SU661329A1 - Gas chromatorgraph for analysis of admixtures - Google Patents

Description

The invention relates to chromatography and will find application in the gas and chemical industries in determining the amount of impurities in gases and vapors. In the chromatographic determination of the content of impurities in gases and vapors, pre-concentration of impurities is used. When analyzing the impurities of heavy components relative to the main component of the analyzed product, the accumulation of impurities, their concentration and the progressive analysis of concentrated impurities are evolved. A gas chromatograph for the analysis of impurities with their preconcentration is a complex complex, including an accumulation column placed in a cryothermostat, the output of which is connected to a separation column connected to a detecting device. When accumulation of impurities through the cooled column pitelnuyu column passed analyzed product and the adsorbent column absorbs the impurities contained therein. Next, the impurities are concentrated and introduced into the separation column for an extensive analysis, the results of which are recorded with a detecting device. The concentration of impurities is carried out by feeding a gas propellant into the accumulation column or by heating the storage column in a thermal field whose temperature varies over time and along the length of the column, while simultaneously feeding the carrier gas. This causes desorption of impurities and their compression into a narrow strip at the exit of the cumulative column, from where a sample of impurities in the flow of carrier gas is fed for a downstream analysis to separation column 2. Of the known gas chromatographs for analyzing impurities with their preliminary concentration the closest to the technical essence proposed is a gas chromatograph containing the input line of the analyzed product with a pressure stabilizer installed in it, a cumulative column, the output of which through the valve is connected to the discharge line of the analyzed product and with the inlet of the separation column, a stabilized source of carrier gas, connected through a valve to the inlet of the separation column 3. The prototype chromatograph, as well as other gas chromatographs for the analysis of impurities with their preconcentration, is deficient impurity content, since the measurement accuracy of the prototype chromatograph is determined not only by the stability of the parameters that influence the hydrochloric sample, but also stability and voeproizvodimostyu parameters which affect at npoiieccbi accumulation of impurities, their concentration and the sample introduction concentrated impurities at about pheno- analysis. In order to ensure the accuracy of quantitative determinations of the chromatograph, it is necessary that the following requirements are fulfilled during the preliminary concentration of impurities: a strictly specified amount of the analyzed product should be entered into the accumulative column, the determined components of the impurities should be completely absorbed by the adsorbent or their absorption coefficient should not be the entrainment of impurities from the cumulative column, the width of the band of concentrated impurities and their rate of introduction Yes, the separation column must be constant. The observance of these conditions depends on C1 stability and reproducibility from analysis to analysis of a large number of parameters, in particular, the rate of input of the aim. during the concentration and introduction of samples of impurities for a progressive analysis, it is impossible to directly control and their violation during the operation of the chromatograph leads to uncontrollable in less accurate measurements. The purpose of the invention is to increase the accuracy of quantitative determinations. According to the invention, this objective is achieved in that the gas chromatograph is equipped with a metrological assurance unit, including a standard dispenser, the inlet of which is connected to the sources of standard gas through valves, and the outlet connected through a valve with a stabilized source of carrier gas is connected between the stubs. a pressure chizator on the lisy liner input line and the beginning of the tube with the specified length and volume. The end of the thrubka is connected via a standard detector and an adjustable lined throttle to the valve, one of which is installed at the entrance of the cumulative column and the other at the entrance of the throttle. which is associated with the discharge line of the product being analyzed. The electrical input of this detector is connected to the input of the pulse puller, the output of which is connected to the drive of the standard metering device, as well as to the input of the pulse period meter and the counter input of pulses. The meter outputs are connected to valve actuators at the inlet and outlet of the cumulative column and at the inlet of the metering unit. The installation in the gas chromatograph for analyzing the impurities of the metrological assurance unit allows monitoring all the conversion stages in the instrument of the analyzed product, from its supply to the accumulative column to recording the impurities peaks at the chromatograph output, to directly measure some of the instrument parameters that affect accuracy of quantitative determinations, and other parameters, the direct measurement of which is impossible, to control indirectly, will receive l data for quantitative calculations to determine the concentrations of the components of impurities in the analyzed product, and judge the degree of reliability of the results of analyzes and their suitability for quantitative calculations. The drawing shows the proposed gas chromatograph for the analysis of impurities. The chromatograph contains a cumulative column 1, the output of which through valve 2 is connected to the inlet of separation column 3, the output of which has a detecting device 4. Through the valve 5, the output of column 1 is connected to the discharge line 6 of the analyzed product. The input of the column 3 through the valve 7 is connected to a stabilized source 8 of carrier gas. The chromatograph is equipped with a unit 9 for metrological assurance of analyzes. Block 9 includes a standard metering device 10, which is a calibrated volume, with the help of actuator 1, which is moved between the input and output channels of the metering device. The input channel of the dispenser 10 of the standard through the valves 12 and 13 is connected respectively to the sources 1-4, 15 gas standards I and II, and through the throttle 16 - with the discharge line. The outlet channel of the dispenser 10, connected via valve 17 to the stabilized gas-media source 8, is connected between the pressure stabilizer 18 connected to the source 19 of the analyzed product and the beginning of the tube 20 having a predetermined length and volume. The end of the tube 20 is connected with the serially mounted detector 21 of the standard and an adjustable choke 22, which is connected through the valve 23 to the input of the cumulative column 1, and through the valve 24 and the adjustable choke 25 to the discharge line 6 of the analyzed product. The electrical detector 21 is connected to the input of a pulse driver 26, which converts the signals of the detector into rectangular pulses. The output of the driver 26 pulses through the Converter 27 is connected to the drive of the dispenser 10 of the standard, and directly with the input of the meter 28 period pulses and the input of the counter 29 pulses.

