Method and device for separating azeotrope of ethanol and dimethyl carbonate

Abstract

The invention provides a method and a device for separating azeotrope of ethanol and dimethyl carbonate, and the method comprises the following steps: adding raw materials into an extractive distillation tower for extractive distillation, and then carrying out first heat exchange and condensation on a compressed top gas phase of the extractive distillation tower and a bottom liquid phase of the extractive distillation tower to obtain a dimethyl carbonate product; sequentially carrying out first reboiling, first flash evaporation, two times of heat exchange, second reboiling and second flash evaporation on the heat-exchanged bottom liquid phase of the extractive distillation tower to obtain a second flash evaporation gas phase and a second flash evaporation liquid phase; carrying out second heat exchange on the second flash liquid phase and the first flash liquid phase, condensing, and returning to the extractive distillation tower; and pressurizing the second flash evaporation liquid phase, performing third heat exchange with the first flash evaporation liquid phase after primary heat exchange, and condensing to obtain an ethanol product. The method is low in energy consumption, the solvent is not easy to volatilize, and the ethanol and the dimethyl carbonate in the azeotrope can be effectively separated.

Description

Technical Field

[0001] The invention relates to the technical field of organic separation, in particular to a method and a device for separating an azeotrope of ethanol and dimethyl carbonate. Background Art

[0002] Ethanol and dimethyl carbonate are very important chemical products with excellent solubility. They are common solvents and production raw materials. In the production process of some chemical products, these two substances are often used as mixed solvents. However, under normal pressure conditions, ethanol and dimethyl carbonate form an azeotropic mixture with a composition of 53.94wt% ethanol and 46.06wt% dimethyl carbonate, and an azeotropic temperature of 75.37℃, which makes them difficult to separate. Therefore, developing an efficient and energy-saving method for separating ethanol and dimethyl carbonate has become one of the current research hotspots.

[0003] In terms of separating the azeotropic system of dimethyl carbonate and ethanol, the distillation methods mainly include azeotropic distillation, extractive distillation and pressure swing distillation. Patent CN 201704241 U proposes a pressure swing distillation method for separating azeotropes by changing the pressure, which can recover high-purity ethanol and dimethyl carbonate. However, this method consumes a lot of energy and has extremely high requirements for equipment.

[0004] Compared with other distillation technologies, extractive distillation has the advantages of low energy consumption, simple operation and low equipment investment cost. At present, extractive distillation and pressure swing distillation technology can be used for the separation of this system. Extractive distillation mainly achieves the separation of components by adding a third solvent to change the relative volatility between the original components. Common extraction solvents include ethylene glycol, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and toluene. It has been reported that furfural (FF) can effectively separate the azeotropic system of ethanol and dimethyl carbonate, but its pyrolysis temperature is 125°C. Under normal pressure operation, the bottom temperature may reach about 120°C, at which time FF will decompose, seriously affecting the operation of extractive distillation. Compared with traditional extraction solvents, ionic liquids have the advantages of high stability, non-toxicity and low volatility. In extractive distillation technology, it can reduce equipment investment, simplify process flow and reduce energy consumption. At present, there are relatively few studies on the use of ionic liquids for extractive distillation to separate and reorganize azeotropic systems.

[0005] In summary, the development of an ionic liquid-based extractive distillation method to achieve efficient and energy-saving separation of ethanol and dimethyl carbonate has important practical application value and broad market prospects. Summary of the invention

[0006] The main purpose of the present invention is to provide a method and device for separating the azeotrope of ethanol and dimethyl carbonate, so as to solve the problems of high energy consumption and easy volatility of solvent in the method for separating dimethyl carbonate and ethanol in the prior art.

[0007] In order to achieve the above-mentioned object, according to one aspect of the present invention, there is provided a method for separating the azeotrope of ethanol and dimethyl carbonate, comprising the following steps: step S1, adding the azeotrope of ethanol and dimethyl carbonate and an extractant into an extractive distillation tower, performing extractive distillation to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower; step S2, performing a first compression on the gas phase at the top of the extractive distillation tower to obtain a compressed gas phase at the top of the extractive distillation tower; performing a first heat exchange on the compressed gas phase at the top of the extractive distillation tower and the liquid phase at the bottom of the extractive distillation tower to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower after heat exchange. The liquid phase at the bottom of the tower; step S3, performing a first condensation on the gas phase at the top of the extractive distillation tower after heat exchange to obtain a liquid phase at the top of the extractive distillation tower after condensation, and dividing the liquid phase at the top of the extractive distillation tower after condensation into a first liquid phase at the top of the extractive distillation tower after condensation and a second liquid phase at the top of the extractive distillation tower after condensation; refluxing the first liquid phase at the top of the extractive distillation tower after condensation, and extracting the second liquid phase at the top of the extractive distillation tower after condensation to obtain a dimethyl carbonate product; step S4, performing a first reboiling and a first flash evaporation on the liquid phase at the bottom of the extractive distillation tower after heat exchange in sequence to obtain a first flash gas phase and a first flash evaporation liquid phase; step S5, returning the first flash gas phase to the extraction distillation tower, subjecting the first flashed liquid phase to a second heat exchange to obtain a first flashed liquid phase after a first heat exchange, subjecting the first flashed liquid phase after the first heat exchange to a third heat exchange to obtain a first flashed liquid phase after a second heat exchange; step S6, subjecting the first flashed liquid phase after the second heat exchange to a second reboil and a second flash, in sequence, to obtain a second flashed gas phase and a second flashed liquid phase; wherein the second heat exchange comprises: subjecting the second flashed liquid phase to a second heat exchange with the first flashed liquid phase to obtain a second flashed liquid phase after heat exchange and a first flashed liquid phase after a first heat exchange; subjecting the second flashed liquid phase after heat exchange to a second condensation to obtain a regenerated extractant, and subjecting the regenerated extractant to a second condensation. The raw extractant is returned to the extractive distillation tower; wherein the third heat exchange comprises: performing a second pressurization on the second flash gas phase to obtain a pressurized second flash gas phase, and then performing a third heat exchange on the pressurized second flash gas phase and the first flash liquid phase after the primary heat exchange to obtain a second flash gas phase after heat exchange and a first flash liquid phase after the secondary heat exchange; performing a third condensation on the second flash gas phase after heat exchange to obtain an ethanol product; the extractant comprises an anion component and a cationic component, the cationic component comprises one or more of imidazole, pyrrole and pyridine, and the anion component comprises one or more of organic acid, chloride and tetrafluoroborate.

[0008] Further, in the azeotrope, the weight ratio of ethanol to dimethyl carbonate is (40-60):(40-60); and / or, the extractant includes one or more of 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride and N-octyl-3-methylpyridinium tetrafluoroborate.

[0009] Furthermore, the flow rate of the azeotrope entering the extractive distillation tower is 8000-12000 kg / h, the pressure is 1.0-1.5 bar, and the feed temperature is 40-60°C; and / or, the flow rate of the extractant entering the extractive distillation tower is 25000-35000 kg / h, the pressure is 1.0-1.5 bar, and the feed temperature is 50-80°C; preferably, the weight ratio of the azeotrope to the extractant is (0.2-0.5):1.

[0010] Furthermore, the number of theoretical plates of the extractive distillation tower is 25 to 35; the azeotrope enters from above any one or more plates among the 15th to 25th plates from top to bottom of the extractive distillation tower; the extractant enters from above any one or more plates among the 2nd to 10th plates from top to bottom of the extractive distillation tower; and / or the liquid phase at the top of the extractive distillation tower after the first condensation enters from above any one or more plates among the 1st to 3rd plates from top to bottom of the extractive distillation tower; the first flash gas phase enters from above any one or more plates among the 20th to 25th plates from top to bottom of the extractive distillation tower; and the regenerated extractant enters from above any one or more plates among the 3rd to 9th plates from top to bottom of the extractive distillation tower.

[0011] Further, in step S2, the compression ratio of the first compression is 1 to 2; and / or the temperature of the gas phase at the top of the extractive distillation tower after compression is 80 to 105°C, the temperature of the liquid phase at the bottom of the extractive distillation tower is 80 to 98°C, and the temperature of the gas phase at the top of the extractive distillation tower after compression is higher than the temperature of the liquid phase at the bottom of the extractive distillation tower; the temperature of the liquid phase at the bottom of the extractive distillation tower after heat exchange is 80 to 95°C, and the temperature of the gas phase at the top of the extractive distillation tower after heat exchange is 80 to 100°C; and / or in step S3, the temperature of the liquid phase at the top of the extractive distillation tower after condensation is 85 to 93°C; the volume ratio of the liquid phase at the top of the extractive distillation tower after the first condensation and the liquid phase at the top of the extractive distillation tower after the second condensation is (0.5 to 3):1.

