Preparation method of 2, 6-dihydroxybenzoic acid by external circulation of kettle

Abstract

The invention relates to the technical field of chemical industry, and provides a preparation method of 2, 6-dihydroxybenzoic acid by external circulation of a kettle, which comprises the following steps: S1, under the action of a catalyst, resorcinol and alkali metal salt are subjected to a salt forming reaction in a reaction kettle to obtain a reaction liquid I; and S2, carrying out gas-liquid mixing on the reaction liquid I and carbon dioxide gas introduced from the outside of the reaction kettle, and circulating the mixture out of the kettle back to the reaction kettle in S1 for carboxylation reaction to obtain the 2, 6-dihydroxybenzoic acid. According to the technical scheme, the problems of long reaction time, low yield and low purity of 2, 6-dihydroxybenzoic acid in related technologies are solved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to a method for preparing 2,6-dihydroxybenzoic acid by external circulation in a kettle. Background Art

[0002] 2,6-Dihydroxybenzoic acid is an important organic synthesis intermediate, which is widely used in the fields of medicine, pesticides, dyes, etc. At present, the traditional preparation method of 2,6-dihydroxybenzoic acid mainly has the following problems: the traditional preparation method is usually carried out in a reactor, and the mixing degree of materials during the reaction is limited, which easily leads to excessive or low local concentration, affecting the uniformity and yield of the reaction. At the same time, due to certain limitations of the stirring method in the reactor, it is difficult to achieve efficient mass transfer and heat transfer, resulting in a long reaction time and high energy consumption.

[0003] In addition, the traditional method may produce some by-products during the reaction process, and the accumulation of these by-products will affect the purity and quality of the product. Moreover, it is difficult to control the reaction conditions in the traditional process, which is prone to problems such as unstable reaction and large fluctuations in product quality. Summary of the invention

[0004] The invention provides a method for preparing 2,6-dihydroxybenzoic acid by circulating outside a kettle, which solves the problems of long reaction time, low yield and low purity of 2,6-dihydroxybenzoic acid in the related art.

[0005] The technical solution of the present invention is as follows: The present invention provides a method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle, comprising the following steps: S1. Under the action of a catalyst, resorcinol and an alkali metal salt undergo a salt-forming reaction in a reactor to obtain a reaction solution I; S2, mixing the reaction liquid I with the carbon dioxide gas introduced from outside the reactor, and circulating the mixture back to the S1 reactor through the reactor to perform carboxylation reaction, thereby obtaining 2,6-dihydroxybenzoic acid.

[0006] As a further technical solution, S2 is a process for mixing the reaction liquid I with the carbon dioxide gas introduced outside the reactor, circulating the mixture outside the reactor back to the S1 reactor for carboxylation reaction, and then filtering, washing, and recrystallizing with anhydrous ethanol to obtain 2,6-dihydroxybenzoic acid.

[0007] As a further technical solution, the gas-liquid mixing is carried out in a gas-liquid mixer.

[0008] In the present invention, a gas-liquid mixer is used to shear carbon dioxide gas into small bubbles, thereby increasing its solubility in the reaction liquid 1, allowing it to fully contact with the reactants, increasing the reaction speed, greatly shortening the reaction time, reducing the generation of reaction by-products, and improving the conversion rate of raw materials. The reaction time from heating to the end of the reaction is shortened from the original reaction time of 5 hours to less than 3.5 hours, thereby greatly improving the production efficiency and production stability of 2,6-dihydroxybenzoic acid.

[0009] As a further technical solution, the added amount of the catalyst is 3% to 5% of the mass of resorcinol.

[0010] As a further technical solution, the catalyst includes one or more of magnesium oxide, calcium oxide, and potassium oxide.

[0011] As a further technical solution, the catalyst consists of potassium oxide and magnesium oxide.

[0012] As a further technical solution, the mass ratio of potassium oxide to magnesium oxide is 1~3:1.

[0013] The present invention finds that when the mass ratio of potassium oxide to magnesium oxide is 1-3:1, the generation of by-products can be further reduced, and the yield and purity of 2,6-dihydroxybenzoic acid can be improved.

[0014] As a further technical solution, the mass ratio of potassium oxide to magnesium oxide is 2:1.

[0015] As a further technical solution, the salt-forming reaction is carried out in a solvent, and the solvent includes one or more of water, methanol, and ethanol.

[0016] As a further technical solution, the temperature of the salt-forming reaction is 120°C~140°C, the time is 1h, and the pressure is 0.5~0.8MPa.

[0017] As a further technical solution, the alkali metal salt includes one or more of potassium carbonate, potassium bicarbonate, and sodium carbonate.

[0018] As a further technical solution, the molar ratio of resorcinol to the alkali metal in the alkali metal salt is 1:2-3.

[0019] As a further technical solution, the mass volume ratio of resorcinol to solvent is 1g:15~20mL.

