Low-arsenic ammonium polyphosphate and preparation method thereof

Abstract

The invention provides low-arsenic ammonium polyphosphate and a preparation method thereof, and the method comprises the following steps: preparing an alcohol-water mixed solution, and adding ammonium polyphosphate to obtain an ammonium polyphosphate suspension with the mass volume concentration of 10-70%; and adding hydrogen peroxide into the ammonium polyphosphate suspension, reacting at the temperature of not more than 80 DEG C, separating solids after the reaction, and drying to obtain the low-arsenic ammonium polyphosphate. According to the method, ammonium polyphosphate is oxidized, dissolved and separated, the content of arsenic in ammonium polyphosphate is reduced to 10 ppm, the process is simple, product loss is small, and the requirements of application fields such as textiles with environment-friendly and low-arsenic requirements can be met.

Description

Technical Field

[0001] The invention relates to the field of polyphosphate and arsenic element separation, and to the application field of flame-retardant textiles, and in particular to a low-arsenic ammonium polyphosphate and a preparation method thereof. Background Art

[0002] As we all know, arsenic is a toxic heavy metal, and its accumulation in the environment can cause harm to human health and the ecosystem. Phosphate ore resources are generally accompanied by arsenic, and there is a certain amount of arsenic in the final phosphorus chemical products. Therefore, the arsenic content needs to be removed and controlled during the production of phosphorus chemicals. Since arsenic is a member of the same family as phosphorus and has similar properties, it is difficult to obtain low-arsenic phosphorus. Currently, arsenic removal is a key link in the refining process of high-purity yellow phosphorus. In order to meet environmental protection requirements and application needs, the arsenic in yellow phosphorus is purified. Chemical arsenic removal and oxidative dissolution separation are commonly used in industry to obtain low-arsenic yellow phosphorus. The chemical arsenic removal method is based on the reaction of As and S 2- The characteristic of forming insoluble compounds is to use sulfide as a dearsenicizing agent to precipitate and separate the arsenic in phosphoric acid in the form of arsenic sulfide. The oxidation dissolution separation method is to add an oxidant to liquid yellow phosphorus to oxidize the arsenic in the yellow phosphorus, and then hydrate to form water-soluble arsenous acid (H3AsO3) or arsenic acid (H3AsO4) into the water phase, thereby separating arsenic from phosphorus and achieving the purpose of dearsenicization.

[0003] Chinese patent application CN117865097A (published on April 12, 2024) discloses a method for producing a high-polymerization ammonium polyphosphate flame retardant from wet-process phosphoric acid, which uses a purifier represented by barium carbonate, barium hydroxide or phosphorus sulfide to mix and centrifuge with wet-process phosphoric acid to achieve the purpose of reducing the arsenic content before phosphoric acid polymerization. Japanese patent application JPS5493692A (published on July 24, 1979) discloses a method for purifying yellow phosphorus using nitric acid and sulfuric acid as oxidants, but the oxidant introduced in this method brings undesirable impurities.

[0004] Ammonium polyphosphate is an inorganic polymer containing phosphorus and nitrogen, which has the characteristics of halogen-free flame retardancy, low toxicity and biodegradability. Ammonium polyphosphate has 5 different crystalline forms. Industrial production is mainly based on crystalline type I and crystalline type III. Among them, crystalline type II ammonium polyphosphate has a more stable crystalline form and degree of polymerization, and is widely used as a flame retardant. Crystalline type II ammonium polyphosphate uses phosphorus pentoxide and diammonium hydrogen phosphate as the main raw materials. Since phosphorus pentoxide is directly produced by burning yellow phosphorus, the arsenic element in crystalline type II ammonium polyphosphate mainly comes from its raw material yellow phosphorus. Therefore, using low-arsenic yellow phosphorus as a raw material to produce low-arsenic ammonium polyphosphate is a conventional option in this field. However, low-arsenic yellow phosphorus has high requirements for the quality of phosphate ore. Although my country has abundant phosphate ore resources, the quality of phosphate ore is poor. The output of low-arsenic yellow phosphorus on the market is small and the price is much higher than that of ordinary yellow phosphorus, which limits the output and application of low-arsenic ammonium polyphosphate. At present, there is no existing technology for removing arsenic from ammonium polyphosphate made from ordinary yellow phosphorus as a raw material.

