Anew simulation model for the dynamic performance of gas separation membrane modules is presented. In order to take account of nonideal mixing flows in permeate and residue sides a tanks-in-series model is utilized. As a stable computational scheme, the relaxation method is applied to solve the governing ordinary differential equations for transport across the membrane, mass balance and pressure distributions in a hollow-fiber membrane module. The proposed simulation model and scheme are validated using the experimental data and simulation results hydrogen gas separation and air separation in the literature. Using the proposed simulation model and scheme the dynamic performance of membrane gas separation processes, hydrogen recovery process and two-stage methane separation process with residue recycle, is examined by varying the operating conditions, i.e.. the bulk mixing degree (perfect mixing, plug flow and intermediate mixing), pressure drop and recycle ratio. The computational results indicate that effect of mixing degree in the feed side is more significant as compared with that in the permeate side and less mixing in the feed side results in higher performance. The retentate recycle is found to improve methane recovery efficiency. The proposed simulation model considering nonideal mixing in the membrane module provides more reliable examination of unsteady-state behaviors of hollow-fiber membrane gas separation modules. (c) 2010 Elsevier B.V. All rights reserved.