[0020] As a further technical solution, the carboxylation reaction is carried out at a temperature of 140°C to 160°C, for a time of 2.5 to 3 hours, and at a pressure of 1.3 to 1.6 MPa.

[0021] The working principle and beneficial effects of the present invention are: The addition of the catalyst in the present invention can shorten the reaction time, improve the selectivity of 2,6-dihydroxybenzoic acid, reduce the production cost, and contribute to environmental protection. Moreover, when the catalyst is compounded with potassium oxide and magnesium oxide, the by-products can be further reduced, and the yield and purity of 2,6-dihydroxybenzoic acid can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0023] Figure 1 The present invention is a process flow chart of preparing 2,6-dihydroxybenzoic acid by external circulation in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example 1 A method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle comprises the following steps: S1, 330 mL of anhydrous ethanol, 22 g of resorcinol, 13.8 g of potassium carbonate and 0.66 g of a catalyst were placed in a reactor, and a salt-forming reaction was carried out at 130° C. and a pressure of 0.5 MPa for 1 h to obtain a reaction solution I, wherein the catalyst was magnesium oxide; S2 and carbon dioxide are mixed and sheared with the reaction liquid I through a gas-liquid mixer (the introduction rates of the reaction liquid I and the carbon dioxide gas in the gas-liquid mixer are 1.5 m / s and 10 m / s, respectively), and then introduced from the top of the S1 reactor through an external reaction liquid circulation pump. After reacting for 3 hours at 160° C. and a pressure of 1.6 MPa, 29.29 g of 2,6-dihydroxybenzoic acid is obtained through suction filtration, washing, and recrystallization with anhydrous ethanol. The yield is 94.24% and the purity is 99.1%. The process flow chart of preparing 2,6-dihydroxybenzoic acid by external circulation in this embodiment is as follows: Figure 1 shown.

[0026] Example 2 S1, 400 mL of anhydrous ethanol, 22 g of resorcinol, 15.8 g of potassium carbonate and 0.88 g of a catalyst were placed in a reactor, and a salt-forming reaction was carried out at 135° C. and a pressure of 0.7 MPa for 1 h to obtain a reaction solution I, wherein the catalyst was magnesium oxide; S2 and carbon dioxide were mixed and sheared with the reaction liquid I through a gas-liquid mixer (the introduction rates of the reaction liquid I and the carbon dioxide gas in the gas-liquid mixer were 3 m / s and 12 m / s, respectively), and then introduced from the top of the S1 reactor through a reaction liquid circulation pump outside the reactor. After reacting for 3 hours at 150° C. and a pressure of 1.5 MPa, 29.32 g of 2,6-dihydroxybenzoic acid was obtained through suction filtration, washing, and recrystallization from anhydrous ethanol. The yield was 94.43% and the purity was 99.2%.

[0027] Example 3 S1, 440 mL of anhydrous ethanol, 22 g of resorcinol, 20.7 g of potassium carbonate and 1.1 g of a catalyst were placed in a reactor, and a salt-forming reaction was carried out at 140° C. and a pressure of 0.8 MPa for 1 h to obtain a reaction solution I, wherein the catalyst was magnesium oxide; S2 and carbon dioxide were mixed and sheared with the reaction liquid I through a gas-liquid mixer (the introduction rates of the reaction liquid I and carbon dioxide gas in the gas-liquid mixer were 5 m / s and 15 m / s, respectively), and then introduced from the top of the S1 reactor through a reaction liquid circulation pump outside the reactor. After reacting for 2.5 hours at 145°C and a pressure of 1.3 MPa, 29.35 g of 2,6-dihydroxybenzoic acid was obtained through suction filtration, washing, and recrystallization with anhydrous ethanol. The yield was 94.53% and the purity was 99.2%.

[0028] Example 4 The only difference between this embodiment and embodiment 1 is that the catalyst is potassium oxide.

[0029] Result: 29.44 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 94.72% and a purity of 99.1%.

[0030] Example 5 The only difference between this embodiment and embodiment 1 is that the catalyst is potassium oxide and magnesium oxide in a mass ratio of 1:2.

[0031] Result: 29.72 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 95.82% and a purity of 99.3%.

[0032] Example 6 The only difference between this embodiment and embodiment 1 is that the catalyst is potassium oxide and magnesium oxide in a mass ratio of 4:1.

[0033] Result: 29.81 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 96.11% and a purity of 99.3%.

[0034] Example 7 The only difference between this embodiment and embodiment 1 is that the catalyst is potassium oxide and magnesium oxide in a mass ratio of 3:1.

[0035] Result: 30.27 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 97.69% and a purity of 99.4%.

[0036] Example 8 The only difference between this embodiment and embodiment 1 is that the catalyst is potassium oxide and magnesium oxide in a mass ratio of 2:1.

