US3125852A - - Google Patents

Description

United States Patent Ofi ice 3,125,852 Patented Mar. 24-, 1964 3,125,852 MUNQPRUPELLS .lenning P. Blackwell and Richard C. Doss, Bartlesville,

Okla, assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Aug. 12, 1959, Ser. No. 833,353 18 Claims. (Cl. 6t)35.4)

This invention relates to monopropellant compositions suitable for use in rocket motors. In a further aspect, this invention relates to a method of operating such motors.

Rocket motors are operated by burning a mixture of fuel and oxidant in a combustion chamber and causing the resulting gases to be expelled through a nozzle at high velocity. Liquid propellants are preferred over solid propellants where it is necessary to vary thrust during flight. Liquid propellants are classified as bipropellants and monopropellants and the latter are either a single compound or mixtures of compounds. Monopropellant systems are advantageous in that they require only one tank, one pump, one nozzle, one fuel line, one set of controls, etc. Furthermore, no mixing or proportioning system is required.

The principal elements of a rocket motor utilizing a liquid fuel comprise a combustion chamber, exhaust nozzle, an injection system, and propellant control valves. The propellant gases are produced in the combustion chamber at pressures governed by the chemical characteristics of the propellant, its rate of consumption, and the cross-sectional area of the nozzle throat. The gases are ejected into the atmosphere through the nozzle with supersonic velocity. The function of the nozzle is to convert the pressure of the propellant gases into kinetic energy. The reaction of the discharge of the propellant gases constitute the thrust developed by the rocket motor.

In copending application Serial No. 678,243, filed August 14, 1957, by H. M. Fox, there are disclosed and claimed monopropellant compositions suitable for use in rocket motors and a method of operating such motors using said monopropellants. Broadly speaking, said monopropellant compositions comprise an amine nitrate and a suitable oxidant, for example, nitric acid. We have found that the utility of monopropellants comprising a mixture of an amine nitrate and nitric acid can be enhanced by incorporating a minor amount of a stabilizing agent as defined hereinafter in said mixture. The incorporation of said stabilizing agent increases the storage stability of said mixtures, i.e., the monopropellant mixture can be stored at higher temperatures for longer periods of time. Thus, broadly speaking, the present invention comprises the use of a stabilized mixture of an amine nitrate and nitric acid as a monopropellant.

An object of this invention is to provide an improved monopropellant composition. Another object of this invention is to provide a method of operating rocket motors using said improved monopropellant composition. Still another object of this invention is to stabilize a monopropellant composition comprising a mixture of an amine nitrate and nitric acid. Other aspects, objects, and advantages of the invention will be apparent to those skilled in the art in view of this disclosure.

Thus, according to the invention there are provided improved monopropellant compositions comprising a mixture of (l) a nitric acid oxidant, (2) an amine nitrate,

and (3) a stabilizing agent. Suitable stabilizing agents for use in the practice of the invention are ammonium nitrate, the alkali metal nitrates, ammonium perchlorate, and the alkali metal perchlorates. If desired, mixtures of said stabilizing agents can be employed.

Further according to the invention there is provided a method of operating a rocket motor which comprises the step of injecting the monopropellant compositions of the invention into the combustion chamber of a reaction motor.

Very low concentrations (less than 0.1 weight percent of the monopropellant) of the stabilizing agents of the invention can be used in the practice of the invention with beneficial results. However, it is usually desirable to use higher concentrations. preferred amount of stabilizing agent used will be within the range of 0.1 to 10 weight percent of the monopropellant. However, beneficial efifects result from the use of even smaller amounts, e.g. as low as 0.01 percent, and greater amounts, e.g. 10 to 15 percent, can be used.

