US2855445A - Purification of normal heptane by treating with alkali polysulfide followed by a copper chloride treatment - Google Patents

Description

Oct. 7, 1958 T F. T. OGLE EI'AL 45 PURIFICATION OF NORMAL HEPTANE BY TREATING WITH ALKALI POLYSULFIDE FOLLOWED BY A COPPER CHLORIDE TREATMENT Filed Jan. 10, 1956 mm hm qm om HEM/BELL 3CHHO'1HD BBddOD' HOLVNOILDVBJ mozizmuwd INVENTORS F.T. OGLE C H MIHM Y I/ M f ATTORNEYS HOLVNOILOVHd United States Patent PURIFICATION OF NORMAL HEPTANE BY TREATING WITH ALKALI POLYSULFIDE FOLLOWED BY A COPPER CHLORIDE TREATMENT A Frank T. Ogle and Clifford H. Mihm, Borger, Tex., as-

SlgllOlS to Phillips Petroleum Company, a corporation of Delaware.

Application January 10, 1956, Serial No. 558,225 9 Claims. (Cl. 260-676) This invention relates to a process for sweetening and producing a low odor hydrocarbon product from straightrun or natural gasoline fractions. In one aspect, this invention relates to a multi-step process for treating sour straight-run or natural gasoline fractions to produce a substantially odor-free product. In another of its aspects, this invention relates to a multi-step process comprising the utilization of an alkali metal sulfide or polysulfide solution followed by a fractionation to sweeten straightrun or natural gasoline fractions by removing therefrom sulfur compounds, such as mercaptans, and various other materials, which are responsible for bad odors or sourness of the hydrocarbons. In still another of its aspects, this invention relates to the sweetening of a gasoline fraction comprising normal heptane and isooctane by treating said gasoline in a multi-step process utilizing and alkali metal sulfide or polysulfide solution in the first step, a sand filter and/or a dry copper chloride treater 1n the second step, and fractionation of the efllulent from the second step to produce a low odor normal heptane product.

Various methods and reagents have either been used or proposed for the desulfurization or sweetening of hydrocarbon oils. Chemical reagents that have been used include solutions of sodium plumbite, alkaline sodium hypochlorite, alkali metal sulfides and polysulfides, and dry copper chloride. These reagents have either been used alone or, in some cases, used in combination with another reagent to treat sour hydrocarbon oils. One process that has been used to sweeten gasoline fractions comprised the use of a solution of an alkali metal polysulfide to treat the overhead product from a fractionating column separating normal heptane from isooctane. However, the product obtained from this process was not always entirely satisfactory since a certain amount of residual odor remained in the normal heptane product after treatment with sodium polysulfide. Consequently, this fraction could not be sold as a satisfactory solvent where odor is a problem. The present process obviates this disadvantage of the prior process for producing a low odor normal heptane product that is marketable and meets the specification for commercial grade normal heptane.

One object of this invention is to provide a process for sweetening natural gasoline or fractions thereof. Another object of this invention is to provide a process for sweetening straight-run gasoline or fractions thereof. Another object of this invention is to provide a multi-step process for producing a low odor normal heptane solvent from a natural gasoline fraction. A still further object of this invention is to provide a multi-step process for treating v natural gasolines utilizing alkali metal polysulfide solutions and a fractionation step to produce a substantially odor-free normal heptane product.

Other aspects, ob-

jects, as well as the several advantages of this invention,

are apparent from a study of the disclosure, the drawings and the appended claims.

We have found that sulphur contaimng straight-run or natural gasoline fractions contacted with a sodium polysawed Oct. 7, 1958 sulfidesolution to convert the sulphur compounds to higher boiling sulphur compounds, and subsequently treated in either a sand filter or a dry copper chloride treat'er, still" has sufficient odor to render the product undesirable as a solvent, and that by fractionating the effluent gasoline fractions from .these treatments, a substantially odor-free solvent product is obtained. In accordance with this invention, the odor of sulfur bearing gasolinefractions is substantially eliminated by treating these fractions in a multi-step process utilizing an alkali metal polysulfide solution followed by fractionation, thereby removing sulfur compounds and other materials responsible for the bad, odor and sourness of these hydrocarbons.

As used he reinafter and in the claims, the unqualified term gasoline means either straight-run or natural gasoline or a mixture of the two. The terms natural gasolinefland fstraight-run gasoline are those used in the American Petroleum Institute Glossary of Terms Used in Petroleum Refining, 1953 edition.

