in this work, a novel combination of fixed and fluidized-bed hydrogen-permselective membrane reactors for Fischer-Tropsch synthesis (FTS) has been optimized using Genetic Algorithm (GA). This novel reactor configuration incorporates a fixed-bed FTS reactor with a membrane assisted fluidized-bed FTS reactor. In the proposed configuration, hydrogen is withdrawn from the fresh feed synthesis gas and is injected to the end segment of reactor in order to control dozing of hydrogen along the reactor and prevention of hydrogen waste. A theoretical investigation was performed in order to optimize the reactor performance. maximizing C-5(+) production and at the same time, minimizing the CO2 yield as an undesired product. The optimization was carried out and the results show there is a favorable profile of FTS products along the optimized combined system relative to the conventional fixed-bed single stage FTS reactor. Optimal ratio of reactors length, H-2/CO ratio, catalyst size, shell and tube pressures of second reactor, hydrodynamic parameters, gas phase velocity and temperature profile along the reactor were obtained and 45.9% additional C-5(+) yield was resulted in optimized system relative to conventional fixed-bed single stage FTS reactor. (C) 2009 Elsevier B.V. All rights reserved.