Device for recovering non-condensable gas of dimethyl carbonate rectifying tower

Abstract

The utility model discloses a device for recovering non-condensable gas of a dimethyl carbonate rectifying tower, which comprises a methanol washing tower, a remote liquid level meter is arranged at the lower part of the methanol washing tower, and the bottom of the methanol washing tower is connected with a circulating pump; the upper part of the methanol washing tower is provided with a methanol inlet, the lower part of the methanol washing tower is provided with a non-condensable gas inlet, the non-condensable gas inlet is respectively connected with reflux tanks of the dimethyl carbonate reactive distillation tower, the dimethyl carbonate distillation tower and the dimethyl carbonate product distillation tower, and the top of the methanol washing tower is provided with a gas phase outlet which is connected with a gas phase inlet of the tower top cooler; a condensate outlet of the tower top cooler is connected with a top inlet of the methanol washing tower; bottom solution of the methanol washing tower is connected with the upper portion of the methanol washing tower through a circulating pump, and an outlet pipeline of the circulating pump is connected with the methanol buffer tank. According to the device provided by the utility model, the pollution to the environment is reduced by collecting the non-condensable gas of the dimethyl carbonate rectifying tower; the yield of dimethyl carbonate is increased; the method has the advantages of low investment, small occupied area and simplicity and convenience in operation.

Description

Technical Field

[0001] This utility model relates to a device for recovering non-condensable gas from a dimethyl carbonate distillation column, belonging to the field of chemical technology. Background Technology

[0002] Dimethyl carbonate is a low-toxicity, environmentally friendly, and widely used chemical raw material. It is an important organic synthesis intermediate. Its molecular structure contains functional groups such as carbonyl, methyl, and methoxy groups, giving it a variety of reactivity properties. In production, it is safe, convenient, produces little pollution, and is easy to transport.

[0003] Chinese patent CN209352803U discloses a dimethyl carbonate recovery device, which is mainly for the separation of a mixture of methanol and dimethyl carbonate. This method achieves the separation of methanol and dimethyl carbonate, but does not treat the venting air generated during the separation and storage of methanol and dimethyl carbonate.

[0004] Currently, the production of dimethyl carbonate (DMC) via transesterification, the urea-methanol indirect method, and the methanol oxidative carbonylation synthesis all require the separation of a methanol-DMC mixture. This separation process generates a large amount of non-condensable gas. This non-condensable gas contains a portion of methanol and DMC; directly venting it not only causes environmental pollution but also wastes materials. To recover the methanol and DMC from the non-condensable gas, this invention provides a device for recovering non-condensable gas from a DMC distillation column. Utility Model Content

[0005] This invention provides a device for recovering non-condensable gases from a dimethyl carbonate distillation column. It not only collects and absorbs the non-condensable gases from the dimethyl carbonate distillation column, but also recovers and processes the absorbed liquid, thereby increasing the product yield.

[0006] The technical solution adopted in this utility model is:

[0007] An apparatus for recovering non-condensable gases from a dimethyl carbonate distillation column includes a methanol scrubbing column. A remote level gauge is installed at the bottom of the methanol scrubbing column, and a circulating pump is connected to the bottom of the column. The methanol scrubbing column has a methanol inlet at the top and a non-condensable gas inlet at the bottom, which are connected to the reflux tanks of a dimethyl carbonate reactive distillation column, a dimethyl carbonate distillation column, and a dimethyl carbonate product distillation column, respectively. The top of the methanol scrubbing column has a gas phase outlet connected to the gas phase inlet of a column top cooler. The condensate outlet of the column top cooler is connected to the top inlet of the methanol scrubbing column. The bottom solution of the methanol scrubbing column is connected to the top of the column via a circulating pump to form a mixed liquid circulation, increasing absorption efficiency. The outlet pipeline of the circulating pump is connected to a methanol buffer tank.

[0008] Furthermore, refined methanol is introduced into the methanol washing tower, and the bottom liquid level of the methanol washing tower is controlled at 40% to 70% of the volume of the methanol washing tower.

