Reaction apparatus and preparation method for preparing magnesium hydroxide flame retardant based on gas phase method

Abstract

This invention relates to a reaction apparatus and method for preparing magnesium hydroxide flame retardant using a gas-phase method, belonging to the field of chemical engineering equipment and inorganic non-metallic material preparation technology. The reaction apparatus includes a precursor precision delivery system, a multi-temperature zone laminar flow reaction system, a high-efficiency particle collection system, and a central process control system. The method utilizes the precursor precision delivery system to provide gas-phase flows of magnesium source precursor, hydrolysate, and surface modifier, which are introduced into the multi-temperature zone laminar flow reaction system via three coaxial laminar flow nozzles, where controlled mixing is sequentially completed in the preheating mixing zone. This invention is carried out entirely in a low-pressure laminar flow environment in the gas phase, effectively avoiding particle agglomeration. The prepared magnesium hydroxide flame retardant exhibits uniform primary particle size, good dispersibility, and a high degree of surface organication, significantly improving its compatibility and flame retardant efficiency in a polymer matrix.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering equipment and inorganic non-metallic material preparation technology, specifically to a reaction apparatus and preparation method for preparing magnesium hydroxide flame retardant based on a gas-phase method. Background Technology

[0002] In the field of modern polymer materials science and engineering, flame retardant technology, as a key link in ensuring the safe application of materials, has always been closely linked to the progress of materials science. With increasingly stringent global environmental regulations and a general increase in public awareness of safety, traditional technical routes, represented by halogenated flame retardants, are gradually being restricted by the market and regulations due to their inherent defects, such as the release of toxic and corrosive gases during combustion.

[0003] Developing efficient, environmentally friendly, and low-toxicity halogen-free flame retardants has become an industry consensus and a core research and development direction. Among them, magnesium hydroxide (Mg(OH)2), as a typical inorganic hydroxide flame retardant, has been widely used and extensively studied in the fields of wires and cables, engineering plastics, thermoplastic elastomers, and coatings due to its multiple flame-retardant mechanisms, such as high heat absorption during thermal decomposition, release of non-toxic water vapor to dilute flammable gases, and effective isolation of oxygen by the generated magnesium oxide char layer. In addition, it has the advantages of wide availability and controllable cost.

[0004] To meet the comprehensive requirements of different polymer matrices for flame retardancy, mechanical properties, and processing performance, those skilled in the art have conducted extensive and fruitful work on the preparation and modification of magnesium hydroxide flame retardants. Among these efforts, the liquid-phase precipitation method constitutes the mainstream paradigm of current technological development. Specifically, this method typically uses soluble magnesium salts (such as magnesium sulfate and magnesium chloride) as raw materials, which undergo a precipitation reaction with alkalis (such as sodium hydroxide and ammonia) in an aqueous medium to generate magnesium hydroxide crystal nuclei. The crystal growth process is controlled by adjusting process parameters such as reaction temperature, pH value, and stirring rate. Finally, the product is obtained through washing, filtration, and drying.

[0005] The advantages of this technical approach lie in its mature process, ease of large-scale production, and provision of a convenient reaction platform for subsequent performance optimization. For example, invention patent CN117700838B discloses a technical solution for preparing magnesium aluminum hydroxide via liquid-phase co-precipitation, followed by multi-step chemical modification. This solution aims to improve flame retardancy efficiency by introducing aluminum to form a hydrotalcite structure and grafting nitrogen, phosphorus, and silicon-containing organic functional groups.

[0006] Another invention patent, CN114716828B, discloses a method of loading magnesium hydroxide particles prepared by a liquid-phase method onto the surface of polypyrrole nanotubes. The aim is to utilize the bridging effect of the nanocarrier to improve the interfacial compatibility between the inorganic flame retardant and the organic polymer matrix, thereby optimizing its dispersion state in the matrix. The above technical solutions all demonstrate the profound understanding and active exploration in this field of addressing the problems of magnesium hydroxide's inherent high polarity and poor compatibility with non-polar polymers through chemical composite and surface functionalization methods.

[0007] As application scenarios place increasingly stringent demands on the comprehensive performance indicators of materials, the inherent characteristics of the aforementioned liquid-phase-based technical system at the principle level are gradually revealing its limitations in addressing new challenges. These limitations are not isolated process issues, but rather stem from the fundamental constraints of the physicochemical processes of particle formation in the liquid-phase reaction environment. Because the liquid-phase precipitation process is essentially a complex "nucleation-growth" process, it is highly susceptible to the inhomogeneity of the local microenvironment within the reaction system (such as concentration gradients and temperature fluctuations), resulting in a wide size distribution and difficult-to-precise morphology control of the generated magnesium hydroxide primary particles.

[0008] More importantly, newly formed high specific surface energy nano- or micro-sized particles in liquid media exhibit a strong tendency to spontaneously aggregate due to physical effects such as van der Waals forces. These initial aggregates formed in the liquid phase further dehydrate and solidify during subsequent filtration and drying processes, forming "hard aggregates" that are difficult to dissociate. Existing surface modification technologies, whether through coating or chemical bonding, primarily modify the outer layer of these already formed aggregates. While this can improve their macroscopic compatibility with the polymer matrix to some extent, it is difficult to fundamentally break down the hard aggregate structure between particles. This uneven dispersion at the microscopic level not only significantly reduces the effective specific surface area of ​​the flame retardant, resulting in flame retardant efficiency falling short of theoretical expectations, but also creates stress concentration points in the material, severely degrading the mechanical properties of the final product, such as impact strength and elongation at break. Summary of the Invention

[0009] The purpose of this invention is to provide a reaction apparatus and preparation method for preparing magnesium hydroxide flame retardant based on the gas phase method, which effectively overcomes the technical problems in the prior art when preparing magnesium hydroxide flame retardant by liquid phase method, such as hard agglomeration of particles, wide particle size distribution, and uncontrollable morphology caused by the inherent physicochemical limitations of the liquid phase reaction environment, which in turn affects its dispersibility in the polymer matrix and the final composite material performance.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0011] This invention provides a method for preparing magnesium hydroxide flame retardants based on a gas-phase method, which fundamentally avoids the aggregation problem in the liquid-phase nucleation and growth process. By achieving uniform mixing, controlled nucleation, ordered growth, and in-situ surface functionalization of reactant molecules in a highly controllable gas-phase environment, a magnesium hydroxide flame retardant with uniform primary particle size, controllable crystal form, excellent dispersibility, and strong compatibility with the polymer matrix interface is prepared.

