Feed separation type vapor-liquid coupling type extractive distillation process

Abstract

The invention discloses a feed separation type vapor-liquid coupling type extractive distillation process. A vapor-liquid coupling type extractive distillation device of the process comprises a pre-fractionating tower, an extractive distillation tower and a solvent recovery tower, the vapor-liquid coupling type extractive distillation process comprises the following steps: conveying two strands of first mixtures from a raw material tank, conveying one strand of first mixtures to a pre-fractionating tower, conveying the other strand of first mixtures to an extractive distillation tower, and conveying an azeotropic mixture obtained from the top of the pre-fractionating tower to the extractive distillation tower; the feed separation type vapor-liquid coupling type extractive distillation process is more energy-saving, an intermediate reboiler can be saved under certain conditions, the process is also suitable for a system which is not suitable for a feed separation type extractive distillation energy-saving method, and the application range of feed separation type extractive distillation is expanded.

Description

Technical Field

[0001] The present invention specifically relates to a feed separation type vapor-liquid coupling extraction distillation process. Background Art

[0002] Extractive distillation can change the relative volatility between the components to be separated by adding a solvent, and is usually used to separate azeotropic components or near-azeotropic components. For dilute solutions, a three-column extractive distillation sequence is usually used, including a pre-fractionation column, an extractive distillation column, and a solvent recovery column. At present, the energy-saving methods for extractive distillation include heat integration, heat pump distillation, sidestream withdrawal, vapor-liquid coupling, feed separation, etc. For example, Patent CN 113214038 B proposes a method for separating benzene-n-propanol-water mixture by heat pump extractive distillation. Patent CN 107501085 A proposes a method for separating acetic acid and water mixture by double-effect heat-integrated extractive distillation. Patent CN110885283 A proposes an energy-saving process for separating ethyl acetate-ethanol by heat-integrated extractive distillation with sidestream withdrawal.

[0003] The literature "Comparison of heterogeneous azeotropic distillation and energy-saving extractive distillation for separating the acetonitrile-water mixtures" proposed an energy-saving extractive distillation process with vapor-liquid coupling. The steam at the top of the solvent recovery column was used as the direct steam heating source at the bottom of the pre-fractionation column. Part of the liquid product withdrawn from the bottom of the pre-fractionation column was used as the reflux of the solvent recovery column. Through such a vapor-liquid connection, the pre-fractionation column and the solvent recovery column were vapor-liquid coupled, thus saving a large amount of energy consumption and heat exchanger costs. The literature "Novel energy-saving methods to improve the three-column extractive distillation process for separating ethyl acetate and ethanol using furfural" proposed another energy-saving extractive distillation process with vapor-liquid coupling. The steam at the top of the extractive distillation column was used as the direct steam heating source at the bottom of the pre-fractionation column. Part of the liquid product withdrawn from the bottom of the pre-fractionation column was used as the reflux of the extractive distillation column. Through such a vapor-liquid connection, the pre-fractionation column and the extractive distillation column were vapor-liquid coupled, thus saving a large amount of energy consumption and heat exchanger costs. The literature "Process improvement for three-column extractive distillation by feed split" proposed a feed split type extractive distillation, which saved energy consumption and equipment costs by feeding the components to be separated into the pre-fractionation column and the extractive distillation column respectively. These energy-saving methods can all reduce the energy consumption and costs of extractive distillation.

[0004] However, the application range of the feed split type extractive distillation is limited. Under specific feed conditions, such as the systems of isopropanol-water-DMSO, acetonitrile-water-ethylene glycol, methanol-acetone-water, etc., the method of feed split cannot be used to save energy. For the highly energy-saving process of vapor-liquid coupling type extractive distillation, there is still potential to further reduce energy consumption, but it is more difficult to continue saving energy. Therefore, we propose a feed split type vapor-liquid coupling type extractive distillation process. Summary of the Invention

[0005] The purpose of the present invention is to provide a feed split type vapor-liquid coupling type extractive distillation process to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: A feed separation type vapor-liquid coupling type extractive distillation process. The vapor-liquid coupling type extractive distillation device of this process includes: a pre-fractionating tower, an extractive distillation tower, and a solvent recovery tower;

[0007] The vapor-liquid coupling type extractive distillation process includes the following steps:

