Petroleum constituents

A residuum, often shortened to resid, is the residue obtained from petroleum after nondestmctive distillation has removed all the volatile materials. The temperature of the distillation is usually below 345°C because the rate of thermal decomposition of petroleum constituents is substantial above 350°C. Temperatures as high as 425°C can be employed in vacuum distillation. When such temperatures are employed and thermal decomposition occurs, the residuum is usually referred to as pitch. By inference, the name is used in the same manner as when it refers to the nonvolatile residue from the thermal decomposition of coal tar (3). 

The relationship of electrokinetic phenomena and the movement of petroleum constituents is not of high importance however, it can be important for the transport of some solutes related to a remedial technology such as electroosmosis remediation. 

The amount and types of other contaminants (such as other petroleum constituents) that will also consume oxidant. 

Thiourea inclusion compounds have also found recent applications as diverse as the separation of liquid crystal isomers 84 ), isolation of petroleum constituents 85,86), and the recovery of squalene during olive oil refining87), to cite just a few examples. 

An oil refinery has to blend gasoline. Suppose that the refinery wishes to blend four petroleum constituents into three grades of gasoline A, B9 and C. Determine the mix of the four constituents that will maximize profit. 

Generally, the properties of petroleum constituents varying over the boiling range 0 to >565°C (32 to 1050°F). Variations in density also occur over the range 0.6 to 1.3, and pour points can vary from <0 to >100°C. Although these properties may seem to be of lower consequence in the grand scheme of environmental cleanup, they are important insofar as these properties influence (1) the evaporation rate, (2) the abihty of the petroleum constituents or petroleum product to float on water, and (3) the fluidity or mobility of the petroleum or petroleum product at various temperatures. 

Conventional infrared spectroscopy yields information about the functional features of various petroleum constituents. For example, infrared spectroscopy will aid in the identification of N-H and O-H functions, the nature of polymethylene chains, the C-H out-of-place bending frequencies, and the nature of any polynuclear aromatic systems (Speight, 1999, and references cited therein). 

Nuclear magnetic resonance has frequently been employed for general studies and for the structural studies of petroleum constituents (Bouquet and BaiUeul, 1982 Hasan et al., 1989). In fact, proton magnetic resonance (PMR) studies (along with infrared spectroscopic studies) were perhaps the first studies of the modem era that allowed stmctmal inferences to be made about the polynuclear aromatic systems that occm in the high-molecular-weight constituents of petroleum. 

This chapter deals with the toxicity of petroleum and petroleum products, the effects of petroleum constituents on the environment, individual process wastes, and the means by which petroleum, petroleum products, and process wastes are introduced into the environment. The processes are restricted to those processes by which the common products are produced (Chapter 3). 

The feedstock crude oil is heated to between 65 and 177°C (150 to 350°F) to rednce viscosity and surface tension for easier mixing and separation of the water. The temperature is limited by the vapor pressure of the petroleum constituents. In both methods, other chemicals may be added. Ammonia is often... 

As mentioned above, most oils are buoyant in water. However, in areas with high levels of suspended sediment, petroleum constituents may be transported to the river, lake, or ocean floor through the process of sedimentation. Oil may adsorb to sediments and sink or be ingested by zooplankton and excreted in fecal pellets that may settle to the bottom. Oil stranded on shorehnes also may pick up sediments, float with the tide, and then sink. Most of this process occurs from about 2 to 7 days after the spill. 

Another approach is to consider petroleum constituents in terms of transportable materials, the character of which is determined by several chemical and physical properties (i.e., solubility, vapor pressure, and propensity to bind with soil and organic particles). These properties are the basis of measures of teachability and volatility of individual hydrocarbons. Thus, petroleum transport fractions can be considered by equivalent carbon number to be grouped into 13 different fractions. The analytical fractions are then set to match these transport... 

Corrosivity. An aqueous solution that has a pH less than or equal to 2, or greater than or equal to 12.5, is considered corrosive. Most petroleum constituents and petroleum products are not corrosive, but many of the chemicals used in refineries are corrosive. Corrosive materials also include substances such as sodium hydroxide and some other acids or bases. 

Headspace analysis (EPA 3810, 5021) also works well for analyzing volatile petroleum constituents in soil. In the test method, the soil is placed in a headspace vial and heated to drive out the volatiles from the sample into the headspace of the sample container. Salts can be added for more efficient release of the volatile compounds into the headspace. Similar to water headspace analysis, the soil headspace technique is useful when heavy oils and high analyte concentrations are present, which can severely contaminate purge-and-trap instrumentation. Detection limits are generally higher for headspace analysis than for purge-and-trap analysis. 

Soxhlet extraction (EPA SW-846 3540) is a very efficient extraction process that is commonly used for semivolatile petroleum constituents. In the method, the solvent is heated and refluxed (recirculated) through the soil sample continuously for 16 hours, or overnight. This method generates a relatively large volume of extract that needs to be concentrated. Thus, it is more appropriate for semivolatile constituents than for volatile constituents. Sonication extraction (EPA SW-846 3550) can also be used for semivolatile compounds, and as the name suggests, involves the use of sound waves to enhance analyte transfer from sample to solvent. Sonication is a faster technique than Soxhlet extraction and can require less solvent. 