[0009] Furthermore, the bottom solution of the methanol washing tower is a mixed solution that absorbs the non-condensable gas of dimethyl percarbonate. The outlet of the bottom solution of the methanol washing tower is connected to the top inlet of the methanol washing tower and the methanol buffer tank through a circulation pump. The liquid level of the methanol washing tower and the methanol buffer tank is set to interlock control: during the circulation process, the liquid level and pressure of the methanol washing tower are observed. When refined methanol is fed into the methanol washing tower, the liquid level at the bottom of the tower rises. When the liquid level at the bottom of the methanol washing tower reaches 70% of the volume, the valve of the circulating pump from the bottom of the methanol washing tower to the methanol buffer tank is opened to discharge liquid into the methanol buffer tank. When the liquid level at the bottom of the methanol washing tower reaches 40%-70% of the volume and remains stable, the discharge stops, and the valve of the circulating pump from the bottom of the methanol washing tower to the methanol buffer tank is closed. When the liquid level at the bottom of the methanol washing tower remains above 70% and there is no obvious downward trend, the valve of the circulating pump from the bottom of the methanol washing tower to the methanol buffer tank is manually controlled. Alternatively, if refined methanol is not fed into the methanol washing tower, after a period of operation, the liquid in the bottom of the methanol washing tower absorbs organic matter from the non-condensable gas, causing the liquid level in the bottom of the methanol washing tower to rise slowly. The opening and closing of the valve from the circulating pump of the methanol washing tower bottom to the methanol buffer tank is controlled according to the corresponding liquid level value.

[0010] Furthermore, the vapor phase at the top outlet of the methanol scrubbing tower is sent to the top cooler for cooling. The top cooler is connected to the chilled water supply and return system, and the condensate is recovered to the methanol scrubbing tower.

[0011] Furthermore, the non-condensable gas inlet of the methanol scrubbing tower is connected to the reflux tanks of the dimethyl carbonate reactive distillation tower, the dimethyl carbonate rectification tower, and the dimethyl carbonate product distillation tower, respectively. The non-condensable gases from the dimethyl carbonate reactive distillation tower, the dimethyl carbonate rectification tower, and the dimethyl carbonate product distillation tower enter the methanol scrubbing tower through their respective non-condensable gas venting pipelines. The non-condensable gas entering the methanol scrubbing tower comes into counter-current contact with the methanol falling from the top of the tower, thereby fully absorbing some of the organic matter in the non-condensable gas.

[0012] The operation mode of this utility model is as follows: the non-condensable gas from the dimethyl carbonate distillation column is collected in the lower part of the methanol washing column. A portion of the non-condensable gas is absorbed by the methanol in the column bottom. The unabsorbed non-condensable gas is condensed by the top cooler and then recycled to the methanol washing column for secondary recovery. The material in the column bottom is sent to the top of the column by a circulating pump for tertiary recovery. Finally, the solution in the column bottom is sent to the methanol buffer tank. This not only controls the pollution of the environment by non-condensable gas, but also increases the product yield.

[0013] Specifically, the process in the overhead cooler is as follows: After being cooled by chilled water, the non-condensable gas in the overhead cooler condenses, forming condensate. Due to gravity, the condensate falls to the bottom of a small tank attached to the overhead cooler, while the non-condensable tail gas is located at the top of this tank. The small tank has two outlets: a condensate outlet at the bottom and a tail gas outlet at the upper part. The condensate in the small tank flows by gravity to the methanol scrubbing tower due to its height difference, while the tail gas enters the tail gas scrubbing tower due to its pressure difference.

[0014] The device for recovering non-condensable gases from a dimethyl carbonate distillation column provided by this utility model offers the following benefits:

[0015] (1) The collection of non-condensable gases from the dimethyl carbonate distillation column reduces environmental pollution;

[0016] (2) The material collected from the methanol washing tower is recovered into the system, which increases the yield of dimethyl carbonate;

[0017] (3) It has the practicality of low investment, small footprint and easy operation.

