1,5-dihydroxynaphthalene, its preparation and use

Abstract

The application discloses 1,5-dihydroxynaphthalene and a preparation method and application thereof. The application remarkably improves the efficiency of the 1,5-dihydroxynaphthalene through bentonite nucleation induction, and reduces the generation of by-products, and the purity of the obtained product can be up to 99.6%, and the yield reaches 90%. The method effectively solves the problems of difficult nucleation, many by-reaction products and the like in a traditional process. The application has a wide application prospect in the fields of dyes, medicines and high-performance materials and the like, and has the advantages of mild process conditions, simple operation and good repeatability, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of organic compound preparation, specifically relating to a 1,5-dihydroxynaphthalene, its preparation method, and its application. Background Technology

[0002] 1,5-Dihydroxynaphthalene, as an important organic chemical raw material, has wide applications in many fields such as dyes, pharmaceuticals, and functional materials. For example, in the dye field, it can serve as a key intermediate in the synthesis of high-performance dyes, endowing them with excellent color and fastness; in the pharmaceutical field, it can participate in the synthesis of some compounds with specific pharmacological activities, providing an important material basis for new drug development; in the field of functional materials, it can be used to prepare materials with special optoelectronic properties, applied to novel display technologies, etc.

[0003] Currently, 1,5-dihydroxynaphthalene is mainly produced by the alkaline fusion method using sodium 1,5-naphthalenedisulfonate. This method typically involves direct cooling and crystallization after alkaline fusion, hydrolysis, and acidification. However, in actual production, it has been found that 1,5-dihydroxynaphthalene is difficult to nucleate rapidly in the acidification solution, often remaining in a supersaturated state for a long time, sometimes even precipitating an oily substance before slowly transforming into a solid. This process is not only time-consuming (often requiring several hours or more), but its crystallization behavior is also uncontrollable: once nucleation is triggered, a large number of fine crystals or amorphous precipitates are easily generated due to excessively high local concentrations, leading to difficult filtration, significant washing losses, and some material even remaining in the mother liquor or filter residue, making recovery impossible.

[0004] To improve crystallization, some processes employ seed crystal addition or repeated heating and cooling, but these methods are cumbersome, have poor batch-to-batch reproducibility, and are difficult to adapt to continuous production requirements. More importantly, due to the lack of effective nucleation guidance, the overall yield has long hovered between 80% and 88%, affecting both raw material utilization and increasing the burden on subsequent purification. Therefore, a new method is urgently needed to promote rapid and uniform nucleation of 1,5-dihydroxynaphthalene, shorten the crystallization cycle, and improve solid-liquid separation efficiency, thereby enhancing the overall efficiency and stability of the process. Summary of the Invention

[0005] To address the problem of low production efficiency in the preparation of 1,5-dihydroxynaphthalene in existing technologies, this invention proposes a method for preparing 1,5-dihydroxynaphthalene and its applications. This invention significantly improves the efficiency by adding bentonite during the acidification process, effectively inducing nucleation of 1,5-dihydroxynaphthalene.

[0006] Bentonite is a natural layered silicate mineral with montmorillonite as its main component. Its chemical structure consists of two layers of silicon-oxygen tetrahedra sandwiching a layer of aluminum-oxygen octahedra. Its interlayer crystals carry a permanent negative charge, resulting in a large specific surface area and abundant surface hydroxyl groups. After modification with organic cations (such as hexadecyltrimethylammonium), the interlayer spacing increases, and the surface changes from hydrophilic to hydrophobic, significantly enhancing its adsorption capacity for organic molecules. In the crystallization process of 1,5-dihydroxynaphthalene, organically modified bentonite mainly plays a role in inducing heterogeneous nucleation. The Si–OH and Al–OH hydroxyl groups exposed in the bentonite interlayers can form hydrogen bonds with the phenolic hydroxyl groups in the 1,5-dihydroxynaphthalene molecule, effectively releasing sodium ions; simultaneously, its hydrophobic layers have a certain adsorption effect on the naphthalene ring. This synergistic effect causes 1,5-dihydroxynaphthalene molecules to accumulate in the bentonite interlayers and align in a certain direction, effectively reducing the free energy required for nucleation and promoting rapid and uniform crystal formation. This avoids explosive crystallization or the formation of gel-like substances, and improves crystallization efficiency, crystal regularity, and subsequent solid-liquid separation performance.

