This Article focuses on the optimization of the fabrication procedure and preparation conditions of a polyvinylamine/poly(vinyl alcohol) (PVAm/PVA) blend membrane with respect to its CO2/CH4 separation performance at elevated pressures and the up-scaling of the PVAm/PVA blend flat sheet membrane for pilot scale tests. Experiments show that the optimized membrane preparation conditions for CO2/CH4 separation are different from those for CO2/N-2 separation, especially when operating at elevated pressures, which is considered for applications such as biogas upgrading. The effects of membrane preparation conditions were investigated and membrane CO2/CH4 separation performance was evaluated at elevated pressures (CO2 partial pressure up to 5.6 bar). Up-scaled flat sheet membranes (300 x 300 mm) were prepared using a dip coating procedure. The selection of the support substrate and aging of the membrane were also investigated. A CO2 permeance of up to 0.58 m(3)/ (m(2) h bar), and a CO2/CH4 selectivity of up to 45 were documented at 2 bar with 10% CO2 in feed gas. The membrane showed excellent stability over a 5-month test.