A device and method for separating dimethyl carbonate and methanol azeotrope with low energy consumption

Abstract

The present invention discloses a device and method for separating dimethyl carbonate and methanol, wherein the retentate outlet of a first pervaporation membrane assembly is connected to the inlet of a second pervaporation membrane assembly, the permeate outlet of the first pervaporation membrane assembly is connected to the inlet of a high-pressure distillation tower, the retentate outlet of the second pervaporation membrane assembly is connected to the inlet of an atmospheric distillation tower, and the top fraction outlet of the high-pressure distillation tower is connected to the inlet of the atmospheric distillation tower. The present invention has the advantages of using a method combining two distillation towers and a membrane system for secondary separation to purify dimethyl carbonate and methanol, with low energy consumption, safety, environmental protection, no pollution, and clean production.

Description

Technical Field

[0001] The invention belongs to the field of chemical separation, and in particular relates to a device and a method for separating dimethyl carbonate and methanol azeotropes with low energy consumption. Background Art

[0002] Dimethyl carbonate (DMC) is a green solvent with excellent performance. It can be completely miscible with most ketones, alcohols, ethers and other solvents. DMC is non-toxic and contains functional groups such as methyl and carbonyl in its structure. It can replace highly toxic dimethyl sulfate, methyl chloroformate and phosgene for methylation reaction to synthesize many high value-added downstream products, eliminating the pollution of these highly toxic chemicals to the environment. It is an environmentally friendly organic chemical intermediate and has become a "new cornerstone" in organic synthesis in the new era. With the rapid development of new energy fields at home and abroad, its market demand as the main solvent for electrolyte composition is gradually expanding. At the same time, DMC can be used to prepare high-tech material polycarbonate through processes such as ester exchange and polymerization, becoming an important chemical raw material in the new polycarbonate industry, which will greatly promote the growth of its industrial scale. Because of its high proportion of oxygen in its molecular structure and its good effect of improving octane number, it is considered to be one of the most promising gasoline additives.

[0003] The main production routes of DMC include phosgene method, methanol oxidative carbonylation method, CO 2 Direct synthesis, urea alcoholysis and transesterification. The phosgene method uses highly corrosive and highly toxic radioactive phosgene, which seriously pollutes the environment and poses serious safety hazards during the production process. This method has been gradually eliminated. 2 Both direct synthesis and urea alcoholysis are still limited to the laboratory or thousand tons / year pilot research stage. Oxidative carbonylation includes direct oxidative carbonylation of methanol and indirect oxidative carbonylation. In the indirect oxidative carbonylation, methanol first reacts with NOx to generate methyl nitrite, and methyl nitrite undergoes carbonylation to obtain DMC and N 2 O,N 2 O is then oxidized to NOx. The advantage of this method is low raw material cost, but the disadvantage is also very obvious. 2 O is commonly known as laughing gas, which is neurotoxic and has a greenhouse effect of CO 2The purity of DMC produced by this method is low, and a large number of oxygen-containing compound byproducts (such as dimethyl oxalate, etc.) are generated. The byproducts of the oxidation reaction are common, and the process of separating them into electronic-grade chemicals is difficult. In addition, this route uses precious metal catalysts, which are expensive, and with the promotion of this technology, the price of precious metal catalysts will rise sharply. At the same time, a small amount of highly corrosive nitric acid is produced during the continuous operation of this technology. The liquid phase oxidative carbonylation method mainly uses cuprous chloride as a catalyst. Since cuprous chloride in the reaction system is highly corrosive and has high requirements for equipment, the investment cost is high, and the catalyst is easily deactivated and has a relatively short life.

