Assessment of the Composition and Distillation Properties of

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Assessment of the Composition and Distillation Properties of Thermally Stressed RP-1 and RP-2: Application to Fuel Regenerative Cooling Bret C. Windom and Thomas J. Bruno* Thermophysical Properties Division, National Institute of Standards and Technology, Boulder, Colorado

bS Supporting Information ABSTRACT: In this work, we measured the volatility of thermally stressed samples of RP-1 and RP-2 rocket propellant kerosenes by use of the advanced distillation curve method. This work is part of a large program at NIST and other laboratories geared toward improving the operability of the hydrocarbon component of liquid fuel packages. Measuring the properties of thermally stressed rocket propellant kerosene is a necessary component of this overall effort. This is motivated by the use of the kerosene as a coolant before combustion in the engine. Samples of RP-1 and RP-2 were stressed at 475 and 510 °C, at a pressure of 17 kPa (2500 psi), for residence times of 0.5 min. Volatility measurements revealed significant changes early in the distillation curves, becoming very pronounced at the higher temperature. The volatility measurements were supplemented with chemical analyses and a calculation of the enthalpy of combustion as a function of distillate volume fraction. We note that the increase in volatility is explained by the significant increase of very light (lower molecular mass) components produced during the thermal stress. We also note that the enthalpy of combustion follows the same pattern as the volatility, as we have noted in previous studies.

1. INTRODUCTION In many modern rocket engines, propulsion is achieved by the combustion of kerosene based hydrocarbon fuel and liquid oxygen. In a typical kerosene/liquid oxygen fueled rocket engine, the thrust chambers can exceed temperatures of 3000 K during operation, a temperature level that is much higher than the material limits.1 The thrust chambers are often cooled through a regenerative cooling process in which the fuel or oxidizer is passed through the chamber walls prior to combustion.2 When a kerosene fuel is used as a coolant, the extreme temperatures can have significant effects on the fuel composition. For example, the extreme temperatures experienced by the hydrocarbon fuel can result in coking and in the fouling of the cooling channels. In addition, the decomposition of the fuel can lead to changes in the fuel properties that can affect the fuel performance. To reduce these problems, as well as other corrosive characteristics of the fuel, kerosene based rocket propellants have been reformulated through the years. Despite these efforts, it is still necessary to consider the effect of high temperatures on the kerosene. A large-scale research effort geared toward characterizing the thermophysical properties of kerosene-based fuels (for rocket and aircraft applications) is in progress at the National Institute of Standards and Technology (NIST) as well as other facilities.3 26 The logical paradigm when measuring such thermophysical properties for finished fuels (especially properties that are to be used for model development) is to maintain the fluids in as close to the as-received or pristine condition as possible. In other words, during the course of a measurement, care must be taken to avoid decomposing or changing the fluid sample in any way. On the other hand, as we have discussed above, there are reasons for measuring the properties of fuel that This article not subject to U.S. Copyright. Published 2011 by the American Chemical Society

Figure 1. Schematic detailing the reactor used to produce the thermally stressed RP fluid samples.

has decomposed to a greater or lesser extent under the influence of high temperature.10 One of the most informative and important thermophysical properties that are measured for a complex fluid mixture is the distillation curve. The distillation curve is a graphical depiction of the boiling temperature of a fluid mixture plotted against the volume fraction distilled.27 29 The standard test method for the measurement of the distillation curve, ASTM D-86,30 provides the conventional approach. This method suffers from several drawbacks, however, including large uncertainties in temperature measurements and little theoretical significance.31 To overcome the shortcomings encountered in the ASTM D-86 test method, a new and improved method for distillation curve measurements has been developed.23,31 34 This new advanced distillation curve Received: July 22, 2011 Revised: September 26, 2011 Published: September 28, 2011 5200

dx.doi.org/10.1021/ef201077a | Energy Fuels 2011, 25, 5200–5214

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Figure 2. Chromatograms taken with the GC-MS of the unstressed and the thermally stressed (a) RP-1 and (b) RP-2 samples. The stressed fluids contain much higher concentrations of lighter more volatile hydrocarbons.

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Figure 3. Plot of the aliphatic hydrocarbon family types resulting from the ASTM D-2789 analysis performed on the unstressed and thermally stressed (a) RP-1 and (b) RP-2 samples.

(ADC) measurement provides temperature, pressure, and volume measurements of low uncertainty, allowing for the determination of true thermodynamic state points. This aspect has proven to be highly useful for equation of state development, which has led to surrogate formulations for many complex fuels.16,17,19 In addition, the ADC approach incorporates a composition explicit data channel for each distillate fraction,35 allowing one to sample small volumes (5 25 μL) of distillate during the distillation for additional chemical analyses. Using the appropriate analytical techniques, qualitative, quantitative, and trace compositional analyses can be performed, providing information on how the composition of the fluid varies with distillate fraction and boiling temperature. In addition, an assessment of the energy content and, where needed, corrosivity of the distillate fractions can be performed.36 41 The ADC method has been highly useful in the analysis of many liquid

fuels,23,24,31 33,42 53 including the characterization of RP-1 and RP-2,3,22,32,54 leading to surrogate formulations and equation of state models for these fluids.18,55 In the work reported herein, the ADC method was applied to samples of unstressed and thermally stressed RP-1 and RP-2 to more completely describe the decomposition and its effect on the changes in thermophysical properties that rocket propellants undergo during a regenerative cooling cycle. The thermally stressed samples were created using a reactor that allowed for strict control of the stressing conditions (temperature, pressure, and residence time) experienced by the rocket propellants. The effect of temperature on the decomposition was measured by applying two reaction temperatures, one above and one below 500 °C. Thermodynamically consistent distillation curves were measured for each thermally stressed sample and compared to the respective unstressed mixture. Using the compositional 5202


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Figure 4. Chromatograms following the analysis of the vapor phase collected from the thermally stressed sample of RP-2, generated at 510 °C: (a) obtained by GC-MS; (b and c) obtained on the packed column coupled with the thermal conductivity detector with helium/hydrogen and argon carrier gas.

explicit data channel, the distillate compositions were determined and used to calculate the distillate enthalpies of combustion.

