RU2809978C1 - Method for determining content of organochlorine compounds in an oil sample and installation for its implementation - Google Patents

Abstract

FIELD: analytical chemistry.

SUBSTANCE: invention relates namely to gas chromatography, a method and device for determining the content of organochlorine compounds (OCCs) in an oil sample. To implement a group of inventions for determining the content of organochlorine compounds (OCCs) in an oil sample, an automated oil sample is taken. It is then delivered to the analytical column and the components are separated in the analytical column. Registration of individual components is carried out using an electron capture detector (ECD) of a gas chromatograph. The ECD detector amplifier signal is digitized and displayed as a peak on the chromatogram. An oil sample is taken from the oil flow block, and before delivery to the analytical column, the oil sample is prepared in the oil preparation block by feeding the sample into the container of a vapour-phase sampler with a dosing tap, heating to 90°C, and holding at a given temperature until dynamic equilibrium is achieved between the liquid phase and the evaporated gas phase of the oil sample. Then the evaporated gas phase of the oil sample is dosed from a vapour-phase sampler with a dosing tap to the gas chromatograph by supplying excess pressure of the carrier gas and supplying the evaporated gas phase of the oil sample into the loop of the dosing tap due to the pressure difference. Only the evaporated gas phase of the oil sample is delivered to the analytical column by blowing it with a tenfold volume of carrier gas through a dosing tap.

EFFECT: simplified technology for determining OCCs with an increase in the detection threshold, accuracy and reliability of determining the quantitative and individual composition of OCCs in the oil flow in the pipeline.

3 cl, 1 dwg, 1 tbl

Description

The group of inventions relates to the field of analytical chemistry, namely gas chromatography, which can be used to determine the quantitative and individual composition of organochlorine compounds (hereinafter referred to as COCs) during oil transportation through a pipeline.

There is a known method for determining the content of volatile chemical substances in complex mixtures, including oil and petroleum products, disclosed in document RU 2219541 C1, G01N 30/02, 12/20/2003. In this method, the analyzed mixture is introduced into the evaporator of the chromatograph, located at a temperature from 220 to 350 ° C, the evaporated analyzed mixture is mixed with a flow of carrier gas, chromatographic separation is carried out in a capillary chromatographic column (CC) in the temperature programming mode in the range from 50 to 320 °C, COC is detected at temperatures from 220 to 350°C in an electron capture detector.

The disadvantage of the known solution is the use of an evaporator operating at temperatures from 220 to 350°C, which complicates the design of the chromatograph and leads to the entry of heavy (bitumen) oil fractions into the chromatograph, which requires periodically carrying out a complex procedure for cleaning the chromatograph, which increases the time of preparatory operations for analysis. In addition, it is impossible to carry out such analysis on the stream.

There is a known method for the headspace determination of the mass concentration of carbon tetrachloride, methylene chloride, chloroform, 1,2-dichloroethane, 1.1.2-trichloroethane in bottom sediments using gas chromatography, disclosed in document RU 2581745 C1, G01N 30/00, 04/20/2016, in which preliminary the prepared sample of bottom sediments is dissolved in ethylene glycol, the resulting solution is thermostated at 80°C. The vapor phase above the solution is introduced into the chromatograph using a syringe, chromatographic separation occurs in a capillary CC in the temperature programming mode in the range from 70 to 160°C, the COC is detected using a flame ionization detector.

The disadvantage of this solution is the use of a flame ionization detector, which is difficult to operate, as well as the ability to determine only five COCs, which is not enough to determine COCs in oil and petroleum products; also the disadvantages include the impossibility of carrying out such an analysis on-line.

There is a known method for the qualitative and quantitative determination of organochlorine compounds in petroleum products, disclosed in document CN 108931588 A, G01N 30/02, 04.12.2018. The method involves the following stages: extraction of COC using a special extraction column and a pre-selected solvent, injection of a solvent enriched with COC into the chromatograph; chromatographic separation occurs in a capillary cold chamber by programming the thermostat temperature in the range from 60 to 250°C, using a mass spectrometric detector and helium as a carrier gas. The disadvantages of this solution are the use of an expensive and difficult to operate mass spectrometric detector, as well as the impossibility of performing on-line analysis.

