Monomolecular cracking

As part of the same study selectivity data were provided at 10-100 kPa partial pressures of n-butane at 0-17% conversion over HZSM-5 [90]. With increase in pressure and conversion secondary reactions started to occur. These results are also summarized in Table 13.6. The lowered selectivity to hydrogen, methane and ethane was attributed to increasingly less favorable conditions for monomolecular cracking. The dramatic increase in selectivity to propane which was absent at zero conversion, along with decrease in propylene was considered as signature for bimolecular cracking. More specifically, it was suggested that hydride transfer... 

Bhan, A., Gounder, R., Macht, J., and Iglesia, E. (2008) Entropy considerations in monomolecular cracking of alkanes on acidic zeolites. J. Catal., 253, 221-224. 

Noteworthy are the formation of methane and ethane as well as of hydrogen. MONOMOLECULAR CRACKING... 

The duality of cracking mechanisms is summarized in Fig. 5, where RH paraffin feed, R -C=C = olefinic product, Kq = equilibrium constant of olefin chemisorption. Free Bronsted acid sites HZ interact directly with the paraffin feed by protonation, producing monomolecular cracking. When the acid sites are covered with adsorbed olefins to form... 

With the model developed, we describe alkane adsorption in nanoporous crystalline and ordered acid catalysts with the intention of calculating three mathematical equations, one each for the geometry of the pore system, for describing the adsorption enthalpy and its relation with the activation energy, and for the monomolecular cracking of n-paraffins [97], This methodology can also be applied to other unimolecular reactions. 

In the case of high-acid silica zeolites, Haag has experimentally shown [100] that for monomolecular cracking the apparent or observed activation energy, / obs, is the sum of the heat of adsorption, A//a, of the alkane and the intrinsic activation energy, Emt... 

Within the framework of the transition state theory [112,113], the observed activation energy, Eobs, for a monomolecular catalytic process in the heterogeneous case is Eobs = E0 + A//ads [act. complex], where E0 is the energy of the reaction without a catalyst and A//.lds act. complex] is the adsorption enthalpy of the activated complex [114], In the monomolecular cracking of n-alkanes catalyzed by... 

The product distribution, the rates of total conversion of n- butane, the rates for monomolecular cracking and for dehydrogenation as well as the turnover frequency (TOP) for cracking are compiled in Table 3. For SAP05-3 the selectivity as a function of the reaction temperature is shown in Fig. 2, respectively. 

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