NO122389B - - Google Patents

Description

Soap with reduced color and smell.

The invention relates to a soap with reduced color and smell. It is known that certain of the colored compounds present in fat or low quality fatty acids are not removed by conventional treatment with activated adsorbent materials. The characteristic smell of unperfumed soap is also difficult to remove by treating the fat or fatty acid with an activated adsorbent material. Among the various solutions which have come into use to remove these colored compounds and odorous compounds which are not satisfactorily absorbed, the chemical reduction seems to have been shown some attention, but has so far had no great practical success. Application of non-selective reducing treatments (e.g. hydrogenation in the presence of a nickel catalyst) does not provide a satisfactory solution with regard to removing color and odor,

as this requires an undesirable increase in the melting point of the fat charge. Furthermore, special pressure vessels are required to perform

this hydrogenation.

It is known that certain reducing agents, e.g. alkali metal boron hydrides, decompose at elevated temperatures in aqueous solution

ning, and the decomposition rate increases with increasing temperature and decreases with increasing alkalinity in the solution, based on this knowledge it is surprising to find that low concentrations of alkali metal borohydride can quickly reduce the color and smell of a viscous mixture such as molten soap.

Accordingly, the invention provides a soap which in flow-

end state at any stage during the manufacture of the soap is treated with an alkali metal borohydride, at a pH

value of at least 9.5.

The color of the soap produced by this method can be measured on a 5.84% (w/v) aqueous solution of the soap (on a solids basis) using a Lovibond Tintometer and with a Lovibond 13.3 cm cell. The acceptable color standard depends on the intended use of the manufactured soap. The color can determine

mes expressed in Lovibond red and yellow units, these units being combined into one value (in this description referred to as the "soap color") using the formula: soap color = 10 x (yellow reading) + 30 x (red reading).

The term "soap charge" as defined in the specification refers to the material obtained by saponification of a suitable charge of fat and alkali. The term "fat" can refer to an animal tallow, a vegetable oil such as pal-

meal oil, palm kernel oil or coconut oil, a fish oil or to the fatty acids obtained from such materials by conventional

nell gap technique. Mixtures of these types of fat can be used in the method according to the invention, and a suitable mixture is e.g. based on tallow and up to 20% by weight of an oil, e.g. coconut oil. These types of fat are therefore referred to in the description as the "fat charge". When the fat charge is of low quality, it is desirable that it is given a pre-treatment with an activated earth or another adsorbing bleaching agent (hereafter referred to as a standard bleaching) before the saponification,

as the color thus removed will not compete with it

unadsorbed material towards the borohydride. The color of a low quality bleached tallow can vary from 4.0 yellow, 0.8 red to 15.0 yellow, 2.5 red (measured in a 0.635 cm cell in a Lovibond Tintometer).

Synthetic fatty acids such as such as were obtained by the oxidation of paraffinic hydrocarbons, can also be used for the production of soap according to the invention alone or in mixture with a fat.

A soap charge made from a standard toilet grade bleached tallow or the soap obtained from such tallow may also be treated as herein indicated, especially when it is desired to obtain a product which is practically free of odorous compounds .

The term "alkali metal" is used in this description

to lithium, potassium or sodium. Of the alkali metal borohydrides, the sodium compound is the easiest to obtain commercially. The alkali metal borohydride can be added either in solid form or as an aqueous solution, or as a mixture with soap, or it can be formed in situ from other borohydrides. It is preferably added as a solution in aqueous alkali, and suitable alkalis are 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 soapy system. Due to the large excess of alkali metal ions present in such a system, the borohydride salt will be converted to the alkali metal borohydride.

The alkali metal borohydride is preferably added either towards the end

of the saponification step during the soap manufacture or after the saponification has been completed, as the pH value of the saponification system does not vary as much in these stages as during the initial period of the saponification.

If the borohydride is added during the saponification step, boiling of the saponification system should be continued for an extended period of approx. 30 minutes to ensure complete dispersion of borohydride and maximum reduction of color and odor of the soap charge. The total color and odor reduction depends on the efficiency with which the borohydride spreads through the saponification system as well as the concentration used.

Removal of color and odor can also be carried out after complete saponification as long as the soap is in a liquid state, so that a perfect mixture with the borohydride can be achieved, and as long as the soap's pH value does not fall below approx. 9.5, the preferred pH range being 9.5 - 14.0.

The alkali metal borohydride is preferably added immediately after the soap resulting from the saponification process has been washed or immediately before the step where the soap is dried.

It is necessary to ensure that the temperature of the soapy system is adequately regulated and that sufficient alkali is present in the soapy system to allow the borohydride time to disperse completely and exert its reducing effect before decomposition. If the borohydride is to be mixed with a soapy system which is stirred with normal paddle type stirrers and maintained at 90-100°C, it is preferable that the pH is at least 12.0-14.0. When it comes to continuous or semi-continuous operation where more efficient mixing is used in the pipeline, the pH regulation does not need to be so sharp.

