Comparative Study of Various Sample Preparation Methods for the Determination of Elements in Crude Oils and Petroleum Products by the Spectral Method
Abstract Generated abstract
This paper compares indirect sample preparation procedures for spectral determination of trace metallic impurities in crude oils and petroleum products. Sulfate ashing, direct ashing, ashing according to GOST 1461-59, and ashing with carbon powder as a collector were applied to oil samples from several Western Siberian deposits, with manganese, nickel, lead, titanium, vanadium, and copper determined from prepared ash concentrates. The results indicate that sulfate ashing and carbon powder collector ashing give the most suitable recoveries for the elements studied, while direct ashing and the GOST procedure can lead to partial losses. A comparison with photometric determinations showed satisfactory agreement, and ashing in larger quartz dishes appeared preferable to crucibles because shorter heating reduced element loss.
Full Text
COMPARATIVE STUDY OF VARIOUS SAMPLE PREPARATION METHODS FOR THE DETERMINATION OF ELEMENTS IN OILS AND PETROLEUM PRODUCTS BY A SPECTRAL METHOD
R. D. GLUKHOVSKAYA, L. S. KOLESNIKOVA, Yu. A. KARBAINOV,
L. V. PENEVA
(Presented by the scientific seminar of the Department of Analytical Chemistry)
For the determination of metallic impurities in oils and petroleum products, the spectral method of analysis is widely used; it makes it possible to determine simultaneously a large range of elements over a wide range of concentrations with fairly high sensitivity.
Spectral methods of analysis are divided into direct ones, which provide for the direct analysis of the sample, and indirect ones, associated with concentration (most often with ashing) of the sample. The second group is the most suitable for determining traces of elements, since in this case more than a thousandfold enrichment of the sample is achieved.
Sample preparation is one of the most labor-consuming and critical operations. The accuracy and sensitivity of the analytical results depend to a considerable extent on the choice of the ashing method and on its practical execution.
A large number of works are known in the literature devoted to the spectral determination of elements using various ashing methods [1—5], but when particular impurities are involved it is difficult to give preference to any one of these methods. In this connection, in the present work studies were carried out on a comparative examination of various methods of sample preparation. Below are given the results of analysis of certain deposits of Western Siberia using different variants of sample ashing.
Ashing according to GOST 1461—59 [4]. An ashless paper filter is placed in a previously prepared quartz crucible so that it fits tightly against the bottom and walls of the crucible. The crucible with the filter is weighed, and about 25 g of oil is placed in it. A second ashless filter, folded in the form of a cone with the upper end cut off, is lowered into the oil. After the filter has become impregnated with oil, it is ignited and burned until a dry carbonaceous residue is obtained. The crucible with its contents is transferred to a muffle furnace heated to \(500 \pm 50^\circ\mathrm{C}\) and kept at this temperature until the residue is completely ashed. The ash obtained is analyzed by the spectral method. For this purpose, 100—120 mg of spectrally pure carbon powder is added to the ash and ground in a fluoroplastic mortar in the presence of alcohol for 1.5—2 hours. Part of the mixture obtained is diluted with carbon powder by factors of 10 and 100 and again thoroughly ground to a homogeneous mass.
All prepared concentrates are placed in the channel of the lower electrode (anode). On one plate (UFSH), 2—3 exposures are photographed.
spectra of the prepared samples and standards with concentrations from \(3\cdot 10^{-5}\%\) to \(1\cdot 10^{-2}\%\).
Standards in this work were prepared by grinding the oxides of the corresponding elements with carbon powder by the usual method [5].
The following lines were used as analytical lines:
manganese with wavelength \(2801.06\ \text{Å}\),
titanium \(3088.03\ \text{Å}\),
vanadium \(3185.39\ \text{Å}\),
nickel \(3050.82\ \text{Å}\),
copper \(3247.54\ \text{Å}\),
lead \(2833.07\ \text{Å}\).
The background near the line served as the comparison element.
Sulfate ashing [6]. A corresponding weighed portion of oil is placed in a quartz dish, an equal amount of concentrated sulfuric acid is added, and the mixture is carefully heated on an electric hot plate until a solid carbonaceous mass is obtained. After this, the dish is transferred to a muffle furnace and calcined at a temperature of \(500\pm 50^\circ\text{C}\) until ash is obtained, which is analyzed by the spectral method, as described above.
Direct ashing [7] was carried out by gradually heating the oil sample on an electric hot plate until a solid carbonaceous mass was obtained. The subsequent course of the analysis is analogous to that described earlier.
Ashing using carbon powder as a collector [2, 3, 8, 10]. Into a dish with a weighed portion of oil, 150 mg of spectrally pure carbon powder is placed, and the mixture is gradually heated on an electric hot plate until a solid mass is obtained. The contents of the dish are calcined in a muffle furnace under the same conditions and analyzed according to the procedure described above.
The results of determining manganese, nickel, lead, titanium, vanadium, and copper in Ubinskaya 311 and Yuzhno-Cheremshanskaya oils using the sample-preparation methods described above are given in Table 1.
