Feed separation coupled gas phase feed type extractive distillation process

Abstract

The invention discloses a feed separation coupling gas phase feed type extractive distillation process which 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, meanwhile, a solvent is added into the extractive distillation tower through a pipeline, and a second mixture obtained in the extractive distillation tower is conveyed to a solvent recovery tower; compared with the prior art, the feeding separation coupling gas phase feeding type extractive distillation process disclosed by the invention is more energy-saving, can save a pre-fractionating tower reboiler under specific conditions, is also suitable for a system which is not suitable for a feeding separation type extractive distillation energy-saving method, and expands the application range of feeding separation type extractive distillation.

Description

Technical Field

[0001] The present invention specifically relates to a feed separation coupled gas-phase feed extractive distillation process. Background Technique

[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. At present, the energy-saving methods of extractive distillation include thermal integration, heat pump distillation, side draw, combined column, 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 thermal integration extractive distillation.

[0003] The literature "Increasing the Energy Efficiency of Extractive Distillation" proposes an energy-saving process for extractive distillation using a partial condenser. By setting a partial condenser at the top of the solvent recovery column, a top gas-phase product is obtained and returned to the feed of the pre-fractionation column, thereby saving energy consumption and equipment costs. The literature "Novel energy-saving methods to improve the three-column extractive distillation process for separating ethyl acetate and ethanol using furfural" proposes another energy-saving process for extractive distillation using a partial condenser. By setting a partial condenser at the top of the extractive distillation column, a top gas-phase product is obtained and returned to the bottom feed of the pre-fractionation column, thereby saving energy consumption and equipment costs. The present invention collectively refers to these two methods as gas-phase feed. The literature "Process improvement for three-column extractive distillation by feed split" proposes a feed separation type extractive distillation, which saves energy consumption and equipment costs by feeding the components to be separated to 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 separation type extractive distillation is limited. Under specific feed conditions, such as systems of isopropanol-water-DMSO, acetonitrile-water-ethylene glycol, methanol-acetone-water, etc., the method of feed separation cannot be used to save energy. For the highly energy-saving process of gas-phase feed extractive distillation, there is still potential to further reduce energy consumption, but it is more difficult to continue to save energy. Therefore, we propose a feed separation coupled gas-phase feed extractive distillation process. Summary of the Invention

[0005] The purpose of the present invention is to provide a feed separation coupled gas-phase feed extractive distillation process to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A feed separation coupled gas-phase feed extractive distillation process, and the gas-phase feed extractive distillation device of this process includes: a pre-fractionation tower, an extractive distillation tower, and a solvent recovery tower;

[0007] The gas-phase feed extractive distillation process includes the following steps:

[0008] Two first mixtures are transported from the raw material tank, one is transported to the pre-fractionation tower, and the other is transported to the extractive distillation tower. The azeotropic mixture obtained at the top of the pre-fractionation 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 recovered to the extractive distillation tower for recycling;

[0009] Among them, the gas-phase material obtained in the extractive distillation tower or the solvent recovery tower is transported to the pre-fractionation tower as a steam heat source.

[0010] Preferably, the gas-phase material obtained at the top of the solvent recovery tower through a partial condenser is transported to the bottom of the pre-fractionation tower as a direct steam heat source.

[0011] Preferably, the first distillation product in the first mixture is obtained at the bottom of the pre-fractionation tower, and the second distillation product in the first mixture is obtained at the top of the extractive distillation tower.

[0012] Preferably, the solvent is obtained at the bottom of the solvent recovery tower, and after cooling, it is sent into the extractive distillation tower for recycling.

[0013] Preferably, the gas-phase material obtained at the top of the extractive distillation tower through a partial condenser is transported to the bottom of the pre-fractionation tower as a direct steam heat source.

[0014] Preferably, the first distillation product in the first mixture is obtained at the bottom of the pre-fractionation tower, and the second distillation product in the first mixture is obtained at the top of the solvent recovery tower.

