xtraction of ulfur Corn ydrogen A. P. LIEN, D. A.
M C C A U L A Y , AND
B. L. EVERING
S t a n d a r d Oil Company (Indiana), Whiting, Ind. E x t r a c t i o n of individual organic sulfur compounds with anhydrous liquid hydrogen fluoride shows a n orderly progression with changes i n s u l f u r type, i n molecular weight, or i n configuration of substituent groups. Increased extraction is obtained i n going f r o m mercaptans to disulfides to thio ethers, b u t extraction is decreased with increasing molecular weight of a given type of sulfur compound. Whereas transition from primary to secondary t o tertiary alkyl substituents results i n progressively increased extraction, introduction of t h e phenyl group markedly lowers extraction. These relations are i n keeping with t h e Lewis acid-base concept a n d with f u n d a m e n t a l principles of electronegativity as related t o structure. Besides extraction, certain sulfur compounds undergo i n t r a - a n d intermolecular reactions i n t h e presence of hydrogen fluoride. Addition of olefins t o mercaptans results i n t h e formation of thio ethers soluble i n hydrogen fluoride a n d thereby markedly enhances t h e degree of extraction.
HE action of anhydrous hydrogen fluoride on organic sulfur compounds was first recognized by Hofmann and Stegemann The first systematic study of solutions of individual organic sulfur compounds in liquid hydrogen fluoride was made by Klatt (8). More recent articles (6,10,11) have described the use of hydrogen fluoride as a selective solvent for removal of sulfur compounds from petroleum stocks. However, no published work on extraction of individual sulfur compounds gives an adequate insight into the striking behavior of this inorganic solvent. The purpose of the present work was to provide a background for better understanding of the nature of tho solubility effects exhibited by hydrogen fluoride as applied to selective solvent extraction-for example, of petroleum stocks. Toward this end a systematic study was made of the action of anhydrous hydrogen fluoride toward individual sulfur compounds in hydrocarbon solution, (6), but the role of the solvent was not appreciated.
EXPERIMENTAL METHOD The sulfur compounds studied were purchased from commercial suppliers and were used without further purification. Comparison of physical properties with literature values, when available, indicated purities of 90% or better. The individual sulfur compounds were dissolved in n-heptane t o provide a feed with a sulfur content of about 1.5 weight %. These synthetic blends were treated with 20 volume % of anhydrous hydrogen fluoride (Harshaw Chemical Company, commercial grade, 99.5% pure). I n all runs, except where noted, contacting was carried out at room temperature (21 ' to 26" C.)for a period of 1hour in a 1550-ml. carbon steel bomb equipped with a mechanical stirrer operating a t 1725 r.p.m. (4). After settling, the hydrogen fluoride extract layer was separated from the supernatant hydrocarbon layer by withdrawal through a valve a t the bottom of the reactor. The hydrocarbon layer was washed with ammonium hydroxide and water to remove traces of dissolved hydrogen fluoride. Generally, the extract was recovered by evaporating the bulk of the hydrogen fluoride under a mild
2698
vacuum, neutralizing with ammonium hydrouide, and washing with m t c r . However, in the case of lower boiling materials tht extract layer was poured onto cracked ice and neutralized to rccovcr the organic extract from the hydrogen fluoride solvent. Sulfur analyses on the feed blends and on the raffinates wert obtained by the lamp method (1) and on the extracts by the bomb combustion method (W). Mercaptan (thiol) sulfur wac determined by a modification of the potentiometric titratior method of Tamele and Ryland ( I S ) . EFFECT OF STRUCTURE OM EXTRACTION Sixteen aliphatic sulfur compounds were investigated. The three general types-mercaptans, disulfides, and thio ethers-were all represented by species of various molecular weights and in most cases by straight-chain and branched-chain structures. The results of these experiments, summarized in Table I and shown graphioally in Figure 1, lead to the following genc>ralimtions : 1. Increasing the niolrcular xeight rcbults in a precipito&j decrease in extraction with primary mercaptans and primary disulfides. This effect is less pronounced witla primary thio ethers and tertiary mercaptans. 2. Tertiary mercaptans are much more readily extracted thar: primary mercaptans of tnhe same molecular weight. The one available secondary mercaptan falls between the corresponding primary and tertiary mercaptan. Tertiary mercaptans undergo intermolecular reaction to some extent during extraction to form thio ethers; this reaction will be discussed in more detail in a later section. 3. For a given molecular weight and equal degrees of branching, ease of extraction of the three sulfur typps lies in the order: thioethers >> disulfides > mercaptans.
