A process for the preparation of 3-hydroxypropionitrile

Abstract

The application provides a preparation method of 3-hydroxypropionitrile, and belongs to the technical field of fine chemical preparation. The preparation method comprises the following steps: 1) mixing water, an alkali catalyst and an inorganic salt to obtain a mixed solution; the salt concentration in the mixed solution reaches a saturated or supersaturated state; 2) under stirring, adding acrylonitrile into the mixed solution to perform a hydration reaction; during the reaction, the generated 3-hydroxypropionitrile continuously precipitates from the aqueous phase under the action of salting-out effect, and an independent oil phase is formed; and 3) after the reaction is completed, the oil phase is separated to obtain 3-hydroxypropionitrile. The method provided by the application does not use an organic solvent, the process is simple, the product has high yield and good purity.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical preparation technology, specifically relating to a method for preparing 3-hydroxypropionitrile. Background Technology

[0002] 3-Hydroxypropionitrile (HPN, also known as 2-cyanoethanol) is an important fine chemical intermediate with the molecular formula C3H5NO, a molecular weight of 71.08, a boiling point of 228℃ (slight decomposition), and a relative density of 1.0404 g / cm³. 3 (25℃) It is miscible with solvents such as water, ethanol, and acetone, slightly soluble in diethyl ether, and insoluble in benzene, petroleum ether, and carbon tetrachloride. Hydrogenation of 3-hydroxypropionitrile yields 3-aminopropanol, a key raw material for the synthesis of D-panthenol (D-panthenol is widely used in pharmaceuticals, food additives, and cosmetics). It can also be used to prepare cardiovascular drugs such as propranolol and cyclophosphamide, as well as the antitumor drug cyclophosphamide. Furthermore, 3-hydroxypropionitrile can be used to prepare battery additives such as cyanophosphite, which has significant application value in the lithium-ion battery field.

[0003] Currently, there are three main routes for the chemical synthesis of 3-hydroxypropionitrile (HPN): the reaction of chloroethanol with cyanide, the reaction of ethylene oxide with hydrogen cyanide, and the hydration of acrylonitrile. Among these, the hydration method offers significant advantages, including high atom economy (water and acrylonitrile are added in a 1:1 stoichiometric ratio, with no wasted byproduct atoms), wide availability of acrylonitrile as a raw material, and relatively low price, making it a key focus of research and production both domestically and internationally. However, the core technical challenge facing the industrial application of the acrylonitrile hydration method lies in its poor selectivity. Under alkaline catalysis, acrylonitrile first undergoes an addition reaction with water to generate the target product, 3-hydroxypropionitrile. Simultaneously, the hydroxyl groups in the 3-hydroxypropionitrile molecule are partially activated in the alkaline environment, leading to a Michael addition reaction with unreacted acrylonitrile in the system, generating a di(cyanoethyl) ether byproduct (also known as 3,3'-oxopropionitrile). This cascaded side reaction severely reduces the yield and purity of HPN, representing the biggest technical bottleneck restricting the industrial application of this route. The Michael addition side reaction is thermodynamically spontaneous and difficult to halt. The product 3-hydroxypropionitrile contains an active hydroxyl hydrogen, and acrylonitrile is a strong Michael acceptor. The system is prone to the following side reactions: acrylonitrile + 3-hydroxypropionitrile → dicyandiethyl ether dimerization byproduct; intermolecular addition of acrylonitrile → oligomeric viscous polymer; overhydration → acrylamide impurities. The above side reactions only exist in the acrylonitrile hydration system, which is a unique industry pain point of this system.

[0004] Patent CN1189449C discloses a method for preparing 3-hydroxypropionitrile. This method involves reacting acrylonitrile with water at 80-150℃ and 0.1-0.5 MPa, using a weak base with a pKa (acid dissociation constant: the smaller the pKa, the stronger the acid and the easier it is to donate a proton; the larger the pKa, the weaker the acid and the stronger the corresponding conjugated bond) of 8-12 as a catalyst, to achieve a conversion rate of 40%-80%, obtaining a two-phase mixture. After cooling, the aqueous phase is separated, and acrylonitrile is distilled off from the organic phase. The mixture is then pyrolyzed at 120-160℃ and 0.5-50 kPa, and finally fractionated to obtain 3-hydroxypropionitrile. However, this method relies on multiple thermal operations, including high-temperature and high-pressure reaction, pyrolysis, and fractionation, resulting in high energy consumption and a long process flow.