[0015] Preferably, the solvent added to the extractive distillation tower is the solvent recovered by the solvent recovery tower and the newly added solvent.

[0016] Preferably, the pre-fractionation tower is equipped with a condenser and a reboiler, and the extractive distillation tower or the solvent recovery tower is equipped with a partial condenser and a reboiler.

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

[0018] The feed separation coupled gas-phase feed extractive distillation process disclosed by the present invention is more energy-saving, and is also applicable to systems for which the energy-saving method of feed separation extractive distillation is not applicable, expanding the application scope of feed separation extractive distillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of the present invention;

[0020] Figure 2 is a schematic structural diagram of the present invention.

[0021] In the figure: 1, pre-fractionating column; 2, extractive distillation column; 3, solvent recovery column. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Please refer to Figure 1 、 Figure 2 , the present invention provides a technical solution: a feed separation coupled gas-phase feed extractive distillation process, and the gas-phase feed extractive distillation device of this process includes: a pre-fractionating column 1, an extractive distillation column 2 and a solvent recovery column 3;

[0024] The gas-phase feed extractive distillation process includes the following steps:

[0025] 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. At the same time, 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, and the solvent obtained in the solvent recovery column 3 is recovered to the extractive distillation column 2 for recycling;

[0026] Among them, the gas-phase 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.

[0027] Preferably, the gas-phase material obtained at the top of the solvent recovery column 3 through the partial condenser is transported to the bottom of the pre-fractionating column 1 as a direct steam heat source.

[0028] Preferably, the first distillation product in the first mixture is obtained at the bottom of the pre-fractionating column 1, and the second distillation product in the first mixture is obtained at the top of the extractive distillation column 2.

[0029] 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.

[0030] Preferably, the gas-phase material is obtained at the top of the extractive distillation column 2 through a partial condenser and transported to the bottom of the pre-fractionation column 1 as the direct steam heat source.

[0031] Preferably, the first rectification product in the first mixture is obtained at the bottom of the pre-fractionation column 1, and the second rectification product in the first mixture is obtained at the top of the solvent recovery column 3.

[0032] 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.

[0033] Preferably, the pre-fractionation column 1 is equipped with a condenser and a reboiler, and the extractive distillation column 2 or the solvent recovery column 3 is equipped with a partial condenser and a reboiler.

[0034] Working principle and usage process of the present invention:

[0035] 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. The T1 column is equipped with a condenser and a reboiler (the reboiler can be saved by adjusting the separation ratio of the feed under the condition of relatively low energy consumption in the pre-fractionation column), the T2 column is equipped with a condenser and a reboiler, and the T3 column is equipped with a partial condenser and a reboiler. 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 a suitable 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 (logistics A) in the raw material is obtained at the bottom of the column. 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 from the feed port below the solvent, and the raw material F-2 is fed from 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 gas-phase extraction of product A is obtained at the top of the column and all fed to the bottom of T1 as the direct heating heat source; a solvent with higher purity (logistics S) is obtained at the bottom of the column, cooled by a cooler (COOLER) and then supplemented with a part of fresh solvent (logistics S-MAKEUP) and transported to the upper feed port of T2.

[0036] 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. The T1 column is equipped with a condenser and a reboiler (the reboiler can be saved by adjusting the separation ratio of the feed when the energy consumption of the pre-fractionating column is relatively low). The T2 column is equipped with a partial condenser and a reboiler. The T3 column is equipped with a condenser and a reboiler. 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; a mixture of AB (M-AB) is obtained at the top of the column and transported to T2; a certain product A (logistics A) in the raw material is obtained at the bottom of the column. 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 from the feed inlet below the solvent, and the raw material F-2 is fed from the feed inlet above the M-AB logistics; a vapor-phase draw 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; a mixture of the solvent and raw material B (logistics M-BS) is obtained at the bottom of the column and transported to T3. In T3, product B (logistics B) is obtained at the top of the column; a solvent with a higher purity (logistics S) is obtained at the bottom of the column, cooled by a cooler (COOLER), and then supplemented with a part of fresh solvent (logistics S-MAKEUP) and transported to the upper feed inlet of T2.

