A device and method for producing high-concentration dimethyl carbonate

Abstract

The invention discloses a device and method for producing high-concentration dimethyl carbonate. Low-concentration dimethyl carbonate is separated in a light-removing tower, a part of the light component is refluxed, and the other part and the heavy component are all sent to a methanol fuel tank; a mixture of dimethyl carbonate and methanol is extracted from the side line and sent to a pressure tower. After separation in the pressure tower, high-concentration dimethyl carbonate is obtained in the tower bottom and sent to a refining tower for further purification; a part of the methanol azeotrope containing 15-18% of dimethyl carbonate is distilled from the top of the tower for reflux, and the other part is sent to a normal pressure tower. After separation in the normal pressure tower, a part of the dimethyl carbonate and methanol azeotrope containing 30% concentration is distilled from the top of the tower for reflux, and the other part is sent to a pressure tower; methanol is discharged from the bottom of the tower and sent to a methanol fuel tank. High-concentration dimethyl carbonate is separated in a refining tower, a part of the light component is refluxed, and the other part and the heavy component in the tower bottom are all sent to a methanol fuel tank; high-purity dimethyl carbonate with a content of more than 99.9% is obtained as a product through side line extraction.

Description

Technical Field

[0001] The present invention relates to a device and method for producing high-concentration dimethyl carbonate, and in particular to a device and method for refining and recovering dimethyl carbonate from low-concentration dimethyl carbonate, and in particular to a device and method for refining and recovering dimethyl carbonate from low-concentration dimethyl carbonate produced as a by-product of an ethylene glycol device. Background Art

[0002] In recent years, coal-to-ethylene glycol projects have been hot, and there are more than 40 coal-to-ethylene glycol projects in production and operation or under construction. Most coal-to-ethylene glycol uses coal as raw material, and obtains CO and H2 respectively through gasification, transformation, purification and separation and purification. Among them, CO is synthesized and refined to produce oxalate through catalytic coupling, and then hydrogenated with H2 and refined to obtain ethylene glycol. This process is short and low-cost, and it is the coal-to-ethylene glycol technology that has received the most attention in China. However, in the practice of coal-to-ethylene glycol technology, CO produces dimethyl carbonate as a by-product during carbonylation reaction. The by-product dimethyl carbonate accounts for about 5% to 10% of the ethylene glycol production capacity. Generally, the output of coal-to-ethylene glycol projects is as high as hundreds of thousands of tons or even millions of tons, so the by-product dimethyl carbonate output is considerable. However, these by-product dimethyl carbonates can only be sold as waste due to their low purity.

[0003] High-purity dimethyl carbonate (DMC) is an excellent solvent. It is an environmentally friendly green chemical product that has received widespread attention in recent years. The chemical properties of dimethyl carbonate are very active and it is easy to react with various hydroxyl compounds. It can replace highly toxic phosgene, dimethyl sulfate, methyl chloride, etc. as carbonylating agent and methylating agent, and is a very important organic synthesis intermediate. Dimethyl carbonate has the characteristics of low toxicity, fast evaporation rate, and good compatibility with other solvents. Western Europe has listed it as a non-toxic chemical and vigorously developed its application as a solvent, such as a solvent for special paints, a solvent for high-energy batteries, a solvent for medical production, etc. It can also be used as a spray. Higher-purity dimethyl carbonate can be used as a raw material for the production of lithium battery electrolyte solutions. However, due to the large amount of impurities in dimethyl carbonate produced as a by-product of coal-to-ethylene glycol, its purification method is an urgent problem to be solved. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a device and method for producing high-concentration dimethyl carbonate in view of the shortcomings of the prior art. The method uses low-concentration dimethyl carbonate as a raw material, wherein the dimethyl carbonate content is more than 30%, which is a waste material containing dimethyl carbonate produced in the production process of ethylene glycol; the present invention is a technology for producing high-concentration dimethyl carbonate using low-concentration dimethyl carbonate.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A device for producing high-concentration dimethyl carbonate, comprising a light removal tower, a pressurizing tower, and a refining tower connected in sequence, wherein a low-concentration dimethyl carbonate raw material is sequentially subjected to light removal, pressurization, and refining to obtain a high-purity dimethyl carbonate product, characterized in that:

[0007] The light-removal tower is provided with an exhaust port I at the top and a discharge port I at the bottom, a feed port I is provided at the middle and lower part of one side of the tower wall, a reflux port I is provided at the upper part of the other side of the tower wall, and a discharge port II is provided at the middle and upper part, wherein: the feed port I is connected to a device capable of providing a low-concentration dimethyl carbonate raw material; the exhaust port I is connected to a condenser I and a reflux tank I, the outlet of the reflux tank I is divided into two paths, the first path is connected to the reflux port I, and the second path is connected to a methanol fuel storage tank; the discharge port I is connected to the methanol fuel storage tank;

