Separation method and separation device of dimethyl carbonate and methanol azeotrope

Abstract

The invention relates to a separation method and a separation device for dimethyl carbonate and methanol azeotrope, the separation method comprises the following steps: the dimethyl carbonate and methanol azeotrope is treated by a feed vaporizer and then is introduced into an extractive distillation tower for extractive distillation, and a stripping section of the extractive distillation tower is provided with an intermediate reboiler; at least part of tower top steam of the extractive distillation tower is compressed and heated through a heat pump compressor; the compressed gas phase is used as a heat source to heat a feeding vaporizer and an intermediate reboiler; wherein when the compression ratio of the heat pump compressor is smaller than a preset value, the heat load supplied by the heat source to the feeding vaporizer is larger than that supplied by the heat source to the intermediate reboiler; when the compression ratio of the heat pump compressor is larger than or equal to a preset value, the heat load supplied to the feeding vaporizer by the heat source is smaller than or equal to the heat load supplied to the intermediate reboiler. The separation method can reduce the energy consumption in the separation process.

Description

Technical Field

[0001] The present application relates to the technical field of chemical distillation, and in particular to a method and a device for separating azeotropes of dimethyl carbonate and methanol. Background Art

[0002] Dimethyl carbonate (DMC) is a colorless, odorless, low-volatile liquid that is widely used in organic synthesis, medicine, pesticides, food additives, etc. In addition, as an environmentally friendly solvent, dimethyl carbonate is also widely used in industrial fields such as coatings, inks, rubber, plastics, and electrolytes.

[0003] At present, the methods for preparing dimethyl carbonate mainly include phosgene method, methanol oxidation method, transesterification method and urea alcoholysis method. Among them, the transesterification method has mature technology, has the advantages of non-toxic raw materials, mild reaction conditions and few by-products, and is the most widely used method in industrial production. However, the dimethyl carbonate prepared by the transesterification method usually exists in the form of azeotropes with methanol, and the azeotropes need to be separated. The method for separating dimethyl carbonate and methanol azeotropes mainly includes extractive distillation method. However, the current method for separating dimethyl carbonate and methanol azeotropes by extractive distillation still has the problem of high energy consumption. Summary of the invention

[0004] Based on this, some embodiments of the present application provide a method for separating azeotropes of dimethyl carbonate and methanol, which can reduce the energy consumption of the separation process.

[0005] In addition, some other embodiments of the present application also provide a separation device for use in the above separation method.

[0006] A method for separating an azeotrope of dimethyl carbonate and methanol comprises the following steps:

[0007] The azeotrope of dimethyl carbonate and methanol is treated in a feed vaporizer and then passed into an extractive distillation tower for extractive distillation, wherein the top of the tower is methanol vapor, and the bottom of the tower is dimethyl carbonate and an extractant, and the stripping section of the extractive distillation tower is provided with an intermediate reboiler;

[0008] Compressing at least part of the overhead steam of the extractive distillation tower and raising its temperature through a heat pump compressor;

[0009] Using the compressed gas phase as a heat source to heat the feed vaporizer and the intermediate reboiler;

[0010] Among them, when the compression ratio of the heat pump compressor is less than a preset value, the heat load supplied by the heat source to the feed vaporizer is greater than the heat load supplied to the intermediate reboiler; when the compression ratio of the heat pump compressor is greater than or equal to the preset value, the heat load supplied by the heat source to the feed vaporizer is less than or equal to the heat load supplied to the intermediate reboiler.

[0011] In some of the embodiments, the compression ratio of the heat pump compressor is 1.5~4.

[0012] In some of the embodiments, the compression ratio of the heat pump compressor is 2-3.5.

[0013] In some embodiments, the preset value is 2.5.

[0014] In some embodiments, the compression ratio a of the heat pump compressor is 2≤a<2.5, and the heat load of the heat source is all supplied to the feed vaporizer;

[0015] Alternatively, the compression ratio a of the heat pump compressor is 2.5≤a<3, the heat load of the heat source is supplied to the intermediate reboiler and the feed vaporizer at the same time, and the heat load supplied to the intermediate reboiler is greater than the heat load supplied to the feed vaporizer;

[0016] Alternatively, the compression ratio a of the heat pump compressor is 3≤a≤3.5, and the heat load of the heat source is entirely supplied to the intermediate reboiler.

[0017] In some embodiments, the heat pump compressor is an open heat pump.

[0018] In some embodiments, the vaporization temperature of the intermediate reboiler is 76°C to 90°C.

[0019] In some of the embodiments, the heat transfer temperature difference between the cold and hot sides of the intermediate reboiler is 5°C to 40°C.

[0020] In some of the embodiments, the heat transfer temperature difference between the cold and hot sides of the intermediate reboiler is 8°C to 20°C.

[0021] In some embodiments, the heat transfer temperature difference between the cold and hot sides of the feed vaporizer is 5°C to 40°C.

[0022] In some embodiments, the heat transfer temperature difference between the cold and hot sides of the feed vaporizer is 10°C to 25°C.

[0023] In some embodiments, the extractant comprises propylene carbonate.

[0024] In some embodiments, the extractive distillation tower comprises a distillation section, an extraction section and a stripping section, the number of theoretical plates of the distillation section is 10-35, the number of theoretical plates of the extraction section is 15-50, and the number of theoretical plates of the stripping section is 10-45.

