This work aims to investigate the deactivation of an equilibrated commercial FCC catalyst during the catalytic cracking of heavy fuel oils (HFO) identified as a MARPOL type C residue. For this purpose, we conducted experiments in a batch fluidized bed CREC Riser Simulator under industrially relevant conditions for the evaluation of this reaction parameter on (i) HFO conversion; (ii) product yield (dry gas-LPG-gasoline), and (iii) catalyst deactivation and coke nature. Targeting the reduction of the content of heteroatoms (mainly sulfur) prior to catalytic cracking the ship oil was hydrotreated in a 100 mL stainless steel batch reactor under a continuous hydrogen flow (100 mL min–1) at 400 °C, 80 bar and in the presence of an ex-situ sulfided commercial CoMo/Al2O3 catalyst. The subsequent catalytic cracking of the pre-treated feedstock was carried out under the following operating conditions: 500, 530, and 560 °C; C/O, 5.5; residence time, 3 s. The products were analyzed online through gas chromatography (GC) and the spent catalysts were tested by TG-TPO, LDI FT-ICR/MS, and N2 adsorption-desorption isotherms. The DTG profile obtained from the TG/TPO experiments (consisting of desorption and subsequent combustion step) of spent catalysts reveals a higher concentration of organic species desorbed in the catalysts deactivated at higher cracking temperatures, which can be attributed to a higher amount of retained products inside of the catalyst pores or light coke precursors. We observed a significant rise in the coke content when the temperature is raised from 500 to 530 °C, and a relatively stable coke deposition in the range 530-560 °C. Furthermore, despite an overall lower coke formation, the coke species formed at 560 °C consists of bulkier and more condensed deactivating species, as concluded from the position of the coke combustion peak maxima. LDI FT-ICR/MS analysis of the used catalyst revealed that the species present in the formed coke have mass-to-charge values from 600 to ca. 750 uma, increasing with reaction temperature. The detected species and their corresponding molecular formula predictions reveal aromatics with carbon numbers in the C# = 20-50 range and DBE = 10-40 at 500 °C, increasing up to C#=20-65 and DBE = 15-50 at 530-560 °C. These results showcase a great impact of the temperature variable over the total coke formation and nature in the 500-530 °C, with a reduced effect at more severe conditions.

Compositional insights of the carbonaceous species deposited on the FCC catalyst during the cracking of heavy fuel oils discarded from ships

ACS Spring 2022

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