A kind of synthetic method of sorbic acid

Abstract

The present invention provides a method for synthesizing sorbic acid, and relates to the technical field of organic compound synthesis. The method for synthesizing sorbic acid comprises the following steps: mixing crotonaldehyde, a solvent and a catalyst to obtain a condensation liquid, mixing ketene vapor with an inert gas to obtain a mixed gas; the condensation liquid flows from top to bottom through a packing layer of a condensation device, and the mixed gas passes through the packing layer of the condensation device from bottom to top, and the condensation liquid and the mixed gas undergo a condensation reaction in the packing layer of the condensation device to obtain a mixed reaction liquid containing polyester; the mixed reaction liquid containing polyester is mixed with an acid solution for acid hydrolysis to obtain sorbic acid. The present invention reduces the concentration of ketene at a local reaction site in the condensation reaction by adding an inert gas to ketene, so that the main reaction proceeds smoothly, reduces the generation of coloring substances, and can effectively avoid the problem of the product being oxidized to produce coloring substances due to the shutdown of the device and the entry of air into the condensation device during the reaction.

Description

Technical Field

[0001] The invention relates to the technical field of organic compound synthesis, in particular to a method for synthesizing sorbic acid. Background Art

[0002] Sorbic acid preservatives are non-toxic, highly safe and have good preservative effects. They are internationally recognized as the best food preservatives. So far, there are more than ten process routes for the synthesis of sorbic acid, but not many of them are suitable for industrialization. Industrial production practice has proved that the most successful and economical process route is the "acetic acid cracking-ethylene ketone / crotonaldehyde condensation-polyester acidolysis crystallization" process route.

[0003] The condensation tower in the prior art solution has the following deficiencies: (1) the degree of reaction cannot be controlled, and ketene is easily reacted with impurities such as alpha-vinyl crotonaldehyde, triacetaldehyde and other aldehydes in crotonaldehyde, thereby reducing the yield of polyester and damaging the color and yield of sorbic acid; (2) during or after the condensation reaction, the liquid phase product comes into contact with oxygen, undergoes an oxidation reaction, and generates coloring substances, thereby reducing the yield of polyester and damaging the color and yield of sorbic acid.

[0004] In addition, in order to solve the problem of crude sorbic acid containing a lot of coloring matter and other impurities, the following methods are currently used: Japanese Patent Application Publication No. 54-163516 discloses a method of using urea compounds as inhibitors in polyester decomposition to reduce the formation of coloring matter in polyester decomposition, but the invention requires the addition of urea compounds, which increases the cost of purchasing urea compounds and subsequent separation costs, and increases the operating procedures and costs. Japanese Patent Application Publication No. 9-227447 discloses a method of decomposing polyester in multiple stages at a specific temperature to obtain sorbic acid containing the least tar and easy to purify, but the invention has high requirements for temperature control in the decomposition stage, which increases the operating procedures and costs. The Chinese invention patent ZL00108925.0 authorized to Daicel Chemical Co., Ltd. of Japan adopts the method of controlling the oxygen concentration in the gas phase to be less than 4% by volume, and introducing an inert gas into the gas phase of a container storing a slurry or solution containing sorbic acid or its salt, or into the gas phase of a pipeline adjacent to the container, or into the gas phase of both. The inert gas includes nitrogen, for example, to preserve the slurry or solution containing sorbic acid or its salt. This method can prevent the formation of new color-forming substances in the purification operation of sorbic acid or its salt, minimize the degree of coloration of the obtained sorbic acid, and minimize the possibility of gradual deterioration of color. However, this invention is mainly limited to the hydrolysis stage, and does not consider the application to the condensation stage. Daicel Chemical Industries, Ltd. of Japan has been granted Chinese invention patent ZL99801633.0, "Method for preparing polyester and sorbic acid". It was found that alpha-vinyl crotonaldehyde, triacetaldehyde and other aldehyde impurities exist in crotonaldehyde, which reduces the yield of polyester and damages the color and yield of sorbic acid. It is speculated that the aldehyde is converted into coloring substances during the polyester synthesis process and / or the polyester decomposition process, and a solution for controlling the purity of croton, the raw material of the condensation reaction, is proposed. The invention has strict requirements on the purity of the crotonaldehyde raw material, which significantly increases the cost of the condensation section and reduces the profits of the production enterprise.

