EP3169816A1

EP3169816A1 - Tanning agents

Info

Publication number: EP3169816A1
Application number: EP15762716.7A
Authority: EP
Inventors: Anna Maria Raspolli Galletti; Domenico CASTIELLO
Original assignee: Generale Per La Gestione Del Polo Tecnologico Conciario Societa Consortile A Responsabilita Limitata (poTeCo SCRL) Soc; Laboratori Archa Srl; Universita di Pisa
Current assignee: LABORATORI ARCHA S.R.L.; SOCIETA GENERALE PER LA GESTIONE DEL POLO TECNOLOG; Universita di Pisa
Priority date: 2014-07-18
Filing date: 2015-07-16
Publication date: 2017-05-24
Anticipated expiration: 2035-07-16
Also published as: ES2692324T3; PT3169816T; EP3169816B1; WO2016009387A1

Abstract

The present invention refers to the use as tanning agents for animal pelts of known furan derivatives, which are not toxic and biodegradable, and to a tanning process economically sustainable and comprising a phase of treatment of the pelts directly with aqueous solutions comprising said furan derivatives, obtained by hydrolysis of a lignocellulosic biomass.

Description

TITLE

TANNING AGENTS

DESCRIPTION

Field of the Invention

The present invention generally relates to the field of tanning, and more precisely it relates to novel agents for tanning animal pelts better defined herein below, and to a process of pre-tanning, tanning or re-tanning that uses them and allows obtaining a final product having optimal aesthetic and functional characteristics, also meeting the requirements of health, ecology and environmental safety required today also to the industrial procedures in the tanning field.

State of the Art

It is known that the productive process of the pelts comprises several phases of manufacture, amongst which the tanning phase represents the main phase, that phase wherein the pelt, pre-treated but still putrescible, is subjected to a chemical treatment to render it resistant to microorganisms and to improve its hydrothermal resistance.

The tanning phase is carried out by treating the pelt with tanning agents that, at least in part, combine with the pelt's collagen thus forming transversal links between adjacent peptidic chains in the collagen, and consequently increasing the temperature of gelatinization (Tg) and improving the resistance of the pelt to the proteolytic digestion. The determination of the temperature of gelatinization of a tanned leather is a test to verify the hydrothermal resistance, that is its ability to not deform nor degrade under conditions of elevated temperatures. The type of tanning agent used involves a temperature of gelatinization of the tanned leather more or less high, and therefore more or less good characteristics of the finished product in terms of stability and resistance to mechanical and chemical operations: the higher is the Tg, the higher is the degree of tanning and therefore the stability of the finished product and its resistance. For instance, while leather tanned with chromium salts may have a Tg higher than 100°C, vegetable-tanned leather may have Tg values slightly higher than 70°C.

The chromium salts, opposite their tanning ability accompanied by a relative cheapness and rapidity of processing, require though the use of large amounts of acids, particularly of sulphuric acid, also in form of pre-treatment of the leather to be tanned in a phase known as "pickling" having the purpose of preparing the hides to receive the tanning agent. The environmental impact of this kind of processing is therefore significant, and the additional costs for the disposal of large quantities of sewage strongly affect the manufacture costs.

For these reasons, and in particular for the spread of an increasing ecological sensitivity and attention to the working conditions also in the tanning industry, researchers have tried in recent years to find tanning agents that are natural or at least not harmful for people and for the environment, that produce lower amounts of waste water and consequently less pollution. To this aim also the ever-changing industrial regulations has contributed, requiring the development of products and processes that meet the increasingly stringent requirements in terms of environmental protection and in terms of health and safety of the operators in the industrial processes.

These new tanning agents are on the other hand requested to have efficiency comparable to that of traditional tanning, and a reasonably low cost for not weighing too much on the economy of the production process with substances that, as natural and not harmful, however, have per se a prohibitive cost.

Among the tanning agents alternative to chromium salts, known and used until today, we mention the vegetable tanning, such as tannins, whose use is however strongly limited by the slowness of the processing, by high costs, and by the specific destinations of use of the product that can be obtained with this type of tanning.

