Micellar-enhanced ultrafiltration for the recovery of lactic acid and citric acid from beet molasses with sodium dodecyl sulphate

The feasibility of Micellar-Enhanced UltraFiltration (MEUF) is examined in this study for the recovery of lactic acid and citric acid from synthetic solutions at their natural pH (2.4–3.0) and from beet molasses previously pretreated with activated charcoal at pH=3. Several surfactants were assayed prior to the selection of sodium dodecyl sulphate (SDS). The affinity of SDS micelles for the extraction of organic acids was studied by centrifugal MEUF using 3 kDa regenerated cellulose membranes at 25 °C. Continuous crossflow MEUF was performed using a 5 kDa TiO2 tubular inorganic membrane at 30 °C. A two-parameter linear model, based on pseudophase equilibrium in aqueous solutions, was able to predict monomeric and micellar acid concentrations in both permeate and retentate. Simultaneous recovery of organic acids and removal of SDS for reuse was achieved by treatment of the retentate with sodium hydroxide and subsequent phase separation below the surfactant Krafft temperature. Crossflow MEUF of pretreated molasses was correctly simulated by the model previously developed with synthetic solutions. After the phase separation stage, 79.34% of lactic acid and 55.60% of citric acid contained in the pretreated molasses were recovered in the SDS-free supernatant, 95% of the SDS was separated in the solid phase for reuse and the remaining 5% of the SDS was collected in the permeate.