Low-Temperature Reduced Pressure Continuous Catalytic Distillation Column and Distillation Process for Synthesizing Diacetone Alcohol

Abstract

This invention relates to a low-temperature, reduced-pressure continuous catalytic distillation column and distillation process for synthesizing diacetone alcohol. The low-temperature, reduced-pressure continuous catalytic distillation column includes a catalytic distillation column, a condenser, and a built-in reboiler. The catalytic distillation column comprises a reaction section and a stripping section. The feed inlet of the catalytic distillation column is located between the reaction section and the stripping section. An external condenser is installed at the top of the catalytic distillation column, with its inlet connected to the top outlet and its outlet connected to the side inlet at the top. The built-in reboiler is installed at the bottom of the catalytic distillation column, and a bottom outlet is provided at the bottom of the column. This invention not only significantly improves the reaction conversion rate (>99.9%) but also achieves 100% reaction selectivity, avoiding the generation of byproducts and the decomposition of diacetone alcohol, reducing reaction energy consumption. Furthermore, the product requires no subsequent separation, and the catalyst does not need to be separated and recovered.

Description

Technical Field

[0001] This invention relates to a low-temperature, reduced-pressure continuous catalytic distillation process for synthesizing diacetone alcohol and its catalytic distillation column, belonging to the field of continuous catalytic distillation technology. Background Technology

[0002] Diacetone alcohol, also known as 4-hydroxy-4-methyl-2-pentanone or diacetone alcohol (DAA), possesses the properties and functions of both ketones and alcohols due to its unique molecular structure. It is an important raw material and organic solvent in chemical production. DAA is characterized by its high boiling point, low resistivity, and good electrical conductivity, making it a potentially environmentally friendly solvent that can replace acetone. For example, it can be used as a cleaning solvent or a solvent for cellulose acetate, nitrocellulose, and epoxy resins. Furthermore, it is used in the preparation of dyes, paint thinners, preservatives, wood colorants, rust removers and antifreeze agents, hydraulic oil solvents, and extractants. DAA is also an important chemical intermediate in the preparation of organic products such as methyl isobutyl ketone (MIBK), isopropylacetone, and isophorone. DAA is unstable at high temperatures, decomposing violently into acetone above 120 °C.

[0003] Currently, the traditional industrial process for producing diacetone alcohol from acetone uses batch reactors or fixed-bed reactors, employing catalysts such as alkali metal or alkaline earth metal oxides, hydroxides, or carbonates. This process offers advantages such as simple and inexpensive catalysts and easy operation. However, significant drawbacks include poor selectivity, numerous byproducts, difficult post-processing, and severe environmental pollution. Using heterogeneous catalysts (such as basic anion exchange resins) in conjunction with a fixed-bed process to produce diacetone alcohol offers advantages over homogeneous catalysts, including easier product separation, relative environmental friendliness, and less corrosiveness. However, this process still does not solve the problem of low conversion rates.

[0004] Chinese patent CN 85100473A discloses a batch reactor process for synthesizing diacetone alcohol. Although the reaction time is shortened by using a highly active catalyst and the single-pass conversion rate is increased by lowering the reaction temperature, the yield of diacetone alcohol is still relatively low, about 18-20%, due to the limitation of the equilibrium conversion rate.

[0005] Chinese patent CN 110496414A discloses a continuous reactive distillation equipment and process for synthesizing diacetone alcohol. This process couples the reaction and separation phases through reactive distillation, breaking the limitations of reaction equilibrium and achieving a diacetone alcohol yield far exceeding that of batch reactors and fixed-bed processes. However, this process is atmospheric pressure reactive distillation, requiring high temperatures, which leads to a mismatch between reaction and separation temperatures, incomplete acetone conversion, more byproducts, and high energy consumption. Furthermore, the diacetone alcohol concentration obtained from the bottom of the distillation column is low, necessitating further distillation and separation, increasing equipment costs and energy consumption. In addition, the high temperature in the bottom of the distillation column can cause the decomposition of diacetone alcohol. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a low-temperature vacuum continuous catalytic distillation column and distillation process for synthesizing diacetone alcohol, so as to completely convert acetone to obtain high-purity diacetone alcohol, while not producing by-products.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] This invention relates to a low-temperature, reduced-pressure continuous catalytic distillation column for synthesizing diacetone alcohol, characterized by comprising a catalytic distillation column, a condenser, and a built-in reboiler. The catalytic distillation column includes a reaction section and a stripping section. The feed inlet of the catalytic distillation column is located between the reaction section and the stripping section. An external condenser is installed at the top of the catalytic distillation column, with its inlet connected to the top outlet and its outlet connected to the side inlet at the top of the catalytic distillation column. The built-in reboiler is installed at the bottom of the catalytic distillation column, and a bottom outlet is provided at the bottom of the catalytic distillation column.

