Supercritical fluid extraction and purification process for pentanediol

Abstract

The invention relates to the technical field of pentanediol extraction and purification, in particular to a pentanediol supercritical fluid extraction and purification process which comprises the following specific steps: putting a modified raw material into an extraction kettle, injecting an ethane-methanol mixture, and fully reacting; supercritical ethane dissolved with pentanediol enters a first-stage separation kettle from the extraction kettle, and most of gaseous ethane and a mixture containing pentanediol are separated out; transferring the pentanediol-containing mixture subjected to primary separation and acetone into a secondary separation kettle, after separation is finished, reducing the pressure of the separation kettle, separating the pentanediol solution from the separation kettle, cooling to reach a supersaturated state, and separating out pentanediol crystals; and washing the crystal with cold deionized water, and carrying out vacuum drying to obtain pentanediol. The ethyl chloroformate and the impurities are subjected to esterification reaction, so that the physical and chemical properties of the impurities are different from those of pentanediol, and the pentanediol is separated more efficiently due to different solubility in the subsequent extraction process.

Description

Technical Field

[0001] The invention relates to the technical field of pentanediol extraction and purification, in particular to a pentanediol supercritical fluid extraction and purification process. Background Art

[0002] Pentylene glycol is a key raw material for the synthesis of the fungicide propiconazole, and its purity directly affects the quality and performance of propiconazole. High-purity pentylene glycol can ensure the high efficiency and stability of the fungicide and improve its control effect in agricultural production. As an excellent moisturizer and preservative, pentylene glycol is widely used in cosmetics. Cosmetics have extremely high requirements for the purity and safety of raw materials. Only high-purity pentylene glycol can meet the requirements of cosmetics without irritation and side effects, ensuring the quality of the product and the health of consumers.

[0003] Traditional extraction methods, such as solvent extraction, often require the use of a large amount of organic solvents, which may remain in the product after extraction, affecting the quality and safety of the product. For example, in the food, medicine and other industries, there are strict restrictions on the amount of residual organic solvents in products, and traditional methods are difficult to meet the requirements of high purity and no residue. Some traditional separation methods are not effective in separating substances with similar properties, and it is difficult to obtain high-purity products. For example, pentanediol and other alcohols or impurities with similar structures are relatively close in physical and chemical properties. It is difficult to separate and purify them efficiently using conventional separation methods, resulting in limited product purity and unable to meet the needs of certain high-end application fields. In view of this, we propose a pentanediol supercritical fluid extraction and purification process. Summary of the invention

[0004] The object of the present invention is to provide a pentanediol supercritical fluid extraction purification process to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides a pentanediol supercritical fluid extraction and purification process, comprising the following steps:

[0006] S1.1. Place the modified raw material into an extraction kettle, inject a mixture of ethane and methanol at a flow rate of 1-5 L / min, the extraction temperature is 30-50 ° C, the extraction pressure is 4-8 MPa, the extraction time is 1-3 h, and the stirring device in the extraction kettle is used for stirring at a stirring speed of 100-300 rpm to allow the modified raw material, ethane and methanol to react fully;

[0007] The critical temperature (32.2 °C) and critical pressure (4.88 MPa) of ethane are relatively easy to achieve. In actual operation, ethane can reach the supercritical state without excessive temperature and pressure. Supercritical ethane has a gas-like diffusion coefficient, with a fast diffusion rate, enabling it to quickly penetrate into the pores and internal structures of the raw materials. At the same time, it has good solubility for many organic compounds (such as pentanediol). This solubility can be controlled by adjusting the temperature and pressure, allowing the target substance (pentanediol) to be effectively dissolved from the raw materials during the extraction process, thereby improving the extraction efficiency. Ethane is a relatively chemically stable compound. During the supercritical extraction process, it does not chemically react with most organic compounds such as pentanediol and does not damage the chemical structure of the target substance, ensuring the quality of the product.

[0008] As an entrainer, methanol can enhance the solubility of supercritical ethane for pentanediol. The solubility of supercritical ethane itself for pentanediol is limited, while the addition of methanol changes the polarity of the supercritical fluid, resulting in a significant increase in the solubility of pentanediol in the supercritical ethane-methanol system, which helps to extract pentanediol from the modified raw materials more efficiently and improve the extraction efficiency. Secondly, methanol can have specific interactions with the modified impurities, further expanding the property differences between pentanediol and impurities in the supercritical fluid. In this way, during the extraction process, the selective extraction of pentanediol can be better achieved, reducing the co-extraction of impurities and improving the purity of the product.

