Page 192 - Geochemistry of Oil Field Waters

NITROGEN-FREE ORGANIC COMPOUNDS 179

which is found dissolved in subsurface brines (Marsden and Kawai, 1965).
The major reservoirs in which it is found are marine or lagoonal sedimentary
basins with thick sediments and of wide areal extent. Some of the associated
brines contain more than 80 mg/l of iodide, which is the only commercial
source of iodine in Japan. Some of these brines also contain dissolved
ethane, propane, isobutane, butane, isopentane, and pentane.
An interesting note is that large Soviet deposits of natural gas in a solid
state totaling about 15 trillion m3 were reported to the U.S.S.R. Committee
for Inventions and Discoveries. According to U.S.S.R. investigators, mole-
cules of ground water attract molecules of natural gas and convert them to a
hydrate, which resembles silvery-grey ice, where the pressure is 250 atm and
the temperature 25°C or less. 1 m3 of the hydrate contains up to 200 m3 of
natural gas. These solid hydrate deposits are found in permafrost zones at
depths to 2,500 m. Because of the high electrical resistance, they are
discoverable by geophysical methods. The hydrate can be converted to gas
by sinking a well and reducing the pressure and/or pumping a catalyst such
as methyl alcohol into it (Anonymous, 1970).
The solubility of the hydrocarbons benzene, toluene, o-xylene, rn-xylene,
p-xylene, naphthalene, biphenyl, diphenylmethane, and phenanthrene was
found to increase with increasing silver-ion concentration, indicating that a
slightly soluble 1-1 complex formed (Andrews and Keefer, 1949). Evidence
was obtained that two water-soluble complexes formed with silver and each
aromatic hydrocarbon tested. Potassium nitrate causes a reduction in the
solubility of aromatics in aqueous solutions (salting-out effect), but silver
nitrate increases the solubility of toluene about 73% compared to its solu-
bility in pure water. Apparently this effect with silver ions results from the
formation of n-complexes between the benzene ring and the cation.
Benzene hydrocarbons exhibit a minimum solubility in water near 18°C
which corresponds to a zero heat of solution. The actual volume occupied by
a hydrocarbon with one benzene ring in water solution apparently influences
its degree of solubility, and the larger the molecule the less soluble it is in
water (Bohon and Claussen, 1951). However, naphthalene and biphenyl,
which are larger in size and are multiring compounds, were 7 to 10 times
more soluble, indicating that some property of the benzene ring may in-
fluence the solubility. It was postulated that a positive heat of solution
resulted in the heat of cavity formation, while a negative heat of solution
resulted from the formation of icelike structures around the dissolved
hydrocarbons and/or a n-electron complex of the aromatic nucleus where
the n-electrons functioned as a base and the water as an acid. The heat of
cavitation would predominate above 18°C and would cancel the negative
heat reaction at 18°C , and below 18°C the negative heat would be larger.
A study of the effect that the salts sodium fluoride, sodium chloride,
lithium chloride, ammonium chloride, sodium iodide, cesium chloride,
tetramethylammonium bromide, etc., have upon the activity coefficient of
benzene in aqueous solutions indicates that the salting-out effect varies con-