A separation system and method for dimethyl carbonate and methanol

Abstract

This invention relates to a separation system and method for dimethyl carbonate (DMC) and methanol. A mixture containing DMC and methanol sequentially passes through a DMC purification column and a methanol recovery column connected by pipelines. High-purity DMC is obtained at the bottom of the DMC purification column, and high-purity methanol is obtained at the bottom of the methanol recovery column. Product tanks and condensers are connected to the tops of both the DMC purification column and the methanol recovery column. This invention features a simple process, convenient operation, and can obtain DMC and MeOH products with high purity and high yield. The cross-heat exchange between the top products of the two columns effectively utilizes thermal energy, reducing the overall energy consumption of the process. Furthermore, a hot fluid from the bottom of the DMC purification column is used as the heating medium for a reboiler in the methanol recovery column, effectively utilizing the thermal energy of the hot fluid from the DMC purification column bottom and further reducing energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, specifically relating to a separation system and method for dimethyl carbonate and methanol. Background Technology

[0002] Ethylene glycol, an important chemical raw material, is mainly used in the production of polyethylene terephthalate (PET). The traditional ethylene glycol production route involves producing ethylene oxide from petroleum ethylene, followed by hydration. This route, known as the "petroleum route," has the advantage of mature technology but disadvantages such as high energy consumption and the product cost being heavily influenced by international crude oil prices. Among the various reported ethylene glycol synthesis processes, the route of synthesizing dimethyl oxalate from CO, followed by hydrogenation of dimethyl oxalate to ethylene glycol, has gradually matured. Dimethyl carbonate (DMC) is a byproduct of the CO synthesis of dimethyl oxalate. Methanol (MeOH) is introduced during the separation of dimethyl oxalate and dimethyl carbonate, yielding two products: dimethyl oxalate and DMC-MeOH. To obtain DMC with high purity and high yield, and to improve methanol utilization, the DMC-MeOH needs to be separated.

[0003] Dimethyl carbonate (DMC) is an excellent methylating, carbonylating, hydroxymethylating, and methoxylating agent with highly reactive chemical properties. As an intermediate in organic synthesis, it is widely used in the production of low-boiling-point solvents, cleaning agents, propellants, and solvents for specialty paints. After further processing, it can be used as a gasoline additive, high-energy battery electrolyte, and water treatment agent, and can be used to prepare polycarbonates, pharmaceuticals, pesticides, fragrances, and synthetic lubricants. It is an ideal substitute for highly toxic substances such as phosgene, dimethyl sulfate, and methyl chloroformate, and is hailed as a green chemical product.

[0004] Because DMC-MeOH forms a binary azeotrope, ordinary separation methods are insufficient to achieve the required product separation / purification. The main methods for separating DMC-MeOH include membrane separation, adsorption, azeotropic distillation, extractive distillation, and pressure swing distillation. Membrane separation is complex and expensive, and large-scale industrial application faces many challenges. Adsorption utilizes ion exchange resins to adsorb large amounts of MeOH, significantly increasing the DMC content in the liquid phase after adsorption. However, adsorption is only suitable for DMC-MeOH binary systems with low MeOH content. Azeotropic distillation involves adding an azeotropic agent to the DMC-MeOH azeotrope, causing methanol to form a new azeotrope with a different azeotropic temperature than the original system. The methanol-azeotropic agent azeotrope is then distilled off using the temperature difference, yielding the DMC product. Azeotropic distillation requires specific conditions to form azeotropes, limiting the number of suitable azeotropic agents. Furthermore, it is energy-intensive, highly dependent on the azeotropic composition, and difficult to operate. Extractive distillation, on the other hand, involves adding an extractant to a DMC-MeOH azeotrope with a boiling point higher than all the original components. This extractant exhibits strong compatibility with a particular component and can significantly alter the relative volatility of the original solution components. The advantages of extractive distillation are the ease of extractant selection and the wide range of adjustable extractant dosages. Its disadvantages include the generally high toxicity of the extractant, the large dosage required, the potential impact on product purity, and the high energy consumption associated with extractant recovery.

