Separation method of azeotropic mixture of dimethyl carbonate and methanol
By using the separation method of multi-distillation columns during the separation of dimethyl carbonate and methanol in the azeotropic mixture, propylene glycol methyl ether is reacted with propylene glycol methyl ether, and separation is carried out in multiple distillation columns, the existing solution is solved The problems of high energy consumption and high-pressure tower energy consumption in the technology have achieved stable continuous production and low-cost processes of high-purity DMC.
Patent Information
- Application Number
- CN202411666355.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-20
- Publication Date
- 2025-02-21
AI Technical Summary
The prior art has high energy consumption and high operating costs when separating dimethyl carbonate and methanol azeotropic mixture, and the traditional transformer distillation process has the problem of high-pressure tower energy consumption.
Using a separation method including a reaction distillation tower, a second distillation tower and a third distillation tower, propylene glycol methyl ether is reacted by reacting propylene oxide with methanol, and separated in multiple distillation towers, and finally in the third refinement High purity dimethyl carbonate was obtained from the distillation column.
The high-purity DMC product is obtained stably and continuously, effectively reducing the consumption of heating steam, especially reducing the energy consumption of high-pressure towers, and low process cost.
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Figure CN119490409A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of separation and purification of dimethyl carbonate, and in particular relates to a method for separating an azeotropic mixture of dimethyl carbonate and methanol. Background Art
[0002] Dimethyl carbonate (abbreviated as "DMC") is a green new chemical raw material. It can replace highly toxic substances such as phosgene and methyl chloroformate for carbonylation, carbonyl methoxylation and methylation reactions, and is widely used as an organic synthesis intermediate in pesticides, medicines, polymer synthesis, and battery electrolytes. At present, there are two industrial synthesis methods for dimethyl carbonate. One is the ester exchange route, which is obtained by ester exchange between ethylene carbonate or propylene carbonate and methanol, and propylene glycol and ethylene glycol are co-produced at the same time; the other is the carbonylation oxidation route, which is obtained by carbonylation oxidation reaction of methanol with oxygen and carbon monoxide. In both synthesis methods, methanol cannot be completely converted, and the final crude product will form an azeotropic mixture of dimethyl carbonate and methanol. Therefore, it must be separated and purified to obtain pure DMC.
[0003] Among the current separation technologies, pervaporation, extractive distillation and pressure swing distillation are commonly used methods for separating DMC / methanol azeotropes; among them, pervaporation has high selectivity, simple operation and low energy demand, but its feasibility is limited by membrane performance; extractive distillation is an efficient technology for separating DMC / methanol azeotropes, but the selection and design of suitable entrainers is very difficult, and the introduction of organic solvents into extractive distillation columns may also have negative impacts on the environment or economy; pressure swing distillation is an environmentally friendly process that does not introduce any third components into the system, so this process is very suitable; however, due to the change in pressure, the traditional pressure swing distillation process has high energy consumption and operating costs.
[0004] Therefore, the applicant hopes to seek a more suitable separation process to separate the azeotropic mixture of dimethyl carbonate and methanol. Summary of the invention
[0005] In view of this, the object of the present invention is to provide a method for separating an azeotropic mixture of dimethyl carbonate and methanol, which can stably and continuously obtain a high-purity DMC product, effectively reduce the consumption of heating steam, especially reduce the energy consumption of the high-pressure tower, and have low process cost.
[0006] The technical solution adopted by the present invention is as follows: A method for separating an azeotropic mixture of dimethyl carbonate and methanol, comprising a reaction distillation tower, The second distillation tower and the third distillation tower, wherein The reaction distillation tower is respectively provided with a dimethyl carbonate-methanol azeotrope feed port and a propylene oxide feed port located below the dimethyl carbonate-methanol azeotrope feed port; the rectifying section of the reaction distillation tower is located between the dimethyl carbonate-methanol azeotrope feed port and the tower top, the reaction section of the reaction distillation tower is located between the dimethyl carbonate-methanol azeotrope feed port and the propylene oxide feed port, the stripping section of the reaction distillation tower is located between the propylene oxide feed port and the tower bottom, and the reaction section is filled with a quaternary ammonium salt catalyst; The top discharge end of the reactive distillation tower outputs a dimethyl carbonate-methanol azeotrope at an azeotropic concentration under high pressure, which is used as a feed for the second distillation tower; the bottom discharge end of the reactive distillation tower outputs a mixture of dimethyl carbonate and propylene glycol methyl ether, which is used as a feed for the third distillation tower; The top discharge end of the second distillation tower outputs dimethyl carbonate-methanol azeotrope under low pressure, which is connected to the dimethyl carbonate-methanol azeotrope feed port; the bottom discharge end of the second distillation tower outputs methanol; The top discharge end of the third distillation tower outputs dimethyl carbonate; the bottom discharge end of the third distillation tower outputs a propylene glycol-methyl ether mixture.
