I
ALBERT 1. WILLIAMS and ROBERT D. OFFENHAUER Research and Development laboratory, Socony Mobil Oil Co., Inc., Paulsboro, N. J.
Acidic Components of Catalytically Cracked Distillate Fuel Oil Aromatic thiols separated from catalytically cracked distillate fuel oil promote sediment formation, but of the phenols present only I-naphthol is active in development of color and sediment the crude acid oil was extracted with 92 CATALYTICALLYgrams of sodium hydroxide in 1.7 liters
r
i
cracked distillate fuel oil usually darkens and forms sediment during storage. Removal of acidic components by treatment with alkali metal hydroxides often improves storage stability. The composition of the acids extracted with 5yosodium hydroxide from two catalytically cracked fuels was studied: one from Middle East crudes, the other from West Texas crudes. The composition of the acid oil of Middle East origin was approximately 3 to 1 aromatic thiols to phenols; that of West Texas origin, about 1 to 8. The effect on stability of adding phenol and aromatic thiol fractions, and synthetic compounds, to catalytically cracked distifIate fuel oil was determined. Samples (500 ml.) were stored in a 600-ml. beaker a t 110' F. for 12 weeks. Sediment was determined by filtration, with a reproducibility within d = 2 0 ~ ~Color . was determined on the filtrate. Experimental
Procedure A. This procedure was applied to a catalytically cracked distillate fuel oil (boiling range 430° to 650' F.) from Middle East crudes (Table I). An acid oil containing phenols and aromatic thiols was obtained by extracting 100 gallons of the freshly distilled fuel oi1 with two 1-gallon portions of 5% sodium hydroxide. The acid oil was set free by acidification of the aqueous layer with hydrochloric acid. Acids thus liberated n t r e taken up in 1 liter of peroxide-free ether, in two portions. T o remove entrained oil
of water in two portions. The alkaline extracts were run at once into 400 ml. of 6.2M hydrochloric acid. Liberated acid oil was then taken u p in 450 ml. of ether, in two portions. Because the sodium salts darkened and formed precipitates very rapidly, all of these manipulations were carried out under a nitrogen atmosphere. The combined ether extracts were dried over Drierite and filtered. Ether was removed by distillation through an 8-inch column packed with glass helices. The acid oil remaining (152 grams) was dissolved in 1.5 liters of methanol.
I
3
5
9
7
A saturated solution of lead acetate trihydrate in methanol at 20' C . was added to the methanol solution of acid oil a t room temperature. The addition was continued, with stirring, until precipitation ceased. When the lead thiolides had been filtered off, they were suspended in 700 ml. of methanol and stirred for 15 minutes. The salts were then refiltered and washed on the filter with three 2 0 0 - d . portions of methanol. After drying under vacuum, the yield of lead thiolides was 195 grams. The lead thiolides were refluxed with 43 mi. of concentrated sulfuric acid in 500 ml. of water. During refluxing, steam was passed through the solution
FRACTION N U M B E R II 13 15 17 19
21
23
25
27
290
1.6600
270
1.6400
25C
1.6200
230
1.6000
21c
1.5800
Li W
5
5 W W
!-
1.5600
I90 IO
20
30
40
50
60
70
80
VOLUME PER C E N T D I S T I L L E D
Figure 1 .
Fractional distillation of aromatic thiols separated by Procedure A VOL. 49, NO. 8
AUGUST 1957
1259
Table I.