Table I.
Extraction of Aliphatic Sulfur Compounds
Charge: blend of sulfur compound in n-heptane IIF: 20 volume "/o on blend Sulfur Analyses, Sulfur Mol. wt. % wt, Blend Raffinate Compound" n-Propyl mercaptan 76 1.18 0.36 n-Butyl mercaptan 90 1.23 0.52 n-Octyl mercaptan 146 1.48 1.13 n-Dodecyl memaptan 202 1.38 1.31 aec-B u tyl mereaptau 90 1.41 0.41 0.06 teTt-Butyl mercaptan 90 1.40 0.06 tert-Octyl inercaptanb 146 1.48 tert-Dodeoyl mercaptan6 202 1.53 0.27 Methyl disulfide 94 1.50 0.33 178 1.52 n 95 n-Butyl disulfide 1.15 %-Amyl disulfide 206 1.42 1.41 n-Octyl disulfide 290 1.56 402 1.41 1.39 n-Dodecyl disulfide 178 1.56 0.36 teit-Butyl disulfide 118 1.50 0.02 %-Propyl sulfide 202 1.48 0.16 n-Hexyl sulfide a All normal compounds are primary. b Derived from the corresponding isobutylene polymer.
Sulfur Removsr.
%
70 58 2; 72 !36
96 82 78 37 19 R 1
77 99 90
Additional insight into the effect of molecular structure i? afforded by the experiments on aromatic sulfur compounds shown in Table 11.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1949
Table 11. Extraction of Aromatic Sulfur Compounds Charge: blend of sulfur compound in n-heptane HF: 20 volume % on blend Sulfur Sulfur ' Wt. Sulfur Removal, Compound Blend Raffinate% Phenyl mercaptan 1.49 1.08 28 Benzyl mereaptan 1.50 0.04 97 Phenyl sulfide 1.47 15" Benzyl sulfide 1.50 0:06 96 a Sulfur removal determined both by weight of material extracted and by refractive index change.
w
These results demonstrate a striking difference between the aromatic and aliphatic classes of compounds. Thus, phenyl sulfide, instead of being more completely extracted than the mercaptan, undergoes little extraction. On the other hand the benzyl compounds-both mercaptan and sulfide-are extracted almost completely. A plausible explanation for the above results is provided by the Lewis electronic concept of acids and bases ( 9 ) ,combined with the nucleophilic properties (electronegativities) of the various compounds as predicted from structural relations. If it is assumed that the organic sulfur compounds act toward hydrogen fluoride as bases in the Lewis sense, then the extraction of the various sulfur compounds could be visualized as involving an acid-base type of reaction. For example, with a mercaptan the reaction would be written
.. .. + H:F:
R:C:S:H H
.. ..
