Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By alkyl or aryl transfer between molecules – e.g.,...
Reexamination Certificate
2000-06-27
2002-05-14
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By alkyl or aryl transfer between molecules, e.g.,...
C585S470000, C585S471000
Reexamination Certificate
active
06388158
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of 2,6-dimethylnaphthalene comprising reacting a naphthalene substrate with at least one aromatic hydrocarbon in the presence of a zeolitic catalyst, wherein the naphthalene substrate consists of a cut which, obtained by subjecting suitable petrochemical streams to fractionation, is treated with a bed consisting of a solid acid, before being fed to the synthesis of 2,6-dimethylnaphthalene.
2,6-dimethylnaphthalene is an intermediate for the preparation of 2,6-naphthalenedicarboxylic acid, used for obtaining PEN, polyethylenenaphthalene, a polymeric material much better than PET, polyethyleneterephthalate, for various applications.
DESCRIPTION OF THE RELATED ART
Industrial processes for obtaining 2,6-dimethylnaphthalene are based on its recovery from fractions coming from the reforming of kerosene (JP338535—Nippon Mining; U.S. Pat. No. 963,248—Nippon Mining; JP02247136—Nippon Mining; JP02247137—Nippon Mining; JP02304034—Mitsubishi Oil), or from fractions of FCC oil (Chemical Week, Apr. 11, 1992, page 39; Chemical Marketing Reporter, Dec. 10, 1992; European Chemical News, Sep. 28, 1992, page 30; Chemical Week, Jun. 24, 1992, page 27). In the former case, the dimethylnaphthalenes must be separated by distillation and then the 2,6 isomer is isolated by means of selective absorptions and/or crystallizations. In the latter case, there is an additional problem due to the presence of nitrogen and sulfur which poison the catalysts used for the separation and/or isomerization phases.
There is a synthesis process (U.S. Pat. Nos. 4,990,717; 5,118,892; 5,073,670; 5,030,781; 5,012,024), which, by means of alkenylation, cyclization, dehydrogenation, isomerization steps, results in the selective synthesis of 2,6-dimethylnaphthalene, the first step starting from o-xylene and 1,3-butadiene. Alkylation on the part of butadiene on one of the methyl groups of o-xylene, takes place in the presence of a basic catalyst, with the formation of 5-(o-tolyl)2-pentene. The latter is separated and, in the presence of a zeolitic catalyst (Y-type) containing Pt and Cu, is subjected to an internal cyclization reaction. In this way 1,5-dimethyltetraline is formed, which is subsequently dehydrogenated with the help of a Pt/Re catalyst supported on alumina. This is followed by a separation phase to isolate the 1-5-dimethylnaphthalene, which is then isomerized to 2,6 with another zeolitic catalyst.
As can be seen, there are various passages in this synthesis method. This represents a problem from an economic point of view. In addition there are secondary reactions with every passage (chemical reaction) and consequently separations are necessary to guarantee the purity of the intermediates or end-product. The use of a basic catalyst containing Na and K as such or supported, in this particular process, creates handling and safety problems.
The patent U.S. Pat. No. 5,043,501 relates to a synthesis method of 2,6-dimethylnaphthalene in two steps only. The first step comprises the alkylation of an alkylaromatic with a C
5
olefin in the presence of a zeolitic catalyst (MCM22). The alkylated product is then dehydrocyclized at 400-500° C. with a catalyst consisting of Pt/Ba/K on L zeolite, obtaining a product containing dimethylnaphthalenes which are then isomerized mainly to 2,6; also in this case there are the problems mentioned above.
Another precursor of 2,6-naphthalenedicarboxylic acid (NDC) is 2,6-di-isopropylnaphthalene. The industrial preparation of this intermediate is described in patents U.S. Pat. Nos. 5,003,120; 5,003,122; 5,026,492. A disadvantage of this process is that the oxidation to carboxylic group of the isopropyl function is more expensive than that of the methyl function.