[0007] Preferably, the tower pressure range of the reaction distillation tower is 0.3-0.8 MPa; the tower top temperature range of the reaction distillation tower is 80-120°C; the tower bottom temperature range of the reaction distillation tower is 140-180°C; and the reflux ratio of the reaction distillation tower is set to 0.5-6.
[0008] Preferably, the tower pressure range of the second distillation tower is 0.05-0.3MPa; the tower top temperature range of the second distillation tower is 60-65°C; the tower bottom temperature range of the second distillation tower is 65-70°C; and the reflux ratio of the second distillation tower is set to 2-4.
[0009] Preferably, the tower pressure range of the third distillation tower is 0.05-0.3 MPa; the tower top temperature range of the third distillation tower is 80-100° C.; the tower bottom temperature range of the third distillation tower is 110-140° C.; and the reflux ratio of the third distillation tower is set to 2-4.
[0010] Preferably, the purity of dimethyl carbonate output from the top discharge end of the third distillation tower is ≧99%.
[0011] Preferably, the number of plates of the reactive distillation tower is in the range of 50-65, the number of plates of the second distillation tower is in the range of 50-65, and the number of plates of the third distillation tower is in the range of 30-48.
[0012] Preferably, the top of the reactive distillation tower is connected to a first top condenser provided with a condensation reflux branch, and the bottom of the reactive distillation tower is connected to a first bottom reboiler provided with a reboiling reflux branch; the top of the second distillation tower is connected to a second top condenser provided with a condensation reflux branch, and the bottom of the reactive distillation tower is connected to a second bottom reboiler provided with a reboiling reflux branch; the top of the third distillation tower is connected to a third top condenser provided with a condensation reflux branch, and the bottom of the reactive distillation tower is connected to a third bottom reboiler provided with a reboiling reflux branch; Preferably, the output end of the first top condenser serves as the top discharge end of the reaction distillation tower; the output end of the first bottom reboiler serves as the bottom discharge end of the reaction distillation tower; the output end of the second top condenser serves as the top discharge end of the second distillation tower; the output end of the second bottom reboiler serves as the bottom discharge end of the second distillation tower; the output end of the third top condenser serves as the top discharge end of the third distillation tower; and the output end of the third bottom reboiler serves as the bottom discharge end of the third distillation tower.
[0013] Preferably, the top outlet of the reactive distillation tower is connected to the input end of the second bottom reboiler, and a reflux channel is provided between the second bottom reboiler and the first top condenser.
[0014] Preferably, the feed molar ratio between methanol in the dimethyl carbonate-methanol azeotrope and the alkane in the propylene oxide is 1.5-2.5:1, more preferably 1.8-2.2:1.
[0015] The chemical engineering principles on which the reactive distillation tower of this application is based are as follows: Propylene oxide (as a reaction entrainer) reacts with methanol to produce two propylene glycol monomethyl ether isomers: (1) 2-methoxy-1-propanol and (2) 1-methoxy-2-propanol: ; The propylene glycol methyl ether generated in the initial reaction will continue to react with propylene oxide to generate a series of homologues such as dipropylene glycol methyl ether and tripropylene glycol methyl ether, which are collectively referred to as "propylene glycol methyl ether" in this application.
