A 2-naphthol and its preparation method

Abstract

The present invention relates to the field of chemical engineering technology, and particularly relates to 2-naphthol and a preparation method thereof. In this preparation method, naphthalene and sulfuric acid are used as raw materials to carry out sulfonation reaction and rearrangement reaction to obtain a naphthalene sulfonic acid mixture. 1-Naphthalene sulfonic acid in the naphthalene sulfonic acid mixture is separated by melt crystallization to obtain 2-naphthalene sulfonic acid. Then, the 2-naphthalene sulfonic acid is successively subjected to neutralization, alkali fusion, acidification and refining treatments to obtain 2-naphthol. By utilizing the principle that there is a large difference in the melting points between 2-naphthalene sulfonic acid and 1-naphthalene sulfonic acid, the present invention separates the two by melt crystallization, and 1-naphthalene sulfonic acid can be continuously converted into 2-naphthalene sulfonic acid, which improves the conversion rate of naphthalene and the yield of 2-naphthalene sulfonic acid, is beneficial to increasing the output of 2-naphthol in subsequent preparation, reduces the naphthalene recovery step at the same time, greatly reduces the generation of salt-containing wastewater, reduces the consumption of sulfuric acid, reduces the generation amount of by-product sodium sulfate, and improves the utilization rate of raw materials. The preparation method of the present invention is environmentally friendly, efficient, and the production cost is much lower than that of the traditional process.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical engineering, and particularly relates to 2-naphthol and a preparation method thereof. Background Art

[0002] 2-Naphthol, also known as ethyl naphthol and β-naphthol, is an important organic chemical raw material and dye intermediate. More than 130 dyes and pigments and more than 20 dye intermediates can be directly synthesized from it. In terms of dyes, the main derivatives of 2-naphthol include 2,3-acid, tosyl acid, diazo naphthol sulfonic acid, G-acid, R-acid, γ-acid, J-acid, 2,6-acid, etc.; in terms of medicine and pesticides, 2-naphthol is mainly used for synthesizing anti-inflammatory and analgesic naproxen, herbicide napropamide, plant regulator 2-naphthoxyethylamine, etc. In recent years, downstream products of naphthol have also been used in the synthesis of photosensitive materials and liquid crystal materials, such as hydroxy-1-naphthoic acid, naphthol benzyl ether, 2-hydroxy naphthalene-6-carboxylic acid, etc. It has a very broad market prospect in the applications of medicine, pesticides, rubber auxiliaries, spices, textile printing and dyeing, etc.

[0003] In the synthesis process of 2-naphthol, by-product 1-naphthol is easily generated. However, the boiling point and melting point of 1-naphthol and 2-naphthol are relatively close, and it is difficult to separate the two by physical methods such as distillation. At present, the main relatively mature methods for synthesizing 2-naphthol in industry are the sulfonation-alkali fusion method and the isopropylnaphthalene method. However, with the rise of the concept of green synthetic chemistry, in recent years, some new synthetic process schemes for naphthol have emerged, such as biosynthesis method, direct catalytic synthesis method, superacid catalysis, heteropolyacid catalysis, transition metal oxide catalysis, high-energy radiation catalysis, etc. Although these schemes have achieved certain results, there is still a long way to go before industrial application.

[0004] The industrial production method of 2-naphthol, namely the sulfonation-alkali fusion method, has a mature process. It mainly sulfonates naphthalene to obtain a sulfonation product including 1-naphthalenesulfonic acid (melting point 77-79 °C) and 2-naphthalenesulfonic acid (melting point 91 °C), then transposes to convert part of 1-naphthalenesulfonic acid into 2-naphthalenesulfonic acid, and subsequently neutralizes, alkali-fuses, acidifies 2-naphthalenesulfonic acid, etc. to obtain 2-naphthol. The main disadvantages of this process are: (1) It is necessary to hydrolyze and recover the uncompletely converted 1-naphthalenesulfonic acid. However, the sulfuric acid generated after the hydrolysis of 1-naphthalenesulfonic acid needs to consume a large amount of alkali, and by-product sodium sulfate will be generated at the same time. Moreover, these sodium sulfates are dissolved in water and still require purification steps such as distillation concentration and crystallization, with high energy consumption and a large amount of raw materials required, resulting in a high cost; (2) The naphthalene generated after the hydrolysis of 1-naphthalenesulfonic acid is commonly recovered by steam distillation, with high energy consumption, a large amount of waste water, and it is easy to cause equipment blockage during the recovery process.

[0005] Therefore, there is an urgent need for a more economical and environmentally friendly preparation method for producing 2-naphthol. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a 2-naphthol and its preparation method, so as to solve the technical problems existing in the prior art, such as high energy consumption, low efficiency, and a large amount of by-products in the production of 2-naphthol.