[0007] Specifically, the present invention adopts the following technical solution: a method for preparing 1,5-dihydroxynaphthalene, comprising at least the following steps:

[0008] (1) Sodium 1,5-naphthalenedisulfonate 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; generally, the specific scheme adopted in the prior art is as follows: sodium 1,5-naphthalenedisulfonate is added to molten sodium hydroxide that has been preheated to 290–300°C, the temperature is raised to 310–315°C, and the reaction is stirred 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.

[0009] (2) Add deionized water to the above reaction solution and stir to dilute it; the mass of the deionized water is 8–10 times the mass of sodium 1,5-naphthalenedisulfonate; add 50wt% sulfuric acid dropwise, and control the total amount of sulfuric acid to completely neutralize NaOH and make pH≈2.5–3.0; at this time, sodium 1,5-dihydroxynaphthalene salt is converted into free 1,5-dihydroxynaphthalene, forming a turbid suspension.

[0010] (3) Pump into the first reaction vessel, which contains pre-dispersed organic modified bentonite; control the vessel temperature to 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; under weakly acidic conditions (pH≈3), the organic modified bentonite has a stable structure; its hydrophobic interlayer domains and surface can adsorb 1,5-DHN molecules, providing heterogeneous nucleation sites through hydrogen bonds, promoting microcrystal formation and inhibiting amorphous precipitation.

[0011] Subsequently, the mixture is separated by 10–20 μm filtration. During the filtration process, the scouring effect of the water flow can effectively break the hydrogen bonds between the 1,5-dihydroxynaphthalene crystals and the hydroxyl groups in the bentonite interlayer, causing the formed crystals to desorb from the bentonite surface or interlayer and enter the liquid phase. Organically modified bentonite can be recovered in this process, and the filtrate containing 1,5-dihydroxynaphthalene crystals proceeds to the next step.

[0012] (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.

[0013] 1,5-DHN is a planar polycyclic aromatic hydrocarbon molecule. Its molecular length (major axis), i.e., the diagonal of the naphthalene ring (C1–C8 diagonal), is approximately 7.0–7.4 Å; its molecular width (minor axis), i.e., the width of the naphthalene ring (C4–C5 distance direction), is approximately 4.8–5.2 Å; and its molecular thickness (including H) is approximately 3.2–3.5 Å (van der Waals thickness). Considering tilted insertion or horizontal adsorption, the minimum required space is approximately 6–8 Å. To allow 1,5-DHN to enter the bentonite interlayer, the interlayer spacing d001 must be at least ≥8 Å. Therefore, this invention uses bentonite with an interlayer spacing of 16–20 Å to ensure sufficient insertion space for 1,5-DHN (available height ≈ d001). 001 −2×(silicon oxide layer thickness)≈d 001 −2×4.5 A˚).

[0014] Specifically, the organically modified bentonite is bentonite modified with one of cetyltrimethylammonium bromide (CTAB) or octadecylamine (ODA).

[0015]

[0016] It should be noted that modifying bentonite with organic cations such as hexadecyltrimethylammonium bromide (CTAB) and octadecylamine (ODA) to control the interlayer spacing is a well-known and conventional technique in the field, and is widely used in adsorption, catalysis and composite material preparation. Therefore, the modification method will not be described in detail in this invention.

[0017] In some embodiments of the present invention, the particle size range of the organically modified bentonite is 50–100 μm to match a 10–20 μm filtration system, achieving efficient separation and recycling. Otherwise, nano-sized bentonite will pass through the filter, leading to process failure. Furthermore, it is also necessary to prevent excessively large particles from causing excessively rapid sedimentation and uneven dispersion, affecting their uniformity as nucleation sites. Generally, the bentonite particles are obtained by spray drying and granulation after ion exchange modification of sodium-based bentonite.