Inaccordance with one embodiment of this invention, sulfur containing natural or straight-run gasolines, or fractions thereof, are sweetened by treating said gasolines with an alkali metal polysulfide. solution in the first step of the process, passing said treated gasoline through a sand filter and/or a dry copper chloride treater in the second step, and fractionating the effluent from the second step to produce a low odor overhead product. The in- .vention in accordance with a preferred embodiment pronormal heptane as an overhead product which meets.

specifications as a solvent.

In actual operation, the sulfur containing gasoline fraction is first contacted in any manner causing intimate contact with anaqueous solution comprising an alkali metal polysulfide at a temperature ranging from room temperature, for example, 60 R, up to about 150 F., preferably F. to 120? F., more preferably about F., to remove a substantial. portion of the undesirable sulfur compound originally present in the gasoline fraction. Pressures utilized during the contacting step are normally atmospheric, however, elevated pressures can be employed, ifdes ired. The amount of alkali metal sulfide present in the treating solution preferably ranges from 4 to 6 weight percent, while the amount of sodium hydroxide in the solution ranges from 8 to 12 weight percent; however, concentrations outside of these ranges can be used with satisfactory results. The polysulfide treating solution employed can be prepared by any well-known method in the art. While any alkali metal can be used satisfactorily, we prefer to use sodium. The amount of sodium polysul: fide solution employed to contact the sulfur containing gasoline fraction will ordinarily range from 20 to 60 percent by volume, preferably about 50 percent, of the gasoline fraction being treated.

After the sulfur containing gasoline fraction has been contacted'with'thesodium polysulfidesolution, it can be passed directly to fractionation, but in the preferred mode of operation the desulfurized gasoline is passed through a sand filter to remove treating solution or other undesirable constituents carried along with the gasoline fraction recovered from the settling zone prior to fractionation. In other modes of operation, a zone containing a solid sweetening reagent comprising an absorbent material such as fullers earth impregnated with a solution of a copper salt and a chloride can be used to further treat the hydrocarbons removed from the sodium polysulfide treating zone and/ or the sand filter prior to fractionation. Temperatures employed in the sand filter and the copper chloride treater are preferably the same as the temperature prevailing in the sodium polysulfide contacting and settling zone. Pressures employed are. normally atmospheric, however, elevated pressures, may be utilized, if desired.

Although this invention is applicable to any straight run or natural gasoline exhibiting an odor problem, it is especially applicable to the sweetening of straight run or natural gasoline fractions comprising normal heptane and isooctane fractions which boil within the range between about 200 F. and about 250 F.

The top column temperatures employed in the fractionation zone following the sweetening treatment preferably range from about 240 F. to about 260 F. and a pressure ranging from slightly above atmospheric to two atmospheres or more. The internal reflux to feed ratio employed in the column preferably ranges from 1:1 to 3:1. The amount of feed to the column taken overhead as product preferably ranges from 40 to 80 percent for the most desirable results. If desired, volumes in excess of 80 percent of the feed may be taken overhead and still produce a specification normal heptane with respect to odor. However, it is to be realized that conditions and rates outside of those given above can be employed as will be understood by one skilled in the art with possession of this disclosure.

The present invention will be illustrated by reference to the drawing in which the single figure represents a flow diagram of a preferred mode of operation, wherein a natural gasoline fraction is fractionated to recover a normal heptane-isooctane fraction, this fraction is treated with a sodium polysulfide solution to remove acidic components, especially sulfur and other odor producing compounds, the treated hydrocarbon fraction is filtered and then this fraction is passed to a final fractionation zone wherein a specification normal heptane solvent of very low odor content is removed overhead. Also shown on the drawing are alternate modes of operation wherein the hydrocarbon fraction, after being treated with the sodium polysulfide solution, is either passed directly to a dry copper chloride treater or passed through the sand filter first and then to the dry copper chloride treater. These modes of operation are shown by lines.

Referring now to the drawing, numeral designates a charge line connected into a source of a sour deisoheptanized gasoline fraction, not shown. This sour natural gasoline fraction will ordinarily have a boiling range of from about 200 F. up to about 350 F., or more. The deisoheptanized gasoline fraction is passed through heat exchanger 11, wherein the temperature is raised to 246 F. and passed through line 12 to fractionator 13. The column is operated at a top temperature of 268 F. and 20 p. s. i. g. pressure, and a bottom temperature of 330 F. A kettle product, boiling above about 250 F., is removed via line 14 and passed to subsequent processing, nOt shown. The overhead fraction comprising normal heptane and isooctane, which boils between about 200 F. and 250 F., is removed by line 15 and passed to condenser 16, and then through line 17 to accumulator 18. The condensed overhead product is removed from I the accumulator by line 19 and a portion is returned to column 13 by line 20 to be used as reflux.

