Cryogenic air separation processes rely on differences in boiling points to separate and purify products. The basic process was commercialized early in the 20th century. Since then, numerous process configuration variations have emerged, driven by the desire to produce particular gas products and product mixes as efficiently as possible at various required levels of purity and pressure. These air separation process cycles have evolved in parallel with advances in compression machinery, heat exchangers, distillation technology and gas expander technology.