[0016] The present application adopts a reaction distillation tower (equipped with a dimethyl carbonate DMC / methanol azeotrope feed port and a propylene oxide feed port respectively), a second distillation tower and a third distillation tower as basic separation devices. The reaction distillation tower is divided into a reaction section, a distillation section and a stripping section according to the feed position. The catalyst (specifically, a quaternary ammonium salt catalyst) is loaded into the reaction section; in the reaction section, propylene oxide reacts with methanol to generate propylene glycol methyl ether, and propylene oxide is fully converted in the reaction distillation tower, and separation occurs after the reaction is completed; the distillation section is mainly used to collect methanol, and the methanol is collected at the top of the reaction distillation tower. DMC-methanol azeotrope; the stripping section is used to separate unreacted propylene oxide, methanol, DMC and PGME, and the bottom of the tower is a mixture of propylene glycol methyl ether and DMC; since the boiling point of propylene glycol methyl ether is very different from that of DMC and no azeotrope is formed, the reaction products are easily separated. The present application separates the mixture of propylene glycol methyl ether and DMC by setting a third distillation tower to obtain a high-purity dimethyl carbonate (DMC) product, and effectively reduces the consumption of heating steam, especially reduces the energy consumption of the high-pressure tower, and has a low process cost; In addition, the separation method provided in the present application can realize stable and continuous production. Through implementation verification, in industrial production, the propylene oxide conversion rate can reach more than 99%, and the selectivity can reach more than 94.0%; at the same time, the present application uses propylene oxide as a reactant to synthesize propylene glycol methyl ether (PGME) with methanol, and basically no other side reactions occur in the reaction system. Propylene glycol methyl ether is an environmentally friendly solvent and is widely used in the market. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 It is a schematic diagram of the connection structure of a separation device for an azeotropic mixture of dimethyl carbonate and methanol according to a specific embodiment of the present invention. DETAILED DESCRIPTION
[0018] See also Figure 1 As shown, this embodiment provides an azeotropic mixture of dimethyl carbonate and methanol. The separation method comprises a reaction distillation tower A1, a second distillation tower A2 and a third distillation tower A3, wherein the reaction distillation tower A1 is provided with a dimethyl carbonate-methanol azeotrope feed port 1 and a propylene oxide feed port 2 located below the reaction distillation tower A1; preferably, the feed molar ratio between methanol in the dimethyl carbonate-methanol azeotrope and propylene oxide in the propylene oxide is 1.5-2.5:1, more preferably 1.8-2.2:1; In this embodiment, the distillation section A of the reaction distillation tower A1 is located between the dimethyl carbonate-methanol azeotrope feed port 1 and the tower top, the reaction section B of the reaction distillation tower A1 is located between the dimethyl carbonate-methanol azeotrope feed port 1 and the propylene oxide feed port 2, the stripping section C of the reaction distillation tower A1 is located between the propylene oxide feed port 2 and the tower bottom, and the reaction section B is filled with a quaternary ammonium salt catalyst; the top discharge end of the reaction distillation tower A1 outputs the dimethyl carbonate-methanol azeotrope at an azeotropic concentration under high pressure, which is used as the feed 5 of the second distillation tower A2; the bottom discharge end of the reaction distillation tower A1 The end outputs a mixture of dimethyl carbonate and propylene glycol methyl ether, which is used as the feed 6 of the third distillation tower A3; the top discharge end of the second distillation tower A2 outputs dimethyl carbonate-methanol azeotrope under low pressure, which is connected to the dimethyl carbonate-methanol azeotrope feed port 1; the bottom discharge end 3 of the second distillation tower A2 outputs methanol; the top discharge end of the third distillation tower A3 outputs dimethyl carbonate; the bottom discharge end 4 of the third distillation tower A3 outputs a propylene glycol-methyl ether mixture; preferably, in this embodiment, the purity of dimethyl carbonate output from the top discharge end of the third distillation tower A3 is ≧99%.
[0019] Preferably, in this embodiment, the tower pressure range of the reaction distillation tower A1 is 0.3-0.8MPa; the tower top temperature range of the reaction distillation tower A1 is 80-120°C; the tower bottom temperature range of the reaction distillation tower A1 is 140-180°C; the reflux ratio of the reaction distillation tower A1 is set to 0.5-6; the tower pressure range of the second distillation tower A2 is 0.05-0.3MPa; the tower top temperature range of the second distillation tower A2 is 60-65°C; the tower bottom temperature range of the second distillation tower A2 is 65-70°C; the reflux ratio of the second distillation tower A2 is set to 2-4; the tower pressure range of the third distillation tower A3 is 0.05-0.3MPa; the tower top temperature range of the third distillation tower A3 is 80-100°C; the tower bottom temperature range of the third distillation tower A3 is 110-140°C; the reflux ratio of the third distillation tower A3 is set to 2-4.
