Method for preparing methanol, ethanol and n-propanol from Fischer-Tropsch synthesis water-phase product

Abstract

The invention provides a method for preparing methanol, ethanol and n-propanol from a Fischer-Tropsch synthesis water-phase product, and particularly, the method comprises the following steps: carrying out first rectification on the Fischer-Tropsch synthesis water-phase product to obtain water-containing light alcohol; carrying out extractive distillation on the water-containing light alcohol to obtain light alcohol and extract liquor; and rectifying the obtained light alcohol in sequence, and gradually separating out tower top light components, methanol, ethanol and n-propanol. The method is continuous in operation, the product purity can be selected according to actual market requirements, industrial realization is easy, operation is simple, the recovery rate is high, and economical efficiency is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal chemical industry, and relates to a method for preparing methanol, ethanol and n-propanol by utilizing an aqueous phase product of Fischer-Tropsch synthesis, and specifically relates to a method for refining the aqueous phase product of Fischer-Tropsch synthesis to obtain methanol, ethanol and n-propanol. Background Art

[0002] Given my country's energy situation of being "rich in coal, poor in oil, and limited in natural gas," several indirect coal liquefaction projects have been developed to achieve efficient coal conversion and utilization. The core of indirect coal liquefaction technology is the Fischer-Tropsch synthesis reaction, which involves reacting synthesis gas (CO) and H₂ in the presence of a catalyst and appropriate process conditions to produce oil, chemicals, and aqueous products.

[0003] Fischer-Tropsch synthesis water has a complex component, and its composition is mainly composed of oxygenated organics such as alcohols, aldehydes, ketones, acids and esters, with a total content of 2wt%-30wt%. For example, the Fischer-Tropsch synthesis water obtained by the high-temperature slurry bed Fischer-Tropsch synthesis technology of Zhongke Synthetic Oil Technology Co., Ltd. has oxygenated organics generally lower than 10wt%, and the organic carbon number is less than 8, wherein the content of alcohols (mainly methanol, ethanol, propanol, butanol and amyl alcohol) is about 2wt%, the content of acids (mainly acetic acid, propionic acid, butyric acid and valeric acid) is about 0.76wt%, the content of aldehydes (mainly acetaldehyde and propionic aldehyde) is about 0.14wt%, the content of ketones (mainly acetone) is about 0.07wt%, and the content of esters (mainly ethyl acetate) is about 0.02wt%. In addition, Fischer-Tropsch synthesis water also contains dozens of oxygenated organics with contents lower than 50ppm, which have little impact on the process of Fischer-Tropsch synthesis water treatment and can be ignored.

[0004] If the above-mentioned alcohols are separated from the Fischer-Tropsch synthesis water, the obtained C1-C3 alcohols (methanol, ethanol, propanol) can be used as important basic chemical raw materials, and the C4-C8 alcohols (butanol, pentanol, hexanol, heptanol, octanol) can be used as fuel. This will not only improve the economic benefits of coal-to-oil, but also be beneficial to environmental protection and promote the clean production and development of Fischer-Tropsch synthesis technology.

[0005] At present, the treatment process of Fischer-Tropsch synthesis water mainly includes deoiling the Fischer-Tropsch synthesis water to obtain deoiled Fischer-Tropsch synthesis water, then adding alkaline substances for neutralization treatment to prepare neutralized Fischer-Tropsch synthesis water, which is then introduced into a distillation tower for separation, wherein the bottom of the tower produces synthetic wastewater, and the top of the tower produces water-containing mixed alcohol (Fischer-Tropsch synthesis aqueous phase product, usually with a water content of about 30wt%). This process significantly reduces the organic content in the Fischer-Tropsch synthesis wastewater, ensuring that it is suitable for biochemical treatment; however, further separation of the Fischer-Tropsch synthesis aqueous phase product containing 30wt% water has not yet been achieved, and the quality of the recovered organic product needs to be improved.

[0006] The composition of the aqueous phase product of Fischer-Tropsch synthesis is complex and has a high water content. There are multiple azeotropic systems (except methanol, most alcohols azeotrope with water), which makes further separation more difficult and energy consumption is high. At the same time, the boiling points of ketones, aldehydes and alcohols in the aqueous phase product of Fischer-Tropsch synthesis are similar, which makes the separation process difficult. In addition, the low-carbon alcohol products separated therefrom usually contain other alcohol impurities (such as 2-butanol), aldehydes (such as acetaldehyde), ketones (such as acetone and 2-butanone) and esters (such as ethyl acetate) compounds. The presence of these components also affects the purity of the alcohol product and requires further separation and purification. Therefore, it is particularly necessary to develop an economical and efficient extraction and separation method to achieve effective separation and recovery of the aqueous phase product of Fischer-Tropsch synthesis.

[0007] Regarding the method for separating the aqueous phase products of Fischer-Tropsch synthesis, Chinese patents CN202011496642 and CN202011565616 propose a method for refining ethanol by azeotropic method and extracting propanol by extraction method. This method only separates a single component and fails to take into account the separation of methanol, ethanol and propanol at the same time, resulting in low product utilization. Chinese patent applications CN103044217A and CN103373909A propose a method for processing basic organic raw materials such as acetaldehyde, propionaldehyde, acetone, ethanol, n-propanol and mixed alcohols by subjecting Fischer-Tropsch synthesis water to organic acid distillation separation, ketone-alcohol cutting distillation separation, acetaldehyde refining, propionaldehyde-acetone distillation separation, acetone refining, propionaldehyde refining, anhydrous fusel alcohol separation, alcohol-water separation, aldehyde and ketone hydrogenation reduction, ethanol refining and n-propanol refining, ultimately obtaining acetaldehyde, propionaldehyde, acetone, ethanol, n-propanol and mixed alcohols. Although this method uses distillation to systematically separate and recover non-acidic oxygenated organic matter from the FT synthesis water, the process is complex and difficult to operate, and it is difficult to cope with the fluctuations in the water quality of the FT synthesis aqueous phase product. In addition, due to the low content of aldehydes and ketones in the FT synthesis aqueous phase product, this complex separation process is energy-intensive and costly, and the economic benefits are not significant. Therefore, the relevant technologies in this field still need to be further optimized to achieve more efficient and economical separation goals. Summary of the Invention

[0008] To address the aforementioned problems in the prior art, the present invention proposes a method for refining methanol, ethanol, and n-propanol from the aqueous phase product of Fischer-Tropsch synthesis. The method is simple to operate and has a large throughput. It can produce high-purity alcohol products while ensuring high product yields, meeting the economic requirements of industrial production.

[0009] The present invention provides a method for preparing methanol, ethanol and n-propanol from an aqueous phase product of Fischer-Tropsch synthesis. The method comprises the following steps: subjecting the aqueous phase product of Fischer-Tropsch synthesis to a first distillation to obtain an aqueous light alcohol; subjecting the aqueous light alcohol to extractive distillation to obtain a light alcohol and an extract; and subjecting the obtained light alcohol to sequential distillation to gradually separate a light component from a tower top, methanol, ethanol and n-propanol.

[0010] In a specific embodiment, the method for preparing methanol, ethanol and propanol from the aqueous phase product of Fischer-Tropsch synthesis comprises:

[0011] (1) performing a first distillation on the aqueous phase product of the Fischer-Tropsch synthesis to obtain aqueous light alcohol and aqueous heavy alcohol;

[0012] (2) subjecting the aqueous light alcohol to extractive distillation to obtain light alcohol (preferably having a water content of less than 2 wt %) and an extract;

[0013] (3) treating the light alcohol in step (2) in any one of the following ways to obtain methanol, ethanol and n-propanol:

[0014] a. subjecting the light alcohol described in step (2) to a second distillation to obtain a light component at the top of the tower and a mixed solution Ia of methanol, ethanol and n-propanol; subjecting the mixed solution Ia to a third distillation to obtain crude methanol and a mixed solution IIa of ethanol and n-propanol; subjecting the mixed solution IIa to a fourth distillation to obtain crude ethanol and crude n-propanol;

[0015] b. The light alcohol in step (2) is subjected to a second distillation to obtain a mixed liquid Ib of light components and methanol at the top of the tower, and a mixed liquid IIb of ethanol and n-propanol at the bottom of the tower; the mixed liquid Ib is subjected to a third distillation to obtain crude methanol and light components; the mixed liquid IIb is subjected to a fourth distillation to obtain crude ethanol and crude n-propanol.

[0016] Preferably, the extract can be recovered and reused. For example, the method may further include a step of recovering the extract obtained in step (2), thereby obtaining wastewater and alcohols, which can be reused.

[0017] In some preferred embodiments, the method includes a step of extracting the obtained crude methanol, crude ethanol and crude n-propanol to obtain high-purity methanol, ethanol and n-propanol.

[0018] The separation of the aqueous phase product of Fischer-Tropsch synthesis by the method of the present invention can exhibit the following beneficial effects, but is not limited thereto:

[0019] (1) The method of the present invention is a continuous operation, the purity of the product can be selected according to actual market requirements, it is easy to industrialize, the operation is simple, the recovery rate is high, and the economy is strong.

[0020] (2) The extractant used in the present invention can be recycled and reused, which is simple to recover and effectively reduces the cost of use.

[0021] (3) The wastewater and alcohols produced by the present invention can be recycled, effectively improving product yield, enhancing economic benefits, and being environmentally friendly.

[0022] (4) The method of the present invention can effectively separate the aqueous phase product of Fischer-Tropsch synthesis, improve the economy of coal chemical industry, enrich its product structure, and achieve environmental benefits.

