Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2001-09-12
2002-06-18
Preisch, Nadine (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S237000, C208S238000, C208S219000, C208S223000, C208S222000, C208S196000
Reexamination Certificate
active
06406616
ABSTRACT:
FEDERALLY SPONSORED RESEARCH STATEMENT
Not applicable.
1. Field of the Invention
This invention relates to a process for the removal of organic sulfur compounds by oxidation from hydrocarbon fuels which have relatively low amounts of sulfur present.
2. Background of the Invention
The presence of sulfur in hydrocarbons has long been a significant problem from the exploration, production, transportation, and refining all the way to the consumption of hydrocarbons as a fuel. As government regulations throughout the world increasingly restrict sulfur levels in fuels, the problem of sulfur reduction is being felt by producers, refiners, transporters and marketers of the full range of fuel products, from gasoline and diesel fuel to jet fuel, kerosene, heating oil and heavier fuels. In Western Europe, North America, Japan and other industrial nations the sulfur restrictions on gasoline and on-highway diesel fuel are moving to the ultra-low levels of 30, 15 or even 10 ppm. Consequently, producers, refiners and marketers are seeking low-cost technologies for producing ultra-low sulfur products, with maximum use of existing facilities.
Sulfur can be found in almost any stream within a refinery complex. This is due to the sulfur in the crude oil to be processed. The process technology for removing sulfur that is in almost universal use today is hydrotreating, sometimes referred to as hydrodesulfurization. Hydrotreating, as used herein, is a process whose primary purpose is to reduce the sulfur and/or nitrogen content (and not to change the boiling range) of the feed. While there are many variations and improvements, this technology requires high temperature and pressure in a hydrogen environment and employs advanced catalysts. This process successfully removes the majority of the sulfur compounds in hydrocarbons. However, the substituted thiophenes, especially those having steric hindrance of the sulfur, are particularly difficult and require high severity hydrotreaters having pressures well in excess of 500 psi. Achieving ultra-low sulfur levels requires that most of these difficult-to-hydrotreat compounds be removed, which could drive many refiners to install new hydrotreaters or carry out expensive revamps of their existing hydrotreaters. Gasoline fractions will contain mainly thiophenes and some benzothiophenes but generally little or no dibenzothiophenes. Diesel fractions will contain mainly benzothiophenes and dibenzothiophenes.
The prior art is replete with attempts to reduce the sulfur content of hydrocarbon by both reduction and oxidation of organic sulfur present. Much of this prior art relating to oxidation has taught the use of various peroxides in conjunction with a carboxylic acid and, specifically, the preferred species involved in the practice of this invention; i.e., hydrogen peroxide and formic acid. For example, U.S. Pat. No. 5,310,479 teaches the use of formic acid and hydrogen peroxide to oxidize sulfur compounds in crude oil, limiting the application of the technology only to aliphatic sulfur compounds. There was no hint of the removal of aromatic sulfur compounds. This patent discussion is directed to the removal of sulfur from crude oil rich (about 1-4%) in sulfur compounds. The acid to peroxide ratio was indiscriminately broad and failed to recognize the economic disadvantages to using hydrogen peroxide in attempts to remove large amounts of sulfur, while at the same time failing to recognize the importance of controlling the presence of water to the successful operation. Water was used to extract the sulfones from the treated hydrocarbon in a separate wash step. Further, the prior art also fails to recognize the beneficial effect of limiting the peroxide concentration to low values without compromising either the rate or extent of oxidation of the sulfur compounds.
A recent study entitled “Oxidated Desulfurization of Oils by Hydrogen Peroxide and Heteropolyanion Catalyst,” Collins, et al., published
Journal of molecular Catalysis A: Chemical
, 117 (1997) 397-403, discusses other studies to oxidatively remove sulfur from fuel oil, but large quantities of hydrogen peroxide were required. However, the experimental work did show that unacceptable amounts of hydrogen peroxide were consumed thus suggesting the cost of oxidative reduction of sulfur in feedstocks for diesel fuel to be impermissibly high.
In European Patent Application Publication No. 0565324A1, a method for recovering organic sulfur compounds from liquid oil is described. While the stated objective of the patent publication is to recover the organic sulfur compounds, the treatment involves using a mixture of a number of oxidants, one of which is disclosed as a mixture of formic acid and peroxide. The distillation products, the organic sulfones, are removed by a number of methods including absorption on alumina or silica adsorbent materials. The treatments described are characterized by use of a low ratio of formic acid to the hydrogen peroxide.
While this and other prior art recognize the reaction kinetics and mechanism of hydrogen peroxide and other peroxides with organic sulfur compounds present in various fuels, none recognize the combination of factors necessary to successfully and economically remove relatively small amounts of sulfur present in fuels such as diesel oil, kerosine, gasoline, and light oils down to residual levels approaching zero. While low amounts of sulfur will be construed to mean in the context of this invention, those amounts which are less than about 1500 parts per million, an example demonstrates effective removal of 7000 ppm of sulfur such that the present invention is applicable to higher levels of sulfur. Of course in some instances, the practice of this invention may be economically and technically applicable to the treatment of fuels having a sulfur content at these elevated levels. It has been found in the practice of this invention that the sulfur content of the fuel which is left unoxidized is less than about 10 ppm of sulfur, often as low as about 2 ppm to about 8 ppm. Oxidation alone does not necessarily ensure total removal of the sulfur to the same low residual sulfur values since some of the oxidized sulfur species do have a non-zero solubility in the fuel, and a partition coefficient that defines their distribution in the oil phase in contact with a substantially immiscible solvent phase, whether it is an organic solvent as in prior art, or the high acid aqueous phase of this invention. In addition to the substantially complete and rapid oxidation of the relatively low amounts of sulfur in the fuel feed, the present invention also teaches the substantially complete removal of the oxidized sulfur to residual levels approaching zero, and the recovery of the oxidized sulfur compounds in a form suitable for their practical further disposition in an environmentally benign way. Removal of sulfur by oxidation adds another dimension in that it is desirable that such removal of sulfur be accomplished, without reducing the octane rating of the gasoline, whether it be motor, racing or aviation gasoline. This object is accomplished by the present invention.
In an article, Desulfurization by Selective Oxidation and Extraction of Sulfur-Containing Compounds to Economically Achieve Ultra-Low Proposed Diesel Fuel Sulfur Requirements (Chapados, et al., NPRA Presentation, Mar. 26-28, 2000) the oxidation step involved the reaction of the sulfur in a model compound using dibenzothiophene with a peroxyacetic acid catalyst made from acetic acid and hydrogen peroxide. The reaction with the peroxyacid was conducted at less than 100° C. at atmospheric pressure and in less than 25 minutes. After extraction, the process resulted in a reduction of the sulfur content in the diesel fuel. Still, the cost was indicated to be high with the hydrogen peroxide being the biggest cost item and consumed in the process due in large part to the lack of recognition of the part excessive water plays in the efficient utilization of low amounts of hydrogen peroxide.
SUMMARY OF THE INVENTION
It has been d
DeCanio Stephen J.
Nero Vincent P.
Rappas Alkis S.
Preisch Nadine
Unipure Corporation
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