A separation method based on tetrahydrofuran-methanol-silane-water mixture

Abstract

The present invention relates to a separation method based on tetrahydrofuran methanol silane water mixture, tetrahydrofuran mother liquor is added to crude steam kettle, desalination and decolorization pretreatment are carried out in intermittent crude steaming mode to obtain colorless tetrahydrofuran crude steam liquid; tetrahydrofuran crude steam liquid is sent to extraction tower kettle as feed, water is added in the middle of the tower as extractant to carry out intermittent extractive distillation, and the front fraction of the cut part is temporarily stored in the front fraction tank, and then tetrahydrofuran distillate is collected and temporarily stored in the tetrahydrofuran distillate tank; Tetrahydrofuran distillate is sent to hollow fiber membrane separation unit for separation, and tetrahydrofuran finished product is obtained, and the water in the feed liquid side solution and a small amount of tetrahydrofuran are passed through hollow fiber membrane in the form of steam to obtain permeate, and the permeate is condensed and returned to crude steam tower to reclaim tetrahydrofuran therein again. The advantages of the present invention are simplified process, improved product purity, reduced operating energy consumption, guaranteed extraction water cycle number, safe, efficient and environmentally friendly.

Description

Technical Field

[0001] The invention relates to the technical field of hollow fiber membrane separation applications, in particular to a separation method based on a tetrahydrofuran-methanol-silane-water mixture. Background Art

[0002] Tetrahydrofuran is an important raw material for organic synthesis and a solvent with excellent performance. It is particularly suitable for dissolving PVC, polyvinylidene chloride and butadiene aniline. It is widely used as a solvent for surface coatings, anti-corrosion coatings, printing inks, magnetic tapes and film coatings, and is often used as a reaction solvent.

[0003] Therefore, in the production of some fine chemicals, pharmaceutical APIs, and pesticide intermediates, tetrahydrofuran (THF) is often used as the solvent for the Grignard reaction. After the reaction, the THF contains byproducts from the Grignard reagent reaction and excess reactants, typically including organic compounds such as methanol and silane. Furthermore, water is often added to quench the Grignard reaction, resulting in a THF mother liquor consisting of a tetrahydrofuran-methanol-silane-water mixture. This mixture contains three binary azeotropes: tetrahydrofuran-water, tetrahydrofuran-methanol, and methanol-silane. This makes separation and purification of the THF difficult using conventional processes. Furthermore, the THF used in the Grignard reaction must have a purity of ≥99.9% and a water content of ≤0.05% or even lower. The quality of the separated and purified THF plays a crucial role in the Grignard reaction.

[0004] Currently, most tetrahydrofuran-methanol separation methods use high-boiling-point organic compounds such as ethylene glycol as the extractant. However, tetrahydrofuran-methanol separation processes using water as the extractant, such as the "Environmentally Friendly Tetrahydrofuran Extraction and Distillation Separation Process," disclosed in Chinese Patent Application Publication No. CN115197177A, describe a process for obtaining anhydrous tetrahydrofuran using extractive distillation, membrane separation, and azeotropic distillation. The extraction water is recovered by crude distillation. However, the following problems still exist:

[0005] (1) The existing technology uses a three-step separation technology of extractive distillation-membrane separation-azeotropic distillation, which has a longer purification process, a higher reflux ratio in the extraction tower, and the finished tetrahydrofuran is discharged from the bottom of the azeotropic distillation tower, resulting in lower purity;

[0006] (2) The existing technology has the problem of continuous boiling of tetrahydrofuran in the azeotropic distillation tower, which poses a safety hazard of peroxide accumulation;

[0007] (3) The existing technology requires a separate crude steamer to recover the extraction water, and the extraction water needs to be heated and cooled twice, resulting in high operating energy consumption;

[0008] (4) The existing technology cannot solve the problem of decolorization and desalination of raw materials. High-boiling substances and salts accumulate in the extraction water, affecting the number of extraction water cycles. Summary of the Invention

