Abstract
Removal of nitrogen from methane-rich streams is one of the most energy-intensive gas separations. Nitrogen rejection units are very expensive units and in streams with small and intermediate flowrates, adsorption technologies proved to be an economic alternative, if N-2 is selectively adsorbed in the adsorbent. In this work we have synthesized sodium titanosilicate (Na-ETS-4) and study the effect of exchanging Na with different alkali-earth cations in the structure, namely Sr and Ca. Adsorption equilibrium of CH4 and N-2 and CO2 were measured at 323 K in all the samples. The effect of different activation temperatures was studied in the modified samples. It was observed that activating the adsorbent at high temperatures prior to adsorption tests, the capacity of methane can be reduced. In the Ca-ETS-4 a shift in selectivity was observed: activating the adsorbent at higher temperatures result in an adsorbent with higher selectivity towards nitrogen. In all the samples tested, the loading of carbon dioxide is much higher than the loading of other gases indicating that this gas should be removed from the stream before nitrogen rejection. (C) 2009 Elsevier Inc. All rights reserved.