[0005] Patent CN117682970B introduces hydrophobic solvents (cyclohexane, toluene, ethyl acetate, etc.) into the reaction system, causing acrylonitrile to preferentially dissolve in the organic phase, while the resulting 3-hydroxypropionitrile dissolves in the aqueous phase. This physical isolation between the two phases reduces the contact opportunity between 3-hydroxypropionitrile and acrylonitrile, improving reaction selectivity and achieving a yield of approximately 72%. While this method improves the yield, the introduction of organic solvents increases post-processing separation costs and solvent recovery load, which is inconsistent with the development direction of green chemistry.

[0006] Therefore, it is particularly important to develop a simpler method for the preparation and separation of 3-hydroxypropionitrile that does not use organic solvents, requires no special equipment, and is easy to industrialize. Summary of the Invention

[0007] In view of this, the present invention provides a method for preparing 3-hydroxypropionitrile. The method provided by the present invention does not use organic solvents, and the process is simple, with high product yield and good purity.

[0008] To solve the aforementioned technical problem, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing 3-hydroxypropionitrile, comprising the following steps: 1) Water, an alkaline catalyst, and an inorganic salt are mixed to obtain a mixed solution; the salt concentration in the mixed solution reaches a saturated or supersaturated state; 2) Under stirring conditions, acrylonitrile is added to the above mixed solution to carry out a hydration reaction. During the reaction, the generated 3-hydroxypropionitrile continuously precipitates from the aqueous phase under the salting-out effect, forming an independent oil phase. The inorganic salts include one or more of ammonium sulfate, potassium phosphate, dipotassium hydrogen phosphate, sodium chloride, sodium sulfate, and potassium carbonate; The alkaline catalyst is one or more of sodium carbonate, potassium carbonate, sodium acetate, and sodium hydroxide; 2) Under stirring conditions, acrylonitrile is added to the above mixed solution to carry out a hydration reaction. During the reaction, the generated 3-hydroxypropionitrile continuously precipitates from the aqueous phase under the salting-out effect, forming an independent oil phase. The mass ratio of acrylonitrile to water is 1:2 to 1:10; The hydration reaction is carried out at a temperature of 10℃-40℃ for 1-6 hours. 3) After the reaction is complete, the oil phase is separated to obtain 3-hydroxypropionitrile.

[0009] Preferably, the amount of inorganic salt added in step 1) is such that the salt concentration in the reaction solution reaches 100%-120% of the saturated solubility of the salt at the reaction temperature.

[0010] Preferably, the mass ratio of acrylonitrile to water is 1:3 to 1:5.

[0011] Preferably, the hydration reaction in step 2) is carried out at a temperature of 20°C-30°C and for a time of 4-5.5 hours.

[0012] Preferably, the amount of the alkaline catalyst added is 0.5%-4% of the mass of acrylonitrile.

[0013] Preferably, the pH of the reaction solution is controlled at 9.0-9.5 during the hydration reaction in step 2).

[0014] Preferably, step 3) further includes concentrating the remaining brine phase after separating the oil phase, and recovering the inorganic salts after concentration for recycling.

[0015] Preferably, the inorganic salt is purified or replaced entirely after every 5-10 cycles.

[0016] Preferably, the purification process is activated carbon adsorption.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for preparing 3-hydroxypropionitrile provided by this invention employs a salting-out coupling mechanism to suppress side reactions. 3-hydroxypropionitrile is removed by salting out immediately after generation, achieving "separation upon generation" without the need for additional extraction steps. The reaction-separation process is integrated, and the yield of 3-hydroxypropionitrile is increased while reducing by-products.