[0009] The present invention aims to solve the problems of difficulty, low purity, high energy consumption and great safety hazards in the existing separation and purification of tetrahydrofuran. It provides a separation method based on a tetrahydrofuran-methanol-silane-water mixture, which can simplify the process, improve product purity, reduce operating energy consumption, ensure the number of extraction water cycles, and be safe and environmentally friendly.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A separation method based on a tetrahydrofuran-methanol-silane-water mixture, using water extractive distillation and hollow fiber membrane separation technology, specifically comprising the following steps:

[0012] (1) Crude distillation: Add the tetrahydrofuran mother liquor into the crude distillation kettle and perform desalination and decolorization pretreatment by intermittent crude distillation to obtain a colorless tetrahydrofuran crude distillate, i.e., a tetrahydrofuran-methanol-silane-water mixture;

[0013] (2) Extraction distillation: The crude tetrahydrofuran liquid is fed into the extraction tower as feed, and water is added to the middle of the tower as an extractant for intermittent extraction distillation. Part of the front fraction is cut off and temporarily stored in the front fraction tank, and then the tetrahydrofuran distillate is collected and temporarily stored in the tetrahydrofuran distillate tank. In order to realize the recycling of the extraction water, a rear fraction tank is designed;

[0014] (3) Separation and purification: The tetrahydrofuran distillate is sent to a hollow fiber membrane separation unit for separation to obtain the tetrahydrofuran product. The water and a small amount of tetrahydrofuran in the feed solution pass through the hollow fiber membrane in the form of steam to obtain a permeate. The permeate is condensed and returned to the crude distillation tower to recover the tetrahydrofuran again.

[0015] Furthermore, in the step (1), the methanol content in the tetrahydrofuran mother liquor used for crude distillation is 0.5-8%, and the silane content is 0.1-5%.

[0016] Furthermore, in the step (1), when the tetrahydrofuran mother liquor is crudely distilled, normal pressure or negative pressure operation is adopted, the operating pressure is -0.05 to 0 MPa, the liquid phase product is extracted from the top of the crude distillation tower, and the reflux ratio is controlled at 0.5 to 1.

[0017] Furthermore, in the step (2), during the extraction and distillation process, the volume ratio of the feed amount of the extractant water to the instantaneous evaporation amount of the extraction tower is 1:1 to 1:4, and the reflux ratio of the extraction tower is controlled at 0.1 to 1.5.

[0018] Furthermore, in the step (2), during the extractive distillation process, the volume ratio of the feed amount of extractant water to the instantaneous evaporation amount of the extraction tower is 1:2.

[0019] Furthermore, in the step (2), before collecting the tetrahydrofuran distillate, a certain proportion of the front fraction is cut off, and the cutting ratio of the front fraction accounts for 2 to 8% of the feed amount of each batch.

[0020] Furthermore, in step (2), after the tetrahydrofuran distillate is collected, the organic matter in the tower kettle is continued to be collected as a rear fraction to ensure that the water in the tower kettle can be recycled as an extractant, and the collection ratio of the rear fraction accounts for 3-12% of the feed amount of each batch.

[0021] Furthermore, in step (3), the pressure on the raw material side during the hollow fiber membrane separation process is 250-500 kPa, and the temperature on the raw material side is 5-20° C. higher than the temperature corresponding to the saturated vapor pressure of the system.

[0022] Furthermore, in the step (3), the hollow fiber membrane separation unit uses a water-permeable membrane, which can be an organic membrane or an inorganic membrane.

[0023] Furthermore, in step (3), the hollow fiber membrane separation unit is composed of 1 to 100 hollow fiber membrane separators connected in series, in parallel or in mixed connection to achieve different processing requirements and production capacities.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] (1) The present invention uses hollow fiber membrane separation technology to break the tetrahydrofuran-water azeotropic composition and complete the dehydration of tetrahydrofuran in one step, which has a simple process and a high safety factor;

[0026] (2) The present invention uses water extraction distillation technology to break the azeotropic composition of tetrahydrofuran-methanol and methanol-silane. The extractant is non-toxic and non-flammable and does not introduce other components, thereby ensuring the purity of the final product.

