Chemistry: fischer-tropsch processes; or purification or recover – Liquid phase fischer-tropsch reaction
Reexamination Certificate
2001-01-11
2003-01-07
Warden, Jill (Department: 1743)
Chemistry: fischer-tropsch processes; or purification or recover
Liquid phase fischer-tropsch reaction
C436S060000
Reexamination Certificate
active
06503956
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the area of chemical analysis of Fischer-Tropsch waxes, in particular, the determination of heteroatom content in Fischer-Tropsch waxes.
BACKGROUND OF THE INVENTION
The majority of combustible fuel used in the world today is derived from crude oil. There are several concerns with using crude oil as a fuel source. Crude oil is includes aromatic compounds believed to cause cancer. It also includes sulfur and nitrogen compounds that add to air pollution upon burning.
Combustible liquid fuels can also be prepared from natural gas. This involves converting the natural gas, which is mostly methane, to synthesis gas (syngas), which is a mixture of carbon monoxide and hydrogen. Fischer-Tropsch chemistry is typically used to convert the syngas to a product stream that includes combustible fuel, among other products.
Fischer-Tropsch chemistry tends to produce a broad spectrum of products, ranging from methane to wax. Product slates for syngas conversion over Fischer-Tropsch catalysts (Fe, Co and Ru) are controlled by polymerization kinetics with fairly constant chain growth probabilities, which fix the possible product distributions. Heavy products with a relatively high wax content are produced when chain growth probabilities are high. Methane is produced with high selectivity when chain growth probabilities are low. While methane can be recirculated to ultimately yield combustible liquid fuel, it is typically preferable to form heavy products such as wax. These heavy products can be processed, for example, by hydrocracking followed by oligomerization, to yield combustible liquid fuel.
The catalytic processes used to convert the heavy products are often sensitive to heteroatom poisons, in particular, sulfur and nitrogen. It is advantageous to determine the heteroatom content of Fischer-Tropsch wax and other heavy products before performing catalytic processes on these products.
Chemiluminescence is a conventional technique for measuring nitrogen content in liquid materials. This technique is described, for example, in U.S. Pat. No. 4,018,562, the contents of which are hereby incorporated by reference. Chromatographic methods have also been used to measure nitrogen content, as described, for example, in U.S. Pat. No. 5,612,225, the contents of which are hereby incorporated by reference.
These techniques are designed for the analysis of liquid materials. The types of solids that can be effectively analyzed are those which form a residue and which do not boil during analysis. Erratic results are obtained if the solid materials boil and spatter during the analysis. Thus, it is not readily apparent that one can analyze certain types of solid materials, especially those which spatter or boil, when using these techniques.
The wax and other heavy products from Fischer-Tropsch synthesis are solid materials that melt at relatively high temperatures, and are often subject to spattering or boiling at these temperatures. For these reasons, the analysis of heteroatom content in Fischer-Tropsch heavy products using conventional techniques is extremely difficult and imprecise.
Various methods have been suggested for analyzing solid materials, including dissolving the solids to form a liquid solution, or directly injecting the solids into the analytical equipment. U.S. Pat. No. 4,914,037 describes a process for dispersing a solid in a cool zone by nebulization. None of these methods provide an effective means for analysis of heteroatom content in Fischer Tropsch heavy products.
It would be desirable to have a method for analyzing the heteroatom content of Fischer-Tropsch heavy products. The present invention provides such a method.
SUMMARY OF THE INVENTION
A method for analyzing the heteroatom content of Fischer-Tropsch wax and other heavy products, in particular, nitrogen-containing, substantially paraffinic products, is disclosed. Among other factors, this invention resides in the realization that pre-heat melting avoids many prior problems and surprisingly permits the extension of heretofore liquids-only techniques to solids analysis.
The heteroatom content of Fischer Tropsch heavy products can be determined by melting the sample prior to injection into the analytical instrument used for the analysis. This provides results that are reproducible and accurate.
The melting can be done in any number of ways. When the sample to be analyzed is to be injected into an analytical apparatus, for example, a gas chromatograph (GC), the sample can be melted in an external apparatus prior to injection, or melted in a syringe. Another method is to place the sample in a suitable device, for example, a boat and melt it prior to injection. The melting can be effected by simply moving the device slowly into a heated chamber which allows sufficient time for the sample to melt before it is exposed to the relatively high temperature of the combustion zone, as used in various analytical equipment.
Nitrogen and sulfur determination is preferably carried out using a chemiluminescence detector that detects chemically-bound nitrogen and sulfur. Preferred samples to be analyzed include wax directly obtained from a Fischer-Tropsch synthesis or distilled from a portion of the product of a Fischer-Tropsch synthesis. The wax can also be hydrogenated, denitrified, hydrocracked and/or hydrodesulfirized.
DETAILED DESCRIPTION OF THE INVENTION
A method for analyzing the heteroatom content of Fischer-Tropsch wax and other heavy products, in particular, nitrogen-containing, substantially paraffinic products, is disclosed. The heteroatom content of Fischer Tropsch wax and other heavy products is determined by melting the sample prior to injecting into the analytical instrument used for the analysis. Preferred samples to be analyzed include wax directly obtained from a Fischer-Tropsch synthesis or distilled from a portion of the product of a Fischer-Tropsch synthesis. The wax can also be hydrogenated, denitrified, hydrocracked and/or hydrodesulfurized.
Fischer-Tropsch waxes and other heavy products tend to be substantially paraffinic and may include significant amounts of nitrogen to adversely affect catalysts used to further refine these products, and it is advantageous to reduce the nitrogen content of these products below a threshold value. The terms “nitrogen-containing” and “nitrogen-containing, substantially paraffinic product,” as used herein, refers to a product comprising at least 50% paraffins and at least 1 ppm nitrogen. Unless otherwise specified, all percentages are in weight percent and all parts per million (ppm) are by weight.
When the Fischer-Tropsch products contain nitrogen, the conditions used to reduce the nitrogen content preferably reduce the amount to below about 15 ppm, preferably below 5 ppm, and more preferably, below about 1 ppm. This typically requires that the sample be analyzed both before and after denitrification, to ensure that the denitrification method was successful. Typical methods for denitrification involve hydrotreating, adsorption and extraction.
In Fischer-Tropsch chemistry, syngas is converted to hydrocarbons by contact with a Fischer-Tropsch catalyst under reactive conditions. The Fischer-Tropsch reaction may be effected in a fixed bed, in a slurry bed, or in a fluidized bed reactor. The Fischer-Tropsch reaction conditions may include using a reaction temperature of between 190?C and 340?C, with the actual reaction temperature being largely determined by the reactor configuration. Thus, when a fluidized bed reactor is used, the reaction temperature is preferably between 300?C and 340?C; when a fixed bed reactor is used, the reaction temperature is preferably between 200?C and 250?C; and when a slurry bed reactor is used, the reaction temperature is preferably between 190?C and 270?C.
An inlet synthesis gas pressure to the Fischer-Tropsch reactor of between 1 and 50 bar, preferably between 15 and 50 bar, may be used. The synthesis gas may have a H
2
:CO molar ratio, in the fresh feed, of 1.5:1 to 2.5:1, p
Burns Doane Swecker & Mathis L.L.P.
Chevron U.S.A. Inc.
Siefke Samuel P
Warden Jill
LandOfFree
Determination of heteroatom content in Fischer-Tropsch wax does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Determination of heteroatom content in Fischer-Tropsch wax, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Determination of heteroatom content in Fischer-Tropsch wax will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3047621