[0023] (5) In addition, the method of the present invention has high purity and high recovery rate of methanol, ethanol and n-propanol after optional extraction and separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are a part of the specification and together with the detailed description, provide further explanation of the present invention but are not intended to limit the present invention.

[0025] Figure 1 The present invention is a flow chart of a method for preparing methanol, ethanol and n-propanol from an aqueous phase product of Fischer-Tropsch synthesis according to a specific embodiment of the present invention.

[0026] Description of the reference numerals is as follows:

[0027] T1 is a light alcohol separation tower, T2 is a light alcohol extraction tower, T3 is a light component removal tower (light components include aldehydes, ketones, and esters), T4 is a methanol separation tower, T5 is an ethanol separation tower, T6 is a n-propanol refining tower, T7 is a methanol refining tower, T8 is an ethanol extraction tower, and T9 is an extractant recovery tower;

[0028] 1 is the aqueous product logistics of Fischer-Tropsch synthesis, 2 is the light alcohol logistics with a water content of less than 15 wt%, 3 is the light alcohol logistics with a water content of less than 2 wt%, 4 is the light component logistics, 5 is the methyl, ethyl and propylene glycol mixed alcohol logistics, 6 is the crude methanol logistics, 7 is the refined methanol logistics, 8 is the methyl ethanol logistics, 9 is the ethyl propylene glycol logistics, 10 is the crude ethanol logistics, 11 is the crude n-propanol logistics, 12 is the refined n-propanol logistics, 13 is the n-propanol and heavy component logistics, 14 is the refined ethanol logistics, 15 is the heavy alcohol water logistics, 16 is the extract logistics, 17 is the extract logistics, 18 is the extractant logistics, 19 is the extractant logistics, and 20 is the aqueous alcohol logistics.

[0029] Figure 2 The present invention is a flow chart of a method for preparing methanol, ethanol and n-propanol from an aqueous phase product of Fischer-Tropsch synthesis according to a specific embodiment of the present invention.

[0030] Description of the reference numerals is as follows:

[0031] T1 is a light alcohol separation tower, T2 is a light alcohol extraction tower, T3 is a light component and methanol removal tower (light components include aldehydes, ketones, and esters), T4 is a light component removal tower, T5 is an ethanol separation tower, T6 is a n-propanol refining tower, T7 is a methanol refining tower, T8 is an ethanol extraction tower, and T9 is an extractant recovery tower;

[0032] 1 is the Fischer-Tropsch synthesis aqueous product logistics, 2 is the light alcohol logistics with a water content of less than 15 wt%, 3 is the light alcohol logistics with a water content of less than 2 wt%, 4 is the light component and methanol logistics, 5 is the light component logistics, 6 is the crude methanol logistics, 7 is the ethyl propanol logistics, 8 is the crude ethanol logistics, 9 is the crude n-propanol logistics, 10 is the refined n-propanol logistics, 11 is the n-propanol and heavy component logistics, 12 is the refined methanol logistics, 13 is the methyl ethanol logistics, 14 is the refined ethanol logistics, 15 is the heavy alcohol water logistics, 16 is the extract logistics, 17 is the extract logistics, 18 is the extractant logistics, 19 is the extractant logistics, and 20 is the aqueous alcohol logistics. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described in detail below. The specific embodiments described herein are only used to illustrate and explain the present invention, but are not used to limit the present invention.

[0034] Herein, unless otherwise specified, the term "high purity" refers to a mass purity of 95% or more, and the term "relatively high purity" refers to a mass purity of 80% or more.

[0035] "Fischer-Tropsch synthesis water" refers to the aqueous phase material containing oxygen-containing compounds such as alcohols and aldehydes produced in the Fischer-Tropsch synthesis reaction.

[0036] The present invention is further described below by way of examples, but the present invention is not limited thereto.

[0037] The present invention provides a method for preparing methanol, ethanol and n-propanol from an aqueous phase product of Fischer-Tropsch synthesis. The method comprises the following steps: subjecting the aqueous phase product of Fischer-Tropsch synthesis to a first distillation to obtain an aqueous light alcohol; subjecting the aqueous light alcohol to extractive distillation to obtain a light alcohol and an extract; and subjecting the obtained light alcohol to sequential distillation to gradually separate a light component from a tower top, methanol, ethanol and n-propanol.

[0038] In a specific embodiment, the method for preparing methanol, ethanol and n-propanol from the aqueous phase product of Fischer-Tropsch synthesis according to the present invention comprises:

[0039] (1) performing a first distillation on the aqueous phase product of the Fischer-Tropsch synthesis to obtain aqueous light alcohol and aqueous heavy alcohol;

[0040] (2) subjecting the aqueous light alcohol to extractive distillation to obtain a light alcohol (e.g., wherein the water content is less than 2 wt %) and an extract;

[0041] (3) treating the light alcohol in step (2) in any one of the following ways to obtain methanol, ethanol and n-propanol:

[0042] a. subjecting the light alcohol described in step (2) to a second distillation to obtain a light component at the top of the tower and a mixed solution Ia of methanol, ethanol and n-propanol; subjecting the mixed solution Ia to a third distillation to obtain crude methanol and a mixed solution IIa of ethanol and n-propanol; subjecting the mixed solution IIa to a fourth distillation to obtain crude ethanol and crude n-propanol;

[0043] b. The light alcohol described in step (2) is subjected to a second distillation to obtain a mixed liquid Ib of light components and methanol at the top of the tower, and a mixed liquid IIb of ethanol and n-propanol at the bottom of the tower; the mixed liquid Ib is subjected to a third distillation to obtain crude methanol and light components; and the mixed liquid IIb is subjected to a fourth distillation to obtain crude ethanol and crude n-propanol.

[0044] In a preferred embodiment, in mode a), the mixed liquid IIa is subjected to a fourth distillation to obtain crude ethanol at the top of the tower and crude n-propanol at the bottom of the tower.

[0045] Preferably, the extract of step (2) can be recovered and reused. For example, the method may further include a step of recovering the extract obtained in step (2) to obtain wastewater and alcohols, which can be reused.

[0046] In the present invention, the Fischer-Tropsch synthesis aqueous phase product is a product rich in alcohols containing about 30wt% of water obtained by treating the Fischer-Tropsch synthesis water obtained in the Fischer-Tropsch synthesis. Usually, the Fischer-Tropsch synthesis aqueous phase product is obtained by deoiling, alkali neutralization, and distillation of the Fischer-Tropsch synthesis water. For example, the Fischer-Tropsch synthesis water is subjected to a deoiling step to obtain deoiled Fischer-Tropsch synthesis water, and then an alkaline substance is added thereto for neutralization treatment to prepare neutralized Fischer-Tropsch synthesis water; the water is further allowed to enter a distillation tower for separation, and Fischer-Tropsch synthesis wastewater is produced at the bottom of the tower, while the Fischer-Tropsch synthesis aqueous phase product (containing mixed alcohols, preferably, with a water content of about 30wt%) is obtained at the top of the tower.

[0047] In some embodiments, in step (1), the total content of methanol, ethanol, and n-propanol in the aqueous phase product of the Fischer-Tropsch synthesis is preferably in the range of 50 wt% to 60 wt%, the water content is generally not higher than 35 wt% (preferably not higher than 30 wt%), and the total content of aldehydes, ketones, esters and other alcohols is not higher than 15 wt%.

[0048] In this application, according to the process characteristics of Fischer-Tropsch synthesis, other alcohols may include 2-butanol, isopropanol, butanol, pentanol, etc. Aldehydes, ketones, and esters include, for example, propionaldehyde, n-butyraldehyde, acetone, 2-pentanone, methyl acetate, ethyl acetate, etc.

[0049] The preparation method of the present invention can also be used for a Fischer-Tropsch synthesis aqueous phase product having a total content of methanol, ethanol, and n-propanol of less than 50 wt%.

[0050] In some embodiments, in step (1), the conditions of the first distillation are: top temperature of 70°C-78°C, bottom temperature of 90°C-95°C, top pressure of 100-110 kPa, number of plates of 25-45 (for example, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45), the feed position is the 10th to 25th plate from the top, and the reflux ratio is 0.5-3.

[0051] For example, the top temperature of the first distillation can be selected from 70°C, 71°C, 72°C, 73°C, 74°C, 75°C or 76°C, or any value in the range formed by any two of the above values, such as 75°C-76°C, 74°C-75°C; or, the bottom temperature of the first distillation can be selected from 90°C, 91°C, 92°C, 93°C, 94°C or 95°C, or any value in the range formed by any two of the above values, such as 91°C-92°C, 92°C-93°C; or, the number of plates of the first distillation can be selected from 25, 30, 3 5, 40 or 45, or any value in the range formed by any two of the above values, for example, 25-40; alternatively, the feed position of the first distillation may be the 10th, 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th, 20th, 21st, 22nd, 23rd, 24th or 25th tray from the top, or any value in the range formed by any two of the above values, for example, 10-20; alternatively, the reflux ratio of the first distillation is 0.5, 1, 1.5, 2, 2.5 or 3, or any value in the range formed by any two of the above values, for example, 1.

[0052] In some embodiments, in step (1), the aqueous light alcohol refers to a water content of 2.0 wt% to 15.0 wt%, a total content of C1-C3 light alcohols of not less than 80 wt%, and a total content of aldehydes, ketones, esters and other alcohols of not more than 10 wt%.

[0053] In the present invention, the term "C1-C3 light alcohol" includes methanol, ethanol, isopropanol and n-propanol.

[0054] In some embodiments, the aqueous heavy alcohol in step (1) refers to an aqueous C4-C8 alcohol having a water content of 50 wt% to 60 wt%. In the present invention, the term "C4-C8 alcohol" includes butanol, pentanol, hexanol, heptanol, octanol, etc., such as n-butanol, n-pentanol, n-hexanol, n-heptanol, and n-octanol.

