Commercial-sized modules of the poly(amidoamine) (PAMAM) dendrimer composite membrane with high CO2/N-2 selectivity and CO2 permeance were developed by the in situ modification (IM) method. This method utilizes the interfacial precipitation of membrane materials on the surface of porous, commercially available polysulfone (PSF) ultrafiltration hollow-fiber membrane substrates. A thin layer of amphiphilic chitosan that has a potential affinity for both hydrophobic PSF substrates and hydrophilic PAMAM dendrimers was employed as a gutter layer directly beneath the inner surface of the substrate by the IM method. PAMAM dendrimers were then impregnated into the chitosan gutter layer to form a hybrid active layer for CO2 separation. Scanning electron microscopy (SEM) revealed that the PAMAM/chitosan hybrid layer was coated all through the inner surface of the substrate and that pores of the substrate were completely covered. The thickness of the hybrid layer observed by SEM was 0.6-2.6 mu m. Gas permeation experiments of the PAMAM dendrimer composite membrane were conducted using a humidified CO2 (5%)/N-2 (95%) feed gas mixture at a pressure difference of 97 kPa at ambient temperature. The PAMAM composite membrane exhibited an excellent CO2/N-2 selectivity of 110-170 and a CO2 permeance of 1.5-2.2 x 10(-7) m(3) (STP) m(-2) s(-1) kPa(-1). It was demonstrated that unstable liquid materials such as PAMAM dendrimer can be stabilized in commercial-sized membrane modules by the proposed IM method and that the commercial-sized membrane modules can be used for gas separation under practical operating conditions. A long-term stability test (a separation experiment continuously running for 1000 h) was conducted using an 800-mm module and real exhaust gas at a steel manufacturing plant. It was demonstrated the membrane module was stable for at least 1000 h of exposure to real exhaust gas. (c) 2008 Elsevier B.V. All rights reserved.