[0004] Whether using methanol oxidative carbonylation or CO 2 Direct synthesis, urea alcoholysis, and transesterification all have the problem of separating methanol and DMC azeotropes. The azeotropic temperature of methanol and DMC under normal pressure is 63.7°C, and the azeotropic composition is 70wt% methanol and 30wt% DMC. It is difficult to achieve product refining requirements with ordinary distillation technology. For the separation of methanol and DMC, the main process technologies currently studied are extractive distillation, pressure swing separation, recrystallization, and membrane separation. The most widely used industrial methods are extractive distillation and pressure swing separation. Extractive distillation often introduces high-boiling entrainers outside the system, which is difficult to completely separate and recover in the later stage and will affect product quality. The process operation is relatively complicated. Pressure swing separation uses the pressure change in the process to change the volatility between the azeotropic components to achieve separation, but the operating temperature of the high-pressure distillation process is relatively high, and the energy consumption and heat loss are large. It is urgent to strengthen and upgrade the separation process.

[0005] Patents CN 104370698 A and CN 104370699 A disclose separation of dimethyl carbonate and methanol. Only one pressure tower or atmospheric tower is used on the membrane permeation side. The fraction at the top of the tower also includes dimethyl carbonate. The fraction at the top of the tower directly returns to the reaction distillation tower. The yield of dimethyl carbonate is low, the steam energy consumption is high, and no methanol product is obtained. Patent CN 110404422 A discloses an organic composite membrane for separating methanol and dimethyl carbonate. The service life of the organic composite membrane in industrial applications is much shorter than that of the inorganic composite membrane. Patent CN 101143803A only considers the separation of dimethyl carbonate and methanol by membrane separation, and does not consider the separation of the components at the top of the atmospheric distillation tower and the components on the retentate side of the membrane. The lack of circulation between the streams leads to a low yield of dimethyl carbonate and high energy consumption, which is not conducive to industrial promotion. Patents CN 201823480 U and CN107206286A disclose that the front of dimethyl carbonate and methanol is an atmospheric pressure tower, and the bottom of the tower is methanol product, which violates scientific principles. Theoretically, the atmospheric pressure tower cannot separate the azeotrope of the two, and the bottom of the tower cannot obtain any pure product. If a distillation tower is set at the front of the membrane, it must be a high-pressure tower. The azeotrope contains 70wt% methanol, and the vaporization heat of methanol is very large. If a membrane that preferentially permeates methanol is selected, the energy consumption will be relatively high. Summary of the invention

[0006] The purpose of the present invention is to provide a device and method for separating dimethyl carbonate and methanol azeotropes with low energy consumption suitable for industrial promotion. The device and method adopt a dimethyl carbonate preferential permeation membrane separation technology and a distillation tower combined method for separation, and can simultaneously obtain high-purity dimethyl carbonate and methanol products, thereby improving separation effect and product yield and reducing energy consumption.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A device for separating dimethyl carbonate and methanol, wherein the retentate side outlet of a first pervaporation membrane assembly is connected to the inlet of a second pervaporation membrane assembly, the permeate side outlet of the first pervaporation membrane assembly is connected to the inlet of a high-pressure distillation tower, the retentate side outlet of the second pervaporation membrane assembly is connected to the inlet of an atmospheric distillation tower, and the top fraction outlet of the high-pressure distillation tower is connected to the inlet of the atmospheric distillation tower.

[0009] Furthermore, the first pervaporation membrane assembly and the second pervaporation membrane assembly use dimethyl carbonate-preferentially pervaporation membranes.

[0010] Furthermore, the dimethyl carbonate preferentially permeable pervaporation membrane is a tubular organic-inorganic composite membrane, the carrier of the dimethyl carbonate preferentially permeable pervaporation membrane is alumina, corundum or mullite, the upper layer is alumina, titanium oxide or zirconium oxide; the organic membrane layer is a controllable pore size organic silicon hybrid membrane co-condensed with propyltrimethoxysilane and 1,3-bis(triethoxysilyl)propane.

[0011] Furthermore, the permeate-side outlet of the second pervaporation membrane module is connected to the inlet of the first pervaporation membrane module.

[0012] Furthermore, a heater is provided at the inlet of the first pervaporation membrane assembly.

[0013] Furthermore, the top fraction outlet of the atmospheric distillation tower is connected to the inlet of the first pervaporation membrane assembly.