[0012] Further, in step S4, the liquid phase at the bottom of the extractive distillation tower after heat exchange is subjected to a first reboil to obtain a reboiled liquid phase at the bottom of the extractive distillation tower, the gas phase fraction of the reboiled liquid phase at the bottom of the extractive distillation tower is 0.3-0.5, and the temperature is 85-95°C; and / or a first flash is performed in a first flash tank, the inlet temperature of the first flash tank is 90-100°C; and / or the temperature of the first flash gas phase is 80-95°C.

[0013] Further, in the second heat exchange, the temperature of the first flash liquid phase is 90-95°C, and the temperature of the second flash liquid phase is 210-230°C; and / or in the third heat exchange, the temperature of the first flash liquid phase after one heat exchange is 90-100°C, the temperature of the second flash gas phase is 90-95°C, the compression ratio of the second boost is 0.5-2, and the temperature of the second flash gas phase after boosting is 300-350°C; and / or the temperature of the second flash gas phase after heat exchange is 100-140°C, and the third condensation is carried out in the third condenser, and the temperature of the third condenser is 60-80°C; and / or the temperature of the second flash liquid phase after heat exchange is 100-140°C, and the second condensation is carried out in the second condenser, and the temperature of the second condenser is 50-60°C, and the purity of the extractant in the regenerated extractant is ≥99.9wt%.

[0014] Further, in step S6, the temperature of the first flash liquid phase after the secondary heat exchange is 90-110°C, a second reboiler is performed in the second auxiliary reboiler, the temperature of the second auxiliary reboiler is 210-250°C, and the gas phase fraction of the material after reboiled is 0.5-0.8; and / or a second flash is performed in the second flash tank, the pressure of the second flash tank is 0.01-0.5 bar, and the inlet temperature is 210-240°C.

[0015] Furthermore, the purity of the ethanol product is ≥99.5wt%; and / or the purity of the dimethyl carbonate product is ≥99.9wt%.

[0016] According to another aspect of the present invention, there is provided a device for separating an azeotrope of ethanol and dimethyl carbonate, comprising: an extractive distillation column, a first steam compressor, a first heat exchanger, a throttle valve, a first condenser, a splitter, a first auxiliary reboiler, a first flash tank, a second heat exchanger, a third heat exchanger, a second auxiliary reboiler, a second flash tank, a second steam compressor, a third condenser, and a second condenser;

[0017] The extractive distillation tower has a tower top gas phase outlet, a tower bottom liquid phase outlet, a tower top liquid phase inlet, a tower bottom liquid phase inlet, an extractant inlet, and an azeotrope inlet; the tower top gas phase outlet of the extractive distillation tower is connected to the inlet of the first steam compressor;

[0018] The first heat exchanger has a first hot stream inlet, a first cold stream inlet, a first hot stream outlet, and a first cold stream outlet, the first hot stream inlet is connected to the outlet of the first steam compressor, the first hot stream outlet is connected to the inlet of the throttle valve, the first cold stream inlet is connected to the bottom liquid phase outlet of the extractive distillation tower, and the first cold stream outlet is connected to the inlet of the first auxiliary reboiler;

[0019] The first flash tank has an inlet, a first gas phase outlet and a first liquid phase outlet, the inlet is connected to the outlet of the first auxiliary reboiler, and the first gas phase outlet is connected to the bottom liquid phase inlet of the extractive distillation tower;

[0020] The second flash tank has an inlet, a second gas phase outlet and a second liquid phase outlet, the inlet is connected to the outlet of the second auxiliary reboiler, and the second gas phase outlet is connected to the inlet of the second steam compressor;

[0021] The second heat exchanger has a second hot stream inlet, a second cold stream inlet, a second hot stream outlet, and a second cold stream outlet, the second hot stream inlet is connected to the second liquid phase outlet of the second flash tank, the second hot stream outlet is connected to the inlet of the second condenser, the second cold stream inlet is connected to the first liquid phase outlet of the first flash tank, and the second cold stream outlet is connected to the third cold stream inlet of the third heat exchanger;

[0022] The third heat exchanger has a third hot stream inlet, a third cold stream inlet, a third hot stream outlet, and a third cold stream outlet, the third hot stream inlet is connected to the outlet of the second steam compressor, the third hot stream outlet is connected to the inlet of the third condenser, and the cold stream outlet is connected to the inlet of the second auxiliary reboiler;

[0023] The inlet of the first condenser is connected to the outlet of the throttle valve, and the outlet is connected to the inlet of the splitter; the splitter has a reflux outlet and a production outlet, the reflux outlet is connected to the top liquid phase inlet of the extractive distillation tower, and the production outlet produces dimethyl carbonate product; the outlet of the second condenser is connected to the extractant inlet of the extractive distillation tower, and the outlet of the third condenser produces ethanol product;

[0024] An extractant is added into the extractive distillation tower. The extractant comprises an anion component and a cation component. The cation component comprises one or more of imidazole, pyridine and pyrrole, and the anion component comprises one or more of organic acid, chloride and tetrafluoroborate.

[0025] Furthermore, the extractive distillation tower is a sieve plate tower, preferably one or more of a standard sieve plate tower, a corrugated sieve plate tower, a floating valve sieve plate tower, a mesh sieve plate tower, a spray sieve plate tower, a composite sieve plate tower, a high-efficiency sieve plate tower, a large sieve plate tower and a micro sieve plate tower; the first condenser, the first heat exchanger, the second heat exchanger, the third heat exchanger, the first auxiliary reboiler and the second auxiliary reboiler are independently selected from one or more of a kettle type, a cross flow type and an axial flow type.

[0026] The present invention first compresses the steam at the top of the extractive distillation tower to increase its temperature, and then passes it into the first heat exchanger as a heat source flow to exchange heat with the liquid phase at the bottom of the extractive distillation tower, so that the temperature of the liquid phase at the bottom of the tower increases, and the gas phase fraction is improved, thereby reducing the energy consumption of the subsequent first reboiling process, that is, reducing the additional heat required for the first reboiling, and reducing energy consumption on the basis of ensuring that sufficient heat source is provided for the bottom of the extractive distillation tower. In addition, the present invention specifically utilizes the steam stream at the top of the second flash tank and the liquid phase stream at its bottom to heat the inlet stream of the second flash tank and reduce the energy loss of the second flash tank. Secondly, the present invention specifically adds a top steam compressor at the top of the extractive distillation tower and the top of the second flash tank to pressurize the steam to release the latent heat in the gas phase and increase the heat in the hot stream, and combines with the heat exchanger to fully utilize the heat while saving thermal energy.

[0027] In addition, the specific component extractant of the present invention is non-volatile, non-polluting, easy to prepare, and has a mature production process. It can be combined with the separation process of the present invention to achieve full separation of ethanol and dimethyl carbonate in the azeotrope. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 A schematic flow diagram of separating an azeotrope of ethanol and dimethyl carbonate according to Example 1 of the present invention is shown; and

[0030] The above drawings include the following reference numerals:

[0031] 1. Extraction distillation tower; 2. First steam compressor; 3. First heat exchanger; 4. Throttle valve; 5. First condenser; 6. Divider; 7. First auxiliary reboiler; 8. First flash tank; 9. Second heat exchanger; 10. Third heat exchanger; 11. Second auxiliary reboiler; 12. Second flash tank; 13. Second steam compressor; 14. Third condenser; 15. Second condenser; 16. Pump;

[0032] A. Extractant; B. Azeotrope of ethanol and dimethyl carbonate; C. Dimethyl carbonate product; D. Ethanol product; E. Regenerated extractant. DETAILED DESCRIPTION

[0033] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] Terminology explanation:

[0035] Gas phase fraction: the mass content or mass fraction of the gas phase medium in the gas-liquid two-phase flow, that is, the ratio of the gas phase mass flow rate to the total mass flow rate.

[0036] Compression ratio: the ratio of change in volume of a gas during the compression process.

