A feed-separated thermal integrated extraction distillation process

Abstract

This invention discloses a feed-separated thermally integrated extractive distillation process. This process adjusts the energy consumption distribution of the three distillation columns through feed separation, thereby affecting the thermal integration effect. Simultaneously, the coupling of heat between the three columns during thermal integration alters the impact of feed separation on the total energy consumption of the three columns. Based on the energy savings achieved through thermal integration and feed separation, energy consumption can be further reduced by adjusting parameters. Furthermore, more energy-efficient extractive distillation processes are proposed for the extraction and distillation of acetone and methanol using water as a solvent, and for the extraction and distillation of ethyl acetate and ethanol using furfural as a solvent.

Description

Technical Field

[0001] This invention relates to the field of thermal integrated extraction distillation and separation technology, specifically to a feed-separated thermal integrated extraction distillation process. Background Technology

[0002] Extractive distillation alters the relative volatility of components by adding solvents, and is typically used to separate azeotropic or near-boiling components. Current energy-saving methods for extractive distillation include integrated heat distillation, heat pump distillation, and side-stream extraction. For example, patent CN113214038B proposes a method for separating a benzene-n-propanol-water mixture using heat pump extractive distillation. Patent CN 107501085 A proposes a method for separating an acetic acid and water mixture using double-effect integrated heat distillation. Patent CN 110885283 A proposes an energy-saving process for separating ethyl acetate-ethanol using integrated heat distillation with side-stream extraction. However, there is still potential for further improvements in energy efficiency for integrated heat distillation. Summary of the Invention

[0003] The purpose of this invention is to further improve the energy efficiency of three-tower extractive distillation based on thermal integration technology, and to provide a feed-separated thermally integrated extractive distillation process. This process adjusts the energy consumption distribution of the three distillation columns through feed separation, thereby affecting the effect of thermal integration. Simultaneously, the coupling of heat between the three columns during thermal integration alters the impact of feed separation on the total energy consumption of the three columns. Based on the energy savings achieved through thermal integration and feed separation, energy consumption can be further reduced by adjusting parameters. Furthermore, more energy-efficient extractive distillation processes are proposed for the extraction and distillation of acetone and methanol using water as a solvent, and for the extraction and distillation of ethyl acetate and ethanol using furfural as a solvent.

[0004] The technical solution adopted by the present invention to solve the aforementioned technical problem is as follows:

[0005] In a first aspect, the present invention provides a feed-separated thermal integrated extractive distillation process, which is suitable for situations where the feed composition is far from the azeotropic point and one of the components is present in small quantities. The process flow is as follows: two mixtures are transported from a feed tank, one to a suitable feed position in a pre-fractionation column and the other to a suitable feed position in an extractive distillation column; in the pre-fractionation column, an azeotropic mixture is obtained at the top of the column through parameter adjustment and is then transported to the extractive distillation column, where a certain product from the feed is obtained at the bottom; in the extractive distillation column, the solvent is fed from a suitable position at the top of the column, and through parameter adjustment, a certain product is obtained at the top, while a mixture of solvent and another product is obtained at the bottom and transported to a solvent recovery column; in the solvent recovery column, the product and solvent are separated, the product is obtained at the top, and the solvent is obtained at the bottom, which is then returned to the feed inlet at the top of the extractive distillation column after passing through a solvent cooler for recycling.

[0006] The thermal integration refers to the use of the vapor to be condensed at the top of the solvent recovery tower to heat the reboiler at the bottom of the pre-fractionation tower; or the use of the vapor to be condensed at the top of the extractive distillation tower to heat the reboiler at the bottom of the pre-fractionation tower first, and then the use of the vapor to be condensed at the top of the solvent recovery tower to heat the reboiler at the bottom of the pre-fractionation tower.

[0007] Secondly, the present invention provides a feed-separated thermal integrated extractive distillation process, the process comprising a pre-fractionation column, an extractive distillation column, and a solvent recovery column. The pre-fractionation column has a first condenser at its top and a first reboiler and a fifth reboiler at its bottom, wherein the first reboiler also serves as the condenser for the solvent recovery column. The extractive distillation column has a third condenser and a solvent cooler at its top, and a second reboiler at its bottom. The solvent recovery column has a third reboiler at its bottom. The top of the pre-fractionation column is connected to the first condenser. The feed position of the extractive distillation column is connected, and the extractive distillation column is equipped with a separate feed inlet. The feed is divided into two streams and enters the pre-fractionation column and the extractive distillation column respectively. The bottom of the extractive distillation column is connected to the solvent recovery column via a second reboiler. The vapor to be condensed at the top of the solvent recovery column is connected to the first reboiler of the pre-fractionation column. The bottom of the solvent recovery column is connected to the solvent inlet of the extractive distillation column via a third reboiler and a solvent cooler. Product B is obtained at the top of the solvent recovery column, product B is obtained at the bottom of the pre-fractionation column, and product A is obtained at the top of the extractive distillation column.