A flow-type vapor-phase sampler is known from the prior art, containing a housing with a sampling chamber installed inside the housing in the form of a hollow cylinder without a bottom, to the upper part of which a vapor phase removal pipeline is connected, a reflector is also installed inside the sampling chamber, under which a pipeline for supplying the analyzed oil is vertically connected, in this case, the vapor phase removal pipeline is equipped with a gas phase sampling pump and is designed to be closed by a float valve installed in the sampling chamber above the reflector, disclosed in document RU 201959 U1, G01N 1/22, 01/25/2021. The disadvantage of this device is the impossibility in the presented design of separating the vapor phase from oil during its transportation, and, consequently, of determining the quantitative and individual composition of chemical substances in oil and petroleum products, as well as the impossibility of performing on-line analysis using the proposed device.

The closest analogue of the claimed group of inventions is a method for determining COCs in oil and oil products by the chromatographic method and a device for determining organochlorine compounds in oil and oil products by the chromatographic method disclosed in document RU 2748390 C1, G01N 30/02, 05.25.2021.

A method for determining COCs in oil and petroleum products by the chromatographic method includes bubbling an inert gas through a container filled with the analyzed oil and petroleum products, dividing an inert gas flow saturated with COC vapors into two parallel ones in a chromatograph, chromatographic separation of COCs with boiling points greater than 100°C using a polycapillary CC and chromatographic separation of COCs with boiling points less than 100°C using capillary CC at a temperature from 80 to 100°C in an isothermal mode, installation of a pre-column in front of the capillary CC, from which COCs with boiling points greater than 100°C are removed by backflushing, detection CCA using an electron capture detector (ECD) located at a temperature of 200 to 300°C.

A device for determining organochlorine compounds in oil and petroleum products by the chromatographic method contains a container periodically filled with the analyzed liquid, placed in a thermostat, through which an inert gas is bubbled at a temperature of 60 to 100 ° C, the volumetric flow rate of which is maintained constant using a gas flow stabilizer, chromatograph with a column thermostat, into which an inert gas saturated with COC vapor (sample) is supplied using a thermally insulated or heated supply line, a pre-column to prevent contamination of the capillary CC, ECD and an automated sample supply system.

The disadvantage of this solution is the difficulty in implementing the known method, as well as in the design of the device, since it is necessary to divide the flow of an inert gas saturated with COC vapor in the chromatograph into two parallel ones, and the detection of COC using ECD is carried out at a temperature of 200 to 300°C, the use of such temperature modes complicates the design of the chromatograph and requires the thermostat to be cooled to the initial temperature after each analysis, which increases the time of preparatory operations for analysis and makes it impossible to carry out such analysis on-line.

The objective of the claimed group of inventions is to develop a method and installation for studying the content of COCs in oil in a stream using the chromatographic method.

The technical result of the invention is to optimize the technology for determining chemical toxicants with an increase in the detection threshold, increasing the accuracy and reliability of determining the quantitative and individual composition of chemical pollutants in the oil flow in the pipeline.

The technical result is achieved by the fact that in the method for determining the content of COCs in an oil sample, automated sampling of an oil sample is carried out, delivery of the oil sample to an analytical column, separation of COC components in the analytical column, registration of individual components using an electron capture detector (ECD) of a gas chromatograph, digitization of the amplifier signal ECD detector with its display in the form of a peak on the chromatogram, while the oil sample is taken on the flow from the pipeline through which the oil is transported, and before delivery to the analytical column, the oil sample is prepared by feeding it into the container of a vapor-phase sampler with a dosing tap, heating up to 90°C, and holding at this temperature until dynamic equilibrium is achieved between the liquid phase and the evaporated gas phase of the oil sample, after which the evaporated gas phase of the oil sample is dosed from a vapor-phase sampler with a dosing tap to the gas chromatograph by supplying excess pressure of the carrier gas and supplying the evaporated gas phase of the oil sample into the loop of the dosing tap due to the pressure drop, while only the evaporated gas phase of the oil sample is delivered to the analytical column by blowing it with a tenfold volume of carrier gas through the dosing tap.

