REACTIVITY OF NICKEL PORPHYRINS IN CATALYTIC HYDRODEMETALLATION by ROBERT ADAMS WARE

The kinetics and reaction network of hydrodemetallation (HDM) reactions and the pattern of metal deposition have been investigated using a model residuum oil, consisting of nickel porphyrins (Nietioporphyrin (Ni-EP), Ni-tetraphenylporphyrin (Ni-TPP), and Nitetra(3-methylphenyl)porphyrin (Ni-T3MPP)) dissolved in a clean (N and S free) mineral oil. Reactions were carried out over a commercial CoO-MoO./Y-Al 203 catalyst at 285 345 *C and 4.24 10.44 MPa H2 (600 1500 psig). The porphyrins react via sequential pathways, first involving hydrogenation of peripheral double bonds to "activate" the porphyrin for the final hydrogenolysis steps which fragment the ring and deposit the metal on the catalyst. The extent of initial hydrogenation, the complexity of the reaction pathway, and the overall rate limiting step for metal removal are dependent on the porphyrin structure. One route to deposition with Ni-T3MPP and Ni-TPP is through a non-porphyrinic nickel intermediate. The behavior of a commercial HDS catalyst in promoting HDM reactions is consistent with the dual functionality concept of hydrogenation activity associated with Co and Mo sites and hydrogenolysis (metal deposition) activity associated with acid sites on the support and Mo. The presence of nitrogen (pyridine) and sulfur (CS 2 , sulfided catalyst) did not change the reaction pathway of Ni-T3MPP during HDM but did alter the hydrogenation/hydrogenolysis reaction selectivity. Pyridine preferentially retarded the hydrogenation steps whereas sulfiding the catalyst selectively enhanced the metal deposition steps. The feasibility of controlling the Ni-T3MPP hydrogenation/ hydrogenolysis (metal deposition) reaction selectivity was demonstrated by doping the CoMo/Al 20 3 catlyst. Changes as dramatic as a shift in the overall rate limiting step were possible. Alkali (Cs, Na) neutralized catalyst acidity and drastically reduced the metal deposition activity with only a marginal reduction in the high hydrogenation activity. Sulfur and halogens (I, Cl) added in a reducing environment resulted in high metal deposition activity attributed to an increase in Bronsted acidity on the surface. Hydrogenation activity became successively lower (S>I>Cl) and rate limiting with the halogens and was interpreted as arising from a strong interaction between Mo vacancies and the halogen which deactivated hydrogenation sites. Nickel deposition profiles obtained under diffusion limited conditions reflect the intrinsic reactivity of the nickel porphyrins. At the reactor entrance all profiles were characterized by an internal maxima in the metal deposition pattern, termed M-shape. These maxima shifted to the edge of the catalyst pellets at the end of the reactor bed. The enhanced metal deposition activity of the sulfided catalyst compared to the oxide catalyst was manifested in steeper, more U-shape metal profiles. Theoretical calculations based on sequential HDM reaction schemes coupled with diffusion successfully interpreted the metal profiles. Diffusivities for the nickel species were on the order of 10-6 cm /sec with the hydrogenated intermediates having diffusion coefficients 2 to 3.5 times larger than the starting porphyrin. The impact of the variations in Ni-T3MPP reaction selectivity obtained by doping the catalyst was apparent in metal deposition profiles generated under diffusion limited conditions. Thesis Supervisor: Dr. James Wei Department Head and Warren K. Lewis Professor of Chemical Engineering In Loving Memory of Rosemary J. Wojtowicz Our life together was painfully short yet during this time we lived life to its fullest, enjoying so much in each others company. She brought a special joy and happiness into my life that I would have otherwise not known. The beloved memories of what we did and shared together will always have a special place in my heart. I dedicate this work to Rosie. The example of her accomplishments and the thought of her constant encouragement and companionship have been a continuing source of inspiration for me. As she now lives, so too shall my memories of her. "Blessed are the pure in heart: for they shall see God." Matthew 5:8