[0037] As described in the background of the present invention, there are problems in the prior art of separating dimethyl carbonate and ethanol such as high energy consumption and volatile solvents. In order to solve the above problems, in a typical embodiment of the present invention, a method for separating the azeotrope of ethanol and dimethyl carbonate is provided, comprising the following steps: step S1, adding the azeotrope of ethanol and dimethyl carbonate and an extractant to an extractive distillation tower, performing extractive distillation to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower; step S2, performing a first compression on the gas phase at the top of the extractive distillation tower to obtain a compressed gas phase at the top of the extractive distillation tower; performing a first heat exchange on the compressed gas phase at the top of the extractive distillation tower and the liquid phase at the bottom of the extractive distillation tower to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower after heat exchange. The bottom liquid phase of the distillation tower is taken; step S3, the gas phase at the top of the extractive distillation tower after heat exchange is subjected to a first condensation to obtain the top liquid phase of the extractive distillation tower after condensation, and the top liquid phase of the extractive distillation tower after condensation is divided into a first top liquid phase of the extractive distillation tower after condensation and a second top liquid phase of the extractive distillation tower after condensation; the top liquid phase of the first top liquid phase of the extractive distillation tower after condensation is refluxed, and the top liquid phase of the second top liquid phase of the extractive distillation tower after condensation is extracted to obtain a dimethyl carbonate product; step S4, the bottom liquid phase of the extractive distillation tower after heat exchange is subjected to a first reboil and a first flash evaporation in sequence to obtain a first flash gas phase and a first flash evaporation liquid phase; step S5, the first flash gas phase is returned to the bottom liquid phase of the extractive distillation tower after condensation; The extractive distillation tower is used to perform a second heat exchange on the first flashed liquid phase to obtain a first flashed liquid phase after the first heat exchange, and the first flashed liquid phase after the first heat exchange is subjected to a third heat exchange to obtain a first flashed liquid phase after the second heat exchange; step S6, the first flashed liquid phase after the second heat exchange is subjected to a second reboiling and a second flashing in sequence to obtain a second flashed gas phase and a second flashed liquid phase; wherein the second heat exchange comprises: performing a second heat exchange on the second flashed liquid phase and the first flashed liquid phase to obtain a second flashed liquid phase after the heat exchange and a first flashed liquid phase after the first heat exchange; performing a second condensation on the second flashed liquid phase after the heat exchange to obtain a regenerated extractant, and The regenerated extractant is returned to the extractive distillation tower; wherein the third heat exchange comprises: subjecting the second flash gas phase to a second pressurization to obtain a pressurized second flash gas phase, and then subjecting the pressurized second flash gas phase to a third heat exchange with the first flash liquid phase after the primary heat exchange to obtain a heat-exchanged second flash gas phase and a secondary heat-exchanged first flash liquid phase; subjecting the heat-exchanged second flash gas phase to a third condensation to obtain an ethanol product; the extractant comprises an anion component and a cationic component, the cationic component comprises one or more of imidazole, pyrrole and pyridine, and the anion component comprises one or more of an organic acid, chloride and tetrafluoroborate.

[0038] The present invention adopts an extractant, and extracts and separates the azeotrope of ethanol and dimethyl carbonate in an extractive distillation tower, obtains a gas phase whose main component is dimethyl carbonate at the top of the extractive distillation tower, refluxes it to improve the purity of the dimethyl carbonate product, obtains a liquid phase whose main components are the extractant and ethanol at the bottom of the tower, performs a first reboil and a first flash evaporation, separates the gas phase whose main component is ethanol, and enters the extractive distillation tower for further separation, provides sufficient heat for the extractive distillation tower, promotes mass transfer and heat transfer between components, and realizes component separation. The liquid phase obtained by the first flash evaporation is subjected to a second flash evaporation to separate the ethanol product and regenerate the extractant, and the regenerated extractant is recycled.

[0039] In the extractive distillation process, the amount of condensed water used at the top of the extractive distillation tower and the amount of low-pressure steam used in the reboiling process at the bottom of the tower are mainly large, and the energy consumption of the solvent recovery process using the extractive distillation tower is large. In the prior art, double-effect distillation is usually used to reduce energy consumption, but the hot and cold energy consumption cannot be fully matched, and the investment cost is high. The present invention first compresses the steam at the top of the extractive distillation tower to heat it up, and then passes it into the first heat exchanger as a heat source flow to exchange heat with the liquid phase at the bottom of the extractive distillation tower, so that the temperature of the liquid phase at the bottom of the tower is increased, and the gas phase fraction is increased, thereby reducing the energy consumption of the subsequent first reboiling process, that is, reducing the additional heat required for the first reboiling, and reducing energy consumption on the basis of ensuring that sufficient heat source is provided for the bottom of the extractive distillation tower. In addition, the present invention particularly utilizes the steam stream at the top of the second flash tank and the liquid phase stream at its bottom to heat the inlet stream of the second flash tank, thereby reducing the equipment investment cost of the second flash tank. Secondly, the present invention particularly adds a top steam compressor at the top of the extraction distillation tower and the top of the second flash tank to pressurize the steam to release the latent heat in the gas phase and increase the heat in the hot flow stream, and combines with a heat exchanger to fully utilize the heat while saving thermal energy.

[0040] In the prior art, the energy consumption of the extraction and distillation process without a heat pump is 4500-5000kW, while the energy consumption of the extraction and distillation process with a heat pump added in the present invention is 2000-2500kW, saving about 45%-60%. Compared with the ordinary extraction and distillation tower, the present invention adopts the heat pump process and the heat integration energy-saving means, reduces the energy consumption of the extraction and distillation tower and the overall process energy consumption, and achieves energy saving.

[0041] It should be noted that the heat pump process in the present invention includes: the top and bottom of the extractive distillation tower do not include traditional reboilers and condensers, but use a compressor to raise the temperature of the condensed steam to match the temperature of the bottom of the tower, which effectively improves the heat utilization rate of the entire system and also significantly reduces energy consumption. In addition, the heat integration process in the present invention involves heat exchange between the cold and hot streams between the extractant recovery process and the extractive distillation tower, as well as heat exchange in the process section itself, which can optimize energy utilization, realize energy recovery and reuse, reduce energy consumption, and improve production efficiency.

[0042] In addition, conventional extractants, such as furfural, chlorobenzene and xylene, are volatile, especially at 50-100°C during the extraction and distillation process, they are prone to decomposition, which seriously affects the operation of the extraction and distillation, and requires a large amount of extractant to continue the extraction and distillation process, which is costly. Compared with conventional extractants, the specific component extractant of the present invention is non-volatile, pollution-free, easy to prepare, and has a mature production process because the ionic liquid itself has the characteristic mechanism of molten salt, and can be combined with the separation process of the present invention to achieve full separation of ethanol and dimethyl carbonate in the azeotrope.

[0043] The separation method of the present invention is suitable for a mixture of ethanol and dimethyl carbonate. In a preferred embodiment, in the azeotrope, the weight ratio of ethanol to dimethyl carbonate is (40-60):(40-60).

[0044] In a preferred embodiment, the extractant includes one or more of 1-butyl-3-methylimidazolium acetate (code: C108A203), 1-butyl-3-methylimidazolium chloride (code: C108A001) and N-octyl-3-methylpyridinium tetrafluoroborate (code: C20FA101). Under the above conditions, the extractant has better thermal stability, can be extracted more stably, and has better extraction effect.

[0045] In a preferred embodiment, the flow rate of the azeotrope entering the extractive distillation tower is 8000-12000 kg / h, the pressure is 1.0-1.5 bar, and the feed temperature is 40-60°C; and / or, the flow rate of the extractant entering the extractive distillation tower is 25000-35000 kg / h, the pressure is 1.0-1.5 bar, and the feed temperature is 50-80°C; preferably, the weight ratio of the azeotrope to the extractant is (0.2-0.5): 1. Under the above conditions, the azeotrope and the extractant can be more fully contacted, which is more conducive to improving the separation efficiency and separation effect.

[0046] After a large number of experiments and software calculation simulations, the inventors obtained a more practical material inlet position in the extractive distillation tower. In a preferred embodiment, the number of theoretical plates of the extractive distillation tower is 25 to 35; the azeotrope enters from above any one or more plates from the 15th to the 25th from top to bottom of the extractive distillation tower; the extractant enters from above any one or more plates from the 2nd to the 10th from top to bottom of the extractive distillation tower; and / or the liquid phase at the top of the extractive distillation tower after the first condensation enters from above any one or more plates from the 1st to the 3rd from top to bottom of the extractive distillation tower; the first flash gas phase enters from above any one or more plates from the 20th to the 25th from top to bottom of the extractive distillation tower; the regenerated extractant enters from above any one or more plates from the 3rd to the 9th from top to bottom of the extractive distillation tower. Under the above conditions, the temperature distribution in the extractive distillation tower is more uniform, the plate load is smaller, the operating energy consumption is smaller, the stability is better, the relative volatility of ethanol is higher, the extraction effect of the extractant on dimethyl carbonate is better, the separation effect of ethanol and dimethyl carbonate is better, and the product purity is higher.

[0047] In order to more fully release the latent heat of the vapor at the top of the extractive distillation tower, thereby saving energy more fully, in a preferred embodiment, in step S2, the compression ratio of the first compression is 1 to 2; and / or the temperature of the gas phase at the top of the extractive distillation tower after compression is 80 to 105°C, the temperature of the liquid phase at the bottom of the extractive distillation tower is 80 to 98°C, and the temperature of the gas phase at the top of the extractive distillation tower after compression is higher than the temperature of the liquid phase at the bottom of the extractive distillation tower; the temperature of the liquid phase at the bottom of the extractive distillation tower after heat exchange is 80 to 95°C, and the temperature of the gas phase at the top of the extractive distillation tower after heat exchange is 80 to 100°C. Under the above conditions, more heat is exchanged in the first heat exchanger, the gas phase fraction of the bottom stream of the extractive distillation tower is closer to the flow required for reflux, the power of the auxiliary reboiler is smaller, less additional heat needs to be introduced, and the energy saving effect is better.

