Ammonium pyrophosphate (APP)
Ammonium pyrophosphate (APP), with the chemical formula (NH₄)₂H₂P₂O₇, is a white crystalline salt. It is an inorganic compound formed by the condensation of two orthophosphate groups, belonging to the ammonium polyphosphate family. Below is a detailed introduction to ammonium pyrophosphate:
Properties
Physical Properties: Ammonium pyrophosphate appears as a white powder or lumps. Its density is 2.39 g/cm³, and it has a melting point of 190°C. It is soluble in water but insoluble in organic solvents like ethanol and acetone. Its aqueous solution exhibits weak acidity.
Chemical Properties: Ammonium pyrophosphate is stable under normal conditions but decomposes upon heating to release ammonia and phosphoric acid. It reacts with acids to form corresponding ammonium salts and releases carbon dioxide. It also reacts with bases to produce ammonia and phosphates.
Synthesis Methods
Ammoniation of Phosphoric Acid: Concentrated phosphoric acid is reacted with ammonia. By controlling the reaction conditions, such as temperature and the molar ratio of ammonia to phosphoric acid, ammonium pyrophosphate can be synthesized. For example, introducing ammonia gas into aqueous phosphoric acid at 170°C, followed by continuous addition of wet-process phosphoric acid and ammonia gas, yields ammonium polyphosphate as a melt, which contains ammonium pyrophosphate.
Condensation of Monoammonium Phosphate: Monoammonium phosphate is condensed with urea or other condensing agents to produce ammonium pyrophosphate. For instance, heating a mixture of monoammonium phosphate and urea at 210°C for about 1 hour can yield ammonium polyphosphate containing ammonium pyrophosphate.
Applications
Flame Retardants: Ammonium pyrophosphate is a widely used inorganic flame retardant. When heated, it decomposes to form a protective layer on the surface of materials, inhibiting combustion. It is commonly used as a flame retardant in intumescent paints and coatings, polyolefins, polyurethanes, and thermosets. It can also be applied to textiles, papers, fibers, and wood products for fireproofing.
Fertilizers: As a source of phosphorus and nitrogen, ammonium pyrophosphate can be used as a fertilizer to provide essential nutrients for plant growth, promoting healthy development.
Food Additives: Ammonium pyrophosphate is used as a leavening agent in the food industry. It releases carbon dioxide when reacting with moisture and heat, helping to create a light and fluffy texture in baked goods. It also functions as a buffering agent and emulsifier to regulate pH and improve food stability.
Other Applications: It is used in the production of ceramics, where it serves as a flux to lower the melting point of ceramic glazes. In the water treatment industry, it acts as a dispersant and stabilizer to prevent scaling and corrosion. Additionally, it is used in the pharmaceutical industry as a pH调节剂 and in the manufacture of certain chemical reagents.
Safety Information
Ammonium pyrophosphate is generally recognized as safe (GRAS) by the FDA when used in appropriate amounts in food products. However, it is irritating to the skin, respiratory system, and eyes. In case of contact with the skin or eyes, immediate rinsing with water is recommended. It is also important to avoid inhaling its dust. While it is non-flammable, it may release toxic gases such as ammonia and phosphoric acid when heated to high temperatures.
Market Outlook
The market for ammonium pyrophosphate is primarily driven by its demand in flame retardants, fertilizers, and food additives. With increasing environmental awareness and the promotion of green chemistry, the demand for inorganic flame retardants like ammonium pyrophosphate is expected to grow. Additionally, its applications in emerging fields such as high-performance polymers and nanomaterials are being actively explored, further expanding its market potential.