A method for the preliminary separation of dimethyl oxalate in ethylene glycol production from synthesis gas

Abstract

The present invention discloses a device for the preliminary separation of ethylene glycol dimethyl oxalate from synthesis gas, comprising a dimethyl oxalate synthesis reactor, an absorption tower, and a condenser located at the top of the absorption tower. The absorption tower is provided with a filler, a gas distributor, and a liquid distributor. The gas phase and liquid methanol in the absorption tower are fully contacted in the filler, and heat exchange is performed to reduce the gas phase temperature. After the gas phase temperature is reduced, the gas phase that does not contain dimethyl oxalate and DMC is discharged outward through the gas outlet of the condenser. After cooling, the dimethyl oxalate and DMC form a liquid and flow down to the bottom of the absorption tower, and then are sent to an external distillation section for further purification. The liquid methanol absorbs heat and becomes gaseous and enters the condenser with the circulating gas phase for condensation, thereby preventing DMO from crystallizing into a solid state due to excessively low temperature and clogging equipment and pipelines. The device solves the problem of dimethyl oxalate being difficult to separate in the gas phase and avoids the situation where crystallization and clogging of pipelines and equipment occurs due to the use of circulating water to condense dimethyl oxalate.

Description

Technical Field

[0001] The invention relates to the technical field of dimethyl oxalate separation, and in particular to a method for preliminarily separating dimethyl oxalate in synthesis gas to ethylene glycol. Background Art

[0002] Ethylene glycol is an important chemical raw material, primarily used in the production of polyester, polyester resin, desiccant, plasticizer, surfactant, synthetic fiber, cosmetics, and explosives. It is also used as a solvent for dyes and inks, as an antifreeze agent for engines, as a gas dehydrator, and in the manufacture of resins. It is also used as a wetting agent in cellophane, fiber, leather, and adhesives. It can be used to produce synthetic resin PET, fiber-grade PET (i.e., polyester fiber), and bottle flake-grade PET for mineral water bottles. It can also be used to produce alkyd resins and glyoxal, and is also used as an antifreeze agent. Besides being used as an automotive antifreeze, it is also used for industrial cooling, generally referred to as a refrigerant. It can also be used as a condensing agent, similar to water. Therefore, the efficient conversion of coal or natural gas into chemical raw materials such as ethylene glycol reduces dependence on petroleum resources, contributing to an optimized energy and resource structure and is of great significance.

[0003] In recent years, with the gradual maturity of syngas-to-ethylene glycol technology, China's ethylene glycol consumption continued to grow in 2018, with net imports reaching approximately 10 million tons and production exceeding 7.2 million tons. One-third of this came from coal (syngas)-to-ethylene glycol. Syngas-to-ethylene glycol has been widely used in the polyester and chemical fiber industry, becoming a significant component of China's ethylene glycol production capacity. By the beginning of 2019, 22 coal (syngas)-to-ethylene glycol projects had been put into operation in China, with a total annual production capacity of 4.48 million tons. These syngas-to-ethylene glycol projects have generally achieved stable, high-load operation.

[0004] However, in the process of producing ethylene glycol dimethyl oxalate from synthesis gas, dimethyl oxalate has a melting point of 54°C. When the temperature drops below 54°C, it becomes a solid state, and its melting point decreases after dissolving in methanol. During the dimethyl oxalate synthesis process, the reactor outlet gas phase contains Mn, N, CO, N, dimethyl oxalate, dimethyl carbonate, etc. Dimethyl oxalate and dimethyl carbonate need to be separated from the recycle gas. Conventional cooling to induce phase transition and convert dimethyl oxalate and dimethyl carbonate into liquid state for separation is difficult to control, which can easily cause dimethyl oxalate to fall below its melting point, resulting in equipment and pipeline blockage. Summary of the Invention

[0005] In order to solve one or more technical problems existing in the prior art, the purpose of this application is to provide a method for the preliminary separation of dimethyl oxalate in the synthesis of ethylene glycol from synthesis gas, which solves the problem that dimethyl oxalate is difficult to separate in the gas phase and avoids the use of circulating water to condense dimethyl oxalate, causing crystallization and clogging of pipelines and equipment.

[0006] To solve the above existing technical problems, this application adopts the following technical solutions:

[0007] A method for the preliminary separation of dimethyl oxalate in ethylene glycol production from synthesis gas comprises a dimethyl oxalate synthesis reactor, an absorption tower connected to the gas outlet of the dimethyl oxalate synthesis reactor via a pipeline, and a condenser arranged at the top of the absorption tower. The absorption tower is provided with a packing, a gas distributor, and a liquid distributor, wherein the liquid distributor and the gas distributor are respectively arranged above and below the packing.

