A method of obtaining a permanent trace volatile compounds in the gas stream

 

The invention relates to the field of gas analysis and can be used for calibration of gas analysis equipment. The inventive gas stream is saturated to a predetermined equilibrium concentration by bubbling contact the gas stream with a solution of volatile compounds in low volatile solvent. The saturation of the gas stream to an equilibrium concentration of vapors of volatile substances carry out the sequential contact of the gas stream with at least three fixed portions of a solution of volatile substances in low volatile solvent in which the concentration of volatile substances in low volatile solvent sequentially decreases from the first portion of the solution to the next or remains constant, except for the first portion, in which the concentration of volatile substances above. In addition, in the method of obtaining a permanent trace volatile compounds in the gas stream, the concentration of volatile substances in low volatile solvent may be the same in all portions, but the volume of the first portion to exceed the amount of the subsequent portions, and the resulting gas stream is saturated vapors of volatile substances, can be diluted with gas. The technical result of the invention is to improve lichnosti substances in low volatile solvent. 3 C.p. f-crystals, 3 ill., table 1.

The invention relates to the field of gas analysis and can be used for calibration of gas analysis apparatus, in particular for the calibration of gas chromatography detectors, the creation of artificial gas-vapor mixtures in the development of methods of environmental analysis and in applications where it is necessary the creation of a constant concentration of vapours of substances in gas-diluent.

In 60-ies of the method was developed [O'keefe, A. E., G. G. Ortman // Anal. Chem. 1966. V. 38. R. 760] obtaining the known trace of volatile substances in a stream of inert gas based on gas diffusion through a tube made of Teflon. The method was used to obtain the calibration mixtures with known content as the concentration of various gases (e.g., SO2With4H10), and vapors of volatile substances (pentane, benzene, and others).

The disadvantage of this method is the complexity of manufacturing capsules, the duration of the establishment of the equilibrium concentration of the substance in the flow, a relatively high flow rate of the diluent gas.

There is also known a method of preparation of the calibration mixtures for gas chromatography, in which the original fugitive vidcast, in which is dissolved the original substance [Pankov A. G., Trubin A. M. , Berezkin Century, and others, Ed. mon. The USSR 603898. // Bul. Fig. 15 from 25.04.78].

However, the known method does not provide consistency of trace volatile compounds in the flow of the diluent gas, as the concentration of the original substance continuously decreases according to the exponential law, which limits the scope of application of this method for metrological support gas analysis measurements.

Closest to the claimed invention, the set of essential characteristics is a method of obtaining a gas-vapor mixtures by passing a flow of the diluent gas through a solution with a given concentration of volatile substances in low volatile solvent. When this occurs, the saturation of the gas stream vapors of volatile substances to the equilibrium concentrations. After making contact the gas stream with a solution depleted in volatiles volatile substances portion of the liquid solution is continuously separated from the gas-vapor stream and the original solution [Berezkin Century BC, Budantseva M. Auth. mon. Of the USSR. 697922 // bul. Fig. 42 from 15.11.79].

The disadvantage of this method is the need for a significant amount of the solution Le is dinamicheskim method. It is important to note that the amount of recoverable volatile component affects the accuracy of maintaining a given level of flow parameters of a solution of volatile substances in low volatile solvent, and the flow of the diluent gas.

The present invention is to improve the accuracy of preparation of gas mixtures by the dynamic method, as well as reducing the costs of initial solutions of volatile substances in low volatile solvent.

This problem is solved due to the fact that the method of obtaining a permanent trace volatile compounds in the gas stream where the gas stream is saturated to a predetermined equilibrium concentration by bubbling contact the gas stream with a solution of volatile compounds in low volatile solvent and the saturation gas flow to the equilibrium concentration of vapors of volatile substances carry out the sequential contact of the gas stream with at least three fixed portions of a solution of volatile substances in low volatile solvent in which the concentration of volatile substances in low volatile solvent sequentially decreases from the first portion of the solution to the next or remains constant, except for the first portion, in which the concentration of volatile substances is the volume of the first portion exceeds the amount of the subsequent, and the resulting gas stream is saturated vapors of volatile substances, are mixed with a gas stream containing no target components.

When the task is created technical result, which is the saturation flow of the diluent gas vapors of volatile substances to the equilibrium concentration by successive bubble contact the gas stream with at least three fixed portions of a solution of volatile substances in low volatile solvent, the concentration of which sequentially decreases from the first portion of the solution to the next or remains constant except for the first portion of the solution in which the concentration of volatile substances above that allows to reduce considerably the solution flow rate of volatiles in low volatile solvent and to improve the accuracy of preparation of gas mixtures by the dynamic method.

The proposed method is illustrated by drawings. In Fig. 1 shows a diagram of a device for obtaining permanent trace volatile compounds in the gas stream, where 1 - gas treatment unit, 2 - line gas diluent, 3, 4, 5 is connected in series bubblers, 6 - line gas for dilution of the saturated vapors of volatile substances in the gas flow 7 is exist in the gas stream from time where 1 - heptane; 2 - methylbenzene; 3 - ethylbenzene. In Fig. 3 - experimental concentration dependence of heptane in the gas stream from time to time.

The method is as follows.

