Recovery process of mixed solution containing tetrahydrofuran and methanol

Abstract

The invention discloses a recovery process of a mixed solution containing tetrahydrofuran and methanol, and belongs to the technical field of recovery and separation of mixed solvents, and the recovery process is characterized by comprising the following steps: S1, pumping a clarified tetrahydrofuran-methanol mixed solution into a first-stage extractive distillation tower, adding a first-stage extractant, and controlling the temperatures of a tower kettle and a tower top to obtain a second-stage extractive distillation tower; distilling off a tetrahydrofuran crude product from the tower top, discharging a methanol-water solution from the tower bottom, and rectifying and purifying a mixed solution of methanol and water; s2, pumping the tetrahydrofuran crude product into a second-stage extractive distillation tower, adding a second-stage extractant, controlling the temperature of a tower kettle and the tower top, distilling off tetrahydrofuran steam from the tower top, and discharging a second-stage extractant solution from the tower bottom; s3, condensing the tetrahydrofuran steam, and rectifying to obtain high-purity tetrahydrofuran; the primary extraction agent is water or a mixed solution of water and ethanol; the secondary extraction agent is dihydric alcohol, and the problem that a tetrahydrofuran-methanol azeotropic system is difficult to separate is solved through double extractive distillation and constant-pressure operation.

Description

Technical Field

[0001] This invention relates to the field of mixed solvent recovery and separation technology, and in particular to a recovery process for a mixed solution containing tetrahydrofuran and methanol. Background Technology

[0002] In the chemical industry, the separation and recovery technology of mixed azeotropic systems has always been a key research focus. With the continuous development of the chemical industry, the demand for the efficient recovery and utilization of various mixed solutions is increasing. Effectively separating and recovering components in mixed azeotropic systems can not only improve resource utilization and reduce production costs, but also reduce environmental pollution, promoting the chemical industry towards a green and sustainable development direction. Among the many mixed azeotropic systems requiring separation and recovery, the mixed azeotropic system composed of tetrahydrofuran and methanol has significant research value. Tetrahydrofuran and methanol are widely used in many chemical production processes, and their effective separation and recovery can bring significant economic and social benefits to related industries.

[0003] Existing technologies for azeotropic mixtures of tetrahydrofuran and methanol often employ various separation and recovery techniques. These include extractive distillation, which uses extractants such as sodium hydroxide, n-heptane, and dimethyl sulfoxide as extractants. The extractants selectively alter the relative volatility of the components, followed by distillation for recovery. Pressure swing distillation is another common method, employing a dual-tower pressure swing mode. It utilizes the effect of pressure on the azeotropic composition, typically purifying tetrahydrofuran through initial separation in an atmospheric pressure column and purification in a high-pressure column. Pervaporation membrane separation utilizes specialized membrane materials such as P84 polyimide-cellulose acetate blends, achieving separation based on the selective permeation characteristics of the membrane for methanol. Additionally, there is an azeotropic distillation + phase separation process, which combines extractive distillation columns, azeotropic distillation columns, and phase separation units to achieve multi-component solvent recovery through multiple separations.

[0004] However, existing separation and recovery technologies have many drawbacks. For example, sodium hydroxide is costly and has poor recovery efficiency; n-heptane is flammable and volatile, and its extraction efficiency decreases significantly when the water content is high; dimethyl sulfoxide has poor stability under high temperature, acidic, and high pressure conditions and is easily decomposed, which not only leads to extractant loss but also introduces impurities. Pressure swing distillation requires high-pressure tower equipment, which significantly increases investment costs and operating energy consumption. Multiple extraction distillation + phase separation operations are complex, resulting in low production efficiency and high energy consumption. Pervaporation membrane replacement is expensive, and the unit's processing capacity is limited, making it difficult to meet the needs of large-scale industrial production. Moreover, phase separation operations are affected by the miscibility of tetrahydrofuran with water and methanol, making it difficult to achieve the expected separation effect and often requiring repeated operations, which adversely affects product quality. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a recovery process for a mixed solution containing tetrahydrofuran and methanol. By employing dual extraction distillation and constant pressure operation, it overcomes the difficulty in separating the tetrahydrofuran-methanol azeotropic system.

