Catalytic cracking reaction, modeling

Figure 6. The Mobil series of catalytic cracking reaction models, a) The Mobil 3-Lump model b) the Mobil 10-Lump model (4,5,7).

Catalytic cracking reactions involve the combined effects of reaction and adsorption phenomena. Thus, adequate kinetic modelling should consider heterogeneous representations distinguishing between the chemical species, reactants and products, distributed between gas/solid phases. 

A rare earth metal-exchanged Y-type (REY) zeolite catalyst was found to be an effective catalyst for the catalytic cracking of heavy oil. The influence of the reaction conditions and the catalytic properties of REY zeolite on the product yield and on gasoline quality have been described above. In this section, a reaction pathway is proposed for the catalytic cracking reaction of heavy oil, and a kinetic model for the cracking reaction is developed [14,33]. 

We have shown that additive coke (Cat]j) has much less impact on catalyst activity than catalytic coke (Ccal) at the same coke-on-catalyst level, but the initial catalyst deactivation rate during ARO cracking is greaier than ihat of VGO cracking because of the fast deposition of additional coke on the caialyst surface. The general correlations developed in this paper can be conveniently u sod in the modeling of catalytic cracking reaction kinetics. 

The model we describe in this work has the objective of constituting a preliminary study for the development of models that are able to explain, at the same time, both the product distribution and the decay of activity that is observed in the catalytic cracking reactions the description of the decay of activity implies also that on is able to estimate the amount of coke deposited on the surface of the catalyst. 

The method is applied for the catalytic cracking reactions and the kinetic parameters of a five-lump model are determined by using successively NLRA with various 3- and 4-lump kinetic models. 

The results described in this review demonstrate the importance of novel tools for kinetic modelling and catalyst development. In this context it is proposed to adopt the Riser Simulator to effectively represent the catalytic cracking reactions which take place in a FCC riser reactor. The technique allows for similar conditions to be used such as temperature, catalyst to oil ratio, partial pressure of hydrocarbons, solids loading and reaction time as those used in commercial units. Moreover, the contacting of the hydrocarbons with the catalyst is more representative of riser cracking where the catalyst moves in time with the vapours, than that achieved in the MAT test. 

Liguras, D.K. and Allen, D.T., "Structural Models for Catalytic Cracking. 1. Model Compound Reactions. 2. Reactions of Simulated Oil Mixtures", Ind. Eng. Chem. Res. 28,665-683 (1989). 

Figure 7. Detailed lumping model for catalytic cracking reaction (52),...

An analogous situation occurs in the catalytic cracking of mixed feed gas oils, where certain components of the feed are more difficult to crack (less reactive or more refractory) than the others. The heterogeneity in reactivities (in the form of Equations 3 and 5) makes kinetic modelling difficult. However, Kemp and Wojclechowskl (11) describe a technique which lumps the rate constants and concentrations into overall quantities and then, because of the effects of heterogeneity, account for the changes of these quantities with time, or extent of reaction. First a fractional activity is defined as... 

Induced heterogeneity model, 30 241, 251 Industrial catalytic cracking, 6 271 Industrial reactions see also specific reactions... 

A number of mechanistic modeling studies to explain the fluid catalytic cracking process and to predict the yields of valuable products of the FCC unit have been performed in the past. Weekman and Nace (1970) presented a reaction network model based on the assumption that the catalytic cracking kinetics are second order with respect to the feed concentration and on a three-lump scheme. The first lump corresponds to the entire charge stock above the gasoline boiling range, the second... 

The fluid catalytic cracking (FCC) is a very dynamic nnit that is typically the major conversion process in a refinery. Proper modeling and nnderstanding of unit capabilities represents a tremendons opportunity to improve the overall nnit operation and minimize unit emissions. The combustion chemistry in the FCC regenerator that produces environmental pollntants is extremely complex as nnmerons interactions and reactions occnr between the various chemical species. 

Recently, Takenaka et studied a series of base metal catalysts supported on various ceramic oxides for catalytic cracking of kerosene fuel. Yields of H2 and methane from a model kerosene fuel (52 wt% n-Ci2, 27 wt% diethylbenzene and 21 wt% t-butylcyclohexane) over various base metals at 600°C are shown in Figure 33. Ni/Ti02 showed the highest catalytic activity for the cracking reaction of kerosene fuel, and also maintained a better performance for the kerosene feed that contained benzothiophene. However, the catalytic performance of the... 

Figure 1731. Fluidized bed reactor processes for the conversion of petroleum fractions, (a) Exxon Model IV fluid catalytic cracking (FCC) unit sketch and operating parameters. (Hetsroni, Handbook of Multiphase Systems, McGraw-Hill, New York, 1982). (b) A modem FCC unit utilizing active zeolite catalysts the reaction occurs primarily in the riser which can be as high as 45 m. (c) Fluidized bed hydroformer in which straight chain molecules are converted into branched ones in the presence of hydrogen at a pressure of 1500 atm. The process has been largely superseded by fixed bed units employing precious metal catalysts (Hetsroni, loc. cit.). (d) A fluidized bed coking process units have been built with capacities of 400-12,000 tons/day.

All the previously cited models and works also consider, and some explicitly cite, this assumption—that the catalyst activity varies with time-on-stream (or with coke concentration [12]) in the same manner or with the same deactivation function (VO for all reactions in the network. That is, a nonselective deactivation model is always used. Corella et al. (16) have recently demonstrated that in the FCC process this assumption is not true and that it would be better to use a selective deactivation model. Another work (17) also shows how this consideration, when applied to catalytic cracking, influences the yield-conversion curves. Nevertheless, to avoid an additional complication, we will use in this chapter a nonselective deactivation model with the same a—t kinetic equation and deactivation function (VO for all the cracking reactions of the network. 

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