US3396537A - Hybrid fuel ii - Google Patents

Description

United States Patent 3,396,537 HYBRID FUEL II Kenneth J. Lissant and Thomas J. Bellos, St. Louis, Mo., assignors to Petrolite Corporation, Wilmington, Del., a corporation of Delaware N0 Drawing. Filed Aug. 14, 1963, Ser. No. 302,001 25 Claims. (Cl. 60--216) This invention relates to emulsions of hydrazine and hydrazine derivatives, rocket and jet fuels prepared therefrom, and to the use thereof in rocket and jet propulsion. More particularly this invention relates to such fuels having the characteristics of both liquid and solid fuels (i.e. they are hybrid solid-liquid fuels). Still more particularly this invention relates to hybrid solid-liquid fuels which are especially prepared emulsions of hydrazine or hydrazine derivatives and a second combustible and/or volatile material which is immiscible with said first combustible material, said emulsion being prepared by means of an emulsifying agent capable of forming an emulsion which has the characteristics of a solid fuel when at rest and a liquid fuel when force is exerted on it, such as by the shear of pumping, mixing, etc. This invention also relates to said hybrid fuels containing certain finely divided solids suspended therein, such as for example metals, salts, etc.

In the field of rocket and jet fuel propulsion two general types of fuels are usedsolid fuels and liquid fuels. Both types have intrinsic advantages and disadvantages. For example it is highly advantageous to combine the storability and stability of solid fuels with the higher specific impulse and controllability of liquid fuels. The hybrid fuels of this invention provide an improved fuel composition combining many advantages of both types of fuel.

Liquid fuels are used in combination with oxidizing agents, such as for example liquid oxygen (LOX), red fuming nitric acid, etc. While these combinations yield high specific impulse, it is also known that if the density of the fuel is increased such as by the use of certain combustible metals or metal compounds suspended in the fuels, and the solid-liquid mixture is used in conjunction with the appropriate oxidizing agent, the combination yields a much higher specific impulse. In practice the use of such combinations presents problems since the solid must be kept uniformly suspended in the liquid to obtain consistent performance. Attempts have been made to suspend the solids in the liquids by increasing the viscosity of the liquids, for example by the use of polymeric materials, but it was soon discovered that simply increasing the Newtonian viscosity of the liquid does not solve the problem since the settling of the solid was only slowed and not actually prevented. It was found necessary to produce gels or thixotropic compositions which under low shear behave like elastic solids and yet under high shear flow freely enough to be pumpable.

However, the use of gels only partly solved the problem. If a gel was prepared which is stiff enough to suspend the solids it was often too thick to pump. If a gelling agent was subjected to high shear in pumping or in manufacture, it often permanently lost enough of its gelling action so that it allowed the solids to separate. Since gels are sticky, they do not flow from the fuel tanks cleanly, as much as a hold up having been experienced. In addition, materials used to produce gels are usually difiicult to dissolve in the liquid fuel and gels sometimes become tender on ageing. Furthermore the reproducibility of properties from batch to batch in gelled compositions is often poor.

This invention produces a stiffened liquid fuel by an entirely different mechanism. In the practice of this in- 3,395,537 Patented Aug. 13, 1968 vention an emulsion is made of the principal liquid fuel in a small amount of a second combustible or volatile, immiscible liquid. These emulsions are characterized by having a very low volume percent of external phase, and are highly thixotropic. Although they appear to be elastic solids, having much the consistency of a gelatin gel when at rest, they can however be easily pumped under low pump pressures. Thus, they can be considered to be hybrid fuels.

The hybrid fuels of this invention are high internal phase-low external phase emulsions. The internal phase contains hydrazine, a hydrazine derivative, a mixture of hydrazine and/or its derivatives, or a mixture of hydrazine and/ or its derivatives with other compatible liquids, with or without the addition of an appropriate solid admixed therein. The external phase consists of any immiscible oily phase liquid, that is non-reactive with the internal fuel phase. These emulsions are prepared with an appropriate emulsifier.

The internal phase of the emulsion of this invention may be primarily hydrazine or may be a derivative of hydrazine such as monomethylhydrazine, monoethylhydrazine, unsymmetrical dimethylhydrazine, etc. Mixtures of hydrazine with one or more of its derivatives may also be used. Other miscible fuels such as methyl or ethyl alcohol may also be incorporated. The particular mixture or pure fuel chosen for a given fuel will be dictated by many considerations such as cost, availability, density, melting or boiling point, potential specific impulse with the oxidizer selected, and other considerations. It may be desirable to use an emulsion fuel without solid loading simply to take advantage of the physical properties of the combination or it may be desirable to incorporate finely divided solids into the composition to increase the density of the fuel or to increase specific impulse.

Hydrazine as employed herein in the claims includes hydrazine itself as well as hydrazine compositions and derivatives, for example, those of the formula where the Rs which may be the same or different are hydrogen or a substituted group, for example an alkyl group, but preferably methyl or ethyl.

Thus, the emulsion has two phases, an external oily phase and an internal hydrazine phase. Each phase must be combustible or volatile when employed as a jet or rocket fuel. The two phases must be immiscible, and mutually nonreactive under conditions of transport and storage.

A minor but sufiicient amount of emulsifier is added to form the emulsion, for example from 0.055% by volume such as from 0.l4%, but preferably from 0.23% of emulsifier, based on total volume of emulsion.

The emulsions of this invention are hydrazine-in-oil emulsions in which hydrazine is the internal phase of the emulsion. They contain, for example, at least hydrazine by volume of the emulsion, such as at least preferably at least but can contain at least by volume or greater, and the oily phase is the external phase of the emulsion. Thus, hydrazine comprises a major proportion of the emulsion and the oily phase a minor proportion of the emulsion. Since it is desirable in preparing hydrazine fuels to have the composition contain as much hydrazine as possible consistent with forming an emulsion having the desired properties, the composition employed generally contains at least 9095% hydrazine.

By employing a suitable emulsifier it is also possible to prepare an emulsion in which the hydrocarbon is a major part of the emulsion and hydrazine is a minor part of the emulsion. Thus the hydrocarbon can also comprise the internal phase and hydrazine the external phase of the emulsion so that the ratios stated above could apply inversely to the hydrazine and hydrocarbon.

