Controlled synthesis process of high-temperature-resistant sodium metaantimonate crystal structure

Abstract

The application relates to the technical field of inorganic chemical materials, and discloses a control synthesis process of a high-temperature-resistant sodium meta-antimonate crystal structure, which comprises the following steps: dispersing diantimony trioxide in a sodium hydroxide aqueous solution with an initial concentration of 6.5-8.0 mol / L, adding sodium meta-aluminate as a crystal lattice directing agent to prepare a precursor bottom solution; heating the bottom solution and maintaining turbulent stirring, performing double-flow path synchronous compensation, adding hydrogen peroxide aqueous solution drop by drop and synchronously adding sodium hydroxide; dynamically setting the coupling relationship of the alkali supplementing rate, the oxidation rate and the reaction stoichiometric ratio, and real-timely offsetting the dilution effect of reaction generated water and solvent water, so that the free sodium hydroxide concentration of the mother liquor in the whole reaction process is maintained to be above 6.0 mol / L until the reaction endpoint is reached; the application dynamically clamps the reaction boundary, blocks the path of the lattice gap water or the surface hydroxyl group, and prepares anhydrous sodium meta-antimonate without a crystallization water removal step in the whole temperature range, so that the foaming problem in high-temperature processing is solved.

Description

Technical Field

[0001] This invention relates to a controlled synthesis process for sodium metaantimonate crystal structure resistant to high temperatures, belonging to the field of inorganic chemical material preparation technology. Background Technology

[0002] Sodium metaantimonate, with its high refractive index, is widely used in photovoltaic glass clarification and flame-retardant modification of engineering plastics. Current industrial production primarily employs a liquid-phase oxidation method, using antimony trioxide as a raw material. This involves oxidation and oxidation in a sodium hydroxide solution. The process utilizes a high-concentration alkaline environment to suppress antimony ion hydrolysis, resulting in cubic sodium metaantimonate crystals that meet the thermal stability requirements of downstream applications. However, for high-end engineering plastics like LCPs or high-temperature nylon flame retardants requiring processing above 300 degrees Celsius without precipitation or foaming, the traditional liquid-phase oxidation method suffers from fundamental limitations. The liquid-phase synthesis system is a dynamically changing physicochemical field. The oxidation of sodium metaantimonate releases a large amount of chemical water, and industrial-grade hydrogen peroxide introduces solvent water. As the reaction progresses, solute consumption and solvent increase lead to liquid-phase volume expansion, nonlinear decay of the effective molar concentration of sodium hydroxide, and increased water activity. Later in the reaction, during crystal shell growth, the liquid-phase environment slides into the thermodynamically stable region of hydrated sodium pyroantimonate or sodium hydroxyantimonate, inevitably embedding lattice water or hydroxyl defects into the outermost layer of the crystal.

[0003] In terms of oxidant selection and dehydration process optimization, existing technical solutions also have significant shortcomings and cannot fundamentally solve the lattice defect problem. For example, Chinese invention patent CN106745245B discloses a method for preparing sodium pyroantimonate and sodium metaantimonate. This method uses ozone as an oxidant to prepare sodium pyroantimonate, and then prepares sodium metaantimonate by microwave dehydration. Ozone has a high oxidation potential, which helps to reduce trivalent antimony residue. Microwave dehydration can avoid yellowing caused by traditional high-temperature calcination. However, this solution still obtains sodium metaantimonate through subsequent physical dehydration after the formation of sodium pyroantimonate. This approach does not change the thermodynamic environment in which hydration or hydroxyl defects are formed due to the decay of alkali concentration and the increase of water activity when the crystal grows in the liquid phase. The lattice defects are already formed in the oxidation crystallization stage, and the subsequent dehydration operation is only a compensatory measure.

[0004] Therefore, in an unsteady liquid-phase reaction system with strong exothermic reaction and continuous water production, overcoming the kinetic inevitability of natural decay of chemical potential, locking the anhydrous thermodynamic environment for crystal growth throughout the process, and preparing sodium antimonate with uniform lattice, no hydration defects, and good dispersibility has become the technical problem to be solved by this invention. 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 controlled synthesis process for a high-temperature resistant sodium metaantimonate crystal structure, comprising the following steps:

[0006] Step S1: Construct a high-alkalinity precursor solution by dispersing antimony trioxide powder in an aqueous sodium hydroxide solution with an initial molar concentration of 6.5 mol / L to 8.0 mol / L, and adding sodium aluminate accounting for 0.5% to 1.5% of the molar amount of antimony atoms in antimony trioxide as a lattice directing agent, and forming a homogeneous precursor solution under mechanical stirring.

