Abstract:
One exemplary embodiment can be a process for treating a liquid hydrocarbon stream. The process can include passing the liquid hydrocarbon stream previously contacted with a solvent having an alkanolamine consisting of diethanolamine, a methyl diethanolamine, or a mixture thereof, and an alkali to a vessel. Generally, the vessel contains a coalescing zone for removing at least one of hydrogen sulfide and carbonyl sulfide.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to a process for treating a liquid hydrocarbon stream. 
     DESCRIPTION OF THE RELATED ART 
     Often, hydrocarbon streams are treated to remove sulfur-containing compounds, such as mercaptans. Generally, mercaptans are removed because of their malodorous scent. Additionally, it is usually desirable to remove other compounds, such as carbonyl sulfide. As such, additional equipment may be utilized to remove these other compounds. Such equipment may be provided solvents for removing these compounds. The provided solvents may be limited to particular types and can carryover to downstream units causing upsets. It would be preferable to overcome such shortcomings by reducing the number of equipment pieces, minimize upsets of downstream units, and provide more flexibility with respect to solvents. Thus, improving operability and efficiency of such processes is desirable. 
     SUMMARY OF THE INVENTION 
     One exemplary embodiment can be a process for treating a liquid hydrocarbon stream. The process can include passing the liquid hydrocarbon stream previously contacted with a solvent having an alkanolamine consisting of diethanolamine, a methyl diethanolamine, or a mixture thereof, and an alkali to a vessel. Generally, the vessel contains a coalescing zone for removing at least one of hydrogen sulfide and carbonyl sulfide. 
     Another exemplary embodiment may be a process for treating a liquid hydrocarbon stream. The process can include passing the liquid hydrocarbon stream previously contacted with a solvent including a diethanolamine, an alkali, and water to a contacting zone, and passing the contacted stream to a coalescing zone having a hydrophilic mesh for removing at least one of hydrogen sulfide and carbonyl sulfide. 
     A further exemplary embodiment can be a process for treating a liquid hydrocarbon stream. The process can include passing the liquid hydrocarbon stream previously contacted with a solvent including an alkanolamine consisting of a diethanolamine, a methyl diethanolamine, or a mixture thereof, and an alkali through a contacting zone, passing the contacted stream to a vessel containing a coalescing zone for removing at least one of hydrogen sulfide and carbonyl sulfide, and passing a stream from the vessel to an extraction zone. 
     The embodiments disclosed herein can remove carbonyl sulfide upstream instead of downstream of an extraction zone. Hence, the embodiments herein can reduce the overall cost of the process by eliminating downstream equipment, such as a carbonyl sulfide settler, a sand filter, and/or a water wash of hydrocarbon product streams. Moreover, carryover to downstream units can be minimized preventing upsets in those units. Additionally, solvent flexibility can be increased, such as allowing the use of diethanolamine, sodium hydroxide, and water solutions. Furthermore, existing units may be revamped to use the diethanolamine, sodium hydroxide, and water solution solvents instead of a caustic-water solution. 
     DEFINITIONS 
     As used herein, the term “stream” can include various hydrocarbon molecules, such as straight-chain, branched, or cyclic alkanes, alkenes, alkadienes, and alkynes, and optionally other substances, such as gases, e.g., hydrogen, or impurities, such as heavy metals, and sulfur and nitrogen compounds. The stream can also include aromatic and non-aromatic hydrocarbons. Moreover, the hydrocarbon molecules may be abbreviated C1, C2, C3 . . . Cn where “n” represents the number of carbon atoms in the one or more hydrocarbon molecules. Furthermore, a superscript “+” or “−” may be used with an abbreviated one or more hydrocarbons notation, e.g., C3 +  or C3 − , which is inclusive of the abbreviated one or more hydrocarbons. As an example, the abbreviation “C3 + ” means one or more hydrocarbon molecules of three carbon atoms and/or more. In addition, the term “stream” may be applicable to other fluids, such as aqueous and non-aqueous solutions of alkaline or basic compounds, such as sodium hydroxide. 
     As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones. 
     As used herein, the term “rich” can mean an amount of at least generally about 50%, and preferably about 70%, by mole, of a compound or class of compounds in a stream. If referring to a solute in solution, e.g., one or more disulfide compounds in an alkaline solution, the term “rich” may be referenced to the equilibrium concentration of the solute. As an example, about 5%, by mole, of a solute in a solvent may be considered rich if the concentration of solute at equilibrium is about 10%, by mole. 
