Rectification device and vinyl acetate production system

Abstract

The utility model relates to the technical field of chemical rectification, and discloses a rectification device which comprises a rectification unit (1) and an extraction unit (3), a gas phase distillation outlet (101) of the rectification unit (1) is connected with an extraction unit inlet (303) of the extraction unit (3), and a raffinate phase liquid outlet (304) of the extraction unit (3) is connected with a reflux liquid inlet (102) of the rectification unit (1). The rectification device can reduce and stabilize the content of water and other impurities in vinyl acetate distilled by the vinyl acetate refining rectification tower, so that the energy consumption and the production cost are reduced.

Description

Technical Field

[0001] The utility model relates to the field of chemical distillation, in particular to a distillation device and a vinyl acetate production system. Background Art

[0002] In the vinyl acetate production process, the distillation column feed primarily consists of three materials: the synthesis reaction liquid (generally including acetaldehyde, vinyl acetate, acetic acid, water, acetylene, and other impurities), the recovered liquid (generally including acetaldehyde, vinyl acetate, water, and other impurities), and the filtered supernatant (generally including acetaldehyde, vinyl acetate, acetic acid, water, and other impurities). The synthesis reaction liquid in the distillation column feed comes from the reaction liquid storage tank and is pumped into the distillation column by the reaction liquid feed pump. The recovered liquid primarily comes from the raffinate overflow from the extraction column overhead and is pumped from the recovered liquid feed pump along with the reaction liquid into the distillation column. The filtered supernatant comes from the filtered supernatant tank and is pumped into the distillation column by the filtrate pump.

[0003] The main function of the distillation tower is to remove acetaldehyde (Ald) from the reaction liquid and filtered clear liquid from the top of the tower, and to desorb acetylene dissolved in the reaction liquid. After being sent to the synthesis process for recycling, the gas phase distilled from the top of the distillation tower is partially condensed in the distillation tower's partial condenser. The uncondensed gas from the partial condenser is cooled and condensed in the distillation tower's full condenser. The uncondensed gas from the full condenser is cooled and condensed in the distillation tower's tail gas condenser. The condensate from the partial condenser, full condenser, and tail gas condenser contains vinyl acetate, acetaldehyde, and a small amount of water. It enters the distillation tank of the distillation tower and is discharged by the distillation pump. Part of it is metered back through a flow meter, and the rest is controlled by the distillation tank level meter and metered through the feed flow meter to the lower part of the extraction tower. The liquid phase out of the distillation tower kettle (generally containing vinyl acetate, acetic acid, a small amount of acetaldehyde and water) is controlled by the distillation tower liquid level recording and adjustment table and pumped to the vinyl acetate refining distillation tower for feeding through the distillation tower kettle liquid pump, and further separated in the vinyl acetate refining distillation tower.

[0004] The existing vinyl acetate distillation process uses a fraction of the condensate from the distillation column to reflux, while the remainder is fed to an extraction column for distillation. To improve distillation efficiency, technicians feed the recovered liquid overflowing from the extraction column through the distillation column's raw material inlet for further distillation. However, the ethyl acetate obtained through this process has been largely unrecognized for its high and fluctuating water content. Utility Model Content

[0005] The technical problem to be solved by the present invention is to provide a distillation device that can reduce and stabilize the water content in vinyl acetate and reduce energy consumption and production costs in response to the problem that the water content of vinyl acetate prepared by the existing distillation tower process has always fluctuated and is on the high side.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides a distillation device, including a distillation unit and an extraction unit, the gas phase distillation outlet of the distillation unit is connected to the extraction unit inlet of the extraction unit, and the extract phase liquid outlet of the extraction unit is connected to the reflux liquid inlet of the distillation unit.

[0007] Preferably, it also includes a recovery liquid storage unit connected between the raffinate phase outlet and the reflux inlet, the recovery liquid storage unit inlet of the recovery liquid storage unit is connected to the raffinate phase outlet, and the recovery liquid storage unit outlet is connected to the reflux inlet through a reflux pipeline.

[0008] Preferably, the system further comprises a reflux control valve provided on the reflux pipeline and a recovery liquid pump provided between the reflux control valve and the liquid outlet of the recovery liquid storage unit.

[0009] Preferably, a polymerization inhibitor inlet is provided in the pipeline between the raffinate phase outlet and the liquid inlet of the recovery liquid storage unit.

[0010] Preferably, the distillation unit is also provided with a reaction liquid feed port and a filtered clear liquid feed port, the reflux liquid inlet, the reaction liquid feed port and the filtered clear liquid feed port are arranged in sequence from top to bottom, the gas phase distillation outlet is arranged at the top of the distillation unit, and the reaction liquid feed port and the filtered clear liquid feed port are arranged on the side wall of the distillation unit.

[0011] Preferably, a reflux branch pipe is provided on the pipeline between the gas phase distillation outlet and the extraction unit inlet, and the outlet of the reflux branch pipe is connected to the reflux liquid inlet.

[0012] Preferably, a liquid storage unit is provided between the gas phase distillation outlet and the extraction unit inlet.

