CO2/CH4 separation by means of Matrimid hollow fibre membranes

CO2/CH4 mixtures separation was investigated using Matrimid (R) 5218 hollow fibre membranes and measuring the membrane flux feeding singly CH4 and CO2 and their mixtures, with CH4 concentration ranging from 5 to 70 % molar. Specific attention was paid to membrane properties at a high temperature (up to 75 degrees C) and feeding humidified streams, not yet particularly investigated, in a pressure range 400-600 kPa. The membrane properties were restored when water vapour was removed and temperature decreased stating the excellent hydro-thermal stability of these membranes. Maps of the separation performance were also calculated for a range of operating conditions wider than the experimental one paying specific attention to the feed/ permeate pressure ratio further to membrane selectivity and permeance. Single and multistage membrane separation systems were investigated using these maps. The prepared Matrimid (R) 5218 hollow fibres showed very good performance in terms of flux and selectivity for temperatures up to 60 degrees C, also in steam saturated conditions, allowing a methane concentration meeting the specification for its injection into the grid.