2. EXPERIMENTAL SECTION 2.1. Thermally Stressed Samples. The RP-1 sample used in this work was supplied by the Air Force Research Laboratory, Propulsion Directorate at Wright Patterson Air Force Base. This sample, designated RP-1-4572, was the focus of extensive research in which thermophysical and transport property measurements were made pursuant to the development of a thermophysical property model in the framework of the Refprop computer program.18,55 This sample was pink in color because of the presence of a dye, azobenzene-4-azo-2-naphthol. The RP2 sample was supplied from Edwards Air Force Base, and similar to the

case of the RP-1 sample, it was used for extensive measurements and modeling and for the development of the Refprop-based model.55 This sample, designated as RP-2-EAFB, was clear and colorless, containing no dye. Before the RP-1 and RP-2 were thermally stressed, the starting fluids were analyzed by gas chromatography (GC) with mass spectrometry (MS) detection (30 m capillary column with a 1 μm coating of stationary phase, 5% phenyl dimethyl polysiloxane). Samples were injected with a syringe into a split/splitless injector set with a 50 to 1 split ratio. The injector operated at 300 °C with a constant head pressure of 55.2 kPa (8 psi). A temperature program beginning at 50 °C, followed by a temperature ramp of 3 °C/min to 90 °C, and then a temperature ramp of 10 °C/min to 225 °C was used in the analysis. These analyses were unremarkable, revealing the expected kerosene distribution of linear and branched aliphatic compounds, with very few aromatic or 5203


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Table 1. Comparison of the Initial Boiling Temperatures for Unstressed and Thermally Stressed RP-1 and RP-2 Samplesa sample (pressure)

vapor rise (° C)

unstressed RP-1 (83.4 kPa)

203.5

RP-1-TS-475 (83.9 kPa) RP-1-TS-510 (82.9 kPa)

Table 3. Representative Distillation Curve Data for Unstressed and Thermally Stressed RP-2 Samplesa distillate

95.9 48.7

vol.

RP-2 unstressed

fraction,

(83.2 kPa), Tk

(%)

(°C)

RP-2-TS-475

RP-2-TS-510

(83.4 kPa), Tk distillate vol. (83.8 kPa), Tk (°C)

fraction, (%)

0.025

204.8

162.1

RP-2-TS-475 (83.4 kPa)

92.9

5

205.8

196.5

16

122.9

RP-2-TS-510 (83.8 kPa)

44.4

unstressed RP-2 (83.2 kPa)

204.7

0.025

(°C) 70.5

10

207.2

200.8

21

148.0

These temperatures have been corrected to 1 atm (101.325 kPa) with the Sydney Young equation. The pressures at which the measurements were made are provided in the first column to permit recovery of the actual measured temperature. The uncertainties are discussed in the text.

15

208.4

203.5

26

163.6

20

209.7

205.9

31

175.7

25

211.2

208.3

36

185.8

30 35

212.7 214.2

210.3 212.4

41 46

192.8 198.7

Table 2. Representative Distillation Curve Data for Unstressed and Thermally Stressed RP-1 Samplesa

40

216.0

214.4

51

203.9

45

217.9

216.6

56

208.4

50

219.8

218.5

61

213.0

55

222.0

221.3

66

217.1

60

224.4

223.8

71

221.6

65

227.0

226.9

76

226.4

229.5 233.1

230.0 233.8

81 86

231.7 238.4

a

distillate RP-1-TS-475

RP-1-TS-510

vol.

RP-1 unstressed

fraction,

(83.4 kPa), Tk

(%)

(°C)

(°C)

fraction, (%)

(°C)

0.025

203.7

153.6

0.025

71.3

70 75

(83.9 kPa), Tk distillate vol. (82.9 kPa), Tk

5

205.0

197.6

16

135.1

80

237.3

238.7

91

248.1

10

206.4

200.7

21

154.0

85

242.0

244.4

96

261.9

15

207.8

203.5

26

167.7

90

247.7

252.0

-

20

209.2

205.7

31

177.2

25

210.6

207.7

36

186.0

30

212.3

209.5

41

192.2

35 40

213.9 215.6

211.1 213.1

46 51

198.3 203.5

45

217.4

215.0

56

208.7

50

219.3

217.0

61

213.1

55

221.3

219.2

66

217.7

60

223.5

221.8

71

222.5

65

226.1

224.4

76

227.5

70

229.4

227.2

81

234.1

75 80

232.1 235.9

231.2 235.2

86 91

242.9 253.5

85

240.7

241.1

96

269.6

90

246.9

250.4

-

-

a

These temperatures have been corrected to 1 atm with the Sydney Young equation. The pressures at which the measurements were made are provided to permit recovery of the actual measured temperatures. The uncertainties are discussed in the text.

alkene compounds. The results are important nonetheless in that they furnish the context for all subsequent examinations. Two solvents were used in this study. Acetone was used as a solvent during the analysis of the unstressed fluids. The acetone was obtained from a commercial supplier. Prior to use, the acetone was analyzed by gas chromatography (30 m capillary column of 5% phenyl dimethyl polysiloxane having a thickness of 1 μm, temperature program from 50 to 170 °C, 5 °C/min) using flame ionization detection (FID) and mass spectrometric detection. These analyses revealed the purity to be approximately 99.9%, and the acetone was used without further purification. Carbon disulfide was used during the GC-FID analysis of the stressed rocket propellants. Carbon disulfide has a very weak response from a FID (as a result of the lack of C H bonds), and therefore, it did

-

a

These temperatures have been corrected to 1 atm with the Sydney Young equation. The pressures at which the measurements were made are provided to permit recovery of the actual measured temperatures. The uncertainties are discussed in the text.

not mask any of the peaks representing the volatile components contained within the stressed rocket propellants during the GC-FID measurements. The carbon disulfide was a high pressure liquid chromatography (HPLC) grade from a commercial supplier, and following a similar analysis performed on the acetone, the carbon disulfide was shown to have a purity of approximately 99.9%. All necessary safety precautions were taken when handling these flammable liquids. Of special concern is the use of carbon disulfide as a solvent. This fluid is highly flammable and volatile, and it was only handled in small quantities in a fume hood. After each needle puncture of a septum vial containing this solvent, the septum cap was replaced. The reactor built to thermally stress the rocket propellants, which has been described in greater detail elsewhere,56 is schematically depicted in Figure 1. In brief, this device consists of a high pressure syringe pump capable of generating 55 MPa (8,000 psig), at constant flow rates that may be specified on the pump controller. The pressurized fluid is delivered into a high temperature reactor consisting of a 25 cm length of 1.6 mm (1/16 in.) 316 L stainless steel capillary tubing. The reactor is capable of generating a controlled temperature of up to 600 °C, with uncertainties of less than 1 °C at temperatures below 475 °C and uncertainties of approximately 5 °C at temperatures between 500 and 600 °C. Downstream from the reactor, the fluid is directed via a stainless steel capillary tube into a chilled water bath heat exchanger (set to approximately 5 °C) to quench the reaction and cool the thermally stressed fluid prior to entering the pressure control. From the heat exchanger, the fluid is directed into a back pressure regulator (made from polyether ether ketone, PEEK), which may be set to achieve a range of desired back pressures. Downstream from the back pressure regulator, the fluid passes into a collection vessel (polyethylene bottle). The combination of a syringe pump control 5204


