A method for preparing electronic grade isopropanol by membrane dehydration and co-solvent dehydration in series

Abstract

The application provides a method for preparing electronic-grade isopropyl alcohol by membrane dehydration and co-boiler dehydration in series, which comprises the following steps: feeding isopropyl alcohol liquid containing less than 20% water into a first rectifying tower, heating to a tower top pressure of 0.8 MPa, and feeding the binary azeotrope of isopropyl alcohol and water obtained at the tower top into a membrane dehydration assembly; after passing through the membrane dehydration assembly, most of the separated water is condensed and then fed into a waste water tank, and the remaining isopropyl alcohol with low water content is condensed and then fed into a reflux tank, mixed with cyclohexane in the tank to form a mixed material, and then pumped to the upper part of the first rectifying tower to exchange with the newly fed material, so that the ternary azeotrope of cyclohexane, isopropyl alcohol and water is formed at the tower top, and then dehydrated by the membrane dehydration assembly; the dehydrated ternary azeotrope is fed into the reflux tank, and then into the first rectifying tower, and the cycle is repeated. The application only needs one tower to separate isopropyl alcohol, and can prepare anhydrous electronic-grade isopropyl alcohol with a water content of less than 100 ppm, and the tower height only needs to be about 20 meters, which greatly reduces the production difficulty and production cost.

Description

Technical Field

[0001] This invention relates to the field of chemical separation technology, specifically to a method for preparing electronic-grade isopropanol by a series of membrane dehydration and azeotropic agent dehydration. Background Technology

[0002] Isopropanol is widely used as a solvent or raw material in the production of chemical, pharmaceutical, pesticide intermediates, and semiconductors. During the production process, a certain amount of mixed solution of isopropanol and water is generated. For the separation of isopropanol and water, conventional distillation has been used both domestically and internationally. That is, isopropanol wastewater is pumped to an azeotropic distillation column. The top of the column yields an azeotrope of isopropanol and water, while the bottom is wastewater. Conventional distillation can only obtain the azeotropic composition of isopropanol and water (87% wt of isopropanol and 13% wt of water). The price of the isopropanol and water azeotrope is not high, and the economic return is low.

[0003] Isopropanol azeotropically reacts with water, and conventional distillation methods cannot completely separate it from water. Currently, commercially available methods include azeotropic dehydration with azeotropic agents, two-column pressure-swing continuous distillation, membrane dehydration, and extractive distillation, each with its own advantages and disadvantages. For example, with azeotropic dehydration, the aqueous phase carries away some of the organic phase, requiring repeated distillation cycles to ensure a high yield; two-column pressure-swing distillation is only suitable when the azeotropic ratio of the organic phase changes significantly after pressure change, such as with tetrahydrofuran; membrane dehydration is suitable for many solvents, but it cannot remove water to very low levels, generally only reaching industrial-grade levels of around 0.5%, and further reductions require significant costs; extractive distillation has a limited application range, and the high boiling point of the extractant leads to high energy consumption during recycling, and it is difficult to handle high-boiling-point impurities in the feedstock that need to be separated.

[0004] For example, patent CN 115554721A provides a tetrahydrofuran purification device and method integrating tower and membrane dehydration. In the process flow of this application, the aqueous tetrahydrofuran feed solution is preheated and fed into the first distillation column. The vapor phase of the top of the first distillation column can be directly fed into the membrane dehydration device. The tetrahydrofuran after membrane dehydration can be vapor phase collected and condensed in the reboiler at the bottom of the second distillation column. The vapor phase of the top of the second distillation column can be vapor phase collected and condensed in the reboiler at the bottom of the third distillation column. It requires the use of two distillation columns for tetrahydrofuran dehydration. Although it can theoretically obtain tetrahydrofuran with a water content of less than 100 ppm, in practice, the height of the second distillation column needs to reach more than 100 meters to achieve the above technical effect. A column height of more than 100 meters is very difficult in actual production, and the production cost and equipment cost are very high. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing electronic grade isopropanol by a series of membrane dehydration and azeotropic agent dehydration, which requires only one tower to separate isopropanol and prepare anhydrous electronic grade isopropanol with a water content of <100ppm, and the tower height only needs to be about 20 meters, which greatly reduces the production difficulty and production cost.