[0006] The present invention provides a recovery process for a mixed solution containing tetrahydrofuran and methanol, which adopts the following technical solution: A recovery process for a mixed solution containing tetrahydrofuran and methanol includes the following steps: S1. Pump the clarified tetrahydrofuran-methanol mixture into a primary extractive distillation column, add the primary extractant, and control the column bottom temperature at 80-100℃ and the column top temperature at 58-60℃ under constant pressure. Distill off the crude tetrahydrofuran from the top of the column and discharge the methanol-water solution from the bottom of the column. Purify the methanol-water mixture by distillation. S2. Pump the crude tetrahydrofuran into a two-stage extractive distillation column, add the secondary extractant, and control the column bottom temperature at 120-140℃ and the column top temperature at 65-67℃ under constant pressure. Tetrahydrofuran vapor is distilled off the top of the column, and the secondary extractant solution is discharged from the bottom of the column. S3. High-purity tetrahydrofuran is obtained by condensing tetrahydrofuran vapor and then distilling it. The primary extractant is water or a mixture of water and ethanol; The secondary extractant is a diol.

[0007] Further preferred options include replacing the primary and secondary extractive distillation columns (packed columns) with plate columns (sieve plate columns, valve columns). Replacing existing packed columns with plate columns provides greater operational flexibility and is suitable for operating conditions with large fluctuations in throughput, without requiring changes to core process parameters.

[0008] A further preferred embodiment can combine the methanol distillation column and the extractant recovery column into a multifunctional distillation column. The column body is divided into upper and lower sections. The upper section is the rectification section, with a controlled temperature of 64-65℃, and methanol product is collected at the top of the column. The lower section is the stripping section, with a controlled temperature of 100℃, and 1,2-propanediol or ethylene glycol is discharged from the bottom of the column. Recovered water is collected from the side stream (at 1 / 3 of the column height from the top). In a preferred embodiment, the weight ratio of the primary extractant to the tetrahydrofuran-methanol mixture is (0.6-1.8):1.

[0009] In a preferred embodiment, the diol is one of ethylene glycol and 1,2-propanediol.

[0010] In a preferred embodiment, the weight ratio of ethylene glycol to crude tetrahydrofuran is (0.8-2.2):1.

[0011] In a preferred embodiment, the weight ratio of 1,2-propanediol to crude tetrahydrofuran is (1.2-2.5):1.

[0012] In a preferred embodiment, the conditions for distilling the methanol-water mixture in step S1 are: the top temperature of the column is 64-65°C.

[0013] In a preferred embodiment, the distillation conditions in step S3 are: the top temperature of the column is 66-67°C.

[0014] In a preferred embodiment, the secondary extractant solution is pumped into a recovery tower, with a top temperature of 100°C and a bottom temperature of 197-198°C.

[0015] In a preferred embodiment, the constant pressure is -0.05~0.1 MPa.

[0016] By adopting the above technical solution, utilizing the characteristic that the azeotrope formed by water and tetrahydrofuran does not azeotrope with methanol, water or water-ethanol is used as the primary extractant in the primary extractive distillation column. This breaks the tetrahydrofuran-methanol azeotropic equilibrium, achieving preliminary separation of methanol from the tetrahydrofuran-water azeotrope. Simultaneously, leveraging the high selectivity of ethylene glycol for tetrahydrofuran and its boiling point difference with water, ethylene glycol is selected as the secondary extractant. This allows for further separation of tetrahydrofuran and water in the secondary extractive distillation column, effectively improving the recovery efficiency and purity of tetrahydrofuran and methanol. If 1,2-propanediol is used as the secondary extractant, it can also achieve separation of tetrahydrofuran and water based on its related properties, achieving good recovery results while enabling extractant recycling and reducing auxiliary material consumption. Furthermore, this application simplifies process control and reduces safety risks through constant pressure operation.

[0017] In summary, the present invention has the following beneficial effects: 1. This application solves the problems of high cost, flammability, easy decomposition, and pollution of existing extractants by using water and diol as dual non-toxic and low-cost extractants.

[0018] 2. This application utilizes the characteristic that water azeotropically reacts with tetrahydrofuran but not with methanol to precisely design a two-stage extractive distillation process, which efficiently breaks the azeotropic equilibrium of tetrahydrofuran-methanol, avoids the complex process of multiple extractive distillations and phase separation operations, improves production efficiency, and reduces energy consumption.

