Synthesis method of superfine sodium antimonate flame retardant for engineering plastics

Abstract

The invention relates to the technical field of inorganic fine chemical engineering, and discloses a synthesis method of a superfine sodium antimonate flame retardant for engineering plastics, which comprises the following steps: dissolving antimony trioxide, adding sodium gluconate, and stirring at a constant temperature of 43-47 DEG C to prepare a coordination equilibrium precursor solution; pumping the precursor solution and the hydrogen peroxide solution into a three-stage pipeline type high-shear dispersion machine, and controlling the gap between a stator and a rotor to be 0.2-0.3 mm and the rotating speed to be 4000-4500 rpm for reaction; according to the preparation method disclosed by the invention, a chemical coordination potential barrier is constructed by virtue of constant-temperature aging so as to delay a reaction induction period, coordination equilibrium is broken by virtue of mechanical energy dissipation of a high-shear field, nucleation is instantaneously initiated, and the problem that an oxidation reaction rate is mismatched with a micro-mixing rate is solved; the narrowing of the particle size distribution and the regularization of the morphology of the product are realized.

Description

Technical Field

[0001] This invention relates to a method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics, belonging to the field of inorganic fine chemical technology. Background Technology

[0002] Sodium metaantimonate, as an important inorganic flame retardant synergist, is widely used in polyethylene terephthalate and polyamide engineering plastics systems. Current industrial preparation mainly involves reacting antimony trioxide with sodium hydroxide to prepare sodium antimony oxide solution, followed by the addition of hydrogen peroxide for precipitation. As engineering plastic end products evolve towards thinner walls and greater precision, stringent requirements are placed on the uniformity of flame retardant filler particle size distribution and the regularity of microstructure. The core constraint of traditional liquid-phase oxidation precipitation processes lies in the mismatch between chemical reaction kinetics and the microscopic mixing scale of the fluid. The reaction rate constant between antimony oxide ions and hydrogen peroxide is extremely high, far exceeding the microscopic mixing rate of fluids in conventional industrial stirring equipment. This time scale difference leads to explosive nucleation of the oxidant at local contact interfaces before it is physically dispersed throughout the system, resulting in extremely uneven local supersaturation and a wide particle size distribution in the product.

[0003] Existing attempts to improve the reaction mainly focus on physical strengthening and end-of-pipe modification. Physical strengthening aims to increase stirring speed and shorten mixing time, but is limited by fluid viscosity and energy consumption, making it difficult to overcome the microsecond-level reaction time barrier. End-of-pipe modification involves adding surfactants to the reaction system, but in the highly exothermic and instantaneous oxidation environment, surfactants cannot accurately occupy the surface of newly formed crystal nuclei, failing to intervene in the competition between crystal nucleation and growth kinetics from the source. In addition to attempts at physical mixing, existing technologies attempt to improve product quality by changing the oxidation path or post-processing, but do not address the fundamental problem of reaction kinetic mismatch. For example, Chinese invention patent CN106745245B discloses a method for treating antimony pyrolysis. The preparation methods of sodium tartarate and sodium metaantimonate employ ozone low-temperature oxidation and microwave dehydration technology. Although the high oxidation potential of ozone and the low-temperature heating characteristics of microwaves solve the problems of low product purity and yellowing after high-temperature calcination, the core oxidation precipitation process is still limited by the conventional stirred tank system. The reaction cycle is as long as several hours. The long-cycle reaction mode lacks a spatiotemporal constraint mechanism for the instantaneous formation of crystal nuclei and cannot establish a uniform supersaturation field at the microscale. As a result, crystal growth is still controlled by random local concentration fluctuations. Such improvements are difficult to achieve directional induction of crystal micromorphology. The products inevitably have problems such as wide particle size distribution, easy formation of irregular needle-like or plate-like structures, and easy formation of hard agglomerates.

[0004] Therefore, the technical problem to be solved by this invention is how to achieve spatiotemporal matching of reaction kinetics and physical mixing process without sacrificing production efficiency through process mechanism innovation, so as to prepare sodium metaantimonate with uniform particle size and regular morphology. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics, the method comprising the following steps:

[0006] Step 1: Dissolve antimony trioxide powder in an aqueous sodium hydroxide solution with a mass concentration of 18% to 20% to prepare a sodium antimony base solution; add sodium gluconate to the sodium antimony base solution, controlling the mass ratio of sodium gluconate to antimony trioxide to be 0.03:1 to 0.04:1; place in a temperature environment of 43℃ to 47℃ and stir at a constant temperature for 35 minutes to 45 minutes to obtain a coordination equilibrium precursor solution;

[0007] Step 2: Pump the coordination equilibrium precursor solution and the hydrogen peroxide solution with a mass concentration of 12% to 18% into the shear chamber of the three-stage inline high-shear disperser.

