A process for the purification of acetaldehyde

Abstract

The present application relates to a kind of acetaldehyde purification process.The device includes: extraction column, acetaldehyde refining column, acetaldehyde refining column in the middle, middle separation ware and middle heat exchanger.In the device, by the setting of middle separation ware height and three baffles, the residence time of middle liquid is increased, the layering effect is improved, acetic acid vinyl is extracted from the upper layer of middle separation ware, the lower layer of acetaldehyde water returns to the lower tray of acetaldehyde refining column, the extraction amount of acetaldehyde water is reduced, thereby the energy consumption is reduced;by middle heat exchanger, the temperature of acetaldehyde refining column middle liquid is reduced to 5-15 ℃, after further layering in acetaldehyde refining column distillation tank, into the extraction column kettle, the kettle temperature of extraction column is reduced from 25-30 ℃ to 10-15 ℃, the extraction effect of extraction column is improved;The kettle of acetaldehyde refining column is directly connected with steam for heating, the problem of stable heat supply affected by reboiler blockage is solved, the stable operation of acetaldehyde refining column is ensured, and the equipment investment is also reduced.

Description

[0001] This case is a divisional application of patent application number 202111669665.8, entitled "An Acetaldehyde Purification Device and Process Thereof". Technical Field

[0002] This invention belongs to the field of chemical equipment, and specifically relates to an acetaldehyde purification process. Background Technology

[0003] Currently, the main methods for preparing vinyl acetate include the ethylene method and the acetylene method. The acetylene method primarily involves two processes: fluidized bed and fixed bed gas-phase synthesis. In the fluidized bed gas-phase synthesis of vinyl acetate, a mixture of acetylene and acetic acid gases reacts at a certain temperature in a fluidized bed reactor using activated carbon as a carrier and zinc acetate as a catalyst. The reacted gas mixture exiting the reactor passes through a powder separator to separate the catalyst powder, then enters a gas separation tower. The second stage of the separation tower collects the synthesis reaction liquid, while the first stage collects a filtrate containing a large amount of activated carbon powder with zinc acetate. This filtrate is then purified by distillation and filtration to obtain a clear filtrate. The synthesis reaction liquid and the clear filtrate are then processed in a vinyl acetate coarse separation tower. The bottom material is further purified to obtain vinyl acetate, while the top material, containing vinyl acetate, acetaldehyde, and water, enters an extraction tower and an acetaldehyde purification tower for further purification to obtain the product acetaldehyde. To recover vinyl acetate from the acetaldehyde purification tower, it can be obtained by separating it from the middle section of the acetaldehyde purification tower. Because the midstream extract of the acetaldehyde refining tower contains acetaldehyde, vinyl acetate, and water, direct vapor-phase extraction of the midstream extract presents the following problems: First, the extraction volume is large; second, the temperature of the midstream extract in the acetaldehyde refining tower is 35-60℃, which is high and makes it difficult for vinyl acetate and acetaldehyde water in the midstream extract to separate, thus affecting the extraction efficiency of the extraction tower if the midstream extract is directly extracted and cooled to 5-15℃ to separate vinyl acetate and acetaldehyde water before re-distillation to recover vinyl acetate, a large amount of cooling is required, resulting in increased energy consumption. Furthermore, the acetaldehyde refining tower involved in the above process uses a reboiler for heat exchange; vinyl acetate or polyaldehydes in the feed can easily clog the reboiler, affecting not only the heat exchange efficiency but also the stable operation of the acetaldehyde refining tower. In addition, the extraction tower requires a large amount of demineralized water as the extractant to separate acetaldehyde and vinyl acetate. The operating temperature of the extraction tower is relatively low, at 5-15℃, while the temperature of the demineralized water is usually 25-35℃. A large amount of chilled water is needed for cooling, otherwise the extraction effect of the extraction tower will be affected. Furthermore, the use of demineralized water will also cause a large amount of wastewater to be generated in the bottom of the extraction tower. Summary of the Invention

[0004] The first technical problem this invention aims to solve is that the acetaldehyde refining tower not only produces a large volume of collected liquid, but also suffers from difficulty in separating vinyl acetate and water due to the high temperature of the collected liquid. This necessitates a large amount of cooling to lower the collected liquid to 5-15°C to separate the vinyl acetate and water before re-distillation to recover vinyl acetate, ultimately increasing energy consumption. The second technical problem this invention aims to solve is that the acetaldehyde refining tower uses a reboiler for heating, but the vinyl acetate or polyaldehydes in the feed clog the reboiler, affecting both heat exchange efficiency and the stable operation of the acetaldehyde refining tower. The third technical problem this invention aims to solve is that the extraction tower requires a large amount of demineralized water as the extractant to separate acetaldehyde and vinyl acetate. The demineralized water requires a large amount of chilled water for cooling; without cooling, the extraction efficiency of the extraction tower is affected, and the use of demineralized water also generates a large amount of wastewater in the extraction tower bottom. Therefore, this invention provides an acetaldehyde purification device, and further provides an acetaldehyde purification process using this device.

[0005] This invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides an acetaldehyde purification apparatus, which includes: an extraction tower, an acetaldehyde refining tower, a first condenser for the acetaldehyde refining tower, a second condenser for the acetaldehyde refining tower, an acetaldehyde refining tower distillation tank, an acetaldehyde refining tower midstream collection tank, a wastewater treatment system, a midstream collection separator, and a midstream collection heat exchanger.

