US3041154A - Mixture of alkali metal salts of fatty acids having improved solubility in liquid hydrocarbons - Google Patents

Description

ite States Patented June 26, 1962 This invention relates to chemical compositions, and more particularly to compositions comprising alkali metal salts of branched chain carboxylic acids having improved solubility in liquid hydrocarbon media over the solubility exhibited by individual alkali metal salts of carboxylic acids in general.

The alkali metal salts such as the lithium, sodium and potassium salts of aliphatic carboxylic acids are normally quite insoluble in hydrocarbon media such as petroleum hydrocarbon fractions or aromatic hydrocarbons such as benzene -and toluene, and the usual expedients which have been employed in the art to improve solubility. of materials in hydrocarbon solvents, such as by increasing the carbon content of the aliphatic chain and/ or by employing branched hydrocarbon chains for the carboxylic acid, have been found to give little or no improved solubility for' these alkali metal carboxylates. Various solublizing agents such as alcohols or other polar solvents have been suggested, and, while these do increase the amount of alkali metal carboxylates which may be dissolved in a hydrocarbon solvent, such mixtures are not entirely'satisfactory because they must be used in large amounts to produce even relatively low concentrations in the fuel.

It is an object of the present invention to provide chemical compositions comprising alkali metal salts of branched chain carboxylic acids having materially improved solubilities in liquid hydrocarbon media over the solubility exhibited by any individual alkali metal salt -of the same branched chain carboxylic acid without the addition of other types of solvents to the hydrocarbon media. A further object of the invention is to provide mixtures of alkali metal salts of branched chain carboxylic acids which have enhanced solubility in liquid hydrocarbon media over the solubility exhibited by the individual salts or what would be expected to be the combined solubilities of such salts, and to produce liquid hydrocarbon compositions containing a greater amount of alkali metal salts of branched chain carboylic acids in solution than it has heretofore been possible to obtain.

According to the present invention, the solubility of an alkali metal salt of a branched chain carboxylic acid in liquid hydrocarbon media can be greatly increased by incorporating into such liquid hydrocarbon media an alkali metal salt of at least one other branched chain carboxylic acid so'that liquid hydrocarbon solutions of alkali metal salts of branched chain carboxylic acids can be obtained in which at least one of the carboxylates is present in an amount at least twice as great as its solubility alone in the same media. Aswill be illustrated in the examples, this invention makes possible increasing the actual amount of the alkali metal in a hydrocarbon solution of its salts up to several thousand times the amount normally obtainable by the use of one salt alone. 7

This invention is based on the discovery that, when alkali metal salts of two different branched chain car: boxylic acids are brought together in aliquid hydrocarbon media, particularly petroleum hydrocarbons boiling inthe distillate fuel range, the solubility of the two salts is much greater than the expected sum of the solubilities of the individual salts. These may differ with respect to the carboxylate portion of the molecule or with respect to both the alkali metal and the carboxylate por-i tion of the molecule. The larger the number of salts in such mixture, the greateris the total solubility of such salts in the hydrocarbon media, as will be pointedout hereinafter.

The alkali metal salts of branched chain carboxylic acids have been found to effectively improve the combustion characteristics of distillate hydrocarbon fuels. These alkali metal carboxylates are'especially useful in fuels for spark ignition engines and particularly in in: creasing the knock resistance of the fuel. For this use they are normally employed in quantities which provide from about 0.0025 to about 2 grams (prefer-ably 0.01 to Thesefuels may be any of the various gasolines of commercev 1.5 grams) of the alkali metal per liter of fuel.

including the clear stock or those containing additives, or it may be a finished commercialfuel containing additives normally associated with such fuels as antioxidants,, corrosion inhibitors, anti-icing agents, antiknock agents such as tetraethyllead, and the scavenging agents for such antiknock compounds.