[0007] To achieve the above purpose and other related purposes, the present invention provides a preparation method of 2-naphthol. Using naphthalene and sulfuric acid as raw materials, a sulfonation reaction and a rearrangement reaction are carried out to obtain a naphthalene sulfonic acid mixture. The 1-naphthalene sulfonic acid in the naphthalene sulfonic acid mixture is separated by melt crystallization, and 2-naphthalene sulfonic acid is obtained. The 2-naphthalene sulfonic acid is successively subjected to neutralization, alkali fusion, acidification and refining treatments to obtain 2-naphthol.

[0008] Optionally, the melt crystallization successively includes four processes: direct cooling, primary cooling, secondary cooling and heating for sweating.

[0009] In the present invention, the melt crystallization process is divided into four processes, namely direct cooling, primary cooling, secondary cooling and heating for sweating. Among them, the purpose of direct cooling is to cool the naphthalene sulfonic acid mixture still in a high-temperature state after the rearrangement reaction to the state to be crystallized. The primary cooling is to slowly cool until crystals are formed, that is, the 2-naphthalene sulfonic acid with a higher melting point in the naphthalene sulfonic acid mixture begins to crystallize. The secondary cooling is to further slowly cool until the crystallization of 2-naphthalene sulfonic acid is completed, and the mother liquor containing a large amount of 1-naphthalene sulfonic acid is discharged. Then, heating for sweating is carried out to discharge the residual 1-naphthalene sulfonic acid in the 2-naphthalene sulfonic acid crystals through the sweating liquid, so as to separate the 1-naphthalene sulfonic acid in the naphthalene sulfonic acid mixture and obtain 2-naphthalene sulfonic acid.

[0010] Optionally, the target temperature of the direct cooling is 95-105°C.

[0011] Optionally, the cooling rate of the primary cooling process is 0.5°C / 3-5 min.

[0012] Optionally, the cooling rate of the secondary cooling process is 0.1°C / 1-2 min.

[0013] Optionally, the heating rate of the heating for sweating process is 0.1°C / 3-5 min.

[0014] The preparation method of the present invention includes the following steps:

[0015] S1. Sulfonation and rearrangement: Sulfuric acid is added to naphthalene to obtain a mixture. The mixture is heated and kept warm for the first time to carry out a sulfonation reaction to obtain a sulfonation product. The sulfonation product is purified, and then the sulfonation product is heated and kept warm for the second time to carry out a rearrangement reaction to obtain a naphthalene sulfonic acid mixture;

[0016] S2. Separation: The obtained naphthalene sulfonic acid mixture is subjected to melt crystallization. After direct cooling, primary cooling, and secondary cooling, the crystallization mother liquor is removed to obtain 2-naphthalene sulfonic acid crystals. Then, the temperature of the 2-naphthalene sulfonic acid crystals is raised for sweating, and the sweating liquid is removed to obtain 2-naphthalene sulfonic acid.

[0017] S3. Preparation of 2-naphthol: The obtained 2-naphthalene sulfonic acid is mixed with a sodium sulfite solution, and successively subjected to a neutralization reaction, cooling crystallization, and filtration to obtain sodium 2-naphthalene sulfonate. Then, the sodium 2-naphthalene sulfonate is mixed with an alkali and heated for reaction to obtain sodium 2-naphtholate. The sodium 2-naphtholate is acidified, and the acidified solution is phase-separated to obtain crude 2-naphthol. Finally, the crude 2-naphthol is refined to obtain the product 2-naphthol.

[0018] In the present invention, the refining treatment of the crude 2-naphthol includes distillation dehydration and vacuum distillation of the crude 2-naphthol to purify the crude 2-naphthol.

[0019] Optionally, in step S1, the molar ratio of naphthalene to sulfuric acid is 1.05 - 1.2:1.

[0020] Optionally, in step S1, the sulfuric acid is concentrated sulfuric acid or fuming sulfuric acid.

[0021] In the present invention, the sulfuric acid is added dropwise, and the dropping rate of the sulfuric acid is 54 - 108 mL / h. Adding the sulfuric acid in a dropping manner and controlling the dropping rate can avoid the sublimation of naphthalene due to too rapid temperature rise of the solution.

[0022] Optionally, in step S1, it is heated to 110 - 120 °C for the first time, and the holding time for the first time is 1.5 - 2 h.

[0023] Optionally, in step S1, it is heated to 150 - 165 °C for the second time, and the holding time for the second time is 2 - 2.5 h.

[0024] Optionally, in step S1, the purification includes azeotropic distillation and vacuum distillation.

[0025] In the present invention, the sulfonation product of the sulfonation reaction is purified. The purification process includes azeotropic distillation and vacuum distillation. Azeotropic distillation can carry out water to remove the water in the sulfonation product, and vacuum distillation can remove the residual solvent and unreacted naphthalene. The excess naphthalene is continuously used as a raw material for reaction to improve the utilization rate of the raw material.

[0026] Optionally, in step S1, the azeotropic agent used in the azeotropic distillation includes n-heptane.

[0027] In the present invention, the dosage of n-heptane is 160 - 200 g.

[0028] Optionally, in step S1, the reflux time of the azeotropic distillation is 5 to 6 h.

