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Vol. 17, No. 2
*Distributionof Sulfur in the Fractions Derived from Crude Petroleum' By A. P. Bjerregaard EMPIRE REFINERIES, INC.,OKMULGEE, OKLA.
ULFUR is one of the minor constituents of most crude Notes on Distillation Methods Used petroleum oils as they are found in nature. Its presence has a decided influence on some of the superficial Unless otherwise stated, the crudes were distilled in the properties of the oils derived from the crudes. It is therefore laboratory from a horizontal cylindrical iron still 10 inches in of interest to know how the sulfur present distributes itself diameter and 24 inches long, fitted with a perforated steam through the fractions obtainable by fractional distillation of pipe lying on its inside bottom, with the perforations looking the crude. downward, and heated by a gas burner. A vapor tower of I n the present article no attempt is made to indicate the 63.5 mm. (2.5-inch) iron pipe, 76.2 cm. (2.5 feet) long, filled nature of the individual orhalf wav UT) with 16-mm. ganic or inorganic sulfur (6/~-inc6) keel balls was A number of American crudes and one Mexican crude and compounds present, but it provided, also a by-pass their distillation derivatives have been examined for their pipe and suitable valves. deals solely with the quessulfur content, and the relation between the sulfur content Only the very light fractions tion of the distribution of of the crude and its distillation derivatives is shown. were passed through the the sulfur in the various The sulfur tends to accumulate in the higher boiling vapor tower. While the fractions into which the fractions. lightest fractions were discrude petroleum oil may be In the case of crudes with relatively high sulfur content tilling no steam was injected divided by distillation. there is always a decided loss of sulfur in the uncondensed into the oil. As soon as all All the sulfur determinagases during the distillation. There is a further distillations herein reported were the lightest fractions had tion loss of sulfur in redistilling the benzine. distilled, and usually a t a made by burning the oil in In distilling down to coke a still larger proportion of the temperature in the oil of an oxygen bomb calorimsulfur is lost in the uncondensed gases. about 177" C. (350" F.), eter, with a little water The effect of free elementary sulfur on gasoline when resteam was admitted through in the bottom, precipitating, distilled is shown-namely, when steam is not used addithe perforated pipe into the and weighing as barium tional volatile sulfur compounds are formed. oil, and soon thereafter the sulfate. All the necessary vapors were passed directly and usual precautions were into the condenser without passing through the vapor tower. observed throughout, to insure accurate results. But in some cases no steam was used. The condenser conCrude Petroleum Oils Used sisted of a coil of 25.4-mm. (1 inch) pipe set in a tank of water. A charge of 18.2 liters (4 gallons) of crude was used. (1) Elbing crude from the northern part of Butler County, Kansas, distilled with fire and steam to residual oil. The fractions collected consisted of (a) benzine, equivalent ( 2 ) Elbing crude distilled without steam to coke. to raw gasoline; (b) rerun distillate, equivalent to raw kero(3) Augusta and El Dorado crude from central part of Butler sene (sometimes (a) and (b) were taken together as one fracCounty, Kansas, distilled with fire and steam to residual oil. (4)Billings crude from Noble County, Oklahoma, distilled tion, also called benzine); (c) gas oil; (d) wax distillate; with fire and steam to residual oil. (e) residuum (this was coke in some cases). (5) Healdton crude from Carter County, Oklahoma, distilled The benzine was redistilled from a large Engler flask to with fire and steam t o residual oil. (6) Hull heavy crude from Liberty County, Texas, distilled t o obtain the gasoline and kerosene, and the residue left in the flask is called benzine bottoms. In the two distillations of residual oil with fire and steam. (7) Hull heavy crude from Liberty County, Texas, distilled to Hull crude, Nos. 6 and 7, there was but very little benzine, coke without steam. strictly speaking, and a heavier cut called rerun distillate (8) Panuco Mexican Crude, distilled with fire and steam to was also made. These two cuts from this crude were not residual asphalt. further redistilled. In the case of the samples procured from the refinery, In Table I the crudes are numbered to correspond with the foregoing descriptions. Crudes 1, 2, 4, 6, 7, and 8 were dis- substantially the same procedure was practiced on a large tilled in the laboratory. Crudes 3 and 5 were distilled in a scale. The temperatures of distillation differed with different oils, refinery and the fractions procured and analyzed. None of these fractions had been refined otherwise than by distilla- and are shown in Table IV. tion. Results I n addition, some gasoline derived from crude from Deaner The amount of sulfur in the accompanying tables is given Pool (Okfuskee County), Oklahoma, to which elementary in several forms of statement. In the first place, the per cent sulfur had been added is included, thus: of sulfur by weight as found by the original determination is TABLE 11-Gasoline plus sulfur distilled with steam and fire. stated; secondly, the amount of sulfur in each fraction calOriginal gasoline contained 0.05 per cent sulfur, more sulfur culated on the basis of sulfur in the crude as 100 per cent is added to make 0.442 per cent. given; and subsidiary to this is also shown the proportion of TABLE 111-Same gasoline plus sulfur distilled with fire only. sulfur in the fractions from the redistillation of benzine on the Received August 28, 1924. Presented under the title "Distribution same basis of sulfur in crude being 100 per cent. of Sulfur in Petroleum Fractions as Compared with the Original Crude" beThe method of making the calculations was as follows: fore the Division of Petroleum Chemistry a t the 68th Meeting of the AmeriSince the yields had been determined originally by volume it can Chemical Society, Ithaca, N. Y., September 8 t o 13, 1924.
