Aromatic fractions

As the temperatures of the distillation cuts increase, the problems get more complicated to the point where preliminary separations are required that usually involve liquid phase chromatography (described earlier). This provides, among others, a saturated fraction and an aromatic fraction. Mass spectrometry is then used for each of these fractions. 

In the manufacture of base oils, one of the refining operations is to extract with the aid of an appropriate solvent (furfural most often) the most aromatic fractions and the polar components. When free of solvent, the extracted aromatic fraction can eventually be refined, particularly to remove color or to thicken it, or still further, to fractionate it. The term, aromatic extract is used in every case. 

Although most aromatic modified C-5 resins are typically higher softening point resins, certain appHcations, such as adhesives, require lower softening points. Copolymerization of a C-8—C-10 vinyl aromatic fraction with piperylenes in the presence of a C-4—C-8 mono-olefin chain-transfer stream yields resins with softening points ranging from 0—40°C (44). A particular advantage of these Hquid resins is the fact that they eliminate the need for plasticizers or oils in some pressure sensitive adhesive appHcations. 

G-9 Aromatic Petroleum Resins. Feedstocks typically used for aromatic petroleum resin synthesis boil in the approximate range of 100—300°C at atmospheric pressure, with most boiling in the 130—200°C range. The C-9 designation actually includes styrene (C-8) through C-10 hydrocarbons (eg, methylindene). Many of the polymerizable monomers identified in Table 1 for coumarone—indene type cmdes from coal tar are also present in aromatic fractions from cracked petroleum distillates. Therefore, the technology developed for the polymerization of coal-tar cmdes is also appHcable to petroleum-derived aromatic feedstocks. In addition to availabiHty, aromatic petroleum resins offer several advantages over coumarone—indene resins. These include improved color and odor, as weU as uv and thermal stabiHty (46). 

Superffex C t lytic Crocking. A new process called Superflex is being commercialized to produce predorninantiy propylene and butylenes from low valued hydrocarbon streams from an olefins complex (74). In this process, raffinates (from the aromatics recovery unit and the B—B stream after the recovery of isobutylene) and pyrolysis gasoline (after the removal of the C —Cg aromatics fraction) are catalyticaHy cracked to produce propylene, isobutylene, and a cmde C —Cg aromatics fraction. AH other by-products are recycled to extinction. 

The symbols f and f correspond to total fraction of and hybridi2ed carbon, respectively, f represents the fraction of carbon in aromatic rings f , the fraction in carbonyls, b > 165 ppm the aromatic fraction that is protonated the aromatic fraction that is nonprotonated f, the phenoHc or phenohc ether carbon, 6 = 150-165 ppm f, the alkylated aromatic carbon, 6 = 135-150 ppm , the aromatic bridgehead carbon f represents the fraction of CH or CH2 aUphatic carbon f, the CH or nonprotonated aUphatic carbon and f, the aUphatic carbon bound to oxygen, b — 50-90 ppm. 

The preseparation utilized a 5 pim cyano column (250 cm X 4.6 mm i.d.) and a 5 p.m silica column (250 cm X 4.6 mm i.d.) in series, followed by GC analysis on an SE-54 column (25 m X 0.2 mm i.d., 0.33 p.m film thickness). The SFC system separated the aviation sample into two peaks, including saturates and single-ring aromatics as the first peak, and two-ring aromatic fractions as the second peak. These fractions were selectively cut and then transferred to the GC unit for further analysis. (Figure 12.20). 

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

Figure 14.18 Typical GC cliromatogram of the separated mono-aromatics fraction of a middle distillate sample the numbers indicate the retention time of the various -alkanes.

Figure 14.19 Typical GC chromatogram of the separated di-aromatics fraction of a middle distillate sample Peak identification is as follows 1, naphthalene 2, 2-methylnaphthalene 3, 1-methylnaphthalene 4, biphenyl 5, C2-naphthalenes 6, C3-naphthalenes 7, C4-naph-thalenes 8, C5+-naphthalenes 9, benzothiophene 10, methylbenzothiophenes 11, C2-ben-zotliiopIrenes. Note the clean baseline between naphthalene and the methylnaphthalenes, which means that no overlap with the previous (mono-aromatics) fraction has occuned.

Viscosity indicates the chemical composition of an oil sample. As the viscosity of a sample increases, paraffins increase, hydrogen content increases, and the aromatic fraction decreases. 

The aromatic fractions of natural gas condensate reacted with a-olefins to give alkylarenes which were converted to sodium sulfonates or to ethanolamine sulfonates. The naphthene-paraffin fractions of the gas condensate reacted with PC13 and 02 to give RPOCl2, which reacted with triethanolamine to give N-a-... 

