Wet-process phosphoric acid demetalization method and industrial grade II type ammonium polyphosphate product synthesis method

Abstract

The invention relates to the technical field of ammonium polyphosphate synthesis, in particular to a wet-process phosphoric acid demetalization method and a synthesis method of an industrial grade II type ammonium polyphosphate product. The wet-process phosphoric acid demetallization method comprises the following steps: metal impurities in wet-process phosphoric acid are extracted and removed by adopting a mixed extraction agent, the mixed extraction agent comprises an extraction agent and a diluent in a volume ratio of (1-5): 1, the extraction agent is selected from one or more of di (2-ethylhexyl) phosphate, tributyl phosphate and n-butyl alcohol, and the diluent is selected from one or more of tributyl phosphate and n-butyl alcohol. The diluent is selected from one or two of dodecane and xylene; after the extraction is completed, standing for phase separation, and removing aluminum impurities from a water phase by adopting ammonium fluoride and fluosilicic acid. The wet-process phosphoric acid demetallization method is matched with desulfurization acid radical treatment, the obtained pretreated wet-process phosphoric acid is prepared through the synthesis method, an industrial grade II-type ammonium polyphosphate product with the higher polymerization degree can be obtained, and the flame retardant effect of the product is better.

Description

Technical Field

[0001] The invention relates to the technical field of ammonium polyphosphate synthesis, and in particular to a wet phosphoric acid demetallization method and a synthesis method of an industrial-grade type II ammonium polyphosphate product. Background Art

[0002] Ammonium polyphosphate (APP) is a highly efficient halogen-free phosphorus flame retardant with high nitrogen and phosphorus mass fractions, good flame retardant effect, high decomposition temperature, etc. It has the dual functions of acid source and gas source in typical halogen-free intumescent flame retardants. In recent years, it has gradually become one of the research hotspots in the field of flame retardancy and has been widely used in many fields such as materials, coatings, flame retardants and fire extinguishing agents. As the basic material of intumescent flame retardants, ammonium polyphosphate is widely used in the flame retardant industry. As the global flame retardants are developing towards halogen-free, intumescent flame retardants with ammonium polyphosphate as the main raw material are becoming more and more popular in the industry, especially the demand for type II ammonium polyphosphate with high polymerization degree is becoming increasingly strong.

[0003] The traditional method for synthesizing ammonium polyphosphate is to use thermal phosphoric acid or phosphorus pentoxide and urea as raw materials for condensation reaction, but the production process of thermal phosphoric acid and phosphorus pentoxide is often accompanied by high pollution and high energy consumption. Therefore, from the perspective of environmental protection and energy conservation and emission reduction, technicians have developed a method for synthesizing ammonium polyphosphate using wet phosphoric acid and urea as raw materials. However, the sulfate and metal impurities such as iron, magnesium, and aluminum present in wet phosphoric acid will affect the polymerization degree of the synthesized ammonium polyphosphate, and the product is difficult to meet the standard requirements of industrial-grade type II ammonium polyphosphate. For this reason, it is necessary to pretreat the wet phosphoric acid before synthesis to control the impurity content in the wet phosphoric acid raw material. The existing pretreatment process usually uses the method of adding phosphate slurry / calcium hydrogen phosphate to wet phosphoric acid for desulfurization, and then uses an extractant to remove metal impurities after desulfurization. Since a large amount of metal impurities and miscellaneous acids are adsorbed in the extractant during the extraction process, if the extraction is not well controlled, there will be emulsification, the extractant is difficult to recover, and the loss of the extractant increases, resulting in high economic costs. Summary of the invention

[0004] Aiming at the technical problems that before ammonium polyphosphate is synthesized from wet-process phosphoric acid and urea as raw materials, impurities in wet-process phosphoric acid affect the polymerization degree of the product, and the extractant in the demetallization treatment of wet-process phosphoric acid is difficult to recover, the present invention provides a wet-process phosphoric acid demetallization method and a method for synthesizing an industrial-grade type II ammonium polyphosphate product.

[0005] In a first aspect, the present invention provides a method for demetallization of wet phosphoric acid, comprising the following steps: A mixed extractant is used to extract and remove metal impurities, such as iron impurities, magnesium impurities, etc., in wet-process phosphoric acid. The mixed extractant includes an extractant and a diluent in a volume ratio of 1 to 5:1, wherein the extractant is selected from one or more of di(2-ethylhexyl) phosphate (D2EHPA), tributyl phosphate (TBP), and n-butanol, and the diluent is selected from one or more of dodecane and xylene; After the extraction is completed, the phases are allowed to stand and separated, and the aqueous phase is taken and ammonium fluoride and fluorosilicic acid are used to remove aluminum impurities; Take the oil phase and add alkali solution, the volume ratio of the oil phase to the alkali solution is 10-15:1, separate the phases to obtain the alkali-washed organic phase and the alkali-washing liquid, then add desalted water to the alkali-washed organic phase, separate the phases, and obtain the regenerated mixed extractant.

[0006] Furthermore, the extraction ratio (O / A), that is, the volume ratio of the mixed extractant and the wet-process phosphoric acid is 3~7:1.

[0007] Furthermore, the extraction temperature is 40-60° C., the extraction time is 20-60 min, and stirring is performed during the extraction. The stirring method is preferably mechanical stirring, more preferably stirring with a stirring paddle, and the stirring speed is 200-300 rpm.