[0012] A method for preparing magnesium hydroxide flame retardant based on a gas-phase method is disclosed, which is carried out through a reaction apparatus. The reaction apparatus structurally includes a precursor precision delivery system, a multi-temperature zone laminar flow reaction system, a high-efficiency particle collection system, and a central process control system. These four systems are functionally and data-flow-interdependent, forming a complete and continuous preparation process.

[0013] Specifically, the precursor precision delivery system is designed to inject various precursor substances participating in the chemical reaction into the reaction system at a precise, repeatable, and stable gas-phase molar flow rate. The precursor precision delivery system consists of three independent subsystems: a magnesium source precursor delivery subsystem, a hydrolysate delivery subsystem, and a surface modifier delivery subsystem.

[0014] The magnesium source precursor delivery subsystem includes a 316L stainless steel bubbler containing a liquid organic magnesium precursor, specifically dimethylmagnesium (Mg(CH3)2). The bubbler is surrounded by a circulating water bath jacket. A constant temperature water bath system with an accuracy of ±0.1℃ maintains the bubbler temperature at a preset value. At this temperature, the saturated vapor pressure of dimethylmagnesium is approximately 35 mmHg, ensuring a constant saturated vapor pressure. A first carrier gas, specifically 99.999% pure argon, with its flow rate precisely controlled by a mass flow controller, is introduced below the liquid surface of the bubbler. The bubbling process carries away the saturated dimethylmagnesium vapor, forming a magnesium source precursor gas phase flow.

[0015] The hydrolysate delivery subsystem is configured as a liquid mass flow controller connected to an ultrapure water storage tank. The controller injects liquid water at a set micro-flow rate into a flash evaporator installed on the pipeline. The flash evaporator is heated to 120°C, causing the liquid water to vaporize instantly and mix with a second carrier gas (99.999% pure argon gas) whose flow rate is precisely controlled by a second mass flow controller, forming a water vapor gas phase flow with precise concentration.

[0016] The surface modifier delivery subsystem is structurally and operationally identical to the magnesium source precursor delivery subsystem. Its bubbler contains a liquid organosilane coupling agent, specifically vinyltrimethoxysilane (VTMS). A third carrier gas (99.999% pure argon), controlled by a third mass flow controller, carries out saturated vinyltrimethoxysilane vapor, forming a surface modifier gas phase flow. All pipelines in the three subsystems are constructed of 316L stainless steel and are continuously heated to a temperature 10°C above the boiling point of each precursor to prevent condensation on the pipe walls.

[0017] Furthermore, the multi-temperature zone laminar flow reaction system is the core execution unit of the method of this invention. Its main body is a horizontally placed quartz tube with an inner diameter of 100 mm and a length of 1500 mm. Three independently temperature-controlled resistance wire heating furnaces are fitted around the outside of the quartz tube, thus forming three physicochemical process zones with different functions and temperatures along the axial direction inside the quartz tube: a preheating mixing zone, a nucleation growth zone, and a modification and ripening zone. The three gaseous fluids output from the precursor precision delivery system are introduced into the inlet end of the quartz tube through a specially designed three-coaxial laminar flow nozzle. From the inside out, this nozzle consists of a central tube, a first annular tube, and a second annular tube.

[0018] The magnesium source precursor gaseous flow is introduced through a central tube; a separate isolation carrier gas, namely pure argon, is introduced through a first annular tube, forming a dynamic gas sheath around the magnesium source precursor gaseous flow; the water vapor gaseous flow and the surface modifier gaseous flow are pre-mixed before entering the nozzle, and then introduced together through a second annular tube. This coaxial laminar flow injection method ensures that the reactants flow in parallel laminar flow in the initial stage of entering the reaction chamber. The subsequent mixing process mainly relies on molecular diffusion. Under low pressure of 5 kPa and 300°C, the gas phase diffusion coefficient of reactant molecules increases significantly. It is estimated that at laminar flow rates, reactants can achieve uniform molecular-level mixing through radial diffusion before entering the nucleation growth region. This lays the physical foundation for achieving a uniform and controllable chemical reaction.

[0019] In a preferred embodiment of the present invention, the three temperature zones of the multi-temperature zone laminar flow reaction system have clearly defined process parameter settings. The preheating mixing zone, i.e., the first temperature zone, is set and maintained at 110°C.

[0020] Within this region, the three gaseous fluids are heated together to the reaction initiation temperature while maintaining laminar flow. Simultaneously, the effect of the isolating gas gradually weakens, and the reactant molecules begin to mix initially and slowly through radial diffusion. The nucleation and growth region, also known as the second temperature zone, is the core area for magnesium hydroxide particle formation, and its temperature is precisely controlled between 280°C and 350°C. Under this temperature and low-pressure environment (total chamber pressure maintained at 5 kPa), the thoroughly mixed dimethylmagnesium vapor and water vapor undergo a vigorous gas-phase hydrolysis reaction. The chemical reaction equation is as follows:

[0021] Mg(CH3)2(g) + 2H2O(g) → Mg(OH)2(s) + 2CH4(g).

[0022] Because the reactant concentration is precisely controlled at an extremely low level by the precursor delivery system, the Mg(OH)₂ molecules or small molecule clusters generated in the reaction form crystal nuclei through a homogeneous nucleation mechanism, and continue to grow by adsorbing reactant molecules during subsequent flow. The extremely low gas-phase supersaturation and long molecular free path fundamentally suppress collisions and aggregation between newly formed crystal nuclei, resulting in the formation of dispersed, independent primary magnesium hydroxide particles. The modified ripening zone, i.e., the third temperature zone, is set and maintained at 180°C.

[0023] In this region, the hydroxyl groups (-OH) on the surface of the already formed magnesium hydroxide nanoparticles undergo an in-situ chemical grafting reaction with vinyltrimethoxysilane molecules in the gas phase. The hydrolysis product of vinyltrimethoxysilane (silanol) undergoes a condensation reaction with the hydroxyl groups on the Mg(OH)2 surface, forming a chemically bonded, siloxane-based, organically functionalized layer on the particle surface. This in-situ surface modification process occurs after particle formation and before any possible agglomeration, ensuring that each native particle receives a sufficient and uniform surface coating. Simultaneously, the heat treatment process in this temperature range also serves to mature the magnesium hydroxide lattice and improve its crystal integrity.