[0009] Preferably, the reaction section of the catalytic distillation column is divided into three sections, each with a height of 4–6 m. The stripping section of the catalytic distillation column (T101) has 3–5 trays. The absolute operating pressure of the catalytic distillation column (T101) is 12–15 kPa. The reflux method at the top of the column is total reflux. The top temperature of the catalytic distillation column (T101) is 0–10 °C, the bottom temperature is 100–110 °C, and the space velocity of the catalytic distillation column is 0.45–0.64 h⁻¹. -1 .

[0010] Preferably, the catalyst in the catalytic packing installed in the above-mentioned reaction section is a hydroxide-type macroporous alkaline resin. The reaction section is divided into three sections: the first section is filled with 828 resin, and the second and third sections are filled with D296 resin.

[0011] Preferably, the above-mentioned condenser uses an ethylene glycol aqueous solution at -15 to -20 °C as the condensate.

[0012] Preferably, the above-mentioned built-in reboiler is a single-tube, single-shell tubular overflow reboiler. The reboiler is built into the column body and is located 0.5 m below the stripping section. The tube size is φ38 mm and the tube length is 1~1.5 m. A gas overflow pipe is installed in the middle, and its cross-sectional area is 1%~5% of the column cross-sectional area. The opening of this pipe is 3~8 cm higher than the openings of other tubes.

[0013] The present invention utilizes the distillation column to synthesize diacetone alcohol using a low-temperature, reduced-pressure, continuous catalytic distillation process, characterized by the following steps: (1) Acetone enters the catalytic distillation column (T101) through the feed inlet between the reaction section and the stripping section. The acetone is heated and vaporized, then enters the reaction section. Under the action of the catalyst in the catalytic packing, a condensation reaction occurs. The unreacted light component acetone is distilled off from the top of the column and condensed in the condenser. The condensate is completely refluxed to the top of the catalytic distillation column and re-enters the reaction section for further reaction, forming an acetone enrichment zone in the reaction section; (2) The diacetone alcohol generated in the reaction section enters the stripping section through the separation action of the catalytic packing. In the stripping section, the acetone entrained in the diacetone alcohol is further separated. After the acetone returns to the reaction section to continue the reaction, the diacetone alcohol enters the tube side of the built-in reboiler, and the shell side of the reboiler is provided with heat source by heating steam; (3) The built-in reboiler of the catalytic distillation column (T101) adopts a single tube-pass single shell-pass tubular overflow reboiler. After the diacetone alcohol is partially vaporized by the single tube-pass single shell-pass tubular overflow reboiler, a part of the vapor phase enters the stripping section of the catalytic distillation column (T101) to provide heat source for the whole column. The unvaporized diacetone alcohol enters the bottom of the catalytic distillation column from the tube side of the reboiler due to gravity. The bottom of the column does not provide an additional heat source. The diacetone alcohol product is directly taken out from the bottom of the column, which shortens the residence time of diacetone alcohol in the bottom of the column and the reboiler and avoids the high-temperature decomposition of diacetone alcohol.

[0014] The process of this invention has an acetone conversion rate of >99.9%, a diacetone alcohol product purity of >99.9%, and does not produce byproducts such as isopropylidene acetone during the reaction.

