Preparation of high activity catalysts; the catalysts and...

Details Preparation of high activity catalysts; the catalysts and... Preparation of high activity catalysts; the catalysts and...

1998-09-15

2001-12-18

Killos, Paul J. (Department: 1621)

Chemistry: fischer-tropsch processes; or purification or recover

Group viii metal containing catalyst utilized for the...

C518S700000, C585S734000, C208S028000, C044S281000

Reexamination Certificate

active

06331575

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process, or method, for the production of a high activity catalyst by dispersion of a catalytic metal, or metals, particularly copper or an Iron Group metal, notably cobalt, or both a catalytic metal and rhenium onto a refractory inorganic oxide support, notably titania; the catalyst; its reduction, and use of the catalyst for conducting carbon monoxide hydrogenation reactions, especially Fischer-Tropsch reactions.
BACKGROUND
Carbon monoxide hydrogenation reactions are well known. For example, Fischer-Tropsch synthesis processes, or processes for the catalytic conversion of synthesis gas, i.e., a mixture of hydrogen and carbon monoxide, to high quality distillate fuels or mixtures of C
5
+ liquid hydrocarbons are well known. For example, the Group VIII non-noble metals, iron, cobalt, and nickel have been widely used to catalyze Fischer-Tropsch reactions, and these metals have been deposited on various supports, and promoted with various other metals. In U.S. Pat. No. 4,568,663, e.g., there is disclosed a process of this type which utilizes a highly active catalyst composition constituted of cobalt-rhenium-titania, Co—Re—TiO
2
. This catalyst is made, e.g., by impregnating a concentrated aqueous solution of cobalt nitrate and perrhenic acid onto a titania support by the conventional incipient wetness method, drying, and then calcining to decompose the nitrate salt to the oxide. Several important functions are served by the rhenium. A major function is served by rhenium during the calcination of the catalyst, during which cobalt nitrate decomposes to cobalt oxide, in that it causes the cobalt oxide to become more highly dispersed. It also preserves the cobalt oxide in highly dispersed state under high temperature oxidizing conditions, such as is found useful for regenerating cobalt catalysts. It is also a function of the rhenium to lower the temperature of the reduction of cobalt oxide to the zero valence state, which is required to achieve full activity. Rhenium makes it easier to more fully reduce the cobalt. High dispersal, and full reduction of the cobalt results in a more active catalyst. This result however does not come without cost, for rhenium is a relatively expensive commodity. Thus, there exists a need for means to better disperse the cobalt with a lesser amount of rhenium, find means for recovering the rhenium, or find other more available, less expensive materials for promoting the dispersion, and reduction of the metals.
SUMMARY OF THE INVENTION
The present invention, which meets this and other needs, relates to a novel process for the preparation of a catalyst useful for the hydrogenation of carbon monoxide, especially to a Fischer-Tropsch catalyst, the catalyst, and process for the use of this catalyst for conducting such reactions, especially Fischer-Tropsch synthesis reactions, i.e., reactions for the production of C
5
+ liquid hydrocarbons from hydrogen and carbon monoxide. In the preparation of the Fischer-Tropsch catalyst, a preformed particulate refractory inorganic solids support is impregnated with (a) a compound, or salt, of a catalytic metal, or metals, suitably copper or an Iron Group metal and (b) a polyol or polyhydric alcohol. And preferably, a preformed particulate refractory inorganic solids support, preferably titania, is impregnated with (a) a compound, or salt, of a catalytic metal, or metals, suitably copper or an Iron Group metal, (b) a polyol, or polyhydric alcohol, and (c) a compound, or salt, of rhenium. In impregnating the support, the support is contacted, preferably, with a single solution containing both (a) and (b), or all of (a), (b), and (c), respectively. The polyol is sufficient to distribute the compound or salt of the catalytic metal, copper or Iron Group metal in highly dispersed form, onto the support; and, the rhenium, when added, is sufficient to produce full reduction of the dispersed metal. Whereas rhenium has been used in the past to produce both of these functions, a far lesser amount of rhenium is required to produce both dispersion and reduction of the metal when the rhenium is used in conjunction with the polyol.
Polyols useful in the practice of this invention are characterized as molecules containing straight carbon chains, at least two carbon atoms of which bears a hydroxyl group; the preferred polyols having the following empirical formula:
C
n
H
2n+2
O
x
where n is an integer ranging from 2 to about 6, and x is an integer ranging from 2 to n. In other words, n is 2, 3, 4, 5 or about 6, and 2≦x ≦ n this including such polyols as 2,3-dihydroxybutane, 2,3,4-trihydroxypentane, 2,2-dihydroxyhexane, 2,2,4-trihydroxyhexane, and including more preferably the sugar alcohols; most preferably those alcohols having the formula
HOCH
2
—(CHOH)
n′
—CH
2
OH
where n′ is an integer defining the number of CHOH groups, or groups in a straight chain of carbon atoms each of which bears a hydrogen and a hydroxyl group, n′ ranging from 0 to about 4, and more preferably from about 2 to about 4. Exemplary of polyhydric alcohols, or polyols, useful in the practice of this invention are glycol, a dihydric alcohol; glycerol, a trihydric alcohol; tetritols such as erythritol, threitol, and the like; pentitols, such as ribitol, arabinitol, xylitol, and the like; and hexitols, such as allitol, dulcitol, gluciotol, sorbitol, mannitol, and the like.
It has been found that the copper or Iron Group metal can be more effectively dispersed onto the support via use of the polyol than with rhenium, as a consequence of which no rhenium is required to effect a full, and complete dispersion of the catalytic metal, or metals. However, some rhenium is generally useful, and sometimes required since its presence enables a more complete and full reduction of the dispersed copper or Iron Group metal to the zero valent state. Accordingly, in the preferred practice of this invention, a small amount of a compound or salt of rhenium, and both a compound or salt of copper or an Iron Group metal and a polyol are employed to disperse the copper or Iron Group metal, and rhenium, into the solids support component of the catalyst during the impregnation; dispersion of the copper or Iron Group metal into the preformed catalyst resulting from the presence of the polyol, while the rhenium is effective in permitting full reduction of the catalyst after calcination. The copper or Iron Group metal compound, and rhenium compound, are thus effectively dispersed during the impregnation step, and during calcination the polyol is removed by combustion leaving behind crystallites of well dispersed oxides of the copper or Iron Group metal and the rhenium. Essentially complete reduction of the crystal-lites of the metals is achieved on contact of the calcined catalyst with a reducing agent, e.g., hydrogen. Surprisingly, in the preparation of a catalyst it is found that considerably less rhenium is required overall when prepared with a polyol to produce a full, similar level of activity in a reduced copper or Iron Group metal/rhenium catalyst of given composition, used in a carbon monoxide hydrogenation or Fischer-Tropsch reaction, than with a reduced catalyst of corresponding composition, used in a similar carbon monoxide hydrogenation or Fischer-Tropsch reaction at similar process conditions, made in a preparation otherwise similar except that the catalyst was made without use of a polyol.
DETAILED DESCRIPTION
The catalysts are formed by deposition of the catalytic metal, or metals, on a previously pilled, pelleted, beaded, extruded, spray dried, or sieved support material by the impregnation method. In preparing the catalysts, the metals are deposited from solutio-n on the support in preselected amounts to provide the desired absolute amounts, and weight ratios of the metals being deposited. Catalysts constituted of cobalt and rhenium supported on titania, or a titania-containing support, silica, etc. with or without the addition of an additional metal, or metals, promoter or modifier, e.g.,

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