Petroleum Hydrocarbons and Fuel Additives

There are different approaches to estimating the toxicity of various PHs. One method is to examine the known individual compounds in each PH fraction, based on the data collected for a limited number of compounds and assuming the known materials are representative of the entire mixture. A second method is to divide the mixture into several fractions that contain substances with similar chemical and physical properties, which therefore are considered to have comparable toxicity. A third approach is to consider the entire mixture. The actual content of each mixture depends mainly on the origin of the PH and the distillate fractions. 

The direct exposure pathways of humans to PH following a leak are described in Fig. 4.8. Once released to the surface and subsurface environment, PHs can reach humans directly as vapors, solutes, or adsorbed on particles. 

Hexane represents the aliphatic group. Most of the aliphatic compounds are branched, bnt the same trend of low solubility that decreases with increasing C nnmber is typical of all snbstances in this gronp. Due to their very low solubility, these compounds hardly partition to water and migrate mainly as vapors, as a separate phase, or adsorbed on particnlate matter. In very high concentrations (thousands of ppm), hexane is a lethal narcotic to humans (HCN 2005). High-level exposnre affects several enzyme fnnctions, which lead to increased liver weight. No data on octane toxicity are available, and it is considered nontoxic. 

In general, becanse of the combination of solubility and toxicity characteristics, aromatic componnds are the major group of PH contaminants in groundwater. However, dne to the large amounts of PH released to the environment and lack of information, mnch more research is needed to understand the behavior and toxicity of these complex mixtnres and their potential effect on the subsurface environment. 

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Table 5 Solubilities and other properties of select petroleum hydrocarbons and fuel additives. 

Mixtures constitute a category of solvents produced by distillation and cracking of petroleum. The group includes gasoline, petroleum ether, rubber solvent, petroleum naphtha, mineral spirits, white spirits, Stoddard solvent, kerosene, and jet fuels (Lilis 1992). Gasolines are mixtures of alkanes, cycloalkanes, alkenes, aromatic hydrocarbons, and antiknock additives. 

Shale Oil. In the United States, shale oil, or oil derivable from oil shale, represents the largest potential source of Hquid hydrocarbons that can be readily processed to fuel Hquids similar to those derived from natural petroleum. Some countries produce Hquid fuels from oil shale. There is no such industry in the United States although more than 50 companies were producing oil from coal and shale in the United States in 1860 (152,153), and after the oil embargo of 1973 several companies reactivated shale-oil process development programs (154,155). Petroleum supply and price stabiHty has since severely curtailed shale oil development. In addition, complex environmental issues (156) further prohibit demonstration of commercial designs. 

In the lightening of petroleum hydrocarbon oil, esters of mercaptocarboxyhc acids can modify radical behavior during the distillation step (58). Thioesters of dialkanol and trialkanolamine have been found to be effective multihinctional antiwear additives for lubricants and fuels (59). Alkanolamine salts of dithiodipropionic acid [1119-62-6] are available as water-soluble extreme pressure additives in lubricants (60). 

Fuel modification in terms of volatility, hydrocarbon types, or additive content. Some of the fuels currently being used are liquefied petroleum gas (LPG), liquefied natural gas (LNG), compressed natural gas (CNG), fuels with alcohol additives, and unleaded gasoline. The supply of some of these fuels is very limited. Other fuel problems involving storage, distribution, and power requirements have to be considered. 

NMHC. A large number of hydrocarbons are present in petroleum deposits, and their release during refining or use of fuels and solvents, or during the combustion of fuels, results in the presence of more than a hundred different hydrocarbons in polluted air (43,44). These unnatural hydrocarbons join the natural terpenes such as isoprene and the pinenes in their reactions with tropospheric hydroxyl radical. In saturated hydrocarbons (containing all single carbon-carbon bonds) abstraction of a hydrogen (e,g, R4) is the sole tropospheric reaction, but in unsaturated hydrocarbons HO-addition to a carbon-carbon double bond is usually the dominant reaction pathway. 

Current EPA analytical methods do not allow for the complete speciation of the various hydrocarbon compounds. EPA Methods 418.1 and 8015 provide the total amount of petroleum hydrocarbons present. However, only concentrations within a limited hydrocarbon range are applicable to those particular methods. Volatile compounds are usually lost, and samples are typically quantitated against a known hydrocarbon mixture and not the specific hydrocarbon compounds of concern or the petroleum product released. By conducting EPA Method 8015 (Modified) using a gas chromatograph fitted with a capillary column instead of the standard, hand-packed column, additional separation of various fuel-ranged hydrocarbons can be achieved. 

Fuel oils are petroleum products that are used in many types of engines, lamps, heaters, furnaces, stoves, and as solvents. Fuel oils come from crude petroleum and are refined to meet specifications for each use. Fuel oils are mixtures of aliphatic (open chain and cyclic compounds that are similar to open chain compounds) and aromatic (benzene and compounds similar to benzene) petroleum hydrocarbons. In addition, they may contain small amounts of nitrogen, sulfur, and other elements as additives. The exact chemical composition (i.e., precise percentage of each constituent) of each of the fuel oils discussed in this profile may vary... 

We believe it has been shown that this method for infrared analysis of hydrocarbons collected on charcoal tubes and vapor monitors is a valid and acceptable one. Further work is being done to validate the method for other hydrocarbons such as petroleum naphtha, Stoddard solvent, and other JP aviation fuels. Additionally, work is being done to determine the 3M monitor sampling rate for JP-4. 

Eckart and co-workers have published a series of papers on laboratory studies of biodesulfurization of petroleum and petroleum fractions. The ability of various aerobic mixed cultures to desulfurize Romashkino crude oil (1.69 wt.% S) was addressed by Eckart et al. (21). After 5 days of incubation at 30°C in sulfur-free mineral medium with oil as sole source of carbon and sulfur, approximately 55% of the total sulfur was recovered in the aqueous phase from two of the most active cultures. In another study, gas oil (1.2 to 2 wt.% S), vacuum distillates (1.8 to 2 wt.% S) and fuel oil (up to 4 wt.% S) were used as sole carbon and sulfur sources for the oil-degrading microorganisms (36). The addition of an emulsifying agent was required to enhance desulfurization. Sulfur removals of up to 20% from the gas oil, 5% from the vacuum distillates, and 25% from the fuel oil were observed after 5 to 7 days of incubation. In a later study (37). approximately 30% of the sulfur was removed from fuel-D-oil by a mixed population of bacteria. The removal of benzothiophene, dibenzothiophene and naphthobenzothiophene was shown by high resolution MS analysis. Hydrocarbon degradation was observed in each of these studies. For example, in the latter study with fuel-D-oil, the decreases in the n-alkane and aromatic content were 59% and 14%, respectively. 

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