High purity diaminodiphenylmethane and a method for purifying the same

Abstract

This invention provides a high-purity diaminodiphenylmethane and its purification method, belonging to the field of diaminodiphenylmethane purification technology. The invention involves dissolving crude diaminodiphenylmethane in an organic solvent, adding a hydrophilic liquid bridging agent, and shearing and mixing to form aggregated sodium chloride solid particles under capillary liquid bridging forces. The resulting initial clear liquid, free of solid particles, is obtained by filtration. The initial clear liquid is cooled to the nucleation temperature to precipitate a suspension containing defective crystal nuclei. This suspension is heated to a ripening temperature and stirred at a constant temperature to dissolve the defective crystal nuclei and release 2,4-diaminodiphenylmethane into the liquid mother liquor. After molecular recombination, a well-structured crystal slurry is obtained. This well-structured crystal slurry is cooled to the crystallization endpoint temperature, and high-purity diaminodiphenylmethane is obtained through solid-liquid separation and drying.

Description

Technical Field

[0001] This invention belongs to the field of diaminodiphenylmethane purification technology, specifically relating to a high-purity diaminodiphenylmethane and its purification method. Background Technology

[0002] High-purity diaminodiphenylmethane is used as a curing agent for high-performance epoxy resins, an intermediate for polyurethanes, and a monomer material for specialty polymers. Its purity directly affects the physical properties and chemical reliability of downstream products. In high-precision chemical applications, the purity of 4,4-diaminodiphenylmethane must reach an extremely high proportion, and to ensure polymer network regularity, the total content of 2,4-diaminodiphenylmethane must be controlled to an extremely low limit. To prevent electrochemical migration in circuit packaging, the chloride ion content must be strictly limited.

[0003] When treating crude diaminodiphenylmethane containing organic isomer byproducts and inorganic salt solid particles using unidirectional cooling recrystallization, extremely small inorganic salt solid particles can easily penetrate conventional filter media. This often results in the introduction of large amounts of aqueous washing processes to remove inorganic salts, leading to the generation of large amounts of wastewater containing organic amines. Furthermore, unidirectional cooling recrystallization struggles to achieve both efficient separation of organic isomer byproducts and high overall yield of the target product. Continuous unidirectional cooling causes a large amount of organic isomer byproducts to be encapsulated within the crystal lattice of the target product, necessitating multiple recrystallization operations to achieve the desired purity standard. This results in a significant loss of the target product from the liquid mother liquor during the repeated solid-liquid separation processes. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a high-purity diaminodiphenylmethane and its purification method.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for purifying high-purity diaminodiphenylmethane, comprising the following steps:

[0006] S1: Crude diaminodiphenylmethane is mixed with an organic solvent and heated to dissolve the crude diaminodiphenylmethane. A hydrophilic liquid crosslinking agent is added and sheared and mixed under stirring conditions to obtain a polymerized mixture.

[0007] S2: Filter the aggregated mixture to separate the solid phase and retain the liquid phase to obtain the initial clear liquid;

[0008] S3: Cool the initial clear liquid to the nucleation temperature at the first cooling rate, and precipitate the initial solid phase through liquid-solid phase transformation to obtain a suspension containing defective crystal nuclei;

[0009] S4: The suspension containing defective crystal nuclei is heated to the ripening temperature and stirred at a constant temperature to promote partial dissolution of the solid phase and molecular recombination, resulting in a well-structured crystal slurry.

[0010] S5: Cool the well-structured slurry to the final crystallization temperature at the second cooling rate to obtain the final crystallization mixture;

[0011] S6: Perform solid-liquid separation on the final crystallization mixture to obtain the final solid phase, and wash and dry the final solid phase to obtain high-purity diaminodiphenylmethane.

[0012] Preferably, in step S1, the organic solvent is an aromatic organic solvent whose molecular structure contains a benzene ring structure, including toluene or xylene;

[0013] Preferably, the hydrophilic liquid crosslinking agent is a polar liquid compound containing two or more hydroxyl groups in its molecular structure, and the hydrophilic liquid crosslinking agent includes glycerol, ethylene glycol, diethylene glycol or polyethylene glycol.

[0014] Preferably, in step S1, the ratio of crude diaminodiphenylmethane to organic solvent is 1g:3mL to 1g:8mL; the target heating temperature is 100℃ to 150℃; the added mass of hydrophilic liquid crosslinking agent is 0.1wt% to 0.8wt% of the mass of crude diaminodiphenylmethane; and the continuous stirring time for shear mixing is 10min to 60min.

[0015] Preferably, in step S2, filtration is carried out under the condition that the material temperature is maintained in the range of 100°C to 150°C; filtration includes introducing inert gas into the feed chamber of the filtration device to increase the internal pressure of the feed chamber to 0.1MPa to 0.5MPa to form the filtration driving pressure.

[0016] Preferably, in step S3, the first cooling rate ranges from 0.5℃ / min to 2.0℃ / min; the nucleation temperature ranges from 60℃ to 90℃.

[0017] Preferably, in step S4, the heating rate of the suspension containing defective crystal nuclei to the maturation temperature is 0.2℃ / min to 1.0℃ / min; the maturation temperature is a temperature value 5℃ to 15℃ higher than the nucleation temperature, and the range of the maturation temperature is 65℃ to 105℃; the duration of constant temperature stirring is 0.5h to 4.0h.

[0018] Preferably, in step S5, the second cooling rate ranges from 0.1℃ / min to 0.5℃ / min; and the crystallization endpoint temperature ranges from 20℃ to 40℃.

[0019] Preferably, in step S6, washing the final solid phase includes introducing a low-temperature aromatic organic solvent into the cavity of the solid-liquid separation device to uniformly spray the surface of the final solid phase. The temperature of the low-temperature aromatic organic solvent is maintained in the range of 0°C to 10°C, and the volume of the low-temperature aromatic organic solvent introduced is 0.5 to 2 times the volume of the final solid phase.

[0020] Preferably, in step S6, the drying is carried out in a closed drying chamber of a vacuum drying device. The conditions for vacuum drying include an absolute pressure of 1 kPa to 10 kPa inside the closed drying chamber, a temperature of 60°C to 100°C inside the closed drying chamber, and a holding time of 2 h to 8 h.

[0021] Another technical solution provided by the present invention is a high-purity diaminodiphenylmethane, which is prepared by the above purification method.

[0022] The high-purity diaminodiphenylmethane purification method provided by this invention, through changing the physical morphology of inorganic impurity particles and intervening in the crystallization thermodynamic evolution process of the target product, achieves a technological advancement by obtaining high-purity diaminodiphenylmethane solid that meets the requirements of extremely low impurity limits in a single purification process without generating an aqueous washing waste liquid. Specifically, it has the following beneficial effects:

[0023] After crude diaminodiphenylmethane is mixed with an organic solvent to form a liquid phase, a hydrophilic liquid bridging agent is added and shear mixing is performed under stirring conditions. Under the shear force provided by mechanical stirring, the hydrophilic liquid bridging agent is dispersed into tiny droplets. These droplets, suspended in the liquid phase, specifically wet the surface of sodium chloride solid particles, which are also hydrophilic, creating capillary liquid bridges between adjacent sodium chloride solid particles. These capillary liquid bridges cause isolated sodium chloride solid particles to aggregate, forming larger aggregate particles. This invention causes undissolved fine sodium chloride solid particles to undergo physical volume expansion, generating aggregate particles that cannot penetrate the microporous structure of the filter medium and are thus trapped on the feed side surface of the filter medium. Compared to the prior art, which relies on introducing a large amount of aqueous phase to wash and dissolve sodium chloride solid particles, generating massive amounts of wastewater, this invention achieves the physical interception and stripping of sodium chloride solid particles without introducing an external aqueous phase system, resulting in a significant improvement in environmental friendliness.

