Title of Invention	A NOVEL COMPOSITIONS FOR CHROME TANNING OF HIDES/SKINS
Abstract	The present Invention provides a novel composition for chrome tanning of hides and/or skins thereby avoiding the conventional pickling operation and generation of large amounts of TDS in the waste water. In the process of the present invention the delimed hides and skins are treated with the claimed composition without affecting the tanning potency of the tanning salt followed by subsequent pH adjustment of the hides and skins with water only thereby eliminating the pickling operation and use of alkali for basification.

Title of Invention

A NOVEL COMPOSITIONS FOR CHROME TANNING OF HIDES/SKINS

Abstract

The present Invention provides a novel composition for chrome tanning of hides and/or skins thereby avoiding the conventional pickling operation and generation of large amounts of TDS in the waste water. In the process of the present invention the delimed hides and skins are treated with the claimed composition without affecting the tanning potency of the tanning salt followed by subsequent pH adjustment of the hides and skins with water only thereby eliminating the pickling operation and use of alkali for basification.

Full Text	Field of the invention The present invention relates to a novel composition for chrome tanning of hides/ skins. The invention further relates to an improved process for chrome tanning using the said composition. The present process is envisaged to have tremendous application potential in the tanning industry for substantial reduction of chlorides, chromium and total dissolved solids in the waste streams. The process will enhance the economic and environmental benefits to chrome tanning. Background of the invention and Description of Prior Art Salted hides and skins are the major raw materials for the tanning industry. In leather making process the first operation carried out is removal of the 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. 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. Till now, no viable and cost effective solution is available for secured treatment of total dissolved solids. Minimising or eliminating total dissolved solids in the effluents has been a topic of research interest for quite sometime. Gupta et al. (Journal of Indian Leather Technologists Association, 41, 24-26,1992) developed a pickle free alum - chrome combination tanning system using only 2% of salt thereby reducing use of salt to an extent of 8%. However use of aluminium in the system impairs the feel and softness of the leathers. Further the addition of salt is not eliminated completely. Our co pending Indian Patent application No 177 Del 2002 and US Patent 7,063,728 describes an improved process for making chrome tanned leathers whereby a mixture of conventional tanning salt and alkali metal salt is used at a pH in the range of 5.5. The method involved use of alkali dissolved in water and added in feeds of equal installments to attain a pH of 4.0 - 4.2 for completion of tanning wherein the acid liberated during hydrolysis of chromium is neutralized. However the alkali requirements vary depending up on hydrolysis of chrome salt. Such variations are likely to result in either excess alkali or insufficient alkali at any point of time since alkali is added in equal quantities. These variations can affect the physical properties and surface characteristics of the leather adversely. Objectives of the invention The main objective of the present invention is thus to provide a tanning composition, which obviates the limitations as stated above. Another objective of the present invention is to provide a process for chrome tanning without resorting to pickling. Yet another objective of the present invention is to provide a process applicable to both hides and skins. Summary of the invention Accordingly, the present invention provides a novel composition for chrome tanning of hides and/or skins, wherein the said composition comprising: [a] basic chromium sulfate, having Or2O3 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 invention further provides an improved process for chrome tanning characterized in that it uses the said composition, wherein the steps comprise: (a) conditioning delimed hides and/or skins to a pH in the range of 5.0 to 5.5 by conventional methods followed by treatment with 7.5 to 12.0% w/w of the composition as claimed claim 1 for a period of 2 to 4 hours; (b) adjusting the pH of the treated hides and/or skins as obtained in step (a) in the range of 4.0 to 4.2 by controlled addition of not less than 40% w/w water to obtain the chrome tanned hides and/or skins. Detailed description of the invention The process is described below in detail. The delimed hides and skins are conditioned to a pH in the range of 5-5.5 by conventional method. Alkali earth metal oxide and alkali metal salt of organic acid having carbon chain of length not more than three are mixed with basic chromium sulfate in a ratio in the range of 10:0.25:0.88 to 10:0.38:1.25 to yield the claimed composition and the conditioned hides and skins are treated with 7.5 -12.0% of this composition under agitation for a period not less than 2 Hrs without addition of water, when the tanning salt penetrates the cross section of the hides and skins under processing producing blue colouration at the cross section. The pH