[0008] The pressurized tower is provided with an exhaust port II at the top and a discharge port III at the bottom, a feed port II is provided at the middle and lower part of one side of the tower wall, and a reflux port II is provided at the upper part of the other side of the tower wall, wherein: the feed port II is divided into two paths, the first path is connected to the discharge port II of the light removal tower; the exhaust port II is connected to the condenser II and the reflux tank II, the outlet of the reflux tank II is divided into two paths, the first path is connected to the reflux port II, and the second path is connected to the atmospheric pressure tower;

[0009] The atmospheric pressure tower is provided with an exhaust port III at the top and a discharge port IV at the bottom, a feed port III is provided at the middle and lower part of one side of the tower wall, and a reflux port III is provided at the upper part of the other side of the tower wall, wherein: the feed port III is connected to the second path of the outlet of the reflux tank II; the exhaust port III is connected to the condenser III and the reflux tank III, the outlet of the reflux tank III is divided into two paths, the first path is connected to the reflux port III, and the second path is connected to the second path of the feed port II of the pressurized tower; the discharge port IV is connected to the methanol fuel storage tank;

[0010] The refining tower is provided with an exhaust port IV at the top and a discharge port V at the bottom, a feed port IV is provided at the middle and lower part of one side of the tower wall, a reflux port IV is provided at the upper part of the other side of the tower wall, and a discharge port VI is provided at the middle and upper part, wherein: the feed port IV is connected to the discharge port III of the pressurized tower; the exhaust port IV is connected to a condenser IV and a reflux tank IV, the outlet of the reflux tank IV is divided into two paths, the first path is connected to the reflux port IV, and the second path is connected to a methanol fuel storage tank; the discharge port V is connected to the methanol fuel storage tank; and the discharge port VI is connected to a product storage tank.

[0011] The lightness removal tower, pressure tower, atmospheric pressure tower and refining tower described in the present invention are all conventional equipment commercially available in the art or equipment with corresponding functions.

[0012] The present invention also provides a method for producing high-concentration dimethyl carbonate, comprising the following steps:

[0013] (1) Light and heavy removal: Low-concentration dimethyl carbonate feedstock enters the light removal tower through the feed port I and is separated in the light removal tower. After separation, a light component is obtained at the top of the tower, a heavy component is obtained at the bottom of the tower, and a primary crude product is obtained at the middle and upper part of the tower wall. The light component is methylal and part of methanol, which are discharged from the exhaust port I at the top of the tower and condensed by the condenser I to obtain liquid methylal and part of methanol, and then enter the reflux tank I. Part of the material in the reflux tank I is refluxed from the reflux port I to the light removal tower for recycling, and the other part is sent to the methanol fuel tank; the heavy component is oxalate, which is discharged from the discharge port I at the bottom of the tower and then sent to the methanol fuel tank; the primary crude product is a mixture of dimethyl carbonate and methanol, which is discharged from the discharge port II at the middle and upper part of the tower wall and sent to the pressurized tower through the feed port II;

[0014] (2) Pressurized azeotropic distillation: The primary crude product in the light removal tower enters the pressurized tower, where it is pressurized for azeotropic distillation. Since methanol and dimethyl carbonate are azeotropic, the azeotropic ratio of methanol and dimethyl carbonate can be increased by pressurization, so that almost all of the methanol is azeotropically taken out with the least amount of dimethyl carbonate. A methanol azeotrope containing dimethyl carbonate with a mass content of 15-18% is obtained at the top of the tower, and dimethyl carbonate with a mass concentration of 98.95%-99.05% is obtained in the bottom of the tower; a dimethyl carbonate with a mass content of 15 The methanol azeotrope containing dimethyl carbonate of 98.95% to 18% is discharged from the exhaust port II at the top of the tower and condensed in the condenser II to obtain the liquid methanol azeotrope containing dimethyl carbonate, which then enters the reflux tank II. A part of the material in the reflux tank II is refluxed from the reflux port II to the pressure tower for recycling, and the other part is discharged and enters the atmospheric pressure tower from the feed port III; the dimethyl carbonate with a mass concentration of 98.95% to 99.05% is discharged from the discharge port III at the bottom of the tower and fed into the refining tower through the feed port IV;