The sour normal heptane-isooctane fraction recovered from fractionator 13 is passed through line21 to heat exchanger 22, which may be either a heater or cooler depending upon the temperature of the liquid withdrawn mixing loop. In this example, the stream leaving heat exchanger 22 is at 98 F. A mixture of sodium polysulfide and sodium hydroxide removed from settling zone 27 by line 28 is mixed at a ratio of 1:1 with the sour normal heptane-isooctane fraction in line 24, passed through centrifugal pump 25 and therein intimately mixed and then passed through line 26 and back to settling zone 27. It is to be understood that the mixing device utilized may be any type of mixing device available on the market and may include jet mixers, stirrers, contacting towers, and the like. The settling zone 27 is of sufiicient capacity to allow a residence time for separation by gravity between the contacted normal heptane-isooctane fraction and the aqueous sodium polysulfide solution. The intimate mixing obtained in pump 25 and line 26 serves to remove hydrogen sulfide, mercaptans, and the like, from the sour gasoline fraction and causes solution thereof into the aqueous sodium polysulfide solution. The treating solution utilized for contacting the sour gasoline fraction normally contains 4 to 6 weight percent sodium polysulfide and between 8 to 12 weight percent sodium hydroxide. The contacting may be carried out continuously or intermittently. As shown on the drawing, conduit 29 and a valve (not shown) is provided for the addition of make-up sodium hydroxide and, also, conduit 30 and a valve (not shown) is provided to remove spent treating solution for continuous operations. With intermittent operation, the unit is shut down and the spent solution removed and then recharged with new treating agent. The contacting temperature preferably used will range between F. and about 120 5., more preferably about F.

The treated normal heptane-isooctane fraction is withdrawn from settling zone 27 via line 31 and passed to sand filter 32, wherein at least a portion of any treating agentor other deleterious materials carried over with the hydrocarbon fraction is removed. The hydrocarbon fraction is removed from the filter by line 33, passed through heat exchanger 34, line 35, heat exchanger 36 and thence to fractionator 38 via line 37. A kettle product comprising isooctane and high boiling oxidized sulfur compounds is removed by line 39 and passed in indirect heat exchange with the feed to column 38 through heat exchanger 34, and then passed to subsequent treatment, not shown. The kettle product will generally boil above about 220 F. An over .ead fraction comprising normal heptane and having a boiling range between about 200 F. and about 220 F. is removed from column 33 by line 40 and passed to condenser 4-1 and then through line 42 to accumulator 43. The amount of normal heptane product taken overhead may range as high as 80, or more, volume percent of the feed to column 33 and still produce a pro-duct of very low odor. The normal heptane recovered is removed from accumulator 43 by line 44 and part removed by line 46 as specification product, and the remainder is returned to column 38 by line 45 to be used as reflux. The amount of internal reflux used in column 38 preferably ranges from 1:1 to 3:1 based on normal heptane to the feed. The column is operated with a top temperature of 249 F. and a pressure of 12 p. s. i. g., and bottom temperature of 276 F. In the event the normal heptane product does not meet specification where extremely high purity is desired as to odor, boiling range, sulfur content, etc-., it can be recycled either to the sodium polysulfide treating zone or to the feed to fractionation zone 38.

As previously mentioned, the present invention also contemplates an alternative operation, wherein a dry copper chloride treater such as described in U. S. Patent 2,264,220, Schulze, filed November 9, 1938, and issued November 25, 1941, is used either as a secondary sweeten ing treatment following the sodium polysulfide treatment, or in series following the sand filter. In the first instance, the treated hydrocarbon recovered from settling zone 27 is passed through line 31, thence through line 4-7 to dry copper chloride treater 48 and removed by line 40 and introduced into line 33, and then passed to fractionator 38. Also, the treated hydroc: rbon fraction removed from zone 27 by line 31 can be passed through sand filter 32 first, and then through line 50 and 47 to copper chloride treater 48 and introduced into line 33 as previously described. When using the dry copper chloride treater, as a secondary sweetening step, the ratio of sodium polysulfide solution to hydrocarbon will generally range from 40 to 60 percent, preferably 50 percent, by volume.

