A purification process for ethyl formate

Abstract

The application belongs to the field of separation and purification, and particularly relates to a purification process of ethyl formate, and preparation of a molecular sieve with an aluminum-doped surface; the surface of the molecular sieve is modified to obtain a modified molecular sieve, then the modified molecular sieve is combined with a porous polymer and loaded on a porous matrix to prepare a separation membrane, and a purified material is obtained, and the purified material is used for separation and purification; the process has low energy consumption, high separation factor, and the separation material can be repeatedly used, and has low use cost.

Description

Technical Field

[0001] This invention belongs to the field of separation and purification, and specifically relates to a purification process for ethyl formate. Background Technology

[0002] Ethyl formate is an important industrial raw material, used as a pharmaceutical intermediate in drug synthesis, in the production of coatings and paints, as an insecticide fumigant in agriculture, and as a flavoring and fragrance in the food industry, finding wide application in numerous fields. Industrially, ethyl formate is typically produced by the esterification of formic acid and ethanol. The process mainly involves the direct esterification of formic acid and ethanol under sulfuric acid catalysis, followed by neutralization, washing with water, and distillation to obtain the final product. During this production process, the product ethyl formate and unreacted ethanol form an azeotrope under normal pressure, which is difficult to separate using ordinary distillation methods, resulting in high energy consumption in ethyl formate production. Existing extractive distillation studies have yielded ethyl formate with a purity of 90%, not exceeding the azeotropic content of ethyl formate and ethanol, and require the addition of azeotropic agents or extractants. The separation of these additives themselves introduces additional consumption and costs. Furthermore, due to the high compatibility of ethanol and water, ethyl formate also contains water that is difficult to remove, creating a ternary system that further complicates the purification of ethyl formate. Summary of the Invention

[0003] To address the problems of high difficulty, high energy consumption, and low product purity in the separation and purification of ethyl formate in existing technologies, this invention discloses a highly efficient and low-energy-consumption purification process for ethyl formate. The purification materials used are of high strength and can be reused repeatedly. The technical solution is as follows:

[0004] A purification material for ethyl formate is prepared by preparing an aluminum-doped molecular sieve; the surface of the molecular sieve is modified to obtain a modified molecular sieve; then the modified molecular sieve is combined with a porous polymer and loaded onto a porous matrix to form a separation membrane, thereby obtaining the purification material.

[0005] Furthermore, the preparation of the molecular sieve includes the following steps:

[0006] a. Place tetrapropylammonium hydroxide in sodium hydroxide solution, mix well, add tetraethyl orthosilicate, mix well, and stir for 6-10 h; after crystallization for 48-72 h, wash the product thoroughly and dry to obtain the precursor;

[0007] b. Disperse the precursor in water, add sodium hydroxide solution and mix thoroughly, add sodium aluminate, mix evenly, and crystallize for 10-24 hours; wash the product thoroughly, dry it, and calcine it at 500-600℃ for 5-8 hours to obtain the molecular sieve.

[0008] Furthermore, the concentration of the sodium hydroxide solution in step a is 0.15~0.17 mol / L; the mass ratio of tetrapropylammonium hydroxide to tetraethyl orthosilicate is 1.2~1.5:1.

[0009] Furthermore, in step b, the mass ratio of the precursor to sodium hydroxide is 1:0.08~0.15; and the mass ratio of the precursor to sodium aluminate is 1:0.08~0.12.

[0010] Furthermore, it crystallizes at 160~190℃.

[0011] Furthermore, the preparation of the purified material includes the following steps: surface grafting modification of molecular sieve and γ-methacryloyloxypropyltrimethoxysilane to obtain modified molecular sieve;

[0012] Polyvinylidene fluoride was placed in dimethyl sulfoxide and mixed evenly. Polyvinyl alcohol was then added. Under a nitrogen atmosphere, the system was heated until the polyvinyl alcohol was completely dissolved and ultrasonically mixed for 3-5 hours. Modified molecular sieves were added and ultrasonically mixed until the system was homogeneous. Azobisisobutyronitrile was added and mixed thoroughly for 0.5-1 hours to obtain a homogeneous liquid.

