Leather Chemicals: With a Difference
First in the World of Mineral Syntans
Secure Chrome Management
- Two mineral synthetic tanning agents (syntans) with no international equivalents were designed, developed
- Alcrotan is an innovative light fast Cr – Al syntan. This product ensures uptake of more than 90% of chromium and aluminium
- Alutan is an aluminium based syntan with irreversible binding of aluminium(III), which affords fuller leathers making suede processing easy with color richness
- Marketed as Balsyn ACE and Balsyn AL with a turn over of 7 crores per annum
- Alutan in combination with BCS makes zero waste tanning a reality
Clarichrome and Claritan AL
- A high exhaust chrome tanning salt through designed alterations in the manufacture of BCS has been developed and commercialized
- Marketed by M/s. Golden Chemicals Ltd., the product offers above 85% exhaustion of chromium
- Enables a saving in 20 – 25% of post-tanning chemicals
- A chrome based tanning agent Clarichrome developed
- The product exhibits higher chrome uptake and also ensures reduction in wet finishing chemicals
- An aluminium based product Cleartan AL developed for white leathers
- The product resists precipitation up to pH 5.5-6.0 and enables dyeing of leathers to rich shades and has been commercialized to M/s Quinn Group of Companies
|Chrome Syntans with a Difference
- An Organo–Chromium complex wherein the polymeric backbone is built up without using formaldehyde
- A homogeneous chemical formulation with 16– 18% Cr2O3, and withstands precipitation to pH 5.5 – 6.0
- Product formulated for use in pickle free tanning, thereby reducing the total dissolved solids (TDS) load by 50–60% and chlorides load by 98 -99% from the identified stream
- Leathers are fuller, softer with smoother grain and meet the BIS norms
- The increase in product cost (~20%) is offset by the reduction in wet finishing chemicals with added environmental benefits
- Technology transferred to M/s. Balmer Lawrie & Co.
- Zirconium based white syntan for irreversible binding to the collagen matrix
- The product has a metal oxide content of 20±2% and withstands precipitation to pH 6
- The product can be used as both self-tanning agent and also in combination with chromium
- It finds use as a chrome saver and gives fuller leathers with no drawn grain
- The leathers can be dyed to rich shades readily
Silica Based Syntans
- A self tanning agent containing chromium and silica in suitable ligand environment
- Offers above 105oC shrinkage temperature at 1.0% metal oxide
- The tanned leathers have excellent softness, suppleness, stretch, fluffy and smooth grain
- Obviates the negative characteristics associated with both chromium and silica tannage
- The product has additional advantage of reducing the offer of fatliquors
- It is possible to obtain sheep like character from a goatskin upon tanning with this tanning agent
Products from Wastes
|Natural Shades from Iron Syntans
- A novel chromium-iron based self tanning agent with 27% metal oxide (Cr2O3 and Fe2O3) developed
- Product withstands precipitation up to pH 6.5 and offers shrinkage temperature of 115oC
- Exhibits exhaustion level of more than 90% for both the metals
- Enables development of rich shades (black to brown) when treated with tannins
- Evades the usage of expensive and polluting dyestuffs
Products & Processes Developed (2000-2009)
- Chrome shaving contributes to 9–10% of the raw material processing and accounts for 0.8 million tons of waste globally
- Current usage is only in the area of leather boards, building materials and hydrolyzed products
- Stringent regulations call for safe disposal of chrome bearing solid wastes
- Chrome shavings have been used as reductant in BCS manufacture in the place of molasses and sulfurdioxide
- The product has 18–20% Cr2O3 content and exhibits high uptake of chromium
- This methodology provides a green route to the utilization of chrome shavings
- Semi-continuous chrome recovery system - A semicontinuous chrome recovery system based on sodium carbonate has been developed for large volumes of chromium based wastewaters with varying concentrations of chromium. The method has been commercialized.
- Minimum waste chrome tanning method - Chrome management system based on the high exhaust chrome tanning followed by pickle-tan closed loop has been developed and implemented in 12 commercial tanneries all over the country. It has been demonstrated that this methodology provides a saving of Rs 2000/- per ton of raw material processed.
- Utilization of chrome shavings for BCS manufacture - Chrome shavings have been used as reductant in BCS manufacture in the place of molasses and sulfurdioxide. The product has 18–20% Cr2O3 content and exhibits high uptake of chromium.This methodology provides a green route to the utilization of chrome shavings, which accounts for 0.8 million tons of waste globally.
- Recovery of chromium from vegetable-chrome composite waste solution – An approach for the recovery of chromium from spent semi-chrome solutions has been developed. The vegetable tannins have been removed prior to chromium through either oxidative or reductive approaches followed by precipitation. The treated semi-chrome liquor, after the removal of vegetable tannins rendered the chromium recovery process more feasible.
