analysis of organometallic gasoline additives with the

5508This article not subject to U.S. Copyright. Published 2010 by the American Chemical Society pubs.acs.org/EF

Energy Fuels 2010, 24, 5508–5513 : DOI:10.1021/ef1006403Published on Web 09/09/2010

Analysis of Organometallic Gasoline Additives with the Composition-Explicit

Distillation Curve Method

Thomas J. Bruno* and Evgenii Baibourine

Thermophysical Properties Division, National Institute of Standards and Technology (NIST), Boulder, Colorado 80305

Received May 25, 2010. Revised Manuscript Received August 17, 2010

Problems associated with pre-ignition of fuel in a spark-ignition engine have been documented for manyyears and include poor performance and structural damage in engines. These problems were addressed inthe past by adding organometallic additives, such as tetraethyl lead (TEL), to the fuel.While this additive isbanned, others are permitted in some jurisdictions. Two such additives are ferrocene (FC) and methylcy-clopentadienyl manganese tricarbonyl (MMT). In this paper, we apply the advanced distillation curveapproach to the analysis of these two additives (at concentrations of 20 and 40 mg/L) in a typical gasoline.We observe that neither additive affects the volatility of gasoline until the 55% distillate volume fraction.Subsequent to this fraction, we note temperature departures from the base gasoline that progress from 1 to7 �C for FC and from approximately 1 to 4 �C for MMT. We further note, with the composition-explicitdata channel of the advanced distillation curve (ADC), that the additives are not found in the distillate untilafter the 55% distillate volume fraction and that the concentration in the distillate increases as thedistillation proceeds to completion.

Introduction

When gasoline is used as a fuel in high-compression spark-ignition (SI) engines, the phenomenon known as pre-ignition(manifest by engine knock) often causes serious performanceproblems, which can ultimately lead to structural problems inengines.1 These difficulties have been recognized for decadesand are important issuesbecause high compression ratios inSIengines are associated with high operational efficiency. Formany years, pre-ignition was addressed with the additionof the organometallic additive, tetraethyl lead (TEL), to gaso-line.2,3 The use of TEL was phased out because of health andenvironmental concerns, although this additive is still used inthe general aviation gasoline avgas 100LL.4 Since this additivewas phased out in automobile fuel, pre-ignition (and thesubsequent engine knock) has been prevented primarily bygasoline formulation with higher concentrations of aromaticcompounds, although other organometallic additives are alsoused for this purpose in some jurisdictions. After-marketadditives with organometallic components are also used byautomotive enthusiasts.

Two common organometallic additives that are still used asgasoline additives are dicyclopentadienyl iron [ferrocene

(FC)] and methylcyclopentadienyl manganese tricarbonyl[tricarbonyl[(1,2,3,4,5-η5)-1-methyl-2,4-cyclopentadien-1-yl]-manganese (MMT)].5 FC is the classical example of a metal-locene “sandwich” compound, consisting of a central ironatom between two cyclopentadienyl rings. Indeed, the dis-covery of ferrocene, with its interesting structure, is oftenargued to be the practical beginning of the field of organo-metallic chemistry. It was first prepared accidentally in 1951and is a remarkably stable compound that has been used as ananti-knock additive in SI engines and as an anti-soot additivefor diesel engines. It is still commercially available as anadditive for some vintage automobiles in the U.K.Moreover,it is permitted as a large-scale additive inRussia at levels up to37 mg/L, and it is also used in South Africa.6 The structureand representative properties of FC are provided in Table 1.

The other common organometallic additive used instead ofTEL is the organomanganese compound, MMT. This com-poundwasbanned as a gasoline additive in theU.S. from1977to 1995, and although it is rarely used in the U.S. for thispurpose now, it is nevertheless permitted up to concentrationsof 8.3 mg/L. Except for a regulatory hiatus between 1997 and1998, it has been used in Canada since 1976, where it ispermitted up to 18 mg/L, and it has recently been used inAustralia.7 The toxicity of this additive has been the subject ofcontroversy for many years. Studies suggest that MMT ishighly toxic in a concentrated form, with the liver and kidneysas the target organs. The main exposure route when MMT isapplied as a gasoline additive is dermal absorption andinhalation. Dermal absorption occurs mainly after accidentalgasoline spills and through the (improper) use of gasoline as asolvent. The inhalation route occurs mainly from the inten-tional inhalation of gasoline vapors as a recreational drug.