Another class of tanning agents alternative to chromium salts, which has a lower environmental impact, is that of aldehydes. Among the aldehydes reported in the literature for this use we mention the furaldehyde or furfural, which is also the only molecule of the furan type described in the literature for this application, as far as the Applicants are aware. We cite for example the patent US 2,976,1 11 in which the use of furfural as a tanning agent of animal leather is described; in this patent described are various experimental examples of tanning wherein furfural in pure form is always used, without water or other tanning agents. The patent US 2,976,1 1 1 clearly teaches to use pure furfural as tanning agent, without water or other solvents, also teaching that the this kind of tanning gives better results if the furfural is re-purified by distillation after about four cycles of tanning, with definitely disadvantageous consequences on the processing costs. That patent also indicates that the furfural exerts a tanning activity at pH values lower than 6.4, and that the addition of salt (NaCI) improves the quality of the leather, without however giving a quantitative indication of the extent of the tanning process but simply claiming good product characteristics of the finished product.

For these reasons nowadays, as far as the Applicants are aware of, it is still unsolved the technical problem of having available efficacious tanning agents that are really ecologic and can be used in aqueous solution, able to yield a tanned products of high quality, which is also stable and hydrothermally resistant as required for the product to be used in any kind of applications.

Summary of the Invention

Now the Applicants have found that furan derivatives of formula (I) depicted hereinafter, in the form of an aqueous solution directly obtainable by hydrolysis of biomasses, can be used efficiently as tanning agents in processes of pre-tanning, tanning or re-tanning of animal pelts with a considerable increase of the temperature of gelatinization of the pelts, thus giving to them characteristics of better stability and hydrothermal resistance.

Advantageously, the above said tanning agents are products nontoxic for people nor harmful for the environment, in some cases being also indicated for alimentary use, that do not create problems connected to the safety of use and to the health of operators using them; they can also be obtained by simple processes of conversion, that are environmentally sustainable and have low cost, starting from renewable raw materials, even waste materials, present on the territory.

Particularly advantageous is the fact that the use as tanning agents according to the invention is related to the aqueous solutions directly obtained from the hydrolysis of biomasses comprising the above said derivatives.

It is thus subject of the present invention the use of furan derivatives as tanning agents of animal pelts, as defined in the first of the claims here attached.

A process of pre-tanning, tanning or re-tanning of animal pelts comprising a phase of treatment of said pelt with a furan derivative as defined in the independent claim 6 here attached, is a further subject of the present invention. Further important characteristics of the use of the present furan derivatives as tanning agents and of the process according to the invention are reported in the following detailed description.

Brief description of the Figures

The Figures from 1 to 4 and the Figure 6 are graphs showing the variation of the temperature of gelatinization (Tg) with the pH of the tanning solution for the tanned leather (values indicated with - A- in Figures 1 and 2 and with -♦- in Figure 3, 4 and 6) and for the starting pickled leather, still non tanned (values indicated with -·-), for several tanning agents. In particular:

- Figure 1 : the tanning agent used is pure furfural, not in aqueous solution (comparison Example 1 ),

- Figure 2: the tanning agent used is furfural in aqueous solution (comparison

Example 2),

- Figure 3: the tanning agent used is an aqueous solution of HMF obtained by hydrolysis of fructose for alimentary use (Example 3).

Detailed description of the invention

The furan derivatives, whose use as tanning agents in the form of aqueous solution obtained by hydrolysis of sugars or of lignocellulosic biomass is subject of the present invention, may be represented by the following general formula (I):

(I)

wherein R1 and R2, equal or different between each other, are selected from an aldehyde group CHO and a group hydroxymethyl -CH₂-OH.

The compound of formula (I) wherein R1 is hydroxymethyl and R2 is an aldehyde group is a furan derivative C6 known as 5-hydroxymethyl-2-furaldehyde, also known as 5-hydroxymethylfurfural or 5-(hydroxymethyl)-2-furaldehyde or 5-(hydroxymethyl)-2- furancarboxaldehyde, indicated in the following and in the attached figures as HMF. Regarding the toxicological aspects and the risk to exposure, the HMF is present in many foods of the human diet, for instance in coffee, dried fruit (particularly in prunes), in bakery products, in beer, in cereals and bread. The HMF is accepted by the European Union as a flavouring agent of food [FL No. 13,139 in the EU Register of Flavouring Substances, of the European Commission Decision 1999/217/EC]. No carcinogenic or genotoxic effects on humans have been highlighted and in general the potential toxicity of the HMF is low. Several experiments on animals have shown no adverse effects with levels of daily intake of 80-100 mg per kg of body weight [K. Abraham et al., Mol. Nutr. Food Res. 2011 , 55, 667-678]. The HMF is also highly biodegradable, that is an extremely important aspect for use in the field of tanning.