' As stated before, we have found that byfractionating the normal heptane-isooctane fraction, under controlled conditions, the residual odor compounds remaining in the hydrocarbon fraction after contacting with sodium polysulfide which converts the sulphur compounds to higher boiling sulphur compounds, and either sand filtering or treatment by dry copper chloride, can be removed in the kettle product from the fractionation zone and a substantially odor-free normal heptane product taken overhead. The odor in the feed to the fractionating column has ranged from moderate to very strong, whereas the overhead product obtained has only a slight odor. As shown by the specific example, the reflux ratio was varied from 1:1 to 3:1 based on the feed, and as much as 80 volume percent of the feed was taken overhead, a product of very low odor was still produced.

EXAMPLE I A sour normal heptane-isooctane fraction having a strong odor was treated first with sodium polysulfide and then sweetened in a second treater with dry copper chloride followed by fractionation to recover a very low odor n-heptane product, which would meet specifications as a solvent. The sodium polysulfide solution contained 4-6 weight percent sulfide and 8-12 weight percent sodium hydroxide- The contacting temperature was 100 F. The amountof treating solution used to contact the normal heptane-isooctane fraction was 50 volume percent of the hydrocarbon fraction. The normal heptane-isooctane fraction was then passed over a reagent of fullers earth impregnated with a solution of cupric chloride at a temperature of 100 F. The normal heptane-isooctane was then passed to a 3-foot I. D., SO-tray, bubble-cap fractionating column. The column conditions used were as follows: a feed temperature ranging from 250290 F., overhead vapor temperature ranging from 250260 F., kettle product temperature ranging from 270-300 F., and a top column pressure of about 30 p. s. i. a. The odor of the normal heptane-isooctane feed to the column as well as the odor of the overhead product and other properties of various normal heptane samples are shown in Table I.

from an ASTM D2l6-53 distillation to dry on the filter paper for 2.5 minutes in a room free of noticeable air currents.

It will be noted from the above table that, in all cases, an overhead product having an odor of from passable to excellent was produced. All fractionations produced product which met the specifications for commercial grade normal heptane except the one at an internal reflux to feed ratio of 3/1 with percent of the feed taken overhead. However, even in this one case, the ASTM distillation dry point specification of 210 was exceeded by only one degree which is within the reproducibility of the test method. However, it will be noted that all of the other properties of this sample passed the specification.

The specification for commercial grade normal heptane is shown in Table II.

Table 11 Property Maximum and Test Method Minimum Limits i -iterat s t mi 200 F n1 a o g om n.

. Dry Point max. 210 F }ASTM D216 Vapor Pressure at F max. 2.0 p. s. i AS'IM D323 52. Color; Saybolt min. +30 ASTM D156-531.

ur Content, weight max. 0.01 ASIM D1266-53T.

Pass ASTM D-53T. sweet N GAA Doctor Test. Nonvolatfle Matter, g/100 max. 0.0010 ASTM D268-49.

without departing from the spirit or scope of the disclosure or from the scope of the claims.

We claim:

. 1. Aprocess of treating a sulfur-containing gasoline fraction boiling within a range of about 200 F. to about 250 F. consisting essentially of normal heptane and isooctane which comprises contacting said gasoline fraction with an aqueous sodium polysulfide solution to convert a substantial portion of said sulfur compounds to higher boiling sulphur compounds, separating the contacted gasoline fraction from the sodium polysulfide solution, passing said gasoline fraction through a sand filter zone, and passing said gasoline fraction containing residual odor compounds to a fractionation zone to remove said residual odor compounds and isooctane as kettle product and recovering a substantially odor-free normal heptane fraction as overhead product having less than 0.01 weight percent sulphur.

2. A process of treating a sulfur-containing gasoline fraction boiling within a range of about 200 F. to about 250 F. consisting essentially of normal heptane and iso- Table 1 Overhead Internal Product Dry Total Odor Odor Test Number Reflux to Rate, IBP, Point, Color Sulfur, Index Index Feed Vol. Per- F. F. Saybolt Wt. PerofFeed of OHP Ratio cent of cent Feed The odor indices were determined by averaging the numerical index ratings reported by the odor panel members.

Numerical indicos for the odor tests were: very slight odor 1,

slight odor 2, moderate odor 3, and strong odor 4. An odor index of 1.9 or less is a passable value.

The Phoenix Metal Cap Companys Residual Distillation Residue Odo-r Test was used to obtain the odor rating of all samples. The procedure for the test is to determine the residual odor remaining on Whatman Number 1 filter paper after allowing a few drops of the residue said gasoline fraction through a dry copper chloride treating zone, and passing said gasoline-fraction containing residual odor compounds to a fractionation Zone to remove said residual odor compounds and isooctane as kettle product and recovering a substantially odor-free normal heptane fraction as overhead product having less than 0.01 weight percent sulphur.

