1.ApplicationNumber: US-37219953-A
1.PublishNumber: US-2768929-A
2.Date Publish: 19561030
3.Inventor: CAPELL ROBERT G.
WRIGHT JAMES H.

4.Inventor Harmonized: CAPELL ROBERT G()
WRIGHT JAMES H()

5.Country: US
6.Claims:

7.Description:
(en)United States Patent REFINING OF SULFUR BEARING MINERAL OILS WITH DIALKYLPOLYSULFIDE Robert G. Capell, Pittsburgh, and James H. Wright, Penn Township, Allegheny County, Pa., assignors'to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application August 3, 1953, Serial No. 372,199
8 Claims. (Cl. 196-24) This invention relates to refiningof sulfur bearing mineral oils and more particularly to treatment of crude or I,
refined mineral oils or components thereof which contain sulfur determinable as elemental sulfur, in order to reduce the sulfur content of the oils and otherwise to provide a product of improved quality. v ,7
Sulfur may exist in elemental as well as combinedfor'm in a variety of mineral oils, including both crude'rnineral oils and fractions thereof. By way of example, it may be mentioned that elemental sulfur has been heretofore observed in distillate fractions of petroleum oils. This sulfur has hitherto been considered to result largely from the oxidation of hydrogen sulfide dissolved in the fraction, rather than from the presence of elemental sulfur in the original crude oil from which the fraction was derived. However, recently completed investigations have shown that elemental sulfur may be present in certain crude.
petroleum oils. It is therefore possible that the sulfur found in distillate fractions has its origin in elemental resulting from the reaction of sulfur'and hydrocarbons,
is objectionable not only perfse, but also in view of 'the fact thatit maybe easily reoxidizedto thefhighly corrosive, elemental sulfur. i
More specific difficulties resulting from thepr esenc e of elemental sulfur (or compounds derived therefroml in crude or refined mineral oils are corrosion of pipe lines,
of storage vessels, and of distillation and other refining facilities." Catalysts contacted bysuch oils during'process ing of the latter may lose activity at an accelerated rate. Sulfur-bearing lubricating oils or greases may lead to corrosion of lubricated bearing surfaces. Sulfur-bearing fuels, e. g., gasoline, kerosene and diesel oils, mayexhibit a strong. tendency toward haze and gum formation. Also, the lead-susceptibility of such gasolines is'often low. The combustionproducts of such fuels may also lead to corrosion of metal surfaces contacted thereby. 1" f Although aqueous solutions of alkali metal or alkaline earth polysulfides may be used in treating certain elemental sulfur-containing oils, such inorganic polysulfides are relatively inefficient as regards the extent of sulfur removal; In addition, use of .such solutions, particularly those of relatively high concentrations, may lead to the formation of highly stable emulsions and/or foaming of the treated oils, and the serious difiiculties attendant thereto.
I It is a primary object of this inventionto-provide a simple and highly efficient process for refining mineral tion.
able.
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oils containing objectionable amounts of sulfur determinable as'elemental sulfur. Additional objects are to reduce maintenance costs, due to corrosion by'sulfur and sulfur compounds, for pipe lines, storage facilities, and distillation and other refining equipment. Otherobjects are to reduce the corrosivity of, and to improve the odor, the stability, and the over-all quality of mineral oils which have been treated according to the herein disclosed inven- A detailed object ofthe invention is to provide a processof the kind indicated which will not lead to the formation of highly stable emulsions. I I
These and other objects are achieved by our invention which relates to a process for refining a mineral oil containing sulfur determinable as elemental sulfur. Briefly,
the process includes the steps of contacting a mineral oil of this kind with an organic'polysulfide which contains at least one linkageper molecule of the kind Sn',.-n
being an integer of at least 2. After the contacting is completed, desulfurized oil is separated from the mixture 'under 'conditions at Whichthe organic polysulfide and "the oil "are'su'bstantial'ly immiscible. 5
Althoughthe foregoing description is fullyindicative of the'nature of the invention to those skilled in the art,
which contain sulfur determinable as elemental sulfur. Such sulfur is determinable by the polarographic method,
the procedure for which is described in detail in the article entitled Elemental sulfur in crude oil by Eccleston, Morrison and Smith appearing in the Analytical Chemistry, vol. 24, November 1952, at page 1745 et seq. Sulfur determinable as elemental sulfur by the polarographic -method may include loosely combined sulfur which acts as elemental sulfur, as Well as elemental sulfur itself. Theinventiomof course, includes treatment of mineral oils containing such combined sulfur, as well as elemental sulfur. j
Thus, the process of this invention may be applied to sulfur-containing mineral oils of the above-identified :type,
"whether crude orrefined, and including not onlyicrude petroleumoils and fractions thereof, such as gas oil, kerosene, naphtha, gasolines, LPG, topped crudes, fuel oils, lubricating oils, bright stock, and individual hydrocarbon -.oil constituents of the foregoing oils, e. g., ben,zene, heptane, decane and the like, but also sulfur-bearing oils 'obtained from the liquefaction of various coals, or oils obtained from the destructive distillation of coal or oil shale. The invention is especially important as applied to petroleum oils, since the normal usage of such oils renders malodorous and corrosive characteristics highly undesir- The invention is of particular utility in treating sulfur-bearing, crude petroleum oils, since such oils normally contain .greater'concentrations of sulfur determin able as elemental'sulfur than distillate oils derived therefrom. Accordingly, damage toequipment from such sulfur is potential-1y greatest in the instance of such oils.