[0005] After the condensation of ketene / crotonaldehyde is completed, the polyester enters the acid hydrolysis process, and the resulting crude sorbic acid usually contains a variety of coloring substances and other impurities, which seriously affect the appearance and quality of the product. It is necessary to purify it by activated carbon absorption, distillation or recrystallization, which brings a heavy processing burden and economic cost, and is accompanied by the loss of a large amount of sorbic acid. In order to solve the problem of high content of coloring substances and other impurities in crude sorbic acid and high removal cost, those skilled in the art are in urgent need of developing a new production process for sorbic acid, reducing the generation of coloring substances and impurities in the production process of sorbic acid, and reducing production costs. Summary of the invention

[0006] The object of the present invention is to provide a method for synthesizing sorbic acid to solve the problem that the crude sorbic acid obtained after condensation and acid hydrolysis of ketene / crotonaldehyde contains a variety of coloring substances and other impurities.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for synthesizing sorbic acid, comprising the following steps:

[0009] 1) crotonaldehyde, a solvent and a catalyst are mixed to obtain a condensation liquid, and ketene vapor is mixed with an inert gas to obtain a mixed gas; the condensation liquid flows through a packing layer of a condensation device from top to bottom, and the mixed gas passes through the packing layer of the condensation device from bottom to top, and the condensation liquid and the mixed gas undergo a condensation reaction in the packing layer of the condensation device to obtain a mixed reaction liquid containing polyester;

[0010] 2) The mixed reaction liquid containing the polyester is mixed with an acid solution for acid hydrolysis to obtain sorbic acid.

[0011] Preferably, the mass ratio of crotonaldehyde, solvent and catalyst in the condensation liquid is 1-2:1.5-5:0.005-0.01.

[0012] Preferably, the volume ratio of the ketene vapor to the inert gas is 20-30:70-80;

[0013] The inert gas is nitrogen and / or argon.

[0014] Preferably, the feed amount of the condensation liquid is 15 to 20 m 3 / h, the amount of the mixed gas introduced is 200-1000m 3 / h.

[0015] Preferably, the condensation reaction is carried out at a temperature of 40 to 60° C. and a pressure of 25 to 50 kPa.

[0016] Preferably, the filler of the packing layer is one or more of ball rings, trapezoidal rings, structured ceramics and silicon carbide foam;

[0017] The particle size of the filler is 10 to 60 mm.

[0018] Preferably, the outer diameter of the packing layer of the condensation device is 200-1000 mm, and the height of the packing layer is 6-20 m.

[0019] Preferably, the volume ratio of the mixed reaction liquid to the acid solution is 0.5-1.5:0.5-2.0.

[0020] Preferably, the acid hydrolysis temperature is 100-118° C. and the time is 40-100 min.

[0021] Preferably, the acid solution is a hydrochloric acid solution or a sulfuric acid solution;

[0022] The concentration of the acid solution is 10-36 wt %.

[0023] The present invention has at least the following beneficial effects:

[0024] After a certain proportion of inert gas is added to the condensation reaction gas ketene, the concentration of ketene is effectively diluted. During the reaction with the liquid phase containing crotonaldehyde, the concentration of ketene at the local reaction site is effectively reduced, so that the main reaction proceeds smoothly, and the amount and degree of conversion of high-boiling point impurities such as alpha-vinyl crotonaldehyde, trimeraldehyde and other aldehydes contained in crotonaldehyde into coloring substances during the condensation process is reduced; and the problem of condensation reaction products being oxidized to produce coloring substances due to air entering the condensation equipment during the condensation reaction due to reasons such as vacuum pump failure or emergency shutdown of the device can be effectively avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of one cycle of the condensation reaction in step 1) of the present invention. DETAILED DESCRIPTION

[0026] The present invention provides a method for synthesizing sorbic acid, comprising the following steps:

[0027] 1) crotonaldehyde, a solvent and a catalyst are mixed to obtain a condensation liquid, and ketene vapor is mixed with an inert gas to obtain a mixed gas; the condensation liquid flows through a packing layer of a condensation device from top to bottom, and the mixed gas passes through the packing layer of the condensation device from bottom to top, and the condensation liquid and the mixed gas undergo a condensation reaction in the packing layer of the condensation device to obtain a mixed reaction liquid containing polyester;

[0028] 2) The mixed reaction liquid containing the polyester is mixed with an acid solution for acid hydrolysis to obtain sorbic acid.

