US2334549A - Refining mineral oils - Google Patents

Description

Nov. 16, 1943. G. R. GILBERT REFINING MINERAL OIL Filed July 5. 1941 Halls Patented Nov. 16, 1943 REFINING MINERAL `oIns George R. Gilbert, Baytown, Tex., assi-gno;e to Standard Oil Development Company, a Ycor-11o:

ration of Delaware Application July 5, 1941, Serial. No.. 4.91.1167

11 Claims. l('Cl. 19a-133,).

The present invention is concerned with the refining of mineral oils. The invention more particularly relates to an improvedprocess for the removal of objectionable sulfurr compounds from petroleum oils, particularly from petroleum oils boiling in the motor fuel and heating oil boiling ranges. In accordance 'with the present process objectionable sulfur compoundsas, for example, mercaptans are removed from petroleum oils containing the same by treating `the oil with an alkali metal plumbite solution under conditions to form oilvsoluble, preferably basic lead mercaptides. The oil containing the lead mercaptidesis then distilled under conditions adapted to remove overhead a distillate free of mercaptan and lead compounds. The bottoms fraction containing the soluble .lead mercaptides is treated in a manner to separate the lead which is usually accomplished by the addition offree sulfur or an equivalent means.

It is known in the art to renne petroleum oils by various distillation, cracking and `rfilated operations. For example, it is known to remOYe .objectionable sulfur compounds from `petroleum oils boiling in the motor fuel and heating .oil lboiling ranges utilizing various precedurevs. tOne operation comprises contacting the oil with a mineral acid, as, for example, sulfuric acid under conditions to remove .the sulfur compounds and other objectionable constituents. This Process, however, is not entirelysatisfactory, since the acid, suchfas sulfuric acid, also tendsto remove desirable constituents which have relativelyhigh octane numbers. Another conventional operation employed for the removal of mercaptan compounds is to contact the oil with a .so-called vdoctor solution which comprisesV a sodium vplumbite solution. The sodium plumbite .solution is generally prepared by saturating a to Baume sodium hydroxide solution with lead oxide.

In -this latter operation the mercaptans Vdissolved in the oil react with the sodium plumbite .under conditions to form oil-soluble neutral lead mercaptides. The spent doctor solution islseplarated and the oil is then treated in a manner .to remove therefrom the soluble lead compounds. This is accomplished by a number of procedures, such as by oxidation, by means of hydrgen peroxidaand the like. However, the conventional method is to add free sulfur under conditions to precipitate the lead as lead sulde, and to form the corresponding alkyl disuldes. The precipitated lead sulde is removed from thev oil which contains dissolvedtherein relatively innoGuOlls lvvliereinr 4the ligljiter boiling constituents Vthe ,doctor treating stage,

alkyl vdfisulndes.-Y This eperation, however. nos: sesses severaldisadveaieses @meer which, that the .precipitated lead, snode ,is fleesulent an@ rather diilculttc ,remore from the treated Oil. Another disadvantage is that it yis .desirable te add the theoretical amount ,of sulfur to the oil in order to precipitate the ,total quantity of Iead as ,lead sulfide.. 1f, an insuieient amount of sulfur be adderall. the lead. compounds ere 119i removed frcmthe eil which ,results .in the predueticn of an inferior product. having relatively poerproperiies.. Qn ine etherhand, if enexes of sulfur he added, the exeess sulfur 4remains 'dissolved in theoil which materially increases'the eerresiveness ef the eil.- .Eerthsrmere .the eficess sulfur dsselvedin the eil substantially de.-

creases the susceptibility ,0.f the 011 iowerdkiliksuppressing agents, such ,as tetraeihvl lead ,and the like. However., ,when .adding the vtheoretical correct amount efsillflllihe reaction reeeeds rather slowly and the .sepesiiy .O f the .sweetenmg equipment musibereleiivelv leise Ignorder to overcomethe disadvantages of these procedures, Various alternate Procedures' h've been suggested. o ,For example,` ithasbeen v`suggested that avdstiilation,stagebe employed in conjunction With-the conventional doctor treatins preses.4 slows-ver. an operation f this character, is'not satisfactory dueto thefact that when the oilvcont'aining lthe alkyl disulfides is distilled,

the disuldes tend to decompose, The sulfur compounds lareremoved overhead With'fthe oil, resulting inthevproduction of a product Whichis not satisfactory, It has also'been proposedrto distill the doibr-Washed oil while injecting steam into the still. `This, operation has not been successful, sincethe lead mercaptides tend tohydrolyzheninvthe presence of steam and l-an oil which isnotlsweet to the doctor test is recovered overbssd.