[0007] Specifically, the distillate pipeline from the top of the vinyl acetate crude fractionation tower is connected to the lower inlet of the extraction tower; the upper inlet of the extraction tower is connected to the acetaldehyde water synthesis pipeline; the bottom outlet of the extraction tower is connected to the inlet of the acetaldehyde refining tower; the extraction tower recovery liquid pipeline from the upper outlet of the extraction tower is connected to the inlet of the vinyl acetate crude fractionation tower; the top outlet of the acetaldehyde refining tower is connected to the inlet of the first condenser of the acetaldehyde refining tower; the bottom outlet of the acetaldehyde refining tower is connected to the wastewater treatment system; the upper outlet of the first condenser of the acetaldehyde refining tower is connected to the gas phase inlet of the second condenser of the acetaldehyde refining tower; and the condensate outlet pipeline of the first condenser of the acetaldehyde refining tower is connected to the condensate outlet pipeline of the second condenser of the acetaldehyde refining tower (preferably...). The distillation tank of the acetaldehyde refining tower (after confluence) is connected to the inlet of the distillation tank. The outlet pipeline of the distillation tank is divided into two branches: one connects to the acetaldehyde pipeline, and the other returns to the top of the acetaldehyde refining tower. A midstream separator for midstream liquid phase collection is installed in the middle of the acetaldehyde refining tower. The acetaldehyde water outlet (lower aqueous phase outlet) of the midstream separator returns to the acetaldehyde refining tower. The vinyl acetate liquid outlet (upper outlet) of the midstream separator is connected to the inlet of the midstream heat exchanger. The outlet of the midstream heat exchanger is connected to the top inlet of the midstream tank of the acetaldehyde refining tower. The upper outlet of the midstream tank of the acetaldehyde refining tower is connected to the lower inlet of the extraction tower via a pipeline. The bottom outlet of the intermediate tank is connected to the wastewater treatment system. Preferably, the bottom of the acetaldehyde refining tower is connected to the steam inlet pipeline.

[0008] Preferably, the intermediate separation unit is located at the 25th-30th tray of the acetaldehyde refining tower, more preferably at the 29th-30th tray.

[0009] Preferably, a pipe cap is installed at the 25th-30th tray of the acetaldehyde refining tower, and the bottom ring of the pipe cap is sealed to the acetaldehyde refining tower. An intermediate separation device is connected to the side of the tower wall connected to the connection of the acetaldehyde refining tower.

[0010] Preferably, the height of the intermediate sampling separator is 800-1000mm, for example, about 912mm.

[0011] Preferably, the intermediate-stage separator employs three baffles. The first baffle is located at the top of the inner side of the intermediate-stage separator, the second baffle is located at the bottom of the inner side of the intermediate-stage separator, and the third baffle is located at the top of the inner side of the intermediate-stage separator. The second baffle intersects with the first and third baffles (preferably, the first, second, and third baffles are all vertically arranged), effectively separating vinyl acetate and acetaldehyde water into layers. The intermediate-stage separator in the acetaldehyde refining tower uses three layers of baffles (three baffles) and an interface regulator to control the stratification of vinyl acetate and acetaldehyde water. After stratification, the upper layer of vinyl acetate liquid enters the intermediate-stage heat exchanger and then enters the intermediate-stage tank of the acetaldehyde refining tower, while the lower layer of acetaldehyde water returns to the acetaldehyde refining tower. In the acetaldehyde refining tower, a cap is added at the 25th-30th tray. The bottom of the cap is sealed to the acetaldehyde refining tower. An intermediate recovery separator is connected to the side of the tower wall at the connection point, ensuring that all the condensed liquid falling from the upper tray (e.g., tray 30) at the cap location enters the intermediate recovery separator. The gas phase continues to rise from the cap, and the condensed liquid is collected and flows into the intermediate recovery separator. When the liquid reaches the first baffle, the aqueous phase flows into the second baffle through the gap below the baffle. When the intermediate liquid reaches the upper edge of the second baffle, the baffle extends the stratification time. After stratification, the upper vinyl acetate liquid overflows into the third baffle. By adjusting the interface regulator, the upper vinyl acetate liquid is collected through the outlet between the second and third baffles. The lower acetaldehyde water returns to the lower tray (e.g., tray 29) of the acetaldehyde refining tower after passing through the third baffle, ensuring the stratification effect and reducing the amount of acetaldehyde water collected. That is, the rising airflow enters, for example, a 30-layer tray through the pipe cap, and the condensate is separated into layers by the intermediate-stage separator. The interface height between the upper vinyl acetate liquid and the lower acetaldehyde water is adjusted by the intermediate-stage interface regulator to facilitate the extraction of the upper vinyl acetate liquid. The lower aqueous phase (acetaldehyde water) flows back to the acetaldehyde purification tower (for example, a 29-layer tray) through the acetaldehyde water outlet. The upper vinyl acetate is connected to the inlet of the intermediate-stage heat exchanger through a pipeline via the upper ethyl acetate liquid outlet.

[0012] Preferably, the produced fluid from the intermediate-stage recovery process is cooled by heat exchange through an intermediate-stage heat exchanger.

[0013] Preferably, an interface regulator is installed inside the intermediate recovery separator. By setting the interface regulator, the stratification height of the intermediate recovery liquid inside the intermediate recovery separator is adjusted, so that the upper layer of vinyl acetate liquid is extracted through the outlet at the top of the intermediate recovery separator and enters the intermediate recovery heat exchanger.

[0014] Preferably, chilled water is introduced into the heat exchanger. The upper layer of vinyl acetate (35-60℃) enters the heat exchanger and is cooled by chilled water to a temperature of 5-15℃. After further stratification in the distillation tank of the acetaldehyde refining column, it enters the bottom of the extraction column, reducing the bottom temperature of the extraction column from 25-30℃ to 10-15℃, thereby improving the extraction efficiency of the extraction column.

[0015] Preferably, the bottom outlet of the extraction tower is connected to the inlet of the acetaldehyde refining tower after passing through a heat exchanger. The heat exchanger is preferably a condenser from the vinyl acetate refining tower to utilize the waste heat from the distillation vapor phase of the vinyl acetate refining tower. Specifically: the top distillation vapor phase outlet line of the vinyl acetate refining tower is connected to the upper inlet of the vinyl acetate refining tower condenser; the condensate outlet of the vinyl acetate refining tower condenser is connected to the vinyl acetate condensate outlet line; the lower inlet of the vinyl acetate refining tower condenser is connected to the bottom outlet of the extraction tower; and the upper outlet of the vinyl acetate refining tower condenser is connected to the inlet of the acetaldehyde refining tower. By exchanging heat with the distillation vapor phase of the vinyl acetate refining tower, the feed temperature of the acetaldehyde refining tower is increased from 5-15℃ to 40-60℃, reducing the steam consumption of the acetaldehyde refining tower and the circulating water consumption of the vinyl acetate refining tower.