[0018] Meanwhile, no organic solvents were added during the entire reaction process, avoiding the safety, environmental and economic problems caused by the use of organic solvents, which is more in line with the trend of green chemistry development.

[0019] Furthermore, the aqueous phase after salting out can be recycled after evaporation and concentration, resulting in extremely low salt loss, which not only reduces costs but also achieves near-zero emissions. Attached Figure Description

[0020] Figure 1 The gas chromatogram of the crude 3-hydroxypropionitrile obtained in Example 1; Figure 2 The reaction solution, after standing and separating into layers, forms a three-layer structure: organic phase, brine phase, and saturated salt. Detailed Implementation

[0021] The technical solutions in specific embodiments of the present invention will be described in detail and completely below. Obviously, the described embodiments are only some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0022] This invention provides a method for preparing 3-hydroxypropionitrile, comprising the following steps: 1) Water, an alkaline catalyst, and an inorganic salt are mixed to obtain a mixed solution; the salt concentration in the mixed solution reaches a saturated or supersaturated state; 2) Under stirring conditions, acrylonitrile is added to the above mixed solution to carry out a hydration reaction. During the reaction, the generated 3-hydroxypropionitrile continuously precipitates from the aqueous phase under the salting-out effect, forming an independent oil phase. 3) After the reaction is complete, the oil phase is separated to obtain 3-hydroxypropionitrile.

[0023] In a conventional acrylonitrile hydration reaction (without salting-out coupling), the generated 3-hydroxypropionitrile dissolves in the reaction solution and continues to contact with unreacted acrylonitrile. Due to the presence of a basic catalyst in the reaction system, the hydroxyl groups of the 3-hydroxypropionitrile are partially activated, generating an oxonium (-CH₂CH₂O). - The activated oxygen anion acts as a nucleophile, attacking the C=C double bond of acrylonitrile to generate the byproduct di(cyanoethyl) ether. Main reaction: CH2=CH-CN + H2O → HO-CH2-CH2-CN (3-hydroxypropionitrile)

[0024] Side reaction: HO-CH2-CH2-CN + OH - - O-CH2-CH2-CN+H2O;

[0025] Then: - O-CH2-CH2-CN+CH2=CH-CN→NC-CH2-CH2-O-CH2-CH2-CN (dicyanoethyl ether).

[0026] The rate of the side reaction is positively correlated with the product of the concentrations of 3-hydroxypropionitrile and acrylonitrile in the solution. Therefore, in a conventional system, as the reaction proceeds, the concentration of 3-hydroxypropionitrile gradually increases, and the rate of the side reaction also accelerates, leading to the formation of a large number of byproducts.

