1, 5-dihydroxynaphthalene as well as preparation method and application thereof

Abstract

The invention discloses 1, 5-dihydroxy naphthalene as well as a preparation method and application thereof. Through bentonite nucleation induction, the efficiency is remarkably improved, the generation of byproducts is reduced, the purity of the obtained product can reach 99.6%, and the yield reaches 90%. The method effectively solves the problems of difficult nucleation, more side reaction products and the like in the traditional process. The method is mild in process condition, simple and convenient to operate, good in repeatability and suitable for industrial production, and has wide application prospects in the fields of dyes, medicines, high-performance materials and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of organic compound preparation, and particularly relates to 1,5-dihydroxynaphthalene and a preparation method and application thereof. BACKGROUND

[0002] 1,5-dihydroxynaphthalene is an important organic chemical raw material, which has a wide range of applications in dyes, medicines, functional materials and many other fields. For example, in the field of dyes, it can be used as a key intermediate for synthesizing high-performance dyes, giving the dyes excellent color and fastness; in the field of medicine, it can be used for the synthesis of some compounds with specific pharmacological activity, providing an important material basis for new drug research and development; in the field of functional materials, it can be used for the preparation of materials with special photoelectric properties, and applied in new display technology and other aspects.

[0003] At present, 1,5-dihydroxynaphthalene is mainly prepared by sodium 1,5-naphthalene disulfonate alkali fusion method. After the completion of alkali fusion, hydrolysis and acidification, it is usually directly cooled and crystallized. However, it is found in actual production that 1,5-dihydroxynaphthalene is difficult to nucleate rapidly in the acidification liquid, and often remains in a supersaturated state for a long time, even first precipitates an oily substance, and then slowly converts into a solid. This process not only takes a long time (often more than several hours), but also the crystallization behavior is uncontrollable: once nucleation is triggered, a large number of fine crystals or amorphous precipitates are easily generated due to the local high concentration, resulting in difficult filtration, large washing loss, and part of the material even remains in the mother liquor or filter residue and cannot be recovered.

[0004] In order to improve the crystallization effect, some processes use the method of adding crystal seeds or repeatedly raising and lowering the temperature, but the operation is complicated, the reproducibility between batches is poor, and it is difficult to meet the needs of continuous production. More importantly, due to the lack of effective nucleation guidance, the overall yield has been hovering between 80% and 88% for a long time, which not only affects the utilization rate of raw materials, but also increases the burden of subsequent purification. Therefore, a new method is needed to promote the rapid and uniform nucleation of 1,5-dihydroxynaphthalene, shorten the crystallization period, and improve the solid-liquid separation efficiency, so as to improve the overall efficiency and stability of the process. SUMMARY

[0005] In view of the problem of low production efficiency in the preparation of 1,5-dihydroxynaphthalene in the prior art, the present application provides a kind of 1,5-dihydroxynaphthalene and its preparation method and application. The present application effectively induces the nucleation of 1,5-dihydroxynaphthalene by adding bentonite in the acidification process, and significantly improves its efficiency.

[0006] Bentonite is a natural layered silicate mineral with montmorillonite as the main component. Its chemical structure is composed of two layers of silicon-oxygen tetrahedron sandwiching one layer of aluminum-oxygen octahedron. Its crystal layer has a permanent negative charge, a large specific surface area and a large number of surface hydroxyl groups. After modification by organic cations (such as hexadecyl trimethyl ammonium), the interlayer spacing is expanded, the surface is changed from hydrophilic to hydrophobic, and the adsorption capacity for organic molecules is significantly enhanced. In the crystallization process of 1,5-dihydroxynaphthalene, the organic modified bentonite mainly plays the role of heterogeneous nucleation induction. The exposed Si-OH, Al-OH and other hydroxyl groups in the interlayer of bentonite can form hydrogen bonds with the phenolic hydroxyl groups in the 1,5-dihydroxynaphthalene molecules, effectively removing sodium ions; at the same time, its hydrophobic layer has a certain adsorption effect on the naphthalene ring. This synergistic effect makes the 1,5-dihydroxynaphthalene molecules accumulate in the interlayer of bentonite and arrange in a certain direction, effectively reducing the free energy required for nucleation, promoting the rapid and uniform formation of crystal nuclei. Thus, explosive crystallization or gel formation is avoided, and the crystallization efficiency, crystal regularity and subsequent solid-liquid separation performance are improved.

