Physical/Chemical Properties of Petroleum Hydrocarbons Relating to Groundwater Contamination

Chemical Composition

petroleum products are characterized by:

boiling range
carbon number

gasoline

volatile hydrocarbons (boiling points between 36 and 173° C)
principal components
branched chain paraffins (alkanes)
cycloparaffins (cycloalkanes)
aromatics (e.g., BTX = benzene, toluene, xylene)
composition varies with source

diesel (Number 2 fuel oil)

flash points between 110 and 190° C
principal components
unbranched paraffins (staight chain alkanes)
low amounts of aromatic compounds

Physical Properties

physical form and density (e.g., alkane chains)

<17 carbons -> liquids with density < water (1)
>18 " solids -> (20°C) waxes

solubilities decrease as C number increases

pentane (C=5) solubility = 360 ppm (20C)
hexane (C=6) " = 13 "
decane (C=9) " = 0.009 "

vapor pressures decrease as C number increases

methane (C=1) gas @ 20°C
ethane (C=2) "
propane (C=3) "
butane (C=4) "
pentane (C=5) liquid @ 20°C (vp = 430 mm Hg)
hexane (C=6) " (vp = 120 " ")
decane (C=10) " (vp = 3 " ")

BTX ( most important petroleum hydrocarbon contaminants)

benzene solubility =1780 ppm & vp = 76 mm Hg @ 20°C
toluene 515 22
xylene " 175 to 198 6

 

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