[0029] Optionally, in step S1, the pressure of the vacuum distillation is 0.085 to 0.095 MPa.

[0030] Optionally, in step S1, the temperature of the vacuum distillation is 70 to 100 °C.

[0031] Optionally, in step S3, the base is solid sodium hydroxide.

[0032] Optionally, in step S3, the target temperature of the heating is 325 to 400 °C.

[0033] In the present invention, the reaction time for mixing and heating 2-naphthalenesulfonic acid with a base is 0.8 to 1.2 h.

[0034] Optionally, the crystallization mother liquor and the sweating liquid in step S2 are mixed with the sulfonation product in step S1 for a transposition reaction.

[0035] In the present invention, the crystallization mother liquor and the sweating liquid obtained by melt crystallization of the naphthalenesulfonic acid mixture contain 1-naphthalenesulfonic acid. Transferring the crystallization mother liquor and the sweating liquid to step S1 for a transposition reaction with the sulfonation product can enable the separated 1-naphthalenesulfonic acid to continue the transposition reaction to convert it into 2-naphthalenesulfonic acid, thereby improving the raw material conversion rate.

[0036] Optionally, in step S3, the product of the neutralization reaction includes sulfur dioxide gas, and the sulfur dioxide gas is used to acidify the 2-naphthol sodium.

[0037] Optionally, in step S3, the aqueous phase of the phase separation treatment is a sodium sulfite solution, and the sodium sulfite solution is used for a neutralization reaction with the 2-naphthalenesulfonic acid.

[0038] The present invention also provides a 2-naphthol prepared by the preparation method as described above.

[0039] Advantages of the present invention:

[0040] By utilizing the principle that there is a large difference in the melting points of 2-naphthalenesulfonic acid and 1-naphthalenesulfonic acid, the present invention separates the two by melt crystallization. Moreover, the separated 1-naphthalenesulfonic acid can be continuously converted into 2-naphthalenesulfonic acid, improving the conversion rate of naphthalene and the yield of 2-naphthalenesulfonic acid, which is beneficial to increasing the output of 2-naphthol in the subsequent preparation. At the same time, the naphthalene recovery step is reduced, and the generation of salty wastewater is greatly reduced. The preparation method of the present invention is environmentally friendly, efficient, and the production cost is much lower than that of the traditional process.

[0041] In the process of preparing 2-naphthol, the present invention reduces the consumption of sulfuric acid, decreases the generation amount of by-product sodium sulfate, and improves the utilization rate of raw materials by recycling sulfur dioxide gas and sodium sulfite solution. While further reducing costs, the production process becomes more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic structural diagram of the production system for preparing 2-naphthol in Embodiments 1 to 3 of the present invention.

[0043] DESCRIPTION OF THE REFERENCE NUMERALS

[0044] Sulfonation kettle 11, rearrangement kettle 12, melt crystallizer 13, neutralization kettle 21, solid-liquid separator 22, alkali hydrolysis kettle 23, acidification kettle 24, phase separator 31, distillation kettle 32, raw material inlet A, raw material inlet B, product outlet P. DETAILED DESCRIPTION OF THE INVENTION

[0045] The following will illustrate the embodiments of the present invention with reference to the drawings and specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, rather than for limiting the protection scope of the present invention.

[0046] The present invention provides a method for preparing 2-naphthol. Using naphthalene and sulfuric acid as raw materials, a sulfonation reaction and a rearrangement reaction are carried out to obtain a naphthalenesulfonic acid mixture. 1-naphthalenesulfonic acid in the naphthalenesulfonic acid mixture is separated by melt crystallization to obtain 2-naphthalenesulfonic acid. The 2-naphthalenesulfonic acid is successively subjected to neutralization, alkali fusion, acidification, and refining treatments to obtain 2-naphthol.

[0047] Among them, the melt crystallization successively includes four processes: directly cooling the naphthalenesulfonic acid mixture to 95 - 105°C, performing primary cooling at a cooling rate of 0.5°C / 3 - 5 min, performing secondary cooling at a cooling rate of 0.1°C / 1 - 2 min, and performing heating and sweating at a heating rate of 0.1°C / 3 - 5 min.

[0048] In an embodiment of the present invention, the method for preparing 2-naphthol includes the following steps:

[0049] S1. Sulfonation and rearrangement: Sulfuric acid is added to naphthalene according to a molar ratio of naphthalene to sulfuric acid of 1.05 - 1.2:1 to obtain a mixture. The mixture is heated to 110 - 120 °C for the first time and kept warm for 1.5 - 2 h to carry out the sulfonation reaction, obtaining a sulfonation product. The sulfonation product is subjected to azeotropic distillation and vacuum distillation, and then the sulfonation product is heated to 150 - 165 °C for the second time and kept warm for 2 - 2.5 h to carry out the rearrangement reaction, obtaining a naphthalenesulfonic acid mixture. Among them, n-heptane is used as the azeotropic agent for azeotropic distillation, and the reflux time is 5 - 6 h; the pressure of vacuum distillation is 0.085 - 0.095 MPa, and the temperature is 70 - 100 °C.

