A method for producing isophorone by gas-phase condensation of acetone

Abstract

This invention discloses a method for producing isophorone by gas-phase condensation of acetone, comprising the following steps: (1) preheating and vaporizing acetone feedstock, most of the preheated and vaporized acetone feedstock sequentially enters the upper and lower solid base catalyst beds of a fixed-bed reactor for condensation reaction, and a small portion of the preheated and vaporized acetone feedstock is used as quench gas and directly mixed with the reaction gas from the upper solid base catalyst bed, and condensed in the lower solid base catalyst bed of the fixed-bed reactor; (2) the unreacted acetone obtained from the outlet of the fixed-bed reactor is recycled back to the inlet of the fixed-bed reactor by vacuum flash evaporation and acetone removal tower; (3) the bottom liquid phase obtained from the acetone removal tower in step (2) is dehydrated by a partition-type water separator and a dehydration tower, and the resulting oil phase is sequentially distilled and separated by a negative pressure deisopropylidene acetone tower, a trimethylbenzene removal tower and an isophorone tower to obtain isophorone product.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a method for producing isophorone by gas-phase condensation of acetone. Background Technology

[0002] Isophorones are mainly used to produce isophorone diamine and isophorone diisocyanate, and are commonly used as intermediates in paints, inks, coatings, solvents, and the chemical synthesis of pharmaceuticals and pesticides. Therefore, research on isophorone production processes is of great significance for addressing the demand for isophorone products and the development of downstream products. There are two main synthetic routes for isophorone. One is the isopropylidene acetone method, which uses isopropylidene acetone and ethyl acetoacetate as raw materials under alkaline conditions, employing a phase transfer catalyst, and proceeding through cyclization and hydrolysis reactions to obtain isophorone. The isopropylidene acetone method has relatively mild reaction conditions and can be carried out at room temperature and lower temperatures. It is relatively simple to operate, but the raw material price is high, resulting in high production costs and making industrialization difficult. The other is the acetone condensation method, which, under alkaline catalyst and high temperature conditions, involves acetone undergoing alkaline condensation, dehydration, conjugated addition, intramolecular condensation, and subsequent dehydration reactions to finally obtain isophorone. This route has already achieved industrial-scale production. Acetone condensation can be divided into three types: ① pressurized liquid-phase condensation in alkaline solution; ② solid catalyst heterogeneous catalytic condensation; ③ gas-phase condensation-liquid-phase condensation combined method.

[0003] Initially, the liquid-phase condensation method used calcium oxide, sodium ethoxide, and sodium amide as catalysts. In recent years, alkali metal hydroxides have become the main catalysts. Patents US2334226 and US2399976 describe the use of 20% NaOH solution as a catalyst at a temperature of 150℃, a pressure of 1.1 MPa, and a reaction time of 3 hours, achieving an acetone conversion rate of 17% and an isophorone selectivity of 39%. High-concentration alkaline solutions can accelerate the reaction rate, but they also generate a large number of byproducts, leading to a decrease in isophorone selectivity. Mao Liqiu et al. [Hunan Normal University, Journal of Natural Sciences, 2000, 23(3)] found that under reaction conditions of 250℃ and 3.5 MPa, using 0.7% KOH as a catalyst, the acetone conversion rate was 67.5%, and the isophorone selectivity was as high as 92.7%. Dong Yuhang et al. [Guangzhou Chemical Industry, 2011, 39(15)] studied the effects of different reaction temperatures, NaOH concentrations, reaction times, and acetone-to-water ratios on the yield of isophorone. They found that in the liquid-phase reaction, the acetone condensation reaction is a multi-step series equilibrium reaction; increasing the alkali concentration can relatively reduce the temperature and pressure, but excessively high alkali concentrations will lead to a decrease in the selectivity of isophorone. Patent CN102367223 describes the reaction product of acetone liquid-phase condensation under the action of an organic pyridine-based quaternary ammonium strong base catalyst, which is then distilled to obtain isophorone.

