Background and overview[1]
Monopotassium phosphate is also known as potassium dihydrogen phosphate, potassium primary phosphate, and S⍥rensen’spotassiumphosphate. Colorless orthorhombic or tetragonal crystal. Relative molecular mass 136.09. Relative density 2.338. Melting point 252.6℃. Refractive index 1.5095 (20℃). Stable in dry air and deliquescent. Dehydration begins when heated to 200°C, and is converted into potassium metaphosphate (KPO3)n at 240-260°C. It becomes transparent glass when melted. Insoluble in ethanol, soluble in water (14.8 at 0℃, 18.3 at 10℃, 22.6 at 20℃, 25.1 at 25℃, 28.0 at 30℃, 33.5 at 40℃, 50.1 at 60℃, 70.4 at 80℃, 90℃ Time 83.5). The pH of a 1% aqueous solution is 4.6.
Purpose[2]
Potassium dihydrogen phosphate is widely used in industry, agriculture, medicine, and food industries. In industry, it is often used as bacterial culture agent and yeast culture agent. In agriculture, potassium dihydrogen phosphate is a high-concentration and efficient phosphorus-potassium compound fertilizer. It has high nutritional content (P and K active ingredients >90%), stable chemical properties, odorless, tasteless, non-toxic, and easy to use. It is soluble in water and does not clump, making it suitable for a variety of soils and crops. Among food additives, potassium dihydrogen phosphate is one of the important varieties of food phosphates. It is used as a quality improver, fermentation accelerator, flavoring agent, buffering agent and as a leavening agent together with dipotassium hydrogen phosphate. It is used as a mineral element additive to supplement phosphorus and potassium in feed additives, especially in fish feed.
1. Agriculture
Potassium dihydrogen phosphate is a high-concentration phosphorus-potassium compound fertilizer and high-quality chlorine-free potash fertilizer. It provides both phosphorus and potassium and is suitable for various soils and crops. It has high nutritional content, w(P2O5) is 52%, w(K2O) is 34%, the nutrients H2PO4 and K+ can be fully absorbed by crops, and does not contain impurities and residues. Potassium dihydrogen phosphate has a very low salt rubber antioxidant value and is an ideal foliar fertilizer. In addition, it is used in a small amount and can be widely used for seed soaking, root soaking, medicinal seed dressing, irrigation and foliar spraying. It has significant effects on crops in accelerating grain filling, promoting metabolism, resisting dry and hot winds and preventing lodging. It is used as base fertilizer for crops and foliar spray fertilizer in the middle and late stages of crops. It is widely used in various grains, cash crops, fruits, vegetables, etc. (such as: rice, wheat, corn, sugar cane, soybeans, cotton, flax, fruits, vegetables and tobacco. and other crops), especially suitable for tobacco, citrus, tea and other chlorine-resistant crops. It is an excellent fertilizer variety designated by the Ministry of Agriculture for promotion and development. In recent years, potassium dihydrogen phosphate has not only been found to have significant yield increase, drought resistance, and cold tolerance effects, but it has also been found to have special effects on the prevention and control of crop diseases and insect pests. Therefore, it has been rapidly developed and widely used in recent years. In my country, potassium dihydrogen phosphate is widely used for sprinkler irrigation of fruits, vegetables, tobacco and other crops. This type of consumption is mostly concentrated in Northeast China, Xinjiang, Inner Mongolia and other places. It is estimated that the amount of potassium dihydrogen phosphate used in agriculture in my country is about 50,000 to 60,000 t/a. It is expected that the consumption of agricultural potassium dihydrogen phosphate will reach 80,000 t/a in the next five years.
2. Chemical industry
In the chemical industry, potassium dihydrogen phosphate is widely used. It can be used as raw material for manufacturing potassium metaphosphate and other potassium salts; as culture agent, enhancer, leavening agent and fermentation aid for brewing yeast. In the fermentation industry, it is used as bacterial culture agent, buffer regulator and nutrient agent, mainly used in the production of monosodium glutamate, wine, alcohol, citric acid, enzyme preparations, yeast, starch and sugar. Industrial grade potassium dihydrogen phosphate is mainly used in the production of the above aspects. The consumption of potassium dihydrogen phosphate in my country’s chemical industry is about 30,000 to 40,000 t/a. It is estimated that the consumption of potassium dihydrogen phosphate in the chemical industry will reach 50,000 t/a in the next five years.