I have, howevennow discovered `that providing the oilgbecontactedwiztli a doctor solution in an initial stageundervspei-c conditions and then distilled'in l a y secondary ystage under restricted conditions, it is possible -to Vremove overhead'from the secondary stage a sweet idistillate Which may be employed a motorfuel. -The processvof my inventionrnay be read-ily understood byreference .to tne'attached drawing illustrating embodiments of the same, Yliigure lfill-ustrates a processwherein the total fraction boiling in thefmotorfuel boiling 4range, is vdoctor treated, While-Figure-2-illus` trates arpreferred adaptation ofthe invention by-,pass

Referring specifically to Figure l, it is assumed that the feed oil is a crude petroleum oil. It is also assumed that it is desired to produce a sweetened product having a final boiling point in the range from about 400 to 425 F. The feed oil is introduced into distillation zone I by means of feed line 2. Temperature and pressure conditions are adjusted in zone I adapted to remove overhead by means of line 3 constituents having a nal boiling point in the range from about 450 to about 475 F. and to remove by means of l Il line 4 constituents boiling above this range. The

vaporous product removed by means of line 3 Yisl condensed in zone 5 and introduced into separation Zone E wherein uncondensed constituents are separated from the condensate and removed overhead by means of line 1. The condensate having a final boiling point in the range from about 450 to 475 F. is mixed with a quantity of doctor solution which is withdrawn from doctor storage 9 and introduced into line 8 by means of line I0. The amount of doctor solution added is adjusted so that the mercaptans completely react with the doctor solution to form basic lead mercaptides. This is accomplished by utilizing an appreciable excess of doctor solution as compared to the oil. For the purpose of description it is assumed that 10 volumes of 20 Baume caustic solution saturated with lead oxide is used per volume of oil.

The mixture is passed through mixing zone I I and introduced into separation zone 22. In separation zone 22 the spent plumbite solution is separated from the lead-containing oil and is removed by means of line 23. The treated oil is removed from separation Zone 22 by means of line 24 and introduced into distillation zone I2.

Temperature and pressure conditions are adjusted in zone I2 so as to remove overhead by means of line I3 a vaporous product substantially ,completely free of mercaptan compounds and other objectionable sulfur compounds. For purposes of illustration it is assumed that temperature and pressure conditions in zone I2 are adjusted to remove overhead by means of line I3 a vaporous product having a final boiling point in the range from about 400 to about 425 F. The vaporous product removed overhead is passed through condensing zone I4 and introduced into separation zone I5 wherein the uncondensed con- -stituents are separated from the condensate and removed by means of line IS. The condensate is removed by means of line I'I and further refined and handled as desired. The bottoms are removed from distillation zone rI2 by means of line v I8 and passed into treating zone I9 wherein the lead mercaptides are treated in a manner to precipitate the lead. This is preferably accomplished by means of sulfur which is introduced by means of line 20. The lead sulfide is removed by means of line 2|, combined with the spent doctor solution withdrawn from zone 22 by means of line 23 and the mixture passed to regeneration zone 24 wherein the same is treated and recycled to storage zone S. The spent doctor solution is regenerated by separating entrained hydrocarbon from it by any suitable means, such as by centrifuging, and then blowing the solution with an oxygencontaining gas, such as air. Additional caustic or lead oxide may be added to replace alkali and lead which may have been removed during the treating operation.

Referring specifically to Figure 2 which illustrates a preferred adaptation of the present invention, the condensate removed from separation zone 6 by means of line 8 is introduced into a llead mercaptides.

`about 315 F. in distilling the Oil.

distillation zone 30 rather than directly into the doctor treating stage as illustrated in Figure 1. Temperature and pressure conditions are adjusted in distillation Zone 30 to remove overhead by means of line 3| the relatively lower boiling hydrocarbon constituents. The relatively higher boiling hydrocarbon constituents are removed from zone 30 by means of line 32 and mixed with a doctor solution which is introduced by means of line I0. The mixture is passed through doctor treating zone II and handled as described with .respect to Figure l, except that the overhead removed from distillation zone I2 is preferably combined with the overhead removed from zone 30. However, under certain conditions the overhead removed from Zone 3l) may be removed from the system by means of line S3. When operating as described with respect to Figure 2, the amount removed overhead from distillation zone 30 may vary considerably but generally comprises from about 20% to 60% of the total feed to the distillation zone.

