Fractionation of mineral oils

EXPOSURE ROUTES inhalation ingestion cigarette smoke condensate automobile exhaust soot emissions from coal and gas works and electric plants aromatic fraction of mineral oil commercial solvents, waxes, petrolatum, creosote, coal tar, petroleum asphalt, coal tar pitch charcoal broiled barbecued, or smoke meats and fish certain vegetables and vegetable oils coffee... 

Mineral oils have very low acute toxicities, i.e. oral LD50 values of around lOg/kg. They are not absorbed via the skin and are insufficiently volatile to produce harmful vapours at room temperature. Additives are used in small quantities for specific properties but these do not normally affect the health and safety characteristics. Dermatitis may be caused by repeated or prolonged contact of mineral oils with the skin. Such contact with higher boiling fractions over many years can result in warty growths which may become... 

The development of reliable methods for structural analysis of mixtures is very laborious. Physical data of pure compounds may serve as a base for the investigations. It has, however, been proved that not in all cases can these data be simply correlated with those of the mixtures. Thus correlations of physical data of pure, individual hydrocarbons often prove not to be valid in the analysis of mineral oils. In this case physical constants of mineral oil fractions of widely different origin form a more reliable basis for the structural analysis, provided that their structure has been determined by absolute methods. 

A solution to the problem of determining the composition of mineral oil fractions, especially those of high molecular weight, is provided by dealing with the oil fractions in a statistical way, i.e. some characteristic structural elements in the mixture are defined and determined by appropriate means. 

More detailed knowledge of the composition of mineral oils can be obtained by splitting the oils into as narrow fractions as possible by means of fractionation, thermodiffusion, chromatography, extraction and other means. On the opposite page a scheme is given as an illustration of the application of distillation techniques in the investigation of mineral oils and polymerized fatty oils. 

RING ANALYSIS AND CARBON-TYPE ANALYSIS OF MINERAL OIL FRACTIONS a. Analytical hydrogenation of mineral oils... 

In normal cases the hydrogenation of mineral oil fractions can be used as an analytical tool for a quantitative transformation of aromatic rings into the corresponding naphthenes. 

When the problem of establishing the structure of hydrogenated products has been solved, more complicated mixtures, e.g. aromatic-containing fractions, can be considered. The existing methods of determining the composition of mineral oil fractions have been developed according to this scheme. The methods presented below are treated in principle in chronological order. 

By means of equation (24) it is possible to calculate the value of %Ca of mineral oil fractions if molecular weight and hydrogen content of both the original and the saturated fraction are known. Olefinic compounds should be absent. 

By means of equations (30) and (36) it is possible to calculate the number of aromatic rings per average molecule of mineral oil fractions with Ra < 1 and Ra > 1, respectively, from the molecular weights and the percentages of carbon atoms in aromatic structure. The calculated values are not exact values since it is assumed that the multiple ring systems are kata-condensed however, this often seems to be the case. 

In the n-d-M method use is made of three physical constants, namely the refractive index n (measured for the sodium D-line), the density d in g/ml and the molecular weight M, for the determination of the composition of mineral oil fractions. 

In the last few years the kinematic viscosity and its temperature dependence have been used for the determination of the composition of mineral oil fractions. The first steps in this field were made by Boelhouwer, Van Steenis and Waterman13, who... 

The cross-sections can be used for the determination of the carbon-type composition of mineral oil fractions in the following way. 

Though these graphs are convenient to use it is a drawback that for each structural element a different graph has to be employed. Therefore the nomogram method in general seems to be the most attractive method for determining the values of the various structural elements of mineral oil fractions. 

In this section it will be shown that it is not only possible to determine the chemical structure of mineral oil fractions from physical constants, but also to predict the values of other physical constants, That it is possible to correlate the physical constants of... 

As has been stated above the lines for equal values of the ultrasonic sound velocity of mineral oil fractions in the log v -(n — d) graph are straight. Therefore it is possible to construct a nomogram with the parallel coordinates log v% and (n — 0.181 d), the value of 0.181 in the function (n — 0.181 d) being somewhat more accurate than in the function (n — d). 

For the determination of the surface tension from the viscosity, the refractive index and the density of mineral oil fractions two cross-sections have, in general, to be used. The value of can be obtained by linear interpolation between values read from the... 

The lines for equal values of o in the different cross-sections are parallel to the n axis. This means that the surface tension at a constant value of the viscosity and the density is independent of the refractive index and in fact of any other pl sical constant, i.e. the viscosity and the density are the only two physical constants of mineral oil fractions that are necessary to determine the value of the surface tension of these fractions. text continued on p. 48... 

The fact that only the two physical constants, viscosity and density, are necessary to determine the surface tension of mineral oil fractions, enabled Cornelissen, Harva and Waterman21 to construct a diagram with the coordinates log vand da4°. This diagram has been constructed by projecting the surfaces of equal values of the surface tension in the log v-n-d space model on the log v-d coordinate plane. In the diagram lines of equal values of the surface tension (at 20°C) were constructed (Fig. 43). 

Not only the viscosity but also the temperature dependence of the viscosity can be related to the structure of mineral oil fractions. 

The viscosity-temperature relationship of mineral oil fractions, and in fact of many other liquids, can be represented by a formula proposed by Cornelissen and Waterman24... 

It should be pointed out that this method for ring analysis and branching analysis is based exclusively on reliable data of n, d, M and a of pure individual hydrocarbons, and holds, within the limits of accuracy of the determination, for widely differing types of branched as well as non-branched saturated hydrocarbon mixtures. It is particularly recommended for the structural analysis of saturated polymers, where other statistical methods (w- -M-method, v-n-d-method, etc.) fail because they have been developed for mineral oils, and are based on correlations of physical data of mineral oil fractions that always show approximately the same small degree of branching 1-2 branchings per molecular weight = 100. 

The application of several methods for structural analysis of mineral oils is, in general, limited to those fractions in which no structural elements are present in larger quantities than normally occur in mineral oil fractions. In highly aromatic concentrates, for instance, the normal analytical methods (n-d-M v-n-d) may give inaccurate results, because different types of aromatics may influence the physical constants of the oil differently. 

Van Nes and Van Westen42 described the physical constants and elementary composition of intermediates in the complete hydrogenation of a large number of mineral oil fractions. These data were used by Geelen8 to study the behaviour of mono- and di-aromatics during catalytic hydrogenation. 

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