[0008] Further, ammonium fluoride and fluorosilicic acid are added to the aqueous phase to remove aluminum impurities, and the amount of ammonium fluoride and fluorosilicic acid added is 1 to 2 times the theoretical amount. The reaction formula for removing aluminum impurities by ammonium fluoride and fluorosilicic acid is 6NH4F+H2SiF6+2Al 3+ +6Na + +2H2O=2Na3AlF6↓+SiO2↓+6NH4 + +6H + Before removing aluminum impurities, the aluminum content in the water phase is first measured, and then the theoretical addition amounts of ammonium fluoride and fluorosilicic acid can be calculated based on the reaction formula.

[0009] Furthermore, the alkali solution is a 5wt% to 20wt% sodium hydroxide solution.

[0010] Furthermore, the volume ratio of the alkaline washing organic phase to the desalted water is 1-5:1.

[0011] In a second aspect, the present invention provides a method for synthesizing an industrial-grade type II ammonium polyphosphate product, wherein the wet-process phosphoric acid demetallization method is used to pretreat a wet-process phosphoric acid raw material. That is, the present invention provides an application of the wet-process phosphoric acid demetallization method in synthesizing an industrial-grade type II ammonium polyphosphate product. The wet-process phosphoric acid raw material referred to in the present invention refers to wet-process phosphoric acid used as a raw material for an industrial-grade type II ammonium polyphosphate product.

[0012] Further, the synthesis method comprises the following steps: (1) Wet phosphoric acid desulfurization: Adding a desulfurizing agent to the wet-process phosphoric acid raw material, wherein the desulfurizing agent is selected from one or both of phosphate slurry and calcium hydrogen phosphate, stirring and then standing to obtain clarified desulfurized wet-process phosphoric acid; (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is mixed with a mixed extractant, wherein the volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 3-7:1, and the mixture is extracted while being stirred. The extraction temperature is controlled to be 40-60°C, the extraction time is 20-60 min, the stirring speed is 200-300 rpm, and the mixture is allowed to stand for phase separation after extraction; Taking the aqueous phase, adding fluorosilicic acid and ammonium fluoride, wherein the amount of ammonium fluoride and fluorosilicic acid added is 1 to 2 times the theoretical amount, to obtain pretreated wet-process phosphoric acid; The oil phase is taken and washed with alkali solution, the volume ratio of the oil phase to the alkali solution is 10-15:1, after washing 1-3 times, the phases are separated to obtain an alkali-washed organic phase and an alkali-washing solution, desalted water is added to the alkali-washed organic phase, the volume ratio of the alkali-washed organic phase to the desalted water is 1-5:1, after washing 1-3 times, the phases are separated to obtain a regenerated mixed extractant; (3) Pretreated wet-process phosphoric acid and urea are mixed in a reactor at a molar ratio of 1:1.8-3.2, and prepolymerized at 100-130°C for 10-30 min. The gas generated during the prepolymerization is extracted with a vacuum pump, and the pressure in the reactor is maintained at ≤0.09 MPa. The temperature is then raised to 200-250°C, and the reaction is continued for 60-180 min. The obtained white solid is ammonium polyphosphate.

[0013] Furthermore, in step (1), the amount of desulfurizer added is 1 to 2 times the theoretical amount. The theoretical amount is determined based on the minimum amount of desulfurizer that can remove all sulfur impurities in wet phosphoric acid. The principles of desulfurization of phosphate slurry and calcium hydrogen phosphate are: Ca3(PO4)2+3H2SO4=3CaSO4↓+2H3PO4, 2CaHPO4+H2SO4=CaSO4↓+Ca(H2PO4)2.

[0014] Furthermore, after step (2), the contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid are tested, and step (3) is performed after the requirements are met.

[0015] Furthermore, the phosphorus pentoxide content in the wet-process phosphoric acid raw material of step (1) is 20wt%~25wt%; Step (2) before demetallization, the desulfurized wet-process phosphoric acid is concentrated to a phosphorus pentoxide content of 36.2 wt% to 50.7 wt%; In step (3), before mixing with urea, the pretreated wet-process phosphoric acid is concentrated to a phosphorus pentoxide content of ≥ 61.5 wt%.

[0016] Furthermore, the gas (containing ammonia gas) generated during the prepolymerization process in step (3) is sent to a tail gas scrubber for treatment to obtain ammonia water as a by-product. The ammonia water can be used for self-use or exported, thereby increasing the economic benefits of the synthesis method.

[0017] Furthermore, the method further comprises step (4): after the white solid prepared in step (3) is cooled, the solid is crushed and packaged to obtain a type II product that meets the HG / T 2770-2020 industrial ammonium polyphosphate standard. The type II product that meets the HG / T 2770-2020 industrial ammonium polyphosphate standard in the present invention refers to an ammonium polyphosphate product that meets the type II product index requirements specified in the HG / T 2770-2020 industrial ammonium polyphosphate standard. The specific index requirements are shown in Table 1 below.

[0018] Table 1 Index requirements for HG / T 2770-2020 industrial ammonium polyphosphate type II products

[0019] The beneficial effects of the present invention are: The wet phosphoric acid demetallization method provided by the present invention can effectively remove metal impurities such as iron, magnesium, aluminum and the like in the raw materials. The mixed extractant used overcomes the shortcomings of the existing extractants, such as high viscosity, poor fluidity and difficulty in phase separation when used directly. The mixed extractant has the effects of easy separation, easy regeneration and recycling, greatly reduces the production cost, reduces the discharge of wastewater containing the extractant, and is more environmentally friendly and economical.

[0020] The invention uses the wet-process phosphoric acid demetallization method in combination with desulfate treatment to obtain pretreated wet-process phosphoric acid, which can obtain an industrial-grade type II ammonium polyphosphate product with a higher degree of polymerization compared with conventional wet-process phosphoric acid that directly reacts without pretreatment. The average degree of polymerization reaches 80-120, so the product has a better flame retardant effect.