*To whom correspondence should be addressed. E-mail: [email protected].(1) Guibet, J.-C.; Faure-Birchem, E. Fuels and Engines: Technology,

Energy, Environment; Editions Technip: Paris, France, 1999.(2) Report on Carcinogens;Background Document for “Lead and

Lead Compounds”; National Toxicology Program, National Institute ofEnvironmental Health Sciences: Research Triangle Park, NC, 2003.(3) Tetraethyl lead. In Material Safety Data Sheet (MSDS) 402699;

Sigma-Aldrich: St. Louis, MO, Jan 2, 2006.(4) Lovestead, T. M.; Bruno, T. J. Application of the advanced

distillation curve method to aviation fuel avgas 100LL. Energy Fuels2009, 23, 2176–2183.(5) Linstrom, P. J.; Mallard, W. G. NIST Chemistry WebBook;

National Institute of Standards and Technology (NIST), Gaithersburg MD,June 2005; NIST Standard Reference Database Number 69, http://webbook.nist.gov.

(6) Oudijk, G. Personal communication, May 2, 2010.(7) Gidney, J. T.; Twigg, M. V.; Kittleson, D. B. Effect of organome-

tallic fuel on nanoparticle emission from a gasoline passenger car.Environ. Sci. Technol. 2010, 44, 2562–2569.

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Energy Fuels 2010, 24, 5508–5513 : DOI:10.1021/ef1006403 Bruno and Baibourine

Exposure to manganese in the exhaust is a potential cause ofmanganism, the symptoms ofwhich are similar toParkinson’sdisease.8 This condition is relatively well-understood, since itwas observed in the early 1800s among miners and smelters.More modern manifestations of manganism are seen amongwelders who are exposed to metal fumes. In more recentstudies performed on rats, it appears that manganese oxidenanoparticles (approximate size of 31 nm) can translocatedirectly to the brain along the olfactory system, bypassing theblood-brain barrier.7We note that this compound, like TEL,is chemically stable in solution (in gasoline, for example) but isunstable when exposed to sunlight.6 The structure and repre-sentative properties of MMT are also provided in Table 1.

The development of replacements for the organometallicadditives used in some gasolines requires a sound under-standing of the fuel properties that these additives will influ-ence. Because these additives are present at a relatively lowconcentration in the commercial mixtures, the influence onmany of the bulk thermophysical properties (density, vaporpressure, and transport properties) is slight. When individualowners of vintage vehicles prepare fuels for their own use,however (usually by splash blending in the vehicle tank), theconcentration and the subsequent effect on properties may befar less well-defined. Even in these cases, the effects of the

additives onpropertieswill be subtle.Oneproperty that canbeusedasadiagnostic is the composition-explicit distillationcurve.This measurement, introduced in 2006, can relate thermodyna-mically consistent temperatures of vaporization with the con-centration of the organometallic additives, as a function of thedistillate volume fraction.9-13 The ability to link these twoquantities is significant, because the distillation curve measuredwith thismethod canbemodeledwith an equation of state,14-18

whichcan thenbe related to thevapor emergenceof theadditive.We also note that, during the injection process (before com-bustion), fuel will undergo a droplet vaporization process simi-lar todistillation.Thus, the volatility has application in thedeve-lopment of combustion models.19

The composition-explicit distillation curve, also called theadvanced distillation curve (ADC) method, is an improve-ment over classical approaches.20-22 This technique features(1) a composition-explicit data channel for each distillatefraction (for qualitative, quantitative, and trace analysis),(2) temperature measurements that are true thermodynamicstate points that can be modeled with an equation of state, (3)temperature, volume, and pressure measurements of lowuncertainty suitable for equation of state development, (4)consistencywith a centuryof historical data, (5) an assessmentof the energy content of each distillate fraction, and (6) acorrosivity assessment of each distillate fraction. Clearly, it isnot always needed or desirable to apply all aspects of theADCmetrology in every application. For highly finished fuels, such

Table 1. Data on the Additives Studied in This Worka

a In this table, INChI is the international chemical identifier andRMM is the relative molecular mass.

(8) Manganism, http://www.healthdangers.com/toxic-substances/welding-fumes/index.htm (accessed in 2010).

(9) Bruno, T. J. Improvements in the measurement of distillationcurves;Part 1: A composition-explicit approach. Ind. Eng. Chem. Res.2006, 45, 4371–4380.

