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Adventures in Thermochemistry

Adventures in Thermochemistry. James S. Chickos * Department of Chemistry and Biochemistry University of Missouri-St. Louis Louis MO 63121 9. McDonnell Planetarium. Applications of the Correlation-Gas Chromatographic Method Objectives: To go where no one else has gone

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Adventures in Thermochemistry

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  1. Adventures in Thermochemistry James S. Chickos* Department of Chemistry and Biochemistry University of Missouri-St. Louis Louis MO 63121 9 McDonnell Planetarium

  2. Applications of the Correlation-Gas Chromatographic Method • Objectives: To go where no one else has gone • 1. Evaluation of the vaporization enthalpies of large molecules • Application of Correlation-Gas Chromatography to a Tautomeric Mixture –Acetylacetone • 3. Evaluation of the Vaporization Enthalpy of Complex Hydrocarbon Mixtures

  3. VAPORIZATION ENTHALPIES OF COMPLEX MIXTURES The use of gas-chromatography to measure the vaporization enthalpy of complex hydrocarbon mixtures Vaporization Enthalpies of High Energy Density Fuels for Aerospace Propulsion RP-1, JP-7, JP-8

  4. Why is it important to know the ∆lgHm(298.15 K) of complex mixtures as found in aviation fuels? The most obvious role for aviation fuel in advanced aircraft is for propulsion. A second and increasingly important role is as an airframe coolant in supersonic aircraft. Recently there has been an interest in finding endothermic fuels which initially undergoes an endothermic reaction to form secondary products that are subsequently used for propulsion.

  5. RP-1 (Rocket Propellant 1) Refined petroleum, a mixture of complex hydrocarbons

  6. A GC plot of RP-1 without standards Compound number distribution for RP-1 without standards

  7. Physical properties of RP-1 • Approx. formula C12H23.4 • Boiling range (F) 350-525 • Freezing point (F) -56 • Flash point (F) 155 • Net heating value (btu/lb) 18,650 • Specific gravity (70F) 0.806 • Critical T (F) 770 • Critical P (psia) 315 • Preliminary composition • n-paraffins (wt%) 2.1 • i-paraffins 27.1 • naphthenes 62.4 • aromatics 8.4

  8. Application of the GC method to a complex mixture For a mixture of i structurally related components, the following relationship applies: ln(to/t1) = ln(A1)- slngHm(Tm)1 /RT ln(to/t2) = ln(A2)- slngHm (Tm)2 /RT … ln(to/ti) = ln(Ai)- slngHm(Tm)i /RT Multiplying each component by its mole fraction, ni and summing over all i components result in the following equation: ∑ni ln(to/ti) = ∑ni ln(Ai)- ∑ni slngHm(Tm)i/RT A plot of ∑ni ln(to/ti) versus 1/Tshouldresult in a straight line with a slope of - slngHm(Tm)mix. When several structurally related standards are included in the mixture, a plot of ln(to/ti) versus 1/Tfor each standard should also result in a linear plot. The slngHm(Tm) term for each standard can be correlated to its respective vaporization enthalpy. From the correlation equation andslngHm(Tm)mix of the mixture, the vaporization enthalpy of the ensemble, lgHm(Tm)mix, can be determined. This assumes that the enthalpy of mixing is small

  9. 5 6 A GC Plot of RP-1 with 6 Standards RP-1 with standards: 1. n-octane 2. nonene 3. n-decane 4. naphthalene 5. n-dodecane 6. n-tridecane 3 4 1 2 3 4 5 6 2

  10. A plot of natural logarithm of the reciprocal adjusted retention times for (top to bottom): ,n- octane;  , nonene; , n-decane;  , naphthalene;  , n-dodecane; , n-tridecane.

  11. Equations resulting from a linear regression of ln(to/ta) versus (1/T)K-1 Compound ln(to/ta)=- slngHm/RT + ln(Ai) n-octane ln(to/ta)= (-3887.5/T) + (11.064 ± 0.008) r2=0.9995 1-nonene ln(to/ta)= (-4222.9/T) + (11.159 ± 0.010) r2=0.9993 n-decane ln(to/ta)= (-4687.9/T) + (11.655 ± 0.010) r2=0.9994 naphthalene ln(to/ta)= (-4965.5/T) + (11.176 ± 0.008) r2=0.9997 n-dodecane ln(to/ta)= (-5566.1/T) + (12.685 ± 0.010) r2=0.9996 n-tridecane ln(to/ta)= (-6018.6/T) + (13.232 ± 0.010) r2=0.9997 slngHm(Tm) = lgHm(Tm) + slnHm(Tm) to = 1 min Tm = 368 K

  12. A demonstration of the application of the method for a 1:1 molar mixture of n-Octane and n-Tridecane Vaporization enthalpy of n-Octane = 41560J/mol Vaporization enthalpy of n-Tridecane = 67062J/mol Vaporization enthalpy of 1:1 Mixture = 54120J/mol (assume ideal mixing) [0.5×41560+0.5×67062]

