Discussion on two oxygen analysis methods for chlorine gas
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The company has two manufacturing sites. At the site where I work, the method used to determine the oxygen content in chlorine is as follows: chlorine gas is drawn from a ball tank and fed into a chromatograph using a ten-way valve, such that the oxygen content reaches around 0.5%. At the branch office, after analyzing the purity of chlorine gas, the remaining gas is collected using a latex tube; 40 μL of the sample gas is drawn in with a 50 μL micropipette and sent to the chromatograph for analysis, showing an oxygen content of around 0.4%. The difference between the two methods is around 0.1%–0.2%. 1. The first method wears out the ball tank and corrodes the ten-way valve; the ball tank needs to be replaced every four shifts on average, while the ten-way valve has a lifespan of around 8 months. The advantages are also prominent: quantitative sampling results in low analysis errors. 2. The second method reduces corrosion to the chromatography column, but the injection error is relatively large. Which method do people prefer, the two options?
This post was last edited by northwester on 2021-3-9 09:28. 1. The first method requires replacing the ball valve; it causes corrosion to the ten-way valve, with the ball valve needing to be replaced every four shifts on average, while the lifespan of the ten-way valve is around 8 months. The advantages are also prominent: quantitative sampling results in low analysis errors. 2. The second method reduces corrosion to the chromatography column, but the injection error is relatively large. Which method do people prefer, the two options? Looking at the issue from two perspectives, pure chlorine clearly has low corrosivity; it is only the water vapor that exacerbates its effects. On one hand, try to reduce the moisture content in the chlorine sample you are analyzing by keeping the sampling point dry. On the other hand, from an analytical perspective, the valves should be made of materials such as PTFE; the absence of water and moisture means that corrosion should be minimal. The pipelines should be made of Hastelloy, as PTFE pipelines can provide long-term corrosion resistance. Clearly, direct sampling, backflow of chlorine gas, and analysis of oxygen and nitrogen using a molecular sieve column are appropriate for errors. After absorption by the alkaline solution, the residual chlorine is very low; however, due to the small amount of gas remaining and the small injection volume, the accuracy is naturally a bit lower. But a chromatographic spectrum is sufficient; the cost is obviously lower. It depends on your specific requirements. For high accuracy, direct injection is used; the sampling port and the chromatograph are modified to extend their lifespan. If the accuracy is low, improve the absorption device to collect more residual gas; this way, the volume of the sample taken will be larger and the error will be smaller. If you have any questions, feel free to leave me a message.
Hello, sir. Most of our chlorine samples are chlorine that comes directly from the electrolyzer, without being dried, and they contain saltwater. We have also considered using sulfuric acid (or phosphorus pentoxide) to dry chlorine gas during sampling or injection; however, it’s inconvenient to carry a lot of equipment with you when sampling, and there is a risk that the drying process may not be complete during injection. Moreover, sulfuric acid is corrosive, while phosphorus pentoxide releases toxic substances upon decomposition. I have an idea: could silicone be used to dry chlorine gas? For sampling, a drying tube filled with silicone could be used – silicone does not react with chlorine gas, it is non-toxic, and it’s convenient to handle in solid form. I’m not sure if this would work Looking forward to your answer