A method for producing high-pH sodium tetrapolyphosphate

Abstract

This invention provides a method for producing high pH sodium tetrapolyphosphate. Water is heated to ≥90℃, and a certain amount of liquid alkali is added. Sodium carbonate, liquid alkali, and phosphoric acid are then simultaneously added to a neutralization reactor. A chemical reaction is carried out under stirring. Ammonium phosphate is added as a catalyst. The degree of neutralization (K value) of the neutralization solution is adjusted to 2.65±0.1, and the specific gravity of the neutralization solution is adjusted to 1.6-1.7 g / cm³. 3 The reaction continues until the solution becomes viscous; the resulting viscous solution is then spray-dried, dehydrated, and polymerized to obtain a sodium tetrapolyphosphate semi-finished product; the sodium tetrapolyphosphate semi-finished product is then rapidly cooled to produce glassy sodium tetrapolyphosphate, which is then crushed and sieved to obtain the final sodium tetrapolyphosphate product. Using the feeding method of this invention, the pH value of the obtained product can reach 8.7-9.0, exhibiting a significant chelating ability for calcium ions.

Description

A method for producing high pH sodium tetrapolyphosphate Technical Field

[0001] This invention relates to a method for producing high pH sodium tetrapolyphosphate, and more particularly to a method for producing food-grade sodium tetrapolyphosphate. Background Technology

[0002] In the 1960s, my country began producing sodium polyphosphate, mainly tripolyphosphate. However, the production technology for sodium polyphosphates with higher polyphosphate content (tetrapolyphosphate, pentapolyphosphate, and even higher polyphosphates) was virtually nonexistent in China and remained largely undeveloped. Surveys show that my country currently has relatively few phosphate varieties, mainly concentrated on phosphoric acid and its sodium, potassium, and calcium salts. The United States has over 140 varieties, and Japan over 100. Developing sodium tetrapolyphosphate production technology would help improve the competitiveness of my country's phosphate varieties. my country's food industry has increasingly higher requirements for food additives. For sodium tripolyphosphate, there are higher requirements for its density, pH value, and ability to complex metal ions. Sodium tetrapolyphosphate, as a food additive, functions similarly to sodium tripolyphosphate, and can be used as a binder, emulsifier, ion masking (chelating) agent in meat products to prevent fat oxidation. Sodium tetrapolyphosphate complexes with Ca... 2+ Sodium tetrapolyphosphate (STP) has stronger properties and better fluidity, and its multiple uses cannot be replaced by sodium tripolyphosphate (TTP) and sodium hexametaphosphate (HTP). In addition, STP has wide industrial applications, increasing the fluidity of cement, glass, and other slurries. Due to its stronger complexing power, STP has a stronger dissolving and cleaning ability, making it suitable as a cleaning agent for radiation contamination; this application is also gaining attention.

[0003] Sodium tetrapolyphosphate has a wide range of applications and plays a unique role in certain areas. However, research on sodium tetrapolyphosphate production processes is largely lacking both domestically and internationally. The product of this invention is directly produced from a sodium hexametaphosphate production line using melt polymerization. The main adjustments are made to process parameters such as the sodium-to-phosphorus ratio in the neutralization liquid, polymerization temperature, and polymerization time, along with the selection of certain equipment. The cost is not significantly different from that of producing sodium hexametaphosphate. Sodium tetrapolyphosphate is about 10%-20% more expensive than sodium tripolyphosphate, resulting in better economic benefits and a promising market prospect in the future.

[0004] Currently, my country lacks a national standard for sodium tetrapolyphosphate, and the pH value of most products in the industry falls between 7.8 and 8.2. Domestic sodium tetrapolyphosphate chemical plants maintain the pH value of their products within the range of 8.2-8.5, with many manufacturers' products having pH values ​​close to the lower limit, affecting their applicability in testing and resulting in lower selling prices.