[0005] On the other hand, with the development of modern materials, materials represented by crystalline type II ammonium polyphosphate are increasingly being used in the textile field due to their flame retardant properties and stability. Using ammonium polyphosphate or modified ammonium polyphosphate as a coating for textile fabrics to improve the flame retardant properties of the product puts higher requirements on the arsenic content of ammonium polyphosphate. EU REACH regulations, International Textile Ecology Research and Testing Association The U.S. Consumer Product Safety Improvement Act (CPSIA), GB18401-2010 "National Textile Product Basic Safety Technical Specifications" and other laws and regulations have established corresponding safety standards to limit the arsenic content in textiles to protect the health and safety of consumers. For products that directly contact the skin (such as underwear, bed sheets, etc.), the arsenic content should not exceed 0.5 mg / kg; for products that do not directly contact the skin, the arsenic content should not exceed 1.0 mg / kg. The arsenic content of phosphorus-containing flame retardants used in textiles is usually required to be controlled below the detection limit (less than 10 mg / kg). Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a method for preparing low-arsenic ammonium polyphosphate based on a low-temperature oxidation water-soluble process route, which can efficiently remove arsenic impurities while avoiding destroying the stability of crystalline type II ammonium polyphosphate and introducing foreign impurities; another purpose of the present invention is to provide ammonium polyphosphate prepared by the aforementioned method, which has an arsenic content of no more than 10 mg / kg.

[0007] Technical solution: In order to achieve the above-mentioned purpose, the present invention provides a method for preparing low-arsenic ammonium polyphosphate, comprising: preparing an alcohol-water mixed solution with alcohol and water, adding ammonium polyphosphate to the alcohol-water mixed solution to obtain an ammonium polyphosphate suspension with a mass volume concentration of 10-70%; adding hydrogen peroxide to the ammonium polyphosphate suspension, maintaining the reaction at a temperature lower than the boiling point of the alcohol-water mixed solution, separating the solid after the reaction, eluting it with an alcohol solution, and heating and drying to obtain the low-arsenic ammonium polyphosphate.

[0008] The present invention utilizes hydrogen peroxide as an oxidant to oxidize the arsenic in the crystalline II-type ammonium polyphosphate into water-soluble arsenic acid or arsenous acid, and then removes it in combination with a physical method, thereby achieving the purpose of arsenic removal. The introduction of hydrogen peroxide does not bring exogenous impurities, and can be completely removed in subsequent processes such as solid separation and drying. Nevertheless, the use of the oxidizing properties of hydrogen peroxide to remove arsenic in ammonium polyphosphate requires overcoming additional problems: on the one hand, hydrogen peroxide, as a strong oxidant, can decompose to produce oxygen, and the temperature of the reaction process must be controlled to ensure that a stable oxidation reaction is maintained; on the other hand, although the crystalline II-type ammonium polyphosphate has low water solubility, as the temperature increases in water, the water solubility will increase sharply, accompanied by an increase in the degree of hydrolysis, which leads to excessive loss of ammonium polyphosphate in the arsenic removal process. In addition, the inventors also found that the use of this method to remove arsenic from ammonium polyphosphate can also significantly improve the whiteness of the product, which is more conducive to the application of the low-arsenic ammonium polyphosphate prepared by the method in the textile field.

[0009] As a further optimization of the present invention, the ammonium polyphosphate is crystalline type II ammonium polyphosphate, with a degree of polymerization of not less than 1000 and a water solubility of not more than 0.5g / 100g water. As a further optimization of the present invention, the ammonium polyphosphate also has the following properties: 95% glycolic acid value ≤ 1.0mgKOH / g, pH = 5.5-7.5, whiteness 85-90.

