Chemistry: fischer-tropsch processes; or purification or recover – Liquid phase fischer-tropsch reaction
Reexamination Certificate
2000-10-27
2002-03-19
Padmanabhan, Sreeni (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Liquid phase fischer-tropsch reaction
C585S734000, C585S700000, C585S752000, C208S057000, C208S133000, C208S161000, C518S706000
Reexamination Certificate
active
06359018
ABSTRACT:
FIELD OF THE INVENTION
This invention is generally in the area of the Fischer-Tropsch synthesis, particularly in the area of hydroprocessing of Fischer-Tropsch waxy products.
BACKGROUND OF THE INVENTION
The majority of fuel today is derived from crude oil. Crude oil is in limited supply, and fuel derived from crude oil tends to include nitrogen-containing compounds and sulfur-containing compounds, which are believed to cause environmental problems such as acid rain.
Natural gas is an abundant source of hydrocarbon fuels, lubricating oils, all chemicals and chemical feedstocks. One method of using natural gas in this way involves converting the gas to synthesis gas (“syngas”). For example, in a Fischer-Tropsch process, the syngas produced from a natural gas source is converted to a product stream that includes a broad spectrum of products, ranging from methane to wax. The resulting wax can be hydroprocessed to form lower molecular weight products in the distillate fuel and lubricating oil range. The hydroprocessing is carried out by passing the wax downwardly through one or more catalyst beds, with a cocurrent hydrogen enriched gas stream. The liquid hydrocarbon feed “trickles” down through the catalyst beds and exits the reactor bottom after the desired upgrading is achieved (i.e., a downflow reactor).
In some cases, the feeds prepared for hydroprocessing contain particulate contaminants from upstream processing, such as catalyst fines, catalyst support and the like, upstream equipment (rust and scale), and/or from the source (e.g., crude oil, coal ash) in a wide range of sizes and concentrations. These particulates can cause serious operating difficulties when introduced with the feed into a fixed-bed, trickle-flow hydroprocessing reactor. The most frequent difficulty is pressure drop build-up and eventual plugging of the flow-paths through the catalyst beds as the catalyst pellets filter out the feed particulates. Such build-up can cause significant economic loss in lost production and replacement catalyst costs.
Fischer-Tropsch wax and heavy products, especially those from slurry and fluid bed processes, may contain particulate contaminants such as catalyst fines, which are not adequately removed by filters provided for that purpose. Removing these particulates prior to hydroprocessing is complicated by the viscosity and temperature of the wax stream leaving the Fischer-Tropsch reactor. It would be advantageous to provide an efficient process for hydroprocessing the wax and heavy products from Fischer-Tropsch syntheses that overcomes the need to have nearly complete removal of the particulate contaminants from the heavy products prior to hydroprocessing. The present invention provides such a process.
SUMMARY OF THE INVENTION
The invention provides the described advantages as well as many others obvious to the ordinary skilled artisan. An integrated process for hydroprocessing a Fischer-Tropsch product containing particulate contaminates such as catalyst fines, is disclosed. The process involves performing Fischer-Tropsch synthesis and obtaining a hydrocarbon fraction which contains particulate contaminants. The fraction is subjected to hydroprocessing conditions, preferably upflow hydroprocessing conditions, using a catalyst bed which, through judicious selection of hydroprocessing catalysts and/or flow conditions, permits passage of the particulate contaminants through the bed. Particulate contaminants remaining in the liquid products recovered from hydroprocessing are then removed from the hydroprocessed liquid product, for example by filtration, centrifugation and/or distillation, which is significantly easier than filtering the particulate contaminants from the Fischer-Tropsch synthesis product.
The present method is effective for removing contaminants from any Fischer-Tropsch product stream, regardless of boiling range. In one embodiment, the invention is directed to producing and hydroprocessing heavy Fischer-Tropsch products rich in linear hydrocarbons with a chain length above C
20
. In producing a desirable distillate fuel composition, a Fischer-Tropsch product is hydroprocessed to remove oxygenates, to form isoparaffins through hydroisomerization of the normal paraffins in the heavy Fischer-Tropsch products, and/or to crack the heavy Fischer-Tropsch products to reduce their boiling point range. Hydroisomerization improves the cold properties (e.g., pour point, cloud point, cold filter plugging point (CFPP)) of the products. The hydroprocessing steps may include hydrodewaxing, hydrocracking, hydroisomerization, hydrotreating and other processes. Standard known hydroprocessing catalysts are employed in catalytically effective amounts.
According to the invention, a process is provided for upgrading a Fischer-Tropsch product, wherein the process comprises subjecting syngas to Fischer-Tropsch synthesis conditions, recovering a hydrocarbon fraction from the Fischer-Tropsch synthesis, wherein the fraction further comprises particulate contaminants, subjecting the fraction to hydroprocessing conditions and forming an upgraded product stream which includes at least a portion of the particulate contaminants, and removing at least a portion of the particulate contaminants from the upgraded product stream.
DETAILED DESCRIPTION
An integrated process for producing a liquid hydrocarbon stream from a Fischer-Tropsch process is disclosed. The integrated process involves performing Fischer-Tropsch synthesis, preferably under conditions which favor formation of wax and heavy products (i.e., using a catalyst with high chain growth probabilities), and obtaining hydrocarbon fraction including particulate contaminants such as catalyst fines. Fischer-Tropsch processes that have slurry or fluidized bed reactors are particularly subject to entrained catalyst particulates. The fraction is subjected to hydroprocessing conditions, preferably upflow hydroprocessing conditions, using a catalyst bed which, through judicious selection of hydroprocessing catalysts and/or flow conditions, permits passage of the particulate contaminants. The resulting products are liquid hydrocarbon products which still include the particulate contaminants. At least a portion of the particulate contaminants are then removed from the liquid product, for example by filtration, centrifugation and/or distillation, which is significantly easier than filtering the particulate contaminants from the Fischer Tropsch products.
The catalysts, reactants, reaction conditions and methods for preparing and isolating desired compounds are discussed in more detail below.
In addition to methane, natural gas includes some heavier hydrocarbons (mostly C
2-5
paraffins) and other impurities, e.g., mercaptans and other sulfur-containing compounds, carbon dioxide, nitrogen, helium, water and non-hydrocarbon acid gases. The methane and/or ethane can be isolated and used to generate syngas. Various other impurities can be readily separated. Inert impurities such as nitrogen and helium can be tolerated. The methane in the natural gas can be isolated, for example in a demethanizer, and then de-sulfurized and sent to a syngas generator.
Methane (and/or ethane and heavier hydrocarbons) can be desulfurized and sent through a conventional syngas generator to provide synthesis gas. Typically, synthesis gas contains hydrogen and carbon monoxide, and may include minor amounts of carbon dioxide and/or water.
The presence of sulfur, nitrogen, halogen, selenium, phosphorus and arsenic contaminants in the syngas is undesirable. For this reason, it is preferred to remove sulfur and other contaminants from the feed before performing the Fischer-Tropsch chemistry or other hydrocarbon synthesis. Means for removing these contaminants are well known to those of skill in the art. For example, ZnO guard beds are preferred for removing sulfur impurities. Means for removing other contaminants are well known to those of skill in the art.
The Fischer-Tropsch products tend to include linear hydrocarbons with a chain length above C
20
. For use in distillate fuel co
Moore, Jr. Richard O.
O'Rear Dennis J.
Parimi Krishniah
Chevron U.S.A. Inc
Klaassen Alan W.
Padmanabhan Sreeni
Parsa J.
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