[0007] Step S2: Establish an isochemical potential oxidation crystallization field, heat the precursor liquid to 98°C to 105°C and maintain turbulent stirring, perform dual-flow synchronous compensation operation, add hydrogen peroxide aqueous solution with a mass fraction of 35% to 50% to the precursor liquid at a constant rate in the first flow path, and add solid sodium hydroxide with a purity of not less than 98% or concentrated sodium hydroxide solution with a concentration of not less than 48% to the second flow path simultaneously.

[0008] Step S3: Dynamically control the reaction boundary and set the coupling relationship between the addition rate of sodium hydroxide in the second flow path and the dropping acceleration rate of hydrogen peroxide aqueous solution in the first flow path and the stoichiometric ratio of the reaction. This ensures that the amount of sodium hydroxide added per unit time can offset the dilution effect caused by the water generated in the reaction and the water brought in by the hydrogen peroxide aqueous solution. The concentration of free sodium hydroxide in the reaction mother liquor is maintained above 6.0 mol / L throughout the entire oxidation reaction process until the redox potential of the reaction system jumps and stabilizes in the range of -200 mV to -100 mV.

[0009] Step S4: Solid-liquid separation and mother liquor closed loop. The slurry obtained in step S3 is separated by hot filtration. The separated high-temperature mother liquor is directly returned to step S1 for recycling. The filter cake is washed and dried to obtain anhydrous sodium metaantimonate.

[0010] Preferably, in step S1, the liquid-solid ratio of antimony trioxide to sodium hydroxide aqueous solution is controlled between 3:1 and 5:1; in step S2, the speed of turbulent stirring is controlled between 300 rpm and 500 rpm, the dropping time of hydrogen peroxide aqueous solution is controlled between 2 hours and 4 hours, and the aging time after the dropping is completed is not less than 2 hours.

[0011] Preferably, in step S1, sodium aluminate serves as a heteroepitaxial growth site, inducing antimony octahedrons to stack along the three-dimensional compact direction of the anhydrous cubic crystal system; the precursor solution does not contain organic dispersants or polymeric surfactants.

[0012] Preferably, in step S3, the alkali replenishment rate of the second flow path follows a linear coupling rule based on water-material balance, which is defined by the following formula: ,in, This refers to the mass addition rate of sodium hydroxide in the second flow path, converted to pure sodium hydroxide. The volumetric droplet acceleration rate of the hydrogen peroxide aqueous solution in the first flow path. The preset dilution compensation factor; dilution compensation factor The amount of water produced is determined based on the water content of the hydrogen peroxide aqueous solution and the stoichiometric amount of water produced by the oxidation reaction.

[0013] Preferably, in step S2, the feed ports of the first flow path and the second flow path are symmetrically distributed in the reactor space, and the feed point is located in the intersection area of ​​the tangential flow and the radial flow formed by the stirring blades.

[0014] Preferably, in step S3, silver / silver chloride is used as a reference electrode to monitor the redox potential, and the criteria for determining the reaction endpoint also include the complete change of the slurry color from grayish-white to pure white; the entire reaction process is carried out under normal pressure, and the temperature of the reaction system is always kept at a slight boiling state.

[0015] Preferably, in step S4, before returning to step S1, the high-temperature mother liquor is only replenished with the consumed amount of antimony trioxide and sodium hydroxide to adjust to the initial feed state, without evaporation and concentration. The filter cake is washed with deionized water at a temperature of 60 to 80 degrees Celsius until the pH value of the washing liquid drops to between 7.0 and 8.0.

[0016] Preferably, in step S1, the antimony trioxide raw material is cubic with an average particle size D50 of 1.0 micrometer to 2.0 micrometer and a purity of not less than 99.8%; the anhydrous sodium metaantimonate product has a cubic or hexagonal crystal structure and a thermal weight loss rate of less than 0.1% in the range of 300 degrees Celsius to 350 degrees Celsius.

[0017] Preferably, the dynamic clamping reaction boundary step locks the thermodynamic environment of crystal growth in the stable region of anhydrous sodium antimonate, blocking the formation pathway of interstitial water or surface hydroxyl groups.

[0018] Preferably, the process is used to prepare a flame retardant synergist to be added to engineering plastics, including liquid crystal polymers or high-temperature nylon; the resulting anhydrous sodium metaantimonate crystals have native monodisperse properties and do not require calcination at temperatures above 600 degrees Celsius.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. A dynamic reaction system coupled with oxidation rate and base potential compensation is constructed to avoid the problem of continuous deterioration of the liquid phase environment caused by the introduction of water from the reaction and solvent in traditional wet processes. The water activity of the reaction system is maintained below the thermodynamic formation threshold of hydrated antimonate throughout the oxidation and crystallization process. This ensures that the crystal remains in the stable growth region of the anhydrous cubic crystal system throughout the entire time window from initial nucleation to final shell growth. Dynamic boundary condition locking eliminates the core-shell structure of dry inside and wet outside caused by the sliding of the conventional product into the hydrated region in the later stage of the reaction. It avoids the intercalation of lattice gaps or surface hydroxyl groups. The sodium metaantimonate crystals obtained are free from heat-sensitive water-containing defects under high-temperature processing environment, exhibiting structural inertness and anti-foaming properties. This solves the problem of matrix degradation and bubble generation caused by flame retardants in the extrusion of engineering plastics.

