Background and overview[1-2]
Potassium diacid salt of phosphoric acid (KH2PO4), containing phosphorus (P2O5 sub>)52%, potassium (K2O) 34%, it is white or light yellow crystal, relative density at 20℃ is 2.39, weak hygroscopicity, good physical properties, easily soluble in water, aqueous solution Acidic, pH 3~4. The melting point of potassium dihydrogen phosphate is 253℃. When heated to ℃, it can dehydrate to generate potassium metaphosphate. The aqueous solution of potassium dihydrogen phosphate can react with silver nitrate to form a yellow silver precipitate of dihydrogen phosphate, which can be used as an identification reaction. Potassium dihydrogen phosphate contains two nutrients: phosphorus and potassium. It has stable chemical properties, is non-toxic and harmless, and is not easy to agglomerate. It is widely used in fertilizing crops, especially cash crops. It can improve the taste of cash crops and It can significantly increase the yield and is an excellent fertilizer variety. my country is the main consumer of potassium dihydrogen phosphate, but potassium dihydrogen phosphate, which accounts for nearly 50% of consumption, needs to be imported from abroad. There are few domestic manufacturers of potassium dihydrogen phosphate, mainly distributed in Sichuan and Hubei provinces, and their scale is not large. Most manufacturers in my country use the neutralization method to produce potassium dihydrogen phosphate, using thermal phosphoric acid or purified wet phosphoric acid and potassium alkali as raw materials. The cost is high, which limits their development; the production scale of manufacturers using metathesis and ion exchange methods is also the same. Below 10,000 t/a; with the advancement of organic solvent extraction technology, the number of manufacturers using this method to produce potassium dihydrogen phosphate will gradually increase. The preparation methods of potassium dihydrogen phosphate mainly include neutralization method, extraction method, metathesis method and direct method. The neutralization method has many industrial applications. The metathesis method requires recrystallization and purification because the product contains chlorine. The direct method has higher requirements for phosphate rock. In comparison, there is currently more research on the extraction method and there will be greater development. .
Apply[2]
1. Application of potassium dihydrogen phosphate in agriculture
With the in-depth promotion of the Ministry of Agriculture’s “Potassium Supplementation Project” and “Soil Testing and Fertilization” technology across the country, the demand for KH2PO4 in agriculture has also increased. Potassium is an essential nutrient element for plant growth. KH2PO4 is a chlorine-free, high-concentration binary compound fertilizer that can effectively provide the P and K nutrients needed by plants. Its salt content is low and it does not burn the roots of flowers, rice, corn, sweet potatoes, cotton, wheat and other crops. KH2PO4 is an ideal crop fertilizer. It is often used on rice, corn, wheat, cotton, sweet potatoes, flowers, etc. through foliar spraying, seed soaking, fertilizer soaking roots, seed dressing, base fertilizer, top dressing, etc. to promote metabolism and increase plant height. , enhance the photosynthesis of stems, leaves and fruit moss, make the fruits plump and bright in color, and have the effects of ripening, cold resistance, drought resistance, wind resistance, and yield increase. KH2PO4 is a one-time dissolved fertilizer with the advantages of low dosage, easy absorption, high fertilizer efficiency, and quick results. It is especially beneficial to the growth of chlorine-resistant crops such as tea, tobacco, citrus, flowers, etc., improving crop quality and economic benefits. KH2PO4 can not only improve soil fertility, but also has cold and drought resistance effects on plants. Some studies have found that KH2PO4 also has certain effects on plant pest control and disease prevention. As a high-efficiency compound fertilizer, potassium dihydrogen phosphate can improve the quality of agricultural products and increase yields by mastering the spraying method and timing. Appropriate spraying based on soil properties, climate and other factors can improve the quality of agricultural products and increase yields. Taking rice as an example, spraying potassium dihydrogen phosphate during the booting stage of rice can promote early maturity of rice by 3 to 4 days. On average, the weight of every 1,000 rice grains can be increased by 1g, and the yield can be increased by 3.80% to 4.55%. Spraying potassium dihydrogen phosphate once in each period can promote early maturity of rice by 5 to 9 days. On average, the quality of every 1,000 rice grains can be increased by 1g, the rice setting rate can be increased by 0.72% to 1.62%, and the yield can be increased by 6.81% to 9.29%.
The effect of spraying potassium dihydrogen phosphate on wheat growth cannot be ignored. Its mechanism of action on wheat can be divided into yield increase, quick-acting effect, resistance to lodging and cold, resistance to diseases and insect pests, wind and drought resistance, and increase in yield and quality. effect. In the north, compared with previous staged fertilization, the absorption rate of potassium dihydrogen phosphate sprayed by wheat is close to 100%. Spraying potassium dihydrogen phosphate during the growth period of wheat can provide adequate nutritional supplements to wheat and reduce nutrients between wheat plants. Competition, improve ear setting rate and increase yield. Research has found that wheat absorbs potassium dihydrogen phosphate sprayed very quickly. The leaf surface absorption rate can reach 50% in 1 hour. The absorption is close to saturation in 48 hours. It is converted into energy through photosynthesis. The absorption is basically completed in 96 hours. Spray potassium dihydrogen phosphate. It can increase the concentration of body fluids in wheat plants, reduce the freezing point of body fluids, thicken plant cells, and enhance the toughness of internodes, so it has the effect of cold resistance and lodging resistance. The crops can quickly absorb nutrients, the activity of plant cells is increased, the function of branches is enhanced, and sufficient nutrients are guaranteed. It can carry out a large number of chemical reactions in plants and enhance immunity and resistance. Spraying potassium dihydrogen phosphate reduces wheat transpiration, increases leaf moisture, enhances hot wind and drought resistance, and increases wheat chlorophyll content. Through a series of chemical reactions such as light reaction and carbon reaction, starch and sugar continue to accumulate, thus Improved wheat yield and quality.