[0048] In order to more conveniently control the flow rate, pressure and flow rate of the gas phase at the top of the extractive distillation tower after heat exchange and to further reduce energy consumption, in a preferred embodiment, before the first condensation step, step S2 also includes the step of passing the gas phase at the top of the extractive distillation tower after heat exchange through a throttle valve, and the valve outlet pressure of the throttle valve is 0.9 to 1 bar.

[0049] In a preferred embodiment, in step S3, the temperature of the top liquid phase of the extractive distillation tower after condensation is 85-93°C; the volume ratio of the top liquid phase of the first extractive distillation tower after condensation to the top liquid phase of the second extractive distillation tower after condensation is (0.5-3): 1. Under the above conditions, the energy consumption of the distillation tower and the equipment investment can be not significantly increased on the basis of ensuring the stable operation of the extractive distillation tower, high separation efficiency and high product purity.

[0050] In a preferred embodiment, the liquid phase at the bottom of the extractive distillation tower after heat exchange is subjected to a first reboil to obtain a reboiled liquid phase at the bottom of the extractive distillation tower, wherein the gas phase fraction of the reboiled liquid phase at the bottom of the extractive distillation tower is 0.3-0.5 and the temperature is 85-95° C. Under the above conditions, it is more conducive to improving the heat transfer efficiency in the extractive distillation tower, reducing energy consumption, further more conducive to improving the stability and separation efficiency of the extractive distillation, and saving energy.

[0051] In a preferred embodiment, the first flash is carried out in the first flash tank, and the inlet temperature of the first flash tank is 90-100°C; and / or the temperature of the first flash gas phase is 80-95°C. Under the above conditions, it is more conducive to improving the recovery rate of the extractant and the flash effect, and it can also reduce energy consumption and improve product quality. If the pressure or inlet temperature of the first flash tank is too high, although it is conducive to improving the recovery rate of the extractant, it is easy to cause the extractant to fail and excessive energy consumption. If it is too low, it will affect the flash effect and the recovery rate of the extractant.

[0052] In order to more fully recover the heat of the second flash vapor phase and liquid phase, in a preferred embodiment, in the second heat exchange, the temperature of the first flash liquid phase is 90-95°C, and the temperature of the second flash liquid phase is 210-230°C; and / or in the third heat exchange, after one heat exchange, the temperature of the first flash liquid phase is 90-100°C, the temperature of the second flash vapor phase is 90-95°C, the compression ratio of the second boost is 0.5-2, and the temperature of the second flash vapor phase after boosting is 300-350°C.

[0053] In a preferred embodiment, the temperature of the second flash gas phase after heat exchange is 100-140°C, the third condensation is carried out in the third condenser, and the temperature of the third condenser is 60-80°C; and / or the temperature of the second flash liquid phase after heat exchange is 100-140°C, the second condensation is carried out in the second condenser, and the temperature of the second condenser is 50-60°C. Under the above conditions, the second flash gas phase after heat exchange is more convenient for practical use, and the temperature of the second flash liquid phase after heat exchange is more in line with the minimum recovery temperature for obtaining a high-purity extractant, which is more conducive to the extractive distillation process. In a preferred embodiment, the purity of the extractant in the regenerated extractant is ≥99.9wt%. It should be noted that the specific type of extractant of the present invention has a high boiling point (such as 300-400°C), and the loss after the entire extractive distillation process is negligible (the loss is less than 1kg / h), and no additional extractant needs to be added.

[0054] For the purpose of fully separating ethanol and the extractant, in a preferred embodiment, in step S6, the temperature of the first flash liquid phase after the secondary heat exchange is 90-110°C, a second reboiler is performed in the second auxiliary reboiler, the temperature of the second auxiliary reboiler is 210-250°C, and the gas phase fraction of the material after reboiled is 0.5-0.8; and / or a second flash is performed in the second flash tank, the pressure of the second flash tank is 0.01-0.5 bar, and the inlet temperature is 210-240°C.

[0055] In a preferred embodiment, the purity of the ethanol product is ≥99.5 wt %; and / or the purity of the dimethyl carbonate product is ≥99.9 wt %.

[0056] In another typical embodiment of the present invention, a device for separating the azeotrope of ethanol and dimethyl carbonate is also provided, comprising: an extractive distillation tower 1, a first steam compressor 2, a first heat exchanger 3, a throttle valve 4, a first condenser 5, a splitter 6, a first auxiliary reboiler 7, a first flash tank 8, a second heat exchanger 9, a third heat exchanger 10, a second auxiliary reboiler 11, a second flash tank 12, a second steam compressor 13, a third condenser 14, and a second condenser 15; the extractive distillation tower 1 has a top gas phase outlet, a bottom liquid phase outlet, a top liquid phase inlet, a bottom liquid phase inlet, an extractant inlet, and an azeotrope inlet; the top gas phase outlet of the extractive distillation tower 1 is connected to the inlet of the first steam compressor 2; The first heat exchanger 3 has a first hot stream inlet, a first cold stream inlet, a first hot stream outlet, and a first cold stream outlet, the first hot stream inlet is connected to the outlet of the first steam compressor 2, the first hot stream outlet is connected to the inlet of the throttle valve 4, the first cold stream inlet is connected to the bottom liquid phase outlet of the extractive distillation tower 1, and the first cold stream outlet is connected to the inlet of the first auxiliary reboiler 7; the first flash tank 8 has an inlet, a first gas phase outlet and a first liquid phase outlet, the inlet is connected to the outlet of the first auxiliary reboiler 7, and the first gas phase outlet is connected to the bottom liquid phase inlet of the extractive distillation tower 1; the second flash tank 12 has an inlet, a second gas phase outlet and a second liquid phase outlet, and the inlet is connected to the outlet of the second auxiliary reboiler 11, The second gas phase outlet is connected to the inlet of the second steam compressor 13; the second heat exchanger 9 has a second hot stream inlet, a second cold stream inlet, a second hot stream outlet, and a second cold stream outlet, the second hot stream inlet is connected to the second liquid phase outlet of the second flash tank 12, the second hot stream outlet is connected to the inlet of the second condenser 15, the second cold stream inlet is connected to the first liquid phase outlet of the first flash tank 8, and the second cold stream outlet is connected to the third cold stream inlet of the third heat exchanger 10; the third heat exchanger 10 has a third hot stream inlet, a third cold stream inlet, a third hot stream outlet, and a third cold stream outlet, the third hot stream inlet is connected to the outlet of the second steam compressor 13, and the third hot stream outlet is connected to the third condenser The inlet of the first condenser 5 is connected to the outlet of the throttle valve 4, and the outlet is connected to the inlet of the splitter 6; the splitter 6 has a reflux outlet and a production outlet, the reflux outlet is connected to the top liquid phase inlet of the extractive distillation tower 1, and the production outlet produces dimethyl carbonate product; the outlet of the second condenser 15 is connected to the extractant inlet of the extractive distillation tower 1, and the outlet of the third condenser 14 produces ethanol product; the extractant is added to the extractive distillation tower 1, and the extractant includes an anion component and a cationic component, the cationic component includes one or more of imidazole, pyridine and pyrrole, and the anion component includes one or more of organic acid, chloride and tetrafluoroborate.

[0057] The present invention adopts an extractant, and extracts and separates the azeotrope of ethanol and dimethyl carbonate in an extractive distillation tower 1, obtains a gas phase whose main component is dimethyl carbonate at the top of the extractive distillation tower, refluxes it through a splitter 6 to improve the purity of the dimethyl carbonate product, obtains a liquid phase whose main components are the extractant and ethanol at the bottom of the tower, sends it to a first auxiliary reboiler 7 for a first reboil, and then sends it to a first flash tank 8 for a first flash, separates the gas phase whose main component is ethanol, and allows it to enter the extractive distillation tower 1 for further separation, provides sufficient heat for the extractive distillation tower 1, promotes mass transfer and heat transfer between components, and realizes component separation. The liquid phase of the first flash tank 8 is sent to a second flash tank 12 for a second flash, separates the ethanol product, regenerates the extractant, and recycles the regenerated extractant.