Amine nitrates suitable for use in the practice of the invention include, among others, piperidine nitrate, pyridine nitrate, and amine nitrates having a structural formula wherein: each R and each R is selected from the group consisting of acyclic, alicyclic, and aromatic hydrocarbon radicals containing from 1 to 8 carbon atoms, and hydrogen, at least one R being one of said hydrocarbon radicals; and R" is selected from the group consisting of and RNR lg! L I JZ radicals wherein R is defined as above, y is an integer of from 1 to 3, z is an integer of from 1 to 3, and n is an integer of from 1 to 5 the total number of carbon atoms in the molecule does Generally speaking, the 1 not exceed 40, and the total number of amino nitrogen atoms in the molecule does not exceed 10.

Examples of amine nitrates suitable for use in the practice of the invention include, among others, the following:

Methylamine nitrate Dimethylamine nitrate Trimethylamine nitrate Ethylamine nitrate Diethylamine nitrate Triethylamine nitrate Propylamine nitrate Dipropylamine nitrate Tripropylamine nitrate Isopropylarnine nitrate Tertiary butylamine nitrate Isobutylamine nitrate Cyclopentylamine nitrate Cyclohexylamine nitrate Cyclooctylamine nitrate Dicyclohexylamine nitrate Tricyclohexylamine nitrate 4-cyclohexenylamine nitrate Phenylamine nitrate Diphenylamine nitrate Tri-n-butylamine nitrate N,N-di-n-octyl-p-tolylamine nitrate o-Methylbenzylamine nitrate N,N,N',N-tetramethylethane-1,2-diamine dinitrate N,N,N,N'-tetraethylethane-1,2-diamine dinitrate N,N,N,N'-tetra-n-octylethane-l,2-diamine dinitrate N,N,N',N'-tetramethylpropane-l,Z-diamine dinitrate N,N,N'N'-tetramethylpropane-1,3-diamine dinitrate N,N,N,N-tetraethylpropane-1,3-diamine dinitrate N,N,N',N-tetrabutylpropane-1,3-diamine dinitrate N,N,N,N'-tetrahexylpropane-1,3-diamine dinitrate N,N,N,N'-tetramethylbutane-1,4-diamine dinitrate N,N,N,N'-tetracyclohexylbutane-1,4-diamine dinitrate N,N,N,N-tetraphenylbutane-1,4-diamine dinitrate N,N,N',N-tetraphenyl-n-4-octene-1,3-diamine dinitrate N,N,N,N'-tetracyclohexylhexane-2,6-diamine dinitrate N,N,N',N'-tetramethyl-2-butenel ,4-diamine dinitrate N,N,N,N--tetramethyl-2-butyne-1,4-diamine dinitrate N,N,N',N'-tetramethyl-2-0ctene-4,S-diamine dinitrate N-phenyl-N-n-octylethane-1,2-diamine dinitrate N,N,N',N-tetra-n-0ctyloctane l,Z-diamine dinitrate N,N-di(2-ethylhexyl)-2-butene-1,4-diamine dinitrate N,N,N,N'-tetraethyl-4-octyne-1,3-diamine dinitrate Bis-(N,N-dimethylaminoethyl)ether dinitrate Bis- (N,N-di-n-octylamino-n-butyl) ether dinitrate N-cyclohexylaminopropyl N-phenylaminopropyl ether dinitrate N-Z-ethylphenylaminoethyl amino-n-butyl ether dinitrate Bis (amino-n-butyl ether dinitrate Bis(N,N-di-2-ethylcyclohexylamino-n-butyl)thioether dinitrate Bis(aminoethyl)thioether dinitrate Bis(N,N-dimethylaminoethyl)thioether dinitrate N,N,N,N-tetramethyl-1,3-diamine-2-propanol dinitrate N,N,N,N-tetraethyl-1,9-diamino--nonanol dinitrate N,N,N'-tri-(2-ethylcyclohexyl) -.1,4-diamino-2-butanol dinitrate N,N,N',N',N"-pentamethyldiethylenetriamine trinitrate N,N',N"-tricyclohexyldiethylenetriamine dinitrate N,N,N-tri-n-octyldiethylenetriamine trinitrate N,N,N,N',N",N-hexamethylpropane-1,2,3-triamine trinitrate N ,N ,N ,N ,N ,N ,N ,N ,N ,N -decamethylpentanel,2,3,4,5-pentamine pentanitrate N ,N ,N ,N ,N -pentaethyltetraethylenepentamine pentanitrate N-ethyl-Z-butynylamine nitrate N-methyl-Z-butynylamine nitrate Di(2-butynyl)amine nitrate N-hexyl-Z-propynylamine nitrate N-propyl-3-hexynylamine nitrate As used herein the term alkali metal nitrates includes sodium nitrate, potassium nitrate, lithium nitrate, rubidium nitrate, and cesium nitrate. The term alkali metal erchlorates includes sodium perchlorate, potassium perchlorate, lithium perchlorate, rubidium perchlorate and cesium perchlorate.