[0008] Step 3: Control the gap between the stator and rotor of the three-stage pipeline high-shear disperser to 0.2 mm to 0.3 mm, and control the rotor speed to 4000 rpm to 4500 rpm, so that sodium antimonate slurry is discharged from the outlet.

[0009] Step four: The discharged sodium metaantimonate slurry is directly introduced into an aging tank at a temperature of 25°C to 30°C for aging. The aged sodium metaantimonate slurry is then subjected to solid-liquid separation, washing, and airflow drying to obtain ultrafine sodium metaantimonate flame retardant.

[0010] Preferably, in step one, the preparation process of the sodium antimonyate base solution includes: dissolving antimony trioxide powder at a temperature of 90°C to 95°C until the solution is clear, lowering the solution temperature to a temperature range of 43°C to 47°C, and then adding sodium gluconate.

[0011] Preferably, in step two, the hydrogen peroxide solution is injected at the stator sidewall of the first-stage shear chamber of the three-stage inline high-shear disperser; the ratio of the flow rate of the coordination equilibrium precursor solution pumped into the main inlet to the flow rate of the hydrogen peroxide solution pumped into the shear chamber is controlled so that the molar ratio of hydrogen peroxide to antimony in the reaction system is maintained at 2.2:1 to 2.4:1.

[0012] Preferably, in step three, the average residence time of the coordination equilibrium precursor solution and the hydrogen peroxide solution in the shear chamber is 0.001 seconds to 0.005 seconds, and the average residence time is calculated by dividing the effective volume of the shear chamber by the total feed flow rate.

[0013] Preferably, in step three, the rotor speed and the clearance between the stator and rotor must satisfy the following shear rate constraint conditions: ,in, Shear rate, in reciprocal of seconds ( ); The rotor diameter of the three-stage inline high-shear disperser is in millimeters. ); The rotor speed, measured in revolutions per minute (rpm). ); The gap between the stator and rotor, in millimeters (mm). ).

[0014] Preferably, in step four, the aging time is 1.5 to 2 hours, and the stirring linear speed is maintained at 1.5 to 2 meters per second during the aging process.

[0015] Preferably, in step four, the washing process uses deionized water until the conductivity of the washing liquid is less than 150 Siemens per centimeter, and the inlet air temperature for air drying is controlled at 140°C to 160°C.

[0016] Preferably, the ultrafine sodium metaantimonate flame retardant prepared by the synthesis method has a laser particle size distribution D50 of 0.4 micrometers to 0.6 micrometers, a particle size distribution span of less than 1, and a cubic crystal morphology.

[0017] Preferably, the synthesis method further includes: before the solid-liquid separation in step four, adding a surface modifier to the aging tank, wherein the surface modifier is a silane coupling agent or a titanate coupling agent, and the amount of surface modifier added is 0.5% to 0.1% of the solid mass in the sodium metaantimonate slurry.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. In the ultrafine sodium metaantimonate flame retardant of engineering plastics, constant temperature aging within a specific temperature range and time window forces antimonyite ions and organic ligands to achieve thermodynamic coordination equilibrium, constructing a reaction-inert chelate precursor structure. The chemical conformational change introduces a kinetic delay in the oxidation reaction, extending the reaction induction period to a time greater than the characteristic time of fluid micro-mixing. The chemical delay mechanism, combined with the instantaneous mechanical energy dissipation of the pipeline high shear field, strictly restricts the oxidation nucleation process to occur within the high-energy region of shear force tearing coordination bonds. This reverses the kinetic mismatch state in traditional liquid-phase precipitation where the reaction rate is faster than the mixing rate, ensuring the spatial homogeneity of supersaturation within the reaction system, eliminating the differences in crystal nucleation caused by local concentration gradients, and obtaining a homogeneous product with an extremely narrow particle size distribution and no coarse particles.

[0020] 2. The precursor in the deep coordination state generates a steric hindrance effect at the moment of crystal nucleation. The coordinating groups preferentially adsorb and pin to the highly active crystal face of sodium metaantimonate crystal based on the difference in crystal surface energy, reducing the lattice packing rate in this direction. The selective growth inhibition mechanism causes the crystal to grow along the low-energy surface, forming a highly regular cubic morphology. From the perspective of crystallography, this prevents the formation of needle-like or plate-like irregular particles and reduces the tendency of powder surface energy to form hard agglomerates.