[0013] A uniform liquid is flowed onto a substrate to form a film, which is then allowed to stand for 1-2 hours and then frozen to obtain a frozen membrane material. The dimethyl sulfoxide in the frozen membrane material is completely replaced with water, and the wetted membrane material is dried with hot air at 70-85°C. After drying, the membrane material is thoroughly washed with hot water and then dried to obtain the purified material.

[0014] Furthermore, the mass ratio of the molecular sieve to γ-methacryloyloxypropyltrimethoxysilane is 1:0.15~0.25; the mass ratio of the modified molecular sieve to polyvinylidene fluoride is 1:2~4; the mass ratio of polyvinylidene fluoride to dimethyl sulfoxide is 1:1.5~3; and the mass ratio of polyvinylidene fluoride to polyvinyl alcohol is 1:0.1~0.2.

[0015] Furthermore, the freezing process involves freezing at -15°C or below for 8 to 12 hours.

[0016] A purification process for ethyl formate using the above-mentioned purification material includes the following steps: loading the purification material into a membrane module and controlling the feed solution at 35~45℃; after negative pressure permeation for 1~3 hours, raising the temperature of the feed solution to below 60℃, and collecting the permeate during the process.

[0017] Furthermore, the feed flow rate is 10~50 mL / min; the membrane is removed and treated at 50~80℃ and -0.04~-0.08 MPa for 1~3 h to complete regeneration.

[0018] By adopting the above scheme, the method of the present invention has the following advantages:

[0019] 1. Compared with distillation and extraction, the purification process of this invention has low energy consumption, the purification material is stable and easy to separate, it will not introduce other impurities that are also liquids, and the separation accuracy is high, the product purity is high; the purified material has high strength, strong stability, long service life, can be easily regenerated, and can be used in industrial applications.

[0020] 2. The purification process of this invention involves staged heating. At lower temperatures, it facilitates the permeation of smaller water molecules. At higher temperatures, molecular motion accelerates, increasing the permeation performance of ethanol. Meanwhile, the water content in the feed solution is lower, reducing competition between water and ethanol for the channels, increasing the permeation flux, and decreasing the probability of ethyl formate permeation. This avoids the problems of decreased separation factor and high energy consumption associated with continuously maintaining high temperatures to increase flux.

[0021] 3. The purification material of this invention has a strong affinity for ethanol, and the difference in properties between ethyl formate and ethanol causes ethanol in the material to preferentially permeate, thereby separating ethanol from ethyl formate. Simultaneously, the purification material of this invention does not easily swell in ethyl formate, giving it considerable mechanical strength and structural stability. Its suitable affinity and hydrophobicity result in high permeability and separation factor.

[0022] 4. In the purification material of this invention, the pores inside the molecular sieve are not completely modified. The silanol groups present therein have a stronger interaction with ethanol than ethyl formate, making it easier for ethanol to enter the pores and thus separate from ethyl formate. Furthermore, alumina is introduced onto the surface of the molecular sieve, which can change the polarity of the molecular sieve surface, thereby changing the interaction between the membrane and the components to be separated and improving the separation factor. Alumina also more easily attracts ethanol, which has a smaller molecular volume and contains alcohol hydroxyl groups, further improving the separation factor.

[0023] 5. In the purification material of the present invention, the pores of the polymer and the molecular sieve are matched with those of ethanol. Ethanol and water molecules can easily pass through, while ethyl formate, which has a larger volume, is more easily blocked. This promotes the separation of ethyl formate from difficult-to-remove impurities from a physical perspective, resulting in high reliability and strong selectivity.

