Search

An extended dual kinetic model allows to fit the n-heptane cracking results working in a wide range of reaction conditions. The duality of the model is provided by the contribution of monomolecular and bimolecular cracking mechanisms. It takes into account the role played by the olefins formed on the global cracking or added within the feed. Furthermore by means of this model and the kinetic parameters obtained when cracking n-heptane on ZSM-5, it has been observed that, while some characterization techniques show a homogeneous zeolite surface from the point of view of the active sites, rigorous kinetic experiments point to the possibility that the reactant sees a heterogeneous surface with, at least, two groups of cracking active sites. Those differentiated active sites give different cracking rates and different activation energies for the process and, in the case of ZSM-5, could be assimilated to sites pointing to the 10R channels and sites pointing into the crossing of the 10R channels, mainly due to differences in kid site location and confinement effects. (C) 2015 Elsevier Inc. All rights reserved., Financial support by the Ministerio de Economia y Competitividad of Spain (MINECO) [Programa Estatal (Project MAT2012-31657) and Programa Consolider-Ingenio 2010 (Project MULTICAT)] is gratefully acknowledged.

Steam catalytic cracking of naphtha in smaller FCC units can be considered an option to produce more ethene and propene. These units will operate at high reaction temperatures and in the presence of steam. The profitability of these units could be improved with the use of new catalysts with higher activity and hydrothermal stability, without compromising the selectivity to light olefins. We have explored the possibilities of IM-5 zeolite for high temperature steam catalytic cracking (SCC) of a naphtha, as an alternative to commonly used ZSM-5 zeolite. So, we compare the catalytic activity, the effect of operating variables of the process and the yields of interest products between the two zeolites, the IM-5 zeolite and the best of ZSM-5 zeolites studied previously for SCC reaction. Furthermore, we study post-synthesis treatment of zeolite with phosphorous containing precursors to enhance the hydrothermal stability, and the effect of it on the catalytic activity and the yield of products. It can be seen as the use of the zeolite proposal improve the catalytic activity with respect to the best of ZSM-5 zeolite in SCC process, without compromising the yield to products of interest. Furthermore, the incorporation of phosphorous has a large effect on hydrothermal stability of zeolite, showing this zeolite as an important competitor to the ZSM-5 zeolite for steam catalytic cracking of naphtha., Financial support by the Ministerio de Ciencia e Innovacion of Spain (MICINN) [Programa Nacional (Project MAT2006-14274-C02-01) and Programa Consolider-Ingenio 2010 (Project MULTICAT)] is gratefully acknowledged.

One option to produce more ethene and propene can be to crack naphtha type fractions in dedicated smaller FCC units. We present here the results obtained for high temperature steam catalytic cracking (SCC) of a representative naphtha product (n-heptane) with ZSM-5. It has been found that under those conditions the presence of steam produces an irreversible dealumination of the zeolite as well as a reversible deactivation due to the interaction of water with active sites with a negative effect on protolytic cracking. A kinetic decay model that takes into account the two phenomena has been developed. The apparent activation energy is lower in the presence of steam. It appears that whilst the presence of steam is vital when processing heavy feeds to achieve a better feed dispersion and a more effective catalytic cracking in conventional fluid catalytic cracking (FCC) units, in the case of steam catalytic cracking of naphtha (n-heptane) the presence of steam has a negative effect on the final performance of the catalyst. On the other hand, whilst steam does not modify ethene and propene selectivity, significantly decreases H 2 and CH 4 formation, as well as formation of potential coke precursors., Financial support by the Ministerio de Ciencia e Innovacion of Spain (MICINN) (Project MAT2006-14274-C02-01) and Consolider-Ingenio 2010 (Project MULTICAT) is gratefully acknowledged.

In order to increase ethene and propene, naphtha steam catalytic cracking has been considered. The cracking of C 5-C 12 n-alkanes with ZSM-5 has been studied in absence and in presence of steam and the influence of the operation variables was studied. Irreversible catalyst deactivation by dealumination also occurs in the reactor when the cracking is carried out in the presence of steam. To diminish steam deactivation, the influence of zeolite Si/Al framework and a postsynthesis treatment by phosphorous have been studied and optimized. Much more stable catalyst can be achieved that result in an increase in activity without penalty for production of ethene and propene., Financial support by the Ministerio de Ciencia e Innovacion of Spain (MICINN) (Project MAT2006-14274-C02-01) and by Consolider-Ingenio 2010 (Project MULTICAT) is gratefully acknowledged.