Chromatographic Fractionation of Crude Petroleum Oils CLARENCE KARR, JR., W. D. WEATHERFORD, JR., and R. G. CAPELL industrial Research, University o f Pittsburgh, Pittsburgh, Pa.
M e l l o n Institute o f
The application of the technique of elution chromatography to the fractionation of undiluted virgin crude oils has been investigated, and typical data are presented demonstrating the type and extent of fractionation obtained using alumina and bauxite adsorbents. An apparatus was developed to facilitate the fractionation of virgin crude oils by elution chromatography. The alumina and bauxite adsorbents have been found satisfactory for separating hydrocarbon components from high-sulfur crude oils in a colorless, sulfur-free, metal-free, fractionated state, while yielding sulfur compound concentrates and asphaltic fractions. Certain hydrocarbon classes, such as paraffins and mononuclear aromatics, may be recovered directly uncontaminated by other hydrocarbon classes by proper selection of cut points.
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S CONJUNCTION with a program for isolating and examinfication of crude oils by means of chromatography. However, thi'i ing the sulfur compounds of certain crude petroleums, the procedure involved heating the crude oil to 150" C. or highei authors have found that the techniques of elution chromabefore analysis, which process alters some constituents; some tography may be employedfor fractionatingundiluted virgin crude asphalt was removed before analysis and hence could not enter petroleum oils on activated alumina and bauxite. This paper into the fractionation; and dilute (less than 10%) solutions of describes these techniques and presents typical data demonthe crudes were employed. Kats and Sidorov (6) have studied strating the type and extent of fractionation achieved. fluorescence spectra of crude oils while they are adsorbed on Around 1900 Day (2) was the first to demonstrate the analytical alumina in a chromatographic column. Schuldiner (IO) has possibilities of crude oil chromatography. He employed percolarecently shown that crude oils can be identified by their spot tion-Le., frontal analysis-of a crude petroleum oil up into a chromatograms on white blotting paper, the fluorescence colors finely divided fuller's earth or clay and showed that the material being particularly characteristic. None of these or other modern near the top of the column retained less sulfur and color than the authors, exclusive of the authors of the present work, have used original crude oil. Engler and Albrecht ( 4 ) improved Day's elution chromatography to its best ability and demonstrated that technique by allowing the oil to emerge from the top of the crude oils can be fractionated by this technique into their characcolumn and collecting portions a t fixed intervals. Gilpin and teristic components and various classes of hydrocarbona. Cram ( 5 ) a t Johns Hopkins University found that when crude EXPERIMENTAL oil was forced up into a column of fuller's earth, the top of the column contained more saturated aliphatic hydrocarbons, farThe procedures employed in the chromatographic fractionather down there were more aromatics and unsaturated subtion of undiluted crude oils may be briefly described as follows: stances, and sulfur and nitrogen compounds increased steadily The crude oil charge is introduced into the top of an adsorbent toward the bottom. These and other early workers never bed having in these experiments about six times the bulk volume achieved their desired goal of separating crude oils into the of the charge. The adsorbent bed may be initially filled with npentane in order to reduce heat effects during charge introducvarious classes of compounds present. In the light of presentday chromatography theory it is known that it would have been impossible to achieve Table I. Comparison of Chromatographic Fractionation of Various Crude Oils on their goal by the percolation Activated Alumina , technique. Crude oil The use of an elution techName Pipeline McElroy Kuwait Baxterville" Source West Texas West Texas Near E a s t Mississippi nique for a t least part of the Sulfur, a t . 7' 1.4 2.4 2.6 2.8 crude oil chromatographic fracFscosity a t 100' F . , cs. 4.79 5.82 9.86 822.7 tionation appears to have been 35.0 8.8 sOOo F. distillate, vol. % 45.3 42.7 initiated in 1944 by Mukherjee n-Pentane eluate 58 41 74 68 Yield, u t . % b a n d I n d r a (7, 8). T h e i r 0.18 0.20 0.10 Sulfrir content. wt. % 0.16 method, however, employed Colorless Color Colorless Colorless Colorless Fluorescence under iiltraviolet dilute (lye) solutions of the Pale blue light Pale blue Pale blue Pale blue Pleavant Pleasant Odor Pleasant Pleasant crudes and percolation to obtain the first fraction. MoreBenzene eluate Yield, a t . % 20 24 31 45 over, the fractions were studied Sulfur content. wt. % 4.6 6.4 5.9 4.7 Color Dark red Brown Brown-black Brown only qualitatively by their Fluorescence under ultraviolet colors in natural and ultraGreen-brown Brown light Green-blue Green Odor UnplPasant Mildly unpleasant hlildly unpleasant, asphaltic hlildly asviolet light. Elution chromaphaltic tography was used in part by Ethyl alcohol-benzene eluate Bogulovskaya and VelikovskiI 6 9 11 14 Yield, wt. % 5,4 Sulfur content, wt. % 4.0 6.6 -. 4.. 7 ( 1 ) but regular solvent extracColor Black Brown-black Brown-black Black Fluorescence under ultraviolet tion procedures (Soxhlet apBrown Brown Green-brown light paratus) were employed for Mild burnt Phenolic Asphaltic Asphaltic Odor removing much of the material a Diluted with a n equal volume of n-pentane. b Corrected for light ends losses. from the adsorbent. Schneider (9) described a method of rlawi-
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V O L U M E 26, NO. 2, F E B R U A R Y 1 9 5 4
253 matter, GO to 100 mesh). Both adsorbents were reactivated before use by heating for a t least 4 hours a t about 215" C. Simple chromatographic columns of two different sizes were employed in this work. Small scale runs were made using about 10 ml. oi charge oil in a 60-cm. long column, having an inside diameter of 12 mni. Larger scale, semicontinuous runs nere made using about 7 5 ml. of charge oil in a 130-cm. long column, having an inside diameter of 22 mm. A slight positive pressure was sometimes eniploj rd to speed the introduction of charge into these columns, but gravity flow was usually satisfactory during the elution steps.
tion. The crude oil components are then eluted from the column in a fractionated state as solutions by successive eluants of increasing elutive power, the volume of each eluant being about ten times that of the charge oil. The removal of the crude oil components from activated alumina by this elution procedure is essentially quantitative, as evidenced by the good material balances obtained and the fact that the natural R hite color of the alumina is restored at the end oi a ryrlr. The three eluants normally used in this procedure were purified n-pentane (or diisopropl I), thiophene-free benzene, and 25 volume yo absolute ethyl alcohol in thiophene-free benzene. Two different adsorbents were employed for the crude oil fractionation-namely, activated alumina (Alcoa, Grade F-20, 80 to 200 mesh), and activated bauxite (regular iron Pororel, 2y0 volatile
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Eluant Recycle Line for Atmospheric Pressure
Small Scale Runs. In small scale runs, the product solutions were freed of eluant by room temperature evaporation in open
Nitrogen Bleed during Reduced Pressure Operotion of Stills and Stripper
Nitrogen Bleed or Vacuum
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Shut -off Valve for Reduced Pressure Operotion of S t i l l s and Stripper
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11 I,
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II
Distilled Eluant Condenser
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illed Eluant I-0 f f Receiver Condenser
Feed Reservoir
Bulb Connection Normolly Casr
1
Eluont Feed Rotometer (pyrex -kovor fittings. tef Ian gaskets)
Thermowell
Reflux Control Stopcock
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;on d8nsoblc ~ g h Eluotc t Receiver I my be joc Let ed)
Adsorption Column
Nitrogen Inlet ( f o r priming g a s reservdr)
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Heat Exchanqe Jocket
B y - p o r i Line (for s t a r t - u p of stills)
dE.rine
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Reservoir
.Pocked Eluant Clean-up S t i l l Thermowell Pocked Eluont Topping S t i l l
Fluorometer Cell
rhermawell
1P
./L r
-
- Reboil
Control Stopcock
Thermowell
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Reboiler /
Nitrogen i n l e t (to prevent bum ping )
Reriduol Eluotc Receiver
igures 1 and 2 was developed. Detailed results of a typical C rude ail fractionation with this unit are presented in Table 11. OPERATING PRINCIPLES. During elution operations in this a,pparatus, eluant and volatile components me continuously Stripped from the eluate solution a t temperatures less than 100' C. an d the valat,ilized fraction is passed in sequence through two eontinuous stills for removal of materials less volatile and more Y.olatile than the eluant. All of the components eluted from the C olumn are recovered, substantially free from eluant, in the Ymious eluate fractions, except for those charge constituents nihich cannot be easily separated from the eluant by distillation. 1'he recovered eluant. is continuously recycled to the adsorption eolumn. DESIGNFEATCRES. This apparatus was designed so t h a t flow r ate8 in the various parts of the unit would he self-regulating a iter the operating conditions were set and its performance has b een satisfactory. This self-regulation feature is important bec %use of the inherent unsteady-state nature of elution chromaography. t< The distillation columns are 1 inch in diameter (inside), and are packed with L/s-inch, single-turn, horasilieste glass helices.
1'he packed lengths are 4 feet 2 inches and 2 feet 9 inches for the eluant clean-uo still and eluant tonnine still. resoectivelv. The r eboilers, stripber, and vaporizers .&e h ~ a t e d ' ~ ~ -Tmterhr ith mixt ures of saturated steam and air s n t hese insulating heaters is adjusted so that the outer s k n temerature of the&ss apparatus, when empty and drv, i s somewhat igher than the boiling point of the eluant to be used, hut never h ieher than the eluate striDDer temDerature. 1vacuum pump, manoskt, and &uum gage are provided so hat the stripper and stills may he operated a t reduced pressures lower operating temperatures are desired. During reduced presUTB operations, the feed reservoir and adsorption column are isotted from the vacuum system, the eluate solution flow rate is ianudly controlled with the adsorption column outlet stopcock, nd the recovered eluant is collected in a draaoff mceiver.
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Figure 2. SemieontinuorLS Elution Chromatography AppiIratUB
V O L U M E 2 6 , NO. 2, F E B R U A R Y 1 9 5 4
Miilurrr of Aromatic-free Paraffins and Nophfhenn
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255
M i i l u r n of Eswntially Purr Mononuclear Aromatics
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duit, thereby allowing brine to flow from the gas reservoir, which is initially filled with brine, through the lower conduit int,o the brine chamber until the liquid level increases sufficiently t o immerse the open ends of both gas reservoir conduits. I n operation, the liquid level oscillates only a few millimeters, and therefore the gas inlet pressure is maintained essentially constant a t that pressure existing in the brine reservoir. RESULTS
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IO 20 30 40 50 60 Weight Per Cent of Total Crude Eluted withn-Pentonc
1
64.2
Figure 3. Chromatographic Fractions of a West Texas Crude Oil Eluted from Activated Bauxite with n-Pentane
Table 111. Chromatographic Fractions of a West Texas Crude Oil Eluted from -4ctivated Bauxite with n-Pentane
Fraction 1 to 8 (inclusive) 9 10 11 12
(8nslyaed by ultraviolet spectroscopy) Moles per Liter of Aromatics Mononuclear Dinuclear Trinuclear
wt. 7c of Crude 44.7
5.6
4
:,3 0.4
5
3.2
3 4
< 10-4 x 10-3 x 10-3