I**
[
H
a
I,
E * * ]+[
R:C:S:H
I
AH8
1
&H
CH3
Group (R) Phenyl n-Hexyl Benzyl a
Interpolated value from Figure 1
0 50
I
I
100
160
200
I
I
250
300
MOLECULAR WEIGHT
HH
CHa- ? t -S-H
CH8-b
The marked effect of a phenyl group to reduce and of the benzyl group to enhance the electron density around an attached sulfur atom is shown by the following summary:
Figure 1. Effect of Structure and Molecular Weight on Extraction of Sulfur Compounds
:F:]-
The reaction of hydrogen fluoride with sulfur compounds to form an ionized complex was postulated by Klatt (8) when he found that the boiling point elevation of individual sulfur compounds in hydrogen fluoride was greater than would be expected from simple solution. The present study shows that the degree of extraction of sulfur compounds from hydrocarbon solution can be correlated with the nucleophilicproperties of the compounds as predicted from molecular structure- With regard to the effect of substitution or structural change on reactivity with hydrogen fluoride, the important consideration is the electron density at an active point, such as the sulfur atom, in the molecule; thus with increasing electron density there will be a resulting increase in the nucleophilic (basic) properties of the compound. Increased branching a t the carbon atom next to an active point-that is, transition from primary to secondary to tertiary alkyl groups-results in increased electron density a t the active group. For example, the following resonating structures can be written for a tertiary alkyl sulfur compound:
&Ha
2699
With mercaptans the phenyl group results in lower basicity than the n-alkyl group of the same number of carbon atoms. Introduction of the second phenyl group into the molecule, as in diphenyl sulfide, lowers still further the basic properties of the sulfur atom. The benzyl group, by contrast, provides a high electron density, so that both mercaptan and thio ether are essentially completely extracted. Both these effects can be explained by resonance of the attached groups with the ring. When the sulfur is directly attached to the ring resonance may occur between the following structures:
As a result of the contribution of the two ionic forms, the electron density around the sulfur atom is much less than is the case for an aliphatic mercaptan. When the sulfur atom is attached to a benzyl group the following resonating structures are possible:
CHa CH3-&+ S-H AH3
CH3
l CH-C S-H *- I +
CH3
CHs
cH3-(i +
g-H H3
Since there are fourresonatingionicstructures,their contribution toward the actual structure of the resonance hybrid is much greater than is the case with a primary alkyl group in which only one form is possible. Hence, a tertiary alkyl group attached to the sulfur atom results in a higher electron density than a primary alkyl group; a secondary alkyl group should provide a:: intermediate effect.
The positive carbonium ion is stabilized by resonance with the ortho- and paraquinoid structures and, therefore, makes a large contribution toward the structure of the actual hybrid. Hence the electron density around the sulfur atom is much greater than it would be for a n-alkyl mercaptan. The present studies indicate that with increasing molecular weight the molecule is extracted to a lesser extent. This result could not be predicted on the basis of electron densities about the sulfur atom since the inductive effects of alkyl groups increase slightly with increasing molecular weight (7). However, it is
INDUSTRIAL AND ENGINEERING CHEMISTRY
2700
possible to explain this anomaly by making the reasonable assumption that two equilibria are involved: one a physical distribution of unchanged sulfur compound (and also of the sulfonium complex) between two phases, and the other a chemical equilibrium between the sulfur compound and the sulfonium complex. Thus, for a mercaptan, the following equilibria are in force:
+HF
Hydrocarbon phase -
d
RSH
_ _ - - - _ _ _ --
- --
-
I
__
-
__
Vol. 41, No. 12
REACTION OF SULFUR COMPOUNDS IN THE PRESENCE OF HYDROGEN FLUORIDE During the course of the above studies on hydrogen fluoride extraction, it was found in general that the primary straightchain sulfur compounds were recovered from the extract unchanged. In branched-chain and benzyl derivatives, hoivever, processes other than simple extraction occurred, as shown by extensive rearrangement. In order to elucidate specifically the reactions t,hat were taking place, several runs were carried out with results as shown in Table IV and discussed below.
HFphase
BENZYL MERCAPTAN
The horizontal arrows represent the chemical equilibria and the vertical arrows the physical equilibria. The equilibrium const,ant of the chemical reaction is determined by the electron density about the sulfur atom. Since the electron density increases only slightly with increasing molecular weight of the side chain, it is possible that it is overbalanced by the physical equilibrium which would be shifted toward the hydrocarbon phase with increasing length of a nonpolar, alkyl side chain, As regards the principal types of sulfur compounds, it would be predicted that thio ethers are more basic than mercaptans. This follows from the generally accepted theory that substitution of an alkyl group for hydrogen produces an electronic displacement away from the substituent ( 7 ) . This is actually the order of extraction obtained with these two classes in the present work. The same order of complex formation was found by Klatt (8) with ethyl mercaptan arid ethyl sulfide, as measured by boiling point elevation of solutions in hydrogen fluoride. There is no direct evidence in the literature concerning the basicity of disulfides ot,her t,han the results of the present study, which orients them as being slightly more basic t,han mercaptans of the same molecular weight.
A copious amount of hydrogen sulfide was present in the reaction products. Except for a small portion, the extract was hexanesoluble and on recrystallization yielded yellow-white crystals. Sulfur analyses and melting points, including a mixed melting point with pure benzyl sulfide, indicated these crystals to be benzyl sulfide.
