Method and system for separating and recycling waste liquid of EVA device

Abstract

The invention belongs to the technical field of recycling of waste liquid containing vinyl acetate and isododecane, and discloses a method and a system for separating and recycling waste liquid of an EVA (Ethylene Vinyl Acetate) device. The EVA device waste liquid is conveyed to a rectifying machine for rectification separation, vinyl acetate steam is obtained at the top, fraction liquid is obtained after condensation, one part of fraction liquid flows back into the rectifying machine, and the other part of fraction liquid serves as a vinyl acetate product to be extracted; the rectification residual liquid is conveyed to a first flash tank for flash evaporation, so that part of isododecane and residual vinyl acetate are subjected to flash evaporation to form mixed flash evaporation gas, and the mixed flash evaporation gas is extracted from the top of the first flash evaporation tank and sent back to the reboiler to heat kettle liquid; and heating first flash evaporation residual liquid discharged from the bottom of the first flash evaporation tank, feeding the first flash evaporation residual liquid into a second flash evaporation tank for flash evaporation, evaporating residual isododecane from the top of the second flash evaporation tank, and condensing to obtain an isododecane product. According to the method, the waste liquid of the EVA device is treated by adopting a separation method combining supergravity reduced-pressure rectification with two-stage flash evaporation, so that the self-polymerization reaction of vinyl acetate in the separation process is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling waste liquid containing vinyl acetate and isododecane, and in particular to a method and system for separating and recycling waste liquid from an EVA device, which reduces vinyl acetate self-polymerization by lowering the separation temperature and shortening the heating time. Background Art

[0002] EVA (ethylene-vinyl acetate copolymer) is the main raw material for encapsulation films in solar photovoltaic modules. In recent years, with the rapid development of my country's photovoltaic industry, the demand for EVA has also increased. my country's annual EVA production has exceeded 2 million tons, but for every 100,000 tons of EVA produced, 1,000 to 2,000 tons of waste liquid containing vinyl acetate will be generated. This type of waste liquid is a hazardous waste and is currently mostly treated by incineration, which not only wastes precious resources but also causes environmental pollution.

[0003] The waste liquid generated by the existing vinyl acetate refining and recovery unit of the EVA device generally contains 60-70% vinyl acetate (boiling point 73°C), 20-30% isododecane (boiling range 170°C-200°C), and 5-10% (boiling range 400-600°C) lubricating oil (mainly high-boiling-point alkanes). Due to the large difference in boiling points of these components, distillation can generally be used to separate and recover these components. However, the main problem with using existing conventional distillation tower systems to separate and recover vinyl acetate and isododecane from the waste liquid of the EVA device is that, because vinyl acetate is a heat-sensitive component, operating at excessively high separation temperatures and excessively long heating times can easily cause vinyl acetate to self-polymerize and form viscous polymers, which can easily lead to problems such as blockage of the distillation tower and reduced heat transfer efficiency in the reboiler, thereby affecting the stable operation of the distillation separation equipment.

[0004] Thermal autopolymerization of vinyl acetate affects two main aspects: First, a vinyl acetate polymer layer easily forms on the surface of the reboiler steam heating tubes, affecting heat transfer efficiency. Due to the presence of high-boiling-point isododecane and lubricating oil in the wastewater, the boiling point of the distillation residue increases as the vinyl acetate concentration decreases. Existing distillation technologies in the reboiler use high-temperature steam to indirectly heat the kettle liquid. The steam temperature in the heating tubes is generally 20-30°C higher than the kettle liquid temperature. Therefore, even under reduced pressure, if the vinyl acetate concentration in the kettle liquid is to be reduced to a very low concentration, such as below 2%, the surface temperature of the reboiler steam heating tubes will exceed the temperature at which vinyl acetate autopolymerization will occur. When the heating steam temperature is too high, the vinyl acetate in the stagnant layer of the kettle liquid on the surface of the steam heating tube easily self-polymerizes, forming a polymer layer that adheres to the surface of the heating tube, thereby reducing the heat transfer efficiency of the heating tube. To achieve the same evaporation effect, as the thin polymer layer on the reboiler surface thickens, the reboiler steam temperature must be continuously increased. This increase in temperature leads to more severe vinyl acetate self-polymerization and a decrease in heat transfer efficiency, ultimately causing the reboiler to malfunction. Secondly, existing distillation tower systems, whether in the distillation tower or the reboiler, have large liquid holdups, slow material flow rates, and long residence times. In addition, there are dead spots in the material flow, which cause the material to be heated for a long time, greatly increasing the risk of vinyl acetate self-polymerization even at relatively safe distillation operating temperatures. Therefore, to reduce the risk of vinyl acetate self-polymerization during the distillation operation, the distillation operating temperature must be controlled at a low level, which inevitably sacrifices the vinyl acetate recovery rate. As a result, the wastewater discharged from the vinyl acetate distillation and separation unit of current EVA plants generally contains a high concentration of vinyl acetate.