[0016] Secondly, the present invention provides an acetaldehyde purification process, comprising the following steps: a reaction solution for synthesizing vinyl acetate by the calcium carbide acetylene method (components: 45-50% acetic acid, 45-50% vinyl acetate, 1.0-2.5% acetaldehyde, 0.8-1.8% acetylene, 0.01-0.1% water, a small amount of carbon powder and zinc acetate, temperature 10-40℃), and a filtered clear liquid (components: 85-95% acetic acid, 5-10% vinyl acetate, 0.01-0.1% water, containing carbon powder and zinc acetate, temperature 85-95℃) are distilled in a vinyl acetate crude fractionation column to obtain a distillate from the top of the vinyl acetate crude fractionation column (containing 85-90% vinyl acetate, 5-10% acetaldehyde and a small amount of water 1.0-2.0%, etc., temperature 5-15℃). The distillate from the top of the vinyl acetate crude fractionation column is then used as one of the raw materials to enter the lower part of the extraction column. The function of the extraction tower is to initially separate acetaldehyde and vinyl acetate. The feed to the extraction tower includes the distillate from the vinyl acetate crude fractionation tower (temperature 5-15℃, containing 85-95% vinyl acetate, 5-10% acetaldehyde, and a small amount of water 1.0-2.0%) and the upper layer of vinyl acetate collected from the acetaldehyde refining tower after heat exchange in the intermediate heat exchanger (temperature 5-15℃, containing 60-80% vinyl acetate, 10-20% acetaldehyde, and 5-10% water). Acetaldehyde water (low-temperature acetaldehyde water from the synthesis water washing tower, acetaldehyde content 2-5%, temperature 0-10℃) is added as the extractant at the top inlet of the extraction tower. Because acetaldehyde is miscible with water, while the solubility of acetaldehyde in vinyl acetate and vinyl acetate in water is very low, the distillate from the vinyl acetate crude fractionation tower is added from the bottom of the extraction tower. The vinyl acetate, which has a lower density, moves upward, while the acetaldehyde, which has a higher density, gradually dissolves in the acetaldehyde water added from the top of the tower and moves downward. The two materials alternately pass through the packing in the tower, contacting each other countercurrently. The acetaldehyde gradually diffuses into the water and falls to the bottom of the tower. After extraction, the bottom component of the extraction tower (components: water 80-90%, acetaldehyde 5.0-10.0%, vinyl acetate 1.0-5.0%, temperature 5-15℃) exchanges heat with the distillate phase from the vinyl acetate refining tower in the condenser of the vinyl acetate refining tower. After the feed temperature is increased to 40-60℃, it enters the middle section of the acetaldehyde refining tower. The top component of the extraction tower (components: vinyl acetate 80-90%, acetaldehyde 1.0-5.0%, water 0.5-1.5%, temperature 5-15℃) is returned to the vinyl acetate coarse separation tower as the recovery liquid from the extraction tower. The feed to the acetaldehyde refining tower is the bottom liquid from the extraction tower. The function of the acetaldehyde refining tower is to refine acetaldehyde and recover vinyl acetate.After treatment in the acetaldehyde refining tower, the liquid phase in the middle section of the tower is collected by the intermediate recovery separator (35-60℃). The acetaldehyde water separated by the intermediate recovery separator is returned to the acetaldehyde refining tower. The upper layer of vinyl acetate liquid separated by the intermediate recovery separator enters the intermediate recovery heat exchanger for heat exchange and cooling to 5-15℃, and then enters the top of the intermediate recovery tank of the acetaldehyde refining tower. The upper outlet component of the intermediate recovery tank of the acetaldehyde refining tower (i.e., the stratified upper vinyl acetate liquid) enters the lower part of the extraction tower. The bottom component of the acetaldehyde refining tower and the bottom outlet component of the intermediate recovery tank of the acetaldehyde refining tower both enter the wastewater treatment system. The top component of the acetaldehyde refining tower (16-20℃) enters the inlet of the first condenser of the acetaldehyde refining tower and is cooled by chilled water (temperature -6~-3℃). After condensation, the vapor phase outlet component of the first condenser of the acetaldehyde refining tower enters the inlet of the second condenser of the acetaldehyde refining tower (cooled to -5 to 5°C in the second condenser of the acetaldehyde refining tower) (the reason for setting up two condensers is that the cooling capacity of one condenser is insufficient). The outlet component of the second condenser of the acetaldehyde refining tower (pure acetaldehyde, acetaldehyde ≥ 98.5%, -5 to 5°C) and the condensate outlet component of the first condenser of the acetaldehyde refining tower are combined and enter the distillation tank of the acetaldehyde refining tower. A portion of the qualified acetaldehyde (acetaldehyde ≥ 98.5%) can be collected from the bottom outlet of the distillation tank of the acetaldehyde refining tower and sent for sale. The unqualified (acetaldehyde < 98.5%) can be returned to the acetaldehyde refining tower for reprocessing. The other portion is returned to the top of the acetaldehyde refining tower 3 as reflux.

[0017] In the above process, synthetic acetaldehyde water (acetaldehyde water from the synthesis process, with an acetaldehyde content of 2-5% and a temperature of 0-10℃) is used as the extractant at the top of the extraction tower. Existing extraction towers use 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℃, a large amount of chilled water is needed to cool the demineralized water (temperature 25-35℃) to the operating temperature of the extraction tower; otherwise, the extraction efficiency will be affected. Furthermore, using demineralized water also generates a large amount of wastewater in the bottom of the extraction tower. Using synthetic acetaldehyde water (acetaldehyde water from the synthesis process, with an acetaldehyde content of 2-5% and a temperature of 0-10℃) as the extractant at the top of the extraction tower not only reduces the consumption of demineralized water in the extraction tower but also allows for the recovery of acetaldehyde from the synthetic acetaldehyde water.

[0018] In the above process, acetaldehyde water and vinyl acetate solution form an interface in the tower due to their different densities. The interface between acetaldehyde water and vinyl acetate solution is controlled at a specified position by an interface regulator in the extraction tower.

[0019] In the above process, the acetylene tail gas at the top of the extraction tower is returned to the synthesis process.