[0029] The process flow and reaction process schematic diagram of the present invention are as follows Figure 1 shown.

[0030] In the present invention, a liquid distribution plate is provided on the top of the condensation device, and a heat exchange coil is provided on the inner wall of the condensation device.

[0031] During the synthesis process, the condensation liquid is distributed to the packing layer through the liquid distribution plate, flows through the packing layer from top to bottom, spreads and disperses as a continuous liquid film on the packing surface, and contacts in reverse with the ethylene ketone gas entering from the bottom of the condensation device and flowing from bottom to top, a condensation reaction occurs, and heat is released. The reaction heat is removed through the heat exchange coil on the inner wall of the device. After the condensation reaction, the condensation liquid enters the condensation kettle at the bottom of the tower and is circulated to the top of the tower again through the circulation pump. After 8 to 12 cycles of reaction and reaching the reaction end point, the reaction is terminated and the material is discharged once and transported to the evaporator feed storage tank through a pump. The tail gas escaping from the top of the condensation tower is absorbed by the tail gas absorption device and then discharged.

[0032] In the present invention, the description of the liquid distribution plate, heat exchange coil, circulating pump and other devices in the condensation device is not considered as limiting the present invention.

[0033] In the present invention, the mass ratio of crotonaldehyde, solvent and catalyst in the condensation liquid is 1-2:1.5-5:0.005-0.01, preferably 1.2-1.8:2-4.5:0.006-0.009, further preferably 1.4-1.6:2.5-4:0.007-0.008, and more preferably 1.5:3-3.5:0.007-0.008.

[0034] In the present invention, the volume ratio of the ketene vapor to the inert gas is 20-30:70-80, preferably 22-28:72-78, more preferably 24-26:73-77, and more preferably 25:74-76.

[0035] In the present invention, the inert gas is nitrogen and / or argon.

[0036] In the present invention, the feed amount of the condensation liquid is 15 to 20 m 3 / h, preferably 16 to 19 m 3 / h, more preferably 17 to 18 m 3 / h; the amount of the mixed gas introduced is 200 to 1000m 3 / h, preferably 300-800m 3 / h, more preferably 400 to 700 m 3 / h, more preferably 500 to 600 m 3 / h.

[0037] In the present invention, the temperature of the condensation reaction is 40-60°C, preferably 43-58°C, more preferably 45-55°C, more preferably 48-52°C; the pressure is 25-50kPa, preferably 30-45kPa, more preferably 35-40kPa.

[0038] In the present invention, the filler of the packing layer is one or more of ball rings, trapezoidal rings, structured ceramics and silicon carbide foam.

[0039] In the present invention, the particle size of the filler is 10 to 60 mm, preferably 20 to 50 mm, and more preferably 30 to 40 mm.

[0040] In the present invention, the outer diameter of the packing layer of the condensation device is 200-1000 mm, preferably 300-900 mm, more preferably 400-800 mm, and more preferably 500-600 mm; the height of the packing layer is 6-20 m, preferably 8-18 m, more preferably 10-16 m, and more preferably 12-14 m.

[0041] In the present invention, the volume ratio of the mixed reaction solution to the acid solution is 0.5-1.5:0.5-2.0, preferably 0.7-1.3:0.8-1.8, more preferably 0.8-1.2:1.0-1.5, and more preferably 1.0:1.2.

[0042] In the present invention, the acid hydrolysis temperature is 100-118°C, preferably 103-115°C, more preferably 105-112°C, and more preferably 108-110°C; the time is 40-100 min, preferably 50-90 min, more preferably 60-80 min, and more preferably 65-75 min.

[0043] In the present invention, the acid solution is a hydrochloric acid solution or a sulfuric acid solution.

[0044] In the present invention, the concentration of the acid solution is 10 to 36 wt %, preferably 15 to 30 wt %, and more preferably 20 to 25 wt %.

