I
R. D. OFFENHAUER, J. A. BRENNAN, and
R.
C. MILLER
'Research and Development Laboratory, Socony Mobil Oil Co., Inc., Paulsboro, N. J.
Sediment Formation in Catalytically Cracked Disti!!ate Fuel Oils J
Removal of either aromatic thiols and 1-naphthol or pyrroles from the fuel oils studied practically eliminates sediment formation
UNTREATED
and uninhibited catalytically cracked distillate fuels are usually unstable when stored in the presence of air. The color darkens and a highly colored organic sediment forms that emulsifies oil, rust, and water. The resulting sludge clogs oil burner nozzles and screens. Domestic fuels are frequently blends of these cracked components with straight-run stocks. Usually, in such a blend, the straight-run acts merely as a diluent, most of the sediment coding from the cracked stock, especially if the straight-run stock is low in nitrogen.
Effect of Components on Fuel Oil Stability
Aromatic Thiols. Aromatic thiols in a catalytically cracked fuel (boiling range 430 to 650 F.) contribute to sediment formation (9) (Table I). Their removal with alkali improves stability. Reblending the aromatic thiols from acidified caustic extract of fuel oil brings the amount of sediment formed back to the original level. Addition of pure aromatic thiols (exact structure unimportant) to caustic washed cracked oil causes sediment formation (7 7). T o bring the aromatic thiol content to nil required 3 weeks a t 110' F. exposed to air but with no agitation, 2 days when stirred with oxygen, and only 4 hours when dodecyltoluene sulfonic acid was added. The aromatic thiol content of catalytically cracked oil drops during storage. At 110' F. with access to air but without agitation, the thiol content of a sample dropped to nil in 3 weeks. Stirring with oxygen reduced the time required to 2 days. Addition of dodecyltoluenesulfonic acid further reduced the time to 4 hours. In storage, sediment began to appear only after the aromatic thiol content had dropped below the original value. Concentrated alkali (>35%) is more effective for removal of phenols and aromatic thiols than dilute alkali ( 3 ) . The alkali salts separate in a third phase between the oil and caustic layers. This treatment does not affect pyrrole content.
S as-SH,
% Catalytically cracked fuel 10% NaOH washed 50% KOH washed
0.029 0.005 0'0005
Aliphatic thiols in the fuel oil range are not removed by this method. However, when added to the catalytic component, they do not increase sediment formation (9). Diary1 disulfides do not cause sediment in thiol-free fuel, hence they are not intermediates in sediment formation involving aromatic thiols (Table I). Pyrroles, present in all of the cracked oils discussed here, have been reported to increase sediment formation when added to a whole oil (8). Their presence, however, in a thiol-free oil is relatively harmless (Table I). A sample of oil was treated with alkali Table 1. Effect of Aromatic Thiols and Disulfides on Stability of Catalytically Cracked Fuel Oil from Middle East CrudeaIb Sediment, Sample Mg./Liter Blank A (0.017% S as -SH) 200 A' (A washed with 5% RaOH) 85 A' plus benzenethioIb 0.52 g./literD 164 1.05 g./liter 269 2.63 g./liter 445 A' plus xylenethiolsC 0.66 g./lite# 210 1.32 g./liter 366 3.29 g./liter 519 A' plus diphenyldisulfide, 0.52 g./literc 83 Blank B 166 ,B' (B washed with 43% KOH) 35 With KOH extract reblended 191 Blank C 190 C' (C washed with 50% KOH) 29 Plus dimesityl disulfided, 0.42 g./liteP 35 a All experiments were made on freshly cracked r e h e r y samples in the absence of air. These oils were variable in quality from day to day, which made it necessary t o include blanks with each treatment. 12-week stability at llOo F. (11). Eastman Kodak Co. Combined cuts 10 and 11 from Middle East fuel oil thiols (11). e Prepared by method of Bourgeois (9); m.p. 124O to 125O U.