[0007] Specifically, the present application adopts the following technical scheme: a preparation method of 1,5-dihydroxynaphthalene, at least comprising the following steps: (1) reacting 1,5-naphthalene disulfonic acid sodium with molten sodium hydroxide at 290-320°C to replace the sulfonic acid group by alkali fusion to generate 1,5-dihydroxynaphthalene sodium salt; generally, the specific scheme adopted in the prior art is: adding 1,5-naphthalene disulfonic acid sodium into molten sodium hydroxide which has been preheated to 290-300°C, heating to 310-315°C, and keeping stirring for 2 hours to obtain a molten reaction liquid containing 1,5-dihydroxynaphthalene sodium salt; wherein the mass ratio of 1,5-naphthalene disulfonic acid sodium to sodium hydroxide is 0.6-0.8:1.

[0008] (2) adding deionized water into the above reaction liquid and stirring to dilute; the mass of deionized water is 8-10 times that of 1,5-naphthalene disulfonic acid sodium; adding 50wt% sulfuric acid dropwise, controlling the total sulfuric acid dosage to be completely neutralized NaOH and pH≈2.5-3.0; at this time, 1,5-dihydroxynaphthalene sodium salt is converted into free 1,5-dihydroxynaphthalene, forming a turbid suspension.

[0009] (3) pumping into a first reaction tank, which has been pre-dispersed with organic modified bentonite; controlling the tank temperature to be 80-100°C, and stirring for 20-30 minutes to form 1,5-dihydroxynaphthalene crystal grains in the interlayer of bentonite; wherein the dosage of organic modified bentonite is 5-10% of the mass of 1,5-naphthalene disulfonic acid sodium; under weakly acidic conditions (pH≈3), the structure of organic modified bentonite is stable; its hydrophobic interlayer domain and surface can adsorb 1,5-DHN molecules, provide heterogeneous nucleation sites through hydrogen bonds, promote the formation of microcrystals, and inhibit amorphous precipitation.

[0010] Subsequently, the mixed solution is separated by filtration through 10-20 μm filter, and in the process of filtration, the flushing effect of water flow can effectively destroy the hydrogen bond between the 1,5-dihydroxynaphthalene crystal grains and the interlayer hydroxyl of the bentonite, so that the formed crystal grains are detached from the surface or interlayer of the bentonite and enter the liquid phase; in the process, the organic modified bentonite can be recovered, and the filtrate containing the 1,5-dihydroxynaphthalene crystal grains enters the next step.

[0011] (4) The filtrate is pumped into the second reaction tank, and slowly cooled to 40-50℃ at a cooling rate of 1-2℃ / min, and kept for 30-40 minutes; and then 1,5-dihydroxynaphthalene crystals are collected by suction filtration or centrifugation.

[0012] 1,5-DHN is a planar polycyclic aromatic molecule, the molecular length (long axis), i.e. the diagonal line of naphthalene ring (C1-C8 diagonal line) ≈7.0-7.4Å; the molecular width (short axis), i.e. the width of naphthalene ring (C4-C5 distance direction) ≈4.8-5.2Å; the molecular thickness (including H) ≈3.2-3.5Å (van der Waals thickness); if considering inclined insertion or lying adsorption, the required minimum space is about 6-8Å. In order to make 1,5-DHN enter the interlayer of bentonite, the interlayer spacing d001 at least needs to be ≥8Å. Therefore, the bentonite with interlayer spacing of 16-20Å is used in the present application to ensure the insertion space of 1,5-DHN (available height ≈d 001 -2×(silicon-oxygen layer thickness) ≈d 001 -2×4.5 A˚).

[0013] Specifically, the organic modified bentonite is one of hexadecyl trimethyl ammonium bromide (CTAB) and octadecylamine (ODA) modified bentonite. It should be noted that the modification of bentonite with organic cations such as hexadecyl trimethyl ammonium bromide (CTAB) and octadecylamine (ODA) to control the interlayer spacing is a common and conventional technical means in the art, which is widely used in the fields of adsorption, catalysis and composite material preparation, etc. Therefore, the modification method is not described in detail in the present application.

[0014] In some embodiments of the present application, the particle size of the organic modified bentonite is in the range of 50-100 μm, so as to match the 10-20 μm filtration system and realize efficient separation and recycling. Otherwise, the nanoscale bentonite will pass through the filter, resulting in process failure. In addition, it is also necessary to prevent the particles from being too large to cause rapid sedimentation and uneven dispersion, which affects the uniformity of the nucleation sites. Generally, after ion exchange modification of sodium-based bentonite, the bentonite particles are prepared by spray drying.

[0015] In some embodiments of the present application, in step 2, the amount of sulfuric acid is 0.6-0.7 times the molar amount of NaOH.