[0025] In some of the embodiments, the top operating pressure of the extractive distillation tower is atmospheric pressure, the reflux ratio is 0.2-2, and the bottom temperature is 110° C.-120° C.

[0026] A separation device for dimethyl carbonate and methanol azeotrope, used in the above separation method, the separation device comprising:

[0027] A feed vaporizer for vaporizing the azeotrope of dimethyl carbonate and methanol;

[0028] An extractive distillation tower, connected to the feed vaporizer, for extracting and distilling the azeotrope of dimethyl carbonate and methanol after the vaporization treatment;

[0029] an intermediate reboiler, connected to the extractive distillation tower, and used for reboiling the liquid in the stripping section of the extractive distillation tower;

[0030] The heat pump compressor is connected to the extractive distillation tower, the feed vaporizer and the intermediate reboiler, and is used to compress and heat at least part of the top steam of the extractive distillation tower, and use the compressed gas phase as a heat source to heat the feed vaporizer and the intermediate reboiler.

[0031] In the conventional technology, after the extractive distillation of dimethyl carbonate and methanol azeotrope, the top steam (i.e., the methanol steam after separation) is condensed by the top condenser to recover methanol, and the bottom of the tower recovers dimethyl carbonate and the extractant. In order to ensure the gas-liquid phase equilibrium in the extractive distillation tower, it is also necessary to set a bottom reboiler to vaporize the bottom material again. However, the above method has the problem of high energy consumption. The above-mentioned method for separating dimethyl carbonate and methanol azeotropes in some embodiments of the present application is to extract and distill the azeotrope, and at least part of the top steam after the extractive distillation is compressed and heated by a heat pump compressor, and it is used as a heat source for heating the feed vaporizer and the intermediate reboiler, thereby reducing the steam consumption of the bottom reboiler and the cooling water consumption of the top condenser. By adjusting the heat pump compression ratio and the heat load of the feed vaporizer and the intermediate reboiler, the energy is fully utilized, and the energy consumption of the separation process is significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 A schematic flow chart of a method for separating an azeotrope of dimethyl carbonate and methanol according to some embodiments of the present application;

[0034] Figure 2 A schematic diagram of a structure of a device for separating an azeotrope of dimethyl carbonate and methanol according to some embodiments of the present application;

[0035] Explanation of the reference numerals: feed vaporizer 210 , extractive distillation tower 220 , intermediate reboiler 230 , tower top condenser 240 , heat pump compressor 250 , reflux tank 260 , tower top delivery pump 270 , tower bottom reboiler 280 and tower bottom delivery pump 290 . DETAILED DESCRIPTION

[0036] In order to facilitate the understanding of the present application, the present application will be described more comprehensively below in conjunction with the specific embodiments. The preferred embodiments of the present application are provided in the specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0038] Unless otherwise specified or there is a contradiction, the terms and phrases used in this application have the following meanings:

[0039] In this application, "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0040] In the description of the present application, “plurality” means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined.

[0041] In this application, "one or several" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more of the listed items.

[0042] In this application, the percentage concentration involved, unless otherwise specified, refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of the component.

[0043] In this document, "further", "further", "particularly", "for example", "such as", "example", "for example", etc. are used for descriptive purposes, indicating that the previous and subsequent technical solutions are related in terms of the content covered, but should not be understood as a limitation on the previous technical solution, nor can it be understood as a limitation on the protection scope of this document. In this document, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0044] Herein, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If multiple "optional" items appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" item is independent of each other. In this application, descriptions such as "optionally contain", "optionally include", etc. mean "contain or not contain". "Optional component X" means that component X exists or does not exist, or means that component X is contained or not contained.

[0045] When a numerical range is disclosed in this application, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in this application should be understood to include any and all subranges included therein.

[0046] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0047] The terms "including" and "having" and any variations thereof in the embodiments of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or components that are inherent to these processes, methods, products, or devices.

[0048] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0049] In the flowchart of the present application, although the various steps are displayed in sequence as indicated by the arrows, these steps are not necessarily performed in the order indicated by the arrows. Unless otherwise clearly stated in the text, the execution of these steps is not strictly restricted in order and they can be performed in other orders. Moreover, at least part of the steps in the figure may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily performed at the same time, but can be performed at different times. Their execution order is not necessarily sequential, but can be performed in turn or alternately with other steps or at least part of other sub-steps or stages.

[0050] The methods for separating dimethyl carbonate and methanol azeotropes mainly include high-low pressure distillation and extractive distillation. The high-low pressure distillation method uses high-pressure equipment, and both the equipment cost and the operating cost are higher than the extractive distillation method. However, although the current extractive distillation method has lower fixed costs and operating costs than the high-low pressure distillation method, it is still a high-energy consumption operating unit due to the large amount of methanol and dimethyl carbonate, and the extractive distillation tower requires a certain reflux ratio. Therefore, there is an urgent need for a method that can effectively separate dimethyl carbonate and methanol azeotropes and reduce energy consumption.

[0051] Based on this, the first aspect of the present application provides a method for separating the azeotrope of dimethyl carbonate and methanol, see Figure 1 , including the following steps:

[0052] Step S110: the azeotrope of dimethyl carbonate and methanol is treated in a feed vaporizer and then passed into an extractive distillation tower for extractive distillation, wherein the top of the tower contains methanol vapor and the bottom of the tower contains dimethyl carbonate and an extractant. The stripping section of the extractive distillation tower is provided with an intermediate reboiler.

