Determination method of coulometric sulfur analyzer Hebi Hongtai
2.1 Key points
The coal sample is burned and decomposed in the purified air flow under the high temperature not lower than 1150 ℃ and the action of the catalyst. The generated sulfur dioxide is coulometrically titrated with iodine and bromine generated from electrolytic potassium iodide and potassium bromide solutions. The electricity consumed by electrogenerated iodine and electrogenated bromine is integrated by the coulomb integrator and displays the milligrams of sulfur contained in the coal sample.
2.2 Instruments and reagents
2.2.1 Equipment
The automatic sulfur measuring instrument based on coulometric titration includes the following parts:
a. Sample delivery program controller: coal samples can be moved forward and backward according to the specified program.
b. High temperature furnace: use silicon carbon tube or silicon carbon rod as the heating element, with a high temperature zone (1150 ± 5 ℃) of not less than 90mm long The combustion tube needs to withstand temperatures above 1300 ° C. A platinum rhodium-platinum thermocouple is used. The burning boat is made of porcelain with a temperature resistance above 1300 ° C.
c. Stirrer and electrolytic cell: the stirrer speed is 500r / min, continuously adjustable. The electrolytic cell is about 12cm high and the capacity is about 400mL. There are two platinum electrolysis electrodes with an area of ​​150mm2 and two platinum indicator electrodes with an area of ​​15mm2. Indicator electrode response time should be less than 1s.
d. Coulomb integrator: the integral linearity within the range of electrolytic current 0 to 350mA should be ± 0.1%. Nixie tubes with 5 to 6 digits display milligrams of sulfur or printers with at least 5 digits.
e. Air purification system: about 1500mL / min of air supplied by the pump is purified and dried by a tube containing sodium hydroxide and discoloration silica gel.
2.2.2 Reagents
2.2.2.1 Potassium iodide (GB 1272-77): analytically pure.
2.2.2.2 Potassium bromide (GB 649-77): analytically pure.
2.2.2.3 Glacial acetic acid (GB 676-78): analytically pure.
2.2.2.4 Tungsten trioxide: chemically pure.
2.2.2.5 Color-changing silica gel: industrial products.
2.2.2.6 Sodium hydroxide (GB 629-77): chemically pure.
2.2.2.7 Electrolyte: 5g each of potassium iodide and potassium bromide, 10mL of glacial acetic acid, and 250-300mL of distilled water.
2.3 Test preparation
2.3.1 After connecting the power supply, heat the high-temperature furnace to 1150 ℃, and take another set of calibrated platinum rhodium-platinum thermocouple pyrometers to measure the position and length of the high-temperature zone in the combustion tube and the pre-decomposition position at 600 ℃.
2.3.2 Adjust the program controller so that the pre-decomposition and high-temperature decomposition positions are at 600 ℃ and 1150 ℃ respectively in the high-temperature furnace.
2.3.3 Fill the combustion tube with aluminum silicate wool with a thickness of 3mm, located at the rear end of the high temperature zone. Fill the exit of the combustion tube with clean, dry glass fiber wool.
2.3.4 Assemble the program controller, high temperature furnace (with combustion tube inside), coulomb integrator, agitator, electrolytic cell and air purification system.
Silicone rubber tube should be used to seal the glass-to-glass port of the combustion tube, piston and electrolytic cell.
2.3.5 Start the air supply and suction pump, and adjust the pumping speed to 1000mL / min. Then close the piston between the electrolytic cell and the combustion tube. If the pumping speed drops below 500mL / min, it means that the electrolytic cell, drying tube and other parts are airtight. Otherwise, it is necessary to recheck the components such as the electrolytic cell.
2.4 Test procedure
2.4.1 Control the furnace temperature at 1150 ± 5 ℃.
2.4.2 Adjust the pumping speed of the suction pump to 1000mL / min. Under the conditions of gas supply and pumping, pour 250 ～ 300mL of electrolyte into the electrolytic cell. After starting the stirrer, turn the knob to the automatic electrolysis position.
2.4.3 Weigh about 0.05g of coal sample with a particle size of less than 0.2mg in porcelain boat (weigh to 0.0002g), and cover the coal sample with a thin layer of tungsten trioxide. Place the boat on the quartz tray for sample delivery, turn on the program controller, the quartz tray will automatically enter the furnace, and the coulometric titration will start immediately. The integrator shows the milligrams of sulfur or the percentage of sulfur printed by the printer.
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