S
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INDUXTRIAL A N D E144 YNEERING CHEMISTRY
February, 1925
became necessary t o convert them into yields by weight by means of the specific gravity. With these data a t hand the weight of sulfur in grams in each fraction was calculated and from this the percentage by weight was further calculated. I n most cases the sulfur has a tendency to accumulate in the benzine, wax distillate, and residuum fractions-in other words, the extreme fractionewhereas the intermediate fraction, which is called gas oil, contains relatively little sulfur. Where the distillation was carried to coke, most of the sulfur accumulated in the wax distillate fraction and relatively little remained in the coke. of S u l f u r in Fractions from V a r i o u s C r u d e Oils Sulfur on Fraction on Sulfur in sulfur in crude per fraction per crude per Specific cent by cent by cent by gravity volume weight weight Fractions f r o m Crude 1
T a b l e I-Distribution
PRODUCT
Crude 0.32 Benzine 46.3 0.10 13.3 Gas oil 6.6 3.3 0.17 Wax disfillate 34.3 0.34 37.0 Residuum 8.3 22.2 0.69 Water 1.0 Loss in distilling crude 3.5 24.2 Total in Crude 1 100.0 100.0 Fi'actions f r o m benzine redistilled without steam (Crude 1 ) Gasoline 0.7467 18.0 0.04 1.8 Naphtha 0.7792 9.8 0.04 1.1 Kerosene 16.5 0.07 0.8123 2.9 Benzine bottoms 0.8586 1.3 1.10 3.3 Loss in redistilling benzine 0.7 4.2 Total in benzine 46.3 13.3 Fractions f r o m Crude 2 Crude 0.8498 0.32 Benzine 0.7805 46.3 0.10 13.3 Gas oil 0.8498 0.17 6.6 3.7 Wax distillate 0.8811 0.36 38.4 45.2 Coke 1.50 0.9 5.6 , 1.18 Water 1.0 Loss in distilling crude 6.8 32.2 Total in Crude 2 100.0 100.0 Fractions from Crude 3 Crude 0.8555 0.29 Benzine 0.7852 50.0 0.10 15.73 Gas oil 0.19 6.45 0.8571 10.0 Residuum 0.8973 30.0 0.40 56.45 Loss in distilling crude 1.0 21.37 Total in Crude 3 100.0 100.00 Fractions from benzine redistilled with steam and fire 3) - (Crude . Gasoline 0.7443 16.0 0.03 1.61 Naphtha 0.7779 6.0 0.04 .80 Kerosene 0.8137 17.0 0.07 4.03 Benzine bottoms 0.8256 10.0 0.11 3.63 Loss in redistilling benzine 1.0 5.66 Total in benzine 50.0 15.73 Fractions from Crude 4 Crude 0.8008 0.108 Benzine 0.7831 80.0 0.062 44.9 Residuum 0.9418 18.0 0.282 54.1 Loss in distilling crude 2.0 1.0 Total in Crude 4 100.0 100.0 Fractions from benzine redistilled without steam (Crude 4 ) Gasoline 0.7459 44.0 0.040 11.6 Kerosene 0.8142 18.0 0.041 5.4 Benzine bottoms 0.8514 16.0 0.093 11.6 Loss in redistilling benzine 2.0 16.3 Total in benzine 80.0 44.9 Fractions f r o m Crude 5 Crude 0.8718 0.73 0.09 1.0 Gasoline 0.7459 9.4 1.0 0.12 Naphtha 0.7883 6.2 0.08 8.9 Kerosene 0.8153 1.0 0.34 4.5 2.0 Prime distillate 0.8294 0.57 18.1 Gas oil 0.8545 23.7 1.04 63.6 43.0 Residuum 0.9082 13.3 4.3 Losses Total in Crude 5 100.0 100.0 Fractions f r o m Crude (i Crude 0.8849 0.340 6.5 0.054 1.00 Benzine 0.7870 19.7 0.075 3.66 Rerun distillate 0.8132 6.5 0.225 3.98 Gas oil 0.8509 29.8 0.217 18.94 Wax distillate 0,8800 34.6 0.657 71.76 Residuum 0.9516 Loss in distilling crude 2.9 0.66 Total in crude 6 100.0 100.00
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143
T a b l e I-(Concluded)
PRODUCT
Fraction on Sulfur in crude per fraction per Specific cent b y cent b y gravity volume weight Fractions f r o m Crude 7
Crude Benzine Rerun distillate Gas oil Wax distillate Wax.tailings Coke Loss in distilling crude Total in Crude 7
Sulfur on sulfur in crude per cent b y weight
6.5 19.7 6.5 55.7 1.1 1.4