[0058] In the extractive distillation process, the amount of condensed water used at the top of the extractive distillation tower and the amount of low-pressure steam used in the reboiling process at the bottom of the tower are mainly large, and the energy consumption of the solvent recovery process using the extractive distillation tower is large. In the prior art, double-effect distillation is usually used to reduce energy consumption, but the hot and cold energy consumption cannot be fully matched, and the investment cost is high. The present invention first compresses the steam at the top of the extractive distillation tower to heat it up, and then passes it into the first heat exchanger 3 as a heat source flow to exchange heat with the liquid phase at the bottom of the extractive distillation tower, so that the temperature of the liquid phase at the bottom of the tower is increased, and the gas phase fraction is increased, thereby reducing the energy consumption of the subsequent first reboiling process, that is, reducing the additional heat required for the first reboiling, and reducing energy consumption on the basis of ensuring that sufficient heat source is provided for the bottom of the extractive distillation tower. In addition, the present invention particularly utilizes the steam stream at the top of the second flash tank 12 and the liquid phase stream at its bottom to heat the inlet stream of the second flash tank 12, thereby reducing the equipment investment cost of the second flash tank 12. Secondly, the present invention particularly adds a first steam compressor 2 and a second steam compressor 13 at the top of the extractive distillation tower 1 and the top of the second flash tank 12, respectively, to pressurize the steam, release the latent heat in the gas phase, increase the heat in the hot flow, and combine the first heat exchanger 3, the second heat exchanger 9, and the third heat exchanger 10 to fully utilize the heat while saving thermal energy.

[0059] In the prior art, the energy consumption of the extraction and distillation process without a heat pump is 4500-5000kW, while the energy consumption of the extraction and distillation process with a heat pump added in the present invention is 2000-2500kW, saving about 45%-60%. Compared with the ordinary extraction and distillation tower, the present invention adopts the heat pump process and the heat integration energy-saving means, reduces the energy consumption of the extraction and distillation tower and the overall process energy consumption, and achieves energy saving.

[0060] It should be noted that the heat pump process in the present invention includes: the top and bottom of the extractive distillation tower do not include traditional reboilers and condensers, but use a compressor to raise the temperature of the condensed steam to match the temperature of the bottom of the tower, which effectively improves the heat utilization rate of the entire system and also significantly reduces energy consumption. In addition, the heat integration process in the present invention involves heat exchange between the cold and hot streams between the extractant recovery process and the extractive distillation tower, as well as heat exchange in the process section itself, which can optimize energy utilization, realize energy recovery and reuse, reduce energy consumption, and improve production efficiency.

[0061] In addition, conventional extractants, such as furfural, chlorobenzene and xylene, are volatile, especially at 50-100°C during the extractive distillation process, they are prone to decomposition, which seriously affects the operation of the extractive distillation, and requires a large amount of extractant to continue the extractive distillation process, which is costly. Compared with conventional extractants, the specific component extractant of the present invention is non-volatile, pollution-free, easy to prepare, and has a mature production process because the ionic liquid itself has the characteristics of a molten salt, and can be combined with the separation process of the present invention to achieve full separation of ethanol and dimethyl carbonate in the azeotrope.

[0062] In a preferred embodiment, the extractive distillation tower 1 is a sieve plate tower, preferably one or more of a standard sieve plate tower, a corrugated sieve plate tower, a floating valve sieve plate tower, a mesh sieve plate tower, a spray sieve plate tower, a composite sieve plate tower, a high-efficiency sieve plate tower, a large sieve plate tower and a micro sieve plate tower; the first condenser 5, the first heat exchanger 3, the second heat exchanger 9, the third heat exchanger 10, the first auxiliary reboiler 7, and the second auxiliary reboiler 11 are independently selected from one or more of kettle type, cross flow type and axial flow type.

[0063] Typically but not limiting, the weight ratio of the azeotrope to the extractant is 0.2:1, 0.3:1, 0.4:1, 0.5:1 or a range consisting of any two of them; in the azeotrope, the weight ratio of ethanol to dimethyl carbonate is 40:60, 45:55, 50:50, 55:45, 60:40 or a range consisting of any two of them.

[0064] Typically but not limiting, in step S2, the compression ratio of the first compression is 1, 1.5, 2 or a range consisting of any two of them.

[0065] Typically but not limiting, the gas phase fraction of the liquid phase at the bottom of the extractive distillation tower after reboiled is 0.3, 0.35, 0.4, 0.45, 0.5 or a range consisting of any two of them, and the temperature is 85°C, 90°C, 95°C or a range consisting of any two of them.

[0066] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0067] Example 1

[0068] The flow chart for separating the azeotrope of ethanol and dimethyl carbonate is shown in Figure 1 .

[0069] In the azeotrope B of ethanol and dimethyl carbonate, the weight percentage of ethanol is 50wt%, and the weight percentage of dimethyl carbonate is 50wt%. The flow rate of the azeotrope is 10000kg / h, the feed temperature is 50°C, and the feed pressure is 1.2bar. The flow rate of the extractant A (1-butyl-3-methylimidazole acetate, code: C108A203) is 29640kg / h, the feed temperature is 50°C, and the feed pressure is 1.2bar.

[0070] The number of theoretical plates of the extractive distillation tower is 30, the top temperature is 90°C, and the bottom temperature is 93°C.

[0071] Step S1, adding the azeotrope from above the 18th plate from top to bottom of the extractive distillation tower 1, and adding the extractant from above the 3rd plate from top to bottom of the extractive distillation tower 1, performing extractive distillation to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower.

[0072] Step S2, subjecting the top gas phase of the extractive distillation tower to a first compression through the first steam compressor 2, and controlling the compression ratio to 1.29:1, the temperature of the compressed top gas phase of the extractive distillation tower is 98°C, and then entering the first heat exchanger 3, and performing a first heat exchange with the bottom liquid phase of the extractive distillation tower to obtain the top gas phase of the extractive distillation tower after heat exchange and the bottom liquid phase of the extractive distillation tower after heat exchange, the gas phase fraction of the bottom liquid phase of the extractive distillation tower after heat exchange is 0.41, the temperature of the top gas phase of the extractive distillation tower after heat exchange is 98°C, and the heat exchange of the first heat exchanger 3 is 4697.82kW.

[0073] Step S3, the gas phase at the top of the extractive distillation tower after heat exchange is depressurized through a throttle valve 4, the valve outlet pressure of the throttle valve 4 is 1 bar, and the first condensation is performed through a first condenser 5 to obtain a liquid phase at the top of the extractive distillation tower after condensation, and the temperature of the liquid phase is 90°C, and the liquid phase is divided into two parts, namely, a first liquid phase at the top of the extractive distillation tower after condensation and a second liquid phase at the top of the extractive distillation tower after condensation, through a splitter 6, and the volume ratio of the two parts is 1:1, and the liquid phase at the top of the extractive distillation tower after the first condensation is returned to the extractive distillation tower, and enters from above the first tower plate from top to bottom of the extractive distillation tower; the liquid phase at the top of the second extractive distillation tower after condensation is extracted to obtain a dimethyl carbonate product C with a purity of 99.9wt%.

[0074] Step S4, the liquid phase at the bottom of the extractive distillation tower after heat exchange is sent to the first auxiliary reboiler 7, and continued to be heated to obtain the liquid phase at the bottom of the extractive distillation tower after reboil, the temperature of which is 93°C, the gas phase fraction is 0.47 at this time, and the power of the first auxiliary reboiler 7 is 728.30kW. The liquid phase at the bottom of the extractive distillation tower after reboiled is sent to the first flash tank 8 for the first flash evaporation, the load of the first flash tank 8 is set to 0 cal / sec, and the inlet temperature is set to 97°C, to obtain the first flash gas phase and the first flash liquid phase.

[0075] Step S5, returning the first flash gas phase (mainly composed of ethanol and having a temperature of 93°C) to the extractive distillation tower 1, and entering from above the last plate from top to bottom of the extractive distillation tower; sending the first flash liquid phase (mainly composed of extractant and ethanol and having a temperature of 93°C) to the second heat exchanger 9 for a second heat exchange to obtain the first flash liquid phase after the first heat exchange, and sending the first flash liquid phase after the first heat exchange to the third heat exchanger 10 for a third heat exchange to obtain the first flash liquid phase after the second heat exchange.

[0076] Step S6, the first flash liquid phase after the secondary heat exchange is sent to the second auxiliary reboiler 11 for second reboiling, the temperature of the second auxiliary reboiler 11 is 220° C., the gas phase fraction of the material after reboiled is 0.69, and then enters the second flash tank 12 for second flash evaporation, the load of the second flash tank 12 is 0 cal / sec, the pressure is 0.01 bar, and the inlet temperature is 220° C. The top vapor (second flash vapor phase) of the second flash tank 12 is ethanol with a purity of 99.5wt%, and the bottom liquid phase (second flash liquid phase) is a regenerated extractant with a purity of 99.9wt%, and the temperature is 219° C.