[0021] The synthesis of the industrial-grade type II ammonium polyphosphate product of the present invention adopts a two-step operation of prepolymerization and polymerization, and uses urea as a reaction raw material, which not only serves as a nitrogen source but also can act as a condensation agent. Therefore, there is no need to additionally introduce ammonia. Compared with the traditional reactor synthesis method, the introduction of ammonia gas can avoid increasing the pressure in the reactor. Instead, a negative pressure form is adopted, which effectively reduces the risk of explosion of the reactor and increases the safety factor of production operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 The present invention provides a flow chart of a method for synthesizing an industrial-grade type II ammonium polyphosphate product. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0025] A wet phosphoric acid demetallization method comprises the following steps: (1) Using a mixed extractant to extract and remove metal impurities such as iron impurities and magnesium impurities in wet-process phosphoric acid, the volume ratio of the mixed extractant to the wet-process phosphoric acid is 3 to 7:1, and the mixed extractant includes an extractant and a diluent in a volume ratio of 1 to 5:1, wherein the extractant is selected from one or more of di(2-ethylhexyl) phosphate (D2EHPA), tributyl phosphate (TBP), and n-butanol, and the diluent is selected from one or two of dodecane and xylene; Extraction was performed while stirring with a stirring paddle, the stirring speed was controlled to be 200-300 rpm, the extraction temperature was 40-60°C, and the extraction time was 20-60 min; (2) After the extraction is completed, the phases are allowed to stand and separate, and the water phase is taken to detect the residual aluminum content in the water phase. The theoretical amount of fluorosilicic acid and ammonium fluoride to be added is calculated based on the test results, and ammonium fluoride and fluorosilicic acid are added at 1 to 2 times the theoretical amount to remove aluminum impurities; (3) Add alkali solution to the oil phase, wherein the alkali solution is a 5wt% to 20wt% sodium hydroxide solution, and the volume ratio of the oil phase to the alkali solution is 10 to 15:1. Separate the phases to obtain an alkali-washed organic phase and an alkali-washing liquid. Add desalted water in a volume ratio of 1 to 5:1 to the alkali-washed organic phase, and separate the phases to obtain a regenerated mixed extractant.

[0026] A method for synthesizing an industrial-grade type II ammonium polyphosphate product, such as Figure 1 As shown, the following steps are included: (1) Wet phosphoric acid desulfurization: Using wet-process phosphoric acid with a phosphorus pentoxide content of 20wt% to 25wt% as a raw material, detecting the contents of sulfate, iron, magnesium, and aluminum impurities in the wet-process phosphoric acid raw material, firstly calculating the theoretical amount of the required desulfurizer according to the sulfate content, the desulfurizer is selected from one or two of phosphate slurry and calcium hydrogen phosphate, adding the desulfurizer to the wet-process phosphoric acid raw material according to 1 to 2 times of the theoretical amount, stirring and then standing to obtain clarified desulfurized wet-process phosphoric acid; (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is concentrated to a phosphorus pentoxide content of 36.2 wt% to 50.7 wt%, and then mixed with a mixed extractant, wherein the volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 3 to 7:1, and the mixed extractant comprises an extractant and a diluent in a volume ratio of 1 to 5:1, wherein the extractant is selected from one or more of di(2-ethylhexyl) phosphate (D2EHPA), tributyl phosphate (TBP), and n-butanol, and the diluent is selected from one or two of dodecane and xylene; Extraction is performed while stirring with a stirring paddle, the stirring speed is controlled to be 200-300 rpm, the extraction temperature is 40-60°C, the extraction time is 20-60 min, and after extraction, the mixture is allowed to stand for phase separation; Taking a water phase, detecting the residual aluminum content in the water phase, calculating the theoretical addition amount of fluorosilicic acid and ammonium fluoride according to the detection result, adding ammonium fluoride and fluorosilicic acid at 1 to 2 times of the theoretical addition amount, removing aluminum impurities, and obtaining pretreated wet-process phosphoric acid; The oil phase is taken and washed with alkali solution, wherein the alkali solution is a 5wt% to 20wt% sodium hydroxide solution, and the volume ratio of the oil phase to the alkali solution is 10 to 15:1. After washing 1 to 3 times, the phases are separated to obtain an alkali-washed organic phase and an alkali-washing liquid. Desalted water is added to the alkali-washed organic phase, and the volume ratio of the alkali-washed organic phase to the desalted water is 1 to 5:1. After washing 1 to 3 times, the phases are separated to obtain a regenerated mixed extractant. (3) The content of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid is detected, and the pretreated wet-process phosphoric acid that meets the requirements is concentrated to a phosphorus pentoxide content of ≥61.5wt%, and then mixed with urea in a reactor at a molar ratio of 1:1.8~3.2, and prepolymerized at 100~130°C for 10~30min. The gas generated during the prepolymerization process is extracted by a vacuum pump and sent to a tail gas washing tower for treatment to obtain ammonia water as a by-product. During the prepolymerization process, the pressure in the reactor is maintained at ≤0.09MPa, and then the temperature is raised to 200~250°C, and the reaction is continued for 60~180min. The white solid obtained is ammonium polyphosphate; (4) After the white solid prepared in step (3) is cooled, it is crushed and packaged to obtain a Type II product that meets the HG / T 2770-2020 industrial ammonium polyphosphate standard.