[0055] In a specific embodiment, the water content of the aqueous light alcohol is 5.0wt%-15.0wt%, for example, 5.0wt%, 5.5wt%, 6.0wt%, 6.5wt%, 7.0wt%, 7.5wt%, 8.0wt%, 8.5wt%, 9.0wt%, 9.5wt%, 10wt%, 10.5wt%, 11.0wt%, 11.5wt%, 12.0wt%, 12.5wt%, 13.0wt%, 13.5wt%, 14.0wt%, 14.5wt% or 15.0wt%, or any value in the range formed by any two of the above values. Preferably, the water content of the aqueous light alcohol is 10.0wt%-15.0wt%.

[0056] In some embodiments, in step (2), the extractant is selected from one or more of ethylene glycol, glycerol, diethylene glycol, and ethylene glycol (95 wt%) + potassium acetate (5 wt%). Preferably, the extractant is ethylene glycol.

[0057] In some embodiments, the operating conditions of the extraction in step (2) are as follows: the number of theoretical plates is 30-45, the feed position is the 20th to 35th plate from the top, the extractant feed position is the 5th to 15th plate from the top, the reflux ratio is 0.5-2, the top pressure is controlled at 100-110 kPa, the top temperature is 70°C-78°C, the bottom temperature is 145°C-160°C, and the agent-to-material ratio is 1:1 to 5:1.

[0058] For example, the number of theoretical plates for extraction is 30-45, preferably 30-40, such as 30, 35, 40 or 45, or any value in the range formed by any two of the above values. Alternatively, the feed position for extraction can be the 20th to 35th, preferably 20-30th, such as the 20th, 21st, 22nd, 23rd, 24th, 25th, 26th, 27th, 28th, 29th, 30th, 31st, 32nd, 33rd, 34th or 35th plate, or any value in the range formed by any two of the above values. Alternatively, the feed position for the extractant in the extraction is the 5th to 15th, preferably 5th to 10th plate, such as the 5th, 6th, 7th, 8th, 9th, 10th, 11th, 12th, 13th, 14th or 15th plate, or any value in the range formed by any two of the above values. Alternatively, the reflux ratio in the extraction is 0.5-2, preferably 0.5-1, for example, 0.5, 1, 1.5 or 2. Alternatively, the top temperature of the extraction column is 70°C-78°C, preferably 73°C-74°C, 74°C-75°C, for example, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C or 78°C, or any value in the range formed by any two of the above values. Alternatively, the bottom temperature of the extraction column is 145°C-160°C, preferably 150°C-155°C, 152°C-155°C, 149°C-152°C, for example, 145°C, 148°C, 149°C, 150°C, 152°C, 153°C, 154°C, 155°C, 158°C or 160°C, or any value in the range formed by any two of the above values. Alternatively, the extraction dose-to-material ratio is 1:1 to 5:1, preferably 2:1 to 3:1, for example 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, or any value in the range formed by any two of the above values.

[0059] Light alcohol is obtained at the top of the column. The extract is obtained at the bottom of the column. The light alcohol obtained in step (2) has a water content of less than 2 wt%, a total content of methanol, ethanol, and n-propanol of greater than 93 wt% (preferably greater than 95 wt%), and other oxygen-containing organic components preferably less than 5 wt%.

[0060] In some embodiments, in mode a) of step (3), the conditions for the second distillation are: tower top temperature 52°C-59°C, tower bottom temperature 74°C-77°C, tower top pressure 100-110 kPa, number of tower plates 30-60, feed position 15-30th tower plate from the top, and reflux ratio 6-12.

[0061] In a specific embodiment, in mode a) of step (3), the top temperature of the second distillation may be 52°C, 53°C, 54°C, 55°C, 56°C or 57°C, for example, 55°C-58°C, 56°C-57°C or 57°C-58°C; or, the bottom temperature may be 74°C, 75°C, 76°C or 77°C, for example, 75°C-76°C; or, the number of plates is 30, 35, 40, 45, 50, 55 or 60, for example, 40-60; or, the feed position is the 20th-30th plate from the top, for example, the 20th, 25th or 30th plate; or, the reflux ratio is 10.

[0062] In some embodiments, the light fraction obtained at the top of the tower in step (3) a) mainly includes acetaldehyde, propionaldehyde, acetone, methyl acetate, butyraldehyde, methanol, etc. The reason for the presence of a small amount of methanol is that acetone and methanol form an azeotrope. In order to remove acetone as much as possible, a small amount of methanol is inevitably lost. The amount of methanol loss can vary depending on the acetone removal rate and can be determined by comprehensively considering the content of the raw material components.

[0063] The total content of methanol, ethanol and n-propanol in the obtained mixed solution Ia was 95 wt %.

[0064] In some embodiments, in mode b) of step (3), the conditions for the second distillation are: tower top temperature 58°C-65°C (e.g., 59°C-62°C), tower bottom temperature 75°C-82°C (e.g., 79°C-81°C), tower top pressure 100-110 kPa (e.g., 100 kPa), number of tower plates 60-90 (e.g., 80), feed position 40-50th tower plate from the top (e.g., 42), and reflux ratio 3-6 (e.g., 5).

[0065] In the b) method of step (3), in the second distillation, the light components include acetaldehyde, propionaldehyde, methyl acetate, ethyl acetate, etc. The content of methanol in the mixed solution Ib is not less than 80 wt %. The obtained mixed solution Ib may contain small amounts of ethanol, n-propanol, isopropanol, etc.

[0066] The total content of ethanol and n-propanol in the obtained mixed solution IIb of ethanol and n-propanol was 96 wt %.

[0067] In some embodiments, in the method a) of step (3), the conditions of the third distillation are: tower top temperature 40°C-65°C, tower bottom temperature 58°C-80°C, tower top pressure 35-110 kPa, tower plate number 40-80, feed position 15-45 tower plates, and reflux ratio 8-10.

[0068] In a specific embodiment, in the a) mode of step (3), the top temperature of the third distillation may be 40°C, 42°C, 43°C, 44°C, 45°C, 50°C, 52°C, 55°C, 60°C, 62°C, 64°C, or 65°C, for example, 42°C-43°C, 43°C-44°C, or 64°C-65°C; or the bottom temperature may be 58°C, 59°C, 60°C, 65°C, 70°C, 75°C , 76℃, 77℃, 78℃, 79℃ or 80℃, for example, 58℃-59℃ or 79℃-80℃; or, the number of tower plates is 40, 45, 50, 55, 60, 65, 70, 75 or 80, for example, 40-60; or, the feed position is the 20th-45th tower plate from the top, for example, the 20th, 25th, 30th, 35th, 40th or 45th tower plate; or, the reflux ratio is 8, 9, 10.

[0069] In some embodiments, in mode a) of step (3), the crude methanol contains not less than 85 wt% of methanol, not more than 8 wt% of ethanol, not more than 5 wt% of other oxygen-containing compounds (acetone, methyl acetate, ethyl acetate, butyraldehyde, etc.) and a small amount of impurities.

[0070] The obtained mixed solution IIa mainly contains ethanol, n-propanol, isopropanol and the like.

[0071] The total content of ethanol and n-propanol in the obtained mixed solution IIa was 96 wt %.

[0072] In some embodiments, in mode b) of step (3), the conditions of the third distillation are: tower top temperature 47°C-50°C (e.g., 48°C-50°C), tower bottom temperature 63°C-65°C (e.g., 64°C-65°C), tower top pressure 100-110 kPa, number of tower plates 30-50 (e.g., 40), feed position 15-25th tower plate from the top (e.g., 24), and reflux ratio 9-12 (e.g., 10).

[0073] In some embodiments, in mode b) of step (3), the crude methanol contains not less than 90 wt% of methanol, not more than 5 wt% of ethanol, not more than 5 wt% of other oxygen-containing compounds (acetone, methyl acetate, ethyl acetate, butyraldehyde, etc.) and a small amount of impurities.

[0074] In some embodiments, in mode b) of step (3), in the third distillation, the light components include acetaldehyde, propionaldehyde, methyl acetate, ethyl acetate, etc.

[0075] In some embodiments, in the a) and b) modes of step (3), the conditions of the fourth distillation are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, number of tower plates 30-90, feed position 13-50th tower plate from the top, and reflux ratio 2-6.

[0076] In some embodiments, in the a) method of step (3), the conditions of the fourth distillation are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, number of tower plates 30-80, feed position 13-50th tower plate from the top, and reflux ratio 2-6.

[0077] In a specific embodiment, in mode a) of step (3), the top temperature of the fourth distillation may be 76°C, 77°C, 78°C or 79°C, for example, 77°C-78°C; or, the bottom temperature may be 95°C, 96°C, 97°C or 98°C, for example, 97°C-98°C; or, the number of plates is 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 or 80, for example, 40-80; or, the feed position is the 15th to 25th plate from the top, for example, the 20th, 24th, 25th, 30th, 35th or 40th plate; or, the reflux ratio is 2.

[0078] In some embodiments, in mode b) of step (3), the conditions of the fourth distillation are: tower top temperature 76°C-80°C (e.g., 77°C-78°C), tower bottom temperature 95°C-98°C (e.g., 97°C-98°C), tower top pressure 100-110 kPa, number of tower plates 60-90 (e.g., 80), feed position 30-50th tower plate from the top (e.g., 40th), and reflux ratio 2-6 (e.g., 5).

[0079] In some embodiments, in the methods a) and b) of step (3), the crude ethanol contains not less than 95 wt% ethanol, and small amounts of water, isopropanol, n-propanol, and other components. To ensure that the n-propanol does not contain water, ethanol and water are azeotropically removed to remove all water and enter the crude ethanol stream.

