Abstract:
One exemplary embodiment can be a process for purifying a disulfide oil. The process can include obtaining at least a portion of a disulfide oil coalesced from an alkaline stream, and passing the at least a portion of the disulfide oil through a mesh for recovering a purified disulfide oil stream.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention generally relates to a process for purifying a disulfide oil and an apparatus relating thereto. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Often, hydrocarbon and gas streams are treated to remove sulfur-containing compounds, such as one or more thiol compounds. Generally, such compounds are removed because of their malodorous scent. 
         [0003]    A thiol compound can be designated R—S—H where R is often a light hydrocarbon radical such as methyl or ethyl. Typically, thiol compounds concentrate in hydrocarbon liquid streams separated in a process facility. Many processes can be used to remove thiols and other sulfur-containing compounds. Often, such processes can use a caustic stream contacting the hydrocarbon stream in an extractive system. 
         [0004]    After use, the caustic stream may be regenerated. As such, air may be used for oxidizing the thiol compounds to disulfide oils. The unreacted components of the air stream, e.g. nitrogen, oxygen, and other inert gases, are separated from the caustic and disulfide oils. Often, a separation vessel allows the separation of a disulfide oil stream that contains remnants of caustic, which are desirably removed from the disulfide oil. 
         [0005]    Often, it is desirable to minimize the number of equipment pieces to accomplish this task. A separate sand filter may be used to remove remnant amounts of caustic from the disulfide oil. As a consequence, it would be desirable to minimize the number of separate equipment pieces while removing undesirable components from disulfide oils in an economic and efficient manner to simplify construction and lower costs. 
       SUMMARY OF THE INVENTION 
       [0006]    One exemplary embodiment can be a process for purifying a disulfide oil. The process can include obtaining at least a portion of a disulfide oil coalesced from an alkaline stream, and passing the at least a portion of the disulfide oil through a mesh for recovering a purified disulfide oil stream. 
         [0007]    Another exemplary embodiment may be an apparatus. The apparatus can include a separation vessel. The separation vessel can include a base coupled to a first stack and a second stack. Often, the first stack includes a mesh and the second stack includes a packing. 
         [0008]    A further exemplary embodiment can be a process for purifying a disulfide oil. The process can include sending a spent alkaline solution from an extractor vessel to an oxidation vessel, and sending an effluent from the oxidation vessel to a separation vessel. Often, the separation vessel has a base, a first stack, and a second stack. Usually, the second stack receives the effluent. 
         [0009]    The embodiments disclosed herein can provide a vessel incorporating a stack for removing impurities, such as an alkaline liquid, e.g. caustic, to recover a purified disulfide oil. Such a design can reduce capital costs by combining functions into a single vessel and eliminate other equipment, such as a sand filter. Incorporating all the components into a single vessel can eliminate interconnecting piping due to the inclusion of a sand filter, as well as associated piping connection errors, and simplify maintenance by eliminating backwashing of the sand filter. 
       Definitions 
       [0010]    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. 
         [0011]    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. 
         [0012]    As used herein, the term “vapor” can mean a gas or a dispersion that may include or consist of one or more hydrocarbons. 
         [0013]    As used herein, the term “rich” can mean an amount of generally at least about 50%, and preferably about 70%, by mole, of a compound or class of compounds in a stream. With respect to extraction, an alkaline solution or a disulfide oil stream may be “rich” if such a liquid is at least partially saturated with one or more compounds, such as thiol compounds. 
         [0014]    As used herein, the term “substantially” can mean an amount of generally at least about 80%, preferably about 90%, and optimally about 99%, by mole, of a compound or class of compounds in a stream. 
         [0015]    As used herein, the term “lean” may mean a liquid, such as an alkaline solution or a disulfide oil stream, substantially devoid of one or more impurities, such as one or more thiol compounds or alkali. 
         [0016]    As used herein, the term “thiol” can include a mercaptan and a salt thereof, such as a mercaptide. A thiol can be of the formula RSH or a salt 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. 
         [0017]    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, an adsorber, or a vessel, can further include one or more zones or sub-zones. 
         [0018]    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. 
         [0019]    As used herein, the term “immiscible” means two or more phases that cannot be uniformly mixed or blended. 
         [0020]    As used herein, the term “phase” means 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 gases, liquids, and/or suspension phases. 
         [0021]    As used herein, the term “killed carbon steel” generally means a carbon steel deoxidized by the addition of aluminum, ferrosilicon, or other suitable compounds while the mixture is maintained at melting temperature until all bubbling ceases. Typically, the steel is quiet and begins to solidify at once without any evolution of gas when poured into ingot molds. 