[0008] The specific process is as follows: one feedstock is fed to the feed position of the pre-fractionation column, and another feedstock is fed to the feed position of the extractive distillation column. The two components in the material to be separated are A and B, and the solvent is S. In the pre-fractionation column, by adjusting the reflux ratio, the number of trays, the feed position, and the top outlet position, an azeotropic mixture AB is obtained at the top of the column. The azeotropic mixture AB is then fed to the extractive distillation column, and a certain product B from the feedstock is obtained at the bottom of the column.

[0009] In an extractive distillation column, the solvent is fed from the solvent inlet at the top of the column. By adjusting the reflux ratio, the number of trays, the feed tray position, and the solvent ratio, a certain product A is obtained at the top of the column; a mixture BS of the solvent and another product B is obtained at the bottom of the column and is sent to the solvent recovery column.

[0010] In the solvent recovery tower, product B is separated from solvent S. By adjusting the reflux ratio, the number of trays, and the feed tray position, product B is obtained at the top of the tower, and solvent S is obtained at the bottom. After passing through the solvent cooler, it is returned to the solvent inlet at the top of the extractive distillation tower for recycling. The vapor to be condensed at the top of the solvent recovery tower is used to heat the first reboiler at the bottom of the pre-fractionation tower. The operating pressure of the pre-fractionation tower is lower than that of the solvent recovery tower to ensure that there is a sufficient temperature difference between the top temperature of the solvent recovery tower and the bottom temperature of the pre-fractionation tower for thermal integration. Thermal integration is regulated by adjusting the distribution ratio of the feed flow rate between the pre-fractionation tower and the extractive distillation tower.

[0011] Thirdly, the present invention provides a feed-separated thermal integrated extractive distillation process, comprising a pre-fractionation column, an extractive distillation column, and a solvent recovery column. A first condenser is installed at the top of the pre-fractionation column, and a first reboiler and a fourth reboiler are installed at the bottom of the pre-fractionation column, wherein the first and fourth reboilers also serve as condensers for the extractive distillation column and the solvent recovery column, respectively. A solvent cooler is installed in the extractive distillation column, and a second reboiler is installed at the bottom of the extractive distillation column. A third reboiler is installed at the bottom of the solvent recovery column. The top of the pre-fractionation column is cooled by the solvent from the extractive distillation column via the first condenser. The feed is connected to the pre-fractionation column and then enters the extractive distillation column. The extractive distillation column has a separate feed inlet. The feed is divided into two streams and enters the pre-fractionation column and the extractive distillation column respectively. The bottom of the extractive distillation column is connected to the solvent recovery column via the second reboiler. The vapor to be condensed at the top of the extractive distillation column is connected to the first reboiler of the pre-fractionation column. The vapor to be condensed at the top of the solvent recovery column is connected to the fourth reboiler of the pre-fractionation column. The bottom of the solvent recovery column is connected to the solvent inlet of the extractive distillation column via the third reboiler and the solvent cooler. Product B is obtained at the top of the solvent recovery column, and product A is obtained at the top of the extractive distillation column.

[0012] An auxiliary condenser is installed on the piping between the top of the extractive distillation column and the first reboiler of the pre-fractionation column, and / or on the piping between the top of the solvent recovery column and the fourth reboiler of the pre-fractionation column.

[0013] The specific process flow is as follows: one feedstock is fed to the appropriate feed position of the pre-fractionation column, and another feedstock is fed to the appropriate feed position of the extractive distillation column. The two components in the material to be separated are A and B, and the solvent is S. In the pre-fractionation column, by adjusting the reflux ratio, number of trays, feed position, and top outlet position, an azeotropic mixture is obtained at the top of the column, which is then fed to the extractive distillation column. The bottom of the column yields a certain product A from the feedstock.

[0014] In an extractive distillation column, the solvent is fed from a suitable position at the top of the column. By adjusting the reflux ratio, the number of trays, the feed tray position, and the solvent ratio, a certain product A is obtained at the top of the column; a mixture of solvent and another product BS is obtained at the bottom of the column and is sent to the solvent recovery column.