In summary, a wide volume ratio of emulsion phases can be employed so that the ratios of hydrazine to hydrocarbon can range from 98:2 to 2:98. The emulsion can be a hydrazine-in-hydrocarbon emulsion as well as bydrocarbon-in-hydrazine emulsion. However, in jet and rocket propulsion it is generally desirable to have as high a hydrazine ratio as possible and to have hydrazine in the internal phase and hydrocarbon or another oily material in the external phase of the emulsion.

Practically, the choice of a liquid hydrocarbon in the oily phase for use in a rocket or jet engine is based largely on availability and cost, and on this basis a petroleum hydrocarbon in the gasoline-kerosene range is the preferred material. Aliphatic hydrocarbons from petroleum (gasoline, or kerosene) are the cheapest and most abundant liquid fuels for rockets. The simpler aromatic hydrocarbons (benzene, toluene) are also abundant, have higher densities, and in general give more thermal energy per pound on combustion so that they produce somewhat more thrust per pound of fuel. Aliphatic hydrocarbons, from the standpoint of structure and heat of combustion, could be expected not to differ appreciably one from another in the energy they could contribute to a jet motor. Unsaturated hydrocarbons which are endothermic (that is, which have negative heats of formation) will, of course, liberate this heat during combustion and contribute to higher exhaust velocities. The highest calculated value of specific impulse for a hydrocarbon burned with oxygen is for diacetylene, HCECCECH, which gives 271 pound-seconds per pound. This is the highest that can be expected from any carbonaceous fuel burned with liquid oxygen at 300 p.s.i.a. A more usual value (that for normal octane) is about 240 pound-seconds per pound.

The term oily" phase as herein employed, is intended to include a vast number of substances, both natural and artificial, possessing widely different physical properties and chemical structure. All of the substances included within this term are practically insoluble in water, possess a characteristic greasy touch and have a low surface tension. These include the animal oils of both land and sea animals; vegetable oils, both drying and non-drying; petroleum or minerals oils of various classes, including those of open chain hydrocarbons, cyclic hydrocarbons or cycloparafiins, with or without the presence of solid paraffins and asphalts and various complex compounds, and which may or may not contain sulphur or nitrogenous bodies or may or may not be halogenated, resin oils and wood distillates including the distillates of turpentine, rosin spirits, pine oil, and acetone oil; various oils, obtained from petroleum products, such as gasolenes, naphthas, gas fuel, lubricating and heavier oils; coal distillate, including benzene, toluene, xylene, solvent naphtha, creosote oil and anthracene oil and ethereal oils.

Furthermore, the presence of the usual amounts of anti-knock compounds or other conventional fuel additives in the oil does not adversely affect the usefulness of the oil for our purposes.

We have also found that the choice of oily phase materials is not limited to hydrocarbons since esters such as dibutyl phthalate, diethylmaleate, tricresylphosphate, acrylic and methacrylic esters, natural esters, and the like have been employed by us successfully in the prepartion of useful emulsions. Tung oil, oiticica oil, castor oil, linseed oil, poppyseed oil, soyabean oil, animal and vegetable oils such as cottonseed oil, corn oil, fish oils, walnut oils, pineseed oils, olive oil, coconut oil, degras, and the like, may also be used.

In preparing hydrazine emulsions it is often desirable to suspend certain finely divided combustible solids therein. When these metals or metallic compounds are suspended in the fuel, they impart valuable properties thereto. These will be discussed more fully hereinafter.

The emulsions of the present invention possess the following advantages:

(1) N0nadhesive.-They tend not to stick to the sides of the container. Thus hold up in fuel tanks is minimixed.

(2) Viscosity-The apparent rest viscosity is greater than 1000 cp., generally in the range of 10,000100,000 or greater. However, under low shear, they will flow with a viscosity approaching that of the liquid phases. On removal of shear, the recovery to original apparent rest viscosity is nearly instantaneous. The hysteresis loop is very small.

(3) Temperature stability-Increased temperature has little effect on viscosity until the critical stability temperature is reached at which the points emulsion breaks into its liquid components. This permits a wide temperature range of operation.

(4) Shear stability-Emulsions may be subjected repeatedly to shear without degradation so long as the critical shear point is not reached. At this point the emulsion breaks. However, the critical shear point is sufficiently high to permit pumping at high rates.

(5) Quality c0ntr0l.With these emulsions it is easy to reproduce batches with identical properties due to the absence of any gel structure.

(6) Metering, heat transfer, and nozzle spray characteristics-Since emulsions can be broken with high shear, this can be done at the turbopump, giving completely liquid flow from that point on. This will permit metering by conventional means and will preclude laminar fiow with attendant reduction of heat transfer capability, resulting in completely liquid nozzle flow and combustion characteristics.

(7) Solid l0ading.Emulsions will flow well even with high solids loading since they have a broad range between rest viscosity and viscosity under modest shear.

In contrast to very high volume percent solid loading in gels or slurries which result in a putty, our emulsions can suspend such solids in the internal phase while allowing the external phase to govern fiowability.

(8) Recovery of hydrazine or its derivatives.-When gelling agents are dissolved in the fuel, distillation is required to recover the original component. With emulsions, application of high shear or high temperature to break the emulsion, and a subsequent decantation or drawoff operation, is all that is required. This is significant in considering a storable weapon system. It would be a simple matter to exhaust a missile, break the fuel emulsion, and remake it periodically as required.

(9) Safety.-If the external phase is kerosene or other nontoxic material, less hydrazine vapor is released from a spill until some of the external phase evaporates whereas the vapor pressure of a material is not greatly changed by conventional gelling.

