A novel formaldehyde-free synthetic chrome tanning agent for pickle-less chrome tanning: Comparative study on syntan versus modified basic chromium sulfate

An eco-friendly synthetic chrome tanning salt has been prepared through various routes for application at delimed stage viz., conventional preparation using basic chromium sulphate, sulfonated aromatic hydrocarbon, poly carboxylic acid and organic ligands (product 1); in-situ preparation in the manufacture of BCS by introducing the above ingredients excluding pre-made BCS (product 2); in-situ preparation in the manufacture of BCS by introducing the above ingredients excluding pre-made BCS and aromatic hydrocarbon (product 3). A comparative study has been made for their technical aptness, economic viability and environmental friendliness. It has been found that all the products can be used after deliming without the fear of surface deposition. Fullness of the leathers tanned with the products containing aromatic hydrocarbon (AHC) is generally higher than the product without AHC. The scanning electron microscopic (SEM) studies and visual analysis support the above view. ne analysis of the identified process streams show that the TS, Cl- and chromium loads are curtailed by 80, 99 and 94%, respectively. The strength and bulk properties of the crust leathers are similar or improved when the integrated product/process is employed. The techno-economic viability study reveals. that the chemicals, water, time and power requirements for tanning are reduced by nearly 50% for all the products. However, product 3 tanned leathers need adequate filling during post tanning as conventionally processed. Hence, in spite of its low cost criteria, the use of product 3 is disregarded for tanning skins for fullness-based products. Products 1 and 2 enable the reduction of post tanning syntans by 50% thus reducing the cost of leather production considerably. Especially, product 2 offers a profit oriented pickle-less chrome tanning process.