[0015] In the solvent recovery tower, the product and solvent are separated. By adjusting the reflux ratio, the number of trays, and the feed tray position, product B is obtained at the top of the tower and solvent S is obtained at the bottom of the tower. The solvent obtained at the bottom of the solvent recovery tower is returned to the upper feed port of the extractive distillation tower after heat exchange with the stream collected from the top of the pre-fractionation tower in the solvent cooler for recycling.

[0016] The vapors to be condensed at the top of the extractive distillation column and the solvent recovery column are used to heat the bottom of the pre-fractionation column. The operating pressure of the pre-fractionation column is lower than that of the extractive distillation column and the solvent recovery column to ensure that there is a sufficient temperature difference between the top temperature of the extractive distillation column and the bottom temperature of the pre-fractionation column for thermal integration. Thermal integration is regulated by adjusting the distribution ratio of the feed flow rate between the pre-fractionation column and the extractive distillation column.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] The feed-separated, thermally integrated extractive distillation process of this invention is more energy-efficient, has a higher degree of thermal integration, and results in a lower bottom temperature in the extractive distillation column. This process is applicable to acetone / methanol / water (solvent) systems and ethyl acetate / ethanol / furfural (solvent) systems. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of one embodiment of the feed separation thermal integrated extraction distillation process of the present invention.

[0020] Figure 2 This is a process flow diagram of another embodiment of the feed separation thermal integrated extraction distillation process of the present invention. Detailed Implementation

[0021] The present invention will be further explained below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of protection of this application.

[0022] This invention's extractive distillation process is suitable for situations where the feed composition is far from the azeotropic point and one of the components is present in small quantities. The process flow is as follows: two mixtures are fed from a feed tank; one is fed to a suitable feed position in a pre-fractionation column, and the other to a suitable feed position in an extractive distillation column. In the pre-fractionation column, by adjusting parameters, an azeotropic mixture is obtained at the top and fed to the extractive distillation column, where a specific product from the feed is obtained at the bottom. In the extractive distillation column, the solvent is fed from a suitable position at the top. By adjusting parameters, a specific product is obtained at the top, and a mixture of solvent and another product is obtained at the bottom, which is then fed to a solvent recovery column. In the solvent recovery column, the product and solvent are separated. The product is obtained at the top, and a high-purity solvent is obtained at the bottom, which is then returned to the feed inlet at the top of the extractive distillation column after passing through a solvent cooler for recycling.

[0023] The aforementioned thermal integration refers to using the vapor to be condensed at the top of the solvent recovery tower to heat the reboiler at the bottom of the pre-fractionation tower; or first using the vapor to be condensed at the top of the extractive distillation tower to heat the reboiler at the bottom of the pre-fractionation tower, and then using the vapor to be condensed at the top of the solvent recovery tower to heat the reboiler at the bottom of the pre-fractionation tower; since the solvent obtained from the bottom of the solvent recovery tower needs to be condensed and recycled, it can be used for some low-temperature streams in the heating process.

[0024] like Figure 1 As shown, the feed-separated thermal integrated extractive distillation process of the present invention includes a pre-fractionation column 1, an extractive distillation column 2, and a solvent recovery column 3. The pre-fractionation column 1 has a first condenser 11 at its top and a first reboiler 12 and a fifth reboiler 13 at its bottom. The first reboiler 12 also serves as the condenser for the solvent recovery column 3. The extractive distillation column has a third condenser 21 and a solvent cooler 22 at its top and a second reboiler 23 at its bottom. The solvent recovery column 3 has a third reboiler 31 at its bottom. The top of the pre-fractionation column is connected to the first reboiler 12. A condenser 11 is connected to the feed position of the extractive distillation column. The extractive distillation column is equipped with a separate feed inlet. The feed is divided into two streams and enters the pre-fractionation column and the extractive distillation column respectively. The bottom of the extractive distillation column is connected to the solvent recovery column via a second reboiler. The vapor to be condensed at the top of the solvent recovery column is connected to the first reboiler 12 of the pre-fractionation column. The bottom of the solvent recovery column is connected to the solvent feed inlet of the extractive distillation column via a third reboiler and a solvent cooler. Product B is obtained at the top of the solvent recovery column, product B is obtained at the bottom of the pre-fractionation column, and product A is obtained at the top of the extractive distillation column.

