Acid catalyst with a sulfated zirconia base and its uses

Details Acid catalyst with a sulfated zirconia base and its uses Acid catalyst with a sulfated zirconia base and its uses

2000-07-10

2002-09-10

Wood, Elizabeth D. (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Sulfur or compound containing same

C502S218000, C502S219000, C502S220000, C502S221000, C502S222000, C502S223000

Reexamination Certificate

active

06448198

ABSTRACT:

This invention relates to an acid catalyst that contains a substantial amount of sulfated zirconia and at least one hydrogenating transition metal as well as to its uses in hydrocarbon transformation chemical reactions requiring the use of an acid type catalyst, such as for example those of isomerization, alkylation, oligomerization or yet dehydration reactions of light hydrocarbons, but also hydrocracking or hydroisomerization reactions of heavier hydrocarbons.
In the following, the term “sulfated zirconia” does not mean zirconium sulfate or zirconyle stoichiometric sulfate, but zirconium (zirconium dioxide) more or less sulfated, where the sulfate content can be less than that of the above-mentioned stoichiometric compounds.
BACKGROUND OF THE INVENTION
As known, the oil industry uses many methods to modify hydrocarbon structures in order to obtain molecules whose properties are suitable for the sought use. These procedures usually call for one or more catalysts that have to be specifically adapted to the chemical transformation one wants to complete, as well as to the requirements tied to the implementation of the method.
Many of these hydrocarbon transformation chemical reactions are done with an acid type catalyst. Such is the case, for example, of reactions taking place in the isomerization process of paraffin, which applies mostly to light gasolines and allows for the transformation of linear paraffin into ramified paraffin, whose octane number is higher.
In this method, the acid catalysts most used today are catalysts with an aluminum chloride base supported on alumina (meaning deposited on an alumina support). Indeed, these extremely active catalysts make it possible to obtain an isomerization reaction at low temperatures, around 150° C., with a thermodynamic balance that is very favorable to the formation of the sought products.
However, this type of catalyst does have a certain number of inconveniences tied in particular to the fragile nature of its active sites. Indeed, the aluminum chloride is a very unstable compound: it is irreversibly destroyed by water, oxygen, oxygen-containing or sulfur compounds. These products must therefore be entirely eliminated from the load being treated, which is quite costly and restricting. Furthermore, the loading of the reactors when starting the unit or, when the catalyst has been replaced, must be done in perfectly anhydrous conditions, without any trace of water or oxygen. Moreover, the preservation of the active sites during the operation requires a constant injection of dopants such as hydrochloric acid or other chlorine products; the excess acid must then be removed when leaving the reactor and invariably creates a corrosion problem. Lastly, despite all these precautions, the catalyst is progressively destroyed and must be replaced periodically since it is not regenerable.
This is why the research relating to acid catalysts has looked to the creation of new compounds with catalytic properties similar to those of the aluminum chloride but without having the same inconveniences as the latter. This is specifically the case of the sulfated zirconia.
Thus, U.S. Pat. No. 3,032,599 (Phillips Petroleum) is one of the first patents to describe the application of sulfated zirconia to isomerization and alkylation of hydrocarbons: the proposed catalysts are made entirely of zirconia gel, possibly containing small quantities of a metallic promoter. They are prepared by the precipitation of a zirconyle salt in solution in water, by an addition to the base. The zirconia gel obtained is then sulfated and then activated at approximately 500° C. These catalysts do indeed show acid catalytic properties but, however, they are not very satisfactory. Indeed, they have a low surface area, which can explain their relatively mediocre performance as far as isomerization reactions are concerned. Furthermore, these powdery catalysts are for the most part unusable as such in an industrial reactor.
Also, U.S. Pat. No. 3,132,110 (Union Oil) describes the properties of a series of acid catalysts with a base of hydrated zirconia containing sulfate radicals, pure or preferably combined with alumina. The preparation methods of these catalysts rest mostly on the decomposition of a zirconia sulfate salt in solution in water, by the hydrolysis in a basic medium or by thermal decomposition. The catalysts obtained in this manner are indeed active in a good number of reactions requiring the use of an acid catalyst, and have the advantage of being perfectly regenerable. Nevertheless, their activity has proved to be relatively limited and these catalysts must be used at high temperatures, for example over 370° C. in the case of the isomerization reaction of paraffin. Well, at such temperatures, not only is this reaction disadvantaged thermodynamically but, in addition, the catalyst's deactivation speed is accelerated by depositing coke on its surface.
Along the same lines of replacing aluminum chloride based catalysts in isomerization with more stable catalytic compounds, U.S. Pat. No. 4,406,821 (Exxon) proposes a catalyst consisting of a sulfated oxide deposited on an alumina support. This oxide is preferably a tungsten or hafnium oxide, but can also be a niobium, thallium, zirconium oxide, or a mixture thereof. This catalyst is prepared by impregnation of the alumina support with a solution of a salt of the chosen metal, followed by a calcination at a high temperature, then a sulfation using a sulfuric acid water solution. The catalyst obtained by this method does possess the acid properties and it performs particularly well in the etherification reactions of phenols. Nevertheless, these catalysts are not well adapted to the isomerization reaction of paraffin at low temperatures, where their activity seems to be limited.
In general, the acid catalysts proposed in the prior art and which could replace the alumina chloride based isomerization catalysts are therefore quite unsatisfactory due to their lack of activity.
Continuing her research in the field of sulfated zirconia based catalysts, the petitioner has issued the hypothesis that the lack of activity of the formulas proposed to date was tied to the actual structure of these catalysts that do not present enough accessible active sites to the reactive molecules. She has deduced that this was due to a maladjusted porosity and to a catalyst surface area too small in the prior art's catalysts, and an incapacity to control these parameters.
This is why the petitioner has focused her efforts on the problem, at the time unsolved, of improving the exchanges between the active catalyst sites and the molecules to be converted. She assumed it was necessary to succeed in modifying the structure of these sulfated zirconia based catalysts, and she then focused on creating catalysts that have a more adequate porosity and surface area, appropriate for giving them a better activity compared to what has been accomplished to date. In doing so, she has also discovered a certain number of original methods for controlling the porosity of these catalysts and shaping them so as to obtain the desired active structures.
SUMMARY OF THE INVENTION
So, the applicant has perfected a solid acid catalyst, containing a substantial quantity of supported or mass sulfated zirconia and at least one hydrogenating transition metal. This catalyst is different in that the said sulfated zirconia is in a crystallized form and shows a surface area greater than or equal to 135 m
2
/g, preferably greater than or equal to 150 m
2
/g, a pore volume greater than or equal to 0.16 cm
3
/g, preferably greater than or equal to 0.2 cm
3
/g, and more preferably greater than or equal to 0.25 cm
3
/g and an average pore diameter greater than or equal to 20 Angstroms (20×10
−10
m).
Here and in the following, the characteristics of the surface area, the pore volume and the average pore diameter are mentioned in reference to the method of determination called B.E.T. (Brunauer, Emmett, Teller) by adsorption of nitrogen, well known to any person skill

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