[0050] S2. Separation: The obtained naphthalenesulfonic acid mixture is subjected to melt crystallization, directly cooled to 95 - 105 °C, and then cooled at a rate of 0.5 °C per 3 - 5 min for the first-stage cooling until crystals are formed, and then cooled at a rate of 0.1 °C per 1 - 2 min for the second-stage cooling until crystallization is completed. The crystallization mother liquor is removed, and then heated and sweated at a rate of 0.1 °C per 3 - 5 min. After the heating and sweating are completed, the sweating liquid is removed to obtain 2-naphthalenesulfonic acid.

[0051] S3. Preparation of 2-naphthol: The obtained 2-naphthalenesulfonic acid is mixed with a sodium sulfite solution, and subjected to a neutralization reaction, cooling crystallization, and filtration in sequence to obtain sodium 2-naphthalenesulfonate. Then, sodium 2-naphthalenesulfonate is mixed with solid sodium hydroxide and heated to 325 - 400 °C for reaction to obtain sodium 2-naphthoxide. Then, sodium 2-naphthoxide is acidified, and the acidified solution is phase-separated to obtain crude 2-naphthol. Finally, the crude 2-naphthol is subjected to a refining treatment to obtain the product 2-naphthol.

[0052] Among them, in step S1, the sulfuric acid is added at a dropping rate of 54 - 108 mL / h.

[0053] In step S1, the amount of n-heptane used is 160 - 200 g.

[0054] In step S3, the reaction time for the reaction of heating the mixture of sodium 2-naphthalenesulfonate and alkali is 0.8 - 1.2 h.

[0055] In another embodiment of the present invention, the crystallization mother liquor and sweating liquid in step S2 are mixed with the sulfonation product in step S1 to carry out the rearrangement reaction.

[0056] In yet another embodiment of the present invention, the product of the neutralization reaction in step S3 includes sulfur dioxide gas, and the sulfur dioxide gas is used to acidify sodium 2-naphthoxide.

[0057] In still another embodiment of the present invention, the aqueous phase in the phase separation treatment in step S3 is a sodium sulfite solution, and the sodium sulfite solution is recycled for use in the neutralization reaction with 2-naphthalenesulfonic acid.

[0058] The present invention also provides 2-naphthol prepared by the preparation method as described above.

[0059] The present invention will be described in detail below by way of specific examples. It should also be understood that the following examples are only used to specifically illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific values in the following examples. It should be understood that in the following examples, only the specific situation of using concentrated sulfuric acid and naphthalene as raw materials for the reaction is listed, and those skilled in the art can also choose fuming sulfuric acid and naphthalene as raw materials for the reaction.

[0060] In the present invention, the chemical reaction equations involved are as follows:

[0061] Sulfonation reaction:

[0062] Rearrangement reaction:

[0063] Neutralization:

[0064] Alkali fusion:

[0065] Acidification:

[0066] In the present invention, the production system as Figure 1 shown is used to prepare 2-naphthol. The production system includes a 2-naphthalenesulfonic acid preparation unit, a 2-naphthol preparation unit, and a purification unit.

[0067] Please refer to Figure 1 , the 2-naphthalenesulfonic acid preparation unit includes a sulfonation kettle 11, a rearrangement kettle 12, and a melt crystallizer 13 that are connected in sequence. The sulfonation kettle 11 is used for the sulfonation reaction of raw material naphthalene and sulfuric acid, the rearrangement kettle 12 is used for the rearrangement reaction of the sulfonation product obtained from the sulfonation reaction, and the melt crystallizer 13 is used to separate 1-naphthalenesulfonic acid and 2-naphthalenesulfonic acid in the naphthalenesulfonic acid mixture.

[0068] Please continue to refer to Figure 1, the sulfonation kettle 11 is provided with a raw material inlet A and a raw material inlet B. The raw material inlet A is used to add naphthalene into the sulfonation kettle 11, and the raw material inlet B is used to add sulfuric acid into the sulfonation kettle. The melt crystallizer is also provided with a liquid outlet for discharging crystal mother liquor and sweating liquid. The liquid outlet is communicated with the rearrangement kettle 12 through a circulation pipeline for transporting the discharged crystal mother liquor and sweating liquid into the rearrangement kettle 12 for rearrangement reaction.

[0069] Please continue to refer to Figure 1 , the 2-naphthol preparation unit includes a neutralization kettle 21, a solid-liquid separator 22, an alkali hydrolysis kettle 23, and an acidification kettle 24 that are connected in sequence. The neutralization kettle 21 is used for the neutralization reaction of 2-naphthalenesulfonic acid and sodium sulfite solution. The solid-liquid separator 22 is used for filtering the product of the neutralization reaction. The alkali hydrolysis kettle 23 is used for mixing the filtered sodium 2-naphthalenesulfonate with alkali for alkali fusion. The acidification kettle 24 is used for acidifying the sodium 2-naphtholate obtained in the alkali fusion process to prepare 2-naphthol.