Melting point, C. Mixed melting point, Sulfur, nt. 70
' C.
Benzyl Mercaptan Liquid
25:8
HexaneSoluble Product 47-48 48
Benzyl Sulfide 49
14:9
12.3
The reaction that occurred in this case is as follows:
+ HzS
2CeHsCHzSE-I +(CfiHjCHz)zS
The hexane-insoluble portion of the extract was probably a highly condensed material formed by chain alkylation of successive molecules. This reaction, which is known for the oxygen analog, benzyl alcohol (IW),can be pictured as follows:
nC6H;CIIzSH
+Ce"CH,(Ce"CH,)n-i
SH
+
(n-1)
H2S
EFFECT OF ACID STRENGTH ON EXTRACTION In the above correlations, the relative basicities of a number of sulfur compounds have been compared to an acid of fixed strength (99.570 hydrogen fluoride). If now the strength of t,he acid is increased-for example, by use of an activat,or-the degree of extraction of a given sulfur compound likewise should be increased. The addition of boron trifluoride to hydrogen fluoride has been shown by Burk ( 3 ) to provide a highly effective desulfurizing medium for petroleum stocks. The data in Table I11 demonstrate quantitatively the activating influence of boron trifluoride on the extraction of an individual sulfur compound.
Table 111. Effect of BF3 on Extraction Charge: phenyl sulfide in n-heptane
HF BFI moles/atom sulfur H F on feed blend vol. % Phenyl sulfide in blend, wt. % Sulfide extractiona, 5% Determined by weight of extract.
0.0 20.0 8.Q 15
HF
+
BFs 1.12 30.8 8.7 93
Whereas hydrogen fluoride alone removes little phenyl sulfide, addition of boron trifluoride results in almost complete extraction. This action is postulated t o occur in the following inannri :
THIOPHENE
Thiophene is almost completely removed by hydrogen fluoride from its solution in heptane but is destroyed in the process; hydrogen sulfide is evolved and a light-brown, brittle solid is formed. This solid is apparently soluble in hydrogen fluoride, but it is insoluble in all common organic solvents. Its sulfur content of 28.6Tc, compared to 38.27, for pure thiophene, indicates that diacetylene might have appeared as an intermediate reaction product; possible reactions of the diacetylene intermediate include polymerization and readdition of hydrogen sulfide, as well as alkylation with thiophene to form a solid, cross-linked high molecular weight product. IZlatt (8) also observed that a highly condensed solid was formed when thiophene was contacted with hydrogen fluoride, although he reported the polymer to be insoluble both in hydrogen fluoride and in organic solvents. ter t -BUTY L MERCAPTAN
The organic extract was fractionated on a thirty-plate column and was found to have the following composition: Fraction 83-64.5' C. 64.5-143' C. 143-144' C. 144' C . +
Vol. % of Extract 64 6
28 3
n "u"
1.4230
1.4100
1.4420
....
Composition tert-Butyl Cnknown"mercaptan tert-Butyl sulfide
,.............
a Probably diiaobutylene plus sulfur compourids.
In the presence of a base (in this case a sulfur compound) the strongly electrophilic boron trifluoride attracts the fluorine atoin of hydrogen fluoride and, in forming a coordination complex therewith, markedly reduces the electron density of the fluoride ion; the proton is thereby released and made more available for coordination with the electrons of the sulfur atom.
About two thirdsof the mercaptan was extracted unchanged and most of the remainder reacted to form the thio ether according to the following equation:
HF
2(CH3)aCSH I _ (CHS)3 C-S-C
(CH,),
+ HzS
2701
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1949 T a b l e IV.
ether. The experimental verification of this reaction is discussed in the following section.
R e a c t i o n of S u l f u r C o m p o u n d s (Temperature: 20' t o 25' C . )
Sulfur, Wt. % WLa. HF, RaffiGrams Grams Charge nate
Compound Benzyl mercaptan 20 24 Thiophene tert-Butvl mercaotan 233 tert-Octyl mercaptan n-Octyl mercaptan
*
*
}
48
Sulfur Removal,
%
100 140 348
1.50 2 68
0.042 0.05
97 98
150
6.3
0.413
93
..
...
