Determination of the Elemental Composition of Oils by Gas Chromatography
Abstract Generated abstract
This study examines the application of gas chromatography to elemental analysis of oils, focusing on determination of carbon and hydrogen as principal oil components. An apparatus with a closed helium system was constructed, samples were combusted with nickel oxide at 900 to 950°C, water was converted to acetylene with calcium carbide, and gaseous products were separated on silica gel and quantified using sucrose calibration. Tests on model organic compounds and several oils showed carbon values close to theoretical or classical analytical results, while hydrogen determinations were less accurate, apparently because of incomplete water conversion. The method was found to reduce analysis time to about 40 to 50 minutes and to provide accuracy generally comparable with classical methods, although heavy oil residues required improved combustion conditions.
Full Text
DETERMINATION OF THE ELEMENTAL COMPOSITION OF OILS BY GAS CHROMATOGRAPHY
V. A. KUZNETSOVA, N. P. ZARUBINA, L. A. ZHAROVA
(Presented by the scientific-methodological seminar of the organic departments of the Faculty of Chemical Technology)
The elemental composition is one of the indicators of the quality of oil, its commercial properties, and the geochemical characteristics of an oil field.
At present, the elemental composition of oils in most laboratories is determined by classical methods. These methods provide high accuracy; however, they are lengthy and labor-intensive. One of the most promising directions in elemental analysis is the use of gas chromatography for determining the final decomposition products.
The task of our work is to transfer known methods of elemental analysis using gas chromatography to the elemental analysis of oil. This stage of the work included determination of the principal components of oil—carbon and hydrogen.
To carry out elemental analysis, an apparatus was constructed, based on the scheme described by A. V. Nepryakhina and coauthors [1, 2]. The scheme of the apparatus is shown in the figure. A closed-volume system was implemented. Combustion of the weighed sample was carried out in an at-
Fig. 1. Diagram of the elemental-analysis apparatus. 1 — helium cylinder, 2 — reducer, 3 — fine-control valve, 4 — carrier-gas dryer, 5 — rotameter, 6 — detector, 7 — three-way valves, 8 — shutoff valves, 9 — combustion tube, 10 — heating furnace, 11 — reactor, 12 — chromatographic column, 13 — recorder.
helium atmosphere. Specially prepared nickel oxide [3] was used as the oxidizing agent.
A weighed portion of the substance to be analyzed, together with the oxidizing agent, is placed in the combustion tube (9). The system is purged with helium until the air is completely displaced, which is recorded on the chart tape. Then the combustion volume is isolated by closing the shutoff valves (7, 8), and the flow of carrier gas is directed past the combustion unit. Combustion is carried out at a temperature of 900–950°C for 5–7 min.
To convert water into acetylene, calcium carbide placed in the reactor (11) is used.
The gaseous products are separated on a chromatographic column filled with silica gel; the temperature in the thermostat is 100°C. The calculation is carried out from the titer determined for the standard substance, which is sucrose.
The procedure was developed and tested on individual organic substances. As is seen from Table 1, this method gives an acceptable error for carbon.
Table 1
Carbon and hydrogen content in organic compounds
| Substance | Carbon content, % | Carbon content, % | Hydrogen content, % | Hydrogen content, % |
|---|---|---|---|---|
| calculated | found | calculated | found | |
| Benzoic acid | 59.0 | 59.8 | 4.9 | 4.1 |
| Salicylic acid | 52.1 | 52.7 | 4.4 | 3.6 |
| Undecane | 84.6 | 85.3 | 15.4 | 14.8 |
The maximum deviation from the theoretical content is 0.8% abs. The error for hydrogen increases, which can be explained by the incomplete conversion of water into acetylene.
The results of oil analysis for the determination of carbon and hydrogen using gas chromatography (Table 2) are in agreement
Table 2
Carbon and hydrogen content in oil and oil residue
(I — determined by the classical method, II — determined using gas chromatography)
| Object of study | Carbon | Carbon | Hydrogen | Hydrogen |
|---|---|---|---|---|
| I | II | I | II | |
| Pervomaiskaya oil | 86.1 | 86.2 | 12.4 | 12.0 |
| Varieganskaya oil | 86.2 | 86.7 | 12.8 | 12.0 |
| Puglatynskaya oil | 86.9 | 85.6 | 12.6 | 11.9 |
| Oil residue above 350°C | 86.8 | 84.6 | 11.6 | 10.4 |
with the data of the classical method. However, for the heavy oil residue boiling above 350°C, low results were obtained for both carbon and hydrogen, which is evidently explained by an incorrectly chosen combustion regime.
Conclusions
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The possibility of using gas chromatography for the determination of C and H in oil has been demonstrated.
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It has been established that this method reduces the analysis time to 40–50 min and provides an accuracy commensurate with that of the classical method.
Literature
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A. V. Nepryakhina et al. In: Methods for the Analysis of Organic Compounds of Oil, Their Mixtures, and Derivatives. Moscow, Nauka, 1969.
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I. K. Chudakova et al. Ibid.
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M. N. Chumachenko. Determination of the Elemental Composition of Organic Substances Using Gas Chromatography. Abstract of a dissertation submitted for the degree of Candidate of Chemical Sciences. Moscow, 1966.