US3542823A - Production and treatment of soap - Google Patents

Description

United States Patent US. Cl. 260-418 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the production of a soap of improved colour and odour which includes the step of treating a soap containing system at any stage during the production of the soap with an alkali metal borohydride at a pH of at least 9.5. The soap containing system is preferably treated With anaqueous alakli solution containing 0.01-0.30% sodium borohydide by weight of the fat charge immediately after it leaves the washing unit.

This invention relates to a process for the preparation of a soap and, in particular, it relates to a process for the preparation of a soap of improved colour and odour.

It is known that certain of the coloured compounds present in low grade fats or fatty acids are not removed by a conventional treatment with activated adsorbent materials. The characteristic odour of unperfumed soap is also diflicult to remove by treatment of the fat or fatty acid with an activated adsorbent material. Of the various solutions that are applicable to the problem of removing these coloured compounds and odoriferous compounds which are not satisfactorily absorbed, that of chemical reduction seems to have been given some consideration, but hitherto has not met with any great practical success.- Application of non-selective reducing treatments (for example hydrogenation in the presence of a nickel catalyst) does not provide a useful solution as the removal of colour and odour requires an undesirable increase in the melting point of the fat charge. Furthermore, specialized pressure vessels are required to carry out this hydrogenation treatment.

Certain reducing agents, such as the alkali metal borohydrides, are known to decompose at elevated temperatures in aqueous solution, the rate of decomposition increasing with increasing temperature and decreasing with increasing alkalinity of the solution. In view of this knowledge, it is surprising to find that low concentrations of alkali metal borohydride can rapidly reduce the colour and odour of a viscous medium like molten soap.

Accordingly this invention provides a process for the preparation of a soap which includes the step of treating a soap containing system at any stage during the manufacture of the soap with an alkali metal borohydride, at a pH of at least 9.5.

The colour of the soap obtained from this process is conveniently measured on a 5.84% w./v. aqueous solution of the soap (dry basis) with the aid of a Lovibond Tintometer using a Lovibond 13.3 cms. cell. The acceptable standard of colour depends on the purpose to which the soap produced is to be applied. The colour is determinable in terms of Lovibond red and yellow unitsthese units being combined to form one value (referred to in this specification as the soap colour) by use of the formula:

soap colour= (yellow reading) +30 X (red reading) ice The term soap charge, as defined in this specification refers to the material obtained by saponification of a suitable charge of fat and alkali. The term fat may refer to an animal tallow, a vegetable oil such as palm oil, palm kernel oil or coconut oil, a fish oil or to the fatty acids obtained from such materials by a conventional splitting technique. Mixtures of these fats may be used in the process of this invention-a convenient mixture, for example, being based on tallow and up to 20% W./w. of an oil such as coconut oil. These fats are henceforth referred to in the specification as the fat charge. When the fat charge is of a low grade, it is desirable that it be given a pre-treatment with an activated earth or other adsorbent bleaching agent (referred to henceforth in this specification as a standard bleaching treatment) before saponification, as the colour thus removed will not then compete with the unsorbed material for the borohydride. The colour of a bleached low grade tallow may vary from 40 yellow, 0.8 red to 15.0 yellow, 2.5 red (when measured in a 0.635 cm. cell of a Lovibond Tintometer).

Synthetic fatty acids, such as those obtained by the oxidation of paraflinic hydrocarbons, may also be used in the process of this invention alone or in admixture with a fat.

A soap charge prepared from a toilet grade standard bleached tallow or the soap obtained from such a tallow may also be treated by the process of this invention particularly when it is desired to obtain a product essentially free of odoriferous compounds.

The term alkali metal in this specification is to be taken as referring to lithium, potassium, or sodium. Of the alkali metal borohydrides, the sodium derivative is commercially most readily available. The alkali metal borohydride may be added in the process of this invention either in solid form, or as an aqueous solution, or as a blend with soap, or it may be formed in situ from other borohydrides. Preferably it is added as a solution in aqueous alkali-suitable alkalies being sodium hydroxide or potassium hydroxide.

By in situ formation of an alkali metal borohydride is meant the addition of a borohydride salt, other than an alkali metal salt, to a soap containing system. Due to the large excess of alkali metal ions which are present in such a system, the borohydride salt will be converted to the alkali metal borohydride.

The alkali metal borohydride is conveniently added either towards the end of the saponification stage of the soap manufacture or after the saponification has been completed, as, at these points, the pH of the saponification system does not vary so widely as during the initial period of saponification.

