1. Separation Processes;King,1980
2. An Introduction to Separation Science;Karger,1973
3. R.M. Milton, U.S. Patents 2,882,243 and 2,882,244 (1959).
4. The sorption of polar and non-polar gases by zeolites
5. C.W. Skarstrom, U.S. Patent 2,944,627 (1960) (filed in 1958).