         [0022]    As depicted, process flow lines in the FIGURE can be referred to interchangeably as, e.g., lines, pipes, liquids, oils, solutions, alkalines, caustic, catalyst, branches, portions, feeds, products, or streams. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0023]    The FIGURE is a schematic depiction of an exemplary apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring to the FIGURE, an exemplary apparatus  100  for removing one or more sulfur-containing compounds, such as one or more thiol compounds, from a hydrocarbon stream  20  is depicted. Typically, the apparatus  100  can include an extractor vessel  120 , an oxidation vessel  160 , and a separation vessel  200 . The vessels, lines and other equipment of the apparatus  100  can be made from any suitable material, such as carbon steel, killed carbon steel, stainless steel, or titanium. 
         [0025]    The hydrocarbon stream  20  is typically in a liquid phase and can include a liquefied petroleum gas or a naphtha hydrocarbon. Typically, the hydrocarbon stream  20  contains sulfur compounds in the form of one or more thiol compounds and/or hydrogen sulfide. Generally, the apparatus  100  can also include a caustic prewash vessel. Exemplary apparatuses having at least a caustic prewash vessel, an extractor vessel, and an oxidation vessel for removing sulfur-containing compounds from a hydrocarbon stream are disclosed in, e.g., U.S. Pat. No. 7,326,333 and US 2010/0122936. These vessels can be in direct or indirect communication with each other as well as a separation vessel. 
         [0026]    A hydrocarbon stream  20  can be an effluent from, for example, a separate prewash vessel. The hydrocarbon stream  20  can include hydrogen sulfide and one or more C2-C8 hydrocarbons. Usually, the hydrocarbon stream  20  can include up to about 100 ppm, by weight, hydrogen sulfide. Generally, the hydrocarbon stream  20  is combined with a stream  26  including water from a stream  30  and an alkaline solution stream  28 , as hereinafter described, for removing, e.g., hydrogen sulfide. The alkali can be any caustic material, such as sodium hydroxide and potassium hydroxide, or ammonia, and is usually added to a liquid, e.g., water, to form an alkaline solution. The streams  20  and  26  are combined as an extractor feed  50 . The extractor feed  50  can enter the extractor vessel  120 . The extractor vessel  120  can include a lower prewash section  130 , and an upper extractor section  150 . The extractor feed  50  can enter the lower prewash section  130 . A predominately hydrocarbon phase can rise while the alkaline solution can fall in the prewash section  130 . The alkaline solution can be withdrawn via an alkaline solution withdrawal line  134  with a portion  138  being purged and another portion  136  being recycled. A transfer conduit  140  can transfer the hydrocarbon phase into the upper extractor section  150 , which can be contacted with an alkaline solution  152 , as hereinafter described, for extracting one or more thiol compounds from the hydrocarbon phase into the alkaline phase. 
         [0027]    The hydrocarbon product  154  mostly free of one or more thiol compounds can be withdrawn from the top of the upper extractor section  150  while a spent alkaline solution including one or more thiol compounds can be withdrawn via a line  156 . The spent alkaline solution  156  can be combined with an oxidation catalyst  158  and an air stream  162 . The oxidation catalyst  158  can be any suitable oxidation catalyst, such as a sulfonated metal phthalocyanine. However, any suitable oxidation catalyst can be used such as those described in, e.g., U.S. Pat. No. 7,326,333. The oxidation catalyst  158 , the air stream  162 , and the spent alkaline solution  156  can be combined in a line  164  before entering the oxidation vessel  160 . The spent aqueous alkaline solution and air mixture is distributed in the oxidation vessel  160 . In the oxidation vessel  160 , the one or more thiol compounds may catalytically react with oxygen and water to yield an alkaline solution and organic disulfides. Optionally, the oxidation vessel  160  can include packing, such as carbon rings, to increase the surface area for improving contact between the spent alkaline solution and catalyst. 
         [0028]    Afterwards, an effluent  180  from the oxidation vessel  160  can be withdrawn from the top of the oxidation vessel  160 . The effluent  180  can include an alkaline solution, one or more hydrocarbons, one or more sulfur compounds, and a gas. Typically, the effluent  180  can include a gas phase, a liquid disulfide phase, and a liquid aqueous alkaline solution phase, but may also be referenced as an alkaline stream  180 , as the alkaline solution can be a primary component. Generally, the gas phase includes air with at least some oxygen depletion. In the gas phase, the oxygen content can be about 5-about 21%, by mole. 
         [0029]    The effluent  180  can be received in the separation vessel  200 . The separation vessel  200  can serve as a disulfide separator. The separation vessel  200  can include a base  210 , a first stack  240 , and a second stack  280 . The separation vessel  200  can be operated at any suitable conditions, such as no more than about 60° C. and about 250-about 500 kPa, preferably about 350-about 450 kPa. 
