Organic solvent-water minimum azeotrope system energy-saving separation device and method
By combining the thermal integration method of the distillation tower and the molecular sieve membrane dehydration equipment, the problem of high energy consumption for separation of organic solvents and water is solved, and an efficient and low-cost separation effect is achieved.
Patent Information
- Application Number
- CN202510268097.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-07
- Publication Date
- 2025-07-11
AI Technical Summary
The prior art uses high energy consumption when separating the lowest constant boiler system of organic solvents from water and conventional methods to introduce new impurities or recycles, resulting in high production costs.
An organic solvent-water minimum constant boiler is used to energy-saving separation device, combined with a complete set of equipment for dehydration of 1# distillation tower, 2# distillation tower and molecular sieve membrane, through thermal integration and selective penetration of molecular sieve membrane, the efficient separation of organic solvents and water is achieved and energy consumption is reduced.
It realizes high-quality continuous separation of organic solvents and water, reduces energy consumption and production costs, has a wide range of applications, does not introduce new impurities, and has significant energy-saving effects.
Smart Images
Figure CN120285601A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the fields of chemical separation and waste liquid recovery and treatment, and particularly relates to an energy-saving separation device and method for an organic solvent-water minimum azeotrope system. Background Art
[0002] In industries such as pharmaceuticals, pesticides, and coatings, various organic solvents are widely used, such as methanol, ethanol, isopropanol, tetrahydrofuran, acetone, ethyl acetate, acetonitrile, and so on. These solvents often discharge from production devices or workshops in the form of waste liquid containing water. Enterprises need to recover and reuse the organic solvents therein to reduce production costs, and at the same time reduce the amount and treatment concentration of the waste liquid to facilitate the design of subsequent environmental protection facilities.
[0003] Many of the above-mentioned organic solvents form minimum azeotropes with water, and it is difficult to obtain the recycled product with the required purity by ordinary distillation. Currently, common methods include extractive distillation, azeotropic (or azeotropic) distillation, and pressure swing distillation, etc. Extractive distillation requires the addition of an extractant, and azeotropic distillation requires the addition of an azeotropic agent (or called azeotropic agent, entrainer). The addition of these third components will introduce new impurities, which is unacceptable to some production enterprises. Pressure swing distillation does not introduce new substances, but it can only be used for systems where the azeotropic composition changes greatly with pressure. At the same time, there is a circulating material flow between the two towers, and the energy consumption is relatively large.
[0004] Pervaporation and vapor permeation technologies are a new type of membrane separation technology. It is a process of separation achieved by utilizing the different adsorption and diffusion rates of each component on the membrane surface under the driving force of the chemical potential gradient of the mixture components. Compared with traditional separation technologies, pervaporation technology has the characteristics of high energy efficiency, high recovery rate, simple operation, environmental protection and safety, etc. The pore diameter of the NaA zeolite membrane is about 0.41 nm, which is larger than the kinetic diameter of water molecules (about 0.29 nm) and smaller than the molecular diameters of most organic solvents. And NaA zeolite has super hydrophilicity. Water molecules are selectively adsorbed and permeate through the membrane, which is particularly suitable for the separation of organic solvents and water. The membrane dehydration equipment contains different numbers of membrane modules and can directly separate the vapor phase taken out from the top of the distillation column. However, the separated organic solvent is still in a gaseous state and needs to be further condensed and cooled to obtain a liquid product. In the current conventional distillation + membrane separation system, the condensation heat of the organic vapor cannot be utilized, resulting in a large amount of cold and heat utility consumption, especially when the amount of waste liquid to be treated is large, which makes the production cost of the enterprise remain high. Summary of the Invention
[0005] The purpose of the present invention is to solve the above-mentioned technical deficiencies, so as to provide an energy-saving separation device and method for an organic solvent-water minimum azeotrope system, which can effectively separate the azeotrope system of organic solvent and water in the waste liquid, and greatly reduce the energy consumption, bringing greater economic benefits to enterprises.
