Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By contact with solid sorbent
Patent
1998-01-07
2000-10-17
Griffin, Walter D.
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By contact with solid sorbent
585823, 585532, 585533, 502 80, 502 81, 502 85, 502408, 502410, C07C 712, C07C 202, B01J 2012, B01J 2116
Patent
active
061334979
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
The invention pertains to a catalyst for removing olefins from aromatic compounds or mixtures of aromatic compounds.
Benzene, toluene and the xylenes (BTX), the most important industrial aromatic compounds, are manufactured virtually exclusively nowadays via the catalytic or thermal conversion of suitable mineral oil fractions.
In the case of so-called catalytic reforming, a paraffinic naphtha fraction is treated at approximately 400.degree. C. with catalysts that have been coated with a noble metal. Aromatic compounds are formed from the saturated hydrocarbons during this catalytic process. These aromatic compounds are then separated from the non-aromatic compounds by means of extraction or, as the case may be, crystallization and then they are processed further by distillation.
The sulfolane process (Ullmann's Encyclopadie der Technischen Chemie, Volume 8 (1974), page 395) has gained acceptance as the most important process for the extraction-based separation of benzene/toluene mixtures.
In addition to the desired aromatic compounds, small quantities of olefins are also formed during catalytic reforming. These olefins, whose concentration lies below 1% as a rule, interfere with further processing and have to be removed. Since the undesired olefins have approximately the same boiling points as the aromatic compounds, separation by means of distillation is not possible.
Catalytic treatment with alkaline earth aluminum silicates, e.g. activated smectites in granular form, has gained acceptance on a world wide basis as an economical process for the removal of these olefins. In this connection, the stream of aromatic compounds is fed through a solid bed reactor at approximately 150-200.degree. C. The granular materials act as a catalyst in this way; the undesired olefins are transformed into higher boiling products which can then be separated with ease by means of distillation.
It is known that natural or synthetic alkaline earth aluminum silicates are used preferentially as catalysts which are suitable for the removal of olefins. Thus the most widely different processes have been described using acid-activated bentonites (bleaching earths). In this connection, reference may be made, for example, to GB-1 162 945 and DE-C-22 36 996. The commercial products for the purification of aromatic compounds are generally granulated acid-activated bentonites in the form in which they are used for refining edible oils. As a rule, the products are supplied in a grain size range between 0.3 and 0.6 mm; their specific surface area varies between 200 and 400 m.sup.2 /g; their ion exchange capacity (IEC) varies between 30 and 60 milli-equivalents/100 g.
In addition to the acid-activated bentonites, that are preferably used, use can also be made of synthetic silicates such as Al silicates, Mg silicates and Zr silicates.
The use of zeolites for the removal of olefins from fractions of aromatic compounds is described in U.S. Pat. No. 4,795,550. Zeolites are certainly very reactive but the formation of polymeric by-products takes place in their narrow system of pores and this leads to very rapid deactivation of the catalyst bed.
The working life of acid-activated bentonites in fixed bed reactors varies very markedly depending on the process conditions and lies between several weeks and a year. After this, so much catalytic activity has been lost as a result of deactivation processes that exchange of the catalyst is necessary. The process operators of such aromatic plants are therefore interested in a highly active catalyst which excels by virtue of a long working life.
The task of the present invention is to develop catalysts for removing olefins from aromatic compounds or mixtures of aromatic compounds on the basis of smectites with a constant, high catalytic activity and thus a long working life.
The subject of the invention is thus a catalyst based on acid-activated smectitic clay minerals for removing olefins from aromatic compounds or mixtures of aromatic compounds which is characterized by the feature that th
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Engelhardt Thomas
Flessner Uwe
Hahn Reinhard
Zschau Werner
Cox Scott R.
Griffin Walter D.
Sud-Chemie A.G.
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