[0080] In some embodiments, in the a) and b) modes of step (3), the crude n-propanol at the bottom of the tower contains not less than 90 wt% of n-propanol, and the remainder is 2-butanol, 2-methyl-1-propane, 2-hexanone, 1-(1-ethoxy)-propane and other components.

[0081] In some embodiments, the extractant recovery is to remove alcohols (propanol, butanol, etc.) and water from the extract to recover an extractant with a mass purity greater than 99.5%. The alcohols and water can be returned to step (1) to improve the recovery rate of n-propanol.

[0082] In some embodiments, the extractant recovery is carried out using an extractant recovery tower: the theoretical number of plates is 10-20 (e.g., 10, 15, or 20), the feed position is the 5th to 10th plate from the top (e.g., the 5th or 7th), the top pressure is controlled to be 10 KPa-30 KPa (e.g., 10 KPa or 20 KPa), the top temperature is 37°C-60°C (e.g., 37°C-39°C, 50°C-52°C), the bottom temperature is 120°C-160°C (e.g., 129°C-131°C, 147°C-148°C), the reflux ratio is 2-4 (e.g., 2 or 3), a hydrous alcohol stream is obtained at the top of the tower, and an extractant stream is obtained at the bottom of the tower.

[0083] In some preferred embodiments, the crude methanol, crude ethanol and crude n-propanol are optionally distilled again to obtain methanol, ethanol and n-propanol with higher purity.

[0084] In some preferred embodiments, the conditions for methanol refining are: the number of theoretical plates is 35-80 (e.g., 40 or 80), the feed position is the 10th to 40th plate from the top (e.g., the 20th or 40th plate), the top pressure is controlled at 100-110 kPa, the top temperature is 62°C-65°C (e.g., 63.5°C-64.5°C, 64°C-65°C), the bottom temperature is 68°C-73°C (e.g., 69°C-70°C, 69.5°C-71°C, 69.5°C-73°C), and the reflux ratio is 2-5 (e.g., 3, 4). Through methanol refining, refined methanol with a purity greater than 95 wt% can be obtained at the top of the tower, and a small amount of methanol, ethanol, etc. can be obtained at the bottom of the tower.

[0085] In some preferred embodiments, the n-propanol refining conditions are as follows: the number of theoretical plates is 35-80 (e.g., 40 or 80), the feed position is the 20th to 45th plate from the top (e.g., the 20th, 40th, or 42nd plate), the top pressure is controlled at 100-110 kPa, the top temperature is 95° C.-98° C. (e.g., 96° C.-97° C., 95° C.-97.5° C., 96.5° C.-97.5° C.), the bottom temperature is 96° C.-102° C. (e.g., 97° C.-99° C., 98° C.-99° C.), and the reflux ratio is 5-10 (e.g., 5, 6, or 10). At the top of the tower, n-propanol with a purity greater than 98% is obtained, and at the bottom of the tower, an alcohol stream containing a small amount of propanol and 2-butanol, 2-methyl-1-propanol, 2-hexanone, etc. is obtained.

[0086] In some preferred embodiments, the same extractant as in step (2) is used to extract crude ethanol, and the extraction conditions may be: the theoretical number of tower plates is 30-40 (e.g., 40), the feed position is the 20th-30th plate from the top (e.g., the 30th), the extractant feed position is 5-10 plates from the top (e.g., the 10th), the top pressure is controlled to be 100-110 kPa, the top temperature is 77°C-79°C (e.g., 77.5°C-78°C, 77.5°C-78.5°C), the bottom temperature is 140-158°C (e.g., 144°C-146°C, 149°C-151°C, 156°C-157°C), the agent-to-material ratio is 0.9-1.2:1 (e.g., 0.9:1, 1:1, 1.2:1), and the reflux ratio is 2-3 (e.g., 2). A refined ethanol stream with a purity greater than 99% is obtained at the top of the tower, and an extract stream containing water, isopropanol, 2-pentanone, etc. is obtained at the bottom of the tower. In a preferred embodiment, the extractant is ethylene glycol.

[0087] In some preferred embodiments, the bottom stream of the secondary distillation of crude methanol can be returned to the third distillation for recycling.

[0088] The method provided by the present invention is described in detail below with reference to the accompanying drawings, but the present invention is not limited thereto.

[0089] The following combination Figure 1 The present invention is further described.

[0090] The Fischer-Tropsch synthesis aqueous product stream 1 enters the light alcohol separation tower T1 for the first distillation, obtaining a light alcohol stream 2 with a water content of less than 15 wt% at the top of the tower and a heavy alcohol water stream 15 at the bottom of the tower;

[0091] Light alcohol stream 2 enters light alcohol extraction tower T2 for extraction with an extractant, obtaining light alcohol stream 3 with a water content of less than 2 wt% at the top of the tower and extract stream 16 at the bottom of the tower;

[0092] Light alcohol stream 3 enters light component removal tower T3 for secondary distillation, obtaining light component stream 4 at the top and methyl, ethyl and propylene glycol mixed alcohol stream 5 at the bottom;

[0093] The methyl, ethyl and propylene glycol mixed alcohol stream 5 enters the methanol separation tower T4 for third distillation, obtaining a crude methanol stream 6 at the top of the tower and an ethylene-propylene glycol stream 9 at the bottom of the tower;

[0094] The ethylene propanol stream 9 enters the ethanol separation tower T5 for fourth distillation, and a crude ethanol stream 10 is obtained at the top of the tower, and a crude n-propanol stream 11 is obtained at the bottom of the tower;

[0095] Optionally, the crude n-propanol stream 11 enters the n-propanol refining tower T6 for refining, and a refined n-propanol stream 12 is obtained at the top of the tower, and a n-propanol and heavy component stream 13 is obtained at the bottom of the tower;

[0096] The crude methanol stream 6 enters the methanol refining tower T7 for refining, and the refined methanol stream 7 is obtained at the top of the tower, and the methyl ethanol stream 8 is obtained at the bottom of the tower;

[0097] The crude ethanol stream 10 enters the ethanol extraction tower T8 and is subjected to extractive distillation using an extractant, obtaining a refined ethanol stream 14 at the top of the tower and an extract stream 17 at the bottom of the tower.

[0098] The extract streams 16 and 17 are mixed and fed into the extractant recovery tower T9 for recovery. The top of the tower produces the aqueous alcohol stream 20, and the bottom of the tower produces the extractant streams 18 and 19. Optionally, the extractant streams 18 and 19 are fed to the light alcohol extraction tower and / or the ethanol extraction tower.

[0099] The following combination Figure 2 The present invention is further described.

[0100] The Fischer-Tropsch synthesis aqueous product stream 1 enters the light alcohol separation tower T1 for the first distillation, and a light alcohol stream 2 with a water content of less than 15 wt% is obtained at the top of the tower, and a heavy alcohol water stream 15 is produced at the bottom of the tower;

[0101] Light alcohol stream 2 enters light alcohol extraction T2 for extraction with an extractant, obtaining light alcohol stream 3 with a water content of less than 2 wt% at the top of the tower, and extract stream 16 at the bottom of the tower;

[0102] Light alcohol stream 3 enters light component removal and methanol tower T3 for secondary distillation, obtaining light component and methanol stream 4 at the top of the tower and ethylene propanol stream 7 at the bottom of the tower;

[0103] The light component and methanol stream 4 enters the light component removal tower T4 for third distillation, obtaining light component stream 5 at the top of the tower and crude methanol stream 6 at the bottom of the tower;

[0104] The ethylene propanol stream 7 enters the ethanol separation tower T5 for the fourth distillation, and the crude ethanol stream 8 is obtained at the top of the tower, and the crude n-propanol stream 9 is obtained at the bottom of the tower;

[0105] Optionally, the crude n-propanol stream 9 enters the n-propanol refining tower T6 for refining, and a refined n-propanol stream 10 is obtained at the top of the tower, and an n-propanol and heavy component stream 11 is obtained at the bottom of the tower.

[0106] The crude methanol stream 6 enters the methanol refining tower T7 for refining, and the refined methanol stream 12 is obtained at the top of the tower, and the methyl ethanol stream 13 is obtained at the bottom of the tower;

[0107] The crude ethanol stream 8 enters the ethanol extraction tower T8 and is subjected to extractive distillation using an extractant, obtaining a refined ethanol stream 14 at the top of the tower and an extract stream 17 at the bottom of the tower.

[0108] The extract streams 16 and 17 are mixed and fed into the extractant recovery tower T9 for recovery. The top of the tower produces the aqueous alcohol stream 20, and the bottom of the tower produces the extractant streams 18 and 19. Optionally, the extractant streams 18 and 19 are fed to the light alcohol extraction tower and / or the ethanol extraction tower.

[0109] The content of the present invention can be exemplified by the following numbered paragraphs:

[0110] 1. A method for preparing methanol, ethanol and n-propanol from an aqueous phase product of Fischer-Tropsch synthesis, the method comprising:

[0111] (1) performing a first distillation on the aqueous phase product of the Fischer-Tropsch synthesis to obtain aqueous light alcohol and aqueous heavy alcohol;

[0112] (2) extracting and rectifying the aqueous light alcohol to obtain light alcohol and an extract;

[0113] (3) treating the light alcohol in step (2) in any one of the following ways to obtain methanol, ethanol and n-propanol:

[0114] a. subjecting the light alcohol described in step (2) to a second distillation to obtain a light component at the top of the tower and a mixed solution Ia of methanol, ethanol and n-propanol; subjecting the mixed solution Ia to a third distillation to obtain crude methanol and a mixed solution IIa of ethanol and n-propanol; subjecting the mixed solution IIa to a fourth distillation to obtain crude ethanol and crude n-propanol;

[0115] b. The light alcohol described in step (2) is subjected to a second distillation to obtain a mixed liquid Ib of light components and methanol at the top of the tower, and a mixed liquid IIb of ethanol and n-propanol at the bottom of the tower; the mixed liquid Ib is subjected to a third distillation to obtain crude methanol and light components; and the mixed liquid IIb is subjected to a fourth distillation to obtain crude ethanol and crude n-propanol.