[0009] S1.2. The supercritical ethane dissolved with pentanediol enters the first-stage separation kettle. The first-stage separation kettle maintains a temperature of 35 - 50 °C and the pressure is reduced to 2 - 4 MPa, separating out most of the gaseous ethane and the mixture containing pentanediol.

[0010] The mixture containing pentanediol after the first-stage separation and acetone are transferred to the second-stage separation kettle. The temperature of the second-stage separation kettle is 25 - 40 °C, the pressure is 1.5 - 3 MPa, and it is stirred at a speed of 100 - 200 rpm for 15 - 30 min. After stirring evenly, it is left to stand for 1 - 2 h.

[0011] After the first-stage separation, there may still be some impurities that are difficult to separate in the mixture. The addition of acetone can adjust the difference in the solubility of the supercritical fluid for pentanediol and impurities, making it easier for pentanediol to separate from the impurities. Secondly, acetone has different polarities and chemical properties. It can form specific intermolecular interactions with pentanediol, enhancing the selective separation effect of pentanediol in the second-stage separation kettle. After stirring evenly and leaving it to stand, this interaction can play a more sufficient role, enabling pentanediol to aggregate more stably during the separation process and improving the product purity.

[0012] S1.3. After the separation is completed, reduce the pressure in the separation kettle, separate the pentanediol solution with a purity of 90 - 95% from the separation kettle, cool it to reach a supersaturated state, and precipitate pentanediol crystals;

[0013] S1.4. Wash the crystals with cold deionized water to remove the impurities adsorbed on the surface; then carry out vacuum drying, the drying temperature is 30 - 40 °C, and the drying time is 4 - 6 h to obtain pentanediol.

[0014] Preferably, in S1.1, the modified raw material is obtained by crushing the raw material containing pentanediol with a crusher, the rotation speed of the crusher is 1000 - 3000 rpm, the crushing time is 15 - 30 min, and the powder particle size is 0.5 - 5 mm; then carry out vacuum drying, the drying temperature is 40 - 60 °C, and the drying time is 2 - 4 h;

[0015] Put the dried raw material into a reaction vessel, add boric acid, and stir with a magnetic stirrer at a speed of 50 - 100 rpm for 15 - 30 min; then add ethyl chloroformate and stir with a magnetic stirrer for a reaction time of 2 - 4 h; after the reaction is completed, wait for the mixture to cool to room temperature, and adjust the pH of the mixture to 7 - 9 with a 1 - 5 mol / L sodium bicarbonate solution; wash the mixture with deionized water 3 - 5 times, stir and let it stand for layering, the stirring speed is 200 - 400 rpm, and the stirring time is 10 - 30 min to remove the unreacted ethyl chloroformate, boric acid and by - products; then carry out vacuum drying, the drying temperature is 50 - 70 °C, and the drying time is 3 - 6 h to obtain the modified raw material.

[0016] Ethyl chloroformate can react with the impurities in the raw material. If the impurities contain active functional groups such as hydroxyl groups, they will undergo an esterification reaction with ethyl chloroformate to form carbonate compounds; this reaction changes the chemical structure of the impurities, making the physical and chemical properties such as polarity and solubility of the impurities change, increasing the property difference from the target product pentanediol. In subsequent separation processes such as supercritical fluid extraction, it is more conducive to separating pentanediol from the impurities and improving the purity of pentanediol; ethyl chloroformate can selectively react with the impurities, reducing the impact on pentanediol to a certain extent. By adding boric acid in the early stage to protect pentanediol (boric acid forms a borate complex with pentanediol, reducing the reaction activity of the hydroxyl group of pentanediol), ethyl chloroformate mainly acts on the impurities, thus realizing the modification of the impurities and creating conditions for effectively separating the impurities and pentanediol in the subsequent steps; due to the change in the properties of the impurities modified by ethyl chloroformate, in the subsequent cooling, pH adjustment and subsequent possible extraction and separation steps, the impurities can be more easily removed from the mixture or separated from pentanediol.

