A solar-energy-derived strained hydrocarbon as an energetic hypergolic fuel

Article abstract of DOI:10.1039/c4ra08868a

Quadricyclane (QC), synthesized from photoisomerization and commonly used for solar-energy conversion and storage, is found to be an excellent hypergolic fuel. The ignition delay time of QC-N₂O₄ is 29 ms, which is decreased to 18 ms by addition of boron nanoparticles. Importantly, quadricyclane has 18.9% higher specific impulsion than currently used but dangerous dimethylhydrazine. This journal is

Full text of DOI:10.1039/c4ra08868a

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A solar-energy-derived strained hydrocarbon as an
energetic hypergolic fuel†
Cite this: RSC Adv., 2014, 4, 50998
a
a
a
ab
Lun Pan,‡ab Ren Feng,‡ Hao Peng, Xiu-tian-feng E, Ji-Jun Zou,
Li Wangab
*
and Xiangwen Zhangab
Received 19th August 2014
Accepted 6th October 2014
DOI: 10.1039/c4ra08868a
www.rsc.org/advances
Quadricyclane (QC), synthesized from photoisomerization and hydrides.2,4 However, many energetic ILs are still costly to
commonly used for solar-energy conversion and storage, is found to synthesize and have difficulty in scale up. Therefore, searching
be an excellent hypergolic fuel. The ignition delay time of QC–N2O4 is for easily scale-up and relatively green hypergolic fuels is still
29 ms, which is decreased to 18 ms by addition of boron nanoparticles. necessary for the future practical applications.
Importantly, quadricyclane has 18.9% higher specific impulsion than
Hydrocarbons have the advantages of stability and safety, and
are easy to handle, transport and store.1a,5 But most of them are
not hypergolic and have low specic impulse, compared with
hydrazine-based fuels. Only a few hydrocarbons, like ethyl-
idenenorbornene (EN, density of 0.793 g cmꢀ3), are reported to
be hypergolic.6 Quadricyclane (tetracyclo[3.2.0.02,7.04,6]heptane,
QC), a strained and caged hydrocarbon with high density of
0.982 g mLꢀ1,7 is a colorless and ammable liquid with a boiling
point of 108 ꢁC and a freezing point below ꢀ40 ꢁC. QC molecule
contains two three-membered ring, one four-membered ring
and two ve-membered ring structures (Scheme 1). The bond
angles in the three-membered ring and four-membered ring are
in the range of 59.9–90.0ꢁ (Scheme 1), much smaller than the
normal 109.5ꢁ. With such strained and caged structure, QC
possesses energy of 44.35 MJ kgꢀ1, which is much higher than
the currently used high-density jet fuel JP-10 (exo-tricyclo
[5.2.1.02,6] decane, 42.10 MJ kgꢀ1) (Scheme 1). More importantly,
currently used but dangerous dimethylhydrazine.
Hypergolic liquid propellants are widely used in rockets, satel-
lites and spaceships because of their simplicity and excellent
reliability.1 Hypergolic fuels are chemical compounds or species
that can be automatically ignited under ambient conditions
upon contacting with an oxidant. To realize hypergolicity, both
the fuel and oxidant have to be highly active. The ignition delay
(ID), namely the period between the contacting of fuel/oxidant
and the presence of the rst ame, is the most important
parameter in evaluating the potential of a hypergolic fuel.2 In
currently used hypergolic bipropellants, the fuels are hydrazine
and its methylated derivatives (mostly unsymmetrical dimeth-
ylhydrazine, UDMH) and the oxidants are dinitrogen tetroxide
(N2O4) and white fuming nitric acid (WFNA).1,3 Unfortunately,
hydrazine and its derivatives are very difficult to handle because
they are extremely toxic and have a high risk of detonation and
explosion.3
Recently, many efforts have been devoted to develop envi-
ronmentally benign hypergolic fuels. One promising alternative
is energetic ionic liquids (ILs) that composed by highly active
cations and/or anions such as dicyanoborate and metal
aKey Laboratory for Green Chemical Technology of the Ministry of Education, School of
Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China.