[0019] 3. The recovery process of this application operates under constant pressure throughout, which makes the process easier to control and reduces equipment investment and safety risks compared to pressure swing distillation; compared to membrane separation, the process of this application is more suitable for large-scale industrial production.

[0020] 4. The recycling process of this application can simultaneously achieve high-purity recovery of tetrahydrofuran and methanol, and the recycling rate of the extractant is ≥99%, significantly reducing energy consumption and auxiliary material costs.

[0021] 5. It has good adaptability to fluctuations in the composition of tetrahydrofuran and methanol mixed solutions, requires no adjustment of core processes, has a wide range of industrial applications, and can guarantee product quality. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments. All reagents, unless otherwise specified, are commercially available conventional reagent products. Example 1

[0023] A recovery process for a mixed solution containing tetrahydrofuran and methanol includes the following steps: S1. Pretreatment: The mixture of tetrahydrofuran, methanol, and water (at normal pressure, the proportion of tetrahydrofuran in the mixture is 70 wt%, the proportion of methanol is 25 wt%, and the proportion of water is 5 wt%) is filtered at normal temperature and pressure to remove solid impurities and obtain a clear mixture. S2. Pump the clarified mixture into the primary extractive distillation column, and add the primary extractant (industrial grade pure water, purity ≥99%). The weight ratio of water to mixture is 0.6:1. Under a constant pressure of 0.05 MPa, control the temperature of the column bottom at 80℃ and the temperature of the column top at 58-60℃. Distill off the crude tetrahydrofuran from the top of the column and discharge the methanol-water solution from the bottom of the column. S3. Pump the methanol-water solution into the methanol distillation column. Under a constant pressure of 0.06 MPa, the temperature at the top of the column is 64-65℃. Collect the distillate to obtain the methanol product. Recycle the water at the bottom of the column as the primary extractant. S4. Pump the crude tetrahydrofuran into a secondary extractive distillation column, add the secondary extractant (industrial grade ethylene glycol, purity ≥99%), the mass ratio of ethylene glycol to crude tetrahydrofuran is 0.8:1, under a constant pressure of 0.05MPa, control the column bottom temperature at 120℃ and the column top temperature at 65-67℃, tetrahydrofuran vapor is distilled from the top of the column, and ethylene glycol-water solution is discharged from the bottom of the column; S5. After condensing the tetrahydrofuran vapor, pump it into the tetrahydrofuran distillation column. Under a constant pressure of 0.05 MPa, the top temperature of the column is 66-67℃. Collect the distillate to obtain the tetrahydrofuran product. S6. Pump the ethylene glycol-water solution into the extractant recovery tower. Under a constant pressure of 0.05 MPa, the temperature at the top of the tower is 100°C. Collect the recovered water. The temperature at the bottom of the tower is 197-198°C. Collect the recovered ethylene glycol. Example 2

[0024] A recovery process for a mixed solution containing tetrahydrofuran and methanol includes the following steps: S1. Pretreatment: The mixture of tetrahydrofuran, methanol, and water (at normal pressure, the proportion of tetrahydrofuran in the mixture is 70 wt%, the proportion of methanol is 25 wt%, and the proportion of water is 5 wt%) is filtered at normal temperature and pressure to remove solid impurities and obtain a clear mixture. S2. Pump the clarified mixture into the primary extractive distillation column, and add the primary extractant (industrial grade pure water, purity ≥99%). The weight ratio of water to mixture is 1.2:1. Under a constant pressure of 0.05 MPa, control the temperature of the column bottom at 90℃ and the temperature of the column top at 58-60℃. Distill off the crude tetrahydrofuran from the top of the column and discharge the methanol-water solution from the bottom of the column. S3. Pump the methanol-water solution into the methanol distillation column. Under a constant pressure of 0.08 MPa, the temperature at the top of the column is 64-65℃. Collect the distillate to obtain the methanol product. Recycle the water at the bottom of the column as the primary extractant. S4. Pump the crude tetrahydrofuran into a secondary extractive distillation column, add the secondary extractant (industrial grade ethylene glycol, purity ≥99%), the mass ratio of ethylene glycol to crude tetrahydrofuran is 1.5:1, under a constant pressure of 0.05MPa, control the column bottom temperature at 130℃ and the column top temperature at 65-67℃, tetrahydrofuran vapor is distilled from the top of the column, and ethylene glycol-water solution is discharged from the bottom of the column; S5. After condensing the tetrahydrofuran vapor, pump it into the tetrahydrofuran distillation column. Under a constant pressure of 0.05 MPa, the top temperature of the column is 66-67℃. Collect the distillate to obtain the tetrahydrofuran product. S6. Pump the ethylene glycol-water solution into the extractant recovery tower. Under a constant pressure of 0.05 MPa, the temperature at the top of the tower is 100°C. Collect the recovered water. The temperature at the bottom of the tower is 197-198°C. Collect the recovered ethylene glycol. Example 3