[0015] (3) Pressure swing separation: The methanol azeotrope containing dimethyl carbonate with a mass content of 15-18% enters the atmospheric pressure tower. As the pressure decreases, the azeotropic ratio of methanol and dimethyl carbonate decreases, and a methanol azeotrope containing dimethyl carbonate with a mass content of 29.95%-30.05% is obtained at the top of the tower, and methanol with a purity of more than 99.5% is obtained at the bottom of the tower; the methanol azeotrope containing dimethyl carbonate with a mass content of 29.95%-30.05% is discharged from the exhaust port III at the top of the tower and condensed by the condenser III to obtain a liquid methanol azeotrope containing dimethyl carbonate, which then enters the reflux tank III. A part of the material in the reflux tank III is refluxed from the reflux port III to the atmospheric pressure tower for recycling, and the other part is discharged and returned to the pressure tower for recycling treatment from the feed port II; the methanol with a purity of more than 99.5% is discharged from the discharge port IV at the bottom of the tower and sent to the methanol fuel tank, which is sold as a product or returned to the oxalate system of the ethylene glycol production device for use;

[0016] (4) Refining: Dimethyl carbonate with a mass concentration of 98.95%-99.05% enters a refining tower and is separated in the refining tower to obtain a light component at the top of the tower, a heavy component at the bottom of the tower, and a product at the middle and upper part of the tower wall; the light component is discharged from the exhaust port IV at the top of the tower and condensed in the condenser IV to obtain a liquid light component, which then enters the reflux tank IV. A part of the material in the reflux tank IV flows back to the refining tower from the reflux port IV for recycling, and the other part is discharged and sent to a methanol fuel tank; the heavy component is discharged from the discharge port V at the bottom of the tower and sent to a methanol fuel tank; the product is a high-purity dimethyl carbonate with a mass content of more than 99.9%, which is discharged from the discharge port VI at the middle and upper part of the side wall and sent to a product storage tank.

[0017] In the above technical solution, in step (1), the mass concentration of dimethyl carbonate in the low-concentration dimethyl carbonate raw material is above 30%, and the dimethyl carbonate-containing waste material generated in the production process of ethylene glycol is preferably used.

[0018] In the above technical scheme, in step (1), the lightness removal tower has the following operating conditions: the tower top temperature is 95-105°C, and the pressure is 0.00-0.03MpaG; the tower bottom temperature is 110-130°C, and the pressure is 0.00-0.0.05MpaG.

[0019] In the above technical solution, in step (1), the reflux ratio of the lightness removal tower is 50-60.

[0020] In the above technical solution, in step (2), the operating conditions of the pressurized tower are: the top temperature is 130-140°C, and the pressure is 0.80-1.00MpaG; the bottom temperature is 170-190°C, and the pressure is 0.80-1.00MpaG.

[0021] In the above technical solution, in step (2), the reflux ratio of the pressurized tower is 2 to 4.

[0022] In the above technical scheme, in step (3), the operating conditions of the atmospheric pressure tower are: the tower top temperature is 60-65°C, and the pressure is 0.00-0.03MpaG; the tower bottom temperature is 60-70°C, and the pressure is 0.00-0.05MpaG.

[0023] In the above technical solution, in step (3), the reflux ratio of the atmospheric pressure tower is 1.5-3.

[0024] In the above technical scheme, in step (4), the refining tower has the following operating conditions: the tower top temperature is 80-100°C, and the pressure is 0.00-0.03MpaG; the tower bottom temperature is 85-95°C, and the pressure is 0.00-0.05MpaG.

[0025] In the above technical solution, in step (4), the reflux ratio of the refining tower is 25-35.

[0026] The advantages of the technical solution of the present invention are:

[0027] (1) The low-concentration dimethyl carbonate raw material of the present invention can be waste generated in the production process of ethylene glycol. The waste is hazardous waste and can only be sold at a low price, resulting in a waste of dimethyl carbonate, a decrease in economic benefits and environmental pressure. Therefore, the present invention has obvious economic benefits and environmental advantages.

[0028] (2) The low-concentration dimethyl carbonate raw material of the present invention does not require a high concentration of dimethyl carbonate, and the concentration of dimethyl carbonate can be no less than 30%.

