Method gas chromatographic determination of nitrous oxide in gases

 

The invention relates to analytical chemistry, and in particular to methods gas chromatographic determination of nitrous oxide, and can be used in chemical industry for analytical control of the production of mineral fertilizers. The separation of the analyzed mixture is performed in the flow of carrier gas through column chromatography, where the sorbent according to the invention used zeolite Sakh moisture content of 13 to 17 wt.%, obtained by heat treatment of the original zeolite Sakh on THE 38-10281-80 under vacuum at 100 ° C for 1.5 h and then cooled with an overlap of helium in a closed flask, which was conducted by heat treatment, and further modification of its polyethylene glycol-1000, taken in an amount of 0.5 to 1% by weight of zeolite. Achieved selectivity, efficiency and high sensitivity determination of nitrous oxide 2 mg/m3(0.5 MAC). The method can be implemented in automatic mode on the chromatograph mass production. 5 C.p. f-crystals, 5 tab., 1 Il.

The invention relates to analytical chemistry, and in particular to methods gas chromatographic determination of nitrous oxide, and can be used in chemical nitrous oxide in the exhaust gas, formed during the drying of mineral nitrogen fertilizers, which is important for early detection of the beginning of decomposition of fertilizers and environmental control of the composition of gas emissions and air of the working area.

In the production of complex mineral fertilizers on the stage of granulation and drying use flue gases. The approximate composition of the resultant exhaust gases in the process of granulation and drying complex NPK fertilizers: nitrogen 80 mol.%, oxygen 10 mol.%, carbon dioxide 10 mol.%, as well as admixtures of oxides of nitrogen and other compounds. By increasing the content of nitrous oxide in the exhaust gas is judged on the beginning of the decomposition of fertilizers, thereby it is possible to prevent the danger of spontaneous combustion and explosion.

Control over the content of nitrous oxide in the gas emissions and in the air of working zones are necessary due to the fact that nitrous oxide is it harmful substances hazard class 3 with maximum 5 mg/m3in terms of nitrogen dioxide.

Known methods of determining the nitrous oxide method getaccountinfo chromatography on silica gel, activated carbon, aluminium oxide and polymeric sorbents [anwaar B. I., Drugov Y. C. Gas chromatography of inorganic substances. - M.: Chemistry, 1976, S. 29-31]. These methods are not morisogo of carbon dioxide and nitrogen, as silica gel and activated carbon peak of nitrous oxide in the chromatogram has a retention time close to the retention time of the peak of carbon dioxide, and poorly separated from the peak of the main component is nitrogen. Aluminum oxide irreversibly adsorb carbon dioxide, which leads to getting results with large error. When using polymeric sorbents nitrous oxide eluted after carbon dioxide, and on the chromatogram peak nitrous oxide is covered by the “tail” of the peak of the carbon dioxide that prevents quantification of nitrous oxide.

The known method of gas chromatographic determination of nitrous oxide in the presence of oxide and carbon dioxide, methane, oxygen and nitrogen using zeolite CAA with a programmed temperature increase of the column from 50 to 400[S. Thorburn J Chromatogr., 1969, 42. No. 15, S. 389]. While nitrous oxide is well defined in the presence of nitrogen and carbon dioxide. However, the method is complicated in hardware design, it has a low sensitivity and cannot be automated.

Closest to the proposed combination of essential characteristics is a well-known method of gas chromatographic determination of suites on a chromatographic column, filled with sorbent, representing the zeolite Sah, calcined in a stream of helium at a temperature of 350C for 4 h [Kurmanbekov E., Levchuk B. C. "Chromatographic method of analysis of camerahouse nitrogen" in Proc. of Gas chromatography in chemistry and petrochemistry. - M.: A.V.Topchiev Institute of petrochemical synthesis Russian Academy of Sciences USSR, 1985, S. 106-111]. In the known method specified optimal conditions analysis: column length of 2 m, diameter 4 mm, filled with the aforementioned sorbent; to register the component using a heat conductivity detector; carrier gas helium, flow rate of 50 cm3/ min; column temperature room.

