Title of Invention	A PROCESS FOR THE PREPARATION OF A NOVEL CHROMIUM-IRON COMPLEX FOR USE IN LEATHER INDUSTRY
Abstract	A process for the preparation of a novel chromium-iron complex for use in leather industry by mixing a salt of iron with that of hexavalent chromium in water, treating the reaction mixture with sulphuric acid, adding reducing agent and organic ligand to the reaction mixture either simultaneously or in succession, in one or more installments, maintaining the temperature in the range of 85 to 105°C, ageing the reaction mixture for 8-12 hrs, pH is maintained at 2.5 to 2.8, subjecting the resulting suspension to separation process by known method followed by conventional drying of the final liquor to form the chromium-iron complex.

Title of Invention

A PROCESS FOR THE PREPARATION OF A NOVEL CHROMIUM-IRON COMPLEX FOR USE IN LEATHER INDUSTRY

Abstract

A process for the preparation of a novel chromium-iron complex for use in leather industry by mixing a salt of iron with that of hexavalent chromium in water, treating the reaction mixture with sulphuric acid, adding reducing agent and organic ligand to the reaction mixture either simultaneously or in succession, in one or more installments, maintaining the temperature in the range of 85 to 105°C, ageing the reaction mixture for 8-12 hrs, pH is maintained at 2.5 to 2.8, subjecting the resulting suspension to separation process by known method followed by conventional drying of the final liquor to form the chromium-iron complex.

