Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By isomerization
Reexamination Certificate
1999-04-12
2001-11-06
Knode, Marian C. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By isomerization
C585S481000, C585S482000, C585S906000
Reexamination Certificate
active
06313363
ABSTRACT:
The present invention relates to the field of processes for isomerising aromatic compounds containing eight carbon atoms.
In known processes for isomerising aromatic compounds containing eight carbon atoms, a feed which is relatively depleted in para-xylene with respect to the thermodynamic equilibrium of the mixture (i.e., where the para-xylene content is substantially lower than that of the mixture at thermodynamic equilibrium at the temperature under consideration, the mixture comprising at least one compound selected from the group formed by meta-xylene, ortho-xylene, para-xylene and ethylbenzene) and generally rich in ethylbenzene with respect to the same mixture at thermodynamic equilibrium, is introduced into a reactor containing at least one catalyst, under temperature and pressure conditions suitable for producing at the reactor outlet a composition containing aromatic compounds containing eight carbon atoms which is as close as possible to the mixture at thermodynamic equilibrium at the temperature of the reactor.
Para-xylene and possibly ortho-xylene, namely the desired isomers as they are of great importance in particular for the synthetic fibre industry, are then separated from that mixture. The meta-xylene and ethylbenzene can then be recycled to the isomerisation reactor inlet so as to increase the production of para-xylene and ortho-xylene. If ortho-xylene is not to be recovered, it is recycled with the meta-xylene and ethylbenzene.
However, there are a number of problems when isomerising aromatic compounds containing eight carbon atoms per molecule, caused by secondary reactions. Thus in addition to the main isomerisation reaction, hydrogenation reactions can be seen, such as hydrogenation of aromatic compounds to naphthenes, and naphthene ring opening reactions which lead to the formation of paraffins having at most the same number of carbon atoms per molecule as the naphthenes from which they originate. Cracking reactions are also observed, such as paraffin cracking reactions which lead to the formation of light paraffins typically containing 3 to 5 carbon atoms per molecule, also dismutation and transalkylation reactions which lead to the production of benzene, toluene, aromatic compounds containing 9 carbon atoms pre molecule (for example trimethylbenzenes) and heavier aromatic compounds.
The totality of such secondary reactions greatly reduces the yields of the desired products.
The quantity of secondary products formed (essentially naphthenes typically containing 5 to 8 carbon atoms, paraffins typically containing 3 to 8 carbon atoms, benzene, toluene, and aromatic compounds containing 9 to 10 carbon atoms per molecule) depends on the nature of the catalyst and the operating conditions of the isomerisation reactor (temperature, partial pressures of hydrogen and hydrocarbons, feed flow rate).
The skilled person is well aware that in some catalytic processes, catalyst activation and/or selectivisation procedures must be carried out to optimise the performances of the catalyst.
As an example in the case of a catalyst containing a metal from group VIII of the periodic table (“Handbook of Physics and Chemistry”, 45
th
edition, 1964-65), such as platinum, pre-treating the catalyst with hydrogen sulphide (H
2
S) is well known. The sulphur contained in the hydrogen sulphide molecule becomes fixed on the metal and endows it with improved catalytic properties.
In conventional processes for isomerising aromatic compounds containing eight carbon atoms, a mixture of xylenes and ethylbenzene is brought into contact with a suitable catalyst, generally containing a noble group VIII metal and a zeolite, in order to bring the mixture of aromatic compounds containing eight carbon atoms to a composition which is as close as possible to the composition corresponding to thermodynamic equilibrium at the temperature under consideration.
SUMMARY OF THE INVENTION
The present invention concerns a process for activating catalysts for isomerising aromatic compounds containing eight carbon atoms comprising at least one sulphurization step and at least one passivation step using ammonia, carried out in any order, the sulphurization step normally being preceded by reduction of the metal compound contained in the catalyst.
The invention also concerns a process for isomerising aromatic compounds containing eight carbon atoms in which the catalyst used is activated, comprising at least one sulphurization step and at least one passivation step using ammonia, and an apparatus for carrying out the process.
We have discovered, surprisingly, that catalytic performances—in particular the para-xylene yield—are substantially improved in this type of catalyst when such catalysts are used in a pre-sulphurized or sulphurized form after introduction into the reactor and when they undergo passivation in the presence of ammonia (NH
3
) or an ammonia precursor.
The process of the present invention has a number of advantages over the prior art, among them a reduction in the loss of aromatic compounds containing eight carbon atoms by side reactions of dismutation, transalkylation, hydrogenation and cracking. Further, carrying out the process of the present invention means that lower temperature and pressure conditions can be used with the catalyst, also higher HSVs (wt of feed/weight of catalyst/hour).
The procedure for activating the catalyst of the present invention is applicable to all catalysts for isomerising aromatic compounds containing eight carbon atoms which contain at least one metal or compound of a metal from group VIII selected from iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium. indium and platinum, and preferably at least one noble metal or compound of a metal from group VIII, preferably selected from platinum and palladium, and optionally at least one metal or compound of a metal selected from metals or compounds of metals from groups IIIA and IVA.
The catalyst may contain a zeolite. In this case, the invention is of particular application to catalysts containing at least one zeolite with a mordenite, MFI, EUO or mazzite structure type such as omega zeolite.
More particularly, this activation procedure can be applied to a catalyst comprising at least one zeolite with structure type EUO, for example EU-1 zeolite. The zeolite with structure type EUO which is used contains silica and at least one element T selected from the group formed by aluminium, iron, gallium and boron, preferably aluminium and boron, and in which the global Si/T atomic ratio is about 5 to 100, preferably about 5 to 80, and more preferably about 5 to 60. More particularly, this activation process can be applied to a catalyst comprising at least one zeolite with structure type MOR. Zeolite with structure type MOR has an Si/Al ratio of less than 20, preferably in the range 5 to 15.
When the catalyst contains a zeolite, the zeolite represents a weight of 1% to 90%, preferably 3% to 60%, and more preferably 4% to 40% with respect to the total weight of the catalyst. The weight content of the group VIII element(s) is generally about 0.01% to 2.0% with respect to the total catalyst weight, preferably about 0.05% to 1.0% with respect to the total catalyst weight. This group VIII element is preferably selected from the group formed by platinum and palladium. The element is usually platinum. The catalyst can be formed using a matrix, in a content which forms the complement of 100% by weight of the catalyst.
When the catalyst used in the present invention is formed with a matrix, the matrix is generally selected from the group formed by natural clays (for example kaolin or bentonite), synthetic clays, magnesia, aluminas, silicas, silica-aluminas, titanium oxide, boron oxide, zirconia, aluminium phosphates, titanium phosphates, and zirconium phosphates, preferably from elements of the group formed by aluminas and clays. This matrix can be a simple compound or a mixture of at least 2 of these compounds.
In the particular case where the catalyst contains a zeolite, for example a zeolite with structure type EUO, the ze
Alario Fabio
Benazzi Eric
Joly Jean-Francois
Lacombe Sylvie
Magne-Drisch Julia
Dang Thuan D.
Institut Francais du Pe'trole
Knode Marian C.
Millen White Zelano & Branigan P.C.
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