iliVALY TICAL EDITIOM
104
Vol. 2 , K O . 1
Determination of Sulfur in Gasoline‘ Graham Edgar and George Calingaert ETHYLGASOLISECORPORATION, YONXERS, N. Y .
HE A. S.T. Ill. Method Several modifications of the standard apparatus for around the upper part of D90-26T for the deterthe determination of sulfur in gasoline are described. the \Tick and bent to pass mination of sulfur in These devices seem to have certain distinct advantages through the glass tube and naphthas and illuminating Over the s t a d a r d (A. T. M.) method. The results cut through the groove of oils mas adopted s e v e r a l obtained are essentially the same as those obtained by the cork. If the wick is not the stmdard method. years ago by the U. S. Goyt o o t i g h t , t h e flame m a y ernment (Bur. Mines, Tech. be easily adjusted a t any Paper 323B), and is now in general use in the petroleum time by slight movement of the wire. industry. The principle of the method-the burning of a VOLUMETRIC MEASUREMEKT OF GASOLIXE,WITH ADJUSTtypes of lamp are illustrated in Figure known weight of fuel and the absorption and titration of JIEKT OF FLAME-TWO the sulfur trioxide formed-is sound, but its application 2 which permit volumetric determination of the gasoline by the method as specified is probably not so simple burned and also allow simple adjustment of the height of and dependable as might be desired for routine opera- the flame. One of theqe (2-a) consists of a 10-cc. graduate, tion. Several articles have recently appeared on the subject, fitted with a grooved cork and a glass tube of about 5 mm. relating both to the type of apparatus which can be used outside diameter and about 1 mm. wall thickness extending and to the effectiveness of the method in detecting the sul- from an inch (2.5 cm.) above the cork nearly t o the bottom fur present in certain specific forms. of the graduate. The tube contains a tightly fitting round The attention of the nriters was wick cut off flush with the top of the tube. A cooling decalled t o the difficulty of using the vice, which regulates the height of the flame, slips over the method, particularly in a small labora- upper part of the glass tube. This may be made by punchtory where no plant facilities (such as ing a hole (with punch and die) in a brass strip, 1 mm. thick, large capacity vacuum system) were 10 mm. wide, and 130 mni. long. The punch should leave available, and where the chemist must a collar about 1.5 mm. high around the hole, which should perform other duties in addition to fit snugly but not too tightly over the glass tube. The brass running a few sulfur determinations. strip is bent over tn-ice to form two “wings,” which hold The modifications of the A. S. T. 11. the device in position by friction. The exact dimensions method described herein were developed are probably not essential. il short brass tube, fitting in order to produce an equipment snugly over the glass tube and soldered to the wings, has easy to operate and one which would also been employed satisfactorily, and this is the device give essentially the same results as illustrated in Figure 2-a and 2-b. The collar is shown in the standard method. The question of Figure 4-b. efficacy of the A. S.T. hl. method in The second lamp (2-b) is similar t o the first, except that B~~~~~ with Devi& detecting certain classes of sulfur comthe glass tube is attached as a side arm to the lower part for Adjusting Height pounds was not considered, and it is of a 5-cc. graduate. of Flame presumable that the present method is little, if any, different from the regular A. S. T. 11. method in this respect. It seems unnecessary to discuss a t great length the difficulties in the use of the standard method which it was found desirable to overcome. The authors are fully aware that under certain conditions the method is satisfactory, particularly where only a few determinations are t o be run simultaneously and where one operator is able t o devote full time 2b t o them. The chief difficulties which become apparent when large numbers of determinations are run simultaneously are: (1) the lack of a simple means of adjusting the height of the flame; ( 2 ) pulsations in the flow of air; (3) uncertainty in the blank determination because of the absence of means of determining the volume of air input. The modifications to be described were designed to minimize these difficulties. They comprise three separate parts of the equipment, and can be used jointly, or any one or two can be used with the remaining features of the A. S. T. hl. Figure 2-Two Burners Permitting Volumetric Measurement of Gasoline and Adjustment of method. Height of Flame
T
-
Lamps
ADJUSTMENT OF F L a h r E WITH STAKDARD LAJIP-A simple method of adjustment of the flame with the standard lamp is illustrated in Figure 1.2 It consists of an iron mire looped 1
Received September 18, 1929. H I,. Alexander, of this laboratory.
