Process for increasing cobalt catalyst hydrogenation...

Details Process for increasing cobalt catalyst hydrogenation... Process for increasing cobalt catalyst hydrogenation...

2000-08-01

2002-10-15

Parsa, Jafar (Department: 1621)

Chemistry: fischer-tropsch processes; or purification or recover

Including regeneration of catalyst

C518S700000, C518S715000, C502S020000, C502S022000, C502S023000, C502S241000, C502S325000, C502S326000, C208S015000, C208S018000, C208S061000, C208S133000

Reexamination Certificate

active

06465529

ABSTRACT:

1. FIELD OF THE INVENTION
A process for the preparation of catalyst precursors, and catalysts made therefrom useful for conducting carbon monoxide hydrogenation reactions, especially Fischer-Tropsch reactions, and products made from such catalysts. It also relates to a process for producing, reactivating and/or increasing the activity of catalysts for use in conducting such reactions.
2. BACKGROUND
Processes for the hydrogenation of carbon monoxide to produce waxy and/or oxygenated products for upgrading to highly valued chemical materials and/or hydrocarbon fuels are well documented in the technical and patent literature. For example, in the Fischer-Tropsch (F-T) process, it is well known that the carbon monoxide component of synthesis gas can be catalytically converted by reaction with the hydrogen to reduction products constituting a range of waxy liquid hydrocarbons; hydrocarbons which can be readily upgraded to transportation fuels. In these processes, e.g., catalysts constituted of Group VIII metals (Periodic Table of the Elements, Sargent-Welch Scientific Company, Copyright 1968), notably the Iron Group metals, particularly iron, ruthenium and cobalt, are generally preferred for the synthesis of C
5
+ hydrocarbons; and copper has become the catalytic metal of choice for alcohol synthesis. These metals can exist in multiple valence states, and each state can display quite different behavior from the others during the reduction treatments, hence impacting the catalytic properties of the active catalyst. Each of the metals can be promoted or modified with an additional metal, or metals, or oxide thereof, to improve, e.g., the activity and/or selectivity of the catalyst in conducting these reactions.
Iron Group metal surfaces exhibit higher activities for catalytic reactions such as hydrogenation, methanation and F-T synthesis when catalysts on which these metals are dispersed are subjected to high temperature oxidation, and subsequent reduction. Recent art can be found in Applied Catalysis, A, General 175 (1998) pp. 113-120 and references therein. U.S. Pat. Nos. 4,492,774; 4,399,234; 4,493,905; 4,585,789; 4,088,671; 4,605,679; 4,670,414 and EPO 253924 disclose activation of cobalt catalysts by means of a reduction/oxidation/reduction (R-O-R) cycle, resulting in an increase in activity for F-T synthesis. Thus, typically such catalyst, e.g., supported reduced Co in the form of either a freshly prepared catalyst, or a low activity or deactivated catalyst, is contacted at high temperatures ranging from about 300° to about 600° C. with a gaseous oxygen-containing stream to oxidize the metal, or metals, to a metal oxide form, e.g., Co
3
O
4
. Precautions are taken during such treatments to control the exothermicity of the reaction to avoid sintering of the oxide metal particles, an effect which can be detrimental to the activity of the catalyst. On reduction, i.e., on completion of the oxidation-reduction cycle, the dispersed oxide particles, e.g., the Co
3
O
4
, of the catalyst are reduced to dispersed metallic particles and the activity is increased or the fresh catalyst activated.
Considerable progress has been made in the development of catalysts, and processes, these providing good activity, and selectivity in alcohol synthesis, and in the conversion of hydrogen and carbon monoxide to distillate fuels, predominantly C
5
+ linear paraffins and olefins, with low concentrations of oxygenates. Nonetheless, there remains a pressing need for improved catalysts, and processes; particularly processes for activating and regenerating such catalysts.
3. SUMMARY OF THE INVENTION