(10) Bruno, T. J.; Smith, B. L. Improvements in the measurementof distillation curves;Part 2: Application to aerospace/aviation fuelsRP-1 and S-8. Ind. Eng. Chem. Res. 2006, 45, 4381–4388.

(11) Bruno,T. J.Method and apparatus for precision in-line samplingof distillate. Sep. Sci. Technol. 2006, 41 (2), 309–314.

(12) Bruno, T. J.; Smith, B. L. Enthalpy of combustion of fuels as afunction of distillate cut: Application of an advanced distillation curvemethod. Energy Fuels 2006, 20, 2109–2116.

(13) Smith, B. L.; Bruno, T. J. Advanced distillation curve measure-mentwith amodel predictive temperature controller. Int. J. Thermophys.2006, 27, 1419–1434.

(14) Huber, M. L.; Smith, B. L.; Ott, L. S.; Bruno, T. J. Surrogatemixture model for the thermophysical properties of synthetic aviationfuel S-8: Explicit application of the advanced distillation curve. EnergyFuels 2008, 22, 1104–1114.

(15) Huber, M. L.; Lemmon, E. W.; Diky, V.; Smith, B. L.; Bruno,T. J. Chemically authentic surrogate mixture model for the thermo-physical properties of a coal-derived liquid fuel. Energy Fuels 2008, 22,3249–3257.

(16) Huber,M. L.; Lemmon, E.; Kazakov, A.; Ott, L. S.; Bruno, T. J.Model for the thermodynamic properties of a biodiesel fuel. EnergyFuels 2009, 23, 3790–3797.

(17) Huber, M. L.; Lemmon, E.; Ott, L. S.; Bruno, T. J. Preliminarysurrogatemixturemodels for rocket propellants RP-1 andRP-2.EnergyFuels 2009, 23, 3083–3088.

(18) Huber, M. L.; Lemmon, E. W.; Bruno, T. J. Surrogate mixturemodels for the thermophysical properties of aviation fuel Jet-A. EnergyFuels 2010, 24, 3565–3571.

(19) Bruno, T. J. Thermodynamic, transport and chemical propertiesof “reference” JP-8. In Book of Abstracts, Army Research Office andAir Force Office of Scientific Research, 2007 Contractor’s Meeting inChemical Propulsion; Crystal City, VA, 2007.

(20) Bruno, T. J.; Ott, L. S.; Smith, B. L.; Lovestead, T. M. Complexfluid analysis with the advanced distillation curve approach. Anal.Chem. 2010, 82, 777–783.

(21) Bruno, T. J.; Ott, L. S.; Lovestead, T. M.; Huber, M. L. Thecomposition explicit distillation curve technique: Relating chemicalanalysis and physical properties of complex fluids. J. Chromatogr., A2010, 1217, 2703–2715.

(22) Bruno, T. J.; Ott, L. S.; Lovestead, T. M.; Huber, M. L. Relatingcomplex fluid composition and thermophysical properties with theadvanced distillation curve approach. Chem. Eng. Technol. 2010,33 (3), 363–376.

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as gasoline, it is usually unnecessary to assess corrosivity asa function of the distillate fraction. We have applied this

metrology to gasolines, diesel fuels, aviation fuels, rocketpropellants and surrogates, and renewable gas turbinefuels.4,9-11,13-17,23-47 Moreover, the method has also beenapplied to the volatility simulation of heavy oils.48

In prior work, we applied the ADC to the study of avgas100LL, the anti-knock properties of which derive from theaddition of TEL.4 That study included the thermodynami-cally consistent temperature grid, the enthalpy of combustionas a function of the distillate cut, and the tracking of TELcontent through the distillation curve. We then extended thiswork to cover aviation gasolines in development that do notcontain TEL and used the ADC as the means of comparisonof the properties.49 Here, we present a study of two concen-trations each of FC and MMT in a representative 91 AIwinter-quarter gasoline. Here, we focus on tracking the FCand MMT contents through the distillation curve. The otheraspects of the ADC (temperature grid, energy content, etc.)are very similar to our prior published work on gasoline andgasoline mixed with various additives.31,38

Experimental Section

The gasoline used as the base fluid in this work was a 91 AI(anti-knock index, the average of the motor and research octanenumbers) winter-quarter gasoline formulated with no oxygenateadditive. It was obtained from a commercial source and usedwithout purification. This fluid was analyzed by gas chromatog-raphy (30 m capillary column of 5% phenyl-95% dimethylpolysiloxane, having a thickness of 1 μm, with a temperatureprogram from 50 to 170 �C, at 7 �C/min) separately with flameionization detection (GC-FID) and mass spectrometric detec-tion (GC-MS).50,51 This analysis showed a large fraction ofaromatic constituents, consistent with the relatively high anti-knock index number. Although no specific tests were performedfor olefin content, the GC-MS measurement mentioned abovewas consistent with a very low olefin content. Wemaintained thegasoline in a sealed container at 7 �C, to minimize moistureuptake and to ensure that no compositional changes would occurduring the course of our measurements.