1.00 3.66 3.98 62.79 2.32 4.64
9.1 100.0
100.00
21.61
Fractions from Crude 8 Crude 5.32 Benzine 0.743 6.5 2.23 Gas oil 53.6 Residual asphalt 6.34 38.4 Loss in distilling crude 1.5 Total in Crude 8 100.0 Fractions from benzine redistilled without steam (Crude 8 ) Gasoline 1.5 0.28 0.7455 0.71 Naphtha 0.7796 1.2 0.92 Kerosene 0.8086 3.3 0.97 Benzine bottoms 0.8724 0.5 Loss in redistilling benzine 0 Total in benzine 6.5
-
0.76 19.96 51.16 28.12
100.00 0.06 0.13 0.46 0.08 0.03 0.76
One reason for the accumulation of sulfur in the benzine was the fact that the hydrogen sulfide of the crude concentrated itself in that fraction in so far as it was not lost in the distillation process. The loss of sulfur is very marked in Crudes 1,2, 5,6, and 8. These are all crudes containing relatively high percentages of sulfur, whereas Crudes 4 and 6 show a small loss of sulfur accompanied by a small proportion of sulfur in the crude. I n redistilling the benzine into gasoline, the sulfur has a tendency to increase with the heavier ends and also to accumulate in the very light ends. The presence of hydrogen sulfide of course partly accounts for the accumulation of sulfur in the light ends and its accumulation in the heavier ends must be due to the higher boiling point of the sulfur components as compared with the other hydrocarbons. T a b l e 11-Solu
PRODUCT Solution
20% 40% 60% Last over Residue and loss Total T a b l e 111-Solution
PRODUCT Solution
gg
20%
90%
Last over Residue and loss Total
tion of S u l f u r in Gasoline, Distilled w i t h Fire and Steam
Specific gravity
Sulfur in Fraction fraction per cent per cent by vol. by wt.
0.7567 0.7463 0.7495 0.7539 0.7620 0.7703 0,7783
20 20 20 20 10 S
0.442 0.027 0.022 0.022 0.025 0,037 0.174
2 %1
Sulfur on Sulfur on original total sulfur sulfur (0.05%) per cent per cent by wt. by wt.
1.19 0.90 0.90 1.19 0.90 3.88 91.04
10.5 7.9 7.9 10.5 7.9 34.2 21.1
100.00
1oo.o
of S u l f u r in Gasoline, Distilled w i t h Fire O n l y
(No Steam)
Specific gravity
0.7567 0.7467 0.7479 0.7567 0,7640 0.7736 0,7892
Fraction per cent by vol.
20 20 20 20 10 S 2 100
-
Sulfur in fraction per cent by wt.
0.442 0.127 0.085 0.046 0.070 0.080 0.235 Gain.
Sulfur
on total
sulfur per cent by wt.
5.67 3.88 2.09 3.28 1.79 5.67 77.62 lo0.00
Sulfur on original sulfur
(0.05%)
per cent by wt.
50.0 34.2 18.4 28.9 15.8 50.0
__
. . . ..... ... 197.3 97.3
Tables I1 and I11 give data where elementary sulfur was dissolved in gasoline and the resulting solution was distilled in two ways. I n Table 11 are given the results of distilling this solution of sulfur with steam and sufficient fire to prevent condensation of water in the distilling flask. It will be
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noted that there is an accumulation of sulfur in the first over and especially in the last over-namely, at the higher temperature; also there is a distinct loss of sulfur, 21 per cent as compared with the original amount of sulfur in the gasoline (0.05 per cent). There is also a large accumulation of sulfur in the distilling flask in the form of a sticky residue, as indiTable IV-Highest
Temperatures Attained i n the Oil in Distilling At end of wax distillate At end of gas oil cut cut
O c. O F. c. ’F. 680 304.5 304.5 580 645 340.5 Low red heat 550 288 b 660 343 b 550 288 490 264.5 515 268.5 740 393 400a 204.5 Gasoline (Table 11) 3000 149 Gasoline (Table 111) a Highest temperature attained in the vapor as gasoline. b No wax distillate separated.