[0013] Preferably, the reflux branch is provided between the liquid storage unit outlet of the liquid storage unit and the extraction unit inlet.

[0014] Preferably, the extraction unit is further provided with an extractant liquid inlet, and the extractant liquid inlet is located above the extraction unit inlet and below the raffinate phase liquid outlet.

[0015] A second aspect of the present invention provides a vinyl acetate production system, comprising the distillation device described in the first aspect.

[0016] Through the above technical solution, the beneficial effects of the utility model are:

[0017] The utility model provides a distillation device, in which the raffinate phase outlet of the extraction unit is connected to the reflux inlet of the distillation unit, the components of the raffinate phase in the extraction unit and the reflux liquid of the distillation unit are basically similar, and compared with feeding the recovered liquid (i.e., the raffinate phase) from the raw material inlet of the distillation unit, the raffinate phase is directly refluxed into the reflux inlet of the distillation unit. The direct reflux of the raffinate phase can not only play the role of reflux of the distillation unit, but also reduce the amount of heating and distillation required by the distillation unit, and at the same time reduce the total steam consumption of the distillation unit, reduce the circulation amount of light components in the distillation unit in the distillation device, reduce the water content entering the distillation unit, improve the distillation quality and effect of the subsequent vinyl acetate refining distillation tower, reduce and stabilize the water content in the vinyl acetate distilled from the vinyl acetate refining distillation tower, and thus reduce energy consumption and production costs.

[0018] Other technical features and technical effects of the present invention will be further described in the following specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 It is a simplified structural diagram of the distillation device in the present utility model;

[0021] Figure 2 This is a connection diagram of an embodiment of the distillation device in the present invention;

[0022] Figure 3 It is a connection diagram of an implementation method of the distillation device in the present utility model.

[0023] Description of Reference Numerals

[0024] 1 Distillation unit 101 gas phase distillation outlet

[0025] 102 reflux inlet 103 reaction liquid feed inlet

[0026] 104 filtered liquid feed port 2 liquid storage unit

[0027] 201 liquid storage unit liquid inlet 202 liquid storage unit liquid outlet

[0028] 3 Extraction unit 301 Extraction phase liquid outlet

[0029] 302 Extractant inlet 303 Extraction unit inlet

[0030] 304 Raffinate phase outlet 4 Recovery liquid storage unit

[0031] 401 Recovery liquid storage unit liquid outlet 402 Recovery liquid storage unit liquid inlet

[0032] 5 Return pipe 6 Return control valve

[0033] 7 Recovery liquid pump 8 Distillation pump

[0034] 9 Liquid storage unit control valve 10 Condenser

[0035] 11 Reflux branch DETAILED DESCRIPTION

[0036] The following is a detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0037] In the description of this utility model, it should be noted that, unless otherwise expressly specified or limited, the terms "connection" and "connected" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection, indirect connection through an intermediate medium, abutment, internal communication between two elements, or interaction between two elements. For those skilled in the art, the specific meanings of the above terms in this utility model can be understood according to specific circumstances.

[0038] It should be understood that the terms "upper," "lower," "front," "back," "inner," and "outer" and the like, indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They are not intended to indicate or imply that the devices or elements referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of the aforementioned features.

[0039] The utility model provides a distillation device, see Figure 1 The direction of the arrow in the figure is the flow direction of the liquid in the distillation device, which includes a distillation unit 1 and an extraction unit 3. The gas phase distillation outlet 101 of the distillation unit 1 is connected to the extraction unit inlet 303 of the extraction unit 3, and the extract phase liquid outlet 304 of the extraction unit 3 is connected to the reflux liquid inlet 102 of the distillation unit 1.

[0040] It should be noted that the reflux inlet 102 is the reflux inlet 102 of the distillation unit 1 during self-reflux, and can be set in the middle and upper part of the distillation unit 1. After the reflux inlet 102 is connected to the raffinate phase outlet 304, the raffinate phase is used to replace the reflux liquid to reflux the distillation unit 1; the raw material inlet refers to the position near the middle or middle and upper part of the distillation unit 1, and is lower than the height of the reflux inlet 102. The material entering from the raw material inlet needs to be distilled, separated and purified by the distillation unit 1.

