Method for separating ethanol-isopropanol-n-propanol mixture and rectification device

Abstract

The invention provides a method for separating an ethanol-isopropanol-n-propanol mixture and a rectification device, and belongs to the technical field of extractive rectification. According to the method, 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM] [BF4] is adopted as an extraction agent, during extraction and separation by the method, the mass fraction of n-propyl alcohol can reach 99.9%, the mass fraction of ethanol is 99.87%, and the recovery rate of the extraction agent exceeds 99.9%; compared with a common organic extraction agent, the organic extraction agent has a better separation effect, high-purity ethanol and n-propanol can be obtained, and the problem of environmental pollution caused by volatilization of the common organic solvent can be avoided; the method has good application in extraction separation and recycling of an ethanol-isopropanol-n-propanol mixture.

Description

Technical Field

[0001] This invention belongs to the field of extraction distillation technology, specifically relating to a method and distillation apparatus for separating a mixture of ethanol, isopropanol, and n-propanol. Background Technology

[0002] Ethanol, n-propanol, and isopropanol are three common alcohol compounds with similar physicochemical properties, but some differences exist, which determine the difficulty of separating them in distillation. The difficulty of separating ethanol, n-propanol, and isopropanol in distillation mainly depends on their differences in boiling points and relative volatility. Ethanol has a boiling point of 78.37℃, n-propanol has a boiling point of 97.15℃, and isopropanol has a boiling point of 82.45℃. From the boiling point perspective, ethanol and isopropanol are relatively close (difference of about 4℃), while the difference between ethanol and n-propanol is significant (difference of 19℃). Therefore, separating ethanol and n-propanol is relatively easy, while separating ethanol and isopropanol is more difficult. Relative volatility is an important parameter for measuring the ease of separating two components in distillation. Ethanol and isopropanol have relatively low relative volatility because they are short-chain alcohols with similar molecular structures and polarities, resulting in similar volatility behavior. Ethanol and n-propanol have relatively high volatility because n-propanol has a longer carbon chain, a higher boiling point, and lower volatility. Ethanol does not form azeotropes with n-propanol or isopropanol, therefore azeotropy has little impact on their separation. Ethanol and isopropanol are both short alcohols with similar molecular structures and polarities, making them prone to entrainment during distillation, increasing the difficulty of separation. n-Propanol has a longer carbon chain, stronger intermolecular forces, and a more pronounced difference from ethanol, making it easier to separate by distillation.

[0003] Therefore, there is a need to develop a method and production apparatus for separating a mixture of ethanol, isopropanol, and n-propanol. Summary of the Invention

[0004] To address some shortcomings in existing technologies, this invention provides a method and distillation apparatus for separating a mixture of ethanol, isopropanol, and n-propanol. The invention uses 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] as the extractant. During extraction and separation, the method achieves a n-propanol mass fraction of 99.9% and an ethanol mass fraction of 99.87%, with an extractant recovery rate exceeding 99.9%. Compared to ordinary organic extractants, it exhibits better separation performance, yielding high-purity ethanol and n-propanol, and avoids the environmental pollution problems caused by the volatilization of ordinary organic solvents. It has excellent applications in the extraction, separation, and recycling of ethanol-isopropanol-n-propanol mixtures.

[0005] To achieve the above-mentioned technical objectives, the present invention employs the following technical means: This invention first provides the application of 1-butyl-3-methylimidazolium tetrafluoroborate in the extraction and separation of ethanol-isopropanol-n-propanol mixtures.

[0006] The present invention also provides a method for separating a mixture of ethanol-isopropanol-n-propanol, wherein the method uses 1-butyl-3-methylimidazolium tetrafluoroborate, or a composite solvent consisting of 1-butyl-3-methylimidazolium tetrafluoroborate and an organic solvent, as the extractant.

