Chemistry of inorganic compounds – Zeolite – Organic compound used to form zeolite
Reexamination Certificate
2001-05-07
2004-04-20
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Organic compound used to form zeolite
C423SDIG003, C502S060000
Reexamination Certificate
active
06723301
ABSTRACT:
TECHNICAL FIELD
This invention relates to a new EUO-structural-type zeolite that has a specific chemical composition of its crystalline framework and a specific nitrogen ratio. The invention also relates to the use of the zeolite as a catalyst in the main processes for transformation of hydrocarbons that uses the refining of petroleum and petrochemistry. It is used in particular in the processes for isomerization of aromatic compounds with 8 carbon atoms that are also called “C8-aromatic fractions.”
PRIOR ART
The isomerization of xylenes of ethylbenzene or a mixture of xylenes and ethylbenzene requires the presence of an acid function and a metal of group VIII. The main purpose of the isomerization of the C8-aromatic fractions is to produce the paraxylene that is the most desired isomer because of its application particularly in the textile industry. The isomerization reaction of the C8-aromatic compounds leads to parasitic reactions that result from the opening of naphthene rings that may or may not be followed by cracking or else reactions of dismutation and/or transalkylation of the C8 aromatic compounds that generate undesirable aromatic compounds.
Catalysts for isomerization of aromatic compounds with 8 carbon atoms were already described. U.S. Pat. No. 4,723,051 and U.S. Pat. No. 4,665,258 describe, for example, optimized formulations with a mordenite zeolite base and a metal of group VIII, but they result in catalysts with which the parasitic reactions are non-negligible. These catalysts lack selectivity of paraxylene in favor of the above-mentioned parasitic reactions that constitute net losses for the desired isomerization reaction.
Other works have shown that the EUO-structural-type zeolites have improved catalytic performance levels, in particular in terms of activity, when said zeolites are used as a catalyst in the isomerization reactions of C8-aromatic fractions. In particular, European Patent Application EP-A-0 923 987 of the applicant relates to catalysts that are prepared with an EUO-structural-type zeolite that has good dispersion and good mechanical resistance of the metal of group VIII and that provide good selectivities.
The EUO-structural-type zeolites are described in the prior art (W. M. Meier and D. H. Olson, “Atlas of Zeolites Structure Types,” 4th Edition, 1996) and have a monodimensional microporous network, whose diameter of the pores is 4.1×5.7 Å (1 Å=1 angstrom=1.10
−10
m) N. A. Briscoe et al. taught that these monodimensional channels have lateral pockets with a depth of 8.1 Å and a diameter of 6.8×5.8 Å (zeolites, 8, 74, 1988).
The EUO-structural-type zeolites comprise the EU-1 zeolite, the TPZ-3 zeolite, and the ZSM-50 zeolite and generally have the following formula in anhydrous form: 0-100 XO
2
: 0-10 T
2
O
3
: 0-20 R
2
O: where R represents a cation of valence n, X represents silicon and/or germanium, T represents at least one element that is selected from among aluminum, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese.
In general, the methods for preparation of EUO-structural-type zeolites comprise the mixing in aqueous medium of a source of an element X, a source of an element T, a source of an alkaline metal and a nitrogen-containing organic compound that acts as a structuring agent.
The EU-1 zeolite, described in European Patent Application EP-A-0 042 226, is prepared by using as a structuring agent either the alkylated derivative of an &agr;-&ohgr; diammonium polymethylene or a degradation product of said derivative or else precursors of said derivative, whereby the structuring agent is found after synthesis in the intracrystalline pores of said zeolite (A. Moini et al, Zeolites, 14, 1994). This EU-1 zeolite preferably has an X/T ratio of between 5 and 75.
The TPZ-3 zeolite, described in European Patent Application EP-A-0 051 318, is prepared by using the same structuring agent family as the one that is employed for synthesizing the EU-1 zeolite. In particular, the use of the compound 1,6-N,N,N,N′,N′,N′-hexamethylhexamethylene diammonium is described. This TPZ-3 zeolite preferably has an X/T ratio of between 10 and 125.
The synthesis processes that use an alkylated derivative of an &agr;-&ohgr; ammonium polymethylene as a nitrogen-containing organic compound result in obtaining zeolites, after synthesis, that generally have an N/Si ratio that is greater than 0.07.
The ZSM-50 zeolite, described in documents EP 0 159 845 and U.S. Pat. No. 4,640,829, is prepared by using as a structuring agent the dibenzyldimethylammonium derivative (DBDMA), which is contained in the intracrystalline pores of said zeolite (A. Thangaraj et al., Zeolites, 11, 1991). This zeolite has an X/T ratio that is greater than 50.
The EUO-structural-type zeolites differ essentially by the nature of the nitrogen-containing organic structuring agent that is present in the solid, after synthesis, and therefore by their respective N/T ratio.
Thus, an EUO zeolite that is obtained with the DBDMA derivative is distinguished essentially, after synthesis, from the EUO zeolites that are synthesized with the &agr;-&ohgr; diammonium polymethylene compounds, by the nature of the cation that is present in the intracrystalline pores. It is also known in the literature that the structure of an EUO zeolite, obtained with DBDMA, differs from that of an EUO zeolite that is obtained with the &agr;-&ohgr; diammonium polymethylene compounds by the arrangement of aluminum atoms within the crystalline network (W. Souverijns et al., Microporous Materials, 4, 123-130, 1995).
Whereas the family of structuring agents used for synthesizing the EU-1 and TPZ-3 zeolites seems to promote obtaining zeolites with a low Si/Al ratio, structuring agents such as the DBDMA promote obtaining zeolites with a high Si/Al ratio. Thus, U.S. Pat. No. 4,640,829 describes a method for preparation of a zeolite that has an Si/Al ratio that is greater than 125 and teaches that DBDMA is particularly effective for promoting nucleation and the growth of crystals of ZSM-50 zeolites that have a high Si/Al ratio. It is also reported that with an Si/Al ratio that is less than 125, the product that is obtained for the most part does not contain the ZSM-50 zeolite. Likewise, Rao et al. (Zeolites, 9, 483-490, 1989) described the synthesis of an EUO-structural-type zeolite with a mixture of benzyldimethylamine and benzyl chloride, precursors of dibenzyldimethylammonium chloride, whereby the zeolite that is obtained has a crystallinity rate that is better, the higher the SiAl ratio. Rao further teaches that for numerous catalytic applications, it is preferable to use zeolites that have a high Si/Al ratio.
SUMMARY OF THE INVENTION
This invention is based on the discovery of a new EUO-structural-type zeolite that comprises at least one element X that is selected from among silicon and germanium and at least one element T that is selected from among aluminum, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese. The zeolite of the invention is characterized in that it has an X/T ratio of between 5 and 50, preferably between 6 and 35, more preferably between 7 and 30, and even more preferably between 7 and 26 and in that it has an N/X ratio of between 0.010 and 0.065. The zeolite according to the invention is a new EUO-structural-type zeolite. It is differentiated from EU-1 and TPZ-3 zeolites in that it has, after synthesis, a lower N/X ratio, and it is differentiated from the ZSM-50 zeolite by its low X/T ratio. The invention also relates to the use of said zeolite as an element of a catalyst that is used in the processes for transformation of hydrocarbons and in particular in the processes for isomerization of C8-aromatic compounds.
ADVANTAGE OF THE INVENTION
The EUO-structural-type zeolite according to the invention that has low X/T and N/X ratios and that is used subsequently as a catalyst, combined with at least one binder, at least one metal
Alario Fabio
Kolenda Frederic
Merlen Elisabeth
Rouleau Loïc
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Sample David
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