E-mail: jj_zou@tju.edu.cn; Fax: +86-22-27892340; Tel: +86-22-27892340
bCollaborative Innovative Center of Chemical Science and Engineering (Tianjin),
Tianjin 300072, China
† Electronic supplementary information (ESI) available: Detailed procedure of
experiment, the results of ignition process and the calculated procedure of heat
of formation, heat of combustion, specic impulsion and volumetric specic
impulsion for the fuels. See DOI: 10.1039/c4ra08868a
Scheme 1 Molecular structure of QC from different views (top),
photoisomerization of NBD to QC and properties of QC (below).
‡ These authors contributed equally to this work.
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this strained molecule is endowed with high chemical reactivity time of QC–WFNA binary system is 98 ms (Table 1). In partic-
than the norbornene unit of EN, suggesting a possibility of ular, the ID time of QC–N2O4 binary system is only 29 ms, this
hypergolity.
The major way to synthesize QC is the photoisomerization time is approximately 50 ms for the practical applications.1,2a
intermolecular [2 + 2] cycloaddition of norbornadiene (NBD),7
Energetic colloidal particles have been widely studied as the
superior hypergolicity is very encouraging because the target ID
see Scheme 1, which has been regarded as a promising strategy additive of fuels to increase the combustion energy.1e,8 In
for solar-energy conversion and storage for a long time.7 particular, boron (B) particles are reported to enhance the
Recently, the potential application of QC in propulsion has been
recognized due to its high density and high containing energy.
Although many researchers consider QC as the promising fuel,
Table 1 The ID time of QC-based hypergolic liquid bipropellant
the hypergolicity of QC has not been discovered. Here for the
rst time, we report that solar-energy-derived QC is an excellent
hypergolic fuel with short ID time and high impulse, which is
promising for practical applications.
Entry
Fuela
Oxidant
ID timeb (ms)
1
2
3
4
5
6
QC
QC
QC + C
QC + B
QC + C
QC + B
N2O4
WFNA
N2O4
N2O4
WFNA
WFNA
29
98
27
18
73
68
QC with purity of 99.0% was synthesized via the photoin-
duced [2 + 2] intermolecular cycloaddition of NBD in the pres-
ence of photosensitizer [4,40-bis(diethylamino)benzophenone].
The photoreaction was conducted in a closed cylindrical quartz
vessel with inner irradiation. A 1000 W xenon lamp-based solar
simulator was positioned inside the vessel and cooled by
circulating water jacket. A mixture containing 2 L NBD and 10 g
photosensitizer was suspended under magnetic stirring. Aer
24 h photoreaction, the product was transferred to a rotatory
evaporator to get QC (99.0%) with yield of 96.2%. Its molecular
structure is conrmed by 1H and 13C NMR [1H NMR (CDCl3, 400
MHz), d: 2.02, dd, J ¼ 1.5 Hz, 2H; 1.49, d, J ¼ 4.4 Hz, 4H; 1.35, m,
2H; 13C NMR (101 MHz, CDCl3), d: 32.1, 23.1, 14.8].
a
Abbreviations: QC, quadricyclane; C, carbon; B, boron. b As measured
from the time the drop hits the oxidizer until the rst sign of a ame.
ꢁ
Hypergolic drop tests were conducted at ca. 10 C to deter-
mine the ignition delay. A droplet (ca. 0.05 mL) of QC was
injected in a vial containing oxidizer in large excess (0.5 mL of
98% WFNA or N2O4). The ID time was determined using a
OLYMPUS I-SPEED TR high speed camera at 1000 frames per
second. The extremely powerful and intense single ame
appears upon the contacting of fuel and oxidant (Fig. 1). The ID
Fig. 2 QC suspensions containing well dispersed 0.25 wt% carbon (C)
and boron (B) nanoparticles.
Fig. 3 Ignition process of QC suspension with N2O4 recorded by
Fig. 1 Ignition process of QC–N2O4 and QC–WFNA recorded by high-speed camera. The fuel droplets are marked by green circles. The
high-speed camera. The fuel droplets are marked by green circles.
amount of B or C nanoparticles in QC is 0.25 wt%.