[0020] In the above process, since vinyl acetate has low solubility in water at low temperatures, and low temperatures can prevent the acetaldehyde dissolved in water from escaping, the extraction tower is equipped with a jacket, which is circulated with chilled water for cooling to maintain a low temperature (5-15℃) throughout the tower and improve the selectivity of water for acetaldehyde.

[0021] In the above process, the liquid phase in the middle of the acetaldehyde refining tower is collected. The collected liquid is separated into an upper layer of vinyl acetate and a lower layer of acetaldehyde water in the middle collector separator. The upper layer of vinyl acetate is collected through the middle outlet of the middle collector separator, and the lower layer of acetaldehyde water is returned to the acetaldehyde refining tower. The vinyl acetate liquid (temperature 30-60℃) is cooled to 5-15℃ by heat exchange with chilled water in the middle collector heat exchanger, and then enters the middle collector tank of the acetaldehyde refining tower. After separation, the upper layer of vinyl acetate is pumped from the middle collector of the acetaldehyde refining tower to the extraction tower for feeding. The reason for setting up the intermediate heat exchanger and the intermediate collection tank of the acetaldehyde refining tower is that the upper layer of vinyl acetate extracted from the intermediate separator still contains a small amount of acetaldehyde and water. Since high temperature is not conducive to the separation of vinyl acetate and acetaldehyde water, it is necessary to exchange heat through the intermediate heat exchanger to separate the vinyl acetate and acetaldehyde water into layers. After the heat exchange cools the liquid to 5-15℃, it enters the intermediate collection tank of the acetaldehyde refining tower. After separation, the upper layer of vinyl acetate enters the bottom of the extraction tower, which lowers the temperature of the bottom of the extraction tower from 25-30℃ to 10-15℃, thereby improving the extraction effect of the extraction tower.

[0022] In the above process, the wastewater from the acetaldehyde refining tower is sent to the wastewater treatment system, and the treated wastewater is sent to the filtration chamber to wash the filter.

[0023] In the above process, 1.0-5.0% alkali solution is added to the feed of the acetaldehyde refining tower to control the feed pH value at 6.5-7.5, which prevents acetaldehyde from self-polymerizing in the acetaldehyde refining tower and reduces the COD of the tower bottom from 5000-7000 to 1000-3000, so that the wastewater from the acetaldehyde refining tower bottom meets the requirements for being sent to the wastewater treatment system.

[0024] In the above process, the pH value of the synthesized acetaldehyde water is controlled at 6.5-7.5 to prevent the self-polymerization of the synthesized acetaldehyde water and improve the extraction effect of the extraction tower.

[0025] In the above process, the feed to the acetaldehyde refining tower undergoes heat exchange through the distillate vapor phase of the vinyl acetate refining tower. The feed temperature to the acetaldehyde refining tower is 5-15℃. Direct feeding increases steam consumption. After heat exchange, the feed temperature to the acetaldehyde refining tower is increased to 40-60℃, reducing the steam consumption of the acetaldehyde refining tower and the circulating water consumption of the condenser of the vinyl acetate refining tower.

[0026] In the above process, after the temperature of the liquid collected in the acetaldehyde refining tower is reduced to 5-15℃, the temperature of the extraction tower bottom is reduced from 25-30℃ to 10-15℃ to improve the extraction effect of the extraction tower.

[0027] The technical solution of the present invention has the following advantages:

[0028] (1) In the acetaldehyde purification device of the present invention, by setting a mid-stage separator with three baffles in the acetaldehyde refining tower at the 25th-30th layer, the residence time of the mid-stage liquid (i.e., the middle component of the acetaldehyde refining tower) is increased, and the stratification effect of the upper layer of vinyl acetate and the lower layer of acetaldehyde water is improved; by setting an interface regulator to adjust the stratification interface height of the upper layer of vinyl acetate and the lower layer of acetaldehyde water in the mid-stage separator, the upper layer of vinyl acetate is collected through the outlet above the mid-stage separator and enters the mid-stage heat exchanger; the mid-stage separator collects the upper layer of vinyl acetate, and the lower layer of acetaldehyde water phase returns to the lower tray of the acetaldehyde refining tower, reducing the amount of acetaldehyde water collected, thereby reducing energy consumption; in addition, by collecting vinyl acetate through the mid-stage liquid phase, the self-polymerization of vinyl acetate after falling into the tower bottom and causing blockage of the tower bottom and tray is avoided, thereby reducing energy consumption.

[0029] (2) In the acetaldehyde purification device of the present invention, the upper layer of vinyl acetate extracted by the intermediate separation enters the intermediate heat exchanger and is cooled by chilled water to reduce the temperature to 5-15°C. After further stratification in the distillation tank of the acetaldehyde refining tower, the upper layer of vinyl acetate enters the bottom of the extraction tower, reducing the bottom temperature of the extraction tower from 25-30°C to 10-15°C, thereby improving the extraction effect of the extraction tower.

[0030] (3) In the acetaldehyde purification device of the present invention, the bottom of the acetaldehyde refining tower is directly heated by steam, which reduces the investment in equipment (reboiler), solves the problem of the reboiler blockage affecting the stable supply of heat, ensures the stable operation of the acetaldehyde refining tower, and adopts the method of direct steam heating, which can preheat the acetaldehyde refining tower before feeding, replace the air in the tower, and prevent vinyl acetate in the material entering the acetaldehyde refining tower from self-polymerizing when it falls into the bottom of the tower due to the low temperature of the bottom of the tower.

[0031] (4) In the acetaldehyde purification device of the present invention, the top of the extraction tower uses synthetic acetaldehyde water (acetaldehyde water from the synthesis process, with an acetaldehyde content of 2-5% and a temperature of 0-10℃) as the extractant, which not only reduces the consumption of demineralized water in the extraction tower, but also allows for the recovery of acetaldehyde from the synthetic acetaldehyde water. Attached Figure Description

[0032] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0033] Figure 1 This is a schematic diagram of the acetaldehyde purification device in Embodiment 1 of the present invention.

[0034] Figure 2 This is an enlarged view of the internal structure of the mid-process separator in Embodiment 1 of the present invention.