  13. For a 1:1 mixture of n-Octane and n Tridecane ∑niln(to/ti)= ∑niln(Ai)- ∑nislngHm(Tm)i/RT T/K (1/T) K-1 ln(to/ta)niln(1/ti) (ni = 0.5) n-octane n-decane n-octane/n- tridecane 354.0 0.002825 0.0761 -3.7705 -1.847 358.9 0.002786 0.2278 -3.5357 -1.654 363.9 0.002748 0.3756 -3.3070 -1.466 369.0 0.002710 0.5234 -3.0783 -1.277 374.1 0.002673 0.6673 -2.8556 -1.094 379.2 0.002637 0.8073 -2.6390 -0.9158 384.2 0.002603 0.9396 -2.4343 -0.7474

  14. ∑niln(to/ti)= 12.1498 ± 0.003 – 4954/T (1:1 octane: tridecane)

  15. A plot of lgHm(298.15 K) vs slngHm(368 K) for the remaining standards dodecane naphthalene decane nonene lgHm(298.15 K) = (1.444  0.092)slngHm(368 K) – (4818  746); r2 = 0.9919

  16. Vaporization enthalpies calculated for the standards and for 1:1 mixture of n-Octane/n-Tridecanea lgHm(298.15 K) = (1.444  0.092)slngHm(368 K) – (4.82 3.7); r2 = 0.9919 (2) aenthalpies in kJ /mol bcalculated for a 1:1 mixture of n-octane/n-tridecane

  17. Approximation of the Mol Fraction 8 C 13C FID detector response is proportional to the number of carbon atoms

  18. The observed correlation between the number of carbon atoms present in the standards and the natural logarithm of their adjusted retention time at T = 364 K. The point that falls off the line is naphthalene, all others are n-alkanes/alkenes. The area of each peak was adjusted for carbon number based on its retention time. mol fraction = area(i)/[Nc(i)/Σiareai/Nc(i) DETECTOR BIAS where Nc = -1.218.ln(1/ta) + 8.39

  19. Slope Intercept slngHm(368 K) lgHm(298.15 K) lit lgHm(298.15K) calcd octane -383878 10.880.01 31.91 41.56 41.8 nonene -416284 11.050.01 34.60 45.5 45.8 decane -461584 11.490.01 38.37 51.42 51.3 naphthalene -488448 10.960.01 40.60 55.65 54.8 dodecane -546458 12.410.01 45.42 61.52 61.7 tridecane -589743 12.910.01 49.03 66.68 67.0 RP-1 -4640100 10.580.03 38.57 51.61.2 RP-1a -462694 11.580.03 38.45 51.51.2 lgHm(298.15 K)/kJmol-1 = (1.4720.041) slngHm(368 K) –(5.1450.59); r2 =0.9970 The slopes, intercepts, enthalpies of transfer, and enthalpies of vaporization of the standards and those calculated for RP-1; enthalpies in kJ.mol-1 a adjusted for detector bias

  20. Samples of JP-7 and JP-8 already contain substantial amounts of n-alkanes as identified by GCMS and retention time studies. n-Undecane, n-dodecane, n- tridecane, and n-tetradecane were identified and used as internal standards for JP-7 STANDARDS CHOSEN FOR JP-7 C11 C12 C13 C14

  21. n-decane through to n-pentadecane were similarly identified and used as standards in JP-8. Similar in composition to Jet A used in commercial aviation STANDARDS CHOSEN FOR JP-8 C11 C12 C13 C14 C15

  22. lgHm(298.15 K) kJ.mol-1 Approximate Formula Massa g .mol-1 lgHm(298.15 K) kJ.kg-1 calcd lgHm(298.15 K) kJ.kg-1 (lit) RP-1 C12H23.4 51.5 167.4 308 291, 246b JP-7 C12H25 55.9 169 331 330c JP-8 C11H21 65.4 153 428 A comparison of vaporization enthalpies of RP-1, JP-7, and JP-8 with literature values a reference Edwards, T. “Kerosene Fuels for Aerospace Propulsion-Composition and Properties” b reference CPIA Liquid Propellant Manual c reference “Aviation Fuel Properties” CRC Report No 530, Society of Automotive Engineers, Inc.

  23. The vaporization enthalpy of JP-10, A High Energy Density Rocket Fuel

  24. ∆glHm (298.15 K) exo-THDCPD 49.1 ± 2.3 endo-THDCPD 50.2 ± 2.3 The enthalpies of vaporization and sublimation of exo- and endo-tetrahydrodicyclopentadienes at T = 298:15K Chickos,J. S.; Hillesheim, D.; Nichols, G. J. Chem. Thermodyn. 2002, 34, 1647–1658.

  25. RJ-4 A High Energy Density Rocket Fuel Standards Used decane exo-tetrahydrodicyclopentadiene endo-tetrahydrodicyclopentadiene n-tetradecane lgHm(298.15 K) = 55.3 ± 1.0 kJ/mol Chickos, J.S. Wentz, A. E.; Hillesheim-Cox, D. Zehe, M. J. Ind. Eng. Chem.2003, 42, 2874-7

  26. Acknowledgments Tim Edwards, Wright Patterson Air Force Base W. Hanshaw, P. Umnahanant, and D. Hillesheim-Cox Solutia STARS program support for A. E. Wentz. Fundacāo para a Ciệncis e a Tecnologia (Portugal) support for D. Hillesheim-Cox NASA

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