A method for removing volatiles from high boiling monomers, polymers

Abstract

This invention relates to the field of polymer devolatification. To address the problems of high devolatification temperatures and vacuum limitations in volatile matter evaporation during polymer devolatification, which prevent further reduction of residual volatile matter, this invention discloses a method for removing volatiles from high-boiling-point monomers and polymers. The method involves removing small-molecule volatiles from the substance to be devolatified in a devolatification device with a vacuum environment. The devolatification device includes an evaporation surface and a condensation surface. The condensation surface is covered with an absorbent liquid film formed by a thin-film fluid. The substance to be devolatified flows on the evaporation surface, forming an evaporation liquid film and being heated. Small-molecule volatiles in the substance escape and are absorbed by the absorbent liquid film, flowing away from the devolatification device with the absorbent liquid film. This method can obtain polymers with lower volatile matter at lower devolatification temperatures and has lower dependence on the vacuum level during devolatification.

Description

Technical Field

[0001] This invention relates to the field of polymer de-oxidation, and more particularly to a method for removing volatiles from high-boiling-point monomers and polymers. Background Technology

[0002] The removal of volatile impurities and solvents from heat-sensitive biological products, the removal of residual monomers from polymers, and the removal of volatile small molecules from high-boiling-point small molecule products are all key steps in chemical production. Current devolatilization processes involve placing the liquid to be devolatilized in a low-pressure or vacuum environment, heating it to a temperature higher than the boiling point of the volatiles to form an evaporation surface, causing the volatiles to escape from the evaporation surface, and then condensing the vaporized volatiles back into liquid on a condensation surface.

[0003] However, the substance to be devolatile is essentially a dilute solution of volatiles. According to Henry's Law, the solubility of volatiles in the substance to be devolatile is directly proportional to its equilibrium partial pressure. The vapor pressure of a low-concentration volatile substance, under the influence of the liquid being devolatile, is much lower than that of the pure substance. The liquid phase on the condensing surface is the volatile substance, and its boiling point is related to the gas pressure; the lower the gas pressure, the lower the boiling point. Therefore, the evaporation behavior of the volatile substance on the condensing surface limits the vacuum limit of the devolatile removal equipment. Simultaneously, to ensure liquid flow on the condensing surface, the freezing point of the substance to be devolatile also limits the temperature of the condensing surface, thus affecting the evaporation of the volatile substance on the condensing surface. Taking the devolatile removal of silicone oil as an example, the freezing point of silicone oil is 18℃. When the actual volatile content in the silicone oil is reduced to 1%, the vapor pressure of the organosilicon cyclic compound at 18℃ on the condensing surface is the limit of the actual vacuum degree of the devolatile removal process. For example, the vapor pressure of octamethylcyclotetrasiloxane at 18℃ is 1.6 mmHg, approximately 230 Pa. If a higher vacuum level is achieved, the organosilicon cyclic compounds cannot condense and will instead enter the vacuum pump system, disrupting its operation and ultimately leading to an even worse vacuum level. The required vacuum level for descaling must be lower than the vapor pressure of the dilute silicone oil solution containing the organosilicon cyclic compounds. Henry's Law states that its vapor pressure is only one percent of the vapor pressure of the pure substance. Therefore, even using a well-functioning four-stage series short-path distillation apparatus, it is still impossible to obtain silicone oil with less than 1000 ppm of residual organosilicon cyclic compounds.

[0004] For example, the patent CN103642045A, published in Chinese patent literature, entitled "A High-Efficiency Method for Removing Low-Molecular-Weight Silicone Oil," describes a method where a semi-finished silicone oil is pumped from a buffer tank to a preheater for preheating, then evaporated in a falling film evaporator, and finally enters a conventional vacuum separation system. In this system, a primary separation occurs, followed by a secondary separation in a high-vacuum separation system's thin-film evaporator. The final silicone oil product overflows from the bottom of the evaporator, is cooled, and then enters a product storage tank. The low-molecular-weight components from the primary and secondary separations are recovered via a condenser. This method uses a two-stage separation system to improve the removal efficiency, but this efficiency is highly dependent on the vacuum level of the equipment, requiring complex and costly equipment. Furthermore, during the volatilization process in the high-vacuum separation system, the evaporation surface is still limited by Henry's Law, requiring a high heating temperature to obtain silicone oil with a low residual amount of volatiles. Therefore, this method is not suitable for the volatilization of heat-sensitive small-molecule compounds. Summary of the Invention

