Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the...
Reexamination Certificate
1999-08-12
2001-04-10
Richter, Johann (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
C518S700000, C502S325000, C502S326000
Reexamination Certificate
active
06214890
ABSTRACT:
The present invention relates to the field of catalysts used for the synthesis reactions of hydrocarbons starting from a mixture of gas containing carbon monoxide and hydrogen, generally called a Fischer-Topsch synthesis.
Therefore, the present invention relates to the use of a catalyst comprising at least one support and at least one group VIII metal in a synthesis process for hydrocarbons using a mixture containing carbon monoxide and hydrogen and optionally carbon dioxide denoted as CO—(CO
2
)—H
2
.
DESCRIPTION OF THE PRIOR ART
The properties of the supported metallic catalysts, i.e. catalysts comprising one or more metals deposited on a support chosen from refractory oxides, carbon, polymers or any other material, are conditional upon a set of parameters, such as for example, the size of the metallic particles.
A large number of examples exist in the literature demonstrating the influence of the size of metallic crystallites on the activity of the final catalyst. This aspect has been described in extensive detail in “Catalysis by Metals and Alloys”, V. Ponec, E. Bond, Study in Surface Science and Catalysis, Volume 95, page 280, 1995. On the other hand, the reduction in the size of these crystallites is often linked to an increase in the reaction between the metal and the support.
The catalysts used for the conversion of synthesis gas into hydrocarbons, operated at high temperature and under pressure (known in the literature under the name Fischer-Tropsch synthesis) require specific crystallites size conditions.
Thus the group VIII metals of the periodic classification of the elements, such as iron, ruthenium, cobalt, nickel catalyse the conversion of CO—(CO
2
)—H
2
mixtures (i.e. the CO—H
2
mixtures optionally containing CO
2
, called synthesis gas) into liquid and/or gaseous hydrocarbons,
For these reactions it is necessary to have catalysts the size of the metallic particles of which is controlled, i.e. the size of the particles and the distribution of particles as a function of the size is not random, in order to optimise the activity and the selectivity of the catalyst.
The conventional preparation methods for the supported metallic catalysts used for the Fischer-Tropsch synthesis consist of depositing a metallic salt or a metal-ligand coordination complex onto the support, then carrying out an activation stage consisting of one or more thermal treatments carried out under air or under hydrogen, which leads to a poor distribution of the size of the particles.
The Patent Application EP 0736326 A describes a new preparation method for a cobalt catalyst obtained by drying at a pressure lower than atmospheric pressure: the sizes of the cobalt particles obtained are comprised between 10 and 17 nm.
The Patent Application EP 0174696 A describes a preparation process for a cobalt-based Fischer-Tropsch catalyst where the cobalt is distributed such that &Sgr;Vp/&Sgr; Vc<0.85 (&Sgr;V being the quantity of Co contained in the periphery of the solid, &Sgr;Vc being the quantity of Co contained in the whole solid). The inventor shows that this distribution favours the formation of C5+. The catalyst is prepared by impregnation of the support (preferably silica) already immersed in water for 30 seconds, and can contain a promoter, preferably zirconium.
The U.S. Pat. No. 4,977,126 also describes a method of surface dispersion by vaporisation of a liquid in which the metallic compound is dissolved. A peripheral layer is thus formed.
Other U.S. Pat. No. 4,605,679 and U.S. Pat. No. 4,729,981 and the Patent Application EP 0535790A describe modifications to the reduction/activation stage.
However, the distribution in size of the group VIII metal particles and their interaction with the support are not very well controlled by these different techniques.
It is therefore advantageous, in order to increase the activity of the catalysts when using them in a hydrocarbons synthesis process, to have supported metallic catalysts for which the average size and their size distribution is controlled and the interactions with the supports limited, thanks to a new preparation method. In fact, it has been shown in the literature that the interaction between the metal or metals constituting the catalyst and the support used affect the reducibility and activity of the catalyst (cf. Z. Karpiniski, Adv. Catal. Vol. 37, p. 45, 1990).
This interaction between the metal and the support can be defined by a set of characterization techniques known to a person skilled in the art. For example, programmed thermoreduction which consists of determining the reduction temperature of the supported metal oxide can be mentioned. In fact it has been shown that the more the reduction temperature of the supported metal oxide is increased the more the interaction between the metal and the support is increased.
SUMMARY OF THE INVENTION
A new synthesis process for hydrocarbons using a mixture of synthesis gas containing carbon monoxide and hydrogen and optionally carbon dioxide in the presence of a catalyst comprising a support, at least one VIII group metal, i.e. groups 8, 9 and 10 of the new periodic classification (Handbook of Chemistry and Physics, 76
th
edition, 1995-1996, on the inside front page) has been discovered and is the subject of the present invention, said process being characterised in that at least 80% of the group VIII metallic particles of the catalyst are of a size comprised between D−(D.0.2) and D+(D.0.2), where D represents the average size of the particles.
The metallic particles of the catalyst generally have an average size greater than 1 nm.
The process according to the invention is therefore carried out in the presence of a catalyst having an improved reducibility, i.e. the temperature necessary for the reduction of the catalyst is lower than the temperature necessary for the reduction of the catalyst according to the prior art. In fact the catalyst used in the synthesis process for hydrocarbons according to the invention has a reduction in the interaction between the group VIII metal and the support relative to the catalysts of the prior art, which allows an increase in the activity.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to the use of a catalyst in a synthesis process for hydrocarbons. The catalyst is characterized in that at least 80% of the particles of at least one group VIII metal have a size comprised between D−(D.0.2) and D+(D.0.2), where D represents the average size of the particles.
The catalyst is synthesized for example by the preparation of a colloidal suspension in aqueous phase, of at least one oxide of group VIII metal or metals to be supported, followed by the deposition of said suspension on a support, followed by the optional reduction of the oxide or oxides thus supported,
In a preparation method for the catalyst used in the process according to the invention, the colloidal suspension of at least one metallic oxide of a group VIII metal is prepared in aqueous phase. With regard to other preparation methods for colloidal suspensions, this method uses water as a solvent, which has an advantage as regards safety, and leads to savings in terms of the cost of the process.
More particularly, the preparation method for the catalyst used in the process according to the present invention includes several stages:
a) preparation of a colloidal suspension of at least one metallic oxide, in aqueous phase,
b) deposition of the colloidal suspension by impregnation on a support,
c) drying at a temperature less than or equal to 250° C.
d) optional calcination at a temperature ranging up to 700° C.
e) optional reduction
In stage a) the colloidal suspension is obtained for example by hydrolysis of at least one metallic cation of at least one group VIII metal in an aqueous medium, which leads to the formation of oxide or hydroxide particles in suspension.
Preferably, the hydrolysis can be carried out for example by neutralization of an aqueous solution containing a precursor salt of a group VIII metal capable of leading to the metallic hydroxide or
Didillon Blaise
Roy Magalie
Uzio Denis
Verdon Catherine
Institut Francais du Pe'trole
Millen White Zelano & Branigan
Parsa J.
Richter Johann
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