[0029] (3) The product of the present invention has excellent quality: the product meets the requirements of the national standard for high-quality dimethyl carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : Process flow chart of the method of the present invention;

[0031] Figure 2 It is a schematic diagram of the overall structure of the device of the present invention;

[0032] Among them: 1 is a lightness removal tower, 2 is a pressure tower, 3 is a normal pressure tower, and 4 is a refining tower. DETAILED DESCRIPTION

[0033] The specific implementation of the technical solution of the present invention is described in detail below, but the present invention is not limited to the following description:

[0034] The present invention provides a device for producing high-concentration dimethyl carbonate, comprising a light removal tower 1, a pressurizing tower 2, and a refining tower 4 connected in sequence, wherein a low-concentration dimethyl carbonate raw material is sequentially subjected to light removal, pressurization, and refining to obtain a high-purity dimethyl carbonate product, such as Figure 2 As shown:

[0035] The light-removal tower 1 is provided with an exhaust port I at the top and a discharge port I at the bottom, a feed port I is provided at the middle and lower part of one side of the tower wall, a reflux port I is provided at the upper part of the other side of the tower wall, and a discharge port II is provided at the middle and upper part, wherein: the feed port I is connected to a device capable of providing a low-concentration dimethyl carbonate raw material; the exhaust port I is connected to a condenser I and a reflux tank I, the outlet of the reflux tank I is divided into two paths, the first path is connected to the reflux port I, and the second path is connected to a methanol fuel storage tank; the discharge port I is connected to the methanol fuel storage tank;

[0036] The pressurized tower 2 is provided with an exhaust port II at the top and a discharge port III at the bottom, a feed port II is provided at the middle and lower part of one side of the tower wall, and a reflux port II is provided at the upper part of the other side of the tower wall, wherein: the feed port II is divided into two paths, the first path is connected to the discharge port II of the light removal tower 1; the exhaust port II is connected to the condenser II and the reflux tank II, the outlet of the reflux tank II is divided into two paths, the first path is connected to the reflux port II, and the second path is connected to the atmospheric pressure tower 3;

[0037] The atmospheric tower 3 is provided with an exhaust port III at the top and a discharge port IV at the bottom, a feed port III is provided at the middle and lower part of one side of the tower wall, and a reflux port III is provided at the upper part of the other side of the tower wall, wherein: the feed port III is connected to the second path of the outlet of the reflux tank II; the exhaust port III is connected to the condenser III and the reflux tank III, the outlet of the reflux tank III is divided into two paths, the first path is connected to the reflux port III, and the second path is connected to the second path of the feed port II of the pressurized tower 2; the discharge port IV is connected to the methanol fuel storage tank;

[0038] The refining tower 4 is provided with an exhaust port IV at the top and a discharge port V at the bottom, a feed port IV is provided at the middle and lower part of one side of the tower wall, a reflux port IV is provided at the upper part of the other side of the tower wall, and a discharge port VI is provided at the middle and upper part, wherein: the feed port IV is connected to the discharge port III of the pressurizing tower 2; the exhaust port IV is connected to the condenser IV and the reflux tank IV, the outlet of the reflux tank IV is divided into two paths, the first path is connected to the reflux port IV, and the second path is connected to the methanol fuel storage tank; the discharge port V is connected to the methanol fuel storage tank; the discharge port VI is connected to the product storage tank.

[0039] The present invention also provides a method for producing high-concentration dimethyl carbonate, the flow chart of which is as follows: Figure 1 As shown, the following steps are included:

[0040] (1) Light and heavy removal: Low-concentration dimethyl carbonate feedstock enters the light removal tower 1 through the feed port I, and is separated in the light removal tower. After separation, a light component is obtained at the top of the tower, a heavy component is obtained at the bottom of the tower, and a primary crude product is obtained at the middle and upper part of the tower wall; the light component is methylal and part of methanol, which are discharged from the exhaust port I at the top of the tower and condensed by the condenser I to obtain liquid methylal and part of methanol, and then enter the reflux tank I. Part of the material in the reflux tank I is refluxed from the reflux port I to the light removal tower for recycling, and the other part is sent to the methanol fuel tank; the heavy component is oxalate, which is discharged from the discharge port I at the bottom of the tower and then sent to the methanol fuel tank; the primary crude product is a mixture of dimethyl carbonate and methanol, which is discharged from the discharge port II at the middle and upper part of the tower wall and sent to the pressurized tower 2 through the feed port II;

[0041] (2) Pressurized azeotropic distillation: The primary crude product in the light removal tower enters the pressurized tower 2, where it is pressurized for azeotropic distillation. Since methanol and dimethyl carbonate are azeotropic, the azeotropic ratio of methanol and dimethyl carbonate can be increased by pressurization, so that almost all of the methanol is azeotropically taken out with a minimum amount of dimethyl carbonate. A methanol azeotrope containing dimethyl carbonate with a mass content of 15-18% is obtained at the top of the tower, and dimethyl carbonate with a mass concentration of 98.95%-99.05% is obtained in the bottom of the tower; a dimethyl carbonate with a mass content of 15 The methanol azeotrope containing dimethyl carbonate of 98.95% to 18% is discharged from the exhaust port II at the top of the tower and condensed in the condenser II to obtain the liquid methanol azeotrope containing dimethyl carbonate, which then enters the reflux tank II. A part of the material in the reflux tank II is refluxed from the reflux port II to the pressure tower for recycling, and the other part is discharged and enters the atmospheric pressure tower 3 from the feed port III; the dimethyl carbonate with a mass concentration of 98.95% to 99.05% is discharged from the discharge port III at the bottom of the tower and fed into the refining tower 4 through the feed port IV;