[0021] 3. Establishing thermodynamic pre-equilibrium locks the chemical potential of the precursor solution into a stable state, decoupling the correlation between product quality and fluctuations in raw material dissolution rate or upstream stirring efficiency. Chelating the precursor forms a homogenized concentration of free ions in the solution, ensuring that the initial state of subsequent oxidation reactions is independent of minor disturbances in the operation process. Based on the chemical equilibrium anti-interference mechanism, the stability of the process system to changes in operating conditions is improved, ensuring a stable output of flame retardant products with consistent crystal form and particle size even in continuous industrial production, despite batch differences in raw materials or minor drifts in equipment parameters. During the synthesis process, the organic coordinating groups that participate in lattice construction in situ are ultimately chemically bonded and remain on the surface of sodium antimonate crystals, forming a stable organic-inorganic interface transition layer. This structure transforms the hydrophilic surface of the inorganic powder into an oleophilic surface with good wettability to the engineering plastic melt, reducing the interfacial tension between the filler and the polymer matrix. The inherent surface characteristics promote the fluid-like dispersion of the flame retardant in the resin matrix, avoiding stress concentration points caused by filler agglomeration, maintaining high flame retardant performance while maintaining the original impact toughness and mechanical strength of the matrix material. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall process flow and key parameters of the synthesis method of ultrafine sodium metaantimonate flame retardant of the present invention.

[0023] Figure 2 This is a trend curve showing the effect of high shear speed on the product particle size D50 and distribution span Span value of the present invention.

[0024] Figure 3 This is a material interaction timing and reaction logic diagram of the preparation process of the coordination equilibrium precursor solution of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] This invention proposes a method for synthesizing ultrafine sodium antimonate flame retardants for engineering plastics. By constructing a coordination equilibrium precursor of antimonate ions and organic ligands within a specific thermodynamic temperature range, a kinetic induction period for the oxidation reaction is artificially introduced. This equilibrium is then disrupted by the mechanical energy dissipation of a high-shear dispersion device, thereby achieving spatiotemporal matching between the chemical reaction rate and the fluid micro-mixing rate. The method mainly includes three core stages: preparation of the coordination equilibrium precursor, high-shear coupled oxidation reaction, and controlled aging post-treatment. The preparation of the coordination equilibrium precursor solution addresses the contradiction between the extremely high reactivity of antimonate ions in the aqueous phase and the limited micro-mixing capacity of industrial-grade mixing equipment. The preparation process strictly controls the concentration and temperature fields of the raw materials, selecting those with a purity greater than or equal to... Antimony trioxide powder was used as the antimony source, and ion-exchange membrane grade sodium hydroxide was selected to prepare a solution with a mass concentration of [missing information]. to In a sodium hydroxide aqueous solution, antimony trioxide is added to a hot alkaline solution, and the mass concentration of antimony in the system is controlled to be within a certain range. to Within the range, the solution temperature is raised to to Stir until the solution is completely clear, ensuring that antimony trioxide is completely converted into free sodium antimonyite; then proceed to the critical thermodynamic pre-equilibrium construction stage, cooling the clarified sodium antimonyite base solution and precisely stabilizing it at... to Within a constant temperature range, sodium gluconate was added to the solution as a coordination-crystal blocking agent. The amount of sodium gluconate added was precisely calculated to control the mass ratio with antimony trioxide at a specific ratio. to After adding the complexing agent, in to Maintain constant temperature and low speed stirring under the ambient temperature. minutes to This constant-temperature aging process, lasting for minutes, is the core control point of this process. Its function is to provide the time and energy required to overcome the activation energy barrier of the coordination reaction, thus allowing the free antimonyite ions in the solution to reach a metastable state. After conformational adjustment and coordination assembly with gluconate ions, it is transformed into a thermodynamically stable antimonylic acid-gluconate cyclic chelate precursor. The formation of this chelate structure reduces the electron cloud density and reactivity of the central antimony atom, setting the necessary chemical kinetic energy barrier for subsequent oxidation reactions.

