US2321947A - Manufacture of soap - Google Patents

Description

atented June 35, 1943 UNETED STATES ?AT direct and mesne assignments, to The Sharples Corporation, Philadelphia, has a corporation of Delaware No Drawing. Application April 23, 1941, :Serial No. 389,888

(c1. zen-412.5)

19 Claims.

The present invention pertains to the manufacture of soap, and is mor particularly concemed with the purification of the product known as nigre, obtained in the soap-making process.

In accordance with the conventional procedure for making soap by the full boiled" or settled process, an oil or fat is initially boiled with a quantity of caustic. soda solution which is somewhat lessthan the amount which would theoretically be required for complete saponification. When the alkali has been substantially completely utilized in converting the fat into soap, the soap .formed by reaction of the caustic soda with the fat, and unsaponified oil or fat, are grained out or salted outby the addition of concentrated brine or dry salt. The action of the brine is to cause the soap to precipitate in the form of soap curds, and these curds rise to the top of the soap kettle. This permits withdrawal from the bottom of the kettle f the "spent lye, which is the water solution of salt, glycerine, and any slight excess of alkali which may be present, together with some impurities and coloring matter. This spent lye is subjected to special treatment for glycerine recovery.

The soap curd remaining in th kettle at the end of these operations is treated with a further quantity of caustic soda solution to complete the saponification of any neutral fat which may not have been saponified in the previous treatment. After saponification is completed by boiling the resulting mixture, the soap is again grained by addition of salt or a further quantity of caustic soda solution, and the soap curds are again separated from the resulting aqueous After completion of saponiiicaticn of the fat by a series of saponification steps such as discussed above, called changes, and washing the product in one or more additional changes with a brine solution, there is obtained a soap-containing mass which contains grained soap, water, free alkali (unneutralized sodium hydroxide), salt, and miscellaneous foreign matter including an undesirable quantity of dirt and other-undesired impurities. It is necessary that the quantity of free alkali, salt and foreign matter in the soap-containing mass be materially reduced in order to obtain an acceptable grade of soap, regardless of whether this soap is to be used as a toilet soap or a laundry soap. In order to attain this result, the soap-maker subjects this mass to a fitting or finishing operation.

much smaller proportion of salt, free alkali and dirt than the soap-containing mass from which it is produced. This neat soap is subjected to further treatment, which varies in accordance with the type of soap being produced, in manufacturing the desired commercial product, but these steps do not concern us in the present discussion.

The free alkali, salt and foreign impurities from the original saponified product are, for the most part, retained in the lower stratified layer, or nigre. These impurities are present in the nigre to an objectionable extent, and this material cannot therefore be directly utilized in producing the familiar soaps of commerce. Re gardless of whether the nigre or equivalent substance is produced by the above or some other sequence of steps, it contains a very large proportion of soap, and any soap-making process which failed to utilize the soap values of the nigre would, therefore, be highly uneconomical.

In conventional soap-making procedure, the nigre is mixed with a further quantity of fat and lye in the manufacture of a further batch of soap, and is treated along with this further quantity of fat and lye, in one of the earlier saponi-' fication steps discussed above. By operating in this fashion, the'soap contained in the nigre becomes a part of the next batch of soap, and is, for the most part, retained in the neat soap of the succeeding batch, upon the performance of the fitting step on that batch. The utilization of the nigre in this manner has the disadvantage,

The fitting operation is accomplished by add= however, that it results in the degrading of the next batch of soap by addition to the ingredients of that batch of the least desirable constituents of the preceding batch. In the interests of economy, the nigre is recycled to a succeeding soapmaking batch as long as this may be continued without impairing the quality of the soap derived from the succeeding batches to too great an extent. It is self-evident from the above discussion, however, that the amount of impurities in the nigre as well as in the resulting neat soap increases progressively as the recycling of the nigre is continued, and this recyclingoperation must, accordingly, ultimately be discontinued.

