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A molecular design approach based on isothermal titration calorimetry (ITC) and molecular modeling (MM) was investigated for the development of new extractants in liquid-liquid extraction (LLX) systems. The molecular designs were validated in LLX experiments. Key in the regeneration of a solvent by temperature-swing back-extraction is the temperature dependency of the complexation equilibrium, which is related to the enthalpy of complexation ∆ H. The relation between the molecular structure of extractants and the thermodynamics of complexation in LLX was studied for extraction of acetic acid by basic extractants and 4-cyanopyridine by phenols. For the basic extractants longer alkyl chains and additions of rings decreased ∆ H, whereas for the phenols the acidity of the phenolic proton, and hence the complexation enthalpy, could be increased by electron withdrawing substituents. Using ∆ H as determined with ITC, the temperature dependency of the liquid-liquid equilibrium could indeed be described. Also enthalpy-entropy compensation (EEC) could be observed in the data obtained by ITC, i.e. for extractants of the same family with a larger enthalpy, an opposite effect on the entropic contribution was observed. Unlabelled Image • Interactions of acids with bases were studied, including acetic acid and 4-cyanopyridine. • Molecular modeling (MM) and Isothermal Titration Calorimetry (ITC) were combined. • Effect of molecular structure of extractant on the thermodynamics of complexation was determined. • A high enthalpy of complexation is key for effective temperature-swing regeneration of solvent. • Enthalpy-entropy compensation was observed for small changes in extractant molecular structure. [ABSTRACT FROM AUTHOR]

Highlights • Solvents were selected for extractive distillation of polar close-boiling mixtures. • Three mixtures (acid–acid), (ether–amine), and (alcohol–ketone) were studied. • Solvent functional groups were selected based on expected interactions. • Deviations from Raoult could be related to the intermolecular interactions. • With isothermal titration calorimetry, the intermolecular interactions were studied. Graphical abstract Abstract Solvent selection is key in extractive distillation process development and solvent effects are often predicted based on the activity coefficients at infinite dilution. For close-boiling polar systems with strong or specific interacting species, standard simulation tools, e.g. using UNIFAC or COSMO-RS, often predict poor as the activity coefficients at infinite dilution not always reflect the selectivity in the process. For these systems, a heuristic solvent selection method in which molecular properties such as acidity, hydrogen bonding and polarity are applied is desired as first estimate in the solvent selection. To explore the key parameters for such a first selection, solvent effects on the relative volatility (α) were measured for three different industrially relevant polar mixtures, valeric acid – 2-methylbutyric acid, diethylmethylamine – diisopropylether, and 2-butanol – 2-butanone. For each of the cases the effect of potential solvents on α was measured in an ebulliometer. For the acids, the difference in p K a of 0.1 was too small to separate based on acidity with a moderately basic solvent. Stronger basic solvents resulted in thermal and chemical instability. Although the solvent methyl-2-methyl butyrate is not suitable as a solvent because of reactivity, this structurally similar solvent showed selectivity, indicating also in extractive distillation the like dissolves like phenomenon can be applied to induce selectivity. A larger difference in basicity of the mixture components (amine–ether mixture) and a difference in hydrogen bonding affinity between the mixture components (ketone–alcohol mixture) allowed for increasing α based on differences in acidity and hydrogen bonding, respectively. [ABSTRACT FROM AUTHOR]

