Ammonium polyphosphate is a polyphosphate containing N and P, referred to as APP. According to its degree of polymerization, it can be divided into three types: low polymerization, medium polymerization and high polymerization. When the degree of polymerization is below 20, it is called oligomerization and is water-soluble. When the degree of polymerization is above 50, it is called polymerization and can be used as a flame retardant. In the 1980s, considering factors such as price and cost, oligomeric water-soluble APP was mainly used for flame retardancy on cellulosic materials such as paper and wood. High polymerization ammonium polyphosphate is widely used in intumescent fire retardant coatings, polyethylene, polypropylene, polyurethane, epoxy resin, rubber products, fiberboards and dry powder fire extinguishing agents. It is a safe and efficient nitrogen-phosphorus non-halogen smoke suppressant. Flame retardants.
Agricultural ammonium polyphosphate (APP, ammonium polyphosphate) is a low-N, high-P polyphosphate with a near-neutral pH and its general chemical formula is (NH4)n+2PnO3n+1. According to the degree of polymerization, APP can be divided into three types: oligopolymerization, medium polymerization and high polymerization; the higher the degree of polymerization, the smaller the water solubility. Usually, when n20, it is water-insoluble.
At present, APP Agriculture has entered the field of chemical fertilizers as a new type of fertilizer and is often used as the basic phosphate fertilizer for preparing high-concentration liquid compound fertilizers. Solid ammonium polyphosphate products are generally composed of 20-30% orthophosphate, 40-50% pyrophosphate (P2O74-), 10-15% tripolyphosphate (P3O105-) and 3-5% tetrapolyphosphate. and polyphosphates composed of more than four polymers. Liquid ammonium polyphosphate products generally contain higher amounts of tripolyphosphate and phosphate ions than granular products, but the composition varies. The common range is 30-40% orthophosphate, 50-55% pyrophosphate, and A portion of tripolyphosphate and tetrapolyphosphate. The commonly used liquid APP ratios abroad are: 8-24-0, 10-34-0, 11-37-0, 11-44-0, 8-28-0, etc. (as shown in Table 2), and the solid ratio is 18-58- 0.
Environmentally friendly and efficient liquid fertilizer
The degree of polymerization of ammonium polyphosphate used as fertilizer is usually 5-18. The short chain is fully water-soluble. It includes ammonium phosphate, ammonium pyrophosphate, ammonium tripolyphosphate and ammonium tetrapolyphosphate. The degree of polymerization is higher. High, longer chain ammonium polyphosphate solvents are only present in small amounts. Ammonium polyphosphate fertilizer has the following advantages: First, it has high nitrogen and phosphorus nutrient content, near-neutral pH value, and high safety factor for crop use; second, it has high solubility, and can be configured with liquid fertilizers with higher phosphorus content, and has a lower crystallization temperature and is more convenient for production. It is easy to use; third, it has a chelating effect on metal ions, which can prevent phosphorus and metal impurities in the solution from forming precipitation. Adding trace elements to the liquid fertilizer is conducive to making high-concentration and high-quality liquid fertilizer, and the phosphorus is not easily absorbed into the soil. The iron, calcium and other metal ions are fixed and can complex trace amounts of calcium and magnesium in the water. When used in hard water areas with high water calcium in the north, there will be no blocking of the dropper nozzle when industrial monoammonium phosphate is used as the raw material; fourthly, Although it is not directly absorbed by plants in the soil, it can be slowly hydrolyzed into orthophosphate in the soil and then used by plants. The phosphorus utilization rate is relatively high and it is a long-term fertilizer.
The development and advantages of APP as fertilizer
In recent years, APP has gradually entered the field of liquid fertilizer production, and has been widely used in developed countries such as the United States and Europe.
There are currently 130 factories in the United States producing agricultural APP, with an annual output of 2 million tons. Other countries include Belgium, France, Russia, etc. These basic liquid fertilizers can be mixed with nitrogen solutions and potassium fertilizers to produce liquid compound fertilizers. However, at present, there are still few companies specializing in the production of agricultural ammonium polyphosphate fertilizers in my country. Its properties, composition and production methods are still controversial, and there are large gaps in product quality, quantity and application scope.
Comparison of APP production at home and abroad
APP agricultural ammonium polyphosphate is an important phosphorus raw material for the development of water-soluble fertilizers. It has the following advantages:
(1) The phosphorus nutrient content is high, the pH value is nearly neutral, and the pH value is 6.5-7.5. It has a high safety factor for crop use and good activity of mineral elements.
(2) It has high solubility, solubility ≥150g/100g of water, and can be configured with liquid fertilizer with higher phosphorus content; the crystallization temperature is low, and it is easy to produce and use.
(3) It has a chelating effect on metal ions, which can prevent metal impurities in the solution from forming precipitation. Adding trace elements to liquid fertilizer is beneficial to making high-concentration and high-quality liquid fertilizer. Phosphorus is not easily fixed by metal ions such as iron and calcium in the soil. Instead, it can form soluble complexes with ineffective trace elements in the soil and be absorbed and utilized by plants.
