Two-Step Fractionation of a Model Technical Lignin by Combined Organic Solvent Extraction and Membrane Ultrafiltration

A fractionation method for technical lignin wasdeveloped, combining organic solvent extraction and membraneultrafiltration of the solvent soluble component. Thismethod was validated on a commercial wheat straw/Sarkandagrass lignin (Protobind 1000) using 2-butanone (MEK) as thesolvent for both the extraction and the ultrafiltrationoperations. The parent lignin and the different obtainedfractions were fully characterized in terms of chemicalcomposition and physicochemical properties by gel permeationchromatography, gas chromatography/mass spectrometry (GC/MS), pyrolysis-GC/MS, total phenol contents, 31Pnuclear magnetic resonance (31P NMR), thermogravimetric analysis, differential scanning calorimetry analysis, and Fouriertransforminfrared spectroscopy. The results show that the proposed process allows a straightforward recovery of the differentlignin fractions as well as a selective control over their molecular mass distribution and related dependent properties. Moreover,the operating flexibility of the Soxhlet/ultrafiltration process allows the treatment of lignins from different feedstocks using thesame installation just by modulating the choice of the solvent and the membrane porosity with the best characteristics. This isone of the most important features of the proposed strategy, which represents a new fractionation approach with the potentialto improve lignin valorization for materials science and preparative organic chemistry applications.