US2340157A

US2340157A - Refining of oil

Info

Publication number: US2340157A
Application number: US442776A
Authority: US
Inventors: Jr Richard Bradley Thacker
Original assignee: Sinclair Refining Co
Current assignee: Sinclair Refining Co
Priority date: 1942-05-13
Filing date: 1942-05-13
Publication date: 1944-01-25
Anticipated expiration: 1961-01-25

Description

Jan. 2%5, 1944. R. B. THACKER, JR

REFINING OF OIL Filed May 13, 1942 INVENTOR Patented Jan. 25, 1944 Y UNITED STATES PATENT OFFICE REFINING oF on.

Richard Bradley Thacker, Jr., Houston, Tex., as-

signor to Sinclair Refining Company, New York, N. Y., a corporation of Maine Appncation May 13, 1942,',s'rialNo-4-i2n7s 9 claims. (ci. ies-a9) This invention relates to the refining of petroleum oils and more particularly to an improved process for the refining of petroleum distillates such as gasoline containing undesirable sulfur compounds, for example mercaptans.

The presence of mercaptans in gasoline was early recognized as objectionable' because of their oensive odor and corrosive nature.- Petroleum distillates containing such objectionable sulfur compounds are known as sour distillates and the process of freeing sour distillates of these sulfury compounds is known as sweetening The sweetening of these sour petroleum distillates has been the object of a multitude of proposed processes.

For many years, the so-called doctor treatment has been generally regarded as the most eicient method of sweetening such distillates. In the conventional doctor treatment, the sour distillate is subjected to prolonged intimate contact with an aqueous solution of caustic soda and litharge (sodiumplumbite), so-called fdoctor solution, at or near atmosphericl temperature. A typical doctor solution is'one produced by admixing 125 pounds of caustic soda, '70 pounds of litharge and 125 gallons of water. The amount of this solution added to the oil is usually predetermined by tests in which additional doses are added to a sample of the distillate until it does not further darken. Almost invariably elemental sulfur is nally added to the distillate to complete the doctor breakJ Care is taken to avoid adding excess sulfur as the presence of sulfur renders the finished distillate corrosive.

Though the doctor treatment is generallyeffective in sweetening sour distillates, it has been found to have disadvantages with respect to the refining of modern gasoline motor fuels. Specically, gasoline so sweetened has been found to be impaired as to its anti-knock properties, as to its susceptibility to improvement of its antiknock values by the addition of tetraethyl lead, hereinafter referred to as T. E. L., and as to its susceptibility to the action of oxidation inhibitors of the type frequently added to improve stability in storage.

.- In an eiort to improvethe distillate product, and to avoid the impairment of the characteristics just mentioned, a modied doctor treatment has been proposed according to which thev distillate is treated with the doctor solution at an` elevated temperature and under sufficient pressure to maintain the distillate substantially in the liquid phase, no sulfur being added to eifect the break. Though this modified doctor treatment has been found to be an improvement over the conventional `doctor treatment, ,it nevertheless has several disadvantages and is subject to certain operating limitations.

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I have found that when this modified treatment is carried out in the absence of air or oxygen, thel distillate is not completely rsweetened Within commercially practicalvtime limits. Under such conditions, an equilibrium is approached at which the vreaction rate becomes negligible, for practical purposes, when about of the mercaptans has been extracted by the doctor solution and about 20% is retained in the eliluent lgasoline, probably as sodium and lead mercaptides. When air is present during the treatment, the distillate may be completely sweetened withinprac-tical time limits but the rened distillate is not improved in octane number and stability nor in susceptibility to improvement by the addition of T. E. L. or oxidation inhibitor.

In accordance .with my presenty invention, the distillate is readily and completely sweetened with substantial improvement, with respect to the above-mentioned desirable properties, over the untreated product as Well as over conventionally treated doctor sweetened gasoline.