[0027] After the precursor is constructed, a kinetically matched oxidation reaction coupled with a shear field is performed. This step utilizes a three-stage inline high-shear disperser as the core reactor. This equipment generates intense hydraulic shear and turbulent vortices through the high-speed relative motion between the stator and rotor. The process settings precisely adjust the gap between the stator and rotor to... to And set the rotor speed to to Under this operating condition, the fluid shear rate within the rotor-stator gap is... Will exceed The prepared coordination equilibrium precursor solution was fed into the main feed inlet of a high-shear disperser at a constant flow rate using a volumetric pump, while simultaneously diluting the mass concentration to [a specific value]. to The hydrogen peroxide solution is pumped into the shear chamber through a dedicated injection channel located on the stator sidewall of the first-stage shear chamber. A feed control strategy ensures a constant flow ratio between the two materials, maintaining the molar ratio of hydrogen peroxide to antimony in the reaction system at a certain level. to Within the reaction chamber, high-intensity mechanical shear forces tear apart the fluid film, instantly dispersing hydrogen peroxide into micron- or even nano-sized droplets, achieving a uniform distribution of the oxidant at the microscale. Simultaneously, extremely high shear energy dissipation forcibly breaks the weak coordination bonds of the antimonylate-gluconic acid chelate, instantly releasing highly reactive antimonylate ions. Since the oxidant is now uniformly present at the microscale mixing level, the reaction is no longer diffusion-controlled but instead erupts synchronously throughout the entire system for nucleation. This mechanism of mixing followed by release allows the reaction system to achieve a uniform distribution of the oxidant at the microscale mixing level. The ratio of reaction rate to mixing rate, which is reduced to less than [a certain value], is a key parameter in traditional Chinese medicine. This level fundamentally eliminates the wide particle size distribution caused by uneven local supersaturation, and the average residence time of the reactants in the shear chamber is extremely short, controlled within... to During this period, it is ensured that the nucleated crystals quickly leave the high-energy region to avoid overgrowth; the sodium metaantimonate slurry generated by the reaction is discharged from the disperser outlet and immediately enters the low-temperature aging and post-treatment stage, and the discharged slurry is directly introduced into the pre-cooled and maintained temperature. to In the aging tank, the low-temperature environment rapidly freezes the thermal aging process of the crystals, preventing small crystals from dissolving and recrystallizing into large particles. In the aging tank, the slurry... to Aging at stirring speed Hours to During this period, the previously displaced gluconate ions will preferentially adsorb and pin to the sodium antimonate crystals with the fastest growth rate, based on the difference in crystal surface energy. Crystal planes restrict lattice stacking in that direction through steric hindrance. This selective adsorption mechanism of crystal planes allows crystals to grow only along low-energy planes, eventually developing into highly regular cubic morphologies.

[0028] After aging, the slurry undergoes solid-liquid separation using a plate and frame filter press, and the filter cake is washed in multiple stages of countercurrent washing with deionized water. The control standard for the washing endpoint is that the conductivity of the washing liquid drops to less than [value missing]. To ensure that residual water-soluble sodium salts are fully removed, the washed and qualified wet filter cake is sent to an airflow dryer, where the inlet air temperature is [temperature value missing]. to Under certain conditions, the product is instantaneously dried to obtain the final ultrafine sodium metaantimonate flame retardant product. The product obtained by this process is analyzed using a laser particle size analyzer, and its median diameter is... Stable distribution to The range, and the particle size distribution span is less than Scanning electron microscopy revealed that the product exhibited a uniform cubic structure with no obvious needle-like or flaky particles and no hard agglomerates. This microstructure is based on the excellent dispersibility and flowability of the flame retardant in engineering plastic matrices. In applications requiring further improved compatibility with organic matrices, a surface modification step can be introduced during the aging stage before solid-liquid separation, i.e., adding a certain amount of sodium antimonate solids relative to the mass of the sodium antimonate solids to the aging tank. to The silane coupling agent or titanate coupling agent is stirred and mixed. Within minutes, in-situ coating is completed using the residual active hydroxyl groups on the product surface. The thermodynamic steady-state determination of the coordination equilibrium precursor solution preparation process uses the evolution of solution transmittance as the quantitative characterization basis for the reaction endpoint. The engineering determination procedure involves continuously monitoring the transmittance of the solution at 450 nm wavelength using an online spectrophotometer during the isothermal aging process. If the transmittance change rate is less than 0.5% / min for more than 5 minutes, it is determined that the antimonyite and gluconate ions in the system have completed conformational adjustment and reached thermodynamic coordination equilibrium, initiating the subsequent high-shear transport program. This procedure ensures that the determination of the reaction initiation state is not dependent on a fixed time setting, but adaptively adjusts based on the real-time chemical equilibrium state of the system, eliminating the need for the antimony or alkali concentrations of the raw materials to be within the industrially permissible range. Fluctuations such as ±5% can lead to deviations in the degree of reaction. The micro-mixing consistency control in the high-shear coupled oxidation reaction stage uses the real-time current load of the main motor of the high-shear disperser as an indirect characterization of the energy dissipation density in the reaction zone. A linkage feedback mechanism between current fluctuations and the stator-rotor gap and feed flow rate is established to compensate for the drift in operating conditions caused by equipment wear or changes in fluid viscosity. If the main motor current deviates from the set reference value by more than 5%, the control system automatically fine-tunes the stator-rotor gap or hydrogen peroxide injection flow rate according to the preset response algorithm until the current value returns to the reference range. This dynamic compensation mechanism ensures that the shear stress applied to the fluid micro-element is always maintained at the level of tearing coordination bonds and triggering homogeneous nucleation energy level, regardless of changes in raw material batches during continuous production.