Another variation of the preceding method is to apply HPLC to fractionate the cleaned-up aliphatic-aromatic fraction from flash colurim separation of soluble organic matter as it is performed in the Chevron laboratory, for example, as described in Reference 2. A Waters HPLC system equipped with a preparative Whatman Partisil 10 silica column (9.4 X 500 mm), a HPLC pump, and two detectors for separation monitoring (a UV and refractive index detector) are used, giving three fractions of aliphatic hydrocarbons, mono-, di-, and triaromatics and polar compounds. The hrst two fractions are eluted with hexane, whereas polar compounds are eluted with... 

Each oil-dispersant combination shows a unique threshold or onset of dispersion [589]. A statistic analysis showed that the principal factors involved are the oil composition, dispersant formulation, sea surface turbulence, and dispersant quantity [588]. The composition of the oil is very important. The effectiveness of the dispersant formulation correlates strongly with the amount of the saturate components in the oil. The other components of the oil (i.e., asphaltenes, resins, or polar substances and aromatic fractions) show a negative correlation with the dispersant effectiveness. The viscosity of the oil is determined by the composition of the oil. Therefore viscosity and composition are responsible for the effectiveness of a dispersant. The dispersant composition is significant and interacts with the oil composition. Sea turbulence strongly affects dispersant effectiveness. The effectiveness rises with increasing turbulence to a maximal value. The effectiveness for commercial dispersants is a Gaussian distribution around a certain salinity value. 

Recent investigations have indicated that the aliphatic carbon fraction, rather than aromatic fraction, was strongly correlated to HOC sorption. For instance, the sorption of phenanthrene was related to nonpolar aliphatic carbon fraction, excluding poly(methylene), but was very strongly correlated with the content of the amorphous nonpolar aliphatic domains including amorphous poly(methylene) (Mao et al. 2002). In other words, the rubbeiy, relatively low-density, and amorphous nonpolar aliphatic carbon domains are excellent for phenanthrene partitioning (Figs. 3 and 4). 

A two-component plot of the 13C/12C isotope ratio from the saturated and aromatic fractions of five samples previously identified (Table 4.8 and Figure 4.12) is pre-... 

LC-MS has been used to study various aromatic fractions from coal derived liquids, and there are also a number of reports on its use in the analysis of porphyrin mixtures [601,602]. The early work by Dark et al. [601] using LC-MS for coal-derived liquids was mainly concerned with the separation and identification of polycyclic aromatic components. However, it is interesting to note that... 

The methods include the use of mass spectrometry to determine (1) the hydrocarbon types in middle distillates (ASTM D2425) (2) the hydrocarbon types of gas oil saturate fractions (ASTM D2786) (3) the hydrocarbon types in low-olefin gasoline (ASTM D2789) and (d) the aromatic types of gas oil aromatic fractions (ASTM D3239). 

Leaching processes introduce hydrocarbon into the water phase by solubility and entrainment. Leaching processes of petroleum products in soils can have a variety of potential scenarios. Part of the aromatic fraction of a petroleum spill in soil may partition into water that has been in contact with the contamination. 

In contrast to traditional methods for total petroleum hydrocarbons that report a single concentration number for complex mixtures, the fractionation methods report separate concentrations for discrete aliphatic and aromatic fractions. The petroleum fraction methods available are GC-based and are thus sensitive to a broad range of hydrocarbons. Identification and quantification of aliphatic and aromatic fractions allows one to identify petroleum products and evaluate the extent of product weathering. These fraction data also can be used in risk assessment. 

Another method (EPA 3611) that focuses on the to separation of groups or fractions with similar mobility in soils is based on the use of alumina and silica gel (EPA 3630) that are used to fractionate the hydrocarbon into ahphatic and aromatic fractions. A gas chromatograph equipped with a boiling-point column (nonpolar capillary column) is used to analyze whole soil samples as weU as the aliphatic and aromatic fractions to resolve and quantify the fate-and-transport fractions. The method is versatile and performance based and therefore can be modified to accommodate data quality objectives. 

On the other hand, the complex mixture of petroleum hydrocarbons potentially present in an air sample can be minimized by separation of the sample into aliphatic and aromatic fractions, and then these two major fractions are separated into smaller fractions based on carbon number. Individual compounds (e.g., benzene, toluene, ethylbenzene, xylenes, MTBE, naphthalene) are also identified using this method. The range of compounds that can be identified includes C4 (1,3-butadiene) through C12 (n-dodecane). 

Few analytical methods are available for the determination of total petroleum hydrocarbons in biological samples, but analytical methods for several important hydrocarbon components of total petroleum hydrocarbons may be modified. Most involve solvent extraction and saponification of lipids, followed by separation into aliphatic and aromatic fractions on adsorption columns. Hydrocarbon groups or target compounds are determined by gas chromatography-flame ionization or... 

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