         [0030]    The base  210  can have any suitable dimensions. Typically, the base  210  may have a length greater than a height creating an interior space containing one or more coalescer elements  222 . Usually, the one or more coalescer elements  222  can include at least one of a metal mesh, one or more glass fibers, sand, or an anthracite coal to facilitate separation of immiscible liquids of similar density. Generally, the base  210  has a top  214  and a bottom  218 . Typically, the stacks  240  and  280  are, independently, coupled to the top  214  of the base  210  at any suitable angle. Preferably, each stack  240  and  280  are coupled at a substantially perpendicular orientation with respect to a length of the base  210 . Usually, a level indicator controller  268  is coupled to the base  210  and communicates to a control valve  270  coupled to a line  272  containing a withdrawn disulfide or disulfide oil stream. 
         [0031]    The first stack  240  may be any suitable dimension for receiving a disulfide oil and be substantially cylindrical in shape having one or more walls forming a void. The first stack  240  may contain a mesh  244  positioned near the base of the first stack  240 . The mesh  244  can be made from any suitable material, such as metal. The metal may be carbon steel and/or stainless steel. The mesh  244  can be coated or uncoated. Usually, the height of the first stack  240  may be greater than the width. 
         [0032]    The second stack or another stack  280  can be any suitable dimension for receiving the three-phase effluent  180 . Typically, the height of the second stack  280  can be greater than the width. Generally, the second stack  280  is substantially cylindrical in shape having one or more walls forming a void. At least a portion of a distributor  284  can be inserted into the void and a packing  288  may be positioned near the top of the second stack  280 . Often, the distributor  284  can be any suitable distributor, such as respectively, a pipe with same or different sized slots for distributing the effluent  180  in the second stack  280 . The distributor  284  can be placed below the packing  288  and can be any suitable distributor, such as an elongated pipe with one or more slots, or a distributor as disclosed in, e.g., U.S. Pat. No. 5,237,823 or U.S. Pat. No. 5,470,441. Although not depicted, a wash oil may be provided to the second stack  280  via a distributor, as disclosed in, e.g., US 2010/0122936. Usually, the packing  288 , such as carbon rings, is used to increase the surface area for slowing fluid flow and facilitate condensation. Generally, the liquid phases fall downward toward the base  210  and the gas phase rises upward in the second stack  280  through the packing  288 . 
         [0033]    In operation, a hydrocarbon stream  20  may be combined with the stream  26  including a combined alkaline solution stream  28  that can enter the lower prewash section  130  of the extractor vessel  120 . The hydrocarbon can rise and pass through the transfer conduit  140  to the upper extractor section  150  while the alkaline solution may fall and be withdrawn via the line  134  with a portion recycled and a portion purged. The hydrocarbon product  154  can be withdrawn from the top of the extractor vessel  120 . 
         [0034]    Alkaline solution rich in one or more thiol compounds from the upper extractor vessel  150  can be sent via a line  156  and be combined with the oxidation catalyst  158  and the air stream  162  prior to entering the oxidation vessel  160 . The three-phase effluent  180  from the oxidation vessel  160  can be sent to the separation vessel  200 . 
         [0035]    The effluent  180  can separate in the second stack  280  with the gases rising forming a spent gas phase  296 , including excess air and disulfide oil vapors, and the liquids falling towards the base  210  forming a liquid phase  294 , thus creating separate phases. A gas-liquid interface  292  may be present in the second stack  280 . The gases can rise in the second stack  280  and pass through the packing  288  removing any entrained liquid. Afterwards, the gases can pass through a line  298 . 
         [0036]    The liquids can enter the base  210 , which may include one or more coalescer elements  222 . The various liquid phases can pass through the one or more coalescer elements  222  and be separated into a disulfide oil  260  and a lean alkaline solution  266  forming a disulfide oil/alkaline solution interface  262 , thus separate phases. Generally, the disulfide phase can rise and enter the first stack  240 . 
         [0037]    At least a portion, preferably all, of the disulfide oil can pass through the mesh  244  in the first stack  240  removing substantially all of the alkali, often caustic, present in the disulfide oil to purify the disulfide oil. Often, it is desirable to have no more than about 1 ppm, by weight, of a cation, such as sodium, present in a disulfide oil stream  272 . The cation may be representative of the alkali present in the disulfide oil stream  272 . A gas may be present in the first stack  240  forming a gas/disulfide oil interface  252  with the gas being at a pressure of about 300-about 600 kPa. The level of the interface  262  in the base  210  can be controlled by the level indicator controller  268  and the valve  270  that may control the amount of a disulfide stream  272  exiting the first stack  240 . The gas can exit the first stack  240  as a spent gas stream  248  and be combined with the spent gas stream  298  to form a combined spent gas stream  300 . As such, the gas can be sent or optionally blended with fuel gas for use as a fuel in a heater or furnace. 
         [0038]    Generally, the lean alkaline solution  266  can exit the bottom  218  of the base  210  through a line  226  and be split into separate branches  142  and  152 . The regenerated alkaline solution in the line  142  can be combined with the alkaline solution  136 , and be added to the hydrocarbon stream  20 . Another branch  152  can be provided to the upper extractor section  150  of the extractor vessel  120 , as described above. 
         [0039]    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. 
         [0040]    In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. 
         [0041]    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.