This need and others are achieved in accordance with the present invention relating to an Aqueous Low Temperature Oxidation (ALTO) process for the preparation of, or the activation or reactivation of a cobalt catalyst. The process requires, beginning with a cobalt catalyst or catalyst precursor constituted of a composite having a particulate solid support, or powder component, and a metal, or metals component, inclusive of cobalt at least a portion of which is present as metallic cobalt, catalytically active for conducting carbon monoxide hydrogenation reactions, especially F-T synthesis reactions, contacting the catalyst or catalyst precursor with an oxidant in the presence of water, at sufficiently low temperature to avoid complete evaporation of the water. On reduction, the hydrogenation activity of the cobalt catalyst or catalyst precursor is increased. The hydrogenation activity, especially the carbon monoxide hydrogenation activity of the catalyst precursor, is increased by oxidizing and converting at least initially all or a portion of the metal, or metals component of the catalyst or catalyst precursor to cationic or oxy-anionic species. By oxidation, as used in the ALTO process is meant the conversion of a catalytic metal species to an ionic state, e.g., the conversion of the Co
o
species to a Co
2+
species.
The ALTO process can be effected by contacting the catalyst or catalyst precursor in the presence of water at reaction conditions with gaseous oxidants or by using water-soluble or water miscible oxidants. Typically, the aqueous oxidizing liquid is water to which an oxidant is added. On contact of the catalyst or catalyst precursor with the aqueous oxidizing liquid, it is found that the catalytic metal(s) component thereof, at least a portion of that which is present as metallic cobalt, is transformed to a multitude of metal salts or compounds, including but not limited to metal hydroxides, nitrates, metal oxy-anions, oxyhydroxides, and the like. On reduction of the oxidized metal species, as may be produced by contact and treatment of the oxidized catalyst or catalyst precursor with hydrogen or a hydrogen containing gas, the oxidized metal, or metals is reduced to metallic metal or metals, e.g., Co; and the catalyst or regenerated catalyst thereby activated. Optionally, the oxidized catalyst or catalyst precursor may be dried. The metal compounds or salts formed during drying may be converted to metal oxides, i.e., CoO or Co
3
O
4
. In yet another option, the oxidized catalyst or catalyst precursor may be dried and calcined in an oxidizing atmosphere to obtain yet another oxidized catalyst precursor containing metal oxide or metal oxides, e.g., Co
3
O
4
. In both options, the catalyst or regenerated catalyst is activated by reduction of the oxidized catalysts or catalyst precursors. The catalyst precursors made from the catalyst or catalyst precursor via aqueous oxidation are useful for improving the performance, e.g., activity or selectivity of the activated or regenerated catalysts in carbon monoxide hydrogenation, especially F-T synthesis reactions.
The exothermicity of the ALTO treatment is effectively controlled by the high heat capacity and high heat transfer properties of a sufficient volume of liquid water. The reaction may be carried out at incipient wetness conditions or with an excess of water, resulting in a catalyst/water slurry. Upon completion of the reaction, excess water is eliminated by either filtration, decantation or by evaporation. By excess water is meant any water in excess of the volume necessary for filling the pore volume of the oxidized catalyst.
During the oxidation treatment, other metal salts or metal oxy-anion derivatives, e.g., perrhenic acid or salts, may be formed. When such salts or oxo-anions derivatives are soluble, it is preferable to use the evaporation or the incipient wetness methods in order to retain such metal salts on the catalyst surface. On completion of the oxidation treatment, the oxidized catalyst is then dried.
The metal compounds or salts as well as any metal oxy-anion(s) are intimately dispersed on the surface of the support, hence providing upon reduction with hydrogen or a hydrogen containing gas, metal (or metals) crystallites which are highly active species in carbon monoxide hydrogenation. Optionally, when the oxidized catalyst or catalyst precursor is calcined, the metal compounds or salts are converted to oxide particle

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