The amount of alkali metal borohydride to be used to improve the color and smell of the soap is in the range of 0.01-0.30% by weight of the fat charge in the soap. Addition of borohydride in excess of 0.30% by weight of the fat charge is of course also effective, but will probably not be completely economical.

Boron hydrides decompose in an aqueous environment to form borate ion and hydrogen. Adequate safety measures should be taken in view of the possible fire hazard associated with the development of hydrogen and the associated problem with regard to foam formation. The formation of foam can be controlled by a) gradual addition of the borohydride to the soap-containing system in a vessel with a volume sufficient for unlimited

expansion of the soapy system or

b) adding the borohydride to the soap immediately before the stage when it is pumped into a drying unit and keeping the soap

in this drying unit under pressure until it is sprayed to a further processing unit (e.g. a vacuum chamber or a cooling drum) or

c) addition of the borohydride to the soap at the exit from the washing unit and degassing by injecting the treated soap

in the adjustment pan.

Borate ion can be easily removed from the treated soap by water washing, although its presence has no adverse effect on the soap or any material (eg perfume) to be added to the soap at a later stage of manufacture. A further advantageous feature of the soap according to the invention lies in the fact that the addition of the borohydrides can be so easily incorporated into a normal soap manufacturing process. It may be necessary to make the soap-making machinery fireproof in view of the possible risk associated with the evolution of small amounts of hydrogen.

Amount of adsorbent used in the standard bleaching

of a fat charge of low quality, is preferably approx. 6% by weight

of the fat charge. Fuller's earth is a preferred bleaching agent, but other adsorbing earths or bleaching carbon can also be used.

The color and odor of the treated soap depends on the amount and type of adsorbent bleach (if any) used in the pretreatment of the fat charge, the amount of alkali metal borohydride used, the time and temperature of the treatment with the borohydride, pH value in the soapy mixture during the treatment with borohydride and the effectiveness of the mixing of the soapy mixture.

A further beneficial effect achieved when the borohydride is added during the saponification step is that the resulting glycerol liquor is almost as white as water.

In the following, the invention will be explained with the help of

examples.

EXAMPLE 1.

A low quality tallow was treated with 4 different

amounts (ranging from 1-6% by weight) of Fuller's earth for 5 minutes at 105-110°C, followed by 5 minutes at 110-115°C. After filtering off the Fuller's earth, the tallow obtained from each of the 4 different bleaching trials was divided into 3 aliquots in beakers,

each aliquot containing 20 parts by weight of bleached tallow. After melting these tallow samples in 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 trial. This mixture was kept on the boiling water bath and stirred until it was completely saponified. 9 parts by volume of the 30% aqueous sodium hydroxide solution

addition was added to the remaining 2 samples from each bleach

search. These mixtures were then saponified in the same manner.

40 minutes after the addition of the sodium hydroxide solution

1 part by volume of the above-mentioned 30% aqueous sodium hydroxide solution containing 0.01 part by weight of sodium borohydride was added,

while stirring to the second sample from each of the saponified,

bleached sebum samples. 1 part by volume of the 30% aqueous sodium

hydroxide solution containing 0.02 part by weight of sodium borohydride was likewise added to the third sample of each of the saponified bleached tallow samples.

After 1 hour, 10 parts by volume of water were added to each of the 12 saponified samples, and the resulting mixtures were homogenized by rapid stirring. The homogenized mixtures were then transferred to larger beakers, 290 parts by volume of distilled water added to each and the soap dissolved by heating to approx. 75°C. The color of each of the resulting soap solutions was determined by Lovibond colorimetry in a 13.3 cm cell. The results obtained are listed in the table below:

EXAMPLE 2.

A fat charge containing 92.5% by weight tallow (which was bleached

when treated with 6 wt% adsorbent soil) with a Lovibond yellow reading of 11.7 and a Lovibond red reading of 1.4 in a 5.1 cm cell, and 7.5 wt% coconut oil was saponified at 95°C

in a conventional soap vat. The soap thus produced was separated from the lye and washed in a conventional washing unit with salt water containing 1% (w/v) sodium hydroxide. As the washed soap exited the washing unit, it was treated with an aqueous 5.0% (w/v) sodium hydroxide solution containing 10% by weight sodium borohydride, in an amount sufficient to provide 0.1% sodium borohydride based on the weight of the original saponified fat charge. The borohydride-treated soap was then adjusted, neutralized, heated and dried according to standard practice.

The soap color of the soap that was produced in the above process

search was 37, while the color of a soap made from a similar fat charge that had not been treated with borohydride was 60.

In a further experiment, the soap was washed with salt water containing

held 2% (w/v) sodium hydroxide. The color of the un-

traded soap was 54. The color of the soap treated with 0.1% by weight sodium borohydride was 43.

