GB/T 3208-1982 Microcoulometric determination of total sulfur content in benzene products
Some standard content:
National Standard of the People's Republic of China
Micro-coulomb method for determining the total sulfur content of benzene-type products
This standard is applicable to the determination of sulfur content of coking benzene, coking benzene and pyrolysis benzene with a sulfur content of 10-1000ppm. 1 Test principle
L:DC 668.735
GB 3208-82
The sample is mixed and burned with oxygen in the combustion tube, so that the sulfur in the sample is converted into sulfur oxides and carried into the titration cell by the carrier gas. The following reaction occurs in the oxidation cell:
1 1SO.+ H,O-→SO, +31 +2H
When the sulfur is consumed, the indicating reference electrode pair indicates this change and transmits the sign to the microcoulomb counter, which outputs a corresponding current to the electrolytic anode-electrolytic cathode electrode pair. The following reaction occurs on the electrolytic anode: 31--2e -1;
To replenish the sulfur consumed, the sulfur is returned to the electrolytic titration cell to restore the concentration before titration. The amount of electricity consumed by the electrolysis is the product of the microcoulomb number and the selected charge range. According to Faraday's law of electrolysis, the sulfur content of the sample can be screened out by calibration of the sample.
2 Reagents
2.1 Potassium iodide: analytical grade.
2.2 Glacial acetic acid: analytical grade.
2.3 Iodine: analytical grade.
2.4 Mn: analytically pure.
2.5 Distilled water: use 1L distilled water or deionized water, the water resistance should be greater than 1M. 2.6 Nitrogen: as carrier gas
2.7 Oxygen: as the reaction gas.
2.8 Azoles: purity should not be less than 98%.
2.9 Electrolyte: dissolve 0.5 ml potassium hydroxide in 1L distilled water, add 0.5 ml glacial acid, put into a brown bottle, store in a cool place, and use for 2 to 3 months. 2.10 Organic sulfur standard solution: 2.10.1 Design method of thiophene standard solution: WxCx Sulfur content of thiophene solution: WxCx (m), g Issued by National Bureau of Standards on September 23, 1982, xh (m), implemented on July 1, 1983, purity of thiophene, %; Original age of sulfur; Specific gravity of thiophene: Volume of the container used, ml; Density of thiophene, /ml: GB 3208-82, g/ml.
2.10.2 Prepare a standard solution of sulfur content of 1000ppm: use a needle to draw up a solution (purity is 98%, specific gravity is 1.062), accurately weigh about 2.33g on an analytical balance, put it into a 1000ml bottle filled with about 500ml of water, and dilute to the scale line.
2.33 ×0.98 ×-
Sulfur content of standard solution of sulfur
(1000-
×10h=:1002（ppm）
0×0.866-2.33
According to the required sulfur content of the standard solution, the 1000Ppm standard solution of sulfur can be diluted into 500ppm, 100ppm and 50ppm, etc. by using a pipette and a volumetric dilution machine.
Note: Due to the low melting point of sulfur, the standard solution of sulfur should be re-made after one month of use. 8 Instruments and equipment
3.1 Microcoulombmeter
It can measure the potential of the electrolytic anode-reference electrode pair, and then compare this potential with the given bias voltage, and then convert this potential into a corresponding current and add it to the electrolytic anode-electrolytic cathode electrode pair. 1, so that it electrolyzes to produce: 1:. The detection range should include 10 ~ 1000PpI. Note: All micro-solenoids that meet the above test specifications can be used. 3.2 Quartz combustion tube.
3.3 Combustion furnace: The furnace temperature can be kept constant at 900=20℃3.4 Titration cell, as shown in Figure 1.
There is an indicator-reference electrode pair in the cell, whose function is to calibrate the concentration of the cell, and an electrolytic electrode-electrolytic resistor pair, whose function is to maintain a constant concentration of 1. The indicator electrode is a half-cell, and the reference electrode is a 1-wire cell in the front of the saturated electrolyte. The electrolytic anode is made of nanosheets, and the electrolytic cathode is made of platinum wire. The electrolytic cathode is connected to the central chamber of the titration cell through glass or gold electroplating.
Porous capillary bundle
Electrode
Electrolysis cathode
Non-capillary bundle
Indicator electrode
Electrolysis anode
Porous capillary bundle
Figure 1 Schematic diagram of titration cell
8.5 Electromagnetic stirrer.
3.6 Recorder: Full scale can be 1mV, 5mV or 10mV. 3.7 Shoulder-acting sample injector: Sample delivery speed is about 0.1~0.5ul/s. 3.8 Micro syringe: 10l.
GB3208-82
4 Test steps ((Take SKD-1 microcoulometer as an example) Refer to the schematic diagram of the device for measuring total sulfur content by microcoulomb method (as shown in Figure 2) Quartz combustion tube Silicon rubber plug
Recorder
Full titration cell
—Sensitive gas
Schematic diagram of the device for measuring total sulfur by microcoulometric method
4.1 Turn on the power of the microcoulometer.
4.2 Carefully insert the quartz combustion tube into the combustion chamber and connect the reaction gas and carrier gas lines. Turn on the power of the temperature controller and keep the furnace temperature constant at 900±20℃.
