DEVELOPMENT OF A MECHANISTIC PICTURE OF THE HYDRODEMETALLIZATION REACTION OF METALLO-TETRAPHENYLPORPHYRIN ON A MOLECULAR-LEVEL

Vanadyl- and nickel-tetraphenylporphyrins (VO-TPP and Ni-TPP) have oft en been used as model compounds for the metallo-porphyrin (-like) frac tion in heavy oil residua. The goal of the present work was to validat e and to extend the present-known reaction mechanism for the hydrodeme tallization (HDM) of metallo-tetraphenylporphyrins (M-TPP). Based on m olecular-modelling calculations and GC-MS analysis, new reaction inter mediates could be identified and an extended reaction mechanism for th e hydrodemetallization of metallo-TPP proposed. The mechanism proceeds via three hydrogenation steps on beta-pyrrole positions of the porphy rinic structure to a meso-bridge-hydrogenated structure. After an acid attack, ring opening, and a possible elimination of a tolyl group, th e final product before metal removal is an open-chain molecule, Metal removal and further conversion leads to monopyrrole-containing molecul es and metal deposition on the catalyst surface.