RU2451288C1 - Method of determining sulphur content in diesel fuel - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: fuel sample is placed in a closed volume, analysis is carried out and the amount of sulphur is determined by comparing the obtained results with a calibration curve plotted beforehand, wherein analysis is carried out using ultrasonic signals at resonance frequency between two sensors placed inside a cell and the amount of sulphur-containing impurities in the diesel fuel is determined from the mathematically processed difference between the power of the input and output signals by comparing with the calibration curve of the absorption coefficient versus sulphur concentration.

EFFECT: possibility of designing a method for rapid determination of quantitative content of sulphur-containing compounds in diesel fuel, which does not require expensive equipment and high time expenses and is environmentally safe.

3 cl, 1 dwg

Description

The invention relates to the study of diesel fuels using electrical means and can be used in the oil refining industry, in the storage and sale of fuels in various fields where operational monitoring of its quality is required. Organic sulfur compounds are a natural component of crude oil. During thermal exposure in the process of oil refining, sulfur and its compounds get into oil products in various concentrations. Sulfur compounds poison expensive automobile exhaust gas neutralizers, cause corrosion of equipment, released into the atmosphere, sulfur oxides during combustion create environmental problems. Emission of sulfur compounds into the atmosphere resulting from the combustion of petroleum products is subject to environmental control in all developed countries.

The most “old” method for determining sulfur in petroleum products, the so-called. “The bomb method” [1]. The technology for its implementation is as follows:

- a portion of the test product is burned in a calorimetric bomb filled with compressed oxygen;

- the sulfur dioxide resulting from combustion is absorbed by the alkali previously poured into the bomb;

- oxidize the formed sulfites to sulfates;

- determine sulfur gravimetrically by precipitation with barium chloride BaSO ₄ ;

- weigh the precipitate BaSO ₄ and from the ratio of the molar masses of the elements included in the formula, directly calculate the sulfur content.

The method is applicable to products with low volatility that can be weighed in an open crucible. For light petroleum products its use is very difficult, because Accurate weighing is possible only in a closed vessel, for example, in a gelatin capsule, which itself contains sulfur, causing a significant error. The method is not applicable to products containing elements that form insoluble sulfates upon combustion, which will interfere with the precipitation stage (iron, aluminum, calcium, lead, etc.); they are often included in additives. The method is also not applicable to waste oils containing wear metals.

Known closer, current method, called as the "Lamp method" [2]. The technology for its implementation is as follows:

- preliminary build calibration dependencies for a series of suspensions with different concentrations of barium sulfate, measuring the optical density of the suspension with a photometer at a wavelength of 450 nm. Suspensions stabilize with glycerol;

- the sample is burned in a closed system using a lamp with a cotton wick, in an artificial atmosphere of 30% oxygen and 70% carbon dioxide to prevent the formation of nitrogen oxides, which introduce a positive error in the determination with a titrimetric end;

- the resulting sulfur dioxide is absorbed and oxidized to sulfuric acid by treatment with hydrogen peroxide. The solution was purged with air to remove dissolved carbon dioxide. Sulfur is determined as sulfate by titration with sodium hydroxide or gravimetrically by precipitation as BaSO ₄ . It is allowed to burn the sample in air, but the end of the method should be gravimetric, i.e. more labor intensive (Appendix A2 to ASTM D1266). The burning time of the test product in ASTM D1266 is not specified. Necessary requirements are combustion of the sample without soot formation and complete combustion of the entire sample, since heavy sulfur-containing compounds are concentrated in heavy residues;

- barium sulfate, formed after adding a solution of barium chloride to the absorbing solution, is determined by measuring the optical density of the suspension with a photometer at a wavelength of 450 nm and comparing the results with previously constructed calibration dependences of the optical density on the content of barium sulfate in the suspension.

This method is extremely time-consuming, as it involves a complicated procedure for preparing calibration suspensions, and for evaporating the absorbing solution. All glassware involved in the analysis requires extremely thorough cleaning.

Common disadvantages of the known methods are:

- high cost of equipment;

- analysis in stationary conditions;

- high cost of analysis;

- the need for a significant investment of time;

- the need for a sufficiently high qualification of staff.

The problem to which the claimed method is directed, and the technical result of its use are associated with the development of a method for the rapid determination of the quantitative content of sulfur-containing compounds in diesel fuel, which does not require expensive equipment, time-consuming and environmentally friendly.