[0020] Preferably, in this embodiment, the number of plates of the reactive distillation tower A1 is in the range of 50-65, the number of plates of the second distillation tower A2 is in the range of 50-65, and the number of plates of the third distillation tower A3 is in the range of 30-48.
[0021] Preferably, in this embodiment, the top of the reaction distillation tower A1 is connected to a first top condenser B1 provided with a condensation reflux branch, and its bottom is connected to a first bottom reboiler C1 provided with a reboiling reflux branch; the top of the second distillation tower A2 is connected to a second top condenser B2 provided with a condensation reflux branch, and its bottom is connected to a second bottom reboiler C2 provided with a reboiling reflux branch; the top of the third distillation tower A3 is connected to a third top condenser B3 provided with a condensation reflux branch, and its bottom is connected to a third bottom reboiler C3 provided with a reboiling reflux branch; further preferably, in this embodiment, the output end of the first top condenser B1 serves as the top of the reaction distillation tower A1. discharging end; the output end of the first bottom reboiler C1 serves as the bottom discharging end of the reaction distillation tower A1; the output end of the second top condenser B2 serves as the top discharging end of the second distillation tower A2; the output end of the second bottom reboiler C2 serves as the bottom discharging end of the second distillation tower A2; the output end of the third top condenser B3 serves as the top discharging end of the third distillation tower A3; the output end of the third bottom reboiler C3 serves as the bottom discharging end of the third distillation tower A3; further preferably, in this embodiment, the top outlet of the reaction distillation tower A1 is connected to the input end of the second bottom reboiler C2, and a reflux channel is arranged between the second bottom reboiler C2 and the first top condenser B1.
[0022] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.
[0023] On the basis of the above implementation contents, in order to verify the technical effects achieved by this application, this application further proposes the following embodiments: Embodiment 1: This embodiment 1 provides a separation method of dimethyl carbonate and methanol azeotropic mixture The specific implementation process is as follows: The reactive distillation tower A1 is set to 60 theoretical plates, the feed port 1 of dimethyl carbonate-methanol azeotrope is set on the 24th plate, and the feed port 2 of propylene oxide is set on the 44th plate. The molar ratio of methanol and propylene oxide in the dimethyl carbonate-methanol azeotrope is 2:1, the operating pressure is 0.6 MPa, the reflux ratio is 1.36, the tower top temperature is 111.8°C, and the tower bottom temperature is 170.5°C.
[0024] The second distillation tower A2 is provided with 60 theoretical plates, and the feed port 5 of the dimethyl carbonate-methanol mixture is provided on the 24th plate. The operating pressure of the second distillation tower T2 is 0.1 MPa, the reflux ratio is 2.33, the tower top temperature is 62.8 °C, and the tower bottom temperature is 66.1 °C. The mass composition of the bottom product of the second distillation tower A2 is: 99.92% methanol and 0.17% dimethyl carbonate.
[0025] The third distillation tower A3 is provided with 40 theoretical plates, and the feed port 6 of the dimethyl carbonate-propylene glycol methyl ether mixture is provided on the 20th plate. The operating conditions of the third distillation tower T3 are: operating pressure of 0.1 MPa, reflux ratio of 3.62, tower top temperature of 90.1°C, and tower bottom temperature of 120.5°C. The mass composition of the top product of the third distillation tower A3 is: dimethyl carbonate 99.6%, methanol 0.4%. The mass composition of the bottom product of the third distillation tower T3 is: propylene glycol methyl ether mixture 99.92%, dimethyl carbonate 0.18%.
[0026] According to calculation, the conversion rate of propylene oxide is 99.5%, and the selectivity of 1-methoxy-2-propanol is 95.1%.
