Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1997-08-22
2001-02-27
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S20800M, C208S209000, C208S213000
Reexamination Certificate
active
06193877
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the hydrodesulfurization (HDS) of multiple condensed ring heterocyclic organosulfur compounds found in petroleum and petrochemical streams. HDS is preferably conducted in a mixed bed containing: (a) a Ni-based catalyst on an inorganic refractory support, and (b) a hydrogen sulfide sorbent material. The desulfurized stream can then be passed to further processing, including aromatics saturation and/or ring opening.
BACKGROUND OF THE INVENTION
Hydrodesulfurization is one of the fundamental processes of the refining and chemical industries. The removal of feed sulfur by conversion to hydrogen sulfide is typically achieved by reaction with hydrogen over non-noble metal sulfides, especially those of Co/Mo and Ni/Mo, at fairly severe temperatures and pressures to meet product quality specifications, or to supply a desulfurized stream to a subsequent sulfur sensitive process. The latter is a particularly important objective because some processes are carried out over catalysts which are extremely sensitive to poisoning by sulfur. This sulfur sensitivity is sometimes sufficiently acute as to require a substantially sulfur free feed. In other cases environmental considerations and mandates drive product quality specifications to very low sulfur levels.
There is a well established hierarchy in the ease of sulfur removal from the various organosulfur compounds common to refinery and chemical streams. Simple aliphatic, naphthenic, and aromatic mercaptans, sulfides, di- and polysulfides and the like surrender their sulfur more readily than the class of heterocyclic sulfur compounds comprised of thiophene and its higher homologs and analogs. Within the generic thiophenic class, desulfurization reactivity decreases with increasing molecular structure and complexity. While simple thiophenes represent the more labile sulfur types, the other extreme, sometimes referred to as “hard sulfur” or “refractory sulfur,” is represented by the derivatives of dibenzothiophene, especially those mono- and di-substituted and condensed ring dibenzothiophenes bearing substituents on the carbons beta to the sulfur atom. These highly refractory sulfur heterocycles resist desulfurization as a consequence of steric inhibition precluding the requisite catalyst-substrate interaction. For this reason these materials survive traditional desulfurization and poison subsequent processes whose operability is dependent upon a sulfur sensitive catalyst. Destruction of these “hard sulfur” types can be accomplished under relatively severe process conditions, but this may prove to be economically undesirable owing to the onset of harmful side reactions leading to feed and/or product degradation. Also, the level of investment and operating costs required to drive the severe process conditions may be too great for the required sulfur specification.
A recent review (M. J. Girgis and B. C. Gates,
Ind. Eng. Chem
., 1991, 30, 2021) addresses the fate of various thiophenic types at reaction conditions employed industrially, e.g., 340-425° C. (644-799° F.), 825-2550 psig. For dibenzothiophenes the substitution of a methyl group into the 4-position or into the 4- and 6-positions decreases the desulfurization activity by an order of magnitude. These authors state, “These methyl-substituted dibenzothiophenes are now recognized as the organosulfur compounds that are most slowly converted in the HDS of heavy fossil fuels. One of the challenges for future technology is to find catalysts and processes to desulfurize them.”
M. Houalla et al,
J Catal
., 61, 523 (1980) disclose activity debits of 1-10 orders of magnitude for similarly substituted dibenzothiophenes under similar hydrodesulfurization conditions. While the literature addresses methyl substituted dibenzothiophenes, it is apparent that substitution with alkyl substituents greater than methyl , e.g., 4, 6-diethyldibenzothiophene, would intensify the refractory nature of these sulfur compounds. Condensed ring aromatic substituents incorporating the 3,4 and/or 6,7 carbons would exert a comparable negative influence. Similar results are described by Lamure-Meille et al, Applied Catalysis A: General, 131, 143, (1995) based on analogous substrates.
Mochida et al, Catalysis Today, 29, 185 (1996) address the deep desulfurization of diesel fuels from the perspective of process and catalyst designs aimed at the conversion of the refractory sulfur types, which “are hardly desulfurized in the conventional HDS process.” These authors optimize their process to a product sulfur level of 0.016 wt. %, which reflects the inability of an idealized system to drive the conversion of the most resistant sulfur molecules to extinction. Vasudevan et al, Catalysis Reviews, 38, 161(1996) in a discussion of deep HDS catalysis report that while Pt and Ir catalysts were initially highly active on refractory sulfur species, both catalysts deactivated with time on oil.
In light of the above, there is a need for a desulfurization/ring-opening process capable of converting feeds bearing the refractory, condensed ring sulfur heterocycles at relatively mild process conditions to streams containing substantially no sulfur. Such streams will not deactivate the ring opening catalyst.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a process for the substantially complete desulfurization of a stream selected from petroleum and chemical streams containing condensed ring sulfur heterocyclic compounds, which process comprises contacting said stream with a catalyst system comprised of: (a) a hydrodesulfurization catalyst comprised of an effective amount of Ni on an inorganic refractory support; and (b) a hydrogen sulfide sorbent material; wherein the hydrodesulfurization conditions include temperatures from about 40° C. to 500° C., and pressures from about 100 to 3,000 psig.
In a preferred embodiment of the present invention the hydrodesulfurization catalyst and the hydrogen sulfide sorbent are present in a mixed bed.
In yet another preferred embodiment of the present invention a second catalyst is present having an aromatic saturation function.
In yet another preferred embodiment of the present invention the hydrode-sulfurized feedstream is subjected to a ring opening step.
In still another preferred embodiment of the present invention there is provided a catalyst bed, downstream of, or mixed with, the bed that contains the hydrogen sulfide sorbent.
In another preferred embodiment of the present invention, the hydrogen sulfide sorbent is selected from supported and unsupported metal oxides, spinels, zeolitic based materials, and layered double hydroxides.
DETAILED DESCRIPTION OF THE INVENTION
Feedstocks suitable for being treated by the present invention are those petroleum based feedstocks which contain condensed ring sulfur heterocyclic compounds, as well as other ring compounds, including multi-ring aromatic and naphthenic compounds. Such compounds are typically found in petroleum streams boiling in the distillate range and above. Non-limiting examples of such feeds include diesel fuels, jet fuels, heating oils, and lubes. Such feeds typically have a boiling range from about 150 to about 600° C., preferably from about 175 to about 400° C. It is preferred that the streams first be hydrotreated to reduce sulfur contents, preferably to less than about 1,000 wppm, more preferably less than about 500 wppm, most preferably to less than about 200 wppm, particularly less than about 100 wppm sulfur, ideally to less than about 50 wppm. It is highly desirable for the refiner to upgrade these types of feedstocks by removing as much of the sulfur as possible, as well as to open ring compounds to produce paraffins.
It is well known that so-called “easy” sulfur compounds, such as non-thiophenic sulfur compounds, thiophenes, benzothiophenes, and non-beta dibenzothiophenes can be removed without using severe process conditions. The prior art teaches that substantially more severe conditions are needed to remove the so-called “hard”
Baird Jr. William C.
Chen Jingguang
Daage Michel
Ellis Edward S.
Klein Darryl P.
Exxon Research and Engineering Company
Griffin Walter D.
Hughes Gerard J.
Naylor Henry E.
Preisch Nadine
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