[0025] The specific process is as follows: One feedstock is fed to the feed position of the pre-fractionation column, and another feedstock is fed to the feed position of the extractive distillation column. The materials to be separated contain two components, A and B, and the solvent is S. In the pre-fractionation column, by adjusting parameters such as the reflux ratio, number of trays, feed position, and top collection, an azeotropic mixture AB is obtained at the top of the column and is fed to the extractive distillation column; the bottom of the column yields a product B from the feedstock. In the extractive distillation column, the solvent is fed from the solvent inlet at the top of the column. By adjusting parameters such as the reflux ratio, number of trays, feed tray position, and solvent ratio, a product A is obtained at the top of the column; the bottom of the column yields a mixture BS of the solvent and another product B, which is fed to the solvent recovery column. In the solvent recovery column, product B is separated from solvent S. By adjusting parameters such as the reflux ratio, number of trays, and feed tray position, this product B is obtained at the top of the column, and a higher purity solvent S is obtained at the bottom of the column. After passing through a solvent cooler, it is returned to the solvent inlet at the top of the extractive distillation column for recycling. The vapor to be condensed at the top of the solvent recovery tower is used to heat the reboiler at the bottom of the pre-fractionation tower. The operating pressure of the pre-fractionation tower is lower than that of the solvent recovery tower to ensure that there is a sufficient temperature difference between the top temperature of the solvent recovery tower and the bottom temperature of the pre-fractionation tower for thermal integration. Thermal integration can be adjusted by adjusting the distribution ratio of the feed flow rate between the pre-fractionation tower and the extractive distillation tower.

[0026] like Figure 2The diagram illustrates another embodiment of the feed-separated thermal integrated extractive distillation process of the present invention, comprising a pre-fractionation column 1, an extractive distillation column 2, and a solvent recovery column 3. The pre-fractionation column 1 has a first condenser 11 at its top and a first reboiler 12 and a fourth reboiler 14 at its bottom, which also serve as condensers for the extractive distillation column 2 and the solvent recovery column 3, respectively. The extractive distillation column has a solvent cooler 22 and a second reboiler 23 at its bottom. The solvent recovery column 3 has a third reboiler 31 at its bottom. The top of the pre-fractionation column is connected to the solvent in the extractive distillation column via the first condenser 11. The feed is connected to a cooler and then enters the extractive distillation column. The extractive distillation column has a separate feed inlet, and the feed is split into two streams that enter the pre-fractionation column and the extractive distillation column respectively. The bottom of the extractive distillation column is connected to the solvent recovery column via a second reboiler. The vapor to be condensed at the top of the extractive distillation column is connected to the first reboiler 12 of the pre-fractionation column, and the vapor to be condensed at the top of the solvent recovery column is connected to the fourth reboiler 14 of the pre-fractionation column. The bottom of the solvent recovery column is connected to the solvent inlet of the extractive distillation column via a third reboiler 31 and a solvent cooler 22. Product B is obtained at the top of the solvent recovery column, product A is obtained at the bottom of the pre-fractionation column, and product A is obtained at the top of the extractive distillation column. An auxiliary condenser 32 is installed on the pipeline between the top of the extractive distillation column and the first reboiler 12 of the pre-fractionation column, and / or on the pipeline between the top of the solvent recovery column and the fourth reboiler 14 of the pre-fractionation column.

[0027] The specific process is as follows: One feedstock is fed to a suitable feed position in the pre-fractionation column, and another feedstock is fed to a suitable feed position in the extractive distillation column. The materials to be separated contain two components, A and B, and the solvent is S. In the pre-fractionation column, by adjusting parameters such as the reflux ratio, number of trays, feed position, and top product, an azeotropic mixture is obtained at the top and fed to the extractive distillation column; the bottom of the column yields product A from the feedstock. In the extractive distillation column, the solvent is fed from a suitable position at the top of the column. By adjusting parameters such as the reflux ratio, number of trays, feed tray position, and solvent ratio, product A is obtained at the top of the column; the bottom of the column yields a mixture of the solvent and another product, BS, which is then fed to the solvent recovery column. In the solvent recovery tower, the product and solvent are separated. By adjusting parameters such as the reflux ratio, number of trays, and feed tray position, product B is obtained at the top of the tower, while a high-purity solvent S is obtained at the bottom. The solvent obtained from the bottom of the solvent recovery tower is returned to the upper feed inlet of the extractive distillation tower after heat exchange with the stream collected from the top of the pre-fractionation tower in solvent cooler 22 for recycling. The vapors to be condensed at the top of the extractive distillation tower and the solvent recovery tower are used to heat the bottom of the pre-fractionation tower. The operating pressure of the pre-fractionation tower is lower than that of the extractive distillation tower and the solvent recovery tower to ensure that there is a sufficient temperature difference between the top temperature of the extractive distillation tower and the bottom temperature of the pre-fractionation tower for thermal integration. Thermal integration can be adjusted by changing the distribution ratio of the feed flow rate between the pre-fractionation tower and the extractive distillation tower.