[0007] Preferably, the method includes: (1) The ethanol-isopropanol-n-propanol mixture enters from the middle of the n-propanol distillation column (B1). The bottom of the column is collected by the RE-1-OUT stream to obtain n-propanol with a mass fraction of more than 99.9%. The ethanol and isopropanol flow out from the top of the column and are sent to the extractive distillation column (B2). A mixture of ethanol, isopropanol and a small amount of n-propanol is obtained at the top of the column. (2) After the mixture obtained at the top of the column in step (1) is cooled to room temperature by the first heat exchanger (COOLER-1), it is introduced into the extractive distillation column (B2), and an extractant is added to it. After extractive distillation, the mixture is separated, and ethanol with a mass fraction of more than 99.87% is collected at the top of the column. The bottom outlet of the extractive distillation column (B2) is connected to a flash tank. The bottom liquid is flashed in the flash tank to obtain a high-purity extractant. Isopropanol is collected at the top of the flash tank. A circulation pipeline is set up to reintroduce the extractant into the extractive distillation column (B2) via the second heat exchanger (COOLER-2) and a mixer.

[0008] Preferably, in step (1), the theoretical number of plates of the n-propanol distillation column (B1) is set to 35 to 45, and the feed position of the ethanol-isopropanol-n-propanol mixture is the 3rd to 9th plate.

[0009] Preferably, in step (1), the top condenser of the n-propanol distillation column (B1) is a total condenser with a temperature of 76.0℃~78.0℃, a pressure of 0.5~1.5 bar, and a total pressure drop of 0.1~0.5 bar. The reboiler is a batch-type reboiler with a molar reflux ratio of 0.5~1.5, a reboiler temperature of 98.0℃~102.0℃, and a heat load of 50~70kW. After separation in the column, the bottom of the column can yield n-propanol with a mass fraction exceeding 99.9%.

[0010] Preferably, in step (2), the theoretical number of trays of the extractive distillation column (B2) is set to 40 to 60, and the feed position of the mixed liquid is the 8th to 15th tray.

[0011] Preferably, in step (2), the top condenser of the extractive distillation column (B2) is a total condenser with a temperature of 75.0℃~80.0℃, a pressure of 0.5~1.5 bar, and a total pressure drop of 0.1~0.5 bar. The reboiler is a kettle-type reboiler with a molar reflux ratio of 1.2 to 2.0. The reboiler temperature is 85.0℃ to 91.0℃, and the heat load is 555 to 65 kW.

[0012] Preferably, in step (2), the temperature of the flash tank is set to 200℃~260℃, the pressure is set to 0.01~0.05bar, and the heat load is 10~15kw.

[0013] The present invention also provides a distillation apparatus for the above method, the distillation apparatus comprising: a n-propanol distillation column (B1), an extractive distillation column (B2), and a flash tank; The n-propanol distillation column (B1) is provided with an ethanol-isopropanol-n-propanol mixture inlet and outlet, and the outlet is connected to the first inlet of the extractive distillation column (B2) via the first heat exchanger (COOLER-1). The extractive distillation column (B2) is equipped with a first inlet, a second inlet, and an outlet. A circulation pipeline is provided between the extractive distillation column (B2) and the flash tank (FLASH). The outlet of the extractive distillation column (B2) is connected to the inlet of the flash tank (FLASH). The outlet of the flash tank (FLASH) is connected to the second inlet of the extractive distillation column (B2) via the second heat exchanger (COOLER-2).

