Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By ring formation from nonring moiety – e.g. – aromatization,...
Reexamination Certificate
2000-02-14
2003-01-07
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By ring formation from nonring moiety, e.g., aromatization,...
C585S400000, C585S411000
Reexamination Certificate
active
06504069
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing dimethyltetralin useful as a raw material of naphthalenedicarboxylic acid used for producing plastics such as polyesters.
Dimethyltetralin is converted to dimethylnaphthalene by dehydrogenation. Therefore, dimethyltetralin is a very important compound useful as a raw material of naphthalenedicarboxylic acid which is used for the production of plastics such as polyesters. For instance, polyethylene 2,6-naphthalate produced from 2,6-naphthalenedicarboxylic acid and ethylene glycol is suitably used for the production of films or fibers having more excellent heat resistance and mechanical properties than those of polyethylene terephthalate. Naphthalenedicarboxylic acid used as a raw material of plastics has been required to be isomerically highly pure. Therefore, dimethylnaphthalene used as a raw material of naphthalenedicarboxylic acid is also required to be isomerically highly pure. More specifically, the dimethylnaphthalene includes ten isomers, i.e., 1,2-1,3-, 1,4-, 1,5-, 1,6-, 1,7-, 1,8-, 2,3-, 2,6- and 2,7-isomers, according to the positions of two methyl groups. If an isomer is to be used as a raw material of naphthalenedicarboxylic acid, it is required to be isomerically highly pure, i.e., required to be free from the other isomers.
Dimethylnaphthalene is obtained by separation of high-boiling fractions from petroleum refining, separation of coal tars, alkylation of naphthalene, reaction of alkyl benzene and olefin, etc.
Since dimethylnaphthalene contained in high-boiling fractions from petroleum refining or coal tars is a mixture of isomers, an isomerization step or a complicated isomer-separating step is required to separate a desired single isomer of dimethylnaphthalene from the isomeric mixture. Based on easiness of interconversion between isomers, 10 isomers of dimethylnaphthalene (hereinafter may be referred to as “DMN”) are classified into the following four groups. Although the isomers are relatively easily isomerized to another in the same group, isomerization between different groups is difficult to take place. Further, in addition to the great difficulty in separating an aimed dimethylnaphthalene isomer from the other isomers, it is very difficult to separate and recover the aimed isomer in a high purity from the high-boiling fractions from petroleum refining and coal tars, because the fractions and coal tars actually contain many components other than dimethylnaphthalene isomers,
Group A: 1,5-DMN, 1.6-DMN and 2,6-DMN
Group B: 1,7-DMN, 1.8-DMN and 2,7-DMN
Group C: 1,3-DMN, 2,3-DMN and 1,4-DMN
Group D: 1,2-DMN
Alkylation of naphthalene is performed usually in the presence of a solid acid catalyst such as zeolite and silica alumina. In this method, monomethylnaphthalene, trimethylnaphthalene, etc. are by-produced with dimethylnaphthalene, and therefore, the selectivity to dimethylnaphthalene is not so high. In addition, the resultant dimethylnaphthalene is a mixture of many isomers. Thus, like the separation of high-boiling fractions from petroleum refining and the separation of coal tars, the alkylation of naphthalene fails to produce a specific dimethylnaphthalene isomer in a high yield.
To remedy the above problems, there have been proposed methods of producing a specific dimethylnaphthalene isomer from alkyl benzene and olefin via multiple steps. For instance, Japanese Patent Application Laid-Open No.
2-96540
discloses a method of producing 2,6-dimethylnaphthalene from m-xylene, propylene and carbon monoxide. U.S. Pat. No. 5,008,479 discloses a method of producing 2,6-dimethylnaphthalene from toluene, butene and carbon monoxide.
Japanese Patent Application Laid-Open No. 49-134634 discloses a method of producing 5-(o-tolyl)-pent-2-ene from o-xylene and butadiene; Japanese Patent Application Laid-Open No. 50-89353 discloses a method of producing 1,5-dimethyltetralin by cyclizing 5-(o-tolyl)-pent-2-ene; and Japanese Patent Application Laid-Open No. 48-67261 discloses a method of producing 1,5-dimethylnaphthalene by dehydrogenating 1,5-dimethyltetralin. By combining these teachings, isomerically highly pure 1,5-dimethylnaphthalene can be obtained from o-xylene and butadiene.
