A method for purifying analytical pure salicylic acid

Abstract

The application discloses a method for purifying analytical pure salicylic acid, which comprises the following steps: adding salicylic acid, deionized water and activated carbon into an autoclave, then introducing inert gas, stirring and dissolving under the conditions of pressurization and heating, removing the activated carbon through filtration, introducing the obtained filtrate into a crystallizer to crystallize, finally centrifugally dewatering, and drying the obtained salicylic acid wet crystal in a drier to obtain the analytical pure salicylic acid. The application effectively improves the salicylic acid dissolving speed and the solubility in water by dissolving the salicylic acid under the condition of pressurization, so that excellent purification effect can be achieved through one recrystallization, and the salicylic acid purified through the method has high purity, good quality and high yield, and is a high-quality analytical pure salicylic acid.

Description

Technical Field

[0001] This invention relates to the field of chemical purification technology, and in particular to a method for purifying analytical grade salicylic acid. Background Technology

[0002] Salicylic acid, also known as 2-hydroxybenzoic acid, has the molecular formula C7H6O3 and is a fat-soluble organic acid. It is a toxic, white, needle-like crystal or monoclinic prismatic crystal with a characteristic phenolic odor. It is readily soluble in ether, ethanol, and propanol, and slightly soluble in cold water. Salicylic acid is an important chemical raw material with wide applications in pharmaceuticals, cosmetics, and pesticides.

[0003] The purity requirement for analytical grade salicylic acid is ≥99.5%. Current salicylic acid purification methods mostly employ recrystallization, but due to the low solubility of salicylic acid in water, the overall yield is low. To obtain high-quality salicylic acid, multiple recrystallization processes are sometimes necessary, leading to even lower yields. Currently, the industry lacks an effective purification method for salicylic acid. Summary of the Invention

[0004] This invention provides a purification method for analytical grade salicylic acid, which can solve the above-mentioned problems in the purification of salicylic acid in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides a purification method for analytical grade salicylic acid, comprising the following steps:

[0006] Industrial-grade salicylic acid, deionized water, and activated carbon were added to a high-pressure reactor, and then an inert gas was introduced. The mixture was stirred and dissolved under pressure and heating conditions. The activated carbon was removed by filtration, and the resulting filtrate was introduced into a crystallizer for crystallization. Finally, the mixture was centrifuged to remove water, and the resulting wet salicylic acid crystals were transferred to a desiccator for drying to obtain the analytical grade salicylic acid.

[0007] In a preferred embodiment of the present invention, the pressurized pressure is 1 to 10 MPa, preferably 3 to 6 MPa.

[0008] In a preferred embodiment of the present invention, the heating temperature is 85-100°C.

[0009] In a preferred embodiment of the present invention, the crystallization process conditions are: temperature 5-25°C, stirring speed 15-30 r / min, and time 120-180 min.

[0010] In a preferred embodiment of the present invention, the drying process conditions are as follows: vacuum low-temperature drying, first drying at a temperature of 30-50°C for 1-2 hours, and then heating to 50-80°C for 2-5 hours.

[0011] In a preferred embodiment of the present invention, the filtration method is as follows: open the discharge port at the bottom of the high-pressure reactor, and use the pressure inside the high-pressure reactor to discharge the dissolved solution together with the activated carbon.

[0012] In a preferred embodiment of the present invention, the outlet of the autoclave is connected to the inlet of the crystallizer via a pipe, and a filter is installed on the pipe between the autoclave and the crystallizer.

[0013] In a preferred embodiment of the present invention, the mass ratio of salicylic acid to the volume ratio of deionized water is 1g:5-10mL.

