Processes And Apparatus For Separating Treated Gasoline Range Hydrocarbons From Spent Alkali Solution (UOP)

Processes And Apparatus For Separating Treated Gasoline Range Hydrocarbons From Spent Alkali Solution (UOP)
United States Patent Application 20160115393
Smith; Edward Fraser ;   et al.   April 28, 2016
Applicant: UOP
Abstract
Processes and apparatus are provided for treating gasoline range hydrocarbons containing mercaptans to convert the mercaptans to organic disufides. The process involves contacting treated gasoline range hydrocarbons comprising organic disulfides with a coalescing material and separating refined gasoline range hydrocarbons and organic disulfides from spent alkali using a separation device. The apparatus comprises a treatment vessel suitable for housing a catalyst therein for producing treated gasoline range hydrocarbons comprising organic disulfides, as well as a separation device and coalescing material therein for separating gasoline range hydrocarbons and organic disulfides from spent alkali.
TECHNICAL FIELD
[0001] 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.
BACKGROUND
[0002] Gasoline range hydrocarbons are a mixture of primarily hydrocarbons having from four to twelve carbons per molecule (i.e., C.sub.5-C.sub.12 hydrocarbons) and have a boiling point range of from about 28 to about 221.degree. C. (about 82 to about 430.degree. 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 C.sub.5-C.sub.6 hydrocarbons and having a boiling point range of from about 28 to about 68.degree. C. (about 826 to about 155.degree. F.). Heavy naphtha is a mixture containing primarily C.sub.7.sup.-C.sub.12 hydrocarbons and having a boiling point range of from about 79 to about 221.degree. C. (about 175 to about 430.degree. 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.
[0003] 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.
[0004] 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.
[0005] 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.
BRIEF SUMMARY
[0006] 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.
[0007] 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.
[0008] 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.
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