,
I
Reaction Productsb Benzyl sulfide Resin tert-Butyl sulfide thio andethers 'la
'''
a Dissolved i n n-heptane except f o r tert-butyl mercaptan, where pentane was used. b Hydrogen sulfide also formed i n every case.
This reaction is probably reversible under the conditions of extraction] so that the ratio of unchanged mercaptan to thio ether is a function of the partial pressure of hydrogen sulfide. t e r t - O C T Y L MERCAPTAN
+ n - O C T Y L MERCAPTAN
Since the extraction results in Table I indicate essentially complete removal of tertiary mcrcaptans and very incomplete removal of normal primary mercaptans, i t might be supposed that hydrogen fluoride would afford separation between the two types. I n an experiment designed to obtain quantitative data, a n-heptane blend of equal weights of normal and tertiary octyl mercaptan was contacted with 30 volume % ' hydrogen fluoride, with results as shown in Table IV. Total desulfurization was 93%] whereas only about 60% was expected on the basis of extraction characteristics of the two individual sulfur compounds. The extent of desulfurization, together with the presence of copious quantities of hydrogen sulfide in the product, indicated that reaction had occurred to convert the relatively insoluble normal primary mercaptan into a molecular species more soluble in hydrogen fluoride. The properties of the organic extract, as set forth in Table V, disclose that the principal products thus formed were thio ethers.
T a b l e V. Fractionation of Mixed Octyl M e r c a p t a n Extract Boilinog Mercaptan Point, C. Extract, 9, (9 Rim.) Vol. % Wt. %
4
*
52- 88 88- 99 99-109 109-116
4.8 4.8 4.9 5.2
9.8 1.0 0.27 0.15
116-119
54.6
119-162 162-170 170
10.8 10.0 4.9
0.0 0.79 1.4
..
Total 5. Wt. %
.
Probable Composition
14.71 15 5 Unchanged mercaptan plus 15:4\ higher boiling thio ethers 14.9 14.8
i::}
..
C a R S R , theoretical S = 15.8% C I S R S R ,theoretical S = 12.4% Residue
The potentiometric titrations showed that only 3 to 4% of the total extract consisted of mercaptan. The principal product was a 12-carbon thio ether, most of the remaining product being a 16-carbon thio ether. These results demonstrate that the mercaptans were almost completely converted, and the high degree of extraction obtained (Table IV) correlates well with the previously demonstrated solubility of thio ethers in hydrogen fluoride. The formation of the principal product, 12-carbon thio ether, may be represented by the following two step equation :
+ L-CBHI~SH+CsH17SCdHs + t-C4HgSH + H2S n-CaHi7SH + t-C4HaSH +CSHI~SC~HQ
n-CsH1,SH
(1) (2)
The fact that the alkylation of the n-mercaptan with an S-carbon tertiary mercaptan takes place in increments of four carbon atoms and with loss of hydrogen sulfide points to the strong possibility that alkylation of a normal mercaptan could be accomplished with isobutylene or isobutylene polymer to yield the thio
REACTIONS BETWEEN SULFUR COMPOUNDS AND OLEFINS Heptane solutions of two mercaptans, n-dodecyl and n-octyl, were contacted with hydrogen fluoride alone and with hydrogen fluoride in the presence of added diisobutylene as shown in Table VI. The effect of the added olefin on desulfurization is strikingly shown by the fact that total sulfur removal in the case of n-dodecyl mercaptan was 98yo with added olefin as compared with 5% in the absence of olefin. I n the case of n-octyl mercaptan the corresponding figures are 98 and 24yo,
Table VI.
Reaction-Extraction w i t h Mercaptan-Olefin Mixtures HF: 20 volume % on blend
Blend Mercaptan moles Diisobutylgne, moles 8 i n n-C7 blend, wt. % Raffinate Total S, wt. % S removal, % Mercaptan S, wt. % R S H removal, Yo Extract Refractive index, ngo Specific gravity Boiling range, C . Total 8 wt. % Meroap'tan 8, wt. %
n-Dodecyl
Mercaptan n-Dodecyl n-Octyl
0.208 0.238 1.39
0.212
0.03 98 0.004 99.7
1.31 5
1.4573 0.832 286-292 10.0
0.0
0.0
1.38
... I . .