[0024] The high-efficiency particle collection system functions to efficiently separate and collect in-situ surface-modified magnesium hydroxide nanoparticles suspended in the carrier gas from the gas flow without pollution. This system is connected in series to the outlet of a multi-temperature zone laminar flow reaction system. The high-temperature mixed gas flow after the reaction first passes through a cooling pipe section fitted with a water-cooled jacket, where the temperature is rapidly reduced from 180°C to 60°C to terminate all chemical reactions and prevent further particle growth or morphological changes.

[0025] The cooled airflow then enters a pulse-jet baghouse dust collector made of polytetrafluoroethylene (PTFE) membrane filter media. The filter bags of this dust collector have a filtration accuracy of 0.1 micrometers, effectively intercepting all generated magnesium hydroxide particles. The reaction byproduct, methane gas, and unreacted carrier gas pass through the filter bags, are extracted by a vacuum pump connected to the end of the system, and are discharged after treatment by a tail gas treatment device. The dust collector is equipped with a timed pulse-jet system, which uses high-pressure nitrogen gas to momentarily reverse-jet impact the filter bags, shaking the powder deposited on the inner surface of the filter bags into a conical collection hopper below. The bottom of the collection hopper is connected in series with a star-shaped discharge valve and a double-layer airlock valve. This structure ensures that the collected powder remains isolated from the external atmosphere during continuous or semi-continuous discharge, thus protecting its hydrophobic surface and preventing moisture absorption or contamination.

[0026] The central process control system serves as the command and monitoring hub for the entire manufacturing process. This system is based on a Siemens S7-1500 series programmable logic controller (PLC) and equipped with a touchscreen human-machine interface (HMI). The system contains a pre-written complete process control program organized using a sequential function chart (SFC) logical structure.

[0027] The system's input signals include: real-time flow feedback values ​​from all mass flow controllers, temperature sensor (K-type thermocouple) signals from the constant temperature water bath and each heating furnace, and absolute pressure sensor (capacitive diaphragm gauge) signals from the reaction chamber.

[0028] The system's output signals include: flow setting commands (4-20mA current signals) for all mass flow controllers, control signals for the power of each heater (using PID algorithm to control the on / off state of solid-state relays), control signals for the opening of the vacuum pump throttle valve, and control signals for the solenoid valves of the pulse backflushing system.

[0029] Operators input a complete set of process formula parameters (including the flow rate of each carrier gas, the temperature of the precursor source, the temperature of each reaction zone, the reaction pressure, the pulse backflushing cycle, etc.) through the human-machine interface. The system can then automatically execute the entire process from system vacuuming, charging protective gas, heating, stabilizing parameters, injecting precursors, carrying out the reaction, collecting products, to the final cooling and purging. It also monitors all key parameters in real time and triggers alarms and safety interlocks when deviations occur, ensuring a high degree of automation, accuracy, and repeatability in the preparation process.

[0030] The specific operation steps of the gas-phase method for preparing magnesium hydroxide flame retardant provided by this invention are as follows:

[0031] The first step is system initialization and preparation.

[0032] The central process control system was activated to perform a vacuum leak test on the entire reaction and collection system. After the leak test passed, the internal pressure of the system was evacuated to below 1 Pa using a vacuum pump. Then, high-purity argon gas was repeatedly introduced and the system was evacuated three more times to thoroughly remove air and moisture from the system. Finally, argon gas was introduced into the system to atmospheric pressure and maintained at a slight positive pressure.

[0033] The second step is to set and stabilize the process parameters.

[0034] The preset process formula is downloaded via the human-machine interface. The system automatically starts each heating unit and the constant temperature water bath, heating the three temperature zones of the multi-zone laminar flow reaction system, all pipeline heating cables, and the precursor bubbler to the target temperature according to the set heating rate. Simultaneously, the vacuum pump is started and controlled by a throttle valve to precisely regulate and stabilize the pressure within the reaction chamber at 5 kPa. During this process, each mass flow controller only opens the carrier gas channel, introducing pure argon gas into the system to stabilize the gas flow. This stabilization process lasts for 30 minutes to ensure that all temperature and pressure parameters reach a highly stable state.

[0035] The third step is precursor injection and reaction initiation.

[0036] Once all parameters stabilize, the central process control system simultaneously activates three carrier gas streams—one for dimethylmagnesium, one for water vapor, and one for vinyltrimethoxysilane—according to a preset program, precisely setting their flow rates to the process values. For example, the first carrier gas flow rate for dimethylmagnesium is set to 200 sccm, while the bubbler temperature is increased to 40.0℃ (at which temperature the saturated vapor pressure of dimethylmagnesium is approximately 70 mmHg). The second carrier gas flow rate for water vapor is 200 sccm (while the liquid water flow controller is set to 0.2 g / min), and the third carrier gas flow rate for vinyltrimethoxysilane is 20 sccm. These three gaseous fluid streams are injected into the reaction chamber through three coaxial laminar flow nozzles, sequentially completing the preheating and mixing, gas-phase hydrolysis nucleation and growth, in-situ surface modification, and maturation processes in the preheating mixing zone, nucleation and growth zone, and modification and maturation zone.

[0037] The fourth step is product collection and unloading.

[0038] The reacted and modified magnesium hydroxide particles are carried by the airflow into a high-efficiency particle collection system and captured by PTFE filter bags. The central process control system automatically initiates a pulse backflushing program based on a set time period (e.g., every 10 minutes) or signals from the differential pressure sensors on both sides of the filter bags, collecting the powder into the collection hopper below. During or after the preparation process, operators can use the control system to activate the rotary valve and double-layer airlock valve to transfer the product from the collection hopper to a sealed sample container while isolating it from the atmosphere.

[0039] Step 5: System shutdown and cleanup.

