12-4+Melamine+Introduction




 * = Melamine  ||
 * = [[image:150px-Melamine.png width="273" height="217"]] ||= [[image:file:///C:/DOCUME%7E1/com04/LOCALS%7E1/Temp/moz-screenshot-2.png]][[image:Melamine-3D-balls.png width="240" height="214"]] ||
 * IUPAC name

Other names

Molecular formula

Molar mass

Appearance

Density

Melting point

Boiling point

Solubility in water ||= 1,3,5-Triazine-2,4,6-triamine 2,4,6-Triamino-s-triazine Cyanurotriamide Cyanurotriamine Cyanuramide

C3H6N6

126.12 g/mol

White solid

1574 kg/m3

345 °C, 618 K, 653 °F (decomposition)

Sublimes

3.240 g/l (20 °C) || **Melamine** is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses. Melamine is also a metabolite of cyromazine, a pesticide. It is formed in the body of mammals who have ingested cyromazine. It has been reported that cyromazine can also be converted to melamine in plants. Melamine combines with cyanuric acid and related compounds to form melamine cyanurate and related crystal structures, which have been implicated as contaminants or biomarkers in Chinese protein adulterations.

Etymology
The German word //melamin// was coined by combining the names of 2 other chemical products: Melam (a distillation derivative of ammonium thiocyanate) and Amine.

Uses
Melamine is combined with formaldehyde to produce <span class="wiki_link_ext">melamine resin, a very durable <span class="wiki_link_ext">thermosetting plastic used in <span class="wiki_link_ext">Formica , and <span class="wiki_link_ext">melamine foam , a <span class="wiki_link_ext">polymeric cleaning product. The end products include countertops, <span class="wiki_link_ext">dry erase boards, fabrics, <span class="wiki_link_ext">glues , housewares, guitar saddles, guitar nuts, and flame retardants. Melamine is one of the major components in Pigment Yellow 150, a colorant in inks and plastics. Melamine also enters the fabrication of melamine poly-sulfonate used as <span class="wiki_link_ext">superplasticizer for making high-resistance <span class="wiki_link_ext">concrete. Sulfonated <span class="wiki_link_ext">melamine formaldehyde (SMF) is a polymer used as <span class="wiki_link_ext">cement admixture to reduce the water content in concrete while increasing the fluidity and the workability of the mix during its handling and pouring. It results in concrete with a lower porosity and a higher mechanical strength exhibiting an improved resistance to aggressive environments and a longer life-time. The use of melamine as fertilizer for crops had been envisaged during the '50s and '60s because of its high nitrogen content (2/3). However melamine is much more expensive to produce than other common nitrogen fertilizers, such as <span class="wiki_link_ext">urea. To be effective as a fertilizer, it is essential that the plant nutrients are released or made available in a manner that matches the needs of the growing crop. The nitrogen mineralization process for melamine is extremely slow, making this product both economically and scientifically impractical for use as a fertilizer. Melamine derivatives of <span class="wiki_link_ext">arsenical drugs are potentially important in the treatment of African <span class="wiki_link_ext">trypanosomiasis. Melamine use as <span class="wiki_link_ext">non-protein nitrogen (NPN) for cattle was described in a 1958 patent. In 1978, however, a study concluded that melamine "may not be an acceptable non-protein N source for ruminants" because its <span class="wiki_link_ext">hydrolysis in cattle is slower and less complete than other nitrogen sources such as <span class="wiki_link_ext">cottonseed meal and urea. Melamine is sometimes illegally added to food products in order to increase the apparent protein content. Standard tests such as the <span class="wiki_link_ext">Kjeldahl and <span class="wiki_link_ext">Dumas tests estimate protein levels by measuring the nitrogen content, so they can be misled by adding nitrogen-rich compounds such as melamine.

Synthesis
Melamine was first synthesized by the German chemist <span class="wiki_link_ext">Justus von Liebig in 1834. In early production, first <span class="wiki_link_ext">calcium cyanamide is converted into <span class="wiki_link_ext">dicyandiamide, then heated above its melting temperature to produce melamine. However, today most industrial manufacturers use <span class="wiki_link_ext">urea in the following reaction to produce melamine: ** 6 (NH2)2CO → C3H6N6 + 6 NH3 + 3 CO+ ** It can be understood as two steps. First, urea decomposes into <span class="wiki_link_ext">cyanic acid and ammonia in an <span class="wiki_link_ext">endothermic reaction :
 * (NH2)2CO → HCNO + NH3 **

Then, cyanic acid polymerizes to form melamine and carbon dioxide: ** 6 HCNO → C3H6N6 + 3 CO2 ** The second reaction is <span class="wiki_link_ext">exothermic but the overall process is endothermic. The above reaction can be carried out by either of two methods: <span class="wiki_link_ext">catalyzed gas-phase production or <span class="wiki_link_ext">high pressure liquid-phase production. In one method, molten urea is introduced onto a <span class="wiki_link_ext">fluidized bed with catalyst for reaction. Hot <span class="wiki_link_ext">ammonia gas is also present to fluidize the bed and inhibit deammonization. The effluent then is cooled. Ammonia and <span class="wiki_link_ext">carbon dioxide in the off-gas are separated from the melamine-containing slurry. The slurry is further concentrated and crystallized to yield melamine. Major manufacturers and licensors such as <span class="wiki_link_ext">DSM, <span class="wiki_link_ext">BASF , and <span class="wiki_link_ext">Eurotecnica have developed some proprietary methods. The off-gas contains large amounts of ammonia. Therefore melamine production is often integrated into urea production which uses ammonia as feedstock. Crystallization and washing of melamine generates a considerable amount of waste water, which is a pollutant if discharged directly into the environment. The waste water may be concentrated into a solid (1.5–5% of the weight) for easier disposal. The solid may contain approximately 70% melamine, 23% oxytriazines (<span class="wiki_link_ext">ammeline, <span class="wiki_link_ext">ammelide , and <span class="wiki_link_ext">cyanuric acid ), 0.7% polycondensates (<span class="wiki_link_ext">melem , <span class="wiki_link_ext">melam , and <span class="wiki_link_ext">melon ). In the <span class="wiki_link_ext">Eurotecnica process, however, there is no solid waste and the contaminants are decomposed to <span class="wiki_link_ext">ammonia and <span class="wiki_link_ext">carbon dioxide and sent as off gas to the upstream <span class="wiki_link_ext">urea plant; accordingly, the waste water can be recycled to the melamine plant itself or used as clean cooling water make-up.
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