US2411832A - Water-insoluble soaps - Google Patents

Description

Patented N09. 26, 1946 WATER-INSOLUBLE SOAPS Hooper Linford, Manhattan Beach, and William J. Baral, Long Beach, Calif., assignors to Union Oil Company of California, Los Angeles, Calif.,

a corporation of California No Drawing. Application July 2'7, 1942 Serial No. 452,418

7 Claims.

This invention relates to improvements in the process for preparation of soaps which are relatively water-insoluble from soaps which are relatively water-soluble, by metathesis; a preferred embodiment being improvements in the process of metathesizing sodium naphthenate and copper sulfate to form the water-insoluble copper naphthenate.

The uses of such soaps are many and varied. Copper naphthenate is at present in great demand for treatment of burlap sacks to retard rotting. Other water-insoluble 'soaps to which our invention is applicable have been employed as components of inks, paints, driers, fungicides, adhesives, dyes, pigments, lubricants, fuels, ointments, etc.

Metathesis, or double decomposition, is a common type of chemical reaction which may be illustrated by the following equation:

In applying this general equation to the specific example of the preceding paragraph, AX would represent the' sodium naphthenate, BY the coper sulfate, AY the sodium sulfate, and BX the copper naphthenate. The driving force of the reaction may be considered to be the insolubility of one of the reaction products (in this example the copper naphthenate), and the completeness of the reaction will depend on the relative degree of insolubility of one of the products (or its .effective removal from the system) as compared with that of the reactants. The invention is applicable, therefore, to the preparation of any soap which may be formed bythe above type of reaction, i. e., to the formation of a water-insoluble soap from the corresponding water-soluble soap and a relatively water-soluble salt of the desired metal. The organic acid constituent of the soaps involved is preferably a relatively strong organic acid having a dissociation constant greater than about 10-, as for example a fatty acid, naphthenic acids extracted from petroleum, a product of oxidation of petroleum fractions, a sulfonic acid derived by sulfuric acid treatment of petroleum fractions, or any other similar organic acid; however, it may be a relatively weak acid such as the "phenols extracted from petroleum, an alcohol, mercaptan, imide, etc., in some instances. The metals most commonly forming water-insoluble soaps are the polyvalent metals such as copper, lead, tin, aluminum, iron, zinc,

barium, chromium, etc., although monovalent metals such as silver may also be included. These mentioned are merely examples, and the inven- 2 tion is applicable to the soaps of many other metals and organic acids.

The term salts is sometimes used to describe some of the metal-organic compounds which we refer to as soaps, but we prefer to use the term soaps in this application to avoid confusion with the inorganic salts suchas copper sulfate and sodium chloride, etc., which are also involved in the reactions. As a second item of nomenclature, the terms soluble and insoluble as used in this specification, except when qualified, shall be construed to mean water-soluble or water-insoluble, respectively. Similar- 1y, by naphthenic acids is meant the usual mixture which may contain some acids of other types such as the acyclic arachidie acids for example.

In the past, the commonly used method of preparing a water-insoluble soap such as copper naphthenate by metathesis, has involved mixing equivalent proportions of water solutions of sodium naphthenate and copper sulfate, with added naphtha as a gathering agent for the water-in soluble soap, agitating until the reaction is complete, settling, drawing off the water layer, washing the oil-copper naphthenate layer with water, filtering, and if desired, removing the added naphtha by distillation.

The above process has several features which are decidedly objectionable froma commercial standpoint. One of the worst of these is the tendency of the reaction mixture and the water washing mixtures to form emulsions which are extremelyslow in breaking. This makes the entire process a very slow one, increases costs, and tends to cause high material losses. There is also a distinct fire hazard involved where, naphtha is present in the open kettlesnormally employed in the metathesis step;

, It is theprincipal object of this invention to provide improvements. in the above process of preparing insoluble soaps which eliminate many of its defects." These improvements canbe more clearly understood after considering the following description of the complete improved process, which for convenience is outlined as a series of steps and is exemplified by a description of copper napthenate, this being a preferred form of the invention.

