Mineral oils: processes and products – Chemical conversion of hydrocarbons – Reforming
Reexamination Certificate
2001-07-02
2003-09-23
Norton, Nadine G. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Reforming
C208S138000, C208S133000, C208S134000, C208S015000, C502S325000, C502S326000, C502S327000, C502S328000, C502S333000, C502S334000, C502S339000
Reexamination Certificate
active
06623626
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and composition for opening naphthenic rings of naphthenic ring-containing compounds such as distillate. In particular, this invention relates to the use of a catalyst composition comprising a combination of a naphthene ring isomerizing catalyst, preferably containing Pt and/or Pd in an amount effective to isomerize a C
6
naphthene ring compound to a C
5
naphthene ring compound, and a naphthene ring opening catalyst, preferably containing Ir in an amount effective to ring open naphthene ring compounds.
BACKGROUND OF THE INVENTION
There is an increasing demand for hydrocarbons boiling in the distillate boiling point range (“distillate”). Distillates typically contain paraffins, naphthenes, and aromatics. For fuel quality parameters such as cetane number, gravity and emissions, paraffins are the most desirable components, followed by naphthenes, followed by aromatics. The least desirable are multi-ring aromatic compounds. There is also an increasing demand for paraffinic solvents arising from their low toxicity and biodegradability. Consequently, it is desirable to reduce the cyclic compound content of hydrocarbon solvent blends, in general, and to convert naphthenes to paraffins, in particular. The general process of converting naphthenes to paraffins is referred to herein as ring opening.
Refinery processes that produce distillate fuels often have a limited capability to produce high quality and yields of distillate fuel. For example, conventional hydrogenation processes saturate aromatic rings to form naphthenes, thereby increasing the cetane number and increasing the API gravity (i.e., lowering the density). However, single ring and multi-ring naphthenes have generally lower cetane values and are denser than paraffins having substantially the same number of carbon atoms. The greater density of naphthenes results in reduced volume of the distillate fuel blend relative to compositions containing similar concentrations of paraffins instead of naphthenes. Hydrocracking catalysts, typically composed of hydrogenation metals supported on acidic supports, are also effective for aromatics hydrogenation and for ring opening by cracking. However, cracking tends to make lower boiling point products, including a significant quantity of undesired gas by-products, which lowers the overall boiling range and limits the volume of final distillate product. In fact, hydrocracking products generally do not contain more distillate boiling range paraffins than the hydrocracking feeds. Moreover, a significant portion of the total paraffin concentration in the final product of conventional hydrocracking processes, including gas by-products, are relatively low molecular weight compounds that are outside the distillate boiling range. Thus, the apparent increase in distillate boiling range paraffins and improved distillate fuel quality may result primarily from a combination of the hydrogenation of aromatics and a concentration of paraffins in a reduced volume of distillate product, the latter arising from removing the undesired paraffin gas by-product, i.e., the low boiling point paraffin gas components.
There is therefore a need for selective ring opening processes for converting single and multi-ring aromatic species, including alkyl functionalized derivatives thereof, into distillate boiling range paraffins without producing a significant amount of undesirable low boiling point saturated species. Selectivity for ring opening is related to the propensity for cleavage of a ring bond which results in product molecules having an equivalent number of carbon atoms and at least one less ring than the original molecule, rather than cleavage of a bond which results in a product molecule having fewer carbons than the original molecule. A perfectly selective ring opening process would give only ring bond cleavage to produce molecules having an equivalent number of carbon atoms and at least one less ring than the original molecule. For example, from a hydrocarbon stream containing only single ring naphthenes of n number of carbon atoms, the product from perfect ring opening selectivity would contain only paraffins of n number of carbon atoms. Thus, the greater number of product molecules from a ring opening process having an equivalent number of carbon atoms and at least one less ring than the original molecule, the greater the selectivity for ring opening.
Conventional ring opening processes use a wide range of catalysts, including bifunctional metal hydrogenation-acidic catalysts. However, distillate quality may be improved by controlling paring isomenzations and subsequent dealkylations in order to limit the number of lower cetane, highly branched paraffins that may result from conventional ring opening.
Some conventional processes for forming an improved distillate employ Ir catalysts for opening naphthene ring compounds. Even though distillates such as diesel, jet fuel and heating oil contain at least about 20 vol. %, generally about 20 to about 40 vol. % of C
6
naphthenes, the conventional processes open C
6
naphthenes at low rates, if at all. This problem is exacerbated with hydrotreated distillates because they have a still greater concentration of C
6
naphthenes. In order to overcome this problem of poor opening of C
6
naphthene rings, U.S. Pat. No. 5,763,731 teaches using Ir along with at least one acidic co-catalyst, preferably a zeolite, to isomerize the C
6
naphthene rings to C
5
rings. However, since the resulting C
5
ring structure will typically bear increased numbers of substituents, such as alkyl groups, this approach increases the volume of branched paraffins upon ring opening. In addition, the presence of an acidic co-catalyst has a tendency to isomerize any naturally present linear paraffin into a branched paraffin, often resulting in a ring-opened product that has an undesirably high concentration of branched paraffins. Moreover, the process results in increased light saturated gas production, particularly at high temperature.
Another conventional process, set forth in U.S. Pat. No. 5,811,624, uses Ir along with at least certain transition metals for isomerizing C
6
naphthene rings to C
5
naphthene rings, with the Ir component being particularly effective for opening the C
5
naphthene rings. However, the product contains a significant concentration of branched paraffins, which leads to a lower product cetane number.
There is still a need, therefore, for a ring opening process and catalyst which provide a much higher degree of linearity in the ring opened product.
SUMMARY OF THE INVENTION
In one embodiment, a ring opening catalyst system and process of this invention is provided to form a product higher in linear paraffin functionality compared to conventional ring opening catalysts and processes. The process accomplishes this by providing a naphthene ring opening catalyst system comprising a naphthene ring isomerizing catalyst containing a catalytically active naphthene ring isomerization metal supported on a first catalyst support in an amount effective to isomerize a C
6
naphthene ring-containing compound to a C
5
naphthene ring-containing compound. The catalyst system further comprises a naphthene ring opening catalyst containing a catalytically active naphthene ring opening metal, preferably a Group VIII such as Ir, Pt, Ru, Rh and more preferably Ir, supported on a second catalyst support in an amount effective to ring open a naphthene ring-containing compound.
The isomerizing catalyst and the ring opening catalyst may be mixed together or provided in a stacked bed arrangement. Preferably, the catalytically active isomerization metal is at least one of Pt and Pd. In one embodiment, the isomerizing catalyst contains from about 0.1 to about 2.0 wt. % Pt, Pd, or a combination thereof. Preferably, the ring opening catalyst contains from about 0.01 to about 0.5 wt. % Ir.
In one embodiment, the isomerization and ring opening metals are present at a weight ratio of 50-99 parts of isomerization metal to 50-1 parts of rin
Baird Jr. William C.
Chen Jingguang G.
McVicker Gary B.
ExxonMobil Research and Engineering Company
Hughes Gerald J.
Kliebert Jeremy J.
Norton Nadine G.
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