RU2361200C1 - Gas chromatographic method of determining mass concentration of impurities in natural gas - Google Patents

Abstract

FIELD: physics; measurement.

SUBSTANCE: invention pertains to gas chromatographic analysis methods. A sample of natural gas is preselected. Impurities are concentrated on an absorbing sorbent and thermal desorption of the impurities into a chromatographic column is done. Preselection of the sample of natural gas is done by concentrating impurities of natural gas in a sorbent tube with activated silica gel KCK and valves. The sorbent tube is put into a heated thermal desorption unit with needles, through which the valves in the sorbent tube open, and desorbed impurities are eluated into the chromatographic column. The proposed method is realised using a chromatographic system of determining mass concentration of impurities in natural gas, consisting of gas chromatography, a chromatographic packed column, 10 dock crane-switches, evaporator, detector, aspirator and a sampling device. The sampling device contains a reservoir where the sorbent tube with valves is put at its ends and activated silica gel KCK. The device is provided with two needles, through which valves of the sorbent tube open when taking samples. The thermal desorption unit has two needles, through which valves of the sorbent tube open during analysis.

EFFECT: increased accuracy, as well as possibility of gas chromatographic determination of mass concentration of moisture and methanol impurities in natural gas.

8 cl, 5 dwg

Description

The invention relates to methods for gas chromatographic analysis.

Known methods of gas chromatographic analysis, including sampling, preliminary concentration of impurities on an absorbing sorbent and subsequent desorption of impurities in a chromatographic column.

For example, there is a known method for gas chromatographic analysis of a mixture of gases and vapors (ed. St. USSR No. 1200932, class B01D 15/08, application No. 3747321 / 23-26 of March 16, 84, publication date 12/30/85, bull. No. 48), consisting in passing the flow of the mixture through the sorbent with intermediate heating of the stream for several minutes at a temperature of 120-400 ° C, and before heating, the stream is cooled to 10-20 ° C. This method is effective in the quantitative determination of the content of impurities in gas mixtures, however, it does not allow to determine the content of microconcentrations of moisture in natural gas.

A known method of chromatographic analysis of substances, which consists in repeatedly passing the sample in the flow of the mobile phase through two series-connected chromatographic columns, moreover, the sample after passing through the column is mixed with an eluent stream, the eluting force of which is less than the eluting force of the mobile phase (ed. St. USSR No. 1187836, C. B01D 15/08, application No. 3782596 / 23-26 of 05.16.84, publication date 10/30/85, bull. No. 40). This method is used in preparative chromatography to separate difficult-to-separate components, but is not applicable for determining the microquantities of moisture in gases.

The patent (RU No. 2102742, class G10N 30/08, application No. 95118672/25 dated October 31, 1995, publication date January 20, 98, bull. No. 2) proposes a method for gas chromatographic analysis of mixtures, which consists in preliminary concentration of the sample on an absorbent sorbent in vapors of distilled water, collecting the resulting after desorption of the medium in a receiver of variable volume and subsequent input into the chromatograph. As the sorbent, a carbon fiber sorbent is used. The disadvantage of this analysis method is the inability to determine the moisture impurity content in gases due to the use of distilled water as a stripping agent.

The closest analogue to the proposed invention is the "Method for gas chromatographic analysis of the content of impurities in gases and a device for its implementation" according to patent RU No. 22210073, class. G01N 30/08, B01D 15/08, application No. 2002116995/28 of 06.25.2002, publication date 08/10/2003, bull. Number 22.

The essence of the method consists in the preliminary sampling of the test medium, the concentration of impurities on an absorbing sorbent and subsequent thermal desorption of impurities in a chromatographic column. Activated alumina is used as a sorbent.

The disadvantage of this method is the inability to jointly determine the mass concentration of methanol and moisture in natural and industrial gases due to the adsorption of methanol on the walls of the container into which the gas is preliminarily sampled.

The closest analogue of the claimed sorption tube is a sorption tube containing a housing with a sorbent in the inner part of the housing (see, for example, Sorption tube ST 223, http://pribors.narod.ru/p/pribs894.htm, http: // www .atmosfera-npk.ru, sorption tube in patent application US 2006/0039827 A1, IPC G01N 30/60, publication date 02/23/2006).

The disadvantages of the sorption tube is the lack of rapid sealing of the internal volume and the deposition of methanol on the inner walls of the tube.

The closest analogue of the claimed thermal desorber is a thermal desorber containing a housing with a container for accommodating the sorption tube, a platinum resistance thermometer at the opposite ends of the lid housing and which is part of the Chromatek chromatographic complex (see, for example, http://www.chromatec.ru) .

The disadvantage of the thermal desorber is the inability to open the valves of the sorption tube after placing it in the thermal desorber.

