SARA fractionation

Istas - Flores, C. A., Buenrostro-Gonzalez, E., Lira-Galeana, C., (2005), Comparisons between open column chromatography and HPLC. SARA fractionations in petroleum. Energy Fuels, 19, 2080-2088. 

An atmospheric residue from heavy crude oil was used in order to obtain different fractions by means of chromatographic separation. Table 5.1 shows the properties of the heavy crude and its atmospheric residue. Asphaltenes were obtained by precipitation with -heptane in a pressurized system (25kg/cm ), with nitrogen as inert at temperature of 60°C and constant stirring. SARA fractionation was carried out in two chromatographic columns packed with clay and alumina. More details about the fractionation procedure are reported elsewhere (Alvarez et al., 2011). 

The results of TGA for atmospheric residue and its SARA fractions are shown in Figure 5.2, from which the following observations can be done ... 

Coke Yield for Atmospheric Residue and Its SARA Fractions at Heating Rate of 8°C/min... 

Alvarez, E., Marroquin, G., Trejo, F., Centeno, G., Aneheyta, J., Diaz, J.A.I. 2011. Pyrolysis kinetics of atmospheric residue and its SARA fractions. Fuel 90 3602-3607. 

SARA (Saturates, Aromatics, Resins, Asphaltenes) analysis is widely practiced on heavy fractions such as vacuum and atmospheric residues and vacuum distillates for two purposes ... 

Figure 2.3. SARA-type analysis (showing two additional fractions, carbenes and carboids, that are generally recognized as the results of thermal processes).

Although most facilities that refine crude petroleum in the United States produce a fuel oil. no. 1 fraction (HSDB 1991), only producers that market fuel oil no. 1 as an end product are listed as commercial manufacturers. These manufacturers include Claiborne Gasoline Company (Claiborne and Union Parish, Louisiana), Continental Oil Company (Acadia Parish, Louisiana), Sun Production Company (Starr County, Texas), Exxon Corporation (Pledger County, Texas), Atlantic Richfield Company (New York, New York), and Shell Oil Company (Houston, Texas) (HSDB 1991). Since fuel oils nos. 1, 1-D, 2, 2-D, and 4, and fuel oil UNSP are not required to be reported under SARA Section 313, there are no data for these fuel oils in the 1990 Toxics Release Inventory (TRI90 1992). 

Fig. 5 HPLC of extravirgin olive oil unsaponifiable and collected fractions. A = fraction containing alkanols (6 and 9 min) S = fraction containing sterols (10 and 18 min). (Reprinted from Ref. 7 with the kind permission of Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

In general terms, group-type analysis of petroleum is often identified by the acronyms for the names PONA (paraffins, olefins, naphthenes, and aromatics), PIONA (paraffins, Ao-paraffins, olefins, naphthenes, and aromatics), PNA (paraffins, naphthenes, and aromatics), PINA (paraffins, Ao-paraffins, naphthenes, and aromatics), or SARA (saturates, aromatics, resins, and asphaltenes). However, it must be recognized that the fractions produced by the use of different adsorbents will differ in content and will also be different from fractions produced by solvent separation techniques. 

SARA separation a method of fractionation by which petroleum is separated into saturates, aromatics, resins, and asphaltene fractions. 

The extracts were fractionated by a Preparative Liquid Chromatography method - PLC-8 [2], in eight distinct chemical classes FI-saturated hydrocarbons (HC), F2-monoaromatics, F3-diaromatics, F4-triaromatics, F5-polynuclear aromatics, F6-resins, F7-asphaltenes and F8-asphaltols. This method, proposed by Karam et al. as an extension of SARA method [4], was especially developed for coal-derived liquids. It combines solubility and chromatographic fractionation, affording discrete, well-defined classes of compounds which are readable for direct chromatographic and spectroscopic analysis. 

Similar solubility phenomena can also be observed for the resins. The sample for resin separation after removal of asphaltenes is normally applied as a solution in nC5. However, after the removal of the oil, the fractions obtained from the ion exchangers show a marked decline in solubility in the same solvent. Also, if resin separation is done by the SARA method, the tetrahydro-furan fraction is hardly soluble in nC5. This again shows the solubility criterion to be a function of several variables the removal of some of the solubilizing components of the resins renders the remainder insoluble. 

Figure 6.3 Relative viscosity as a function of the fraction of large spheres in a bimodal distribution of particle sizes with a 5 1 ratio of diameters, at various total volume percentages of particles. The arrow P Q illustrates the 50-fold reduction in viscosity that occurs when monosized particles in a 60 vol% suspension are replaced by a 50-50 mixture of large and small spheres. The arrow P S shows that if monosized spheres are replaced by a bimodal size distribution, the concentration of spheres can be increased from 60% to 75% without increasing the viscosity. (Reprinted from Barnes et al., An Introduction to Rheology (1989), with kind permission from Elsevier Science - NL, Sara Burger-hartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

Figure 6.24 The normalized first normal stress difference N /[4>risp / n 2p) — 1.8)] versus shear rate for glass fibers of aspect ratios p — 276 and 552 in Newtonian solvents, namely, glucose wheat syrup and epoxy resin. For p — 276, the volume fraction (j) is in the range 0.0002-0.0011 and for p = 552,

Rock samples were extracted using methylene chloride and a Soxhlet apparatus and the resulting extract was further fractionated by a semi-quantitative SARA separation. After asphaltenes were removed from the concentrated extract by precipitation with excess pentane, the pentane soluble portion of the sample was separated by medium-pressure liquid chromatography (MPLC) using a deactivated silica gel precolumn and an activated silica gel main column by eluting the saturate and aromatic hydrocarbon fractions from the activated silica column with hexane in the forward and back-flush modes respectively. Polar nonhydrocarbons were backflushed from the precolumn with methylene chloride-methanol. Carbon isotopes were done on a subset of hydrocarbon fractions at Coastal Sciences Labs, Austin, TX (Table 3). 

