US2645603A - Gasoline treating - Google Patents

Description

July 14, 1953 J. M. CRANMER 2,645,603

' GAsoLINE TREATING Filed March 1, 195o fuma Patented July 14, 1953 s assignor to sSocony-Vacuum Oil Companygln- -corporated,i-New, York, N. Y., a corporation of Application March 1, 1950, Serial No. 147,088

.-The presentinventionrelates to the treatment .Y of gasoline and other light petroleum products containing mercaptans and moreUparticularly-to Aanrimprovernent in theprocesses'ior'treating lgasoline and other Vlow boiling petroleum` products to remove mercaptansand provide a-nished y product having alowered disulfide content.

They art is `well acquainted Vwith ythe various methods. forremoving mercaptansfrom vgasoline and other `light 'fractions of petroleum including kerosene and the like.- -In general these methods .f for producing gasoline and the like having a low mercaptan contentcomprise contacting the hyi `drocarbon mixture with an alkaline solution i which contains or can be devoidof solutizers such as alkali metal isobutyrataalkali metal alkyl phenolates and others-wellknown to the art to remove a major portion of :the mercaptan content Vof the untreated hydrocarbon mixture-and c to provide amixture of hydrocarbonshaving a lowered -rnercaptan content.

The importance of the removal-of mercaptans from gasoline, in particular, has increased with the greater-demand -for gasolines of high octane or high anti-knock rating dueV to -the'fact that the increase in octaneV rating'obtained by the addition of tetra-ethyl lead isl decreased bythe presence of mercaptans in the finished gasoline.

The methods presently vemployed to remove mercaptans from gasoline and the like are ineffective for the removal of disuldes` which are'theoxiydation products of the mercaptans originally present in the gasoline. Consequently, whenever a portion of the mercaptans present in the gasoline is converted to disuldes prior to or during treatment for the removal of mercaptans, that A portion of the mercaptan content of the gasoline which has been converted to disuliides isnot Aremoved from the gasoline and remains in the treated gasoline.

These disulfides are equally harmful in that they diminish' theefiect of the addition of tetra-ethyl lead. In fact, some evi- 4dence has been offered ,to support the view that disuldes are more effective in reducing the effectof tetra-ethyl lead upon `the octane rating than the mercaptans from which they, are derived.

It has now beendiscoveredthat gasoline and other mixtures of hydrocarbons containing mercaptans which prior to or during treatment are subjected to conditions under which oxidation of themercaptans to disuliides takes place may be n treated to inhibit this oxidation and providey a gasoline of lowered disulfide content. In conjunction with the treatment to inhibit this internal .oxidation,. it is also desirable r'to treat `the '-extraction'solution in such a manner as tereduce the disulfide content ofv the extracting; solution at least to a level which provides a low reentry value :for the disuldes.

`Among the more recent methods for ytreating gasoline to remove mercaptans is the tanninsolu- L-at--temp-eratures-of the order of about A130 F. i As a resultofthis treatment the mercaptans which were originally present vinthegasoline-and are present in the aqueous solution as rnercaptides are oxidized-to disuldesi a major portion of which can be separated from-the aqueous alkaline solution by settling andV decantation. HOW- ever, these disuldes have a determinablesolubility in the aqueous alkalinesolutions and as a consequence the disulde content ofthe regenerated aqueous alkaline solution builds up to a poi-nt i Where in contact with fresh,isour gasoline results in the extraction of disuldesfrom'the aqueous solution by the sour gasoline. Thisdenitely can be overcome by washing the regenerated aqueous alkaline solution with a petroleum fraction to extract `the disuldes before the regenerated aqueous alkaline solution is contacted with fresh, sour gasoline. In general, the disulfide content of the regenerated aqueous alkaline solutionis kept below about one-two' perl cent disulfide sulfur and preferably about 0.1to 0.3 percent disul- -de sulfur.' Although removalv of Ythe disuldes from theregenerated Vaqueous-alkaline solution 4'lowers the disulde-content of the treated` gasoline, an-undesirable amount ofmercaptans are converted to disuldes prior to or during contact Withthe aqueous alkaline solution. Since these v disuldes are more soluble `inj thelgasoline than 'in the aqueous alkaline solution, the aqueous alkaline solution does not extract Ithe'disuliides and they remain in the gasoline to increasel'the amount of tetra-ethyl lead, which must be added per unit of gasoline to produce thefdesired octane rating. Since the disuldes produced in this manner arisefrom the oxidation of a portion of the original `mei'captan .content of the gasoline,

#it is desirable; and inA factnecessary, in orderto Y drocarbon mixture.

methyl and ethyl `mercaptansobtain the highest octane rating for a particular gasoline with the lowest addition of tetra-ethyl lead to inhibit the oxidation of the mercaptans or to eliminate it entirely.

Therefore, it is an object of the present invention to provide a method for inhibiting the internal oxidation of the mercaptans in sour gasoline prior to or during treatment with aqueous alkaline solutions for the removal of mercaptans.