[0004] The mainstream industrial method currently used is liquid-phase condensation, typically carried out at 200-250℃ and 3-4 MPa. A typical process flow is as follows: Figure 1 As shown.

[0005] Process Description: Acetone, water, and KOH solution are fed into the reactor. The temperature is controlled at 423-573 K and the pressure at 3.0-3.5 MPa. After reacting for 1.5-2 hours, the material is sent to atmospheric distillation column 1 to distill off unreacted acetone and water. The condensed material is then returned to the reactor to continue the reaction. The bottom material of distillation column 1 is sent to a separator for phase separation. The lower alkaline layer is sent to alkaline wastewater treatment, and the upper organic phase is sent to atmospheric distillation column 2. Diacetone alcohol and isopropylidene acetone are distilled off at the top of the column and returned to the reactor to continue the reaction. Crude isophorone product is extracted from the middle of the column, and the bottom of the column contains high-boiling-point substances.

[0006] The challenge of liquid-phase condensation lies in the presence of both oil and water phases within the system, requiring vigorous stirring to ensure sufficient contact between the two phases. Furthermore, the condensation process is a series of reactions, resulting in numerous byproducts and consequently, low selectivity for isophorone. Therefore, early liquid-phase processes primarily focused on addressing the impact of the oil-water dual-phase system, reducing residence time distribution, avoiding side reactions at high catalyst concentrations, and removing colored substances from isophorone.

[0007] Currently, the reaction vessel and distillation column are commonly combined into one, converted into a reactive distillation column, with unreacted acetone at the top of the column cooled and refluxed to the lower reaction vessel. This improved process achieves an acetone conversion of 6-10%, isophorone selectivity of 60-70%, isopropylidene acetone selectivity of 6-8%, and diacetone alcohol selectivity of 15-18%. Liquid-phase condensation reactive distillation has advantages such as high coupling degree, simple catalyst preparation, and good selectivity, making it suitable for industrial production. However, it also has some problems, such as the need for pressurized conditions for the reaction, high requirements for distillation column operation and control, the tendency of alkaline solutions to corrode equipment and difficulties in separation and recovery, low single-pass acetone conversion, and high production costs.

[0008] Two types of magnesium-aluminum composite oxide catalysts were reported in 1998: one for gas-phase and one for liquid-phase [(Mg 2+ ) 1-x (Al 3+ (OH) - )2] x+ [(OH - )] x- (H2O) n and Mg used for liquid-phase reactions 1-x Al x O 1+xCatalyst. Under reaction conditions of 200℃, 2.5MPa, and 1h, the acetone conversion rate was 38%, and the isophorone selectivity was 51%. In recent years, with the development of microchannel reactor technology, the application of microchannel reactors in the acetone liquid-phase condensation method has become a new research direction. Wanhua Polyurethane Co., Ltd., through microchannel reaction technology, achieved an acetone conversion rate of 22.7% and an isophorone mass fraction as high as 91.3% in the high-boiling fraction under conditions of 280℃, 8.3MPa, and a reaction liquid residence time of 5min. Patent CN200910102119.9 reported that by pressurizing acetone and KOH solution to 8.0-20.0MPa and preheating it to 280-320℃, a supercritical reaction was carried out in a tubular reactor for 1-3min, ultimately achieving an α-isophorone selectivity of 93%. However, achieving homogeneous reactions using the supercritical method requires harsh conditions, a complex process, extremely high material requirements, and high equipment investment. Furthermore, the side reaction rate is accelerated under high temperature and pressure, making the process difficult to control and posing a problem for the treatment of waste alkali.

[0009] In general, most industrial-scale plants employ the potassium hydroxide / sodium hydroxide liquid-phase catalytic condensation method. While this process is mature, the liquid-phase reactor is a high-pressure device with a complex internal structure, resulting in high manufacturing costs. Furthermore, waste alkali treatment poses pollution risks, the operation of the reaction distillation column is difficult to control, acetone conversion is low, and reaction time is long. Therefore, an increasing number of researchers are turning their attention to developing environmentally friendly solid-phase catalytic condensation methods.

