For various reasons intel est in adsorption-based prepurification units has continued to increase in air separation industries. This has led to significant development efforts in this area with the objective of generating optimized designs rather than simply workable designs. Emphasis has been placed on the ability to optimize for both energy and capital cost. This paper presents the background to the design of these units. It shows how an extensive program of practical measurements made on a purpose-built large-scale test rig followed by detailed theoretical work to ensure correct interpretation of the information gathered has made it possible to understand this temperature swing adsorption process and at the same time to develop robust and confident designs.