. yThe process of mypresent invention consists primarily of two major steps. In the rst stage of the treatment the distillate is brought into intimate contact with doctor solution at an` elevated temperature with the complete exclusion of air. In the second stage, the distillate from the first stage, Which has been separated from the major portion of the doctor solution, isintimately contacted with a suspension of lead sulde in vcaustic solution, valso at an elevated temperature, and in the presence of controlled amounts of added air.

My new vtwo-step process of the present invention is particularly adapted to continuous operation, -especially as an integral part of modern unitary refining .operations where it is advantageous to pass the Vdistillate from the distilling orfractionating operation directly to lthe sweetening operation. Under such conditions, the distillate, contains no airn or. oxygenand, therefore, it may be passed directly from thestabilizer or debutanizer, for instance, tothe first stage of my process, only the adjustment of its temperature being required. Where Ysuch distillate ispassed directly to the modied doctorrtreatment at an elevated temperature, discussed above, in the absenceof oxygen, the distillate is not completely sweetened. When treated in the prese-nce of air, the sulfur content is not reduced and the distillate is not improved to the maximum extent with respect to octane nurnber and stability and susceptibility to improvement by addition of T. E. L. and inhibitors.

The two steps of my improved process are peculiarly interrelated and dependent one on the other in such a way that chemical reagents active in the second stage are supplied for the most part from the first stage of the process and the In general, the process is as follows: In the first stage, the distillate which is devoid of oxygen or l air and preheated to a temperature of about 180 F. to 260 F., is brought into intimate contact with doctor solution, advantageously at` about the same temperature as the distillate, under a pressure sufficient to maintain the distillate substantially in the liquid phase. For best results, the doctor solution should usually be of about B. to 30 B. gravity and contain not less than 1 pound of litharge per barrel. The intimate admixing of the distillate may with advantage be effected by passing the distillate, and doctor solution together through orifice plate mixers. From thence the mixture may be passed to an enlarged chamber or extraction tower in which a substantial body of the mixture is vmaintained and wherein separation of the foul doctor solution from the distillate is effected by settling. Air is rigorously excluded from this first stage of the process.

Instead of admixing the distillate with the doctor solution, prior to their introduction into the extraction tower, as just described, the intimate contacting of the distillate with doctor solution may be effected by passing the vliquids through the extraction tower in generally countercurrent directions.

In this stage of the operation approximately V 80% of the mercaptans originally present in the distillate are extracted or separated from the distillate with the doctor solution. About of the mercaptans remain in the distillate probably in solution as mercaptides. Consequently, the product from the first stage of the process is not Sweet.

In the second stage of the process, the remaining mercaptans or mercaptides are converted to mono-sulfides or di-suldes by controlled air oxidation in the presence of lead sulfide and without the addition of elemental sulfur. This is accomplished with advantage by bringing the distillate passing from the first stage of the operation, and from which the foul doctor solution and the major portion of the mercaptans have been separated, into intimate contact with a controlled amount of air and a suspension of lead sulfide in doctor solution. After separation from the slurry, for example by settling, the distillate is sweet, though it may contain some doctor solution and lead sulfide in suspension. 'I'his distillate from the second stage may with advantage be washed with fresh or lregenerated doctor solution to remove the lead sulde and, after being completely clarified by settling, is passed to rundown tankage. y

In the carrying out of my two-stage process, the composition o f the doctor solution is important. This solution should usually contain the equivalent of not less than about 1 pound of litharge per barrel and a minimum of caustic sufficient to dissolve more than the minimum of litharge., However, its concentration may be varied somewhat depending upon the mercaptan sulfur content of the distillate, the operating temperature and the duration of the contact with the distillate.

Without limiting my invention to any theory as to the precise nature of the chemical reactions involved, it is my present belief that the reactions occurring in the rst stage of the process may be represented generally by the following equations:

(n RsH NaOH RsNa Hgo (2) msn zntzrbo2 2(RS)2Pb LiNaOH (3) (RS)2Pb Heat RQS -l- PbS where R represents a hydrocarbon radical.

