Biomass, a renewable carbon source, is converted to energy such as bioethanol by employing a chemical reaction such as acidic, basic or ionic liquid pretreatment followed by enzymatic hydrolysis. The goal of the chemical reaction is to improve accessibility and decrease hindrance to enzymatic breakdown and thereby increase overall efficiency. Understanding the structural changes to biomass components such as cellulose, hemicellulose and lignin in the nano- to meso-scale during these chemical reactions is critical for increasing biomass conversion efficiencies. Specifically, ex-situ studies showed the formation of lignin globules and the aggregation of cellulose fibers due to dilute acid pretreatment of biomass. However, no insights into the processes that drive these structural changes were obtained. For this purpose, a pressure reaction cell was developed and used to monitor morphological and structural changes as they occur by placing in a neutron beam and collecting time-resolved small-angle neutron scattering data. This study was first applied to study steam explosion pretreatment, SEP. Changes to cellulose morphology occurred mainly in the heating phase of pretreatment, whereas changes in lignin morphology occurred mainly in the holding and cooling phases. In particular, water is irreversibly expelled from cellulose macrofibrils as the elemental fibers coalesce during heating and lignin aggregates begin to appear and increase in number during the holding phase, which continues to grow into the cooling phase. And, this phase separation starts at ~140 °C during SEP. These results support previous MD simulations that suggest that lignin aggregation occurs during SEP as soon as lignin has phase separated from hemicellulose. This experiment demonstrates the unique information that in-situ SANS pretreatment studies can provide and the potential to extent these types of studies to other chemical reactions.

In-situ visualization of structural changes to biomass during chemical reactions using neutron scattering

253rd National Meeting (2017)

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