Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Gallium containing
Reexamination Certificate
2000-04-04
2001-05-08
Dunn, Tom (Department: 1764)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Gallium containing
C502S063000, C502S064000, C502S071000, C502S077000, C502S085000
Reexamination Certificate
active
06228789
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to water vapor treated metal promoted zeolites. In a more specific aspect it relates to water vapor treated zinc promoted zeolite/alumina compositions. In another aspect it relates to a process for converting non-aromatic hydrocarbons to lower olefin and aromatic hydrocarbons in the presence of a water vapor-treated metal promoted zeolite
It is known to catalytically crack non-aromatic gasoline boiling range hydrocarbons to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene, and xylenes i.e. BTX) in the presence of zeolite catalysts such as ZSM-5, as is described in an article by N.Y. Chen et al in Industrial & Engineering Chemistry Process Design and Development, Volume 25, 1986, pages 151-155. The reaction product of this catalytic cracking process contains a multitude of hydrocarbons such as unconverted C5+ alkanes, lower alkanes (methane, ethane, propane), lower alkenes (ethylene and propylene), C6-C8 aromatic hydrocarbons (benzene, toluene, xylenes, and ethylbenzene), and C9+ aromatic hydrocarbons. Depending upon the relative market prices of the individual reaction products, it can be desirable to increase the yield of certain of the more valuable products relative to the others. Generally it is desirable to enhance the yield of ethylene, propylene and BTX.
Many zeolite catalyst modification techniques are known to enhance one characteristic or another of the catalyst, but they generally tend to cause an undesirable deterioration in other desired characteristics such as selectivity or catalyst life.
Zinc promoted zeolite catalysts for conversion of lower value hydrocarbons to higher value materials such as lower olefins and BTX are well known. Such catalysts, however, deteriorate rapidly during use due to zinc loss and coke formation. A zinc promoted catalyst resistant to zinc loss as a result of a water vapor treatment in the presence of alumina is disclosed in Japanese patent 7-29948, published Apr. 5, 1995. Such catalysts are commercially available from Asahi Chemical Industry Co. under the designation “ALPHA” catalyst.
Coke formation during zeolite catalyzed aromatization of hydrocarbons has continued to be a problem, however.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved zeolite catalyst.
It is a further object of this invention is to provide an improved process for the conversion of hydrocarbons.
It is yet a further object of this invention is to provide a zeolite catalyst which is resistant to coke formation during hydrocarbon conversion processes; and
It is still yet a further object of this invention is to provide a zeolite catalyst that gives a low coke production rate without a sacrifice in other characteristics such as catalyst life or selectivity.
In accordance with one embodiment of this invention, a promoted zeolite is produced by subjecting a zinc promoter to a high temperature water vapor treatment in the presence of alumina to produce a promoter component and thereafter silylating a zeolite/promoter component composition. In accordance with another embodiment of this invention, a promoted zeolite is produced by combining zeolite, a zinc or gallium promoter and a binder which is capable of forming a spinel with the zinc or gallium promoter, to give a zeolite/promoter/binder composition; subjecting the zeolite/promoter/binder composition to a high temperature water vapor treatment to give a zeolite/spinel promoter composition and thereafter silylating the zeolite/spinel promoter composition.
DETAILED DESCRIPTION OF THE INVENTION
Surprisingly, it has been found that silylation of certain water vapor treated metal promoted zeolites results in a catalyst which exhibits greatly reduced coke formation when used in hydrocarbon conversion processes. For instance, silylation of a zeolite having a water vapor treated zinc-alumina component gives such a catalyst. More remarkably, this reduced coking is accomplished without a sacrifice in the selectivity to desired products.
In accordance with this invention there are three methods, referred to hereinafter as method (1) method (2) and method (3) to provide the zeolite/promoter component composition to be silylated, which methods can be briefly described as follows:
(1) Mix a zeolite, a zinc promoter and alumina; and subject the resulting mixture to a high temperature water vapor treatment to give a zeolite/promoter component composition ready for silylation.
(2) Premix a zinc promoter and alumina; subject the resulting premix to a high temperature water vapor treatment to give a promoter component; and thereafter combine the promoter component with a zeolite to give a zeolite/promoter component composition ready for silylation.
(3) Mix a zeolite, a zinc or gallium promoter and a binder capable of forming a spinel with the zinc or gallium promoter; and subject the resulting mixture to a high temperature water vapor treatment to give a zeolite/spinel promoter composition ready for silylation.
Alternatively, in the practice of methods (2) and (3), a commercial spinel can be utilized as the promoter component. Zinc aluminate spinel, for instance is widely used in industry and is readily available in commercial quantities
The zeolite starting material used in the composition of the invention includes any zeolite which is effective in the conversion of non-aromatics to aromatics when contacted under suitable reaction conditions with non-aromatic hydrocarbons. Preferably, the zeolite has a constraint index (as defined in U.S. Pat. No. 4,097,367, which is incorporated herein by reference) in the range of about 0.4 to about 12, preferably about 2-9. Generally, the molar ratio of SiO
2
to Al
2
O
3
in the crystalline framework of the zeolite is at least about 5:1 and can range up to infinity. Preferably the molar ratio of SiO
2
to Al
2
O
3
in the zeolite framework is about 8:1 to about 200:1, more preferably about 40:1 to about 70:1. Preferred zeolites include ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-35, ZSM-38, and mixtures thereof ZSM-5 zeolite is also known as “MFI” or “Pentasil” zeolite. The zeolites can also be described as crystalline aluminosilicates. Suitable aluminosilicates generally have a medium pore size, generally being an effective fine porous size of 5-6.5 angstroms, although small (generally 3-5 Å) or large pore (generally 7-8 Å) zeolites can also be used. The presently preferred zeolite is ZSM-5. While currently less preferred, silicoaluminophosphate zeolites such as SAPO-11 can also be used.
The zinc or gallium promoter component can be in the form of elemental zinc or gallium, a salt, oxide or hydroxide or it can be an organic compound. Preferably the metal is zinc. Examples of suitable modifiers include zinc oxide, zinc nitrate, zinc chloride, zinc acetate, zinc oxalate, zinc acetylacetonate hydrate, zinc bromide, zinc carbonate, zinc hydroxide, zinc borate, zinc silicate, zinc aluminate, zinc chromite, zinc cyclohexanebutyrate dihydrate, zinc 2-ethylhexanoate, zinc fluoride, zinc hexafluoroacetylacetonate dihydrate, zinc iodide, zinc molybdate, zinc naphthenate, zinc perchlorate hexahydrate, zinc phosphate hydrate, zinc phosphide, zinc protoporphyrin, zinc sulfate monohydrate, zinc sulfide, zinc telluride, zinc tetrafluoroborate hydrate, zinc titanate, zinc trifluoromethanesulfonate and alklyzincs as well as corresponding compounds of gallium such as gallium oxide, gallium chloride and gallium nitrate. Currently preferred are zinc chloride and zinc nitrate. Mixtures of two or more zinc compounds, two or more gallium compounds or a mixture of one or more zinc compounds and one or more gallium compounds can also be used.
The suitable amount of zinc or gallium promoter for the present invention is generally 1-10 wt % as metal based on the total weight of the zeolite/promoter component composition, with 1-6 wt % being preferred. By total weight of the zeolite/promoter component composition is meant the calcined product containing the zeolite and the promote
Drake Charles A.
Wu An-hsiang
Dunn Tom
Phillips Petroleum Company
Scott Reece A.
Stewart Charles W.
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