Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By addition of extraneous agent – e.g. – solvent – etc.
Reexamination Certificate
2001-08-25
2003-07-22
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By addition of extraneous agent, e.g., solvent, etc.
C208S211000, C208S212000, C208S219000, C208S220000, C208S221000, C208S222000, C208S223000, C208S224000, C208S240000
Reexamination Certificate
active
06596914
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of removing sulfur- and nitrogen-containing compounds from petroleum liquids and particularly to a method of desulfurization of fuel oils using aqueous acetic acid.
2. Description of Related Art
Environmental concerns have driven the need to remove many impurities from hydrocarbon based distillate fuels. Sulfur- and nitrogen-containing compounds are of particular interest because of their tendencies to produce precursors to acid rain and airborne particulate material. In addition, sulfur in particular can poison the catalysts used on automobiles and trucks to remove pollutant species. Several processes have been proposed in the past to deal with the problem of removing of these compounds from fuels. The most prevalent and common industrial process, and only large scale desulfurization process used to treat liquid fuels in refineries, is that of treating the fuel under high temperatures and high pressures with hydrogen. This process is called hydrotreating and has received extensive attention since its original invention in Germany before the Second World War. Literature describing this technology is immense, amounting to thousands of patents and scientific and engineering publications.
Briefly stated, hydrotreating is a process in which a petroleum fraction is heated, mixed with hydrogen, and fed to a reactor packed with a particulate catalyst. Temperatures in the reactor typically range from 600 to 700° F. (315 to 370° C.). At these temperatures, some or all of the feed may vaporize, depending on the boiling range of the feed and the pressure in the unit. For heavier feeds, it is common for the majority of the feed to be liquid. Reaction pressures range from as low as 500 psig (pounds per square inch, gauge) to as high as 2500 psig depending on the difficulty of removing the sulfur. In the manufacture of distillate fuels such as diesel or jet fuel, pressures higher than 800 psig are common. The feed and hydrogen mixture typically flows downward through the reactor, passing around and through the particulate catalyst. Upon leaving the reactor, the mixture of treated fuel and hydrogen flows through a series of mechanical devices to separate and recycle the hydrogen, remove poisonous hydrogen sulfide generated in the reaction, and recover the desulfurized product. Hydrotreating catalysts slowly lose activity with use, and must be removed and replaced every two to three years.
As used in large integrated refineries, hydrotreating is very effective, relatively inexpensive, and rather inefficient at removing the “refractory” substituted benzo- and di-benzo-thiophenes. However, in small refineries, and especially those with limited capabilities, it can be prohibitively expensive because of the effects of scale-up economics. When process equipment is built, it typically costs much less than twice as much to build a unit with twice the capacity; engineers typically estimate that doubling the size increases the cost by only about 50%. The converse of the scale-up effect occurs when processes are scaled down; smaller process units are only slightly less expensive to build than larger ones. Thus the investment for a small 5,000 barrel per day (bpd) hydrotreater is about 25% of a 40,000 bpd hydrotreater and not 12.5% of the cost of the much larger unit; hence the unitary cost of the smaller unit is approximately twice that of the larger unit.
Because of the way processes are operated and controlled, the manpower costs for the smaller unit are roughly the same as those of the larger one.
Another cost problem faced by small refiners is the lack of an inexpensive hydrogen source. Hydrotreating typically consumes 200 to 500 scfb (standard cubic feet per barrel) of hydrogen, and may consume as much as 1000 scfb. Manufacture of hydrogen from natural gas typically costs about $3 per 1000 scf, adding about $0.60 to as much as $3.00 to the cost of treating a barrel of feed for a small refinery. In large refineries, hydrogen is often available as a byproduct of the gasoline manufacturing process known as platinum reforming. As such, it is virtually free. In small refineries with no platinum reformer, a dedicated hydrogen manufacturing plant must be installed, adding to the refinery operator's investment burden and operating costs.
These economics favor those who wish to operate at large scale, but they make hydrotreaters prohibitively expensive for smaller refineries. This is one of the factors contributing to the closure of small refineries under the pressure of tightening environmental regulations. Some small refineries have survived by changing product mix to emphasize low value products such as asphalt, selling liquid products to large refineries to use as intermediates.
In order to continue to operate successfully, refineries and others have explored alternatives to hydrotreating. One idea that has been explored involves oxidizing the sulfur and nitrogen compounds in a distillate then removing them by selective extraction. This approach has met with only limited success primarily because of problems of non-selectivity of oxidants or the extraction solvents, problems that led to unacceptably high processing costs.
The complete removal of sulfur present in feedstock as sulfides, disulfides and mercaptans, is recognized as relatively easy, and comparatively inexpensive processes can accomplish this goal. Considerably more problematic are the family of “refractory sulfur compounds.” These compounds include the benzothiophenes and dibenzothiophenes and their mono-, di- and tri-substituted homologues with alkyl groups containing from one to 12 carbons. They are typically encountered within a boiling range of 220-350° C., molar weight range of 134-300 Dalton, and carbon number of 8-24. These compounds have very high sulfur levels (in the range of 11-24 wt %). For example, the thiophenes found in Light Atmospheric Gas Oil (LAGO) from Alaska North Slope Crude containing about 5000 ppm sulfur typically have the following inspection:
Carbons
C8-C9
C10
C-11
C-12
C13+
Total
MW Range
134-148
162
176
184-190
204-218
Fraction, wt %
5
34
27
26
8
100
In U.S. Pat. No. 3,847,800, Guth and Diaz proposed a process for treating diesel fuel that used oxides of nitrogen as the oxidant. However, nitrogen oxides have several disadvantages that can be traced to the mechanism by which they oxidize distillates. In the presence of oxygen, nitrogen oxides initiate a very non-selective form of oxidation termed auto-oxidation. Several side reactions also take place including the creation of nitro-aromatic compounds, oxides of alkanes and arylalkanes, and auto-oxidation products. Thus, nitrogen oxide based oxidants do not yield the appropriately oxidized sulfur compounds in distillate hydrocarbons without creating many undesirable byproducts.
The Guth and Diaz patent also proposes the use of methanol, ethanol, a combination of the two, and mixtures of these and water as an extraction solvent for polar molecules. Although these have proved to be acceptable extraction solvents for some polar compounds, they do not perform as well as others.
U.S. Pat. No. 4,746,420, issued to Darian and Sayed-Hamid also proposes the use of a nitrogen oxides to oxidize sulfur- and nitrogen-containing compounds followed by extraction using two solvents—a primary solvent followed by a cosolvent that is different from the primary. The sulfur and nitrogen results published in this patent are consistent with those expected from incomplete oxidation of these compounds followed by extraction.
In European Patent Application number 93302642.9 to Aida titled Method for Recovering Organic Sulfur Compounds from a Liquid Oil, Aida claims many oxidants as being essentially equal in their ability to oxidize sulfur- and nitrogen-containing compounds. However, it has been discovered that many of these oxidants are not sele
Bonde Steve
Dolbear Geoffrey E.
Gore Walter
Skov Ebbe R.
Griffin Walter D.
Nguyen Tam M.
Tavella Michael
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