1,6-dihydroxynaphthalene, a process for its preparation and use thereof

Abstract

This invention discloses a method for preparing 1,6-dihydroxynaphthalene and its applications. Addressing the problems of low product purity, low yield, and wide crystal size distribution in existing technologies, this invention utilizes the spatial confinement and shape-selective effect of the MCM-41 mesoporous molecular sieve membrane to construct a coupled process of "confined nucleation within the membrane—controlled growth outside the membrane." In this method, an acidified 1,6-dihydroxynaphthalene solution is passed through an MCM-41 membrane. Utilizing the matching relationship between the pore size and the solute molecule size, molecules are forced to pre-order within the pores, lowering the nucleation energy barrier and preferentially forming highly uniform nanocrystal nuclei, while simultaneously blocking isomers and large molecular impurities. The outflowing nanocrystal seeds serve as epitaxial growth nuclei, guiding the subsequent crystallization process. This invention achieves molecular-level purification from the nucleation source, significantly shortens the induction period, and greatly improves product purity (>99.3%).

Description

Technical Field

[0001] This invention belongs to the field of synthesis and purification of fine organic chemicals, specifically relating to a method for preparing 1,6-dihydroxynaphthalene with high yield and high selectivity by using sodium 1,6-naphthalenedisulfonate as a raw material, followed by alkali fusion and acidification, and then inducing crystallization using an MCM-41 mesoporous molecular sieve membrane with regular nanopores. The resulting product has significantly higher purity than traditional processes, making it particularly suitable for the synthesis of high-end dyes, organic optoelectronic materials, and pharmaceutical intermediates where stringent purity requirements for raw materials are necessary. Background Technology

[0002] 1,6-Dihydroxynaphthalene, an important aromatic diphenol compound, is a key structural unit in the synthesis of many high-performance chemicals. In the textile industry, it is an indispensable intermediate in the preparation of certain blue and black acidic mordant dyes. These dyes are widely used for dyeing high-grade protein fibers such as wool and silk due to their excellent wet fastness and color richness. Furthermore, its rigid planar conjugated structure and two reactive phenolic hydroxyl groups give it great potential in the field of functional materials, serving as a core framework for constructing liquid crystal molecules, organic semiconductor polymers, and certain pharmaceutical active molecules.

[0003] The mainstream industrial route for large-scale production of 1,6-dihydroxynaphthalene is the alkaline fusion hydrolysis method using sodium 1,6-naphthalenedisulfonate. This process typically involves mixing sodium 1,6-naphthalenedisulfonate with excess solid sodium hydroxide and carrying out a melt reaction at high temperature (approximately 300-350°C under normal or pressurized conditions), causing the sulfonic acid groups to be replaced by hydroxyl groups to generate disodium salt of 1,6-dihydroxynaphthalene. The crude product is then obtained by acidification with sulfuric acid. Although this route is direct, it has long been plagued by several thorny problems in actual production, severely restricting product quality and production efficiency.

[0004] The primary problem is the difficulty in separating positional isomer impurities. Under harsh reaction conditions of high temperature and strong alkali, the hydrolysis and substitution reaction of the sulfonic acid group does not occur exclusively at the 1,6 position. Inevitably, a certain proportion of isomers such as 1,5-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, and 2,7-dihydroxynaphthalene are generated. These isomers are extremely similar to the target product in molecular weight, polarity, and especially in solubility behavior in common solvents (such as water and alcohols). During subsequent acidification crystallization, they readily co-crystallize with the 1,6-isomer, forming mixed crystals or solid solutions. Common methods such as cooling crystallization and solvent recrystallization have extremely low separation efficiency. To obtain a product with a purity higher than 98.5%, up to four to six repeated recrystallization operations are often required. This not only leads to an exceptionally lengthy process and a dramatic increase in solvent consumption, but also suppresses the final product yield to a low level of 70-80%, resulting in the loss of a large amount of material during repeated purification cycles and high production costs.

