WO2015104716A1

WO2015104716A1 - A composition for water free, pickle free chrome tanning of hides/skins

Info

Publication number: WO2015104716A1
Application number: PCT/IN2014/000555
Authority: WO
Inventors: Chellappa Muralidharan
Original assignee: Council Of Scientific & Industrial Research
Priority date: 2014-01-13
Filing date: 2014-08-29
Publication date: 2015-07-16
Also published as: CN106414777A; ZA201605336B; EP3094754A1; EP3094754B1; TR201809066T4; BR112016016270A2; CN106414777B; IN2014DE00085A

Abstract

The present disclosure provides a composition for water free, pickle free chrome tanning of hides/skins comprising of basic chrome sulphate, alkali metal salt of organic acid and polyhydric alcohol for chrome tanning of hides and/or skins. The chrome tanning process ensures avoiding use of water and the conventional pickling operation. It 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 disclosure is therefore envisaged to play a crucial role in enhancing the economic and environmental benefits associated with chrome tanning.

Description

A COMPOSITION FOR WATER FREE, PICKLE FREE CHROME TANNING

OF HIDES/SKINS

FIELD OF INVENTION

[0001] 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

[0002] 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 l ike ammonium chloride for removal of residual l ime. The operation is called deliming, which is usually carried out in tanning drum. The resulting del imed hides and skins are subjected to pickl ing using 1 0% salt (al l 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. Whi le 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. Alkal ine 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.

[0003] 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 pickl ing and chrome tanning contribute significantly for total dissolved sol ids in the effluent during chrome tanning. Presence of large quantities of total dissolved sol ids 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 sol ids 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.

10004) Indian patent application no. 1 77/DEL/2002, and US Patent 7,063,728 describe an improved process for making chrome tanned leathers whereby the del imed 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).

[0005J I ndian patent appl ication no. 2 108/DEL/2008 describes a novel chrome composition comprising essential ly three components - [a] basic chrom ium sulfate, having Cr₂0₃ 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 neutral ized. Thus, the major feature of using this composition in chrome tanning involves avoiding pickling Operation, thereby ensuring that effluent is not loaded with enormous salin ity as well as TDS.

[0006] 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

[0007] 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.

[0008] Another objective of the present disclosure is to provide a process for chrome tanning without resorting to use of water for tanning.

[0009] Yet another objective of the present disclosure is to provide a tanning process without resorting to pickling. SUMMARY OF THE INVENTION

[00010] 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 Cr₂0₃ 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 [00011] In an embodiment of the present disclosure the composition has pH iin the range of 1 -6.

[00012] In another embodiment of the present disclosure Cr₂0₃: S0₄ ratio is in the range of 1 :2.2 to 1 :2.6.

[00013] 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.

[00014] In sti ll another embodiment of the present disclosure the polyhydric alcohol used is selected from sorbitol, mannitol, glycerine.

[00015] 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 .

[00016] In stil l another embodiment of the present disclosure the acid used for acidification of polyhydric alcohol is selected from sulfuric acid, acetic acid, formic acid.

|00017] In sti ll 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 del imed hide/skin with 1 0 to 20% w/w of the said composition for a period in the range of 1 - 1 2 hours, preferably under stirring condition to obtain the chrome tanned hide/skin.

DETAILED DESCRIPTION OF THE INVENTION |00018] 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 fol lowing 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. > Cr₂0₃ : S0₄ ratio is 1 :2.2 to 1 :2.6

100019) 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 I - 12 hrs to get chrome tanned hide/skin.

[00020) The inventive step of the present invention l ies in providing a dispersion to enable the chrome tanning process to be carried out not only without adding water, but also eliminating the pickl ing and basification operations.

EXAMPLES

[00021 | 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

[00022] 700 grams of basic chromium sulfate, 2 1 0 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

> Cr₂0₃ : S0₄= 1 :2.2

> pH of the dispersion = 6.0

The composition was then used for chrome tanning of delimed goat skins.

10 delimed goat skins weighing 12 kilos were taken in a tanning drum. The skins were then agitated with the above composition for 2 hours to complete chrome tanning.

EXAMPLE 2

[00023J 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 1 860 grams of the tanning composition. The product was stored in an air tight bottle. The composition was found to exhibit the fol lowing characteristics: Ratio of basic chromium sul fate, alkali metal salt of organic acid and alcohol = 1 : 0.5 :0.83

> Cr₂0₃ : S0₄ = 1 :2.4

> pH of the dispersion =4.0

The composition was then used for chrome tanning of del imed sheep skins. 10 delimed sheep skins weighing 8 kilos were taken in a tanning drum. The skins were then agitated with the above composition for 8 hours to complete chrome tanning.

EXAMPLE 3

[00024] 1 8.0 kgs. of basic chromium sulfate, 6 kgs sodium citrate were mixed together and dispersed in 1 3.0 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

> Cr₂0₃-: S0₄= 1 :2.6

pH of the dispersion = 1 .0

The composition was then used for chrome tanning of delimed cow hides.

10 delimed cow hides weighing 200 kilos were taken in a drum. The hides were then agitated with the above tanning composition for a period of 12 hours to complete chrome tanning.

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 environmental ly friendly.

Claims

I/WE CLAIM:

1 . A composition for water free, pickle free chrome tanning of h ides/skins comprising:

[a] basic chromium sulfate, having Cr₂0₃ content in the range of 2 1 -25 % (weight / weight of basic chromium sulfate)

[b] alkal i 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 .

2. The composition as claimed in claim 1 , wherein the composition has pH in the range of 1 -6.

3. The composition as claimed in claim 1 , wherein the alkali metal salt of organic acid is selected from sodium formate, sodium acetate, sodium citrate.

4. The composition as claimed in claim I , wherein in the polyhydric alcohol is selected from sorbitol, mannitol, glycerine.

5. 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.

6. A process for chronie tanning of hides/skins by treating del imed hide/skin with 10 to 20% w/w of the composition as claimed in claim 1 for a period in the range of I - 12 hours, preferably under stirring condition to obtain the chrome tanned hide/skin.