[0014] Preferably, the feed inlet of the n-propanol distillation column (B1) is located on the 3rd to 9th trays; the outlet is located at the top of the column and the bottom of the column. The bottom of the column is connected to a stream RE-1-OUT. High-purity n-propanol flows out from the bottom of the column through the stream RE-1-OUT, while ethanol and isopropanol flow out from the top of the column and are sent to the extractive distillation column (B2). The concentrate inlet of the extractive distillation column (B2) is located at the 8th to 15th trays; the second inlet is located at the 44th tray, through which the extractant enters; a stream DIS-2-OU is provided at the top of the column, from which high-purity ethanol flows out, and isopropanol and extractant [BMIM][BF4] flow out through the bottom of the column and are sent to the flash tank. A mixing chamber (MIXER) is connected between the second heat exchanger (COOLER-2) of the flash tank and the second inlet of the extractive distillation column (B2) via a RECYCLE stream. The mixing chamber is connected to the extractant inlet via a MAKEUP stream. The extractant, purified by the flash tank, is returned to the mixing chamber (MIXER) via the RECYCLE stream, and any extractant lost during the process is replenished by the MAKEUP stream. Isopropanol and a small amount of extractant are collected from the top of the flash tank.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention is the first to use extractive distillation to separate components with similar boiling points, and the first to use 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] as an extractant to separate the ethanol-isopropanol system. This invention employs a flash evaporator to recover ionic liquids, which, compared to distillation columns used with organic solvents as extractants, achieves the desired purification effect while saving on equipment investment. Attached Figure Description

[0016] Figure 1 This is a screening diagram for ionic liquids.

[0017] Figure 2 This represents the interaction parameters between molecular groups.

[0018] Figure 3 The diagram shows the process flow and distillation apparatus for using 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] as the extractant.

[0019] Figure labels: n-Propanol distillation column B1, extractive distillation column B2, flash tank, heat exchanger COOLER-1, heat exchanger COOLER-2, mixer MIXER.

[0020] Figure 4 The effect of feed location and reflux ratio of the thickener on key components.

[0021] Figure 5 The effect of feed location and reflux ratio on key components in an extractive distillation column.

[0022] Figure 6 This is a process flow diagram using ethylene glycol as the extractant.

[0023] Figure labels: n-Propanol distillation column B1, extractive distillation column B2, solvent recovery column B3, heat exchanger COOLER-1, heat exchanger COOLER-2, mixer MIXER. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0025] Example 1: Selectivity (S) is an important criterion for analyzing and evaluating the separation ability of an extractant. For the separation of two-component systems, selectivity refers to the ratio of the activity coefficients of the two components, which can be expressed by the following formula: , These are the activity coefficients of component 1 and component 2 in the extractant, respectively. For a system where the gas phase is an ideal gas and the liquid phase is a non-ideal solution: These are the saturated vapor pressures of component 1 and component 2 at the equilibrium temperature, respectively, which can be calculated using the Antoni equation; Where: P is pressure; T is temperature. This invention utilizes COSMOthermX software to perform selectivity calculations on ionic liquids with different cation and anion compositions, and plots the results graphically, as shown below. Figure 1 As shown, the selectivity of [BMIM][BF4] is relatively high at 1.476.

[0026] The simulation uses the UNIFAC-Lei model, such as Figure 2 As shown, input the interaction parameters of the relevant groups.

[0027] Combination Figure 1 and Figure 2 It is known that 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] has a good separation effect as an extractant for separating the ethanol-isopropanol system.

[0028] Example 2: This embodiment first provides a distillation apparatus for separating a mixture of ethanol, isopropanol, and n-propanol, such as... Figure 3 As shown, the distillation apparatus includes: The n-propanol distillation column (B1) is provided with an ethanol-isopropanol-n-propanol mixture inlet and outlet, and the outlet is connected to the first inlet of the extractive distillation column (B2) via the first heat exchanger (COOLER-1). The extractive distillation column (B2) is equipped with a first inlet, a second inlet, and an outlet. A circulation pipeline is provided between the extractive distillation column (B2) and the flash tank (FLASH). The outlet of the extractive distillation column (B2) is connected to the inlet of the flash tank (FLASH). The outlet of the flash tank (FLASH) is connected to the second inlet of the extractive distillation column (B2) via the second heat exchanger (COOLER-2).