[0006] This invention is implemented as follows:

[0007] A method for preparing electronic-grade isopropanol using a series of membrane dehydration and azeotropic agent dehydration processes is disclosed. The preparation system includes a first distillation column, a membrane dehydration assembly, a first condenser, a second condenser, a reflux tank, a reflux pump, a first reboiler, a pumping pump, a second distillation column, a third condenser, and a second reboiler. The top of the first distillation column is connected to the membrane dehydration assembly. One side of the membrane dehydration assembly is connected to a wastewater tank via the first condenser, and the other side is connected to the reflux tank via the second condenser. The reflux tank is connected to the upper part of the first distillation column via the reflux pump.

[0008] The bottom of the first distillation column is connected to the middle of the second distillation column via a pump. The bottom of the first distillation column is connected to the first reboiler. The top of the second distillation column is connected to a third condenser, and the bottom is connected to the second reboiler. The height of the first distillation column is less than or equal to 20m.

[0009] The preparation method steps are as follows:

[0010] Step 1: The isopropanol feed solution with a water content of less than 20% is fed into the first distillation column through the feed inlet. After the first distillation column is heated and distilled, the binary azeotrope of isopropanol and water obtained at the top of the column enters the membrane dehydration unit. The pressure inside the first distillation column is 0.8 MPa.

[0011] Step 2: Most of the water separated after passing through the membrane dehydration unit is condensed in the first condenser and enters the wastewater tank. The remaining isopropanol with a water content of 1.5%-0.5% is condensed in the second condenser to 40±2℃ and then enters the reflux tank. The mixture formed by mixing isopropanol with a water content of less than 1.5%-0.5% with cyclohexane in the reflux tank is pumped to the upper part of the first distillation column by the reflux pump, and the reflux pump is controlled to pump the mixture at a fixed flow rate.

[0012] Step 3: After the mixture exchanges gas and liquid with the fresh feed in the first distillation column, a ternary azeotrope of cyclohexane, isopropanol, and water is formed at the top of the column. The composition of the ternary azeotrope is as follows: water 10.19%, isopropanol 29.41%, and cyclohexane 60.40%.

[0013] Next, the gas-phase ternary azeotrope enters the membrane dehydration unit from the top of the first distillation column for dehydration. After dehydration, the moisture content of the ternary azeotrope is reduced to 1%, and then it enters the reflux tank and is sent back to the first distillation column by the reflux pump. This cycle continues.

[0014] Step 4: The water content of the liquid isopropanol at the bottom of the first distillation column is less than 100 ppm. It is then pumped into the second distillation column for deweighting to obtain the finished product.

[0015] Furthermore, cyclohexane should be added to the reflux tank slowly, and the amount of cyclohexane added to the reflux tank should be based on the temperature at the feed inlet of the first distillation column. If the temperature at the feed inlet of the first distillation column is greater than 137°C, continue to add cyclohexane until the cyclohexane in the first distillation column drops to the feed inlet position, so that its temperature is maintained between 130 and 137°C.

[0016] The present invention has the following advantages:

[0017] This invention requires only one tower to separate isopropanol and prepare anhydrous electronic-grade isopropanol with a water content of <100ppm. The tower height only needs to be about 20 meters, which greatly reduces the production difficulty and cost. It overcomes the problem that the separation of anhydrous isopropanol with a water content of <100ppm is very difficult and the production and equipment costs are very high in the actual production of anhydrous isopropanol. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a schematic diagram of the preparation system for the method of preparing electronic-grade isopropanol by tandem membrane dehydration and azeotropic agent dehydration according to the present invention.