Table 1
| Ashing method | Mn | Ni | Pb | Ti | V | Cu |
|---|---|---|---|---|---|---|
| Sulfate | \(1.5\cdot 10^{-5}\) | \(3.0\cdot 10^{-4}\) | \(2.0\cdot 10^{-6}\) | \(7.1\cdot 10^{-6}\) | \(4.5\cdot 10^{-4}\) | \(4.6\cdot 10^{-5}\) |
| Direct | \(1.5\cdot 10^{-5}\) | \(1.3\cdot 10^{-4}\) | \(1.9\cdot 10^{-6}\) | \(5.5\cdot 10^{-6}\) | \(2.5\cdot 10^{-4}\) | \(3.6\cdot 10^{-5}\) |
| GOST 1461-59 | \(1.7\cdot 10^{-5}\) | \(1.5\cdot 10^{-4}\) | \(1.7\cdot 10^{-6}\) | \(5.9\cdot 10^{-6}\) | \(3.6\cdot 10^{-4}\) | \(3.4\cdot 10^{-5}\) |
| With collector | \(3.9\cdot 10^{-5}\) | \(2.6\cdot 10^{-4}\) | \(2.1\cdot 10^{-6}\) | \(6.5\cdot 10^{-6}\) | \(8.3\cdot 10^{-4}\) | \(4.1\cdot 10^{-5}\) |
| Ubinskaya 311 | Ubinskaya 311 | Ubinskaya 311 | Ubinskaya 311 | Ubinskaya 311 | Ubinskaya 311 | Ubinskaya 311 |
| Sulfate | \(1.3\cdot 10^{-4}\) | \(3.3\cdot 10^{-3}\) | \(2.0\cdot 10^{-4}\) | \(3.3\cdot 10^{-4}\) | \(2.5\cdot 10^{-3}\) | \(4.2\cdot 10^{-4}\) |
| Direct | \(1.1\cdot 10^{-4}\) | \(2.1\cdot 10^{-3}\) | \(1.4\cdot 10^{-4}\) | \(4.3\cdot 10^{-4}\) | \(1.9\cdot 10^{-3}\) | \(3.0\cdot 10^{-4}\) |
| GOST 1461-59 | \(1.3\cdot 10^{-4}\) | \(2.0\cdot 10^{-3}\) | \(2.3\cdot 10^{-4}\) | \(4.9\cdot 10^{-4}\) | [[unclear: value appears as \(2.3\cdot 1,^{-3}\)]] | \(3.2\cdot 10^{-4}\) |
| With collector | \(3.2\cdot 10^{-4}\) | \(3.8\cdot 10^{-3}\) | \(2.5\cdot 10^{-4}\) | \(5.0\cdot 10^{-4}\) | \(3.5\cdot 10^{-3}\) | [[unclear: value appears as \(4.2\cdot 11^{-4}\)]] |
| Yu.-Cheremshanskaya | Yu.-Cheremshanskaya | Yu.-Cheremshanskaya | Yu.-Cheremshanskaya | Yu.-Cheremshanskaya | Yu.-Cheremshanskaya | Yu.-Cheremshanskaya |
It is evident from Table 1 that, for the determination of manganese, nickel, lead, titanium, vanadium, and copper, the most rational methods are acid ashing and ashing with a collector (carbon powder). Direct ashing and ashing according to GOST 1461—59 lead to partial loss of some elements.
Comparison of the sulfate method of ashing a sample of oil from the Myldzhinskoye field, carried out in quartz dishes with a capacity of 200 ml and in crucibles with a capacity of 75 ml, showed (Table 2) a certain underestimation of the results obtained when ashing in crucibles. This is apparently due to
Table 2
| Ashing method | Mn | Ni | Pb | Ti | V | Cu |
|---|---|---|---|---|---|---|
| Found, % | Found, % | Found, % | Found, % | Found, % | Found, % | |
| Sulfate in dishes | $4.5\cdot10^{-4}$ | $2.7\cdot10^{-4}$ | $1.7\cdot10^{-5}$ | $2.2\cdot10^{-5}$ | $8.3\cdot10^{-4}$ | $4.5\cdot10^{-4}$ |
| Sulfate in crucibles | $4.1\cdot10^{-4}$ | $2.5\cdot10^{-4}$ | $1.2\cdot10^{-5}$ | $2.1\cdot10^{-5}$ | $7.5\cdot10^{-4}$ | $3.5\cdot10^{-4}$ |
| Data of photometric determination | $5.7\cdot10^{-4}$ | $2.6\cdot10^{-4}$ | — | $3.2\cdot10^{-5}$ | $6.7\cdot10^{-4}$ | — |
longer ashing. The samples placed in a crucible were ashed for 3–4 hours longer than in dishes, which led to partial loss of elements.
Conclusions
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The results of the photometric determination presented in Table 2 agree satisfactorily with the data of spectral analysis.
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A comparative study has been carried out of certain indirect methods of preparing oil samples for spectral analysis.
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It has been found that the most suitable methods are sulfate ashing and ashing using carbon powder as a collector.
LITERATURE
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