Determination of Sulfur in Fuel Oils An Instrumental Analysis Experiment Richard C. Graham, John K. Robertson, a n d W. David Loehle Science Research Laboratory and Department of Chemistry, U.S. Military Academy, West Point, NY 10996
The recent enerev crisis has forced accelerated research on alternatives, suchas those derived from coal, shale-oil, and synthetic hydrocarbons, to the use of foreign imported oils. T h e use of such fuels requires that many preliminary properties of the fuels be determined and related to various limitations placed upon industry by such government regulations as T h e Clean Air Act. A major problem in the use of these alternative fuels is the sulfur content of the fuel. Recent investigations (1-3) have shown that sulfur oxidation products, traditionally considered innocuous, are present in the atmosnhere. One recent paper (3)indicates that such potentiallv ckinogenic compo~ndsas monomethyl sulfate add dimethyl sulfate are present in the atmosphere or a t least in particulate matter produced by the comh&ion of low sulfu; coal. The increased presence of sulfur oxides has caused increased acidity of rain, the recognition of which has resulted in increased emphasis being placed upon the acid rain problem (4) by everyone from the President (5) to the National Atmospheric Deposition Program' (6). Coupled with the student's desire to oerform meanineful work. this emohasis sueeests an "" experiment for an instrumental analysis laboratory to determine the sulfur content of fuels. Such an experiment was used with great success in the physical chemistry and instrumental analvsis courses2 a t the U S . Militarv Academv. Communication a t "The Second National ~ y k p o s i u mi n Ion Chromatographic Analysis of Environmental Pollutants, 1978" (7, 8)led us to believe that modification of ASTM methods (9) could he adapted easilv and rapidlv for use in a classroom e u v i r o u m e n t . ~ ~ nofe the major idvintages to the use of this technique is the exposure to the combined use of two pieces of equipment to obtain a desired result. Safety Considerations As with all experiments in chemistry, some consideration must be given to the safety aspects of the experiment. T h e use of t h e Parr combustion bomb h a s several steps which could be notentiallv daneerous a n d t o which narticular attention must be paid. The following considerations have been summarized from Salzherg et al. ( l l ) , Shoemaker and Garland (12),and the instruction manual for the Parr homh (13). Sample size should he limited to nomore than about 0.75 If i t is-felt t h a t t h e energy which is liberated w h e n testing a particular substance may exceed several hund r e d c d o r i e s o r t h e h e a t content of t h e substance i s unknown, thought should be given t o reacting only a small fraction of w h a t would h e considered a full charee. One of the major considerations is that theiuterior of the homh, the cap, and all threads should be free of corrosion and grease or oil. The ignition wire should be attached firmly to the electrode and care should he taken that the ignition wire does
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The National Atmospheric Deposition Program is a network designed to monitor changes in precipitation chemistry and also to determine any effectson the environment of the increased acidity in the rain. Ttm physical chemisrry come at USMA incudes a one-wee* olock on introducuon lo lnstrumenlal analysis. The bloc* ncludes instruction on gas and ion chromatography and atomic absorption spectrophotometry. 340
Journal of Chemical Education
not touch the sample cup. After charging the homh with the buffer and securing the cap with the screw rinr, the entire Iwmh assembly shc;uld he swurelv rlnmprd in I he hrnrh tup atcess~~ry that is clamped to the hench top. After shtvkini: to see that the oxveen reeulator is functionine ,.. ...orooerlv. . . . slowlv charge thr bomb with uxyArn by upenini: the \,ent and alloxine the oxvern to t!soar)e for ?-:I min. CAIJTIOZI: do not aliow a n y s m o k i n g n e a r t h e apparatus. The pressure durinr this . ~ u r. a i .n .rprocess should not exceed 5 atm. Upon cumplering rhe purge, lower the pressure rozeri~and doit. the vent un thr bnml~.Slowlv raise the prrisure lu 25 atm. 110 not allow any sudden surges o r allow the pressure to exceed 33 atm. I t il does, shut oil the rerulau~rand vent the l n ~ n i l ~ . When the bomb contains 25 atmospheres, turn off the regulator and use the line purge valve on the regulator to allow excess pressure in the line to escape. Monitor the pressure gauge prior to pressure relief to assure there is no leakage. If there is leakwe. vent and check all seals. If there is no leakaee. remove the ffiing line. Securely clamp the bomb in the hench too rack and olace a oortahle shield in front of the bomb. ~ i n n e cthe t electrodesafrom the control box. Only depress the fire button for 5-10 see:. auv . loneer mav burn out the load resistor. B e s u r e t h a t hands, face, etc., a r e kept away from t h e top of t h e bomb during t h e ignition sequence a n d e n s u r e t h a t t h e portable shield is in place. The ignition may be checked by cautiously touching the bomb-warmth indicates that combustion has occurred. If not, depress the button for an additional 5-10 sec. If still no combustion, vent the homh and check the ignition wire for tightness and see that it is not touchina the sample cup. After allowing sufficient time for complete reaction (15-30 sec), the homb may be shaken to allow the buffer to absorb the combustion gases. Carefully and slowly vent the excess pressure before removing the screw ring and cap.
