Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By ring formation from nonring moiety – e.g. – aromatization,...
Reexamination Certificate
2001-06-01
2002-10-29
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By ring formation from nonring moiety, e.g., aromatization,...
C585S410000
Reexamination Certificate
active
06472576
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to the production of dimethylnapthalene. In particular, it relates to a process for preparing 2,6-dimethylnapthalene by dehydrogenation and cyclization of 1-(p-tolyl)-2-methylbutane or 1-(p-tolyl)-2-methylbutene) in the presence of a catalyst.
2. Description of Related Art
2,6-dimethylnapthalene (in the following also abbreviated “2,6-DMN”) is a desirable raw material required for the production of 2,6-naphthalene dicarboxylic acid. Said carboxylic acid can be obtained by oxidation using known oxidation processes (see for example U.S. Pat. No. 5,183,933, Harper et al.). 2,6-naphthalene dicarboxylic acid is an important intermediate in the manufacture of speciality polymers, such as poly(ethylene naphthalate) (PEN) and liquid crystal polymers. The cost of PEN depends strongly on the price of 2,6-naphthalene dicarboxylic acid and, thus, on the price of its raw material 2,6-DMN. Therefore, for the economics of the process, it is essential that 2,6-DMN of high purity and good quality is selectively produced with an inexpensive process.
At present, 2,6-DMN is prepared by a multistep synthesis which starts by alkylation of o-, m- or p-xylene with 1- or 2-butene or, preferably, butadiene to yield 5-(o-, m-, or p-tolyl)-pent-1 (or -2-)-ane or -ene, which is subsequently converted to 1,5-, 1,6-, 2,5- or 2,6- dimethyltetralin. The tetralins are dehydrogenated to the corresponding dimethylnaphthalenes, and isomerized to yield 2,6-dimethylnapthalene (2,6-DMN). This prior art is discussed by Sikkenga et al. who disclose multi-step liquid phase syntheses for the cyclisation of specific alkenyl benzenes to one or more specific dimethyl tetralins in the presence of suitable solid acid cyclisation catalysts, such as acidic crystalline zeolites, followed by dehydrogenation to corresponding dimethylnapthalene(s) and isomerization of the resulting dimethylnaphthalenes to the desired specific dimethylnapthalene (cf. U.S. Pat. Nos. 5,073,670, 5,401,892, 5,118,892, 5,012,024 and 5,030,781 and Published PCT Application WO 89/12 612.
A problem associated with most of the prior art methods is the utilisation of l-(o-, m-, or p-tolyl) pent-1-or-2-ene type straight-chained alkenylated compounds as a starting material, which results in the use of an acidic cyclisation catalyst. Consequently, after dehydrogenation the product stream contains several dimethylnaphthalenes, and a subsequent step of isomerisation and/or separation is required. It has therefore been highly desired to improve the selectivity of the cyclisation step in the aforesaid multistep processes, and even more desirable also to decrease the number of necessary process steps in order to achieve a more economic performance.
To that end, EP 0 430 714 B1 (Mitsubishi Gas Chemicals) suggests a process for producing 2,6-dimethylnapthalene by subjecting 2-methyl-1-(p-tolyl)-butene, 2-methyl-1-(p-tolyl)-butane or a mixture of thereof to cyclization and dehydrogenation in the presence of (a) a catalyst comprising lead oxide and/or indium oxide and aluminum oxide; (b) a catalyst comprising lead oxide and/or indium oxide, aluminum oxide and alkali metal oxide and/or alkaline earth metal oxide; (c) a catalyst comprising lead oxide and/or indium oxide, aluminum oxide and at least one oxide of the metals: iron, tin antimony, chromium, zinc, vanadium, nickel or cobalt; or (d) a catalyst comprising lead oxide and/or indium oxide, aluminum oxide, an oxide of iron, tin antimony, chromium, zinc, vanadium, nickel and/or cobalt and an oxide of alkali metal and/or alkaline earth metal. A later patent, EP 0 546 266 B1, discloses the use of a catalyst comprising a platinum component and at least one component selected from alkali metals or alkaline earth metals and supported on alumina. Finally , EP 0 557 722 B1 discloses the use of a catalyst which comprises palladium, alkali metal compound and aluminum oxide. In the catalyst, 0.05-20 wt-% of palladium together with 0.1-20 wt-% of alkali metal is supported on alumina, and the catalyst is used in cyclisation dehydrogenation reaction at 350-700 ° C. in the presence of a solvent/diluent such as toluene, benzene, steam or the like to suppress side reactions such as polymerisation.