[0005] Compared to other DMC-MeOH separation methods, pressure swing distillation has advantages such as not requiring the addition of other substances, avoiding the problems of extractant or azeotropic agent recovery and product purity in extractive distillation and azeotropic distillation technologies, having a wider allowable range of operating pressure fluctuations, and simpler process. Therefore, it has been widely used in DMC industrial production.

[0006] Patent CN101462961A invented a process for synthesizing ethylene glycol and co-producing dimethyl carbonate using syngas as a raw material; however, the problem is that the purity of the obtained dimethyl carbonate is low. Patent CN200710064633 discloses a method for separating a dimethyl carbonate-methanol mixture using a membrane with different permeation selectivity for methanol and dimethyl carbonate. However, the purity of the obtained stream does not demonstrate high economic efficiency.

[0007] For the reasons mentioned above, the key to separating dimethyl carbonate and methanol in the syngas-to-ethylene glycol process lies in how to obtain high-purity dimethyl carbonate while increasing the yield of dimethyl carbonate and reducing the energy consumption for product separation. Summary of the Invention

[0008] The purpose of this invention is to provide a separation system and method for dimethyl carbonate and methanol to solve the above problems. The process is simple and easy to operate, and it can obtain DMC and MeOH products with high purity and high yield, while reducing energy consumption, which is beneficial for industrial applications.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A separation system for dimethyl carbonate and methanol includes a DMC purification column, a methanol recovery column, and a cross heat exchanger disposed between the DMC purification column and the methanol recovery column.

[0011] The tops of both the DMC refining tower and the methanol recovery tower are connected to product tanks and condensers. The top product of the DMC refining tower and the top product of the methanol recovery tower exchange heat through the cross heat exchanger.

[0012] The product from the top of the DMC refining tower after heat exchange in the cross heat exchanger is fed into the methanol recovery tower. The product from the top of the methanol recovery tower after heat exchange in the cross heat exchanger is fed into the DMC refining tower. By introducing the cross heat exchanger, the product from the top of the methanol recovery tower and the product from the top of the DMC refining tower exchange heat, thereby improving the thermal energy utilization rate.

[0013] In existing syngas-to-ethylene glycol industries, the separation process of dimethyl carbonate and methanol generally does not include a cross heat exchanger. To improve heat utilization, this invention makes a corresponding improvement: the top product of the methanol recovery tower and the top product of the DMC purification tower exchange heat through a cross heat exchanger before being mixed with crude DMC and fed into the DMC purification tower. The top product of the DMC purification tower, after heat exchange, is then fed into the methanol recovery tower. Through heat exchange, both hot and cold streams reach suitable feed temperatures. This arrangement effectively utilizes the thermal energy of the hot material at the top of the DMC purification tower, reducing the energy consumption of the entire process.

[0014] Preferably, both the DMC refining tower and the methanol recovery tower are equipped with reboilers in their bottoms.

[0015] Preferably, the DMC refining column has one reboiler in its reboiler, and the methanol recovery column has two reboilers in its reboiler. The DMC refining column's reboiler is divided into two streams of product. One stream of product is connected to one of the reboilers in the methanol recovery column's reboiler via a pipeline, serving as the heating medium for that reboiler. The pipeline is equipped with an adjustable flow control valve. Using one stream of hot fluid from the DMC refining column's reboiler as the heating medium for one reboiler in the methanol recovery column effectively utilizes the thermal energy of the hot fluid from the DMC refining column's reboiler, further reducing energy consumption.

[0016] Preferably, the cross heat exchanger is one of a shell-and-tube heat exchanger, a coaxial heat exchanger, or a coil heat exchanger.

[0017] A method for separating dimethyl carbonate and methanol, comprising using the separation system described above, wherein a mixture containing dimethyl carbonate and methanol is fed into the DMC purification tower, high-purity dimethyl carbonate product is obtained at the bottom of the DMC purification tower, and high-purity methanol is obtained at the bottom of the methanol recovery tower.

