EP3094754B1

EP3094754B1 - A composition for water free, pickle free chrome tanning of hides/skins

Info

Publication number: EP3094754B1
Application number: EP14786723.8A
Authority: EP
Inventors: Chellappa Muralidharan
Original assignee: Council of Scientific and Industrial Research CSIR
Current assignee: Council of Scientific and Industrial Research CSIR
Priority date: 2014-01-13
Filing date: 2014-08-29
Publication date: 2018-03-28
Anticipated expiration: 2034-08-29
Also published as: EP3094754A1; CN106414777A; WO2015104716A1; IN2014DE00085A; TR201809066T4; BR112016016270A2; CN106414777B; ZA201605336B

Description

FIELD OF INVENTION

The present disclosure relates to a composition for water free, pickle free chrome tanning of hides/skins for improved chrome tanning process. The present disclosure further relates to a process for chrome tanning using the said composition, whereby the tanning process is carried out as a waterless, salt free system without adding any additional medium. The present disclosure is envisaged to have tremendous application potential in the tanning industry to ensure eco-benign leather processing that does not add to environmental pollution. The present disclosure is therefore envisaged to play a crucial role in enhancing the economic and environmental benefits associated with chrome tanning.

BACKGROUND OF THE INVENTION

Salted hides and skins are the major raw materials for the tanning industry. In leather making process, the first operation carried out is the removal of salt in the hides and skins through repeated washings. The hair and flesh are loosened by treatment with lime and sodium sulfide or enzyme and then removed using knives. The hides and skins are then agitated with acid salts like ammonium chloride for removal of residual lime. The operation is called deliming, which is usually carried out in tanning drum. The resulting delimed hides and skins are subjected to pickling using 10% salt (all percentages mentioned are on the basis of weight of hides and skins) and 1% mineral acid in the hitherto known process, in order to bring down the pH of the delimed stock, which is around 8.0 to 2.8 to 3.0 to facilitate uptake as well as penetration of chrome tanning salt (commonly known as basic chromium sulfate - BCS) in the cross section of the hides and skins to be tanned. While the penetration of BCS in hides and skins during chrome tanning is carried out at pH 2.8 to 3.0, the same is raised to 3.8 to 4.0 for fixation, which is known as basification in the industry. Alkaline salts of weak organic acids which are normally referred to as masking salts are added during chrome tanning process to prevent surface fixation of chromium in hides and skins. All these operations are carried out in aqueous medium. It is very important in this regard that a significant portion of the chemicals used in the process is let out in the effluent. Thus, considering the fact that in tanning alone, nearly 150-200% w/w (on the weight of hides and skins) of water is used, the conventional chrome tanning process is associated with generation of enormous amount of waste water containing a lot of unabsorbed chemicals leading to significant pollution as well as disposal problem. This obviously leads to an alarming situation especially in view of the ever growing scarcity of usable water.
The major limitation associated with the conventional chrome tanning process is the generation of effluents with significant quantities of total dissolved solids due to lowering and raising of pH, chlorides and unfixed chromium. In fact pickling and chrome tanning contribute significantly for total dissolved solids in the effluent during chrome tanning. Presence of large quantities of total dissolved solids in effluent makes the treatment of tannery effluents a cost ineffective proposal. Secured treatment of total dissolved solids has remained a major challenge to the tanning industry till now. This has prompted the researchers to explore possibilities for minimization or elimination of total dissolved solids in the effluents for the survival of the industry. A system with less or no water has thus emerged as a prominent research option in this regard in recent time.
Indian patent application no. 177/DEL/2002 , and US Patent 7,063,728 describe an improved process for making chrome tanned leathers whereby the delimed hides or skins are treated with a mixture of basic chromium sulfate and alkali metal salt of organic acid, to ensure a chrome tanning process devoid of pickling operation, thereby leading to minimization of total dissolved soilds (TDS).
Indian patent application no. 2108/DEL/2008 describes a novel chrome composition comprising essentially three components - [a] basic chromium sulfate, having Cr₂O₃ content in the range of 21-25% (weight / weight of basic chromium sulfate),
[b] alkali earth metal oxide; and[c] alkali metal salt of organic acid having carbon chain of length in the range of one to three; wherein the ratio of [a] : [b] : [c] is in the range of 10:0.25:0.88 to 10:0.38:1.25. The method of using this composition for tanning purpose involves use of alkali dissolved in water and added in feeds of equal installments to attain a pH of 4.0 - 4.2 in aqueous medium for completion of tanning wherein the acid liberated during hydrolysis of chromium is neutralized. Thus, the major feature of using this composition in chrome tanning involves avoiding pickling operation, thereby ensuring that effluent is not loaded with enormous salinity as well as TDS.
The major limitation of these hitherto known developments is that the processes require to be used in aqueous medium. In other words, the tanning process generates huge amounts of waste water that requires further treatment before disposal even though it may not be containing high amounts of TDS. It is thus evident that the need for a chrome tanning process requiring no water has remained a challenge and is a deserving subject matter for research.

OBJECTIVES OF THE INVENTION

The main objective of the present disclosure is to provide a composition for water free, pickle free chrome tanning of hides/skins for improved chrome tanning process which obviates the limitations as stated above.
Another objective of the present disclosure is to provide a process for chrome tanning without resorting to use of water for tanning.
Yet another objective of the present disclosure is to provide a tanning process without resorting to pickling.

