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Hyperbranched Poly(amidoamine) as an Efficient Macroinitiator for Thermal Cracking and Heat-Sink Enhancement of Hydrocarbon Fuels Guijin He,† Xi Wu,† Dengfeng Ye,† Yongsheng Guo,† Shenlin Hu,‡ Yu Li,‡ and Wenjun Fang*,† †

Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, People’s Republic of China Science and Technology on Scramjet Laboratory, The 31st Research Institute of China Aerospace Science and Industry Corporation (CASIC), Beijing 100074, People’s Republic of China

‡

S Supporting Information *

ABSTRACT: One of the amidoamine-structured hyperbranched polymers is developed as an efficient macroinitiator to enhance the endothermic capacity of hydrocarbon fuels to meet the stringent cooling requirement of hypersonic aircrafts. Hyperbranched poly(amidoamine) (PAMAM) is treated with palmitoyl chloride to modify a lipophilic shell on the hydrophilic core, and the amphiphilic product, palmitoyl-hyperbranched poly(amidoamine) (PPAMAM), can be well-dissolved in hydrocarbon fuels. The long alkyl chains in PPAMAM break away from the core at about 200 °C, and the PAMAM core destructs around 400 °C. The high decomposition temperature of the core enables PPAMAM to be performed as a macroinitiator for hydrocarbon fuels. Thermal cracking of methylcyclohexane (MCH) from 600 to 720 °C with the addition of PPAMAM is carried out in an electrically heated tubular reactor under the pressure of 3.5 MPa. Significant improvements of the conversion, gas yield, and heat sink of MCH with PPAMAM are observed. The conversion of MCH is increased from 39.5 to 56.3 wt % at 690 °C, and the corresponding heat sink has been raised from 2.48 to 2.91 MJ/kg. Furthermore, PPAMAM with the optimum molecular weight is employed for the cracking of aviation kerosene. The heat sink is also improved significantly in comparison to that from the thermal cracking of bare kerosene, which confirms the effective application of PPAMAM in endothermic hydrocarbon fuels.

1. INTRODUCTION Efficient thermal management is essential when designing modern engines used for advanced hypersonic or supersonic aircrafts.1,2 To achieve the active cooling requirement for aircrafts with high flight Mach numbers (>5 Mach), endothermic hydrocarbon fuels with an additional chemical heat sink gained from endothermic cracking reactions have been developed.3−6 The cracking of a hydrocarbon fuel is usually carried out at a relatively high temperature to reach a high cracking conversion. However, severe coking may happen in the cracking process under a high temperature, and it is extremely harmful to the engines.7−10 Thus, various techniques that can obtain the same conversion of a hydrocarbon fuel at a lower cracking temperature are in urgent need. According to the radical chain mechanism for the cracking of hydrocarbons, the overall reaction rate is determined by the C− C bond cleavage step.11,12 The addition of initiators is considered as an effective method to increase the rate of thermal cracking because they can produce active primary free radicals to initiate the cracking reaction at a lower temperature.13 These homogeneous initiators can be dissolved in hydrocarbon fuels to avoid the disadvantages of heterogeneous catalysts, such as deposition.14,15 Many efforts have been devoted to the enhancement effect of initiators on the conversion and the heat sink of hydrocarbon fuels.16−19 Wickham et al.18 reported that some commercial initiators (azo/proxide compounds) with the content of 2 wt % could improve the cracking rate of n-heptane and the product distributions were affected in an unremarkable degree. The accelerating effects of triethylamine and tributylamine on nheptane were investigated by Wang et al.20−22 The cracking © XXXX American Chemical Society

