Individual Hydrocarbon Composition of Gasoline Fractions of Gas Condensate from the Luginets Field

V. A. Kuznetsova, N. M. Smolyaninova

(Presented by the scientific-methodological seminar of the KhTF)

Knowledge of the individual hydrocarbon composition of light fractions of oils and gas condensates makes it possible to orient oneself correctly in choosing the most rational methods for their use.

Below are presented the results of a study of the hydrocarbon composition of the broad fraction (initial boiling point—122°C) of gas condensate from the Luginets field, located in Tomsk Oblast.

The fractions subjected to study were obtained by atmospheric rectification of the condensate on an ARN-2 unit.

The individual hydrocarbon composition was determined by the method of gas–liquid chromatography on a “Khrom-2” chromatograph with a flame-ionization detector.

The analysis was carried out on a capillary column 200 m long and with an internal diameter of 0.5 mm according to the method developed by M. I. Ivanova¹. Vacuum oil VM-4, applied from a 10% solution in benzene onto the walls of a copper capillary, was used as the stationary phase. The carrier gas was nitrogen, at a rate of 1 ml/min.

Chromatograms were recorded at temperatures of 22 and 95°C for the 28–60°C fraction, at 35 and 68°C for the 60–95°C fraction, and at 35, 50, and 95°C for the 95–122°C fraction.

The results of the analysis are given in the table.

In all, 78 components were identified in the fraction studied, of which only 58 were included in the indicated table; the remaining 20 represent minor impurities (traces) of various hydrocarbons that entered this fraction owing to the low efficiency (20 theoretical plates) of the rectification column. It follows from the table that the composition of the cut studied includes about 63% methane hydrocarbons, among which alkanes of normal structure predominate (55%, calculated on the sum of methane hydrocarbons). Among the iso compounds, monosubstituted ones predominate—73% of the sum of isoparaffins.

Z. K. Olenina and A. A. Petrov² consider that for the majority of gas condensates of the Soviet Union the sum of cyclohexane hydrocarbons in light fractions considerably exceeds the sum of cyclopentane hydrocarbons,

Table

Individual hydrocarbon composition of the gasoline fraction (28–122°C) of gas condensate from the Luginets field

and the ratio of the sum of cyclohexanes to the sum of cyclopentanes lies within the range from 2.33 to 4.49, and this ratio is characteristic only of condensates from gas-condensate fields.

Our data show that in the gasoline fraction of the Luginets gas condensate the content of five-membered naphthenes is 2.5 times greater than that of six-membered ones, i.e., this condensate does not obey the regularity indicated above.

However, it should be noted that there is a relatively high concentration of methylcyclohexane in the fraction (5.90%), which, in combination with a significant content of normal alkanes, in the opinion of the same authors, may serve as a criterion making it possible to distinguish gas condensates from oils.

Among the five-membered naphthenic hydrocarbons, cyclopentane and some of its close homologues of composition C₆—C₈ were found, of which the maximum amount is accounted for by methylcyclopentane (7.95%).

The exceptionally low content of aromatic hydrocarbons in the investigated distillate of the Luginets condensate—only 0.41%—is noteworthy.

The data on the individual composition of the broad hydrocarbon fraction (b.p.—122°C) of the Luginets gas condensate make it possible

to regard it as an especially favorable feedstock for pyrolysis, since this cut is distinguished by a negligible content of aromatics and a high content of paraffinic hydrocarbons, which in pyrolysis give maximum yields of ethylene and other unsaturated compounds.

A significant amount of naphthenic hydrocarbons, with a predominance of five-membered representatives, determines the advisability of using narrow fractions of the cut under study to obtain aromatic hydrocarbons by the platforming method.

Conclusions

1. The individual hydrocarbon composition of the broad fraction (b.p.—122°C) of Luginets gas condensate was determined using a capillary column.

2. It was established that the fraction under study contains 33.84% normal and 28.8% isoparaffinic hydrocarbons, 36.25% naphthenic hydrocarbons, and 0.41% aromatic hydrocarbons.

3. Among the methane hydrocarbons, n-paraffins predominate; among the naphthenic hydrocarbons, five-membered naphthenes predominate.

4. It was shown that gasoline fractions of Luginets gas condensate can serve as feedstock for pyrolysis and platforming.

1. M. I. Ivanova. Use of gas–liquid chromatography for determining the individual composition of straight-run gasolines boiling below 150°C. Dissertation, Irkutsk, 1967. ↩

2. Z. K. Olenina, A. A. Petrov. Some features of the individual composition of gas condensates. Neftekhimiya, 7, No. 3, 1967. ↩