[0025] A recovery process for a mixed solution containing tetrahydrofuran and methanol includes the following steps: S1. Pretreatment: The mixture of tetrahydrofuran, methanol, and water (at normal pressure, the proportion of tetrahydrofuran in the mixture is 70 wt%, the proportion of methanol is 25 wt%, and the proportion of water is 5 wt%) is filtered at normal temperature and pressure to remove solid impurities and obtain a clear mixture. S2. Pump the clarified mixture into the primary extractive distillation column, and add the primary extractant (industrial grade pure water, purity ≥99%). The weight ratio of water to mixture is 1.8:1. Under a constant pressure of 0.1 MPa, control the temperature of the column bottom at 100℃ and the temperature of the column top at 58-60℃. Distill off the crude tetrahydrofuran from the top of the column and discharge the methanol-water solution from the bottom of the column. S3. Pump the methanol-water solution into the methanol distillation column. Under a constant pressure of 0.1 MPa, the temperature at the top of the column is 64-65℃. Collect the distillate to obtain the methanol product. Recycle the water at the bottom of the column as the primary extractant. S4. Pump the crude tetrahydrofuran into a secondary extractive distillation column, add the secondary extractant (industrial grade ethylene glycol, purity ≥99%), the mass ratio of ethylene glycol to crude tetrahydrofuran is 2.2:1, under a constant pressure of 0.1 MPa, control the column bottom temperature to be 140℃ and the column top temperature to be 65-67℃, tetrahydrofuran vapor is distilled from the top of the column, and ethylene glycol-water solution is discharged from the bottom of the column; S5. After condensing the tetrahydrofuran vapor, pump it into the tetrahydrofuran distillation column. Under a constant pressure of 0.1 MPa, the temperature at the top of the column is 66-67℃. Collect the distillate to obtain the tetrahydrofuran product. S6. Pump the ethylene glycol-water solution into the extractant recovery tower. Under a constant pressure of 0.05 MPa, the temperature at the top of the tower is 100°C. Collect the recovered water. The temperature at the bottom of the tower is 197-198°C. Collect the recovered ethylene glycol. Example 4

[0026] A recovery process for a mixed solution containing tetrahydrofuran and methanol differs from Example 1 in that, in step S2, the primary extractant is a mixture of water and ethanol with an ethanol content of 10 wt%, while all other steps are the same as in Example 1. Example 5

[0027] A recovery process for a mixed solution containing tetrahydrofuran and methanol differs from Example 1 in that, in step S4, 1,2-propanediol is used as the secondary extractant, the mass ratio of 1,2-propanediol to crude tetrahydrofuran is 1.2:1, and the bottom temperature of the secondary extractive distillation column is 125°C. All other aspects are the same as in Example 1. Example 6

[0028] A recovery process for a mixed solution containing tetrahydrofuran and methanol differs from Example 1 in that, in step S4, 1,2-propanediol is used as the secondary extractant, the mass ratio of 1,2-propanediol to crude tetrahydrofuran is 1.2:1, and the bottom temperature of the secondary extractive distillation column is 135°C. All other aspects are the same as in Example 1. Example 7

[0029] A recovery process for a mixed solution containing tetrahydrofuran and methanol differs from Example 1 in that, in step S4, 1,2-propanediol is used as the secondary extractant, the mass ratio of 1,2-propanediol to crude tetrahydrofuran is 2.5:1, and the bottom temperature of the secondary extractive distillation column is 145°C. All other aspects are the same as in Example 1.