[0017] Boric acid forms a borate complex with the hydroxyl groups of pentanediol. The formation of this complex selectively reduces the reactivity of the hydroxyl groups of pentanediol. In a reaction system containing ethyl chloroformate, pentanediol might originally undergo an esterification reaction with ethyl chloroformate. However, due to the formation of the borate, the nucleophilicity of the hydroxyl group decreases, significantly reducing the extent to which pentanediol participates in the esterification reaction. This helps to retain the original structure of pentanediol and reduce its loss during the chemical modification of impurities, thereby facilitating the subsequent acquisition of a high-purity pentanediol product. The reaction conditions for the formation of the borate complex between boric acid and pentanediol are relatively mild, without introducing overly complex reaction condition control requirements, and this borate complex is reversible. After the chemical modification reaction is completed, by appropriately adjusting the pH value of the reaction system, such as adding an appropriate amount of base (such as sodium hydroxide solution), the borate can be decomposed to release pentanediol again. This can effectively modify the impurities without affecting the structure and properties of pentanediol.

[0018] Preferably, the mass ratio of boric acid to the raw material is 0.02 - 0.1:1.

[0019] Preferably, the mass ratio of ethyl chloroformate to the raw material is 1 - 3:1.

[0020] Preferably, after adding ethyl chloroformate, the speed of the magnetic stirrer is 100 - 300 rpm, and the temperature is 60 - 80 °C.

[0021] Preferably, in S1.1, the mass ratio of ethane to methanol in the ethane-methanol mixture is 5 - 7:1.

[0022] Preferably, in S1.1, the mass ratio of the modified raw material to the ethane-methanol mixture is 1:10 - 20.

[0023] Preferably, in S1.2, before the supercritical ethane dissolved with pentanediol enters the first separation kettle, the purity of pentanediol is 40 - 60%.

[0024] Preferably, in S1.2, the purity of pentanediol in the mixture containing pentanediol after the first separation is 60 - 80%.

[0025] Preferably, in S1.3, the pressure of the separation kettle is reduced to 0.1 - 1 MPa, and the reduction rate is 0.1 - 0.5 MPa per minute.

[0026] Compared with the prior art, the beneficial effects of the present invention:

[0027] 1. In this pentanediol supercritical fluid extraction and purification process, ethyl chloroformate can effectively change the chemical properties of impurities. For impurities containing active functional groups such as hydroxyl groups, it reacts with them to form carbonate compounds. This change in structure makes the physicochemical properties such as polarity and solubility of the impurities significantly different from those of pentanediol. In the subsequent extraction process, due to the property differences, the solubilities of pentanediol and the modified impurities in supercritical ethane are different, thus achieving more efficient separation.

[0028] 2. In this pentanediol supercritical fluid extraction and purification process, boric acid can form a borate complex with the hydroxyl groups of pentanediol, reducing the reaction activity of the pentanediol hydroxyl groups. Thus, during the chemical modification of impurities, the reaction of pentanediol itself is greatly reduced, and the original structure of pentanediol is retained, providing a guarantee for obtaining high-purity pentanediol products in the subsequent steps; moreover, the reaction conditions for the formation of the borate complex between boric acid and pentanediol are mild and can be decomposed under appropriate conditions, enabling the borate to release pentanediol again without affecting the structure and properties of pentanediol. Specific embodiments

[0029] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] The raw material containing pentanediol is the crude product of epoxypentane hydrolysis.

[0031] Example 1: A pentanediol supercritical fluid extraction and purification process, including the following steps:

[0032] S1.1. Crush the crude product of epoxypentane hydrolysis with a crusher. The rotation speed of the crusher is 2000 rpm, the crushing time is 20 min, and the powder particle size is 2 mm; then carry out vacuum drying, the drying temperature is 50 °C, and the drying time is 4 h;

[0033] The dried pentane hydrolysis crude product was placed in a reaction container, and boric acid was added in a mass ratio of 1:0.03 to the pentane hydrolysis crude product, and stirred at 100 rpm with a magnetic stirrer for 30 minutes; then ethyl chloroformate was added in a mass ratio of 1:2 to the pentane hydrolysis crude product, and stirred at 200 rpm with a magnetic stirrer at 60°C for 4 hours; after the reaction was completed, the mixture was cooled to room temperature, and the pH of the mixture was adjusted to 8 with sodium bicarbonate at a concentration of 2 mol / L; the mixture was washed with deionized water for 5 times, stirred and allowed to stand for stratification at a stirring speed of 300 rpm and a stirring time of 20 minutes to remove unreacted ethyl chloroformate, boric acid and by-products; and then vacuum dried at a drying temperature of 60°C and a drying time of 5 hours to obtain a modified pentane hydrolysis crude product;

