Method of measuring volume fraction of nitrogen oxide in gaseous mixtures

FIELD: chemical industry.

SUBSTANCE: during process of taking sample from technological pipe-line, absorption of water vapors and nitrogen oxides (II) and (IV) are conducted simultaneously. For the purpose the chemical agents are used which don't absorb nitrogen oxide and don't react with it. Chromatographic measurement of volume fraction of nitrogen oxide (I) is carried out by means of industrial chromatograph having heat-conductance detector by using column of thickness of 5 m and diameter of 3 mm. The column is filled with polysorbent; temperature of column's thermostat is 20-30 C and temperature of evaporator is 100C. Hydrogen is used as a gas-carrier. Concentrations of nitrogen oxide, measured by the method, belong to range of 0, 05-0, 50% of volume fraction. Method excludes aggressive affect of corrosion-active components on sensitive parts of chromatograph. Method can be used under industrial conditions for revealing factors influencing process of forming of nitrogen oxide at the stage of catalytic oxidation of ammonia and searching for optimal conditions for minimizing effluent of ammonia into atmosphere.

EFFECT: high reproduction; simplification; improved efficiency of operation.

3 ex

 

The invention relates to the chemical industry and can be used to determine the volume fraction of oxide of nitrogen (I) - N2O in multicomponent gas mixtures containing nitrogen oxides, water vapor, nitrogen, oxygen, ammonia, carbon dioxide and other impurities.

The method for determination of nitrogen oxide (I) in a mixture of gases containing oxides of nitrogen and carbon (RJ Chemistry, joint volume, №22(1), 1966), based on the use of two columns, one of which contains silica gel with 10-20% glycerol or triethanolamine, and the second filled with molecular sieve 5A. Gases leaving the first column, pass through one of the chambers of katharometer, while the carrier gas (Mr) passes through the second, after exiting the second column gases get into the second chamber of katharometer, and the carrier gas passes through the first. Both thermostated column.

The composition of the gas mixture: O2N2CH4, NO, N2O, CO, CO2

The carrier gas - helium

First column: length 5 m, gasket - silica gel with 10% tea, work temperature of the column is 20°C.

Second column: length 4 m, gasket - molecular sieve, the operating temperature of the column is 10°C.

The disadvantages of the method:

1. The necessity of special construction materials chromatograph due to the oxidation of nitric oxide with oxygen to oxide, which in turn is aerodactyl with structural materials chromatograph and removes them from the system.

2. The need to use saheliwomen systems to maintain the temperature of the column 10°C.

3. The inability to use method for gas mixtures containing water vapor, as a result of reactions:

which leads to corrosion of sensitive elements chromatograph and removes them from the system.

The method for determination of nitrogen oxide (I), consisting of the following: oxides of nitrogen in a mixture with inert gases were separated on a specially treated molecular sieves 5A (R.N. Dietz Analyt.Chem., 1968, v.40, No. 10, R-1578).

The chromatographic column was kept for 20 hours at 300°With removal of water and activation of the adsorbent. Then passed through a column of helium and oxygen for oxidation of nitric oxide to oxide. Such treatment allows at room temperature to separate NO and N2O. nitrogen Dioxide irreversibly adsorbed by molecular sieves and does not interfere with the determination.

The disadvantages of the method:

1. The complexity of this method for routine determination of nitrogen oxide (I) in the production environment due to the length and complexity of preparation.

2. The inability to use method for gas mixtures containing water vapor, as a result of reactions (1, 2).

Known way to determine the value of nitrogen oxide (I), to prevent correlating the impact of nitric oxide and nitrogen dioxide on the threads of katharometer and design chromatograph, in which the objective is achieved by application of indirect chromatographic determination of NO and NO2, attempting to analyze the derivatives of these substances.

Thus, nitrogen dioxide can be defined after interaction with organophosphorus compounds (Doring S.E. EA. - Acta. chim. Acad. Sci. Hung., 1973, Bd. 45, No. 2, s.89).

The disadvantages of the method:

1. The distortion of the measurement result due to the reaction:

2. The inability to use method for gas mixtures containing water vapor, as a result of reactions (1, 2).

Closest to the present invention is a method for determining the nitrogen oxide (I) in mixtures containing H2O2N2CH4, CO, CO2, NO, NO2consisting in the following: the analysis is carried out by dilution of the mixture with helium using a device with three columns (Berezkin V.G., Gavrichev B.C. “Analysis of gases containing oxides of nitrogen”. Institute of petrochemical synthesis, Russian Academy of Sciences USSR - Head. Lab., 1971, V.37, №8, s).