[0116] 2. The method as described in paragraph [1], wherein, in method a), the mixed liquid IIa is subjected to a fourth distillation to obtain crude ethanol at the top of the tower and crude n-propanol at the bottom of the tower.

[0117] 3. The method as described in paragraph [1] or [2], wherein the extract of step (2) is recovered and reused.

[0118] 4. The method as described in any one of paragraphs [1] to [3], wherein the Fischer-Tropsch synthesis aqueous phase product is an alcohol-rich product with a water content of less than 35 wt% obtained by treating the Fischer-Tropsch synthesis water obtained in the Fischer-Tropsch synthesis.

[0119] 5. The method as described in paragraph [4], wherein the Fischer-Tropsch synthesis aqueous phase product is obtained by deoiling, alkali neutralization, and distillation of Fischer-Tropsch synthesis water.

[0120] 6. The method according to any one of paragraphs [1] to [5], wherein in step (1), the total content of methanol, ethanol and n-propanol in the aqueous phase product of Fischer-Tropsch synthesis is between 50 wt% and 60 wt%, the water content is not higher than 35 wt%, and the total content of aldehydes, ketones, esters and other alcohols is not higher than 15 wt%.

[0121] 7. The method of any one of paragraphs [1] to [6], wherein in step (1), the conditions for the first distillation are: tower top temperature 70°C-78°C, tower bottom temperature 90°C-95°C, tower top pressure 100-110 kPa, number of tower plates 25-45, feed position 10-25th tower plate from the top, and reflux ratio 0.5-3.

[0122] 8. The method of paragraph [7], wherein the top temperature of the first distillation column is selected from 70°C, 71°C, 72°C, 73°C, 74°C, 75°C or 76°C, or any value in the range formed by any two of the above values; or

[0123] The bottom temperature of the first distillation column is selected from 90°C, 91°C, 92°C, 93°C, 94°C or 95°C, or any value in the range formed by any two of the above values; or

[0124] The number of plates in the first distillation is selected from 25, 30, 35, 40 or 45, or any value in the range formed by any two of the above values; or

[0125] The feed position of the first distillation is the 10th, 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th, 20th, 21st, 22nd, 23rd, 24th or 25th tray from the top, or any value in the range formed by any two of the above values; or

[0126] The reflux ratio of the first distillation is 0.5, 1, 1.5, 2, 2.5 or 3, or any value within the range formed by any two of the above values.

[0127] 9. The method of any one of paragraphs [1] to [8], wherein in step (1), the aqueous light alcohol has a water content of 2.0 wt% to 15.0 wt% and a total C1-C3 light alcohol content of not less than 80 wt%.

[0128] 10. The method of any one of paragraphs [1] to [9], wherein the water content of the aqueous light alcohol is 10.0 wt% to 15.0 wt%.

[0129] 11. The method according to any one of paragraphs [1] to

[10] , wherein in step (2), the extractant is selected from one or more of ethylene glycol, glycerol, diethylene glycol, and ethylene glycol + potassium acetate.

[0130] 12. The method of paragraph

[11] , wherein the extractant is ethylene glycol.

[0131] 13. The method according to any one of paragraphs [1] to

[12] , wherein in step (2), the extraction operating conditions are as follows: the number of theoretical plates is 30-45, the feed position is the 20th to 35th plate from the top, the extractant feed position is the 5th to 15th plate from the top, the reflux ratio is 0.5-2, the top pressure is controlled at 100-110 kPa, the top temperature is 70°C-78°C, the bottom temperature is 145°C-160°C, and the agent-to-material ratio is 1:1 to 5:1.

[0132] 14. The method of paragraph

[13] , wherein the number of theoretical plates of the extraction is 30-40; or

[0133] The extraction feed position is 20-30 trays from the top; or,

[0134] The extraction agent is fed into the extraction tray 5-10 from the top; or

[0135] The reflux ratio in the extraction is 0.5-1; or,

[0136] The extraction tower top temperature is 73℃-75℃; or,

[0137] The bottom temperature of the extraction tower is 149°C-155°C; or

[0138] The extraction agent-material ratio is preferably 2:1 to 3:1.

[0139] 15. The method according to any one of paragraphs [1] to

[14] , wherein light alcohol is obtained at the top of the column and the extract is obtained at the bottom of the column.

[0140] 16. The method according to any one of paragraphs [1] to

[15] , wherein the light alcohol obtained in step (2) has a water content of less than 2 wt %, and a total content of methanol, ethanol and n-propanol of greater than 93 wt %.

[0141] 17. The method according to any one of paragraphs [1] to

[16] , wherein in step (3) a), the conditions for the second distillation are: tower top temperature 52°C-59°C, tower bottom temperature 74°C-77°C, tower top pressure 100-110 kPa, number of tower plates 30-60, feed position 15-30th tower plate from the top, and reflux ratio 6-12.

[0142] 18. The method of paragraph

[17] , wherein, in step (3) a), the top temperature of the second distillation tower is 55°C-58°C, 56°C-57°C, or 57°C-58°C; or

[0143] The bottom temperature is 75℃-76℃; or

[0144] The number of plates is 40-60; or

[0145] The feed position is the 20th to 30th tray from the top; or

[0146] The reflux ratio is 10.

[0147] 19. The method according to any one of paragraphs [1] to

[16] , wherein in step (3) b), the conditions for the second distillation are: tower top temperature 58°C-65°C, tower bottom temperature 75°C-82°C, tower top pressure 100-110 kPa, number of tower plates 60-90, feed position 40-50th tower plate from the top, and reflux ratio 3-6.

[0148] 20. The method as described in paragraph

[19] , wherein in step (3) b), the conditions for the second distillation are: tower top temperature 59°C-62°C, tower bottom temperature 79°C-81°C, tower top pressure 100 kPa, number of tower plates 80, feed position 42nd tower plate from the top, and reflux ratio 5.

[0149] 21. The method of any one of paragraphs [1] to

[18] , wherein in step (3) a), the conditions for the third distillation are: tower top temperature 40°C-65°C, tower bottom temperature 58°C-80°C, tower top pressure 35-110 kPa, number of tower plates 40-80, feed position 15-45 tower plates, and reflux ratio 8-10.

[0150] 22. The method of paragraph

[21] , wherein, in step (3) a), the top temperature of the third distillation is 42°C-43°C, 43°C-44°C, or 64°C-65°C; or

[0151] The tower bottom temperature is 58°C-59°C or 79°C-80°C; or

[0152] The number of plates is 40-60; or

[0153] The feed position is the 20th to 45th tray from the top; or

[0154] The reflux ratio is 8, 9, and 10.

[0155] 23. The method of any one of paragraphs [1] to

[18] , wherein in step (3) a), the crude methanol contains not less than 85 wt% of methanol; or, the total content of ethanol and n-propanol in the obtained mixed solution IIa is 96 wt%.

[0156] 24. The method of any one of paragraphs [1] to

[16] , wherein in step (3) b), the conditions for the third distillation are: tower top temperature 47°C-50°C, tower bottom temperature 63°C-65°C, tower top pressure 100-110 kPa, number of tower plates 30-50, feed position 15-25 from the top, and reflux ratio 9-12.

[0157] 25. The method as described in paragraph

[24] , wherein, in mode b) of step (3), the conditions for the third distillation are: tower top temperature 48°C-50°C, tower bottom temperature 64°C-65°C, tower top pressure 100-110 kPa, number of tower plates 40, feed position 24th tower plate from the top, and reflux ratio 10.

[0158] 26. The method of any one of paragraphs [1] to

[16] , wherein in the methods a) and b) of step (3), the conditions for the fourth distillation are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, number of tower plates 30-90, feed position 13-50th tower plate from the top, and reflux ratio 2-6.

[0159] 27. The method of paragraph

[26] , wherein in step (3) a), the fourth distillation conditions are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, number of trays 30-80, feed position 13-50 from the top, reflux ratio 2-6; or

[0160] In the b) mode of step (3), the conditions of the fourth distillation are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, tower plate number 60-90, feed position 30-50th tower plate from the top, and reflux ratio 2-6.

[0161] 28. The method according to any one of paragraphs [1] to

[27] , further comprising the step of recovering the extractant, wherein the extractant recovery is carried out using an extractant recovery tower: the number of theoretical plates is 10-20, the feed position is the 5th to 10th plate from the top, the top pressure is controlled to be 10 KPa-30 KPa, the top temperature is 37°C-60°C, the bottom temperature is 120°C-160°C, the reflux ratio is 2-4, and a water-containing alcohol stream is obtained at the top of the tower, and an extractant stream is obtained at the bottom of the tower.

[0162] 29. The method according to any one of paragraphs [1] to

[28] , wherein the method comprises the step of further distilling the obtained crude methanol, crude ethanol and crude n-propanol.