[0006] To achieve the above object, the technical solution provided by the present invention is as follows:
[0007] On the one hand, the present invention provides an energy-saving separation device for an organic solvent-water minimum azeotrope system. The device includes: a feed liquid conveying pipeline, a 1# distillation column device, a 2# distillation column device, and a molecular sieve membrane dehydration complete set of equipment; the 1# distillation column device includes a 1# distillation column and its supporting 1# distillation column reboiler, and the 2# distillation column device includes a 2# distillation column and its supporting 2# distillation column condenser and 2# distillation column reboiler; the molecular sieve membrane dehydration complete set of equipment is a complete set of equipment, including a membrane module, a permeate condenser, a permeate tank, a permeate pump, and a vacuum unit;
[0008] The feed liquid conveying pipeline is divided into two branches. The first branch is connected to the material inlet of the 1# distillation column, and a second preheater is provided on the first branch; the second branch is connected to the material inlet of the 2# distillation column, and a third preheater is provided on the second branch;
[0009] The gas-phase outlet at the top of the 1# distillation column is connected to the gas-phase material inlet of the molecular sieve membrane dehydration complete set of equipment; the liquid-phase outlet at the bottom of the 1# distillation column is divided into two branches. The first branch is communicated with the cold fluid side inlet of the 1# distillation column reboiler, and the cold fluid side outlet of the 1# distillation column reboiler is communicated with the bottom return port of the 1# distillation column. The second branch is communicated with the hot side inlet of the second preheater, and the material in the second branch is taken out after heat exchange with the second preheater; the liquid-phase outlet at the bottom of the 2# distillation column is also divided into two branches. The first branch is communicated with the cold fluid side inlet of the 2# distillation column reboiler, and the cold fluid side outlet of the 2# distillation column reboiler is communicated with the bottom return port of the 2# distillation column. The material at the bottom of the column is heated and then returned to the bottom of the column to form rising steam. The second branch is communicated with the hot side inlet of the third preheater, and the material in the second branch is taken out after heat exchange with the third preheater.
[0010] Further, the gas-phase outlet at the top of the 2# distillation column is connected to the hot fluid side inlet of the 2# distillation column condenser. The hot fluid side outlet of the 2# distillation condenser is divided into two paths, which are respectively connected to the top reflux port of the 1# distillation column and the top reflux port of the 2# distillation column.
[0011] Further, the gas-phase material outlet of the molecular sieve membrane dehydration complete set of equipment is communicated with the hot fluid side inlet of the 2# distillation column reboiler.
[0012] Further, a first preheater is also provided on the pipeline of the first branch of the feed liquid conveying pipeline before the second preheater. The hot fluid side outlet of the 2# distillation column reboiler is communicated with the hot side inlet of the first preheater, and the organic solvent product is obtained by taking out the hot side outlet of the first preheater.
[0013] Further, a first preheater is also provided on the pipeline before the branch of the feed liquid conveying pipeline. The hot fluid side outlet of the reboiler of the 2# rectification column is communicated with the hot side inlet of the first preheater, and the organic solvent finished product is taken out from the hot side outlet of the first preheater.
[0014] Further, the gas-phase material inlet of the molecular sieve membrane dehydration complete set of equipment is the membrane module inlet, and the gas-phase material outlet of the molecular sieve membrane dehydration complete set of equipment is the organic phase outlet of the membrane module. The permeate side outlet of the membrane module is communicated with the hot fluid side inlet of the permeate condenser. The liquid phase outlet of the hot fluid side of the permeate condenser is communicated with the inlet of the permeate tank. The outlet of the permeate tank is communicated with the inlet of the permeate pump. The outlet of the permeate pump is connected to the waste water discharge main pipe. The gas-phase outlet of the hot fluid side of the permeate condenser is communicated with the inlet of the vacuum unit, and the outlet of the vacuum unit is connected to the tail gas discharge main pipe.
[0015] On the other hand, the present invention also proposes an energy-saving separation method for an organic solvent-water minimum azeotrope system, which is carried out by using the energy-saving separation device for an organic solvent-water minimum azeotrope system as described above, and includes the following process steps:
[0016] A) Send a part of the feed liquid containing the organic solvent-water minimum azeotrope system to the 1# rectification column equipment. After separation, the organic solvent-water mixed vapor close to the azeotropic composition is obtained at the top of the 1# rectification column, and the water containing a small amount of organic solvent is obtained at the bottom of the column.
[0017] B) Send the organic solvent-water mixed vapor in step A) into the molecular sieve membrane dehydration complete set of equipment for continuous dehydration and purification to obtain the organic solvent vapor with the required purity, and collect the separated water by vacuum condensation on the permeate side of the membrane dehydration equipment.
[0018] C) Send the remaining part of the feed liquid to the 2# rectification column equipment for separation. The water containing a small amount of organic solvent is separated at the bottom of the 2# rectification column. After the top vapor is condensed, a part of it returns to the top of its own column for reflux, and the rest is taken out and used as the top reflux liquid of the 1# rectification column.
[0019] D) Use the organic solvent vapor in step B) as the heat source of the reboiler of the 2# rectification column to realize heat integration. The organic solvent is condensed here and further cooled in the first preheater to obtain the finished product.