[0005] Therefore, the present invention is proposed to address the problems of easy self-polymerization of vinyl acetate and low recovery rate in the existing distillation separation process of vinyl acetate. Summary of the Invention

[0006] In order to overcome the shortcomings and deficiencies of the prior art and to meet the need for separating vinyl acetate and isododecane from waste liquid of an EVA device, the primary purpose of the present invention is to provide a method for separating waste liquid of an EVA device.

[0007] Another object of the present invention is to provide a separation system for waste liquid from an EVA device.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for separating and recovering waste liquid from an EVA device comprises the following steps:

[0010] (1) EVA device waste liquid is transported as feed to a distillation machine, and distillation separation is carried out under reduced pressure. Vinyl acetate vapor is obtained at the top of the distillation machine, and condensed in a condenser to obtain vinyl acetate distillate. Part of the distillate is refluxed into the distillation machine, and part is extracted as vinyl acetate product;

[0011] (2) The distillation residue of step (1) is transported as a feed to a first flash tank, and flashed under reduced pressure and isothermal conditions to flash a portion of the isododecane and the residual vinyl acetate into a mixed flash gas; the mixed flash gas is pumped out from the top of the first flash tank by a first flash vacuum pump and returned to a reboiler for heating the kettle liquid;

[0012] (3) The first flash residual liquid discharged from the bottom of the first flash tank is heated and sent to the second flash tank as feed, and flashed under reduced pressure and adiabatic conditions to evaporate isododecane from the top of the second flash tank. After condensation in the second flash condenser, the condensate is obtained as the isododecane product, and the non-condensable steam is pumped out by the second flash vacuum pump, and the second flash residual liquid is discharged from the bottom of the second flash tank.

[0013] Preferably, the distillation machine is a high gravity distillation machine;

[0014] The process parameters of the distillation separation are as follows:

[0015] Feed flow rate: 100~300kg / h;

[0016] Distillation operating pressure: 10~20kPa;

[0017] Condensation temperature: 10-20°C;

[0018] Reboiler liquid temperature: 90~110℃;

[0019] Reflux ratio: 1-4;

[0020] The distillation machine motor speed is: 500~1000r / min.

[0021] Preferably, in the vinyl acetate fraction liquid of step (1), the vinyl acetate content is ≥99.9%, the isododecane content is ≤0.1%, and the lubricating oil component content is 0%, calculated by mass percentage.

[0022] Preferably, the vinyl acetate content in the distillation residue of step (2) is ≤2% by mass.

[0023] Preferably, the separation process parameters of the flash evaporation in step (2) are as follows:

[0024] Feed flow rate: 100-350 kg / h, preferably 124-310 kg / h;

[0025] Flash pressure: 1~10kPa;

[0026] Flash gas vacuum pump discharge pressure: 20~30kPa;

[0027] Flash temperature: 100~120℃.

[0028] Preferably, the mass flow rate of the mixed flash gas in step (2) is 50 to 80% of the feed flow rate of the distillation residue.

[0029] Preferably, the separation process parameters of the flash evaporation in step (3) are as follows:

[0030] Feed flow rate: 50-70 kg / h, preferably 62-64 kg / h;

[0031] Flash pressure: 10~20kPa;

[0032] Feed liquid temperature: 250~300℃.

[0033] Preferably, in terms of mass percentage, the vinyl acetate content in the first flash tank residue in step (3) is ≤0.1%; the isododecane content in the condensate in step (3) is ≥98%, the vinyl acetate content is ≤0.1%, and the lubricating oil alkane component content is ≤1%; and the isododecane content in the second flash tank residue in step (3) is ≤10%.

[0034] A separation and recovery system for waste liquid from an EVA device comprises an ultra-gravity distillation system, a first flash evaporation system and a second flash evaporation system connected in sequence;

[0035] The supergravity distillation system comprises a supergravity distillation machine (1), a reboiler (2), a motor (3), a fraction condenser (5) and a vacuum distillation vacuum pump (6); a steam distributor (4) is provided inside the reboiler (2); the first flash evaporation system comprises a first flash tank (7), a first steam heater (9) and a first flash vacuum pump (10); the second flash evaporation system comprises a second flash tank (8), a second steam heater (11), a second flash gas condenser (12), a second flash vacuum pump (13) and a second flash residual liquid cooler (14);

[0036] The residual liquid outlet of the reboiler (2) is connected to the inlet of the first flash tank (7) through a pipeline; the steam outlet at the top of the first flash tank (7) is connected to the gas phase inlet of the reboiler (2) through a pipeline; the bottom outlet of the first flash tank (7) is connected to the inlet of the second flash tank (8) through a pipeline, and a second steam heater (11) is provided on the pipeline.