• Study of interactions related to LLX of phenol and phenolics. • High distribution ratios were obtained, reduced by especially polar impurities. • Homoconjugate competition weakens the primary hydrogen bond of phenol and extractant. • ITC, NMR and IR showed that interaction with phenol is based on hydrogen bonding, • Physical LLX-based separation is challenging and reactive extraction may be required. Renewable phenol can be obtained from pyrolytic bio-oil, which contains not only phenol, but also other phenolic compounds, oxygenates and carboxylic acids. For applications of renewable phenol in production of polycarbonates, it is required to upgrade and separate intermediate products and phenol. To support separation and purification approaches for bio-based phenol, interactions related to separation and purification of phenol and phenolics have been studied together with extraction results, focusing on phenol separation from low concentration aqueous streams by liquid-liquid extraction. The effect of the presence of other components and the effect of the substitution of the phenols were studied at 293 < T /K < 333. High phenol distribution ratios were obtained, the presence of especially polar impurities decreased the distribution ratios for phenol. Increasing the ratio of phenol to extractant weakened the primary hydrogen bond as a result of homoconjugate competition of phenol. Analysis with isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy showed that interaction with phenol is based on hydrogen bonding, not proton transfer. Thus extractants with a high hydrogen bond basicity have a high potential. This explains that, although 2-nitrophenol and thiophenol have a lower pK a value than phenol, their interaction with the phosphine oxide extractant is weaker. [ABSTRACT FROM AUTHOR]

• A solvent screening approach for extractive distillation was developed and validated. • The approach combines Isothermal Titration Calorimetry (ITC) and Molecular Modeling (MM). • Three cases of polar mixtures were applied for development and validation of approach. • Effects of potential solvents on the relative volatility were successfully predicted. • Guidelines for solvent selection based on ITC and MM reduce required labor, time and material. A solvent screening approach for extractive distillation, combining isothermal titration calorimetry (ITC) and molecular modeling (MM), was investigated based on three close-boiling mixture cases. The investigated mixtures are octanoic acid (HOct) and levulinic acid (HLev); diethylmethylamine (DEMA) and diisopropylether (DIPE); 2-butanol (2-BuOH) and 2-butanone (2-BuO). Solvent effects were predicted based on ITC and MM. The correlation between the interaction energy of the solvent and mixture constituents and the effect on the relative volatility (validated with VLE experiments) was shown. Successful solvents showed moderate interactions (between binary mixture interaction energy and −60 kJ/mol, with MM calculated). Too low interaction energy lacks effect and too high interaction energy compromised regeneration. For mixtures without strong intermolecular interactions (e.g. 2-BuOH and 2-BuO), a preferential exothermic interaction with the high-boiling component is needed. The developed method with solvent selection guidelines offers an effective approach for systems with strong non-idealities. [ABSTRACT FROM AUTHOR]

• Diluent and temperature-swing regeneration processes applied for extraction of succinic acid with TOA and TOPO in MIBK. • Swing in acid distribution between extraction and regeneration more important than acid distribution itself. • Regeneration process based on gaseous anti-solvent ethane is most efficient, requiring only 21% of the energy of evaporation. • Combination of evaporation of MIBK and temperature-swing strongly reduces required energy input and results in higher product purity. Solvent regeneration processes for liquid-liquid extraction of succinic acid (HSuc) from aqueous streams were investigated. Tri -n- octyl amine (TOA) and tri -n- octyl phosphine oxide (TOPO) in methyl isobutyl ketone (MIBK) showed good extraction. For 20 wt% TOA in MIBK, addition of pentane at anti-solvent-to-solvent ratio of 1 (vol/vol) decreased K D from 10.2 to 0.46, applying ethane at 30 bar decreased K D to 0.45 and increasing the temperature to 60 °C decreased K D to 1.6. Evaporation of MIBK from a solvent of 40 wt% TOA in MIBK decreased K D from 10.2 to 4.0. For these processes, capital investments and energy requirements were calculated for 10 kiloton per year at a concentration factor of 5. Costs of all processes to obtain the product at maximum solubility are less than evaporation (2600 kJ/kg product at maximum solubility). A combination of a swing in diluent and temperature results in higher product concentrations after back-extraction, and reduced the energy input to obtain the pure HSuc to 19 MJ/kg. The ethane-based process is most effective with 13 MJ/kg to obtain the pure HSuc product. Although additional capital investments for compressors and pumps are required, only 110 days of production are required for return on investments. [ABSTRACT FROM AUTHOR]