[0018] In some embodiments of the present invention, in step 2, the amount of sulfuric acid used is 0.6–0.7 times the molar amount of NaOH.

[0019] In some embodiments of the present invention, the crystalline 1,5-dihydroxynaphthalene is further purified using methanol, the specific steps of which are as follows:

[0020] (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;

[0021] (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.

[0022] The advantages of this invention are: by introducing bentonite with a specific interlayer spacing, this invention effectively induces the nucleation of the target product and promotes the orderly growth of crystals. The crystallization reaction can achieve a yield of 90% in about 1 hour. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the induction principle of the present invention;

[0024] Figure 2 This is a scan of bentonite after catalysis;

[0025] Figure 3 XRD pattern of modified bentonite;

[0026] Figure 4 The HPLC chromatogram of the product of Example 1;

[0027] Figure 5 The HPLC chromatogram of the product in Example 2;

[0028] Figure 6 The HPLC chromatogram of the product in Example 3;

[0029] Figure 7 The image shows the HPLC chromatogram of the product from Example 4. Detailed Implementation

[0030] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0031] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0032] The embodiments of the present invention will be further described below with reference to several examples.

[0033] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0034] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0035] In the following examples, the CTAB-modified bentonite (CTAB-BT) used was prepared through the following steps:

[0036] (1.1) Weigh 1 kg of sodium bentonite, add 9 L of deionized water, stir at room temperature for 2 hours to prepare a 10% suspension slurry. Calculate the required amount of cetyltrimethylammonium bromide (CTAB) based on 1.2 times the cation exchange capacity (CEC) of bentonite, and dissolve it in 1 L of 50°C hot water to prepare a CTAB solution.

[0037] (1.2) Heat the bentonite slurry to 70–80°C, and slowly add CTAB solution dropwise while stirring for at least 1 hour. After the addition is complete, continue to stir and maintain the temperature at 70–80°C for 2 hours to complete the ion exchange.

[0038] (1.3) After the reaction is complete, filter the filter cake using a plate and frame filter press (filter cloth pore size ≤ 20 μm). Wash the filter cake 2-3 times with hot deionized water at 60°C until no pale yellow precipitate is formed when silver nitrate is added to the wash solution, indicating that Br⁻ has been washed away.

[0039] (1.4) The washed filter cake is re-pulverized, water is added to adjust the solid content to 25%–30%, and the mixture is passed through a 100-mesh sieve to obtain a uniform slurry. The slurry is fed into a centrifugal spray drying tower, and the inlet air temperature is controlled at 220–240°C, the outlet air temperature at 90–100°C, and the centrifugal disc speed at 10,000–12,000 rpm for granulation and drying. The dried powder is collected and passed through a 250-mesh sieve (approximately 61 μm pore size) and a 300-mesh sieve (approximately 48 μm pore size) in sequence. The particles between the two sieves are collected to obtain CTAB modified bentonite product with a particle size of 50–60 μm.

[0040] X-ray diffraction (XRD) Figure 3Analysis shows that the (001) crystal plane diffraction peak is located at 2θ ≈ 4.7°–5.2°, and the interlayer spacing d is calculated. 001 The value is 17–19 Å, indicating that CTAB has been successfully inserted into the interlaminar space and achieved effective expansion.

[0041] In the following examples, the ODA-modified bentonite (ODA-BT) used was prepared through the following steps:

[0042] (1.1) Weigh 1 kg of sodium bentonite, add 9 L of deionized water, stir at room temperature for 2 hours to prepare a homogeneous 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 bentonite; dissolve ODA in 100 L of 50°C hot water to prepare a solution.

[0043] (1.2) Heat the bentonite slurry to 75–80°C, and slowly add ODA solution dropwise while stirring for at least 1 hour. After the addition is complete, continue to keep the mixture at 75–80°C and stir for 2 hours to complete the organic modification.