[0024] This invention employs a method of heating a suspension containing defective crystal nuclei to a ripening temperature while maintaining constant temperature stirring. The temperature increase of the suspension to the ripening temperature induces a slightly unsaturated state in both the solid and liquid phases, promoting the preferential dissolution of primary solid crystal nuclei with high surface energy, lattice defects, and embedded 2,4-diaminodiphenylmethane molecules. During dissolution, the embedded 2,4-diaminodiphenylmethane molecules are released into the liquid mother liquor. Simultaneously, 4,4-diaminodiphenylmethane molecules dissolved in the liquid mother liquor migrate to and orderly adhere to the surface of the more structurally complete primary solid crystal nuclei, healing the lattice defects. This invention causes the dissolution and molecular recombination of primary solid crystal nuclei, eliminating the 2,4-diaminodiphenylmethane molecules embedded within the solid particles and directly generating a well-structured crystal slurry. Compared to the prior art, where continuous unidirectional cooling leads to the mechanical encapsulation of 2,4-diaminodiphenylmethane molecules and requires multiple recrystallizations resulting in significant loss of the target product, this invention eliminates the organic isomer encapsulation defect through a single warming and ripening process. This technological advancement achieves a more stable overall yield with higher purification while avoiding repeated recrystallization operations.

[0025] This invention integrates the shearing and mixing of a hydrophilic liquid bridging agent to obtain a coalesced mixture, and the heating of a suspension containing defective crystal nuclei to a ripening temperature while maintaining constant temperature stirring. The coalesced mixture is filtered to completely intercept the coalesced particles, ensuring that the initial clear liquid delivered to the crystallization stage no longer contains suspended sodium chloride solid particles. This particle-free initial clear liquid provides a uniform thermodynamic environment for the molecular recombination process when the suspension containing defective crystal nuclei is heated to the ripening temperature, eliminating the physical interference of sodium chloride solid particles as heterogeneous nucleation sites, which could induce uncontrolled crystal growth and secondary encapsulation of impurities. Simultaneously, the dense solid-phase crystal particles formed during subsequent cooling of the well-structured crystal slurry are less likely to trap trace amounts of chloride ions in the liquid mother liquor on their outer surface and within their pores. The interaction between the aggregation interception induced by the hydrophilic liquid bridging agent and the ripening and recombination in a slightly unsaturated state produces a combined effect that ensures that the final high-purity diaminodiphenylmethane solid achieves extremely low levels of both organic isomer content and inorganic chloride ion residue, which is beyond the simple superposition of the effects achieved by desalination or organic isomer removal alone. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of a method for purifying high-purity diaminodiphenylmethane;

[0028] Figure 2 This is a process diagram for purifying high-purity diaminodiphenylmethane;

[0029] Figure 3 This is a temperature-time control timing diagram of a high-purity diaminodiphenylmethane purification method. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0032] Unless otherwise specified, all raw materials described below may be commercially available or prepared using conventional methods in the art. Exemplary commercially available specifications are as follows: glycerol (analytical grade AR, ≥99.0%), methanol (chromatographic grade HPLC, ≥99.9%), and toluene (analytical grade AR, ≥99.5%).

[0033] Application Overview:

[0034] The fundamental reason for the difficulty in removing inorganic salts and the low efficiency in separating organic isomers in traditional unidirectional cooling recrystallization processes lies in the fact that extremely fine inorganic salt particles lack the intrinsic driving force for physical volume aggregation in hydrophobic organic solvents, while organic isomers with very similar molecular structures are prone to co-precipitation and mechanical encapsulation under continuous supersaturated cooling. Based on this analysis, this invention achieves effective physical interception of inorganic salt solid particles without introducing an external aqueous washing process, while simultaneously eliminating the encapsulation defects of co-precipitated organic isomers within a single crystallization cycle, thus achieving both high-purity diaminodiphenylmethane solids and maintaining a high overall purification yield.

[0035] Exemplary method:

[0036] like Figures 1 to 3 As shown, a method for purifying high-purity diaminodiphenylmethane includes the following steps:

[0037] S1: Crude diaminodiphenylmethane is mixed with an organic solvent and heated to dissolve the crude diaminodiphenylmethane. A hydrophilic liquid crosslinking agent is added and sheared and mixed under stirring conditions to obtain a polymerized mixture.

[0038] S2: Filter the aggregated mixture to separate the solid phase and retain the liquid phase to obtain the initial clear liquid;

[0039] S3: Cool the initial clear liquid to the nucleation temperature at the first cooling rate, and precipitate the initial solid phase through liquid-solid phase transformation to obtain a suspension containing defective crystal nuclei;

[0040] S4: The suspension containing defective crystal nuclei is heated to the ripening temperature and stirred at a constant temperature to promote partial dissolution of the solid phase and molecular recombination, resulting in a well-structured crystal slurry.

[0041] S5: Cool the well-structured slurry to the final crystallization temperature at the second cooling rate to obtain the final crystalline mixture;

[0042] S6: Perform solid-liquid separation on the final crystallization mixture to obtain the final solid phase, and wash and dry the final solid phase to obtain high-purity diaminodiphenylmethane.

[0043] The following is a detailed explanation of each step.

[0044] In step S1, the crude diaminodiphenylmethane is a solid mixture obtained by acid-catalyzed condensation of aniline and formaldehyde followed by alkali neutralization. The crude diaminodiphenylmethane includes 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane, polymeric byproducts, and sodium chloride solid particles. Aromatic organic solvents are hydrophobic organic solvents whose molecular structure contains a benzene ring. Aromatic organic solvents include toluene, xylene, and other aromatic solvents with similar dissolving properties.

[0045] Hydrophilic liquid crosslinking agents are polar liquid compounds that have a boiling point higher than that of aromatic organic solvents under normal pressure, contain two or more hydroxyl groups in their molecular structure, and are not miscible with aromatic organic solvents in the temperature range of 100℃ to 150℃. Hydrophilic liquid crosslinking agents include glycerol, ethylene glycol, diethylene glycol, polyethylene glycol, and other polar liquid compounds with similar polymerization properties.

[0046] Sodium chloride solid particles in crude diaminodiphenylmethane do not dissolve in aromatic organic solvents. 4,4-Diaminodiphenylmethane, 2,4-diaminodiphenylmethane, and polymeric byproducts in crude diaminodiphenylmethane dissolve in aromatic organic solvents heated to 100°C to 150°C. Sodium chloride solid particles remain suspended in a dispersed state in the liquid phase in aromatic organic solvents at 100°C to 150°C.

[0047] Step S1 involves dispersing the soluble components of crude diaminodiphenylmethane in an aromatic organic solvent, while simultaneously causing the sodium chloride solid particles suspended in the liquid phase to aggregate and form aggregated particles.

[0048] Specifically, crude diaminodiphenylmethane and an aromatic organic solvent are added to the same container to form an initial mixture. The ratio of crude diaminodiphenylmethane to the aromatic organic solvent is 1 g:3 mL to 1 g:8 mL. The initial mixture is subjected to continuous mechanical stirring while being heated to 100°C to 150°C and maintained at this temperature range until the soluble components in the initial mixture dissolve.

[0049] The molecular structures of 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane, and their polymeric byproducts contain nonpolar benzene ring groups. These benzene ring groups share similarities with the molecular structures of aromatic organic solvents. Based on the principle of "like dissolves like," when heated to 100°C to 150°C in aromatic organic solvents, the increased thermal motion of the molecules overcomes intermolecular forces, allowing them to disperse in the aromatic organic solvent and form a homogeneous liquid phase. Sodium chloride solid particles, being ionic crystals, do not exhibit matching intermolecular forces with nonpolar aromatic organic solvents. Therefore, sodium chloride solid particles do not dissolve in aromatic organic solvents at 100°C to 150°C and remain suspended as independent solid particles in the homogeneous liquid phase.

[0050] A hydrophilic liquid crosslinking agent was added to the initial mixture at a temperature maintained between 100°C and 150°C. The mass of the hydrophilic liquid crosslinking agent added was 0.1 wt% to 0.8 wt% of the crude diaminodiphenylmethane. Continuous mechanical stirring was applied to the initial mixture after adding the hydrophilic liquid crosslinking agent. The shear force provided by the mechanical stirring caused the hydrophilic liquid crosslinking agent to form dispersed droplets in the initial mixture. The stirring time was 10 min to 60 min.