Since water tends to retard combustion of the acid with the fuel, the nitric acid is preferably substantially free of water. Thus, the presently most preferred oxidant is anhydrous nitric acid. However, other more dilute nitric acids can be used in the practice of the invention. White fuming nitric acids and red fuming nitric acids of varying concentrations are available commercially, and all are useful in the practice of this invention. White fuming nitric acid usually contains about to 99 weight percent HNO from 0 to 2 weight percent N0 and up to about 10 weight percent water. Red fuming nitric acid usually contains about 70 to 90 weight percent HNO from 2 to 25 weight percent N0 and up to about 10 weight percent water. Of course, mixtures of the above described acids can be employed to give an acid having an intermediate composition, and all are useful in the practice of this invention. Thus, it has been found that nitric acids of all types containing at least about 70 Weight percent HNO are useful as an oxidant in the practice of the invention.

The monopropellants used in the practice of the present invention are preferably near stoichiometric mixtures of the nitric acid and the amine nitrate. The ratio of fuel component to oxidant can be in the range of 0.75 to 1.25 times that of the stoichiometric amount. A slightly fuel-rich mixture is usually required to give optimum rocket motor performance.

The monopropellants of the invention can be prepared by adding the stabilizer salt to the fluid mixture compris ing the amine nitrate and the nitric acid. It is also within the scope of the invention to employ any other suitable order of mixing said ingredients, e.g., adding the stabilizer salt to the nitric acid and then adding the amine nitrate to the resulting mixture. In preparing said monopropellants of the invention it is preferred that the mixing of said ingredients be carried out at temperatures below 50 C., e.g., 0 to 30 C.

Amine nitrates can be prepared by several methods. One method is to react an amine with nitric acid. Another method which can be employed is to form a salt of the amine, such as hydrochloride or an acetate, and then react the amine salt with nitric acid.

EXAMPLE I A number of runs were made in which polyamine compounds were reacted with nitric acid to form the corresponding amine nitrates. These runs were carried out according to the following procedure.

An amount of the pure polyamine compound was charged to a flask, after which an amount of aqueous nitric acid was charged slowly to said flask by means of a dropping funnel. The temperature of the flask contents was maintained within the range of from O to 10 C. by means of an ice bath and by adjusting the rate of addition of the nitric acid to keep the temperature of the reaction mass below 10 C. During the addition of the nitric acid, the flask contents were stirred vigorously. After the nitric acid had been charged, the flask contents were stirred for several minutes to insure complete reaction, after which said fiask contents were poured into approximately 5 times its volume of chilled acetone (10 to 25 C.). The amine nitrate precipitated out. This precipitate was recovered by filtration, washed with cold acetone or ether, and dried in a vacuum desiccator at room temperature. The melting point and stability of the amine nitrate were then determined. None of the amine nitrates which were prepared were found to be shock sensitive to the blow of a hammer. The results of these runs are given below in Table I.