[0014] The beneficial effects of this invention are: This invention provides a purification method for analytical grade salicylic acid, which effectively improves the dissolution rate and completeness of salicylic acid in water by dissolving it under pressure, so that excellent purification effect can be achieved after one recrystallization. The salicylic acid purified by the method of this invention has high purity, good quality and high yield, and is a high-quality analytical grade salicylic acid. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the equipment used in the purification method of analytical grade salicylic acid according to the present invention;

[0016] The components in the attached diagram are labeled as follows: 1. Autoclave, 2. Pipeline, 3. Crystallizer, 4. Filter. Detailed Implementation

[0017] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0018] Please see Figure 1 The embodiments of the present invention include:

[0019] This invention discloses a high-pressure purification method for preparing analytical grade salicylic acid. By using high pressure conditions, the solubility of salicylic acid in deionized water is increased, thereby promoting the rapid and complete dissolution of salicylic acid in deionized water. Then, purification by recrystallization helps to improve the recrystallization effect of salicylic acid, thus improving the yield and quality of salicylic acid purification.

[0020] Specifically, the purification method of the present invention includes the following steps:

[0021] According to the ratio of salicylic acid mass to deionized water volume of 1g: 5-10mL, industrial-grade salicylic acid, deionized water and activated carbon are added to autoclave 1. Then, inert gas (such as nitrogen, helium, etc.) is introduced to replace the air in the autoclave. The inert gas is continued to be introduced until the pressure in the autoclave reaches 1-10MPa, preferably 3-6MPa. Under this pressure condition, the temperature in the autoclave is raised to 85-100℃, and then stirred for 30-60 minutes to fully and completely dissolve the added industrial-grade salicylic acid.

[0022] The bottom of the aforementioned high-pressure reactor 1 has a discharge port, which is connected to the crystallizer 3 via a pipe 2, and a filter 4 is installed on the pipe 2.

[0023] Open the discharge port at the bottom of the high-pressure reactor to allow the dissolved solvent and activated carbon to be discharged into pipe 2 under the pressure of inert gas inside the high-pressure reactor. After being filtered by the filter 4, the resulting filtrate enters the crystallizer 3 for crystallization. The specific crystallization process conditions are as follows: the crystallization temperature is adjusted to 5-25°C by the refrigerant in the crystallizer jacket, the stirring speed is set to 15-30 r / min, and crystallization is carried out for 120-180 min at this temperature and stirring rate.

[0024] After crystallization, the salicylic acid wet crystals are centrifuged and dehydrated. The resulting salicylic acid wet crystals are then transferred to a desiccator for drying to obtain the analytical grade salicylic acid. The specific drying process conditions are as follows: in a vacuum drying oven, under a vacuum of -5 to -10 MPa, the mixture is first dried at a temperature of 30 to 50°C for 1 to 2 hours, and then heated to 50 to 80°C for 2 to 5 hours.

[0025] Example 1

[0026] Add 1 kg of industrial-grade salicylic acid, 10 kg of deionized water, and 10 g of activated carbon to autoclave 1, and turn on the stirring device. First, purge the autoclave 1 with nitrogen gas for 10 minutes to replace and remove the air inside. Then, cover the autoclave and close the vent valve. Continue to purge with nitrogen gas until the pressure inside the autoclave reaches 3 MPa. Under constant pressure, turn on the heating device to raise the temperature inside the autoclave to 90°C. Stir continuously for 60 minutes under the conditions of maintaining temperature and pressure to ensure that the industrial-grade salicylic acid is fully dissolved and the activated carbon fully adsorbs and dissolves the released impurities.

[0027] Open the valve at the bottom outlet of the autoclave. Under the pressure inside the autoclave, the material is forced into the filter, and the filtered liquid is forced into crystallizer 3. Set the jacket refrigerant temperature of crystallizer 3 to 10℃ and the stirring speed to 20 rpm. Crystallize for 180 minutes under these conditions. After crystallization, centrifuge and dehydrate, collect the mother liquor separately, and transfer the resulting wet salicylic acid product to a drying oven with a vacuum of -10MPa for low-temperature drying. First, adjust the temperature of the drying oven to 30℃ and dry at this temperature for 1 hour. Then, raise the temperature of the drying oven to 80℃ and continue drying for 2 hours to obtain 0.9551 kg of the finished product, with a yield of 95.51%.