[0035] Wherein: 1—Extraction tower, 2—Acetaldehyde refining tower, 3—Mid-stage separator, 4—Mid-stage heat exchanger, 5—Mid-stage tank of acetaldehyde refining tower, 6—First condenser of acetaldehyde refining tower, 7—Second condenser of acetaldehyde refining tower, 8—Distillation tank of acetaldehyde refining tower, 9—Condenser of vinyl acetate refining tower, 10—Wastewater treatment system, 11—Pipe cap, 12—First baffle plate, 13—Second baffle plate, 14—Third baffle plate. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In the description of the invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] like Figure 1 As shown, the acetaldehyde purification apparatus of the present invention includes: an extraction tower 1, an acetaldehyde refining tower 2, an acetaldehyde refining tower first condenser 6, an acetaldehyde refining tower second condenser 7, an acetaldehyde refining tower distillation tank 8, an acetaldehyde refining tower midstream collection tank 5, a wastewater treatment system 10, a midstream collection separator 3, and a midstream collection heat exchanger 4.

[0039] Specifically, the distillate pipeline from the top of the vinyl acetate crude fractionation tower is connected to the lower inlet of extraction tower 1; the upper inlet of extraction tower 1 is connected to the acetaldehyde water synthesis pipeline; the bottom outlet of extraction tower 1 is connected to the (middle) inlet of acetaldehyde refining tower 2; the extraction tower recovery liquid pipeline from the upper outlet of extraction tower 1 is connected to the inlet of the vinyl acetate crude fractionation tower; the top outlet of acetaldehyde refining tower 2 is connected to the inlet of the first condenser 6 of the acetaldehyde refining tower; the bottom outlet of acetaldehyde refining tower 2 is connected to the wastewater treatment system 10; the gas phase outlet of the first condenser 6 of the acetaldehyde refining tower is connected to the inlet of the second condenser 7 of the acetaldehyde refining tower; and the condensate outlet pipeline of the first condenser 6 of the acetaldehyde refining tower is connected to the second condenser 7 of the acetaldehyde refining tower. The condensate outlet pipelines are merged and connected to the inlet of the acetaldehyde refining tower distillation tank 8. The outlet pipeline of the acetaldehyde refining tower distillation tank 8 is divided into two lines: one line is connected to the acetaldehyde pipeline, and the other line returns to the top of the acetaldehyde refining tower 2. A midstream separator 3 is installed in the middle of the acetaldehyde refining tower 2. The lower acetaldehyde water outlet of the midstream separator 3 returns to the acetaldehyde refining tower 2. The upper vinyl acetate liquid outlet of the midstream separator 3 is connected to the inlet of the midstream heat exchanger 4. The outlet of the midstream heat exchanger 4 is connected to the top inlet of the midstream tank 5 of the acetaldehyde refining tower. The upper outlet of the midstream tank 5 of the acetaldehyde refining tower is connected to the lower inlet of the extraction tower 1 via a pipeline. The bottom outlet of the midstream tank 5 of the acetaldehyde refining tower is connected to the wastewater treatment system 10.

[0040] In another preferred embodiment, the bottom of the acetaldehyde refining tower 2 is connected to a steam inlet line.

[0041] In yet another preferred embodiment, the intermediate separation unit 3 is located at the 25th-30th tray of the acetaldehyde refining tower 2, preferably at the 29th-30th tray.

[0042] In another preferred embodiment, such as Figure 2 As shown, a pipe cap 11 is installed at the 29th-30th tray of the acetaldehyde refining tower 2. The bottom ring of the pipe cap 11 is sealed and welded to the acetaldehyde refining tower 3. The intermediate separator 3 is welded to the side of the tower wall connected to the weld at the weld of the acetaldehyde refining tower 2.

[0043] In another preferred embodiment, the height of the intermediate sampling separator 3 is 800-1000 mm, for example, about 912 mm. Preferably, as Figure 2As shown, the intermediate mining separator 3 employs three baffles. The first baffle 12 is located at the top of the inner side of the intermediate mining separator 3, the second baffle 13 is located at the bottom of the inner side of the intermediate mining separator 3, and the third baffle 14 is located at the top of the inner side of the intermediate mining separator 3. The second baffle 13 intersects with the first baffle 12 and the third baffle 14. Preferably, the first baffle 12, the second baffle 13, and the third baffle 14 are all vertically arranged. A pipe cap 11 is installed between layers 25 and 30 of the acetaldehyde refining tower 2. The lower end of the pipe cap 11 is completely welded to the acetaldehyde refining tower 2. The intermediate-stage separator 3 is welded to the side of the tower wall adjacent to the weld. The rising airflow enters, for example, the 30th layer of the tower through the pipe cap 11. After the condensate passes through the intermediate-stage separator 3 and is separated into layers, the residence time is extended by the baffle plate to facilitate the separation of the upper vinyl acetate liquid and acetaldehyde water. The interface height is adjusted by the intermediate-stage interface regulator. The lower aqueous phase (acetaldehyde water) flows back to the acetaldehyde refining tower 2 (for example, the 29th layer of the tower) through the acetaldehyde water outlet (flange pipe). The upper vinyl acetate is connected to the inlet of the intermediate-stage heat exchanger 4 through the upper ethyl acetate liquid outlet.

[0044] In yet another preferred embodiment, chilled water is introduced into the heat exchanger 4.

[0045] In another preferred embodiment, the bottom outlet of extraction column 1 is connected to the inlet of acetaldehyde purification column 2 after passing through a heat exchanger. The heat exchanger is preferably the vinyl acetate purification column condenser 9, to utilize the waste heat from the distillation vapor phase of the vinyl acetate purification column. Specifically: the top distillation vapor phase outlet line of the vinyl acetate purification column is connected to the upper inlet of the vinyl acetate purification column condenser 9; the condensate outlet of the vinyl acetate purification column condenser 9 is connected to the vinyl acetate condensate outlet line; the lower inlet of the vinyl acetate purification column condenser 9 is connected to the bottom outlet of extraction column 1; and the upper outlet of the vinyl acetate purification column condenser 9 is connected to the inlet of acetaldehyde purification column 2.