... ... ... .*. ...
0.206 0.212 1.41 0.03 98 0.00 100 1.4568 0.873 265-2635
...
0.0
n-Octyl 0,208 0.0 1.48 1.13 24 1.17 21 .,.
...
... ..,
...
Potentiometric titration of the raffinates from the runs with added olefin showed essentially 1 0 0 ~ mercaptan o removal, which indicates that the small amounts of residual sulfur compounds are unextracted reaction products of mercaptan and olefin. The absence of mercaptan sulfur in the extracts from the same runs provides a final proof of quantitative conversion of the original mercaptans. The physical properties of the extract from n-dodecyl mercaptan are roughly those of a 16-carbon thio ether, while those of the extract from n-octyl mercaptan are typical of a 12carbon thio ether. The sulfur content (10%) of the extract from n-dodecyl mercaptan is somewhat less than that of a 16-carbon thio ether (12,4761, probably because some isobutylene polymer or hydrogen transfer product is present. Both extracts formed crystalline sulfones and mercuric chloride complexes. These properties of the extracts demonstrate that a hydrogen fluoride-soluble thio ether is formed by reaction of an olefin with a mercaptan under the influence of hydrogen fluoride. Since the diisobutylene used appeared to depolymerize and provide isobutylene fragments for reaction with the mercaptan, the final reaction would be pictured as: RSH
+ (CHa)2C = CH2 +RSC(CH3)s CONCLUSIONS
The extraction of organic sulfur compounds with anhydrous liquid hydrogen fluoride shows an orderly progression with changes in molecular weight, configuration of substituent group or type of sulfur compound. This orderly arrangement is in keeping with the Lewis acid-base concept and with the fundamental principles of electronegativity as related to structure. It therefore provides a means of predicting with reasonable accuracy the ease of extraction of sulfur compounds that have not been investigated experimentally. Besides extraction, certain sulfur compounds undergo intraand intermolecular reactions in the presence of hydrogen fluoride. With difficultly extractable mercaptans, addition of olefins results in the formation of thio ethers soluble in hydrogen fluoride, and thereby markedly enhances the degree of extraction.
2702
INDUSTRIAL AND ENGINEERING CHEMISTRY
These findings, in addition to their theoret,ical interest, have important applications to the extraction of sulfur compounds from petroleum.
ACKNOWLEDGMENT The authors wish to thank B. H. Shoemaker and R. F. Marschner of this laboratory and H. C. Brown of Purdue University for their advice and encouragement during the course of t,his work.
LITERATURE CITED (1) Am. SOC.Testing Material, “A.S.T.M. Standards on Petroleum Products and Lubricants,” p. 37, D 9-47T, Philadelphia, Pa., 1947. i2) Ibid., p , 472, D 894-46T.
Vol. 41, No. 12
(3) Burk, R. E., U.S. Patent 2,343,841 (March 7, 1944). (4) Evering, B. L., and d’Ouville, E. L , d . Am. Chem. &c., 71, 440 (1949). (5) Foster, A. L., Oil Gas J . , 44, 96 (June 15, 1946). (6) Hofrnann, F.,and St,egemarin, W., Brit. Patent, 292,432 (June 25, 1927). ( 7 ) Ingold, C. K., Chem. Rev., 15, 225 (1934). (8) Klatt, W., Z . anorg. u.allgem. Chem., 232, 404 (1937). (9) Lewis, J., J . Franklin In.st., 226, 293 (1938). (10) Scafe, E. T., Petroleum Refiner, 25, 413 (1946). (11) Schneider, K. W., and Gottsohall, H . , ErdBl u a Aohla, 1, 74 (1948) (12) Schriner, R. L., and Berger, A., J . OTO.Chena., 6, 305 (1941). (13) Taniele, M . , and Kyland, L. B., IND. EXG.CHEM., ANAL.ED., 8, 16 (1036). ~
RECJIVFD M a y 16, 1949
CATALYTIC DESULFURIZATIQN OF CRUD J. H.HALE, M. C. SIMMONS1, AND F. P.WHISENHUNT Petroleum Experiment Station, Bureau of Mines, Bartlesville, Okla. Experiments have indicated that the composition and Properties of crude oil can be improved greatly by catalytic desulfurization. Table I shows some of the changes that would be brought about by treating 100 barrels of Slaughter crude oil in a bauxite catalytic desulfurizer under the conditions given. The sulfur content of the oil would be reduced Sl.Sq’,. The most active types of sulfur compounds are the ones removed by the treatment ; therefore corrosion problems would be reduced in the subsequent refining of the oil. The products distilled from the oil would have improved properties. The gasoline would have
an A.S.T.M. motor-method clear octane number 6.8 units higher, and also an increased lead susceptibility. The volumes of gasoline and gas oil would be increased at the expense of the residual material, thus reducing the amount of bottoms from the distillation. A limited amount of experimental work using hydrogen and an operating pressure of 225 pounds per square inch gage with bauxite, cobalt molybdenum bauxite, and zinc molybdenumbauxite catalysts showed that better desulfurization could be obtained in this way and that the prepared catalysts give the best results.