[0029] Preferably, the feed inlet of the n-propanol distillation column (B1) is located on the 3rd to 9th trays; the outlet is located at the top of the column and the bottom of the column. The bottom of the column is connected to a stream RE-1-OUT. High-purity n-propanol flows out from the bottom of the column through the stream RE-1-OUT, while ethanol and isopropanol flow out from the top of the column and are sent to the extractive distillation column (B2). The concentrate inlet of the extractive distillation column (B2) is located at the 8th to 15th trays; the second inlet is located at the 44th tray, through which the extractant enters; a stream DIS-2-OU is provided at the top of the column, through which high-purity ethanol flows out, and isopropanol and extractant [BMIM][BF4] flow out through the bottom of the column and are sent to the flash tank. A mixing chamber (MIXER) is connected between the second heat exchanger (COOLER-2) of the flash tank and the second inlet of the extractive distillation column (B2) via a RECYCLE stream. The mixing chamber is connected to the extractant inlet via a MAKEUP stream. The extractant, purified by the flash tank, is returned to the mixing chamber (MIXER) via the RECYCLE stream, and any extractant lost during the process is replenished by the MAKEUP stream. Isopropanol and a small amount of extractant are collected from the top of the flash tank.

[0030] This embodiment also provides a method for separating an ethanol-isopropanol-n-propanol mixture using the above-described distillation apparatus. The method includes using 1-butyl-3-methylimidazolium tetrafluoroborate or a composite solvent composed of 1-butyl-3-methylimidazolium tetrafluoroborate and an organic solvent as the extractant.

[0031] Specifically, the method includes: (1) The raw material mixture is fed into the n-propanol distillation column (B1) via a feeder. The bottom of the column yields n-propanol with a mass fraction exceeding 99.9%, and the top of the column yields a mixture of ethanol, isopropanol, and a small amount of n-propanol. The theoretical number of trays in the n-propanol distillation column (B1) is set to 40, and the ethanol-isopropanol-n-propanol mixture is fed onto the 6th tray. The top condenser of the n-propanol distillation column (B1) is a total condenser with a temperature of 78.0℃ and a pressure of 1 bar, resulting in a total pressure drop of 0.1 bar. The reboiler is a kettle-type reboiler with a molar reflux ratio of 1.5, a reboiler temperature of 99.4℃, and a heat load of 63.1528kw.

[0032] (2) After the mixture obtained from the top of the column in step (1) is cooled to room temperature by the first heat exchanger (COOLER-1), it is introduced into the extractive distillation column (B2). An extractant is added to it, and after extractive distillation, the mixture is separated. Ethanol with a mass fraction of more than 99.87% is collected from the top of the column. The bottom outlet of the extractive distillation column (B2) is connected to a flash evaporator. The bottom liquid is flashed to obtain a high-purity extractant. A circulation pipeline is set up to reintroduce the extractant into the extractive distillation column (B2) through the second heat exchanger (COOLER-2). The theoretical number of plates in the extractive distillation column (B2) is set to 45, and the feed position of the mixture is the 11th plate. The condenser at the top of the extractive distillation column (B2) is a total condenser with a temperature of 78.0℃ and a pressure of 1 bar, and the pressure drop of the entire column is 0.1 bar. The reboiler is a kettle-type reboiler with a molar reflux ratio of 1.5. The temperature of the reboiler is 90.4℃, and the heat load is 59.8026kw.

[0033] The temperature of the flash tank was set to 300℃, the pressure to 0.01 bar, and the heat load to 12.7826 kW.

[0034] Example 3: Operation process and discharge situation when the feed flow rate is 100 kg / h This embodiment takes a feed flow rate of 100 kg / h as an example, comparing Example 2 and Example 3. Figure 3 The distillation methods and distillation apparatus mentioned in the text will be explained in detail.

[0035] like Figure 4 As shown, by plotting the concentrations of key components extracted from the top and bottom of the column, and their relationship with the reflux ratio and feed location, the optimal reflux ratio and feed location of the n-propanol distillation column (B1) and the extractive distillation column (B2) are analyzed and determined.