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Experimental Samples of fuel oil used in the power plant at the US. Military Academy were obtained. An accurately weighed portion of approximately 0.5 g was placed in the cup portion of a PARR model 1108 oxygen combustion bomb. Then 25 ml of a0.003 M NaHCOal0.0024 M NazCOs buffer solution was placed in the bottom of the bomb. The homb was assembled for electrical ignition. The bomb was then charged with 25 atm of oxygen; apurge time of 2-4 min with the vent valve partially open was allowed. The presence of the buffer in the calorimeter allowed for absorption of the sulfur trioxide into an aqueous medium. The bomb was shaken for several minutes after ignition to effect complete scrubbing of the gas phase by the eluent. The homb was then disassembled and theeluentwashed into a 250-ml volumetric flask and diluted tovolume with the CO:?/HCO; buffer. The i00-@Iinjection loop of a Model 14 DIONEX ion chmmatograph (1C) was loaded with the solution, and the sulfatelevel in each sample was determined using 0.003 M NaHCO:r/0.0024 M NazCOa as the eluent at a flow rate of 20%(92.0 mllhr). Results of analvsis of standards of 20,50,100, and 200 ppm SO:-(prepared fromanhydrous K2S01)were used to construct a calibration curve (see figure). Results and Discussion \Vith rhr large exreas of oxygen present in thv I ~ o m11rior l~ to coml~ustion,all of rhe s ~ ~ l l ' u isr presumahls onidi7ed to sulfur trioxide. The resulting oxide is scrubbed from Lhe gas
Table 1. Summary of Results Without Shaking (Values are % sulfur in fuel oil sample)
1.23 0.90 1.32
0.39' 0.80' 1.15
1.11 0.95 1.04 With Shaking mass fuel oil
mass fuel oil
1.88 1.88
0.5370 0.5370
0.4849
1.84
0.4147
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0.4849 0.4995
1.84
0.4147
1.86 1.94
0.4274
X = 1.89 s = 0.042
% sulfur
0.6744 0.6744 0.7370 0.7370
1.93 1.90
0.5152 0.5152
1.91
1.95
0.6131
1.92 1.90
0.6406
1.91
0.6406 0.4324 0.4324
1.10
S = 0.15
% sullur
mass tuel oil
0.6131
?=
0.4995
0.4274
1.87
1.85 1.84
Army Petroleum Activity Analysis (10) (by ASTM D-1552)i =1.89,s = 0.04
'lncornplete cornburtion-
values not used in statistical calculations.
Table 2. SulfurAnalysis of Mher Fuels
Calibration curve tor determination of SO:fuel ails.
