A vinyl acetate rectification column, a vinyl acetate rectification system and a production system

Abstract

The application discloses a vinyl acetate rectification tower, which comprises a rectification tower body and a reboiler, a feeding pipe for flowing material from the rectification tower body to the reboiler is arranged in communication between the bottom of the reboiler and the bottom of the rectification tower body, and the bottom of the feeding pipe is connected with a discharging branch pipe used for being in communication with a vinyl acetate rectification tower. The present application solves the problem that the vinyl acetate rectification tower in the prior art is frequently maintained during shutdown, thereby shortening the operation cycle.

Description

Technical Field

[0001] This invention relates to equipment for purifying vinyl acetate, specifically a vinyl acetate distillation column.

[0002] The present invention also relates to a purification device for vinyl acetate, specifically a vinyl acetate distillation system.

[0003] The present invention also relates to equipment for producing vinyl acetate, specifically a vinyl acetate production system. Background Technology

[0004] Concentrated acetylene derived from natural gas is used as a raw material. After purification, it is mixed with acetic acid in a fixed-bed reactor using zinc acetate / activated carbon as a catalyst. The reaction proceeds through mixing and condensation to produce crude vinyl acetate (approximately 40% vinyl acetate and 60% acetic acid). The crude vinyl acetate is then purified by distillation to obtain refined vinyl acetate. The vinyl acetate distillation column is the main equipment used for vinyl acetate purification. The column consists of the column body and a reboiler. The crude vinyl acetate in the column body enters the reboiler for heating. Because vinyl acetate's physical properties make it prone to polymerization at high temperatures, a certain amount of polymerization inhibitor is added during the vinyl acetate preparation process to reduce clogging of the distillation column body.

[0005] Chinese patent document CN105964008A discloses a high-purity vinyl acetate separation system, comprising a third distillation column and a fourth distillation column, which are connected together. A reboiler is connected to the bottom of the third distillation column, and a first distillate condenser and a second distillate condenser are sequentially connected to the top of the fourth distillation column. The distillation columns employ inclined perforated trays, which are installed horizontally with double overflow. The inclined perforated trays fully utilize the available space within the column, including the trays, downcomers, and distributors, maximizing phase contact area and minimizing pressure drop, thereby improving tray efficiency. The inclined perforated tray is a novel tray designed based on a summary of the advantages and disadvantages of various trays. The tray has several rows of parallel inclined perforations, from which vapor flows out. The orifices are oriented in the same direction, with adjacent rows having opposite orifice directions, arranged in an alternating pattern. This design increases gas velocity and reduces mist entrainment. Furthermore, the airflow from adjacent rows of angled orifices creates a mutual restraining effect on the liquid flow. This not only eliminates the phenomenon of the liquid being pushed to one side of the tower wall due to continuous airflow acceleration, but also tends to create a multi-pass flow, increasing the length of the liquid flow channel, resulting in good gas-liquid contact, a low and uniform liquid layer, and significantly improving the efficiency and production capacity of the trays. Moreover, the angled orifice trays are less prone to clogging, making them particularly suitable for the self-polymerizing vinyl acetate in this system.

[0006] Chinese patent document CN113563188A discloses a method for recovering vinyl acetate from vinyl acetate waste liquid, specifically involving a vinyl acetate distillation system, including a preheater, a distillation column, a thin-film evaporator, and a reflux tank. The vinyl acetate waste liquid feedstock is pumped to the preheater, and after preheating, it is conveyed to the bottom inlet of the distillation column for distillation. Distillation is then performed. After distillation, the liquid at the bottom of the distillation column is continuously conveyed to the thin-film evaporator via a bottom pump for evaporation. The heat medium for the thin-film evaporator is steam, and the operating pressure is atmospheric pressure or slightly negative pressure. The thin-film evaporator serves as a reheater for the distillation process. The bottom material of the distillation column undergoes secondary evaporation and recovery, which improves the recovery rate and avoids blockage of the reboiler at the bottom of the distillation column. The liquid from the bottom of the distillation column is continuously fed to the top distributor of the thin-film evaporator, and heating is turned on. By controlling the temperature of the evaporator, the vapor phase after evaporation by the scraped film evaporator is returned to the distillation column, and the liquid phase is sent to the residue tank as residual liquid. After the vapor at the top of the distillation column is completely condensed by the condenser, the condensate is collected in the reflux tank. At the outlet of the reflux tank, a portion of the condensate is returned to the distillation column through the reflux pipeline via the reflux pump, and the other portion of the condensate is pumped to the cooler for cooling. After cooling, the recovered vinyl acetate product is obtained. The beneficial effects of this prior art solution are as follows: by sequentially setting up equipment such as a preheater, a distillation column, a thin-film evaporator, and a reflux tank, vinyl acetate in the vinyl acetate waste liquid generated during EVA production is recovered. The overall process is simple and has low operating costs. It effectively avoids the blockage at the bottom of the distillation column caused by tar, polymerization inhibitors, and vinyl acetate polymers in the prior art, and effectively recovers vinyl acetate, realizing resource reuse.