To achieve the specified technical result in the method, including the conclusion of the sample in a closed volume in the form of a cell, conducting research with it, determining the amount of sulfur is carried out by comparing the results with a pre-prepared calibration dependence, the studies are carried out using ultrasonic signals with a resonant frequency between two sensors placed inside the cell with a breakdown, and the mathematically processed difference in the power of the input and output signals by comparing with the caliber the exact dependence of the absorption coefficient on the sulfur concentration determines the amount of sulfur-containing impurities in diesel fuel. When conducting studies, the most optimal values of the resonant frequency ν _p = (5 ± 0.5) MHz and temperature t = (20 ± 1) ° C are adopted. In mathematical processing, the absorption coefficient α is determined from the formula:

where L is a fixed distance between two sensors, Pin and Pout are the power of the input and output signals.

A distinctive feature of the proposed method is the use of the revealed properties of diesel fuel - to change the absorption coefficient α depending on the concentration of sulfur-containing impurities in it when ultrasonic signals pass through it with a resonant frequency ν _p .

The technical implementation of the proposed method is presented in the drawing in the form of an installation that includes an ultrasound generator 1, a temperature-controlled cell 2 with a sample of diesel fuel, an ultrasound emitter 3, an ultrasound receiver 4, a thermostat 5, a comparison device 6, a display 7 of a comparison device, an output power determination sensor 8 Pout signal, sensor 9 determine the power of the input signal Pin.

The method is as follows. The thermostat 5 maintains the set temperature in cell 2 during the study of diesel fuel. Ultrasonic generator 1 generates an alternating voltage with a resonant frequency ν _p . This voltage is supplied to the ultrasound emitter 3, which directs the ultrasonic wave through the cell with diesel fuel to the ultrasound receiver 4. The power sensor 9 determines the power of the input signal Pin, the power sensor 8 detects the power of the output signal Pout. Both signals are fed to a comparison device 6, where they are mathematically processed and the absorption coefficient α is determined. Knowing the absorption coefficient α and having pre-compiled calibration curves (in electronic form or on paper in the form of a table), it is easy to determine the amount of sulfur-containing impurities in diesel fuel.

In contrast to attenuation, which includes the scattering of sound by inhomogeneities and other types of non-dissipative losses, absorption only includes dissipative losses. For liquids, the absorption coefficient α, m ^-1 is

,

,

where ρ ₀ is the density, kg / m ³ ; f is the frequency, Hz; η — dynamic viscosity, Pa · s; η 'is the coefficient of bulk viscosity, Pa · s; ν is the speed of sound, m / s; æ - coefficient of thermal conductivity, W / (K · m); c _p - specific heat at constant pressure, J / (K · kg). There are no direct methods for measuring the coefficient of bulk viscosity η '. The only way to determine it is to compare experimental absorption with that calculated by classical theory. This part of the absorption is due to the relaxation processes of the thermodynamic transition of a fluid from one state to another under bulk compression and tension in a sound wave. According to the thermodynamic principle of the uniform distribution of energy over the degrees of freedom, the energy of the translational motion passes to the internal degrees of freedom, exciting them. In this regard, the kinetics of the relaxation transition is characterized by a certain lag in time of the change in the system parameters when one of them changes - the relaxation time - τ. The lag is determined by the molecular mechanisms of restoring the statistical equilibrium of the molecules of a substance. Irreversible processes of restoration of equilibrium are accompanied by energy dissipation, causing anomalous (non-classical) absorption of sound wave energy [3].

The conducted studies show that chemical impurities influence the bulk viscosity η 'very significantly. In particular, for diesel fuel, such impurities are sulfur-containing substances with the presence of chemical bonds С-S (carbon - sulfur) in them. The presence of a resonant frequency ν _p for sulfur-containing substances, at which an increase in the absorption of the intensity of the ultrasonic signal is observed, allows us to develop a method for the rapid determination of the presence of sulfur-containing substances in diesel fuel. At the resonant frequency ν _p , the power of the input signal Pin and the power of the output Pout after the passage of ultrasound through diesel fuel containing sulfur is compared. Further, according to the formula,

where L is the distance that ultrasound travels in diesel fuel, the absorption coefficient α is determined for its subsequent comparison with previously constructed calibration dependences.

