The conceptual design for a full-scale air separation unit is discussed in terms of specific surface area and feasibility of manufacturing. The concept with highest specific surface area was found to be that using multi-channel monoliths, followed by that using tube-and-plate assemblies, and by that using single-hole tubes, and finally by that with hollow fibres. The basic unit size is, however, dependent on the maximum gas velocity allowed in the module (25 m/s). In this case, the number of modules required to house 5000 m(2) of membrane surface area follows a different order. A minimum of 32 modules is required when using single-hole tubes, followed by the concept with multi-channel monoliths (39 modules), and that with multiple tube-and-plate assemblies in one module (120 modules). The hollow fibre concept leads to about 1800 modules. A further discussion on the (dis)advantages of these concepts in relation with the manifolding, sealing, and the possibility of using a sweep/reactive gas is presented. We conclude that the concept using single-hole tubes is preferred for the production of oxygen with and without a sweep gas, and also for the partial oxidation of gaseous hydrocarbons using a reactive sweep gas. (c) 2005 Elsevier B.V. All rights reserved.