[0037] Result: 30.35 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 98.05% and a purity of 99.5%.

[0038] Example 9 The only difference between this embodiment and embodiment 1 is that the catalyst is potassium oxide and magnesium oxide in a mass ratio of 1:1.

[0039] Result: 30.21 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 97.50% and a purity of 99.4%.

[0040] Example 10 The only difference between this embodiment and embodiment 6 is that the catalyst is potassium oxide and calcium oxide in a mass ratio of 4:1.

[0041] Result: 29.54 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 95.14% and a purity of 99.2%.

[0042] Comparative Example 1 The only difference between this embodiment and embodiment 6 is that the carbon dioxide gas is directly introduced into the S1 reactor.

[0043] Result: 28.41 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 91.13% and a purity of 98.8%.

[0044] Comparative Example 2 The only difference between this comparative example and Example 1 is that no catalyst is added.

[0045] Result: 28.56 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 91.24% and a purity of 98.4%.

[0046] Compared with Example 1, the carbon dioxide gas in Comparative Example 1 was directly introduced into the reactor. As a result, the yield of Comparative Example 1 was lower than that of Example 1, indicating that the use of a gas-liquid mixer to perform gas-liquid mixing outside the reactor in the present invention can improve the yield and purity of 2,6-dihydroxybenzoic acid.

[0047] Compared with Example 1, no catalyst was added in Comparative Example 2. As a result, the yield of 2,6-dihydroxybenzoic acid in Example 1 was higher than that in Comparative Example 2, indicating that the addition of a catalyst can improve the yield and purity of 2,6-dihydroxybenzoic acid.

[0048] Compared with Example 1, the catalyst in Example 4 is potassium oxide, and the catalyst in Example 5 is potassium oxide and magnesium oxide. As a result, the yield of 2,6-dihydroxybenzoic acid in Examples 4 and 5 is higher than that in Example 1, indicating that when the catalyst is potassium oxide, the yield of 2,6-dihydroxybenzoic acid can be further improved, and when the catalyst is composed of potassium oxide and magnesium oxide, the yield of 2,6-dihydroxybenzoic acid can be further improved, so that 2,6-dihydroxybenzoic acid has a higher purity.

[0049] Compared with Example 5, Examples 6 to 9 changed the mass ratio of potassium oxide and magnesium oxide. As a result, the yields of 2,6-dihydroxybenzoic acid in Examples 7 to 9 were all higher than those in Examples 5 to 6, indicating that when the mass ratio of potassium oxide to magnesium oxide was 1 to 3:1, the yield of 2,6-dihydroxybenzoic acid could be further improved, so that 2,6-dihydroxybenzoic acid had a higher purity.

[0050] Compared with Example 6, Example 10 replaces magnesium oxide with an equal amount of calcium oxide. As a result, the yield of 2,6-dihydroxybenzoic acid in Example 6 is higher than that in Example 10, indicating that when the catalyst is composed of potassium oxide and magnesium oxide, the yield of 2,6-dihydroxybenzoic acid can be better improved, so that 2,6-dihydroxybenzoic acid has a higher purity.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle, characterized in that: The following steps are involved: S1. Under the action of a catalyst, resorcinol and an alkali metal salt undergo a salt-forming reaction in a reactor to obtain a reaction solution I; S2, mixing the reaction liquid I with the carbon dioxide gas introduced from outside the reactor, and circulating the mixture back to the S1 reactor through the reactor to perform carboxylation reaction, thereby obtaining 2,6-dihydroxybenzoic acid.

2. The method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 1, characterized in that: The added amount of the catalyst is 3% to 5% of the mass of resorcinol.

3. A method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 1, characterized in that: The catalyst includes one or more of magnesium oxide, calcium oxide and potassium oxide.

4. A method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 3, characterized in that: The catalyst consists of potassium oxide and magnesium oxide.

5. A method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 4, characterized in that: The mass ratio of potassium oxide to magnesium oxide is 1-3:

1.

6. The method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 1, characterized in that: The salt-forming reaction is carried out in a solvent, and the solvent includes one or more of water, methanol and ethanol.

7. The method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 1, characterized in that: The alkali metal salt includes one or more of potassium carbonate, potassium bicarbonate and sodium carbonate.

8. The method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 1, characterized in that: The molar ratio of the resorcinol to the alkali metal in the alkali metal salt is 1:1-1.

5.

9. The method for preparing 2,6-dihydroxybenzoic acid by external circulation of a kettle according to claim 1, characterized in that: The mass volume ratio of the resorcinol to the solvent is 1g:15-20mL.

10. The method for preparing 2,6-dihydroxybenzoic acid by external circulation in an autoclave according to claim 1, characterized in that: The carboxylation reaction is carried out at a temperature of 140° C. to 160° C., for a time of 2.5 to 3 hours, and at a pressure of 1.3 to 1.6 MPa.

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