[0016] In some embodiments of the present application, the crystallized 1,5-dihydroxynaphthalene is further refined using methanol, and the specific steps are as follows: (a) 1,5-dihydroxynaphthalene is mixed with methanol, activated carbon and antioxidant 1010 are added, and the temperature is raised to 65°C, and after 15-30 min, the filtrate is heated at 65°C; wherein 3L of methanol is used per kilogram of 1,5-dihydroxynaphthalene; the mass of antioxidant 1010 and activated carbon is 1% of 1,5-dihydroxynaphthalene, respectively; (b) 5 times the amount of water is added to the filtrate under stirring, and the temperature is lowered to 25°C, and then 1,5-dihydroxynaphthalene refined product is obtained by filtration, and after drying, pure 1,5-dihydroxynaphthalene is obtained.

[0017] The present application has the advantages that: the present application effectively induces the nucleation of the target product by introducing bentonite with a specific interlayer spacing, promotes the ordered growth of the crystal, and the crystallization reaction can reach a yield of 90% in about 1 hour. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The induction principle of the present application is shown in the figure; Figure 2 The scanning diagram of the bentonite after catalysis is shown in the figure; Figure 3 The XRD diagram of the modified bentonite is shown in the figure; Figure 4 The HPLC spectrum of the product of Example 1 is shown in the figure; Figure 5 The HPLC spectrum of the product of Example 2 is shown in the figure; Figure 6 The HPLC spectrum of the product of Example 3 is shown in the figure; Figure 7 The HPLC spectrum of the product of Example 4 is shown in the figure. DETAILED DESCRIPTION

[0019] The following examples are used to further illustrate the present application, and the purpose is to illustrate the present application, but should not be interpreted as limiting the scope of the present application. The following uses weight parts and weight percentage unless otherwise specified.

[0020] The raw materials used in the present application are conventional commercially available products unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0021] The following examples are used to further illustrate the present application, and the purpose is to illustrate the present application, but should not be interpreted as limiting the scope of the present application. The following uses weight parts and weight percentage unless otherwise specified.

[0022] It should be clear that the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0023] The terminology used in the present application embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in this present application and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0024] In the following examples, the CTAB-modified bentonite (CTAB-BT) used was prepared by the following steps: (1.1) Take 1 kg of sodium-based bentonite, add 9 L of deionized water, and stir at room temperature for 2 hours to prepare a 10% suspension slurry. Calculate the amount of cetyltrimethylammonium bromide (CTAB) required at 1.2 times the cation exchange capacity (CEC) of the bentonite, dissolve it in 1 L of 50°C hot water to prepare a CTAB solution.

[0025] (1.2) Slowly add the CTAB solution to the bentonite slurry while stirring, and the dropwise addition time should be no less than 1 hour. After the dropwise addition is complete, continue to stir at 70-80°C for 2 hours to complete the ion exchange.

[0026] (1.3) After the reaction is complete, filter the cake using a plate and frame filter press (filter cloth aperture ≤ 20 μm). Wash the filter cake with 60°C hot deionized water for 2-3 times until the washings are free of pale yellow precipitate when silver nitrate is added, indicating that Br⁻ has been washed out.

[0027] (1.4) Re-slurry the washed filter cake, add water to adjust the solid content to 25%-30%, and pass it through a 100-mesh sieve to obtain uniform slurry. Send the slurry to a centrifugal spray drying tower, control the inlet air temperature at 220-240°C, the outlet air temperature at 90-100°C, and the centrifugal disc speed at 10,000-12,000 rpm, and perform granulation and drying. Collect the dried powder, pass it through a 250-mesh sieve (aperture about 61 μm) and a 300-mesh sieve (aperture about 48 μm) in sequence, and take the particles between the two sieves, i.e., the CTAB-modified bentonite product with a particle size of 50-60 μm.

[0028] X-ray diffraction (XRD, Figure 3 ) analysis shows that the (001) crystal face diffraction peak is located at 2θ ≈ 4.7°-5.2°, and the calculated interlayer spacing d 001 is 17-19 Å, indicating that CTAB has been successfully inserted into the interlayer and effectively expanded.

[0029] In the following examples, the ODA-modified bentonite (ODA-BT) used was prepared by the following steps: (1.1) Take 1 kg of sodium bentonite, add 9 L of deionized water, and stir at room temperature for 2 hours to prepare a uniform slurry with a solid content of 10%. Calculate the required amount of octadecylamine (ODA) based on 1.2 times the cation exchange capacity (CEC) of the bentonite; dissolve ODA in 100 L of hot water at 50°C to prepare a solution.

[0030] (1.2) Warm the bentonite slurry to 75-80°C, and slowly add the ODA solution under stirring, with a dropwise addition time of not less than 1 hour. After the addition is complete, continue to stir at 75-80°C for 2 hours to complete the organic modification.

[0031] (1.3) After the reaction is complete, filter the cake using a plate and frame filter press (filter cloth aperture ≤20 μm). Wash the cake with 60°C hot deionized water for 2-3 times until the washings are silver nitrate-free, ensuring the removal of unreacted ODA and byproducts.

[0032] (1.4) Re-slurry the washed cake, adjust the solid content to 25%-30%, pass through a 100-mesh sieve to obtain a uniform slurry. Send the slurry to a centrifugal spray drying tower, control the inlet air temperature at 230-250°C, the outlet air temperature at 95-105°C, and the centrifugal disc speed at 8,000-10,000 rpm, and perform granulation and drying.

[0033] (1.5) Collect the dry powder, pass it through a 180-mesh sieve (aperture about 80 μm) and a 230-mesh sieve (aperture about 60 μm) in sequence, and take the material between the two sieves, i.e. the ODA-modified bentonite product with a particle size of 60-80 μm.

[0034] Seal and store in a dry place.

[0035] Take samples for characterization: XRD measurement shows that the (001) diffraction peak is located at 2θ ≈ 4.4°-4.9° ( Figure 3 ), and the interlayer spacing d 001 is calculated to be 18-20 Å, indicating that ODA has been effectively inserted into the interlayer and fully expanded.

[0036] Example 1 (1) Add 5.4 g of sodium 1,5-naphthalene disulfonate to molten sodium hydroxide preheated to 290-300°C, heat to 310-315°C, and stir for 2 hours to obtain a molten reaction liquid containing sodium 1,5-dihydroxynaphthalene salt; wherein the mass ratio of sodium 1,5-naphthalene disulfonate to sodium hydroxide is 0.6:1.

[0037] (2) Add deionized water to the above reaction solution and stir to dilute; the mass of the deionized water is 8 times the mass of the 1,5-naphthalenedisulfonic acid sodium salt; add 50 wt% sulfuric acid, the amount of which is 0.6 times the molar amount of NaOH, and the pH is about 2.5; (3) Pump into the first reaction tank, which has CTAB-BT dispersed therein in advance; control the tank temperature to be 100°C and stir for 20 minutes to form 1,5-dihydroxynaphthalene crystal grains between the layers of the bentonite; wherein the amount of CTAB-BT is 5% of the mass of the 1,5-naphthalenedisulfonic acid sodium salt; Subsequently, the mixed solution is separated by filtration through a 10 μm filter to recover the organically modified bentonite, and the filtrate containing the 1,5-dihydroxynaphthalene crystal grains is passed to the next step.

[0038] (4) Pump the filtrate into the second reaction tank, and slowly reduce the temperature to 50°C at a rate of 2°C / min, and maintain the temperature for 30 minutes; collect the 1,5-dihydroxynaphthalene crystals 2.34 g by suction filtration or centrifugation.

[0039] Thus, the actual yield reaches 90% in 50 minutes from nucleation to crystallization.

[0040] (5) Use methanol for purification, and the specific steps are as follows: Mix the 1,5-dihydroxynaphthalene with methanol, add activated carbon and antioxidant 1010, and heat to 65°C, maintain the temperature for 15-30 min, and then filter at 65°C; wherein 3 L of methanol corresponds to 1 kg of 1,5-dihydroxynaphthalene; the mass of the antioxidant 1010 and the activated carbon is each 1% of the mass of the 1,5-dihydroxynaphthalene; (b) Add 5 times the amount of water to the filtrate under stirring, and cool to 25°C, and then filter to obtain 1,5-dihydroxynaphthalene refined product, and dry to obtain pure 1,5-dihydroxynaphthalene.

[0041] The HPLC spectrum of the product is shown in Figure 4 According to the HPLC spectrum (detection wavelength 254 nm), a sharp, symmetrical and dominant area peak appears at about 5.979 min, the retention time of which is consistent with that of the 1,5-dihydroxynaphthalene standard under the same chromatographic conditions, indicating that the main component in the sample is 1,5-dihydroxynaphthalene, and the peak area of other impurity peaks (such as 12.2 min and 14.8 min) in the figure is very small, and the purity is 99.6%.

[0042] To verify whether 1,5-dihydroxynaphthalene crystal grains are successfully formed between the layers of the CTAB-BT in the first reaction tank without pressure filtration, we further analyzed the CTAB-BT in step 3 without filtration. After 20 minutes of stirring reaction, the sample was observed by scanning electron microscopy (SEM) (as shown in Figure 1SEM images clearly show that there are many fine particles attached to the CTAB-BT surface, which strongly suggests the successful formation of 1,5-dihydroxynaphthalene crystal grains, confirming the effective nucleation of 1,5-dihydroxynaphthalene between the layers of bentonite.