[0029] Example 1: In preparing sodium metaantimonate flame retardant for the production of high-strength flame-retardant ABS composites, the production scenario requires the flame retardant to maintain uniform dispersion in the ABS matrix even under extremely high processing shear rates, while avoiding stress concentration points due to local agglomeration, which would lead to a decrease in the notched impact strength of the final product. The direct challenge in this application scenario is that conventional sodium metaantimonate, due to its excessively rapid oxidation reaction rate during synthesis, results in a wide micro-particle size distribution and a high tendency to form hard agglomerates. These agglomerates cannot be broken up by melt shear force during injection molding, severely impairing the mechanical properties of the composite material. To address these issues, this example employs the synthesis process detailed in the aforementioned specific embodiments. In the coordination precursor preparation stage, antimony trioxide is dissolved in hot alkaline solution and then cooled to... And add relative to the mass of antimony trioxide Sodium gluconate, at this point the system does not immediately oxidize, but rather... Stirring at constant temperature This operation, lasting several minutes, allows sufficient time for the antimonyite ions in the solution to overcome the energy barrier and form a thermodynamically stable chelate precursor structure with the gluconate ions. This precursor solution and the hydrogen peroxide solution are then synchronously pumped into the stator-rotor gap. Rotation speed is In a high-shear disperser.

[0030] In this crucial step, the high-shear disperser functions not only as a mixing device but also as a precise trigger for the chemical reaction. On one hand, the coordination structure formed by sodium gluconate acts like a chemical lock, temporarily sealing the reactivity of antimonyite and maintaining its temporary kinetic inertness to oxidants. On the other hand, the disperser provides high shear rates... The shear rate acts like a mechanical key, physically tearing the coordinate bonds within an extremely short microsecond time. This synergistic mechanism of chemical retardation and physical activation ensures that the oxidation nucleation reaction occurs only in the microscopic region with the highest shear energy, and that the oxidant has already achieved molecular-level homogeneous mixing throughout the entire system by the time it occurs. The sodium metaantimonate powder obtained after low-temperature aging, washing, and drying has a median diameter... for And the particle size distribution span is less than When this product was applied to ABS composite materials, its notched impact strength was improved compared to the control group using commercially available sodium antimonate, under the same flame retardant rating. By artificially regulating the matching of reaction kinetics and micro-mixing scale, the micro-morphology of flame retardants can be precisely controlled.

[0031] Example 2: This example demonstrates an experiment conducted to maximize the preservation of the impact toughness of the matrix material without sacrificing the flame retardant rating. The test platform was equipped with precise temperature control and online particle size monitoring. The reaction vessel system, and a unit with a rated speed of up to The three-stage inline high-shear disperser's data acquisition system consists of a high-precision mass flow meter, thermocouple sensors, and a real-time data logger, capable of... The sampling period is used to monitor temperature, flow rate and rotation speed fluctuations in the reaction process in real time to ensure the traceability of process parameters; the experimental design covers three dimensions of comparative verification: first, the effect verification of coordination-crystalline blocking agent; second, the exploration of the influence law of shear field strength; and finally, the gradient evaluation of comprehensive performance.

[0032] In the first stage, two parallel experiments were set up. The control group (comparison sample group 1) used the traditional direct drop method, that is, in Hydrogen peroxide was added dropwise directly to the sodium antimonyate solution without adding any complexing agent. The sample group (experimental group 1) of this invention strictly followed the aforementioned specific implementation method. Sodium gluconate was introduced and aged at a constant temperature. Minutes later, oxidation was carried out again in a high-shear field. After the same post-processing procedure, both groups of products were characterized using a laser particle size analyzer. The particle size distribution of sample group 1 was found to be wider. Value up to Furthermore, electron microscopy reveals a large number of particles exceeding [a certain size]. Irregular aggregates, compared to the product in test group 1. converges to , Value dropped to The crystal exhibits a highly uniform cubic morphology, a difference that directly confirms the decisive role of the coordination pre-equilibrium step in suppressing explosive nucleation and controlling crystal growth; the second stage focuses on the influence of shear rate on nucleation kinetics, and a series of rotational speed gradients are set while keeping other conditions constant. , , The experimental results show that as the rotational speed increases, the product particle size exhibits a non-linear decreasing trend; when the rotational speed is lower than... At this point, the particle size reduction is not significant, and the distribution remains relatively wide, indicating that the shear energy at this stage is insufficient to completely break the limitations of reaction diffusion at the micro-mixing scale. However, when the rotational speed exceeds [a certain value], [the particle size reduction is not significant, and the distribution remains relatively wide]. (corresponding shear rate) At this time, the particle size rapidly homogenizes and stabilizes. Around this performance inflection point, the emergence of this point strongly supports the engineering rationale for limiting the rotational speed range, proving that only in the high-intensity mechanical energy dissipation region can the simultaneous tearing of coordination bonds and micro-mixing be achieved, thereby triggering homogeneous nucleation; finally, sodium metaantimonate samples prepared by different processes were blended and extruded with ABS resin and brominated epoxy resin respectively to prepare standard test strips, with the same amount of flame retardant added ( Under these conditions, all specimens met the UL94V-0 flame retardant standard. However, in the cantilever beam notched impact strength test, the specimen using the flame retardant from the control group 1 showed an impact strength lower than that of the pure ABS matrix. Microscopic observation of the fracture surface revealed significant debonding, indicating that coarse particles were the source of stress concentration and crack propagation. In contrast, the specimen using flame retardant group 1 showed a high impact strength retention rate. Furthermore, the fracture surface exhibits typical ductile fracture characteristics. See Table 1, which summarizes the key physical properties of sodium metaantimonate prepared under different process conditions and its application performance data in ABS composite materials.