[0034] The crude product of hydrolysis of modified pentylene oxide was placed in an extraction kettle, and an ethane-methanol mixture with a mass ratio of 1:15 to the crude product of hydrolysis of modified pentylene oxide was injected at a flow rate of 3 L / min, the mass ratio of ethane to methanol in the mixture was 6:1, the extraction temperature was 40°C, the extraction pressure was 4 MPa, the extraction time was 3 h, and the stirring device in the extraction kettle was used for stirring at a stirring speed of 200 rpm to allow the crude product of hydrolysis of modified pentylene oxide, ethane and methanol to fully react;

[0035] S1.2, supercritical ethane containing 60% pentanediol is introduced from the extraction kettle into a primary separation kettle, the temperature of the primary separation kettle is maintained at 35°C, the pressure is reduced to 3MPa, and most of the gaseous ethane and the mixture containing pentanediol are separated;

[0036] The mixture containing 80% pentanediol and acetone after primary separation was transferred to a secondary separation kettle, the temperature of the secondary separation kettle was 25°C, the pressure was 2MPa, and the mixture was stirred at a speed of 150rpm for 30min. After stirring evenly, the mixture was allowed to stand for 2h.

[0037] S1.3, after the separation is completed, the pressure of the separation kettle is reduced to 1 MPa at a rate of 0.3 MPa / min, and the reduction rate is, the pentanediol solution with a purity of 95% is separated from the separation kettle, cooled to reach a supersaturated state, and pentanediol crystals are precipitated;

[0038] S1.4. Wash the crystals with cold deionized water to remove impurities adsorbed on the surface; then vacuum dry the crystals at a drying temperature of 40°C for 6 hours to obtain pentanediol.

[0039] Embodiment 2: A pentanediol supercritical fluid extraction purification process comprises the following steps:

[0040] S1.1. The crude product of pentane hydrolysis was crushed by a pulverizer at a speed of 2000 rpm for 20 min to obtain a powder particle size of 2 mm; the powder was then vacuum dried at a drying temperature of 50°C for 4 h;

[0041] The dried pentane hydrolysis crude product was placed in a reaction container, and boric acid was added in a mass ratio of 1:0.05 to the pentane hydrolysis crude product, and stirred at a speed of 100 rpm with a magnetic stirrer for 30 minutes; then ethyl chloroformate was added in a mass ratio of 1:2 to the pentane hydrolysis crude product, and stirred at a speed of 200 rpm with a magnetic stirrer at 60°C for 4 hours; after the reaction was completed, the mixture was cooled to room temperature, and the pH of the mixture was adjusted to 8 with sodium bicarbonate at a concentration of 2 mol / L; the mixture was washed with deionized water for 5 times, stirred and allowed to stand for stratification, the stirring speed was 300 rpm, the stirring time was 20 minutes, and the unreacted ethyl chloroformate, boric acid and by-products were removed; and then vacuum dried at a drying temperature of 60°C and a drying time of 5 hours to obtain a modified pentane hydrolysis crude product;

[0042] The crude product of hydrolysis of modified pentylene oxide was placed in an extraction kettle, and an ethane-methanol mixture with a mass ratio of 1:15 to the crude product of hydrolysis of modified pentylene oxide was injected at a flow rate of 3 L / min, the mass ratio of ethane to methanol in the mixture was 6:1, the extraction temperature was 40°C, the extraction pressure was 4 MPa, the extraction time was 3 h, and the stirring device in the extraction kettle was used for stirring at a stirring speed of 200 rpm to allow the crude product of hydrolysis of modified pentylene oxide, ethane and methanol to fully react;

[0043] S1.2, supercritical ethane containing 60% pentanediol is introduced from the extraction kettle into a primary separation kettle, the temperature of the primary separation kettle is maintained at 35°C, the pressure is reduced to 3MPa, and most of the gaseous ethane and the mixture containing pentanediol are separated;

[0044] The mixture containing 80% pentanediol and acetone after primary separation was transferred to a secondary separation kettle, the temperature of the secondary separation kettle was 25°C, the pressure was 2MPa, and the mixture was stirred at a speed of 150rpm for 30min. After stirring evenly, the mixture was allowed to stand for 2h.