[0020] Further, the organic solvent in the organic solvent-water feed liquid forms a binary azeotrope with the lowest bubble point with water, and the concentration of the organic solvent is lower than the azeotropic composition; the membrane material selected for the membrane module in the molecular sieve membrane dehydration complete set of equipment is the NaA type molecular sieve membrane.
[0021] Further, even further, the organic solvent is a common organic solvent such as ethanol, isopropanol, n-butanol, ethyl acetate, acetonitrile, tetrahydrofuran, benzene, toluene, etc. that can form a minimum azeotrope with water. It should be noted that common organic solvents that do not form an azeotrope with water, such as methanol, acetone, etc., are also applicable to this method.
[0022] Further, in step A), the operating pressure of the column in the #1 rectification tower equipment is 0.05 - 0.6 MpaG, preferably 0.09 - 0.3 MPaG, and the operating temperature is related to and corresponds to the type of organic solvent in the feed liquid and the operating pressure; in step C), the operating pressure of the column in the #2 rectification tower equipment is lower than that of the #1 rectification tower, and the bottom operating temperature of the column in the #2 rectification tower equipment in step C) is 10°C - 50°C lower than the temperature of the organic solvent vapor in step D), preferably 20°C - 30°C.
[0023] Further, the ratio of the organic solvent - water feed liquid sent to the #1 rectification tower equipment and the #2 rectification tower equipment satisfies that the organic solvent vapor in step D) is just used as the heat source for the reboiler at the bottom of the #2 rectification tower equipment.
[0024] The purpose of setting the #2 rectification tower equipment is to utilize the latent heat of the organic vapor purified by the molecular sieve membrane dehydration complete set of equipment in step B) to achieve heat integration, thereby reducing the consumption of heat medium (fresh steam, heat transfer oil, etc.) and cooling water.
[0025] The organic solvent finished product is obtained at the outlet of the hot fluid side of the reboiler of the #2 rectification tower; the tail gas outlet of the molecular sieve membrane dehydration complete set of equipment is connected to the main tail gas discharge pipe, and the permeate outlet of the molecular sieve membrane dehydration complete set of equipment is connected to the main waste water pipe.
[0026] When the device of the present application works:
[0027] 1) A part of the liquid to be treated is pumped to the middle of the #1 rectification tower. The bottom material of the tower is heated by the reboiler of the #1 rectification tower and then returns to the bottom of the tower to form rising vapor, which contacts the falling liquid phase in the tower to achieve mass transfer and heat transfer. The light component mixture close to the azeotropic composition is concentrated at the top of the tower and then taken out and sent into the molecular sieve membrane dehydration complete set of equipment, and the water containing a small amount of organic solvent is taken out from the bottom of the tower;
[0028] 2) The remaining part of the liquid to be treated is pumped to the middle of the #2 rectification tower. The bottom material of the tower is heated by the reboiler of the #2 rectification tower and then returns to the bottom of the tower to form rising vapor. Similarly, the light and heavy components are separated in the tower. The light component mixture close to the azeotropic composition at the top of the tower is condensed by the condenser of the #2 rectification tower. A part of the condensed liquid phase returns to the top of its own tower, and the other part is sent as the reflux liquid of the #1 rectification tower to the reflux port at the top of the #1 rectification tower; the water containing a small amount of organic solvent is taken out from the bottom of the tower;
[0029] 3) The organic solvent vapor purified by the molecular sieve membrane dehydration complete set of equipment is used to heat the reboiler of the 2# distillation column, and itself is condensed, changing from the vapor phase to the liquid phase. The water vapor on the permeate side of the membrane dehydration complete set of equipment is condensed and discharged, and after being combined with the water in the reboilers of the 1# and 2# distillation columns, it goes to the sewage treatment station or is further utilized.
[0030] Further optimized, to better reduce the consumption of cold / hot utility, the device of the present application further includes heat exchangers for cold / hot fluid heat exchange, including a first preheater, a second preheater, and a third preheater. The second preheater and the third preheater are respectively located on the first branch and the second branch of the feed liquid conveying pipeline. Regarding the position of the first preheater, there are two schemes. Scheme 1: The first preheater is arranged on the pipeline of the first branch of the feed liquid conveying pipeline before the second preheater; Scheme 2: The first preheater is arranged on the pipeline before the feed liquid conveying pipeline branches.
[0031] For the said Scheme 1: The feed liquid entering the 1# distillation column is first preheated by the organic solvent condensate after heating the reboiler of the 2# distillation column by the first preheater, and then further preheated by the product withdrawn from the bottom of the 1# distillation column by the second preheater and then enters the middle of the 1# distillation column; the feed liquid entering the 2# distillation column is preheated by the product withdrawn from the bottom of the 2# distillation column by the third preheater and then enters the middle of the 2# distillation column.