[0008] Two first mixtures are transported from the raw material tank. One is transported to the pre-fractionating tower, and the other is transported to the extractive distillation tower. The azeotropic mixture obtained at the top of the pre-fractionating tower is transported to the extractive distillation tower. At the same time, the solvent is added to the extractive distillation tower through a pipeline. The second mixture obtained in the extractive distillation tower is transported to the solvent recovery tower, and the solvent obtained in the solvent recovery tower is recycled to the extractive distillation tower for reuse;

[0009] Wherein, a part of the first distillation product in the first mixture obtained at the bottom of the pre-fractionating tower is transported to the extractive distillation tower or the solvent recovery tower as reflux;

[0010] The gaseous material obtained in the extractive distillation tower or the solvent recovery tower is transported to the pre-fractionating tower as steam heat source.

[0011] Preferably, the gaseous material obtained at the top of the solvent recovery tower is transported to the bottom of the pre-fractionating tower as a direct steam heat source.

[0012] Preferably, a part of the first distillation product in the first mixture obtained at the bottom of the pre-fractionating tower is transported to the solvent recovery tower as reflux, and the remaining part is taken out through a pipeline. The second distillation product in the first mixture is obtained at the top of the extractive distillation tower.

[0013] Preferably, the solvent obtained at the bottom of the solvent recovery tower is cooled and then sent into the extractive distillation tower for recycling.

[0014] Preferably, the gaseous material obtained at the top of the extractive distillation tower is transported to the bottom of the pre-fractionating tower as a direct steam heat source.

[0015] Preferably, a part of the first distillation product in the first mixture obtained at the bottom of the pre-fractionating tower is transported to the extractive distillation tower as reflux, and the remaining part is taken out through a pipeline. The second distillation product in the first mixture is obtained at the top of the solvent recovery tower.

[0016] Preferably, the solvent added to the extractive distillation tower is the solvent recovered by the solvent recovery tower and the newly added solvent.

[0017] Preferably, a condenser is installed on the pre-fractionating tower, and a reboiler is installed in the extractive distillation tower or the solvent recovery tower.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] The feed separation type vapor-liquid coupling extraction distillation process of the present invention is more energy-saving. Under some conditions, an intermediate reboiler can be saved, and it is also applicable to systems where the energy-saving method of feed separation type extraction distillation is not applicable, expanding the application range of feed separation type extraction distillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of the present invention;

[0021] Figure 2 is a schematic structural diagram of the present invention.

[0022] In the figure: 1, pre-fractionation tower; 2, extractive distillation tower; 3, solvent recovery tower. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Please refer to Figure 1 , Figure 2 , the present invention provides a technical solution: a feed separation type vapor-liquid coupling extraction distillation process, and the vapor-liquid coupling extraction distillation device of this process includes: a pre-fractionation tower 1, an extractive distillation tower 2 and a solvent recovery tower 3;

[0025] The vapor-liquid coupling extraction distillation process includes the following steps:

[0026] Two first mixtures are transported from the raw material tank, one is transported to the pre-fractionation tower 1, and the other is transported to the extractive distillation tower 2. The azeotropic mixture obtained at the top of the pre-fractionation tower 1 is transported to the extractive distillation tower 2. At the same time, the solvent is added to the extractive distillation tower 2 through a pipeline. The second mixture obtained in the extractive distillation tower 2 is transported to the solvent recovery tower 3, and the solvent obtained in the solvent recovery tower 3 is recovered to the extractive distillation tower 2 for recycling;

[0027] Among them, a part of the first distillation product in the first mixture obtained at the bottom of the pre-fractionation tower 1 is transported to the extractive distillation tower 2 or the solvent recovery tower 3 as reflux;

[0028] The gas-phase material obtained in the extractive distillation tower 2 or the solvent recovery tower 3 is transported to the pre-fractionation tower 1 as steam heat source.

[0029] Preferably, the gas-phase material obtained at the top of the solvent recovery tower 3 is transported to the bottom of the pre-fractionation tower 1 as a direct steam heat source.

[0030] Preferably, a part of the first rectification product in the first mixture obtained at the bottom of the pre-fractionation column 1 is transported to the solvent recovery column 3 as reflux, and the remaining part is withdrawn through a pipeline. The second rectification product in the first mixture is obtained at the top of the extractive distillation column 2.