[0005] Secondly, the reaction system is complex and contains various impurities. The alkaline fusion reaction medium contains high concentrations of inorganic salts, such as the reaction byproduct sodium sulfite, unreacted sodium hydroxide, and sodium sulfate generated after acidification. These inorganic salts may be mixed in with organic products in microcrystalline form or encapsulated within rapidly growing crystals, making them difficult to remove completely by simple washing. Furthermore, in a high-temperature alkaline environment, raw materials or intermediates may undergo trace amounts of oxidation, condensation, and other side reactions, generating quinone-based colored impurities or oligomers. These organic impurities, along with trace amounts of metal ions that may be introduced from raw materials or equipment, not only affect the appearance of the product (causing it to turn grayish or yellowish) but also adversely affect its subsequent applications. For example, in the synthesis of high-purity dyes, these impurities may interfere with the localization selectivity of the coupling reaction, reducing the dye's color and intensity; in the preparation of optoelectronic materials, they may become charge traps or lattice defect centers, impairing the material's carrier mobility and device stability.

[0006] To address these issues, those skilled in the art have made various attempts. For example, optimizing the temperature curve of the alkali fusion reaction, the excess ratio of sodium hydroxide, and the stirring intensity has been attempted to improve the selectivity of the main reaction, but with limited success, failing to fundamentally eliminate the formation of isomers. Some studies have employed column chromatography (such as silica gel columns or alumina columns) for laboratory-scale purification. While high-purity samples can be obtained, the process is cumbersome, requires large amounts of solvent, and has extremely low processing capacity, making it completely uneconomical for industrial scale-up. Other technical solutions attempt to add seed crystals or specific surfactants during the crystallization stage to control crystal morphology, but this primarily improves physical properties and has negligible effect on intrinsic separation based on molecular structure (such as distinguishing between 1,6- and 1,5- isomers).

[0007] Therefore, there is an urgent need to develop an innovative process technology that can achieve efficient separation at the molecular level, particularly selectively promoting the crystallization of the target 1,6-isomer while inhibiting or eliminating the co-extrusion of other isomers and impurities. This would allow for the direct acquisition of ultra-high purity 1,6-dihydroxynaphthalene products while simplifying the process and increasing yield. This invention aims to overcome this technological bottleneck. Summary of the Invention

[0008] To address the problems of low product purity, lengthy traditional recrystallization purification process, large yield loss, and difficulty in obtaining crystals with uniform particle size in existing technologies, this invention provides a novel approach and method for preparing 1,6-dihydroxynaphthalene.

[0009] The core of this invention lies in the creative integration of the nano-confinement effect of mesoporous molecular sieve membranes with the solution crystallization process. This invention does not treat the MCM-41 membrane as a simple filtration medium, but rather designs it as a "nanoscale structured reaction field" and a "molecular sieve," inducing nucleation in the initial stage of crystallization and the nucleation process, thereby achieving confined directional nucleation within the membrane and homogeneous epitaxial growth outside the membrane.

[0010] This invention provides a method for preparing high-purity 1,6-dihydroxynaphthalene, comprising the following steps: Step (1): Alkali fusion reaction Sodium 1,6-naphthalenedisulfonate, sodium hydroxide, and water were added to a high-pressure reactor at a mass ratio of 1:(1.8-2):(1.2-2) and thoroughly mixed. The reaction was carried out at 300°C to 320°C for 2 to 2.5 hours. Under these conditions, the sulfonic acid groups of sodium 1,6-naphthalenedisulfonate were quantitatively substituted with hydroxyl groups, converting it into the disodium salt of 1,6-dihydroxynaphthalene. This step employed a specific material ratio to ensure sufficient alkalinity to drive the reaction to completion, while controlling the water content to maintain suitable viscosity and mass transfer efficiency of the reaction system.

[0011] Step (2): Acidification precipitation After the reaction was complete, the system was cooled to 80°C. While stirring, concentrated sulfuric acid was slowly added for acidification, precisely adjusting the pH to a weakly acidic range of 2-3. At this point, sodium 1,6-dihydroxynaphthalene salt was converted into free 1,6-dihydroxynaphthalene molecules. Due to the low solubility of the free product in acidic aqueous solution, the system rapidly changed from a homogeneous state to a supersaturated state, forming a fine suspension or emulsion, providing the thermodynamic driving force for subsequent crystallization.

[0012] Step (3): Membrane-induced restricted nucleation (the key and essence of this invention) The suspension obtained in step (2) was further cooled and kept constant at approximately 80°C. This temperature was chosen to balance molecular diffusion rate, membrane material stability, and supersaturation control for subsequent crystallization. The supersaturated solution was then passed through a device equipped with an MCM-41 mesoporous molecular sieve membrane. The MCM-41 membrane has a highly ordered one-dimensional hexagonal pore structure with uniform pore size, preferably 2-3 nanometers.

[0013] This step preferably controls the transmembrane pressure differential within a low range of 0.1 to 0.3 bar. This moderate pressure ensures continuous solution permeation while preventing membrane pore deformation or forced penetration of impurities caused by high pressure.

[0014] During this process, a series of synergistic physicochemical effects occurred: 1. Spatial Confinement and Molecular Pre-assembly: 1,6-Dihydroxynaphthalene is a planar aromatic molecule. Its dimensions (estimated molecular planar projection length approximately 0.74 nm, width approximately 0.40 nm, and thickness approximately 0.35 nm) form a "loosely confined" relationship with the pore diameter of MCM-41 (2-3 nm). When the molecule flows into the nanopores with the solution, its translational and rotational degrees of freedom are physically constrained by the pore walls. More importantly, strong hydrogen bonds can form between the phenolic hydroxyl groups (-OH) at both ends of the molecule and the abundant silanol groups (Si-OH) on the inner walls of the pores. This specific interaction acts like a "molecular lock," driving the 1,6-dihydroxynaphthalene molecule to adopt an energy-optimal arrangement: its molecular plane (naphthalene ring plane) is parallel to the radial direction of the pores and "attached" to the pore walls. This highly ordered monolayer or multilayer molecular arrangement pre-formed in the nanospace greatly reduces the conformational entropy change that needs to be overcome during subsequent molecular aggregation, laying the foundation for homogenized nucleation.

[0015] 2. Reduced nucleation energy barrier and generation of uniform crystal nuclei: Within the confined space of the pores, the local concentration of pre-ordered molecules is significantly higher than in the bulk solution, and the π-π stacking interaction between molecules is effectively enhanced at a fixed orientation. This dual effect of "concentration enrichment" and "fixed orientation" works synergistically to significantly reduce the critical Gibbs free energy required to form stable crystal nuclei. Therefore, compared with the random and difficult homogeneous nucleation in the bulk solution, the nucleation process can occur more easily and in greater quantities at a lower supersaturation level within the MCM-41 pores, generating nanocrystalline nuclei with highly uniform size, structure, and orientation.

[0016] Step (4): Controlled epitaxial growth and product collection Collect the solution rich in uniform nanocrystal nuclei flowing from the permeate side of the MCM-41 membrane. Transfer this solution to a crystallization vessel, stop heating, and allow it to cool slowly to room temperature (approximately 20-25°C) under gentle stirring. During the cooling process, the overall supersaturation of the solution gradually increases. At this point, the numerous highly uniform nanocrystal nuclei already present in the solution, originating from the membrane process, become the sole dominant growth centers. Solute molecules use these nuclei as templates for epitaxial growth. Due to the high uniformity of the nuclei themselves, the resulting macroscopic crystals exhibit excellent particle size distribution and complete crystal form. After complete crystal precipitation, the crystals are filtered, washed with a small amount of low-temperature deionized water to remove trace amounts of mother liquor and inorganic salts adhering to the surface, and finally vacuum dried at a suitable temperature (e.g., 50-60°C) to obtain a high-purity 1,6-dihydroxynaphthalene product.

[0017] As a further optimization of the present invention, for applications requiring extremely high purity (such as semiconductor material precursors), a refining step can be added after the above crystallization step: the crude product is dissolved in methanol, a small amount of activated carbon and antioxidant (such as antioxidant 1010) are added for decolorization and stabilization treatment, and after hot filtration, an antisolvent (such as water) is added to the filtrate for secondary crystallization, which can further improve the purity to over 99.9%.

[0018] The present invention also provides a high-purity 1,6-dihydroxynaphthalene product prepared by the above method, and the application of the product in the preparation of high-performance acid dyes, organic optoelectronic materials and pharmaceutical intermediates.

[0019] Compared with the prior art, the present invention has the following significant advantages: 1. Revolutionary improvement in purity: Through the shape-selective sieving and induced nucleation of the MCM-41 membrane, most isomers and macromolecular impurities are eliminated at the source, so that the purity of the product after one crystallization can be stably reached above 99.3%, and can reach up to 99.8%, which is far superior to the purity level that traditional processes require multiple recrystallizations to achieve.