[0027] Embodiment 2: This embodiment 2 provides a separation method of dimethyl carbonate and methanol azeotropic mixture The specific implementation process is as follows: The reactive distillation tower A1 is set to have 58 theoretical plates, the feed port 1 of dimethyl carbonate-methanol azeotrope is set on the 22nd plate, and the feed port 2 of propylene oxide is set on the 42nd plate. The molar ratio of methanol and propylene oxide in the dimethyl carbonate-methanol azeotrope is 2:1, the operating pressure is 0.6 MPa, the reflux ratio is 1.34, the tower top temperature is 112.1°C, and the tower bottom temperature is 169.5°C.
[0028] The second distillation tower A2 is provided with 58 theoretical plates, and the feed port 5 of the dimethyl carbonate-methanol mixture is provided on the 23rd plate. The operating pressure of the second distillation tower T2 is 0.1 MPa, the reflux ratio is 2.35, the tower top temperature is 63.1°C, and the tower bottom temperature is 65.8°C. The mass composition of the bottom product of the second distillation tower A2 is: 99.94% methanol and 0.15% dimethyl carbonate.
[0029] The third distillation tower A3 is provided with 38 theoretical plates, and the feed port 6 of the dimethyl carbonate-propylene glycol methyl ether mixture is provided on the 19th plate. The operating conditions of the third distillation tower T3 are: operating pressure of 0.1 MPa, reflux ratio of 3.73, tower top temperature of 89.5°C, and tower bottom temperature of 119.8°C. The mass composition of the top product of the third distillation tower A3 is: dimethyl carbonate 99.6%, methanol 0.4%. The mass composition of the bottom product of the third distillation tower T3 is: propylene glycol methyl ether mixture 99.91%, dimethyl carbonate 0.09%.
[0030] According to calculation, the conversion rate of propylene oxide is 99.6%, and the selectivity of 1-methoxy-2-propanol is 95.3%.
[0031] Embodiment 3: This embodiment 3 provides a separation method of dimethyl carbonate and methanol azeotropic mixture The specific implementation process is as follows: The reactive distillation tower A1 is set to have 56 theoretical plates, the feed port 1 of dimethyl carbonate-methanol azeotrope is set on the 20th plate, and the feed port 2 of propylene oxide is set on the 40th plate. The molar ratio of methanol and propylene oxide in the dimethyl carbonate-methanol azeotrope is 2:1, the operating pressure is 0.6 MPa, the reflux ratio is 1.32, the tower top temperature is 112.5°C, and the tower bottom temperature is 169.1°C.
[0032] The second distillation tower A2 is provided with 56 theoretical plates, and the feed port 5 of the dimethyl carbonate-methanol mixture is provided on the 21st plate. The operating pressure of the second distillation tower T2 is 0.1 MPa, the reflux ratio is 2.38, the tower top temperature is 63.3°C, and the tower bottom temperature is 66.3°C. The mass composition of the bottom product of the second distillation tower A2 is: 99.95% methanol and 0.05% dimethyl carbonate.
[0033] The third distillation tower A3 is provided with 36 theoretical plates, and the feed port 6 of the dimethyl carbonate-propylene glycol methyl ether mixture is provided on the 18th plate. The operating conditions of the third distillation tower T3 are: operating pressure of 0.1 MPa, reflux ratio of 3.80, tower top temperature of 89.3°C, and tower bottom temperature of 120.3°C. The mass composition of the top product of the third distillation tower A3 is: dimethyl carbonate 99.6%, methanol 0.4%. The mass composition of the bottom product of the third distillation tower T3 is: propylene glycol methyl ether mixture 99.92%, dimethyl carbonate 0.08%.
[0034] According to calculation, the conversion rate of propylene oxide is 99.8%, and the selectivity of 1-methoxy-2-propanol is 95.5%.
[0035] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.
[0036] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.