[0036] The feed liquid enters the n-propanol distillation column (B1) from the 6th theoretical plate. The mass composition of the feed liquid is: 99.7 wt% ethanol, 0.142 wt% isopropanol, and 0.147 wt% n-propanol. The flow rate is 100 kg / h, and the molar reflux ratio is 1.5. Figure 5 Analysis revealed that the distillate, after being cooled, was introduced into the extractive distillation column from the 11th tray.

[0037] The extractive distillation column has 45 theoretical plates. The extractant 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] enters from the 44th theoretical plate at a flow rate of 99.82 kg / h. The extractive distillation column operates at atmospheric pressure with a molar reflux ratio of 1.6. The top temperature of the extractive distillation column is 78.0℃, and the bottom temperature is 90.4℃. Ethanol with a mass fraction of 99.87% is obtained at the top of the column. The bottom liquid of the extractive distillation column enters a flash evaporator for flash distillation at a temperature of 300℃ and a vacuum degree of 0.01 bar. 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] with a mass fraction of over 99.9% is obtained at the bottom of the flash evaporator and is recycled back to the extractive distillation column for reuse.

[0038] Example 4: Operation process and discharge situation when the feed flow rate is 200 kg / h This embodiment takes a feed flow rate of 200 kg / h as an example, comparing Example 2 and Example 3. Figure 3 The distillation methods and distillation apparatus mentioned in the text will be explained in detail. Figure 4 and Figure 5 The results of the effects of feed location and reflux ratio on key components in the concentration column and extractive distillation column were presented based on... Figure 4 and Figure 5 The analysis revealed the feed location, leakage rate, and feed location of the extractive distillation column, as detailed below: The feed concentrate has 40 theoretical plates. The feed liquid enters from the 6th theoretical plate, with a composition of 99.7 wt% ethanol, 0.142 wt% isopropanol, and 0.147 wt% n-propanol. The flow rate is 200 kg / h, and the molar reflux ratio is 1.3. The top temperature of the concentrate is approximately 78.0℃, and the bottom temperature is approximately 90.4℃. The n-propanol is collected from the bottom of the concentrate with a mass fraction of 99.9%. The distillate is cooled and introduced from the 11th plate. The extractive distillation column has 45 theoretical plates. The extractant 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] enters from the 44th theoretical plate at a flow rate of 199.64 kg / h. The extractive distillation column operates at atmospheric pressure with a molar reflux ratio of 1.6. The top temperature of the extractive distillation column is 78.0℃, and the bottom temperature is 90.4℃. Ethanol with a mass fraction of 99.87% is obtained at the top of the column. The bottom liquid of the extractive distillation column enters the solvent recovery tank for flash distillation at a temperature of 300℃ and a vacuum degree of 0.01 bar. 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] with a mass fraction of over 99.9% is obtained at the bottom of the tank and is recycled back to the extractive distillation column for reuse.

[0039] Example 5: Operation process and discharge conditions when the feed flow rate is 300 kg / h This embodiment takes a feed flow rate of 300 kg / h as an example, comparing Example 2 and Example 3. Figure 3The distillation methods and distillation apparatus mentioned in the text will be explained in detail. Figure 4 and Figure 5 The results of the effects of feed location and reflux ratio on key components in the concentration column and extractive distillation column were presented based on... Figure 4 and Figure 5 The analysis revealed the feed location, leakage rate, and feed location of the extractive distillation column, as detailed below: The feed concentrate has 40 theoretical plates. The feed liquid enters from the 6th theoretical plate, with a composition of 99.7 wt% ethanol, 0.142 wt% isopropanol, and 0.147 wt% n-propanol. The flow rate is 300 kg / h, and the molar reflux ratio is 1.3. The top temperature of the concentrate is approximately 78.0℃, and the bottom temperature is approximately 90.4℃. The n-propanol is collected from the bottom of the concentrate with a mass fraction of 99.9%. The distillate is cooled and introduced from the 11th plate. The extractive distillation column has 45 theoretical plates. The extractant 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] enters from the 44th theoretical plate at a flow rate of 299.46 kg / h. The extractive distillation column operates at atmospheric pressure with a molar reflux ratio of 1.6. The top temperature of the extractive distillation column is 78.0℃, and the bottom temperature is 90.4℃. Ethanol with a mass fraction of 99.87% is obtained at the top of the column. The bottom liquid of the extractive distillation column enters the solvent recovery tank for flash distillation at a temperature of 300℃ and a vacuum degree of 0.01 bar. 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] with a mass fraction of over 99.9% is obtained at the bottom of the tank and is recycled back to the extractive distillation column for reuse.

