Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the...
Reexamination Certificate
1999-09-17
2001-05-22
Richter, Johann (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
C518S700000, C502S326000
Reexamination Certificate
active
06235798
ABSTRACT:
This invention relates to the use of a catalyst that comprises at least one substrate, at least one metal of group VIII in the form of metal particles, in a process for synthesis of hydrocarbons from a mixture that comprises CO—(CO
2
)—H
2
(i.e., a mixture that comprises CO—H
2
that optionally comprises CO
2
, called synthesis gas), more particularly the use that makes it possible to carry out the conversion of synthesis gas into a mixture of saturated linear hydrocarbons that essentially consist of C5′ hydrocarbons (i.e., that have at least 5 carbon atoms per molecule) or more specifically into a mixture of essentially linear and saturated hydrocarbons that contain at least 25% by weight of C5′ hydrocarbons relative to all of the hydrocarbons that are formed. The invention also relates to the catalyst that is used as well as its preparation process.
It is known to one skilled in the art that the synthesis gas can be converted into hydrocarbons in the presence of catalyst that contains transition metals. This conversion that is operated at high temperature and under pressure is known in the literature under the name of Fiecher-Tropsch synthesis. Metals of group VIII of the periodic table, such as iron, ruthenium, cobalt and nickel thus catalyze the transformation of CO—(CO
2
)—H
2
mixtures (i.e., a CO—H
2
. mixture that optionally comprises CO
2
, called synthesis gas) into liquid and/or gaseous hydrocarbons.
The products that are prepared by Fischer-Tropsch synthesis in the presence of catalysts that comprise metals of group VIII have a very wide distribution in terms of molecular weight.
Thus, only a small proportion of products that are obtained are located in the range of the middle distillates that consist of kerosene and gas oil fractions, whereby the kerosene fraction or fractions consist(s) of a hydrocarbon mixture whose boiling points are between 140° C. and 300° C., and whereby the gas oil fraction or fractions consist(s) of a hydrocarbon mixture with boiling points of between 180° C. and 370° C. during an atmospheric distillation as carried out on a crude by one skilled in the art.
Significant efforts have been undertaken since 1973 to improve the yield of middle distillates that are based on the conversion of the synthesis gas.
Various methods have been described and developed in the prior art that are intended to improve the distribution of metal to limit the diffusional phenomena inside the grain. The substrate is then coated or covered so that the metal remains on the periphery of the grain.
Patent Application EP 0174696 A describes a process for preparation of a Fischer-Tropach catalyst with a cobalt base, where the cobalt is distributed in such a way that &Sgr;Vp/&Sgr;Vc <0.86 (whereby &Sgr;Vp is the quantity of Co that is contained in the periphery of the solid, and whereby &Sgr;Vc is the quantity of Co that is contained in the entire solid). The inventor shows that this distribution promotes the formation of C5
+
. The catalyst is prepared by impregnation of the substrate (preferably silica) that is already immersed in water for 30 seconds and can contain a promoter, preferably zirconium.
U.S Pat. No. 5,036,032 describes the preparation of a catalyst with a cobalt base that makes it possible to increase the dispersion of cobalt over the outside surface of the substrate. The preparation method makes it possible to increase the density of surface active sites by using a precursor of sufficient viscosity to prevent penetration in the pores by capillary action. The direct reduction without a calcination stage makes it possible to increase the dispersion. SiO
2
is preferred as a substrate. The diffusional limitations are thus avoided.
U.S. Pat. No. 4,977,126 also describes a surface dispersion method by vaporization of a liquid in which the metal compound is dissolved. A peripheral layer thus is formed.
Other U.S. Pat. No. 4,605,679, U.S. Pat. No. 4,729,981, EP 0 535 790 A describe modifications of the reduction stage/activation.
Finally, Patent Application EP 0 736 326 A describes a new method for preparation of the catalyst with cobalt that comprises an impregnation stage that is followed by a drying stage of the catalyst under a pressure that is less than the atmospheric pressure.
The influence of the size of the particles on the activity of the catalyst was widely discussed in the literature. In the case of the transformation of synthesis gas into liquid and/or gaseous hydrocarbons, it was shown that the specific activity was independent of the dispersion of the metal and the nature of the substrate [E. Iglesia, Applied Catalysis A: General 161 (1997) 59].
The specific activity corresponds to the activity of the catalyst that is brought back to the number of metal atoms that are accessible to the number of molecules to be transformed. The number of accessible metal atoms can be determined by techniques for chemisorption of sampler molecules (oxygen, hydrogen, carbon monoxide) or from the size of the particles that is determined by electronic microscopy. Theme different techniques are well known to one skilled in the art.
This invention relates to a process for synthesis of hydrocarbons from a mixture that comprises carbon monoxide and CO—H
2
hydrogen, optionally carbon dioxide CO
2
, in the presence of a catalyst that comprises a substrate and particles of at least one metal of group VIII of the periodic table of elements that is (are) deposited on the substrate, characterized in that at least a portion of the particles of the metal of group VIII of the catalyst are not isolated relative to one another.
The applicant discovered, surprisingly enough, that when at least a portion of the metal particles is not isolated relative to the other particles that are deposited on the substrate but that the particles form agglomerates or aggregates, the catalyst has a selectivity of C5
+
that is improved relative to a catalyst that has isolated particles. The particles of the catalyst according to the invention are generally between 50 and 500 Å in size, preferably between 60 and 400 Å. The catalyst according to the invention has a selectivity of C5
+
that is improved relative to a catalyst that comprises isolated particles that are between 50 and 500 Å in size and relative to a catalyst that has isolated particles that are greater than 500 Å in size. These particles can be dispersed on the periphery or inside the pores of the substrate or at the same time on the periphery and inside the pores.
The aggregation state between metal particles is defined by the existence of at least one contact zone between at least two particles. The aggregation state is characterized by an analysis by microscopy with transmission of the catalyst before or after reduction of the active phase.
For the catalyst according to the invention, analysis by microscopy shows that at least 60% of the particles, preferably 80% of the particles, and even more preferably 90% of the particles have at least one contact zone with at least one other particle, and preferably with at least two other particles. The particles are preferably deposited in the form of essentially spherical agglomerates that are between 500 and 100,000 Å in size. They can also be used in the form of clusters or streams or any other configuration to have at least one contact zone with at least one other particle, preferably with two other particles
This invention involves a catalyst that is used in Fischer-Tropsch synthesis whose performances are particularly stable and which after reduction under hydrogen results in the conversion of the synthesis gas into a linear and saturated hydrocarbon mixture that contains at least 50% by weight of C5
+
hydrocarbons and at least 20% of methane relative to all. of the hydrocarbons that are formed.
The conditions of use of said catalysts for the synthesis of hydrocarbons are usually as follows:
The catalyst that comprises at least one metal of group VIII that is impregnated on a substrate is dried and then calcin
Marion Marie-Claire
Roy Magalie
Insitut Francais du Petrole
Millen White Zelano & Branigan P.C.
Parsa J.
Richter Johann
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