Chemistry of hydrocarbon compounds – Miscellaneous process – e.g. – indeterminate modification of a...
Reexamination Certificate
2001-11-06
2003-05-27
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Miscellaneous process, e.g., indeterminate modification of a...
C585S734000, C208S950000, C518S728000
Reexamination Certificate
active
06570047
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
Field of the Invention
The invention relates to a slurry hydrocarbon synthesis process which includes liquid isomerization in an external downcomer reaction loop. More particularly the invention relates to a slurry Fischer-Tropsch type of hydrocarbon synthesis process, in which the synthesized hydrocarbon slurry liquid in the synthesis reactor is circulated through at least one external downcomer reactor, in which it reacts with hydrogen in the presence of a hydroisomerization catalyst, and preferably a monolithic catalyst, to hydroisomerize the liquid and reduce its pour point. The liquid then passes back into the synthesis reactor.
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 hot reactive slurry in a hydrocarbon synthesis reactor. The slurry comprises synthesized hydrocarbons which are liquid at the synthesis reaction conditions and in which is dispersed a particulate Fischer-Tropsch type of catalyst. The H
2
and CO react in the presence of the catalyst and form hydrocarbons. The hydrocarbon liquid is continuously or intermittently withdrawn from the reactor and pipelined to one or more downstream upgrading operations. The upgraded products may include, for example, a syncrude, various fuels and lubricating oil fractions and wax. The downstream upgrading includes fractionation and conversion operations, typically comprising hydroisomerization, in which a portion of the molecular structure of at least some the hydrocarbon molecules is changed. It would be an improvement if the synthesized hydrocarbon slurry liquid could be hydroisomerized to reduce its pour and melt points, which make it more transportable by pipeline, before it is transferred to downstream operations.
SUMMARY OF THE INVENTION
The invention relates to a slurry Fischer-Tropsch type of hydrocarbon synthesis process, in which a portion of the synthesized hydrocarbon slurry liquid is passed out of the synthesis reactor and into at least one external downcomer reactor, in which it reacts with hydrogen in the presence of a hydroisomerization catalyst, and preferably a monolithic hydroisomerization catalyst, to hydroisomerize the liquid, which is then passed back into the three-phase slurry (main slurry body) in the synthesis reactor. The slurry liquid, which comprises synthesized hydrocarbons that are liquid at the synthesis reaction conditions, comprises mostly normal paraffins and the hydroisomerization reduces its pour and melt points, thereby making it more pumpable and pipelineable. By downcomer reactor is meant that all or most of the slurry circulation between it and the synthesis reactor is achieved by density-driven hydraulics, in which the density of the downflowing slurry is greater than in the synthesis reactor. Slurry densification is achieved by removing at least a portion of the gas bubbles from the slurry, thereby densifying the slurry, before it is passed into the downcomer reactor. The one or more downflow reactors may each be a simple, substantially vertical, hollow fluid conduit or pipe. The process comprises contacting hot slurry from the main slurry body, with means for removing gas bubbles, and preferably both gas bubbles and at least a portion of the particulate solids from the slurry liquid which, along with a hydrogen treat gas, is then passed out of the synthesis reactor and down into the one or more external downcomer reactors. The hydroisomerization catalyst is located in the interior of the downcomer reactor and comprises the hydroisomerization reaction zone. This hydroisomerized hydrocarbon liquid of reduced pour point is then passed back into the main slurry body in the synthesis reactor. Thus, the synthesized hydrocarbon liquid is passed out of the synthesis reactor, down into and through the interior of the one or more external downcomer reactors and back into the synthesis reactor. The downcomer reactor is in fluid communication with the main slurry body inside the synthesis reactor, via upper and lower conduit portions opening into respective upper and lower portions of the synthesis reactor. This enables hydroisomerization of the slurry liquid (i) in an external reaction loop which depends from, and is therefore part of, the synthesis reactor and (ii) while the synthesis reactor is producing hydrocarbons, but without interfering with the hydrocarbon synthesis reaction. The concentration of hydroisomerized hydrocarbon liquid in the synthesis reactor continues to increase until equilibrium conditions are reached. When the reactor reaches equilibrium, it is possible for the slurry liquid being removed from it to comprise mostly hydroisomerized hydrocarbons of reduced pour point. In some cases, no further hydroisomerization of the liquid hydrocarbon product withdrawn from the hydrocarbon synthesis reactor is necessary. Thus, the process of the invention will reduce and in some cases even eliminate the need for a separate, stand-alone hydroisomerization reactor and associated equipment, downstream of the synthesis reactor. If a downstream hydroisomerization reactor is needed, it will be smaller than it would be if the synthesized hydrocarbon liquid passed into it was not at least partially hydroisomerized. While all of the hydroisomerized hydrocarbon liquid is typically returned back into the main slurry body with which it mixes, in some embodiments a portion of the hydroisomerized liquid will be passed from the downcomer reactor directly to downstream operations.
Hydroisomerizing the slurry liquid in one or more external loops permits the use of heat exchange means associated therewith to adjust the hydroisomerization temperature to be different (e.g., higher) from that in the synthesis reactor. A higher hydroisomerization temperature enables the use of a less expensive, non-noble metal hydroisomerization catalyst. The gas bubble and preferably the slurry gas bubble and particulate solids removal means is preferably located in the main slurry body and may comprise the same or separate means. While various filtration means may be used to separate the slurry liquid from at least a portion of the catalyst and any other particles, before the slurry is passed down into the hydroisomerization zone, in the practice of the invention the use of filtration means may be avoided by using known slurry solids reducing means that do not employ filtration. Gas bubble and solids removal means suitable for use with the present invention are known and disclosed in, for example, U.S. Pat. Nos. 5,866,621 and 5,962,537, the disclosures of which are incorporated herein by reference. Simple gas bubble removing means are disclosed in U.S. Pat. Nos. 5,382,748; 5,811,468 and 5,817,702, the disclosures of which are also incorporated herein by reference. Removing gas bubbles from the slurry densities it and, if properly employed in connection with feeding the densified slurry down into and through the downcomer reactor (e.g., the slurry is densified sufficiently vertically above the external hydroisomerization zone), provides a density-difference driven hydraulic head to circulate the slurry from inside the synthesis reactor, down into and through the external downcomer reactor and back into the synthesis reactor. Removing gas bubbles from the slurry prior to hydroisomerization also reduces the CO and water vapor content of the flowing fluid, which could otherwise react with the hydroisomerization hydrogen and also adversely effect the hydroisomerization catalyst. A monolithic hydroisomerization catalyst having a minimal solid cross-sectional area perpendicular to the flow direction of the fluid, minimizes the pressure drop of the fluid flowing down and across the catalyst surface. Removing catalyst and other solid particles, such as inert heat transfer particles, from the slurry upstream of the hydroisomerization zone, reduces scouring of the monolithic catalys
Clark Janet Renee
Feeley Jennifer Schaefer
Mart Charles John
Wittenbrink Robert Jay
ExxonMobil Research and Engineering Company
Griffin Walter D.
Marin Mark D.
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