HMF may be obtained from the conversion of the cellulosic fraction of the raw biomass or from the dehydration of monosaccharides C6, such as glucose or fructose, or of the polysaccharides such as sucrose, cellobiose, inulin or cellulose, in the presence of acid catalysts, that can be homogeneous, organic or inorganic, or heterogeneous. The hydrolysis may be carried out under conditions of homogeneous catalysis by using one or more protic acids as catalysts at high temperatures, or under conditions of heterogeneous catalysis by using one or more heterogeneous acid catalysts at high temperature. Examples of catalysts of possible use are hydrochloric acid, sulphuric acid, phosphoric acid, oxalic acid, ionic exchange acid resins, niobium phosphate, zirconium phosphate, titanium phosphate, niobium oxide, to be used at temperatures comprised for instance between 70°C and 200°C.

Alternatively, the hydrolysis of the above said mono- and polysaccharides and of the raw biomass in order to obtain aqueous solutions containing HMF, can be effectively carried out even in the absence of acid catalyst, operating in the presence of only water at temperatures typically above 150°C. Even under these conditions it is observed the depolymerisation of the saccharides with cyclization to furan derivatives.

We note that until today the industrial production of anhydrous high-purity HMF has encountered difficulties because of the significant energy costs due to the fact that the pure product must be obtained by concentration of aqueous solutions; furthermore, the highly concentrated HMF is less stable, must be stored at low temperature because it tends to form soluble polymers and humins [B. Duan et al., Green Chemistry, 2014, 16 (5), 2835 - 2845], thus making the purification stage as the most complex and expensive stage of the whole process for the synthesis of HMF. For these reasons the present tanning process, that allows using HMF in aqueous solution directly obtained from lignocellulosic biomasses or from saccharides or polysaccharides mixtures without any purification and even without a complete conversion of all the starting saccharides and polysaccharides, represents a considerable economic advantage, because the raw HMF, not purified and in aqueous solution, is a product which is available also at low cost and it can be easily prepared, by a single-step process, and it can be used as such [J. J. Wang et al. Aiche Journal , 20 3, 59, 2558 - 2566].

According to the present invention by "biomass" is meant the biodegradable fraction of products, wastes and residues of biological origin, of lignocellulosic nature, thus containing saccharides and polysaccharides as main components; preferably, it is meant a product selected from among a mixture of pure carbohydrates or of raw sugars, single raw sugars, syrup of fructose and glucose, cellulose, inulin, amid, cellobiose and raw materials, also waste materials, containing carbohydrates, even with low purity grade; it is further meant raw products, also waste products, such as the giant cane {Arundo donax L), rice, miscanthus, corn, sorghum, Jerusalem artichoke, the wastes of sugar factories, the wastes of food industry and of wood and paper processing.

The present process allows therefore using directly the aqueous solutions obtained by hydrolysis of such a biomass, carried out on aqueous solutions of the biomass or of the saccharidic mixtures by using the conventional heating as well as the irradiation with microwaves in the presence of acidic homogeneous or heterogeneous catalysts, or in the presence of water only by auto-hydrolysis. The irradiation with microwaves is a preferred system of heating of the aqueous starting solution because it allows a great energy saving (up to 85 times more than the conventional heating), and a considerable reduction of the reaction time (Dallinger et al., Chem. Rev. 2007, 107, 2563); this process is particularly interesting, with a view to a sustainable process, when water is used as the reaction medium.

The compound of formula (I) wherein R1 and R2 are hydroxymethyl groups is a furan derivative C6, the 2,5-bis-hydromethyl-furaldehyde known as BHMF; this acronym BHMF is used in the following and in the attached figures to identify the product in question.