3. A process of treating a sulfur-containing normal heptane-isooctane natural gasoline fraction boiling within a range of about 200 F. to 250 F. comprising the steps of contacting said hydrocarbon fraction with an aqueous sodium polysulfide solution containing from 4 to 6 weight percent sodium sulfide and 8 to 12 weight percent sodium hydroxide at a temperature within a range of 80 F. to 120 F, to convert the sulphur compounds to higher boiling sulphur compounds, separating the contacted hydrocarbon fraction from the polysulfide solution, passing said hydrocarbon fraction through a sand filter zone to remove a portion of the undesirable components remaining in said hydrocarbon fraction, passing said hydrocarbon fraction containing residual odor compounds to a fractionation zone to remove isooctane and high boiling residual odor compounds as kettle product, and recovering a very low odor normal heptane product having less than 0.01 Weight percent sulphur overhead.

4. A process of treating a sulfur-containing normal heptane-isooctane natural gasoline fraction boiling within a range of about 200 to 250 F. comprising the steps of contacting said hydrocarbon fraction with an aqueous sodium polysulfide solution containing from 4-6 weight percent sodium sulfide and 8-12 weight percent sodium hydroxide at a temperature within a range of 80-120 F., to convert the sulphur compounds to high boiling sulphur compounds separating the contacted hydrocarbon fraction from the polysulfide solution, passing said hydrocarbon fraction through a dry copper chloride treating zone to remove a portion of the undesirable components remaining in said hydrocarbon fraction, passing said hydrocarbon fraction containing residual odor compounds to a fractionation zone to remove isooctane and high boiling residual odor compounds as kettle product, and recovering a very low odor normal heptane product having less than 0.01 weight percent sulphur overhead.

5. A process of treating a sulfur-containing normal heptane-isooctane natural gasoline fraction boiling within a range of about 200 to 250 F. comprising the steps of contacting said hydrocarbon fraction with an aqueous sodium polysulfide solution containing from 4-6 weight percent sodium sulfide and 8-12 weight percent sodium hydroxide at a temperature within a range of 80-120 E, to convert the sulphur compounds to higher boiling sulphur compounds separating the contacted hydrocarbon fraction from the polysulfide solution, passing said hydrocarbon fraction through a sand filter zone and then through a dry copper chloride treating zone to remove a portion of the undesirable components remaining in said hydrocarbon fraction, passing said hydrocarbon fraction containing residual odor compounds to a fractionation zone to remove isooctane and high boiling residual odor compounds as kettle product, and recovering a very low odor normal heptane product having less than 0.01 weight percent sulphur overhead.

6. A process of treating a sulphur-containing normal heptane-isooctane natural gasoline fraction boiling within a range of about 200 to 250 F. comprising the steps of contacting said hydrocarbon fraction with an aqueous sodium polysulfide solution containing from 4-6 weight percent sodium sulfide and 8-12 weight percent sodium hydroxide at a temperature within a range of 80-120 F., to convert the sulphur compounds to higher boiling sulphur compounds separating the contacted hydrocarbon fraction from the polysulfide solution, passing said hydrocarbon fraction through a sand filter zone to remove a portion of the undesirable components remaining in said hydrocarbon fraction, passing said hydrocarbon fraction containing residual odor compounds to a fractionation zone operating with an internal reflex-to-feed ratio ranging between 1:1 and 3:1, 21 top column temperature ranging from 240 F. to 260 F., a pressure ranging from atmospheric to two atmospheres, or more, and recovering from 40 to volume percent of the feed overhead as a substantially odor-free normal heptane product having less than 0.01 weight percent sulphur.

7. A process for treating a sulfur-containing straightrun gasoline boiling fraction boiling above 200 F. comprising the steps of fractionating said gasoline to remove hydrocarbons boiling above 250 F. as kettle product and recovering overhead a normal heptane-isooctane fraction boiling between 200 F. and 250 F., contacting said hydrocarbon fraction with an aqueous sodium polysulfide solution containing from 4-6 weight percent sodium sulfide and 8-12 weight percent sodium hydroxide at a temperature within a range of 80-120 F., to convert the sulphur compounds to higher boiling sulphur compounds separating the contacted hydrocarbon fraction from the polysulfide solution, passing said hydrocarbon fraction through a sand filter Zone to remove a portion of the undesirable components remaining in said hydrocarbon fraction, passing said hydrocarbon fraction containing residual odor compounds to a fractionation zone operating with an internal refiux-to-feed ratio ranging between 1:1 and 3:1, a top column temperature ranging from 240 F. to 260 F., a pressure ranging from atmospheric to two atmospheres, or more, and recovering from 40 to 80 volume percent of the feed overhead as a substantially odor-free normal heptane product having less than 0.01 weight percent sulphur.