Preliminary studies show that the most optimal values when using the proposed method are the measurement temperature t = 20 ° C and the resonant frequency ν _p = 5 MHz.

The table shows the data for the determination of α at various frequencies at a temperature of t = 20 ° C. To diesel fuel with high purification from sulfur-containing substances with their initial concentration C = 0.010%, these substances were added in their complex content with a gradually increasing concentration up to C = 0.1%. As can be seen from the results, their further increase does not make sense in relation to the claimed method. The measurements were carried out in triplicate. Column 6 shows the relative error ε determined from 3 dimensions.

Table C% L, m P _input , W P _out , W α ε,% 0.010 0.1 one 0,999 0.015 6 0.015 0.1 1,000 0.983 0.017 7 0,020 0.1 1,000 0.975 0,025 6 0,025 0.1 1,000 0.960 0,041 8 0,030 0.1 1,000 0.946 0.056 7 0,035 0.1 1,000 0.934 0,068 8 0,040 0.1 1,000 0.920 0,083 8 0,045 0.1 1,000 0.908 0,096 7 0,050 0.1 1,000 0.894 0,112 8 0,055 0.1 1,000 0.883 0.124 8 0,060 0.1 1,000 0.874 0.135 7 0,065 0.1 1,000 0.869 0.140 6 0,070 0.1 1,000 0.868 0.142 7 0,075 0.1 1,000 0.865 0.145 7 0,080 0.1 1,000 0.863 0.147 5 0,085 0.1 1,000 0.862 0.148 6 0,090 0.1 1,000 0.861 0.150 6 0,095 0.1 1,000 0.860 0.151 5 0,100 0.1 1,000 0.860 0.151 5 0.105 0.1 1,000 0.861 0.150 6

As can be seen from the results shown in the Table, the absorption coefficient α uniquely determines the quantitative presence of sulfur-containing substances in concentrations from 0.010% to 0.080%, after which a significant increase in α with a further increase in sulfur content is not observed. Perhaps this is due to the saturation phenomenon, when the used input signal power Pin is no longer enough for the resonant excitation of an ever-increasing number of C-S bonds. Meanwhile, the determination of sulfur in the claimed concentration range from 0.010% to 0.080% is quite sufficient for modern diesel fuel, with an acceptable error ε <9%.

Example

The studies of sulfur content in the experimental setup at t = 20 ° C and at ν _p = 5 MHz showed that the absorption coefficient of diesel fuel α at a distance between the sensors in the cell L = 10 cm was α _x = 0,092. Then, using the values given in the Table, we find the reference dependence of α on C. Using it, we determine that α _x corresponds to the presence of sulfur-containing substances in a concentration of C _x = 0.043%. Taking into account the relative error ε = 8%, the value of the desired concentration falls into the interval C _x = (0.043 ± 0.0003)%. Installation setup and measurement took 10 minutes. The volume of the used cell with diesel fuel did not exceed 50 ml.

Information sources

1. ASTM D129-00 (2005) “Standard Method for the Determination of Sulfur in Petroleum Products (General Bomb Method)”, GOST 3877-88 “Petroleum Products. Method for determination of sulfur by burning in a calorimetric bomb. "

2. ASTM D1266-98 (2003), GOST R 51859-2002. "The standard method for the determination of sulfur in petroleum products by the lamp method." GOST 19121-73 "Petroleum products. Method for determination of sulfur by burning in a lamp. "

3. "Physical quantities." Directory. - M .: Energoatomizdat, 1991, p. 134.

Claims (3)

1. The method of determining the sulfur content in diesel fuels, including the conclusion of a fuel sample in a closed volume, conducting research and determining the amount of sulfur by comparing the results with a pre-prepared calibration dependence, characterized in that the studies are carried out using ultrasonic signals with a resonant frequency between two sensors, placed inside the cell, and according to the mathematically processed difference in the power of the input and output signals, by comparing with the calibration d dependence of the absorption coefficient on the concentration of sulfur impurities determine the amount of sulfur in diesel fuel. 2. The method according to claim 1, characterized in that when conducting research, the resonant frequency is taken (5 ± 0.5) MHz at a temperature of (20 ± 1) ° C. 3. The method according to claim 1, characterized in that in mathematical processing the absorption coefficient α is determined from the formula

where L is a fixed distance between the sensors;
Pvh and Pvyh are the input and output signal powers.