Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
1999-11-30
2001-12-25
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
C208S050000, C208S086000, C208S087000, C208S089000, C208S132000
Reexamination Certificate
active
06332975
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method for making anode grade coke and particularly to heating in a delayed coker vessel a resin-containing stream obtained by solvent deasphalting a petroleum residue feedstock containing sulfur and metal contaminants.
BACKGROUND OF THE INVENTION
The economics of petroleum production and refining are requiring that more usable materials be obtained from petroleum residues of ever worsening characteristics, primarily sulfur content, metal content and asphaltene content of the petroleum residues, resulting from the atmospheric and vacuum distillation of petroleum feedstocks. The distillation of the petroleum feedstock tends to concentrate the contaminants into the petroleum residue.
Common ways of improving the yield of distillate products and disposing of the residue have involved hydrotreating. Hydrotreating involves reacting the petroleum residue with hydrogen in the presence of a catalyst to convert the petroleum residue into a higher proportion of more valuable lower-boiling products. The residue remaining after the lower-boiling products are removed from the hydrotreater effluent generally has a lower sulfur and metal content.
Another process commonly used to treat petroleum residue is delayed coking. In this process, the petroleum residue is heated and subjected to destructive thermal cracking to produce valuable lower-boiling petroleum distillate products, and forming a solid carbonaceous residue known as coke. Coke with a high sulfur and/or metal content is generally subject to combustion as a fuel. “Fuel grade coke” is not generally suitable for other purposes.
Higher quality coke grades such as anode grade coke generally have lower sulfur and metal content. For example, anode grade coke generally has a sulfur content less than 3 weight percent, a nickel content less than 200 ppm, a vanadium content less than 350 ppm and a total metals content less than 500 ppm. In addition, anode grade coke which is suitable for use as making a carbon anode which can be used in aluminum manufacture, for example, must also have an HGI grindablility index greater than 70, a bulk density of at least 50 lbs/ft
3
, and a volatile carbonaceous material content of less than 10 or 12 weight percent. It is more desirable to produce anode grade coke since this is a higher value product than fuel grade coke.
Particularly with high sulfur, high metals residues, one approach has been suggested to hydrotreat the residue which removes the sulfur and metal so that the coke obtained by destructive thermal cracking of is the hydrotreated residue is within specifications for anode grade coke. Unfortunately, however, it is known that hydrotreating of the petroleum residue feedstock affects the physical characteristics of the coke, which can make the coke unsuitable for the anode manufacturing process. Therefore, for the production of anode grade coke, feedstocks have been historically limited to virgin residues with inherently low sulfur and metals content. Petroleum residues are generally comprised of saturate, aromatic, resin and asphaltene fractions. Hydrotreating a petroleum residue is known to convert a portion of the resin fraction to saturates. The data below in Table 1 are based on the feed and product from a commercial hydrotreating unit and illustrate this change:
TABLE 1
Resin fraction (wt %)
Saturates fraction (wt %)
Virgin petroleum
35
14
residue
Hydrotreated residue
13
33
It is generally accepted that the type of change in composition illustrated above can make the hydrotreated residue unsuitable for anode grade coke production.
It is also known to subject petroleum residue fractions to solvent extraction to separate the residue fraction into a deasphalted oil fraction and an asphaltene fraction, and sometimes into a third resin fraction. It has been known to hydrotreat and/or catalytically crack the deasphalted oil and/or resin fractions, and treat the asphaltene fraction in a delayed coker. However, as far as applicants are aware, no one has previously tried to improve the quality of coke produced in the delayed coker by feeding the resin-containing fraction from the solvent deasphalting of the petroleum residue to a delayed coker unit.
U.S. Pat. No. 5,013,427 to Mosby et al. discloses hydrotreating a petroleum residue feed with a resin fraction from a solvent extraction unit together in a residue hydrotreating unit, feeding a first portion of the residue hydrotreating unit bottoms fraction to the solvent extraction unit, and a second portion of the hydrotreated residue to a coker unit. Similar disclosures are found in U.S. Pat. Nos. 4,940,529 to Beaton et al.; 5,124,027 to Beaton et al.; 5,228,978 to Taylor et al.; 5,242,578 to Taylor et al.; 5,258,117 to Kolstad et al.; and 5,312,543 to Taylor et al.
SUMMARY OF THE INVENTION
The present invention involves the discovery that the quality of coke made from a high sulfur and/or high metals petroleum residue feedstock can be upgraded by solvent deasphalting and heating a resin-containing stream obtained thereby in a delayed coker to make anode grade coke. While the sulfur and metals levels of the residue may be reduced by hydrotreating and/or solvent deasphalting as appropriate for producing coke meeting anode grade coke specifications for sulfur and metals, we have found that other anode grade coke specifications such as volatile carbonaceous material content, bulk density and grindability are not easily met. We believe the aromatic content of the resin fed to the coker in our invention results in the improved properties of the coke obtained by coking the resin-containing stream. In the process according to our invention, the residue feedstock is solvent deasphalted to form a deasphalted oil stream, an optional but preferred separate resin stream, and an asphaltene-rich stream, and the resin-containing stream is coked in a delayed coker, preferably with hydrotreating of (1) a minor portion of the residue feedstock wherein the hydrotreated residue is fed to the delayed coker with the resin-containing stream, (2) the resin-containing stream wherein the resin-containing stream is fed to the delayed coker, or (3) a major portion of the residue feedstock wherein the hydrotreated residue is fed to the solvent deasphalting unit.
Broadly, the present invention provides a process for preparing anode grade coke from a petroleum residue feedstock containing sulfur and metal contaminants, comprising: (1) solvent deasphalting the residue feedstock to produce (a) a deasphalted oil stream, a resin stream essentially free of asphaltenes and an asphaltene-rich stream, or (b) a deasphalted oil stream comprising resin and an asphaltene rich stream; (2) feeding a process stream comprising the resin stream or the resin comprising deasphalted oil stream directly to a delayed coker; and (3) heating the process stream in the delayed coker under delayed coking conditions to form a batch of the anode grade coke. The process stream fed to the delayed coker can be essentially free of hydrotreated material.
In another embodiment, the present invention provides a process for preparing anode grade coke from a petroleum residue feedstock containing sulfur and metal contaminants. The process includes the steps of: (1) hydrotreating a first process stream consisting essentially of a first portion of the residue feedstock to produce a hydrotreated residue stream of reduced sulfur and metal content; (2) solvent deasphalting a second portion of the residue feedstock to produce a deasphalted oil stream, a resin stream essentially free of asphaltenes and an asphaltene-rich stream; (3) feeding the hydrotreated residue stream together with a second process stream comprising the resin stream to a delayed coker; and (4) heating the hydrotreated residue stream and the second process stream in the delayed coker under delayed coking conditions to form a batch of the anode grade coke. The second process stream can further comprise a minor portion of the deasphalted oil stream and/or a minor portion of the asphaltene-r
Abdel-Halim Tayseer
Floyd Raymond H.
Low Jim Y.
Moretta Jon C.
Silverman Michael A.
Kellogg Brown & Root, INC
Kellogg Brown & Root, Inc.
Yildirim Bekir L.
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