[0037] Vapor-phase feed extractive distillation is actually the recovery and reuse of the partial latent heat of the vapor 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 used in combination with the vapor-phase feed, energy can only be saved by affecting the loads of the three reboilers. However, when used in combination with the vapor-phase feed, the latent heat to be recovered can be increased on the basis of affecting the loads of the three reboilers, thus producing a better energy-saving effect and better economic benefits.

[0038] Effect Example 1:

[0039] In this effect example, dimethyl sulfoxide is used as the solvent to separate isopropanol and water by the process of the present invention. The specific 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 6 - 10, the feed position is 3 - 6, the operating pressure is 50 - 101.3 kPa, the reflux ratio is 0.01 - 0.1, the top temperature of the column is 60 - 81 °C, the bottom temperature of the column is 80 - 102 °C, the total feed amount of the raw materials is 200 - 300 kmol / h, and a water product (component A) with a molar purity of 0.999 - 0.9999 is drawn from the bottom of the column.

[0040] The number of theoretical plates of the extractive distillation column is 45 - 55, and the feed positions are 4 - 7, 40 - 45, 46 - 50 (wherein, the solvent feed port position is 4 - 7; the raw material feed position is 46 - 50; the feed position of the overhead product stream of the pre-fractionation column is 40 - 45), the operating pressure is 101.3 kPa, the reflux ratio is 0 - 1.5, the overhead temperature is 80 - 84 °C, the bottom temperature is 128 - 130 °C, and the overhead product is isopropanol product (Component B) with a molar purity of 0.999 - 0.9999.

[0041] The number of theoretical plates of the solvent recovery column is 13 - 18, the feed position is 4 - 8, the operating pressure is 120 - 130 kPa, the reflux ratio is 0.1 - 0.3, the overhead temperature is 105 - 120 °C, the bottom temperature is 200 - 220 °C, the overhead steam (Component A) with a molar purity of 0.999 - 0.9999 is taken out through a partial condenser and all sent to the bottom of the pre-fractionation column as a direct heat source, and the solvent with a molar purity of 0.99999 is taken out at the bottom of the column. The solvent taken out at the bottom of the column is cooled by a solvent cooler and then recycled back to the extractive distillation column together with the make-up solvent through the solvent feed port of the extractive distillation column.

[0042] This example can save 5 - 10% of energy compared with the original gas-phase feed technology; the original feed separation technology has no energy-saving effect on this system under the same conditions, but on the basis of the gas-phase feed technology, the feed separation technology can be used to save energy again; in addition, a reboiler of the pre-fractionation column can be omitted.

[0043] Example 2 of the effect:

[0044] In this example of the effect, furfural is used as the solvent in the extractive distillation process to separate ethyl acetate and ethanol by extractive distillation. The specific process is as Figure 2 shown. In this example of the effect, the molar fraction of ethyl acetate in the feed composition is 0.2 - 0.3, and the molar fraction of ethanol is 0.7 - 0.8. The number of theoretical plates of the pre-fractionation column is 15 - 23, the feed position is 6 - 10, the operating pressure is 40 - 60 kPa, the reflux ratio is 1 - 2, the overhead temperature is 40 - 53 °C, the bottom temperature is 50 - 62 °C, the raw material feed rate is 200 - 300 kmol / h, and the ethanol product (Component A) with a molar purity of 0.995 - 0.999 is taken out at the bottom of the column.