[0031] Preferably, the solvent is obtained at the bottom of the solvent recovery column 3, cooled and then sent into the extractive distillation column 2 for recycling.

[0032] Preferably, the gas-phase material obtained at the top of the extractive distillation column 2 is transported to the bottom of the pre-fractionation column 1 as a direct steam heat source.

[0033] Preferably, a part of the first rectification product in the first mixture obtained at the bottom of the pre-fractionation column 1 is transported to the extractive distillation column 2 as reflux, and the remaining part is withdrawn through a pipeline. The second rectification product in the first mixture is obtained at the top of the solvent recovery column 3.

[0034] Preferably, the solvent added to the extractive distillation column 2 is the solvent recovered by the solvent recovery column 3 and the newly added solvent.

[0035] Preferably, a condenser is installed in the pre-fractionation column 1, and a reboiler is installed in the extractive distillation column 2 or the solvent recovery column 3.

[0036] The working principle and usage process of the present invention:

[0037] In the present invention, as Figure 1 shown, T1 is the pre-fractionation column, T2 is the extractive distillation column, and T3 is the solvent recovery column. A condenser is installed in the T1 column, a condenser and a reboiler are installed in the T2 column, and a reboiler is installed in the T3 column. The technological process of this method is as follows: The raw materials (a mixture of A and B, logistics AB) are respectively transported from the raw material tank to the appropriate positions of T1 and T2. In T1, the raw material (F-1) is fed from an appropriate position of the column; the mixture of AB (M-AB) is obtained at the top of the column and transported to T2; a certain product A in the raw material is obtained at the bottom of the column, part of which is withdrawn as the product logistics (logistics A), and part of which is transported to T3 as the top reflux of T3. In T2, the solvent (logistics F-S) is fed from a suitable position in the upper part of the column, the M-AB logistics is fed at the feed port below the solvent, and the raw material F-2 is fed at the feed port below the M-AB logistics; the product B (logistics B) is obtained at the top of the column; the mixture of the solvent and the raw material A (logistics M-BS) is obtained at the bottom of the column and transported to T3. In T3, the gaseous phase of product A is obtained at the top of the column and all is fed as a direct heating heat source to the bottom of T1; the solvent with higher purity (logistics S) is obtained at the bottom of the column, cooled by a cooler (COOLER) and then supplemented with part of the fresh solvent (logistics S-MAKEUP) and then transported to the upper feed port of T2.

[0038] In the present invention, as Figure 2As shown in the figure, T1 is the pre-fractionating column, T2 is the extractive distillation column, and T3 is the solvent recovery column. A condenser is installed in T1 column, a reboiler is installed in T2 column, and a condenser and a reboiler are installed in T3 column. The technological process of this method is as follows: The raw materials (a mixture of A and B, stream AB) are respectively transported from the raw material tank to the appropriate positions of T1 and T2. In T1, the raw material (F-1) is fed from the appropriate position of the column; the mixture of AB (M-AB) is obtained at the top of the column and transported to T2; a certain product A in the raw material is obtained at the bottom of the column, part of which is taken out as the product stream (stream A), and part of which is transported to T2 as the top reflux of T2. In T2, the solvent (stream F-S) is fed from a suitable position in the upper part of the column, the M-AB stream is fed at the feed inlet below the solvent, and the raw material F-2 is fed at the feed inlet above the M-AB stream; the vapor-phase extraction of product A is obtained at the top of the column, and all of it is fed as the direct heating heat source to the bottom of T1; the mixture of the solvent and raw material B (stream M-BS) is obtained at the bottom of the column and transported to T3. In T3, product B (stream B) is obtained at the top of the column; a solvent with higher purity (stream S) is obtained at the bottom of the column, cooled by a cooler (COOLER), and then supplemented with part of the fresh solvent (stream S-MAKEUP) and transported to the upper feed inlet of T2.

[0039] Vapor-liquid coupled extractive distillation is actually the recovery and reuse of the partial latent heat of the gas phase. The feed separation affects the distribution of the heat loads of the three columns by distributing the feeds of the two columns. If it is not combined with vapor-liquid coupling, only the energy is saved by affecting the loads of the three reboilers. However, when combined with vapor-liquid coupling, the latent heat to be recovered can be increased on the basis of saving energy by affecting the loads of the three reboilers, thus producing a better energy-saving effect and better economic benefits.

