Free of salt high-pressure deliming of animal hides
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RESEARCH ARTICLE
Free of salt high-pressure deliming of animal hides Michael Prokein 1 & Adrian Chrobot 1 & Manfred Renner 1 & Eckhard Weidner 1,2 Received: 3 April 2020 / Accepted: 15 June 2020 # The Author(s) 2020
Abstract The wastewater pollution of tanneries is of high concern. The investigation of technologies to minimize the consumption of chemicals in the leather production process can reduce the environmental burden. We focus on the reduction of ammonium salts in the leather production process. Salt-free deliming of animal hides with compressed carbon dioxide as deliming agent is performed for the first time in a technical scale 20-L drum. As a result, CO2-deliming at 30 bar and 30 °C is two times faster than conventional deliming. In addition, the deliming efficiency is slightly improved. The initial calcium (Ca) content of the hides of 8 g/kg reaches the lowest value of 2 g/kg after a process time of 3 h. However, a process time of 60 min is sufficient to reach an elimination of 50 wt% of the initial lime. The resulting Ca-content of 4 g/kg after 60 min CO2-deliming at 30 bar is comparable with the Ca-content of conventional delimed hide. We clarify that the ampholytic character of the collagen itself enables a buffering of the pH-value at pH-7. The stable pH-value supports the selection of specific bating enzymes that decompose noncollagen proteins. No buffering salts contaminate the wastewater. The high-pressure CO2-deliming process has high potential to reduce wastewater emissions, save costs for chemicals, and process time in industrial beamhouse applications. Keywords High-pressure . CO2 . Leather . Deliming . Ammonium nitrogen emissions
Introduction The production from raw animal hide to leather goods consists of 4 main categories: beamhouse, tanning, wet end, finishing. Each category includes a variety of working steps consuming high amounts of water and process chemicals (Joseph and Nithya 2009). In the beamhouse, raw hide is prepared for the tanning process by soaking, liming, unhairing, deliming, bating, and pickling. During the preparation, hairs are removed and the hide is modified in chemical containing aqueous solutions, called floats. All chemicals used in the beamhouse are lost with the wastewater (Buljan et al. 2000, Black et al. 2013). As a result, beamhouse processing causes environmental challenges in developing countries and/or enormous costs in Responsible Editor: Philippe Garrigues
modern tanneries. According to estimations, the costs of environmental protection measures in European tanneries account for 4.3% of their turnover while their profit margin is just about 5% (Cotance 2012). The use of dense carbon dioxide promises a high potential to reduce the environmental burden caused by the leather production process as already reviewed and highlighted by several authors (Sathish et al. 2016; Hu and Deng 2016; Renner et al. 2009; Renner et al. 2012). Recently, we demonstrated a CO2-intensified low-emission tanning process to produce high-quality leather in a 1700-L drum at 30 bar
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