Patent Application
20160115393
The disclosure generally relates to processes and apparatus for treating gasoline range hydrocarbons, and more particularly relates to processes and apparatus for separating treated gasoline range hydrocarbons from spent alkali solution.
Gasoline range hydrocarbons are a mixture of primarily hydrocarbons having from four to twelve carbons per molecule (i.e., C5-C12 hydrocarbons) and have a boiling point range of from about 28 to about 221° C. (about 82 to about 430° F.). Gasoline range hydrocarbons are very similar to and include full range naphtha, which further includes light and heavy naphthas. More particularly, light naphtha is a mixture containing primarily C5-C6 hydrocarbons and having a boiling point range of from about 28 to about 68° C. (about 826 to about 155° F.). Heavy naphtha is a mixture containing primarily C7-C12 hydrocarbons and having a boiling point range of from about 79 to about 221° C. (about 175 to about 430° F.). Gasoline range hydrocarbons are generally straight chain or branched alkanes, with small amounts of cyclic alkanes and aromatic-type hydrocarbons. Gasoline range hydrocarbons and full range naphtha are typically liquids under normal conditions, i.e., room temperature and atmospheric pressure, and are widely useful, for example, as fuel for internal combustion engines, feedstock for production of olefins, diluent for asphalt production, cleaning solvents, and lighter fluid, among other things.
Particularly when derived from petroleum, gasoline range hydrocarbons often contain undesirable components including, without limitation, sulfur compounds such as mercaptans (R—mSH), which adversely affect various refining steps and end uses. Among the conventional methods for addressing problems presented by the presence of mercaptans in gasoline range hydrocarbons is treatment of the gasoline range hydrocarbons, chemically, by contact with a base (alkali) in the presence of a catalyst to convert mercaptans to organic disulfides, which do not present the same difficulties as mercaptans. In some cases, the base is sometimes a strong base such as a caustic provided as a dilute aqueous solution (e.g., from about 0.5 to about 5 percent by weight caustic) which is typically added continuously to the incoming gasoline range hydrocarbons prior to entering a treatment containing suitable catalyst. Alternatively, a weak base such as ammonia provided as a dilute aqueous solution (e.g., from about 0.2 to about 3 percent by weight ammonia) which may be continuously added to the incoming gasoline range hydrocarbons.
Such conversion of the mercaptans is typically followed by separation of spent alkali from the treated gasoline range hydrocarbons now containing organic disulfides to prevent the alkali from adversely affecting further processing steps and downstream process apparatus. However, full separation of the spent alkali is generally not accomplished and there is typically some alkali carryover into the refined gasoline range hydrocarbon product. The refined gasoline range hydrocarbons are often sent to a fractionation column and reboiler apparatus assembly for separation and production of different hydrocarbon range products, such as light naphtha or heavy naphtha, but the presence of carryover alkali is likely to damage the reboiler. To remove carryover alkali prior to sending the refined gasoline range hydrocarbons to the fractionation column and reboiler assembly, refined gasoline range hydrocarbons from a mercaptan treatment stage are typically provided to a sand filter or water wash vessel specifically to remove carryover alkali (e.g., alkali derivatives such as sodium, potassium or ammonium) before sending the refined gasoline range hydrocarbons to the fractionation column and reboiler assembly.
Accordingly, it is desirable to provide processes and apparatus that facilitate conversion of mercaptans in gasoline range hydrocarbons to organic disulfides using alkali, and subsequent separation of spent alkali prior to further processing. In addition, it is desirable to provide processes and apparatus that increase the efficiency of separation of spent alkali from treated gasoline range hydrocarbons. Furthermore, other desirable features and characteristics of the processes and apparatus contemplated and disclosed herein will become apparent from the subsequent detailed description and appended claims, taken in conjunction with the accompanying drawings.
