The objective of the study was to investigate alkali lignin polymerization/depolymerization pathways in subcritical water (SW) without additives. Following a SW treatment at 200, 250, 275 and 300 °C, the products were subjected to a comprehensive suite of analyses addressing the product speciation and molecular weight (MW) distribution. The MW reduction (1.4 times) in the solid products following the SW treatment indicated a surprisingly reduced impact of cross-linking/repolymerization at 300 °C and lower temperatures. This was further confirmed by thermal carbon analysis (TCA) showing a reduction in pyrolytic charring after the SW treatment. The TD-Py gas chromatography analysis of the SW treated lignin indicated that the solid residue is less oxygenated than the initial lignin (23 vs. 29% as confirmed by elemental analysis). Thus, deoxygenation rather than re-polymerization appears to be the main process route in the absence of catalysts within the temperature range considered.

Department of Chemistry University of North Dakota 151 Cornell St Grand Forks ND 58202 USA

Department of Chemistry University of North Dakota 151 Cornell St Grand Forks ND 58202 USA; 3M Center Building 260 3A 05 Saint Paul MN 55119 USA

Department of Chemistry University of North Dakota 151 Cornell St Grand Forks ND 58202 USA; Agilent Technologies Inc 2850 Centerville Rd Wilmington DE 19808 1610 USA

Department of Chemistry University of North Dakota 151 Cornell St Grand Forks ND 58202 USA; PREOL a s Terezínská 1214 410 02 Lovosice Czech Republic

Department of Chemistry University of North Dakota 151 Cornell St Grand Forks ND 58202 USA; Sciex Minneapolis MN 58203 USA

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