Polyoxometalate (POM)-aided modification of lignin from wheat straw biorefinery

Abstract

The oxidative modification of Biolignin (BL) has been investigated to make it more suitable as an adsorbent for transition/heavy metals. BL is a by-product of a wheat straw organosolv process for the production of pulp, ethanol, and pentoses (CIMV S.A. pilot plant, Levallois Perret, France). It was subjected to oxidation by a polyoxometalate (POM) H-3[PMo12O40], aiming at the increment of oxygen-containing adsorption-active sites. The POM oxidation of BL was performed under moderate conditions (1 bar, 60-90 degrees C, and 200 degrees C) with the co-oxidants O-2 or H2O2. The resulting lignin functionality and structure was evaluated by pyrolysis-gas chromatography/mass spectrometry, solid-state C-13 nuclear magnetic resonance, Fourier transform infrared, and chemical analysis. The condensation degree of BL and its COOH and aliphatic OH group contents increased significantly, whereas the polymer structure was maintained. Under optimal conditions with POM/H2O2, the sorption capacity of lignins toward Cd(II) and Pb(II) was increased threefold and twofold, respectively.