[0032] For the said Scheme 2: The raw feed liquid is first preheated by the organic solvent condensate after heating the reboiler of the 2# distillation column by the first preheater, and after preheating, it is divided into two paths to enter the 1# distillation column and the 2# distillation column respectively. The feed liquid entering the 1# distillation column is further preheated by the product withdrawn from the bottom of the 1# distillation column by the second preheater and then enters the middle of the 1# distillation column; the feed liquid entering the 2# distillation column is preheated by the liquid discharged from the bottom of the 2# distillation column by the third preheater and then enters the middle of the 2# distillation column.
[0033] Further optimized, on the basis of the device of the present application, a reflux drum and a reflux pump for the 2# distillation column can be set. The process material condensed by the condenser of the 2# distillation column is connected to the inlet of the reflux drum of the 2# distillation column, the outlet of the reflux drum of the 2# distillation column is connected to the inlet of the reflux pump of the 2# distillation column, and the outlet of the reflux pump of the 2# distillation column is divided into two paths and connected to the top reflux ports of the 1# distillation column and the 2# distillation column respectively. After adding this setting, the natural reflux at the top is changed to forced reflux, which can reduce the requirement for the storey height of the construction site.
[0034] In the present invention, the reboilers of the 1# and 2# distillation columns are heated by steam, heat transfer oil or other heat media, and the refrigerant of the condenser of the 2# distillation column transfers heat by using circulating cooling water, low-temperature water or other refrigerants.
[0035] Due to the adoption of the above technical solutions, the beneficial effects obtained by the present invention are:
[0036] The process of the present invention is simple and can achieve high-quality continuous separation of organic solvent-water azeotropic systems. Compared with traditional extractive distillation and azeotropic distillation, it does not introduce new components such as extractants and entrainers and does not contaminate the products; compared with pressure-swing distillation, it has a wider application range and significantly reduced energy consumption; compared with the conventional single-column distillation + membrane separation combined process, it makes full use of the latent heat of the secondary steam, further reducing the energy consumption and production cost, and this advantage is more obvious when the feed liquid treatment volume is large, providing a new way for the low-cost separation of azeotropic systems.
[0037] The present invention adopts a combined method of distillation + molecular sieve membrane dehydration to effectively separate azeotropic systems and obtain high-purity organic solvents. Compared with azeotropic distillation or extractive distillation, it does not introduce a third component and does not contaminate the products; at the same time, heat integration is adopted, and the energy-saving effect is more significant compared with pressure-swing distillation and the conventional single-column distillation + membrane dehydration combined process. Brief Description of the Drawings
[0038] Figure 1 and Figure 2 is a schematic structural diagram of an energy-saving separation device for an organic solvent-water minimum azeotropic system of the present invention;
[0039] In the figure: 10. 1# distillation column; 11. 1# distillation column reboiler; 20. 2# distillation column; 21. 2# distillation column condenser; 22. 2# distillation column reboiler; 30. Molecular sieve membrane dehydration complete set of equipment; 31. Membrane module; 32. Permeate condenser; 33. Vacuum unit; 34. Permeate tank; 35. Permeate pump; 41. First preheater; 42. Second preheater; 43. Third preheater. Detailed Embodiments
[0040] The following further illustrates the present invention with specific embodiments, but the protection scope of the present invention is not limited thereto.
[0041] The present invention provides an energy-saving separation device and method for an organic solvent-water minimum azeotropic system. The device of the present invention includes: a feed liquid conveying pipeline, a 1# distillation column device, a 2# distillation column device, and a molecular sieve membrane dehydration complete set of equipment, and also includes several heat exchangers for preheating the feed liquid.
[0042] The 1# rectification tower equipment includes the 1# rectification tower 10 and the 1# rectification tower reboiler 11. The 2# rectification tower equipment includes the 2# rectification tower 20, the 2# rectification tower condenser 21 and the 2# rectification tower reboiler 22. The molecular sieve membrane dehydration complete equipment includes a membrane module 31, a permeate condenser 32, a vacuum unit 33, a permeate tank 34 and a permeate pump 35. The heat exchangers for preheating the feed liquid include a first preheater 41, a second preheater 42 and a third preheater 43. It should be noted that the equipment in the molecular sieve membrane dehydration complete equipment is typical equipment, and the configurations of different professional manufacturers are different. However, as long as the corresponding design and selection are made, it will not affect the effects obtained by implementing the method of this application.