[0021] 2. The strong exfoliation effect of the antimony species hydration layer by the high concentration of sodium hydroxide environment, combined with the heterogeneous induction effect of trace aluminum species, forms a synergistic mechanism. The constant high alkaline potential field inhibits the coordination tendency of antimony ions and water molecules, clearing the competitive hydration barrier for aluminum-oxygen tetrahedral-dominated heteroepitaxial growth. The intervention of aluminum species guides the crystal to stack along the three-dimensional dense direction of the anhydrous structure, avoiding the formation path of layered water-bearing structures. The synergistic effect of the two changes the crystal growth mode from explosive amorphous precipitation to controlled layered epitaxial growth. Based on the regular polyhedral morphology and uniform particle size distribution of the product, the original monodisperse microcrystalline structure does not need to undergo the high-temperature calcination process that leads to hard agglomeration, thus possessing the dispersibility and flow compatibility of the polymer matrix.

[0022] 3. By using a real-time compensation strategy for solute consumption and solvent dilution during the reaction process, the chemical requirements for maintaining the crystal growth environment and the engineering requirements for mother liquor recycling are unified in the same operating unit. After the reaction, the mother liquor is consistent with the starting feed solution in terms of chemical composition and concentration potential. It can be directly reused as the base liquid for the next batch of reaction without the need for high-energy evaporation and concentration or complex preparation. The process compensation replaces the atom-economical path of back-end treatment to maintain the long-term stability of the reaction kinetic environment between batches, reduce water consumption and waste liquid discharge in industrial production, and achieve the unification of inorganic synthesis process quality control and green manufacturing. Attached Figure Description

[0023] Figure 1 This is a flowchart of the isochemical potential controlled synthesis process of high-temperature resistant sodium metaantimonate according to the present invention;

[0024] Figure 2 This is a comparison chart of the high-temperature extrusion processing stability of LCP samples processed using different techniques according to the present invention.

[0025] Figure 3 This is a schematic diagram of the structure of the dual-flow-path reaction device and the closed-loop circulation principle of the mother liquor of the present invention. Detailed Implementation

[0026] The following embodiments are further explanations and illustrations of the present invention and do not constitute any limitation on the present invention.

[0027] This invention proposes a controlled synthesis process for high-temperature resistant sodium metaantimonate crystal structures, comprising four core steps: construction of a high-alkalinity precursor solution, heteroepitaxial lattice guidance, isochemical potential dual-flow-path oxidation crystallization, and high-temperature mother liquor closed-loop circulation. By clamping the liquid phase chemical potential boundary in a dynamic reaction field, the dilution effect caused by solute consumption and solvent increment during conventional wet oxidation is eliminated, thereby locking the thermodynamic growth environment of anhydrous cubic or hexagonal sodium metaantimonate across the entire temperature range. In the first stage of the process, namely the construction of the high-alkalinity precursor solution, a reaction slurry is prepared by dispersing cubic antimony trioxide powder in an aqueous sodium hydroxide solution. The initial molar concentration of the sodium hydroxide solution is strictly set within the range of 6.5 mol / L to 8.0 mol / L, and the liquid-to-solid ratio is controlled between 3:1 and 5:1. The establishment of this initial high-concentration alkaline environment aims to utilize the strong solvation binding effect of the high-concentration electrolyte on water molecules to suppress the initial water activity of the system below the formation threshold of hydrated antimonate, thereby blocking... In the early formation pathway of the bond, sodium aluminate, accounting for 0.5% to 1.5% of the molar amount of antimony atoms in antimony trioxide, is introduced as a lattice directing agent in this high-alkalinity substrate. The aluminum-oxygen tetrahedral species dissociated from the sodium aluminate in the system, taking advantage of the difference and compatibility with the antimony-oxygen octahedron in coordination geometry, act as induction sites for heteroepitaxial growth, guiding the generated sodium aluminate crystals to stack along the three-dimensional dense direction of the anhydrous structure, rather than along the direction of the layered aqueous structure, thereby establishing the lattice framework of the anhydrous phase in the early stage of nucleation.