[0046] Example 1

[0047] like Figure 1As shown, the acetaldehyde purification apparatus of this embodiment includes: an extraction tower 1, an acetaldehyde refining tower 2, an acetaldehyde refining tower first condenser 6, an acetaldehyde refining tower second condenser 7, an acetaldehyde refining tower distillation tank 8, an acetaldehyde refining tower midstream recovery tank 5, a wastewater treatment system 10, a midstream recovery separator 3, and a midstream recovery heat exchanger 4; wherein, the distillate pipeline from the top of the vinyl acetate crude fractionation tower is connected to the lower inlet of the extraction tower 1, the upper inlet of the extraction tower 1 is connected to the synthetic acetaldehyde water pipeline, the bottom outlet of the extraction tower 1 is connected to the middle inlet of the acetaldehyde refining tower 2, the extraction tower recovery liquid pipeline from the upper outlet of the extraction tower 1 is connected to the inlet of the vinyl acetate crude fractionation tower, the top outlet of the acetaldehyde refining tower 2 is connected to the inlet of the acetaldehyde refining tower first condenser 6, the bottom outlet of the acetaldehyde refining tower 2 is connected to the wastewater treatment system 10, and the gas phase outlet of the acetaldehyde refining tower first condenser 6 is connected to the inlet of the acetaldehyde refining tower second condenser 7. Next, the condensate outlet pipeline of the first condenser 6 of the acetaldehyde refining tower and the condensate outlet pipeline of the second condenser 7 of the acetaldehyde refining tower merge and connect to the inlet of the distillation tank 8 of the acetaldehyde refining tower. The outlet pipeline of the distillation tank 8 of the acetaldehyde refining tower is divided into two paths: one path connects to the acetaldehyde product pipeline, and the other path returns to the top of the acetaldehyde refining tower 2. A midstream separator 3 is installed at the 30th tray in the middle of the acetaldehyde refining tower 2. The lower acetaldehyde aqueous phase outlet of the midstream separator 3 returns to the 29th tray of the acetaldehyde refining tower 2. The upper vinyl acetate liquid outlet of the midstream separator 3 is connected to the inlet of the midstream heat exchanger 4 (the midstream separator 3 has two outlets). The outlet of the midstream heat exchanger 4 is connected to the top inlet of the midstream tank 5 of the acetaldehyde refining tower. The upper outlet of the midstream tank 5 of the acetaldehyde refining tower is connected to the lower inlet of the extraction tower 1 via a pipeline. The bottom outlet of the midstream tank 5 of the acetaldehyde refining tower is connected to the wastewater treatment system 10.

[0048] Among them, such as Figure 2 As shown, a pipe cap 11 is installed at the 30th tray of the acetaldehyde refining tower 2. The bottom ring of the pipe cap 11 is sealed and welded to the acetaldehyde refining tower 2. The intermediate separator 3 is welded to the side of the tower wall connected to the weld at the weld of the acetaldehyde refining tower 2.

[0049] The bottom of the acetaldehyde refining tower 2 is connected to the steam inlet pipeline.

[0050] Among them, the height of the intermediate-scale separator 3 is 912mm, such as Figure 2 As shown, the intermediate mining separator 3 uses three baffles. The first baffle 12 is located at the top of the inner side of the intermediate mining separator 3, the second baffle 13 is located at the bottom of the inner side of the intermediate mining separator 3, and the third baffle 14 is located at the top of the inner side of the intermediate mining separator 3. The second baffle 13 intersects with the first baffle 12 and the third baffle 14. The first baffle 12, the second baffle 13, and the third baffle 14 are all vertically arranged.

[0051] Among them, the interface regulator is installed in the middle mining separator 3.

[0052] Chilled water is introduced into heat exchanger 4.

[0053] The bottom outlet of extraction column 1 is connected to the inlet of acetaldehyde refining column 2 via a heat exchanger. The heat exchanger is preferably the vinyl acetate refining column condenser 9, to utilize the waste heat from the distillation vapor phase of the vinyl acetate refining column. Specifically: the top distillation vapor phase outlet line of the vinyl acetate refining column is connected to the upper inlet of the vinyl acetate refining column condenser 9; the condensate outlet of the vinyl acetate refining column condenser 9 is connected to the vinyl acetate condensate outlet line; the lower inlet of the vinyl acetate refining column condenser 9 is connected to the bottom outlet of extraction column 1; and the upper phase outlet of the vinyl acetate refining column condenser 9 is connected to the inlet of acetaldehyde refining column 2.

[0054] The above-mentioned apparatus is used to purify acetaldehyde from the reaction solution and filtrate of the calcium carbide acetylene synthesis process according to the following procedure:

[0055] The reaction solution for synthesizing vinyl acetate via the calcium carbide-acetylene method (components: acetic acid 45-50%, vinyl acetate 45-50%, acetaldehyde 1.0-2.5%, acetylene 0.8-1.8%, water 0.01-0.1%, small amount of carbon powder and zinc acetate, temperature 10-40℃), and the filtered clear liquid (components: acetic acid 85-95%, vinyl acetate 5-10%, water 0.01-0.1%, containing carbon powder and zinc acetate, temperature 85-95℃). After being purified by the vinyl acetate crude fractionation column, the distillate from the top of the vinyl acetate crude fractionation column (containing 85-95% vinyl acetate, 5-10% acetaldehyde, and a small amount of water 1.0-2.0%, etc., at a temperature of 5-15℃) is obtained. This distillate then enters the lower part of extraction column 1 (the function of extraction column 1 is to initially separate acetaldehyde and vinyl acetate. Its feed includes the distillate from the vinyl acetate crude fractionation column (temperature 5-15℃, containing 85-95% vinyl acetate, 5-10% acetaldehyde, and a small amount of water 1.0-2.0%, etc., at a temperature of 5-15℃). The process involves adding an extractant (containing 5-95% vinyl acetate, 5-10% acetaldehyde, and a small amount of water, 1.0-2.0%) from the acetaldehyde refining tower's separator and the upper layer of vinyl acetate (temperature 40-60℃, containing 60-80% vinyl acetate, 10-20% acetaldehyde, and 5-10% water, etc.) to the top inlet of extraction tower 1. This extractant is then used to synthesize acetaldehyde water (low-temperature acetaldehyde water from the synthesis water washing tower, acetaldehyde content 2-5%, temperature 0-10℃). Since acetaldehyde is miscible with water, but its solubility in vinyl acetate and vinyl acetate in water is very low, the distillate from the vinyl acetate coarse fractionation tower is added from the bottom of extraction tower 1. The lower density vinyl acetate in this solution moves upwards, while the higher density acetaldehyde in the solution gradually dissolves in the acetaldehyde water added from the top of the tower, moving downwards. The two materials alternately pass through the packing material in the tower, contacting each other counter-currently. The acetaldehyde gradually diffuses into the water and settles at the bottom of the tower.After extraction, the bottom component of extraction column 1 (components: water 80-90%, acetaldehyde 5.0-10.0%, vinyl acetate 1.0-5.0%, temperature 5-15℃) exchanges heat with the distillate phase from the vinyl acetate refining column in the condenser 9 of the vinyl acetate refining column. After the feed temperature is increased to 40-60℃, it enters the middle section of the acetaldehyde refining column 2. The top component of extraction column 1 (components: vinyl acetate 80-90%, acetaldehyde 1.0-5.0%, water 0.5-1.5%, temperature 5℃) enters the middle section of the acetaldehyde refining column 2. The liquid from the acetaldehyde purification tower (at -15℃) is used as the recovered liquid in the extraction tower and enters the vinyl acetate coarse separation tower. The middle liquid phase of the acetaldehyde purification tower 2 is collected by the intermediate recovery separator 3 (35-60℃). After stratification, the lower layer of acetaldehyde water returns to the acetaldehyde purification tower 2, and the upper layer of vinyl acetate liquid enters the intermediate recovery heat exchanger 4 for heat exchange and cooling to 5-15℃ (the function of the acetaldehyde purification tower 2 is to purify acetaldehyde and recover vinyl acetate). Then it enters the top of the intermediate recovery tank 5 of the acetaldehyde purification tower. The upper outlet component of the intermediate recovery tank 5 of the acetaldehyde purification tower (i.e., the upper layer after stratification) Vinyl acetate enters the lower part of extraction tower 1. The bottom components of acetaldehyde refining tower 2 and the bottom outlet components of acetaldehyde refining tank 5 both enter wastewater treatment system 10. The top components (16-20℃) of acetaldehyde refining tower 2 enter the upper inlet of the first condenser 6 of acetaldehyde refining tower. After condensation by chilled water (temperature -6 to -3℃), the gaseous outlet components of the first condenser 6 of acetaldehyde refining tower enter the second condenser 7 of acetaldehyde refining tower (cooled to -5 to 5℃ in the second condenser 10). The condensate outlet components (refined acetaldehyde, acetaldehyde ≥ 98.5%, -5~5℃) of the second condenser 7 of the acetaldehyde refining tower and the condensate outlet components of the first condenser 6 of the acetaldehyde refining tower are combined and then enter the distillation tank 8 of the acetaldehyde refining tower. A portion of the qualified acetaldehyde (acetaldehyde ≥ 98.5%) at the bottom outlet of the distillation tank 8 can be sold externally, while the unqualified (acetaldehyde < 98.5%) can be returned to the acetaldehyde refining tower 2 for reprocessing, and the other portion is returned to the top of the acetaldehyde refining tower 2 as reflux.

[0056] As shown in Example 1, in the acetaldehyde purification device of this example, the residence time of the middlings liquid is increased by the height of the middlings separator and the setting of the baffles, which improves the stratification effect. The middlings separator extracts the upper layer of vinyl acetate liquid, and the lower aqueous phase (acetaldehyde water) is returned to the lower tray of the acetaldehyde refining tower, reducing the amount of acetaldehyde water extracted by about 20,000 t / year, thereby reducing energy consumption, such as reducing steam consumption by 2,000-3,000 t / year, and also improving the acetaldehyde separation effect of the acetaldehyde refining tower. In addition, by extracting vinyl acetate from the middlings liquid phase, the amount of vinyl acetate recovered can reach 5,000-5,500 t / year, avoiding the phenomenon of self-polymerization of vinyl acetate after falling into the bottom of the acetaldehyde refining tower, which causes blockage of the bottom and trays, thereby reducing energy consumption, such as reducing steam consumption by 3,000-4,000 t / year. The temperature of the midstream liquid in the acetaldehyde refining tower is reduced to 5-15℃ by using a midstream heat exchanger, and the temperature of the extraction tower bottom is reduced from 25-30℃ to 10-15℃, improving the extraction efficiency of the extraction tower. Steam is directly introduced into the bottom of the acetaldehyde refining tower for heating, solving the problem of reboiler blockage affecting the stable heat supply, ensuring the stable operation of the acetaldehyde refining tower, and reducing equipment investment. If a reboiler is used for heating, it cannot operate stably normally; if blockage occurs, it requires boiling with caustic soda for at least 24 hours, and the operation poses significant safety risks. Synthetic acetaldehyde water (acetaldehyde water from the synthesis process, with an acetaldehyde content of 2-5% and a temperature of 0-10℃) is used as the extractant at the top of the extraction tower. This not only reduces the consumption of demineralized water in the extraction tower by 70,000-80,000 tons / year, but also allows for the recovery of acetaldehyde from the acetaldehyde synthesis water, with a recovered acetaldehyde amount of 1,700-2,000 tons / year.