Step 1.-Preparation of the water soluble soap solution Kerosene and gas oil fractions from a California crude oil were each extracted with aqueous caustic soda solution originally containingabout 6 lbs. NaOH per bbl.,, until the bulk of the caustic 'fers from the conventional in each case was converted to sodium naphthenate by the naphthenic acids present in the oil fractions and the resulting solution had a basicity to phenolphthalein equivalent to an NaOH content of about 0.5 lb. per bbl. These crude soaps were then blended, and the blend Was acidified with sulfuric acid to obtain a supernatant layer of "crude acids having an acid number of about 150 mg. KOH per gram. The crude acids were then" separated and distilled, taking a heart out comprising about a 5% to 80% overhead fraction, this material being designated distilled crude acids and. having an acid number of about 1'75 mg. KOH per gram. A charge of about 30 tons (175 bbls.) of these distilled crude acids was then introduced into an agitator equipped for heating, cooling, and agitation, and the calculated equivalent amount of caustic, namely about 92 tons (500 bbls.) of an aqueou caustic soda solution containing lbs. of NaOH per bbl. was added. The mixture was heated to a temperature between 150 F. and 175 F. and agitated for about 2 hours to complete the saponification, and the pH of the resulting solution was adjusted to 8.0 by

addition of a small quantity of caustic (naphthenic acids may be required in some instances).

Step 2.-Formation of the insoluble soap by metathesz's To the above prepared aqueous sodium naph- Step 3.--Purification of the insoluble soap The above copper naphthenate soap phase, which carried with it small amounts of water and other impurities such as water-soluble salts, was charged to a shell still, in which it was heatedjust sufficiently to boil off all of the water. This also effectively precipitated the water-soluble salts. About 200 bbls. of mineral spirits, was then added and the charge was mixed, and settled until clear. The clear solution of copper naphthenate in mineral spirits, which was the desired. product in this example, was decanted,

leaving in the still a small residue of copper naphthenate solution plus the settled solid impurities. The still was then flushed with mineral spirits (which was drawn off into an auxiliary tank, allowed to settle, and used as the diluent for the next batch of copper naphthenate), and finally flushed with water and steam.

It may be observed that the above'process difprocess in the following particulars:

v (l) The precipitating salt employed in the metathesisis used in the form of a solid instead of an aqueous solution. This eliminates the step trated salt solution and a supernatant phase consisting of nearly pure insoluble soap. These two concentrated phases occupy a relatively small volume, and have very little tendency to emulsify.

(3) No water washing is used. It has been found that removal of inorganic impurities including the water soluble salts by dehydrating and settling is fully as effective and much more rapid than the usual water washing, and also results in a product soap completely free from water, andtherefore having improved oil solubility characteristics.

' The invention therefore resides in the production and separation of the Water-insoluble soap phase by the addition of solid salt to the reaction mixture in the absence of any added oil or naphimpurities; in the combination of these steps;

and in an improvement designed to facilitate the separation of the water-insoluble soap phase from the aqueous phase described below.

The invention has been illustrated by the metathesis of sodium naphthenate and copper sulfate to produce copper naphthenate. However, the inventionis applicable to the preparation of a very large variety of soaps as indicated above. The following description is intended to show the reasons for some of the operating conditions used in the above preparation of copper naphthenate, and to clarify the operating conditions which may be used in other preparations.

In the extraction of petroleum fractions with caustic soda to form the crude soaps as in Step 1 above, it is desirable to employ a solution of such strength as to minimize emulsification of the two phases which may otherwise result in loss of sodium naphthenate to the oil and in excessive entrainment of oil in the crude soaps. Some entrainment always occurs, however, as evidenced by the fact that the crude acids cracked out from the crude soaps as described above, may contain about 25% or 30% of unsaponifiables such as entrained oil and unstable asphaltic or resinous materials.

The crude acids or crudesoaps may be used in place of the distilled crude acids or the soaps made therefrom in our process, particularly when the petroleum fractions being extracted are clean distillates of relatively low molecular weight, such as kerosene, stove oil, etc., and the percent of unsaponifiables is relatively low, self below about 20%. It is preferable, however, especially where cracked, residual, or high molecular weight stocks are extracted, to use the distilled crude acids as described above, since these are free from high molecular weight materials, unstable materials, etc., which might cause excessive emulsification in the succeeding metathesis. The distilled crude acids described usually contain about 15% to 20% of dissolved entrained oil of moderate molecular weight (kerosene to gas oil). This is not a necessary part of the invention however, since as described below, our process is also applicable to highly refinednaphthenic acids, which contain 3% or less of .un- 'saponifiables, as well as to organic acids other than naphthenic acids, which may containno oil. It has been found, moreover, that the presence of such normally entrained oil of moderate molecular weight (a portion of the stock being extracted) is, not analogous to the presence. ofa

tracted; while in the other series the oil was a naphtha (mineral spirits). The degree of emulsification experienced in the metathesis step in each experiment was measured by the volume of emulsion cuff remaining after 2 hours of settling, expressed as a percent of the volume of the clear supernatant copper naphthenatc soap phase. The results follow:

Resulting per cent emulsion based on clear soap phase Weight per cent oil added based on acid content In presence Infprgsfrace of added n i ner al parent oil Spirits These data show clearly one of the advantages of operating without added naphtha, as well as the difference between the low boiling oilsadded in conventional processes, and the parent oil normally present in extracted naphthenic acids, when each is present in relatively small quantities. When naphtha is employed as a gathering agent in the conventional processes, incidentally, it is common practice to add 100% by weight or more on the above basis.

The strength of the caustic soda or other base used to form the aqueous solution of the watersoluble soapis limited by the following considerations. It should be strong enough to keep the volume of the solution at a reasonably low value, and to minimize emulsion tendencies; yet it should not be so strong as to interfere seriously with the freedom of contact between the watersoluble soap and the added salt, either by salting on the water-soluble soap or by imparting excessive viscosity or emulsifiability to the solution. Bases having strengths of about 0.2 M to 2.0 M (mols per liter) have been found generally satisfactory.

In the neutralization of naphthenic acids, using caustic soda as above, it is desirable to stop at an end point pH of about 8.0. This is done to insure minimum acid loss with maximum utilization of caustic, and to eliminate complications resulting from precipitation ofinsoluble metal oxides or hydroxides. Similar considerations will dictate the pH to be used as an end point in other preparations. For example, in neutralizing weaker acids such as the petroleum phenols, it may be desirable to stop at a much higher pH, e. g, 10 or higher. If too high a pH is employed, however, there may be a side reaction involving considerable precipitation of an insoluble metal hydroxide during the metathesis step when certain metal salts are added, and this could cause contamination of the water-insoluble soap phase with free organic acids, or even prevent appreciable metathesis of the waterinsoluble soap.

The most common bases employed for formation of the soluble soaps are those of the alkali metals, especially sodium and potassium, and

soluble soap phase may be either the upper or the lower layer after stratification. In the above copper naphthenate example, it was the upper layer, while in a similar preparation of lead naphthenate, it was the lower layer. Obviously, there will be other preparations or variations in operating conditions which will result in approximately equal specific gravities for both the insoluble soap phase and the aqueous phase, thus making the rate of Stratification extremely slow. In this event the specific gravity of one of the phases must be modified.

The specific gravity of the aqueous phase may be modified by a change in the concentration of the base used to saponify the organic acid in the preparation of the soluble soap. For example, the

refined naphthenic acids containing about 3% 0f unsaponifiables described above were saponified as in Step 1 above by reaction with caustic of about 15 lbs. NaOH per bbl. strength (1 M) in one experiment, and with caustic of about 3 lbs. Na'OI-Iper bbl. strength (0.2 M) in a second experiment. In the subsequent metathesis as in Step 2 above, the insoluble soap phase stratified above the aqueous phase in the first experiment, and below the aqueous phase in the second experiment. Similar. modification of the specific gravity of the aqueous phase could be accomplished by adding either water or a water soluble salt or heavy brine to the reaction mixture during Step 2, 7 g

The specific gravity of the insolublesoap phase may also be modified to avoid equal specific gravities of the two phases. The addition of naphtha as in conventional processes tends to reduce the specific gravity of this soap phase, but it may have the disadvantage of increasing emulsification tendencies as noted above. The addition of small amounts of parent oil would be preferable, in preparing naphthenate soaps.

We have found a means of modifying the specific gravity of the insoluble soap phase. however. which is believed to be novel, and which has an additional beneficial effect in reducing emulsification tendencies, which effect may be due to modification of the existing interfacial tension. The addition of carbon tetrachloride to the reaction mixture in amounts as low as a few percent or possibly as high as of the volume of the aqueous phase will cause the insoluble soap phase to stratify below the aqueous phase in instances where the two phases normally have approximately equal specific gravities, and will also markedly decrease tendencies toward emulsification. The carbon tetrachloride will then accompany the insoluble soap to the subsequent purification as in Step 3 above, where it may be distilled off with the entrained water and reused, etiher after separation'from the distillate water layer, or in conjunction with that layer. Other solvents which are suitable for this purpose are those organic liquids which are stable, non-reactive, water-insoluble, and miscible with the water-insoluble soap under the conditions of use, and which have specific gravities above about 1.2, and boiling points between about F. and

