Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material. The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO2. The composite PVAm/PSfHF membranes having a 0.7-1.5 mu m PVAm selective layer, showed CO2/N-2 selectivity between 100 and 230. The selectivity was attributed to the CO2 facilitated transport imposed by PVAm selective layer. The CO2 permeance changed from 0.006 to 0.022 m(3)(STP)/(m(2) barh) in direct correlation with CO2 permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40 nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO2 partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO2/N-2 selectivity ranged between 20 and 500 and the CO2 permeance from 0.11 to 2.3 m(3)(STP)/(m(2) bar h) depending on the operating conditions. For both PVAm/PSf and PVAm/PPO membranes, the CO2 permeance was similar with the CO2 permeance of uncoated hollow fiber supports, confirming that the CO2 diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2 mu m thin and water swollen PVAm, selective layer. A dynamic transfer of the CO2 diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO2 diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2 [mu m, PVAm top layer becomes the CO2 diffusion rate limiting step. (C) 2009 Elsevier B.V. All rights reserved.