[0027] (3) The present invention cuts off part of the front fraction before collecting the tetrahydrofuran distillate, and the methanol remaining in the last distillation in the tower and the silane in the material can be collected as the front fraction, thereby ensuring the stability of the subsequent tetrahydrofuran distillate during collection, while preventing silane from mixing into the tetrahydrofuran distillate and affecting the separation performance and service life of the hollow fiber separation membrane;

[0028] (4) After the extraction and distillation, the present invention recycles the extraction water by collecting the post-distillate, thereby avoiding secondary heating and cooling of the extraction water and reducing operating energy consumption;

[0029] (5) The present invention adopts a crude distillation method to decolorize and desalt the tetrahydrofuran mother liquor, remove the organic heavy components and salts, and avoid the organic heavy components and salts produced by the reaction from being brought into the subsequent extraction and distillation, thereby ensuring that the extractant water can be recycled, further reducing waste liquid discharge, and being safe and environmentally friendly. DETAILED DESCRIPTION

[0030] Example 1

[0031] To make the present invention more clear, a separation method based on a tetrahydrofuran-methanol-silane-water mixture of the present invention is further described below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] A separation method based on a tetrahydrofuran-methanol-silane-water mixture, comprising the following steps, characterized in that:

[0033] (1) sending the tetrahydrofuran mother liquor after the reaction to a crude distillation kettle, performing desalination and decolorization pretreatment by intermittent crude distillation, and collecting the tetrahydrofuran crude distillate from the top of the tower, i.e., a tetrahydrofuran-methanol-silane-water mixture, and sending it to a tetrahydrofuran crude distillate tank for collection;

[0034] (2) The crude tetrahydrofuran liquid is fed into the extraction tower as feed, water is added to the extraction tower as an extractant, and intermittent extractive distillation is performed, the reflux ratio is controlled to be 1, and the volume ratio of the water flow rate in the tower to the instantaneous evaporation volume of the tower is controlled to be 1:1, 1:2, 1:3 and 1:4 respectively. The front fraction is cut at a ratio of 5% of the feed amount and temporarily stored in the front fraction tank, and then the tetrahydrofuran distillate is collected and temporarily stored in the tetrahydrofuran distillate tank, and finally the rear fraction is collected at a ratio of 8% of the feed amount and placed in the rear fraction tank;

[0035] (3) The tetrahydrofuran distillate is heated and vaporized in an evaporator at a feed rate of 200 kg / h, and then superheated to 10°C in a superheater and fed into a hollow fiber membrane separation unit for separation to obtain a tetrahydrofuran product. The gauge pressure on the feed liquid side is 0.35 MPa, and the pressure on the permeate side is controlled at 800 Pa. The water content of the finished product is ≤0.03%. The water in the feed liquid solution and a small amount of tetrahydrofuran pass through the hollow fiber membrane in the form of steam to obtain a permeate. The permeate vapor is condensed and returned to the crude distillation kettle to re-recover the tetrahydrofuran.

[0036] In extractive distillation, when tetrahydrofuran distillate with different water addition ratios is used as the feed of the membrane separation unit, the water content of the obtained tetrahydrofuran distillate, the required number of membrane modules for separation, the purity of the tetrahydrofuran product and the methanol content are shown in Table 1.

[0037] Water addition ratio in extractive distillation 1:1 1:2 1:3 1:4 Water content of tetrahydrofuran distillate wt.% 4.5 5.1 5.8 6.5 Number of membrane separators required 2 3 3 4 Purity of finished tetrahydrofuran % 99.9 99.95 99.96 99.96 Methanol content in finished tetrahydrofuran % 0.045 0.030 0.026 0.021

[0038] As can be seen from the table, controlling the water addition ratio of the extractive distillation tower within an appropriate range can effectively optimize the required membrane area of the entire equipment and the quality of the final tetrahydrofuran product.

