104 for the removal of carbon dioxide and other impurities and then passed as stream 105 in a cryogenic rectification plant the cryogenic rectification plant illustrated in fig1 comprises a single column 106 and a top condenser 108 it is preferred in the practice of this invention that the cryogenic rectification plant comprise one column although plants comprising more than one column may be employed column 106 preferably is operating at a pressure within the range of from 40 to 140 pounds per square inch absolute psia within column 106 the feed air is separated by cryogenic rectification into product nitrogen vapor ad a nitrogen containing liquid the product nitrogen vapor is withdrawn from the upper portion of column 106 having a purity of at least 99 percent nitrogen up to a purity of 99 9999 percent nitrogen or greater a portion 126 of product nitrogen vapor 109 is passed into top condenser 108 wherein it is condensed against nitrogen containing liquid and then passed as stream 117 back into column 106 as reflux if desired a portion 120 of stream 117 may be recovered as product liquid nitrogen 118 nitrogen containing liquid having a nitrogen concentration generally within the range of from 60 to 70 percent is removed from the lower portion of column 106 as stream 107 reduced in pressure through valve 134 and passed as stream 127 into top condenser 108 wherein it boils to carry out the.