4.3 Open the valves of the gas cylinder and oxygen cylinder, adjust the pressure relief valve outlet pressure barrier 1~2kg/cm2, and adjust the steady flow rate to keep the nitrogen flow rate constant at 160ml/min and the oxygen flow rate constant at 40ml/min. 4.4 First clean the titration cell, install the reference electrode, rinse the titration cell with electrolyte 2 to 3 times, and then add the electrolyte to the titration tank. Add 1 volume of electrolyte to keep the liquid level about 1cm above the sheet electrode. The two sheet electrodes and the electrolytic cathode should be on the same plane. Note: Installation of reference electrode: add about 2g iodine into the reference electrode chamber, then add electrolyte into the titration cell, open the side plug of the reference electrode chamber, inject electrolyte into the reference electrode chamber, wait for the electrolyte to fill the chamber, and ensure that there are no bubbles between the iodine and the reference electrode, carefully insert the reference electrode with vacuum grease (or vaseline) pre-coulombed on the grinding door. 4.5 Place the titration cell on the electromagnetic stirrer, and connect the titration cell to the ferrite tube through a silicone rubber plug with holes or a spherical grinding mouth. 4.6 Turn on the power of the stirrer, recorder and injector, turn on the stirrer switch, and adjust the stirring speed to stir a slight vortex. 4.7 Connect the two ends of the microcoulometer input line to the reference electrode and the indicator electrode respectively, and connect the two ends of the microcoulometer output lead to the electrolytic anode and the electrolytic cathode respectively.
4.8 According to the sulfur content range of the sample, refer to the data in Table 1, and first inject 5μ sample, roughly calculate the sulfur content, and then select the relevant parameters of the coulometer.
4.9 The method of adjusting the bias voltage is: according to the sulfur content of the sample, adjust the bias voltage to an appropriate value (generally between -90 and -130mV) according to Table 1. When measuring high-sulfur samples, the bias voltage must be lower, and when measuring low-sulfur samples, the bias voltage must be higher. Put the detection and the range in the appropriate position. At this time, the signal shows negative overlimit, then use a 10μl syringe to inject a quantitative sulfur standard (the sulfur content of the standard sample is closer to the sulfur content of the sample, the more sensitive it is), and the peak shape is tail-bearing (as shown in Figure 3, A). The bias voltage can be appropriately increased and the detection voltage can be reduced. Then use the compensation voltage to adjust the signal to stabilize near zero (generally the absolute value of the signal is less than 2), and a symmetrical peak shape can be obtained on the recorder (as shown in Figure 3, B). When an over-peak is obtained (as shown in Figure 3), the bias voltage and the detection voltage are appropriately reduced to obtain a symmetrical peak shape. The symmetrical peak shape indicates that the bias voltage and other operating conditions are well selected. After 1 to 2 minutes of waiting, the sample can be injected for analysis. The standard signal is a positive over-limit. After the peak is obtained, adjust the peak shape in the same way as above.
Note: (1) Negative limit: that is, the words "-8.8.7." are displayed on the electronic display, and the first and second digits are optional. ② Positive limit, that is, the words "9,8,9." are displayed on the left, and the first and second digits are also optional. The display shows
Sample content range [
(ppm)
1000 ~ 100
100~10
4.10 Calibration
-100-120
120～-130
GB 3208--82
SKD-1 Digital Coulometric Titration Instrument Operation Number Selection Gate
Disk Range
Time (min)
Figure 3, Typical Peak Shape of Sulfur
Detection Range
microvolt/ Before each analysis, a standard sample with a similar boiling range and sulfur content to the sample to be tested is used for calibration. Each calibration is repeated at least three times, and the "electricity range" and the displayed value of the electricity are recorded. Each injection is 5μ, and the injection speed is about 0.1 μl/s. The recovery rate of sulfur in the general standard sample should be above 80%. If the recovery rate is lower than 80%, the instrument operating parameters should be checked to see if they are appropriate and if the concentration of the standard solution has changed. The recovery rate K (%) is calculated according to formula (2): K
96500x
recovery rate of sulfur in standard solution, %,
measured quantity of electricity, uC:
-quantity range, which can be 1, 2, 5, 10 and 20, the value of quantity displayed on the microcoulomb meter, μC, the redox capacity of sulfur, g!
Faraday constant, C/mol,
volume of standard solution injection, μl,
density of standard solution, /ml,
sulfur content of standard solution, ppm.
4.11 Sample analysis
After calibration with standard sample, analyze the sample with a 10-liter syringe under the same operating conditions, injecting 5μl each time, repeat the measurement three times, and record the "electric mouse range" and quantity displayed value, and take the arithmetic average of the three measurements. Calculation of test results
The sulfur content S of the sample is calculated as follows:
Wherein: S—sulfur content of the sample, P
GB3208-82
C standard—sulfur content in the standard solution, ppm;
Q standard—the amount of electricity consumed when measuring the standard sample, μC; Q sample—the amount of electricity consumed when measuring the sample, μC. 6 Test errorbzxZ.net
The ratio of the range of the three measurement results of the same sample to its average value shall not exceed 5.4%. Additional remarks:
This standard was proposed by the Ministry of Metallurgical Industry of the People's Republic of China. This standard was drafted by Anshan Thermal Energy Research Institute. The main drafter of this standard is Lu Xiuyun.
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