It is evident, however, that the greatest obstacle in the wide-scale use of PEN lies in the cost of the monomer, 2,6-naphthalene dicarboxylic acid (NDC) (2,6-Naphthalene Dicarboxylic Acid Precursors, May 1993, Chem Systems; High Performance Polyesters, November 1996, Chem Systems; H. P. Muhs, Polyesters Technologies for Fibres & Packaging, De Witt Petrochemical Review, 1997; J. Caldwell, PEN Outlook & Review, De Witt Petrochemical Review, 1998). It is therefore understandable how important it is, regardless of the preparation procedure followed, to be able to intervene in one or more steps of these procedures to obtain a simple and inexpensive selective synthesis of 2,6-dimethylnaphthalene.
The same Applicant, in co-pending Italian patent application MI98A000809 filed on Apr. 17, 1998, described a process for the preparation of 2,6-dimethylnaphthalene starting from naphthalene, methylnaphthalenes, dimethylnaphthalenes, trimethylnaphthalenes and/or polymethylnaphthalenes carried out under at least partially liquid phase conditions and in the presence of suitable aromatic hydrocarbons, catalyzed by a zeolite of the MTW structural type (abbreviation IZA), which allows the selective synthesis of 2,6-dimethylnaphthalene in a single step.
MTW zeolites in particular, when used under the process conditions of this patent application, are more active than the zeolites used according to the conditions described in the known art, especially with respect to BEA and MFI zeolites considered by the known art as being the best catalysts for the preparation of 2,6-dimethylnaphthalene.
BRIEF SUMMARY OF THE INVENTION
The Applicant has now found, and this is an object of the present invention, that it is possible to effect these syntheses, again regardless of the particular procedure followed, using a feeding stream which can be obtained simply and at very competitive costs.
The present invention, in fact, relates to the use, in the synthesis of 2,6-dimethylnaphthalene, of a naphthalene cut obtained by the fractionation of petrochemical streams and the subsequent acid treatment of the product thus obtained.
The present invention relates in particular to a process for the preparation of 2,6-dimethylnaphthalene which comprises reacting, with at least one aromatic hydrocarbon, a mixture of naphthalenes comprising a cut obtained by the fractionation of suitable petrochemical streams and the subsequent treatment of the product thus obtained with a solid acid.
Significant and relatively “clean” quantities of naphthalenes are contained in fractions such as FOK (Fuel Oil Cracking), LCO (Light Cicle Oil) and heavy fractions from catalytic reforming which are not widely exploited at the moment (for example FOK is used as fuel in certain cases). These form an economic source of naphthalenes which can be separated by distillation. For this purpose FOK or LCO petrochemical streams are subjected to fractionation to obtain the specific cut, which contains at least 20% of useful naphthalenes (mainly naphthalene and methylnaphthalenes). During this fractionation, which is carried out using conventional distillation methods, other components are inevitably separated together with the useful naphthalenes. These distill together with the useful naphthalenes because their boiling points fall within the temperature range corresponding to the separation of the cut in question.
Using this cut as naphthalene source for the synthesis of 2,6-dimethylnaphthalene, we have found that, operating according to the object of the present invention, the life of the catalyst can be considerably increased when the feeding to the synthesis of 2,6-dimethylnaphthalene is treated on a pre-bed consisting of solid acid.
DETAILED DESCRIPTION OF THE INVENTION
The present invention therefore relates to an improved process for the preparation of 2,6-dimethylnaphthalene comprising the following steps:
fractionation of a petrochemical stream selected from FOK and LCO;
treatment of the naphthalene cut thus obtained with an acid catalyst;
sending the product thus obtained for reaction with the desired aromatic hydrocarbon in the presence of a catalyst of a zeolitic nature.
Mention has been made of the meaning of the FOK and LCO fractions. As specified, these are subjected to fractionation according to the conventional
Mansani Riccardo
Pazzuconi Giannino
Perego Carlo
Enichem S.p.A.
Griffin Walter D.
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