Energy & Fuels and a back pressure regulator can provide a controlled, constant flow rate at any desired nominal pressure. In this way, the residence time can also be controlled. We realize that the wetted surface we have chosen in this work (316 L stainless steel) may not be the first choice for all applications. Indeed, copper alloys often form the rocket engine bells through which fuel is circulated as a coolant. As we discussed in detail elsewhere, we can vary the surface as needed, and this study should therefore be viewed as an initial application on a particular surface, to which we have no inherent limitation. Both rocket propellants (RP-1 and RP-2) were thermally stressed at two temperatures, 475 and 510 °C, both at a constant pressure of 17.2 MPa (2500 psi). Approximately 1 L of thermally stressed fluid was produced at each reactor temperature, which is enough fluid for a full range of thermophysical property measurements. For clarity, we will refer to these thermally stressed samples with the suffix “TS”, and the temperature of the thermal stress. Thus, for example, RP-1-TS-475 refers to the sample of RP-1 that has been thermally stressed at 475 °C. We caution the reader inter alia that this notation is not to be confused with the TS series of rocket propellants. The thermally stressed fluids were found to contain dissolved and entrained gaseous species. Indeed, as we have noted previously, a significant gaseous fraction was produced in the reactor and could actually be observed as fluid entered the collection vessel.56 More detail regarding the handling of this aspect will be provided later; however, we note that the collected liquid had a significant potential for off-gassing during storage. Because of this possibility, care was taken to prevent component loss from the recovered thermally stressed liquid. This was done by storing the samples in tightly sealed bottles at approximately 5 °C. Moreover, samples were maintained in the absence of light to prevent photobleaching. The formation of coke or carbonaceous build-up during the thermal stress processes did not pose significant problems, even at 510 °C. We noted occasionally that the back pressure regulating valve accumulated small deposits of coke particulates, but these were easily removed by exercising the valve periodically. The extent of coking was never more than a few observable particles. 2.2. Advanced Distillation Curve Measurements. The method and apparatus for ADC measurements has been reviewed in detail elsewhere (see the references previously cited), and thus, only a limited description of a typical measurement is provided herein. In brief, 200 mL of each sample fuel was placed into the boiling flask with a 200 mL volumetric pipet (equipped with an automatic pipet) for each distillation curve measurement. Thermocouples were then inserted into the proper locations to monitor Tk, the temperature in the fluid, and Th, the temperature of the vapor at the bottom of the takeoff position in the distillation head. Enclosure heating was then commenced with a fourstep program based upon a previously measured distillation curve and knowledge of the neat sample composition. Volume measurements were made in a level-stabilized receiver, and sample aliquots were collected at the receiver adapter hammock. Because the measurements of the distillation curves were performed at an elevation of ∼1650 m, resulting in an ambient atmospheric pressure of ∼83 kPa (measured with an electronic barometer), temperature readings were adjusted for what should be obtained at standard atmospheric pressure (1 atm = 101.325 kPa). This adjustment was done with the modified Sydney Young equation, in which the constant term was assigned a value of 0.000109.57 59 This value corresponds to a carbon chain of 12. The pressure adjustment resulted in a typical temperature adjustment of approximately 8 °C. The actual measured temperatures are easily recovered from the Sydney Young equation at each measured atmospheric pressure that is reported for every measurement throughout this work. To accompany the temperature data grid on the distillation curves with the composition channel information, sample aliquots were

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withdrawn for selected distillate volume fractions and chemically analyzed. To accomplish this, aliquots of approximately 7 μL of emergent fluid were withdrawn from the sampling hammock in the receiver adapter with a blunt-tipped chromatographic syringe and added to a crimp-sealed vial containing a known mass (approximately 1 mL) of solvent (acetone for the unstressed fuels and carbon disulfide for the thermally stressed fluids). Distillate samples were withdrawn at the first drop of fluid from the condenser and then at the 10, 50, and 80% volume fractions, for a total of four sample aliquots for each fluid mixture.

3. RESULTS AND DISCUSSION 3.1. Thermally Stressed Sample Composition. As we discussed above and in more detail elsewhere, the thermal stress process produces numerous gaseous and light products (low molecular mass linear and branched alkanes, hydrogen, etc.). Indeed, at 510 °C, we noted that 50% (mass/mass) of the output from the reactor (and the subsequent chilled heat exchanger) was gaseous and was not collected in the liquid that was recovered. Rather, during the thermal stress process, this product was simply vented (through a carbon cartridge) because our primary interest was the stressed liquid. We did, however, characterize (by chemical analysis) both the gaseous product and the thermally stressed liquid for the RP-1 and RP-2 that was stressed at 510 °C. 3.1.1. Thermally Stressed Liquid Analysis. The chromatograms acquired following the GC-MS analysis on the neat unstressed and stressed RP-1 and RP-2 liquid samples are provided in Figure 2, showing distinct differences. Most notable is the extent of decomposition in the stressed fluids, shown by the higher concentration of smaller and more volatile molecules (those eluting at retention times less than 5 min). Both RP-1 and RP-2 samples stressed at 510 °C undergo much more extensive decomposition into smaller components than do the samples thermally stressed at 475 °C. This result highlights the interesting and different decomposition chemistry that occurs at approximately 500 °C, which has been observed in prior thermal decomposition kinetics measurements on these fluids. While a detailed peak by peak comparison can be made for each fuel, a survey comparison can be done with an analysis method that is based on ASTM Method D-2789.60 In this method, one uses the GC-MS to classify hydrocarbon samples into six different types, based entirely on the fragmentation behavior observed in mass spectra. The six different moieties are paraffins, monocycloparaffins, dicycloparaffins, alkylbenzenes (or aromatics), indanes and tetralins, and naphthalenes. While this method has many limitations and sources of uncertainty (we have reviewed the pitfalls elsewhere33) and is only specified for use on low olefinnic gasoline samples, it is routinely used for all types of fuel. Interpretation of these results should primarily emphasize fuel to fuel (or sample to sample) comparisons and secondarily emphasize detailed comparisons among the moieties within a given fuel. The results from this procedure performed on the unstressed and thermally stressed RP-1 and RP-2 samples can be seen in Figure 3. As indicated in Figure 3, both fluid types (RP-1 and RP-2) undergo similar compositional transitions as a result of the thermal stress. For both fuels, the concentration of paraffins declines, the monocycloparaffin and naphthalenic content is relatively constant, and we observe an increase in dicycloparaffins and alkybenzenes. The most notable changes in composition occur with the reduction of paraffins and the increase in alkybenzenes in both fluids as the thermal stress temperature is 5205


