US3539311A - Aluminum soap thickeners with surface active agents - Google Patents

Description

United States Patent 3,539,311 ALUMINUM SOAP THICKENERS WITH SURFACE ACTIVE AGENTS Leonard Cohen, Baltimore, Md., and William T. Gregory,

Rushville, Ill., assignors to the United States of America as represented by the Secretary of the Army N0 Drawing. Filed June 8, 1955, Ser. No. 514,136 Int. Cl. C101 7/02 US. Cl. 44-7 6 Claims The invention described herein may be manufactured and used by and for the Government of the United States of America for governmental purposes without the payment to us of any royalty thereon.

This invention relates to the thickening of gasoline by aluminum soaps.

Gasoline, thickened or gelled by small quantities (about 1 to 12%) of aluminum soaps of higher carboxylic acids, is important as an incendiary in warfare. Various aluminum soaps have been used, the best-known being napalm, the aluminum soap of a mixture of oleic and naphthenic acids and coconut-oil fatty acids, disclosed and claimed in US. Pat. No. 2,606,107 to Louis F. Fieser. More recently, improved results have been obtained by the use of about 0.75 to 4% of aluminum octoates, notably aluminum di- (2-ethyl hexoate) and the isooctoates disclosed in applications, Ser. Nos. 321,747 and 466,242, filed Nov. 20, 1952 and Nov. 1, 1954, respectively, by Leonard Cohen, now Pats. 2,741,629 and 2,718,462, respectively.

One advantage of these thickened gasolines over other incendiary fuels lies in the fact that they may be produced in the field by mixing the dry soap with gasoline. The proper amount of soap is added to a batch of gasoline and the mixture agitated until thickening occurs. The gel is then allowed to stand, or cure, for a certain length of time. During the curing period the gel develops elasticity.

It is desirable that the time of mixing, or vortex time, and the cure time be as short as possible, particularly to make it possible to use continuous rather than batch mixing and to make prompt use of the filled bombs or flamethrowers. It is also desirable that the gel be as high in consistency as possible for a given amount of thickening agent, that it be highly elastic, and that it be stable over a long period of time.

In application Ser. No. 514,135 filed June 8, 1955 by us jointly with Leo Finkelstein and Sidney Magram, we have shown that the vortex time and the cure time can be shortened, while retaining or enhancing the other desirable properties, by adding to the gasoline prior to the addition of the aluminum soap, a small amount of a nonionic surface-active agent, prefera'bly accompanied by water, particularly when the aluminum soap is aluminum hydroxy di 2-ethyl hexoate) We have also found that similarly improved results can be obtained by adding a small amount of a fatty acid having at least three carbon atoms, those having from six to being preferred. The straight-chain acids were found to be most effective, notably caproic, heptoic, caprylic, pelargonic and capric acids. The branched-chain acids such as Z-ethyl butyric, 2-ethyl hexoic, and 3,5,5-trimethyl hexoic were somewhat less effective than the straight-chain acids.

An essential feature of our invention is the addition with the acid of small amounts of water, the ratio of water to acid ranging from 10:90 to :85. In the case of the higher acids it may be desirable to employ a cosol- 3,539,311 Patented Nov. 10, 1970 vent in order to maintain the mutual solubility of water and acid over a wide temperature range. Isopropanol and the diethyl ether of ethylene glycol are suitable cosolvents. Suitable blends for the addition to gasoline may have the following compositions (by weight) 2 Fatty acid: H O: 15% 10% Cosolvent:- 100% Such a blend has proved effective in the proportion of about 1 part blend to 10 parts aluminum soap.

While the peptization of aluminum soaps by fatty acids to hasten the formation of hydrocarbon gels has been previously known, the use of small amounts of water produces very different and improved results and is believed to involve a completely different mechanism. Whereas peptization of aluminum soaps by fatty acids involved the use of acid and soap in a minimum effective ratio of 1:4, by weight, the addition of the water permits the use, as noted above, of an acid/water/cosolvent blend in a ratio of blend to soap of only 1:10, by Weight. Since the blend is less than 50% acid, this means that the ratio of acid to soap is less than 1:20.

Still more important is the change in the gel itself. The use of acid alone as peptizer causes a reduction in the consistency of the gel as measured by a Gardner Mobilometer, while the use of an acid blend with water causes an increase of gel consistency due to improved curing of the gel.

It is believed that the mechanism of interaction between surface-active agents or fatty acids involving the use of water differs completely from simple peptization of aluminum soaps by polar compounds such as fatty acids in the formation of hydrocarbon gels. In the process of peptization it has been found that the aluminum soap micelles are reduced in size and molecular weight by the action of the chemically polar peptizer, thereby rendering them more readily soluble in hydrocarbons with a resulting decrease of gel consistency. In the process of formation of aluminum soaps by aqueous metathesis from sodium soap and aluminum salts in the presence of excess sodium hydroxide, aluminum hydroxide is formed with the aluminum soap. This aluminum hydroxide is hydrophilic in nature and obstructs access of the hydrocarbons to the aluminum soap thereby retarding gelation. It is believed that the addition of surface-active agents or acids containing water causes hydration and addition "by chemisorption of the lipophilic agent or acid to the surface of the aluminum hydroxide, thereby eliminating the obstruction of access to the aluminum soap by the hydrocarbon solvents. While we believe the above explanation to be correct, we do not Wish to be bound by theory.

The following example shows the improvement produced by our invention:

EXAMPLE In a laboratory mixer, four percent of aluminum hydroxy di-(2-ethyl hexoate), which-had been formed by reacting aluminum sulfate or aluminum chloride and sodium 2-ethyl hexoate in an aqueous solution of sodium hydroxide, was added to gasoline and the electric stirrer rotated at a fixed speed. As the mixture thickens, the level of the vortex rises about the rod of the stirrer. The time was noted for the level to rise from a predetermined initial level to a fixed point on the rod. This time is used as the vortex time. While the test is empirical in its choice of conditions, it is useful because it gives a quantitative measure of the time a thickener must be mixed in the field before it is allowed to stand or cure. The cure time was then determined by allowing the mixture to stand and noting the point at which elasticity develops.

Finally, the gel was allowed to stand for 24 hours and the consistency was then determined using a Gardner Mobilometer.

The experiment was then repeated in the same manner except that there was first added to the gasoline 0.4%, by weight, an acid/water/cosolvent blend, as described above, prior to the introduction of the aluminum soap.

Results of the tests are shown in the following table:

Ratio, water acid Vortex Gardner time, Curetime, consistency minutes minutes after 24 hrs.

Acid

None (control) O p Heptoic z 12288 Capryllc {010:90

cno

Pelargonic {gigzgg Cap1'ic 10592 num hydroxy di-(Z-ethyl hexoate), the amount of said aluminum hydroxy di-(Z-ethyl hexoate) being about one to twelve percent by weight of the gasoline and the amount of the first-named fatty acid being about five percent by weight of the aluminum di-(Z-ethyl hexoate), stirring the mixture until thickening occurs, and then allowing the thickened mixture to stand until it develops elasticity.

2. A process as defined in claim 1 wherein the firstnamed fatty acid is a straight-chain acid.

3. A process as defined in claim 1 wherein the firstnamed acid is caproic acid.

4. A process as defined in claim 1 wherein the firstnamed acid is caprylic acid.

5. A process as defined in claim 1 wherein the firstnamed acid is pelargonic acid.

6. A process as defined in claim 1 wherein the firstnamed acid is capric acid.

References Cited UNITED STATES PATENTS 2,390,609 12/1945 Minich 252-316 2,492,173 12/1949 Mysels 44-7 X 2,718,462 9/1955 Cohen 447 2,751,284 6/1956 Hill.

FOREIGN PATENTS 544,729 4/ 1942 Great Britain.

LELAND A. SEBASTIAN, Primary Examiner U.S. Cl. X.R.

Claims (1)

1. A PROCESS OF GELLING GASOLINE COMPRISING ADDING TO SAID GASOLINE A BLEND OF WATER AND A FATTY ACID CONTAINING FROM 6 TO 10 CARBON ATOMS PER MOLECULE, THE RATIO OF WATER TO ACID RANGING FROM 10:90 TO 15:85 THEN ADDING ALUMINUM HYDROXY DI-(2-ETHYL HEXOATE), THE AMOUNT OF SAID ALUMINUM HYDROXY DI-(2-ETHYL HEXOATE) BEING ABOUT ONE TO TWELVE PERCENT BY WEIGHT OF THE GASOLINE AND THE AMOUNT OF THE FIRST-NAMED FATTY ACID BEING ABOUT FIVE PERCENT BY WEIGHT OF THE ALUMINUM DI-(2-ETHYL HEXOATE), STIRRING THE MIXTURE UNTIL THICKENING OCCURS, AND THEN ALLOWING THE THICKENED MIXTURE TO STAND UNTIL IT DEVELOPS ELASTICITY.