[0005] In response to the problem of low pH value in existing sodium tetrapolyphosphate products, this study investigates the pH value of sodium tetrapolyphosphate products and controls the high pH value between 8.8 and 9.5. Summary of the Invention

[0006] The purpose of this invention is to provide a process for preparing sodium tetrapolyphosphate using sodium carbonate, liquid alkali, and food-grade phosphoric acid as raw materials, through steps such as spray drying, polymerization, quenching, and sieving. This process is characterized by readily available raw materials, low cost, and the ability to achieve industrial-scale production.

[0007] The specific process is as follows:

[0008] (1) Neutralization reaction: After heating the water to ≥90℃, add a certain amount of liquid alkali, and then simultaneously add sodium carbonate, liquid alkali and phosphoric acid to the neutralization reactor. Stir and carry out the chemical reaction. Add ammonium phosphate, adjust the degree of neutralization K value of the neutralization solution to 2.65±0.1, and adjust the specific gravity of the neutralization solution to 1.6-1.7 g / cm³. 3 Continue the reaction until the solution becomes viscous;

[0009] (2) Polymerization reaction: The viscous solution obtained by neutralization is spray-dried and dehydrated, and then polymerized to obtain sodium tetrapolyphosphate semi-finished product;

[0010] (3) Rapid cooling generation: The sodium tetrapolyphosphate semi-finished product is rapidly cooled to generate glassy sodium tetrapolyphosphate, and then the sodium tetrapolyphosphate product is obtained by crushing and screening.

[0011] In this step, a certain amount of liquid alkali is added after the water is heated to ≥90℃. The purpose is to adjust the pH value of the product and protect the equipment. If acid is added first, it is easy to corrode the equipment and carry the impurities from the corrosion into the product. This also lays the groundwork for eliminating the carbon dioxide byproduct produced by the reaction of sodium carbonate and phosphoric acid in the later stages.

[0012] The sodium carbonate mentioned in this invention is a food-grade product with a purity of 99% or higher, the liquid alkali is an alkali solution with a purity of 45-48%, and the phosphoric acid is wet-process phosphoric acid, which is usually a product with a mass concentration of 85%.

[0013] In this case, the higher the purity, the higher the purity of the product, and it does not introduce unnecessary impurities such as metal ion impurities.

[0014] In some embodiments, step (1) of the present invention is carried out in a neutralization reactor. During the neutralization reaction, the mass ratio of sodium carbonate, liquid alkali and phosphoric acid in the raw materials is 0.5-1:2-3:4-5.

[0015] During the simultaneous addition of sodium carbonate, liquid alkali, and phosphoric acid, the feed is continuous according to the theoretical values ​​corresponding to the neutralization reaction formula. The sodium carbonate is added continuously, i.e., at a rate of 0.5-2 tons / hour, and the chemical reaction proceeds simultaneously.

[0016] The entire neutralization reaction process can be represented by the following reaction equation:

[0017] 4H3PO4+3Na2CO3→2NaH2PO4+2Na2HPO4+3CO2↑+2H2O

[0018] 3H3PO4+5NaOH→2NaH2PO4+Na2HPO4+5H2O

[0019] 2NaH2PO4 + 2Na2HPO4 → Na6P4O 13 +3H2O

[0020] In some embodiments, the stirring speed during the stirring reaction is varied, i.e., stirring at 50-200 r / min for 30-90 min, then at 300-500 r / min for 90-180 min, and then at 250-350 r / min for 30-90 min.

[0021] As a preferred option, the stirring speed during the stirring reaction is carried out in a variable speed stirring mode, that is, stirring at 100-200 r / min for 30-60 min, then stirring at 400-500 r / min for 90-180 min, and then stirring at 250-300 r / min for 30-60 min.

[0022] In the above stirring process, low-speed stirring is carried out during the continuous feeding of sodium carbonate and promotes the early reaction. After the sodium carbonate is fed, the stirring speed is increased to carry out the middle reaction process. Finally, the stirring speed is reduced again to carry out the later reaction process and to adjust the K value and specific gravity.

[0023] The purpose of the variable-speed stirring described above is to accelerate the production of sodium tetrapolyphosphate, and at the same time, to remove as much carbon dioxide as possible from the neutralization slurry as possible through rapid stirring.

