Carbon membranes from cellulose and metal loaded cellulose

The focus of this work was to find a low-cost precursor for carbon molecular sieve (CMS) membranes, and a simple way of producing them. In addition, several ways of modifying a carbon material are described. The modification method used in this study was metal doping of carbon. CMS membranes were formed by vacuum carbonization of cellulose and metal loaded cellulose. Metal additives include oxides of Ca, Mg, Fe(III) and Si, and nitrates of Ag, Cu and Fe(III). The carbon membrane containing Fe-nitrate has promising separation performance for the gas pairs O-2/N-2 and CO2/CH4. Carbon containing nitrates of Cu or Ag show high selectivity, but reduced O-2 and CO2 permeability compared to carbon with Fe-nitrate. Element analysis indicates that Cu migrates to the carbon surface, creating an extra layer resistance to gas transport. A silver mirror is also seen on the surface of Ag-nitrate-containing carbon. However, the Ag- and Cu-containing membranes show a high H-2 permeability. Adding metal oxides makes the carbon membranes retard the transport of easily condensable gases (e.g. CO2). This can be exploited for enhanced H-2/CO2 separation efficiency. (C) 2005 Published by Elsevier Ltd.