[0042] (3) Pressure swing separation: The methanol azeotrope containing dimethyl carbonate with a mass content of 15-18% enters the atmospheric pressure tower 3. As the pressure decreases, the azeotropic ratio of methanol and dimethyl carbonate decreases, and a methanol azeotrope containing dimethyl carbonate with a mass content of 29.95%-30.05% is obtained at the top of the tower, and methanol with a purity of more than 99.5% is obtained at the bottom of the tower; the methanol azeotrope containing dimethyl carbonate with a mass content of 29.95%-30.05% is discharged from the exhaust port III at the top of the tower and condensed in the condenser III to obtain a liquid methanol azeotrope containing dimethyl carbonate, which then enters the reflux tank III. A part of the material in the reflux tank III is refluxed from the reflux port III to the atmospheric pressure tower for recycling, and the other part is discharged and returned to the pressure tower for recycling treatment from the feed port II; the methanol with a purity of more than 99.5% is discharged from the discharge port IV at the bottom of the tower and sent to the methanol fuel tank, which is sold as a product or returned to the oxalate system of the ethylene glycol production device for use;

[0043] (4) Refining: Dimethyl carbonate with a mass concentration of 98.95%-99.05% enters the refining tower 4, where it is separated to obtain a light component at the top of the tower, a heavy component at the bottom of the tower, and a product at the middle and upper part of the tower wall; the light component is discharged from the exhaust port IV at the top of the tower and condensed in the condenser IV to obtain a liquid light component, which then enters the reflux tank IV. A part of the material in the reflux tank IV flows back to the refining tower from the reflux port IV for recycling, and the other part is discharged and sent to the methanol fuel tank; the heavy component is discharged from the discharge port V at the bottom of the tower and sent to the methanol fuel tank; the product is high-purity dimethyl carbonate with a mass content of more than 99.9%, which is discharged from the discharge port VI at the middle and upper part of the side wall and sent to the product storage tank.

[0044] The present invention will be described below in conjunction with specific embodiments:

[0045] Embodiment 1:

[0046] A method for producing high-concentration dimethyl carbonate specifically comprises the following steps:

[0047] (1) Light and heavy removal: Low-concentration dimethyl carbonate raw material (raw material composition, see Table 1) enters the light-removal tower through the feed port I and is separated in the light-removal tower; after separation, a light component is obtained at the top of the tower, which is methylal and part of methanol, which is discharged from the exhaust port I and condensed by the condenser I to obtain liquid methylal and part of methanol and enter the reflux tank I; a part of the material in the reflux tank is returned to the light-removal tower from the reflux port I (reflux ratio is 56) for recycling, and the other part is connected to the methanol fuel tank; after separation, a heavy component is obtained at the bottom of the tower, which is oxalate, which is discharged from the discharge port I and sent to the methanol fuel tank; a mixture of dimethyl carbonate and methanol is taken from the side line of the light-removal tower and sent to the pressurized tower 2 through the discharge port II and the feed port II.

[0048] Table 1 shows the composition of low concentration dimethyl carbonate raw materials

[0049]

[0050]

[0051] The operating conditions of the light-removal tower are: the tower top temperature is 97°C and the pressure is 0.02MpaG; the tower bottom temperature is 118°C and the pressure is 0.02MpaG.

[0052] (2) Pressurized azeotropic distillation: The material from the outlet II of the light removal tower enters the pressurized tower 2. In the pressurized tower, since methanol and dimethyl carbonate are azeotropic, the azeotropic ratio of methanol and dimethyl carbonate can be increased by pressurization, so that almost all of the methanol can be azeotropically taken out with the least amount of dimethyl carbonate. The tower kettle obtains dimethyl carbonate with a concentration of 99%, which is sent to the refining tower 4 through the outlet III for further purification. The azeotropic mixture containing 15-18% of dimethyl carbonate and methanol is discharged from the exhaust port II at the top of the tower and condensed by the condenser II to obtain a liquid methanol azeotropic mixture containing dimethyl carbonate, which enters the reflux tank II. A part of the material in the reflux tank II is refluxed from the reflux port II (reflux ratio is 3) to the pressurized tower for recycling, and the other part is discharged and enters the atmospheric tower 3 through the feed port III.