- Pickle-less chrome tanning – Pickle-less chrome tanning has been developed through optimization of the pH and the amount of masking agents required for tanning the cowhides using commercially available basic chromium sulfate without pickling. It has been observed that the penetration and distribution of chromium is much better for pH 5.0 as compared to other systems.
- Narrow pH leather processing –An attempt has been made to develop a method for processing leathers in a narrow range of pH viz., 4.0-8.0. A process for dehairing at a pH around 8.0 using commercial formulation enzyme with grain side application has been explored. The process enjoys an environmental benefit due to significant reduction of COD load in the effluent.
- Chromium-silica tanning agent, Silchrome - A self tanning agent containing chromium and silica in suitable ligand environment, which offers above 105oC shrinkage temperature at 1.0% metal oxide has been demonstrated. The tanned leathers have excellent softness, suppleness, stretch, fluffy and smooth grain. It is possible to obtain sheep like character from a goatskin upon tanning with this tanning agent
- Chrome- Iron tanning agent, Spectratan FE - A new chrome-iron tanning agent as a chrome saver has been developed. The negative attributes associated with iron tanning such as deterioration of strength and darkening of color on ageing are negated with this product. It is possible to evade the usage of expensive and polluting dyestuffs. Variety of shades have been developed by treating with vegetable tanning materials.
- Chromite ore processing method - The method relates to a process for simultaneous recovery of chromium and iron from Chromite Ore Processing Residue (COPR) and more particularly, relates to an economical and environment-friendly process for recovering chromium as a chromate salt and iron as an iron salt from non-leachable Chromite Ore Processing Residue and avoids landfilling of toxic metals.
- Organo-aluminium complex for self tanning, Alsyn - A formaldehyde free aluminium syntan as an alternative to chromium has been developed. It is an organo-aluminium complex wherein the polymeric backbone is built up without using formaldehyde with 10-12% Al2O3 content. The product withstands precipitation up to pH 5.5-7.0. The product can be directly used after deliming without a pickling process. Thus this integrated tanning process completely avoids pickling thereby reducing the total dissolved solids load apart from eliminating the chrome pollution.
- Three step leather processing - The approach involves, removal of hair and flesh as well as fibre opening using biocatalysts and sodium hydroxide at pH 8.5 for cow hides. This is followed by a pickle free chrome tanning, which does not require a basification step. Hence, this tanning technique involves primarily three steps namely dehairing, fibre opening and tanning leading to near zero waste tanning method.
- Utilization of seaweeds for the removal of chromium - The removal of chromium from tannery effluent has been carried out using two abundantly available brown seaweeds namely; Sargassum wightii and Turbinaria spp. The Sargassum and Turbinaria species exhibited a maximum uptake of 35 and 31mg of chromium per gram of seaweeds respectively. The chromium-loaded seaweed was advantageously used as a reductant for the manufacture of basic chromium sulfate thus providing a holistic solution.
- Ecofriendly bioprocess for leather processing – This process is basically an enzyme only dehairing and fibre opening without the use of lime and sulphide. The methodology enables significant reduction in the pollution load of the beamhouse operations and also the lime sludge. The reduction in process time and usage of chemicals are other salient features of this process. In addition, another unit operation used in conventional leather making (deliming) is completely avoided thereby enhancing the productivity.
- Solid wastes for the treatment of liquid pollutants - Fleshing from animal hides/skins is one such waste that is high in protein content. Raw fleshing complexed with iron has been used for removal of chromium(VI). The adsorption capacity of iron treated fleshing is 51 mg of chromium(VI) per gram of fleshing.
- Integrated wet finishing process - A compact wet finishing process has been developed for making both upper and garment leathers. The process provides leathers having comparable or even better physical and bulk properties to that derived from conventional wet finishing process. Importantly, the water consumption is reduced by 73% for processing 1 metric ton of wet blue shaved leathers, which is one of the pioneering achievements.
- Silica enhanced enzymatic dehairing - A lime and sulfide-free dehairing process using a commercial enzyme formulation with the activation of a silicate salt has been developed. Enhancement of enzyme activity by the addition of silicate has been demonstrated through activity measurements. Hair removal is found to be complete and experimental leathers are comparable to that of control leathers. The process also enjoys a significant reduction in pollution load and techno-economic feasibility.
- Transposed process for making leather – This methodology involves reversing the leather process sequence from its conventional processing. This avoids several basification and neutralization steps thereby reducing the TDS load in the wastewaters. The reductions in water usage and process time are the other salient benefits. The methodology provides a means for the distribution of chemicals thereby the quality of the final leathers are slightly better.