Flow Diagram for Separation o f Aromatic Thiols from a Catalytically Cracked Fuel Oil o f Middle East Origin (Procedure A) Cat. cracked fuel oil, 298,000 g r a m s ; 0.015%o thiol S ; 45 grams thiol S ~-
[
2 gal. 5 % N a O H
Hydrochloric acid
Acid oil, 152 g r a m s ; 17.057, S, 26 grams
Caustic-washed oil 298,000 g r a m s ; 0.0057, thiol S , 15 grams thiol S
Methanol solution of l e a d acetate
1
Lead thiolides, 195 g r a m s
I
A
Dilute sulfuric acid ; ether extraction
Phenols in methanol
Aromatic thiols, 115 grams ; 21.317' S, 24.5 grams S Fractional distillation, 20 mm. H g Fractions 1-28 of aromatic thiols
Table It. Flow Diagram for Separation o f Phenols and Aromatic Thiols from a Catalytically Cracked Fuel Oil o f West Texas Origin (Procedure B) Cat. cracked fuel oil, 134,000 g r a m s ; 0.009% thiol S, 12 g r a m s thiol S 2 gal. 5 7 , N a O H
Hydrochloric acid Caustic-washed oil, 134,000 g r a m s ; 0.0047, thiol S, 6 rrrams thiol S
I
Percolated in n-pentane over silica gel
I Methanol I
Benzene I Aromatic thiols, 12.7 g r a m s ; 21.75Yo S, 2.76 grams S
Fractional distillation a t 20 mm. H g
I 1 260
Fractions 1--8of aromatic thiols
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
Phenols, 131 g r a m s ; 0.66% S, 0.87 grams S, 0.000% thiol S Fractional distillation at 10 mm. Fractions 1-41 of phenols
ACIDIC C O M P O N E N T S O F D I S T I L L A T E FUEL O I L to assist decomposition and avoid bumping. The pale yellow thiols rose to the surface, and lead sulfate (116.5 grams) settled out. Regenerated thiols were extracted into 600 ml. of ether, in three portions. Removal of the ether through an 8-inch column left 115 grams of thiols. The thiols (107 grams) were distilled (under nitrogen a t 20 mm. of mercury) through a 115-cm. glass column packed with 1/8-inch glass helices. Each of the 28 fractions taken was 3 ml. in volume; 80% (weight) of the sample was collected as distillate (Figure 1). Procedure B. This procedure was applied to a catalytically cracked distillate fuel oil (boiling range 450' to 650" F.) from West Texas crudes (Table 11). A purified acid oil was obtained from 45 gallons of this fuel oil by Procedure A. The acid oil (178 grams) was dissolved in 560 ml. of n-pentane. An 8foot glass column (1.5 inches in inside diameter) was charged with 1900 grams of Davison commercial grade silica gel. After the column had been flushed with nitrogen, it was prewetted with npentane. The pentane solution of acid oil was then percolated under nitrogen ( 8 ) . The adsorbate was washed with 2.3 liters of n-pentane. Thiols were then removed by desorption with 2.3 liters of benzene. Phenols were desorbed by 1.8 liters of methanol. The aromatic thiols, in benzene solution, were extracted by 900 ml. of 5% aqueous sodium hydroxide, used in three portions. After the thiols had been liberated by excess iced hydrochloric acid (6N), they were taken up in 400 ml. of ether. Removal of the dried ether by distillation left 12.7 grams of thiols. The thiols (IO grams) were distilled (under nitrogen at 20 mm. of mercury) through a 46-cm. column packed with glass helices. Seven distillate fractions were obtained (Figure 2). Phenols were salted from the methanol solution by the addition of 5 liters of concentrated aqueous salt solution. The phenols were extracted by two 500-ml. portions of n-pentane. After the combined pentane solutions had been washed with 6 liters of water, the phenols were extracted by 2.5 liters of 5yo sodium hydroxide, used in three portions. Phenols were freed by iced 6 N hydrochloric acid and taken u p in 600 ml. of ether. Removal of the ether, after drying over Drierite, left 131 grams of phenols. T h e phenols (100 grams) were distilled (under nitrogen) into 41 fractions, through a 115-cm. glass column packed with glass helices. Fractions through ' point) were 34 (at the 79.5 weight % distilled at 10 mm. of mercury pressure. The pressure was then reduced to 3 mm. of mercury for the remaining fractions (Figure 3).
290
I
2
3
FRACTION NUMBER 4 5 6
7
a
280
I.6400
2 70
1.6300
260
1.6200
U 250 2
1.6100
dW
240
1.6000
230
1.5900
220
1.5800
210
1.5700
9
f
W-
2
I-
a 2
W
t-
x
I$
a
200 0
Figure 2.