[0043] The feed liquid conveying pipeline is divided into two paths. The first path of feed liquid is connected to the feed port of the 1# rectification tower 10 through a pipeline. The bottom outlet of the 1# rectification tower 10 is communicated with the inlet of the cold fluid side of the 1# rectification tower reboiler 11 and there is a side draw. The outlet of the cold fluid side of the 1# rectification tower reboiler 11 is communicated with the bottom return port of the 1# rectification tower 10. The gas phase outlet at the top of the 1# rectification tower is connected to the gas phase material inlet of the molecular sieve membrane dehydration complete equipment 30. The second path of feed liquid is connected to the feed port of the 2# rectification tower 20 through a pipeline. The bottom outlet of the 2# rectification tower 20 is communicated with the inlet of the cold fluid side of the 2# rectification tower reboiler 22 and there is a side draw. The outlet of the cold fluid side of the 2# rectification tower reboiler 22 is communicated with the bottom return port of the 2# rectification tower 20. The bottom material is heated and then returned to the bottom of the tower to form rising steam. The gas phase outlet at the top of the 2# rectification tower 20 is connected to the inlet of the hot fluid side of the 2# rectification tower condenser 21. The outlet of the hot fluid side of the 2# rectification tower condenser 21 is divided into two paths, which are respectively connected to the top reflux port of the 1# rectification tower 10 and the top reflux port of the 2# rectification tower 20. The gas phase material outlet of the molecular sieve membrane dehydration complete equipment 30 is communicated with the inlet of the hot fluid side of the 2# rectification tower reboiler 22, and the finished organic solvent is obtained at the outlet of the hot fluid side of the 2# rectification tower reboiler 22. The tail gas outlet of the molecular sieve membrane dehydration complete equipment 30 is connected to the main tail gas discharge pipe, and the permeate outlet of the molecular sieve membrane dehydration complete equipment is connected to the main waste water pipe.
[0044] The gas phase material inlet of the molecular sieve membrane dehydration complete equipment 30 is the inlet of the membrane module 31, and the gas phase material outlet of the molecular sieve membrane dehydration complete equipment 30 is the organic phase outlet of the membrane module 31. The permeate side outlet of the membrane module 31 is communicated with the inlet of the hot fluid side of the permeate condenser 32. The liquid phase outlet of the hot fluid side of the permeate condenser 32 is communicated with the inlet of the permeate tank 34. The outlet of the permeate tank 34 is communicated with the inlet of the permeate pump 35. The outlet of the permeate pump 35 is connected to the main waste water discharge pipe. The gas phase outlet of the hot fluid side of the permeate condenser 32 is communicated with the inlet of the vacuum unit 33, and the outlet of the vacuum unit 33 is connected to the main tail gas discharge pipe.
[0045] Example 1
[0046] The feed liquid to be treated (waste liquid) contains 30% acetonitrile (mass percentage, the same below), and the rest is water. The temperature of the feed liquid is 30°C, the treatment capacity is 14.6 t / h, and the required purity of acetonitrile after separation is 98%, and the acetonitrile content in water is <0.5%. Note: Acetonitrile and water will form an azeotrope, and the azeotropic composition at atmospheric pressure is: 84% acetonitrile and 16% water.
[0047] 65% (mass percentage) of the feed liquid is sent to the 1# distillation column. The operating pressure at the top of the 1# distillation column is 0.09 MPa (gauge pressure, the same below), the operating temperature at the top is 93°C. The vapor with 81.4% (wt.) acetonitrile content and 18.6% (wt.) water content is drawn from the top of the column. This vapor is sent to the NaA molecular sieve membrane dehydration complete set of equipment. After adsorption and permeation, high-purity acetonitrile vapor is obtained, and at the same time, a permeate with an acetonitrile content of <0.5% (wt.) (i.e., the separated water) is obtained. The reboiler at the bottom of the column is heated by 0.6 MPa saturated steam; the remaining 35% of the feed liquid is sent to the 2# distillation column. The operating pressure at the top of the 2# distillation column is -0.06 MPa, the operating temperature at the top is 52°C, and the operating temperature at the bottom is 75°C. 1.8 t / h of acetonitrile-water mixture is drawn from the top of the 2# distillation column and sent to the top of the 1# distillation column for reflux. The acetonitrile vapor from the membrane dehydration equipment is used to heat the reboiler of the 2# distillation column, providing heat for the 2# distillation column to form rising vapor inside the column, and the acetonitrile vapor from the membrane dehydration equipment itself is condensed. The condensed acetonitrile flows into the hot fluid side of the first preheater to heat the feed liquid entering the 1# distillation column. The feed liquid is heated from 30°C to 48°C and then enters the second preheater, and is further heated to 95°C by the liquid drawn from the bottom of the 1# distillation column and then enters the middle inlet of the 1# distillation column. The liquid drawn from the bottom of the 2# distillation column enters the inlet of the hot fluid side of the third preheater to heat the feed liquid entering the 2# distillation column to 57°C.