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the device for non-condensable gas recovery in a dimethyl carbonate distillation column according to the present invention.

[0020] Figure 2 This is a flowchart of the dimethyl carbonate production process.

[0021] In the diagram: 1 is a methanol washing tower, 2 is a circulating pump, 3 is a tower top cooler, 4 is chilled water supply, 5 is chilled water return, 6 is a remote level gauge, 7 is a remote thermometer, 8 is a remote pressure gauge, 9 is a methanol buffer tank, 10 is a tail gas washing tower, 11 is methanol, 12 is non-condensable gas from a reactive distillation tower, 13 is non-condensable gas from a dimethyl carbonate distillation tower, 14 is non-condensable gas from a dimethyl carbonate product distillation tower, 15 is a reactive distillation tower, 16 is a reactive distillation tower reflux tank, 17 is a pressurized distillation tower, 18 is a pressurized distillation tower reflux tank, 19 is a dimethyl carbonate distillation tower, 20 is a dimethyl carbonate distillation tower reflux tank, 21 is a dimethyl carbonate product distillation tower, 22 is a dimethyl carbonate product distillation tower reflux tank; 23 is a dimethyl carbonate synthesis feedstock premix; 24 is a high-boiling-point mixture; 25 is a qualified dimethyl carbonate outflow pipeline. Detailed Implementation

[0022] The embodiments of this utility model will be described in detail below with reference to the examples. The following examples are only used to illustrate this utility model and should not be regarded as limiting the scope of this utility model. Example

[0023] Existing process: A company uses a urea-methanol indirect method to produce DMC. During the operation of the dimethyl carbonate reactive distillation column, dimethyl carbonate distillation column, and dimethyl carbonate product column, non-condensable gas is generated. The non-condensable gas contains a small amount of organic matter such as dimethyl carbonate and methanol. The emission of unrecovered non-condensable gas has an adverse impact on the working environment of the operators, causes pollution to the surrounding environment, and the dimethyl carbonate yield is not high.

[0024] like Figure 1 As shown, this utility model provides a device for recovering non-condensable gas from a dimethyl carbonate distillation column, including a methanol washing column 1. A remote level gauge 6 is installed at the bottom of the methanol washing column, and a circulation pump 2 is connected to the bottom of the methanol washing column 1. The methanol washing column 1 has a methanol inlet 11 at the top and a non-condensable gas inlet at the bottom. The non-condensable gas inlet is connected to a reflux tank 16 of a dimethyl carbonate reactive distillation column, a reflux tank 20 of a dimethyl carbonate distillation column, and a reflux tank 22 of a dimethyl carbonate product distillation column, respectively. The top of the methanol washing column 1 has a gas phase outlet, which is connected to the gas phase inlet of a column top cooler 3. The column top cooler 3 is connected to a chilled water supply 4 and a chilled water return 5. The condensate outlet of the column top cooler 3 is connected to the top inlet of the methanol washing column 1. The bottom solution of the methanol washing column 1 is connected to the top of the methanol washing column 1 through the circulation pump 2 to form a mixed liquid circulation, which increases the absorption efficiency. The outlet pipeline of the circulation pump 2 is connected to a methanol buffer tank 9.

[0025] Further, refined methanol is introduced into methanol washing tower 1, and the bottom liquid level of methanol washing tower 1 is controlled at 40%~70% of the volume of methanol washing tower. The bottom solution of methanol washing tower is a mixed solution that absorbs non-condensable gas from dimethyl percarbonate. The bottom solution outlet of methanol washing tower is connected to the top inlet of methanol washing tower and methanol buffer tank through a circulation pump. The liquid levels of methanol washing tower and methanol buffer tank are interlocked. During the circulation process, when the liquid level of methanol washing tower rises to 70%, the valve of methanol washing tower bottom circulation pump to methanol buffer tank is opened to send the material of methanol washing tower to methanol buffer tank. When the liquid in the bottom of methanol washing tower is discharged for a certain period of time and the liquid level in the bottom of methanol washing tower remains stable at 40%-70%, the discharge is stopped and the valve of methanol washing tower bottom circulation pump to methanol buffer tank is closed by interlock. Or, when the liquid in the bottom of methanol washing tower is lower than 40%, the discharge is stopped and the valve of methanol washing tower bottom circulation pump to methanol buffer tank is closed by interlock.