[0053] The operating conditions of the pressurized tower 2 are: the tower top temperature is 136°C and the pressure is 0.90MpaG; the tower bottom temperature is 177°C and the pressure is 0.90MpaG.

[0054] (3) Pressure-swing separation: A 15-18% azeotrope of dimethyl carbonate and methanol enters the atmospheric tower 3 through the feed port III. As the pressure decreases, the azeotropic ratio of methanol and dimethyl carbonate decreases. A 30% azeotrope of dimethyl carbonate and methanol is discharged from the exhaust port III at the top of the tower and condensed by the condenser III to obtain a liquid methanol azeotrope containing dimethyl carbonate, which then enters the reflux tank III. A part of the material in the reflux tank III is refluxed from the reflux port III (reflux ratio is 2) to the atmospheric tower for recycling, and the other part is discharged and returned to the pressure tower through the feed port II for recycling. Methanol with a purity of about 99.5% flows out of the tower bottom, is sent out of the boundary area through the discharge port IV, and is sold as a product or returned to the oxalate system of the ethylene glycol production device for use.

[0055] The operating conditions of the atmospheric pressure tower (3) are: the tower top temperature is 63°C and the pressure is 0.01MpaG; the tower bottom temperature is 65°C and the pressure is 0.03MpaG.

[0056] (4) Refining: Dimethyl carbonate with a concentration of 99% from the bottom of the pressure tower enters the refining tower 4, and after separation in the refining tower; the light component is discharged from the exhaust port IV at the top of the tower and condensed by the condenser IV to obtain a liquid light component, which then enters the reflux tank IV. A part of the material in the reflux tank IV is refluxed from the reflux port IV (the reflux ratio is 30) to the refining tower for recycling, and the other part is discharged and sent to the methanol fuel tank; the heavy component is discharged from the discharge port V at the bottom of the tower and sent to the methanol fuel tank; the high-purity dimethyl carbonate with a content of more than 99.9% is obtained as a product through the side line and sent to the product tank through the discharge port VI.

[0057] The operating conditions of the refining tower 4 are as follows: the tower top temperature is 83°C and the pressure is 0.01MpaG; the tower bottom temperature is 90°C and the pressure is 0.02MpaG.

[0058] In the product of this embodiment, the quality of dimethyl carbonate is higher than the quality of the superior product in the national standard of dimethyl carbonate (GB / T33107-2016), and its components are shown in Table 2.

[0059] Table 2 Dimethyl carbonate product composition

[0060] Serial number composition content 1 Dimethyl carbonate ≧99.9％ 2 water ≤0.015％ 3 Methanol ≤0.010％

[0061] Embodiment 2:

[0062] A method for producing high-concentration dimethyl carbonate specifically comprises the following steps:

[0063] (1) Light and heavy removal: Low-concentration dimethyl carbonate raw material (raw material composition, see Table 3) enters the light-removal tower 1 through the feed port I and is separated in the light-removal tower; after separation, a light component is obtained at the top of the tower, which is methylal and part of methanol, which is discharged from the exhaust port I at the top of the tower and condensed by the condenser I to obtain liquid methylal and part of methanol, and then enters the reflux tank I. A part of the material in the reflux tank I is refluxed from the reflux port I (reflux ratio is 57) to the light-removal tower for recycling, and the other part is sent to the methanol fuel tank; after separation, a heavy component is obtained at the bottom of the tower, which is oxalate, which is discharged from the discharge port I and sent to the methanol fuel tank; a mixture of dimethyl carbonate and methanol is taken from the side line of the light-removal tower and sent to the pressurized tower 2 through the discharge port II and the feed port II.

[0064] Table 3 Low concentration dimethyl carbonate raw material composition

[0065]

[0066] The operating conditions of the light-removal tower (1) are: the tower top temperature is 96°C and the pressure is 0.019MpaG; the tower bottom temperature is 117°C and the pressure is 0.02MpaG.

[0067] (2) Azeotropic distillation: The material from the outlet II of the light removal tower enters the pressure tower. In the pressure tower, due to the azeotropic reaction of methanol and dimethyl carbonate, the azeotropic ratio of methanol and dimethyl carbonate can be increased by pressurization, so that almost all of the methanol can be azeotropically taken out with the least amount of dimethyl carbonate. The tower kettle obtains dimethyl carbonate with a concentration of 99%, which is sent to the refining tower 4 through the outlet III for further purification. The azeotropic mixture containing 15-18% of dimethyl carbonate and methanol is discharged from the exhaust port II at the top of the tower and condensed in the condenser II to obtain a liquid methanol azeotropic mixture containing dimethyl carbonate, which enters the reflux tank II. A part of the material in the reflux tank II is refluxed from the reflux port II (reflux ratio is 3) to the pressure tower for recycling, and the other part is discharged and enters the atmospheric tower 3 through the feed port III.