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Figure 5. Measured distillation curves for the unstressed and stressed samples of RP-1. The curves represent the temperature of the boiling fluid, indicated as Tk. All the temperatures were adjusted to 1 atm using the modified Sydney Young equation. The uncertainty is discussed in the text.

Figure 6. Measured distillation curves for the unstressed and stressed samples of RP-2. The curves represent the temperature of the boiling fluid, indicated as Tk. All the temperatures were adjusted to 1 atm using the modified Sydney Young equation. The uncertainty is discussed in the text.

increased. Overall, the hydrocarbon classification analysis reveals a trend of an increasing C/H ratio as the stressing temperature is increased. This trend is expected as the vapor phase analysis (discussed in detail below) revealed a release of hydrogen during the decomposition. 3.1.2. Gaseous Sample Analysis. To analyze the gaseous phase, we first had to separately collect the gas while ensuring that there was no contamination with the liquid. Any contamination with liquid would skew the analysis toward heavier components and make any conclusions invalid. Simply sampling the headspace of the polyethylene bottle in which the liquid was collected was not a viable approach, because this vessel was initially filled with air and the gaseous product could not be assumed to have fully displaced the air. Collection for analysis

was therefore done with a specially designed two phase separator collection manifold that has been described elsewhere.61 This device, called P2SC, physically separates and collects both the gas and liquid flows exiting the heat exchanger, with no cross contamination. The gas phase that was recovered with the P2SC was analyzed with two types of chromatographic methods: a GC-MS method utilizing a capillary column and a series of packed column methods utilizing thermal conductivity detection (TCD). For the GC-MS method, the same column and method from the liquid analyses (described earlier) were used, with the exception of column temperature, which was held isothermally at 0 °C. Column cooling was achieved by use of a vortex chiller fitted to the chromatographic oven. The packed column analyses utilized 5206


Energy & Fuels a 5A molecular sieve at (60/80 mesh, column 6.35 mm o.d., 3 m in length, isothermal at 150 °C, flash vaporization inlet isothermal at 175 °C with a head pressure of 137.9 kPa (20 psi), and thermal conductivity detector operated at 250 °C). Measurements were made with two different carrier gases: a helium/ hydrogen mixture (91.5/8.5 vol/vol) and argon. The different carrier gases allowed us to more easily detect species with varying thermal conductivities. The chromatograms following the GC-MS and the GC-TCD analysis of the gas phase sample collected during the thermal stressing of the RP-2 at 510 °C are provided in Figure 4 (results for RP-1-TS-510 are similar). The GC-MS analysis enabled the identification of hydrocarbons as large as methyl butane in the vapor phase; however, this method was less effective in the separation of smaller molecules. Complementary to the GC-MS analysis, the packed column analyses separated the smaller components, indicating the presence of hydrogen, carbon monoxide, methane, ethane, oxygen, and nitrogen. The oxygen and nitrogen species most likely originated from air dissolved within the unstressed fluids. 3.2. Initial Boiling Behavior. During the initial heating of each sample during the distillation, the behavior of the fluid was carefully observed. Typically, during the early stages of an ADC measurement performed on a complex fluid, the first bubbles will appear intermittently and are rather small. Sustained bubbling occurs subsequent to onset, characterized by larger, more vigorous bubbles. Finally, in most cases, the vapor then rises into the distillation head, causing an immediate response on the Th thermocouple. This is the initial boiling temperature (IBT) of the fluid. In this work, however, we noted that the thermally stressed samples presented a behavior contrary to this usual pattern. Instead, for these fluids, no sudden rise in the head temperatures was noticed. Rather than exhibiting a sudden jump, the head temperature was observed to rise gradually, in a fashion similar to that of the fluid temperature (Tk). Moreover, the vapor was not observed to rise into the head, as is the usual observation with the ADC approach. For the thermally stressed fluids, the first indication of vaporization was the observation of a fluid film on the inside wall of the chilled condenser (or, in some cases, in the chilled receiver). Because this was the first indication that material had boiled (that is, a phase change occurred that caused fluid to leave the kettle), the corresponding Tk temperature was designated as the vapor rise temperature (and, therefore, the IBT) for the thermally stressed samples. The vapor rise temperatures for each RP-1 and RP-2 fluid are provided in Table 1. The uncertainties of the vapor rise temperatures were less than 0.5 °C for the unstressed fluids and less than 2 °C for the thermally stressed fluids. The initial boiling temperatures for the two rocket propellants are similar and undergo comparable transitions as a result of the thermal stressing. The thermal stressing temperature plays a significant role in the reduction of the initial boiling temperatures, as seen by the dramatic decrease in the IBT of the TS-510 fluids. 3.3. Distillation Curve Measurements. For each fluid sample, between two and four distillations were performed. The distillation data for each of the RP-1 and RP-2 samples are presented in Tables 2 and 3, and the curves are presented in Figures 5 and 6, respectively. The average uncertainties for temperatures were below 1 °C for both of the unstressed fluids and also for the fluids stressed at 475 °C. The uncertainties for the fluids stressed at 510 °C were somewhat higher, at approximately 2 °C. The higher concentration of dissolved gaseous