Table 1 Run No. Amine Charged N, ,N-tetramethylpropane-1,2-diamine. ,N-tetramethylbutane-1,3-diamine ,N-tetramethyibutane-1,3-diamine ,N-tetramethyl-2-butyne-1,4-diamine ,N N ,N'-tetramethylethane-1,2-diamine -dimethylethy1ene-1,2-diamme ,N',N-tetramethyl-2-butene-1 4-diamine N ,N-tetraethylpropane-LB-diamine 1 In this run, the amine was dissolved in an equal volume of acetone.

EXAMPLE II Monopropellant mixtures were prepared with anhydrous nitric acid obtained by distillation of red fuming nitric acid in the presence of sulfuric acid. Analyses of typical batches of the distilled acid showed that the product contained more than 99.8 weight percent HNO and less than 0.2 weight percent oxides of nitrogen.

Said monopropellants were prepared by dissolving an amine salt in separate portions of freshly prepared acid and then incorporating a stabilizing agent of the invention in the solution. The storage stability of the monopropellants thus prepared was measured by the following procedure.

A small glass tube, constructed from fii-inch I.D. glass pipe which will withstand a pressure greater than 1000 p.s.i.g. is filled about two-thirds full (about 6 ml.) with the monopropellant to be tested. Said tube is fitted with a safety head containing a blowout disk which will rupture at about 200 p.s.i. pressure. The small glass bomb is then placed in a constant temperature bath containing cold Water and is connected to a pressure recorder and to a supply of compressed nitrogen gas. The pressure in said bomb is then increased to about 75 p.s.i.g. with nitrogen to check the system for leaks and, after checking, the pressure in said bomb is reduced to 20 p.s.i.g. The temperature in the constant temperature bath, which can be regulated to maintain a temperature of 200 F., is increased and the time at which a temperature of 200 F. is reached is taken as the start of the test. The test is terminated when the pressure in said bomb exceeds 100 p.s.i.g., or when the blow-out disk is ruptured (the pressure rise is often rapid after 100 p.s.i.g. is reached). The storage life of the monopropellant being tested is recorded as the time necessary for the pressure in said bomb to increase from 20 to 100 ps.i.g. at a temperature of 200 F.

Table II given below shows the weight percent of amine salt and of stabilizer salt which was mixed with the. anhydrous nitric acid to prepare the monopropellants. is approximately the stoichiometric ratio, i.e. the acid is sufficient to oxidize the amine salt completely to carbon dioxide, nitrogen, and water.

Comparison of runs 1 and 2 shows that the storage.

stability of the monopropellant is increased from 22.2 to 53 hours by use of ammonium nitrate. Comparison of run 3 with runs 4 and 5 shows that the storage stability of the monopropellant was increased from 0.7 to 17.25 and from 0.7 to 13.7 hours by use of ammonium perchlorate and ammonium nitrate, respectively. These runs illustrate the benefits which are obtained in the practice of the invention.

The ratio of amine salt to acid in these mixtures.

Percent Yield of Mols Ni- Aqueous Mols Amine M.P. of trio Acid Acid (Wt. Amine Nitrate, Amine N1- Charged Percent Charged Percent trate C HNOa) 0.606 40. 5 0. 275 96. 3 220-221 O. 606 33. 4 0.275 92. 3 177-179 0. 606 40. 5 0.275 95.0 115-116 1.19 70. O 0. 578 97.0 115-116 0.6 41. 0. 285 96. 4 145-146 0. 6 41. 0 0.285 76. 142-143 0. 43 70.0 0.208 98. 7 173-174 0. 4O 70. 0 0. 183 94. 3 173-174 0.51 70. 0 1 0.25 72.0 88-93 0. 51 70. 0 0. 85. 2 120-124. 0.51 70. 0 0. 25 91. 2 113-114 '0. 70 70. 0 0. 23 80. 0 162-163 0. 53 70. 0 0. 173 65. 3 104-106 0. 505 60. 0 0. 5 not 125 recorded 0. 44 70. 0 0. 21 179-180 0. 42 70. 0 0.2 97. 0 157. 5-159. 5