[0077] The second flashed liquid phase is sent to the second heat exchanger 9 as a hot stream to perform a second heat exchange with the first flashed liquid phase. The temperature of the first flashed liquid phase after the first heat exchange is 95° C., and the temperature of the second flashed liquid phase after the heat exchange is 137° C. The heat exchanged in the second heat exchange is 1826.27 KW. The second flashed liquid phase after the heat exchange is then sent to the second condenser 15 to be condensed to 50° C. to obtain a regenerated extractant E with a purity of 99.9 wt%. The regenerated extractant is returned to the extractive distillation tower 1 through a pump 16 and enters from above the third plate from top to bottom of the extractive distillation tower to recycle the regenerated extractant.

[0078] The second flash vapor phase is sent to the second steam compressor 13 for supercharging, and the compression ratio of the second supercharging is 0.72. The temperature of the second flash vapor phase after supercharging is 327°C. Then it is sent to the third heat exchanger 10 as a hot stream to perform a third heat exchange with the first flash liquid phase after the first heat exchange to obtain the second flash vapor phase after heat exchange and the first flash liquid phase after the second heat exchange. The temperature of the first flash liquid phase after the first heat exchange is 95°C, the temperature of the second flash vapor phase after heat exchange is 137°C, and the temperature of the first flash liquid phase after the second heat exchange is 93°C. The heat exchanged in the third heat exchange is 2390KW. Then the second flash vapor phase after heat exchange is passed through the third condenser 14 for a third condensation. The temperature of the third condenser is 79°C to obtain ethanol product D with a purity of 99.5wt%.

[0079] Example 2

[0080] The flow chart for separating the azeotrope of ethanol and dimethyl carbonate is shown in Figure 1 .

[0081] In the azeotrope of ethanol and dimethyl carbonate, the weight percentage of ethanol is 45wt%, and the weight percentage of dimethyl carbonate is 55wt%. The flow rate of the azeotrope is 10000kg / h, the feed temperature is 50°C, and the feed pressure is 1.2bar. The flow rate of the extractant (1-butyl-3-methylimidazolium chloride, code: C108A001) is 31616kg / h, the feed temperature is 50°C, and the feed pressure is 1.2bar.

[0082] The number of theoretical plates of the extractive distillation tower is 34, the top temperature is 90°C, and the bottom temperature is 87°C.

[0083] Step S1, adding the azeotrope from above the 20th plate of the extractive distillation tower 1, and adding the extractant from above the 5th plate from top to bottom of the extractive distillation tower 1, performing extractive distillation to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower.

[0084] Step S2, the gas phase at the top of the extractive distillation tower is subjected to a first compression through the first steam compressor 2, and the compression ratio is controlled to be 1.4:1. The temperature of the gas phase at the top of the extractive distillation tower after compression is 100°C, and then enters the first heat exchanger 3 to perform a first heat exchange with the liquid phase at the bottom of the extractive distillation tower to obtain the gas phase at the top of the extractive distillation tower after heat exchange and the liquid phase at the bottom of the extractive distillation tower after heat exchange. The temperature of the liquid phase at the bottom of the extractive distillation tower after heat exchange is 84°C, the gas phase fraction is 0.44, the temperature of the gas phase at the top of the extractive distillation tower after heat exchange is 99°C, and the heat exchange of the first heat exchanger 3 is 4866kW.

[0085] Step S3, the gas phase at the top of the extractive distillation tower after heat exchange is depressurized through a throttle valve 4, the valve outlet pressure of the throttle valve 4 is 1 bar, and the first condensation is performed through a first condenser 5 to obtain a liquid phase at the top of the extractive distillation tower after condensation, and the temperature of the liquid phase is 90°C, and the liquid phase is divided into two parts, namely, a first liquid phase at the top of the extractive distillation tower after condensation and a second liquid phase at the top of the extractive distillation tower after condensation, through a splitter 6, and the volume ratio of the two parts is 1.2:1, and the liquid phase at the top of the extractive distillation tower after the first condensation is returned to the extractive distillation tower, and enters from above the first tower plate from top to bottom of the extractive distillation tower; the liquid phase at the top of the second extractive distillation tower after condensation is extracted to obtain a dimethyl carbonate product with a purity of 99.9wt%.

[0086] Step S4, the liquid phase at the bottom of the extractive distillation tower after heat exchange is sent to the first auxiliary reboiler 7, and is continuously heated to obtain the liquid phase at the bottom of the extractive distillation tower after reboil, the temperature of which is 87°C, the gas phase fraction is 0.48 at this time, and the power of the first auxiliary reboiler 7 is 840.2kW. The liquid phase at the bottom of the extractive distillation tower after reboil is sent to the first flash tank 8 for the first flash evaporation, the load of the first flash tank 8 is set to 0 cal / sec, and the inlet temperature is set to 90°C, to obtain the first flash gas phase and the first flash liquid phase.

[0087] Step S5, returning the first flash gas phase (mainly composed of ethanol and having a temperature of 87°C) to the extractive distillation tower 1, and entering from above the last plate from top to bottom of the extractive distillation tower; sending the first flash liquid phase (mainly composed of extractant and ethanol and having a temperature of 90°C) to the second heat exchanger 9 for a second heat exchange to obtain the first flash liquid phase after the first heat exchange, and sending the first flash liquid phase after the first heat exchange to the third heat exchanger 10 for a third heat exchange to obtain the first flash liquid phase after the second heat exchange.

[0088] Step S6, the first flash liquid phase after the secondary heat exchange is sent to the second auxiliary reboiler 11 for the second reboiling, the temperature of the second auxiliary reboiler 11 is 221° C., the gas phase fraction of the material after reboiling is 0.65, and then enters the second flash tank 12 for the second flash evaporation, the load of the second flash tank 12 is 0 cal / sec, the pressure is 0.05 bar, and the inlet temperature is 221° C. The top vapor (second flash vapor phase) of the second flash tank 12 is ethanol with a purity of 99.5wt%, and the bottom liquid phase (second flash liquid phase) is a regenerated extractant with a purity of 99.9wt%, and the temperature is 221° C. The second flash liquid phase is sent to the second heat exchanger 9 as a hot stream to perform a second heat exchange with the first flash liquid phase. After one heat exchange, the temperature of the first flash liquid phase is 94°C, and the temperature of the second flash liquid phase after the heat exchange is 134°C. The heat exchanged in the second heat exchange is 1840KW. The second flash liquid phase after the heat exchange is then sent to the second condenser 15 to be condensed to 50°C to obtain a regenerated extractant with a purity of 99.9wt%. The regenerated extractant is returned to the extractive distillation tower 1 through the pump 16 and enters from above the 5th tower plate from top to bottom of the extractive distillation tower to recycle the regenerated extractant. The second flash gas phase is sent to the second steam compressor 13 for pressurization. The second pressurized The compression ratio is 0.8, and the temperature of the second flash vapor phase after pressurization is 320°C. It is then sent to the third heat exchanger 10 as a hot stream to perform a third heat exchange with the first flash liquid phase after the first heat exchange to obtain the second flash vapor phase after heat exchange and the first flash liquid phase after the second heat exchange. The temperature of the first flash liquid phase after the first heat exchange is 94°C, the temperature of the second flash vapor phase after heat exchange is 118°C, and the temperature of the first flash liquid phase after the second heat exchange is 94°C. The heat exchanged in the third heat exchange is 2401KW. The second flash vapor phase after heat exchange is then passed through the third condenser 14 for a third condensation. The temperature of the third condenser is 79°C to obtain an ethanol product with a purity of 99.5wt%.

[0089] Example 3

[0090] The flow chart for separating the azeotrope of ethanol and dimethyl carbonate is shown in Figure 1 .

[0091] In the azeotrope of ethanol and dimethyl carbonate, the weight percentage of ethanol is 50wt%, and the weight percentage of dimethyl carbonate is 50wt%. The flow rate of the azeotrope is 12000kg / h, the feed temperature is 50°C, and the feed pressure is 1.2bar. The flow rate of the extractant (N-octyl-3-methylpyridinium tetrafluoroborate, code: C20FA101) is 29283kg / h, the feed temperature is 78°C, and the feed pressure is 1.1bar.

[0092] The number of theoretical plates of the extractive distillation tower is 32, the top temperature is 90°C, and the bottom temperature is 93°C.

[0093] Step S1, adding the azeotrope from above the 20th plate of the extractive distillation tower 1, and adding the extractant from above the 5th plate from top to bottom of the extractive distillation tower 1, performing extractive distillation to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower.

[0094] Step S2, the gas phase at the top of the extractive distillation tower is subjected to a first compression through the first steam compressor 2, and the compression ratio is controlled to be 1.5:1. The temperature of the gas phase at the top of the extractive distillation tower after compression is 103°C, and then enters the first heat exchanger 3 to perform a first heat exchange with the liquid phase at the bottom of the extractive distillation tower to obtain the gas phase at the top of the extractive distillation tower after heat exchange and the liquid phase at the bottom of the extractive distillation tower after heat exchange. The temperature of the liquid phase at the bottom of the extractive distillation tower after heat exchange is 93°C, the gas phase fraction is 0.5, the temperature of the gas phase at the top of the extractive distillation tower after heat exchange is 90°C, and the heat exchange of the first heat exchanger 3 is 2390kW.

