NISTIR 6659
`Thermodynamic, Transport, and Chemical
`Properties of “Reference” JP-8
`
`Thomas J. Bruno
`Marcia Huber
`Arno Laesecke
`Eric Lemmon
`Mark McLinden
`Stephanie L. Outcalt
`Richard Perkins
`Beverly L. Smith
`Jason A. Widegren
`
`National Institute of Standards and Technology
`United States Department of Commerce
`
`UTC-2014.001
`
`GE v. UTC
`Trial IPR2016-01301
`
`

`

`
`
`UTC-2014.002
`
`UTC-2014.002
`
`

`

`NISTIR 6659
`
`Thermodynamic, Transport, and Chemical
`
`Properties of “Reference” JP—8
`
`Thomas J. Bruno
`
`Marcia Huber
`
`Arno Laesecke
`
`Eric Lemmon
`
`Mark McLinden
`
`Stephanie L- Outcalt
`Richard Perkins
`
`Beverly L. Smith
`Jason A. Widegren
`
`Physical and Chemical Properties Division
`National Institute of Standards and Technology
`
`325 Broadway
`Boulder, CO 80305-3337
`
`July 2010
`
`
`
`US. DEPARTMENT OF COMNIERCE
`
`ijv Locke, Secretary
`
`NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY
`
`Patrick D. Gallagher; Director
`
`UTC—2014.003
`
`

`

`
`
`UTC-2014.004
`
`UTC-2014.004
`
`

`

`Table of Contents
`
`Accomplishments and New Findings……………………………………………………… ... 1
`Chemical Analyses of JP-8 and Jet-A samples …………………………………………… .... 1
`Thermal Decomposition………………………………………………………………….. ...... 6
`Thermal Decomposition of Jet-A-4658………………………………………………. ........... 6
`Thermal Decomposition of Propylcyclohexane ………………………………… ................. 13
`Thermophysical Property Measurements on Methylcyclohexane ..............................................
`and Propylcyclohexane……………………………………………………… ....................... 17
`Compressed Liquid Density Measurements for Methyl-
`and Propylcyclohexane……………………………………………………… ....................... 17
`Viscosity Measurements of Methyl- and Propylcyclohexane……………………….. ........... 24
`Sound Speed Measurements of Methyl- and Propylcyclohexane……………………. .......... 28
`Thermal Conductivity of Methyl- and Propylcyclohexane …………………………... ........ 31
`Thermophysical Property Measurements on Jet-A, JP-8 and S-8……………………….. .... 34
`Distillation Curves of Jet-A, JP-8 and S-8………………………………………… .............. 34
`Density Measurements of Compressed Liquid Jet-A, JP-8 and S-8………………….. ......... 59
`Viscosity Measurements of Jet-A Fuels at Ambient Pressure…………………… ................. 71
`Thermal Conductivity Measurements of the Compressed
` Liquid Aviation Fuels ………………………………………………………… .................... 80
`Heat Capacities of Jet Fuels S-8 and JP-8……………………………………. ..................... 83
`Development of the Thermodynamic and Transport Model……………………….. ............. 86
`References…………………………………………………………………………. .............. 98
`Appendix 1: Thermal Conductivity Measurements for Aviation Fuels …………. .............. 102
`
`UTC-2014.005
`
`

`

`
`
`UTC-2014.006
`
`UTC-2014.006
`
`

`

`Accomplishments and New Findings:
`
`This report will not necessarily be presented in the order in which work was performed,
`but rather we will progress from the general topics to the more specific topics. Thus, the
`chemical analysis and the thermal decomposition measurements that were made, which
`necessarily affect all conclusions that can be drawn from all subsequent measurements,
`will be presented first. Then, we will present the property measurement work on the pure
`fluids that were needed to support model development. Subsequent to this section, we
`present the measurements on the actual aviation fuels, and then finally the
`thermodynamic and transport modeling results.
`
`Chemical Analyses of JP-8 and Jet-A samples:
`
` A
`
` A
`
` total of five individual samples of representative aviation fuels (one JP-8, three Jet-A,
`one Fischer Tropsch synthetic fuel, S-8) were obtained from the Air Force Research
`Laboratory for this work. The sample of JP-8 was POSF-3773, directly from the Wright
`Patterson Air Force Base flight line. The three samples of Jet-A were POSF -3602, -3638
`and -4658, the latter being a composite mixture prepared by AFRL. The synthetic
`Fischer Tropsch fuel was POSF-4734.
`
` chemical analysis was done on each of the fluid samples by gas chromatography mass
`spectrometry (30 m capillary column of 5% phenyl polydimethyl siloxane having a
`thickness of 1 µm, temperature program from 90 to 250 °C, 10 °C per minute). Mass
`spectra were collected for each peak from 15 to 550 RMM (relative molecular mass)
`units1, 2. Chromatographic peaks made up of individual mass spectra were examined for
`peak purity, then the mass spectra were used for qualitative identification. Components
`in excess of 0.5 mole percent were selected for identification and tabulated for each fluid.
`In addition to this detailed analysis, the hydrocarbon type classification based on ASTM
`D-2789 was performed. These results figure in the overall mixture characterization, and
`are also used for comparisons with the chemical analyses of individual distillate fractions
`(discussed in the section on distillation curves). In addition, this approach to
`characterizing the mixtures allows the development of fluid mixture files for equation of
`state development, which will be described later.
`
`The chemical analysis typically allows the identification of between 40 and 60 percent
`(by mass) of the fluid components. There are usually numerous minor components that
`cannot be identified because of their low concentrations, and other cases in which
`chromatographic peak overlap prevents reliable identification of even the more abundant
`components. An example of the summary of a chemical analysis for Jet-A (the results for
`Jet-A-4658) is provided in Table 1. Since this fluid represents a composite of samples of
`Jet-A, additional information is provided for this fluid. In this table, peaks are labeled by
`numbers or letters. Lettered peaks are relatively minor but are included for a specific
`reason, such as to provide a budget for the highly volatile components. The peak profile
`describes how the peak was handled for mass spectral determination. This is typically a
`single (S) point, an average (A) or both. The correlation coefficient is a numerical figure
`of merit describing the match of the analyte peak with a library entry. It is important to
`
`UTC-2014.007
`
`

