BEA and MOR as additives for light olefins production

The use of MFI-based additives in the fluid catalytic cracking (FCC) process in order to increase both-the production of light olefins and gasoline octane number-has been commercially proven. It is well known that impregnation by phosphorus increases the stability of aluminum atoms of H-MFI zeolite framework, resulting in higher yields of desired products. This paper discusses the possibility of combining either beta (BEA) or mordenite (MOR) zeolites-before and after treatment-with phosphoric acid (P/AI ratio of 1) with the conventional MFI-based additive. Zeolite samples were characterized by nitrogen adsorption, X-ray diffraction (XRD) and Al-27 and P-31 solid state NMR before and after hydrothermal treatment. Such treatment was responsible for decreases in zeolite surface area, crystallinity and also in the number of framework tetrahedral aluminum species of all samples. After impregnation with phosphoric acid and hydrothermal treatment, besides other species, both H-MOR/P/St and H-BEA/P/St presented resonance signals at 38 and -30 ppm at the Al-27 and P-31 MAS NMR spectra, respectively, which can be attributed to tetrahedral aluminum and phosphorus in AIPO's-like crystalline structures. After being mixed with an equilibrium FCC catalyst, the laboratory performance of the different additives was investigated using a gasoil feedstock and a fixed-bed micro activity test unit. Similarly to what was previously reported for H-MFI/P/St, the phosphoric acid treatment improved the performance of H-MOR/P/St and H-BEA/P/St zeolites with an expressive increase in lighter products yields in detriment of naphtha. The results suggest that, besides classical tetrahedral aluminum in the framework (Altet-f), other aluminum species also take part in the improvement of the zeolites performance. (c) 2006 Elsevier B.V. All rights reserved.