[0020] The numbers in the image are as follows:

[0021] 1. First distillation column; 2. Membrane dehydration assembly; 3. First condenser; 4. Second condenser; 5. Reflux tank; 6. Reflux pump; 7. First reboiler; 8. Pump; 9. Second distillation column; 10. Third condenser; 11. Second reboiler; 12. Wastewater tank; 13. Feed inlet. Detailed Implementation

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] like Figure 1 As shown, this invention relates to a method for preparing electronic-grade isopropanol by a series of membrane dehydration and azeotropic agent dehydration. The preparation system structure includes a first distillation column 1, a membrane dehydration assembly 2, a first condenser 3, a second condenser 4, a reflux tank 5, a reflux pump 6, a first reboiler 7, a pump 8, a second distillation column 9, a third condenser 10, and a second reboiler 11. The top of the first distillation column 1 is connected to the membrane dehydration assembly 2. One side of the membrane dehydration assembly 2 is connected to a wastewater tank 12 via the first condenser 3, and the other side is connected to the reflux tank 5 via the second condenser 4. The reflux tank 5 is connected to the upper part of the first distillation column 1 via the reflux pump 6.

[0025] The bottom of the first distillation column 1 is connected to the middle of the second distillation column 9 via a pump 8. The bottom of the first distillation column 1 is connected to the first reboiler 7. The top of the second distillation column 9 is connected to the third condenser 10, and the bottom is connected to the second reboiler 11. The height of the first distillation column 1 is less than or equal to 20m.

[0026] The preparation method steps are as follows:

[0027] Step 1: The isopropanol feed solution with a water content of less than 20% is fed into the first distillation column 1 through the feed inlet 13. After the first distillation column 1 is heated and distilled, the binary azeotrope of isopropanol and water obtained at the top of the column enters the membrane dehydration unit 2. The pressure inside the first distillation column 1 is 0.8 MPa.

[0028] Step 2: Most of the water separated after passing through the membrane dehydration module 2 is condensed by the first condenser 3 and enters the wastewater tank 12. The remaining isopropanol with a water content of 1.5%-0.5% is condensed to 40±2℃ by the second condenser 4 and enters the reflux tank 5. The mixture formed by mixing the isopropanol with a water content of less than 1.5%-0.5% with the cyclohexane in the reflux tank 5 is pumped to the upper part of the first distillation column 1 by the reflux pump 6, and the reflux pump 6 is controlled to pump the mixture at a fixed flow rate.

[0029] Step 3: After the mixture exchanges gas and liquid with the fresh feed in the first distillation column 1, a ternary azeotrope of cyclohexane, isopropanol, and water is formed at the top of the column. The composition of the ternary azeotrope is as follows: water 10.19%, isopropanol 29.41%, and cyclohexane 60.40%.

[0030] Next, the gaseous ternary azeotrope enters the membrane dehydration unit 2 from the top of the first distillation column 1 for dehydration. After dehydration, the moisture content of the ternary azeotrope is reduced to 1%, and then it enters the reflux tank 5 and is sent back to the first distillation column 1 by the reflux pump 6. This cycle continues.

[0031] Step 4: The water content of the liquid isopropanol at the bottom of the first distillation column 1 is less than 100 ppm. It is then pumped into the second distillation column 9 by pump 8 to remove excess water and obtain the finished product.

[0032] Cyclohexane should be added slowly to reflux tank 5, and the amount added should be based on the temperature at the feed inlet 13 of the first distillation column 1. If the temperature at the feed inlet 13 of the first distillation column 1 is greater than 137°C, continue adding cyclohexane until the temperature in the first distillation column 1 drops to the feed inlet 13, maintaining its temperature between 130 and 137°C. After the first addition of cyclohexane to the required height of the first distillation column 1, no further additions are made. If the feed inlet temperature exceeds 137°C during subsequent production, add cyclohexane in appropriate amounts to maintain the temperature between 130 and 137°C.