The toluene used as a solvent for the organometallic com-pounds (prepared as analytical standards) was obtained from acommercial source and was analyzed by gas chromatography(30 m capillary column of 5% phenyl-95% dimethyl polysilox-ane, havinga thickness of 1μm,witha temperatureprogramfrom50 to 150 �C, at 7 �C/min) separately with two separate detectionmethods: flame ionization detection and mass spectrometricdetection. This analysis demonstrated that the fluid purity ex-ceeded the 99.9%certificationprovidedby themanufacturer, andit was used as received.

The FC and MMT used in this work were obtained from acommercial source and were analyzed by gas chromatography(30 m capillary column of 5% phenyl-95% dimethyl polysilox-ane, havinga thickness of 1μm,witha temperatureprogramfrom

(23) Huber,M. L.; Lemmon, E.; Bruno, T. J. Effect of RP-1 composi-tional variability on thermophysical properties. Energy Fuels 2009, 23,5550–5555.(24) Lovestead, T. M.; Bruno, T. J. Comparison of the hypersonic

vehicle fuel JP-7 to the rocket propellants RP-1 and RP-2 with theadvanced distillation curve method. Energy Fuels 2009, 23 (7), 3637–3644.(25) Ott, L. S.; Bruno, T. J. Corrosivity of fluids as a function of

distillate cut: Application of an advanced distillation curve method.Energy Fuels 2007, 21, 2778–2784.(26) Ott, L. S.; Smith, B. L.; Bruno, T. J. Advanced distillation curve

measurements for corrosive fluids: Application to two crude oils. Fuel2008, 87, 3055–3064.(27) Ott, L. S.; Smith, B. L.; Bruno, T. J. Advanced distillation curve

measurement: Application to a bio-derived crude oil prepared fromswine manure. Fuel 2008, 87, 3379–3387.(28) Ott, L. S.; Smith, B. L.; Bruno, T. J. Composition-explicit

distillation curves of mixtures of diesel fuel with biomass-derived glycolester oxygenates: A fuel design tool for decreased particulate emissions.Energy Fuels 2008, 22, 2518–2526.(29) Ott, L. S.; Hadler, A.; Bruno, T. J. Variability of the rocket

propellants RP-1, RP-2, and TS-5: Application of a composition- andenthalpy-explicit distillation curve method. Ind. Eng. Chem. Res. 2008,47 (23), 9225–9233.(30) Ott, L. S.; Bruno, T. J. Variability of biodiesel fuel and compar-

ison to petroleum-derived diesel fuel: Application of a composition andenthalpy explicit distillation curvemethod.Energy Fuels 2008, 22, 2861–2868.(31) Smith, B. L.; Bruno, T. J. Improvements in the measurement of

distillation curves: Part 3;Application to gasoline and gasoline þmethanol mixtures. Ind. Eng. Chem. Res. 2007, 46, 297–309.(32) Smith, B. L.; Bruno, T. J. Improvements in the measurement of

distillation curves: Part 4;Application to the aviation turbine fuel Jet-A. Ind. Eng. Chem. Res. 2007, 46, 310–320.(33) Smith,B. L.; Bruno,T. J. Composition-explicit distillation curves

of aviation fuel JP-8 and a coal-based jet fuel. Energy Fuels 2007, 21,2853–2862.(34) Smith, B. L.; Bruno, T. J. Application of a composition-explicit

distillation curve metrology to mixtures of Jet-A þ synthetic Fischer-Tropsch S-8. J. Propul. Power 2008, 24 (3), 619–623.(35) Smith, B. L.; Ott, L. S.; Bruno, T. J. Composition-explicit

distillation curves of diesel fuel with glycol ether and glycol esteroxygenates: A design tool for decreased particulate emissions. Environ.Sci. Technol. 2008, 42 (20), 7682–7689.(36) Smith, B. L.; Ott, L. S.; Bruno, T. J. Composition-explicit