The process of the present invention may be widely varied. It is to be understood that the respective zones may comprise any suitable number and arrangement of units. The process may be readily adapted for the removal of mercaptan compounds from any feed oil containing the same. Itis, however, particularly adapted for the removal of mercaptan compounds from petroleum oils boiling in the range from about F. to about 650 F., particularly from oils boiling in the motor fuel boiling range from about 100 F. to about 420 F. The feed oil may be secured from an initial distillation operation ormay be secured from thermal cracking operations, from catalytic cracking operations or from various alkylation and isomerization operations.

Although the feed oil to the doctor treating zone may boil in the range of the boiling range desired in the final refined product, in general, it is preferred that the feed oil entering the treating zone have a final boiling point at least 5 F., preferably from 25 F. to 50 F. above the final boiling point desired in the final refined product.

Although any alkali metal plumbite solution may be employed', in general, it is preferred that the solution comprise a sodium plumbite solution which is prepared by saturating a 10 to 30 Baume sodium hydroxide solution with lead oxide. The amount of doctor solution employed is suflicient so that the mercaptan compounds present in the feed oil will be converted to lead mercaptides, preferably to the basic lead mercaptides.

The doctor treated oil containing dissolved therein the soluble basic lead mercaptides is distilled under conditions to remove overhead an essentially mercaptan-free oil and to remove as a bottoms a relatively small stream containing the In general, the oil is distilled in a vacuum,y the pressure of which is in the range from less than l inch mercury absolute pressure to about atmospheric pressure. When treating oils boiling in the range from about 100 F. to about 450 F., the vacuum conditions are adjusted so that the temperature in the bottom of the distillation zone does not exceed about 250 F. and preferably is less than about 200 F., in the range from about F. to 175 F. When higher boiling oils, such as kerosene fractions, are being `treated in accordance with my invention, it may be necessary to employ a still temperature of It is to be understood that different conditions will be required for different oils. Thus, higher vdistillation temperatures will be required when kerosene or heating oils are being treated by my process than are needed for oils boiling in the gasoline boiling range. However, the distillation conditions are to be so adjusted by application of vacuurn so that decomposition of lead mercaptides is at a minimum.

The oil stream removed from the bottom of the distillation zone may be treated by any suitable means such as with hydrogen peroxide and the like ina manner to remove the lead compounds therefrom. The stream likewise may be treated with an excess amount of sulfur in order to secure a rapid precipitation of the lead sulde, since the relatively high boiling oil may be readily incorporated in fuel oils 'rather than employed in motor fuels. However, if desired, this relatively small quantity of oil may be treated with the correct amount of sulfur and a mercaptan-free and lead-free oil removed by means of line 25 and combined with the oil removed from zone I by means of line 26. Y Other adaptations of the present process may be employed. For example, the process may be readily adapted for the recovery of mercaptans from `the oil containing a high concentration of mercaptides by treating the same with a mineral acid. Furthermore, the leaded oil may be employed for the production of lead carbonate by blowing the same with carbon dioxide.

In order to further illustrate my invention the following examples are given which should not be construed as limiting the same in any manner whatsoever.

Example 1 Mercaptan-containing oils having a final boiling point of about 375 F. and about 400 F. were blended 'and the blend treated with a 50% excess by volume of doctor solution 'under conditions to form basic lead mercaptides. The doctor treated oil was distilled under vacuum conditions taking cuts overhead. The distillation operation was conducted under conditions wherein no steam was added during the time the iirst 10% out was taken overhead. Steam was employed in removing overhead the remaining 10% cuts. The first 10% cut was substantially freeof sulfur compounds while the remaining cuts contained sulfur compounds.

A second portion of the doctor treated oil was rerun without the addition of steam, and with the application of sufficient vacuum to maintain a bottoms temperature not exceeding 190 F. The rst 0 to 10% fraction was removed under atmospheric pressure. All fractions, up to 99% overhead, were sweet to the doctor test. The composite overhead condensate had a zero reactive sulfur test. No degradation in color was observed. The remaining '1% bottoms were also lfound to be doctor sweet and contained some heavy, dark sediment.

An voperation similar to that described was conducted except that the mercaptan-containing Vfeed 'oil was 'not treated with a doctor solution. Only the initial 0 to 35% overhead cut was found to be doctor sweet.

From the above it is apparent that a iini'shed product freed to the desired extent of objectionable sulfur compounds may be readily `produced by doctor treating the feed oil, followed by distilling the doctor treated oil undervacuum conditions in the absence of steam, wherein the ltempi-irature at 'the bottom of the distillation Zone is' maintained below about'200F.

Example 2 A petroleum oil boiling in the kerosene boiling range, containing 36 mg. of mercaptan sulfur per hundred m1. of oil and having a total sulfur content of 0.13 percent by weight was distilled under a maximum vacuum of 25 inches of mercury without the use of steam. The temperature at the bottom of the distillation zone did not exceed about 315 F., and a fraction comprising 0 to 95% of the feed oil was removed overhead. On testing this 95 per cent overhead fraction for mercaptan sulfur content, it was found to contain 33 mg. per hundred ml. of oil. The total suifur'content of this fraction was 0,115 per cent by weight. y

' Another portion of this kerosene feed was treated ywith a doctor solution in an amount so that about 44.5 per cent of the total lead meroaptides formed in the oil were basic mercaptides. The leaded oil was distilled under a. vacuum of 25 inchesof mercury (maximum) andl at 1a maximlum bottoms temperature of about 315 F. No steam was employed during the distillation. A fraction corresponding to 95 percent of the treated oil was taken overhead. This fraotion had a mercaptan sulfur content of only 0.6 and a total sulfur content ofonly 0.075 per cent by Weight.

' A portion of the 5 per cent bottom fraction was washed with .a dilute aqueous hydrochloric acid solution (of approximately 5 per cent by weight strength) to regenerate the mercaptan. The oil was washed free from acid with water. O n testing the bottoms fraction it was found to have a mercaptan sulfur content of 544 mg. per 100 ml. of oil.

Another portion of the kerosene stool; having a mercaptan sulfur contentof 36 mg. per 100 ml. was treated with doctor solution in suflicient lquantity so that 83.5fper cent of the total lead mercaptides in the oil werey in the basic form rather than as neutral mercaptides.

l 'Ihe leaded oil was distilled under a maximum vacuum of 25 inches of mercury Without employment of steam and a 95.6 per centfr'action was takenoverhead at a maximum bottoms temperature of 315 F. On testing'this 95.6 per cent fraction, it was found to be sweet to the doctor test and contained only 0.077 per .cent

by Yweight of to-tal sulfur.

It is apparent that when distilling a leaded oil under vacuum and employing steam very little if any reduction in veither mercaptan or total sulfur content is effected. On the other hand, when'the oil is leadedand distilled under vacuum without the use of steam substantially all of the oil' can be distilled overhead to obtain a product sweet to the doctor test and having a'mercaptan sulfur` and total sulfur content appreciably vlower than that obtainedl when distillingr under vacuum and employing steam. Itwill be further observed that when the Aoil is leaded with a Vsufficient amount of doctor solution so that the mercaptides formed are substantially in the basic form, vthe. reduction in mercaptan sulfur and ltotal sulfur content is appreciably greater and that these compounds may be substantially completely removed from the oil.

' A further advantage of this method of treating oil is that the mercaptans are concentrated inthe bottoms fractions, which fractions corg mineral acid, such as hydrochloric acid or sulfuric acid, whereby the lead lsalt is precipitated out of the solution and the mercaptans are'left in a concentrated form in the hydrocarbon fraction.

Example 4 In order to determine whether the lead might be recovered for further use such as in the paint industry or in the wood preserving industry, a portionof the lead mercaptide concentrate was acidiiied by contacting it with carbonio acid gas. A precipitate of PbCOs was thus obtained, which after thorough washing with a hydrocarbon fraction (boiling between 200 and 400 F.)4 was of a white color. Such a material is useful as a pigment in the paint industry. When it is desired to convert the lead mercaptide to alkyl disulfide, sulfur is employed rather than carbonio acid gas.

Example 5 A portion of the lead mercaptide concentrate was mixed with a slight excess of elementary sulfur and a concentrate of alkyl disulfides was obtained.

Ercample 6 A high octane cracked naphtha boiling in the motor fuel boiling range which had a mercaptan sulfur content of 21 mg. per 100 ml. of oil and a total sulfur content of 0.091 per cent by weight was distilled under a maximum vacuum of 25 inches of mercury at a maximum bottoms temperature of 250 F. without employing steam to obtain a 0 to 96.5 per cent overhead fraction. On testing this fraction for sulfur content it was found to contain l1 mg. of mercaptansulfur per 100 ml. and a total sulfur content of 0.068 per cent by weight. y

A second portion of the charge stock having a mercaptan sulfur content of 21 mg. per 100 ml. of oil was treated with an amount of doctor solution to form basic lead meroaptides. The oil was then distilled under a maximum vacuum of 25 inches of mercury and a maximum temperature of 250 F. without employing steam to obtain a 96.5 per cent overhead fraction. This overhead fraction was tested for sulfur content and was found to contain 1.5 mg. of mercaptan sulfur per 100 ml. of oil and 0.057 per cent by weight of total sulfur.

A third portion 0f the sour charge stock was doctor sweetened and the lead mercaptides formed in the oil were broken out using a slight excess of the theoretical quantity of the sulfur. The resultant sweet stockA was distilled under vacuum (25 inches of mercury) at a maximum bottoms temperature of 250 F. without employing steam to obtain a 0 to 96.5 per cent overhead fraction. This fraction gave a positive reaction to the doctor test and was found to contain less than 1 mg. of mercaptan sulfur per 100 ml. of oil; the total sulfur was 0.063 per cent by weight. l

From the above it is apparent that when practicing my invention, a product of appreciably lower mercaptan sulfur and total sulfur content may be obtainedl even though the oil is not sweetened prior to distillation as long as the critical conditions of distillation that I have specied are employed.

What I claiml as new and wish to protect by Letters Patent is:

l. Process for the removal of sulfur compounds from mineral oil fractions which comprises contacting the same in an initial stage with an alkali metal plumbite solution under conditions to form lead mercaptides, separating the oil from the plumbite solution and distilling the same in the absence of steam and under vacuum at a temperature below 250 F. in a secondary stage under conditions to remove overhead a sweetened product.

2. Process as defined by claim 1 in which said oil boils in the motor fuel boiling range.

3. Process as defined by claim 1 in which said oil passed to the initial stage has a iinal boiling point at least 5 F. above the final boiling point of the oil removed overhead in the secondary stage.

4. Process for the removal of mercaptan compounds from petroleum oils containing the same which comprises contacting a petroleum oil in an initial stage with an excess of sodium plumbite solution under conditions to form basic lead mercaptides, separating the treated oil from the partially spent sodium plumbite solution and distilling the same in a secondary stage in the absence of steam and under vacuum at a temperature below 250 F. under conditions to remove overhead a distillate free of mercaptan compounds and to remove as a `bottoms a relatively small quantity of higher boiling oil constituents containing dissolved therein the basic lead mercaptides, treating the bottom stream in a manner to remove the lead compounds therefrom, combining the lead compounds with said partially spent sodium plumbite solution and recycling the same to the systern.

5. Process as dened by claim 4, in which said feed oil boils in the motor fuel boiling range.

6. Process as dened by claim 4, in which the f iinal boiling point of the feed oil to the initial stage is at least 5 F. higher than the iinal boiling point of the distillate removed overhead in said secondary stage.

'7. Process as dened by claim 4, in which the lead compounds are removed from the stream withdrawn from the bottom of said secondary stage by the addition of excess free sulfur.

8. Process as defined by claim 4, in which the lead compounds are removed from the stream withdrawn from the bottom of said secondary stage by the addition of free sulfur controlled so that the oil withdrawn is substantially free of lead and contains no free sulfur.

9. A process for the removal of sulfur compounds from mineral oil which comprises preparing a fraction having a substantially higher final boiling temperature than is desired in the finished oil, treating the fraction with an alkali metal plumbite solution in water to form lead mercaptides, separating the oil from the plumbite solution, and distilling from the plumbite-treated oil under Vacuum and at a temperature below 250 F., a fraction having a iinal boiling point lower than that of the fraction rst separated, to take overhead a substantially sulfur-free distillate and leave behind as bottoms a solution of mercaptides in heavy oil.

10. A process for the removal of sulfur compounds from mineral oil which comprises preparing a fraction having a substantially higher final boiling temperature than is desired in the iinished oil, treating the fraction with an alkali metal plumbite solution in Water to form lead mercaptides, separating the oil from the plumbite solution, and distilling from the plumbite-treated oil under conditions of reduced pressure and at a temperature below 250 F., a fraction having a nal boiling point lower than that of the fraction rst; separated, to take overhead a substantially sulfur-free distillate and leaving behind as bottoms a solution of mercaptides in heavy oil.

11. A process for the removal `of sulfur compounds from mineral oil which comprises preparing a fraction having a substantially higher nal boiling temperature than is desired in the iinished oil, treating the fraction with an alkali metal plumbite solution in Water to form lead mercaptides, separating the oilfrom the plumbite solution, and distilling from the plumbitetreated oil under conditions of reduced pressure, freedom from Water and temperatures below about 250 F. and below that at which serious decomposition of mercaptides occurs, a fraction having a nal boiling point lower than that of the fraction rst separated, to take overhead a substantially sulfur-free distillate and leave behind as bottoms a solution of mercaptides in heavy oil.

GEORGE R. GILBERT.

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