. As previously indicated, satisfactory treating materials for the purposes" of this invention are organic polysulfides -containing at least one -Sn' linkage per molecule,
where n is an integer of at least 2. Such polysulfides apparently combine with elemental sulfur through a mech- I anism not fully understood to form compounds or' complexes corresponding to higher polysulfides, i. e., poly- .sulfides having a greater number of sulfur atoms'pe molecule. I I
Taking up the polysulfide treating materials in more detail, it is essential for the purposes of this invention that t y ibe Qr anienely u i l s Alt u h taqueeusi qli t e of inorganic sulfides and polysulfides are capable of removing sulfur from petroleum oil, it has been found that organic polysulfides are distinctly superior to such inorganic polysulfides, especially insofar as completeness of elemental sulfur removal is concerned. Moreover, our organic polysulfides are normally used in substantially anhydrous form, thereby avoiding appreciable formation of highly stable emulsions.
It is also necessary for the purposes of this invention 7 that thetreating agent be a polysulfide, i. e., disulfides or higher polysulfidesmust be employed. The use of polysulfides is essential tothis invention, since, unlike inorganic monosulfides, organic monosulfides exhibit little .Qr. .110. ii r. lem tal s l ur P actical tre C OI IClllQlO DS Forthis reason'thqactive, elemental sulfurabsorbing linkages are thosein which n is an t e vf at estl-ii,
A has been ndicat wetr et ng e t ui e e -the r es 9 thisf nten e a these rg ni p y- ,i fit e tt i h. a e. S bs nt ally i s u en r. mmis e si /1th ag lbe nstr e d a the con ions. ofisep a I2 ad tiam, o cou se} th polys lfi ee e emal sulfur Product also should .beim eral -,9i1-ins lu 2le.-u d the a a s t g s. .11 ener l, eoil-so ubi ty haracterli i s 9 bffifil de d f in on y iu en m er of s f r n qms per. mql s ar s b n a y the. s m
This conveniences the separation of oil from unreacted and ,r aet d i fiatin m e a since c ndi o t w h the ,unreacted polysulfide is immiscible with the oil are also those at which the reacted polysulfide is immiscible with t l, r i
Organic polysulfides which are substantially mineral ,oi-l-insoluble at, atmospheric temperatures are distinctly preferred for economic reasons. However, the invention includes the use. of polysulfides having appreciable mineral .oil solubility at the contacting conditions, so long as these polysulfides are substantially mineral oil-insoluble at the separation conditions. In such instances, it is necessary to adjust the conditions ofseparationin accordance with conventional principles to reduce the solubility or miscibility of the materials to the desired degree, Thus, the
oil-solubilityor miscibility of the materialsjmayfbe 'reduced, for example, byrcducingthetemperature'of the oil being treated, or by addition of an extraneous materia'lto produce asort of salting out1of the polys'ulfide (and it sadjditlion product with sulfur) from the oil.
T he property of oil-insolubility or immiscibility for'the l polysulfides isof gr eat importance, since it is by virtue ofith s property thatphysical separationof thetreated oil fl q h u ur-beari g m rials is effected. Thisseparatl0l dlstipguishes the subject invention from many 'sul- I fur reat ng procedures which do, not remove sulfurous.
components, from the oil, but merely transform them.
