A method for continuously synthesizing benzoic acid from a sodium benzoate mother liquor

Abstract

This invention discloses a method for the continuous synthesis of benzoic acid from sodium benzoate mother liquor, comprising the following steps: (1) continuously pumping sodium benzoate mother liquor into a high-temperature acidification kettle, adding hydrochloric acid dropwise, controlling the pH value to 1~2, and the reaction temperature to 97~100℃; (2) overflowing the acidification mother liquor into a cooling kettle #1 to reduce the temperature to 70~80℃; (3) overflowing part of the acidification mother liquor in the cooling kettle #1 into a dispersion kettle as a dispersion mother liquor, and overflowing part of the acidification mother liquor into a cooling kettle #2; reducing the temperature to below 40℃; adding crude benzoic acid to the dispersion kettle to increase the concentration of benzoic acid, and then returning it to the high-temperature acidification kettle; (4) centrifuging the acidification mother liquor in the cooling kettle #2 into a centrifuge and then discharging it into a crude benzoic acid buffer tank, part of the crude benzoic acid into the dispersion kettle, and the remaining crude benzoic acid dried and discharged to obtain the finished benzoic acid. This invention utilizes continuous high-temperature acidification of sodium benzoate mother liquor and increases the concentration of benzoic acid during high-temperature acidification, resulting in high-quality benzoic acid with high production efficiency.

Description

Technical Field

[0001] This invention relates to the field of benzoic acid preparation technology, and more specifically to a method for the continuous synthesis of benzoic acid from sodium benzoate mother liquor. Background Technology

[0002] Benzoyl chloride is a very important industrial raw material and organic synthesis intermediate. Due to the highly reactive acyl chloride group (-COCl) in its molecule, it readily undergoes acylation reactions with compounds containing active hydrogen (such as -OH, -NH2), and therefore has a wide range of applications in many industrial fields, mainly in the production of peroxide initiators and modified resins (such as the production of dibenzoyl peroxide).

[0003] Since unreacted benzoyl chloride exists in the mother liquor as sodium benzoate during synthesis, and the benzoic acid obtained from acidification can be collected as a byproduct, this increases the economics of production and effectively reduces the organic matter in the mother liquor. Currently, benzoic acid is obtained by intermittent acidification at room temperature followed by washing and centrifugation. This method results in low benzoic acid content, high moisture content, low production efficiency, high drying load in the later stages, and poor quality of benzoic acid. Therefore, developing a continuous synthesis process for benzoic acid is crucial. Summary of the Invention

[0004] The purpose of this patent is to provide a method for the continuous synthesis of benzoic acid from sodium benzoate mother liquor. The synthesis method provided by this patent is simple to operate, highly efficient, and provides accurate data.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for the continuous synthesis of benzoic acid from sodium benzoate mother liquor includes the following steps: (1) The sodium benzoate mother liquor was continuously pumped into the bottom of the high-temperature acidification kettle, and hydrochloric acid was continuously added dropwise to the high-temperature acidification kettle. The pH value was controlled at 1~2 by an online pH meter, and the reaction temperature was 97~100℃. Benzoic acid dissolved in large quantities at 97~100℃, and liquid benzoic acid oil droplets (pale yellow) appeared in it. There was basically no solid in the acidification mother liquor. (2) The acidification mother liquor in the high-temperature acidification kettle overflows into the No. 1 cooling kettle, and the No. 1 cooling kettle reduces the temperature of the acidification mother liquor to 70~80℃; (3) Part of the acidification mother liquor in the No. 1 cooling kettle overflows into the dispersion kettle as dispersion mother liquor, and part of the acidification mother liquor overflows into the No. 2 cooling kettle; the No. 2 cooling kettle lowers the temperature of the acidification mother liquor to below 40°C; the crude benzoic acid from step (4) is added to the dispersion kettle to increase the concentration of benzoic acid in the dispersion mother liquor, and then it is refluxed into the high-temperature acidification kettle; (4) The acidified mother liquor in the No. 2 cooling kettle is centrifuged and then discharged into the crude benzoic acid buffer tank. Part of the crude benzoic acid enters the dispersion kettle, and the remaining crude benzoic acid is dried and discharged to obtain the finished benzoic acid.

