Deactivation continuous catalyst regeneration

Reactions with reversible catalyst deactivation calling for continuous catalyst regeneration... 

Depending on tlie time. scale of deactivation, the catalytic activity can be restored in different ways. For example, in fluid catalytic cracking, where the deactivation is very fast, a recirculating leacTor is used for continuous catalyst regeneration. However, if the deactivation is slow and constant conversion is desired 10 meet certain environmental regulations as in VOCoxidation, the temperature level can be used to compensate fur the loss of intrinsic catalytic activity. Under such additions, the deactivation effects are measured by the temperature increase required to maintain constant conversion. 

Reactions with reversible deactivation requiring continuous catalyst regeneration and high selectivity... 

Alternative catalysts for this reaction are polymer-supported alkyl sulfonic acids [231], even if they show lower performances than the zeolite. Two of the problems in the reactions are the need to vaporize the reactant and the periodic regeneration of the rapidly deactivating zeolite catalysts. It was thus proposed recently that continuous catalytic Friedel-Crafts acylation can be performed in the biphasic medium of an ionic liquid and supercritical carbon dioxide [232]. 

Not only does the decreasing catalyst activity lead to a loss of productivity, it is also often accompanied by a lowering of the selectivity. Therefore, in industrial processes great efforts are made to avoid catalyst deactivation or to regenerate deactivated catalyst. Catalyst regeneration can be carried out batchwise or preferably continuously while the process is running. 

Catalyst regeneration also provides a means of maintaining overall catalyst activity within systems with rapid catalyst deactivation. Deactivated catalyst particles can be continuously removed from a reaction zone while regenerated catalyst from a regeneration zone is continuously recycled back to the reaction zone in a flow scheme similar to that shown in Fig. 

Kesults from reaction experiments are shown in Figure 2. For both feedstocks, the sulphur conversions decrease with increasing time on stream. After 50 hours on stream, both catalysts were regenerated by burning the coke. When the catalysts were put back on stream, deactivation continued. Regeneration was performed again, after 90 hours on stream. This was followed by another on stream period, during which deactivation continued. 

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