[0027] Example 1 (1) Wet phosphoric acid desulfurization: Wet-process phosphoric acid with a phosphorus pentoxide content of 21wt% was used as a raw material, and the contents of sulfate, iron, magnesium, and aluminum impurities in the wet-process phosphoric acid raw material were detected (as shown in Table 2). The wet-process phosphoric acid raw material was transported to a desulfurization tank by a pump, and the theoretical amount of phosphate slurry required for desulfurization was calculated according to the sulfate content, and the phosphate slurry was added to remove sulfate. The phosphate slurry was added according to 1.4 times the theoretical amount, and stirred for 50 minutes with a stirring paddle at a stirring speed of 180r / min, and then allowed to stand for 150 minutes. After the desulfurization reaction was completed, the material was filtered to obtain clarified desulfurized wet-process phosphoric acid; (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is sent to a concentration kettle ① and concentrated to a phosphorus pentoxide content of 43.5wt%, and then sent to an extraction reactor, using di(2-ethylhexyl) phosphate (D2EHPA) and dodecane in a volume ratio of 3:1 as a mixed extractant, and the volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 5:1, and extraction is carried out while stirring with a stirring paddle, the stirring speed is controlled to be 200rpm, the extraction temperature is 50°C, the extraction time is 30min, and after standing for 60min, phase separation is performed to obtain an extracted organic phase and an aqueous phase; Taking the aqueous phase, detecting the residual aluminum content in the aqueous phase, and then pumping the aqueous phase into a refining kettle, calculating the theoretical addition amount of fluorosilicic acid and ammonium fluoride according to the detection results, adding ammonium fluoride and fluorosilicic acid at 1.5 times the theoretical addition amount, further removing the metal impurity aluminum, and obtaining pretreated wet-process phosphoric acid; The oil phase is pumped to the alkaline washing kettle, and 5wt% sodium hydroxide solution is added for washing. The volume ratio of the oil phase to the alkaline solution is 15:1. After washing twice, the phases are separated to obtain an alkaline washing organic phase and an alkaline washing solution. Desalted water is added to the alkaline washing organic phase. The volume ratio of the alkaline washing organic phase to the desalted water is 4:1. After washing twice, the phases are separated to obtain a regenerated mixed extractant. (3) The contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid were tested (as shown in Table 3). The pretreated wet-process phosphoric acid that met the requirements was transported to a concentration kettle ② and concentrated to a phosphorus pentoxide content of 61.5 wt%. Urea was weighed and put into a prepolymerization reactor. The pretreated wet-process phosphoric acid and urea were mixed with a stirring paddle in a molar ratio of 1:1.8 to obtain a transparent clear liquid. The mixed solution was prepolymerized in the prepolymerization reactor. The temperature in the prepolymerization reactor was raised to 124° C. and the reaction was carried out for 25 min. During the prepolymerization process, a large amount of bubbles were generated due to the formation of ammonia gas. The ammonia gas was extracted with a vacuum pump to maintain the pressure in the reactor at 0.085 MPa. The extracted ammonia gas was sent to a tail gas scrubber for treatment to obtain ammonia water as a byproduct. Subsequently, the material after the prepolymerization was transported to a polymerization curing reactor and the temperature was further raised to 230° C. for polymerization curing. The reaction was carried out for 140 min to obtain a white solid, which was ammonium polyphosphate. (4) After the white solid prepared in step (3) is cooled, it is sent to a crushing system through a conveying system, crushed, and packaged. The prepared ammonium polyphosphate product is tested according to the test method described in HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0028] Example 2 (1) Wet phosphoric acid desulfurization: Wet-process phosphoric acid with a phosphorus pentoxide content of 24wt% was used as a raw material, and the contents of sulfate, iron, magnesium, and aluminum impurities in the wet-process phosphoric acid raw material were detected (as shown in Table 2). The wet-process phosphoric acid raw material was transported to a desulfurization tank by a pump, and the theoretical addition amount of the desulfurizer phosphate slurry required was calculated according to the sulfate content, and the phosphate slurry was added to remove the sulfate. The phosphate slurry was added according to 1.5 times the theoretical addition amount, and stirred for 45 minutes with a stirring paddle at a stirring speed of 150r / min, and then allowed to stand for 180 minutes. After the desulfurization reaction was completed, the material was filtered to obtain clarified desulfurized wet-process phosphoric acid; (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is sent to a concentration kettle ① to be concentrated to a phosphorus pentoxide content of 47.1wt%, and then sent to an extraction reactor, using di(2-ethylhexyl) phosphate (D2EHPA) and xylene in a volume ratio of 4:1 as a mixed extractant, and the volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 6:1, and extraction is carried out while stirring with a stirring paddle, the stirring speed is controlled to be 230rpm, the extraction temperature is 50°C, the extraction time is 30min, and after standing for 70min, phase separation is performed to obtain an extracted organic phase and an aqueous phase; Taking the aqueous phase, detecting the residual aluminum content in the aqueous phase, and then pumping the aqueous phase into a refining kettle, calculating the theoretical addition amount of fluorosilicic acid and ammonium fluoride according to the detection results, adding ammonium fluoride and fluorosilicic acid at 1.5 times the theoretical addition amount, further removing the metal impurity aluminum, and obtaining pretreated wet-process phosphoric acid; The oil phase is pumped to an alkali washing kettle, and a 10wt% sodium hydroxide solution is added for washing. The volume ratio of the oil phase to the alkali solution is 10:1. After washing twice, the phases are separated to obtain an alkali-washed organic phase and an alkali-washing solution. Desalted water is added to the alkali-washed organic phase. The volume ratio of the alkali-washed organic phase to the desalted water is 5:1. After washing twice, the phases are separated to obtain a regenerated mixed extractant. (3) The contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid were tested (as shown in Table 3). The pretreated wet-process phosphoric acid that met the requirements was transported to a concentration kettle ② and concentrated to a phosphorus pentoxide content of 65.2 wt%. Urea was weighed and put into a prepolymerization reactor. The pretreated wet-process phosphoric acid and urea were mixed with a stirring paddle in a molar ratio of 1:2 to obtain a transparent clarified liquid. The mixed solution was prepolymerized in the prepolymerization reactor. The temperature in the prepolymerization reactor was raised to 124° C. and the reaction was carried out for 30 min. During the prepolymerization process, a large amount of bubbles were generated due to the formation of ammonia gas. The ammonia gas was extracted with a vacuum pump to maintain the pressure in the reactor at 0.075 MPa. The extracted ammonia gas was sent to a tail gas scrubber for treatment to obtain ammonia water as a byproduct. Subsequently, the material after the prepolymerization was transported to a polymerization curing reactor and the temperature was further raised to 230° C. for polymerization curing. The reaction was carried out for 160 min to obtain a white solid, which was ammonium polyphosphate. (4) After the white solid prepared in step (3) is cooled, it is