Structural Determination by XAFS Spectroscopy of Non-Porphyrin Nickel and Vanadium in Maya Residuum, Hydrocracked Residuum and Toluene-Insoluble Solid

Abstract

The local structure of non-porphyrin Ni and V in Maya residuum, hydrocracked residuum, and toluene-insoluble solid were determined by XAFS spectroscopy. In residuum, the first coordination shell of non-porphyrin V is similar to that for vanadyl tetraphenylporphyrin with four N at a distance of 2.08 Å and one O at 1.67 Å. Similarly, the first coordination shell of Ni non-porphyrin is similar to that in nickle tetraphenylporphyrin, i.e., four N at a distance of 1.90 Å. The Ni and V coordination geometries are remarkably stable toward thermal cracking, catalytic hydrogen, and H2S. After hydrocracking to about 60% conversion of the residuum, the local coordination of Ni and V in the hydrocracked residuum is little changed. During hydrocracking, approximately 1% of the residuum is converted to toluene-insoluble solid, which contains high levels of Ni and V. Approximately 10% of the Ni and V in the solid is still present in a porphyrin-type coordination geometry, while the remaining Ni and V has an octahedral coordination. In the latter, the V coordination contained one O at 1.64 Å, four N at 2.14 Å, and one N (or O) at 1.96 Å, and the Ni coordination contained six N at 2.09 Å. Ni or V sulfides are not formed in the toluene-insoluble solid.