Full Text	The present invention relates to a process for the preparation of a novel chromium-iron complex for use in Leather industry. It has potential use predominantly as a self-tanning agent for hides and skins. The complex may also be used as a natural aid for developing various shades by adding external aids other than dyes during post tanning operations on leathers tanned with this complex. Conventional chrome tanning practices give rise to an uptake of only 50-60% of chromium offered. The poor uptake of chromium in tanning has resulted in wide scale ecological concerns and economic loss. As reported by Chandrasekaran {Leather Science, 34, 91, 1987) several methods have been evolved over the vh years for better management of chromium in leather industry. Among the several options considered, the chrome saver approach and the development of mineral alternatives to chromium have been gaining momentum. Many products based on metal ions like aluminium, titanium, zirconium and iron have been reported in the past by Covington (Chemical Society Reviews,26, 73, 1997), to have tanning potency. But these products lack the ability to withstand pH conditions above 5.5, as described by Heidemann (Fundamentals of Leather Manufacture, Eduard Roether KG publications 1st edition, Chapter 11, 1993). Though several efforts have been taken to overcome these drawbacks, universal availability and high cost have forced researchers to look for other alternatives as well. As reported by Percy et al (The Analyst, 123, 41, 1998), the subject of iron tanning has been of great academic interest in view of the existence of iron-protein combinations in nature and the ease with which iron forms complex ions. Knapp (Journal of American Leather Chemists Association, 16, 658, 1921) obtained a number of patents covering iron tanning, but all his attempts to manufacture iron-tanned leather failed because the resulting feather was not only brittle and thin but also found to deteriorate with ageing. When used as a tanning agent iron has a tendency to hydrolyze and precipitate as hydrated oxide or as a highly basic salt. Casaburi (Journal of Society of International Leather Trades ,, t and Chemists, 3, 61, 1919) postulated that the poor results obtained in iron tannage were due to incomplete removal of uncombined ferric salts from the leather. Further iron tanned leathers have been reported to darken on ageing. Thorstensen and Theis (Journal of American Leather Chemists Association, 44(12), 841, 1942) reported that the addition of masking salts to an iron tannage reduced the hydrolysis of iron salt. Ruppenthal and Malik (Journal of American ^Leather Technologists and Chemists, 38, 148, 1943) have reported that a combination of chromium and iron tannage could be advantageous for obtaining leathers of good shrinkage temperature. They found that an iron pretannage followed by chrome tanning leaves very little iron in the effluent while a chrome pretannage followed by iron tanning leaves very little chromium in the effluent. This could be due to the fact that both iron and chromium follow the same tanning mechanism, and when separately offered for tanning, one hinders the fixation of the other. Recently Platon et al (Proceedings of the International Union of Leather Technologists and Chemists Society Congress, 405, 1993) have reported the development of heterocomplexes of chromium and iron with glucose as the reducing agent. As reported by Thorstensen and Theis (Journal of American Leather Chemists Association, 44(12), 841, 1942), mineral tanning agents containing iron without masking agents are known to deteriorate the leather on ageing. Thus the limitation of these complexes is that they are not stable against hydrolysis. Moreover, the absence of organic ligands leads to the offer of 2.2% metal oxide for tanning to produce leather of shrinkage temperature of maximum of 107°C. Under such conditions the amount of chromium in the effluent (as chromium) has been found to be 875 ppm. This high discharge of chromium in the environment certainly generates great ecological concerns. Dyeing improves the aesthetic value of leather. The increasing awareness of harmful effects of the conventional dyes has brought in a need for ecofriendly dyes throughout the world. The ban on arylamine based dyes has also motivated the leather dyers to look for better options, which include the use natural dyes. Although natural stuff like Log-wood, Fustic and hypernic have in the past been used in dyeing of leather, yet they are not free from certain limitations like limited availability as well as limited potential variation of shade. Thorstensen (Practical Leather Technology, Krieger publishing company, 4h edition, Florida, 1993). reported that in the presence of iron salts, the condensed tannins produce greenish black colour, while the hydrolysable tannins produce blue-violet colour. The main objective of the present invention is to provide a process for the preparation of a novel chromium-iron complex for use in feather industry, which obviates the drawbacks stated above. Another objective of the present invention is to prepare a mineral tanning agent having an active ingredient capable of giving near zero wastage of metal salt. Yet another objective of the present invention is to exploit the ability of chromium and iron to form mixed oxo complexes in the presence of organic ligands which when used would resist darkening/deterioration of leather on ageing. Still another objective of the present invention is to develop a tanning salt which when used in tanning gives an exhaustion of more than 90% of the metal salts employed. Yet another objective of the present invention is to develop a tanning salt which can be used to produce leathers of various shades by treating with eco-friendly natural stuff other than dyes. Accordingly the present invention provides a process for the preparation of a novel chromium-iron complex for use in leather industry, which comprises i) mixing a salt of iron with that of hexavalent chromium in water, ii) treating the reaction mixture, as formed in step (i), with sulphuric acid, iii) adding reducing agent such as herein described and organic ligand to the reaction mixture as formed in step(ii), either simultaneously or in succession, in one or more installments, maintaining the temperature in the range of 85 to 105°C, iv) ageing the reaction mixture, as formed in step (iii), for 8-12 hrs, pH is maintained at 2.5 to 2.8, v) subjecting the resulting suspension,as formed in step (iv), to separation process by known method followed by conventional drying of the final liquor to form the chromium-iron complex. In an embodiment of the present invention, the salt of hexavalent chromium used may be sodium dichromate, potassium dichromate, ammonium dichromate. In another embodiment of the present invention, the iron salt used may be such as ferrous sulphate, ferrous ammonium sulphate, ferric s.ulphate. In yet another embodiment of the present invention, the amount of iron salt used may be such as 0.1 - 2.0 moles of iron per mole of chromium. In still another embodiment of the present invention, the amount of water added to the reaction mixture may be such as 15-30 moles of water per mole of chromium. In yet another embodiment of the present invention, the amount of sulphuric acid used may be such as 1.3 -1.5 moles per mole of chromium. In yet another embodiment of the present invention, the reducing agent used may be such as molasses, glucose, sodium sulphite, sodium bisulphite, either individually or in combination. In still another embodiment of the present invention, the amount of reducing agent may be in the range of 0.1 -0.2 moles per mole of chromium. In yet another embodiment of the present invention, the organic ligand used may be such as citric acid, phthalic acid, tartaric acid, oxalic acid, lactic acid, any alkali metal salt of these acids, either individually or in combination. In still another embodiment of -the present invention, the amount of organic ligand used may be 0.1 -1.0 mole per mole of chromium. In yet another embodiment of the present invention, the temperature of the reaction mixture to be maintained, while adding the reducing agent and the organic ligands may be in the range of 85-105°C. In still another embodiment of the present invention, the pH of the slurry after ageing may be in the range of 2.5-2.8. In yet another embodiment of the present invention, the process of separation of the suspension may be such as filtration, gravity precipitation, centrifugajion. In still another embodiment of the present invention, the process for drying of the final liquor may be such as drum drying, spray drying, air drying effected at 130-260°C over a period of 3-60 seconds. Accordingly the present invention provides a novel chromium-iron complex prepared by the process described above. 0.1 - 2.0 moles of a salt of iron per mole of chromium is mixed with that of hexavalent chromium and 15-30 moles of water per mole of chromium is added to the reaction mixture with continuous stirring. Sulphuric acid calculated as 1.3-1.5 moles per mole of chromium is then added to the reaction mixture while continuing the stirring. 0.1-0.2 mole of a reducing agent per mole of chromium and 0.1-1.0 mole of organic ligand per mole of chromium are added to the above reaction mixture either simultaneously or in different successions, in one or more installments, with continuous stirring over a period of minimum 1 hr. Stirring is continued for minimum 1hr even after the complete addition of the above agents. The resultant mixture is then allowed to settle. After a period of 8-12 hrs, pH of the resulting suspension is checked to be in the range of 2.5-2.8. This suspension is then subjected to separation process by known method followed by conventional drying of the final liquor, obtained thereby, for 3-60 sec at a temperature in the range of 130-260°C to get the chromium-iron complex powder. The novelty of the present invention lies in selecting the starting materials and in providing a process to prepare a chrome-iron matrix in the form of an oxo bridged complex with additional complexing provided by organic ligands, thereby ensuring, unlike conventional iron based tanning agents, absence of any darkening/deterioration of the leathers on ageing, and facilitating higher uptake of both chromium and iron resulting not only in the reduction of pollution problem but also in raising the shrinkage temperature of leather above 105°C, with an additional option of developing various shades for leathers on treatment with non-dye external aids including eco-friendly vegetable tanning materials. The invention is described in detail in the following examples, which are provided by way of illustration only and therefore should not be construed to limit the scope of the present invention. Example I 141.4 gms of ferrous sulphate was stirred with 303,gms of sodium dichromate in a flask fitted with a stirrer. 550 ml of water was added to the above mass with continuous stirring. 153 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 41 gms of molasses was added to 41 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period, of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 95°C. A mixture of 10 gms of tartaric acid and 11.1 gms of phthalic acid was added to this reaction mixture over a period of 10 minutes. 50 gms of molasses was added to 50 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes. A mixture of 9 gms of tartaric acid and 10 gms of phthalic acid was added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 105°C. The stirring was continued for another 2 hrs after the complete addition of the organic ligands. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium (VI) could be detected. The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be 2.7. This mixture was then filtered through a cloth and the filtrate was spray dried at a temperature of 260°C with contact time of 3 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 5.5% on pelt weight and the resultant leathers were found to have a shrinkage temperature of 120°C, exhibiting an exhaustion of 91 and 90% for iron and chromium respectively. The tanned leathers were subsequently treated with 2% Babool extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of pale grayish colour. Example II 565.5 gms of ferrous sulphate was stirred with 303 gms of sodium dichromate in a flask fitted with a stirrer. 600 ml of water was added to the above mass with continuous stirring. 153 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 41 gms of molasses was added to 41 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over •* a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 85°C. A mixture of 59 gms of sodium tartarate and 44.4 gms of phthalic acid was added to the reaction mixture over a period of 10 minutes. f-j 50 gms of molasses was added to 50 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes. A mixture of 58 gms of sodium tartarate and 40 gms of phthalic acid was added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 100°C. The stirring was continued for another 2 hrs after the complete addition of the organic ligands. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 10 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be 2.6. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with contact time of 60 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning the pickled goat skins at an offer of 3.5% on pelt weight and the resultant leathers were found to have a shrinkage temperature of 108°C, exhibiting an exhaustion of 92 and 94% for iron and chromium respectively. The tanned leathers were subsequently treated with 3% Myrobalan extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of intense black colour. Example III 417 gms of ferrous sulphate was stirred with 147.1 gms of potassium dichromate in a flask fitted with a stirrer. 480 ml of water was added to the above mass with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 43.2 gms of molasses was added to 44 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 60 minutes with continuous stirring. Simultaneously, a mixture of 63 gms of oxalic acid and 115 gms of sodium tartarate was added to the reaction mixture over a period of 20 minutes. The temperature of the reaction mixture was noted to be 102°C. The stirring was continued for another 2 hrs after the complete addition of organic ligands. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be 2.2. 10 gms of sodium carbonate was added to the mixture over a period of 15 min and the stirring was continued for 30 min. The pH was found to be 2.5. ,••; The resulting mixture was then filtered through a cloth and the filtrate was spray dried at 260°C with contact time of 4 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 5% on pelt weight and resulting leathers were found to have a shrinkage temperature of 109°C, exhibiting an exhaustion of 90 and 94% for iron and chromium respectively. The tanned leathers were subsequently treated with 4% wattle extract as an • •- ¥?** external colouring aid in the post tanning wet bath. The resultant leathers were of light grey colour. Example IV 556 gms of ferrous sulphate was stirred with 126 gms of ammonium dichromate in a flask fitted with a stirrer. 520 ml of water was added to the above mass with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 24 gms of molasses was added to 24 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. Simultaneously, a mixture of 74 gms of citric acid and 16.5 gms of oxalic acid was added to the reaction mixture over a period of 10 minutes. The temperature of the reaction mixture was noted to be 88°C. 20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 20 minutes. Simultaneously, 70 gms of citric acid and 15 gms of oxalic acid were then added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 100°C.The stirring was continued for another 1 hr after complete addition. Then 3 gms of sodium sulphite was added to the mixture and the stirring was continued for another 45 minutes.' A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 8 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be 2.0. 13 gms of sodium carbonate was then added to the mixture over a period of 20 minutes with continuous stirring. The stirring was continued for another 30 minutes and the pH was found to be 2.6. The resulting mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with contact time of 50 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 7% on pelt weight and the resulted leathers were found to have a shrinkage temperature of 107°C, exhibiting an exhaustion of 92 and 94% for iron and chromium, respectively. The tanned leathers were subsequently treated with 2% Myrobalan extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of black colour. Example V 392.16 gms of ferrous ammonium sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 30 gms of glucose was added to 30 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 60 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 98°C. 75 gms of tartaric acid was added to the reaction mixture over a period of 20 minutes. 5 gms of sodium bisulphite was added over a period of 5 minutes. The temperature of the reaction mixture was noted to be 103°C. The reaction mixture was stirred continuously for 2 hrs after complete addition. A 10% solution of the above mass was subjected to diphenyl carbazide test, whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.8. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with contact time of 55 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 4.5% on skin weight and resulted leathers were found to have a shrinkage temperature of 112°C, exhibiting an exhaustion of 91 and 95% for iron and chromium respectively. The tanned leathers were subsequently treated with 3% quebracho extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of slightly dark grey colour. Example VI 200 gms of ferric sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 360,ml of water was added to the above mass with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 24 gms of molasses was added to 24 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 90°C. A mixture of 8 gms of tartaric acid, 8 gms of phthalic acid and 4 gms of lactic acid was added to the reaction mixture over a period of 15 minutes. 20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes. A mixture of 7 gms of tartaric acid, 8.6 gms of phthalic acid and 5 gms of lactic acid was added to the above mass over a period of 15 minutes. The temperature of the reaction mixture was noted to be 101°C. The srirring was continued for another 2 hrs after the complete addition of organic ligands. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 9 hrs. The pH of the 1:1 aqueous solution of the above mixture was checked and found to be 2.6. The resulting mixture was then filtered through a cloth and the filtrate was spray dried at 260°C with contact time of 3 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 6% on pelt weight and resulted leathers was found to have a shrinkage temperature of 117°C, exhibiting an exhaustion of 92 and 94% for iron and chromium, respectively. The tanned leathers were subsequently treated with 3% chestnut extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of dark black colour. Example VII 278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 300 ml of water was added to the above mass with continuous stirring. 75 ml of98% sulphuric acid was added slowly to the above reaction mixture. 24 gms of molasses was added to 24 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 93°C. A mixture 20 gms of tartaric acid and 24 gms of citric acid was added to the reaction mixture over a period of 15 minutes. 20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes. A mixture of 17.5 gms of tartaric acid and 24 gms of citric acid were added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 103°C. The stirring was continued for another 90 minutes after complete addition of organic ligands. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.7. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with a contact time of 60 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 5% on xfc pelt weight and resulted leathers with a shrinkage temperature of 114°C,' exhibiting an exhaustion of 93 and 96% for iron and chromium respectively. The tanned leathers were subsequently treated with 2% potassium ferrocyanide as an external colouring aid in the post tanning wet bath. The resultant leathers were of Prussian blue colour. Example VIII 278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 270 ml of water was added to the above mass ,' with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 15 gms of glucose was added to 20 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 90°C. A mixture of 40 gms of phthalic acid and 20 gms of lactic acid was added to the reaction mixture over a period of 10 minutes. 15 gms of glucose was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes. A mixture of 43 gms of phthalic-acid and 25 gms of lactic acid was added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 99°C. The stirring was continued for another 2 hrs after complete addition of the organic ligands. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was checked and found to be 2.6. The resulting mixture was then filtered through a cloth and the filtrate was spray dried at a temperature of 260°C with a contact time of 3 sec. The resulting .-chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 3.5% on pelt weight and resulted leathers were found to have a shrinkage temperature of 108°C, exhibiting an exhaustion of 93 and 95% for iron and chromium, respectively. The tanned leathers were subsequently treated with 2% sodium thiocyanate as an external colouring aid in the post tanning wet bath. The resultant leathers were of yellow colour. Example IX 278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture. 23 gms of molasses was added to 23 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 95°C. 60 gms of sodium tartarate and was added to the reaction mixture over a period of 15 minutes. 20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes. 55 gms of sodium tartarate was added to the above mass over a period of 15 minutes. The temperature of the reaction mixture was noted to be 103°C. The stirring was continued for another 2 hrs after the complete addition of the organic ligand. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 11 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.8. This mixture was then filtered through a cloth and the filtrate was spray dried at a temperature of 260°C with a contact time of 3 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 7.5% on pelt weight and the resulted Jeathers were found to have a shrinkage temperature of 120°C, exhibiting an exhaustion of 90 jnd 91% for iron and chromium, respectively. The tanned leathers were subsequently were treated with 5% myrobalan extract as an external colouring aid in the post tanning wet bath. The resultant leathers were in dark blue colour. Example X 278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 400 ml of water was added to the above mass with continuous stirring. 