to remove the acid oils, then pyrroles, indoles, and possibly other components were removed by treating with formalin in 5% sulfuric acid. A somewhat similar treatment (7) ~, removed diolefins and sulfur compounds from fuels. Reblending the acid oils did not restore the sediment-forming ability of the oil (Table 11). Indoles, shown to be present by Sauer (6),would be expected to react like pyrroles, though not as rapidly. Addition of indole to a pyrrole-free oil containing the alkali extract caused sediment formation (Table 11), whereas several basic heterocyclics had little effect. During the 12-week storage test period at 110' F., the pyrrole content of several samples of fuel oil determined by the method of Thompson (70) dropped to approximately half the original value. Pyrroles were present after the test period in the 14 cases tested. Phenols. Most phenols in the fuel oil range have no effect on sediment formation. An exception is 1-naphthol, which can form sediment in the absence of both pyrroles and aromatic thiols (Table 111). The presence of l-naphtho1 and a methyl-1-naphthol in a catalytic fuel oil has been reported ( 7 7). Sulfonic Acids. The addition of sulfonic acids, which can be formed in the oil through oxidation of aromatic thiols, causes rapid color formation and sedimentation in the presence of oxygen. Dichloroacetic acid, trichloroacetic acid, and sulfurous acid have also shown this effect. When oxygen is excluded, this effect is not seen.
Nature of Sediment The sediment is believed to be composed of sulfonic acids formed through oxidation of the aromatic thiols plus the basic condensate formed by the action of oxygen and acids on the pyrroles and indoles (4). It is a dark powder that forms a dark brown or purple solution in chloroform, acetone, or acetone-methanol. It is insoluble in paraffins. On heating, the sediment decomposes without melting >175' C. The distillate VOL. 49, NO. 8
AUGUST 1957
1265
from the decomposition products gives a posidve pyrrole test with Ehrlich's reagent (TO), expected from known reactions of pyrrole condensates. Analyses of sediments from widely different sources show similarities with respect to carbon, hydrogen, and oxygen (Table IV). Nitrogen and sulfur are always present, but in varying amounts. An oil in which 4-chlorobenzenethiol, prepared by the method of Tarbell (7), was substituted for the original thiols gave sediment. Analysis of the sediment showed chlorine to sulfur ratio of 3.85'30 to 4.75% (3 to 4). This experiment shows that most of the sulfur in the sediment comes from the aromatic thiols in the oil. The excess sulfur may correspond to that sulfur not accounted for as sulfonic acid in Table V. A sediment sample titrated for basic nitrogen with perchloric acid in acetic acid (5) and for acidic groups with potassium hydroxide in isopropyl alcohol showed basic nitrogen as 16 and acidic groups as 31. expressed as potassium hydroxide per gram of sediment. A comparison of sulfonic acid sulfur with total sulfur is shown for a number of sediment samples in Table V. This comparison assumes that all acid groups are from sulfonic acids. Approximately two thirds of the sulfur can be accounted for as sulfonic acid groups. The nature of the rest of the sulfur is not known. Assuming molecular weights of 100 to 200 for the indoles, pyrroles, and thiols in the fuel oils, calculations from Table IV data show that the products from these can account for no more than half the total sediment weight. The identity of the other half is not known. Identification of 2-Naphthalenesulfonic Acid, The sediment from an oil in which the original thiols were replaced
Table II. Effect on Stability of Pyrrole Removal and Replacement with Other Nitrogen Compounds in Catalytically Cracked Fuel Oil from Middle East Crude" dediment, LMMg./Liter Sample Blank A A' (A washed with 43y0 KOH) A" (A' treated with formalin in 5% H2S04) Plus K O H extract from A
287 48
Blank B 3' (B washed with 50% KOH, treated with formalin-5% HtSOp, and reblended with K O H extract) B' plus nitrogen compounds @.01% Indoleb Pyridineb Z-Picolineb Quinolineb Quinaldineb
180
w
8 30
55 241
56 39 85 62
12-week stability at llOo F.
' Eastman Kodak Co.
Table 111. Effect of 1-Naphthol on Stability of Thiol-Free Catalytically Cracked Fuel Oil from Middle East Crude" Sediment, Mg./Liter
Sample Blank A A9i(A washed with 43% KOH) A' plus 1-naphthole, 0.17 g./liter
261
Blank B B P(B washed with 5% NaOH) B' plus I-naphthol, 0.25 g./liter
149 78 155
a
58 124
12-week stability at 1IOo F. Eastman Xodak Co.
Table
IV.
Analysis of Sediments from Fuel Oil Blends Containing Catalytically Cracked Components from Various Crude Oils"
Crude Source
C, %
H, %
0, %
N, %
S, %
West Texas California Middle East Middle East (cracked component only)
76.9
8.7 8.5 8.5
1.8 3.1.
2.1
1.9 1.3 4.1
0.7
78.5 77.5
6.7 6.9 6.9
76.1
6.3
7.7
3.4
2.6
2.5
*
...
