Simultaneous Lignin Fractionation and Functionalization under Mild Conditions via Reactive Extraction

Reactive extraction (REx) is a promising route to simultaneously fractionate and upgrade (functionalize) lignin under mild conditions. In this work, hydrothermally treated wood solids (T = 180 °C, t = 45 min, liquid-to-solid ratio = 1) were refluxed for 1 h using acetic acid, formic acid, and ethanol as solvent-reagents. In addition, Amberlyst 15 (Amb-15) was tested as a heterogeneous acid catalyst for REx. The design of the reaction setup allowed to minimize product losses, even when Amb-15 was used, which could be easily removed from the reaction mixture. The extracted lignins showed appreciable amounts of native linkages (28.8-46.4/100 Ar), molar masses of 2.8-13.7 kDa (M _w), and total hydroxy group contents of 4.6-5.8 mmol/g. HSQC NMR analysis proved the incorporation of ethoxy, acetyl, and formyl groups in the extracted lignins in 1.2-2.0/100 Ar, 39.2-39.4/100 Ar, and 12.6-15.4/100 Ar, respectively. The molar masses of the residual cellulosic solids ranged from DP_w of 2900 to 1000, and ¹³C NMR solid-state and solution-state NMR analyses confirmed the functionalization of the residual cellulosic solids as well, though to a low extent.