distillation curves of commercial biodiesel fuels: Comparison of petro-leum derived fuel with B20 and B100. Ind. Eng. Chem. Res. 2008, 47 (16),5832–5840.(37) Bruno,T. J.;Wolk,A.;Naydich,A. Stabilization of biodiesel fuel

at elevated temperature with hydrogen donors: Evaluation with theadvanced distillation curve method. Energy Fuels 2009, 23, 1015–1023.(38) Bruno, T. J.; Wolk, A.; Naydich, A. Composition-explicit dis-

tillation curves for mixtures of gasoline with four-carbon alcohols(butanols). Energy Fuels 2009, 23, 2295–2306.(39) Bruno,T. J.;Wolk,A.;Naydich,A.Analysis of fuel ethanol plant

liquor with the composition explicit distillation curve approach. EnergyFuels 2009, 23 (6), 3277–3284.(40) Bruno, T. J.;Wolk, A.; Naydich, A.; Huber,M. L. Composition-

explicit distillation curves for mixtures of diesel fuel with dimethylcarbonate and diethyl carbonate. Energy Fuels 2009, 23 (8), 3989–3997.(41) Hadler, A. B.; Ott, L. S.; Bruno, T. J. Study of azeotropic

mixtures with the advanced distillation curve approach. Fluid PhaseEquilib. 2009, 281, 49–59.(42) Bruno, T. J.; Wolk, A.; Naydich, A. Composition-explicit dis-

tillation curves for mixtures of gasoline and diesel fuel with γ-valer-olactone. Energy Fuels 2010, 24, 2758–2767.(43) Bruno, T. J.; Smith, B. L. Evaluation of the physicochemical

authenticity of aviation kerosene surrogate mixtures. Part 1: Analysis ofvolatility with the advanced distillation curve. Energy Fuels 2010, 24,4266–4276.(44) Bruno, T. J.; Huber, M. L. Evaluation of the physicochemical

authenticity of aviation kerosene surrogate mixtures. Part 2: Analysisand prediction of thermophysical properties. Energy Fuels 2010, 24,4277–4284.(45) Windom, B. C.; Lovestead, T. M.; Riggs, J. R.; Nickell, C.;

Bruno, T. J. Assessment of the compositional variability of RP-1 andRP-2 with the advanced distillation curve approach. In Proceedings ofthe 57th Joint Army-Navy-NASA-Air Force (JANNAF) Conference;Colorado Springs, CO, May 2010.

(46) Bruno, T. J.; Baibourine, E.; Lovestead, T. M. Comparison ofsynthetic isoparaffinic kerosene turbine fuels with the composition-explicit distillation curve method. Energy Fuels 2010, 24, 3049–3059.

(47) Lovestead, T. M.; Windom, B. C.; Bruno, T. J. Investigating theunique properties of cuphea-derived biodiesel fuel with the advanceddistillation curve method. Energy Fuels 2010, 24, 3665–3675.

(48) Satyro, M. A.; Yarranton, H. Oil characterization from simula-tion of experimental distillation data.Energy Fuels 2009, 23, 3960–3970.

(49) Windom,B.C.; Lovestead, T.M.; Bruno,T. J. Application of theadvanced distillation curve method to the development of unleadedaviation gasoline. Energy Fuels 2010, 24, 3275–3284.

(50) Bruno, T. J.; Svoronos, P. D. N. CRCHandbook of Basic Tablesfor Chemical Analysis, 2nd ed.; CRC Press (Taylor and Francis Group):Boca Raton, FL, 2004.

(51) Bruno, T. J.; Svoronos, P. D. N.CRCHandbook of FundamentalSpectroscopic Correlation Charts; CRC Press (Taylor and Francis Group):Boca Raton, FL, 2006.

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50 to 225 �C, at 7 �C/min) with mass spectrometric detection inscanmode from 20 to 550RMMunits. For these analyses, toluenesolutions of the organometallic compounds were injected. Thepurity of the FCwas verified as being 98% (mass/mass). Althoughthe purity specification for MMT was listed as greater than 88%(mass/mass), our analysis indicated apurity of approximately 95%(mass/mass). Both additives were used as received.

Themixtures of gasoline with the organometallic additives wereprepared as stock solutions at 23 �C in mixing cylinders. Concen-trations of 20 and 40 mg/L were prepared for each additive. Theseconcentrations, while not exactlymatching those used industrially,were chosen to cover the entire practical range. Once prepared, themixtures were maintained in sealed containers. The FC did notaffect the appearance of the gasoline to any noticeable extent;however, theMMTproduced a very slight cloudiness at the 40mg/Lconcentration.This solutionwasnevertheless stable, andnosolidphase settled or precipitated out. No such cloudiness was observedwith the 20 mg/L solution of MMT.

