Leather manufactures – Processes
Reexamination Certificate
2002-11-19
2004-03-23
Welch, Gary L. (Department: 3765)
Leather manufactures
Processes
C069S022000, C069S024000, C008S09410R
Reexamination Certificate
active
06708531
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel eco-friendly bio-process for leather processing. More particularly, the present invention provides an eco-friendly beam house process for de-hairing of leather using commercially available enzymes that obviates the use of lime and other alkalis. The present invention also provides an alternate process for opening the fibres of leather using commercially available enzymes. The present invention further provides a three-step process for tanning hide or skin in a narrow pH range of from about 7.5 to about 8.5.
BACKGROUND AND PRIOR ART REFERENCES
Conventional leather processing involves a number of unit processes and operations namely soaking, liming (dehairing), reliming (fibre opening), deliming, pickling, chrome/vegetable tanning, rechroming, neutralisation, retanning, dyeing and fatliquoring. Liming-reliming processes are the inevitable steps in leather processing. The main objectives of liming are the removal of hair, flesh and splitting of fibre bundles by chemical and physical means. To achieve these, lime and sodium sulphide are employed along with substantial quantity of water. Various application methods include pit, paddle, drum and painting on flesh side. Generally, liming-reliming process liquors contribute to 50-70% of the total biochemical oxygen demand (BOD) and chemical oxygen demand (COD) load from a tannery wastewater and 15-20% in the case of total solids (TS) load as reported by Aloy et al (Tannery and Pollution, Centre Technique Du Cuir: Lyon, France, 1976). Apart from this, a great deal of solid wastes containing lime sludge, fleshings, and hair are generated. The extensive use of sulphide bears unfavorable consequences on environment and the efficacy of effluent treatment plants as reported by Colleran et al (Antonie van Leeuwenhoek, 67, 29, 1995).
Several lime and sulphide free liming methods have evolved during the past century. Bose and Dhar (Leather Science, 2, 140, 1955; 21, 39, 1974) have reviewed the use of enzymes such as proteolytic, amylolytic, etc from various sources namely animal, mold, bacterial and plant for dehairing hides and skins. However, these methods include the use of lime. Rosenbusch (Das Leder, 16, 237, 1965) has reported the use of chlorine dioxide for dehairing. Morera et al (Journal of the Society of Leather Technologists and Chemists, 81, 70, 1997) have studied the use of hydrogen peroxide in alkaline medium for dehairing by oxidation mechanism. However, the reduction in pollution load especially COD is not significant. Sehgal et al (Journal of the Society of Leather Technologists and Chemists, 80, 91, 1996) have developed a non-enzymatic sulphide free dehairing process using 1% nickel carbonate, 1% sodium hydroxide, 5% lime and kaolin along with water by painting. However, disposal or recovery of nickel compounds poses serious health problems. Schlosser et al (Journal of the Society of Leather Technologists and Chemists, 70, 163, 1986) have reported the use of lacto-bacillus based enzymes at acidic conditions for dehairing. This method leads to the solubilisation of collagen at the experimental conditions. Valeika et al (Journal of the Society of Leather Technologists and Chemists, 81, 65, 1997; 82, 95, 1998) have attempted to replace lime for dehairing using sodium hydroxide and sodium sulphide. They also found that the addition of salts such as sodium chloride, sodium sulphate, sodium formate or sodium hydrogen phosphate influence the extent of hair removal as well as opening up of the dermis structure. Commercial application of these methods is not popular in the global leather sector. However, enzyme-assisted lime-sulphide dehairing is being followed in some parts of the world. Nevertheless, only partial replacement of sulphide has been feasible in such kind of applications. All these methods are applicable for only dehairing of skins/hides in leather processing. The dehaired pelts require fibre opening. Conventionally the fibre opening is obtained by treatment with lime through osmotic swelling. Monshemier et al (U.S. Pat. No. 4,294,087, 1981) have developed a process for dehairing using a mixture of alkali and enzyme at a pH range of 11-13, where hair is recovered and the opening up of fibre bundles is carried out through osmotic swelling. However, this process requires deliming as practised for conventional leather processing.
Liming removes all the interfibrous materials especially proteoglycans and produces a system of fibres and fibrils of collagen which are clean as described by Campbell et al (Journal of American Leather Chemists Association, 68, 96, 1973). This is achieved by the alkali action as well as osmotic pressure built up in the skin matrix. Hence, in principle, it is possible to produce pelt by removing the protein-carbohydrate conjugates through enzyme action. Steven (Biochimica Biophysica Acta, 97, 465, 1965) and Burton et al (Journal of the Society of Leather Technologists and Chemists, 37, 82, 1953) have shown that &agr;-amylase has specific activity on carbohydrate containing proteins such as proteoglycans.
Conventional leather processing involves a number of unit processes and operations. It includes a combination of single and multi-step processes that employs as well as expels various biological, organic and inorganic materials as described by Germann (Science and Technology for Leather into the Next Millennium, Tata McGraw-Hill Publishing Company Ltd., New Delhi, 1999, p. 283). Conventional method of pre-tanning and tanning processes involve 7-8 steps comprising soaking, liming, reliming, deliming, bating, pickling, chrome tanning and basification and discharge enormous amount of pollutants. This accounts for nearly 90% of the total pollution from a tannery as analyzed by Aloy et al (Tannery and Pollution, Centre Technique Du Cuir, Lyon, France, 1976). This includes biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), sulphides, chlorides, sulphates, chromium, etc. This is primarily due to the fact that the conventional leather processing employs ‘do-undo’ process schemes such as swell-deswell (liming-deliming); pickle-depickle (pickling-basification) as described by Bienkewicz (Physical Chemistry of Leather Making, Krieger Publishing, Malabar, Fla., 1983). In other words, conventional methods employed in, leather processing subject the skin/hide to wide variations in pH. Such pH changes demand the usage of acids and alkalis, which leads to the generation of salts. This results in a net increase in COD, TDS, chlorides, sulphates and other minerals in tannery wastewaters as reported by Thanikaivelan et al (Journal of the Society of Leather Technologists and Chemists, 84, 276, 2000). Further, toxic gases like ammonia and hydrogen sulphide are also emitted. Apart from this, a great deal of solid wastes like lime sludge from tannery and chrome sludge from effluent treatment plant are being generated. This happens to be a major stumbling block for many of the tanners around the world due to the stringent environmental regulations.
Attempts have been made to either reduce the pollution or replace the toxic chemicals by revamping the individual processing steps. Conventional liming-reliming process liquors contribute to 50-70% of the total biochemical oxygen demand (BOD) and chemical oxygen demand (COD) load from a tannery wastewater and 15-20% in the case of total solids (TS) load as reported by Aloy et al (Tannery and Pollution, Centre Technique Du Cuir, Lyon, France, 1976). Apart from this, a great deal of solid wastes containing lime sludge, fleshings, and hair are generated. The extensive use of sulphide bears unfavorable consequences on environment and the efficacy of effluent treatment plants as reported by Colleran et al (Antonie van Leeuwenhoek, 67, 29, 1995). Several lime and sulphide free liming methods have evolved during the past century. Bose and Dhar (Leather Science, 2, 140, 1955; 21, 39, 1974) have reviewed the use of enzymes such as proteolytic, amylolytic, etc from various sources n
Nair Balachandran Unni
Ramasami Thirumalachari
Rao Jonnalagadda Raghava
Thanikaivelan Palanisamy
Council of Scientific and Industrial Research
Merchant & Gould P.C.
Welch Gary L.
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