[0040] Effect Example 1:

[0041] Dimethyl sulfoxide is used as the solvent for the extractive distillation to separate isopropanol and water.

[0042] In this effect example, dimethyl sulfoxide is used as the solvent to extract and distillate to separate isopropanol and water by the feed separation type vapor-liquid coupled extractive distillation process. The specific technological process is as Figure 1 shown. In this effect example, the mole fraction of isopropanol in the feed composition is 0.1 - 0.3, the mole fraction of water is 0.7 - 0.9, the number of theoretical plates of the pre-fractionating column is 5 - 10, the feed position is 3 - 6, the operating pressure is atmospheric pressure, the reflux ratio is 0 - 0.1, the top temperature of the column is 75 - 85 °C, the bottom temperature of the column is 95 - 105 °C, the total feed amount of the raw materials is 200 - 300 kmol / h, and water (component A) with a mole purity of 0.999 - 0.9999 is taken out at the bottom of the column, part of which is taken out as the product, and part of which is used as the top reflux of the solvent recovery column.

[0043] The number of theoretical plates of the extractive distillation column is 44 - 55, and the feed positions are 3 - 6, 35 - 42, 43 - 46 (wherein, the solvent feed port position is 3 - 6; the raw material feed position is 43 - 46; the feed position of the overhead product stream from the pre - fractionation column is 35 - 42). The operating pressure is atmospheric pressure, the reflux ratio is 0.5 - 1, the overhead temperature is 80 - 85 °C, the bottom temperature is 130 - 135 °C, the raw material feed rate is 40 - 50 kmol / h, and the overhead product is isopropanol product (Component B) with a molar purity of 0.999 - 0.9999.

[0044] The number of theoretical plates of the solvent recovery column is 12 - 15, the feed position is 4 - 7, the operating pressure is 120 - 150 kPa, the reflux ratio is 0.1 - 0.3, the overhead temperature is 100 - 110 °C, the bottom temperature is 195 - 205 °C. The overhead product is steam (Component A) with a molar purity of 0.999 - 0.9999, which is all sent to the bottom of the pre - fractionation column as a direct heat source. The solvent recovered from the bottom of the column has a molar purity of 0.99999. After the solvent recovered from the bottom of the column is cooled by a solvent cooler, it is recycled back to the extractive distillation column together with the make - up solvent through the solvent feed port of the extractive distillation column.

[0045] This example can save 4 - 8% energy compared with the original vapor - liquid coupling process; under the same conditions of the original feed separation technology, there is no energy - saving effect for this system, but on the basis of the vapor - liquid coupling technology, the feed separation technology can be used for further energy - saving; in addition, a reboiler of the pre - fractionation column can be omitted.

[0046] Example 2 of the effect:

[0047] Using furfural as the solvent to separate ethyl acetate and ethanol.

[0048] In this example, furfural is used as the solvent to extractively distill and separate ethyl acetate and ethanol by the feed - separation type heat - integrated extractive distillation process. The specific process is as Figure 2 shown. In this example, the mole fraction of ethyl acetate in the feed composition is 0.1 - 0.3, and the mole fraction of ethanol is 0.7 - 0.9. The number of theoretical plates of the pre - fractionation column is 13 - 20, the feed position is 3 - 8, the operating pressure is 40 - 60 kPa, the reflux ratio is 0.5 - 1.5, the overhead temperature is 50 - 60 °C, the bottom temperature is 55 - 65 °C, the raw material feed rate is 200 - 300 kmol / h. The ethanol (Component A) recovered from the bottom of the column has a molar purity of 0.99 - 0.995, part of which is taken out as the product, and part of which is used as the reflux at the top of the solvent recovery column.

[0049] The number of theoretical plates of the extractive distillation column is 60 - 70, and the feed positions are 4 - 8, 35 - 45, 50 - 60 (wherein, the solvent feed port position is 4 - 8; the raw material feed position is 35 - 45; the feed position of the overhead product of the pre-fractionation column is 50 - 60). The operating pressure is 200 - 300 kPa, the reflux ratio is 0.1 - 1, the overhead temperature is 95 - 110 °C, the bottom temperature is 145 - 160 °C, the raw material feed rate is 20 - 50 kmol / h, and ethanol (component A) with a molar purity of 0.99 - 0.995 is taken as the overhead product, which is all sent to the bottom of the pre-fractionation column as a direct heat source.

