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Manufacture, Importation and Use

1. Manufacture

Formaldehyde is manufactured in Australia by catalytic oxidation of methanol. Two methods are used; one uses a silver catalyst and the other a metal oxide catalyst. As formaldehyde is produced in gas form, it is absorbed into water during manufacture. The aqueous solutions are called formalin and the concentrations of formaldehyde in formalin range from 37% to 54%. Four companies manufacture formaldehyde at five sites around Australia. Information on the location of the plants, manufacturing techniques and the formaldehyde concentrations in formalin produced are summarised in Table 7.1.

Company	Location	State	Manufacture technique	% Formaldehyde in formalin
Woodchem	Oberon	NSW	Metal oxide catalyst	37
Orica	Deer Park	VIC	Metal oxide catalyst	54
Hexion	Laverton	VIC	Silver catalyst	54
Hexion	Gibson Island	QLD	Silver catalyst	50
Dynea	Dardanup	WA	Silver catalyst	37

Some manufacturers also dilute the 50% and 54% formalin to as low as 26% for use or sale.

Manufacturing process

Formaldehyde manufacture involves a series of continuous, enclosed processes designed to facilitate the oxidation of methanol over a catalyst. The processes for the two manufacturing methods used in Australia are similar and are shown in Figure 7.2.

Figure 7.1: Quantities of formaldehyde manufacture in Australia

70
60

tonnes x 1000

50
40
30
20
10
0

2000 2001 2002 Mean

Year

Figure 7.2: Formaldehyde manufacturing process

Raw materials used in formaldehyde manufacture are methanol, water, air and catalysts. Liquid methanol is fed into a vaporising chamber where it is mixed with water and air (oxygen). The contents of the chamber are maintained at a desired temperature range through the addition of steam. The vaporised methanol is then directed to the top of an exothermic reaction chamber. The reaction generates heat that is used to sustain the temperature of the catalyst and generate steam for use in resin manufacture. Hot gaseous formaldehyde is cooled as it exits the reaction chamber. It is then passed to absorption towers where formaldehyde is absorbed into recirculating water. By careful control of temperature and/or flows into the absorber tower the required concentration of formalin is achieved in the base of the tower. Formalin is then passed through a distillation tower where any remaining methanol is removed. Decanting of formalin is via pump and closed pipe system to either storage tanks on site or loaded to tankers or drums for road transport.
Most of the gas exiting the top of the absorber tower is recycled through the process again. This lowers the oxygen level of the gas stream so that it can be maintained below the explosive range for the methanol/air mix. Exhaust gases pass over a catalytic converter to minimise emissions of formaldehyde, methanol and by-products that remain. The whole manufacturing process is controlled by a computer system operated by workers in a control room.
The metal oxide process involves the oxidation of vaporised methanol using air whereas the silver catalyst process involves partial oxidation and dehydrogenation of vaporised methanol in air using steam and granulated silver. Table 7.2 shows the similarities and differences between these two manufacturing techniques.
Table 7.2: Comparison between silver catalyst process and metal oxide process (Kroschwitz & Howe-Grant, 1994; IARC, 1995)

Metal oxide process Silver catalyst process No. of reactions One Two
Reaction type Exothermic Exothermic (overall) Exothermic (50-60%)

Endothermic (40-50%)

Reaction CH₃OH + ½O₂ →HCHO + H₂O

∆H = -156 kJ (-37.28 kcal)

1. 
   CH₃OH + ½O₂ →HCHO + H₂O
   

∆H = -156 kJ (-37.28 kcal)



Temperature in reaction chamber

2. 
   CH₃OH →HCHO + H₂₇
   

∆H = +85 kJ (20.31 kcal)
270-370^oC 500-700^oC

Pressure Atmospheric Atmospheric

By-products formed

Carbon monoxide Dimethyl ether Carbon dioxide Formic acid

Carbon monoxide Carbon dioxide Methyl formate Formic acid Hydrogen

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