Recovery of chitosan from aqueous acidic solutions by salting-out: Part 1. Use of inorganic salts

We describe a novel and easy-to-use approach based on salting-out to efficiently recover chitosan from aqueous acidic solutions. Inorganic salts of the Hofmeister series salted-out chitosans of 30 kiloDaltons (kDa), 240 kDa (35 cP) and a 70 cP form of the biopolymer dissolved in dilute HCl or acetic acid. The efficiency generally followed the ranking order of the Hofmeister’s salts ( SO 4 2 - > H 2 PO 4 - ≅ HPO 4 2 - > NO 3 - ) . Temperature (4 °C, room temperature, 50 °C) did not markedly affect the process. Ammonium sulfate was the most efficient salting-out agent of chitosans over a wide range of molecular sizes (2300 Da to >240,000 Da). The solubility (dilute HCl or acetic acid) of the salted-out chitosans varied from readily soluble to nearly insoluble. The choice of the Hofmeister’s salt(s) for salting-out chitosans must take into account, (1) the efficiency of recovery, and (2) the molecular size of the chitosans to be recovered.