[0027] The applicant discovered that the molecular structure of hydroxypropionitrile is HO-CH2-CH2-CN, containing one hydroxyl group (-OH) and one cyano group (-CN). The hydroxyl group can form hydrogen bonds with water molecules, giving 3-hydroxypropionitrile a certain degree of water solubility; however, the cyano group and the ethylidene chain have a certain degree of hydrophobicity, making 3-hydroxypropionitrile generally moderately polar. In ordinary aqueous solutions, 3-hydroxypropionitrile can dissolve uniformly (water solubility ≥10g / 100mL at 20℃). However, when a high concentration of inorganic salt is added, water molecules are "robbed" by salt ions, disrupting the hydrogen bond network of 3-hydroxypropionitrile. Its solubility in water decreases sharply, and hydrophobic interactions between 3-hydroxypropionitrile molecules become dominant. This causes it to precipitate from the aqueous phase as an organic phase and aggregate into a new organic layer, forming a two-phase three-layer or two-phase two-layer structure. (The addition of high-concentration inorganic salt causes strong hydration between salt ions and water molecules, disrupting the hydrogen bond network between 3-hydroxypropionitrile and water, leading to a sharp decrease in the solubility of 3-hydroxypropionitrile. Driven by the salting-out effect, 3-hydroxypropionitrile molecules aggregate and precipitate from the brine phase, forming an independent organic phase. After the reaction solution settles, it separates into layers: the upper layer is the 3-hydroxypropionitrile organic phase, and the lower layer is the brine phase. When the salt concentration exceeds the saturation solubility, the excess inorganic salt settles at the bottom as a solid phase or a supersaturated solution, forming a three-layer structure of organic phase-brine phase-saturated salt phase, as shown in the diagram.) Figure 2 As shown; when the salt is just or nearly saturated and dissolved, a two-layer structure of organic phase and salt water phase is formed. The preparation method of 3-hydroxypropionitrile provided by this invention uses a salting-out coupling mechanism to suppress side reactions. Specifically, a high concentration of inorganic salt is pre-placed in the reaction solution to keep the reaction solution saturated or nearly saturated. As the reaction proceeds, the generated 3-hydroxypropionitrile precipitates immediately as an independent oil phase under the salting-out effect and is removed from the aqueous phase. This means: (1) The equilibrium concentration of 3-hydroxypropionitrile in the aqueous phase is significantly reduced: As 3-hydroxypropionitrile is continuously salted out, its equilibrium concentration in the reaction solution is always maintained at an extremely low level. (2) The contact opportunity between 3-hydroxypropionitrile and acrylonitrile is greatly reduced: once 3-hydroxypropionitrile is formed, it is "isolated" into the organic phase, while acrylonitrile is mainly dissolved in the aqueous phase (or distributed at the liquid-liquid interface), and the contact probability between the two is significantly reduced. (3) Side reactions are suppressed at the source: Since the concentration of 3-hydroxypropionitrile in the aqueous phase is continuously controlled at an extremely low level, the rate of the side reaction of Michael addition with acrylonitrile is greatly reduced.

[0028] The method provided by this invention involves salting out during the reaction process, utilizing the salting-out effect to simultaneously achieve the dual goals of product separation and side reaction suppression, realizing the "precipitation upon formation" of 3-hydroxypropionitrile and maximally suppressing side reactions from the source. High-yield, high-purity 3-hydroxypropionitrile product is obtained with extremely simple operation without introducing organic solvents or using special equipment.

[0029] This invention involves mixing water, an alkaline catalyst, and an inorganic salt to obtain a mixed solution; the salt concentration in the mixed solution reaches a saturated or supersaturated state. In this invention, the inorganic salt preferably includes one or more of ammonium sulfate, potassium phosphate, dipotassium hydrogen phosphate, sodium chloride, sodium sulfate, and potassium carbonate, more preferably ammonium sulfate. In this invention, the amount of inorganic salt added is preferably such that the salt concentration in the reaction solution reaches 100%-120% of the saturated solubility of the salt at the reaction temperature.

[0030] In this invention, inorganic salts are further selected as salting-out agents based on the following principles: (1) High solubility: The higher the solubility of salt in water, the higher the salt concentration that can be achieved, and the more significant the salting-out effect. The typical solubility of salting-out agents in water at 20℃ is as follows: ammonium sulfate about 75g / 100mL water, potassium phosphate about 120g / 100mL water, and sodium chloride about 36g / 100mL water.

[0031] (2) Strong hydration capacity: The higher the charge density and the smaller the radius of an ion, the stronger its hydration capacity. Polyvalent anions (such as SO42-) 2- PO4 3- The hydration capacity of ions is significantly stronger than that of monovalent anions (such as Cl-). - ).

[0032] (3) Chemical inertness: The salt should not react chemically with the reactants acrylonitrile or 3-hydroxypropionitrile, and should not interfere with the normal progress of the hydration reaction.

[0033] (4) Cost and environmental protection: Salt should be cheap and readily available, and the brine phase after salting out can be recycled and reused through evaporation and concentration to achieve near-zero emissions.

[0034] Based on the above principles, this invention preferably uses one or more of the following: ammonium sulfate ((NH4)2SO4), potassium phosphate (K3PO4), dipotassium hydrogen phosphate (K2HPO4), sodium chloride (NaCl), sodium sulfate (Na2SO4), and potassium carbonate (K2CO3). Among these, ammonium sulfate has good water solubility (approximately 75g / 100mL water at 20℃) and strong hydration capacity (SO4). 2- It has the advantages of being a high-valence anion, low price, good chemical inertness, non-toxic and harmless, making it the most preferred salting-out agent.