[0020] 2. Significantly improved yield: Membrane-induced nucleation significantly lowers the nucleation energy barrier, shortens the induction period, and makes the crystallization process more complete, reducing the amount of product residue in the mother liquor. The overall yield can be consistently above 90%, which is a significant improvement over the traditional process (70-80%).

[0021] 3. Excellent crystal quality: Based on the epitaxial growth of uniform nanocrystal seeds, the resulting product has a narrow crystal size distribution, complete crystal shape, and good fluidity, which is beneficial for subsequent processing and use.

[0022] 4. Simplified process flow: It eliminates the repeated recrystallization and related dissolution, filtration and drying unit operations in the traditional process, which greatly shortens the production cycle and reduces energy consumption and solvent consumption.

[0023] 5. Easy to scale up and operate continuously: The membrane crystallization unit is easy to design and integrate in a modular manner, which lays the foundation for the continuous and automated production of this process in the future and has good prospects for industrial application. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the system structure described in this invention.

[0025] Figure 2 The image shows the small-angle XRD pattern of the MCM-41 molecular sieve membrane used in this invention, with the horizontal axis representing 2θ and the vertical axis representing intensity.

[0026] Figure 3 This is a schematic diagram of the structure of the MCM-41 molecular sieve membrane assembly 3 in the system described in this invention.

[0027] Figure 4 The high-performance liquid chromatography (HPLC) chromatogram of the product obtained in Example 1 shows that the purity corresponding to the percentage of the main peak area is 99.34%.

[0028] Figure 5 The image shows the HPLC chromatogram of the crude product obtained after membrane crystallization in Example 2, with a purity of 99.37%.

[0029] Figure 6 The image shows the HPLC chromatogram of the product obtained in Example 3, with a purity of 99.35%.

[0030] Figure 7 The image shows the HPLC chromatogram of the product obtained in Example 4, with a purity of 99.79%.

[0031] Figure 8 The image shows the HPLC chromatogram of the product obtained in Example 5, with a purity of 99.36%. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments and comparative experiments. These embodiments are used to illustrate the technical solutions and effects of the present invention more specifically, and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, the reagents, raw materials and equipment used in the present invention are all commercially available.

[0033] The preparation of MCM-41 membranes generally employs a combination of the sol-gel method and evaporation-induced self-assembly (EISA) technology. Specifically, MCM-41 membranes are prepared on the surface of porous alumina (α-Al₂O₃) supports. The core process involves using a surfactant (template) to form micelles in the sol (the alkyl chain (C16) length of hexadecyltrimethylammonium bromide (CTAB) determines the size of the resulting micelle core; after hydrolysis, polycondensation, and calcination, the theoretical pore size of the resulting silica channels is approximately 2.5-3.0 nm). During the drying process after coating, as the solvent evaporates, the micelles co-assemble with the inorganic silicon source, forming an ordered liquid crystal phase structure on the support surface. Finally, the template agent is removed by high-temperature calcination, leaving a mesoporous silica membrane with a regular hexagonal channel structure. Specific preparation steps can be found in the following existing techniques: Step 1: Synthesize MCM-41 coating sol Dissolve 2.0 g of CTAB (template agent) in a mixture of 90 g of deionized water and 40 g of anhydrous ethanol, and stir vigorously in a 35°C water bath until a clear solution is formed. While stirring vigorously, slowly add 8.5 g of TEOS dropwise (approximately 1 drop / second) to the above solution.

[0034] After the addition was complete, the pH of the mixture was adjusted to approximately 2.0 using 0.1 M HCl or dilute ammonia (acidic conditions are beneficial for forming a denser film with fewer defects). The mixture was stirred continuously at 35°C for 24 hours to obtain a uniform, slightly opalescent, and stable MCM-41 precursor sol.

[0035] Step 2: Carrier surface pretreatment and coating The cleaned and dried α-Al₂O₃ support was preheated at 500°C for 1 hour to remove physically adsorbed water and enhance the activity of surface hydroxyl groups, which facilitates sol adhesion. The support was then vertically immersed in the sol for 60 seconds to ensure it was fully wetted. The support was then smoothly and vertically lifted out of the liquid surface at a constant speed (generally 2-4 cm / min).