[0040] After the predetermined production time is completed, the control system first shuts off all precursor deliveries, maintaining only carrier gas flow for a few minutes to purge residual reactants from the pipelines and reaction chamber. Subsequently, the system gradually shuts down the heating unit and vacuum system according to a preset program. After the system cools to room temperature, it is then filled with argon gas for protection.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The entire process of this invention is carried out in a low-pressure gas-phase environment, avoiding the uncontrollable local concentration gradients and van der Waals forces between particles present in liquid-phase methods, thus preventing the formation of hard agglomerates at the source. The prepared magnesium hydroxide flame retardant consists of highly monodisperse nanoparticles with a hexagonal, plate-like shape and a primary particle size in the range of 50-100 nanometers, chemically coated with organosilane. Due to their excellent dispersibility and surface organic affinity, these particles can achieve molecular-level dispersion when melt-blended with polymer matrices such as polypropylene and polyethylene, significantly increasing the effective contact area of ​​the flame retardant. This allows for excellent flame retardant effects at relatively low addition levels, while minimizing the negative impact on the mechanical properties of the composite material. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 This is a system block diagram of the preparation method of the present invention.

[0045] Figure 2 This is a schematic diagram of the structure of the multi-temperature zone laminar flow reaction system of the present invention.

[0046] Figure 3 This is a schematic diagram of the precursor precision conveying system of the present invention.

[0047] Figure 4 This is a schematic flowchart of the preparation method of the present invention.

[0048] Figure 5 These are SEM and TEM images of the present invention.

[0049] Figure 6 This is a SEM image of Comparative Example 1 of the present invention.

[0050] Figure label:

[0051] 10- Precision conveying system for precursors; 11- Magnesium source precursor conveying subsystem; 12- Hydrolyzing agent conveying subsystem; 13- Surface modifier conveying subsystem; 14- Bubblehead; 15- Mass flow controller; 16- Flash evaporator; 20- Multi-temperature zone laminar flow reaction system; 21- Quartz tube; 22- Resistance wire heating furnace; 23- Preheating mixing zone; 24- Nucleation growth zone; 25- Modification and ripening zone; 26- Triaxial laminar flow nozzle; 30- High-efficiency particle collection system; 40- Central process control system. Detailed Implementation

[0052] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0053] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0054] Example 1:

[0055] See Figures 1-6 This embodiment discloses a method for preparing magnesium hydroxide flame retardant based on a gas-phase method. The method achieves controlled mixing of reactant molecules, homogeneous nucleation and growth of magnesium hydroxide particles, and subsequent in-situ surface functionalization in a gas-phase environment, thereby preparing magnesium hydroxide flame retardant powder with excellent performance.

[0056] The reaction apparatus used for the gas-phase preparation of magnesium hydroxide flame retardant, upon which the preparation method is based, includes:

[0057] A precursor precision delivery system 10 is used for a repeatable and stable gas-phase molar flow rate supply of various chemical substances required for the reaction;

[0058] A multi-temperature zone laminar flow reaction system 20 serves as the core site for chemical reactions and physical processes;

[0059] A high-efficiency particulate collection system 30 is used to efficiently separate and protect the generated products from the gas stream;

[0060] And a central process control system 40, which acts as the nerve center of the entire system, coordinating and monitoring all operations.

[0061] The precursor precision delivery system 10 is used to achieve precise control of the gas phase concentration of three key precursor substances: magnesium source, hydrolysant and surface modifier, to ensure the uniformity of particle size and controllable morphology of the final product.

[0062] The precursor precision delivery system 10 consists of three functionally independent subsystems: a magnesium source precursor delivery subsystem 11, a hydrolysate delivery subsystem 12, and a surface modifier delivery subsystem 13. The magnesium source precursor delivery subsystem 11 includes a 316L stainless steel bubbler 14, which contains a liquid organic magnesium precursor, specifically dimethylmagnesium (Mg(CH3)2) in this embodiment. The bubbler 14 is externally designed with a circulating water bath jacket. An external constant-temperature water bath system with a temperature control accuracy of ±0.1℃ maintains its overall temperature at a preset value, for example, 25.0℃. This constant temperature ensures that the saturated vapor pressure of dimethylmagnesium within the bubbler remains at a stable level. A high-purity argon gas with a purity of 99.999% is used as the first carrier gas. Its flow rate is precisely measured and controlled by a high-precision mass flow controller 15. The first carrier gas is introduced through an immersion tube that extends below the liquid surface of the bubbler 14. By generating fine bubbles in the liquid dimethylmagnesium, it carries out saturated dimethylmagnesium vapor, thereby forming a magnesium source precursor gas phase flow with a constant molar flow rate.

[0063] The hydrolysate delivery subsystem 12 provides precisely concentrated water vapor. Unlike the magnesium source delivery subsystem, it employs a dedicated liquid mass flow controller directly connected to an ultrapure water storage tank. This liquid mass flow controller can stably pump liquid water at extremely low flow rates, such as 0.2 g / min. The pumped liquid water is injected into a small flash evaporator 16 connected in series in the pipeline. The flash evaporator 16 is filled with high specific surface area metal packing to increase the heat exchange area and is precisely heated and maintained at 120°C by an external heating jacket. At this temperature, the minute amount of injected liquid water instantly vaporizes, forming pure water vapor.

[0064] Simultaneously, a second carrier gas (also 99.999% pure argon) with its flow rate precisely controlled by a second mass flow controller 15 is also introduced into the flash evaporator 16. This gas mixes thoroughly with the newly generated water vapor, ultimately forming a hydrolysate gaseous flow with a precisely known water vapor concentration and a stable flow rate. This avoids the steam flow pulsation problem caused by liquid level fluctuations or uneven boiling in traditional steam generators.

[0065] The surface modifier delivery subsystem 13 is basically the same as the magnesium source precursor delivery subsystem 11 in structure and working principle. Its bubbler 14 contains a liquid organosilane coupling agent, specifically vinyltrimethoxysilane (VTMS) in this embodiment.

[0066] A third carrier gas (99.999% pure argon), controlled by a third mass flow controller 15, carries saturated vinyltrimethoxysilane vapor in a bubbling manner, forming a surface modifier gaseous flow. To ensure that all precursors exist in gaseous form throughout the transport process from the source to the reactor, and to avoid concentration changes due to condensation caused by local temperature drops, all pipelines in the three subsystems are made of corrosion-resistant 316L stainless steel and are electrically heated throughout. The heating temperature is set and maintained at a temperature at least 10°C above the boiling point of each precursor, for example, 130°C, thereby ensuring the accuracy and stability of the precursor molar flow rate.