[0014] Furthermore, the heat from the top of the high-pressure distillation tower is used to heat the reboiler of the atmospheric distillation tower.

[0015] Furthermore, the permeate-side outlet of the first pervaporation membrane module is connected to a first condenser, and the permeate-side outlet of the second pervaporation membrane module is connected to a second condenser.

[0016] Furthermore, the first pervaporation membrane assembly and the second pervaporation membrane assembly are driven by a vacuum system.

[0017] The present invention also provides a method for separating dimethyl carbonate and methanol, comprising:

[0018] The raw material enters the first pervaporation membrane assembly, and after pervaporation treatment, the first permeate obtained enters the high-pressure distillation tower for distillation treatment, and the first retentate enters the second pervaporation membrane assembly; the second retentate obtained by the second pervaporation membrane assembly enters the atmospheric distillation tower for distillation treatment; dimethyl carbonate is obtained at the bottom of the high-pressure distillation tower; and methanol is obtained at the bottom of the atmospheric distillation tower.

[0019] Preferably, the operating temperature of the first pervaporation membrane module is 40-60°C.

[0020] Preferably, the operating temperature of the second pervaporation membrane module is 40-60°C.

[0021] Preferably, the concentration of dimethyl carbonate in the raw material is 20-30 wt %, and the raw material enters the first pervaporation membrane module in the form of gas phase or liquid phase.

[0022] The concentration of dimethyl carbonate in the first permeate is 40-90 wt %, the concentration of dimethyl carbonate in the permeate obtained by the second membrane assembly is 20-40 wt %, and the concentration of dimethyl carbonate in the second retentate is 0.5-20 wt %.

[0023] Preferably, the absolute pressure of the vacuum system is 1000~10000Pa.

[0024] Preferably, the reflux ratio of the high-pressure distillation tower is 0.5-5, the operating pressure is 0.2-0.7 MPa, and the tower top temperature is 90-130°C.

[0025] Preferably, the reflux ratio of the atmospheric distillation tower is 0.5-5, the operating pressure is 0.01-0.1 MPa, and the tower top temperature is 60-70°C.

[0026] The present invention has the following beneficial effects:

[0027] 1. The present invention adopts an organic-inorganic composite membrane that preferentially permeates dimethyl carbonate. The composite membrane can effectively break the bottleneck of methanol-dimethyl carbonate azeotropy, change the relative volatility of the azeotrope, and significantly reduce steam energy consumption. The higher the selectivity of the membrane for dimethyl carbonate, the lower the steam energy consumption. The selectivity and stability of the membrane selected in the present invention are better than the membranes reported in the literature.

[0028] 2. The device used in the present invention is provided with a two-stage membrane separation system, the first-stage permeate enters the high-pressure tower, and the second-stage permeate is mixed with the raw material and enters the first-stage membrane system. The heat at the top of the high-pressure tower is used to heat the tower kettle of the atmospheric tower. The membrane separation system and the high-low pressure distillation tower are matched with each other. The steam consumption of dimethyl carbonate per ton in the traditional pressure swing distillation process is about 7.2 tons under the condition of heat recycling. The steam energy consumption of the present invention is only 30-50% of that of the traditional pressure swing distillation process, and the processing capacity of the high-pressure tower is only 40% of that of the high-pressure tower of the traditional pressure swing distillation process, and the processing capacity of the atmospheric tower is only 60% of that of the atmospheric tower of the traditional pressure swing distillation process.

[0029] 3. The device and process of the present invention can reduce the operating pressure and processing capacity of the high-pressure tower, improve the yield of dimethyl carbonate, and further reduce the separation difficulty and tower load.

[0030] 4. The present invention adopts continuous operation, and can simultaneously obtain two products of dimethyl carbonate and methanol with a purity of ≥99.5wt%. All materials are circulated and separated in the system, with high yield and no three wastes generated.

[0031] 5. The distillation tower and membrane process proposed in the present invention takes investment and operation costs into consideration and is suitable for industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of a device for separating dimethyl carbonate and methanol.