[0037] Preferably, in the supergravity distillation system, the kettle liquid outlet of the supergravity distillation machine (1) is connected to the feed liquid inlet of the reboiler (2) through a pipeline, and the gas phase outlet of the reboiler (2) is connected to the gas phase inlet of the supergravity distillation machine (1) through a pipeline to form a loop; the top of the supergravity distillation machine (1) is connected to the fraction condenser (5) through a pipeline, and the outlet of the fraction condenser (5) is divided into two paths, one of which is connected to the vacuum distillation vacuum pump (6) and the other is used for the extraction and reflux of the vinyl acetate product;

[0038] In the first flash evaporation system, a first steam heater (9) is provided at the bottom of the first flash evaporation tank (7), and the top of the first flash evaporation tank (7) is connected to the first flash evaporation vacuum pump (10) through a pipeline;

[0039] In the second flash system, the top of the second flash tank (8) is connected to the second flash gas condenser (12) and the second flash vacuum pump (13) through pipelines in sequence, and the bottom of the second flash tank (8) is connected to the second flash residual liquid cooler (14) through a pipeline.

[0040] The method of the present invention is used to separate vinyl acetate and isododecane components in waste liquid of an EVA device, wherein the purity of vinyl acetate is not less than 99.9% and the recovery rate is not less than 95%, and the purity of isododecane is not less than 98% and the recovery rate is not less than 90%.

[0041] The present invention utilizes high-gravity distillation equipment in place of conventional distillation towers to reduce the heating time of vinyl acetate distillation and lower the risk of autopolymerization. High-gravity distillation equipment replaces gravity with centrifugal force, enhancing the mass transfer process and significantly increasing the number of theoretical plates per unit volume. While achieving equivalent separation efficiency, the high-gravity distillation equipment is only 5-10% of the height of a conventional distillation tower, with a liquid holdup of approximately 10% and a residence time of approximately 1 / 10 of that of a conventional distillation tower. Furthermore, the high-speed flow of material within the high-gravity field creates a self-cleaning effect, further reducing the likelihood of blockages and dead zones within the high-gravity distillation system.

[0042] To address the existing problem of indirect heating of the kettle liquid in reboilers using high-temperature steam, which results in excessively high surface temperatures on the heat transfer tubes and dead zones in the kettle liquid, which can easily lead to vinyl acetate self-polymerization, the present invention proposes a method of separating high-temperature isododecane vapor from the distillation residue after vinyl acetate separation and directly introducing it into the reboiler to heat the kettle liquid. The advantages of direct heating of the kettle liquid include: firstly, direct heating eliminates the need for indirect heat transfer through heating tubes, completely avoiding the problem of vinyl acetate self-polymerization caused by excessively high steam heating tube surfaces; secondly, the introduced heating gas fully agitates the kettle liquid in the reboiler, avoiding dead zones and resolving the problem of the kettle liquid remaining in the reboiler for an extended period of time.

[0043] The present invention uses a reduced-pressure isothermal flash evaporation method to separate isododecane gas from the distillation residue, which is used to heat the kettle liquid. The flash tank has a simple structure and produces almost no pressure loss, thereby minimizing the isododecane evaporation temperature and reducing the occurrence of autopolymerization. Furthermore, even if autopolymerization occurs in the flash tank, it is unlikely to clog, has minimal impact on the operation of the flash tank, and is very easy to clean and maintain. Therefore, using the separation scheme proposed in the present invention to treat EVA plant wastewater can effectively reduce the risk of autopolymerization of vinyl acetate.

[0044] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0045] 1. Use a super-gravity distillation machine to treat the waste liquid generated by the EVA device. Since the super-gravity distillation machine rotates at high speed and does not require traditional fillers, the material flows quickly in the distillation tower and the residence time is only about one-tenth of that of similar distillation tower equipment. This greatly shortens the heating time of vinyl acetate and reduces the chance of self-polymerization of vinyl acetate.

[0046] 2. High-temperature isododecane vapor is directly introduced into the supergravity reboiler to heat the kettle liquid, avoiding the occurrence of vinyl acetate self-polymerization reaction due to excessive temperature on the surface of the reboiler steam heating tube. At the same time, a large amount of high-temperature isododecane gas is blown in from the bottom of the reboiler, which can fully stir the kettle liquid in the reboiler, avoid dead corners of the kettle liquid flow in the reboiler, accelerate the circulation of the kettle liquid, and effectively reduce the risk of vinyl acetate self-polymerization in the reboiler.

[0047] 3. A large amount of isododecane vapor is introduced into the kettle liquid in the reboiler of the ultra-gravity distillation unit as a heat source, which increases the isododecane concentration in the kettle liquid and relatively reduces the concentration of vinyl acetate in the kettle liquid, and is also used to reduce the probability of vinyl acetate self-polymerization.