The present invention provides hydrocarbon solutions of alkali metal branched chain carboxylates that are visually clear, homogeneous, stable liquids containing.

amounts of the alkali metal far in excess of any quantity conceivable by heretofore known methods, making possible the preparation of master mixes for further -dilution. For example, solutions containing up to about 50% by weight of the salts have been obtained simply by adding the multiplicity of alkali metal branched carboxylates to the liquid hydrocarbon medium, giving as high as 20 grams of alkali metal per liter in hydrocarbon solution. The carboxylates may be added thereto separately as the individual salts or they may be, mixed -beforehand. Alternately,the corresponding individual acids may first be mixed and converted to the same mixture of alkali metal salts. .Such mixture of salts may be prepared in situ in a liquid hydrocarbonfor example by the action of an alkali metal hydride on the acids. The.

new hydrocarbon solutions of the present invention will contain at least two alkali metal salts in amounts'at least twice their individual solubilities in the same hydro-' carbon, although as pointed out above, by this invention, hydrocarbon solutions of alkali metal branched chaiir.

carb-oxylates may be produced containing up-to 50% weight of salts in the solution.

Any of the usual techniques may be employed to facilita-te the solubilization process, e.g. the solvent-solute system may be heated or agitated, under abrading conditions if desired, as in the presence of steel balls or clean dry sand, to increase the surface area of thesolid phase and thereby speed upits rate of solution. Also, the salts may first be dissolved in a solvent such as alcohblgethers,

esters or ketones, the solution added to the hydrocarbon medium and thesolvent then removed. Conveniently,

an alcohol, eg, CHQOH, CgHgOl-I or other solvent boiling lower than thehydrocarbon and separable therefrom (as by distillation) may be used. The solvent, which is not essential to this invention, need not be removed if its presence is desirable for another purpose, for example where alcohol is used to serve as an anti-icing agent in motor fuels. I l The alkali metal carboxylates. with which invention is concerned are the lithium, sodium and potassium salts of branched, chain carboxylic acids in which the radical attached to the carbon atom of thecarboxyl group is an open branched chain aliphatic hydrocarbon radical More particularly, th e branched acids may contain .up to,-

36 carbon atoms and will have at least one branch in its carbon skeleton within the first'4 carbon atoms of the main chain, counting from and including the carboxyl carbon atom. The branched acids are those having open branched carbon skeletons and may be secondary or tertiary acids or branched chain primary acids. Secondary and tertiary acids, by definition, are branched on the carbon atom adjacent to the carboxyl carbon atom, while branched chain primary acids have their first branch on a carbon atom more remote from the carboxyl group. For reasons of availability, branched acids having up to about 20 carbon atoms are preferred.

Representative acids from which the alkali metal carboxylate may be derived are:

2-methylpropanoic 2,2-dimethylpropanoic (pivalic) 3-methylbutanoic (isovaleric) Z-ethylbutanoic 2,2-dimethylbutanoic 2,3-dimethylbutanoic 3,3-dimethylbutanoic 4-methylpentanoic Z-ethyl-Z-methylbutanoic 4,5-dimethylhexanoic 2-ethylhexanoic 3-ethylpent-2-enoic acid 3-ethylpent-3-enoic acid 2,2,4,4-tetramethylpentanoic 3,5,5-trimethylhexanoic 2-ethyl-4,4-dimethylpentanoic 4-ethyl-5,5-dimethylhexanoic 2,2-diethylhexanoic 2-isopropyl-5-methylhexanoic 2-propylheptanoic 2-isobutyl-4-methylpentanoate 2-heptylnonanoic 2-hexyldecanoic Z-ethyl-Z-butyldecanoic 2-methyldodecanoic 2,2-dimethylhexadecanoic 2,2-dimethyloctadecanoic.

Mixtures of branched chain acids such as obtained by various methods described in the art may be employed, such as mixtures obtained by oxidizing branched chain aldehydes and primary alcohols produced on carboxylating olefins (particularly branched chain olefins) with carbon monoxide and hydrogen, by the well-known Oxoprocess. Oxo products obtained from polymers and copolymers of propylene and butylene-for example, the C alcohol from propylene-butylene dimer, the C alcohol from tripropylene, and C alcohol from tetrapropylene and the C alcohol from pentapropylene, are readily available. Such products, including representative mixed acids that may be obtained therefrom, are more particularly described in US. Patents 2,815,355, 2,824,836 and 2,751,361.