Similarly, the reactions occurring in the second stage may be generally represented as follows:

second stage of the operation. An elevated temperature is required to obtain these reactions in a reasonable time. 'Ihe lead sulde appears to act as a catalyst for the Reactions 4 and 5. The lead sulfide is formed in the first stage of the operation and a portion of it passes over into the second stage with the distillate.

The 'foul doctor solution from the rst stage of the process may with advantage be passed to a conventional regenerating system and the regenerated doctor solution therefrom used for the iinalwashing of the distillate from the second stage.V After separation from this distillate, the regenerated doctor solution may be used for treating the distillate in the first stage.

The optimum treating temperature will depend largely upon the proportion of mercaptans to be converted; for example in treating a distillate containing 30 to 35 milligrams ol mercaptans per c. c., a temperature of 220 F. has been found to give the highest removal of mercaptans. For distillates of lower mercaptan content, the temperature may be lowered and, for distillates of higher mercaptan content, the temperature should be raised. Accordingly, a distillate containing only 20 milligrams of mercaptan sulfur per 100 c. c. can be treated successfully down to 4 milligrams or lower at a temperature of F., while, for a distillate containing 40 milligrams per 100 c. c., it may be necessary to raise the temperature to 230 F., or the throughput may b'e cut to allow a longer time of contact of the doctor solution and the distillate.

Thenecessary `pressure will depend upon the volatility of the distillate and the temperature employed. In operating with a 5 pound to 6 pound 'vapor pressure debutanizer bottoms distillate, a pressure of 60 pounds per square inch 'has been found to be suflicient to insure even operating conditions. Actually, the distillate could be kept in a liquid state at a much lower pressure. However, by using this higher pressure in the extractor tower, the foul doctor solution may be forced therefrom to the regenerating system and from thence back to the final washing operation by means of the pressure within the extractor tower, thus avoiding the necessity of using pumps for that purpose.

The proportion of doctor solution radded to the raw distillate before entering the extractor tower may with advantage be about 10% to 20% by volume. This proportion is not particularly critical but `preferably should be 10% or over in order to insure propenand complete Ycontact of the distillate with the doctor solution before entering the extraction tower. The extractive capacity of a given apparatus depends somewhat upon the thoroughnessl of the mixing of the distillate with the doctor solution before entering the extraction tower or during its' passage through the tower and generally is increased as the thoroughness of the mixing is increased.

The proportion of air introduced into rthe second stage of the operation should be carefully controlled. Enough oxygen must be introduced to oxidize the mercaptans present but an excess amount of air is objectionable' because of the difculty in recovering gasoline from the eluent air and also because the blackstrap in the treating solution will be oxidized and the sweetening reaction changed 'in such a manner that the improvementsobtained from the rst stage of the treatment are lost. The optimum proportion of air to be used will be found to vary with the characteristics of'the different distillates being treated. It may be stated generally that for each thousand barrels of distillate about 75 cubic feet of air per milligram of mercaptan sulfur per 100 millilitersof distillate should be used.

The process of my present invention will be further described with referenceto a specic method oi operation, graphically represented by the ow sheet constituting the accompanying drawing.

In this flow sheet, the raw distillate which may, for instance, be stabilizer or debutanizer bottoms preheated to a temperature of about 180 Vto 260 F., is passed to the system through the line l. Doctor solution, advantageously at approximately the temperature of the distillate,

is introduced into the system through line 2 in starting up the operation, is combined with the raw distillate in line I, and passes together therewith through the mixer conventionally indicated at 3, which may with advantage consist of a series of orifice plate mixers and in which the distillate and doctor solution are intimately admixed. From the mixer the admixed distillate and doctor` solution pass through line d into the chamber 5 which on theow sheet is designated extraction tower. The admixture is preferably introduced into the lower part of the tower at a point spaced from `the bottomso as to provide av relatively quiescent zone at the bottom of the tower to facilitate separation of the distillate from the doctor solution. The admixture may be introduced directly into the tower as indicated or with advantage through a spray head, not shown. Within this tower, the distillate separates from the doctor solution by gravity and passes from the top of the tower through the line 6. u

In the operation of the extraction tower, as just described, the admixed doctor solution and sour distillate flow generally concurrently through the tower., rspent doctor solution settling out in the bottom of ythe tower. An alternative arrangement which may be used with. advantage is to pass the raw distillate umnixedwith doctor solution directly into the lower portion of the extraction Atower and to introduce the doctor solution into the upper portion of the tower so that they pass through the towerA in intimate contact and in a generally countercurrent direction.