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species within TS-510 fluids increased the uncertainty of the temperature measurements by making it difficult to reproducibly condense and collect the sample during distillation. Upon completing the distillation of the TS-510 fluids, it was noticed that there was a deficit of approximately 10% of the distillate volume in the receiver. After first noting this behavior, additional steps were taken to ensure the efficient capture of highly volatile species. These steps included lowering the receiver temperature, adding additional insulation to the head, and eliminating all potential gaps in the apparatus. Despite these changes, the observation of the apparent loss was persistent and repeatable, with a duplicate curve essentially overlying the initial measurement. Evidence pointed to sample loss occurring very early in the measurement, most probably the result of off-gassing of very volatile species that were either dissolved or entrained in the liquid. This suggests that the TS-510 distillation curves would be skewed along the x-axis (the distillate volume fraction) by a volume corresponding to the loss. This behavior was not encountered with the TS-475 fluids or in any previous application of the ADC. A simple experiment was designed to approximate the amount or fraction of the TS-510 fluid that was lost during the distillation (or rather at the very early stage of the distillation). This was done so that an appropriate shift in the measured volume fractions could be devised. To do this, weighed autosampler vials (well sealed with a silicone/Teflon sandwich septum) of the TS-510 samples were placed in a GC oven. A small piece of uncoated fused silica tubing was inserted through the septum to serve as a vent, so that any dissolved or entrained gases could escape. The temperature of the vial inside the oven was then increased to 130 °C; this target temperature was chosen to approximate the temperature measured at the 5% distillate volume fractions for the TS-510 samples. The vial remained in the oven for approximately one hour, to approximate the time of an ADC measurement. Upon reweighing the vials, we noted the loss of approximately 13% (mass/mass) of the sample. To convert this mass loss into a volume, we focused on the gaseous products analysis discussed earlier and presented in Figure 4. On the basis of this product suite, we used a composite density of 0.6 g/mL for this lost mass. Thus, to account for the gases that escaped prior to the measured 5% volume fraction, the TS-510 distillation curves presented in Figures 5 and 6 were reconfigured with a positive shift of 11% in distillate volume fraction. The differences in the distillation curves between the unstressed and stressed fluids are striking. The temperatures marking the first drop of distillate from the condenser are much lower for the TS-475 samples than for the unstressed samples. Following the first drop, however, the TS-475 curves approach the unstressed sample distillation curves and nearly coincide by the 20% distillate volume fraction. The extent of decomposition in the TS-475 samples clearly only affects the earliest temperatures of the distillation curve. Very different behavior is seen for the TS-510 samples. The more advanced thermal decomposition, resulting in a large suite of lighter components, results in distillation curves uniformly lower in temperature. For both RP-1 and RP-2, the TS-510 curves have a much lower first drop temperature than the corresponding unstressed fluids, indeed approaching approximately 70 °C. The TS-510 curves do not approach the unstressed curves until the 70 80% distillate volume fractions. The large difference between the TS-475 and TS-510 distillation curves is an additional indication of the 5207


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Figure 7. Distillate fraction chromatograms collected during the distillation of the (a) unstressed RP-1, (b) RP-1-TS-475, and (c) RP-1-TS-510. Side by side comparisons on the basis of fraction (for example, 50% compared to 50%) are provided in Figure S1 in the Supporting Information.

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Figure 8. Distillate fraction chromatograms collected during the distillation of the (a) unstressed RP-2, (b) RP-2-TS-475, and (c) RP-2-TS-510. Side by side comparisons on the basis of fraction (for example, 50% compared to 50%) are provided in Figure S2 in the Supporting Information.

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Figure 9. Molar combustion enthalpies for the distillate fractions withdrawn during the distillations of the unstressed and thermally stressed (a) RP-1 and (b) RP-2 samples. The uncertainty is discussed in the text.

difference in chemistry that occurs when kerosene rocket propellants are stressed below and above 500 °C. 3.4. Distillate Composition. To provide a better picture of the decomposition and its effect on the distillation curve, the compositions of selected distillate fractions were measured using GC-FID and GC-MS. Each distillate volume aliquot was analyzed with GC-FID (30 m capillary column with a 1 μm coating of stationary phase, 5% phenyl dimethyl polysiloxane) with external standards to determine the compound concentrations. The quantitative GC-FID analyses were performed by injecting 3 μL of the solvent/sample mixtures from the crimp-sealed vials into a split injector (15 to 1 split ratio) with an automatic sampler. The injector operated at 300 °C and a constant head pressure of 82.7 kPa (12 psi). An oven temperature program with a 3 min soak at 50 °C, followed by a temperature ramp of 4 °C/min

to 90 °C, and then a temperature ramp of 5 °C/min to 225 °C was used. High-purity nitrogen was used as the carrier and makeup gas, and the detector was maintained at 275 °C for all the analyses performed with the GC-FID. The composition of the distillate fractions was determined by identifying peaks in the chromatograms produced with the GC-MS, with aid from the NIST/EPA/NIH Mass Spectral Database, and also on the basis of retention times.62,63 The series of chromatograms of the distillate fractions for each of the RP-1 and RP-2 samples can be seen in Figures 7 and 8, respectively. The thermally stressed samples have a far greater number of highly volatile components (indicated by peaks with lower retention times) in the first drop of the distillation than the unstressed fluids. This explains the large temperature differences early in the distillation curves of the thermally stressed samples 5210


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Table 4. Total Enthalpy of Combustion, Presented in kJ/ mol, for Four Distillate Volume Fractions of the Two Thermally Stressed RP-1 fuels and the Unstressed RP-1 Fuela

Table 6. Total Enthalpy of Combustion, Presented in kJ/g, for Four Distillate Volume Fractions of the Two Thermally Stressed RP-1 Fuels and the Unstressed RP-1 Fuela

distillate distillate vol. fraction, (%) 0.025

a

RP-1

RP-1 unstressed, RP-1-TS-475, vol. fraction, RP-1-TS-510, ( kJ/mol)

( kJ/mol)

(%) 0.025

( kJ/mol) 3371 (169)

distillate vol.

unstressed,

fraction, (%)

( kJ/g)

0.025

( kJ/g)

RP-1-TS-

fraction, (%) 510, ( kJ/g)

6372 (319)

3494 (175)

43 (2)

45 (2)

10

6718 (336)

6393 (320)

21

4340 (217)

10

43 (2)

43 (2)

21

44 (2)

50 80

7120 (356) 7689 (384)

7105 (355) 7655 (383)

61 91

6663 (333) 7658 (383)

50 80

43 (2) 43 (2)

43 (2) 43 (2)

61 91

43 (2) 43 (2)

Neat

7135 (357)

6741 (337)

Neat

5601 (280)

Neat

43 (2)

44 (2)

Neat

44 (2)

a

The uncertainties are presented in parentheses.