is then adjusted in the range of 4-4.2 by controlled addition of not less than 40% w/w of water to complete chrome tanning process. In an embodiment of the present invention, the proportion of alkali earth metal oxide and basic chromium sulfate in the composition may be in the range of 1:26 to 1:40. In another embodiment of the present invention, the alkali earth metal oxide used may be selected from CaO and MgO. In yet another embodiment of the present invention, the proportion of alkali metal salt of organic acid and basic chromium sulfate in the composition may be in the range of 1:8 to 1:11.5. In still another embodiment of the present invention, the alkali metal salt of organic acid used may be selected from sodium formate, sodium acetate, sodium citrate, potassium formate, and potassium acetate. In still another embodiment of the present invention, the Cr2 O3 : SO4 of the basic chromium sulfate may be 1:2.2 to 1:2.6. The inventive step of the present invention lies in treating hides and skins under processing at a pH the range of 5-5.5 with the claimed composition without affecting the tanning potency of the tanning salt followed by subsequent pH adjustment of the hides and skins with water only thereby eliminating the pickling operation and use of alkali for basification. 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 10 delimed goat skins weighing 10 kilos were taken in a drum. 30 gms of formic acid dissolved in 300ml. of water was added to drum and the skins were agitated for a period of 20 minutes to attain a pH of 5.5. The skins were then agitated with 780 gms of tanning composition consisting of 700 gms of basic chromium sulfate, 17.5 gms of MgO and 62.5 gms of sodium formate for a period of 3 hours. The cross section of the skin was checked and found to be blue in color indicating complete penetration of chromium. The pH of the skins were then adjusted to 4.2 by adding 4 L of water to the drum, where in the skins were agitated continuously, in 16 equal installments over a period of 80 minutes to complete chrome tanning. Example 2 10 delimed sheep skins weighing 8 kilos were taken in a drum. 30 gms of acetic acid dissolved in 300ml. of water was then added to drum and the skins were agitated for a period of 15 minutes to attain a pH of 5.0. The skins were then agitated with 930 gms of the tanning composition consisting of 800 gms of basic chromium sulfate, 30 gms of CaO and 100 gms of sodium acetate for a period of 2 hours. The cross section of the skin was checked and found to be blue in color indicating complete penetration of chromium. The pH of the skins were adjusted to 4.0 by adding to drum 4.0 L of water, in 8 equal installments over a period of 80 minutes to complete chrome tanning. Example - 3 10 delimed cow hides weighing 100 kilos were taken in a drum. 500 gms of formic acid dissolved in 5.0 L of water was then added to the drum and the hides were agitated for a period of 30 minutes to attain a pH of 5.2. The hides were then agitated with 11.1 kgs. of tanning composition consisting of 10.0 kgs. Of basic chromium sulfate, 300 gms of MgO and 700 gms of sodium citrate for a period of 4 hours. The cross section of the hides were checked and found to be blue in color indicating complete penetration of chromium. The pH of the hides were adjusted to 4.0 by adding to drum 45 L of water, in 10 equal installments over a period of 100 minutes to complete chrome tanning. The advantages of the present invention are the following: 1. It is a versatile composition which is applicable to pickle free chrome tanning. 2. Complete avoidance of sodium chloride addition during tanning is effected. 3. It ensures that uneven stains do not appear on the leather. 4. The process is cost effective and environmentally friendly. We claim: 1. A novel composition for chrome tanning of hides and/or skins, wherein the said composition comprising: [a] basic chromium 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. 2. A composition as claimed in claim 1, wherein the proportion of alkali earth metal oxide and basic chromium sulfate is preferably in the range of 1:26 to 1:40. 3. A composition as claimed in claiml, wherein the alkali earth metal oxide used is selected from CaO and MgO. 4. A composition as claimed in claiml, wherein the proportion of alkali metal salt of organic acid and basic chromium sulfate is preferably in the range of 1:8 to 1:11.5. 5. A composition as claimed in claiml, wherein the alkali metal salt of organic acid used is selected from sodium formate, sodium acetate, and sodium citrate. 6. A composition as claimed in claim 1, wherein in the Cr2O3 : SO4 ratio of 1:2.2 to 1:2.6. 7. An improved process for chrome tanning characterized in that it uses the composition as claimed in claim 1, wherein the steps comprise: (c) conditioning delimed hides and/or skins to a pH in the range of 5.0 to 5.5 by conventional methods followed by treatment with 7.5 to 12.0% w/w of the composition as claimed claim 1 for a • period of 2 to 4 hours; (d) adjusting the pH of the treated hides and/or skins as obtained in step (a) in the range of 4.0 to 4.2 by controlled addition of not less than 40% w/w water to obtain the chrome tanned hides and/or skins. 8. A novel composition and process for chrome tanning of hides/skins substantially as herein described with reference to the foregoing examples.