[0044] (1.3) After the reaction is complete, filter the filter cake using a plate and frame filter press (filter cloth pore size ≤20 μm). Wash the filter cake 2-3 times with hot deionized water at 60°C until no precipitate is formed when silver nitrate is added to the wash solution, ensuring the removal of unreacted ODA and byproducts.

[0045] (1.4) The washed filter cake is re-pulped, and the solid content is adjusted to 25%–30%. The slurry is passed through a 100-mesh sieve to obtain a uniform slurry. The slurry is fed into a centrifugal spray drying tower, and the inlet air temperature is controlled at 230–250°C, the outlet air temperature at 95–105°C, and the centrifugal disc speed at 8,000–10,000 rpm for granulation and drying.

[0046] (1.5) Collect the dry powder and pass it through a 180-mesh sieve (approximately 80 μm in diameter) and a 230-mesh sieve (approximately 60 μm in diameter) in sequence. Take the material between the two sieves to obtain ODA-modified bentonite products with a particle size of 60–80 μm.

[0047] Store in a sealed container in a dry place.

[0048] Sampling for characterization: XRD analysis showed that the (001) diffraction peak was located at 2θ ≈ 4.4°–4.9°. Figure 3 ), calculate the interlayer spacing d 001 The value is 18–20 Å, indicating that ODA has been effectively inserted into the interlayer and achieved sufficient expansion.

[0049] Example 1

[0050] (1) Add 5.4 g of sodium 1,5-naphthalenedisulfonate to molten sodium hydroxide preheated to 290–300 °C, raise the temperature to 310–315 °C, and stir 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 0.6:1.

[0051] (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 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.

[0052] (3) Pump into the first reaction vessel, which contains pre-dispersed CTAB-BT; control the vessel temperature at 100℃ 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;

[0053] 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.

[0054] (4) 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 2.34g of 1,5-dihydroxynaphthalene crystals by filtration or centrifugation.

[0055] Therefore, the total time from nucleation to crystallization is 50 minutes, and the actual yield reaches 90%.

[0056] (5) Refining with methanol, the specific steps are as follows:

[0057] 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.

[0058] (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.

[0059] The HPLC chromatogram of the product is as follows Figure 4As shown in the HPLC chromatogram (detection wavelength 254 nm), a sharp, symmetrical, and predominantly large peak appears at approximately 5.979 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 1,5-dihydroxynaphthalene. Other impurity peaks in the chromatogram (such as those at 12.2 min and 14.8 min) have extremely small peak areas, indicating a purity of 99.6%.

[0060] To verify whether 1,5-dihydroxynaphthalene crystals successfully formed in the interlayer of the unfiltered CTAB-BT in the first reaction vessel, we further analyzed the unfiltered CTAB-BT from step 3. After 20 minutes of stirring, the sample was observed using a scanning electron microscope (SEM) (e.g., Figure 1 As shown in the image, the SEM image clearly shows that there are many fine particles attached to the surface of CTAB-BT. The presence of these particles strongly suggests the successful formation of 1,5-dihydroxynaphthalene crystals, confirming the effective nucleation of 1,5-dihydroxynaphthalene in the bentonite layers.

[0061] Example 2

[0062] (1) Add 5.4 g of sodium 1,5-naphthalenedisulfonate to molten sodium hydroxide preheated to 290–300 °C, raise the temperature to 310–315 °C, and stir 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 0.8:1.

[0063] (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;

[0064] (4) Pump into the first reaction vessel, which contains pre-dispersed ODA-BT; control the vessel temperature at 80°C and stir for 30 minutes to form 1,5-dihydroxynaphthalene crystals between the bentonite layers; wherein, the amount of ODA-BT is 10% of the mass of sodium 1,5-naphthalenedisulfonate;

[0065] Subsequently, the mixture was filtered through a 20μm filter screen to separate the organically modified bentonite, and the filtrate containing 1,5-dihydroxynaphthalene crystals proceeded to the next step.

