The 30-40% aqueous solution of formaldehyde (methanal) is called formalin and has the chemical formula HCHO.
The raw material for formalin production is methanol which produced from natural gas at high temperature (260°C) and high pressure (100 atm pressure). Methanol is then passed through evaporator and is evaporated. This vaporized methanol is mixed with air and passed through a catalyst chamber in which methanal is produced. This methanal gas is dissolved in water of an absorbing tower and 30-40% aqueous solution of methanal, i.e., formalin is produced which is collected at the lower portion of the absorbing tower. Unused methanol vapor is again passed to the evaporator for re-production through a condenser.
Flow-diagram for the manufacture of formalin