2D NMR characterization of wheat straw residual lignin after dilute acid pretreatment with different severities

TY - JOUR

T1 - 2D NMR characterization of wheat straw residual lignin after dilute acid pretreatment with different severities

AU - Jensen, Anders

AU - Cabrera Orozco, Yohanna

AU - Hsieh, Chia-Wen

AU - Nielsen, John

AU - Ralph, John

AU - Felby, Claus

PY - 2017/6/27

Y1 - 2017/6/27

N2 - The chemical characteristics of wheat straw lignin pretreated under dilute acid conditions were compared. After pretreatment, the lignin content of the solid residue increased as temperature increased (from 160°C to 190°C) and with the amount of acid added (0%, 0.25%, or 1% H2SO4). Pretreatment at 190°C with increasing concentrations of acid catalyst led to a decrease in glucan content, whereas the glucan content remained almost constant at 160°C pretreatment regardless of the acid concentration. The xylan content decreased in proportion with increased acid concentration and pretreatment temperature. The residual lignins were characterized by solution-state, two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy and size-exclusion chromatography (SEC). Results showed that more ether bonds were cleaved with increased pretreatment temperature and lower pH, whereas the levels of carbon-carbon bonded structures (e.g. phenylcoumaran and resinol units) were hardly affected. With a pretreatment of 160°C and 1% H2SO4, the majority of the β-O-4 bonds were cleaved. In addition, lignin depolymerization was more evident than repolymerization at higher pretreatment temperatures and lower pH. Documenting lignin structural changes as a function of pretreatment parameters provides a tool for biorefineries to gain flexibility in processing parameters with full control over the final properties of the products.

AB - The chemical characteristics of wheat straw lignin pretreated under dilute acid conditions were compared. After pretreatment, the lignin content of the solid residue increased as temperature increased (from 160°C to 190°C) and with the amount of acid added (0%, 0.25%, or 1% H2SO4). Pretreatment at 190°C with increasing concentrations of acid catalyst led to a decrease in glucan content, whereas the glucan content remained almost constant at 160°C pretreatment regardless of the acid concentration. The xylan content decreased in proportion with increased acid concentration and pretreatment temperature. The residual lignins were characterized by solution-state, two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy and size-exclusion chromatography (SEC). Results showed that more ether bonds were cleaved with increased pretreatment temperature and lower pH, whereas the levels of carbon-carbon bonded structures (e.g. phenylcoumaran and resinol units) were hardly affected. With a pretreatment of 160°C and 1% H2SO4, the majority of the β-O-4 bonds were cleaved. In addition, lignin depolymerization was more evident than repolymerization at higher pretreatment temperatures and lower pH. Documenting lignin structural changes as a function of pretreatment parameters provides a tool for biorefineries to gain flexibility in processing parameters with full control over the final properties of the products.

U2 - 10.1515/hf-2016-0112

DO - 10.1515/hf-2016-0112

M3 - Journal article

SN - 0018-3830

VL - 71

SP - 461

EP - 469

JO - Holzforschung

JF - Holzforschung

IS - 6

ER -