Editing Adsorption (section)

===Zeolites===

[[Zeolite]]s are natural or synthetic crystalline [[aluminosilicate]]s, which have a repeating pore network and release water at high temperature. Zeolites are polar in nature.

They are manufactured by [[hydrothermal synthesis]] of sodium aluminosilicate or another silica source in an [[autoclave]] followed by ion exchange with certain cations (Na<sup>+</sup>, Li<sup>+</sup>, Ca<sup>2+</sup>, K<sup>+</sup>, NH<sub>4</sub><sup>+</sup>). The channel diameter of zeolite cages usually ranges from 2 to 9 [[angstrom|Å]]. The ion exchange process is followed by drying of the crystals, which can be pelletized with a binder to form macroporous pellets.

Zeolites are applied in drying of process air, CO<sub>2</sub> removal from natural gas, CO removal from reforming gas, air separation, [[catalytic cracking]], and catalytic synthesis and reforming.

Non-polar (siliceous) zeolites are synthesized from aluminum-free silica sources or by dealumination of aluminum-containing zeolites. The dealumination process is done by treating the zeolite with steam at elevated temperatures, typically greater than {{convert|500|C|F|sigfig=2}}. This high temperature heat treatment breaks the aluminum-oxygen bonds and the aluminum atom is expelled from the zeolite framework.