Crude
... ...
s
Vol. 17, No. 2
cated in the column in Table I1 headed “Sulfur on total SUIfur,” in which 91 per cent, of the sulfur has accumulated in the residue (including some loss). ’ When this same solution‘ of‘sulfur was distilled without steam and therefore at slightly higher temperatures, reaction took place between the sulfur and the hydrocarbons, with the result that all the distillates contained larger proportions of sulfur and there was a gain of sulfur in the fractions amounting to nearly 100 per cent of the original sulfur present (0.05 per cent). Here also the sulfur has a tendency to accumulate in the first and last fractions, and there is a tendency for the, increase in the sulfur content to begin at the 80 per cent over point in both these cases. I n the case of distillation without steam there was an evolution of hydrogen sulfide during the distillation of the last portion, and this last portion was of a yellow color, indicating a considerable reaction between the sulfur and the oil.
Nitrogen Oxides in Sulfuric Acid‘ By E. M. Jones TENNESSEE COPPER Co., COPPERHILL, TENN.
YDYGER2 has recently shown the nitrometer to be unsatisfactory for determining the oxides of nitrogen in commercial sulfuric acid. His solution of the problem was to distil off the oxides of nitrogen, by heating the acid with ferrous sulfate, into pure, concentrated sulfuric ’ acid and titrate with permanganate. The. writer recently had occasion to investigate the same problem. The method used at this plant for estimating the dissolved oxides was to titrate directly the acid containing them with permanganate. This method gave results that were so much higher than nitrometer results that it was believed the permanganate was titrating other substances such as ferrous iron or dissolved sulfur dioxide. The amount of dissolved sulfur dioxide was found to be negligible, and qualitative tests showed that ferrous iron was absent. A consideration of the reaction between nitroso sulfuric acid and ferrous sulfate will show that the two could not exist together a t the temperature of acid coming from a Glover tower. 2FeS04 PHNOSO4 = Fea(SO4)a f &Soil f 2N0 Ferric iron was present in an appreciable quantity. Impure commercial sulfuric acid used in a nitrometer is usually colored a more or less pronounced blue, although C. P. acid with a pure nitrate never gives this color. This blue is due to the iron present in the acid. It is a compound of nitric oxide and ferrous iron, and is broken up only on heating.3 I n other words, it is the familiar ring test for nitrates. As a compound is formed between the nitric oxide and the ferrous sulfate, the amount of nitric oxide evolved will be less than it should be, and the results will be low. This accounted for the difference between the permanganate titration and the nitrometer results. To demonstrate that iron present in the acid caused a large error, a weighed portion of standard potassium nitrate and a small amount of
N
+
1 Received
July 21, 1924. Bull. f&%alion ind. chim. Belg., 2, 367 (1923). a Treadwell-Hall, “Analytical Chemistry,” Vol. I , p. 331. The color of the ring in this test for nitrates varies with the concentration of ferrous sulfate. A relatively large amount of ferrous sulfate will produce a brown ring while with decreasing amounts of ferrous sulfate the ring is red, then purple, and with very small amounts is blue. In commercial sulfuric acid the amount of ferrous or ferric iron is very small. 2
ferric sulfate were placed in the decomposition bulb of a nitrometer with C . P. 95 per cent sulfuric acid. The amount of nitric oxide measured in the buret was considerably less than it should have been for the amount of nitrate used. The same low results were obtained using ferrous sulfate. The blue color appears instantly with ferrous sulfate, but takes a few seconds to appear with ferric sulfate, due, no doubt, to the time required to reduce the ferric iron to the ferrous condition. The conclusion is that the nitrometer cannot be used t o eetimate nitrogen oxides in commercial sulfuric acid containing iron, with any degree of accuracy. It is absolutely worthless for small amounts of nitrogen oxides under those conditions. Method
The following method will accurately estimate small amounts of nitrogen oxides in sulfuric acid. It is a modification of Devarda’s method, as used by Allen4 and further modified for this work. The apparatus consists of a distillation flask of about 1 liter capacity connected to a condenser. A 2-hole stopper fits in the neck of the flask. The condenser is connected through one of these holes and a separating funnel with a stopcock fits in the other. Enough strong caustic (40 per cent NaOH, on which a blank has been previously run) to more than neutralize the sample of acid to be used is placed in the flask with a few drops of indicator and 5 grams of Devarda’s alloy. The flask is stoppered and the condenser connected. The sample of acid is placed in the funnel and allowed to run slowly into the hydroxide. Care should be taken in adding the sample, for the violent reaction between the acid and the strong caustic tends to cause the contents of the flask to boil over. (The acid sample should not be diluted with water, for dilution will liberate the dissolved nitrogen oxides.) When the action has slowed down the flask is heated until all the ammonia is driven over. One hour will complete the distillation. This method will determine the dissolved nitrogen oxides in sulfuric acid, and also any ammonium salts present. TO determine the latter, of course, the alloy is omitted. 4
Scott, “Methods of Analysis,” Vol. I , p. 346.