[0007] Preferably, in step (1), the sodium benzoate solution is preheated to 85~90°C by a continuous pump into a heat exchanger before entering the high-temperature acidification reactor.

[0008] Preferably, a benzoic acid heat preservation vessel is provided between the heat exchanger and the high-temperature acidification vessel, and the sodium benzoate solution preheated by the preheater enters the benzoic acid heat preservation vessel and then overflows into the high-temperature acidification vessel.

[0009] Preferably, the benzoic acid content in the material inside the high-temperature acidification reactor is 3-7% by mass, which serves as seed crystals for benzoic acid. The benzoic acid that precipitates upon cooling has a good morphology, high quality, and low water content.

[0010] Preferably, in step (3), the overflow from the No. 1 cooling vessel to the dispersion vessel is adjusted by the weight of the mother liquor in the dispersion vessel measured by the dispersion vessel weighing module to regulate the opening of the regulating valve for the overflow to the dispersion vessel.

[0011] Preferably, the mass percentage of benzoic acid in the mother liquor of the dispersion vessel is 10% to 20%.

[0012] Preferably, the centrifuges include centrifuge #1 and centrifuge #2; the cooling kettle #2 discharges material to centrifuges #1 and #2 according to the liquid level, and switches between discharges to meet the continuous condition.

[0013] Preferably, it also includes a sodium benzoate mother liquor tank, which is connected to the heat exchanger. After the centrifugal mother liquor produced by the centrifuge in step (4) is returned to the sodium benzoate mother liquor tank, it is preheated by the heat exchanger and then enters the medium-high temperature acidification kettle.

[0014] Preferably, in step (4), the crude benzoic acid is dried using a rake dryer under vacuum at a temperature of 40-50°C and a negative pressure of -0.09-0.1 MPa for 1 hour to obtain a benzoic acid product with a content of >99%, moisture content of <0.5%, and whiteness of >80.

[0015] As can be seen from the above technical solution, compared with the prior art, the present invention uses continuous high-temperature acidification of sodium benzoate mother liquor, increases the concentration of benzoic acid during high-temperature acidification, and adds seed crystals, resulting in crude benzoic acid with better morphology and lower moisture content, thus reducing the subsequent drying load. This process requires less labor, has high production efficiency, and produces high-quality, stable benzoic acid. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a process flow diagram of the continuous synthesis of benzoic acid from sodium benzoate mother liquor according to the present invention.

[0018] In the diagram: 1. Sodium benzoate mother liquor tank; 2. Sodium benzoate mother liquor transfer pump; 3. Preheater; 4. Hydrochloric acid high-level tank; 5. Benzoic acid insulated kettle; 6. High-temperature acidification kettle; 7. Online pH meter; 8. Online thermometer; 9. Cooling kettle #1; 10. Cooling kettle #2; 11. Online level gauge; 12. Centrifuge #1; 13. Centrifuge #1; 14. Crude benzoic acid buffer tank; 15. Centrifugal mother liquor receiving tank; 16. Centrifugal mother liquor transfer pump; 17. Rake dryer; 18. Washing mother liquor receiving tank; 19. Dispersion kettle; 20. Dispersion kettle discharge pump. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: like Figure 1As shown, this embodiment of the invention provides a method for the continuous synthesis of benzoic acid from sodium benzoate mother liquor. The sodium benzoate mother liquor is transported to a sodium benzoate mother liquor tank 1 for storage. The sodium benzoate mother liquor transfer pump 2 pumps the sodium benzoate mother liquor through a preheater 3 into a benzoic acid heat preservation kettle 5, preheating it to 85~90℃. The preheated solution overflows through an overflow pipe to a high-temperature acidification kettle 6. Simultaneously, the material dispersion mother liquor in the dispersion kettle 19 is pumped to the high-temperature acidification kettle 6 through a dispersion kettle discharge pump 20. The flow rate is controlled by a regulating valve. The high-temperature acidification kettle 6 is heated to 97~100℃ by interlocking the opening of the steam regulating valve with an online thermometer 8. The pH is adjusted to 1~2 by interlocking the opening of the bottom valve regulating valve of the hydrochloric acid high-level tank 4 with an online pH meter 7. At this time, the material is in a molten state. Then, the material overflows from the high-temperature acidification reactor to the No. 1 cooling reactor 9 and is cooled to 70~80℃. The material in the No. 1 cooling reactor 9 is controlled by the regulating valve. Part of it flows to the dispersion reactor 19 to provide dispersion mother liquor, and the remaining material flows to the No. 2 cooling reactor 10 and is cooled to below 40℃. The bottom valve of the No. 2 cooling reactor 10 is controlled by the online liquid level gauge 11, and the material is discharged to the centrifuge for centrifugation. The centrifuged mother liquor is sent to the centrifuged mother liquor receiving tank 15 and pumped back to the system by the centrifuged mother liquor transfer pump 16. The solid is put into the benzoic acid crude product buffer tank 14. After centrifugation, the process water valve is opened for rinsing. The water washing mother liquor is collected in the water washing mother liquor receiving tank 18 and discharged from the system. The crude benzoic acid is intermittently added to the dispersion reactor 19 to prepare a 10%~20% benzoic acid solution. The remainder is put into the rake dryer 17 for drying and discharged into a ton bag for sampling and content analysis.

