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Energies 2018, 11(2), 376; https://doi.org/10.3390/en11020376

Changes in Lignin Chemistry of Switchgrass due to Delignification by Sodium Hydroxide Pretreatment

1
Biological and Agricultural Engineering, Campus Box 7625, North Carolina State University, Raleigh, NC 27695-7625, USA
2
Department of Forest Biomaterials, Campus Box 8001, North Carolina State University, Raleigh, NC 27695-8001, USA
*
Author to whom correspondence should be addressed.
Received: 19 December 2017 / Revised: 30 January 2018 / Accepted: 1 February 2018 / Published: 6 February 2018
(This article belongs to the Section Energy Sources)
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Abstract

Switchgrass was pretreated with sodium hydroxide (NaOH) at various concentrations and pretreatment times to investigate how delignification caused by NaOH affects its lignin chemistry. NaOH resulted in significant delignification ranging from 44.0 to 84.6% depending on pretreatment intensity. While there was no significant glucan loss due to NaOH pretreatment, higher NaOH concentrations removed xylan by up to 28.3%. Nitrobenzene oxidation (NBO) was used to study changes in lignin chemistry, and indicated that at higher NaOH concentrations, the amount of 4-hydroxygenzaldehyde (Hy) degraded from p-hydroxyphenyl propanol (H) lignin units was significantly reduced (p < 0.05). However, amounts of syringic (SA) and vanillic (VA) acids generated from syringyl (S) and guaiacyl (G) degradation were greater at higher NaOH concentration. S/G ratio (=0.62 raw switchgrass) did not significantly (p > 0.05) change with 15 min pretreatment, but it increased to 0.75 and 0.72, respectively, with 30 and 60 min pretreatments (p < 0.05). Increase in NaOH concentration did not significantly (p > 0.05) change S/G ratio, but H/G ratio (=0.48 raw switchgrass) decreased significantly to 0.14 regardless of pretreatment times. Overall, the H unit was found to be more susceptible to NaOH than S and G unit monolignols. Though changes in lignin chemistry due to NaOH concentration were observed, their impact on cellulolytic enzyme action during hydrolysis could not be fully understood. Further studies on lignin isolation may help to determine how these changes in lignin chemistry by NaOH impact cellulolytic enzymes. View Full-Text
Keywords: switchgrass; lignin chemistry; syringyl; guaiacyl; p-hydroxyphenyl; lignin monomer ratio; nitrobenzene oxidation switchgrass; lignin chemistry; syringyl; guaiacyl; p-hydroxyphenyl; lignin monomer ratio; nitrobenzene oxidation
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Jung, W.; Savithri, D.; Sharma-Shivappa, R.; Kolar, P. Changes in Lignin Chemistry of Switchgrass due to Delignification by Sodium Hydroxide Pretreatment. Energies 2018, 11, 376.

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