The method and apparatus for the distillation curve measure-ment has been reviewed in a number of sources; therefore, anadditional general description will not be provided here.9-11,13 Therequired fluid for the distillation curve measurement (in each case,200mL) was prepared as a stock solution with the additive, so thatthe concentrations would be repeatable for successive measure-ments. This fluid was placed into the boiling flask with a 200 mLvolumetric pipet. The thermocouples were then inserted into theproper locations tomonitorTk, the temperature in the fluid, andTh,the temperature at the bottom of the takeoff position in the distilla-tion head. Enclosure heating was then commenced with a four-stepprogram based on a previously measured distillation curve.

Because the measurements of the distillation curves were per-formed at local ambient atmospheric pressure (approximately 83kPa,measuredwithan electronicbarometer), temperature readingswere corrected for what should be obtained at standard atmo-spheric pressure. The pressure adjustments were performed withthe modified Sydney Young equation, in which the constant termwas assigned a value of 0.000119.52-55 This value corresponds to an-alkane carbon chain of 8, which is a reasonable representative formotor gasoline.

Volumemeasurements weremade in the level-stabilized receiver,and sample aliquots were collected at the receiver adapter ham-mock. In the course of this work, we focused primarily on trackingthe concentration of the organometallic additive through the dis-tillation curve. Because we have performed numerous distillationsof the base gasoline fluid in prior work, we only measured threereplicate curves for each additive concentration studied here.

Results and Discussion

Initial Boiling Temperatures. During the initial heating ofeach sample in the distillation flask, the behavior of the fluidwas carefully observed. Direct observation through the flask

window or through the bore scope allowed for the measure-ment of the onset of boiling for each of the mixtures(measured withTk). Typically, to ascertain the initial boilingbehavior, wemeasure the onset of bubbling, the temperatureat which bubbling is sustained, and the temperature at whichthe vapor rises into the distillation head. This can be notedvisually or by the rapid increase in the temperature of thethermocouple thatmonitorsTh.We have shown that this lasttemperature is actually the initial boiling temperature (theIBT, an approximation of the bubble point temperature atambient pressure) of the initial fluid. This measurement issignificant for a mixture because it can be modeled with anequation of state. Experience with previousmixtures, includ-ing n-alkane standard mixtures that were prepared gravime-trically, indicates that the uncertainty in the onset ofbubbling and sustained bubbling temperatures is approxi-mately 1 �C. The uncertainty in the vapor rise temperaturewas 0.3 �C. The initial boiling temperatures for the mixturesof gasoline with FC and MMT are provided in Table 2,where the vapor rise temperatures are shown. These tem-peratures are averages of five separate measurements. Wenote that these temperatures vary little with the additiveconcentration and are essentially unchanged from the vaporrise temperature of a typical 91 AI winter-quarter gasoline.Indeed, the vapor rise temperature for the base gasoline usedhere was found to be 64.7 �C. These observations indicatethat the addition of these two additives has a minimal effecton the very early vaporization behavior of gasoline.

Distillation Curves. Representative distillation curve datafor the mixtures of 91 AI winter-quarter gasoline and thisgasoline with 20 and 40mg/L of FC andMMTare presentedin Table 3. For eachmixture, five complete distillation curveswere measured. Distillation data are presented in both Tk

(measured directly in the fluid) and Th (measured in thedistillation head). The Tk data are true thermodynamic statepoints, while the Th data allow for a comparison to earliermeasurements. In this table, the estimated uncertainty (witha coverage factor k= 2) in the temperatures was 0.3 �C. Wenote that the experimental uncertainty of Tk is always some-what lower than that ofTh, but as a conservative position, weuse the higher value for both temperatures. The uncertaintyin the volume measurement that was used to obtain thedistillate volume fraction is 0.05 mL in each case. Therepeatability in the pressure measurement (assessed by log-ging a pressure measurement every 15 s for the duration ofa typical distillation) was 0.001 kPa. The relatively lowuncertainties in the measured quantities facilitate modelingthe results, for example, with an equation of state.

We note from the data that the additives have no dis-cernible effect on the vaporization temperatures of themixtures early in the distillation curves, but as the distillationprogresses, the effect appears to become more pronounced.This can be illustrated in panels a and b of Figure 1, in whichthe latter portions of the curves are represented graphically.Here, we see that the presence of the additive increases the

Table 2. Initial Boiling Behavior of Gasoline Mixtures with FC and MMTa

observed temperaturegasoline þ 20 mg/LFC (�C, at 83.49 kPa)

gasoline þ 40 mg/LFC (�C, at 83.90 kPa)

gasoline þ 20 mg/LMMT (�C, at 83.42 kPa)

gasoline þ 40 mg/LMMT (�C, at 83.5 kPa)

onset 43.5 45.2 53.8 41.9sustained 63.5 63.7 61.1 61.7vapor rise 64.8 65.5 64.2 65.0

aThe temperatures have been adjusted to standard atmospheric pressure with the Sydney Young equation. The vapor rise temperatures are the initialboiling temperatures of each mixture. The uncertainty is discussed in the text.

(52) Ott, L. S.; Smith, B. L.; Bruno, T. J. Experimental test of theSydney Young equation for the presentation of distillation curves.J. Chem. Thermodyn. 2008, 40, 1352–1357.(53) Young, S. Correction of boiling points of liquids from observed

to normal pressures. Proc. Chem. Soc. 1902, 81, 777.(54) Young, S. Fractional Distillation; Macmillan and Co., Ltd.:

London, U.K., 1903.(55) Young, S. Distillation Principles and Processes; Macmillan and

Co., Ltd.: London, U.K., 1922.

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vaporization temperatures for both the 20 and 40 mg/Lmixtures. We also note that a much greater change in the

vaporization temperature occurs when 40 mg/L of eachorganometallic additive is present. The additive that is solidat room temperature, FC, has a noticeable effect beginningat the 55% distillate volume fraction, while the effect of theMMT is not pronounced until the 70% distillate volumefraction. For FC, the departure in the vaporization tempera-ture, beginning at the 55% distillate volume fraction, rangesfrom 1 to 7 �C, with an average of 3.7 �C. For MMT, thedeparture ranges from just below 1 to 4 �C, with an averageof 1.1 �C.

As examination of the behavior of the temperatures Tk

and Th, together as a function of the distillate cut, is alsoinstructive. We have demonstrated that a convergence ofthese temperatures is indicative of the presence of anazeotrope.41We note fromTable 3 that no such convergenceis found with the mixtures that we have measured.

Composition Channel. The composition-explicit datachannel of the ADC is a functional means of explaining theappearance of distillation curves in terms of the chemicalcomposition of the distillate over the course of a distillation.We used this channel by withdrawing 7 μL samples ofselected distillate fractions and dissolving this aliquot in aknown mass of solvent (n-tetradecane). This solvent waschosen because it causes no chromatographic interferencewith the sample matrix (fractions of gasoline). We thenanalyzed these samples by GC-MS, using similar chroma-tographic conditions used to verify the purity of the addi-tives. Instead of scanning mode, however, we used selectedion monitoring. For FC, we monitoredm/z 56, 121, and 186,while for MMT, we monitored m/z 79, 134, 162, and 218.Five replicates of each sample were measured. The analysisfor each of the additives was standardized with fourmixturesof each additive in toluene, applied as external standards.A calibration curve was developed from these solutions (r2=0.998) and was designed to bracket the analytical samples.The results of these analyses are provided as histograms inFigure 2. The combinedmass fraction uncertainty (includingthe calibrations and analyte concentrations) ranged from30% at the very low concentrations to less than 2% at thehigher concentrations (coverage factor k = 2). The uncer-tainty is indicated by the bars on the figure.

Table 3. Representative Distillation Curves for Gasoline Mixtures with FC and MMTa

gasoline þ 20 mg/LFC (82.31 kPa)

gasoline þ 40 mg/LFC (83.59 kPa)

gasoline þ 20 mg/LMMT (82.9 kPa)

gasoline þ 40 mg/LMMT (83.5 kPa)

distillate volumefraction (%) Tk (�C) Th (�C) Tk (�C) Th (�C) Tk (�C) Th (�C) Tk (�C) Th (�C)

