Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the... – Iron containing catalyst
Reexamination Certificate
2003-03-25
2004-09-07
Parsa, J. (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
Iron containing catalyst
C518S715000, C518S719000, C585S502000, C585S510000, C585S529000
Reexamination Certificate
active
06787577
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the production of highly branched products from a slurry-type Fischer-Tropsch unit, an integrated process for increasing the yield of lube base oils, and a novel potassium promoted iron catalyst.
BACKGROUND OF THE INVENTION
The market for lubricating base oils of high paraffinicity is continuing to grow due to the high viscosity index, oxidation stability, and low volatility relative to viscosity of these molecules. Feedstocks having these preferred properties include the waxy products produced from the Fischer-Tropsch process which make them ideal candidates for processing into lube base stocks. Accordingly, the hydrocarbon products recovered from the Fischer-Tropsch process have been proposed as feedstocks for preparing high quality lube base oils. Because these waxy feeds have a high pour point, they must be dewaxed to low pour point to meet base oil specifications. See, for example, U.S. Pat. No. 6,080,301 which describes a premium lube base oil having a high non-cyclic isoparaffin content prepared from Fischer-Tropsch waxes by hydroisomerization dewaxing and solvent dewaxing. The dewaxing operation improves the pour point of the product. Unfortunately, when catalytic dewaxing is used a significant amount of wax cracking will usually take place during the dewaxing operation. This wax cracking which occurs in association with the catalytic dewaxing process cracks the molecules into lower molecular weight products, and, consequently, the final yield of lube base oil suffers. In order to limit the loss of the commercially valuable lube base oil product, it is usually desirable to operate the catalytic dewaxing unit at the lowest severity which will produce the product having the desired viscosity index and pour point.
As discussed in U.S. Pat. No. 6,090,989, the degree of branching present on the molecule and the position of the branches have a significant impact on the properties of the lube base stock. In general, the greater degree of branching in the product recovered from the Fischer-Tropsch unit, the less severe the dewaxing operation must be in order to produce lube base oils having the desired properties. Accordingly, in order to maximize the yield of lube base oils, it is advantageous to operate the Fischer-Tropsch unit in a mode which maximizes the branching of the products. The ability to increase the molecular branching is not only advantageous for increasing the yield of lube base oils, but also benefits the lighter cuts derived from the Fischer-Tropsch product. For example, branching in Fischer-Tropsch derived naphtha will increase the octane rating, branching in Fischer-Tropsch derived jet will improve the freeze point, and branching in Fischer-Tropsch derived diesel is known to improve the pour point. See U.S. Pat. No. 5,506,272.
The type of branching present in the carbon backbone of the molecules is important in determining the properties of the lube base oil product. See S. J. Miller,
Wax Isomerization for Improved Lube Oil Quality,
1 st Intl. Conf. on Refining Processing, AlChE, New Orleans (1998). Significant deviation from the ideal branch structure will usually result in a loss of benefit. For those Fischer-Tropsch products which are intended as feed for a hydrocracking operation an additional advantage for the presence of branching is that the branching renders the molecule easier to crack.
Several commercial methods are used to provide the desired branching in the hydrocarbon molecules recovered from the Fischer-Tropsch process. The high temperature Fischer-Tropsch process which is carried out in the vapor phase will produce lower molecular weight olefinic products within the C
3
to C
8
range. The olefinic products of the high temperature Fischer-Tropsch process may be sent through oligomerization and hydrogenation steps which will produce a highly branched iso-paraffinic product. The products recovered from the high temperature Fischer-Tropsch process may contain a significant amount of branching. However, the high temperature Fischer-Tropsch process is not ideal for producing higher molecular weight products in the lubricating base oil boiling ranges. As already noted, the majority of the hydrocarbons produced are within the C
3
to C
8
range. In order to produce hydrocarbons in the molecular weight range of lubricating base oils almost all of the products must be sent through an oligomerization operation. In addition, the product from the high temperature Fischer process will usually contain significant amounts of aromatics which must be removed in order to prepare a high quality lube base oil.
In contrast to the high temperature Fischer-Tropsch process, the low temperature Fischer-Tropsch process, which is conducted in the liquid phase, will yield higher molecular weight products with low branching, with lower olefinicity than the high temperature Fischer-Tropsch process, and with virtually no aromatics. While the low temperature Fischer-Tropsch process will produce products within the lube base oil boiling range, due to the low level of branching, such products do not possess the desired low pour point characteristics. In order to meet these desired values for the products, a catalytic dewaxing operation is usually necessary in order to introduce the proper branching into the molecule. The relatively severe conditions at which the catalytic dewaxing unit must be operated results in a significant yield loss of the higher molecular weight products due to wax cracking. In addition, since the products derived from a low temperature Fischer-Tropsch operation have lower olefinicity, there will be fewer olefins to oligomerize to lube and consequently a lower lube yield or, alternatively, a dehydrogenation step will be needed to increase the olefin level of the Fischer-Tropsch products.
While a Fischer-Tropsch reaction may be suitably conducted in either a fixed bed reactor, slurry bed reactor, or a fluidized bed reactor, fixed bed reactors and slurry bed reactors are preferred for low temperature Fischer-Tropsch processes. Fluidized bed reactors are preferred for high temperature Fischer-Tropsch processes. Although the low temperature Fischer-Tropsch process is generally considered as being carried out at a temperature between 160 degrees C. and 250 degrees C. while the high temperature Fischer-Tropsch process is usually conducted at temperatures between 250 degrees C. and 375 degrees C., in actuality, the temperature range for the two processes will overlap. A good comparison of the high temperature and low temperature Fischer-Tropsch processes is presented in B. Jager and R. Espinoza,
Advances in Low Temperature Fischer
-
Tropsch Synthesis, Catalysts Today
23 (1995) pp 17-28.
Precipitated iron catalysts promoted with potassium have been described in the literature for use in Fischer-Tropsch synthesis. However, U.S. Pat. No. 4,994,428 teaches that the amount of potassium present should be limited to less than 0.6 weight percent. Higher levels of potassium are taught to offer no benefit in selectivity and to increase the production of undesirable oxygenated by-products. Copper is known to serve as an induction promoter, i.e., reduce the catalytic induction period, in a slurry-type potassium promoted iron catalyst. Copper and potassium promoted iron catalysts have been described in the literature as being selective for alpha olefins. See U.S. Pat. No. 5,100,856. U.S. Pat. No. 4,639,431 describes an iron/zinc Fischer-Tropsch catalyst promoter with copper which is useful for producing olefins.
U.S. Pat. No. 4,617,320 describes a potassium promoted iron catalyst containing a SAPO which is taught as useful for promoting branching in Fischer-Tropsch derived products boiling in the range of transportation fuels.
The dual catalyst composition taught in this reference is a pelleted catalyst that is intended for use in a fixed bed and, consequently, would not be suitable for use in a slurry-type Fischer-Tropsch synthesis process.
The present invention utilizes a novel iron-based Fischer-Tropsch catal
Davis Burtron H.
Miller Stephen J.
Ambrosius James W.
Chevron U.S.A. Inc.
Parsa J.
LandOfFree
Process for the production of highly branched... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the production of highly branched..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the production of highly branched... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3192286