[0028] The process of establishing an isochemical potential oxidation crystallization field is the core step in overcoming the dilution effect of traditional reaction processes. It is initiated by heating the precursor solution to 98-105°C and maintaining turbulent stirring at 300-500 rpm. This step abandons the conventional operation of simply adding an oxidant dropwise, instead implementing a dual-flow-path synchronous compensation operation. In the first flow path, a 35%-50% hydrogen peroxide aqueous solution is added dropwise at a constant rate to initiate the oxidation reaction. In the second flow path, solid sodium hydroxide with a purity of not less than 98% or a concentrated sodium hydroxide solution with a concentration of not less than 48% is added simultaneously. During this process, the rate of sodium hydroxide addition in the second flow path is not constant or arbitrarily set, but follows a linear coupling rule based on water-material balance. This rule requires the second flow path to have a mass addition rate equivalent to pure sodium hydroxide. The formula must be satisfied The defined quantitative relationship, among which is the volumetric droplet acceleration rate of the hydrogen peroxide aqueous solution in the first flow path, and the dilution compensation coefficient. The calculated value is determined by the water content of the hydrogen peroxide aqueous solution and the stoichiometric water production of the oxidation reaction. By executing this dynamic clamping procedure, the amount of alkali added per unit time can offset the dilution effect of the reaction-generated water and hydrogen peroxide solvent water on the system in real time and accurately, and maintain the concentration of free sodium hydroxide in the reaction mother liquor above the critical dehydration threshold of 6.0 mol / L throughout the entire oxidation reaction process, ensuring that the growth of the crystal from the core to the shell is always in the anhydrous thermodynamic stability region.

[0029] The endpoint of the oxidation reaction is determined using a dual anchoring mechanism of electrochemical and optical signals. When the monitoring system shows that the redox potential of the reaction system suddenly rises from a negative value and stabilizes in the range of -200 mV to -100 mV, and the slurry color changes completely from grayish-white at the beginning of the reaction to pure white, the reaction is considered complete and the dual-flow path feeding is stopped. Afterward, the slurry continues to age in a slightly boiling state for no less than 2 hours, utilizing the Oswald ripening effect to further eliminate fine grains and regulate crystal morphology. The solid-liquid separation and mother liquor closed-loop process after the reaction embodies the atom economy and engineering closed-loop logic of this process. The high-temperature mother liquor obtained by hot filtration, due to the dynamic alkali addition operation based on solute consumption and solvent increment compensation implemented in the preceding steps, maintains a high degree of consistency between the sodium hydroxide concentration and the initial feed concentration. Therefore, this high-temperature mother liquor does not require further high-temperature filtration. The energy-efficient evaporation and concentration operation only requires the addition of antimony trioxide and trace amounts of sodium hydroxide for preparation. The solution can then be directly returned to the first stage as a precursor for the next batch. The filter cake is washed with deionized water at 60°C to 80°C until the pH of the washing solution drops to between 7.0 and 8.0. After drying, anhydrous sodium metaantimonate is obtained. The resulting anhydrous sodium metaantimonate product exhibits a regular cubic or hexagonal crystal structure. Due to the blocking of interstitial water and surface hydroxyl groups during the synthesis process, the product exhibits extremely high thermal stability in the high-temperature range of 300°C to 350°C, with a thermal weight loss rate of less than 0.1%. The average particle size D50 is controlled between 1.0 μm and 2.0 μm, possessing native monodisperse characteristics. It is suitable as a flame retardant synergist in liquid crystal polymers or high-temperature nylon and other engineering plastics.

[0030] Example 1: In the application of flame retardant modification for high-performance liquid crystal polymer (LCP) precision connectors, traditional sodium metaantimonate flame retardants are facing severe challenges in processing stability. During the production of such precision electronic components, the processing temperature of the matrix resin needs to be maintained above 320°C for extended periods, and the melt is subjected to extremely high shear stress within micron-level flow channels. Under such harsh conditions, commercially available sodium metaantimonate products, due to residual structural water deep within their crystal lattice or adsorbed hydroxyl groups on their surface, are highly susceptible to dehydration condensation reactions under the combined effects of high temperature and shear, releasing trace amounts of water vapor. This in-situ generated water vapor forms microbubbles in the melt, directly causing appearance defects such as silver streaks on the connector surface. This not only severely affects the product yield but also induces hydrolysis in the matrix resin. Degradation leads to a catastrophic decrease in the mechanical strength of materials, failing to meet the zero-defect requirements for dimensional accuracy and mechanical properties in high-end electronic connectors. To address these challenges, this invention employs an isochemical potential-controlled oxidation crystallization process as described in the aforementioned specific embodiments to achieve full-lifecycle anhydrous structure locking of the microstructure of sodium metaantimonate. During this process, a high-alkalinity precursor solution with an initial concentration of 7.5 mol / L is constructed. The strong solvation binding effect of high-concentration sodium hydroxide on water molecules suppresses the water activity of the system below the thermodynamic formation threshold of hydrated antimonate. Based on this, in the oxidation crystallization stage, this process does not follow the traditional one-pot method of unidirectional oxidant addition, but instead activates a core dual-flow-path synchronous compensation mechanism.