The technical result is also achieved by the fact that the installation for determining the content of COCs in an oil sample contains an oil flow block in which an oil sample is taken, an oil pressure reduction block connected to it, an oil sample preparation block connected to the oil pressure reduction block, containing a vapor-phase sampler with a metering valve and connected to it a container with carrier gas and a container for recycling the evaporated gas phase of an oil sample, connected to a waste oil sample withdrawal line with a drain/fill tank, a connected return line for used oil samples to the oil flow block, and designed for heating an oil sample to 90°C, holding it at this temperature until dynamic equilibrium is achieved between the liquid phase and the evaporated gas phase of the oil sample, and dosing the evaporated gas phase of the oil sample by supplying excess pressure of the carrier gas and supplying the evaporated gas phase of the oil sample to a loop of a dosing tap due to a pressure difference, a chromatographic unit connected to the oil sample preparation unit, as determined by the chemical composition, containing a chromatograph and a personal computer, while the units are connected through pipelines on which measuring instruments are installed.

In a particular version of the installation for determining the content of COCs in an oil sample, the oil flow block contains containers with oil and a pumping unit, forming a circulation circuit for pumping oil.

The essence of the group of inventions is illustrated by a drawing, which shows a technological diagram of a laboratory installation for determining the content of chemical substances in an oil sample.

The positions on the figure indicate the following:

1 - container with carrier gas;

2 - containers with oil;

3 - oil drain/fill tank;

4 - pressure reduction block;

5 - headspace sampler;

6 - chromatographic unit;

7 - container for recycling the evaporated gas phase of an oil sample;

8 - pumping unit;

9 - level scale;

10 - flow meter;

11 - pressure reducer;

12- ball valve;

13 - needle valve;

14 - means of measuring pressure, temperature;

15 - manual selection;

16 - input of the measuring probe;

17 - pumping circulation circuit.

The oil industry uses a large number of different oilfield reagents: clay stabilizers, surfactants, emulsifiers, demulsifiers, viscosity modifiers, corrosion inhibitors, asphalt and paraffin resin inhibitors, detergents, bactericides, etc. Many reagents contain COCs as a constituent component.

COCs are organic compounds in which one or more atoms are replaced by chlorine atoms. Highly volatile COCs are a group of COCs whose boiling point is below 204°C. Of the halogen-containing compounds contained in oil, it is the COCs that create the greatest problems, since they are an additional source of hydrochloride corrosion of oil refining installations in addition to inorganic chlorides. When oil is processed at high temperatures, they are often destroyed with the formation of corrosive hydrogen chloride, and partially with the formation of lighter compounds distributed among oil fractions.

The greatest activity of COCs is observed in installations for preliminary hydrotreatment of raw materials, diesel fuel, gas fractionation and reforming. The boiling limits of COCs basically coincide with the boiling limits of gasoline fractions, so the main damage is observed in catalytic reforming units due to the high corrosion rate caused by the formation of hydrogen chloride (hydrochloric acid) - HCl, and partial deactivation of catalysts. Hydrochloric acid is a strong corrosive agent; in addition, hydrogen chloride interacts with ammonia, which is formed during the hydrogenation of nitrogen compounds that are traditionally present in oil. The result is ammonium chloride (NH ₄ Cl), a white powdery substance that clogs equipment. As a result, the equipment of hydrotreating units, as well as pre-hydrotreating units of feedstock from catalytic reforming and isomerization units, is subject to additional wear due to hydrochloride corrosion, and is also clogged with ammonium chloride deposits.

