Ammonium and potassium are also the predominant cations in the cation removal process, which includes the acidifying and neutralizing steps in the waste-disposal process. The process includes 20-30° F regeneration, usually by CO 2, with no net accumulation of CO 2.
Titanium (titanite) and chromium (eudialite) are added to the feed in order to increase the catalytic activity of the zeolite. The ammonium ions are exchanged with the alkali metal cations, making the zeolite difficult to regenerate by steam. Carbon dioxide would be the preferred regeneration gas for the ammonium cations, but since carbon dioxide tends to dissolve into water, the reaction of ammonium with carbon dioxide becomes difficult when the solution volume goes up.
The most stable catalysts can be made from mixtures of rare-earth oxides, aluminum oxide and silica. In a typical zeolite synthesis, a aqueous solution of the oxides are reacted at a pH of around 12. A NH 4 OH solution is then added and the resulting gel is autoclaved or steamed at 200-300° C, followed by calcination at 600-800° C to finish the crystallization process. The zeolite can be further treated with stronger solutions to incorporate other metal ions such as calcium, vanadium, iron, nickel, etc. The zeolite can also be modified with various chemical treatments and composites to enhance their catalytic activity.
Amberlite XAD-2 is obtained by removing the sand fraction of honeysuckle stem bark with chloroform as the solvent. Amberlite XAD-7 is produced from the resinoids with the same solvent as the previous method.
Synthetic layered and organosilicate zeolites are formed using metal oxides as the seed material, followed by the incorporation to zeolitic frameworks of alkyl groups to be incorporated as pore formers. d2c66b5586