[0051] Hydrophilic liquid bridging agents contain multiple hydroxyl groups in their molecular structure. These hydroxyl groups are highly polar, and the hydrophilic liquid bridging agents are immiscible with nonpolar aromatic organic solvents within a temperature range of 100°C to 150°C. Under the shear force provided by mechanical stirring, the hydrophilic liquid bridging agents are dispersed into independent microdroplets, which are suspended in a homogeneous liquid phase. Sodium chloride solid particles carry a polar charge on their surface, making them highly hydrophilic. When hydrophilic liquid bridging agent droplets suspended in the liquid phase collide with sodium chloride solid particles, the droplets wet the surface of the sodium chloride solid particles, forming continuous liquid bridges between adjacent sodium chloride solid particles. Cohesive forces exist between the liquid molecules within the liquid bridge, causing the liquid bridge to tend to contract. This contraction tendency exerts a pulling force on adjacent sodium chloride solid particles towards the center of the liquid bridge; this pulling force towards the center of the liquid bridge is called capillary bridging force. Capillary liquid bridging forces bring adjacent sodium chloride solid particles closer together. Multiple sodium chloride solid particles aggregate together under the continuous action of capillary liquid bridging forces, forming aggregated particles.

[0052] In step S1, the mixture is transformed from a heterogeneous initial mixture containing undissolved solids into a coalesced mixture containing a homogeneous liquid phase and aggregated particles. The homogeneous liquid phase contains dissolved 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane, and polymeric byproducts. The solid particles in the coalesced mixture are aggregated particles formed by the agglomeration of sodium chloride solid particles, which are suspended in the homogeneous liquid phase.

[0053] The solubility of 4,4-diaminodiphenylmethane in aromatic organic solvents decreases with decreasing material temperature. When the material temperature is below 100℃, 4,4-diaminodiphenylmethane precipitates from the aromatic organic solvent, forming solid particles. The sodium chloride aggregate particles contain chloride ions, which will enter the solid product along with the sodium chloride solid particles. Step S2 separates the sodium chloride aggregate particles in the aggregated mixture from the homogeneous liquid phase while keeping 4,4-diaminodiphenylmethane dissolved in the aromatic organic solvent, thus removing the solid component carrying chloride ions from the material.

[0054] Step S2 also involves a filter medium and a filter device. The filter medium is a porous solid material with a uniformly interconnected microporous structure, including woven filter cloth, sintered metal filter plates, and porous ceramic filter plates. The filter device is a closed container that can contain the filter medium and apply filtration driving pressure to the feed fluid. The interior of the filter device is divided into two independent chambers, an inlet chamber and an outlet chamber, by the filter medium.

[0055] Specifically, the coalesced mixture is fed into the feed chamber of the filter device while maintaining its temperature between 100°C and 150°C. An inert gas is introduced into the feed chamber to increase the internal pressure to 0.1 MPa to 0.5 MPa, creating a filtration driving pressure. This pressure forces the coalesced mixture into contact with the feed surface of the filter medium. The homogeneous liquid phase in the coalesced mixture passes through the microporous structure of the filter medium and enters the discharge chamber of the filter device. Sodium chloride agglomerates in the coalesced mixture cannot pass through the microporous structure of the filter medium and remain and accumulate on the feed surface of the filter medium.

[0056] Whether solid particles can pass through the microporous structure of a porous medium depends on the relative size of the solid particles' equivalent particle size and the micropore size of the porous medium. When the equivalent particle size of the solid particles is larger than the micropore size of the porous medium, the solid particles cannot pass through the microporous structure and are intercepted on the feed side surface of the porous medium. Similarly, sodium chloride aggregate particles have an equivalent particle size larger than the micropore size of the filter medium; therefore, the sodium chloride aggregate particles cannot pass through the microporous structure of the filter medium and are intercepted on the feed side surface of the filter medium.

[0057] Sodium chloride aggregates accumulate on the feed side of the filter medium, forming a filter cake layer with a continuous porous structure. The equivalent pore size between the particles in the filter cake layer is larger than the molecular size of aromatic organic solvents but smaller than the equivalent particle size of unagglomerated sodium chloride solid particles. Aromatic organic solvents containing dissolved solutes can penetrate the interparticle pores of the filter cake layer, while incompletely agglomerated sodium chloride solid particles cannot penetrate the interparticle pores and are intercepted on the feed side of the filter cake layer.

[0058] Under the continuous action of the filtration driving pressure, the homogeneous liquid phase in the agglomerated mixture passes through the filter medium and enters the discharge chamber of the filtration device, thus completing the filtration. The liquid phase in the discharge chamber of the filtration device is collected to obtain the initial clarified liquid. The temperature of the initial clarified liquid is maintained between 100℃ and 150℃. The dispersion medium of the initial clarified liquid is an aromatic organic solvent, and the initial clarified liquid contains dissolved 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane, and polymeric byproducts. The solid component on the feed side surface of the filter medium is a sodium chloride agglomerated filter cake, which contains agglomerated sodium chloride solid particles and adsorbed aromatic organic solvents.

[0059] The solubility of 4,4-diaminodiphenylmethane in aromatic organic solvents exhibits a monotonically decreasing trend as the material temperature decreases. Lowering the material temperature reduces the solubility of 4,4-diaminodiphenylmethane in aromatic organic solvents. When the actual concentration of 4,4-diaminodiphenylmethane exceeds the saturation solubility of 4,4-diaminodiphenylmethane at the corresponding temperature, the material becomes supersaturated.

[0060] Supersaturation is the ratio of the actual concentration of the solute in a solution to the saturated solubility of the solute at the corresponding temperature. Supersaturation is also the thermodynamic driving force for the precipitation of the solute from the liquid phase to form solid-phase nuclei. The metastable region is the temperature-concentration range between the saturated solubility curve and the supersolubility curve. Supersaturated solutions in the metastable region will not spontaneously nucleate; nuclei will only form under external disturbances. When the supersaturation of the solution exceeds the critical value corresponding to the supersolubility curve, the solution enters the unstable region, and the solution will spontaneously generate a large number of primary nuclei.

[0061] Step S3 involves steadily reducing the temperature of the initial clear liquid at a set rate, causing the initial clear liquid to move from a dissolved saturated state to a supersaturated unstable state, triggering the aggregation of 4,4-diaminodiphenylmethane molecules to form primary crystal nuclei, resulting in a suspended material comprising solid crystal nuclei and a liquid phase.

[0062] Specifically, the initial clarified liquid obtained in step S2 is transferred to a sealed container equipped with a temperature control jacket, temperature measuring element, and mechanical stirring device. During the initial clarified liquid transfer, the material temperature is continuously maintained within the temperature range of 100℃ to 150℃ to ensure that all solutes in the initial clarified liquid remain in a dissolved state. The first cooling rate is the rate of temperature decrease of the material per unit time, and the value of the first cooling rate ranges from 0.5℃ / min to 2.0℃ / min. Cooling medium is introduced into the temperature control jacket of the sealed container. Through heat exchange between the temperature control jacket and the inside of the container, the temperature of the initial clarified liquid decreases steadily according to the set first cooling rate. During the cooling process, continuous mechanical stirring is applied to the material. The mechanical stirring action ensures that the temperature and solute concentration at all locations within the material are uniformly distributed, and there are no areas with excessively low temperatures or excessively high solute concentrations within the material.

[0063] As the material temperature steadily decreases, the saturated solubility of 4,4-diaminodiphenylmethane in aromatic organic solvents continuously decreases, while the ratio of the actual concentration of 4,4-diaminodiphenylmethane in the material to its saturated solubility at the corresponding temperature continuously increases, indicating a continuous rise in the supersaturation of the material. The nucleation temperature is the critical temperature at which the solution transitions from the metastable region to the unstable region at the corresponding solute concentration. Under the temperature conditions corresponding to the nucleation temperature, the supersaturation of the solution reaches the critical value for spontaneous nucleation. The nucleation temperature ranges from 60℃ to 90℃. When the material temperature drops to the nucleation temperature, the supersaturation of the material reaches the critical value corresponding to the supersolubility curve, and the solution enters the unstable region.

