PROPANE

H3C CH3 CASRN: 74-98-6; DOT: 1978; DOT label: Flammable gas; molecular formula: C3H8; FW: 44.10; RTECS: TX2275000; Merck Index: 12, 7982 Physical state, color, and odor: Colorless, very flammable gas with a characteristic odor. Usually shipped as a compressed liquid in inexpensive container. An odor threshold concentration of 1,500 ppmv was reported by Nagata and Takeuchi (1990). Melting point (°C): -189.7 (Weast, 1986) Boiling point (°C): -42.1 (Weast, 1986) Density (g/cm3): 0.505 at 20 °C (Chevron Phillips, 2005) Diffusivity in water (x 10-5 cm2/sec): 1.16 at 25 °C (quoted, Hayduk and Laudie, 1974) Dissociation constant, pKa: ≈ 44 (Gordon and Ford, 1972) Flash point (°C): -105 (Hawley, 1981) Lower explosive limit (%): 2.1 (NIOSH, 1997) Upper explosive limit (%): 9.5 (NIOSH, 1997) Heat of fusion (kcal/mol): 0.842 (Dean, 1987) Henry’s law constant (atm⋅m3/mol): 0.706 at 25 °C (Hine and Mookerjee, 1975) Ionization potential (eV): 10.94 (Lias, 1998) 11.12 (Svec and Junk, 1967) Soil organic carbon/water partition coefficient, log Koc: Unavailable because experimental methods for estimation of this parameter for aliphatic hydrocarbons are lacking in the documented literature

ow 2.36 (Hansch et al., 1975) Solubility in organics (vol %): Alcohol (790 at 16.6 °C and 754 mmHg), benzene (1,452 at 21.5 °C and 757 mmHg), chloroform (1,299 at 21.6 °C and 757 mmHg), ether (926 at 16.6 °C and 757 mmHg), and turpentine (1,587 at 17.7 °C and 757 mmHg) (Windholz et al., 1983). Solubility in water: 62.4 mg/kg at 25 °C (shake flask-GC, McAuliffe, 1963, 1966) At 0 °C, 0.0394 vol/unit volume of water at 19.8 °C (Claussen and Polglase, 1952) 1.50 mM at 25 °C (shake flask-GC, Barone et al., 1966) 3.46, 1.53, and 0.84 mM at 4, 25, and 50 °C, respectively (Kresheck et al., 1965) Vapor density: 2.0200 g/L at 0 °C, 1.8324 g/L at 25 °C (Windholz et al., 1983) 1.52 (air = 1) Vapor pressure (mmHg): 7,904 at 27.6 °C (Francis and Robbins, 1933) 6,460 at 20 °C, 8,360 at 30 °C (quoted, Verschueren, 1983) Environmental fate: Biological. In the presence of methane, Pseudomonas methanica degraded propane to 1propanol, propionic acid, and acetone (Leadbetter and Foster, 1959). The presence of carbon dioxide was required for “Nocardia paraffinicum” to degrade propane to propionic acid (MacMichael and Brown, 1987). Propane may biodegrade in two pathways. The first is the formation of propyl hydroperoxide, which decomposes to 1-propanol followed by oxidation to propanoic acid. The other pathway involves dehydrogenation to 1-propene, which may react with water giving propanol (Dugan, 1972). Microorganisms can oxidize alkanes under aerobic conditions (Singer and Finnerty, 1984). The most common degradative pathway involves the oxidation of the terminal methyl group forming the corresponding alcohol (1-propanol). The alcohol may undergo a series of dehydrogenation steps forming an aldehyde (propionaldehyde), then a fatty acid (propionic acid). The fatty acid may then be metabolized by β-oxidation to form the mineralization products carbon dioxide and water (Singer and Finnerty, 1984). Photolytic. When synthetic air containing propane and nitrous acid was exposed to artificial sunlight (λ = 300-450 nm), propane photooxidized to acetone with a yield of 56% (Cox et al., 1980). The rate constants for the reaction of propane and OH radicals in the atmosphere at 298 and 300 K were 1.11 x 10-12 cm3/molecule⋅sec (DeMore and Bayes, 1999) and 1.3 x 10-12 cm3/molecule⋅sec (Hendry and Kenley, 1979). Cox et al. (1980) reported a rate constant of 1.9 x 10-12 cm3/molecule⋅sec for the reaction of gaseous propane with OH radicals based on a value of 8 x 10-12 cm3/molecule⋅sec for the reaction of ethylene with OH radicals. Chemical/Physical. Incomplete combustion of propane in the presence of excess hydrogen chloride resulted in a high number of different chlorinated compounds including, but not limited to alkanes, alkenes, monoaromatics, alicyclic hydrocarbons, and polynuclear aromatic hydrocarbons. Without hydrogen chloride, 13 nonchlorinated polynuclear aromatic hydrocarbons were formed (Eklund et al., 1987). Complete combustion in air yields carbon dioxide and water. Exposure limits: NIOSH REL: TWA 1,000 ppm (1,800 mg/m3), IDLH 2,100 ppm; OSHA PEL: TWA 1,000 ppm (1,800 mg/m3); ACGIH TLV: TWA 2,500 ppm (adopted).