Table 5. Total Enthalpy of Combustion, Presented in kJ/ mol, for Four Distillate Volume Fractions of the Two Thermally Stressed RP-2 Fuels and the Unstressed RP-2 Fuela

0.025

( kJ/mol)

( kJ/mol)

fraction, (%)

6506 (325)

3293 (165)

6690 (334)

6467 (323)

21

0.025

4072 (204)

50 80

7088 (354) 7698 (385)

6982 (349) 7698 (385)

61 91

6680 (334) 7617 (381)

Neat

7271 (364)

7030 (337)

Neat

6258 (313)

RP-2

3189 (159)

distillate vol.

unstressed,

fraction, (%)

( kJ/g)

0.025 10 50

The uncertainties are presented in parentheses. a

compared to the unstressed samples. The 10% distillate volume fraction chromatograms of the TS-475 samples resemble the 10% distillate volume fraction chromatograms of the unstressed fluids, but they still have a somewhat higher number of more volatile components. This observation explains the sharp rise in the TS-475 distillation curves and also the convergence of the TS-475 curves with those of the unstressed fluids by the 20% volume fraction. The TS-475 and unstressed 50% and 80% volume fraction distillate chromatograms appear to be nearly identical, thus, explaining the overlay of the TS-475 and unstressed distillation curves following the 20% volume fraction. For the TS-510 samples, the 21% volume fraction chromatogram is made up of a much higher number of smaller, more volatile components, than either the TS-475 or the unstressed 10% volume fraction chromatogram. This explains the significantly lower distillation temperatures measured for the TS-510 distillation curves in this region. The 61% distillate volume fraction chromatograms of the TS-510 samples begin to resemble the 50% volume fraction chromatograms of the TS-475 and unstressed samples, but we still note a preponderance of lighter components. The 91% distillate volume fraction chromatograms of the TS-510 samples resemble those of the 80% volume fraction of the TS-475 and the unstressed fluid samples, explaining the convergence that occurs with all three distillation curves at later volume fractions. 3.5. Enthalpy of Combustion. As we have previously demonstrated, it is possible to supplement the distillation curve with thermochemical data, with the information available from the composition explicit data channel. We calculate a fractional enthalpy of combustion on the basis of the measured mole fractions of the individual components in the distillate cuts. One simply multiplies the measured mole fraction by the pure

45 (2)

Table 7. Total Enthalpy of Combustion, Presented in kJ/g, for Four Distillate Volume Fractions of the Two Thermally Stressed RP-2 Fuels and the Unstressed RP-2 Fuela

( kJ/mol)

10

0.025


distillate vol. RP-2 unstressed, RP-2-TS-475, distillate vol. RP-2-TS-510, fraction, (%)

a

RP-1-TS-475, distillate vol.

RP-2-TS-475, distillate vol. ( kJ/g)

43 (2)

45 (2)

43 (2) 43 (2)

43 (2) 43 (2)

RP-2-TS-

fraction, (%) 510, ( kJ/g) 0.025 21 61

45 (2) 44 (2) 43 (2)

80

43 (2)

43 (2)

91

43 (2)

Neat

43 (2)

43 (2)

Neat

43 (2)


component enthalpy of combustion. The enthalpy of combustion of the individual (pure) components is taken from a reliable database compilation. We have discussed the contributions to the overall uncertainty of the total enthalpy of combustion elsewhere.39 The main sources of uncertainty in the enthalpy of combustion calculation here are due to (1) uncertainty in the values tabulated for the individual enthalpy of combustion values for each component, (2) uncertainty in the measured mole fraction, and (3) the uncertainty arising from the absence of data for experimental enthalpy of combustion for some of the constituents. There is also uncertainty in neglecting the enthalpy of mixing; however, this value has been shown previously to be less than 0.01% of the enthalpy of combustion. Additionally, there may be uncertainty in the enthalpy of combustion as a result of the inability to resolve very closely related isomers via the analytical protocol, the complete misidentification of a component, and neglecting components present at very low concentrations. In past work, we determined that neglecting peaks with total uncalibrated area percentages of up to 4% increased the uncertainty of the calculated enthalpy by only 1.5%. Thus, neglecting minor components in the rocket propellant distillate fractions does not significantly affect the uncertainty of the total enthalpy of combustion. In view of these sources of uncertainty, the overall combined uncertainty in our total enthalpy of combustion calculations (with the coverage factor k = 2)64 was less than 5%. The uncertainty is dominated by the analytical measurement and determination of the component mole fractions. The molar based combustion enthalpies for each RP-1 and RP-2 fluid are presented in Figure 9, with the data provided in Tables 4 and 5, respectively. The molar enthalpies of combustion 5211


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Table 8. Total Enthalpy of Combustion, Presented in kJ/L, for Four Distillate Volume Fractions of the Two Thermally Stressed RP-1 Fuels and the Unstressed RP-1 Fuela RP-1 distillate vol.

unstressed,

fraction, (%)

( kJ/L)

0.025

a

RP-1-TS-475, distillate vol. RP-1-TS-510, ( kJ/L)

35887 (1794) 29001 (1450)

fraction, (%) 0.025

( kJ/L) 28731 (1437)

10

36417 (1821) 35790 (1789)

21

31802 (1590)

50 80

36877 (1844) 36937 (1847) 37089 (1854) 37229 (1861)

61 91

36518 (1826) 37188 (1859)

Neat

36828 (1841) 35831 (1792)

Neat

34050 (1703)


Table 9. Total Enthalpy of Combustion, Presented in kJ/L, for Four Distillate Volume Fractions of the Two Thermally Stressed RP-2 Fuels and the Unstressed RP-2 Fuela RP-2 distillate vol.

unstressed,

fraction, (%)

( kJ/L)

0.025 10 50

a

RP-2-TS-475, distillate vol. RP-2-TS-510, ( kJ/L)

36975 (1849) 28600 (1430) 37399 (1870) 36906 (1845) 38036 (1902) 37991 (1900)

fraction, (%) 0.025

( kJ/L) 28314 (1416)

21 61

31215 (1561) 37502 (1875)

80

38250 (1912) 38207 (1910)

91

38286 (1914)

Neat

38020 (1901) 37643 (1882)

