Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-08-13
2001-08-21
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S20800M, C208S236000, C208S240000, C208S242000, C208S196000, C585S857000, C585S864000
Reexamination Certificate
active
06277271
ABSTRACT:
FIELD OF THE INVENTION
The field of art to which this invention pertains is the desulfurization of hydrocarbonaceous oils to produce low concentrations of residual sulfur.
BACKGROUND OF THE INVENTION
There is an increasing demand to reduce the sulfur content of hydrocarbonaceous oil to produce products which have very low concentrations of sulfur and are thereby marketable in the ever more demanding marketplace. With the increased environmental emphasis on the requirement for more environmentally friendly transportation fuels, those skilled in the art have sought to find feasible and economical techniques to reduce the sulfur content of hydrocarbonaceous oil to low concentrations.
Traditionally, hydrocarbons containing sulfur have been subjected to a catalytic hydrogenation zone to remove sulfur and produce hydrocarbons having lower concentrations of sulfur. Hydrogenation to remove sulfur is very successful for the removal of the sulfur from hydrocarbons that have sulfur components that are easily accessible to contact with the hydrogenation catalyst. However, the removal of sulfur components which are sterically hindered becomes exceedingly difficult and therefore the removal of sulfur components to a sulfur level below about 100 ppm is very costly by known current hydrotreating techniques. It is also known that a hydrocarbonaceous oil containing sulfur may be subjected to oxygenation to convert the hydrocarbonaceous sulfur compounds to compounds containing sulfur and oxygen, such as sulfoxide or sulfone for example, which have different chemical and physical characteristics which make it possible to isolate or separate the sulfur-bearing compounds from the balance of the original hydrocarbonaceous oil. For example, see a paper presented at the 207
th
American Chemical Society Meeting in San Diego, Calif. on Mar. 13-17, 1994 entitled “Oxidative Desulfurization of Liquid Fuels” by Tetsuo Aida et al. The disadvantage to this approach is that the isolated sulfur-bearing compounds are still not useful as a sulfur-free material and therefore the yield of a sulfur-free material from the original hydrocarbonaceous oil is less than desirable and therefore uneconomic.
INFORMATION DISCLOSURE
U.S. Pat. No. 2,769,760 (Annable et al) discloses a hydrodesulfurization process which reduces the organic sulfur concentration in a hydrocarbon feedstock. The resulting hydrocarbon product from the first stage hydrodesulfurization zone contains sulfur and is subsequently introduced into a second stage partial desulfurization and/or chemical reaction wherein the second stage treatment is conducted at a temperature of approximately 450° F. and at atmospheric pressure in the absence of hydrogen. The contact material for the reaction in the second stage is of the same type as used for the hydrodesulfurization reaction. Preferred contact materials contain cobalt and molybdenum. The main thrust of the '760 patent is for the production of sweet naphthas. The exemplification of the invention in the '760 patent utilizes a hydrocarbon feedstock having an end boiling point of 425° F. The patent does not disclose the removal of sulfur compounds from a hydrocarbon by oxidation and extraction steps.
Published European Patent Application No. 565324 discloses a method of recovering an organic sulfur compound from a liquid oil wherein the method comprises treating the liquid oil containing an organic sulfur compound with an oxygen agent and separating the oxidized organic sulfur compound by separation means such as distillation, solvent extraction and/or adsorption means. A principal objective of the invention of the '324 reference is to recover organic sulfur compounds which are industrially useful in the fields of production of medicines, agricultural chemicals, and heat-resistant resins, for example. This objective contemplates the use of the organic sulfur compounds as produced. The '324 reference teaches that hydrogenation with hydrogen at high temperature and pressure cannot be employed when it is intended to isolate the organic sulfur compound from the mineral oil in such a state that the original chemical structure is maintained as much as possible to thereby utilize the organic sulfur compounds. The '324 reference teaches the undesirability of the use of hydrodesulfurization and fails to disclose that a suitable feedstock for the process of the '324 reference has been subjected to a hydrodesulfurization step.
U.S. Pat. No. 3,551,328 (Cole et al) discloses a process for reducing the sulfur content of heavy hydrocarbon petroleum fractions by oxidizing the sulfur compounds present in such heavy hydrocarbon fractions and contacting the heavy hydrocarbon fractions containing such oxidized sulfur compounds with a lower paraffinic hydrocarbon solvent in a concentration sufficient to separate the oxidized sulfur compounds from the heavy hydrocarbon fractions and recovering a heavy hydrocarbon fraction of reduced sulfur content. The '328 patent teaches that it is particularly well adaptable to the treating of crude oils and topped or reduced crude oils containing large quantities of asphaltenic material and it is especially advantageous when applied to the treating of atmospheric or vacuum tower bottoms. The patent also teaches that such feedstocks which are contaminated by the presence of excessive concentrations of various non-metallic and metallic impurities detrimentally affect various catalytic systems employed for the conversion of such heavy hydrocarbon fractions.
SUMMARY OF THE INVENTION
The present invention provides a process for the desulfurization of hydrocarbonaceous oil wherein the hydrocarbonaceous oil is contacted with a hydrodesulfurization catalyst in a hydrodesulfurization reaction zone to reduce the sulfur level to a relatively low level and then contacting the resulting hydrocarbonaceous stream from the hydrodesulfurization zone with an oxidizing agent to convert the residual, low level of sulfur compounds into sulfur-oxidated compounds.
The remaining oxidizing agent is decomposed and the resulting hydrocarbonaceous oil stream containing the sulfur-oxidated compounds is separated to produce a stream comprising the sulfur-oxidated compounds and a hydrocarbonaceous oil stream having a reduced concentration of sulfur-oxidated compounds. At least a portion of the sulfuroxidated compounds is recycled to the hydrodesulfurization reaction zone.
In a preferred embodiment of the present invention, the hydrocarbonaceous effluent stream from the hydrodesulfurization zone is contacted with an aqueous oxidizing solution to convert the residual, low level of sulfur compounds into sulfuroxidated compounds. The resulting hydrocarbonaceous oil stream containing the sulfur-oxidated compounds is treated to decompose any residual oxidizing agent and is contacted with a selective solvent having a greater selectivity for the sulfur-oxidated compounds than for the sulfur-free hydrocarbonaceous oil to produce a solvent containing at least a portion of the sulfur-oxidated compounds and a hydrocarbonaceous oil stream having a reduced concentration of sulfur-oxidated compounds. At least a portion of the sulfur-oxidated compounds is recycled to the hydrodesulfurization reaction zone.
The present invention discloses a novel integrated process which is capable of easily and economically reducing the sulfur content of hydrocarbonaceous oil while achieving high recovery of the original feedstock. Important elements of the present invention are the minimization of the cost of hydrotreating in the integrated two-stage desulfurization process and the ability to economically desulfurize a hydrocarbonaceous oil to a very low level while maximizing the yield of the desulfurized hydrocarbonaceous oil.
One embodiment of the invention may be characterized as a process for the desulfurization of a hydrocarbonaceous oil which process comprises: (a) contacting the hydrocarbonaceous oil with a hydrodesulfurization catalyst in a hydrodesulfurization reaction zone at hydrodesulfurization conditions to p
Cutts, Jr. John G.
Griffin Walter D.
Nguyen Tam M.
Spears, Jr. John F.
Tolomei John G.
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