* This method was devised by
In using either of these lamps the graduate is filled with gasoline, and the brass collar is pushed down until its upper edge is 5 to 10 mm. below the top of the glass tube. The burner is lighted, and after it has been allowed to burn for a minute or longer, the brass collar is raised until a flame of the desired height is obtained. This usuaily requires
January 15, 1930
IAt7DCXTRIdLA S D ESGINEERIXG CHEXISTRY
bringing the top of the collar 1 to 2 mm. below the edge of the glass tube (apparently the brass collar cools the upper part of the wick, thus decreasing the flow of gasoline). The lamp is then placed under the absorption tube and the volume of gasoline is read. The volume is again read a t the end of the operation, and the weight of gasoline calculated from the specific gravity of the gasoline. It should be noted that 1%-ithlamp 2-b the actual volume of gasoline is read directly, while lamp 2-a must be calibrated to allow for the volume of the glass tube and wick. With forty lamps tested by this laboratory the conversion factor was 0.82; i. e., if the volume read on the graduate is 1.0 cc. the actual volume used is 0.82 cc. I n an average determination in which 3 cc. or more of gasoline are burned, the accuracy of measurement is about 1 per cent, which is 3u quite sufficient for ordinary work. The apparatus may be adapted to the usual weighing method if desired.
i
!Voles-(1) T h e best results have been obtained with t h e wick fitting tightly in t h e t u h e a n d c u t flush with t h e top of t h e glass t u b e (2) T h e wick is 50 tight t h a t i t cannot be easily removed a n d does not dry readily T h e best way t o clean i t from residual gasoline before a new sample is r u n is t o p u t about 5 cc of t h e new sample in t h e lamp and t o suck it through t h e wick by inserting over t h e glass t u b e a piece of rubber tubing connected t o a water pump.
105
embodying ( a ) a manifold fitted with t h e requisite number of connections, each provided with a regulating valve: ( b ) a balancinj: t a n k of several gallons capacity t o minimize sudden fluctuations in t h e air flow; (c) a 10-inch (25.4-cm.) mercury manometer connected with t h e air t a n k ; ( d ) a valve connecting t h e air t a n k with outside air, in o r d u t o regulate t h e suction by bleeding in surplus air. If t h e manifold is so constructed t h a t t h e linear velocity of air is substantially constant throughout t h e piping, t h e capacity of t h e pump need not be more t h a n 20 per cent above t h e air consumption (0.07 cubic feet or 0.002 cu. m. per minute per burner) t o afford very easy regulation. These appliances are equally desirable with t h e standard a n d with modified apparatus. Without t h e m a pumping capacity greatly in excess of actual requirements (300 t o 500 per cent) is indispensable t o provide satisfactory regulation of t h e air flow.
Elimination of Blank Determinations
Lamps 2-a and 2-6 are readily adaptable to a device for eliminating the necessity of running a blank determination. This is illustrated in Figure 4 , and consists of a modified chimney, extending entirely over the lamp, and fitting over a cork which is attached to the lower part of the lamp cylinder (4-a)or the side arm (44). h side tube on the chimney serves as air inlet. A brass rod, soldered t o the cooling device of the lamp, passes through the cork and serves t'o regulate the flame. I n the use of this chimney, the inlet tube is connected t o a tower containing soda lime t o remove acid vapors. Act'ivated charcoal may be added, if other substances vAiich might yield acid on burning are suspected of being present in the air. The lamp is lighted and adjusted as usual, and connected with the absorption syst'em imme-
Absorption Tube Figure
3-New
Absorption System Complete
The absorption system (Figure 3) consists of a tube of Jena glass ( 3 4 ) with a porous fritted glass disk sealed into the cower portion. (The tube is described by the manufacturers as a mercury filter.) The tube is fitted a t the upper end with a spray trap 1 3 4 ) and a t the lower end is connected with a 150-cc. Erlenmeyer flask (3-e) which in turn iq connected with an A. S. T. h1. type absorption chimney ( 3 - 4 by means of a rubber stopper. When the lamp is ready, a rubber stopper is inserted in the bottom of the chimney, 10 cc. of sodium carbonate solution are measured into the absorption tube, and the tube is then connected t o the spray trap. Suction is applied gently and the rubber stopper is removed. If the rubber stopper is not used, a small amount of the solution may filter through the porous disk