Neat

36139 (1807)


tracked during the distillation for each fluid follow trends similar to those of the distillation curves. This observation, which has been reported in our earlier work, results from the molar enthalpy of combustion of a hydrocarbon, similar to the case of the boiling temperatures, being dependent on the size of the molecules or, more specifically, the number of hydrogen carbon bonds that are present. The enthalpies of combustion for the first drop of the thermally stressed samples are significantly less than the enthalpies of combustion of the first drop of the unstressed fluids. Similar to the distillation curves, the molar enthalpies of combustion of the TS-475 samples increase sharply between the first drop and the 10% volume fraction and approach the values of the unstressed samples. The molar enthalpies of combustion of the 50% and 80% volume fractions for the TS-475 and unstressed samples are nearly identical. The distillate TS-510 molar enthalpies of combustion are well below the enthalpies of the unstressed distillates and do not approach the TS-475 and unstressed values until approximately the 80% distillate volume fraction. The presentation of the thermochemical information in units of kJ/mol is useful for design, stoichiometric, and modeling studies because thermochemical information presented in this way represents fundamental values easily applied to the individual component mole fractions. A practical engineering alternative would be to present ΔHc in terms of mass or volume, expressed in kJ/g or kJ/L, respectively. The conversion to a per-mass basis requires only the relative molecular mass (RMM) of the constituents of each sample; the uncertainty of this calculation remains less than 5%. The distillate per-mass enthalpies of combustion for the RP-1 and RP-2 samples are presented in Tables 6 and 7 and are nearly identical for every sample.

The presentation of the data on a per-volume basis is also valuable. The conversion to a per-volume basis requires both the RMM and the density of the constituents of each sample at each distillate temperature. Here, reliable density data of the constituents of each sample are available as a function of the distillation temperatures, and the uncertainty of this calculation remains less than 5%.65 The volumetric enthalpy of combustion data calculated for the distillate fractions can be seen in Tables 8 and 9 for the RP-1 and RP-2 fluids, respectively. The per-volume enthalpies of combustion follow a trend similar to that of the per-molar enthalpy of combustion. The volumetric enthalpies of combustion for the unstressed fluids remain nearly constant within experimental uncertainty throughout the distillation. The TS475 fluids have a lower per-volume enthalpy of combustion in the first drop then rapidly approach the values of the unstressed fluids. The early volume fractions of the TS-510 fluids contain less energy per volume than the unstressed fluids. As the distillation progresses, the per-volume enthalpies of combustion for the TS-510 samples slowly approach the values of the other two fluids before nearly converging around the 60% volume fraction.

4. CONCLUSION Using the advanced distillation curve method, this study focused on describing the changes in volatility one can expect when a typical rocket propellant is thermally stressed. A representative sample of both RP-1 and RP-2 was thermally stressed at two temperatures, 475 and 510 °C, both at a constant pressure of 17 kPa (2500 psi). Initial chemical analysis showed that the composition of the two rocket propellants underwent dramatic changes following the thermal stressing. An increase in the concentration of shorter more volatile hydrocarbons was noticed for each of the thermally stressed fluids, with the TS-510 fluids having a much higher concentration of these resulting molecules. The distillation curves reflected these changes in composition. The distillation curves of the TS-475 fluids experienced lower boiling temperatures at the initial volume fractions before approaching the distillation curves of the unstressed fluids around the 20% volume fraction. The distillation curves of the TS-510 fluids experienced lower boiling temperatures than the TS-475 samples and did not approach the unstressed distillation curves until around the 80% volume fraction. Gas chromatography analysis of the distillate samples showed a higher concentration of volatile components in the stressed fluids, which was responsible for the decreased boiling temperatures. The composition of the distillate fractions was quantitatively determined and used to calculate the enthalpies of combustion at selected volume fractions. The molar and volume based enthalpies of combustion followed trends similar to those of the distillation curves, with the thermally stressed fluids having lower initial values before approaching the enthalpies of combustion for the unstressed fluids at higher volume fractions. The massbased enthalpies of combustion were identical and underwent no discernible change during the distillation for all the fluids. These results provide a better insight into the changes in physical properties that can be expected in rocket propellants during a typical regenerative cooling process. ’ ASSOCIATED CONTENT

bS

Supporting Information. Additional chromatograms collected during the distillation of unstressed RP-1, RP-1-TS-475,

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Energy & Fuels unstressed RP-2, and RP-2-TS-475. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT The financial support of the Air Force Research Laboratory (MIPR-F1SBAA0138G001) is gratefully acknowledged. B.C.W. gratefully acknowledges a National Academy of Sciences/ National Research Council Postdoctoral Associateship. ’ REFERENCES (1) Bates, R. W.; Edwards, T.; Meyer, M. L. Heat Transfer and Deposition Behavior of Hydrocarbon Rocket Fuels. 41st Aerospace Sciences Meeting and Exhibit, Reno, NV, 2003. (2) Salakhutdinov, G. M. Development of Methods of Cooling Liquid Propellant Rocket Engines (ZhRDs), 1903 1970. In History of Rocketry and Astronautics; Skoog, A. I., Ed.; American Astronautics Society: San Diego, 1990; pp 115 122. (3) Lovestead, T. M.; Windom, B. C.; Nickell, J. R. R. C.; Bruno, T. J. Assessment of the Compositional Variability of RP-1 and RP-2 with the Advanced Distillation Curve Approach. Energy Fuels 2010, 24, 5611– 5623. (4) Billingsley, M.; Edwards, J. T.; Shafer, L. M.; Bruno, T. J. Extent and Impacts of Hydrocarbon Fuel Compositional Variability for Aerospace Propulsion Systems. 46th AIAA/ASME/SAE/ASEEJoint Propulsion Conference and Exhibit, Paper AIAA 2010 6824; Nashville, TN, 2010. (5) Bruno, T. J.; Huber, M. L.; Laesecke, A.; Lemmon, E. W.; Perkins, R. A. Thermochemical and Thermophysical Properties of JP-10, NIST-IR 6640; National Institute of Standards and Technology: United States, 2006. (6) Bruno, T. J. Thermodynamic, Transport and Chemical Properties of “Reference” JP-8. In Book of Abstracts, Contractor’s Meeting in Chemical Propulsion; Army Research Office and Air Force Office of Scientific Research: United States, 2006; pp 15 18. (7) Bruno, T. J. The Properties of S-8. In Final Report for MIPR F4FBEY6237G001; Air Force Research Laboratory, 2006. (8) Bruno, T. J.; Laesecke, A.; Outcalt, S. L.; Seelig, H.-D.; Smith, B. L. Properties of a 50/50 Mixture of Jet-A + S-8, NIST-IR-6647; National Institute of Standards and Technology : United States, 2007. (9) Bruno, T. J. Thermodynamic, Transport and Chemical Properties of “Reference” JP-8. In Book of Abstracts, Contractor’s Meeting in Chemical Propulsion; Army Research Office and Air Force Office of Scientific Research: United States, 2007. (10) Bruno, T. J.; Billingsley, M; Bates, R. D. Findings and Recommendations from the Joint NIST/AFRL Workshop on Rocket Propellants and Hypersonic Vehicle Fuels; National Institute of Standards and Technology, September, 2008. (11) Bruno, T. J.; Huber, M. L.; Laesecke, A.; Lemmon, E. W.; McLinden, M. O.; Outcalt, S. L.; Perkins, R.; Smith, B. L.; Widegren, J. A. Thermodynamic, Transport, and Chemical Properties of “Reference” JP-8, NISTIR 6659; National Institute of Standards and Technology: Gaithersburg, MD. 2010. (12) Bruno, T. J.; Smith, B. L. Evaluation of the Physicochemical Authenticity of Aviation Kerosene Surrogate Mixtures Part I: Analysis of Volatility with the Advanced Distillation Curve. Energy Fuels 2010, 24, 4266–4276. (13) Bruno, T. J.; Huber, M. L. Evaluation of the Physicochemical Authenticity of Aviation Kerosene Surrogate Mixtures Part II: Analysis and Prediction of Thermophysical Properties. Energy Fuels 2010, 24, 4277–4284.

