RU2267124C1 - Colorimetric method of determination of presence of iron in motor petrol - Google Patents

Abstract

FIELD: methods of analysis of materials, motor petrols in particular.

SUBSTANCE: proposed method includes drawing sample, conversion of iron into liquid phase, addition of 1-2 drops of potassium ferricyanide (III) indicator at concentration of 5-10 mass-% followed by estimation of presence of iron by change of tint of aqueous phase; conversion of iron into aqueous phase is carried out by addition of oxidant solution to sample at ratio of 1:10-15; solution is prepared by mixing 11.25 g of potassium iodide, 7.5 g of potassium iodate, 45 ml of concentrated hydrochloric acid and diluting with distilled water to 200 cm³; then solution is mixed for 1-3 min and distilled water is added at ratio of 4:1 relative to oxidant solution volume; indicative of presence of iron is change in tint of aqueous phase after addition of indicator from yellow-green to blue-green.

EFFECT: enhanced reliability of determination.

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Description

The invention relates to methods for the analysis of materials, in particular motor gasolines, mainly for the presence of iron, and can be used at gas stations, petrol bases and storage facilities and other enterprises consuming and producing motor gasolines.

The authors were faced with the task of developing an express method for the analysis of gasoline, which allows one to determine the presence of iron in it with an acceptable degree of reliability of the results.

It is known that in the Russian Federation at present, to increase the octane number of gasoline, additives are widely used, which include ferrocene. Iron-containing additives based on derivatives of ferrocene (A.M. Danilov, "Additives and additives", M .: Chemistry, 1996, p.100, 187) are part of many additives for motor gasolines, are carriers of the antiknock effect. The iron content in gasoline is limited by regulatory documents (ND) (no more than 40 mg / dm ³ ) [A.S. Safonov, A.I. Ushakov, I.V. Chechkenev. Automotive fuels: Chemotology. Operational properties. Range. - SPb., 2002, p.222]. An increase in the iron content in gasoline leads to a negative effect on the fuel systems and engine of the car (significantly reduce the life of spark plugs, catalytic converters and oxygen sensors (lambda probes), increase wear on engine parts, and increase gum formation).

Currently, there are a number of methods for determining the iron content in gasoline.

The most sensitive method for determining iron in gasoline (the range of detectable concentrations is from 1 to 400 mg / dm ³ ) is the atomic absorption method [L. M. Zamilova, V. I. Sokolova, T. G. Biktimirova, I. I. Ryzhenko. Atomic absorption determination of iron in petroleum products. Chemistry and technology of fuels and oils, 1990, No. 10, p.31-32]. The definition consists in the fact that a sample previously prepared for analysis is atomized and the iron content is measured by the resonance absorption of the analytical iron line (248.8 nm) in the atomic spectra of the analyzed sample.

The disadvantage of this method is the complexity of the hardware design (expensive device, gas lines of acetylene and air), which affects the cost of the control method. In addition, as practice has shown, there are cases when it is urgent to determine not the quantity, but the qualitative presence of iron.

The closest and taken as a prototype is the express method for the qualitative determination of iron in gasoline containing ferrocene or its derivatives [O. M. Panady, V. E. Emelyanov, E. V. Aleksandrova, S. N. Onoychenko. The definition of iron in gasoline, "Chemistry and technology of fuels and oils", 1996, No. 5, p.51]. The express method is based on the color reaction of potassium hexacyanoferrate (III) K ₃ [Fe (CN) ₆ ] with ferrocene in an acidic medium. The analysis is carried out as follows. A few drops of the test gasoline are treated with acetic acid (~ 3 ml) and two to three drops of a 10% aqueous solution of K ₃ [Fe (CN) ₆ ] are added. The appearance of a green color in the water layer indicates the presence of ferrocenes with a content of more than 2 mg / dm ³ (0,0002%), with a higher content (> 100 mg / dm ³ ) of ferrocene, a turnbule blue precipitate is formed.

The disadvantage of this method is the low reliability of the obtained determination results on various brands of gasoline. So, if gasoline contains other additives, such as monomethylaniline (MMA), methyl tert-butyl ether (MTBE) and alcohols, then in the range of iron content of 2-10 mg / dm ^{3 the} color of the aqueous layer indicates its absence (yellow) . At present, it is precisely such gasolines that are increasingly being used.

The technical result of the invention is to increase the reliability of the results of determining the presence of iron in gasoline of various brands.