[0163] 30. The method of paragraph

[29] , wherein the methanol refining conditions are: the number of theoretical plates is 35-80, the feed position is the 10th to 40th plate from the top, the top pressure is controlled at 100-110 kPa, the top temperature is 62°C-65°C, the bottom temperature is 68°C-73°C, and the reflux ratio is 2-5; or

[0164] The conditions for refining n-propanol are: the theoretical number of plates is 35-80, the feed position is the 20th to 45th plate from the top, the top pressure is controlled at 100-110 kPa, the top temperature is 95°C-98°C, the bottom temperature is 96°C-102°C, and the reflux ratio is 5-10; or

[0165] The same extractant as in step (2) is used to extract crude ethanol. The extraction conditions may be as follows: the theoretical number of tower plates is 30-40, the feed position is the 20th-30th tower plate from the top, the extractant feed position is 5-10 plates from the top, the tower top pressure is controlled to be 100-110 kPa, the tower top temperature is 77° C.-79° C., the tower bottom temperature is 140-158° C., the agent-to-material ratio is 0.9-1.2:1, and the reflux ratio is 2-3.

[0166] 31. The method of paragraph

[30] , wherein the bottom stream of the secondary distillation of crude methanol is returned to the third distillation for recycling.

[0167] Example

[0168] Unless otherwise specified, the reagents, materials and devices involved in the following examples are all commercially available in the art; the conventional operations involved in the following examples can be found in patents, patent applications and publications disclosed in the art (for example, He Yongde, ed., "Modern Coal Chemical Technology Handbook", Chemical Industry Press, 2003, but not limited thereto).

[0169] Example 1

[0170] according to Figure 1 In the process shown, the Fischer-Tropsch synthesis aqueous product stream 1 (composition is shown in Table 1) enters the light alcohol separation tower T1. Under the conditions of 25 theoretical plates, a reflux ratio of 1, and a feed position of the 13th plate from the top, the top operating pressure is controlled to be 100 KPa, the top temperature is 75°C-76°C, and the bottom temperature is 91°C-92°C. A light alcohol stream 2 with a water content of less than 15 wt% is produced from the top of the tower, and the water content in this embodiment is 13.5 wt%. A heavy alcohol water stream 15 is produced from the bottom of the tower.

[0171] A light alcohol stream 2 with a water content of 13.5 wt% enters a light alcohol extraction tower T2, which is an extractive distillation tower. Ethylene glycol is used as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 1, a dose-to-material ratio of 3:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 18 of the 10th plate from the top, the top pressure of the tower is controlled to be 100 KPa, the top temperature of the tower is 73°C-74°C, and the bottom temperature of the tower is 152°C-155°C. A light alcohol stream 3 with a water content of less than 2 wt% is obtained at the top of the tower. In this embodiment, the water content of the light alcohol stream 3 is 0.8 wt%, and an extract stream 16 is obtained at the bottom of the tower.

[0172] The light alcohol stream 3 with a water content of 0.8 wt% enters the light component removal tower T3. Under the conditions of 40 theoretical plates, a reflux ratio of 10, and a feed position of the 20th plate from the top, the top pressure is controlled to be 100 KPa, the top temperature is 56-57 ° C, and the bottom temperature is 75-76 ° C. A light component stream 4 is obtained at the top of the tower, and an methyl, ethyl, and propylene glycol mixed alcohol stream 5 is obtained at the bottom of the tower.

[0173] A mixture of methyl, ethyl and propylene glycol stream 5 enters the methanol separation tower T4. Under the conditions of 40 theoretical plates, a reflux ratio of 9, and a feed position of the 20th plate from the top, the tower top pressure is controlled at 40 kPa, the tower top temperature is 42°C-43°C, and the tower bottom temperature is 58°C-59°C. A crude methanol stream 6 is obtained at the tower top. In this embodiment, the ethanol content in the tower top stream is 4.08%, and an ethylene-propylene glycol stream 9 is obtained at the tower bottom.

[0174] The ethyl propanol stream 9 enters the ethanol separation tower T5. Under the conditions of 40 theoretical plates, a reflux ratio of 2, and a feed position of the 20th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 77°C-78°C, and the bottom temperature is 97°C-98°C. Crude ethanol stream 10 is obtained at the top of the tower, and crude n-propanol stream 11 is obtained at the bottom of the tower.

[0175] The crude n-propanol stream 11 enters the n-propanol refining tower T6. Under the conditions of 80 theoretical plates, a reflux ratio of 6, and a feed position of the 40th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 96-97°C, and the bottom temperature is 98-99°C. Refined n-propanol stream 12 is obtained at the top of the tower, and n-propanol and heavy component stream 13 is obtained at the bottom of the tower.

[0176] The crude methanol flow 6 enters the methanol refining tower T7. Under the conditions of 80 theoretical plates, a reflux ratio of 3, and a feed position of the 40th plate from the top, the top pressure is controlled at 100 KPa, the top temperature is 64-65°C, and the bottom temperature is 69-70°C. Refined methanol flow 7 is obtained at the top of the tower, and methyl ethanol flow 8 is obtained at the bottom of the tower.

[0177] The crude ethanol stream 10 enters the ethanol extraction tower T8, which is an extractive distillation tower using ethylene glycol as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 2, a reagent-to-material ratio of 1:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 19 of the 10th plate from the top, the top pressure of the tower is controlled to be 100 kPa, the top temperature of the tower is 77.5°C-78°C, and the bottom temperature of the tower is 156°C-157°C. Refined ethanol stream 14 is obtained at the top of the tower, and extract stream 17 is obtained at the bottom of the tower.

[0178] The extract streams 16 and 17 are mixed and enter the extractant recovery tower T9. Under the conditions of 15 theoretical plates, a reflux ratio of 3, and a feed position of the 7th plate from the top, the top pressure is controlled at 20 kPa, the top temperature is 50°C-52°C, and the bottom temperature is 147°C-148°C. The aqueous alcohol stream 20 is obtained at the top of the tower, and the extractant streams 18 and 19 are obtained at the bottom of the tower, which are then sent to the light alcohol extraction tower and the ethanol extraction tower.

[0179] The main logistics data and products separated according to the above conditions are shown in Table 1, and the recovery rates are shown in Table 5.

[0180] Table 1 Data of main logistics of Example 1

[0181]

[0182] Example 2

[0183] The composition of the aqueous phase product of Fischer-Tropsch synthesis remains unchanged, but the theoretical plate number, feed position, reflux ratio, operating pressure, etc. of the distillation tower are changed. Figure 1 In the process shown, the Fischer-Tropsch synthesis aqueous product stream 1 (composition is shown in Table 1) enters the light alcohol separation tower T1. Under the conditions of 40 theoretical plates, a reflux ratio of 1, and a feed position of the 20th plate from the top, the top operating pressure is controlled to be 100 KPa, the top temperature is 74°C-75°C, and the bottom temperature is 92°C-93°C. A light alcohol stream 2 with a water content of less than 14 wt% is produced from the top of the tower, and the water content in this embodiment is 13.5 wt%. A heavy alcohol water stream 15 is produced from the bottom of the tower.

[0184] A light alcohol stream 2 with a water content of 13.5 wt% enters a light alcohol extraction tower T2, which is an extractive distillation tower. Ethylene glycol is used as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 1, a dose-to-material ratio of 2.5:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 18 of the 10th plate from the top, the top pressure of the tower is controlled to be 100 KPa, the top temperature of the tower is 74°C-75°C, and the bottom temperature of the tower is 149°C-152°C. A light alcohol stream 3 with a water content of less than 2 wt% is obtained at the top of the tower. In this embodiment, the water content is 1.2 wt%, and an extract stream 16 is obtained at the bottom of the tower.

[0185] The light alcohol stream 3 with a water content of 1.2 wt% enters the light component removal tower T3. Under the conditions of 40 theoretical plates, a reflux ratio of 10, and a feed position of the 20th plate from the top, the top pressure is controlled at 100 KPa, the top temperature is 56°C-57°C, and the bottom temperature is 75°C-76°C. A light component stream 4 is obtained at the top of the tower, and an methyl, ethyl, and propylene glycol mixed alcohol stream 5 is obtained at the bottom of the tower.

[0186] A mixture of methyl, ethyl and propylene glycol stream 5 enters the methanol separation tower T4. Under the conditions of 40 theoretical plates, a reflux ratio of 8, and a feed position of the 20th plate from the top, the tower top pressure is controlled at 40 kPa, the tower top temperature is 43°C-44°C, and the tower bottom temperature is 58°C-59°C. A crude methanol stream 6 is obtained at the tower top. In this embodiment, the ethanol content in the tower top stream is 7.75 wt%, and an ethylene-propylene glycol stream 9 is obtained at the tower bottom.

[0187] The ethyl propanol stream 9 enters the ethanol separation tower T5. Under the conditions of 40 theoretical plates, a reflux ratio of 2, and a feed position of the 20th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 77°C-78°C, and the bottom temperature is 97°C-98°C. Crude ethanol stream 10 is obtained at the top of the tower, and crude n-propanol stream 11 is obtained at the bottom of the tower.

[0188] The crude n-propanol stream 11 enters the n-propanol refining tower T6. Under the conditions of 80 theoretical plates, a reflux ratio of 10, and a feed position of the 40th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 95°C-97.5°C, and the bottom temperature is 97°C-99°C. Refined n-propanol stream 12 is obtained at the top of the tower, and n-propanol and heavy component stream 13 is obtained at the bottom of the tower.

[0189] The crude methanol flow 6 enters the methanol refining tower T7. Under the conditions of 80 theoretical plates, a reflux ratio of 4, and a feed position of the 40th plate from the top, the top pressure is controlled to be 100 kPa, the top temperature is 63.5°C-64.5°C, and the bottom temperature is 69.5°C-73°C. Refined methanol flow 7 is obtained at the top of the tower, and methyl ethanol flow 8 is obtained at the bottom of the tower.