In conventional procedure, when the nigre becomes degraded to a point at which recycling in manufacture of a particular grade of soap is impossible, the nigre, instead of being entirely discarded, is mixed with fat and alkali entering into the making of an inferior grade of soap, and the recycling of the nigre in the manufacture of this inferior grade of soap is continued until the nigre becomes too poor to be used further in this operation. While the exact sequence of steps of recycling the nigre and/or passing it to a saponification step in manufacture of an inferior grade of soap varies considerably, depending upon the, quality of soap to be produced and other considerations, the above discussion covers the general principle of re-use of the nigre to recover the soap which it contains.

The above discussion afiords an approach to a statement of the nature of the present invention. A feature of the invention is the removal of foreign impurities from the nigre before recycling the nigre to the succeeding soap-making batch, thereby avoiding progressive increase in the amount of foreign impurities in successive batches of nigre, and permitting continuation of the operation of recycling the nigre, without the degradation which'has occurred in prior artpractice.

By the practice of the invention, the soapmaker is able to perform an effective removal of impurities from the nigre. At the same time, he-is able to effect removal of impurities from the nigre-by a procedure which involves utilization of materials whichordinarily enter the soap-making process, thereby permitting all of the materials introduced for the purpose of assisting in removal of impurities from the nigre to be utilized in the manufacture of coap.

Further advantages of the invention will be evident from the following discussion, and the manner in which these advantages have been attained will also be evident from that discussion.

The present invention rests upon the discovery that it is possible to effect removal of practically all of the undesired impurities fromthe nigre provided material constituting a source of acid is first mixed with the nigre and reacted with the alkali of the nigre to reduce the free alkali content of the nigre. Thus, in the practice of the invention, an acid or ester is mixed with the nigre, and the resulting mixture is preferably heated to a temperature sumciently high to effect fairly rapid reaction between the free alkali of the nigre and the acid or ester employed to reduce the free alkali concentration.

In the preferred practice of the invention, a high molecular organic acid or ester is added to the nigre for reaction with the free alkali which is present. The resulting mixture is then heated to a temperature which may be in the neighbor-- hood of the boiling point of water, in order to cause reaction between the free alkali and source of acid to produce soaps oi the acids or esters employed. when the quantity of free alkali has been substantially reduced or entirely eliminated by neutralization by the acid or ester, it will be found that most of the foreign impurities may be removed by appropriate treatment.

Among the preferred materials which may be used for neutralization of the free alkali of the nigre in the practice of the invention are the various fatty acids and fats, and other high molecular organic acids and esters thereof, such as the various oils and fatty acids which ordinarily enter into the soap-making operation. Thus, cocoanut oil, tallow, cottonseed oil, corn oil, palm kernel oil, soya bean oil, rosin, or any one of a large number of other organic esters or acids obtained by splitting of such esters may be used in the practice of the invention. We have obtained our best results by the use of cocoanut oil or cocoanut oil fatty acids in this connection, since the neutralization of free alkali by cocoanut oil or cocoanut oil acids results in production of a mass from which undesired impuritreatment, such as the application of centrifugal force.

In the preferred practice of the invention, a suflicient amount of the material constituting the source of neutralizing acid is added to the nigre to eiiect substantially complete neutrali-' zation of the freealkali, and even an exces the material constituting the sourcevof acid may be used, in order to assist in obtaining rapid and complete reaction of the acid with the alkali present.

After a substantial proportion of the free alkali has been neutralized by the operations discussed above, the resulting mixture is subjected to a separating operation which, in the preferred embodiment of the invention, involves centrifugation. When the treated nigre is subjected to high centrifugal force, practically all of the undesired impurities are removed, and the resulting purified mixture may then be recycled directly to the first or any subsequent saponification step of the soap-making process, and subjected to further treatment together with the alkali and fat employed in the subsequent soap-making operation.

