Slurry hydrocarbon synthesis process with increased catalyst...

Details Slurry hydrocarbon synthesis process with increased catalyst... Slurry hydrocarbon synthesis process with increased catalyst...

1998-08-14

2001-09-04

Yildirim, Bekir L. (Department: 1764)

Chemistry: fischer-tropsch processes; or purification or recover

Including regeneration of catalyst

Solvent utilized

C518S715000, C585S733000, C585S638000, C502S030000, C502S031000, C502S053000

Reexamination Certificate

active

06284807

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to a hydrocarbon synthesis process with increased catalyst life. More particularly, the invention relates to a slurry catalytic hydrocarbon synthesis process employing a supported cobalt metal catalyst in which catalyst half life is increased by using a syngas feed containing less than fifty parts per billion of nitrogenous, catalyst deactivating species.
2. Background of the Invention
Slurry hydrocarbon synthesis (HCS) processes are known. In a slurry HCS process a synthesis gas (syngas) comprising a mixture of H
2
and CO is bubbled up as a third phase through a slurry in a reactor in which the slurry liquid comprises hydrocarbon products of the synthesis reaction and the dispersed, suspended solids comprise a suitable Fischer-Tropsch type hydrocarbon synthesis catalyst. Reactors which contain such a three phase slurry are sometimes referred to as “bubble columns”, as is disclosed in U.S. Pat. No. 5,348,982. Irrespective of whether the slurry reactor is operated as a dispersed or slumped bed, the mixing conditions in the slurry will typically be somewhere between the two theoretical conditions of plug flow and back mixed. It is also known that Fischer-Tropsch type catalysts useful for forming hydrocarbons from a syngas are rapidly, but reversibly deactivated by certain nitrogenous species in the syngas feed, particularly HCN and NH
3
. Syngas made from hydrocarbon feedstocks which contain nitrogen (i.e., natural gas) or nitrogen containing compounds (i.e., resids, coal, shale, coke, tar sands, etc.) invariably contains HCN and NH
3
which contaminate the reactive slurry and deactivate the catalyst. Certain oxygenates and carbonaceous compounds which are formed in the slurry as by-products of the HCS reaction are also believed to cause rapid deactivation. Deactivation of such catalysts by HCN and NH
3
may be reversed and catalytic activity restored (rejuvenated) by contacting the deactivated catalyst with hydrogen or a hydrogen containing gas (rejuvenating gas). Deactivation of such catalysts by these species is reversible and catalytic activity is restored (the catalyst rejuvenated) by contacting the deactivated catalyst with hydrogen either continuously or intermittently as is disclosed, for example, in U.S. Pat. Nos. 5,260,239; 5,268,344 and 5,283,216. While methods have been suggested for reducing the HCN and NH
3
content of syngas down to about 0.1 ppm (100 ppb) by catalytic hydrolysis (U.S. Pat. No. 4,769,224) and chemical scrubbing (U.S. Pat. No. 5,068,254), it has now been found that even as little as 100 vppb of a combined total of HCN and NH
3
in the syngas will result in a catalyst half life of only four days for the case of a supported Co metal catalyst in an HCS slurry. It has now been found that reducing the level of the HCN and NH
3
catalyst poisons in the syngas below 50 ppb produces increased catalyst life and requires less catalyst rejuvenation. A method for achieving such low levels has also been found and is disclosed in U.S. Pat. No. 6,107,353.
SUMMARY OF THE INVENTION
The present invention relates to a slurry hydrocarbon synthesis (HCS) process employing a supported cobalt metal catalyst in which the short term catalyst half life is at least 10 days, preferably at least 30 and more preferably at least 40 or more days. By short term half life is meant that the catalytic activity caused by reversible deactivation of the catalyst is 50% that of fresh catalyst and that this loss is substantially restored (the catalyst rejuvenated) by contacting the deactivated catalyst with a rejuvenating gas comprising H
2