sent to a crushing system through a conveying system, crushed, and packaged. The prepared ammonium polyphosphate product is tested according to the test method described in HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0029] Example 3 (1) Wet phosphoric acid desulfurization: Wet-process phosphoric acid with a phosphorus pentoxide content of 25wt% was used as a raw material, and the contents of sulfate, iron, magnesium, and aluminum impurities in the wet-process phosphoric acid raw material were detected (as shown in Table 2). The wet-process phosphoric acid raw material was transported to a desulfurization tank by a pump, and the theoretical amount of phosphate slurry required for desulfurization was calculated according to the sulfate content, and the phosphate slurry was added to remove sulfate. The phosphate slurry was added at 1.2 times the theoretical amount, and stirred for 60 minutes with a stirring paddle at a stirring speed of 150r / min, and then allowed to stand for 180 minutes. After the desulfurization reaction was completed, the material was filtered to obtain clarified desulfurized wet-process phosphoric acid; (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is sent to a concentration kettle ① to be concentrated to a phosphorus pentoxide content of 48.2wt%, and then sent to an extraction reactor, using tributyl phosphate (TBP) and dodecane in a volume ratio of 4:1 as a mixed extractant, and the volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 5:1, and extraction is carried out while stirring with a stirring paddle, the stirring speed is controlled to be 230rpm, the extraction temperature is 50°C, the extraction time is 30min, and after standing for 45min, phase separation is performed to obtain an extracted organic phase and an aqueous phase; Taking a water phase, detecting the residual aluminum content in the water phase, and then pumping the water phase into a refining kettle, calculating the theoretical addition amount of fluorosilicic acid and ammonium fluoride according to the detection results, adding ammonium fluoride and fluorosilicic acid at 1.7 times the theoretical addition amount, further removing the metal impurity aluminum, and obtaining pretreated wet-process phosphoric acid; The oil phase is pumped to the alkaline washing kettle, and 5wt% sodium hydroxide solution is added for washing. The volume ratio of the oil phase to the alkaline solution is 13:1. After washing three times, the phases are separated to obtain an alkaline washed organic phase and an alkaline washing solution. Desalted water is added to the alkaline washed organic phase. The volume ratio of the alkaline washed organic phase to the desalted water is 5:1. After washing three times, the phases are separated to obtain a regenerated mixed extractant. (3) The contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid were tested (as shown in Table 3). The pretreated wet-process phosphoric acid that met the requirements was transported to a concentration kettle ② and concentrated to a phosphorus pentoxide content of 68.8 wt%. Urea was weighed and put into a prepolymerization reactor. The pretreated wet-process phosphoric acid and urea were mixed with a stirring paddle in a molar ratio of 1:1.8 to obtain a transparent clear liquid. The mixed solution was prepolymerized in the prepolymerization reactor. The temperature in the prepolymerization reactor was raised to 128° C. and the reaction was continued for 30 min. During the prepolymerization process, a large amount of bubbles were generated due to the formation of ammonia gas. The ammonia gas was extracted with a vacuum pump to maintain the pressure in the reactor at 0.085 MPa. The extracted ammonia gas was sent to a tail gas scrubber for treatment to obtain ammonia water as a byproduct. Subsequently, the material after the prepolymerization was transported to a polymerization curing reactor and continued to be heated to 250° C. for polymerization curing. The reaction was continued for 140 min to obtain a white solid, which was ammonium polyphosphate. (4) After the white solid prepared in step (3) is cooled, it is sent to a crushing system through a conveying system, crushed, and packaged. The prepared ammonium polyphosphate product is tested according to the test method described in HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0030] Comparative Example 1 (1) Wet phosphoric acid desulfurization: The same wet-process phosphoric acid raw material as in Example 3 was used and transported to the desulfurization tank by a pump. The theoretical amount of phosphate slurry added to remove sulfate was calculated according to the test data. The phosphate slurry was added to remove sulfate. The amount of phosphate slurry added was 1.2 times the theoretical amount. The mixture was stirred with a stirring paddle for 60 minutes at a stirring speed of 150 r / min, and then allowed to stand for 180 minutes. After the desulfurization reaction was completed, the material was filtered to obtain clarified desulfurized wet-process phosphoric acid. (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is sent to a concentration kettle ① to be concentrated to a phosphorus pentoxide content of 48.2wt%, and then sent to an extraction reactor, using tributyl phosphate (TBP) as an extractant, the volume ratio of the extractant to the desulfurized wet-process phosphoric acid is 5:1, and the extraction is carried out while stirring with a stirring paddle, the stirring speed is controlled to be 230rpm, the extraction temperature is 50°C, the extraction time is 30min, and the phases are separated after standing for 15h, and the extracted organic phase and the aqueous phase are obtained by phase separation; Taking a water phase, detecting the residual aluminum content in the water phase, and then pumping the water phase into a refining kettle, calculating the theoretical addition amount of fluorosilicic acid and ammonium fluoride according to the detection results, adding ammonium fluoride and fluorosilicic acid at 1.7 times the theoretical addition amount, further removing the metal impurity aluminum, and obtaining pretreated wet-process phosphoric acid; The oil phase is pumped to the alkaline washing kettle, and 5wt% sodium hydroxide solution is added for washing. The volume ratio of the oil phase to the alkaline solution is 13:1. After washing three times, the phases are separated to obtain an alkaline washed organic phase and an alkaline washing solution. Desalted water is added to the alkaline washed organic phase. The volume ratio of the alkaline washed organic phase to the desalted water is 5:1. After washing three times, the phases are separated to obtain a regenerated mixed extractant. (3) The contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid were tested (as shown in Table 3). The pretreated wet-process phosphoric acid that met the requirements was transported to a concentration kettle ② and concentrated to a phosphorus pentoxide content of 68.8 wt %. The phosphoric acid was then pumped into a prepolymerization reactor. Urea was weighed and put into the prepolymerization reactor. The pretreated wet-process phosphoric acid and urea were mixed with a stirring paddle in a molar ratio of 1:1.8 to obtain a transparent clear liquid. The mixed solution was prepolymerized in the prepolymerization reactor. The temperature in the prepolymerization reactor was raised to 128° C. and the reaction was continued for 30 min. During the prepolymerization process, a large amount of bubbles were generated due to the formation of ammonia. The ammonia-containing gas was extracted with a vacuum pump to maintain the pressure in the reactor at 0.085 MPa. The extracted ammonia-containing gas was sent to a tail gas scrubber for treatment to obtain ammonia water as a byproduct. Subsequently, the material after the prepolymerization was transported to a polymerization curing reactor and continued to be heated to 250° C. for polymerization curing. The reaction was continued for 140 min to obtain a white solid. (4) After the white solid prepared in step (3) is cooled, it is