[0033] Table 1: Comparison of physical properties and application performance of sodium metaantimonate under different process conditions

[0034]

[0035] Example 3: This example combines Figures 1 to 3 A method for synthesizing an ultrafine sodium metaantimonate flame retardant for engineering plastics is described, such as... Figure 1 As shown, this process involves preparing the raw materials in the sodium antimonyate base solution preparation stage. Mixed with a 18%-20% NaOH solution, dissolved until clear at 90-95℃, it enters the coordination equilibrium precursor construction stage. The key is the addition of sodium gluconate as a coordination agent, followed by isothermal aging at 43-47℃ to establish thermodynamic stability. Then, a high-shear coupled oxidation reaction is carried out. The precursor solution and a 12%-18% hydrogen peroxide solution are simultaneously pumped into a three-stage inline high-shear disperser, where the shear rate... Under kinetic conditions, mechanical energy dissipation is used to break the coordination equilibrium, and the reaction products then enter a low-temperature aging and crystal facet control step. Aging is carried out at 25-30℃ for 1.5-2.0 hours. Selective adsorption of gluconate crystal faces induces the formation of a regular cubic morphology. Finally, after solid-liquid separation and airflow drying, the washing conductivity is controlled to <150. Under conditions of a dry air inlet temperature of 140-160℃, the final output D50 is 0.4-0.6. , Ultrafine sodium antimonyate flame retardant with a cubic structure and a particle size <1.0.

[0036] like Figure 2As shown, the curves, with rotational speed (rpm) on the x-axis and particle size index on the y-axis, depict the nonlinear relationship between shear strength and product quality using the solid line D50μm and the dashed line Span value. Data shows that in the low rotational speed range of 1000rpm to 3000rpm, as the rotational speed increases, D50 decreases from 2.15μm to 1.25μm, and the Span value decreases from 1.85 to 1.4. A clear performance inflection point appears at 4000rpm, where D50 decreases to 0.5μm and the Span value reaches its lowest point at approximately 0.9. Subsequently, as the rotational speed further increases to 5000rpm and 6000rpm, although D50 decreases slightly, it tends to plateau around 0.45μm, while the Span value rebounds to 1.35, indicating that excessively high rotational speeds trigger secondary agglomeration or crystal breakage. Figure 3 As shown, five interacting components are arranged vertically: antimony trioxide, sodium hydroxide solution, dissolution reaction vessel, sodium gluconate, and precursor solution, demonstrating the process from antimony trioxide with a purity ≥99.8%... The process begins with adding powdered antimony to a dissolving reactor and then adding a 18%-20% NaOH solution. The reaction system is heated and controlled at 90-95°C. Through continuous stirring, the antimony concentration is dissolved until it reaches 90-100 g / L, and the solution is confirmed to be clear. Completely convert to sodium antimonynate, begin cooling to the target temperature of 43-47℃, add sodium gluconate at a mass ratio of 0.03:1 to 0.04:1, maintain constant temperature and stir at low speed for 35-45 minutes, finally the coordination reaction is completed, antimonynate and gluconate form a chelate precursor, establish thermodynamic steady state and form a chemical kinetic energy barrier, so that the reactivity is temporarily sealed to obtain the precursor solution.