[0040] Comparative Example 1: Separation of key components when ethylene glycol is used as the extractant This comparative study investigated the effect of ethylene glycol as the extractant on the separation effect of a mixture of ethanol, isopropanol, and n-propanol. The specific steps are as follows: like Figure 6 As shown, the feed concentration tower has 40 theoretical plates. The feed liquid enters from the 8th theoretical plate and has a composition of 99.7 wt% ethanol, 0.142 wt% isopropanol, and 0.147 wt% n-propanol. The concentration column has a flow rate of 100 kg / h and a molar reflux ratio of 1.5. The top temperature of the concentration column is 78.0℃ and the bottom temperature is 99.4℃. Propanol is distilled off at the top. The extractive distillation column has 60 theoretical plates. Ethylene glycol, the extractant, enters from the 4th theoretical plate at a flow rate of 99.82 kg / h. The extractive distillation column operates at atmospheric pressure with a molar reflux ratio of 1.7. The top temperature of the extractive distillation column is 78.0℃ and the bottom temperature is 191.7℃. Ethanol is obtained at the top. The liquid from the bottom of the extractive distillation column enters the solvent recovery column from the 6th theoretical plate. The top temperature of the solvent recovery column is 78.5℃ and the bottom temperature is 200.1℃. Ethylene glycol with a mass fraction of over 99.9% is obtained at the bottom of the solvent recovery column and can be recycled back to the extractive distillation column for reuse.

[0041] The comparison of the separation situation with ionic liquids is shown in Table 1.

[0042] Table 1. Effects of different extractants on the separation of key components composition FEED RE-1-OUT DIS-2-OU RECYCLE <![CDATA[[BMIM][BF4]]]> 0.00000 0.00000 0.00000 0.99998 ethanol 0.99711 0.00000 0.99875 0.00002 Isopropanol 0.00142 0.00000 0.00124 0.00000 n-Propanol 0.00147 1.00000 0.00000 0.00000 Ethylene glycol 0.00000 0.00000 0.00000 0.99976 ethanol 0.99711 0.00000 0.99751 0.00023 Isopropanol 0.00142 0.00000 0.00248 0.00001 n-Propanol 0.00147 1.00000 0.00000 0.00000 Table 1 shows the effect of different extractants on the separation of key components. As can be seen from Table 1, when ionic liquid is used as the extractant, the purity of ethanol is increased to 99.875% and the solvent recovery rate exceeds 99.99%.

[0043] In summary, this invention uses the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] to replace the traditional solvent as the extractant, which can achieve better separation effect; the 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] has excellent application in the separation of ethanol and isopropanol.

[0044] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

Application of 1,1-Butyl-3-methylimidazolium tetrafluoroborate in the extraction and separation of ethanol-isopropanol-n-propanol mixtures.

2. A method for separating a mixture of ethanol, isopropanol, and n-propanol, characterized in that, The method uses 1-butyl-3-methylimidazolium tetrafluoroborate, or a composite solvent consisting of 1-butyl-3-methylimidazolium tetrafluoroborate and an organic solvent, as the extraction solvent.