Full Text

Field of the invention
The present invention relates to a novel composition for chrome tanning of hides/ skins. The invention further relates to an improved process for chrome tanning using the said composition. The present process is envisaged to have tremendous application potential in the tanning industry for substantial reduction of chlorides, chromium and total dissolved solids in the waste streams. The process will enhance the economic and environmental benefits to chrome tanning.
Background of the invention and Description of Prior Art
Salted hides and skins are the major raw materials for the tanning industry. In leather making process the first operation carried out is removal of the 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.
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. Till now, no viable and cost effective solution is available for secured treatment of total dissolved solids. Minimising or eliminating total dissolved solids in the effluents has been a topic of research interest for quite sometime.
Gupta et al. (Journal of Indian Leather Technologists Association, 41, 24-26,1992) developed a pickle free alum - chrome combination tanning system using only 2% of salt thereby reducing use of salt to an extent of 8%. However use of aluminium in the system impairs the feel and softness of the leathers.
Further the addition of salt is not eliminated completely. Our co pending Indian Patent application No 177 Del 2002 and US Patent 7,063,728 describes an improved process for making chrome tanned leathers whereby a mixture of conventional tanning salt and alkali metal salt is used at a pH in the range of 5.5. The method involved use of alkali dissolved in water and added in feeds of equal installments to attain a pH of 4.0 - 4.2 for completion of tanning wherein the acid liberated during hydrolysis of chromium is neutralized. However the alkali requirements vary depending up on hydrolysis of chrome salt. Such variations are likely to result in either excess alkali or insufficient alkali at any point of time since alkali is added in equal quantities. These variations can affect the physical properties and surface characteristics of the leather adversely.
Objectives of the invention
The main objective of the present invention is thus to provide a tanning
composition, which obviates the limitations as stated above.
Another objective of the present invention is to provide a process for chrome
tanning without resorting to pickling.
Yet another objective of the present invention is to provide a process
applicable to both hides and skins.
Summary of the invention
Accordingly, the present invention provides a novel composition for chrome tanning of hides and/or skins, wherein the said composition comprising:
[a] basic chromium sulfate, having Or2O3 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 invention further provides an improved process for chrome tanning characterized in that it uses the said composition, wherein the steps comprise:
(a) conditioning delimed hides and/or skins to a pH in the range of 5.0 to 5.5 by conventional methods followed by treatment with 7.5 to 12.0% w/w of the composition as claimed claim 1 for a period of 2 to 4 hours;
(b) adjusting the pH of the treated hides and/or skins as obtained in step (a) in the range of 4.0 to 4.2 by controlled addition of not less than 40% w/w water to obtain the chrome tanned hides and/or skins.
Detailed description of the invention
The process is described below in detail.
The delimed hides and skins are conditioned to a pH in the range of 5-5.5 by conventional method. Alkali earth metal oxide and alkali metal salt of organic acid having carbon chain of length not more than three are mixed with basic chromium sulfate in a ratio in the range of 10:0.25:0.88 to 10:0.38:1.25 to yield the claimed composition and the conditioned hides and skins are treated with 7.5 -12.0% of this composition under agitation for a period not less than 2 Hrs without addition of water, when the tanning salt penetrates the cross section of the hides and skins under processing producing blue colouration at the cross section. The pH is then adjusted in the range of 4-4.2 by controlled addition of not less than 40% w/w of water to complete chrome tanning process.
In an embodiment of the present invention, the proportion of alkali earth metal oxide and basic chromium sulfate in the composition may be in the range of 1:26 to 1:40.
In another embodiment of the present invention, the alkali earth metal oxide used may be selected from CaO and MgO.
In yet another embodiment of the present invention, the proportion of alkali metal salt of organic acid and basic chromium sulfate in the composition may be in the range of 1:8 to 1:11.5.
In still another embodiment of the present invention, the alkali metal salt of
organic acid used may be selected from sodium formate, sodium acetate,
sodium citrate, potassium formate, and potassium acetate.
In still another embodiment of the present invention, the Cr2 O3 : SO4 of the
basic chromium sulfate may be 1:2.2 to 1:2.6.
The inventive step of the present invention lies in treating hides and skins
under processing at a pH the range of 5-5.5 with the claimed composition
without affecting the tanning potency of the tanning salt followed by
subsequent pH adjustment of the hides and skins with water only thereby
eliminating the pickling operation and use of alkali for basification.
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 10 delimed goat skins weighing 10 kilos were taken in a drum. 30 gms of formic acid dissolved in 300ml. of water was added to drum and the skins were agitated for a period of 20 minutes to attain a pH of 5.5. The skins were then agitated with 780 gms of tanning composition consisting of 700 gms of basic chromium sulfate, 17.5 gms of MgO and 62.5 gms of sodium formate for a period of 3 hours. The cross section of the skin was checked and found to be blue in color indicating complete penetration of chromium. The pH of the
skins were then adjusted to 4.2 by adding 4 L of water to the drum, where in the skins were agitated continuously, in 16 equal installments over a period of 80 minutes to complete chrome tanning.
Example 2 10 delimed sheep skins weighing 8 kilos were taken in a drum. 30 gms of acetic acid dissolved in 300ml. of water was then added to drum and the skins were agitated for a period of 15 minutes to attain a pH of 5.0. The skins were then agitated with 930 gms of the tanning composition consisting of 800 gms of basic chromium sulfate, 30 gms of CaO and 100 gms of sodium acetate for a period of 2 hours. The cross section of the skin was checked and found to be blue in color indicating complete penetration of chromium. The pH of the skins were adjusted to 4.0 by adding to drum 4.0 L of water, in 8 equal installments over a period of 80 minutes to complete chrome tanning.
Example - 3 10 delimed cow hides weighing 100 kilos were taken in a drum. 500 gms of formic acid dissolved in 5.0 L of water was then added to the drum and the hides were agitated for a period of 30 minutes to attain a pH of 5.2. The hides were then agitated with 11.1 kgs. of tanning composition consisting of 10.0 kgs. Of basic chromium sulfate, 300 gms of MgO and 700 gms of sodium citrate for a period of 4 hours. The cross section of the hides were checked and found to be blue in color indicating complete penetration of chromium. The
pH of the hides were adjusted to 4.0 by adding to drum 45 L of water, in 10 equal installments over a period of 100 minutes to complete chrome tanning.
The advantages of the present invention are the following:
1. It is a versatile composition which is applicable to pickle free chrome tanning.
2. Complete avoidance of sodium chloride addition during tanning is effected.
3. It ensures that uneven stains do not appear on the leather.
4. The process is cost effective and environmentally friendly.

