A primary methanol recovery device in dimethyl carbonate production

Abstract

The utility model relates to a primary methanol recovery device in dimethyl carbonate preparation. Its technical scheme is: the lower part of dimethyl carbonate reaction tower is connected to the side line of primary propylene glycol tower through pipeline and first material transfer pump, the top of primary propylene glycol tower is connected to the middle and lower part side line of dimethyl carbonate reaction tower through reflux pipeline, the bottom of primary propylene glycol tower is connected to flash tank through pipeline, the top of flash tank is connected to vacuum buffer tank through pipeline and condenser, the top of vacuum buffer tank is connected to vacuum pump through pipeline, the bottom of flash tank is connected to the middle and upper part side line of propylene glycol rectification tower through pipeline and second material transfer pump. Advantageous effects are: the utility model increases a first flash tank between the discharge of primary propylene glycol tower and propylene glycol rectification tower, and the flash methanol gas phase enters vacuum buffer tank after condensation through condenser, thereby realizing methanol recovery, avoiding methanol loss in subsequent rectification process, and playing the role of cost reduction and benefit increase.

Description

Technical Field

[0001] This utility model relates to the field of dimethyl carbonate production technology, and in particular to a primary methanol recovery device in the preparation of dimethyl carbonate. Background Technology

[0002] Dimethyl carbonate (DMC) is produced by transesterification of methanol and propylene carbonate in the presence of a catalyst. The products include DMC and 1,2-propanediol. During the reaction, methanol acts as the carrier in the methanol-dimethyl carbonate azeotropic system, and is often in excess. The excess methanol and propylene glycol, one of the reaction products, are then fed into a primary propylene glycol column for atmospheric pressure flash evaporation to recover methanol from the top of the column.

[0003] Due to the low flash evaporation efficiency, 5%-10% of methanol still enters the propylene glycol distillation system from the bottom of the primary propylene glycol column, and is eventually distilled from the top of the distillation column to obtain low-concentration primary methanol with low usability. Utility Model Content

[0004] The purpose of this invention is to address the aforementioned deficiencies in the existing technology by providing a primary methanol recovery device for the preparation of dimethyl carbonate, which recovers primary methanol from the reaction production section, reduces material loss in the dimethyl carbonate production process, and achieves cost reduction and efficiency improvement.

[0005] The present invention discloses a primary methanol recovery device for the preparation of dimethyl carbonate, the technical solution of which includes a dimethyl carbonate reaction tower (1), a first transfer pump (2), a primary propylene glycol tower (3), a flash tank (4), a second transfer pump (5), a propylene glycol distillation tower (6), a condenser (7), and a vacuum buffer tank (9). The lower part of the dimethyl carbonate reaction tower (1) is connected to the side line of the primary propylene glycol tower (3) through pipelines and the first transfer pump (2). The top of the primary propylene glycol column (3) is connected to the lower middle side line of the dimethyl carbonate reaction column (1) via a reflux line. The bottom of the primary propylene glycol column (3) is connected to the flash tank (4) via a line. The top of the flash tank (4) is connected to the vacuum buffer tank (9) via a line and a condenser (7). The top of the vacuum buffer tank (9) is connected to the vacuum pump (10) via a line. The bottom of the flash tank (4) is connected to the upper middle side line of the propylene glycol distillation column (6) via a line and a second feed pump (5).

[0006] Preferably, the top of the vacuum pump (10) is connected to the exhaust gas treatment system (11) via an exhaust gas pipeline.

[0007] Preferably, the top of the flash tank (4) is connected to the tube inlet of the condenser (7) via a pipeline, and the tube outlet of the condenser (7) is connected to the vacuum buffer tank (9) via a pipeline.

[0008] Preferably, the shell-side inlet of the condenser (7) is connected to the circulating cooling water pipe (8), and the shell-side outlet of the condenser (7) is connected to the circulating water storage tank through a pipeline.

[0009] Preferably, the bottom of the vacuum buffer tank (9) is provided with a primary methanol outlet and a first control valve (12).

[0010] Preferably, a second control valve (13) is installed on the reflux line connected to the top of the primary propylene glycol tower (3).

[0011] Preferably, the above-mentioned flash tank (4) is a vacuum flash tank of level one or above, and the height-to-diameter ratio of the flash tank (4) is designed to be greater than 2.5.