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a
Table 2 Calculated propulsion properties of QC, UDMH and EN with stoichiometric amount of N2O4
Fuel
QC
UDMH
EN
Heat of formation of
307.8 (ref. 6a and 7c)
84.0 (ref. 13)
102.3 (ref. 6a)
ꢀ43.01
fuel (kJ molꢀ1
)
Heat of combustion of
ꢀ44.35
ꢀ31.02
fuel (kJ gꢀ1
)
Mol ratio of fuel/N2O4
2/9
1/2
1/6
Density of fuel (g mLꢀ1
)
0.982
1.32
305
0.793
1.14
297
0.896
1.30
298
Density of propellant (g mLꢀ1
Specic impulsion (s)
Volumetric specic
)
402
337
388
impulsion (kg s Lꢀ1
)
a
The detailed calculated procedures are shown in ESI.
hypergolic performance of some ILs.8a,9 Herein we explored B ms. QC–N2O4 shows 18.9% higher volumetric specic impul-
(averaged size: 30 nm) and carbon (C, averaged size: 35 nm) sion than UDMH–N2O4. This hydrocarbon is easy to synthesize
nanoparticles as both energetic and ignition additives to on large scale, safe to handle, transport and store, and therefore
enhance the hypergolic performance of QC. Surface modica- is a promising relatively benign and energetic hypergolic fuel.
tion using surfactant can stabilize the particles in hydrocarbon This work gives the hint that high-strained and caged hydro-
fuels. As shown in Fig. 2, the TOPO-modied nanoparticles can carbons with high energy, low vapor pressure and low risk may
be well dispersed in QC aer sonication. The addition of NPs be serve as new hypergolic liquid fuel to substitute currently
has no effects on the viscosity of fuel (1.6 mPa s and 1.7 mPa s used hydrazine-based fuels.
for QC and QC + 0.25 wt% NPs, respectively). Fuels containing
NPs show signicantly reduced ID time (Fig. 3, S1 in ESI†). As
shown in Table 1, C particles make the ID time decreased to 27
Acknowledgements
ms and 73 ms for QC–N2O4 and QC–WFNA systems, respec-
tively. Surprisingly, in the presence of B particles, the ID time is
decreased from 29 ms to 18 ms for N2O4 and from 98 ms to 68
ms for WFNA, respectively.
The authors appreciate the supports from the National Natural
Science Foundation of China (21222607) and the Program for
New Century Excellent Talents in Universities (NCET-09-0594).
L. Pan thanks the support from the Scholarship Award for
Excellent Doctoral Student granted by Ministry of Education of
China (2011).
Considering the excellent hypergolicity of QC–N2O4, we
further estimated the propulsion performance using the
method reported in literature.6 As shown in Table 2, the
computed specic impulse of QC is higher than UDMH and EN
due to the high heat of combustion, attributed to the existence
of extra energy embedded in the strained cages. Moreover, the
density of QC is much higher than UDMH, so its volumetric
specic impulsion, that is specically important for volume
limited aerospace vehicles, is 18.9% higher than that of UDMH.
Although the QC oral acute toxicity is determined as
moderated class, no deaths occurred for rabbits following 24 h
dermal exposure to the EPA limit dose.10 This indicates that the
major risk comes from oral ingestion rather than dermal
exposure. Besides, the vapor pressure of QC (4.5 kPa at 29 ꢁC)11
is much lower than that of UDMH (22.3 kPa at 25 ꢁC),12 therefore
this presents a lower ash exposition risk and harmfulness in
the applications. At present stage, the price of QC may be
double of UDMH. But it is still promising when consider the
promotion in propulsion and better safety.
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In summary, we explored a new kind of hypergolic liquid fuel
based on strained QC. The ID time of QC–N2O4 system is 29 ms,
satisfying the requirement of practical applications. The addi-
tion of boron nanoparticles further decreases the ID time to 18
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