[0053] Step S120: compressing at least part of the top steam of the extractive distillation tower through a heat pump compressor to increase the temperature.

[0054] Step S130: using the compressed gas phase as a heat source to heat the feed vaporizer and the intermediate reboiler.

[0055] Among them, when the compression ratio of the heat pump compressor is less than a preset value, the heat load supplied by the heat source to the feed vaporizer is greater than the heat load supplied to the intermediate reboiler; when the compression ratio of the heat pump compressor is greater than or equal to the preset value, the heat load supplied by the heat source to the feed vaporizer is less than or equal to the heat load supplied to the intermediate reboiler.

[0056] In the conventional technology, after the extractive distillation of dimethyl carbonate and methanol azeotrope, the top steam is condensed by the top condenser to recover methanol, and the bottom of the tower recovers dimethyl carbonate and the extractant. In order to ensure the gas-liquid phase equilibrium in the extractive distillation tower, it is also necessary to set a bottom reboiler to vaporize the bottom material again. However, the above method has the problem of high energy consumption. The above-mentioned method for separating dimethyl carbonate and methanol azeotropes in some embodiments of the present application extracts and distills the azeotrope, compresses and heats the top steam after the extractive distillation through a heat pump compressor, and uses it as a heat source for heating the feed vaporizer and the intermediate reboiler, thereby reducing the steam consumption of the bottom reboiler and the cooling water consumption of the top condenser. By adjusting the heat pump compression ratio and the heat load of the feed vaporizer and the intermediate reboiler, the energy is fully utilized, which significantly reduces the energy consumption of the separation process.

[0057] In addition, in some related technologies, after the azeotrope of dimethyl carbonate and methanol is separated by an extractive distillation tower, the top vapor is compressed and used for heating the tower bottom reboiler. However, due to the large difference between the top temperature and the tower bottom temperature, when the top vapor is compressed and used for heating the tower bottom reboiler, the compression ratio is large and the energy consumption is high. In some embodiments of the present application, the top vapor is compressed and used for heating the intermediate reboiler and the feed vaporizer, and the heat load of the two is adjusted according to different compression ratios, so that the energy is fully utilized and the energy consumption is significantly reduced.

[0058] In some embodiments, the compression ratio of the heat pump compressor is 1.5 to 4. For example, the compression ratio of the heat pump compressor may be, but is not limited to, 1.5, 1.6, 2, 2.1, 2.3, 2.5, 2.7, 2.8, 3, 3.2, 3.3, 3.5, 3.8, 4, or a range consisting of any two of these values. Optionally, the compression ratio of the heat pump compressor is 2 to 3.5.

[0059] In some embodiments, the preset value is 2.5.

[0060] In some embodiments, the compression ratio a of the heat pump compressor is 2≤a<2.5, and the heat load of the heat source is all supplied to the feed vaporizer; or, the compression ratio a of the heat pump compressor is 2.5≤a<3, and the heat load of the heat source is supplied to the intermediate reboiler and the feed vaporizer at the same time, and the heat load of the intermediate reboiler is greater than the heat load supplied to the feed vaporizer; or, the compression ratio a of the heat pump compressor is 3≤a≤3.5, and the heat load of the heat source is all supplied to the intermediate reboiler. With the above arrangement, the heat loads of the feed vaporizer and the intermediate reboiler are adjusted according to different compression ratios, which is conducive to further reducing energy consumption and costs.

[0061] The above preset value is obtained based on conventional electricity prices and steam prices, combined with the characteristics of the intermediate reboiler and the feed vaporizer. By adjusting the heat load of the intermediate reboiler and the feed vaporizer according to the compression ratio according to the above preset value, it is beneficial to reduce energy consumption and cost. It can be understood that if the electricity price and steam price in different regions or at different times vary significantly, the preset value is not limited to 2.5, and a suitable preset value can be selected to make full use of energy and achieve a reduction in operating costs and energy consumption.

[0062] In some embodiments, the compressed gas phase is condensed after heat exchange and used as reflux and extraction at the top of the tower. Another portion of the top vapor is not compressed and directly condensed in a top condenser and used as reflux and extraction at the top of the tower.

[0063] In some embodiments, the tower top steam is divided into the first steam and the second steam, the first steam is compressed and heated by the heat pump compressor, and the second steam is directly condensed by the tower top condenser, wherein the proportion b of the first steam is greater than or equal to the proportion c of the second steam. Specifically, the greater the compression ratio, the higher the temperature of the tower top steam after compression, and the higher proportion of steam will be used to heat the vaporizer and the intermediate reboiler. That is, the greater the compression ratio, the greater the proportion b of the first steam.

[0064] In some embodiments, the compression ratio a<2.5, and the ratio of the proportion b of the first steam to the proportion c of the second steam is b:c=(1~4):1. In addition, at the same compression ratio, the proportions of the first steam and the second steam are different under different heat load distribution ratios. For example, when the compression ratio is 2.1, when the heat load of the heat source is all used for the feed vaporizer, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 3.6:1; when the heat load of the heat source is all used for the intermediate reboiler, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 1.1:1; when the heat load of the heat source is used for half of the intermediate reboiler and half of the feed vaporizer, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 1:1.

[0065] In other embodiments, the compression ratio a is 2.5≤a<3, and the ratio of the proportion b of the first steam to the proportion c of the second steam is b:c=(5~10):1. For example, when the compression ratio is 2.7, when the heat load of the heat source is all used for the feed vaporizer, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 6.2:1; when the heat load of the heat source is all used for the intermediate reboiler, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 5.3:1; when the heat load of the heat source is used for the intermediate reboiler and the feed vaporizer half each, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 6.5:1.