[0005] To overcome the problems of high devolatilization temperatures and vacuum limitations in the evaporation of volatiles during polymer devaporization in existing technologies, which prevent further reduction of volatile residues, this invention provides a method for removing volatiles from high-boiling-point monomers and polymers. This method can obtain polymers with lower volatile content at lower devolatilization temperatures, has lower dependence on vacuum during devolatilization, and can be widely applied to polymer devolatilization, condensation reaction devolatilization to prepare ultra-high molecular weight polymers, devolatilization of other high-boiling-point organic compounds, and low-temperature devolatilization of thermosensitive products.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for removing volatiles from high-boiling-point monomers and polymers involves removing small-molecule volatiles from the substance to be removed in a vacuum-environment removal device. The removal device includes an evaporation surface and a condensation surface. The surface of the condensation surface is covered with an absorbent liquid film formed by a thin-film fluid. The substance to be removed flows on the evaporation surface to form an evaporation liquid film and is heated. After the small-molecule volatiles in the substance escape, they are absorbed by the absorbent liquid film and flow away from the removal device with the absorbent liquid film.

[0008] This invention couples falling film absorption to the distillation process of the degassing device. A non-volatile film fluid, miscible with volatile substances, covers the condensation surface of the degassing device, forming a low-temperature film fluid that absorbs volatiles. In this way, the condensation surface becomes a dilute solution with a temperature much lower than that of the volatile substances on the evaporation surface. This allows the condensed small-molecule volatiles to be dissolved by the film fluid, and the vapor pressure of the dilute solution is only one-thousandth of that of the volatiles at the condensation temperature. This breaks the limitation of the vapor pressure of small-molecule volatiles on the condensation surface on the vacuum degree of the degassing device, making the degassing of the substance more thorough.

[0009] Preferably, the substance to be removed is a liquid polymer, a fusible polymer, or a thermosensitive small molecule compound.

[0010] In the process of distillation devolatilization, when the vacuum degree is constant, the amount of small molecule volatiles removed increases with the increase of the temperature of the substance to be devolatilized. However, the temperature of the substance to be devolatilized cannot be increased indefinitely. At high temperatures, the substance to be devolatilized is prone to oxidation, decomposition, polymerization and cross-linking. Compared with the traditional distillation devolatilization method, the method of the present invention improves the devolatilization efficiency. When the evaporation surface temperature is the same, the product obtained by the present invention has a lower residual amount of small molecules. Therefore, the present invention can obtain a product with a low residual amount of small molecule volatiles at a lower devolatilization temperature, consumes less energy, and can also avoid the decomposition of the substance to be devolatilized at a higher temperature. It can be used for the devolatilization of thermosensitive small molecule compounds.

[0011] Preferably, the substance to be removed is polymethylsiloxane, polymethylphenylsiloxane, polyphenylsiloxane, polyester, acrylate monomer, or methacrylate monomer.

[0012] Preferably, the thin-film fluid is the substance to be desorbed or the substance to be desorbed after preliminary devolvation.

[0013] The thin-film fluid on the condenser surface is used to absorb small volatile molecules that evaporate from the material to be removed. The material to be removed and the material to be removed after preliminary devolatification can absorb the volatiles. At the same time, the evaporation behavior of the material to be removed on the condenser surface will not introduce other impurities into the material to be removed on the evaporation surface.

[0014] Preferably, the thin-film fluid is a volatile solvent with a saturated vapor pressure of less than 10 Pa at the condensation surface temperature.

[0015] Besides the substances to be removed, thin-film fluids can also be high-boiling-point, low-vapor-pressure solvents with good solubility for volatile components. For example, polyoxypropylene-ethylene ether, ethylene glycol, and liquid chlorinated paraffin have high boiling points and can absorb small-molecule volatiles in polymethylsiloxane, polymethylphenylsiloxane, polyphenylsiloxane, polyester, acrylate monomers, and methacrylate monomers, and can also be used as thin-film fluids.

[0016] Preferably, the evaporation surface and the condensation surface are arranged in parallel opposite directions, and the substance to be removed and the thin film fluid can flow from top to bottom on the evaporation surface and the condensation surface respectively under the action of gravity.