[0037] Example 4: This example uses a standardized process window optimization experiment to verify the nonlinear influence of the core control variables—shear rate (characterized by rotational speed) and residence time—on the nucleation and growth kinetics of sodium metaantimonate crystals during high-shear dispersion. This experiment aims to demonstrate that the process parameter range defined in the claims is not arbitrarily chosen, but rather an optimal solution based on a rigorous physicochemical mechanism trade-off. The experiment uses the same reaction platform system as in Example 2, fixing the components of the coordination precursor (sodium gluconate to antimony trioxide mass ratio of...). ) and reaction temperature ( (This refers to a test group where the rotational speed of a pipeline high-shear disperser was adjusted in a gradient manner.) Five test groups were set up with rotational speeds of [missing information]. , , , and Simultaneously, by adjusting the feed flow rate, the average residence time of the reactants in the shear chamber is kept within a certain range. to During the experiment, the particle size distribution of the product was monitored in real time using an online laser particle size analyzer, and the crystal morphology was observed using a scanning electron microscope (SEM).

[0038] Data shows that when the speed is lower than (At lower shear rates), the system is in a mixing-dominated region, and uneven local supersaturation leads to differences in nucleation rates, resulting in different products. Generally greater than And the distribution span Value exceeds The microstructure exhibits obvious irregular polycrystalline aggregate characteristics, which increases with rotational speed. to Range (corresponding to shear rate) The system enters the optimal window for kinetic matching. Within this range, extremely high mechanical energy dissipation not only enables molecular-level mixing of reactants at the microsecond level but also provides activation energy sufficient to break coordination bonds, triggering explosive nucleation of the entire system. At this point, the products... convergence to about, Value dropped to Below, the crystals exhibit a highly regular cubic morphology; however, when the rotational speed is further increased to When the residence time is too long, although the particle size further decreases, the excessively high shear energy causes secondary agglomeration of the newly formed crystal nuclei or crystal breakage, resulting in... The value actually increases, and energy consumption also increases, making it uneconomical for industrial applications. The appearance of this performance inflection point confirms the importance of rotor speed ( to The scientific validity and necessity of limiting the shear gap parameter indicate that the parameter range is an optimal working window that balances nucleation quality and energy efficiency, effectively avoiding uneven mixing under low shear and crystal damage under excessively high shear. See Table 2, which summarizes the key particle size indexes and morphological characteristics of sodium metaantimonate under different shear rates, and intuitively presents the nonlinear relationship between process parameters and microstructure.

[0039] Table 2: Comparison of particle size and morphology characteristics of sodium metaantimonate at different shear rates

[0040]

[0041] Example 5: To ensure the process robustness of this synthesis method under different production batches and fluctuations in raw material sources, this example constructs and implements a standardized offline calibration procedure for the stability of coordination precursors. By quantitatively monitoring the evolution of the transmittance of the precursor solution, the optimal aging time window required to achieve thermodynamic pre-equilibrium under different raw material conditions is determined, thereby providing a reproducible process control basis for industrial production. This calibration procedure can be performed on a precision constant-temperature optical monitoring platform, and a series of preparations with different initial antimony concentrations ( to ) and alkali concentration ( to A sodium antimonyate-based solution was used to simulate potential raw material fluctuations in industrial production. Sodium gluconate (mass ratio fixed) is added under constant temperature conditions. ), and immediately start stirring, using an online spectrophotometer (wavelength set to ), The transmittance of the solution was continuously recorded over time. The data showed that in the initial stage after the addition of the ligand, the transmittance would fluctuate briefly due to local supersaturation and the formation of metastable coordination intermediates. As the aging time increased, antimonyite and gluconate gradually completed coordination and recombination, and the transmittance curve tended to stabilize, indicating that the system had reached thermodynamic coordination equilibrium.

[0042] Through dynamic fitting analysis of multiple sets of data, an empirical correlation model between transmittance stabilization time and initial antimony concentration was established. Based on this model, the following on-site process control logic was established: In actual production, if the raw material antimony concentration fluctuates within... Within this period, the standard aging time is set as follows: minutes; if the concentration deviation exceeds Then the aging time needs to be dynamically adjusted based on the real-time transmittance monitoring results until the transmittance change rate is less than 1%. And continue After at least 1 minute, the subsequent high-shear oxidation step can be started.

[0043] Example 6: This example introduces a dual mechanism of dimensionless standard number correlation calibration and online energy consumption response monitoring to achieve accurate mapping and dynamic correction of process parameters. During the engineering scale-up stage, based on the principle of similarity compatibility, the Reynolds number is used... With power level As a core scale-up criterion, the characteristic values ​​of fluid shear stress at the optimal reaction speed were measured on a laboratory-scale high-shear device. Using a computational fluid dynamics (CFD) simulation model, the stator and rotor structure of the industrial-grade reactor were optimized to ensure that it could still generate an equivalent microscopic turbulent dissipation rate under high-throughput conditions. After the equipment was installed, a rigorous hydraulic commissioning process was carried out: using pure water as the medium, the equivalent shear speed and critical cavitation margin of the industrial equipment were calibrated by gradually increasing the rotational speed and monitoring the pressure pulsation spectrum at the stator outlet, thereby establishing a correction coefficient matrix for converting laboratory parameters to industrial parameters.

