Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G19/00—Refining hydrocarbon oils in the absence of hydrogen, by alkaline treatment
  • C10G19/08—Recovery of used refining agents

Definitions

• This invention relates to a process for regenera ⁇ ting an alkaline stream containing mercaptan compounds.
• a number of hydrocarbon streams produced by refining operations or natural gas processing operations contain mercaptan sulfur compounds and are commonly treated to remove such mercaptan sulfur compounds in order to reduce odor and/or corrosivity associated with these acidic species.
• alkyl and aryl mercaptans are generally removed from such hydrocarbon streams by washing or contacting such streams with an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.
• the sulfur compounds are removed into the alkaline stream as mercaptides, i.e. the metal salts of the mercaptans.
• the alkaline solution containing the mercaptides is then separated from the hydrocarbon stream.
• regenerate is meant the removal of most, if not all, of the mercaptides in the alkaline stream, which may be accomplished by oxidizing the mercaptides to disulfides. The disulfides, which are relatively insoluble in the alkaline solution, may then be removed therefrom as an organic layer.
• a catalyst is generally employed. Any suitable catalyst known to those skilled in the art may be utilized, including, for example, any of the catalysts disclosed in U.S. Patent No.
• a typical process for conventionally regenerating the alkaline stream involves the use of an oxidation zone, which typically involves a column having suitable contacting means such as trays with bubble caps, or suitable packing material such as Raschig rings and the like.
• the alkaline stream in the column is contacted with air in the presence of the oxidation catalyst whic is generally contained in the alkaline stream to be regenerated, in order to oxidize the mercaptides to disulfides.
• oxidation zones are relatively large columns which are very expensive to construct and maintain.
• the various methods used to regenerate the caustic typically do so by oxidizing the mercaptides to disulfides, generally in the presence of an oxidation catalyst such as certain metal chelates, including, for example, cobalt phthalocyanine disulfonate.
• an oxidation catalyst such as certain metal chelates, including, for example, cobalt phthalocyanine disulfonate.
• Such processes produce a mixture of regenerated caustic and disulfides which must be separated before the regenerated caustic can be reused.
• the oxidation of mercaptides to disulfides and the separation of the regenerated caustic from the disulfides is accomplished in separate steps. Also, the separation is typically not complete, i.e. excessive disulfides remain in the caustic solution and and regenerated caustic remains in the disulfides.
• the dispersion is passed through a coalescing system and then to a settling tank whereby the disulfide compounds are separated from the alkaline solution. While most of the disulfides are removed in the settling tank, in some cases the settling step may be followed by a naphtha wash to remove disulfides still retained in the alkaline solution.
• U.S. Patent No. 2,853,432, Glei , et al. discloses the regeneration of used alkaline reagents by oxidizing same using a phthalocyanine catalyst.
• a phthalocyanine catalyst For example, 'mercaptides contained in a caustic solution were oxidized to disulfides, which were then withdrawn from the regeneration zone by skimming or by dissolving in a suitable solvent such as naphtha.
• U.S. Patent No. 3,574,093, Strong relates to a multi-step process wherein the spent caustic generated by treating a low-boiling hydrocarbon stream for mercaptan removal is thereafter used in a second treating step wherein a higher boiling sour distillate is sweetened.
• the mercaptans in the sour distillate are oxidized to disulfides.
• the disulfides exit the treating stage in the hydrocarbon stream along with those mercaptides which had been previously extracted from the low boiling hydrocarbon stream.
• the higher boiling stream is sweetened and the partially spent alkaline stream is regenerated at the same time.
• the regenerated caustic is then introduced into a separation zone from which the disulfide phase is recovered from the caustic zone.
• the coalescence of the disulfide compound into a separate phase is stated to be extremely difficult without the use of coalescing agents.
• a high residence time is used in the separation zone to further facilitate this phase separation.
• U.S. Patent No. 3,758,404, Clonts; U.S. Patent No. 3,977,829, Clonts; and U.S. Patent No. 3,992,156, Clonts are directed to methods and apparatus for liquid-liquid mass transfer between immiscible liquids.
• a first liquid is introduced onto the upstream surface portion of a plurality of fibers extending generally along and secured within a conduit.
• a second liquid, immiscible with said first liquid is flowed through the conduit cocurrently with the first liquid, thereby dragging a film of the first liquid along the fibers.
• the two liquids are collected at the downstream end of the conduit in a collection vessel or gravity separator.
• a large surface area is generated between the two liquids and mass transfer between the two liquids is facilitated.
• a component of either of the liquids may be transferred either into or out of the liquid film as it moves along the fibers.
• the mass transfer may also occur as the result of a chemical reaction at the interface between the liquids, such as the removal of acidic constituents from a hydrocarbon by reaction with a base in an aqueous solution, or the transfer may be without a chemical reaction, such as by extraction from one liquid to another.
