Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Hydrocarbon is contaminant in desired hydrocarbon
Patent
1997-09-30
2000-12-26
Tran, Hien
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Hydrocarbon is contaminant in desired hydrocarbon
585820, 585823, 585829, 585520, 585532, 585533, 502 79, 502 80, 502 81, 502 85, 502 60, C07C 7163
Patent
active
06166278&
DESCRIPTION:
BRIEF SUMMARY
The invention concerns the use of naturally acid smectites to eliminate olefins from aromatics or aromatic mixtures.
The most significant industrial aromatics benzene, toluene and xylenes (BTX) are now almost exclusively produced by catalytic or thermal conversion of appropriate petroleum fractions.
In so-called catalytic reforming a paraffinic naphtha fraction is treated at about 400.degree. C. with noble metal-coated catalysts. Aromatics are formed from the saturated hydrocarbons during this catalytic process. These aromatics are then separated from the nonaromatics by extraction or crystallization and further processed by distillation.
The sulfolane process has emerged as the most important process for extractive separation of benzene-toluene mixtures (Ullmann's Encyklopadie der Technischen Chemie, Vol. 8 (1974), p. 395).
Limited amounts of olefins are also formed during catalytic reforming in addition to the desired aromatics. These olefins, whose content generally lies below 1%, interfere with subsequent processing and must be removed. Since the undesired olefins have roughly the same boiling points as the aromatics, distillative separation is not possible.
Catalytic treatment with alkaline earth metal aluminosilicates, for example, activated smectites in granulate form, has emerged as an economical process worldwide for elimination of these olefins. The aromatic stream is passed through a fixed bed reactor at about 150-200.degree. C. The granulates act as catalyst; the undesired olefins are converted to higher boiling products that can then be easily separated by distillation.
It is known that natural or synthetic alkaline earth metal aluminosilicates are preferably used as suitable catalysts for elimination of olefins. A wide variety of methods have been described using acid-activated bentonites (bleaching earth). For example GB-1 162 945 and DE-C-22 36 996 can be referred to in this connection. The commercial products for aromatic purification are generally granulated acid-activated bentonites, like those used for refining of edible oils. The products are generally supplied in a particle size range between 0.3 and 0.6 mm, with specific surface between 200 and 400 m.sup.2 /g and ion exchange capacity (IEC) between 30 and 60 meq./100 g.
Synthetic silicates, like Al silicates, Mg silicates, Zr silicates, can also be used in addition to the preferred acid-activated bentonites.
The use of zeolites to eliminate olefins from aromatic fractions is described in U.S. Pat. No. 4,795,550. Zeolites are definitely very reactive; however, formation of polymer byproducts that lead to very rapid deactivation of the catalyst bed occurs in their narrow pore system.
The lifetime of acid-activated bentonites in fixed bed reactors varies very sharply, depending on the process conditions, and lies between a few weeks and 1 year. By that point so much catalytic activity has been lost by the deactivation process that replacement of the catalyst is necessary. Process operators of such aromatic units are therefore interested in a highly active catalyst characterized by a long lifetime.
The goal of the present invention is to develop catalysts for elimination of olefins from aromatics or aromatic mixtures based on smectites with constant high catalytic activity and thus longer lifetime.
The object of the invention is the use of naturally acid smectites to eliminate olefins from aromatic or aromatic mixtures. Naturally acid smectites are known, but have only been used thus far as bleaching earth. It has been surprisingly found that they are also suitable as catalysts for the aforementioned purpose.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE shows results of the performance of Comparison Examples 1 and 2 and Examples 1, 2 and 3.
A naturally acid smectite having the following properties is preferably used: 40 to 80 meq./100 g, in which the portion of the IEC of Al.sup.3+ ions is about 5 to 70 meq./100/g, the proportion of the IEC of the alkali ions is less than about 2.0 meq./100 g and the proportion of the IEC of the alkali
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Engelhardt Thomas
Flessner Uwe
Hahn Reinhard
Zschau Werner
Cox Scott R.
Preisch Nadine
Sud-Chemie A.G.
Tran Hien
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