Natural Hydrogen Donors in Petroleum Resids

Abstract

A new method of measuring the donor hydrogen concentration and reactivity relative to tetralin was devised using dehydrogenation by 2−3-dichloro-5,6-dicyano-p-benzoquinone. Petroleum resids were found to contain high concentrations of natural hydrogen donors, and more are generated during thermolysis from substituted naphthenes in the resid. In contrast to the expected low concentration, the donor hydrogen concentration in the asphaltene fraction was found to be equivalent to the concentration in the full resid. However, the donor hydrogens in asphaltenes are more reactive than in any other fraction of the resid. This requires modifying the phase-separation mechanism for coke formation and the average chemical structure of asphaltenes. Thermal conversion of resid fractions in the presence of a super reactive hydrogen donor, 1,2,3,4-tetrahydroquinoline, showed that the selectivity to distillable liquids can be increased but the formation of polyaromatic cores cannot be prevented. In addition, reactive hydrogen donors greatly reduce the thermal reaction rate by reducing the free-radical concentration. On the basis of these and previous results, methods to increase visbreaker conversion and to inhibit thermal cracking are described and the concept of an economic optimum conversion in resid hydroconversion is proposed.