[0024] 6. The molecular sieve in the purification material of this invention can not only be used for the separation and purification of ethyl formate, but also serve as a packing material to improve membrane strength. Simultaneously, the polymer surrounding the molecular sieve ensures its full dispersion, isolates interactions between molecular sieves, and promotes uniform distribution. This guarantees a high permeation flux while maintaining a high separation factor, avoiding a decrease in the separation factor caused by agglomeration or local deficiencies. This solves the problem of molecular sieves easily agglomerating, resulting in a small proportion in the material and limited potential for improving the separation factor.

[0025] 7. The present invention first prepares an aluminum-free silicon-based precursor, then treats the surface with an alkaline solution to ionize some of the silicon on the surface of the precursor, and then exchanges it with aluminum through the difference in solubility. Finally, it is calcined so that only a local area of ​​the molecular sieve surface has a high aluminum content, so that aluminum can directly contact the raw material to be separated and retain more active sites of silicon for modification.

[0026] 8. This invention uses polyvinyl alcohol and dimethyl sulfoxide together to create pores, forming a polyvinylidene fluoride framework that allows the raw materials to be separated to fully contact the molecular sieve. Based on the pores created by dimethyl sulfoxide, the change in the physical state of polyvinyl alcohol caused by the viscosity change from low to high temperature is utilized to maintain and promote the connectivity of the channels during the thermal crosslinking process of hot air drying, reducing collapse and resulting in high permeability of the formed pores.

[0027] 9. The polyvinylidene fluoride skeleton in the purification material of the present invention has good solvent resistance and strength in ethyl formate, which can greatly ensure the pore size and the stability of the molecular sieve, avoid uncontrollable cracks between the molecular sieve and the polymer skeleton due to swelling, and has a high separation index and good purification effect. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: (1) Take 3g of tetrapropylammonium hydroxide and place it in 0.16mol / L sodium hydroxide solution. After mixing evenly, add 2g of tetraethyl orthosilicate and mix evenly. Stir for 8h. After crystallizing at 180℃ for 48h, wash the product thoroughly and dry it to obtain the precursor. Take 1.5g of the precursor and disperse it in water. Add 10mL of 0.4mol / L sodium hydroxide solution and mix thoroughly. Add 0.15g of sodium aluminate and mix evenly. Crystallize at 180℃ for 18h. Wash the product thoroughly and dry it. Calcine at 550℃ for 6h to obtain the molecular sieve.

[0030] (2) Take 1.2g of molecular sieve and place it in 200mL of methanol for ultrasonic dispersion. Add 60mL of ammonia water diluted 50 times and then add 0.25g of γ-methacryloyloxypropyltrimethoxysilane. React at 50℃ for 6h. Wash the product with ethanol and water 3 times and dry it to obtain the modified molecular sieve.

[0031] (3) Place 3g of polyvinylidene fluoride 17-88 in 7g of dimethyl sulfoxide, mix evenly, add 0.45g of polyvinyl alcohol, heat the system to 80℃ under nitrogen atmosphere, after the polyvinyl alcohol is completely dissolved, sonicate and mix for 4h; add 1g of modified molecular sieve, sonicate until the system is uniform, add azobisisobutyronitrile, mix thoroughly for 0.5h to obtain a uniform liquid;

[0032] (4) A uniform liquid is flowed onto a polytetrafluoroethylene substrate with a pore size of 0.2µm to form a film. The film is allowed to stand for 1 hour and then frozen at -18℃ for 12 hours to obtain a frozen membrane. The frozen membrane is then immersed in water and replaced with dimethyl sulfoxide. The immersion and replacement operation is repeated 5 times. The wet membrane after replacement is dried with hot air at 70~85℃. After drying, the membrane is thoroughly washed with hot water and dried to obtain the purified material.

[0033] Example 2: The difference from Example 1 is as follows:

[0034] (2) Take 1.2g of molecular sieve and place it in 200mL of methanol for ultrasonic dispersion. Add 60mL of ammonia water diluted 50 times and then add 0.18g of γ-methacryloyloxypropyltrimethoxysilane. React at 50℃ for 6h. Wash the product with ethanol and water 3 times and dry it to obtain the modified molecular sieve.

