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Difficulty: Very hardNitrogen Gas, Nitrogen Cycle, and Oxides of Nitrogen

Arrange the following sequential stages involved in the industrial isolation of pure nitrogen gas from atmospheric air via fractional distillation in the correct chronological order, from ambient air intake to nitrogen gas collection.

  1. 1Removal of dust, atmospheric moisture, and carbon(IV) oxide gas to prevent solid blockage of refrigeration pipework during cooling.
  2. 2Compression of the purified gaseous air to high pressure (approximately 200 atm200\text{ atm}) followed by repeated cooling and expansion through a fine jet to form liquid air at −200 ∘C-200\text{ }^\circ\text{C}.
  3. 3Introduction of the liquid air into a fractionating column and gradual warming of the mixture.
  4. 4Selective vaporization and collection of nitrogen gas at the top of the column at its boiling point of −196 ∘C-196\text{ }^\circ\text{C} (77 K77\text{ K}), leaving behind argon and liquid oxygen.

Answer

The correct chronological order of the process is: 1. Removal of dust, moisture, and carbon(IV) oxide; 2. Compression and Joule-Thomson expansion to produce liquid air; 3. Feeding liquid air into a fractionating column and gradual warming; 4. Selective vaporization and collection of nitrogen gas at -196 °C.
The industrial preparation of nitrogen gas relies on fractional distillation of liquid air. Ambient air must first be purified of water vapor and carbon(IV) oxide to prevent cryogenic equipment blockages caused by solid ice formation. The clean air is compressed under high pressure (around 200 atmospheres) and subjected to rapid Joule-Thomson expansion, which cools it repeatedly until it condenses into liquid air at approximately −200 ∘C-200\text{ }^\circ\text{C}. When liquid air is fed into a fractionating column and warmed gradually, nitrogen gas boils off first at −196 ∘C-196\text{ }^\circ\text{C} (77 K77\text{ K}) due to having a lower boiling point than argon (−186 ∘C-186\text{ }^\circ\text{C}) and oxygen (−183 ∘C-183\text{ }^\circ\text{C}).

Step-by-Step Solution

1
Identify the initial purification stage required before gas liquefaction.
Air is scrubbed to remove dust, water vapor, and CO2CO_2.
Freezing points of water (0 ∘C0\text{ }^\circ\text{C}) and carbon(IV) oxide (−78.5 ∘C-78.5\text{ }^\circ\text{C}) are much higher than liquefaction temperature, meaning they would solidify and clog cryogenic tubes if not removed first.
2
Determine the phase change process of purified gaseous air into liquid air.
Purified air is compressed to ∼200 atm\sim 200\text{ atm} and allowed to expand through a fine nozzle.
The Joule-Thomson expansion causes progressive cooling until air liquefies around −200 ∘C-200\text{ }^\circ\text{C}.
3
Analyze the fractionating column feed and thermal gradient.
Liquid air enters the fractionating column and is warmed slowly.
Gradual heating drives components with lower boiling points to vaporize first.
4
Compare boiling points to establish which component distills first.
Nitrogen boils off at −196 ∘C-196\text{ }^\circ\text{C}, followed by argon (−186 ∘C-186\text{ }^\circ\text{C}) and oxygen (−183 ∘C-183\text{ }^\circ\text{C}).
Nitrogen has the lowest boiling point, so it boils off first as a gas at the top of the column.

Key Concept

Fractional Distillation of Liquid Air for Industrial Production of Nitrogen
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Topics

Nitrogen Gas, Nitrogen Cycle, and Oxides of Nitrogen

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