This `alternative method of operation 4may be carried out, in the apparatus diagrammatically represented in the drawing, by closing the valve in line 2 nearest the juncture with line I and passing the doctor solution directly into the upper part of the extraction tower through line 2. With this arrangement the raw distillate may be by-passed around the mixer 3 through line 4', by the proper adjustment of the valve shown, and from thence directly into the lower portion of the extraction tower through line 4 Without 'previous mixing with the doctor solution.

l It is desirable to maintain a considerable volume and depth of doctor solution within the tower so as to insure sufficiently prolonged rcontact between the doctor solution and the distillate passing therethrough. The vlevel of the doctor solution may be maintained by means of an automatic level control conventionally `indicated on the ilow sheet at 1, the level lpreterably being maintained near the upper end of the chamber, as indicated.

Foul doctor solution which separates from Athe distillate in the chamber 5 iswithdrawn therefrom through line 8 to a conventional regenerating system. u

. The above-described treatment of the raw distillate with doctor solution constitutes the first stage of the process. The raw distillate passing to this first stage of the process is free rfrom air or oxygen and no air or oxygen is permitted to enter the apparatus during this stage of the operation. The distillate passing from the upper end of the chamber 5 through theline 6 usually contains a considerable proportion of mercaptans, probably as sodium mercaptides and lead mercaptides. It also contains'a small amount of lead sulfide and doctor solution. As this partially reined distillate passes from the chamber 5 through the line li there is injected into it acontrolled amount of air from the line 9 and a slurry oi lead sulfide and doctor lsolution from line It. The 'admixture of distillate, lead sulfide slurry and air 'are then passed through the mixer Il, which may with advantage be of the type previously described, and into the settling chamber I2 which on the flow sheet is designated settler.

The air entering this second stage of 'the operation will, of course, be under pressure and may be supplied from any convenient source; In starting up the operation, the lead sulde slurry may be supplied from a convenient source, for instance from an outside source through line I 3. However, as the operation progresses, the lead sulfide-doctor solution vslurry accumulates in the bottom of the settler I2 'by kreason of the slurry introduced as such and valso 'the lead sulde and doctor solution carried'ove'r by the distillate from the first stage 'of the operation. When a suiicient amount of this slurry has collected in the settler I2, the introduction of leadv sulfide slurry through the pipe I3 may be -discontinued, the valve therein being closed and the slurry from settler I2 continuously circulated through lines l@ and Ill by means of the pump l5. As this slurry accumulates; it may be drawn 01T continuously or from time toj time from the cycle through' valved connection IB into the line 8 leading to the'doctor regenerating system. The level of the slurry in settler l2 may be observed by means of gauge glass Il.

The optimum concentration of the blackstrap or lead sulfide suspension is somewhat dependent upon the type and concentration of mercaptans in the distillate. If too low a concentration of lead sulde be maintained, the desirable octane characteristics and inhibitor susceptibility obtained by the first stage of the treatment may not be fully retained.

The distillate which passes from settler Al2 through the line I8 contains substantially no mercaptans but may contain small amounts of lead sulde and doctor solution. For the removal of such lead sulfide, the distillate may be washed with fresh or regenerated doctor solution introduced into the line I3 through line i9 and passes together with the distillate through the mixer 20, which may with advantage be of the type previously described. From thence the mixture enters the settler 2| wherein the distillate is clarified and passes from the settler' through line 22 to rundown tankage. The level within the settler 2l may be observed by the gauge glass 23.