[0010] The key to the solid-phase catalytic condensation process for producing isophorone lies in the selection of the catalyst and the separation of the products. Currently reported catalysts mainly include magnesium-aluminum composite oxides, mixed oxides, molecular sieves, and titanium dioxide, among which magnesium-aluminum composite oxides are considered the most promising catalysts for industrial application. Since the 1990s, numerous related patents have been reported both domestically and internationally, such as CN101698147A, CN102258994A, CN113731393A, US 005849957A, and EP0597693A1. Compared to the traditional acetone liquid-phase condensation method, the solid-phase catalytic condensation method uses a solid base catalyst, eliminating the problem of alkali catalyst treatment. The products are mainly isophorone, isopropylidene acetone, water, and a small amount of high-boiling polymers. It employs a fixed-bed process at atmospheric or low pressure, resulting in mild operating conditions, a simple process flow, and ease of achieving continuous industrial production, aligning with the trend of environmentally friendly industrialization. However, actual industrial-scale plants are few, and the process is essentially still in the research stage.

[0011] CN102633612A discloses a method for preparing isophorone under atmospheric pressure. Acetone is heated and vaporized, then enters a reactor for a condensation reaction. The product is distilled and enters a receiving tank, where it undergoes distillation, decoking, phase separation, and rectification to obtain the final product, isophorone. The atmospheric pressure reactor is preheated to 220-350℃, and a solid catalyst is added and heated to a molten state while maintaining a certain liquid level. Acetone is then introduced into the reactor for reaction, with a material residence time of 1-2 hours. The atmospheric pressure reduces the initial investment in equipment selection and avoids the operational difficulties associated with higher pressures. However, it suffers from intermittent operation, making continuous production impossible. Reference [Nanjing University of Technology, Master's Thesis, Gu Jinfeng] reports a gas-solid catalytic condensation method, the basic process of which is as follows: Figure 2 As shown. This method has simple post-processing, no pollution, and is easy to scale up for production, but it suffers from problems such as rapid catalyst deactivation, difficulty in regenerating agglomerates, and low selectivity for isophorone.

[0012] CN107573227A discloses an acetone gas-solid multiphase condensation method-divider column separation technology, which can solve the azeotropic problem of the product and effectively separate acetone, isophorone, isopropylidene acetone, water and a small amount of high-boiling polymers. Theoretically, the purity of the separated product can reach 99.6%, but this process technology has not yet been industrially verified.

[0013] In 2011, the 10,000 t / a isophorone unit was put into operation. The catalyst used was an alkaline metal oxide supported on a lanthanum oxide-neodymium oxide-alumina rare earth composite; calcium oxide or magnesium oxide. Compared with existing technologies, the catalyst has the advantages of a wide operating range, strong adaptability, and low β-isophorone content in the reaction products, but the preparation cost of the catalyst is relatively high. The condensation products are mainly isophorone, isopropylidene acetone, water, and a small amount of high-boiling polymers. Product separation adopts an azeotropic extraction separation process, and the process flow is as follows. Figure 3 As shown.

[0014] Since the condensation of acetone to isophorone is a multi-step reaction, with each elementary reaction being an equilibrium reaction, the principle of chemical equilibrium can be utilized to first condense acetone in the gas phase at a relatively low temperature (50-70℃) to form isopropylacetone, and then condense isopropylacetone with acetone in the liquid phase under high pressure (1.0-2.0 MPa, 150-180℃) to obtain isophorone, which can effectively improve the yield of isophorone. CN103467263A discloses a method in which acetone is fed into a first reaction tower to undergo a condensation reaction to produce a diacetone alcohol mixture. The mixture flows out of the first reaction tower and is then pumped into a heat exchanger for heating to induce a dehydration reaction of the diacetone alcohol, yielding a mixture of acetone and isopropylidene acetone. The acetone and isopropylidene acetone mixture, along with the remaining diacetone alcohol mixture and an alkaline catalyst, are fed into a second reaction tower. After cooling, the reaction liquid is separated into a gas phase, an oil phase, and an aqueous phase. These are then neutralized and distilled to obtain the final product, isophorone. The first step involves a low reaction temperature, with the reactants being gaseous and the products being liquid. An alkaline anion exchange resin is used as the catalyst. The second step, a liquid-phase condensation reaction, uses an alkaline catalyst. Compared to the traditional liquid-phase method, the gas-liquid co-processing method offers relatively milder reaction conditions in the liquid-phase reaction section. However, it adds the first-stage reaction equipment and shares the same disadvantages as the liquid-phase method. Therefore, the industrial application of the gas-liquid co-processing method is limited. Summary of the Invention

