Lignocellulose deconstruction using glyceline and a chelator-mediated Fenton system

Non-edible plant biomass (lignocellulose) is a valuable precursor for liquid biofuels, through the processes of pretreatment and saccharification followed by fermentation into products such as ethanol or butanol. However, it is difficult to gain access to the fermentable sugars in lignocellulose, and this problem is principally associated with limited enzyme accessibility. Hence, biomass pretreatments that destroy native cell wall structure and allows enzyme access are required for effective biomass conversion techniques. This research studied two novel pretreatment methods on two wood species: 1) a deep eutectic solvent (DES) that, under heat, swells lignocellulose and partially solubilizes cell wall materials by causing breakage of lignin-carbohydrate linkages and depolymerization of the biomass components, and 2) a chelator-mediated Fenton reaction (CMF) that chemically modifies the nanostructure of the cell wall through a non-enzymatic cell wall deconstruction. After pretreatment, utilizing analytical techniques such as nuclear magnetic spectroscopy, wide angle x-ray scattering, and gel permeation chromatography, samples were analyzed for chemical and structural changes in the solubilized and residual materials. After single stage DES (choline-chloride-glycerol) and two stage, CMF followed by DES pretreatments, lignin/carbohydrate fractions were recovered, leaving a cellulose-rich fraction with reduced lignin and hemicellulose content as determined by compositional analysis. Lignin and heteropolysaccharide removal by DES was quantified and the aromatic-rich solubilized biopolymer fragments were analyzed as water insoluble high molecular weight fractions and water-ethanol soluble low molecular weight compounds. After pretreatment for the hardwood sample, enzyme digestibility reached a saccharification yield of 78% (a 13-fold increase) for the two stage (DES/CMF) pretreated biomass even with the presence of some lignin and xylan remained on the pretreated fiber; only a 9-fold increase was observed after the other sequence of CMF followed by DES treatment. Single stage CMF treatment or single stage DES pretreatment improved 5-fold glucose yield compared to the untreated sample for the hardwood sample. The enhancement of enzymatic saccharification for softwood was less than that of hardwoods with only 4-fold increase for the sequence CMF followed by DES treatment. The other sequence of treatments reached up to 2.5-fold improvement. A similar result was determined for the single stage CMF treatment while the single stage DES treatment reached only 1.4-fold increase compared to the untreated softwood. Hence, all these pretreatments presented different degrees of biopolymer removal from the cell wall and subsequent digestibility levels; synergistic effects were observed for hardwood particularly in the sequence DES followed by CMF treatment while softwoods remained relatively recalcitrant. Overall, these studies revealed insight into two novel methods to enhance lignocellulosic digestibility of biomass adding to the methodology to deconstruct cell walls for fermentable sugars.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Macromolecular Science and Engineering

Department dc:contributor.department

Chemistry

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2017

Author dc:creator

• Orejuela, Lourdes Magdalena

Chairs dc:contributor.committeechair

• Renneckar, Scott Harold
• Goodell, Barry

Committee members dc:contributor.committeemember

• Frazier, Charles E.
• Helm, Richard F.
• Edgar, Kevin J.

• Deep eutectic solvent (DES)
• chelator-mediated Fenton system (CMF)
• pretreatment
• biomass saccharification
• structural analysis

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

vt_gsexam:13945

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/81255