[0033] The following will be combined with the appendix Figure 1 The technical solution of the present invention will be clearly and completely described in detail with specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0034] Comparative Example 1

[0035] Isopropanol membrane dehydration + conventional distillation dehydration:

[0036] The first distillation column maintains a binary azeotropic composition until membrane dehydration at the top. After membrane dehydration, isopropanol with a water content of less than 1.0% is obtained. This low-water-content isopropanol then goes to the second atmospheric azeotropic distillation column. The composition at the top of the column is (87% IPA, 13% water), and the temperature at the top is 80.18℃. The bottom of the column is basically IPA. To achieve a bottom isopropanol water content of less than 100ppm (boiling point of about 82.05℃), the theoretical height of the second atmospheric azeotropic distillation column needs to be more than 100 meters, resulting in very high production and construction costs. Example 1

[0037] This invention relates to membrane dehydration tandem azeotropic agent dehydration:

[0038] The ternary azeotropic ratio of IPA, water and cyclohexane at 8 atmospheres is: water 10.19%, isopropanol 29.41%, cyclohexane 60.40%, with an azeotropic temperature of 129.09℃.

[0039] Assuming the feed composition is IPA 85.3% : water 14.7% :

[0040] With the addition of cyclohexane as an azeotropic agent, the first distillation column maintains a ternary azeotropic composition before dehydration at the top membrane: 10.19% water, 29.41% isopropanol, and 60.40% cyclohexane, with an azeotropic temperature of 129.09℃. The isopropanol at the bottom of the column has a water content of less than 100 ppm (boiling point 146.80℃), requiring the first distillation column to be only about 20 meters high.

[0041] Production process:

[0042] First, add a certain amount of cyclohexane to the reflux tank, and then proceed with the following steps;

[0043] Step 1: The feed solution consisting of 85.3% IPA and 14.7% water is fed into the first distillation column through the feed inlet. After the first distillation column is heated and distilled, the binary azeotrope of isopropanol and water obtained at the top of the column enters the membrane dehydration unit. The pressure inside the first distillation column is 0.8 MPa.

[0044] Step 2: Most of the water separated after passing through the membrane dehydration unit is condensed in the first condenser and enters the wastewater tank. The remaining isopropanol with a water content of about 1% is condensed in the second condenser to 40°C (the temperature to which it is condensed) and then enters the reflux tank. The mixture formed by mixing the isopropanol with a water content of about 1% with cyclohexane in the reflux tank is pumped to the upper part of the first distillation column by the reflux pump, and the reflux pump is controlled to pump the mixture at a fixed flow rate.

[0045] Step 3: After the mixture exchanges gas and liquid with the new feed in the first distillation column, a ternary azeotrope of cyclohexane, isopropanol, and water is formed at the top of the column. The composition of the ternary azeotrope is as follows: water 10.19%, isopropanol 29.41%, and cyclohexane 60.40%. The amount of cyclohexane added to the reflux tank is based on the temperature at the feed inlet of the first distillation column. If the temperature at the feed inlet of the first distillation column is greater than 137°C, cyclohexane is added continuously until the cyclohexane in the first distillation column drops to the feed inlet position, so that its temperature is maintained between 130 and 137°C.

[0046] Next, the gas-phase ternary azeotrope enters the membrane dehydration unit from the top of the first distillation column for dehydration. After dehydration, the moisture content of the ternary azeotrope is reduced to 1%, and then it enters the reflux tank and is sent back to the first distillation column by the reflux pump. This cycle continues.

[0047] Step 4: The water content of the liquid isopropanol at the bottom of the first distillation column is less than 100 ppm. It is then pumped into the second distillation column for deweighting to obtain the finished product.

[0048] Finally, the top of the first distillation column is recycled for dehydration, and the anhydrous IPA (water content <100ppm) at the bottom of the column enters the second distillation column to remove heavy components and obtain high-quality IPA.

[0049] If the isopropanol feed solution contains more than 20% water, the isopropanol feed solution should first be dehydrated in an atmospheric distillation column to obtain an azeotropic composition of isopropanol (87wt% isopropanol, 13wt% water) before entering the first distillation column.

[0050] When Comparative Example 1 is dehydrated to 1% using membrane dehydration, the top material is directly re-distilled to the azeotropic ratio using a second azeotropic distillation column, and isopropanol with less than 100 ppm water content is obtained from the bottom of the second azeotropic distillation column, that is, isopropanol (boiling point at atmospheric pressure 82.05℃) and isopropanol azeotrope (azeotropic temperature at atmospheric pressure 80.18℃) are separated by two columns. The boiling points of the two are very close, making them difficult to separate. Theoretically, about 400 plates are needed.

