A method for preparing phosphine by pyrolysis of sodium hypophosphite based on raw material pretreatment

Abstract

This invention provides a method for preparing phosphine by pyrolysis of sodium hypophosphite based on raw material pretreatment. The pretreatment method includes mechanical activation and dry granulation of sodium hypophosphite. First, sodium hypophosphite powder is subjected to intermittent ball milling under an inert atmosphere to form primary activated sodium hypophosphite. Subsequently, it is granulated through steps such as tableting, crushing, and sieving to obtain a particle size of 0.8–1.2 mm, a porosity of 20%–35%, and a bulk density of 0.75–0.95 g / cm³. 3 Granular sodium hypophosphite. The pyrolysis method, based on pretreatment, involves staged heating and pyrolysis under inert gas protection. The resulting phosphine is purified through multi-stage condensation and low-temperature distillation to obtain high-purity phosphine gas. This method significantly reduces the pyrolysis initiation temperature, increases the phosphine release rate and yield, and reduces side reactions and impurity entrainment. It boasts advantages such as high raw material utilization, concentrated and controllable pyrolysis reaction, and high product purity, making it suitable for the efficient and safe preparation of phosphine.

Description

Technical Field

[0001] This invention relates to the field of phosphine preparation technology, and more specifically to a method for preparing phosphine by pyrolysis of sodium hypophosphite based on raw material pretreatment. Background Technology

[0002] Phosphine (PH3) is an important industrial raw material widely used in electronics, chemicals, and pharmaceuticals, playing a crucial role, especially in the semiconductor industry. Due to its strong reducing properties, flammability, and toxicity, safety and purity are paramount during its preparation and recycling.

[0003] Currently, the main methods for preparing phosphine include calcium phosphide hydrolysis, white phosphorus reaction with alkali metals, electrolysis, and hypophosphite pyrolysis. Among these, the pyrolysis of sodium hypophosphite (NaH2PO2) to prepare phosphine has attracted increasing attention due to its readily available raw materials, low cost, and simple operation. This reaction, under heating conditions, produces phosphine and the byproduct phosphate. The main reaction is as follows: 2NaH2PO2 → Na2HPO4 + PH3↑.

[0004] Existing sodium hypophosphite pyrolysis processes generally suffer from the following technical problems: the raw materials are usually in powder form, highly hygroscopic, and prone to clumping or agglomeration during storage and reaction, causing uneven heating and localized overheating, which affects pyrolysis efficiency and phosphine yield. Furthermore, the dense internal structure of the raw materials lacks effective gas escape channels, easily leading to poor gas release, localized temperature increases, and the induction of side reactions, generating complex solid byproducts such as pyrophosphate. These byproducts reduce the selectivity of the main reaction and may also clog the reaction system, affecting the continuity and stability of equipment operation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing phosphine by pyrolysis of sodium hypophosphite based on raw material pretreatment, so as to at least solve the problem of moisture absorption of sodium hypophosphite powder raw material, avoid agglomeration during the pyrolysis reaction, and prevent local overheating after agglomeration from affecting the pyrolysis efficiency and inducing side reactions, thereby ensuring the stable operation of the process equipment.

[0006] On one hand, the present invention provides a raw material pretreatment method for preparing phosphine by pyrolysis of sodium hypophosphite, the method comprising the following steps: S100 is used to mechanically activate sodium hypophosphite to obtain primary activated sodium hypophosphite. S200 Granulates the primary activated sodium hypophosphite to obtain granular sodium hypophosphite; The mechanical activation is a ball milling process.

[0007] Preferably, the ball milling process is carried out in an inert gas environment, and the ball milling process is intermittent ball milling, with milling for 2 to 10 minutes, resting for 2 to 5 minutes, and repeated 5 to 10 times at a speed of 300 to 500 rpm.

[0008] Preferably, the granulation method includes: S201 compresses the primary activated sodium hypophosphite into tablets; S202 is used to crush and sieve the tableted product to obtain granular sodium hypophosphite.

[0009] Preferably, the granular sodium hypophosphite has a D50 of 0.8–1.2 mm and a porosity of 20%–35%.

[0010] Preferably, the bulk density of the granular sodium hypophosphite is 0.75-0.95 g / cm³. 3 .

[0011] On the other hand, the present invention provides a method for preparing phosphine by pyrolysis of sodium hypophosphite. Before pyrolysis, the sodium hypophosphite raw material is treated using a raw material pretreatment method. The method for preparing phosphine by pyrolysis includes the following steps: S300 pre-dries the granular sodium hypophosphite; S400 places dried granular sodium hypophosphite in a reactor and heats it under an inert gas atmosphere to carry out a pyrolysis reaction; The S500 performs multi-stage condensation and collection of phosphine gas produced by pyrolysis. The S600 process purifies the collected phosphine through distillation to obtain a high-purity phosphine product.

[0012] Preferably, the pyrolysis is divided into four stages, specifically including: During the preheating stage of S401 raw material, the temperature is 80-110℃, the heating rate is 25-30℃ / min, and the holding time is 30-60min. During the S402 activation and heating stage, the temperature is between 110 and 160℃, and the heating rate is 20 to 25℃ / min. During the S403 pyrolysis stage, the temperature is 160-200℃, the heating rate is 10-15℃ / min, and the holding time is 60-120min. During the final stage of S404 reheating, the temperature is between 200 and 210℃, the heating rate is 5 to 10℃ / min, and the holding time is 10 to 15min.

[0013] Preferably, the multi-stage condensation is provided with three stages of condensation: the first stage condensation temperature is 0 to -20°C, the second stage condensation temperature is -90 to -30°C, and the third stage condensation temperature is below -90°C.

[0014] Preferably, the distillation step employs a two-stage cryogenic distillation column, with the top temperature of the first distillation column being -110 to -100°C and the top temperature of the second distillation column being -90 to -85°C, and the distillation pressure being controlled at 0.1 to 0.3 MPa.

[0015] Beneficial effects: This invention provides a method for preparing phosphine from sodium hypophosphite via pyrolysis based on raw material pretreatment. On one hand, by pretreating the sodium hypophosphite powder raw material using a combination of mechanical activation and dry granulation, the problem of easy agglomeration of the powder raw material in existing processes is solved. This further avoids uneven heating during subsequent pyrolysis, reduces side reactions, and thus improves pyrolysis efficiency and product purity. Mechanical activation effectively disperses agglomerated sodium hypophosphite raw material. Simultaneously, ball milling introduces lattice defects, increasing pyrolysis reactivity, lowering the pyrolysis initiation temperature, and further improving pyrolysis efficiency, ensuring complete pyrolysis of sodium hypophosphite at a lower temperature. On the other hand, dry granulation forms particles with a specific particle size range and pore structure, improving the heating uniformity of the raw material during pyrolysis, avoiding localized overheating and coking, and providing microscopic channels for the phosphine product, reducing the risk of side reactions caused by untimely discharge of the phosphine product. By combining ball milling and dry granulation, the reactivity of sodium hypophosphite raw material is improved, enabling the sodium hypophosphite to be heated more evenly during the pyrolysis reaction while also allowing for smoother gas discharge, thereby further improving pyrolysis efficiency and avoiding side reactions.

[0016] On the other hand, during the pyrolysis stage of the pretreated sodium hypophosphite feedstock, combined with the structural optimization of sodium hypophosphite, the pyrolysis reaction process was made more stable by rationally controlling the heating rate and the holding time at each stage. This resulted in more uniform and controllable phosphine release, effectively suppressing local overheating and the occurrence of side reactions caused by local overheating, thereby improving the yield and purity of phosphine. Furthermore, the product was processed using a combination of multi-stage condensation and low-temperature distillation, further improving the recovery rate and purity of phosphine. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, 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 this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a process flow diagram for Example 1. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the content.

[0021] This invention provides a raw material pretreatment method for preparing phosphine by pyrolysis of sodium hypophosphite, the method comprising the following steps: S100 is used to mechanically activate sodium hypophosphite to obtain primary activated sodium hypophosphite. S200 Granulates the primary activated sodium hypophosphite to obtain granular sodium hypophosphite; The mechanical activation is ball milling, which is carried out in an inert gas environment. The ball milling is intermittent, with milling for 2-10 minutes, resting for 2-5 minutes, and repeated 5-10 times at a speed of 300-500 rpm.

[0022] In this invention, ball milling is used to mechanically activate sodium hypophosphite, aiming to improve the physical structure of the sodium hypophosphite powder and enhance its pyrolysis performance. Sodium hypophosphite is a highly hygroscopic powdery solid, prone to agglomeration, which affects the stability and efficiency of subsequent reactions. Therefore, during ball milling, an inert gas is introduced into the reaction system to purge air, preventing moisture absorption and agglomeration of the raw material. Simultaneously, the continuous introduction of inert gas removes heat during ball milling, further ensuring the purity and conversion efficiency of the final product.

[0023] Furthermore, the ball milling is conducted intermittently to avoid the raw material temperature rising too quickly due to continuous operation, thus reducing raw material agglomeration or premature decomposition. Inert ball milling media such as zirconium oxide are selected during ball milling.

[0024] After ball milling, the crystal structure of sodium hypophosphite changes at the microscopic level. The collisions and friction during ball milling cause dislocations, cracks, or boundary defects in the crystal lattice, forming a large number of surface active sites, increasing surface activity, and reducing the pyrolysis initiation temperature by 5-10°C compared to the untreated raw material.