The acids may also be those mixtures obtained by carboxylating olefins such as Z-methylpentene-l, 2,6-dimethylheptene-3, decene-l, mixed nonenes e.g. tripropylene, mixed dodecenes, e.g. tetrapropylene, and the like, with water and carbon monoxide in the presence of acid catalysts. Typical mixed acids are more particularly described in US. Patents 2,158,031, 2,419,131 and 2,831,877; French Patent 1,130,080, and by H. Koch in Brennstofi chemie 36, 321 (1955) and Fette-Seifen-Anstrichmittel 59, 493 (1957).

Mixed acids made by applying the Guerbet reaction to a mixture of primary alkanols also provide alkali metal carboxylates exhibiting the unusual solubility characteristics of the present invention. In the overall process, primary alcohols having at least two hydrogen atoms on the carbon atom adjacent to the CH OH group are transformed by heating with alkaline reagents to carboxylic acids having twice the number'of carbon atoms as the original alcohol and having an alkyl branch on the carbon atom adjacent to the carboxyl group. For example, U.S. Patent 2,829,177 discloses the Guerbet condensation of C C and C Oxo alcohols to the corre sponding C C and C branched alcohols. These may be oxidized to the carboxylic acids by heating with caustic, as described in Ber. 56, 1739 (1923) for the preparation of heptadecanoic acid from heptadecyl alcohol. U.S. Patent 2,293,649 describes the one-step conversion of certain primary alcohols, e.g. octadecyl, to higher branched chain acids, e.g. hexadecyl Z-eicosanic acid, on heating with sodium.

As stated above, the individual lithium, sodium or potassium salt of a branched chain carboxylic acid as defined and exemplified above, shows extremely limited solubility in liquid hydrocarbons. In terms of the alkali metal, the solubility of such a species will usually be in the range of 0.001 to 0.0001 gram of metal per liter of solution. In this respect, these salts of the branched chain acids are no diiferent than those of the straight chain fatty acid series. However, the branched chain salts are remarkably different in that they mutually increase the solubility of one another to a level many times the sum of the individual solubilities to give even as much as 20 grams of alkali metal per liter, whereas mixtures of the corresponding salts of the fatty acid series (straight chain) show no appreciable increase.

Employed according to the present invention, two single salts, lithium carboxylates for example, Whose additive solubility (i.e. the sum of the intrinsic solubilities) is of the order of 0.001 gram of lithium per liter, will provide a dissolved lithium content which will be much greater than the expected additive solubility. It has also been discovered that by increasing the complexity of the system by adding a third, then a fourth, etc. component, the mutual solubilizing effect is markedly increased. In this way solubility increases of several hundred to a thousand times the additive solubility have been achieved.

It should be understood that each of the solutions produced may be used to bring into solution still another (diiferent) alkali metal carboxylate which may be a single salt or mixture of such salts. In other words, a hydrocarbon solution of an alkali metal salt of a branched chain carboxylic acid as defined will effectively take into solution still another alkali metal salt of a branched chain carboxylic acid as defined, in amounts greatly exceeding its intrinsic solubility.

Practically speaking, the relative quantities of each of the salts employed in the starting mixture is immaterial to the operability of the solubilization process. A combination of two or more salts as defined will dissolve, at least in part, to provide a concentration of alkali metal (in solution as a salt of two or more carboxylic acids) which is greater than the sum of the intrinsic solubilities of the individual salts that make up the mixture. Generally, however, it is desirable, from a practical point of view, in effecting solution of one salt by another, to add them to the solvent in the mol ratio within the range of from 1 to 5 to 1 to 5, with the optimum of about 1 to 1.

Where more complex mixtures of salts are employed, that is, where a number of salts are dissolved in the hydrocarbon solvent, each salt appears to be capable of increasing the solubility of another salt in the mixture in the same way, for, as illustrated in the following examples, where complex mixtures such as of the C salts are used, the solubility in the hydrocarbon of any other salt added to the mixture is tremendously increased. Of course the exact number of individual salts in these normallyoccuring mixtures is not known. Where only three individual salts were employed such as in Example 4, the total amount of lithium put in solution in the isooctane was 900 times greater than was indicated by the individual solubilities in the same solvent.