[0068] The operating conditions of the pressurized tower 2 are: the tower top temperature is 134°C and the pressure is 0.88MpaG; the tower bottom temperature is 175°C and the pressure is 0.91MpaG.

[0069] (3) Pressure swing separation: The azeotrope of dimethyl carbonate and methanol with a mass content of 15-18% enters the atmospheric tower 3 through the feed port III. As the pressure decreases, the azeotropic ratio of methanol and dimethyl carbonate decreases. The azeotrope of dimethyl carbonate and methanol with a concentration of about 30% is discharged from the exhaust port III at the top of the tower and condensed in the condenser III to obtain a liquid azeotrope of methanol containing dimethyl carbonate, which then enters the reflux tank III. A part of the material in the reflux tank III is refluxed from the reflux port III (the reflux ratio is 2) to the atmospheric tower for recycling, and the other part is discharged and returned to the pressure tower for recycling through the feed port II. Methanol with a purity of about 99.5% flows out of the tower bottom, is sent out of the boundary area through the discharge port IV, and is sold as a product or returned to the oxalate system of the ethylene glycol production device for use.

[0070] The operating conditions of the atmospheric pressure tower 3 are as follows: the tower top temperature is 63°C and the pressure is 0.01MpaG; the tower bottom temperature is 65°C and the pressure is 0.03MpaG.

[0071] (4) Refining: Dimethyl carbonate with a concentration of 99% enters the refining tower 4. After separation in the refining tower, the light component is discharged from the exhaust port IV at the top of the tower and condensed in the condenser IV to obtain the liquid light component, which then enters the reflux tank IV. A part of the material in the reflux tank IV is refluxed from the reflux port IV (the reflux ratio is 30) to the refining tower for recycling, and the other part is discharged and sent to the methanol fuel tank; the heavy component is discharged from the discharge port V at the bottom of the tower and sent to the methanol fuel tank; the high-purity dimethyl carbonate with a content of more than 99.9% is obtained as a product through the side line and sent to the product tank through the discharge port VI.

[0072] The operating conditions of the refining tower 4 are as follows: the tower top temperature is 83°C and the pressure is 0.01MpaG; the tower bottom temperature is 90°C and the pressure is 0.02MpaG.

[0073] The refining tower (1).

[0074] In the product of this embodiment, the quality of dimethyl carbonate is higher than the quality of the superior product in the national standard of dimethyl carbonate (GB / T33107-2016), and its composition is shown in Table 4.

[0075] Table 4 Dimethyl carbonate product composition

[0076] Serial number composition content 1 Dimethyl carbonate ≧99.9％ 2 water ≤0.015％ 3 Methanol ≤0.010％

