This study investigates the recovery and purification of lactic acid from corn stover subcritical water hydrolysates using a hybrid separation process based on niosome-assisted ultrafiltration. Agricultural residues such as corn stover represent abundant lignocellulosic biomass that can be valorised to produce high-value chemicals within a more sustainable biorefinery framework. However, hydrolysates generated during thermochemical treatment contain complex mixtures of organic acids and degradation products, making selective separation of lactic acid challenging. In this work, different sorbitan-based niosomes were formulated using Span 60, Span 80 and Tween 80, and their physicochemical properties were characterized through particle size distribution and zeta potential measurements. Ultrasonication time strongly influenced vesicle formation, and stable systems were obtained after approximately 45 minutes of treatment. Encapsulation experiments performed with synthetic solutions showed that the non-dissociated form of lactic acid exhibited higher encapsulation efficiencies than the lactate form, particularly for Span 60-based niosomes. The influence of competing organic acids such as formic and acetic acids was also evaluated, revealing a decrease in selectivity under multicomponent conditions.
Niosome-assisted ultrafiltration experiments were subsequently conducted using Span 60 niosomes and a tubular ceramic membrane with both synthetic and real corn stover hydrolysate. Process performance was assessed through permeate flux and retention factors for the different organic acids. Results showed that operational parameters such as pH and contact time significantly affected separation efficiency. Acidic conditions favoured higher retention due to increased encapsulation of the protonated acid species, while longer contact times up to 1.5 h did not modify retention values, indicating that this contact time was sufficient to reach equilibrium between the continuous phase and the niosomal vesicles.
Overall, the results demonstrate that niosome-assisted ultrafiltration constitutes a promising solvent-free for the recovery of lactic acid from lignocellulosic hydrolysates, contributing to the development of sustainable biomass valorisation processes within future biorefineries and circular bioeconomy systems
