Process for the synthesis of alkylated aromatic hydrocarbons

Details Process for the synthesis of alkylated aromatic hydrocarbons Process for the synthesis of alkylated aromatic hydrocarbons

1992-01-24

1994-02-22

Pal, Asok

Chemistry of hydrocarbon compounds

Aromatic compound synthesis

By condensation of entire molecules or entire hydrocarbyl...

585446, 585467, 502344, C07C 266

Patent

active

052889360

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field Of The Invention
The present invention relates to a process for the manufacture of alkylated aromatic hydrocarbons. It relates more particularly to the manufacture of alkylated aromatic hydrocarbons with an alkyl chain containing at least four carbon atoms by reacting an aromatic hydrocarbon substituted by a short-chain alkyl group containing 1 to 3 carbon atoms with an olefin in the presence of a catalyst.
2. Description Of Related Art
A process for the synthesis of alkylated aromatic compounds, consisting in condensing an aromatic hydrocarbon substituted by a group containing a saturated carbon atom bonded to at least one hydrogen atom with an unsaturated hydrocarbon (U.S. Pat. No. 2,758,140, V. N. Ipatieff et al;) column 2, lines 19 to 45 and column 23, claim 1) has been known for a long time. The process can be performed in the presence of contact agents, such as alumina.
However, this known process has the disadvantage of giving rise to poor selectivities and to relatively low yields of the alkylated aromatic compounds (columns 5 and 6, Table 1).
In British Patent GB-1,259,535 there is a description of a process for alkylating aromatic hydrocarbons in the presence of a catalyst containing an alkali metal or an alkali metal hydride deposited on alumina. The catalyst is prepared before the alkylation reaction by mixing the metal with alumina under a nitrogen atmosphere, followed by a heat treatment at 300.degree. C. for several hours (page 2, lines 15 to 20 and lines 38 to 44). European Patent Application EP-A1-0,328,940 discloses a similar process for the synthesis of alkylated aromatic hydrocarbons, where the catalyst is also prepared in a preliminary stage consisting in treating an alumina with an alkali metal and an alkali metal hydroxide at a temperature of 200.degree. to 600.degree. C. in the presence of small quantities of moisture and in an inert gaseous atmosphere (claim 1, page 12).
These processes have the disadvantage of requiring an additional stage for preparing the catalyst immediately before it is employed in the alkylation reaction. Apart from the additional costs linked with the equipment and the thermal energy which are needed for the heat treatment, these processes involve difficulties in handling the catalysts, as the latter generally have the disadvantage of being pyrophoric.


SUMMARY OF THE INVENTION

The invention is intended to overcome these disadvantages by providing a process which makes it possible to obtain selectivities close to 100% with alkylated aromatic hydrocarbon yields which exceed 90% without requiring the prior preparation of the catalyst.
The invention relates to a process for the synthesis of alkylated aromatic hydrocarbons with a saturated alkyl chain containing at least four carbon atoms comprising reacting an aromatic hydrocarbon substituted by a saturated short-chain alkyl group containing one to three carbon atoms with an olefin in the presence of a catalyst comprising at least one alkali metal or an alkali metal hydride impregnated onto an alumina support, wherein the catalyst is prepared in the reaction medium in the presence of the aromatic hydrocarbon substituted by the saturated short-chain alkyl group by mixing anhydrous alumina with the alkali metal or with the alkali metal hydride, and the olefin is then introduced to start the reaction.
The invention is directed to the preparation of aromatic hydrocarbons alkylated by a linear or branched saturated alkyl chain containing more than four and, preferably, not at least eight carbon atoms. It is applicable, in particular, to the preparation of benzene-related hydrocarbons alkylated by a saturated and branched alkyl chain containing five carbon atoms. It is very particularly suited to the preparation of amylbenzenes, such as, for example, tert-amylbenzene.


DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

An aromatic hydrocarbon alkylated with a short chain alkyl group, employed as the starting material according to the invention, is intended to denote any ar

REFERENCES:
patent: 2758140 (1956-08-01), Ipatieff et al.
patent: 4962254 (1990-10-01), Fukao et al.

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