[0064] In the liquid phase, 4,4-diaminodiphenylmethane molecules undergoing random thermal motion aggregate through intermolecular forces, forming molecular aggregates with sizes exceeding the critical nucleus radius. The critical nucleus radius is the minimum size at which a nucleus can stably exist in the liquid phase. When the size of the molecular aggregate is smaller than the critical nucleus radius, it spontaneously dissolves back into the liquid phase; when the size of the molecular aggregate is larger than the critical nucleus radius, it can stably exist in the liquid phase and becomes a primary nucleus capable of further growth. Simultaneously, a large number of primary nuclei larger than the critical nucleus radius are generated within the material, and these primary nuclei are dispersed in the liquid phase.

[0065] Under conditions of high supersaturation, the adhesion rate of solute molecules to the surface of the primary crystal nucleus is dominated by the kinetic rate of molecular thermal motion, not by the matching degree between molecular structure and crystal lattice. The molecular structures of 2,4-diaminodiphenylmethane and 4,4-diaminodiphenylmethane are highly similar. 2,4-diaminodiphenylmethane molecules migrate to the surface of the primary crystal nucleus along with 4,4-diaminodiphenylmethane molecules. Some 2,4-diaminodiphenylmethane molecules are embedded in the interstitial and defect positions of the primary crystal nucleus's lattice, while others are adsorbed onto the surface and grain boundaries of the primary crystal nucleus. Together, the 2,4-diaminodiphenylmethane molecules and the primary crystal nucleus of 4,4-diaminodiphenylmethane form solid particles.

[0066] Once the material temperature steadily decreases to the set nucleation temperature and a large number of primary crystal nuclei are generated within the material, cooling stops. The material transforms from a homogeneous, initially clear liquid without solid particles into a suspension containing solid primary crystal nuclei and a liquid mother liquor. This suspension contains defective crystal nuclei. The solid component in the suspension containing defective crystal nuclei consists of primary crystal nuclei containing 2,4-diaminodiphenylmethane, with the solid particles dispersed in the liquid mother liquor. The liquid mother liquor in the suspension containing defective crystal nuclei is an aromatic organic solvent, containing dissolved unprecipitated 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane, and polymeric byproducts.

[0067] 2,4-Diaminodiphenylmethane molecules are adsorbed on the surface and at the grain boundaries of the primary solid nuclei. These primary nuclei contain lattice defects such as interstitial crystals and dislocations. The temperature of the suspension containing the defective nuclei is the nucleation temperature set in step S3, ranging from 60°C to 90°C. Smaller solid particles dissolve in the solution, and the resulting solute molecules reprecipitate on the surface of larger solid particles, increasing the average size and decreasing the total number of solid particles in the material. Step S4 adjusts the temperature of the suspension containing the defective nuclei to the set ripening temperature, causing the solid-liquid two-phase material to enter a slightly unsaturated state. This promotes the dissolution and molecular recombination of some solid particles, resulting in a mixture containing solid crystal particles with a complete lattice structure and a liquid mother liquor.

[0068] Specifically, the maturation temperature is a temperature value that is 5°C to 15°C higher than the nucleation temperature set in step S3, and the range of the maturation temperature is 65°C to 105°C.

[0069] Under continuous mechanical stirring of the suspension containing defective crystal nuclei, a heating medium is introduced into the temperature-controlled jacket of the sealed container holding the suspension. Through heat exchange between the temperature-controlled jacket and the interior of the container, the temperature of the suspension containing defective crystal nuclei is steadily increased to the set ripening temperature at a heating rate of 0.2℃ / min to 1.0℃ / min. During the heating process, the mechanical stirring action ensures that the temperature and solute concentration are uniformly distributed throughout the solid-liquid two-phase material containing the suspension, preventing any areas of excessively high temperature or excessively low solute concentration.

[0070] Once the temperature of the suspension containing defective crystal nuclei reaches the set aging temperature, heating is stopped, and the temperature of the suspension containing defective crystal nuclei is maintained within ±0.5℃ of the set aging temperature. Meanwhile, mechanical stirring is continuously performed for 0.5h to 4.0h.

[0071] When the temperature of the suspension containing defective crystal nuclei is raised to the set aging temperature, the saturated solubility of 4,4-diaminodiphenylmethane in aromatic organic solvents increases. The solid-liquid two-phase material of the suspension containing defective crystal nuclei enters a slightly unsaturated state. In this slightly unsaturated state, the actual concentration of 4,4-diaminodiphenylmethane in the liquid mother liquor is lower than the saturated solubility of 4,4-diaminodiphenylmethane at the set aging temperature. The primary solid crystal nuclei in the suspension containing defective crystal nuclei exhibit significant differences in particle size distribution. Primary solid crystal nuclei with smaller equivalent particle sizes have higher surface energy and higher saturated solubility. Primary solid crystal nuclei with numerous lattice defects and embedded 2,4-diaminodiphenylmethane molecules also have higher surface energy and higher saturated solubility. In a slightly unsaturated material environment, the saturated solubility of solid primary crystal nuclei with smaller equivalent particle size and more lattice defects is higher than the actual concentration of 4,4-diaminodiphenylmethane in the liquid mother liquor. The solid primary crystal nuclei with smaller equivalent particle size and more lattice defects spontaneously dissolve, and the 4,4-diaminodiphenylmethane molecules in the solid primary crystal nuclei with smaller equivalent particle size and more lattice defects, together with the 2,4-diaminodiphenylmethane molecules embedded in the crystal lattice, detach from the solid particles and enter the liquid mother liquor.

[0072] Solid primary nuclei with larger equivalent particle size and more complete lattice structure have lower surface energy and lower saturation solubility. The saturation solubility of these nuclei is lower than the actual concentration of 4,4-diaminodiphenylmethane in the liquid mother liquor. 4,4-diaminodiphenylmethane molecules dissolved in the liquid mother liquor spontaneously migrate to the surface of these nuclei, arranging themselves according to lattice matching rules and attaching to the solid particles. This fills and regularizes the lattice structure of the solid particles, healing lattice defects such as interstitial spaces and dislocations. In contrast, the spatial structure of 2,4-diaminodiphenylmethane molecules is asymmetric. 2,4-diaminodiphenylmethane molecules cannot match the regular lattice formed by 4,4-diaminodiphenylmethane, and therefore cannot attach to the surface of solid particles with a complete lattice structure. Consequently, 2,4-diaminodiphenylmethane molecules remain in the liquid mother liquor.

[0073] In step S4, the solid-liquid two-phase material of the suspension containing defective crystal nuclei transforms from a suspension containing primary solid crystal nuclei with a wide equivalent particle size distribution and numerous lattice defects into a mixture containing solid crystal particles with a narrow equivalent particle size distribution and a complete lattice structure and a liquid mother liquor. This mixture is a well-structured crystal slurry. The solid component in the well-structured crystal slurry consists of solid crystal particles formed from 4,4-diaminodiphenylmethane. There are no embedded 2,4-diaminodiphenylmethane molecules within the lattice of these solid crystal particles, and no adsorbed 2,4-diaminodiphenylmethane molecules on their surfaces. The liquid mother liquor in the well-structured crystal slurry is an aromatic organic solvent, containing dissolved unprecipitated 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane released from the solid particles, and polymeric byproducts.

[0074] In step S5, the second cooling rate is the rate of temperature decrease of the material per unit time, and the value of the second cooling rate ranges from 0.1℃ / min to 0.5℃ / min. The crystallization endpoint temperature is the target temperature for material cooling, and the value of the crystallization endpoint temperature ranges from 20℃ to 40℃. Step S5 steadily reduces the temperature of the solid-liquid two-phase material containing the well-structured crystal slurry to the crystallization endpoint temperature according to the set second cooling rate, so that the supersaturation of the material is always maintained within the low supersaturation range of the metastable region. This promotes the orderly attachment and growth of 4,4-diaminodiphenylmethane molecules dissolved in the liquid phase onto the surface of the existing solid phase crystal particles with complete crystal lattice structure, while 2,4-diaminodiphenylmethane molecules are continuously retained in the liquid mother liquor, resulting in a solid-liquid two-phase mixture with the solid phase ratio reaching its maximum.