The pulse counter is designed to measure the number of pulses received at its input, and has m outputs. In the initial state, all its outputs, except for the zero, have no signals, and there is a single signal at the zero output. When pulses are fed to the input of the counter 29, a single signal is successively transferred from one output to another, and the output number, on which a single signal is present, is equal to the number of pulses fed to the input of the counter 29. At the output of the pulse period meter 28, signals are generated that are proportional to the time intervals (periods) between adjacent pulses coming in at its input.

The outputs of the pulse counter 29 are connected via converters 30-32, respectively, to valve actuators 12 and 13 at the inlet of the standard metering device 10, and to valve actuators 5 and 23 at the input and output of the cumulative column 1.

Transducers 27, 30-32 serve to convert incoming signals to their inputs into control commands.

The operation of the chromatograph is controlled by a software device (not shown), which in the required time sequence produces control commands.

The chromatograph works as follows.

Preliminary data on the range of impurity concentrations in the analyzed product determine the required dosing volume Q, i.e., the amount of the analyzed product that must be passed through cumulative column 1 to accumulate impurities in an amount sufficient for reliable measurement by a detecting device 4 chromatograph. By means of the pressure stabilizer 18, a constant pressure PO of the analyzed product is established in the tube 20 and the portion q of the product is determined, while in the tube:

H where V is the volume of the tube 20;

R is gas constant;

T - absolute temperature.

Thereafter, the number of n portions g is determined, which must be supplied to cumulative column 1 to provide the required dosing volume Q of the product being analyzed:

(2)

P

The input of the converter 32 is connected to the n-th output of the pulse counter 29 (), and the inputs of the converters 30 and 31 to the outputs of the counter 29 located between its zero and (n-1) th outputs. In the drawing, converter 30, connected to valve 12 on the standard 1 supply line, is connected to the zero (p-3) th, (p-2) -th, and (p-1) -th outputs, and the input of the converter 31 connected to the valve 13 on the standard II supply line is connected to the remaining outputs of the counter 29.

Next, adjust the conductivity of the adjustable throttle 22, so as to provide the desired input rate of the analyzed product in the cumulative column 1.

0 Adjust the conductivity of the adjustable throttle 25 so that the speed of the analyzed product when it is fed through the column 1 and through the choke 25 is approximately the same, which is ensured with equal conductivities of the chokes 25 and the column at the accumulation temperature. The conductivity of the adjustable throttle 16 is adjusted so that the flow rate of the gas-gas is sufficient to ensure full flushing of the calibrated volume.

Q gas-reference between the cycles of the dispenser 10 standard.

In the initial state, the valve 7 and the valve 12 connected via the converter 30 to the zero output of the pulse counter 29 are open, and the remaining valves are closed. The carrier gas is fed to the separation column 3, where the separation of impurities that enter the column 3 in the previous cycle occurs. The standard gas 1 from source 14 flows through the calibrated volume of the metering device 10 of the standard. The accumulation column 1 is cooled to a temperature at which impurities accumulate.

At the beginning of the cycle of operation of the chromatograph, open the valve 24, and the analyzed product from the source 19 through the stabilizer 18, the dispenser 10, the tube 20, the detector 21, the throttles 22 and 25 will go to the discharge line 6. In this case, the tube 20 is flushed and at the same time balancing the measuring circuit of the detector 21 of the standard

 (balancing node not shown). After the end of balancing, preambles are accumulated, for which a command K is sent, through which valve 24 closes and valves 5 and 23 open. The flow of the analyzed product from source 19 through stabilizer 18, dispenser 10, tube 20, detector 21 and throttle 22 will be sent to cumulative column 1, where the sorption of impurities occurs, and from it into the discharge line 6. Due to the equality of flow rates

 of the analyzed product through the throttle 25 and through column 1, the switching of the flow will not cause an imbalance in the measuring circuit of the detector 21 of the standard.