The advantages obtained by the practice of the invention will now be apparent. In the first place, the neutralization of the free alkali by addition of an acid has the effect, for reasons which we do not fully understand, of making it possible to remove the dirt and other undesired impurities almost completely from the nigre. By reason of the accomplishment of this result, it is possible to effect recycling of the nigre almost indefinitely to succeeding soap-making batches. and to effect improvements both in the quality of the soap produced and in the economics of the soap-making process. But these results are accomplished, in contradistinction to previously proposed methods of purifying the nigre, in a manner which introduces no additional expense to the fundamental steps of the soap-making operation. By using, as the ester or acid added to the nigre to reduce the quantity of free alkali present, a material which normally enters into the soap-making operation, we are able to effect removal of undesired impurities from the nigre without addingany expense whatever, for the same quantity of ester or acid would be utilized and the same heat required to effect reaction if the free alkali were neutralized by return of the mm to the succeeding soap-making operation without first adding the fat or acid. Thus, when the ordinary soap-making fats or acids are used to precondition the nigre for clarification, this preconditioning step merely involves effecting saponification of a part of the fat or acid to be used in the ensuing soap-making operation at a slightly earlier stage than would otherwise be the procedure.

Various modifications will be obvious to those skilled in the art. Instead of using, as a source of acid to neutralize the free alkali of the nine.

an ester or acid such as ordinarily used in soapmaking, other esters or acids capable of furnishing an acid radical for combination with the free alkali may be employed. Thus, aliphatic and aromatic sulfonic acids such as have recently come into wide use as washing, wetting and emulsifying agents may be added to the nigre for reaction with the free alkali to furnish the appro-' priate salts of such acids, or a wide variety of other organic and inorganic acids and esters may ties may be readily separated by appropriate be employed.

- in combination with the performance of the step of neutralizing the free alkali with an acid, and that advantageous results are obtained in some cases by diluting with water the mixture of nigre and added acid.

Example I A mass of soap nigre was placed in a large kettle and heated to 210 F. The nigre ,was thoroughly agitated during the heating period,

' and this agitation was continued during the feed of the nigre to a centrifugal separator at a rate of 1680 lbs. per hour. Prior to centrifugation, the nigre contained 1.3% solids, and after centrifugation it contained 0.8% solids. 38.5% of the solids of the nigre were thus obtained as a bowl deposit in the centrifugal separator.

A sufficient quantity of cocoanut oil was next added to the nigre remaining in the kettle to effect neutral zation of all of the free alkali of the nigre. Stirring and heating were continued for an hour after addition of the cocoanut oil, in order to insure neutralization of all of the free nigre was neutralized with cocoanut oil fatty alkali. The resulting nigre was next passed through the centrifugal under conditions identical with the treatment of the unneutralized portion of the nigre which had previously been subjected to centrifugation. In this centrifugation, only 0.1% of solids remained in the centrifuged nigre. Approximately 92% of the content of solids was thus removed from the portion ofthe nigre neutralized with cocoanut oil.

Example II In an operation conducted in a manner analogous to that of Example I, a sample of nigre containing 1.6% of solids was centrifuged without prior neutralization of alkali, with the result that the nigre effluent from the centrifugal contained 0.9% solids, representing a removal of 43.7% of the content of solids., In' a second operation, involving treatment of the same nigre after neutralization with hydrochloric acid, the nigre effluent from the centrifugal contained only 0.1%

acids, and this second sample was then subjected to similar centrifugation, with the result that the solids content was reduced to 0.4%, representing an 87.1% removal of solids.

Example V A sample of nigre containing 2.2% solids was centrifuged without prior neutralization, and approximately 50% of the solids content was removed. in this operation. A second sample was neutralized with tallow acids, and the content of solids was reduced to 0.5%, representing a solids removal of 77.3%.

Example!!! A sample-of nigre containing 0.9% solids was centrifuged without pro-treatment, with. removal of approximately 50% of the solids. A similar samplewas then neutralized by treatment with cocoanut oil and centrifuged, with the result that all but 0.01% of the solids wereremoved, repre- 'senting a 99% removal of solids.

Example VII A nigre sample containing 1.2% solids was neutralized with cocoanut oil fatty acids and centrifuged, with the result that the content of solids was reduced to 0.03%, representing a 97.5% removal of solids.

Still further modifications will be obvious to those skilled in the art, and we do not therefore wish to be limited except by the scope of the following claims.

When reference is made in these claims to a source of acid this expression is used in the same sense as on pages 2 and 3 of this specifiof solids, representing removal of 93.7% of the content of solids in the centrifugal.