7; Acccrdmgly, suitable iorganic' polysulfides are aliphatic pable of imparting ,mineral 'oil-insolubility to the'compound,,and where n is at least 2. "Theorganic radicals attached to. the;Snlinkages maybe aliphatic or arornati'c. and. identical or dissimilar.
They also may, and normally :will, contain substituents, unsaturated linkages,
and/ or elements other than carbon and hydrogen, includingnitrogen, halogens, sulfur, oxygenor phosphorous, -yvhich do notmateriallyinterfere with the. sulfur-combining properties of the polysulfide linkage,'and which do not impart appreciable oil-solubility to the over all'come pound. Organic disulfides of. the type indicated are especially advantageous,'not only because of their g eater ayailahility, relatiyely lower cost, and ease of reaction with elemental sulfur, but also because the disulfides possess greatest capacity for taking up elemental sulfur. Specific examples of polysulfides which are suitable for the purposes of this invention are organic disulfides such as diacetyl disulfide, dithiodiglycol, i. e., bis-( 8- hydr'oxye'thyl) disulfide, or 2,2-dithiodiethanol,' formamidine disulfide, thiuram disulfide, "tetramethylthiuram di lfide blew-a n rr i nie a dlfil fid (swin 'and esters thereof, especially lower' alkyl esters, bis-(p- ,nitrophenyl) clisulfide, dinitrobenzyl disulfide,-dibenzoyl disulfide, alkyl dithiocarbamates, bis- (nitr'ophenoXythionophosphorus) disulfide; trisulfi des such as bis (nitro-ptolyl)"tris'ulfide;"tetra'sulfides corresponding to the diand trisulfides mentioned above, and in addition, various proprietary poly'sulfide fubberswhich' are, in essence, polymeric tetrasulfides, e. g.,
Thiokol A cnzouz srqn Particularly preferred are the'bis-(alkanol) disulfides, and especially those wherein thealk anol substituents contain five or less'ca'rbon atoms of which dithio digly'col is representative. c c
u The compounds listed above are representative of the various classes of p'olysul fi des which are eifectiveitreating agents in the process of this invention. Certain of the named compounds can be obtained commercially, as, for eXample,"dithiodiglycol or the polysulfide rubbers; thei re mainder can be easily prepared by conventional methods.
In this connection, it'is considered that the preparation "of the: various polysulfides disclosed neednot be discussed in detail, since such preparation entirely con- I ventional, and since numerous such procedures have beendisclos ed in the literature. In the interest of clarity, -however, it will be briefly mentioned that organic poly sulfides in general may be prepared by reaction of organic I sulfates or halides with alkali metal polysulfides. V Higher poly sulfides may also be prepared by addition of ele fmenta l sulfur to lower polysulfides. Additionally, disulfides may be prepared by mild oxidation of mercaptans or I th ioph enols, including; substituted members from each I class. Trisulfides rn ay be prepared by'the reaction of thionylchloride or sulfuryl chloride with sulfhydryl com- :pounds. Tetrasulfidcs may be prepared by reacting sulfur chloride with mercaptans or thiophenols r I Our experimental work has shown that the organic polysulfides take up elemental sulfur eXtrernely'readily atordinary, atmospheric :temperatures and otherwise achieve ahigh degree of sulfur removal, Thusyusually satisfactory processing temperatures are the normally encountered' atmospheric temperatures, e g., those betwjeeniabout 40" about F. Somewhat lower for higherctemperatures can be used, if desired. Where vsulfur removal tends to be sluggish or relatively incomplete, an iimprovement inre sultsusually can he obtained :by moderate heating of the oilpolysulfidemixtur c, e g., tobetween about 100? and about F., preferably in ,admirrture with a small monst r a nitrogenbase cata lyst, e. g., amomniaora ba sic amine. I z The treatment contact timel and the oil;polys ulfide ratio,may vary quite widely, depending largely on the type of contacting p-rocedure employ ed. Thus, it has been 'found that batch agitation of less than :5 by volume polysulfide with an oil containing substantial proportions of elemental sulfur 5 for as little as five minutes was entirely adequate to eff ect subs tantiallycomplete removal of elemental sulfur from the oil, The invention, of course, includes the use of shorter or longer contacttimes Under certain conditions, as in -the in stance of afi'ioilzhaving a veryzhigh' elementals f t QI tent, or in the instance of an extremely low polysulfidezoil ratio, a somewhat longer contact time, e. g., up to.say,' 60 "minutes or more, may be desirable.