• the patents teach the introduction of an aqueous caustic solution onto the * fibers and the flowing of gasoline containing acidic components cocurrently therewith. The acidic components of the gasoline react with a d are absorbed by the caustic.
• the object of the present invention is to provide an improved method of regenerating an alkaline stream such as an aqueous caustic solution containing mercaptan sulfur compounds, such as occurs in alkaline streams used in removing mercaptans from hydrocarbon distillates.
• an alkaline stream such as an aqueous caustic solution containing mercaptan sulfur compounds, such as occurs in alkaline streams used in removing mercaptans from hydrocarbon distillates.
• the present invention provides a process for regenerating an aqueous stream of alkali metal hydroxide containing mercaptide compounds, characterized by intro- ducing an aqueous stream of alkali metal hydroxide containing mercaptide compounds and an oxidation catalyst onto an upstream end of a plurality of fibers positioned longitudi ⁇ nally within a conduit, a downstream end of the fibers extending out of the conduit making contact with a regenerated alkali metal hydroxide liquid in a collection vessel?
• the present invention results in an efficient compact regeneration system for regenerating spent alkaline solutions.
• entrainment of the alkaline solution in the solvent/disulfide mixture is avoided since the method of contacting the caustic with the oxygen required for regeneration is not dispersive in nature.
• Yet another advantage of the present invention is that of entrainment of disulfide in the regenerated caustic is avoided. Thus, separate washing steps to remove such entrained materials are unnecessary.
• less equipment is required for the regeneration process of this invention than with methods known to the art, and the equipment which is utilized in the practice of the present invention is smaller in size and simpler to operate than that utilized in prior art processes. Therefore, equipment investment and costs of operation are substantially lower.
• Fig. 1 is a schematic flow diagram of a process for regenerating an alkaline stream according to the present invention.
• a mass transfer apparatus M includes a bundle B of substantially continuous elongated fibers mounted in a shroud S and contained within a conduit 10.
• the conduit 10 has an outlet flange 10b that is adapted for connection or placement with a mating flange 11a of collection vessel 11.
• a fluid distribution means 12 is mounted within an upper position of conduit inlet assembly 10a for distributing the mercaptide-containing aqueous alkaline solution to be regenerated from the spent alkaline feed line 8 onto the fibers within the bundle B.
• a second solution line 14 is attached to the conduit inlet assembly 10a for delivering the oxygen-containing solvent into the conduit inlet.
• the conduit outlet 10b is attached to mounting flange 11a of the collection vessel 11.
• Shroud S contains fiber bundle B which extends partly within the confines of the collection vessel 11.
• Other mechanical details of the mass transfer apparatus are not necessary to an understanding of the invention and reference may be made to the aforementioned patents for further additional mechanical details.
• the positioning of the downstream end of the bundle B within the collection vessel 11 is such that it is within the regenerated alkaline solution which is collected as a lower layer in the collection vessel 11.
• Collection vessel 11 contains a lower layer 18 of regenerated alkaline solution and an upper layer 20 of hydrocarbon solvent containing disulfides. Collection vessel 11 is preferably maintained at conditions which avoid the separation of gases from the liquids therein.
• the fibers that comprise the bundle B are selected to meet two criteria.
• the fiber material must be preferentially wetted by the aqueous alkaline solution introduced by feed line 8 and the fibers must be of a material that will not contaminate the process or be destroyed by it, such as by corrosion. Accordingly, inasmuch as the present invention deals with aqueous alkaline solutions containing sulfur compounds, metallic fibers and, in particular, stainless steel or special corrosion resistant alloy fibers, are preferably employed.
• the spent alkaline streams which may be regenerated according to the present invention include, for example, spent aqueous potassium hydroxide solutions and spent aqueous sodium hydroxide solutions, i.e. caustic.
• Such alkaline solutions are widely used * for treatment- of a ' variety of mercaptan containing hydrocarbon streams, including liquid petroleum gas (LPG), butanes, butenes, gasoline streams and naphthas and the like.
• LPG liquid petroleum gas
• spent alkaline solutions resulting from the treatment of the aforementioned hydrocarbon streams can typically contain a number of different mercaptan sulfur compounds, including., for example, such mercaptans as methyl mercaptan, ethyl mercaptan, n-propyl mercaptan, iso-propyl mercaptan, n-butyl mercaptan, and thiophenol.
• Alkali metal sulfides can also be present in such spent alkaline solutions due to the presence of hydrogen sulfide in the hydrocarbon streams which were previously treated with the alkaline solution. The presence of such sulfides does not adversely affect the efficiency of the present invention.
• the spent alkaline stream containing an oxidation catalyst is flowed through line 8 into the inlet 10a and to the fluid distribution means 12 and onto the upstream end of the fiber bundle 6 as illustrated in Fig. 1.
