glycol from industrial grade 1, 2-propylene glycol

Abstract

According to the method, industrial-grade 1, 2-propylene glycol co-produced by a dimethyl carbonate process through a transesterification method is taken as a raw material, and purification processes of activated carbon adsorption impurity removal, deodorant impurity removal and rectification impurity removal are carried out, so that various indexes such as chromaticity, odor, purity and ultraviolet light transmittance of the obtained 1, 2-propylene glycol product reach the quality indexes of an imported pharmaceutical-grade 1, 2-propylene glycol product. According to the method disclosed by the invention, the pharmaceutical grade propylene glycol can be prepared with high quality, and a good development prospect and huge economic benefits are undoubtedly brought to the propylene glycol industry.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical industry, and particularly relates to a method for preparing pharmaceutical-grade 1,2-propylene glycol from industrial-grade 1,2-propylene glycol. BACKGROUND

[0002] 1,2-propylene glycol (PG for short) is an important chemical raw material, which has multiple uses: in the food industry, 1,2-propylene glycol can be used as a food emulsifier, stabilizer, thickening agent, etc., and also can be used as a solvent for food colorants and flavorings; in the pharmaceutical industry, 1,2-propylene glycol can be used as an excipient, preservative, softening agent, etc., and also can be used as a solvent for some medical supplies such as penicillin and vitamins; in industry, 1,2-propylene glycol is not only a raw material for surfactants, demulsifiers, emulsifiers, but also is an important raw material for epoxy resins, polyurethane resins, unsaturated polyesters, etc.

[0003] Currently, the production process of 1,2-propanediol can be divided into "hydration method" and "ester exchange method". The "hydration method" process uses propylene oxide and water as raw materials, and carries out pressurized reaction under the action of no catalyst or acidic catalyst, and then the 1,2-propanediol is obtained after purification. The "hydration method" process is simple, short process, and the quality of the produced 1,2-propanediol is better. At present, the pharmaceutical grade 1,2-propanediol sold on the market is mainly produced by "hydration method". The "ester exchange method" production process uses propylene carbonate and methanol as raw materials, and sodium methoxide as catalyst to produce dimethyl carbonate and co-produce 1,2-propanediol. Since the "ester exchange method" is a co-production process, a set of device produces dimethyl carbonate and 1,2-propanediol at the same time, which has obvious cost advantage; but there are more side reactions, so the 1,2-propanediol produced by "ester exchange method" is easy to discolor, has strong irritating smell, and the quality of propylene glycol product is poor, only reaches industrial grade standard, and is difficult to meet the requirements of pharmaceutical grade. This is mainly because the product 1,2-propanediol produced by ester exchange method contains various trace impurities, including 1-methoxy-2-propanol, 2-methoxy-1-propanol, 1-hydroxy-2-propanone, 1-(2-propenyloxy)-2-propanol, 3-(1,3-dimethylbutoxy)-2-butanol, 1-(2-methoxy-1-methyl-ethoxy)-2-propanol, 1-(2-allyloxy-1-methyl-ethoxy)-2-propanol, 1-(2-methoxypropoxy)-2-propanol, 1,2-dimethoxypropane, 4-hydroxy-4-methyl-2-pentanone, methoxy-acetic acid ethyl ester, etc., the total amount of impurities is about 0.2%~0.3%, and the content of some impurities is as low as 0.005%. These impurities are of many types and small amounts, which are difficult to remove. At present, the ester exchange method has occupied the dominant position in the domestic industrial production due to its process advantage of being able to co-produce dimethyl carbonate and 1,2-propanediol, but the 1,2-propanediol is mainly industrial grade, which cannot meet the requirements of pharmaceutical grade propylene glycol, and cannot be applied in the industries of medicine, food, essence, perfume, cosmetics and high-grade resin. The 1,2-propanediol produced by ester exchange method cannot meet the pharmaceutical grade, and has low sales price and poor economic benefit. Therefore, refining the industrial grade 1,2-propanediol to meet the quality requirements of pharmaceutical grade, and then reaching the quality level of imported 1,2-propanediol, will greatly promote the production operation of dimethyl carbonate device by ester exchange method and improve the economic benefit of the device.