3. Pharmaceutical industry
In medicine, potassium dihydrogen phosphate is used as a bacterial culture agent; used to acidify urine and used as a nutritional agent; and also used in the production of penicillin, oxytetracycline, gallinin, etc. Hebei China Resources Pharmaceutical Co., Ltd. is inviting bids to expand production to 10,000t/a based on the existing pharmaceutical grade potassium dihydrogen phosphate of 500t/a. As a pharmaceutical production base, Hebei Province has great potential for demand for this product. According to preliminary estimates, the annual consumption of potassium dihydrogen phosphate in the pharmaceutical industry in Hebei Province alone reaches 8,000t. The 15,000 t/a potassium dihydrogen phosphate project of Inner Mongolia Tuoketuo Hua’ao Chemical Co., Ltd. is constructed in conjunction with the production of CSPC. The annual consumption of potassium dihydrogen phosphate in the national pharmaceutical industry is approximately 12,000 tons. It is expected that the consumption of potassium dihydrogen phosphate in the pharmaceutical industry will reach 20,000 t/a in the next five years.
4. Food industry
In the food industry, potassium dihydrogen phosphate is used as an additive and nutritional flavoring additive for baked goods. It is mainly used in the manufacture of baked goods, monosodium glutamate, baking powder, etc. Food grade potassium dihydrogen phosphate is generally used in this field. The national consumption of potassium dihydrogen phosphate in the food field is about 15,000 t/a. It is expected that the consumption of potassium dihydrogen phosphate in the food industry will also increase in the next five years.
5. Feed industry
In the feed industry, potassium dihydrogen phosphate is mainly used as a mineral element additive to supplement phosphorus and potassium, especially in fish feed. With the rapid development of the fish breeding industry in recent years, the dosage of potassium dihydrogen phosphate as a fish feed additive has increased rapidly, and the dosage of potassium dihydrogen phosphate in this field will also increase.
Preparation method[3]
At present, there are many production methods of potassium dihydrogen phosphate at home and abroad, mainly including neutralization method, extraction method, metathesis method, ion exchange method, direct method, electrolysis method, crystallization method and P.K.F. method.
1) Neutralization method. The neutralization method uses high-concentration thermal phosphoric acid to react with potassium hydroxide or potassium carbonate to generate potassium dihydrogen phosphate based on the principle of acid-base neutralization. Process flow: Prepare potassium hydroxide or potassium carbonate into a solution with a mass fraction of approximately 30%, gradually add thermal phosphoric acid with a mass fraction of approximately 50% under constant stirring, and control the reaction temperature to 80~100°C and the pH of the reaction solution. It is 4~5. After the reaction is completed, potassium dihydrogen phosphate is obtained through filtration, heating and concentration, cooling and crystallization, centrifugal separation, and drying. The crystallization mother liquor is returned to the concentration process for reuse. Reaction principle:
Advantages: short process flow, mature technology, simple operation, good product quality, and low energy consumption. Disadvantages: The production cost of raw ACE liquid calcium and zinc is high, and its promotion and application are greatly limited.
2) Extraction method. The extraction method is a method that can selectively use a certain solvent for extraction and separation to prepare potassium dihydrogen phosphate during the interphase transfer process based on the different solubilities of a certain substance in different solvents. This method is divided into inorganic extraction method and organic extraction method. Due to the immature technology of the inorganic extraction method, the purity of potassium dihydrogen phosphate produced is not high, so it is difficult to popularize and apply it. The organic extraction method is relatively mature and is one of the commonly used methods for preparing refined potassium dihydrogen phosphate in industrial production. The mass fraction of potassium dihydrogen phosphate in the product is as high as over 99%. The organic solvent extraction method uses H3PO4 and KCl as raw materials and uses the selectivity of organic extractants to extract H3PO4 or HCl. Reaction principle:
Advantages: low energy consumption, and the obtained potassium dihydrogen phosphate product has better quality. Disadvantages: The recovery rate of phosphorus is low, and organic solvents are expensive and difficult to recycle. They cause certain pollution to the environment and are not environmentally friendly.
