Feed separation type combined tower extractive distillation method

Abstract

The invention relates to the technical field of extractive distillation separation, and provides a feed separation type combined tower extractive distillation method. The method comprises two forms, one form is that one combined tower is matched with one extractive distillation tower, and the other form is that one combined tower is matched with one solvent recovery tower. By reasonably distributing feeding positions and accurately regulating and controlling operation parameters of each tower, high-efficiency separation of a mixture is realized; compared with the prior art, the energy-saving effect is remarkably improved, and an intermediate reboiler can be saved under specific conditions; especially, the method breaks through the traditional limitation, and can also effectively play a role in the systems such as an isopropanol-water-DMSO system, an acetonitrile-water-ethylene glycol system and the like which cannot be applied by the existing feed separation type extractive distillation energy-saving method, so that the application range of feed separation type extractive distillation is greatly expanded, and the method is suitable for industrial production. The method has remarkable technical advantages and economic value.

Description

Technical Field

[0001] The present invention relates to the technical field of extractive distillation separation, and particularly relates to an extractive distillation method for a feed separation type combined tower. Background Technique

[0002] Extractive distillation is to change the relative volatility between 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 heat integration, heat pump distillation, sidestream withdrawal, combined tower, 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 method for separating ethyl acetate-ethanol by heat integrated extractive distillation with sidestream withdrawal. In addition, a variety of combined extractive distillation energy-saving methods have been proposed in the literature, such as reducing energy consumption and equipment costs by combining a pre-fractionation tower and a solvent recovery tower or an extractive distillation tower; 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 tower and the extractive distillation tower respectively.

[0003] However, the application range of feed separation type extractive distillation is limited. Especially when dealing with certain specific systems (such as isopropanol-water-DMSO, acetonitrile-water-ethylene glycol, methanol-acetone-water, etc.), the energy-saving effect cannot be achieved. In addition, although the combined tower extractive distillation method already has a high energy-saving efficiency, there are still great challenges in further reducing energy consumption on the existing basis. Summary of the Invention

[0004] To solve the technical problems existing in the background technique, the present invention proposes an extractive distillation method for a feed separation type combined tower to solve the problems of limited application range of feed separation type extractive distillation and difficulty in further energy saving of combined tower extractive distillation in the prior art, achieve a more energy-saving effect, and expand the application range of feed separation type extractive distillation.

[0005] An extractive distillation method for a feed separation type combined tower proposed by the present invention:

[0006] The first form: a combined tower is paired with an extractive distillation tower

[0007] Feeding step:

[0008] Two streams of the mixture to be separated are led out from the raw material tank, one is sent to a predetermined feeding position at the upper part of the combined tower, and the other is sent to a predetermined feeding position of the extractive distillation column;

[0009] Separation steps of the combined tower:

[0010] In the combined tower, the operating parameters are adjusted and controlled. An azeotropic mixture is obtained at the top of the tower and sent to the extractive distillation column; the first target product in the raw material is separated at a specific position in the middle of the combined tower; the solvent is obtained at the bottom of the tower, and after being cooled by a solvent cooler, it is sent to the extractive distillation column for recycling;

[0011] Separation steps of the extractive distillation column:

[0012] In the extractive distillation column, the solvent is fed from a preset position at the upper part of the tower, the azeotropic mixture is fed from a preset position below the solvent feeding position, and the raw material mixture is fed below the azeotropic mixture feeding position; by adjusting and controlling the operating parameters, the second target product is obtained at the top of the tower, and a mixture of the solvent and the third target product is obtained at the bottom of the tower, and this mixture is sent back to a specific position at the lower part of the combined tower.

[0013] The operating parameters of the combined tower, including the number of theoretical plates, feeding position, operating pressure, reflux ratio, reboiler heat load, top temperature, bottom temperature, and raw material feeding rate, are adjusted according to the characteristics of the system to be separated and the separation requirements;

[0014] The operating parameters of the extractive distillation column, including the number of theoretical plates, feeding position, operating pressure, reflux ratio, reboiler heat load, top temperature, bottom temperature, and raw material feeding rate, are also adjusted according to the characteristics of the system to be separated and the separation requirements.