rate and conversion can be promoted significantly by the addition of these amines (2−10 wt %). Liu et al.23 compared the performance of three initiators for the cracking of ndodecane under supercritical conditions. With an increasing initiator concentration up to 2%, the conversion of n-dodecane increased remarkably and then was kept stable against the additional amount. These small molecular initiators start to decompose at much lower temperatures (for azo compounds, 50−65 °C;24 for peroxide compounds, 50−100 °C25) and come into notable accelerating effects only at a large addition quantity (>2 wt %). In contrast, a macroinitiator with an adequate structure and degree of polymerization can solve the problem faced by small molecular initiators. In the previous work,26 palmitoyl-modified hyperbranched polyglycerol was applied to the initiator-aided cracking of n-tridecane and kerosene. This kind of macroinitiator with a hyperbranched structure could not only be well-dissolved in hydrocarbon fuels but also play the role of “radical package”, which supplies a great amount of radicals with a small addition quantity (usually lower than 0.1 wt %). Therefore, it is meaningful to develop the promising family of hyperbranched macromolecular initiators for endothermic propellants. As a continuous work, a hyperbranched polymer, poly(amidoamine) (PAMAM), is prepared via Michael addition polymerization and polycondensation27−29 in this paper. The molecular weight of PAMAM is tuned by changing the feeding ratio of ethylenediamine versus methyl acrylate. The solubility Received: March 14, 2017 Revised: June 1, 2017 Published: June 2, 2017 A

DOI: 10.1021/acs.energyfuels.7b00751 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels

Figure 1. Synthesis of PPAMAM via amidation of PAMAM with palmitoyl chloride. PAMAM samples. The linear poly(methyl methacrylate)s (PMMAs) with a series of molecular weights were used as standards for calibration. Before the GPC analyses, the PAMAM samples were treated to achieve the transformation of the primary amine into tertiary amine to prevent the primary-amine-terminated PAMAMs from absorption on the column.30 The tertiary-amine-terminated PAMAM was dissolved in water at the concentration of 5.0 mg/mL, and water was employed as the eluent under the flow rate of 1.0 mg/min. Thermal behaviors of the polymers were investigated by differential scanning calorimetry (DSC, TA Instruments, New Castle, DE, U.S.A.) with the scanning rate of 10 °C/min at a temperature from −70 to 100 °C. Thermal stability for PAMAM and PPAMAM was checked on thermogravimetric analysis (TGA, TA Instruments, New Castle, DE, U.S.A.). The scanning temperature range was set from the room temperature to 600 °C under a nitrogen atmosphere with the heating rate of 5 °C/min. 2.5. Thermal Cracking of Hydrocarbon Fuels. The thermal cracking for PPAMAM hydrocarbon fuels was investigated via an electrically heated method. The details can be found in our previous work.26,31 The fuels flow through a tubular reactor that was designed to simulate the cooling channel in the practical aircrafts. The flow rate of 1.0 g/s was controlled by a high-pressure constant flow pump (P500, China). Then, the tube was heated by a current from a direct current power supply to raise the outlet temperature of the fuel. A series of welded K-type thermocouples were used to detect the wall temperatures of the reactor. A backpressure valve was applied to control the system pressure at 3.5 MPa to ensure that the fuel was cracked under a supercritical condition. The cracked fuel was quenched to room temperature by a two-stage water-cooling system. The gaseous and liquid products were separated in a gas−liquid separator. Each cracking test was performed 3 times under the given conditions to confirm the repeatability and evaluate the uncertainty. In the previous work,26 we had proven the accelerating effect of a macroinitiator, palmitoyl-modified hyperbranched polyglycerol (PHPG), on a paraffinic hydrocarbon of n-tridecane and aviation kerosene. Because the naphthenic hydrocarbons are also important components of aviation kerosene, as a continuous work, we investigated the thermal cracking performance of PPAMAM on the model naphthenic hydrocarbon of MCH. The conversion and gas yield obtained from the thermal cracking are considered as the indicators, which are calculated from the following equations:

of the polymer in hydrocarbons is controlled by the modification with palmitoyl groups to form palmitoylPAMAM (PPAMAM), which contains a “core−shell” structure.29 The thermal cracking performances of methylcyclohexane (MCH) or a kerosene-based fuel with and without PPAMAM under different conditions are discussed. It is expected to provide fundamental information for the development of novel macroinitiators and advanced hydrocarbon fuels with high endothermic capacity.

