About fractional distillation of liquid air

[dttom]

This's one of my exam question, the model answer said that noble gases could be obtained from the fractional distillation of liquid air, while I doubt if this statement is correct, though may be due to my misconception.

 

During the fractional distillation of liquid air, after purification of incoming air, the air mainly contain noble gases, nitrogen and oxygen, while the purified air is continuously compressed and expanded, made to a temperature of about 200 'C, which noble gases are not liquefied yet; later the liquid air (containing N2 and O2 only now) is heated and nitrogen and oxygen are obtained at different position of the fractionating column.

 

What I have in my mind is that the procedures after obtaining the liquid air (composed of N2 and O2) are known as fractional distillation of liquid air, but not including the extraction of noble gases, which are not obtained from the 'liquid air'.

 

Could anyone correct me if I have got any mistake, or any opinion would be appreciated.