[0048] After the above process treatment, the purity of the separated acetonitrile is 98% (wt.). The water with an acetonitrile concentration of about 0.5% (wt.) is obtained at the bottoms of the 1# distillation column and the 2# distillation column; the consumption of fresh steam is about 3 t / h. Under the same treatment capacity and treatment target, the comparison with the pressure swing distillation and the conventional single-column distillation + membrane dehydration combined process is shown in the following table:
[0049]
[0050] As can be seen from the above comparison table, the fresh steam consumption of the method of the present invention is about 37.0% less than that of the conventional single-column distillation + membrane dehydration combined process under the corresponding conditions, and about 85.4% less than that of the pressure swing distillation process, and the energy-saving effect is remarkable.
[0051] Example 2
[0052] The feed liquid (waste liquid) to be processed contains 40% (mass percentage, the same below) of tetrahydrofuran, and the rest is water. The temperature of the feed liquid is 25°C, the processing capacity is 6 t / h, and it is required that the purity of tetrahydrofuran after separation is 99.5%, and the content of tetrahydrofuran in water is <0.3%. Note: Tetrahydrofuran and water will form an azeotrope, and the azeotropic composition under normal pressure is: 95% of tetrahydrofuran and 5% of water.
[0053] 73.3% of the feed liquid is sent to the 1# distillation column. The operating pressure at the top of the 1# distillation column is 0.35 MPa (gauge pressure, the same below), the operating temperature at the top is 114°C, and the composition of the vapor drawn from the top of the column is 90.8% (wt.) of tetrahydrofuran and 9.2% (wt.) of water. This vapor is sent to the NaA molecular sieve membrane dehydration complete equipment. After adsorption and permeation, high-purity tetrahydrofuran vapor is obtained, and at the same time, a permeate with a tetrahydrofuran content of <0.3% (wt.) (i.e., the separated water) is obtained. The reboiler at the bottom of the column is heated by 0.8 MPa saturated steam; the remaining 26.7% of the feed liquid is sent to the 2# distillation column. The operating pressure at the top of the 2# distillation column is normal pressure, the operating temperature at the top is 64°C, and the operating temperature at the bottom is 98°C. About 670 kg / h of the tetrahydrofuran-water mixture is drawn from the top of the 2# distillation column and sent to the top of the 1# distillation column for reflux. The tetrahydrofuran vapor from the membrane dehydration equipment is used to heat the reboiler of the 2# distillation column to provide heat for the 2# distillation column to form rising vapor inside the column, and the tetrahydrofuran vapor from the membrane dehydration equipment is condensed by itself. The condensed tetrahydrofuran enters the hot fluid side of the first preheater to heat the feed liquid entering the 1# distillation column. The feed liquid is heated from 25°C to 50°C and then enters the second preheater, and is further heated to 108°C by the liquid drawn from the bottom of the 1# distillation column and then enters the middle inlet of the 1# distillation column. The liquid drawn from the bottom of the 2# distillation column enters the inlet of the hot fluid side of the third preheater to heat the feed liquid entering the 2# distillation column to 68°C.
[0054] After the above process treatment, the purity of the separated tetrahydrofuran is 99.5%. Water with a tetrahydrofuran concentration of about 0.3% (wt.) is obtained at the bottoms of the 1# distillation column and the 2# distillation column; the consumption of fresh steam is about 1.15 t / h. Under the same processing capacity and processing target, the comparison with the extractive distillation (using DMF as the extractant) and the conventional single-column distillation + membrane dehydration combined process is shown in the following table:
[0055]
[0056] As can be seen from the above comparison table, the fresh steam consumption of the method of the present invention is about 91.9% less than that of the extractive distillation process using DMF as the extractant under the corresponding conditions, and about 40.7% less than that of the conventional single-column distillation + membrane dehydration combined process, and the energy-saving effect is remarkable.
[0057] Example 3
[0058] The ethanol content in the aqueous ethanol solution to be treated is 60% (mass percentage, the same hereinafter), the rest is water, the temperature of the feed liquid is 25°C, and the treatment capacity is 6.67 t / h. It is required that the purity of ethanol after separation is 99.5%, and the ethanol content in water is <0.4%. Note: Ethanol and water will form an azeotrope, and the azeotropic composition under normal pressure is: ethanol 95.6%, water 4.43%.
