The role of choline chloride in biomass delignification by the deep eutectic solvent (DES) containing lactic acid was investigated. In this study, the influence of choline chloride on the pulping of Eucalyptus globulus chips was determined. Pulping experiments were performed at 120 °C for 8 hours with a DES to wood ratio of 20:1. Various experiments were performed to study the influence of choline chloride on lignin solubility, cleaving reactions and mass transfer in order to gain understanding of the observed pulping results. It was found that the chloride anion is the active component of choline chloride. In fact, the inexpensive salt NaCl performed as well as choline chloride in that respect. Furthermore, choline chloride it is already effective in a 1:250 molar ratio to lactic acid. It was found by studies on milled wood lignin (MWL) that choline chloride increases the cleavage rate of β-O-4, and thereby increases the delignification rate of biomass. Furthermore, choline chloride slightly decreased the solubility of lignin in DES and due to an increase in viscosity decreased the estimated mass transfer coefficient. Overall, the delignification rate of eucalyptus by lactic acid increased by the addition of halide salts.

Separation of volatile fatty acids (VFAs) from fermented wastewater is challenging, due to low VFA concentrations in mineral-rich streams. As a result, separation capacity and selectivity with traditional solvents and adsorbents are both compromised. In this study, using a complex artificial model solution mimicking real fermented wastewaters, it is shown that a simple and robust adsorption-based separation technique can retain a remarkable capacity and selectivity for VFAs. Four types of polystyrene-divinylbenzene-based resins (primary, secondary, and tertiary amine-functionalized, and nonfunctionalized) were examined as the adsorbents. The presence of chloride, sulfate, and phosphate salts resulted in coadsorption of their acidic forms HCl, H₂SO₄, and H₃PO₄ on amine-functionalized adsorbents, and severely reduced the VFA capacity. With the nonfunctionalized adsorbent, almost no mineral acid coadsorption was observed. This together with a high total VFA capacity of up to 76 g/kg in equilibrium with the model solution containing a total VFA concentration of 1 wt % resulted in a very high selectivity for the VFAs. Nitrogen-stripping with various temperature profiles was applied to regenerate the adsorbent, and study the potential for fractionation of the VFAs during regeneration. Butyric acid (HBu) was obtained in mole fractions of up to 0.8 using a stepwise increase in the stripping temperature from 25 °C via 120 to 200 °C. During four successive adsorption–regeneration cycles, no reduction in the adsorption capacity was observed.

The infinite dilution activity coefficient, γ_i^∞, is often applied to characterize solvent-solute interactions, and when accurately predicted, it can also serve as an early stage solvent selection tool. Ample data is available on the use of a variety of models, which complicates decision making on which model to apply when. A comparative study was performed for eight predictive models at 298.15K, including the Hildebrand parameter and the Hansen Solubility Parameters. Also, three Group Contribution Methods based on UNIFAC, COSMO-RS, the Abraham model and the MOSCED model were evaluated. The MOSCED model and the Abraham model are overall most accurate for respectively molecular solvents and ionic liquids, with Average Relative Deviations of 16.2±1.35% and 65.1±4.50%. Therefore, cautious decision making based on predicted γ_i^∞ in ionic liquids should always be done, due to the expected significant deviations. A MOSCED model for ionic liquids could be a potential approach for higher accuracy.

Production of volatile fatty acids (VFAs) by fermentation is a potential sustainable alternative for conventional petrochemical routes to VFAs. Due to the low VFA content of fermentation broths, robust and economical separation technology has to be devised to recover the VFA. Liquid–liquid extraction of VFAs with the phosphonium phosphinate ionic liquid (IL) [P_666,14][Phos] allows good VFA extractability. For an extraction process using [P_666,14][Phos] to be green, it is essential to efficiently regenerate the solvent and recover the VFA. To obtain insight into the (strong) intermolecular interactions between [P_666,14][Phos] and acetic acid, selected as a model VFA, ¹H NMR, ³¹P NMR, FT-IR and isothermal titration calorimetry (ITC) were applied. The observations were used to interpret operations to recover acetic acid from the IL, which included evaporation at elevated temperature under vacuum, possibly assisted by nitrogen stripping, in situ esterification and back-extraction with volatile bases. Through evaporative regeneration with nitrogen stripping, HAc could be removed, but only down to an HAc/IL molar ratio of 1. The remaining molar equivalent of HAc–IL interacts tightly with the IL by partial proton transfer and strong hydrogen bonding interactions with the phosphinate anion. Back-extraction of HAc with trimethylamine (TMA) and subsequent decomposition of the HAc–TMA complexes allowed for successful IL regeneration. This process uses ten times less amine (TMA) than conventional amine-based extraction processes (e.g. tri-n-octyl amine), and provides a sustainable process route to obtain pure carboxylic acids from highly diluted aqueous solutions without generating large streams of byproducts. Further valorization via in-line vaporization/catalytic ketonization or via in-line thermal decomposition and ketonization of the TMA–HAc salt was also demonstrated, showing the potential of the VFAs as a green platform for bio-based chemicals.