2. EXPERIMENTAL SECTION 2.1. Materials. Ethylenediamine, methyl acrylate, magnesium sulfate, and palmitoyl chloride were purchased from Aladdin Chemical Reagent Corporation. Triethylamine, chloroform, methanol, and ethyl ether were purchased from Sinopharm Chemical Reagent Corporation. All of the reagents were used as received without further purification. 2.2. Preparation of PAMAM. Methyl acrylate (MA, 25.83 g, 0.3 mol) was added dropwise into a mixture of ethylenediamine (EDA, 18.03 g, 0.3 mol) and methanol (30 mL) with magnetic stirring. The system was kept stirring at 25 °C for 48 h, followed with the removal of most methanol. The mixture was then kept in an oil bath for 1 h at 60 °C, 2 h at 100 °C, 2 h at 120 °C, and 2 h at 140 °C on a rotary evaporator under vacuum to generate macromolecules. The crude product was redissolved in 50 mL of methanol, followed by precipitation in 300 mL of ethyl ether. After the separation from the ether layer, the final product was obtained as a viscous yellow liquid. 2.3. Modification of PAMAM. A typical modification procedure of PAMAM with palmitoyl chloride (Figure 1) is as follows:29,36 Freshly distilled palmitoyl chloride (1.5 mol equiv per −NH2 group) was dissolved in 12 mL of chloroform and then was added slowly into a solution with 2 g of PAMAM in 24 mL of chloroform and 6 mL of triethylamine. The reaction was performed at 35 °C for 24 h with magnetic stirring. The crude product was redissolved in chloroform and washed with saturated brine 3 times to remove palmitates. The organic layer was dried with magnesium sulfate and treated with rotatory vaporization to obtain a yellow waxy solid product. 2.4. Characterizations of PAMAM and PPAMAM. The structures of PAMAM and PPAMAM were characterized with nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The 1H NMR spectra were recorded on a Bruker AVANCE III 500 MHz NMR spectrometer with methanol-d4 and chloroform-d as the solvents for PAMAM and PPAMAM, respectively. The FTIR spectra of the polymers were recorded on a Nicolet iS10 spectrometer. Gel permeation chromatography (GPC, Waters, Milford, MA, U.S.A.) was applied to determine the number-average molecular weights (M̅ n) and molecular weight distributions of the

conversion = (m0 − m1c1)/m0 × 100%

(1)

where m0 is the mass of MCH injected into the channel at a given time interval, m1 is the mass of liquid residues over the same time interval, and c1 is the mass fraction of MCH in the liquid residues, which is determined by gas chromatography/mass spectrometry (GC/MS) analyses. B


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Energy & Fuels It is noted that the coking phenomena in the thermal cracking of all of the experimental fuels with/without the addition of PPAMAM are insignificant as a result of the low experimental temperatures (600− 720 °C). The generated coke per unit mass of injected fuel is lower than 20 μg/g, which is a low value. Therefore, the gas yield can be calculated as follows:

gas yield = (m0 − m1)/m0 × 100%

(2)

Gas chromatography (GC 9790, Fuli, China) was applied for the analyses of gaseous products. The content of H2 was determined by GC equipped with a stainless-steel column and a thermal conductivity detector (TCD). The mass fractions of gaseous hydrocarbons were determined by GC equipped with a capillary column and a flame ionization detector (FID), of which the heating program was set from 50 to 120 °C at the rate of 5 °C/min after an initial isothermal period of 3 min. The components of the liquid products were determined by GC/ MS (Agilent 7890/5975C, Santa Clara, CA, U.S.A.) installed with a capillary column. The column was heated from 50 to 260 °C at the rate of 10 °C/min. The transfer line temperature was 250 °C, and the quadrupole temperature was kept at 150 °C. The mass scanning range was set from 35 to 350 amu. The mass fraction of each product was calculated by an area normalization method to convert the peak areas of GC/MS signals. The heat sink of a hydrocarbon fuel was calculated from the principle of energy conservation32