[0075] Specifically, a cooling medium is introduced into the temperature-controlled jacket of the sealed container holding the well-structured crystal slurry. Through heat exchange between the temperature-controlled jacket and the interior of the container, the temperature of the solid-liquid two-phase material containing the well-structured crystal slurry steadily decreases at a set second cooling rate. During the cooling process, the well-structured crystal slurry is continuously mechanically stirred. The mechanical stirring action ensures that the temperature and solute concentration at all locations within the solid-liquid two-phase material containing the well-structured crystal slurry are uniformly distributed, and there are no areas with excessively low temperatures or excessively high solute concentrations within the solid-liquid two-phase material containing the well-structured crystal slurry.

[0076] As the temperature of the well-structured slurry in the solid-liquid two-phase material steadily decreases, the saturated solubility of 4,4-diaminodiphenylmethane in aromatic organic solvents continuously decreases. The ratio of the actual concentration of 4,4-diaminodiphenylmethane in the material to its saturated solubility at the corresponding temperature continuously increases, and the supersaturation of the material slowly rises. The set second cooling rate keeps the supersaturation of the material within the low supersaturation range of the metastable region. Within the low supersaturation range of the metastable region, the material will not spontaneously generate new primary crystal nuclei; only the attachment of solute molecules and crystal growth can occur on the surface of existing solid-phase crystal particles.

[0077] 4,4-Diaminodiphenylmethane molecules dissolved in the liquid phase migrate to the surface of solid crystal particles in the well-structured slurry through random thermal motion. The spatial structure of 4,4-diaminodiphenylmethane molecules is symmetrical, perfectly matching the lattice structure of the solid crystal particles. These molecules adhere orderly to the surface of the solid crystal particles according to their lattice arrangement, causing the particle size to continuously increase. Conversely, 2,4-diaminodiphenylmethane molecules have an asymmetrical spatial structure and do not match the lattice structure of the solid crystal particles. Therefore, 2,4-diaminodiphenylmethane molecules cannot adhere orderly to the surface of the solid crystal particles and remain trapped in the mother liquor.

[0078] Through step S5, the well-structured slurry, consisting of solid-liquid two-phase materials, transforms from a well-structured slurry containing solid crystal particles with complete lattice structure and uniform particle size into a solid-liquid two-phase mixture with the solid phase proportion reaching its maximum. This mixture is the final-state crystallization mixture. The solid phase component in the final-state crystallization mixture consists of solid crystal particles formed from 4,4-diaminodiphenylmethane. These solid crystal particles have a complete lattice structure and contain no embedded 2,4-diaminodiphenylmethane molecules. The liquid mother liquor in the final-state crystallization mixture is an aromatic organic solvent, which contains dissolved unprecipitated 4,4-diaminodiphenylmethane, 2,4-diaminodiphenylmethane, and polymeric byproducts.

[0079] Step S6 involves solid-liquid separation, where the solid crystal particles in the final crystallization mixture are physically separated from the liquid mother liquor. The 2,4-diaminodiphenylmethane and polymeric byproducts contained in the liquid mother liquor are discharged along with the liquid mother liquor. Step S6, by completing the solid-liquid two-phase separation of the final crystallization mixture, surface washing of the solid crystal particles, and solvent removal of the solid crystal particles, yields a solid 4,4-diaminodiphenylmethane product.

[0080] This step also involves a solid-liquid separation device, which is a device that can realize the physical separation of solid and liquid phases, including centrifuges, plate and frame filters, and vacuum filtration devices.

[0081] Specifically, the final crystallized mixture obtained in step S5 is conveyed to a solid-liquid separation device. A separation driving force is applied to the final crystallized mixture, including centrifugal force, pressure difference, and vacuum negative pressure. This driving force causes the liquid mother liquor in the final crystallized mixture to pass through the filter medium of the solid-liquid separation device and exit the cavity of the device. The solid crystal particles in the final crystallized mixture cannot pass through the filter medium and remain and accumulate on its surface. The equivalent particle size of the solid crystal particles is larger than the micropore size of the filter medium, preventing them from passing through its microporous structure and trapping them on its surface. The 2,4-diaminodiphenylmethane and polymeric byproducts dissolved in the liquid mother liquor are discharged from the cavity of the solid-liquid separation device along with the liquid mother liquor, completing the physical separation of the solid crystal particles from the impurity-containing liquid mother liquor.

[0082] After the liquid mother liquor is discharged from the solid-liquid separation device, a low-temperature aromatic organic solvent is introduced into the device. The temperature of the solvent is maintained between 0°C and 10°C, and the volume of the solvent introduced is 0.5 to 2 times the volume of the solid crystal particles accumulated on the filter medium surface. The solvent is uniformly sprayed onto the surface of the solid crystal particles, wetting the outer surface and pores between the particles, and displacing the residual liquid mother liquor film adhering to the particle surface. The resulting mixed liquid passes through the microporous structure of the filter medium and is discharged from the solid-liquid separation device. The 2,4-diaminodiphenylmethane and polymeric byproducts contained in the residual liquid mother liquor adhering to the solid crystal particles are discharged from the device along with the displaced mixed liquid, thus completing the removal of surface impurities from the solid crystal particles.

[0083] After washing, the solid crystal particles accumulated on the surface of the filter media are removed from the solid-liquid separation device and transferred to the sealed drying chamber of the vacuum drying device. The sealed drying chamber is connected to a vacuum unit, which can reduce the absolute pressure inside the chamber to 1 kPa to 10 kPa. The chamber is equipped with a temperature-controlled heating component, which can stably maintain the temperature inside the chamber within the range of 60°C to 100°C. The absolute pressure inside the chamber is reduced to 1 kPa to 10 kPa, while the temperature is stably maintained within the range of 60°C to 100°C for 2 to 8 hours. In the low-pressure environment, the boiling point of aromatic organic solvents decreases with decreasing ambient pressure. The residual aromatic organic solvents on the outer surface and in the internal pores of the solid crystal particles evaporate upon heating, forming organic solvent vapor. This vapor is continuously extracted from the sealed drying chamber by the vacuum unit, achieving the separation of residual organic solvents from the solid crystal particles.

[0084] After vacuum drying, the pressure inside the sealed drying chamber is restored to atmospheric pressure, and the dried solid material is removed to obtain high-purity diaminodiphenylmethane solid. The main component of the high-purity diaminodiphenylmethane solid is 4,4-diaminodiphenylmethane.

[0085] In the following examples and comparative examples, the crude diaminodiphenylmethane used was produced by aniline-formaldehyde hydrochloric acid catalytic condensation and controlled water washing process, as detailed below:

[0086] M1: In a reactor equipped with a mechanical stirrer and temperature control device, 186.0 g of aniline and 60.0 g of a 30% hydrochloric acid aqueous solution were added. The mixture was stirred at a constant temperature of 30°C for 30 min to form an aniline hydrochloride solution. Subsequently, under the condition of 30°C and continuous stirring, 81.0 g of a 37% formaldehyde aqueous solution was added dropwise at a uniform rate over a fixed time of 60 min.

[0087] M2: After the addition is complete, raise the internal temperature of the reactor to 70°C and keep it at that temperature for 120 minutes. Then, raise the temperature to 100°C and keep it at that temperature for 180 minutes to complete the molecular rearrangement and condensation reaction.

[0088] M3: Reduce the material temperature to 60℃, slowly add 68.0g of 30% sodium hydroxide aqueous solution for neutralization until the pH of the aqueous phase of the system reaches 8.0, then stop adding alkali.

[0089] M4: Stop stirring and let stand for 30 minutes to allow the material to separate into layers. Discard the lower layer of salt-rich water phase and retain the upper organic phase. Add only 50.0 mL of deionized water to the organic phase for a single, short wash (stir for 5 minutes, let stand to separate the layers, and drain the water to separate them; by limiting the amount and number of washes, the residual sodium chloride in the organic phase is precisely controlled at the target level). Transfer the washed organic phase to a vacuum distillation apparatus to remove unreacted aniline and residual water under an absolute pressure of 5 kPa and a temperature of 150 °C. The solid cooled residue at the bottom of the distillation is the desired crude diaminodiphenylmethane.

[0090] The determination showed that the initial purity of 4,4-diaminodiphenylmethane in the crude diaminodiphenylmethane was 86.50%, the initial content of 2,4-diaminodiphenylmethane was 10.20%, and the initial chloride ion content was 3500 ppm.

