Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2000-06-01
2003-04-22
Dang, Thuan D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S015000, C208S25400R
Reexamination Certificate
active
06551501
ABSTRACT:
FIELD OF INVENTION
The present invention relates to hydrotreating of diesel fuels and in particular to improvement of those processes in a staged process.
BACKGROUND
The need to produce extremely clean transportation fuels is continually increasing. Future standards are being set, which cannot be achieved with existing process equipment. Although improved commericial catalysts are available, they are not sufficiently active to meet the increasingly more strict requirements for high quality commercial fuels, and thus modifications of process equipment are also necessary. Such changes in process equipment will be expensive and there is a need to identify novel processes to meet these requirements.
DETAILED DESCRIPTION
Overall Process Description
It is in the context of the above problems that the present invention was conceived. When the sulphur level must be lowered to less than 500 ppm sulphur, the conversions that are required involve desulphurization of highly substituted dibenzothiophenes, especially those in which the substituents are present on the aromatic rings adjacent to the heterocyclic sulphur atom. We will refer to such compounds as refractory sulphur compounds (RS-compounds). A typical example of such a compound is 4,6-dimethyldibenzothiophene (46 DMDBT). We have found that the conversion of the most refractory sulphur (RS) compounds (such as 46 DMDBT) in diesel fuels is made even more difficult by the presence of certain other components found in normal feeds to diesel hydrotreaters. Such compounds are referred to as inhibitors for hydrodesulphurization (HDS).
We have discovered that if such inhibitors are selectively removed from the feed and the feed containing less inhibitors is hydrotreated under typical commercial conditions used in today's refineries, then the RS-compounds can be readily removed by hydrotreating using conventional catalyst loadings and process conditions. The degree to which the inhibitors are removed will depend on the particular adsorbent used and the cost of the removal process. In many instances, it is not necessary to remove all of the inhibitors to experience the benefits of our combined process. For ease of discussion, we will refer to diesel fuels which have been contacted with adsorbents for the inhibitors as “inhibitor free” diesel fuels, however, we do not mean to imply that 100% of the inhibitors have been removed.
FIGS. 2 and 3
and Example 1 illustrate this point.
Hydrotreating Process
The hydrotreating step of the combined process scheme of this invention, shown in
FIG. 1
, can be any conventional hydrotreating process. This includes fixed or ebulated bed operations at conventional operating conditions such as temperatures in the range of 250° C. to 450° C., preferably 300° C. to 380° C. Pressures are also conventional such as 20-60 atm of hydrogen, and preferably below 40 atm of hydrogen. Higher temperatures and pressures will also provide the benefits of the present invention, however, lower pressures and temperatures are preferred to avoid yield losses of valuable diesel fuels and to avoid the need for construction of new process equipment in order to achieve extremely strict sulphur standards such as less than 300 ppm sulphur or even more strict sulphur standards of less than 50 ppm sulphur.
Catalysts used in the hydrotreating step are preferably those employed conventionally, such as mixed cobalt and/or nickel and molybdenum sulphides supported on alumina and mixed nickel and tungsten sulphides supported on alumina or silica. The combined process of this invention will also benefit newly developed catalysts such as those containing ruthenium sulfide and catalysts using novel supports such as silica-aluminas, carbons or other materials. For details on the state of the art in conventional hydrotreating processes, we refer to “Hydrotreating Catalysis—Science and Technology”, by H. Topsøe, B.S. Clausen and F. E. Massoth, Springer-Verlag Publishers, Heidelberg, 1996.
Inhibitor Removal Processes
It is possible to envision many ways of removing materials, which inhibit the hydrotreating process, especially the hydrodesulphurization of RS-compounds. However, the removal of inhibitors should be done in a practical way if this principle is to be realized commercially. The method used for inhibitor removal should be highly selective for only the inhibitors and should not remove the valuable components of the diesel fuel or other non-inhibiting components of the diesel fuel. An alternative process would be to selectively remove the RS-compounds as described in U.S. Pat. No. 5,454,933. However, in that patent the yield of diesel fuel was not specified, and in attempting to duplicate this patent, we have observed that the adsorbent carbon, though showing some selectivity for RS-compounds, has a high capacity for all diesel fuel components. When one attempts to recover the valuable diesel fuel components, the RS-compounds are also released, as the strength of adsorption is not high. Thus, it may be possible to concentrate the RS-compounds, but not remove them specifically. There are many different classes of materials that can inhibit the HDS of RS-compounds.
It is well known that certain basic compounds such as quinolines and acridines inhibit HDS reactions (see H. Topsøe, B. S. Clausen and F. E. Massoth, “Hydrotreating Catalysis—Science and Technology”, Springer-Verlag publishers, Berlin 1996; M. J. Girgis and B. C. Gates, Ind. Eng. Chem. Res., pp. 2021-2058, Vol. 30 No. 9, 1991; D. D. Whitehurst, T. Isoda and I. Mochida, Advances in Catalysis, pp. 345-471, Vol. 42, 1998; and references therein). However, any compound that will compete with RS-compounds for adsorption on the catalytic site will inhibit the HDS of the RS-compound. Thus, in addition to basic compounds, other strongly adsorbing species in the diesel fuel that is to be hydrotreated will lower the rate of removal of sulphur from the diesel fuel. We have found that such inhibitors are all highly polar materials that may be selectively removed from the hydrocarbons and RS-compounds by various adsorbents. By polar compounds we mean classical basic compounds such as were described above, including their benzo-analogs. These may be identified in diesel fuels by titration with strong acids in non-aqueous media. Other inhibitors include acidic nitrogen species, such as carbazoles, indoles and their benzo-analogs. Such acidic N-compounds can be identified by titration with strong bases in non-aqueous media. Still other inhibitors include amphoteric compounds such as hydroxyquinolines, and still other neutral compounds containing more than one nitrogen in an aromatic ring system or compounds which contain both oxygen and nitrogen in the same molecule. Further, inhibitors need not contain nitrogen, but may e.g. be composed of highly polar oxygen containing species.
Thus, it is possible to devise adsorption processes, which will selectively remove certain chemical classes of inhibitors or selectively remove essentially all inhibitor molecules by virtue of their polar nature. We have devised several different means to achieve selective inhibitor removal from diesel fuels using either their chemical properties or their polar properties. The particular method that is preferred will depend on the particular situation and the specific diesel fuel that is to be processed. However, the most preferred general method for inhibitor removal is based on their polar nature. The following text describes the various methods we have devised for use in the combined process of this invention.
Liquid Adsorbent Processes
In the present invention, our approach is to selectively remove the inhibitors for RS-compound conversion and then selectively desulphurize the inhibitor free feed in conventional HDS operations. We have found that only certain adsorbents have the selectivity desired.
Liquid adsorbents can be identified using their solvent parameters, f
d
, f
p
and f
h
, as defined by Teas [see J. P. Teas, “Graphic Analysis of Resin Solubilities”, J. Paint Technology 19, 40 (1968)].
Brorson Michael
Cooper Barry H.
Knudsen Kim Grøn
Whitehurst Darrell Duayne
Zeuthen Per
Dang Thuan D.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Haldor Topsoe A/S
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