Hydroprocessing of the LDPE thermal cracking oil into transportation fuels over Pd supported on hierarchical ZSM-5 catalyst

Abstract

The oil obtained by LDPE thermal cracking, which is formed by linear olefins and paraffins with a broad carbon atom range, has been upgraded by hydroprocessing over Pd/ZSM-5 catalysts. As a consequence of this treatment, gasoline and diesel range hydrocarbons are produced with an enhanced content of isoparaffins and aromatics, while the presence of olefins is strongly reduced. The use of hierarchical zeolitic supports with a secondary porosity has a positive effect on the catalytic activity in the main reactions taking place (hydrogenation, hydroisomerization, cracking, oligomerization and aromatization), which is assigned to the higher reactant accessibility achieved with the hierarchical ZSM-5 compared to a nanocrystalline ZSM-5 sample used as reference. On the other hand, the acidic features of the zeolite have been controlled by variation of the Si/Al ratio in the 30–300 range, which has allowed adjusting the extension of the metal and acid sites catalyzed reactions.In overall, the use of Pd/h-ZSM-5 catalysts allows the hydroprocessing of the LDPE thermal cracking oil to be conducted in an effective way improving significantly the feed properties regarding its potential use in the formulation of transportation fuels. Thus, adjusting the catalyst properties and the operating conditions it is possible to achieve a high selectivity towards liquid fuels (over 95%), avoiding excessive cracking, and to control their composition leading to high isoparaffins and aromatics content with a low share of olefinic compounds. Finally, a reaction scheme has been proposed taking into account the main transformations occurring during the hydroprocessing treatment.