[0039] Example 2

[0040] A separation method based on a tetrahydrofuran-methanol-silane-water mixture, comprising the following steps, characterized in that:

[0041] (1) sending the tetrahydrofuran mother liquor after the reaction to a crude distillation kettle, and performing desalination and decolorization pretreatment by intermittent crude distillation, and collecting the tetrahydrofuran crude distillate, i.e., a tetrahydrofuran-methanol-silane-water mixture, from the top of the crude distillation tower, into a tetrahydrofuran crude distillate tank for collection;

[0042] (2) The crude tetrahydrofuran liquid is fed into the extraction tower as feed, water is added to the extraction tower as an extractant, and intermittent extractive distillation is performed. The reflux ratio is controlled to be 1, and the volume ratio of the water flow rate in the tower to the instantaneous evaporation volume of the tower is controlled to be 1:2. The front fraction is cut at a ratio of 2%, 4%, 6%, and 8% of the feed amount and temporarily stored in the front fraction tank, and then the tetrahydrofuran distillate is collected and temporarily stored in the tetrahydrofuran distillate tank. Finally, the rear fraction is collected at a ratio of 8% of the feed amount and is put into the rear fraction tank;

[0043] (3) The tetrahydrofuran distillate is heated and vaporized in an evaporator at a feed rate of 100 kg / h, and then superheated to 10° C. in a superheater and fed into a hollow fiber membrane separation unit for separation to obtain a tetrahydrofuran product. The feed liquid side pressure is 0.5 MPa, the permeate side pressure is controlled at 500 Pa, and the finished product water content is ≤0.02%. The water in the feed liquid side solution and a small amount of tetrahydrofuran pass through the hollow fiber membrane in the form of steam to obtain a permeate. The permeate vapor is condensed and returned to the crude distillation kettle to re-recover the tetrahydrofuran.

[0044] After different amounts of fore fractions were taken out during the extractive distillation process, the purity and silane content of the obtained tetrahydrofuran product, the change in membrane operating performance, and the tetrahydrofuran yield are shown in Table 2.

[0045]

[0046] As can be seen from the table, controlling the proportion of the front fraction removed during the extraction distillation process within an appropriate range can effectively extend the service life of the membrane and optimize the quality and yield of the final tetrahydrofuran product.

[0047] Example 3

[0048] A separation method based on a tetrahydrofuran-methanol-silane-water mixture, comprising the following steps, characterized in that:

[0049] (1) sending the tetrahydrofuran mother liquor after the reaction to a crude distillation kettle, performing desalination and decolorization pretreatment by intermittent crude distillation, and collecting the tetrahydrofuran crude distillate from the top of the crude distillation tower into a tetrahydrofuran crude distillate tank for collection;

[0050] (2) The crude tetrahydrofuran liquid is fed into the extraction tower as feed, and water is added to the extraction tower as an extractant for intermittent extractive distillation. Fresh water and wastewater after the last batch of fractions cut off at 5%, 9% and 12% are used as extractants. The reflux ratio is controlled to be 1.2, and the volume ratio of the water flow rate in the tower to the instantaneous evaporation volume of the tower is controlled to be 1:3. The front fraction is cut off at a ratio of 6% of the feed amount and temporarily stored in the front fraction tank, and then the tetrahydrofuran distillate is collected and temporarily stored in the tetrahydrofuran distillate tank. Finally, the rear fraction is collected at a ratio of 5% of the feed amount and put into the rear fraction tank;

[0051] (3) The tetrahydrofuran distillate is heated and vaporized in an evaporator at a feed rate of 300 kg / h, and then superheated to 15°C in a superheater and sent to a hollow fiber membrane separation unit for separation to obtain a tetrahydrofuran product. The feed side pressure is 0.35 MPa, the permeate side pressure is controlled at 800 Pa, and the water content of the finished product is ≤0.03%. The water in the feed side solution and a small amount of tetrahydrofuran pass through the hollow fiber membrane in the form of steam to obtain a permeate. The permeate vapor is condensed and returned to the crude distillation kettle to re-recover the tetrahydrofuran.

[0052] Table 3 shows the purity and methane content of the tetrahydrofuran products obtained by using different extraction waters in the extractive distillation process.

[0053] Residual fraction removal ratio % Fresh 5 9 12 Extraction water COD mg / L 50 8510 2240 1680 Purity of finished tetrahydrofuran % 99.94 99.76 99.89 99.92 Methanol content in finished tetrahydrofuran % 0.025 0.077 0.038 0.028

[0054] As can be seen from the table, by controlling the proportion of the fraction removed from the extraction distillation process within an appropriate range, the recycling of the extraction water can be achieved.

