Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By isomerization
Reexamination Certificate
2000-08-02
2002-10-15
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By isomerization
C585S482000
Reexamination Certificate
active
06465705
ABSTRACT:
The present invention relates to a process for isomerising aromatic C8 cuts, i.e., hydrocarbon cuts containing 8 carbon atoms, in the presence of a catalyst containing a mordenite which is slightly or not dealuminated and a binder. This mordenite is at least partially in its acid form, in an amount generally of 3% to 60%, preferably 5% to 40% by weight, and the binder, which is preferably alumina, is generally present in an amount of 40% to 97%, preferably 60% to 95% by weight. The Si/Al atomic ratio of the mordenite is less than 20, preferably in the range 5 to 15, and more preferably in the range 5 to 10. The catalyst also contains at least one metal from group VIII of the periodic table, preferably selected from the group formed by palladium and platinum, in an amount, expressed with respect to the catalyst, generally in the range 0.01% to 2% by weight, preferably in the range 0.05% to 1.0% by weight The element or elements can be deposited on the zeolite or on the binder, preferably selectively on the binder. Finally, the catalyst further contains at least one metal from group III of the periodic table, namely selected from gallium, indium and thallium, preferably indium. The catalyst can optionally also contain at least one metal from group IV of the periodic table, selected from germanium, tin and lead, preferably tin. The present invention also relates to a catalyst used for isomerising C8 aromatic cuts and to a process for its preparation.
Zeolites used in processes for isomerising aromatic C8 cuts include ZSM-5, used alone or mixed with other zeoletes such as mordenite. Such catalysts have been described in U.S. Pat. Nos. 4,467,129, 4,482,773 and European patent EP-B-0 138 617. Other catalysts are based on mordenite and have been described, for example, in U.S. Pat. Nos. 4,723,051, 4,665,258 and French patent FR-A-2 477 903. While the activity of ZSM-5 is excellent due to the size of its channels, mordenite is more active.
The lack of selectivity of mordenite can be attenuated by optimising formulations and/or specific treatments as has been described, for example, in the Applicant's patent FR-A-2 691 914. Those techniques reduce dismutation side reactions.
Isomerisation of xylenes to ethylbenzene requires the presence of a group VIII metal. Optimised formulations based on mordenite and a group VIII metal lead to catalysts with which side reactions remain non negligible. As an example, naphthene ring opening which may or may not be followed by cracking can be cited. The development of more selective catalysts is thus of particular importance.
The Applicant has discovered that, surprisingly, a catalyst for isomerising aromatic C8 cuts containing a mordenite zeolite with an Si/Al atomic ratio of less than 20, preferably in the range 5 to 15, more preferably in the range 5 to 10, at least one group VIII metal, preferably selected from the group formed by palladium and platinum, more preferably platinum, in an amount, expressed with respect to the catalyst, generally in the range 0.01% to 2%, preferably in the range 0.05% to 1.0% by weight, said catalyst further comprising at least one group III metal in an amount, expressed with respect to the catalyst, generally in the range 0.01% to 2%, preferably in the range 0.05% to 1.0% by weight, leads to substantially improved performances, mainly in terms of selectivity, with respect to catalysts comprising mordenite and at least one metal selected from group VIII for isomerising aromatic C8 cuts.
The present invention thus provides a process for isomerisation of aromatic C8 cuts in the presence of a catalyst comprising: a support containing
3% to 60%, preferably 5% to 40% by weight with respect to the support, of at least one zeolite with a mordenite structure characterized in that its Si/Al molar ratio is less than 20, preferably in the range 5 to 15, more preferably in the range 5 to 10;
in general, 40% to 97%, preferably 60% to 95% by weight with respect to the support, of at least one binder, preferably alumina;
in general 0.01% to 2%, preferably 0.05% to 1.0% by weight with respect to the catalyst, of at least one metal from group VIII of the periodic table, preferably selected from the group formed by platinum and palladium, more preferably platinum;
in general, 0.01% to 2%, preferably 0.05% to 1.0% by weight, with respect to the catalyst, of at least one metal from group III of the periodic table, preferably indium;
optionally, 0.01% to 2%, preferably 0.05% to 1.0% by weight with respect to the catalyst, of at least one metal from group IV of the periodic table, preferably tin.
Any zeolite with a mordenite structure which is known to the skilled person is suitable for the present invention. Thus, for example, the zeolite used as a base to prepare the catalyst of the present invention is a “large pore” mordenite in its sodium form, or a “small pore” mordenite in its sodium form with the required specifications as regards the Si/Al ratio. Thus, in accordance with the present invention, the Si/Al ratio is less than 20, preferably in the range 5 to 15 and more preferably in the range 5 to 10. At least one ion exchange step can then be carried out in at least one solution of NH
4
NO
3
to obtain a zeolite with a greater or lesser residual sodium content.
This zeolite constitutes part of the composition of the catalyst support in an amount of 3% to 60% by weight, preferably 5% to 40% by weight, the complement to 100% by weight consisting of the binder in the catalyst support.
The binder (or matrix) in the support for the catalyst of the present invention is generally selected from elements of the group formed by clays, magnesia, aluminas, silicas, titanium oxide, boron oxide, zirconia, aluminium phosphates, titanium phosphates, zirconium phosphates and silica aluminas. Coal can also be used. The binder is preferably alumina.
The metals can be introduced either all in the same manner or using different techniques, at any moment during the preparation, before or after forming, and in any order. Further, intermediate treatments such as calcining and/or reduction can be carried out in between depositing the different metals.
The present invention also concerns a process for preparing a catalyst which can be carried out using any method which is known to the skilled person. At least one element from group VIII is introduced into the support, preferably to the binder, before or after forming. In general, the matrix and zeolite are mixed followed by forming. Forming is generally followed by calcining, generally at a temperature in the range 250° C. to 600° C. At least one element from group VIII of the periodic table is introduced after calcining by deposit on the support, preferably selectively onto the binder. Said elements are preferably almost completely deposited on the binder in a manner known to the skilled person by controlling the parameters used during deposition, such as the nature of the precursor used to carry out deposition. Further, at least one element from group III and optionally at least one element from group IV are added. Elements from group VIII and groups III, and optionally group IV can be added separately or simultaneously in at least one unitary step. When at least one group III element and at least one optional group IV element are separately added, it is preferable that it/they is/are added prior to the group VIII element.
The group VIII elements are deposited on the pre-formed zeolite-matrix mixture using any technique which is known to the skilled person. Deposition is, for example, carried out by dry impregnation, excess impregnation or ion exchange. Any precursor is suitable for depositing these elements. As an example, anion exchange can be carried out using hexachloroplatinic acid and/or hexachloropalladic acid in the presence of a competing agent, for example hydrochloric acid.
At least one other metal selected from group III and optionally at least one metal selected from group IV are also introduced. Any deposition technique which is known to the skilled person and any precursors are suitabl
Alario Fabio
Merlen Elisabeth
Dang Thuan D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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