GOST R 51858 “Oil. General technical conditions" provides for the mandatory determination, in addition to traditional physical and chemical indicators (density, content of mechanical impurities, water, chloride salts, hydrogen sulfide and mercaptans, saturated vapor pressure), also the content of chemical substances. The specified GOST establishes the norm of organic chlorides in the fraction of oil boiling up to 204 ° C - no more than 10 ppm.

Most often, COCs are found in large quantities in organic solvents (for example, toluene), water repellents based on N-alkyldimethylbenzylammonium chloride, in lubricating additives for drilling fluids based on waste oils, as well as acids, which are industrial wastes in the technological processes of which COCs are present. COS is found in small quantities in corrosion inhibitors, bactericides, and complex action inhibitors.

When determining the content of the mass fraction of organic chlorides in oilfield chemicals using X-ray fluorescence spectrometry, energy dispersive spectrometry, microcoulometric titration, reduction with sodium biphenyl and subsequent potentiometric titration, the problem of separating organic chlorides from inorganic ones arises.

The proposed technical solutions consist in developing the principle of influencing oil during the preparation of an oil sample taken from the oil flow from the pipeline. Since oil cannot be directly introduced into a gas chromatograph, it is first necessary to isolate the gas phase of the oil, and it is also necessary to ensure the separation of the determined COCs into the gas phase. At the same time, to correctly determine the content of COCs in oil, it is necessary to achieve a dynamic equilibrium between the liquid phase of oil and the gas phase of oil, as well as to determine and select the optimal parameters of the technological process for preparing an oil sample to ensure the possibility of determining the content of COCs in oil using a gas chromatograph during its transportation through a pipeline , as well as in the development of an appropriate implementation option for equipment for preparing an oil sample.

The proposed method is carried out in several stages:

1. taking a single sample of oil from an oil stream;

2. supplying the selected oil sample to the container of a vapor-phase sampler with a dosing tap, where it is heated to a temperature of 90°C;

3. holding the selected liquid oil sample at a given temperature for a certain time until dynamic equilibrium is achieved between the liquid phase and the evaporated gas phase of the oil sample;

4. dosing of the evaporated gas phase of an oil sample from a vapor-phase sampler with a dosing tap to a gas chromatograph by supplying excess pressure of the carrier gas;

5. supplying the evaporated gas phase of an oil sample due to a pressure difference into the loop of the dosing tap, by purging it with a carrier gas in a volume exceeding its volume by 10 times;

6. delivery of the evaporated gas phase of the oil sample by the carrier gas that picked it up through the dosing valve and its delivery to the analytical column for further separation of the chemical substances;

7. separation of components in an analytical column;

8. registration of individual components using an ECD gas chromatograph;

9. digitization of the signal by the amplifier of the ECD detector and displaying it as a peak on the chromatogram.

Upon completion of the analysis, the recording of the chromatogram stops, the gas chromatograph software automatically processes the data obtained and produces the results obtained in the form of concentration values for each of the components determined by the chromatograph.

The proposed installation for determining the COC content in an oil sample is a complex system designed for the preparation of an oil sample taken from a flow continuously moving through a pipeline, and the subsequent determination of COC in the oil sample by gas chromatography. Control of the operating mode of the installation, reception and recording of chromatographic data is carried out using certified Chromos software installed on a personal computer.

The proposed installation for determining the COC content in an oil sample includes the following components:

- an oil flow block consisting of a pipeline, or, in a particular case (if the installation is laboratory, shown in the drawing), of tanks with oil (2), and a pumping unit (8), forming a circulation circuit for pumping oil;

- block for reducing (reducing) oil pressure (4);

- an oil sample preparation unit containing a vapor-phase sampler (5) with a metering valve and a container with carrier gas (1) connected to it and a container for recycling the evaporated gas phase of the oil sample (7), connected to the waste oil sample withdrawal line (with drain/fill tank (3)) connected to the line for returning waste oil samples to the oil flow block;

- a chromatographic unit according to the determination of COC (6) with the ability to output information to a personal computer, which includes a laboratory gas chromatograph or an industrial gas chromatograph (depending on the type of installation used) and a personal computer;

- pipelines connecting the installation blocks and measuring instruments installed on them, such as a flow meter (10), pressure and temperature measuring instruments (14), pressure gauges, electronic scales, graduated cylinders, volumetric flasks, digital multimeter.