[0015] The second form: One combined tower is paired with one solvent recovery tower

[0016] Feeding steps:

[0017] Two streams of the mixture to be separated are transported from the raw material tank, one is transported to a predetermined feeding position at the upper part of the combined tower, and the other is transported to a predetermined position at the lower part of the combined tower;

[0018] Separation steps of the combined tower:

[0019] In the combined tower, the solvent is fed from a preset position at the lower part of the tower. By adjusting and controlling the operating parameters, the azeotropic mixture is withdrawn from the top of the tower and returned to the predetermined feeding position of the combined tower; the first target product in the raw material is separated at a specific position in the middle of the combined tower; a mixture of the solvent and the second target product is obtained at the bottom of the tower, and this mixture is transported to the predetermined feeding position of the solvent recovery tower.

[0020] Separation steps of the solvent recovery tower:

[0021] In the solvent recovery column, by adjusting the operating parameters, the second target product is obtained at the top of the column, and the solvent is obtained at the bottom of the column. The solvent is cooled by a solvent cooler and then sent to a combination column for recycling.

[0022] The operating parameters of the combination column, including the number of theoretical plates, feed location, operating pressure, reflux ratio, reboiler heat load, condenser heat load, top temperature, bottom temperature, and raw material feed rate, are adjusted according to the characteristics and separation requirements of the material system to be separated.

[0023] The operating parameters of the solvent recovery column, including the number of theoretical plates, feed location, operating pressure, reflux ratio, reboiler heat load, condenser heat load, top temperature, and bottom temperature, are adjusted according to the characteristics and separation requirements of the material system to be separated.

[0024] Preferably, the method is applicable to material systems that are not applicable to the existing energy-saving methods of extractive distillation with feed separation, including the isopropanol-water-DMSO system, the acetonitrile-water-ethylene glycol system, and the methanol-acetone-water system.

[0025] In the present invention, an extractive distillation method with a feed separation type combination column is proposed. Compared with the prior art, the extractive distillation method with a feed separation type combination column of the present invention has significant beneficial effects. This method is more energy-saving and can save an intermediate reboiler under certain conditions. At the same time, it is also applicable to material systems that are not applicable to the energy-saving methods of extractive distillation with feed separation, greatly expanding the application range of extractive distillation with feed separation.

[0026] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Description of the Drawings

[0027] Figure 1 It is a process flow diagram of the method for combining a combination column with an extractive distillation column in the present invention;

[0028] Figure 2 It is a process flow diagram of the method for combining a combination column with a solvent recovery column in the present invention. Detailed Description of the Invention

[0029] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar symbols represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as limiting the present invention.

[0030] As Figure 1 - Figure 2 shown, an extractive distillation method with a feed separation type combination column

[0031] First aspect: Embodiment of a combined tower with an extractive distillation column:

[0032] The extractive distillation method includes a combined tower and an extractive distillation column; the process of the method is as follows: Two mixtures are conveyed from a raw material tank, one is conveyed to a suitable feeding position at the upper part of the combined tower, and the other is conveyed to a suitable feeding position of the extractive distillation column; In the combined tower, through parameter adjustment, an azeotropic mixture is obtained at the top of the tower and conveyed to the extractive distillation column, a certain product in the raw material is obtained at a certain position in the middle of the tower, and the solvent is obtained at the bottom of the tower. After passing through the solvent cooler, it is sent to the extractive distillation column for recycling; In the extractive distillation column, the solvent is fed from a suitable position at the upper part of the tower, the azeotropic mixture is fed at a suitable position below the solvent, and the raw material mixture is fed below the azeotropic mixture. Through parameter adjustment, a certain product is obtained at the top of the tower, and a mixture of the solvent and another product is obtained at the bottom of the tower, which is conveyed back to a certain position at the lower part of the combined tower.