[0012] The beneficial effects of this invention are as follows: By adding a flash tank between the primary propylene glycol tower discharge and the propylene glycol distillation tower, the flashed methanol vapor phase is condensed by a condenser and then enters a vacuum buffer tank to achieve methanol recovery, avoiding methanol loss during subsequent distillation. In short, this invention first recovers methanol from a high-concentration methanol mixture and then flashes a low-concentration methanol mixture under vacuum, which saves energy and reduces the operating load of the vacuum pump, while achieving effective methanol recovery and reducing costs and increasing efficiency. Attached Figure Description

[0013] Figure 1 This is a connection diagram of this utility model; In the diagram above: 1. Dimethyl carbonate reaction tower; 2. First feed pump; 3. Primary propylene glycol tower; 4. Flash tank; 5. Second feed pump; 6. Propylene glycol distillation tower; 7. Condenser; 8. Circulating cooling water pipe; 9. Vacuum buffer tank; 10. Vacuum pump; 11. Tail gas treatment system; 12. First control valve; 13. Second control valve. Detailed Implementation

[0014] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0015] Example 1, referring to Figure 1This utility model discloses a primary methanol recovery device for the preparation of dimethyl carbonate, comprising a dimethyl carbonate reaction tower 1, a first transfer pump 2, a primary propylene glycol tower 3, a flash tank 4, a second transfer pump 5, a propylene glycol distillation tower 6, a condenser 7, and a vacuum buffer tank 9. The lower part of the dimethyl carbonate reaction tower 1 is connected to the side line of the primary propylene glycol tower 3 via pipelines and the first transfer pump 2. The top of the primary propylene glycol tower 3 is connected to the lower middle side line of the dimethyl carbonate reaction tower 1 via a reflux pipeline. The bottom of the primary propylene glycol tower 3 is connected to the flash tank 4 via pipelines. The top of the flash tank 4 is connected to the vacuum buffer tank 9 via pipelines and the condenser 7. The top of the vacuum buffer tank 9 is connected to a vacuum pump 10 via pipelines. The bottom of the flash tank 4 is connected to the upper middle side line of the propylene glycol distillation tower 6 via pipelines and the second transfer pump 5.

[0016] The top of the aforementioned vacuum pump 10 is connected to the exhaust gas treatment system 11 via an exhaust gas pipeline.

[0017] The top of the flash tank 4 is connected to the tube inlet of the condenser 7 via a pipeline, and the tube outlet of the condenser 7 is connected to the vacuum buffer tank 9 via a pipeline.

[0018] The shell-side inlet of the condenser 7 is connected to the circulating cooling water pipe 8, and the shell-side outlet of the condenser 7 is connected to the circulating water storage tank via a pipeline.

[0019] The bottom of the aforementioned vacuum buffer tank 9 is equipped with a primary methanol outlet and a first control valve 12.

[0020] A second control valve 13 is installed on the reflux line connected to the top of the primary propylene glycol column 3.

[0021] The aforementioned flash tank 4 is a single-stage vacuum flash tank. The height-to-diameter ratio of the flash tank 4 is designed to be greater than 2.5, and the design size of the top pipe opening is not less than DN300mm.

[0022] When this utility model is used, the bottom of the dimethyl carbonate reaction tower 1 is fed to the primary propylene glycol tower 3 by the first transfer pump 2. Excess methanol and one of the reaction products, propylene glycol, enter the primary propylene glycol tower 3 for atmospheric pressure flash evaporation to recover methanol from the top of the tower and then send it to the dimethyl carbonate reaction tower 1 for recycling. Then, a flash tank 4 is added to the process from the discharge of the primary propylene glycol column 3 to the propylene glycol distillation column 6. The height-to-diameter ratio of the flash tank is designed to be greater than 2.5, and the top pipe opening is designed to be no less than DN300, which facilitates the improvement of methanol flashing efficiency. The flashed methanol vapor phase is then condensed by the condenser and enters the vacuum buffer tank 9. Methanol is recovered at the bottom of the vacuum buffer tank 9, and the methanol that is not completely recovered at the top of the primary propylene glycol column 3 is further recovered here to avoid methanol loss during subsequent distillation. In addition, the tail gas at the top of the vacuum buffer tank 9 enters the tail gas system 11 for further treatment.