The closest analogue of the claimed sampling device is a sample gas sampling device containing a housing with a container for accommodating the sorption tube and at opposite ends of the lid body (see, for example, the invention according to patent RU No. 2210073, class G01N 30/08, B01D 15 / 08, application No. 2002116995/28 of 06.25.2002, publication date 08/10/2003, bull. No. 22).

The disadvantage of the sampling device is the inability to open the valves of the sorption tube after placing it in the sampling device and closing the valves of the sorption tube after pumping the required dose of natural gas through the sorption tube.

Thus, the known methods of chromatographic analysis of the content of impurities in gases are pre-sampling in containers and further concentration of impurities on an absorbent sorbent. However, these methods are not suitable for the joint determination of methanol and moisture in natural gas, since the sampling of natural gas in a metal container leads to the adsorption of methanol vapor on its walls, and the passage of natural gas through ordinary sorption tubes leads to the instantaneous absorption of moisture from air onto the sorbent . These methods make the sample unrepresentative and the analysis unreliable.

The objective of the present invention is to provide a gas chromatographic method for determining the mass concentration of methanol impurities and moisture in natural gas in the concentration range of 1.5 × 10 ^-3 -2.0 g / m ³ or 1-2500 ppm.

The technical result is expressed in providing gas chromatographic determination of the mass concentration of methanol and moisture impurities in natural gas with high accuracy.

The essence of the method consists in the preliminary sampling of natural gas, the concentration of impurities on an absorbent sorbent and subsequent thermal desorption of impurities in a chromatographic column, while the preliminary sampling of natural gas is carried out by means of a sampling device by concentrating natural gas impurities in a sorption tube with activated KSK silica gel and with valves , place the sorption tube in a heated thermal desorber with needles, through which the valves are opened in the sorption tube sponge, and desorbed impurities are eluted into the chromatographic column.

The implementation of the claimed method is carried out by means of a chromatographic complex for determining the mass concentration of impurities in natural gas, consisting of a gas chromatograph, a chromatographic nozzle column, a 10-port switch crane, an evaporator, a detector, an aspirator, and a sampling device that contains a container for accommodating a sorption tube with valves at its ends and activated KSK silica gel and is equipped with two needles providing opening of sorption tube valves during sampling SRI and thermodesorbers provided with two needles, ensuring the opening of valves of the sorption tube when implementing the analysis.

The sorption tube of the sampling device contains a housing, in the middle of the inner part of the housing there is a sorbent of activated KSK silica gel, at the ends of the housing are two valves.

A thermal desorber containing a housing with a capacity for accommodating the sorption tube, a platinum resistance thermometer and at opposite ends of the lid body, is equipped with two needles with internal channels installed in the lids and providing opening of the sorption tube valves during analysis.

The natural gas sampling device, comprising a housing with a container for accommodating the sorption tube and at opposite ends of the lid body, is equipped with needles with internal channels installed in the lids and providing opening of the sorption tube valves when sampling natural gas.

The essence of the method of gas chromatographic determination of the mass concentration of impurities in natural gas and a device for its implementation is illustrated by drawings, where

figure 1 shows a structural diagram of a chromatographic complex for determining the mass concentration of impurities in natural gas;

figure 2 - thermal desorber in cross section;

figure 3 - sampling device in cross section;

figure 4 - sorption tube in cross section;

figure 5 is an example of the results of chromatographic analysis of natural gas.

The chromatographic complex for determining the mass concentration of impurities in natural gas consists of a gas chromatograph with an integrated thermal desorber 1, a sorption tube 2 with valves, a chromatographic nozzle column 3, a 10-port switch crane 4, an evaporator 5, detector 6 (Fig. 1), a device for sampling 7 and aspirator 13 (figure 3). The lines for supplying carrier gas ГН1 from the first line, carrier gas ГН2 from the second line, carrier gas ГН3 from the third line are connected to the 10-port crane switch 4.

The concentration of methanol and moisture from natural gas is carried out on a sorption tube 2 with a sorbent (figure 4). The sorption tube 2 contains a housing 27, in the middle of the inner part of the housing 27 there is a sorbent that is made of activated KSK silica gel 28, at the ends of the housing 27 there are two valves 14 and 15 (Figs. 3, 4).

This design allows you to maintain the tightness of the sorption tube 2 inside the sampling device 7 before and after sampling, as well as after removing the sorption tube 2 from the sampling device 7 before starting the analysis of the sample.

The valves 14 and 15 of the sorption tube 2 can be made in the form of ball valves, each of which contains a ball 25, one or two sealing rings 24 of elastic material, located between the ledge in the inner part of the housing 27 of the sorption tube 2 and the ball 25, which is pressed by a spring 26 to the nearest sealing ring 24. The sealing rings 24 are fixed inside the housing 27 with sleeves 23 and threaded bushings 22 mounted at the ends of the housing 27.