[0033] Figure 1 In the figure, T1 is the combined tower, T2 is the extractive distillation column. The T1 tower is equipped with a condenser, a reboiler and an intermediate reboiler (M-REB), and the T2 tower is equipped with a condenser and a reboiler. The process of this method is as follows: The raw materials (a mixture of A and B, stream AB) are respectively conveyed from the raw material tank to the suitable positions of T1 and T2. In T1, the raw material (F-1) is fed from a suitable position at the upper part of the tower; The mixture of AB (M-AB) is obtained at the top of the tower and conveyed to T2; A certain product A (stream A) in the raw material is obtained by side stream withdrawal in the middle of the tower; The solvent with higher purity (stream S) is obtained at the bottom of the tower. After being cooled by the cooler (COOLER) and supplemented with some fresh solvent, it is conveyed to the upper feeding port of T2. In T2, the solvent (stream F-S) is fed from a suitable position at the upper part of the tower, the M-AB stream is fed at the feeding port below the solvent, and the raw material F-2 is fed at the feeding port below the M-AB stream; Product B (stream B) is obtained at the top of the tower; A mixture of the solvent and raw material A (stream M-AS) is obtained at the bottom of the tower, which is conveyed to the feeding port below the side stream withdrawal of T1.

[0034] Second aspect: Embodiment of a combined tower with a solvent recovery tower:

[0035] The method includes a combined tower and a solvent recovery tower. The process of the method is as follows: Two mixtures are conveyed from a raw material tank, one is conveyed to a suitable feeding position at the upper part of the combined tower, and the other is conveyed to a suitable position at the lower part of the combined tower; In the combined tower, the solvent is fed from a suitable position at the lower part of the tower. Through parameter adjustment, the azeotropic mixture is withdrawn from the top of the tower and returned to a suitable position for feeding in the combined tower. A certain product in the raw material is obtained at a certain position in the middle of the tower, and a mixture of the solvent and another product is obtained at the bottom of the tower, which is conveyed to a suitable position of the solvent recovery tower; In the solvent recovery tower, through parameter adjustment, another product is obtained at the top of the tower, and the solvent is obtained at the bottom of the tower. After passing through the solvent cooler, it is sent to the combined tower for recycling.

[0036] Figure 2 Among them, T1 is a combined tower, T2 is a solvent recovery tower. T1 tower is equipped with a condenser and a reboiler, and T2 tower is equipped with a condenser and a reboiler. The process flow 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 two appropriate positions of T1. In T1, the raw material F-1 is fed from a suitable position in the upper part of the tower, the raw material F-2 is fed from a suitable position in the lower part of the tower, and the solvent is fed from a suitable position between F-1 and F-2; a mixture of AB (M-AB) is obtained at the top of the tower and is circulated and transported to a position below the feed of F-2 in T1; a certain product A (logistics A) in the raw material is taken out from the side line in the middle of the tower; a mixture of the solvent and raw material A (logistics M-AS) is obtained at the bottom of the tower and is transported to T2; in T2, the logistics M-BS is fed from a certain appropriate position; product B (logistics B) is obtained at the top of the tower; a solvent with higher purity (logistics S) is obtained at the bottom of the tower, cooled by a cooler (COOLER), and then after supplementing part of the fresh solvent, it is transported to T1.

[0037] Example 1: Extractive distillation separation of isopropanol and water using dimethyl sulfoxide as a solvent

[0038] In this example, dimethyl sulfoxide is used as a solvent to extract and distillate the separation of isopropanol and water by the feed separation type combined tower extraction distillation method. The specific method process is as Figure 1 shown. In this 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 combined tower is 20 - 30, the feed positions are (2 - 5, 10 - 15), where the feed position of the raw material F-1 is 2 - 5, and the feed position of the water and solvent mixture is 10 - 15. The operating pressure is 50 - 101.3 kPa, the reflux ratio is 0.001 - 0.1, the top temperature of the tower is 60 - 80 °C, the bottom temperature of the tower is 190 - 210 °C, the raw material feed rate is 200 - 300 kmol / h, the side line extraction position in the middle of the tower is 3 - 9, and water (component A) with a molar purity of 0.999 - 0.9999 is obtained.

