This paper investigates the alternative of precombustion capture of carbon dioxide from integrated gasification combined cycle (IGCC) plants using membrane reactors equipped with H 2-selective zeolite membranes for the water gas shift reaction. Specifically, a one-dimensional and isothermal membrane reactor model is developed. This model is used for simulation and optimization studies considering cocurrent and countercurrent modes of reactor operation. The simulation results indicate successful countercurrent cases that satisfy all of the specified targets and constraints. With use of this developed model, a novel optimization problem is formulated and solved to guide the selection of the optimal reactor design among typical scenarios of operation. The optimization results suggest as optimal solution a reactor design with a preshift followed by a membrane reactor. The obtained optimal design enables a more efficient membrane use by placing it in the optimal location. This design also results in savings of as high as 25% (in the range of 10-25%) in terms of membrane material when compared to the original membrane reactor design. For the price range of zeolite membranes considered on the order of $1000-10-000/m 2 and for large-scale applications, in which the membrane surface areas are on the order of 2000 m 2, 25% of savings implies cost reductions on the order of millions of dollars (as high as $5-000-000 in this case).