Thermal and Structural Characterization of Coke Deposition on Spent NiMo Catalyst Used During Catalytic Upgrading of Heavy Oil

Abstract

Catalyst deactivation has become a major concern in the refining industry globally. The deactivation of hydroprocessing catalyst by coke deposition reduces its useful life, the on-stream time of the process involved and the profitability of upgrading heavy oils to useful products. There are various methods used in thermal and structural characterization but for the purpose of this research journal, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) were carried out on both fresh and spent NiMo catalyst. The TGA results of the spent catalyst samples indicates the presence of coke species with the major portion of the species being ‘medium’ and ‘hard’ coke (second and third stage). There was also no significant change in loss of weight with change in heating rate. In comparison to the fresh catalyst, the SEM micrograph of the used catalyst indicates the formation of poor porous-structure and block-shaped crystallites depicting the sintering of particles because of the higher calcination temperature. O–C–O bond stretching vibrations with an anatase morphology were observed using FTIR on the spent catalyst sample confirming the presence of the coke species while the XRD results showed the formation and nature of carbonaceous deposits on the spent catalyst’s surfaces. A rutile phase with a tetragonal symmetry was detected for spent NiMo diffraction peaks, with the major phase indicating the presence of Carbon with a hexagonal phase.