The present invention relates generally to natural products, particularly natural products requiring treatment before they may be used in a functional manner. More particularly, the present invention relates to natural products obtained from animals, such as for example skins, hides and the like. Even more particularly, the present invention relates to a process for pickling hides and skins as part of the tanning process, and to a method for preparing a pickling solution. The present invention finds particular application in pickling and tanning naturally occurring hides or skins to produce durable leather.

Although the present invention will be described with particular reference to a pickling solution for use in treating hides and skins of animals, it is to be noted that the scope of the present invention is not so limited, but rather the scope is more extensive so as to include other pickling solutions and uses of the pickling solution other than those specifically described.

Leather is a natural product which is derived from the hides or skins of many animals. However, before the hides or skins are useful, they must be treated. One such treatment is tanning. Hides and skins need to be tanned in order to produce leather which has the durability and thermal stability normally required of leather goods, which is to say that the properties of the hides and skins need to be modified before they are useful, which modification is achieved by tanning. The most widely practised tanning procedure involves treatment of the hides and skins with chromium salts. However, to promote uniform penetration of

the chromium salts into the collagen matrix of the skins and hides without precipitation, the hides and skins require a pickling or acidification treatment or pretreatment. Traditionally, the pickling or acidification treatment involves the use of a mineral acid, such as for example hydrochloric acid, sulphuric acid or the like, or an organic acid, such as formic acid, or more commonly a mixture of sulphuric and formic acids, together with the addition of a salt, usually sodium chloride, to prevent swelling of the hides or skins which would otherwise occur when the collagen is exposed to an acid medium. Although traditional pickling treatments are effective and employ materials which are inexpensive, such treatments suffer from serious disadvantages in that they result in the production of tannery effluents which have a high salt concentration. The disposal of the high salt effluent presents a serious environmental problem, particularly for tanneries situated in-land, or in areas where there is insufficient water or rainfall to effectively dilute the effluent to acceptable levels for safe or convenient disposal.

In the past, attempts to overcome this disadvantage have involved the use of various organic sulphonic acids as replacements for the salts to suppress the swelling which accompanies pickling the hides or skins with agents such as sulphuric and/or formic acid. In one particular instance, a condensate of a sulphonated phenol with a formaldehyde- urea prepolymer had been considered as a salt alternative. Other attempts have led to the introduction of commercially available pickling agents such as PICALTAL marketed by BASF, SELLA AN P from Ciba-Geigy, and other similar materials which are examples which are based on naphthalene sulphonic acids or oligomeric phenol sulphonic acid sulphones which are useful in reducing or counteracting the tendency towards swelling whilst allowing tanning of the hides or skins to take place. Unfortunately, the use of

such materials has a major disadvantage in that they tend to become ineffective in acidic conditions of below about pH 3, or otherwise impart undesirable characteristics, such as fullness or stiffness, to the pickled stock, or hinder the rate of or uniformity of penetration of the collagen matrix, all of which result in uneven pickling of the hides or skins or in the skins or hides exhibiting some other undesirable property.

In the past, among the compounds investigated by other workers in attempts to replace salt in pickling solutions were phenol sulphonic acids. However, the results of these previous investigations obtained at that time were not encouraging and tended to indicate that the sulphonic acids tested might not be suitable as alternatives to salt in pickling treatments prior to tanning. In fact, some investigators found that phenol sulphonic acid gave swelling values that were close to those obtained when using sulphuric acid in the absence of any additional salt, which clearly indicated the unsuitability of these materials. This was confirmed by other investigators who found that marked swelling occurred when hides were pickled with phenol sulphonic acid. It is to be noted that hides pickled with sulphuric acid alone will swell in excess of 50% of the delimed weight of the hide whereas when a salt/sulphuric acid mixture is used not only is there no swelling but there is also deswelling to about -10% of the original delimed weight of the hide.

Therefore, there was a need for a pickling solution which was as least as effective as the traditional sulphuric acid/salt treatment but which did not result in an effluent of high salt concentration. Furthermore, there was a need for an alternative pickling agent to traditional agents which produced desirable characteristics in the leather.

Surprisingly, it has now been found that phenol mono-, di-

and trisulphonic acids either alone or in combination with each other in the absence of excess or large amounts of sulphuric acid, give deswelling of hides and skins comparable to that obtained when using conventional pickling regimes involving the use of salt or involving the use of commercially available salt-alternative treatments as mentioned previously. More importantly, it has been discovered that such sulphonic acids do not possess the undesirable properties of the prior art compounds, which made using such prior art compounds inconvenient to the tanner. Furthermore, it has been discovered that the leather products exhibited no undesirable properties. In addition, it was discovered that the phenol mono-, di- and trisulphonic acids of the present invention could be added rapidly to the skins or hides being treated without swelling taking place since such materials rapidly penetrated the collagen matrix and were effective at a pH below 3 without causing swelling of the skin or hides.