[0051] The membrane dehydration tandem azeotropic agent dehydration method of the present invention has a ternary azeotropic point (63.8°C at atmospheric pressure) of isopropanol, water and cyclohexane, which is nearly 20 degrees different from the boiling point of isopropanol (82.05°C at atmospheric pressure), making them easy to separate. Therefore, only one tower is needed to separate isopropanol, and the tower height only needs to be about 20 meters.

[0052] In summary, this invention requires only one tower to separate isopropanol and prepare anhydrous electronic-grade isopropanol with a water content of <100ppm. Moreover, the tower height only needs to be about 20 meters, which greatly reduces the production difficulty and production cost. It overcomes the problem that the separation of anhydrous isopropanol with a water content of <100ppm is very difficult and the production and equipment costs are very high in the actual production of anhydrous isopropanol.

[0053] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing electronic-grade isopropanol by a series of membrane dehydration and azeotropic agent dehydration, characterized in that: The preparation system structure includes a first distillation column, a membrane dehydration assembly, a first condenser, a second condenser, a reflux tank, a reflux pump, a first reboiler, a pumping pump, a second distillation column, a third condenser, and a second reboiler; the top of the first distillation column is connected to the membrane dehydration assembly; one side of the membrane dehydration assembly is connected to a wastewater tank through the first condenser, and the other side is connected to the reflux tank through the second condenser; the reflux tank is connected to the upper part of the first distillation column through the reflux pump; The bottom of the first distillation column is connected to the middle of the second distillation column via a pump. The bottom of the first distillation column is connected to the first reboiler. The top of the second distillation column is connected to a third condenser, and the bottom is connected to the second reboiler. The height of the first distillation column is less than or equal to 20m. The preparation method steps are as follows: Step 1: The isopropanol feed solution with a water content of less than 20% is fed into the first distillation column through the feed inlet. After the first distillation column is heated and distilled, the binary azeotrope of isopropanol and water obtained at the top of the column enters the membrane dehydration unit. The pressure inside the first distillation column is 0.8 MPa. Step 2: Most of the water separated after passing through the membrane dehydration unit is condensed in the first condenser and enters the wastewater tank. The remaining isopropanol with a water content of 1.5%-0.5% is condensed in the second condenser to 40±2℃ and then enters the reflux tank. The mixture formed by mixing isopropanol with a water content of less than 1.5%-0.5% with cyclohexane in the reflux tank is pumped to the upper part of the first distillation column by the reflux pump, and the reflux pump is controlled to pump the mixture at a fixed flow rate. Step 3: After the mixture exchanges gas and liquid with the fresh feed in the first distillation column, a ternary azeotrope of cyclohexane, isopropanol, and water is formed at the top of the column. The composition of the ternary azeotrope is as follows: water 10.19%, isopropanol 29.41%, and cyclohexane 60.40%. Next, the gas-phase ternary azeotrope enters the membrane dehydration unit from the top of the first distillation column for dehydration. After dehydration, the moisture content of the ternary azeotrope is reduced to 1%, and then it enters the reflux tank and is sent back to the first distillation column by the reflux pump. This cycle continues. Step 4: The water content of the liquid isopropanol at the bottom of the first distillation column is less than 100 ppm. It is then pumped into the second distillation column for deweighting to obtain the finished product.

2. The method for preparing electronic-grade isopropanol by a series of membrane dehydration and azeotropic agent dehydration according to claim 1, characterized in that: Cyclohexane should be added slowly to the reflux tank, and the amount of cyclohexane added should be based on the temperature at the feed inlet of the first distillation column. If the temperature at the feed inlet of the first distillation column is greater than 137°C, continue to add cyclohexane until the cyclohexane in the first distillation column drops to the feed inlet position, so that its temperature is maintained between 130 and 137°C.

Images