Closed-loop and chromium-free leather for the circular economy through refining sustainably available plant food waste

Currently, 80% (1700 km2) of global leather manufacture is tanned with chromium (III) salts, which are not renewable and problematic to recover at end-of-life (Covington 2007). Commercial vegetable tanning agents are extracted from cultivated stocks, which are insufficient to replace the current consumption of chromium (III) salts. Further expansion of existing plantations is not a sustainable method to generate sufficient tannin extracts to meet current demands. Therefore, alternative bio-based waste sources are required to effectively reuse resources and reduce the need for new fossil-based inputs and reduce the environmental footprint of leather manufacture. Literature supports the presence of tannins in coffee waste. Low et al (2015) and Bhoite et al (2013) confirm the presence of both condensed and hydrolysable tannins with C13 NMR and MS data. This observation can be extended to many waste streams in the food and beverage sector. Underpinning tanning application has been demonstrated through trials by Baskar at ICLT, which shows the extracted coffee waste replaces conventional veg tannins which includes both tanning and retanning stages. Typical concentrations of tannins required to fully tan are more than 30% of the hide weight, therefore, the use of waste sources has the potential to replace a significant quantity of leather processing chemicals. Currently at TRL 3, the project aim is to develop a scalable leather manufacturing process with tannins extracted from food and beverage wastes thus replacing Cr and plantation crop tanning agents.