[0031] While adding 50% hydrogen peroxide solution, the second flow path simultaneously injects an ultra-high concentration of sodium hydroxide solution into the reaction system based on a real-time calculated dilution compensation coefficient. This crucial intervention acts as a precise chemical potential stabilizing valve, counteracting the dilution effect of the reaction-generated water and oxidant solvent water on the mother liquor's alkali concentration in real time. This keeps the free sodium hydroxide concentration above the critical dehydration threshold of 6.0 mol / L throughout the entire reaction process. This dynamic locking of the liquid phase chemical potential boundary ensures that the sodium metaantimonate crystals remain in the thermodynamically stable region of the anhydrous cubic crystal system at every growth moment, from the initial formation of the crystal nucleus to the final closure of the crystal shell, thereby completely blocking interstitial water or surface water at the source. The formation pathway of hydroxyl defects; the anhydrous sodium metaantimonate crystals prepared by this process showed decisive performance advantages in application verification. When added to the LCP matrix at a mass fraction of 5% and subjected to high-temperature extrusion granulation, even after being processed at 340°C for 30 minutes, the melt surface remained smooth as a mirror, without any visible bubbles or silver streaks, indicating that the flame retardant completely eliminates the risk of heat-sensitive moisture release under extreme thermal conditions. The mechanical property test results further confirmed that, compared with the control group that added conventional products, the tensile strength retention rate of the LCP composite material using the product of this invention was increased by more than 15%, and the elongation at break did not show a significant decrease in brittleness.

[0032] Example 2: In a real high-temperature extrusion processing verification experiment, a set of control experiments was designed to systematically investigate the effect of isochemical potential controlled oxidation process on the integrity of sodium metaantimonate crystal structure and its processing stability in a high-temperature polymer matrix. The experimental group (sample group of this invention) was prepared using the process of this invention, that is, during the oxidation process, dual-flow-path synchronous compensation was strictly implemented to keep the concentration of free sodium hydroxide in the mother liquor above 6.0 mol / L throughout the process; Control group 1 (conventional process sample group) simulated the traditional one-time high-alkali method. Although the initial alkali concentration was also 7.5 mol / L, only hydrogen peroxide was added dropwise in one direction during the oxidation process, without synchronous alkali replenishment. Operation: Control group 2 (low-alkali process sample group) simulated the condition of insufficient alkali concentration in the later stage of the reaction, and the alkali concentration was controlled between 4.5 mol / L and 5.5 mol / L throughout the reaction process; The crystal structure and thermal stability of the three groups of samples were characterized. Observation using high-resolution transmission electron microscopy (HRTEM) revealed that the crystals of the experimental group exhibited a regular cubic morphology with clear lattice fringes extending to the edges and no amorphous layer was observed; while the crystal edges of control group 1 and control group 2 both had varying degrees of blurred areas, showing an amorphous hydration layer of about 5-15 nm thick. Further thermogravimetric analysis (TGA) data are shown in Table 1.

[0033] Table 1: Comparison of Thermogravimetric Loss Data for Sodium Metaantimonate Prepared by Different Processes

[0034]

[0035] Referring to the data in Table 1, the weight loss rate of the experimental group in the critical processing temperature range of 300℃ to 350℃ was only 0.08%, which was lower than 0.45% of control group 1 and 1.25% of control group 2. This result confirms that maintaining a high-alkali environment through dual-flow synchronous compensation effectively blocks the formation of interstitial water and surface hydroxyl groups, eliminating the heat-sensitive weight loss source at high temperatures. The three groups of samples were mixed with LCP resin at an addition amount of 5% and subjected to high-temperature granulation tests in a twin-screw extruder. The temperature of each zone of the extruder was set at 330℃-340℃ and the screw speed was 300 rpm. The monitoring data of the processing process and the evaluation results of the finished product appearance are as follows.

[0036] Table 2: Comparison of High-Temperature Extrusion Processing Performance of LCP Composites

[0037]

[0038] Referring to the results in Table 2, the experimental group showed minimal melt pressure fluctuation (±0.2 MPa) during high-temperature and high-shear processing, with a smooth extruded strip surface and no pores in the cross-section, indicating that the flame retardant did not undergo decomposition and dehydration in the matrix. In contrast, control groups 1 and 2 experienced unstable melt pressure and foaming due to the release of residual hydroxyl groups or water of crystallization in the crystal structure at high temperatures, which seriously affected the processing quality of the material.