[0008] The gas phase of the synthesis gas after the reaction in the dimethyl oxalate synthesis reactor enters the absorption tower, and then is evenly distributed through the gas distributor and rises into the packing.

[0009] The gaseous methanol in the absorption tower is cooled by the condenser and then flows back into the absorption tower and is evenly distributed through the liquid distributor before entering the packing. The gas phase and liquid methanol in the absorption tower are fully contacted and heat-exchanged in the packing to reduce the gas phase temperature. After the gas phase temperature is reduced, the gas phase that does not contain dimethyl oxalate and DMC is discharged outward through the gas outlet of the condenser.

[0010] After cooling, dimethyl oxalate and DMC form liquids and flow down to the bottom of the absorption tower, and are then sent to an external distillation section for further purification. Liquid methanol absorbs heat and becomes gaseous, entering the condenser with the circulating gas phase for condensation, thereby preventing DMO from crystallizing into a solid state due to excessively low temperature and clogging equipment and pipelines.

[0011] Optionally, the gas distributor includes a distribution pipe, a conduit, a plurality of branch pipes and an arc plate, the branch pipes are arranged through the distribution pipe, the conduit is arranged on the branch pipe, and each arc plate is arranged on the periphery of the distribution pipe.

[0012] Optionally, the gas distributor further includes a plurality of fixed channel steels, and each of the branch pipes is fixed by the corresponding fixed channel steel.

[0013] Optionally, a gas-liquid separation tank is further provided at the gas outlet end of the condenser, and the liquid separated by the gas-liquid separation tank flows back into the absorption tower, and the gas discharged from the condenser is subjected to secondary separation in the gas-liquid separation tank before flowing out to the subsequent system.

[0014] Optionally, the filler is composed of a plurality of corrugated metal plates.

[0015] Optionally, the temperature of the condenser is 35-40°C.

[0016] Optionally, the absorption tower controls the water content to be less than 500 ppm.

[0017] Optionally, the outlet temperature of the dimethyl oxalate synthesis reactor is 110-130°C, and the circulating gas volume is 150,000 Nm 3 / h.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention can effectively evenly distribute the gas phase and liquid phase, effectively separate dimethyl oxalate and DMC through methanol, completely condense the dimethyl oxalate in the circulating gas, and prevent dimethyl oxalate from being carried into the subsequent system. This prevents dimethyl oxalate from generating oxalic acid upon contact with water in the subsequent system, thereby reducing the difficulty of treating alcohol-containing wastewater in the subsequent system. Furthermore, the present invention can save circulating water for cooling the product gas and reduce steam consumption in the distillation unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a process flow chart of the present invention;

[0021] Figure 2 Schematic diagram of the gas distributor in the present utility model;

[0022] In the figure: 1. dimethyl oxalate synthesis reactor; 2. absorption tower; 3. gas distributor; 4. packing; 5. liquid distributor; 6. condenser; 7. gas-liquid separation tank; 8. distribution pipe; 9. conduit; 10. branch pipe; 11. fixed channel steel; 12. arc plate. DETAILED DESCRIPTION

[0023] Below, the present application is further described in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0024] In the description of this application, it should be understood that the terms "up", "down", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on this application.

[0025] The terms "first," "second," and the like in this application are used to distinguish similar objects, and are not used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of this application can be implemented in an order other than that illustrated or described herein, and that the objects distinguished by "first," "second," and the like are generally of the same type, and do not limit the number of objects; for example, the first object can be one or more. In addition, "and / or" in the specification and claims refers to at least one of the connected objects, and the character " / " generally indicates that the objects connected are in an "or" relationship.

[0026] like Figure 1 As shown, a method for the preliminary separation of dimethyl oxalate in ethylene glycol production from synthesis gas comprises a dimethyl oxalate synthesis reactor 1, an absorption tower 2 connected to the gas outlet of the dimethyl oxalate synthesis reactor 1 through a pipeline, and a condenser 6 arranged at the top of the absorption tower 2. The absorption tower 2 is provided with a packing 4, a gas distributor 3 and a liquid distributor 5. The liquid distributor 5 and the gas distributor 3 are respectively arranged above and below the packing 4. The gas phase of the synthesis gas after the reaction in the dimethyl oxalate synthesis reactor 1 enters the absorption tower 2, and then rises to the packing 4 after being evenly distributed by the gas distributor 3. The outlet circulating gas of the dimethyl oxalate synthesis reactor 1 contains N2 (nitrogen), CO (carbon monoxide), CO2 (carbon dioxide), NO (nitric oxide), MN (nitrous oxide), and the like. The gaseous methanol in the absorption tower 2 is cooled by the condenser 6 and then refluxed into the absorption tower 2 and is evenly distributed through the liquid distributor 5 before entering the packing 4. The gas phase and liquid methanol in the absorption tower 2 are fully contacted and heat-exchanged in the packing 4 to reduce the gas phase temperature. After the gas phase temperature is reduced, the gas phase not containing dimethyl oxalate and DMC is discharged to the outside through the gas outlet of the condenser 6. After cooling, dimethyl oxalate and DMC form a liquid and flow down to the bottom of the absorption tower 2, and are then sent to the external distillation section for further purification. The liquid methanol absorbs heat and becomes a gaseous state. It enters the condenser 6 with the circulating gas phase for condensation, thereby preventing DMO from crystallizing into a solid state due to excessively low temperature and clogging equipment and pipelines.

