The paper introduces a procedure for the preliminary design and optimization of membrane modules made of dense metal permeator tubes for hydrogen separation from gas mixtures. Based on the mass transfer mechanisms of hydrogen into the metal lattice, the design procedure establishes the relationships among the dimensionless parameters related to the geometry (tube diameter, length and wall thickness) and the operating conditions (pressure, temperature, flow rates of feed and permeate streams, etc.). The concept of maximum hydrogen recovery and its dependence on pressure and dilution of feed stream is introduced and discussed. Similarly, the decrease of the driving force with the increase of the required hydrogen recovery factor is showed. The influence of the operative conditions on the minimum required tube wall thickness is also determined. Particularly, the operation at high temperature reduces significantly the Pd-alloy tensile strength thus increasing the minimum Pd-tube thickness. Finally, the model is applied to a case study of a Pd-membrane module separating ultra pure hydrogen from a gas stream coming from the methane reforming. A sensitive analysis is carried out by using the expressions and the graphs of dimensionless parameters defined by the design procedure introduced in this paper. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.