[0095] Step S3, the gas phase at the top of the extractive distillation tower after heat exchange is depressurized through a throttle valve 4, the valve outlet pressure of the throttle valve 4 is 1 bar, and the first condensation is performed through a first condenser 5 to obtain a liquid phase at the top of the extractive distillation tower after condensation, and the temperature of the liquid phase is 90°C, and the liquid phase is divided into two parts, namely, a first liquid phase at the top of the extractive distillation tower after condensation and a second liquid phase at the top of the extractive distillation tower after condensation, through a splitter 6, and the volume ratio of the two parts is 3:1, and the liquid phase at the top of the extractive distillation tower after the first condensation is returned to the extractive distillation tower, and enters from above the first tower plate from top to bottom of the extractive distillation tower; the liquid phase at the top of the second extractive distillation tower after condensation is extracted to obtain a dimethyl carbonate product with a purity of 99.9wt%.

[0096] Step S4, the liquid phase at the bottom of the extractive distillation tower after heat exchange is sent to the first auxiliary reboiler 7, and is continuously heated to obtain the liquid phase at the bottom of the extractive distillation tower after reboil, the temperature of which is 93°C, the gas phase fraction is 0.48 at this time, and the power of the first auxiliary reboiler 7 is 784kW. The liquid phase at the bottom of the extractive distillation tower after reboil is sent to the first flash tank 8 for the first flash evaporation, the load of the first flash tank 8 is set to 0 cal / sec, and the inlet temperature is set to 92°C, to obtain the first flash gas phase and the first flash liquid phase.

[0097] Step S5, returning the first flash gas phase (mainly composed of ethanol and having a temperature of 90°C) to the extractive distillation tower 1, and entering from the top of the last plate of the extractive distillation tower from top to bottom; sending the first flash liquid phase (mainly composed of extractant and ethanol and having a temperature of 93°C) to the second heat exchanger 9 for a second heat exchange to obtain the first flash liquid phase after the first heat exchange, and sending the first flash liquid phase after the first heat exchange to the third heat exchanger 10 for a third heat exchange to obtain the first flash liquid phase after the second heat exchange.

[0098] Step S6, the first flash liquid phase after the secondary heat exchange is sent to the second auxiliary reboiler 11 for the second reboiling, the temperature of the second auxiliary reboiler 11 is 225° C., the gas phase fraction of the material after reboiling is 0.32, and then enters the second flash tank 12 for the second flash evaporation, the load of the second flash tank 12 is 0 cal / sec, the pressure is 0.01 bar, and the inlet temperature is 225° C. The top vapor (second flash vapor phase) of the second flash tank 12 is ethanol with a purity of 99.5wt%, and the bottom liquid phase (second flash liquid phase) is a regenerated extractant with a purity of 99.9wt%, and the temperature is 224° C. The second flash liquid phase is sent to the second heat exchanger 9 as a hot stream to perform a second heat exchange with the first flash liquid phase. After one heat exchange, the temperature of the first flash liquid phase is 98°C, and the temperature of the second flash liquid phase after the heat exchange is 120°C. The heat exchanged in the second heat exchange is 2385KW. The second flash liquid phase after the heat exchange is then sent to the second condenser 15 to be condensed to 50°C to obtain a regenerated extractant with a purity of 99.9wt%. The regenerated extractant is returned to the extractive distillation tower 1 through a pump 16 and enters from above the 5th tower plate from top to bottom of the extractive distillation tower to recycle the regenerated extractant. The second flash gas phase is sent to the second steam compressor 13 for pressurization. The second pressurized pressure The reduction ratio is 0.75, and the temperature of the second flash vapor phase after pressurization is 336°C, and then it is sent to the third heat exchanger 10 as a hot stream to perform a third heat exchange with the first flash liquid phase after the first heat exchange to obtain the second flash vapor phase after heat exchange and the first flash liquid phase after the second heat exchange. The temperature of the first flash liquid phase after the first heat exchange is 98°C, the temperature of the second flash vapor phase after heat exchange is 136°C, and the temperature of the first flash liquid phase after the second heat exchange is 100°C. The heat exchanged in the third heat exchange is 1820KW, and then the second flash vapor phase after heat exchange is passed through the third condenser 14 for a third condensation. The temperature of the third condenser is 79°C to obtain an ethanol product with a purity of 99.5wt%.

[0099] Comparative Example 1

[0100] The only difference from Example 1 is:

[0101] Without heat pump, a condenser is used at the top of the extractive distillation tower and a reboiler is used at the bottom of the tower to replace the first steam compressor in Example 1. The energy consumption of the extractive distillation process without heat pump is 4500-5000 kW.

[0102] After analysis, it can be seen that this patent uses excellent ionic liquid as an extractant and adopts a heat pump to separate azeotropes, which greatly saves energy consumption. By using heat pump extraction distillation and thermal coupling to save energy on the entire process, it can save more than 30% energy compared to the original process.

[0103] As can be seen from the above, the present invention first compresses the steam at the top of the extractive distillation tower to increase its temperature, and then passes it into the first heat exchanger as a heat source flow to exchange heat with the liquid phase at the bottom of the extractive distillation tower, so that the temperature of the liquid phase at the bottom of the tower increases, and the gas phase fraction is increased, thereby reducing the energy consumption of the subsequent first reboiling process, that is, reducing the additional heat required for the first reboiling, and reducing energy consumption on the basis of ensuring that sufficient heat source is provided for the bottom of the extractive distillation tower. In addition, the present invention specifically utilizes the steam stream at the top of the second flash tank and the liquid phase stream at its bottom to heat the inlet stream of the second flash tank and reduce the energy loss of the second flash tank. Secondly, the present invention specifically adds a top steam compressor at the top of the extractive distillation tower and the top of the second flash tank to pressurize the steam to release the latent heat in the gas phase, increase the heat in the hot stream, and combine with the heat exchanger to fully utilize the heat while saving thermal energy. In addition, the specific component extractant of the present invention is non-volatile, pollution-free, easy to prepare, and has a mature production process, and can be combined with the separation process of the present invention to achieve the full separation of ethanol and dimethyl carbonate in the azeotrope. In addition, it can be seen that when each process parameter is within the preferred range of the present invention, ethanol and dimethyl carbonate in the azeotrope can be more fully separated, and the product purity is higher.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for separating an azeotrope of ethanol and dimethyl carbonate, characterized in that: The following steps are involved: Step S1, adding the azeotrope of ethanol and dimethyl carbonate and an extractant into an extractive distillation tower to perform extractive distillation to obtain a gas phase at the top of the extractive distillation tower and a liquid phase at the bottom of the extractive distillation tower; Step S2, performing a first compression on the extractive distillation tower top gas phase to obtain a compressed extractive distillation tower top gas phase; The compressed extractive distillation tower top gas phase and the extractive distillation tower bottom liquid phase are subjected to a first heat exchange to obtain a heat-exchanged extractive distillation tower top gas phase and a heat-exchanged extractive distillation tower bottom liquid phase; Step S3, performing a first condensation on the gas phase at the top of the extractive distillation tower after heat exchange to obtain a condensed extractive distillation tower top liquid phase, and dividing the condensed extractive distillation tower top liquid phase into a first condensed extractive distillation tower top liquid phase and a second condensed extractive distillation tower top liquid phase; refluxing the first condensed extractive distillation tower top liquid phase, and extracting the second condensed extractive distillation tower top liquid phase to obtain a dimethyl carbonate product; Step S4, sequentially performing a first reboiling and a first flash evaporation on the liquid phase at the bottom of the extractive distillation tower after the heat exchange to obtain a first flash gas phase and a first flash liquid phase; Step S5, returning the first flash vapor phase to the extractive distillation tower, subjecting the first flash liquid phase to a second heat exchange to obtain a first flash liquid phase after a primary heat exchange, subjecting the first flash liquid phase after a primary heat exchange to a third heat exchange to obtain a first flash liquid phase after a secondary heat exchange; Step S6, subjecting the first flashed liquid phase after the secondary heat exchange to a second reboil and a second flash, to obtain a second flashed gas phase and a second flashed liquid phase; The second heat exchange comprises: performing the second heat exchange on the second flashed liquid phase and the first flashed liquid phase to obtain the second flashed liquid phase after the heat exchange and the first flashed liquid phase after the first heat exchange; performing a second condensation on the second flashed liquid phase after the heat exchange to obtain a regenerated extractant, and returning the regenerated extractant to the extractive distillation tower; The third heat exchange comprises: performing a second pressurization on the second flash gas phase to obtain a pressurized second flash gas phase, and then performing the third heat exchange on the pressurized second flash gas phase and the first flash liquid phase after the primary heat exchange to obtain a heat-exchanged second flash gas phase and the second flash liquid phase after the secondary heat exchange; performing a third condensation on the heat-exchanged second flash gas phase to obtain an ethanol product; The extractant includes an anion component and a cationic component, wherein the cationic component includes one or more of imidazole, pyrrole and pyridine, and the anion component includes one or more of an organic acid, chloride and tetrafluoroborate.

