A process for separating butyl acetate, n-propanol and water using extractive pressure swing distillation

Abstract

The present application relates to a method for separating butyl acetate, n-propanol and water by extractive pressure swing rectification. For the strong non-ideal ternary system containing butyl acetate, n-propanol and water, glycerol is used as an extractant to break the rectification boundary. In turn, n-propanol is extracted in the first extractive rectification column, and butyl acetate is extracted in the second extractive rectification column. Then, water is recovered through a solvent recovery column, and the extractant realizes closed loop circulation. The present application realizes efficient and high-purity separation of a ternary azeotrope, and has certain reference value for the separation of other alcohol-ester-containing azeotropes.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation and purification, specifically relating to a method for separating butyl acetate, n-propanol and water using extractive pressure swing distillation. Background Technology

[0002] Industrial wastewater containing butyl acetate and n-propanol is frequently generated in industrial production and related processes. Butyl acetate and n-propanol, as important organic solvents and chemical intermediates, are widely used in coatings, adhesives, pharmaceuticals, and fine chemicals. Achieving efficient recovery of this system not only aligns with green chemical principles but also creates significant economic benefits. However, this system exhibits extremely high thermodynamic non-ideal behavior. The butyl acetate / n-propanol / water ternary system contains up to four azeotropic compounds, including three binary azeotropes and one ternary azeotrope. These complex azeotropic behaviors create stringent thermodynamic limitations, making effective separation difficult using traditional distillation methods. Direct discharge of such mixtures not only wastes valuable organic resources but also poses serious challenges to the atmospheric and aquatic environments due to the characteristics of volatile organic compounds. Currently, extractive distillation, with its wide solvent selection range, high operational stability, and excellent performance in handling complex multi-component azeotropic systems, has become one of the most effective methods for separating such mixtures. However, there is still room for optimization in terms of energy efficiency and equipment investment in traditional extractive distillation processes. For example, while pressure swing distillation can achieve separation by utilizing the pressure-dependent properties of azeotropic composition, it often involves high energy consumption. Furthermore, in extractive distillation, directly cooling the high-calorific-content circulating solvent with cooling water leads to significant energy waste. Although existing research has proposed thermal integration techniques, effectively combining solvent selection, pressure swing operation strategies, and multi-stage sensible heat recovery remains a significant design challenge for specific pressure-sensitive systems. Therefore, there is an urgent need to develop a highly efficient and energy-saving integrated separation process that, by deeply exploring the pressure-sensitive characteristics of the system and combining it with a multi-stage waste heat recovery scheme, can fundamentally achieve green and efficient separation of the butyl acetate / n-propanol / water azeotropic system. Summary of the Invention

[0003] [Technical problem to be solved] The purpose of this invention is to provide a method for separating a ternary azeotropic mixture of butyl acetate, n-propanol, and water. This system comprises three binary azeotropes and one ternary azeotrope, exhibiting strong thermodynamic non-ideals. This invention aims to solve the distillation boundary limitations caused by the complex azeotropic behavior. Furthermore, by combining pressure sensitivity analysis with multi-stage sensible heat recovery technology, it overcomes the bottlenecks of high energy consumption and energy waste caused by solvent circulation cooling in traditional extractive distillation, achieving high-purity resource recovery of butyl acetate, n-propanol, and water.

[0004] Technical solution

[0005] This invention proposes a method for separating butyl acetate, n-propanol, and water using extractive pressure swing distillation. Utilizing glycerol as the extractant, the relative volatility of the components is significantly increased under reduced pressure, breaking the azeotropic limitation. This process employs a three-tower continuous distillation sequence to achieve efficient separation.