[0048] 4. Flash separation is used to separate the circulating isododecane used to heat the kettle liquid and the residual vinyl acetate vapor from the ultra-gravity distillation residue. Under the condition of the same distillation rate, the flash operation is beneficial to lowering the separation temperature and reducing the separation time, which is beneficial to reducing the risk of vinyl acetate self-polymerization during the separation process.

[0049] 5. Using the present invention, vinyl acetate in the distillation residue is separated by flash distillation and returned to the distillation unit, thereby improving the vinyl acetate recovery rate (over 96%). Furthermore, since the vinyl acetate concentration in the residue is reduced to a very low level after the first-stage flash distillation separation, the residue can be flash distilled at a higher temperature, achieving a higher isododecane recovery rate (over 94%).

[0050] 6. Because the first-stage flash distillation reduces the concentration of vinyl acetate in the second-stage flash distillation feed (below 0.1%), it also reduces the amount of vinyl acetate entering the second-stage flash gas, thereby improving the purity of the regenerated isododecane product, and the isododecane content is greater than 98%.

[0051] 7. Most of the existing single-set EVA plants in my country have an annual production capacity of only 100,000 tons, and the annual waste solvent generation is generally only 1,000 to 2,000 tons. If the existing continuous feed distillation tower is used to recover vinyl acetate, the size of the distillation tower is too small, and the operation and maintenance of the tower will be relatively difficult. If an intermittent distillation tower is used to separate and recover vinyl acetate, not only is the operation cumbersome, but the purity of the distillation product is also unstable, making it difficult to reuse it in the EVA polymerization system. If the high-gravity distillation and flash separation technology proposed in the present invention is used to treat the waste liquid generated by the EVA plant, it can achieve continuous feeding of small batches of waste liquid and continuous discharge of products. The operation is convenient and stable, and the space and site required for the equipment are small, which is conducive to the promotion and application of the technology and can meet the waste liquid treatment needs of EVA plants of all scales in China. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Flow chart of the separation process of the present invention; wherein, 1 is a supergravity distillation machine, 2 is a reboiler, 3 is a motor, 4 isododecane vapor distributor, 5 is a fraction condenser, 6 is a vacuum distillation vacuum pump, 7 is a first flash tank, 8 is a second flash tank, 9 is a first flash gas heater, 10 is a first flash vacuum pump, 11 is a first flash residual liquid heater, 12 is a second flash gas condenser, 13 is a second flash vacuum pump, and 14 is a second flash residual liquid cooler.

[0053] Figure 2 The left figure is the distillation residue sample; among them, the left figure is the ultra-gravity distillation residue (Example 1), and the right figure is the distillation residue of the conventional distillation tower (Comparative Example 1). DETAILED DESCRIPTION

[0054] The present invention will be described in further detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0055] The technical parameters of the ultra-gravity distillation machine are as follows:

[0056] The number of rotating bed layers is 3, and the feed port is set in the middle layer.

[0057] The number of theoretical plates in the rectifying section of the rectifying machine is 25, and the number of theoretical plates in the stripping section is 10.

[0058] The reboiler is directly heated by introducing 20-30 kPa high-temperature flash steam of isododecane and vinyl acetate mixture.

[0059] The waste liquid raw material used for distillation is produced in the EVA device. Analysis shows that the waste liquid contains 70% vinyl acetate, 20% isododecane and 10% lubricating oil.

[0060] Gas chromatography analysis conditions: An HP-5 (30 m × 0.32 mm × 0.25 μm) or similar weakly polar column was used as the analytical column, with a 1 μL injection volume, an inlet temperature of 250°C, a vaporizer temperature of 300°C, and a split ratio of 30:1. The column temperature was initially set at 35°C (held for 1 min), then increased at a rate of 15°C / min to 185°C, and then at a rate of 20°C / min to 300°C (held for 3 min). The carrier gas was N2 at a flow rate of 1.60 mL / min. The detector combustion air flow rate was 400 mL / min, the hydrogen flow rate was 30 mL / min, and the detector temperature was 280°C. Vinyl acetate and isododecane with a purity greater than 99.95% were used as standards for qualitative and quantitative analysis.

[0061] Example 1

[0062] 200kg / h of EVA device waste liquid enters the machine from the feed port of the supergravity distillation machine. The vacuum pump is adjusted to control the operating pressure of the distillation machine to about 10kPa, and the condensation temperature of the distillate steam is about 10℃. After the distillation process stabilizes, the flow rate of the vinyl acetate distillate liquid obtained by condensing the distillate steam is 272kg / h. The reflux ratio is adjusted to 1, that is, the flow rate of vinyl acetate refluxed to the distillation machine is 136kg / h, and the flow rate of the vinyl acetate distillate product produced as a product is 136kg / h.

[0063] The mixed flash vapor of isododecane and vinyl acetate from the first flash tank (temperature 100°C, flow rate 248 kg / h, pressure 20 kPa) is directly introduced into the isododecane vapor distributor at the bottom of the reboiler, heating the kettle liquid in the reboiler to boiling temperature (approximately 90°C). The flow rate of the distillation residue discharged from the reboiler is controlled at 310 kg / h, and the flow rate of the mixed flash vapor is 80% of the distillation residue flow rate.