Table II 5 COMPOSITION OF MONOPROPELLANTS AND STORAGE STABILITY Amine Wt. Per- Storage Nitrate in cent Stahi- Stability, Run Amine Monopro- Stabilizer lizer in hr. at 200 No. Nitrate pellant, Monopro- F. Wt. Perpellant cent A 29.3 0 0 22. 2 A 27.8 NH NO3 7.1 b 53 13 36 0 0 0. 7 B 35. 8 NH4C104. 1 a 1. 7 17. 25 B 35.8 NHiNo3 1.1 13. 7

' Solution was saturated with the salt at room temperature (2025 0.).

EXAMPLE III Ammonium nitrate in the amount of 0.15 gram was dissolved in 14.85 grams (9.9 m1.) of essentially anhydrous nitric acid (prepared as described in Example II above). The storage stability at 200 F. of said solution was determined in accordance with the procedure described in Example 11 above and was found to be 2.2 hours. A control run made on said anhydrous acid containing no ammonium nitrate showed that the storage stabilityat 200 F. of said acid containing no ammonium nitrate was 28 hours.

Thus ammonium nitrate does not stabilize nitric acid but surprisingly will stabilize the monopropellants comprising an amine nitrate dissolved in nitric acid.

-It is to be realized that the storage stability test at 200 F. is a very severe test. The stabilizing agents of the invention are effective for increasing the storage stability at temperatures lower than 200 F. Sincethe monopropellants of the invention may possibly be used or stored under desert conditions, 200 F. has been chosen as a reasonable, yet severe, maximum temperature at which to measure storage stability.

Various modifications of the invention can be made, or followed, by those skilled in the art in view of the above disclosure. Such modifications are believed to be within the spirit and scope of the invention.

We claim:

1. A monopropellant composition consisting essentially of a mixture of (1) a nitric acid oxidant containing at least weight percent HNO;.,, (2) an amine nitrate selected from the group consisting of pyridine nitrate, piperidine nitrate, and amine nitrates characterized by a formula selected from the group consisting of wherein: each R and each R is selected from the group consisting of acyclic, alicyclic, and aromatic hydrocarbon radicals containing from 1 to 8 carbon atoms, and hydrogen, at least one R being one of said hydrocarbon radicals; and R" is selected from the group consisting of (a) alkylene, alkenylene, and alkynylene hydrocarbon radicals containing from 2 to 8 carbon atoms wherein the carbon atoms attached to the nitrogen atoms are attached to adjoining carbon atoms by single valence bonds, and (b) "'X-]- R"' radicals wherein each R'" is an alkylene radical containing from 2 to 4 carbon atoms, and each X is selected from the group consisting of oxygen, sulfur, and

radicals wherein R is defined as above, y is an integer of from 1 to 3, z is an integer of from 1 to 3; and n is an integer of from 1 to 5; the total number of carbon atoms in the molecule does not exceed 40, and the total number of amino nitrogen atoms in the molecule does not exceed 10, and (3) a stabilizing agent selected from the group consisting of ammonium nitrate, the alkali metal nitrates, ammonium per chlorate, the alkali metal perchlorates, and mixtures thereof; the ratio of said amine nitrate to said nitric acid oxidant in said mixture being withn the range of 0.75 to 1.25 times that of the stoichiometric amount, and said stabilizing agent being present in an amount within the range of 0.01 to 15 weight percent of said mixture.

2. The composition of claim 1 wherein said stabilizing agent is present in an amount within the range of 0.1 to weight percent of said nitric acid oxidant.

