Comparison between membrane filtration and antisolvent addition methods for the recovery and recycling of a deep eutectic solvent after biomass pretreatment

Deep eutectic solvents (DESs) are green solvents with several advantages, including biodegradability, low toxicity, and tunability. However, their industrial application is hindered by the lack of efficient recovery and recycling technologies. The most common DES recovery method involves antisolvent addition, which is often solvent-intensive. Membrane technology offers a promising alternative, potentially reducing solvent consumption. In this study, the delignification performance of recycled DES (choline chloride:lactic acid, 1:9) was compared between antisolvent-based and membrane-based recovery methods. To the best of our knowledge, this is the first attempt to recycle spent DES after wood delignification-rather than a model lignin-DES solution-using membrane technology with low solvent addition (DES:ethanol, 1:0.7). Although the DES recycled via ultrafiltration extracted 15 % less lignin in the third cycle compared to the DES recovered by antisolvent addition, our results demonstrate that DES can be effectively recycled without inducing precipitation. The reduction in delignification performance of the recycled DES was addressed by extra antisolvent addition and replenishment of acid content. These modifications had a greater effect on the membrane-based recycled DES than on the antisolvent-based DES, increasing lignin extraction by 4 % and 16 %, respectively, as the latter contained fewer residual solids. Even partial removal of residual solids in the recovered DES, achieved by adding water and replenishing lactic acid to its original level, restored the efficiency of the recycled DES to 78 % lignin extraction, compared to 82 % for pristine DES.