[0045] S1.3, after the separation is completed, the pressure of the separation kettle is reduced to 1 MPa at a rate of 0.3 MPa / min, and the reduction rate is, the pentanediol solution with a purity of 95% is separated from the separation kettle, cooled to reach a supersaturated state, and pentanediol crystals are precipitated;

[0046] S1.4. Wash the crystals with cold deionized water to remove impurities adsorbed on the surface; then vacuum dry the crystals at a drying temperature of 40°C for 6 hours to obtain pentanediol.

[0047] Embodiment 3: A pentanediol supercritical fluid extraction purification process comprises the following steps:

[0048] S1.1. The crude product of pentane hydrolysis was crushed by a pulverizer at a speed of 2000 rpm for 20 min to obtain a powder particle size of 2 mm; the powder was then vacuum dried at a drying temperature of 50°C for 4 h;

[0049] The dried pentane hydrolysis crude product was placed in a reaction container, and boric acid was added in a mass ratio of 1:0.1 to the pentane hydrolysis crude product, and stirred at a speed of 100 rpm with a magnetic stirrer for 30 minutes; then ethyl chloroformate was added in a mass ratio of 1:2 to the pentane hydrolysis crude product, and stirred at a speed of 200 rpm with a magnetic stirrer at 60°C for 4 hours; after the reaction was completed, the mixture was cooled to room temperature, and the pH of the mixture was adjusted to 8 with sodium bicarbonate at a concentration of 2 mol / L; the mixture was washed with deionized water for 5 times, stirred and allowed to stand for stratification, the stirring speed was 300 rpm, the stirring time was 20 minutes, and the unreacted ethyl chloroformate, boric acid and by-products were removed; and then vacuum dried at a drying temperature of 60°C and a drying time of 5 hours to obtain a modified pentane hydrolysis crude product;

[0050] The crude product of hydrolysis of modified pentylene oxide was placed in an extraction kettle, and an ethane-methanol mixture with a mass ratio of 1:15 to the crude product of hydrolysis of modified pentylene oxide was injected at a flow rate of 3 L / min, the mass ratio of ethane to methanol in the mixture was 6:1, the extraction temperature was 40°C, the extraction pressure was 4 MPa, the extraction time was 3 h, and the stirring device in the extraction kettle was used for stirring at a stirring speed of 200 rpm to allow the crude product of hydrolysis of modified pentylene oxide, ethane and methanol to fully react;

[0051] S1.2, supercritical ethane containing 60% pentanediol is introduced from the extraction kettle into a primary separation kettle, the temperature of the primary separation kettle is maintained at 35°C, the pressure is reduced to 3MPa, and most of the gaseous ethane and the mixture containing pentanediol are separated;

[0052] The mixture containing 80% pentanediol and acetone after primary separation was transferred to a secondary separation kettle, the temperature of the secondary separation kettle was 25°C, the pressure was 2MPa, and the mixture was stirred at a speed of 150rpm for 30min. After stirring evenly, the mixture was allowed to stand for 2h.

[0053] S1.3, after the separation is completed, the pressure of the separation kettle is reduced to 1 MPa at a rate of 0.3 MPa / min, and the reduction rate is, the pentanediol solution with a purity of 95% is separated from the separation kettle, cooled to reach a supersaturated state, and pentanediol crystals are precipitated;

[0054] S1.4. Wash the crystals with cold deionized water to remove the impurities adsorbed on the surface; then perform vacuum drying at a drying temperature of 40 °C and a drying time of 6 h to obtain pentanediol.

[0055] Comparative Example 1

[0056] Adopt the method of Example 3 with unmodified raw materials.

[0057] Comparative Example 2

[0058] Adopt the method of Example 3 and remove ethyl chloroformate.

[0059] Comparative Example 3

[0060] Adopt the method of Example 3 and remove boric acid.

[0061] Comparative Example 4

[0062] Adopt the method of Example 3 and remove methanol.

[0063] The present invention relates to a purification process of pentanediol by supercritical fluid extraction with modified raw materials. The specific test effects are as follows:

[0064] According to GB / T 36788-2018, measure the purity and recovery rate of pentanediol in the raw materials by gas chromatography. Higher purity and recovery rate indicate a high content of pentanediol in the sample and a reliable analysis method, which is suitable for applications with high quality requirements.