[0035] In this invention, the alkaline catalyst is one or more of sodium carbonate, potassium carbonate, sodium acetate, and sodium hydroxide, preferably sodium acetate. The use of weakly alkaline sodium acetate helps to moderate the alkalinity of the reaction system. Weakly alkaline conditions ensure sufficient catalytic activity for the hydration main reaction while effectively inhibiting the deprotonation of the hydroxyl group in 3-hydroxypropionitrile, reducing the equilibrium concentration of reactive oxygen anions, thereby slowing down the rate of the Michael addition side reaction and improving reaction selectivity. In this invention, the amount of alkaline catalyst added is preferably 0.5%-4% of the mass of acrylonitrile.

[0036] After obtaining the mixed solution, acrylonitrile is added to the mixed solution under stirring to carry out a hydration reaction. In this invention, the mass ratio of acrylonitrile to water is 1:2-1:10, preferably 1:3-1:5. The reaction temperature of the hydration reaction is 10℃-40℃, preferably 20-30℃; the reaction time is 1-6 h, preferably 4-5.5 h. In this invention, the pH of the reaction solution during the hydration reaction is preferably controlled at 9.0-9.5. Within this pH range, sufficient catalytic activity can be ensured to maintain a reasonable reaction rate, while excessive alkalinity can be avoided to prevent over-activation of the hydroxyl groups of 3-hydroxypropionitrile, which would accelerate side reactions, thus achieving a good balance between reaction rate and selectivity.

[0037] In this invention, after separating the oil phase, the remaining brine phase is preferably concentrated, and the inorganic salts are recovered and recycled. By recovering and recycling the inorganic salts, production costs can be further reduced. To avoid impurities carried in the repeatedly recycled inorganic salts affecting product purity, the inorganic salts are preferably purified or replaced entirely after every 5-10 cycles. The purification process is preferably performed using activated carbon adsorption.

[0038] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] The experimental reagents and instruments used in each of the embodiments and comparative examples are as follows: Chemicals: Acrylonitrile (AN): analytical grade, purity ≥99.0%; 3-hydroxypropionitrile (HPN) standard: purchased from Maclean's, purity ≥98%; Ammonium sulfate ((NH4)2SO4): reagent grade, purchased from Maclean's, purity ≥99.0%; Potassium phosphate (K3PO4): reagent grade, adamas, purity ≥99.0%; Sodium chloride (NaCl): superior grade reagent, purchased from Maclean's, purity ≥99.8%; Sodium sulfate (Na2SO4): reagent grade, purchased from Maclean's, purity ≥98.0%; Potassium carbonate (K2CO3): reagent grade, purchased from Maclean's, purity ≥99.0%; Sodium hydroxide (NaOH): reagent grade, purchased from Maclean's, purity ≥98.0%; Anhydrous sodium carbonate (Na2CO3): reagent grade, purchased from Maclean's, purity ≥99.9%.

[0040] Gas chromatograph: Agilent 7890B, DB-1701 capillary column (30m×0.32mm×0.25μm), temperature program: 50℃ for 5 min, then increase to 200℃ at 10℃ / min and hold for 8 min; FID detector, detector temperature 250℃, injection port temperature 250℃.

[0041] Example 1 In a 500mL quick-opening reactor equipped with a stirrer and temperature sensor, add 150mL of deionized water, 112g of ammonium sulfate (to bring the initial salt concentration to approximately 75g / 100mL water, close to saturation), and 4.0g of sodium carbonate (Na₂CO₃). Stir until the solids are completely dissolved to form a saturated salt solution. Maintain the temperature at 25℃, add 53.0g of acrylonitrile (approximately 1.0mol) at once, purge the air in the reactor three times with nitrogen, and react for 5 hours.