[0039] Example 3: This example combines Figures 1 to 3 The controlled synthesis process of a high-temperature resistant sodium antimonate crystal structure is described, such as... Figure 1 As shown, the controlled synthesis process of this high-temperature resistant sodium metaantimonate crystal structure is based on dispersion Starting with raw materials, the process proceeds to step S1 to construct a high-alkalinity precursor solution. Sodium aluminate is added as a lattice directing agent, and the initial concentration is controlled at 6.5 to 8.0 M. The system is heated to a micro-boiling state of 98 to 105 degrees Celsius and turbulent stirring is established. The process then proceeds to step S2, the isochemical potential controlled oxidation stage. The core operation involves simultaneous compensation of dual flow paths and dynamic clamping of the reaction boundary. The key indicator is to maintain NaOH ≥ 6.0 M throughout the process until a sudden jump in ORP potential is detected and the slurry color turns pure white. The reaction slurry then proceeds to step S3 for crystal maturation. After micro-boiling aging for more than 2 hours to eliminate fine crystals and defects, the mixture is filtered while hot and proceeds to step S4 for solid-liquid separation. The separated high-temperature mother liquor is returned to step S1 through a closed-loop circulation circuit without the need for evaporation and concentration, and only the consumed amount is replenished. The separated filter cake is washed, dried, and packaged to obtain anhydrous sodium antimonate product.

[0040] like Figure 2 As shown, the left vertical axis represents performance index values. The legend distinguishes between the extruder appearance score (out of 10) and the die head melt pressure fluctuation (in MPa). Data shows that the test group samples had an extruder appearance score close to 10 and extremely low die head melt pressure fluctuation, close to 0.2 MPa. Control group 1, however, saw its appearance score drop to 6 and pressure fluctuation increase to 1.5 MPa. Control group 2 performed the worst, with an appearance score below 2 and pressure fluctuation approaching 4.0 MPa. Figure 3 As shown, the main body of the reaction device is a reactor with a heating jacket and a motor-driven stirrer. The top of the reactor has symmetrically distributed first and second flow path feed ports, which are used for inputting feed. With NaOH, the vessel contains... NaOH and The precursor liquid is formed and the liquid level is displayed. After the reaction is completed, the slurry is discharged from the bottom outlet of the reactor and enters the solid-liquid separation unit for hot filtration. The separated solid phase is filter cake, i.e. anhydrous sodium metaantimonate, while the liquid phase is used as a high-temperature mother liquor circulation flow and is directly returned to the reactor along the return pipeline to participate in the construction of the next batch of precursor liquid.

[0041] Example 4: To address the issue of dilution compensation coefficient in the industrial-scale production of high-temperature resistant sodium metaantimonate. To address the identified engineering black box issues and verify the closed-loop stability of the high-temperature mother liquor under non-evaporation concentration conditions, this embodiment constructs a standardized parameter calibration procedure based on thermodynamic water-material balance. In a 500-liter Hastelloy pilot-scale reactor equipped with a precision mass flow meter and an online refractometer, the dynamic hydration behavior of the reaction system under micro-boiling conditions at 98°C to 105°C is quantitatively modeled. This procedure identifies three core variables affecting the water activity of the system: the flux of solvent water introduced by the hydrogen peroxide solution... Chemical water flux generated by oxidation reaction And the natural evaporation water flux under specific stirring power and temperature. Based on the above variables, the dilution compensation coefficient is established. The engineering calculation logic aims to precisely counteract the dilution effect caused by the increase in purified water through the addition of solid sodium hydroxide in the second flow path. This control logic is quantified into the following mass balance relationship: ,in, The mass addition rate of solid sodium hydroxide in the second flow path. The target molar concentration of the mother liquor was set (7.5 mol / L in this example). The coefficient of solution volume increase caused by dissolving a unit mass of sodium hydroxide is used in actual calibration. This is achieved by adding deionized water to the reaction vessel and heating it to 102 degrees Celsius while maintaining reflux. The inherent evaporation rate under these conditions is then measured. With a flow rate of 12.5 L / h, and considering the constant dripping acceleration rate of 50% mass fraction hydrogen peroxide in the first flow path, the system calculates that the net water increment is only 5.7 L / h.

[0042] Based on this calculation result, the alkali replenishment rate of the second flow path is set. Three consecutive batches of oxidation crystallization cycle experiments were conducted. After each batch of reaction, the crystals were separated by hot filtration. The filtrate was not subjected to any additional evaporation and concentration steps. Instead, antimony trioxide and trace amounts of sodium hydroxide were added to correct the initial volume, and the filtrate was directly used as the base liquid for the next batch. The monitoring data of key indicators of the mother liquor from the three batches of cycle experiments showed that the sodium hydroxide concentration of the mother liquor at the reaction endpoint remained stable in a very narrow range of 7.4 mol / L to 7.6 mol / L, without the concentration decay phenomenon commonly seen in conventional processes. Moreover, due to the precise coupling of the micro-boiling evaporation effect and the alkali replenishment operation, the total liquid volume fluctuation of the system was less than 3%. By establishing a precise water-material balance model, dynamic clamping and mother liquor closed-loop can be unified in the same thermodynamic process, achieving long-term and stable locking of the growth environment of anhydrous sodium metaantimonate without introducing a high-energy-consuming evaporation process.