[0064] Gas chromatography analysis of the recovered regenerated vinyl acetate product revealed a vinyl acetate content of 99.91% by mass, an isododecane content of 0.05%, and no detectable lubricating oil paraffins. Chromatographic analysis of the distillation residue discharged from the reboiler revealed a content of 91.02% isododecane and 1.75% vinyl acetate. The parameters of the high-gravity distillation unit and the distillation process are summarized in Table 1. The parameters of a conventional distillation tower of equivalent capacity and the process are also listed in Table 1.

[0065] Table 1 Comparison of two distillation equipment and process parameters

[0066]

[0067] Conclusion: Comparison of the two distillation separation data listed in Table 1 shows that, in the conventional vacuum distillation tower system, due to its higher tower height and greater pressure drop, under the same vacuum conditions at the top of the tower, the temperature of the kettle liquid in the reboiler is 15°C higher than that of the supergravity distillation, the average residence time of the material in the distillation process is 11 minutes longer, and the heating heat source temperature of the kettle liquid is 20°C higher. Therefore, in the conventional distillation process, more vinyl acetate may undergo self-polymerization reaction, resulting in the vinyl acetate recovery rate obtained by supergravity distillation being 1.26% higher than that of the conventional distillation tower system. It can be seen that the distillation separation of vinyl acetate by the present invention is more conducive to reducing vinyl acetate self-polymerization. In addition, Figure 2 The color of the distillation residue also shows that the material in the traditional distillation tower system has undergone more serious self-polymerization and oxidation reactions, so the color is darker.

[0068] The distillation residue discharged from the reboiler of the ultra-gravity distillation machine enters the first flash tank at a flow rate of 310 kg / h for isothermal flash evaporation. Water vapor at 110°C is introduced into the first flash tank heater, and the steam flow rate is adjusted to maintain the flash evaporation operating temperature at around 100°C. The first flash vacuum pump is adjusted to control the flash tank pressure to around 1 kPa, and the vacuum pump exhaust pressure is controlled to around 20 kPa. The mixed flash gas of isododecane and vinyl acetate discharged from the vacuum pump has a flow rate of 248 kg / h, and the flash gas temperature is 100°C and the pressure is 20 kPa. It is sent to the ultra-gravity reboiler and introduced into the isododecane vapor distributor to directly heat the kettle liquid.

[0069] The first flash residue discharged from the bottom of the first flash tank has a flow rate of 62 kg / h. It is heated to 250°C with 260°C steam and then enters the second flash tank for adiabatic flash evaporation. Further isododecane separation is achieved by flash evaporation. The second flash vacuum pump is adjusted to maintain the flash operating pressure at 10 kPa. The flashed isododecane gas exiting the top of the flash tank is pumped out by the second flash vacuum pump and condensed in the second flash condenser. The condensation temperature is controlled to achieve a regenerated isododecane flow rate of 38 kg / h. The non-condensable vapor in the condenser is pumped out by the second flash vacuum pump. The second flash residue discharged from the bottom of the second flash tank has a flow rate of 23 kg / h. After being cooled to room temperature in the second flash residue cooler, it is sent to the waste liquid treatment system.

[0070] The first flash gas was analyzed by gas chromatography and found to contain 97.81% isododecane and 2.08% vinyl acetate. The flash residue contained 64.21% isododecane and 0.03% vinyl acetate.

[0071] Gas chromatography analysis of the second flash gas condensate revealed, by mass percentage, 98.63% isododecane, 0.01% vinyl acetate, and 0.47% lubricant oil alkanes. Chromatographic analysis of the second flash raffinate discharged from the second flash tank revealed 9.86% isododecane, 86.65% lubricant oil alkanes, and no vinyl acetate. The recovery rate of isododecane was 93.70%.

[0072] Conclusion: The two-stage flash distillation method for isododecane separation allows the first-stage flash distillation to simultaneously separate the isododecane and also flash off most of the vinyl acetate in the distillation residue, returning it to the distillation system. Therefore, this solution not only solves the problem of heat source in the distillation unit's reboiler, but also improves vinyl acetate recovery. Furthermore, since the vinyl acetate concentration in the feed liquid of the second flash tank is reduced, the second flash feed liquid can be heated to a higher temperature, resulting in a higher isododecane recovery rate.

[0073] Example 2

[0074] 200kg / h of EVA device waste liquid enters the machine from the feed port of the supergravity distillation machine. The vacuum pump is adjusted to control the pressure on the top of the distillation machine to about 20kPa, and the condensation temperature of the distillate is about 20℃. After the distillation process stabilizes, the flow rate of the vinyl acetate distillate liquid obtained by condensing the distillate steam is 675kg / h. The reflux ratio is adjusted to 4, that is, the flow rate of the vinyl acetate distillate refluxed to the distillation machine is 540kg / h, and the flow rate of the vinyl acetate distillate produced as a product is 135kg / h.