[0070] Please continue to refer to Figure 1 , the neutralization kettle 21 is communicated with the outlet of the melt crystallizer 13 for feeding 2-naphthalenesulfonic acid into the neutralization kettle 21. The neutralization kettle 21 is communicated with the acidification kettle 24 for transporting the sulfur dioxide gas obtained from the neutralization reaction to the acidification kettle 24 to acidify the sodium 2-naphtholate.

[0071] Please continue to refer to Figure 1 , the purification unit includes a phase separator 31 and a distillation kettle 32 that are connected in sequence. The phase separator 31 is used for phase separation of the acidified solution. The distillation kettle 32 is used for refining the crude 2-naphthol obtained from the phase separation.

[0072] Please continue to refer to Figure 1 , the phase separator 31 is communicated with the acidification kettle 24 for feeding the acidified solution into the phase separator 31. The phase separator 31 is also communicated with the neutralization kettle 21 for transporting the sodium sulfite solution obtained from the phase separation to the neutralization kettle 21 for neutralization reaction. The distillation kettle 32 is also provided with a product outlet P. After the refining process is completed, the product 2-naphthol is obtained through the product outlet P.

[0073] In the present invention, the naphthalene used is refined naphthalene. Before mixing the refined naphthalene with concentrated sulfuric acid, the refined naphthalene is heated to dissolve it into a liquid. Among them, the target temperature of heating is 80 - 90 °C.

[0074] Example 1

[0075] This example provides a method for preparing 2-naphthol, including the following steps:

[0076] S1. Sulfonation and rearrangement: 142.2 g of refined naphthalene was added to a four-necked flask according to a molar ratio of refined naphthalene to sulfuric acid of 1.1:1, and heated to 85 °C to dissolve the refined naphthalene. Then the refined naphthalene was added to a sulfonation kettle, and 54 mL (i.e., 100 g) of concentrated sulfuric acid with a concentration of 98 wt% was added dropwise to the refined naphthalene at a dropping rate of 80 mL / h to obtain a mixture. The mixture was heated to 115 °C for the first time and kept warm for 1.8 h to carry out the sulfonation reaction to obtain a sulfonation product. Subsequently, 180 g of n-heptane was added to the sulfonation product, and refluxed at 115 °C for 5.5 h for azeotropic distillation to remove water; then the pressure of the sulfonation product system was adjusted to 0.090 MPa, and the sulfonation product was subjected to vacuum distillation at a temperature of 85 °C to remove the unreacted refined naphthalene; then the purified sulfonation product was transferred to a rearrangement kettle for secondary heating to 158 °C and secondary insulation for 2.2 h to carry out the rearrangement reaction to obtain a naphthalenesulfonic acid mixture.

[0077] S2. Separation: The obtained naphthalenesulfonic acid mixture was added into the crystallization tube of a melt crystallizer and directly cooled to 100 °C. Subsequently, it was cooled at a rate of 0.5 °C / 4 min for the first-stage cooling. When the temperature was cooled to 88.0 °C, crystals were observed to form. The crystals were white thin flakes. Then it was cooled at a rate of 0.1 °C / 1.5 min for the second-stage cooling. When the temperature was cooled to 82 °C, the crystallization was completed. 33.5 g of the crystallization mother liquor was poured out to obtain 2-naphthalenesulfonic acid crystals. Then it was heated and sweated at a rate of 0.1 °C / 4 min to 88.8 °C, and 29.3 g of the sweating liquid was poured out to obtain the first-grade product of 2-naphthalenesulfonic acid.

[0078] After detection, the mass of the first-grade product of 2-naphthalenesulfonic acid was 143.2 g, and the purity of 2-naphthalenesulfonic acid was 98.71%.

[0079] S3. Preparation of 2-naphthol: The obtained 2-naphthalenesulfonic acid was added dropwise to a sodium sulfite solution for a neutralization reaction. Subsequently, it was cooled for crystallization and filtered to obtain sodium 2-naphthalenesulfonate. Then sodium 2-naphthalenesulfonate was mixed with solid sodium hydroxide and heated to 360 °C for a reaction for 1 h to obtain sodium 2-naphthoxide. Then sodium 2-naphthoxide was acidified, and the acidified solution was phase-separated to obtain crude 2-naphthol. Finally, the crude 2-naphthol was distilled to remove water and subjected to vacuum distillation to obtain the second-grade product of 2-naphthol.

[0080] After detection, the mass of the second-grade product of 2-naphthol was 94.0 g, the purity of 2-naphthol was 99.20%, the yield was 95.29%, and the content of 1-naphthol in the second-grade product was 0.006%.