Example III treated sample was reduced in solids content from 1.4% to 0.8%, representing removal of 42.8% of the solids, while the neutralized sample was reduced to 0.4% solids content, representing a 71.4% solids removal.

Example IV A sample of nigre containing 3.1% of solids was heated and centrifugedas in Example I with out prior neutralization of the free alkali, with the result that approximately 50% of the solids wereremoved. A second sample of this same cation, to indicate either a free acid, or an ester capable of furnishing an acid radical for combination with the free alkali of the nigre. When reference is made to treatment of the nigre with acid or reaction of the free alkali of the nigre with acid, treatments and reactions by which soap is formed by the action of the free alkali upon any of theabove-mentioned sources of acid is included.

We claim:

1. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of acid to said nigre and reactingthe acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre, the reaction between the acid and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the nigre. l

2. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of acid to said nigre and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre by centrifugation, the reaction between the acid and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the nigre.

3. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of acid to saidnigre and reacting the acid with the free alkali of the nigre until the free alkali has been substantially completely neutralized, and theretreated nigre, the reaction between the acid and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the nigre.

4. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of acid to said nigre and reacting the acid with the free alkali of the nigre until the free alkali has been substantially completely neutralized, and thereafter removing insoluble impurities from the acid treated nigre by centrifugation, the reaction between the acid and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the nigre.

5. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of organic acid to said nigre and reacting the acid withthe free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre by centrifugation, the reaction between the acid and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the nigre.

'7. In the separation of insoluble impurities from a soap nigre containing free alkali, the

process comprising adding a source of a soap-.

forming organic acid to said nigre and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre.

8. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of a soapforming organic acid to said nigre and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre by centrifugation.

9. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of a higher aliphatic soap-forming acid to said nigre, and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre.

10. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of a higher aliphatic soap-forming acid to said nigre and reacting the acid with the free alkali of the nigre until said free alkali is substantially completely neutralized, and thereafter removing insoluble impurities from the acid treated nigre.

11. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of cocoanut oil acid to said nigre and reacting the acid with enema? after removing insoluble impurities from the acid the free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre.

12. In the separation of insoluble impurities from a soap nigre containing free alkali, the process comprising adding a source of cocoanut oil acid to said nigre and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, and thereafter removing insoluble impurities from the acid treated nigre by centrifugation.

,13. In the separation of insoluble impurities from a soapnigre containing free alkali, the process comprising adding a source of cocoanut oil acid to said nigre and reacting the acid with the free alkali of the nigre until said free alkali is substantially completely neutralized, and thereafter removing insoluble impurities from the acid treated nigre by centrifugation.

14. In the manufacture of soap, the process comprising, saponifying a source of soap-forming acid, separating a nigre containing free alkali from the saponified mass, adding a source of acid to said nigre and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, thereafter removing insoluble impurities from the acid treated nigre, and mixing the purified nigre with other constituents in the manufacture of a further quantity of soap, the reaction between the acid .and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the nigre.

15. In the manufacture of soap, the process comprising, saponifying a source of soap-forming acid, separating a nigre containing free alkali from the saponified mass, adding a source of acid to said nigre and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, thereafter removing insoluble impurities from the acid treated nigre, and mixing the purified nigre with a further quantity of a source of acid and of alkali in the manufacture of a further quantity of soap, the reaction between the acid and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the-nigre.

16. A process as defined in claim 14, in which the source of acid added to the nigre is a source of cocoanut oil acids. 4

17. A process as defined in claim 14, in which the source of acid added to the nigre is a source of higher fatty acids. 1

18. A process as defined in claim 14, in which the source of acid added to the nigre is a source of soap-forming acid.

19. In the manufacture of soap, the process comprising, saponifying a source of soap-forming acid, separating a nigre containing free alkali from the saponified mass, adding a source of acid to said nigre and reacting the acid with the free alkali of the nigre until the quantity of said free alkali is substantially reduced, thereafter removing insoluble impurities from the acid treated nigre by centrifugation, and mixing the purified nigre with other constituents in the manufacture of a further quantity of soap, the reaction between the acid and nigre constituents being conducted in such a manner as to avoid substantial splitting of the soap of the nigre.

LEOPOLD SENDER. JAMES H. WILSON.