[0041] Existing vinyl acetate distillation processes mostly use a method of feeding three parts of materials, namely, a synthesis reaction liquid (including acetaldehyde, vinyl acetate, acetic acid, water, acetylene and other impurities), a recovered liquid (including acetaldehyde, vinyl acetate, water and other impurities), and a filtered supernatant (including acetaldehyde, vinyl acetate, acetic acid, water and other impurities), from the raw material inlet of the distillation unit 1. However, this feeding method causes the recovered liquid to pass through the tower plates of the distillation unit 1 again, increasing the amount of materials that need to be heated and separated on the tower plates, and increasing the amount of hot steam generated during the distillation process, which in turn leads to large fluctuations and high water content in the discharge material. This is something that has not been paid attention to by those skilled in the art. The inventors of the present invention unexpectedly discovered this problem during the research process and found that the components of the raffinate phase and the reflux liquid of the distillation unit are basically similar. By directly refluxing the raffinate phase into the reflux inlet 102 of the distillation unit 1, the direct reflux of the raffinate phase can reduce the total steam consumption of the distillation unit 1 while playing the role of reflux of the distillation unit 1, reduce the circulation amount of the light components in the distillation unit 1 in the distillation device, and reduce the water content entering the distillation unit 1 (the recovered liquid, i.e., the raffinate phase, contains a certain amount of water, while the existing process is that the recovered liquid is fed from the raw material inlet and contains a certain amount of water, and the reflux of the distillation unit 1 itself also contains a certain amount of water), thereby improving the distillation quality and effect of the subsequent vinyl acetate refining distillation tower, reducing and stabilizing the water content in the vinyl acetate distilled from the vinyl acetate refining distillation tower, and thus reducing energy consumption and production costs. When the distillation device provided by the above basic technical solution is in operation, taking the distillation process of vinyl acetate as an example, it includes the following processes:

[0042] The distillation process for vinyl acetate is a fluidized bed gas-phase synthesis process for vinyl acetate. This process involves reacting a mixture of acetylene and acetic acid in a fluidized bed reactor under heating conditions using activated carbon as a carrier and zinc acetate as a catalyst. During the reaction, the reacted mixed gas is discharged from the top of the reactor, separated by a powder separator, and then fed to a gas separation tower. The first stage of the separation tower produces a filtrate containing a large amount of activated carbon powder containing zinc acetate. The second stage of the separation tower produces a synthesis reaction liquid. The filtrate produced from the first stage is treated by distillation and filtration to produce a clear filtrate. After the synthesis reaction liquid and clear filtrate are treated in distillation unit 1, the bottom material of distillation unit 1 is fed to a vinyl acetate refining distillation tower for further refining to produce vinyl acetate. The top material of distillation unit 1, containing vinyl acetate, acetaldehyde, water, and other impurities, enters extraction unit 3. The extract from extraction unit 3 is refined in an acetaldehyde refining tower to produce the acetaldehyde product.

[0043] For example, in the vinyl acetate distillation process, the distillation unit 1 utilizes a distillation tower, and the extraction unit 3 utilizes an extraction tower. The distillation tower is a conventional distillation tower used in fluidized bed processes. The distillation tower removes acetaldehyde (Ald) from the synthesis reaction liquid from the top of the tower, while simultaneously feeding the acetylene (C2H2) dissolved in the synthesis reaction liquid after desorption into the vinyl acetate synthesis process for recycling. The synthesis reaction liquid contains 0.2-2.5 wt% acetaldehyde, 35.0-55.0 wt% vinyl acetate, 43.1-62.4 wt% acetic acid, 0.02-1.5 wt% water, and small amounts of acetylene and other impurities. The material exiting the vapor phase distillation outlet 101 at the top of the distillation tower enters the extraction tower. The upper raffinate phase in the extraction tower contains 90.0-95.0 wt% vinyl acetate, 2-3.5 wt% acetaldehyde, 0.8-1.0 wt% water, and other impurities. The lower extract phase contains 1.0-3.0 wt% vinyl acetate, 3.0-5.0 wt% acetaldehyde, and 92.0-96.0 wt% water. The raffinate phase overflows the extraction tower through the reflux inlet 102 of the distillation tower and refluxes into the distillation tower. The non-condensable acetylene gas (C2H2) in the distillation tower, along with a small amount of acetaldehyde (Ald), is returned to the acetylene gas recovery tank in the vinyl acetate synthesis process. The liquid phase of the bottom of the distillation tower is discharged from the bottom, and the acetaldehyde content of the bottom liquid phase is 0.003-0.005wt%, the vinyl acetate VAC content is 50.0-55.0wt%, the acetic acid content is 48.0-50.0wt%, and the water content is 0.05-0.08wt%. The bottom liquid is sent to the vinyl acetate refining distillation tower for feeding, and is further separated in the vinyl acetate refining distillation tower.

[0044] In one embodiment of the present invention, a condenser 10 is provided at the top of the distillation unit 1. Condenser 10 includes a partial condenser, a complete condenser, and an off-gas condenser. During the distillation process of the gas phase at the top of the distillation unit 1, it is first partially condensed in the partial condenser (the cooling medium is circulating water). The uncondensed gas in the partial condenser is further cooled and condensed in the complete condenser (the cooling medium is chilled water). The uncondensed gas in the complete condenser is cooled and condensed in the off-gas condenser (the cooling medium is chilled water). The condensate flowing out of the partial condenser, the condensate flowing out of the complete condenser, and the condensate from the off-gas condenser enter the extraction unit 3. A feed flow meter is provided on the extraction unit 3. The feed flow meter records the amount of condensate fed into the extraction unit 3 via the extraction unit inlet 303. The extractant in the extraction unit 3 can be deionized water or an acetaldehyde aqueous solution. The extraction tower in the existing vinyl acetate distillation process uses a large amount of demineralized water as the extractant to separate acetaldehyde and vinyl acetate. Because the extraction tower operates at a relatively low temperature of 5-15°C, a large amount of chilled water is required to cool the demineralized water (temperature 25-35°C) to the extraction tower operating temperature, otherwise the extraction efficiency of the extraction tower will be affected. In addition, the use of demineralized water also causes a large amount of wastewater to be generated in the extraction tower kettle. Preferably, the top of the extraction tower uses the acetaldehyde aqueous solution from the synthesis water scrubber (acetaldehyde water from the synthesis process, acetaldehyde content 1.0-3.0wt%, temperature 0-10°C) as the extractant. This not only reduces the consumption of demineralized water in the extraction tower, but also allows the acetaldehyde aqueous solution from the acetaldehyde synthesis process water scrubber to be recycled, saving water resources.

