Sodium hexametaphosphate with high total phosphate content and preparation method

Abstract

The invention provides sodium hexametaphosphate with high total phosphate content and a preparation method thereof. The method comprises the following steps: at the initial stage of reaction, firstly adding a certain amount of liquid caustic soda into a neutralization pot, heating, then adding a reaction accelerator sodium ammonium hydrogen phosphate tetrahydrate and sodium hexametaphosphate seed crystal, stirring for a period of time, simultaneously adding phosphoric acid and a sodium carbonate suspension, and adding a certain amount of a catalyst phosphotungstic acid to prepare neutralized slurry which is colorless sticky liquid with the specific gravity of 1.6-1.8 and the pH value of 3.8-4.0; filtering to remove impurities, and quenching through a double-roller quenching machine after agglomeration. The sodium hexametaphosphate with high total phosphate content is prepared through the steps of a primary crusher, an elevator, a winnowing crusher, a rotary vibration sieve and the like. According to the method, raw materials are pretreated, a reaction accelerator is introduced, the pH value of neutralized slurry is optimized, a novel catalyst is introduced, the parameters such as the agglomeration temperature, the proportion of raw materials and clinker and shock cooling are optimized, and particularly, the reaction accelerator and the novel catalyst are introduced, and the proportion of the raw materials and the clinker is optimized. The method is simple in technological process, high in equipment adaptability and easy to realize industrial production.

Description

Technical Field

[0001] The invention relates to a method for preparing sodium hexametaphosphate with a high total phosphate content, and in particular to a method for producing high-end food-grade sodium hexametaphosphate. Background Art

[0002] Sodium hexametaphosphate has a wide range of uses, and food-grade sodium hexametaphosphate is mainly used in the field of food additives. The national standard GB1886.4-2020 sodium hexametaphosphate requires a total phosphate content of ≥67%, and the industry usually reaches a maximum of 68%. However, some high-end customers require the total phosphate content in the product to reach 69-70%. The main reason why the quality requirements of high-end customers cannot be met at present is that the production process parameters of sodium hexametaphosphate have not been adjusted to the most ideal level.

[0003] The present invention directly produces on the existing food-grade sodium hexametaphosphate production line, mainly optimizes the production process parameters such as reaction accelerator, crystal seed, catalyst, neutralization slurry pH value, melting temperature, raw and clinker ratio, residence time, etc., to produce sodium hexametaphosphate with high total phosphate content. The price of sodium hexametaphosphate with high total phosphate content is about 3% higher than that of ordinary sodium hexametaphosphate, with good economic benefits and good market prospects. Summary of the invention

[0004] The purpose of the present invention is to provide a production process for preparing sodium hexametaphosphate with a high total phosphate content by optimizing process parameters, such as introducing a reaction accelerator and a new catalyst, shortening the reaction time, and increasing the total phosphate content in the product. The production process is characterized by easy availability of raw materials, low cost, strong equipment adaptability, no need for additional equipment, and can achieve industrial production.

[0005] The specific process is as follows: A method for preparing sodium hexametaphosphate with a high total phosphate content comprises the following steps: Pretreatment stage: At the beginning of the reaction, add a certain amount of alkali solution into the neutralization pot, raise the temperature to 30-40°C, add the reaction accelerator sodium phosphate salt and sodium hexametaphosphate seeds, and stir evenly.

[0006] Neutralization reaction stage: add phosphoric acid and soda ash suspension to the neutralization pot at the same time for neutralization reaction, add a certain amount of new catalyst phosphotungstic acid, and the qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered and removed for use after secondary filtration.

[0007] Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw materials to clinker is controlled, the temperature in the high-temperature melting tank is controlled at 650±20℃, and the raw materials are preliminarily dehydrated using the clinker to obtain the semi-finished product of sodium hexametaphosphate.

[0008] Quenching and post-processing stage: The semi-finished sodium hexametaphosphate in the molten state is physically cooled by a double-roll quenching machine, and then post-processed by a primary crusher, an elevator, an air separation crusher, a rotary vibrating screen, etc. to obtain the product expected by this patent.

[0009] In some embodiments, the neutralization reaction is carried out in a neutralization pot or a neutralization reactor. Specifically, an alkaline solution is first added to the neutralization pot, and sodium phosphate salt and sodium hexametaphosphate seeds are added under heating conditions. The heating condition is 30-40°C, which helps to promote uniform mixing of the sodium phosphate salt and sodium hexametaphosphate seeds in the alkaline solution.

[0010] The alkaline solution is selected from liquid alkali or dilute soda ash solution; wherein the concentration of the liquid alkali is 32-48%, and the concentration of the soda ash solution is 30-35%.

[0011] The sodium phosphate salt is selected from sodium ammonium hydrogen phosphate tetrahydrate; the mass fraction of the sodium phosphate salt is 0.75-1.5%.

[0012] The sodium hexametaphosphate seed crystal is 0.1-1%.

[0013] The dosage of the catalyst phosphotungstic acid is 0.8-1.5‰.

[0014] When the temperature of the material in the neutralization pot is raised, the alkali source and the phosphorus source are added simultaneously to cause a neutralization reaction.

[0015] The mass fraction of phosphoric acid in step (2) is 75% or more, more preferably 85% or more, and more preferably 95% or more; The mass fraction of the soda ash suspension is greater than 30%, more preferably greater than 35%, and further preferably greater than 40%.

[0016] In some embodiments, the neutralization reaction process also includes a stirring process. During the stirring process, the speed is first slow and then fast, wherein the stirring speed is 200-300 r / min in the initial stage, the reaction is 0.5h, the stirring speed is 450-500 r / min in the middle stage of the reaction, the reaction is 0.5-1h, and the stirring speed is about 350-450 r / min in the late stage of the reaction, and the reaction is 0.2-0.5h.

[0017] In some embodiments, the catalyst is added at the early stage of the reaction, that is, the new catalyst is added at the same time as the phosphoric acid and soda ash solutions are added and stirred evenly.

[0018] In order to improve the reaction process, reduce local reaction blind spots, increase the total phosphate content of the product, make the sodium hexametaphosphate product have better uniformity and stability, and maximize the catalytic effect on the neutralization material, this patent will heat the alkali solution at the beginning of the reaction, add a reaction accelerator and seed crystals, add soda ash suspension and phosphoric acid into the neutralization pot at the same time, and immediately add a new catalyst.

[0019] Adjust the pH value of the white viscous neutralization slurry obtained in step (1) to 3.8-4.0, and adjust the specific gravity of the neutralization liquid to 1.7 g / cm 3 .

[0020] In the actual implementation of the present invention, because the neutralization degree K value of the sodium hexametaphosphate neutralization slurry varies greatly, even after the reaction is completed, the k value of the neutralization slurry detected twice before and after also has a difference of 0.2-0.5, which is easy to mislead production, prolong the reaction time, and cause uneven and unstable products, making it difficult to achieve refined production, and increasing production costs. What is unexpected in this patent is that when the monitoring method of the neutralization slurry is replaced, especially when the pH of the neutralization slurry is 3.8-4.0, the error of the repeated measurement before and after is not more than 0.1, which is qualified, and a stable sodium hexametaphosphate product can be obtained, and all indicators are qualified.

[0021] In some embodiments, the melt polymerization reaction temperature is 670°C ± 20, and the residence time is extended by 10-15min. The ratio of raw material to clinker is controlled at 1 / 2-2 / 3 (ratio is raw material: clinker). Those skilled in the art know that the reaction process of the present application is a continuous feeding and discharging process. In the present application, clinker refers to adding the qualified neutralized slurry in the present application to the polymerization reactor, and then heating it to 670°C ± 20 for melt polymerization. At this time, the material in the reactor is clinker, and then adding the qualified neutralized slurry in the present application. At this time, the slurry is raw material. After the raw material is added, the ratio of raw material to clinker is controlled to 1 / 2-2 / 3, and the reaction is carried out for 10-15min for discharging.

[0022] Here, the temperature difference between clinker and raw material is used to achieve the initial dehydration of raw material with clinker, shorten the reaction time, improve the reaction process and increase the product output. In actual production, the clinker is generally controlled at about 50%. If it is all clinker, safety accidents are prone to occur. If it is all raw material, it is easy to affect product quality and output, and sodium hexametaphosphate with a high total phosphate content will also be prepared.