[0017] The condensing surface and the evaporating surface are set parallel to each other. After the volatile substances evaporate from the evaporating surface, they only need to diffuse a distance of centimeters or even millimeters to reach the condensing surface. This eliminates the pressure difference in the pipeline, significantly improves the actual vacuum degree of the evaporating surface, and improves the evaporation efficiency.

[0018] Preferably, the distance between the evaporation surface and the condensation surface is 0.5-500 mm.

[0019] More preferably, the distance between the evaporation surface and the condensation surface is 2-30 mm.

[0020] Preferably, the vacuum level of the vacuum environment is 0.01-1000 Pa.

[0021] Preferably, the thickness of the evaporating liquid film is 0.05-0.2 mm.

[0022] Preferably, the volume ratio of the substance to be removed to the thin film fluid is (1-9):1.

[0023] Therefore, the present invention has the following beneficial effects: (1) The present invention covers the condensation surface of the devolatilization device with a non-volatile and miscible thin film fluid that is miscible with volatile substances, forming a low-temperature thin film fluid that absorbs volatiles, breaking the limitation of the vapor pressure of small molecule volatiles on the surface of the condenser on the vacuum degree of the short-path distillation system, making the polymer devolatilization more thorough; (2) Compared with the existing short-path distillation process, polymers with lower volatiles or high-boiling-point products can be obtained at a lower devolatilization temperature, and can be widely used in the devolatilization of polymers, the devolatilization of condensation reaction to prepare ultra-high molecular weight polymers, the devolatilization of other high-boiling-point organics, and the low-temperature devolatilization of thermosensitive products. Detailed Implementation

[0024] The present invention will be further described below with reference to specific implementation methods.

[0025] Example 1

[0026] A method for removing small molecule volatiles from octadecyl acrylate, comprising the following steps:

[0027] (1) Heat transfer oil is introduced into the evaporation jacket of the 300-type double-film short-path distillation equipment and heated to 140°C. 30°C circulating cooling water is introduced into the condensation jacket. The distance between the evaporation surface and the condensation surface is 15mm.

[0028] (2) Start the multi-stage Roots vacuum unit, set the pump head pressure to 15Pa, and continuously pump 300 kg of crude octadecyl acrylate into the double-membrane short-path distillation equipment at a flow rate of 40 kg / hour. The crude octadecyl acrylate contains 3% acrylic acid and 1% p-toluenesulfonic acid by mass. 90% of the crude octadecyl acrylate is diverted to the falling film evaporation surface preheated to 140℃, and 10% of the crude octadecyl acrylate is diverted to the falling film absorption surface at 30℃. Since the condensation surface is a dilute solution of volatiles, the vapor pressure is much lower than the saturated vapor pressure of volatiles. At this time, the vacuum degree of the double-membrane short-path distillation equipment is 25Pa.

[0029] (3) Collect the octadecyl acrylate finished product obtained from the drain outlet of the falling film evaporation surface and the octadecyl acrylate absorbent obtained from the drain outlet of the falling film absorption surface, respectively.

[0030] Testing revealed that a total of 259 kg of octadecyl acrylate finished product was collected, containing 0.2% acrylic acid and 0.1% p-toluenesulfonic acid; and 41 kg of octadecyl acrylate absorbent solution was collected, containing 20.6% acrylic acid and 6.8% p-toluenesulfonic acid.

[0031] Example 2

[0032] A method for removing small molecule volatiles from octadecyl acrylate, comprising the following steps:

[0033] (1) Heat transfer oil is introduced into the evaporation jacket of the 300-type double-film short-path distillation equipment and heated to 140°C. 30°C circulating cooling water is introduced into the condensation jacket. The distance between the evaporation surface and the condensation surface is 500 mm.

[0034] (2) Start the multi-stage Roots vacuum unit, set the pump head pressure to 15Pa, and continuously pump 300 kg of crude octadecyl acrylate into the double-membrane short-path distillation equipment at a flow rate of 40 kg / hour. The crude octadecyl acrylate contains 3% acrylic acid and 1% p-toluenesulfonic acid by mass. 90% of the crude octadecyl acrylate is diverted to the falling film evaporation surface preheated to 140℃, and 10% of the crude octadecyl acrylate is diverted to the falling film absorption surface at 30℃. Since the condensation surface is a dilute solution of volatiles, the vapor pressure is much lower than the saturated vapor pressure of volatiles. At this time, the vacuum degree of the double-membrane short-path distillation equipment is 25Pa.