[0066] In some other embodiments, the compression ratio a is 3≤a<3.3, and the ratio of the proportion b of the first steam to the proportion c of the second steam is b:c=(15-20):1. For example, when the compression ratio is 3, when the heat load of the heat source is all used for the feed vaporizer, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 16.9:1; when the heat load of the heat source is all used for the intermediate reboiler, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 19.7:1; when the heat load of the heat source is used for the intermediate reboiler and the feed vaporizer half each, the ratio b of the proportion b of the first steam to the proportion c of the second steam is about 19.6:1.

[0067] In some other embodiments, when the compression ratio a≥3.3, all the vapor from the top of the tower is compressed and heated by the heat pump compressor.

[0068] In some embodiments, the heat pump compressor is an open heat pump. An open heat pump is a heat pump that directly compresses the material. It is understood that in other embodiments, the heat pump compressor may also be a closed heat pump that uses a compressed intermediate medium. Preferably, the heat pump compressor is an open heat pump.

[0069] In some embodiments, the vaporization temperature of the intermediate reboiler is 76°C to 90°C. For example, the vaporization temperature of the intermediate reboiler may be, but is not limited to, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, or a range consisting of any two of these values. Optionally, the vaporization temperature of the intermediate reboiler is 83°C to 90°C. Further optionally, the vaporization temperature of the intermediate reboiler is 85°C to 90°C.

[0070] In some embodiments, the heat transfer temperature difference between the cold and hot sides of the intermediate reboiler is 5°C to 40°C. In the present application, the heat transfer temperature of the intermediate reboiler refers to the difference between the temperature T1 of the compressed gas phase after heat exchange with the intermediate reboiler and the vaporization temperature T2 of the intermediate reboiler, that is, T1-T2. By setting up an intermediate reboiler, heat is input into the tower using a low-grade heat source to reduce the consumption of tower bottom steam. By selecting a suitable heat transfer temperature difference, the low compression ratio of the heat pump compressor is guaranteed, and the heat exchange area of ​​the intermediate reboiler is not too large.

[0071] In one example, the heat transfer temperature difference between the cold and hot sides of the intermediate reboiler can be, but is not limited to, 5°C, 8°C, 10°C, 12°C, 15°C, 18°C, 20°C, 22°C, 25°C, 30°C, 35°C, 40°C, or a range consisting of any two of these values. Optionally, the heat transfer temperature difference between the cold and hot sides of the intermediate reboiler is 8°C to 20°C.

[0072] In some embodiments, the heat transfer temperature difference between the cold and hot sides of the feed vaporizer is 5°C to 40°C. In the present application, the cold and hot heat transfer temperatures of the feed vaporizer refer to the difference between the temperature T3 of the compressed gas phase after heat exchange with the feed reboiler and the vaporization temperature T4 of the feed reboiler, that is, T3-T4. By vaporizing the feed, heat is input into the tower using a low-grade heat source to reduce the consumption of steam in the tower bottom. Selecting an appropriate cold and hot heat transfer temperature difference can ensure a low compression ratio of the heat pump compressor and ensure that the heat exchange area of ​​the feed vaporizer is not too large.

[0073] In one example, the heat transfer temperature difference between the cold side and the hot side of the feed vaporizer can be, but is not limited to, 5°C, 8°C, 10°C, 12°C, 15°C, 18°C, 20°C, 22°C, 25°C, 30°C, 35°C, 40°C, or a range consisting of any two of these values. Optionally, the heat transfer temperature difference between the cold side and the hot side of the feed vaporizer is 10°C to 25°C.

[0074] In one example, the vaporization temperature of the feed vaporizer is 71° C. It is understood that this vaporization temperature is obtained based on the conventional ratio of the azeotrope of dimethyl carbonate and methanol output from the reactive distillation column.

[0075] In some embodiments, the feed thermal state of dimethyl carbonate and methanol azeotrope can be supercooled, saturated liquid phase and saturated gas phase, and different states correspond to different heat loads of the vaporizer and the intermediate reboiler. By setting the feed thermal state, adjusting the heat load of the feed vaporizer and the intermediate reboiler, the steam consumption of the tower bottom and the power consumption of the heat pump compressor are adjusted to optimize the operating cost.

[0076] In some embodiments, the extractant used for extractive distillation includes propylene carbonate. The extractant can change the relative volatility of dimethyl carbonate and methanol, thereby achieving the separation of azeotropes. Propylene carbonate, the raw material for preparing dimethyl carbonate by ester exchange, is used as an extractant. In the subsequent separation process, there is no need to worry about the poor separation effect causing the material returned to the reaction distillation tower to affect the reaction effect. In the traditional method, diethyl carbonate is used as an extractant. This material is not a raw material for preparing dimethyl carbonate by ester exchange, and may affect the reaction effect due to incomplete separation. And because of the poor separation effect, the crude methanol needs to be separated and purified through an additional separation tower, which has a complicated process, high equipment investment, and increased cost and energy consumption.

[0077] In some embodiments of the present application, the extractant includes propylene carbonate, and methanol that meets the purity requirements can be obtained using an extraction distillation tower. The equipment cost is low, and energy can be fully utilized while achieving effective separation of dimethyl carbonate and methanol azeotropes, thereby significantly reducing the energy consumption and cost of the separation process.

