Chemistry: fischer-tropsch processes; or purification or recover – Including regeneration of catalyst
Reexamination Certificate
2000-06-02
2001-11-27
Richter, Johann (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Including regeneration of catalyst
C518S700000, C518S715000, C502S020000
Reexamination Certificate
active
06323248
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to a slurry hydrocarbon synthesis process, which includes increasing the activity of fresh catalyst in-situ in the slurry liquid, during the synthesis reaction. More particularly the invention relates to a slurry Fischer-Tropsch hydrocarbon synthesis process for producing hydrocarbons from a synthesis gas, wherein the activity of fresh synthesis catalyst added to the slurry reactor is increased in-situ in the slurry during the synthesis reaction.
2. Background of the Invention
The slurry Fischer-Tropsch hydrocarbon synthesis process is now well known and documented, both in patents and in the technical literature. This process comprises passing a synthesis gas which comprises a mixture of H
2
and CO, up into a reactive slurry comprising a hot, synthesized hydrocarbon liquid, in which a suitable, particulate Fischer-Tropsch type of catalyst is dispersed and suspended, at reaction conditions effective for the H
2
and CO to react and form liquid hydrocarbons. The hydrocarbon liquid is continuously withdrawn from the reactor and upgraded by one or more upgrading steps, which include fractionation and conversion operations such as hydroconversion, in which a portion of the molecular structure of at least some of the hydrocarbon molecules is changed. The upgraded products may include, for example, a syncrude, various fuels and lubricating oil fractions and wax. During the synthesis reaction, the presence of reversibly deactivating catalyst species present in the synthesis gas, such as NH
3
and HCN, causes a reduction in catalyst activity. This activity loss is reversible and may be restored in-situ in the reactor by rejuvenation, as is known and disclosed, for example, in U.S. Pat. No. 5,283,216; 5,811,363; 5,811,468; 5,817,702; 5,821,270; 5,844,005 and 5,958,986. Catalyst rejuvenation is achieved by passing hydrogen or a hydrogen treat gas into the bottom of a vertically oriented, hollow conduit or tube immersed in the slurry or external of the synthesis reactor in a separate vessel. This sets up a slurry circulation in the tube, in which the hydrogen gas contacts the catalyst particles in the slurry liquid, thereby rejuvenating them by restoring at least part of their activity. Some of the activity loss is permanent, which ultimately requires catalyst regeneration or replacement. One of the advantages of the slurry process, is the ability to add and remove catalyst without taking the reactor off-line and thereby stopping the synthesis reaction. U.S. Pat. No. 5,292,705 discloses that the activity of a fresh Fischer-Tropsch type of hydrocarbon synthesis catalyst can be increased by treatment with hydrogen in a hydrocarbon liquid, including in-situ in the hydrocarbon synthesis slurry in the synthesis reactor. The hydrogen treatment for increasing the catalytic activity is preferably conducted in the absence of CO. Thus, in this process, if the catalyst activity is increased by treatment in-situ in the hydrocarbon synthesis slurry in the slurry synthesis reactor, the synthesis reactor is not producing hydrocarbons while the activity of the fresh catalyst is increased. It would be an improvement to the art if the activity of fresh catalyst added to the reactor could be increased while the reactor is producing hydrocarbons and without adversely effecting the selectivity or productivity of the synthesis reaction.
SUMMARY OF THE INVENTION
The present invention relates to a process for increasing the activity, and therefore the productivity, of a fresh hydrocarbon synthesis catalyst above its initial value, by contacting it with hydrogen or a hydrogen treat gas, in-situ in the hydrocarbon synthesis slurry used for synthesizing hydrocarbons in the slurry Fischer-Tropsch hydrocarbon synthesis reactor, while the reactor is producing hydrocarbons from the synthesis gas feed. This is achieved by adding the fresh catalyst to the hydrocarbon synthesis slurry in, or external of, the synthesis reactor and circulating a portion of the slurry containing the fresh catalyst up through one or more catalyst activity increasing means, the interior of which is isolated from the slurry body in the synthesis reactor. Hydrogen or a hydrogen treat gas is passed into the means, in which it contacts the fresh catalyst particles in the flowing slurry and increases their activity. By fresh catalyst is meant one that is new and has not been used, or has been in use only for a relatively short period of time and has an activity of at least 85%, preferably at least 90% and more preferably at least 95% of the initial value of a new and unused catalyst. By initial value is meant the lined out activity level the fresh catalyst exhibits when first added to the slurry, extrapolated back to zero time. The activity is calculated based on the extent of CO conversion and, for a given catalyst, is effected by the space velocity, temperature, and partial pressure of the reactants and reaction products, as well as the hydrodynamics in the slurry reactor. 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. In contrast to the process disclosed in U.S. Pat. No. 5,292,705, in which the synthesis reactor is off-line and not producing hydrocarbons while increasing the activity of the fresh catalyst in-situ in the slurry in the synthesis reactor, in the process of the invention the activity of the fresh catalyst is increased in-situ in the slurry in the synthesis reactor without interrupting or interfering with the hydrocarbon synthesis reaction. This is made possible, because the catalyst activity increasing zone, even if it is wholly immersed in the slurry body in the synthesis reactor, is isolated from it. The catalyst activity increasing process of the invention eliminates the need for (i) the addition of heat to the reactor, (ii) additional hydrogen capacity and (iii) compressors to deliver sufficient hydrogen to the reactor to maintain slurry circulation and catalyst dispersion in the slurry liquid while increasing the catalyst activity.
In the process of the invention, the fresh catalyst in the form of solid particles or slurried in an appropriate hydrocarbon liquid, is added to the hydrocarbon synthesis slurry. The hydrocarbon synthesis slurry containing the fresh catalyst is contacted with a hydrogen treat gas in one or more catalyst activity increasing zones, in which it contacts the fresh catalyst particles and increases their activity. The slurry containing the activity increased catalyst is then returned to the hydrocarbon synthesis slurry body (hereinafter “slurry body”) in the hydrocarbon synthesis reactor. In one embodiment, the fresh catalyst is added to the hydrocarbon synthesis slurry, by adding it to the slurry body in the reactor, with a portion of the slurry body, now containing the fresh catalyst, circulated from the slurry body up through and out of the one or more catalyst activity increasing zones and back into the slurry body. In another embodiment, the fresh catalyst is added to the hydrocarbon synthesis slurry in the one or more zones, as the hydrocarbon synthesis slurry and hydrogen treat gas pass up and through the zones, with the slurry containing the activity increased fresh catalyst then returned back to the slurry body in the synthesis reactor. Thus, the expression “the fresh catalyst is added to the hydrocarbon synthesis slurry” is meant to include one or both of these two embodiments. By “hydrocarbon synthesis slurry” is meant either the slurry body in the synthesis reactor, or slurry withdrawn from the slurry body with or without gas bubble removal prior to passing it into the one or more catalyst activity increasing zones or means. The hydrocarbon synthesis slurry comprising the slurry body in the synthesis reactor comprises catalyst particles and gas bubbles dispersed in a hydrocarbon slurry liquid.
The catalyst activity increasing means may comprise a h
Mart Charles John
Neskora Daniel Ray
ExxonMobil Research and Engineering Company
Parsa J.
Richter Johann
Simon Jay
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