A tower containing six ideal plates, a reboiler, and a total condenser is used to separate, partially, oxygen from air at 65 lb_ƒ/in.² gauge. It is desired to operate at reflux ratio (reflux to product) of 2.6 and to produce a bottom product containing 51 wt% oxygen. The air is fed to the column at 65 lb_ƒ/in.² gauge and 30 percent vapor by mass. The enthalpy of oxygen-nitrogen mixtures at this pressure is given Table 21.8. Compute the composition of the overhead if the vapors are just condensed but not cooled.

Table 21.8

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TABLE 21.8 Enthalpy of oxygen-nitrogen at 65 lb, /in. gauge Liquid Temperature, C -163 -165 -167 -169 -171 -173 -175 -177 -178 N₂, wt% 0.0 7.5 17.0 27.5 39.0 52.5 68.5 88.0 100.0 H, cal/g mol 420 418 415 410 398 378 349 300 263 N₂, wt% 0.0 19.3 35.9 50.0 63.0 75.0 86.0 95.5 100.0 Vapor H,, cal/g mol 1.840 1,755 1,685 1,625 1,570 1515 1,465 1,425 1,405