Although low polysulfidezoil ratios have been found satisfactory, it is not necessarily implied that low ratios are always to be preferred. For example, in procedures involving a solid contact material, e. g., percolation of the sulfur-bearing oil through a particulatebed of polysulfide, or contact filtration utilizing a particulate material, the quantity of polysulfide contacted by a particular portion of oil may be quite large. The same would be generally true in instances of continuous oil desulfurization using liquid polysulfides, e. g., such as would result from the use of continuous liquid-liquid contacting means. However, it should be noted that from the standpoint of total oil contacted by polysulfide, the po'lysulfide:oil ratio in the instances noted above would be considerably lower. I a I As indicated in connection with the, previous description of the invention, the polysulfide and oil are separated following the desulfurization treatment. In the instance of liquid polysulfides this may be accomplished by utilizing to advantagerthe immiscibility of the materials and the difference in their specific gravity. Thus,- separation may be carried out in a batch-wise fashion, as by gravity settling, or continuously, as with centrifugal separators, or alternatively, as with time-settling tanks used in concurrent contacting, i. e., tanks of sufficient volume to provide the desired settling time while streams.
of separated materials are continuously withdrawn from the top and bottom of the tank, or the combination contacting and separating tanks used in liquid-liquid countercurrent contacting. Moderate heating of mixtures containing heavy oils may facilitate separation by reducing the viscosity of the oil. Where the solubility of the polysulfide is increased materially by heating, or inother instances, it may be preferred to reduce the viscosity of the oil by dilution. In the instance of relatively oilsoluble polysulfides for desulfurizing oils, the oil temperature is reduced during separation.
to organic polysulfide molecules must ultimately result in the saturation of the latter with respect to elemental sulfur. At this stage, or at any more convenient previous stage of partial saturation, it may be desirable to effect regeneration of the saturated or partially'saturated polysulfides to lower, less sulfur-saturated polysulfides. This may be accomplished by conventional methods; thus, for example, pentasulfides and tetrasulfides may be regenerated to trisulfides by distillation. Disulfides can be regenerated from trisulfides and higher polysulfides by acidification of the polysulfides to be regenerated (e. g., to a pH of about 6 or lower), and moderate heating, followed by extraction of the polysulfide with a hydrocarbon solvent or carbon'disulfide to remove sulfur from the polysulfide. Alternatively, the extraction may be carried out with water, alcohols, glycols, ketones orthe like to remove the polysulfide from the sulfur.
Although regeneration of the polysulfide may be desirable, it is not essential and may be dispensed with,"if desired. In such instances, the exhausted polysulfide may be merely replaced with fresh polysulfide.-
Although disulfides are preferred from the standpoint of 'sulfur capacity, trisulfides are preferred in regenerative processes, since they are more highly stable than other polysulfides. In such instances, the trisulfide may be sulfided to any desired degree and is thenregenerated to the trisulfideform. r 1
The principles of the subject invention :may be utilized in producing and recovering elemental sulfur from mineraloils. .Inthis modification, a mineral oil, e. g.,. a crude petroleum oil, is contacted with a suitable organic polysulfide, e. g., dithiodiglycol, and separation is effected as indicated above. After the desired degree of sulfursaturation of the polysulfide has been reached, the poly- As is obvious, the step-wise addition of sulfur atoms.
a the dithiodiglycol would be a multiple of that illustrated sulfide-sulfur product is regenerated as described above, and elemental sulfur is separated therefrom by one of the extraction methods disclosed or other suitable. separation procedure. The regenerated polysulfide is then recycled to the contacting step Where it is again used to remove sulfur from fresh, sulfur-bearing oil.
Various advantages of the invention may be more easily understood by reference to the following specific examplesf Example I Two hundred and fifty parts by volume of a McElroy (West Texas) crude petroleum oil containing sulfur determinable as elemental sulfur by the polarographic methodwas agitated with 60 parts by volume of dithio-- dig'lycol for five minutes at room temperature, following which the mixture was allowed to settle; After separation ofthe mixture by decanting, the oil'was analyzed for elemental sulfur. The extent of elemental sulfur removal obtainedis indicated below:
Percent Before After Elemental Treatment Treatment Sulfur Removed Total Sulfur, Percent by Weight- 2. 45 1:99 Elemental Sulfur .percent 0. 443 0. 0318 93 The odor of the desulfurized oil was noted have changed from foul to sweet following the treatment.
