Extraction of low-concentration bio-based diols and dicarboxylic acids using ionic liquid-based aqueous two-phase systems: Experimental and theoretical studies

Biochemical pathways to generate renewable and high value-added diols and dicarboxylic acids have attracted increasing interest. However, the diols/dicarboxylic acids usually exist in the form of low-concentration aqueous solution after the bioprocesses, causing the issues of low efficiency and high energy consumption in the separation and recovery of these highly hydrophilic bioproducts. Here, we developed an aqueous two-phase system (ATPS) consisting of ionic liquid (IL) and inorganic salt for efficient extraction of the bio-based diols and dicarboxylic acids. The optimal salt, IL, and extractant to feed volume ratio were K4P2O7, [Bmim][C12H23O2], and 1:4, respectively. The selected IL showed large capacity and good reusability, with the highest dehydration rate reaching up to 97.6%. More importantly, the IL-based ATPS exhibited effectiveness and high efficiency in the separation of various low-concentration diols and dicarboxylic acids, with the recovery exceeding 91.9%. To explore the extraction mechanism, the structural and interactions analyses were conducted by DFT calculations. The strength of hydrogen bond interactions formed between diols/dicarboxylic acids and ILs and those between salts and water largely determines the extraction performance. Moreover, three descriptors that can well represent the H-bond basicity and polarizability/dipolarity of ILs were established to facilitate the IL evaluation and screening.