[0021] Specific parameter control: Based on a 3m³ reactor size test, the feed flow rate of sodium benzoate mother liquor (2% sodium benzoate concentration) was controlled at 1000 kg / h. The temperature of the high-temperature acidification reactor was controlled at 97℃, the preheating temperature at 85℃, and the pH of the high-temperature acidification reactor at 2. After adding benzoic acid to the dispersion reactor, the benzoic acid mass percentage in the high-temperature acidification reactor was increased to 3%. The No. 1 cooling reactor was cooled to 70℃, and the No. 2 cooling reactor was cooled to 35℃. 130 kg / h of the mother liquor from the No. 1 cooling reactor was input into the dispersion reactor, along with 11 kg / h of crude benzoic acid. The mass concentration of the mother liquor in the dispersion reactor was controlled at 10%, until the flow rate of the high-temperature acidification reactor was 142 kg / h. Excluding the reuse in the dispersion reactor, 20.8 kg of crude benzoic acid was obtained per hour, with a purity of 91% and a moisture content of 8.6%. After drying for 1 hour, 19 kg of crude benzoic acid was obtained, with a purity of 99.4%, a moisture content of 0.3%, a whiteness of 82, and a benzoic acid recovery rate of 94.4%.

[0022] Example 2: The synthesis steps were consistent with those in Example 1, with specific parameter control as follows: Based on a 3m³ reactor, the feed flow rate of sodium benzoate mother liquor (2% sodium benzoate) was controlled at 1500 kg / h. The high-temperature reactor temperature was controlled at 98°C, the preheating temperature at 87°C, and the pH of the high-temperature acidification reactor at 1.5. After adding benzoic acid to the dispersion reactor, the benzoic acid mass percentage in the high-temperature acidification reactor was increased to 5%. The No. 1 cooling reactor was cooled to 75°C, and the No. 2 cooling reactor was cooled to 37°C. 399 kg / h of the No. 1 cooling reactor mother liquor was input into the dispersion reactor, along with 51 kg / h of crude benzoic acid. The concentration of the mother liquor in the dispersion reactor was controlled at 10%, until the flow rate in the high-temperature acidification reactor reached 450 kg / h. Excluding the reuse of the dispersion reactor, 30.7 kg of crude benzoic acid was obtained per hour, with a content of 92.5% and a moisture content of 7.2%. After drying for 1 hour, 28.5 kg was obtained, with a content of 99.4% and a moisture content of 0.2%, a whiteness of 84, and a benzoic acid recovery rate of 94.4%.

