Ionic liquid-mediated aqueous two-phase system to enhance the partitioning of lignin

The aqueous two-phase system (ATPS) is a promising and efficient alternative platform for the extraction, separation, and purification of biomolecules and bioproducts. In this work, four different imidazolium-based ionic liquids with Cl- as anions and with different cations with aqueous Na2CO3 (inorganic salt) acting as the salting out agent were used to form the ATPS for the partitioning of lignin. The effects of the cation core and the length of the alkyl side chain of the ionic liquids on the formation of the ATPS were investigated using the phase diagram determined by the cloud point titration method, and the corresponding tie lines were measured and reported. It was found that the hydrophobicity of the ionic liquids plays a major role in the phase formation. The effects of the concentrations of IL, Na2CO3, and lignin as well as temperature on the partition coefficient and the extraction efficiency of lignin in the IL-mediated ATPS were investigated, and the optimum conditions were established. It was found that the high extraction efficiency (similar to 99 %) and partition coefficient (similar to 47) of lignin in the IL-mediated ATPS were achieved with the following parameters: Na2CO3 40 % (w/w); [HMIM]Cl 0.4 mol/L; lignin 0.006 mol/L; and at a temperature of 328 K. The thermodynamic study on lignin partitioning in the IL-mediated ATPS was also investigated by varying the temperature range from 298-328 K, from which it was observed that the partitioning of lignin in the ATPS increases with an increase in temperature. This suggests that the process is endothermic in nature.