`

`understand that this number is not necessarily the best measure of the “goodness of fit”.
`The confidence indicator, ranging from high (H), moderate (M) to uncertain (U) is a more
`reliable indicator, since it is based on more factors, including chromatographic behavior.
`The area percentages provided are uncalibrated, raw area counts on the total ion
`chromatogram.
`
`For comparison, the summary analyses for S-8-4734 is provided in Table 2, and for JP-8-
`3773 is provided in Table 3. For these fluids we provide a synopsis only, without the
`chromatographic details. We note that occasionally, it is not possible to determine the
`isomerization of a branched hydrocarbon on the basis of the mass spectrum of the
`chromatographic peak. In these cases, we have used the variable “x” to note the
`uncertainty. For example, x-methyl dodecane simply indicates uncertainty in the position
`of the methyl group on the hydrocarbon backbone.
`
`Table 1: A chemical analysis for Jet-A-4658 performed with gas chromatography – mass
`spectrometry, used for fuel characterization, and for the development of mixture equations of state.
`
`Peak
`Profile
`
`Correlation
`Coefficient
`
`Confidence
`
`Name
`
`CAS No.
`
`S
`S
`S
`S
`S
`
`S
`S
`
`S
`S
`S
`S
`S & A
`S & A
`S
`
`S
`A
`
`S
`
`A
`
`72.9
`76.9
`71.6
`29.2
`41.9
`
`44.0
`31.1
`
`12.4
`37.6
`33.9
`NA
`NA
`7.97
`35.8
`
`10.7
`5.27
`
`27.8
`
`13.7
`
`n-heptane
`methyl cyclohexane
`2-methyl heptane
`Toluene
`cis-1,3-dimethyl
`cyclohexane
`n-octane
`1,2,4-trimethyl
`cyclohexane
`4-methyl octane
`1,2-dimethyl benzene
`n-nonane
`?
`x-methyl nonane
`4-methyl nonane
`1-ethyl-3-methyl
`benzene
`2,6-dimethyl octane
`1-methyl-3-(2-
`methylpropyl)
`cyclopentane
`1-ethyl-4-methyl
`benzene
`1-methyl-2-propyl
`cyclohexane
`
`142-82-5
`108-87-2
`592-27-8
`108-88-3
`638-04-0
`
`111-65-9
`2234-75-5
`
`2216-34-4
`95-47-6
`111-84-2
`
`NA
`17301-94-9
`620-14-4
`
`2051-30-1
`29053-04-1
`
`622-96-8
`
`4291-79-6
`
`H
`H
`H
`H
`H
`
`H
`H
`
`H
`H
`H
`U
`H
`M1
`H
`
`H
`U2
`
`M2
`
`M2
`
`2
`
` Area
`Percentage
`
`0.125
`0.198
`0.202
`0.320
`0.161
`
`0.386
`0.189
`
`0.318
`0.575
`1.030
`0.321
`0.597
`0.754
`1.296
`
`0.749
`0.285
`
`0.359
`
`0.370
`
`2.351
`2.945
`
`3.036
`3.169
`3.527
`3.921
`4.066
`4.576
`4.655
`
`4.764
`4.836
`
`5.012
`
`5.049
`
`
`
`
`
`Retention
`Time,
`min
`1.726
`1.878
`2.084
`2.144
`2.223
`
`Peak
`No.
`
`a
`b
`c
`1
`d
`
`2
`e
`
`3
`4
`5
`6
`7
`8
`9
`
`10
`11
`
`12
`
`13
`
`UTC-2014.008
`
`