Hsink = (Pinput − Ploss)/M 0

Figure 3. FTIR spectra of (a) PAMAM and (b) PPAMAM.

becomes weaker after the amidation. The typical peak of (CH2)14 clearly appears at 640 cm−1. The results reflect the successful amidation of PAMAM with palmitoyl chloride.34 The M̅ n values of the PAMAM samples vary from 5300 to 26 800 (Table 1). A higher molecular weight of polymer was

(3)

Table 1. Characterizations of Synthesized PAMAM and PPAMAM Samples

where Pinput and Ploss are the input power and heat loss, respectively (J/ s) and M0 is the mass flow rate of the injected fuel (1.0 g/s). The relationship between Ploss and wall temperature is predetermined by heating the empty tube. The wall temperatures were detected in detail by a series of K-type thermocouples that were welded on the tube wall.33

3. RESULTS AND DISCUSSION 3.1. Structure Identification of PAMAM and PPAMAM. Typical 1H NMR spectra for PAMAM and PPAMAM and the corresponding analyses on signals for various groups are shown in Figure 2. After the modification, signals for the hexadecyl group on PPAMAM appear around δH = 0.8−1.7 ppm and the signal peak for the −NH−CO− group that is connected with hexadecyl can be observed at δH = 7.4 ppm. The FTIR spectra of PAMAM and PPAMAM are shown in Figure 3. It is observed that the −NH2 band (∼3250 cm−1)

polymer

nEDA/nMA

M̅ na

Tgb (°C)

PAMAM-1 PAMAM-2 PAMAM-3 PPAMAM-1 PPAMAM-2 PPAMAM-3

1:3 1:2 1:1

5300 8500 26800

−36.5 −32.5 −28.8

Tmb (°C)

sizec (nm)

34.3 38.6 41.2

5.04 8.27 11.25 6.82 10.27 15.38

a

Determined by GPC. bDetermined by DSC. cDetermined by DLS with the Z-average size.

generated with the ratio of EDA/MA approaching 1:1. The results of dynamic light scattering (DLS) quantitatively show that the size of PAMAM increases with increasing the molecular weight. 3.2. Thermal Properties of PAMAM and PPAMAM. Typical DSC curves of PAMAM and PPAMAM are shown in Figure 4. The melting points of the PPAMAM samples appear at 34.3−41.2 °C. From the DSC analysis results shown in Table 1, a higher glass transition temperature of PAMAM with a higher molecular weight can be observed because the intramolecular hydrogen bond interaction of PAMAM becomes stronger as the molecular weight increases. Furthermore, TGA is used to investigate the thermal stability of PAMAM and PPAMAM. During the decomposition of PPAMAM, the dissociation of the hexadecyl chains happens at first, and subsequently, the PAMAM core destructs around 400 °C (Figure 5), showing a high decomposition temperature. Thus, the reactive radicals released from PPAMAM are expected to promote the thermal cracking of hydrocarbon fuels at a high temperature. As shown in Figure S1 of the Supporting Information, the onset cracking temperature of the PAMAM core (270 °C) is found to be lower than that of PHPG (301 °C) as a result of the weaker bond dissociation energy of C−N (305 kJ/mol) than C−O (326 kJ/mol). As a potential macroinitiator, PPAMAM is expected to promote the

Figure 2. 1H NMR spectra of (a) PAMAM and (b) its palmitoylmodified product PPAMAM. C