[0036] Step 3: Drying and Self-Assembly Immediately after stretching, the wet film was placed in a sealed container with a small cup of ethanol inside to maintain a certain vapor pressure. It was then allowed to age at room temperature for 24-48 hours. During this process, the ethanol and water slowly evaporated, inducing micelles and silicon species to undergo highly ordered self-assembly on the carrier surface, forming a preliminary mesoscopic structure.

[0037] Step 4: Template agent removal and film curing The aged membrane was placed in a muffle furnace and calcined by programmed temperature increase to completely remove the CTAB template agent, resulting in an MCM-41 mesoporous molecular sieve membrane loaded on an α-Al2O3 support.

[0038] The orderliness of the mesoscopic structure was verified by small-angle X-ray diffraction (SA-XRD). Figure 2 As shown, the characteristic peaks of the (100) crystal plane of MCM-41 are sharp, indicating that the channel arrangement is highly ordered.

[0039] The purification method of the present invention is carried out in a membrane filtration system, which includes a constant temperature feed unit for containing and transporting materials, an MCM-41 molecular sieve membrane module for realizing molecular sieving and induced crystallization, a driving fluid transport unit, and a collection unit for collecting the purified permeate.

[0040] like Figure 1 The circulating membrane filtration system used in this embodiment mainly includes a constant-temperature feed tank 1, a circulating pump 2, an MCM-41 molecular sieve membrane module 3, a permeate collection tank 5, and connecting pipes 4. The outlet of the constant-temperature feed tank 1 is connected in sequence to the circulating pump 2 and the feed-side inlet of the MCM-41 molecular sieve membrane module 3 via pipes 4; the permeate-side outlet of the membrane module 3 is connected to the permeate collection tank 5 via pipes.

[0041] The MCM-41 molecular sieve membrane module 3 is a tubular ceramic membrane module, wherein the MCM-41 molecular sieve membrane layer is coated on the inner surface of a porous α-Al2O3 ceramic tube by a sol-gel method, and the pore size of the membrane is approximately 2.5 nm.

[0042] The circulating pump 2 is a diaphragm pump or a peristaltic pump. Its selection must meet the requirements of low shear force and small pulsation in order to avoid damaging the nanocrystal nuclei in the solution to be purified.

[0043] The constant temperature liquid tank 1 is equipped with a jacket, and the temperature of the material in the tank is maintained at 80℃ ± 2℃ by an external circulating water bath.

[0044] During operation, the suspension from the acidification step is injected into the constant-temperature feed tank 1 and kept at a constant temperature of 80°C. The circulation pump 2 is started, and the feed solution flows through the MCM-41 molecular sieve membrane module 3 (…). Figure 3 When the transmembrane pressure difference is driven, the solvent, 1,6-dihydroxynaphthalene monomer, and nanocrystal nuclei oriented within the membrane pores permeate through the membrane into the permeate collection tank 5.

[0045] Example 1 (1) In a high-pressure reactor with stirring, add 100g of sodium 1,6-naphthalenedisulfonate, 180g of sodium hydroxide and 120g of deionized water, and stir to mix the materials evenly.

[0046] (2) In a sealed reactor, the internal temperature is raised to 300°C by programmed heating. The reaction is stirred at this temperature for 2.5 hours to complete the alkali melting process.

[0047] (3) After the reaction is complete, the system is cooled to 80°C using a jacket cooling system. While stirring, 50 wt% sulfuric acid aqueous solution is slowly added dropwise until the pH of the reaction mixture stabilizes at around 2.5. At this point, the system becomes a grayish-white suspension.

[0048] (4) Pump the suspension into the constant temperature feed tank 1 and maintain it at 80°C. Start the circulation pump 2 and control the transmembrane pressure difference to 0.2 bar to induce crystallization.

[0049] (5) Collect the permeate through the permeate collection tank 5, transfer it to a clean crystallization vessel, stop heating, and let it cool naturally overnight to room temperature (about 25°C) with slow stirring.

[0050] (6) Collect the precipitated white crystals by vacuum filtration, rinse the filter cake twice with a small amount of cold water at 5°C, and then place the filter cake in a vacuum drying oven and dry it at 55°C for 6 hours.