[0028] The pressures of the various columns in the above-mentioned thermal integration are different to meet the temperature difference of the thermal integration, which is achieved by reducing the pressure of the pre-fractionation column or increasing the pressure of the extractive distillation column / solvent recovery column.

[0029] Preferably, when the material to be separated is an acetone and methanol system, the mass fraction of acetone is 0.1-0.4%; when the material to be separated is an ethyl acetate and ethanol system, the mass fraction of ethyl acetate is 0.1-0.4%.

[0030] Example 1: Separation of acetone and methanol by extractive distillation using water as a solvent

[0031] This embodiment uses water as a solvent and a feed-separated thermal integrated extraction distillation process to extract and separate acetone and methanol. The specific process is as follows: Figure 1 As shown, in this embodiment, the feed composition contains 0.2% acetone and 0.8% methanol by mass. The pre-fractionation column has 34 theoretical plates, feed position 14, operating pressure of 101.3 kPa, reflux ratio of 2.7, total heat load of the first reboiler 12 and the fifth reboiler 13 of 11968 kW, top temperature of 55°C, bottom temperature of 69°C, feed rate of 1161 kmol / h, and methanol (component B) with a molar purity of 0.995 is collected from the bottom of the column.

[0032] The extractive distillation column has a theoretical plate number of 92, with feed points at 44, 77, and 81 (solvent feed point at 44; feed feed point at 81; and feed point for the top effluent from the pre-fractionation column at 77). The operating pressure is 101.3 kPa, the reflux ratio is 2.4, the heat load of the second reboiler 23 is 7996 kW, the top temperature is 56 °C, the bottom temperature is 91 °C, the feed rate is 189 kmol / h, and the top effluent is acetone (component A) with a molar purity of 0.994.

[0033] The solvent recovery tower has a theoretical plate count of 35, a feed position of 26, an operating pressure of 202.6 kPa, a reflux ratio of 1.4, a heat load of 6856 kW for the third reboiler 31, a heat load of -6267 kW for the condenser (the first reboiler 12 of the pre-fractionation tower acts as a condenser here), a top temperature of 83°C, a bottom temperature of 124°C, and methanol (component B) with a molar purity of 0.999 is collected from the top of the tower. Water with a molar purity of 0.9999 is collected from the bottom of the tower. The solvent water collected from the bottom of the tower is cooled by the solvent cooler 22 and then recycled back to the extractive distillation tower along with the makeup solvent through the solvent feed inlet of the extractive distillation tower.

[0034] During the distribution process, installing only a reboiler with a lower energy consumption of 5701kW in the bottom of the pre-fractionation tower is sufficient to match the load of the condenser at the top of the solvent recovery tower with the heat of the bottom of the pre-fractionation tower, so that all the heat load of the steam at the top of the solvent recovery tower is used to heat the bottom of the pre-fractionation tower.

[0035] In this embodiment, a feed separation type thermal integration method is adopted to achieve the purpose of separating acetone and methanol by extractive distillation with water as solvent under the premise of lower cost and energy consumption. The recoverable heat is 6267kW, and the total energy consumption of the reboiler in the pre-fractionation column is 11968kW. Since 6267kW of heat can be recovered, an additional 5701kW reboiler can be set to achieve heat matching. The temperature of the extractive distillation column bottom is 91℃.

[0036] Original heat integration technology (without feed separation, other connection methods such as...) Figure 1 (As shown) Under the same conditions, the recoverable heat is 4600kW, the total energy consumption of the pre-fractionation column reboiler is 13081kW, and the temperature of the extractive distillation column bottom is 93℃.

[0037] Therefore, the feed separation-type thermal integration method in this embodiment can recover more heat while reducing the heat consumption of the system itself, resulting in lower annual costs and better energy-saving performance. This embodiment also achieves a higher degree of thermal integration and lower bottom temperature in the extractive distillation column. This represents an improvement of over 4% compared to existing standalone thermal integration technologies.

[0038] Example 2: Separation of ethyl acetate and ethanol using furfural as a solvent

[0039] This embodiment uses furfural as a solvent and employs a feed-separation type thermal integrated extraction distillation process to separate ethyl acetate and ethanol. The specific process is as follows: Figure 2 As shown, in this embodiment, the feed composition contains 0.25% ethyl acetate and 0.75% ethanol by mass. The pre-fractionation column has 16 theoretical plates, feed position 6, operating pressure of 49 kPa, reflux ratio of 0.93, reboiler (12 and 14) heat load of 2574 kW, column top temperature of 54°C, column bottom temperature of 62°C, feed rate of 270 kmol / h, and ethanol (component A) with a molar purity of 0.995 is collected from the bottom of the column.