[0006] The present invention proposes a method for separating ternary azeotropes, characterized in that the apparatus for implementing this process mainly comprises the following parts: The system comprises an extractive distillation column 1 (column 1), an extractive distillation column 2 (column 2), a solvent recovery column (column 3), a first condenser, a second condenser, a third condenser, a first reboiler, a second reboiler, a third reboiler, a circulating cooler, a first pump, a second pump, and a third pump. The piping connections are as follows: the feed line is connected to the middle of column 1, and the first circulating extractant line is connected to the upper part of column 1. The vapor at the top of column 1 is condensed by the first condenser and divided into a reflux line and a butyl acetate product collection line. A portion of the bottom product is returned to the column via the first reboiler, and the other portion is connected to the lower part of column 2 via the first pump. The second circulating extractant line... The pipeline is connected to the upper part of the tower 2. The vapor at the top of the tower 2 is condensed by the second condenser and then divided into a reflux pipeline and a n-propanol product collection pipeline. Part of the bottom product of the tower 2 is returned to the tower via the second reboiler, and the other part is connected to the upper part of the tower 3 via the second pump. The vapor at the top of the tower 3 is condensed by the third condenser and then divided into a reflux pipeline and a water product collection pipeline. Part of the bottom product of the tower 3 is returned to the tower via the third reboiler, and the other part is connected to the fresh extractant replenishment pipeline via the third pump and the circulating cooler to form a total circulation pipeline. The total circulation pipeline is divided into a first circulating extractant pipeline and a second circulating extractant pipeline. The method for separating ternary azeotropic substances using the above-mentioned apparatus includes the following steps: (1) The raw material containing butyl acetate, n-propanol and water, as well as the extractant glycerol, are fed into column 1. The relative volatility is changed by glycerol, and high-purity butyl acetate is separated from the top of the column. (2) The mixture (n-propanol, water and glycerol) at the bottom of column 1 enters column 2, and under the action of the second extractant, pure n-propanol is separated from the top of the column; (3) The bottom material of tower 2 (a mixture of water and glycerol) enters tower 3, and high-purity water is separated from the top of the tower, while the recovered glycerol extractant is obtained from the bottom of the tower; (4) The glycerol at the bottom of tower 3 is cooled and then recycled to tower 1 and tower 2 for continued use.

[0007] 2. The method according to claim 1, wherein the extractant is glycerol.

[0008] 3. The method according to claim 1, characterized in that: the number of theoretical plates in tower 1 is 87; the number of theoretical plates in tower 2 is 34; and the number of theoretical plates in tower 3 is 5.

[0009] According to another preferred embodiment of the present invention, the column 1 has 87 theoretical plates, the raw material feed position is the 36th plate, and the extractant feed position is the 3rd plate; the column 2 has 34 theoretical plates, the raw material feed position is the 28th plate, and the extractant feed position is the 3rd plate; the column 3 has 5 theoretical plates, and the feed position is the 3rd plate.

[0010] According to another preferred embodiment of the present invention, the extractant is glycerol.

[0011] Beneficial effects

[0012] The present invention has the following beneficial effects: (1) This invention discovers and utilizes the significant enhancement effect of glycerol on the selectivity of butyl acetate / n-propyl acetate / water system under reduced pressure by performing pressure sensitivity analysis on the system.

[0013] (2) This process achieves complete recycling of the extractant glycerol, and the purity of each product (butyl acetate, n-propanol, and water) reaches more than 99.9 mol%, effectively realizing the resource-based treatment of industrial wastewater and clean production. Attached Figure Description

[0014] Appendix Figure 1 A schematic diagram of the process flow for the extraction and separation of butyl acetate / n-propanol / water azeotrope by pressure swing distillation; In the diagram, there are extraction distillation column 1 (column 1), extraction distillation column 2 (column 2), solvent recovery column (column 3), first condenser, second condenser, third condenser, first reboiler, second reboiler, third reboiler, circulating cooler, first pump, second pump, and third pump; numbers 1 to 32 represent various material pipelines. Detailed Implementation

[0015] The following description, in conjunction with the accompanying drawings, is intended to further illustrate the scope of the invention but is not intended to limit its scope. Example 1

[0016] The feed flow rate is 100 kmol / h, and its molar composition is 0.34% butyl acetate, 0.33% n-propanol, and 0.33% water. The feed enters extractive distillation column one (column 1). Extractive distillation column one (column 1) has a total of 87 theoretical plates. The feed enters from the 36th theoretical plate, and the circulating extractant glycerol enters from the 3rd plate. The operating pressure is set at 0.0229 atm. The molar purity of the n-propanol product produced at the top of the column is greater than or equal to 99.9%. Extractive distillation column two (column 2) has a total of 34 theoretical plates. The mixture from the bottom of column 1 enters from the 28th plate, and the second stream of circulating glycerol enters from the 3rd plate. The operating pressure is 0.0809 atm. The molar purity of the butyl acetate product collected at the top of the column also reaches ≥99.9 mol%. The solvent recovery tower (tower 3) has a total of 5 theoretical plates, with the feed located on the 3rd plate. It operates at a pressure of 0.0102 atm. High-purity aquatic products are collected from the top of the tower, while the high-temperature glycerol recovered from the bottom is cooled by a circulating cooler. The entire process achieves a completely closed-loop circulation of the extractant glycerol, and the purity of all recovered components is consistently above 99.9 mol%. Example 2