[0035] Example 3: The difference from Example 1 is as follows:

[0036] (2) Take 1.2g of molecular sieve and disperse it in 200mL of methanol by ultrasonication. Add 60mL of ammonia water diluted 50 times and then add 0.3g of γ-methacryloxypropyltrimethoxysilane. React at 50℃ for 6h. Wash the product with ethanol and water 3 times and dry it to obtain the modified molecular sieve.

[0037] Example 4: The difference from Example 1 is as follows:

[0038] (3) Place 2g of polyvinylidene fluoride 17-88 in 7g of dimethyl sulfoxide, mix evenly, add 0.45g of polyvinyl alcohol, heat the system to 80℃ under nitrogen atmosphere, and after the polyvinyl alcohol is completely dissolved, sonicate and mix for 4h; add 1g of modified molecular sieve, sonicate until the system is uniform, add azobisisobutyronitrile, mix thoroughly for 0.5h to obtain a uniform liquid.

[0039] Example 5: The difference from Example 1 is as follows:

[0040] (3) Place 3g of polyvinylidene fluoride 17-88 in 4.5g of dimethyl sulfoxide, mix evenly, add 0.45g of polyvinyl alcohol, heat the system to 80℃ under nitrogen atmosphere, after the polyvinyl alcohol is completely dissolved, sonicate and mix for 4h; add 1g of modified molecular sieve, sonicate until the system is uniform, add azobisisobutyronitrile, mix thoroughly for 0.5h to obtain a uniform liquid.

[0041] Example 6: The difference from Example 1 is as follows:

[0042] (3) Place 3g of polyvinylidene fluoride 17-88 in 9g of dimethyl sulfoxide, mix evenly, add 0.45g of polyvinyl alcohol, heat the system to 80℃ under nitrogen atmosphere, and after the polyvinyl alcohol is completely dissolved, sonicate and mix for 4h; add 1g of modified molecular sieve, sonicate until the system is uniform, add azobisisobutyronitrile, mix thoroughly for 0.5h to obtain a uniform liquid.

[0043] Example 7: The difference from Example 1 is as follows:

[0044] (3) Place 3g of polyvinylidene fluoride 17-88 in 7g of dimethyl sulfoxide, mix evenly, add 0.3g of polyvinyl alcohol, heat the system to 80℃ under nitrogen atmosphere, and after the polyvinyl alcohol is completely dissolved, sonicate and mix for 4h; add 1g of modified molecular sieve, sonicate until the system is uniform, add azobisisobutyronitrile, mix thoroughly for 0.5h to obtain a uniform liquid.

[0045] Example 8: The difference from Example 1 is as follows:

[0046] (3) Place 3g of polyvinylidene fluoride 17-88 in 7g of dimethyl sulfoxide, mix evenly, add 0.6g of polyvinyl alcohol, heat the system to 80℃ under nitrogen atmosphere, after the polyvinyl alcohol is completely dissolved, sonicate and mix for 4h; add 1g of modified molecular sieve, sonicate until the system is uniform, add azobisisobutyronitrile, mix thoroughly for 0.5h to obtain a uniform liquid.

[0047] Comparative Example 1: The difference from Example 1 is that:

[0048] (1) Take 3g of tetrapropylammonium hydroxide and place it in 0.16mol / L sodium hydroxide solution. After mixing evenly, add 2g of tetraethyl orthosilicate and mix evenly. Stir for 8h. After crystallizing at 180℃ for 48h, wash the product thoroughly and dry it to obtain the precursor. Take 1.5g of the precursor and disperse it in water. Add 10mL of 0.4mol / L sodium hydroxide solution and mix thoroughly. Add 0.25g of sodium aluminate and mix evenly. Crystallize at 180℃ for 18h. Wash the product thoroughly and dry it. Calcine at 550℃ for 6h to obtain the molecular sieve.