As the process continues the doctor solution separated from the distillate and accumulating in the settler 2| is with advantage used for the treatment of the raw distillate in the nrst stage of the process and for this purpose may be continuously withdrawn from settler 2| through lines 24 andadmixed with the raw distillate passing to the system through line I by means of pump 25. -At this point the supply of doctor solution to the system through line 2 may be discontinued or reduced to an amount sulicient only to compensate for operating losses.

YIn a large commercial operation carried out iii-apparatus comprising a cylindrical extraction tower andl settlers each approximately 9 feet in diameter and 32 feet long, satisfactory results have been obtained by charging distillate to the rst stage of the operation at a temperature of about 220 F. at the rate of about 220 barrels per hour. The doctor solution charged to the first stage of the operation was at the same temperature and was charged atthe rate of about 45 barrels per hour. Air was charged to the second stage of the operation at the rate of 220 cubic feet per hour and the slurry of lead sulfide and doctor solution was circulated from the bottom of the first settler into the stream of distillate passing to the second stage at the rate of about 45 barrels per hour. The final washing of the sweet distillate from the secondvstage of the operation was accomplished by admixing therewith regenerated doctor solution at the `rate of about 45 barrels per hour. The mixture Aof distillate and doctor solution is introduced v into `the extraction tower through a spray nozzle at approximately 4 feet from the bottom of the tower and the level of the doctor solution in the tower is maintained at about 6 feet from the top of the tower.

My improved two-step process is independent of the particular method employed for regenerating the foul doctor solution. This regeneration may be accomplished by the conventional method which consists essentially of heating the foul doctor solution to a temperature of, say, 275 F., and blowing it with a small quantity of air. By this treatment the sulfur compounds dissolved in the doctor solution are volatilized and driven 01T, the sodium and lead compounds being oxidized to litharge and caustic soda. This regenerating operation is well known to the art and need not be herein described in greater detail.

In order to maintain the required treating temperature throughout the process, it is desirable that the apparatus in which the operation is carried out be thoroughly insulated against heat losses. However, if necessary, conventional heat exchange apparatus may be installed between the stages of the operation for the adjustment of the temperature.

The results obtained by the treatment of sour petroleum distillate by my improved two-step process may be illustrated by the following data concerning a specific operation in which the raw distillate treated was mixed debutanizer bottoms. v In this operation, the distillate and the doctor solution were each preheated to about 230 prior to being admixed and this temperature was substantially maintained in the rst stage of the operation. The temperature of the distillate stream passing from the second stage of the operation was approximately 225 F. A pressure of about 58 pounds per square inch was maintained throughout.

The distillate was charged to the operation at a rate of approximately one barrel per hour and the doctor solution was admixed with this distillate at the rate of about 0.30 barrel per hour. Airvwas charged to the second stage at the rate of approximately 1.2 cubic feet per hour.

The doctor solution, admixed with the distillate entering the ilrst stage of the operation, was regenerated solution from the final settling operation previously described. The character and composition of this regenerated doctor solution and of the foul doctor solution withdrawn from the rst stage of the operation were, respectively, as tabulated below:

lgrersg? Foul doctor tion charged solution from to iirst stage rst Stage Gravity 25 24.5 NaOH grains per 1iter. 174 172 NagCO e di- 54 54 Mercaptan sulfur mgs. per c. c.. 32 57.6 Organic acids 0.3 0.3 PbO in solution und per barrel.. 2 2 Soluble PbO.. d 2 2 0.8 1.0

The gravity, Reid vapor pressure and mercaptan sulfur content of the feed and of the stream of distillate Vfrom the first and second stages of the operation, respectively, and of that passing to rundown tankagewere as follows:

Thev octane number of the raw distillate and of the distillate in various stages of renement, as determined by the motor method, and also the susceptibility of these distillates to improvement in octane value 4by the addition of T.1'E L., were as recorded in the-following tabulation:

From From Torun- Octane No. Feed. rst. second down v stage stage tankage Neat 67.3 67 4+0. 1 67.4-1-0. 1 67.4+0.1 +I C. c T` E. L 72.8 73'2+0:4 -73'.'2+0.4 73;2+0`.4 +2 c. c T E..L 75. 0. 75 4+0.4 75.4+0.4 75. Hf-0.4 +3 c. C T. E. L 76.7 77 8+1. 1 77. 8+l. 1 77. 8+l. l

Theboiling point characteristics `of .the raw distillate and of the distillate in. Various. stages of treatment wereas indicated below:

As a further example, stabilized cracked distillate from Mid-Continent and WestTexas-New Mexico crude was treated, by the processV` of the present invention, in a large commercial operation having `a capacity of about 9000 barrels per day at a temperature of 225.F.-230 F.. and a pressure of 55 pounds per square inch. The doctor solution was admixed with the raw distillate charged to the rst stage of the operationln an amount approximating by volume of a raw distillate. Air was supplied to the second stage at the .rate` of approximately 4000 cubic feet per day.

The gravity and composition. of .regenerated doctor solution charged to the rst. stage,A and of the foul doctor solution withdrawn from the rst The characteristics and composition of the raw distillate, the partially rened distillate from the first and second stages of the operation, re` H spectively, and of fthe.. refined distillate; passing' to rundown tankage were as follows:

From From To run- Feed rst second down stage stage tankage A. P. I. gravity 53.6 53.6 53.3 53.1 R. V. P. at 100 F 5.0 5.0 4.8 4. 5 Mercaptan suliur mgs./100 c. c 28.8 6. 7 0.0 0.0 Mercaptan sulfur reduction per cent 76. 8 100 100 Sulfur 0.099 0. 077 0.077 0. 077 Oxygen bomb timeminutes 30 90 180 180 From the above data it appears that the distillate Was entirely freed of mercaptan sulfur and that the total sulfur content was very substantially reduced. Further, the increased stability of the treated distillate over that of the raw distillate is indicated by the standard oxygen bomb induction test, according to which the oxygen bomb'timewas .increased from `30 minutes for the raw distillate. tof180 minutes for the completely treated distillate. A

The improvement in octane value and susceptibility. to improvement in octane value by the addition of T. E. L. appears from the following tabulation, the octane values having been determined by the motor method:

The distillation characteristics of the raw feed andof the partially rened distillate from the rst and second. stages of the operation, respectively, appear from the following tabulation:Y

, From first From second Feed stage stage lnitialboilng point 111 110 108 10 F 176 177 177 50F 276 279 278 'F 36S 366 364 End point.. 405 406 406 Per cent recover 98. 5 98. 5 98. 5

As previously stated, the gravity of the doctor solution used in my improved process may vary from about 10 to about 30 Baume. I usually prefer to use a doctor solution' having a gravity of about 18 to 25 B. and carrying not less than 3 pounds of litharge per barrel. Best results are usually obtained when the caustic content of the doctor solution is 20 pounds per barrel or higher. Howevenl have obtained satisfactory results using va doctor solution containing as llow yas 5 pounds of caustic soda and only 1/2 pound of litharge per barrel.

Though. the treatment of sour petroleum distillate with a suspension of lead suliide in caustic solution for sweetening the distillate had been previously proposed, suchv treatment alone does not usually'resultin a reduction of the sulfur content of the distillate, only the condition ofthe sulfur present being modified.. By my improved two-step-.proces'slof the present invention, not only is the distillate sweetened, but its sulfur con-tentis substantially reduced.

I claim:

l. Aprocessvfor the treatment of light 'petroleum distillates containing undesirable sulfur compounds'. to eliminate vsaidv sul-furl compounds therefrom, comprising intimately contacting thel distillate at an elevated temperature and in the absence of oxygen with an aqueous solution of caustic soda and litharge, separating the distillate from the aqueous solution, intimately contacting the separated distillate at an elevated temperature and in the presence of oxygen With a suspension of lead sulde in aqueous caustic soda solution and thereafter separating the distillate.