[0023] In some embodiments, the smelting temperature is controlled to be stable at 660°C ± 10, which can reduce the production of sodium trimetaphosphate, sodium tetrametaphosphate and other inactive ingredients. At the same time, considering the temperature bearing capacity of the smelting pool, and reducing the corrosion of the equipment in the smelting pool under high temperature conditions, and the entry of harmful impurities into the product, the maximum smelting temperature is preferably controlled below 670°C. By controlling the ratio of raw and clinker, the initial dehydration of the neutralized slurry is achieved, and the reaction progress is improved.

[0024] Those skilled in the art know that the raw materials for obtaining sodium hexametaphosphate also include sodium tripolyphosphate and / or disodium hydrogen phosphate, and the sodium tripolyphosphate and / or disodium hydrogen phosphate are added to the neutralization reaction stage. In actual production, unqualified sodium tripolyphosphate and / or disodium hydrogen phosphate are often used as the reaction raw materials for hexametaphosphate to reasonably control the production costs of enterprises.

[0025] A technical solution of the present invention is to provide a sodium hexametaphosphate with a high total phosphate content, which is prepared by the described method, wherein the total phosphate content of the sodium hexametaphosphate is above 69.0%, more preferably above 69.0%, more preferably above 70.0%, and more preferably above 71.0%. DETAILED DESCRIPTION

[0026] Example 1 When preparing sodium hexametaphosphate with a high total phosphate content, no catalyst is added and other factors remain unchanged.

[0027] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 0.75% sodium ammonium phosphate tetrahydrate as a reaction promoter and 1% sodium hexametaphosphate seed (calculated based on the yield of sodium hexametaphosphate calculated based on the amount of raw material phosphoric acid used), and stir evenly.

[0028] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, without adding the new catalyst phosphotungstic acid, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered for secondary use after impurities are removed.

[0029] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:2, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0030] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 67.4%. (The total phosphorus phosphate content of ≥67.0% is qualified in the national standard GB1886.4-2020).

[0031] Example 2 When preparing sodium hexametaphosphate with a high total phosphate content, 0.8‰ catalyst was added, and the other contents remained unchanged compared with Example 1.

[0032] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 0.75% sodium ammonium phosphate tetrahydrate as a reaction accelerator and 1% sodium hexametaphosphate seed, and stir evenly.

[0033] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, add 0.8‰ catalyst phosphotungstic acid, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered and removed for use.

[0034] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:2, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0035] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roller quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 70.2%. (The total phosphorus phosphate content in the national standard GB1886.4-2020 is ≥67.0% as qualified).

[0036] Example 3 When preparing sodium hexametaphosphate with a high total phosphate content, 1.5‰ catalyst was added, and the other contents remained unchanged compared with Example 1.

[0037] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 0.75% sodium ammonium phosphate tetrahydrate as a reaction accelerator and 1% sodium hexametaphosphate seed, and stir evenly.

[0038] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, add 1.5‰ catalyst phosphotungstic acid, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered for secondary use after impurities are removed.

[0039] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:2, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0040] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 70.5%. (The total phosphorus phosphate content of ≥67.0% in the national standard GB1886.4-2020 is qualified).

[0041] Example 4 When preparing sodium hexametaphosphate with a high total phosphate content, 1.8‰ catalyst was added, and the other contents remained unchanged compared with Example 1.

[0042] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 0.75% sodium ammonium phosphate tetrahydrate to promote the reaction and 1% sodium hexametaphosphate seed, and stir evenly.

[0043] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, add 1.8‰ catalyst phosphotungstic acid, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered for secondary use after impurities are removed.

[0044] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:2, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0045] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 69.1%. (The total phosphorus phosphate content of ≥67.0% is qualified in the national standard GB1886.4-2020).

[0046] Example 5 When preparing sodium hexametaphosphate with a high total phosphate content, 0.5‰ catalyst is added, and the other contents remain unchanged compared with Example 1.

[0047] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 0.75% sodium ammonium phosphate tetrahydrate as a reaction accelerator and 1% sodium hexametaphosphate seed, and stir evenly.

