Melamine (chemical formula: C3H6N6), commonly known as melamine, protein extract, IUPAC named "1,3, 5-triazine-2,4, 6-triamino-melamine", is a triazine nitro-containing heterocyclic organic compound used as a chemical raw material. It is a white monoclinic crystal, almost odorless, slightly soluble in water (3.1g/L at room temperature), soluble in methanol, formaldehyde, acetic acid, hot glycol, glycerin, pyridine, etc., insoluble in acetone, ether, harmful to the body, can not be used for food processing or food additives. However, recently in Qinghai, Gansu, Jilin and other provinces, melamine milk powder exceeded the standard by more than 500 times. It is likely that the "Sanlu problem milk powder" that has not been completely destroyed is processed and sold.
Substance definition
Chinese Pinyin: s ana ju qing an Melamine (English name: Melamine) is a triazine molecular diorama
Nitrogen containing heterocyclic organic compounds, important nitrogen heterocyclic organic chemical raw materials. Referred to as triamine, commonly known as melamine, protein essence, also known as 2,4, 6-triamino-1,3, 5-triazine, 1,3, 5-triazine-2,4, 6-triamine, 2,4, 6-triaminourea, melamine, cyanamide triamide. More English names: 1,3, 5-triazine-2,4,6-triamine; 2,4, 6-triamino-1,3,5-triazine; 2,4, 6-triamino-s-triazine; Aero; Cyanuramide; Cyanuric triamide; Cyanurotriamide; Cyanurotriamine; DG 002 (amine); Hicophor PR; Isomelamine; Melamine; NCI-C50715; Pluragard; Pluragard C 133; s-Triazine, 2,4,6-triamino-; Teoharn; Theoharn; Virset 656-4;
Molecular structure
Chemical formula (molecular formula) C3H6N6 Molecular weight 126.15 CAS login number 108-78-1 EINECS login number
Physical property
Melamine is pure white monoclinic crystal, odorless, density 1.573g/cm3 (16℃). Atmospheric melting point 354℃, rapid heating decomposition; Rapid heating sublimation, sublimation temperature 300℃. Solubility in water increases with the increase of temperature, at 20℃, about 3.3 g/L, that is, slightly soluble in cold water, soluble in hot water, very slightly soluble in hot ethanol, insoluble in ether, benzene and carbon tetrachloride, soluble in methanol, formaldehyde, acetic acid, hot glycol, glycerol, pyridine and so on.
Chemical property
Non-combustible and stable at room temperature. It is weakly alkaline (pH =8), and can form melamine salts with hydrochloric acid, sulfuric acid, nitric acid, acetic acid, oxalic acid, etc. In the neutral or slightly alkaline case, condensation with formaldehyde to form a variety of hydroxymethyl melamine, but in the slightly acidic (pH 5.5 ~ 6.5) and hydroxymethyl derivatives of polycondensation reaction to produce resin products. In case of hydrolysis of strong acid or strong base aqueous solution, the amine group is gradually replaced by the hydroxyl group, which becomes a cyanuric acid diamide, further hydrolysis to cyanuric acid monoamide, and finally cyanuric acid.
Synthesis technology
Melamine was first synthesized by Liebig in 1834, and the early synthesis used dicyandiamide method: calcium cyanamide (CaCN2) was prepared from calcium carbide (CaC2), and calcium cyanamide dimerized after hydrolysis to produce dicyandiamide, and then heated and decomposed to produce melamine. At present, due to the high cost of calcium carbide, dicyandiamide method has been eliminated. Compared with this method, urea method has low cost and is widely used at present. Urea with ammonia as the carrier, silica gel as the catalyst, boiling reaction at 380-400℃ temperature, first decomposition to cyanic acid, and further condensation to produce melamine. The reaction formula is: 6 CO (NH2)2 → silica gel, high temperature C3H6N6 + 6 NH3↑ + 3 CO2↑ The generated melamine gas is cooled and captured to obtain crude products, and then dissolved, remove impurities, recrystallization to obtain finished products. Urea method for the production of melamine consumes about 3800kg of urea and 500kg of liquid ammonia per ton of products.
Process classification
According to different reaction conditions, melamine synthesis process can be divided into high pressure method (7-10MPa, 370-450℃, liquid phase), low pressure method (0.5-1MPa, 380-440℃, liquid phase) and atmospheric pressure method (<0.3MPa, 390℃, gas phase) three categories. Most foreign melamine production processes are named after technology development companies, Such as Germany's BASF Process (BASF Process), Austria's Linz Process (Chemical Linz Process), Lurgi process (Lurgi Process), the United States Allied Signal Chemical company chemical law (Allied Signal) Chemical, the Nissan Process in Japan, Stamicabang in the Netherlands. Both DSM method) and so on. According to the different synthetic pressure, these production processes can be basically divided into three processes: high pressure method, low pressure method and normal pressure method. At present, the world's advanced technology and strong competitiveness are mainly Japan's new Nissan method and Italy's Allied-Eurotechnica high pressure method, the Netherlands DSM low pressure method and Germany BASF atmospheric pressure method. Melamine production enterprises in China mostly use semi-dry atmospheric pressure process, which uses urea as raw material below 0.1MPa, about 390℃, with silica gel as a catalyst to synthesize melamine, and make melamine crystallize in the condensate, and the crude product is dissolved, filtered and crystallized into finished products.