[0045] The distillation device provided by the present invention directly uses the raffinate phase in the extraction unit 3 as the reflux liquid of the distillation unit 1 to enter from the reflux liquid inlet 102 of the distillation unit 1, and the gas phase at the top of the distillation unit 1 enters the extraction unit 3 through the gas phase distillation outlet 101 for extraction and separation. Compared with the raffinate phase being fed directly from the reflux liquid inlet 102 to the distillation unit 1 as the recovered liquid and being fed from the raw material inlet of the distillation unit 1, the direct reflux of the raffinate phase can play the role of reflux of the distillation unit 1 while reducing the amount of gas entering the distillation unit 1. By increasing the feed amount of element 1 (and reducing the water content in the feed amount at the same time), when the feed amounts of other components in the distillation unit 1 remain unchanged, it is equivalent to reducing the total amount of water entering the distillation unit 1 and the total amount of materials that need to be heated in the distillation unit 1, thereby reducing the total steam consumption of the distillation unit 1, reducing the circulation amount of light components in the distillation unit 1 in the distillation device, improving the distillation quality and effect of the subsequent vinyl acetate refining distillation tower, reducing and stabilizing the water content in the vinyl acetate distilled from the vinyl acetate refining distillation tower, and thus reducing energy consumption and production costs.

[0046] In a specific embodiment of the present invention, see Figure 2, further comprising a recovery liquid storage unit 4 connected between the raffinate phase outlet 304 and the reflux inlet 102. The recovery liquid storage unit inlet 402 of the recovery liquid storage unit 4 is connected to the raffinate phase outlet 304, and the recovery liquid storage unit outlet 401 is connected to the reflux inlet 102 via a reflux line 5. Collecting the raffinate phase in the recovery liquid storage unit 4 and then recirculating the raffinate phase via the reflux line 5 can improve the stability of the raffinate phase supply in the distillation apparatus, further enhancing the operational stability of the distillation unit 1.

[0047] As a specific embodiment of the present invention, it also includes a reflux control valve 6 arranged on the reflux pipeline 5 and a recovery liquid pump 7 arranged between the reflux control valve 6 and the liquid outlet 401 of the recovery liquid storage unit. The reflux control valve 6 can control the opening and closing of the reflux pipeline 5, which is convenient for the inspection and maintenance of the distillation device; the recovery liquid pump 7 can quickly transport the recovery liquid in the recovery liquid storage unit 4 to the distillation unit 1, thereby increasing the speed of material transportation. During operation, the flow rate of the recovery liquid in the reflux pipeline 5 can be adjusted according to the material balance principle while improving the stability of material transportation. Preferably, the recovery liquid pump 7 is arranged close to the liquid outlet 401 of the recovery liquid storage unit, and the flow rate of the reflux recovery liquid can be adjusted in time according to the change of the liquid level in the recovery liquid storage unit 4, thereby improving the stability of material transportation.

[0048] As a specific embodiment of the present invention, a polymerization inhibitor inlet is provided in the pipeline between the raffinate phase outlet 304 and the recovery liquid storage unit inlet 402. After being added, the polymerization inhibitor enters the recovery liquid storage unit 4 and then enters the distillation unit 1 through the reflux line 5, thereby preventing vinyl acetate from self-polymerizing in the distillation unit 1.

[0049] As a specific embodiment of the present invention, the distillation unit 1 is further provided with a reaction liquid feed port 103 and a filtered clear liquid feed port 104. The reflux liquid feed port 102, the reaction liquid feed port 103, and the filtered clear liquid feed port 104 are arranged in sequence from top to bottom. The gas phase distillation outlet 101 is arranged at the top of the distillation unit 1, and the reaction liquid feed port 103 and the filtered clear liquid feed port 104 are arranged on the side wall of the distillation unit 1. During operation, the recycled liquid enters the distillation unit 1 from the reflux liquid feed port 102, the synthetic reaction liquid enters the distillation unit 1 from the reaction liquid feed port 103, and the filtered clear liquid enters the distillation unit 1 from the filtered clear liquid feed port 104. The reaction liquid feed port 103 and the filtered clear liquid feed port 104 are arranged on the side wall of the distillation unit 1, and the reaction liquid feed port 103 is arranged above the filtered clear liquid feed port 104. For example, when the distillation unit 1 is a distillation tower, the reaction liquid feed inlet 103 and the filtered clear liquid feed inlet 104 can be arranged with two or four tower plates between them. When they are separated by two or four tower plates, the reaction liquid feed inlet 103 and the filtered clear liquid feed inlet 104 can be arranged on the same side of the distillation unit 1. When they are separated by three tower plates, the reaction liquid feed inlet 103 and the filtered clear liquid feed inlet 104 can be arranged on different side walls of the distillation unit 1. Arranging the reaction liquid and the filtered clear liquid to enter the distillation unit 1 at different positions according to the different material compositions in the reaction liquid and the filtered clear liquid can improve the distillation effect of the tower plates and avoid the accumulation of materials on the same tower plate, which affects the distillation effect of the reaction liquid and the filtered clear liquid.