The compositions of this invention are adapted to provide Working concentrations of the alkali metal in soluble form in media consisting essentially of liquid hydrocarbons boiling in the distillate fuel range. The liquid hydrocarbon medium may be parafiinic, isoparafiinic, olefinic, naphthenic, arocatic, or blends thereof. For example, it may be heptane, isooctane, diisobutylene, benzene, toluene, kerosene, gasoline, diesel oil or jet fuel oil and mixtures of these materials. The solutions may be used as such or as additives for gasoline or other fuels.

The following procedure was used for determining solubility of the salts and mixtures of salts in the various media mentioned. A quantity of the salt or mixture was added to the solvent and stirred or otherwise agitated for one hour at room temperature. This solution was allowed to stand for at least two days in a closed container. A portion of the liquid phase was then removed, centrifuged for 15 minutes at 1850 rpm. and the resulting clear liquid analyzed for its metal content.

The following examples are given to illustrate the invention. Par-ts used are by weight unless otherwise specified.

EXAMPLE 1 One-half gram each of lithium 2, 2,4,4-tetramethylpentanoate and lithium 3,5,5-trimethylhexanoate was added to 100 ml. of isooctane and the mixture stirred for 2 days at 27 C. The resulting liquid phase contained 0.024 gram of dissolved salt (0.01 gram of lithium per liter of solution), which corresponds to about 27 times the additive solubilities of the two salts determined separately in control experiments.

EXAMPLE 2 Twenty (20) milligrams of a 1:1 mixture of lithium 2,2,4,4-tetramethylpentanoate and 3,5,5-trimethylhexanoate was dissolved in 2 ml. of methanol and the solution added to 120 ml. of isooctane. The resulting mixture was distilled under reduced pressure at 30 to 40 C. to remove the methanol completely and to concentrate the solution to a volume of about 8 ml. At 27 C. the lithium content of this clear solution corresponded to 0.09 gram of lithium per liter. By this method of putting the salts in solution, the total amount of salt solubilized is 9 times greater than obtained by the procedure of Example 1.

EXAMPLE 3 EXAMPLE 4 To 100 ml. of isooctane was added 0.5 gram of each of the following lithium salts having the individual solubilities tabulated below:

Lithium Carboxylate: g?}l? g$ &

2,2,4,4tetramethylpentanoate 0.0001 3,5,5-tn'methylhexanoate 0.0003 2-hexyldecanoate 0.0001

The mixture was stirred at 27 C. After 2 days, a small quantity of solid remained undissolved. This dissolved lithium content of the liquid phase, in grams per liter, was 0.45 or 900 times the sum of the individual solubilities shown above, determined in control experiments.

EXAMPLE 5 The procedure of Example 4 was repeated on a mixture consisting of 0.5 gram of each of the following: lithium 2-hexyldecanoate, lithium 2,2-dirnethylhexadecanoate and 2,2-dimethyloctadecanoate. The solubility of the mixture is isooctane, after 2 days, corresponded to 0.31 gram of lithium per liter, or about 150 times the sum of the individual solubilities as found in separate experiments.

EXAMPLE 6 The procedure of Example 4 was employed on a mixture consisting of 0.5 gram each of lithium 2,2-dimethylpropanoate, lithium 2,2,4,4-tetramethylpentanoate and lithium 2,Z-dimethyloctadecanoate. After 2 days, the isooctane solution contained 0.17 gram. of lithium per liter, or about 170 times the sum of the individual solubilities as found in separate experiments.

EXAMPLE 7 The procedure of Example 4 was repeated on a mixture containing 0.5 gram each of the following nine lithium carboxylates: 4

3,5 ,S-trimethylhexanoate 2,2,4,4-tetramethylpentanoate 2-propylheptanoate 2-isopropyl-S-methylhexanoate 4-ethyl-5,5-dimethylhexanoate 2-isobutyl-4-methylpentanoate 2-methyldodecanoate 2-hexyldecanoate 2,2-dimethyloctadecanoate.