[0024] In some embodiments, the amount of ammonium phosphate added is 0.75-1.5‰ of the sodium tetrapolyphosphate product mass. The sodium tetrapolyphosphate product mass refers to the theoretical value obtained based on the added amounts of the above-mentioned raw materials and the reaction formula.

[0025] In some preferred embodiments, the ammonium phosphate is added during the middle of the reaction, that is, during the rapid stirring process at 300-500 r / min or during the rapid stirring process at 400-500 r / min.

[0026] In some embodiments, the spray drying is carried out in a spray drying tower at a temperature controlled at 320-350°C. This drying process achieves dehydration of the viscous solution to below 0.5%, more preferably to 0.1%.

[0027] After drying, polymerization is carried out in a polymerization furnace. The material is transported to the polymerization furnace by a screw conveyor, and the polymerization temperature is controlled at 550-650℃. The polymerization reaction residence time is 15-35 min, and the polymerization furnace speed is controlled at about 10-20 r / min.

[0028] The quenching process involves rapidly cooling the sodium tetrapolyphosphate semi-finished product to room temperature within 20±5 minutes using a quenching machine. Specifically, the polymerized semi-finished product is transported to the quenching machine for cooling, and then subjected to subsequent crushing and screening processes to obtain the desired sodium tetrapolyphosphate product.

[0029] This invention is carried out on an existing sodium tripolyphosphate production line, with relatively simple processes and equipment, easy operation, and the ability to achieve industrial-scale production. The sodium tetrapolyphosphate product produced by this invention plays a role in the field of food additives, and also plays a more significant role in the field of detergents.

[0030] One of the key technical points of this invention is the feeding method: first, liquid alkali is added, then phosphoric acid, liquid alkali, and sodium carbonate are added together. Another key technical point is the new catalyst, ammonium phosphate. The final product has a pH value of approximately 8.8, and under preferred conditions, it reaches around 9.0.

[0031] The quality standards for the produced sodium tetrapolyphosphate products are as follows:

[0032] Detailed Implementation

[0033] Example 1

[0034] First, add 1 ton of process water to the neutralization reactor and heat it to approximately 90°C with steam. Start the stirring at 100 rpm. Add 1 ton of 48% liquid alkali. Then, simultaneously add 3 tons of sodium carbonate, 6 tons of liquid alkali, and 12 tons of 85% phosphoric acid to the neutralization reactor. Control the sodium carbonate feeding rate, adding it at a uniform rate of 1 ton every 0.5 hours. After feeding, stir the reaction for 30 minutes at 400 rpm to allow the chemical reaction to occur. Add 18.75 kg of ammonium phosphate, and the reaction time is 3 hours. During the later stages of the reaction, increase the stirring speed to 250 rpm and stir for another 30 minutes, adjusting the neutralization degree (K value) of the neutralization solution to 2.65 ± 0.1. Adjust the specific gravity of the neutralization solution to 1.7 g / cm³. 3 The reaction continues until the solution becomes viscous. The resulting viscous solution is then transferred to a spray drying tower for preliminary dehydration, with the tower top temperature controlled at 330°C. It is then conveyed to a polymerization furnace via a screw conveyor, where the polymerization temperature is controlled at 600°C, the polymerization reaction residence time is 25 minutes, and the furnace rotation speed is controlled at approximately 20 r / min. The polymerized semi-finished product is then transferred to a quencher for cooling. During the quenching process, the sodium tetrapolyphosphate semi-finished product is rapidly cooled to room temperature within 20 minutes, with the quencher rotation speed controlled at 25 r / min. Subsequent crushing and sieving processes yield the desired sodium tetrapolyphosphate product.

