Polyvinylamine (PVAm) was modified using a cross-linking agent containing carriers piperazine (PIP). Attenuated total reflectance fourier transform infrared, elemental analyzer, and X-ray diffraction were used to characterize the PIP-modified PVAm. The PVAm-PIP/polysulfone (PS) composite membrane was developed by coating PVAm-PIP mixed solutions with different mass ratios of PIP/PVAm (m(PIP)/m(PVAm)) on the PS ultrafiltration membrane. The effects of m(PIP)/m(PVAm) (from 0.715 to 2.860) in the coating solutions and wet coating thickness on the gas performance of the PVAm-PIP/PS composite membrane were investigated. The PVAm-PIP/PS composite membrane prepared showed higher performance than other membranes reported in the literature due to the large increase of the introducing carrier concentration and low crystallinity. Moreover, the separation performance stability of the PVAm-PIP/PS composite membrane was investigated and no deterioration in the membrane permselectivity was observed. Finally, the economic evaluation of the membrane with the highest performance prepared was carried out. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 215-228, 2013