[0043] Example 2 (1) 5.4 grams of 1,5-naphthalene disulfonic acid sodium salt was added to molten sodium hydroxide preheated to 290-300°C, heated to 310-315°C, and stirred for 2 hours to obtain a molten reaction liquid containing 1,5-dihydroxynaphthalene sodium salt; wherein the mass ratio of 1,5-naphthalene disulfonic acid sodium salt to sodium hydroxide was 0.8:1.

[0044] (3) Deionized water was added to the above reaction liquid and stirred to dilute; the mass of deionized water was 10 times that of 1,5-naphthalene disulfonic acid sodium salt; 50wt% sulfuric acid was added dropwise, the amount of sulfuric acid was 0.6-0.7 times the molar amount of NaOH, and the pH was about 2.5; (4) Pumped into the first reaction tank, ODA-BT was pre-dispersed in the first reaction tank; the tank temperature was controlled at 80°C, and stirred for 30 minutes to form 1,5-dihydroxynaphthalene crystal grains between the layers of bentonite; wherein the amount of ODA-BT was 10% of the mass of 1,5-naphthalene disulfonic acid sodium salt; Subsequently, the mixed liquid was filtered and separated through a 20μm filter screen, and the organic modified bentonite was recovered, and the filtrate containing 1,5-dihydroxynaphthalene crystal grains entered the next step.

[0045] (5) The filtrate was pumped into the second reaction tank, and the temperature was slowly reduced to 40°C at a rate of 1°C / min, and kept for 40 minutes; after filtration or centrifugation, 2.31g of 1,5-dihydroxynaphthalene crystal was collected. The HPLC spectrum of the product is shown in Figure 5 According to the HPLC spectrum (detection wavelength 254 nm), a sharp, symmetrical and area-dominant main peak appeared at about 6.053 min, which was consistent with the retention time of the 1,5-dihydroxynaphthalene standard under the same chromatographic conditions, indicating that the main component in the sample was the target product, and the purity was 99.1%.

[0046] In this example, the total time from nucleation to crystallization was 70 minutes, and the actual yield reached 89%.

[0047] Example 3 (1) 5.4 grams of 1,5-naphthalene disulfonic acid sodium salt was added to molten sodium hydroxide preheated to 290-300°C, heated to 310-315°C, and stirred for 2 hours to obtain a molten reaction liquid containing 1,5-dihydroxynaphthalene sodium salt; wherein the mass ratio of 1,5-naphthalene disulfonic acid sodium salt to sodium hydroxide was 0.6:1.

[0048] (2) Add deionized water to the above reaction solution and stir to dilute; the mass of the deionized water is 8 times the mass of the 1,5-naphthalenedisulfonic acid sodium salt; drop 50wt% sulfuric acid, the amount of sulfuric acid is 0.6 times the molar mass of NaOH, pH≈2.5; (3) Pump into the first reaction tank, the first reaction tank is pre-dispersed with CTAB-BT; control the tank temperature to be 90℃, stir for 20 minutes, and form 1,5-dihydroxynaphthalene crystal grains between the layers of bentonite; wherein, the amount of CTAB-BT is 7% of the mass of 1,5-naphthalenedisulfonic acid sodium salt; Subsequently, the mixed solution is separated by 10μm filtration, and the organic modified bentonite is recovered, and the filtrate containing 1,5-dihydroxynaphthalene crystal grains enters the next step.

[0049] (4) Pump the filtrate into the second reaction tank, slowly reduce the temperature to 40℃ at a cooling rate of 2℃ / min, and keep the temperature for 40 minutes; collect 1,5-dihydroxynaphthalene crystals 2.30g by suction filtration or centrifugation.

[0050] Thus, the actual yield reaches 89% from nucleation to crystallization within 60 minutes.

[0051] (5) Use methanol for refining, the specific steps are as follows: Mix 1,5-dihydroxynaphthalene with methanol, add activated carbon and antioxidant 1010, heat to 65℃, keep the temperature for 15-30min, and then filter at 65℃; wherein, 3L of methanol corresponds to 1kg of 1,5-dihydroxynaphthalene; the mass of antioxidant 1010 and activated carbon is 1% of 1,5-dihydroxynaphthalene respectively; (b) Add 5 times the amount of water to the filtrate under stirring, cool to 25℃, and filter to obtain 1,5-dihydroxynaphthalene refined product, and dry to obtain pure 1,5-dihydroxynaphthalene.