[0190] The crude ethanol stream 10 enters the ethanol extraction tower T8, which is an extractive distillation tower with ethylene glycol as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 2, a dose-to-material ratio of 1.2:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 19 of the 10th plate from the top, the top pressure of the tower is controlled to be 100 kPa, the top temperature of the tower is 77.5°C-78°C, and the bottom temperature of the tower is 149°C-151°C. Refined ethanol stream 14 is obtained at the top of the tower, and extract stream 17 is obtained at the bottom of the tower.

[0191] The extract streams 16 and 17 are mixed and enter the extractant recovery tower T9. Under the conditions of 10 theoretical plates, a reflux ratio of 2, and a feed position of the 5th plate from the top, the top pressure is controlled at 30 kPa, the top temperature is 59°C-60°C, and the bottom temperature is 157°C-160°C. A water-containing alcohol stream 20 is obtained at the top of the tower, and extractant streams 18 and 19 are obtained at the bottom of the tower, which are then sent to the light alcohol extraction tower and the ethanol extraction tower.

[0192] The main logistics data and products separated according to the above conditions are shown in Table 2, and the recovery rates are shown in Table 5.

[0193] Table 2 Data of main logistics of Example 2

[0194]

[0195]

[0196] Example 3

[0197] The composition of the aqueous phase product of Fischer-Tropsch synthesis remains unchanged, but the theoretical plate number, feed position, reflux ratio, operating pressure, etc. of the distillation tower are changed. Figure 1 In the process shown, the Fischer-Tropsch synthesis aqueous product stream 1 (composition is shown in Table 1) enters the light alcohol separation tower T1. Under the conditions of 40 theoretical plates, a reflux ratio of 1, and a feed position of the 20th plate from the top, the top operating pressure is controlled to be 100 KPa, the top temperature is 74°C-75°C, and the bottom temperature is 92°C-93°C. A light alcohol stream 2 with a water content of less than 14 wt% is produced from the top of the tower, and the water content in this embodiment is 13.5 wt%. A heavy alcohol water stream 15 is produced from the bottom of the tower.

[0198] A light alcohol stream 2 with a water content of 13.5 wt% enters a light alcohol extraction tower T2, which is an extractive distillation tower. Ethylene glycol is used as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 1, a dose-to-material ratio of 2:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 18 of the 10th plate from the top, the top pressure of the tower is controlled to be 100 KPa, the top temperature of the tower is 74°C-75°C, and the bottom temperature of the tower is 150°C-155°C. A light alcohol stream 3 with a water content of less than 2 wt% is obtained at the top of the tower. In this embodiment, the water content is 1.5 wt%, and an extract stream 16 is obtained at the bottom of the tower.

[0199] The light alcohol stream 3 with a water content of 1.5 wt% enters the light component removal tower T3. Under the conditions of 40 theoretical plates, a reflux ratio of 10, and a feed position of the 20th plate from the top, the top pressure is controlled at 100 KPa, the top temperature is 57°C-58°C, and the bottom temperature is 75°C-76°C. A light component stream 4 is obtained at the top of the tower, and an methyl, ethyl, and propylene glycol mixed alcohol stream 5 is obtained at the bottom of the tower.

[0200] A mixture of methyl, ethyl and propylene glycol stream 5 enters the methanol separation tower T4. Under the conditions of 80 theoretical plates, a reflux ratio of 9, and a feed position of the 40th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 64°C-65°C, and the bottom temperature is 79°C-80°C. A crude methanol stream 6 is obtained at the top of the tower. In this embodiment, the ethanol content in the top stream is 6.08 wt%, and an ethylene-propylene glycol stream 9 is obtained at the bottom of the tower.

[0201] The ethyl propanol stream 9 enters the ethanol separation tower T5. Under the conditions of 80 theoretical plates, a reflux ratio of 2, and a feed position of the 40th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 77°C-78°C, and the bottom temperature is 97°C-98°C. Crude ethanol stream 10 is obtained at the top of the tower, and crude n-propanol stream 11 is obtained at the bottom of the tower.

[0202] The crude n-propanol stream 11 enters the n-propanol refining tower T6. Under the conditions of 40 theoretical plates, a reflux ratio of 10, and a feed position of the 20th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 96.5°C-97.5°C, and the bottom temperature is 98°C-99°C. Refined n-propanol stream 12 is obtained at the top of the tower, and n-propanol and heavy component stream 13 is obtained at the bottom of the tower.

[0203] The crude methanol flow 6 enters the methanol refining tower T7. Under the conditions of 40 theoretical plates, a reflux ratio of 4, and a feed position of the 20th plate from the top, the top pressure is controlled to be 100 kPa, the top temperature is 63.5°C-64.5°C, and the bottom temperature is 69.5°C-71°C. Refined methanol flow 7 is obtained at the top of the tower, and methyl ethanol flow 8 is obtained at the bottom of the tower.

[0204] The crude ethanol stream 10 enters the ethanol extraction tower T8, which is an extractive distillation tower with ethylene glycol as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 2, a dose-to-material ratio of 0.9:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 19 of the 10th plate from the top, the top pressure of the tower is controlled to be 100 kPa, the top temperature of the tower is 77.5°C-78.5°C, and the bottom temperature of the tower is 144°C-146°C. Refined ethanol stream 14 is obtained at the top of the tower, and extract stream 17 is obtained at the bottom of the tower.

[0205] The extract streams 16 and 17 are mixed and enter the extractant recovery tower T9. Under the conditions of 10 theoretical plates, a reflux ratio of 2, and a feed position of the 5th plate from the top, the top pressure is controlled at 10 kPa, the top temperature is 37°C-39°C, and the bottom temperature is 129°C-131°C. A water-containing alcohol stream 20 is obtained at the top of the tower, and extractant streams 18 and 19 are obtained at the bottom of the tower, which are then sent to the light alcohol extraction tower and the ethanol extraction tower.

[0206] The main logistics data obtained by separation under the above conditions are shown in Table 3, and the recovery rate is shown in Table 5.

[0207] Table 3 Data of main logistics of Example 3

[0208]

[0209] Example 4

[0210] The composition of the aqueous phase product of Fischer-Tropsch synthesis remains unchanged, but the order of distillation tower setting, number of theoretical plates, feed position, reflux ratio, operating pressure, etc. are changed. Figure 2 In the process shown, the Fischer-Tropsch synthesis aqueous product stream 1 (composition is shown in Table 1) enters the light alcohol separation tower T1. Under the conditions of 40 theoretical plates, a reflux ratio of 1, and a feed position of the 20th plate from the top, the top operating pressure is controlled to be 100 KPa, the top temperature is 74°C-75°C, and the bottom temperature is 92°C-93°C. A light alcohol stream 2 with a water content of less than 15 wt% is produced from the top of the tower, and the water content in this embodiment is 13.5 wt%. A heavy alcohol water stream 15 is produced from the bottom of the tower.

[0211] A light alcohol stream 2 with a water content of 13.5 wt% enters the light alcohol extraction T2, which is an extractive distillation tower with ethylene glycol as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 1, a dose-to-material ratio of 3:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 18 of the 10th plate from the top, the top pressure of the tower is controlled to be 100 KPa, the top temperature of the tower is 74°C-75°C, and the bottom temperature of the tower is 150°C-155°C. A light alcohol stream 3 with a water content of less than 2 wt% is obtained at the top of the tower. In this embodiment, the water content is 0.8 wt%, and an extract stream 16 is obtained at the bottom of the tower.

[0212] The light alcohol stream 3 with a water content of 0.8 wt% enters the light component removal and methanol tower T3. Under the conditions of 80 theoretical plates, a reflux ratio of 5, and a feed position of the 42nd plate from the top, the top pressure is controlled at 100 KPa, the top temperature is 59°C-62°C, and the bottom temperature is 79°C-81°C. A light component and methanol stream 4 is obtained at the top of the tower, and an ethylene propylene glycol stream 7 is obtained at the bottom of the tower.

[0213] The light component and methanol stream 4 enter the light component removal tower T4. Under the conditions of 40 theoretical plates, 10 reflux ratio and the 24th plate from the top, the top pressure is controlled at 100 KPa, the top temperature is 48-50 ° C and the bottom temperature is 64-65 ° C. The light component stream 5 is obtained at the top of the tower and the crude methanol stream 6 is obtained at the bottom of the tower.

[0214] The ethyl propanol stream 7 enters the ethanol separation tower T5. Under the conditions of 80 theoretical plates, a reflux ratio of 5, and a feed position of the 40th plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 77°C-78°C, and the bottom temperature is 97°C-98°C. Crude ethanol stream 8 is obtained at the top of the tower, and crude n-propanol stream 9 is obtained at the bottom of the tower.

[0215] The crude n-propanol stream 9 enters the n-propanol refining tower T6. Under the conditions of 80 theoretical plates, a reflux ratio of 5, and a feed position of the 42nd plate from the top, the top pressure is controlled at 100 kPa, the top temperature is 96.5°C-97.5°C, and the bottom temperature is 98°C-99°C. Refined n-propanol stream 10 is obtained at the top of the tower, and n-propanol and heavy component stream 11 is obtained at the bottom of the tower.

[0216] The crude methanol flow 6 enters the methanol refining tower T7. Under the conditions of 40 theoretical plates, a reflux ratio of 4, and a feed position of the 20th plate from the top, the top pressure is controlled to be 100 kPa, the top temperature is 63.5°C-64.5°C, and the bottom temperature is 69.5°C-71°C. Refined methanol flow 12 is obtained at the top of the tower, and methyl ethanol flow 13 is obtained at the bottom of the tower.