[0025] Furthermore, ball milling of sodium hypophosphite results in smaller particle size and more uniform distribution of the powder, which is more conducive to tableting.

[0026] Preferably, the granulation method includes: S201 compresses the primary activated sodium hypophosphite into tablets; S202 is used to crush and sieve the tableted product to obtain granular sodium hypophosphite.

[0027] Preferably, the granular sodium hypophosphite has a D50 of 0.8–1.2 mm, and the D50 can be 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, or 1.2 mm; and a porosity of 20%–35%, and the porosity can be 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%.

[0028] Preferably, the bulk density of the granular sodium hypophosphite is 0.75–0.95 g / cm³. 3 The bulk density can be 0.76 g / cm³. 3 0.77g / cm 3 0.78g / cm 3 0.79g / cm 3 0.80g / cm 3 0.81 g / cm 3 0.82g / cm 3 0.83g / cm 3 0.84 g / cm 3 0.85g / cm 3 0.86 g / cm 3 0.87g / cm 3 0.88g / cm 3 0.89g / cm 3 0.90g / cm 3 0.91g / cm 3 0.92g / cm 3 0.93g / cm 3 0.94g / cm 3 0.95g / cm 3 .

[0029] In this invention, primary activated sodium hypophosphite powder is loaded into a mold and pressed into tablets using a tableting device. Preferably, a stainless steel tableting mold with a diameter of 50-100 mm is used, and the tablets are pressed into tablets under a pressure of 5-10 MPa for 30-60 seconds. No binders or additives are added during the tableting process to ensure system purity and prevent impurities from affecting subsequent pyrolysis. Preferably, the tablet thickness is 2-5 mm. Specifically, the tableting process improves the efficiency of subsequent particle shaping. The dense structure formed by tableting reduces powder flying, and the increased surface hardness helps control the particle size during breakage.

[0030] Further, the tableted product is crushed using a knife-type or roller crusher to form granular sodium hypophosphite raw material with a particle size of 0.5–3 mm. The crushed product is then graded using a standard sieve, passing through a 14-20 mesh sieve to collect particles of 0.8–1.2 mm, yielding granular sodium hypophosphite. The sieved fine powder is re-pressed for reuse, while larger particles can be further crushed and re-sieved to ensure the acquisition of granular sodium hypophosphite of the target size. A D50 of 0.8–1.2 mm is chosen because within this particle size range, sodium hypophosphite has a suitable bulk density and gas escape channels, which can improve heating uniformity and pyrolysis efficiency. When the particle size is less than 0.8 mm, it is still prone to agglomeration during pyrolysis; when the particle size is greater than 1.5 mm, it leads to poor heat transfer efficiency and hinders gas diffusion, causing the phosphine product to accumulate inside the raw material and be difficult to disperse. Furthermore, excessively large particle sizes can lead to incomplete local reactions, thus inducing side reactions.

[0031] Furthermore, the porosity of granular sodium hypophosphite, between 20% and 35%, facilitates the smooth release of phosphine products, reduces the risk of side reactions caused by gas retention, and also improves the permeability and heat transfer uniformity of the granular bed in the pyrolysis reactor. Additionally, controlling the bulk density of granular sodium hypophosphite to 0.75-0.95 g / cm³ is beneficial. 3 Within this range, it is also an important condition to ensure the smooth release of phosphine products. At this packing density, the granular sodium hypophosphite has a loose but not loose structure, with good gas channels. While ensuring the heat transfer contact area, it can improve the efficiency and stability of the pyrolysis reaction.

[0032] This invention pretreats sodium hypophosphite powder raw materials through mechanical activation and dry granulation. Mechanical activation significantly enhances the surface activity of the raw material, lowering the decomposition initiation temperature of sodium hypophosphite by 5-10°C, effectively reducing side reactions while ensuring complete reaction and improving pyrolysis efficiency. Dry granulation controls the porosity, particle size distribution, and bulk density of granular sodium hypophosphite, providing good filling performance and gas exit channels in the reactor, further improving the escape efficiency and heat transfer uniformity of the phosphine product. Simultaneously, the granulated sodium hypophosphite maintains good mechanical stability during pyrolysis, further inhibiting agglomeration and coking. Compared to the original powder, granular sodium hypophosphite also reduces dust and byproduct entrainment, preventing powdery materials from entering the condensation zone and causing blockages or impurity entrainment. The pretreated raw material provides a solid foundation for an efficient, safe, and controllable pyrolysis process for sodium hypophosphite. Furthermore, the present invention also provides a method for preparing phosphine by pyrolysis of sodium hypophosphite. After pretreatment of the sodium hypophosphite raw material, the method for preparing phosphine by pyrolysis includes the following steps: S300 pre-dries the granular sodium hypophosphite; S400 places dried granular sodium hypophosphite in a reactor and heats it under an inert gas atmosphere to carry out a pyrolysis reaction; The S500 performs multi-stage condensation and collection of phosphine gas produced by pyrolysis. The S600 process purifies the collected phosphine through distillation to obtain a high-purity phosphine product.

