Benzene Emissions Factors - Office of Air Quality Planning and Standards, U.S. - Gulf Oil Spill Danger For Coastal States

3.1 NATURE OF POLLUTANT
Benzene is a clear, colorless, aromatic hydrocarbon that has a characteristic
sickly sweet odor. It is both volatile and flammable. Chemical identification information for
benzene is found in Table-3-1. Selected physical and chemical properties of benzene are
presented in Table 3-2 .4-7
Benzene contains 92.3 percent carbon and 7.7 percent hydrogen (by mass). The
benzene molecule is represented by a hexagon formed by six sets of carbon and hydrogen
atoms bonded together with alternating single and double bonds.
3-2
TABLE 3-1. CHEMICAL IDENTIFICATION OF BENZENE
Chemical Name Benzene
Synonyms Benzol, phenyl hydride, coal naphtha,
phene, benxole, cyclohexatriene
Molecular formula C H 6 6
Identification numbersa
CAS Registry 71-43-2
NIOSH RTECS CY 1400000
DOT/UN/NA UN 1114; Benzene (Benzol)
DOT Designation Flammable liquid
Source: References 4 and 5.
a Chemical Abstract Services (CAS); National Institute of Occupational Safety and Health (NIOSH); Registry of
Toxic Effects of Chemical Substances (RTECS); Department of Transportation/United Nations/North American
(DOT/UN/NA).
The chemical behavior of benzene indicates that the benzene molecule is more realistically
represented as a resonance-stabilized structure:
in which the carbon-to-carbon bonds are identical. The benzene molecule is the cornerstone
for aromatic compounds, all of which contain one or more benzene rings.8
Because of its resonance properties, benzene is highly stable for an unsaturated
hydrocarbon. However, it does react with other compounds, primarily by substitution and, to
a lesser degree, by addition. Some reactions can rupture the molecule or result in other groups
cleaving to the molecule. Through all these types of reactions, many commercial chemicals
are produced from benzene.8 The most common commercial grade of benzene contains 50 to
3-3
TABLE 3-2. PHYSICAL AND CHEMICAL PROPERTIES OF BENZENE
Property Value
Molecular weight 0.17 lbs (78.12 g)
Melting point 41.9(F (5.5(C)
Boiling point at 1 atmosphere (760 mm Hg) 176.18(F (80.1(C)
Density, at 68(F (20(C) 0.0141 lb/ft3 (0.8794 g/cm3)
Physical state (ambient conditions) Liquid
Color Clear
Odor Characteristic
Viscosity (absolute) at 68(F (20(C) 0.6468 cP
Surface tension at 77(F (25(C) 0.033 g/cm3 (28.18 dynes/cm3)
Heat of vaporization at 176.18(F (80.100(C) 33.871 KJ/Kg·mol (8095 Kcal/Kg·mol)
Heat of combustion at constant pressure and 41.836 KJ/g (9.999 Kcal/g)
77(F (25(C) (liquid C H to liquid H O and 6 6 2
gaseous CO ) 2
Odor threshold 0.875 ppm
Solubility:
Water at 77(F (25(C) Very slightly soluble (0.180 g/100 mL,
1800 ppm)
Organic Solvents Soluble in alcohol, ether, acetone, carbon
tetrachloride, carbon disulfide, and acetic
acid
Vapor pressure at 77(F (25(C) 95.2 mm Hg (12.7 kPa)
Auto ignition temperature 1044(F (562(C)
Flashpoint 12(F (-11.1(C) (closed cup)
Conversion factors (Vapor weight to volume) 1 ppm = 319 mg/m3 at 77(F (25(C);
1 mg/L = 313 ppm
Source: References 4, 5, 6, and 7.
3-4
100 percent benzene, the remainder consisting of toluene, xylene, and other constituents that
distill below 248(F (120(C).4
Laboratory evaluations indicate that benzene is minimally photochemically
reactive in the atmosphere compared to the reactivity of other hydrocarbons. Reactivity can be
determined by comparing the influence that different hydrocarbons have on the oxidation rate
of nitric oxide (NO) to nitrogen dioxide (NO ), or the relative degradation rate of various 2
hydrocarbons when reacted with hydroxyl radicals (OH), atomic oxygen or ozone. For
example, based on the NO oxidation test, the photochemical reactivity rate of benzene was
determined to be one-tenth that of propylene and one-third that of n-hexane.9
Benzene shows long-term stability in the atmosphere.8 Oxidation of benzene
will occur only under extreme conditions involving a catalyst or elevated temperature or
pressure. Photolysis is possible only in the presence of sensitizers and is dependent on
wavelength absorption. Benzene does not absorb wavelengths longer than 1.1x10-5 inches (in)
(275 nanometers [nm]).8
In laboratory evaluation, benzene is predicted to form phenols and ring cleavage
products when reacted with OH, and to form quinone and ring cleavage products when reacted
with aromatic hydrogen.6 Other products that are predicted to form from indirect reactions
with benzene in the atmosphere include aldehydes, peroxides, and epoxides. Photodegradation
of NO produces atomic oxygen, which can react with atmospheric benzene to form phenols.

My Last Attempt... I hope the NFO gets out there...