This technical result is achieved by the fact that in the known rapid method for the qualitative determination of the presence of iron in gasoline, including sampling, the conversion of iron into the aqueous phase and the addition of an indicator, according to the invention, the conversion of iron into the aqueous phase is carried out by adding, in a ratio of 1: 10- 15 to the sample, an oxidizing solution obtained by mixing 11.25 g of potassium iodide, 7.5 g of potassium iodide, 45 ml of concentrated hydrochloric acid and diluting with distilled water to 200 cm ³ , stirring for 1-3 min and adding distilled water taken in a ratio of 4: 1 to the volume of the oxidizing agent solution, while the presence of iron is judged by the color change of the aqueous phase after adding the indicator from yellow-green to blue-green.

The essence of the invention boils down to the fact that the claimed method uses a well-known high-quality reaction to iron (II) with the formation of a precipitate of Turnbull blue (Fe ₃ [Fe (CN) ₆ ] ₂ ) [I.K. Tsitovich. Course of analytical chemistry. M .: "Higher School", 1972, p.144]. Since iron is in the organic phase (gasoline) in the form of an organometallic complex (ferrocene), it is necessary to destroy the organometallic complex to form Fe ^{2+ ions} , which then interact with the indicator (potassium hexacyanoferrate (III)), staining the aqueous solution from yellow green to blue. The destruction is achieved by using, as an oxidizing agent (the organic part of the complex), a hydrochloric acid solution of iodine monochloride, identified during the research. The appearance of a yellow-green color already indicates the presence of iron in gasoline. With increasing iron content in gasoline, the color from yellow-green changes through blue-green to blue, that is, the higher the iron content, the closer the color to blue.

Thus, the invention contributes to an increase in the number of methods for determining the presence of iron in gasoline of various grades with increasing reliability. The authors of the combination of well-known and distinctive features in the scientific, technical and patent literature were not found.

The starting materials for the implementation of the method are:

the oxidizing agent is a hydrochloric acid solution of iodine monochloride (orange), prepared as follows: 11, 25 g of potassium iodide (TU 6-09-2008-77) are weighed into a flask with a capacity of 100 cm ³ , 45 ml of concentrated hydrochloric acid and 7.5 g are added potassium iodide (GOST 4232-77), shaken and adjusted to the mark with distilled water. The resulting clear orange solution is diluted twice with distilled water (the solution is stored for 2-3 months);

indicator - 5-10% solution of potassium hexacyanoferrate (III) (GOST 4206-75);

distilled water.

Potassium hexacyanoferrate (III) (potassium hexacyanoferriate, potassium iron-hydrogen sulfide, potassium ferricyanide, red blood salt) K ₃ [Fe (CN) ₆ ], a reagent known in analytical chemistry, is commercially available.

To substantiate the claimed operational parameters, samples (No. 1-11) were prepared (Table 1) by mixing ferrocene — Fe (C ₅ H ₅ ) ₂ with pure gasoline (without iron additives). The presence of iron was determined by the claimed method (the results are presented in table 2).

Table 1 The composition of the tested samples of gasoline Sample No. Base gasoline The content of Fe, mg / DM ³ 1 AI-80 0 2 - "- 5 3 AI-92 + MMA 5 4 AI-92 7 5 AI-92 10 6 AI-95 + MMA + MTBE 5 7 AI-95 + MMA + MTBE 10 8 AI-95 fifteen nine AI-98 + alcohols + MTBE 10 10 - "- fifty eleven - "- twenty

The method was carried out as follows.

Example 1. Take 10 cm ³ sample No. 5 containing 10 mg / DM ³ iron, add 1 cm ³ solution of iodine monochloride, shake for 1 min, add 4 cm ³ distilled water, the aqueous phase becomes pale yellow-green color, add 1 drop of a 5% solution of potassium hexacyanoferrate (III), after which it is thoroughly shaken. The color of the water layer changes from yellow-green to blue-green, which indicates the presence of iron. The final conclusion about the presence of iron is carried out after 5-7 minutes.

Example No. 2. 10 cm ^{3 of} sample No. 6 containing 5 mg / dm ^{3 of} iron was taken, 1 cm ^{3 of a} saturated solution of iodine monochloride was added, shaken for 1 min, 4 cm ^{3 of} distilled water was added, the aqueous phase turned pale yellow-green, 2 drops added 5% potassium hexacyanoferrate (III) solution, after which it is thoroughly shaken. The color of the water layer changes from yellow-green to green, which indicates the presence of iron. The final conclusion about the presence of iron is carried out after 5-7 minutes.

