Mineral oils: processes and products – Chemical conversion of hydrocarbons – Reforming
Patent
1997-12-15
1999-10-19
Griffin, Walter D.
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Reforming
208134, 208135, 208136, 208137, 208138, 585418, 585419, 585420, 585421, C10G 35085
Patent
active
059683457
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the catalytic conversion of hydrocarbons into aromatic compounds to be used for the reforming of gasolines and the production of aromatics.
In more precise manner, it relates to a process of this type using as catalyst a catalyst which comprises a matrix consisting of .eta. transition alumina or .gamma. transition alumina, or a mixture of these two aluminas, at least one doping metal chosen from the group made up of alkali and alkaline-earth metals, at least one halogen, at least one noble metal and at least one promoter metal.
2. Description of the Background
Catalyst reforming is a process which can be used to obtain improved octane ratings of petroleum fractions, in particular of heavy distillation gasoline by conversion of n-paraffins and naphthenes into aromatic hydrocarbons.
Catalyst reforming therefore entails the conversion firstly of C.sub.7 -C.sub.10 n-paraffins into aromatics and light paraffins, and secondly of C.sub.7 -C.sub.10 naphthenes into aromatics and light paraffins. These reactions are illustrated in particular by the conversion through dehydrogenation of cyclohexanes and dehydroisomerization of alkyl cyclopentanes to give aromatics, for example methyl cyclohexane giving toluene, and by the conversion through cyclization of n-paraffins into aromatics, for example n-heptane giving toluene.
During catalytic reforming, cracking reactions of heavy n-paraffins into light paraffins also take place, leading in particular to C1-C4 products, chiefly propane and isobutane: these reactions are detrimental to the yield of reformed product.
Finally, coke formation also takes place through condensation of aromatic nuclei to form a solid product rich in carbon which is deposited on the catalyst.
These reforming catalysts are extremely sensitive, in addition to coke, to various poisons likely to deteriorate their activity: in particular sulphur, nitrogen, metals and water.
When coke is deposited on the surface of the catalyst it leads to loss of activity in the course of time which gives rise to higher operating temperatures, a lower yield of reformed product and a higher yield of gas.
On this account, and taking into consideration the regeneration of the catalyst, the process of catalytic reforming can be implemented in two different manners: in semi-regenerative or cyclical manner and in continuous manner. In the former, the process is carried out in a fixed bed, and in the latter in a mobile bed.
In the semi-regenerative process, to offset the loss of activity of the catalyst, the temperature is gradually increased then the installation is stopped to proceed with regenerating the catalyst by eliminating the coke. In cyclical reforming which is in fact a variant of the semi-regenerative process, the installation comprises several reactors in series and each is put out of operation in turn, the coke deposits are eliminated from the catalyst placed out of circuit and the catalyst is regenerated while the other reactors remain in operation.
In continuous reforming, the reactors used are mobile bed reactors operating at low pressure (less than 15 bars), which allows for considerably improved yields of reformed product and hydrogen by promoting aromatization reactions to the detriment of cracking reactions, coke formation on the other hand being greatly accelerated. The catalyst passes through the reactors, then through a regenerating section.
On account of the chemical reactions that take place during reforming processes, a bifunctional catalyst must be used which combines two types of activity namely the hydrogenating-dehydrogenating activity of a metal, in particular a noble metal such as platinum, possibly in conjunction with other metals such as rhenium or tin, so-called promoter metals, this metal being deposited on the surface of a porous matrix. This matrix of alumina contains a halogen, preferably a chloride, which provides the necessary acidic function for isomerizations, cyclizations and crack
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Alario Fabio
Deves Jean-Marie
Euzen Patrick
Griffin Walter D.
Institut Francais du Pe'trole
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