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Physical & Chemical properties

Vapour pressure

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Description of key information

The vapour pressure of pure formaldehyde is ca 5176 - 5186 hPa at 25°C (gas)
The vapour pressure of a 55% aqueous solution is 14 hPa at 20 °C and 92 hPa at 50 °C.
The partial pressure of formaldehyde over water is 1.2 hPa and 1.3 hPa at 20 °C for 30 % and 50 % formaldehyde in aqueous solution respectively.

Key value for chemical safety assessment

Additional information

Vapour pressure pure formaldehyde

Nine individual sources were identified containing information on the vapour pressure of pure formaldehyde.

At 25 °C the reported vapour pressures were 5186 hPa (HSDB 2015, Boublik 1984), between 5176 and 5185 hPa (Gestis 2015), 5186.24 hPa (EPA 2008) and 5176.9 hPa (SYKE 2015).

At 20 °C the reported vapour pressures were 4378 and 4420 hPa (Gestis 2015), 4378.7 hPa (Knovel 2012), between 4378 and 4420 hPa (RömppChemie 2015)

In the CRC (2010) the vapour pressure is published at various temperatures, i.e.: 5490, 2360, 846, and 13 hPa at 26.85, 1.85, -23.15 and -88.15 °C respectively.

According to the online Reaxys database (2015) citing Spence (1935) and Mali (1925) the vapour pressure at -22.3, -34.5, -91 and -109.5 °C is 885.66, 551, 13 and 0.126 hPa respectively.

In addition SYKE reports a vapour pressure at -88 °C of 13.3 hPa

Vapour pressure aqueous formaldehyde solutions

Six individual sources were identified containing information on the vapour pressure of aqueous formaldehyde solutions.

In a study from BASF (1988) the determination of the vapor pressure was carried out by a dynamic method, based on the principle of Cottrell pump. According to this study the vapour pressure of a 55% aqueous solution is 14 hPa at 20 °C and 92 hPa at 50 °C.

This data is supported by a study from Walker (1967) in which the the partial pressure of formaldehyde over water is 1.2 hPa and 1.3 hPa at 20 °C for 30 % and 50 % formaldehyde respectively. According to BASF (1974) the calculated pressure is 0.9857, 1.1322, 1.3187 hPa at 20 °C for a 30 %, 40% and 50% formaldehyde solution. In another study from BASF (1965) in which the vapor pressure was determined, the vapor pressures were 1.2 and 5.6 hPa at 20 and 40 °C respectively (partial pressure formaldehyde over water).

According to the online database Gestis (2015) is the vapour pressure 2 hPa at 20 °C.

The EPA (2008) report published a vapor pressure of 1.73 hPa at 20 °C for a 37% formaldehyde solution in water with 0.5% to 15% methanol. At 36.7 °C the reported vapor pressure is 89.3 - 117.3 hPa.