5 80.3 69.5 80.7 66.2 79.7 72.8 78.9 69.610 86.2 79.7 85.4 75.7 85.9 78.6 84.6 76.915 91.8 86.1 90.9 83.0 91.8 85.3 89.8 84.220 97.4 92.2 97.7 90.6 97.5 91.3 96.0 90.725 102.3 98.3 102.9 96.6 102.3 96.5 100.3 98.130 107.1 103.4 108.1 101.1 107.5 101.7 106.3 103.935 111.7 108.7 113.1 106.7 112.3 107.2 111.0 108.940 116.1 113.4 116.7 111.0 116.3 112.1 115.0 114.645 120.2 117.6 121.2 115.4 120.2 115.7 119.1 117.450 124.3 121.4 125.2 119.6 124.2 119.8 124.0 122.055 128.5 124.4 129.2 122.9 127.3 124.0 127.3 126.260 132.2 128.1 134.0 127.5 131.6 128.4 131.9 130.565 136.7 131.7 138.9 131.4 136.7 134.2 136.9 135.570 142.1 136.3 146.3 137.1 143.4 139.9 143.8 144.175 148.0 142.0 154.3 139.7 150.4 145.6 150.7 152.280 156.8 150.7 163.1 150.9 158.0 152.8 159.4 160.185 166.2 161.5 173.2 156.3 166.8 160.9 170.9 169.6

aThe temperatures have been adjusted to standard atmospheric pressure with the Sydney Young equation. The vapor rise temperatures are the initialboiling temperatures of each mixture. The uncertainty is discussed in the text.

Figure 1. Latter portion of the distillation curves of mixtures of 91 AIwinter-quarter gasoline with (a) FC and (b) MMT. For comparison,data for gasoline with no organometallic additive are also shown.

5513


In the early distillate volume fractions and continuing up tothe 60% fraction, we do not detect any additive in the distillate.This is consistent with the temperature grid of the distillationcurves, in which little difference is seen between the two concen-trations of the additives early in the vaporization. Subsequent tothe 60%distillate volume fraction, the additive can be observedin the distillate, increasing in concentration until the vaporiza-tion is completed.We note that a similar behavior was observedwith themore common anti-knock additive, TEL, in our earliermeasurements on high-performance aviation gasoline 100LL.There, we only observed appreciable TEL after the 60% distil-late volume fraction.4 The results that we observe here differ inthe absolute concentrations observed in the distillate. Here, forFC and MMT, we observe concentrations that are 2 orders of

magnitude lower than what was observed for TEL. The mainreason for this is the much higher concentration of TEL that isused in aviation gasoline. The starting concentration of TEL inthe sample of 100LL that was examined in our earlier studywas560mg/L, a 14-fold higher concentration of additive than whatwe have studied here. For operational and environmentalreasons, FC and MMT used today are applied at much lowerconcentrations than TEL used in aviation gasoline. We wereunable to study the differences in aviation gasoline with andwithout TEL, because the base stock is not generally available.

The analytical results complement and, in fact, explain thedistillation curve results. The departures from the vaporiza-tion temperatures of the base gasoline are observed only inthe distillate volume fractions in which the organometallicadditive is found.Moreover, the magnitude of the departureis consistent with the additive concentration.

Conclusions

In this paper, we presented an analysis of gasoline mixtureswith two organometallic anti-knock additives, FC andMMT.We found that these two additives, at the concentrationstypically applied or recommended as anti-knock additives ingasoline, have little effect on the early regions (from 0 to 50%distillate volume fraction) of the distillation curves. Theadditives do appear to affect the latter portion of the curves,producing somewhat higher vaporization temperatures. Thispart of the distillation curve of gasoline is associated with thedesign and specification of fuel economy and power outputparameters.We note that the temperature departure from thebase gasoline is larger for the additive that is solid at roomtemperature (FC). The vaporization behavior that is observedfor these two additives is similar to that of TEL in high-performance aviation gasoline. The composition-explicit datachannel of the ADC confirms the presence of substantialorganometallic additive in the distillate of this late vaporiza-tion region. The major significance of these results will be inthe thermophysical property modeling of gasolines withorganometallic additives. Here, capturing the subtle volatilitybehavior is critical.We note inter alia that gasoline containingthese additives that might be used as accelerants (or ignitableliquids) in arson fires will likely leave the additive in theevaporation or weathering pattern likely to be found in thefire debris.

Acknowledgment. A Professional Research Experience Pro-gram Undergraduate Fellowship at the National Institute ofStandards and Technology is gratefully acknowledged by E.B.

Figure 2. Histogram showing the measured concentrations of (a)FC and (b)MMTas a function of the distillate volume fraction. Theuncertainty is discussed in the text.

analysis of organometallic gasoline additives with the

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