[0028] Comparative Example 1

[0029] Add 1 kg of industrial-grade salicylic acid, 10 kg of deionized water, and 10 g of activated carbon to the reactor, and turn on the stirrer. Turn on the heating device to raise the temperature inside the autoclave to 90°C, and stir continuously for 60 minutes under the condition of heat preservation. At this time, most of the salicylic acid has not dissolved, and even with continued stirring, most of the salicylic acid still cannot dissolve.

[0030] The material in the reactor was filtered through a filter, and the filtrate was transferred to a crystallizer. The jacket refrigerant temperature of the crystallizer was set to 10°C, and the stirring speed was set to 20 rpm. Crystallization was carried out under these conditions for 180 minutes. After crystallization, the product was centrifuged and dehydrated. The mother liquor was collected separately, and the resulting wet salicylic acid product was transferred to a vacuum drying oven at -10 MPa for drying. The oven temperature was first adjusted to 50°C, and drying was carried out at this temperature for 1 hour. Then, the oven temperature was increased to 80°C, and drying was continued for 2 hours, yielding 0.352 kg of the final product, with a yield of 35.2%.

[0031] The salicylic acid obtained in Example 1 and Comparative Example 1 was subjected to performance testing, and the results are shown in Table 1 below.

[0032] Table 1

[0033]

[0034]

[0035] As shown in Table 1, the industrial-grade salicylic acid obtained by the purification method of the present invention meets the standard requirements, with a purity of 99.98%, which is higher than the standard requirement of 99.5%, and a product yield of over 95.5%. In contrast, although the quality of the traditional method is comparable to that of the pressurized method, the product yield is significantly different.

[0036] This invention provides a purification method for analytical grade salicylic acid, which has the following beneficial effects:

[0037] 1. By using a pressurization method, salicylic acid is dissolved in deionized water under pressurized conditions, which effectively improves the dissolution rate and the completeness of dissolution.

[0038] 2. The pressure inside the autoclave is used to transfer the material to the filter, realizing the unit's filtration operation. This avoids the use of high-energy-consuming and high-noise pumps, which helps to reduce energy consumption.

[0039] 3. Using water as a solvent, the resulting mother liquor can be reused twice, and less waste liquid is generated, making the entire process green and environmentally friendly.

[0040] 4. Excellent purification effect: The purified salicylic acid has high purity and quality, with a high yield of over 95.5%.

[0041] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for purifying analytical grade salicylic acid, characterized in that, Includes the following steps: Salicylic acid, deionized water, and activated carbon were added to a high-pressure reactor, and then an inert gas was introduced. The mixture was stirred and dissolved under pressure and heating conditions. The pressure was 3-6 MPa, and the heating temperature was 85-100°C. The activated carbon was removed by filtration, and the resulting filtrate was introduced into a crystallizer for crystallization. Finally, the mixture was centrifuged to remove water, and the resulting wet salicylic acid crystals were transferred to a desiccator for drying to obtain analytical grade salicylic acid.

2. The purification method for analytical grade salicylic acid according to claim 1, characterized in that, The crystallization process conditions are: temperature 5-25℃, stirring speed 15-30 r / min, and time 120-180 min.

3. The purification method for analytical grade salicylic acid according to claim 1, characterized in that, The drying process conditions are as follows: vacuum low-temperature drying, first drying at a temperature of 30-50℃ for 1-2 hours, and then heating to 50-80℃ for 2-5 hours.

4. The purification method for analytical grade salicylic acid according to claim 1, characterized in that, The filtration method is as follows: open the discharge port at the bottom of the high-pressure reactor, and use the pressure inside the high-pressure reactor to discharge the dissolved solution along with the activated carbon.

5. The purification method for analytical grade salicylic acid according to claim 4, characterized in that, The outlet of the autoclave is connected to the inlet of the crystallizer via a pipe, and a filter is installed on the pipe between the autoclave and the crystallizer.

6. The purification method for analytical grade salicylic acid according to claim 1, characterized in that, The salicylic acid mentioned is industrial grade salicylic acid.

7. The purification method for analytical grade salicylic acid according to claim 6, characterized in that, The mass ratio of the salicylic acid to the volume ratio of the deionized water is 1 g: 5-10 mL.

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