[0050] Taking the vinyl acetate distillation process as an example, the raffinate phase in the reflux liquid inlet 102 has an acetaldehyde content of 2.0-3.5 wt%, a vinyl acetate content of 90.0-95.0 wt%, a water content of 0.8-1.0 wt% and other impurities; the synthesis reaction liquid in the reaction liquid feed inlet 103 has an acetaldehyde content of 0.2-2.5 wt%, a vinyl acetate content of 35.0-55.0 wt%, an acetic acid content of 43.1-62.4 wt%, a water content of 0.02-1.5 wt%, a small amount of acetylene and other impurities; the filtrate in the supernatant inlet 104 has an acetaldehyde content of 0.1-1.0 wt%, a vinyl acetate content of 5.0-15.0 wt%, an acetic acid content of 82.0-93.0 wt%, a water content of 0.02-1.5 wt% and other impurities. The synthetic reaction liquid feed in the distillation unit 1 comes from the reaction liquid storage tank and is pumped out by the reaction liquid feeding pump into the distillation unit 1; the recovered liquid mainly comes from the raffinate phase overflowing from the upper part of the extraction unit 3; the upper raffinate phase in the extraction tower contains 90.0-95.0wt% vinyl acetate, 2.0-3.5wt% acetaldehyde, 0.8-1.0wt% water, and other impurities; the lower extract phase contains 1.0-3.0wt% vinyl acetate, 3.0-5.0wt% acetaldehyde, and 92.0-96.0wt% water; the filtered supernatant comes from the filtered supernatant tank and is pumped out by the filtrate pump into the distillation unit 1.

[0051] As a specific embodiment of the present invention (see Figure 3 ), a distillation pump 8 and a liquid storage unit control valve 9 are provided between the gas phase distillation outlet 101 and the extraction unit inlet 303. The distillation pump 8 can adjust the pumping rate of the distillate (i.e., the condensate from the condenser 10) according to the principle of material balance. In addition, the liquid storage unit control valve 9 can be controlled to open and close according to the amount of condensate, thereby improving the stability of material transportation.

[0052] As a specific embodiment of the present invention, a reflux branch pipe 11 is provided on the pipeline between the gas phase distillation outlet 101 and the extraction unit inlet 303, and the outlet of the reflux branch pipe 11 is connected to the reflux liquid inlet 102. The flow in the reflux branch pipe 11 is controlled by the liquid storage unit control valve 9. The liquid storage unit control valve 9 can be a three-way valve, which can transport all the condensate in the distillation unit 1 to the extraction unit 3 for extraction and stratification, or send half of the condensate to the extraction unit 3 for extraction and stratification, and the other half enters the distillation unit 1 through the reflux branch pipe 11 for direct reflux. The provision of the reflux branch pipe 11 can prevent the distillation unit 1 from maintaining stable operation when a malfunction occurs in the extraction unit 3.

[0053] As a specific embodiment of the present invention, the extractant inlet 302 is arranged at the upper middle part of the extraction unit 3, and a pipeline connected to the extractant inlet 302 is provided in the extraction unit 3, extending into the interior of the extraction unit 3, and the pipeline bends downward at the center position of the cross section of the extraction unit 3, and the end of the downward-bent pipeline is connected to a downward liquid distributor, so that the liquid is fully mixed and the extraction effect is improved; the extraction unit inlet 303 is arranged at the bottom near the bottom, and a pipeline connected to the extraction unit inlet 303 is provided in the extraction unit 3, extending into the interior of the extraction unit 3, and the pipeline bends upward at the center position of the cross section of the extraction unit 3, and the end of the upward-bent pipeline is connected to an upward liquid distributor, so that the liquid is fully mixed and the extraction effect is improved.

