From nature to innovation : natural phenolic compounds as performance promoter in membrane fabrication and modification

Abstract

Membrane technologies underpin modern biorefineries’ core activities and are fundamental in exploiting the full potential of lignocellulosic biomass by enabling the separation and extraction of diverse high-value products across wood-based biorefineries. However, due to the complexity of such biorefineries’ streams, membrane fouling remains one of the main bottlenecks, diminishing their broader applicability. Moreover, enhancing membrane performance without compromising the critical trade-off between permeability and selectivity continues to be a goal-directed objective in membrane development and modification. By focusing on natural phenolic compounds – including lignin, an underutilized byproduct from the paper industry, and vanillin – this work unlocks new potentials for biomass valorization to directly address these identified challenges in membrane technology.

In line with the primary objective of this dissertation to enhance membrane permeability without detriment to its other performances, i.e., rejection, the dual strategy of physical surface modification using vanillin and integration of DES-lignin within the polyethersulfone (PES) structure has successfully met our goal-directed objectives, enhancing the flux while preserving the integrity of the membrane’s rejection capabilities. Remarkably, using just 0.25 wt% DES-lignin in the PES membrane structure distinctly improved both the rejection and pure water flux, offering a promising pathway in membrane fabrication and modification that does not compromise essential performance metrics, i.e., trade-off challenge between permeability and selectivity.

Leveraging vanillin as a potent antifouling agent, this study explores its efficacy in modifying the surface of a commercial ultrafiltration membrane (UH004 P) and in developing a novel polyethersulfone (PES) ultrafiltration membrane to enhance membrane performance. Vanillin was shown to significantly improve membrane hydrophilicity and mitigate fouling tendencies, which are crucial for prolonging the operational life of membrane systems and minimizing fouling in biorefinery streams.

Using a deep eutectic solvent, a green solvent, DES-lignin was effectively extracted from birch wood and integrated into the PES and poly (lactic acid) (PLA) matrices to tailor the membranes’ architecture and performance. Incorporating up to 1% DES-lignin into PES membranes significantly enhances their hydrophilicity and antioxidant properties, improving permeability by approximately 30% without detriment to their selectivity. Lignin-enriched PLA membranes show promise for the fabrication of biodegradable membranes, showcasing enhanced hydrophilicity, surface negative charge, and rejection properties, though the inherent trade-off between selectivity and flux remains a challenge to be further investigated. Utilizing DES-lignin in the development of biodegradable ultrafiltration membranes offers a sustainable alternative to conventional fossil-based materials, supporting the global transition toward renewable and environmentally friendly solutions.

The knowledge acquired from this dissertation illuminates the practical implications and effectiveness of incorporating natural phenolic compounds into membranes, providing pivotal insights that guide the future development of membrane technology and its expansion across various sectors.