[0078] In some embodiments, the extractive distillation column includes a distillation section, an extraction section and a stripping section, the theoretical plate number of the distillation section is 10 to 35, the theoretical plate number of the extraction section is 15 to 50, and the theoretical plate number of the stripping section is 10 to 45. By selecting appropriate distillation sections, extraction sections and stripping sections, and cooperating with extractants, azeotropes can be effectively separated, and separation efficiency and purity can be improved.

[0079] Specifically, the extractive distillation tower is divided into three sections: upper, middle and lower. The upper section is the distillation section, the middle section is the extraction section, and the lower section is the stripping section. The feed inlet of the extractant is the boundary layer between the distillation section and the extraction section, and the feed inlet of the azeotrope of dimethyl carbonate and methanol is the boundary layer between the extraction section and the stripping section.

[0080] In one example, the number of theoretical plates in the rectification section may be, but is not limited to, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, or a range consisting of any two of these values. The number of theoretical plates in the extraction section may be, but is not limited to, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 45, 48, 50, or a range consisting of any two of these values. The number of theoretical plates in the stripping section may be, but is not limited to, 10, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 45, or a range consisting of any two of these values.

[0081] In some embodiments, the top operating pressure of the extractive distillation tower is normal pressure, the reflux ratio is 0.2-2, and the bottom temperature is 110° C.-120° C. It can be understood that the top temperature of the extractive distillation tower is the temperature of methanol vapor, which is 65° C. The above operating conditions are mild, do not require complex pressurizing equipment and vacuum equipment, have a low reflux ratio, and have low energy consumption.

[0082] It is understood that in this application, normal pressure refers to the pressure under standard atmospheric pressure, that is, 101.325 kilopascals (kPa), or about 1 atmosphere (atm). Using normal pressure operation and avoiding the use of high-pressure equipment is conducive to further reducing costs.

[0083] In one example, the reflux ratio may be, but is not limited to, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, or a range consisting of any two of these values.

[0084] In some embodiments, the azeotrope of dimethyl carbonate and methanol is obtained from the top of a transesterification reaction distillation tower.

[0085] The above-mentioned separation method of dimethyl carbonate and methanol azeotrope has at least the following advantages:

[0086] (1) A heat pump compressor is used to compress a large amount of low-temperature heat source at the top of the tower and then use it to heat the feed vaporizer and the intermediate reboiler, reducing the steam consumption of the tower bottom reboiler and the cooling water consumption of the tower top condenser. Furthermore, by adjusting the heat pump compression ratio and the heat load distribution ratio between the feed vaporizer and the intermediate reboiler, energy utilization is maximized to achieve the optimal operating cost.

[0087] (2) Propylene carbonate, the raw material for preparing dimethyl carbonate by the ester exchange method, is used as an extractant to change the relative volatility of dimethyl carbonate and methanol, thereby achieving effective separation of the azeotrope. In the subsequent separation process, there is no need to worry about the poor separation effect causing the material returned to the reaction distillation tower to affect the reaction effect.

[0088] (3) In the above separation method, an extractive distillation tower is used to separate methanol under normal pressure, with simple equipment and low fixed cost.

[0089] The second aspect of the present application provides a separation device for dimethyl carbonate and methanol azeotrope, which is used in the separation method of the first aspect. Specifically, the separation device includes: a feed vaporizer, an extractive distillation tower, an intermediate reboiler and a heat pump compressor.

[0090] The feed vaporizer is used to vaporize the azeotrope of dimethyl carbonate and methanol. The extractive distillation tower is connected to the feed vaporizer and is used to extract and distill the azeotrope of dimethyl carbonate and methanol after the vaporization. The intermediate reboiler is connected to the extractive distillation tower and is used to reboil the liquid in the stripping section of the extractive distillation tower. The heat pump compressor is connected to the extractive distillation tower, the feed vaporizer and the intermediate reboiler, and is used to compress and heat at least part of the top steam of the extractive distillation tower, and use the compressed gas phase as a heat source to heat the feed vaporizer and the intermediate reboiler.

[0091] The specific feed vaporizer, extractive distillation tower, intermediate reboiler and heat pump compressor are the same as those in the first aspect described above and will not be described in detail.

[0092] In some embodiments, the separation device further comprises a tower top condenser and a tower bottom reboiler. The tower top condenser is used to condense the remaining uncompressed tower top steam. The tower bottom reboiler is used to reheat and vaporize the tower bottom material to maintain the gas-liquid balance in the extractive distillation tower.

[0093] Furthermore, the separation device also includes a reflux tank, a tower top delivery pump and a tower bottom delivery pump. The reflux tank is used to recover the liquid condensed by the tower top condenser and the liquid after heat exchange with the intermediate reboiler and the feed vaporizer. The tower top delivery pump is used to deliver the liquid in the reflux tank to the reactive distillation tower. The tower bottom delivery pump is used to deliver the liquid dimethyl carbonate and the extractant at the bottom of the tower to the downstream separation tower for separation and recovery of the extractant.

[0094] It can be understood that in this application, tower bottom and tower bottom have the same meaning, both refer to the bottom of the tower, and can be used interchangeably.

[0095] Specifically, see Figure 2 , Figure 2 The figure is a schematic diagram of a structure of a separation device for dimethyl carbonate and methanol azeotrope. Figure 2 In the embodiment, the separation device includes: a feed vaporizer 210, an extractive distillation tower 220, an intermediate reboiler 230, a tower top condenser 240, a heat pump compressor 250, a reflux tank 260, a tower top delivery pump 270, a tower bottom reboiler 280 and a tower bottom delivery pump 290.

