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

1. Evaluation of the vaporization enthalpies of large molecules 2. Application of Correlation-Gas Chromatography to a Tautomeric

Mixture –Acetylacetone3. Evaluation of the Vaporization Enthalpy of Complex

Hydrocarbon Mixtures

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

Why is it important to know the ∆Why is it important to know the ∆llggHHmm(298.15 K) of complex (298.15 K) of complex

mixtures as found in aviation fuels?mixtures as found in aviation fuels?

The most obvious role for aviation fuel in advanced aircraft is for The most obvious role for aviation fuel in advanced aircraft is for propulsion. propulsion.

A second and increasingly important role is as an airframe coolant A second and increasingly important role is as an airframe coolant in supersonic aircraft.in supersonic aircraft.

Recently there has been an interest in finding endothermic fuels Recently there has been an interest in finding endothermic fuels which initially undergoes an endothermic reaction to form which initially undergoes an endothermic reaction to form secondary products that are subsequently used for propulsion.secondary products that are subsequently used for propulsion.

• RP-1 (Rocket Propellant 1)

Refined petroleum, a mixture of complex hydrocarbons

A GC plot of RP-1 without standards

Compound number distribution for RP-1 without standardsCompound number distribution for RP-1 without standards

0

1000000

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1 10 19 28 37 46 55 64 73 82 91 100 109 118

Compound Number

Are

a

• 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•

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)- sln

gHm(Tm)1 /RT ln(to/t2) = ln(A2)- sln

gHm (Tm)2 /RT … ln(to/ti) = ln(Ai)- sln

gHm(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/T should result 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/T for 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

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

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1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 121Compound Number

Are

a

3 4

5

6

2 1 2 3 4 5 6

1/T, K-1

0.00255 0.00260 0.00265 0.00270 0.00275 0.00280 0.00285

Ln(1

/t c)

-5

-4

-3

-2

-1

0

1

2

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

Equations resulting from a linear regressionEquations resulting from a linear regression

of ln(of ln(ttoo//ttaa) versus (1/) versus (1/TT)K)K-1-1

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) = l

gHm(Tm) + slnHm(Tm)

to = 1 min Tm = 368 K

A demonstration of the application of the method for a 1:1 A demonstration of the application of the method for a 1:1 molar mixture of n-Octane and n-Tridecanemolar mixture of n-Octane and n-Tridecane

Vaporization enthalpy of n-Octane = 41560J/molVaporization enthalpy of n-Octane = 41560J/mol

Vaporization enthalpy of n-Tridecane = 67062J/molVaporization enthalpy of n-Tridecane = 67062J/mol

Vaporization enthalpy of 1:1 Mixture = 54120J/mol Vaporization enthalpy of 1:1 Mixture = 54120J/mol (assume ideal mixing) (assume ideal mixing) [0.5×41560+0.5×67062][0.5×41560+0.5×67062]

For a 1:1 mixture of n-Octane and n Tridecane For a 1:1 mixture of n-Octane and n Tridecane ∑ ∑nniiln(ln(ttoo//ttii)= ∑n)= ∑niiln(Aln(Aii)- ∑n)- ∑niislnsln

ggHHmm((TTmm))ii/R/RTT

TT/K/K (1/T) K (1/T) K-1 -1 ln(ln(ttoo//ttaa)) nniiln(1/ln(1/ttii) (n) (ni i = 0.5)= 0.5)

n-octane n-decane n-octane/n- tridecane n-octane n-decane n-octane/n- tridecane 354.0354.0 0.002825 0.002825 0.0761 0.0761 -3.7705 -3.7705 -1.847 -1.847 358.9358.9 0.002786 0.2278 -3.5357 -1.654 0.002786 0.2278 -3.5357 -1.654 363.9363.9 0.002748 0.3756 -3.3070 -1.466 0.002748 0.3756 -3.3070 -1.466 369.0369.0 0.002710 0.5234 -3.0783 -1.277 0.002710 0.5234 -3.0783 -1.277 374.1374.1 0.002673 0.6673 -2.8556 -1.094 0.002673 0.6673 -2.8556 -1.094 379.2379.2 0.002637 0.8073 -2.6390 -0.9158 0.002637 0.8073 -2.6390 -0.9158 384.2384.2 0.002603 0.9396 -2.4343 -0.7474 0.002603 0.9396 -2.4343 -0.7474