[0054] Taking the vinyl acetate distillation process as an example, the extractant in extraction unit 3 is a low-temperature acetaldehyde aqueous solution from a synthetic water scrubber. The low-temperature acetaldehyde aqueous solution contains 1.0-3.0 wt% acetaldehyde, 96.0-98.0 wt% water, and a small amount of acetylene. The low-temperature acetaldehyde aqueous solution enters through extractant inlet 302 and is separated and purified based on the principle that acetaldehyde is miscible with water and its solubility in vinyl acetate is lower than its solubility in water. The distillate from distillation unit 1 enters the bottom of extraction unit 3 through extraction unit inlet 303 at the bottom of extraction unit 3. The vinyl acetate in the distillate has a low density and moves upward. During this upward movement, the acetaldehyde gradually dissolves in the low-temperature acetaldehyde aqueous solution, which is fed from the top and continuously flows downward. The two streams alternate in countercurrent contact within extraction unit 3 through packing (packing is provided in the extraction unit). Acetaldehyde gradually diffuses into the low-temperature acetaldehyde aqueous solution and settles in the lower portion of extraction unit 3, improving the separation of acetaldehyde and vinyl acetate.

[0055] As a specific embodiment of the present invention, see Figure 3 , a liquid storage unit 2 is provided between the gas phase distillation outlet 101 and the extraction unit inlet 303. Preferably, a condenser is further provided between the gas phase distillation outlet 101 and the liquid storage unit 2. The liquid storage unit 2 can collect the condensate obtained by condensing the gas phase distilled from the gas phase distillation outlet 101 through the condenser into the liquid storage unit 2, and then stably feed the condensate into the extraction unit 3, which can improve the stability of the condensate supply in the extraction unit 3, improve the stability of the residual phase components in the extraction unit 3, and thus improve the stability of the distillation device. Exemplarily, the condenser can be arranged near the gas phase distillation outlet 101 of the distillation unit 1, or near the liquid inlet end of the liquid storage unit 2, to condense the gas phase material into a liquid state, which can improve the stability of the operation of the device.

[0056] As a specific embodiment of the present invention, a reflux branch 11 is disposed between the liquid storage unit outlet 202 and the extraction unit inlet 303 of the liquid storage unit 2. The flow of condensate passing through the reflux branch 11 is controlled by the liquid storage unit control valve 9, and the flow can be monitored by setting a liquid level recording and adjustment table. The liquid storage unit control valve 9 can be a three-way valve that can transfer all of the condensate in the liquid storage unit 2 to the extraction unit 3 for extraction and stratification, or transfer half of the condensate to the extraction unit 3 for extraction and stratification, while the other half flows directly back into the distillation unit 1 through the reflux branch 11. The provision of the reflux branch 11 ensures that the distillation unit 1 can maintain stable operation even if a malfunction occurs in the extraction unit 3.

[0057] As a specific embodiment of the present invention, the raffinate phase outlet 304 is disposed at the top of the extraction unit 3, above the extractant inlet 302. The distillate from the rectification unit 1 enters the bottom of the extraction unit 3 through the extraction unit inlet 303 at the bottom of the extraction unit 3, with components with lower density moving upward. The raffinate phase outlet 304 is disposed at the top of the extraction unit 3, preferably near the top, and the extractant inlet 302 is located below the raffinate phase outlet 304. This increases the contact time between the distillate and the extractant, thereby improving the removal of impurities.

[0058] As a specific embodiment of the present invention, the extraction unit 3 is further provided with an extraction phase outlet 301, which is located below the extraction unit inlet 303. When the extraction unit 3 is in operation, low-density components accumulate in the upper portion of the extraction unit 3, overflowing from the extraction phase outlet 304 into the recovery liquid storage unit 4. The extraction phase then passes through the extraction phase outlet 301 from the bottom of the extraction unit 3, extracting impurities and delivering them to other processing steps. The location of the extraction phase outlet 301 below the extraction unit inlet 303 allows for the timely separation of low-density components from impurities in the material flowing into the extraction unit inlet 303, preventing the low-density components from being discharged from the extraction phase outlet 301, thereby improving the extraction effect.

[0059] A second aspect of the present invention provides a vinyl acetate production system comprising the distillation apparatus described in the first aspect. The production system further comprises a vinyl acetate refining distillation tower, an acetaldehyde removal tower, an acetaldehyde refining tower stock liquid tank, an inhibitor storage tank, an acetic acid refining tower, and the like, connected in series according to the material flow. The production system can also be connected in series with equipment in the vinyl acetate synthesis process and other related processes according to the material flow.