[0007] Chinese patent document CN206414785U discloses an energy-saving vinyl acetate distillation system, including a vinyl acetate distillation column, a first reboiler, a first condenser, a second condenser, an acetic acid refining distillation column, a second reboiler, a third condenser, a fourth condenser, a high-pressure hot water tank, and a primary steam generator. The vinyl acetate distillation column has an inlet for feeding a mixture of vinyl acetate and acetic acid. A vapor phase outlet discharges vaporized vinyl acetate, which is then sent to the second condenser for condensation and collection. A vapor phase mixture is discharged from the top of the column and sent to the first condenser for reflux or distillation. The liquid phase outlet at the bottom of the column is connected to the material inlet of the first reboiler. The primary steam generator generates primary steam. The steam inlet of the first reboiler is connected to one end of a first steam pipe, and the other end of the first steam pipe is connected to the primary steam generator. The liquid phase outlet of the first reboiler discharges condensate. The material outlet of the first reboiler is connected to the vapor phase inlet at the bottom of the vinyl acetate distillation column. The material inlet of the acetic acid refining distillation column... The inlet is used to feed crude acetic acid. The vaporous material discharged from the top vapor outlet of the acetic acid refining distillation column is refluxed or distilled out via the third condenser. Vaporous acetic acid is discharged from the vapor outlet of the acetic acid refining distillation column and sent to the fourth condenser for condensation and collection. The bottom liquid outlet is connected to the material inlet of the second reboiler, and the material outlet of the second reboiler is connected to the bottom vapor inlet of the acetic acid refining distillation column. The steam inlet of the second reboiler is connected to one end of the second steam pipe, and the other end of the second steam pipe is connected to the primary steam... The generating apparatus connects the condensate from the steam exchanged in the second reboiler to the inlet of the high-pressure warm water tank via the liquid phase outlet of the second reboiler. The high-pressure warm water tank discharges condensate from its outlet, and its outlet is connected to a first steam pipe via a secondary steam inlet pipe. This allows the secondary steam from the high-pressure warm water tank to be introduced into the first reboiler. A first regulating valve is installed on the first steam pipe, and a second regulating valve is installed on the secondary steam inlet pipe. These valves are used to control the temperature within the vinyl acetate distillation column. This prior art incorporates a high-pressure warm water tank to recover and collect the secondary steam used in the crude acetic acid refining and distillation process. This secondary steam, with a temperature reaching 110°C, can effectively heat vinyl acetate to the gas phase. Therefore, primary steam is not required for heat exchange during crude acetic acid refining and distillation, significantly saving primary steam and energy.

[0008] When using the above-mentioned existing technology, the vinyl acetate distillation column is still prone to frequent reboiler blockage, which requires frequent shutdowns for maintenance, resulting in a short operating cycle. Furthermore, frequent shutdowns for maintenance lead to increased maintenance costs, and shutdowns also cause production interruptions, resulting in reduced production efficiency and increased production costs. Summary of the Invention

[0009] The purpose of this invention is to provide a vinyl acetate distillation column, a vinyl acetate distillation system, and a production system to solve the problem that the vinyl acetate distillation column in the prior art has frequent shutdowns for maintenance, resulting in a short operating cycle.

[0010] To achieve the above objectives, the basic solution of the present invention provides a vinyl acetate distillation column, including a distillation column body and a reboiler. A feed pipe is connected between the bottom of the reboiler and the bottom of the distillation column body to allow material to flow from the distillation column body toward the reboiler. A discharge branch pipe is connected to the bottom of the feed pipe and is used to communicate with the acetic acid distillation column.

