Filling with a mixture of carbon dioxide and argon gas

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This post was last edited by touchskyyy on 2019-5-13 at 14:13. I’ve seen that some industrial gas filling stations offer mixed bottled gases of carbon dioxide and argon (with the volume fractions of carbon dioxide and argon being 20% and 80% respectively). I have a few questions for the experts here: 1. When carbon dioxide (a high-pressure liquefied gas) and argon (a noble gas) are mixed in one bottle, can it be ensured that the volume fractions of the various components in the resulting mixed gas remain at 20% carbon dioxide and 80% argon? 2. What filling method can ensure safety? Since liquefied gases are filled based on their mass according to specified filling coefficients (the critical temperature of carbon dioxide is 31 degrees Celsius), permanent gases are filled based on pressure; improper methods of mixed filling can pose a risk to the safety of the cylinders. My question is that carbon dioxide is a high-pressure liquefied gas; at room temperature, its pressure exceeds 5.7 MPa (the saturated vapor pressure at 20°C), so it exists in a liquid state ； Argon is in a compressed gas state at room temperature and 5.7 MPa. When using the gas, open the gas cylinder; the concentration of the gas that emerges is not a constant ratio. For example, at 20°C and a total pressure of 10 MPa, most of the carbon dioxide in the bottle is in liquid form, while argon is in gas form. At this point, the molar fractions of carbon dioxide and argon in the gas phase should be equal to the ratio of their respective partial pressures. Carbon dioxide is at saturation, with a partial pressure in the gas phase of 5.7 MPa ； The partial pressure of argon is 10-5.7=4.3MPA. Then calculate the volume ratio. As the total pressure in the cylinder decreases over time until it drops to 5.7 MPa, pure carbon dioxide is released from the cylinder. Is there anything wrong with such an idea? ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Separator. There is another idea: at 20°C, when carbon dioxide and argon are stored in a steel cylinder in a volume ratio of 20% to 80% (i.e., a molar ratio), the partial pressure of carbon dioxide may be lower than its saturated vapor pressure at 20°C; therefore, it can be concluded that no liquid phase exists in the cylinder due to the low concentration of carbon dioxide. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Separator Line: In accordance with HG/T3728-2004 \"Mixed Gases for Welding – Argon-Carbon Dioxide\", when the volume fraction of carbon dioxide is less than or equal to 30%, the filling pressure shall not exceed 13.5±0.5 MPa. Following the second approach, under the most severe conditions, the operating temperature for the steel cylinder is set at -5°C; the saturated vapor pressure at -5°C is 3.05 MPa. The molar ratio of carbon dioxide to argon is: 20% : 80%. The total pressure is 14 MPa; therefore, the partial pressure of carbon dioxide is 14*0.2=2.8 MPa. This pressure is lower than the saturated vapor pressure at -5°C; therefore, the carbon dioxide in the bottle is in an unsaturated state, with no liquid phase present. I originally wanted to ask a question; while working through it, I came up with my own ideas, tested them, and finally reached a conclusion. But I would still ask all the teachers to take a look and see if the reasoning is correct and if the conclusions are right.