Selective Ring Opening of Naphthenic Molecules

Abstract Ring opening as practiced in hydrocracking of naphthenic molecules results from multiple cleavages of both endo- and exocyclic C–C bonds. Selective ring opening requires that only one endocyclic C–C bond per naphthene ring be severed, preserving thereby reactant molecular weight. The products of selective ring opening are alkanes and alkylnaphthenes. Over hydrocracking catalysts the yield of alkanes with the same number of carbon atoms as the reactant naphthenes is unacceptably low as a result of extensive dealkylation of alkylnaphthenes and secondary cracking of alkanes. Alkylcyclopentanes, in contrast, selectively ring open by hydrogenolysis over a number of noble metal catalysts. Under similar reaction conditions the selective ring-opening rates of alkylcyclohexanes are, however, one to two orders slower than those of alkylcyclopentanes. Addition of a ring-contraction acidity function converts alkylcyclohexanes into more easily ring-opened alkylcyclopentanes, greatly facilitating selective ring opening. Selective ring-opening rates and selectivities are optimum when ring isomerization occurs by a nonbranching ring contraction. Branching ring contraction, creating increased numbers of ring substituents, is detrimental to both ring-opening rates and selectivities. When an effective acidity function is coupled with a high-activity hydrogenolysis metal, such as iridium, the resulting bifunctional catalyst system greatly outperforms conventional hydrocracking catalysts for the selective conversion of naphthenes to alkanes.

[1]  D. R. Stull,et al.  The chemical thermodynamics of organic compounds , 1969 .

[2]  Z. Paâl,et al.  Reactions of alkylcyclopentanes over pt catalysts , 1989 .

[3]  B. Gates,et al.  Chemistry of catalytic processes , 1979 .

[4]  A. Stanislaus,et al.  Aromatic Hydrogenation Catalysis: A Review , 1994 .

[5]  P. Tétényi,et al.  A new classification of metal catalysts in skeletal reactions of hydrocarbons , 1977, Nature.

[6]  R. Baker,et al.  Chemisorption properties of iridium on alumina catalysts , 1980 .

[7]  J. Penninger New aspects of the mechanism for the thermal hydrocracking of indan and tetralin , 1982 .

[8]  B. Coq,et al.  Competitive reaction of methylcyclohexane and n-hexane over alumina-supported platinum, iridium and ruthenium catalysts , 1995 .

[9]  S. Ernst,et al.  Large pore molecular sieves: Chapter 5 Catalytic test reactions for probing the pore width of large and super-large pore molecular sieves , 1994 .

[10]  Bjorn Donnis,et al.  AROMATIC SATURATION OF DISTILLATES: AN OVERVIEW , 1996 .

[11]  Robert J White,et al.  Selective Hydrocracking of C9- to C12-Alkylcyclohexanes on Acidic Catalysts. Evidence for the Paring Reaction , 1962 .

[12]  G. Mcvicker,et al.  Conversion of methylcyclopentane and acyclic hexanes over supported platinum catalysts: I. Isomerization kinetics and hydrogenolysis selectivities , 1988 .

[13]  Peter A. Jacobs,et al.  Hydroisomerization and hydrocracking. 2. Product distributions from n-decane and n-dodecane , 1981 .