Example 11 Percent Crude Oil Elemental Sulfur Ori inal O. 443 First 95 parts aliquot 0. 0361 Third 25 parts aliquot. 0. 0404 Fifth 25 parts aliquot 0. 0410 At the-end of the experiment the sulfur content of the dithiodiglycol was approximately 8% by weight. A still greater capacity for elemental sulfur is indicated by the fact that the portion of elemental sulfur absorbed by the dithiodiglycol in this experiment corresponds to less than one mol of added sulfur per mol dithiodiglycol. Accordingly, the theoretical capacity for elemental sulfur by in the foregoing experiment] Example III The reduction of co-rrosivity of sulfur-bearing oils by our process was illustrated by subjecting a sample of a West Texas pipe-line crude oil having atotal sulfur .co 1 1-- tent of 1.47 and-an elementalsulfur content of 008 72% by weight before treatment and a sample of the McEl-roy greases.
details of-whi'chare well known to: those skilled in the art. However, in order that the results-indicatedabove may be easily evaluated, it may be mentioned briefly'that the-test involves immersion of a polished copper strip in a sample of the oil being tested followed by heating of the sample at a selected temperature and for a selected time characteristic of the material being tested. At the end of the test the copper strip is removed and compared with a reference strip. The tested strip is rated according to its appearance with a number 0, l, 2, 3, 4 or 4+ for. various degrees of corrosion. The foregoing numbers correspond respectively to no tarnish, slight tarnish, moderate tarnish, dark tarnish, slight corrosion and pronounced corrosion.
The copper strips employed in the testing of the samples mentioned abovereceived the rating indicated in the tabulation below;
MeElroy West Texas Crude Crude Before After Before After Treat- Treat- Treat- Treatment ment ment ment ASTM D-130-5QT, 3 hours, 122 F... 4+ 4+ 0 The results of this test indicate that the corrosion-causing materials in the oil have been effectively eliminated.
Example IV The suitability of the present invention for removing elemental sulfur from low-boiling hydrocarbons was illustrated by agitating a benzene solution containing 1.3% elemental sulfur with approximately 25% by volume of dithiodiglycol for about five minutes and allowing settling to take place. The degree ofdesulfurization obtained is indicated in the results presented below:
Benzene Benzene Percent Before After Elemen- Treat- Treattal Sulfur ment ment Removed Percent Elemental Sulfur 1, 30 0.0618 95 Example V Before After Percent 'Ireat- Treat- Elemenment ment; ta l Sulfur Removed Percent Total Sulfur 2. 44 2. 08 67 Percent Elemental Sulfur 0. 443 0.141 67 The-percentsulfur determinable as elemental sulfur for the samples tested in each of the foregoing examples was determined by the Eccleston polarographic method, cited supra.
As indicated inthe foregoing examples, treatment of elemental sulfur-containing"mineral oils according to the process of tiiis invention provide not only a material reduction in elemental sulfur content, but also an improvement' in odor, and a reduction in corrosivity of the oil. As further shown, the use of orga'nic polysulfides produces markedly superior'results 'as compared withthe use of inorganic polysulfides, It is to be understood that other organic polysulfides of the type disclosed herein can be'esubstitut'ed for themorganic polysulfide employed in the foregoing illustrative. examples. 1
The invention is not-limited to the use of any particulan contacting apparatus: As indicatedabove, the desulfurizationumaybe carried out. by batch agitation of -oil and polysulfide; or substantially continuously by percolation of. the sulfur-bearing oil through a bed of particulate, solid polysulfideor liquid polysulfide supported on a particu late carrier, e. -g., pumice, clay, or the like, or by liquid polysulfide extraction in any efiicient liquid-liquid contacting apparatus, either of the concurrent or countercurrent type. These and other commonly utilized contacting and separating-systems may be employed with-ap-- propriate adaptation to the requirements of the particular materials utilized in this process. Such systemsform-nopart of this invention and need, not bedescribedin detail. Inpassing, it is tobe noted that small portions ofpolysulfide which remain in the oil following separation there-- of maybe'removed, if desired-by solventextraction of the oilwith water or other oil-immiscible solvent for the polysulfide.
Th'e-above-described invention produces a distinct improvement in the quality of the oil products produced. Costs of maintenance due to corrosion by sulfur and sulfur compounds of-distillation equipment, other refining equipment; and pipe line andstorage facilities are reduced greatly by the use of the invention.
Numerous variations of the subject process may be re-- sorted to without departing from the spirit of the invention." Accordingly,-only such limitations should be imposed thereon as are indicated by the appended claims.
We claim:
1. A process ofrefining a mineral oil-which contains sulfur determinable as elemental sulfur, comprising contacting saidoil with an organic polysulfide desulfurizing agent that 'is normally substantially insoluble in said .oil. and which contains at least one linkage per molecule of the kind Sn--, where n is an integer of at least 2, and then separating an oil phase of relatively reducedsulfur content that is substantially free from said desulfurizing agent-from an oil-insoluble, organic polysulfide-containing phase-of relatively-increased sulfur content.
2. A-process of refining a crude'petroleum oil which contains-sulfur determinable as elemental sulfur, comprising contactingsaid oil-With an organic polysulfide desulfurizing agent that is normally substantially insolublein said oil and which contains at least one linkage per. molecule of thekind -Sn where-n is an integer of at least 2, and then separating an oilphaseof relatively reduced sulfur content that is substantially free-from said desulfurizing agent from an oil-insoluble, organic polysulfide-containing phase of relatively increased sulfur content.
I 3. A process of refining a mineral oil which containssulfur determinable as elemental sulfur, comprising con-- tacting said-oil with analipha-tic organic polysulfide def sulfurizing agent which .is normally substantially insoluble insaid oil and which contains at least-one linkage per molecule of the kind 'Sn, wheren is 2, and thenseparatingan-oil phaseof relatively reduced sulfur content that-is substantially free from said-desulfurizing agent from an oil-insoluble, organic polysulfide-containing phase of relatively increased sulfur content.
4. A process of refining a mineral oil which contains sulfur determinable as elemental sulfur, comprising contacting said oil with a bis-(alkanol) polysulfide desulfurizing-agent which'contains at least one linkage per molecule of the kind Sn, where n is 2, and which is normally substantiallyv insoluble in said oil, and then separating an' oil phase of relatively reduced sulfur content that is substantially free from said desulfurizingagent from. an oil-insoluble, organic polysulfide-containing phase of relatively increased sulfur content.
'5. 'A process of refining a mineral oil which contains sulfur determinable as elemental sulfur, comprising-con-' 9 tacting said oil with dithiodiglycol, and then separating an oil phase of relatively reduced sulfur content from an oilinsoluble phase.
6. A process of refining a crude petroleum oil containing sulfur determinable as elemental sulfur, comprising contacting said oil with dithiodiglycol, and then separating an oil phase of relatively reduced sulfur content from an oil-insoluble phase.
7. A process of refining a mineral oil which contains sulfur determinable as elemental sulfur, comprising contacting said oil with an organic trisulfide desulfurizing agent that is normally substantially insoluble in said oil and which contains at least one linkage per molecule of the kind -Sn-, where n .is 3, separating an oil phase of relatively reduced sulfur content that is substantially free from said desulfurizing agent from an oil-insoluble, organic polysulfide-containing phase of relatively increased sulfur content, subjecting sulfur-enriched material obtained from said separating to a regenerative treatment to liberate elemental sulfur and said trisulfide, separating the sulfur from the trisulfide and again contacting addi- 10 tional mineral oil with the recovered trisulfide as described. 8. A method of refining a mineral oil and recovering elemental sulfur from mineral oil containing sulfur determinable as elemental sulfur comprising contacting said oil with an organic polysulfide desulfurizing agent that is normally substantially insoluble in said oil and which contains at least one linkage per molecule of the kind -Sn-, where n is an integer of at least 2, separating an oil phase of relatively reduced sulfur content that is substantially free from said desulfurizing agent from an oilinsoluble, organic polysulfide-containing phase of relatively increased sulfur content, subjecting sulfur-enriched material obtained from said separating to a regenerative treatment to liberate elemental sulfur, and then separating the thus liberated elemental sulfur.
References Cited in the file of this patent UNITED STATES PATENTS