[0050] The number of theoretical plates of the solvent recovery column is 18 - 25, the feed position is 6 - 10, the operating pressure is 40 - 80 kPa, the reflux ratio is 0.1 - 1, the overhead temperature is 55 - 65 °C, the bottom temperature is 140 - 150 °C, ethyl acetate (component B) with a molar purity of 0.99 - 0.995 is taken as the overhead product, and furfural with a molar purity of 0.99999 is taken from the bottom of the column. The furfural taken from the bottom of the column is recycled back to the extractive distillation column together with the supplementary solvent.

[0051] In the literature, the TAC (total annual cost) of the original vapor-liquid coupling column technology was 2462 k$ / y under the conditions of a total feed flow rate of 300 kmol / h and a molar fraction of ethyl acetate in the feed of 0.25. The TAC of this example of the effect is 2404 k$ / y, which can save 2.4%. Under the same conditions, the original feed separation technology in the literature can save 2.3%. This example of the effect saves more, so it is considered that the coupling effect of the two methods is better.

[0052] Although the embodiments and examples of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A feed separation type vapor-liquid coupling extraction and distillation process, characterized in that, The vapor-liquid coupling extractive distillation device of this process includes: a pre-fractionating column (1), an extractive distillation column (2), and a solvent recovery column (3); The vapor-liquid coupling extractive distillation process comprises the following steps: Two first mixtures are transported from the raw material tank, one is transported to the pre-fractionating column (1), and the other is transported to the extractive distillation column (2). The azeotropic mixture obtained at the top of the pre-fractionating column (1) is transported to the extractive distillation column (2). Meanwhile, the solvent is added to the extractive distillation column (2) through a pipeline. The second mixture obtained in the extractive distillation column (2) is transported to the solvent recovery column (3). The solvent obtained in the solvent recovery column (3) is recovered to the extractive distillation column (2) for recycling; Among them, a part of the first rectification product in the first mixture obtained at the bottom of the pre-fractionating column (1) is transported to the extractive distillation column (2) or the solvent recovery column (3) as reflux; The gaseous material obtained in the extractive distillation column (2) or the solvent recovery column (3) is transported to the pre-fractionating column (1) as a steam heat source.

2. The feed separation type vapor-liquid coupling extraction distillation process according to claim 1, characterized in that: The gaseous material obtained at the top of the solvent recovery column (3) is transported to the bottom of the pre-fractionating column (1) as a direct steam heat source.

3. The feed separation type vapor-liquid coupling extractive distillation process according to claim 2, characterized in that: A part of the first rectification product in the first mixture obtained at the bottom of the pre-fractionating column (1) is transported to the solvent recovery column (3) as reflux, and the remaining part is taken out through a pipeline. The second rectification product in the first mixture is obtained at the top of the extractive distillation column (2).

4. The feed separation type vapor-liquid coupling extractive distillation process according to claim 1, characterized in that: The solvent is obtained at the bottom of the solvent recovery column (3), and after being cooled, it is sent into the extractive distillation column (2) for recycling.

5. The feed separation type vapor-liquid coupling extractive distillation process according to claim 1, characterized in that: The gaseous material obtained at the top of the extractive distillation column (2) is transported to the bottom of the pre-fractionating column (1) as a direct steam heat source.

6. A feed separation type vapor-liquid coupling extractive distillation process according to claim 5, characterized in that: A part of the first rectification product in the first mixture obtained at the bottom of the pre-fractionating column (1) is transported to the extractive distillation column 2 as reflux, and the remaining part is taken out through a pipeline. The second rectification product in the first mixture is obtained at the top of the solvent recovery column (3).

7. A feed separation type vapor-liquid coupling extraction distillation process according to claim 1, characterized in that: The solvent added to the extractive distillation column (2) is the solvent recovered by the solvent recovery column (3) and the newly added solvent.

8. A feed separation type vapor-liquid coupling extractive distillation process according to claim 1, characterized in that: A condenser is installed on the pre-fractionating column (1), and a reboiler is installed in the extractive distillation column (2) or the solvent recovery column (3).

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