Hydrogen development meant that the 20 tons of soap that had been produced in each of the above experiments where borohydride was used swelled to a volume that would otherwise have contained 35 tons of soap.

EXAMPLE 3.

A fat charge that contained 92.5 wt% tallow (which was

bleached by treatment with 6 wt% adsorbent soil) with a Lovibond yellow reading of 6.0 and a Lovibond red reading of

0.9 in a 5.1 cm cell, and 7.5 wt% coconut oil was saponified at 95°C in a conventional soap pot. The soap thus produced was separated from the lye and then washed with salt water containing 1% (w/v) sodium hydroxide. Aqueous 5% (w/v) sodium hydroxide solution containing 10% by weight sodium borohydride

(in an amount sufficient to give 0.02% by weight of sodium borohydride based on the original fat charge) was added to half of the soap as it emerged from the washing unit. The color of the soap thus treated was 26 = (1.4 c + 0.4 R). The color of the remaining soap not treated with sodium borohydride was 39 = (2.1 C + 0.6 R).

EXAMPLE 4.

A 1.5 tonne soap charge was produced by saponification of

a fat charge consisting of 85% by weight of tallow and 15% by weight of coconut oil. The liquor was separated from the soap charge and the soap washed with brine containing 1% (w/v) sodium hydroxide, adjusted and conveyed to the heat exchanger unit before being dried, milled and kneaded.

Sodium borohydride was dissolved in cold aqueous 4% (w/v) sodium hydroxide solution in an amount sufficient to give a 15% w/v solution. Sufficient of this solution was used to give a borohydride amount corresponding 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 were taken of the treated soap after it had been dried, milled and kneaded, and they were examined for free alkalinity and soap color. Similar samples of untreated soap were examined in the same way.

The foam problem was largely overcome by this procedure.

EXAMPLE 5.

A 113 kg fat charge containing 80% by weight standard bleached toilet grade tallow and 20% by weight standard bleached coconut oil was saponified. The soap thus obtained was separated from the lye, washed and adjusted. This soap had a free alkali content of 0.01%.

An 18 kg sample of this soap was heated to 90°c. 750 ml of a 10% by weight sodium borohydride solution in aqueous 5%

(w/v) sodium hydroxide solution was gradually added to the heated soap with stirring (this was equivalent to an addition of 0.1% sodium borohydride based on the weight of fatty material in the soap). An additional 420 ml of the aqueous 5% sodium hydroxide solution (which increases the amount of free alkali to 0.5% w/v) was also added to the soapy system to reduce the amount of suds.

Another 18 kg sample was treated in the same way, but with

half the volume of borohydride solution.

The treated soap was adjusted, milled and kneaded and the smell assessed by a panel of assistants who were asked to smell with their eyes closed (this to prevent the influence of color-in differences) and to express their opinion as to which soap had the strongest smell. Since the samples were unperfumed, the panel members' judgment was a direct measure of the strength of the unwanted base odor. The bars of soap which were found to have a stronger smell were given a grade of +1, 0 was given for "no difference" and -1 for bars of soap with a weaker smell. The marks given by each panel member for each soap were added together to give the total mark for each soap. A low number indicated little base odor and a high number indicated strong base odor.

The experimental patterns contained soap bars that were not relevant in connection with the invention, and the results for these soap bars were picked out. The odor ratings for the series were therefore not always evenly distributed around zero as they would have been in a full comparative analysis.

A difference of twice the standard deviation is significant

at the 5% probability level.

EXAMPLE 6.

Another 18 kg sample of the soap from Example 5 was heated

to 90°C. 880 ml of a 10% by weight potassium borohydride solution in water

dig 5% (w/v) sodium hydroxide solution was gradually added

added to the soap while stirring (which corresponds to an addition of

0.08% by weight potassium borohydride based on the weight of the fat charge). Additional 320 ml of the aqueous 5% sodium hydroxide solution

(which increases the amount of free alkali to 0.5% w/v) was also added to the soapy system to reduce the amount of foam.

This experiment was repeated with 3 other 18 kg samples of the soap

from Example 5, with the exception that the amount of potassium borohydride solution added was reduced. The amounts of potassium borohydride used in each case were respectively 0.02, 0.04 and 0.06% by weight of the fat charge. The odor value for each sample was determined as follows:

A panel of 10 members was asked to compare the smell

on the samples of the soaps that had been treated by the method in this example, with a sample of untreated soap, and to grade

the samples after the achieved degree of deodorisation. The following table shows the number of members who were able to place each sample in the correct place.

Claims (1)

Soap with reduced odor and colour, characterized in that the soap in a liquid state is added at any stage during the production to an amount of alkali metal borohydride, which is equal to 0.01-0.30% by weight of the fat charge at a pH value of at least 9.5.