[0042] As acrylonitrile was added dropwise and the reaction proceeded, oily droplets gradually appeared on the upper layer and coalesced to form an oil layer. After the reaction was completed, the mixture was allowed to stand and separate into layers. The upper oil phase was the crude 3-hydroxypropionitrile. The lower brine phase was collected for recycling. The obtained crude 3-hydroxypropionitrile was analyzed by gas chromatography, and the specific chromatogram is shown below. Figure 1 As shown.

[0043] Analytical results (gas chromatography with internal standard method): 3-hydroxypropionitrile purity 95.19%, yield 90.3%, and di(cyanoethyl) ether content of byproduct 4.07%.

[0044] The yield calculation is as follows: 3-hydroxypropionitrile yield (%) = (actual mass of 3-hydroxypropionitrile / theoretical mass of 3-hydroxypropionitrile) × 100%. The theoretical mass of 3-hydroxypropionitrile is calculated based on the amount of acrylonitrile fed: acrylonitrile molecular weight is 53.06, 3-hydroxypropionitrile molecular weight is 71.08, theoretical mass of 3-hydroxypropionitrile = mass of acrylonitrile fed × (71.08 / 53.06).

[0045] Purity and byproduct content: Both were determined by gas chromatography with internal standard method. The internal standard was n-butanol or n-dodecane. The standard curve was calibrated with 3-hydroxypropionitrile standard and di(cyanoethyl) ether standard.

[0046] Example 2 The lower brine phase from Example 1 was collected and placed in an evaporator. It was evaporated and concentrated to approximately 40% of its original volume at 80°C and 0.08 MPa, resulting in the precipitation of some ammonium sulfate crystals. The crystals were recovered by filtration, and a small amount of fresh ammonium sulfate (5% of the initial amount) was added before returning the mixture to the reactor for a second reaction under the conditions of Example 1.

[0047] Analysis results: 3-hydroxypropionitrile purity 94.5%, yield 89.0%, and di(cyanoethyl) ether content 4.5%. Compared with fresh salt (Example 1), the byproduct content increased from 4.07% to 4.5%, indicating that the salt phase can still maintain good reaction performance when recycled, and the salt recovery rate can reach over 95%.

[0048] Example 3 To verify the long-term recycling performance of the salt phase, the lower salt phase after the reaction in Example 2 was recycled three more times, with 5% fresh ammonium sulfate added each time to compensate for mechanical losses. The results are summarized in Table 1: Table 1

[0049] Experimental results show that with increasing cycle number, a small amount of organic impurities accumulate in the salt phase, leading to a slight decrease in yield and purity. However, within 5 cycles, the yield of 3-hydroxypropionitrile remains above 84%, and the product purity remains above 90%, demonstrating excellent salt phase recycling performance. It is recommended to perform activated carbon adsorption treatment or replace the entire salt phase every 5-10 cycles to ensure stable product quality.

[0050] Example 4 The difference from Example 1 is that 2.0 g of sodium hydroxide was used instead of sodium carbonate, while other conditions remained the same as in Example 1. Analytical results: 3-hydroxypropionitrile purity 93%, yield 85%, di(cyanoethyl) ether content 5.5%. Higher conversion rate was achieved under strong base catalysis, but slightly more byproducts were produced.

[0051] Example 5 The difference from Example 1 is that 5.0 g of potassium carbonate was used instead of sodium carbonate, while other conditions were the same as in Example 1. Results: 3-hydroxypropionitrile purity was 94.5%, yield was 89.0%, and di(cyanoethyl) ether content was 3.2%.

[0052] Example 6 The difference from Example 1 is that 5.0 g of sodium acetate was used as a catalyst, and the pH was maintained at 9.0-9.5 with 0.05 mol / L sodium hydroxide during the reaction. Other conditions were the same as in Example 1. Results: 3-hydroxypropionitrile purity was 95.48%, yield was 91.5%, and di(cyanoethyl) ether content was 4.10%.