[0043] Example 5: In the engineering deployment project of migrating the high-temperature sodium metaantimonate synthesis process from the laboratory scale to a thousand-ton-scale industrial production line, establishing standardized offline calibration and data filling procedures is a prerequisite for ensuring production stability. Considering the engineering reality of reactor scale-up, a pilot-scale reaction model with a volume of 50 liters and geometrically similar to the actual production equipment was constructed. Precision calorimetry was used to determine the natural evaporation water flux under different combinations of stirring power density (0.5 to 2.0 kW / m³) and reaction temperature (98 to 105 degrees Celsius). Through a series of orthogonal experiments, a characteristic curve of the evaporation rate as a function of operating parameters was plotted, and this curve was fitted into an empirical formula and entered into the core database of the production control system (DCS). This procedure, through controlled offline experiments, provides a basis for online calculation of the dilution compensation coefficient. It provides a set of basic parameters supported by measured data, eliminating the risk of water and material balance runaway caused by theoretical estimation errors.

[0044] When the above process is first deployed at a newly built off-site production base, a strict on-site pre-deployment calibration / commissioning procedure can be implemented. This procedure requires that, before formal feeding, a blank test run of no less than 48 hours be conducted using deionized water to simulate the reaction medium under set stirring and heating conditions. Through multiple temperature sensors and level gauges installed at different heights and orientations inside the reactor, the uniformity of heat distribution and level fluctuations of the system are monitored and recorded in real time. This is used to calibrate the temperature control PID parameters and level compensation algorithm in the DCS system. At the same time, the actual mixing time of the reactor is determined by the tracer method to confirm whether the location of the dual-flow path feeding point is in the optimal intersection area of ​​the tangential and radial flows formed by the stirring blades. If necessary, the angle and depth of the feeding pipe are fine-tuned. Only when all monitoring indicators are stable within the preset tolerance range for 24 consecutive hours and the mixing efficiency reaches the specified standard is the system allowed to enter the formal feeding production stage. This ensures that each new production line can stably produce high-quality sodium metaantimonate products that meet the full-lattice anhydrous standard from the first batch.

[0045] Example 6: To ensure that the high-temperature sodium metaantimonate synthesis process has clear calibration basis for key process parameters such as stirring power density and natural evaporation water flux in industrial deployment, this example constructs a reactor kinetic calibration and adaptive parameter generation procedure based on dimensionless linear number correlation. This procedure identifies the core variables affecting the mass transfer efficiency and evaporation rate of the system: reactor inner diameter D, impeller diameter d, stirring speed N, and fluid Reynolds number. Based on these geometric and physical parameters, a power metric is established. and mixed time standard The calibration model is based on this core. In actual operation, deionized water is added to the target production reactor to the designed level. The stirring speed N (ranging from 0.5 to 5.0 Hz) is adjusted in a gradient manner at room temperature. The input power P is measured in real time using a torque sensor mounted on the stirring shaft, and the result is calculated according to the formula... Calculate the power number under different fluid conditions. ,in For fluid density, by plotting The characteristic curve determines whether the reactor has reached a fully turbulent state (i.e., Critical Reynolds number (approaching a constant) and the corresponding rotation speed Set as the minimum speed limit for process operation.

[0046] For natural evaporation water flux This key parameter affecting the accuracy of dilution compensation is calibrated using thermodynamic calibration procedures. The medium inside the reactor is heated to the specified micro-boiling temperature range (98 to 105 degrees Celsius), a constant stirring speed is maintained, all inlet and outlet valves are closed, and the liquid level drop per unit time is continuously recorded using a precision level gauge. Combined with the cross-sectional area of ​​the reaction vessel Calculate the natural evaporation rate under this operating condition. This calibration process needs to be repeated at different liquid levels (30%, 50%, 80%) to establish... The correction function that varies with the liquid level is ultimately the result of the calibration above. and The correction function is entered into the DCS control system as a dilution compensation coefficient. The basic input parameters for the real-time calculation module are used in this procedure to ensure that the isochemical potential microenvironment consistent with the pilot-scale experiment can be reproduced in reactors of different specifications by transforming general chemical engineering principles into quantitative calibration steps for specific equipment.

[0047] 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.

