Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-06-07
2001-06-12
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S211000, C208S212000, C208S217000, C208S226000
Reexamination Certificate
active
06245221
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the hydrodesulfurization (HDS) of multiple condensed ring heterocyclic organosulfur compounds present in petroleum and petrochemical streams over noble metal-containing catalysts under relatively mild conditions. The noble metal is selected from Pt, Pd, Ir, Rh and polymetallics thereof. The catalyst system also contains a hydrogen sulfide sorbent material.
BACKGROUND OF THE INVENTION
Hydrodesulfurization is one of the fundamental processes of the refining and petrochemical 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 petrochemical 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 process capable of converting feeds bearing refractory, condensed ring sulfur heterocycles at relatively mild process conditions to products containing substantially no sulfur.
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, at a temperature from about 40° C. to 500° C. and a pressure from about 100 to 3,000 psig, with a catalyst system comprised of: (a) a hydrodesulfurization catalyst comprised of a noble metal selected from the group consisting of Pt, Pd, Ir, Rh and polymetallics thereof, on an inorganic refractory support; and (b) a hydrogen sulfide sorbent material
In a preferred embodiment of the present invention, the noble metal is selected from Pt, Pd, Ir, and polymetallics thereof.
In another preferred embodiment of the present invention the hydrodesulfurization catalyst and the hydrogen sulfide sorbent are present in a single mixed bed.
In still another preferred embodiment of the present invention said hydrogen sulfide sorbent flows through a bed of said noble metal catalyst with the feedstream.
In yet another preferred embodiment of the present invention the hydrogen sulfide sorbent material is selected from supported and unsupported metal oxides, spinels, zeolitic based materials, and layered double hydroxides.
REFERENCES:
patent: 5925239 (1999-06-01), Klein et al.
Baird Jr. William C.
Chen Jingguang
Daage Michel
Ellis Edward S.
Hantzer Sylvain S.
Exxon Research and Engineering Company
Griffin Walter D.
Hughes Gerard J.
Nguyen Tam M.
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