Japanese Patent Application Laid-Open No. 1-503389 discloses a method of isomerizing 1,5-dimethylnaphthalene to obtain a mixture of 1,5-dimethylnaphthalene, 1,6-dimethylnaphthalene and 2,6-dimethylnaphthalene, and then separating highly pure 2,6-dimethylnaphthalene by crystallization from the mixture. The proposed method utilizes the isomerization and crystallization between the three dimethylnaphthalene isomers belonging to the same isomerization group mentioned above, and therefore, can be carried out more advantageously as compared to the isomerization and crystallization between isomers belonging to different groups. Many studies have been made on the development of industrial production methods of 2,6-dimethylnaphthalene, because it is the most notable isomer as a raw material for 2,6-naphthalenedicarboxylic acid.
A method of producing dimethylnaphthalene from xylene and butadiene comprises a step of alkenylating one of two methyl groups of xylene to obtain 5-tolyl-pent-2-ene, a step of cyclizing 5-tolyl-pent-2-ene to obtain dimethyltetralin, a step of dehydrogenating dimethyltetralin to obtain dimethylnaphthalene, a step of isomerizing dimethylnaphthalene, and a step of crystallizing followed by separation.
Regarding the production of dimethyltetralin by cyclization of 5-(oolyl)-pent-2-ene, Japanese Patent Application Laid-Open No.
49-93348
proposes to carry out the cyclization at 180 to 350° C. in liquid phase using a solid phosphoric acid.
Japanese Patent Application Laid-Open No. 3-500052 teaches that a cyclization at 120 to 250° C. in liquid phase in the presence of a catalyst such as a platinum- or copper-modified ultra-stabilized Y-type zeolite (USY) produces dimethyltetralin in a yield of 95% or more. It also discloses, as preferred solvents optionally used, a solvent having a boiling point of about 270° C. or higher, exemplified by paraffin such as tetradecane, aromatic hydrocarbon such as anthracene and a mixture thereof.
Japanese Patent Application Laid-Open No. 6-56709 discloses that dimethyltetralin can be obtained in a high yield by vapor-phase cyclization at 100 to 400° C. using a catalyst comprising mordenite and silica to completely prevent the dimerization of 5-tolyl-pent-2-ene. However, the vapor-phase cyclization requires several considerations in achieving a sufficiently high reaction temperature, using a considerably large amount of diluent, reducing reaction pressure, etc.
Japanese Patent Publication No. 49-11385 teaches that dimethyltetralin can be obtained in a high yield by carrying out the cyclization at lower temperatures in the absence of solvent using a cation exchange resin as a catalyst. However, since the catalyst is effective only up to 150° C., the working temperature range of the catalyst is limited to narrow range. In addition, since cation exchange resins are generally expensive, the proposed method is costly disadvantageous for industrial use.
As described above, dimethyltetralin can be produced by cyclizing 5-tolyl-pent-2-ene which is obtained by alkenylating a side chain of xylene with butadiene, and then dehydrogenating the resultant dimethyltetralin. When 5-tolyl-pent-2-ene is cyclized to dimethyltetralin in liquid phase, dimerization of 5-tolyl-pent-2-ene is likely to occur, thereby failing to obtain dimethyltetralin in a high yield. Also, when an aromatic hydrocarbon is used as a solvent for the cyclization in the presence of a catalyst conventionally used, the selectivity to dimethyltetralin is low due to the reaction of 5-tolyl-pent-2-ene with the aromatic hydrocarbon. It is reported that vapor-phase cyclization of 5-tolylpent-2-ene can prevent the production of high-boiling compounds. However, the vapor-phase cyclization known in the art should be carried out under limited reaction conditions because sufficiently high temperature is required.
Although a
Fushimi Norio
Kyuuko Youichi
Takagawa Makoto
Antonelli Terry Stout & Kraus LLP
Griffin Walter D.
Mitsubishi Gas Chemical Company Inc.
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