If the borohydride is added during the saponification stage, boiling of the saponification system should be continued for a further period of about 30 minutes to ensure complete dispersion of borohydride and maximum reduction of colour and odour of the soap charge. The total colour and odour reduction is dependent on the effectiveness with which the borohydride is spread through the saponification system as well as the level used.

Colour and odour removal can also be effected after the completion of saponification as long as the soap is still in a fluid state ot permit adequate mixing with the borohydride and as long as the pH of the soap does not fall below about 9.5, a preferred range of pH being 9544.0.

The alkali metal borohydride is preferably added immediately after the soap derived from the saponification process has been washed or immediately prior to the stage when the soap is dried. Alternatively it is possible to add the borohydride to the soap immediately after the end of 3 the drying stage or at the milling stage (with accompanying pigment.)

It is necessary to ensure that the temperature of the soap containing system is adequately controlled and that there is sufficient alkali present in the soap-containing system to allow time for the borohydride to disperse completely and to carry out its reducing action before decomposition. If the borohydride is to be mixed with a soap containing system that is being stirred with normal paddle-type stirrers and maintained at 90-100 C. it is preferable that the pH be at least 12.0-14.0. With continuous or semi-continuous processing where more efiicient inline mixing is employed pH control need not be quite so stringent.

The amount of alkali metal borohydride to be used for the improvement of the colour and odour of soap, preferably lies within the range of 0.005-0.30% by weight of the total fatty acid content of the soap used. A particularly preferred amount of borohydride for the treatment of a soap obtained from a toilet grade standard bleached tallow lies within the range 0.02-0.10% by weight of the fat charge. Addition of borohydride in excess of 0.30% by weight of the fat charge is, of course, also effective but is less likely to be economically attractive.

Borohydrides decompose in aqueous media with the formation of borate ion and hydrogen. Adequate precautions should be taken in view of possible fire hazards associated with the evolution of hydrogen and the associated problem of foam formation. The foam formation may be controlled by (a) gradual addition of the borohydride to the soap containing system in a vessel having a volume sufiicient to allow for any expansion of the soap containing system or (b) adding the borohydride to the soap immediately prior to the stage when it is to be pumped into a drier unit and to maintain the soap in this drier unit under pressure until it is sprayed onto a further processing unit The invention is now further illustrated with reference to the following examples.

EXAMPLE 1 A low grade tallow was treated with four different percentage proportions (ranging from 1-6% w./W.) of fullers earth for 5 minutes at 105 1l0 C. followed by 5 minutes at 110-115 C. After filtration from the fullers earth, the tallows obtained from each of the four bleaching level experiments were divided into three aliquots in beakers, each aliquot containing 20 parts by weight of bleached tallow. After melting these samples of tallow on a boiling water bath, 10 parts by volume of a 30% w./v. aqueous sodium hydroxide solution were added to the first sample from each bleaching level experiment. This mixture was maintained on the boiling water bath and stirred until completely saponified. 9 parts by volume of the 30% w./v. aqueous sodium hydroxide solution were added to the remaining two samples from each bleaching level experiment. These mixtures were subsequently similarly saponified.

minutes after the addition of the sodium hydroxide solution, one part by volume of 30% w./v. aqueous sodium hydroxide solution containing 0.01 part by weight of sodium borohydride was added with stirring to the second sample of each of the saponifying bleached tallows. One part by volume of 30% w./v. aqueous sodium hydroxide solution containing 0.02 part by weight of sodium borohydride was similarly added to the third sample of each of the saponifying bleached tallows.

After one hour, 10 parts by volume of water were added to each of the 12 saponified samples and the mixtures thus obtained were homogenised by rapid stirring. The homogenised mixtures were then transferred to larger beakers, 290 parts by volume of distilled water added to each and the soap dissolved by heating to about 75 C. The colour of each of the derived soap solutions was determined by Lovibond colorimetry in a 13.3 cms. cell.

(such as a vacuum chamber or a chilling drum) or 40 The results obtained were tabulated as below:

Percent bleaching earth 1 2 4 6 Percent sodium borohydride.. 0 0.05 0.1 0 0.05 0 0.05 0 0.05 0.1 Lovibond Yellow 29 27 15 7.4 6.3 4.0 3.2 2.8 1.5 1.5 Lovibond Red 1.0 1.0 0 8 1.6 1.0 0.8 0.6 0.6 0.3 0.2

(0) adding the borohydride to the soap as it leaves the EXAMPLE 2 washing unit and degasing by spraying the treated soap into the fitting pan.