In a laboratory setup, the oil flow unit includes two oil tanks (2). Each of the tanks has its own oil pumping circuit (17). Pumping in each circuit is provided by a pumping unit (8).

The pressure reduction unit (4) is a pressure regulator that reduces the pressure at the outlet of the unit and allows for stable sampling and sample preparation over the entire specified pressure range.

The oil sample preparation unit contains an electromagnetic valve (not shown in the figure), which allows you to dose the amount of sample for its preparation in a vapor-phase sampler (5), and which is a calibrated heated container equipped with fittings for introducing the sample, emptying the container, and supplying the gas phase for analysis and purging of the container.

The spent sample withdrawal line contains a drain/fill tank (3) and is connected to the return line of spent oil samples to the oil flow block.

The chromatographic unit (6) consists of a chromatograph and a personal computer and analyzes the vapor phase of the prepared sample from a headspace sampler.

The implementation of the claimed group of inventions occurs as follows.

Before starting research from the oil flow block, a single oil sample is taken from the oil flow piping the connection unit. Next, the oil sample is transferred through a pipeline to transfer the sample to the sample preparation unit.

In the case of laboratory tests, one of the containers (2) of the oil flow block is filled with the test oil. The selection of a working tank for pumping oil is carried out manually using shut-off valves. Next, the pump unit (8) is turned on, and the required flow rate of the oil pumping circuit (17) is set. The establishment of the required pumping mode is controlled using a flow meter (10) and a pressure gauge. After the flow in the oil pumping circuit (17) is established, sampling starts. During transportation through the pipeline, the sample pressure is reduced in the pressure reduction unit (4) to the specified value. The solenoid valve opens and the sample flows through the pipeline into the oil sample preparation unit. To control the temperature and pressure in the pipeline, a thermometer and a pressure gauge are installed after the pressure reduction block (4). Next, in the sample preparation unit, the sample is heated to 90°C and kept in a vapor-phase sampler (5), where an equilibrium distribution of the analyzed chemical substances occurs between the liquid and gas phases, and then the gas phase is supplied to the chromatographic unit (6). To ensure that the sample is supplied to the chromatograph, a carrier gas is supplied to the headspace sampler, which can be used, for example, nitrogen or argon until a specified pressure drop is achieved. Due to the excess pressure in the headspace sampler, the equilibrium gas phase from the headspace sampler enters the dosing loops of the chromatograph dosing valves, the output gas lines of which are connected to the atmosphere. In order to displace atmospheric air from the sample line and dosing loops of the dosing taps, as well as the components of the previous sample, the dosing taps are purged with a volume of carrier gas equal to at least ten times the volume of the gas phase; this will ensure complete emptying of the dosing taps to ensure an increase in the threshold detection, accuracy and reliability of determining the quantitative and individual composition of chemical substances, due to the complete cleaning of dosing taps from the previous sample.

The remaining liquid part of the sample from the vapor-phase sampler (5) is sent to the spent sample withdrawal line, which contains a drain/fill tank (3) and a line for returning spent oil samples to the oil flow block connected to it.

Next, in the chromatographic unit (6), the COC is analyzed and the results are automatically displayed on a personal computer in the form of a chromatogram.

An example of a specific implementation of the proposed technical solutions:

For analysis, either a laboratory gas chromatograph “Chromos GC-1000” or an industrial gas chromatograph “CHROMOS PGH-1000.1” with ECD is used, depending on the installation used. An information and computing system is used to collect and process analysis results.

Chromatographic columns operate in isothermal mode. During tests on a laboratory installation, it was found that at low column temperatures (50-70°C), light COCs are well separated, but they condense in the column and heavier COCs do not come out. On the contrary, at high temperature (140°C) COCs are separated and heavy components are recorded, but due to the similar time of release of light COCs, they are not divided into peaks, but come out as one combined peak, which makes it impossible to identify light COCs.