Additionally, the sorption tubes 2 can be sealed with plugs, which allow to maintain tightness during transportation from the place of sampling to the place of analysis and vice versa (for example, from a gas field to the laboratory). This, in turn, gives a number of advantages, expressed in the exclusion of moisture on the sorbent from the air, in the elimination of the loss of concentrated impurities during transportation, which allows you to determine the concentration of the analyzed components at the level of 1 ppm.

The housing 27 of the sorption tube 2 can be equipped with a protrusion 29, which eliminates the incorrect location of the tube 2 in the sampling device 7 and the thermal desorber 1 (figure 4).

The sorption tube 2 is placed in the sampling device 7 and then in the thermal desorber 1 in a certain position. This is due to the following. When passing the analyzed gas through the sorption tube, impurities of the sample are usually adsorbed at the beginning of the inner part of the housing of the sorption tube filled with a sorbent (in the claimed sorption tube 2, activated KSK silica gel). The desorption of impurities from the sorbent is carried out in the opposite direction to reduce the blurring of the chromatographic zone and obtain narrow symmetric peaks of the analyzed components. In known tubes, a graphic image is applied at one end, which in no way excludes errors in the placement of the sorption tube in the thermal desorber when it is inserted from the wrong end, which should be introduced first into the thermal desorber. The presence of the protrusion 29, for example, in the form of a ring or part thereof at one end of the housing of the sorption tube 2 automatically ensures the fulfillment of this condition (figure 4).

To ensure the operation of the claimed sorption tube 2, a natural gas sampling device 7 (Fig. 3) and a thermal desorber 1 (Fig. 2) were developed. A feature of the natural gas sampling device 7 and thermal desorber 1 is the presence of needles 10, 11 (FIG. 3) and 19, 20 (FIG. 2), which open the ball valves 14 and 15 in the sorption tube 2 during sampling and analysis.

The thermal desorber 1 contains a housing 17 with a container for accommodating the sorption tube 2, a platinum resistance thermometer 18 and lids 16 and 30 at the opposite ends of the housing 17. The thermal desorber 1 is equipped with two needles 19, 20 with internal channels installed in the covers 16, 30 and allowing valves to open 14, 15 of the sorption tube 2 in the analysis (figure 2). The thermal desorber 1 is located on the chromatograph 21 and is connected to a 10-port crane switch 4 (Fig.1, 2).

In one embodiment of the thermal desorber 1, grooves are made at the ends of the needles 19, 20 with internal channels, with a direction from the internal channel to the outside of each needle 19, 20.

The natural gas sampling device 7 comprises a housing with a container for accommodating the sorption tube 2 and the lid 8, 31 at opposite ends of the housing. The sampling device 7 of natural gas is equipped with needles 10 and 11 with internal channels installed in the lids 8, 31 and providing opening of the valves 14, 15 of the sorption tube 2 when sampling natural gas. In the middle of the casing of the sampling device 7, a natural gas discharge line 9 is connected before sampling (Fig. 3).

In one embodiment of the sampling device 7, grooves are made at the ends of the needles 10, 11 with internal channels, with a direction from the internal channel to the outside of each needle 10 and 11.

The separation of the components occurs on a packed chromatographic column (figure 1). C1-C10 hydrocarbons, benzene, toluene, acetone and moisture do not interfere with the determination of methanol. Toluene interferes with the determination of water.

The method of gas chromatographic determination of the mass concentration of impurities in natural gas is as follows.

The chromatograph is calibrated through an evaporator 5 using methanol solutions in water and water solutions in dried acetone. The calibration coefficient is calculated by the formula

where K _{gr, i} is the calibration coefficient in the i-th calibration solution for methanol (water), mg;

With _{gr, i} is the concentration of methanol (water) in the i-th calibration solution, mg / ml;

V _{gr, i} - sample volume of the i-th calibration solution, µl;

S _{gr, i} - peak area of methanol (water) of the i-th calibration solution, y.e.