[0052] The HPLC spectrum of the product is shown in Figure 6 According to the HPLC spectrum (detection wavelength 254 nm), a sharp, symmetrical and dominant area main peak appears at about 6.259min, and the retention time is consistent with that of the 1,5-dihydroxynaphthalene standard under the same chromatographic conditions, indicating that the main component in the sample is the target product. In addition, the peak area of other impurity peaks in the figure is very small, indicating that the product has high purity, and the purity is 99.1%.

[0053] Example 4 (1) Add 5.4 grams of 1,5-naphthalenedisulfonic acid sodium salt to molten sodium hydroxide preheated to 290-300℃, heat to 310-315℃, and keep stirring for 2 hours to obtain a molten reaction solution containing 1,5-dihydroxynaphthalene sodium salt; wherein, the mass ratio of 1,5-naphthalenedisulfonic acid sodium salt to sodium hydroxide is 0.8:1.

[0054] (3) Add deionized water to the above reaction solution and stir to dilute; the mass of the deionized water is 10 times the mass of sodium 1,5-naphthalenedisulfonate; add 50wt% sulfuric acid, the amount of sulfuric acid is 0.6–0.7 times the molar amount of NaOH, and the pH is approximately 2.5; (4) Pump into the first reaction tank, in which ODA-BT is pre-dispersed; control the tank temperature at 100°C and stir for 30 minutes to form 1,5-dihydroxynaphthalene crystals between the bentonite layers; wherein, the amount of ODA-BT is 8% of the mass of sodium 1,5-naphthalene disulfonate; subsequently, the mixture is filtered and separated through a 20μm filter screen, the organic modified bentonite is recovered, and the filtrate containing 1,5-dihydroxynaphthalene crystals enters the next step.

[0055] (5) Pump the filtrate into the second reaction vessel and slowly reduce the temperature to 50°C at a rate of 2°C / min. Keep the temperature for 30 minutes. Collect 2.28g of 1,5-dihydroxynaphthalene crystals by filtration or centrifugation.

[0056] Therefore, the total time from nucleation to crystallization was 60 minutes, and the actual yield reached 87.8%.

[0057] (5) Refining with methanol, the specific steps are as follows: 1,5-Dihydroxynaphthalene was mixed with methanol, activated carbon and antioxidant 1010 were added, the mixture was heated to 65°C, kept at that temperature for 15-30 minutes, and then hot-filtered at 65°C. Each kilogram of 1,5-dihydroxynaphthalene corresponds to 3 L of methanol; the mass of antioxidant 1010 and activated carbon is 1% of the mass of 1,5-dihydroxynaphthalene. (b) Add 5 times the amount of water to the filtrate while stirring, cool to 25°C, filter to obtain 1,5-dihydroxynaphthalene refined wet product, and dry to obtain pure 1,5-dihydroxynaphthalene.

[0058] The HPLC chromatogram of the product is as follows Figure 7 As shown in the HPLC chromatogram (detection wavelength 254 nm), a sharp, symmetrical, and predominantly large peak appears at approximately 6.049 min. Its retention time is consistent with that of the 1,5-dihydroxynaphthalene standard under the same chromatographic conditions, indicating that the main component in the sample is the target product. Based on the peak area, its purity is calculated to be 99.3%.

[0059] Comparative Example 1: Preparation of 1,5-dihydroxynaphthalene without bentonite (1) Same as in Example 1, 5.4 g of sodium 1,5-naphthalenedisulfonate was added to molten sodium hydroxide that had been preheated to 290–300°C, the temperature was raised to 310–315°C, and the mixture was stirred and kept warm for 2 hours to obtain a molten reaction solution containing sodium 1,5-dihydroxynaphthalene salt; wherein the mass ratio of sodium 1,5-naphthalenedisulfonate to sodium hydroxide was 0.6:1.

[0060] (2) Same as in Example 1, add deionized water to the above reaction solution and stir to dilute; the mass of the deionized water is 8 times the mass of sodium 1,5-naphthalenedisulfonate; add 50wt% sulfuric acid, the amount of sulfuric acid is 0.6 times the molar amount of NaOH, and the pH is approximately 2.5; (3) Pump into the first reaction vessel, control the vessel temperature at 100℃, and stir for 20 minutes; (4) Pump the solution into the second reaction vessel and slowly reduce the temperature to 50°C at a rate of 2°C / min, and maintain the temperature for 30 minutes; collect 1.07 g of 1,5-dihydroxynaphthalene crystals by filtration or centrifugation. The actual yield corresponds to approximately 41.2% of the theoretical yield based on sodium 1,5-naphthalenedisulfonate starting material.

