Flux decline in crossflow ultrafiltration-based diafiltration process for lignin recovery from a deep eutectic solvent comprised of lactic acid and choline chloride

This study investigates a continuous ultrafiltration (UF)-based diafiltration (DF) method to separate and purify lignin from a deep eutectic solvent (DES) containing lactic acid and choline chloride after biomass delignification. A crossflow setup with a polyether sulfone UF membrane with a molecular weight cut off of 5000 Da was used to evaluate flux decline and fouling in this process. Under different pressure, feed flowrate, lignin, and DES concentrations, lignin rejection is around 0.90. Higher lignin and DES concentrations increase filtration resistance, and thus decrease flux at constant pressure. On the basis of a previously setup model based on dead-end filtration, a modeling approach was further developed to predict the system size required to implement UF-DF on a large scale. The results shows that at a constant pressure, the membrane system's area increases as the cake layer thickness over the membrane's surface increases.