3) Metathesis method. The metathesis method uses K+ in KCl and H2PO4- in orthophosphate MH2PO4 (M can be Na+ or NH4+) to prepare KH2PO4 through a metathesis reaction. Reaction principle:
The product KH2PO4 can be separated according to the phase diagram of the MCl-KH2PO4-H2O system. The raw materials used are different and the process conditions are also different. Advantages: simple production equipment and operation methods, low production cost, environmental protection and no pollution. Disadvantages: The product is of poor quality and can only be used in agriculture.
4) Ion exchange method. The ion exchange method usually uses potassium chloride solution to adsorb the corresponding anions and cations from the solution through a styrene-based cation (or anion) exchange resin, and then replaces the ammonium dihydrogen phosphate solution through the resin, so that K+ and H2PO4- are transferred to Combine on the same side to obtain a solution of potassium dihydrogen phosphate. The potassium dihydrogen phosphate solution is then heated and concentrated, cooled and crystallized, centrifuged, and dried to obtain the finished potassium dihydrogen phosphate. The crystallization mother liquor is returned to the concentration process for reuse. Reaction principle:
Advantages: The raw materials are cheap, and the cost is reduced by 1/3 compared with the neutralization method. Disadvantages: large water evaporation, high energy consumption, expensive resin, and large one-time investment.
5) Direct method. It is generally believed at home and abroad that the direct method is a very economical method for producing potassium dihydrogen phosphate because this method can directly make full use of the phosphorus in the phosphate rock and convert it into phosphoric acid and potassium dihydrogen phosphate. Israel, the United States, Japan, France and other countries have successively conducted research and development on this method. Compared with other methods, the raw materials of this method are much cheaper, and the method is straightforward and simple. This method uses phosphate rock, sulfuric acid, and potassium chloride as raw materials. It first uses potassium chloride and sulfuric acid to prepare potassium hydrogen sulfate, and then uses excess sulfuric acid and potassium hydrogen sulfate to react with phosphate rock powder under certain conditions to obtain phosphoric acid and The mixture of potassium dihydrogen phosphate is finally concentrated by heating and then precipitated with methanol to separate the phosphoric acid to obtain a crude product of potassium dihydrogen phosphate.
6) Electrolysis method. The electrolysis method usually uses potassium chloride (or potassium sulfate) and phosphoric acid as raw materials. Through the two-step reaction of electrolysis and metathesis in the electrolytic cell, H2PO4- or K+ selectively permeates the ion exchange membrane to obtain KH2PO4. In the first step, electrolysis occurs, and the cathode and anode produce high-purity hydrogen and chlorine respectively; in the second step, a metathesis reaction occurs, and K+ and H2PO4- combine to obtain KH2PO4. Reaction principle:
Advantages: The process flow is short and simple, the equipment is weakly corroded, and the potassium dihydrogen phosphate product obtained has high purity. Disadvantages: slight pollution to the environment, many technical difficulties need to be overcome, and currently only suitable for small-scale production.
7) Crystallization method. The crystallization method uses the different solubility of KH2PO4 in the H3PO4-KH2PO4-KCl-H2O system at different temperatures to obtain potassium dihydrogen phosphate crystals. It is usually produced by direct reaction of KCl and thermal phosphoric acid. Reaction principle:
As the hydrogen chloride gas is continuously removed during the reaction, the chemical reaction equilibrium moves to the right, causing the chemical reaction to continue to the right. Advantages: The production cost is better than the neutralization method and the production cost is lower. Disadvantages: It is highly corrosive to equipment, requires a large one-time investment, causes certain pollution to the environment, and the resulting product is of poor quality.
8) P.K.F method. The P.K.F method uses phosphate rock, potassium salt, and fluorosilicic acid as raw materials. It utilizes the fluoride of the main metal impurities in the phosphate rock (such as Ca, Al, Fe, Mg, etc.) which are generally difficult to dissolve in water, thereby producing potassium dihydrogen phosphate. Preparation and separation, while producing potassium dihydrogen phosphate, the main metal impurities can be eliminated at one time. Reaction principle:
It is a one-time elimination of impurities. Reaction principle:
