RU2292546C1 - Method of evaluating induction period of motor gasolines - Google Patents

Abstract

FIELD: petroleum product test methods.

SUBSTANCE: invention relates to petroleum product testing area and mainly to evaluation of chemical stability of motor gasolines to provide methods applicable in research institutions, in refinery laboratories, and at enterprises dealing with development and application of motor fuels as well as with problems concerning preservation of automobile gasolines during storage and transportation periods. In a method of evaluating induction period of motor gasolines from sample oxidation time at 100°C calculated in terms of a mathematic relationship using an informational parameter of the sample, the latter is content of unsaturated hydrocarbons Cn, which is preliminarily determined in the sample, and sample oxidation time at 100°C (τ100) is calculated in terms of following relationship: τ100 = k1Ln(Cn)+k2, where k1 and k2 are empirical constants.

EFFECT: accelerated motor gasoline induction period evaluation without reduction in requirements to accuracy and reliability and increased determination safety.

1 dwg, 3 tbl

Description

The invention relates to the field of testing of petroleum products, mainly to assess the chemical stability of motor gasolines, and can be used in research organizations, in laboratories of oil refineries and in organizations involved in the development and use of motor fuels, and for assessing the persistence of motor gasolines during storage and transportation.

One of the main operational properties of motor gasolines, which determine the stability of quality indicators during storage, is chemical stability, which characterizes the ability to withstand oxidative processes during storage and use (by the length of the induction period of oxidation and the content of actual resins) [B.V. Belyanin, V.N. .Erikh. Technical analysis of oil products and gas. L .: Chemistry, 1979, p. 84].

Unsaturated hydrocarbons exhibit the greatest propensity for oxidation and gum formation from hydrocarbon composition [A.S. Safonov, A.I. Ushakov, N.D. Yuskovets. Automotive Maintenance Materials. St. Petersburg: Gidromethioizdat, 1998, p.145]. The content of unsaturated hydrocarbons is judged by the iodine number, i.e. by the amount of iodine (in grams) to 100 grams of the analyzed fuel [GOST 2070. Light petroleum products. Method for determination of iodine numbers and unsaturated hydrocarbon content].

A known method for determining the induction period of fuel oxidation by heating its predetermined amount (10 cm ³ ) to a predetermined temperature (200 ° C), thermostating with periodic selection (after 1 min) of fuel portions (1 cm ³ volume) and determination in them (chromatographically) the content of dissolved oxygen with subsequent fixation of the induction period according to the difference between the start time of heating and the moment of a sharp decrease in the content of dissolved oxygen (by 3-5%) relative to its solubility in fuel [ed. No. 1049804, G 01 N 33/22].

In the known method it should be noted the high complexity associated with the need for periodic sampling of fuel to determine the content of dissolved oxygen.

There is also a method for determining the induction period of fuel oxidation by the time interval from the beginning of the exposure of the fuel sample in an airtight container with a given ratio of liquid and gas phases (gas phase - atmospheric air at atmospheric pressure, the volume of which is 40-50% of the tank volume) to a sharp decrease in the information gas parameter. At least 2 tests of each fuel sample are carried out, the first of which is carried out at a constant temperature of 170 ° C, and the temperature of the second test is selected depending on the start time of the linear portion of the kinetic dependence of the oxygen consumption on the oxidation of the first test sample. On the basis of 2 tests, time periods are determined for a given fuel sample for which a conditionally set amount of oxygen would be consumed in excess of its initial amount in the tank, and the induction period τ _{100 of} oxidation at a temperature of 100 ° C is calculated on the basis of the mathematical dependence [patent No. 2175131 G 01 N 33/22].

The disadvantages of the method are: the complexity of the calculations; the dependence of the results on the accuracy of constructing the linearity of the kinetic dependences of the absorption of oxygen concentration in the gas phase; decrease in the sensitivity of the method of determination due to the limited reproducibility of the results by the temperature range of the test (120-220 ° C), the volume of the gaseous medium (40-50%) and the time interval of the flow rate of a conditionally set amount of oxygen 1.5-1.7 times higher than the initial amount gas phase capacity.

The closest in technical essence and taken as a prototype is the standard method for determining the induction period of gasoline oxidation [GOST 4039-88. Gasolines are automobile. Methods for determining the induction period], characterizing the tendency of gasoline to oxidize and gum under storage conditions.

The essence of the method (method B) is to determine the time interval during which a sample of the analyzed gasoline, which is in an oxygen atmosphere at a pressure of 700 kPa (7 kgf / cm ² ) and a temperature of 100 ° C, is not oxidized.

In the prototype, a sample of motor gasoline with a volume of (50 ± 1) cm ³ , aged at a temperature of (20 ± 5) ° C and filtered through a paper filter, is poured into a glass vessel previously placed in a test container (bomb), with a ratio of liquid and gas volumes phases V _W : V _g = 1: 5. The test container (bomb) is filled with oxygen until overpressure (700 ± 20) kPa (7 ± 0.2 kgf / cm ² ) is created and placed in a heating water bath having a constant temperature (100 ± 2) ° С. The kinetic dependence of the change in oxygen pressure on the oxidation time is removed.

For the induction period at an average test temperature of (100 ± 2) ° C, the time interval from the beginning of the holding of the test container (bomb) in the heating water bath to the appearance of the inflection point on the pressure change curve, characterized by a moment at which, after the previous pressure drop of 14, 0 kPa in 15 minutes, the same or greater pressure drop is observed over the next 15 minutes.

The calculation of the induction period at a temperature of 100 ° C is as follows:

if the average test temperature is more than 100 ° C, the induction period (IP ₁₀₀ ) in minutes at 100 ° C is calculated by the formula (1):

if the average test temperature is below 100 ° C, the induction period (IP ₁₀₀ ) in minutes at 100 ° C is calculated by the formula (2):

where IP ₁₀₀ is the induction period at a test temperature of 100 ° C, min;

IP _{(100 + Δt)} - induction period at an average test temperature above 100 ° C, min;

IP _(100-Δt) - induction period at an average test temperature below 100 ° C, min;

Δt is the algebraic difference of the average test temperature and 100 ° С, ° С.

The test result is the arithmetic mean of two consecutive definitions.

As a disadvantage of the prototype, we note:

along with the long duration of the determination (up to 5 days for straight-run gasolines and catalytic reforming and cracking gasolines) increased safety requirements associated with the use of oxygen;

to increase the sensitivity of the test, taking into account the reproducibility of the results obtained, high requirements are imposed on the preliminary preparation of the used test equipment:

- the glass vessel is washed with a mixture of toluene with acetone, kept for 6 hours in a medium of potassium dichromate and concentrated sulfuric acid and a thermostat at a temperature of (140 ± 10) ° С for 1 hour;

- the test container (bomb) is washed with a mixture of toluene with acetone, dried and checked for leaks at an excess pressure of 700 kPa (7.0 kgf / cm ² ) for 10 min;

the inadequacy of the results obtained in assessing the propensity for oxidation of motor gasolines containing a significant amount of oil refined petroleum products, since in the oxidation process, fixed during the determination of the induction period, low molecular weight primary oxidation products are formed that slightly affect the propensity of motor gasolines to oxidize;

during the test, the temperature of the heating water bath is constantly monitored to an accuracy of 0.1 ° C, the pressure in the test container (bomb) is continuously measured or counted with an interval of not more than 15 minutes.

The technical result is a reduction in the time for determining the induction period of gasoline without reducing the requirements for accuracy and reliability, improving the safety of the evaluation method.

The specified technical result is achieved by the fact that in the method for evaluating the induction period of motor gasolines by the time interval of oxidation of the sample at 100 ° C, calculated by mathematical dependence using the determined information index of the sample, according to the invention, the content of unsaturated hydrocarbons C _n in the sample of the analyte is determined as the information index motor gasoline and oxidation time interval τ ₁₀₀ samples of gasoline at 100 ° C was calculated by the following dependence imosti:

where τ ₁₀₀ is the time interval for the oxidation of the sample of the analyzed gasoline at 100 ° C, min;

With _n is the content of unsaturated hydrocarbons in the sample of the analyzed automobile gasoline, vol.%;

k ₁ = -197.18 - constant coefficient (obtained experimentally);

k ₂ = 951.09 - constant coefficient (obtained experimentally).

The technical essence of the claimed method consists in the use of an empirical formula that reflects the established dependence of the values of the induction period τ ₁₀₀ on the content of unsaturated hydrocarbons C _n in the sample of analyzed automobile gasoline.

The drawing shows the dependence of the change in the induction period of gasoline on the content of unsaturated hydrocarbons.

The claimed method by determining the content of unsaturated hydrocarbons in the samples of the analyzed gasoline excludes a long oxidation process, increases the safety of the evaluation method by eliminating the use of pure oxygen and high pressure test equipment.

The method is as follows.

Example 1. A sample of unleaded brand gasoline Regular-92 with a volume of 7.5 ml is placed in an Fourier transform IR interferometer and the content of unsaturated hydrocarbons C _n in the sample is determined by absorption of infrared (IR) radiation in the wavelength range from 2.7 to 15, 4 μm [ASTM D 5845 "Standard verification method for determining the content of oxygenates, aromatic and olefinic compounds in the infrared absorption spectrum"]. The content of unsaturated hydrocarbons With _n is 13.2 vol.%.

The time interval for the oxidation of gasoline, calculated by the calculated dependence, corresponds to 442.32 min:

where τ ₁₀₀ is the time interval for the oxidation of the sample of the analyzed gasoline at 100 ° C, min;

With _n is the content of unsaturated hydrocarbons in the sample of the analyzed automobile gasoline, vol.%;

k ₁ = -197.18 - constant coefficient (obtained experimentally);

k ₂ = 951.09 - constant coefficient (obtained experimentally).