[0026] Furthermore, the non-condensable gas inlet of the methanol scrubbing tower is connected to the reflux tank 16, reflux tank 20, and reflux tank 22 of the dimethyl carbonate reactive distillation tower, respectively. The non-condensable gases from the dimethyl carbonate reactive distillation tower 15, dimethyl carbonate distillation tower 19, and dimethyl carbonate product distillation tower 21 enter the methanol scrubbing tower 1 through the non-condensable gas vent lines of the dimethyl carbonate reactive distillation tower reflux tank 16, dimethyl carbonate distillation tower reflux tank 20, and dimethyl carbonate product distillation tower reflux tank 22, respectively. The non-condensable gas entering the methanol scrubbing tower comes into counter-current contact with the methanol falling from the top of the tower, thereby fully absorbing some of the organic matter in the non-condensable gas.

[0027] To address the aforementioned existing process, the device for recovering non-condensable gases from the dimethyl carbonate distillation column provided by this invention was adopted. This resulted in a reduction of the pungent odor in the on-site operating environment, a significant increase in the top product from the reactive distillation column, and a reduction in production consumption. Figure 1 The apparatus shown receives non-condensable gas from the 12-reactive distillation column, the 13-dimethyl carbonate distillation column, and the 14-dimethyl carbonate product distillation column of the dimethyl carbonate synthesis unit, which is connected to the lower part of methanol scrubbing tower 1 via pipelines. Methanol scrubbing tower 1 has a methanol inlet at its upper part. The non-condensable gas entering the methanol scrubbing tower comes into counter-current contact with the methanol falling from the top of the tower, thereby fully absorbing some of the organic matter in the non-condensable gas. Methanol scrubbing tower 1 has a gas phase outlet at its top, which connects to the gas phase inlet of the tower top cooler 3. The tower top cooler 3 is connected to the chilled water supply 4 and chilled water return 5. The condensate outlet of the tower top cooler 3 is equipped with a small tank. Compared to a separate condensate collection tank at the outlet of the tower top cooler 3, this design reduces the equipment's footprint, facilitating full utilization of the site space, reducing the difficulty of on-site equipment installation, and simplifying later maintenance. The small tank attached to the cooler has two outlets: a condensate outlet at the bottom and a tail gas outlet at the upper middle part of the tank.

[0028] Figure 2 The unit in the middle is a dimethyl carbonate synthesis apparatus, mainly comprising a reactive distillation column 15, a pressurized distillation column 17, a dimethyl carbonate distillation column 19, and a dimethyl carbonate product distillation column 21; the main synthesis process is described below:

[0029] First, the premix 23 of dimethyl carbonate synthesis feedstock enters the reactive distillation column 15 for reactive distillation to synthesize dimethyl carbonate. The low-boiling-point azeotrope of dimethyl carbonate and methanol is collected from the top of the column and sent to the reactive distillation column reflux tank 16. The non-condensable gas from the reactive distillation column 15 is connected to the methanol washing column 1 through the top pipeline of the reactive distillation column reflux tank 16. The bottom product of the reactive distillation column 15 is a high-boiling-point mixture 24, which proceeds to the next process.

[0030] A portion of the material from the reactive distillation column reflux tank 16 is fed to the pressurized distillation column 17 for distillation. The top product of the pressurized distillation column 17 is mostly methanol, with a small amount of dimethyl carbonate, and enters the pressurized distillation column reflux tank 18. A portion of the material from the pressurized distillation column reflux tank 18 is fed to the reactive distillation column 15 for distillation. The bottom product of the pressurized distillation column 17 contains a large amount of dimethyl carbonate and a small amount of methanol. The bottom product of the pressurized distillation column 17 enters the dimethyl carbonate distillation column 19 for distillation.