Processes and apparatus are provided for treating gasoline range hydrocarbons comprising mercaptans to produce refined gasoline range hydrocarbons comprising organic disulfides. In an exemplary embodiment, the process comprises the steps of: providing a gasoline feed stream comprising gasoline range hydrocarbons and mercaptans; adding alkali to the gasoline feed stream to form a feed mixture; adding an oxygen-containing gas to the feed mixture; and contacting the feed mixture with a catalyst capable of converting mercaptans to organic disulfides to produce a treated gasoline stream comprising the organic disulfides and spent alkali. The process further comprises, separating the gasoline range hydrocarbons from the spent alkali using a separation device to produce a refined gasoline stream comprising the gasoline range hydrocarbons and the organic disulfides; and contacting the treated gasoline stream with a coalescing material for encouraging the spent alkali to coalesce in an aqueous phase and separate from the gasoline range hydrocarbons in an organic phase which combines with the treated gasoline stream.
In another exemplary embodiment, the process for treating gasoline range hydrocarbons comprises the steps of: providing a gasoline feed stream comprising gasoline range hydrocarbons and mercaptans; adding alkali to the gasoline feed stream to form a feed mixture; adding an oxygen-containing gas to the feed mixture; and contacting the feed mixture with a catalyst capable of converting mercaptans to organic disulfides to produce a treated gasoline stream comprising the organic disulfides and spent alkali. Additionally, the process comprises, separating the gasoline range hydrocarbons from the spent alkali using a separation device to produce a refined gasoline stream comprising the gasoline range hydrocarbons and the organic disulfides; and contacting the treated gasoline stream with a coalescing material for encouraging the spent alkali to coalesce in an aqueous phase and separate from the gasoline range hydrocarbons in an organic phase which combines with the treated gasoline stream. The process further comprises distilling the refined gasoline stream to produce a light naphtha stream and a heavy naphtha stream, and subjecting the heavy naphtha stream to a hydroprocessing stage for removal of unwanted constituents.
In an exemplary embodiment, the apparatus for treating gasoline range hydrocarbons comprising mercaptans comprises a treatment vessel. More particularly, the treatment vessel comprises: an interior having a catalyst situated therein, wherein said catalyst is capable of converting mercaptans to organic disulfides in the presence of alkali, and an inlet in fluid communication with the interior for allowing a gasoline feed stream comprising gasoline range hydrocarbons, mercaptans, alkali and an oxygen-containing gas to enter the interior and contact the catalyst and produce treated gasoline range hydrocarbons. The treatment vessel comprises a separation device situated in a bottom portion of the treatment vessel and capable of separating refined gasoline comprising organic disulfides from spent alkali in the treated gasoline range hydrocarbons, the separation device having an outlet for allowing the treated gasoline to exit the interior, and coalescing material situated proximate the separation device and capable of encouraging the spent alkali to coalesce in an aqueous phase and separate from the gasoline range hydrocarbons in an organic phase which combines with the treated gasoline stream. Moreover, the treatment vessel includes an outlet located at the bottom thereof for allowing the spent alkali to exit the interior of the treatment vessel.
The processes and apparatus contemplated herein will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the processes and apparatus contemplated and described herein, nor the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
In processes and apparatus for treating gasoline range hydrocarbons with alkali to convert potentially harmful mercaptans often contained therein to less detrimental organic disulfides, it is desirable to maximize and enhance the separation of the resulting refined gasoline range hydrocarbons, now containing organic disulfides, from spent alkali. The processes and apparatus contemplated herein accomplish this goal by adding coalescing material to the vessel within which conversion of the mercaptans to organic disulfides and separation of the refined gasoline range hydrocarbons and spent alkali occur. Thus, after alkali and oxygen are added to the gasoline range hydrocarbons containing mercaptans, they are contacted with a catalyst to facilitate conversion of the mercaptans, followed by contacting the resulting treated gasoline range hydrocarbons with the coalescing material.