[0077] The above examples are only for illustrating the technical concept and technical features of the present invention, and cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing high-concentration dimethyl carbonate, characterized in that: The following steps are involved: (1) Light and heavy removal: a low-concentration dimethyl carbonate raw material enters a light removal tower (1) through a feed port I, and is separated in the light removal tower (1). After separation, a light component is obtained at the top of the tower, a heavy component is obtained at the bottom of the tower, and a primary crude product is obtained at the middle and upper part of the tower wall; the light component is methylal and part of methanol, which are discharged from an exhaust port I at the top of the tower and condensed by a condenser I to obtain liquid methylal and part of methanol, and then enter a reflux tank I. A part of the material in the reflux tank I is refluxed from the reflux port I to the light removal tower (1) for recycling, and the other part is sent to a methanol fuel tank; the heavy component is oxalate, which is discharged from a discharge port I at the bottom of the tower and sent to a methanol fuel tank; The primary crude product is a mixture of dimethyl carbonate and methanol, which is discharged from the discharge port II in the upper middle part of the tower wall and fed into the pressure tower (2) through the feed port II; (2) Pressurized azeotropic distillation: The primary crude product in the light-removal tower (1) enters the pressurized tower (2), and is subjected to azeotropic distillation by pressurization in the pressurized tower (2). Since methanol and dimethyl carbonate are azeotropic, the azeotropic ratio of methanol and dimethyl carbonate can be increased by pressurization, thereby almost all of the methanol is azeotropically removed with a minimum amount of dimethyl carbonate, and a methanol azeotrope containing dimethyl carbonate with a mass content of 15 to 18% is obtained at the top of the tower, and dimethyl carbonate with a mass concentration of 98.95% to 99.05% is obtained in the bottom of the tower; The methanol azeotrope containing dimethyl carbonate with a mass content of 15-18% is discharged from the exhaust port II at the top of the tower and condensed in the condenser II to obtain a liquid methanol azeotrope containing dimethyl carbonate, which then enters the reflux tank II. A part of the material in the reflux tank II is refluxed from the reflux port II to the pressure tower for recycling, and the other part is discharged and enters the atmospheric pressure tower (3) from the feed port III; Dimethyl carbonate with a mass concentration of 98.95%-99.05% is discharged from the outlet III at the bottom of the tower and fed into the refining tower (4) through the feed port IV; the operating conditions of the pressure tower (2) are: the tower top temperature is 130-140°C, the pressure is 0.80-1.00MpaG; the tower bottom temperature is 170-190°C, and the pressure is 0.80-1.00MpaG; the reflux ratio of the pressure tower (2) is 2-4; (3) Pressure swing separation: The methanol azeotrope containing dimethyl carbonate with a mass content of 15-18% enters the atmospheric pressure tower (3). As the pressure decreases, the azeotropic ratio of methanol and dimethyl carbonate decreases, and the methanol azeotrope containing dimethyl carbonate with a mass content of 29.95%-30.05% is obtained at the top of the tower, and methanol with a purity of more than 99.5% is obtained at the bottom of the tower; The methanol azeotrope containing dimethyl carbonate with a mass content of 29.95%-30.05% is discharged from the exhaust port III at the top of the tower and condensed by the condenser III to obtain the liquid methanol azeotrope containing dimethyl carbonate, which then enters the reflux tank III. A part of the material in the reflux tank III is refluxed from the reflux port III to the atmospheric tower for recycling, and the other part is discharged and returned to the pressurized tower through the feed port II for recycling. Methanol with a purity of more than 99.5% is discharged from the discharge port IV at the bottom of the tower and sent to the methanol fuel tank to be sold as a product or returned to the oxalate system of the ethylene glycol production device for use. (4) Refining: Dimethyl carbonate with a mass concentration of 98.95%-99.05% enters a refining tower (4) and is separated in the refining tower (4). A light component is obtained at the top of the tower, a heavy component is obtained at the bottom of the tower, and a product is obtained at the middle and upper part of the tower wall. The light component is discharged from an exhaust port IV at the top of the tower and condensed in a condenser IV to obtain a liquid light component, which then enters a reflux tank IV. A part of the material in the reflux tank IV flows back to the refining tower from the reflux port IV for recycling, and the other part is discharged and sent to a methanol fuel tank. The reflux ratio of the refining tower (1) is 25-35. The heavy component is discharged from a discharge port V at the bottom of the tower and sent to a methanol fuel tank. The product is a high-purity dimethyl carbonate with a mass content of more than 99.9%, which is discharged from a discharge port VI at the middle and upper part of the side wall and sent to a product storage tank.

2. The method for producing high-concentration dimethyl carbonate according to claim 1, characterized in that: In step (1), the mass concentration of dimethyl carbonate in the low-concentration dimethyl carbonate raw material is above 30%.

3. The method for producing high concentration dimethyl carbonate according to claim 2, characterized in that: The low-concentration dimethyl carbonate raw material is waste material containing dimethyl carbonate generated in the production process of ethylene glycol.

4. The method for producing high-concentration dimethyl carbonate according to claim 1, characterized in that: In step (1), the operating conditions of the light-removal tower (1) are as follows: the tower top temperature is 95-105° C., and the pressure is 0.00-0.03 MpaG; the tower bottom temperature is 110-130° C., and the pressure is 0.00-0.05 MpaG; and the reflux ratio of the light-removal tower (1) is 50-60.

5. The method for producing high-concentration dimethyl carbonate according to claim 1, characterized in that: In step (3), the operating conditions of the atmospheric pressure tower (3) are: the tower top temperature is 60-65°C, and the pressure is 0.00-0.03MpaG; the tower bottom temperature is 60-70°C, and the pressure is 0.00-0.05MpaG; and the reflux ratio of the atmospheric pressure tower (3) is 1.5-3.

6. The method for producing high-concentration dimethyl carbonate according to claim 1, characterized in that: In step (4), the refining tower (4) has the following operating conditions: the tower top temperature is 80-100°C, and the pressure is 0.00-0.03MpaG; the tower bottom temperature is 85-95°C, and the pressure is 0.00-0.05MpaG.

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