[0031] The top of dimethyl carbonate distillation column 19 contains a low-boiling-point azeotrope of dimethyl carbonate and methanol, which enters the dimethyl carbonate distillation column reflux tank 20. A portion of the material in the reflux tank 20 is transferred to the pressurized distillation column 17 for further distillation. The bottom of dimethyl carbonate distillation column 19 contains high-purity dimethyl carbonate, which enters the dimethyl carbonate product distillation column 21 for further distillation. The non-condensable gas from dimethyl carbonate distillation column 19 is connected to the methanol washing column 1 via a pipeline at the top of the reflux tank 20.

[0032] The overhead feed of dimethyl carbonate product distillation column 21 contains a large amount of dimethyl carbonate. This overhead feed enters the dimethyl carbonate product distillation column reflux tank 22.

[0033] A portion of the material is fed to dimethyl carbonate distillation column 19. The dimethyl carbonate product distillation column 21 contains qualified dimethyl carbonate. This qualified dimethyl carbonate is collected through the qualified dimethyl carbonate collection pipeline 25. The non-condensable gas from the product distillation column 21 is connected to the methanol washing column 1 through the top pipeline of the dimethyl carbonate product distillation column reflux tank 22.

[0034] The specific processing procedure includes the following steps: The non-condensable gas vent lines of the dimethyl carbonate reactive distillation column reflux tank, the dimethyl carbonate distillation column reflux tank, and the dimethyl carbonate product column reflux tank are connected to the lower part of the methanol scrubbing tower. The non-condensable gases from the top of the reactive distillation column, the dimethyl carbonate distillation column, and the dimethyl carbonate product column enter the methanol scrubbing tower through the non-condensable gas vent lines of these three columns, respectively. The methanol scrubbing tower contains 40% (liquid level) of refined methanol. The methanol in the bottom of the scrubbing tower absorbs some organic matter. The gas phase is condensed by the top cooler, and the condensate is returned to the methanol scrubbing tower for secondary recovery. The tail gas is sent to the tail gas scrubbing tower. Unabsorbed dimethyl carbonate is circulated back to the top of the methanol scrubbing tower by the bottom circulation pump for three-stage recovery. The material in the bottom of the methanol scrubbing tower is intermittently fed into the methanol buffer tank as feed to the reactive distillation column.

[0035] Commissioning steps:

[0036] 1. Open the valve on the pipeline from refined methanol to the methanol washing tower, and introduce refined methanol until the liquid level reaches 40%;

[0037] 2. Open the chilled water return valve on the top condenser of the methanol washing tower;

[0038] 3. Open the valves for the non-condensable gas from the top of the reactive distillation column, the dimethyl carbonate distillation column, and the dimethyl carbonate product column to the methanol scrubbing column;

[0039] 4. Open the valve of the methanol washing tower to the reboiler circulation pump;

[0040] 5. Start the circulating pump in the bottom of the methanol washing tower to put the methanol washing tower into a self-circulating state;

[0041] 6. After the reactive distillation column, dimethyl carbonate distillation column, and dimethyl carbonate product column are heated, the non-condensable gas at the top of each column is sent to the methanol washing column.