[0015] Beneficial effects of the present invention

[0016] This invention achieves a match between the separation temperature and the reaction temperature by reducing pressure, which significantly improves the selectivity of the reaction. Furthermore, the product does not require subsequent separation, resulting in low energy consumption and minimal equipment investment.

[0017] This invention utilizes a single-tube, single-shell, tubular reboiler built into the catalytic distillation column as the reboiler heating device, which shortens the heating time of diacetone alcohol and avoids its thermal decomposition into acetone. This achieves the advantages of high product purity and stable quality, and the diacetone alcohol collected from the reboiler of the catalytic distillation column can be used as a qualified product. Its gas overflow pipe can realize smooth countercurrent flow of vapor and liquid, while ensuring smooth flow of both vapor and liquid phases at high flow rates.

[0018] Furthermore, compared to traditional batch reactors and fixed-bed processes, it solves the problems of low conversion rate, incomplete conversion of acetone, and the need for subsequent product separation in the reaction process; compared to atmospheric pressure catalytic distillation column processes, it solves the problems of multiple by-products, poor selectivity, incomplete conversion of acetone, and the need for subsequent product separation, reducing the need for a diacetone alcohol distillation column and significantly reducing equipment investment; at the same time, it lowers the reaction temperature, avoids the re-decomposition of diacetone alcohol into acetone, and also reduces energy consumption.

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow and catalytic distillation column structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the cross-sectional structure connecting the reboiler and the distillation column of the present invention. Detailed Implementation

[0022] To make the above features and advantages of the present invention more apparent and understandable, the present invention will be further described below through specific embodiments and in conjunction with the accompanying drawings.

[0023] This invention relates to a low-temperature, reduced-pressure continuous catalytic distillation column for synthesizing diacetone alcohol, comprising a catalytic distillation column A1, a condenser A2, and a built-in reboiler A3. The reboiler A3 (also called a reboiler) is used to vaporize the liquid again; it is a single-tube, single-shell, tubular reboiler with overflow capability. The catalytic distillation column A1 comprises a reaction section A11 and a stripping section A12. The feed inlet 1 of the catalytic distillation column is located between the reaction section A11 and the stripping section A12. An external condenser A2 is installed at the top of the catalytic distillation column. The inlet 2 of the condenser is connected to the top outlet of the catalytic distillation column, and the outlet of the condenser is connected to the side inlet 3 at the top of the catalytic distillation column. The built-in reboiler A3 is installed at the bottom of the catalytic distillation column, and a bottom outlet 4 is provided at the bottom of the catalytic distillation column.

[0024] The reaction section of the catalytic distillation column can be divided into three sections, each with a height of 4–6 m. The stripping section of the catalytic distillation column (T101) has 3–5 trays. The absolute operating pressure of the catalytic distillation column (T101) can be 12–15 kPa. The reflux method at the top of the column is total reflux. The top temperature of the catalytic distillation column (T101) can be 0–10 ℃, the bottom temperature can be 100–110 ℃, and the space velocity of the catalytic distillation column can be 0.45–0.64 h⁻¹. -1 .

[0025] The catalyst in the catalytic packing installed in reaction section A11 is a hydroxide-type macroporous alkaline resin. The reaction section is divided into three sections. Specifically, the first section is filled with 828 resin, and the second and third sections are filled with D296 resin.

[0026] The condenser mentioned above uses ethylene glycol aqueous solution at -15 to -20 ℃ as the condensate.

[0027] This application introduces a built-in reboiler A3 (a single-pass, single-shell, tube-type overflow reboiler) located on the inner circumferential wall A13 of the distillation column. The built-in reboiler A3 is constructed as a sealed cylindrical shell (the outer circumferential wall of the cylindrical shell contacts the inner circumferential wall of the distillation column). A rising overflow pipe A31 is installed in the middle between the upper and lower surfaces of the shell. Multiple tubes A32 are arranged around the outer circumference of the rising overflow pipe A31, forming a cavity between the cylindrical shell, the rising overflow pipe A31, and the tubes A32. This cavity circulates heat with a heat source outside the distillation column. In this application, the built-in reboiler A3 is positioned 0.5 m below the stripping section. The tubes A32 have a diameter of φ38 mm and a length of 1~1.5 m. m, in which a gas overflow pipe A31 is installed in the middle, the cross-sectional area of ​​which is 1% to 5% of the cross-sectional area of ​​the tower, and the opening of the pipe is 3 to 8 cm higher than the openings of other tubes; the gas overflow pipe A31 can realize the smooth counter-current flow of gas and liquid, and at the same time ensure the smooth flow of the two phases of gas and liquid under high flow rate.