. Catalyst activity is defined in terms of the CO conversion to hydrocarbons. Thus, if under a given set of HCS conditions fresh catalyst produces a CO conversion of 80 mole %, the catalyst half life is realized when the conversion drops to 40%, as a result of contact with the reversibly deactivating nitrogenous species in the synthesis gas (syngas) feed. By reversibly deactivating nitrogenous species is meant HCN, NH
3
and mixture thereof. It is also an embodiment of the process of the invention that the catalyst will have a long term half life of at least 100 days and preferably at least 200 days. It has been found that there is also an unrejuvenable catalyst activity loss which occurs over time, which cannot be restored by contacting the catalyst with H
2
, but which can be restored by regeneration. The unrejuvenable, but regenerable loss in catalyst activity drops continuously, so that eventually the catalyst has a CO conversion activity at its long term half life only half or 50% of fresh catalyst and this long term activity loss cannot be restored (the catalytic activity cannot be rejuvenated) by contacting the deactivated catalyst with H
2
or a H
2
containing rejuvenating gas. Thus, by long term half life is meant the time it takes the catalyst to have only half the activity of fresh catalyst and that this activity loss, while reversible, is not restored by a rejuvenation process in which the deactivated catalyst is contacted with H
2
or an H
2
containing gas. Instead, the catalyst has to be separated from the slurry and regenerated by processes that include oxidation or burning, rereduction of the catalytic metal(s) and, optionally, passivation in CO and/or syngas. Thus, long term loss of catalyst activity in the context of the invention is regenerable, but not rejuvenable with H
2
. Further, regenerable activity loss is different from irreversible catalyst activity loss due to, for example, sulfur poisoning, which requires catalyst replacement. The relatively long short term and long term catalyst life in the practice of the invention is achieved by using a syngas feed in which the total level of the catalyst deactivating nitrogenous species HCN, NH
3
and mixture thereof is less than 50 vppb (volume parts per billion), preferably less than 20 vppb, and still more preferably less than 10 vppb. A slurry HCS catalyst useful in the practice of the invention comprises a catalytically active cobalt component dispersed and supported on a particulate inorganic refractory oxide carrier or support, and preferably as a thin catalytically active surface layer, ranging in thickness from about 5-200 microns. It is also preferred that the catalyst have a productivity of at least 150 hr
−1
at 200° C., preferably at least 500 hr
−1
and more preferably at least 1000 hr
−1
. By productivity is meant the standard volume of CO converted per volume of catalyst per hour. In a further embodiment, the catalyst employed in the process of the invention will have a methane selectivity of less than 10 mole % and preferably less than 5 mole %. This means that less than 10% of the CO converted is converted to methane. In one embodiment the catalyst comprises catalytically effective amounts of Co and one or more of Re, Ru, Fe, Ni, Th, Zr, Hf, U, Mg and La on a suitable inorganic support material, and preferably one which comprises one or more refractory metal oxides. Preferred supports for Co containing catalysts comprise titania and titania-silica composites, particularly when employing a slurry HCS process in which higher molecular weight, primarily paraffinic liquid hydrocarbon products are desired. Useful catalysts and their preparation are known and illustrative, but nonlimiting examples may be found, for example, in U.S. Pat. Nos. 4,568,663; 4,663,305; 4,542,122; 4,621,072 and 5,545,674, with those disclosed in U.S. Pat. No. 5,545,674 being particularly preferred.
An HCS slurry process of the invention comprises reacting a syngas which contains HCN, HN
3
or mixture thereof in the presence of a solid, particulate HCS catalyst in a slurry which comprises the catalyst and gas bubbles in a hydrocarbon slurry liquid, at reaction conditions effective to produce hydrocarbons from the syngas, wherein the total amount of HCN, HN
3
or mixture thereof in the syngas is less than 50 vppb, preferably less than 20 vppb and more preferably less that 10 vppb to achieve a short ter

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