Department of Computer, Control and Management Engineering

Nitrogen production from air by membrane gas separation processes is a mature technology which is applied in numerous industrial sectors (chemical, food, aeronautics, space.). Depending on the nitrogen purity requirements (typically between 90 and 99.9%), single stage or multistage membrane process configurations are used. A very large number of advanced membrane materials have been recently reported, showing increasing permeability and/or selectivity for air separation applications (i.e. trade-off limits of dense polymeric materials for the O2/N2 gas pair) compared to the commercially available membranes. The interest of these new materials in terms of nitrogen production cost and their impact in terms of process configuration are reported through a process synthesis study. Based on a tailor made optimization methodology and program, the production cost and associated optimal process configuration are first identified for two standard O2/N2 separation membranes at four different levels of N2 purity (90, 95, 99, 99.9%). The same strategy is then performed with advanced trade-off membrane materials, with the possibility to combine different materials in multistaged systems. The impact in terms of nitrogen production cost for the different purities and the corresponding optimal membrane materials and process configurations are discussed. Surprisingly, a medium membrane selectivity combined to a high permeability is shown to systematically offer the best set of performances, for mono or multistaged systems. Vacuum operation and recycling loops are shown to generate lower N2 production costs.