[0049] Process Example: The purification material is loaded into the membrane module, the feed temperature is controlled at 40°C, the feed is pumped in and flows through the membrane module, the pressure on the permeate side is maintained at -0.4MPa, and after 2 hours of negative pressure permeation, the feed temperature is raised to 65°C and permeation continues until the ethanol content in the feed is less than 0.1%, and the permeate is collected.

[0050] Process Comparison Example 1: The purification material was loaded into the membrane module, the feed temperature was controlled at 40℃, the feed was pumped in and flowed through the membrane module, the pressure on the permeate side was maintained at 300Pa, and after negative pressure permeation for 2 hours, the feed temperature was raised to 85℃ and permeation continued until the ethanol content in the feed was less than 0.1%, and the permeate was collected.

[0051] Process Comparison Example 2: The purification material is loaded into the membrane module, the feed temperature is controlled at 60℃, the feed is pumped in and flows through the membrane module, the vacuum on the permeate side is maintained, and negative pressure permeation is carried out until the ethanol content in the feed is less than 0.1%, and the permeate is collected.

[0052] Example Sample Testing: A feed solution composed of 90 wt% methyl formate, 9 wt% ethanol, and 1 wt% water was prepared. The purification materials from each example and comparative example were used, and experiments were conducted according to the process examples. The purification material from Example 1 was used, and experiments were conducted according to Process Comparative Example 1 and Process Comparative Example 2. The mass of the purified material permeating per unit membrane area per unit time was measured, and the permeation flux was calculated. The separation factor was calculated using the formula: (Concentration of ethanol and water in the permeate / Concentration of ethyl formate in the permeate) / (Concentration of ethanol and water in the feed solution / Concentration of ethyl formate in the feed solution). The results are as follows:

[0053] Compared to Example 1, Comparative Example 1 involved more aluminum substitution during molecular sieve preparation, resulting in increased permeation flux but a significantly decreased separation factor. This indicates that excessive aluminum substitution can negatively impact the pore structure of the molecular sieve, enlarging the pore size and reducing the selectivity of the feed solution to be separated. The decreased water content in the permeate also reflects the influx of more ethyl formate into the permeate. During molecular sieve modification, Example 2 had a lower coupling agent content, while Example 3 had a higher coupling agent content. Example 2 had a higher permeation flux than Example 3, and Example 3 had a higher separation factor. However, compared to Example 1, the increase in permeation flux in Example 2 was not significant, while the decrease in separation factor was more pronounced. Meanwhile, Example 3 showed a significant increase in separation factor, but a significant decrease in permeation flux, indicating that the separation efficiency of Examples 2 and 3 was lower than that of Example 1.

[0054] In Example 4, the low polyvinylidene fluoride (PVDF) content resulted in a reduced membrane thickness. While the permeate flux increased significantly, the separation factor decreased markedly. In Example 5, the low dimethyl sulfoxide (DMSF) content significantly reduced the permeate flux, increasing the separation factor, although the increase was not substantial compared to Example 1. In Example 6, the high dimethyl sulfoxide (DMSF) content increased the permeate flux, but significantly reduced the separation factor and the water content in the permeate. Combining Examples 5 and 6, it can be seen that DMSF directly affects the porosity and pore size of the purification material. More DMSF increases porosity and flux, but also increases pore size, thus decreasing the separation factor. However, less DMSF is also detrimental to pore shaping. In Example 7, less polyvinyl alcohol (PVA) was used in the preparation, while in Example 8, more was used. The permeate flux of Example 7 was lower than that of Example 8, but the separation factor was higher. Although Example 8 had a high permeate flux, the separation factor decreased drastically, indicating that PVA is beneficial for pore stability, but excessive PVA increases pore size and affects the selectivity of the membrane material.