• a suitable hydrocarbon solvent containing a dissolved oxygen-containing gas such as air, is flowed through line 14, into the conduit inlet 10a, and then cocurrently with and in intimate contact with the alkaline stream, passing over the fibers of the fiber bundle B contained within conduit 10, and then into the collection vessel 11.
• the mercaptides contained in the spent alkaline solution are oxidized to disulfides and the disulfides are extracted into the hydrocarbon solvent and are thus removed from the alkaline solution.
• the oxidation reaction will occur at temperatures of from ambient to about 150 ⁇ F.
• the preferred operating temperature is from about 100°F to about 130°F.
• residence time in the fiber bundle may be rather short, from about thirty second to about three minutes. Preferred residence -times are from about one to about two minutes.
• the oxidation catalyst contained in the alkaline stream may be any suitable oxidation catalyst known to those skilled in the art and preferably comprises a metal phthalocyanine dissolved or suspended in the alkaline stream entering the system through the line 8.
• Metal phthalocyanines that may be employed include cobalt phthalocyanine and vanadium phthalocyanine or sulfonated or carboxylated derivatives thereof.
• a preferred catalyst comprises cobalt phthalocyanine disulfonate.
• the catalyst concentration will vary depending in part on the level of mercaptides in the alkaline stream, as will be understood by those skilled in the art.
• the amount of cobalt phthalocyanine disulfonate may range from about 10 to about 1,000 ppm by weight of the alkaline solution.
• the oxygen required for the oxidation of the mercaptides is introduced into the system through line 15 by dissolving oxygen or an oxygen-containing gas, such as air, in the hydrocarbon solvents stream 14. In the fiber bundle B, the oxygen is transferred from the hydrocarbon stream into the alkaline solution. Oxygen thus is available for chemical reaction with the mercaptides in the presence of the oxidation catalyst contained in the spent alkaline stream as the respective fluids move through the mass transfer apparatus M.
• the amount of oxygen provided is at least equal to the stoichiometric amount and generally is provided in excess of the stoichiometric amount.
• the pressure in the system is maintained at a level such that the desired amount of oxygen can be dissolved into the hydrocarbon stream without exceeding the solubility limits for oxygen or the oxygen-containing gas in the hydrocarbon.
• Typical system back pressures range from 10 psig to 100 psig with system back pressures of from about 25 psig to about 75 psig typically being sufficient for most normal mercaptide loadings.
• Any suitable organic solvent which is immiscible with the aqueous alkaline stream and does not otherwise adversely affect the overall process may be utilized.
• many of the hydrocarbon streams described above as being treatable for mercaptan removal with alkaline streams may be employed as the solvent.
• the regenerated alkaline stream being immiscible with the solvent, separates and collects as a bottom layer 18 and the hydrocarbon solvent, now containing disulfides, accumulates as an upper layer 20 in the collection vessel 11.
• the interface 21 between the solvent and regenerated alkaline solution may vary, but it is preferred that the interface remain above the lower or downstream end of the fiber bundle B as illustrated in Fig. 1.
• the solvent and the regenerated alkaline streams are withdrawn separately from the collection vessel 11.
• the regenerated alkaline stream 17 is recycled for further use, for example, in further contacting of ercaptan-containing hydrocarbon streams.
• the addition of fresh, alkaline solution may also be necessitated due to the dilution effect resulting from the oxidation of the mercaptides wherein water is a co-product of the oxidation reaction.
• the hydrocarbon solvent containing disulfide compounds may be processed further to- recover the disulfide component therefrom, may be discarded in an environmentally safe manner, or may be recycled to the inlet line 14 for further use in the process of the present invention.
• the solvent loses its effectiveness as its level of disulfides increases, it may be desirable to remove some of. the disulfide-containing solvents such as through line 19 and to add fresh, lean solvent such as through line 23 from time to time or in a continuous mode, in order to maintain the proper efficiency of extraction of disulfides.
• the present method of regenerating alkaline streams is quite superior to conventional processes employing separate zones to effect the oxidation and separation steps inherent in the overall regeneration process.
• the use of a suitable fiber bundle contacting device in the present invention provides for a compact process and results in reduced capital costs.
• parameters including the rates of mass transfer of oxygen into the alkaline stream to provide the oxygen for the catalytic oxidation of the mercaptides to disulfides and the extraction of the resulting disulfide from the alkaline stream into the solvent.
• Such parameters as the surface area of the fiber bundle B, the rate of flow of streams entering the lines 8 and 14, the amounts of dissolved oxygen in either of the reactant streams, the amount of catalyst contained in the alkaline stream, residence time of the respective materials within the mass transfer apparatus M, and temperature and pressure conditions may be varied depending on the chemical composition of sulfur compounds contained in the alkaline stream to be regenerated, the type of hydrocarbon solvent used, and other factors as will be appreciated by those skilled in the art.
