Phases of hydrocarbons in a compressed gas cylinder

In summary, the conversation discusses the process of selecting gas mixtures for calibrating a gas chromatograph. The gas mixture in question has 95% methane, 1% each of carbon dioxide, butane, and acetylene, and 2% nitrogen. The gas cylinder will be pressurized at 1345 psig and the calibration will be done at room temperature. The critical temperatures of methane and nitrogen are below room temperature, but it is uncertain if the other compounds will be in liquid or gas phase at this pressure. The speaker plans to use a two-stage pressure regulator to lower the pressure to below 125 psig, but this may not ensure that all compounds are in gas phase.
  • #1
temaire
279
0
I'm currently in the process of selecting gas mixtures to calibrate a gas chromatograph. One of the gas mixtures I'm interested in has the following composition by percent volume:

methane (CH4): 95%
carbon dioxide (CO2): 1%
butane (C4H10): 1%
acetylene (C2H2): 1%
nitrogen (N2): 2%

The gas cylinder pressure is 1345 psig. I plan on calibrating the gas chromatograph at room temperature (24oC) and need to ensure that all compounds in the cylinder are in gas phase. I know that the CH4 and N2 will be in gas phase since their critical temperatures are well below room temperature. However, I'm unsure about whether the CO2, butane, and acetylene are in liquid or gas phase. For example, CO2 has a critical point of ~ 31oC and 1070 psi. Since the gas cylinder will be pressurized above this at 24oC, will it be in liquid phase? Am I approaching this problem the right way?
 
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  • #2
temaire said:
Am I approaching this problem the right way?

Depends . Are you going to use the mixture at that pressure or expand down to a much lower pressure for feeding into the gas chromatograph ?
 
  • #3
Nidum said:
Depends . Are you going to use the mixture at that pressure or expand down to a much lower pressure for feeding into the gas chromatograph ?

I will be installing a two-stage pressure regulator on the gas cylinder and the outlet pressure will be below 125 psig. However, I don't think this addresses the issue of some of the compounds in the cylinder remaining in liquid phase. I need to make sure that there isn't any liquid to begin with.
 

1. What are the different phases of hydrocarbons in a compressed gas cylinder?

The three phases of hydrocarbons in a compressed gas cylinder are liquid, gas, and solid. The liquid phase occurs when the hydrocarbons are compressed into a liquid state due to high pressure. The gas phase occurs when the pressure is released, causing the hydrocarbons to expand and become a gas. The solid phase can occur when the temperature is extremely low and the hydrocarbons freeze into a solid state.

2. How do the phases of hydrocarbons affect the pressure inside a compressed gas cylinder?

The different phases of hydrocarbons can greatly affect the pressure inside a compressed gas cylinder. When the hydrocarbons are in their liquid phase, the pressure will be high due to the compression. Conversely, when the hydrocarbons are in their gas phase, the pressure will decrease as the gas expands. The solid phase does not typically have a significant impact on pressure unless the temperature changes significantly.

3. Can the phases of hydrocarbons change inside a compressed gas cylinder?

Yes, the phases of hydrocarbons can change inside a compressed gas cylinder depending on the temperature and pressure conditions. For example, as the temperature increases, the hydrocarbons may transition from a liquid to a gas phase. Similarly, if the pressure decreases, the hydrocarbons may transition from a gas to a liquid phase.

4. How do the phases of hydrocarbons affect the storage and transport of compressed gas cylinders?

The phases of hydrocarbons can greatly impact the storage and transport of compressed gas cylinders. For safety reasons, it is important to ensure that the hydrocarbons remain in a stable phase. This means keeping them at a consistent pressure and temperature to prevent phase changes. Additionally, the type of phase can also affect the amount of gas that can be stored in a cylinder.

5. What safety precautions should be taken when handling compressed gas cylinders with hydrocarbons?

When handling compressed gas cylinders with hydrocarbons, it is important to wear appropriate protective gear, such as gloves and safety glasses. It is also important to be aware of the phase of the hydrocarbons and handle the cylinder accordingly. If the hydrocarbons are in a gas phase, for example, it is important to handle the cylinder carefully to prevent sudden pressure release. Additionally, cylinders should be stored and transported in a well-ventilated area to prevent the buildup of flammable gases.

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