[0039] The number of theoretical plates of the extractive distillation tower is 45 - 55, and the feed positions are 3 - 8, 35 - 42, 43 - 48 respectively (where the solvent feed port position is 3 - 8; the feed position of the overhead product stream of the pre-fractionation tower is 35 - 42; the raw material feed position is 43 - 48). The operating pressure is 50 - 101.3 kPa, the reflux ratio is 0.1 - 1, the top temperature of the tower is 65 - 85 °C, the bottom temperature of the tower is 112 - 132 °C, the raw material feed rate is 40 - 70 kmol / h, and isopropanol (component B) with a molar purity of 0.999 - 0.9999 is obtained at the top of the tower.

[0040] In the original combined tower technology in the literature, the mole fraction of isopropanol in the feed composition is 0.2, and the energy consumption is 2850.3 kW under the condition of a feed flow rate of 250 kmol / h. The energy consumption of this example under the same feed conditions and the same product composition is 2263.8 kW, with an energy saving of 21%; the original feed separation technology has no energy-saving effect on this system under the same feed conditions, but the feed separation technology can be used on the basis of the combined tower technology to save energy; in addition, an intermediate reboiler of a combined tower is also omitted.

[0041] Example 2: Using furfural as a solvent to separate ethyl acetate and ethanol

[0042] In this example, furfural is used as a solvent, and the extractive distillation method of a feed separation type combined tower is used to extract and distillate ethyl acetate and ethanol. The specific method process is as Figure 2 shown. In this example, the mole fraction of ethyl acetate in the feed composition is 0.2 - 0.3, and the mole fraction of ethanol is 0.7 - 0.8. The number of theoretical plates of the combined tower is 65 - 80, and the feed positions are 5 - 10, 20 - 30, 40 - 45, 50 - 60 respectively (where the feed port of F-1 raw material is 5 - 10, and the solvent feed port position is 20 - 30; the feed position of F-2 raw material is 40 - 45; the recycle feed position at the top of the tower is 50 - 60). The operating pressure is 40 - 60 kPa, the reflux ratio is 11 - 2, the top temperature of the tower is 40 - 60 °C, the bottom temperature of the tower is 90 - 110 °C, the raw material feed amount of F-1 is 200 - 300 kmol / h, F-2 is 20 - 60 kmol / h, and the middle side draw position of the tower is 15 - 25, obtaining ethanol (component A) with a molar purity of 0.995 - 0.999.

[0043] The number of theoretical plates of the solvent recovery tower is 15 - 25, the feed position is 5 - 9, the operating pressure is 40 - 60 kPa, the reflux ratio is 0.1 - 1, the top temperature of the tower is 50 - 60 °C, the bottom temperature of the tower is 130 - 140 °C, the top draw has a molar purity of 0.995 - 0.999 of ethyl acetate (component B), the bottom draw has a molar purity of 0.99999 of furfural, and the furfural drawn from the bottom of the tower together with the supplementary solvent is recycled back to the extractive distillation tower.

[0044] In the original combined tower technology in the literature, the mole fraction of ethyl acetate in the feed composition is 0.25, and the energy consumption is 7176.6 kW under the condition of a feed flow rate of 300 kmol / h. The energy consumption of this example under the same feed conditions and the same product composition is 4030 kW, with an energy saving of 44%; in the original feed separation technology, when the mole fraction of ethyl acetate in the feed composition is 0.25 and the feed flow rate is 300 kmol / h, the energy consumption is 5971 kW, and the energy consumption without feed separation is 6176 kW, and the energy saving rate is only 3.3%. In addition, an intermediate reboiler of a combined tower is omitted.

[0045] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

[0046] As mentioned above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent replacements or changes, and should be covered within the protection scope of the present invention.