[0048] 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 process for the controlled synthesis of a high temperature resistant sodium metaantimonate crystal structure, characterized in that, The method comprises the following steps: Step S1, constructing a high-alkaline precursor solution, dispersing antimony trioxide powder in a sodium hydroxide aqueous solution with an initial molar concentration of 6.5 mol / L to 8.0 mol / L, and adding sodium aluminate accounting for 0.5% to 1.5% of the molar amount of antimony in the antimony trioxide as a crystal lattice directing agent, to form a homogeneous precursor solution under mechanical stirring; Step S2, establishing an isochemical potential oxidation crystallization field, heating the precursor solution to 98°C to 105°C and maintaining a turbulent stirring state, performing a double-flow synchronous compensation operation, the first flow path drops a hydrogen peroxide aqueous solution with a mass fraction of 35% to 50% into the precursor solution at a constant rate, and the second flow path synchronously adds solid sodium hydroxide with a purity of not less than 98% or a concentrated sodium hydroxide solution with a concentration of not less than 48%; Step S3, dynamically clamping the reaction boundary, setting a coupling relationship between the addition rate of sodium hydroxide in the second flow path and the drop rate of the hydrogen peroxide aqueous solution in the first flow path and the reaction stoichiometric ratio, so that the amount of sodium hydroxide added per unit time can real-time offset the dilution effect caused by the reaction generated water and the water brought in by the hydrogen peroxide aqueous solution, and the free sodium hydroxide concentration of the reaction mother liquor in the whole oxidation reaction process is maintained at more than 6.0 mol / L, until the oxidation-reduction potential of the reaction system jumps and stabilizes in the interval of -200 mV to -100 mV; Step S4, solid-liquid separation and mother liquor closed loop, hot filtration separation of the slurry obtained in step S3, the separated high-temperature mother liquor is directly returned to step S1 for recycling, and the filter cake is washed and dried to obtain anhydrous sodium metaantimonate.

2. The process as claimed in claim 1, wherein the process for the controlled synthesis of sodium meta-antimonate crystal structure having high temperature resistance is characterized by, In step S1, the liquid-solid ratio of antimony trioxide to sodium hydroxide aqueous solution is controlled to be between 3:1 and 5:1; in step S2, the rotating speed of the turbulent stirring is controlled to be between 300 rpm and 500 rpm, the drop time of the hydrogen peroxide aqueous solution is controlled to be between 2 hours and 4 hours, and the aging time after the drop is completed is not less than 2 hours.

3. The controlled synthesis process of a high-temperature resistant sodium metaantimonate crystal structure according to claim 1, characterized in that, In step S1, sodium aluminate acts as a heterogeneous epitaxial growth site to induce the accumulation of antimony oxygen octahedrons along the three-dimensional dense direction of anhydrous cubic crystal system; the precursor solution does not contain organic dispersants or high molecular surfactants.

4. The process as claimed in claim 1, wherein the process for the controlled synthesis of sodium meta-antimonate crystal structure having high temperature resistance is characterized by, In step S3, the alkali make-up rate of the second flow path follows a linear coupling rule based on water material balance, which is defined by the following formula: wherein, is the mass addition rate of the second flow path converted into pure sodium hydroxide, is the volume drop rate of the hydrogen peroxide aqueous solution in the first flow path, is a preset dilution compensation coefficient; the dilution compensation coefficient is determined according to the water content of the hydrogen peroxide aqueous solution and the stoichiometric water production of the oxidation reaction.

5. The controlled synthesis process of a high-temperature resistant sodium metaantimonate crystal structure according to claim 1, characterized in that, In step S2, the feeding ports of the first flow path and the second flow path are symmetrically distributed in the reactor space, and the feeding points are located in the intersection area of the tangential flow and the radial flow formed by the stirring paddle.

6. The controlled synthesis process of a high-temperature resistant sodium metaantimonate crystal structure according to claim 1, characterized in that, In step S3, the silver / silver chloride is used as the reference electrode for monitoring the oxidation-reduction potential, and the determination standard of the reaction endpoint also includes the complete change of the slurry color from off-white to pure white; the whole reaction process is carried out in a normal pressure environment, and the temperature of the reaction system is always maintained at a micro-boiling state.

7. The controlled synthesis process of a high-temperature resistant sodium metaantimonate crystal structure according to claim 1, characterized in that, In step S4, before being returned to step S1, the high-temperature mother liquor only adds consumed antimony trioxide and sodium hydroxide to adjust to the initial dosing state, and does not perform evaporation concentration operation; the filter cake is washed with deionized water with a temperature of 60°C to 80°C until the pH value of the washing liquid is reduced to 7.0 to 8.

0.

8. The controlled synthesis process of a high-temperature resistant sodium metaantimonate crystal structure according to claim 1, characterized in that, In step S1, the raw material of antimony trioxide is cubic crystal, the average particle size D50 is 1.0-2.0 microns, and the purity is not less than 99.8%; the crystal structure of the product of anhydrous sodium metaantimonate is cubic or hexagonal, and the thermal weight loss rate in the range of 300-350 DEG C is less than 0.1%.

9. The controlled synthesis process of a high-temperature resistant sodium metaantimonate crystal structure according to claim 1, characterized in that, The dynamic clamping reaction boundary step locks the thermodynamic environment of crystal growth in the stable zone of anhydrous sodium metaantimonate, and blocks the formation path of interlattice water or surface hydroxyl.

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