The disadvantages of this method are the low efficiency of the sorbent used and the low sensitivity of the determination of nitrous oxide, especially in the presence of large concentrations of nitrogen and carbon dioxide, as well as the duration of the analysis. A significant drawback of this method is also low selectivity determination of nitrous oxide in the presence of carbon dioxide, which is first adsorbed and then “go” in the background. These shortcomings do not allow to automate the known method.

An object of the invention is the development of effective, selective, vysokochuvstvitel who I am in the process of granulation and drying fertilizers, and in the air of working zone of the production of complex fertilizers.

The technical problem is solved in that in the method of gas chromatographic determination of nitrous oxide in gases, including separation of the analyzed mixture in the flow of carrier gas to the chromatographic column filled with the adsorbent, which includes zeolite Sah, and registration of components according to the invention in use as a sorbent zeolite Sakh moisture content of 13 to 17 wt.%, modified by polyethylene glycol-1000, taken in an amount of 0.5-1.0% by weight of zeolite.

As the analyzed mixture may use the exhaust gases of the process of granulation and drying compound fertilizer containing nitrous oxide.

As the analyzed mixture may use the air of the working zone of the production of complex mineral fertilizers, containing a mixture of nitrous oxide.

Zeolite Sakh moisture content of 13 to 17 wt.% can be obtained by heat treatment of the original zeolite Sakh on THE 38-10281-80 under vacuum at 100 ° C for 1.5 h and then cooled with an overlap of helium in a closed tank in which heat treatment was carried out.

To register nitrous oxide can use the detector to the detector constant recombination velocity.

Optimal conditions of chromatographic analysis is shown in table 1.

To obtain zeolite Sakh moisture content of 13 to 17 wt.% the original zeolite Sakh on THE 38-10281-80 crushed, selected fraction of 0.25 to 0.5 mm, covered in heat resistant glass round bottom flask, which is placed in a temperature of 100With muffle furnace, and kept under vacuum for 1.5 hours then the zeolite is cooled to room temperature with an overlap of helium in a closed flask, in which heat treatment was performed.

For sorbent sample of polyethylene glycol-1000 (PEG-1000) in an amount of 0.5-1.0% by weight of zeolite was dissolved in chloroform, pour the prepared solution zeolite Sakh moisture content of 13 to 17 wt.% and evaporate the solvent in a fume hood in a water bath with periodic stirring to obtain a dry granular mass, and then dried in a drying Cabinet at 100 ° C to constant weight.

Thus prepared sorbent fill chromatographic column and condition in the flow of carrier gas for 6 h at a temperature of 200C.

Below are examples of explanatory Technica and nitrogen. For more accurate values of the retention times of individual components using pure substance.

Example 1 (the present method). The sample gases are analyzed under the conditions shown in table 1.

Example 2 (control). The same sample analyzed in terms of one of the known methods using zeolite CAA modified by polyethylene glycol-1000.

Example 3 (control, prototype). Gas chromatographic separation of components of the same tests carried out on a column of zeolite Sah treated in a stream of helium at a temperature of 350C for 4 h, but, unlike the prototype, under the conditions shown in table 1.

The test results of the separation properties of the used sorbents are given in tables 2-4.

Notes to table 2: -N2/N2O-the degree of completeness of the separation of nitrogen and nitrous oxide, as defined by p. 42 GOST 17567-81;- the analysis time is set as the output peak CO2.

Examples 4-8. To establish the optimum moisture content of the zeolite to achieve maximum values of selectivity and separation efficiency, and maximum detection sensitivity the table 1. As sorbent use zeolite Sakh with different moisture content.

To obtain zeolite Sakh with different moisture content change processing mode of the original zeolite. The residual moisture content determined by gravimetric method.

The results are shown in table 3.

The test results for examples 1-8 are presented in tables 2 and 3 show that only the zeolites Sakh moisture content of 13 to 17 wt.% let the maximum extent possible to solve the technical problem and provide good (see table 3,=1) separation of the sample components with a minimum analysis time and the maximum detection sensitivity of nitrous oxide.