[0010] Further, the alcohol in the alcohol-water mixed solution is methanol and / or ethanol, and the volume concentration of the alcohol in the alcohol-water mixed solution is 20-85%. The inventors found that the alcohol component of the appropriate ratio is conducive to improving product quality and yield. As a preferred embodiment of the present invention, the ratio of alcohol and water in the alcohol-water mixed solution needs to be controlled within a suitable range. As a preferred embodiment of the present invention, the alcohol is selected from ethanol, and the volume concentration of ethanol in the preferred alcohol-water mixed solution is 60-85%. Too high an alcohol component ratio will lead to a decrease in arsenic removal efficiency, while too low an alcohol component ratio will increase the water solubility of ammonium polyphosphate and hydrolysis during the reaction, thereby leading to a decrease in yield and an increase in indicators such as acid value and water solubility, and causing the obtained low-arsenic ammonium polyphosphate to deteriorate in performance. As the best embodiment of the present invention, the volume concentration of ethanol is 70-80%.

[0011] Furthermore, the hydrogen peroxide described in the present invention is a hydrogen peroxide aqueous solution with a volume concentration of 1-28%. As a further optimization of the present invention, the hydrogen peroxide described in the present invention is a hydrogen peroxide aqueous solution with a volume concentration of 5-20%.

[0012] Furthermore, the mass ratio of the ammonium polyphosphate to the hydrogen peroxide is 100:(0.1-3.0). As a further optimization of the present invention, the mass ratio of the ammonium polyphosphate to the hydrogen peroxide is 100:(0.5-2.0).

[0013] Further, the reaction is carried out at a temperature lower than the boiling point of the alcohol-water mixed solution, generally, maintained at 40-75° C., and the preferred reaction time is 1-4 hours. As a preferred embodiment of the present invention, the reaction is carried out on an ammonium polyphosphate suspension prepared based on a 70-80% ethanol-water solution at a temperature not exceeding 75° C. for 2 hours.

[0014] Furthermore, the solid separation includes centrifugation or filter pressing; the moisture content of the material after the solid separation is controlled below 10wt%.

[0015] Furthermore, the alcohol solution used for elution is an ethanol solution with a volume concentration of 70-90%, preferably an ethanol solution with a volume concentration of 85%.

[0016] Furthermore, the heating drying is flash drying at 120-160°C, preferably flash drying at a temperature not exceeding 150°C.

[0017] The present invention provides low-arsenic ammonium polyphosphate prepared by the above method, which can be applied to flame-retardant textiles, flame-retardant decorative materials (such as wallpaper, wall cloth) and other products with low arsenic requirements. The low-arsenic ammonium polyphosphate has at least the following properties:

[0018] Arsenic content ≤10mg / kg;

[0019] Water solubility ≤ 0.5g / 100g water;

[0020] 95% glycolic acid value ≤1.0mg KOH / g;

[0021] pH = 5.5-7.5;

[0022] Whiteness ≥92.

[0023] The present invention provides a new ammonium polyphosphate arsenic removal process, which avoids the problems of large yellow phosphorus loss, high cost, high equipment requirements, etc. compared with the traditional yellow phosphorus as the starting point for arsenic removal. The present invention also solves the problems of reduced yield, easy hydrolysis, high acid value, etc. caused by ammonium polyphosphate in the low-temperature oxidation water-soluble arsenic removal process, and further improves the whiteness of the product. DETAILED DESCRIPTION

[0024] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments. The measurement method of the test data in the following embodiments is as follows:

[0025] pH value test method: Take 10wt% low-arsenic ammonium polyphosphate suspension, stir for 30min at 25±1℃, and test with a pH meter;

[0026] Water solubility test: Take 10wt% low-arsenic ammonium polyphosphate suspension, stir for 30min at 25±1℃, filter, obtain the filtrate, dry it, and express it as the weight of the product dissolved in 100g water;

[0027] 95% ethanol acid value test: Take low-arsenic ammonium polyphosphate and fully leaching it with 95% ethanol solution. The separated filtrate is titrated with potassium hydroxide-ethanol standard titration solution, and the value is expressed as the number of milligrams of potassium hydroxide required to neutralize 1g of the product;

[0028] Arsenic content test: Take 0.2g of low-arsenic ammonium polyphosphate and completely digest it with nitric acid and hydrogen peroxide, and then test it according to the GB / T35828-2018 inductively coupled plasma mass spectrometry (ICP-MS) method.