Although the selectivity of the process has been somewhat increased by the art suggested in above-mentioned patents, further improvement is still required. There is also a need for an inexpensive process which provides for easy separation of by-products. In particular the formation of alkyl-substituted indanes and indenes should be minimized.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for manufacturing 2,6-DMN with improved yield and selectivity by cyclisation of an alkenylbenzene (alkyl-benzene), 1-(p-tolyl)-2-methylbutene (1-(p-tolyl)-2-methylbutane).
It is a second object of the present invention to provide a novel catalyst which is suitable for use in, e.g., dehydrocyclisation reactions.
It is a third object of the present invention to provide a new use of activated carbon.
These and other objects, together with the advantages thereof over known processes, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed.
The present invention is based on the finding that a key feature in selectivity enhancement of dehydrocyclisation reactions is the composition of the heterogeneous catalyst. By neutralisation of acid sites present on supports of catalysts for dehydrocyclisation it becomes possible to suppress unwanted cracking reactions as well as undesired acid catalysed condensation reactions. Surprisingly, it has further been found that high activity and good selectivity is obtained with inexpensive catalysts consisting essentially of activated carbon. Thus, such materials which traditionally have been used as supports for noble metal catalyst have turned out to possess high activity for dehydrocyclisation as such (without any catalytically active metal species). The activity of the activated carbon is further increased when it is neutralized or otherwise modified so as to produce non-acidic carbon. When a noble metal is deposited on such a support a non-acidic noble metal catalyst is obtained on which the reaction proceeds only on the metallic sites.
The present invention also provides a novel kind of catalyst comprising chromium deposited on an active carbon support. This catalyst is useful for dehydrocyclisation reactions.
The present invention provides considerable advantages. Thus, the selectivity is improved compared to that of bifunctional systems, wherein two types of active sites, the metallic and acidic, operate simultaneously offering diverse reaction routes. Activated carbon is an inexpensive catalyst that is readily available. Furthermore, it has been found that advantageous results are obtained by employing a highly dispersed catalyst for ring closure in dehydrocyclisation. Monofunctional non-acidic well-dispersed noble metal catalysts are therefore suitable for dehydrocyclisation of a specific methyl-alkenylbenzene, such as 1-(p-tolyl)-2-methylbutene, to form 2,6-DMN in one step.
The present process provides for easy separation of by-products and the formation of alkyl-substituted indanes and indenes is minimized.
DETAILED DESCRIPTION OF THE INVENTION
The present invention primarily relates to an improved method for manufacturing 2,6-DMN in one step instead of by a multistep synthesis, that is, to convert alkenylbenzene (alkylbenzene), 1-(p-tolyl)-2-methylbutene (1-(p-tolyl)-2-methylbutane) by dehydrocyclisation to 2,6-DMN. The catalysts described herein can, however, also be employed in conventional multistep-synthesis methods, although that application is not particularly preferred.
The present one-step reaction is carried out in the presence of a solid dehydrocyclisation catalyst comprising an essentially neutral support at an elevated temperature and ambient pressure in gaseous phase using a gas mixture as a car
Bergström Christer
Niemelä Marita
Cohen & Pontani, Lieberman & Pavane
Dang Thuan D.
Optatech Corporation
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