Claims

1. A combined extraction and rectification method for a feed separation type combined tower, characterized in that It includes a combined tower and an extractive distillation tower. The specific method steps are as follows: Feeding step: Two streams of the mixture to be separated are led out from the raw material tank. One stream is sent to a predetermined feeding position at the upper part of the combined tower, and the other stream is sent to a predetermined feeding position of the extractive distillation tower. Separation step of the combined tower: In the combined tower, the operating parameters are adjusted and controlled. An azeotropic mixture is obtained at the top of the tower and sent to the extractive distillation tower. The first target product in the raw material is separated at a specific position in the middle of the combined tower. The solvent is obtained at the bottom of the tower. After being cooled by a solvent cooler, the solvent is sent to the extractive distillation tower for recycling. Separation step of the extractive distillation tower: In the extractive distillation tower, the solvent is fed from a preset position at the upper part of the tower, the azeotropic mixture is fed from a preset position below the solvent feeding position, and the raw material mixture is fed below the azeotropic mixture feeding position. By adjusting and controlling the operating parameters, the second target product is obtained at the top of the tower, and a mixture of the solvent and the third target product is obtained at the bottom of the tower. This mixture is sent back to a specific position at the lower part of the combined tower.

2. The extractive distillation method of the feed separation combined tower according to claim 1, wherein The operating parameters of the combined tower, including the number of theoretical plates, feeding position, operating pressure, reflux ratio, reboiler heat load, top temperature of the tower, bottom temperature of the tower, and raw material feeding rate, are adjusted according to the characteristics of the system to be separated and the separation requirements. The operating parameters of the extractive distillation tower, including the number of theoretical plates, feeding position, operating pressure, reflux ratio, reboiler heat load, top temperature of the tower, bottom temperature of the tower, and raw material feeding rate, are also adjusted according to the characteristics of the system to be separated and the separation requirements.

3. A method for extractive distillation in a feed separation type combined tower, characterized in that, It includes a combined tower and a solvent recovery tower. The specific method steps are as follows: Feeding step: Two streams of the mixture to be separated are transported from the raw material tank. One stream is transported to a predetermined feeding position at the upper part of the combined tower, and the other stream is transported to a predetermined position at the lower part of the combined tower. Separation step of the combined tower: In the combined tower, the solvent is fed from a preset position at the lower part of the tower. By adjusting and controlling the operating parameters, the azeotropic mixture is taken out at the top of the tower and returned to the predetermined feeding position of the combined tower. The first target product in the raw material is separated at a specific position in the middle of the combined tower. A mixture of the solvent and the second target product is obtained at the bottom of the tower and sent to the predetermined feeding position of the solvent recovery tower. Separation step of the solvent recovery tower: In the solvent recovery tower, by adjusting and controlling the operating parameters, the second target product is obtained at the top of the tower, and the solvent is obtained at the bottom of the tower. After being cooled by a solvent cooler, the solvent is sent to the combined tower for recycling.

4. The extractive distillation method of the feed separation type combined tower according to claim 3, characterized in that The operating parameters of the combined tower, including the number of theoretical plates, feeding position, operating pressure, reflux ratio, reboiler heat load, condenser heat load, top temperature of the tower, bottom temperature of the tower, and raw material feeding rate, are adjusted according to the characteristics of the system to be separated and the separation requirements. The operating parameters of the solvent recovery tower, including the number of theoretical plates, feeding position, operating pressure, reflux ratio, reboiler heat load, condenser heat load, top temperature of the tower, bottom temperature of the tower, are adjusted according to the characteristics of the system to be separated and the separation requirements.

5. The extractive distillation method of the feed separation type combined tower according to claim 1 or 3, characterized in that, The method is applicable to systems that are not applicable to the existing energy-saving methods of feed separation type extractive distillation, including the isopropanol - water - DMSO system, the acetonitrile - water - ethylene glycol system, and the methanol - acetone - water system.

Images