STUDY OF THE COMPOSITION OF ALKANE AND ISOALKANE HYDROCARBONS IN LIGROIN FRACTIONS OF SELECTED CRUDE OILS FROM FIELDS IN TOMSK OBLAST

S. I. Khoroshko, V. A. Kuznetsova, G. A. Lagotskaya

(Presented by the Scientific-Methodological Seminar of the organic departments of the Faculty of Chemical Technology)

The composition of the ligroin fraction of crude oil \((150—200^\circ\mathrm{C})\) is very difficult to study because of the presence of a large number of \(C_{10}—C_{11}\) isomers having similar physicochemical properties. Complete identification of all ligroin components has so far been impossible. Some progress in this field has been achieved owing to the great capabilities of capillary chromatography using calibration mixtures (isomerizates) as “secondary standards” [1].

Dearomatized samples of petroleum ligroins from the Olen’e and Sredne-Nyurol’sk fields were studied. The investigation was carried out in two stages: 1. Study of the composition of calibration mixtures. 2. Qualitative identification of alkane and isoalkane hydrocarbons of ligroin on the basis of the known composition of isomerizates. The calibration mixtures were obtained by isomerization of n-decane and n-undecane in the presence of \(\mathrm{AlBr_3}\) as catalyst. The method of E. K. Bryanskaya, V. A. Zakharenko, and Al. A. Petrov [2] was taken as the basis. Analysis of the isomerizates was performed on a “Khrom-2” chromatograph with a flame-ionization detector. The chromatographic column was a copper capillary 0.5 mm in diameter and 100 m long; the stationary phase was squalane, and the carrier gas was nitrogen. Identification of the isomerizate components was carried out using the Kovats retention-index system.

According to A. A. Martynov and M. S. Vigdergauz [3], the isoalkanes of composition \(C_{10}\) have been decoded. To identify \(C_{11}\) isoalkanes, the “similarity” method was applied, based on observed regularities in changes in Kovats index values when the molecule chain is lengthened by one methyl group, and consisting in the fact that isoalkanes with branches identical relative to the terminal groups have index values differing by 100 units. “Similarity” is also observed in the order of elution of groups of isomers.

Analysis of the ligroin samples was carried out under the same conditions as for the isomerizates. The components of the paraffin-naphthene portion of the ligroin were identified by comparing their retention characteristics with the Kovats indices of isoalkanes in the isomerizate.

The results of the study are presented in the table. It is seen from the table that the n-undecane isomerizate contains 21 hydrocarbons of composition \(C_{10}\) and 26 alkanes \(C_{11}\). The ligroin samples contain 16 alkanes \(C_{10}\) and 20—\(C_{11}\).

Table 1

Kovats indices of alkanes and isoalkanes of the isomerizate and of the ligroins of the Olen’ya and Sredne-Nyurol’skaya crudes

Continuation of Table 1

Conclusions

1. A study was carried out of the composition of the isomerizates of n-decane and n-undecane by capillary gas chromatography. The isoalkanes \(C_{10}\) were completely decoded, and \(C_{11}\) partially.

2. The composition of the paraffin–naphthene portion of the ligroins of two oils from fields in Tomsk Oblast was studied. In the ligroin sample of Olenya oil, 59 alkanes of composition \(C_9\)—\(C_{11}\) were found; in the ligroin sample of Sredne-Nyurolskaya oil, 68. Hydrocarbons of weakly branched structures predominate.

LITERATURE

1. Bryanskaya E. K., Oleinina Z. K., Petrov A. A. Collection “Methods for the Analysis of Organic Compounds of Petroleum, Their Mixtures and Derivatives.” Issue 2, 1969, 7–20.

2. Bryanskaya E. K., Zakharenko V. A., Petrov A. A. “Neftekhimiya,” vol. IV, No. 5, 1966, 729.

3. Martynov A. A., Vigdergauz M. S. “Neftekhimiya,” vol. X, No. 5, 1970, 763–772.