Once the catalyst has completed its life or cycle length it will be withdrawn from the process and at this stage, the catalyst is termed as “spent catalyst”. During normal operation of the unit heavy metals, coke, and other poisonous elements get stick on the catalyst surface and make it unable to continue normal reactions.
Once the catalyst is declared as spent then the most preferable treatment is to regenerate it and re-use it in the same process. The catalyst can regenerated 2~3 times depending upon the operation conditions. It is better to regenerate the maximum possible times. It will save the cost of the fresh catalyst and also will the environment.
The second option is to regenerate and reuse in some other process with less severe working conditions. Further, the regenerated catalyst can be sold in the market.
Furthermore, if the catalyst cannot be regenerated, then the costly metals are recovered from the catalyst, and the remaining are disposed of in landfills. But landfilling is the least preferred method because of its very negative effects on the environment