Using numerical simulations, a new membrane reactor is proposed for the direct synthesis of propylene oxide (PO) in liquid phase. The reactor is a combination of two consecutive catalytic reactor units, one for the hydrogen peroxide (H2O2) synthesis on a Pd/SiO2 catalytic membrane layer, and the second for the conversion of hydrogen peroxide with propylene (C3H6) to PO on a titanium silicalite-1 (TS-1) catalytic layer. The membrane reactor is described numerically by a set of kinetic-diffusion mass balance equations. The optimization of the reactor design is achieved by determining membrane pore size, thickness and gas pressures which provide conversion and selectivity performance comparable to the industrial requirements. An optimal pore size of 0.2-0.4 mu m was found for the Pd/SiO2 membrane layer. The results show that a Pd/SiO2 membrane thickness of 250 pm and a TS-1 layer of 100 pm are necessary to ensure conversion and selectivity performance of the catalytic membrane reactor comparable to the industrial ones. Calculated these optimized dimensions of the membrane reactor, a total membrane area of 84,000 m(2) is required for the production of 300 kton/year of propylene oxide. (C) 2015 Elsevier Ltd. All rights reserved.