[0015] The purpose of this invention is to overcome the following defects in the prior art and provide a method for producing isophorone by gas-phase condensation of acetone.

[0016] (1) Currently, the traditional alkali liquid-phase compression method used in industry has problems such as high pressure reaction, high reactor manufacturing cost, pollution from waste alkali treatment, difficulty in controlling the operation of the reaction distillation tower, low acetone conversion rate, complex products leading to increased separation difficulty, and long reaction time.

[0017] (2) Solve the problem of azeotropic separation of isophorone, isopropylidene acetone, water and a small amount of high-boiling polymer in the gas-solid phase condensation process for preparing isophorone; the problem of reduced isophorone selectivity caused by increased polymer in traditional atmospheric pressure high temperature distillation separation; and the problem of long process and product contamination and reduced product purity caused by the addition of pyridine extractant in product separation.

[0018] The technical solution of the present invention is as follows:

[0019] A method for producing isophorone by gas-phase condensation of acetone includes the following steps:

[0020] (1) The acetone feedstock is preheated and vaporized. Most of the preheated and vaporized acetone feedstock enters the upper and lower solid base catalyst beds of the fixed bed reactor for condensation reaction. A small portion of the preheated and vaporized acetone feedstock is used as cold quench gas and directly mixed with the reaction gas from the upper solid base catalyst bed to carry out condensation reaction in the lower solid base catalyst bed of the fixed bed reactor.

[0021] The catalyst packed in the above solid base catalyst bed is a magnesium-aluminum composite oxide modified with zirconium oxide and lanthanum oxide;

[0022] (2) The unreacted acetone obtained from the outlet of the above fixed-bed reactor is recycled back to the inlet of the above fixed-bed reactor by vacuum flash evaporation and acetone removal tower.

[0023] (3) The bottom liquid phase obtained from the acetone removal tower in step (2) is dehydrated by a partition-type water separator and a dehydration tower. The resulting oil phase is then subjected to distillation separation by a negative pressure deisopropylidene acetone tower, a detrimethylbenzene tower and an isophorone tower to obtain isophorone product.

[0024] In a preferred embodiment of the present invention, the fixed-bed reactor is a tubular adiabatic reactor, which is divided into two layers: an upper section and a lower section. The interlayer is an empty tube mixing section, in which acetone quench tubes are installed.

[0025] More preferably, the catalyst packing height-to-diameter ratio in the upper and lower sections of the solid alkali catalyst bed of the fixed bed reactor is 2-3:1.

[0026] In a preferred embodiment of the present invention, the partition-type water separator is provided with multiple partitions to form an overflow flow; the coarsely separated aqueous phase flows to the upper part and the oil phase flows to the bottom; the oil-water mixture is fed from one end of the partition-type water separator, and the aqueous phase and oil phase are discharged from the upper and lower parts of the other end respectively, realizing multi-stage near-static oil-water separation.

[0027] In a preferred embodiment of the present invention, the condensation reaction conditions in step (1) are: reaction pressure 0.2-0.5 MPa, reaction temperature 260-350 °C, and feed liquid hourly velocity 0.8-1.8 h.