into the Erlenmeyer. This does not, however, affect the determination except b y decreasing the amount of solution available for absorption. The air flow is then regulated t o secure a good flame and satisfactory contact between the air and the solution. This usually corresponds t o a height of liquid and air bubbles of 6 to 12 cm. in the absorption tube. When sufficient gasoline has been burned, the lamp is removed and the air flow is stopped, whereupon the sodium carbonate solution begins t o filter slowly through the glass disk into the Erlenmeyer flask. If the operator will blow gently through the rubber tube a t the top of the spray trap, the liquid will immediately run down into the flask. The trap, the tube, and the chimney are rinsed into the flask as per 4. S. T. 11. specifications, the tube is disconnected, and the solution in the flask is titrated. T h e lamp should n o t be allowed t o smoke, b u t if smoking .Votes-(1) should occur soot will collect a t t h e bottom of t h e glass disk and interfere with t h e suction This soot m a y be removed b y allowing t h e lower p a r t of t h e t u b e t o stand in cleaning fluid overnight. (2) I n running a large number of determinations simultaneously there are many advantages in t h e use of a well-constructed suction system
Figure 4-Chimneys
and Lamps Designed to Avoid t h e S e c e s s i t y of Blank Determinations
dintely after the air flow has been started. Further adjustment of tlic flnine may he readily niatli., without cli:connectinc any part of the apparatus, by manipulating ?he brass rod attached to the cooliiig clip of the lamp. With this assembly of apparatus no blank deterininstion 13 neccwtry. Xofc-Kith very volatile Zasolincs t h e cooling d e \ icc ,hown ia Figures 2 - 0 and 2 - t is h3rdL.r sufficient t o regulate the flanie p r o x r ! ? , when t h e lamp is used in t h e entirely enclosed chimney. T h e coo!in; surface i e therefore i n c r e a d h y inserting a coil of very thin bras5 stri;, held t o the nings or t h e hrn..; clip l > y il d r o p of solder. T h i i d e v i c e i- i::u-trated in Figure .1-1. T h i s type of coolin.: device mag also i e u 5 d \rirliout t h e entirely cnclo,ed chimr.ey. i i desired.
Experimental Results
I n order to test t!ie accuracy of the metliocl, soluticws wcrc prcpnrcd of pure c:iri)on diaulfiile :iiid of purc tliiopliciic in normal 1iq)t:iiic. Dtwrminstions were made by variou.;
d S A L I'TICd L EDI T I O S
106
modifications of the above method and also hy the regular -4.S.T. 11. method. C o n t e n t of C a r b o n Disulfide a n d T h i o p h e n e by R e g u l a r a n d Modified M e t h o d s SULFUR FOVND Lam ABSORBER CHIXISEY
T a b l e I-Sulfur
SULFUR PRESEKT
CARBOX D I S U L F I D E
Pcr c e n t
Per cenl 0.195 0.188 0.185
0.19s 0 198 0.198
4-b 2-b
2 3
4-b Standard
A . S. T. 31.standard
T-ol. 2, s o . I
I t \Till be noted that, the two methods give very close results, with a slight tendency for the modified method to give higher results. The average of twenty determinations shows a value about 0.003 higher. llthougli this difference is small enough bo be within the limit, of accuracy, its tendency to be always in t,he same direction is probably not accidental. It can probably be att,ributed to the greater efficiency of absorption in the filter tube than in the bead absorber. Discussion
THIOPHENE
0 100 0,100 0.100 0.257 0.257 0,257
0 096 0.097 0 101 0,255 0 257 0,255
A . S. T . A I . standard 3 Standard 3 Standard A . S. T. SI. standard 3 4-b 3 Standard
2-b 4-b 4-b 2-b
The results, shown in Table I, agree very well with each other and with the theoretical. It should be noted that all the data on solutions of thiophene are closer t o the theoretical values than those on solutions of carbon bisulfide. Thib suggests t h a t solutions of pure thiophene would serve excellently for the calibration of any sulfur lamps. Since the method was designed primarily as a practical substitute for the A. S. T. AI, method, i t is of greater interest to compare the results obtained by both methods. A number of determinations were run simultaneously on samples of commercial gasolines, one determination being made by the standard A. S.T. AI. method, and one by the modified method, using lamps 2-a and 2 4 , without the entirely enclosed chimney. Blank determinations were run for each method and corrections made accordingly. The determinations were made in a routine way with no special precautions. Characteristic results are shown in Table 11. T a b l e 11-Comparison of S u l f u r C o n t e n t of C o m m e r c i a l G a s o l i n e s b y E t h y l G a s o l i n e a n d A . S. T. M . M e t h o d s
KO.
A . S.T. h f , I~ETHOD Per cent 0.126 0.113
0,079 0.082
0 0 0 0 0 0
034 068 103 134 129 101
ETHYL
ETHYL
A. S. T. 31. G.ASOLISE
GASOLINE LfETHOD
S O .
AfETHOD
Per cent 0.136
11
Per cenl 0 05s 0 096 0,0i6
0.109 0.085 0,086 0.034 0.068 0.1Oi 0.141 0.135 0.099
12
13
14 15 16 17
0.075 O.Oi6 0.085 0 087 0 009
19 20
0 150 0 082
18
AlETIiOD Per cent 0 05; 0 100 0 084 0 083 0 090 0 094 0 083 0 012 0 144 0 0i6
A Laboratory Shaker' Henry E. Bent CHEXZICAL LABORATORIES, HARIA R D UNIVERSITY, CAMBRIDGE, S14sq
HE shaker shon n in the accompanying figure has been in continuous uae for the last two years, during aliich time it has required no attention aside from occasional oiling. It consists of a 6-foot (1.8-meter) 0.5-inch (1.3-cm.) steel rod, pivoted a t one end, the other being held by six heavy screen door springs. The rod with attached appaiatu; vibrates with its own period, a small impulqe approximately in phase being imparted by a sniall spring actuated by a constant-speed motor. The period of the shaker is made to approximate that of the crank by means of an adjustable 1%-eightwhich slides on the steel rod. $pparatus is attached directly to the rod by ordinary clamps. The shaker is noiseless, the slight noise from the motor being tlie only sound. Rapid shaking of delicate glass apparatus is possible inasmuch as the drive is not direct but through springs. The amplitude may easily be varied by a 1
Received November 8, 1929
The following advantages may be claimed for the devices described above over the standard apparatus: (1) Lamp 1 permits ready adjustment of the flame d u i h g the progress of the determination. ( 2 ) Lamps 2-a and 2-b permit ready adjustnient of tlie flame during the determination and also allon- tlie amount of fuel burned to be determined by volume rather than by weight'. thus saving considerable time when a nuniber of determinations are made simultaneously. They are also more readily adaptable for use with the special chimney (Figure 4) than the standard lamp Jvould be. (3) The absorption tube (Figure 3 ) gives very excellent contact between the air and the soda solution which should make for very efficient absorption of the sulfur trioxide. The air flow through it, is entirely free from pulsations, making the flame burn more steadily than it does with the standard set-up. Titration of the soda at' the end of the deterniination is effected in a flask, and is much more comfortably made than in tlie standard absorption tube. (4) The modified chimney permits the elimination of tlie lilank determination, which is not only advantageous from tlie standpoint of saring time, but, also increases the accuracy of the determination, since with the standard apparatus there is no way of knoning whether the volume of air passing through the blank is identical with that passing through the actual determinations, and this makes the correction for blanks somewhat uncertain if quite pure air is not available. .is pointed out above, these devices may all be uaed together or any one or more of them may be coniliined vMi parts of the standard apparatus. Sote-The complete apparatus described abox-e, consistingof I d m p 4 - b , chimney 4 - b , and absorption system 3, may now be obtained from the Vonkers Laboratory Supply Co., 515-132nd St., S e w York, PI'. 1 ' .
slight shift in the sliding weight which changes the natural period. A4tthe pivot the angular motion is about 3 degrees. Connections for gas, water, or even a glass line may be made a t this point, in the latter case using a spiral. A 'jao-hp. c o n s t a n t - s p e e d m o t o r n-as found to supply inore than sufficient power. The other materials are easily obtained and require very little time for assembling. The frequency of shaking was about 200 r. p. ni., the amplitude 4 inches (10 em.); and t,he weight 3 kg. Aside from stiffening of the rod, which is necessary a t higher frequencies, a wide range of speed and amplitude is possible.
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