Feasibility of nano- and ultrafiltration for processing biomass streams

Abstract

The increasing global interest in biorefineries is driven by their ability to generate biobased chemicals with high economic value. The literature review objectives of this thesis was to summarize the recovery technologies of different bioproducts, such as hemicellulose, lignin, phenolic compounds and acetic acid, from biorefineries, specifically emphasizing the use of ultrafiltration (UF) and nanofiltration (NF) to recover acetic acid and phenolic compounds. These membrane-based techniques offer notable advantages, such as enhanced energy efficiency and selectivity, in comparison to traditional distillation methods for product recovery.

In the experimental part of this thesis, the aim was to perform fractionation of phenolic compounds using UF and NF and test their feasibility. Autumn leaves from maple trees in Finland are a rich source of phenolic compounds, which possess significant antioxidant, anti-inflammatory, and antimicrobial properties, making them valuable. The selection of ultrafiltration and nanofiltration membranes was primarily determined by their molecular cut-off values of membrane 100 kDa, 1 kDa and about 400 Da. Dead-end cell was used for filtration, and parameters such as flux, changes in pure water permeability and solution retention were monitored.

To evaluate membrane fouling, contact angle measurements were conducted. The extracted solution underwent thorough analysis using UV and IR spectroscopy, enabling comprehensive characterization of the phenolic compounds. This analytical approach allowed for a detailed understanding of the chemical composition and properties of the extracted substances, providing insightful information on the nature and purity of the phenolic compounds in the mixture. However, the filtration experiments using maple leaf extract showed challenges in fractionating polyphenols due to membrane fouling and the presence of foulants such as lignin, tannins and aromatic compounds