[0028] More preferably, in step (1): the acetone raw material is pressurized to 0.2-0.5 MPa by a centrifugal pump and then sent to a preheater to raise the temperature to 200-220°C. 70-90% of the acetone is then heated to 260-300°C by an electric heater and sent to the solid alkali catalyst bed in the upper section of the fixed bed reactor for condensation reaction. 10-30% of the acetone is sent to the empty tube mixing section between the upper and lower sections of the fixed bed reactor by a quench tube and mixed with the reaction gas from the solid alkali catalyst bed in the upper section. The temperature after mixing is adjusted to 280-320°C in the solid alkali catalyst bed in the lower section of the fixed bed reactor.

[0029] More preferably, in step (2): the mixture obtained from the outlet of the fixed bed reactor is cooled to 55-80°C by a two-stage heat exchanger, and then sent to a flash tank after being depressurized to atmospheric pressure. Unreacted gaseous acetone is separated from the top of the flash tank, and then pressurized to 0.2-0.5MPa by a pipeline pump and sent back to the inlet of the fixed bed reactor or cooled and sent to an acetone storage tank for later use.

[0030] In a further preferred embodiment, in step (2): the liquid phase at the bottom of the flash tank is sent to the acetone stripping tower for distillation and separation, the acetone recovered at the top of the tower is pumped back to the reactor inlet by a pipeline pump, and the liquid phase at the bottom of the tower is sent to a partition-type horizontal water separator; the acetone stripping tower operates at atmospheric pressure, with a top temperature of 55-80℃ and a bottom temperature of 80-95℃.

[0031] In a further preferred embodiment, in step (3): the wastewater at the bottom of the dehydration tower is sent to the sewage treatment system, and the oil-water phase at the top of the dehydration tower is sent back to the partition-type horizontal water separator; the dehydration tower operates at atmospheric pressure, with a top temperature of 90-105℃ and a bottom temperature of 100-110℃.

[0032] In a further preferred embodiment, the distillation separation of the isopropylidene-removed acetone column, the trimethylbenzene-removed column, and the isophorone-removed column is all operated under negative pressure conditions with a vacuum degree of 10-20 kPa. The isopropylidene-removed acetone, trimethylbenzene-removed acetone, and isophorone products with a purity greater than 98% are collected from the top of the columns, respectively, with a reflux ratio of 3-5. Specifically, the top temperature of the isopropylidene-removed acetone column is 90-105℃, and the bottom temperature is 115-130℃; the top temperature of the trimethylbenzene-removed acetone column is 135-150℃, and the bottom temperature is 145-160℃; the top temperature of the isophorone-removed acetone column is 145-160℃, and the bottom temperature is 165-180℃.

[0033] The beneficial effects of this invention are:

[0034] 1. Compared with the atmospheric pressure gas-solid phase condensation method, this invention, based on the gas phase reaction mechanism, increases the reaction pressure to facilitate the reaction direction with reduced volume, thereby increasing the reaction rate and thus increasing the unit production capacity. The condensation reaction adopts a fixed-bed reactor with a pressure of 0.2-0.5MPa and a reaction temperature of 260-350℃. The equipment has a simple structure and low manufacturing cost.

[0035] 2. The present invention uses a magnesium-aluminum composite oxide modified with zirconium oxide and lanthanum oxide as a catalyst, which has high activity and high selectivity, and reduces the troublesome catalyst post-processing problem caused by traditional methods; the acetone is fed in stages, which can solve the problem of excessive temperature rise in a single stage of the adiabatic reactor causing an increase in polymerization products; the fixed-bed reactor is used, and the production operation is simple.

[0036] 3. This invention employs reduced-pressure flash evaporation to recover unreacted acetone and a multi-stage static separation technology using a baffle-type horizontal water separator for oil-water phase separation. The material exiting the low-pressure reactor enters the atmospheric-pressure flash tank, which is slightly above the boiling point of acetone, enabling rapid separation and recovery of large quantities of unreacted acetone. Increasing the height of the baffle-type horizontal water separator allows for multi-stage quasi-static oil-water phase separation, reducing the problems of excessive load on subsequent distillation and reduced separation purity caused by oil-water azeotropy.