Any suitable emulsifier can be employed. The emulsifiers which we most usually employ in the practice of our invention are generally known as Oxyalkylated surfactants or more specifically polyalkylene ether or polyoxyalkylene surfactants. Oxyalkylated surfactants as a class are well known. The possible sub-classes and specific species are legion. The methods employed for the preparation of such Oxyalkylated surfactants are also too well known to require much elaboration. Most of these surfactants contain, in at least one place in the molecule and often in several places, an alkanol or a polyglycolether chain. These are most commonly derived by reacting a starting molecule, possessing one or more oxyalkylatable reactive groups, with an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide, or higher oxides, epichlorohydrin, etc. However, they may be obtained by other methods such as shown in US. Patents 2,588,771 and 2,596,091-3, or by esterification or amidification with an Oxyalkylated material, etc. Mixtures of oxides may be used as well as successive additions of the same or different oxides may be employed. Any oxyalkylatable material may be employed. As typical starting materials may be mentioned alkyl phenols, phenolic resins, alcohols, glycols, amines, organic acids, carbohydrates, mercaptans, and partial esters of polybasic acids. In general, the art teaches that, if the starting material is water-soluble, it may be converted into an oil-soluble surfactant by the addition of polypropoxy or polybutoxy chains. If the starting material is oil-soluble, it may be converted into a chains. Subsequent additions of ethoxy units to the water-soluble surfactant by the addition of polyethoxy chains tend to increase the Water solubility, While, subsequent additions of high alkoxy chains tend to increase the oil solubility. In general, the final solubility and surfactant properties are a result of a balance between the oil-soluble and water-soluble portions of the molecule.

In the practice of our invention we have found that emulsifiers suitable for the preparation of high internal phase ratio emulsions may be prepared from a wide variety of starting materials. For instance, if we begin with an oil-soluble material such as a phenol or a long chain fatty alcohol and prepare a series of products by reaction with successive portions of ethylene oxide, we find that the members of the series are successively more water-soluble. We find also that somewhere in the series there will be a limited range where the products are useful for the practice of our invention. Similarly it is possible to start with water or a water-soluble material such as polyethylene glycol and add, successively, portions of propylene oxide. The members of this series will be progressively less water-soluble and more oil-soluble. Again there will be a limited range Where the materials are useful for the practice of our invention.

In general, the compounds which would be selected for testing as to their suitability are oxyalkylated surfactants of the general formula wherein Z is the oxyalkylatable material, R is the radical derived from the alkylene oxide which can be, for ex ample, ethylene, propylene, butylene, epichlorohydrin and the like, n is a number determined by the moles of alkylene oxide reacted, for example 1 to 2000 or more and m is a whole number determined by the number of reactive oxyalkylatable groups. Where only one group is oxyalkylatable as in the case of a monofunctional phenol or alcohol ROH, then m=1. Where Z is water, or a glycol, m=2. Where Z is glycerol, m=3, etc.

In certain cases, it is advantageous to react alkylene oxides with the oxyalkylatable material in a random fashion so as to form a random copolymer on the oxyalkylene chain, i.e. the [(OR), OH] chain such as AABAAABBABABBABBA-. In addition, the alkylene oxides can be reacted in an alternate fashion to form block copolymers on the chain, for example -BBBAAABBBAAAABBBB or BBBBAAACCCAAAABBBB- where A is the unit derived from one alkylene oxide, for example ethylene oxide, and B is the unit derived from a second alkylene oxide, for example propylene oxide, and C is the unit derived from a third alkylene oxide, for example, butylene oxide, etc. Thus, these compounds include terpolymers or higher copolymers polymerized randomly or in a blockwise fashion or many variations of sequential additions.

Thus, (OR) in the above formula can be written -A B C or any variation thereof, wherein a, b and c are 0 or a number provided that at least one of them is greater than 0.

It cannot be overemphasized that the nature of the oxyalkylatable starting material used in the preparation of the emulsifier is not critical. Any species of such material can be employed. By proper additions of alkylene oxides, this starting material can be rendered suitable as an emulsifier and its suitability can be evaluated by plotting the oxyalkyl content of said surfactant versus its performance, based on the ratio of the oil to hydrazine which can be satisfactorily incorporated into hydrocarbon as a stable emulsion. By means of such a testing system any oxyalkylated material can be evaluated and its proper oxyalkylation content determined.

REPRESENTATIVE EXAMPLES OF Z No. Z

RC-O- 3 RO 4 RS- [I H R-O-N i 6 R-CN\ 7 1'1 R-N- 9 Phenol-aldehyde resins. 10 O (Ex: Alkylene oxide block polymers).

O t X=O, -S, -CH -H, etc.

R-SCHzCQ- RPO4H RPO4= PO4= Iii 1s-.. R. s0m

1. a ma i t 1s RCN N 19 Polyol-derived (Ex: glycerol, glucose, pentaerithrytol). 20 Anhydrohexitau or anhydrohexide derived (Spans and Tweens). Polycarboxylic derived.

22 ((3HCH2O)n amine Examples of oxyalkylatable materials derived from the above radicals are legion and these, as Well as other oxyalkylatable materials, are known to the art. A good source of such oxyalkylatable materials, as well as others, can be found in Surface Active Agents and Detergents, vols. 1 and 2, by Schwartz et al., Interscience Publishers (vol. 1, 1949, vol. 2, 1958), and the patents and references referred to therein.

In general, the base oxyalkylatable material is tested for solubility in Water or toluene, or any other suitable oily material. If it is water soluble, it is oxyalkylated with propylene or butylene oxide until it is just oil soluble, with representative samples being collected as its oxyalkylate content is increased. These samples are tested according to the test shown in Example 88 and its optimum performance mapped as herein described. If the oxyalkylatable material is oil-soluble, then it is oxyalkylated with ethylene oxide until it is just water-soluble, with representative samples being collected as its oxypropylation or oxybutylation content is increased. These samples are similarly tested. This procedure can thereupon be repeated with another alkylene oxide until opposite solubility is achieved, i.e., if the material is water-soluble it is oxypropylated or oxybutylated until it is oil-soluble. If the prior oxypropylated or oxybutylated material is oil-soluble, it is treated with ethylene oxide until it is water-soluble. This can be repeated in stages each time changing the material to one of opposite solubility by using a hydrophile oxide (i.e., EtO) for an oil-soluble material and a hydrophobe oxide (i.e., Pro or BuO) for water solubility. The same procedure and tests are employed at each stage, proceeding each time to oxyalkylation to opposite solubility.