[0059] 63% of the feed liquid is sent to the 1# distillation column. The operating pressure at the top of the 1# distillation column is 0.13 MPa (gauge pressure, the same hereinafter), the operating temperature at the top is 101°C, and the composition of the vapor drawn from the top of the column is 88.4% (wt.) ethanol and 11.6% (wt.) water. This vapor is sent to the NaA molecular sieve membrane dehydration complete equipment. After adsorption and permeation, high-purity ethanol vapor is obtained, and at the same time, a permeate with an ethanol content of <0.4% (wt.) (i.e., the separated water) is obtained. The reboiler at the bottom of the column is heated by 0.5 MPa saturated steam; the remaining 37% of the feed liquid is sent to the 2# distillation column. The operating pressure at the top of the 2# distillation column is -0.05 MPa, the operating temperature at the top is 62°C, and the operating temperature at the bottom is 81°C. Approximately 1636 kg / h of ethanol-water mixture is drawn from the top of the 2# distillation column and sent back to the top of the 1# distillation column. The ethanol vapor from the membrane dehydration equipment is used to heat the reboiler of the 2# distillation column to provide heat for the 2# distillation column to form rising vapor inside the column, and the ethanol vapor from the membrane dehydration equipment is condensed by itself. The condensed ethanol enters the hot fluid side of the raw material preheater, heating the feed liquid from 25°C to 53°C, and then it is divided into two paths. One path is further heated to 72°C by the liquid drawn from the bottom of the 1# distillation column and then enters the inlet in the middle of the 1# distillation column. The other path is heated to 57°C by the liquid drawn from the bottom of the 2# distillation column and then enters the inlet in the middle of the 2# distillation column.
[0060] After the above process treatment, the purity of the separated ethanol is 99.5%. The water with an ethanol concentration of approximately 0.4% (wt.) is obtained at the bottom of the 1# distillation column and the 2# distillation column; the consumption of fresh steam is approximately 2.71 t / h. Under the same treatment capacity and treatment target, the comparison with the azeotropic distillation (using cyclohexane as the entrainer) and the conventional single-column distillation + membrane dehydration combined process is shown in the following table:
[0061]
[0062]
[0063] As can be seen from the above comparison table, the fresh steam consumption of the method of the present invention is approximately 94.6% less than that of the azeotropic distillation process using cyclohexane as the entrainer under the corresponding conditions, and approximately 34.1% less than that of the conventional single-column distillation + membrane dehydration combined process, with significant energy-saving effects.
[0064] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention (such as the heat exchange scheme between cold / hot streams, the specific composition of the molecular sieve membrane dehydration equipment, etc.). The scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. An energy-saving separation device for an organic solvent-water minimum azeotrope system, characterized in that, The device includes: a feed liquid conveying pipeline, a No. 1 rectification tower device, a No. 2 rectification tower device, and a molecular sieve membrane dehydration complete set of equipment; the No. 1 rectification tower device includes a No. 1 rectification tower and its supporting No. 1 rectification tower reboiler, and the No. 2 rectification tower device includes a No. 2 rectification tower and its supporting No. 2 rectification tower condenser and No. 2 rectification tower reboiler; the molecular sieve membrane dehydration complete set of equipment includes a membrane module, a permeate condenser, a permeate tank, a permeate pump, and a vacuum unit; The feed liquid conveying pipeline is divided into two branches. The first branch is connected to the material inlet of the No. 1 rectification tower, and a second preheater is arranged on the first branch; the second branch is connected to the material inlet of the No. 2 rectification tower, and a third preheater is arranged on the second branch; The gas-phase outlet at the top of the No. 1 rectification tower is connected to the gas-phase material inlet of the molecular sieve membrane dehydration complete set of equipment; the liquid-phase outlet at the bottom of the No. 1 rectification tower is divided into two branches. The first branch is communicated with the cold fluid side inlet of the No. 1 rectification tower reboiler, and the cold fluid side outlet of the No. 1 rectification tower reboiler is communicated with the return port at the bottom of the No. 1 rectification tower. The second branch is communicated with the hot side inlet of the second preheater, and the material in the second branch is taken out after heat exchange with the second preheater; the liquid-phase outlet at the bottom of the No. 2 rectification tower is also divided into two branches. The first branch is communicated with the cold fluid side inlet of the No. 2 rectification tower reboiler, and the cold fluid side outlet of the No. 2 rectification tower reboiler is communicated with the return port at the bottom of the No. 2 rectification tower. The material at the bottom of the tower is heated and then returned to the bottom of the tower to form rising steam. The second branch is communicated with the hot side inlet of the third preheater, and the material in the second branch is taken out after heat exchange with the third preheater.
2. An energy-saving separation device for an organic solvent-water minimum azeotrope system according to claim 1, characterized in that, The gas-phase outlet at the top of the No. 2 rectification tower is connected to the hot fluid side inlet of the No. 2 rectification tower condenser. The hot fluid side outlet of the No. 2 rectification condenser is divided into two paths and is respectively connected to the reflux port at the top of the No. 1 rectification tower and the reflux port at the top of the No. 2 rectification tower.