[0055] The present invention adopts distillation and hollow fiber membrane separation technology, combines traditional processes with new separation technologies, adopts hollow fiber membrane separation technology instead of other technologies to break the tetrahydrofuran-methanol azeotrope, adopts water extraction distillation technology instead of other flammable and toxic extractant technologies to break the tetrahydrofuran-methanol and methanol-silane azeotropes, does not add any additional components, and is highly efficient, energy-saving, and environmentally friendly.

[0056] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A separation method based on a tetrahydrofuran-methanol-silane-water mixture, using water extractive distillation and hollow fiber membrane separation technology, the specific steps are as follows, characterized in that: include: (1) Crude distillation: Add tetrahydrofuran mother liquor into a crude distillation kettle, wherein the methanol content of the tetrahydrofuran mother liquor used for crude distillation is 0.5~8wt% and the silane content is 0.1~5wt%. Crude distillation is carried out under normal pressure or negative pressure, and the operating pressure is -0.05~0MPa. The liquid phase product is extracted from the top of the crude distillation tower, and the reflux ratio is controlled at 0.5~1. The crude distillation is carried out by intermittent crude distillation to perform desalination and decolorization pretreatment, thereby obtaining a colorless tetrahydrofuran crude distillate, i.e., a tetrahydrofuran-methanol-silane-water mixture; (2) Extraction distillation: The crude tetrahydrofuran liquid is fed into the extraction tower as feed, and water is added to the middle of the tower as an extractant for intermittent extraction distillation. The volume ratio of the feed amount of the extractant water to the instantaneous evaporation amount of the extraction tower is 1:1~1:

4. The reflux ratio of the extraction tower is controlled at 0.1~1.

5. A portion of the front fraction is cut off and temporarily stored in the front fraction tank, and then the tetrahydrofuran distillate is collected and temporarily stored in the tetrahydrofuran distillate tank; (3) Separation and purification: The tetrahydrofuran distillate is sent to the hollow fiber membrane separation unit for separation. During the hollow fiber membrane separation process, the pressure on the raw material side is 250~500kPa, and the temperature on the raw material side is 5~20℃ higher than the temperature corresponding to the saturated vapor pressure of the system to obtain the finished tetrahydrofuran. The water and a small amount of tetrahydrofuran in the solution on the feed side pass through the hollow fiber membrane in the form of steam to obtain the permeate. The permeate is condensed and returned to the crude distillation tower to recover the tetrahydrofuran again.

2. The separation method based on a tetrahydrofuran-methanol-silane-water mixture according to claim 1, wherein: In the step (2), during the extraction and distillation process, the volume ratio of the feed amount of the extractant water to the instantaneous evaporation amount of the extraction tower is 1:

2.

3. The separation method based on tetrahydrofuran-methanol-silane-water mixture according to claim 1 or 2, characterized in that: In the step (2), before collecting the tetrahydrofuran distillate, a certain proportion of the front fraction is cut off, and the cutting ratio of the front fraction accounts for 2-8% of the feeding amount of each batch.

4. The separation method based on tetrahydrofuran-methanol-silane-water mixture according to claim 1 or 2, characterized in that: In the step (2), after the tetrahydrofuran distillate is collected, the organic matter in the tower kettle is continued to be collected as a rear fraction to ensure that the water in the tower kettle can be recycled as an extractant. The collection ratio of the rear fraction accounts for 3-12% of the feed amount of each batch.

5. The separation method based on tetrahydrofuran-methanol-silane-water mixture according to claim 1 or 2, characterized in that: In the step (3), the hollow fiber membrane separation unit adopts a water-permeable membrane, which is an organic membrane or an inorganic membrane.

6. The separation method based on a tetrahydrofuran-methanol-silane-water mixture according to claim 1 or 2, characterized in that: In the step (3), the hollow fiber membrane separation unit is composed of 1 to 100 hollow fiber membrane separators connected in series, in parallel or in mixed connection to achieve different processing requirements and production capacities.

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