2. The method according to claim 1, characterized in that: In the azeotrope, the weight ratio of the ethanol to the dimethyl carbonate is (40-60):(40-60); and / or, The extractant includes one or more of 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride and N-octyl-3-methylpyridinium tetrafluoroborate.

3. The method according to claim 1 or 2, characterized in that: The flow rate of the azeotrope entering the extractive distillation tower is 8000-12000 kg / h, the pressure is 1.0-1.5 bar, and the feed temperature is 40-60° C.; and / or, The flow rate of the extractant entering the extractive distillation tower is 25000-35000 kg / h, the pressure is 1.0-1.5 bar, and the feed temperature is 50-80°C; Preferably, the weight ratio of the azeotrope to the extractant is (0.2-0.5):

1.

4. The method according to any one of claims 1 to 3, characterized in that The number of theoretical plates of the extractive distillation tower is 25 to 35; The azeotrope enters from above any one or more plates from the 15th to the 25th from the top to the bottom of the extractive distillation tower; the extractant enters from above any one or more plates from the 2nd to the 10th from the top to the bottom of the extractive distillation tower; and / or The liquid phase at the top of the extractive distillation tower after the first condensation enters from above any one or more tower plates among the 1st to 3rd from the top to the bottom of the extractive distillation tower; the first flash gas phase enters from above any one or more tower plates among the 20th to 25th from the top to the bottom of the extractive distillation tower; the regenerated extractant enters from above any one or more tower plates among the 3rd to 9th from the top to the bottom of the extractive distillation tower.

5. The method according to any one of claims 1 to 4, characterized in that In the step S2, The compression ratio of the first compression is 1 to 2; and / or the temperature of the gas phase at the top of the extractive distillation tower after compression is 80 to 105°C, the temperature of the liquid phase at the bottom of the extractive distillation tower is 80 to 98°C, and the temperature of the gas phase at the top of the extractive distillation tower after compression is higher than the temperature of the liquid phase at the bottom of the extractive distillation tower; the temperature of the liquid phase at the bottom of the extractive distillation tower after heat exchange is 80 to 95°C, the temperature of the gas phase at the top of the extractive distillation tower after heat exchange is 80 to 100°C; and / or In the step S3, The temperature of the liquid phase at the top of the extractive distillation tower after condensation is 85-93° C.; the volume ratio of the liquid phase at the top of the first extractive distillation tower after condensation to the liquid phase at the top of the second extractive distillation tower after condensation is (0.5-3):

1.

6. The method according to any one of claims 1 to 5, characterized in that In the step S4, The liquid phase at the bottom of the extractive distillation tower after heat exchange is subjected to the first reboiling to obtain a liquid phase at the bottom of the extractive distillation tower after reboiling, wherein the gas phase fraction of the liquid phase at the bottom of the extractive distillation tower after reboiling is 0.3-0.5 and the temperature is 85-95° C.; and / or The first flash is carried out in a first flash tank, the inlet temperature of the first flash tank is 90-100° C.; and / or The temperature of the first flash gas phase is 80-95°C.

7. The method according to any one of claims 1 to 6, characterized in that In the second heat exchange, the temperature of the first flash liquid phase is 90-95° C., and the temperature of the second flash liquid phase is 210-230° C.; and / or In the third heat exchange, the temperature of the first flash liquid phase after the first heat exchange is 90-100° C., the temperature of the second flash gas phase is 90-95° C., the compression ratio of the second pressurization is 0.5-2, and the temperature of the second flash gas phase after the pressurization is 300-350° C.; and / or The temperature of the second flash gas phase after the heat exchange is 100-140° C., the third condensation is performed in the third condenser, and the temperature of the third condenser is 60-80° C.; and / or The temperature of the second flash liquid phase after the heat exchange is 100-140° C., the second condensation is carried out in the second condenser, the temperature of the second condenser is 50-60° C., and the purity of the extractant in the regenerated extractant is ≥99.9wt%.

8. The method according to any one of claims 1 to 7, characterized in that In step S6, The temperature of the first flash liquid phase after the secondary heat exchange is 90-110° C., the second reboiler is used for the second auxiliary reboiler, the temperature of the second auxiliary reboiler is 210-250° C., and the gas phase fraction of the material after reboiler is 0.5-0.8; and / or The second flash evaporation is carried out in a second flash tank, the pressure of the second flash tank is 0.01-0.5 bar, and the inlet temperature is 210-240°C.

9. The method according to any one of claims 1 to 8, characterized in that The purity of the ethanol product is ≥99.5wt%; and / or the purity of the dimethyl carbonate product is ≥99.9wt%.

10. A device for separating an azeotrope of ethanol and dimethyl carbonate, characterized in that: include: Extraction distillation tower (1), first steam compressor (2), first heat exchanger (3), throttle valve (4), first condenser (5), splitter (6), first auxiliary reboiler (7), first flash tank (8), second heat exchanger (9), third heat exchanger (10), second auxiliary reboiler (11), second flash tank (12), second steam compressor (13), third condenser (14), second condenser (15); The extractive distillation tower (1) has a tower top gas phase outlet, a tower bottom liquid phase outlet, a tower top liquid phase inlet, a tower bottom liquid phase inlet, an extractant inlet, and an azeotrope inlet; the tower top gas phase outlet of the extractive distillation tower (1) is connected to the inlet of the first steam compressor (2); The first heat exchanger (3) has a first hot stream inlet, a first cold stream inlet, a first hot stream outlet, and a first cold stream outlet, the first hot stream inlet is connected to the outlet of the first steam compressor (2), the first hot stream outlet is connected to the inlet of the throttle valve (4), the first cold stream inlet is connected to the bottom liquid phase outlet of the extractive distillation tower (1), and the first cold stream outlet is connected to the inlet of the first auxiliary reboiler (7); The first flash tank (8) has an inlet, a first gas phase outlet and a first liquid phase outlet, the inlet is connected to the outlet of the first auxiliary reboiler (7), and the first gas phase outlet is connected to the liquid phase inlet at the bottom of the extractive distillation tower (1); The second flash tank (12) has an inlet, a second gas phase outlet and a second liquid phase outlet, the inlet is connected to the outlet of the second auxiliary reboiler (11), and the second gas phase outlet is connected to the inlet of the second steam compressor (13); The second heat exchanger (9) has a second hot stream inlet, a second cold stream inlet, a second hot stream outlet, and a second cold stream outlet, the second hot stream inlet is connected to the second liquid phase outlet of the second flash tank (12), the second hot stream outlet is connected to the inlet of the second condenser (15), the second cold stream inlet is connected to the first liquid phase outlet of the first flash tank (8), and the second cold stream outlet is connected to the third cold stream inlet of the third heat exchanger (10); The third heat exchanger (10) has a third hot stream inlet, a third cold stream inlet, a third hot stream outlet, and a third cold stream outlet, the third hot stream inlet is connected to the outlet of the second steam compressor (13), the third hot stream outlet is connected to the inlet of the third condenser (14), and the cold stream outlet is connected to the inlet of the second auxiliary reboiler (11); The inlet of the first condenser (5) is connected to the outlet of the throttle valve (4), and the outlet is connected to the inlet of the splitter (6); the splitter (6) has a reflux outlet and a production outlet, the reflux outlet is connected to the top liquid phase inlet of the extractive distillation tower (1), and the production outlet produces dimethyl carbonate product; The outlet of the second condenser (15) is connected to the extractant inlet of the extractive distillation tower (1), and the outlet of the third condenser (14) produces an ethanol product; An extractant is added into the extractive distillation tower (1), wherein the extractant comprises an anion component and a cationic component, wherein the cationic component comprises one or more of imidazole, pyridine and pyrrole, and the anion component comprises one or more of organic acid, chloride and tetrafluoroborate.

11. The device according to claim 10, characterized in that The extractive distillation tower (1) is a sieve plate tower, preferably one or more of a standard sieve plate tower, a corrugated sieve plate tower, a floating valve sieve plate tower, a mesh sieve plate tower, a spray sieve plate tower, a composite sieve plate tower, a high-efficiency sieve plate tower, a large sieve plate tower and a micro sieve plate tower; The forms of the first condenser (5), the first heat exchanger (3), the second heat exchanger (9), the third heat exchanger (10), the first auxiliary reboiler (7), and the second auxiliary reboiler (11) are independently selected from one or more of kettle type, cross flow type and axial flow type.

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