[0040] The extractive distillation column has a theoretical plate number of 70, with feed points at 10, 38, and 57 (solvent feed point at 10; feed feed point at 38; and feed point at the top of the pre-fractionation column at 57). The operating pressure is 278 kPa, the reflux ratio is 0.41, the heat load of the second reboiler is 1741 kW, the heat load of the condenser (i.e., the first reboiler 12 on the pre-fractionation column) is -1376 kW, the top temperature is 106 °C, the bottom temperature is 162 °C, the feed rate is 30 kmol / h, and the top product is ethanol (component A) with a molar purity of 0.995.

[0041] The solvent recovery tower has a theoretical plate count of 26, a feed position of 9, an operating pressure of 177 kPa, a reflux ratio of 0.87, a third reboiler heat load of 1157 kW, a condenser (i.e., the fourth reboiler 14 of the pre-fractionation tower) heat load of -1198 kW, a top temperature of 95 °C, and a bottom temperature of 186 °C. The top product is ethyl acetate (component B) with a molar purity of 0.995, and the bottom product is furfural with a molar purity of 0.99999. The furfural from the bottom product exchanges heat with the stream from the top product of the pre-fractionation tower and is then recycled back to the extractive distillation tower along with the makeup solvent.

[0042] In the thermal integration of the three columns, the combined load of the top condenser of the extractive distillation column and the top condenser of the solvent recovery column is comparable to, and almost equal to, the load of the reboiler at the bottom of the pre-fractionation column. Therefore, only one auxiliary condenser 32 with very low energy consumption of -0.3kW needs to be installed in the solvent recovery column or the extractive distillation column.

[0043] Table 1. Energy consumption of all reboilers in the entire process of each embodiment.

[0044] Example 1 2 Total energy consumption (kW) for extractive distillation process (no feed, separation, no heat integration) 25045 6176 Total energy consumption (kW) of thermally integrated extraction distillation process (no feed separation with thermal integration) 21425 3146 Total energy consumption (kW) of a feed-separated extractive distillation process (with feed separation but no integrated heating) 25045 5971 Total energy consumption (kW) of a feed-separated, thermally integrated extractive distillation process (with both feed separation and thermal integration). 20553 2959 The energy saving rate of the heatless integrated process with feed separation compared to the heatless integrated process without feed separation is higher. 0 3.3％ Compared to a feed-separated thermally integrated process, the feed-separated thermally integrated process achieves higher energy savings. 4.1％ 5.9％ The energy saving rate of the feedless separation and thermal integration process compared to the feedless separation and thermal integration process 14.5％ 49.1％ A process with feed separation and thermal integration offers higher energy savings compared to a process with feed separation but without thermal integration. 17.9％ 50.4％

[0045] The feed-separation type thermally integrated extractive distillation method of this invention is more energy-efficient than existing thermally integrated extractive distillation technologies and feed-separation type extractive distillation technologies. The improvement of the existing feed-separation type extractive distillation method is reflected in the following: feed-separation type extractive distillation was originally unsuitable for the system in Example 1. The energy-saving principle of feed separation is changed by the heat coupling during the thermal integration process of this invention, making the feed separation method applicable to this system, expanding the applicability of the feed-separation type extractive distillation method, and achieving the goal of separating acetone and methanol using water as a solvent through extractive distillation with lower energy consumption and lower cost. For the system in Example 2, the energy-saving rate of feed-separation type extractive distillation is increased from 3.3% to 5.9% by this invention, resulting in improved energy-saving effect. The improvement of the existing thermally integrated extractive distillation method of this invention is reflected in the following: the energy-saving effect of both Example 1 and Example 2 is significantly improved; the reboiler temperature of the feed-separation type thermally integrated extractive distillation column in the examples is lower than that without feed-separation thermal integration; and the degree of thermal integration in the feed-separation type thermally integrated extractive distillation in Example 1 is higher.

[0046] In this invention, the two methods of thermal integration and feed separation are coupled together, which enhances the energy-saving effect and thus significantly improves the energy saving rate and reduces the operating cost. In particular, in Example 1, simple feed separation cannot achieve the purpose of energy saving. When feed separation and thermal integration are coupled, the energy saving rate can be significantly reduced, achieving a 1+1 greater than 2 effect, and the energy saving effect is significant.