3. The composition of claim 1 wherein said stabilizing agent is ammonium nitrate.

4. The composition of claim 1 wherein said stabilizing agent is sodium nitrate.

5. The composition of claim 1 wherein said stabilizing agent is potassium nitrate.

6. The composition of claim 3 wherein said amine nitrate is N,N,N',N'-tetraethylpropane-1,3-diamine dinitrate.

7. The composition of claim 3 wherein said amine nitrate is N,N,N',N'-tetramethylpropane-1,3-diamine dinitrate.

8. The composition of claim 1 wherein said stabilizing agent is ammonium perchlorate.

9. The composition of claim 1 wherein said stabilizing agent is sodium perchlorate.

10. The composition of claim 1 wherein said stabilizing agent is potassium perchlorate.

11. The composition of claim 8 wherein said amine nitrate is N,N,N,N'-tetraethylpropane-1,3-diamine dinitrate.

12. The composition of claim 8 wherein said amine ni- 8 trate is N,N,N',N-tetramethylpropane-1,3-diamine dinitrate.

13. In the method for development of thrust by the combustion of a monopropellant in the combustion chamber of a reaction motor, the step comprising injecting into said combustion chamber a mixture of (1) a nitric acid oxidant containing at least 70 weight percent HNO;,, (2) an amine nitrate selected from the group consisting of pyridine nitrate, piperidine nitrate, and amine nitrates characterized by a formula selected from the group consisting of wherein: each R and each R is selected from the group consisting of acyclic, alicyclic, and aromatic hydrocarbon radicals containing from 1 to 8 carbon atoms, and hydrogen, at least one R being one of said hydrocarbon radicals; and R" is selected from the group consisting of (a) alkylene, alkenylene, and alkynylene hydrocarbon radicals containing from 2 to 8 carbon atoms wherein the carbon atoms attached to the nitrogen atoms are attached to adjoining carbon atoms by single valence bonds, and (b) {-R"X-} R"'- radicals wherein each R is an alkylene radical containing from 2 to 4 carbon atoms, and each X is selected from the group consisting of oxygen, sulfur, and

radicals wherein R is defined as above, y is an integer of from 1 to 3, z is an integer of from 1 to 3, and n is an integer of from 1 to 5; the total number of carbon atoms in the molecule does not exceed 40, and the total number of amino nitrogen atoms in the molecule does not exceed 10, and (3) a stabilizing agent selected from the group consisting of ammonium nitrate, the alkali metal nitrates, ammonium perchlorate, the alkali metal perchlorates, and mixtures thereof; the ratio of said amine nitrate to said nitric acid oxidant in said mixture being within the range of 0.75 to 1.25 times that of the stoichiometric amounts, and said stabilizing agent being present in an amount within the range of 0.01 to 15 weight percent of said mixture.

14. The method of claim 13 wherein said stabilizing agent is ammonium nitrate.

15. The method of claim 13 wherein said stabilizing agent is ammonium perchlorate.

16. The method of claim 14 wherein said amine nitrate is N,N,N',N'-tetraethylpropane-1,3-diamine dinitrate. 17. The method of claim 15 wherein said amine nitrate is N,N,N',N'-tetramethylpropane-1,3-diamine dinitrate.

18. The method of claim 13 wherein said stabilizing agent is present in an amount within the range of 0.1 to 10 percent by weight of said mixture.

References Cited in the file of this patent UNITED STATES PATENTS 2,951,335 Stengel Sept. 6, 1960

Claims (1)

13. IN THE METHOD FOR DEVELOPMENTG OF THRUST BY THE COMBUSTION OF A MONOPROPELLANT IN THE COMBUSTION CHAMBER, OF A REACTION MOTOR, THE STEP COMPRISING INJECTING INTO SAID COMBUSTION CHAMBER A MIXTURE OF (1) A NITRIC ACID OXIDANT CONTAINING AT LEAST 70 WEIGHT PERCENT HNO3, (2) AN AMINE NITRATE SELECTED FROM THE GROUP CONSISTING OF PYRIDINE NITRATE, PIPERIDINE NITRATE, AND AMINE NITRATES CHARACTERIZED BY A FORMULA SELECTED FROM THE GROUP CONSISTING OF