BHMF may be obtained by hydrogenation of HMF solutions in water. The selective hydrogenation of the formyl group at position 2 of the HMF brings to the formation of the BHMF that is also an important building - block in the synthesis of polymers and in particular of polyurethanes [C. Moreau et al. Top. Catal., 2004, 27, 11 - 30]. This reaction may be carried out with good yields by using sodium borohydride (NaBH₄) in stoichiometric amount but also formalin under aqueous basic conditions (F. W. Lichtenthaler et al. GreenChem., 2001 , 3, 201 - 209; L. Cottier et al. Synth. Commun., 2003, 33, 4285 - 4295). Further reactions suitable for selective obtainment of BHMF are those reactions using platinum supported on carbon as hydrogenation catalyst (V. Schiavo et al. Bull. Soc. Chim. Fr., 1991, 704 - 711 ). Starting from neutral aqueous solutions of HMF, in order to obtain the selective hydrogenation yielding BHMF, preferred is the use of platinum catalysts, which guarantees the hydrogenation of the formyl group also avoiding at the same time the hydrogenation of the furan ring.

A further tanning agent according to the present invention is the compound of formula (I) wherein R1 and R2, equal between each other, are an aldehyde group. It is a dialdehyde known as 2,5-diformylfurane, that may be obtained by oxidation of HMF, using for instance air or oxygen as the oxidising agent, in the presence of oxidation catalysts based on metals such as ruthenium, gold, palladium, platinum (C.A. Antonyaraj et al. Journal Industrial Engineering Chem. 19 (3), 20113, p1056-1059).

The Applicants have carried out experiments, described in the following examples, in order to verify the tanning ability of the above said compounds of formula (I) depending on the main conditions used for the tanning process of bovine, sheep and goat skins and of exotic leathers prepared for the tanning phase by a preparatory phase (riviera phase), previously subjected to picking at the end of the preparatory phase or just subjected to deliming and maceration in the preparatory phase, without being then subjected to pickling with agents commonly used in this processing phase. As a matter of fact it has been found that tanning agents according to the invention can also be used as agents for pickling and pre-tanning agents, for example in processes of vegetable- tanning and chrome-tanning. The tanning agents of the invention can also be used both as the only tanning agents of the processing, or in combination with other tanning agents.

The above said compounds of formula (I) may be used as tanning agents alone as well as in mixture with each other, in the form of aqueous solution directly obtained from a biomass of lignocellulosic nature or in general from products containing mixtures of saccharides or polysaccharides. According to a preferred embodiment of the present invention, as tanning agents are used aqueous solutions directly obtained from biomass or from saccharides, in particular from fructose, by heating in the presence of a suitable catalyst, optionally subjected to a subsequent hydrogenation, thus comprising HMF or mixtures of HMF and BHMF in concentration higher than 10 g/litre, and preferably comprised between 20 and 300 g/litre.

It was verified that the possible presence of other components in such aqueous solutions, in particular of non-hydrolysed sugars does not hinder the tanning process, but may actually improve the characteristics of the treated leather.

The tanning process with the present compounds of formula (I) may be carried out at temperature comprised between about 5°C and about 60°C, in a range of pH comprised between 2 and 8, using the single pure compound, or the mixtures thereof, or the respective aqueous solutions directly obtained from a biomass or from saccharide mixtures as described above.

To get a comparison it was tested also furfural, the only furan aldehyde disclosed in the literature as tanning agent, as mentioned above. It was so found that its tanning ability is scarce, and much lower than the ability shown by the compounds of formula (I), as illustrated in detail in the following.

The invention is described in the following by means of the showing example 3 without being however limited to it, but it is meant that the amounts and percentages of the disclosed reagents may be varied, as well as the type of reactors used, always remaining within the scope of the present invention.

EXAMPLE 1 (COMPARISON)

The tanning performances of furfural, when used in pure form, not in aqueous solution, were evaluated by comparison with what described in patent US 2,976,111. To do this a tanning test was carried out with pure furfural on pickled dehydrated skin, which should also absorb more effectively the tanning agent.

The test was carried out in the absence of water by using 78.2 g of pickled bovine leather and 10 g of furfural (14.8 % of furfural with respect to the weight of the leather).

The experimental procedure used in this test was as follows:

• measuring the temperature of gelatinization Tg of the dehydrated pickled leather, that is of 66°C;

- addition of 10 g of furfural;

• introduction of the dehydrated pickled leather to be treated;

• 15 hours of agitation with a rotary shaker, so as to obtain a uniform penetration of the tanning agent in the leather;

• evaluation of the penetration of the tanning agent, of the pH and of the Tg;

· progressive and gradual basification to evaluate the behaviour of the Tg of the leather with the variation of the pH values.

The variation of Tg with the pH is represented in Figure 1.

It is evident from Figure 1 not an increase but a decrease of at least 2°C of Tg of the leather treated with furfural with respect to the pickled leather, throughout the whole pH range in which the study was performed. The resulting leather does not show any evidence of the stabilization and firmness that are typical of tanned leather.

EXAMPLE 2 (COMPARISON) The tanning performances of the furfural in aqueous solution were also evaluated. To this aim a tanning test with this product was carried out on pickled calfskin.

The test was carried out by using 54 grams of pickled leather, 100 ml of water, and 13.5 grams of furfural.

The experimental procedure used for this test was as follows:

• measuring the temperature of gelatinization Tg of the pickled leather, which was of 61 °C;

• introduction of the pickled leather in solution of 100 ml of water at density of 7°Be;

• acidification up to pH 3.2 with formic acid;

• addition of 13.5 g of furfural;

• 15 hours of agitation with rotary shaker, to obtain a uniform penetration of the tanning agent into the leather;

· evaluation of the penetration of the tanning agent, of pH and of Tg;

• progressive and gradual basification in order to evaluate the behaviour of the Tg of the leather with the variation of the pH values.

The trend of the Tg with the variation of pH is represented in Figure 2.

From Figure 2 is evident not an increase but a decrease of Tg of the leather treated with furfural with respect to the pickled leather throughout the whole range of pH wherein the study was carried out. The leather obtained in the tanning test with furfural in aqueous solution has a consistency very similar to the pickled leather as such, without any evidence of the stabilization and firmness typical of a tanned leather.

EXAMPLE 3

10.2 grams of fructose for alimentary use was dissolved in 34 ml of water and

2.71 grams of niobium phosphate were added as heterogeneous acid catalyst. The suspension was heated up to 150°C in a microwave reactor MARS 6 (CEM) for a reaction time of 15 minutes. The resulting suspension was then rapidly cooled, the heterogeneous catalyst removed by filtration and the resulting solution, subjected to HPLC analysis, had a concentration of HMF of 46.1 g/litre, while the residual fructose was present in the solution in concentration of 234.2 g/litre. The process was repeated several times in order to have available a sufficient amount of HMF for carrying out tanning tests. The so obtained solution was concentrated under vacuum and an aqueous solution was obtained having a concentration of HMF equal to 82.02 g/litre, while the residual fructose was present in the solution with a concentration of 450.30 g/litre.

90 ml of this solution, obtained by hydrolysis of fructose for alimentary use as described above, was used in a tanning process on a sample of pickled pelt of calfskin weighting 29.5 grams, by using the 25% by weight of HMF, calculated in percentage with respect to the weight of the pelt.

The experimental procedure used in this tanning test was as follows:

• basification of the solution up to pH 3.2;

• increment of salinity up to a density of 7°Be;

· introduction of the pelt sample;

• 15 hours of agitation with rotary shaker;

• evaluation in terms of penetration of the tanning agent, of pH and of Tg;

• progressive and gradual basification in order to evaluate the behaviour of the Tg of the pelt with the variation of pH.

During the experimental procedure the variation of Tg with pH was carefully studied, as schematically showed in Figure 3. From the graph in Figure 3 it is evident how the better value of end Tg (Tg at the end of the tanning process) is obtained at pH of 7.4-7.8 with an increase of the temperature of gelatinization (ATg at the end of the tanning process) of 9.5°C that corresponds to 16.1% when expressed in terms of percentage with respect to the Tg of the pickled pelt.