[0033] Among them, 1 is the first pervaporation membrane assembly, 2 is the second pervaporation membrane assembly, 3 is the high-pressure distillation tower, 4 is the atmospheric distillation tower, 5 is the first condenser, 6 is the second condenser, 7 is the reboiler of the high-pressure distillation tower, 8 is the reboiler of the atmospheric distillation tower, 9 is the heater, and 10 is the vacuum system. The arrows in the figure represent the direction of material flow, and the dotted arrows represent the direction of heat supply. DETAILED DESCRIPTION

[0034] The present invention is further explained below in conjunction with the examples. The following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0035] like Figure 1 A device for separating dimethyl carbonate and methanol is shown, wherein the retentate side outlet of the first pervaporation membrane assembly 1 is connected to the inlet of the second pervaporation membrane assembly 2, the permeate side outlet of the first pervaporation membrane assembly 2 is connected to the inlet of a high-pressure distillation tower 3, the retentate side outlet of the second pervaporation membrane assembly 2 is connected to the inlet of a atmospheric distillation tower 4, and the top fraction outlet of the high-pressure distillation tower 3 is connected to the inlet of the atmospheric distillation tower 4.

[0036] The first pervaporation membrane assembly 1 and the second pervaporation membrane assembly 2 use dimethyl carbonate-preferential pervaporation membranes.

[0037] The permeate-side outlet of the second pervaporation membrane module 2 is connected to the inlet of the first pervaporation membrane module 1 .

[0038] A heater 9 is provided at the inlet of the first pervaporation membrane module 1 .

[0039] The top fraction outlet of the atmospheric distillation tower 4 is connected to the inlet of the first pervaporation membrane module 1 .

[0040] The heat at the top of the high-pressure distillation tower 3 is used to heat the reboiler 8 of the atmospheric distillation tower 4 .

[0041] The permeate-side outlet of the first pervaporation membrane module 1 is connected to a first condenser 5 , and the permeate-side outlet of the second pervaporation membrane module 2 is connected to a second condenser 6 .

[0042] The first pervaporation membrane module 1 and the second pervaporation membrane module 2 are driven by a vacuum system 10 .

[0043] Example 1

[0044] The above device is used to heat the raw material containing 30wt% dimethyl carbonate and methanol to 50℃ and then enter the membrane assembly. The organic silicon hybrid membrane / alumina ceramic co-condensed with propyltrimethoxysilane and 1,3-bis(triethoxysilyl)propane is used to preferentially permeate dimethyl carbonate pervaporation membrane, and separated by two-stage membrane assembly. The downstream side of the membrane adopts the method of vacuuming and condensing to form the vapor partial pressure difference of the components on the upstream and downstream sides of the membrane. The permeate vapor enters the first and second condensers respectively under the vacuum unit absolute pressure of 5000Pa to obtain the first and second permeates. The dimethyl carbonate concentration in the first permeate is 50wt%, and it enters the high-pressure distillation tower for treatment. The dimethyl carbonate concentration in the second permeate is 28wt% and mixed with the raw material containing 30wt% dimethyl carbonate and methanol and then returns to the first pervaporation membrane assembly for cyclic treatment.

[0045] The first permeate is transported to the middle of the high-pressure distillation tower by the tower feed pump. The high-pressure distillation tower is operated at a pressure of 0.2MPa, a reflux ratio of 1, a tower top temperature of 130°C, and the tower bottom reboiler is heated and vaporized. After full reflux and stable operation, part of the condensation is refluxed to the top of the high-pressure distillation tower. A methanol mixture containing 20% ​​dimethyl carbonate is produced from the tower top, and a 99.8wt% DMC product is produced from the tower bottom. The tower top product enters the atmospheric pressure tower for treatment. The heat of the tower top product is provided to the tower bottom reboiler of the atmospheric pressure distillation tower.

