Fluid catalytic cracking conversion effects

Table V. Effect of Conversion Level in Fluid Catalytic Cracking Using ...

With this decision made, Ashland set out to develop a new residual oil conversion process which could effectively produce a greater amount of transportation fuel from each barrel of crude processed. It was concluded that a new process would take the best features from the fluid catalytic cracking process and couple them with innovative improvements in related key areas such as unique... 

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. 

The catalysts used in Fluid Catalytic Cracking (FCC) are reversibly deactivated by the deposition of coke. Results obtained in a laboratory scale entrained flow reactor with a hydrowax feedstock show that coke formation mainly takes place within a time frame of milliseconds. In the same time interval conversions of 30-50% are found. After this initial coke formation, only at higher catalyst-to-oil ratios some additional coke formation was observed. In order to model the whole process properly, the coke deposition and catalyst deactivation have to be divided in an initial process (typically within 0.15 s) and a process at a larger time scale. When the initial effects were excluded from the modeling, the measured data could be described satisfactory with a constant catalytic activity. 

Data obtained in fixed-bed reactors and in continuous high-velocity coil-t ype reactors (fluid catalyst) indicate that the catalytic cracking of gas oils is approximately a first-order reaction, but that the apparent order approaches two because of the effect of nonhomogeneity of the feed and because of the increasing dilution of reactant with cracked products as conversion increases at constant total pressure (73). The extent of reaction is determined by the intrinsic activity of the catalyst surface, reaction time at the surface, temperature, and susceptibility of the feed to cracking. Superficial contact time in the reactor is of little consequence. The effective time of reaction is the time spent by oil on the active surface of the catalyst. For a given extent of adsorption, the reaction time should be inversely proportional to weight space velocity and should also be a function of the reactant partial pressure. Results of experiments with... 

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