75 mf of 98% sulphuric acid was added slowly to the .above reaction mixture. 23 gms of molasses was added to 23 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 89°C. 33 gms of oxalic acid was added to the reaction mixture over a period of 10 minutes. 20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes. 30 gms of oxalic acid was added to the reaction mixture over a period of 15 minutes. The temperature of the reaction mixture was noted to be 104°C. The stirring was continued for another 2 hrs after the complete addition of the organic ligand. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.8. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with a contact time of 54 sec. The resulting chromium-iron complex powder was stored in a plastic container. This product was used for tanning pickled goat skins at an offer of 3% on pelt weight and resulted leathers were found to have a shrinkaae temoerature of 110°C, exhibiting an exhaustion of 93 and 96% for iron and chromium, respectively. The tanned leathers were subsequently and were treated with 4% ammonium thiocyanate as an external colouring aid in the post tanning wet bath. The resultant leathers were of dark brown colour. The advantages of the present invention are the following 1. The chromium-iron complex of the present invention exhibits good solubility in water and is a potential self tanning agent 2. The process of the present invention provides a simple process to prepare a matrix of Chromium and iron with additional complexing through organic ligands, thereby ensuring that the leathers manufactured by using this product do not darken/deteriorate on ageing. 3. Fuller leathers with no drawn grain appearance are produced by using the complex as a self tanning agent. 4. The product exhibits around 90-95% exhaustion of both chromium and iron and produces leathers with shrinkage temperature above 105°C. 5. Shelf life of the product is about 15-24 months. 6. Various shades can be produced on the leathers tanned by the chromium-iron complex of the present invention, when the tanned leathers produced thereby are treated with non-dye external aids including eco-friendly vegetable tanning materials during the post tanning operations, thereby achieving dyeing leathers without using conventional dyes. 7. Unlike the conventional iron tanned or other iron combination tanned leathers, those produced by using the tanning .salt of the present invention exhibit smoother surface. We claim : 1. A process for the preparation of a novel chromium-iron complex for use in leather industry, which compcisep vi) mixing a salt of iron with that of hexavalent chromium in water, vii) treating the reaction mixture, as formed in step (i), with sulphuric acid, viii) adding reducing agent such as herein described and organic ligand to the reaction mixture as formed in step(ii), either simultaneously or in succession, in one or more installments, maintaining the temperature in the range of 85 to 105°C, ix) ageing the reaction mixture, as formed in step (iii), for 8-12 hrs, pH is maintained at 2.5 to 2.8, x) subjecting the resulting suspension,as formed in step (iv), to separation process by known method followed by conventional drying of the final liquor to form the chromium-iron complex. 2. A process, as claimed in claim 1, wherein the salt of hexavalent chromium used is sodium dichromate, potassium dichromate, ammonium dichromate. 3. A process, as claimed in claims 1 & 2, wherein the iron salt used is ferrous sulphate, ferrous ammonium sulphate, ferric sulphate. 4. A process, as claimed in claims 1 to 3, wherein the amount of iron salt used is 0.1 - 2.0 moles of iron per mole of chromium. 5. A process, as claimed in claims 1 to 4, wherein the amount of water added to the reaction mixture is 15-30 moles of water per mole of chromium. 6. A process, as claimed in claims 1 to 5, wherein the amount of sulphuric acid used is 1.3 -1.5 moles per mole of chromium. 7. A process, as claimed in claims 1 to 6, wherein the reducing agent used is molasses, glucose, sodium sulphite, sodium bisulphite, either individually or in combination. 8. A process, as claimed in claim 1 to 7, where in the amount of reducing agent is in the range of 0.1 -0.2 moles per mole of chromium. 9. A process, as claimed in claims 1 to 8, wherein the organic ligand used is citric acid, phthalic acid, tartaric acid, oxalic acid, lactic acid, any alkali metal salt of these acids, either individually or in combination. 10. A process, as claimed in claims 1 to 9, wherein the amount of organic ligand used is 0.1 - 1.0 mole per mole of chromium. 11. A process, as claimed in claims 1 to 10, wherein the pH of the slurry after ageing is in the range of 2.5-2.8. 12. A process, as claimed in claims 1 to 12, wherein the process of separation of the suspension may be filtration, gravity precipitation, centrifugation. 13. A process, as claimed in claims 1 to 12, wherein the process for drying of the final liquor may be drum drying, spray drying, air drying effected at 130- 260°C over a period of 3-60 seconds. 14. A process for the preparation of a novel chromium-iron complex for use in leather industry, substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for the preparation of a novel chromium-iron complex for use in Leather industry. It has potential use predominantly as a self-tanning agent for hides and skins. The complex may also be used as a natural aid for developing various shades by adding external aids other than dyes during post tanning operations on leathers tanned with this complex.
Conventional chrome tanning practices give rise to an uptake of only 50-60% of chromium offered. The poor uptake of chromium in tanning has resulted in wide scale ecological concerns and economic loss. As reported by Chandrasekaran {Leather Science, 34, 91, 1987) several methods have been evolved over the
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years for better management of chromium in leather industry. Among the several options considered, the chrome saver approach and the development of mineral alternatives to chromium have been gaining momentum.
Many products based on metal ions like aluminium, titanium, zirconium and iron have been reported in the past by Covington (Chemical Society Reviews,26, 73, 1997), to have tanning potency. But these products lack the ability to withstand pH conditions above 5.5, as described by Heidemann (Fundamentals of Leather Manufacture, Eduard Roether KG publications 1st edition, Chapter 11, 1993). Though several efforts have been taken to overcome these drawbacks, universal
availability and high cost have forced researchers to look for other alternatives as well.
As reported by Percy et al (The Analyst, 123, 41, 1998), the subject of iron tanning has been of great academic interest in view of the existence of iron-protein combinations in nature and the ease with which iron forms complex ions. Knapp (Journal of American Leather Chemists Association, 16, 658, 1921) obtained a number of patents covering iron tanning, but all his attempts to manufacture iron-tanned leather failed because the resulting feather was not only brittle and thin but also found to deteriorate with ageing. When used as a tanning agent iron has a tendency to hydrolyze and precipitate as hydrated oxide or as a highly basic salt. Casaburi (Journal of Society of International Leather Trades
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and Chemists, 3, 61, 1919) postulated that the poor results obtained in iron tannage were due to incomplete removal of uncombined ferric salts from the leather. Further iron tanned leathers have been reported to darken on ageing. Thorstensen and Theis (Journal of American Leather Chemists Association, 44(12), 841, 1942) reported that the addition of masking salts to an iron tannage reduced the hydrolysis of iron salt. Ruppenthal and Malik (Journal of American ^Leather Technologists and Chemists, 38, 148, 1943) have reported that a combination of chromium and iron tannage could be advantageous for obtaining leathers of good shrinkage temperature. They found that an iron pretannage followed by chrome tanning leaves very little iron in the effluent while a chrome
pretannage followed by iron tanning leaves very little chromium in the effluent. This could be due to the fact that both iron and chromium follow the same tanning mechanism, and when separately offered for tanning, one hinders the fixation of the other.
Recently Platon et al (Proceedings of the International Union of Leather Technologists and Chemists Society Congress, 405, 1993) have reported the development of heterocomplexes of chromium and iron with glucose as the reducing agent. As reported by Thorstensen and Theis (Journal of American Leather Chemists Association, 44(12), 841, 1942), mineral tanning agents containing iron without masking agents are known to deteriorate the leather on ageing. Thus the limitation of these complexes is that they are not stable against hydrolysis. Moreover, the absence of organic ligands leads to the offer of 2.2% metal oxide for tanning to produce leather of shrinkage temperature of maximum of 107°C. Under such conditions the amount of chromium in the effluent (as chromium) has been found to be 875 ppm. This high discharge of chromium in the environment certainly generates great ecological concerns.
Dyeing improves the aesthetic value of leather. The increasing awareness of harmful effects of the conventional dyes has brought in a need for ecofriendly dyes throughout the world. The ban on arylamine based dyes has also motivated the leather dyers to look for better options, which include the use natural dyes.
Although natural stuff like Log-wood, Fustic and hypernic have in the past been used in dyeing of leather, yet they are not free from certain limitations like limited availability as well as limited potential variation of shade. Thorstensen (Practical Leather Technology, Krieger publishing company, 4h edition, Florida, 1993). reported that in the presence of iron salts, the condensed tannins produce greenish black colour, while the hydrolysable tannins produce blue-violet colour.
The main objective of the present invention is to provide a process for the preparation of a novel chromium-iron complex for use in feather industry, which obviates the drawbacks stated above.
Another objective of the present invention is to prepare a mineral tanning agent having an active ingredient capable of giving near zero wastage of metal salt.
Yet another objective of the present invention is to exploit the ability of chromium and iron to form mixed oxo complexes in the presence of organic ligands which when used would resist darkening/deterioration of leather on ageing.
Still another objective of the present invention is to develop a tanning salt which when used in tanning gives an exhaustion of more than 90% of the metal salts employed.
Yet another objective of the present invention is to develop a tanning salt which can be used to produce leathers of various shades by treating with eco-friendly natural stuff other than dyes.
Accordingly the present invention provides a process for the preparation of a novel chromium-iron complex for use in leather industry, which comprises
i) mixing a salt of iron with that of hexavalent chromium in water,
ii) treating the reaction mixture, as formed in step (i), with sulphuric acid,
iii) adding reducing agent such as herein described and organic ligand to the reaction mixture as formed in step(ii), either simultaneously or in succession, in one or more installments, maintaining the temperature in the range of 85 to 105°C,
iv) ageing the reaction mixture, as formed in step (iii), for 8-12 hrs, pH is maintained at 2.5 to 2.8,
v) subjecting the resulting suspension,as formed in step (iv), to separation process by known method followed by conventional drying of the final liquor to form the chromium-iron complex.
In an embodiment of the present invention, the salt of hexavalent chromium used may be sodium dichromate, potassium dichromate, ammonium dichromate.
In another embodiment of the present invention, the iron salt used may be such as ferrous sulphate, ferrous ammonium sulphate, ferric s.ulphate.
In yet another embodiment of the present invention, the amount of iron salt used may be such as 0.1 - 2.0 moles of iron per mole of chromium.
In still another embodiment of the present invention, the amount of water added to the reaction mixture may be such as 15-30 moles of water per mole of chromium.
In yet another embodiment of the present invention, the amount of sulphuric acid used may be such as 1.3 -1.5 moles per mole of chromium.
In yet another embodiment of the present invention, the reducing agent used may be such as molasses, glucose, sodium sulphite, sodium bisulphite, either individually or in combination.
In still another embodiment of the present invention, the amount of reducing agent may be in the range of 0.1 -0.2 moles per mole of chromium.
In yet another embodiment of the present invention, the organic ligand used may be such as citric acid, phthalic acid, tartaric acid, oxalic acid, lactic acid, any alkali metal salt of these acids, either individually or in combination.
In still another embodiment of -the present invention, the amount of organic ligand used may be 0.1 -1.0 mole per mole of chromium.
In yet another embodiment of the present invention, the temperature of the reaction mixture to be maintained, while adding the reducing agent and the organic ligands may be in the range of 85-105°C.
In still another embodiment of the present invention, the pH of the slurry after ageing may be in the range of 2.5-2.8.
In yet another embodiment of the present invention, the process of separation of the suspension may be such as filtration, gravity precipitation, centrifugajion.
In still another embodiment of the present invention, the process for drying of the final liquor may be such as drum drying, spray drying, air drying effected at 130-260°C over a period of 3-60 seconds.
Accordingly the present invention provides a novel chromium-iron complex prepared by the process described above.
0.1 - 2.0 moles of a salt of iron per mole of chromium is mixed with that of hexavalent chromium and 15-30 moles of water per mole of chromium is added to the reaction mixture with continuous stirring. Sulphuric acid calculated as 1.3-1.5 moles per mole of chromium is then added to the reaction mixture while continuing the stirring. 0.1-0.2 mole of a reducing agent per mole of chromium and 0.1-1.0 mole of organic ligand per mole of chromium are added to the above reaction mixture either simultaneously or in
different successions, in one or more installments, with continuous stirring over a period of minimum 1 hr. Stirring is continued for minimum 1hr even after the complete addition of the above agents. The resultant mixture is then allowed to settle. After a period of 8-12 hrs, pH of the resulting suspension is checked to be in the range of 2.5-2.8. This suspension is then subjected to separation process by known method followed by conventional drying of the final liquor, obtained thereby, for 3-60 sec at a temperature in the range of 130-260°C to get the chromium-iron complex powder.
The novelty of the present invention lies in selecting the starting materials and in providing a process to prepare a chrome-iron matrix in the form of an oxo bridged complex with additional complexing provided by organic ligands, thereby ensuring, unlike conventional iron based tanning agents, absence of any darkening/deterioration of the leathers on ageing, and facilitating higher uptake of both chromium and iron resulting not only in the reduction of pollution problem but also in raising the shrinkage temperature of leather above 105°C, with an additional option of developing various shades for leathers on treatment with non-dye external aids including eco-friendly vegetable tanning materials.
The invention is described in detail in the following examples, which are provided by way of illustration only and therefore should not be construed to limit the scope of the present invention.
Example I
141.4 gms of ferrous sulphate was stirred with 303,gms of sodium dichromate in a flask fitted with a stirrer. 550 ml of water was added to the above mass with continuous stirring. 153 ml of 98% sulphuric acid was added slowly to the above reaction mixture.
41 gms of molasses was added to 41 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period, of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 95°C.
A mixture of 10 gms of tartaric acid and 11.1 gms of phthalic acid was added to this reaction mixture over a period of 10 minutes. 50 gms of molasses was added to 50 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes.
A mixture of 9 gms of tartaric acid and 10 gms of phthalic acid was added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 105°C. The stirring was continued for another 2 hrs after the complete addition of the organic ligands. A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium (VI) could be detected.
The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be
2.7. This mixture was then filtered through a cloth and the filtrate was spray dried at a temperature of 260°C with contact time of 3 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 5.5% on pelt weight and the resultant leathers were found to have a shrinkage temperature of 120°C, exhibiting an exhaustion of 91 and 90% for iron and chromium respectively.
The tanned leathers were subsequently treated with 2% Babool extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of pale grayish colour.
Example II
565.5 gms of ferrous sulphate was stirred with 303 gms of sodium dichromate in a flask fitted with a stirrer. 600 ml of water was added to the above mass with continuous stirring. 153 ml of 98% sulphuric acid was added slowly to the above reaction mixture.
41 gms of molasses was added to 41 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over
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a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 85°C.
A mixture of 59 gms of sodium tartarate and 44.4 gms of phthalic acid was added to the reaction mixture over a period of 10 minutes.
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50 gms of molasses was added to 50 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes.
A mixture of 58 gms of sodium tartarate and 40 gms of phthalic acid was added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 100°C. The stirring was continued for another 2 hrs after the complete addition of the organic ligands.
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 10 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be 2.6. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with contact time of 60 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning the pickled goat skins at an offer of 3.5% on pelt weight and the resultant leathers were found to have a shrinkage temperature of 108°C, exhibiting an exhaustion of 92 and 94% for iron and chromium respectively.
The tanned leathers were subsequently treated with 3% Myrobalan extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of intense black colour.
Example III
417 gms of ferrous sulphate was stirred with 147.1 gms of potassium dichromate in a flask fitted with a stirrer. 480 ml of water was added to the above mass with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture.
43.2 gms of molasses was added to 44 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 60 minutes with continuous stirring. Simultaneously, a mixture of 63 gms of oxalic acid and 115 gms of sodium tartarate was added to the reaction mixture over a period of 20 minutes. The temperature of the reaction mixture was noted to be 102°C.
The stirring was continued for another 2 hrs after the complete addition of organic ligands.
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be
2.2. 10 gms of sodium carbonate was added to the mixture over a period of 15 min and the stirring was continued for 30 min. The pH was found to be 2.5.
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The resulting mixture was then filtered through a cloth and the filtrate was spray dried at 260°C with contact time of 4 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 5% on pelt weight and resulting leathers were found to have a shrinkage temperature of 109°C, exhibiting an exhaustion of 90 and 94% for iron and chromium respectively.
The tanned leathers were subsequently treated with 4% wattle extract as an
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external colouring aid in the post tanning wet bath. The resultant leathers were of light grey colour.
Example IV
556 gms of ferrous sulphate was stirred with 126 gms of ammonium dichromate in a flask fitted with a stirrer. 520 ml of water was added to the above mass with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture.
24 gms of molasses was added to 24 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over
a period of 20 minutes with continuous stirring. Simultaneously, a mixture of 74 gms of citric acid and 16.5 gms of oxalic acid was added to the reaction mixture over a period of 10 minutes. The temperature of the reaction mixture was noted to be 88°C.
20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 20 minutes. Simultaneously, 70 gms of citric acid and 15 gms of oxalic acid were then added to the above mass over a period of 10 minutes. The temperature of the
reaction mixture was noted to be 100°C.The stirring was continued for
another 1 hr after complete addition. Then 3 gms of sodium sulphite was
added to the mixture and the stirring was continued for another 45 minutes.'
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 8 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and was found to be 2.0. 13 gms of sodium carbonate was then added to the mixture over a period of 20 minutes with continuous stirring. The stirring was continued for another 30 minutes and the pH was found to be 2.6. The resulting mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with contact time of 50 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 7% on pelt weight and the resulted leathers were found to have a shrinkage temperature of 107°C, exhibiting an exhaustion of 92 and 94% for iron and chromium, respectively.
The tanned leathers were subsequently treated with 2% Myrobalan extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of black colour.
Example V
392.16 gms of ferrous ammonium sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture.
30 gms of glucose was added to 30 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 60 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 98°C.
75 gms of tartaric acid was added to the reaction mixture over a period of 20 minutes. 5 gms of sodium bisulphite was added over a period of 5 minutes. The temperature of the reaction mixture was noted to be 103°C.
The reaction mixture was stirred continuously for 2 hrs after complete addition.

A 10% solution of the above mass was subjected to diphenyl carbazide test, whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.8. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with contact time of 55 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 4.5% on skin weight and resulted leathers were found to have a shrinkage temperature of 112°C, exhibiting an exhaustion of 91 and 95% for iron and chromium respectively.
The tanned leathers were subsequently treated with 3% quebracho extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of slightly dark grey colour.
Example VI
200 gms of ferric sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 360,ml of water was added to the above mass with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture.
24 gms of molasses was added to 24 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 90°C.
A mixture of 8 gms of tartaric acid, 8 gms of phthalic acid and 4 gms of lactic acid was added to the reaction mixture over a period of 15 minutes. 20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes.
A mixture of 7 gms of tartaric acid, 8.6 gms of phthalic acid and 5 gms of lactic acid was added to the above mass over a period of 15 minutes. The temperature of the reaction mixture was noted to be 101°C. The srirring was continued for another 2 hrs after the complete addition of organic ligands.
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 9 hrs. The pH of the 1:1 aqueous solution of the above mixture was checked and found to be 2.6. The resulting mixture was then filtered through a cloth and the filtrate was spray dried at 260°C with contact time of 3 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 6% on pelt weight and resulted leathers was found to have a shrinkage temperature
of 117°C, exhibiting an exhaustion of 92 and 94% for iron and chromium, respectively.
The tanned leathers were subsequently treated with 3% chestnut extract as an external colouring aid in the post tanning wet bath. The resultant leathers were of dark black colour.
Example VII
278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 300 ml of water was added to the above mass with continuous stirring. 75 ml of98% sulphuric acid was added slowly to the above reaction mixture.
24 gms of molasses was added to 24 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 93°C.
A mixture 20 gms of tartaric acid and 24 gms of citric acid was added to the reaction mixture over a period of 15 minutes.
20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes.
A mixture of 17.5 gms of tartaric acid and 24 gms of citric acid were added to the above mass over a period of 10 minutes. The temperature of the reaction
mixture was noted to be 103°C. The stirring was continued for another 90 minutes after complete addition of organic ligands.
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected. The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.7. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with a contact time of 60 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 5% on
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pelt weight and resulted leathers with a shrinkage temperature of 114°C,' exhibiting an exhaustion of 93 and 96% for iron and chromium respectively.
The tanned leathers were subsequently treated with 2% potassium ferrocyanide as an external colouring aid in the post tanning wet bath. The resultant leathers were of Prussian blue colour.
Example VIII
278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate
in a flask fitted with a stirrer. 270 ml of water was added to the above mass