When the concentration of iron gasoline in the initial sample is 20 mg / dm ³ or more, after carrying out all the determination steps, blue flakes are formed at the interface and in the volume of the aqueous phase, then they fall to the bottom. The test results of the samples are presented in table 2.

table 2 The test results of the samples of the claimed method No. Samples No. The sequence of technological operations and operational parameters 1 2 3 4 5 6 7 8 nine 10 eleven 1 2 3 4 5 6 7 8 nine 10 eleven 12 thirteen 1 Sample volume, cm ³ The definition of the claimed method 10 10 twenty fifteen twenty 10 fifteen 10 twenty fifteen 10 2 The amount of oxidizing agent, cm ³ 1 1 2 2 * 2 1 1,5 3 * 2 1,5 0.5 * 3 Mixing time min 2 2 2 2 1 3 1 1 2 1 0.5 * 4 Dilution 1: 4 1: 8 * 1: 4 1: 4 1: 4 1: 4 1: 4 1: 4 1: 4 1: 4 1: 4 5 The volume of the aqueous phase, cm ³ 4 8 8 8 8 4 6 12 8 6 2 6 The color of the aqueous phase before the indicator yellow yellow yellow yellow yellow-green yellow yellow-green yellow yellow-green green yellow 7 Number of indicator, cap. 1 1 1 2 2 2 1 2 5* 2 2 8 The color of the aqueous phase with indicator yellow yellow green yellow blue-green green blue-green yellow blue-green syn. yellow nine Conclusions about the presence of iron - - + - + + + - + + - 10 The content of Fe, mg / DM ³ AAC ** 0 5 5 7 10 5 10 fifteen 10 fifty twenty eleven Comparability with real Fe content + - + - + + + - + + - * - tests conducted in conditions that go beyond the boundaries of the parameters of the proposed method.
** - to confirm the reliability of the results of the proposed method, the amount of iron is determined on AAS.

From the test results of the samples shown in table 2, we can see that the dilution of the aqueous phase is more than 1: 4 (sample No. 2), excess oxidizing agent (samples No. 4 and 8), the mixing time is less than 1 minute (sample No. 11) leads to unreliable results of the determination, an excess of the indicator does not affect the reliability of the results, but there is no need for an overrun of the indicator.

To confirm the technical result obtained - to increase the reliability of the results of determining the presence of iron in gasoline of various grades in the range of iron content of 2-10 mg / dm ³ , in gasolines containing other additives, samples No. 3, 6, 7, 9 were presented, presented in the table 1, according to the prototype method. The results of the study are presented in table 3. As can be seen from the results, this method does not allow to reliably determine the presence of iron in gasolines containing additives, in addition to ferrocene, also monomethylaniline, MTBE and alcohols.

Table 3 The gasoline test results of the claimed method and the known prototype No. The sequence of technological operations and operational parameters Samples No. 3 6 7 nine 1 2 3 4 5 6 1 The content of Fe, mg / DM ³ 5 5 10 10 2 The volume of acetic acid, ml 3 3 3 3 3 Number of indicator, cap. 2 3 2 3 4 The color of the aqueous phase with indicator yellow yellow yellow yellow 5 Conclusions about the presence of iron - - - - 6 Comparability with real Fe content - - - -

Thus, the application of the invention will expand the list of grades of gasoline, which can reliably determine the presence of iron.

Claims (1)

A colorimetric method for determining the presence of iron in motor gasolines, including sampling, transferring iron to the aqueous phase, adding 1-2 drops of potassium hexacyanoferrate (III) indicator with a concentration of 5-10 wt.%, And subsequent assessment of the presence of iron by changing the color of the aqueous phase, characterized in that the transfer of iron into the aqueous phase is carried out by adding in a ratio of 1: 10-15 to the sample a solution of an oxidizing agent obtained by mixing 11.25 g of potassium iodide, 7.5 g of potassium iodide, 45 ml of concentrated hydrochloric acid, and thinner distilled water to 200 cm ³ , stirring for 1-3 minutes and adding distilled water taken in a ratio of 4: 1 to the volume of the oxidizing solution, while the presence of iron is judged by the color change of the aqueous phase after adding the indicator from yellow-green to blue green.