Although the amount of oxyalkylated material present in the emulsion has been stated to be 0.05- volume percent, but preferably 0.2-3%, larger amounts can also be employed if desired. However, economics generally restrict the amount employed to the ranges indicated.

The exact range which is useful for the practice of our invention will vary with the starting emulsifier base and the sequence of alkylene oxides used to achieve the polyalkylene ether chains. It should also be noted that materials useful in the practice of our invention can be made by other well-known methods besides oxyalkylation such as the esterification of a polyalkylene ether alcohol, reaction of carboxylic acids with oxyalkylated amines, etc. Thus, the term oxyalkylated includes any means of attaching the oxyalkyl group to a molecule. Any method of attaching oxyalkyl groups to a molecule can be employed.

We have also found that the optimum range of effectiveness for any particular emulsifier series will vary with the particular oily phase and also with the composition of the hydrazine phase which is employed.

To illustrate the variety of materials that may be used as emulsifiers in the practice of our invention the following examples are presented. It should be noted that these examples are simply illustrative and should not be construed as imposing limitations on the scope of the invention.

Example 1 The same general procedure was employed as described in U.S. Patent 2,572,886, Example 1a, columns 9 and 10, except that the starting material was n-decanol. Propylene oxide was added first in a weight ratio of 1.96 parts of oxide to one part of n-decanol, and ethylene oxide was then added in a ratio of 2.61 parts of oxide to one part of n-decanol. The final product was a viscous amber liquid.

Examples 2 through 8 were prepared in the same manner as Example 1 except that the relative amounts of ndecanol, propylene oxide, and ethylene oxide added in the order given were as listed in Table I.

TABLE I Weight Weight Weight Ex. No. n-deeanol Propylene Ethylene Oxide Oxide 1 None 2. 72

In Table II a series of examples are given in which a crude alkyl (C -C phenol was treated with ethylene oxide in the method of Example 1.

TABLE II One part by weight of crude phenol foots was reacted with the parts shown in the table of ethylene oxide.

Examples 22 through 33 were made by the same general method described in Example 1 except that the starting material Was glycerine. The proportions of reactants are listed in Table III. The alkylene oxides were added in the order given reading from left to right.

TABLE III One part by weight glyeerine to Ex. N 0. Parts Parts Parts Butylene Propylene Ethylene Oxide Oxide Oxide Example 34 A mixed nonyl-butyl phenol-acid catalyzed-formaldehyde resin was prepared by the method of U.S. Patent 2,499,370, Example 1a.

Examples 35 through 48 were prepared by stepwise oxyalkylation of the resin produced in Example 34 by the procedure described in U.S. Patent 2,499,370, Example 1b, except that the proportions of oxides used were as listed in Table IV. The oxides used were as listed in Table IV. The oxides used were as listed in Table IV. The oxides were added in the order given reading from left to right.

TABLE IV Moles of Propylene Moles of Ethylene Example No. Oxide per phenolic Oxide per phenolic unit of starting resin unit of starting resin Examples 49, 50, 51

Polyepichlorohydrin-amine compounds were prepared by the methods described in application 820,116, filed June 15, 1959, and assigned to Petrolite Corporation, De Groote and Cheng.

Example 49 is Example 18b of said application.

Example 50 is Example 19b of said application.

Example 51 is Example of said application.

9 Example 52 The product of Example 49 was treated as in Example 1 except that the starting material was treated with 2.16 parts of propylene oxide, 3.31 parts of ethylene oxide and finally with 19.6 parts of propylene oxide in the order given.

Example 53 The product of Example 50 was treated as in Example 1 except that 2.24 parts of propylene oxide, 2.85 parts of ethylene oxide, and 24.3 parts of propylene oxide were used in the order given.

Example 54 Percent Additional Ethylene Oxide Based on Starting Material Starting Material Example No. Product ot Example 66 The procedure of Example 1 was employed except that 1,3-butanediol was the starting material and 3.0 parts of butylene oxide, 322 parts of propylene oxide, and 16.6 parts of ethylene oxide were employed in the order given.

Example 67 The general procedure of Example 1 was employed except that the starting material was triethylene glycol and that 5.1 parts of butylene oxide, 30.0 parts of propylene oxide, and 22 parts of ethylene oxide were used in the order given.

Example 68 The same general procedure as Example 1 was employed except that the starting material was tetraethylene glycol and that 5.1 parts of butylene oxide, 300 parts of propylene oxide, and 14.0 parts of ethylene oxide were used in the order given.

Example 69 One part of dipropylene glycol was treated with 29.8 parts of propylene oxide and 20.5 parts of ethylene oxide in this order according to the general procedure of Example 1.

Example 70 One part by weight of castor oil Was treated with 6.8 parts of propylene oxide according to the procedures mentioned above.

Example 71 One part by weight of crude tall oil was treated with 3.27 parts of ethylene oxide according to the procedures mentioned above.

Example 72 One mole of stearyl alcohol was treated with 3.12 moles of ethylene oxide and then the resulting material was reacted with 1.5 moles sulfamic acid to convert the terminal hydroxyl to a sulfate group.

Example 73 The procedure of Example 1 was employed except that the starting material was hexadecanol and 1.2 parts of propylene oxide and 1.5 parts of ethylene oxide added in the order given.

Example 74 The compound and procedure of Example 73 was employed except that the amount of ethylene oxide in the second addition was 1.8 parts.

Example 75 The procedure of Example 1 was employed except that the starting material was tridecyl alcohol and 1.35 parts by weight of propylene oxide and 4.01 parts by weight of ethylene oxide were employed in the order given.

Example 76 Commercial didodecylphenol was treated in the manner of Example 1 with 0.64 part of ethylene oxide.

Example 77 The procedure of Example 76 with didodecylphenol was used, except that 0.85 part of ethylene oxide were em ployed.

Example 78 The procedure of Example 76 with didodecylphenol was employed, except that 1.06 parts of ethylene oxide were employed.

Example 79 The procedure of Example 1 was employed to treat one parts of methoxytripropylene glycol with 5.1 parts of ethylene oxide and 35.0 parts of propylene oxide.