8. A process for recovering a substantially odor-free, low sulphur content normal heptane product from a sulphur-containing natural or straight-run gasoline fraction boiling above about 200 F. comprising the steps of fractionating said gasoline fraction to remove a hydrocarbon fraction boiling above about 250 F. as kettle product, and recovering overhead a normal heptaneisooctane fraction boiling between about 200 F. and about 250 F., contacting said normal heptane-isooctane fraction with an aqueous sodium polysulfide solution containing from 4-6 weight percent sodium sulfide and 8-12 weight percent sodium hydroxide within a temperature range of 80-120 P. so as to convert the sulphur compounds in said fraction to higher boiling sulphur compounds, separating said normal heptane-isooctane fraction from said polysulfide solution by gravity in a settling zone, passing said normal heptane-isooctane fraction containing high boiling sulphur compounds and residual odor compounds to a filtering zone to remove a portion of the undesirable components remaining in said fraction removed from said contacting, passing said fraction to a dry copper chloride treating zone to further sweeten said fraction, passing said normal heptane-isooctane fraction containing high boiling sulphur compounds and residual odor compounds to a fractionation zone to remove isooctane and high boiling sulphur compounds and residual odor compounds as kettle product, and recovering from 40 to 80 volume percent of the fractionation zone feed overhead as a substantially odor-free normal heptane product having less than 0.01 weight percent sulphur.

9. A process for recovering a substantially odor-free, low sulphur content normal heptane product from a sulphur-containing normal heptane-isooctane natural gasoline hydrocarbon fraction boiling within a range of about 200 to about 250 F., comprising the steps of contacting said fraction with an aqueous sodium polysulfide solution containing from 4-6 weight percent sodium sulfide and 8-12 weight percent hydroxide at a temperature within the range of 80-120 P. so as to convert the sulphur compounds in said fraction to higher boiling sulphur compounds, passing the mixture to a settling zone so as to separate said hydrocarbon fraction containing higher boiling sulphur compounds from said polysulfide solution, passing said hydrocarbon fraction through a filtering zone to remove at least a portion of the undesirable components remaining in said hydrocarbon fraction removed from said settling zone, passing said hydrocarbon fraction containing high boiling sulphur compounds and residual odor compounds to a fractionation zone to remove isooctane and high boiling sulphur and residual odor compounds as kettle product, and 1 '10 recovering from 40-80 volume percent of the fractionation zone feed overhead as a substantially odor-free normal heptane product having less than 0.01 weight percent sulphur.

References Cited in the file of this patent UNITED STATES PATENTS Fischer et a1. Ian. 20, 1931 Schulze Nov. 25, 1941

Claims (1)

1. 2. A PROCESS OF TREATING A SULFUR-CONTAINING GASOLINE FRACTION BOILING WITHIN A RANGE OF ABOUT 200*F. TO ABOUT 250*F. CONSISTING ESSENTIALLY OF NORMAL HEPTANE AND ISOOCTANE WHICH COMPRISES CONTACTING SAID GASOLINE FRACTION WITH AN AQUEOUS SODIUM POLYSULFIDE SOLUTION TO CONVERT A SUBSTANTIAL PORTION OF SAID SULFUR COMPOUNDS TO HIGHER BOILING SULPHUR COMPOUNDS, SEPARATING THE CONTACTED GASOLINE FRACTION FROM THE SODIUM POLYSULFIDE SOLUTION, PASSING SAID GASOLINE FRACTION THROUGH A DRY COPPER CHLORIDE TREATING ZONE, AND PASSING SAID GASOLINE-FRACTION CONTAINING RESIDUAL ODOR COMPOUNDS TO A FRACTIONATION ZONE TO REMOVE SAID RESIDUAL ODOR COMPOUNDS TO A FRACTIONATION ZONE TO REMOVE PRODUCT AND RECOVERING A SUBSTNATIALLY ODOR-FREE NORMAL HEPTANE FRACTION AS OVERHEAD PRODUCT HAVING LESS THAN 0.01 WEIGHT PERCENT SULPHUR.

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