Process for selective hydrogenation of ethylbenzene
AssigneeChevron Research Company
InventorDerek L. Ransley
Life of this patent
Estimating the term…
Abstract
An improved process for selective hydrogenation of ethylbenzene which employs a rhodium catalyst and mild reaction conditions, and is especially useful to reduce the concentration of ethylbenzene in mixtures comprising ethylbenzene and at least one xylene isomer.
Drawings
Claims14
A process for selectively hydrogenating ethylbenzene in a C.sub.8 aromatic mixture comprising ethylbenzene and at least one xylene isomer, which comprises heating said mixture with hydrogen in the presence of a catalyst consisting essentially of rhodium until from about 5% to about 60% of said mixture is hydrogenated.
An improved process for preparing a ethylbenzene reduced C.sub.8 aromatic mixture which comprises heating a C.sub.8 aromatic feed mixture comprising ethylbenzene and at least one xylene isomer with hydrogen in the presence of a rhodium catalyst until from about 5% to about 60% of the feed mixture is hydrogenated, and separating the hydrogenated non-aromatic fraction comprising ethylcyclohexane.
6 Sep 1994Estimated · howhidePre-1995 term; greater of 17 years from grant or 20 years from filing when eligible. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.
Of the platinum group metals: ruthenium, rhodium, osmium or iridium
Life of this patent
Term ended 6 Sep 1994 (estimated)
Priority31 Dec 1975
Granted6 Sep 1977
Term ended6 Sep 1994
Priority31 Dec 1975
Granted6 Sep 1977
Term ended6 Sep 1994
Application filedUS 05/645,586
GrantedUS 4,046,824 A
Term endedEstimated
USPTO file history isn’t available for this patent, so only indexed dates are shown.
Description1,529 words
Summary1,224 words
#Para-xylene is in demand as a precursor in the production of terephthalic acid and dimethyl terephthalate which are, in turn, used in the manufacture of polyester resins. Mixtures containing substantial guantities of ethylbenzene and xylene isomers are prepared by catalytic reforming of petroleum fractions and catalytic isomerization of xylenes. Typical processes for separating p-xylene from C.sub.8 aromatic mixtures involve fractional crystallization. In order to provide an improved feedstock for para-xylene crystallization processes it is desirable to reduce the concentration of ethylbenzene in the aromatic mixture. Ethylbenzene acts as a diluent in crystallization minimizing the production of p-xylene from a given size crystallization apparatus and lowering the eutectic temperature of the mixtue which, if obtained, results in a higher viscosity slurry and a lower density difference between the p-xylene crystals and the mother liquor. Thus, the presence of ethylbenzene impedes the separation of p-xylene crystals.
#It is known that the boiling points of the C.sub.8 aromatics are very close. In particular, ethylbenzene boils at about 136.degree. C., p-xylene at about 138.degree. C., m-xylene at about 139.degree. C., and o-xylene at about 144.degree. C. While ethylbenzene can be separated from xylene isomers by fractional distillation, typical ethylbenzene fractionators contain 300 to 400 actual trays and require about a 25-50 to 1 feed ratio.
#Accordingly, there is a continuing need to provide a process for reducing the concentration of ethylbenzene in C.sub.8 aromatic mixtures, thereby providing a more efficient less expensive p-xylene crystallization feedstock. One approach to the separation of ethylbenzene and xylenes has been to hydrogenate the C.sub.8 mixture prior to separation. Interest in this approach stems from the greater difference in boiling points between ethylcyclohexane and the dimethyl cyclohexanes than between ethylbenzene and the xylenes. U.S. Pat. No. 2,282,231 describes such a process. While complete hydrogenation of the C.sub.8 mixture is satisfactory, it suffers certain shortcomings. For example, it is suggested that the feedstock should not contain o-xylene. Thus, the C.sub.8 mixture should first be distilled to separate the o-xylene fraction. It is also necessary to reform the resulting substituted cyclohexanes to xylenes in order to obtain the desired p-xylene-containing mixture. Thus, an additional step is required. These shortcomings could be overcome by providing a hydrogenation process which selectively hydrogenates ethylbenzene in a C.sub.8 aromatic mixture.
Detailed description305 words
#The following examples further illustrate the practice of this invention.
#In the following examples, the reactions were run in the liquid phase with 10 to 27 ml of a 0.5% rhodium catalyst on an alumina support. Samples were analyzed by gas phase chromatography using a 100 feet by 0.02 inch coated column at 70.degree. C. The reactions were run in a 0.5 inch-diameter reactor equipped with pressure and heating means. The following table summarizes the results of typical runs.