[0096] The steps of separation using the above separation device are as follows: the azeotrope of dimethyl carbonate and methanol enters the boundary layer between the extraction section and the stripping section of the extractive distillation tower 220 after being treated by the feed vaporizer 210, the extractant enters the boundary layer between the distillation section and the extraction section, the azeotrope of dimethyl carbonate and methanol and the extractant are subjected to extractive distillation in the extractive distillation tower 220 to separate methanol and dimethyl carbonate, the top steam is high-purity methanol, at least part of the top steam is compressed by the heat pump compressor 250 and used as a heat source for heating the feed vaporizer 210 and the intermediate reboiler 230, and the gas phase after heat exchange is depressurized and enters the reflux tank 260. The remaining top steam enters the reflux tank 260 after being condensed by the top condenser 240 to obtain methanol of satisfactory purity, and the methanol in the reflux tank 260 is returned to the reactive distillation tower (not shown) through the top delivery pump 270. The bottom of the tower contains dimethyl carbonate and an extractant, and the bottom of the tower is also provided with a tower bottom reboiler 280 to heat and vaporize the dimethyl carbonate and the extractant in the bottom of the tower again by external steam heating, and the vaporized materials are returned to the extractive distillation tower 220. The liquid phase material is output to the downstream separation tower (not shown) through the bottom delivery pump 290 for separation to recover the extractant. Since the boiling points of dimethyl carbonate and the extractant are greatly different, the separation of dimethyl carbonate and the extractant is relatively easy.

[0097] In order to make the purpose and advantages of the present application clearer, the separation method of dimethyl carbonate and methanol azeotrope of the present application and its effect are further described in detail below in conjunction with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and shall not be used to limit the present application. The following examples do not include other components except inevitable impurities unless otherwise specified. The drugs and instruments used in the examples are conventionally selected in this area unless otherwise specified. The experimental methods for which specific conditions are not specified in the examples are implemented according to conventional conditions, such as the conditions described in the literature, books, or the methods recommended by the manufacturer.

[0098] Example 1

[0099] This embodiment provides a method for separating the azeotrope of dimethyl carbonate and methanol, using Figure 2The separation device shown in the figure performs separation, comprising the following steps:

[0100] The dimethyl carbonate and methanol azeotrope obtained at the top of the reactive distillation tower is fed into the extracting distillation tower 220 through the interface between the extracting section and the stripping section after passing through the feed vaporizer 210, and propylene carbonate is used as an extractant to enter through the interface between the extracting section and the extracting section of the extracting distillation tower 220. The extracting distillation tower 220 has a theoretical plate number of 25 in the extracting section, a theoretical plate number of 45 in the extracting section, and a theoretical plate number of 30 in the stripping section.

[0101] The top steam of the extractive distillation tower 220 is divided into two parts. One part is compressed by the heat pump compressor 250 and used for heat exchange with the feed vaporizer 210 and the intermediate reboiler 230. The material after heat exchange is decompressed and enters the reflux tank 260; the other part of the top steam is condensed by the top condenser 240 and enters the reflux tank 260. Methanol that meets the purity requirements is obtained at the top of the tower and returned to the reactive distillation tower. Among them, the top operating pressure is normal pressure, the reflux ratio is 0.43~0.55, the top steam temperature is 65℃, and the heat pump compression ratio is 2.1. The cold material vaporization temperature of the intermediate reboiler 230 is 76℃, and the heat transfer temperature difference between cold and hot is 10℃. The tower bottom is dimethyl carbonate and extractant, and the tower bottom material temperature is 114℃. The tower bottom is provided with a tower bottom reboiler 280, and the dimethyl carbonate and extractant in the tower bottom are heated and vaporized again by external steam heating, and the vaporized material is returned to the extractive distillation tower 220. The liquid phase is output to the downstream separation tower through the tower bottom delivery pump 290 for separation and recovery of the extractant.

[0102] Under the above conditions, the heat load of the feed vaporizer 210, the intermediate reboiler 230, the power of the heat pump compressor 250, the power of the tower top condenser 240 and the tower bottom reboiler 280 and the unit ton operating cost under different azeotropic feed heat states are shown in Table 1:

[0103] Table 1

[0104]

[0105] Note: Steam price is 174.28 ¥ / t, cooling water price is 0.24 ¥ / t, and electricity cost is 0.62 ¥ / kW·h.

[0106] Example 2

[0107] This embodiment provides a separation method of dimethyl carbonate and methanol azeotrope, which is similar to the separation method of Example 1, except that the cold material vaporization temperature of the intermediate reboiler 230 is 83° C. and the compression ratio of the heat pump compressor 250 is 2.7. Other conditions are the same as those of Example 1 and will not be repeated.

[0108] Under the above conditions, the heat load of the feed vaporizer 210, the intermediate reboiler 230, the power of the heat pump compressor 250, the power of the tower top condenser 240 and the tower bottom reboiler 280 and the unit ton operating cost under different azeotropic feed heat states are shown in Table 2:

[0109] Table 2

[0110]

[0111] Note: Steam price is 174.28 ¥ / t, cooling water price is 0.24 ¥ / t, and electricity cost is 0.62 ¥ / kW·h.