[0023] Example 3: The synthesis steps were consistent with those in Example 1, with specific parameter control as follows: Based on a 3m³ reactor, the feed flow rate of sodium benzoate mother liquor (2% sodium benzoate) was controlled at 2000 kg / h. The high-temperature reactor temperature was controlled at 100℃, the preheating temperature at 90℃, and the pH of the high-temperature acidification reactor at 1. After adding benzoic acid to the dispersion reactor, the benzoic acid mass percentage in the high-temperature acidification reactor was increased to 7%. The No. 1 cooling reactor was cooled to 80℃, and the No. 2 cooling reactor was cooled to 40℃. 652.5 kg / h of the No. 1 cooling reactor mother liquor was input into the dispersion reactor, along with 116.5 kg / h of crude benzoic acid. The concentration of the mother liquor in the dispersion reactor was controlled at 20%, until the flow rate in the high-temperature acidification reactor reached 769 kg / h. Excluding the reuse of the dispersion reactor, 41 kg of crude benzoic acid was obtained per hour, with a content of 92.8% and a moisture content of 6.9%. After drying for 1 hour, 38.2 kg was obtained, with a content of 99.5% and a moisture content of 0.2%, a whiteness of 85, and a benzoic acid recovery rate of 95%.

[0024] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0025] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for the continuous synthesis of benzoic acid from sodium benzoate mother liquor, characterized in that, Includes the following steps: (1) The sodium benzoate mother liquor is continuously pumped into the bottom of the high-temperature acidification kettle, and hydrochloric acid is continuously added dropwise to the high-temperature acidification kettle to control the pH value to 1~2 and the reaction temperature to 97~100℃; (2) The acidification mother liquor in the high-temperature acidification kettle overflows into the No. 1 cooling kettle, and the No. 1 cooling kettle reduces the temperature of the acidification mother liquor to 70~80℃; (3) Part of the acidification mother liquor in the No. 1 cooling kettle overflows into the dispersion kettle as dispersion mother liquor, and part of the acidification mother liquor overflows into the No. 2 cooling kettle; the No. 2 cooling kettle lowers the temperature of the acidification mother liquor to below 40°C; the crude benzoic acid from step (4) is added to the dispersion kettle to increase the concentration of benzoic acid in the dispersion mother liquor, and then it is refluxed into the high-temperature acidification kettle; (4) The acidified mother liquor in the No. 2 cooling kettle is centrifuged and then discharged into the crude benzoic acid buffer tank. Part of the crude benzoic acid enters the dispersion kettle, and the remaining crude benzoic acid is dried and discharged to obtain the finished benzoic acid.

2. The method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to claim 1, characterized in that, In step (1), the sodium benzoate solution is preheated to 85~90℃ by a heat exchanger via a continuous pump before entering the high-temperature acidification reactor.

3. The method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to claim 2, characterized in that, A benzoic acid insulated vessel is provided between the heat exchanger and the high-temperature acidification vessel. The sodium benzoate solution preheated by the preheater enters the benzoic acid insulated vessel and then overflows into the high-temperature acidification vessel.

4. A method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to any one of claims 1 to 3, characterized in that, The mass percentage of benzoic acid in the material inside the high-temperature acidification reactor is 3-7%.

5. A method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to any one of claims 1 to 3, characterized in that, In step (3), the overflow from the No. 1 cooling vessel to the dispersion vessel is adjusted by the weight of the mother liquor in the dispersion vessel measured by the dispersion vessel weighing module to regulate the opening of the regulating valve of the overflow to the dispersion vessel.

6. A method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to any one of claims 1 to 3, characterized in that, The mass percentage of benzoic acid in the mother liquor of the dispersion vessel is 10%~20%.

7. A method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to any one of claims 1 to 3, characterized in that, The centrifuges include centrifuge #1 and centrifuge #2; the cooling kettle #2 discharges material to centrifuges #1 and #2 according to the liquid level, and switches between the discharge to meet the continuous condition.

8. A method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to any one of claims 2 to 3, characterized in that, It also includes a sodium benzoate mother liquor tank, which is connected to the heat exchanger. In step (4), the centrifugal mother liquor produced by the centrifuge flows back to the sodium benzoate mother liquor tank and is preheated by the heat exchanger before entering the medium-high temperature acidification kettle.

9. The method for continuous synthesis of benzoic acid from sodium benzoate mother liquor according to claim 1, characterized in that, In step (4), the crude benzoic acid is dried using a rake dryer under vacuum at a temperature of 40-50°C and a negative pressure of -0.09-0.1 MPa for 1 hour to obtain a benzoic acid product with a content of >99%, moisture content of <0.5%, and whiteness of >80.

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