[0047] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A feed-separation type thermal integrated extractive distillation process for separating acetone and methanol using water as a solvent, characterized in that, The system includes a pre-fractionation column, an extractive distillation column, and a solvent recovery column. The pre-fractionation column has a first condenser at its top and a first and fifth reboiler at its bottom, with the first reboiler also serving as the condenser for the solvent recovery column. The extractive distillation column has a third condenser and a solvent cooler at its top and a second reboiler at its bottom. The solvent recovery column also has a third reboiler at its bottom. The top of the pre-fractionation column is connected to the feed position of the extractive distillation column via the first condenser. The extractive distillation column has a separate feed inlet, and the feed is split into two streams that enter the pre-fractionation column and the extractive distillation column respectively. The bottom of the extractive distillation column is connected to the solvent recovery column via the second reboiler. The vapor to be condensed at the top of the solvent recovery column is connected to the first reboiler of the pre-fractionation column. The bottom of the solvent recovery column is connected to the solvent feed inlet of the extractive distillation column via the third reboiler and the solvent cooler. Product B is obtained at the top of the solvent recovery column, product B is obtained at the bottom of the pre-fractionation column, and product A is obtained at the top of the extractive distillation column. The specific process is as follows: one feedstock is fed to the feed position of the pre-fractionation column, and another feedstock is fed to the feed position of the extractive distillation column. The two components in the material to be separated are A and B, and the solvent is S. In the pre-fractionation column, by adjusting the reflux ratio, the number of trays, the feed position, and the top outlet position, an azeotropic mixture AB is obtained at the top of the column. The azeotropic mixture AB is then fed to the extractive distillation column, and a certain product B from the feedstock is obtained at the bottom of the column. In an extractive distillation column, the solvent is fed from the solvent inlet at the top of the column. By adjusting the reflux ratio, the number of trays, the feed tray position, and the solvent ratio, a certain product A is obtained at the top of the column; a mixture BS of the solvent and another product B is obtained at the bottom of the column and is sent to the solvent recovery column. In the solvent recovery tower, product B is separated from solvent S. By adjusting the reflux ratio, the number of trays, and the feed tray position, product B is obtained at the top of the tower, and solvent S is obtained at the bottom. After passing through the solvent cooler, it is returned to the solvent inlet at the top of the extractive distillation tower for recycling. The vapor to be condensed at the top of the solvent recovery tower is used to heat the first reboiler at the bottom of the pre-fractionation tower. The operating pressure of the pre-fractionation tower is lower than that of the solvent recovery tower to ensure that there is a sufficient temperature difference between the top temperature of the solvent recovery tower and the bottom temperature of the pre-fractionation tower for thermal integration. Thermal integration is regulated by adjusting the distribution ratio of the feed flow rate between the pre-fractionation tower and the extractive distillation tower.

2. The feed-separation type thermal integrated extraction distillation process according to claim 1, characterized in that, In the extraction and distillation separation of acetone and methanol using water as a solvent, the mass fraction of acetone is 0.1-0.4%.

3. The feed-separated thermal integrated extraction distillation process according to claim 1, characterized in that, The feed composition contains 0.2% acetone and 0.8% methanol. The pre-fractionation column has 34 theoretical plates, feed position 14, operating pressure of 101.3 kPa, reflux ratio of 2.7, total heat load of the first and fifth reboilers of 11968 kW, top temperature of 55℃, bottom temperature of 69℃, feed rate of 1161 kmol / h, and methanol with a molar purity of 0.995 is collected from the bottom of the column. The extractive distillation column has 92 theoretical plates, a solvent inlet at position 44, a feed inlet at position 81, and the pre-fractionation column has a feed inlet at position 77. The operating pressure is 101.3 kPa, the reflux ratio is 2.4, the heat load of the second reboiler is 7996 kW, the top temperature is 56 °C, the bottom temperature is 91 °C, the feed rate is 189 kmol / h, and the top product is acetone with a molar purity of 0.

994. The solvent recovery tower has a theoretical plate number of 35, a feed position of 26, an operating pressure of 202.6 kPa, a reflux ratio of 1.4, a heat load of 6856 kW for the third reboiler, a heat load of -6267 kW for the condenser (which is also the first reboiler of the pre-fractionation tower), a top temperature of 83°C, a bottom temperature of 124°C, and methanol with a molar purity of 0.999 is collected from the top of the tower, while water with a molar purity of 0.9999 is collected from the bottom of the tower.