[0075] The mixed flash vapor of isododecane and vinyl acetate from the first flash tank (temperature 120°C, flow rate 248 kg / h, pressure 30 kPa) is directly introduced into the isododecane vapor distributor at the bottom of the reboiler, heating the kettle liquid in the reboiler to boiling temperature (about 110°C). The flow rate of the distillation residue discharged from the reboiler is controlled at 310 kg / h, and the flow rate of the mixed flash vapor is 80% of the distillation residue flow rate.

[0076] Gas chromatography analysis of the recovered regenerated vinyl acetate product revealed a vinyl acetate content of 99.95%, an isododecane content of 0.02%, and no detectable lubricating oil paraffins. Chromatographic analysis of the distillation residue discharged from the reboiler revealed a content of 90.97% isododecane and 1.54% vinyl acetate. The parameters of the high-gravity distillation unit and the distillation process are summarized in Table 2. The parameters of a conventional distillation tower of equivalent capacity and the process are also listed in Table 2.

[0077] Table 2 Comparison of two distillation equipment and process parameters

[0078]

[0079] Conclusion: Comparing the separation results of the two distillation schemes in Table 2 shows that, due to the higher tower height and greater pressure drop in the conventional vacuum distillation system, the reboiler liquid temperature in the reboiler is 4°C higher than that in the high-gravity distillation reactor under the same vacuum conditions at the top of the tower, and the material resides in the distillation process for 10 minutes longer. As a result, the conventional distillation process may cause more vinyl acetate to undergo self-polymerization, resulting in a vinyl acetate yield reduction of approximately 1.16% compared to high-gravity distillation. Therefore, the distillation separation of vinyl acetate using the present invention is more effective in reducing vinyl acetate self-polymerization.

[0080] The distillation residue discharged from the reboiler of the ultra-gravity distillation machine enters the first flash tank at a flow rate of 310 kg / h for isothermal flash evaporation. Water vapor at 120°C is introduced into the steam heater of the first flash tank, and the steam flow rate is adjusted to maintain the flash evaporation operating temperature at about 110°C. The first flash vacuum pump is adjusted to control the flash pressure to about 10 kPa, and the exhaust pressure of the vacuum pump is controlled to 30 kPa. The mixed flash gas of isododecane and vinyl acetate discharged from the vacuum pump (temperature of 110°C, flow rate of 248 kg / h, pressure of 30 kPa) is sent to the ultra-gravity reboiler and introduced into the isododecane vapor distributor to directly heat the kettle liquid.

[0081] The first flash residue discharged from the bottom of the first flash tank has a flow rate of 64 kg / h. It is heated to 300°C with 320°C steam and then enters the second flash tank for adiabatic flash evaporation. The isododecane is further separated by flash evaporation. The second flash vacuum pump is adjusted to maintain the flash operating pressure at 20 kPa. The flashed isododecane gas from the top of the flash tank is pumped out by the second flash vacuum pump and condensed in the second flash gas condenser. The condensation temperature is controlled at approximately 50°C, resulting in a regenerated isododecane flow rate of 39 kg / h. The non-condensable vapor in the condenser is pumped out by the second flash vacuum pump. The second flash residue discharged from the bottom of the second flash tank has a flow rate of 22 kg / h. After being cooled to room temperature in the second flash residue cooler, it is sent to the waste liquid treatment system.

[0082] Gas chromatography analysis of the second flash gas condensate revealed, by mass percentage, 98.11% isododecane, 0.02% vinyl acetate, and 0.78% lubricant oil alkanes. Chromatographic analysis of the flash residue discharged from the second flash tank revealed 9.80% isododecane, 86.91% lubricant oil alkanes, and no vinyl acetate. The recovery rate of isododecane was 95.65%.

[0083] Conclusion: The two-stage flash distillation method not only achieves the separation and recovery of isododecane, but also improves the recovery rate of vinyl acetate and effectively increases the purity of the isododecane product obtained in the second flash distillation. Furthermore, due to the reduced vinyl acetate concentration in the second flash distillation feed, isododecane can be separated at a higher flash distillation temperature, resulting in a higher isododecane recovery rate.

[0084] Example 3

[0085] 200kg / h of EVA device waste liquid enters the machine from the feed port of the supergravity distillation machine. The vacuum pump is adjusted to control the operating pressure of the distillation machine to about 10kPa, and the condensation temperature of the distillate steam is about 10℃. After the distillation process stabilizes, the flow rate of the vinyl acetate distillate liquid obtained by condensing the distillate steam is 272kg / h. The reflux ratio is adjusted to 1, that is, the flow rate of vinyl acetate refluxed to the distillation machine is 136kg / h, and the flow rate of the vinyl acetate distillate product produced as a product is 136kg / h.