[0091] Example 1:

[0092] This embodiment provides a method for purifying diaminodiphenylmethane, including the following steps:

[0093] S1: Crude diaminodiphenylmethane and toluene were added to the same container at a ratio of 1 g:5 mL to form an initial mixture. The initial mixture was continuously stirred at 150 rpm while being heated to 120°C and maintained at this temperature until the soluble components dissolved. Glycerol was added to the initial mixture at 120°C, with an addition mass of 0.1 wt% of the crude diaminodiphenylmethane. The mixture after adding glycerol was then continuously stirred at 150 rpm for 30 minutes to obtain a polymerized mixture.

[0094] S2: With the temperature of the coalesced mixture maintained at 120°C, the coalesced mixture is fed into the feed chamber of a filtration device. The filter medium of the filtration device is woven filter cloth. Nitrogen gas is introduced into the feed chamber of the filtration device, increasing the internal pressure to 0.3 MPa. This forces the coalesced mixture into contact with the feed side surface of the filter medium. The homogeneous liquid phase in the coalesced mixture passes through the microporous structure of the filter medium and enters the discharge chamber of the filtration device. Solid particles in the coalesced mixture are intercepted on the feed side surface of the filter medium. The liquid phase in the discharge chamber of the filtration device is collected to obtain the initial clear liquid.

[0095] S3: Transfer the initial clarified liquid to a sealed container equipped with a temperature control jacket, temperature sensing element, and mechanical stirring device. Maintain the material temperature at 120℃ throughout the initial liquid transfer. Circulate cooling medium through the temperature control jacket of the sealed container to allow the initial clarified liquid temperature to decrease steadily at a rate of 1.0℃ / min. During the cooling process, apply continuous mechanical stirring at a speed of 50 rpm. Stop cooling when the material temperature drops to 75℃, resulting in a suspension containing defective crystal nuclei.

[0096] S4: Under continuous mechanical stirring of the suspension containing defective crystal nuclei, a heating medium is introduced into the temperature-controlled jacket of the sealed container holding the suspension, causing the temperature of the suspension to rise steadily to 85℃ at a rate of 0.5℃ / min. Once the temperature of the suspension reaches 85℃, heating is stopped, and the temperature is maintained stable within the range of 85℃ ± 0.5℃, while continuous mechanical stirring at a speed of 50 rpm is performed for 2.0 hours, resulting in a well-structured crystal slurry.

[0097] S5: Cooling medium is introduced into the temperature-controlled jacket of the sealed container holding the well-structured crystal slurry, causing the temperature of the solid-liquid two-phase material containing the well-structured crystal slurry to decrease steadily at a cooling rate of 0.3℃ / min. During the cooling process, the well-structured crystal slurry is continuously mechanically stirred at a speed maintained at 50 rpm. When the temperature of the solid-liquid two-phase material containing the well-structured crystal slurry steadily drops to 25℃, cooling is stopped, yielding the final crystallized mixture.

[0098] S6: The final crystallization mixture is fed into a centrifuge at 3000 rpm for 10 minutes to separate the liquid mother liquor from the solid crystal particles. The liquid mother liquor is discharged from the centrifuge chamber, while the solid crystal particles accumulate on the inner wall of the centrifuge drum. After the liquid mother liquor is discharged, toluene at 5°C is introduced into the centrifuge chamber at a volume equal to the volume of the solid crystal particles. The toluene is evenly sprayed onto the surface of the solid crystal particles to complete surface washing. The washed liquid mixture is then discharged from the centrifuge chamber. The washed solid crystal particles are removed from the centrifuge and transferred to the sealed drying chamber of a vacuum drying device. The absolute pressure inside the sealed drying chamber is reduced to 5 kPa, while the temperature inside the sealed drying chamber is stably controlled at 80°C for 4 hours. After the heat preservation and pressure holding time is completed, heating and vacuum extraction are stopped, the pressure inside the sealed drying chamber is restored to normal pressure, and the dried solid material is taken out to obtain high-purity diaminodiphenylmethane solid.

[0099] Example 2:

[0100] This embodiment refers to the entire operation process of Embodiment 1. The difference between this embodiment and Embodiment 1 is that when adding glycerol to the initial mixing system at a temperature maintained at 120°C, the added mass of glycerol is 0.3 wt% of the mass of crude diaminodiphenylmethane.

[0101] Example 3:

[0102] This embodiment refers to the entire operation process of Embodiment 1. The difference between this embodiment and Embodiment 1 is that when adding glycerol to the initial mixing system at a temperature maintained at 120°C, the added mass of glycerol is 0.8 wt% of the mass of crude diaminodiphenylmethane.

[0103] Example 4:

[0104] This embodiment refers to the entire operation process of Embodiment 1. The difference between this embodiment and Embodiment 1 is that when adding glycerol to the initial mixture at a temperature maintained at 120°C, the added mass of glycerol is 0.3 wt% of the crude diaminodiphenylmethane. When the temperature of the suspension containing defective crystal nuclei reaches 85°C, the heating is stopped, and the temperature of the suspension containing defective crystal nuclei is maintained within the range of 85°C ± 0.5°C. At the same time, mechanical stirring is continuously performed at a speed of 50 rpm for 0.5 h, resulting in a well-structured crystal slurry.

[0105] Example 5:

[0106] This embodiment refers to the entire operation process of Embodiment 1. The difference between this embodiment and Embodiment 1 is that when adding glycerol to the initial mixture at a temperature maintained at 120°C, the added mass of glycerol is 0.3 wt% of the mass of crude diaminodiphenylmethane. When the temperature of the suspension containing defective crystal nuclei reaches 85°C, the heating is stopped, and the temperature of the suspension containing defective crystal nuclei is maintained within the range of 85°C ± 0.5°C. At the same time, mechanical stirring is continuously performed at a speed of 50 rpm for 4.0 h, resulting in a well-structured crystal slurry.

[0107] Comparative Example 1:

[0108] This comparative example follows the entire operation process of Example 1. The difference between this comparative example and Example 1 is that the initial mixture is heated to 120°C and maintained until the soluble components are dissolved. Glycerol is not added, and continuous mechanical stirring is applied directly to the initial mixture. The mechanical stirring speed is 150 rpm and the stirring time is 30 min to obtain an aggregated mixture.

[0109] Comparative Example 2:

[0110] This comparative example follows the entire operation process of Example 1. The difference between this comparative example and Example 1 is that when adding glycerol to the initial mixture at a temperature maintained at 120°C, the added mass of glycerol is 0.05 wt% of the mass of crude diaminodiphenylmethane.

[0111] Comparative Example 3:

[0112] This comparative example follows the entire operation process of Example 1. The difference between this comparative example and Example 1 is that when adding glycerol to the initial mixture at a temperature maintained at 120°C, the added mass of glycerol is 1.0 wt% of the mass of crude diaminodiphenylmethane.

[0113] Comparative Example 4:

[0114] This comparative example follows the entire operation process of Example 1. The difference between this comparative example and Example 1 is that when adding glycerol to the initial mixture at a temperature maintained at 120°C, the added mass of glycerol is 0.3 wt% of the crude diaminodiphenylmethane. After the material temperature drops to 75°C to obtain a suspension containing defective crystal nuclei, the temperature is not increased. Instead, a cooling medium is directly introduced into the temperature-controlled jacket of the sealed container containing the suspension containing defective crystal nuclei, so that the temperature of the solid-liquid two-phase material containing the suspension containing defective crystal nuclei decreases steadily at a cooling rate of 0.3°C / min. During the cooling process, mechanical stirring is continuously applied to the suspension containing defective crystal nuclei, and the mechanical stirring speed is maintained at 50 rpm. When the temperature of the solid-liquid two-phase material containing the suspension containing defective crystal nuclei drops steadily to 25°C, the cooling is stopped, and the final crystallized mixture is obtained.