[0065] Through the above standards, the obtained data are shown in Table 1:

[0066] Table 1 Purity and recovery rate of pentanediol in Examples 1-3 and Comparative Examples 1-4

[0067] Example / Comparative Example Purity % Recovery Rate % Example 1 98.8 91.4 Example 2 99.0 91.7 Example 3 99.2 92.8 Comparative Example 1 80.1 56.3 Comparative Example 2 83.2 58.9 Comparative Example 3 84.9 60.2 Comparative Example 4 89.7 68.1

[0068] It can be seen from Table 1 that pentanediol in Examples 1-3 shows significantly high purity and high recovery rate; taking Example 3 as the optimal example and combining with Comparative Example 1, it can be seen that the purity and recovery rate of pentanediol in the unmodified raw materials are significantly reduced;

[0069] In the unmodified raw materials, the physicochemical properties of pentanediol and impurities may be relatively similar. During extraction or other separation processes, it is difficult to effectively distinguish pentanediol from impurities, and they will be extracted together, resulting in a high impurity content in the final product, thereby reducing the purity of pentanediol; impurities may react with pentanediol to form by-products, which may lead to the loss of pentanediol or make the subsequent separation process of pentanediol more complicated, thus reducing the recovery rate of pentanediol; without modifying the raw materials, the active functional groups (such as hydroxyl groups) of pentanediol are easily exposed, making it more likely to undergo side reactions, resulting in changes or losses in the structure of pentanediol itself. This will not only reduce the amount of pentanediol finally recovered but also may introduce new impurities, further reducing the purity of pentanediol.

[0070] Comparing Example 3 with Comparative Example 2, it can be seen that when ethyl chloroformate is removed, the purity and recovery rate of pentanediol in the raw materials are significantly reduced;

[0071] Ethyl chloroformate can change the chemical structure of impurities, causing different dissolution behaviors of impurities and pentanediol during processes such as supercritical fluid extraction. When ethyl chloroformate is removed, the selectivity of the supercritical fluid for pentanediol and impurities is poor, and it is unable to effectively separate pentanediol from impurities. This will result in the extraction of pentanediol and impurities together during the separation process, reducing the purity of pentanediol. Moreover, due to the inability to accurately extract pentanediol, the recovery rate will also be affected; there are active functional groups (such as hydroxyl groups) in the pentanediol molecule. In the absence of ethyl chloroformate, these active functional groups are more easily exposed, making pentanediol more likely to undergo unnecessary chemical reactions with other reagents or impurities during the reaction, such as esterification reactions and oxidation reactions. These reactions will lead to changes or losses in the structure of pentanediol, thereby reducing the recovery rate of pentanediol; at the same time, the by-products generated by the reaction will mix into the product, reducing the purity of pentanediol.

[0072] Further comparing Example 3 with Comparative Example 3, it can be seen that when boric acid is removed, the purity and recovery rate of pentanediol in the raw materials are significantly reduced;

[0073] During the process, boric acid can form a borate complex with the hydroxyl groups of pentanediol, reducing the reactivity of pentanediol. In subsequent steps, pentanediol is less likely to react with other chemicals. When boric acid is removed, pentanediol undergoes esterification, condensation and other reactions with some active groups in the impurities. These side reactions can cause pentanediol to be converted into other compounds, thereby reducing the recovery rate of pentanediol and also its purity. Without the protection of boric acid, the chemical stability of pentanediol itself becomes worse, making it more vulnerable to environmental factors (such as temperature, humidity, pH, etc.) and prone to chemical changes, which in turn results in the loss of pentanediol and a decrease in its purity. The presence of boric acid may affect the solubility of pentanediol in certain solvents. When boric acid is removed, the solubility of pentanediol may change. In subsequent separation steps such as extraction or washing, pentanediol may not dissolve well in a specific solvent phase, leading to its ineffective separation from impurities.

[0074] Combining the optimal Example 3 with Comparative Example 4 shows that when methanol is removed, the purity and recovery rate of pentanediol in the raw material decrease significantly.

[0075] Methanol is an important entrainer in this system. It can change the polarity of supercritical ethane. Supercritical ethane itself is non-polar. After adding methanol, its polarity can be appropriately increased, thereby enhancing its solubility in pentanediol. Since pentanediol is a compound with polar groups (hydroxyl groups), when methanol is removed, the polarity of supercritical ethane decreases, and its solubility in pentanediol decreases, resulting in pentanediol not being fully extracted from the modified raw material and a significant decrease in the recovery rate.