Therefore, it is an aim of the present invention to provide a pickling agent which is useful for pickling hides or skins, which results in leather products having desirable properties, but which does not produce an effluent having an unacceptably high salt content. Additionally, it is an aim of the present invention to provide a method of making a pickling agent having desirable properties.

According to a first aspect of the present invention there is provided a method of treating a naturally derived product prior to performing a subsequent treatment wherein the naturally derived product is treated with an agent to modify a property or characteristic of the naturally derived product, characterised in that the treatment by the agent is effective at a final pH of or below 3.4 and in that the agent comprises at least one or more of phenol mono-, di- or trisulphonic acid or derivatives thereof, either singly or in combination, including combination with

other materials.

According to a further aspect of the present invention there is provided a method of preparing a treatment agent suitable for use in treating a naturally derived product comprising contacting a phenol mono-, di- or trisulphonic acid or derivative thereof, either singly or in combination, including combination with other materials including oleum or a sulphuric acid, characterised in that the agent is effective in use at a final pH of 3.4 or less.

Typically, the naturally derived product is a hide or skin, more typically a hide or skin useful in producing leather or a leather product.

Typically, the treatment agent for use with the hide or skin is a pickling or acidifying agent. Typically, the subsequent treatment is a tanning treatment. Typically, the tanning treatment can be any type of tanning treatment or more particularly a chromium tanning treatment or vegetable tanning treatment.

Typically, the agent is a pickling agent and comprises essentially pure phenol mono-, di- or trisulphonic acid or derivatives thereof. More typically, the pickling agent comprises a further acidic material. Typically, the further acidic material is sulphuric acid or oleum or a material derived from them.

By use of the term "essentially pure" in the context of the present invention is meant a phenol sulphonic acid agent which before application to the hides or skins is associated with up to and no more than about 1 g, preferably less than about 0.6 g, more preferably less than about 0.4 g of sulphuric acid, oleum or equivalent thereof per 1 g of the phenol sulphonic acid or mixture thereof.

By use of the term "derivatives" is meant any salt or partial salt or compound of the phenol sulphonic acids, or any such derivatives having functional groups equivalent to the phenol sulphonic acids, such as for example compounds having a benzene ring substituted with a sulphonic acid, carboxylate, ester, alkyl, hydroxyl or thiol group.

More typically, the pickling agent comprises a mixture of monosulphonic acid and disulphonic acid, optionally together with trisulphonic acid, or any combination thereof.

Typically, the amount of disulphonic acid in the agent is maximised in order to facilitate reduction in the amount of swelling. More typically, the ratio of monosulphonic acid to disulphonic acid is from about 100:1 to 1:100, preferably about 50:1 to 1:50, more preferably about 1:1 by weight. However, the relative ratios of disulphonic to monosulphonic acid can deviate from these ranges. It is to be noted that phenol trisulphonic acid can be present as well as phenol monosulphonic acid and disulphonic acid.

Typically, phenol sulphonic acids or mixtures of the present invention contain less than 1 g sulphuric acid or oleum per gram of phenol sulphonic acid, and are readily prepared when phenols are sulphonated with oleum and/or sulphuric acid.

Typically, the pickling treatment can have a duration of up to about 48 hours or more, typically up to about 24 hours.

In one embodiment of the present invention, when oleum is used as a sulphonating agent, the concentration of the sulphonic acid in the resultant product mix is increased. It is to be noted that the amount of phenol di- and trisulphonic acid relative to the amount of monosulphonic acid is increased. However, the amount of phenol

trisulphonic acid is relatively small compared to the amounts of phenol mono- and disulphonic acids. The concentration of sulphur trioxide in the oleum can, of course, be varied, and while the use of oleum containing, say, 65% sulphur trioxide will give a very effective pickling agent, it has to be kept in mind that because the product will contain less associated sulphuric acid, more of the pickling agent will have to be used in the pickling treatment to achieve the desired level of acidification. In practice, for most purposes, oleum typically containing about 20% to 25% sulphur trioxide is effective.

In another embodiment, reaction temperatures for producing the pickling agent of the present invention will typically be in the range of from 0°C to 200°C, preferably in the range 80°C to 140°C. In addition, it is preferred to use in excess of 2 moles of sulphuric acid in the reaction mixture to maximise the amount of phenol disulphonic acid, and optionally to assist in acidification of the pickling step.

