Formalin is the name given to the 37% concentrated solution of formaldehyde gas in water. Since it is not safe to transport formaldehyde in gaseous form, it is transported and stored in aqueous solution. Since formaldehyde can form short paraformaldehyde polymer chains in formalin, some methanol is added to it. Formalin contains a very small amount of formaldehyde monomer. Since formaldehyde reacts with water, most of the formaldehyde solution is in the form of methanediol .
Paraformaldehyde is formed when water evaporates from formalin under reduced pressure and separates. It is a polymer, a white solid with the formula HO(CH2O)xH (x is about 30). When this polymer is heated, it turns into gaseous formaldehyde. Therefore, gas is a suitable source for obtaining formaldehyde.
|Formaldehyde concentration||Min 37% by wt.|
|Methanol content||2-10% by wt.|
|PH||2.5 – 4.2|
|Storage life at 35-45 C||6 months|