[0217] The crude ethanol stream 8 enters the ethanol extraction tower T8, which is an extractive distillation tower with ethylene glycol as the extractant. Under the conditions of 40 theoretical plates, a reflux ratio of 2, a dose-to-material ratio of 1:1, a feed position of the 30th plate from the top, and an entry position of the circulating extractant stream 19 of the 5th plate from the top, the top pressure of the tower is controlled to be 100 kPa, the top temperature of the tower is 77.5°C-78.5°C, and the bottom temperature of the tower is 144°C-146°C. Refined ethanol stream 14 is obtained at the top of the tower, and extract stream 17 is obtained at the bottom of the tower.

[0218] The extract streams 16 and 17 are mixed and enter the extractant recovery tower T9. Under the conditions of 10 theoretical plates, a reflux ratio of 2, and a feed position of the 5th plate from the top, the top pressure is controlled at 10 kPa, the top temperature is 37°C-39°C, and the bottom temperature is 129°C-131°C. A hydrous alcohol stream 20 is obtained at the top of the tower, and extractant streams 18 and 19 are obtained at the bottom of the tower, which are then sent to the light alcohol extraction tower and the ethanol extraction tower.

[0219] The main logistics data and products separated according to the above conditions are shown in Table 4, and the recovery rates are shown in Table 5.

[0220] Table 4 Data of main logistics of Example 4

[0221]

[0222] Table 5 Recovery of Example 1-Example 4

[0223]

Claims

1. A method for preparing methanol, ethanol and n-propanol from an aqueous phase product of Fischer-Tropsch synthesis, the method comprising: (1) performing a first distillation on the aqueous phase product of the Fischer-Tropsch synthesis to obtain aqueous light alcohol and aqueous heavy alcohol; (2) extracting and rectifying the aqueous light alcohol to obtain light alcohol and an extract; (3) treating the light alcohol in step (2) in any one of the following ways to obtain methanol, ethanol and n-propanol: a. subjecting the light alcohol described in step (2) to a second distillation to obtain a light component at the top of the tower and a mixed solution Ia of methanol, ethanol and n-propanol; subjecting the mixed solution Ia to a third distillation to obtain crude methanol and a mixed solution IIa of ethanol and n-propanol; subjecting the mixed solution IIa to a fourth distillation to obtain crude ethanol and crude n-propanol; b. The light alcohol described in step (2) is subjected to a second distillation to obtain a mixed liquid Ib of light components and methanol at the top of the tower, and a mixed liquid IIb of ethanol and n-propanol at the bottom of the tower; the mixed liquid Ib is subjected to a third distillation to obtain crude methanol and light components; and the mixed liquid IIb is subjected to a fourth distillation to obtain crude ethanol and crude n-propanol.

2. The method according to claim 1, wherein The Fischer-Tropsch synthesis aqueous product is an alcohol-rich product with a water content of less than 35 wt% obtained by treating the Fischer-Tropsch synthesis water obtained in the Fischer-Tropsch synthesis; optionally, the Fischer-Tropsch synthesis aqueous product is obtained by deoiling, alkali neutralization, and distillation of the Fischer-Tropsch synthesis water; preferably, the total content of methanol, ethanol, and n-propanol in the Fischer-Tropsch synthesis aqueous product is 50 wt%-60 wt%, and the water content is not higher than 35 wt%.

3. The method according to claim 1 or 2, wherein In step (1), the conditions of the first distillation are: tower top temperature 70°C-78°C, tower bottom temperature 90°C-95°C, tower top pressure 100-110 kPa, number of tower plates 25-45, feed position 10-25th tower plate from the top, and reflux ratio 0.5-3; Preferably, the top temperature of the first distillation is selected from 70°C, 71°C, 72°C, 73°C, 74°C, 75°C or 76°C, or any value in the range formed by any two of the above values; or, The bottom temperature of the first distillation column is selected from 90°C, 91°C, 92°C, 93°C, 94°C or 95°C, or any value in the range formed by any two of the above values; or The number of plates in the first distillation is selected from 25, 30, 35, 40 or 45, or any value in the range formed by any two of the above values; or The feed position of the first distillation is the 10th, 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th, 20th, 21st, 22nd, 23rd, 24th or 25th tray from the top, or any value in the range formed by any two of the above values; or The reflux ratio of the first distillation is 0.5, 1, 1.5, 2, 2.5 or 3, or any value within the range formed by any two of the above values.

4. The method according to any one of claims 1 to 3, wherein In step (2), the extractant is selected from one or more of ethylene glycol, glycerol, diethylene glycol, and ethylene glycol + potassium acetate; The operating conditions of the extraction are: the number of theoretical plates is 30-45, the feed position is the 20th to 35th plate from the top, the extractant feed position is the 5th to 15th plate from the top, the reflux ratio is 0.5-2, the top pressure is controlled at 100-110 kPa, the top temperature is 70°C-78°C, the bottom temperature is 145°C-160°C, and the agent-to-material ratio is 1:1 to 5:

1.

5. The method according to any one of claims 1 to 4, wherein In the method a) of step (3), the conditions for the second distillation are: tower top temperature 52°C-59°C, tower bottom temperature 74°C-77°C, tower top pressure 100-110 kPa, number of trays 30-60, feed position 15-30 trays from the top, and reflux ratio 6-12; Preferably, in the mode a) of step (3), the top temperature of the second distillation tower is 55°C-58°C, 56°C-57°C or 57°C-58°C; or, The bottom temperature is 75℃-76℃; or The number of plates is 40-60; or The feed position is the 20th to 30th tray from the top; or The reflux ratio is 10.

6. The method according to any one of claims 1 to 4, wherein In the b) mode of step (3), the conditions for the second distillation are: tower top temperature 58°C-65°C, tower bottom temperature 75°C-82°C, tower top pressure 100-110 kPa, tower plate number 60-90, feed position 40-50th tower plate from the top, and reflux ratio 3-6; Preferably, in mode b) of step (3), the conditions for the second distillation are: tower top temperature 59°C-62°C, tower bottom temperature 79°C-81°C, tower top pressure 100 kPa, number of tower plates 80, feed position 42nd tower plate from the top, and reflux ratio 5.

7. The method according to any one of claims 1 to 5, wherein In the method a) of step (3), the conditions of the third distillation are: tower top temperature 40°C-65°C, tower bottom temperature 58°C-80°C, tower top pressure 35-110 kPa, tower plate number 40-80, feed position 15-45 tower plates, and reflux ratio 8-10; Preferably, in the mode a) of step (3), the top temperature of the third distillation is 42°C-43°C, 43°C-44°C or 64°C-65°C; or, The tower bottom temperature is 58°C-59°C or 79°C-80°C; or The number of plates is 40-60; or The feed position is the 20th to 45th tray from the top; or The reflux ratio is 8, 9, and 10.

8. The method according to any one of claims 1 to 4, wherein In the b) mode of step (3), the conditions of the third distillation are: tower top temperature 47°C-50°C, tower bottom temperature 63°C-65°C, tower top pressure 100-110 kPa, tower plate number 30-50, feed position 15-25th tower plate from the top, and reflux ratio 9-12; Preferably, in mode b) of step (3), the conditions for the third distillation are: tower top temperature 48°C-50°C, tower bottom temperature 64°C-65°C, tower top pressure 100-110 kPa, number of tower plates 40, feed position 24th tower plate from the top, and reflux ratio 10.

9. The method according to any one of claims 1 to 4, wherein In the methods a) and b) of step (3), the conditions for the fourth distillation are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, number of trays 30-90, feed position 13-50th tray from the top, and reflux ratio 2-6; Preferably, in the method a) of step (3), the conditions of the fourth distillation are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, number of tower plates 30-80, feed position 13-50th tower plate from the top, reflux ratio 2-6; or, In the b) mode of step (3), the conditions of the fourth distillation are: tower top temperature 76°C-80°C, tower bottom temperature 95°C-98°C, tower top pressure 100-110 kPa, tower plate number 60-90, feed position 30-50th tower plate from the top, and reflux ratio 2-6.

10. The method according to any one of claims 1 to 9, wherein The method further includes a step of recovering the extractant, wherein the extractant recovery is performed using an extractant recovery tower: the theoretical number of plates is 10-20, the feed position is the 5th to 10th plate from the top, the tower top pressure is controlled to be 10KPa-30KPa, the tower top temperature is 37°C-60°C, the tower bottom temperature is 120°C-160°C, the reflux ratio is 2-4, and the aqueous alcohol stream is obtained at the tower top and the extractant stream is obtained at the tower bottom; or, The method comprises the steps of rectifying the obtained crude methanol, crude ethanol and crude n-propanol again; Preferably, the conditions for methanol refining are: the theoretical plate number is 35-80, the feed position is the 10th-40th plate from the top, the top pressure is controlled to be 100-110 kPa, the top temperature is 62°C-65°C, the bottom temperature is 68°C-73°C, and the reflux ratio is 2-5; or The conditions for refining n-propanol are: the theoretical number of plates is 35-80, the feed position is the 20th to 45th plate from the top, the top pressure is controlled at 100-110 kPa, the top temperature is 95°C-98°C, the bottom temperature is 96°C-102°C, and the reflux ratio is 5-10; or The same extractant as in step (2) is used to extract crude ethanol. The extraction conditions may be as follows: the theoretical number of tower plates is 30-40, the feed position is the 20th-30th tower plate from the top, the extractant feed position is 5-10 plates from the top, the tower top pressure is controlled to be 100-110 kPa, the tower top temperature is 77° C.-79° C., the tower bottom temperature is 140-158° C., the agent-to-material ratio is 0.9-1.2:1, and the reflux ratio is 2-3.

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