[0060] As a relatively preferred embodiment of the present invention, see Figure 3Taking the distillation process of vinyl acetate as an example, the arrow in the figure indicates the direction of liquid flow, and a distillation device is provided, comprising a distillation unit 1, a liquid storage unit 2, and an extraction unit 3 connected in sequence, wherein the raffinate phase outlet 304 of the extraction unit 3 is connected to the reflux inlet 102 of the distillation unit 1; and further comprising a recovery liquid storage unit 4 connected to the raffinate phase outlet 304 of the extraction unit 3, wherein the recovery liquid storage unit outlet 401 of the recovery liquid storage unit 4 is connected to the reflux inlet 102 of the distillation unit 1 through a reflux pipeline 5. It also includes a reflux control valve 6 provided on the reflux pipeline 5 and a recovery liquid pump 7 provided between the reflux control valve 6 and the liquid outlet 401 of the recovery liquid storage unit; a pipeline between the raffinate phase outlet 304 and the liquid inlet 402 of the recovery liquid storage unit is provided with an inhibitor inlet; a pipeline between the liquid storage unit 2 and the extraction unit 3 is provided with a distillation pump 8 and a liquid storage unit control valve 9; a reflux inlet 102, a reaction liquid feed inlet 103 and a filtered clear liquid feed inlet 104 are provided on the distillation unit 1 from top to bottom; the distillation unit 1 is also provided with a gas phase distillation outlet 101, the gas phase distillation outlet 101 is provided at the top of the distillation unit 1, a condenser 10 is provided above the gas phase distillation outlet 101, a reaction liquid feed inlet 103 and a filtered clear liquid feed inlet 104 are provided on the side wall of the distillation unit 1; an extraction unit inlet 303 and an extractant inlet 302 are provided on the extraction unit 3, the liquid storage unit outlet 202 of the liquid storage unit 2 is connected to the extraction unit inlet 303, and the liquid storage unit outlet 202 of the liquid storage unit 2 is connected to the extraction unit inlet 303. The pipeline is connected to a reflux branch pipe 11, the outlet of which is connected to the reflux inlet 102 of the distillation unit 1. The extractant inlet 302 is located above the extraction unit inlet 303. The extraction unit 3 is also provided with an extract phase outlet 301, which is located below the extraction unit inlet 303. The raffinate phase outlet 304 is provided at the top of the extraction unit 3, which is located above the extractant inlet 302. Each control valve is provided with a corresponding liquid level recording and adjustment table.

[0061] When the above-mentioned distillation device is in operation, taking the distillation process of vinyl acetate as an example, the acetaldehyde content in the synthesis reaction liquid is 0.2-2.5wt%, the vinyl acetate content is 35.0-55.0wt%, the acetic acid content is 43.1-62.4wt%, the water content is 0.02-1.5wt%, and a small amount of acetylene and other impurities; the acetaldehyde content in the recovered liquid is 2.0-3.5wt%, the vinyl acetate content is 90.0-95.0wt%, the water content is 0.8-1.0wt% and other impurities; the acetaldehyde content in the filtered supernatant is 0.1-1.0wt%, the vinyl acetate content is 5.0-15.0wt%, the acetic acid content is 82.0-93.0wt%, the water content is 0.02-1.5wt% and other impurities. The synthesis reaction liquid enters the distillation unit 1 through the reaction liquid feed port 103, and the filtered supernatant enters the distillation unit 1 through the filtered supernatant feed port 104. After the synthesis reaction liquid and the filtered clear liquid are rectified for a period of time in the distillation unit 1, the gas phase at the top of the distillation unit 1 is distilled out through the gas phase distillation outlet 101 and enters the partial condenser (the cooling medium is circulating water) in the condenser 10 to be partially condensed. The uncondensed gas in the partial condenser is cooled and condensed by the full condenser (the cooling medium is chilled water) in the condenser 10. The uncondensed gas in the full condenser is cooled and condensed by the tail gas condenser (the cooling medium is chilled water) in the condenser 10. The vinyl acetate (VAC) content in the partial condenser condensate, the full condenser condensate and the tail gas condenser condensate is 80.0-92.0wt%, the acetaldehyde (Ald) content is 6.0-8.0wt%, and a small amount of water (H2O) and other impurities enter the liquid storage unit 2. The liquid level recorder in liquid storage unit 2 activates liquid storage unit control valve 9 and distillation pump 8 based on liquid control. Distillate from rectification unit 1, driven by distillation pump 8, flows through the feed flow recorder on extraction unit 3 and enters the bottom of extraction unit 3 from extraction unit inlet 303 at its lower portion. The extractant in extraction unit 3 is a low-temperature acetaldehyde aqueous solution from a synthetic water scrubber. The low-temperature acetaldehyde aqueous solution has a temperature of 5±5°C and contains 1.0-3.0 wt% acetaldehyde, 96.0-98.0 wt% water, and a small amount of acetylene. The low-temperature acetaldehyde aqueous solution enters through extractant inlet 302. Separation and purification are performed based on the principle that acetaldehyde is miscible with water and its solubility in vinyl acetate is lower than its solubility in water. Vinyl acetate, with its low density, moves upward. During this upward movement, acetaldehyde gradually dissolves in the low-temperature acetaldehyde aqueous solution, which is fed from the top of the tower and continuously flows toward the bottom. The acetaldehyde, dissolved in the low-temperature acetaldehyde aqueous solution, continues to move downward. The two streams of materials are alternately contacted in countercurrent through the packing in the extraction unit 3 , and the acetaldehyde in the distillate of the rectification unit 1 gradually diffuses into the water and falls into the lower part of the extraction unit 3 .The extract phase at the bottom of extraction unit 3 flows into the acetaldehyde refining tower raw liquid tank through the extract phase outlet 301. Vinyl acetate accumulates in the upper portion of extraction unit 3. Recovered liquid (raffinate phase) overflows from the raffinate outlet 304 and, along with the polymerization inhibitor, enters the recovered liquid storage unit 4. The liquid level recorder in the recovered liquid storage unit 4 controls the opening of the reflux control valve 6 based on the recovered liquid level in the recovered liquid storage unit 4, while simultaneously starting the recovered liquid pump 7. Based on the principle of material balance, the recovered liquid is fed through the reflux line 5 to the reflux inlet 102, achieving recovered liquid reflux. In this embodiment, the distillate from the rectification unit 1 has substantially similar component contents to the raffinate phase, both containing a large amount of vinyl acetate, a small amount of acetaldehyde, and a small amount of water. Furthermore, the corresponding vinyl acetate content in both is similar. Therefore, the raffinate phase can be used as reflux for the rectification unit 1.