[0053] Example 7 In a 500mL quick-opening reactor equipped with a stirrer and temperature sensor, add 150mL of deionized water, 135g of potassium phosphate, and 4.0g of sodium carbonate (Na₂CO₃). Stir until the solids are completely dissolved to form a saturated salt solution. Maintain the temperature at 40℃ and add 53.0g of acrylonitrile (approximately 1.0mol) at once. Purge the air in the reactor with nitrogen three times and react for 5 hours. After the reaction is complete, allow the mixture to stand and separate into layers. The upper oil phase is the crude 3-hydroxypropionitrile.

[0054] Analysis results: 3-hydroxypropionitrile purity 93.24%, yield 86%, and di(cyanoethyl) ether content of byproduct 5.11%.

[0055] Example 8 In a 1000mL quick-opening reactor equipped with a stirrer and temperature sensor, add 500mL of deionized water, 195g of sodium chloride, and 4.0g of sodium carbonate (Na₂CO₃). Stir until the solids are completely dissolved to form a supersaturated salt solution (with a small amount of NaCl suspended). Maintain the temperature at 20℃, and add 53.0g of acrylonitrile (approximately 1.0mol) at once. Replace the air in the reactor with nitrogen three times, and react for 5 hours. After the reaction is complete, allow the mixture to stand and separate into layers; the upper oil phase is the crude 3-hydroxypropionitrile.

[0056] Analytical results: 3-hydroxypropionitrile purity 92.5%, yield 85.6%, and di(cyanoethyl) ether content of byproduct 4.91%.

[0057] Example 9 In a 500mL quick-opening reactor equipped with a stirrer and temperature sensor, add 150mL of deionized water, 155g of potassium carbonate, and 5g of potassium carbonate (K2CO3) (totaling 160g). Stir until the solids are completely dissolved to form a saturated salt solution. Maintain the temperature at 15℃, then add 53.0g of acrylonitrile (approximately 1.0mol) at once. Purge the air in the reactor with nitrogen three times and react for 5 hours. After the reaction is complete, allow the mixture to stand and separate into layers. The upper oil phase is the crude 3-hydroxypropionitrile.

[0058] Analysis results: 3-hydroxypropionitrile purity 93.61%, yield 86%, and di(cyanoethyl) ether content of byproduct 4.8%.

[0059] Comparative Example 1 Traditional aqueous phase reaction + organic solvent extraction (without salting out) In a 500 mL quick-opening reactor equipped with a stirrer and temperature sensor, 200 mL of deionized water and 4.0 g of sodium carbonate (Na₂CO₃) were added and stirred until dissolved. The temperature was maintained at 25 °C, and 53.0 g of acrylonitrile (approximately 1.0 mol) was added in a single batch. After reacting for 4 hours, the mixture was extracted with ethyl acetate (3 × 100 mL), and the organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was recovered by vacuum distillation (119-121 °C / 0.8 kPa) to obtain 3-hydroxypropionitrile.

[0060] Analytical results: 3-hydroxypropionitrile purity was 88.5%, yield was 73.2% (with some loss during extraction and distillation), and the content of the byproduct di(cyanoethyl) ether was 8.5%. Compared with Example 1, this comparative example did not use salting out, but adopted conventional organic solvent extraction-distillation separation. The yield and purity were significantly lower than those of this invention, the byproduct content was much higher than that of the coupled process of this invention, and it involved the use and recovery of organic solvents, making the operation more complicated.

[0061] Comparative Example 2 Direct distillation without salting out (without separating byproducts) The reaction conditions were the same as in Comparative Example 1, but extraction was not performed after the reaction; instead, vacuum distillation was carried out directly (119-121℃ / 0.8kPa). Since the boiling points of 3-hydroxypropionitrile and the byproduct di(cyanoethyl) ether are approximately 228℃ and 250℃, respectively, complete separation is difficult to achieve with ordinary distillation. Furthermore, during vacuum distillation, 3-hydroxypropionitrile is prone to polymerization and decomposition at high temperatures (close to its boiling point).

[0062] Analysis results: Only about 65% of the fraction could be obtained, and the purity of 3-hydroxypropionitrile in the fraction was less than 70%. A large amount of byproducts and polymers remained at the bottom of the vessel. This method is not suitable for industrial production.