Example 80 Two parts of paratertiarybutylphenol were mixed with one part of nonylphenol and one part by weight of this mixture was reacted with 2.36 parts of ethylene oxide according to the method outlined above.

Esters of oxyalkylates may also be employed, such as shown in the following examples:

Example 81 674.0 grams of the material of Example 80, 7.6 grams of diglycollic acid, 2 drops of 15% HCl, and 20 ml. of toluene were heated together in a one liter flask fitted with stirrer, heating mantle, and a Dean-Stark trap and condenser at 160 C. for eight hours. The bulk of the toluene was then stripped oil and the result was a light brown, viscous liquid.

Example 82 A three-necked Pyrex glass flask was fitted with a stirrer, a thermometer, a Dean-Stark trap and condenser, and a gas pll'ge inlet. Into the flask was put a mixture consistmg 0 Material of Example 13 g 197 Material of Example 10 g Maleic anhydride Q 25 Benzene ml 100 Paratoluenesulfonic acid g 1 The flask was purged with nitrogen and the mixture heated, while stirring, at 160 C. to C. for 12 hours.

Example 83 The equipment and procedure of Example 82 were used except that 544 g. of the material of Example 6, 33 g. of

maleic anhydride, 2 g. of paratoluenesulfonic acid, and 70 ml. of benzene were used.

Example 84 One gram of paratoluene sulfonic acid, 450 g. of the material of Example 73, 25 g. of maleic anhydride, and 70 ml. of benzene were employed according to the general procedure of Example 82.

Example 85 24.5 g. of phthalic anhydride, 321 g. of the material of Example 18, 1 g. of paratoluene sulfonic acid, and 100 ml. of toluene were employed according to the general procedure of Example 82.

It should be noted that emulsifiers other than oxyalkylates may be used. The practice of this invention is not to be construed as limited to the employment of oxyalkylates as emulsifiers.

For example, the following non-oxyalkylate may be employed.

Example 86 The apparatus of Example 82 was charged with: Morpholine g 14.5 Triethylenetetramine monohydroxyethyl g 31.5 Oleic acid g 94.5 Toluene ml 100 The mixture was heated, with stirring, at 160 C. for 8 hours. 15 ml. of water were removed in the Dean-Stark trap. 85 ml. of toluene were then stripped out of the mixture. The result was a dark brown liquid.

Thus, any emulsifier capable of forming the emulsion of this invention can be employed. It is the function of the emulsifier rather than its specific composition that is of interest in forming these emulsions. Therefore a tedious recital of all classes of emulsifiers is omitted.

As is quite evident, new emulsifiers will be constantly developed which could be useful in this invention. It is therefore not only impossible to attempt a comprehensive catalogue of such compositions, but to attempt to describe the invention in its broader aspects in terms of specific chemical names of its components used would be too voluminous and unnecessary since one skilled in the art could by following the testing procedures described herein select the proper agent. This invention lies in the use of suitable emulsifiers in preparing the compositions of this invention and their individual composition is important only in the sense that their properties can effect these emulsions. To precisely define each specific emulsifier in light of the present disclosure would merely call for chemical knowledge within the skill of the art in a manner analogous to a mechanical engineer who prescribes in the construction of a machine the proper materials and the proper dimensions thereof. From the description in this specification and with the knowledge of a chemist, one will know or deduce with confidence the applicability of emulsifiers suitable for this invention by means of the evaluation tests set forth herein. In analogy to the case of a machine wherein the use of certain materials of construction or dimensions of parts would lead to no practical useful result, various materials will be rejected as inapplicable where others would be operative. We can obviously assume that no one will wish to make a useless composition or will be misled because it is possible to misapply the teachings of the present disclosure in order to do so. Thus, any emulsifier that can perform the function stated herein can be employed.

One of the new and novel aspects of the present invention is the ease with which the emulsions can be prepared. While a few instances of emulsions of over 70 to 75% internal phase have been known to the art, they are difficult to prepare and tend to be unstable. Most of them are laboratory curiosities and not well adapted to large-scale, commercial production.

Present practice for the commercial production of emulsions of even moderately high internal phase ratio calls for the use of a colloid mill or other method of extremely high shear. Paint mills, high speed cone mills, and roller mills are employed. These methods require the use of expensive equipment and the utilization of large amounts of power. Even with these methods, the internal phase ratio seldom exceeds 70% internal phase.

On the contrary, in the practice of our invention only the simplest equipment is required. Actually useful and novel emulsions with internal phase ratios of over 90%, and even over 95% to 99%, can be made by simple hand stirring with a paddle or spoon. In actual practice a wide variety of mixing devices may be used. The following examples will illustrate the great advantages to be gained by the practice of our invention. The examples should not be construed as limitations on the methods which may be employed.

Example 87 Ten ml. of kerosene and 2 ml. of the material of Example 1 were mixed by shaking in a pint jar. Ten ml. of hydrazine was added and the mixture shaken until all the hydrazine had emulsified. Additional amounts of hydrazine were added, with shaking, until a total of 250 ml. of hydrazine had been added. The result was a stiff, almost translucent jelly. This material was found to be stable over the range 10 C. to 50 C. for several weeks. It is an hydrazine-in-oil emulsion as shown by the fact that it can be diluted with kerosene to form a thin, white dispersion of hydrazine in kerosene.

For the preparation of small laboratory batches of emulsions we prefer to use a kitchen-type mixer, such as the Model C3, Kitchen Aid Mixer manufactured by the Hobart Manufacturing Company. This mixer uses a two quart glass mixing bowl and a Wire beater with a planetary motion. Our testing procedure is as follows:

Example 88 Ten ml. of the oily phase is mixed with a suitable amount, usually 2 ml. to 4 ml., of the emulsifier in a glass mixer bowl. With the mixer running at a speed setting of 2 to 6, the hydrazine phase is slowly added to the bowl. Initial additions should be made in small amounts, allowing the mixer ample time to incorporate hydrazine into the emulsion. As the amount of material in the bowl increases, the mixing action is more efficient and further additions may be made more rapidly. When the mixer will no longer produce an emulsion without a free hydrazine phase, the limit of the test is considered to have been reached.

