Fluid catalytic cracking catalyst deactivation

Sodium Deactivation of Fluid Catalytic Cracking Catalyst... 

Contaminant-Metal Deactivation and Metal-Dehydrogenation Effects During Cyclic Propylene Steaming of Fluid Catalytic Cracking Catalysts... 

Improved Methods for Testing and Assessing Deactivation from Vanadium Interaction vvith Fluid Catalytic Cracking Catalyst... 

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

Several reactor types have been described [5, 7, 11, 12, 24-26]. They depend mainly on the type of reaction system that is investigated gas-solid (GS), liquid-solid (LS), gas-liquid-solid (GLS), liquid (L) and gas-liquid (GL) systems. The first three arc intended for solid or immobilized catalysts, whereas the last two refer to homogeneously catalyzed reactions. Unless unavoidable, the presence of two reaction phases (gas and liquid) should be avoided as far as possible for the case of data interpretation and experimentation. Premixing and saturation of the liquid phase with gas can be an alternative in this case. In homogenously catalyzed reactions continuous flow systems arc rarely encountered, since the catalyst also leaves the reactor with the product flow. So, fresh catalyst has to be fed in continuously, unless it has been immobilized somehow. One must be sure that in the analysis samples taken from the reactor contents or product stream that the catalyst docs not further affect the composition. Solid catalysts arc also to be fed continuously in rapidly deactivating systems, as in fluid catalytic cracking (FCC). 

Recent literature shows a growing trend to include free alumina in the formulation of fluid catalytic cracking (FCC) products. Over the last dozen years, FCC catalysts containing free alumina have been cited in the open and patent literature for benefits including (1) enhanced catalyst reactivity and selectivity (1-3). (2) more robust operation in the presence of metals in the petroleum feedstock (4-7). (3) improved attrition resistance (8.9). (4) improved hydrothermal stability against steam deactivation during regeneration (2.8). (5) increased pore volume and decreased bulk density (8), and (6) reduction of SOx emissions (10). 

The main problem in case of thermocatalytic cracking of polymers is the activity loss of catalysts therefore first-order kinetics is applicable only with some simplifications in thermocatalytic cases. On the other hand there is a relation modelling the fluid catalytic cracking taking into consideration the catalyst deactivation in refineries [31] ... 

Fluid catalytic cracking (FCC) (Fig. 13.5) was first introduced in 1942 and uses a fluidized bed of catalyst with continuous feedstock flow. The catalyst is usually a synthetic alumina or zeolite used as a catalyst. Compared to thermal cracking, the catalytic cracking process (1) uses a lower temperature, (2) uses a lower pressure, (3) is more flexible, (4) and the reaction mechanism is controlled by the catalysts. Feedstocks for catalytic cracking include straight-run gas oil, vacuum gas oil, atmospheric residuum, deasphalted oil, and vacuum residuum. Coke inevitably builds up on the catalyst over time and the issue can be circumvented by continuous replacement of the catalyst or the feedstock pretreated before it is used by deasphalting (removes coke precursors), demetallation (removes nickel and vanadium and prevents catalyst deactivation), or by feedstock hydrotreating (that also prevents excessive coke formation). 

Suib et at. (25, 254) reported the different effects of nickel and vanadium on the catalytic activity and selectivity for the fluid catalytic cracking by a photoluminescence technique and showed that the method is useful in predicting the catalyst deactivation caused by the deposition of metals on surfaces. The activity of the catalyst decreases monotonically with increasing vanadium content. With 1.5 wt% of V, the catalystad lost most of its activity, and with 2.0 wt% of V it became almost completely inactive. Such a deactivation of the catalyst was irreversible, with the extent being closely associated with the surface area covered with vanadium. Moreover, the extent of the deactivation was found to depend on the aging temperature, which was accelerated when aging was carried out under the same conditions normally sized in hydrothermal reactions. 

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. 

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