[0051] (7) Weigh the product to obtain 43.5 grams of dried product. Perform HPLC analysis on a sample; the results are as follows: Figure 4As shown, the purity of 1,6-dihydroxynaphthalene is 99.34% calculated using the area normalization method. Based on the amount of sodium 1,6-naphthalenedisulfonate fed, the yield in this step exceeds 90%.

[0052] Example 2 (1) The reaction steps are the same as in Example 1. The amount of materials added is: 100g of sodium 1,6-naphthalenedisulfonate, 200g of sodium hydroxide, 200g of water, reaction temperature 320℃, and reaction time 2 hours.

[0053] (2) The acidification and membrane-induced crystallization steps are the same as in Example 1.

[0054] (3) After crystallization, filtration, washing, and drying, 44 grams of product were obtained with an HPLC purity of 99.37%. Figure 5 ).

[0055] (4) To further improve purity, refining is performed: The crude product and methanol are mixed at a mass ratio of 1:2.4, and then 1% by mass of powdered activated carbon and an equal mass of antioxidant 1010 are added. The temperature is raised to 65°C and stirred for 30 minutes. The activated carbon is removed by filtration while hot.

[0056] (5) Slowly add the clarified filtrate to 5 times its volume of deionized water while stirring. Fine crystals will precipitate during this process. Then cool the system to 25°C, continue stirring for 1 hour, and then filter.

[0057] (6) Collect refined wet products, dry them to obtain the final product, and the purity is increased to over 99.9% by HPLC detection.

[0058] Example 3 The effects of different material ratios were investigated.

[0059] (1) Feeding: 100 g of sodium 1,6-naphthalenedisulfonate, 200 g of sodium hydroxide, and 200 g of water. Other reaction and acidification conditions are the same as in Example 1.

[0060] (2) Membrane-induced crystallization (80°C, pressure difference 0.2 bar) and post-treatment are the same as in Example 1.

[0061] (3) The product was obtained with an HPLC purity of 99.35% ( Figure 6 The yield was similar to that of Example 1. This indicates that the reaction proceeded effectively within the stated ratio range.

[0062] Example 4 (1) The feeding and acidification conditions are the same as in Example 1; the reaction temperature is 310℃ and the time is 2.5 hours.

[0063] (2) The acidified suspension at 70°C was subjected to transmembrane induced crystallization, while other conditions remained unchanged.

[0064] (3) After treatment, crystallization is performed to obtain the product. HPLC analysis ( Figure 7 The purity is shown to be 99.79%.

[0065] Example 5 (1) In a high-pressure reactor with stirring, add 400g of sodium 1,6-naphthalenedisulfonate, 800g of sodium hydroxide and 600g of deionized water, and stir to mix the materials evenly.

[0066] (2) In a sealed reactor, the internal temperature is raised to 300°C by programmed heating. The reaction is stirred at this temperature for 2.5 hours to complete the alkali melting process.

[0067] (3) After the reaction is complete, the system is cooled to 80°C using a jacket cooling system. While stirring, a 50% sulfuric acid aqueous solution is slowly added dropwise until the pH of the reaction mixture stabilizes at around 2.5. At this point, the system becomes a grayish-white suspension.

[0068] (4) Pump the suspension into the constant temperature feed tank 1 and maintain the temperature. Start the circulation pump 2 and control the transmembrane pressure difference to 0.1 bar to induce crystallization.

[0069] (5) Collect the permeate, transfer it to a clean crystallization vessel, stop heating, and let it cool naturally overnight to room temperature (about 25°C) with slow stirring.

[0070] (6) Collect the precipitated white crystals by vacuum filtration, rinse the filter cake twice with a small amount of cold water at 5°C, and then place the filter cake in a vacuum drying oven and dry it at 55°C for 6 hours.

[0071] (7) The product was obtained with an HPLC purity of 99.36% ( Figure 8 ).

[0072] Comparative Example 1 (No membrane induction, conventional crystallization) (1) The feeding and reaction conditions are the same as in Example 1.

[0073] (2) After acidification, without any membrane treatment, the suspension at 50°C is directly cooled to room temperature for crystallization.

[0074] (3) The product is obtained after filtration, washing and drying.