[0037] 4. The isopropylidene-removing acetone tower, trimethylbenzene-removing tower, and isophorone tower in this invention employ negative pressure operation for distillation separation. Byproducts are separated by reduced pressure distillation, which saves energy and improves the purity and yield of isophorone products. At the same time, it solves the problems of long process, extractant addition and recovery, product contamination and reduced product purity caused by the traditional azeotropic extraction separation method. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the process flow of the pressurized liquid-phase condensation method in an alkaline solution, as described in the background art of this invention.

[0039] Figure 2 This is a schematic diagram of the solid catalyst heterogeneous catalytic condensation-reactive distillation separation process in the background art of the present invention.

[0040] Figure 3 This is a schematic diagram of the solid catalyst heterogeneous catalytic condensation-azeotropic extraction separation process in the background art of this invention.

[0041] Figure 4 This is a process flow diagram of Embodiment 1 of the present invention.

[0042] Figure 5 This is a graph showing the 800-hour operating data from Example 1 of the present invention, illustrating the acetone conversion rate and the selectivity of the product after deducting the aqueous phase. Wherein, CON: acetone conversion rate, MO: isopropylidene acetone, C9: trimethylbenzene, IP: isophorone, C12: polymerization product. Detailed Implementation

[0043] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0044] Example 1

[0045] The process flow of this embodiment is as follows: Figure 4 As shown, the specific steps include the following:

[0046] (1) Acetone feedstock from the storage tank is pressurized to 0.2 MPa (gauge pressure) by a feed pump and preheated to 220±5℃ by a preheater. Acetone with a fractional flow rate of 80±5% (volume flow rate) is mixed with acetone recycled from the flash tank and acetone removal tower via a pipeline pump and then heated to 280±5℃ by an electric heater before being fed into the top inlet of the fixed-bed reactor for condensation reaction. Acetone with a fractional flow rate of 20±5% (volume flow rate) from the preheater outlet is fed into the interlayer of the fixed-bed reactor through a quench pipe, mixed with the reaction gas from the upper outlet, and then enters the lower reaction bed for condensation reaction. The temperature after mixing is controlled to 290±5℃. The temperature of the mixture at the outlet of the fixed-bed reactor is 310±5℃, and its main components are water, isopropylidene acetone, mesitylene, isophorone, polymerization products, and unreacted acetone.

[0047] Specifically, the fixed-bed reactor described above is a tubular adiabatic reactor, divided into upper and lower sections, with an empty tube mixing section in between, equipped with acetone quench tubes. The catalyst packed in both the upper and lower sections of the fixed-bed reactor is a La₂O₃ / MgO-Al₂O₃ composite oxide catalyst, with a height-to-diameter ratio of 2:1 for both sections. The condensation reaction conditions are: reaction pressure 0.2 MPa, reaction temperature 300 ± 5 °C, and feed liquid hourly space velocity 1.0 h⁻¹.

[0048] (2) The mixture obtained from the outlet of the fixed bed reactor is cooled to 60±5℃ by two-stage heat exchangers, and then sent to the flash tank after being depressurized to atmospheric pressure. Unreacted gaseous acetone is separated from the top of the flash tank and pressurized to 0.2MPa by a pipeline pump and sent back to the inlet of the fixed bed reactor or cooled and sent to the acetone storage tank for later use.

[0049] (3) The liquid phase at the bottom of the flash tank is fed into the acetone stripping tower for further removal of unreacted acetone. The liquid phase at the bottom of the acetone stripping tower is then fed into a baffle-type horizontal water separator. The acetone recovered at the top of the acetone stripping tower is collected in the main inlet pipe of the aforementioned pipeline pump. The acetone stripping tower operates at atmospheric pressure, with a top temperature of 60±5℃ and a bottom temperature of 90±5℃.

