Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Sulfur or compound containing same
Reexamination Certificate
1999-09-22
2001-09-11
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Sulfur or compound containing same
C502S217000, C502S218000, C502S219000, C502S220000, C502S221000, C502S222000, C502S223000
Reexamination Certificate
active
06288006
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the presulphurization of the catalysts which are employed chiefly in the treatment of hydrocarbons and for oil refining.
BACKGROUND OF THE INVENTION
The industrial operations employing the catalysts to which the present invention relates consist very particularly in performing a hydrotreating of hydrocarbon feedstocks at elevated temperature and under a high pressure of hydrogen, in the presence of appropriate catalysts, in order to convert organosulphur compounds by hydrodesulphurization (HDS) operations with formation of hydrogen sulphide, and organonitrogen compounds by hydrodenitrogenation (HDN) operations with formation of ammonia.
These catalysts are generally based on metals of groups VI B and VIII of the Periodic Classification of the elements, such as molybdenum, tungsten, nickel and cobalt. The most commonly used hydrotreating catalysts are formulated from cobalt-molybdenum (Co—Mo), nickel-molybdenum (Ni-Mo) and nickel-tungsten (Ni—W) systems on porous inorganic supports such as aluminas, silicas and silicoaluminas. These catalysts, manufactured industrially in very large tonnages, are supplied in their oxide forms (for example cobalt oxide-molybdenum oxide catalysts on alumina, symbolized in the form Co-Mo/alumina). However, these catalysts are active in the hydrotreating operations only in the form of metal sulphides; consequently they must be presulphurized before being employed.
The presulphurization of hydrotreating catalysts is an important stage in the activation of these catalysts to obtain their maximum performance in HDS and in HDN. As indicated by the authors of Hydrotreating Catalysis (Catalysis, vol. 11, 1996, p. 25, edited by J. R. Anderson and M. Boudart), practical experience has shown that the sulphurization procedure can have a significant influence on the activity and the stability of the catalyst, and many efforts have been devoted to improving the sulphurization procedures.
Conventional sulphurization procedures consist in treating the catalysts in oxide forms with sulphur compounds in the presence of hydrogen, in specified temperature conditions. In the operating conditions employed and in the presence of hydrogen, the sulphur compounds generate hydrogen sulphide which ensures the conversion of the metal oxides to sulphides. In the case of the metals concerned of groups VI B and VIII this conversion in the presence of hydrogen is reflected in a change to a reduced state; thus, for example, molybdenum, which in oxide form is in the Mo
6+
state, is reduced in sulphide form to the Mo
4+
state. In the case of the hydrotreatment catalysts which contain metals such as molybdenum, tungsten, nickel and cobalt, the chemical reactions which involve hydrogen sulphide and hydrogen for the reductive conversions of the metal oxides to sulphides can be schematized as follows:
The presulphurization of a catalyst with hydrogen sulphide mixed with hydrogen is the most direct method and has formed the subject-matter of a number of patents: U.S. Pat. No. 3,016,347, U.S. Pat. No. 3,140,994, GB 1 309 457, U.S. Pat. No. 3,732,155, U.S. Pat. No. 4,098,682, U.S. Pat. No. 4,132,632, U.S. Pat. No. 4,172,027, U.S. Pat. No. 4,176,087, U.S. Pat. No. 4,334,982 and FR 2 476 118. This method is generally practised at the laboratory stage, but the use of hydrogen sulphide presents major difficulties which rule out its use on any industrial sites.
Industrial procedures for the sulphurization of catalysts are generally performed under hydrogen pressure with liquid feedstock containing sulphur compounds as sulphurizing agents.
The method chiefly employed in the past by refiners consisted in presulphurizing the catalysts with the sulphur-containing oil feedstocks. This technique had considerable disadvantages because of the difficulty of converting the sulphur compounds to hydrogen sulphide. To avoid the reduction of the catalysts by the hydrogen, the presulphurizations, which started at low temperature, had to be conducted slowly to obtain a complete sulphurization of the catalysts at elevated temperature.
Sulphur-containing additives have been proposed for improving the presulphurization of the catalysts. The method consists in incorporating a sulphur compound (spiking agent) in a feedstock such as a naphtha, in a special cut such as a VGO (vacuum gas oil) or an LGO (light gas oil). U.S. Pat. No. 3,140,994 was the first to claim the use of compounds of various kinds which are liquid at ambient temperature: carbon disulphide, thiophene, mercaptans, dialkyl disulphides and diaryl disulphides. Organic sulphides, in particular dimethyl sulphide, have also formed the subject-matter of claims. Dimethyl disulphide (DMDS) has been particularly recommended for the presulphurization of catalysts, while Patent EP 64429 claims an effective method of sulphurization with dimethyl disulphide.
H. Hallie (Oil and Gas Journal, Dec. 20, 1982, pp 69-74) has reviewed these procedures of sulphurization under hydrogen which are performed directly in the hydrotreating reactors. These various techniques of presulphurization of catalysts, known as “in situ”, have been compared and work has shown that presulphurization with a liquid feedstock to which has been added a sulphurizing agent which has the property of decomposing at low temperature (spiked feedstock) is the best sulphurization technique. The technique without an additional sulphurizing agent (unspiked feedstock) gives a less active sulphur-containing catalyst. The preferred sulphurizing agent added to the feedstock is dimethyl disulphide.
Organic polysulphides have also been claimed as sulphurizing agents for the presulphurization of catalysts. U.S. Pat. No. 4,725,569 describes a method of employing organic polysulphides of RS
x
R′ type (it being possible for R and R′ to be identical or different and x being equal to or greater than 3), which consists in impregnating the catalyst at ambient temperature with a solution containing the polysulphide, then removing the inert solvent and, finally, performing the sulphurization, under hydrogen, of the catalyst charged into the hydrotreating reactor. In Patent EP 298 111 the polysulphide of RS
n
R′ type is injected during the presulphurization of the catalyst diluted in a liquid feedstock in the presence of hydrogen. The use of functionalized mercaptans such as mercaptocarboxylic acids or esters, dithiols, aminomercaptans and hydroxymercaptans, as well as of thiocarboxylic acids or esters, is also described in Patent EP 289 211 for the presulphurization of catalysts.
New techniques of presulphurization of catalysts have been developed more recently. These procedures are divided into two stages. In a first stage, known as “ex situ”, the catalyst is preactivated in the absence of hydrogen outside the refinery after having been impregnated with a sulphurizing agent. The complete sulphurization of the catalyst is performed in the hydrotreating reactor in the presence of hydrogen. The ex-situ presulphurization relieves the refiner of injecting a sulphurizing agent during the sulphurization of the catalyst under hydrogen. The ex-situ techniques developed at present employ organic polysulphides or sulphur as sulphur-containing materials.
Eurecat has been the first company to industrialize an ex-situ technique of presulphurization of catalysts, based on the use of polysulphides of the RS
n
R′ type (it being possible for R and R′ to be identical or different and n≧3), which has formed the subject-matter of Patent EP 130 850. This process consists in impregnating the catalyst in oxide form with a solution composed of organic polysulphides such as TPS 37 or TNPS (tert-nonyl polysulphides) marketed by Elf Atochem, diluted in a hydrocarbon of the white spirit type. This preliminary stage of incorporation of a sulphur compound of a particular kind in the catalyst is supplemented by a heat treatment of the catalyst in the absence of hydrogen at temperatures not exceeding 150° C. This operation has the effect of removi
Elf Aquitaine Exploration Production France
Smith , Gambrell & Russell, LLP
Wood Elizabeth D.
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