Abstract
The solid–liquid equilibrium (SLE) behavior and liquid–liquid extraction (LLX) abilities of deep eutectic solvents (DESs) containing (a) thymol and L-menthol, and (b) trioctylphosphine oxide (TOPO) and L-menthol were evaluated. The distribution coefficients (KD) were determined for the solutes relevant for two biorefinery cases, including formic acid, levulinic acid, furfural, acetic acid, propionic acid, butyric acid, and L-lactic acid. Overall, for both cases, an increasing KD was observed for both DESs for acids increasing in size and thus hydrophobicity. Furfural, being the most hydrophobic, was seen to extract the highest KD (for DES (a) 14.2 ± 2.2 and (b) 4.1 ± 0.3), and the KD of lactic acid was small, independent of the DESs (DES (a) 0.5 ± 0.07 and DES (b) 0.4 ± 0.05). The KD of the acids for the TOPO and L-menthol DES were in similar ranges as for traditional TOPO-containing composite solvents, while for the thymol/L-menthol DES, in the absence of the Lewis base functionality, a smaller KD was observed. The selectivity of formic acid and levulinic acid separation was different for the two DESs investigated because of the acid–base interaction of the phosphine group. The thymol and L-menthol DES was selective towards levulinic acid (Sij = 9.3 ± 0.10, and the TOPO and L-menthol DES was selective towards FA (Sij = 2.1 ± 0.28).
Highlights
It is estimated that in the chemical industry, about 20 million metric tons of organic solvents are produced annually [1]
In line with the global sustainable development goals, defined in the Brundtland Report as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”, solvents should be considered that have a low impact on the environment and society [2]
deep eutectic solvents (DES) were applied in a liquid-liquid extraction operation in two bio refinery-relevant cases that entailed solutes of formic acid, levulinic acid, furfural, acetic acid, propionic acid, butyric acid, and L-lactic acid
Summary
It is estimated that in the chemical industry, about 20 million metric tons of organic solvents are produced annually [1]. In line with the global sustainable development goals, defined in the Brundtland Report as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”, solvents should be considered that have a low impact on the environment and society [2]. For this reason, the search to identify newly sustainable, bio-derived, organic solvents is of the utmost importance. Typical hydrolysis products [4,7,13] include formic acid, levulinic acid, and furfural, formed via sugars and
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