[0004] CN101906020A discloses that the by-product of ester exchange method 1,2-propanediol and the desalted water added with a deodorant are sent into a reaction rectifying tower, the deodorant is one of the compounds of alkylamine, hydroxylamine, hydrazine, 2,4-dinitrophenylhydrazine or a mixture of several, and the reaction is carried out by using the deodorant and the trace impurities in 1,2-propanediol to remove the odor. The 1,2-propanediol obtained by rectification has no obvious odor, but the ultraviolet light transmittance at 220 nm is not reported. Through the experiment of the applicant repeating the disclosed patent, the ultraviolet light transmittance at 220 nm of the obtained 1,2-propanediol is 40%, which is obviously lower than the ultraviolet light transmittance at 220 nm of the imported medical grade 1,2-propanediol of Dow Chemical Company, which is 75%, and the product quality needs to be further improved. CN116462573A discloses a high-efficiency and low-temperature method for preparing medical grade 1,2-propanediol. The main steps include: 1. mixing and adsorption: adding ethanol into industrial grade 1,2-propanediol to reduce the viscosity, then adding solid adsorbent (such as activated carbon, zeolite, adsorption resin, etc.) to adsorb impurities, after adsorption, filtering and collecting the liquid phase; 2. azeotropic distillation: adding water into the liquid phase to form an azeotrope with ethanol, then heating to the azeotropic temperature (78.1℃), and evaporating water and ethanol to obtain medical grade 1,2-propanediol with high purity. However, the patent does not report the odor and light transmittance of 1,2-propanediol. Li Ling (1,2-propanediol catalytic refining process, Tianjin University master thesis, 2004) used a fixed bed reactor to screen solid acid catalysts, and found that when the catalytic conditions were atmospheric pressure, liquid hourly space velocity 0.98 h-1, and reaction temperature 100℃, using amorphous aluminum silicate as the catalyst to treat 1,2-propanediol could achieve good impurity removal effect, and the best impurity removal effect was achieved when the content of silicon dioxide reached 40%. Based on this catalyst, Li Ling also determined the rectification operation conditions, i.e. when the tower top pressure was 50 mmHg and the reflux ratio was 2, the best impurity removal effect was achieved, and the purity of the obtained 1,2-propanediol reached 99.9494%, meeting the requirements of medical grade, but the odor and ultraviolet light transmittance were not reported. Liu Jing (Study on the removal of odor of industrial grade 1,2-propanediol solution, Qingdao University of Science and Technology master thesis, 2014) in order to find out the reason for the irritating odor of 1,2-propanediol produced by the ester exchange method, first determined the composition of the impurities in 1,2-propanediol by GC-MS, then treated 1,2-propanediol by vacuum batch rectification. The experimental results show that when the reflux ratio is 3 and the tower top pressure is 73 kPa, the top product has a strong irritating odor, while the 1,2-propanediol at the bottom of the tower has no odor and the purity is close to 99.9%, which is considered to meet the requirements of medical grade.The applicant believes that it is difficult to remove trace impurities by simple distillation, and the industrial 1,2-propanediol is also obtained by distillation. If the odor can be removed by simple distillation, the 1,2-propanediol byproduct of dimethyl carbonate by ester exchange method can be obtained by distillation to obtain pharmaceutical grade 1,2-propanediol. In fact, the factory cannot do it at present.

[0005] Therefore, there is an urgent need in the art for a low-cost, simple-to-operate method for preparing pharmaceutical grade 1,2-propanediol from industrial grade 1,2-propanediol. SUMMARY

[0006] The present application aims to overcome the defects in the prior art, and the quality of the obtained pharmaceutical grade 1,2-propanediol cannot be compared with that of imported 1,2-propanediol. By simple refining technology, industrial grade 1,2-propanediol is prepared into pharmaceutical grade 1,2-propanediol, reaching the quality level of imported 1,2-propanediol.

[0007] The present application is a method for preparing pharmaceutical grade 1,2-propanediol from industrial grade 1,2-propanediol, which comprises three parts of activated carbon adsorption of impurities, removal of odorants to remove odor impurities, and distillation to remove trace impurities. The main steps of the preparation method are: (1) mixing and adsorbing industrial grade 1,2-propanediol with activated carbon for a period of time; (2) separating the solid-liquid compound of step 1 to obtain filtrate 1; (3) adding an odor removal agent to the filtrate 1 and reacting at a certain temperature and time; (4) adding the mixture of step 3 to a distillation column for distillation, and taking the middle fraction as pharmaceutical grade 1,2-propanediol.

[0008] The activated carbon is one or a mixture of wood activated carbon, bamboo activated carbon, coal activated carbon, and coconut shell activated carbon, and the amount is 1% to 10% of the mass of 1,2-propanediol, and the adsorption is carried out at 20°C to 60°C for 20 to 180 minutes.

[0009] The solid-liquid separation is one of sedimentation, centrifugal separation, plate and frame filtration, and membrane filtration.

[0010] The odor removal agent is one or a mixture of monoethanolamine, diethanolamine, triethanolamine, diisopropyl ethanolamine, N-methyl diethanolamine, and diethanol monoisopropylamine.

[0011] The amount of odor removal agent added is 5 to 50 mg / L of the filtrate 1.

[0012] The reaction temperature is 40 to 80°C, and the reaction time is 30 to 120 minutes.

[0013] The theoretical plate number of the rectification tower is 10-40, and the pressure is 5-20 kPa.

[0014] The reflux ratio of the rectification tower is 0.5-5.0.