[0027] In the present invention, the esterification tower outlet gas phase enters the dimethyl oxalate synthesis reactor 1, generates a mixed gas such as dimethyl oxalate, methanol, and DMC through a catalytic reaction, and enters the absorption tower 2. After the gas phase at the top outlet of the absorption tower 2 passes through the overhead condenser 6, a certain saturated gas phase methanol is condensed and then returned to the absorption tower 2 to absorb and condense the dimethyl oxalate in the product gas, and is sent to the subsequent dimethyl oxalate distillation unit for deep separation. MN, NO, inert gases, etc. that are not absorbed by methanol return to the esterification tower for reaction. The present invention can effectively evenly distribute the gas phase and liquid phase in the absorption tower 2, effectively separate dimethyl oxalate and DMC through methanol, and condense all dimethyl oxalate in the circulating gas. No dimethyl oxalate is brought into the rear system, preventing dimethyl oxalate from generating oxalic acid corrosion equipment in the rear system when it encounters water, thereby reducing the difficulty of treating alcohol-containing wastewater in the rear system. At the same time, it is possible to save circulating water for cooling the product gas and reduce steam consumption in the distillation unit.

[0028] Among them, such as Figure 2 As shown, the gas distributor 3 includes a distribution pipe 8, a conduit 9, several branch pipes 10 and an arc plate 12. The branch pipe 10 is arranged through the distribution pipe 8, the conduit 9 is arranged on the branch pipe 10, and each of the arc plates 12 is arranged on the periphery of the distribution pipe 8; the gas distributor 3 also includes several fixed channel steels 11, and each of the branch pipes 10 is fixed by the corresponding fixed channel steel 11.

[0029] Among them, the distribution pipe 8 is connected to the branch pipe 10. When the gas phase enters the distribution pipe 8, it flows into each branch pipe 10 through the distribution pipe 8, and then is discharged outward through the conduit 9 on the branch pipe 10. The gas phase is evenly distributed in the same plane of the absorption tower 2 through the conduit 9. Among them, each branch pipe 10 is installed with a number of conduits 9 that protrude 5 to 10 mm upward. The conduits 9 can control the flow direction of the airflow while distributing the gas phase directly into the filler 4 to avoid the gas phase from flowing downward. An arc plate 12 is installed on the periphery of the distribution pipe 8. The arc plate 12 can support the connection of the branch pipe 10 to avoid separation of the branch pipe 10 from the distribution pipe 8. The fixed channel steel 11 can support and fix each branch pipe 10 in the absorption tower 2 to prevent the branch pipe 10 from tilting.

[0030] A further improvement is that a gas-liquid separation tank 7 is also provided at the gas outlet end of the condenser 6, and the liquid separated by the gas-liquid separation tank 7 is refluxed into the absorption tower 2, and the gas discharged from the condenser 6 is subjected to secondary separation by the gas-liquid separation tank 7 before flowing out to the subsequent system.

[0031] When the gas phase continues to be discharged with liquid, the liquid will accumulate at the low point of the pipeline. When it accumulates to a certain level, it will cause a high pressure difference in the system, which will seriously cause liquid hammer in the pipeline and equipment, leading to damage. Therefore, the gas-liquid separation tank 7 can effectively perform secondary filtration on the liquid methanol brought out from the outlet of the condenser 6 to avoid the subsequent discharge of liquid in the gas phase, which will lead to accumulation at the low point of the pipeline.

[0032] At the same time, the filler 4 is composed of a plurality of metal corrugated plates. The filler 4 arranged regularly by the metal corrugated plates can better increase the gas-liquid contact area and achieve a better heat exchange effect.

[0033] A further improvement is that the temperature of the condenser 6 is 35-40°C.

[0034] If the temperature is lower than 35℃, a large amount of circulating water will be used, which will be heated in the subsequent system, consuming steam and circulating water, and increasing production costs. If the temperature is higher than 40℃, the methanol cannot be completely condensed, and a large amount of methanol will go to the subsequent system with the gas phase. The amount of reflux methanol is insufficient, and the dimethyl oxalate in the absorption tower 2 cannot be completely condensed, and will be brought into the subsequent system with the gas phase.