[0035] (3) Collect the octadecyl acrylate finished product obtained from the drain outlet of the falling film evaporation surface and the octadecyl acrylate absorbent obtained from the drain outlet of the falling film absorption surface, respectively.

[0036] Testing revealed that a total of 260 kg of octadecyl acrylate finished product was collected, containing 0.74% acrylic acid and 0.22% p-toluenesulfonic acid; 40 kg of octadecyl acrylate absorbent solution was collected, containing 17.3% acrylic acid and 6.1% p-toluenesulfonic acid.

[0037] Example 3

[0038] A method for removing small molecule volatiles from octadecyl acrylate, comprising the following steps:

[0039] (1) The 300 type double-film short-path distillation equipment has heat transfer oil in the evaporation jacket and is heated to 140°C, and 30°C circulating cooling water in the condensation jacket. The distance between the evaporation surface and the condensation surface is 2mm.

[0040] (2) Start the multi-stage Roots vacuum unit, set the pump head pressure to 15Pa, and continuously pump 300 kg of crude octadecyl acrylate into the double-membrane short-path distillation equipment at a flow rate of 40 kg / hour. The crude octadecyl acrylate contains 3% acrylic acid and 1% p-toluenesulfonic acid by mass. 90% of the crude octadecyl acrylate is diverted to the falling film evaporation surface preheated to 140℃, and 10% of the crude octadecyl acrylate is diverted to the falling film absorption surface at 30℃. Since the condensation surface is a dilute solution of volatiles, the vapor pressure is much lower than the saturated vapor pressure of volatiles. At this time, the vacuum degree of the double-membrane short-path distillation equipment is 25Pa.

[0041] (3) Collect the octadecyl acrylate finished product obtained from the drain outlet of the falling film evaporation surface and the octadecyl acrylate absorbent obtained from the drain outlet of the falling film absorption surface, respectively.

[0042] Testing revealed that a total of 262 kg of octadecyl acrylate finished product was collected, with an acrylic acid content of 0.12% and no p-toluenesulfonic acid content detected; 38 kg of octadecyl acrylate absorbent solution was collected, with an acrylic acid content of 22.8% and a p-toluenesulfonic acid content of 7.8%.

[0043] Example 4

[0044] A method for removing small molecule volatiles from methyl silicone oil, comprising the following steps:

[0045] (1) Heat transfer oil is introduced into the evaporation jacket of the 300-type double-film short-path distillation equipment and heated to 180°C. 30°C circulating cooling water is introduced into the condensation jacket. The distance between the evaporation surface and the condensation surface is 25mm.

[0046] (2) Turn on the diffusion vacuum pump with cryogenic equipment, set the pump head pressure to 12Pa, and continuously pump 300 kg of crude methyl silicone oil into the double-film short-path distillation equipment at a flow rate of 40 kg per hour. The viscosity of the crude methyl silicone oil is 200cp and it contains 12% volatile matter by mass. 90% of the crude methyl silicone oil is diverted to the falling film evaporation surface preheated to 180°C, and 10% of the crude methyl silicone oil is diverted to the falling film absorption surface at 30°C. Since the condensation surface is a dilute solution of volatile matter, the vapor pressure is much lower than the saturated vapor pressure of volatile matter. At this time, the vacuum degree of the double-film short-path distillation equipment is 25Pa.

[0047] (3) Collect the finished methyl silicone oil obtained from the drain outlet of the falling film evaporation surface and the methyl silicone oil absorbent obtained from the drain outlet of the falling film absorption surface, respectively.

[0048] Testing revealed that a total of 225 kg of finished methyl silicone oil was collected, with no odor and a volatile content of 0.05%; 65 kg of methyl silicone oil absorbent was collected, with a volatile content of 55.2%.

[0049] Example 5

[0050] A method for removing small molecule volatiles from vinyl silicone oil, comprising the following steps:

[0051] (1) Heat transfer oil is introduced into the evaporation jacket of the 300-type double-film short-path distillation equipment and heated to 170°C. 20°C circulating cooling water is introduced into the condensation jacket. The distance between the evaporation surface and the condensation surface is 30mm.