[0112] Example 3

[0113] This embodiment provides a method for separating dimethyl carbonate and methanol azeotropes, which is similar to the separation method of Example 1, except that the cold material vaporization temperature of the intermediate reboiler 230 is 87° C., and the compression ratio of the heat pump compressor 250 is 3. Other conditions are the same as those of Example 1 and will not be repeated.

[0114] Under the above conditions, the heat load of the feed vaporizer 210, the intermediate reboiler 230, the power of the heat pump compressor 250, the power of the tower top condenser 240 and the tower bottom reboiler 280 and the unit ton operating cost under different azeotropic feed heat states are shown in Table 3:

[0115] Table 3

[0116]

[0117] Note: Steam price is 174.28 ¥ / t, cooling water price is 0.24 ¥ / t, and electricity cost is 0.62 ¥ / kW·h.

[0118] Example 4

[0119] This embodiment provides a separation method of dimethyl carbonate and methanol azeotrope, which is similar to the separation method of Example 1, except that the cold material vaporization temperature of the intermediate reboiler 230 is 90° C. and the compression ratio of the heat pump compressor 250 is 3.3. Other conditions are the same as those of Example 1 and will not be repeated.

[0120] Under the above conditions, the heat load of the feed vaporizer 210 and the intermediate reboiler 230, the power of the heat pump compressor 250, the power of the tower top condenser 240 and the tower bottom reboiler 280 and the unit ton operating cost under different azeotropic feed heat states are shown in Table 4:

[0121] Table 4

[0122]

[0123] Note: Steam price is 174.28 ¥ / t, cooling water price is 0.24 ¥ / t, and electricity cost is 0.62 ¥ / kW·h.

[0124] Comparative Example 1

[0125] Comparative Example 1 provides a separation method of dimethyl carbonate and methanol azeotrope, which is similar to the separation method of Example 1, except that a heat pump scheme is not adopted, that is, a feed vaporizer, an intermediate reboiler and a heat pump compressor are not provided. The overhead steam is directly condensed by the overhead condenser, and the tower kettle reboiler reboils the liquid in the kettle to maintain the gas-liquid balance in the kettle. At this time, the tower kettle reboiler power is 14663kW, the tower top condenser power is 13541kW, and the unit ton product operating cost is 413.5¥ / t.

[0126] It is understood that in the above table, the feed vaporization rate refers to the ratio of the material vaporized in the dimethyl carbonate and methanol azeotrope to the total material. If the feed vaporization rate is 0, dimethyl carbonate and the methanol azeotrope are not vaporized. If the feed vaporization rate is 1, dimethyl carbonate and the methanol azeotrope are all vaporized.

[0127] The following table is explained by taking Table 4 as an example. In Table 4, the feed vaporization rate is selected as 0.1. According to the feed flow rate of 41.4t / h and the feed temperature of 48.6℃, the required feed vaporizer thermal power is calculated to be 1733kW when the vaporization rate is 0.1. At this vaporization rate, when the number of tower plates and feed position are fixed, the reflux ratio required to achieve the separation requirements of the top and bottom of the tower is calculated. The maximum intermediate reboiler input power can be obtained by selecting the intermediate reboiler temperature. After setting the maximum input power, the tower kettle reboiler power and the tower top condenser power can be obtained. The heat pump power is calculated based on the set compression ratio.

[0128] As can be seen from Table 1, when the cold material vaporization temperature of the intermediate reboiler 230 is selected to be 76°C, a distillation scheme with a compression ratio of 2.1 for the heat pump compressor 250 is adopted, under different feed heat states, the cooling water energy consumption can be reduced to 21.6%~47.3% of Comparative Example 1, the tower bottom steam energy consumption can be reduced to 35.0%~58.5% of Comparative Example 1, and the unit ton operating cost can be reduced to 45.6%~64.6% of Comparative Example 1. Under this heat pump compression ratio of 2.1, when all the heat pump heat load is allocated to the feed vaporizer 210, the unit ton product operating cost is the lowest.

[0129] It can be seen from Table 2 that when the cold material vaporization temperature of the intermediate reboiler 230 is selected to be 83°C, a distillation scheme with a compression ratio of 2.7 for the heat pump compressor 250 is adopted, and under different feed heat states, the cooling water energy consumption can be reduced to 11.6%~14.8% of Comparative Example 1, the tower bottom steam energy consumption can be reduced to 25.7%~28.4% of Comparative Example 1, and the unit ton operating cost can be reduced to 42.1%~43.9% of Comparative Example 1. Under this compression ratio, when the feed vaporization rate is selected to be 0.3, that is, when the heat load ratio of the feed vaporizer 210 and the intermediate reboiler 230 is 1:2, the unit ton product operating cost is the lowest.

[0130] It can be seen from Table 3 that when the cold material vaporization temperature of the intermediate reboiler 230 is selected to be 87°C, a distillation scheme with a compression ratio of 3 for the heat pump compressor 250 is adopted. Under different feed heat conditions, the cooling water energy consumption can be reduced to 4.1%~4.8% of Comparative Example 1, the tower bottom steam energy consumption can be reduced to 14.9%~19.3% of Comparative Example 1, and the unit ton operating cost can be reduced to 34.2%~40.1% of Comparative Example 1. Under this compression ratio, when all the heat pump heat load is allocated to the intermediate reboiler 230, the unit ton product operating cost is the lowest.

