US2776250A - Fractionation of crude petroleum oil - Google Patents

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United States "Patent FRACTIONATION 0F CRUDE PETROLEUM OIL :Robert G. Capell, Clarence Karr, Jr., and William D. Weatherford, Jr., Pittsburgh, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application June 24, 1952, Serial No. 295,354

3 Claims. (Cl. 196-147) The present invention relates to the fractionation of crude petroleum and more particularly to a method of separating the constituents of crude petroleum on the basis of molecular types by chromatographic fractionation.

The frictionation of crude oil by distillation has a number of disadvantages. For example, fractional distillation separates the crude constituents according to boiling points or molecular weights rather than according to molecular types so that it is impossible by distillation alone to obtain from most crudes, motor fuel fractions or cracking stock fractions free from undesirable substances such as sulfur compounds or metal compounds boiling in the same temperature ranges as the desired fractions. Consequently in conventional refinery operations, it is necessary, following the recovery of desired fractions by distillation, to subject such fractions to further refining for the removal of undesirable materials which distill with the desired materials. Molecular types such as sulfur compounds, diolefins and active monoolefins formed on distillation, aromatics, metal compounds, and asphaltic and resinous materials are distributed among several of the distillation fractions. Relatively expensive and complicated procedures must be applied to each of the fractions to separate the desired types from the undesirable ones. Thus it is conventional to subject gasoline fractions to copper sweetening to convert mercaptans to less obnoxious sulfur compounds or to processes for the removal of sulfur. In the case of kerosenes it is the usual practice to remove aromatics by sulfur doxide extraction or by. heavy acid treatment. When gas oils charged to catalytic cracking units contain metals, these metals deposit on the cracking catalyst and can have an adverse effect. posits, unlike coke deposits, cannot be removed by oxidative regeneration, and it is therefore desirable to prepare metal-free cracking stocks. Lubricating oil stocks are subjected to several refining processes to produce salable lubricants.

Another characteristic of distillation fractionation which is frequently undesirable is the resulting thermal decomposition of at least some of the crude oil constituents. In fractionating a crude oil into several fractions by distillation fractionation, it is impossible to recover many of the valuable chemicals of the crude petroleum in their natural state because they are thermally decomposed under the conditions necessary for this type .of distillation.

Our present process has none of the indicated disadvantages of fractional distillation. By our process it is possible to separate the constituents of a crude oil ac- ..cording to molecular types and obtain fractions which .consist essentially of compounds that occur naturally in .crude oil, that is, compounds which have undergone no thermal conversion during the fractionation process, and it is possible to separate compounds which are desirable a particular refinery product from those which are un- Such metal de- I 2,776,250 i atented Jan. 1, 1957 desirable. Thus, for example, by our process it is possible to obtain from a total crude oil, fractions such as: essentially pure paraffins; essentially pure mononuclear aromatics; essentially colorless, sulfur-free, oxygen-free and metal-free hydrocarbons; sulfur compound concentrates which are essentially asphalt-free and metal-free; sulfur compound concentrates which are essentially color less and metal-free; and mixtures which are rich in sulfur, asphalt and metals. Certain of these fractions are ideal sources of motor fuels, cracking stocks, lubricating oil stocks, and other valuable products. Other of the fractions have importance from the petro-chemical point of view since they contain high concentrations of valuable naturally occurring petroleum compounds.

We have discovered in accordance with the invention that crude oils can be separated into a plurality of valuable fractions without substantial destruction of the compounds existing in the crude oil by subjecting the crude oil to elution chromatography as described more fully hereinafter. An important feature of the invention is based upon the discovery that an alumina adsorbent material, especially bauxite, is markedly superior to other adsorbents for the fractionation of crude petroleum oils.

Our process in genera-l comprises passing into contact with a bed of adsorbent material selected from the group consisting of activated alumina and activated bauxite a liquid comprising at least about 25 percent by volume crude oil in an amount which penetrates no more than about percent of the adsorbent bed. The bed is then contacted with a series of eluant liquids of successively increasing eluting powers. Each eluate is collected as it emerges from the bed either as one fraction or in a number of successively collected portions to obtain fractions of unconverted natural petroleum compounds.

An important element in our process is the maximum quantity of oil to be fractionated which can be charged to the adsorbent bed. In other words, the ratio of charge to adsorbent is important. This ratio is important because if an excessive volume of charge is introduced to the column, the fractionation will begin as a percolation process and it will be impossible to obtain sharp unmixed fractions which are obtainable by our process. To avoid mere percolation of any of the oil, it is necessary that the amount of charge be substantially less than the amount necessary to penetrate the entire bed. Therefore, when the charging of the crude oil is terminated and the introduction of the first eluant is begun, there must still be a portion of the bed which is unpenetrated by the charge oil.

In our process the liquid mixture comprising crude oil is introduced to the adsorbent bed at either extremity thereof in an amount which is insufiicient to penetrate the entire bed. The oil must penetrate no more than about 90 percent of the bed. There is no lower limit for the amount of oil that can be charged as far as obtaining sharp fractions in concerned. However, to use the capacity of the column most efficiently the amount should not be unreasonably small. In general, it can be said that the amount of oil charged should be that which will penetrate from about 5 to 90 percent of the adsorbent bed. It will be understood, however, that the extent of penetration within this range adapted to accomplish desirable fractionation will vary depending upon such factors as the specific composition of the crude oil, the particular adsorbent used, and the equipment employed. Accordingly, in many cases the process should be carried out in such manner that the charge oil penetrates substantially less than 90 percent of the adsorbent bed.

The simplicity and efficiency of our process are at their greatest when undiluted, untreated total crude oil is the charge mixture. However, in addition to total crude.

the charge stock for our process can also be topped or reduced crude oil, deasphalted crude, or mixtures of such stocks with total crude. The preparation of these stocks does not involve the use of distillations severe enough to cause any important decomposition of their valuable constituents, and it will be understood that when unconverted naturally occurring petroleum compounds are referred to herein and in the claims, the compounds present in topped, reduced or deasphalted crude oils are included. While it is generally unnecessary to dilute such stocks for fractionation by our process, it may be desirable to moderately dilute very viscous liquids so that they will pass readily through the adsorptive bed. Heavy stocks which might require dilution are total crudes of very high viscosity such as Mississippi crude, or topped or reduced crudes. The diluent can in general be any solvent for the crude oil which is not so strongly adsorbed in the adsorbent bed as to inactivate the bed for fractionating the crude oil. Suitable diluents include liquids such as hydrocarbons of the naphtha, kerosene, gas oil, or fuel oil ranges. Among the possible nonhydrocarbon diluents might be mentioned halogenated hydrocarbons or nitrobenzene. It is also possible to dilute ,a high viscosity stock with a lighter crude oil if desired. Still another possibility is the use of a low viscosity product of our process as the diluent.