,' with continuous stirring. 75 ml of 98% sulphuric acid was added slowly to the
above reaction mixture.
15 gms of glucose was added to 20 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 90°C.
A mixture of 40 gms of phthalic acid and 20 gms of lactic acid was added to the reaction mixture over a period of 10 minutes. 15 gms of glucose was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes.
A mixture of 43 gms of phthalic-acid and 25 gms of lactic acid was added to the above mass over a period of 10 minutes. The temperature of the reaction mixture was noted to be 99°C. The stirring was continued for another 2 hrs after complete addition of the organic ligands.
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was checked and found to be 2.6. The resulting mixture was then filtered through a cloth and the filtrate was spray
dried at a temperature of 260°C with a contact time of 3 sec. The resulting
.-chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 3.5% on pelt weight and resulted leathers were found to have a shrinkage temperature
of 108°C, exhibiting an exhaustion of 93 and 95% for iron and chromium, respectively.
The tanned leathers were subsequently treated with 2% sodium thiocyanate as an external colouring aid in the post tanning wet bath. The resultant leathers were of yellow colour.
Example IX
278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 75 ml of 98% sulphuric acid was added slowly to the above reaction mixture.
23 gms of molasses was added to 23 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 95°C. 60 gms of sodium tartarate and was added to the reaction mixture over a period of 15 minutes.
20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes.
55 gms of sodium tartarate was added to the above mass over a period of 15 minutes. The temperature of the reaction mixture was noted to be 103°C. The stirring was continued for another 2 hrs after the complete addition of the organic ligand.
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 11 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.8. This mixture was then filtered through a cloth and the filtrate was spray dried at a temperature of 260°C with a contact time of 3 sec. The resulting chromium-iron complex powder was stored in a plastic container.
This product was used for tanning pickled goat skins at an offer of 7.5% on pelt weight and the resulted Jeathers were found to have a shrinkage temperature of 120°C, exhibiting an exhaustion of 90 jnd 91% for iron and chromium, respectively.
The tanned leathers were subsequently were treated with 5% myrobalan extract as an external colouring aid in the post tanning wet bath. The resultant leathers were in dark blue colour.
Example X
278 gms of ferrous sulphate was stirred with 149 gms of sodium dichromate in a flask fitted with a stirrer. 400 ml of water was added to the above mass
with continuous stirring. 75 mf of 98% sulphuric acid was added slowly to the
.above reaction mixture.
23 gms of molasses was added to 23 ml of water taken in a beaker and the mixture was added drop by drop by a dropping funnel to the above mass over a period of 20 minutes with continuous stirring. The temperature of the resulting mixture was noted to be 89°C.
33 gms of oxalic acid was added to the reaction mixture over a period of 10 minutes.
20 gms of molasses was added to 20 ml of water taken in a beaker and the mixture was added to the above mass over a period of 30 minutes.
30 gms of oxalic acid was added to the reaction mixture over a period of 15 minutes. The temperature of the reaction mixture was noted to be 104°C.
The stirring was continued for another 2 hrs after the complete addition of the organic ligand.
A 10% solution of the above mass was subjected to diphenyl carbazide test whereby no chromium(VI) could be detected.
The reaction mixture thus formed was aged for 12 hrs. The pH of the 1:1 aqueous solution of the above mixture was then checked and found to be 2.8. This mixture was then filtered through a cloth and the filtrate was drum dried at 130°C with a contact time of 54 sec. The resulting chromium-iron complex powder was stored in a plastic container.