Claims
1. A method for separating an azeotropic mixture of dimethyl carbonate and methanol, characterized in that: It includes a reaction distillation tower (A1), a second distillation tower (A2) and a third distillation tower (A3), wherein: The reaction distillation tower (A1) is provided with a dimethyl carbonate-methanol azeotrope feed port (1) and a propylene oxide feed port (2) located below the dimethyl carbonate-methanol azeotrope feed port (1) and the tower top; the reaction section (B) of the reaction distillation tower (A1) is located between the dimethyl carbonate-methanol azeotrope feed port (1) and the propylene oxide feed port (2); the stripping section (C) of the reaction distillation tower (A1) is located between the propylene oxide feed port (2) and the tower bottom; and the reaction section (B) is filled with a quaternary ammonium salt catalyst; The top discharge end of the reactive distillation tower (A1) outputs a dimethyl carbonate-methanol azeotrope at an azeotropic concentration under high pressure, which is used as a feed (5) for the second distillation tower (A2); the bottom discharge end of the reactive distillation tower (A1) outputs a mixture of dimethyl carbonate and propylene glycol methyl ether, which is used as a feed (6) for the third distillation tower (A3); The top discharge end of the second distillation tower (A2) outputs dimethyl carbonate-methanol azeotrope at low pressure, which is connected to the dimethyl carbonate-methanol azeotrope feed port (1); the bottom discharge end (3) of the second distillation tower (A2) outputs methanol; The top discharge end of the third distillation tower (A3) outputs dimethyl carbonate; the bottom discharge end (4) of the third distillation tower (A3) outputs a propylene glycol-methyl ether mixture.
2. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 1, characterized in that: The tower pressure range of the reaction distillation tower (A1) is 0.3-0.8 MPa; the tower top temperature range of the reaction distillation tower (A1) is 80-120°C; the tower bottom temperature range of the reaction distillation tower (A1) is 140-180°C; and the reflux ratio of the reaction distillation tower (A1) is set to 0.5-6.
3. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 1 or 2, characterized in that: The tower pressure range of the second distillation tower (A2) is 0.05-0.3 MPa; the tower top temperature range of the second distillation tower (A2) is 60-65°C; the tower bottom temperature range of the second distillation tower (A2) is 65-70°C; and the reflux ratio of the second distillation tower (A2) is set to 2-4.
4. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 1 or 2, characterized in that: The tower pressure range of the third distillation tower (A3) is 0.05-0.3MPa; the tower top temperature range of the third distillation tower (A3) is 80-100°C; the tower bottom temperature range of the third distillation tower (A3) is 110-140°C; and the reflux ratio of the third distillation tower (A3) is set to 2-4.
5. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 1, characterized in that: The purity of dimethyl carbonate output from the top discharge end of the third distillation tower (A3) is ≥ 99%.
6. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 1, characterized in that: The number of plates of the reactive distillation tower (A1) is in the range of 50-65, the number of plates of the second distillation tower (A2) is in the range of 50-65, and the number of plates of the third distillation tower (A3) is in the range of 30-48.
7. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 1, characterized in that: The top of the reaction distillation tower (A1) is connected to a first top condenser (B1) provided with a condensation reflux branch, and the bottom of the tower is connected to a first bottom reboiler (C1) provided with a reboiling reflux branch; the top of the second distillation tower (A2) is connected to a second top condenser (B2) provided with a condensation reflux branch, and the bottom of the tower is connected to a second bottom reboiler (C2) provided with a reboiling reflux branch; the top of the third distillation tower (A3) is connected to a third top condenser (B3) provided with a condensation reflux branch, and the bottom of the tower is connected to a third bottom reboiler (C3) provided with a reboiling reflux branch.
8. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 7, characterized in that: The output end of the first tower top condenser (B1) serves as the tower top discharge end of the reaction distillation tower (A1); the output end of the first tower bottom reboiler (C1) serves as the tower bottom discharge end of the reaction distillation tower (A1); the output end of the second tower top condenser (B2) serves as the tower top discharge end of the second distillation tower (A2); the output end of the second tower bottom reboiler (C2) serves as the tower bottom discharge end of the second distillation tower (A2); the output end of the third tower top condenser (B3) serves as the tower top discharge end of the third distillation tower (A3); and the output end of the third tower bottom reboiler (C3) serves as the tower bottom discharge end of the third distillation tower (A3).
9. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 8, characterized in that: The top outlet of the reactive distillation tower (A1) is connected to the input end of the second bottom reboiler (C2), and a reflux channel is provided between the second bottom reboiler (C2) and the first top condenser (B1).
10. The method for separating the azeotropic mixture of dimethyl carbonate and methanol according to claim 1, characterized in that: The feed molar ratio between methanol in the dimethyl carbonate-methanol azeotrope and the alkane in propylene oxide is 1.5-2.5:1, more preferably 1.8-2.2:1.