SUMMARY OF THE INVENTION

Accordingly, the present disclosure provides a composition for water free, pickle free chrome tanning of hides/skins, wherein said composition comprises:

[a] basic chromium sulfate, having Cr₂O₃ content in the range of 21-25 % (weight / weight of basic chromium sulfate)
[b] alkali metal salt of organic acid having carbon chain of length in the range of one to three;
[c] polyhydric alcohol previously acidified with acid;

In an embodiment of the present disclosure the composition has pH iin the range of 1-6.
In another embodiment of the present disclosure Cr₂O₃: SO₄ ratio is in the range of 1:2.2 to 1:2.6.
In yet another embodiment of the present disclosure the alkali metal salt of organic acid used is selected from sodium formate, sodium acetate, sodium citrate.
In still another embodiment of the present disclosure the polyhydric alcohol used is selected from sorbitol, mannitol, glycerine.
In still another embodiment of the present disclosure the ratio of polyhydric alcohol and basic chromium sulfate is in the range of 0.3:1 to 1:1.
In still another embodiment of the present disclosure the acid used for acidification of polyhydric alcohol is selected from sulfuric acid, acetic acid, formic acid.
In still another embodiment of the present disclosure a process for chrome tanning characterized in that it uses the said composition, wherein the steps comprise treatment of delimed hide/skin with 10 to 20% w/w of the said composition for a period in the range of 1-12 hours, preferably under stirring condition to obtain the chrome tanned hide/skin.

DETAILED DESCRIPTION OF THE INVENTION

Basic chromium sulfate is mixed with alkali metal salt of organic acid having carbon chain of length one to three in a ratio in the range of 1:0.25 to 1:0.5 and then mixed with acidified polyhydric alcohol, characterized by carbon chain length of 3-6, adjusted at a pH in the range of 1-6. The amount of polyhydric alcohol is in a ratio 0.3:1 to 1:1 with basic chromium sulfate. The mixture is preferably subjected to stirring for a period of 20 minutes to obtain the novel tanning composition. The composition exhibits the following characteristics:

➢ pH of the dispersion = 1-6.
➢ Preferable proportion of basic chromium sulfate and alkali metal salt of organic acid is 1:0.25 to 1:0.5.
➢ Cr₂O₃ : SO₄ ratio is 1:2.2 to 1:2.6

The composition is used for chrome tanning. Delimed hides and skins are treated with 10-20 % w/w, of the novel tanning composition without addition of water under agitation for a period of 1-12 hrs to get chrome tanned hide/skin.
The inventive step of the present invention lies in providing a dispersion to enable the chrome tanning process to be carried out not only without adding water, but also eliminating the pickling and basification operations.

EXAMPLES

The invention is described in detail with reference to the examples given below which should not however be construed to limit the scope of the present invention.

EXAMPLE 1

700 grams of basic chromium sulfate, 210 grams of sodium formate were mixed together and dispersed in 270 grams of sorbitol previously acidified with 50 grams of acetic acid by stirring for 30 minutes to yield 1230 grams of tanning composition. The product was stored in an air tight bottle. The composition was found to exhibit the following characteristics:

➢ Ratio of basic chromium sulfate, alkali metal salt of organic acid and alcohol = 1:0.3:0.46
➢ Cr₂O₃ : S04= 1:2.2
➢ pH of the dispersion = 6.0

EXAMPLE 2

800 grams of basic chromium sulfate and 400 grams of sodium acetate were mixed together and dispersed in 600 grams of glycerine previously acidified with 60 grams of formic acid, by stirring for a period of 20 minutes to yield 1860 grams of the tanning composition. The product was stored in an air tight bottle. The composition was found to exhibit the following characteristics:

➢ Ratio of basic chromium sulfate, alkali metal salt of organic acid and alcohol = 1: 0.5:0.83
➢ Cr₂O₃ : SO₄ = 1:2.4
➢ pH of the dispersion =4.0

EXAMPLE 3

18.0 kgs. of basic chromium sulfate, 6 kgs sodium citrate were mixed together and dispersed in 13.0 kilos of mannitol previously acidified with 1.0 kg of sulfuric acid, by stirring for a period of 40 minutes to yield 38.0 kgs of tanning composition. The product was stored in an air tight bottle. The composition was found to exhibit the following characteristics:

➢ Ratio of basic chromium sulfate, alkali metal salt of organic acid and alcohol = 1:0.3:0.78
➢ Cr₂O₃ : SO₄= 1:2.6
➢ pH of the dispersion = 1.0

ADVANTAGES OF THE INVENTION

1. It is a versatile composition which is applicable to water-free, pickle-free chrome tanning.
2. Shelf life of the composition is about 3 months.
3. Complete avoidance of water and sodium chloride addition during tanning is affected.
4. It ensures that uneven stains do not appear on the leather.
5. The process is cost effective and environmentally friendly.

Claims

A composition for water free, pickle free chrome tanning of hides/skins comprising:
[a] basic chromium sulfate, having Cr₂O₃ content in the range of 21-25 % (weight / weight of basic chromium sulfate)

[b] alkali metal salt of organic acid having carbon chain of length in the range of one to three;

[c] polyhydric alcohol previously acidified with acid;
wherein the ratio of [a] : [b] : [c] is in the range of 1:0.25:0.3 to 1:0.5: 1.
The composition as claimed in claim 1, wherein the composition has pH in the range of 1-6.
The composition as claimed in claim 1, wherein the alkali metal salt of organic acid is selected from sodium formate, sodium acetate, sodium citrate.
The composition as claimed in claim 1, wherein the polyhydric alcohol is selected from sorbitol, mannitol, glycerine.
The composition as claimed in claim 1, wherein the acid used for acidification of polyhydric alcohol is selected from sulfuric acid, acetic acid, formic acid.
A process for chrome tanning of hides/skins by treating delimed hide/skin with 10 to 20% w/w of the composition as claimed in claim 1 for a period in the range of 1-12 hours, preferably under stirring condition to obtain the chrome tanned hide/skin.