[0018] Preferably, the bottom temperature of the DMC refining tower is 125.0-200.0℃, and the bottom temperature of the methanol recovery tower is 45.0-90.0℃. More preferably, the bottom temperature of the DMC refining tower is 130.0-195.0℃, and the bottom temperature of the methanol recovery tower is 55.0-80.0℃.

[0019] Preferably, the top pressure of the DMC refining column is 0.25-3.0 MPa, and the top pressure of the methanol recovery column is 0.01-0.30 MPa. More preferably, the top pressure of the DMC refining column is 0.40-2.0 MPa, and the top pressure of the methanol recovery column is 0.06-0.20 MPa. This invention employs a high-pressure distillation followed by low-pressure distillation to separate dimethyl carbonate and methanol, resulting in a high-purity dimethyl carbonate product with a high yield, and a high-purity methanol product.

[0020] Preferably, the DMC refining tower has 15-45 trays and a top reflux ratio of 1.5-25, and the methanol recovery tower has 5-35 trays and a top reflux ratio of 1.2-15.

[0021] A mixture containing dimethyl carbonate (DMC) and methanol (MeOH) with DMC content ranging from 0.5% to 65% by mass and the balance being MeOH yields a dimethyl carbonate product with a purity greater than 99.99%, a methanol content of less than 5 ppm, a dimethyl carbonate yield greater than 99.9%, and a methanol product with a purity greater than 99.9%.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1) The process is simple and easy to operate, and DMC and MeOH products can be obtained with high purity and high yield, which is conducive to industrial application.

[0024] 2) After cross-heat exchange, the top product of the methanol recovery tower and the top product of the DMC refining tower reach the appropriate feed temperature, effectively utilizing the thermal energy of the hot material at the top of the DMC refining tower and reducing the energy consumption of the entire process.

[0025] 3) A hot fluid from the bottom of the DMC refining tower is used as the heating medium for a reboiler in the methanol recovery tower, which can effectively utilize the thermal energy of the hot fluid from the bottom of the DMC refining tower and further reduce energy consumption; in addition, a flow regulating valve is installed on this hot fluid pipeline, making operation flexible and convenient. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a dimethyl carbonate and methanol separation system according to an embodiment of the present invention.

[0027] In the diagram: 1-DMC refining tower; 2-Methanol recovery tower; 3-Cross heat exchanger; 4-Product tank; 5-Condenser; 6-Transfer pump; 7-Reboiler; 8-Control valve. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] like Figure 1 As shown, a separation system for dimethyl carbonate and methanol includes a DMC refining tower 1, a methanol recovery tower 2, and a cross heat exchanger 3 located between the DMC refining tower 1 and the methanol recovery tower 2. The tops of both the DMC refining tower 1 and the methanol recovery tower 2 are connected to product tanks 4 and condensers 5, and one or more transfer pumps 6 are installed in the pipelines. The top product of the DMC refining tower 1 and the top product of the methanol recovery tower 2 exchange heat through the cross heat exchanger 3. The top product of the DMC refining tower 1 after heat exchange through the cross heat exchanger 3 enters the methanol recovery tower 2 as feed, and the top product of the methanol recovery tower 2 after heat exchange through the cross heat exchanger 3 enters the DMC refining tower 1 as feed. The DMC refining column 1 is equipped with one reboiler 7, and the methanol recovery column 2 is equipped with two reboilers 7. The reboiler of the DMC refining column 1 is divided into two streams of product. One stream of product is connected to one of the reboilers 7 in the methanol recovery column 2 via a pipeline, serving as the heating medium for that reboiler 7. The pipeline is equipped with an adjustable flow control valve 8. The cross heat exchanger 3 is one of a shell-and-tube heat exchanger, a coaxial heat exchanger, or a coil heat exchanger.

[0031] A method for separating dimethyl carbonate and methanol in a syngas-to-ethylene glycol process, wherein the liquid mixture containing DMC-MeOH from the oxalate synthesis section has the following composition (mass fraction): methanol 86.12% and dimethyl carbonate 13.88%, and the separation system and method of the present invention are used to perform distillation separation of the above product liquid.