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Energy & Fuels

propylene in the mass fraction is observed to be the highest at high temperatures, and it is followed by that of ethylene. It is also notable that the yield of H2 increases against the molecular weight of PPAMAM (Figure 8), which indicates that the PPAMAM initiators can promote the dehydrogenation of MCH. The components in the liquid products after the cracking of MCH are mainly classified into α-olefins, cycloalkanes, cycloalkenes, and aromatics according to the GC/MS analyses, the relative contents of which are shown in Figure S2 of the Supporting Information. The components from liquid residues for the cracking of MCH at different temperatures are present in Table S1 of the Supporting Information. The amount of cycloalkene is observed to be higher than those of other species at each temperature, except for that at 720 °C. As the temperature increases, the dehydrogenation of cycloalkane/ cycloalkene and condensation reactions are significantly promoted and an increase of the amount of aromatics is exponentially generated.35 The α-olefins and cycloalkenes exhibit the change trends of intermediates against the temperature. At the given temperature, with the increase of the molecular weight of PPAMAM, the production of cycloalkenes and aromatics is improved, which also shows the cracking promotion of MCH. It can be concluded that hydrogen atoms on cyclohexane of MCH are abstracted first by the primary radicals obtained from PPAMAM and cycloalkenes are then formed. As the temperature goes up, deeper dehydrogenation of cycloalkanes/cycloalkenes and cyclization of α-olefins leads to the formation of benzene, toluene, and other aromatics. To further confirm the cracking enhancement of MCH by PPAMAM, different addition quantities of PPAMAM-1 are applied and the results are shown in Figure 9. Significant improvements of the conversion and gas yield for the cracking of MCH with PPAMAM-1 can be observed. Because of the higher radical concentration, the higher conversion and gas yield appear with a higher PPAMAM-1 addition quantity. For the same conversion of 50% (Figure 9a), the corresponding

Figure 4. Typical DSC curves of (a) PAMAM-1 and (b) PPAMAM-1.

cracking of hydrocarbon fuels under lower temperatures than those of PHPG. 3.3. Influence of PPAMAM on the Thermal Cracking of MCH. The values of conversion and gas yield for the thermal cracking of MCH with the addition of different PPAMAM initiators are compared in Figure 6. The addition quantity of each PPAMAM sample is 0.03 wt %. It is observed that the introduction of such a hyperbranched polymer can lead to an enhancement effect on the cracking of MCH. Both the conversion and gas yield are promoted with increasing the molecular weight of PAMAM. As an example, the conversion at 690 °C is raised from 39.5 to 56.3 wt % with the existence of PPAMAM-3 and the corresponding gas yield is raised from 18.6 to 30.0 wt %. This promotion effect is ascribed to the higher local concentration of free radicals, which are obtained from the decomposition of PPAMAM containing a PAMAM core with a higher molecular weight. The main components in the gaseous products, hydrogen, methane, ethane, ethylene, propane, propylene, C4 alkanes, and alkenes, are determined and shown in Figure 7. The yield of

Figure 5. Typical TGA curves of PAMAM and PPAMAM. D


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Energy & Fuels

Figure 6. (a) Conversion and (b) gas yield for the thermal cracking of MCH with different PPAMAM initiators.

Figure 7. Major gaseous products from the cracking of MCH with different PPAMAM samples.

temperature can be lowered from 701 to 678 °C in the presence of 0.12 wt % PPAMAM-1, which reflects its good initiation effect. The amount of coke can be reduced because of the lower reaction temperature. 3.4. Heat-Sink Enhancement of MCH with PPAMAM. It has been proven that PPAMAM promotes the cracking of MCH, and the enhancement can be tuned by changing its molecular weight or addition amount. Investigations on the heat sink of MCH that contains 0.03 wt % PPAMAM are performed, and the results are presented in Figure 10a. It can be found that the heat-sink enhancement is significant in the presence of the PPAMAM initiator, especially at the temperatures from 660 to 690 °C. The values of the heat sink are increased from 2.48 to 2.91 MJ/kg with 0.03 wt % PPAMAM-3 at 690 °C. The enhancement as high as 17.3% indicates that the PPAMAM initiator is an effective additive to improve the heat sink of MCH. To further validate this effect, the heat-sink values of MCH containing PPAMAM-1 with different addition quantities are measured, with the results shown in Figure 10b. The heat sink can be elevated from 2.48 to 2.95 MJ/kg at 690

Figure 8. Hydrogen yield from the cracking of MCH cracked with different PPAMAM samples. E


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Energy & Fuels

Figure 9. (a) Conversion and (b) gas yield for the cracking of MCH with different addition quantities of PPAMAM-1.