[0076] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A pentanediol supercritical fluid extraction and purification process, characterized in that: The following steps are involved: S1.

1. Place the modified raw material into an extraction kettle, inject a mixture of ethane and methanol at a flow rate of 1-5 L / min, the extraction temperature is 30-50 ° C, the extraction pressure is 4-8 MPa, the extraction time is 1-3 h, and the stirring device in the extraction kettle is used for stirring at a stirring speed of 100-300 rpm to allow the modified raw material, ethane and methanol to react fully; S1.2, supercritical ethane containing pentanediol enters the primary separation kettle from the extraction kettle, the primary separation kettle is maintained at a temperature of 35-50°C, the pressure is reduced to 2-4MPa, and most of the gaseous ethane and the mixture containing pentanediol are separated; The mixture containing pentanediol and acetone after the primary separation is transferred to a secondary separation kettle, the temperature of the secondary separation kettle is 25-40°C, the pressure is 1.5-3MPa, and the mixture is stirred at a speed of 100-200rpm for 15-30min. After stirring evenly, the mixture is allowed to stand for 1-2h; S1.

3. After the separation is completed, the pressure of the separation kettle is reduced, and the pentanediol solution with a purity of 90-95% is separated from the separation kettle, and cooled to reach a supersaturated state, and pentanediol crystals are precipitated; S1.

4. Wash the crystals with cold deionized water to remove impurities adsorbed on the surface; then vacuum dry the crystals at a temperature of 30-40°C for 4-6 hours to obtain pentanediol.

2. The pentanediol supercritical fluid extraction and purification process according to claim 1, characterized in that: In S1.1, the modified raw material is a raw material containing pentanediol that is crushed by a pulverizer at a speed of 1000-3000 rpm for 15-30 min to obtain a powder particle size of 0.5-5 mm; and then vacuum dried at a drying temperature of 40-60° C. for 2-4 h. The dried raw material is placed in a reaction container, boric acid is added, and the mixture is stirred at a speed of 50-100 rpm for 15-30 minutes with a magnetic stirrer; ethyl chloroformate is then added, and the reaction time is stirred for 2-4 hours with a magnetic stirrer; after the reaction is completed, the mixture is cooled to room temperature, and the pH value of the mixture is adjusted to 7-9 with sodium bicarbonate with a concentration of 1-5 mol / L; the mixture is washed with deionized water for 3-5 times, stirred and allowed to stand for stratification, the stirring speed is 200-400 rpm, the stirring time is 10-30 minutes, and unreacted ethyl chloroformate, boric acid and by-products are removed; and vacuum drying is performed at a drying temperature of 50-70° C. and a drying time of 3-6 hours to obtain a modified raw material.

3. The pentanediol supercritical fluid extraction and purification process according to claim 2, characterized in that: The mass ratio of the boric acid to the raw material is 0.02-0.1:

1.

4. The pentanediol supercritical fluid extraction and purification process according to claim 2, characterized in that: The mass ratio of the ethyl chloroformate to the raw material is 1-3:

1.

5. The pentanediol supercritical fluid extraction and purification process according to claim 2, characterized in that: After the ethyl chloroformate is added, the speed of the magnetic stirrer is 100-300 rpm and the temperature is 60-80°C.

6. The pentanediol supercritical fluid extraction and purification process according to claim 1, characterized in that: In S1.1, the mass ratio of ethane to methanol in the ethane and methanol mixture is 5-7:

1.

7. The pentanediol supercritical fluid extraction and purification process according to claim 1, characterized in that: In the S1.1, the mass ratio of the modified raw material to the ethane-methanol mixture is 1:10-20.

8. The pentanediol supercritical fluid extraction and purification process according to claim 1, characterized in that: In S1.2, before the supercritical ethane containing pentanediol enters the primary separation kettle from the extraction kettle, the purity of pentanediol is 40-60%.

9. The pentanediol supercritical fluid extraction and purification process according to claim 1, characterized in that: In S1.2, the purity of pentanediol in the mixture containing pentanediol after the primary separation is 60-80%.

10. The pentanediol supercritical fluid extraction and purification process according to claim 1, characterized in that: In S1.3, the pressure of the separation kettle is reduced to 0.1-1 MPa, and the reduction rate is 0.1-0.5 MPa / minute.