     As used herein, the term “substantially” can mean an amount of at least generally about 80%, preferably about 90%, and optimally about 99%, by mole, of a compound or class of compounds in a stream. 
     As used herein, the term “coupled” can mean two items, directly or indirectly, joined, fastened, associated, connected, or formed integrally together either by chemical or mechanical means, by processes including stamping, molding, or welding. What is more, two items can be coupled by the use of a third component such as a mechanical fastener, e.g., a screw, a nail, a bolt, a staple, or a rivet; an adhesive; or a solder. 
     As used herein, the term “coalescer” may be a media containing an optionally coated metal mesh, glass fibers, or other material to facilitate separation of immiscible liquids of similar density. 
     As used herein, the term “immiscible” can mean two or more phases that cannot be uniformly mixed or blended. 
     As used herein, the term “phase” may mean a liquid, a gas, or a suspension including a liquid and/or a gas, such as a foam, aerosol, or fog. A phase may include solid particles. Generally, a fluid can include one or more gas, liquid, and/or suspension phases. 
     As used herein, the term “alkali” can mean any substance that in solution, typically a water solution, has a pH value greater than about 7.0, and exemplary alkali can include sodium hydroxide, potassium hydroxide, or ammonia. Such an alkali in solution may be referred to as “an alkaline solution” or “an alkaline” and includes caustic, i.e., sodium hydroxide in water. 
     As used herein, the term “parts per million” may be abbreviated herein as “ppm” and “weight ppm” may be abbreviated herein as “wppm”. 
     As used herein, the term “mercaptan” typically means thiol and may be used interchangeably therewith, and can include compounds of the formula RSH as well as salts thereof, such as mercaptides of the formula RS − M +  where R is a hydrocarbon group, such as an alkyl or aryl group, that is saturated or unsaturated and optionally substituted, and M is a metal, such as sodium or potassium. 
     As used herein, the weight percent or ppm of sulfur, e.g., “wppm-sulfur” is the amount of sulfur, and not the amount of the sulfur-containing species unless otherwise indicated. As an example, methylmercaptan, CH 3 SH, has a molecular weight of 48.1 with 32.06 represented by the sulfur atom, so the molecule is about 66.6%, by weight, sulfur. As a result, the actual sulfur compound concentration can be higher than the wppm-sulfur from the compound. 
     As used herein, the term “lean” can describe a fluid optionally having been treated and desired levels of sulfur, including one or more mercaptans and one or more disulfides for treating one or more C1-C15 hydrocarbons. 
     As used herein, the term “liquefied petroleum gas” can refer to one or more C1-C4 hydrocarbons, typically one or more C3-C4 hydrocarbons, having a boiling point of about −160-about 0° C. at atmospheric pressure. 
     As used herein, the term “naphtha” can refer to one or more C5-C12 hydrocarbons having a boiling point of about 25-about 190° C. at atmospheric pressure. 
     As used herein, the term “kerosene” can refer to one or more C9-C15 hydrocarbons having a boiling point of about 160-about 275° C. at atmospheric pressure. 
     As used herein, the terms “degrees Celsius” may be abbreviated “° C.” and the term “kilopascal” may be abbreviated “KPa” and all pressures disclosed herein are absolute. 
     As depicted, process flow lines in the figures can be referred to, interchangeably, as, e.g., lines, pipes, branches, distributors, streams, effluents, feeds, products, portions, catalysts, withdrawals, recycles, suctions, discharges, and caustics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of an exemplary apparatus for removing carbonyl sulfide. 
         FIG. 2  is a schematic depiction of another exemplary apparatus for removing carbonyl sulfide. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an apparatus  100  can include a contacting zone  120 , a vessel  140 , such as a prewash vessel  140 , and an extraction zone  200 . A liquid hydrocarbon stream  50 , such as a liquefied petroleum gas, a naphtha, or a kerosene, containing one or more sulfur compounds, such as one or more thiol compounds or hydrogen sulfide, may be provided to the apparatus  100 . Usually, the liquid hydrocarbon stream  50  can be rich or substantially include one or more C1-C15 hydrocarbons, and can be substantially in a liquid phase. The liquid hydrocarbon stream  50  may also contain about 50-about 500 ppm, by weight, carbonyl sulfide and be combined with a solvent or recycle stream  60 , as hereinafter described, to form a combined stream  80  before entering the contacting zone  120 . 
     The contacting zone  120  can include any suitable device, such as a jet educator mixer, a structured column packing, a random packing, a sieve tray, and/or a static mixer. In this exemplary embodiment, a static mixer  124  can thoroughly blend the components of the streams  50  and  60 . A contacted stream  90  from the contacting zone  120  may be passed to the vessel or prewash vessel  140 . 