Figure 10. Heat sink for the cracking of MCH with (a) different PPAMAM initiators and (b) different addition quantities.

Figure 11. (a) Gas yield and (b) alkene ratio for the thermal cracking of aviation kerosene with different addition quantities of the PPAMAM-3 initiator.

°C with the addition of 0.12 wt % PPAMAM-1. The change trends of heat sink values are in good agreement with those of the conversions of MCH shown in Figure 9. 3.5. Practical Application of PPAMAM to Aviation Kerosene. The sample of PPAMAM-3 is further optimized to be the macroinitiator for cycloalkane-based aviation kerosene, which contains 76.1 wt % decalin. The gas yield and alkene ratio in the gaseous products from the thermal cracking of kerosene are shown in panels a and b of Figure 11, respectively. It is observed that the gas yield and alkene ratio are significantly raised with the addition of PPAMAM-3. A higher production of alkene from a hydrocarbon fuel generally indicates a better

endothermic capacity, which suggests that PPAMAM-3 has the potential to enhance the endothermic capacity of kerosene. The effects of PPAMAM-3 on the heat sink of kerosene are presented in Figure 12. With the addition of 0.06 wt %, the heat sink of the kerosene-based fuel is increased from 2.16 to 2.41 MJ/kg at 630 °C, from 2.57 to 2.73 MJ/kg at 660 °C, and from 2.91 to 3.08 MJ/kg at 690 °C. It is worth noting that, during all of the cracking processes, stable conditions of operation pressures and temperatures can be kept for more than 1800 s (Figure S3 of the Supporting Information) and the coke amount of per gram of cracked fuel is lower than 20 μg/g. Thus, it can be concluded that PPAMAM as a macroinitiator F


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Energy & Fuels Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the National Natural Science Foundation of China (91441109 and J1210042) is greatly appreciated by the authors.