For the separation of carbon dioxide and nitrogen dioxide in the known method uses a method of reaction gas chromatography. The column used for the separation of oxides of nitrogen from other gases, is filled Akti the new coal SKT. Eluruume from her H2About2N2, CO, NO, CH4pass the second column with molecular sieve 5A. Undivided band of nitrogen dioxide and carbon dioxide, and the band of nitric oxide (I), leaving after methane, are routed through castigados crane in the reactor filled with copper. In the reactor, nitrogen dioxide and oxides of nitrogen (I) fully restored to elemental nitrogen. Components not had time to leave the second column until the switching gas lines, remain in it. Two peaks of nitrogen, formed from nitrogen dioxide and oxide of nitrogen (I), are formed on the third column filled with activated carbon SKT.

The separation is performed using a gas chromatograph with thermal conductivity detector. Through the column is skipped, the flow of helium with a speed of 32 ml/min

First column: length 2 m, thermostatically at a temperature of 145°C.

Second column: the length is 1 m, the temperature of the room.

Third column: length 0.2 m, the temperature of -150°C.

The second and third columns are placed outside thermostat chromatograph.

The reactor is a quartz tube 32×0.7 cm, filled recovered in the flow of hydrogen in copper and heated to 900°C.

The disadvantages of the method.

1. The complexity of the use of this method in an industrial environment due to the bulkiness set the Cai and the complexity of measurement in this way, due to the selection and constant torque switching columns.

2. Poor reproducibility due to deviation of the heights of the peaks at 10% of the height calibration of the instrument due to a change in the position of the zero line between the moments of switching due to the lack of indemnification resistances in the gas stream.

3. The complexity of the use of this method in industrial settings due to the need to maintain a high temperature (900° (C) in the reactor recovery.

4. The inability to use method for gas mixtures containing water vapor, as a result of reactions (1) and (2).

The General lack of analogs and prototypes is a systematic error in the determination taking place because of the possibility of the occurrence of the following reactions in the selected sample containing water vapor:

as well as reactions (1) and (2), in which the nitric oxide (I) may either be formed, either to rot or absorb, due to prolonged contact of the components of the gas mixture.

The main problem solved by the invention is the ability to determine the volume fraction of oxide of nitrogen (I) in gas mixtures containing water vapor, excluding the impact of corrosion sensitive components on the e elements chromatograph, the results of chromatographic analysis for a short time at affordable and cheap domestic chromatographic phase, achieving high reproducibility with low complexity.

This technical result is achieved by the fact that in the process of sampling from the process piping at the same time is the absorption of water vapor and oxides of nitrogen (II and IV), which eliminates the reactions (1, 2-4, 5), and the effects of corrosion of the sample gas on the device design. Use the sinks, not sorbing and not interacting with nitric oxide (I).

Sampling is carried out in Teflon sampler through the system sinks of water vapor and oxides of nitrogen (II) and (IV).

Example 1. Determination of nitric oxide (I) in the gas mixture after the recovery boiler nitrous gases; the gas temperature (T)=300°C, composition of the gas mixture, vol.%: NO - 5,370, NO2- 3,820, O2- 4,29, N2- 69,60, N2On - 16,410, N2O to be determined.

Sampling shall be subject to the prior absorption of the gas mixture of water vapor, oxides of nitrogen (II) and (IV), which is achieved by the sequential transmission of the gas mixture through Askari (h, TU 6-09-4128-75) - to absorb water vapor; chromic anhydride for oxidation of nitric oxide (II) in nitric oxide (IV) according to reaction (3); triethylene glycol (TU 6-09-1981-72 for absorption of nitrogen oxide (IV); for more precise drying gas is passed through engeron, the residual content of water vapor in a sample of 0.002 mg/L. the velocity of the gas through the absorber w=100 h-1.

Selection of prepared gas is produced in Teflon sampler. Determination of volume fraction of nitric oxide (I) in the analyzed sample is performed by gas chromatography. Operating mode chromatograph Color - 100”: the temperature of the column thermostat - 20°C; evaporator temperature is 100°; current bridge - 200 mA; the speed of the carrier gas (H2) - 30 ml/min; volume of injected sample to 2 ml; speed chart tape - 240 mm/h; chromatographic column with Polisorb length 5 m, diameter 3 mm, Calculate the volume fraction of nitric oxide (I) is conducted by the method of absolute calibration using a passported gas mixture. The results of the three parallel definitions volume fraction of N2O the following: 0,50; 0,51; 0,50. Time yield N2O on the chromatogram 3 minutes.