(4) Although it is not directly absorbed by plants in the soil, it can be slowly hydrolyzed into orthophosphate in the soil and then used by plants. It is a slow-soluble, long-acting fertilizer.
(5) It can be made into foliar fertilizer for foliar spraying on crops. Agricultural ammonium polyphosphate is used as a fertilizer. The application rate can be 3 times higher than that of orthophosphate, but it will not burn the leaves. The neutral solution can remain on the leaves for several days without being evaporated or salted out.
Problems with hydrolysis of APP agricultural ammonium polyphosphate
Orthophosphate can be directly absorbed and utilized by plants, but pyrophosphate, tripolyphosphate, tetrapolyphosphate, etc. can only be absorbed and utilized by plants after they are hydrolyzed to orthophosphate. The hydrolysis reaction controls the absorption of phosphorus by plants. . The hydrolysis of polyphosphate is mainly affected by factors such as enzymes, temperature, pH value, and metal ions.
(1) Phosphatase in soil is the key enzyme for the hydrolysis of pyrophosphate. Phosphatase can catalyze the hydrolysis of ammonium polyphosphate very quickly, and the hydrolysis rate is 106 times faster than without enzyme catalysis.
(2) Temperature is an important factor affecting the hydrolysis of agricultural ammonium polyphosphate.��, the higher the temperature, the faster the polyphosphate hydrolyzes. Under the same pH conditions, the hydrolysis rate of ammonium tripolyphosphate is 27 times faster than that at normal temperature; in soil, the hydrolysis rate of polyphosphate at different temperatures is: 10℃＜20℃＜30℃. There is an activation energy for breaking between P-O-P chains in phosphate. Every time the temperature increases by 5°C, the chemical reaction rate doubles.
(3) The hydrolysis of agricultural ammonium polyphosphate is affected by pH value. The lower the pH value, the faster the polyphosphate hydrolyzes. When the temperature is lower than 25°C and the pH is near neutral (pH=6.4), the agricultural ammonium polyphosphate solution is very stable. In a low pH environment, the P-O-P chain reacts with (H3O)+ and hydrolysis is accelerated.
(4) Metal ions can catalyze the hydrolysis of agricultural ammonium polyphosphate, and the hydrolysis rate decreases as the activity of metal ions decreases (K+＜Na+＜Ca2+＜Mg2+＜Al3+). Metal ions can activate phosphorus atoms in agricultural polyphosphates and increase the number of activated molecules in the reaction.
(5) The content of heavy metals is low, it can passivate heavy metals in the soil, improve the soil, and is safe and environmentally friendly.
Good quality improvement and yield increase
Urea phosphate is a phosphate double salt produced by the reaction of phosphoric acid and urea under certain conditions. Its solubility changes greatly with temperature, and it can be frozen or vacuumed. The production process is simple.
Urea phosphate is a phosphate with multiple uses: first, it is a good-quality acidic fertilizer. The urea contained in it will not be quickly decomposed by urease, which improves N utilization; phosphorus is not easily decomposed due to the complexation of urea. Fixed in the soil, the utilization rate of phosphorus is high. Secondly, it is an ideal feed additive for ruminants. The toxicity to animals is 1.5-2 times that of urea. Cattle and sheep fed with urea phosphate can increase lactation by 11%, increase body weight by 15%-30%, and enhance disease resistance. Mortality rate reduced. Thirdly, urea phosphate can be heat treated to obtain its derivative urea – ammonium polyphosphate. More than 50% of P2O5 is polyphosphate, which is a good high-concentration nitrogen-phosphorus liquid fertilizer and a good phosphorus-nitrogen flame retardant. Finally, it can be used as a method to purify phosphoric acid. Phosphate urea is treated with arkema nitric acid and oxalic acid to obtain purified phosphoric acid and urea nitrate or urea oxalate. The purified phosphoric acid can then be further processed to obtain food-grade phosphoric acid.
Water-soluble ammonium polyphosphate has also been tested as a liquid fertilizer. For example, in the alkaline soil in the suburbs of Urumqi, Xinjiang, the fertilizer efficiency of using ammonium polyphosphate liquid fertilizer to root jute-skinned cantaloupe is higher than that of solid diammonium phosphate with the same nutrient content. The yield increase effect is 3.0%-8.4% higher, and the yield per mu is 228. -254 kg of melon, and can improve the quality of the crop and increase the sugar content by about 3.2%. Through experiments, it was found that liquid fertilizer is easier to mix and apply than solid fertilizer, and the uniformity after application is higher than that of solid fertilizer. The acidity of ammonium polyphosphate (pH is 5.92) is conducive to the improvement of fertilizer efficiency, and the fertilizer efficiency is higher than solid fertilizers with equal nutrient content. The fertilizer diammonium phosphate can significantly increase production, and the fertilizer utilization rate is also improved accordingly.