[0045] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0046] Example 1

[0047] The crotonaldehyde, toluene solvent and catalyst (zinc chloride) were mixed in a mass ratio of 2:1.6:0.01 to prepare a condensation liquid. The condensation reaction was carried out in a condensation reaction device. During the reaction, the condensation liquid flowed from top to bottom through the packing layer of the condensation device (the outer diameter of the packing layer was 500 mm and the height of the packing layer was 12 m). The packing layer was filled with a packing ball ring with a particle size of 25 mm. The condensation liquid feed amount was 15 m 3 / h, the reaction gas (the volume fraction of ketene is 20%, and the volume fraction of inert gas nitrogen is 80%) flows from bottom to top through the packing layer of the condensation device, and the feed rate is 1000m 3 / h(such as Figure 1 The temperature in the condensation device is 50° C. and the pressure is 30 kPa. After 8 cycles of reaction, the reaction is completed to obtain a mixed reaction liquid containing polyester.

[0048] The mixed reaction liquid was evaporated at 110°C for 2 hours to remove impurities and remove excess crotonaldehyde and toluene solvent (the yield of polyester was 82.3% based on ethylene ketone), and then acid-hydrolyzed with 25% hydrochloric acid, the volume ratio of hydrochloric acid to the reaction liquid after evaporation and impurity removal was 1:1, and the reaction liquid containing sorbic acid was obtained after acid hydrolysis at 105°C for 1 hour; after activated carbon adsorption, it was separated and purified to finally obtain a sorbic acid product, the sorbic acid yield based on polyester was 84.2%, and the product transmittance was 80.2%.

[0049] Example 2

[0050] The crotonaldehyde, toluene solvent and catalyst (zinc chloride) were mixed in a mass ratio of 2:1.6:0.01 to prepare a condensation liquid. The condensation reaction was carried out in a condensation reaction device. During the reaction, the condensation liquid flowed from top to bottom through the packing layer of the condensation device (the outer diameter of the packing layer was 600 mm and the height of the packing layer was 13 m). The packing layer was filled with a packing trapezoidal ring with a particle size of 40 mm. The condensation liquid feed amount was 20 m 3 / h, the reaction gas (30% by volume of ketene and 70% by volume of inert gas helium) flows from bottom to top through the packing layer of the condensation device, with a feed rate of 900m 3 / h, the temperature in the condensation device was 52°C, the pressure was 31 kPa, and the reaction was completed after 10 cycles of reaction to obtain a mixed reaction liquid containing polyester.

[0051] The mixed reaction liquid was evaporated at 108°C for 2.5 hours to remove impurities and remove excess crotonaldehyde and toluene solvent (the yield of polyester was 81.9% based on ethylene ketone), and then acid-hydrolyzed with 25% hydrochloric acid, the volume ratio of hydrochloric acid to the reaction liquid after evaporation and impurity removal was 1:1, and the reaction liquid containing sorbic acid was obtained after acid hydrolysis at 108°C for 0.9 hours; after activated carbon adsorption, it was separated and purified to finally obtain a sorbic acid product, the sorbic acid yield based on polyester was 84.4%, and the product transmittance was 79.8%.

[0052] Comparative Example 1

[0053] Crotonaldehyde, toluene solvent and catalyst (zinc chloride) were mixed in a ratio of 2:1.6:0.01 to prepare a condensation liquid. The condensation reaction was carried out in a condensation reaction device. During the reaction, the condensation liquid flowed from top to bottom through the packing layer of the condensation device (the outer diameter of the packing layer was 500 mm and the height of the packing layer was 12 m). The packing layer was filled with packing ball rings with a particle size of 25 mm. The condensation liquid feed amount was 15 m 3 / h, the reaction gas (ketene content 100%) flows from bottom to top through the packing layer of the condensation device, and the feed rate is 200m 3The temperature in the condensation device was 50° C. and the pressure was 30 kPa. After 8 cycles of reaction, the reaction was completed to obtain a mixed reaction liquid containing polyester.

[0054] The mixed reaction liquid was evaporated at 110°C for 2 hours to remove impurities and remove excess crotonaldehyde and toluene solvent (the yield of polyester was 78.1% based on ethylene ketone), and then acid-hydrolyzed with 25% hydrochloric acid, the volume ratio of hydrochloric acid to the reaction liquid after evaporation and impurity removal was 1:1, and the reaction liquid containing sorbic acid was obtained after acid hydrolysis at 105°C for 1 hour; after activated carbon adsorption, the reaction liquid was separated and purified to finally obtain a sorbic acid product, the sorbic acid yield based on polyester was 84.3%, and the product transmittance was 70.6%.