sent to a crushing system through a conveying system, crushed, and packaged. The prepared ammonium polyphosphate product is tested according to the test method described in HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0031] Comparative Example 2 (1) Wet phosphoric acid desulfurization: The same wet-process phosphoric acid raw material as in Example 3 was used and transported to the desulfurization tank by a pump. The theoretical amount of phosphate slurry added to remove sulfate was calculated according to the test data. The phosphate slurry was added to remove sulfate. The amount of phosphate slurry added was 1.2 times the theoretical amount. The mixture was stirred with a stirring paddle for 60 minutes at a stirring speed of 150 r / min, and then allowed to stand for 180 minutes. After the desulfurization reaction was completed, the material was filtered to obtain clarified desulfurized wet-process phosphoric acid. (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is sent to a concentration kettle ① to be concentrated to a phosphorus pentoxide content of 48.2wt%, and then sent to an extraction reactor, using tributyl phosphate (TBP) and kerosene in a volume ratio of 4:1 as a mixed extractant, and the volume ratio of the extractant to the desulfurized wet-process phosphoric acid is 5:1, and extraction is carried out while stirring with a stirring paddle, the stirring speed is controlled to be 230rpm, the extraction temperature is 50°C, the extraction time is 30min, and the phases are separated after standing for 90min, and the extracted organic phase and the aqueous phase are obtained by phase separation; Taking a water phase, detecting the residual aluminum content in the water phase, and then pumping the water phase into a refining kettle, calculating the theoretical addition amount of fluorosilicic acid and ammonium fluoride according to the detection results, adding ammonium fluoride and fluorosilicic acid at 1.7 times the theoretical addition amount, further removing the metal impurity aluminum, and obtaining pretreated wet-process phosphoric acid; The oil phase is pumped to the alkaline washing kettle, and 5wt% sodium hydroxide solution is added for washing. The volume ratio of the oil phase to the alkaline solution is 13:1. After washing three times, the phases are separated to obtain an alkaline washed organic phase and an alkaline washing solution. Desalted water is added to the alkaline washed organic phase. The volume ratio of the alkaline washed organic phase to the desalted water is 5:1. After washing three times, the phases are separated to obtain a regenerated mixed extractant. (3) The contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid were tested (as shown in Table 3). The pretreated wet-process phosphoric acid that met the requirements was transported to a concentration kettle ② and concentrated to a phosphorus pentoxide content of 68.8 wt %. The phosphoric acid was then pumped into a prepolymerization reactor. Urea was weighed and put into the prepolymerization reactor. The pretreated wet-process phosphoric acid and urea were mixed with a stirring paddle in a molar ratio of 1:1.8 to obtain a transparent clear liquid. The mixed solution was prepolymerized in the prepolymerization reactor. The temperature in the prepolymerization reactor was raised to 128° C. and the reaction was continued for 30 min. During the prepolymerization process, a large amount of bubbles were generated due to the formation of ammonia. The ammonia-containing gas was extracted with a vacuum pump to maintain the pressure in the reactor at 0.085 MPa. The extracted ammonia-containing gas was sent to a tail gas scrubber for treatment to obtain ammonia water as a byproduct. Subsequently, the material after the prepolymerization was transported to a polymerization curing reactor and continued to be heated to 250° C. for polymerization curing. The reaction was continued for 140 min to obtain a white solid. (4) After the white solid prepared in step (3) is cooled, it is sent to a crushing system through a conveying system, crushed, and packaged. The prepared ammonium polyphosphate product is tested according to the test method described in HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0032] Comparative Example 3 (1) Wet phosphoric acid desulfurization: The same wet-process phosphoric acid raw material as in Example 3 was used and transported to the desulfurization tank by a pump. The theoretical amount of phosphate slurry added to remove sulfate was calculated according to the test data. The phosphate slurry was added to remove sulfate. The amount of phosphate slurry added was 1.2 times the theoretical amount. The mixture was stirred with a stirring paddle for 60 minutes at a stirring speed of 150 r / min, and then allowed to stand for 180 minutes. After the desulfurization reaction was completed, the material was filtered to obtain clarified desulfurized wet-process phosphoric acid. (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is sent to a concentration kettle ① to be concentrated to a phosphorus pentoxide content of 48.2wt%, and then sent to an extraction reactor, using tributyl phosphate (TBP) and dodecane in a volume ratio of 4:1 as a mixed extractant, and the volume ratio of the extractant to the desulfurized wet-process phosphoric acid is 5:1, and extraction is carried out while stirring with a stirring paddle, the stirring speed is controlled to be 230rpm, the extraction temperature is 50°C, the extraction time is 30min, and the phases are separated after standing for 45min, and the extracted organic phase and the aqueous phase are obtained by phase separation; Taking a water phase, detecting the residual aluminum content in the water phase, and then pumping the water phase into a refining kettle, calculating the theoretical addition amount of fluorosilicic acid and ammonium fluoride according to the detection results, adding ammonium fluoride and fluorosilicic acid at 1.7 times the theoretical addition amount, further removing the metal impurity aluminum, and obtaining pretreated wet-process phosphoric acid; The oil phase is pumped to the alkaline washing kettle, and 5wt% sodium hydroxide solution is added for washing. The volume ratio of the oil phase to the alkaline solution is 13:1. After washing three times, the phases are separated to obtain an alkaline washed organic phase and an alkaline washing solution. Desalted water is added to the alkaline washed organic phase. The volume ratio of the alkaline washed organic phase to the desalted water is 5:1. After washing three times, the phases are separated to obtain a regenerated mixed extractant. (3) The contents of sulfate and impurities such as iron, magnesium, and aluminum in the pretreated wet-process phosphoric acid were tested (as shown in Table 3), and the pretreated wet-process phosphoric acid that met the requirements was transported to the concentration kettle ② and concentrated to a phosphorus pentoxide content of 68.8 wt %, and then injected into the polymerization and curing reactor. At the same time, urea was weighed and mixed with the pretreated wet-process phosphoric acid and urea in a molar ratio of 1:1.8 using a stirring paddle to obtain a transparent clear liquid. The temperature in the polymerization and curing reactor was raised to 250° C. and the reaction was carried out for 170 min. During the reaction, a large amount of bubbles were generated due to the formation of ammonia gas. The ammonia-containing gas was extracted with a vacuum pump to maintain the pressure in the reactor at 0.085 MPa. The extracted ammonia-containing gas was sent to the tail gas scrubber for treatment to obtain a by-product ammonia water. After the reaction was completed, a white solid was obtained. (4) After the white solid prepared in step (3) is cooled, it is sent to a crushing system through a conveying system, crushed, and packaged. The prepared ammonium polyphosphate product is tested according to the test method described in HG / T 2770-2020 Industrial Ammonium Polyphosphate Standard. The results are shown in Table 4.

