Petroleum separation into four fractions

Coal liquids, petroleum crudes, and their distillation cuts have been separated into four or five fractions by SEC (5 15). The SEC fractions were analyzed by use of GC. The procedure was performed manually. It was inefficient, and susceptible to human error. The automated fraction collection followed by injection of the fraction into the GC reduces analysis time, and offers an option for collection of the desired number of fractions at predetermined time intervals. The manual collection of up to 10 one-ml fractions is also used in order to study the effectiveness of the automated method. 

In their study of the petroleum ether-extractable material (8% of tobacco weight) from tobacco which was chromato-graphically separated into eight fractions (see Table XXV-8), Severson et al. (3616) identified PAHs in the pyrolysates from fractions F-2 and F-3 (containing phytosterol derivatives) and from fractions F-5 and F-6 (containing unbound phytosterols). Their PAH data for these four pyrolysates from phytos-terol-rich tobacco fractions showed high yields of chrysene vs. those in the pyrolysates from the essentially phytosterol-free fractions (F-1, F-2, F-7, and F-8). 

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. 

Petroleum can be fractionated into four generic types of materials representing general chemical properties. These include saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes. The standard ASTM separation procedure (D2007) for isolating the asphaltenes and the other components in petroleum is based on solubility behavior and chromatography, as shown in Fig. 5. Commerically, many refineries utilize solvent separations to produce a solvent deasphalted oil which has lower impurity levels. 

Additionally, classes (or types) of hydrocarbons were, and still are, determined based on the capability to isolate them by separation techniques. The four fractional types into which petroleum is subdivided are paraffins, olefins, naphthenes, and aromatics (PONA). Paraffinic hydrocarbons include both normal and branched alkanes, whereas olefins refer to normal and branched alkenes that contain one or more double or triple carbon-carbon bonds. Naphthene (not to be confused with naphthalene) is a term specific to the petroleum industry that refers to the saturated cyclic hydrocarbons (cycloalkanes). Finally, the term aromatics includes all hydrocarbons containing one or more rings of the benzenoid structure. 

Scheme 1. Convenient separation of petroleum into four major fractions.

Petroleum is a naturally occurring oily, flammable liquid composed principally of hydrocarbons (50-98%) with the remainder consisting of organic compounds, oxygen, nitrogen, sulfur, and traces of metal salts. Petroleum is usually found beneath the earth s surface and occasionally in pools above the surface. Unrefined petroleum is called crude oil. Petroleum is separated by distillation into the following four major fractions ... 

---