[0029] Example 1

[0030] In a 500L reactor, add 150kg of ammonium polyphosphate (crystalline type II, degree of polymerization >1000, water solubility ≤0.34g / 100g water, arsenic content 21ppm, 95% ethanol acid value ≤0.45mg KOH / g, pH = 6.7, whiteness 90), 150kg of 70% volume concentration ethanol aqueous solution, stir for 2 hours at room temperature; after adding 7.5kg of 20% concentration hydrogen peroxide, heat to 75°C, react for 2h, cool, centrifuge, and rinse with 85% anhydrous ethanol solution. The final material moisture content is 5wt%.

[0031] The wet material is flash dried at a drying temperature of 150°C to obtain ammonium polyphosphate with low arsenic content.

[0032] Example 2

[0033] In a 500L reactor, 90kg of ammonium polyphosphate (same as in Example 1) and 210kg of 80% volume concentration ethanol aqueous solution were added, and stirred at room temperature for 1h; after adding 9.0kg of 5% concentration hydrogen peroxide, the temperature was raised to 50°C, reacted for 4 hours, cooled, centrifuged, and rinsed with 85% anhydrous ethanol solution. The final material moisture content was 4wt%.

[0034] The wet material is flash dried at a drying temperature of 150°C to obtain ammonium polyphosphate with low arsenic content.

[0035] Example 3

[0036] In a 500L reactor, 120kg of ammonium polyphosphate (same as in Example 1) and 180kg of 30% volume concentration ethanol aqueous solution were added, and stirred at room temperature for 1h; after adding 12.0kg of 20% concentration hydrogen peroxide, the temperature was raised to 50°C, reacted for 1 hour, cooled, centrifuged, and rinsed with 85% anhydrous ethanol solution. The final material moisture content was 9wt%.

[0037] The wet material is flash dried at a drying temperature of 150°C to obtain ammonium polyphosphate with low arsenic content.

[0038] Example 4

[0039] In a 500L reactor, 135kg of ammonium polyphosphate (same as in Example 1) and 165kg of 60% volume concentration ethanol aqueous solution were added, and stirred at room temperature for 1h; after adding 20.3kg of 10% concentration hydrogen peroxide, the temperature was raised to 60°C, reacted for 2 hours, cooled, centrifuged, and rinsed with 85% anhydrous ethanol solution. The final material moisture content was 6wt%.

[0040] The wet material is flash dried at a drying temperature of 150°C to obtain ammonium polyphosphate with low arsenic content.

[0041] Example 5

[0042] In a 500L reactor, 135kg of ammonium polyphosphate (same as in Example 1) and 165kg of 50% volume concentration ethanol aqueous solution were added, and stirred at room temperature for 1h; after adding 9.0kg of 15% concentration hydrogen peroxide, the temperature was raised to 60°C, reacted for 2 hours, cooled, centrifuged, and rinsed with 85% anhydrous ethanol solution. The final material moisture content was 7wt%.

[0043] The wet material is flash dried at a drying temperature of 150°C to obtain ammonium polyphosphate with low arsenic content.

[0044] Comparative Example 1

[0045] Crystalline type II ammonium polyphosphate, degree of polymerization ≥1000, Hangzhou Jieersi Flame Retardant Chemical Co., Ltd.

[0046] Comparative Example 2

[0047] In a 500L reactor, add 120kg of ammonium polyphosphate (same as Example 1) and 180kg of 15% volume concentration ethanol aqueous solution, and stir at room temperature for 1h; slowly add 7.5kg of 20% concentration hydrogen peroxide, heat to 40°C, react for 2 hours, cool, centrifuge, and rinse with 85% anhydrous ethanol solution. The final material moisture content is 10wt%.

[0048] The material was flash dried at a drying temperature of 150° C. to obtain Comparative Example 2.

[0049] Comparative Example 3

[0050] In a 500L reactor, add 120kg of ammonium polyphosphate (same as in Example 1) and 180kg of 90% volume concentration ethanol aqueous solution, and stir at room temperature for 1h; slowly add 6.0kg of 20% concentration hydrogen peroxide, heat to 60°C, react for 2 hours, cool, centrifuge, and rinse with 85% anhydrous ethanol solution. The final material moisture content is 2wt%.

[0051] The material was flash dried at a drying temperature of 150° C. to obtain Comparative Example 3.