Borate ion is readily removable from the treated soap by aqueous washing although its presence has no deleterous effect on the soap or any material (such as perfume) that is to be added to the soap at a later stage in its preparation. A further advantageous feature of the process of this invention lies in the fact that it is so readily incorporated into a normal soap manufacturing process. Flame-proofing of the soap-making machinery may be necessary in view of the possible hazard associated with the evolution of small volumes of hydrogen.

The amount of adsorbent agent used in the standard bleaching treatment of a low grade fat charge is preferably about 6% by weight of the fat charge. Fullers earth is a preferred bleaching agent, but other adsorbent earths or bleaching carbons may be used.

The colour and odour of the treated soap depends on the amount and type of adsorbent bleaching agent (if any) that is usd in the pre-treatment of the fat charge, the amount of alkali metal borohydride used, the time and temperature of the treatment with the borohydride, the pH of the soap containing mixture during the borohydride treatment and the efficiency of mixing the soap containing mixture.

A further beneficial effect that is obtained when the borohydride is added during the saponification stage is that the derived glycerine lye is almost water white.

A fat charge containing 92.5% w./w. tallow (that had been bleached by treatment with 6% W./W. adsorbent earth) having a Lovibond Yellow reading of 11.7 and a Lovibond Red reading of 1.4 in a 5.1 cm. cell and 7.5% w./w. coconut oil was saponified at C. in a conventional soap pan. The soap thus prepared was separated from the lye and washed, in a conventional washing unit, with brine containing 1% w./v. sodium hydroxide. As the washed soap passed out of the washing unit it was treated with an amount of aqueous 5.0% w./v. sodium hydroxide solution containing 10 w./ w. sodium borohydride-sufiicient to provide 0.1% sodium borohydride based on the weight of the fat charge originally saponified. The borohydride treated soap was subsequently fitted, neutralised, heated and dried according to standard practice.

The soap colour of the soap prepared in the above experiment was 37, while the soap colour of a soap prepared from a similar fat charge which was not treated with borohydride, was 60.

In a further experiment the soap was washed with brine containing 2% w./v. sodium hydroxide. The soap colour of the untreated soap was 54. The colour of the soap that had been treated with 0.1% w./w. sodium borohydride was 43.

Hydrogen evolution inflated the 20 tons of soap that were prepared in each of the above experiments where borohydride was used, to the volume that would have been occupied by 35 tons of soap.

EXAMPLE 3 A fat charge containing 92.5% w./w. tallow (that had been bleached by treatment with 6% w./w. adsorbent earth) having a Lovibond Yellow reading of 6.0 and a Lovibond Red reading 0.9 (measured in a 5.1 cm. cell), pan. 7.5% w./w. coconut oil was saponified at 95 C. in a conventional soap pan. The soap thus prepared was separated from the lye and subsequently washed with brine containing 1% w./v. sodium hydroxide. Aqueous 5% w./v. sodium hydroxide solution containing w./w. sodium borohydride (in an amount sufiicient to provide 0.02% sodium borohydride by weight of the original fat charge) was added to half the soap as it left the washing unit. The soap colour of the soap treated in this way was 26=(1.4 Y+0.4 R). The soap colour of the remaining soap that had not been treated with sodium borohydride was 39=(2.1 Y+0.6 R).

EXAMPLE 4 A 1.5 ton soap charge was prepared by saponification of a fat charge comprising 85% w./w. tallow and w./w. coconut oil. The lye was separated from this soap charge and the soap washed with brine containing 1% w./v. sodium hydroxide, fitted and passed on to the heat exchanger unit prior to drying, milling and plodding.

Sodium borohydride was dissolved in cold aqueous 4% -w./v. sodium hydroxide solution in an amount sufficient to provide a 15 w./w. solution. Sufiicient of this solution was used to provide an amount of borohydride equal to 0.1% by Weight of the fat charge. This solution was injected into the soap line immediately before the pump feeding the heat exchanger unit over a period of 30 minutes. Samples of the treated soap were taken, after they had been dried, milled and plodded and examined for free alkalinity and soap colour. Comparative samples of untreated soap were similarly examined.

The problem of foaming was largely overcome by this process.

EXAMPLE 5 A 250 lb. fat charge comprising 80% w./w. toilet grade standard bleached tallow and w./w. standard bleached coconut oil was saponified. The soap thus obtained was separated from the lye, washed and fitted. The soap thus obtained had a free alkali content of 0.01%.

