Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And additional al or si containing component
Reexamination Certificate
2000-01-24
2003-01-14
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And additional al or si containing component
C502S064000, C502S074000, C502S079000
Reexamination Certificate
active
06506703
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to depositing catalyst metals into zeolite substrates to produce non-acidic, zeolite based hydrocarbon processing catalysts. More particularly, the present invention is directed to a method for loading and uniformly distributing Group VIII catalyst metals into large/medium pore zeolites via ion exchange with exchangeable cations in the zeolite to make non-acidic hydrocarbon processing catalyst. Specifically, this invention is a method for loading platinum into zeolite L, X, Y, and ZSM-5 catalysts to make non-acidic monofunctional reforming catalysts.
BACKGROUND OF THE INVENTION
Reforming is a major petroleum refining process used to raise the octane rating of naphtha streams, for blending into motor gasoline and to produce light aromatics from paraffins and naphthenes in naphtha which are then extracted and used to make chemical Intermediate products.
Reforming reactions include dehydrogenation, isomerization and dehydrocyclization, i.e., aromatization. Reforming catalysts are particularly effective in aromatizing naphthenes paraffins.
Reforming catalysts also crack paraffins to light hydrocarbons and methane. However, cracking is undesirable since it produces fuel gas which has less valued than paraffins. Cracking liquids to gases is undesirable since gas fuels are worth less than liquid fuels. Catalysts with more propensity to aromatize and less propensity to crack are said to have high selectivity.
Reforming catalysts deactivate progressively during normal operation due to deposition of coke on the catalyst and agglomeration of the noble catalytic metals dispersed in the catalyst. Periodically, the catalyst is regenerated to recover activity by burning off the accumulated coke and redispersing the catalytic metals.
Currently, the most widely used commercial reforming catalysts are comprised of a Group VIII metal, such as platinum, or platinum plus a second catalytic metal typically rhenium or iridium, dispersed on alumina. These catalysts are bifunctional, i.e., they have two types of catalyst sites: metal sites and strong acid sites.
The catalytic metal sites are one or more Group VIII metal, such as platinum. Additional metals, such as rhenium or iridium are dispersed on the alumina to enhance or modify the activity of the catalytic metal. The acid sites are typically a halogen such as chlorine which is adsorbed on to the alumina substrate. The dehydrogenation and dehydrocyclization reactions occur on the metal sites and the isomerization reactions occur on the acid sites. The undesirable reactions, cracking and coking, also occur on the acid sites.
Bifunctional catalysts aromatize C
8
paraffins very well but they do not aromatize C
6
paraffins to benzene and C
7
paraffins to toluene well. A new class of reforming catalysts has been developed which aromatizes C
6
and C
7
paraffins to aromatics with great facility, significantly better than bifunctional catalysts.
These new catalysts employ zeolites, highly structured crystalline alumina/silica materials, as the substrate for the catalyst noble metal rather than alumina, which is amorphous. These new zeolite catalysts are monofunctional as they contain few acid sites and both the dehydrocyclization and isomerization reactions are catalyzed on the noble metal sites.
Unwanted acidity is introduced into the catalyst when the catalytic metals are reduced to activate the catalyst. Acidity impairs catalyst performance and accelerates deactivation. Catalyst performance is further impaired by detrital material which is deposited in the micropores of the zeolites when it is formed into aggregates. Current loading processes deposit additional detrital matter in the catalyst.
U.S. Pat. No. 4,568,656 describes. an immersion process for loading platinum onto a Zeolite-L wherein a nonplatinum metal salt is added to the platinum containing loading solution in an amount (A) such that following the exchange of platinum from the loading solution into the Zeolite-L to cause a release of nonplatinum metal from the Zeolite-L back into the loading solution in an amount (A′), that the following conditions apply,
A
+
A
′
Z
=
0.3
A
′
X
to
1.2
A
′
X
wherein X is the amount of loading solution to fill the total pore volume of the Zeolite-L to incipient wetness and Z is the amount of loading solution used for the total immersion of the Zeolite-L. The loading process is said to reduce the number of acid sites formed in the catalyst when it undergoes activation by reduction of its platinum content.
SUMMARY OF INVENTION
The present invention is directed to methods for loading catalytic metals into zeolites.
The metal loading process of the present invention removes detrital matter. Moreover, the present process precludes or minimizes deposition of detrital matter during metal loading.
The present invention is particularly useful for loading Group VII noble metals into large pore zeolites or medium pore zeolites to make a hydrocarbon processing catalyst. Most particularly, this invention is useful for depositing platinum into zeolite L, X, Y, or ZSM-5 to make a monofunctional (non-acidic) catalyst which is effective for reforming light naphtha hydrocarbons into aromatics.
In one embodiment, the present invention is an ion exchange process for dispersing or loading catalytically active noble metals into zeolites to make hydrocarbon processing catalysts.
More specifically, the present invention is directed to an ion exchange method for loading catalyst metals into zeolites which involves maintaining a predetermined amount of non-catalytic metal exchangeable cations in the loading solution while simultaneously controlling the end point pH within a specified range.
The ion exchange method for loading catalytic metals into zeolite catalyst in accordance with the present invention results in catalyst that exhibits higher activity and selectivity than can be achieved with alternative loading procedures.
One problem with current loading processes is that they introduce unwanted acidity into the catalyst. Acidity reduces the yield and selectivity of the catalyst to desired products by promoting cracking of the feed, and accelerating deactivation by inducing coke formation on the surfaces of the catalyst.
The unwanted acidity is induced after the catalyst is charged to the process reactor during reduction of the catalyst prior to introducing the hydrocarbon feed to initiate reaction. During catalyst reduction, the noble metal cations which were ion exchanged into the zeolite during metal loading are reduced to their zero valent state by contact with hydrogen. The noble metals vacate the ion exchange sites in the zeolite which they had occupied as cations. To maintain electrical charge balance the zeolite captures hydrogen ions which are present in the background and these hydrogen ions are the undesirable acid sites. A preferred process for activating zeolite based catalysts is described in U.S. Pat. No. 4,717,700.
In the present invention, unwanted acidity in the catalyst is avoided by formulating the loading solution so that non-noble metal cations are added to the catalyst in addition to the noble metals. The non-noble metal cations are added as a salt admixed into the catalyst. When the noble metal cations are reduced, these excess non-noble metal cations dissociate from their salt and occupy the zeolite ion exchange sites vacated by the noble metals. Thus, unwanted acidity in the catalyst is precluded or minimized. A reasonable excess of non-noble metal cations over the amount of ion exchange sites is required to ensure exclusion of hydrogen ions. However, too large an excess of non-noble metal cation salt is to be avoided because salts clog the zeolite passages and interfere with diffusion of reactants and products to and from the active catalytic sites thus impairing catalytic activity.
Another problem with current loading procedures is that they do not remove detrital material, e.g., amorphous alumina and silica, in the catalyst deposited w
Clem Kenneth Ray
Fung Shun Chong
Kao Jar-Lin
Vanderspurt Thomas Henry
Exxon Mobil Chemical Patents Inc.
Ildebrando Christina
Silverman Stanley S.
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