[0028] The present invention uses the distillation column to synthesize diacetone alcohol by low-temperature vacuum continuous catalytic distillation process, which is carried out in the following steps: (1) Acetone enters the catalytic distillation column (T101) from the feed inlet between the reaction section and the stripping section. The acetone is heated and vaporized and enters the reaction section. Under the action of the catalyst in the catalytic packing, a condensation reaction is carried out. The unreacted light component acetone is distilled off from the top of the column and condensed in the condenser. The condensate is completely refluxed to the top of the catalytic distillation column and enters the reaction section again for reaction, forming an acetone enrichment zone in the reaction section; (2) The diacetone alcohol generated in the reaction section enters the stripping section through the separation action of the catalytic packing. In the stripping section, the acetone entrained in the diacetone alcohol is further separated. The ketone returns to the reaction section to continue the reaction, and the diacetone alcohol enters the tube side of the built-in reboiler. The shell side of the reboiler is provided with heat source by heating steam. (3) The built-in reboiler of the catalytic distillation column (T101) adopts a single tube-pass single shell-pass tubular overflow reboiler. After the diacetone alcohol is partially vaporized by the single tube-pass single shell-pass tubular overflow reboiler, a part of the vapor phase enters the stripping section of the catalytic distillation column (T101) to provide heat source for the whole column. The unvaporized diacetone alcohol enters the bottom of the catalytic distillation column from the tube side of the reboiler due to gravity. The bottom of the column does not provide an additional heat source. The diacetone alcohol product is directly taken out from the bottom of the column, which shortens the residence time of diacetone alcohol in the bottom of the column and the reboiler and avoids the high-temperature decomposition of diacetone alcohol.

[0029] The process of this invention has an acetone conversion rate of >99.9%, a diacetone alcohol product purity of >99.9%, and does not produce byproducts such as isopropylidene acetone during the reaction.

[0030] This invention achieves a match between the separation temperature and the reaction temperature by reducing pressure, which significantly improves the selectivity of the reaction. Furthermore, the product does not require subsequent separation, resulting in low energy consumption and minimal equipment investment.

[0031] This invention utilizes a single-tube, single-shell, tubular reboiler built into the catalytic distillation column as the reboiler heating device, which shortens the heating time of diacetone alcohol and avoids its thermal decomposition into acetone. This achieves the advantages of high product purity and stable quality, and the diacetone alcohol collected from the reboiler of the catalytic distillation column can be used as a qualified product. Its gas overflow pipe can realize smooth countercurrent flow of vapor and liquid, while ensuring smooth flow of both vapor and liquid phases at high flow rates.

[0032] Furthermore, compared to traditional batch reactors and fixed-bed processes, it solves the problems of low conversion rate, incomplete conversion of acetone, and the need for subsequent product separation in the reaction process; compared to atmospheric pressure catalytic distillation column processes, it solves the problems of numerous by-products, poor selectivity, incomplete conversion of acetone, and the need for subsequent product separation, reducing the need for one diacetone alcohol distillation column and significantly reducing equipment investment; at the same time, it lowers the reaction temperature and residence time of diacetone alcohol, preventing diacetone alcohol from decomposing back into acetone, and also reducing energy consumption.