[0081] Example 2

[0082] This example provides a method for preparing 2-naphthol, including the following steps:

[0083] S1. Sulfonation and rearrangement: Add 135.8 g of refined naphthalene into a four-necked flask according to the molar ratio of refined naphthalene to sulfuric acid of 1.05:1, heat it to 90 °C to dissolve the refined naphthalene, and add the refined naphthalene into the sulfonation kettle. Then, dropwise add 54 mL (i.e., 100 g) of concentrated sulfuric acid with a concentration of 98 wt% into the refined naphthalene at a dropping rate of 54 mL / h to obtain a mixture. Heat the mixture to 120 °C for the first time and keep it warm for 1.5 h to carry out the sulfonation reaction to obtain a sulfonation product. Subsequently, add 160 g of n-heptane to the sulfonation product, reflux at 120 °C for 5 h for azeotropic distillation to remove water; then adjust the pressure of the sulfonation product system to 0.085 MPa, and keep the temperature at 100 °C to carry out vacuum distillation on the sulfonation product to remove the unreacted refined naphthalene; then transfer the purified sulfonation product to the rearrangement kettle for secondary heating to 165 °C and secondary insulation for 2 h to carry out the rearrangement reaction to obtain a naphthalenesulfonic acid mixture.

[0084] S2. Separation: Add the obtained naphthalenesulfonic acid mixture into the crystallization tube of the melt crystallizer, directly cool it to 95 °C, and then carry out primary cooling at a rate of 0.5 °C / 5 min. When the temperature drops to 88.5 °C, it is observed that crystals are formed. The crystals are white thin flakes. Then carry out secondary cooling at a rate of 0.1 °C / 2 min. When the temperature drops to 81.8 °C, the crystallization is completed. Pour out 32.9 g of the crystallization mother liquor to obtain 2-naphthalenesulfonic acid crystals. Then carry out temperature-raising sweating at a rate of 0.1 °C / 5 min to 89.0 °C, and pour out 30.1 g of the sweating liquid to obtain the primary product 2-naphthalenesulfonic acid.

[0085] After detection, the mass of the primary product 2-naphthalenesulfonic acid is 142.8 g, and the purity of 2-naphthalenesulfonic acid is 99.03%.

[0086] S3. Preparation of 2-naphthol: Drop the obtained 2-naphthalenesulfonic acid into the sodium sulfite solution for a neutralization reaction, then cool it for crystallization and filter to obtain sodium 2-naphthalenesulfonate. Then mix sodium 2-naphthalenesulfonate with solid sodium hydroxide and heat it to 400 °C for a reaction for 0.8 h to obtain sodium 2-naphthoxide. Then acidify sodium 2-naphthoxide and carry out phase separation on the acidified solution to obtain crude 2-naphthol. Finally, carry out distillation dehydration and vacuum distillation on the crude 2-naphthol to obtain the secondary product 2-naphthol.

[0087] After detection, the mass of the secondary product 2-naphthol is 93.8 g, the purity of 2-naphthol is 99.42%, and the yield is 95.25%. Among them, the content of 1-naphthol in the secondary product is 0.005%.

[0088] Example 3

[0089] This example provides a method for preparing 2-naphthol, including the following steps:

[0090] S1. Sulfonation and rearrangement: 155.2 g of refined naphthalene was added to a four-necked flask according to a molar ratio of refined naphthalene to sulfuric acid of 1.2:1, and heated to 80 °C to dissolve the refined naphthalene. Then the refined naphthalene was added to a sulfonation kettle, and 54 mL (i.e., 100 g) of concentrated sulfuric acid with a concentration of 98 wt% was added dropwise to the refined naphthalene at a dropping rate of 108 mL / h to obtain a mixture. The mixture was heated to 110 °C for the first time and kept warm for 2 h to carry out the sulfonation reaction to obtain a sulfonation product. Subsequently, 200 g of n-heptane was added to the sulfonation product, and refluxed at 110 °C for 6 h for azeotropic distillation to remove water; then the pressure of the sulfonation product system was adjusted to 0.095 MPa, and the sulfonation product was subjected to vacuum distillation at a temperature of 70 °C to remove the unreacted refined naphthalene; then the purified sulfonation product was transferred to a rearrangement kettle for secondary heating to 150 °C and secondary insulation for 2.5 h to carry out the rearrangement reaction to obtain a naphthalenesulfonic acid mixture.

[0091] S2. Separation: The obtained naphthalenesulfonic acid mixture was added to the crystallization tube of a melt crystallizer and directly cooled to 105 °C. Subsequently, it was cooled at a rate of 0.5 °C / 3 min for the first-stage cooling. When the temperature was cooled to 87.7 °C, crystals were observed to form. The crystals were white thin flakes. Then it was cooled at a rate of 0.1 °C / 1 min for the second-stage cooling. When the temperature was cooled to 82.5 °C, the crystallization was completed. 35.1 g of the crystallization mother liquor was poured out to obtain 2-naphthalenesulfonic acid crystals. Then it was heated and sweated at a rate of 0.1 °C / 3 min to 88.3 °C, and 28.4 g of the sweating liquid was poured out to obtain the first-grade product of 2-naphthalenesulfonic acid;

[0092] After detection, the mass of the first-grade product of 2-naphthalenesulfonic acid was 143.9 g, and the purity of 2-naphthalenesulfonic acid was 98.67%.

