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Catalytic degradation of polyethylene: catalytic behaviour of parent restructured and pillared clays towards metal-exchanged derivatives.

Elisabetta Borsella ,  Giorgio Perez ,  Anthony A. Tomlinson ,  Patrizia Cafarelli ,  Adriana De Stefanis 

Istituto per lo Studio dei Materiali Nanostrutturati (ISMN-CNR), Monterotondo, Roma I-00016, Italy


The catalytic cracking of medium density polyethylene was carried out on modified (restructured, pillared, and/or metal exchanged) clays. It has been oserved that the spectra of the products depend on the clay used (montmorillonite and beidellite, pure montmorillonite, or saponite), on the pillars (alumina and iron-aluminium-oxides) and on metal exchange, if any.The pyrolysis of PE is known to follow the random chain scission route, resulting in mainly oligomers and dimers leading, depending on the catalyst used, to higher aliphatics and/or aromatics. The extensive screening on PE cracking has evidenced a major difference between montmorilonite and saponite based materials. Either pillared or restructured montmorillonite ones show production of aliphatics, meanwhile the saponite-based that of aromatics. These latter have the same behaviour of the H-ZSM-5. Zn-exchanged zeolites are known to promote propene cyclisation and in general to favour aromatisation routes. The active zinc species has been identified with Zn(OH)+ bond to Brönsted acid sites and displaying Lewis acidity. ZnO crystallite are inert and present outside the catalyst framework. The formation of the active species can be correlated to the acidic sites present on the different catalysts frameworks. Considering the temperature (300°C) utilised, the presence of dominant Brönsted acidity of different force can be claimed for the results on montmorillonites. In confirmation of this the Zn-exchange (which gives Lewis acidity) gives an inversion of products on FAMO and HMO and to a lesser extent on K10®, known to contain both acidities. On the contrary the aromatics production on saponites should be ascribed to the presence of Lewis acidity, in which case the Zn-exchange leads to inactive ZnO crystallite presence hindering the access and decreasing aromatics production. AZA, produced from a bentonite (mixed montmorillonite beidellite) shows an intermediate behaviour.


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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium D, by Elisabetta Borsella
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-07-02 12:09
Revised:   2009-06-07 00:48