[0067] Furthermore, the main body of the multi-temperature zone laminar flow reaction system 20 is a horizontally placed quartz tube 21 with an inner diameter of 100 mm and an effective heating zone length of 1500 mm. High-purity quartz is selected as the material for the reaction tube, as it possesses excellent chemical inertness at high temperatures, good thermal stability, and tolerance to sudden temperature changes. Three independently programmable resistance wire heating furnaces 22 are sequentially mounted on the outside of the quartz tube 21 along its axial direction. By setting different temperature parameters for these three resistance wire heating furnaces 22, three clearly defined continuous processing zones with different physicochemical conditions can be constructed inside the quartz tube 21 along the airflow direction: a preheating mixing zone 23, a nucleation growth zone 24, and a modification and ripening zone 25.

[0068] The three gaseous fluids output from the precursor precision delivery system 10 are introduced through a specially designed triaxial laminar flow nozzle 26 located at the inlet end of the quartz tube 21. The triaxial laminar flow nozzle 26 consists of three concentrically arranged tubes, from the inside out: a central tube, a first annular tube, and a second annular tube. With this structural design, the reactants flow in parallel laminar flow at the nozzle outlet, and the subsequent process of achieving uniform mixing through molecular diffusion takes approximately 0.1 to 0.5 seconds.

[0069] The specific airflow distribution scheme is as follows:

[0070] The magnesium source precursor gaseous flow carrying dimethylmagnesium is introduced through the innermost central tube; a separate pure argon gas, whose flow rate is precisely controlled by a mass flow controller, is introduced through the middle first annular tube as a barrier gas; while the hydrolysate gaseous flow and the surface modifier gaseous flow are pre-mixed by a static mixer before entering the nozzle, and then introduced together through the outermost second annular tube.

[0071] In the initial stage at the nozzle exit, the highly reactive magnesium source precursor gas stream is enveloped by an inert argon sheath, physically isolating it from the outer water vapor-containing reaction gas stream. The gas streams enter the reaction chamber in a near-parallel laminar flow state; their mixing relies not on turbulent counterflow, but primarily on the slow radial diffusion of molecules. This controlled, gradual mixing mode creates the initial conditions for the uniform and controllable execution of subsequent chemical reactions, effectively avoiding explosive nucleation and uncontrolled growth caused by excessively high local concentrations.

[0072] In a preferred embodiment of the present invention, the multi-temperature zone laminar flow reaction system 20 has three temperature zones with precisely optimized process parameters. The preheating mixing zone 23, i.e., the first temperature zone, is set and stably maintained at 110°C. In this zone, the three coaxial gas streams are uniformly heated to near the reaction initiation temperature while maintaining laminar flow. As the gas streams advance, the effect of the argon gas in the central sheath gradually weakens due to radial diffusion, allowing the dimethylmagnesium molecules in the central tube and the water vapor molecules in the second annular tube to begin preliminary, mild interpenetration and mixing. This temperature ensures that all components remain in the gas phase and is significantly lower than the activation energy of the hydrolysis reaction, thereby ensuring that the mixing process takes place under conditions where no significant chemical reaction occurs.

[0073] The subsequent nucleation and growth zone 24, the second temperature zone, is the core region for the formation of magnesium hydroxide particles. The temperature in this region is precisely controlled within a narrow range, typically between 280°C and 350°C, for example, 300°C. Simultaneously, the total pressure of the entire reaction chamber is precisely maintained at a low pressure, for example, 5 kPa, through a downstream vacuum pump and throttling valve system. Under this specific high-temperature, low-pressure environment, the thoroughly mixed dimethylmagnesium vapor undergoes a violent and irreversible gas-phase hydrolysis reaction with water vapor. The chemical reaction equation is as follows:

[0074] Mg(CH3)2(g) + 2H2O(g) → Mg(OH)2(s) + 2CH4(g).

[0075] The temperature of the nucleation and growth zone is set at 300℃ based on the principles of gas-phase reaction kinetics, and this is based on the following considerations:

[0076] 1) The activation energy for the reaction of dimethylmagnesium with water vapor is approximately 50 kJ / mol, and the reaction rate constant reaches a practical level at 300℃;

[0077] 2) Excessively high temperatures (>350℃) may cause magnesium hydroxide to decompose, while excessively low temperatures (<280℃) will result in incomplete reaction;

[0078] 3) Verification using the Arrhenius equation shows that 300℃ is the optimal reaction temperature window.

[0079] Because the reactant concentration is precisely controlled at an extremely low level by the precursor delivery system 10, the gas-phase supersaturation of the reaction system is also in a low and controlled state. This favors the formation of crystal nuclei from Mg(OH)₂ molecules or small molecule clusters through a homogeneous nucleation mechanism. Furthermore, the low-pressure environment significantly increases the mean free path of gas molecules, greatly reducing the probability of collisions and aggregation between newly formed crystal nuclei. Therefore, each crystal nucleus can grow independently during subsequent flow by continuously adsorbing surrounding reactant molecules, ultimately forming dispersed primary magnesium hydroxide particles with an extremely narrow particle size distribution.

[0080] Finally, when the gas stream carrying the newly generated magnesium hydroxide nanoparticles enters the modified curing zone 25, i.e., the third temperature zone, its temperature is set and maintained at 180°C. This zone serves a dual function.

[0081] Firstly, in-situ surface modification is performed. Vinyltrimethoxysilane molecules in the gas phase exhibit good thermal stability at this temperature (their thermal decomposition initiation temperature is above 200℃), and their methoxy group (-OCH3) partially hydrolyzes to form a more reactive silanol group (-Si-OH). This silanol group undergoes a condensation reaction with the abundant hydroxyl groups (-Mg-OH) on the surface of magnesium hydroxide nanoparticles, removing one water molecule and forming a chemically bonded -Mg-O-Si- structure on the particle surface. This creates an organic coating layer on the surface of each native particle, primarily composed of siloxane and containing vinyl functional groups. Because this modification process occurs after particle formation and before any possible aggregation or collection, it ensures extremely uniform and complete coating of each native particle.

[0082] Secondly, it plays a role in lattice ripening. The 180℃ heat treatment helps newly formed magnesium hydroxide crystals, which may have lattice defects, to relax and reconstruct, thereby improving their crystal integrity and thermal stability.

[0083] After the reaction process is completed, the carrier gas contains in-situ surface-modified magnesium hydroxide nanoparticles and gaseous byproduct methane. The function of the high-efficiency particle collection system 30 is to efficiently separate the solid-phase product from the gaseous substance. The high-efficiency particle collection system 30 is connected in series at the outlet of the multi-temperature zone laminar flow reaction system 20.

