Exo-tetrahydrotricyclopentadiene, a high density liquid fuel

A high density fuel for airbreathing or bi-propellant engines consisting of xo-tetrahydrotricyclopentadiene (EXO-THTC) alone and in mixtures with other high density fuels. Processes for their preparation are also disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to an improved high density liquid airbreather and 
bi-propellant engine fuels. Further, it also relates to an improved high 
density liquid airbreather fuel alone and with mixtures of other high 
density liquid airbreather fuels that allows a customizing ability to 
prepare such fuels for certain end uses. 
High density fuels for airbreathing engines are necessary for use in 
military jet aircraft and missiles in order to obtain greater efficiency. 
Greater efficiency is an ever sought after goal for such end uses in order 
to obtain greater range through higher density, that is, more energy per 
unit fuel volume. Further, a higher flash point for added safety to avoid 
premature ignition and, improved physical and chemical properties are also 
sought after goals. 
Several high density fuels are known in the art. With perhaps Cannell, U.S. 
Pat. No. 4,059,644, being one recent example of a process for preparing 
such fuels and a fuel product by such process. Cannell shows a method for 
preparing high density fuels by oligomerization of a mixture of 
cyclopentadiene dimer and methylcyclopentadiene dimer to their co-trimer 
followed by hydrogenation of the oligomerization product. And, even though 
many high density fuels are available, even greater density fuels with 
higher flash points for safer use are sought to yield a reliable high 
density fuel with greater range in a safe manner. Moreover, other existing 
fuels that may be classed as competitive are either considerably lower in 
volumetric heating value (related to missile range) or are considerably 
more expensive. 
SUMMARY OF THE INVENTION 
A new and improved high density fuel for airbreathing engines and a process 
for preparing it are illustrated in the present invention. In accordance 
with this invention, a new and improved high density fuel for airbreathing 
engines and a process for preparing it, consisting of pure 
exo-tetrahydrotricyclopentadiene (EXO-THTC) alone and in combination with 
mixtures of other high density fuels are illustrated. 
OBJECTS OF THE INVENTION 
It is an object of this invention to provide a new and improved high 
density fuel for airbreathing engines consisting of EXO-THTC. 
Another object of this invention provides new and improved high density 
fuel for airbreathing engines consisting of EXO-THTC and in combination 
with mixtures of other high density fuels. 
Still another object of this invention provides processes for preparing the 
new and improved high density fuel for airbreathing engines. 
These and other objects are accomplished in the present invention by 
providing new and improved high density fuels consisting of pure EXO-THTC 
alone and in combination with other high density fuels and, processes for 
preparing said new and improved high density fuels. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The starting materials for preparing the high density fuels of this 
invention are the readily available endo, and exo, isomers of 
tetrahydrotricyclopentadiene, melting point 48.9.degree. C., made by 
distilling the trimer fraction from the product of heating 
dicyclopentadiene in a closed system at about 170.degree. C., followed by 
catalytic hydrogenation of the reaction mixture. These starting compounds 
are readily available as products from cracking or pyrolysis of petroleum 
distillates, naphthas, kerosenes, etc.

EXAMPLE 1 
Dicyclopentadiene (C.sub.10 H.sub.12 --three rings) is added to a closed 
system and heated to a temperature of 170.degree. C. Tricyclopentadiene, 
tetracyclopentadiene and pentacyclopentadiene are obtained as the reaction 
mixture. Analyses show tricyclopentadiene having five rings and a C.sub.15 
H.sub.18 structure, tetracyclopentadiene having seven rings and a C.sub.20 
H.sub.24 structure and pentacyclopentadiene having nine rings and a 
C.sub.25 H.sub.30 structure. 