3. The method according to claim 2, characterized in that, The method includes: (1) The ethanol-isopropanol-n-propanol mixture enters from the middle of the n-propanol distillation column (B1). The bottom of the column is collected by the RE-1-OUT stream to obtain n-propanol with a mass fraction of more than 99.9%. The ethanol and isopropanol flow out from the top of the column and are sent to the extractive distillation column (B2). A mixture of ethanol, isopropanol and a small amount of n-propanol is obtained at the top of the column. (2) After the mixture obtained at the top of the column in step (1) is cooled to room temperature by the first heat exchanger (COOLER-1), it is introduced into the extractive distillation column (B2), and an extractant is added to it. After extractive distillation, the mixture is separated, and ethanol with a mass fraction of more than 99.87% is collected at the top of the column. The bottom outlet of the extractive distillation column (B2) is connected to a flash tank. The bottom liquid is flashed in the flash tank to obtain a high-purity extractant. Isopropanol is collected at the top of the flash tank. A circulation pipeline is set up to reintroduce the extractant into the extractive distillation column (B2) via the second heat exchanger (COOLER-2) and a mixer.

4. The method according to claim 3, characterized in that, In step (1), the theoretical number of trays of the n-propanol distillation column (B1) is set to 35 to 45, and the feed position of the ethanol-isopropanol-n-propanol mixture is the 3rd to 9th tray. The top condenser of the n-propanol distillation column (B1) is a total condenser with a temperature of 76.0℃~78.0℃ and a pressure of 0.5~1.5 bar, and a total pressure drop of 0.1~0.5 bar. The reboiler is a batch reboiler with a molar reflux ratio of 0.5~1.5, a reboiler temperature of 98.0℃~102.0℃, and a heat load of 50~70kw. After separation by the column, the bottom of the column can obtain n-propanol with a mass fraction of more than 99.9%.

5. The method according to claim 3, characterized in that, In step (2), the theoretical number of trays of the extractive distillation column (B2) is set to 40 to 60, and the feed position of the mixed liquid is the 8th to 15th tray; The extractive distillation column (B2) uses a total condenser at the top, with a temperature of 75.0℃~80.0℃, a pressure of 0.5~1.5 bar, and a total pressure drop of 0.1~0.5 bar. The reboiler is a kettle-type reboiler with a molar reflux ratio of 1.2 to 2.0; the reboiler temperature is 85.0℃ to 91.0℃ and the heat load is 555 to 65 kW.

6. The method according to claim 3, characterized in that, In step (2), the temperature of the flash tank is set to 200℃~260℃, the pressure is set to 0.01~0.05 bar, and the heat load is 10~15 kW.

7. A distillation apparatus for use in the method according to any one of claims 2 to 6, characterized in that, The distillation apparatus includes: n-Propanol distillation column (B1), extractive distillation column (B2), and flash evaporator; The n-propanol distillation column (B1) is provided with an ethanol-isopropanol-n-propanol mixture inlet and outlet, and the outlet is connected to the first inlet of the extractive distillation column (B2) via the first heat exchanger (COOLER-1). The extractive distillation column (B2) is equipped with a first inlet, a second inlet, and an outlet. A circulation pipeline is provided between the extractive distillation column (B2) and the flash tank (FLASH). The outlet of the extractive distillation column (B2) is connected to the inlet of the flash tank (FLASH). The outlet of the flash tank (FLASH) is connected to the second inlet of the extractive distillation column (B2) via the second heat exchanger (COOLER-2).

8. The apparatus according to claim 7, characterized in that, The feed inlet of the n-propanol distillation column (B1) is located on the 3rd to 9th trays; the outlet is located at the top of the column and at the bottom of the column, and the bottom of the column is connected to a stream RE-1-OUT for the n-propanol to flow out.

9. The apparatus according to claim 7, characterized in that, The concentrate inlet of the extractive distillation column (B2) is located at the 8th to 15th trays; the second inlet for the extractant is located at the 44th tray; and the top of the column is equipped with a stream DIS-2-OU for ethanol outflow.

10. The apparatus according to claim 7, characterized in that, The flash tank's second heat exchanger (COOLER-2) and the extractive distillation column's second inlet are connected by a mixing mixer via a RECYCLE stream, and the mixing mixer is connected to the extractant inlet via a MAKEUP stream.

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