Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-10-19
2001-05-01
Myers, Helane (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S228000, C208S230000, C208S235000, C208S236000, C208S237000, C208S227000
Reexamination Certificate
active
06224750
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a biological process for removing sulfur compounds from a hydrocarbon stream. The invention more directly relates to a process for removing sulfur compounds from a hydrocarbon stream through the use of an aqueous caustic stream which is regenerated in a biological reaction zone. The invention specifically relates to the production of very low sulfur hydrocarbon products through the use of a purified stream of caustic which has been regenerated in an aerobic bioreactor.
BACKGROUND OF THE INVENTION
Unprocessed hydrocarbons derived from crude oil and natural gas tend to contain a number of sulfur compounds. These compounds or the sulfur they contain must be removed before the hydrocarbons are suitable for use. There are two prime reasons for this. First, the release of sulfur or sulfur compounds into the atmosphere is a significant environmental concern which is coming under increased regulatory constraints. Second, sulfur must be at a very low concentration in various hydrocarbon streams in order to meet the quality standards for these hydrocarbon products. It is therefore necessary for petroleum refineries, gas processing plants and other industrial facilities to remove sulfur compounds of various types from raw material fractions and from partially processed hydrocarbon fractions such as hydrogen-rich gas streams, natural gas, diesel fuel, naphtha and LPG. This need to remove the sulfur compounds is independent of whether the hydrocarbons are intended for use as a motor fuel or as a petrochemical feedstock.
Many different techniques such as hydrotreating are widely used for removing sulfur compounds from hydrocarbon streams. Most of these techniques include a step in which a liquid phase or gas phase hydrocarbon stream is contacted with an aqueous stream containing a dissolved alkaline material. The aqueous stream, commonly referred to as “caustic” is employed to remove acidic sulfur compounds from both vapor phase or liquid phase process streams. The result is the formation of a sulfur-rich alkaline aqueous stream; that is, one containing an increased concentration of a sulfur compound such as hydrogen sulfide. The rich aqueous stream must be regenerated so that it can be reused. The subject invention provides a process for regenerating hydrogen sulfide rich alkaline aqueous streams in a manner which converts the hydrogen sulfide to recovered elemental sulfur. To accomplish this, the subject invention passes the hydrogen sulfide rich aqueous stream into a biological reaction zone, a term which is used herein to describe both single reactor and multiple reactor apparatus. It may contain zones for performing both aerobic and anaerobic reactions. This biological reaction zone employs naturally occurring microorganisms that catalyze the conversion of sulfur compounds to elemental sulfur which is physically removed. The subject invention then purifies the treated aqueous stream to remove additional elemental sulfur.
RELATED ART
An overview of the application of biological treatment to sulfur-containing waste streams such as sulfidic caustic generated in a petroleum refinery is found in paper No. AM-98-27 presented at the 1998 NPRA Annual Meeting held Mar. 15-17, 1998 in San Francisco, Calif. This reference describes the use of a bioreaction zone which may comprise both anaerobic and aerobic sections or a single aerobic section for the treatment of waste streams containing sulfates or hydrogen sulfide. The reference describes in general terms the application of this biotechnology to the treatment of waste streams generated in several different treatment processes. The reference also presents a schematic diagram of a bioreactor suitable for use in the process.
A simplified process flow diagram and a brief description of the application of biotreating to gas streams containing hydrogen sulfide is provided at page 89 of the August 1998 edition of
Hydrocarbon Processing.
The description refers to the recycling of “sulfur-free” aqueous solution thus showing a lack of recognition of the subject invention. The reference treats a gas stream which would not be expected to pick up elemental sulfur from the aqueous solution.
Processes for the conversion of sulfur-containing compounds present in aqueous streams including sulfidic caustic used in scrubbing H
2
S from a process stream are described in U.S. Pat. Nos. 5,366,633; 5,518,619; and, 5,637,220 issued to C. J. N. Buisman. These references describe the conversion of the sulfur compounds to elemental sulfur. U.S. Pat. No. 5,366,633 indicates that a separator
7
can be used to treat the effluent of the reactor
4
to separate elemental sulfur from the process liquid, The text indicates the elemental sulfur can be removed by physical separation such as settling, centrifuging, flocculation or filtration. However, there is believed to be no disclosure in these references of methods to produce high purity liquid-phase hydrocarbon products, to remove trace amounts of suspended elemental sulfur still present in the treated aqueous stream after the initial physical separation or of techniques to adopt this technology to treating liquid-phase hydrocarbon feed streams instead of water.
BRIEF SUMMARY OF THE INVENTION
It has now been found that aqueous caustic solutions which have been regenerated by means of the previously cited biotechnology contain a small but significant amount of elemental sulfur which is carried over due to incomplete separation of particulate sulfur from the bioreactor effluent and possibly formed after the separation. Further, it has been determined that at least a portion of this sulfur readily dissolves in a hydrocarbon stream which is subsequently being treated by the regenerated caustic. The result is the hydrocarbon stream picks up sufficient dissolved elemental sulfur that the level of sulfur contamination can cause the treated hydrocarbon to fail standard product quality test methods. In summary it has been found that the freshly regenerated aqueous solution, which is supposed to readily remove sulfur compounds from the feed hydrocarbon, unexpectedly gives up elemental sulfur to the feed stream
The subject invention centers around the elimination of this carryover elemental sulfur in the treated aqueous stream. One broad embodiment of the subject invention may be characterized as a process which comprises passing a feedstream comprising hydrocarbons and sulfur-containing compounds through an extraction zone in which at least a major portion of the sulfur-containing compounds are removed from the feedstream by contact with an aqueous treatment stream, and thereby producing a hydrocarbon product stream containing less than about 3 wt. ppm combined hydrogen sulfide and elemental sulfur and a rich aqueous treatment stream; passing the rich aqueous treatment stream into a biological reaction zone in which elemental sulfur is formed, and forming a biological reaction zone effluent stream comprising particulate elemental sulfur; separating particulate elemental sulfur from the biological reaction zone effluent stream and thereby forming a partially regenerated treatment stream comprising an aqueous alkaline solution and entrained elemental sulfur; and contacting the partially regenerated treatment stream with a liquid-phase wash stream comprising a hydrocarbon in a contacting zone and removing entrained elemental sulfur from the partially regenerated treatment stream and thereby forming the aqueous treatment stream employed in the extraction zone.
REFERENCES:
patent: 4033410 (1977-07-01), Kauffman
patent: 4055400 (1977-10-01), Stambaugh et al.
patent: 4391608 (1983-07-01), Dondelewski
patent: 4708620 (1987-11-01), Bricker
patent: 4722432 (1988-02-01), Weston et al.
patent: 5017279 (1991-05-01), Oswald et al.
patent: 5582714 (1996-12-01), Forte
Arena Blaise J.
Pittman Rusty Mark
Myers Helane
Spears, Jr. John F.
Tolomei John G.
UOP LLC
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