[0050] Specifically, the aforementioned baffle-type water separator is equipped with multiple baffles to form an overflow flow; the coarsely separated aqueous phase flows to the top and the oil phase flows to the bottom; the oil-water mixture is fed from one end of the baffle-type water separator, and the aqueous and oil phases are discharged from the top and bottom of the other end respectively, realizing multi-stage near-static oil-water separation.

[0051] (4) After static oil-water separation in the bottom of the acetone removal tower, the aqueous phase exiting from the upper part of the other end of the baffle-type water separator is sent to the dehydration tower. The wastewater at the bottom of the dehydration tower is sent to the sewage treatment system, and the mixture of acetone and water at the top of the dehydration tower is returned to the baffle-type water separator. The dehydration tower operates at atmospheric pressure, with a top temperature of 95±5℃ and a bottom temperature of 105±5℃.

[0052] (5) The oil phase exiting from the bottom of the other end of the partition-type horizontal water separator is sequentially distilled and separated by a negative pressure-operated isopropylidene-removing acetone tower, a trimethylbenzene-removing tower, and an isophorone tower. The isopropylidene-removing acetone tower, trimethylbenzene-removing tower, and isophorone tower distillation separation are operated under negative pressure conditions with a vacuum degree of 20 kPa. The specific steps are as follows:

[0053] A. The oil phase exiting from the bottom of the other end of the aforementioned partition-type horizontal water separator is sent to an isopropylidene acetone stripping tower. A reflux condenser is installed at the top of the tower with a reflux ratio of 3-5, and qualified isopropylidene acetone with a purity greater than 95% is collected. The heavy phase mixture at the bottom of the tower enters a trimethylbenzene stripping tower. The top temperature of the isopropylidene acetone stripping tower is controlled at 100±5℃, and the bottom temperature is controlled at 120±5℃.

[0054] B. The heavy phase mixture at the bottom of the isopropylidene-acetone stripping column enters the trimethylbenzene stripping column, which is equipped with a reflux condenser at the top with a reflux ratio of 3-5, and produces qualified trimethylbenzene with a purity greater than 95%; the heavy phase mixture at the bottom enters the isophorone stripping column. The temperature at the top of the trimethylbenzene stripping column is 140±5℃, and the temperature at the bottom is 150±5℃.

[0055] C. The heavy phase mixture from the bottom of the trimethylbenzene removal tower enters the isophorone tower. A reflux condenser is installed at the top of the tower with a reflux ratio of 3-5, and qualified isophorone with a purity greater than 95% is collected. The polymer heavy component from the bottom of the tower is sent to the waste tank in the tank area. The top temperature of the isophorone removal tower is 150±5℃, and the bottom temperature is 170±5℃.

[0056] Testing showed that the acetone single-pass conversion rate in Example 1 was 35-40%. The mass composition of the effluent from the fixed-bed reactor was 23-25% water, 20-22% isopropylidene acetone, 3-5% mesitylene, 50-52% isophorone, and 3-5% polymerization products. The selectivity of the aqueous phase products was: 20-25% isopropylidene acetone, 5-10% mesitylene, 65-70% isophorone, and 5-10% polymerization products. 800h operating data are as follows... Figure 5 As shown.

[0057] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for producing isophorone by gas-phase condensation of acetone, characterized in that: Includes the following steps: (1) The acetone feedstock is preheated and vaporized. Most of the preheated and vaporized acetone feedstock enters the upper and lower solid base catalyst beds of the fixed bed reactor for condensation reaction. A small portion of the preheated and vaporized acetone feedstock is used as quench gas and directly mixed with the reaction gas from the upper solid base catalyst bed to carry out condensation reaction in the lower solid base catalyst bed of the fixed bed reactor. The fixed bed reactor adopts a tubular adiabatic reactor, which is divided into upper and lower sections. The interlayer is an empty tube mixing section with acetone quench tubes. The catalyst packed in the above solid base catalyst bed is a magnesium-aluminum composite oxide modified with zirconium oxide and lanthanum oxide; (2) The unreacted acetone obtained from the outlet of the above fixed-bed reactor is recycled back to the inlet of the above fixed-bed reactor by vacuum flash evaporation and acetone removal tower; (3) The bottom liquid phase obtained from the acetone removal tower in step (2) is dehydrated by a partition-type water separator and a dehydration tower. The resulting oil phase is then subjected to distillation separation by a negative pressure-operated isopropylidene removal acetone tower, a trimethylbenzene removal tower, and an isophorone tower to obtain isophorone product. The partition-type water separator is equipped with multiple partitions to form an overflow flow. The coarsely separated water phase flows to the top, and the oil phase flows to the bottom. The oil-water mixture is fed from one end of the partition-type water separator, and the water phase and oil phase are discharged from the top and bottom of the other end, respectively, to achieve multi-stage near-static oil-water separation.