Sampling of the analyzed natural gas is carried out on a sorption tube 2 filled with activated silica gel KSK 28. To do this, unscrew the cover 8 from the sampling device 7. The sorption tube 2, preconditioned and cooled, is placed in the sampling device 7. Install the cover 8 on the device body sampling 7. Attach one end of the sampling device 7 to the aspirator 13, the second end of the sampling device 7 to a closed valve 12 for purging with natural or other analyzed gas, and to the middle parts of the body of the sampling device 7 attach a gas discharge line 9. When screwing the cover 8 of the sampling device 7 to a certain position, the sampling device 7 is sealed, but the valves 14, 15 of the sorption tube 2 still remain closed. Open the valve 12 and purge the sampling device 7 with natural gas with the discharge of gas into line 9 for about several minutes (two minutes are enough). This also removes the air previously located in the sampling device 7. Excess gas is released into the atmosphere. After purging, line 9 is closed and the cover 8 of the sampling device 7 is twisted to the stop. Needles 10, 11 with internal channels enter the sorption tube 2, press the valves 14, 15 of the sorption tube 2 and open them. The grooves on the ends of the needles 10, 11 with a direction from the inner channel to the outside of the needle provide guaranteed gas flow around the surface of the valves 14, 15 after they are opened. The gas flows through the activated silica gel KSK 28 of the sorption tube 2. Using an aspirator 13, for example a bellows or similar, the required volume of natural gas is pumped through the activated silica gel KSK 28 of the sorption tube 2 in the range 100-600 cm ³ (for example, to determine a methanol concentration of more than 0 , 2 g / m ^{3 it is} enough to pump 100 cm ^{3 of} natural gas). After gas sampling, the valves 14, 15 of the sorption tube 2 are closed by unscrewing the cover 8 of the sampling device 7 after closing the valve 12. The sorption tube 2 is removed from the sampling device 7 and, if necessary, additionally sealed with plugs.

Then, the sorption tube 2 after moving to the chromatograph 21 and removing the plugs (if they were used if necessary) is placed in a thermal desorber 1 heated to a certain temperature (for example, up to 180 ° C). When screwing the cover 16 of the thermal desorber 1, the needles 19, 20 with internal channels located on the covers 16, 31 of the thermal desorber 1 open the valves 14, 15 of the sorption tube 2. The sorption tube 2 is heated for about 1 minute. After the 10-port faucet switch 4 is switched to the analysis mode, a carrier gas, for example helium, begins to flow through the thermal desorber 1 and the sorption tube 2. The impurities are desorbed from the heated KSK silica gel 28 and the desorbed impurities are eluted into chromatographic column 3, and then to detector 6 of the chromatographic complex.

The mass concentration of impurities is calculated by the formula

where K _gr - the average value of the calibration coefficient of methanol (water);

S is the value of the peak area of methanol (water) in the chromatogram, cu;

V _g - the value of the volume of natural gas pumped through the sorption tube,

cm ³ ;

Y is the mass concentration of methanol (water) in natural gas, g / m ³ .

As an example of the results of chromatographic analysis of natural gas, Fig. 5 shows a chromatogram of analysis of natural gas on a column with 10% TCEP on chromosorb T (T _c = 120 ° C) after concentration on a sorption tube with KSK silica gel.

The claimed method of gas chromatographic determination of the mass concentration of impurities in natural gas and a device for its implementation can be used for analysis of other impurities in a gas or air environment.

Claims (8)

1. The method of gas chromatographic determination of the mass concentration of impurities in natural gas, including preliminary sampling of natural gas, concentration of impurities on an absorbing sorbent and subsequent thermal desorption of impurities in a chromatographic column, characterized in that the preliminary sampling of natural gas is carried out by means of a sampling device by concentration of natural impurities gas in the sorption tube with activated KSK silica gel and with valves, place the sorption tube in rety thermodesorbers with needles by which the valve is opened in the sorption tube and eluted with desorbed impurities into the chromatographic column. 2. A chromatographic complex for determining the mass concentration of impurities in natural gas, consisting of a gas chromatograph, a chromatographic nozzle column, a 10-port switch crane, an evaporator, a detector, a thermal desorber, a sampling device and an aspirator, characterized in that the sampling device contains a container for accommodating the sorption tube with valves at its ends and with activated KSK silica gel, equipped with two needles with internal channels that open the sorption valves tubes during sampling; the thermal desorber is equipped with two needles with internal channels, providing opening of the sorption tube valves during analysis. 3. A sorption tube containing a housing, a sorbent, characterized in that the sorbent in the middle of the inner part of the housing is made of activated KSK silica gel, two valves are located at the ends of the housing. 4. The sorption tube according to claim 3, characterized in that on the outer side of one of the ends of the housing there is a protrusion in the form of a ring or part thereof. 5. A thermal desorber comprising a body with a container for accommodating the sorption tube, a platinum resistance thermometer and at opposite ends of the lid body, characterized in that it is equipped with two needles with internal channels installed in the lids and providing opening of the sorption tube valves during analysis. 6. The thermal desorber according to claim 5, characterized in that at the ends of the needles with internal channels grooves are made with a direction from the internal channel to the outside of the needle. 7. A device for sampling natural gas, comprising a housing with a container for accommodating the sorption tube and at opposite ends of the lid body, characterized in that it is equipped with needles with internal channels installed in the lids and providing opening of the sorption tube valves when sampling natural gas. 8. The device for sampling natural gas according to claim 6, characterized in that at the ends of the needles with internal channels grooves are made with a direction from the internal channel to the outside of the needle.

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