[0033] Table 2 Impurity detection results of wet-process phosphoric acid raw materials in various embodiments and comparative examples

[0034] Table 3 Impurity detection results of pretreated wet-process phosphoric acid in various embodiments and comparative examples

[0035] Table 4 Performance indicators of industrial grade II ammonium polyphosphate products of various embodiments and comparative examples

[0036] It can be seen from Table 4 that the removal effect of impurities such as iron, magnesium, aluminum, and sodium in the wet-process phosphoric acid pretreated by the wet-process phosphoric acid demetallization method of the present invention is good, and the treatment efficiency is high; the industrial-grade type II ammonium polyphosphate products prepared by the synthesis method of the present invention all meet the requirements of the HG / T 2770-2020 industrial ammonium polyphosphate standard.

[0037] In the extraction step of Comparative Example 1, only TBP is used as the extractant, and no diluent is added. The other conditions are consistent with those of Example 3. The finally generated ammonium polyphosphate does not meet the HG / T 2770-2020 industrial ammonium polyphosphate standard. The reason is that it is extremely difficult to separate the phases after the extraction reaction in step (2) is completed. The organic phase and the aqueous phase are separated only after standing for 15 hours. The phosphoric acid in the separated aqueous phase contains a large amount of TBP, resulting in that when phosphoric acid and urea react with urea subsequently, phosphoric acid and urea can only condense into short-chain ammonium polyphosphate, and short-chain ammonium polyphosphate cannot condense into long-chain ammonium polyphosphate. Therefore, the ammonium polyphosphate generated in Comparative Example 1 has a low degree of polymerization and cannot meet the HG / T2770-2020 industrial ammonium polyphosphate standard.

[0038] Comparative Example 2 uses kerosene as a diluent, but the resulting ammonium polyphosphate does not meet the HG / T 2770-2020 industrial ammonium polyphosphate standard. Compared with xylene and methane, kerosene has better fluidity and better synergy with the extractant. Therefore, using kerosene as a diluent will increase the impurity ion content of the pretreated wet-process phosphoric acid. The higher impurity ions cause the quality of the resulting ammonium polyphosphate to fail to meet the HG / T 2770-2020 industrial ammonium polyphosphate standard.