Excessive dilution of the crude oil must be avoided because .the. adsorbent column capacity is inefficiently employed when a large amount of diluent liquid is added to the crude oil to be separated. It is not possible to specify proper degrees of dilution which will be suitable for all the heavy stocks because of the wide variations in viscosity of such stocks. However, the crude should not be diluted to a concentration below about 25 percent by volume. In more dilute concentrations than this, the maximum efficiencyof the column for fractionating crude oils is not obtained.

An important element of our process is the particular adsorbent materials employed because the class of adsorbents which we use is essential to the production of substantially sulfur-free, metal-free, oxygen-free and colorless fractions which are characteristic of our process. The adsorbent in our process is an alumina or bauxite. The adsorbent aluminas which can be used are those available commercially as alumina and which analyze 99.0 percent A1203 on a volatile-free basis and materials which consist predominantly of alumina such as those which consist of alumina and a minor amount of other compounds, such as silica. Bauxites, which can be obtained commercially in adsorbent form under such trade names as Porocel and Florite, are well-known products, and are activated by heat treating bauxite ores.

Theadsorbent is preferably employed in granulated form. We have found that excellent yields are obtained when the particle size is between about and 200 mesh. Very small particles are undesirable because the chilicultyof removing all of the charge liquid from the adsorbent bed increases as the proportion of fines increases. The adsorbent material is preferably disposed in an elongated vertical column. It is activated before use as by heating to an elevated temperature for several hours. The temperature of activation is not critical, but we have foundthat temperatures between about 250 and 1400" -F., and preferably between about 400 and 800 F, give good results.

Immediately following introduction of the crude oil charge, the development of the chromatogram is begun by introducing the first eluant liquid to the bed. This first eluant is chosen according to its elutive power to produce the typeof first fraction desired. To assist in the selection of the proper sequence of eluant liquids, they can be conveniently grouped according to their relative elutive'powers. The following table lists a suitable grouping of several typesof eluantliquids:

TABLE I Weak Eluants Moderate Eluants Strong Eluants n-pentane. hot weak eluant. hot moderate eluants. mixed pentanes. weak eluant modmoderate eluant petroleum ether. crate eluant. strong eluant. parafiinic mixture. carbon tetrachloride. 25% ethanol in benoyclohcxane. zene.

maphthenic mixture. ethanol.

benzene. methanol.

aromatic mixture. solvent polar compound. polar solvent.

If it is desired to obtain a first fraction which is substantially colorless, sulfur-free, metal-free, and oxygenfree, and adsorbent column should be first eluted with a weak eluant, such as one of those ofthe first column of Table I whch will not excessively elute undesired substances from the column. This is our preferred procedure. However, if a large first fraction is desired, e. g., a deasphalted crude, and there is no objection to its containing substances such as sulfur compounds, :1 moderately strong first eluant can be chosen, such as an eluant from the second column of Table I. The volume of the eluant employed in each stage depends upon the desired separation but is preferably at least about one to five times the volume of the charge liquid. Much larger volumes of eluant can be employed, of course, but without improving the fractionation to any important degree. Following the elution with a first stage eluant, the bed is contacted with a second stage eluant of stronger elution power to recover a second fraction and thereafter, if desired with a third eluant of still stronger eluting power to recover a third fraction. More eluants can be used if more fractions are desired. The final eluant, if desired, can be a strongly adsorbed liquid which acts as a displacer liquid to displace all remaining adsorbed substances from the adsorbent bed.

It will be noted from Table I above that a moderate eluant mixed with a weak eluant yields a moderate eluant, and a strong eluant mixed with a moderate eluant yields a strong eluant. Thus, the elutive power of a weak or moderate eluant is greatly increased by the addition of even very minor amounts of a stronger eluant. Accordingly, for the efiicient recovery of fractions of weak- 1y adsorbed substances such a paraflins, naphthenes, and mononuclear aromatics without the inclusion of more strongly adsorbed substances such as sulfur compounds it is important that the eluant employed be a weak eluant which is uncontaminated by any stronger eluant which would cause the elution of undesired substances with the weak eluant fraction. The mixture of two or more eluants having about the same order of elutive powers is not usually objectionable but the inclusion of even a very small quantity, e. g. 0.5 percent, of a strong eluant can form. a.mixture having a much stronger elutive power than the major constituents of weak elutive power. This principle governs the purity of eluants that can be used for elutingthe first fractions from the adsorbent bed. Thus, to obtain the total weak eluant fraction as a colorless, sulfur-free, and metal-free fraction, it is essential thatthe first eluant be a weak eluant such as a parafiin liquid which contains no appreciable quantity of stronger eluants-such as aromatics or polar compounds. The weak eluant can in most cases, however, consist of mixtures of paraffins. It is clear from these facts that it is important in .a cyclic process in accordance with our invention to recover the eluants from the products substantially uncontaminated by liquids with a higher order of eluting power before again using them as eluants in another cycle. The described effect of the addition of a strong eluant to a weak eluant has the advantage of making it possible to employ as the moderate or strong eluants, mixtures .which are predominantly relatively inexpensive paralfins and-.whichcontain only minor amounts, sufficient to give the desired eluting power, of more expensive stronger eluants such as aromatics or polar solvents.

The importance in our process of using first stage eluants which are unmixed with stronger eluants is related to the previously mentioned important element of the process, the maximum charge to adsorbent ratio. Thus if the volume of charge introduced to the adsorbent bed before elution is begun exceeds the capacity of the bed, the charge in the bell will in effect be eluted by the portion of charge which exceeds the capacity of the bed. Since the charge comprises a crude oil and therefore con tains substances which are moderate or strong eluants, the bed will be first eluted by a moderate or strong eluant. It is, of course, essential in our process that the bed be elutive by a series of eluants of successively increasing elutive powers and therefore the elution of the bed by a portion of the charge itself before the first stage elution with a weak eluant would make it impossible to obtain the proper fractionation of the charge. In addition, poor recovery of weakly adsorbed substances would result from elution with a portion of the charge itself, since these substances would be distributed throughout the bed owing to their presence in the entering charge.

As mentioned above, the alumina or bauxite adsorbent employed in our process can be an activated alumina adsorbent which is substantially pure alumina or one which consists predominantly of alumina or it can be the activated natural alumina, bauxite. We have discovered, however, that bauxite is especially valuable in the present process. We have found that when using bauxite, the separation between sulfur compounds and hydrocarbons free from sulfur is especially sharp. Thus, when activated bauxite is employed as the adsorbent material, we have found that a weak paraffinic eluant will not desorb substantial amounts of sulfur from the adsorbent. It is therefore possible in accordance with the invention to recover the entire eluate obtained with the weak eluant as a colorless, substantially sulfur-free and metal-free fraction which contains substantially all of the paraffinic, naphthenic and mononuclear aroma-tic compounds of the crude oil.

As described, it is possible in our process to separate a crude oil into a small number of fractions by recovering the entire liquid eluted by an eluant as a single fraction. However, it is usually preferred to take advantage of the differences in adsorbabili-ty of the crude oil constituents and collect the liquid issuing from the adsorbent bed in each elution stage in a number of portions. Thus, because of their differences in adsorbability certain types of compounds will emerge from the column first, and other types will follow successively depending upon their strengths of adsorbability. If proper cuts are made of the emerging liquid, it is possible to collect fractions of substantially single types of petroleum compounds. This technique can be applied to any of the elution stages of our process and has particular application in fractionating crude petroleum for the recovery of valuable petrochemicals.

We have found that a first-stage Weak paraffinic eluant will elute some sulfur compounds from alumina adsorbent bed. However, we have discovered that sulfur is not eluted by the paraffinic liquid uniformly throughout the Weak eluant stage, but rather that sulfur compounds begin to appear in the eluate only after a considerable quantity of eluate has emerged from the bed. We have also discovered that the occurrence of sulfur in the eluate corresponds closely With the occurrence of compounds which fluoresce in ultraviolet light. Consequently, We are able to collect a sulfur-free fraction by observing the fluores cence under ultraviolet light of the emerging eluate and separating the collected material when fluoroescence first appears.

cessively increasing eluting powers, for example, by ani eluant ffom the second column of Table I, and then by an eluant from the third column of Table I. In each of these elutions the volume of the eluant is preferably about one to five times the volume of the charge oil, although larger volumes of eluant can be used.

The fractionation process of our invention can be readily adapted to continuous or cyclic operation. In such a case, following the final elution with a strong eluant the adsorbent bed is purge-d of the strong eluant to prepare :for the next cycle. It is possible to remove centain final stage eluants from the bed simply by wash-- ing the bed with the first stage eluant for the next cycle.

However, other final stage eluants must be removed in. stages. Thus, for example, in a process employing n-pentane, benzene, and ethanol as the first, second, and:

third stage eluants respectively, it is impossible or impracticable to remove completely the ethanol remaining: in the bed after the final elution by merely purging the: bed with cold pentane. A suitable procedure is to waslr the bed with benzene after the ethanol elution to remove the ethanol and then with pentane to remove the benzene before commencing the next fractionation cycle.

At the start of our fractionation process, the adsorbent bed can be either dry or wet but it is preferred to prewet the bed with the first stage eluant or with a Weaker eluant before introducing the crude oil to be fractionated. Prewetting is desirable for several reasons. In a cyclic process it assists in removing from the bed the last traces bed is eluted with a series of additional eluants of sucof the final stage eluant of the previous fractionation cycle. Prewett-ing also causes the crude oil charge to penetrate more readily the adsorbent bed and reduces channeling in the bed. Still further, prewetting reduces or eliminates the heat of wetting when the crude oil is introduced to the bed. The heat evolved on contacting a crude oil with a dry adsorbent bed can raise the tempenature of particles of oil in contact with the adsorbent sufficiently to cause thermal decomposition of some of the desired constituents of the crude oil. Since one of the important advantages of our process is the fractionation of crude oil without thermal decomposition of its valuable components, it would thus be desirable to avoid introducing the charge to a dry bed if the heat of wetting would be such as to cause substantial thermal decomposition.

In the continuous operation of our process, a plurality of adsorbent beds can be employed so that the charge oil can be introduced to one or another of the beds at all times while the other beds are undergoing elution or purging. Small quantities of materials may be unremovable from the bed by the usual eluting solvents and in such cases the bed can at intervals be subjected to regeneration such as by burning to remove accumulated carbonaceous deposits.

We have fractionated several different crude oils by our process and also by unsatisfactory processes using nonalumina adsorbents, i. e. adsorbents other than bauxite or alumina.

Tables 1H, III, IV, and V below record the inspection data for the West Texas, McElroy West Texas, Kuwait, and Baxtervill-e, Mississippi, crude oils respectively which we have fractionated.

TABLE 11 West Texas crude Gravity, API at 60 F 35.2 Viscosity, F, centistokes 4.79 Sulfur, wt. percent 1.40 Chlorides, as NaCl, lbs./ 1000 bbl 21.8 ASTM distillation:

I.B.P 118 F. 10% 248 F. 20% 316 F. 30% 375 F., 45.3% over at 500 F.

40% 466 F., 58.1% over at 590 F.

BLE ontinu ASTM distillation:

TABLE 111 McElroy West Texas crude We have fractionated the West Texas crude oil of Table F FY DAPIO at II above in accordance with our process using granular Vlscosltyq activated alumina as the adsorbent and using four succemlstokes cessive eluant liquids: n-pentane, carbon tetrachloride, benzene, and a mixture of 25 percent by volume of ethanol l l" Percent: in benzene. The procedure followed is described in EX- ge gengf amplelbelow. chlorides, as NaCl, lbs/1000 bbl Nil Examplel ASTM distillation: The total undiluted West Texas crude oil was intro- P 0 R duced at the top of a column of 80-200 mesh activated 2 R alumina in the amount of about 0.15 volume of crude 5% 0 oil per volume of adsorbent. The charge penetrated 10% F about 35 percent of the bed. Immediately after lntro- 20% 0. duction of the entire crude oil charge, the column Was 30% F eluted by introducing at the top of the column about 9 40% 0 parts by volume of n-pentane per part of charge 011. 453% 0 F ,(obviouscmcking) The entire amount of liquid eluted In this stage was recovered as a single fraction. Following elution with TABLE n-pentane the column was eluted successively with about Kuwait crude equal amounts of carbon tetrachloride, benzene, and a Gravity at F 5 solution of 25 percent ethanol in benzene. In each stage Viscosity the entire eluate solution was collected as a single frac- Centistokcs 9:36 tion and the eluant was evaporated from the crude oil U S traction by heating the solution to 50-60 C. while sweepsulfur Wt Percent 259 mg its surface with a stream of nitrogen. In each stage chlorides, as Nacl, 1bs /1O00|bb1 of the chromatographic fractionation, the liquids were passed through the adsorbent column by gravity flow and AsTMdlstl'nat'lom O no channeling difiiculties were encountered. The frac- P 106 tionation was carried out at room temperature or about 10% 256 77 1; 392 The results of the Example I fractionation of the West Texas crude oil are recorded in Table VI below in terms 590 40 of the yields and characteristics of each fraction obtained. TABLE V It will be noted from Table VI that material losses were substantial. These losses resulted from the evapora- Baxtewllle Cmde tion of the light ends of the crude oil while separating Gravity, API at F 15.8 the eluant liquid from the crude oil fraction. The ad- Viscosity, F.: 45 sorbent bed after the final elution with the ethanol-ben- Centistokes 822.7 zene mixture had the same white appearance that it had S, U. S -e 3801.0 at the start of the process, thus indicating that the crude Sulfur, wt. percent 2.83 oil charge had been substantially entirely removed from Chlorides, as NraCl, lbs./ 1000 bbl '10 the bed.

TABLEVI Eluant. n-pentant CClt benzene 26% ethanol in benzene Mass Recovery:

Wt. Percent 01 Charge 48. 5 15.1 5. 3 6. 6

Total Wt. Percent 75. 5

Sulfur Content, Wt. Percent 0. '19 4. s4 5. 29 3. 72

Sulfur Recovery:

Wt. Percent of Sulfur in Charge 6.6 47. 4 20. 2 17. 7

Total Wt. Percent 91. 9

Appearance colorlessoiL. darl; orange. dark brown black tar. Odor pleasant"... tuiz fleasantn asg halticuu asplfialtitlrand p cue to. ititi iiiiiifiift t t fiiifi i fiiiiiii31111133333: 53% blue T Carbon Content, Wt. Percent... Hydrogen Content, Wt. Percent Oxygen Content, Wt. Percent Corrected Mass Recovery: I Wt. Percent oi charge. 73

1 All material losses were light ends.

From Table VI above it can be seen that our process produced a colorless fraction amounting to 73 percent 10 teristics of each fraction Obtained are given in Table VIIbelow.

TABLE VII Re- Corrected S S Recovery, Re- Content, covery, Fraction Wt. covery 1 Wt. Wt. Fluorescence Crude 011 No. Eluant Percent Wt. Percent Percent Appearance Odor Under U. V.

of Percent of of S in Light Charge of Fraction Charge Charge 1 n-petane 49. 7 64. 2 0. 08 1. 7 Grgofless Pleasant. None.

1 2 benzene 25. 4 25. 4 6. 32 67. 4 Dark orange Unpleasant Blue. McElroy Crude, 2.38% S 011.

, 3 25 vol. percent 10. 4 10. 4 5. 31 23. 2 Brown- Asphaltlc- Brown.

ethanol in black benzene. semi-solid.

Total Recovery 85. 5 100. 92. 3

1 n-pentane 40. 6 56. 4 0. 0.8 Colorless Pleasant. None.

01 2 benzene 30. 3 30.3 5.15 60.2 Brown oil Unpleasant Green-blue. Kuwalt Crude, 259% S 3 vol. percent 13. a 13v 3 6.05 31.1 Brown- Asphaltic... Brown.

ethanol in black benzene. semi-solid.

Total Recovery 84. 2 100. 0 92. 1

1 All material losses were light ends.

by weight of the crude oil charge based on corrected mass recovery calculations. This large fraction obtained from the high sulfur West Texas crude oil contained only 0.19 percent by weight sulfur and was oxygen free. The

pleasant odor of this eluate substantiates its low sulfur analysis. The carbon tetrachloride eluate contained 4.34

percent sulfur and thus had a high concentration of sulfur compounds. On an estimated average molecular weight of 446 for this carbon tetrachloride eluate, the

calculated sulfur compound content is about 60 percent, assuming one sulfur atom in each sulfur compound molecule. Therefore, this eluate is a valuable source of sulfur-containing chemicals. The benzene eluate contained 5.29 percent sulfur and contained an even higher proportion of sulfur compounds than the carbon tetrachloride eluate. four fractions obtained increase successively in average molecular weight and that the ratio of carbon to hydrogen increases correspondingly, the latter ratio indicating the increased aromaticity and decreased paraflinicity of each successive eluate.

We have fractionated the McElroy West Texas crude of Table III above and the Kuwait crude of Table IV by our process using our preferred adsorbent, bauxite. The procedure employed is described in Example II below.

Example II The adsorbent in each fractionation was the 60-100 mesh activated bauxite known commercially as Regular Iron Porocel. In each fractionation the crude oil was introduced to the adsorbent column in the manner described in Example I, in a charge to adsorbent ratio of about 0.14:1. This amount of oil penetrated about percent of the bed. In each run after introduction of the undiluted total crude oil charge, the column was eluted with three successive eluants, n-pentane, benzene, and a mixture of 25 volume percent ethanol in benzene. In each elution stage the eluant to charge volume ratio was 10:1 or greater. The recovered eluate solutions were placed in shallow vessels under a ventilating hood to separate the eluants from the crude oil fractions by evaporation. The results of fractionating the McElroy and Kuwait crude oils in terms of quantities and charac- It should also be noted in Table VI that the l In Table VII above it can be seen that our fractionation process gave excellent results in fractionating the Mc- Elroy and Kuwait crude oils, both of which have high sulfur contents, but which differ in other respects. The table shows that there was obtained from the McElroy crude a n-pentane eluate comprising 49.7 percent of the original crude. When corrections are made for the losses in evaporating to separate the eluant from recovered fractions the yield is about 64 percent. This large fraction was colorless and substantially sulfur free.

Table VII also shows the production of a large colorless and sulfur-free fraction from the Kuwait crude oil. The n-pentane eluate of the Kuwait crude amounted to 40.6 percent of the original crude or about 56 percent, with corrections made for losses of light ends in evaporating to remove the eluant. It should be observed that in fractionating the McElroy and Kuwait crudes with bauxite as the adsorbent, the entire pentane eluate in each fractionation was substantially sulfur free so that a collection of the pentane eluate in a plurality of portions to segregate sulfur compounds was unnecessary.

We have also fractionated in accordance with our process the three crude oils of Tables III, IV, and V, using activated alumina as the adsorbent as described in Example III below.

Example III The McElroy, Kuwait, and Baxterville crude oils of Tables III, IV, and V, respectively, were fractionated as described in Example I, using -200 mesh activated alumina as the adsorbent. In each fractionation the adsorbent column was eluated in three stages, the eluants in the order of their use being, n-pentane, benzene, and a mixture of 25 percent ethanol in benzene. In each elution stage the eluant to charge ratio was about 10: 1. The McElroy and Kuwait crudes were charged undiluted to the adsorbent column but the high viscosity Baxterville crude oil was diluted wtih an equal volume of n-pentane to cause it to pass more easily into the adsorbent bed. The results of these fractionations in terms of the quantities and characteristics of the fractions obtained are recorded in Table VIII below.

TABLE VIII Recovery, Corrected Sulfur Sulfur Frac- Wt. Per- Recovery, Content, Recovery, Fluorescence Crude 011 tion cent of Wt. Per- Wt. Pcr- Wt. Per- Appearance Odor under U. V.

No. Charge cent of cent of cent of S Light Charge Fraction in Charge 1 51.0 67.7 0.18 3.9 golorlessflOlL. geasantnguh lgzitle blue. 2 23.3 23.3 6. 53 63.9 rown np easan ue-green. McEmy Crude 238% 3 9.0 9.0 6.70 25.3 Brown-black Asphaltlc Brown.

semi-solid.

Total Recovery 83.3 100.0 93.1

1 44.7 58.3 0.20 3.5 golorless 01i{l 6l 1 gleasantninn gialggpe. 2 29.8 29.8 6.00 69.1 rownac np easan g rown. Kuwa omdermm 3 1119 11.9 s43 25.0 Brown-black Aspha1tic Brown.

semi-solid.

Total Recovery 86.4 100. 0 97. 6

1 41.5 0.10 1.5 Colorless O1l Pleasant Pale blue. 2 45.2 4.74 76.7 Highly: vllscous Mild asphaltic Brown. Bat 1110 (1,2. S. ac oi.

X erv e m e 83% 3 14.0 4.68 23.3 Black tar Mild burnt Do.

odor.

Total Recovery 100.7 101. 5

I All material losses were light ends.

The results recorded in Table VIII show that our process employing activated alumina as the adsorbent is applicable to crude oils of widely varying characteristics. Each of the crude oils fractionated had a high sulfur content but our process produced from each crude a large fraction of very low sulfur content colorless oil and the sulfur was concentrated in the strongly adsorbed fractions of the crude. The results are particularly surprising with the Baxtcrville crude. From this very heavy, highly carbonaceous crude oil it was possible to obtain a fraction comprising 41.5 percent of the crude oil which was colorless and contained only 0.10 percent sulfur.

We have also fractionated the West Texas crude of Table II using five different adsorbent materials as described in Example IV below.

Exampie IV The West Texas crude of Table II was fractionated using five different adsorbent materials. Two of the adsorbents used were adsorbents of our process, namely activated alumina and activated bauxite. The three other adsorbents were non-alumina adsorbents, namely, 30170 mesh Florisil (a synthetic magnesium silicate), 30-170 mesh fullers earth, and 28-200 mesh silica gel. Three successive eluants were used in each fractionation: n-pentane benzene, and 25 percent ethanol in benzene, The charge to adsorbent ratio in each farctionation was about 0.15 to 1 which in each case was sufficient to cause penetration of from about 30 to 40 percent of the bed by the charge oil. In each eluti'on stage the eluant to charge ratio was 1011 or greater. In the fractionations with activated alumina, with Florisil, and with fullers earth, the n-pentane eluate was collected in two successive portions in order to isolate fluorescence in the second portion. The results of these five fractionations in terms of quantities and characteristics of the fractions obtained are given in Table IX below for the bauxite and alumina fractionations and in Table X below for the fractionations with the non-alumina absorbents.

TABLE IX Absorbent Activated Bauxite (Porocel, Activated Alumina (80-200 mesh) 60-100 mesh) Eluant n-pentane benzene 25% ethanol n-pentane benzene 25% ethanol in benzene in benzene Mass Recovery:

Wt. Percent of Charge 55.3 21.1 8.1 44.3 9.6 19.6 0.0

Total, Wt. Percent 84. 5 79. 5

Sulfur Content: Wt. Percent 0.03 4.35 4.82 0.02 0. 4.72 4. 56

Sulfur Recovery:

Wt. Percent of Sulfur in charge 1.12 65. 5 27. 9 0. 6 3. 4 60. 4 19. 8

Total Wt. Percent 94.6 90.2

Appearance colorless orange oil. black tar colorless colorless darlllr red black tar.

o1 o' 0' 0' Odor pleasant," unpleasant asphaltic pleasant..- pleasant unpleasant asphgltic phenolic. Fluorescence (Under ultraviolet light) trace of trace of greenbrown.

blue. blue. Corrected MassReoovery: 2 Wt. Percent 13 20 6.

of Charge.

2 All material losses were light ends.

TABLE X Adsorbent Florisil (30-170 mesh) Fuller's Earth (30-170 mesh) Silica Gel (28-200 mesh) 25% etha- 25% etha- 25% etha- Eluant n-pentane benzene nol in n-pentane benzene n in n-pentane benzene 1101 in benzene benzene benzene Mass Recovery:

Wt. Percent of Charge 12. 4 54. 7 12.0 7 1 15.2 46. 4 l0. 5 8. 6 58. 4 23. 3 1. 1

Total, Wt.

Percent 86.2 80. 7 82.8

Sulfur Content, Wt.

Percent 0. 33 1. 24 4. 61 3. 0.31 1. 29 5.05 3. 41 0. 74 3. 91 3. 4O

Sulfur Recovery:

Wt. Percent of S in Charge 2. 9 48. 8 39. 9 16.1 3. 4 43. 0 37. 9 21.0 31.0 65. 5 2. 6

Total, Wt.

Percent 107.7 105.3 99.1

Appearance colorless pale yel- Orangeblack tar colorless colorless orange black tar brownbrownblack oil. low oil. red oil. oil. oil. oil. blf-ck bliick tar.

or o1 Odor pleasant unpleasunpleasasphaltic pleasant slightly unpleasasphaltic pleasant unpleasphenolic.

ant. ant and and pheunpleasant. and pheant.

aisphalnolic. ant. nolic.

c. Fluorescence (under trace of blue yellow brown.-... trace of blue yellow.- brown....- mixed... mixed... mixed.

ultraviolet light). blue. blue. Corrected Mass Re- 75 24 1.1.

covery: 2 Wt. Percent of Charge.

1 Pentane eluate collected in two successive portions to isolate most of fluorescence in latter portion.

1 All material losses were light ends.

that the lowest sulfur fraction obtained with the alumina V adsorbent contained only 0.02 percent sulfur and amounted to 44.3 weight percent of the charge, or 61 weight percent of the charge based on corrected mass recovery.

The data in Tables IX and X show the complete difference in kind of our process from processes employing non-alumina adsorbents. With the non-alumina adsorbents it is impossible to obtain in any substantial yield a pentane eluate which is substantially sulfur-free as in our process. As Table X shows, the pentane eluate of the silica gel process eluted a fraction having a sulfur content of 0.74 percent. In collecting this fraction the poor colorretention properties of the silica gel adsorbent were clear- 1y demonstrated. Even the first drop of the first fraction emerging from the adsorbent was dark colored. There was no colorless material at all. Table X shows that in the Florisil and fullers earth processes, lower sulfur contents than with the silica gel process were obtained by collecting the pentane eluate in two portions. Thus, the first portion of the pentane eluate in the Florisil process had a sulfur content of 0.33 percent and in the fullers earth process a sulfur content of 0.31 percent. However, the yields of these relatively low sulfur fractions were very low, namely 12.4 percent of the charge (uncorrected) in the Florisil process and 15.2 percent of the charge (uncorrected) in the fullers earth process. These results compare very unfavorably with the results of our process listed in Table IX.

In the foregoing examples, we have described the use of relatively high ratios of eluant to charge. These ratios can be considerably lower than used in the foregoing examples. As we have stated, the eluant to charge ratio in each elution stage is preferably from about 1 to 5 volumes of eluant per volume of charge. Increasing the volume of eluant, or, in other words, the eluant to charge ratio, increases the liquid eluted from the column in each elution stage. However, a very high percentage of the material recoverable in an elution stage, e. g. 99 percent, can be eluted by about 5 volumes of eluant per volume of charge so that the use of a larger volume of eluant is generally not economically worthwhile. Example V below describes a fractionation in which we used somewhat lower charge to eluant ratios than in the previous examples.

Example V The McElroy crude of Table IH above was fractionated in a column of -200 mesh activated alumina using three successive eluants: n-pentane, benzene, and 25 volume percent ethanol in benzene. The charge to adsorbent volume ratio was about 0.15 to l and about 35 percent of the adsorbent column was penetrated by the charge oil. In the first elution stage n-pentane was introduced to the column in the amount of 6.8 volumes per volume of charge. The n-pentane eluate was collected in two portions in order to isolate fluorescence in the second portion. The separation of this cluate was at the point at which 5.7 volumes of n-pentane per volume of charge had been introduced. Thereafter, 1.1 volumes were used. The benzene was used in the amount of 5.0 volumes per volume of charge and the ethanol-benzene eluant was used in the amount of 7.0 volumes per volume of charge. The results of this fractionation in terms of quantities and characteristics of the fraction obtained are given in Table XI below.

TABLE XI Eluant Recov- Total S Elemen- S Recov- Fluoresto charge cry, wt. Content, tal S Conery, wt. cencc under Crude Oil Fraction Eluant ratio, percent wt. pertent, wt. percent Appearance Odor Ultra-vio- No. volJvol. of charge cent of percent of of sulfur let light fraction fraction in charge 1 (a). n-pentanc 5. 7 49. 6 0. 011 0. 00001 0.2 colorless oil pleasant..." none. 1 (b) 1.1 19. 7 0. 53 0.011 4.4 do do pale blue.

McElroy Crude, 2.38% total 6. 8 69. 3

S, 0.506% elemental S.

2 benzene 5.0 20.0 6. 40 55. 4 brown o1l unpleasant blue-green. 3 vol. percent 7.0 10.0 7. 90 33.2 brown-black asphaltlc brown.

ethanol in bensemi-solid.

zone. Total Recovery" 99. 9 93. 2

Table XI shows that the n-pentane fraction obtained with the 6.8 to 1 eluant to charge ratio amounted to 69.3 percent of the crude oil charged. The table also shows that 99.9 percent of the crude oil was recovered in the three elution stages. There were no substantial material losses in this fractionation.

The results in Table XI show very clearly another valuable characteristic of our process. This characteristic is in the production of a fraction which is free of elemental sulfur. Elemental sulfur is known to be the most undesirable form of sulfur present'in crude oil because of its highly corrosive nature. Therefore, the reduction of the volumes per volume of charge. When 2.8 volumes of eluant per volume of charge had been introduced, the emerging eluate began to show light blue fluorescence in ultraviolet light, and the eluate emerging from the column thereafter was collected separately. After this point, 1.4 volumes of the first eluant per volume of charge were added. After the first stage elution, the adsorbent bed was eluted with benzene in the amount of 6.7 volumes per volume of charge and then with a mixture of volume percent ethanol in benzene in the amount of 51 volumes per Volume of charge. The results of this fractionation are given in Table XII, below.

TABLE XII Eluant Recov- Sulfur Sulfur Fluoresto cry, Content, Recovcenee Crude Oil Fraction Eluant Charge Wt. Wt. cry, Wt. Appearance Odor under N0. Ratio, Percent Percent Percent U. V. vol./vol. o of S in Light Charge Fraction Charge 2,3 dimethyl butane. 2. 8 33.9 0.008 0.19 Colorless oil... pleasant... none. 1.4 42.0 0.29 8. 52 do do pale blue.

4. 2 75. 9 West Texas Crude, 1.40% S... I

benzene 6. 7 22. 5 3. 86 60. 7 Brown 01l unpleasant bluegreen. 35 Vol. percent eth- 5.1 7. 54 3. 17. 92 Brown-black asphaltie brown.

anol in benzene. semi-solid;

Total Recovery 105. 9 87. 3

elemental sulfur content in motor fuel or cracking stock fractions is even more important than the reduction of combined sulfur content. Table XI shows that in Example V the first portion of the n-pentane eluate which amounted to 49.6 percent of the crude, contained less than 0.00001 weight percent elemental sulfur, as compared with the McElroy crude oil charge which contained 0.506 weight percent elemental sulfur.

The results of Table XI are also of interest in con- Example VI The West Texas crude of Table II was fractionated in a column of 80200 mesh activated alumina, using a charge to adsorbent ratio of 0.20 voiumc of charge per volume of adsorbent. This quantity of charge penetrated about 40 percent of the adsorbent bed. Immediately after introduction of the crude oil charge, the bed was eluted with 2,3-dimethyl butane in the amount of 4.2

Table XII shows that the same excellent results are obtained using the'branched chain paraffin, 2,3-dimethyl butane, as the first stage weak eluant, as are obtained with normal pentane. Thus, the two portions of the weak eluant fraction amounted to about 75.9 weight percent of the charge oil. This fraction was a colorless oil of pleasant odor, the first portion of which had a negligible sulfur content of only 0.008 weight percent. Table XII also shows the excellent results obtained with rather low eluant to charge ratios. Excellent fractionation and high recoverieswere obtained using only 4.2 parts of first stage eluant per part of charge and 6.7 and 5.1 parts of eluant per part of charge in the second and third clution stages, respectively. It will be noted that the total recovery exceeds. lOO percent. The probable explanation is that each eluate fraction contained a small amount of uncvaporated eluant.

It must also be understood that the colorless, low sulfur fractions. obtained with the first-stage eluants by our process are substantially metal-free and contain substantially all of the mononuclear aromatic compounds of the original crude. The characteristic of our process of producing metal-free fractions is very important because if metalsare present in liquids subjected to catalytic treatments such. as cracking, such metals can have a seriously' adverseeffect on the; catalysts. For these reasons the substantially metal-free fractions of our process, when distilled, yield' ideal catalytic cracking stocks.

The metal contents of the fractions obtained in our process are illustrated by vanadium analyses on the fractions obtained in fractionating the total West Texas crude oil of Table II above in accordance with our process using three eluants, namely n-pentane, benzene, and

18 oil can be performed in such a manner. However, as we have mentioned, it is preferable in our process to take advantage of the diiferences in adsorbability of the various petroleum compounds which cause such compounds to 25 percent ethanol in benzene. The analyses were made iislle successively from the 601112111 and to Collect the qon composite eluate fractions from several different fraculd from the adsorbent column 11 Several POI'UOIIS Which tionations of the mentioned West Texas crude. The cof'ltalll elthel a Single WP a YP ofcompoundsvanadium contents of these fractions are listed in Table Thls procedure of collqctmg h llould emerging t the XIII below. The West Texas crude oil before fractionaadsorbent Column durlng elutlofl 111 Several Portions tion contained 0.000380 percent by weight vanadium. be PP to y One all the ellltlOIl Stages 0111' fractionation process. We have collected the first stage TABLE XIII eluate in a fractionation of the West Texas crude of Table II through bauxite, in accordance with our process, in Fraction Recovery Vanadium 2 533? twelve different portions. The procedure employed is de- Wt. Per Content of Wt. Per- 16 scrlbed Exmple VII belowcent of Appearance Fraction, cent of No. Eluant o n t ie Wt.Percent vat ai m Example VII In I'll e Oil The West Texas crude was introduced to a column of 60-100 mesh activated bauxite (Regular Iron Porocel) 1-- n-pentane. 75 ok les s oi l nfl 8. $821 in a charge to adsorbent ratio of 0.15 volume of crude oil 3:: g g gl f ag 0100738 97+ per volume of adsorbent. About percent of the colinbenumn was penetrated by the 011. Immediately after introduction of the charge, the column was eluted with n-pentane in the amount of 6.0 volumes per volume of charge. Fr m Ta le XIII a v It can be Seen that the 9 25 The liquid emerging from the column was collected in less first fraction which is eluted from the column with twelve portions, the first eleven of which each contained ll-pentane and Whlch cofltalns about 75 We1ght P t about 5.5 weight percent of crude oil charged and the of the crude oil charged, was substantially v l twelfth of which contained 3.2 weight percent of the free. The value for vanadium contentof th1s fraction crude. The results of this fractionation are given in which is listed in Table XIII is the minimum detectable Table XIV below.

TABLE XIV Rings per Molecule Aromatics, Moles per Liter 1 Fluorescence Wt. Molecu- (Van Nes and Van (Lipkin and under Fraction N0. Percent lar Weston Method) 2 Martin) 3 Ultra-violet of Crude Weight Light Mono- Di- Tri- Aromatic Naph- Aromatic nuclear nuclear nuclear thenic 5.5 320 o 0 as 245 0 0.4 5.6 215 0 0.6 2:1 3%?) 3 8:2 5.5 255 0 0.5 5.7 230 0 0.6 5.5 240 0 0.6 5. 6 255 4 10- 10- 10- 0 0. 6 5. 3 260 5 10- 10- 10- 0 0. 7 5.4 360 3 2 10- 4x10- 0.6 1.2 3.2 400 4 10- 1. 5X10 0.9 0.9

Total 64.2

1 Determined by ultraviolet light absorption spectroscopy. 2 K. Van N as and H. A. Van Weston, Aspects of the Constitution of Mineral Oils, Elsevier Publishing Co., Inc, New York,

5 M. R. Llpkin and C. C. Martin, Ind. Eng. Chem, Anal. Ed., vol. 19, p. 183, 1947.

quantity of vanadium by the analytical method employed. However, it is probable that the fraction was actually completely free of vanadium and, in any event, the vanadium content of this fraction was less than 1 percent of the vanadium present in the original crude oil. The benzene fraction was also quite low in vanadium as the table shows, while the third fraction which was eluted with the ethanol-benzene mixture constituted about 5 percent of the original crude and contained nearly all of the vanadium present in the original crude. Table XIII shows that concentration of vanadium in the third fraction is about 19 times the concentration of vanadium in the crude oil, so that in any process for the recovery of vanadium from petroleum, this third fraction is a considerably better material for the process than the original crude oil.

In each of the foregoing examples we have described recovering the eluate fractions in either one or, in the case of the pentane eluates, two portions. Such a procedure may often be desired and, as the examples and tables show, an excellent primary fractionation of crude From the results of Table XIV it can be seen that the first portion of the pentane eluate consisted entirely of paraffins, since no aromatic or naphthenic rings were indicated. Fractions 2 through 8 inclusive were mixtures of parafi'ins and naphthenes as indicated by the presence of naphthenic rings and the absence of aromatic rings. The extremely low aromatic content of the first 8 fractions is conclusively indicated by the sensitive ultraviolet light absorption spectroscopy analysis. Fractions 11 and 12 contained high concentrations of mononuclear aromatics. The dinuclear aromatic contents of these fractions were low and the trinuclear aromatic contents were very low. From this table it can be seen that the n-pentane eluate could be collected in three portions to obtain a paraflinic portion, a portion consisting essentially of parafiins and naphthenes, and a highly aromatic portion.

In each of the foregoing examples, I though VII inclusive, the fractionations described were carried out at room temperature or from about 70 to F. and the liquids were passed through the adsorbent columns by gravity flow. It should be understood, however, that other operating conditions can be employed in our process. Thus, f r example, hot eluants can be used in certain of the on stages. Heating an eluant liquid increases its itivc power and, therefore, it is possible to use the same ciuant liquid for two or more clution stages by introducing it to the adsorbent bed at successively higher temperatures for the successive elution stages. It should be understood also that in our process pressure can be applied to the liquid inlet end of the adsorbent bed or vacuum to the exit end if desired, to increase the rate of How through the bed above the normal rate of gravity flow.

From the foregoing description of our invention it can be seen that we have developed a process which can be of great value to the petroleum refiner. Our process makes it possible to place the paraffinic, naphthenic and mononuclcar aromatic compounds of crude oil in fractions of the crude separate from the sulfur and metal compounds. The sulfur-containing components of the crude are segregated from the non-sulfur components without subjecting them to elevated temperatures. In this Way the contamination of non-sulfur-containing fractions by the decomposition of labile sulfur compounds during distillation is avoided, and also many valuable sulfur compounds can be recovered in their natural state for use as chemical agents or intermediates. Still further, it is possible with out process to se :arate a crude petroleum oil into a large number of fractions diifering according to molecular type by making appropriate cuts in each eluate emerging from the adsorbent bed.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof; therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for separating crude petroleum oil into low and 'high sulfur content fractions of unconverted, naturally-occurring petroleum compounds which comprises passing into contact with a bed of adsorbent material selected from the group consisting of activated alumina and activated bauxite, a charge liquid comprising at least about 25 percent by volume of a sulfur-containing crude oil in an amount which penetrates no more than about 90 percent of the adsorbent bed, then contacting said adsorbent bed with a wholly paraffinic eluant liquid in an amount at least as great as the amount of charge liquid, recovering from the bed with said paraffinic eluant liquid a parafiinic fraction of the crude oil of low sulfur content, thereafter contacting said bed with at least one additional eluant liquid, each eluant liquid having stronger eluting power than the eluant used before it, and recovering from the bed with an eluant liquid of stronger eluting power than said paraffinic eluant a fraction of said crude oil of high sulfur content.

2. The process according to claim 1 in which substantially all of the paraflinic, naphthenic and mononuclear aromatic compounds of the crude oil are recovered in at least one fraction with said parafiinic eluant liquid and substantially all of the polynuclear aromatics and sulfur components of the crude oil are recovered in at least one other fraction with a stronger eluant.

3. A process for separating crude petroleum into low and high sulfur-content fractions of natural unconverted petroleum compounds which comprises passing into contact with a bed of activated alumina, a liquid comprising at least about 25 percent by volume crude oil in an amount which penetrates no more than about 90 percent of the alumina bed, then contacting said alumina bed with a wholly paraflinic eluant liquid, collecting eluate emerging from said bed until the eluate begins to show fluorescence under ultraviolet light, separately collecting the remaining liquid eluted by said paraflinic liquid, thereafter contacting said bed with a series of eluants of successively increasing eluting powers, and recovering separately each eluted fraction of unconverted natural petroleum compounds.

References Cited in the file of this patent UNITED STATES PATENTS 2,390,917 Brcth et al. Dec. 11, 1945 2,395,491 Mavity Feb. 26, 1946 2,441,572 Hirschler et al. May 18, 1948 2,509,486 Danforth May 30, 1950 2,571,936 Paterson et al, Oct. 16, 1951 2,574,434 Greentree et al. Nov. 6, 1951 OTHER REFERENCES Pringsheim et al.: Luminescence of Liquids and Solids, Interscience Publishers, New York, N. Y. (1943), pages 72 and 73.

Australian Chemical Institute, Journal and Proceedings, vol. 14, pages 61-7 (1946). Abstracted in Chem. Abs, vol. 41, column 4913b (1947).

Cassidy: Adsorption and Chromatography, page 183 (1951), Intcrscience Publishers Inc., 250 Fifth Avenue, New York 1, New York.

Claims (1)

1. A PROCESS FOR SEPARATING CRUDE PETROLEUM OIL INTO LOW AND HIGH SULFUR CONTENT FRACTIONS OF UNCONVERTED, NATURALLY-OCCURING PETROLEUM COMPOJUNDS WHICH COMPRISES PASSING INTO CONTACT WITH A BED OF ASDORBENT MATERIAL SELECTED FROM THE GROUP CONSISTING OF ACTIVATED ALUMINA AND ACTIVATED BAUXITE, A CHARGE LIQUID COMPRISING AT LEAST ABOUT 25 PERCENT BY VOLUME OF A SULFUR-CONTAINING CRUDE OIL IN AN AMOUNT WHICH PERETRATES NO MORE THAN ABOUT 90 PERCENT OF THE ADSORBENT BED, THEN CONTACTING SAID ADSORBENT BED WITH A WHOLLY PARAFFINIC ELUANT LIQUID IN AN AMOUNT AT LEAST AS GREAT AS THE AMOUNT OF CHARGE LIQUID, RECOVERING FROM THE BED WITH SAID PARAFFINIC ELUANT LIQUID A PARAFFINIC FRACTION OF THE CRUDE OIL OF LOW SULFUR CONTENT, THEREAFTER CONTACTING SAID BED WITH AT LEAST ONE ADDITIONAL ELUANT LIQUID, EACH ELUANT LIQUID HAVING STRONGER ELUTING POWER THAN THE ELUANT USED BEFORE IT, AND RECOVERING FROM THE BED WITH AN ELUANT LIQUID OF STRONGER ELUTING POWER THAN SAID PARAFFINIC ELUANT A FRACTION OF SAID CRUDE OIL OF HIGH SULFUR CONTENT.