[0048] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, add 0.7‰ catalyst phosphotungstic acid, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered for secondary use after impurities are removed.

[0049] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:3, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0050] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 68.3%. (The total phosphorus phosphate content of ≥67.0% in the national standard GB1886.4-2020 is qualified).

[0051] Example 6 When preparing sodium hexametaphosphate with a high total phosphate content, 0.8‰ catalyst and 1.0% sodium ammonium phosphate tetrahydrate are added, while other factors remain unchanged.

[0052] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 1.0% reaction accelerator sodium ammonium phosphate tetrahydrate and 1% sodium hexametaphosphate seed, and stir evenly.

[0053] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, and add 0.8‰ catalyst phosphotungstic acid. React until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid. The qualified neutralization slurry is filtered and removed for use.

[0054] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:3, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0055] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 69.8%. (The total phosphorus phosphate content of ≥67.0% is qualified in the national standard GB1886.4-2020).

[0056] Example 7 When preparing sodium hexametaphosphate with a high total phosphate content, 0.8‰ catalyst and 1.5% sodium ammonium phosphate tetrahydrate are added, while other conditions remain unchanged.

[0057] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 1.5% reaction accelerator sodium ammonium phosphate tetrahydrate and 1% sodium hexametaphosphate seed, and stir evenly.

[0058] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, add 0.8‰ catalyst phosphotungstic acid, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered and removed for use.

[0059] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:3, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0060] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 70.5%. (The total phosphorus phosphate content of ≥67.0% in the national standard GB1886.4-2020 is qualified).

[0061] Example 8 When preparing sodium hexametaphosphate with a high total phosphate content, 0.8‰ catalyst and 2.0% sodium ammonium phosphate tetrahydrate are added, while other factors remain unchanged.

[0062] (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 2.0% reaction accelerator sodium ammonium phosphate tetrahydrate and 1% sodium hexametaphosphate seed, and stir evenly.

[0063] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, and add 0.8‰ catalyst phosphotungstic acid. React until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid. The qualified neutralization slurry is filtered and removed for use.

[0064] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:3, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0065] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 70.3%. (The total phosphorus phosphate content of ≥67.0% in the national standard GB1886.4-2020 is qualified).

[0066] Example 9 In the actual production process, unqualified pentasodium (sodium tripolyphosphate) is often used as the raw material for hexametaphosphate. The unqualified pentasodium is: for example, the pH value, product particle size, whiteness, system waste, screen material, etc. of sodium tripolyphosphate do not meet the national standards or customer requirements. The preparation method of sodium hexametaphosphate includes the following steps: (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 0.75% sodium ammonium phosphate tetrahydrate as a reaction accelerator and 1% sodium hexametaphosphate seed, and stir evenly.

[0067] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, add sodium tripolyphosphate accounting for 22% of the total mass of phosphoric acid and soda ash suspension, add 1.5‰ catalyst phosphotungstic acid, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered for secondary use after impurities are removed.

[0068] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:2, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0069] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 70.9%. (The total phosphorus phosphate content of ≥67.0% in the national standard GB1886.4-2020 is qualified).

[0070] Example 10 In the reagent production process, unqualified pentasodium (sodium tripolyphosphate) is often used as a raw material for hexametaphosphate. The unqualified pentasodium is: for example, the pH value, product particle size, whiteness, system waste, screen material, etc. of sodium tripolyphosphate do not meet the national standards or customer requirements. The preparation method of sodium hexametaphosphate includes the following steps: (1) Pretreatment stage: At the beginning of the reaction, add a certain amount of 32% liquid alkali into the neutralization pot, raise the temperature to 30°C, add 0.75% sodium ammonium phosphate tetrahydrate as a reaction accelerator and 1% sodium hexametaphosphate seed, and stir evenly.

[0071] (2) Neutralization reaction stage: Add 85% phosphoric acid and 40% soda ash suspension to the neutralization pot at the same time, add sodium tripolyphosphate accounting for 22% of the total mass of phosphoric acid and soda ash suspension, and react until the neutralization slurry has a specific gravity of 1.7 and a pH value of 3.8-4.0. The qualified neutralization slurry is a colorless viscous liquid after retesting. The qualified neutralization slurry is filtered for secondary use after impurities are removed.