Pre-cook weight or volumetric several solutions of a given concentration, consisting of a mixture or individual volatile compounds in low volatile liquid. Fill them bubblers 3, 4 and 5, and the concentration of volatile compounds in the first bubbler 3 more than in the bubblers 4 and 5, or the volume of solution in the bubbler 3 more than subsequent bubblers at the same concentration of volatile compounds in low volatile liquid in all the bubblers. After that, when the temperature (temperature in thermostat 25o(C) sequentially passed through the United bubblers flow of the diluent gas (nitrogen) at a constant speed F=50 cm3/min, which can be diluted to a predetermined concentration in the gas line 8, by changing the ratio of flow in the gas lines 2 and 6 using a choke 7. After the initial displacement of the gas environment of the bubblers in the system installed equilibrium gas stream with a constant concentration of volatile compounds, which can be used in precise analytical and f is a mini dimensions.

Material-balance equation for the migration process gas volume dVGof the vessel (n-1) concentration of the ith volatile component, is equal to CG(n-1)in vessel n concentration of the i-th component WithG(n)can be represented in the form (CG(n-1)-CG(n))dVG=(VG(n)+KcVL(n)dCG(n)wherethe distribution constant of the i-th component between mobile (gas) and stationary (liquid) phases; VG(n)and VL(n)- the volumes of gas and liquid phases in the vessel n, respectively.

Experimental evaluation of the proposed and known methods of obtaining permanent trace volatile compounds in the gas stream was conducted by comparing the results of the preparation of gas mixtures by the dynamic method on three examples. It was identified the following characteristics and parameters: - amount of solution of volatile compounds in low volatile solvent Vpcm3to obtain a constant concentration of these substances in the flow of the diluent gas output during the same time,, h; - average concentrations of volatile compounds in the gas stream to at least n=10 measurements.


the relative error of the measure or confidence interval measurements Withcfwhen P=0.95 and f=n-1, in percent=Sr-t(P,f)100,
where t(P,f) - factor of normalized deviations Student.

Example 1. Fill the first bubbler 3 solution containing 2.5% vol. heptane, toluene and ethylbenzene in tridecane and bubblers 4 and 5 with a solution containing 2 vol.% heptane, toluene and ethylbenzene in tridecane. The amount of solution in each bubbler 23 cm3. The total quantity of solution was Vp=233=69 cm3for time=10 h with a constant concentration of volatile compounds in the gas stream. For a known way at a flow rate of a liquid solution of 1.0 cm3/mines the quantity of solution to=10 h will be Vare shown the experimental dependence of the concentration of volatile substances in the gas stream from the time bubble contact the diluent gas with the solution, obtained by the proposed method. The concentration of ethylbenzene is more than three times less than the concentration of heptane, which is caused by different values of the constants distribution Toc(Ativinsole)>(gahana)
Example 2. Fill 20 cm3in each of the three bubblers following individual solutions of volatile substances. Bubbler 3 - 2,6%, bubbler 4 - 2,3%, the bubbler 5 - 2,0% heptane in vaseline oil, respectively. The quantity of solution Vp= 203=60 cm3when=8 h with constant concentration of heptane in nitrogen. For a known way, the flow rate of the liquid solution was maintained at a level of 1.15 cm3/min. for=8 h the spent solution Vp=1,15860=552 cm3.

In Fig.3 shows obtained by the proposed method experimental concentration dependence of heptane in the gas stream from time to time.

Example 3. Fill 35 cm3in the bubbler 3, and bubblers 4 and 5 to 20 cm3solution of heptane in tridecane with the same concentration of 2.0 vol.%. The quantity of solution Vp= 260+35=75 cm3when7,060=672 cm3.

The results of the experiments of examples 1, 2 and 3 are summarized in table Comparative data experimental verification of known and proposed method".

From the table it is seen that the proposed method provides a permanent trace volatile compounds in the gas stream at a much lower number of initial solution Vpon average more than 8-9 times, and ethylbenzene - 26.1 times. In addition, improved the accuracy of the produced concentrations of volatile substances more than 3 times, for example 2, the error is reduced to15 times. This is due to the replacement in the proposed method, two mobile gas and liquid phases in a system consisting of several portions of the stationary solution of volatile compounds in low volatile solvent, through which consistently bubbled gas stream.

Using the proposed method to obtain constant concentrations of volatile compounds in the gas flow allows you to:
1. To increase the accuracy of the concentrations of volatile substances in the gas flow of diluent through better uletuchat solvent.

2. To significantly reduce the initial solution to obtain the same amount of gas mixtures with a constant concentration of individual components or volatile substances in the gas stream due to the sequential contact of a gas stream with stationary portions of the liquid solution.

3. To organize metrological support gas analysis and chromatographic measurements at the exact analytical and physico-chemical studies.


Claims

1. A method of obtaining a permanent trace volatile compounds in the gas stream where the gas stream is saturated to a predetermined equilibrium concentration by bubbling contact the gas stream with a solution of volatile compounds in low volatile solvent, characterized in that the saturation of the gas stream to an equilibrium concentration of vapors of volatile substances carry out the sequential contact of the gas stream, at least three fixed portions of a solution of volatile substances in low volatile solvent.

2. A method of obtaining a permanent trace volatile compounds in the gas stream under item 1, characterized in that the concentration of volatile substances in mnoy, except for the first portion, in which the concentration of volatile substances above.

3. A method of obtaining a permanent trace volatile compounds in the gas stream under item 1, characterized in that the volume of the first portion exceeds the amount of the subsequent.

4. A method of obtaining a permanent trace volatile compounds in the gas stream on the PP.1-3, characterized in that the gas stream is saturated vapors of volatile substances, are mixed with the gas stream that does not contain the target components.

 

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