2. Application of potassium dihydrogen phosphate in the food industry
According to the U.S. Food and Chemical Pharmacopoeia (FCC), the functions of phosphates in the food industry can be divided into 15 categories, including sour agents, anti-caking agents, antioxidants, buffers, dough improvers, emulsifiers, and hardening agents. Agents, moisturizers, starter cultures, nutrients, preservatives, chelating agents, modified starch additives, tissue improvers, and fermented foods. Potassium dihydrogen phosphate plays a role in the food industry, the one-time investment is relatively large. In addition, for every 1 ton of potassium dihydrogen phosphate produced, more than 4 tons of 6% dilute ammonium chloride solution is produced as a by-product. When the output is large, post-processing is very troublesome; during the production process, the resin is also easily poisoned and needs to be replaced entirely, which brings problems to production. trouble and increased costs. The domestic unit that develops the process for producing potassium dihydrogen phosphate by ion exchange is the Hubei Institute of Chemistry. In 1980, the ion exchange method developed by the institute to produce potassium dihydrogen phosphate won the National Invention Award. The institute conducted intermediate tests of 500t/a and 1000t/a ion exchange method to produce potassium dihydrogen phosphate in Huangmei County and Wuhan City inorganic salt chemical plants respectively. According to the assessment, the production cost was 1/3 lower than that of the neutralization method at that time, and the product w (KH2PO4)>98%. At present, the domestic manufacturer that uses the ion exchange method to produce potassium dihydrogen phosphate is Tianjin Binhai Welfare Chemical Plant, with a production capacity of 1,000t/a.
4. Metathesis method: The metathesis method currently referred to at home and abroad mainly refers to the essence of the reaction, which is the metathesis reaction between potassium ions in potassium chloride and dihydrogen phosphate in sodium or ammonium orthophosphoric acid to form dihydrogen phosphate. Potassium production process. Its chemical reaction formula is:
The reacted material liquid can be separated into potassium dihydrogen phosphate according to the NH4ClKH2PO4H2O or NaClKH2PO4H2O system phase diagram.
1) Sodium dihydrogen phosphate metathesis method. The process involves reacting phosphoric acid with sodium carbonate to prepare sodium dihydrogen phosphate and then reacting with potassium chloride to generate potassium dihydrogen phosphate. It is to dissolve potassium chloride, add sodium carbonate and phosphoric acid in proportion, stir thoroughly, adjust the pH to 4-5, heat and concentrate to 110°C, and then cool and crystallize, centrifuge, and dry to obtain the product KH2PO4. The process flow See Figure 4.
This method is characterized by simple production equipment, gentle reaction conditions, easy operation, no pollution, and reliable quality. It is said that the cost can be reduced by more than 1,000 yuan per ton compared with the neutralization method. The product quality of this method is not as good as that of the neutralization method and will contain a small amount of sodium chloride. Recovering sodium chloride from the mother liquor after separation of KH2PO4 crystallization requires high energy consumption and low value.
2) Ammonium dihydrogen phosphate metathesis method. The process involves reacting phosphoric acid with ammonium bicarbonate to prepare ammonium dihydrogen phosphate and then reacting with potassium chloride to generate potassium dihydrogen phosphate. It is to add water, potassium chloride and ammonium bicarbonate in proportion, then add a specified amount of phosphoric acid, stir thoroughly, adjust the pH value, heat and concentrate to 110°C, and then crystallize by cooling, centrifugal separation, and drying to obtain the product. KH2PO4, the mother liquor obtained by centrifugal separation is concentrated into a multi-element compound fertilizer containing nitrogen, phosphorus, potassium and other elements. This process has no three wastes emissions, and the production cost is 1,600 yuan/t lower than the neutralization method, and 1,000 yuan/t lower than the crystallization method, extraction method, and ion exchange method. However, the product quality is not as good as the neutralization method, extraction method, and ion exchange method, and it can only be used for agricultural purposes. Therefore, the value of its products will be much lower than other methods. Currently, Jiaozuo University is transferring the 6000t/a metathesis production technology. At present, domestic manufacturers that use the potassium chloride metathesis method to produce potassium dihydrogen phosphate include Xuzhou Runjia Dongfang Chemical Co., Ltd. (formerly Jiangsu Northern Chlor-Alkali Group Dongfang Chemical Factory), with a production capacity of 1,000t/a.
5. Direct method: The process of producing potassium dihydrogen phosphate using phosphate rock, sulfuric acid and potassium salt as raw materials was first announced by the Irish Golding Fertilizer Company at the technical meeting of the International Phosphate Manufacturers Association and is considered It is a relatively economical method to produce potassium dihydrogen phosphate. Subsequently, Israel, the United States, Japan and other countries have successively conducted research and development. This method reacts sulfuric acid with potassium chloride to produce potassium bisulfate and hydrogen chloride. Hydrogen chloride is absorbed by water as a by-product of hydrochloric acid, while potassium bisulfate and excess sulfuric acid react with phosphate rock to produce potassium dihydrogen phosphate, hydrofluoric acid and phosphoric acid. The mixed liquid and phosphogypsum are added to the silicon tetrafluoride obtained by defluorination of SiO2, and water (or sodium hydroxide) is used to absorb the by-product fluosilicic acid (or sodium fluosilicate). The reaction formula is as follows:
Main reference materials
[1] Encyclopedia of Chinese Agriculture·Agricultural Chemistry Volume
[2] Research progress on the preparation and application of potassium dihydrogen phosphate
[3] Current status and prospects of potassium dihydrogen phosphate in my country