This product was used for tanning pickled goat skins at an offer of 3% on pelt weight and resulted leathers were found to have a shrinkaae temoerature of 110°C, exhibiting an exhaustion of 93 and 96% for iron and chromium, respectively.
The tanned leathers were subsequently and were treated with 4% ammonium thiocyanate as an external colouring aid in the post tanning wet bath. The resultant leathers were of dark brown colour.
The advantages of the present invention are the following
1. The chromium-iron complex of the present invention exhibits good
solubility in water and is a potential self tanning agent
2. The process of the present invention provides a simple process to
prepare a matrix of Chromium and iron with additional complexing
through organic ligands, thereby ensuring that the leathers
manufactured by using this product do not darken/deteriorate on
ageing.
3. Fuller leathers with no drawn grain appearance are produced by using
the complex as a self tanning agent.
4. The product exhibits around 90-95% exhaustion of both chromium and
iron and produces leathers with shrinkage temperature above 105°C.
5. Shelf life of the product is about 15-24 months.
6. Various shades can be produced on the leathers tanned by the
chromium-iron complex of the present invention, when the tanned
leathers produced thereby are treated with non-dye external aids
including eco-friendly vegetable tanning materials during the post
tanning operations, thereby achieving dyeing leathers without using
conventional dyes.
7. Unlike the conventional iron tanned or other iron combination tanned leathers, those produced by using the tanning .salt of the present invention exhibit smoother surface.