[0115] Comparative Example 5:

[0116] This comparative example follows the entire operating procedure of Example 1. The difference between this comparative example and Example 1 is that when adding glycerol to the initial mixture at a temperature maintained at 120°C, the added mass of glycerol is 0.3 wt% of the crude diaminodiphenylmethane. When the temperature of the suspension containing defective crystal nuclei reaches 85°C, the heating is stopped, and the temperature of the suspension containing defective crystal nuclei is maintained within the range of 85°C ± 0.5°C. At the same time, mechanical stirring is continuously performed at a speed of 50 rpm for 0.3 h, resulting in a well-structured crystal slurry.

[0117] Comparative Example 6:

[0118] This comparative example follows the entire operating procedure of Example 1. The difference between this comparative example and Example 1 is that when adding glycerol to the initial mixture at a temperature maintained at 120°C, the added mass of glycerol is 0.3 wt% of the crude diaminodiphenylmethane. When the temperature of the suspension containing defective crystal nuclei reaches 85°C, the heating is stopped, and the temperature of the suspension containing defective crystal nuclei is maintained within the range of 85°C ± 0.5°C. At the same time, mechanical stirring is continuously performed at a speed of 50 rpm for 4.5 hours to obtain a well-structured crystal slurry.

[0119] Experimental Example 1:

[0120] 1. Sample preparation

[0121] The test samples used in this experiment included 11 groups, namely crude diaminodiphenylmethane from the same batch, and high-purity diaminodiphenylmethane solids prepared using the methods described in Examples 1, 2, 3, 4, 5, Comparative Examples 1, 2, 3, 4, 5, 6, and 7. All examples and comparative examples used the same batch of crude diaminodiphenylmethane as the raw material. The initial purity of 4,4-diaminodiphenylmethane in the crude product was 86.50%, the initial content of 2,4-diaminodiphenylmethane was 10.20%, and the initial chloride ion content was 3500 ppm. The environmental conditions, reagent specifications, and instrument parameters used in the preparation of all samples were kept consistent.

[0122] 2. Experimental Methods

[0123] Purity of 4,4-diaminodiphenylmethane and content of 2,4-diaminodiphenylmethane: High-performance liquid chromatography (HPLC) was used. The instrument employed was an HPLC system equipped with a UV detector, a C18 reversed-phase column, a methanol-water solution (60:40 v / v), a detection wavelength of 254 nm, a column temperature of 30 °C, a mobile phase flow rate of 1.0 mL / min, and an injection volume of 20 μL. Before testing, the sample was dissolved in chromatographically pure methanol and diluted to the specified concentration. The solution was then filtered through a 0.22 μm organic phase filter to prepare the test solution. Each sample was tested in triplicate, and the arithmetic mean of the three test results was taken as the test value.

[0124] Inorganic chloride ion content: The test was performed using ion chromatography with an ion chromatograph equipped with a conductivity detector. The chromatographic column was an anion exchange column, and the eluent was a 3.5 mmol / L sodium carbonate-1.0 mmol / L sodium bicarbonate solution. The column temperature was 35℃, the eluent flow rate was 1.2 mL / min, and the injection volume was 100 μL. Before testing, the sample was accurately weighed, and ultrapure water was added for ultrasonic extraction for 30 min. After high-speed centrifugation, the supernatant was collected and filtered through a 0.22 μm aqueous filter membrane to prepare the test solution. Each sample was tested in triplicate, and the arithmetic mean of the three results was taken as the test value. The method detection limit was 0.1 ppm.

[0125] Overall purification yield: The formula for calculating the overall purification yield is: Overall purification yield (%) = (Mass of high-purity diaminodiphenylmethane solid obtained × Measured purity of 4,4-diaminodiphenylmethane in the sample) ÷ (Mass of crude diaminodiphenylmethane fed × Measured purity of 4,4-diaminodiphenylmethane in the crude product) × 100%. During the calculation process, all mass data were obtained using an electronic analytical balance with an accuracy of 0.1 mg. The purity data of the sample and crude product were obtained using the aforementioned high-performance liquid chromatography (HPLC) test results. All calculated data were retained to one decimal place.

[0126] The results are shown in Table 1:

[0127] Table 1

[0128]

[0129] Sodium chloride particles in crude diaminodiphenylmethane do not dissolve in high-temperature toluene and remain suspended in the liquid phase in a dispersed state. The microporous structure of the filter medium cannot intercept the non-agglomerated sodium chloride particles, which can pass through the filter medium into the initial supernatant and ultimately remain in the high-purity diaminodiphenylmethane solid. The diaminodiphenylmethane purification method described in Comparative Example 1, without the addition of a hydrophilic liquid bridging agent, yielded a high-purity diaminodiphenylmethane solid with a chloride ion content of 210.0 ppm, which is orders of magnitude different from the chloride ion content of the high-purity diaminodiphenylmethane solid prepared in the example group with the addition of a hydrophilic liquid bridging agent.

[0130] When the amount of hydrophilic liquid bridging agent added is at the critical low value of 0.05 wt%, the chloride ion content of the high-purity diaminodiphenylmethane solid prepared by the diaminodiphenylmethane purification method described in Comparative Example 2 is 85.0 ppm. The addition amount of 0.05 wt% is insufficient to provide a sufficient volume of dispersed droplets, failing to wet all sodium chloride solid particles in the liquid phase. Most sodium chloride solid particles remain suspended in the liquid phase in an isolated form, unable to form aggregates that can be intercepted by the filter medium. During filtration, a large number of sodium chloride solid particles still penetrate the filter cloth and enter the initial clear liquid, ultimately leading to an increase in the chloride ion content of the high-purity diaminodiphenylmethane solid.

[0131] When the amount of hydrophilic liquid bridging agent added is in the range of 0.1wt% to 0.8wt%, the chloride ion content of the high-purity diaminodiphenylmethane solid prepared by the diaminodiphenylmethane purification methods described in Examples 1, 2, and 3 is in the range of 1.1ppm to 5.2ppm, and the total purification yield is in the range of 81.2% to 83.5%. The hydrophilic liquid bridging agent in the range of 0.1wt% to 0.8wt% can form a sufficient number of uniformly sized dispersed droplets under the shearing action of mechanical stirring. These droplets can wet the sodium chloride solid particles in the liquid phase, and through capillary liquid bridging force, the sodium chloride solid particles agglomerate into aggregate particles that can be intercepted by the filter medium. The aggregate particles are retained in the filter cake during filtration, significantly reducing the chloride ion content entering the initial clear liquid. Simultaneously, the hydrophilic liquid bridging agent does not form a continuous liquid film, preventing the aggregate particles from breaking or the target product from being entrained, thus maintaining a stable total purification yield of the high-purity diaminodiphenylmethane solid. The diaminodiphenylmethane purification method described in Example 2, with an addition amount of 0.3 wt%, produces high-purity diaminodiphenylmethane solid with the lowest chloride ion content among the same series of test samples.

[0132] When the amount of hydrophilic liquid bridging agent added is at the critical high value of 1.0 wt%, the chloride ion content of the high-purity diaminodiphenylmethane solid prepared by the diaminodiphenylmethane purification method described in Comparative Example 3 is 28.0 ppm, and the total purification yield is 71.4%. Excessive hydrophilic liquid bridging agent forms a continuous polar liquid film in the liquid phase. This polar liquid film encapsulates the formed sodium chloride agglomerates. Under the shearing action of mechanical stirring, the agglomerates are broken down into smaller particles, resulting in penetration during filtration and an increase in the chloride ion content of the high-purity diaminodiphenylmethane solid. Furthermore, excessive hydrophilic liquid bridging agent adsorbs some of the dissolved 4,4-diaminodiphenylmethane. Simultaneously, the filter cake formed by the excessive hydrophilic liquid bridging agent and the agglomerates clogs the micropores of the filter medium, causing a large amount of liquid phase containing the target product to be retained in the filter cake during filtration, ultimately leading to a decrease in the total purification yield of the high-purity diaminodiphenylmethane solid.

[0133] During rapid cooling and nucleation, the material is in a state of high supersaturation. 2,4-Diaminodiphenylmethane molecules become embedded in the lattice defects of the 4,4-diaminodiphenylmethane crystal nuclei. Without a reheating and ripening process, the 2,4-diaminodiphenylmethane molecules embedded in the lattice cannot be released into the liquid phase and ultimately remain in the high-purity diaminodiphenylmethane solid. The diaminodiphenylmethane purification method described in Comparative Example 4 did not include a reheating and ripening process. The high-purity diaminodiphenylmethane solid obtained had a 2,4-diaminodiphenylmethane content of 2.85% and a 4,4-diaminodiphenylmethane purity of 96.80%, which are significantly different from the corresponding indicators of the high-purity diaminodiphenylmethane solid obtained in the example group that included a reheating and ripening process.