[0015] The beneficial effects of the present application are: using industrial-grade 1,2-propanediol co-produced in dimethyl carbonate process by ester exchange method as raw material, through the purification process of activated carbon adsorption, impurity removal and rectification, finally the color, odor, purity and ultraviolet transmittance and other indicators reach the quality indicators of imported pharmaceutical-grade 1,2-propanediol product. DETAILED DESCRIPTION

[0016] The present application will be further described by examples, and the purpose is only to better understand the content of the present application. Therefore, the examples do not limit the protection scope of the present application: Example 1

[0017] In a 1000ml flask, 500g of 1,2-propanediol co-produced in dimethyl carbonate process by ester exchange method was added, and 2% of coconut activated carbon was added at 50℃ to stir and adsorb the raw material. After adsorbing for 30 minutes, filtration was carried out, 20mg / L of triethanolamine was added to the obtained clear night, 20% (wt) of deionized water was added, and stirring was carried out at a temperature of 70℃ for 60 min, and then vacuum rectification was carried out in a rectification tower. The rectification tower was filled with θ ring stainless steel packing, the theoretical plate number was 25, the tower top pressure was 8 kPa, the tower bottom was heated, and the reflux ratio was 1.0. The front fraction water and impurities were removed, and the middle fraction was taken as the 1,2-propanediol product. The product quality indicators are shown in Table 1.

[0018] Example 2 In a 1000ml flask, 500g of 1,2-propanediol co-produced in dimethyl carbonate process by ester exchange method was added, and 3% of wooden activated carbon was added at 40℃ to stir and adsorb the raw material. After adsorbing for 50 minutes, filtration was carried out, 30mg / L of diethanolamine was added to the obtained clear night, 15% (wt) of deionized water was added, and stirring was carried out at a temperature of 70℃ for 80 min, and then vacuum rectification was carried out in a rectification tower. The rectification tower was filled with θ ring stainless steel packing, the theoretical plate number was 25, the tower top pressure was 8 kPa, the tower bottom was heated, and the reflux ratio was 1.0. The front fraction water and impurities were removed, and the middle fraction was taken as the 1,2-propanediol product. The product quality indicators are shown in Table 1.

[0019] Example 3 In a 1000 ml flask, 500 g of 1,2-propanediol co-produced in dimethyl carbonate process by ester exchange method was added, and 4% of bamboo activated carbon was added to the raw material for stirring adsorption treatment at 50°C. After adsorption for 60 minutes, filtration was performed, 40 mg / L of monoethanolamine was added to the obtained clear solution, 25% (wt) of deionized water was added, stirring was performed at a temperature of 80°C for 100 min, and then vacuum rectification was performed in a rectification column. The rectification column was filled with θ ring stainless steel packing, the theoretical plate number was 25, the top pressure was 6 kPa, the bottom of the column was heated, and the reflux ratio was 2.0. The front fraction water and impurities were removed, and the middle fraction was taken as the 1,2-propanediol product. The product quality index is shown in Table 1.

[0020] Example 4 In a 1000 ml flask, 500 g of 1,2-propanediol co-produced in dimethyl carbonate process by ester exchange method was added, and 5% of coal activated carbon was added to the raw material for stirring adsorption treatment at 35°C. After adsorption for 120 minutes, filtration was performed, 15 mg / L of diisopropanolamine was added to the obtained clear solution, 30% (wt) of deionized water was added, stirring was performed at a temperature of 60°C for 120 min, and then vacuum rectification was performed in a rectification column. The rectification column was filled with θ ring stainless steel packing, the theoretical plate number was 25, the top pressure was 6 kPa, the bottom of the column was heated, and the reflux ratio was 2.0. The front fraction water and impurities were removed, and the middle fraction was taken as the 1,2-propanediol product. The product quality index is shown in Table 1.

[0021] Table 1

Claims

1. A process for the preparation of pharmaceutical grade 1,2-propanediol from technical grade 1,2-propanediol, characterized in that, The main steps of the preparation method are: (1) mixing and adsorbing industrial-grade 1,2-propanediol with activated carbon for a period of time; (2) separating the solid-liquid compound of step 1 to obtain filtrate 1; (3) adding a deodorizing agent to the filtrate 1 and reacting at a certain temperature and time; (4) adding the mixture of step 3 to a rectifying column for rectification, cutting off the initial and heavy distillates, and taking the middle distillate as the pharmaceutical-grade 1,2-propanediol.

2. The production method according to claim 1, wherein The activated carbon is one or a mixture of several of wood-based activated carbon, bamboo-based activated carbon, coal-based activated carbon, and coconut shell activated carbon.

3. The production method according to claim 1 or 2, characterized by, The amount of activated carbon used is 1% to 10% of the mass of 1,2-propanediol, and the adsorption is carried out at 20°C to 60°C for 20 to 180 minutes.

4. The production method according to claim 1, wherein The solid-liquid separation uses one of sedimentation, centrifugal separation, plate and frame filtration, and membrane filtration.

5. The production method according to claim 1, wherein The deodorizing agent is one or a mixture of several of monoethanolamine, diethanolamine, triethanolamine, diisopropanolamine, N-methyldiethanolamine, and diethanol monoisopropanolamine.

6. The production method according to claim 1 or 5, wherein The amount of deodorizing agent added is 5 to 50 mg / L of filtrate 1.

7. The production method according to claim 1, wherein The reaction temperature is 40 to 90°C, and the reaction time is 30 to 120 minutes.

8. The production method according to claim 1, wherein The theoretical plate number of the rectifying column is 10 to 50, and the pressure is 5 to 30 kPa.

9. The production method according to claim 1, wherein The reflux ratio of the rectifying column is 0.5 to 5.0.

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