[0093] S3. Preparation of 2-naphthol: The obtained 2-naphthalenesulfonic acid was added dropwise to a sodium sulfite solution for a neutralization reaction. Subsequently, it was cooled and crystallized, filtered to obtain sodium 2-naphthalenesulfonate. Then sodium 2-naphthalenesulfonate was mixed with solid sodium hydroxide and heated to 325 °C for a reaction for 1.2 h to obtain sodium 2-naphtholate. Then sodium 2-naphtholate was acidified, and the acidified solution was phase-separated to obtain crude 2-naphthol. Finally, the crude 2-naphthol was subjected to distillation dehydration and vacuum distillation to obtain the second-grade product of 2-naphthol.

[0094] After detection, the mass of the second-grade product of 2-naphthol was 94.5 g, the purity of 2-naphthol was 99.13%, and the yield was 95.30%. Among them, the content of 1-naphthol in the second-grade product was 0.009%.

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 1 is that: the melt crystallization method was not used to remove 1-naphthalenesulfonic acid from the naphthalenesulfonic acid mixture, and the other preparation conditions and steps were the same as those in Example 1.

[0097] After detection, the mass of the naphthalene sulfonic acid mixture is 195.3 g, the content of 2-naphthalene sulfonic acid in the naphthalene sulfonic acid mixture is 81.56%, the mass of the product 2-naphthol is 113.6 g, the purity of 2-naphthol is 83.44%, and the yield is 85.96%. Among them, the content of 1-naphthol in the product is 15.4%.

[0098] Comparative Example 2

[0099] The difference between this comparative example and Example 1 is that: 1-naphthalene sulfonic acid in the naphthalene sulfonic acid mixture is removed by hydrolysis instead of melt crystallization, that is, the naphthalene sulfonic acid mixture is placed in an acidic water system for hydrolysis to produce naphthalene and sulfuric acid. The specific steps are as follows:

[0100] S1. Sulfonation and rearrangement: Add 142.2 g of refined naphthalene to a four-necked flask according to the molar ratio of refined naphthalene to sulfuric acid of 1.1:1, heat to 85 °C to dissolve the refined naphthalene, add the refined naphthalene to the sulfonation kettle, and then add 54 mL (i.e., 100 g) of concentrated sulfuric acid with a concentration of 98 wt% dropwise to the refined naphthalene at a dropping rate of 80 mL / h to obtain a mixture. Heat the mixture to 115 °C for the first time and keep it warm for 1.8 h to carry out the sulfonation reaction to obtain a sulfonation product. Then transfer the purified sulfonation product to the rearrangement kettle for secondary heating to 158 °C and secondary insulation for 2.2 h to carry out the rearrangement reaction to obtain a naphthalene sulfonic acid mixture;

[0101] S2. Hydrolysis: Place the obtained naphthalene sulfonic acid mixture in an acidic water system for hydrolysis reaction. After the hydrolysis reaction is completed, pass steam into the obtained hydrolysis reaction solution to remove the unreacted refined naphthalene and naphthalene produced by the hydrolysis reaction to obtain the primary product 2-naphthalene sulfonic acid;

[0102] After detection, the mass of the primary product 2-naphthalene sulfonic acid is 169.3 g, and the purity of 2-naphthalene sulfonic acid is 91.35%.

[0103] The remaining preparation conditions and steps are the same as those in Example 1. After detection, the mass of the secondary product 2-naphthol is 104.3 g, the purity of 2-naphthol is 93.76%, the yield is 91.34%, and among them, the content of 1-naphthol in the secondary product is 1.3%.

[0104] It can be seen from Examples 1 to 3 that the purity of 2-naphthalene sulfonic acid prepared in Examples 1 to 3 all reaches 98.67% and above, the purity of 2-naphthol prepared from 2-naphthalene sulfonic acid all reaches 99.13% and above, and the yields are all above 95%. At the same time, the content of 2-naphthol in the product is all below 0.01%. This result shows that the 2-naphthalene sulfonic acid prepared by the preparation method of the present invention has high purity, the 2-naphthol prepared from 2-naphthalene sulfonic acid has high purity, high yield, and the content of the by-product 1-naphthol is extremely low.

[0105] As can be seen from Example 1 and Comparative Examples 1-2, in Comparative Example 1, the naphthalenesulfonic acid mixture was not subjected to melt crystallization treatment. The purity of 2-naphthalenesulfonic acid in the naphthalenesulfonic acid mixture was 81.56%, and the purity and yield of 2-naphthol were 83.44% and 85.96% respectively, which were much lower than those in Example 1. In Comparative Example 2, the traditional process was used to hydrolyze naphthalenesulfonic acid. Among them, the purity of 2-naphthalenesulfonic acid was 91.35%, and the purity and yield of 2-naphthol were 93.76% and 91.34% respectively, which were higher than those in Comparative Example 1 but still lower than those in Example 1. This result shows that the present invention separates 1-naphthalenesulfonic acid from the naphthalenesulfonic acid mixture by melt crystallization, improves the purity of 2-naphthalenesulfonic acid, and further improves the purity of 2-naphthol.