3. An energy-saving separation device for an organic solvent-water minimum azeotropic system according to claim 2, characterized in that, The gas-phase material outlet of the molecular sieve membrane dehydration complete set of equipment is communicated with the hot fluid side inlet of the No. 2 rectification tower reboiler.
4. An energy-saving separation device for an organic solvent-water minimum azeotrope system according to claim 3, characterized in that, A first preheater is also arranged on the pipeline of the first branch of the feed liquid conveying pipeline before the second preheater. The hot fluid side outlet of the No. 2 rectification tower reboiler is communicated with the hot side inlet of the first preheater, and the organic solvent product is obtained by taking out from the hot side outlet of the first preheater.
5. The energy-saving separation device for an organic solvent-water minimum azeotropic system according to claim 3, wherein A first preheater is also arranged on the pipeline before the feed liquid conveying pipeline is branched. The hot fluid side outlet of the No. 2 rectification tower reboiler is communicated with the hot side inlet of the first preheater, and the organic solvent product is obtained by taking out from the hot side outlet of the first preheater.
6. An energy-saving separation device for an organic solvent-water minimum azeotrope system according to claim 4 or 5, characterized in that, The gas-phase material inlet of the molecular sieve membrane dehydration complete set of equipment 30 is the inlet of the membrane module, and the gas-phase material outlet of the molecular sieve membrane dehydration complete set of equipment is the organic phase outlet of the membrane module. The outlet on the permeate side of the membrane module is communicated with the hot fluid side inlet of the permeate condenser. The hot fluid side liquid-phase outlet of the permeate condenser is communicated with the inlet of the permeate tank. The outlet of the permeate tank is communicated with the inlet of the permeate pump. The outlet of the permeate pump is connected to the waste water discharge main pipe. The hot fluid side gas-phase outlet of the permeate condenser is communicated with the inlet of the vacuum unit. The outlet of the vacuum unit is connected to the tail gas discharge main pipe.
7. An energy-saving separation method for an organic solvent-water minimum azeotrope system, which is carried out by using the energy-saving separation device for the organic solvent-water minimum azeotrope system as described in claim 6, characterized in that, It includes the following technological steps: A) Part of the feed liquid containing an organic solvent - water minimum azeotrope system is sent to the 1# distillation column equipment. After separation, an organic solvent - water mixed vapor close to the azeotropic composition is obtained at the top of the 1# distillation column, and water containing a small amount of organic solvent is obtained at the bottom of the column. B) The organic solvent - water mixed vapor described in step A) is sent to the molecular sieve membrane dehydration complete set of equipment for continuous dehydration and purification to obtain an organic solvent vapor with a purity meeting the requirements. The separated water is collected by vacuum condensation on the permeate side of the membrane dehydration equipment. C) The remaining part of the feed liquid is sent to the 2# distillation column equipment for separation. Water containing a small amount of organic solvent is separated at the bottom of the 2# distillation column. After the top vapor is condensed, a part of it is returned to the top of its own column for reflux, and the rest is taken out and used as the top reflux liquid of the 1# distillation column. D) The organic solvent vapor described in step B) is used as the heat source of the reboiler of the 2# distillation column to achieve heat integration. The organic solvent is condensed here and further cooled in the first pre - heater to obtain the finished product.
8. An energy-saving separation method for an organic solvent-water minimum azeotrope system according to claim 7, characterized in that The organic solvent in the organic solvent - water feed liquid forms a binary azeotrope with the lowest bubble point with water, and the concentration of the organic solvent is lower than the azeotropic composition. The membrane material selected for the membrane module in the molecular sieve membrane dehydration complete set of equipment is NaA type molecular sieve membrane.
9. The energy-saving separation method for an organic solvent-water minimum azeotrope system according to claim 8, characterized in that, In the 1# distillation column equipment described in step A), the operating pressure of the column is 0.05 - 0.6 MpaG, preferably 0.09 - 0.3 MPaG. In the 2# distillation column equipment described in step C), the operating pressure of the column is lower than that of the 1# distillation column. In the 2# distillation column equipment described in step C), the bottom operating temperature of the column is 10°C - 50°C lower than the temperature of the organic solvent vapor described in step D), preferably 20°C - 30°C.
10. A method for energy-saving separation of an organic solvent-water minimum azeotrope system according to claim 8, characterized in that, The ratio of the organic solvent - water feed liquid sent to the 1# distillation column equipment and the 2# distillation column equipment satisfies that the organic solvent vapor described in step D) just serves as the heat source of the reboiler at the bottom of the 2# distillation column equipment.