2. The method as described in claim 1, characterized in that: The catalyst packing height-to-diameter ratio in the upper and lower sections of the solid alkali catalyst bed of the fixed bed reactor is 2-3:

1.

3. The method as described in claim 1 or 2, characterized in that: The condensation reaction conditions in step (1) are: reaction pressure 0.2-0.5 MPa, reaction temperature 260-350℃, and feed liquid hourly space velocity 0.8-1.8 h⁻¹. -1 .

4. The method as described in claim 3, characterized in that: In step (1): the acetone raw material is pressurized to 0.2-0.5 MPa by a centrifugal pump and then sent to a preheater to raise the temperature to 200-220℃. 70-90% of the acetone is then heated to 260-300℃ by an electric heater and sent to the solid alkali catalyst bed in the upper section of the fixed bed reactor for condensation reaction. 10-30% of the acetone is sent to the empty tube mixing section between the upper and lower sections of the fixed bed reactor by a quench tube and mixed with the reaction gas from the solid alkali catalyst bed in the upper section. The temperature after mixing is adjusted to 280-320℃ in the solid alkali catalyst bed in the lower section of the fixed bed reactor.

5. The method according to claim 4, wherein: In step (2): the mixture obtained from the outlet of the fixed bed reactor is cooled to 55-80°C by a two-stage heat exchanger, and then sent to a flash tank after being depressurized to atmospheric pressure. Unreacted gaseous acetone is separated from the top of the flash tank and then pressurized to 0.2-0.5MPa by a pipeline pump and sent back to the inlet of the fixed bed reactor or cooled and sent to an acetone storage tank for later use.

6. The method as described in claim 5, characterized in that: In step (2): the liquid phase at the bottom of the flash tank is sent to the acetone stripping tower for distillation and separation, the acetone recovered at the top of the tower is pumped back to the reactor inlet by a pipeline pump, and the liquid phase at the bottom of the tower is sent to a partition-type water separator. The acetone stripping tower operates at atmospheric pressure, with a top temperature of 55-80℃ and a bottom temperature of 80-95℃.

7. The method as described in claim 6, characterized in that: In step (3): the wastewater at the bottom of the dehydration tower is sent to the sewage treatment system, and the oil-water phase at the top of the dehydration tower is sent back to the partition-type horizontal water separator; the dehydration tower operates at atmospheric pressure, with a top temperature of 90-105℃ and a bottom temperature of 100-110℃.

8. The method as described in claim 7, characterized in that: The distillation separation of the isopropylidene-removed acetone column, the trimethylbenzene-removed column, and the isophorone column is all operated under negative pressure conditions with a vacuum degree of 10-20 kPa. The isopropylidene-removed acetone, trimethylbenzene, and isophorone products with a purity greater than 98% are collected from the top of the columns, respectively, with a reflux ratio of 3-5. Specifically, the top temperature of the isopropylidene-removed acetone column is 90-105℃, and the bottom temperature is 115-130℃; the top temperature of the trimethylbenzene-removed column is 135-150℃, and the bottom temperature is 145-160℃; the top temperature of the isophorone-removed column is 145-160℃, and the bottom temperature is 165-180℃.

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