[0035] Example 2

[0036] First, add 1 ton of process water to the neutralization reactor and heat it to approximately ≥90℃ with steam. Start stirring at 100 rpm. Add 1 ton of 48% liquid alkali. Then, simultaneously add 3 tons of sodium carbonate, 6 tons of liquid alkali, and 12 tons of 85% phosphoric acid to the neutralization reactor. Control the sodium carbonate feeding rate, adding it at a uniform rate of 1 ton every 0.5 hours. After feeding, stir for 30 minutes at 500 rpm to allow the chemical reaction to occur. Add 25 kg of ammonium phosphate, and the reaction time is 3 hours. During the later stages of the reaction, increase the stirring speed to 300 rpm and stir for another 30 minutes, adjusting the neutralization degree (K value) of the neutralization solution to 2.65 ± 0.1. Adjust the specific gravity of the neutralization solution to 1.7 g / cm³. 3The reaction continues until the solution becomes viscous. The resulting viscous solution is then transferred to a spray drying tower for preliminary dehydration, with the tower top temperature controlled at 330°C. It is then conveyed to a polymerization furnace via a screw conveyor, where the polymerization temperature is controlled at 600°C, the polymerization reaction residence time is 25 minutes, and the furnace rotation speed is controlled at approximately 20 r / min. The polymerized semi-finished product is then transferred to a quencher for cooling. During the quenching process, the sodium tetrapolyphosphate semi-finished product is rapidly cooled to room temperature within 20 minutes, with the quencher rotation speed controlled at 25 r / min. Subsequent crushing and sieving processes yield the desired sodium tetrapolyphosphate product.

[0037] Example 3

[0038] First, add 1 ton of process water to the neutralization reactor and heat it to approximately 90°C with steam. Start stirring at 100 rpm. Add 1 ton of 48% liquid alkali. Then, simultaneously add 3 tons of sodium carbonate, 6 tons of liquid alkali, and 12 tons of 85% phosphoric acid to the neutralization reactor. Control the sodium carbonate feeding rate, adding it at a uniform rate of 1 ton every 0.5 hours. After feeding, stir for 30 minutes at 450 rpm to allow the chemical reaction to occur. Add 37.5 kg of ammonium phosphate, and the reaction time is 3 hours. During the later stages of the reaction, increase the stirring speed to 250 rpm and stir for another 30 minutes, adjusting the neutralization degree (K value) of the neutralization solution to 2.65 ± 0.1. Adjust the specific gravity of the neutralization solution to 1.7 g / cm³. 3 The reaction continues until the solution becomes viscous. The resulting viscous solution is then transferred to a spray drying tower for preliminary dehydration, with the tower top temperature controlled at 330°C. It is then conveyed to a polymerization furnace via a screw conveyor, where the polymerization temperature is controlled at 600°C, the polymerization reaction residence time is 25 minutes, and the furnace rotation speed is controlled at approximately 20 r / min. The polymerized semi-finished product is then transferred to a quencher for cooling. During the quenching process, the sodium tetrapolyphosphate semi-finished product is rapidly cooled to room temperature within 20 minutes, with the quencher rotation speed controlled at 25 r / min. Subsequent crushing and sieving processes yield the desired sodium tetrapolyphosphate product.

[0039] Example 4

[0040] The method and steps are the same as in Example 1, except that ammonium phosphate is not added.

[0041] Example 5

[0042] The method and steps are the same as in Example 1, except that an excess of 50 kg of ammonium phosphate is added.

[0043] Example 6

[0044] The method and steps are the same as in Example 1, except that ammonium phosphate and sodium carbonate are added together, and the mixture is stirred continuously at 200 r / min for 5 h 40 min until the degree of neutralization K value is 2.65 ± 0.1. The specific gravity of the neutralized solution is then adjusted to 1.7 g / cm³. 3 about.

[0045] Example 7

[0046] The method and steps are the same as in Example 1, except that sodium carbonate, liquid alkali, and phosphoric acid are added simultaneously and reacted for 30 minutes. The stirring speed is then increased to 400 r / min, and the reaction is continued for 4 hours and 10 minutes until the degree of neutralization (K value) is 2.65 ± 0.1. The specific gravity of the neutralized solution is then adjusted to 1.7 g / cm³. 3 about.

[0047] Determination of product quality indicators under different process parameters:

[0048]

[0049] Note: Chelating ability: The number of cations (g) complexed by 100g of polyphosphate.

[0050] Comparative analysis showed that when the polymerization temperature was controlled at around 610℃, the product exhibited better whiteness, pH value, water-insoluble matter, chelating ability, and other indicators.

