Mark W. Ackley, Salil U. Rege, Himanshu Saxena
Praxair, Inc., 175 East Park Drive, Tonawanda, NY 14151, USA
Received 22 July 2002; received in revised form 21 October 2002; accepted 22 October 2002
There are many natural zeolites of which a small number including clinoptilolite, chabazite, mordenite, erionite, ferrierite and phillipsite offer the greatest promise for gas separation. Patents and other literature have been surveyed to identify the bulk separation and purification processes for which these zeolites have potential. The abundance and low raw material cost of natural zeolites have rarely offset such disadvantages as variable composition, low purity and often poorer separation performance compared to the more-favored synthetic zeolites. The results of the present study in- dicate that these natural zeolites are particularly well suited for trace-gas removal. In contrast, they are less likely to provide competitive performance in bulk separations. Clinoptilolite and chabazite are judged the most versatile, while also offering unique adsorption characteristics. Effective and efficient methods for screening all types of adsorbents are presented for various gas separations. Natural zeolites must demonstrate unique or superior performance to be serious contenders in commercial separations. Use of these methods should enhance such opportunities. The importance of including relevant process considerations in the analyses is demonstrated through application to processes for a bulk separation (O2 production from air) and purification (removal of trace levels of N2O from air). The results are not encouraging for the use of natural zeolites in air separation. Conversely, clinoptilolite and chabazite outperform commercially available synthetics in N2O removal from air.