[0084] First, the high-temperature mixed gas carrying the products passes through a cooling pipe section fitted with a circulating water-cooled jacket, where its temperature is rapidly reduced from 180°C to 60°C in a short time. This quenching step aims to completely terminate any potential chemical reactions and "freeze" the size and morphology of the particles, preventing sintering between particles during slow cooling. The cooled gas flow then enters a pulse-jet bag filter. The pulse-jet bag filter is equipped with multiple filter bags made of polytetrafluoroethylene (PTFE) membrane filter media. PTFE membrane filter media has natural hydrophobicity and extremely low surface energy, effectively preventing the adhesion of unmodified hydrophilic particles. Simultaneously, its surface micropores achieve a filtration precision of 0.1 micrometers, completely intercepting all generated magnesium hydroxide nanoparticles. Reaction byproducts such as methane, unreacted carrier gas, and excess water vapor pass smoothly through the filter bags, are extracted by a vacuum pump connected to the end of the system, and are safely discharged after treatment by a tail gas treatment device (such as a combustion furnace).

[0085] To achieve continuous or semi-continuous production, the pulse-jet bag filter is equipped with a pulse-jet system that starts on a timed or differential pressure basis. When the central process control system 40 detects that the pressure difference between the inside and outside of the filter bag reaches a set threshold or a preset time period, it instantly opens the high-pressure nitrogen valve. A powerful nitrogen pulse impacts the filter bag from the top, causing the powder layer deposited on the inner surface of the filter bag to vibrate and fall off, dropping into the conical collection hopper below by gravity. To ensure that the collected highly active nanoparticles with hydrophobic surfaces do not come into contact with the outside atmosphere and thus degrade their performance, a precision unloading valve assembly is designed at the bottom of the collection hopper. The unloading valve assembly consists of a star-shaped unloading valve and a double-layer airlock valve connected in series. During unloading, the star-shaped unloading valve quantitatively feeds the powder into the sealed chamber between the two airlock valves. Then, the upper airlock valve closes and the lower airlock valve opens, discharging the powder into the sample container below. This ensures that the inside of the collection hopper remains isolated from the external atmospheric environment, thereby maximizing the protection of the product's surface condition.

[0086] The central process control system 40 is based on a high-performance Siemens S7-1500 series programmable logic controller (PLC) and is equipped with a touch screen human-machine interface (HMI) as the window for operation and monitoring.

[0087] In terms of software, the central process control system 40 pre-programs a complete process control program based on Sequential Function Chart (SFC) logic. The system's input signals comprehensively cover all key process parameters, including real-time flow feedback values ​​from all mass flow controllers 15, temperature signals from K-type thermocouples in the constant temperature water bath, each resistance wire heating furnace 22, and the pipeline heating tape, as well as the absolute pressure signal measured by the capacitor film gauge inside the reaction chamber. The output signals of the central process control system 40 precisely control all actuators, including: sending 4-20mA current signals to all mass flow controllers 15 to set their flow rates; precisely controlling the power of each heating unit by adjusting the on / off duty cycle of solid-state relays through a PID (Proportional-Integral-Derivative) control algorithm; controlling the opening of the downstream throttle valve of the vacuum pump to stabilize the chamber pressure; and triggering the solenoid valves of the pulse backflushing system according to a time sequence.

[0088] Operators only need to select or input a complete set of process formulation parameters on the human-machine interface, and the system can automatically execute the entire process from system leak detection, vacuuming, gas filling protection, programmed temperature rise, parameter stabilization, precursor injection, reaction proceeding, product collection, to final safe cooling and purging. It also monitors, records, and displays trends of all key parameters in real time. When any parameter deviates from the preset safety range, the system immediately triggers an audible and visual alarm and executes corresponding safety interlock actions, such as cutting off the precursor supply, thereby ensuring a high degree of automation, accuracy, safety, and repeatability of the entire preparation process.

[0089] To facilitate a better understanding of the present invention by those skilled in the art, the present invention will be further described below in conjunction with specific embodiments:

[0090] The aim is to prepare a highly dispersed hexagonal flake-shaped magnesium hydroxide nanoflame retardant modified in situ by vinyltrimethoxysilane.

[0091] The first step is system initialization and preparation.

[0092] Upon starting the central process control system 40, the automatic vacuum leak detection program is first executed to confirm that the entire system is airtight (vacuum pressure drop less than 1 x 10⁻⁶). -2 After leak detection, the system pressure was evacuated to below 1 Pa using a vacuum pump and maintained for 30 minutes for degassing. Then, 99.999% pure argon gas was introduced into the system to 100 kPa, followed by evacuation to 1 Pa. This purging-evacuation process was repeated three times to thoroughly remove any residual air and moisture from the system. Finally, the system was filled with argon gas to a slightly positive pressure state for later use.

[0093] The second step is to set and stabilize the process parameters.

[0094] The preset process formula is downloaded via the human-machine interface. The system automatically starts all heating units. The three temperature zones of the multi-temperature zone laminar flow reaction system 20 are set to the following temperatures: 110℃ for the preheating mixing zone 23, 300℃ for the nucleation and growth zone 24, and 180℃ for the modification and ripening zone 25. The constant temperature water bath temperature of the magnesium source precursor bubbler 14 is set to 40.0℃, and the constant temperature water bath temperature of the surface modifier bubbler 14 is set to 30.0℃. The temperature of the hydrolysate flash evaporator 16 is set to 120℃. The temperature of all pipeline heating tapes is uniformly set to 130℃. The system heats up according to the preset heating rate (e.g., 10℃ / minute). At the same time, the vacuum pump is started and PID regulation is performed through the throttle valve to precisely control and stabilize the pressure in the reaction chamber at 5.0 kPa. During this process, each mass flow controller 15 only opens the carrier gas channel to introduce pure argon gas into the system to establish a stable gas flow field. The entire parameter stabilization process lasts 30 minutes to ensure that fluctuations in all temperature and pressure parameters are within the set allowable values.

[0095] The third step is precursor injection and reaction initiation.

