Houdry process coke deposit

The first successful catalytic cracking process was the Houdry process, announced in 1933 (132) and commercialized in 1936 (172). This was a fixed-bed process employing, at first, an activated bentonite clay as catalyst. It had been known previously that certain types of decolorizing clays catalyzed the decomposition of hydrocarbon oils (165,188), but a carbonaceous deposit rapidly accumulated on the clay and seriously impaired its activity. During his early work in France, between 1927 and 1930, Houdry found that catalyst activity could be maintained at a satisfactory level by carefully burning off the carbonaceous deposit, or coke, at frequent intervals before the concentration became high enough to interfere seriously with the desired catalytic reactions. 

Entrained catalyst is removed from the product off-gas by means of cyclones. The catalyst circulates continuously from the reactor to the regenerator and vice versa by means of transfer lines. Coke deposited on the catalyst is burnt off in the regenerator however, because the amount of coke is relatively small, additional fuel must be burnt in the regenerator to satisfy the thermal requirements of the endothermic dehydrogenation reaction. However, while this approach is similar to that in the Houdry process, FED does not have a catalyst reduction step with hydrogen before proceeding to the dehydrogenation cycle lack of this step is believed to be somewhat detrimental to the overall performance of the process. 

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