[0086] The mixed flash vapor of isododecane and vinyl acetate from the first flash tank (temperature 100°C, flow rate 64 kg / h, pressure 20 kPa) is directly introduced into the isododecane vapor distributor at the bottom of the reboiler, heating the kettle liquid in the reboiler to boiling temperature (approximately 90°C). The flow rate of the distillation residue discharged from the reboiler is controlled at 128 kg / h, and the flow rate of the mixed flash vapor is 50% of the distillation residue flow rate.

[0087] Gas chromatography analysis of the recovered regenerated vinyl acetate product revealed a vinyl acetate content of 99.90% by mass, an isododecane content of 0.01%, and no lubricating oil paraffins. Chromatographic analysis of the distillation residue discharged from the reboiler revealed a content of 91.12% isododecane and 1.78% vinyl acetate. The parameters of the high-gravity distillation unit and the distillation process are summarized in Table 3. The parameters of a conventional distillation tower of equivalent capacity and the process are also listed in Table 3.

[0088] Table 3 Comparison of two distillation equipment and process parameters

[0089]

[0090]

[0091] Conclusion: Comparing the separation results of the two distillation schemes in Table 3 shows that, due to the higher tower height and greater pressure drop, the conventional vacuum distillation system, under the same vacuum conditions at the top of the tower, has a 4°C higher temperature in the reboiler than the still in the high-gravity distillation reactor, and the material resides in the distillation process for 11 minutes longer. Therefore, the conventional distillation process may cause more vinyl acetate to undergo self-polymerization, resulting in a vinyl acetate yield that is approximately 1% lower than that of high-gravity distillation. Therefore, the distillation separation of vinyl acetate using the present invention is more effective in reducing vinyl acetate self-polymerization.

[0092] The distillation residue discharged from the reboiler of the high-gravity distillation machine enters the first flash tank for isothermal flash evaporation at a flow rate of 124 kg / h. 110°C steam is introduced into the steam heater of the first flash tank, and the steam flow rate is adjusted to maintain the flash operating temperature at approximately 100°C. The first flash vacuum pump is adjusted to control the flash pressure to approximately 10 kPa, and the vacuum pump exhaust pressure is controlled at 20 kPa. The mixed flash vapor of isododecane and vinyl acetate discharged from the vacuum pump (at a flow rate of 64 kg / h, a temperature of 100°C, and a pressure of 20 kPa) is sent to the high-gravity reboiler and introduced into the isododecane vapor distributor to directly heat the kettle liquid.

[0093] The first flash residue is discharged from the bottom of the first flash tank at a flow rate of 64 kg / h. It is heated to 300°C with 320°C steam and then enters the second flash tank for adiabatic flash evaporation to further separate isododecane. The second flash vacuum pump is adjusted to maintain the flash operating pressure at 20 kPa. The flashed isododecane gas exiting the top of the flash tank is pumped out by the second flash vacuum pump and enters the second flash gas condenser. The condensate temperature is controlled at approximately 40°C, resulting in a regenerated isododecane flow rate of 38.5 kg / h. The flash residue discharged from the bottom of the flash tank has a flow rate of 22.4 kg / h. It is cooled to room temperature in the second flash residue cooler and then sent to the waste liquid treatment system.

[0094] Gas chromatography analysis of the second flash gas condensate revealed, by mass percentage, 98.51% isododecane, 0.03% vinyl acetate, and 0.58% lubricant oil alkanes. Chromatographic analysis of the flash residue discharged from the second flash tank revealed 9.65% isododecane, 86.91% lubricant oil alkanes, and no vinyl acetate. The recovery rate of isododecane was 94.81%.

[0095] Conclusion: The two-stage flash distillation method not only achieves the separation and recovery of isododecane, but also improves the recovery rate of vinyl acetate and effectively increases the purity of the isododecane product obtained in the second flash distillation. Furthermore, due to the reduced vinyl acetate concentration in the second flash distillation feed, isododecane can be separated at a higher flash distillation temperature, resulting in a higher isododecane recovery rate.

[0096] Comparative Example

[0097] A conventional distillation tower was used, and the specific process parameters are shown in Tables 1 to 3.

[0098] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for separating and recovering waste liquid from an EVA device, characterized in that: The steps include: (1) EVA device waste liquid is transported as feed to a distillation machine, and distillation separation is carried out under reduced pressure. Vinyl acetate vapor is obtained at the top of the distillation machine, and condensed in a condenser to obtain vinyl acetate distillate. Part of the distillate is refluxed into the distillation machine, and part is extracted as vinyl acetate product; (2) The distillation residue of step (1) is transported as a feed to a first flash tank, and flashed under reduced pressure and isothermal conditions to flash a portion of the isododecane and the residual vinyl acetate into a mixed flash gas; the mixed flash gas is pumped out from the top of the first flash tank by a first flash vacuum pump and returned to a reboiler for heating the kettle liquid; (3) The first flash residual liquid discharged from the bottom of the first flash tank is heated and sent to the second flash tank as feed, and flash distillation is carried out under reduced pressure and adiabatic conditions, so that isododecane is evaporated from the top of the second flash tank. The condensate obtained after condensation in the second flash condenser is produced as the isododecane product, and the non-condensable steam is pumped out by the second flash vacuum pump, and the second flash residual liquid is discharged from the bottom of the second flash tank.

