Low-chromium- and low-sulphate emission leather tanning intensified by compressed carbon dioxide

The leather industry transforms raw hides and skins into high-performance leather products. This transformation requires a high usage of chemicals. About 90% of all leather products are tanned by basic chromium sulphate tanning agents. The use of large quantities of tanning agent causes elevated chromium and sulphate concentrations in the wastewater of conventional tanneries. This article focuses on the reduction of tanning agent consumed by the chromium tanning procedure. Compressed carbon dioxide is used to intensify the process. Carbon dioxide-intensified tanning at 60 bar allows the production of high-quality leather by using about 50 wt% less of tanning agent compared to the conventional tanning process. The chromium and sulphate concentrations in the wastewater generated by the tanning process are highly reduced. Results of full skin tanning (bull skin; up to 10 square metre per skin) in a high-pressure reactor with a volume of 1700-L are presented for the first time.