300 F, These include allyl iodide, trichlorethane, butyl bromide, etc.

It is obvious from the above disclosure that the occurrence of equal specific gravities of aqueous and insoluble soap phases may be avoided by any suitable combination of the methods described. It should also be noted in this connection that the temperature of the stratifying mixture may play an important part in the relative specific gravities of the two phases, since it has been observed that the co-efiicient of expansion of the insoluble soap phase is frequently much greater than that of theaqueous phase. In fact, mixtures have been prepared in which the insoluble soa phase will stratify above the aqueous phase while hot, yet will sink below the aqueous phase when cold.

It is not necessary in all cases to conduct the metathesis at elevated temperatures, but it generally shortens the reaction time, and may reduce emulsion troubles. It may be necessary, moreover, in some cases, to operate above the melting point ofv one of the constituents. For example, the final step in purifying the waterinsoluble soap, involving separation of solid impurities by settling or filtration, obviously requires liquid phase operation, and this may require elevated temperatures when th desired soap is normally a'solid, and no diluent is present.

The addition of mineral spirits to the dehydrated. soap as shown in the example is not a vital part of the invention, but in case the water-insoluble soap is desired in the form of a solution in mineral spirits or other diluent, it may be of some advantage to add said diluent to th waterinsoluble soap phase (after separation of the aqueous phase), so as toexpedite the settling or filtering of the precipitated salts from the dehydrated soap. It may be of some further advantage to add the diluent before dehydrating, thus providing mixing by convection. Also, if desired in the latter operation. a portion of a suitable diluent may be taken overhead with the water in the dehydration, thus permitting a lower temperature for the dehydration.

It is obvious that many minor modifications in specific procedures other than those mentioned may also be applied without exceedin the scope of the invention defined by the following claims.

We claim:

1. A. process for preparing a relatively water insoluble metal soap of an organic acid which is also capable of form ng a relatively water soluble soap of a second metal, which consists in adding a solid granular salt of said first metal, with agitation, to a water solution of a water soluble soap of said acid and said second metal so as to form said relatively water insoluble soap of said acid and said first metal by metathesis, allowing the reaction mixture to separate into an aqueous phase and an insoluble soap phase, separating said phases and then separating water and solid inorganic impurities from said insoluble soap phase.

2. A process according to claim 1 in which the.

organic acid has a dissociation constant greater than about 10".

- 3. A process for preparing a relatively water insoluble metal soap of naphthenic acids which will also form a relatively water soluble soap of a second metal, which consists in adding a solid granular salt of said first metal, with agitation, to a water solution of a naphthenate of said sec-- ond metal so as to form the naphthenate of said first metal by metathesis, allowing the reaction mixture to separate into an aqueous phase and an insoluble soap phase, separating said phases, heating said insoluble soap phase to effect substantial dehydration thereof and then separating solid inorganic impurities from the dehydrated product.

4. A process according to claim 3 in which a volatile hydrocarbon diluent is added to the insoluble soap phase after its separation from the aqueous phase to facilitate the separation of the impurities,

5. A process according to claim 3 in which the separation of the reaction mixture into an aqueous phase and an insoluble soap phase is effected in the presence of a water insoluble, halogenated organic liquid boiling between about 150 F. and about 300 F. and having a specific gravity greaterthan about 1.2 whereby said insoluble soap phase is dissolved in said halogenated liquid and the solution separates as a lower layer.

6. A process according to claim 3 in which the separation of the reaction mixture into an aqueous phase and an insoluble soap phase is effected in the presence of carbon tetrachloride whereby said insoluble soap phase is dissolved in said carbon tetrachloride and the solution separates as a lower layer.

7. A process for preparing copper naphthenate which consists in reacting an aqueous solution ofsodium naphthenate with a solid granular copper salt at a temperature between about and the initial boiling point of the reaction mixture, with agitation, so as to form copper naphthenate by metathesis, allowing the reaction mixture to separate into an aqueous phase and a copper naphthenate soap phase, separating said phases, heating said copper naphthenate phase to effect substantial dehydration thereof, adding a volatile hydrocarbon diluent to said dehydrated soap phase, separating solid inorganic impurities from said diluted phase, and separating said volatile hydrocarbon diluent from the product.

HOOPER LINFORD. WILLIAM J. BARAL.