Ultraefficient Tanning Process: Role of Mass Transfer Efficiency and Sorption Kinetics of Cr(III) in Leather Processing

Abstract

This study reports on the diffusion and sorption phenomena of Cr(III) in water, propylene carbonate (PC), and a mixture of PC + water during the leather tanning process. The results presented here are based on the molecular diffusion which is fundamental to mass transport. Understanding the basic mechanism of the associated mass transfer phenomenon and quantitative estimation of the same is critical for the overall processing of leather. The results suggest that the mass transfer efficiency of Cr(III) increases with increasing the proportion of PC in the tanning process, and nearly 100% mass transfer efficiency is achieved when water is completely replaced by PC. Further, it has been observed that PC has no effect on hydrolytic behavior and reactivity of Cr(III) toward leather matrix. The diffusivity of Cr(III) (4.5 × 10–5 cm2/s) in 100% propylene carbonate tanning is nearly 4.5 times faster than the 100% water based system (1 × 10–5 cm2/s). The sorption kinetic study reveals that tanning with 100% PC obeys the pseudo-second-order kinetic and the surface sorption is a rate limiting step in contrast to tanning with the 100% water system, where intraparticle diffusion is the rate limiting step. The fitting of kinetic data to various models suggests that the process is complex with more than one mechanism limiting the rate of sorption.