Kinetics of Cracking

Alkanes Framework type apparent (k)/mol) intrinsic Reference 

4 Effect of Pore Size and Acid Site Density on Cracking 

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Model Based on Kinetics of Cracking and Deactivation from Laboratory Tests... 

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. 

In this paper we shall review the information found in the literature concerning the kinetics of cracking of cumene on silica-alumina. We shall also present some new experimental studies which take into account the precautions outlined in the preceding reference. 

The kinetics of crack growth under SMIE conditions may be given by 5... 

Figure 8.24. The kinetics of crack growth for aUoy 1 in high-purity oxygen and argon at 873, 923, and 973 K [37,38],...

Some of the more important methods of failure studies include stress-strain, impact loading, and fatigue. Creep and stress relaxation (Chapter 10) may cause serious damage to engineering materials, but they normally do not result in fracture per se except for creep rupture. Emphasis in this chapter will be on the study of fracture energy, kinetics of crack growth, and molecular mechanisms. The reader is directed to Chapter 13 for a fuller discussion of plastic toughening. 

FIGURE 6. Kinetics of crack propagation for the unloading of a glass ball on polyurethane from / = 50 mN to P — -30 mN, for two temperatures. The dashed line is the theoretical value of the inflection point. (From Reference 10.)... 

Computational chemistry has advanced dramatically in the last decades, due to the increase in the availability of moderately priced hardware and software and may be an alternative or complementary method to study the thermodynamics and kinetics of cracking processes. It is well known that very accurate total and relative energies of molecular species can be obtained at the coupled cluster... 

The deposition of coke on the catalyst results in rapid activity decay and hence a catalyst decay function is multiplied by the intrinsic rate to give the actual rate. It is normally assumed that the same active sites will crack both gas oil and gasoline molecules, therefore the activity decay functions and 2 are assumed equal (Weekman, 1968). In general, the catalyst activity is dependent on the carbon laid down and is thus related to the time the catalyst is exposed to hydrocarbons. Then, to completely describe the kinetics of cracking according to the three lump model involves the determination of the parameters k, ki, kj and the deactivation function. ... 

Kachanov. L.M. (1961) On the kinetics of crack growth. J. Appl. Math. Mech. 25, 739-745 Kalker, J.J. (1975) Aspects of Contact Mechanics , in The Mechanics of the Contact Between Deformable Bodies, ed. by A.D. de Pater, J.J. Kalker (Delft University Press) pp. 1-25 Kalker, J.J. (1977) A survey of the mechanics of contact between solid bodies. J. Appl. Math. Phys. (ZAMP) 57, 13-17... 

Before discussing the kinetics of crack-healing, we describe thermodynamically the experimental conditions associated with the temperature and partial oxygen pressure. Generally SiC oxidation includes active-to-passive transition, where passive oxidation is given by Eq. (1) and active oxidation is given by... 

Whereas all of the above theories [54—68] refer in one way or another to the thermally activated breakage of one kind of molecular bonds as primary fracture event, the Bueche-Halpin theory for the tensile strength of gum elastomers [69] employs the idea that the viscoelastic straining of rubber filaments together with the degree of their ultimate elongation determine the kinetics of crack propagation in an elastomeric solid. 

It is very important to examine the crack surface in order to understand the kinetics of crack growth. Such a study reveals the origin of crack initiation and the direction of crack propagation if crack growth is semi-brittle in manner. Of course, fracture meehanism changes such as brittle, semi-brittle and ductile can also be identified by investigation of fracture surfaces. 

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