In general, we find that emulsifiers which have heretofore been used for the production of conventional emulsions will not permit the incorporation of more than 20 to 30 ml. of internal phase before breaking or inversion occurs. On the contrary, the materials of our invention allow the incorporation of over ml. of internal phase into a stable emulsion and it is quite common to incorporate 200 ml. or more of internal phase. In fact, we do not usually consider a material suitable for practical use if it does not permit the incorporation of at least about 200 ml. of internal phase per 10 volumes of volumes of external phase.

As stated above, a Wide variety of materials may be used as emulsifiers in the practice of our invention. However, not all materials of a particular type are suitable for the production of a specific emulsion. As previously stated, the effectiveness of a particular material varies with the composition of both the internal and external phase. We find that the test oulined in Example 88 a simple and convenient method of establishing the optimum material for a particular system.

In general, in the practice of our invention, our preferred method for selection of materials of optimum effectiveness is to prepare a family of related materials and test them for effectiveness in the particular system that is under consideration. A water-soluble base is oxyalkylated with propylene oxide (PrO) or butylene oxide (BuO) until it just becomes oil-soluble and selected members of the series are tested. An oil-soluble base is treated with ethylene oxide (HO) and similarly tested. A test such as that outlined in Example 88 may be used or any other test that accurately reflects the proposed methods of preparation of the desired emulsion. The results of the tests are then plotted on a model of a multi-dimensional noncommutative composition space that represents the family of materials being used. Such tests and plots reveal the existence of an optimum-performance region in the composition space.

A complete discussion of the use of such noncommutative, composition spaces is found in U.S. Patent 3,083,232, and in the Journal of Chemical Documentation, vol. 3, pp. 103-113 (1963).

As has been previously stated, one of the advantages of our invention is the wide variety of materials that may be incorporated into the compositions and the concomitant variety of properties that may be thus imparted to the final formulations. Four primary variables control the final properties of the formulations. The composition of the external phase, the composition of the internal phase, the emulsifier employed, and the method of mixing. The final formulations are stable, viscous thixotropic emulsions. Thus, it is possible to convert a fluid, mobile liquid such as hydrazine into an extremely viscous form without adding suflicient foreign material to significantly afi'ect its chemical properties. Using the method of Example 87 this fluid material may be converted into a stiff jelly. It should be noted that, although the physical properties of the hydrazine have been drastically modified, the final composition contains less than added material. Thus the fuel rating and the' burning properties of the hydrazine are thus not seriously modified.

The final viscosity of these compositions is a function of the particular emulsifier used, the ratio of the two phases, and the method employed to produce the intimate mixture. Compositions may be formed which vary in consistency from that of thick cream to jellies which are so stitf that they may be cut into pieces and stand unsupported. Thus, the viscosity may be chosen to suit the particular application.

We have prepared emulsions having apparent rest viscosities of at least 1,000 c.p.s., for example, about 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000 or greater, all of which are thixotropic and pumpable u-nder shear.

The preferred embodiment of this invention comprises an emulsion consisting of a minor amount of an external oily phase and a major amount of an internal phase of hydrazine having a combustible finely divided solid dispersed within it. The choice of the solid is dictated primarily by potential specific impulse considerations. The usual practice of this invention would be to select a combination of hydrazine and solids that is mutually nonreactive at storage temperatures and that has potentially the maximum specific impulse. Specific impulse can be defined by the following equation.

The expression for specific impulse (1 and the equations which lead to it are as follows (Fz =total impulse in lb.-sec. and F=mc/g):

where I =Specific impulse, pounds of thrust per pound weight of propellant burned per second.

F=Thrust, lb.

t=Duration of thrust due to burning, sec.

W=Total weight of propellant, lb.

m=Wei-ght of propellant burned per second, lb./ sec.

c=Efiective exhaust velocity of propellant gases, ft./sec. Actual exhaust velocity of propellant gases in the case of rockets (but not for air-breathing jets), ft./ sec. g=Acceleration due to gravity, ft./sec.- R=RM=Universal gas constant, 1544 ft.-lb./(lb.-mole) R=Gas constant per pound weight of propellant gases, ft.-lb./ (1b.) F.). T =Combustion chamber temperature, R. M=Average molecular weight of propellant gases. v=C /C C =Heat capacity of propellant gases at constant pressure, B.t.u./ (1b.) F.). C =Heat capacity of propellant gases at constant volume, B.t.u./(-lb.) F.). P =Pressure of propellant gases at nozzle exit, p.s.i. P -Pressure of propellant gases in combustion chamber,

p.s.i.

Having selected the best available combination of solids and hydrazine and having calculated the optimum proportion of the two to be used, one then selects a liquid for the external phase that is non-reactive with either hydrazine or solids, is immiscible with hydrazine and not a solvent for the solids. Using the methods detailed elsewhere in these specifications, one then selects an appropriate emulsifier for the system. This emulsifier is then dissolved or dispersed in the external phase liquid and the mixture of solid and hydrazine mixed into this liquid by any of the methods elsewhere described.

Examples of combustible finely divided solids elements which are of interest when combined with appropriate liquid fuels are lithium, beryllium, boron, carbon, sodium, magnesium, aluminum, silicon, etc. The hydrides or nitrides of the above elements, when they are solids, may be employed. These are generally employed as finely divided solids, for example, having a particle size of less than about 200 microns, such as less than about microns, for example from about 0.5 to 50 microns, but preferably from about 1 to 10 microns.

The amount of finely divided solids and to the fuel can vary widely such as from about 5 to 200 g. or more per 100 volumes of emulsions, for example from about 10 to 180 g., such as from about 15 to 140 g. but preferably about 20 to g.

The following examples are presented as non-limiting examples illustrating the practice of this invention where finely divided solids are employed therein.

Example 89 10 ml. of kerosene and 3 ml. of compound are mixed in a pint glass jar. This jar is clamped onto a ringstand and a split disc stirrer mounted so that the blades just clear the bottom of the jar. A Sargent Cone-drive stirrer set at about speed is used to drive the stirrer blades.

90 g. of aluminum powder (Reynolds 400) is weighed into a 400 ml. beaker and 200 ml. of hydrazine added. This mixture is stirred with a spatula until it is homogeneous.