[0035] A further improvement is that the water content in the absorption tower 2 is controlled to be less than 500 ppm to prevent dimethyl oxalate from reacting with water to form oxalic acid, which may cause equipment corrosion and shorten the service life of the equipment.

[0036] Further improvement is that the outlet temperature of the dimethyl oxalate synthesis reactor 1 is 110-130 ° C, the circulating gas volume is 150,000 Nm 3 At this temperature and circulation rate, the methanol refluxed from the top of the absorption tower 2 and entered the gas phase at the bottom of the absorption tower 2 achieve heat balance. The dimethyl oxalate at the bottom has high purity and low methanol content, which reduces the steam consumption of dimethyl oxalate purification in the subsequent system. At the same time, the dimethyl oxalate can be completely condensed and absorbed into the liquid phase.

[0037] The above-mentioned embodiments are only preferred embodiments of the present application and cannot be used to limit the scope of protection of the present application. Any non-substantial changes and replacements made by technicians in this field based on the present application shall fall within the scope of protection required by the present application.

Claims

1. A method for the preliminary separation of dimethyl oxalate in ethylene glycol produced from synthesis gas, the method using an apparatus for the preliminary separation of dimethyl oxalate in ethylene glycol produced from synthesis gas, characterized in that: The device comprises a dimethyl oxalate synthesis reactor (1), an absorption tower (2) connected to the gas outlet of the dimethyl oxalate synthesis reactor (1) through a pipeline, and a condenser (6) arranged at the top of the absorption tower (2); a filler (4), a gas distributor (3) and a liquid distributor (5) are provided in the absorption tower (2); the liquid distributor (5) and the gas distributor (3) are respectively arranged above and below the filler (4); The gaseous phase of the synthesis gas after the reaction in the dimethyl oxalate synthesis reactor (1) enters the absorption tower (2) for circulation, and then is evenly distributed by the gas distributor (3) and rises into the filler (4). The gaseous methanol in the absorption tower (2) is cooled by the condenser (6) and then flows back into the absorption tower (2) and is evenly distributed by the liquid distributor (5) and enters the filler (4). The gaseous phase and liquid methanol in the absorption tower (2) are circulated in the filler (4). After sufficient contact and heat exchange, the gas phase temperature is lowered. After the gas phase temperature is lowered, the gas phase that does not contain dimethyl oxalate and dimethyl carbonate is discharged outward through the gas outlet of the condenser (6). After cooling, dimethyl oxalate and dimethyl carbonate are formed into liquid form and flow down to the bottom of the absorption tower (2), and then sent to the external distillation section for further purification. The liquid methanol absorbs heat and becomes gaseous and enters the condenser (6) with the circulating gas phase for condensation, thereby preventing dimethyl oxalate from being crystallized into a solid state due to excessively low temperature and clogging equipment and pipelines. The gas distributor (3) includes a distribution pipe (8), a conduit (9), a plurality of branch pipes (10) and an arc plate (12). The branch pipes (10) are arranged on the distribution pipe (8). Each branch pipe (10) is equipped with a plurality of conduits (9) protruding upward by 5 to 10 mm. The conduits (9) can control the flow direction of the gas flow while distributing the gas phase directly into the filler (4) to avoid the gas phase from descending. Each arc plate (12) is arranged on the periphery of the distribution pipe (8).

2. The method for preliminary separation of dimethyl oxalate in synthesis gas to ethylene glycol according to claim 1, characterized in that: The gas distributor (3) further comprises a plurality of fixed channel steels (11), and each branch pipe (10) is fixed by a corresponding fixed channel steel (11).

3. The method for preliminary separation of dimethyl oxalate in synthesis gas to ethylene glycol according to claim 1, characterized in that: The gas outlet end of the condenser (6) is further provided with a gas-liquid separation tank (7), and the liquid separated by the gas-liquid separation tank (7) flows back into the absorption tower (2), and the gas discharged from the condenser (6) is subjected to secondary separation by the gas-liquid separation tank (7) before flowing out to the subsequent system.

4. The method for preliminary separation of dimethyl oxalate in synthesis gas to ethylene glycol according to claim 1, characterized in that: The filler (4) is composed of a plurality of metal corrugated plates.

5. The method for preliminary separation of dimethyl oxalate in synthesis gas to ethylene glycol according to claim 1, characterized in that: The temperature of the condenser (6) is 35-40°C.

6. The method for preliminary separation of dimethyl oxalate in synthesis of ethylene glycol from synthesis gas according to claim 1, characterized in that: The absorption tower (2) controls the water content to be less than 500 ppm.

7. The method for preliminary separation of dimethyl oxalate in synthesis of ethylene glycol from synthesis gas according to claim 1, characterized in that: The outlet temperature of the dimethyl oxalate synthesis reactor (1) is 110-130°C, and the circulating gas volume is 150,000 Nm 3 / h.

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