Pump air through a filter to remove dust and other contaminants. Cool the air in stages until it reaches a temperature of -79 degrees Celsius. At this point, the carbon dioxide will become solid and drop from the cooled air, leaving nitrogen, oxygen and argon in the air.
Continue cooling the air until it reaches a temperature of -200 degrees Celsius and becomes liquid.
Pump the liquid air into a fractionating column. Create a marginal amount of heat at the bottom of the column. As the air becomes heated, the Nitrogen will convert to gas when it reaches temperatures above -196 degrees Celsius, rising to the top of the column and though a collection pipe at the top.
Maintain a temperature in the bottom of the column below -183 degrees Celsius so the oxygen remains liquid. Pump the liquid oxygen from the bottom of the column into a separate fractionating column.
Create a marginal amount of heat in the column and slowly raise the temperature of the liquid oxygen to convert the remaining element, argon, into gas and separate it from the liquid oxygen. Pump the pure liquid oxygen into a separate storage tank.