More particularly, in an exemplary embodiment, a process for treating gasoline range hydrocarbons comprising mercaptans comprises providing a gasoline feed stream comprising gasoline range hydrocarbons and mercaptans (R—SH). Gasoline range hydrocarbons are a mixture of primarily C5-C12 hydrocarbons having a boiling point range of from about 28 to about 221° C. (about 82 to about 430° F.). Other unwanted constituents such as, without limitation, carbon dioxide, sulfur compounds besides mercaptans, and others, may also be present in the gasoline feed stream. Furthermore, gasoline range hydrocarbons include light naphtha which is a mixture containing primarily C5-C6 hydrocarbons having a boiling point range of from about 28 to about 68° C. (about 82 to about 155° F.), as well as heavy naphtha which is a mixture containing primarily C7-C12 hydrocarbons having a boiling point range of from about 79 to about 205° C. (about 175 to about 430° F.).
The process further involves adding alkali and oxygen-containing gas to the gasoline feed stream to form a feed mixture. The feed mixture is next contacted with a catalyst capable of converting mercaptans to organic disulfides to produce a treated gasoline stream comprising the gasoline range hydrocarbons, the organic disulfides and spent alkali. The gasoline range hydrocarbons and organic disulfides are separated from the spent alkali using a separation device to produce a refined gasoline stream comprising the gasoline range hydrocarbons and the organic disulfides.
The process contemplated herein further comprises contacting the treated gasoline stream with a coalescing material for encouraging the spent alkali to coalesce in an aqueous phase and separate from the gasoline range hydrocarbons in an organic phase which combines with the treated gasoline stream. More particularly, without intending to be bound by theory or mechanism, contacting the treated gasoline stream with the coalescing material encourages formation of droplets (coalescence) of aqueous phase containing spent alkali so that the aqueous phase with spent alkali preferentially sinks to the bottom and leaves the treatment vessel. Accordingly, separation of spent alkali from the treated gasoline range hydrocarbons is increased to produce a refined gasoline stream containing less alkali (e.g., alkali derivatives such as sodium, potassium or ammonium) carryover and eliminating the need for alkali removal in a sand filter unit or water wash vessel prior to further separation, such as for example in a fractionation column and reboiler assembly. In some embodiments of the process contemplated and described herein, the treated gasoline stream is contacted with the coalescing material immediately before or immediately after separating the gasoline range hydrocarbons from the spent alkali using the separation device. In some embodiments of the process, for example where the feed mixture is contacted with an aqueous solution of dilute sodium hydroxide (i.e., the alkali is dilute sodium hydroxide) to produce the treated gasoline stream, and after the treated gasoline stream is contacted with the coalescing material and subjected to separation using the separation device, the refined gasoline stream comprises less than about 0.1 ppm sodium.
The coalescing material may be any material known now or in the future which is hydrophilic and facilitates aqueous-organic phase separation in liquid-liquid systems. For example, in some embodiments of the process contemplated herein, the coalescing material is a mesh or nonwoven fiber blanket, corrugated sheet or a combination thereof, made of metal such as stainless steel, and coated with a hydrophilic substance such as hydrophilic polymer. In such embodiments, the coalescing material overlays at least a portion of the separation device. Suitable coalescing materials are commercially available, for example, under the tradename COALEX, from Koch Otto York, a Koch-Glitsch business group, located in Houston, Tex., U.S.A. In other embodiments of the process contemplated herein the coalescing material comprises the hydrophilic substance, e.g., hydrophilic polymer, which is applied to at least a portion of the separation device such as by spray coating, dip coating, rolling or brushing.
In some conventional processes for treating gasoline range hydrocarbons comprising mercaptans, the spent alkali is further subjected to gravity separation. The processes contemplated and described herein that involve contacting the treated gasoline stream with coalescing material enhance separation of the refined gasoline range hydrocarbons from the spent alkali to a degree which may reduce or eliminate the need for such gravity separation. At a minimum, the gravity separation will be more efficient and less likely to be adversely affected by carryover alkali (i.e., alkali derivatives such as sodium, potassium or ammonium) from the mercaptan conversion stage of the process.