[0045] The number of theoretical plates of the extractive distillation column is 60 - 80, and the feeding positions are 5 - 9, 35 - 45, 53 - 63 respectively (wherein, the solvent feeding port position is 5 - 9; the raw material feeding position is 35 - 45; the feeding position of the overhead product of the pre - fractionation column is 53 - 63), the operating pressure is 300 - 400 kPa, the reflux ratio is 0.5 - 1.5, the overhead temperature is 111 - 120 °C, the bottom temperature is 164 - 174 °C, the raw material feeding rate is 20 - 35 kmol / h, and ethanol (component A) with a molar purity of 0.995 - 0.999 is taken out from the overhead through a partial condenser and all is sent to the bottom of the pre - fractionation column as a direct heat source.

[0046] The number of theoretical plates of the solvent recovery column is 18 - 24, the feeding position is 5 - 9, the operating pressure is 45 - 55 kPa, the reflux ratio is 0.5 - 1.5, the overhead temperature is 50 - 60 °C, the bottom temperature is 130 - 140 °C, ethyl acetate (component B) with a molar purity of 0.995 - 0.999 is taken out from the overhead, and furfural with a molar purity of 0.99999 is taken out from the bottom of the column. The furfural taken out from the bottom of the column together with the supplementary solvent is recycled back to the extractive distillation column.

[0047] This example of effect can save 4 - 6% of energy compared with the original gas - phase feeding technology; under the same conditions as the original feeding separation technology, it can save 3.3% of energy, and the energy - saving rate is higher.

[0048] Although the embodiments and examples of effects 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-coupled gas-phase feed extractive distillation process, characterized in that, The gas phase feed type extraction distillation device of the process comprises: a pre-fractionation tower (1), an extraction distillation tower (2) and a solvent recovery tower (3); The gas phase feed extractive distillation process includes the following steps: Two first mixtures are transported from a raw material tank, one of which is transported to the pre-fractionation tower (1) and the other 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); a solvent is simultaneously added to the extractive distillation tower (2) through a pipeline; the second mixture obtained in the extractive distillation tower (2) is transported to a solvent recovery tower (3); and the solvent obtained in the solvent recovery tower (3) is recovered to the extractive distillation tower (2) for recycling; The gaseous material obtained in the extractive distillation tower (2) or the solvent recovery tower (3) is transported to the pre-fractionation tower (1) to serve as a steam heat source.

2. The feed separation-coupled gas-phase feed extractive distillation process according to claim 1, wherein: The top of the solvent recovery tower (3) is passed through a partial condenser to obtain gaseous materials, which are transported to the bottom of the pre-fractionation tower (1) as a direct steam heat source.

3. The feed separation-coupled gas-phase feed extractive distillation process according to claim 2, wherein: The first distillation product in the first mixture is obtained at the bottom of the pre-fractionation tower (1), and the second distillation product in the first mixture is obtained at the top of the extractive distillation tower (2).

4. A feed separation-coupled gas-phase feed extractive distillation process according to claim 1, characterized in that: The solvent is obtained in the bottom of the solvent recovery tower (3), and after cooling, is sent to the extraction distillation tower (2) for recycling.

5. A feed separation-coupled gas-phase feed extractive distillation process according to claim 1, characterized in that: The top of the extractive distillation tower (2) is passed through a partial condenser to obtain gaseous materials, which are transported to the bottom of the pre-fractionation tower (1) as a direct steam heat source.

6. The extractive distillation process of a feed separation coupling gas-phase feed according to claim 5, characterized in that: The first distillation product in the first mixture is obtained at the bottom of the pre-fractionation tower (1), and the second distillation product in the first mixture is obtained at the top of the solvent recovery tower (3).

7. A feed separation-coupled gas-phase feed extractive distillation process according to claim 1, wherein: The solvent added to the extractive distillation tower (2) is the solvent recovered by the solvent recovery tower (3) and the newly added solvent.

8. The feed separation coupled gas-phase feed extractive distillation process according to claim 1, characterized in that: The pre-fractionation tower (1) is equipped with a condenser and a reboiler, and the extractive distillation tower (2) or the solvent recovery tower (3) is equipped with a decondenser and a reboiler.

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