[0052] (2) Start the multi-stage Roots vacuum unit, set the pump head pressure to 15Pa, and continuously pump 300 kg of crude vinyl silicone oil into the double-film short-path distillation equipment at a flow rate of 40 kg per hour. The viscosity of the vinyl silicone oil is 80cp and it contains 12% volatile matter by mass. 90% of the crude vinyl silicone oil is diverted to the falling film evaporation surface preheated to 170°C, and 10% of the crude vinyl silicone oil is diverted to the falling film absorption surface at 20°C. Since the condensation surface is a dilute solution of volatile matter, the vapor pressure is much lower than the saturated vapor pressure of volatile matter. At this time, the vacuum degree of the double-film short-path distillation equipment is 25Pa.

[0053] (3) Collect the vinyl silicone oil product obtained from the drain outlet of the falling film evaporation surface and the vinyl silicone oil absorbent obtained from the drain outlet of the falling film absorption surface, respectively.

[0054] Testing revealed that a total of 224 kg of vinyl silicone oil was collected, which was odorless and contained 0.05% volatile matter; 66 kg of vinyl silicone oil absorbent was collected, which contained 55.2% volatile matter.

[0055] Example 6

[0056] A method for removing small molecule volatiles from vinyl silicone oil, comprising the following steps:

[0057] (1) Heat transfer oil is introduced into the evaporation jacket of the double-film short-path distillation equipment and heated to 175°C. 20°C circulating cooling water is introduced into the condensation jacket. The distance between the evaporation surface and the condensation surface is 30mm.

[0058] (2) Start the multi-stage Roots vacuum unit, set the pump head pressure to 15Pa, and continuously pump 300 kg of crude vinyl silicone oil into the double-film short-path distillation equipment at a flow rate of 40 kg per hour. The viscosity of the vinyl silicone oil is 50cp, and it contains 13% volatile matter by mass. 90% of the crude vinyl silicone oil is diverted to the falling film evaporation surface preheated to 175°C, and 10% of the crude vinyl silicone oil is diverted to the falling film absorption surface at 20°C. Since the condensation surface is a dilute solution of volatile matter, the vapor pressure is much lower than the saturated vapor pressure of volatile matter. At this time, the vacuum degree of the double-film short-path distillation equipment is 25Pa.

[0059] (3) Collect the vinyl silicone oil product obtained from the drain outlet of the falling film evaporation surface and the vinyl silicone oil absorbent obtained from the drain outlet of the falling film absorption surface, respectively.

[0060] Testing revealed that a total of 222 kg of vinyl silicone oil was collected, which was odorless and contained 0.05% volatile matter; 68 kg of vinyl silicone oil absorbent was collected, which contained 57.2% volatile matter.

[0061] Example 7

[0062] A method for removing small molecule volatiles from vinyl silicone oil, comprising the following steps:

[0063] (1) Heat transfer oil is introduced into the evaporation jacket of the double-film short-path distillation equipment and heated to 175°C. 20°C circulating cooling water is introduced into the condensation jacket. The distance between the evaporation surface and the condensation surface is 25mm.

[0064] (2) Start the multi-stage Roots vacuum unit, set the pump head pressure to 15Pa, and continuously pump 300 kg of crude vinyl silicone oil into the double-film short-path distillation equipment at a flow rate of 36 kg / h. The viscosity of the vinyl silicone oil is 50cp, and it contains 13% volatile matter by mass. All the crude vinyl silicone oil flows into the falling film evaporation surface preheated to 175°C, and the liquid chlorinated paraffin flows into the falling film absorption surface at 20°C at a flow rate of 4 kg / h. Since the condensation surface is a dilute solution of volatile matter, the vapor pressure is much lower than the saturated vapor pressure of volatile matter. At this time, the vacuum degree of the double-film short-path distillation equipment is 25Pa.

[0065] (3) Collect the vinyl silicone oil product obtained from the drain outlet of the falling film evaporation surface and the liquid chlorinated paraffin absorbent obtained from the drain outlet of the falling film absorption surface, respectively.

[0066] Testing revealed that a total of 261 kg of vinyl silicone oil was collected, which was odorless and contained 0.06% volatile matter; 75 kg of liquid chlorinated paraffin absorbent was collected, which contained 51.8% volatile matter.

[0067] As can be seen from the test results of the above embodiments, the method of the present invention can effectively reduce the volatile content in the substance to be devolatiled. Compared with the traditional devolatiled method, the present invention further reduces the residual volatiles after devolatiled treatment.