[0051] pH detection conditions: Weigh 1.00 g ± 0.01 g of sample into a 100 mL beaker, dissolve in carbon dioxide-free water, transfer to a 100 mL volumetric flask, dilute to the mark with carbon dioxide-free water, and mix well. Pour into a 100 mL dry beaker, and measure the pH of the sample solution using a calibrated pH meter. The test results are considered the arithmetic mean of parallel determinations. The absolute difference between two independent determinations obtained under repeatability conditions should not exceed 0.1.

[0052] Detection conditions for water-insoluble matter: Weigh approximately 10 g of the sample, accurate to 0.01 g, place it in a 400 mL beaker, add 200 mL of water, heat to boiling to dissolve, and while hot, filter through glass sand that has been dried to constant mass at 105 ℃ ± 2 ℃. Wash 10 times with hot water (approximately 20 mL of water each time) until the precipitate is free of phosphate (tested with silver nitrate solution and ammonia solution). Place in an electric thermostatic drying oven and dry to constant mass at 105 ℃ ± 2 ℃.

[0053] Whiteness testing conditions: First, use a white plate to calibrate the whiteness meter. Weigh 10g of sample, press it, and put it into the whiteness meter to test the product whiteness.

[0054] Water absorption rate test conditions: Place 100g sample in a sampling tray for 1 hour, measure the product weight after 1 hour, and calculate the product water absorption rate using the differential method.

Claims

1. A method for producing high pH sodium tetrapolyphosphate, characterized in that, The process includes the following steps: (1) Neutralization reaction: After heating the water to ≥90℃, add a certain amount of liquid alkali, and then simultaneously add sodium carbonate, liquid alkali and phosphoric acid to the neutralization reaction vessel. Stir and carry out the chemical reaction. Add ammonium phosphate, adjust the degree of neutralization K value of the neutralization solution to 2.65±0.1, and adjust the specific gravity of the neutralization solution to 1.6-1.7 g / cm³. 3 Continue the reaction until the solution becomes viscous. During the stirring reaction, the stirring speed is adjusted according to the variable speed stirring method, that is, stirring at 50-200 r / min for 30-90 min, then at 300-500 r / min for 60-180 min, and then at 250-350 r / min for 30-90 min. The ammonium phosphate is added in the middle of the reaction, that is, during the rapid stirring at 300-500 r / min. The amount of ammonium phosphate added is 0.75-1.5‰ of the mass of sodium tetrapolyphosphate product. (2) Polymerization reaction: The viscous solution obtained by neutralization is spray-dried and dehydrated, and then polymerized to obtain sodium tetrapolyphosphate semi-finished product. (3) Rapid cooling generation: The sodium tetrapolyphosphate semi-finished product is rapidly cooled to generate glassy sodium tetrapolyphosphate, and then crushed and sieved to obtain sodium tetrapolyphosphate product.

2. The method for producing high pH sodium tetrapolyphosphate according to claim 1, characterized in that, The mass ratio of sodium carbonate, liquid alkali, and phosphoric acid is 0.5-1:2-3:4-5.

3. The method for producing high pH sodium tetrapolyphosphate according to claim 2, characterized in that, The sodium carbonate is added at a rate of 0.5-2 tons / h and undergoes a chemical reaction.

4. The method for producing high pH sodium tetrapolyphosphate according to claim 1, characterized in that, During the stirring reaction, the stirring speed is adjusted by a variable speed stirring method, that is, stirring at 100-200 r / min for 30-60 min, then at 400-500 r / min for 90-180 min, and then at 250-300 r / min for 30-60 min.

5. The method for producing high pH sodium tetrapolyphosphate according to claim 1, characterized in that, During the spray drying stage, the temperature at the top of the tower is controlled at 320-350℃.

6. The method for producing high pH sodium tetrapolyphosphate according to claim 1, characterized in that, The polymerization temperature is controlled at 550-650℃, the polymerization reaction residence time is 15-35min, and the polymerization furnace speed is controlled at 10-20r / min.

7. The method for producing high pH sodium tetrapolyphosphate according to claim 1, characterized in that, The rapid cooling process involves rapidly cooling the sodium tetrapolyphosphate semi-finished product to room temperature within 20±5 minutes.

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