[0106] In summary, the preparation method of the present invention improves the purity of 2-naphthalenesulfonic acid, and further improves the purity and yield of 2-naphthol. In addition, during the preparation of 2-naphthol, the present invention can recycle sulfur dioxide gas and sodium sulfite solution, reduce the consumption of sulfuric acid, reduce the generation amount of by-product sodium sulfate, improve the raw material utilization rate and economy, and make the production process more efficient and environmentally friendly.

[0107] The above embodiments merely illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of 2-naphthol, characterized in that: Using naphthalene and sulfuric acid as raw materials, a sulfonation reaction and a rearrangement reaction are carried out to obtain a mixture of naphthalenesulfonic acids. 1-Naphthalenesulfonic acid in the mixture of naphthalenesulfonic acids is separated by melt crystallization to obtain 2-naphthalenesulfonic acid. The 2-naphthalenesulfonic acid is successively subjected to neutralization, alkali fusion, acidification and refining treatments to obtain 2-naphthol; The melt crystallization successively includes four processes: direct cooling, primary cooling, secondary cooling and heating for sweating. The target temperature of the direct cooling is 95-105°C, the cooling rate of the primary cooling process is 0.5°C / 3-5 min, the cooling rate of the secondary cooling process is 0.1°C / 1-2 min, and the heating rate of the heating for sweating process is 0.1°C / 3-5 min. After direct cooling, primary cooling and secondary cooling, the mother liquor of crystallization is removed to obtain 2-naphthalenesulfonic acid crystals, and then the 2-naphthalenesulfonic acid crystals are heated for sweating to remove the sweating liquid to obtain 2-naphthalenesulfonic acid.

2. The preparation method according to claim 1, wherein The preparation method includes the following steps: S1. Sulfonation and rearrangement: Sulfuric acid is added to naphthalene to obtain a mixture. The mixture is heated and kept warm once to carry out a sulfonation reaction to obtain a sulfonation product. The sulfonation product is purified, and then the sulfonation product is heated and kept warm twice to carry out a rearrangement reaction to obtain a mixture of naphthalenesulfonic acids; S2. Separation: The obtained mixture of naphthalenesulfonic acids is subjected to melt crystallization. After direct cooling, primary cooling and secondary cooling, the mother liquor of crystallization is removed to obtain 2-naphthalenesulfonic acid crystals, and then the 2-naphthalenesulfonic acid crystals are heated for sweating to remove the sweating liquid to obtain 2-naphthalenesulfonic acid; S3. Preparation of 2-naphthol: The obtained 2-naphthalenesulfonic acid is mixed with a sodium sulfite solution, and successively subjected to a neutralization reaction, cooling crystallization and filtration to obtain 2-naphthalenesulfonate. Then the 2-naphthalenesulfonate is mixed with an alkali and heated to react to obtain 2-naphtholate. The 2-naphtholate is acidified, and the acidified solution is phase-separated to obtain crude 2-naphthol. Finally, the crude 2-naphthol is subjected to a refining treatment to obtain the product 2-naphthol.

3. The preparation method according to claim 2, characterized in that: In step S1, the molar ratio of naphthalene to sulfuric acid is 1.05-1.2:1; and / or, in step S1, the sulfuric acid is concentrated sulfuric acid or fuming sulfuric acid; and / or, in step S1, the first heating is to 110-120°C, and the holding time of the first heat preservation is 1.5-2 h; and / or, in step S1, the second heating is to 150-165°C, and the holding time of the second heat preservation is 2-2.5 h.

4. The preparation method according to claim 2, characterized in that: In step S1, the purification includes azeotropic distillation and vacuum distillation.

5. The preparation method according to claim 4, characterized in that: In step S1, the azeotropic agent used in the azeotropic distillation includes n-heptane; and / or, in step S1, the reflux time of the azeotropic distillation is 5-6 h; and / or, in step S1, the pressure of the vacuum distillation is 0.085-0.095 MPa; and / or, in step S1, the temperature of the vacuum distillation is 70-100°C.

6. The preparation method according to claim 2, characterized in that: In step S3, the alkali is solid sodium hydroxide; and / or, in step S3, the target temperature of the heating is 325-400°C.

7. The preparation method according to claim 2, characterized in that, The preparation method further includes: mixing the crystallization mother liquor and the sweating liquor in step S2 with the sulfonation product in step S1 for a rearrangement reaction; And / or, in step S3, the product of the neutralization reaction includes sulfur dioxide gas, and the sulfur dioxide gas is used to acidify the sodium 2-naphtholate; And / or, in step S3, the aqueous phase obtained by the phase separation treatment is a sodium sulfite solution, and the sodium sulfite solution is used to carry out a neutralization reaction with the 2-naphthalenesulfonic acid.

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