`

`5.291
`5.325
`5.637
`
`5.825
`5.910
`6.073
`6.176
`6.364
`
`S
`S
`S
`
`S
`S
`S & A
`S
`S & A
`
`6.516
`
`S & A
`
`26.3
`37.7
`36
`
`36
`26.9
`NA
`5.01
`25.7
`
`35.6
`
`NA
`20.4
`22.9
`23.2
`NA
`NA
`17.9
`
`22.0
`NA
`22.3
`
`19.6
`19.0
`10.8
`24.1`
`
`3.5
`14.5
`
`NA
`NA
`29.8
`24.7
`
`H
`H
`H
`
`H
`H
`M
`M2
`M2
`
`H
`
`U2
`M3
`H
`H
`U
`U
`M
`
`H
`M
`M
`
`H
`H
`H
`M
`
`M
`M
`
`M
`M
`H
`H
`
`1,2,4-trimethyl benzene
`n-decane
`1-methyl-2-propyl
`benzene
`4-methyl decane
`1,3,5-trimethyl benzene
`x-methyl decane
`2,3-dimethyl decane
`1-ethyl-2,2,6-trimethyl
`cyclohexane
`1-methyl-3-propyl
`benzene
`aromatic
`5-methyl decane
`2-methyl decane
`3-methyl decane
`Aromatic
`Aromatic
`1-methyl-(4-
`methylethyl) benzene
`n-undecane
`x-methyl undecane
`1-ethyl-2,3-dimethyl
`benzene
`n-dodecane
`2,6-dimethyl undecane
`n-tridecane
`1,2,3,4-tetrahydro-2,7-
`dimethyl naphthalene
`2,3-dimethyl dodecane
`2,6,10-trimethyl
`dodecane
`x-methyl tridecane
`x-methyl tridecane
`n-tetradecane
`n-pentadecane
`
`95-63-6
`124-18-5
`1074-17-5
`
`2847-72-5
`108-67-8
`NA
`17312-44-6
`71186-27-1
`
`1074-43-7
`
`NA
`13151-35-4
`6975-98-0
`13151-34-3
`NA
`NA
`99-87-6
`
`1120-21-4
`NA
`933-98-2
`
`112-40-3
`17301-23-4
`629-50-5
`13065-07-1
`
`6117-98-2
`3891-98-3
`
`NA
`NA
`629-59-4
`629-62-9
`
`1.115
`1.67
`0.367
`
`0.657
`0.949
`0.613
`0.681
`0.364
`
`0.569
`
`0.625
`0.795
`0.686
`0.969
`0.540
`0.599
`0.650
`
`2.560
`1.086
`1.694
`
`3.336
`1.257
`3.998
`0.850
`
`0.657
`0.821
`
`0.919
`0.756
`1.905
`1.345
`
`S & A
`S
`S
`A
`S
`S
`S
`
`A
`A
`A
`
`A
`S
`S & A
`S
`
`S
`S
`
`S
`S
`S
`S
`
`6.662
`6.589
`6.728
`6.862
`7.110
`7.159
`7.310
`
`7.626
`7.971
`8.875
`
`9.948
`10.324
`12.377
`12.901
`
`13.707
`14.138
`
`13.834
`13.998
`14.663
`16.86
`
` 1
`
` trailing impurity
`2 highly impure composite peak
`3 there is evidence of an aromatic impurity in this peak
`
`The meaning of the confidence and profile indicators (H, M,U, S, A) are discussed in the
`text.
`
`
`
`3
`
`14
`15
`16
`
`17
`18
`19
`20
`21
`
`22
`
`f
`23
`24
`25
`26
`27
`28
`
`29
`29
`30
`
`31
`32
`33
`33a
`
`33b
`33c
`
`33d
`33e
`34
`35
`
`UTC-2014.009
`
`