[0032] According to the present invention, the above-mentioned liquid mixture enters the DMC purification column 1, and DMC is collected from the bottom of the column at 0.98-1.05 MPa and 170.9℃-173.5℃. The mixture containing DMC-MeOH at the top of the column passes through the cross heat exchanger 3 and enters the methanol recovery column 2. Methanol is collected from the bottom of the methanol recovery column 2 at 0.101-0.122 MPa and 66.8-68.2℃. The mixture containing DMC-MeOH at the top of the column is returned to the DMC purification column 1 through the cross heat exchanger 3. The DMC purification column 1 has 33 trays and a top reflux ratio of 7.5-9, while the methanol recovery column 2 has 28 trays and a top reflux ratio of 3.7-8.

[0033] The composition of each stream and the yields of DMC and MeOH are shown in Table 1.

[0034] Table 1. Composition of each stream and yield of DMC and MeOH.

[0035]

[0036] As shown in Table 1, the method described here for separating dimethyl carbonate and methanol in the syngas-to-ethylene glycol process yields a dimethyl carbonate product with a purity greater than 99.99%, a methanol content of less than 5 ppm, a dimethyl carbonate yield greater than 99.9%, and a methanol product with a purity greater than 99.9%. Furthermore, this separation method is simple, easy to operate, and conducive to industrial application.

[0037] Example 2

[0038] A method for separating dimethyl carbonate and methanol, wherein the liquid mixture containing DMC-MeOH from the oxalate synthesis section has the following composition (mass fraction): methanol 35% and dimethyl carbonate 65%, and the above product liquid is separated by distillation using the separation system and method of the present invention.

[0039] According to the present invention, the above-mentioned liquid mixture enters the DMC purification column 1, and DMC is collected from the bottom of the column at 1.1-1.2 MPa and 193℃-194.5℃. The mixture containing DMC-MeOH at the top of the column passes through the cross heat exchanger 3 and enters the methanol recovery column 2. Methanol is collected from the bottom of the methanol recovery column 2 at 0.23-0.24 MPa and 86.1-88.4℃. The mixture containing DMC-MeOH at the top of the column is returned to the DMC purification column 1 through the cross heat exchanger 3. The DMC purification column 1 has 44 trays and a top reflux ratio of 1.5-3, while the methanol recovery column 2 has 15 trays and a top reflux ratio of 9-11.

[0040] The composition of each stream and the yields of DMC and MeOH are shown in Table 2.

[0041] Table 2 Composition of each stream and yield of DMC and MeOH

[0042]

[0043] As shown in Table 2, the method described here for separating dimethyl carbonate and methanol in the syngas-to-ethylene glycol process yields a dimethyl carbonate product with a purity greater than 99.99%, a methanol content of less than 5 ppm, a dimethyl carbonate yield greater than 99.9%, and a methanol product with a purity greater than 99.89%. Furthermore, this separation method is simple, easy to operate, and conducive to industrial application.

[0044] Example 3

[0045] A method for separating dimethyl carbonate and methanol, wherein the liquid mixture containing DMC-MeOH from the oxalate synthesis section has the following composition (mass fraction): methanol 98.5% and dimethyl carbonate 1.5%, and the above product liquid is separated by distillation using the separation system and method of the present invention.

[0046] According to the present invention, the above-mentioned liquid mixture enters the DMC purification column 1, and DMC is collected from the bottom of the column at 0.65-0.72 MPa and 161.5℃-164.8℃. The mixture containing DMC-MeOH at the top of the column passes through the cross heat exchanger 3 and enters the methanol recovery column 2. Methanol is collected from the bottom of the methanol recovery column 2 at 0.04-0.05 MPa and 45.3-47.7℃. The mixture containing DMC-MeOH at the top of the column is returned to the DMC purification column 1 through the cross heat exchanger 3. The DMC purification column 1 has 18 trays and a reflux ratio of 9.8-13, while the methanol recovery column 2 has 34 trays and a reflux ratio of 1.3-3.5.