[0134] When the aging and holding time is at the critical low value of 0.3 h, the high-purity diaminodiphenylmethane solid prepared by the diaminodiphenylmethane purification method described in Comparative Example 5 has a 2,4-diaminodiphenylmethane content of 1.25% and a 4,4-diaminodiphenylmethane purity of 98.20%. The 0.3 h holding time is insufficient to complete the full thermodynamic molecular exchange process; only extremely small crystals with very high surface energy dissolve. Most of the defective crystals containing 2,4-diaminodiphenylmethane do not completely dissolve, and the 2,4-diaminodiphenylmethane molecules embedded in the crystal lattice are not completely released into the liquid mother liquor. During subsequent cooling, the undissolved defective crystals continue to grow, and impurities are fixed in the product crystals, ultimately leading to an increase in the 2,4-diaminodiphenylmethane content in the high-purity diaminodiphenylmethane solid.

[0135] When the aging and holding time is between 0.5 h and 4.0 h, the 2,4-diaminodiphenylmethane content in the high-purity diaminodiphenylmethane solid prepared by the diaminodiphenylmethane purification methods described in Examples 2, 4, and 5 is between 0.12% and 0.28%, and the 4,4-diaminodiphenylmethane purity is between 99.55% and 99.75%. Within the 0.5 h to 4.0 h range, crystals with smaller particle sizes and more lattice defects in the material dissolve, and 2,4-diaminodiphenylmethane molecules embedded in the lattice are released into the liquid mother liquor. Simultaneously, crystals with larger particle sizes and complete lattice structures remain and heal surface defects, forming well-structured seed crystals. During subsequent cooling, 2,4-diaminodiphenylmethane molecules cannot match the well-structured lattice and are retained in the liquid mother liquor, resulting in a significant reduction in the 2,4-diaminodiphenylmethane content in the high-purity diaminodiphenylmethane solid. The diaminodiphenylmethane purification method described in Example 2, with a heat preservation time of 2.0 h, yielded high-purity diaminodiphenylmethane solid with the lowest 2,4-diaminodiphenylmethane content and the highest 4,4-diaminodiphenylmethane purity among the same series of test samples.

[0136] When the aging and holding time is at the critical high value of 4.5 h, the 2,4-diaminodiphenylmethane content in the high-purity diaminodiphenylmethane solid prepared by the diaminodiphenylmethane purification method described in Comparative Example 6 is 0.32%, and the total purification yield is 72.5%. Excessive heat exposure can cause oxidative polymerization side reactions of diaminodiphenylmethane molecules in the material. The resulting oligomers alter the metastable zone boundary of the solution, interfering with the orderly growth of crystals and causing some 2,4-diaminodiphenylmethane molecules to re-adsorb onto the crystal surface, resulting in an increase in the isomer content in the high-purity diaminodiphenylmethane solid. Furthermore, excessively long isothermal holding time causes continuous evaporation of organic solvents in the material, leading to uncontrolled changes in the supersaturation of the solution. Some target products precipitate prematurely with solvent evaporation and are carried out by the mother liquor. Simultaneously, the excessively long aging process can dissolve some structurally regular crystals, ultimately resulting in a decrease in the total purification yield of the high-purity diaminodiphenylmethane solid.

[0137] In summary, the coalescence desalination process using hydrophilic liquid bridging agents can remove sodium chloride solid particles from the material before the crystallization process, obtaining an initial clear liquid free of inorganic solid impurities. This initial clear liquid ensures a stable thermodynamic environment for the material during subsequent cooling nucleation and reheating ripening processes, preventing uncontrolled heterogeneous nucleation due to the presence of inorganic solid particles and avoiding the formation of numerous defective crystal nuclei, thus providing a uniform and stable material environment. The reheating ripening crystallization process can form crystal particles with larger particle sizes and more complete lattice structures. The complete crystal structure does not contain liquid mother liquor, preventing trace amounts of chloride ions and isomers remaining in the liquid mother liquor from being encapsulated inside the crystal, further reducing the impurity content in high-purity diaminodiphenylmethane solid while ensuring the recovery rate of the target product.

[0138] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for purifying high-purity diaminodiphenylmethane, characterized in that, Includes the following steps: S1: Crude diaminodiphenylmethane is mixed with an organic solvent and heated to dissolve the crude diaminodiphenylmethane. A hydrophilic liquid crosslinking agent is added and sheared and mixed under stirring conditions to obtain a polymerized mixture. S2: Filter the aggregated mixture to separate the solid phase and retain the liquid phase to obtain the initial clear liquid; S3: Cool the initial clear liquid to the nucleation temperature at the first cooling rate, and precipitate the initial solid phase through liquid-solid phase transformation to obtain a suspension containing defective crystal nuclei; S4: The suspension containing defective crystal nuclei is heated to the ripening temperature and stirred at a constant temperature to promote partial dissolution of the solid phase and molecular recombination, resulting in a well-structured crystal slurry. S5: Cool the well-structured slurry to the final crystallization temperature at the second cooling rate to obtain the final crystallization mixture; S6: Perform solid-liquid separation on the final crystallization mixture to obtain the final solid phase, and wash and dry the final solid phase to obtain high-purity diaminodiphenylmethane.

2. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S1, the organic solvent is an aromatic organic solvent containing a benzene ring structure in its molecular structure, including toluene or xylene; the hydrophilic liquid crosslinking agent is a polar liquid compound containing two or more hydroxyl groups in its molecular structure, including glycerol, ethylene glycol, diethylene glycol or polyethylene glycol.

3. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S1, the feeding ratio of crude diaminodiphenylmethane to organic solvent is 1g:3mL to 1g:8mL; the target heating temperature is 100℃ to 150℃; the added mass of hydrophilic liquid crosslinking agent is 0.1wt% to 0.8wt% of the feeding mass of crude diaminodiphenylmethane; and the continuous stirring time for shear mixing is 10min to 60min.

4. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S2, the filtration is carried out under the condition that the material temperature is maintained in the range of 100°C to 150°C; the filtration includes introducing inert gas into the feed chamber of the filtration device to increase the internal pressure of the feed chamber to 0.1MPa to 0.5MPa to form the filtration driving pressure.

5. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S3, the first cooling rate ranges from 0.5℃ / min to 2.0℃ / min; the nucleation temperature ranges from 60℃ to 90℃.

6. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S4, the heating rate of the suspension containing defective crystal nuclei to the maturation temperature is 0.2℃ / min to 1.0℃ / min; the maturation temperature is a temperature value that is 5℃ to 15℃ higher than the nucleation temperature, and the range of the maturation temperature is 65℃ to 105℃; the duration of the constant temperature stirring is 0.5h to 4.0h.

7. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S5, the second cooling rate ranges from 0.1℃ / min to 0.5℃ / min; the crystallization endpoint temperature ranges from 20℃ to 40℃.

8. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S6, washing the final solid phase includes introducing a low-temperature aromatic organic solvent into the cavity of the solid-liquid separation device to uniformly spray the surface of the final solid phase. The temperature of the low-temperature aromatic organic solvent is maintained in the range of 0°C to 10°C, and the volume of the low-temperature aromatic organic solvent introduced is 0.5 to 2 times the volume of the final solid phase.

9. The method for purifying high-purity diaminodiphenylmethane according to claim 1, characterized in that, In step S6, the drying is vacuum drying carried out in a sealed drying chamber of a vacuum drying device. The conditions for vacuum drying include an absolute pressure of 1 kPa to 10 kPa inside the sealed drying chamber, a temperature of 60°C to 100°C inside the sealed drying chamber, and a heat and pressure holding time of 2 h to 8 h.

10. A high-purity diaminodiphenylmethane, characterized in that, The high-purity diaminodiphenylmethane was prepared using a purification method for high-purity diaminodiphenylmethane as described in any one of claims 1 to 9.

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