[0062] For comparison, the applicant used the raffinate phase as the recovered liquid and mixed it with the synthesis reaction liquid for feeding, i.e., the process scheme of the prior art before the technical transformation of the present application. The quality comparison of vinyl acetate (VAC) distilled from the vinyl acetate refining distillation tower before and after the transformation is as follows:

[0063] project water purity Before renovation >0.08wt% 99.80wt% After transformation ≤0.03wt% 99.94wt%

[0064] The distillation device provided in the above preferred embodiment has the following advantages compared with the original device:

[0065] (1) The feed rate of the distillation unit 1 is reduced, and the steam consumption of the distillation unit 1 is correspondingly reduced. Based on the calculation that 5.4 tons of vinyl acetate (VAC) consumes 1 ton of steam, the above-mentioned distillation unit reduces the steam consumption by 1 ton per hour;

[0066] (2) The circulation volume of the light components in the distillation unit 1 is reduced, the load of the distillation section of the distillation unit 1 is reduced, and the tail gas volume of a single column is reduced from the previous 600-700Nm 3 / h dropped to 400-500Nm 3 / h, thereby reducing the load of cleaning and small recovery in the synthesis process.

[0067] The distillation apparatus provided in the preferred embodiment can improve the distillation quality and effect of vinyl acetate (VAC) distilled from the subsequent vinyl acetate refining distillation tower, reduce the amount of material heated in the distillation tower, and thereby reduce and stabilize the content of water and other impurities in vinyl acetate, thereby reducing energy consumption and production costs.

[0068] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention may be subjected to various simple modifications, including combining the specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not further describe various possible combinations. However, these simple modifications and combinations should also be considered as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A distillation device, characterized in that: The invention comprises a distillation unit (1) and an extraction unit (3), wherein the gas phase distillation outlet (101) of the distillation unit (1) is connected to the extraction unit inlet (303) of the extraction unit (3), and the raffinate phase liquid outlet (304) of the extraction unit (3) is connected to the reflux liquid inlet (102) of the distillation unit (1); the distillation device further comprises a recovery liquid storage unit (4) connected between the raffinate phase liquid outlet (304) and the reflux liquid inlet (102), the recovery liquid storage unit inlet (402) of the recovery liquid storage unit (4) is connected to the raffinate phase liquid outlet (304), and the recovery liquid storage unit outlet (401) is connected to the reflux liquid inlet (102) via a reflux pipeline (5).

2. The distillation device according to claim 1, characterized in that It also includes a reflux control valve (6) provided on the reflux pipeline (5) and a recovery liquid pump (7) provided between the reflux control valve (6) and the liquid outlet (401) of the recovery liquid storage unit.

3. The distillation device according to claim 1, characterized in that The pipeline between the raffinate phase outlet (304) and the recovery liquid storage unit inlet (402) is provided with an inhibitor inlet.

4. The distillation device according to any one of claims 1 to 3, characterized in that: The distillation unit (1) is further provided with a reaction liquid feed port (103) and a filtered clear liquid feed port (104); the reflux liquid feed port (102), the reaction liquid feed port (103) and the filtered clear liquid feed port (104) are arranged in sequence from top to bottom; the gas phase distillation outlet (101) is arranged at the top of the distillation unit (1); the reaction liquid feed port (103) and the filtered clear liquid feed port (104) are arranged on the side wall of the distillation unit (1).

5. The distillation device according to claim 4, characterized in that A reflux branch pipe (11) is provided on the pipeline between the gas phase distillation outlet (101) and the extraction unit inlet (303), and the outlet of the reflux branch pipe (11) is connected to the reflux liquid inlet (102).

6. The distillation device according to claim 5, characterized in that A liquid storage unit (2) is provided between the gas phase distillation outlet (101) and the extraction unit inlet (303).

7. The distillation device according to claim 6, characterized in that The reflux branch pipe (11) is arranged between the liquid storage unit liquid outlet (202) of the liquid storage unit (2) and the extraction unit inlet (303).

8. The distillation device according to claim 4, characterized in that The extraction unit (3) is also provided with an extractant liquid inlet (302), and the extractant liquid inlet (302) is located above the extraction unit inlet (303) and below the raffinate phase liquid outlet (304).

9. A vinyl acetate production system, characterized in that: The distillation device comprises the distillation device according to any one of claims 1 to 8.

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