Salting-Out-Assisted Liquid–Liquid Extraction for Nicotine from Its Aqueous Solutions

The complete effectiveness of various inorganic salts (NaCl, KCl, NaBr, KBr, Na2CO3, and Na2SO4) to form two-phase systems was systematically evaluated for separating nicotine from its aqueous solutions. The binodal curve and tie lines for nicotine + salt + water ternary systems were experimentally determined at 298.15 K and atmospheric pressure. The salting-out effectiveness was accounted for by phase diagrams, as well as partition coefficients and recovery percentages of nicotine. The binodal curves obtained experimentally were successfully fitted to the Merchuk model, and the reliability of tie-line data was evaluated using the Othmer–Tobias and Bancroft equations. The results clearly show that all investigated salts, as salting-out media, cause the expansion of the two-phase region and have high partition yield for the separation of nicotine from its aqueous solutions. It is also observed that both cations and anions present an influence on the liquid–liquid equilibrium. The relative tendency of anions to form two-phase systems, CO32– > SO42– > Cl– > Br–, follows the position of anions in the Hofmeister series. Due to the stronger interaction of Na+ with the nicotine nitrogen than K+, the effectiveness order of cations (K+ > Na+) follows the opposite trend with the Hofmeister series. Furthermore, the order Na2CO3 > Na2SO4 > KCl > NaCl > KBr > NaBr for the effective excluded volume (EEV) of different salts is consistent with the size order of the heterogeneous region. Thus, EEV can be used as a predictive tool for the biphase-forming ability of salts. The partition coefficients and recovery percentages of nicotine are found to increase with the increase of temperature and pH. The calculated entropy of the cloud point indicates that the high positive entropy is the driving force for the two-phase formation.