EXAMPLE 8 135 parts by weight of commercial propylene tetramer and 87.4 parts of a hydrated boron trifluoride catalyst (prepared by saturating water with boron trifluoride at room temperature) was charged into a silver-lined autoclave cooled to about C. The autoclave was pressurized to 3000 p.s.i. with carbon monoxide (in large excess), closed, mechanically shaken, and warmed to room temperature where it was held to complete the reaction (about 30 minutes). The autoclave was then vented and its liquid charge removed. The products from five such, runs were combined, washed with water (to remove. boron trifluoride) and distilled to yield the following fractions:

(A) As a small forerun, a mixture of neutraljoil and acid substance;

(B) As the major product (494 parts), an acid fraction consisting substantially of branched chain C car boxylic acids, boiling range 120 C. at 0.3 mm. of Hg, neut. equiv. 223; V

(C) As a minor product, an acid fraction boiling from 112 to 118 C. at 0.1 mm. of Hg and having a neut. equiv. of 357 (corresponding to an average carbon content of 23);

(D) As the distillation residue, an acid fraction, remaining undistilled at 167 c. at 0.08 mm. of Hg and having a neut. equiv. of 520.

Each of fractions B, C and D formed alkali metal salts showing unusually high solubility in liquid hydrocarbon fuels and other organic solvents, as indicated below.

By the above procedure, propylene trimer, diisobutylene, triisobutylene, dodecene-l, mixed tetradecenes and mixed octadece nes were carboxylated to yield multicomponent mixtures of branched chain carboxylic acids whose alkali metal salts also show surprisingly high solubilities in organic solvent.

EXAMPLE 9 The alkali metal salts described below were prepared by neutralizing the acid fractions B, C and D of Example 8 with the stoichiometric quantity of alkali hydroxide in either alcohol or water, followed by removing the solvent in vacuo.

Each lithium salt of fractions B, C and D of Example 8 was soluble in isooctane to the extent of at least 100 grams per liter of solution at room temperature.

The sodium and potassium salts of the C acid frac- 7 tion B were each readily soluble at the. 100 gram liter level in isooctane.

The lithium salt of fraction B was soluble to the extent of at least (a) 100 grams per liter of solution in 'n-heptane, benzene and commercial automotive and aviation gasolines, and (b) 10 to 12 grams per liter of solution in JP-4 jet fuel. 1

EXAMPLE 10 I To 100 ml. of a 0.02 molar solution of the lithium salt I of the C acid fraction described in Example 8 was added 0.5 gram of a lithium carboxylate listedbelow. 1 The mixture was stirred for 4 hours at room temperature, allowed to stand in a closed glass container for days, and its liquid phase after centrifuging analyzed for lithium. The results are tabulated below:

Sollrbilization of Lithium Carboxylates by 0.02 Molar LiC in Isooctane Li carboxylate. Mols of salt solubilized Normal 'aliphaticextracting with 5 volume percent water, 74% of the salt remains unextracted.

I Theembodiments of the invention in which an incluw sive property or privilege is. claimed are defined as follows:

1. A method for increasing the amount of an alkali metal of the group consisting of sodium, potassium and lithium which can be put in solution in the form of a salt in a liquid hydrocarbon media, which comprises inper mol of LiCm Salt' I Acetate 0.00 Caproate 0.00 Stearate 0.00 Branched aliphatic Pivalate 0.50 2-ethylhexanoate 0.24 '2,2,4,4-tetramethylpentanoate 1.02 2-hexyldecanoate 1 0.21

The solubility of each of the above listed pure salts'is substantially nil in isooctanealone. 'The marked solubility of the lithium carboxlates having at least one alkyl branch inthe presence of another salt (LiC is apparent from the above data;

EXAMPLE 11 1965 parts by weight of LiOH-H O was slowly added to a stirred solution of 10,578 parts of the C acid frac' tion described in Example 8 and 10,600 parts of benzene. The resulting mixture was heated to boiling under a reflux condenser equipped with a Dean-Stark trap in which the benzene-water azeotrope was collected and separated, with the benzene layer being returned to the reactor. When water no longer appeared in the distillate (after 24 to 40 hours), the reaction mass was cooled to -60 C. and filtered through cheese cloth to remove trace quantities of insoluble matter. The thus filtered product was a clear amber liquid, mobile at room temperature.

