Controlled atmosphere glove boxes maintain an inert atmosphere free of oxygen and moisture. However, oxygen and moisture may permeate through gloves, which increases the levels of oxygen and moisture in the glove box chamber. Other sources of oxygen and water vapor may come from the material transfer into or out of the glove box chamber. To well maintain the low levels of oxygen and moisture for specific applications, it is mandatory to install a gas purification system that can forcefully circulate the gas in the chamber through an oxygen remover and a moisture purifier.
Oxygen removal from the inert gas such as nitrogen, argon, or helium is based on its chemical reaction with copper to form copper oxide (CuO). The active material is made of finely divided copper particles and catalyst distributed on an alumina matrix.
Moisture (water molecules) is removed by molecular sieves enclosed in a separate container or the same container as that containing the oxygen purifier. Molecular sieves can also remove other gas molecules such as carbon dioxide (CO2), nitrogen dioxide (NO2), hydrogen sulfide (H2S), carbon monoxide (CO) and many organic compounds including alcohols, aromatics, amines, halogenated compounds, oxygenated compounds, hydrocarbons and organic acids.
The lifetime of the oxygen and moisture purifiers depends on the capacity of the purifiers and the amount of oxygen or moisture that comes into the purifiers. The purifiers work effectively until saturation, which can be indicated by the oxygen and moisture analyzers showing the moisture and oxygen levels are unable to be reduced to <1 ppm. To elongate the lifetime, only well controlled atmosphere should be circulated into the purifiers. Otherwise, chamber purging should be performed first before circulating.
To restore the function of purifiers, regeneration of the purifier columns is needed. The moisture absorbed by molecular sieve can be removed by using heat (high temperature), and copper/catalyst is regenerated by using hydrogen to reduce copper oxide to metal copper. Therefore, both are regenerated by heating up while introducing 3-7% hydrogen in nitrogen to the purifiers.
How frequent is the regeneration needed? It greatly depends on how often the gas purification system is used and how regularly new oxygen or moisture are introduced to the chamber enclosure via antechambers and the like.