`

`Table 2: A listing of the major components found in the sample of S-8-4734. The area
`percentages provided are from raw uncorrected areas resulting from the integration of the
`GC-MS total ion chromatogram. When ambiguity exists regarding isomerization, the
`substituent position is indicated as a general variable, x.
`
`
`Name
`
`CAS No.
`
`592-27-8
`
`589-81-1
`
` 0.437
`
`15890-40-1
`
` 0.965
`
`2216-30-0
`
` 1.131
`
`2216-34-4
`
`2216-33-3
`
`111-84-2
`
`15869-96-9
`
`2051-30-1
`
`15869-86-0
`
`17301-94-9
`
`871-83-0
`
`5911-04-6
`
`124-18-5
`
`17302-27-1
`
`62016-18-6
`
`13151-35-4
`
`2847-72-5
`
`6975-98-0
`
`2.506
`
`1.323
`
`1.623
`
`1.035
`
`0.756
`
`1.032
`
`1.904
`
`1.019
`
`1.385
`
`2.050
`
`1.175
`
`1.015
`
`1.315
`
`1.134
`
`1.529
`
`2-methyl
`heptane
`3-methyl
`heptane
`1,2,3-
`trimethyl
`cyclopentane
`2,5-dimethyl
`heptane
`4-methyl
`octane
`3-methyl
`octane
`n-nonane
`
`3,5-dimethyl
`octane
`2,6-dimethyl
`octane
`4-ethyl
`octane
`4-methyl
`nonane
`2-methyl
`nonane
`3-methyl
`nonane
`n-decane
`
`2-5-dimethyl
`nonane
`5-ethyl-2-
`methyl
`octane
`5-methyl
`decane
`4-methyl
`decane
`2-methyl
`
`
`
` Area
` Percentage
` 0.323
`
`Name
`
`CAS No.
`
`n-undecane
`
`1120-21-4
`
`x-methyl
`undecane
`3-methyl
`undecane
`
`5-methyl
`undecane
`4-methyl
`undecane
`2-methyl
`undecane
`2,3-dimethyl
`undecane
`n-dodecane
`
`4-methyl
`dodecane
`x-methyl
`dodecane
`2-methyl
`dodecane
`x-methyl
`dodecane
`n-tridecane
`
`4-methyl
`tridecane
`6-propyl
`tridecane
`x-methyl
`tridecane
`
`NA
`
`1002-43-3
`
`1632-70-8
`
`2980-69-0
`
`7045-71-8
`
`17312-77-5
`
`112-40-3
`
`6117-97-1
`
`NA
`
`1560-97-0
`
`NA
`
`629-50-5
`
`26730-12-1
`
`55045-10-8
`
`NA
`
`n-
`tetradecane
`x-methyl
`tetradecane
`5-methyl
`
`629-59-4
`
`NA
`
`25117-32-2
`
`4
`
` Area
` Percentage
`2.420
`
`1.590
`
`1.15
`
`1.696
`
`1.045
`
`1.072
`
`1.213
`
`2.595
`
`0.929
`
`0.744
`
`1.293
`
`1.281
`
`1.739
`
`0.836
`
`1.052
`
`1.066
`
`1.562
`
`1.198
`
`0.720
`
`UTC-2014.010
`
`

`

`decane
`3-methyl
`decane
`
`
`13151-34-3
`
`1.583
`
`
`
`
`
`tetradecane
`n-
`pentadecane
`x-methyl
`tetradecane
`
`629-62-9
`
`NA
`
`1.032
`
`0.727
`
`
`
`Table 3: A listing of the major components found in the sample of JP-8-3773. The area
`percentages provided are from raw uncorrected areas resulting from the integration of the
`GC-MS total ion chromatogram. When ambiguity exists regarding isomerization, the
`substituent position is indicated as a general variable, x.
`
`
`Compound
`n-heptane
`
`CAS No.
`142-82-5
`
`Area %
` 0.125
`
`methyl
`cyclohexane
`
`2-
`methylheptane
`
`108-87-2
`
`0.198
`
`592-27-8
`
`0.202
`
`0.320
`
`0.161
`
`0.386
`
`0.189
`
`0.318
`
`0.575
`
`1.030
`
`0.597
`
`0.754
`
`1.296
`
`toluene
`
`108-88-3
`
`638-04-0
`
`111-65-9
`
`2234-75-5
`
`2216-34-4
`
`95-47-6
`
`111-84-2
`
`NA
`
`17301-94-9
`
`620-14-4
`
`cis-1,3-
`dimethyl
`cyclohexane
`n-octane
`
`1,2,4-
`trimethyl
`cyclohexane
`4-methyl
`octane
`1,2-dimethyl
`benzene
`n-nonane
`
`x-
`methylnonane
`4-
`methylnonane
`1-ethyl-3-
`methyl
`benzene
`
`
`
`CAS No.
`17312-44-6
`
`Area %
`0.681
`
`71186-27-1
`
`0.364
`
`1074-43-7
`
`0.569
`
`NA
`
`13151-35-4
`
`6975-98-0
`
`13151-34-3
`
`NA
`
`NA
`
`99-87-6
`
`1120-21-4
`
`NA
`
`933-98-2
`
`0.625
`
`0.795
`
`0.686
`
`0.969
`
`0.540
`
`0.599
`
`0.650
`
`2.560
`
`1.086
`
`1.694
`
`Compound
`2,3-dimethyl
`decane
`1-ethyl-2,2,6-
`trimethyl
`cyclohexane
`1-methyl-3-
`propyl
`benzene
`aromatic
`unknown
`5-
`methyldecane
`
`2-
`methyldecane
`3-
`methyldecane
`
`aromatic
`unknown
`aromatic
`unknown
`1-methyl-(4-
`methylethyl)
`benzene
`n-undecane
`
`x-methyl
`undecane
`1-ethyl-2,3-
`dimethyl
`benzene
`
`5
`
`UTC-2014.011
`
`