* * * * *

The present invention was here described with reference to a preferred embodiment. It is to be understood that there may be other embodiments afferent to the same inventive core, as defined by the scope of protection of the claims set out below.

Claims

1. Use of compounds of formula (I), alone or as a mixture thereof, in the form of an aqueous solution

wherein R1 and R2, equal or different between each other, are selected from an aldehyde group CHO and a hydroxymethyl group -CH₂-OH,

as tanning agents for animal pelts, optionally in combination with other tanning agents, wherein said aqueous solution is a solution having a concentration of the compound of formula (I) or of the mixtures thereof not lower than 10 g/litre, directly obtainable by treating a lignocellulosic biomass or a mixture of saccharides and / or polysaccharides in aqueous solution.

2. The use according to claim 1 , wherein said solution directly obtainable from biomasses or from saccharidic mixtures comprises the compound of formula (I) wherein R1 is hydroxymethyl and R2 is an aldehyde group in a concentration not lower than 10 g/litre, and is obtained by acidic hydrolysis of a lignocellulosic biomass or of a mixture of saccharides and/or polysaccharides in aqueous solution.

3. The use according to claim 1 , wherein said solution directly obtainable from biomasses or from saccharidic mixtures comprises the compound of formula (I) wherein R1 and R2, equal between each other, are a hydroxymethyl group, in a concentration not lower than 10 g/litre, and is obtained by acidic hydrolysis of a lignocellulosic biomass or of a mixture of saccharides and/or polysaccharides in aqueous solution, followed by hydrogenation.

4. The use according to claim 2 or 3, wherein said hydrolysis is carried out on aqueous solutions of said biomass or of said mixture of saccharides and/or polysaccharides by heating in the presence of acid catalysts homogeneous or heterogeneous, or in the presence of only water by auto-hydrolysis.

5. The use according to claim 4, wherein said hydrolysis is carried out in the presence of a catalyst selected from the group consisting of hydrochloric acid, sulphuric acid, phosphoric acid, oxalic acid, ionic exchange acidic resins, niobium phosphate, zirconium phosphate, titanium phosphate, and niobium oxide at temperature comprised between 70 and 200°C.

6. The use according to any one of the preceding claims, wherein said aqueous solution comprises part of the starting saccharides in not hydrolysed form.

7. A process for the processing of animal pelts comprising a pre-tanning, tanning and/or re-tanning phase wherein said pelts are treated with one or more compounds of formula (I) as tanning agent in the form of aqueous solution

(I)

wherein R1 and R2, equal or different between each other, are selected from an aldehyde group CHO and a hydroxymethyl group -CH₂-OH, and wherein said solution has a concentration of compound of formula (I) or of mixtures thereof not lower than 10 g/litre, directly obtainable by treating a lignocellulosic biomass or a mixture of saccharides and/or polysaccharides in aqueous solution.

8. The process according to claim 7, wherein said tanning agent is used in combination with other tanning agents.

9. The process according to claim 7 or 8, wherein said pelts are animal pelts previously subjected to pickling in a range of pH comprised between 3.5 and 8.

10. The process according to claim 9, wherein said pelts have been dried after pickling.

11. The process according to claim 9, wherein said pelts are animal pelts previously subjected to deliming and maceration, without subsequent pickling.

12. The process according to claim 7, wherein in said pre-tanning, tanning and/or re-tanning phase said pelts are immersed in said aqueous solution.

13. The process according to claim 7, wherein said aqueous solution directly obtainable from biomasses or from saccharidic mixtures comprises the compound of formula (I) wherein R1 is hydroxymethyl and R2 is an aldehyde group in concentration not lower than 10 g/litre, and is obtained by acidic hydrolysis of a lignocellulosic biomass or of a mixture of saccharides and/or polysaccharides in aqueous solution.

14. The process according to claim 7, wherein said aqueous solution directly obtainable from biomasses or from saccharidic mixtures comprises the compound of formula (I) wherein R1 and R2, equal between each other, are a hydroxymethyl group, in concentration not lower than 10 g/litre, and is obtained by acidic hydrolysis of a lignocellulosic biomass or of a mixture of saccharides and/or polysaccharides in aqueous solution.