Typically, the final pH of the pickled hides or skins is about 3.0 or below.

Typically, the method of treatment and the pickling agent of the present invention may be applied to any of the types or hides or skins currently being processed by conventional techniques, such as for example ovine, porcine, bovine, caprine or like hides or skins, whether green or preserved in any known manner. More typically, the hide or skin may be treated by the pickling agent of the present invention either before or after the hair, wool or other covering or associated material has been removed. Even more typically, the process of the present invention can be used in conjunction or in combination with other technologies or processes conventionally used to prepare hides and skins for tanning.

Typically, the amount of phenol sulphonic acid or acids or mixtures thereof or derivatives thereof to be used may vary widely, but as in conventional acid/salt treatments, the amount used will depend to some extent on the state of the hide or skin to be pickled, the amount of mineral acid or separately introduced organic acid in the preparation, and the desired end pH or the like. Typically, for full thickness delimed hides, 1% to 10% by weight, based on the weight of the delimed hide, of the sulphonic acid or mixture will give satisfactory pickling.

Typically, the hide or skin may be in contact with the phenol sulphonic acid or acids or mixtures thereof for any suitable period, depending on requirements and/or be at any suitable or convenient temperature. For example, delimed hides treated with a pickling solution containing from about 1% to 10% by weight acid will lead to equilibrium pickles exhibiting no swelling in less than 24 hours. Additionally, uniform and even chromium penetration and no swelling of the hides or skins will be exhibited when the chromium or chromium-containing tanning material is applied simultaneously or substantially simultaneously or sequentially with the sulphonic acid or acids or mixtures thereof.

The invention will now be described by way of example with reference to the following examples, which are understood to be illustrative only of the scope of the present invention and not to be taken as restrictive on the generality of the invention described therein.

Further, it is to be noted that in Examples 4 to 8, the reagent weight percentages are based on the weight of the damp delimed hides or skins being treated.

EXAMPLE 1

Preparation of phenol sulphonic acid solution using 22% oleum

To prepare this example of the pickling agent 683 ml of 22% oleum solution was slowly added to 650 g of phenol in a suitable vessel with cooling and stirring while maintaining the reaction temperature below 80°C. After all of the oleum had been added, the mixture was warmed to 80°C and maintained at that temperature whilst stirred for 12 hours. The mixture was then cooled and water was added to make a final volume of 2 L. The resultant solution contained approximately 60% of a phenol sulphonic acid mixture comprising about 1:1 weight ratio of mono- to disulphonic acids.

EXAMPLE 2

Preparation of phenol sulphonic acid solution using sulphuric acid

Concentrated sulphuric acid (2.34 kg) was added slowly with stirring to phenol (1 kg). The temperature rose to 80°C. The mixture was maintained at 120°C for a further 2 to 12 hours. It was cooled and water was added to make up a final volume of 3.08 L.

Analysis showed that this mixture comprised of approximately equimolar quantities of phenol mono- and phenol disulphonic acids.

EXAMPLE 3

Preparation of concentrated phenol sulphonic acid solution A phenol sulphonic acid mixture was prepared as in Example 1 but this time using 65% oleum instead of 22% oleum. The result was a greater concentration of the phenol sulphonic acids and less sulphuric acid being present in the reaction mixture. Also more phenol disulphonic acid was produced than the amount of phenol monosulphonic acid and also a

small amount of trisulphonic acid was produced. For use in the pickling agent, the mixture was diluted to give about a 60% solution of sulphonic acids as in Example 1.

EXAMPLE 4 Equilibrium pickling of full thickness hide

In this example a pickling agent prepared in accordance with the preceding examples was employed to pickle a full thickness hides. A solution of water (35% by weight based on the weight of the delimed hides as indicated previously) and sodium formate (0.5% by weight based on the weight of the delimed hides as indicated previously) was added to delimed hides, which were then drummed for 5 minutes in a suitable drum before adding the solution containing the pickling agent of phenol sulphonic acid mixture as prepared in accordance with Example 1 or Example 2 at a concentration of 4% of the formulation based on the weight of the delimed hides in 10% water by weight based on the weight of the delimed hides as indicated previously. Drumming was continued for 2 to 3 hours, after which formic acid (0.85% by weight based on the weight of the delimed hides as indicated previously) and a suitable amount of sulphuric acid depending on the final pH desired was added. Drumming was continued for a further 12 hours . The pH of the pickling liquor was from about 1.5 to 3, depending on the extent of deliming of the hides and the amount of sulphuric acid added previously. A sample cut was taken from the hide which showed that full penetration of the pickling agent had been achieved. No swelling of the hide was observed.