- Novel bio- tanning agent, Biotan – A bio-tanning agent from collagenous material obtained from the chrome shavings has been developed as an ecobenign tanning agent.
- Pickleless tanning through product and process innovation - A polymeric syntan, which can enable pickle-free chrome tanning using commercial basic chromium sulphate, has been developed. The novel product-process helps to reduce the chemical oxygen demand (COD), total dissolved solids (TDS) and chlorides in the spent tan liquor. Further, the product offers full, soft leathers having a shrinkage temperature comparable to that of conventional chrome tanned leathers. This integrated process provides reduction in chemicals, water, time and power consumption.
- Rare earth based colorants for surface coating applications – A new class of environmentally benign brown rare earth colorants as alternatives to toxic inorganic colorants has been developed. These colorants are based on mixed rare earth oxides. The pigment was compatible with various auxiliaries employed in leather finishing and meets the current requirements for pigments like upgrading of finished leather through excellent covering of surface and improved levelness, no overloading of grain, excellent physical properties, ageing resistance and miscibility with water.
- Wet pink leathers- A way for chrome free tanning – An effective combination tanning system based on zirconium and tetrakis (hydroxymethyl) phosphonium sulphate (THPS) has been explored to produce wet-pink leathers. The leather properties and physical strength characteristics are on par with conventional chrome tanned leathers. The analysis of spent tan liquor shows that there is an interaction between zirconium and THPS resulting in the pink colour of leathers.
- Integration of leather processing –A single step chrome tanning cum wet finishing process has been developed for making upper and garment leathers. The process provides leathers having comparable or even better physical and bulk properties to that derived from conventional multi step process. More specifically, water consumption is reduced by half as that of conventional requirement.
- Multifunctional synthetic tanning agent, Protac M – A multifunctional syntan is a product developed from solid wastes and biodegradable natural materials as an alternative to conventional phenol-formaldehyde based products in retanning for upper leathers. The product provides a synergistic effect on the leather as against unifunctional properties offered by conventional phenol–formaldehyde syntans.
- Bio- tanning process –Environmental constraints on the discharge of toxic metal-ions and poor biodegradable vegetable tannins in the wastewater have become serious issue. In this method, the pelts are tanned using eco-benign bio-molecules other than vegetable tannins to reduce the pollution loads. Performance of the leathers is on par with conventionally processed leathers.
- Colors through use of natural materials – An attempt has been made to develop leathers, colored using natural dyes such as Rhine, Rhine M, Indus, Pacific, Caspian, Henna and modified Logwood. Twenty four shades were developed using combination of seven natural colorants by mordanting with three metal ions. Developed colors have potential value in the global leather market in the context of environmentally benign leather processing.
- Three pot approach for the management of both liquid and solid waste - A three pot solution for chromium, tannins and solid wastes by way of a) the selective removal of tannins from semi-chrome wastewaters by an adsorption process, with chrome shaving being employed as adsorbent, b) employing the tannin adsorbed shaving as reducing agents in the preparation of BCS, b) the precipitation of tannin free chrome liquor as chromium hydroxide, followed by redissolution in sulfuric acid to generate BCS has demonstrated.
- Chemo-enzymatic Process - An integrated chemo-enzymatic methodology has been explored, which would minimize or to some extent eradicate the unsafe chemicals involved in the process to provide a clean environment. The sequence involves an enzymatic dehairing, NaOH based fibre opening and a pickle-less chrome tanning. The modified process results in decrease in COD and TS (total solids) loads as compared with control process.
- Wet oxidation process for color removal in wastewater - Catalytic wet hydrogen peroxide oxidation of anionic dyes has been explored. Copper salen complex encapsulated in zeolite framework has been proven as a good heterogeneous catalyst for removal of colour from commercial tannery wastewater.
- Silicate based fibre opening - The dehairing and fiber opening processes has been designed using enzyme and sodium metasilicate. The amount of sodium metasilicate required for fiber opening is standardized through the removal of proteoglycan, increase in weight, and bulk properties of leathers. It has been found that the extent of opening up of fiber bundles is comparable to that of conventionally processed leathers using a 2% sodium metasilicate solution. The presence of silica in the crust leather enhances the bulk properties of the leather.
- Rationalized Leather processing - The rationalized process developed involves a salt-free curing, lime and sulfide-free beam-house process and post-tanning followed by tanning employing a reverse leather-processing technique. The functional performance of the leathers is found to be on par with that of conventionally processed leathers. The rationalized leather process reduces the usage and discharge of chemicals and also enjoys a significant reduction in pollution loads.