We claim :
1. A process for the preparation of a novel chromium-iron complex for use in
leather industry, which compcisep
vi) mixing a salt of iron with that of hexavalent chromium in water,
vii) treating the reaction mixture, as formed in step (i), with sulphuric acid,
viii) adding reducing agent such as herein described and organic ligand to the reaction mixture as formed in step(ii), either simultaneously or in succession, in one or more installments, maintaining the temperature in the range of 85 to 105°C,
ix) ageing the reaction mixture, as formed in step (iii), for 8-12 hrs, pH is maintained at 2.5 to 2.8,
x) subjecting the resulting suspension,as formed in step (iv), to separation process by known method followed by conventional drying of the final liquor to form the chromium-iron complex.
2. A process, as claimed in claim 1, wherein the salt of hexavalent chromium
used is sodium dichromate, potassium dichromate, ammonium dichromate.
3. A process, as claimed in claims 1 & 2, wherein the iron salt used is ferrous
sulphate, ferrous ammonium sulphate, ferric sulphate.
4. A process, as claimed in claims 1 to 3, wherein the amount of iron salt used
is 0.1 - 2.0 moles of iron per mole of chromium.
5. A process, as claimed in claims 1 to 4, wherein the amount of water added to
the reaction mixture is 15-30 moles of water per mole of chromium.
6. A process, as claimed in claims 1 to 5, wherein the amount of sulphuric acid
used is 1.3 -1.5 moles per mole of chromium.
7. A process, as claimed in claims 1 to 6, wherein the reducing agent used is
molasses, glucose, sodium sulphite, sodium bisulphite, either individually or in
combination.
8. A process, as claimed in claim 1 to 7, where in the amount of reducing agent
is in the range of 0.1 -0.2 moles per mole of chromium.
9. A process, as claimed in claims 1 to 8, wherein the organic ligand used is
citric acid, phthalic acid, tartaric acid, oxalic acid, lactic acid, any alkali metal salt
of these acids, either individually or in combination.

