US2802848A - Soap-making and bleaching process - Google Patents

Description

United States PatentO SOAP-MAKING AND BLEACHING PROCESS Claims priority, applicationGreat Britain February 16, 1954 7 Claims. (CL Isa-41s No Drawing.

This invention relates to the bleaching of soap, particularly the bleaching ofsoap with an alkali metal hypochlorite.

When a soap of good color is required to be produced it is necessary to bleach the oil from which the soap is made with a bleaching earth. The bleaching of oils with a bleaching earth is, however, a laborious and costly process involving filtering of the oil from the earth. It also involves a treatment of the spent earth to recover the considerable amount of oil which is absorbed by the earth during the treatment. Consequently, earth bleaching of oils is adopted in the soap-making industry only when it is desired to produce soaps of the very highest quality, for example, toilet soaps.

The bleaching of oils by treatment with chemical bleaching agents followed by saponification to produce good colored soap or the bleaching of soaps from unbleached oils avoids the abovementioned disadvantages of earth bleaching. As chemical'bleaching agents hypochlorites, and in particular sodium hypochlorite, have been suggested. Such hypochlorites, however, do not'effectively bleach most oils, although in the case of some oils a certain amount of bleaching may take place at very highconcentrations of'hypochlorite. Also, theyare not effective inbleaching soaps from'some oils, suchas red palm oil, unless violent agitation, for example, agitation by a high speed impeller working in a stream of soap, is employed. Also, unlessviol'ent agitation is employed, a soap capable of being-bleachedwith' hypochlorite'te'nds torevert to its unbleached color tin-standing; The .-degr'ee of agitation has'to vbesu'ch that it is not=possible to carry out hypoch-loritetreatment of soaps batchwis'e in the conventional soap-making kettles, but .requiresa special apparatus for pumpingia'stream of hypochlorite into a stream of soap and violently agitating'the two streams:

Also, in soap-making processes, the lye which. separates from the grained soap has an-unspent alkali content which is usually higher in the case of continuous processes than in the case of batch processes, as Well as any impurities such as dirt and coloring matter present in the oil prior to saponification. It is uneconomic to discharge this lye to glycerine recovery without recovering alkali. The unspent alkali in such lye may be neutralized by mixing the lye with an oilhaving a high free fatty acid content. The free fatty acid in this oil :neutralizes the alkali to form a neutral oil-soap mixture. This neutral oil-soap mixture containing all the dirty impurities present in the original oil is then treated, for example, by 'centrifuging to remove the major part of the aqueous con stituents and the dirty impurities. The oil-soap mixture is then added to the oil being saponified in the continuous soap-making process. Although most of the dirt and other impurities is removed from the oil-soap mixture before passing into the continuous soap-making process, a certain amount of impurities is not removed and therefore impurities are continuously being fed back into the soap-making process. Over a period of time there is 2,892,348 Patented Aug. 13 1957 ICC aprogressive build-up of color throughout the continuous soap-making process with consequent contamination of the soap produced. A state of affairs is often arrived at when treatment of the soap as such with most known processes based -on the use of hypochlorite fails to'bleach the soap satisfactorily.

It is an object of the present invention to provide a process of bleaching soaps with a hypochlorite which avoids the above mentioned disadvantages.

The present invention provides aprocess of preparing light-colored soap which includes the steps of contacting an oil, containing free fatty acid and from which the soap is to be formed, with a chlorite, then saponifying the'chlorite-treated oil with alkali and bleaching the resultant soap with ahypochlorite.

The chlorite may be an alkali metal chlorite, such as sodium or potassium chlorite, and is preferably added to the oil in the form of an aqueous solution. Likewise the hypochlorite may be an alkali metal chlorite such as sodium or potassium hypochlorite, and is preferably added'to'the oil in the form of anaqueous solution. desired, thehypochlorite and chlorite may be formed in situ-in the soap and oil respectively, for example, in the case of the hypochlorite, by addingan alkali, such as sodium hydroxide, to the soap and' passing chlorine gas'through it.

The process of the invention may be used for bleaching soapsfrom any vegetable or animal oils containing free'fatty acids; that is to say, it canbe used for so'aps from unrefined oils which generally'cont'ain free acids: It is of particular advantage for decolorizing soaps-made from oil blends which include the acid oils resulting from the splitting of soapwhen the soapstock obtained from crude oils are alkali refined.

When adding the chlorite to the oil and the hypo chlorit'e to the soap it is not necessaryto provide violent agitation. In fact, agitation need only be sufficient to insure'uniform dispersion of the additives throughout the oil and soap respectively. This is in contrast tothe case where hypochlorite' is'usedto bleach soaps from oils not treated with chlorite where violent agitation of a stream of'hypochlorit'e and a stream of soap is essential. The fact that agitation of thesoap andhypochlorite does not have to be violent, and does not involve the use of streams means-that'the operations of treating the oil with chlorite, saponifying and treating the soap with hypochlorite may be carried outin a single vessel, for example,a soapmaking kettle; insoapmaking may be used for saponification. 'For example, the alkali metal hydroxides such as sodium and potassium hydroxide can be used to produce-water soluble soaps whereas alkaline-earth metal hydroxides such as calcium and barium hydroxide canbe used'toproduce water insoluble soaps. Such a vessel should preferably be acid-resistant since the product of the chlorite addition may. attack non-resistant materials and this may, result in lessJeflicient' decolorization of the finished soap than'would otherwise be obtained. The saponification procedure is conventional.

