We have recently developed a two-stage pretreatment comprising an alkaline pre-extraction followed by a Cu-catalyzed alkaline hydrogen peroxide (Cu-AHP) treatment that is effective at pretreating hardwoods at relatively mild reaction conditions. We previously demonstrated that this process is capable of achieving high yields of sugars from enzymatic hydrolysis and high yields of aromatic monomers from the catalytic depolymerization of lignin. In this work, we focus on characterizing how biomass source and reaction conditions used during the alkaline pre-extraction impact the subsequent processing stages as well as lignin yields and properties. Specifically, five hybrid poplars were subjected to alkaline pre-extraction under various conditions including differences in time (15-300 min), temperature (90-155 <sup>o</sup>C), alkali loadings (0.1-0.2 g/g biomass), and solid to liquid ratios (10-20% wt/v) and the impact on lignin recovery and purity was determined. Empirical models were developed to relate lignin extraction and recovery during the pre-extraction stage to reaction severity. For select conditions, lignin properties are assessed and include β-O-4 content determined by <sup>13</sup>C NMR, molecular mass distributions as determined by gel permeation chromatography, and susceptibility to depolymerization to aromatic monomers using thioacidolysis and formic acid-catalyzed depolymerization and these properties are demonstrated to be a function of pre-extraction conditions. Finally, the pre-extracted biomass from select conditions is assessed for its response to the subsequent Cu-AHP treatment and enzymatic hydrolysis and the overall impact of processing conditions on process economics are determined through a technoeconomic analysis.

Evaluating the impacts of two-stage alkaline-oxidative pretreatment of hybrid poplar on lignin properties

2019 Fall National Meeting

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