Chemistry of inorganic compounds – Zeolite – Organic compound used to form zeolite
Reexamination Certificate
2001-05-07
2003-09-09
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Organic compound used to form zeolite
C423S708000, C423S709000, C585S481000, C502S064000, C502S074000
Reexamination Certificate
active
06616910
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for preparation of an EUO-structural-type zeolite that contains, after synthesis, in its intracrystalline pores, a nitrogen-containing organic cation with a chemical formula that is defined and synthesized with nuclei to obtain a zeolite that has a well-determined chemical composition of its crystalline framework. The invention also relates to the zeolite that is prepared by this process and the use of said zeolite in a process for isomerization of aromatic compounds with 8 carbon atoms that are also called “C8-aromatic fractions” in the presence of a catalyst with an EUO zeolite base that is prepared according to the process of this invention.
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. Patents U.S. Pat. Nos. 4,723,051 and 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 mixture 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 application also describes a synthesis process in which the zeolitic nuclei of the same nature or of a different nature from the EU-1 zeolite to be synthesized are introduced into the reaction mixture. 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. The synthesis of the TPZ-3 is optionally carried out in the presence of TPZ-3 zeolite nuclei. This TPZ-3 zeolite preferably has an X/T ratio of between 10 and 125.
The ZSM-50 zeolite, described in documents EP-A-0 159 845 and U.S. Pat. No. 4,640,829, is prepared by using as a structuring agent the dibenzyldimethylammonium derivative (DBDMA) that is contained in the intracrystalline pores of said zeolite (A. Thangaraj et al., Zeolites, 11, 1991).
The synthesis methods of EUO-structural-type zeolites differ essentially by the nature of the organic structuring agent and the natures of the nuclei, when the mixture contains them, as well as by the chemical composition of the mixture (X/T ratio).
Thus, an EUO zeolite that is obtained in a process of preparation that uses the DBDMA derivative is distinguished essentially, after synthesis, from the EUO zeolites that are obtained in a synthesis process with the &agr;-&ohgr; diammonium polymethylene compounds, by the nature of the cation that is present in the intracrystalline pores. It is also described 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. Sowerijns et al,
Microporoups 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, Patent 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 benzyldimethylammonium and benzyl chloride, whereby the zeolite that is obtained has a crystallinity rate that is better, the higher the Si/Al 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 process for preparation of an EUO-structural-type zeolite that is synthesized in the presence of a nitrogen-containing organic structuring agent of the dibenzyldimethylammonium (DBDMA) type and that has an X/T ratio of between 5 and 50 where X is selected from among silicon and germanium and T is selected from among aluminum, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese. The preparation of the zeolite is carried out in the presence of nuclei of at least one zeolitic material of the same structural type as the zeolite to be synthesized and, preferably, of a chemical composition of the crystalline framework that is close to that of the zeolite that is to be synthesized. The zeolite that is obtained by this process according to the invention is a new EUO-structural-type zeolite that has an Si/Al ratio of between 5 and 50, preferably between 6 and 35, more preferably between 7 and 30 and even more preferably between 7 an
Alario Fabio
Kolenda Frederic
Merlen Elisabeth
Rouleau Loïc
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Sample David
LandOfFree
Process for preparation of an EUO-structural-type zeolite,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for preparation of an EUO-structural-type zeolite,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparation of an EUO-structural-type zeolite,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3104796