The amount of chlorite used may be between 0.1% and "10% based'onthe total Weight of oil and fatty acid to "be" reacted with alkali; For'best results the amount of chlorite should 'be 0.5%. The amount of aqueous hypochlorite-(l4% available chlorine) used is preferably betweenv0.2-5% and 20%, i. e., from about 0.04 to 3% of hypochlorite expressed as alkali metal hypochlorite, based on thetotalweight of oil and fatty acid'previously treate'dwith chlorite and for best results 7.5% of aqueous hypochlorite should 'be used. The temperature ofboth" the chlorite treatment and the hypochlorite bleaching should bev between40 C. and 100 C. and preferably about C. The time of contact shouldbebetween-d- Any alkali customarily used minutes and 300 minutes and preferably about 30 minutes, when carrying out the process of the invention batchwise. It is preferred to keep the time of contact between the soap and hypochlorite as short as possible. In one embodiment of the invention suitable for use in combination with a continuous soap-making process, a stream of soap made from chlorite-treated oil containing free fatty acid may be mixed by a suitable form of mixing device with a stream of aqueous solution of hypochlorite. No violent agitation of the soap and hypochlorite is necessary to give a bleached soap, the color of which shows less tendency to deteriorate on standing than do soaps bleached by hypochlorite alone.

In copending application Serial No. 481,709, filed January 13, 1955, there is described a process of bleaching soapstocks obtained in the alkali-refining of animal and vegetable oils, which process consists of treating the soapstock with a hypochlorite and a chlorite.

The process of the present invention is particularly suitable for combining with the process of the aforesaid copending application. In one embodiment of the present invention soapstock treated according to the process of the copending application may be mixed with the chlorite-treated oil containing free fatty acids prior to the reaction with alkali. Such soapstock which contains a considerable proportion of neutral oil is thus directly used in a soap-making process. Hitherto it has been necessary to split such soapstock with mineral acid to covert it into an acid oil by a difiicult and prolonged process, and the acid oil so produced was utilized in the soap-making process. In carrying out this specific embodiment of the process of the present invention the soapstock may be decolorized by the process of the copending application prior to mixing with the chlorite-treated oil utilized in the present invention. Alternatively, the untreated soapstock and material which is to be chloritetreated may be mixed and chlorite and hypochlorite added to the mixture provided the amount of soapstock in the mixture is sufiicient to render the mixture neutral or alkaline. The soap formed after reaction with alkali in this embodiment of the present invention has then, of course, to be treated with hypochlorite.

The process of the present invention is also particularly useful in overcoming the color build-up resulting from the incorporation of the products of neutralization of the lye encountered in the soap-making processes, and which is not overcome by the hypochlorite treatment of soap even when this treatment involves intense agitation such as is mentioned above.

The invention will now be illustrated by the following examples, in which Lovibond color unit readings were obtanied by dissolving the soaps formed in various examples in 70% by volume ethyl alcohol to obtain a by weight of alcoholic soap solution, on which Lovibond color measurements were then made in a 2 inch cell. Parts are by weight.

Example 1 This illustrates the treatment of a crude oil blend to which soapstock has been added. An oil blend of the following composition was prepared:

Parts Crude palm oil 35 Crude palm kernel oil 35 Crude mixed split acid oils 10 blend alkaline and the free fatty acid content of the final blend was 20.6% expressed as oleic acid.

One hundred (100) parts of this oil blend were treated at C. in a reaction vessel fitted with a stirrer with 0.5 parts of sodium chlorite in the form of an aqueous solution of about 50% concentration. Treatment was continued for about 30 minutes. Soap was then prepared by saponification with caustic soda in the normal manner. The lye was allowed to separate and was then removed. The soap was washed and the washings removed. To the soap which had about 60% total fatty matter was added 15% by weight of water and 5% by weight based on the weight of the soap treated (equivalent to about 8.3% by weight of the total fatty matter) of sodium hypochlorite liquor having about 14% by weight available chlorine. The mixture was contained in a glass (or suitably chemically-resistant reaction vessel) fitted with a stirrer and was heated to 60 C. and held at that temperature for about 15 minutes in which time stirring had been taking place. The blended soap was then treated in the usual manner for soap finishing operations. Lovibond color measurements on a 10% alco holic soap solution were then made and are given in the following Table I, which also gives Lovibond measurements made on soaps obtained by saponifying respectively an untreated oil blend, an oil blend treated with 5% bleaching earth and the oil blend treated with 10% hypochlorite only:

The above figures clearly illustrate the better bleaching elfect on soap of the process of the invention over soap from oil treated with 10% hypochlorite and from earth bleached oils.

