Higher-Boiling Constituents

Naphthalene and its homologs are less acutely toxic than benzene but are more prevalent for a longer period during oil spills. The toxicity of different crude oils and refined oils depends not only on the total concentration of hydrocarbons but also the hydrocarbon composition in the water-soluble fraction (WSF) of petroleum, water solubility, concentrations of individual components, and toxicity of the components. The water-soluble fractions prepared from different oils wiU vary in these parameters. Water-soluble fractions (WSFs) of refined oils (e.g.. No. 2 fuel oil and bunker C oil) are more toxic than water-soluble fraction of crude oil to several species of fish (killifish and salmon). Compounds with either more rings or methyl substitutions are more toxic than less substituted compounds, but tend to be less water soluble and thus less plentiful in the water-soluble fraction. 

Among the polynuclear aromatic hydrocarbons, the toxicity of petroleum is a function of its di- and triaromatic hydrocarbon content. Like the single aromatic 

There are indications that pure naphthalene (a constituent of mothballs, which are, by definition, toxic to moths) and alkylnaphthalenes are from three to 10 times more toxic to test animals than are benzene and alkylbenzenes. In addition, and because of the low water solubility of tricyclic and polycyclic (polynuclear) aromatic hydrocarbons (i.e., those aromatic hydrocarbons heavier than naphthalene), these compounds are generally present at very low concentrations in the water-soluble fraction of oil. Therefore, the results of this smdy and others conclude that the soluble aromatics of crude oil (such as benzene, toluene, ethylbenzene, xylenes, and naphthalenes) produce the majority of its toxic effects in the enviromnent. 

The dynamics of oil-in-water dispersion (OWD) are complex and have relevance related to potential toxicity or hazard. In comparing the toxicides to marine animals of oil-in-water dispersions prepared from different oils, not only the amount of oil added but also the concentrations of oil in the aqueous phase and the composition and dispersion-forming characteristics of the parent oil must be taken into consideration. In comparing the potential impacts of spills of different oils on the marine biotic community, the amount of oil per unit water volume required to cause mortality is of greater importance than any other aspect of the crude oil behavior. 

Mixtures of polynuclear aromatic hydrocarbons are often carcinogenic and possibly phototoxic. One way to approach site-specific risk assessments would 

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Currently, the preferred method for the analysis of liquefied petroleum gas, and indeed for most petroleum-related gases, is gas chromatography (ASTM D2163 IP 264). This technique can be used for the identification and measurement of both primary and trace constituents. However, there may be some accuracy issues that arise in the measurement of the higher-boiling constituents due to relative volatility under the conditions in which the sample is held. 

The development of distillation columns with rotating elements, described by Baker et al. (5) and Willingham et al. (70), indicates a trend which probably will be followed in future developments to reduce the time required to reach equilibrium and hence the time for an efficient fractionation. Hickman s (27) type of molecular distillation will certainly acquire increasing importance for analytical uses as one becomes more concerned with the higher boiling constituents. 

DEPHLEGMATION. Partial condensation of vapor from a distillation operation to produce a liquid richer in higher-boiling constituents than the original vapor. The residual vapor is richer in the lower boiling constituents. 

The problems encountered in processing the heavy feedstocks can be directly equated to the amount of complex, higher-boiling constituents in the residual portion of the oil. Refining these feedstocks is not just a matter of applying know-how derived from refining conventional crude oils but requires knowledge of the composition of these more complex feedstocks. 

Smith studied the effect of boiling point differences of various cuts of hexane on miscella (218). Smith also determined the vapor pressure of hexane-soybean oil solutions at high solvent concentrations (211). When making stripping calculations, one should be aware that the last portions of solvent to vaporize consist of higher boiling constituents in that particular cut of solvent. 

In addition to other gases, liquefied petroleum gas may also be contaminated by higher-boiling constituents such as the constituents of middle distillates to lubricating oil. These contaminants become included in the gas during handling and must be prevented from reaching unacceptable levels. Olefins and especially diolefins are prone to polymerization and should be removed. 

The general appearance, or color, of diesel fuel is a useful indicator against contamination by residual (higher boiling) constituents, water, or fine solid particles. Therefore, it is necessary to make a visual inspection that clear fuel is being delivered (ASTM D-4176). 

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