ORK on the catalytic desulfurization of crude oil v a s an outgrowth of Bureau of Mines studies on desulfurization of aviation-gasoline base stocks during IVorld War 11. The idea was conceived that, if an entire crude oil could be desulfurized effectively corrosion problems would be minimized, subsequent desulfurization of the gasoline distillate would not be necessary, a.nd a cracking unit charge stock of low sulfur coiit,ent would be available. This report covers experiments on the desulfurization of Slaughter crude oil over bauxite to establish optimum limits for operating variables, such as temperature and liquid hourly space velocity. Data also were obt’ained for the effect of oil-catalyst ratio on the liquid products and catalyst deposits, but additional data on regeneration of the catalyst would be required to establish the maximum oil-catalyst ratio that should be used. Further development would require pilot scale evaluation of t,he process, preferably on a continuous or cycle basis. Such development, if t h e data !Tarrant it, is deemed outside the scope of the activity of the Bureau of Mines. Sccordiiigly, tlic data are presented as found as a basis for further development.
displacement charge pump with adjushble stroke furnished the desired rates of pumping. The preheater consists of 15 feet of ‘/*-inch, standard black iron pipe coiled so that the coil fits smoothly over a 2-inch pipe placed concentrically in a 4-inch pipe with the bottom closed and the annular space filled with lead. The lead is heated by two 1000-watt strip heaters, cont,rolled by a variable transformer, clamped on opposite sides of the 4-inch pipe. The outside is insulated with high-temperahre pipc insulation. The catalyst chamber is a 5-foot section of 2-inch extra strong pipe with a concentric thermomell made of 1/4-inchpi e extending from the tee at the top of the column to a point 6 incies from the bottom of the chamber. Eight, t’hermocouples are equally spaced throughout the length of the thermowell. The volume of the catalyst chamber is about 2700 ml., of which 2400 ml. are filled with catalyst. As shown in Figure 1, one layer of a,sbcstos listing on the column furnishes the base for a layer of Alundum cement. Three Nichrome-wire heating elements, each covcring a separate vertical portion of the chamber, are wound over the layer of Alundum cement, which is built up between the coils of the heating element and holds them in place. Two layers of asbestos listing and an outside covering of pipe insulation covcr the heating wires. The condensers are st,raight tubes with an outer jacket in which refrigerated water is circulated. The liquid-product receiver is a 2-gallon screwcap bottle like the charge bottle. A smaller receiving bottle is used when the total charge for a run is less than 1 gallon. The gas-washing bot,tles have plastic screw caps with connections for rubber tubing.
APPARATUS Figure 1 shows diagrammatically the small scale bauxitedesulfurization unit used. A 2-gallon screw-cap bottle is the container for the charge. Two 500-ml. Pyrex graduated cylinders, closed at the ends by gasketed-steel plates, drilled and tapped for pipe connections, provide a measure of the volume of oil charged. A positive1
Present address, Shell Oil Company, Houston, Tex.
-
-
-
EXPERIMENTAL PROCEDURE A 2-gallon bottle is placed on the charge line wit,h enough sample to fill the charge lines to the top of the catalyst chamber and to adjust the pumping rate. One of the graduated cylinders is pumped down to the bottom graduation mark, and while the other cylinder is pumping down, the charge bottle is replaced wit,h one containing a weighed aniount of sample. The empty