[0011] With this configuration, when the material at the bottom of the vinyl acetate distillation column flows to the reboiler through the feed pipe, the material at the bottom of the feed pipe will enter the discharge branch pipe and be discharged to the vinyl acetate distillation column. However, the inventors discovered that when the material at the bottom of the distillation column flows to the reboiler through the feed pipe, the heavy components in the material will flow along the bottom of the feed pipe. By setting a discharge branch pipe at the bottom of the feed pipe, the heavy components in the material enter the discharge branch pipe when flowing through the interface between the discharge branch pipe and the feed pipe. This significantly reduces the heavy component content of the material entering the reboiler, thereby reducing the need for shutdown maintenance of the vinyl acetate distillation column due to reboiler malfunction or excessive decrease in heat transfer efficiency.

[0012] Preferably, the discharge branch pipe is located below the feed pipe. This arrangement allows the heavy components in the feed pipe to enter the discharge branch pipe more effectively under gravity, which helps to further reduce the content of heavy components entering the reboiler, thereby further extending the operating cycle of the vinyl acetate distillation column.

[0013] Preferably, a valve is installed on the discharge branch pipe. This arrangement allows for convenient control of the opening and closing of the discharge branch pipe via the valve, thereby regulating the effect of material containing heavy components entering the discharge branch pipe from the feed pipe.

[0014] Preferably, the discharge branch pipe is connected to a pump. This arrangement, with the pump driving the material flow within the discharge branch pipe, facilitates the smoother entry of materials containing heavy components from the feed pipe into the discharge branch pipe, further improving the effect of extending the operating cycle of the vinyl acetate distillation column.

[0015] Preferably, the end of the discharge branch pipe connected to the feed pipe is close to the bottom of the reboiler. With this arrangement, as the material moves within the feed pipe, the heavier components in the material gradually settle and approach the bottom of the feed pipe. By placing the end of the discharge branch pipe connected to the feed pipe close to the bottom of the reboiler, the heavier components in the material within the feed pipe are brought as close as possible to the bottom of the feed pipe and enter the discharge branch pipe, thereby minimizing the amount of heavy components entering the reboiler. This is beneficial for further extending the operating cycle of the vinyl acetate distillation column.

[0016] Preferably, the end of the feed pipe connected to the reboiler is lower than the end of the feed pipe connected to the distillation column body. This arrangement allows as much material as possible from the distillation column body into the reboiler under gravity, eliminating the need for additional power equipment, simplifying the equipment structure, and reducing costs.

[0017] Secondly, the present invention provides a vinyl acetate distillation system for preparing the vinyl acetate distillation system described in the present invention, comprising any of the vinyl acetate distillation columns described above.

[0018] Thirdly, the present invention provides a vinyl acetate production system according to the present invention, comprising a vinyl acetate distillation system and an acetic acid distillation system, wherein the acetic acid distillation system includes a reflux pump for an acetic acid distillation column, and the vinyl acetate distillation system is any of the above-mentioned vinyl acetate distillation systems, and the discharge branch pipe is connected to the reflux pump of the acetic acid distillation column.

[0019] The present invention has the following beneficial effects: 1. Compared with the prior art, the present invention connects a discharge branch pipe to the feed pipe, so that when the material in the distillation column enters the reboiler through the feed pipe, the heavy components in the material will enter the discharge branch pipe and be discharged. This reduces the accumulation of heavy components such as polymers in the reboiler, which can clog the reboiler and cause a serious reduction in the heat transfer efficiency of the reboiler. As a result, the frequency of shutdown maintenance of the vinyl acetate distillation column is reduced, the operating cycle of the vinyl acetate distillation column is significantly extended, and the production cost is reduced.

[0020] 2. In order to solve the problem of short operating cycle of vinyl acetate distillation column, this invention can solve the problem by adding a discharge branch pipe to the existing equipment. The modification to the existing equipment is small, the modification cost is low, and it is simple and easy to implement, which is conducive to large-scale promotion and application.

[0021] 3. This invention connects the discharge branch pipe to the reflux pump of the acetic acid distillation column, allowing the material in the discharge branch pipe to enter the acetic acid distillation column through the reflux pump. This enables the acetic acid component in the material discharged from the discharge branch pipe to be recovered by the acetic acid distillation column, while the heavy components in the material are discharged through the bottom tar pump of the acetic acid distillation column. This avoids the waste of acetic acid and achieves both the extension of the operating cycle of the vinyl acetate distillation column and the recovery of acetic acid. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of an embodiment of a vinyl acetate distillation column according to the present invention; Figure 2 This is a schematic diagram of an embodiment of a vinyl acetate production system according to the present invention. Detailed Implementation