EXAMPLE 5

Non-equilibrium pickle of hides combined with chromium tannage

A solution of water and sodium formate was prepared and added to delimed hides as in Example 4, followed by the addition of the phenol sulphonic acid solution to the hides

also in accordance with Example 4. After drumming for 30 minutes, formic acid (0.85%) was added and sulphuric acid as in Example 4 and drumming continued for a further 30 minutes. 8% by weight of a "33% basic" chromium tanning material (i.e. a tanning powder comprising chromium sulphate in which one third of the sulphate ion content had been replaced by hydroxyl ion) was then added to the drumming vessel and the mixture further drummed. Full penetration was noted after 5 to 7 hours by observing a sample removed from the hide. The pH of the tanning solution was raised to 3.5 to 4.2 by adding magnesium oxide (0.5% to 1.5% depending on the final pH desired). The hides were drained and washed. Shrinkage temperature of the tanned material was >100°C.

EXAMPLE 6

Pickling and chromium tanning of sheepskin pelts A solution of sodium formate (0.5%) and water (35%) was added to delimed pelts and the mixture drummed for 5 minutes. The phenol sulphonic acid mixture prepared in accordance with Example 1 or Example 2 (3.5% in water 10%) was added, and drumming was continued for a further 60 minutes, at which time pickling was close to equilibrium. Formic acid (0.4%) was added and drumming continued for another 30 to 60 minutes. Chromium powder (6% of 33% basic) was added, and full penetration was noted after 2 hours. The pH was raised to 3.5 to 4.2 over 3 hours by adding magnesium oxide, and the hides were drained and washed. Shrinkage temperature of the tanned material was >100°C.

EXAMPLE 7

Low pH pickle of sheepskin pelts

Delimed pelts were drummed with water and sodium formate, then treated with phenol sulphonic acid solution as in Example 6. Drumming was continued for 2 hours and sulphuric acid (0.5%) was added. After further drumming

for 4 hours, antifungal agent was added, and the pelts were drummed for a further 1 hour. At a final pH of 1.2 no swelling was discernible.

EXAMPLE 8 Pickling of woolly sheepskins

As woolly sheepskins need a large float (i.e. a large amount of water) to prevent felting of the wool during processing, reagent concentration is very low and care needs to be taken when adding the phenol sulphonic acid in order to avoid swelling. This problem can be overcome as follows:

a) The woolly sheepskins were drummed in water (20 L per skin) containing sodium formate (2.5 g/L) . After 1 hour, concentrated phenol sulphonic acid mixture (prepared as in Example 3) was added (15 ml/L), and the skins were drummed intermittently overnight. The final pH was 2.7, and no swelling was observed.

b) The woolly sheepskins were drummed for 15 minutes in water (20 L per skin) containing sodium formate (1.5 g/L) and sodium carbonate (2.5 g/L). Phenol sulphonic acid mixture (prepared as in Example 1 or 2) was then added (15 ml/L), and the skins drummed intermittently overnight. The final pH was 3.1, and no swelling was observed.

While the present invention has largely been described with reference to chromium tanning, the invention can be expected to offer advantages when employed in association with other tanning regimes, such as other mineral tannages, vegetable tanning, aldehyde tanning, Syntans tannages, where pickling is required.

ADVANTAGES

The pickling process described herein produces a pickled stock of a quality virtually indistinguishable from that produced in the conventional salt/acid treatments; in addition to its effectiveness in suppressing swelling, it offers the following advantages:

It is salt free, and results in a significant reduction in the Total Dissolved Solids (TDS) in tannery effluent, thus making disposal of waste material more convenient.

- using the method of the present invention, the addition of the pickling agent and the formation of the pickling agent is less hazardous and more convenient since only routine precautions need be taken. No specialised handling precautions or specialised training and experience is required of operators.

It does not require the handling of any solid material.

The agent penetrates hides and skins as rapidly as or more rapidly than the commercial salt alternatives referred to above.

The agents can readily be used with the acids of the conventional salt/acid process.

The agents are exhausted up to 70% or more.

- The pickled stock is compatible with conventional chromium or pickle recycling regimes, or tanning processes.

The agents are inexpensive and easy to make.

The final product obtained by the process of the present invention is just as good as the final product produced by conventional tanning since the quality of the leather produced by the method of the present invention is indistinguishable to that produced in conventional salt/acid tanning.

The pickling formulation and pickling agent of the present invention are biodegradable.