[0033] In detail, granular sodium hypophosphite is dried with hot air at 80-100℃ for 30-60 minutes, and an inert gas is introduced into the reaction system to avoid early oxidation and at the same time remove trace amounts of water of crystallization.

[0034] Preferably, the pyrolysis is divided into four stages, specifically including: During the preheating stage of S401 raw material, the temperature is 80-110℃, the heating rate is 25-30℃ / min, and the holding time is 30-60min. During the S402 activation and heating stage, the temperature is between 110 and 160℃, and the heating rate is 20 to 25℃ / min. During the S403 pyrolysis stage, the temperature is 160-200℃, the heating rate is 10-15℃ / min, and the holding time is 60-120min. During the final stage of S404 reheating, the temperature is between 200 and 210°C, the heating rate is 5 to 10°C / min, and the holding time is 10 to 15min.

[0035] In detail, the dried granular sodium hypophosphite is placed in a reactor and heated for pyrolysis under an inert atmosphere. During the raw material preheating stage, to prevent the sodium hypophosphite from absorbing moisture or undergoing side reactions during heating, an inert gas flow rate of 20–50 mL / min is introduced into the reaction system to further preheat and dry the granular sodium hypophosphite, establishing an anhydrous and oxygen-free reaction environment. Then, the heating stage begins. Initially, this is an activation heating stage where the sodium hypophosphite gradually pyrolyzes. During this stage, the heating rate is relatively fast, and the pyrolysis temperature of sodium hypophosphite has not yet been reached. The main purpose is to activate the raw material, ensure uniform heat distribution, and gradually move into the pyrolysis stage. When the temperature reaches 160℃, the main reaction period begins. At this time, the heating rate is reduced to 10~15℃ / min, and phosphine begins to be released stably and rapidly. During this stage, inert gas is continuously supplied to promote the timely escape of the product phosphine and avoid side reactions caused by excessively high product concentration or local overheating. After holding at this temperature for 1~2 hours, the temperature is further increased to 200-210℃. This stage is the final heating stage, mainly to ensure that sodium hypophosphite reacts completely. The temperature is held for only 10~15 minutes to reduce the occurrence of high-temperature induced side reactions.

[0036] Furthermore, the multi-stage condensation is configured with three stages of condensation: the first stage condensation temperature is 0 to -20°C, the second stage condensation temperature is -90 to -30°C, and the third stage condensation temperature is below -90°C.

[0037] In detail, the phosphine gas produced by pyrolysis undergoes multi-stage condensation and collection. The first-stage condensation temperature is 0~20℃, using ice-salt water or ordinary refrigerant. This stage primarily cools the phosphine mixture, condensing and removing most of the water vapor to prevent icing and blockage in the subsequent low-temperature condensation system. The second-stage condensation uses a dry ice / acetone cold bath or liquid nitrogen jacket for indirect cooling. This stage is the main condensation stage for phosphine. Phosphine has a boiling point of -87.7℃, and within this temperature range, the vast majority of phosphine condenses, achieving centralized recovery of the main product. The third-stage condensation temperature is below -90℃, using direct liquid nitrogen cooling to capture residual phosphine, further improving the recovery rate. Simultaneously, the third-stage condensation section serves as a buffer zone for the condensation system, preventing impact from peak airflow and enhancing the stability and safety of the condensation system.

[0038] Furthermore, the distillation step employs a two-stage cryogenic distillation column, with the top temperature of the first distillation column being -110 to -100°C and the top temperature of the second distillation column being -90 to -85°C, and the distillation pressure being controlled at 0.1 to 0.3 MPa.

[0039] In detail, after multi-stage condensation, the collected crude phosphine gas is sent to a pre-cooling tank at -90°C, with the pressure maintained at 0.1-0.3 MPa. Moderate pressurization facilitates phosphine liquefaction. Subsequently, the pre-cooled crude phosphine liquid is introduced into a two-stage distillation system for further purification. The feed temperature of the first distillation column is -90°C, the top temperature is -110 to -100°C, the bottom temperature is maintained at -90 to -80°C, and the operating pressure is 0.1-0.3 MPa. The reflux ratio of this column is set to 1.5-2.5, and the initial separation of phosphine from low-boiling substances is achieved through condensation reflux control. The phosphine distillate from the bottom of the first distillation column is further fed into the second distillation column for high-purity phosphine purification. The feed temperature of the second distillation column is set at -90 to -80°C, the top temperature is controlled at -90 to -85°C, the bottom temperature is maintained at -80 to -70°C, and the operating pressure is 0.1-0.3 MPa. The second distillation column further separates phosphine and volatile components, thereby obtaining a high-purity phosphine product.