[0033] Examples of the distillation process using the low-temperature vacuum continuous catalytic distillation column for synthesizing diacetone alcohol according to the present invention are as follows:

[0034] Example 1

[0035] The process flow shown in the attached diagram is adopted, wherein the stripping section has 3 theoretical plates, and the reaction section is 12 m high (divided into three sections, each 4 m high). The operating conditions of the catalytic distillation column are: operating absolute pressure of 12 kPa, total reflux at the top of the column, condenser using -20 ℃ ethylene glycol aqueous solution as condensate, and space velocity of 0.45 h⁻¹. -1 The raw material, acetone, is pumped into the catalytic distillation column from the bottom of the reaction section via the feed pipe. It reacts with the catalyst in the reaction section. The temperature at the top of the column is 5.0 ℃, and the temperature at the bottom of the column is 105.6 ℃. The diacetone alcohol produced by the reaction is separated in the stripping section and then vaporized in a single-tube, single-shell tubular overflow reboiler (with built-in reboiler A3). The vapor phase enters the stripping section of the catalytic distillation column, and the liquid phase is collected from the bottom of the column through the outlet pipe, resulting in a product with a diacetone alcohol mass fraction of 99.96%, without the byproduct isopropylidene acetone.

[0036] Example 2

[0037] The process flow shown in the attached diagram is adopted, wherein the theoretical number of plates in the stripping section is 5, the height of the reaction section is 18 m (divided into three sections, each 6 m high), and the operating conditions of the catalytic distillation column are: operating absolute pressure of 12 kPa, total reflux at the top of the column, condenser using -20 ℃ ethylene glycol aqueous solution as condenser, and space velocity of 0.64 h⁻¹. -1 The raw material, acetone, is pumped into the catalytic distillation column from the bottom of the reaction section via the feed pipe. It reacts with the catalyst in the reaction section. The temperature at the top of the column is 5.0 ℃, and the temperature at the bottom of the column is 105.1 ℃. The diacetone alcohol produced by the reaction is separated in the stripping section and then vaporized and separated in a single-tube, single-shell tubular overflow reboiler. The vapor phase enters the stripping section of the catalytic distillation column, and the liquid phase is collected from the bottom of the column through the outlet pipe, yielding a product with a diacetone alcohol mass fraction of 99.92%, without the byproduct isopropylidene acetone.

[0038] Example 3

[0039] The process flow shown in the attached diagram is adopted, wherein the stripping section has 4 theoretical plates, the reaction section is 15 m high (divided into three sections, each 5 m high), and the catalytic distillation column operating conditions are: operating absolute pressure of 15 kPa, total reflux at the top of the column, condenser using -15 ℃ ethylene glycol aqueous solution as condenser, and space velocity of 0.45 h⁻¹. -1 The raw material, acetone, is pumped into the catalytic distillation column from the bottom of the reaction section via a feed pipe, where it reacts with the catalyst. The top temperature of the column is 9.4 ℃, and the bottom temperature is 108.9 ℃. The diacetone alcohol produced in the reaction is separated in the stripping section and then vaporized in a single-tube, single-shell overflow reboiler. The vapor phase enters the stripping section of the catalytic distillation column, while the liquid phase is collected from the bottom outlet pipe, yielding a product with a diacetone alcohol mass fraction of 99.90%, without the byproduct isopropylidene acetone.

[0040] This invention employs catalytic distillation technology, utilizing a vacuum pump to control vacuum, a catalytic distillation column, a condenser, a built-in single-pass overflow reboiler, and several connecting pipes to achieve continuous production. It can directly obtain diacetone alcohol with a purity of not less than 99.9%. By reducing pressure, this invention achieves matching between the separation temperature and the reaction temperature, which not only significantly improves the reaction conversion rate (>99.9%), but also achieves 100% reaction selectivity, avoiding the generation of by-products and the decomposition of diacetone alcohol, reducing reaction energy consumption. In addition, the product does not require subsequent separation, and the catalyst does not require separation and recovery.

[0041] Finally, it should be noted that this invention is not limited to the above-described preferred embodiments. Anyone inspired by this invention can derive various other forms of vacuum continuous catalytic distillation processes and catalytic distillation columns for the synthesis of diacetone alcohol. Those skilled in the art should understand that modifications to the specific embodiments of this invention or equivalent substitutions of some technical features, without departing from the spirit of the invention, should be covered within the scope of the technical solutions claimed in this invention.