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(1) Sobel, D. R.; Spadaccini, L. J. Hydrocarbon fuel cooling technologies for advanced propulsion. J. Eng. Gas Turbines Power 1997, 119, 344−351. (2) Huang, H.; Spadaccini, L. J.; Sobel, D. R. Fuel-cooled thermal management for advanced aeroengines. J. Eng. Gas Turbines Power 2004, 126, 284−293. (3) Bao, W.; Li, X.; Qin, J.; Zhou, W.; Yu, D. Efficient utilization of heat sink of hydrocarbon fuel for regeneratively cooled scramjet. Appl. Therm. Eng. 2012, 33−34, 208−218. (4) Sun, W.; Liu, G.; Wang, L.; Zhang, X. Quasi-homogeneous catalytic cracking of JP-10 over high hydrocarbon dispersible nanozeolites. Fuel 2015, 144, 96−102. (5) Wang, L.; Diao, Z.; Tian, Y.; Xiong, Z.; Liu, G. Catalytic cracking of endothermic hydrocarbon fuels over ordered MESO-HZSM-5 zeolites with Al-MCM-41 shells. Energy Fuels 2016, 30, 6977−6983. (6) Guo, B.; Wang, Y.; Wang, L.; Zhang, X.; Liu, G. Thermal decomposition and kinetics of a high-energy-density hydrocarbon fuel: Tetrahydrotricyclopentadiene (THTCPD). Energy Fuels 2016, 30, 230−238. (7) Edwards, T. Cracking and deposition behavior of supercritical hydrocarbon aviation fuels. Combust. Sci. Technol. 2006, 178, 307−334. (8) DeWitt, M.; Edwards, T.; Shafer, L.; Brooks, D.; Striebich, R.; Bagley, S. P.; Wornat, M. Effect of aviation fuel type on pyrolytic reactivity and deposition propensity under supercritical conditions. Ind. Eng. Chem. Res. 2011, 50, 10434−10451. (9) Liu, G.; Wang, X.; Zhang, X. Pyrolytic depositions of hydrocarbon aviation fuels in regenerative cooling channels. J. Anal. Appl. Pyrolysis 2013, 104, 384−395. (10) Liu, G.; Han, Y. J.; Wang, L.; Zhang, X.; Mi, Z. Solid deposits from thermal stressing of n-dodecane and chinese rp-3 jet fuel in the presence of several initiators. Energy Fuels 2009, 23, 356−365. (11) Watanabe, M.; Tsukagoshi, M.; Hirakoso, H.; Adschiri, T.; Arai, K. Kinetics and product distribution of n-hexadecane pyrolysis. AIChE J. 2000, 46, 843−856. (12) Kalpathy, S. V.; Bagley, S. P.; Wornat, M. J. The effects of temperature on the yields of the major aliphatic and aromatic products of supercritical n-decane pyrolysis. Ind. Eng. Chem. Res. 2015, 54, 7014−7027. (13) Edwards, T. Liquid fuels and propellants for aerospace propulsion: 1903−2003. J. Propul. Power 2003, 19, 1089−1107. (14) Wang, Q.; Hua, X.; Cheng, X.; Li, J.; Li, X. Effects of fuel additives on the thermal cracking of -decane from reactive molecular dynamics. J. Phys. Chem. A 2012, 116, 3794−3801. (15) Meng, F.; Liu, G.; Wang, L.; Qu, S.; Zhang, X.; Mi, Z. Effect of HZSM-5 coating thickness upon catalytic cracking of n-dodecane under supercritical condition. Energy Fuels 2010, 24, 2848−2856. (16) Chakraborty, J. P.; Kunzru, D. High-pressure pyrolysis of nheptane: Effect of initiators. J. Anal. Appl. Pyrolysis 2012, 95, 48−55. (17) Jia, Z.; Wang, Z.; Cheng, Z.; Zhou, W. Experimental and modeling study on pyrolysis of n-decane initiated by nitromethane. Combust. Flame 2016, 165, 246−258. (18) Wickham, D. T.; Engel, J. R.; Rooney, S.; Hitch, B. D. Initiators for endothermic fuels. J. Propul. Power 2008, 24, 55−63. (19) Chang, J.; Fan, L.; Fujimoto, K. Enhancement effect of free radical initiator on hydro-thermal cracking of heavy oil and model compound. Energy Fuels 1999, 13, 1107−1108. (20) Wang, Z.; Lin, R.; Fang, W.; Li, G.; Guo, Y.; Qin, Z. Triethylamine as an initiator for cracking of heptane. Energy 2006, 31, 2773−2790.

Figure 12. Heat sink of aviation kerosene with different addition quantities of the PPAMAM-3 initiator.

has potential application to practical hydrocarbon fuels, especially at the temperature range of 630−720 °C.

4. CONCLUSION An amidoamine-structured macroinitiator, PAMAM, has been synthesized through Michael addition of ethylenediamine and methyl acrylate, followed by polycondensation. The molecular weight of PAMAM was controlled by adjusting the ratio of ethylenediamine to methyl acrylate. The amidation product with palmitoyl chloride, PPAMAM, as a “radical package” for the cracking of a model hydrocarbon fuel MCH and practical aviation kerosene has been checked. The significant effects on the promotion of the conversion, gas yield, and heat sink for the thermal cracking of MCH have been observed. The cracking enhancement can be achieved by tuning the molecular weight or the addition quantity of PPAMAM. It is proven that PPAMAM as a macroinitiator has a practical accelerating effect on endothermic hydrocarbon fuels. The hydrocarbon fuels that contain such a kind of additive are expected to provide high endothermic capability for hypersonic aircrafts.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.7b00751. Comparison of TGA curves of PHPG and PPAMAM (Figure S1), relative contents of liquid products from the cracking of MCH with different PPAMAM samples (Figure S2), temperature and pressure drop during the cracking of kerosene with (a) 0.03 wt % PPAMAM-3 and (b) 0.06 wt % PPAMAM-3 (Figure S3), and components from the liquid residues for the cracking of MCH at different temperatures (Table S1) (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Telephone/Fax: +86-571-88981416. E-mail: [email protected]. cn. ORCID

