Petroleum fractions, higher boiling

Petroleum or mineral oil (kerosene, etc.) are less soluble in alcohol than most oils. They have a low specific gravity and refractive index, and are not saponified by alcoholic potash. The lower boiling fractions can usually be detected by their odour, and the higher boiling fractions remain in the residue on fractional distillation. They are unaffected by fuming nitric acid. 

Methylbenzenes occur in small quantities in naphtha and higher boiling fractions of petroleum. Those presently of commercial importance are toluene, o-xylene, p-xylene, and to a much lesser extent m-xylene. 

In the thermal cracking methods, the higher-boiling petroleum fractions like heavy oils are subjected to high temperature and pressure by which the bigger hydrocarbon molecules break down to yield lower-boiling lighter fractions ... 

For example, if gasoline is suspected to be the sole contaminant, the method will use purge-and-trap sample introduction. If higher-boiling petroleum fractions (diesel, middle distillates, motor oil) are the contaminants, the analysis will use direct injection and hotter oven temperatures. Mixtures or unknown contamination may require both volatile range and extractable range analyses. Alternatively, a single injection can be used to analyze the entire sample, but the extraction method must not use a solvent evaporation step. 

Several thousand compounds are present in petroleum. Few are separated as pure substances. Many of the uses of petroleum can be served by certain fractions from the distillation of crude oil. Typical distillation fractions and their uses are given in Table 7.3 and a distillation unit is shown in Fig. 7.5. The complexity of the molecules, molecular weight, and carbon number increase with the boiling point. The higher boiling fractions are usually distilled in vacuo at lower temperature than their atmospheric boiling points to avoid excessive decomposition to tars. 

Liquid propane is employed as the solvent in this process. The use of a petroleum fraction as a solvent for dewaxing is desirable from the standpoint of the availability and cost of solvent, and the higher boiling hydrocarbon fraction has been employed many years for dewaxing of residual stocks. 

Characterization of Homogeneous Mixtures of Hydrocarbons. In the higher boiling fractions of petroleum, such as the gas oil and lubricant portions, the isolation... 

Of the data that are available, the proportions of the elements in petroleum vary only slightly over narrow limits (Chapter 1). And yet, there is a wide variation in physical properties from the lighter more mobile crude oils at one extreme to the heavier asphaltic crude oils at the other extreme. The majority of the more aromatic species and the heteroatoms occur in the higher boiling fractions of feedstocks. The heavier feedstocks are relatively rich in these higher boiling fractions. 

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