[0046] The second retentate and the top product of the high-pressure distillation tower are transported to the middle of the atmospheric distillation tower by the tower feed pump. The atmospheric distillation tower is operated at a pressure of 0.05MPa, with a reflux ratio of 1 and a top temperature of 65°C. The tower bottom reboiler is heated and vaporized. After full reflux and stable operation, it is condensed by the top condenser and partially refluxed to the top of the atmospheric distillation tower. A methanol mixture containing 25wt% DMC is partially produced, and a 99.5wt% methanol product is produced in the tower bottom. The top product is circulated into the first pervaporation membrane assembly for treatment. The heat of the tower bottom comes from the heat of the top of the high-pressure distillation tower.

[0047] Example 2

[0048] The above device is used to allow 28wt% dimethyl carbonate and methanol gaseous raw materials at 60°C to enter the membrane assembly, and the organic silicon hybrid membrane / alumina ceramic co-condensed with propyltrimethoxysilane and 1,3-bis(triethoxysilyl)propane is used to preferentially permeate dimethyl carbonate pervaporation membrane, and separated by two-stage membrane assembly. The downstream side of the membrane is vacuumed and condensed to form a vapor partial pressure difference between the components on the upstream and downstream sides of the membrane. The permeate vapor enters the first and second condensers respectively under the vacuum unit absolute pressure of 10000Pa to obtain the first and second permeates, and the dimethyl carbonate concentration in the first permeate is 60wt%, which enters the high-pressure distillation tower for treatment. The dimethyl carbonate concentration in the second permeate is 32wt%, and after heating and vaporization, it is mixed with the raw materials containing 28wt% dimethyl carbonate and methanol and returned to the first pervaporation membrane assembly for cyclic treatment.

[0049] The first permeate is transported to the middle of the high-pressure distillation tower by the tower feed pump. The high-pressure distillation tower is operated at a pressure of 0.4MPa, a reflux ratio of 5, a tower top temperature of 90°C, and a tower bottom reboiler for heating and vaporization. After stable operation at full reflux, part of it is condensed and refluxed to the top of the high-pressure distillation tower. The gas phase partially produces a methanol mixture containing 20% ​​dimethyl carbonate and enters the atmospheric pressure tower for treatment. 99.7wt% of DMC product is produced in the tower bottom.

[0050] The second retentate and the top product of the high-pressure distillation tower are transported to the middle of the atmospheric distillation tower by the tower feed pump. The atmospheric distillation tower is operated at a pressure of 0.01 MPa, a reflux ratio of 5, a top temperature of 70°C, and the bottom reboiler is heated and vaporized. After stable operation of full reflux, part of it is refluxed to the top of the atmospheric distillation tower. A methanol mixture containing 26wt% DMC is produced in the gas phase and enters the first permeation vaporization membrane assembly for treatment. A 99.5wt% methanol product is produced in the bottom of the tower.

[0051] Example 3

[0052] The above device is used to heat the raw materials of 20wt% dimethyl carbonate and methanol to 40℃ and then enter the membrane assembly. The organic silicon hybrid membrane / alumina ceramic co-condensed with propyltrimethoxysilane and 1,3-bis(triethoxysilyl)propane is used to preferentially permeate dimethyl carbonate pervaporation membrane, and separated by two-stage membrane assembly. The downstream side of the membrane adopts the method of vacuuming and condensing to form the vapor partial pressure difference of the components on the upstream and downstream sides of the membrane. The permeate vapor enters the first and second condensers respectively under the vacuum unit absolute pressure of 1000Pa to obtain the first and second permeates. The dimethyl carbonate concentration in the first permeate is 40wt%, and it enters the high-pressure distillation tower for treatment. The dimethyl carbonate concentration in the second permeate is 32wt% after heating and vaporization, and mixed with the raw materials containing 20wt% dimethyl carbonate and methanol, and then returns to the first pervaporation membrane assembly for cyclic treatment.