[0052] Comparative Example 4

[0053] In a 500L reactor, 120kg of ammonium polyphosphate (same as in Example 1) and 180kg of 60% volume concentration ethanol aqueous solution were added and stirred at room temperature for 2h; then the temperature was raised to 50°C, reacted for 4h, cooled, centrifuged, and rinsed with 85% anhydrous ethanol solution. The final material moisture content was 6wt%.

[0054] The material was flash dried at a drying temperature of 150° C. to obtain Comparative Example 4.

[0055] Table 1 Experimental data of Examples 1-5 and Comparative Examples 1-4

[0056]

[0057]

[0058] Note: According to GB / T 35828-2018, the arsenic content in the table is tested by inductively coupled plasma mass spectrometry (ICP-MS) with a detection limit of 10 mg / kg. ND means not detected.

[0059] As can be seen from Table 1, by comparing Examples 1-5 and Comparative Example 4, it is found that the addition of hydrogen peroxide is conducive to the effective removal of arsenic in ammonium polyphosphate, and hydrogen peroxide is also conducive to the increase of the whiteness of the final product. From the comparison of Examples 1-5, it is also found that with the increase in the amount of hydrogen peroxide, the whiteness of the final product is positively improved, but it is not good for the acid value, which is easy to cause the acid value to increase. Another important influencing factor is the proportion of alcohol in the alcohol-water mixed solution. The increase in its proportion can reduce the acid value and water solubility of the final product, and can also have a high yield and a small loss of ammonium polyphosphate. However, it is found from Comparative Example 3 that too high an alcohol content is not conducive to the removal of arsenic. The reason for the analysis is that too high an alcohol content affects the precipitation of water-soluble arsenic acid, which ultimately affects the removal efficiency of arsenic.

[0060] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing low-arsenic ammonium polyphosphate, characterized in that: The method comprises: preparing alcohol and water into an alcohol-water mixed solution, adding ammonium polyphosphate to the alcohol-water mixed solution to obtain an ammonium polyphosphate suspension with a mass volume concentration of 10-70%; adding hydrogen peroxide to the ammonium polyphosphate suspension, maintaining a temperature lower than the boiling point of the alcohol-water mixed solution to carry out a reaction, separating a solid after the reaction, eluting it with an alcohol solution, and heating and drying to obtain low-arsenic ammonium polyphosphate.

2. The method for preparing low-arsenic ammonium polyphosphate according to claim 1, characterized in that: The ammonium polyphosphate is crystalline type II ammonium polyphosphate, with a degree of polymerization of not less than 1000 and a water solubility of not more than 0.5 g / 100 g water.

3. A method for preparing low-arsenic ammonium polyphosphate according to claim 1 or 2, characterized in that: The alcohol in the alcohol-water mixed solution is methanol and / or ethanol, and the volume concentration of the alcohol in the alcohol-water mixed solution is 20-85%.

4. The method for preparing low-arsenic ammonium polyphosphate according to claim 3, characterized in that: The hydrogen peroxide is a hydrogen peroxide aqueous solution with a volume concentration of 1-28%.

5. The method for preparing low-arsenic ammonium polyphosphate according to claim 4, characterized in that: The mass ratio of the ammonium polyphosphate to the hydrogen peroxide is 100:(0.1-3.0).

6. A method for preparing low-arsenic ammonium polyphosphate according to any one of claims 1-2, 4-5, characterized in that: The solid separation includes centrifugation or filter pressing, and the moisture content of the material after the solid separation is controlled below 10wt%.

7. A method for preparing low-arsenic ammonium polyphosphate according to any one of claims 1-2, 4-5, characterized in that: The heating drying is flash drying at 120-160°C.

8. Low-arsenic ammonium polyphosphate prepared by the method according to any one of claims 1 to 7.

9. The low-arsenic ammonium polyphosphate according to claim 8, characterized in that The low arsenic ammonium polyphosphate also has the following properties: Arsenic content ≤10mg / kg; Water solubility ≤ 0.5g / 100g water; 95% glycolic acid value ≤1.0mg KOH / g; pH = 5.5-7.5; Whiteness ≥92.

10. Use of the low-arsenic ammonium polyphosphate as claimed in claim 8 in flame-retardant textiles or flame-retardant decorative materials.

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