Thus, it has been established experimentally that it is precisely heating the gas phase of the sample to 90°C that makes it possible to increase the threshold of detection, accuracy and reliability of determining the quantitative and individual composition of chemical substances in the oil flow in the pipeline.

The operating parameters of the laboratory installation and the headspace sampler (hereinafter referred to as the VPS) are indicated in the table.

The measurement cycle time includes the sequential processes of filling the liquid sample, thermostatting the liquid sample in the PFP, the time of pumping nitrogen into the steam space to pressurize the gas space of the PFP, the time of purging the dosing taps with an equilibrium vapor sample, the time of recording the chromatogram, and the switching time.

Thus, the proposed technical solutions ensure the release of the determined COCs into the gas phase during the process of controlled heating and evaporation of oil in an amount sufficient for their determination on a gas chromatograph, by achieving a dynamic equilibrium between the liquid phase of oil and the gas phase of oil.

The proposed technical solutions provide selective determination of COCs; oil hydrocarbons, which are extracted together with COCs into the gas phase in a headspace sampler, do not interfere with the determination of COCs; detection and measurement of COCs in oil is ensured in the required range in order to prevent deterioration in the quality of oil in terms of the mass content of organic chlorides according to the requirements established by GOST R 51858.

Thus, it is possible to determine on a gas chromatograph the content of COCs in oil during its transportation through a pipeline in an automated mode without stopping pumping and without manually taking an oil sample using a simplified technology that excludes the detection of COCs at high temperatures, which complicates the design of the chromatograph and requires cooling after each analysis thermostat to initial temperature.

Claims (3)

1. A method for determining the content of organochlorine compounds (OCC) in an oil sample, including automated sampling of oil, delivery of the oil sample to an analytical column, separation of OCP components in the analytical column, registration of individual components using an electron capture detector (ECD) of a gas chromatograph, digitization of the amplifier signal ECD detector with its display in the form of a peak on the chromatogram, characterized in that the oil sample is taken on stream from the pipeline through which oil is transported, and before delivery to the analytical column, the oil sample is prepared by feeding it into the container of a headspace sampler with a dosing tap , heating to 90°C, and holding at this temperature until dynamic equilibrium is achieved between the liquid phase and the evaporated gas phase of the oil sample, after which the evaporated gas phase of the oil sample is dosed from a vapor-phase sampler with a dosing tap to the gas chromatograph by supplying excess gas pressure - carrier and supplying the evaporated gas phase of the oil sample into the loop of the dosing tap due to the pressure drop, while only the evaporated gas phase of the oil sample is delivered to the analytical column by blowing it with a tenfold volume of carrier gas through the dosing tap. 2. An installation for determining the content of organochlorine compounds (OCC) in an oil sample to implement the method according to claim 1, characterized in that it contains an oil flow block in which an oil sample is taken, an oil pressure reduction block connected to it, connected to the block oil pressure reduction unit for preparing an oil sample, containing a vapor-phase sampler with a metering valve and connected to it a container with a carrier gas and a container for recycling the evaporated gas phase of the oil sample, connected to a waste oil sample withdrawal line with a drain/fill tank connected to it line for returning spent oil samples to the oil flow block, and designed for heating the oil sample to 90°C, holding it at this temperature until dynamic equilibrium is achieved between the liquid phase and the evaporated gas phase of the oil sample, and dosing the evaporated gas phase of the oil sample by applying excess pressure carrier gas and supply of the evaporated gas phase of the oil sample into the loop of the dosing valve due to the pressure drop, a chromatographic unit connected to the oil sample preparation unit, as determined by the chemical composition, containing a chromatograph and a personal computer, while the units are connected through pipelines on which measuring instruments are installed . 3. Installation according to claim 2, characterized in that the oil flow block contains containers with oil, shut-off valves and a pump unit forming a circulation circuit for pumping oil.