Dual function fluid cracking catalyst (DFCC) containing a microporous additive for olefin selectivity

Abstract

When calcined TS-1 granules are added to a commercially available fluid cracking catalyst (FCC) to form a 70% FCC-30% TS-1 mixture, the resulting dual function FCC (DFCC) exhibits enhanced cracking activity and olefin yields. A weak solid acid like TS-1 with very few strong acid sites, catalyzes secondary cracking reactions that remove lighter components in the gasoline boiling range. As a result gasoline octane numbers, olefins (C 3 and C 4 ) and LPG generation increase at all conversion levels investigated. Addition of an air dried expanded bentonite to the FCC produced activity and selectivity changes consistent with a dilution effect. The lack of catalytic activity is attributed to the inadequate hydrothermal stability of this type of expanded clay. Density functional theory (DFT) methods have been used to interpret the data for the adsorption of nitrogen at 77K within the pores of the commercial FCC under study and for the two additives tested, a bentonite expanded with SiO 2 . TiO 2 clusters and a TS-1 molecular sieve. The results obtained are compared with the results of more traditional data treatments and indicate that the DFT model can provide realistic pore volume and surface area estimation in these different porous solids. Both BET and Langmuir methods grossly underestimate the surface area of FCCs and only DFT methods yields reliable surface area and pore volume measurements over the entire micro-meso porosity range investigated. Microcalorimetry results using ammonia as a probe molecule have shown that the calcined TS-1 and (Si,Ti)-bentonite samples contain an heterogeneous distribution of acid sites and that acid sites density is low indicating that these additives are weak solid acids. However, the strength of the strongest acid sites (initial heat) in TS-1 is ∼180 kJ/mol revealing the presence of very few strong sites not present in the expanded bentonite nor in the parent FCC under study.