Example 2. Determination of nitric oxide (1) in the gas mixture after the absorption columns; the temperature of the gas (T)=35°C, composition of the gas mixture, vol.%: NO - 0,095, NO2- 0,016, O2is 2.80, N2- 96,08, N2O - 0,913, N2O to be determined.

Sampling shall be subject to the prior absorption of the gas mixture of water vapor, oxides of nitrogen (II) and (IV), that is consistent is by passing the gas mixture through Askari (h, THE 6-09-4128-75) to absorb water vapor; chromic anhydride for oxidation of nitric oxide (II) in nitric oxide (IV) according to reaction (3); triethylene glycol (TU 6-09-1981-72) for absorption of nitrogen oxide (IV); for thinner drying gas is passed through engeron, the residual content of water vapor in a sample of 0.002 mg/L. the velocity of the gas through the absorber w=600 h-1.

Selection of prepared gas is produced in Teflon sampler. Determination of volume fraction of nitric oxide (I) in the analyzed sample is performed by gas chromatography. Operating mode chromatograph Color - 100”: the temperature of thermostat column - 25°C; evaporator temperature is 100°; current bridge - 200 mA; the speed of the carrier gas (H2) - 30 ml/min; volume of injected sample to 2 ml; speed chart tape - 240 mm/h; chromatographic column with Polisorb length 5 m, diameter 3 mm, Calculate the volume fraction of nitric oxide (I) is conducted by the method of absolute calibration using a passported gas mixture. The results of the three parallel definitions volume fraction of H2About the following: 0,10; 0,10; 0,11. Time yield N2O on the chromatogram 3 minutes.

Example 3. Determination of nitric oxide (I) in the gas mixture after the selective catalytic reactor cleaning; gas temperature (T)=280°C, composition of the gas mixture, vol.%: (NO+NO2) - 0,005, N2About to 1.00, N2O Podles the t definition, N2- the rest.

Sampling shall be subject to the prior absorption of the gas mixture of water vapor, oxides of nitrogen (II) and (IV), which is achieved by the sequential transmission of the gas mixture through Askari (h, TU 6-09-4128-75) to absorb water vapor; chromic anhydride for oxidation of nitric oxide (II) in nitric oxide (IV) according to reaction (3); triethylene glycol (TU 6-09-1981-72) for absorption of nitrogen oxide (IV); for thinner drying gas is passed through engeron, the residual content of water vapor in a sample of 0.002 mg/L. the velocity of the gas through sinks w=1000 h-1.

Selection of prepared gas is produced in Teflon sampler. Determination of volume fraction of nitric oxide (I) in the analyzed sample is performed by gas chromatography. Operating mode chromatograph Color - 100”: the temperature of thermostat column - 25°C; evaporator temperature is 100°; current bridge - 200 mA; the speed of the carrier gas (H2) - 30 ml/min; volume of injected sample to 2 ml; speed chart tape - 240 mm/h; chromatographic column with Polisorb length 5 m, diameter 3 mm, Calculate the volume fraction of nitric oxide (I) is conducted by the method of absolute calibration using a passported gas mixture. The results of the three parallel definitions volume fraction of N2O the following: 0,05; 0,05; 0,05. Time yield N2O on the chromatogram 3 minutes.

<> As seen from the above examples, the proposed method allows to determine the volume fraction of nitric oxide (I) with high reproducibility using serial chromatograph, without contact of the corrosive gas sensitive elements of the chromatograph; the time of peak N2O on the chromatogram does not exceed 3 minutes.

The method of determining the volume fraction of oxide of nitrogen (I) in gas mixtures containing H2About2N2CH4, CO, CO2, NO, NO2including chromatographic determination of volume fraction of oxide of nitrogen (I) N2O taking into account the signal detector thermal conductivity, characterized in that in the process of sampling a gas mixture containing (0,05÷0,50).% N2O and water vapor from the process line at the same time carry out the absorption of water vapor and oxides of nitrogen NO and N2O, using the reagents is not widespread and not entering into the reaction with N2O, the sample volume of 2 ml injected into the chromatographic column with a length of 5 m and a diameter of 3 mm, filled with Polisorb, when the temperature of thermostat column (20÷30)°and the temperature of the evaporator 100°using as a carrier gas hydrogen at a rate of 30 ml/min, detection is carried out with a speed chart tape 240 mm/min and the current bridge detector 200 mA.



 

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