Asphalt is thought of as a colloidal system similar to petroleum, the difference being that the lighter molecules have been removed from asphalt during the refining process. Asphalt can be fractionated into four important fractions saturates, aromatics, resins, and asphaltenes by either the SARA method or the ASTM D4124 process (standard test method for separation of asphalt into four fractions). The fractionated part of saturates and aromatics is generally considered to be gas-oil. The polarity of these four fractions increases from saturates —> aromatics —> resins —> asphaltenes. 

Because the asphalt system is not a true solution, it can be fractionated into saturates, aromatics, resins, and asphaltenes by the solvent fraction method, SARA method, or TLC method. The polarity of these four fractions is increased in the order of saturates, aromatics, resins, asphaltenes. In crude oil, asphaltene micelles are present as discrete or dispersed particles in the oily phase. Although the asphaltenes themselves are insoluble in gas-oil (saturates and aromatics), they can exist as fine or coarse dispersions, depending on the resin content. The resins are part of the oily medium but have a polarity higher than gas-oil. This property enables the molecules to be easily adsorbed onto the asphaltene micelles and to act as a peptizing agent of the colloid stabilizer by charge neutralization. 

Fig. 65. Schematically shown temperature dependence of the fraction of associated monomeric units (p) and of turbidity (t) for s-PMMA (s = 0.91 in butyl acetate on molecular scale the process is very fast subsequent aggregation needs more time. Reproduced from Adv Colloid Int Sci [Ref. 212] by the courtesy of the authors and of Elsevier Science-NL, Sara Burger-hartstraat 25,1055 KV Amsterdam, The Netherlands...

Fukuyama and Terai used a lumped model to study the kinetics of hydroprocessing of VR (7 to 10 MPa 700K). A total of seven lumps comprising hydrocarbon groups was determined by SARA analysis, as well as different fractions of products and a residue. The kinetics parameters were used to identify the most active Fe/AC catalyst. The same catalyst was the most resistant to deactivation. 

Muller et al. used SCS derivatives to study the effects of hydrodesulfurization (HDS) on polycyclic aromatic sulfur heterocycles (PASHs) in bitumen residua. Their experiments concentrated on PASHs, which is a predominant class of SCS in vacuum residue bottoms. Asphaltenes were removed by precipitation, followed by the separation of aromatic fractions from saturated fractions by the saturates, aromatics, resins, and asphalts (SARA) method. Several methods can be deployed as the SARA method depending on the type of petroleum sample, one of the more common for more viscous oils is a combination of two methods ASTM D2007 and ASTM D893. Pentane-insoluble (PI) method ASTM D893 is used first to identify the asphaltene content then ASTM D2007 is used to calculate the saturates, aromatics, and resins. 

A 9.4T FT-ICR MS outfitted with a ThermoFisher Scientific source was used. The vacuum bottom residues were fractionated by the SARA method. Samples were injected at a flow rate of 50-100 pL/min. 

Conversion (upgrading) of bitumen and heavy oils to distillate products requires reduction of the MW and boiling point of the components of the feedstocks. The chemistry of this transformation to lighter products is extremely complex, partly because the petroleum feedstocks are complicated mixtures of hydrocarbons, consisting of 10 to 10 different molecules. Any structural information regarding the chemical nature of these materials would help to understand the chemistry of the process and, hence, it would be possible to improve process yields and product quality. However, because of the complexity of the mixture, the characterization of entire petroleum feedstocks and products is difficult, if not impossible. One way to simpHfy this molecular variety is to separate the feedstocks and products into different fractions (classes of components) by distillation, solubility/insolubility, and adsorption/desorption techniques. For bitumen and heavy oils, there are a number of methods that have been developed based on solubility and adsorption. The most common standard method used in the petroleum industry for separation of heavy oils into compound classes is SARA (saturates, aromatics, resins, and asphaltenes) analysis. Typical SARA analyses and properties for Athabasca and Cold Lake bitumens, achieved using a modified SARA method, are shown in Table 1. For comparison, SARA analysis of Athabasca bitumen by the standard ASTM method is also shown in this table. The discrepancy in the results between the standard and modified ASTM methods is a result of the aromatics being eluted with a... 

Karacan and Kok recently studied the pyrolysis of two crude oils and their SARA fraetions." Differential scanning calorimetry and thermogravimetry techniques were used to evaluate the pyrolysis behaviour of the feedstoeks. The results indicated that the pyrolysis mechanisms depend on the nature of the constituents. Thermogravimetric data showed that asphaltenes are the main contributors to coke formation and that resins are a second contributor. The weight loss for the SARA components was additive. The authors argued that each fraction in a whole crude oil follows its own reaction pathway and there is no interaction or S5mergy between the components. 

In an attempt to correlate the thermal cracking behavior of heavy oils to their properties, Liu et al. studied the thermal cracking of 40 heavy oil fractions obtained by supercritical extraction from six Chinese light crude oils and oils from Oman and Saudi Arabia. The thermal cracking experiments were performed at 410°C, 0.1 MPa N2 for 1 hour. A non-linear regression fit indicated that the thermal cracking of the fractions could be correlated with the H/C, S (wt%), N (wt%) and molecular weight. A similar correlation was obtained with SARA analysis, S, and MW. In this study, the coke yields... 

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