4. A feed-separation type thermal integrated extractive distillation process for separating ethyl acetate and ethanol using furfural as a solvent, characterized in that, The process is used to separate ethyl acetate and ethanol using furfural as a solvent. It includes a pre-fractionation column, an extractive distillation column, and a solvent recovery column. The pre-fractionation column has a first condenser at its top and a first reboiler and a fourth reboiler at its bottom, which also serve as condensers for the extractive distillation column and the solvent recovery column, respectively. The extractive distillation column has a solvent cooler and a second reboiler at its bottom. The solvent recovery column has a third reboiler at its bottom. The top of the pre-fractionation column is connected to the solvent cooler of the extractive distillation column via the first condenser. The feed then enters the extractive distillation column, which has a separate feed inlet. The feed is split into two streams that enter the pre-fractionation column and the extractive distillation column, respectively. The bottom of the extractive distillation column is connected to the solvent recovery column via a second reboiler. The vapor to be condensed at the top of the extractive distillation column is connected to the first reboiler of the pre-fractionation column, and the vapor to be condensed at the top of the solvent recovery column is connected to the fourth reboiler of the pre-fractionation column. The bottom of the solvent recovery column is connected to the solvent inlet of the extractive distillation column via a third reboiler and a solvent cooler. Product B is obtained at the top of the solvent recovery column, and product A is obtained at the top of the extractive distillation column. Install auxiliary condensers on the piping between the top of the extractive distillation column and the first reboiler of the pre-fractionation column and / or on the piping between the top of the solvent recovery column and the fourth reboiler of the pre-fractionation column. The specific process flow is as follows: one feedstock is fed to the appropriate feed position of the pre-fractionation column, and another feedstock is fed to the appropriate feed position of the extractive distillation column. The two components in the material to be separated are A and B, and the solvent is S. In the pre-fractionation column, by adjusting the reflux ratio, number of trays, feed position, and top outlet position, an azeotropic mixture is obtained at the top of the column, which is then fed to the extractive distillation column. The bottom of the column yields a certain product A from the feedstock. In an extractive distillation column, the solvent is fed from a suitable position at the top of the column. By adjusting the reflux ratio, the number of trays, the feed tray position, and the solvent ratio, a certain product A is obtained at the top of the column; a mixture of solvent and another product BS is obtained at the bottom of the column and is sent to the solvent recovery column. In the solvent recovery tower, the product and solvent are separated. By adjusting the reflux ratio, the number of trays, and the feed tray position, product B is obtained at the top of the tower and solvent S is obtained at the bottom of the tower. The solvent obtained at the bottom of the solvent recovery tower is returned to the upper feed port of the extractive distillation tower after heat exchange with the stream collected from the top of the pre-fractionation tower in the solvent cooler for recycling. The vapors to be condensed at the top of the extractive distillation column and the solvent recovery column are used to heat the bottom of the pre-fractionation column. The operating pressure of the pre-fractionation column is lower than that of the extractive distillation column and the solvent recovery column to ensure a sufficient temperature difference between the top temperature of the extractive distillation column and the bottom temperature of the pre-fractionation column for thermal integration. Thermal integration is regulated by adjusting the feed flow rate distribution ratio between the pre-fractionation column and the extractive distillation column. The process feed composition includes ethyl acetate mass fraction of 0.25% and ethanol mass fraction of 0.75%. The pre-fractionation column has 16 theoretical plates, feed position 6, operating pressure of 49 kPa, reflux ratio of 0.93, heat load of the first and fourth reboilers of 2574 kW, top temperature of 54℃, bottom temperature of 62℃, feed rate of 270 kmol / h, and ethanol with a molar purity of 0.995 as the bottom product. The extractive distillation column has a theoretical plate number of 70, a solvent inlet at position 10, a feed inlet at position 38, a pre-fractionation column top feed outlet at position 57, an operating pressure of 278 kPa, a reflux ratio of 0.41, a second reboiler heat load of 1741 kW, a condenser (which is also the first reboiler on the pre-fractionation column) heat load of -1376 kW, a column top temperature of 106 °C, a column bottom temperature of 162 °C, a feed rate of 30 kmol / h, and an ethanol top product with a molar purity of 0.

995. The solvent recovery tower has a theoretical plate count of 26, a feed position of 9, an operating pressure of 177 kPa, a reflux ratio of 0.87, a third reboiler heat load of 1157 kW, a condenser (which is also the fourth reboiler on the pre-fractionation tower) heat load of -1198 kW, a top temperature of 95°C, a bottom temperature of 186°C, and produces ethyl acetate with a molar purity of 0.995 at the top and furfural with a molar purity of 0.99999 at the bottom. The furfural from the bottom is exchanged with the stream from the top of the pre-fractionation tower and then recycled back to the extractive distillation tower along with the makeup solvent.

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