10. A process, as claimed in claims 1 to 9, wherein the amount of organic ligand
used is 0.1 - 1.0 mole per mole of chromium.
11. A process, as claimed in claims 1 to 10, wherein the pH of the slurry after
ageing is in the range of 2.5-2.8.
12. A process, as claimed in claims 1 to 12, wherein the process of separation of
the suspension may be filtration, gravity precipitation, centrifugation.
13. A process, as claimed in claims 1 to 12, wherein the process for drying of
the final liquor may be drum drying, spray drying, air drying effected at 130-
260°C over a period of 3-60 seconds.
14. A process for the preparation of a novel chromium-iron complex for use in leather industry, substantially as herein described with reference to the examples.

Documents:

446-del-1999-abstract.pdf

446-del-1999-claims.pdf

446-del-1999-correspondence-others.pdf

446-del-1999-correspondence-po.pdf

446-del-1999-description (complete).pdf

446-del-1999-form-1.pdf

446-del-1999-form-19.pdf

446-del-1999-form-2.pdf

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Patent Number

216560

Indian Patent Application Number

446/DEL/1999

PG Journal Number

13/2008

Publication Date

28-Mar-2008

Grant Date

14-Mar-2008

Date of Filing

19-Mar-1999

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001,INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	JONNALAGADDA RAGHAVA RAO	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020,INDIA
2	KALARICAL JANARDHANAN SREERAM	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020,INDIA
3	PALANISAMY THANIKAIVELAN	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020,INDIA
4	BALACHANDRAN UNNI NAIR	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020,INDIA
5	THIRUMALACHARI RAMASAMI	CENTRAL LEATHER RESEARCH INSTITUTE, ADYAR, CHENNAI-600 020,INDIA

PCT International Classification Number

C22C 37/06

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA