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JAMES L. JEZL and ARCHIBALD P. STUART Basic Research Division, Research and Development Department, Sun Oil
Co.,Marcus Hook, Pa.
Separation of Sulfur Compounds from Mineral Oil Fractions
Prolonged calcining at 600"to 700"C. may improve the ability of an alumina to remove sulfur compounds from aromatic fractions of mineral oil. Nickelnickel oxide supported on silicaalumina is excellent for removing sulfur compounds from hydrocarbons.
For(
some years, naturally occurring sulfur compounds and certain aromatics have been considered as contributing to the stability of mineral oils. As no methods have been available to separate mixtures of sulfur compounds and aromatics, it has not been possible to separate the effects of these two "natural inhibitors" entirely. Chemical reagents have removed the sulfur compounds but may have altered or removed important aromatic hydrocarbons. The present work was undertaken to develop adsorbents specific for the separation of sulfur compounds in the mineral oil range from their associated hydrocarbons. Much of the previous work on the physical separation of sulfur compounds has been carried on by API Project 48A. Aluminas were used with some success, particularly for lower boiling petroleum distillates (7, 8). Thermal diffusion methods have been used for removing sulfur compounds from low boiling fractions (8), but have been relatively ineffective for mixtures boiling in the lubricating oil range (7). The present study is concerned primarily with low sulfur oils, (0.1 to 0.3%), but preliminary work indicates that the adsorbents developed work equally well for high-sulfur stocks. Presumably the adsorbents could also be used for hydrocarbon fractions lower in boiling range than lubricating oils.
Experimental Details
Properties and carbon type composition of charge stocks are given in Table I. Oil A was a naphthenic coastal oil, and oil B was a paraffin-base oil. Both stocks were low in sulfur. Procedure. Elution chromatography, as described by Hirschler and James (3), was employed. I n a typical run 500 grams of adsorbent was placed in a column to provide a %foot packed section. After the column was washed down with pentane, a charge of 25 grams of oil in 50 ml. of pentane was introduced. The column was developed with 1500 ml. of 4% benzene in pentane, 1000 ml. of 10% benzene in pentane, 1000 ml. of 24% benzene in pentane, 1000 ml. of benzene, 2000 ml. of 50% 2-propanol or ethanol in benzene, and a final wash with acetone, pyridine, or other polar solvent. Cuts of 150-ml. volume were taken at a rate of about 8 ml. per minute. Properties and composition of cuts were determined after solvent was removed. The types and amounts of aromatic hydrocarbons in cuts were determined by ultraviolet spectroscopy against known standards. Runs with larger amounts of oil
~~~
were made by scaling up the quantities of adsorbents and eluents. Because silica gel has a much higher surface area than the aluminas (750 sq. meters per gram, as compared with about 300 to 350 for the aluminas), it
Table 1.
Properties of Oil Stocks Used , in Separation Studies
Oil A Type Naphthenic Density, % '6 0.9340 Refractive - index, nga 1.5153 Refractivity interCePt, nn-d 1 2 1.0483 Viscosity, SUS/ looo F. 603.0 Viscosity, SUS/ 210° F. 55.03 Viscosity-gravity constant 0.886 Av. molecular weight 364 Sulfur, wt. yo 0.26 Total nitrogen, wt. % 0.051 Basic nitrogen, wt. % 0.021 Oxygen, wt. % 0.19 Carbon type analysis (6) % CA 20 % CN 40 % CP 40
Oil B Para5nic 0.8724 1.4848 1.0482 105.7 39.56 0.832 358 0.16 0.029 0.010 0.18 12 27 61
~
Adsorbents Davison Chemical Co. grade 912 (28-200 mesh), activated by heating at 150° C. for 8 hours Alcoa grade F-20 (80-200 mesh) and H-41 (100-200 mesh), activated at 150° C. for 8 hours Heated in mufae furnace at 600" to 700° C. for 24 hours, cooled in nitrogen atmosphere to 150' to ZOOo C., stored in nitrogenfilled containers Water-washed to neutral pH, dried by refluxing with toluene in modified Dean-Stark apparatus, washed with cyclohexene to remove hydrogen and toluene, and with iso-octane to remove cyclohexene Harshaw nickel catalyst Ni-0104 T l/g inch, crushed to powder in nitrogen atmosphere. Partially oxidized nickel metal supported in silica-alumina: Ni 43.6%, NiO 28.2%, Si02 19.9%, 4 2 0 8 2.0%, graphite 4.0%
Silica gel Alumina Calcined alumina Raney nickel
Nickel-nickel oxide
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4 Figure 1. Sulfur content-refractive index chromatograph o f oil A
SILICA GEL
Silica gel gave substantial sulfur removal from saturate fraction only
1.60
was used at a ratio of 8 grams per gram of oil. All other adsorbents were employed at ratios of 20 to 1, except where indicated otherwise. Results. The results with adsorbents studied are summarized in Table 11. Typical sulfur content-refractive index chromatograms are given in Figures 1, 2, and 3. ~
Table II. Selectivity of Adsorbents for Removing Sulfur Compounds from Mineral Oil A
0
20
40
60
80
FRACTION OF OIL DESORBED
1
-4dsorbent H-41 alumina (calcined at 700" C. for 24 hours) H-41 alumina (calcined at 625' C. for 24 hours) Nickel-nickel oxide, supported on silica-alumina F-20 alumina (calcined at 6.50' C. for 24 hours) H-41 alumina (uncalcined) Silica gel F-20 alumina (uncalcined)
IO0
WT.%
1
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H-41ALUMINA (UNCALCINED)
2.0 # G 3 I1.5 $,
1.55-
z
Iz 0
W
(1:
1.501
4
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0
1.0
5 LL
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4 Figure 2.
0 20 40 60 80 100 FRACTION OF OIL DESORBED WT. % 944
85
75 73
54 35 31
Silica gel gave substantial removal of sulfur from the saturate fraction only (first 52.5%). Early aromatic fractions possessed as much sulfur as the charge itself, while the di- and polynuclear aromatic fractions and the resin fractions contained about 1% of sulfur. The first 90% of the oil desorbed contained about 65% of its original sulfur content; for a removal of 35%. H-41 alumina was less effective for separating saturates and aromatics than silica gel, but appreciably better for sulfur removal. Here 54% removal was realized in the first 907, of desorbed oil. Calcined H-41 alumina was less effective in separating hydrocarbon types than the uncalcined material, but definitely superior for sulfur removal. Calcining a t 700' C. removed 93% of sulfur from the first 90% of oil, while calcining a t 625' C. removed 85%. F-20 alumina was inferior to H-41
I
1
W
93
I
1.60
L L
Sulfur Removed at 90% Yield of Desorbed Oil, Wt. %
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Sulfur content-refractive graph o f oil A
index chromato-
H-41 alumina was less effective than silica gel for saturates and aromatics but better for sulfur
SULFUR COMPOUND SEPARATION alumina both in separation of hydrocarbon types and in sulfur removal, giving 31y0 reduction in sulfur in the first 90% of desorbed oil. Calcining a t 650' C . raised this value to 73%. Raney nickel removed an appreciable amount of sulfur from oil, but most of these sulfur compounds could not be removed by elution. Supporting nickel-nickel oxide acted as an adsorbent for both hydrocarbon and sulfur compounds. Its chromatograms were similar to that of H-41 alumina. Sulfur removal was 75% for the first 90% of desorbed oil. Over 85% of the sulfur compounds were easily removed from the adsorbent by alcohol elution, resulting in sulfur recoveries very similar 'to those with aluminas or silica gel. A number of other adsorbents were evaluated but found inferior to those reported. The effectiveness of these adsorbents for removing sulfur is presented in Table I1 in order of decreasing effectiveness. Calcined H-41 alumina was most effective ; supported nickel-nickel oxide was somewhat less effective. H-41alumina is a synthetic product with some silica in its make-up. Presumably other aluminas of similar composition and surface area should serve as well when calcined.
-
H-41 ALUMINA (CALCINED AT 7OO0C
1.60-
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0
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CHARGE r
20 40 60 80 100 FRACTION OF OIL DESORBED WT%
0
Figure 3. Sulfur content-refractive index chromatograph of oil A Properties of Calcined Aluminas
Surface areas, heats of wetting, and x-ray patterns have been determined for calcined H-41 alumina in an attempt to learn why calcining should improve its selectivity for sulfur compounds. Surface areas by the BET method were determined by the Houdry Process Corp.
ti-41 alumina calcined at 700' C. was less effective than calcined material in separating hydrocarbon types, but superior in removing sulfur
cined aluminas form a proportionately stronger adsorption bond with sulfur compounds than with aromatics. Alternatively, a greater number of bonds may be involved with sulfur compounds. Holm and Blue ( 4 ) reported that heattreated aluminas are rather effective hydrogenation dehydrogenation catalysts. Cornelius and others ( 2 ) attribute this property to strained sites created by calcining. In the present case the polarizable sulfur atoms probably can take fuller advantage of such sites than can aromatic hydrocarbons.
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Alumina Adsorbent
Surface Area, Sq. M./G.
Sulfur Removal, Wt. %
Uncalcined Calcined a t 625' C. Calcined at 700° C.
314 282 271
54 85 93
Thus, calcining lowers the surface area to some extent while increasing selectivity. X-ray studies established no discernible change in pattern during calcining, all samples showing only y-alumina. Adsorption studies showed that calcining markedly decreased the ability of the alumina to adsorb benzene selectively from heptane solution. Moreover, while calcining increased the heat of wetting the alumina, this effect was appreciably greater for thiophene than for benzene. This suggests that cal-
Removal of Nitrogen- and Oxygen-Containing Compounds
Although removal of compounds containing nitrogen and oxygen from oil stocks was not, studied extensively, it was observed that good adsorbents for removing sulfur compounds removed oxygen compounds to about the same extent. Nitrogen compounds were removed very readily, particularly by aluminas, whether calcined or not. Oil fractions desorbed by hydrocarbons from alumina or silica gel generally contained less than 0.001% nitrogen. Compounds of nitrogen and oxygen were con-
centrated in the sulfur-rich fractions desorbed by alcohol. Separation of Oils with Multiple Adsorbents
Advantage may be taken of the ability of one adsorbent to separate sulfur compounds from hydrocarbons and of a second adsorbent to separate hydrocarbons into types by employing the two in sequence. The order is not important. If the desulfurizing adsorbent is used first, the sulfur compounds appear as a sulfur-rich concentrate along with resinous material, highly condensed aromatics, etc., as the last fraction to be desorbed. If the hydrocarbonseparating adsorbent is used first, followed by refractionation of the aromatic concentrates on a calcined alumina, sulfur concentrates appear as very small fractions a t the end of each refractionation run. Both techniques were used in this' work. Separation of Naphthenic Oil. Oil A was first desulfurized on a large scale with H-41 alumina which had been calcined a t 700' C. The resultant cuts were combined into concentrates of desulfurized saturates, mononuclear, diVOL. 50, NO. 6
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nuclear, and trinuclear aromatics, and a sulfur concentrate. The hydrocarbon fractions were then individually passed through uncalcined H-41 alumina. Cuts were stripped free of solvent, combined on the basis of refractive index, and analyzed for aromatic types by ultraviolet spectroscopy. Properties of heart cuts of the refractionation runs are given in Table 111. The sulfur-rich nonhydrocarbon fraction, constituting 6% of material in the first fractionation, was also refractionated on uncalcined H-41 alumina (Table IV). Only cut 3 contained sufficient material of sufficiently high sulfur content to be of interest. This cut was calculated to contain over 80% of sulfur compounds. Its relatively large amount of oxygen (1.90%) indicated the presence of oxygen-containing compounds taken out of hydrocarbon fractions. Ultraviolet analyses of cut 3 indicated thiophenes as a major component (30%) with some thioindanes and thiotetralins present. Remaining sulfur compounds may be saturated molecules and would not appear in the ultraviolet scan. Cut 4 contained some diphenyl sulfides and benzothiophenes. This separation technique does not adequately separate sulfur-free tetranuclear and higher aromatics. Separation of Paraffinic-Base Oil. Oil B was first separated into sulfurcontaining hydrocarbon types with silica gel. Blends of cuts were made to give
Table 111.
fractions of saturates, mononuclear, dinuclear, and trinuclear aromatics, and resins. These fractions were individually passed through calcined H-41 alumina to remove sulfur compounds and provide additional purification of the desired hydrocarbon type (Table 111). I n each refractionation sulfur was concentrated in the tail-end cuts, with sulfur contents ranging from 2 to 4y0. These were not processed further. I n both of these runs saturate fractions contained 0.00 to 0.01% sulfur. Mononuclear aromatics contained 0.04 to 0.05% sulfur, dinuclear aromatics 0.07 to 0.15% sulfur, and trinuclear aromatics 0.21 to 0.32% sulfur. This is a substantially better desulfurization than has been obtained by adsorbents. Calcined aluminas have also been successfully used for desulfurizing highsulfur crudes. Conclusions
Two major observations are made in the present work. An alumina may be improved in its ability to remove sulfur compounds from aromatic fractions of mineral oil by calcining a t 600' to 700' C. for a prolonged period. The removal of sulfur is indicated by the following comparison of sulfur contents of aromatic fractions obtained by parallel percolation of the same oil through calcined and uncalcined H-41 alumina.
Properties of Hydrocarbon Types
Hydrocarbon Type Saturates Mononuclear aromatics Dinuclear aromatics Trinuclear aromatics Original oil
55 22 12 5
Refractive Sulfur, index wt. % 1.4865 1.5228 1.5678 1.6216
1.5153
0.01 0.05 0.07 0.21 0.26
Refractive index
Sulfur, wt. %
73 12 7 4
1.4671 1.5098 1.5769 1.6505 1.4848
0.00 0.04 0.15 0.32 0.16
Refractionation of Sulfur-Rich Fraction from Oil A on Uncalcined H-41 Alumina
Fraction 1
2 3
4
5 6
Undesorbed Charge
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Wt. % of Charge 0.48 0.63 6.8 5.6 13.4 5.3
Mononuclear aromatics Dinuclear aromatics Trinuclear aromatics
0.10 0.50
0.07
1.4
0.21
0.02-0.05
hydrocarbons and shows some ability to fractionate hydrocarbon types. This removal appears to be due to physical adsorption because, unlike Raney nickel, it permits these sulfur compounds to be desorbed by polar solvents. The oil fractions obtained in this work have been used in a detailed study of the mutual effects of various hydrocarbon fractions on the oxidation stability of oils ( 5 ) . Acknowledgment
The authors wish to acknowledge the assistance of A. E. Hirschler, who advised on chromatographic procedures, E. J. Rosenbaum and Anne R. Donnell, who supervised the spectroscopic analyses and interpreted spectroscopic data, R. W. King and H. H. King, Jr., who supplied many of the analyses, and J. W. Marshall and H. S. Young, who conducted much of the experimental . work. Literature Cited
Total in oil, wt. %
1st fractionation, H-41 alumina (calcined at 700° C.), 2nd fractionation, H-41 alumina (uncalcined), a 1st fractionation, silica gel. 2nd fractionation, H-41 alumina (calcined at 700' C.)* 0 Does not inrlude 6% of material removed as sulfur-rich fraction (Table IV).
Table IV.
Fraction
Sulfur Content, Wt. % Uncalcined Calcined alumina alumina
Oil Bb
011A"
Total in oil, wt. %c
Nickel-nickel oxide supported on silica-alumina is an excellent material for removing sulfur compounds from
Cumulative Wt. % of Wt. % Original Oil 0.5 1.1 7.9 13.5 26.9 32.3
Sulfur, Wt. %
0.029 0.038 0.41 0.34 0.81 0.32
Too dark Too dark
1.1 5.5 7.36 5.05 2.58 1.11
6.0
Too dark
2.53
67.7
INDUSTRIAL AND ENGINEERING CHEMISTRY
Refractive Index 1.490 1.516 1.545 1.585
(1) Coleman, H. J., Adams, N. G., Eccleston, B. H., Hopkins, R. L., Mikkelson, L., Rall, H. T., Richardson, D., Thompson, C. J., Smith, H. M., Anal. Chern. 28, 1380-4 (1956). -, (2) Cornelius, E. B., Milliken, T. H., Mills, G. A., Oblad, -4.G., J . Phys. Chem. 59, 809-1 3 (1955). (3) Hirschler, A. E., James, R. L., Division of Petroleum Chemistry, 127th Meeting, ACS, Dallas, Tex., April 1956. (4'1 V. C. F.. Blue. R. W.. IND. , , Holm. EN;. CHEM.43,'501-i (1951). ' (5) Jezl, J. L., Stuart, A. P., Schneider, A., Zbid., 50,947 (1958). (6) Kurtz, S. S., Jr., King, R. W., Stout, W. J.. Partikian. D. G.. Skrabek, E. A.; Anal. Chem. 28; 1928-31 (1956). (7) Sun Oil Go., unpublished data. (8) Thompson, C. J., Coleman, H. J., Rall, H. T., Smith, H. M.,Anal. Chem. 27,175-85 (1955). \ -
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RECEIVED for review July 2, 1957 ACCEPTED November 1, 1957 Division of Petroleum Chemistry, 131st Meeting, ACS, Miami, Fla., April 1957.