Examples 9-12. To determine the optimal ratio of sorbent: stationary phase that eliminates sorption of nitrous oxide and carbon dioxide, erosion peaks, and achieved a satisfactory degree of chromatographic separation and high sensitivity of the method, analyze gas samples containing 0.1 and 0.005 mol.% nitrous oxide. Sample containing 0.1 mol.% nitrous oxide, to analyze the chromatograph under the conditions shown in table 1. Samples with a content of 0.005 mol.% nitrous astdr). In addition, calculating the degree of chromatographic separation (R) nitrous oxide with carbon dioxide in accordance with p. 41 GOST 17567-81.

The obtained test results are shown in table 4.

The results of the studies are shown in table 4, show that the optimal content of PEG-1000 on the zeolite Sakh moisture content of 13 to 17 wt.% is 0.5-1.0% by weight of zeolite. Only in this case, achieving a complete separation of nitrous oxide from nitrogen and carbon dioxide and provides high sensitivity analysis 110-4mol.%, that corresponds to the contents of nitrous oxide is about 2 mg/m3.

Example 13 (the present method). The analysis is performed under the conditions of table 1, as the sample used sample gas obtained during the kinetic studies on thermal decomposition of complex nitrogen-phosphorus-potassium fertilizers. The resulting chromatogram is shown in the drawing. The chromatogram indicated:

1 oxygen + nitrogen; 2 - nitrous oxide; 3 - carbon dioxide.

The content of nitrous oxide in the gas, calculated by the method of absolute calibration, 0.5 mol.%.

Examples 14, 15 (the present method). Order PTMG /m3nitrous oxide in the air. Conditions of the analysis in table 1, the registration of nitrous oxide is carried out using DPR. The results are shown in table 5.

Thus, the developed method of determination of nitrous oxide in gases on a chromatographic column containing zeolite Sakh moisture content of 13 to 17 wt.%, modified PEG-1000 in the amount of 0.5-1.0% by weight of zeolite. The proposed method is characterized by expressnet, higher efficiency, selectivity and sensitivity compared to the prototype. The sensitivity of the inventive method for nitrous oxide is 110-4mol.%, (which is equivalent to about 2 mg/m3or 0.5 MPC), while the measurement relative error does not exceed25%, which meets the requirements of GOST 12.1.005-88 to the control methods of air of the working area.

The method can be implemented in automatic mode on the chromatograph mass production.

Quantitative and qualitative analysis by the present method is of particular practical importance for monitoring the process of granulation and drying compound fertilizer to prevent their spontaneous combustion and explosion.

< the proposed method of determination of nitrous oxide in the gas samples make it possible to use this method in the laboratory and directly in production.

Claims

1. Method gas chromatographic determination of nitrous oxide in gases, including separation of the analyzed mixture in the flow of carrier gas to the chromatographic column filled with the adsorbent, which includes zeolite Sah, and registration components, characterized in that the zeolite adsorbent are used Sakh moisture content of 13 to 17 wt.%, modified by polyethylene glycol - 1000, taken in an amount of 0.5-1.0% by weight of zeolite.

2. The method according to p. 1, characterized in that as the analyzed mixture using the exhaust gases of the process of granulation and drying compound fertilizer containing nitrous oxide.

3. The method according to p. 1, characterized in that as the analyzed mixture using the air of the working zone of the production of complex mineral fertilizers, containing a mixture of nitrous oxide.

4. The method according to one of paragraphs.1-3, characterized in that use Sakh moisture content of 13 to 17 wt.%, obtained by heat treatment of the original zeolite Sakh on THE 38-10281-80 under vacuum at 100 ° C for 1.5 h and then cooled with an overlap of helium in a closed tank in which heat treatment was carried out.

5. The method according to one of paragraphs.1, 2 on one of the PP.1-4, characterized in that for the registration of nitrous oxide use the detector constant recombination velocity.

 

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