2. The method for separating and recovering waste liquid from an EVA device according to claim 1, wherein: The distillation machine is a high gravity distillation machine; The process parameters of the distillation separation are as follows: Feed flow rate: 100~300kg / h; Distillation operating pressure: 10~20kPa; Condensation temperature: 10-20°C; Reboiler liquid temperature: 90~110℃; Reflux ratio: 1-4; The distillation machine motor speed is: 500~1000r / min.

3. The method for separating and recovering waste liquid from an EVA device according to claim 1, wherein: Calculated by mass percentage, in the vinyl acetate fraction liquid of step (1), the vinyl acetate content is ≥99.9%, the isododecane content is ≤0.1%, and the lubricating oil component content is 0%.

4. The method for separating and recovering waste liquid from an EVA device according to claim 1, wherein: Calculated by mass percentage, the vinyl acetate content in the distillation residue of step (2) is ≤2%.

5. The method for separating and recovering waste liquid from an EVA device according to claim 1, wherein: The separation process parameters of the flash evaporation in step (2) are as follows: Feed flow rate: 100~350kg / h; Flash pressure: 1~10kPa; Flash gas vacuum pump discharge pressure: 20~30kPa; Flash temperature: 100~120℃.

6. The method for separating and recovering waste liquid from an EVA device according to claim 1, wherein: The mass flow rate of the mixed flash gas in step (2) is 50 to 80% of the feed flow rate of the distillation residue.

7. The method for separating and recovering waste liquid from an EVA device according to claim 1, wherein: The separation process parameters of the flash evaporation in step (3) are as follows: Feed flow rate: 50-70 kg / h; Flash pressure: 10~20kPa Feed liquid temperature: 250~300℃.

8. The method for separating and recovering waste liquid from an EVA device according to claim 7, wherein: In terms of mass percentage, in the residual liquid of the first flash tank in step (3), the vinyl acetate content is ≤0.1%; in the condensate in step (3), the isododecane content is ≥98%, the vinyl acetate content is ≤0.1%, and the lubricating oil alkane component content is ≤1%; in the residual liquid of the second flash tank in step (3), the isododecane content is ≤10%.

9. A separation and recovery system for waste liquid from an EVA device, characterized in that: It includes an ultra-gravity distillation system, a first flash distillation system and a second flash distillation system connected in sequence; The supergravity distillation system comprises a supergravity distillation machine (1), a reboiler (2), a motor (3), a fraction condenser (5) and a vacuum distillation vacuum pump (6); a steam distributor (4) is provided inside the reboiler (2); the first flash evaporation system comprises a first flash tank (7), a first steam heater (9) and a first flash vacuum pump (10); the second flash evaporation system comprises a second flash tank (8), a second steam heater (11), a second flash gas condenser (12), a second flash vacuum pump (13) and a second flash residual liquid cooler (14); The residual liquid outlet of the reboiler (2) is connected to the inlet of the first flash tank (7) through a pipeline; the steam outlet at the top of the first flash tank (7) is connected to the gas phase inlet of the reboiler (2) through a pipeline; the bottom outlet of the first flash tank (7) is connected to the inlet of the second flash tank (8) through a pipeline, and a second steam heater (11) is provided on the pipeline.

10. The separation and recovery system for waste liquid from an EVA device according to claim 9, characterized in that: In the supergravity distillation system, the kettle liquid outlet of the supergravity distillation machine (1) is connected to the feed liquid inlet of the reboiler (2) through a pipeline, and the gas phase outlet of the reboiler (2) is connected to the gas phase inlet of the supergravity distillation machine (1) through a pipeline to form a loop; the top of the supergravity distillation machine (1) is connected to the fraction condenser (5) through a pipeline, and the outlet of the fraction condenser (5) is divided into two paths, one of which is connected to the vacuum distillation vacuum pump (6) and the other is used for the extraction and reflux of the vinyl acetate product; In the first flash evaporation system, a first steam heater (9) is provided at the bottom of the first flash evaporation tank (7), and the top of the first flash evaporation tank (7) is connected to the first flash evaporation vacuum pump (10) through a pipeline; In the second flash system, the top of the second flash tank (8) is connected to the second flash gas condenser (12) and the second flash vacuum pump (13) through pipelines in sequence, and the bottom of the second flash tank (8) is connected to the second flash residual liquid cooler (14) through a pipeline.

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