[0023] A distillation column is a tower-type gas-liquid contact device used for distillation. It utilizes the property that the components in a mixture have different volatility (i.e., different vapor pressures at the same temperature), causing lighter components (low-boiling compounds) in the liquid phase to transfer to the gas phase, while heavier components (high-boiling compounds) in the gas phase transfer to the liquid phase, thus achieving separation. (See Baidu Encyclopedia for details) A reboiler, as the name suggests, vaporizes a liquid once more. It is a special heat exchanger that can exchange heat and has a vaporization space. (See Baidu Encyclopedia for details) The following detailed description illustrates the specific implementation method: The reference numerals in the accompanying drawings include: 1. Distillation column body; 2. Reboiler; 3. Feed pipe; 4. Valve; 5. Discharge branch pipe; 6. Acetic acid distillation column; 7. Reflux pump.

[0024] Example 1: Basic as shown in the attached document Figure 1 The diagram shows a vinyl acetate distillation column, comprising a column body 1 and a reboiler 2. A feed pipe 3 connects the bottom of the reboiler 2 to the bottom of the column body 1. In this embodiment, the end of the feed pipe 3 connected to the reboiler 2 is lower than the end of the feed pipe 3 connected to the column body 1, allowing the material in the column body 1 to flow into the reboiler 2 under gravity, thereby reducing the need for power equipment. In this embodiment, two reboilers 2 are preferably provided, and the two reboilers 2 are located on opposite sides of the column body 1. All reboilers 2 are evenly distributed circumferentially along the column body 1.

[0025] A discharge branch pipe 5 is connected to the bottom of the feed pipe 3. In this embodiment, the discharge branch pipe 5 is located below the feed pipe 3, which facilitates the accumulation of heavy components in the feed pipe 3 on the side connected to the discharge branch pipe 5 under gravity, thus facilitating the entry of heavy components into the discharge branch pipe 5. A valve 4 is installed on the discharge branch pipe 5. In this embodiment, the valve 4 is preferably a ball valve. A pump is connected to the discharge branch pipe 5, which facilitates the suction of heavy components in the feed pipe 3 into the discharge branch pipe 5.

[0026] In this embodiment, each reboiler 2 is provided with a discharge branch pipe 5, thus there are two discharge branch pipes 5 in this embodiment. The connection between each discharge branch pipe 5 and the feed pipe 3 is located at the bottom of the corresponding reboiler 2, thereby facilitating the minimization of heavy components in the feed pipe 3 entering the reboiler 2.

[0027] Example 2: A vinyl acetate distillation system, including a vinyl acetate distillation column. For example... Figure 1 As shown, the vinyl acetate distillation column includes a column body 1 and a reboiler 2, with a feed pipe 3 connecting the bottom of the reboiler 2 to the bottom of the column body 1. In this embodiment, two reboilers 2 are preferably provided, and the two reboilers 2 are located on opposite sides of the column body 1. All reboilers 2 are evenly distributed along the circumference of the column body 1.

[0028] A discharge branch pipe 5 is connected to the bottom of the feed pipe 3. In this embodiment, the discharge branch pipe 5 is located below the feed pipe 3, which facilitates the accumulation of heavy components in the feed pipe 3 on the side connected to the discharge branch pipe 5 under gravity, thus facilitating the entry of heavy components into the discharge branch pipe 5. A valve 4 is installed on the discharge branch pipe 5. In this embodiment, the valve 4 is preferably a ball valve. A pump is connected to the discharge branch pipe 5, which facilitates the suction of heavy components in the feed pipe 3 into the discharge branch pipe 5.

[0029] In this embodiment, each reboiler 2 is provided with a discharge branch pipe 5, thus there are two discharge branch pipes 5 in this embodiment. The connection between each discharge branch pipe 5 and the feed pipe 3 is located at the bottom of the corresponding reboiler 2, thereby facilitating the minimization of heavy components in the feed pipe 3 entering the reboiler 2.

[0030] Example 3: Figure 2 As shown, a vinyl acetate production system includes a vinyl acetate distillation system and an acetic acid distillation system. The vinyl acetate distillation system includes a vinyl acetate distillation column. The vinyl acetate distillation column includes a column body 1 and reboilers 2, with a feed pipe 3 connecting the bottom of the reboiler 2 to the bottom of the column body 1. All reboilers 2 are evenly distributed circumferentially along the column body 1. In this embodiment, two reboilers 2 are preferably provided, and the two reboilers 2 are respectively located on both sides of the column body 1.