[0047] The composition of each stream and the yields of DMC and MeOH are shown in Table 3.

[0048] Table 3 Composition of each stream and yield of DMC and MeOH

[0049]

[0050] As shown in Table 3, the method described here for separating dimethyl carbonate and methanol in the syngas-to-ethylene glycol process yields a dimethyl carbonate product with a purity greater than 99.99%, a methanol content of less than 5 ppm, a dimethyl carbonate yield greater than 99.9%, and a methanol product with a purity greater than 99.99%. Furthermore, this separation method is simple, easy to operate, and conducive to industrial application.

[0051] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A system for separating dimethyl carbonate and methanol, characterized by comprising: The system comprises a DMC refining tower (1), a methanol recovery tower (2) and a cross heat exchanger (3) between the DMC refining tower (1) and the methanol recovery tower (2) connected in sequence according to the feeding direction. The top of the DMC refining tower (1) and the methanol recovery tower (2) is connected with a product tank (4) and a condenser (5), and the top product of the DMC refining tower (1) is condensed by the condenser (5) and then exchanges heat with the condensed top product of the methanol recovery tower (2) by the cross heat exchanger (3). The top product of the DMC refining tower (1) after heat exchange by the cross heat exchanger (3) is fed into the methanol recovery tower (2), and the top product of the methanol recovery tower (2) after heat exchange by the cross heat exchanger (3) is fed into the DMC refining tower (1). The bottom of the methanol recovery tower (2) is provided with a reboiler (7), and one of the bottom products of the DMC refining tower (1) is fed into the reboiler (7) of the methanol recovery tower (2) as the heating medium of the reboiler (7). The pipeline of the bottom product of the DMC refining tower (1) fed into the reboiler (7) of the methanol recovery tower (2) is provided with an adjustable flow regulating valve (8).

2. The system for separating dimethyl carbonate and methanol according to claim 1, wherein The bottom of the DMC refining tower (1) is provided with a reboiler (7).

3. The system for separating dimethyl carbonate and methanol according to claim 2, wherein The bottom of the DMC refining tower (1) is provided with a reboiler (7), and the bottom of the methanol recovery tower (2) is provided with two reboilers (7).

4. The system for separating dimethyl carbonate and methanol according to claim 1, wherein The cross heat exchanger (3) is one of a shell-and-tube heat exchanger, a double-pipe heat exchanger and a coil heat exchanger.

5. A process for separating dimethyl carbonate and methanol, characterized by, The separation system of any one of claims 1-4 is used for separation, and a mixed solution containing dimethyl carbonate and methanol is fed into the DMC refining tower (1) as the feed, high-purity dimethyl carbonate is obtained at the bottom of the DMC refining tower (1), the top product of the DMC refining tower (1) is fed into the methanol recovery tower (2) through the cross heat exchanger (3), and high-purity methanol is obtained at the bottom of the methanol recovery tower (2). The top pressure of the DMC refining tower (1) is 0.25-3.0 MPa, and the top pressure of the methanol recovery tower (2) is 0.01-0.30 MPa. The bottom temperature of the DMC refining tower (1) is 125.0-200.0℃, and the bottom temperature of the methanol recovery tower (2) is 45.0-90.0℃.

6. The method of separating dimethyl carbonate and methanol according to claim 5, wherein The bottom temperature of the DMC refining tower (1) is 130.0-195.0℃, and the bottom temperature of the methanol recovery tower (2) is 55.0-80.0℃.

7. The method of separating dimethyl carbonate and methanol according to claim 5, wherein The top pressure of the DMC refining tower (1) is 0.40-2.0 MPa, and the top pressure of the methanol recovery tower (2) is 0.06-0.20 MPa.

8. The method of separating dimethyl carbonate and methanol according to claim 5, wherein The number of plates of the DMC refining tower (1) is 15-45, and the top reflux ratio is 1.5-25, the number of plates of the methanol recovery tower (2) is 5-35, and the top reflux ratio is 1.2-15.

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