The content of unsaturated hydrocarbons can be determined not only by the absorption of infrared (IR) radiation, but also by calculating the value of the iodine number and the average molecular weight of the test fuel [GOST 2070-82 Light petroleum products. Methods for determination of iodine numbers and unsaturated hydrocarbon content].

The inventive method was studied low-octane, high-octane gasoline, low-stabilized and highly stabilized gasoline fractions.

Analysis of the test results to assess the propensity for oxidation of gasoline of the claimed method and prototype (tables 1) revealed:

the expressed logarithmic dependence of the oxidation time (induction period) of motor gasolines on the content of unsaturated (olefin) hydrocarbons (see drawing);

with an increase in the content of unsaturated hydrocarbons, the propensity to oxidize gasoline increases, decreasing the values of the induction period of oxidation.

Table 1
The test results to assess the propensity for oxidation of gasoline of the claimed method and prototype The name of the sample of gasoline The content of unsaturated hydrocarbons, With _n vol.% The value of ln (C _n ) Induction period at 100 ° C, min

, минThe inventive method

min Prototype GOST 4039, τ ₁₀₀ , min Catalytic Cracking Gasoline (BCC) 29.6 3.3877744 283.09 233 Catalytic reforming gasoline (BCR) 1,6 0.4700036 858.41 870.0 Stable gasoline (BGS) 2,8 1,0296194 748.07 741 Unstabilized Pyrolysis Fractions 43.7 3,7773481 206.27 228 Hydrogenated fraction C ₅ -C ₉ 31.9 3,462606 268.33 324 Normal unleaded gasoline Normal-80 twenty 2,9957323 360.39 342 Unleaded gasoline Regular-92 brands 13,2 2,5802168 442.32 441 Premium unleaded gasoline Premium-95 10.6 2,360854 485.58 496 Thermal Cracking Gasoline (BTK) 34,4 3,5380566 253.46 255 Verification mixture No. 1 * 22.4 3,109061 338.05 314 Notes: * a mixture of stabilized and low-stabilized fractions k ₁ = -197.18; k ₂ = 951.09

The adequacy of the quantitative relationship between the estimated indicators (the induction period of motor gasolines from the content of unsaturated hydrocarbons), the reproducibility of the quantitative determination results, the significance of the equation coefficients were determined using F (Fisher's test) and T (Student's test) statistics (table 2).

Assessment of statistical significance showed:

correlation between the induction period of motor gasolines and the content of unsaturated hydrocarbons;

The claimed method and prototype do not differ in reproducibility;

improving the reproducibility of the evaluation method without reducing the requirements for accuracy and reliability.

Table 3 presents a comparative assessment of the claimed method and prototype for the tendency to oxidize gasoline

Table 3
Comparative assessment of the tendency to oxidize gasoline Indicators The inventive method Prototype GOST 4039 Score indicator oxidation time, min oxidation time, min Test conditions: Duration of determination, min 10 100-3000 Sample volume, ml 7.5 one hundred* Number of samples one 2 The sensitivity of the method: Preliminary sample preparation not required the sample is kept at a temperature of 20 ± 5 ° C and filtered through a paper filter, Test Equipment Requirements not presented - the bomb must withstand a pressure of 1240 kPa at a temperature of 100 ° C for 10-15 minutes; - the gasket must hold a pressure of 700 kPa at a temperature of 100 ° C for 24 hours; - a glass vessel, pre-washed with a mixture of toluene with acetone, kept in a medium of potassium dichromate and concentrated sulfuric acid for 6 hours and a thermostat for 1 hour at a temperature of 140 ± 10 ° C. - pressure valves are washed with a mixture of toluene with acetone and dried; - thermostatic bath with a thermostatic liquid (a mixture of distilled water and glycerin) Determination of unsaturated hydrocarbon content + not determined Oxidizing environment not required oxygen 98-99% Method accuracy 1.5% 5-10% Note - * taking into account parallel definitions.

Thus, the claimed method will reduce the time for determining the induction period of gasoline without reducing the requirements for accuracy and reliability, increase the safety of the evaluation method.

Claims (1)

A method for evaluating the induction period of motor gasolines by the oxidation time interval calculated by the mathematical dependence using the determined informational indicator of the sample, characterized in that the informational content of unsaturated hydrocarbons in the sample of the analyzed automobile gasoline is determined, and the oxidation time interval is calculated by the following dependence:

where τ ₁₀₀ is the time interval for the oxidation of the sample of the analyzed gasoline at 100 ° C, min; With _n is the content of unsaturated hydrocarbons in the sample of the analyzed automobile gasoline, vol.%; k ₁ = -197.18 - constant coefficient (obtained experimentally); k ₂ = 951.09 - constant coefficient (obtained experimentally).