[0131] It can be seen from Table 4 that when the cold material vaporization temperature of the intermediate reboiler 230 is selected to be 90°C, a distillation scheme with a compression ratio of 3.3 for the heat pump compressor 250 is adopted. Under different feed heat conditions, the cooling water energy consumption can be reduced to 0% to 0.2% of Comparative Example 1, the tower bottom steam energy consumption can be reduced to 14.9% to 16.1% of Comparative Example 1, and the unit ton operating cost can be reduced to 36.8% to 39.5% of Comparative Example 1. Under this compression ratio, when all the heat pump heat load is allocated to the intermediate reboiler 230, the unit ton product operating cost is the lowest.

[0132] From the data in Tables 1 to 4, it can be seen that when the steam price is 174.28 ¥ / t, the cooling water price is 0.24 ¥ / t, and the electricity fee is 0.62 ¥ / kW·h, the heat pump compression ratio is selected to be around 3, and the heat load of the heat pump is fully allocated to the intermediate reboiler 230, the lowest operating cost per ton of product can be obtained.

[0133] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0134] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solution of the present application in detail, but it cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the contents of the attached claims, and the description and drawings can be used to explain the contents of the claims.

Claims

1. A method for separating an azeotrope of dimethyl carbonate and methanol, characterized in that: The steps include: The azeotrope of dimethyl carbonate and methanol is treated in a feed vaporizer and then passed into an extractive distillation tower for extractive distillation, wherein the top of the tower is methanol vapor, and the bottom of the tower is dimethyl carbonate and an extractant, and the stripping section of the extractive distillation tower is provided with an intermediate reboiler; Compressing at least part of the overhead steam of the extractive distillation tower and raising its temperature through a heat pump compressor; Using the compressed gas phase as a heat source to heat the feed vaporizer and the intermediate reboiler; Among them, when the compression ratio of the heat pump compressor is less than a preset value, the heat load supplied by the heat source to the feed vaporizer is greater than the heat load supplied to the intermediate reboiler; when the compression ratio of the heat pump compressor is greater than or equal to the preset value, the heat load supplied by the heat source to the feed vaporizer is less than or equal to the heat load supplied to the intermediate reboiler.

2. The method for separating the azeotrope of dimethyl carbonate and methanol according to claim 1, characterized in that: The compression ratio of the heat pump compressor is 1.5-4; Optionally, the compression ratio of the heat pump compressor is 2~3.

5.

3. The method for separating the azeotrope of dimethyl carbonate and methanol according to claim 2, characterized in that: The preset value is 2.

5.

4. The method for separating the azeotrope of dimethyl carbonate and methanol according to claim 3, characterized in that: The compression ratio a of the heat pump compressor is 2≤a<2.5, and the heat load of the heat source is all supplied to the feed vaporizer; Alternatively, the compression ratio a of the heat pump compressor is 2.5≤a<3, the heat load of the heat source is supplied to the intermediate reboiler and the feed vaporizer at the same time, and the heat load supplied to the intermediate reboiler is greater than the heat load supplied to the feed vaporizer; Alternatively, the compression ratio a of the heat pump compressor is 3≤a≤3.5, and the heat load of the heat source is entirely supplied to the intermediate reboiler.

5. The method for separating the azeotrope of dimethyl carbonate and methanol according to any one of claims 1 to 4, characterized in that: The heat pump compressor is an open heat pump.

6. The method for separating the azeotrope of dimethyl carbonate and methanol according to claim 1, characterized in that: The vaporization temperature of the intermediate reboiler is 76°C to 90°C; And / or, the heat transfer temperature difference between the cold and hot sides of the intermediate reboiler is 5°C to 40°C; Optionally, the heat transfer temperature difference between the cold and hot sides of the intermediate reboiler is 8°C to 20°C.

7. The method for separating the azeotrope of dimethyl carbonate and methanol according to claim 1, characterized in that: The heat transfer temperature difference between the cold and hot sides of the feed vaporizer is 5°C to 40°C; Optionally, the heat transfer temperature difference between the cold and hot sides of the feed vaporizer is 10°C to 25°C.

8. The method for separating the azeotrope of dimethyl carbonate and methanol according to claim 1, characterized in that: The extractant includes propylene carbonate.

9. The method for separating the azeotrope of dimethyl carbonate and methanol according to claim 1, characterized in that: The extractive distillation tower is provided with a distillation section, an extraction section and a stripping section, the number of theoretical plates of the distillation section is 10-35, the number of theoretical plates of the extraction section is 15-50, and the number of theoretical plates of the stripping section is 10-45; And / or, the top operating pressure of the extractive distillation tower is normal pressure, the reflux ratio is 0.2-2, and the bottom temperature is 110° C.-120° C.

10. A separation device for dimethyl carbonate and methanol azeotrope, characterized in that: Used in the separation method according to any one of claims 1 to 9, the separation device comprises: A feed vaporizer for vaporizing the azeotrope of dimethyl carbonate and methanol; An extractive distillation tower, connected to the feed vaporizer, for extracting and distilling the azeotrope of dimethyl carbonate and methanol after the vaporization treatment; an intermediate reboiler, connected to the extractive distillation tower, and used for reboiling the liquid in the stripping section of the extractive distillation tower; The heat pump compressor is connected to the extractive distillation tower, the feed vaporizer and the intermediate reboiler, and is used to compress and heat at least part of the top steam of the extractive distillation tower, and use the compressed gas phase as a heat source to heat the feed vaporizer and the intermediate reboiler.

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