[0040] During the two-stage distillation process, the gas escaping from the top of the column is mainly hydrogen, containing trace amounts of phosphine. To ensure safety and environmentally friendly emissions, the top tail gas needs to be treated with an alkaline oxidizing scrubbing solution, preferably an alkaline solution of NaClO2 or KMnO4, to oxidize PH3 into non-toxic and stable phosphate. The scrubbed tail gas can then be treated at high temperature in a combustion tower or safely released through a vacuum exhaust system.

[0041] Example 1 S100 mechanically activates sodium hypophosphite to obtain primary activated sodium hypophosphite. Sodium hypophosphite powder is placed in a ball mill jar, and zirconium oxide inert ball milling media is added. Under closed conditions, high-purity nitrogen is introduced for intermittent ball milling. The ball milling conditions are: ball milling for 5 minutes, standing for 3 minutes, 6 cycles, speed of 400 rpm, and ambient temperature of 25℃. S200 granulates the primary activated sodium hypophosphite to obtain granular sodium hypophosphite; the ball-milled powder is loaded into a tableting mold and pressed at 7 MPa for 40 seconds to obtain a tablet product. After tableting, the tablets are crushed using a knife crusher and sieved through a 14-20 mesh screen to collect particles of 0.8–1.2 mm, obtaining granular sodium hypophosphite. The D50 is 1.0 mm, and the bulk density is 0.85 g / cm³. 3 The porosity was measured to be 28%.

[0042] S300 pre-dries the granular sodium hypophosphite: the granular sodium hypophosphite is placed in a hot air drying oven, the temperature is controlled at 90°C, and dried for 45 minutes under nitrogen protection to remove the water of crystallization.

[0043] S400 places dried granular sodium hypophosphite in a reactor and heats it under an inert gas atmosphere to carry out a pyrolysis reaction. Nitrogen gas is introduced at a rate of 40 mL / min and the reactor is heated. The following reaction stages are reached sequentially in the reactor: S401 raw material preheating stage: heating rate is 25℃ / min, and the temperature is held for 45min after reaching 100℃; S402 activation and heating stage: The heating rate is increased to 20℃ / min, and the temperature is increased to 160℃; S403 pyrolysis stage: The heating rate is adjusted to 12℃ / min, the temperature is raised to 190℃, and held for 90min; S404 reheating stage: Heat to 200℃ and hold for 10 minutes.

[0044] Nitrogen gas is continuously purged during pyrolysis to maintain an inert atmosphere and remove the product gases.

[0045] The S500 performs multi-stage condensation and collection of phosphine gas produced by pyrolysis. The produced phosphine gas passes through a three-stage condensation system in sequence: First-stage condensation: The temperature is controlled at 0℃, and ice-salt water is used for cooling to remove water vapor; Second-stage condensation: The temperature is controlled at -78℃, and a dry ice-acetone cold bath is used to condense most of the phosphine. Third-stage condensation: The temperature is controlled at -196℃, and liquid nitrogen is used for direct cooling to capture residual phosphine.

[0046] The S600 process collects phosphine and then purifies it through distillation to obtain a high-purity phosphine product. The crude phosphine liquid collected by the condensation system is sent to a -90℃ precooling tank for pretreatment, with the pressure controlled at 0.2MPa.

[0047] Operating conditions for the first distillation column: feed temperature -90℃, top temperature -105℃, bottom temperature -85℃, pressure 0.2MPa, reflux ratio 2.0; Operating conditions for the second distillation column: feed temperature -85℃, top temperature -88℃, bottom temperature -75℃, pressure 0.2MPa.

[0048] The gas escaping from the top of the tower is washed with an alkaline solution containing NaClO2 to oxidize the residual pH3, and the remaining gas is discharged into the combustion exhaust system.

[0049] The final product is a high-purity phosphine product with a purity of >99.5%, which meets the requirements for electronic applications, and the phosphine yield is 92%.

[0050] Example 2-12 The steps for preparing phosphine from sodium hypophosphite are the same as in Example 1, with the differences shown in the table below:

[0051] In Examples 1-8, the purity of phosphine was higher than 97%, reaching up to 99.5%, and the yield was 85% to 92%. The temperature of the main pyrolysis stage was between 190°C and 198°C. The pyrolysis process was stable, with few side reactions, smooth gas release, and almost no agglomeration or coking of raw materials.