[0075] Results Analysis: The obtained product had a slightly grayish appearance, an HPLC purity of only about 94.2%, and a yield of approximately 78%. Obvious peaks of the 1,5- and 1,7-dihydroxynaphthalene isomers were detected in the product. This indicates that without membrane-induced selective nucleation and purification, the target product and impurities will co-precipitate, leading to low purity and a large amount of product remaining in the mother liquor with high impurity content, thus impairing the yield. To achieve a purity of over 99%, at least 3-4 subsequent recrystallizations are required, and the overall yield will drop below 65%.

[0076] The success of this invention's "confined nucleation within the membrane—controllable growth outside the membrane" process stems from the precise control of molecular behavior in the early stages of crystallization. The regularized channels of the MCM-41 membrane not only act as a sieve but also as a "nanotemplate" and an "energy barrier lowerer." It forces molecules to pre-order through spatial confinement and stabilizes specific orientations through surface hydrogen bonding; these two factors synergistically significantly reduce the kinetic barriers to nucleation. In dynamic cycles, this "template-based nucleation" and "size sieving" are continuously repeated and reinforced, thereby achieving high-purity, high-yield, and uniform crystallization results on a macroscopic scale.

[0077] This process cleverly avoids the predicament of traditional methods that rely on minute differences in solubility for separation. Instead, it utilizes differences in molecular size, shape, and their interaction with nanopores to achieve a more fundamental and efficient separation. It not only provides a superior new route for the preparation of 1,6-dihydroxynaphthalene, but its "membrane-induced crystallization" concept also offers valuable reference for the preparation of other high-value-added, difficult-to-separate organic isomers or high-purity crystals.

[0078] The above embodiments detail the technical solution, implementation process, and beneficial effects of the present invention. It should be understood that those skilled in the art can make changes, modifications, and adjustments to these embodiments without departing from the principles and spirit of the present invention. All such changes, modifications, and adjustments should fall within the protection scope of the present invention as defined by the appended claims.

Claims

1. A method for preparing 1,6-dihydroxynaphthalene, characterized in that, It includes the following steps: (1) Sodium 1,6-naphthalenedisulfonate, sodium hydroxide and water are mixed evenly and reacted to produce sodium 1,6-dihydroxynaphthalene salt; (2) After cooling to 80℃, add sulfuric acid to acidify to pH = 2-3; (3) Inducing nucleation of the product obtained in step (2); (4) The mixture was then cooled to room temperature to crystallize 1,6-dihydroxynaphthalene. The solid product was collected to obtain 1,6-dihydroxynaphthalene.

2. The method according to claim 1, characterized in that, The method used in step (3) to induce the nucleation of the product obtained in step (2) is as follows: the product obtained in step (2) is passed through an MCM-41 molecular sieve membrane, so that the 1,6-dihydroxynaphthalene molecular plane is arranged parallel to the pore axis.

3. The method according to claim 2, characterized in that, The product obtained in step (2) flows through the MCM-41 molecular sieve membrane under the drive of the circulating pump.

4. The method according to claim 1, characterized in that, The mass ratio of sodium 1,6-naphthalenedisulfonate, sodium hydroxide, and water is 1 : (1.8-2) : (1.2-2).

5. The method according to claim 1, characterized in that, The reaction temperature in step (1) is 300-320℃; the reaction time is 2-2.5 hours.

6. The method according to claim 1, characterized in that, The cross-membrane pressure difference generated when passing through the MCM-41 molecular sieve membrane in step (3) is 0.1 - 0.3 bar.

7. The method according to claim 1, characterized in that, The crystalline 1,6-dihydroxynaphthalene is purified using methanol. The specific steps are as follows: (1) Take 1,6-dihydroxynaphthalene and methanol in a mass ratio of 1:2.4, 1% of activated carbon in mass of 1,6-dihydroxynaphthalene, and antioxidant 1010 in mass equal to that of activated carbon, add them to 1,6-dihydroxynaphthalene, heat to 65℃, keep warm for 15-30 min, and then heat filter at 65℃. (2) Add 5 times the volume of water to the filtrate while stirring, cool to 25°C, filter to obtain 1,6-dihydroxynaphthalene refined wet product, and dry to obtain pure 1,6-dihydroxynaphthalene.

8. A 1,6-dihydroxynaphthalene prepared by the method of claim 1.

9. An application of 1,6-dihydroxynaphthalene as described in claim 8.

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