[0066] (5) Pump the filtrate into the second reaction vessel and slowly cool it to 40°C at a rate of 1°C / min, maintaining the temperature for 40 minutes; collect 2.31 g of 1,5-dihydroxynaphthalene crystals by filtration or centrifugation. The HPLC chromatogram of the product is shown below. Figure 5As shown in the HPLC chromatogram (detection wavelength 254 nm), a sharp, symmetrical, and predominantly large peak appears at approximately 6.053 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 with a purity of 99.1%.

[0067] In this embodiment, the total time from nucleation to crystallization is 70 minutes, and the actual yield reaches 89%.

[0068] Example 3

[0069] (1) Add 5.4 g of sodium 1,5-naphthalenedisulfonate to molten sodium hydroxide preheated to 290–300 °C, raise the temperature to 310–315 °C, and stir 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 0.6:1.

[0070] (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 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.

[0071] (3) Pump into the first reaction vessel, which contains pre-dispersed CTAB-BT; control the vessel temperature at 90°C and stir for 20 minutes to form 1,5-dihydroxynaphthalene crystals between the bentonite layers; wherein, the amount of CTAB-BT is 7% of the mass of sodium 1,5-naphthalenedisulfonate;

[0072] 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.

[0073] (4) Pump the filtrate into the second reaction vessel and slowly reduce the temperature to 40°C at a rate of 2°C / min. Keep the temperature for 40 minutes. Collect 2.30g of 1,5-dihydroxynaphthalene crystals by filtration or centrifugation.

[0074] Therefore, the total time from nucleation to crystallization is 60 minutes, and the actual yield reaches 89%.

[0075] (5) Refining with methanol, the specific steps are as follows:

[0076] 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.

[0077] (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.

[0078] The HPLC chromatogram of the product is as follows Figure 6 As shown in the HPLC chromatogram (detection wavelength 254 nm), a sharp, symmetrical, and predominantly large peak appears at approximately 6.259 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. Furthermore, the peak areas of other impurities in the chromatogram are extremely small, indicating high product purity of 99.1%.

[0079] Example 4

[0080] (1) Add 5.4 g of sodium 1,5-naphthalenedisulfonate to molten sodium hydroxide preheated to 290–300 °C, raise the temperature to 310–315 °C, and stir 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 0.8:1.

[0081] (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;

[0082] (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.

[0083] (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.

[0084] Therefore, the total time from nucleation to crystallization was 60 minutes, and the actual yield reached 87.8%.

[0085] (5) Refining with methanol, the specific steps are as follows:

[0086] 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.

[0087] (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.

[0088] 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%.

[0089] Comparative Example 1: Preparation of 1,5-dihydroxynaphthalene without bentonite

[0090] (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.

[0091] (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;

[0092] (3) Pump into the first reaction vessel, control the vessel temperature at 100℃, and stir for 20 minutes;

[0093] (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.

[0094] 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.

[0095] Comparative Example 2: Preparation of 1,5-dihydroxynaphthalene induced by unmodified bentonite

[0096] (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.

[0097] (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;

[0098] (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;

[0099] 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.

[0100] (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%.

[0101] 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.

[0102] Preparation of 1,5-dihydroxynaphthalene induced by bentonite with large interlayer spacing (Comparative Example 3)

[0103] 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.

[0104] (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.

[0105] (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;

[0106] (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;

[0107] 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.

[0108] (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%.

[0109] 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 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. The interlayer spacing of the organically modified bentonite is 16–20 Å; the organically modified bentonite is bentonite modified with one of cetyltrimethylammonium bromide (CTAB) or octadecylamine (ODA).

2. The preparation method according to claim 1, characterized in that, The particle size range of the organically modified bentonite is 50–100 μm.

3. The preparation method according to claim 1, characterized in that, The organically modified bentonite is obtained by ion-exchange modification of sodium-based bentonite followed by spray drying and granulation.

4. 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.

5. 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.

6. 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.

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