volatility

This article covers the physical property. For other meanings of the same name, see Volatility (disambiguation) .

Volatility (also volatility or evaporation number ) is a dimensionless relative number that describes the evaporation of a solvent .

Evaporation rate

By definition , volatility is given as the ratio of the vapor pressure of the substance in question to the vapor pressure of the highly volatile reference substance diethyl ether (this at 20  ° C and 65 ± 5% relative humidity ):

${\displaystyle {\text{Flüchtigkeit}}={\frac {p_{\text{betrachtet}}}{p_{\text{Diethylether}}}}}$

In Germany, the evaporation rate (VD) is determined according to DIN 53170. The time it takes for a substance to completely evaporate (evaporation time = VDZ) is related to the time it takes diethyl ether to evaporate.

${\displaystyle {\text{VD}}={\frac {VDZ_{\text{betrachtet}}}{VDZ_{\text{Diethylether}}}}}$

A high evaporation rate means relatively slow evaporation, i.e. low volatility. A small evaporation number means faster evaporation, i.e. a relatively high volatility.

Examples of the evaporation rates of solvents (for diethyl ether = 1)

solvent	Evaporation rate
Butyl diglycol	> 1200
2-butoxyethyl acetate	250
Butyl glycol	163
N -methyl pyrrolidone	095
water	080
Test petrol 145-200 (K30)	035
Xylene	017th
1-butanol	033
1-methoxy-2-propanol	028
Butyl acetate (acetic acid n- butyl ester)	011
Ethanol	008.3
Methyl isobutyl ketone	007th
acetone	002
Hexane	001.4

Evaporation rate

In the USA, the evaporation rate (E) is determined over time and in relation to butyl acetate .

${\displaystyle {\text{Flüchtigkeit}}={\frac {t_{\text{90 (Butylacetat)}}}{t_{\text{90 (betrachtet)}}}}}$

with = time, up to 90% of the sample has evaporated. ${\displaystyle t_{\mathrm {90} }}$

Examples of the evaporation rates of solvents (for butyl acetate = 1)

solvent	Evaporation rate
Methyl ethyl ketone	3.8
acetone	5.6
Hexane	8.3
Ethanol, 95%	3.8
naphtha	1.4
Xylene	0.6
2-methyl-1-propanol	0.6
water	0.3
White spirit	0.1

Classification of solvents according to volatility

Comparison of different classifications

In Germany		In the USA
Classification	Evaporation rate	Classification	evaporation rate
very difficult to volatilize	> 50	slow evaporation	<0.8
not very volatile	35… 50	medium evaporation	0.8 ... 3.0
medium volatile	10 ... 35	rapid evaporation	> 3.0
volatile	<10

See also

• relative volatility
• Volatile Organic Compounds (VOCs)
• Volatile and non-volatile acids in wine

Individual evidence

1. ↑ ^{a b} Brock, Groteklaes, Mischke: Textbook of paint technology . Vincentz, Hannover 2000, ISBN 3-87870-569-7 , p. 100 ( limited preview in Google Book search).
2. ↑ ^{a b} MSDS Glossary: ​​Evaporation Rate. Retrieved October 3, 2013 .