`

`2051-30-1
`
`29053-04-1
`
`0.749
`
`0.285
`
`n-dodecane
`
`112-40-3
`
`2,6-dimethyl
`undecane
`
`17301-23-4
`
`3.336
`
`1.257
`
`622-96-8
`
`0.359
`
`n-tridecane
`
`629-50-5
`
`3.998
`
`4291-79-6
`
`0.370
`
`95-63-6
`
`1.115
`
`124-18-5
`
`1.67
`
`1074-17-5
`
`0.367
`
`1,2,3,4-
`tetrahydro-
`2,7-dimethyl
`naphthalene
`2,3-dimethyl
`dodecane
`
`2,6,10-
`trimethyl
`dodecane
`x-methyl
`tridecane
`
`2847-72-5
`
`108-67-8
`
`0.657
`
`0.949
`
`x-methyl
`tridecane
`n-tetradecane
`
`13065-07-1
`
`0.850
`
`6117-98-2
`
`0.657
`
`3891-98-3
`
`0.821
`
`NA
`
`NA
`
`629-59-4
`
`0.919
`
`0.756
`
`1.905
`
`NA
`
`0.613
`
`n-
`pentadecane
`
`629-62-9
`
`1.345
`
`Thermal Decomposition:
`
`Thermal Decomposition of Jet-A-4658:
`
`The thermal decomposition of the aviation fuels has been assessed with an ampoule
`testing instrument and approach that has been developed at NIST3, 4. We note that this
`work is meant strictly to support the physical property measurement work, and not to
`delineate reaction mechanisms. The instrument, shown schematically in Figure 1,
`consists of a 304L stainless steel thermal block that is heated to the desired experimental
`temperature (here, between 250 and 450 °C, although our rate constants were measured
`between 375 and 450 °C). The block is supported in an insulated box with carbon rods;
`the temperature is maintained and controlled (by a PID controller) to within 0.1 °C in
`response to a platinum resistance sensor embedded in the thermal block. The ampoule
`cells consist of 6.4 cm lengths of ultrahigh pressure 316L stainless steel tubing (0.64 cm
`
`
`
`6
`
`2,6-dimethyl
`octane
`1-methyl-3-
`(2-
`methylpropyl)
`cyclopentane
`1-ethyl-4-
`methyl
`benzene
`1-methyl-2-
`propyl
`cyclohexane
`
`1,2,4-
`trimethyl
`benzene
`n-decane
`
`1-methyl-2-
`propyl
`benzene
`4-methyl
`decane
`1,3,5-
`trimethyl
`benzene
`x-methyl
`decane
`
`
`
`UTC-2014.012
`
`

`

`external diameter, 0.18 cm internal diameter) that are sealed on one end with a TIG
`welded stainless steel plug. Each cell is connected to a high-pressure high-temperature
`
`insulation
`
`slots for reactors
`
`stainless steel block
`(one of two)
`
`temperature probe
`
`heaters
`
`graphite supports
`
`ampoule reactor
`
`thermostat
`
`
`
`high-
`pressure —>
`valve
`
`high-
`presslrl'e —’
`ce
`
`PID temperature
`controller
`
`
`
`L‘‘
`
`Figure 1: A schematic diagram showing the ampoule thermal decomposition apparatus
`that was developed at NIST to assess the thermal stability of the aviation fuels studied in
`this work.
`
`valve at the other end with a short length of 0.16 cm diameter 316 stainless steel tubing
`with an internal diameter of 0.02 cm, also TIG welded to the cell. Each cell and valve is
`capable of withstanding a pressure in excess of 105 MPa at the desired temperature. The
`internal volume of each cell is known and remains constant at a given temperature. Fluid
`is added to the individual cell by mass (as determined by an approximate equation of
`state calculation) to give a total pressure of 34 MPa at the final fluid temperature.
`Measurements
`are done by measuring the
`integrated area of an emergent
`chromatographic peak suite that results from the decomposition. This is illustrated in
`Figure 2,
`in which a representative chromatogram of Jet-A is shown along with
`magnified insets of the emergent peak zone.
`In the “as received” sample, there are no
`peaks in the emergent zone, while after thermal stress, the suite develops and is seen to
`grow into the chromatogram as a function of increasing exposure time and temperature.
`
`During the course of this work, we performed kinetic studies on two samples that are
`relevant to the development of the surrogate model for JP-8. First, we measured Jet-A—
`4658, which is the composite Jet-A samples. Next, in order to facilitate the modeling
`process, we found it necessary to measure propylcyclohexaneé. This became important
`because of the need to represent this class of cycloalkane. Before doing any property
`measurements, we needed to assess the thermal stability.
`
`7
`
`UTC—2014.013
`
`