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Energy & Fuels Analysis and Physical Properties of Complex Fluids. J. Chromatogr. 2010, A1217, 2703–2715. (38) Bruno, T. J.; Ott, L. S.; Lovestead, T. M.; Huber, M. L. Relating Complex Fluid Composition and Thermophysical Properties with the Advanced Distillation Curve Approach. Chem. Eng. Technol. 2010, 33, 363–376. (39) Bruno, T. J.; Smith, B. L. Enthalpy of Combustion of Fuels As a Function of Distillate Cut: Application of an Advanced Distillation Curve Method. Energy Fuels 2006, 20, 2109–2116. (40) 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. (41) Ott, L. S.; Bruno, T. J. Modifications to the Copper Strip Corrosion Test for the Measurement of Microscale Samples. J. Sulfur Chem. 2007, 28, 493–504. (42) Bruno, T. J.; Wolk, A.; Naydich, A. Composition-Explicit Distillation Curves for Mixtures of Gasoline with Four-Carbon Alcohols (Butanols). Energy Fuels 2009, 23, 2295–2306. (43) Bruno, T. J.; Wolk, A.; Naydich, A. Analysis of Fuel Ethanol Plant Liquor with the Composition Explicit Distillation Curve Approach. Energy Fuels 2009, 23, 3277–3284. (44) Bruno, T. J.; Wolk, A.; Naydich, A.; Huber, M. L. Composition Explicit Distillation Curves for Mixtures of Diesel Fuel with Dimethyl Carbonate and Diethyl Carbonate. Energy Fuels 2009, 23, 3989–3997. (45) Lovestead, T. M.; Windom, B. C.; Bruno, T. J. Investigating the Unique Properties of Cuphea Derived Biodiesel with the Advanced Distillation Curve Method. Energy Fuels 2010, 24, 3662–3675. (46) Ott, L. S.; Bruno, T. J. Variability of Biodiesel Fuel and Comparison to Petroleum-Derived Diesel Fuel: Application of a Composition and Enthalpy Explicit Distillation Curve Method. Energy Fuels 2008, 22, 2861–2868. (47) Ott, L. S.; Smith, B. L.; Bruno, T. J. Advanced Distillation Curve Measurements for Corrosive Fluids: Application to Two Crude Oils. Fuel 2008, 87, 3055–3064. (48) Ott, L. S.; Smith, B. L.; Bruno, T. J. Advanced Distillation Curve Measurement: Application to a Bio-Derived Crude Oil Prepared from Swine Manure. Fuel 2008, 87, 3379–3387. (49) Ott, L. S.; Smith, B. L.; Bruno, T. J. Composition-Explicit Distillation Curves of Mixtures of Diesel Fuel with Biomass-Derived Glycol Ester Oxygenates: A Fuel Design Tool for Decreased Particulate Emissions. Energy Fuels 2008, 22, 2518–2526. (50) Smith, B. L.; Ott, L. S.; Bruno, T. J. Composition-Explicit Distillation Curves of Diesel Fuel with Glycol Ether and Glycol Ester Oxygenates: Fuel Analysis Metrology to Enable Decreased Particulate Emissions. Environ. Sci. Technol. 2008, 42, 7682–7689. (51) Smith, B. L.; Ott, L. S.; Bruno, T. J. Composition-Explicit Distillation Curves of Commercial Biodiesel Fuels: Comparison of Petroleum Derived Fuel with B20 and B100. Ind. Eng. Chem. Res. 2008, 47, 5832–5840. (52) Windom, B. C.; Lovestead, T. M.; Bruno, T. J. Application of the Advanced Distillation Curve Method to the Development of Unleaded Aviation Gasoline. Energy Fuels 2010, 24, 3275–3284. (53) Bruno, T. J.; Wolk, A.; Naydich, A. Stabilization of Biodiesel Fuel at Elevated Temperature with Hydrogen Donors: Evaluation with the Advanced Distillation Curve Method. Energy Fuels 2009, 23, 1015–1023. (54) Lovestead, T. M.; Bruno, T. J. Comparison of the Hypersonic Vehicle Fuel JP-7 to the Rocket Propellants RP-1 and RP-2 with the Advanced Distillation Curve Method. Energy Fuels 2009, 23, 3637– 3644. (55) Huber, M. L.; Lemmon, E.; Ott, L. S.; Bruno, T. J. Preliminary Surrogate Mixture Models for Rocket Propellants RP-1 and RP-2. Energy Fuels 2009, 23, 3083–3088. (56) Bruno, T. J.; Windom, B. C. Method and Apparatus for the Thermal Stress of Complex Fluids: Application to Fuels. Energy Fuels 2011, 25, 2625–2632. (57) Young, S. Distillation Principles and Processes; Macmillan and Co., Ltd.: London, 1922.

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