[0055] Compared to Example 1, Comparative Example 1 showed an increased permeation flux but a significantly decreased separation factor. At higher temperatures, the space for molecules to pass through increases and molecular motion accelerates, leading to an increased permeation flux. However, ethyl formate also passes through more easily, while the permeation advantage of ethanol and water due to accelerated molecular motion is weakened, resulting in a decreased separation factor. Comparative Example 2, which did not involve staged heating, had a higher permeation flux than Example 1, but a significantly lower separation factor. Compared to Comparative Example 2, Example 1, with its staged heating, was clearly more advantageous.

[0056] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A purification material for ethyl formate, characterized by, The surface of the molecular sieve is doped with aluminum; the molecular sieve is subjected to surface grafting modification with gamma-methacryloxypropyltrimethoxysilane to obtain a modified molecular sieve; The polyvinylidene fluoride is placed in dimethyl sulfoxide, and polyvinyl alcohol is added after uniform mixing; under a nitrogen atmosphere, the system is heated to completely dissolve the polyvinyl alcohol, and ultrasonic mixing is performed for 3-5 hours; the modified molecular sieve is added and ultrasonically mixed until the system is uniform; azobisisobutyronitrile is added and mixed thoroughly for 0.5-1 hour to obtain a uniform liquid; The uniform liquid is formed into a film on a substrate by flow casting, and is allowed to stand and soak for 1-2 hours, and then is frozen to obtain a frozen film; dimethyl sulfoxide in the frozen film is replaced with water, and the soaked film after the replacement is completed is dried by hot air at 70-85°C; after drying, the film is washed with hot water, and a purified material is obtained after drying.

2. The purified material of ethyl formate according to claim 1, characterized in that, The preparation of the molecular sieve comprises the following steps: a. Tetrapropylammonium hydroxide is placed in a sodium hydroxide solution, and tetraethyl orthosilicate is added after uniform mixing; the mixture is stirred for 6-10 hours; after crystallization for 48-72 hours, the product is washed thoroughly and dried to obtain a precursor; b. The precursor is dispersed in water, and a sodium hydroxide solution is added and mixed thoroughly; sodium aluminate is added and mixed uniformly, and then crystallization is performed for 10-24 hours; The product is washed thoroughly and dried, and then is calcined at 500-600°C for 5-8 hours to obtain the molecular sieve.

3. The purified material of ethyl formate according to claim 2, characterized in that, The concentration of the sodium hydroxide solution in step a is 0.15-0.17 mol / L; and the mass ratio of the tetrapropylammonium hydroxide to the tetraethyl orthosilicate is 1.2-1.5:

1.

4. The purified material of ethyl formate according to claim 2, characterized in that, In step b, the mass ratio of the precursor to the sodium hydroxide is 1:0.08-0.15; and the mass ratio of the precursor to the sodium aluminate is 1:0.08-0.

12.

5. The purified material of ethyl formate according to claim 2, characterized in that, Crystallization is performed at 160-190°C.

6. The purified material of ethyl formate of claim 1, wherein, The mass ratio of the molecular sieve to the gamma-methacryloxypropyltrimethoxysilane is 1:0.15-0.25; the mass ratio of the modified molecular sieve to the polyvinylidene fluoride is 1:2-4; the mass ratio of the polyvinylidene fluoride to the dimethyl sulfoxide is 1:1.5-3; and the mass ratio of the polyvinylidene fluoride to the polyvinyl alcohol is 1:0.1-0.

2.

7. The purified material of ethyl formate of claim 1, wherein, The freezing is performed at -15°C or lower for 8-12 hours.

8. A purification process of ethyl formate using the purified material according to any one of claims 1 to 7, characterized by, The purified material is loaded into a membrane module, and the temperature of the feed liquid is controlled at 35-45°C; after negative pressure permeation for 1-3 hours, the temperature of the feed liquid is increased to below 60°C, and the permeate is collected during the process.

9. The purification process of ethyl formate according to claim 8, characterized in that, The feed flow rate is 10-50 mL / min; the membrane is taken out and treated at 50-80°C and -0.04 to -0.08 MPa for 1-3 hours to complete the regeneration.

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