A catalyst is a substance, the presence of which increases the rate of a reaction without being consumed itself; it can be preserved after the reaction. The principal application for catalysts is catalytic, heterogeneous hydration.
There are several reasons for maintaining that a process filter is the appropriate solution for catalyst filtration. The first is safety. The catalyst often has pyropherous properties at the end of a reaction, which means that it can spontaneously ignite in air. In addition, combustible and frequently toxic solvents or reaction participants are used in many organic syntheses. Therefore, the removal of the catalyst from the reaction solution should occur in a closed, inertable system.
The next argument in favour of process filters is efficiency. Since in most cases expensive products come into being in hydration processes, it is preferable to be able to remove these as much as possible from the filter cake. The cascade washing system of a process filter permits first-rate washing with a minimum of washing fluid.
Process flexibility is the final reason for using process filters for catalyst filtration. Since catalysts are mostly very expensive to purchase, it is desirable to preserve them completely after the reaction. They are then either reduced to slurry and returned to the reaction vessel or preserved as dry residue for further reactions. Both techniques can be optimally performed with a process filter, since it is a simple matter to fully dry and withdraw the cake in the filter or suck it out as slurry via a slurry pipe.
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