It is another object of the present invention to provide a method for producing gasoline having a lowered disulde content by inhibiting internal oxidation and by reducing the disulde A tosettler 20 where the disuliides settle out as re-entry value of the regenerated aqueous alka'- line mercaptan extracting solution.

Other objects and advantages will become apparent from the following discussion taken in conjunction with the drawing. In general the aforesaid objects can be accomplished by passing the gasoline directly from the stabilizer to a pre-wash step and then to the mercaptan extracting system and injecting an internal oxidation inhibitor into the gasoline immediately after removal from the stabilizer. The internal oxidation inhibitor preferably is an organic substance soluble in the mixture of hydrocarbons, for example, gasoline, and having a higher oxidation potential than the mercaptans of the hydrocarbon mixture. In other words, the inhibitor of internal oxidation is an organic substance soluble in the hydrocarbon mixture which is morey readily oxidized than the mercaptans of the hy- A satisfactory internal oxidation inhibitor is N,Ndi(secondarybutyl) phenylenediamine available industrially as U. O. P. #5 or Dupont #22. Other internal oxidation inhibitors are N,Ndi(norinalbutyl) -paraphenylenediamine, N,N di(iso butyl) para" phenylenediamine, 2,4-dimethyl-S-tertiary-butyl phenol and 2,6-di(-tertiary butyl) -li-methyl phenol.

In order that those skilled in the art may have a better understanding of the present invention, the use of an internal oxidation inhibitor in the production of gasoline with an increased sensitivity to tetra-ethyl lead will be described in conjunction with the drawing. Gasoline from a stabilizer (not shown) drawn through line I to pre-washer 2. At some point, say 3, on line I upstream from the pre-Washer 2 an internal oxidation inhibitor such as the aforementioned N,N- di(secondarybutyl)phenylenediamine is introduced through conduit 4 by pump 5 from storage tank 6. As those skilled in the art know, prewasher 2 contains an aqueous solution of alkali metal hydroxide of such strength as to remove hydrogen sulfide and light mercaptans such as When the composition of the sour gasoline is such as to make it desirable, the pre-washer can be bi-passed and the gasoline containing the internal oxidation inhibitor can be introduced directly into extractor` I2 through lines 9 and Il by closing valve 'l and opening valves 8 and I0. When the gasoline containing the internal oxidation inhibitor is passed through the pre-washer, the pre-washed gasoline enters line i I and passes to extractor' I2 where itis contacted as it rises therein with an aqueous alkalinesclution preferably containing a solutizer such as an alakil metal alkyl phenolate introduced into extractor I2 through line I3. In a multi-stage extraction, which is usually required, the aqueous alkaline solution introduced into extractor I2 through line i3 is drawn from extractor I li through line I5. The aqueous al-` an upper layer and are withdrawn through line 2 I tostorage or for admixture with cracking stock or for admixture with fuel. The lower aqueous alkaline layer in settler is withdrawn through line 22 to disulfide extractor 23 into which hydrocarbon solvent for disulfides, such as naphtha boiling within the range about 180 to about 450 F. or having a boiling range of about 80 to about 450 F. or-in general a hydrocarbon mixture boiling within the range about 500 and about 750 F.,

' sand barrels of sour is introduced through line 213. The hydrocarbon solvent rising through the regenerated aqueous alkaline solution extracts the dsuldes therein and is withdrawn from the `olisulide extractor 23 through line 25. The extracted regenerated aqueous alkaline solution is withdrawn from eX- tractor 23 through lineZS and introduced into the last stage of the mercaptan removal system extractor lll, The partially demercaptanized gasoline after treatment in extractor i2 passes through line 2l into extractor M and rises through the lean extracted regenerated aqueous alkaline solution and leaves extractor i4 through pipe 28 to be introduced into water washer 29 into which water is introduced through conduit 3Q and. from which water is withdrawn through pipe 3i while the water washed demercaptanized gasoline leaves the water washer 29 through line 32 to a storage or distribution system. Y

Those skilled in the art will understand that one or more mercaptan extractors can be interposed between extractor I2 and Id of the drawing and the aqueous alkaline solution passed through these additional extractors in series therewith and countercurrent to the flowing stream of hydrocarbons being demercaptanized. Those skilled in the art will also understand that a portion of the fouled aqueous alkaline solution; i. e., aqueous alkaline solution containing extracted mercaptans can be removed from eX- tractorvld through line I5 under the control of valve 33 and regenerated when desired. Other variations in thev manipulation of the stream or streams of gasoline or other hydrocarbon mixtures ycontaining the internal oxidation inhibitor can be used without departing from the spirit of this invention.

In general the internal oxidation inhibitor is employed in amounts effective to reduce or eliminate the internal oxidation of the mercaptans in the gasoline to disulndes. t has been found that from 5to about 20 pounds of inhibitor per thougasoline provides satisfactory results. However, it is preferred to use about 8 to about l2 or l5 pounds of inhibitor per thousand barrels of gasoline. Highly satisfactory results have been obtained by using 10 pounds of i N,Ndi(secondarybutyl)phenylenediamine per thousand barrels of sour gasoline. It is also desirable to transfer the sour gasoline from the stabilizer orfrom storage in a closed system so that the amount of oxygen absorbed by the gasoline is kept at a minimum.

I claim:

1. A method of inhibiting internal oxidation of mercaptans to polysuldes in gasoline which comprises drawing gasoline containing mercaptans from a stabilizer, introducing about 5 to about 20 pounds of N,N'-di(secondarybutyl) phenylenediamine per 1,000 barrels of gasoline into said gasoline, contacting said gasoline containing mercaptans and said phenylenediamine in the absence of substantial amounts of air with an alkaline solution to extract a major portion of said mercaptans to obtain a fouled alkaline solution containing said Vextracted mercaptans as rnercaptides and a treated gasoline, separating said treated gasoline from said fouled alkaline solution, Vand regenerating said fouled alkaline solution.

2. A method of inhibiting internal oxidation of mercaptans to polysuldes in gasoline which comprises introducing about 5 to about 20 pounds of N,Ndi(secondarybutyl) phenylenediamine into about 1,000 barrels of gasoline containing mercaptans, contacting said gasoline containing mercaptans and said phenylenediamine in the absence of substantial amounts of air with an alkaline solution to extract said mercaptans and obtain a fouled alkaline solution containing extracted mercaptans as mercaptides, separating said fouled alkaline solution from treated gasoline, passing air through said separated fouled alkaline solution to convert said mercaptides to polysuli'ldes, separating said polysuldes from said alkaline solution, and contacting said alkaline solution in the absence of substantial amounts of air with further amounts of gasoline containing mercaptans and about 5 to about 20 pounds of f.l\T,N-di(secondarybutyl) phenylenediamine.

3. The method set forth and described in claim 2 wherein the alkaline solution after separation of the polysuldes is extracted with an immiscible organic solvent for polysuldes and the solvent separated from the alkaline solution.

4. A method of inhibiting internal oxidation of mercaptans to polysulides in a hydrocarbon mixture which comprises introducing into a hydrocarbon mixture containing mercaptans about 5 to about 20 pounds per 1,000 barrels of said hydrocarbon mixture of an organic compound soluble in said hydrocarbon mixture and being more readily oxidized than said mercaptans, contacting said hydrocarbon mixture containing mercaptans and said organic compound in the absence of substantial amounts of air with an alkaline solution to extract said mercaptans and obtain a fouled alkaline solution containing extracted mercaptans, separating said fouled alkaline solution from treated hydrocarbon mixture, passing air through said separated fouled alkaline solution to convert mercaptans present therein as mercaptides to polysuldes, separating said polysuldes from said alkaline solution, to obtain a regenerated alkaline solution and contacting further amounts of hydrocarbon mixture containing mercaptans and about 5 to about 20 pounds of said organic compound in the absence of substantial amounts of air with said regenerated alkaline solution.

5. The method of inhibiting internal oxidation of mercaptans to polysuliides in a hydrocarbon mixture as set forth and described in claim 4 wherein the regenerated alkaline solution is extracted with an immiscible solvent for polysulfides and said immiscible solvent separated from said regenerated alkaline solution.

6. The method of inhibiting internal oxidation of mercaptans to polysuldes in a hydrocarbon mixture as set forth and described in claim 4 wherein the organic compound more readily oxidized than mercaptans is N,Ndi(secondary butyl) phenylenediamine and the regenerated alkaline solution is extracted with a petroleum fraction.

JOHN MATTHIAS CRANMER.

References Cited in the file 0f this patent UNITED STATES PATENTS Number Name Date 2,257,079 Story Sept. 23, 1941 2,457,635 Bond Dec. 28, 1948 2,552,399 Browder May 8, 1951 OTHER REFERENCES Bond, Oil and Gas J December 8, 1945.

Claims (1)

1. A METHOD OF INHIBITING INTERNAL OXIDATION OF MERCAPTANS TO POLYSULFIDES IN GASOLINE WHICH COMPRISES DRAWING GASOLINE CONTAINING MERCAPTANS FROM A STABILIZER, INTRODUCING ABOUT 5 TO ABOUT 20 POUNDS OF N,N''-DI(SECONDARY-BUTYL) PHENYLENEDIAMINE PR 1,000 BARRELS OF GASOLINE INTO SAID GASOLINE, CONTACTING SAID GASOLINE CONTAINING MERCAPTANS AND SAID PHENYLENEDIAMINE IN THE ABSENCE OF SUBSTANTIAL AMOUNTS OF AIR WITH AN ALKALINE SOLUTION TO EXTRACT A MAJOR PORTION OF SAID MERCAPTANS TO OBTAIN A FOULDED ALKALINE SOLUTION CONTAINING SAID EXTRACTED MERCAPTANS AS MERCAPTIDES AND A TREATED GASOLINE, SEPARATING SAID TREATED GASOLINE FROM SAID FOULED ALKALINE SOLUTION, AND REGENERATING SAID FOULED ALKALINE SOLUTION.

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