[0052] Examples 9-12 show that when the porosity is too high, the particle structure becomes too loose, the thermal contact efficiency decreases, some raw materials are not heated enough, resulting in incomplete pyrolysis; when the porosity is too low, the gas channels are restricted, the escape of phosphine is blocked, and the failure of phosphine to escape in time leads to side reactions; both excessively high and low porosity will lead to a decrease in the purity and yield of phosphine, and at the same time the holding temperature during the pyrolysis stage will also increase.

[0053] When the bulk density is too low, the material is not packed tightly, the heating is uneven, and the escape path of phosphine gas is chaotic, and phosphine is prone to aggregation, leading to side reactions. When the bulk density is too high, the bed is too dense, making it difficult for gas to penetrate, resulting in local heat accumulation and slight coking. Porosity that is too high or too low will lead to a decrease in phosphine purity and yield, and the holding temperature during the pyrolysis stage will also increase.

[0054] In Examples 13-14, the ball milling conditions were adjusted, leading to an increase in pyrolysis temperature. Insufficient ball milling resulted in fewer lattice defect sites in sodium hypophosphite, which failed to achieve the desired reduction in pyrolysis temperature, resulting in slow reaction progress. During pyrolysis, the raw materials were not fully decomposed, leading to a decrease in phosphine purity and yield. When ball milling was excessive, the raw material temperature was too high, causing premature agglomeration and local sintering of sodium hypophosphite, further reducing phosphine purity and yield.

[0055] Comparative Example 1 Sodium hypophosphite was granulated to obtain granular sodium hypophosphite. The ball-milled powder was loaded into a tableting mold and compressed under a pressure of 8 MPa for 40 seconds to obtain the tablet product. After tableting, the tablets were crushed using a knife crusher and sieved through a 14-20 mesh screen to collect particles of 0.8–1.2 mm, obtaining granular sodium hypophosphite. The bulk density was determined to be 0.43 g / cm³. 3 The porosity was measured to be 55%.

[0056] The granular sodium hypophosphite was pre-dried: the granular sodium hypophosphite was placed in a hot air drying oven at 90°C and dried for 45 minutes under nitrogen protection to remove the water of crystallization.

[0057] The dried granular sodium hypophosphite was placed in a reactor and heated under an inert gas atmosphere to carry out a pyrolysis reaction. Nitrogen gas was introduced at a rate of 40 mL / min and the reactor was heated. The following reaction stages were reached sequentially in the reactor: S401 raw material preheating stage: heating rate is 26℃ / min, and the temperature is held for 45min after reaching 100℃; S402 activation and heating stage: The heating rate is increased to 20℃ / min, and the temperature is increased to 160℃; S403 pyrolysis stage: The heating rate is adjusted to 12℃ / min, the temperature is raised to 210℃, and held for 90min; S404 reheating stage: Heat to 220℃ and hold for 10 minutes.

[0058] Nitrogen gas is continuously purged during pyrolysis to maintain an inert atmosphere and remove the product gases.

[0059] The phosphine gas produced by pyrolysis is collected through multi-stage condensation, and the produced phosphine gas passes through a three-stage condensation system in sequence: First-stage condensation: The temperature is controlled at 0℃, and ice-salt water is used for cooling to remove water vapor; Second-stage condensation: The temperature is controlled at -78℃, and a dry ice-acetone cold bath is used to condense most of the phosphine. Third-stage condensation: The temperature is controlled at -196℃, and liquid nitrogen is used for direct cooling to capture residual phosphine.

[0060] The collected phosphine was purified by distillation to obtain a high-purity phosphine product. The crude phosphine liquid collected by the condensation system is sent to a -90℃ precooling tank for pretreatment, with the pressure controlled at 0.2MPa.

[0061] Operating conditions for the first distillation column: feed temperature -90℃, top temperature -105℃, bottom temperature -85℃, pressure 0.2MPa, reflux ratio 2.0; Operating conditions for the second distillation column: feed temperature -85℃, top temperature -88℃, bottom temperature -75℃, pressure 0.2MPa.

[0062] The gas escaping from the top of the tower is washed with an alkaline solution containing NaClO2 to oxidize the residual pH3, and the remaining gas is discharged into the combustion exhaust system.

[0063] The final product obtained was phosphine with a purity >97.3% and a phosphine yield of 76%.

[0064] Compared to Example 1, Comparative Example 1 lacked the ball milling pretreatment process. After tableting, the bulk density was lower, the powder was loose, easily agglomerated, and not densely packed. The porosity was increased, with most of the pores being interparticle pores. The permeability was poor, and gas escape was not smooth. The original powder structure was loose, but there were fewer internal micropores. During the pyrolysis process, there was local overheating. Furthermore, the main decomposition temperature of sodium hypophosphite was higher than that of Example 1, resulting in a decrease in the purity of the final phosphine product.