The alkali added to the gasoline feed stream is an aqueous mixture comprising either dilute caustic or ammonia. Where the alkali is dilute caustic the aqueous mixture contains from about 0.5 to about 5 percent by weight (wt %) caustic, based on the total weight of the aqueous mixture. For example, the dilute caustic may comprise from about 1 to about 4 wt % caustic, or from about 1 to about 3 wt %, or even from about 2 to about 3 wt % caustic. The caustic may be chosen from sodium hydroxide, potassium hydroxide, and mixtures thereof. If ammonia is used, the aqueous mixture should contain from about 0.2 to 3 wt % ammonia, such as from 02 to about 2 wt %, or even from 0.5 to 1 wt % ammonia. The gasoline feed stream and alkali form the feed mixture that is contacted with the catalyst. Additionally, an oxygen-containing gas, such as air or pure molecular oxygen, is typically also added to the feed mixture prior to contacting it with the catalyst to provide oxygen for the conversion reaction of mercaptans to organic disulfides.
Suitable catalysts are any catalysts known now or in the future capable of converting mercaptans to organic disulfides in the presence of caustic or a weak base such as ammonia. Suitable catalysts include the MEROX line of catalysts commercially available from UOP LLC of Des Plaines, Ill., U.S.A., such as without limitation, MEROX FB, MEROX No. 8, MEROX No. 10, MEROX No. 21, and MEROX 31, among others. Furthermore, the catalyst may be either water-soluble liquid or impregnated on activated carbon support material.
In some embodiments, the process further comprises distilling the refined gasoline stream to produce a light naphtha stream and a heavy naphtha stream. The heavy naphtha stream may be subjected to one or more hydroprocessing stages for treatment or removal of additional unwanted constituents such as without limitation, sulfur compounds other than mercaptans.
An exemplary embodiment of an apparatus as contemplated herein for treating gasoline range hydrocarbons comprising mercaptans will now be described with reference to
The treatment vessel 12 also has an inlet 18 in fluid communication with the interior 14 for allowing a feed mixture (not shown per se) comprising gasoline range hydrocarbons, mercaptans and alkali to enter the interior 14 and contact the catalyst 16 to produce treated gasoline range hydrocarbons. In addition, a separation device 20 is situated in a bottom portion 22 of the treatment vessel 12 and is capable of separating refined gasoline comprising organic disulfides from spent alkali. The separation device 20 has an outlet 24 for allowing the refined gasoline stream to exit the vessel interior 14. As used herein, the term “bottom portion” of the treatment vessel 12 means the bottommost one third portion of the treatment vessel 12, while the “bottom” of the treatment vessel 12 means lowest part of the treatment vessel 12. In embodiments where the feed mixture is contacted in the treatment vessel 12 with an aqueous solution of dilute sodium hydroxide (i.e., the alkali is dilute sodium hydroxide) to produce the treated gasoline stream, and after the treated gasoline stream is contacted with the coalescing material 26 and subjected to separation using the separation device 20, the refined gasoline stream comprises less than about 0.1 ppm sodium.
As shown in
In an exemplary embodiment of the apparatus 10 contemplated herein and shown in
The separation device 20 also includes a plurality of lateral conduits, such as six or more lateral conduits 36 shown in
The coalescing material 26 may be any material known now or in the future which is hydrophilic and facilitates aqueous-organic phase separation. For example without limitation, in some embodiments of the apparatus 10 contemplated herein, such as those shown in
In other embodiments of the apparatus 10 contemplated herein, the coalescing material 26 comprises the hydrophilic substance, e.g., hydrophilic polymer, applied directly to at least a portion of the separation device 20, such as on one or more of the plurality of lateral conduits 36. In such embodiments, the coalescing material 26 may be applied by any conventional method such as spray coating, dip coating, rolling, brushing, etc. In still other embodiments of the apparatus 10, the coalescing material, in any form (i.e., whether mesh, non-woven fiber, hydrophilic substance applied as a coating, or mesh or nonwoven fiber coated with a hydrophilic substance), may be positioned within a portion of the separation device 20, such as within the central interior flow path 34 of the manifold conduit 30, or within the interior flow path 40 of one or more of the plurality of lateral conduits 36.
In some embodiments, such as shown in
As also shown in
While at least one exemplary embodiment has been presented in the foregoing detailed description of the processes and apparatus contemplated herein, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the processes and apparatus in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention.
