Monocalcium phosphate

NSP is produced by the reaction of phosphate rock and sulfuric acid. This reaction quickly yields a soHd mass containing monocalcium phosphate monohydrate and gypsum, CaSO 2H20, according to the simplified equation... 

Chemistry and Properties. TSP is essentially impure monocalcium phosphate monohydrate, Ca(H2P0 2 20, made by acidulating phosphate rock with phosphoric acid according to... 

Nitrophosphates are made by acidulating phosphate rock with nitric acid followed by ammoniation, addition of potash as desired, and granulation or prilling of the slurry. The acidulate, prior to ammoniation, contains calcium nitrate and phosphoric acid or monocalcium phosphate according to the foUowiag equations ... 

Some commonly used primary nutrient fertilizers are incidentally also rich sources of calcium. Ordinary superphosphate contains monocalcium phosphate and gypsum in amounts equivalent to all of the calcium originally present in the phosphate rock. Triple superphosphate contains soluble monocalcium phosphate equivalent to essentially all the P2 5 product. Other fertilizers rich in calcium are calcium nitrate [10124-37-5] calcium ammonium nitrate [39368-85-9] and calcium cyanamide [156-62-7]. The popular ammonium phosphate-based fertilizers are essentially devoid of calcium, but, in view of the natural calcium content of soils, this does not appear to be a problem. 

Both monocalcium phosphate and dicalcium phosphate dissolve incongmently in water, disproportionating to more basic calcium phosphate and phosphoric acid. The extent of these reactions varies with the temperature and the amount of water. If water is added gradually to anhydrous monocalcium phosphate, equiUbrium conditions first correspond to a mixture of the anhydrous salt and its monohydrate. After conversion to the monohydrate, further reaction affords dicalcium phosphate plus free phosphoric acid. Dicalcium phosphate decomposes in aqueous solution to the more basic hydroxyapatite and phosphoric acid via intermediate octacalcium phosphate. The compHcated stepwise conversion of the acidic mono- and dicalcium phosphates to hydroxyapatite is summarized in equations 6—9. The kinetics are quite complex. 

Because monocalcium phosphate is incongmently soluble, it is typically contaminated with various amounts (6—10%) of dicalcium phosphate and free phosphoric acid resulting from in-process disproportionation of the monocalcium salt. Free phosphoric acid may render the product hygroscopic, and absorbed water plus acid catalyzes further decomposition to additional free acid and dicalcium phosphate. For this reason, industrial monocalcium phosphate may contain some dicalcium phosphate resulting from excess lime addition and then aged to ensure the removal of residual free phosphoric acid. 

Uses. Commercial monocalcium phosphate is available as both the anhydrous and the monohydrate salts. Most uses are based on acidic properties. Monocalcium phosphate is used to control acidity in powdered drink mixes, as an ingredient in effervescent tablets, as a plastics stabilizer, and in ceramics. Its single largest appHcation is as a leavening agent in bread, cake mixes, and self-rising flour. 

Anhydrous monocalcium phosphate, Ca(H2PObe made in a pan mixer from concentrated phosphoric acid and lime. The high heat of reaction furnishes essentially all the necessary thermal input and subsequent drying is minimized. A small amount of aluminum phosphate or a mixture of sodium and potassium phosphates is added in the form of proprietary stabilizers for coating the particles. Heat treatment converts the coating to a protective polyphosphate (19). 

A number of acidic phosphates which vary in their rate of reaction are available for use in a wide variety of bakery appHcations. These acids, which include monocalcium phosphate, sodium aluminum phosphate, and sodium acid pyrophosphate, release carbon dioxide at a controlled rate to give a certain fraction prior to baking the remaining fraction is released at a specific time during baking. Controlled releasing of carbon dioxide at the time it is needed can also be achieved by a mixture of different types of leavening acids. 

Monocalcium Phosphate. The monohydrate of monocalcium phosphate (MCP) was the first of the phosphates to be used as a leavening... 

Dicalcium Phosphate Dihydrate (DPD). Dicalcium phosphate cHhydrate is completely nonreactive at room temperature. At 65—71°C and in the presence of water, it dehydrates and decomposes into hydroxyapatite and acidic monocalcium phosphate, or a free phosphoric acid (18). It is used to some extent in cake mixes in combination with faster acting acid. Its primary function is to provide acidity late in the baking cycle and thus produce a neutral and palatable product. DPD has an NV of 33. It provides sufficient acidity only in products requiring long baking times. 

Monocalcium phosphate [10031-30-8] Ca(H2P0 2 H2O, used in baking powder (see Bakeryprocesses and leavening agents), is crystallized from a hot reaction mixture of concentrated (electric furnace) phosphoric acid and lime, or it is made by spray-drying a slurry of the product of reaction of lime and phosphoric acid (14). 

By far the largest source of phosphorus is phosphate rock, with some use of phosphatic iron ore, from which phosphorus is obtained as a by-product from the slag. Phosphate rock consists of the insoluble tricalcium phosphate and other materials. For use as a fertilizer, phosphate must be converted to the water soluble form, phosphoric acid (H3PO4) which has three hydrogen atoms, all of which are replaceable by a metal. Tricalcium phosphate, is converted to soluble monocalcium phosphate and to superphosphate, A fertilizer factory, typically, a large installation, characterized by large silos produces year round, but peaks with the demands of the growing season. Phosphorus has many uses other than for fertilizer. 

Irani and Callis (Ref 14) used two parameters of the distribution of ground monocalcium phosphate (which follows the commonly used log normal distribution law) namely, Mg and Og, the geometric mean diameter and the geometric standard deviation, to evaluate the precision and accuracy of electro-formed sieves vs sedimentation as a reference procedure ... 

An unusual example of a process that produces a lot of waste is the intensive rearing of pigs. They need additional phosphorus in their feed for healthy growth, and this is usually added as inorganic phosphorus in the form of monocalcium phosphate (calcium dihydroxy-oxido-oxo-phosphorane). Unabsorbed phosphorus passes through into the manure, and if spread onto fields as a fertiliser can lead to excess phosphorus run-off into rivers and lakes leading to eutrophication. 

The production of a baking powder depended on a system where the reaction could be delayed until required. In 1864 a patent was taken out to use monocalcium phosphate hydrate in making a baking powder. In 1885 sodium aluminium sulfate came to be used. This compound has a low solubility in water at ambient temperatures so it does not start to act until the product has heated up. 

Monocalcium phosphate monohydrate reacts almost as quickly as cream of tartar (potassium acid tartrate). Anhydrous monocalcium phosphate has four-fifths of the reactivity. At ambient temperatures dicalcium phosphate dihydrate, sodium aluminium phosphate and some grades of sodium acid pyrophosphate are essentially unreactive. 

Haynes RJ (1992) Relative ability of a range of crop species to use phosphate rock and monocalcium phosphate as P sources when grown in soil. J Sci Food Agric 60 205-211. doi http // dx.doi.org/10.1002/jsfa.2740600208... 

---