1.3
460
e . .
540
...
Catalytically cracked components accounted for practically all sediment formed. Cryoscopic in 1,1,2,2-tetrabromoethaneafter Soxhlet extraction with n-pentane, and drying.
Table V. Comparison of Total Sulfur in Sediments with Sulfur Calculated from Titration of Acid Groups' Calcd. S as Crude Source Total S, Sulfonic of Sediment % Acids, % Middle Easd Middle EastO Calif orniab West Texas' a
Ash, % Mo1.Wt.B
3.82 4.48 1.58
2.50
2.7 3.0 1.0 1.7
Assuming that all acids are sulfonic
acids.
* Sediments prepared in glass. Field eample of eediment.
1 266
by an equivalent amount of 2-naphthalenethiol contained 2-naphthalenesulfonic acid, proved by the isolation of the acid as its sulfonamide. EXPERIMENTAL. Three liters of fresh catalytically cracked fuel oil from Middle East crude (0.033% sulfur as-SH) was extracted with 200 nil. of 50% potassium hydroxide under nitrogen. The oil, after separation of the bottom potassium hydroxide layer and the intermediate layer of potassium salts, was filtered through paper to remove traces of treating solution. The product was water-
INDUSTRIAL AND ENOlNEERlNG CHEMISTRY
washed and refiltered to remove traces of water. The potassium content of the oil was nil, sulfur as -SH was 0.001%. To the oil, 4.36 grams of 2-naphthalenethiol (Eastman Kodak Co.) was added and the product stored in an open gallon jug a t 110' F. After 3 months the oil was filtered to give a dark brown powder; yield, 429 mg. A 300-mg. sample of the sediment wad refluxed for 4 hours with 2 ml. of phosphorus oxychloride. The product was decomposed by stirring with ice and filtered. The precipitate was extracted with ether, leaving a dark insoluble material. Evaporation of the ether left a semisolid residue. Distillation at 1IOo C. (3 mm. of mercury) gave a colorless solid melting at 69' to 76" C.; yield, 36 mg. (reported for Z-naphthalenesulfcnyl chloride, melting point 76" C.) The sulfonyl chloride was treated with ammonium hydroxide and recrystallized from water to give the sulfonamide, melting point 218.5' C. (reported for 2-naphthalenesulfonamide, 21 7 O '2.). C H Calcd. for C I O H ~ N O ~ S 57.97 4.35 Found
57.49
4.38
Other Evidence for Presence of Sulfonic Acids in Sediment. Sulfonic acids were separated from a sediment obtained from fuel oil storage tank by treatment with warm alkali, followed by neutralization with a cation exchange resin. Prior to use, the resin was washed with water to ensure the absence of acids. Identification was made by infrared spectroscopy, the product giving a strong band a t 1175 cm.-* Literature Cited (1) Arundale, E., Mikeska, L. A., G. S. Patent 2,567,173 (1 949). (2) Bourgeois, E., Abraham, A., Rec. trau. chim. 30,413 (1911). (3) Duval, C. A., Malin, R. T., Kaliclievsky, V. A., Petrobum Rejiner 34, 142-4 (1955). (4) Morton, A. A., "Chemistry of Heterocyclic Compounds," p. 66, Mc-
Graw-Hill, New Yorl;, 1946. ( 5 ) Richter, F. P., Caesar, P. D., Meisel, S. L., Offenhauer, R. D., IND. ENG.CHEM.44.2601 (1952). ( 6 ) Saurr, R. W., Melpolder, F. W., Brown, R. A,, Ibid.. 44, 2606-9 (1952). (7) Tarbell, D. S., Fukushima, D. K., Org. Syntheses Coll. Vol. 3, 809 (1955).
(8) Tdompson, R. B., Chenicek, J. A , Druge, L. W., Symon, T., IND. ENG.CHEM.43, 935-9 (1951). (9) Thompson, R. B., Druge, L. W., Chenicek, J. A., Ibid., 41, 2715-21 (1949).
(10) Thompson,
R. B., Symon, T., Wankat, C., Anal. Chem. 24, 1465
(1952). (11) Williams, A. L.,Offenhauer, R. D., IND.ENG.CHEM.49, 1259 (1957).
RECEIVED for review September 18, 1956 ACCEPTEDJanuary 26, 1957 Division of Petroleum Chemistry, 130th Meeting, ACS, Atlantic City, N. J . . September 1956
