Mineral oils: processes and products – Refining – Metal contaminant removal
Reexamination Certificate
1999-05-17
2002-02-26
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Refining
Metal contaminant removal
C208S182000, C208S293000, C208S301000, C585S820000, C585S835000
Reexamination Certificate
active
06350372
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the removal of mercury and other heavy metals from a mercury-contaminated hydrocarbon feedstream.
BACKGROUND OF THE INVENTION
Hydrocarbon feedstreams, including petroleum crude oils, natural gas, and natural gas condensates, can contain various amounts of mercury. Even in trace amounts, mercury is an undesirable component. The release of mercury by the combustion of mercury-contaminated hydrocarbons pose environmental risks and the accidental release and spill of accumulated mercury can lead to numerous safety hazards. Moreover, the contact of mercury-contaminated feedstreams with certain types of petroleum processing equipment presents additional problems of equipment deterioration and damage. This results when mercury accumulates in equipment constructed of various metals, such as aluminum, by forming an amalgam with the metal. Repair and replacement of the deteriorated processing equipment may be extremely costly.
Numerous methods have been developed for removing mercury from liquid hydrocarbon feedstreams, including petroleum crude oils and natural gas condensates, as well as from hydrocarbon gas streams. For example, U.S. Pat. No. 4,981,577 discloses a process for separating a natural gas wellstream into gaseous and liquid fractions and mixing the hydrogen sulfide containing gaseous fraction (sour gas) with the liquid fraction to form filterable mercury sulfide. However, removal of elemental mercury from gas streams and condensates is relatively facile when compared to the removal of the great variety of mercury compounds, e.g. elemental mercury, inorganic compounds, and organic (alkylated) compounds, often encountered in a far more chemically complex feedstream such as petroleum crude. For example, the particulates and waxy components of a crude oil would likely render a filtering method ineffective due to filter blockage and pore size limitations.
Generally, deleterious metals, such as mercury, are removed from liquid hydrocarbon feedstreams by chemisorption processes which comprise passing the feedstream at elevated temperatures over an adsorbent. U.S. Pat. Nos. 5,107,060 and 5,110,480 describe the removal of mercury from a natural gas condensate containing mercury by contacting the condensate with metals, metal sulfides, or metal oxides on a support such as carbon. The metal component on the adsorbent reacts with the mercury in the condensate feedstream. However, the heavier hydrocarbon fractions of crudes and some condensates may compete too favorably with the mercury and block the active metal sites on the adsorbent, destroying the activity of the adsorbent for mercury removal. Accordingly, these methods require higher temperatures within the adsorbent bed or an increased concentration of the active metal component on the adsorbent.
In particular, the organic (alkylated) mercury compounds present in many crude oil feedstreams are difficult to remove. Unlike elemental mercury and inorganic mercury compounds, the organic mercury compounds are soluble in oil and typically far less reactive than elemental mercury or inorganic mercury compounds. Moreover the solubility and toxicity of the organic mercury compounds makes them dangerous to handle.
EP-A-352,420 describes removing mercury from a natural gas liquid by mixing an aqueous solution of an ammonium or alkali metal sulfide with the liquid hydrocarbon to form insoluble mercury sulfide that can be transferred to the aqueous phase and subsequently separated and removed. In order to remove the organic mercury compounds, the feedstream must be contacted with an adsorbent comprising a heavy metal sulfide. Such a process involves the processing of two relatively immiscible phases, aqueous and oil, and the retention of organic mercury compounds in an adsorbent bed and/or aqueous fraction.
There remains a need to effectively and efficiently treat more complex hydrocarbon feedstreams that contain a variety of mercury compounds, including organic mercury compounds. It has now been discovered that the combination of a feedstream-soluble sulfur compound and an adsorbent is extremely effective in removing mercury from petroleum crudes as well as less complex hydrocarbon feedstreams. In addition, the process has been proven to be effective at moderately low temperatures and has maintained adsorption capacity for prolonged periods of time.
SUMMARY OF THE INVENTION
The invention relates to removing mercury, and other heavy metals such as lead and arsenic, from mercury-contaminated hydrocarbon feedstreams by the combined use of a feedstream-soluble sulfur compound and an adsorbent. As used herein, “feedstream-soluble” refers to a compound that is soluble or miscible in the hydrocarbon feedstream. Generally, the sulfur species is contacted with the hydrocarbon feedstream and both are subsequently passed through an adsorbent bed, which is preferably activated carbon. Typically, the soluble sulfur compounds react readily with the mercury compounds in the feedstream, including the organic (alkylated) mercury compounds found in petroleum crudes, to form mercury sulfide prior to contacting with the adsorbent. The mercury sulfide is readily adsorbed and may be easily recovered from the spent carbon adsorbent.
Accordingly, the process is able to remove mercury from a wide variety of hydrocarbon feedstreams. In particular, it has been discovered that contacting a mercury-contaminated petroleum crude oil feedstream with hydrogen sulfide and then passing that feedstream over activated carbon can effectively remove greater than 99% of the mercury entities in the petroleum crude oil under moderate adsorption temperatures for prolonged periods of time.
DETAILED DESCRIPTION OF THE INVENTION
The hydrocarbon feedstreams to be processed in accordance with the present invention may include any hydrocarbon feedstream containing mercury and/or other heavy metals, and in particular, petroleum crude oils, gas condensates, and gases. The other heavy metals that may be present in these hydrocarbon feedstreams include Pb, Fe, Ni, Cu, V, As, Cd, Sn, Sb, Bi, Se, Te, Co, In, and Tl.
Typically, petroleum crude oils comprise organic, inorganic, and elemental forms of mercury. Crude oils tend to have a brown or black color and a heavy end with an upper end boiling point of greater than about 537° C. and an A.P.I. gravity of less than about 50, more typically, less than about 45. Typical gas condensates comprise organic and elemental forms of mercury. Generally, a gas condensate is a liquid hydrocarbon produced from natural gas and separated from the gas by cooling or various other means of separation. Condensates generally are water-white, straw, or blueish in color with an upper end boiling point of less than about 315° C. and an A.P.I. gravity of greater than about 45. Typical hydrocarbon gas streams, such as natural gas streams, comprise organic and elemental forms of mercury. Generally, the gas streams comprise low molecular weight hydrocarbons such as methane, ethane, propane, and other paraffinic hydrocarbons that are typically gases at room temperature. In preferred embodiments, the process of the present invention may be used to remove mercury from crude oil hydrocarbon feedstreams.
Typically, the feedstreams may comprise about 40 to about 5000 ppb mercury. Some feedstreams may contain from about 2000 to about 100,000 ppb mercury. The mercury content may be measured by various conventional analytical techniques known in the art. For example, cold vapor atomic absorption spectroscopy (CV-AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray fluorescence, or neutron activation may be used to measure mercury content.
According to the present invention, the hydrocarbon feedstream is contacted with a sulfur compound. In preferred embodiments, the sulfur compounds are feedstream soluble or miscible, and in particular, oil soluble or miscible, and may therefore be added to the feedstream as gases, liquids, or an oil soluble solid. Preferred feedstream-soluble compounds which can be e
Degnan Thomas F.
LeCours Steven M.
Brumlik Charles J.
Mobil Oil Corporation
Yildirim Bekir L.
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