[0096] Once all parameters stabilize, the central process control system 40 automatically executes the reaction program. The flow rates of each gas are precisely set: the first carrier gas (argon) for dimethylmagnesium is set to 200 sccm; the second carrier gas (argon) for water vapor is set to 200 sccm, with the corresponding liquid water mass flow controller set to 0.2 g / min; the third carrier gas (argon) for vinyltrimethoxysilane is set to 20 sccm; and the argon flow rate in the intermediate ring of the three coaxial laminar flow nozzles 26 (acting as an isolation gas) is set to 500 sccm. The three precursor gas flows are injected into the reaction chamber through the three coaxial laminar flow nozzles 26, sequentially completing preheating mixing, gas-phase hydrolysis nucleation growth, in-situ surface modification, and ripening processes in each temperature zone. This reaction process lasts for 2 hours.

[0097] The fourth step is product collection and unloading.

[0098] The reacted and modified magnesium hydroxide particles are carried by the gas flow into the high-efficiency particle collection system 30, where they are efficiently captured by PTFE filter bags. The central process control system 40 is set to execute a pulse backflushing program every 10 minutes, using high-pressure nitrogen gas at a pressure of 0.5 MPa to perform a momentary (100 milliseconds) backflushing of the filter bags, collecting the powder into the collection hopper below. After the 2-hour preparation process is completed, the control system activates the star-shaped discharge valve and the double-layer airlock valve to transfer approximately 150 grams of white powder product from the collection hopper to a pre-filled, sealed sample container in an atmosphere-isolated state.

[0099] Step 5: System shutdown and cleanup.

[0100] All precursor deliveries were shut off, with only carrier gas flow maintained for 15 minutes to purge residual reactants from the pipelines and reaction chambers. Subsequently, the system was gradually shut down all heating units and the vacuum system according to a preset program. After the system had completely cooled to room temperature, it was purged with argon for protection until the next use.

[0101] The product obtained in Example 1 was characterized and analyzed. See [link / reference] Figure 5 Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the product was a well-dispersed, regularly shaped hexagonal sheet-like nanoparticle with no obvious hard agglomeration.

[0102] Image analysis software revealed that the average particle size of the original particles was 85 nm, with a particle size distribution coefficient (D90 / D10) of less than 1.5, exhibiting high monodispersity. X-ray diffraction (XRD) analysis showed that the product was well-crystallized brucite magnesium hydroxide, without other impurity phases. Fourier transform infrared spectroscopy (FTIR) analysis showed that, in addition to the characteristic absorption peak of Mg-OH, characteristic peaks of Si-O-Si and -CH=CH2 were also present, proving that vinyltrimethoxysilane was successfully grafted onto the surface of the magnesium hydroxide particles. The contact angle of the powder under water droplets reached as high as 145°, demonstrating excellent hydrophobicity.

[0103] Comparative Example 1:

[0104] For comparison, magnesium hydroxide flame retardants were prepared using the traditional liquid-phase co-precipitation method.

[0105] A 1 mol / L aqueous solution of magnesium chloride (MgCl2) was added dropwise at a constant rate to a vigorously stirred reactor containing a surfactant. The pH of the reactor was precisely controlled by the automatic addition of a 2 mol / L sodium hydroxide (NaOH) solution at a pH of 10.0. The reaction temperature was maintained at 60°C. After the precipitation reaction was complete, the reactor was aged for another 2 hours. The slurry was then filtered and repeatedly washed with deionized water until neutral. The resulting filter cake was dried in a vacuum oven at 80°C for 12 hours to obtain magnesium hydroxide powder. Finally, this powder was dry-mixed with 2% (by weight) vinyltrimethoxysilane in a high-speed mixer to achieve surface modification.

[0106] See the product obtained in Comparative Example 1. Figure 6 Scanning electron microscopy (SEM) revealed that the aggregates were irregularly sized, composed of a large number of tightly packed primary particles, with numerous hard agglomerates that were difficult to disperse. The size of these aggregates ranged from 200 nanometers to 2 micrometers. The water droplet contact angle was approximately 92°, indicating moderate hydrophobicity.

[0107] Verification of the reaction mechanism: Online mass spectrometry monitoring of the concentration of methane, a byproduct of the reaction, confirmed that the hydrolysis reaction achieved a conversion rate of over 95% at 300℃. The surface modification effect was verified by XPS analysis, showing that silicon was uniformly distributed on the particle surface, with a graft density of 2.3 grafts / nm².

[0108] The following performance comparison tests were conducted:

[0109] Magnesium hydroxide powder prepared in Example 1 and Comparative Example 1 were used as flame retardants and melt-blended with polypropylene (PP) matrix using a twin-screw extruder to prepare PP / Mg(OH)2 composite materials with a flame retardant content of 40% (mass fraction). The extruded strips were granulated and then injection molded to prepare standard test specimens for performance testing. The test results are summarized in Table 1 below.

[0110] Table 1:

[0111]

[0112] As can be seen from the comparative data in Table 1 above, the product prepared by the gas-phase method for preparing magnesium hydroxide flame retardant provided by this invention exhibits significantly better dispersion performance in a polypropylene matrix than products prepared using traditional liquid-phase methods. This is due to its nanoscale primary particle size, high monodispersity, regular hexagonal plate morphology, and uniform hydrophobic surface achieved through in-situ chemical bonding. The excellent dispersibility allows each magnesium hydroxide nanoparticle to function as an independent flame-retardant unit, greatly improving the effective specific surface area and flame-retardant efficiency of the flame retardant. Therefore, at the same addition amount, the limiting oxygen index of the composite material in Example 1 is significantly improved, achieving the highest V-0 flame retardant rating. Simultaneously, the excellent dispersibility and enhanced interfacial compatibility significantly reduce the disruption of the polymer matrix continuity caused by inorganic fillers, thereby maximizing the preservation of the mechanical properties of the composite material (such as tensile strength and elongation at break), even surpassing those of composite materials prepared using traditional processes.