[0030] In Examples 5-7 above, the cost was reduced by 10-15% by using 1,2-propanediol instead of ethylene glycol. Example 8

[0031] A recovery process for a mixed solution containing tetrahydrofuran and methanol differs from Example 1 in that, in step S2, the pressure is -0.01 MPa and the top temperature of the column is 55-57°C; in step S4, the pressure is -0.01 MPa and the top temperature of the column is 62-64°C, while all other aspects are the same as in Example 1.

[0032] If there are no solid impurities in the mixture of tetrahydrofuran and methanol, the pretreatment filtration unit can be omitted, and the primary extraction process can be carried out directly.

[0033] When using the recovery process of this application, the primary and secondary extractive distillation columns (packed columns) can be replaced with plate columns (sieve plate columns, valve columns). Replacing the existing packed columns with plate columns provides greater operational flexibility and is suitable for operating conditions with large fluctuations in throughput, without requiring changes to the core process parameters.

[0034] When using the recovery process of this application, the methanol distillation column and the extractant recovery column can be combined into a multi-functional distillation column. The column body is divided into upper and lower sections. The upper section is the rectification section, with the temperature controlled at 64-65℃. Methanol product is collected from the top of the column. The lower section is the stripping section, with the temperature controlled at 100℃. 1,2-propanediol or ethylene glycol is discharged from the bottom of the column. Recovered water is collected from the side stream in the middle of the column (at 1 / 3 of the column height from the top). The overall equipment investment can be reduced by 20%, and the energy consumption can be increased by less than 5%. Product Testing

[0035] The purity and recovery rate of tetrahydrofuran and methanol obtained by distillation in the above examples were tested, and the recycling rate of the secondary extractant was tested. The results are shown in Table 1.

[0036] Table 1. Test Results of Final Product and Secondary Extractant

[0037] Based on the data in Table 1: The methanol recovered in Examples 1-8 of this application has a purity of 99.5% or higher and a methanol recovery rate of 97% or higher. The tetrahydrofuran has a purity of 99% or higher and a tetrahydrofuran recovery rate of 97% or higher. This indicates that the recovery process of this application results in a product with good purity and recovery rate. Furthermore, the recycling rate of the secondary extractant is also above 97%, which improves the utilization of the extractant. In addition, the extractant is non-toxic and harmless, which also reduces the emission risk.

[0038] The embodiments described herein are merely illustrative of preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A recovery process for a mixed solution containing tetrahydrofuran and methanol, characterized in that, Includes the following steps: S1. Pump the clarified tetrahydrofuran-methanol mixture into a primary extractive distillation column, add the primary extractant, and control the column bottom temperature at 80-100℃ and the column top temperature at 58-60℃ under constant pressure. Distill off the crude tetrahydrofuran from the top of the column and discharge the methanol-water solution from the bottom of the column. Purify the methanol-water mixture by distillation. S2. Pump the crude tetrahydrofuran into a two-stage extractive distillation column, add the secondary extractant, and control the column bottom temperature at 120-140℃ and the column top temperature at 65-67℃ under constant pressure. Tetrahydrofuran vapor is distilled off the top of the column, and the secondary extractant solution is discharged from the bottom of the column. S3. High-purity tetrahydrofuran is obtained by condensing tetrahydrofuran vapor and then distilling it. The primary extractant is water or a mixture of water and ethanol; The secondary extractant is a diol.

2. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 1, characterized in that: The weight ratio of the primary extractant to the tetrahydrofuran-methanol mixture is (0.6-1.8):

1.

3. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 1, characterized in that: The diol is one of ethylene glycol and 1,2-propanediol.

4. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 3, characterized in that: The weight ratio of ethylene glycol to crude tetrahydrofuran is (0.8-2.2):

1.

5. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 3, characterized in that: The weight ratio of 1,2-propanediol to crude tetrahydrofuran is (1.2-2.5):

1.

6. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 1, characterized in that: The conditions for distilling the methanol-water mixture in step S1 are: the top temperature of the column is 64-65℃.

7. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 1, characterized in that: The distillation conditions in step S3 are: the top temperature of the column is 66-67℃.

8. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 1, characterized in that: The secondary extractant solution is pumped into the recovery tower, where the top temperature is 100°C and the bottom temperature is 197-198°C.

9. The recovery process for a mixed solution containing tetrahydrofuran and methanol according to claim 1, characterized in that: The constant pressure is -0.05~0.1MPa.

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