∑∑nniiln(ln(ttoo//ttii)= 12.1498 )= 12.1498 ± 0.003 – 4954/± 0.003 – 4954/T T (1:1 octane: tridecane) (1:1 octane: tridecane)

enthalpies of transfer from solution to the vapor; J mol-1

34000 36000 38000 40000 42000 44000 46000 48000

vapo

riza

tion

ent

halp

y(lit

era

ture

); J

mol

-1

44000

46000

48000

50000

52000

54000

56000

58000

60000

62000

64000

llggHHmm(298.15 K) = (1.444 (298.15 K) = (1.444 0.092) 0.092)slnsln

ggHHmm(368 K) – (4818 (368 K) – (4818 746); r 746); r22 = 0.9919 = 0.9919

A plot of llggHHmm(298.15 K) vs (298.15 K) vs slnsln

ggHHmm(368 K) for the remaining standards(368 K) for the remaining standards

dodecane

naphthalene

decane

nonene

Vaporization enthalpies calculated forVaporization enthalpies calculated forthe standards and for 1:1 mixture of the standards and for 1:1 mixture of

n-Octane/n-Tridecanen-Octane/n-Tridecaneaa

slngHm(368 K) l

gHm(298.15 K)

lit

lgHm(298.15 K)

Calcd [eq (2)]

nonene 35.108 45.50 45.9±5.0

decane 38.973 51.42 51.5±5.2

naphthalene 41.281 55.65 54.8±5.3

dodecane 46.274 61.52 62.0±5.7

1:1 mixtureof n-octane/n-tridecane

41.188 54.6±5.3 54.1b

ll

ggHHmm(298.15 K) = (1.444 (298.15 K) = (1.444 0.092) 0.092)slnslnggHHmm(368 K) – (4.82 (368 K) – (4.82 3.7); r3.7); r22 = 0.9919 (2) = 0.9919 (2)

aaenthalpies in kJ /molenthalpies in kJ /mol bbcalculated for a 1:1 mixture of n-octane/n-tridecanecalculated for a 1:1 mixture of n-octane/n-tridecane

Approximation of the Mol Fraction

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1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 121Compound Number

Are

a

8 C

13C

FID detector response is proportional to the number of carbon atoms

DETECTOR BIAS

The observed correlation between the number of carbon atoms present in the standards and the natural logarithm of their adjusted retention time atT = 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 numberbased on its retention time.

mol fraction = area(i)/[Nc(i)/Σiareai/Nc(i)

ln (1/ta )

-4 -3 -2 -1 0 1

N, t

he n

umbe

r of

car

bon

atom

s

7

8

9

10

11

12

13

14

where

Nc = -1.218.ln(1/ta) + 8.39

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

  Slope Intercept slngHm(368 K) l

gHm(298.15 K)lit

lgHm(298.15K)

calcdoctane -383878 10.880.01 31.91 41.56 41.8

nonene -416284 11.050.01 34.60 45.5 45.8

decane -461584 11.490.01 38.37 51.42 51.3

naphthalene -488448 10.960.01 40.60 55.65 54.8

dodecane -546458 12.410.01 45.42 61.52 61.7

tridecane -589743 12.910.01 49.03 66.68 67.0

RP-1 -4640100 10.580.03 38.57   51.61.2

RP-1a -462694 11.580.03 38.45   51.51.2  l

gHm(298.15 K)/kJmol-1 = (1.4720.041) slngHm(368 K) –(5.1450.59); r2

=0.9970

STANDARDS CHOSEN FOR JP-7

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

Adjusted retention time (min)

0 5 10 15 20 25 30 35 40

Mol

Fra

ctio

n

0.00

0.02

0.04

0.06

0.08

0.10

C11 C12 C13 C14

STANDARDS CHOSEN FOR JP-8n-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

Adjusted retention time (min)

0 5 10 15 20 25 30 35 40

Mol

Fra

ctio

n

0.00

0.01

0.02

0.03

0.04

0.05

0.06

C11 C12 C13 C14 C15

  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 Manualc reference “Aviation Fuel Properties” CRC Report No 530, Society of Automotive Engineers, Inc.

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

The enthalpies of vaporization and sublimation of exo- and endo-tetrahydrodicyclopentadienesat T = 298:15KChickos,J. S.; Hillesheim, D.; Nichols,G. J. Chem. Thermodyn. 2002, 34, 1647–1658.

∆glHm (298.15 K)

exo-THDCPD 49.1 ± 2.3endo-THDCPD 50.2 ± 2.3

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

AcknowledgmentsAcknowledgmentsTim Edwards, Wright Patterson Air Force BaseTim Edwards, Wright Patterson Air Force BaseW. Hanshaw, P. Umnahanant, and D. Hillesheim-CoxW. Hanshaw, P. Umnahanant, and D. Hillesheim-CoxSolutia STARS program support for A. E. Wentz.Solutia STARS program support for A. E. Wentz.FundacFundacāo para a Ciệncis e a Tecnologia (Portugal) support for āo para a Ciệncis e a Tecnologia (Portugal) support for D. Hillesheim-Cox D. Hillesheim-Cox NASANASA