The reaction mixture is then hydrogenated in the presence of a 
nickel-on-kieselguhr catalyst and tetrahydrotricyclopentadiene, 
tetrahydrotetracyclopentadiene and tetrahydropentacyclopentadiene are 
obtained. Analyses show tetrahydrotricyclopentadiene having a structure of 
C.sub.15 H.sub.22, a mass of 202.33 and a melting point of 49.degree. C.; 
tetrahydrotetracyclopentadiene having a structure of C.sub.20 H.sub.28, a 
mass of 268.43 and a melting point of approximately 205.degree. C.; and 
tetrahydropentacyclopentadiene having a structure of C.sub.25 H.sub.34 and 
a mass of 334.53. The trimer product yield is maximized by adjusting 
temperature and heating time during cracking and condensing. The trimer 
fraction product, tetrahydrotricyclopentadiene is isomerized by treatment 
with aluminum chloride at a temperature of from 0.degree. C. to 20.degree. 
C. in a methylene chloride solvent to form 
exo-tetrahydrotricyclopentadiene having the following properties: 
formula--C.sub.15 H.sub.22 ; density--1.0376; flash point--121.degree. C.; 
viscosity (cp)--37 at 20.degree. C., 97 at 0.degree. C., and 510 at 
-20.degree. C.; freezing point--below -40.degree. C.; .DELTA.Hc, net, 
Btu/gal.--155,522, .DELTA.Hc, net, Btu/lb.--18,110, %.DELTA.Hc (Btu/gal.) 
(above JP-5)--21 and an estimated cost/lb. (car lots) $3.00. 
EXAMPLE 2 
The exo-tetrahydrotricyclopentadiene product as prepared in Example 1 is 
mixed with an exo-tetrahydrodicyclopentadiene in a sixty to forty weight 
percent ratio. The following properties were obtained upon analysis of 
this mixture: formula--60 weight % C.sub.15 H.sub.22, 40 weight % C.sub.10 
H.sub.16 ; density--0.996; flash point--above 60.degree. C.; viscosity 
(cp)--10 at 20.degree. C., 40 at -18.degree. C. and 170 at -40.degree. C.; 
freezing point--below -40.degree. C.; .DELTA.Hc, net, Btu/gal. 150,600; 
.DELTA.Hc, net, Btu/lb. 18,090; %.DELTA.Hc, Btu/gal. (above JP-5) 17 and 
cost/lb. (car lots) of about $3.00. 
EXAMPLE 3 
The product of Examples 1 and 2 are compared in this example with JP-5 
(C.sub.10 H.sub.19), exo-tetrahydrodicyclopentadiene (EXO-THDC) (C.sub.10 
H.sub.16), and RJ-5 (C.sub.14 H.sub.18.4). The results upon analyses show 
the following properties: 
______________________________________ 
JP-5 EXO--THDC RJ-5 
______________________________________ 
Formula C.sub.10 H.sub.19 
C.sub.10 H.sub.16 
C.sub.14 H.sub.18.4 
Density 0.788-0.845 
0.936 1.08 
at 20.degree. C. 
at 16.degree. C. 
at 16.degree. C. 
Flash Point (.degree.C.) 
60 (min) 56 116 
Viscosity (cp) 
14 17 2000 
at -40.degree. C. 
at -40.degree. C. 
at -40.degree. C. 
Freezing Point (.degree.C.) 
-46 (max) below -40 above -40 
Cost/lb. ($) 
0.20 3 15 
.DELTA.Hc (net) 
(Btu/gal.) 125,000 141,700 161,000 
% .DELTA.Hc (Btu/gal.) 
(above JP-5) 
0 12 23 
______________________________________ 
The pure EXO-THTC and with mixtures illustrate excellent fuels for missiles 
and aircraft that use airbreathing engines as a means of propulsion. 
Further, EXO-THTC is a highly promising, yet inexpensive bi-propellant 
fuel for rocket propulsion, having a high specific impulse and high 
propellant density wherein the stoichiometry for combustion is to CO and 
H.sub.2 O. 
It is noted from the examples that pure EXO-THTC yields the highest heating 
value possible with the exception of RJ-5 wherein the cost is about five 
times as great for substantially equivalent heating value. The "exo" fuels 
exhibit significantly higher heating values and thus greater range 
capability than the JP-5 standard heretofore and at a reasonable cost of 
about one dollar per pound in production quantities. 
Other mixtures of fuels with EXO-THTC are considered within the purview of 
applicants invention and the invention is not considered to be limited to 
the specific examples presented.