The stirrer is then turned on and the hydrazine-aluminurn mixture slowly added to the kerosene solution in the jar. If the emulsion forms, the jar is removed from the clamp and the stirrer worked up and down in the thick emulsion until it appears uniform. If the emulsion is slow to form, a little more kerosene is added.

A screw cap is then put on the jar and the emulsion stored at room temperature and observed daily until it breaks. Measurements of apparent viscosity were made with a Brookfield Viscometer. In certain instances the emulsion will not wet the spindle. This makes measurement of the viscosity by this method invalid.

Ten different emulsifiers were used in this series of tests. These results are summarized in the following Tables I, II, and III.

TABLE I Emulsifier Test; Result No Example No.

Q; 20 mll). of kerosene required. Good emulsion. r o. 84 Makes easily with no additional kerosene.

Excellent. 16 Almost makes with ml. kerosene. Good with ml. 5 73 Takes about half of the hydrazine, then inverts. 6 74 Almost makes 25 ml. kerosene and 1 ml. more reagent. 7 6 Barely makes at ml. kerosene and 4 ml.

reagent. 8 75 Emulsion won't make. 9 77 o. 10 18 Makes at 15 ml. kerosene. Fair emulsion.

TABLE II Test Emulsifier Appearance after Appearance after No. of 24 hrs. 1 week Example No.

1 82 Thick emulsion, No change.

little bleeding. 2 83 Thick, Very little Do.

bleeding. 84 Best of 1, 2, and Stable even on s aking. 16 Some slight bleeding. Breaks on shaking. 73 74 Thin, some bleedin Remakes on shaking.

6 do Do.

77 18 Good; very little Breaks on shaking.

bleeding.

TABLE III Emulsifier Brookfield viscosity after 24 hours, Test No of centipoises Ex. No.

6 r.p.m. 12 r.p.m. 30 r.p.m. 60 r.p.m.

" i l 3,666 "11366 "Q36 "ite "is imb ""tszn ejsba"" as" A remake of No. 3 was spun for 3 minutes at 1700 r.p.m. in a centrifuge with an 8 inch arm. It showed no separation or settling of the solids.

These tests show that the selection of the emulsifier is important in the procedure. While the emulsifier in Test N0. 3 allows the production of a thick stable emulsion with 10 ml. of kerosene as the external phase, Nos. 5, 8, and 9 will not make stable emulsions under these conditions, and Nos. 1, 2, 4, and 10 require more external phase for stability. It can be seen also that while Nos. 1, 2, 3, 6, and 7 were stable for over a week, the rest either broke or were unstable to shaking.

These emulsions are highly thixotropic. The apparent viscosities varying as much as an order of magnitude between the 6 r.p.m. and 60 rpm. readings. It should also be noted that we are able to make stable emulsions with a wide range of viscosities.

The above examples are employed to illustrate the preparation of the emulsion of this invention containing combustible powdered solids which can be employed in jet and rocket fuel. However, it should be understood that powdered aluminum and other powdered solids can be similarly added to other emulsions prepared in accord with this invention, for example, the' emulsions described in the specific example disclosed herein.

As the rate of shear increases the effective viscosity decreases. This is of great importance where the material has to be pumped. It means that a material that, when stationary or at low shear, behaves like a thick jelly, will become fluid while being pumped and regain its viscosity as it slows down. This thixotropy is a general property of the composition of this invention.

Illustrations have already been given of the wide variety of materials that may be used as emulsifiers in the practice of our invention. It should be noted that no single specific emulsifier will necessarily be operative on \all possible phase combinations. However, by the application of a simple laboratory test such as that outlined in Example 88 or 89, anyone skilled in the art can readily ascertain the emulsifier best suited for any particular purpose.

It will often be found that continuing the stirring for a longer period than necessary to form a stable emulsion will often result in a more viscous product. Contrary to general emulsion practice, however, increased shear, will not necessarily make a stiffer composition. In fact, if a method employing extremely high shear is used, an inferior emulsion results. For example, in the method of Example 88 it is often easier to get a satisfactory emulsion using the low speeds on the mixer than it is using high speeds. It is as though the higher shear met-hods prevent the formation of the necessary structure in the composition and may even cause inversion. As a further example may be mentioned the use of pumps as mixers. We have found that la moderate speed pump with some slippage such as a Jabsco pump with a flexible rubber impeller or a Viking pump perform well. However, it is found that if the speed of the pump is increased the effectiveness increases to a point and then falls off sharply. In fact, these emulsions may be broken back to their Component phases by subjecting them to extremely high shear such as by passing thelm through a high speed centrifugal pump or forcing them through a small nozzle. It is one of the advantages of our invention that high speed, high power equipment is not necessary for the production of these products. Colloid nn 'llis and other high shear devices may be eleminiated and simple mixing and blending apparatus or pumps used instead. In field use such emulsions may be made by stirring with a wooden paddle by hand.

In some applications it may be desirable to be able to break the emulsion and reclaim the original phases. In such cases advantage may be taken of the effect of extremely high shear. For instance, thickened fuels of the type enoompassed by this invention are easier to transport and less subject to evaporation, ignition, and spillage than fuels in conventional form. Due to their thixotropy they may be pumped without difficulty. They may be broken back to the original fuel by passing through a nozzle and allowing the small amount of oily phase to settle out. This is not true of gels which have been made from polymers and other materials currently used for such purposes.

Fuels prepared by the practice of our invention also have utility in applications where the sloshing of fuels in storage tanks is a problem. Since the fuels are pumpable and yet viscous they may be used in liquid fuel rockets, jets, and water craft where the shift of weight concomitant with la sudden change in direction will seriously affect the trim of the vessel. The reduced tendency to splash and shift lessens the need for elaborate bulkheads and allows more payload.

Little is to be gained by a detailed description of the jet and rocket engines in which compositions of this type are burned. Recent details of the construction of such engines are not generally available due to security restrictions. A general description of the operation of rocket and jet engines is \given in Encyclopedia of Chemical Technology, published by Interscience Publishers (1951), vol. 6, pages 954-959, under Jet Propulsion Fuels, and in vol. 11, pages 760-778, under Rocket P ropellants.