[0063] Comparative Example 3 Comparison of salting-out effects of low-concentration salts The coupling process of Example 1 was used, but the amount of ammonium sulfate was halved (56g, salt concentration of about 37g / 100mL water, about half of the saturation concentration), while other conditions remained the same.

[0064] Analysis results: No significant oil phase precipitation occurred during the reaction. After the reaction, the system remained homogeneous or had only a very small amount of oil droplets suspended upon standing. Only after adding additional ammonium sulfate to saturation did the oil phase slowly precipitate. Analysis showed that the yield of 3-hydroxypropionitrile was only 72.5%, and the byproduct content was 7.2%. It can be concluded that the salt concentration must reach saturation or supersaturation to produce a significant salting-out effect; low salt concentrations cannot achieve immediate product removal during the reaction process.

[0065] Comparative Example 4 Salting out after reaction In a 500mL quick-opening reactor equipped with a stirrer and temperature sensor, add 200mL of deionized water and 4.0g of sodium carbonate (Na₂CO₃) and stir to dissolve. Maintain the temperature at 25℃ and add 53.0g of acrylonitrile (approximately 1.0mol) all at once. After reacting for 4 hours, add solid sodium chloride (NaCl) in portions, totaling 80g, to the reaction solution until saturation (NaCl solubility is approximately 36g / 100mL water at 20℃). Continue stirring for 15 minutes and let stand for 30 minutes. The system separates into layers, with the upper oil phase separating out.

[0066] Analytical results: 3-hydroxypropionitrile purity 89.5%, yield 79.3%, and di(cyanoethyl) ether content of byproduct 7.1%.

[0067] Table 2 summarizes the process types and test results of each embodiment and comparative example. Table 2 Summary of Experimental Results

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing 3-hydroxypropionitrile, characterized in that, Includes the following steps: 1) Water, an alkaline catalyst, and an inorganic salt are mixed to obtain a mixed solution; the salt concentration in the mixed solution reaches a saturated or supersaturated state; The inorganic salts include one or more of ammonium sulfate, potassium phosphate, dipotassium hydrogen phosphate, sodium chloride, sodium sulfate, and potassium carbonate; The alkaline catalyst is one or more of sodium carbonate, potassium carbonate, sodium acetate, and sodium hydroxide; 2) Under stirring conditions, acrylonitrile was added to the above mixed solution to carry out a hydration reaction. During the reaction, the generated 3-hydroxypropionitrile was continuously precipitated from the aqueous phase under the salting-out effect to form an independent oil phase. The mass ratio of acrylonitrile to water is 1:2 to 1:10; The hydration reaction is carried out at a temperature of 10℃-40℃ for 1-6 hours. 3) After the reaction is complete, the oil phase is separated to obtain 3-hydroxypropionitrile.

2. The preparation method according to claim 1, characterized in that, Step 1) The amount of inorganic salt added is such that the salt concentration in the reaction solution reaches 100%-120% of the saturated solubility of the salt at the reaction temperature.

3. The preparation method according to claim 1, characterized in that, The mass ratio of acrylonitrile to water is 1:3 to 1:

5.

4. The preparation method according to claim 1, characterized in that, The hydration reaction described in step 2) is carried out at a temperature of 20℃-30℃ and for a time of 4-5.5h.

5. The preparation method according to claim 1, characterized in that, In step 2), the pH of the reaction solution is controlled at 9.0-9.5 during the hydration reaction.

6. The preparation method according to claim 1, characterized in that, The amount of the alkaline catalyst added is 0.5%-4% of the mass of acrylonitrile.

7. The preparation method according to claim 1, characterized in that, Step 3) involves separating the oil phase and then concentrating the remaining brine phase. After concentration, the inorganic salts are recovered and recycled.

8. The preparation method according to claim 7, characterized in that, Inorganic salts should be purified or replaced entirely after every 5-10 cycles.

9. The preparation method according to claim 8, characterized in that, The purification process is performed by activated carbon adsorption.

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