• the following are examples illustrating the process of the present invention and are not intended to limit the scope thereof.
• a 15% by weight aqueous solution of sodium hydroxide to which had been added methyl mercaptan in an amount such that the mercaptide concentration was 640, expressed in ppm as sulfur was introduced to the top of the fiber bundle at a flow rate of 164 ml/min.
• the caustic solution also contained 100 ppm of cobalt phthalocyanine disulfonate as an oxidation catalyst.
• kerosene solvent stream into which air had been injected and dissolved.
• the kerosene flow rate was 602 ml/min. and the air injection rate was 0.0096 SCFM.
• the caustic solution and the kerosene solution flowed cocurrently through the fiber bundle. The pressure in the system was maintained
• the regenerated caustic collected as a lower layer and the kerosene collected as an upper layer, both of which were continuously removed, sampled and analyzed for mercaptan. sulfur content and disulfide content. The regenerated caustic was found to contain
• ercaptide-containing caustic solution was prepared from 15% by weight solution hydroxide to which ethyl mercaptan was added in an amount such that the mercaptide concentration was 428, expressed as ppm sulfur.
• the caustic solution also contained 100 ppm of cobalt phthalocyanine disulfonate as an oxidation catalyst. This solution was introduced into the top of the fiber bundle at a flow rate of 170 ml/min. Also introduced into the top of the beaded glass column was a hexane solvent stream into which air had been injected and dissolved. The hexane flow rate was 515 ml/min. and the air injection rate was 0.007 SCFM.
• the pressure in the system was maintained 2 at 3.51 kg/cm (50 psig) and the operating temperature was approximately 41.1°C (106°F) .
• the regenerated caustic was analyzed and was found to contain nil mercaptan sulfur and only 1 ppm as sulfur, disulfide.
• the effluent hexane was analyzed and found to contain 1,700 ppm as sulfur, disulfide. Again, the regeneration of the caustic was very effective both in terms of mercaptide sulfur and disulfide removal.
• Example 2 Utilizing the apparatus and procedures described in Example 1, a synthesized spent caustic containing ethyl mercaptide was regenerated by the process of the present invention and the solvent employed was kerosene. Fifteen percent by weight sodium hydroxide was used to prepare the spent caustic solution to be regenerated, the ethyl mercaptide concentration was 1,230 . pm as sulfur, and the caustic solution contained 100 ppm of cobalt phthalocyanine disulfonate. This spent caustic was introduced into the fiber bundle at a flow rate of 167 ml/min. The kerosene flow rate was 600 ml/min. and the air injection rate 0.0068 SCFM. The pressure in the system was maintained
• the regenerated caustic was found to contain nil mercaptan sulfur and only 6 ppm as sulfur, disulfide.
• the effluent kerosene was found to contain 5,240 ppm as sulfur, disulfide. This demonstrates very effective regeneration of the caustic solution.
• a synthesized spent caustic containing sodium thiophenate (an aromatic mercaptide) was regenerated by the process of the present invention and the solvent employed was hexane.
• Fifteen percent by weight sodium hydroxide was used to prepare the spent caustic solution by adding thiophenol in an amount such that the thiophenate concentra- tion was 1,160 ppm as sulfur, and cobalt phthalocyanine disulfonate was present at a concentration of 100 ppm.
• the spent caustic was introduced into the fiber bundle at a flow rate of 56 ml/min.
• the hexane flow rate was 305 ml/min. and the air injection rate was 0.0062 SCFM.
• the regenerated caustic was found to contain 190 ppm as sulfur, of thiophenate indicating substantial regeneration of the caustic.
• Example 2 Utilizing the apparatus and procedures described in Example 1, a sample of a spent caustic feed to a conven ⁇ tional caustic regeneration unit within a refinery was subjected to the process of the present invention.
• the spent caustic analyzed as follows:
• the spent caustic was introduced into the top of the fiber bundle at a flow rate of 43 ml/min.
• Kerosene was introduced at a flow rate of 218 ml/min. and the air injection rate was 0.0090 SCFM.
• the pressure in the system was maintained
• the regenerated caustic was found to contain nil thiophenate indicating that the regeneration of the caustic was very effective.

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• Organic Chemistry (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
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• 1985
  • 1985-04-10 EP EP19850902236 patent/EP0178320A1/de not_active Withdrawn
  • 1985-04-10 WO PCT/US1985/000611 patent/WO1985004894A1/en unknown
  • 1985-04-22 CA CA000479668A patent/CA1234795A/en not_active Expired
  • 1985-04-25 ES ES542556A patent/ES542556A0/es active Granted

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