[0061] This comparative example demonstrates that, even with strict control of reaction conditions, the nucleation rate of 1,5-dihydroxynaphthalene decreases significantly due to the lack of sufficient heterogeneous nucleation sites in the absence of nucleation promoters such as bentonite. This results in incomplete crystallization, smaller crystal size, and easy encapsulation of impurities from the mother liquor, leading to a lower yield (approximately 41.2%). In contrast, the addition of appropriately modified bentonite in Example 1, utilizing its abundant surface nucleation sites and good dispersibility, significantly improved the nucleation efficiency, achieving a higher yield in the same timeframe. This fully demonstrates the important role of bentonite in improving the nucleation efficiency during the synthesis of 1,5-dihydroxynaphthalene.

[0062] Comparative Example 2: Preparation of 1,5-dihydroxynaphthalene induced by unmodified bentonite (1) Same as in Example 1, 5.4 g of sodium 1,5-naphthalenedisulfonate was added to molten sodium hydroxide that had been preheated to 290–300°C, the temperature was raised to 310–315°C, and the mixture was stirred and kept warm for 2 hours to obtain a molten reaction solution containing sodium 1,5-dihydroxynaphthalene salt; wherein the mass ratio of sodium 1,5-naphthalenedisulfonate to sodium hydroxide was 0.6:1.

[0063] (2) Same as in Example 1, add deionized water to the above reaction solution and stir to dilute; the mass of the deionized water is 8 times the mass of sodium 1,5-naphthalenedisulfonate; add 50wt% sulfuric acid, the amount of sulfuric acid is 0.6 times the molar amount of NaOH, and the pH is approximately 2.5; (3) Pump into the first reaction vessel, which contains pre-dispersed unmodified BT (sodium bentonite with an interlayer spacing of approximately 9.6 Å); control the vessel temperature at 100°C and stir for 20 minutes to form 1,5-dihydroxynaphthalene crystals between the bentonite layers; wherein, the amount of CTAB-BT is 5% of the mass of sodium 1,5-naphthalene disulfonate; Subsequently, the mixture was separated by 10μm filtration, and the organic modified bentonite was recovered. The filtrate containing 1,5-dihydroxynaphthalene crystals was then used in the next step.

[0064] (4) The filtrate was pumped into the second reaction vessel and slowly cooled to 50°C at a rate of 2°C / min, and kept at this temperature for 30 minutes to promote residual nucleation. Finally, after filtration or centrifugation, only 0.99 g of 1,5-dihydroxynaphthalene crystals were obtained, corresponding to a yield of approximately 38.1%.

[0065] This comparative example demonstrates that although unmodified bentonite was introduced as a potential nucleating agent, its small interlayer spacing (~9.6 Å) and lack of interaction with 1,5-DHN prevented it from effectively inducing ordered molecular nucleation. In contrast, CTAB-modified bentonite with an interlayer spacing expanded to 17–19 Å, used in Example 1, significantly improved nucleation efficiency through synergistic hydrogen bonding. This clearly demonstrates that bentonite must undergo organic modification to expand its interlayer spacing and regulate its surface properties in order to effectively exert its nucleation-inducing function.

[0066] Preparation of 1,5-dihydroxynaphthalene induced by bentonite with large interlayer spacing (Comparative Example 3) Following the aforementioned method, sodium bentonite (DODMAC-BT) modified with dioctadecyl dimethylammonium chloride was used. Figure 3 The XRD results show that the (001) diffraction peak is shifted to a very small angle, and the calculated interlayer spacing is much greater than 20 Å, indicating that the interlayer structure is overstretched and tends to be disordered.

[0067] (1) Same as in Example 1, 5.4 g of sodium 1,5-naphthalenedisulfonate was added to molten sodium hydroxide that had been preheated to 290–300°C, the temperature was raised to 310–315°C, and the mixture was stirred and kept warm for 2 hours to obtain a molten reaction solution containing sodium 1,5-dihydroxynaphthalene salt; wherein the mass ratio of sodium 1,5-naphthalenedisulfonate to sodium hydroxide was 0.6:1.

[0068] (2) Same as in Example 1, add deionized water to the above reaction solution and stir to dilute; the mass of the deionized water is 8 times the mass of sodium 1,5-naphthalenedisulfonate; add 50wt% sulfuric acid, the amount of sulfuric acid is 0.6 times the molar amount of NaOH, and the pH is approximately 2.5; (3) Pump into the first reaction vessel, which contains DODMAC-modified BT pre-dispersed; control the vessel temperature at 100°C and stir for 20 minutes to form 1,5-dihydroxynaphthalene crystals between the bentonite layers; wherein, the amount of CTAB-BT is 5% of the mass of sodium 1,5-naphthalenedisulfonate; Subsequently, the mixture was separated by 10μm filtration, and the organic modified bentonite was recovered. The filtrate containing 1,5-dihydroxynaphthalene crystals was then used in the next step.