Example 2 Soaps prepared in a similar manner to that of the last line of the above table were kept for 12 and 15 days, respectively, at 35 C. and 75% relative humidity. Lovibond readings on 10% alcohol soap solutions of samples were taken before and after standing. These readings are given in the following tables, those in Table II relating to storage for 12 days and those in Table III to storage for 15 days:

TABLE II Lovibond Readings on Alcoholic Soap Solutions Yellow Red Soap before storage 0.9 0. 2 Soap after 12 days storage 1. O 0. 2

TABLE III Lovibond Readings on Alcoholic Soap Solutions Yellow Red Soap before storage 1. Soap after 15 days storage 1.

These figures clearly illustrate the absence of color reversion in soaps formed according to the invention.

Example 3 This illustrates the formation of hypochlorite in situ. An oil blend was prepared with the following composition:

Parts Crude palm oil 24.0 Crude tallow 22.5 Crude palm kernel oil 24.0 Crude mixed soft acid oil 9.5

soap was prepared from the treated oil blend, also in the,

manner described in Example 1. The soap was then mixed with about of its weight of water containing the requisite amount of sodium hydroxide which when reacted with chlorine would form the equivalent of about 5% of the weight of soap (having 60% total fatty matter) of sodium hypochlorite liquor having about 14% by weight available chlorine. This mixture was heated to 60 C. and passed through a suitable enclosed mixing apparatus, for example, a centrifugal or other suitable pump. The necessary amount of chlorine gas to react with sodium hydroxide to form the equivalent of about 5% of the sodium hypochlorite liquor (14% by weight available chlorine) based on the weight of soap having a 60% total fatty matter, is fed into the stream of soap/ sodium hydroxide mixture entering the mixing apparatus, for example, into the inlet side of the pump. The bleached soap passes continuously from the outlet of the mixing apparatus and is then subjected to the normal finishing operations for the production of soap. Analogous experiments were carried out with concentrated oil blends and the results obtained are expressed in the fol- The oil treated according to the present invention can be any of those customarily used in making soap. Examples of preferred fatty oils are rapeseed oil, peanut oil, palm oil, coconut oil, tallow, olive oil, palm kernel oil and like oils.

I claim:

1. A process of preparing light-colored soaps which includes the steps of contacting a glyceride oil containing free fatty acid with an alkali metal chlorite, saponifying the chlorite-treated oil with alkali and bleaching the resultant soap with from about 0.04% to about 3% of an alkali metal hypochlorite based on the total weight of chlorite-treated oil.

2. The process of claim 1 in which the chlorite is sodium chlorite and the hypochlorite is sodium hypochlorite.

3. A process of preparing light-colored soaps which includes the steps of contacting a glyceride oil containing free fatty acid with from about 0.1 to 10% of an alkali metal chlorite based on the weight of oil, saponifying the chlorite-treated oil with alkali and bleaching the resultant soap with from about 0.04% to about 3% of an alkali metal hypochlorite based on the total weight of chlorite-treated oil.

4. The process of claim 3 in which the oil is contacted with an aqueous solution of chlorite at a temperature between about 40 and C.

5. The process of claim 4 in which the said chlorite is sodium chlorite and the hypochlorite is sodium hypochlorite.

6. A process of preparing light-colored soap which includes the steps of contacting a glyceride oil containing free fatty acid with an aqueous solution of an alkali metal chlorite at a temperature between about 40 and 100 C., saponifying the chlorite-treated oil with alkali and bleaching the resultant soap by contact with an aqueous solution of an alkali metal hypochlorite at a temperature between about 40 and 100 C., said aqueous solution of alkali metal hypochlorite furnishing from about 0.04% to about 3% of an alkali metal hypochlorite based on the total weight of chlorite-treated oil.

7. The process of claim 6 in which the chlorite is sodium chlorite and the hypochlorite is sodium hypochlorite.

References Cited in the file of this patent UNITED STATES PATENTS Kauffmann Jan. 13, 1942 Stossel et a1 Dec. 2, 1947 Henderson et a1 Oct. 4, 1949 OTHER REFERENCES

Claims (1)

1. A PROCESS OF PREPARING LIGHT-COLOURED SOAPS WHICH INCLUDES THE STEPS OF CONTACTING A GLYCERIDE OIL CONTAINING FREE FATTY ACID WITH AN METAL CHLORITE, SAPONIFYING THE CHLORITE-TREATED OIL WITH ALKALI AND BLEACHING THE RESULTANT SOAP WITH FROM ABOUT 0.04% TO ABOUT 3% OF ALKALLI METAL HYPROCHLORITE BASED ON THE TOTAL WEIGHT OF CHLORITE-TREATED OIL.