LIGNOCELLULOSIC BIOMASS COMPONENTS DECONSTRUCTION WITH REACTIVE OXYGEN SPECIES

Maryam Davaritouchaee

Extensive efforts have been dedicated to enhancing global sustainability through biofuel production from biomass as a renewable feedstock. This dissertation study focused on pretreatment of lignocellulosic biomass with radical oxidation. More specifically, four main radical species including superoxide anion radical (O2•−), sulfate radical (SO42−⦁), hydroperoxide anion (HO2−), and hydroxyl radical (HO•) were investigated for their effectiveness to deconstruct the structure of wheat straw and lignin. First, three persulfate activation systems were designated to pretreat wheat straw and the effects of base, heat, and hydrogen peroxide as activators were evaluated. The generation of reactive oxygen species was monitored, and the reaction variables were optimized. Persulfate-based process, as a novel advanced oxidation system, degraded lignin and hemicellulose and made cellulose available for enzymatic hydrolysis. Second, to provide an insight into the biomass decomposition with radical species, superoxide radical anion, sulfate radical, hydroperoxide anion, and hydroxyl radical were compared. The O2•− resulted in more lignin/hemicellulose modification and degradation. Characterization techniques verified the capabilities of this system to decrease S units of lignin, degrade side-chain linkages of lignin, and remove hemicellulose acetyl groups. Third, selective depolymerization of lignin was investigated to provide new information on lignin unlocking mechanisms during oxidation deconstruction process. The reaction patterns of the oxidative degradation reflected carbon-carbon cleavage and β–O–4 degradation as well as side chain oxidation of lignin. Last, the delignification and enzyme diffusion limited kinetics of oxidation pretreatments were determined experimentally. The results demonstrated that radical species increased sugar recovery by removing lignin but did not have a significant effect on the diffusion of cellulase into cellulose. The present research provides new information on lignin unlocking mechanisms during radical oxidation and fills some of the knowledge gap between biological degradation mechanism and its application to developing engineering solutions. The results further provide insights towards the development of new pretreatment processes for conversion of lignocellulose to fuels and chemicals.

LIGNOCELLULOSIC BIOMASS COMPONENTS DECONSTRUCTION WITH REACTIVE OXYGEN SPECIES

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