Steam Explosion in alkaline medium for gelatine extraction from chromium-tanned leather wastes: time reduction and process optimization

ABSTRACT

Alkaline hydrolysis of chromium-tanned leather wastes (CTLW) is a well-known process that allows the extraction of its most valuable portion: the protein. However, alkaline hydrolysis is time-consuming. It usually takes from 2 to 10 h to be completed. In this work, alkaline hydrolysis was performed in a steam explosion reactor, using CaO as the alkalinizing agent and aiming at a short-time process. Three different temperatures and residence times were tested: 130, 140, and 150°C; 5, 10, and 15 min. When performed at 140°C for 10 min, the steam explosion in alkaline medium resulted in the optimum combination of protein extraction yield (30%) and gelatine quality (viscosity of 2.4 cP at 25°C in a 24.6 g/L protein solution – 39 kDa of molecular mass $\overline{M}$w). Not only a high extraction yield was achieved, but when compared to traditional methods, steam explosion in alkaline medium reduced the process time by a factor that varied from 12 to 36 times. It also reduced chromium content in the gelatine by a factor that varied from 16 to 96 times. Finally, to produce a high quality product, the ash content of the gelatine was reduced from 11.8% (dry basis) to 1.2% (dry basis) through diafiltration. This purification allows the application of the gelatine, for example, in the production of polymeric films.

GRAPHICAL ABSTRACT

KEYWORDS:

• Steam explosion
• gelatine
• leather waste
• processing time reduction
• extraction yield

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors thank to Caxias do Sul University, Federal University of Rio Grande do Sul, and to the National Counsel of Technological and Scientific Development (CNPq – Brazil) for their financial support. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.