A 40 lb. sample of this soap was heated to 90 C. 750 mls. of a 10% w./ w. sodium borohydride solution in aqueous 5% w./v. sodium hydroxide solution was gradually added to the heated soap with stirring (representing an addition of 0.1% sodium borohydride based on the weight of fatty material present in the soap). A further 420 mls. aqueous 5% w./v. sodium hydroxide solution (increasing the amounts of free alkali to 0.5% w./v.) was also added to the soap containing system to reduce the amount of foaming.

A further 40 lb. sample was similarly treated with half the volume of borohydride solution.

The treated soap was fitted, milled and plodded and its odour evaluated by a panel of assistants who were asked to smell the soaps with closed eyes (thus to prevent any influence of colour difference) and to express an opinion as to which soap had the stronger odour. Since the samples were unperfumed the assessment of the panel members was a direct measure of the strength of the undesirable base odour. Each entry was scored +1 for the tablets with the stronger odour, 0 for no difference and -1 for that which had the weaker odour. The scores for each panel member for each soap were added together to arrive at the total score for each soap. A low score indicated little base odour and a high score indicated strong base .odour.

The experimental designs contained soap bars not relevant to the present invention and the results on these soap bars were extracted. The odour scores for any one series did not therefore lie about the zero mean as they would have done in a complete pad comparison analysis.

Addition of borohydride: Odour score Standard error :15.7

A difference of twice the standard error is significant at the 5% probability level.

EXAMPLE 6 A further 40 lb. sample of the soap prepared in Example 5' was heated to C. 880- mls. of a 10% w./w. potassium borohydride solution in aqueous 5% w./v. sodium hydroxide solution was gradually added to the soap with stirring (representing an addition of 0.08% w./w. potassium borohydride based on the weight of the fat charge). A further 320 mls. aqueous 5% w./v. sodium hydroxide solution (increasing the amount of free alkali to 0.5% w./v.) was added to the soap to reduce the amount of foaming.

This experiment was repeated with three further 40 lb. samples of the soap prepared in Example 5, with the exception that the amount of the potassium borohydride solution added was reduced. The amounts of potassium borohydride used in each case, amounted to 0.02%, 0.04% and 0.06% by weight of the fat charge, respectively The odour value of each sample was assessed as follows:

A panel of 10 people was asked to compare the odour of samples of the soaps treated by the process described in this example, with-a sample of untreated soap and to place each sample according to the degree of deodorisation they thought had been achieved. The following table shows the number of people who were able to correctly allot the right position for each sample.

Percent borohydride: No. of correct allotments What is claimed is:

1. In a process for the production of a soap comprising the stages of (a) reacting a fat charge with an alkali,

(b) separating, washing and fitting a soap containing system obtained from stage (a) (c) drying and milling the soap containing system and (d) extruding the dried soap, the improvement which comprises adding an alkali metal borohydride at a pH of at least 9.5 at any stage of said process up to the step of extruding the dried soap.

2. A process as claimed in claim 1 in which the treatment with the alkali metal borohydride is carried out at a pH between 9.5 and 14.0.

3. A process as claimed in claim 1 in which the soap is produced from a fat charge, the main constituent of which is tallow.

4. A proces as claimed in claim 1 in which the soap is produced from a fat charge, a constituent of which is palm oil, palm kernel oil or coconut oil.

5. A process as claimed in claim 1 in which the soap is produced from a fat charge, the constituent of which is the fatty acids obtained from fat by a conventional splitting technique.

6. A process as claimed in claim 1 in which the fat charge is pre-treated with an adsorbent bleaching agent.

7. A process as claimed in claim 1 in which the soap is treated with an alkali metal borohydride after the reaction of the fat charge with alkali is completed.

8. A process as claimed in claim 1 in which the soap is treated with an alkali metal borohydride immediately after it has been washed.

9. A process as claimed in claim 1 in which the soap is treated with an alkali metal borohydride immediately prior to the drying stage.

10. A process as claimed in claim 1 in which the soap is treated with an amount of alkali metal borohydride equal to 0.005-0.30% by weight of the fat charge.

11. A process as claimed in claim 1 in which the soap is treated with an aqueous sodium hydroxide solution of an alkali metal borohydride.

12. A process as claimed in claim 1 in which the soap is treated with sodium borohydride.

References Cited UNITED STATES PATENTS 2,946,813 7/1960 Palmquist 260417 LEWIS GOTTS, Primary Examiner E. G. LOVE, Assistant Examiner US. Cl. X.R. 260417