Yongsheng Guo: 0000-0001-7609-1891 Wenjun Fang: 0000-0002-5610-1623 G


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Energy & Fuels (21) Wang, Z.; Lin, R.; Guo, Y.; Li, G.; Fang, W.; Qin, Z. Tributylamine as an initiator for cracking of heptane. Energy Convers. Manage. 2008, 49, 1584−1594. (22) Wang, Z.; Guo, Y.; Lin, R. Effect of triethylamine on the cracking of heptane under a supercritical condition and the kinetic study on the cracking of heptane. Energy Convers. Manage. 2008, 49, 2095−2099. (23) Liu, G.; Han, Y.; Wang, L.; Zhang, X.; Mi, Z. Supercritical thermal cracking of n-dodecane in presence of several initiative additives: Products distribution and kinetics. Energy Fuels 2008, 22, 3960−3969. (24) Androvič, L.; Bartácě k, J.; Sedlák, M. Recent advances in the synthesis and applications of azo initiators. Res. Chem. Intermed. 2016, 42, 5133−5145. (25) Russell, K. E. Free radical graft polymerization and copolymerization at higher temperatures. Prog. Polym. Sci. 2002, 27, 1007−1038. (26) He, G.; Li, G.; Ying, H.; Guo, Y.; Fang, W. Palmitoyl hyperbranched polyglycerol as a nanoscale initiator for endothermic hydrocarbon fuels. Fuel 2015, 161, 295−303. (27) Han, K.; Yu, B.; Kwak, S. Hyperbranched poly(amidoamine)/ polysulfone composite membranes for Cd(II) removal from water. J. Membr. Sci. 2012, 396, 83−91. (28) Pérignon, N.; Mingotaud, A.; Marty, J.; Rico-Lattes, I.; Mingotaud, C. Chem. Mater. 2004, 16, 4856−4858. (29) Liu, C.; Gao, C.; Yan, D. Formation and stabilization in water of metal nanoparticles by a hyperbranched polymer chemically analogous to PAMAM dendrimers. Chem. Res. Chin. Univ. 2005, 21, 345−354. (30) Cao, L.; Yang, W.; Wang, C.; Fu, S. Synthesis and striking fluorescence properties of hyperbranched poly(amido amine). J. Macromol. Sci., Part A: Pure Appl.Chem. 2007, 44, 417−424. (31) Yue, L.; Wu, J.; Gong, Y.; Hou, J.; Xiong, L.; Xiao, C.; Fang, W. Heat transfer and cracking performance of endothermic hydrocarbon fuel when it cools a high temperature channel. Fuel Process. Technol. 2016, 149, 112−120. (32) Zhang, S.; Qin, J.; Bao, W.; Feng, Y.; Xie, K. Thermal management of fuel in advanced aeroengine in view of chemical recuperation. Energy 2014, 77, 201−211. (33) Yue, L.; Lu, X.; Chi, H.; Guo, Y.; Xu, L.; Fang, W.; Li, Y.; Hu, S. Heat-sink enhancement of decalin and aviation kerosene prepared as nanofluids with palladium nanoparticles. Fuel 2014, 121, 149−156. (34) Zhang, Y.; Peng, H.; Huang, W.; Zhou, Y.; Zhang, X.; Yan, D. Hyperbranched poly(amidoamine) as the stabilizer and reductant to prepare colloid silver nanoparticles in situ and their antibacterial activity. J. Phys. Chem. C 2008, 112, 2330−2336. (35) Singh, O.; Pant, K. Mechanistic modelling of the catalytic pyrolysis of methylcyclohexane. Can. J. Chem. Eng. 2003, 81, 981−992. (36) Shi, Y.; Liang, J.; Liu, L.; He, L.; Tu, C.; Guo, X.; Zhu, B.; Jin, C.; Yan, D.; Han, T.; Zhu, X. A new two−phase route to cadmium sulfide quantum dots using amphiphilic hyperbranched polymers as unimolecular nanoreactors. J. Appl. Polym. Sci. 2011, 120, 991−997.

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