Efficient chemical modeling of the hydrocracking of heavy oils.

摘要

Hydrocracking is an oil upgrading process that can assist in meeting future petroleum products demand. Its optimization would be enhanced by a fundamental understanding of the underlying intrinsic chemistry controlling the reactions of heavy oils during hydrocracking. However, laboratory and modeling approaches are impeded by the complexity of heavy oils.; The complexity of heavy oil feedstocks and their reactions motivates a new approach for the resolution of fundamental pathways, kinetics and mechanisms. Chemical modeling provides the framework for a complimentary attack to this problem. The basic steps in chemical modeling are T, E, T{dollar}sp{lcub}-1{rcub}{dollar}. The transformation of a real system into a model system, T, uses modern analytical chemistry to deduce the components of the real system which are responsible for the fundamental behavior. These model compounds, which mimic the reactive moieties in the real system, are studied experimentally (E) to elucidate their reaction pathways, kinetics and mechanism. Finally, the information obtained from these experiments is organized into a model (T{dollar}sp{lcub}-1{rcub}{dollar}) which includes the fundamental features of the complex system. This work focuses on E.; The reactivity heavy oil feedstocks was studied herein through the use of carefully chosen model compounds which mimic the reactivity of similar moieties in the heavy oil. Chemical modeling led to this set of compounds, whose reactions yielded important kinetics, pathways, and mechanisms in hydrocracking. Because of the complexity of heavy oils, many different reactions will be occurring simultaneously during hydrocracking; however, the model compound results indicate that there are essentially four types of reactions: (1) Hydrogenations which increase the molecular weight. Three-ring and Two-ring structures were observed to undergo this reaction much more readily than did single-ring compounds. For example, the rate of hydrogenation of phenanthrene to either tetrahydrophenanthrene or dihydrophenanthrene was approximately 4.08 times faster than was the hydrogenation of 1-methylnaphthalene to methyltetralins. (2) Isomerizations which provide no change in molecular weight. Two types were observed: six-membered to five-membered ring transformations (such as tetrahydrophenanthrene to methylcyclopentenonaphthalene), and alkyl substituent branching reactions (the number of {dollar}Csb{lcub}16{rcub}{dollar} alkanes produced during the hexadecylnaphthalenes hydrocracking experiment far exceeded the number of hexadecylnaphthalene isomers initially present). (3) Ring-openings which increase the molecular weight by 2 a.m.u. Three-ring structures underwent this reaction more easily than did two-ring structures. Single-ring structures underwent very little ring-opening. (4) Dealkylations which decrease molecular weight (requires 1 mol {dollar}Hsb2{dollar}). The larger the leaving alkyl group, the more easily the dealkylation occurred.; The foregoing results are summarized in terms of linear free energy relationships which should also be a summary of the intrinsic reactivity of heavy oil feedstocks.