[0039] The method of comparative example 3 does not perform prepolymerization, and the other conditions are consistent with those of example 3, and the ammonium polyphosphate finally generated does not meet the HG / T 2770-2020 industrial ammonium polyphosphate standard. The present invention uses urea as both a nitrogen source and a condensing agent in the reaction process. The condensation effect can only be exerted at 100-130°C to cause the ammonium polyphosphate to undergo a chain extension reaction. When the temperature is directly raised to 250°C, the urea has no time to react and is almost completely decomposed or condensed, resulting in very little urea in the material, which inhibits the chain extension reaction of the ammonium polyphosphate, resulting in most of the short-chain ammonium polyphosphate in comparative example 3, which cannot meet the HG / T 2770-2020 industrial ammonium polyphosphate standard.

[0040] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A wet phosphoric acid demetallization method, characterized in that: The steps include: A mixed extractant is used to extract and remove metal impurities in wet-process phosphoric acid, wherein the mixed extractant includes an extractant and a diluent in a volume ratio of 1 to 5:1, wherein the extractant is selected from one or more of di(2-ethylhexyl) phosphate, tributyl phosphate, and n-butanol, and the diluent is selected from one or two of dodecane and xylene; After the extraction is completed, the phases are allowed to stand and separated, and the aqueous phase is taken and ammonium fluoride and fluorosilicic acid are used to remove aluminum impurities; Take the oil phase and add alkali solution, the volume ratio of the oil phase to the alkali solution is 10-15:1, separate the phases to obtain the alkali-washed organic phase and the alkali-washing liquid, then add desalted water to the alkali-washed organic phase, separate the phases, and obtain the regenerated mixed extractant.

2. The wet phosphoric acid demetallization method according to claim 1, characterized in that: The volume ratio of the mixed extractant to the wet-process phosphoric acid is 3-7:

1.

3. The wet phosphoric acid demetallization method according to claim 1, characterized in that: The extraction temperature is 40~60℃, the extraction time is 20~60min, and stirring is performed during extraction.

4. The wet phosphoric acid demetallization method according to claim 1, characterized in that: Ammonium fluoride and fluorosilicic acid are added to the aqueous phase to remove aluminum impurities. The amount of ammonium fluoride and fluorosilicic acid added is 1 to 2 times the theoretical amount.

5. The wet phosphoric acid demetallization method according to claim 1, characterized in that: The volume ratio of the alkaline washing organic phase to the desalted water is 1~5:

1.

6. A method for synthesizing an industrial-grade type II ammonium polyphosphate product, characterized in that: The wet-process phosphoric acid raw material is pretreated by the wet-process phosphoric acid demetallization method as claimed in claim 1.

7. The synthesis method according to claim 6, characterized in that The steps include: (1) Wet phosphoric acid desulfurization: Adding a desulfurizing agent to the wet-process phosphoric acid raw material, wherein the desulfurizing agent is selected from one or both of phosphate slurry and calcium hydrogen phosphate, stirring and then standing to obtain clarified desulfurized wet-process phosphoric acid; (2) Wet phosphoric acid demetallization: The desulfurized wet-process phosphoric acid in step (1) is mixed with a mixed extractant, wherein the volume ratio of the mixed extractant to the desulfurized wet-process phosphoric acid is 3-7:1, and the mixture is extracted while being stirred. The extraction temperature is controlled to be 40-60°C, the extraction time is 20-60 min, the stirring speed is 200-300 rpm, and the mixture is allowed to stand for phase separation after extraction; Taking the aqueous phase, adding fluorosilicic acid and ammonium fluoride, wherein the amount of ammonium fluoride and fluorosilicic acid added is 1 to 2 times the theoretical amount, to obtain pretreated wet-process phosphoric acid; The oil phase is taken and washed with alkali solution, the volume ratio of the oil phase to the alkali solution is 10-15:1, after washing 1-3 times, the phases are separated to obtain an alkali-washed organic phase and an alkali-washing solution, desalted water is added to the alkali-washed organic phase, the volume ratio of the alkali-washed organic phase to the desalted water is 1-5:1, after washing 1-3 times, the phases are separated to obtain a regenerated mixed extractant; (3) Pretreated wet-process phosphoric acid and urea are mixed in a reactor at a molar ratio of 1:1.8-3.2, and prepolymerized at 100-130°C for 10-30 min. The gas generated during the prepolymerization is extracted with a vacuum pump, and the pressure in the reactor is maintained at ≤0.09 MPa. The temperature is then raised to 200-250°C, and the reaction is continued for 60-180 min. The obtained white solid is ammonium polyphosphate.

8. The synthesis method according to claim 7, characterized in that The method further comprises step (4): after the white solid prepared in step (3) is cooled, the white solid is crushed and packaged to obtain a type II product that meets the HG / T 2770-2020 industrial ammonium polyphosphate standard.

9. The synthesis method according to claim 7, characterized in that The phosphorus pentoxide content in the wet-process phosphoric acid raw material of step (1) is 20wt%~25wt%; Step (2) before demetallization, the desulfurized wet-process phosphoric acid is concentrated to a phosphorus pentoxide content of 36.2 wt% to 50.7 wt%; In step (3), before mixing with urea, the pretreated wet-process phosphoric acid is concentrated to a phosphorus pentoxide content of ≥ 61.5 wt%.

10. The synthesis method according to claim 7, characterized in that The gas generated during the prepolymerization process in step (3) is sent to a tail gas scrubber for treatment to obtain ammonia water as a by-product.

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