[0068] Comparative Example 1

[0069] A method for removing small molecule volatiles from vinyl silicone oil, comprising the following steps:

[0070] (1) Heat transfer oil is introduced into the evaporation jacket of the double-film short-path distillation equipment and heated to 170°C. 20°C circulating cooling water is introduced into the condensation jacket. The distance between the evaporation surface and the condensation surface is 25mm.

[0071] (2) Start the multi-stage Roots vacuum unit, set the pump head pressure to 20Pa, and continuously pump 300 kg of crude vinyl silicone oil into the double-film short-path distillation equipment at a flow rate of 40 kg per hour. The viscosity of the vinyl silicone oil is 80cp and it contains 12% volatile matter by mass. Make all the crude vinyl silicone oil flow to the falling film evaporation surface preheated to 170°C. Since the condensation surface is entirely composed of volatile matter, its vapor pressure is the saturated vapor pressure. At this time, the vacuum degree of the double-film short-path distillation equipment is 400Pa.

[0072] (3) Collect the vinyl silicone oil product obtained from the drain outlet of the falling film evaporation surface and the waste liquid obtained from the drain outlet of the falling film absorption surface respectively;

[0073] Testing revealed that a total of 265 kg of vinyl silicone oil was collected, with a volatile content of 0.5%.

[0074] In Comparative Example 1, the vacuum degree of the double-membrane short-path distillation equipment during de-devouring was 400 Pa, lower than that in the example. This is because when the vacuum degree of the double-membrane short-path distillation equipment further decreases, the volatiles in the vinyl silicone oil will not be able to condense on the condensation surface and will enter the vacuum pump system. Therefore, to protect the equipment, the gas pressure in the double-membrane short-path distillation equipment during de-devouring cannot be lower than the saturated vapor pressure of the volatiles. Furthermore, the volatile content in the de-devoured vinyl silicone oil product obtained in Comparative Example 1 is much higher than that in the de-devoured vinyl silicone oil product obtained in Example 7, indicating that the de-devouring method of the present invention has a better de-devouring effect at the same de-devouring temperature.

Claims

1. A method for removing volatile matter, characterized by, A descaling device is used to remove small molecule volatiles from the material to be descaled. The descaling device includes an evaporation surface and a condensation surface. The surface of the condensation surface is covered with an absorbent liquid film formed by a thin-film fluid. The material to be descaled flows on the evaporation surface to form an evaporation liquid film and is heated. The small molecule volatiles in the material to be descaled escape and are absorbed by the absorbent liquid film, then flow away from the descaling device with the absorbent liquid film. The material to be descaled is crude octadecyl acrylate, and the small molecule volatiles are acrylic acid and p-toluenesulfonic acid. The distance between the evaporation surface and the condensation surface is 2-500 mm. 300 kg of crude octadecyl acrylate is continuously pumped into the descaling device at a flow rate of 40 kg / h. 90% of the crude octadecyl acrylate is diverted to the evaporation surface preheated to 140°C, and 10% of the crude octadecyl acrylate is diverted to the condensation surface at 30°C. The finished octadecyl acrylate product obtained from the drain outlet of the evaporation surface and the octadecyl acrylate absorbent obtained from the drain outlet of the absorbent surface are collected separately. The vacuum degree of the descaling device is 25 Pa.

2. The method of claim 1, wherein, The evaporation surface and the condensation surface are arranged in parallel and opposite directions, and the substance to be removed and the thin film fluid can flow from top to bottom on the evaporation surface and the condensation surface respectively under the action of gravity.

3. The method of claim 1 wherein, The finished octadecyl acrylate contains 0.2% acrylic acid and 0.1% p-toluenesulfonic acid.

4. The method of claim 1 wherein, The octadecyl acrylate absorbent contains 20.6% acrylic acid and 6.8% p-toluenesulfonic acid.

5. The method of claim 1 wherein, The distance between the evaporation surface and the condensation surface is 2 mm.

6. The method of claim 1 wherein, The de-lowering device also includes an evaporator jacket, a condenser film jacket, and a multi-stage Roots vacuum unit.

7. The method according to claim 6, characterized in that, 30°C circulating cooling water is introduced into the condensation membrane jacket.

8. The method according to claim 6, characterized in that, The pump head pressure of the multi-stage Roots vacuum unit is 15 Pa.