[0113] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0114] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing magnesium hydroxide flame retardant based on gas-phase method, characterized in that, Includes the following steps: A precursor precision delivery system is used to provide gaseous flow of magnesium source precursor, gaseous flow of hydrolysate and gaseous flow of surface modifier respectively. Three gas-phase flows are introduced into a multi-temperature zone laminar flow reaction system through a three-coaxial laminar flow nozzle. The multi-temperature zone laminar flow reaction system is provided with a preheating mixing zone, a nucleation growth zone and a modification and ripening zone in sequence along the airflow direction. The three gas-phase flows are mixed in a controlled manner in the preheating mixing zone, undergo a gas-phase hydrolysis reaction in the nucleation growth zone to generate magnesium hydroxide particles, and undergo in-situ surface modification of the magnesium hydroxide particles in the modification and ripening zone. The temperature of the nucleation growth zone is set and maintained between 280°C and 350°C, while the total pressure in the multi-temperature zone laminar flow reaction system is maintained at a low pressure environment of 5 kPa. An airflow carrying in-situ surface-modified magnesium hydroxide particles is introduced into a high-efficiency particle collection system to separate and collect the magnesium hydroxide particles from the airflow. The specific steps for providing three-way gas phase flow using a precursor precision delivery system include: The magnesium source precursor is provided in gaseous flow through a magnesium source precursor delivery subsystem; The hydrolysate is provided via a hydrolysate delivery subsystem; The surface modifier is provided in a gaseous flow via a surface modifier delivery subsystem; The magnesium source precursor delivery subsystem, the hydrolysate delivery subsystem, and the surface modifier delivery subsystem are independent of each other and are connected to the three coaxial laminar flow nozzles through pipelines. All pipelines are heated throughout to prevent precursor condensation.

2. The method for preparing magnesium hydroxide flame retardant based on gas-phase method according to claim 1, characterized in that, The structure and working principle of the magnesium source precursor delivery subsystem and the surface modifier delivery subsystem are as follows: The core component is a bubbler containing a liquid precursor. The bubbler is surrounded by a circulating water bath jacket. The temperature of the bubbler is kept constant at a preset value by a constant temperature water bath system to ensure that the saturated vapor pressure of the liquid precursor is constant. One carrier gas, after its flow rate is precisely controlled by a mass flow controller, is introduced into the bubbler below the liquid surface. The saturated precursor vapor is carried out by bubbling, thereby forming a stable flow of the magnesium source precursor gas phase or the surface modifier gas phase.

3. The method for preparing magnesium hydroxide flame retardant based on gas-phase method according to claim 1, characterized in that, The hydrolysate delivery subsystem includes a liquid mass flow controller connected to an ultrapure water storage tank and a flash evaporator installed on the pipeline. The liquid mass flow controller injects liquid water at a set micro-flow rate into the flash evaporator, which is heated to a preset vaporization temperature, so that the liquid water vaporizes instantly. Meanwhile, a second carrier gas is introduced into the flash evaporator after its flow rate is precisely controlled by a second mass flow controller, and mixes with the vaporized water vapor to form the hydrolysate gas phase flow with precise concentration and stable flow rate.

4. The method for preparing magnesium hydroxide flame retardant based on gas-phase method according to claim 1, characterized in that, The main body of the multi-temperature zone laminar flow reaction system is a horizontally placed quartz tube. At least three independently temperature-controlled resistance wire heating furnaces are installed on the outside of the quartz tube. By setting different temperatures for the resistance wire heating furnaces, the preheating mixing zone, nucleation growth zone, and modification and ripening zone are formed axially inside the quartz tube.

5. The method for preparing magnesium hydroxide flame retardant based on gas-phase method according to claim 1 or 4, characterized in that, The specific steps of introducing three gas phase flows through a three-coaxial laminar flow nozzle include: The magnesium source precursor gas phase flow is introduced through the central tube of the three coaxial laminar flow nozzles; An inert gas, which serves as an isolation gas, is introduced through the first annular tube of the three coaxial laminar flow nozzles to form a dynamic gas sheath around the gas phase flow of the magnesium source precursor. After the hydrolysate gaseous flow and the surface modifier gaseous flow are premixed, they are introduced together through the second annular tube of the three coaxial laminar flow nozzles, thereby ensuring that each reactant flows in parallel in a laminar state in the initial stage of entering the reaction chamber, and the subsequent mixing process mainly depends on molecular diffusion.

6. The method for preparing magnesium hydroxide flame retardant based on gas-phase method according to claim 4, characterized in that, The process conditions within the multi-temperature zone laminar flow reaction system are as follows: The temperature of the preheating mixing zone is set and maintained at 110°C so that each gas phase fluid is heated together to the reaction initiation temperature while maintaining laminar flow, and radial diffusion mixing begins.

7. The method for preparing magnesium hydroxide flame retardant based on gas-phase method according to claim 6, characterized in that, The temperature of the modified curing zone is set and maintained at 180°C. Within this zone, surface modifier molecules in the gas phase undergo an in-situ chemical grafting reaction with the hydroxyl groups on the surface of the already generated magnesium hydroxide nanoparticles, forming a chemically bonded organic functionalized layer on the surface of each native particle. Simultaneously, the heat treatment process at this temperature serves to cure the magnesium hydroxide lattice and improve its crystal integrity.

8. The method for preparing magnesium hydroxide flame retardant based on gas-phase method according to claim 1, characterized in that, The steps of the high-efficiency particle collection system specifically include: First, the high-temperature mixed gas flow carrying the magnesium hydroxide particles is passed through a cooling pipe section fitted with a water-cooled jacket to rapidly reduce the gas flow temperature from 180°C to 60°C, so as to terminate all chemical reactions and fix the particle morphology. Subsequently, the cooled airflow is introduced into a particle collection device for solid-gas separation.

9. A reaction apparatus for preparing magnesium hydroxide flame retardant by gas-phase method, used to perform the preparation method of magnesium hydroxide flame retardant by gas-phase method according to any one of claims 1-8, characterized in that, include: A precursor precision delivery system is used to provide magnesium source precursor gas phase flow, hydrolysant gas phase flow and surface modifier gas phase flow with precise and controllable gas phase molar flow rate; The multi-temperature zone laminar flow reaction system is fluidly connected to the precursor precision delivery system. It is used to receive the three gas phase flows and achieve controlled mixing of reactants, gas phase hydrolysis reaction to generate magnesium hydroxide particles, and in-situ surface modification of particles through a preheating mixing zone, a nucleation growth zone and a modification and ripening zone arranged sequentially along the air flow direction. A high-efficiency particle collection system is fluidly connected to the outlet end of the multi-temperature zone laminar flow reaction system, and is used to separate and collect surface-modified magnesium hydroxide particles from the reaction gas stream. The central process control system is connected to the precursor precision conveying system, the multi-temperature zone laminar flow reaction system, and the high-efficiency particle collection system to automatically monitor and control the process parameters of the entire device, including temperature, pressure, flow rate, and collection operation.

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