`

`
`Figure 2: Representative chromatograms showing the usual kerosene component
`distribution, with the insets showing the very early eluting region. Upon thermal stress,
`one notes the development of emergent decomposition peaks.
`
`
`
`
`
`The simplest type of decomposition is a first-order reaction in which a reactant (A)
`thermally decomposes into a product (B), equation 1. The rate law for such a reaction
`can be written in terms of the reactant or the product, equation 2, where [A] is the
`concentration of A, [B] is the concentration of B, k is the reaction rate constant, and t is
`the time. Equation 3 shows the integrated expression in terms of the reactant, where [A]t
`is the concentration of reactant at time t and [A]0 is the initial reactant concentration:
`
`
`Specifically, for a first-order reaction, a plot of ln[A] as a function of t should result in a
`straight line. Additionally, an Arrhenius plot should also yield a straight line.
`
`
`
`8
`
`A  B,
`
`
`
`
`
`
`
`
`
`
`
`−d[A]/dt = d[B]/dt = kt,
`
`
`
`
`
`
`
`
`
`ln[A]t = ln[A]0 − kt.
`
`
`
`
`
`
`
`
`
`(1)
`
` (2)
`
` (3)
`
`
`UTC-2014.014
`
`

`

`The half-life, t0.5, of a decomposition reaction is the time required for half of the reactants
`to become products. For a first-order reaction such as the one shown in equation 1, the
`half-life can be calculated directly from the rate constant, equation 4. A related quantity is
`the time it takes for 1% of the reactants to become products, t0.01. For first-order
`reactions, t0.01 also can be calculated directly from the rate constant, equation 5. The t0.5
`and t0.01 of thermal decomposition are useful because they give a direct measure of the
`time period over which the concentration of thermal decomposition products will reach
`an unacceptable level. Hence, they are useful when deciding what conditions and
`protocols are to be used for property measurements. These quantities are given by:
`
`
`t0.5 = 0.6931/k,
`
`
`
`
`
`
`
`
`
`t0.01 = 0.01005/k.
`
`
`
`
`
`
`
`
`
`(4)
`
` (5)
`
`
`In addition to calculating values for t0.5 and t0.01, rate constants determined over a
`temperature range can be used to evaluate the parameters of the Arrhenius equation,
`equation 6, where A is the pre-exponential factor, Ea is the activation energy, R is the gas
`constant, and T is the temperature. The Arrhenius parameters can then be used to predict
`rate constants at temperatures other than those examined experimentally:
`
`
`k = A exp(−Ea/RT).
`
`
`
`
`
`
`
`
`
`(6)
`
`
`
`Samples of Jet-A-4658 were decomposed in the stainless steel ampoule reactors at 375,
`400, 425 and 450 °C. This temperature range was chosen because it allowed for reaction
`times of a convenient length. At 375 °C the reaction is relatively slow, so reaction times
`ranged from 4 to 24 h. At 450 °C the reaction is much faster, so reaction times ranged
`from 10 to 120 min. The unreacted Jet A was clear and nearly colorless. Mild thermal
`stress (i.e., the shortest reaction times at the lower temperatures) caused the liquid to
`become pale yellow. Severe thermal stress (i.e., the longest reaction times at the higher
`temperatures) caused the liquid to become very dark brown, opaque, and viscous. A small
`amount of dark particulate was regularly seen in the more thermally stressed samples.
`Additionally, low-molecular-weight decomposition products caused a pressurized vapor
`phase to develop inside the reactors. For the more severely stressed samples, it was
`common for the entire liquid sample to be expelled under pressure when the reactor valve
`was opened.
`
` A
`
` separate analysis of this vapor phase was desired, and to accomplish this a gas-liquid
`separator designed at NIST for such work was employed7. This device is shown in
`Figure 3. The gas phase was then analyzed using a gas chromatograph with MS
`detection. Over 30 compounds were identified in the gas phase, with light alkanes being
`the most abundant. Table 4 shows the 10 most abundant compounds, based on total ion
`current in the MS detector. Note that the MS method employed precludes observation of
`methane. The apparent lack of alkene decomposition products is somewhat surprising,
`although it is known that high pressures and long reaction times decrease the yield of
`alkenes from the decomposition of alkanes. The rate of decomposition from alkanes
`
`
`
`9
`
`UTC-2014.015
`
`

`

`
`
`
`Figure 3: A schematic diagram of the gas-liquid separator that was used to examine the
`vapor phase of the thermally stressed Jet-A-4658. More details regarding this device can
`be found in ref 5.
`
`Table 4: A listing of the most abundant compounds found in the vapor phase of
`thermally stressed Jet-A-4658, maintained for 2 hrs. at 450 °C.
`
`
`
`Compound
`butane
`
`pentane
`
`propane
`
`2-methylpropane
`
`2-methylbutane
`
`ethane
`
`hexane
`
`2-methylpentane
`
`methylcyclopentane
`
`3-methylpentane
`
`% of Total Ion Current
`13.0
`
`10.6
`
`10.4
`
`8.6
`
`8.1
`
`6.6
`
`6.4
`
`5.9
`
`3.3
`
`3.2
`
`
`
`are also known to depend on the material used to construct the reactor.
`
`
`
`
`10
`
`UTC-2014.016
`
`