[0044] In actual production debugging, to address the potential changes in rheological properties caused by batch fluctuations in raw materials, the procedure integrates adaptive control logic based on motor current load. The system collects the current signal of the main motor of the high-shear disperser in real time as an indirect characterization of the apparent viscosity and micro-mixing state of the reaction system. When the detected current fluctuation exceeds the preset value... When the threshold is reached, the control system will automatically fine-tune the hydrogen peroxide injection flow rate or the stator-rotor gap based on a pre-embedded feedback algorithm to maintain a constant energy dissipation density within the reaction zone. This dynamic adjustment mechanism based on online response compensates for non-ideal disturbances in the engineering environment, ensuring the particle size distribution of each batch of products. The value is always controlled at Within.

[0045] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics, characterized in that, The method includes the following steps: Step 1: Dissolve antimony trioxide powder in an aqueous sodium hydroxide solution with a mass concentration of 18% to 20% to prepare a sodium antimony base solution; add sodium gluconate to the sodium antimony base solution, controlling the mass ratio of sodium gluconate to antimony trioxide to be 0.03:1 to 0.04:1; place in a temperature environment of 43℃ to 47℃ and stir at a constant temperature for 35 minutes to 45 minutes to obtain a coordination equilibrium precursor solution; Step 2: Pump the coordination equilibrium precursor solution and the hydrogen peroxide solution with a mass concentration of 12% to 18% into the shear chamber of the three-stage inline high-shear disperser. Step 3: Control the gap between the stator and rotor of the three-stage pipeline high-shear disperser to 0.2 mm to 0.3 mm, and control the rotor speed to 4000 rpm to 4500 rpm, so that sodium antimonate slurry is discharged from the outlet. Step four: The discharged sodium metaantimonate slurry is directly introduced into an aging tank at a temperature of 25°C to 30°C for aging. The aged sodium metaantimonate slurry is then subjected to solid-liquid separation, washing, and airflow drying to obtain ultrafine sodium metaantimonate flame retardant.

2. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, In step one, the preparation process of the sodium antimonyate base solution includes: dissolving antimony trioxide powder at a temperature of 90°C to 95°C until the solution is clear, lowering the solution temperature to a temperature range of 43°C to 47°C, and then adding sodium gluconate.

3. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, In step two, the hydrogen peroxide solution is injected at the stator sidewall of the first-stage shear chamber of the three-stage inline high-shear disperser; the ratio of the flow rate of the coordination equilibrium precursor solution pumped into the main inlet to the flow rate of the hydrogen peroxide solution pumped into the shear chamber is controlled so that the molar ratio of hydrogen peroxide to antimony in the reaction system is maintained at 2.2:1 to 2.4:

1.

4. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, In step three, the average residence time of the coordination equilibrium precursor solution and the hydrogen peroxide solution in the shear chamber is 0.001 seconds to 0.005 seconds. The average residence time is calculated by dividing the effective volume of the shear chamber by the total feed flow rate.

5. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, In step three, the rotor speed and the clearance between the stator and rotor must satisfy the following shear rate constraints: ,in, Shear rate, in reciprocal of seconds. ; The rotor diameter of the three-stage inline high-shear disperser is in millimeters. This refers to the rotor speed, measured in revolutions per minute. This refers to the gap between the stator and rotor, measured in millimeters.

6. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, In step four, the aging time is 1.5 to 2 hours, and the stirring speed is maintained at 1.5 to 2 meters per second during the aging process.

7. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, In step four, deionized water is used for the washing process until the conductivity of the washing liquid is less than 150 microsiemens per centimeter, and the inlet air temperature for air drying is controlled at 140°C to 160°C.

8. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, The ultrafine sodium metaantimonate flame retardant prepared by the synthesis method has a laser particle size distribution D50 of 0.4 μm to 0.6 μm, and the particle size distribution span is less than 1. The crystal morphology is cubic structure.

9. The method for synthesizing ultrafine sodium metaantimonate flame retardant for engineering plastics according to claim 1, characterized in that, The synthesis method further includes: before the solid-liquid separation in step four, adding a surface modifier to the aging tank. The surface modifier is a silane coupling agent or a titanate coupling agent, and the amount of surface modifier added is 0.5% to 0.1% of the solid mass in the sodium metaantimonate slurry.

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