[0023] This invention first recovers methanol from a high-concentration methanol mixture, and then flash-evaporates a low-concentration methanol mixture under vacuum. This saves energy and reduces the operating load on the vacuum pump, while achieving effective methanol recovery.

[0024] Example 2: A primary methanol recovery device for dimethyl carbonate preparation mentioned in this utility model includes a dimethyl carbonate reaction tower 1, a first transfer pump 2, a primary propylene glycol tower 3, a flash tank 4, a second transfer pump 5, a propylene glycol distillation tower 6, a condenser 7, and a vacuum buffer tank 9. The lower part of the dimethyl carbonate reaction tower 1 is connected to the side line of the primary propylene glycol tower 3 via a pipeline and the first transfer pump 2. The top of the primary propylene glycol tower 3 is connected to the lower middle side line of the dimethyl carbonate reaction tower 1 via a reflux pipeline. The bottom of the primary propylene glycol tower 3 is connected to the flash tank 4 via a pipeline. The top of the flash tank 4 is connected to the vacuum buffer tank 9 via a pipeline and the condenser 7. The top of the vacuum buffer tank 9 is connected to a vacuum pump 10 via a pipeline. The bottom of the flash tank 4 is connected to the upper middle side line of the propylene glycol distillation tower 6 via a pipeline and the second transfer pump 5.

[0025] The difference from Example 1 is: In this embodiment, the flash tank 4 can be a two-stage vacuum flash tank, which can achieve better methanol recovery. The methanol that is not completely recovered at the top of the primary propylene glycol tower 3 can be further recovered here, avoiding methanol loss during subsequent distillation.

[0026] The above description is merely a preferred embodiment of this utility model. Any person skilled in the art may modify this utility model or modify it into an equivalent technical solution using the technical solutions described above. Therefore, any simple modifications or equivalent transformations made based on the technical solutions of this utility model are within the scope of protection claimed by this utility model.

Claims

1. A primary methanol recovery device for dimethyl carbonate preparation, characterized in that: The system includes a dimethyl carbonate reaction tower (1), a first transfer pump (2), a primary propylene glycol tower (3), a flash tank (4), a second transfer pump (5), a propylene glycol distillation tower (6), a condenser (7), and a vacuum buffer tank (9). The lower part of the dimethyl carbonate reaction tower (1) is connected to the side line of the primary propylene glycol tower (3) via a pipeline and the first transfer pump (2). The top of the primary propylene glycol tower (3) is connected to the middle and lower side line of the dimethyl carbonate reaction tower (1) via a reflux pipeline. The bottom of the primary propylene glycol tower (3) is connected to the flash tank (4) via a pipeline. The top of the flash tank (4) is connected to the vacuum buffer tank (9) via a pipeline and the condenser (7). The top of the vacuum buffer tank (9) is connected to a vacuum pump (10) via a pipeline. The bottom of the flash tank (4) is connected to the middle and upper side line of the propylene glycol distillation tower (6) via a pipeline and the second transfer pump (5).

2. The primary methanol recovery device in the preparation of dimethyl carbonate according to claim 1, characterized in that: The top of the vacuum pump (10) is connected to the exhaust gas treatment system (11) via an exhaust gas pipeline.

3. The primary methanol recovery device in the preparation of dimethyl carbonate according to claim 2, characterized in that: The top of the flash tank (4) is connected to the tube inlet of the condenser (7) via a pipeline, and the tube outlet of the condenser (7) is connected to the vacuum buffer tank (9) via a pipeline.

4. The primary methanol recovery device in the preparation of dimethyl carbonate according to claim 3, characterized in that: The shell-side inlet of the condenser (7) is connected to the circulating cooling water pipe (8), and the shell-side outlet of the condenser (7) is connected to the circulating water storage tank through a pipeline.

5. The primary methanol recovery device in the preparation of dimethyl carbonate according to claim 3, characterized in that: The bottom of the vacuum buffer tank (9) is provided with a primary methanol outlet and a first control valve (12).

6. The primary methanol recovery device in the preparation of dimethyl carbonate according to claim 1, characterized in that: A second control valve (13) is installed on the reflux line connected to the top of the primary propylene glycol tower (3).

7. The primary methanol recovery device in the preparation of dimethyl carbonate according to claim 1, characterized in that: The flash tank (4) is a vacuum flash tank of level one or above, and the height-to-diameter ratio of the flash tank (4) is designed to be greater than 2.5.

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