The role of the desorbent in bulk separation processes in gaseous phase based on displacement chromatography is analyzed in detail. The optimal desorbent is characterized by adsorptivity intermediate between those of the components to be separated. When using such a desorbent, classical chromatography and optimal recycle chromatography yield, according to the equilibrium theory, identical process performance. If a weak or a strong desorbent is used, then optimal recycle chromatography is the most convenient. When the appropriate desorbent can not be found, the use of two desorbents, one strong and the other weak, can lead to improved separation performances with respect to the use of one of the two desorbents alone. The optimal operation involves the use of two separate desorbent pulses of suitable duration, the first constituted by the pure strong desorbent and the second by the pure weak one.