IO
20
30 40 50 60 70 80 WEIGHT PER CENT DISTILLED
90
100
k~ 0:
1.5600
Fractional distillation of aromatic thiols separated by Procedure B
320
1.6500
300
1.6300 ao
0-
6
r
2
I
N k
0 (D
+ 280
1.6100
41
t
bf
260
1.5900
240
1.5700
I--
z
2
' w
P
c
2 a
0
5
a
LL.
220
1.5500
200
1.5300
w
a
0
rn
0
10
20
30
40
WEIGHT PER
Figure 3.
50 60 70 CENT DISTILLED
80
90
100
Fractional distillation of phenols separated by Procedure
Discussion
Comparison of Procedures. The inefficiency of the original 5% caustic extraction leaves much of the thiol sulfur still in the oil; hence, the sample examined contains only the more acidic components. Particularly in the study of the fuel oil of West Texas origin, it seems likely that the most reactive components are lost from the acid oil sample during the acidification. These may be present in only small amounts. While the acid oil is in aqueous alkali, color develops. When the solution is acidified, precipitates form even in cool solutions
B
under nitrogen. The materials responsible are probably those most active in promoting the development of color and sediment during storage of the catalytically cracked distillate fuel oil. Procedure A gives good recoveries of aromatic thiols only when the percentage of phenols in the acid oil is low. Examination of known mixtures of phenols and aromatic thiols shows that phenols increase the solubility of lead thiolides in the methanol solution. Procedure B gives high losses of aromatic thiols even when phenols are nearly absent. Comparison of Acid Oils. The acid oils obtained from catalytically cracked VOL. 49, NO. 8
AUGUST 1957
1261
Table 111. Analyses of Aromatic Thiol Distillates Separated by Procedure A Fraction
c7 %
H, %
1 3 10 16 21 23 24 25 26 27 28
67.47 69.24 69.41 70.67 71.80 72.41 72.42 73.32 73.60 74.08 74.47
6.58
S, 5%
...
7.17 7.35
~ . .
...
...
19.48
...
X 303.27 - 207.21
1
5 8 12 16 20 24 28 30 31 32 35 38 41
$1
1 262
Mixed Thiols
Richest Fraction
3
1
32
10 17
17 17 17
23 28
crystalline solids. The mass spectrum of the thiols of fraction 28 shows mass numbers for naphthalenethiols and methylnaphthalene thiols. As thiols of low vapor pressure in fraction 28 might be missed in a stud). of the mass spectrum, a sample was desulfurized to allow examination of the corresponding hydrocarbons. The desulfurization with Raney nickel gave a hydrocarbon mixture having a hydrogen to carbon atomic ratio of 1.19, compared with 0.975 for the thiols. This was done by refluxing in ethyl alcohol for 5 hours under a hydrogen pressure of 1 atm. The mass numbers for the hvdrocarbons indicate biphenyl, methylbiphenyl, tetrahydronaphthalene. and its mono-: di-, and tsimethyl derivatives, and /or the alkylindan analogs of the tetrahydronaphthalenes. The ultraviolet absorption spectrum resembles that of diluted biphenyl. The absence of naphthalene was explained when it was found experimentally that 2naphthalenethiol went to tetrahydronaphthalene under the conditions used for the desulfurization. The ultraviolet absorption spectrum of fraction 28 (Figure 4) is much like that of fraction 27 and of the liquid remaining in the distillation column. The spectrum resembles that of 2naphthalenethiol (Eastman Kodak Co.) (see Figure 5). .4sample of l-naphthal-
Table VI.