[0017] The feed flow rate is 150 kmol / h, and its molar composition is 0.34% butyl acetate, 0.33% n-propanol, and 0.33% water. The feed enters extractive distillation column one (column 1). Extractive distillation column one (column 1) has a total of 87 theoretical plates. The feed enters from the 36th theoretical plate, and the circulating extractant glycerol enters from the 3rd plate. The operating pressure is set at 0.0229 atm, and the molar purity of the n-propanol product produced at the top of the column is greater than or equal to 99.9%. Extractive distillation column two (column 2) has a total of 34 theoretical plates. The mixture from the bottom of column 1 enters from the 28th plate, and the second stream of circulating glycerol enters from the 3rd plate. The operating pressure is 0.0809 atm, and the molar purity of the butyl acetate product collected at the top of the column also reaches ≥99.9 mol%. The solvent recovery tower (tower 3) has a total of 5 theoretical plates, with the feed located on the 3rd plate. It operates at a pressure of 0.0102 atm. High-purity aquatic products are collected from the top of the tower, while the high-temperature glycerol recovered from the bottom is cooled by a circulating cooler. The entire process achieves a completely closed-loop circulation of the extractant glycerol, and the purity of all recovered components is consistently above 99.9 mol%. Example 3

[0018] The feed flow rate is 200 kmol / h, and its molar composition is 0.34% butyl acetate, 0.33% n-propanol, and 0.33% water. The feed enters extractive distillation column one (column 1). Extractive distillation column one (column 1) has a total of 87 theoretical plates. The feed enters from the 36th theoretical plate, and the circulating extractant glycerol enters from the 3rd plate. The operating pressure is set at 0.0229 atm. The molar purity of the n-propanol product produced at the top of the column is greater than or equal to 99.9%. Extractive distillation column two (column 2) has a total of 34 theoretical plates. The mixture from the bottom of column 1 enters from the 28th plate, and the second stream of circulating glycerol enters from the 3rd plate. The operating pressure is 0.0809 atm. The molar purity of the butyl acetate product collected at the top of the column also reaches ≥99.9 mol%. The solvent recovery tower (tower 3) has a total of 5 theoretical plates, with the feed located on the 3rd plate. It operates at a pressure of 0.0102 atm. High-purity aquatic products are collected from the top of the tower, while the high-temperature glycerol recovered from the bottom is cooled by a circulating cooler. The entire process achieves a completely closed-loop circulation of the extractant glycerol, and the purity of all recovered components is consistently above 99.9 mol%.

[0019] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for extractive distillation to separate a ternary azeotrope of butyl acetate, n-propanol, and water, characterized in that, The apparatus for implementing this method includes an extractive distillation column 1 (column 1), an extractive distillation column 2 (column 2), a solvent recovery column 3 (column 3), a first condenser, a second condenser, a third condenser, a first reboiler, a second reboiler, a third reboiler, a circulating cooler, a first pump, a second pump, and a third pump. The piping connections are as follows: the feed line is connected to the middle of column 1, and the first circulating extractant line is connected to the upper part of column 1. The vapor at the top of column 1 is condensed by the first condenser and divided into a reflux line and a butyl acetate product collection line. A portion of the bottom product is returned to the column via the first reboiler, and the other portion is connected to the lower part of column 2 via the first pump. The second circulating cooler... The cyclic extractant pipeline is connected to the upper part of column 2. The vapor at the top of column 2 is condensed by the second condenser and then divided into a reflux pipeline and a n-propanol product collection pipeline. Part of the bottom product is returned to the column via the second reboiler, and the other part is connected to the upper part of column 3 via the second pump. The vapor at the top of column 3 is condensed by the third condenser and then divided into a reflux pipeline and a water product collection pipeline. Part of the bottom product is returned to the column via the third reboiler, and the other part is connected to the fresh extractant replenishment pipeline via the third pump and the circulating cooler to form a total circulation pipeline. The total circulation pipeline is divided into a first circulating extractant pipeline and a second circulating extractant pipeline. The method for separating ternary azeotropic substances using the above-mentioned apparatus includes the following steps: (1) The raw material containing butyl acetate, n-propanol and water, as well as the extractant glycerol, are fed into column 1. The relative volatility is changed by glycerol, and high-purity butyl acetate is separated from the top of the column. (2) The mixture (n-propanol, water and glycerol) at the bottom of column 1 enters column 2, and under the action of the second extractant, pure n-propanol is separated from the top of the column; (3) The bottom material of tower 2 (a mixture of water and glycerol) enters tower 3, and high-purity water is separated from the top of the tower, while the recovered glycerol extractant is obtained from the bottom of the tower; (4) The glycerol at the bottom of tower 3 is cooled and then recycled to tower 1 and tower 2 for continued use.

2. The method according to claim 1, characterized in that: The extractant is glycerol.

3. The method according to claim 1, characterized in that: Tower 1 has 87 theoretical plates; Tower 2 has 34 theoretical plates; Tower 3 has 5 theoretical plates.

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