A short description of the operation of jet engines is given in the same publication on page 954, and of rocket engines on pages 766-767 thereof and elsewhere. Since the compositions of this invention may be pumped and handled in the same manner as liquids they are used in the same types of engines as conventional liquid fuels. They possess the unique advantages of high density (due to the incorporated solids), stability, restartability, and high specific impulse.

We claim:

1. A jet and rocket thixotropic emulsion fuel comprising (1) a hydrazine, (2) an emulsifiable oil phase material, and (3) an emulsifying agent, said fuel emulsion having the characteristics of a solid fuel when at rest and the characteristics of a liquid fuel when a force is exerted on it.

2. The jet and rocket thixotropic emulsion fuel of claim 1, also including finely divided combustible solids, said fuel emulsion having the characteristics of a solid fuel when at rest and the characteristics of a liquid fuel when a force is exerted on it.

3. The jet and rocket thixotropic emulsion fuel of claim 1, also including finely divided aluminum particles, said fuel emulsion having the characteristics of a solid fuel when at rest and the characteristics of a liquid fuel when a force is exerted on it.

4. A jet and rocket tfhixotropic hydrazine-in-oil emulsion fuel comprising (1) a hydrazine, (2) an emulsifiable oil, and (3) an emulsifying agent, said hydrazine being present in said emulsion fuel in an amount of at least 80% hydrazine by volume of the emulsion, said emulsion having the characteristics of a solid fuel when at rest and the characteristics of a liquid fuel when a force is exerted on it.

5. The jet and rocket thixotropic emulsion fuel of claim 4, also including finely divided combustible solids.

6. The jet and rocket thixotropic emulsion fuel of claim 4, also containing finely divided aluminum particles.

7. A jet and rocket thixotropic hydrazine-in-oil emulsion fuel comprising (1) a hydrazine, (2) an emulsifiable oil, and (3) an emulsifying agent, said hydrazine being present in said emulsion fuel in an amount of at least 90% hydrazine by volume of the emulsion, said emulsion having the characteristics of a solid fuel when at rest and the characteristics of a liquid fuel when a force is exerted on it.

8. The jet and rocket thixotropic emulsion fuel of claim 7, also including finely divided combustible solids.

9. The jet and rocket thixotropic emulsion fuel of claim 7, also containing finely divided aluminum particles.

10. A jet and rocket thixotropic hydrazine-in-hydrocarbon emulsion fuel comprising (1) a hydrazine, (2) an emulsifiable hydrocarbon, and (3) an emulsifying agent, said hydrazine being present in said emulsion fuel in an amount of at least 90% hydrazine by volume of the emulsion, said emulsion having the characteristics of a solid fuel when at rest and the characteristics of a liquid fuel when a force is exerted on it.

11. The jet and rocket thixotropic emulsion fuel of claim 10, also including finely divided combustible solids.

12. The jet and rocket thixotropic emulsion fuel of claim 10, also containing finely divided aluminum particles.

13. A thixotropic emulsion consisting essentially of (1) a hydrazine, (2) an emulsifiable oil phase material, and (3) an emulsifying agent, said emulsion having the characteristics of a solid when at rest and the characteristics of a liquid when a force is exerted on it.

14. The method of providing jet and rocket power comprising burning the fuel of claim 1 in a reaction motor and utilizing the products of combustion as a source of power.

15. The method of providing jet and rocket power comprising burning the fuel of claim 2 in a reaction motor and utilizing the products of combustion as a source of power.

16. The method of providing jet and rocket power comprising burning the fuel of claim 3 in a reaction motor and utilizing the products of combustion as a source of power.

17. The method of providing jet and rocket power comprising burning the fuel of claim 4 in a reaction motor and utilizing the products of combustion as a source of power.

18. The method of providing jet and rocket power comprising burning the fuel of claim 5 in a reaction motor and utilizing the products of combustion as a source of power.

19. The method of providing jet and rocket power comprising burning the fuel of claim 6 in a reaction motor and utilizing the products of combustion as a source of power.

20. The method of providing jet and rocket power comprising burning the fuel of claim 7 in a reaction motor and utilizing the products of combustion as a source of power.

21. The method of providing jet and rocket power comprising burning the fuel of claim 8 in a reaction motor and utilizing the products of combustion as a source of power.

22. The method of providing jet and rocket power comprising burning the fuel of claim 9 in a reaction motor and utilizing the products of combustion as a source of power.

23. The method of providing jet and rocket power comprising burning the fuel of claim 10 in a reaction motor and utilizing the products of combustion as a source of power.

24. The method of providing jet and rocket power comprising burning the fuel of claim 11 in a reaction motor and utilizing the products of combustion as a source of power.

25. The method of providing jet and rocket power comprising burning the fuel of claim 12 in a reaction motor and utilizing the products of combustion as a source of power.

References Cited UNITED STATES PATENTS 2,920,948 l/1960 Weeks 4451 X 2,927,849 3/ 1960 Greblick et al 445l X 3,077,072 2/1963 Rice 447 OTHER REFERENCES Pluronics, Wyandotte Chemicals Corporation, Wyandotte, Mich., received 1958.

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner.

Claims (2)

1. A JET AND ROCKET THIXOTROPIC EMULSION FUEL COMPRISING (1) A HYDRAZINE, (2) AN EMULSIFIABLE OIL PHASE MATERIAL, AND (3) AN EMULSIFYING AGENT, SAID FUEL EMULSION HAVING THE CHARACTERISTICS OF A SOLID FUEL WHEN AT REST AND THE CHARACTERISTICS OF A LIQUID FUEL WHEN A FORCE IS EXERTED ON IT.

3. THE JET AND ROCKET THIXOTROPIC EMULSION FUEL OF CLAIM 1, ALSO INCLUDING FINELY DIVIDED ALUMINUM PARTICLES, SAID FUEL EMULSION HAVING THE CHARACTERISTICS OF A SOLID FUEL WHEN AT REST AND THE CHARACTERISTICS OF A LIQUID FUEL WHEN A FORCE IS EXERTED ON IT.