Chemistry: fischer-tropsch processes; or purification or recover – Liquid phase fischer-tropsch reaction
Reexamination Certificate
2002-01-15
2004-07-06
Parsa, J. (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Liquid phase fischer-tropsch reaction
C208S027000, C208S059000, C208S093000, C208S177000, C208S184000, C208S311000, C208S341000, C436S161000, C702S025000, C702S030000
Reexamination Certificate
active
06759438
ABSTRACT:
The present invention relates to an improved process for producing Fischer Tropsch products through measuring oxygenate concentration using GC-AED.
BACKGROUND OF THE INVENTION
The concentration of total oxygenates in Fischer-Tropsch products often needs to be maintained within established limits for optimal product characteristics. In addition, it may also be necessary to maintain the concentration of specific individual oxygenates within established limits. Therefore, to achieve the desired concentrations, the concentration of oxygenates, often specific individual oxygenates, in a Fischer-Tropsch product must be measured and controlled. The results from an analysis of oxygenates may be used to regulate operation of the Fischer Tropsch process. Accordingly, accurate measurement of oxygenates and control of their levels to desired set points are needed for efficient production of salable products from Fischer-Tropsch products.
There have been a variety of methods used to measure the concentration of oxygenates in Fischer-Tropsch products, including, elemental analysis, Infrared (IR), simple Gas Chromatography (GC), and GC coupled with mass spectrometry (MS). By way of example, U.S. Pat. No. 5,895,506 to Cook, et al. describes the use of Infrared (IR) techniques to monitor various oxygenate and olefin classes in Fischer-Tropsch products. IR techniques, however, have two disadvantages. First, they require calibration; calibration introduces error because the substance used for calibration may not behave exactly as the compounds in the sample. Second, IR techniques measure only the total concentration of each class of compounds (for example, alcohols, acids, etc.); therefore, they do not provide a distribution by carbon number. In performing and controlling a Fischer Tropsch process, a combined analysis by class and carbon number may be required.
GC may also be used to monitor oxygenate concentration. The basic science of gas chromatography has been known for over a century. GC separates different molecules in a mixture into components with different groups, typically sorted by molecular weight or boiling point. Various detectors can be used with GC. If a majority of the components in the mixture are to be measured, several detectors may be used, including a Thermal Conductivity Detector (TCD) or a Flame-Ionization Detector (FID).
When it is desired to measure a specific minority component in the mixture, it is preferable to use a detector that monitors the family of compounds that encompass the minority component. An example of such a detector is Gas Chromatography coupled with a Mass Spectrometry analyzer (GC-MS,) which can determine the specific components that elute from the GC at the same time. By way of example, U.S. Pat. No. 5,600,134 to Ashe et al. describes a method for controlling the bending of blend stocks using GC-MS. The method of Ashe requires a 10-step process for producing a training set of one or more known properties from reference samples. The training set provides a predicted MS value of the one or more properties against which MS information from the blend stocks may be compared. The training set is used to produce a predicted MS value of the desired properties for blend stocks and blend product samples. While GC-MS may be a good tool for identifying the general nature of compounds in a mixture, it can lack sufficient sensitivity for all operations.
In all of the above listed techniques, when control of specific individual oxygenate compounds at low levels is required, these techniques may be inadequate.
As control and measurement of specific individual oxygenate compounds at low levels may be important to producing salable products from Fischer Tropsch processes, there are needed techniques that can accurately and efficiently measure oxygenates and control their concentrations to selected set points.
SUMMARY OF THE INVENTION
The present invention relates to methods for producing a substantially paraffinic Fischer-Tropsch product or a blended Fischer Tropsch product comprising a selected oxygenate concentration, and if required, a selected oxygenate concentration of specific individual oxygenates. The methods of the present invention measure oxygenate concentration using GC-AED. The oxygenate measurements obtained using the GC-AED may be used to adjust and control various processes used to produce, upgrade, or finish Fischer Tropsch products to provide Fischer Tropsch products with a selected oxygenate concentration, and if required, a selected oxygenate concentration of specific individual oxygenates.
The present invention relates to a method for producing a substantially paraffinic Fischer-Tropsch product comprising at least one oxygenated species. In the method, a concentration of oxygenated species in the substantially paraffinic Fischer-Tropsch product is selected. A carbon number distribution of oxygenated species or a class of oxygenated species may also be selected. A Fischer-Tropsch synthesis is performed to provide a Fischer-Tropsch product stream. A substantially paraffinic product stream containing oxygenated species is isolated from the Fischer-Tropsch product stream. The substantially paraffinic product stream is purified, for example, by hydrotreating, hydrocracking, adsorption, extraction, and combinations thereof, to remove a portion of oxygenated species, to provide a substantially paraffinic Fischer-Tropsch product comprising at least one oxygenated species. The substantially paraffinic Fischer-Tropsch product is monitored for concentration of oxygenated species by GC-AED. The substantially paraffinic Fischer-Tropsch product may also be monitored for carbon number distribution or class of oxygenated species by GC-AED. The conditions of the purification are adjusted to ensure that the concentration of the oxygenated species in the substantially paraffinic Fischer-Tropsch product complies with the selected concentration. The conditions of the purification may also be adjusted to ensure that the carbon number distribution or class of the oxygenated species in the substantially paraffinic Fischer-Tropsch product complies with a selected carbon number distribution or class.
An additional aspect of the present invention relates to a method for producing a substantially paraffinic Fischer-Tropsch product comprising no detectable oxygenated species. In that method, a Fischer-Tropsch synthesis is performed to provide a Fischer-Tropsch product stream. A substantially paraffinic product stream containing oxygenated species is isolated from the Fischer-Tropsch product stream. The substantially paraffinic product stream is purified, for example, by hydrotreating, hydrocracking, adsorption, extraction, and combinations thereof, to remove the oxygenated species, to provide a substantially paraffinic Fischer-Tropsch product comprising no detectable oxygenated species. The substantially paraffinic Fischer-Tropsch product is monitored for concentration of oxygenated species by GC-AED. The conditions of the purification are adjusted to ensure that the concentration of the oxygenated species in the substantially paraffinic Fischer-Tropsch product is not detectable.
The present invention also provides a method for preparing a blended Fischer-Tropsch product comprising at least one oxygenated species. In the method a concentration of oxygenated species in the blended Fischer-Tropsch product is selected. A carbon number distribution of oxygenated species or a class of oxygenated species may also be selected. A Fischer-Tropsch synthesis is performed to provide a Fischer-Tropsch product stream. A substantially paraffinic product stream containing oxygenated species is isolated from the Fischer-Tropsch product stream, for example, by distillation. The substantially paraffinic product stream is blended with at least one non-oxygenate containing hydrocarbon stream to provide a blended product comprising at least one oxygenated species. The blended product is monitored for concentration of oxygenated species by GC-AED. The blended product may also be monitored for car
O'Rear D J
Rainis Andrew
Burns Doane Swecker & Mathis L.L.P.
Chevron U.S.A. Inc.
Parsa J.
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