[0031] A discharge branch pipe 5 is connected to the bottom of the feed pipe 3. In this embodiment, the discharge branch pipe 5 is located below the feed pipe 3, which facilitates the accumulation of heavy components in the feed pipe 3 on the side connected to the discharge branch pipe 5 under the action of gravity, thereby facilitating the entry of heavy components into the discharge branch pipe 5. A valve 4 is installed on the discharge branch pipe 5. In this embodiment, the valve 4 is preferably a ball valve.

[0032] In this embodiment, each reboiler 2 is provided with a discharge branch pipe 5, thus there are two discharge branch pipes 5 in this embodiment. The connection between each discharge branch pipe 5 and the feed pipe 3 is located at the bottom of the corresponding reboiler 2, thereby facilitating the minimization of heavy components in the feed pipe 3 entering the reboiler 2.

[0033] The acetic acid distillation system includes a reflux pump 7 for the acetic acid distillation column 6 and a bottom tar pump for the acetic acid distillation column 6. A discharge branch pipe 5 is connected to the reflux pump 7 of the acetic acid distillation column 6, allowing the material in the discharge branch pipe 5 to enter the acetic acid distillation column 6 under the action of the reflux pump 7, thereby recovering acetic acid from the material. Heavy components in the material are then discharged by the bottom tar pump of the acetic acid distillation column 6. This allows the discharge branch pipe 5 to fully utilize the existing pump mechanism to remove heavy components, eliminating the need for a separate pump mechanism, further simplifying the structure and reducing modification costs.

[0034] By using the solution of the present invention, by connecting the discharge branch pipe 5 to the feed pipe 3, the discharge branch pipe 5 removes the heavy components in the feed pipe 3, thereby reducing the accumulation of polymer in the reboiler 2 and the blockage of the reboiler 2 and the serious reduction of the heat exchange efficiency of the reboiler. This significantly extends the operating cycle of the reboiler 2, thereby reducing the frequency of shutdown and maintenance of the vinyl acetate distillation column and reducing production costs.

[0035] Comparing the operational status of the vinyl acetate distillation column before and after adopting this solution: Before adopting this solution, the vinyl acetate distillation column experienced at least one shutdown per year due to reboiler malfunction or a significant reduction in reboiler heat exchange efficiency. After adopting this solution, the vinyl acetate distillation column has not experienced any shutdown for maintenance due to reboiler malfunction or a significant reduction in reboiler heat exchange efficiency for over two years. Therefore, it can be seen that adopting this solution can extend the operating cycle of the vinyl acetate distillation column by at least double, resulting in a significant reduction in maintenance costs and production losses caused by downtime. Furthermore, this invention requires minimal modification to existing equipment and is simple to implement, which helps reduce modification costs and facilitates widespread adoption.

[0036] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics in the solutions is not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A vinyl acetate distillation column, comprising a column body and a reboiler, wherein a feed pipe is connected between the bottom of the reboiler and the bottom of the column body to allow material to flow from the column body toward the reboiler, characterized in that: The bottom of the feed pipe is connected to a discharge branch pipe, which is used to connect to the acetic acid distillation column.

2. The vinyl acetate distillation column according to claim 1, characterized in that: The discharge branch pipe is located below the feed pipe.

3. The vinyl acetate distillation column according to claim 2, characterized in that: A valve is installed on the discharge branch pipe.

4. The vinyl acetate distillation column according to claim 3, characterized in that: The discharge branch pipe is connected to a pump.

5. A vinyl acetate distillation column according to claim 4, characterized in that: The end of the discharge branch pipe that connects to the feed pipe is close to the bottom of the reboiler.

6. A vinyl acetate distillation column according to claim 5, characterized in that: The end of the feed pipe connected to the reboiler is lower than the end of the feed pipe connected to the distillation column body.

7. A vinyl acetate distillation column according to claim 6, characterized in that: The reboilers are evenly distributed around the circumference of the distillation column body.

8. A vinyl acetate distillation system, characterized in that: Includes the vinyl acetate distillation column as described in any one of claims 1 to 7.

9. A vinyl acetate production system, comprising a vinyl acetate distillation system and an acetic acid distillation system, wherein the acetic acid distillation system includes a reflux pump for an acetic acid distillation column, characterized in that: The vinyl acetate distillation system is the vinyl acetate distillation system according to claim 8, and the discharge branch pipe is connected to the reflux pump of the acetic acid distillation column.

10. A vinyl acetate production system according to claim 9, characterized in that: The acetic acid distillation system also includes a tar pump at the bottom of the acetic acid distillation column.

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