[0053] The first permeate is transported to the middle of the high-pressure distillation tower by the tower feed pump. The high-pressure distillation tower is operated at a pressure of 0.7 MPa, a reflux ratio of 0.5, a tower top temperature of 128°C, and is heated and vaporized in the tower bottom reboiler. After stable operation at full reflux, part of it is condensed and refluxed to the top of the high-pressure distillation tower. The gas phase partially produces a methanol mixture containing 20% ​​dimethyl carbonate and enters the atmospheric pressure tower for treatment. 99.7wt% of DMC product is produced in the tower bottom.

[0054] The second retentate and the top product of the high-pressure distillation tower are transported to the middle of the atmospheric distillation tower by the tower feed pump. The atmospheric distillation tower is operated at a pressure of 0.1 MPa, a reflux ratio of 0.5, a top temperature of 60°C, and is heated and vaporized in a reboiler in the tower bottom. After stable operation at full reflux, part of it is refluxed to the top of the atmospheric distillation tower. A methanol mixture containing 26 wt% DMC is produced in the gas phase and enters the first pervaporation membrane assembly for treatment. A 99.5 wt% methanol product is produced in the tower bottom.

Claims

1. A method for separating dimethyl carbonate and methanol, characterized in that: A device for separating dimethyl carbonate and methanol is used, wherein the retentate outlet of a first pervaporation membrane module of the device is connected to the inlet of a second pervaporation membrane module, the permeate outlet of the first pervaporation membrane module is connected to the inlet of a high-pressure distillation tower, the retentate outlet of the second pervaporation membrane module is connected to the inlet of an atmospheric distillation tower, and the top fraction outlet of the high-pressure distillation tower is connected to the inlet of the atmospheric distillation tower; The first pervaporation membrane assembly and the second pervaporation membrane assembly use a dimethyl carbonate-preferential pervaporation membrane; the dimethyl carbonate-preferential pervaporation membrane is a tubular organic-inorganic composite membrane, the carrier of the dimethyl carbonate-preferential pervaporation membrane is alumina, corundum or mullite, the upper layer is alumina, titanium oxide or zirconium oxide; the organic membrane layer is a controllable pore size organic silicon hybrid membrane co-condensed with propyltrimethoxysilane and 1,3-bis(triethoxysilyl)propane; The permeation side outlet of the second pervaporation membrane module is connected to the inlet of the first pervaporation membrane module; The top fraction outlet of the atmospheric distillation tower is connected to the inlet of the first pervaporation membrane assembly; The method comprises: raw materials enter a first pervaporation membrane module, after pervaporation treatment, the first permeate obtained enters a high-pressure distillation tower for distillation treatment, and the first retentate enters a second pervaporation membrane module; the second retentate obtained by the second pervaporation membrane module enters a normal-pressure distillation tower for distillation treatment; dimethyl carbonate is obtained at the bottom of the high-pressure distillation tower; and methanol is obtained at the bottom of the normal-pressure distillation tower.

2. The method according to claim 1, characterized in that The permeate-side outlet of the second pervaporation membrane module is connected to the inlet of the first pervaporation membrane module.

3. The method according to claim 1, characterized in that A heater is provided at the inlet of the first pervaporation membrane module.

4. The method according to claim 1, characterized in that: The heat from the top of the high-pressure distillation tower is used to heat the reboiler of the atmospheric distillation tower.

5. The method according to claim 1, characterized in that: The operating temperature of the first pervaporation membrane module is 40-60°C; the operating temperature of the second pervaporation membrane module is 40-60°C.

6. The method according to claim 1, characterized in that The concentration of dimethyl carbonate in the raw material is 20-30wt%, and the raw material enters the first pervaporation membrane module in the form of gas phase or liquid phase.

7. The method according to claim 1, characterized in that The reflux ratio of the high-pressure distillation tower is 0.5-5, the operating pressure is 0.2-0.7 MPa, and the tower top temperature is 90-130°C; the reflux ratio of the atmospheric distillation tower is 0.5-5, the operating pressure is 0.01-0.1 MPa, and the tower top temperature is 60-70°C.

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