2. A process for the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, comprising intimately contacting the distillate at a temperature of about F. to 260 F. andin the absence of oxygen with an aqueous solution of caustic soda and litharge, separating the distillate from the aqueous solution, intimately contacting the separated distil..

late at a temperature of about 180 F. to 260 F., and in the presence of oxygen with a suspension of lead sulfide in aqueous caustic soda solution and thereafter separating the distillate- 3. A process for the treatment of light pe-v troleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, comprising intimately contacting the distillate at an elevated temperature and in the absence of oxygen with an aqueous solution of sodium plumbite, separating the distillate from the aqueous solution, intimately contacting the separated distillate at an elevated temperature and in the presence of oxygen with a suspension of lead sulfide in aqueous caustic soda solution and thereafter separating the distillate.

4. A process for` the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, comprising intimately contacting the distillate at an elevated temperature, under a pressure sufficient to maintain the distillate substantially in the liquid phase and in the absence of oxygen with an aqueous solution of caustic soda and litharge, separating the distillate from the aqueous solution, intimately contacting the separated distillate at an elevated temperature and in the presence of oygen With a suspension of lead sulfide in aqueous caustic soda solution and thereafter separating the distillate.'

5. A process for the treatment of light pe troleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, comprising intimately contacting the distillate at an elevated temperature and in the absence of oxygen with an aqueous .solution of caustic and litharge having a gravity of about 18 to 25 B., and containing not less than about 3 pounds of litharge per barrel, separating the distillate from the aqueous solution, intimately contacting the separated distillate atan elevated temperature and in the presence of oxygen with a suspension of lead sulfide in aqueous caustic soda solution and thereafter separating the distillate. v

6. A process for the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, comprising intimately contacting the distillate at an elevated temperature and in the. .absence of oxygen With an aqueous solution of caustic soda and litharge, separating the distillate from the aqueous solution, intimately contacting the separated distillate at an elevated temperature and in the presence of oxygen with a suspension of lead sulde in aqueous caustic I soda solution, separating the distillate from the major portion of the aqueous solution and lead suliide,'washing the separated distillate with an aqueous solution of caustic soda and litharge to remove residual lead-sulde and thereafter separating the distillate from the last said solution.

7. A` continuous two-stage process for the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, comprising, as the rst step, intimately contacting the distillateV While at an elevated temperature and in the absence of oxygen with an aqueous solution of caustic soda and litharge and separating the distillate from the solution and, as the second step, vintimately contacting the distillate from the rst stage While at an elevated temperature and in the presence of oxygen with a suspension of lead sulfide in aqueous caustic soda solution and separating the distillate from said suspension, regenerating the foul aqueous solution from the rst stage, Washing the distillate from the second stage with this regenerated solution, separating the distillate from the regenerated solution, and thereafter passing the separated regenerated solution to the rst stage of the operation wherein itis intimately admixed with the distillate feed.

8. A process for the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, `comprising passing the distillate at an elevated temperature and in the absence of oxygen in intimatecontact and generally countercurrent relation with an aqueous solution of caustic soda and litharge, passing the distillate from which the major portion of the aqueous solution has been separated into intimate contact with a suspension of lead sulfide in aqueous caustic solution at elevated temperature and in the presence of oxygen and thereafter separating the distillate.

9. A process for the treatment of light petroleum distillates containing undesirable sulfur compounds to eliminate said sulfur compounds therefrom, comprising intimately contacting the distillate'at an elevatedtemperature and in theabsence of oxygen with an aqueous solution of caustic soda and litharge, separating the distillate from the aqueous solution, intimately contacting the separated distillate at an elevated temperature With air and a suspension of lead sulfide in aqueous caustic solution, the proportion of airv approximating cubic feet of air per thousand barrels of distillate per milligram of mercaptan sulfur per milliliters of distillate, and thereafter separating the distillate.

RICHARD BRADLEY THACKER, JR.