[0072] (3) Melting reaction stage: The qualified slurry is evenly transported to the high-temperature melting furnace, the ratio of raw material to clinker is controlled at 1:2, the temperature in the high-temperature melting tank is controlled at 650±20℃, the raw material is preliminarily dehydrated by the clinker, and a melting reaction occurs under the action of the catalyst to obtain a semi-finished product of sodium hexametaphosphate.

[0073] (4) Quenching and post-processing stage: The semi-finished sodium hexametaphosphate is physically cooled by a double-roll quenching machine at a speed of 70r / min, and then the product expected by this patent is obtained by post-processing such as a primary crusher, an elevator, an air separation crusher, and a rotary vibrating screen. Test: The total phosphate content of the product is 67.3%. (The total phosphorus phosphate content of ≥67.0% is qualified in the national standard GB1886.4-2020).

Claims

1. A method for preparing sodium hexametaphosphate with a high total phosphate content, characterized in that: The steps include: (1) Pretreatment stage: Heat the liquid alkali solution, add the reaction accelerator sodium phosphate and sodium hexametaphosphate seed, and stir to dissolve; (2) Neutralization reaction stage: adding phosphoric acid and soda ash suspension to step (1) simultaneously for neutralization reaction, and adding a certain amount of catalyst phosphotungstic acid to obtain a neutralized slurry; (3) Melt polymerization reaction stage: filtering the qualified neutralized slurry obtained in step (2), and obtaining a semi-finished product of sodium hexametaphosphate by melt polymerization; (4) Quenching and post-processing stage: The sodium hexametaphosphate semi-finished product obtained in the molten state in step (3) is quenched, crushed, and sieved to obtain sodium hexametaphosphate with a high phosphate content.

2. The method for preparing sodium hexametaphosphate with a high total phosphate content according to claim 1, characterized in that: The alkaline solution in step (1) is selected from liquid alkali or pure alkali solution.

3. The method for preparing sodium hexametaphosphate with a high total phosphate content according to claim 1, characterized in that: The sodium phosphate salt is selected from sodium ammonium hydrogen phosphate tetrahydrate; the dosage of the sodium phosphate salt is 0.75-1.5%.

4. The method for preparing sodium hexametaphosphate with a high total phosphate content according to claim 1, characterized in that: The amount of sodium hexametaphosphate seed is 0.1-1%, and the amount of catalyst phosphotungstic acid is 0.8-1.5‰.

5. The method for preparing sodium hexametaphosphate with a high total phosphate content according to claim 1, characterized in that: The mass fraction of phosphoric acid in step (2) is 75% or more, more preferably 85% or more, and more preferably 95% or more; the mass fraction of the soda ash suspension is 30% or more, more preferably 35% or more, and more preferably 40% or more.

6. The method for preparing sodium hexametaphosphate with a high total phosphate content according to claim 1, characterized in that: During the neutralization reaction, the slurry specific gravity is 1.6-1.8, and the pH value of the slurry is 3.8-4.

0.

7. The method for preparing sodium hexametaphosphate with a high total phosphate content according to claim 1, characterized in that: During the melting reaction, the ratio of raw material to clinker is controlled at 1 / 2-2 / 3; the melting temperature is controlled at 650±20°C, the melting reaction time is 25±5min, and the quenching condition is to cool to 50±10°C within 5-10min.

8. The method for preparing sodium hexametaphosphate with a high total phosphate content according to claim 1, characterized in that: The raw materials for obtaining sodium hexametaphosphate also include sodium tripolyphosphate and / or disodium hydrogen phosphate, and the sodium tripolyphosphate and / or disodium hydrogen phosphate are added to the neutralization stage.

9. A sodium hexametaphosphate with a high total phosphate content, characterized in that: The method is prepared by any one of claims 1 to 8.

10. The sodium hexametaphosphate with a high total phosphate content according to claim 9, characterized in that: The total phosphate content of sodium hexametaphosphate is 69.0% or more, more preferably 69.0% or more, more preferably 70.0% or more, and even more preferably 71.0% or more.