[0069] (4) The filtrate was pumped into the second reaction vessel and slowly cooled to 50°C at a rate of 2°C / min, and kept at this temperature for 30 minutes to promote residual nucleation. Finally, after filtration or centrifugation, only 1.2 g of 1,5-dihydroxynaphthalene crystals were obtained, corresponding to a yield of approximately 46%.

[0070] This comparative example shows that when the interlayer spacing of bentonite is excessively spread and much greater than 20 Å, its interlayer structure tends to be disordered, failing to provide an effective ordered template and stable nucleation sites for 1,5-dihydroxynaphthalene molecules, resulting in a significant decrease in nucleation induction efficiency. This result, together with Comparative Example 2 (interlayer spacing too small), demonstrates that there is a clear optimal window (16-20 Å) for the interlayer spacing of bentonite; exceeding this range will prevent the achievement of the efficient crystallization effect of this invention.

Claims

1. A method for preparing 1,5-dihydroxynaphthalene, characterized in that, It should include at least the following steps: (1) Sodium 1,5-naphthalene disulfonate is reacted with molten sodium hydroxide at 290–320°C to generate sodium 1,5-dihydroxynaphthalene salt by alkali fusion substitution of sulfonic acid groups; (2) Add deionized water to the above reaction solution and stir to dilute; the mass of the deionized water is 8–10 times the mass of sodium 1,5-naphthalenedisulfonate; add sulfuric acid with a concentration of 50wt% dropwise, and control the total amount of sulfuric acid to completely neutralize NaOH and make pH≈2.5–3.0; (3) Pump into the first reaction tank, which contains pre-dispersed organic modified bentonite; control the tank temperature at 80–100℃ and stir for 20–30 minutes to form 1,5-dihydroxynaphthalene crystals between the bentonite layers; wherein, the amount of organic modified bentonite is 5–10% of the mass of sodium 1,5-naphthalene disulfonate; Subsequently, the mixture was filtered through a 10–20 μm filter screen to separate the organically modified bentonite, and the filtrate containing 1,5-dihydroxynaphthalene crystals was used in the next step. (4) Pump the filtrate into the second reaction vessel and slowly cool it down to 40-50°C at a rate of 1–2°C / min. Keep it warm for 30-40 minutes. Collect 1,5-dihydroxynaphthalene crystals by filtration or centrifugation.

2. The preparation method according to claim 1, characterized in that, The interlayer spacing of the organically modified bentonite is 16–20 Å.

3. The preparation method according to claim 2, characterized in that, The organically modified bentonite is bentonite modified with one of cetyltrimethylammonium bromide (CTAB) or octadecylamine (ODA).

4. The preparation method according to claim 2, characterized in that, The particle size range of the organically modified bentonite is 50–100 μm.

5. The preparation method according to claim 2, characterized in that, The organically modified bentonite is obtained by ion-exchange modification of sodium-based bentonite followed by spray drying and granulation.

6. The preparation method according to claim 1, characterized in that, In step 2, the amount of sulfuric acid used is 0.6–0.7 times the molar amount of NaOH.

7. The preparation method according to claim 1, characterized in that, Step 1 specifically involves adding sodium 1,5-naphthalenedisulfonate to molten sodium hydroxide preheated to 290–300°C, raising the temperature to 310–315°C, and stirring the mixture for 2 hours to obtain a molten reaction solution containing sodium 1,5-dihydroxynaphthalene salt; wherein the mass ratio of sodium 1,5-naphthalenedisulfonate to sodium hydroxide is 0.6–0.8:

1.

8. The preparation method according to claim 1, characterized in that, The crystalline 1,5-dihydroxynaphthalene is further purified using methanol, and the specific steps are as follows: (a) Mix 1,5-dihydroxynaphthalene with methanol, add activated carbon and antioxidant 1010, heat to 65°C, keep at this temperature for 15-30 min, and then heat filter at 65°C; wherein, each kilogram of 1,5-dihydroxynaphthalene corresponds to 3 L of methanol; the mass of antioxidant 1010 and activated carbon is 1% of the mass of 1,5-dihydroxynaphthalene; (b) Add 5 times the amount of water to the filtrate while stirring, cool to 25°C, filter to obtain 1,5-dihydroxynaphthalene refined wet product, and dry to obtain pure 1,5-dihydroxynaphthalene.

9. A 1,5-dihydroxynaphthalene prepared by the method according to any one of claims 1 to 8.

10. An application of 1,5-dihydroxynaphthalene as described in claim 9.

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