EXAMPLE 12 A complex mixture of isomeric 2-octyldodecan-1-ols obtainable from Oxo-decanol and which has branching in both the octyl and dodecan chains, was oxidized to a mixture of the corresponding C carboxylic acids, boiling range 149160 C. at about 0.1 to 0.2 mm. of Hg. The procedureemployed, involving caustic fusion of the alcohol, was similar to that described by Heiduschka and Ripper, Ber. 56, 1739 (1923) for the conversion of heptadecyl alcohol to heptadecanoic acid.

The lithium salt of the mixed C acid (prepared by neutralizing the acid with lithium hydroxide in alcohol and evaporating the solution to dryness in vacuo) is highly soluble in organic solvents; for example, its solucorporating in the hydrocarbon media at least two alkali metal salts of aliphatic branched open chain carboxylic acids, at least one of which, salts is present in an amount at least twice its individual solubility in such hydrocarbon, the carboxylic acid salts being those in which the carboxy group is attached to a hydrocarbon radical.

2. A method for increasing the amount ofan alkali 7 metal of the, group consisting of sodium, potassium and lithium which can be put in solution in the form of a salt in a liquid hydrocarbon media, which comprises incorporatinginthe hydrocarbon media at least two alkali metal salts of aliphatic branched open chain carboxylic acids, at least 2 of such alkali metal, salts being present in amounts at least twice that of their individual'solubil- I ities in the same hydrocarbon,-the carboxylic acid salts being those in which the carboxy'group is, attached to a hydrocarbon radical.

3. A method for increasing the amount of an alkali metal of the group consisting of sodium, potassium and lithium which can be put in solution in the form of a salt in a liquid hydrocarbon media, which comprises incorporating in the hydrocarbon media at least two alkali metal salts of aliphatic branched open chain carboxylic acids, each salt being present in an amount at least twice that of its individual solubility in the same hydrocarbon, the carboxylic acid salts being those in which the carboxy group is attached to a hydrocarbon radical.

4. A liquid hydrocarbon containing dissolved therein from 0.01 to 20.0 grams of an alkali metal of the group consisting of sodium, potassium and lithium per liter in the form of the alkali metal salts of aliphatic branched open chain carboxylic acids, which solution has been obtained by incorporating in the liquid hydrocarbon a mixture of alkali metal salts of aliphatic branched open chain carboxylic acids, the carboxylic acid salts being those in which the carboxy group is attached to a hydrocarbon radical.

References Cited in the file of this patent UNITED STATES PATENTS 2,151,432 Lyons et al Mar. 21, 1939 2,280,474 Byrkit et al. Apr. 21, 1942 2,616,905 Asseif et al. Nov. 4, 1952 FOREIGN PATENTS 300,156 Great Britain Nov. 6, 1928 312,245 Great Britain May 17, 1929 658,059 France Jan. 22, 1929

Claims (1)

1. 4. A LIQUID HYROCARBON CONTAINING DISSOLVED THEREIN FROM 0.01 TO 20.0 GRAMS OF AN ALKALI METAL OF THE GROUP CONSISTING OF SODIUM, POTASSIUM AND LITHIUM PER LITER IN THE FORM OF THE ALKALI METAL SALTS OF ALIPHATIC BRANCHED OPEN CHAIN CARBOXYLIC ACIDS, WHICH SOLUTION HAS BEEN OBTAINED BY INCORPORATING IN THE LIQUID HYDROCARBON A MIXTURE OF ALKALI METAL SALTS OF ALIPHATIC BRANCHED OPEN CHAIN CARBOXYLIC ACIDS, THE CARBOXYLIC ACID SALTS BEING THOSE IN WHICH THE CARBOXY GROUP IS ATTACHED TO A HYDROCARBON RADICAL.