The techniques employed to extract the analytes of interest can frequently extract interfering compounds. Polar compounds such as animal and plant fats, proteins, and small biological molecules may be identified incorrectly as petroleum constituents. Extract cleanup techniques can be used to remove them. In an ideal situation, only interfering compounds are removed. In reality, some polar petroleum constituents can also be removed. 

Even thongh cleanup procedures are advocated before sample analysis, there can be several limitations to varions cleannp steps. The reasons for decreased effectiveness of cleanup procedures include (1) Sample loading may exceed the capacity of cleanup columns, (2) nonpetrolenm componnds may have chemical strnctnres similar to petroleum constituents and may behave like a petroleum constituent, (3) analytes of interest may be removed dnring the cleanup and (4) no single cleanup technique removes all the chemical interference. 

Once the sample preparation is complete, there are several approaches to the analysis of petroleum constituents in the water and soil (1) leachability or toxicity of the sample, (2) the amounts of total petroleum hydrocarbons in the sample, (3) petroleum group analysis, and (4) fractional analysis of the sample. These methods measure different petroleum constituents that might be present in petroleum-contaminated environmental media. 

Samples are extracted with a suitable solvent (i.e., a solvent with no C-H bonds), and biogenic polar materials are removed with silica gel. Some polar petroleum constituents may be removed as part of the silica gel cleanup. The absorbance of the silica gel eluate is measured at the specified frequency and compared to the absorbance of a standard or standards of known petroleum... 

In the method(s), petroleum constituents are extracted into a suitable solvent. Biogenic polar materials typically may be partially or completely removed with silica gel. The solvent is evaporated and the residue is weighed. This quantity is reported as a percentage of the total soil sample dry weight. These methods are better suited for heavy oil because they include an evaporation step. 

This method (EPA 1664) is a liquid-liquid extraction gravimetric procedure that employs n-hexane as the extraction solvent, in place of 1,1,2-trichloroethane (CFC-113) and/or 1,2,2-trifluoroethane (Freon-113), for determination of the conventional pollutant oil and grease. Because the nature and amount of material determined are defined by the solvent and by the details of the method used for extraction, oil and grease method-defined analytes are used. The method may be modified to reduce interferences and take advantage of advances in instrumentation provided that all method equivalency and performance criteria are met. However, n-hexane is a poor solvent for high-molecular-weight petroleum constituents (Speight, 1999, 2001). Thus, the method will produce erroneous data for samples contaminated with heavy oils. 

Immunoassay methods correlate total petroleum hydrocarbons with the response of antibodies to specific petroleum constituents. Many methods measure only aromatics that have an affinity for the antibody, benzene-toluene-ethylbenzene-xylene, and PAH analysis (EPA 4030, Petroleum Hydrocarbons by Immunoassay). 

The principle behind the test method(s) is that antibodies are made of proteins that recognize and bind with foreign substances (antigens) that invade host animals. Synthetic antibodies have been developed to complex with petroleum constituents. The antibodies are immobilized on the walls of a special ceU or filter membrane. Water samples are added directly to the cell, while soils must be extracted before analysis. A known amount of labeled analyte (typically, an enzyme with an affinity for the antibody) is added after the sample. The sample analytes compete with the enzyme-labeled analytes for sites on the antibodies. After equilibrium is established, the cell is washed to remove any um-eacted sample or labeled enzyme. Color development reagents that react with the labeled enzyme are added. A solution that stops color development is added at a specified time, and the optical density (color intensity) is measured. Because the coloring agent reacts with the labeled enzyme, samples with high optical density contain low concentrations of analytes. Concentration is inversely proportional to optical density. 

Many common environmental methods measure individual petroleum constituents or target compound rather than the entire signal from the total petroleum hydrocarbons. Each method measures a suite of compounds selected because of their toxicity and common use in industry. 

A high-performance liquid chromatography system can be used to measure concentrations of target semi- and nonvolatile petroleum constituents. The system only requires that the sample be dissolved in a solvent compatible with those used in the separation. The detector most often used in petroleum environmental analysis is the fluorescence detector. These detectors are particularly sensitive to aromatic molecules, especially PAHs. An ultraviolet detector may be used to measure compounds that do not fluoresce. 

A gas chromatography-mass spectrometry system is used to measure concentrations of target volatile and semivolatile petroleum constituents. It is not typically used to measure the amount of total petroleum hydrocarbons. The advantage the technique is the high selectivity, or ability to confirm compound identity through retention time and unique spectral pattern. 

Since the term total petroleum hydrocarbons (total petroleum hydrocarbons) includes any petroleum constituent that falls within the measurable amount of petroleum-based hydrocarbons in the enviromnent the information obtained for total petroleum hydrocarbons depends on the analytical method used. Therefore, the difficulty associated with measurement of the total petroleum hydrocarbons is that the scope of the methods varies greatly (Table 8.1). Some methods are nonspecific, whereas others provide results for hydrocarbons in a boiling-point range. Interpretation of analytical results requires an understanding of how the determination was made (Miller, 2000, and references cited therein Dean, 2003). 

Figure 1-3 Simplified representation of the rate of thermal decomposition of petroleum constituents with temperature. 

---