H,
Distilled,
%
%
%
77.22 77.69 78.03 79.08 79.16 79.67 80.03 79.69 80.40 80.56 80.23 80.76 82.34 82.75
8.01 8.48 8.63 9.01 8.87 8.98 8.82 8.84
0 2.4 9.5-11.8 16.5-18 a 7 25.6-28.0 34.8-37.0 44.0-46.2 53 -0-55.3 62 .O-64.3 66.7-69. 2 69.2-71.6 71.6-74.0 79.5-81.6 86.6-89.4 94.8-97.1
6.60 6.45 6.50 6.67 6.45
Toluenethiol Xylenethiol Trimethylbenzenethiol Tetramethylbenzenethiol Polynuclear thiols
Since 195.0 grams of lead thiolide (Table I) give 116.5 grams of lead sulfate, the average equivalent weight is 151. 'This checks the value of 150 obtained from the elemental sulfur analysis. 'The agreement between these results shoil-s that sulfide or disulfide sulfur must be nearly absent. It also establishes the absence of phenols in the mixture. This is confirmed by elemental analyses (0.23y0 oxygen ; 0.06% nitrogen). Aromatic Thiols. The 28 distillate fractions of aromatic thiols of Middle East origin were examined for the molecular structures present. Mass spectra show fractions 1 through 24 to be of the alkylbenzenethiol series. The absence of polynuclear thiols having fused aromatic rings in these 24 fractions is confirmed by ultraviolet spectra. Analyses of some of these fractions are shown in Table 111. Approximate concentrations for the alkylbenzenethiols are calculated from the carbon analyses. For this purpose it is assumed that each fraction consists of only two alkylbenzenethiol formula types, differing by a methylene group. The contribution of each formula type is then estimated by summing the contributions from all fractions (Table IV). Refractive indices and elemental analyses indicate that fractions 25 and 26 are mixtures of mono- and binuclear thiols. Fractions 27 and 28 are mostly white,
B
C,
7.07
5% m Aromatic Thiola
Alkyl groups larger t h a n methyl ale unlikely.
distillate fuel oil from two geographic sources are very different in amount and in sulfur content; the magnitudes of these differences vary from time to time in the cracked fuel oil. In general, the acid oils from the Middle East source are mostly aromatic thiols, while phenols predominate in those from the West Texas source In spite of these differences, thew are close similarities. Comparison of distillation and refractive index curves in Figures 1 and 2 suggests that the aromatic thiols from both samples are of the same types. This is supported by elemental analyses and ultraviolet spectra of the fractions. The average equivalent weight of the aromatic thiols (calculated from the percentage of sulfur) is 147 for those of West Texas origin and 150 for those of Middle East origin. Samples taken at other times show average equivalent weights of 144 and 146 for thiols of Middle East origin. When Procedure A is emplox ed for the separation, the average equivalent weight of the aromatic thiols can be calculated from the weights of lead thiolides and lead sulfate. If A represents the weight of lead thiolide, and B the weight of lead sulfate formed from it, the average equivalent weight of the thiols will be
Fraction
C~HBSH CSHQSH CQHiiSH CioHiaSH
... ...
Table V. Analyses of Phenolic Distillates Separated by Procedure
Aromatic Thiols Postulated for a Catalytically Cracked Distillate Fuel Oil of Middle East Origin
Molecular Formula
22.76 22.68 22.71 19.77
7.78 8.02 7.96 7.88 7.63 6.53 6.01 6.09
2
Table IV.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Phenols Postulated for a Catalytically Cracked Distillate Fuel Oil of West Texas Origin Molecular % in Formula
C;.H?OH C~HQOH CQHiiOH CioHisOH CgHsOH CioHiiOH CiiHtaOH CioH70H CIOH~OH CIZHQOH CiiHQOH CsHuOH I
.
.
1 . .
Phenolic Compoundn Cresols Xylenols Trimethylphenols Tetramethylphenols Indanol Methylindanol a n d / o r tetrahydronaphthol Dimethylindanol a n d / o r tetrahydromethylnaphthol 1-Naphthol 2-Naphthol p-Phenylphenol Methylnaphthol Methylphenylphenol Other polynuclear phenols Sulfur-containing phenols
Alkyl groups larger t h a n methyl are unlikely.
Mixed Phenols