`

`The thermally stressed liquid phase of each sample was analyzed by a gas chromatograph
`equipped with a flame ionization detector. An easily identifiable suite of decomposition
`products had retention times between 2.3 and 2.8 min, Figure 4. The kinetic analysis was
`done based on this suite of peaks. We did not identify all of the individual compounds
`responsible for these peaks, but it is worth noting that pentane and hexane had retention
`times of 2.4 min and 2.5 min under these conditions, which suggests that most of these
`decomposition products had 5-7 carbon atoms. The observed product suite was
`essentially the same at all temperatures, with retention times that were constant to within
`0.01 min. Undoubtedly, there were peaks for decomposition products in the broad
`kerosene “hump” that began around 2.9 min, but use of them for the kinetic analysis was
`impractical because of peak overlap and the lack of baseline resolution. Additionally, we
`did not routinely monitor compounds that were not retained in the liquid phase, including
`vapor-phase products and potential coke deposits.
`
`As mentioned above, the kinetic analysis was done using the emergent suite of
`decomposition products in the liquid phase with retention times between 2.3 and 2.8 min.
`The rate constant, k, at each temperature was determined from data collected at four
`different reaction times, with 3 to 6 replicate decomposition reactions run at each reaction
`time. The value of k was obtained from a nonlinear least-squares fit of these data to
`equation 3. For example, Figure 4 is a plot of the data and curve-fit for 425 °C. Note that
`data were collected at seven time points, but only the first four data points in Figure 4
`were used to determine k. The reason for excluding the later time points was to limit the
`influence of any secondary decomposition reactions on the kinetics. Even though it is
`unlikely that measurements would intentionally be carried out with instrumental
`residence times in excess of the first four time points, this area of the plot is still useful in
`that it represents the chemical decomposition regime that is possible if an instrument or
`engine enters an upset condition resulting in long residence times. Values for t0.5 and t0.01
`are calculated from k by use of equations 4 and 5. The decomposition rate constants at all
`four temperatures, along with values of t0.5 and t0.01, are presented in Table 5. The
`standard uncertainties given were calculated from the standard deviation of replicate
`measurements and from the standard error in the nonlinear fit. The values of t0.01 show
`that physical property measurements at ≥400 °C would require apparatus residence times
`on the order of 5 min or less. On the other hand, at 375 °C a residence time of about half
`an hour may be acceptable. First order rate constants reported for the decomposition of n-
`tetradecane are k = 1.78  10−5 s−1 at 400 °C, k = 1.01  10−4 s−1 at 425 °C, and k = 4.64 
`10−4 s−1 at 450 °C. Within our experimental uncertainty, these are the same as the values
`in Table 5 for Jet A.
`
`An Arrhenius plot of the rate constants is shown in Figure 5. The Arrhenius parameters
`determined from a linear regression of the data are A = 4.1  1012 s−1 and Ea = 220
`kJ·mol−1. The standard uncertainty in Ea, calculated from the standard error in the slope
`of the regression, is 10 kJ·mol−1. The linearity of the Arrhenius plot (r2 > 0.9978) over
`the 75 °C temperature range is an important validation that the assumption of first-order
`kinetics is reasonable. Note that the activation energy for the decomposition of Jet A is
`slightly lower than the values reported for pure C10–C14 n-alkanes; for example, for n-
`dodecane Ea is 260 kJ·mol−1 (with a reported uncertainty of 8 kJ·mol−1).
`
`
`
`11
`
`UTC-2014.017
`
`

`

`100
`
`300
`200
`Reaction Time / min
`
`400
`
`500
`
`200
`
`150
`
`100
`
`50
`
`Product Suite Area
`
`0
`
`0
`
`
`Figure 4: Plot of the corrected area counts of the decomposition product suite as a
`function of time at 425 °C. Only the data at short reaction times (solid symbols) were
`used to determine the rate constant. The error bars represent the standard deviation for
`replicate decomposition reactions at each time point.
`
`
`
`Table 5: Kinetic data for the thermal decomposition of Jet-A-4658.
`
`
`T / °C
`375
`
`400
`
`425
`
`450
`
`
`
`
`
`k / s−1
`5.9  10−6
`3.3  10−5
`1.2  10−4
`4.4  10−4
`
`Uncertainty in k / s−1
`3.9  10−6
`1.8  10−5
`0.6  10−4
`2.3  10−4
`
`t0.5 / h
`33
`
`t0.01 / min
`28
`
`5.8
`
`1.7
`
`0.44
`
`5.0
`
`1.4
`
`0.38
`
`12
`
`UTC-2014.018
`
`