[0065] Comparative Example 2 Sodium hypophosphite was mechanically activated to obtain primary activated sodium hypophosphite. Sodium hypophosphite powder was placed in a ball mill jar, and zirconium oxide inert ball milling media were added. Under closed conditions, high-purity nitrogen was introduced for intermittent ball milling. The ball milling conditions were: 8 min of ball milling, 5 min of standing, 8 cycles, 300 rpm, and 25℃. Pre-dry the activated sodium hypophosphite: Place the granular sodium hypophosphite in a hot air drying oven, control the temperature at 90℃, and dry for 45 minutes under nitrogen protection to remove the water of crystallization.

[0066] The dried, primary activated sodium hypophosphite was placed in a reactor and heated under an inert gas atmosphere to carry out a pyrolysis reaction. Nitrogen gas was introduced at a rate of 40 mL / min and the reactor was heated. The following reaction stages were reached sequentially in the reactor: S401 raw material preheating stage: heating rate is 30℃ / min, and the temperature is held for 45min after reaching 100℃; S402 activation and heating stage: The heating rate is increased to 25℃ / min, and the temperature is increased to 160℃; S403 pyrolysis stage: The heating rate is adjusted to 10℃ / min, the temperature is raised to 205℃, and held for 90min; S404 reheating stage: Heat to 210℃ and hold for 10 minutes.

[0067] Nitrogen gas is continuously purged during pyrolysis to maintain an inert atmosphere and remove the product gases.

[0068] The phosphine gas produced by pyrolysis is collected through multi-stage condensation, and the produced phosphine gas passes through a three-stage condensation system in sequence: First-stage condensation: The temperature is controlled at 0℃, and ice-salt water is used for cooling to remove water vapor; Second-stage condensation: The temperature is controlled at -78℃, and a dry ice-acetone cold bath is used to condense most of the phosphine. Third-stage condensation: The temperature is controlled at -196℃, and liquid nitrogen is used for direct cooling to capture residual phosphine.

[0069] The collected phosphine was purified by distillation to obtain a high-purity phosphine product. The crude phosphine liquid collected by the condensation system is sent to a -90℃ precooling tank for pretreatment, with the pressure controlled at 0.2MPa.

[0070] Operating conditions for the first distillation column: feed temperature -90℃, top temperature -105℃, bottom temperature -85℃, pressure 0.2MPa, reflux ratio 2.0; Operating conditions for the second distillation column: feed temperature -85℃, top temperature -88℃, bottom temperature -75℃, pressure 0.2MPa.

[0071] The gas escaping from the top of the tower is washed with an alkaline solution containing NaClO2 to oxidize the residual pH3, and the remaining gas is discharged into the combustion exhaust system.

[0072] The final product obtained was phosphine with a purity >93.6% and a phosphine yield of 75%.

[0073] Compared to Example 1, Comparative Example 2 lacked the pretreatment procedure of dry granulation, resulting in smaller particle size after ball milling. During pyrolysis, it was prone to agglomeration and coking, and local overheating occurred. The pyrolysis reaction temperature was high, and gas retention led to an increase in side reactions. The yield of phosphine was significantly reduced, and sodium hypophosphite powder appeared in the condensation system.

[0074] Comparative Example 3 Pre-dry the sodium hypophosphite: Place the granular sodium hypophosphite in a hot air drying oven, control the temperature at 90℃, and dry for 45 minutes under nitrogen protection to remove the water of crystallization.

[0075] The dried, primary activated sodium hypophosphite was placed in a reactor and heated under an inert gas atmosphere to carry out a pyrolysis reaction. Nitrogen gas was introduced at a rate of 40 mL / min and the reactor was heated. The following reaction stages were reached sequentially in the reactor: S401 raw material preheating stage: heating rate is 28℃ / min, and the temperature is held for 45min after reaching 100℃; S402 activation and heating stage: The heating rate is increased to 25℃ / min, and the temperature is increased to 150℃; S403 pyrolysis stage: The heating rate is adjusted to 18℃ / min, the temperature is raised to 215℃, and held for 90min; S404 reheating stage: Heat to 220℃ and hold for 10 minutes.

[0076] Nitrogen gas is continuously purged during pyrolysis to maintain an inert atmosphere and remove the product gases.

[0077] The phosphine gas produced by pyrolysis is collected through multi-stage condensation, and the produced phosphine gas passes through a three-stage condensation system in sequence: First-stage condensation: The temperature is controlled at 0℃, and ice-salt water is used for cooling to remove water vapor; Second-stage condensation: The temperature is controlled at -78℃, and a dry ice-acetone cold bath is used to condense most of the phosphine. Third-stage condensation: The temperature is controlled at -196℃, and liquid nitrogen is used for direct cooling to capture residual phosphine.

[0078] The collected phosphine was purified by distillation to obtain a high-purity phosphine product. The crude phosphine liquid collected by the condensation system is sent to a -90℃ precooling tank for pretreatment, with the pressure controlled at 0.2MPa.