At the same time, the Ko command will be fed through the converter 27 to the metering actuator 10 of the standard, the calibrated volume of which will move down and a sample of the gas of the standard I will be introduced into the flow of the analyzed product, after which the calibrated volume will return to its original position. The sample introduced at the beginning of the tube 20 by the flow of the analyzed product will move through the tube 20. When the end of the tube 20 is reached, when a portion of the analyzed product is inserted into column 1 is g, the sample gas of the standard I will go to the detector 21 of the standard and will exit at its output electrical signal in the form of a peak. This signal through the pulse former 26 to the pulse counter 29, the pulse period meter 28 and through the converter 27 to the metering drive 10. The calibrated volume of the dispenser 10 will move down again, a second sample of the standard gas I will be introduced into the analyzed gas flow, after which the volume will return to its original position. A single signal is shifted from zero to the first output of the counter 29 pulses. Valve 12 will close and valve 13 will open. The reference gas II will be supplied from the source 15 to the metering unit 10 of the reference. When the second sample gas of the reference 1 enters the reference detector 21, when the second portion g of the analyzed product is introduced into column 1, the output of the detector 21 again shows . This signal will lead to the introduction of a third sample (reference gas II) at the beginning of tube 20, to the transfer of a single signal from the first to the second output of counter 29 pulses and to the formation of a period of pulses at the output of the meter 28, proportional to the time interval t, between the first and second peaks at the detector output 21. By the value of t | You can determine the velocity of the analyzed gas V | supplied to the cumulative column 1: where C is the proportionality coefficient. Upon receipt of the third sample (gas standard II) in the detector 21, the fourth sample (reference gas II) will automatically enter the beginning of tube 20, a single signal will be transferred to the third output of the counter 29 pulses and a tz signal inversely proportional to speed will be output at the output of the meter 28 Vi of the analyzed product in the interval between the second and third peaks. Similarly, block 9 will continue to work automatically. When a single signal appears at the (p-3) th output of the pulse counter 29, valves 12 and 13 will switch, as a result of which (p-2) -and and (p-1) -th dispenser of the 10 standard are introduced into the stream analyzed product standard gas 1 will be supplied again. On admission of (n-1) sample to the 21 standard detector, a single signal will be generated at the nth output of the pulse counter 29, which through converter 32 will be fed to valve actuators 5 and 23. These the valve is closed and the supply of the product to be analyzed to cumulative column 1 is stopped. The accumulation of impurities and the cycle of operation of the metrological unit 9 is completed. Thus, unit 9 of metrological assurance is performed by distributing in time a cumulative column 1 of a known amount of standard gases and an exact dose of the analyzed product (Q ng), with registration of the feed speed gpQ. When the impurities are concentrated, valve 7 is closed, valves 2 and 17 are opened and column 1 is heated in a thermal field whose temperature varies in time and along the length of the column. The carrier gas will flow through the metering device 10, the tube 20, the detector 21 and the choke 22 into the accumulator column 1 and from it into the separation column 3 and the detecting device 4. The impurities and standard gases I and II will be concentrated in the form of a narrow strip at the column outlet 1 and the flow of carrier gas transferred to the separation column 3, after which the valves 2 and 17 are closed and the valve 7 is opened. With an extensive analysis, a sample of impurities and gas standards I and II will be divided into separate components in column 3, whose peaks will be recorded at the exit by a detecting device 4. On the chromatogram, in addition to the peaks of impurities. contained in the analyzed product, peaks of gaseous standards will be recorded. He I and II. The concentration of each impurity component is equal to the ratio of the peak parameter determining its quantitative content to the volume of the analyzed product introduced into the instrument. The presence in the gas chromatograph of a unit for metrological assurance of analyzes significantly increases the accuracy and reliability of the analyzes. The introduction of gas standards in the analyzed mixture has two objectives. On the one hand, when entering the product to be analyzed into the chromatograph, the standard gases are used as "labels" that allow for the exact dosing of the product. On the other hand, exactly the known number of standards distributed in the analyzed product is introduced. Standards are accumulated, concentrated, separated and recorded under the same conditions as the impurities of the analyzed product, and therefore all factors affecting the quantitative results of the analyzes will affect the impurities and the standards the same: As a result, changes in the parameters of the peaks of the standards (area, height), determining their quantitative content, indicate the deviations of the operating mode of the chromatograph. In particular, a reduction in the area of standards of standards may be due to the ablation of standards, and the investigator