[0042] 7. After the system is put into operation, observe the liquid level, pressure and temperature of the methanol washing tower. ① When the liquid level in the bottom of the methanol washing tower rises to 50% in a short time, in order to prevent the liquid level in the bottom of the tower from rising too fast and eventually flooding the gas phase pipeline, it is necessary to manually adjust and open the valve of the circulating pump from the bottom of the methanol washing tower to the methanol buffer tank in time to maintain the liquid level in the bottom of the methanol washing tower at 40-70%. ② When the valve from the methanol washing tower reboiler circulation pump to the methanol buffer tank is closed and the methanol washing tower reboiler level slowly rises to 70%, the methanol washing tower and methanol buffer tank level interlock is activated, opening the valve from the methanol washing tower reboiler circulation pump to the methanol buffer tank to drain liquid into the methanol buffer tank. After the methanol washing tower reboiler liquid has been drained for a certain period of time and the methanol washing tower reboiler level remains stable at 40%-70%, the draining is stopped and the valve from the methanol washing tower reboiler circulation pump to the methanol buffer tank is closed. Alternatively, if the reboiler level falls below 40% during the draining process, the valve from the methanol washing tower reboiler circulation pump to the methanol buffer tank is closed, stopping the draining into the methanol buffer tank. ③ When the valve from the methanol washing tower reboiler circulation pump to the methanol buffer tank is opened and the methanol washing tower reboiler level slowly drops to 40%, the valve from the methanol washing tower reboiler circulation pump to the methanol buffer tank is closed, stopping the draining into the methanol buffer tank. ④ When the methanol washing tower bottom liquid level is maintained above 70%, and the methanol washing tower and methanol buffer tank are interlocked, open the valve from the methanol washing tower bottom circulation pump to the methanol buffer tank to drain liquid into the methanol buffer tank. If the liquid level does not drop below 70%, manually adjust the valve from the methanol washing tower bottom circulation pump to the methanol buffer tank to lower the methanol washing tower bottom liquid level to within 40%~70%. ⑤ When the methanol washing tower pressure reaches 10kPa, the methanol washing tower gas volume is relatively high. In order to recover organic matter in the non-condensable gas, it is necessary to control the valve on the methanol washing tower pipeline to increase the methanol flow rate. After the methanol flow rate increases, the bottom liquid level rises. To ensure the stability of the bottom liquid level, open the valve from the methanol washing tower bottom circulation pump to the methanol buffer tank to maintain the bottom liquid level within 40%~70%.

Claims

1. A device for recovering non-condensable gases from a dimethyl carbonate distillation column, characterized in that: The system includes a methanol washing tower with a remote level gauge at the bottom and a circulation pump connected to the bottom. The tower has a methanol inlet at the top and a non-condensable gas inlet at the bottom, which are connected to the reflux tanks of a dimethyl carbonate reactive distillation tower, a dimethyl carbonate distillation tower, and a dimethyl carbonate product distillation tower. A vapor outlet at the top connects to the vapor inlet of a top cooler, and the condensate outlet of the top cooler connects to the top inlet of the methanol washing tower. The bottom solution of the methanol washing tower is connected to the top via a circulation pump, creating a mixed liquid circulation system to increase absorption efficiency. The outlet pipeline of the circulation pump is connected to a methanol buffer tank.

2. The apparatus for recovering non-condensable gases from a dimethyl carbonate distillation column according to claim 1, characterized in that: Refined methanol is introduced into the methanol washing tower, and the bottom liquid level of the methanol washing tower is controlled at 40% to 70% of the volume of the methanol washing tower.

3. The apparatus for recovering non-condensable gases from a dimethyl carbonate distillation column according to claim 2, characterized in that: The bottom solution outlet of the methanol washing tower is connected to the top inlet of the methanol washing tower and the methanol buffer tank via a circulation pump. The liquid levels of the methanol washing tower and the methanol buffer tank are interlocked. During the circulation process, when the liquid level of the methanol washing tower rises to 70%, the valve connecting the reboiler circulation pump of the methanol washing tower to the methanol buffer tank is opened, and the material of the methanol washing tower is sent to the methanol buffer tank.

4. The apparatus for recovering non-condensable gases from a dimethyl carbonate distillation column according to claim 1, characterized in that: The vapor phase at the top outlet of the methanol scrubbing tower is sent to the top cooler for cooling. The top cooler is connected to the chilled water supply and return system, and the condensate is recovered back to the methanol scrubbing tower.

5. The apparatus for recovering non-condensable gases from a dimethyl carbonate distillation column according to claim 1, characterized in that: The non-condensable gas inlet of the methanol washing tower is connected to the reflux tank of the dimethyl carbonate reactive distillation tower, the reflux tank of the dimethyl carbonate distillation tower, and the reflux tank of the dimethyl carbonate product distillation tower, respectively.

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