[0057] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An acetaldehyde purification process, wherein the process uses an acetaldehyde purification device, the device comprising: Extraction tower (1), acetaldehyde refining tower (2), acetaldehyde refining tower intermediate collection tank (5), intermediate collection separator (3) and intermediate collection heat exchanger (4); Among them, the lower inlet of the extraction tower (1) is connected to the raw material feed pipeline, the upper inlet of the extraction tower (1) is connected to the extractant pipeline, the bottom outlet of the extraction tower (1) is connected to the inlet of the acetaldehyde refining tower (2), the upper outlet of the extraction tower (1) is connected to the extraction tower recovery liquid pipeline, the top outlet pipeline of the acetaldehyde refining tower (2) is divided into two paths, one path is connected to the acetaldehyde pipeline, and the other path returns to the top of the acetaldehyde refining tower (2). A mid-stage separator (3) is set in the middle of the acetaldehyde refining tower (2). The lower aqueous phase outlet of the mid-stage separator (3) returns to the acetaldehyde refining tower (2). The vinyl acetate liquid outlet of the mid-stage separator (3) is connected to the inlet of the mid-stage heat exchanger (4). The outlet of the mid-stage heat exchanger (4) is connected to the top inlet of the mid-stage tank (5) of the acetaldehyde refining tower. The upper outlet of the mid-stage tank (5) of the acetaldehyde refining tower is connected to the lower inlet of the extraction tower (1) through a pipeline. The intermediate mining separator (3) uses three baffles. The first baffle (12) is located at the top inside the intermediate mining separator (3), the second baffle (13) is located at the bottom inside the intermediate mining separator (3), and the third baffle (14) is located at the top inside the intermediate mining separator (3). The second baffle (13) intersects with the first baffle (12) and the third baffle (14). Its characteristic is that it includes the following steps: The raw material enters the lower part of the extraction tower (1), and the extractant is added to the top inlet of the extraction tower (1). After extraction, the bottom component of the extraction tower (1) enters the middle part of the acetaldehyde refining tower (2). The liquid phase in the middle part of the acetaldehyde refining tower (2) is collected by the intermediate-stage separator (3). After stratification, the lower layer of acetaldehyde water returns to the acetaldehyde refining tower (2), and the upper layer of vinyl acetate liquid enters the intermediate-stage heat exchanger (4) for heat exchange and cooling to 5-15℃. Then it enters the top of the intermediate-stage tank (5) of the acetaldehyde refining tower. The upper outlet component of the intermediate-stage tank (5) of the acetaldehyde refining tower enters the lower part of the extraction tower (1). The top component of the acetaldehyde refining tower (2) is divided into two parts. One part is collected, and the other part is returned to the top of the acetaldehyde refining tower (2) for reflux. The reaction liquid and filtrate of vinyl acetate synthesized by the calcium carbide acetylene method are distilled through a vinyl acetate crude fractionation tower to obtain the top distillate of the vinyl acetate crude fractionation tower. The top distillate of the vinyl acetate crude fractionation tower is then used as a raw material to enter the lower part of the extraction tower (1). The reaction liquid includes 45-50% acetic acid, 45-50% vinyl acetate, 1.0-2.5% acetaldehyde, 0.8-1.8% acetylene, 0.01-0.1% water, carbon powder and zinc acetate. The filtrate includes 85-95% acetic acid, 5-10% vinyl acetate, 0.01-0.1% water, carbon powder and zinc acetate. The top distillate of the vinyl acetate crude fractionation tower includes 85-90% vinyl acetate, 5-10% acetaldehyde and 1.0-2.0% water.

2. The process according to claim 1, characterized in that, The extractant pipeline at the top of the extraction tower (1) is connected to the acetaldehyde water synthesis pipeline. The bottom outlet of the extraction tower (1) is connected to the inlet of the acetaldehyde refining tower (2) after passing through a heat exchanger, which is a vinyl acetate refining tower condenser (9). The vapor phase discharge pipeline from the top of the vinyl acetate refining tower is connected to the upper inlet of the vinyl acetate refining tower condenser (9). The condensate outlet of the vinyl acetate refining tower condenser (9) is connected to the vinyl acetate condensate discharge pipeline. The lower inlet of the vinyl acetate refining tower condenser (9) is connected to the bottom outlet of the extraction tower (1). The upper outlet of the vinyl acetate refining tower condenser (9) is connected to the inlet of the acetaldehyde refining tower (2). After the bottom component of the extraction tower (1) and the distillate phase of the vinyl acetate refining tower exchange heat in the condenser (9) of the vinyl acetate refining tower, the feed temperature is increased to 40-60℃ and then enters the middle part of the acetaldehyde refining tower (2).

3. The process according to claim 1 or 2, characterized in that, Extractant is added to the top inlet of the extraction tower (1) to synthesize acetaldehyde water.

4. The process according to claim 1 or 2, characterized in that, The acetaldehyde purification device also includes: a first condenser (6) of the acetaldehyde refining tower, a second condenser (7) of the acetaldehyde refining tower, and an acetaldehyde refining tower distillation tank (8); wherein, the top outlet of the acetaldehyde refining tower (2) is connected to the inlet of the first condenser (6) of the acetaldehyde refining tower, the bottom outlet of the acetaldehyde refining tower (2) is connected to the wastewater treatment system (10), the gas phase outlet of the first condenser (6) of the acetaldehyde refining tower is connected to the inlet of the second condenser (7) of the acetaldehyde refining tower, the condensate outlet pipeline of the first condenser (6) of the acetaldehyde refining tower and the condensate outlet pipeline of the second condenser (7) of the acetaldehyde refining tower are connected to the inlet of the acetaldehyde refining tower distillation tank (8), the outlet pipeline of the acetaldehyde refining tower distillation tank (8) is divided into two paths, one path is connected to the acetaldehyde pipeline, and the other path returns to the top of the acetaldehyde refining tower (2), and the bottom outlet of the acetaldehyde refining tower distillation tank (5) is connected to the wastewater treatment system (10). Among them, the bottom component of the acetaldehyde refining tower (2) and the bottom outlet component of the acetaldehyde refining tower (5) both enter the wastewater treatment system (10). The top component of the acetaldehyde refining tower (2) enters the upper inlet of the first condenser (6) of the acetaldehyde refining tower. After being condensed by chilled water, the gas phase outlet component of the first condenser (6) of the acetaldehyde refining tower enters the inlet of the second condenser (7) of the acetaldehyde refining tower. The condensate outlet component of the second condenser (7) of the acetaldehyde refining tower and the condensate outlet component of the first condenser (6) of the acetaldehyde refining tower merge and enter the distillation tank (8) of the acetaldehyde refining tower. Part of the acetaldehyde is extracted from the bottom outlet of the distillation tank (8) of the acetaldehyde refining tower, and the other part is returned to the top of the acetaldehyde refining tower (2) for reflux.

5. The process according to claim 1, characterized in that, Chilled water is introduced into the heat exchanger (4).

6. The process according to claim 1, characterized in that, The upper outlet component of the acetaldehyde refining tower (5) enters the bottom of the extraction tower (1), reducing the bottom temperature of the extraction tower from 25-30℃ to 10-15℃.

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