Claims

1. A low-temperature, reduced-pressure continuous catalytic distillation column for synthesizing diacetone alcohol, characterized in that: The catalytic distillation column includes a catalytic distillation column, a condenser, and a built-in reboiler. The catalytic distillation column comprises a reaction section and a stripping section. The feed inlet of the catalytic distillation column is located between the reaction section and the stripping section. An external condenser is installed at the top of the catalytic distillation column, with its inlet connected to the top outlet and its outlet connected to the side inlet at the top. The built-in reboiler is located at the bottom of the catalytic distillation column, and a bottom outlet is located at the bottom. The reaction section of the catalytic distillation column is divided into three sections, each 4–6 m high. The stripping section of the catalytic distillation column (T101) has 3–5 trays. The absolute operating pressure of the catalytic distillation column (T101) is 12–15 kPa, and the top reflux method is total reflux. The top temperature of the catalytic distillation column (T101) is 0–10 °C, and the bottom temperature is 100–110 °C. At ℃, the space velocity in the catalytic distillation column is 0.45~0.64 h⁻¹. -1 The built-in reboiler is a single-pass, single-shell, tubular overflow reboiler. The reboiler is built into the column body and is located 0.5 m below the stripping section. The tube size is φ38 mm and the tube length is 1~1.5 m. A gas overflow pipe is installed in the middle, and its cross-sectional area is 1%~5% of the column cross-sectional area. The pipe opening is 3~8 cm higher than the tube openings of other tubes.

2. The low-temperature vacuum continuous catalytic distillation column for synthesizing diacetone alcohol according to claim 1, characterized in that: The catalyst in the catalytic packing installed in the reaction section is a hydroxide-type macroporous alkaline resin. The reaction section is divided into three sections: the first section is filled with 828 resin, and the second and third sections are filled with D296 resin.

3. The low-temperature vacuum continuous catalytic distillation column for synthesizing diacetone alcohol according to claim 2, characterized in that: The condenser uses an ethylene glycol aqueous solution at -15 to -20 ℃ as the condensate.

4. A distillation process for synthesizing diacetone alcohol using a distillation column according to any one of claims 1-3, characterized in that, The following steps are performed: (1) Acetone enters the catalytic distillation column (T101) through the feed inlet between the reaction section and the stripping section. The acetone is heated and vaporized and enters the reaction section. Under the action of the catalyst in the catalytic packing, a condensation reaction is carried out. The unreacted light component acetone is distilled off from the top of the column and condensed in the condenser. The condensate is completely refluxed to the top of the catalytic distillation column and enters the reaction section again for reaction, forming an acetone enrichment zone in the reaction section; (2) The diacetone alcohol generated in the reaction section enters the stripping section through the separation action of the catalytic packing. In the stripping section, the acetone entrained in the diacetone alcohol is further separated. The acetone returns to the reaction section to continue the reaction. The tube side of the built-in reboiler is used, and the shell side of the reboiler is provided with heat source by heating steam; (3) The built-in reboiler of the catalytic distillation column (T101) adopts a single tube-pass single shell-pass tubular overflow reboiler. After the diacetone alcohol is partially vaporized by the single tube-pass single shell-pass tubular overflow reboiler, a part of the vapor phase enters the stripping section of the catalytic distillation column (T101) to provide heat source for the whole column. The unvaporized diacetone alcohol enters the bottom of the catalytic distillation column from the tube side of the reboiler due to gravity. The bottom of the column does not provide an additional heat source. The diacetone alcohol product is directly taken out from the bottom of the column, which shortens the residence time of diacetone alcohol in the bottom of the column and the reboiler and avoids the high-temperature decomposition of diacetone alcohol.

5. The low-temperature vacuum continuous catalytic distillation process for synthesizing diacetone alcohol according to claim 4, characterized in that: The process achieves an acetone conversion rate of >99.9%, a diacetone alcohol product purity of >99.9%, and does not produce isopropylidene acetone byproducts during the reaction.

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