We claim:
1. A novel composition for chrome tanning of hides and/or skins, wherein
the said composition comprising:
[a] basic chromium 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.
2. A composition as claimed in claim 1, wherein the proportion of alkali earth metal oxide and basic chromium sulfate is preferably in the range of 1:26 to 1:40.
3. A composition as claimed in claiml, wherein the alkali earth metal oxide used is selected from CaO and MgO.
4. A composition as claimed in claiml, wherein the proportion of alkali metal salt of organic acid and basic chromium sulfate is preferably in the range of 1:8 to 1:11.5.
5. A composition as claimed in claiml, wherein the alkali metal salt of organic acid used is selected from sodium formate, sodium acetate, and sodium citrate.
6. A composition as claimed in claim 1, wherein in the Cr2O3 : SO4 ratio of 1:2.2 to 1:2.6.
7. An improved process for chrome tanning characterized in that it uses the composition as claimed in claim 1, wherein the steps comprise:
(c) conditioning delimed hides and/or skins to a pH in the range of
5.0 to 5.5 by conventional methods followed by treatment with
7.5 to 12.0% w/w of the composition as claimed claim 1 for a
• period of 2 to 4 hours;
(d) adjusting the pH of the treated hides and/or skins as obtained in
step (a) in the range of 4.0 to 4.2 by controlled addition of not
less than 40% w/w water to obtain the chrome tanned hides
and/or skins.
8. A novel composition and process for chrome tanning of hides/skins substantially as herein described with reference to the foregoing examples.

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Patent Number

271546

Indian Patent Application Number

2108/DEL/2008

PG Journal Number

09/2016

Publication Date

26-Feb-2016

Grant Date

25-Feb-2016

Date of Filing

08-Sep-2008

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110 001,INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	VICTOR JOHN SUNDAR	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020, INDIA
2	THIRUMALAISAMY RANGASAMY	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020, INDIA
3	CHELLAPPA MURALIDHARAN	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020, INDIA

PCT International Classification Number

C14C

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA