Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And additional al or si containing component
Reexamination Certificate
1999-06-07
2003-09-02
Dunn, Tom (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And additional al or si containing component
C502S065000, C502S066000, C502S062000, C502S063000, C502S073000, C502S074000, C502S085000
Reexamination Certificate
active
06613708
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for modifying zeolite catalysts and catalysts so modified, and more particularly relates, in one embodiment, to methods for modifying zeolite catalysts to make them more selective to the synthesis of para-substituted dialkylbenzenes relative to other dialkylbenzene isomers, as well as useful in other reactions, and catalysts so modified.
BACKGROUND OF THE INVENTION
Of the para-substituted dialkylbenzenes, para-xylene (PX) is of particular value as a large volume chemical intermediate in a number of applications being useful in the manufacture of terephthalates which are intermediates for the manufacture of polyethylene terephthalate (PET). One source of feedstocks for manufacturing PX is by disproportionation of toluene into xylenes. One of the disadvantages of this process is that large quantities of benzene are also produced. Another source of feedstocks used to obtain PX involves the isomerization of a feedstream that contains non-equilibrium quantities of mixed ortho- and meta-xylene isomers (OX and MX, respectively) and is lean with respect to PX content. A disadvantage of this process is that the separation of the PX from the other isomers is expensive.
Zeolites are known to catalyze the reaction of toluene with other reactants to make xylenes. Some zeolites are silicate based materials which are comprised of a silica lattice and, optionally, alumina combined with exchangeable cations such as alkali or alkaline earth metal ions. Although the term “zeolites” includes materials containing silica and optionally alumina, it is recognized that the silica and alumina portions may be replaced in whole or in part with other oxides. For example, germanium oxide, tin oxide, phosphorus oxide, and mixtures thereof can replace the silica portion. Boron oxide, iron oxide, gallium oxide, indium oxide, and mixtures thereof can replace the alumina portion. Accordingly, the terms “zeolite”, “zeolites” and “zeolite material”, as used therein, shall mean not only materials containing silicon and, optionally, aluminum atoms in the crystalline lattice structure thereof, but also materials which contain suitable replacement atoms for such silicon and aluminum, such as gallosilicates, borosilicates, ferrosilicates, and the like.
The term “zeolite, “zeolites”, and “zeolite materials” as used herein, besides encompassing the materials discussed above, shall also include aluminophosphate-based materials. Aluminophosphate zeolites are made of alternating AlO
4
and PO
4
tetrahedra. Aluminophosphate-based materials have lower acidity compared to aluminosilicates. The lower acidity eliminates many side reactions, raises reactants' utilization, and extends catalyst life. Aluminophosphate-based zeolites are often abbreviated as ALPO. Substitution of silicon for P and/or a P—Al pair produces silicoaluminophosphate zeolites, abbreviated as SAPO.
Processes have been proposed for the production of xylenes by the methylation of toluene using a zeolite catalyst. For instance, U.S. Pat. No. 3,965,207 involves the methylation of toluene using a zeolite catalyst such as a ZSM-5. U.S. Pat. No. 4,670,616 involves the production of xylenes by the methylation of toluene with methanol using a borosilicate zeolite which is bound by a binder such as alumina, silica, or alumina-silica. One of the disadvantages of such processes is that catalysts deactivate rapidly due to build up of carbonaceous material and heavy by-products. Another disadvantage is that methanol selectivity to para-xylene, the desirable product, has been low, in the range of 50 to 60%. The balance is wasted on the production of coke and other undesirable compounds.
It has been further demonstrated that alkylaromatic compounds can be synthesized by reacting an aromatic compound such as toluene with a mixture of carbon dioxide (CO
2
), and carbon monoxide (CO) and hydrogen (H
2
) (synthesis gas) at alkylation conditions in the presence of a catalyst system, which comprises (1) a composite of oxides of zinc, copper, chromium, and/or cadmium; and (2) an aluminosilicate material, either crystalline or amorphous, such as zeolites or clays; as disclosed in U.S. Pat. Nos. 4,487,984 and 4,665,238. Such catalyst systems, however, are not capable of producing greater than equilibrium concentrations of para-xylene (PX) in the xylene-fraction product. Typically, the xylene-fraction product contains a mixture of xylene isomers at or near the equilibrium concentration, i.e., 24% PX, 54% MX, and 22% OX. The lack of para-xylene selectivity in alkylation of toluene with syngas can be caused by (1) the acidic sites on the surface outside the zeolite channels, and/or (2) the channel structure not being able to differentiate para-xylene from its isomers. It would be desirable for the toluene alkylation to be more para-selective due to the much higher value of PX compared to that of MX and OX. Furthermore, such processes suffer from catalyst deactivation as well. In addition, the prior art disclosed neither syngas alkylation to alkyl aromatic compounds nor syngas selective alkylation to high purity PX using aluminophosphate-based materials.
It has been recognized that certain zeolites can be modified to enhance their molecular-sieving or shape-selective capability. Such, modification treatments are usually called zeolite selectivation. Selectivated zeolites can more accurately differentiate molecules on the basis of molecular dimension or steric characteristics than the unselectivated precursors. For example, silanized ZSM-5 zeolites adsorbed PX much more preferentially over MX than untreated ZSM-5. It is believed that the deposition of silicon oxide onto zeolite surfaces from the silanization treatment has (1) passivated the active sites on the external surface of zeolite crystals, and (2) narrowed zeolitic pores to facilitate the passage of the smaller PX molecules and prevent the bigger MX and OX molecules from entering or exiting the pores. In this application, the term “para-alkyl selectivation” refers to modifying a catalyst or catalytic reaction system so that it preferentially forms more para-substituted dialkylbenzenes than the expected equilibrium proportions relative to the other isomers.
Zeolite selectivation can be accomplished using many techniques. Reports of using compounds of silicon, phosphorous, boron, antimony, coke, magnesium, etc. for selectivation have been documented. Unfortunately many, if not most of the zeolites used in the prior art have undesirably short active lifetimes before they deactivate and have to be reactivated or replaced.
There remains a need for still further improved processes for catalytic PX synthesis which minimizes or avoids the disadvantages of prior systems, which include low PX selectivity, low methanol selectivity, rapid catalyst deactivation, and the like.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for producing a modified catalyst capable of being more selective to para-substituted dialkyl benzenes in the synthesis of dialkylbenzenes.
Accordingly, it is another object of the present invention to provide a modified catalyst useful in a method for synthesizing para-substituted dialkyl benzenes in high product concentration via alkylation of toluene and/or benzene with a mixture of gases including H
2
, and CO and/or CO
2
and/or methanol.
In carrying out these and other objects of the invention, there is provided, in one form, a method for modifying catalysts involving contacting first component, such as crystalline or amorphous aluminosilicates, substituted aluminosilicates, substituted silicates, crystalline or amorphous aluminophosphates, zeolite-bound zeolites, substituted aluminophosphates, and mixtures thereof with an agent which may be compounds of elements selected from Groups 1 through 16, and mixtures thereof.
DETAILED DESCRIPTION OF THE INVENTION
It has been discovered that catalysts, particularly zeolite catalysts, may be modified using organometallic compounds in such a way to enhance selectivity t
Guan Lili
Long Xiangyun
Ou John D. Y.
Xie Youchang
Yang Xiawan
ExxonMobil Chemical Patents Inc.
Ildebrando Christina
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