[0055] Comparative Example 2

[0056] Crotonaldehyde, toluene solvent and catalyst (zinc chloride) were mixed in a ratio of 2:1.6:0.01 to prepare a condensation liquid. The condensation reaction was carried out in a condensation reaction device. During the reaction, the condensation liquid flowed from top to bottom through the packing layer of the condensation device (the outer diameter of the packing layer was 600 mm and the height of the packing layer was 13 m). The packing layer was filled with a packing trapezoidal ring with a particle size of 40 mm. The condensation liquid feed amount was 20 m 3 / h, the reaction gas (ketene content 100%) flows from bottom to top through the packing layer of the condensation device, and the feed rate is 240m 3 / h, the temperature in the condensation device was 52°C, the pressure was 31 kPa, and the reaction was completed after 10 cycles of reaction to obtain a mixed reaction liquid containing polyester.

[0057] The mixed reaction liquid was evaporated at 108°C for 2.5 hours to remove impurities and remove excess crotonaldehyde and toluene solvent (the yield of polyester was 77.3% based on ethylene ketone), and then acid-hydrolyzed with 25% hydrochloric acid, the volume ratio of hydrochloric acid to the reaction liquid after evaporation and impurity removal was 1:1, and the reaction liquid containing sorbic acid was obtained after acid hydrolysis at 108°C for 0.9 hours; after activated carbon adsorption, the reaction liquid was separated and purified to finally obtain a sorbic acid product, the sorbic acid yield based on polyester was 84.0%, and the product transmittance was 70.9%.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for synthesizing sorbic acid, characterized in that: The following steps are involved: 1) crotonaldehyde, a solvent and a catalyst are mixed to obtain a condensation liquid, and ketene vapor is mixed with an inert gas to obtain a mixed gas; the condensation liquid flows through a packing layer of a condensation device from top to bottom, and the mixed gas passes through the packing layer of the condensation device from bottom to top, and the condensation liquid and the mixed gas undergo a condensation reaction in the packing layer of the condensation device to obtain a mixed reaction liquid containing polyester; 2) The mixed reaction liquid containing the polyester is mixed with an acid solution for acid hydrolysis to obtain sorbic acid.

2. A method for synthesizing sorbic acid according to claim 1, characterized in that, The mass ratio of crotonaldehyde, solvent and catalyst in the condensation liquid is 1-2:1.5-5:0.005-0.

01.

3. A method for synthesizing sorbic acid according to claim 2, characterized in that, The volume ratio of the ketene vapor to the inert gas is 20-30:70-80; The inert gas is nitrogen and / or argon.

4. A method for synthesizing sorbic acid according to claim 2 or 3, characterized in that: The feed amount of the condensation liquid is 15-20m 3 / h, the amount of the mixed gas introduced is 200-1000m 3 / h.

5. A method for synthesizing sorbic acid according to claim 4, characterized in that, The temperature of the condensation reaction is 40-60° C., and the pressure is 25-50 kPa.

6. A method for synthesizing sorbic acid according to claim 5, characterized in that, The filler of the packing layer is one or more of ball rings, trapezoidal rings, structured ceramics and silicon carbide foam; The particle size of the filler is 10 to 60 mm.

7. A method for synthesizing sorbic acid according to claim 6, characterized in that, The outer diameter of the packing layer of the condensation device is 200-1000 mm, and the height of the packing layer is 6-20 m.

8. A method for synthesizing sorbic acid according to claim 7, characterized in that, The volume ratio of the mixed reaction liquid to the acid solution is 0.5-1.5:0.5-2.

0.

9. A method for synthesizing sorbic acid according to any one of claims 6 to 7, characterized in that: The acid hydrolysis temperature is 100-118° C. and the time is 40-100 min.

10. The method for synthesizing sorbic acid according to claim 9, characterized in that: The acid solution is a hydrochloric acid solution or a sulfuric acid solution; The concentration of the acid solution is 10-36 wt %.

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