Visualizing morphological changes to biomass components during steam pretreatment using neutron scattering

Understanding the structural changes in biomass during pretreatment is critical for increasing biomass conversion efficiencies. Our previous work showed the formation of lignin globules and the aggregation of cellulose fibers in pretreated biomass. However, no insights into the processes that drive these structural changes were obtained. A pressure reaction cell that was developed, was used to monitor morphological changes as they occur during steam explosion pretreatment (SEP) by placing in a neutron beam and collecting time-resolved small-angle neutron scattering data. 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. During heating, water is irreversibly expelled from cellulose macrofibrils as the elemental fibers coalesce. Lignin aggregates begin to appear and increase in number during the holding phase. Lignin aggregates continue to appear and increase in size during the cooling phase. These results support previous MD simulations that suggest that lignin aggregation occurs during SEP as soon as lignin has phase separated from hemicellulose (Langan et al., Green Chem., 2014, 16, 63). The results presented here indicate that this phase separation starts at ~140^oC during SEP. This experiment demonstrates the unique information that in situ SANS pretreatment studies can provide. This approach is useful in optimizing the heating, holding and cooling stages of pretreatments to control lignin aggregates and enhance enzyme accessibility to cellulose and therefore the efficiency of biomass conversion (Pingali et al., Cellulose, 2014, 21, 873).  http://www.ornl.gov/science-discovery/clean-energy/research-areas/systems-biology/bioenergy/dynamic-visualization-of-lignocellulose