produced upon the combustion of
phase by the buffer present in the bomb, yielding a sulfuric acid solution. Analytical results in ppm SO:- were converted to percent sulfur in the fuel oils by the following equation: 8.18 xppm SO;= % sulfur mass fuel oil
where the constant (8.18) takes into account the accuracy of the method (98.2%), the volume of eluent (250 ml) used for dilution of the combusted sample, and the factor for the conversion of sulfate to sulfur concentration. Two sets of data were taken under different conditions. Results of these two determinations are given in Table 1.The first set was obtained without vigorous shaking or a time delay bctw'en conihustion i~nddlsassernhi?. of ~ h hr n h . The variabilitv ot the results in the first set r0.9%1.3'bj indicated with the method. This variability was attributed a to insufficient shaking of the bomb prior to disassembly. The second set was obtained using vigorous shaking of the bomb prior to disassembly. An independent analysis of the fuel oil by ASTM method D-1552 ( 1 0 ) found 1.89%sulfur in the oil, and an estimated standard deviation of 0.04. The average of
Fuel
Per Cent Sulfur Content
Shell Hi-Test Gasohol Military No-Lead Kerosene Military Diesel
0.069 0.082 0.075 0.132 0.181
the second set of data from our experiment was 1.89%with a standard deviation of 0.042. As evidenced by the excellent agreement between the ICiParr bomb method and the ASTM D-1552 method, the two methods can be judged to be comnarahle. Similar accounts of comparability of the ASTM ~nethuds( 9 ) and the 1CIl'srr bomh hare been repmed &ewhere ( 7 . 8 ) 'I'he'with ihakinaMdatain'l'nble 1 was treated using paired t-statistics since each of the solutions resulting from combustion and dissolution of the resulting gases was injected twice on the IC. The calculated t was 0.32 and the tablet for 14 degrees of freedom and a = 0.05 (2 tail test) is f2.145. Since the calculated t lies between the values for the tablet, the hypothesis that the duplicate determinations are the same cannot be rejected, thus indicating that the precision of the method is at least 95%. The method can thus be judged to be both accurate and precise. Two steps were taken to maximize the effective use of laboratorv time. The first was that the instructors would iniect the necessary standards in the IC prior to the beginning oithe lab ueriod. These chromatoerams were furnished to the student from which the peak heights were obtained and a calibration curve prepared. The second was that the initial bomb for a two-hour period was filled by the instructors. Subsequent fillings of the bomb were performed by the group of students for the next group to perform the experiment. As a result of these two measures, three groups of 3-4 students each were able to perform all aspects of the experiment (from loading the bomb to calculating the percent sulfur) in a two-hour lab oeriod. With these logistical simplifications, three sections of students could nerform the analvsis durine a six-hour laboratorv period. ~es;lts of the extension of thismethod to additiond fuels are given in Table 2. Such a determination of sulfur in more than one fuel could lead to a discussion on the relative merits of one fuel over another, such as a consideration of the total sulfur emitted by the combustion of each of the fuels. For example, although the sulfur content of gasolines are low relative to the diesel fuels, the total volume of gasoline burned results in a substantial loading of sulfur into the atmosphere. Another experiment could he performed at the same time as Volume 59
Number 4
AWi1 1982
341
this by coupling the Parr bomb with the calorimeter portion of the system to measure the heat produced upon combustion. From the measurement of the heat produced, the BTU equivalent of fuels could be calculated. These values would, of course, be valuable in the discussion on the relative merits of various fuels.
14) Likena, G. E., Chom. and Engr News. 29 (22 November 1976). (5) Carter, . I . "Second . Annual Report on the Environmont to congress: 2 August 1979. 16) Ga1loway.J. N.,Cowling. E. B.,Gorham,E.,snd McFee. W. W.."A NstionslProgram for Assessing the Problem of Atmospheric Deposition (Acid Rain): a report to the Council on Environmenlal Quality, National Atmospheric Deposition P~ogram
Acknowledgment
The analysis of the various types of fuel by Stephen Coma is gratefully acknowledged. Literature Cited (1) Hagan, A. W., and Mohnon. V. A,, Science. 205.1313 11979). (2) Shinn, J.H.,and Lynn,S.,EnvirSci. ond Tech., 13,1062 (1979). (3) Lee, M. L.,Lsfer,D. W.,Rollim,D. K.. Eatough,D.J..and Hanren. L. D.,S&nca,207, 186, 11980).
342
Journal of Chemical Education
p'ivate communication. 111) Sslzberg, H. W., Morrow, J. I., and Cohen, S. R., "Lsborafory C a u m in Physical Chemistry? Academic Preaa, New Yark. 1966, pp. 60-63. (12) Shoemaker. D. P., and Garland, C. W., "ExperimenU in Physical Chemistry." McGrav-Hill.New York. 1962.p~.11&115. 113) "lnstruefion Msnua1,"Parr Combustion Bomb Model 1108.