`

`-7
`
`-9
`
`-11
`
`ln k
`
`-13
`1.35
`
`1.40
`
`1.45
`1000/T
`
`1.50
`
`1.55
`
`
`
`
`Figure 5: Arrhenius plot for the decomposition of Jet-A-4658. The Arrhenius parameters
`determined from the fit to the data are A = 4.1  1012 s−1 and Ea = 220 kJ·mol−1.
`
`Thermal Decomposition of Propylcyclohexane:
`
`
`As mentioned above, we also found it necessary to incorporate some pure component
`property measurements into the model development. Two fluids were chosen to
`represent cyclic branched alkanes: methylcyclohexane and propylcyclohexane. Because
`adequate thermal stability data could be found for methyl cyclohexane, no additional
`measurements were done on this fluid. Propylcyclohexane required measurements,
`however, since no thermal decomposition data could be found.
`
`The ampoule reactors were filled with propylcyclohexane by use of a procedure designed
`to achieve an initial pressure of 34.5 MPa (5000 psi) for all of the decomposition
`reactions. This is important because it mimics the high-pressure conditions during some
`physical property measurements, and it helps ensure that differences in observed
`decomposition rates are not due to differences in pressure. It also allows comparability
`with the jet-A-4658 measurements described above. After filling, air in the void space of
`the reactor was removed by one freeze-pump-thaw cycle. The loaded reactors were then
`inserted into the thermostatted stainless steel block and maintained at the reaction
`temperature for a period of time ranging from 10 min to 32 h. After decomposition, the
`reactors were removed from the thermostatted block and immediately cooled in room-
`temperature water. The thermally stressed propylcyclohexane was recovered and
`analyzed as described below. After each run, the cells and valves were carefully cleaned
`and dried. Blank experiments, in which the cell was loaded as described above but not
`heated, confirmed the effectiveness of the cleaning protocol.
`
`
`
`
`13
`
`UTC-2014.019
`
`

`

`The products of a 40 min decomposition reaction at 450 °C were identified by GC-MS.
`To accomplish this, a short length of glass capillary tubing was connected to the outlet on
`the reactor valve. The valve on the reactor was opened just enough to allow the
`pressurized mixture of gas and liquid in the reactor to escape slowly. Then the end of the
`capillary was briefly pushed through the inlet septum of the split/splitless injection port
`of the GC-MS, directly introducing the decomposed sample by flowing capillary
`injection. The components of the sample were then separated on a 30 m capillary column
`coated with a 0.25 m film of (5%-phenyl)-methylpolysiloxane. The temperature
`program for the separation started with an initial isothermal separation at 35 °C for 6 min,
`followed by a 20 °C/min ramp to 175 °C. The most abundant decomposition products
`identified in this manner are listed in Table 6.
`
`Table 6. Summary of the most abundant decomposition products after 40 min at 450 °C.
`
`
`
`
`
`
`Compound
`
`ethane + propane (not resolved)
`pentane
`methylcyclopentane
`cyclohexane
`cyclohexene
`methylcyclohexane
`methylenecyclohexane
`1-methylcyclohexene
`ethylcyclohexane
`1-methyl-2-propylcyclopentane
`propylcyclohexene (all isomers)
`butylcyclohexane
`1,3-diisopropylcyclohexane
`
`% of Total Ion
`Abundance
`2.3
`0.7
`1.1
`5.5
`3.8
`2.1
`3.4
`4.7
`0.7
`6.9
`2.1
`1.1
`2.8
`
`In order to determine the kinetics of decomposition, the thermally stressed liquid phase of
`every decomposition reaction was analyzed by a gas chromatograph equipped with a
`flame ionization detector (GC-FID). Evaporative losses were minimized by transferring
`the liquid phase into a chilled (7 °C) glass vial and immediately diluting it with a known
`amount of n-dodecane. The resulting n-dodecane solution was typically 5% reacted
`propylcyclohexane (mass/mass). The sample was then analyzed by GC-FID using a 30 m
`capillary column coated with a 0.1 m film of (5 %-phenyl)-methylpolysiloxane. The
`temperature program for the chromatographic separation consisted of an initial isothermal
`separation at 80 °C for 4 min, followed by a 30 °C/min gradient to 250 °C, with an
`additional minute at the final temperature. Figure 6 shows the suite of decomposition
`products that was seen in the chromatograms. The decomposition products were
`essentially the same at all temperatures, with retention times that were constant to within
`
`
`
`14
`
`UTC-2014.020
`
`

`

`0.01 min. Although we did not attempt to identify the individual peaks, the product suite
`observed by GC-FID is consistent with the product suite identified by GC-MS. These
`routine GC-FID analyses allowed us to track the extent of decomposition for each
`reaction. For example, about 20% of the propylcyclohexane had decomposed after 40
`min at 450 °C, but only about 4% of the propylcyclohexane had decomposed after 32 h at
`375 °C.
`
`
`
`unheated propylcyclohexane
`
`after 40 min at 450 °C
`
`
`
`Figure 6: Chromatograms obtained by gas chromatography for unheated
`propylcyclohexane and for decomposed propylcyclohexane. The decomposed sample had
`been maintained at 4