     In this exemplary embodiment, the prewash vessel  140  can be orientated substantially vertical. The prewash vessel  140  can include a coalescing zone  180 , which can include at least one of a mesh and one or more vanes to form a circular disk across an entire cross-section of the prewash vessel  140 . Generally, the coalescing zone  180  may include a hydrophilic media having at least one of a metal mesh that is optionally coated; one or more glass fibers, such as fiberglass; corrugated sheet media; or a metal, such as stainless steel, mesh or wires. One exemplary hydrophilic coated mesh may include a coating sold under the trade designation COALEX or KOCH-OTTO YORK™ separations technology by Koch-Glitsch, LP of Wichita, Kans. 
     Downstream of the prewash vessel  140  may be an extraction zone  200 . The extraction zone  200  can receive a prewashed hydrocarbon stream  140  from the prewash vessel  140 . The extraction zone  200  can include any suitable vessels, such as an extraction vessel and an alkali regeneration zone, including an oxidation vessel and a settler. Typically, the extraction zone  200  can produce a hydrocarbon product stream and a rich alkali stream from the extraction vessel that is sent to the alkali regeneration zone to obtain a lean alkali stream provided back to the extraction vessel. An exemplary extraction zone including an extraction vessel and an alkali regeneration zone are disclosed in, e.g., U.S. Pat. No. 7,381,309. 
     In operation, the liquid hydrocarbon stream  50  can be combined with the solvent stream  60  to form a combined stream  80  provided to the static mixer  124  in the contacting zone  120 . The contacted stream  90  can be provided to the prewash vessel  140 . A hydrocarbon phase  154  can form above and have an interface  152  with an aqueous phase  156 . The hydrocarbon phase  154  may rise and pass through the coalescing zone  180  resulting in the coalescing of aqueous droplets dropping back down to the bottom of the prewash vessel  140 . The prewashed hydrocarbon stream  194  can be withdrawn from the prewash vessel  140  and be provided to the extraction zone  200  to obtain a hydrocarbon product stream  210 . 
     The aqueous phase  156  can fall in the prewash vessel  140  and be withdrawn as a bottom stream  164 . The bottom stream  164  can be split into a purge stream  168  and a portion  170 . A control valve  160  can communicate with a level controller  158  for regulating the level of liquids in the prewash vessel  140 . The portion  170  may be combined with a make-up stream  70 . 
     The make-up stream  70  can include the solvent, which may include an alkali, an alkanolamine, and water. The alkali can include at least one potassium hydroxide, sodium hydroxide, and ammonia. The alkanolamine may include or consist of diethanolamine and/or methyl diethanolamine. A weight ratio of alkali:alkanolamine may be about 1:2-about 2:1 with the balance water. In one preferred embodiment, the make-up stream  70  can have a weight ratio of sodium hydroxide:diethanolamine of about 1:2-about 2:1 with the balance water. 
     The make-up stream  70  can be combined with the portion  170  to form a stream  72  to the suction of a circulating pump  174 . The circulating pump  174  may provide a discharge of the solvent stream  60  combined with the liquid hydrocarbon stream  50 . 
     Referring to  FIG. 2 , another version of the apparatus  100  is depicted. The primary difference in this version as compared to the version discussed above is that the vessel  140  is orientated primarily horizontal instead of vertical. So, many of the elements are the same in the two versions and may not be discussed with respect to this version. As an example, the contacting zone  120  and extraction zone  200  can be substantially identical as discussed above. Usually, the coalescing zone  180  can form a substantially vertical orientated disk dividing the prewash vessel  140  into two chambers allowing the passage of liquid there through. Also, the contacted stream  90  from the contacting zone  120  may be passed through a distributor  94  into the prewash vessel  140 . The distributor  94  can be any suitable device, including a pipe with a series of holes formed about its circumference. The hydrocarbon product stream  210  can be obtained, as described above in the version depicted in  FIG. 1 . 
     In both versions, it is generally desirable to obtain the prewashed hydrocarbon stream  194  having no more than about 1 wppm of sodium, which can represent the amount of solvent carryover to downstream equipment or zones, such as the extraction zone  200 . Moreover, both hydrogen sulfide and carbonyl sulfide may be removed from the hydrocarbon stream. By removing carbonyl sulfide upstream of the extraction zone  200 , additional equipment can be eliminated. 
     Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
     In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.