1.Increased reactant conversion. Recycling the reactants back to the feed to a reactor can significantly increase the overall conversion of the reactant. For certain systems recycle allows the reactor to be operated at low conversion levels, yielding improved selectivity, with recycling of the unreacted reactants making it possible to attain a high overall degree of conversion.
2.Continuous catalyst regeneration. Catalysts are used to increase the rate of chemical reactions, but their effectiveness can diminish with use(catalyst deactivation).Processes that use catalysts that deactivate at a relatively regeneration and recycling of the catalyst. For example,in a a fluidized catalytic cracking(FCC) process(Figure 12.4), the cracking catalyst deactivates almost immediately upon contact with the gas oil feed at the reaction temperature because of the formation of Coke on the surface of the catalyst. Therefore, the deactivated (spent) catalyst is transported to the catalyst regenerator where most of the coke is burned off the surface of the catalyst to restore the activity of the catalyst.