[0079] Operating conditions for the first distillation column: feed temperature -90℃, top temperature -105℃, bottom temperature -85℃, pressure 0.2MPa, reflux ratio 2.0; Operating conditions for the second distillation column: feed temperature -85℃, top temperature -88℃, bottom temperature -75℃, pressure 0.2MPa.

[0080] The gas escaping from the top of the tower is washed with an alkaline solution containing NaClO2 to oxidize the residual pH3, and the remaining gas is discharged into the combustion exhaust system.

[0081] The final product obtained was phosphine with a purity >90.4% and a phosphine yield of 65%.

[0082] Comparative Example 3 did not undergo any raw material pretreatment and directly used powdered sodium hypophosphite for pyrolysis. Due to the uneven particle size distribution and loose packing of the sodium hypophosphite powder, it was highly susceptible to moisture absorption and agglomeration, resulting in significant problems such as coking caused by uneven heat transfer during pyrolysis. Furthermore, the pyrolysis reaction temperature was high, producing numerous byproducts, and a large amount of raw material powder appeared in the condensation system, ultimately leading to low purity and low yield of the phosphine product.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for pretreatment of raw materials for the preparation of phosphine by pyrolysis of sodium hypophosphite, characterized in that, The method includes the following steps: S100 is used to mechanically activate sodium hypophosphite to obtain primary activated sodium hypophosphite. S200 Dry granulation of the primary activated sodium hypophosphite is performed to obtain granular sodium hypophosphite; The mechanical activation is performed by ball milling; the granular sodium hypophosphite has a D50 of 0.8–1.2 mm, a porosity of 20%–35%, and a bulk density of 0.75–0.95 g / cm³. 3 ; The ball milling process is carried out in an inert gas environment. The ball milling process is intermittent, with milling for 2 to 10 minutes, resting for 2 to 5 minutes, and repeated 5 to 10 times at a speed of 300 to 500 rpm.

2. The raw material pretreatment method according to claim 1, characterized in that, The dry granulation method includes: S201 compresses the primary activated sodium hypophosphite into tablets; S202 is used to crush and sieve the tableted product to obtain granular sodium hypophosphite.

3. The raw material pretreatment method according to claim 1, characterized in that, The granular sodium hypophosphite has a D50 of 0.9–1.1 mm, a porosity of 25%–33%, and a bulk density of 0.80–0.92 g / cm³. 3 .

4. The raw material pretreatment method according to claim 1, characterized in that, The granular sodium hypophosphite has a D50 of 1.0–1.1 mm, a porosity of 28%–30%, and a bulk density of 0.85–0.90 g / cm³. 3 .

5. The raw material pretreatment method according to claim 1, characterized in that, Ball mill for 4–8 minutes, let stand for 3–5 minutes, cycle 6–8 times, and rotate at 400–500 rpm.

6. A method for preparing phosphine by pyrolysis of sodium hypophosphite, characterized in that, Prior to pyrolysis, the sodium hypophosphite raw material is treated using the raw material pretreatment method according to any one of claims 1 to 5, and the method for preparing phosphine by pyrolysis includes the following steps: S300 pre-dries the granular sodium hypophosphite; S400 places dried granular sodium hypophosphite in a reactor and heats it under an inert gas atmosphere to carry out a pyrolysis reaction; The S500 performs multi-stage condensation and collection of phosphine gas produced by pyrolysis. The S600 process collects phosphine and then purifies it by distillation to obtain the phosphine product.

7. The method for preparing phosphine by pyrolysis according to claim 6, characterized in that, The pyrolysis is divided into four stages, specifically including: During the preheating stage of S401 raw material, the temperature is 80-110℃, the heating rate is 25-30℃ / min, and the holding time is 30-60min. During the S402 activation and heating stage, the temperature is between 110 and 160℃, and the heating rate is 20 to 25℃ / min. During the S403 pyrolysis stage, the temperature is 160-200℃, the heating rate is 10-15℃ / min, and the holding time is 60-120min. During the final stage of S404 reheating, the temperature is between 200 and 210℃, the heating rate is 5 to 10℃ / min, and the holding time is 10 to 15min.

8. The method for preparing phosphine by pyrolysis according to claim 6, characterized in that, The multi-stage condenser is configured with three stages: the first stage condensation temperature is 0 to -20℃, the second stage condensation temperature is -90 to -30℃, and the third stage condensation temperature is below -90℃.

9. The method for preparing phosphine by pyrolysis according to claim 6, characterized in that, The distillation step employs a two-stage cryogenic distillation column. The top temperature of the first distillation column is -110 to -100°C, and the top temperature of the second distillation column is -90 to -85°C. The distillation pressure is controlled at 0.1 to 0.3 MPa.

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